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Fishery Bulletin

in 3

National Oceanic ar d Atmospheric Administration • National Marine Fisheries Service

APR 'i S

Woods Hole, .Mass.

Vol. 75, No. 1

January 1977

CLARK, STEPHEN H., and BRADFORD E. BROWN. Changes in biomass of finfishes
and squids from the Gulf of Maine to Cape Hatteras, 1963-74, as determined from
research vessel survey data 1*

NELSON, WALTER R., MERTON C. INGHAM, and WILLIAM E. SCHAAF. Larval
transport and year-class strength of Atlantic menhaden, Brevoortia tyrannus . . 23

STRUHSAKER, JEANNETTE W. Effects of benzene (a toxic component of petro-
leum) on spawning Pacific herring, Clupea harengus pallasi 43

HOSIE, MICHAEL J., and HOWARD F. HORTON. Biology of the rex sole, Glypto-
cephalus zachirus, in waters off Oregon 51

HOUDE, EDWARD D. Abundance and potential yield of the round herring, Etru-
meus teres, and aspects of its early life history in the eastern Gulf of Mexico ... 61

HAEFNER, PAUL A., JR. Reproductive biology of the female deep-sea red crab,
Geryon quinquedens, from the Chesapeake Bight 91

PRIST AS, PAUL J., and LEE TRENT. Comparisons of catches of fishes in gill nets in
relation to webbing material, time of day, and water depth in St. Andrew Bay,
Florida 103

WHITE, MICHAEL L., and MARK E. CHITTENDEN, JR. Age determination, repro-
duction, and population dynamics of the Atlantic croaker, Micropogonias
undulatus 109

RICHARDSON, SALLY L., and WILLIAM G. PEARCY. Coastal and oceanic fish
larvae in an area of upwelling off Yaquina Bay, Oregon 125

ROHR, BENNIE A., and ELMER J. GUTHERZ. Biology of offshore hake, Merluccius
albidus, in the Gulf of Mexico 147

NORRIS, KENNETH S., ROBERT M. GOODMAN, BERNARDO VILLA-RAMIREZ,
and LARRY HOBBS. Behavior of California gray whale, Eschrichtius robustus,
in southern Baja California, Mexico 159

PEARCY, WILLIAM G., MICHAEL J. HOSIE, and SALLY L. RICHARDSON. Dis-
tribution and duration of pelagic life of larvae of Dover sole, Microstomas pacificus;
rex sole, Glyptocephalus zachirus; and petrale sole, Eopsetta jordani, in waters off
Oregon 173

TRENT, LEE, and PAUL J. PRISTAS. Selectivity of gill nets on estuarine and
coastal fishes from St. Andrew Bay, Florida 185

MacINNES, J. R., F. P. THURBERG, R. A. GREIG, and E. GOULD. Long-term
cadmium stress in the cunner, Tautogolabrus adspersus 199

LEONG, RODERICK. Maturation and induced spawning of captive Pacific mackerel,
Scomber japonicus 205

(Continued on back cover)

Seattle, Washington

U.S. DEPARTMENT OF COMMERCE

Juanita M. Kreps, Secretary

NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

Robert M. White, Administrator

NATIONAL MARINE FISHERIES SERVICE

Robert W. Schoning, Director

Fishery Bulletin

The Fishery Bulletin carries original research reports and technical notes on investigations in fishery science, engineering, and
economics. The Bulletin of the United States Fish Commission was begun in 1881; it became the Bulletin of the Bureau of Fisheries in
1904 and the Fishery Bulletin of the Fish and Wildlife Service in 1941. Separates were issued as documents through volume 46; the last
document was No. 1103. Beginning with volume 47 in 1931 and continuing through volume 62 in 1963, each separate appeared as a
numbered bulletin. A new system began in 1963 with volume 63 in which papers are bound together in a single issue of the bulletin
instead of being issued individually. Beginning with volume 70, number 1, January 1972, the Fishery Bulletin became a periodical,
issued quarterly. In this form, it is available by subscription from the Superintendent of Documents, U.S. Government Printing Office,
Washington, DC 20402. It is also available free in limited numbers to libraries, research institutions, State and Federal agencies, and
in exchange for other scientific publications.

EDITOR

Dr. Bruce B. Collette

Scientific Editor, Fishery Bulletin

National Marine Fisheries Service

Systematics Laboratory

National Museum of Natural History

Washington, DC 20560

Editorial Committee

Dr. Elbert H. Ahlstrom

National Marine Fisheries Service

Dr. William H. Bayliff

Inter-American Tropical Tuna Commission

Dr. Roger F. Cressey, Jr.
U.S. National Museum

Mr. John E. Fitch

California Department of Fish and Game

Dr. William W. Fox, Jr.
National Marine Fisheries Service

Dr. Marvin D. Grosslein
National Marine Fisheries Service

Dr. Edward D. Houde
University of Miami

Dr. Merton C. Ingham

National Marine Fisheries Service

Dr. Reuben Lasker

National Marine Fisheries Service

Dr. Sally L. Richardson
Oregon State University

Dr. Paul J. Struhsaker

National Marine Fisheries Service

Dr. Austin Williams

National Marine Fisheries Service

Kiyoshi G. Fukano, Managing Editor

The Fishery Bulletin is published quarterly by Scientific Publications Staff, National Marine Fisheries Service, NOAA, Room 450,
1107 NE 45th Street, Seattle, WA 98105. Controlled circulation postage paid at Tacoma, Wash.

The Secretary of Commerce has determined that the publication of this periodical is necessary in the transaction of the public
business required by law of this Department. Use of funds for printing of this periodical has been approved by the Director of the
Office of Management and Budget through 31 May 1977.

Fishery Bulletin

CONTENTS

Vol. 75, No. 1 January 1977

CLARK, STEPHEN H., and BRADFORD E. BROWN. Changes in biomass of finfishes
and squids from the Gulf of Maine to Cape Hatteras, 1963-74, as determined from
research vessel survey data 1

NELSON, WALTER R., MERTON C. INGHAM, and WILLIAM E. SCHAAF. Larval
transport and year-class strength of Atlantic menhaden, Brevoortia tyrannus . . 23

STRUHSAKER, JEANNETTE W. Effects of benzene (a toxic component of petro-
leum) on spawning Pacific herring, Clupea harengus pallasi 43

HOSIE, MICHAEL J., and HOWARD F. HORTON. Biology of the rex sole, Glypto-
cephalus zachirus, in waters off Oregon 51

HOUDE, EDWARD D. Abundance and potential yield of the round herring, Etru-
meus teres, and aspects of its early life history in the eastern Gulf of Mexico ... 61

HAEFNER, PAUL A., JR. Reproductive biology of the female deep-sea red crab,
Geryon quinquedens, from the Chesapeake Bight 91

PRIST AS, PAUL J., and LEE TRENT. Comparisons of catches of fishes in gill nets in
relation to webbing material, time of day, and water depth in St. Andrew Bay,
Florida 103

WHITE, MICHAEL L., and MARK E. CHITTENDEN, JR. Age determination, repro-
duction, and population dynamics of the Atlantic croaker, Micropogonias
undulatus ' 109

RICHARDSON, SALLY L., and WILLIAM G. PEARCY. Coastal and oceanic fish
larvae in an area of upwelling off Yaquina Bay, Oregon 125

ROHR, BENNIE A., and ELMER J. GUTHERZ. Biology of offshore hake, Merluccius
albidus, in the Gulf of Mexico 147

NORRIS, KENNETH S., ROBERT M. GOODMAN, BERNARDO VILLA-RAMIREZ,
and LARRY HOBBS. Behavior of California gray whale, Eschrichtius robustus,
in southern Baja California, Mexico 159

PEARCY, WILLIAM G., MICHAEL J. HOSIE, and SALLY L. RICHARDSON. Dis-
tribution and duration of pelagic life of larvae of Dover sole, Microstomus pacificus;
rex sole, Glyptocephalus zachirus; and petrale sole, Eopsetta jordani, in waters off
Oregon 173

TRENT, LEE, and PAUL J. PRISTAS. Selectivity of gill nets on estuarine and
coastal fishes from St. Andrew Bay, Florida 185

MacINNES, J. R., F. P. THURBERG, R. A. GREIG, and E. GOULD. Long-term
cadmium stress in the cunner, Tautogolabrus adspersus 199

LEONG, RODERICK. Maturation and induced spawning of captive Pacific mackerel,
Scomber japonicus 205

(Continued on next page)

Seattle, Washington

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington,
DC 20402— Subscription price: $11.80 per year ($2.95 additional for foreign mailing). Cost
per single issue — $2.95.

Contents-continued

Notes

AUSTIN, C. BRUCE. Incorporating soak time into measurement of fishing effort in

trap fisheries 213

MISITANO, DAVID A. Species composition and relative abundance of larval and
post-larval fishes in the Columbia River estuary, 1973 218

GUNN, JOHN T., and MERTON C. INGHAM. A note on: "Velocity and transport
of the Antilles Current northeast of the Bahama Islands" 222

CREASER, EDWIN P., JR., and DAVID A. CLIFFORD. Salinity acclimation in the
soft-shell clam, Mya arenaria 225

GRAVES, JOHN. Photographic method for measuring spacing and density within
pelagic fish schools at sea 230

MORROW, JAMES E., ELDOR W. SCHALLOCK, and GLENN E. BERGTOLD.
Feeding by Alaska whitefish, Coregonus nelsoni, during the spawning run 234

FISHER, WILLIAM S., and DANIEL E. WICKHAM. Egg mortalities in wild pop-
ulations of the Dungeness crab in central and northern California 235

Vol. 74, No. 4 was published on 18 February 1977.

The National Marine Fisheries Service (NMFS) does not approve, rec-
ommend or endorse any proprietary product or proprietary material
mentioned in this publication. No reference shall be made to NMFS, or
to this publication furnished by NMFS, in any advertising or sales pro-
motion which would indicate or imply that NMFS approves, recommends
or endorses any proprietary product or proprietary material mentioned
herein, or which has as its purpose an intent to cause directly or indirectly
the advertised product to be used or purchased because of this NMFS
publication.

CHANGES IN BIOMASS OF FINFISHES AND SQUIDS FROM

THE GULF OF MAINE TO CAPE HATTERAS, 1963-74,
AS DETERMINED FROM RESEARCH VESSEL SURVEY DATA

Stephen H. Clark and Bradford E. Brown1

ABSTRACT

Trends in finfish and squid biomass for the 1963-74 period in the International Commission for the
Northwest Atlantic Fisheries (ICNAF) Subarea 5 and Statistical Area 6, as evidenced by autumn
bottom trawl survey data, were reviewed. Commercial statistics reported to ICNAF reveal that
landings for groundfish species of major commercial importance peaked in 1965 and subsequently
declined with shifts in directed effort to major pelagic species (for which landings peaked in 1971).
Trends in landings for species of lesser commercial importance primarily reflect increasing effort
throughout this period.

Relative abundance indices (stratified mean catch in kilograms per tow) from the autumn bottom
trawl survey revealed drastic declines in abundance of haddock, Melanogrammus aeglefinus; silver
hake, Merluccius bilinearis; red hake, Urophycis chuss; and herring, Clupea harengus, during this
period although decreases were observed for nearly all finfish species of commercial importance.
Possible evidence of changes in species composition were also observed, in that white hake, Urophycis
tenuis; Atlantic mackerel, Scomber scombrus; and squids, Loligo pealei and lllex illecebrosus , have
shown pronounced increases in relative abundance in recent years coincident with declines in other
species occupying similar ecological niches. Analysis for four strata sets (Middle Atlantic, southern
New England, Georges Bank, and Gulf of Maine areas) reveal unadjusted declines in biomass ranging
from 37% on Georges Bank to 74% in the Middle Atlantic area; by combining data for all strata, a
decline of 32% was obtained for the 1967-74 period (including the Middle Atlantic section, added in
1967), while for all remaining strata (1963-74) the corresponding figure is 43%. By adjusting biomass
components according to catchability and computing stock size estimates for the entire biomass, a 65%
decline was obtained for all strata (including the Middle Atlantic) using untransformed abundance
indices, and a 66% decline was computed from retransformed abundance indices. For the remaining
strata (Middle Atlantic strata excluded) declines of 47% and 46% were obtained, respectively. By
combining these data sets, the corresponding figures were 51% and 47%. Stock size estimates for 1975
approximated 2.0 x 10e tons, one-fourth of the estimated virgin biomass level and one-half of the level
corresponding to maximum sustainable yield.

The continental shelf waters of the northwest
Atlantic adjacent to the U.S. coast support a
valuable and productive fishery resource. Prior to
1960, this area was exploited almost exclusively
by a coastal fleet of U.S. vessels of under 300 gross
registered tons. Landings averaged less than 500
x 103 tons2 annually (International Commission
for the Northwest Atlantic Fisheries 1953-1961), a
level substantially lower than the estimated
maximum sustainable yield (MSY) of approx-
imately 950 x 103 tons obtained for this area by
various investigators (Au3; Brown et al.4; Brown

•Northeast Fisheries Center, National Marine Fisheries
Service, NOAA, Woods Hole, MA 02543.

2Landings and estimated stock levels in this paper are given in
terms of metric tons.

3Au, D. W. K. 1973. Total sustainable finfish yield from
Subareas 5 and 6 based on yield per recruit and primary pro-
duction consideration. Int. Comm. Northwest Atl. Fish. Annu.
Meet. 1973, Res. Doc. No. 10, Serial No. 2912 (mimeo.), 7 p.

4Brown, B. E., J. A. Brennan, E. G. Heyerdahl, M. D. Gross-

et al. in press). In the early 1960's, however,
distant-water fleets of the U.S.S.R., Poland, and
other nations entered the fishery and as that dec-
ade progressed these fleets underwent continual
modernization and expansion. As a result, fishing
effort and landings have increased greatly in this
area in recent years. Brown et al. (in press) es-
timated that during the 1961-72 period stan-
dardized effort increased sixfold, while landings
more than tripled. Assessments now indicate that
all major stocks in this area are fully exploited and
some, notably haddock, Melanogrammus
aeglefinus, and herring, Clupea harengus, on
Georges Bank and yellowtail flounder, Limanda
ferruginea, off southern New England have been

lein, and R. C. Hennemuth. 1973. An evaluation of the effect of
fishing on the total finfish biomass in ICNAF Subarea 5 and
Statistical Area 6. Int. Comm. Northwest Atl. Fish. Annu. Meet.
1973, Res. Doc. No. 8, Serial No. 2910 (mimeo.), 30 p.

Manuscript accepted September 1976.
FISHERY BULLETIN: VOL. 75, NO. 1, 1977.

FISHERY BULLETIN: VOL.

demonstrably overfished (Hennemuth5; Brown
and Hennemuth6; Schumaker and Anthony7). In
addition, the June 1975 report of the ICNAF
Standing Committee on Research and Statistics
(STACRES) indicates that finfish landings for the
1971-74 period have substantially exceeded the

5Hennemuth, R. C. 1969. Status of the Georges Bank haddock
fishery. Int. Comm. Northwest Atl. Fish. Annu. Meet. 1969, Res.
Doc. No. 90, Serial No. 2256 (mimeo.), 21 p.

sBrown, B. E., and R. C. Hennemuth. 1971. Assessment of the
yellowtail flounder fishery in Subarea 5. Int. Comm. Northwest
Atl. Fish. Annu. Meet. 1971, Res. Doc. No. 14, Serial No. 2599
(mimeo.), 57 p.

7Schumaker, A., and V. C. Anthony. 1972. Georges Bank
(ICNAF Division 5Z and Subarea 6) herring assessment. Int.
Comm. Northwest Atl. Fish. Annu. Meet. 1972, Res. Doc. No. 24,
Serial No. 2715 (mimeo.), 36 p.

MSY point (International Commission for the
Northwest Atlantic Fisheries 1975c).

This expansion in fishing activity in recent
years has stimulated considerable interest in its
possible effects on biomass levels and productiv-
ity. Edwards (1968) developed biomass estimates
for the area extending from Hudson Canyon to the
Nova Scotia shelf (strata 1-40, Figure 1) by ad-
justing 1963-66 U.S. research vessel survey
catches to compensate for availability and vul-
nerability to the survey gear by species and es-
timated that the annual harvest from this area
(1.2 x 106 tons) approximated one-fourth of the
fishable biomass during that period. He also re-
ported a rapid decrease in fishable biomass during

FIGURE 1. — Northwest Atlantic area from Nova Scotia to Cape Hatteras, (a) delineated into strata by depth, and (b) delineated into
major units for analytical purposes, with ICNAF division boundaries superimposed.

CLARK and BROWN: CHANGES IN BIOMASS OF FINFISHES AND SQUIDS

the early and mid-1960's and noted that while the
decrease had obviously been greater in the case of
species for which there were directed fisheries,
declines had nevertheless been general. Gross-
lein8 examined autumn research vessel survey
data (stratified mean catch per tow, pounds) for
the 1963-71 period for southern New England and
Georges Bank (strata 1-12, 13-23, and 25, Figure
1) and observed reductions in abundance of over
90% for haddock and ocean pout, Macrozoarces
americanus, and more moderate reductions in
other components of the groundfish community.
Overall, Grosslein's data indicated declines in
finfish biomass of 62% and 74% for southern New
England and Georges Bank strata, respectively.
Brown et al. (see footnote 4) presented additional
analyses of Grosslein's data and documented
pronounced declines for nearly all groundfish
species or species groups, skates (Raja spp.), and
sea herring; the decline for all species combined
(with individual species weighted by cumulative
landings for the 1962-71 period) was 64%. Brown
et al. (in press) updated these analyses by includ-
ing 1972 data and found an overall decline of 56%.

Since 1950, fishery management in the
northwest Atlantic region has been conducted
under the auspices of ICNAF, an international
body currently consisting of 18 member nations
pledged to cooperate in research and management
of marine fishery resources in the northwest
Atlantic area. This Commission, after considering
the advice of various standing committees and
subcommittees, formulates regulations, estab-
lishes quotas or "total allowable catches" (TAC's),
and handles other matters necessary for the
conservation of fish stocks in the seven regions
composing the ICNAF Convention Area. The
present study is concerned with the southernmost
regions within this area adjoining the U.S. coast
(ICNAF Subarea 5 and Statistical Area 6, Figure
1, hereafter referred to as SA 5 and 6).

In response to accumulating evidence indicat-
ing biomass declines in SA 5 and 6, STACRES in
1973 recommended an overall TAC for this area
for 1974 (International Commission for the
Northwest Atlantic Fisheries 1974d). Accord-

8Grosslein, M. D. 1972. A preliminary investigation of the
effects of fishing on the total fish biomass, and first approxi-
mations of maximum sustainable yield for finfishes in ICNAF
Division 5Z and Subarea 6. Part I. Changes in the relative
biomass of groundfish in Division 5Z as indicated by research
vessel surveys, and probable maximum yield of the total
groundfish resource. Int. Comm. Northwest Atl. Fish. Annu.
Meet. 1972, Res. Doc. No. 119, Serial No. 2835 (mimeo.), 20 p.

ingly, a TAC of 923.9 x 103 tons was adopted by
the Commission for 1974 to stabilize biomass
levels (International Commission for the
Northwest Atlantic Fisheries 1974a); for 1975,
this figure was reduced to 850 x 103 tons (In-
ternational Commission for the Northwest At-
lantic Fisheries 1974b). In addition, STACRES
further recommended that biomass levels, as
measured by bottom trawl surveys, be used to
monitor the effect of this regulation (International
Commission for the Northwest Atlantic Fisheries
1974d).

The validity of such an approach is well
documented. Grosslein (1971) has presented
evidence that abundance indices derived from
bottom trawl surveys are of sufficient accuracy to
monitor major changes in stock size; for selected
groundfish species, current levels of sampling
appear adequate to detect changes on the order of
50%. Similarly, Schumaker and Anthony (see
footnote 7) and Anderson9 have found that trends
in bottom trawl survey data accurately reflect
major changes in stock abundance for pelagic
species (herring and Atlantic mackerel, Scomber
scombrus, respectively).

The objective of the present study was to further
investigate changes in biomass of finfishes and
squids in SA 5 and 6 as evidenced by trends in U.S.
research vessel survey data. In this study, we have
expanded on previous analyses of untransformed
data (Grosslein see footnote 8; Brown et al. see
footnote 4; Brown et al. in press) so as to include all
available data from SA 5 and 6 for the 1963-74
period. In addition, we have attempted to com-
pensate for anomalies in survey catch data and
bias resulting from catchability differences by
transforming and weighting data by species and
summarizing resulting values to provide com-
bined biomass estimates by year. We believe that
the resulting trends obtained are more realistic
than those derived from unadjusted survey data.

In this paper, we define biomass as consisting of
weight of all species of finfishes and squids re-
ported to ICNAF, excluding other invertebrates
and large pelagic species such as swordfish,
Xiphias gladius; sharks other than dogfish
(Squalus acanthias and Mustelus canis); and
tunas, Thunnus spp. We have also chosen to
exclude inshore species such as American eel,

9Anderson, E. D. 1973. Assessment of Atlantic mackerel in
ICNAF Subarea 5 and Statistical Area 6. Int. Comm. Northwest
Atl. Fish. Annu. Meet. 1973, Res. Doc. No. 14, Serial No. 2916
(mimeo.), 37 p.

FISHERY BULLETIN: VOL. 75, NO. 1

Anguilla rostrata; white perch, Morone ameri-
cana; and Atlantic menhaden, Brevoortia
tyrannus. The latter species is an important
component of the biomass, but is taken primarily
inshore in the southern portion of SA 6 and is,
therefore, not of direct interest in the present
study.

The term species, for convenience, refers to both
species and species groups. Terms such as other
pelagics, other fish, and groundfish refer to species
so designated in ICNAF statistical bulletins
(International Commission for the Northwest
Atlantic Fisheries 1965-1973, 1974c, 1975a).

BOTTOM TRAWL SURVEY
PROCEDURES

Autumn bottom trawl survey data have been
collected by the U.S. National Marine Fisheries
Service RV ALBATROSS IV since 1963; the RV
DELAWARE II has also participated infre-
quently. In all of these surveys, both vessels have
used the standard "36 Yankee" trawl with a 1.25-
cm stretched mesh cod end liner. This trawl
measures 10-12 m along the footrope and 2 m in
height at the center of the headrope, and is
equipped with rollers to make it suitable for use on
rough bottom (Edwards 1968).

The area sampled extends from Nova Scotia to
Cape Hatteras. A stratified random sampling
design has been used in this survey (Cochran
1953); thus, the survey area has been stratified
into geographical zones (Figure 1) primarily on
the basis of depth (Grosslein 1969). During 1963-
66, only strata from the New Jersey coast
northward (1-42, Figure 1) were sampled; addi-
tional strata (61-76, Figure 1) were added in
autumn 1967 to cover the mid- Atlantic region
(Grosslein10). An additional section covering part
of the Scotian Shelf was also added in 1968 but is
not considered in this study.

In each cruise, sampling stations were allocated
to strata roughly in proportion to the area of each
stratum and were assigned to specific locations
within strata at random. A 30-min tow was taken
at each station at an average speed of 3.5 knots.
After each tow, weight and numbers captured,
fork length, and other pertinent data were re-
corded for each species. Data were summarized,

'"Grosslein, M. D. 1968. Results of the joint USA-USSR
groundfish studies. Part II. Groundfish survey from Cape
Hatteras to Cape Cod. Int. Comm. Northwest Atl. Fish. Annu.
Meet. 1968, Res. Doc. No. 87, Serial No. 2075 (mimeo.), 28 p.

audited, and transferred to magnetic tape follow-
ing the completion of each survey. The reader is
referred to Grosslein (1969, footnote 11) for
further details concerning survey procedures.

Following procedures given by Cochran
(1953:66) we calculated stratified mean catch per
tow values in terms of weight by

y, = VN 2 [au] (1)

h = V

where yst = stratified mean catch per tow,
Nh = area of the hth stratum,
N = total area of all strata in the set,
ft, — mean catch per tow in the hth

stratum, and
k = number of strata in the strata set.

We calculated the estimated population variance
as

S2 = 1/A7

h = l

Nhyh'-

Nyst2 +1^

/! = !

(Nh

1) +

(Nh - N) (Nh - nh)

(2)

where S2 = estimated population variance,

nh = number of tows in the hth stratum,
s/,2 = variance within the hth stratum, and
yst, N, Nh, yh, and k are defined as before.

We used stratified mean weight per tow
(kilograms) in preference to numbers as an index
of biomass change due to its convenience when
working with different species groups and the
high degree of variability in numbers associated
with fluctuations in recruitment. Obviously,
numbers would also tend to overemphasize the
importance of small organisms in the community
under study, as pointed out by Odum and Smalley
(1959).

RECENT TRENDS IN LANDINGS

Commercial landings as reported to ICNAF
(International Commission for the Northwest
Atlantic Fisheries 1965-1973, 1974c, 1975a,

"Grosslein, M. D. 1969. Groundfish survey methods. NMFS,
Woods Hole, Mass., Lab. Ref. No. 69-2, 34 p.

CLARK and BROWN: CHANGES IN BIOMASS OF FINFISHKS AND SQUIDS

footnote 12) for the major species groups consid-
ered in this paper (principal groundfish, princi-
pal pelagics, flounders, other groundfish, other
pelagics and other fish, and squid, Table 1) are
given in Figures 2 and 3. Effort was concentrated
on principal groundfish during the mid-1960's;
landings peaked at approximately 643 x 103 tons
in 1965, declined to approximately 575 x 103 tons
in 1966, and dropped off sharply thereafter (Fig-
ure 2). Statistical data for individual species
(International Commission for the Northwest
Atlantic Fisheries 1965-73, 1974c, 1975a, see
footnote 12) reveal that this pattern resulted
primarily from great increases in landings of cod,
haddock, and silver and red hake in the mid-
1960's, followed by subsequent declines. Landings
of redfish and pollock have increased somewhat in
more recent years, but not enough to offset de-
clines in the remaining species.

Landings for principal pelagics during this
period (herring and mackerel) declined initially
followed by a subsequent upswing. This can be
attributed primarily to a diversion of USSR effort
from herring to haddock and hake in 1965 and
1966 (Schumaker and Anthony see footnote 7). In
1967, however, the USSR redirected much of its
effort back to the Georges Bank herring stock and
also initiated an intensive mackerel fishery
(Anderson see footnote 9) and other distant water
fleets also began to exploit these species at about
this time. This increase in effort produced in-
creased landings of herring and mackerel to a total

TABLE 1. — Scientific and common names of species considered1
in this study, grouped as in ICNAF statistical bulletins.

"International Commission for the Northwest Atlantic
Fisheries. 1975. Provisional nominal catches in the Northwest
Atlantic, 1974 (Subareas 1 to 5 and Statistical Areas 0 and 6).
Int. Comm. Northwest Atl. Fish. Annu. Meet. 1975, Summ. Doc.
No. 32, Serial No. 3590 (mimeo.), 61 p.

^— ^— Principal groundfish
Principal pelagics

/ \ '
1 \ 1

/ \

/ \ ' ^-'

/ \ ' ^
/ \ 1

/ \ '
/ \ '
/ V

/ AS.

/ N~ — -~">v
/ \

N •
S/

\
\
\
\

63 64 65 66 67 68 69 70 71 72 73 74

YEAR

FIGURE 2. — Landings of principal groundfish and principal
pelagics in ICNAF Subarea 5 and Statistical Area 6, 1963-74.

Common name

Scientific name

Principal groundfish
(except flounders):

Cod

Haddock

Redfish

Silver hake

Red hake

Pollock (saithe)
Flounders:

American plaice

Witch

Yellowtail

Winter flounder

Summer flounder
Other groundfish:

Angler

Cusk

Ocean pout

Sculpins

Scup

Searobins

White hake
Principal pelagics:

Herring

Mackerel
Other pelagics and other fish:

Butterfish

Spiny dogfish

Skates and rays
Squid:

Short-finned squid

Long-finned squid

Gadus morhua
Melanogrammus aegletinus
Sebastes marinus
Merluccius bilinearis
Urophycis chuss
Pollachius virens

Hippoglossoides platessoides
Glyptocephalus cynoglossus
LJmanda ferruginea
Pseudopleuronectes americanus
Paralichthys dentatus

Lophius americanus
Brosme brosme
Macrozoarces americanus
Myoxocephalus spp.
Stenotomus chrysops
Prionotus spp.
Urophycis tenuis

Clupea harengus
Scomber scombrus

Poronotus triacanthus
Squalus acanthias
Raja spp.

///ex illecebrosus
Loligo pealei

1Note that for all groupings except principal groundfish, principal pelagics,
and squid, other species were considered but are not mentioned specifically.

g 70
S

— Fkujnders
Other groundfish

— Other pelages and other fish

Squid

63 64 65 66 67 68 69 70 71

72 73 74

FIGURE 3. — Landings of flounders, other groundfish, other
pelagics and other fish, and squid in ICNAF Subarea 5 and
Statistical Area 6, 1963-74.

FISHERY BULLETIN: VOL. 75, NO. 1

of approximately 667 x 103 tons in 1971 (Figure
2). Landings of herring and mackerel peaked in
1968 and 1972, respectively (International
Commission for the Northwest Atlantic Fisheries
1965-1973, 1974c, 1975a, see footnote 12).

Landings for the remaining species groups
(Figure 3) generally reflect decreasing abundance
in response to increasing effort. Landings of
flounders were relatively constant but did in-
crease until 1969 followed by a gradual decline.
The somewhat anomalous 1969 value resulted
primarily from sharply increased catch of yellow-
tail by distant water fleets (Brown and Henne-
muth see foonote 6). Steadily declining landings of
other groundfish throughout the period of study
can be attributed in part to declining abundance,
while other pelagics and other fish show a general
increase which would appear to be associated with
increased effort as shown later. Squid landings
also increased sharply since 1970.

As TAC's have been imposed for certain stocks
since 1970, their possible influence should be
considered. It is not believed, however, that quota
management affected these trends appreciably.
Species subject to quota management in 1970 and
1971 (i.e., haddock and yellowtail) had already
been seriously depleted, while in 1972 and 1973
TAC's did not appear to be limiting with the ex-
ception of those imposed for haddock, yellowtail,
and herring, and for the latter two species TAC's
were in fact exceeded (International Commission
for the Northwest Atlantic Fisheries 1975c). It
appears likely that TAC's imposed for 1974 had a
greater effect, particularly in the case of herring
and mackerel; also, the overall TAC of 923.9 x 103
tons (referred to above) undoubtedly limited total
catches by nation to some degree although it was
exceeded by approximately 75 x 103 tons (In-
ternational Commission for the Northwest At-
lantic Fisheries 1975c). In summary, however, it
would appear that the influence of quota
management on the overall trends depicted in
Figures 2 and 3 was relatively minor for the level
of effort being exerted which, as noted previously,
increased by a factor of six during the period
1962-72. It is not possible to speculate whether or
not significant additional effort would have been
added in 1973 and 1974 (say from new entrants to
the area), had there not been regulations.

The possible influence of bias upon reported
landings remains to be mentioned. In ICNAF
statistical bulletins, some landings have been
recorded as "not specified," e.g., "groundfish (not

specified)," "other pelagics (not specified)," etc.
Insofar as possible, we have combined these
landings with landings data reported by species
within each species group. In recent years,
however, an improvement has occurred in re-
porting accuracy which appears to have affected
the relative amounts of "not specified" landings
(and thus annual totals as depicted in Figures 2
and 3). For instance, examination of data in
ICNAF statistical bulletins (International
Commission for the Northwest Atlantic Fisheries
1965-1973, 1974c, 1975a) reveals a decrease in the
relative percentage of "not specified" groundfish of
from 15 to 20% of the other groundfish category in
the mid-1960's to approximately 10% in 1970-73,
while for "other fish" a complete reversal of this
trend occurred. The "not specified" proportion of
the total "other fish" category increased from
approximately 10% in the mid-1960's to 25-30%
during 1970-73. This implies that landings for
principal groundfish and other species may have
been erroneously included under other groundfish
to a greater extent in former years, thus biasing
the observed trend for other groundfish down-
ward, while the trend for other pelagics and other
fish may have been biased upward due to inclusion
of previously omitted landings data in more recent
years. The actual extent to which trends depicted
in Figures 2 and 3 were distorted by this factor is
problematical, but it should be noted that for
principal groundfish, principal pelagics, floun-
ders, and squid, more important (and/or more
readily identified) species were involved which
probably were not affected by reporting inac-
curacies to the same degree. Consequently, it is
our judgement that trends for the remaining
species groups were probably not appreciably
biased.

CHANGES IN BIOMASS
Unweighted Analyses

Summaries of survey data by species and area
permit preliminary evaluation of the magnitude
and direction of change in selected biomass
components in recent years and of the degree of
year-to-year variability that may be encountered.
Accordingly, we examined trends for different
species and strata sets and for data summed over
all strata before attempting transformation or
weighting procedures.

Individual strata can be grouped for analysis on

CLARK and BROWN: CHANGES IN BIOMASS OF FINFISHES AND SQUIDS

the basis of stock structure, ecological factors,
exploitation patterns, and availability of survey
data. In the present paper, we have selected four
major strata sets in SA 5 and 6 based on the above
factors (Figure 1) which we considered separately
prior to examination of data for the area as a
whole. These are as follows:

1. Middle Atlantic area (strata 61-76, cor-
responding approximately to ICNAF Di-
visions 6B and C);

2. Southern New England area (strata 1-12,
corresponding approximately to ICNAF
Divisions 6A and Subdivision 5Zw);

3. Georges Bank (strata 13-25, corresponding
approximately to ICNAF Subdivision 5Ze),
and

4. Gulf of Maine (strata 26-30 and 36-40,
corresponding approximately to ICNAF
Division 5Y).

The rationale for this arrangement is based on
differences in faunal assemblages although
exploitation patterns and data availability were
also considered. A number of stock identification
studies support such an arrangement (Wise 1962;
Grosslein 1962; Anthony and Boyar 1968; Ridg-
way et al.13; Anderson14; and others). In addition,

Grosslein's15 study indicated a relatively high
diversity of species in the southern New
England-Middle Atlantic areas in contrast to the
Gulf of Maine, with Georges Bank being a rather
transitional area. Exploitation patterns and
reporting of commercial fishery statistics also
dictate some form of division between Subdivision
5Ze and the Subdivision 5Zw-Statistical Area 6
region and other areas to the north or south (Fig-
ure 1). Finally, the fact that survey data are
nonexistent for Middle Atlantic strata prior to
1967 required a division between this area and the
remainder of SA 5 and 6 for analytical purposes.
Trends in relative abundance from 1963 to 1974
(stratified mean catch per tow [kilograms], U.S.
autumn bottom trawl survey data) are given by
area for selected species in Tables 2-5 and for
major ICNAF categories in Figures 4-9. Pro-
nounced declines of principal groundfish are
evident both on Georges Bank and in the Gulf of
Maine, with lesser declines in the remaining areas
(Figure 4). The trends observed resulted primarily
from declining relative abundance of haddock and
silver and red hake (Tables 2-5). Haddock, in
particular, appears to have greatly decreased on

13Ridgway, G. J., R. D. Lewis, and S. Sherburne. 1969.
Serological and biochemical studies of herring populations in the
Gulf of Maine. Cons. Perm. Int. Explor. Mer, Memo No. 24, 6 p.

14Anderson, E. D. 1974. Comments on the delineation of red
and silver hake stocks in ICNAF Subarea 5 and Statistical Area
6. Int. Comm. Northwest Atl. Fish. Annu. Meet. 1974, Res. Doc.
No. 100, Serial No. 3336 (mimeo.), 8 p.

15Grosslein, M. D. 1973. Mixture of species in Subareas 5 and
6. Int. Comm. Northwest Atl. Fish. Annu. Meet. 1973, Res. Doc.
No. 9, Serial No. 2911 (mimeo.), 20 p.

TABLE 2. — Stratified mean catch per tow (kilograms) for selected species of finfish and squid,
Albatross IV autumn bottom trawl survey data, 1967-74, Middle Atlantic area (strata 61-76).

Species

1967

1968

1969

1970

1971

1972

1973

1974

Principal groundfish:

Silver hake 0.9 0.9 0.1 0.2 0.3 0.5 0.4 '0.0

Red hake 0.1 0.8 0.5 0.2 0.4 0.2 0.1 0.0

Flounders:

Yellowtail 3.4 5.5 3.6 '0.0 0.3 0.1 10.0 0.0

Winter flounder 1.7 1.3 0.6 10.0 0.2 0.1 0.1 0.0

Summer flounder 2.0 1.5 0.8 '0.0 0.4 0.1 0.3 0.8

Other 0.7 2.0 0.6 0 4 0.8 10 1.6 0.5

Other groundfish:

Angler 0.7 0.6 0.3 '0.0 0.1 1.4 0.9 '0.0

Scup 2.6 0.8 8.4 0.1 0.3 3.2 0.2 0.7

Searobins 130.1 13.8 5.4 6.9 3.1 1.7 1.9 1.9

Other 05 0.3 0.3 '0.0 '0.0 '0.0 '0.0 0.0

Principal pelagics:

Herring 0.0 0.0 0.0 0.0 0.0 0.0 '0.0 0.0

Mackerel '0.0 0.1 0.0 00 '0.0 0.0 0.0 0.0

Other pelagics and other fish:

Butterfish 3.6 18.1 3.9 5.4 5.0 4.2 11.0 3.7

Spiny dogfish 47.8 3.1 4.9 0.0 0.0 0.0 '0.0 0 0

Skates and rays 4.0 8 4 29.5 7 0 12.8 6.6 10.4 5.4

Other2 9.8 7.0 4.5 59 9.6 3.1 94 3.3

Squid:

Short-finned squid 0.3 0.2 0.1 0.4 0.2 0.3 '0.0 0.1

Long-finned squid 10.6 9.3 9.2 48 2.5 12.6 11.2 11.1

Total finfish and squid 218.8 73.7 72.7 31.3 36.0 35.1 47.5 27.5

'Less than 0.05.

2Does not include data for tunas, sharks, swordfish, American eel, or white perch.

FISHERY BULLETIN: VOL. 75, NO. 1

TABLE 3. — Stratified mean catch per tow ( kilograms) for selected species of finfish and squid, Albatross IV autumn bottom trawl

survey data, 1963-74, southern New England area (strata 1-12).

Species

1963

1964

1965

1966

1967

1968

1969

1970

1971

1972

1973

1974

Principal groundfish:

Cod

3.0

0.5

0.7

2.9

1.5

0.6

0.1

2.1

'0.0

Haddock

2.7

7.1

1.2

0.1

0.5

'0.0

0.1

0.5

0.1

0.0

'0.0

0.0

Silver hake

5.2

5.7

7.6

4.4

4.8

2.3

2.6

4.6

4.0

3.2

1.3

Red hake

8.1

4.4

5.6

2.9

2.7

4.4

3.9

3.4

6.6

3.0

Flounders:

Yellowtail

12.0

11.8

8.7

11.9

11.1

12.3

137

7.6

26.8

2.6

1.2

Winter flounder

2.4

3.1

2.1

1.5

1.0

1.3

2.4

1.0

3.0

0.5

0.4

Other

4.8

3.8

2.7

1.9

1.7

1.9

1.3

2.9

2.4

2.9

Other groundfish:

Angler

4.4

7.0

6.7

1.9

1.2

2.5

1.5

9.8

2.9

1.0

Ocean pout

0.7

0.4

0.3

1.1

0.6

0.5

0.3

0.1

0.2

0.0

Sculpins

0.3

1.0

1.7

2.5

1.6

1.0

1.4

1.1

0.3

2.2

0.1

Scup

1.3

2.5

0.7

0.5

0.6

0.4

1.6

0.4

0.2

1.9

1.6

1.4

Searobins

1.0

0.8

0.5

0.7

0.3

0.5

0.2

0.3

4.7

0.3

0.1

White hake

0.6

1.2

1.3

1.4

0.6

0.5

0.4

0 1

Other

0.1

'0.0

0.3

'0.0

0.1

0.3

'0.0

0.0

Principal pelagics:

Herring

0.2

'0.0

0.5

1.8

0.1

'0.0

0.0

Mackerel

'0.0

"0.0

'0.0

1.0

0.2

3.9

'0.0

0.1

'0.0

Other pelagics and other fish:

Butlerfish

6.0

4.5

1.5

4.0

6.5

1.1

2.4

6.1

Spiny dogfish

71.2

194 4

93.0

924

969

585

216.5

676

13.2

327

46.1

18.6

Skates and rays

15.8

10.4

11.3

13.6

3.7

1.2

2.3

2.9

6.6

9.1

3.0

Other2

1.9

2.0

0.7

1.7

1.3

4.1

5.1

4,1

3.1

5.3

Squid

Short-finned squid

(3)

40.1

"0.1

«0.1

0 1

0.3

0.6

0 1

Long-finned squid

(3)

«1.2

"16

"22

2.0

122

181

3.6

5.4

167

12.1

Total finfish and squid

137.1

262 6

1525

1468

141.4

108 0

282 5

1116

567

119.1

944

548

'Less than 0.05

2Does not include data for tunas, sharks, swordfish. American eel. or white perch

3Data not recorded

4Squid catches for 1964-66 prorated by species according to relative percentages caught in later years

TABLE 4. — Stratified mean catch per tow (kilograms) for selected species of finfish and squid, Albatross IV autumn bottom trawl

survey data, 1963-74, Georges Bank area (strata 13-25).

Species

1963

1964

1965

1966

1967

1968

1969

1970

1971

1972

1973

1974

Principal groundfish:

Cod

11.0

7.1

7.2

5.0

8.4

5.3

4.9

7.8

6.1

14.2

19.1

5.1

Haddock

51.2

75.2

56.1

21.4

20.5

9.3

5.8

10.6

3.6

5.1

7.2

2.8

Redfish

0.9

4.0

1.1

2.0

2.6

3.5

6.5

4.6

1.9

3.9

2.6

1.9

Silver hake

5.4

1.7

1.6

2.1

1.0

2.2

1.6

2.3

1.2

2.4

1.5

Red hake

7.4

2.2

1.8

1.2

0.8

1.1

1.5

0.9

1.9

1.2

2.8

1.4

Pollock

2.3

2.1

1.7

2.9

1.1

1.0

1.4

0.4

2.2

1.0

1.6

0.4

Flounders:

American plaice

5.5

2.0

1.2

3.3

1.7

1.3

1.1

1.5

0.9

0.4

Witch

1.0

0.5

1.5

0.6

0.9

0.5

1.5

0.5

1.0

1.5

0.4

Yellowtail

8.2

8.4

5.6

2.5

4.5

6.7

5.4

3.0

3.7

4.0

3.8

2.2

Winter flounder

1.8

2.1

2.0

3.6

1.3

1.5

1.7

4.7

1.0

1.5

1.6

1.5

Other

1.0

0.7

0.6

1.1

1.2

1.3

0.4

0.6

1.3

3.5

1.8

Other groundfish:

Angler

3.5

2.6

5.0

5.8

0.5

1.9

1.1

0.7

0.6

1.6

2.2

1.1

Ocean pout

1.7

1.0

0.9

0.2

0.1

'0.0

0.1

'0.0

0.4

0.2

'0.0

Sculpins

3.4

1.8

3.3

2.0

3.8

3.1

4.9

3.1

2.8

3.6

2.0

White hake

1.4

0.5

0.8

'0.0

1.6

1.0

1.8

2.4

2.2

3.5

2.0

Other

0.5

0.6

1.0

0.7

1.0

0.2

0.5

0.1

0.4

0.7

0.3

Principal pelagics:

Herring

1.0

0.2

0.9

1.5

0.6

0.2

'0.0

0.3

0.1

'0.0

Mackerel

'0.0

0.0

0.1

0.2

0.4

0.1

'0.0

0.4

'0.0

0.3

Other pelagics and other fish:

Butlerfish

0.7

1.3

0.3

0.1

0.6

1.0

0.3

0.2

1.1

1.2

0.4

1.0

Spiny dogfish

2.9

3.0

3.5

1.8

2.5

5.6

2.4

3.5

3.3

9.7

36.2

2.2

Skates and rays

31.3

15.0

21.7

17.7

15.2

12.3

8.7

15.7

8.9

15.4

28.9

15.4

Other2

0.5

0.4

0.5

0.4

0.2

0.6

0.9

1.0

2.8

Squid:

Short-finned squid

(3)

"0.2

«0.5

"0.3

0.1

0.3

'0.0

0.2

0.4

0.2

5.0

0.1

Long-finned squid

(3)

40.2

"0.5

"0.4

0.4

1.5

1.1

1.0

1.1

0.1

2.2

Total finfish and squid

142.6

132.7

118.0

80.0

68.7

62.2

51.8

67.3

45.2

72.9

128.8

48.8

'Less than 0.05.

2Does not include data for tunas, sharks, swordfish, American eel, or white perch.

3Data not recorded.

4Squid catches for 1964-66 prorated by species according to relative percentages caught in later years.

CLARK and BROWN: CHANGES IN BIOMASS OF FINFISHES AND SQUIDS

TABLE 5. — Stratified mean catch per tow (kilograms) for selected species of finfish and squid, Albatross IV autumn bottom trawl

survey data, 1963-74, Gulf of Maine area (strata 26-30 and 36-40).

Species

1963

1964

1965

1966

1967

1968

1969

1970

1971

1972

1973

1974

Principal groundfish:

Cod

10.9

14.1

7.4

8.0

5.7

12.0

9.5

10.2

8.0

5.4

5.5

Haddock

39.1

14.2

12.8

10.1

9.8

11.9

7.8

4.3

5 1

3.2

5.3

2.2

Redfish

269

59.1

14.0

31.8

25.7

432

21.3

33.8

25.4

250

17.3

264

Silver hake

28.3

4.8

8.7

4.2

2.0

2.4

3.0

4.0

3.9

Red hake

4.9

0.7

1.0

0.8

0.3

0.1

0.3

0.1

1.0

2.0

0.5

Pollock

8.6

7.8

3.6

2.4

2.9

5.4

13.1

3.6

5.5

5.9

Flounders:

American plaice

6.2

3.6

6.0

6.3

3.5

4.3

3.5

2.5

2.9

2.2

2.9

2.3

Witch

2.5

4.5

2.0

3.7

5.1

3.4

3.2

2.3

1.3

1.6

Other

1.1

0.4

1.0

0.1

'0.0

0.1

1.2

0.3

0.1

0.7

0.2

0.6

Other groundfish:

Angler

3.7

1.6

1.9

3.6

1.7

2.0

4 5

3.1

4.0

1.5

3.6

2.3

Cusk

2.2

1.2

1.3

3.8

1.1

1.8

1.7

2.0

1.8

3.0

1.3

0.5

White hake

7.8

7.9

9.5

4.2

5.8

17.7

16.3

15.3

16.9

15.9

14.0

Other

0.3

0.4

0.6

1.0

0.2

0.5

0.1

0.6

0.3

0.8

0.4

0.3

Principal pelagics:

Herring

0.1

0.2

0.3

0.1

'0.0

"0.0

0.1

0.6

'0.0

Mackerel

'0.0

0.0

'0.0

'00

Other pelagics and other fish:

Spiny dogfish

58.2

10.6

11.8

4.0

22.8

18.3

119

17.3

7.2

8.7

Skates and rays

15.1

9.4

111

17.4

4.9

10.0

14.4

16.2

12.1

7.9

7.6

4.4

Other2

2.5

0.1

0.2

0.3

0.4

0.2

0.1

0.3

0.2

0.3

0.2

Squid:

Short-finned squid

(3)

'•"0.0

"0.2

"0.4

0.1

0.3

0.5

0.2

1.2

Long-finned squid

(3)

"0.0

'•40.0

"0.1

'0.0

'00

Total finfish and squid

221.0

135.6

92.2

108.6

73.0

125.9

112.8

117.8

103.2

106.0

79.6

80.8

'Less than 0.05

2Does not include data for tunas, sharks, swordfish, American eel, or white perch

3Data not recorded.

4Squid catches for 1964-66 prorated by species according to relative percentages caught in later years.

Middle Altanlic
So New England
Georges Bank
Gulf ol Marne

72 73 74

FIGURE 4— Catch of principal groundfish in U.S. autumn bot-
tom trawl surveys for the Middle Atlantic (strata 61-76), 1967-
74, and for southern New England (strata 1-12), Georges Bank
(strata 13-25), and the Gulf of Maine (strata 26-30 and 36-40),
1963-74.

Georges Bank and in the Gulf of Maine and to be
almost nonexistent in southern New England
waters. Relative abundance indices for redfish and
pollock, however, appear to have remained rela-
tively stable (Tables 4, 5). Cod declined somewhat
in the Gulf of Maine but remained relatively sta-
ble in other areas (Tables 3-5).

Catches of flounders indicate substantial de-
clines in relative abundance for all areas (Figure
5) and nearly all species (Tables 2-5) with yellow-
tail declining very sharply in recent years.
Unusually high catches of yellowtail were taken
in southern New England waters in 1972 (Figure
5, Table 3); factors involved are unclear but appear
to reflect changes in availability, as actual in-
creases in abundance do not appear to have oc-
curred (Parrack16).

Data for other groundfish (Figure 6) suggest a
decline in biomass for Middle Atlantic strata, an
increase for Gulf of Maine strata, and relatively
stable levels elsewhere. The observed trend for
Middle Atlantic strata is strongly influenced by
large catches of searobins in 1967 (Table 2) which

16Parrack, M. L. 1973. Current status of the yellowtail floun-
der fishery in ICNAF Subarea 5. Int. Comm. Northwest Atl.
Fish. Annu. Meet. 1973, Res. Doc. No. 104, Serial No. 3067
(mimeo.), 5 p.

FISHERY BULLETIN: VOL. 75, NO. 1

g 25

£ 20

3 15

Middle Atlantic

So Mew England

Georges Bank

Gulf of Mome

FIGURE 5.— Catch of flounders in U.S. autumn bottom trawl
surveys for the Middle Atlantic (strata 61-76), 1967-74, and for
southern New England (strata 1-12), Georges Bank (strata 13-
25), and the Gulf of Maine (strata 26-30 and 36-40), 1963-74.

Middle Atlantic
So New England
Geofges Bonk
Gulf of Mome

66 69 70

YEAR

FIGURE 6. — Catch of other groundfish in U.S. autumn bottom
trawl surveys for the Middle Atlantic (strata 61-76), 1967-74,
and for southern New England (strata 1-12), Georges Bank
(strata 13-25), and the Gulf of Maine (strata 26-30 and 36-40),
1963-74.

continued to decline in succeeding years. Ocean
pout also appear to have declined sharply during
the period of study in southern New England and
Georges Bank strata (Tables 3, 4). Abundance of
white hake, however, appears to have increased
in the Gulf of Maine in recent years (Table 5),
leading to an increase in other groundfish biomass
for these strata.

Principal pelagics appear to have declined in
relative abundance although considerable
fluctuation is evident (Figure 7). Most of this
variation is, however, associated with the pres-
ence of outstanding year-classes of herring in the
early and mid-1960's (Schumaker and Anthony
see footnote 7) and the appearance of an out-
standing year-class of mackerel in 1967 (Anderson
see footnote 9). Considerable fluctuation is also
evident in catches of other pelagics and other fish
(Figure 8, Tables 2-5) although the trend is
generally downward (anomalous peaks relate
primarily to high catches of spiny dogfish in cer-
tain years). Data for squid (Figure 9) indicate
increased abundance although catches of long-
finned squid appear to be lower in 1970 and 1971
in Middle Atlantic strata and from 1970 to 1972 in
southern New England strata than in the years
immediately preceding and following (Tables 2, 3).
The actual degree of change throughout the period
of study is uncertain, however, in that complete
records of catches for squid were not kept prior to
1967.

A summary of trends in relative abundance by
area is given in Tables 6 and 7 and Figure 10. We
computed percentage changes from mean catch
values (averaged over 1967-68 and 1973-74 for
Middle Atlantic strata and 1963-65 and 1972-74
for all other strata sets). We obtained declines of

FIGURE 7.— Catch of principal pelagic species in U.S. autumn
bottom trawl surveys for the Middle Atlantic (strata 61-76),
1967-74, and for southern New England (strata 1-12), Georges
Bank (strata 13-25), and the Gulf of Maine (strata 26-30 and
36-40), 1963-74.

CLARK and BROWN: CHANGES IN BIOMASS OF FINFISHES AND SQUIDS

M-ddle AltantK

— — So New England

Georges Bonk

Gulf of Mome

FIGURE 8. — Catch of other pelagics and other fish in U.S. au-
tumn bottom trawl surveys for the Middle Atlantic (strata GI-
TS), 1967-74, and for southern New England (strata 1-12),
Georges Bank (strata 13-25), and the Gulf of Maine (strata 26-30
and 36-40), 1963-74.

over 90% for certain species, while for all data
combined we obtained declines of 74%, 52%, 37%,
and 41% for the Middle Atlantic, southern New
England, Georges Bank, and Gulf of Maine areas,
respectively. Omission of catches of searobins for
the Middle Atlantic area, however, reduces that
value to 52%. Further omitting data for squid for
all strata sets (as squid catches were inadequately
recorded during the early years of the survey)
provides corresponding declines of 62% , 58% , 38% ,
and 41%. Consequently, even greater declines
may be more realistic than those initially com-
puted.

After examining data for the above strata sets,
we evaluated trends for the entire region by
combining data over all strata (Tables 8, 9) and
compared between means of initial and final
periods (1967-68/1973-74 data for all strata;
1963-65/1972-74 data, Middle Atlantic strata
excluded). For 1967-74, all strata (Table 8), we
observed a decline of 32%, while for 1963-74,

FIGURE 9. — Catch of squid in U.S. autumn bottom trawl surveys
for the Middle Atlantic (strata 61-76), 1967-74, and for southern
New England (strata 1-12), Georges Bank (strata 13-25), and the
Gulf of Maine (strata 26-30 and 36-40), 1963-74.

58 69

YEAR

FIGURE 10.— Catch of total finfish and squid in U.S. autumn
bottom trawl surveys for the Middle Atlantic (strata 61-76),
1967-74, and for southern New England (strata 1-12), Georges
Bank (strata 13-25), and the Gulf of Maine (strata 26-30 and
36-40), 1963-74.

Middle Atlantic strata excluded (Table 9), the
decline is 43% . The corresponding figures are 37%
and 46%, respectively, with squid omitted.

The above data demonstrate that significant
changes in biomass levels occurred in SA 5 and 6
after the early 1960's. It will be noted, however,
that the summaries presented above are biased by
"catchability" differences among species and do

FISHERY BULLETIN: VOL. 75, NO. 1

TABLE 6. — Stratified mean catch per tow (kilograms) for selected species, Albatross IV fall survey data, Middle
Atlantic (1967-68 and 1973-74) and southern New England (1963-65 and 1972-74) areas.1 Mean catch per tow values
represent simple averages of values given in Tables 2 and 3 for these areas and years.

Middle Atlantic

Southern New England

Species

1 967-68 mean

1973-74 mean

% change

1963-65 mean 1972-74 mean

% change

Principal groundfish:

Cod

0.0

1.7

0.8

-53

Haddock

0.0

3.7

20.0

-99

Silver hake

0.9

0.2

-78

2.8

-55

Red hake

0.5

0.1

-80

6.0

3.4

-43

Flounders:

Yellowtail

4.5

20.0

-99

10.8

10.2

- 6

Summer flounder

1.8

0.5

-72

0.5

0.9

+80

Winter flounder

1.5

0.1

-93

2.9

1.3

-55

Other

1.2

1.1

-8

3.3

1.8

-45

Other groundfish:

Angler

0.7

0.5

-29

5.4

4.5

-17

Ocean pout

20.0

- 0

0.5

0.1

-80

Sculpins

0.1

0.0

-100

1.0

0.8

-20

Scup

1.7

0.5

-71

1.5

1.6

Searobins

71.9

1.9

-97

0.7

1.7

+ 143

White hake

0.1

0.0

-100

0.8

0.2

-75

Other

0.3

20.0

-99

0.1

20.0

-99

Principal pelagics:

Herring

0.0

20.0

0.2

20.0

-99

Mackerel

0.1

0.0

-100

20.0

Other pelagics and other fish:

Butterfish

10.9

7.4

-32

4.4

4.9

+ 11

Spiny dogfish

25.5

20.0

-100

119.4

32.5

-73

Skates and rays

6.2

7.9

+ 27

12.5

5.1

-59

Other

8.4

6.4

-24

1.3

4.5

+246

Squid:

Short-finned squid

0.3

0.1

-67

0.1

0.3

+200

Long-finned squid

9.9

11.1

+ 12

1.4

11.8

+ 743

Total finfish and squid

146.5

37.8

-74

184.4

89.2

-52

'Middle Atlantic and southern New England areas represented by strata sets 61-76 and 1-12, respectively
2Less than 0.05.

TABLE 7. — Stratified mean catch per tow (kilograms) for selected species, Albatross IV fall survey data, Georges Bank
and Gulf of Maine areas,1 1963-65 and 1972-74. Mean catch per tow values represent simple averages of values given
in Tables 4 and 5 for these areas and years.

Georges Bank

Gult of Maine

Species

1963-65 mean

1 972-74 mean

% change

1963-65 mean

1 972-74 mean

% change

Principal groundfish:

Cod

8.4

12.8

+52

10.8

6.3

-42

Haddock

60.8

5.0

-92

22.0

3.5

-84

Redfish

2.0

2.8

+40

33.3

22.9

-31

Silver hake

2.9

2.1

-28

13.9

4.7

-66

Red hake

3.8

1.8

-53

2.2

1.0

-55

Pollock

2.0

1.0

-50

6.7

6.8

+ 1

Flounders:

American plaice

2.9

0.7

-76

5.3

2.4

-55

Yellowtail

7.4

3.4

-54

0.4

0.2

-50

Winter flounder

2.0

1.5

-25

0.4

0.3

-25

Witch

0.7

1.0

+43

2.8

1.7

-39

Other

0.8

2.2

+ 175

0.1

20.0

-99

Other groundfish:

Angler

3.7

1.6

-57

2.4

2.5

Cusk

0.3

0.2

-33

1.6

Ocean pout

1.2

0.2

-83

20.0

0.1

+474

Sculpins

2.8

2.7

-4

0.2

White hake

0.9

2.6

+ 189

6.9

15.6

+ 126

Other

0.2

0.3

+50

0.3

0.1

-66

Principal pelagics:

Herring

0.7

20.0

-99

0.6

20.0

-99

Mackerel

20.0

0.2

+ 300

20.0

Other pelagics and other fish:

Spiny dogfish

3.1

16.0

+416

26.9

11.1

-59

Skates and rays

22.7

19.9

-12

11.9

6.6

-45

Other

1.2

2.4

+ 100

0.8

0.2

-75

Squid:

Short-finned squid

0.4

1.8

+350

0.1

0.7

+600

Long-finned squid

0.4

1.1

+ 175

20.0

Total finfish and squid

131.3

83.3

-37

149.6

88.5

-41

'Georges Bank and Gulf of Maine areas represented by strata sets 13-25 and 26-30 and 36-40, respectively.
2Less than 0.05.

CLARK and BROWN: CHANGES IN BIOMASS OF FINFISHES AND SQUIDS

TABLE 8. — Stratified mean catch per tow (kilograms) for selected species of finfish and squid,
Albatross IV autumn bottom trawl survey data, 1967-74, Middle Atlantic, southern New
England, Georges Bank, and Gulf of Maine (strata 61-76, 1-30, and 36-40).

Species

1967

1968

1969

1970

1971

1972

1973
6.4

19 74

Cod

4.5

4.4

5.1

6.4

2.9

Haddock

8.1

5.8

4.0

2.4

2.2

3.3

1.3

Redfish

8.2

136

7.9

11.1

7.9

8.3

5.7

7.7

Silver hake

2.3

2.5

1.8

2.0

2.4

3.6

2.6

1.9

Red hake

1.0

1.6

1.8

1.3

1.7

2.6

1.6

0.7

Pollock

1.2

1.9

4.2

1.2

2.2

2.7

2 1

Yellowtail

4.8

5.6

5.2

1.0

Other flounder

4.6

5.4

5.1

3.5

4.3

4.2

3.5

Herring

0.3

0.1

'0.0

0.3

0.1

'0.0

Mackerel

1.1

'0.0

0.1

'0.0

Other finfish2

809

47.1

892

493

33.6

43.3

54.5

27.4

Short-finned squid

0.2

0.3

0.1

0.3

0.4

0.3

0.4

Long-finned squid

2.8

5.1

6.8

2.1

4.6

5.8

Total finfish and squid

119.2

94.2

131.5

85.8

64 0

86.4

89.9

54.4

'Less than 0.05.

2Does not Include data for tunas, sharks, swordfish, American eel. or white perch.

TABLE 9. — Stratified mean catch per tow (kilograms) for selected species of finfish and squid, Albatross IV autumn bottom trawl
survey data, 1963-74, southern New England, Georges Bank, and Gulf of Maine areas (strata 1-30 and 36-40).

Species

1963

1964

1965

1966

1967

1968

1969

1970

1971

1972

1973

1974

Cod

8.5

7.6

5.6

4.8

5.7

6.4

5.6

6.4

5.7

8.1

3.6

Haddock

31.6

31.2

229

10.5

10.2

7.4

4.7

5.1

3.1

2.8

1.6

Redfish

10.3

23.1

5.8

12.4

10.4

17.1

10.0

14.0

10.0

10.5

7.2

100

Silver hake

13.8

4.1

6.1

3.3

2.7

2.9

2.4

4.4

3.2

2.4

Red hake

6.7

2.3

2.7

1.6

1.2

1.8

2.1

1.6

2.0

3.2

2.0

0.8

Pollock

4.1

3.6

1.9

1.8

1.5

2.3

5.3

1.5

2.7

3.4

2.7

2.2

Yellowtail

6.6

6.5

4.5

3.2

5.2

5.6

5.3

3.6

2.1

Other flounder

6.1

6.7

4.6

5.6

5.8

4.0

5.1

4.8

4.0

Herring

1.0

0.1

0.5

1.2

0.4

0.1

'0.0

0.1

Mackerel

'0.0

0.1

0.4

0.2

1.4

0.1

0.2

0.1

Other finfish2

75.6

89.4

61.8

629

49.8

45.8

97.5

55.5

33.7

49.4

599

306

Short-finned squid

(3)

'"0.0

"0.1

0.2

0.4

0.1

0.3

0.4

0.3

0.4

Long-finned squid

(3)

"0.5

"0.8

"1.0

0.8

4.0

6.2

1.5

2.0

2.5

6.7

4.5

Total finfish and squid

167.0

174.5

119.5

112.1

93.1

99.6

146.6

100.1

70.5

99.8

101.3

61.6

'Less than 0.05.

2Does not include data for tunas, sharks, swordfish. American eel, or white perch

3Data not recorded.

"Squid catches for 1964-66 prorated by species according to relative percentages caught in later years.

not reflect the relative magnitude of various
species within the biomass as a whole. For in-
stance, herring and mackerel together appear to
have constituted over 50% of the biomass present
during this study (Edwards 1968; International
Commission for the Northwest Atlantic Fisheries
1974e, footnote 17) yet account for less than 1% of
the weight taken in autumn bottom trawl surveys.
Furthermore, the aggregated distribution of
finfishes and squid in nature, and the behavior of
the gear employed, insure that catch data for
individual species will seldom be normally dis-
tributed but rather will tend to conform to the
negative binomial or some other contagious form
(Taylor 1953). In the following sections, we utilize
selected transformation and weighting procedures
in attempts to correct for these factors.

^International Commission for the Northwest Atlantic
Fisheries. 1975. Report of the herring working group, April
1975. ICNAF Annu. Meet. 1975, Summ Doc. No. 19, Serial No.
3499 (mimeo.), 31 p.

Weighted Analyses

Catchability differences among species imply
that trends in biomass as defined in this study will
be primarily determined by trends for species most
vulnerable to the survey gear unless adjustments
in terms of catchability are made. Accordingly, we
developed catchability coefficients by year for the
species and species groups in Tables 8 and 9 for use
in computing weighting factors by relating
stratified mean catch per tow by stock to available
estimates of stock size, all computations being in
terms of weight. Annual estimates of stock size
(weight at the beginning of year i) were required
for this purpose for each individual stock for which
TAC's have been established (International
Commission for the Northwest Atlantic Fisheries
1975c); thus, separate estimates were required for
cod in 5Y18 and 5Z, haddock in 5Ze, silver hake in

18Alphanumeric designations refer to divisions and sub-
divisions of SA 5 and 6 given in Figure 1.

FISHERY BULLETIN: VOL. 75, NO. 1

5Y, 5Ze, and 5Zw-SA 6, red hake in 5Ze and
5Zw-SA 6, yellowtail in 5Ze, 5Zw, and SA 6, and
herring in 5Y and 5Z-SA 6. (We considered the
remaining species and species groups indicated as
stocks for the purpose of this analysis.) Silver
hake, herring, and mackerel stock sizes were
available from virtual population analyses in
previous assessments (International Commission
for the Northwest Atlantic Fisheries 1974e, see
footnote 17; Anderson19,20), while annual esti-
mates for haddock and red hake had also been
computed earlier (Hennemuth see footnote 5;
Anderson21; Clark22) using average weight or
mean weight at age data and the relationship:

calculated stock size for each year using Equation
(3); 1964-66 stock sizes were then assumed to be
similar to the 1967-68 average as commercial
abundance indices were stable through this
period. We then obtained values for succeeding
years by adjusting the 1967-68 average by stock
abundance indices based on pre-recruit survey
catches (Brown and Hennemuth see footnote 6;
Parrack23), i.e.,

Stock size in year i = Mean stock size for 1967-68

Abundance index for year i
Mean abundance index for 1967-68

(4)

Ct =N,Fl/Zl(l - expt-ZJ)

(3)

where Ct = landings (number) in year i,

Nt = stock size ( number) at the beginning of

year i,
F- = instantaneous fishing mortality rate

in year i, and
Z = instantaneous total mortality rate in
year i ( =Ft + M, the instantaneous
natural mortality rate).

Approximations of stock size for both long-
finned and short-finned squids are also available
for recent years ( International Commission for the
Northwest Atlantic Fisheries 1975c). We used
these approximations for all years in view of
uncertainty regarding stock size and historical
trends in abundance for these species (Interna-
tional Commission for the Northwest Atlantic
Fisheries 1975c).

Stock size estimates for the remaining species
and species groups are currently unavailable, and
we computed estimates by a variety of procedures.
For yellowtail, we assumed an F value of 1.0 for
the southern New England (5Zw) stock in 1967-68
(M = 0.2 in all cases) based on earlier assessment
work (Brown and Hennemuth see footnote 6), and

19Anderson, E. D. 1975. Assessment of the ICNAF Division 5Y
silver hake stock. Int. Comm. Northwest Atl. Fish. Annu. Meet.
1975, Res. Doc. No. 62, Serial No. 3544 (mimeo.), 13 p.

20Anderson, E. D. 1975. Assessment of the ICNAF Subdivision
5Ze and Subdivision 5Zw-Statistical Area 6 silver hake stocks.
Int. Comm. Northwest Atl. Fish. Annu. Meet. 1975, Res. Doc. No.
94, Serial No. 3574 (mimeo.), 17 p.

"Anderson, E. D. 1974. Assessment of red hake in ICNAF
Subarea 5 and Statistical Area 6. Int. Comm. Northwest Atl.
Fish. Annu. Meet. 1974, Res. Doc. No. 19, Serial No. 3165
(mimeo.), 27 p.

22Clark, S. 1975. Current status of the Georges Bank (5Ze)
haddock stock. Int. Comm. Northwest Atl Fish. Annu. Meet.
1975, Res. Doc. No. 48, Serial No. 3527 (mimeo.), 9 p.

For an estimate of SA 6 stock size, we obtained
values for the 1963-66 period by multiplying the
computed average stock size value for southern
New England by the ratio between mean survey
abundance indices between the SA 6 and southern
New England stock areas and the ratio between
the actual bottom areas considered; we obtained
the remaining values using stock abundance
indices (Parrack see footnote 23) as above. For the
Georges Bank (5Ze) stock, we assumed an F value
of 0.8 in 1964 and 1965 (Brown and Hennemuth
see footnote 6), calculated stock sizes by Equation
(3), and averaged these values to obtain an initial
estimate; we then adjusted this value by means of
commercial abundance indices (Brown and
Hennemuth see footnote 6; Parrack see footnote
23) according to Equation (4) to obtain estimates
for later years. The Cape Cod yellowtail stock was
considered to have been relatively stable in recent
years; we computed an estimate for 1969 by
Equation (3) assuming an F value of 0.8 and added
the resulting value to each Georges Bank stock
size estimate to obtain combined estimates for the
Georges Bank area.

We obtained stock size estimates for the re-
maining stocks from Equation (3) using available
estimates of F and M and historical catch data
(International Commission for the Northwest
Atlantic Fisheries 1965-1973, 1974c, 1975a, see
footnote 12). We computed an average stock size
for the entire 1965-75 period for 5Y cod using
mortality rates reported by Penttila and Gifford24,

23Parrack, M. L. 1974. Status review of ICNAF Subarea 5 and
Statistical Area 6 yellowtail flounder stocks. Int. Comm.
Northwest Atl. Fish. Annu. Meet. 1974, Res. Doc. No. 99, Serial
No. 3335 (mimeo.), 17 p.

24Penttila, J. A., and V. M. Gifford. 1975. Growth and mortal-
ity rates for cod from the Georges Bank and Gulf of Maine areas.
Int. Comm. Northwest Atl. Fish. Annu. Meet. 1975, Res. Doc. No.
46, Serial No. 3525 (mimeo.), 13 p.

CLARK and BROWN: CHANGES IN BIOMASS OF FINFISHES AND SQUIDS

while for 5Z cod we computed an average figure for
the 1970-75 period using mortality rates from the
above paper and obtained values for the remain-
ing years by adjusting this average by commercial
abundance indices reported by Brown and
Heyerdahl.25 We followed an analogous procedure
in the case of "other finfish" by computing a value
for 1967 (chosen to be in the middle of the period)
assuming an F value of 0.4 and M = 0.2; we then
calculated commercial abundance indices from
historical catch data and total effort estimates for
SA 5 and 6 (Brown et al. in press) and obtained
stock size estimates for the remaining years by
adjusting the 1967 value by means of these
abundance indices according to Equation (4), as
above. For redfish, other flounders, and pollock, we
computed average values from Equation (3) using
available sustainable yield estimates and as-
sumed values of F, as follows (M = 0.2 in all cases):

Sustainable

yield estimate

Species

Period

(tons x 10'3)

Redfish

1964-75

16 (Mayo26)

0.4

Other flounders

1964-69

0.7

Other flounders

1970-75

0.9

Pollock

1964-75

2716

0.4

Turning to survey abundance indices, an in-
herent problem in any analysis of trawl data lies
in the fact that the computed means and variances
are seldom, if ever, independent. The present data
are no exception; Grosslein (1971) has found that
in the present survey individual stratum var-
iances are approximately proportional to the
squares of the stratum means, indicating that a
logarithmic transformation is appropriate (Steel
and Torrie 1960). Under these conditions, use of a
logarithmic scale transformation tends to nor-
malize the data and render means and variances
independent, thereby permitting use of paramet-
ric statistical methods (obviously, anomalous
fluctuations in observed trends are also reduced

25Brown, B. E., and E. G. Heyerdahl. 1972. An assessment of
the Georges Bank cod stock (Div. 5Z). Int. Comm. Northwest Atl.
Fish. Annu. Meet. 1972, Res. Doc. No. 117, Serial No. 2831
(mimeo.), 24 p.

26Mayo, R. K. 1975. A preliminary assessment of the redfish
fishery in ICNAF Subarea 5. Int. Comm. Northwest Atl. Fish.
Annu. Meet. 1975, Res. Doc. No. 59, Serial No. 3541 (mimeo.),
31 p.

"Pollock in ICNAF Divisions 4VWX, Subarea 5, and Statis-
tical Area 6 are currently considered as a unit stock. Accord-
ingly, this figure represents the SA 5 and 6 proportion of the
estimated sustainable yield for this stock as determined from
historical catch data.

considerably). Accordingly, we computed strati-
fied mean catch per tow values for all stocks using
In (kilograms + 1) values for each tow; strata sets
used are given by species and stock in Table 10. We
then computed estimates of stratified mean catch
per tow in original units by retransforming as
suggested by Bliss (1967:128) according to the
relation:

E(yst) = exp (yst + S2/2)

(5)

where E(yst) represents the estimated (re-
transformed) stratified mean catch per tow andys,
and S2 represent the stratified mean and the
estimated population variance, respectively, in
logarithmic units, computed as in Equations (1)
and (2) above. We also calculated untransformed
(yst) values for the stocks and strata sets in Table
10 for comparative purposes.

After obtaining stock size estimates and
abundance indices as described above, we com-
puted catchability coefficients for all years by
dividing both untransformed and retransformed
stratified mean catch per tow for year i by the
appropriate stock size value at the beginning of
year i + 1 (or by the computed average stock size).
Deviations from the arithmetic mean were then
plotted by year; where trends were apparent,

TABLE 10. — Strata sets used in computing stratified mean catch
per tow values by stock.

Strata sets

Middle Atlantic

Southern New

Species and stock

north'

England north2

Cod

5Y3

26-30, 36-40

5-30, 36-40

Haddock

5Ze

13-25

Redfish

18, 22, 26-30, 36-40

1-30,36-40

Silver hake

26-30, 36-40

5Ze

13-25

5Zw-6

61-76, 1-12

1-12

Red hake

5Ze

13-25

5Zw-6

61-76, 1-12

1-12

Pollock

61-76, 1-30, 36-40

1-30, 36-40

Yellowtail

5Ze

13-25

5Zw

5-12

69-76, 1-4

1-4

Other flounders

61-76, 1-30, 36-40

1-30. 36-40

Herring

26-30, 36-40

5Z-6

63-76, 1-25

1-25

Mackerel

61-76, 1-30, 36-40

1-30, 36-40

Other finfish

61-76, 1-30, 36-40

1-30, 36-40

Short-finned squid

61-76, 1-30, 36-40

1-30, 36-40

Long-finned squid

61-76, 1-30, 36-40

1-30, 36-40

'Strata for the Middle Atlantic area
2Since 1963 (strata 1-40).
Alphanumeric designations refer to
shown in Figure 1 .

(61-76) added in 1967.

divisions and subdivisions of SA 5 and 6

FISHERY BULLETIN: VOL. 75, NO. 1

linear regressions were fitted to the data to
evaluate the degree of relationship. A significant
(P<0.01) negative trend was obtained for haddock
for both untransformed and retransformed data
(Figure 11). This could have resulted from over-
estimates of stock size in later years or actual
differences in catchability associated with
changing availability as stock size decreased. A
plot of numbers captured per tow by year during
the period of study suggested that actual dif-
ferences in catchability may have occurred (Fig-
ure 11); accordingly, we divided the period of study
into two units (1963-68 and 1969-74) for the
purpose of calculating weighting coefficients for
the species. The dividing line was taken as the
point in which the percentage of tows containing
five haddock or less reached 90%.

In the case of species for which more than one
stock had been defined, some question existed as to

whether coefficients should be computed for the
entire species or on a stock basis. As no consistent
trends had been found for these species over time,
one-way analysis of variance was used to test for
differences between stocks, using years as repli-
cate observations. These tests revealed significant
differences (P<0.05) between individual stocks for
all species except yellowtail (i.e., cod, silver and
red hake, and herring). We therefore retained
individual stocks as discrete units in computing
biomass declines (i.e., no attempt was made to
combine stocks on a species basis).

After obtaining the desired sets of catchability
coefficients for all stocks, we obtained weighting
coefficients by calculating arithmetic means of
untransformed and retransformed sets (Tables 11,
12), using the entire set except in the case of
haddock as explained above. We then computed
biomass estimates by year, viz.

TABLE ll. — Weighting coefficients calculated by stock from untransformed and retrans-
formed survey data, 1967-74, Middle Atlantic, southern New England, Georges Bank, and
Gulf of Maine area (strata 61-76, 1-30, and 36-40).

Calculated from

Species

Untransformed data

Retransformed data'

and

Weighting

Coefficient

Weighting

Coefficient

stock2

coefficient3

of variation4

coefficient3

of variation4

Cod:

39.954

0.31

44.545

0.44

5.160

0.52

3.433

0.50

Haddock5:

5Ze

14.146, 10.193

0.25, 0.46

15.591, 7.461

0.71, 0.56

Redfish

40.063

0.29

49.188

0.32

Silver hake:

8.714

0.80

8.348

0.94

5Ze

0.727

0.30

0.650

0.31

5Zw-6

1.325

0.33

1.101

0.40

Red hake:

5Ze

6.565

0.65

5.384

0.74

5Zw-6

2.341

0.74

1.422

0.71

Pollock

4.069

0.45

1.442

0.37

Yellowtail:

5Ze

17.391

0.24

15.106

0.31

5Zw

45.722

0.79

42.229

0.70

67.795

0.95

39.969

076

Other flounders

10.897

0.18

11.134

0.17

Herring:

0.125

>1.0

0.039

0.97

5Z-6

0.010

>1.0

0.002

0.75

Mackerel

0.015

>1.0

0.005

0.57

Other finfish

12.809

0.31

14.553

0.14

Short-finned squid

0.302

0.37

0.206

0.34

Long-finned squid

5.240

046

4.302

0.65

'Estimated stratified mean catch per tow values computed from transformed data according to the relation,
E(yst) = oxp(yst +S2/2), where yst and S2 represent the mean and estimated population variance, respectively,
on the transformed scale.

2Weighting coefficients calculated by individual stock for cod, haddock, silver hake, red hake, yellowtail, and
herring: stock areas are given in Figure 1 . Stock areas for the remaining species are equivalent to all strata in SA
5 and 6 covered during 1967-74.

/TiM+i]

3Weighting coefficients calculated as n where C, = stratified mean catch per tow (tons) in year/

and S/ + 1 = stock size at the beginning of the following year. All values x 108.

Coefficient of variation calculated over all years.

5Weighting coefficients computed separately for 1967-68 and 1969-74 data due to apparent changes in
catchability.

CLARK and BROWN: CHANGES IN BIOMASS OF FINFISHES AND SQUIDS

46 613

LINEAR

. RETRANSFORMED

1963 64

73 1974

1963

n - 57

_lm_ „b«hJ

1964

n =63

1965

n ■ 66

1966

n - 67

1967

n • 67

)- 1968

)-■ n>69

3 ^2 g g ? Si e 88
^ii i ii i 7 i

^ ~- (\j O V J1 10 ^

1969

II.

n = T3

1970

ll.

n =70

1971

Il—

n .73

1972

n =73

1973

■

n =73

1974

1..

n .74

o m o o o g

1 — (SJ (O ^

i. i i I I

O <f O O -f

"1 f- O O =

i i 7 ~ 8

""go

FIGURE 1 1 .—(Top) Trends in catchability coefficients
calculated by year using untransformed and re-
transformed survey data, and (bottom) distributions
of stratified mean catch per tow in numbers expressed
as relative percentages of the total number of survey
tows by year for Georges Bank haddock.

NUMBERS /TOW

FISHERY BULLETIN: VOL. 75, NO. 1

TABLE 12. — Weighting coefficients calculated by stock from untransformed and retrans-
formed survey data, 1963-74, southern New England, Georges Bank, and Gulf of Maine
area (strata 1-30 and 36-40).

Calculated from

Species
and

Untransformed data

Retransformed data1

Weighting
coefficient

Coefficient

Weighting

Coefficient

stock2

of variation4

coefficient

of variation4

Cod:

42.877

0.31

41 000

0.41

4.918

0.46

3.462

0.47

Haddock5:

5Ze

20.696, 10.193

0.36, 0.46

38.857, 7.461

0.63, 0.56

Redfish

42.776

0.41

46.898

0.34

Silver hake:

7.948

0.79

8.205

0.94

5Ze

0.814

0.49

0.724

0.46

5Zw-6

2.122

0.32

2.116

0.37

Red hake:

5Ze

6.503

0.69

5.380

0.77

5Zw-6

3.644

0.68

3.070

0.62

Pollock

5.174

0.41

2.279

0.46

Yellowtail:

5Ze

17.143

0.28

15.221

0.38

5Zw

39 399

0.77

40.716

0.62

104.145

>1.00

121.231

>1.00

Other flounders

13.016

0.22

14.293

0.25

Herring:

0.178

>1.00

0095

>1.00

5Z-6

0.027

>1.00

0 005

0.94

Mackerel

0 015

>1.00

0 006

056

Other finfish

12.569

0.31

13.648

0.18

Short-finned squid

0 254

0.70

0.177

0.63

Long-finned squid

3.124

0.80

2.099

>1.00

1 Estimated mean catch per tow values computed from transformed data according to the relation, E(yst) =
exP(ysf + S2/2), where yst and S2 represent the mean and estimated population variance, respectively, on the
transformed scale.

2Weightmg coefficients calculated by individual stock for cod, haddock, silver hake, red hake, yellowtail, and
herring, stock areas are given in Figure 1 Stock areas for the remaining species are equivalent to all strata in SA
5 and 6 covered during 1967-74

/=1 [CA+l]

3Weightmg coefficients calculated as ^ where C, = stratified mean catch per tow (tons) in year/

and S, + 1 = stock size at the beginning of the following year All values « 108.

Coefficient of variation calculated over all years

5Weighting coefficients computed separately for 1967-68 and 1969-74 data due to apparent changes in
catchability

k
1

Cv/Wj

.7 = 1 L-

for all i

(6)

where Cy refers to stratified mean catch per tow for
the 7th stock in the itb. year and Wj refers to the
weighting coefficient for thejth stock (Tables 13,
14), summation being over k stocks. For the
purposes of this paper, we consider each computed
estimate as representing stock size at the begin-
ning of the year following collection of the survey
data (i + 1), as catchability coefficients were
calculated by relating catch per tow values in
autumn of year i to stock size at the beginning of
year i + 1 (above). Note that with the exception of
1970 figures for "all data" (Tables 13, 14), values
computed from retransformed data agree
reasonably well with those computed from un-
transformed values; consequently the general

appropriateness of assuming a lognormal dis-
tribution for these data is confirmed.

The average stock size estimate for 1964-66
obtained for all species of 5.0 x 106 tons (Table 14)
is almost identical to that obtained by Edwards
(1968) for the same area and period (5.1 x 106

TABLE 13.— Stock size estimates (tons x 10 3) for ICNAF Sub-
area 5 and Statistical Area 6, 1967-74, Middle Atlantic, southern
New England, Georges Bank, and Gulf of Maine, inclusive
(strata 61-76, 1-30, and 36-40).

Calculated with

Untransformed data

Retransformed data

All

Data for principal

All

Data for principal

Year

data

pelagics excluded

data

pelagics excluded

1968

7,481

1,783

8,012

1,806

1969

3,826

1,795

5,209

1,880

1970

9,555

1,859

5,158

1,750

1971

2,097

1,567

2,964

1,736

1972

3,156

1,331

3,062

1,418

1973

3,136

1.870

3,661

1,825

1974

2,098

1,841

2,541

1,760

1975

1,828

1.107

1,934

1.119

CLARK and BROWN: CHANGES IN BIOMASS OF FINFISHES AND SQUIDS

TABLE 14.— Stock size estimates (tons x 10 3) for ICNAF Sub-
area 5 and Statistical Area 6, 1963-74, southern New England,
Georges Bank and Gulf of Maine, inclusive (strata 1-30 and
36-40).

Calculated with

Untransformed data

Retransformed data

All

Data for principal

All

Data for principal

Year

data

pelagics excluded

data

pelagics excluded

1964

6.616

3,317

7,357

3,640

1965

2.780

2,373

2.677

2.151

1966

5,079

2,088

5,382

2.184

1967

8.331

1.610

7.770

1,605

1968

6,056

1,478

6.431

1,493

1969

3.400

1.787

4,238

1.763

1970

1 1 .490

2.012

5,158

1.867

1971

2,174

1.642

2.828

1.759

1972

2.644

1,411

2.751

1,501

1973

3.231

1.964

3.622

1.937

1974

2.371

2.009

2,717

1.931

1975

2,036

1.217

1.981

1.165

tons). Edwards obtained biomass estimates by
adjusting minimum biomass figures for each
species by a factor accounting for differences in
availability and vulnerability, and although
estimates obtained for individual species by these
methods differed in certain cases it can be seen
that, on the average, results are quite comparable.

The data of Tables 13 and 14 again reveal
pronounced declines. In Table 13 (1968-75, all
strata) comparisons of averages for "all data"
between 1968-69 and 1974-75 reveal a 65% decline
for untransformed data and a 66% decline in the
case of retransformed values; with principal
pelagics excluded, the corresponding figures are
18 and 22%, respectively. In Table 14 (1964-75,
Middle Atlantic strata excluded) comparisons
between averages for "all data" for 1964-66 and
1973-75 reveal declines of 47% and 46% for un-
transformed and retransformed values, respec-
tively, while with principal pelagics excluded the
corresponding figures were 33% and 37%. The
greater decrease for the 1968-75 period for "all
data" might appear somewhat anomalous but
actually results primarily from appearance of the
outstanding 1967 mackerel year class.

As the estimates in Tables 13 and 14 purport to
measure declines in biomass in SA 5 and 6, it
might logically be argued that they could be
combined in some way (use of the 1968-75 data
would be preferable in that survey coverage
extended further to the south). Paired £-tests
indicated no differences between corresponding
stock size estimates in Tables 13 and 14 for the
1968-75 period. Therefore, we combined the
1968-75 estimates in Table 13 with the 1964-67
estimates in Table 14 (Figures 12, 13) and
computed percentage changes between the means

of the 1964-66 and 1973-75 periods, as before. For
"all data," we obtained declines of 51% and 47%
with untransformed and retransformed values;
with herring and mackerel excluded, the cor-
responding figures were 38% and 41%.

Analysis of both untransformed and re-
transformed data yield essentially similar results.
The data of Figures 12 and 13 illustrate the ef-
fectiveness of the transformation in reducing
anomalies caused by variability in the data. For
untransformed estimates (Figure 12) it will be

£ 4.000

FIGURE 12 — Estimates of fishable biomass by year for ICNAF
Subarea 5 and Statistical Area 6, 1964-75, calculated with un-
transformed survey data. Curves were plotted by combining
1968-75 estimates from Table 13 with 1964-67 estimates from
Table 14.

1 1

9.000

^^— Alldolo

Dolo »0f pr-incipoi pdog-cs eicluded

7,000

6.000

5 DOC

4,000

3.000

\ *

2,000

*"--. ____

... ^,- ..

1,000

1 1 I 1 i _J

FIGURE 13.— Estimates of fishable biomass by year for ICNAF
Subarea 5 and Statistical Area 6, 1964-75, calculated with
retransformed survey data. Curves were plotted by combining
1968-75 estimates from Table 13 with 1964-67 estimates from
Table 14.

FISHERY BULLETIN: VOL. 75, NO. 1

noted that an anomalous peak occurs in 1970,
which examination of biomass estimates on a per-
species basis revealed to have been caused by
anomalously high mackerel catches in certain
tows during the 1969 survey. The influence of this
factor appears to have been compensated for by
use of the logarithmic transformation (Figure 13).
On the other hand, the anomalously low data point
for 1965 (Figures 12, 13) appears to have been
caused by anomalously low catches of herring in
that year, a circumstance in which the trans-
formation was ineffective. It does appear, how-
ever, that by and large the transformation was of
definite value in following trends through time,
although estimates for most of the years consid-
ered proved to be similar.

The above analyses clearly indicate that
biomass levels have decreased significantly in SA
5 and 6 in recent years; the trend observed cor-
relates well with increases in fishing effort ob-
served by Brown et al. (in press). In addition, we
have also found evidence indicating that major
changes in species composition have occurred as
well. The apparent increase in white hake
abundance in the Gulf of Maine in recent years
(Table 5) could have resulted from population
increases in response to reductions in other
groundfish species. Similarly, increased mackerel
abundance coincident with declining abundance
of herring (Tables 3, 4) may indicate some form of
species interaction coincident with exploitation,
while apparent increases in abundance of squid
(Tables 2-7, Figure 9) may have occurred in re-
sponse to declining abundance of finfish species.
The relationships involved are unclear at present
and further study is obviously necessary.

Comparisons of annual landings data since 197 1
(over 1.0 x 106 tons) with biomass estimates in
Tables 13 and 14 indicate that the fraction of the
biomass harvested annually has increased sig-
nificantly in recent years (i.e., from less than one-
fifth of the total in the early and mid-1960's to
between one-third and one-half of the total at
present). Furthermore, landings since 1971 have
exceeded the composite MSY figure of 950 x 103
tons calculated by Brown et al. (in press) based on
the Schaeffer yield model. This information,
together with declines in stock size approximating
50% as indicated in this paper, imply that a
significant degree of overfishing has occurred and
that stock size has been reduced below the level
corresponding to MSY. Back-calculations for all
species in Tables 13 and 14 provide an average

stock size estimate of approximately 7.0 x 106tons
prior to 1964, from which (allowing for the U.S.
coastal fishery in previous years) it may be in-
ferred that the actual virgin biomass for this
fishery probably approximated 8.0-9.0 x 106 tons.
Since the Schaeffer yield model postulates that
MSY will be taken at a stock level corresponding
to one-half the maximum (Schaeffer 1954), we
may in turn assume that a stock level of ap-
proximately 4.0-4.5 x 106 tons should be main-
tained for SA 5 and 6 if MSY from this resource is
to be achieved. In contrast, estimates for fishable
biomass in the present paper approximate 2.0 x
106 tons at the start of 1975, implying that a
lengthy period of reduced exploitation is necessary
if stocks are to be rebuilt to the MSY level.

In April 1975, the Assessments Subcommittee
(STACRES) reviewed evidence relating to de-
clines in biomass in SA 5 and 6 in recent years and
concluded that substantial reductions in catch
would be necessary if stocks are to recover (In-
ternational Commission for the Northwest At-
lantic Fisheries 1975c). Accordingly, a TAC of 650
x 103 tons was recommended to ICNAF and
approved at the Seventh Special Commission
Meeting (International Commission for the
Northwest Atlantic Fisheries 1975b) in Sep-
tember. Even with a reduction of this magnitude,
STACRES estimated that a minimum of 7 yr
would be required for this resource to recover to
the MSY point.

ACKNOWLEDGMENTS

We thank Judith Brennan for her helpful
comments and suggestions on data analysis,
Kathryn Paine for her assistance with computer
programming, and Elizabeth Bevacqua and
Maureen Romaszko for numerous tabulations of
the data. Richard C. Hennemuth reviewed the
manuscript and made suggestions for im-
provement. The work of the numerous biologists
and technicians who have participated in Alba-
tross IV autumn bottom trawl surveys and the
processing of the sample data since the beginning
of the program is also sincerely appreciated.

LITERATURE CITED

ANTHONY, V. C, AND H. C. BOYAR.

1968. Comparison of meristic characters of adult Atlantic
herring from the Gulf of Maine and adjacent waters. Int.
Comm. Northwest Atl. Fish. Res. Bull. 5:91-98.

CLARK and BROWN: CHANGES IN BIOMASS OF FINFISHES AND SQUIDS

Bliss, C. I.

1967. Statistics in biology; statistical methods for research
in the natural sciences, Vol. I, 558 p. McGraw-Hill, N.Y.

BROWN, B. E., J. A. BRENNAN, E. G. HEYERDAHL, M. D.
GROSSLEIN, AND R. C. HENNEMUTH.

In press. The effect of fishing on the marine finfish biomass
in the Northwest Atlantic from the eastern edge of the
Gulf of Maine to Cape Hatteras. Int. Comm. Northwest
Atl. Fish. Res. Bull. 12.
Cochran, w. G.

1953. Sampling techniques. John Wiley & Sons, Inc., N.Y.,
330 p.
EDWARDS, R. L.

1968. Fishery resources of the North Atlantic area. In D.
Gilbert (editor), The future of the fishing industry of the
United States, p. 52-60. Univ. Wash. Publ. Fish., New
Ser., 4.

GROSSLEIN, M. D.

1962. Haddock stocks in the ICNAF convention area. Int.
Comm. Northwest Atl. Fish. Redbook 1962, Part III, p.
124-131.

1969. Groundfish survey program of BCF Woods Hole.
Commer. Fish. Rev. 31(8-9):22-35.

1971. Some observations on accuracy of abundance indices
derived from research vessel surveys. Int. Comm.
Northwest Atl. Fish. Redbook 1971, Part III, p. 249-
266.
INTERNATIONAL COMMISSION FOR THE NORTHWEST ATLAN-
TIC FISHERIES.

1953-1973. Statistical Bulletin 1-21.
1974a. Proceedings, Third Special Commission Meeting,
October 1973. ICNAF Proceedings 1974, p. 4-34.

1974b. Proceedings, 24th Annual Meeting, June 1974.

ICNAF Proceedings 1974, p. 107-256.
1974c. Statistical Bulletin 22, 239 p.
1974d. Report of the Standing Committee on Research and

Statistics, October 1973. ICNAF Redbook 1974, p. 5-8.
1974e. Report of the Standing Committee on Research and

Statistics, May-June 1974. ICNAF Redbook 1974, p. 63-

142.
1975a. Statistical Bulletin 23, 277 p.
1975b. Proceedings, Seventh Special Commission Meeting,

September 1975.
1975c. Report of the Standing Committee on Research and

Statistics (STACRES), Annual Meeting-May-June 1975.

ICNAF Redbook 1975, p. 11-111.
ODUM, E. P., AND A. E. SMALLEY.

1959. Comparison of population energy flow of a herbivorous
and a deposit-feeding invertebrate in a salt marsh
ecosystem. Proc. Natl. Acad. Sci. 45:617-622.

SCHAEFFER, M. B.

1954. Some aspects of the dynamics of populations impor-
tant to the management of the commercial marine
fisheries. Bull. Inter- Am. Trop. Tuna Comm. 1:27-56.

Steel, R. G. D., and J. H. Torrie.

1960. Principles and procedures of statistics with special
reference to the biological sciences. McGraw-Hill, N.Y.,
481 p.

Taylor, C. C.

1953. Nature of variability in trawl catches. U.S. Fish Wildl.

Serv., Fish. Bull. 54:145-166.
WISE, J. P.

1962. Cod groups in the New England area. U.S. Fish Wildl.

Serv., Fish. Bull. 63:189-203.

LARVAL TRANSPORT AND YEAR-CLASS STRENGTH OF ATLANTIC
MENHADEN, BREVOORTIA TYRANNUS1

Walter R. Nelson,2 Merton C. Ingham,3 and William E. Schaaf2

ABSTRACT

A Ricker spawner-recruit model was developed for Atlantic menhaden, Brevoortia tyrannus, from data
on the 1955-70 year classes. The number of eggs produced by the spawning stock was calculated as the
independent variable to account for changes in fecundity due to changes in population size and age
structure. A survival index was developed from deviations around the Ricker curve and was regressed
on several environmental parameters to determine their density-independent effects. The recruit-
environment model accounted for over 84% of the variation in the survival index. Zonal Ekman
transport, which acts as a mechanism to transport larval menhaden from offshore spawning areas to
inshore nursery grounds, was the most significant parameter tested. Ricker functions for good and poor
environmental years were developed, indicating the wide range of recruitment that can be expected at
different stock sizes. Comparisons of spawner-recruit relations for Pacific sardine and Atlantic
menhaden indicated striking similarities. Surplus yield for the Atlantic menhaden fishery was cal-
culated from observed and predicted survival, and compared with the actual performance of the fishery.

One of the more intriguing and important prob-
lems in fishery science, that of the relative
influence of spawning stock size and environ-
mental variation on year-class strength, has
resulted in a long-standing controversy among
fishery biologists. The two principal reasons for
investigating the effects of stock size and en-
vironmental change on year-class strength are, of
course, to understand what has happened and to
predict what will happen. Since environmental
conditions will produce varying recruitment at a
given stock size, one must determine both the
reproductive potential under average en-
vironmental conditions, i.e., the density-
dependent spawner-recruit curve, and the effect of
varying environmental conditions, or the
density-independent function. The difficulty
comes, as Clark and Marr (1955) point out, in
separating the relative influences of the two
functions. A prerequisite for such an attempt is a
reliable long-term series of data, adequate to
estimate the size of the spawning stocks, the
number of recruits, the age structure of the
populations, the patterns of environmental var-
iation, and the rate at which the resource is being
harvested.

"MARMAP Contribution No. 88.

2Atlantic Estuarine Fisheries Center, National Marine
Fisheries Center, NOAA, Beaufort, NC 28516.

3Atlantic Environmental Group, National Marine Fisheries
Service, NOAA, Narragansett, RI 02882.

Biologists are in general agreement that the
most critical survival period for many marine
fishes is during the time of egg and larval drift.
Major factors affecting survival during this period
are food (Cushing 1969), cannibalism by filter-
feeding parents (Radovich 1962; Murphy 1967),
and ocean currents (Sette 1943). The first two of
these factors are density dependent and tend to
control population growth. Transport by ocean
currents to or from areas favorable to survival is
density independent and has been used to explain
successful year classes of Atlantic mackerel by
Sette (1943) and Atlantic haddock by Walford
(1938). A relationship between winds and year-
class success for the East Anglian herring fishery
was reported by Carruthers (1938). Cushing
(1969) pointed out that ". . . correlations between
recruitment and winds were often successful for a
period of years, after which they failed catas-
trophically."

Other density-independent factors, such as
temperature, particularly in the sense of long-
term climatic change, have been related to
changes in spawning success and location. For
example, a change in the environment of the Pa-
cific sardine over a period of time which resulted
in a change in normal distribution patterns and a
series of poor year classes was postulated by
Radovich (1962). Sissenwine (1974) documented a
significant relationship between atmospheric
temperature and the recruitment and equilibrium
catch of yellowtail flounder, but did not explain

Manuscript accepted June 1976.

FISHERY BULLETIN: VOL. 75, NO. 1, 1977.

FISHERY BULLETIN: VOL. 75, NO. 1

the mechanism by which temperature anomalies
influence the fishery.

Cushing (1969) listed three sources of variation
which might affect recruitment: year-to-year
environmental changes, larger scale climatic
changes, and differences due to stock density. The
year-to-year effects were considered by Cushing to
be randomly distributed around the stock and
recruitment curve and not of major consequence in
the long-term regulation of fisheries. Over a
number of years, variations around a stock and
recruitment curve may tend to cancel one another
and the fishery may provide a relatively stable
yield. However, when a fishery is overexploited
and subjected to poor survival as a result of en-
vironmental conditions, stock size may be reduced
to a small fraction of that necessary to maintain a
maximum sustainable yield (MSY). Further, with
overcapitalization, fishing effort may remain
high, preventing a resurgence of the stocks by
maintaining a spawning stock too small to pro-
duce a large year class under favorable en-
vironmental conditions. From this standpoint, a
predictive capability, based on knowledge of
density-dependent and density-independent
recruitment could be vital to the maintenance of
adequate stock size through a reduction in effort,
or to the harvesting of surplus population beyond
that necessary to maintain the MSY. Fisheries, in
the generic sense, operate over long periods of
time. Fishermen, fish processors, and consumers
operate on a much shorter time scale and large,
unexpected, year-to-year fluctuations in stock size
have significant economic and social impact.

The Atlantic menhaden, Brevoortia tyrannus, is
a species that has supported a significant fishery
since the middle of the 19th century (Reintjes
1969). Landings from the fishery have been
sampled extensively since 1955 and the major
characteristics of the stocks and the fishery have
been determined. Information for a variety of
stock sizes and from a range of environmentally
different years is available, and the stocks have
been subjected to heavy fishing pressure (Schaaf
and Huntsman 1972).

A study of forecasting methods and the de-
velopment of a forecast for the Atlantic menhaden
fishery was carried out by the National Marine
Fisheries Service (Schaaf et al.4). The manuscript

points out that knowledge of the biology of re-
cruitment of the Atlantic menhaden is needed to
take advantage of strong year classes through the
development of short-term fishing strategies.
Knowledge of poor year classes would also be
beneficial from a standpoint of avoiding excessive
fishing pressure on the stocks.

A single year class is harvested by industry over
a 4- to 5-yr period, and its failure could be masked
to some extent by overfishing of other year classes
taken concurrently, resulting in serious stock
depletion. Conversely, a large year class may lead
to a large increase in fishing effort which con-
tinues after the year class has been harvested,
leading to overcapitalization and overfishing in
subsequent years of reduced stock size. A large
year class, followed by several poor year classes is
potentially disastrous to the fishing industry and
to the stocks. Knowledge of the recruitment pro-
cess and the ability to predict year-class strength
is necessary if the fishery is to operate at the MSY
level.

Detailed information on the composition of
Atlantic menhaden stocks obtained yearly since
1955 shows a range in numbers recruited into the
fishery of from 11.5 billion in 1958 to 0.9 billion in
1967. Although some of the variation in re-
cruitment can be attributed to fluctuations in the
size of the spawning stock (Schaaf and Huntsman
1972), the wide range of fluctuations between
years with similar spawning stock sizes suggests
that environmental factors are influencing the
survival of prerecruits. This study attempts to
identify those factors, determine their relative
influences, and develop a predictive model to
account for the variations between actual and
expected recruitment into the Atlantic menhaden
fishery.

SPAWNING AND
LARVAL DISTRIBUTION

Gravid or running-ripe Atlantic menhaden are
rarely caught and spawning has not been ob-
served. Without conclusive information, the time
and place of spawning has been inferred by the
relative ripeness of maturing ova, the occurrence
of partially spent ovaries, and the distribution and
occurrence of eggs and small larvae.

Higham and Nicholson (1964:262) reported that

"Schaaf, W. E., J. E. Sykes, and R. B. Chapoton. 1973. Forecast
of 1973 Atlantic and Gulf menhaden catches based on the histor-
ical relation of catch and fishing effort. Unpubl. manuscr., 22 p.

Atlantic Estuarine Fisheries Center, National Marine Fisheries
Service, NO A A, Beaufort, NC 28516.

NELSON ETAL.: LARVALTRANSPORTOFB/?£VOO/?77A TYRANNHS

". . . (only 11 specimens containing numerous ripe
ova were encountered in the routine field
examination of several hundred thousand fish
during 4 years of sampling), . . . ." Based on a
sample of approximately 37,000 female menhaden
from all Atlantic coast fishing areas, they con-
cluded, p. 270, "Spawning apparently occurred in
the North Atlantic Area [north of Long Island]
from May to September; in the Middle Atlantic
[south to Cape Hatteras], from March through
May and again in September and October; and in
the South Atlantic [south of Cape Hatteras] , from
October through March." Based on the percent-
ages of sexually active (ripening but not ripe)
females in their samples, it appears that a major-
ity of spawning activities take place in the South
Atlantic Bight. The spawning cycle appears to be
one of limited spawning during a spring north-
ward migration, limited early and late summer
spawning as far north as Cape Cod and occasion-
ally into the Gulf of Maine, increased spawning
activity during a southward fall migration, and
intensive (90-100% sexually active) winter
spawning in the South Atlantic Bight.

Spawning activities through the winter are
difficult to determine because the stocks move
offshore and there is no fishery for menhaden
during that period. This is the only time during
the year that menhaden schools are not available
in coastal waters, and that fact leads to specula-
tion about an offshore spawning migration.

Available information about the distribution of
menhaden eggs and larvae has been reviewed by
Kendall and Reintjes (1975) and Chapoton.5 In-
ferences regarding spawning activities have been
drawn from various surveys of restricted time and
coverage which have been conducted on the east
coast since 1937 (Permutter 1939), primarily in
sounds, bays, and creeks. Only two egg and larval
research efforts have provided large-scale sys-
tematic coverage of major menhaden spawning
areas on the Atlantic coast. Those are the cruises
of the MV Theodore N. Gill (Reintjes 1961) and the
RV Dolphin (Kendall and Reintjes 1975). The
distribution of larvae collected by the Dolphin
cruises is in general agreement with the spawning
cycle documented by Higham and Nicholson
(1964). RV Dolphin cruises covered the entire
continental shelf from Cape Lookout, N.C., to

5Chapoton, R. B. 1972. On the distribution of Atlantic menha-
den eggs, larvae, and adults. Unpubl. manuscr., 69 p. Atlantic
Estuarine Fisheries Center, National Marine Fisheries Service,
NOAA, Beaufort, NC 28516.

Martha's Vineyard, Mass., in 14 transects from
December 1965 to May 1966.

The southern part of the menhaden spawning
range was covered by cruises of the Theodore N.
Gill in 1953 and 1954 (Reintjes 1961). The absence
of menhaden larvae during all but the winter
cruises led Reintjes to conclude that menhaden
spawn along the south Atlantic coast generally
from December to February. The southern limit of
the spawning range of the Atlantic menhaden is
undetermined because a southerly species, the
yellowfin menhaden, Brevoortia smithi, has an
overlapping spawning range. Those larvae col-
lected by the Theodore N. Gill off southern Florida
were probably B. smithi and those collected off
Cape Lookout, the other area of larval concentra-
tion located by the Theodore N. Gill, were un-
doubtedly B. tyrannus. Based on the distribution
of juveniles and adults, it seems safe to assume
that Atlantic menhaden spawn as far south as
northern Florida, but at a low intensity in the ex-
treme southern part of their range. Reintjes
(1969) hypothesized that much of the spawning
takes place south of Cape Hatteras.

Atlantic menhaden appear to spawn over most
of the continental shelf. The general timing se-
quence and location of spawning during migra-
tions indicates that eggs and larvae are subjected
to an open ocean environment for a sufficient
length of time to be affected by oceanic conditions.
Both the Dolphin and Theodore N. Gill cruises
resulted in catches of small larvae from nearshore
to the edge of the shelf. Dolphin records show a
general increase in average size of larvae from
offshore to inshore stations as well as increased
distance offshore from north to south. Major sum-
mer spawning in the New York-New England
area appears to occur well inshore, and large
numbers of eggs and larvae have been taken in
bays and sounds from Long Island north. Matth-
iessen (1974) reported concentrations of eggs that
exceeded 20,000/100 m3 in June 1972 in Nar-
ragansett Bay, R.I., and computed the total pro-
duction of eggs in the Bay during the summer of
1973 as being in excess of 4.64xlOn.

Concentrations of eggs and small larvae are
found progressively nearer the offshore edge of the
shelf during the fall and winter southward migra-
tion. Massmann et al. (1962) found larvae as small
as 7 mm 79 km off Chesapeake Bay, and concluded
that spawning and hatching occurred more than
that distance offshore. Reintjes (1968) reported an
extensive patch of menhaden eggs in Onslow Bay,

FISHERY BULLETIN: VOL. 75, NO. 1

N.C., in December 1966, 40 km from shore and
estimated their age at 8 to 55 h. Theodore N. Gill
cruises resulted in the location of larval menhaden
up to 220 km off Cape Fear, N.C., in February
1954, although most larvae taken during the Gill
cruises were over the shelf. Cruises of the RV
Undaunted during the winter of 1970-71 also
yielded larvae 170-175 km off Cape Fear.

PHYSICAL OCEANOGRAPHY OF
THE SPAWNING REGION

An excellent summary of the oceanography of
the coastal waters of the U.S. east coast was re-
cently prepared by Bumpus ( 1973) and the reader
is referred to that for detailed information. Bum-
pus identified three distinct subdivisions as the
Gulf of Maine, Middle Atlantic Bight (Cape Cod to
Cape Hatteras), and South Atlantic Bight (Cape
Hatteras to Cape Canaveral). Although menha-
den are periodically taken north of Cape Cod,
Mass., migratory intrusions do not occur there
routinely and the area is not one of significant
menhaden spawning activity. A brief summary of
oceanographic conditions in the other two regimes
of significant menhaden spawning activities
follows.

In the Middle Atlantic Bight the Gulf Stream
diverges abruptly toward the northeast, passing
Cape Hatteras, and the space between the Shelf
Water masses and the Gulf Stream left by this
divergence is occupied by the Slope Water mass.
Flow in the Shelf Water and Slope Water is
generally slow and southward, more or less
parallel to the isobaths except for portions of the
Slope Water mass near the Gulf Stream which
have a northward to northeastward motion im-
parted by transfer of momentum from the Gulf
Stream. At Cape Hatteras the southward flowing
waters generally turn to flow northward and an
unknown fraction of these waters becomes en-
trained within the Gulf Stream. The southward
drift of Shelf Water is partly driven by the pres-
sure field developed around river effluent plumes,
and in times of low runoff and southeasterly winds
the flow may be reversed. Menhaden spawning
takes place throughout the Middle Atlantic Bight
and oceanographic conditions there should have a
major influence on the distribution and survival of
eggs and larvae.

In the South Atlantic Bight the Gulf Stream
current forms the seaward boundary of the region
of intensive Atlantic menhaden spawning. The

current's mean position is parallel to and a short
distance (37-74 km in Carolina coastal waters)
from the edge of the continental shelf (180-m
isobath). A mass of Shelf Wa^er which has lower
salinity and lower temperature, except in sum-
mer, than the Gulf Stream water is found
shoreward of the Gulf Stream. Motion of the Shelf
Water mass is generally slow and variable, re-
sponding to local winds, but not customarily
flowing southward, unlike the pattern of flow of
the Shelf Water in the Middle Atlantic Bight.
Occasionally southward flows have been identified
near the coast, and the cuspate formations of
Raleigh Bay, Onslow Bay, and Long Bay suggest
southward flow nearshore as part of a large
counterclockwise eddy in each bay. The existence
of these eddies, although suspected, never has
been conclusively demonstrated. Stefansson et al.
(1971) found, based on geopotential topography
from six cruises in 1966-67, that there was always
an indication of a counterclockwise eddy in
Onslow Bay. The pattern found in Raleigh Bay
was less permanent and influenced by the influx of
Virginian Coastal Water from the north.

LARVAL TRANSPORT

Menhaden larvae, spawned offshore, move into
estuaries before metamorphosing to juveniles,
after traversing long, open ocean distances. The
larvae are 18-22 mm in length when they enter
estuaries after an oceanic phase of IV2 to 2 mo.
Very few small larvae (<12 mm) have been taken
in estuaries along the central and southern U.S.
Atlantic coast, even though eggs and young larvae
have occasionally been taken near shore. The
timimg of larval entrance is apparently controlled
to some extent by the larvae and is somewhat
independent of water movement. During earlier
larval stages, however, there is a passive drift
period in which larval movement is the result of
ocean currents. Based on the rate of fin de-
velopment, the completely passive phase probably
ends when a length of 10-12 mm is reached.
Depending on water temperature, menhaden
reach that length in 30-45 days (William F. Het-
tler pers. commun., Atlantic Estuarine Fisheries
Center).

Currents with an onshore component, par-
ticularly during the passive larval phase, would
seem to be important for transportation of the
larvae from offshore spawning areas to estuarine
nursery grounds. There are no documented

NELSON KT AL.: LARVAL TRANSPORT OFBREVOORT1A TYRANNUS

physiological requirements for estuarine de-
pendence, but metamorphosing larvae are rarely
taken in the ocean, indicating that apparent
requirements (food, shelter, etc.) provided by
estuaries are essential in the life cycle of
menhaden. Transport to the vicinity of estuaries
should increase the opportunity for entering
nursery grounds, resulting in good year classes
from years of strong onshore transport. Weak
onshore transport or water movement offshore
would increase the distance that must be actively
traversed, reduce chances of survival, and result
in a poor year class. If variation in survival is due
to variation in the efficiency of transport of larval
menhaden from offshore areas to estuaries, then
knowledge of the transport mechanisms would be
useful for understanding and predicting variation
in year-class strength.

Menhaden larvae have been found to be more
abundant in the upper 15 m of the water column
than in the underlying 18-33 m in extensive
surveys of our Atlantic shelf waters (Kendall and
Reintjes 1975; Chapoton see footnote 5). It is
assumed, therefore, that they remain in the upper
mixed layer and are transported along with it.
Horizontal transport in the surface layer is
principally the result of extensive quasi-steady-
state currents and local, variable currents, which
are strongly influenced by wind and run-off.
Steady state currents, by definition, cannot be
responsible for year-to-year variation in larval
transport and recruitment, so attention was first
turned to the local, variable currents which are
superimposed on the quasi-steady-state circula-
tion of the surface layer.

In the search for a westward transport
mechanism which varies seasonally and from
year-to-year, wind drift data computed from mean
monthly atmospheric pressure distributions for
the period 1946 to the present were considered
first. In particular, plots of zonal (eastward or
westward) wind-driven (Ekman) transport
produced by the Pacific Environmental Group,
NMFS, NOAA were studied (for method see
Bakun 1973). A grid point (lat. 35°N, long. 75°W)
located about 56 km southeast of Cape Hatteras
was selected as being representative of the wind
field in the area of interest. The seasonal variation
of Ekman transport at lat. 35°N, long. 75°W
generally includes relatively strong WSW-SW-
SSW transport during the first quarter of each
year. Because of the SW-NE trend of the coastline
south of Cape Hatteras, Ekman transports sig-

nificantly west of southwestward (those with a
stronger westward component) would be most
effective in transporting eggs and larvae toward
estuarine nursery areas. Plots of the monthly
zonal transport at this point revealed conditions of
eastward or weak westward transport during most
of the year, shifting to moderate or strong west-
ward transport during January-March; a
periodicity which matched that of spawning of
menhaden south of Cape Hatteras (Figure 1).

In coastal waters of the Middle Atlantic Bight
between Virginia and Long Island, N.Y., com-
putations of monthly zonal Ekman transport
exhibited a pattern similar to that found south of
Cape Hatteras. Monthly zonal Ekman transport
values computed for this area show that stronger
westward transport generally occurs in the
November-February period of menhaden spawn-
ing activities, possibly providing a mechanism for
transporting menhaden larvae into the vicinity of
estuarine environments.

A model of the circulation of the shelf waters off
the Chesapeake Bight was developed and cited for
its application to menhaden year-class strength by
Harrison et al. (1967). The model was used in an
attempt to explain the difference in "production of
young menhaden" in Chesapeake Bay from the
1958 year class, an unusually productive one, and
the 1964 year class, which was well below average.
The model yielded inappropriate surface current
regimes to explain strong shoreward larval
transport in 1957-58, and Harrison et al. chose
near-bottom currents, which appeared more
favorable, as an explanation. As cited earlier, data
collected in comparative net tows indicate that
menhaden larvae are more abundant in the upper
layer than the near-bottom layer, a condition
which weakens the premise on which the argu-
ment is based.

Application of the Ekman drift data to the
problem of explaining the large difference in
menhaden production in Chesapeake Bay in 1958
and 1964 leads to a more satisfactory biological
conclusion than the bottom-layer-transport model
used by Harrison et al. (1967). The average
monthly westward Ekman transports for the
November-March period at two points in the
Middle Atlantic Bight for 1957-58 (Table 1) were
about twice as large as those for 1963-64, qual-
itatively implying that variation in wind-driven
surface layer transport of larvae may be at least
partly responsible for the amount of variation in
menhaden year-class strength.

FISHERY BULLETIN: VOL. 75. NO. 1

5
U

«/»

z
o

►-

z
<

EASTWARD TRANSPORT

WESTWARD TRANSPORT

1969 , 1970 1971 1972 1973 .

I ' " "' ■ .... .1. ... . I., i , 1 1 .1, i

J M I RN.IMMJSN J M M .1 "

JMMJSNJMMJSNJMMJSNJMMJSNJMMJSNJMMJSNJMMJSNJMMJSNJMMJSNJMMJSN

FIGURE 1. — Monthly average zonal Ekman transport at lat. 35°N. long. 75°W, 1955-73. January-March spawning period is shaded.

TABLE 1. — Average westward wind-driven Ekman transport
computed for November-March 1957-58 and 1963-64 at lat.
39°N, long. 72°W and lat. 39°N, long. 75°W. Transports expressed
in metric tons per second per kilometer of front.

Year

Lat. 39°N,
long. 72W

Lat. 39°N,
long. 75°W

1957-58
1963-64

480
250

520
260

SPAWNER-RECRUIT RELATION

Over the 16 yr from 1955 to 1970, there was a
sharp decline in the size of the Atlantic menhaden
spawning stock and the size of resultant year
classes. From 1964 to 1970, the annual catch of
spawning age fish averaged only 14% of the
previous 9 yr. Resultant per-year recruitment
from 1964-70 averaged 42% of that for the previ-
ous 9 yr (Schaaf 1972). A description of the aver-
age relationship between spawning stock size and
recruitment is useful for examining this coinci-
dent reduction and for predicting the expected fate
of the fishery under different exploitation regimes.
A stock-recruit function is also the necessary
starting point for developing an index of survival
(observed recruitment to that expected from

number of spawners) against which one may
assess the impact of density-independent en-
vironmental effects of recruitment. The approach
in this study has been to determine if selected
density-independent environmental factors could
explain deviations from a postulated spawner-
recruit model.

Ricker's (1954) comprehensive study of stock-
recruitment formulated a dome-shaped model,
with strong compensation, resulting in decreased
recruitment at stock sizes beyond some maximum
value. It is described by the equation:

R = Se(Sr~S),Sm

where R = recruitment

S = spawning stock
e = base of natural logarithm
Sr = maximum equilibrium stock
Sm = stock size yielding maximum absolute
recruitment.

Ricker's model states that some stock size (Sm)
produces maximum recruitment, and that, be-
cause of density-dependent mortality and growth,

NELSON ET AL.: LARVAL TRANSPORTOFBfi£VOO/?77A TYRANNUS

stocks greater than Sm produce progressively
fewer recruits. There is a size-dependent fecundity
relationship for Atlantic menhaden (Higham and
Nicholson 1964), and growth rates are slower for
large year classes (Gene R. Huntsman, pers. com-
mun., Atlantic Estuarine Fisheries Center). Also,
adult menhaden are indiscriminate filter feeders
and are known to ingest their own eggs. Calcula-
tion of a density-dependent index for Atlantic
menhaden (i.e., the slope of a regression of InR on
InS ) yields a value of 0.238. This index falls within
the category described by Cushing (1971) as hav-
ing a slightly convex spawner-recruit curve. The
average fecundity of Atlantic menhaden (113,000
eggs per female) calculated from data used in this
study, also places the species in groups which
Cushing describes as having a dome-shaped
spawner-recruit curve. Accordingly, the Ricker
model has been used in this analysis, instead of
models proposed by Beverton and Holt ( 1957), and
others.

Schaaf and Huntsman (1972) presented a
Ricker spawner-recruit curve for Atlantic
menhaden. The same catch data and basically the
same methodology were used in this study, with
one important modification. Instead of using the
estimated total number of spawning age fish as the
independent variable to estimate recruitment, the
potential number of eggs that could be produced
from the spawning stock was used. This annual
potential is influenced by the age distribution of
the spawners and their average size. The potential
number of eggs produced each year and at each age
(Table 2) was calculated from the estimated
number of age 3 and older females (1955-70), their
back-calculated length, and the following fecun-

dity relation from data presented by Higham and
Nicholson (1964):

ME) = 0.3149+0.0176(/)

where E = thousands of eggs produced per female
at length, and
/ = back-calculated length at age of an-
nulus formation for age-3 and older
fish.

Another deviation from the data used on the
original Ricker spawner-recruit curve by Schaaf
and Huntsman (1972) is the calculated number of
recruits in the 1955-70 year classes. The numbers
differ between the two studies because: 1) some
adult menhaden were reaged following the initial
study which brought about slight changes in
estimates of year-class size, 2) the maximum
instantaneous fishing mortality rates were av-
eraged for age-specific exploitation rates for age
2-5 fish and were not weighted for numbers at age
as was done in the earlier study, and 3) the
exploitation rate of age-1 fish was estimated each
year based on the exploitation rate of age 2-5 fish
instead of an estimated exploitation rate of two-
thirds that of older fish as was done in the previous
study. This was necessary because shifts in fishing
area and effort in recent years have increased the
vulnerability of age-1 fish.

The parameters of the Ricker model were es-
timated from a linear regression of ln(i?/S) on S.
Fitting the model (Figure 2) yielded an estimate of
Sm equal to 60 x 1012 eggs. This is equivalent to
531 million spawning females spread over ages
3-6, and would produce an average recruitment of
3.68 billion fish at age 1.

TABLE 2. — Estimated number of eggs produced by spawning
stock of Atlantic menhaden for each year class by age, 1955-70.

Age

Year

8 +

Total

eggs
4.3

x W" -

1955

36.2

72.1

12.6

0.9

0.3

126.4

1956

45.7

11.1

52.8

12.5

3.4

1.1

126.6

1957

15.5

15.1

12.2

13.8

1.8

0.6

59.0

1958

11.4

6.3

6.8

4.9

3.0

0.3

32.7

1959

49.0

10.8

5.0

6.0

2.5

1.1

74.4

1960

18.1

368

12.6

4.7

1.7

0.5

74.4

1961

146.2

5.5

12.0

1.4

0.6

0.2

165.9

1962

23.9

56.7

7.2

6.4

0.9

0.2

95.3

1963

15.4

8.8

12.2

3.3

1.1

0.2

41.0

1964

8.5

3.8

1.9

2.1

0.5

0.1

16.9

1965

7.8

1.7

0.3

0.4

0.2

10.4

1966

3.9

0.9

0.1

5.0

1967

9.7

1.0

0.1

10.8

1968

6.7

2.0

0.2

8.9

1969

9.4

1.4

0.1

10.9

1970

7.7

2.9

0.2

10.8

+ = less than 0.05 x 1012.

20 40 60 80 100 120 140 160 ISO

SIZE OF SPAWNING STOCK {NO OF EGGS * 10'J)

FIGURE 2. — Ricker spawner-recruit relationship for Atlantic
menhaden, 1955-70.

FISHERY BULLETIN: VOL. 75, NO. 1

Because the regression of \n(R/S) onS, as is done
for the Ricker equation, will automatically give a
significant correlation coefficient, a nonlinear
fitting procedure was also applied to the data
(Marquardt 1963). A comparison of the residual
mean squares of the two procedures yielded anF of
1.02, indicating no significant difference in the fit
of the Ricker curve to the spawner-recruit data
between the standard technique and the nonlinear
estimation.

Few published stock-recruitment curves appear
to fit the observed data well, and the one for At-
lantic menhaden is no exception. Application of a
power function of the form R = aSh to the data
resulted in a fit that was not significantly better
from that of the Ricker function. The purpose of
the study, however, is to examine and explain the
deviations from the curve caused by density-
independent factors, to see if they can be predicted,
and consequently to improve upon a management
plan based solely on a long-term, average MSY
concept. The survival index (Table 3) represents
the ratio of observed recruits (the number of age
l's in the population as estimated from the catch of
age l's and estimated exploitation rates) to the
number calculated from the Ricker spawner-
recruit model. This ratio is an index of survival,
independent of density, and should reflect those
environmental effects which influence survival of
menhaden from the time of spawning until the
time of recruitment to the fishery at age 1.

INFLUENCE OF EKMAN TRANSPORT
AND OTHER FACTORS

The influence of transport processes in the
southern part of the spawning range is indicated
in Figure 3 which depicts the Ekman transport
index for the January-March spawning period for
1955-70 and the estimated number of menhaden
recruits at age 1 from the year class. The re-
sponsiveness of survival to transport shows up
well in the Figure where years of strong westward
transport correspond with large year classes, and
weak transport years with smaller year-class size.
Also, increases and decreases in recruitment from
one year to the next generally coincide with an
increase or decrease in westward transport in the
year in which the year class was produced.

The correspondence is weaker in the 1968-70
year classes, although it follows the general
pattern. Intense fishing pressure over a number of
years changed the age structure of the spawning

TABLE 3.— Estimated number of eggs, observed and expected
number of recruits at age 1, and density-independent survival
index for Atlantic menhaden, 1955-70.

No.

No. of observed

No. of expected

Survival

Year

of eggs

recruits (fi0)

recruits (ft. )

index

class

x 1012

x 106

^o Rc

1955

126.4

5,019

2,569

1.95

1956

126 6

4.984

2.568

1.94

1957

56.0

2.538

3,688

069

1958

32.7

11,540

3,166

3.64

1959

74.4

2,007

3.599

056

1960

74.4

2,568

3,598

0.71

1961

165.9

1,553

1,751

089

1962

953

1,740

3.253

0.54

1963

41.0

1.378

3,457

0.40

1964

16.9

1,408

2.134

066

1965

10.4

1,406

1,472

0.96

1966

5.0

1.579

773

2.04

1967

10.8

922

1,505

0.61

1968

8.9

1,324

1,282

1.03

1969

10.9

2,763

1,521

1.82

1970

10.8

1,415

1,499

0.94

stocks to a considerable extent. For example,
approximately 40% of the estimated spawning
stock in 1958 were 4 yr or older. The number of age
4 and older fish in the 1969 spawning population
was only about 9%, and the average number of
eggs per spawning female was about 50,000 less
than in 1958. Thus, fishing pressure brought
about an even greater reduction in spawning
potential than is apparent when considering the
number of spawners alone, because of a reduction
in the average age. This reduction in real spawn-
ing potential reduced the opportunity for a large-
scale response to favorable transport in the 1968-
70 year classes.

Comparison of the density-independent survi-
val index with Ekman transport yields a sur-
prisingly consistent relationship (Figure 4). A

z
o

No. of R«cruitt

130

3
Qr-

Ekman Tramporl— — ^ ^
/ \

I
in

'*"'

"*\

1 1

/
1

\ ■

a.
Z

1 i-*ti '

v /

t i

r^i

— *

\ i

i/t

EAR

CIA

FIGURE 3.— Observed number of Atlantic menhaden recruits at
age 1 and sum of average monthly zonal Ekman transport at lat.
35°N, long. 75°W for January-March of spawning years, 1955-70.

NELSON ET AL : LARVAL TRANSPORT OF BREVOORTIA TYR ANNUS

<
>
>

at
3

lo 46 J6 40- 50 60 70 80

WESTWARD TRANSPORT (METRIC TONS X 10/SEC/KM)

FIGURE 4. — Linear regression of
calculated survival index (observed
recruits/calculated recruits) for Atlan-
tic menhaden on sum of January-March
zonal Ekman transport at lat. 35°N,
long. 75°W, 1955-70.

linear regression of survival indices against
transport values for the January-March spawning
periods at lat. 35°00'N and long. 75°00'W results
in an r of 0.789 significant at the 0.001 level with
14 df (Figure 4). This accounts for approximately
629c (r2 = 0.622) of the variation between observed
and expected recruitment. Since the transport is
indicative of conditions over only a portion of the
total spawning range of Atlantic menhaden, and
since r2 accounts for such a large share of the total
variation in overall recruitment, the actual effect
of transport processes in the southern spawning
area must be of overriding significance for the
survival of spawn south of Cape Hatteras. With
the exception of 1966, the index of survival was
greater than 1.0 only when the Ekman transport
index indicated a strong westward transport for
the January- March period of menhaden spawning
activities south of Cape Hatteras.

The transport data fall conveniently into groups
of 0-200, 200-500, and 500-1,000 metric tons/s- km
of ocean front. Five years of strong westward
transport (>500) were found, and in all of these
years the survival index was greater then 1.0. The
observed recruitment exceeded the expected by an
average of 108%, with the 1958 year class showing
the largest value. In 6 yr of low westward trans-
port (0-200), the survival index was never greater
than 1.0. In 5 yr of moderate or "average" west-
ward transport, (200-500) high survival occurred
in 1 yr, and poor or moderate survival in the other
4 yr, indicating the influence of additional factors
over the spawning range that are operating to
produce variations in year-class strength. The
high index for 1966 may partially result from the
fact that the estimated spawning stock production

of 5 x 1012 eggs was, by far, the lowest of any year
on record (Table 2). Under such low stock size,
density-dependent survival may have exceeded
that indicated by the Ricker curve, creating an
artificially high index of survival. A slight un-
derestimation in the computation of the number of
spawners would also create a very high survival
index, since the slope of the Ricker curve is ex-
tremely steep as spawning stock size approaches
zero (Figure 2).

Transport values at lat. 33°N, long. 78°W,
approximately 200 nautical miles southwest of
lat. 35°N, long. 75°W were also considered. The
data are from a point offshore of Long Bay, S.C.,
the southernmost of the cuspate Carolina bays,
and serves as an indicator of Ekman transport in
the extreme southern part of the Atlantic
menhaden spawning range. A significant corre-
lation existed between transport for the
January-March period and the survival index
(Table 4). Due to the correlation between the two
transport values south of Cape Hatteras, however,
little additional variation is accounted for by the
southernmost transport value (Table 5). Since
transport is a function of wind stress and Coriolis
force, movements of air masses through the
southeastern United States would give parallel
transport values at the two locations, with inten-
sity of transport dependent on variations within
the air mass. The large amount of variation ac-
counted for by the two transport indices south of
Cape Hatteras is sufficient to account for the rela-
tive success or failure of a year class, and supports
the observation that a significant portion of
menhaden spawning takes place south of Cape
Hatteras.

FISHERY BULLETIN: VOL. 75, NO. 1
TABLE 4. — Stepwise regression of survival index of Atlantic menhaden on environmental factors.

Correlation

Individual

Error

Cumulative

Time of

with

level of

Cumulative

mean

percent of

Factor

No.

year

survival index

significance

correlation

square

variance

Zonal Ekman transport

Jan. -Mar

0.789

0.001

0.789

0.298

62.2

lat. 35°N, long. 75°W

Chesapeake Bay

July-Sept.

-0.216

—

0.825

0.271

68.0

discharge

Zonal Ekman transport

Nov -Feb.

0.352

—

0.840

0270

70.6

lat. 39°N, long. 72°W

Zonal Ekman transport

Nov -Feb

0.519

0.05

0896

0.198

80.3

lat. 39°N, long. 75°W

Minimum temp

Jan. -Feb.

-0 177

—

0.914

0.181

83.6

Delaware Bay entrance

Zonal Ekman transport

Jan-Mar.

0.720

0.005

0.919

0.190

84.5

lat. 33°N, long. 78°W

TABLE 5. — Regression coefficients between independent en-
vironmental variables used in the recruit-environment predic-
tive equation for Atlantic menhaden. See description of X's in
Table 4.

0.789

0.645

0.644

-0.333

0.032

0.589

0.701

-0.580

-0.068

0.868

-0.403

0.174

-0.510

0.213

0.023

Wind-driven transport off Delaware Bay was
studied as being representative of menhaden
spawning areas in the Middle Atlantic Bight.
Because the transport values are produced in a 3°
grid by the Pacific Environmental Group, there
were no available data for a point located centrally
on the continental shelf. Two locations were
chosen: one at lat. 39°N, long. 75°W, near the
mouth of Delaware Bay, the other at lat. 39°N,
long. 72°W, near the outer edge of the continental
shelf. The two locations are approximately 260 km
apart in an east-west direction, and are felt to be
representative of Ekman transport over the broad
shelf area near the east-west axis of the Middle
Atlantic Bight.

The entrance of larvae into estuaries of the
Middle Atlantic Bight occurs variably from
September to June, with peak immigration oc-
curring in the winter. Reintjes and Pacheco ( 1966)
reported on 6 yr of larval collection at Indian
River, Del., and showed high rates of influx from
December through March. The peak month varied
from year to year, but stayed within the
December-March period. Correlation coefficients
between summed transport values for
November-February (the peak period of larval
drift) and the survival index (Table 4) are not as
large as those from south of Cape Hatteras, but the
effect of transport on survival at the inshore point
(lat. 39°N, long. 75°W) is significant at the 0.05
level. The transport values from the inshore and

offshore points account for approximately 27% and
12%, respectively, of the total variance in the
survival index for Atlantic menhaden. When
combined with the transports south of Cape
Hatteras, these values for the Middle Atlantic
Bight account for an additional 12+% of the re-
sidual variance. Correlation coefficients are lower
than those found for the South Atlantic Bight, and
may be indicative of: 1) major nearshore spawning
activities, reducing the need for a suitable
transport mechanism; 2) a lower level of spawning
in the area; or 3) a lower level of recruits per
spawner due to mortalities from other en-
vironmental factors in the area.

The model of circulation off Chesapeake Bay
developed by Harrison et al. (1967) and discussed
in the Larval Transport section would be ap-
propriate if larval menhaden were demersal in
nature. However, since larvae are more abundant
in the upper water column, we would expect a
negative relationship between discharge and
survival in the Middle Atlantic Bight because
high surface discharge would impede larval
entrance into estuaries. Chesapeake Bay was
chosen to test that hypothesis because of its im-
portance as a major nursery area. Average
monthly discharge rates from the Susquehanna,
Potomac, and James rivers were used in the test
because they constitute over 90% of the total
inflow into Chesapeake Bay. Discharge during the
third quarter (July-September) of the year pre-
ceding the year-class year was chosen because
there is a lag time of up to 90 days between stream
flow and bay discharge (Harrison et al. 1967). The
influence from run-off would be felt at the mouth of
the Bay in the October-December period when
larvae begin entering in increasing abundance. A
correlation between the survival index and
discharge rate did not result in a significant

NELSON ETAL.: LARVAL TRANSPORT OFBREVOORT1A TYRANNUS

coefficient (Table 4). When combined with the
other factors considered above, Chesapeake Bay
discharge accounts for an additional 6% of the
residual variance in density-independent year-
class strength. A fairer test of the effects of dis-
charge on larval transport would require that we
isolate that portion of the total larval production
that would enter Chesapeake Bay under varying
conditions. Our knowledge of Atlantic menhaden
spawning activities is not sufficient to do this with
reasonable precision.

An absence or reduction in the number of larvae
in estuaries during periods of extreme cold has
been noted by June and Chamberlin (1959) and
Reintjes and Pacheco ( 1966). Kendall and Reintjes
(1975) hypothesized that severe winters, par-
ticularly in the northern segment of the spawning
range, result in heavy kills of overwintering lar-
vae in the estuaries. In addition, laboratory ac-
climation studies have shown high mortality rates
when menhaden larvae were held for several days
at temperatures below 3°C (Lewis 1965). A time
series of minimum mean monthly sea surface
temperatures was located for the mouth of Dela-
ware Bay from National Ocean Survey Tide Sta-
tion Observer Records (U.S. Department of
Commerce 1973). These data were considered
representative of mid-to-northern coastal areas in
the Middle Atlantic Bight. Correlation of the
survival index for the entire population and the
minimum temperature yielded a low correlation
coefficient (Table 4). The correlation is somewhat
of an artifact, however, and probably is biased by
the positive correlation between Ekman transport
and year-class strength. Westward Ekman
transport is generated by winds from the north.
Years of high westward transport in winter
months are years of sustained north winds, which
are associated with cold air masses. Under such
conditions, we would expect cooler sea-surface
temperatures in those years, particularly in or
near shallow estuarine areas. There may be a posi-
tive correlation between temperature and survi-
val, but the relationship probably is masked by the
overriding effects of wind-generated Ekman
transport (Table 5). The low correlation coefficient
could also indicate that only a small portion of the
population would overwinter in northern waters
where temperature stress might be a significant
factor.

If low temperature reduces survival, a transport
mechanism to carry fall-spawned larvae south-
ward along the Middle Atlantic Bight into the

vicinity of estuaries that have milder winter
temperatures would be a positive survival factor.
Therefore, the meridional (north-south) compo-
nent of Ekman transport in the Middle Atlantic
Bight at lat. 39°N, long. 72°W near the edge of the
shelf off Delaware Bay was considered. A corre-
lation between the survival index and the
southward transport for the October-December
spawning period resulted in a coefficient of 0.336,
which accounts for about 10% of the total variance
in density-independent recruitment. However,
the contribution to reduction in residual variance
was minimal, because all of the variation due to
southward transport was accounted for by linearly
related east-west zonal Ekman components al-
ready considered. A relatively steady state
southward transport mechanism exists in the
Middle Atlantic Bight in the form of a southward
flowing current over the shelf (Bumpus 1973).
Because this current is quasi-permanent, vari-
ations in southward Ekman transport may be of
little significance and may only create minor
fluctuations in strength of an existing transport
mechanism.

RECRUIT-ENVIRONMENTAL MODEL

The logic used in the selection of environmental
parameters for inclusion in a model of en-
vironmental effects is depicted schematically in
Figure 5. The heavy line represents an intuitive
weight of density-dependent and density-
independent factors in the survival of menhaden
larvae from the time of spawning through their
oceanic phase. In the upper Middle Atlantic Bight,
for example, spawning takes place close to shore or
in major bays and sounds, reducing or eliminating
the time spent by larvae in the open ocean. This
would reduce dependence on favorable currents
for transport. Under such conditions, environ-
mental factors influencing mortality may be rela-
tively stable, with variation in the number offish
spawning in the area being the probable cause of
most of the variation in the number of recruits
produced. In the South Atlantic Bight, however,
spawning takes place offshore, and dependence on
favorable ocean currents would seem to have
greater weight than spawning stock size on
survival. Large annual variations in transport
would produce large variations in survival in the
South Atlantic Bight at a given stock size. The
lower Middle Atlantic Bight seems to be an in-
tergrade between the two extremes, with sig-

FISHERY BULLETIN: VOL. 75, NO. 1

STOCK SIZE
(Survival Density Dependent)

ENVIRONMENTAL CONDITIONS

(Survival Density Independent)

YEAR-CLASS SUCCESS FACTORS

Actual Survival Index (Ro/Rc)

Predicted Survival Index

FIGURE 5. — Schematic representation of logic used in the de-
velopment of the survival index predictive model. Location of
environmental parameters used in the model is indicated byXn,
description of parameters in Table 4.

nificant spawning taking place farther offshore as
adults migrate southward in the fall. This should
result in increased significance of oceanic trans-
port factors from north to south in the determi-
nation of year-class strength. The hypothesis of
increasing importance of transport as spawning
activities move progressively farther offshore is
supported by the highly significant correlations
between the survival index and transport values
south of Cape Hatteras and similar correlations
which have a lower level of significance off Dela-
ware Bay.

The selection of locations and time periods for
Ekman transport data was based on the availa-
bility of data for specific coordinates, desire for
representation of broad spawning areas, and
estimates of larval drift time and direction (Figure
5). Of the many possible environmental factors
which could influence survival during the oceanic
phase, three (transport, temperature, and river
discharge) were chosen because they appeared to
be factors of major importance and data series
were available for the same period in which vital
statistics of the Atlantic menhaden populations
have been taken.

Q
Z

-j
<
>
>

19SS 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70

FIGURE 6. — Multiple regression of the survival index for Atlan-
tic menhaden on environmental factors, 1955-70. Predictive
equation and listing of environmental factors presented in text.
Correlation coefficients and model data presented in Tables 4
and 6.

TABLE 6. — Data used in recruit-environment predictive model
for Atlantic menhaden. Location of factors identified in Figure 5,
individual factors identified in Table 4.

Year
class

S.I.

Environmental factors

1955

1.95

272

152

2.4

1956

1.94

107

307

271

1.0

1957

0.69

3.4

1958

3.64

124

141

169

0.6

1959

0.56

126

1.5

1960

0.71

121

1.6

1961

0.89

155

129

1.6

1962

0.54

149

1.4

1963

0.40

206

158

-0.3

1964

0.66

120

127

2.0

1965

0.96

1.8

1966

2.04

125

104

1.3

1967

0.61

1.8

1968

1.03

161

0.0

1969

1.82

317

212

0.4

1970

0.94

185

156

0.2

The multiple-regression model developed to
relate recruitment to environmental variables
yields a correlation coefficient of 0.919, significant
at 0.003 with 9 df (Figure 6). Model data are given
in Table 6. The model accounts for over 84% of the
variance in the actual survival indices (Table 4).
Translated into recruits, the model indicates that
over 84% of the variation between actual re-
cruitment into the fishery and expected re-
cruitment during the 1955-70 period is accounted
for by environmental fluctuation. The model is
described by the equation:

S.I. = 0.4148 + 0.0205XJ +0.00530Z2

- 0.00807X3 + 0.00950X4 + 0.23967X5

- 0.02679X6 ± e

where S.I. = survival index computed by dividing
observed recruits by expected re-
cruits

NELSON ET AL.: LARVAL TRANSPORT OFBREVOORTIA TYRANNUS

Xx= sum of monthly average zonal
(westward) Ekman transport rates
for January-March of the year-class
year at lat. 35°N long. 75°W

X2= sum of monthly average zonal
(westward) Ekman transport rates
for January-March of the year-class
year at lat. 33°N, long. 78°W

X3= sum of monthly average zonal
(westward) Ekman transport rates
for November-December of the year
prior to the year class and January-
February of the year-class year at
lat. 39°N, long. 72°W

X4 = sum of monthly average zonal
(westward) Ekman transport rates
for November-December of the year
prior to the year class and January-
February of the year-class year at
lat. 39°N, long. 75°W

X5= minimum mean sea surface temper-
ature at the mouth of Delaware Bay
in the year-class year

X6 = sum of monthly average discharge
rates from Susquehanna, Potomac,
and James rivers in July-September
of the year preceding the year-class
year
e= error term.

The predicted number of recruits for each year is
given by:

Rp - RCI

x S.I.

where Rp =

Rr, =

predicted number of recruits
number of recruits calculated from
the Ricker curve at spawning stock
size in the ith year.

A correlation between the observed number of
recruits (R0) and the predicted recruits (Rp) for
each year yields a coefficient of 0.943 and a slope of
0.914 with no systematic bias around the regres-
sion line. Further evidence of the validity of the
model is the failure of adjustments to increase the
percent of variance accounted for by the en-
vironmental factors. The initial model, based on
judgments of the proper time and location of
environmental parameters, yielded a higher
correlation coefficient than any subsequent mod-
els in which any of the parameters or time-spans
were varied away from those which were consid-

ered the most significant from a biological stand-
point. The parameters were not selected by a
screening process from a large number of vari-
ables, but were selected because of their probable
impact on survival.

The four largest year classes ( 1955, 1956, 1958,
and 1969) during the 16-yr period are accurately
described by the model. The average error of
prediction for these years is 4.3% and the
maximum error is 6.3%. Smaller year classes are
not described with the same degree of accuracy,
although the mean error for the 16-yr period is
reduced from 1.5 billion fish using only the Ricker
curve to 610 million individuals per year by the
model, and the standard error of the mean is re-
duced from 501 to 155 million fish.

The multiple-regression model has a high
correlation coefficient and therefore describes the
data well. Its value for prediction is somewhat
more tenuous and requires testing on a sub-
sequent set of data to determine its accuracy. The
model was not broken into separate time-series
units for testing because of the brevity of the 16-yr
data base.

The model is a first-cut approximation for the
evaluation of transport and other factors. The
number of variables included tends to increase the
R2 value, even though some parameters do not
show individual significance levels when corre-
lated with the survival index. However, only the
Chesapeake Bay discharge has a /3 value of which
±2 standard errors encompasses 0, indicating that
the factor is probably not significant. The other
parameters are associated with the same major air
mass movements, and are therefore interrelated.
A more sophisticated model should be based on
either principal components regression or Ridge
regression techniques to correct for the inter-
dependence of some of the parameters and to
improve the predictive capability. A reduction in
the number of variables used is desirable from a
statistical standpoint because of the short time
span of the data base. Regression of the survival
indices on the three transport values off of Cape
Hatteras (lat. 35°N, long. 75°W) and Delaware
Bay (lat. 39°N, long. 72°W; lat. 39°N, long. 75°W)
yields an R2 of 0.741 (12 df, P<0.001). The ab-
breviated model accounts for a significant portion
of the variance around the spawner-recruit curve.
It describes the data for high and low survival
years nearly as well as the full model and probably
has a similar predictive capability. Determination
of the actual influence of the other factors (dis-

FISHERY BULLETIN: VOL. 75, NO. 1

charge and temperature) which were included
because of their potential biological importance
will require a greater knowledge of spawning
intensities and a longer term data base.

Overall, the model implies a predictive capabil-
ity for large year classes and for extremely poor
year classes. The model provides a satisfactory
indication of the general magnitude of a year class
prior to entering the fishery in 14 of the 16 yr.

For initial model purposes, the survival index
was not computed beyond 1970 because the 1971
year class is still being harvested by the fishery,
and the total catch from that year class necessary
for verification of the number of recruits is not
known. Forecasting in real time can be ac-
complished by inserting the routinely available
environmental data into the survival index
equation. The expected number of recruits for a
given year class is obtained by determining age
structure and abundance of 2-yr-old and older fish
from fishery landings the previous fishing season,
estimating an exploitation and survival rate to
determine the number that will survive to spawn
the next year class, calculating the expected
number of eggs produced, and estimating the
expected number of recruits from the Ricker
function. Multiplying the expected number of
recruits by the predicted survival index gives the
predicted number of recruits. Estimates of the
number of recruits can be made as early as April of
the year-class year, and can be revised when ac-
tual exploitation rates are determined to allow
better estimates of the size of the spawning stock
which produces the year class. Thus, an initial
prediction of the number of recruits can be made
approximately 1 yr before they become available
to the fishery the following spring.

DISCUSSION

Refinement of the predictive capability of the
recruit-environment model is dependent on in-
creased knowledge of the biology of Atlantic
menhaden and on better understanding of the
effects of the many factors that influence dis-
tribution, abundance, and survival. The model is
concerned only with variation introduced into
year-class size during the relatively short life
phase in which larvae are oceanic and before
metamorphosis takes place. The model concen-
trates on those factors which influence larval
distribution and act as a mechanism to transport
larvae into the vicinity of estuarine nursery

grounds, thereby increasing survival. Major
sources of variation such as food availability and
predation have not been directly considered.
However, since these factors are, to some extent,
influenced by the number of larvae produced by
the spawning stock, variations induced by them
should be partially accounted for by the density-
dependent Ricker function. The actual fluctuation
in availability of food could only be determined by
broad-scale surveys over the entire menhaden
spawning range and would require a continuous
time series for a number of years. Likewise, the
determination of predation and cannibalistic
influences would require extensive field surveys
and controlled laboratory experiments.

Problems in determining the influence of
pertinent environmental factors are compounded
by the large geographic range of menhaden
spawning activities. The influence of any one
particular factor at a specific location could only be
determined if the amount of spawning at that
location was known. Comparison of environmen-
tal factors against a survival index for the entire
stock, as has been done in this study, requires the
selection of broad-scale factors having major
influence over large portions of the spawning
range, or the selection of representative data
which provide a generalized environmental index
for a selected factor. Localized variations may be
highly significant, but masked by overall survival
success or failure without knowledge of localized
spawning intensity.

Cushing (1969, 1974) cited failures in attempts
by other authors to correlate year-class strength
and winds (or pressure gradients), and suggested
that variation in wind direction may be a greater
source of variation than the strength of winds from
a single direction. The U.S. east coast is composed
of an almost continuous series of bays and sounds,
which extend both north and south of the major
spawning region for Atlantic menhaden. Under
these circumstances, variations in wind direction
would probably influence the route of larval drift.
However, unless northward or southward larval
movement was extreme, larvae would not be
transported away from suitable nursery areas as
long as there was a significant onshore component
of wind-driven circulation. Thus wind direction
would be a significant factor only if that direction
reduced the westward component of Ekman
transport or if the normal seasonal wind pattern
reversed, generating eastward (offshore) trans-
port.

NELSON ET AL.: LARVAL TRANSPORTOFfifl£VOOft77A TYRANNUS

Comparison with Pacific Sardine

Computed survival indices allow comparisons
between the Pacific sardine and Atlantic
menhaden, in addition to those detailed by
McHugh (1969). Radovich (1962) presented data
for Pacific sardine showing the effect of good,
average, and poor environmental conditions on
the spawner-recruit relationship. He used
maximum and minimum parabolas based on
highest and lowest recruitment years and iden-
tified the area between the curves as indicative of
the effects of the environment as well as spawning
stock size on recruitment. A similar approach,
modified by using the right-hand skewed Ricker
curve yields similar results (Figure 7). Year clas-
ses used in the computation of the maximum and
minimum recruitment curves for Atlantic
menhaden were not selected for high and low
recruitment as was done by Radovich, but were
selected because they represented extremes in the
variation of transport factors. The maximum
recruitment curve was developed from year-class
size during the 3 yr of highest (3^700 metric tons/
skm) southern onshore transport (1955, 1958,
1969). Similarly, the minimum recruitment curve
was computed from year-class size during the 3 yr
of lowest (<100 metric tons/s-km) onshore
transport (1959, 1963, 1967). The two curves
represent a wide range of environmentally in-
duced fluctuation around the stock and re-
cruitment curve calculated from the 1955-70 data
base. No statistical significance can be attached to
the upper and lower curves because each is based
on three data points. However, the figure indicates
the range of variance that masks the density-
dependent function if pertinent environmental
factors are not identified and weighted for effect at
various stock sizes. The greater slope of the
maximum curve is of particular interest, indicat-
ing a significant loss of potential recruits in good
environmental years if adequate stock size is not
maintained.

Additional parallels can be drawn between
Pacific sardine and Atlantic menhaden spawner-
recruit relationships during periods of overfishing
and low survival. A comparison of spawning stock
size and year-class size for the two species linked
in chronological order shows striking similarities
(Figure 8). In each case, there was a period of
several years at high stock size in which the size
appeared to be near or past the maximum needed
to produce large numbers of recruits. A series of

|333-S]/55

SIZE OF SPAWNING STOCK (NO OF EGGS x 10")

FIGURE 7. — Ricker spawner-recruit relationships calculated for
years of good and poor environmental conditions. The upper
curve is calculated from observed recruitment during the three
greater years of Ekman transport, the middle curve is calculated
from the 16-yr data set, and the lower curve is calculated from
observed recruitment during the three lesser years of Ekman
transport.

good year classes ( 1937-39 for sardine; 1955, 1956,
and 1958 for menhaden) was followed by a series of
poor survival years (1940-45 for sardine, 1959-64
for menhaden). These reductions in recruitment,
combined with excessive fishing pressure, reduced
spawning stock size drastically, leading to a re-
stabilization of stock and recruitment around
small stock levels. In the case of menhaden, the
5-yr period of decline reduced the spawning stock
size by an order of magnitude. By 1966, spawning
potential had dropped to a low of 5 x 1012 eggs
from the 1961 high of 165 x 1012. The parallel
between the two sets of data is a cause for concern,
because the decline and apparent restabilization
of Pacific sardine stocks was followed by a com-
plete collapse of the fishery. Henry (1971:23) in his
analysis of the decline of the Atlantic menhaden
fishery stated, "I am concerned that the stocks of
Atlantic menhaden may have been reduced to a
level that is having an adverse effect on recruit-
ment." Clark (1974:14), in a study of the effects of
schooling on population dynamics on small school-
ing species (as in the case with Atlantic menha-
den), concluded that, "A commercial fishery based
on such a species might be expected to experience a
rather spectacular population collapse, which
could be brought on either as a direct result of an
increased fishing effort which suddenly trans-
forms the system into an unstable mode, or as an
indirect result of fishing which reduces resiliency
and renders the population vulnerable to the ef-
fects of random environmental fluctuations." The
possibility of a complete collapse in the Atlantic

FISHERY BULLETIN: VOL. 75, NO. 1

O 7

PACIFIC SARDINE

2 9

39
!

i 3?

40 v\ '

33>
.--'43

\35
34

ATLANTIC MENHADEN

55
%

-'56

FIGURE 8. — Year-class size related to
spawning stock size and linked in
chronological order for Atlantic
menhaden and Pacific sardine. Pacific
sardine figure after Radovich
(1962:134).

SPAWNING STOCK SIZE (BILLIONS OF FISH)

SIZE OF SPAWNING STOCK |NO OF EGGS * 10"l

menhaden fishery, given high fishing effort and
additional years of poor survival, cannot be dis-
counted.

Fortunately, there are significant differences in
the environment, biology, and fishery of Pacific
sardine and Atlantic menhaden. One of the more
important differences is the estuarine depen-
dence of menhaden. In every year, at least some
estuarine systems on the east coast should
provide favorable environments, insuring good
survival of larvae which reach those nursery
grounds. Also, spawning activities spread over the
entire coast should include at least some areas
conducive to survival, reducing the chance of
almost no survival over the entire range. Climatic
change which shifts the distribution of menhaden
spawning activities would not likely shift the
spawning region far enough away from suitable
nursery areas to cause the type of massive failure
that occurred in the sardine fishery. Another
significant factor in the collapse of the sardine
stocks was an increase in the stock size of compet-
ing species, filling the niche in the ecosystem as
the sardine population decreased. Although there
is no fishery for species which are potentially
competitive with Atlantic menhaden and
adequate stock data on such species are not av-
ailable, there are no indications of large increases
in abundance of any coastal pelagic species, and
the niche available to menhaden appears to be
open. However, John Radovich (pers. commun.,
California Department of Fish and Game) points
out that "the value of not having identified an
increase in competitors for the menhaden may be
of little significance because:

1) The sardine collapse and failure to recover
may have happened without a 'competing'
species such as the anchovy.

2) Available forage and habitat may be utilized
through slight increases in the abundance of
several species, and hence go unnoticed.

3) The capacity within a trophic level may vary
considerably so that actual changes in the
abundance of competing species may be
masked by changes in available forage and
habitat."

The menhaden fishery is somewhat self-
regulating, in that low stock levels have brought
about economic conditions which forced a reduc-
tion in effort and closure of processing plants. The
closure of plants in the northeast United States
during the late 1960's reduced fishing effort on
older age-groups, halting the drastic decline in
spawning stock size (Schaaf in press). This action,
plus good survival in 1966 which produced the
spawning stock for the high transport, large year-
class year of 1969, is probably responsible for the
brief resurgence of the fishery in the early 1970's.

Implications for the Fishery

Implications for the fishery are rather
straightforward: in years of poor environmental
conditions recruitment is low regardless of stock
size; extremely low spawning stock sizes in years
of poor environmental conditions result in re-
cruitment below the level needed to maintain the
fishery; favorable environmental years will

NELSON ETAL.: LARVAL TRANSPORT OF BREVOORTIA TYRANNUS

produce exceptional year classes and a propor-
tionally greater harvestable surplus at stock sizes
near the spawning optimum; and a series of poor
environmental years (1959-64), coupled with
excessive fishing pressure, will reduce stock size to
a level which produces little harvestable surplus.

During the 16 yr covered by this study ex-
tremely large year classes were produced in 3 yr
(1955, 1956, and 1958). Favorable conditions in
1969 resulted in a high survival rate, but only
produced 2.7 billion recruits because of small
spawning stock size. In one other year (1966)
survival occurred that was greater than expected,
but at extremely low stock size. In the other 11 yr
recruitment was either near, or well below the
expected level, compounding the stock depletion
caused by excessive fishing pressure. The drastic
reduction in stock size resulted in a restabilization
of the stock-recruitment relationship around a low
stock level. This is evidenced by the steady decline
in catches from 1956 to a low of 162,000 metric
tons in 1969, followed by slightly higher catches in
succeeding years (Table 7). Extremely large
catches in the late 1950's are the result of the
unusual coincidence of 3 high survival years
within a 4-yr span. Average survival over the
16-yr period was much lower, and average year-
class size would be considerably smaller, even at
optimum spawning stock size.

Schaaf and Huntsman (1972) gave MSY es-
timates for Atlantic menhaden of 600,000 metric
tons based on an equilibrium catch-effort curve
from historic data and 380,000 metric tons from a
population-prediction model. The population-
prediction model dampens the effects of large year

classes and probably comes closer to representing
long-term MSY than the higher estimates.

The maintenance of optimum spawning stock
size and several year classes in the spawning stock
is vital to insure adequate response to favorable
environmental conditions. Based on the estimated
survival rates over the 16-yr period, and the
optimum spawning stock size from the Ricker
function, surplus yield was calculated under
conditions which would maintain four spawning
groups (ages 3-6) in the populations. The calcu-
lation of surplus yield is based on an instantane-
ous natural mortality of 0.42 and fishing mortality
of 0.36 spread over 6 yr within a year class (ages
1-6) and assuming that one-half of the age-1 re-
cruits are vulnerable to the fishery. A full
complement of years 1-6, from year-class data
available after 1954, was not obtainable until
1961, when 6-yr-old fish were harvested from the
1955 year class. Under the conditions imposed on
the harvest, the allowable catch, computed for
1961-71, averaged 419,000 metric tons/yr (Table
7). Extremes in the allowable catch would have
ranged fron 227,000 to 633,000 metric tons,
depending on the size of year classes which con-
stituted stock size in a particular year. This catch
is similar to the MSY estimates of Schaaf and
Huntsman (1972), and was computed for a period
in which most of the year classes had less-than-
expected survival. The survival index was well
below 1.0 from 1959 to 1964, a period of six con-
tinuous years, and is reflected by the decline in
surplus stock during that period. Actual catches
made by the fishery from 1955 to 1971 (Table 7)
averaged approximately the same as MSY, but

TABLE 7. — Catch of Atlantic menhaden at MSY for actual survival rates, 1955-70 year classes, fishery
landings, 1955-71, and predicted surplus from recruit-environment model.

Potential catch at Sm

Actual catch by fishery

Predicted catch

Year of

No. in

Wt (thousand

Wt/fish

No. in

Wt (thousand

Wt/fish

Wt (thousand

harvest

billions

metric tons)

(9)

billions

metric tons)

(9)

metric tons)

1955

3.12

641.4

206

1956

3.56

721.1

203

1957

3.51

602.8

172

1958

2.72

510.0

188

1959

5.35

659.1

123

1960

2.78

529 8

191

1961

1.68

632.9

377

2.60

575.9

222

510.9

1962

1.38

488.1

354

2.01

537.7

268

466.7

1963

1.10

4100

373

1.76

346.9

197

412.5

1964

0.88

339.0

385

1.73

269.2

156

392.5

1965

0.76

226.6

298

1.50

273.4

182

295.5

1966

099

254.9

257

1.34

219.6

164

374.2

1967

1.72

367.4

214

0.98

193.5

197

371.5

1968

1.62

472.0

291

1.14

234.8

206

405.1

1969

1.40

426.0

304

0.87

161.6

185

387.0

1970

1.81

464.7

257

1.40

259.3

185

471.5

1971

1.78

525.6

295

0.97

250.3

258

521.6

Mean

1.37

418.8

306

2.20

410.4

178

419.0

were taken by extensive overfishing in the late
1950's and early 1960's, with a resultant decrease
in spawning stock size and age structure. The
average catch from 1955 to 1963 was 596,000
metric tons, well above the MSY level. The fishery
also took greater numbers of fish of smaller size
than was compatible with management to insure
adequate numbers of spawners. Thus overfishing,
which reduced stock size, was compounded by a
series of poor environmental years, further re-
ducing the spawning stock to a level below that
necessary to provide large surplus yields from the
higher survival years of 1966 and 1969. Had
optimum spawning stock size been maintained,
the fishery should have been able to increase its
yield during the 1967-71 fishing seasons by an
average of 231,000 metric tons/yr.

The value of a predictive model lies in its
usefulness for developing strategies to take
advantage of exceptional year classes or to avoid
overexploitation of poor year classes. Catches
based on the number of recruits calculated from
the survival index model are similar to MSY and
to those averaged by the fishery (Table 7).
However, the absolute mean error from the al-
lowable surplus is approximately 134,000 metric
tons/yr for the actual fishery landings (1961-71)
and 48,000 metric tons/yr if harvest had been
limited to the predicted surplus. Some overfishing
would have occurred because of errors in pre-
diction, but it would have been significantly less
than that imposed by the fishery during earlier
years. Fishing at a level necessary to harvest the
predicted surplus would have provided reasonably
stable catches, maintained several age-classes in
the fishery, maintained adequate spawning stock,
and prevented excessive exploitation of the stocks,
all desirable factors in the management of fishery
resources.

ACKNOWLEDGMENTS

The authors acknowledge a debt to the late
Robert L. Dryfoos who was instrumental in the
initiation of this work. We also express our ap-
preciation to David R. Colby for assistance in
computer analyses, to Herbert R. Gordy for the
illustrations, and to Valerie N. Ward for assis-
tance with the manuscript.

FISHERY BULLETIN: VOL. 75, NO. 1

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EFFECTS OF BENZENE (A TOXIC COMPONENT OF PETROLEUM)
ON SPAWNING PACIFIC HERRING, CLUPEA HARENGUS PALLASI

Jeannette W. Struhsaker1

ABSTRACT

When female Pacific herring were exposed to low (parts per billion) levels of benzene for 48 h just prior
to their spawning, a significant reduction occurred in survival of ovarian eggs and resultant embryos
and larvae through yolk absorption. The reduction in survival of ovarian eggs was approximately
10-25%, for embryos from fertilization to hatching, 26%, and for embryos and larvae through yolk
absorption, 43%. Exposure to benzene also induced premature spawning and resulted in aberrant
swimming behavior and disequilibrium in adults of both sexes.

The maximum accumulation of 14C-labeled benzene and/or metabolites in ovarian eggs (14 times
initial concentration in water in 24-48 h; 1.4 /il/g from 0.1 /id/liter) was greater than in later egg and
larval stages as measured in other experiments.

Conservatively estimating the total reduction in survival in these experiments to be approximately
50% through yolk absorption, I surmise that the effect of exposing spawning herring to only one toxic
component of petroleum could have a significant effect on the population. The fish in these experiments
were exposed to relatively high parts per billion levels, but they were exposed for a relatively short
period (48 h); it is probable that in the estuary, if chronically exposed over a longer period of time to low
parts per billion levels of aromatic components, the populations could be seriously affected.

When the spawning female herring is compared with other life history stages, we find that the
spawning stage is clearly the most sensitive of those tested. If fishes prove generally to be most
sensitive to petroleum components during their spawning seasons, fishery management decisions
should take this factor into consideration in protecting the resources.

In studies of pollutant effects on marine or-
ganisms, emphasis should be placed on critical or
sensitive life history stages. With this in view,
research on petroleum effects on fish has been
directed more recently toward egg, embryo, and
larval stages (Kiihnhold 1969, 1972; Evans and
Rice 1974; Struhsaker et al. 1974). Results in
many studies revealed that fish egg and larval
stages were surprisingly resistant to crude oil and
water-soluble and aromatic fractions of crude oil.
Some of this resistance in fish is probably at-
tributable to the presence of enzymes for
metabolic detoxification of components with
ensuing rapid depuration and physiological
homeostasis (Lee et al. 1972; Neff 1975; Korn,
Hirsch, and Struhsaker 1976, footnote 2).

I have observed, as expected, that the effects of
exposure of monoaromatics such as benzene are
more severe at all life history stages if fishes are

'Southwest Fisheries Center Tiburon Laboratory, National
Marine Fisheries Service, NOAA, 3 150 Paradise Drive, Tiburon,
CA 94920.

2Korn, S., N. Hirsch, and J. W. Struhsaker. 1976. The uptake,
distribution, and depuration of 14C-benzene and 14C-toluene in
Pacific herring (Clupea pallasi). Unpubl. manuscr.

otherwise stressed by environmental extremes or
are in poor "condition" from inadequate nutrition.
On this basis it is suggested that the female at
time of spawning may be the most sensitive stage
to toxic oil components. In herring, for example,
the fish often feed poorly for some time prior to
spawning and have low fat and energy reserves
associated with the production of eggs (Blaxter
and Holliday 1963). Anadromous fishes or fishes
such as herring which migrate into estuaries for
spawning may also be exposed to environmental
extremes, particularly to changes in salinity,
which produce additional stress. Further, since
aromatics are highly lipid-soluble, it might be
expected that benzene would accumulate to high
levels in ovarian eggs. These factors could lead to
significant reductions in fecundity and serious
consequences for populations over long chronic
exposures.

The purpose of this experiment was to examine
the effect of benzene on female Pacific herring,
Clupea harengus pallasi Valenciennes, just prior
to spawning. We have also studied benzene effects
on other life history stages of the herring
(Struhsaker et al. 1974; Korn et al. see footnote 2;

Manuscript accepted September 1976.
FISHERY BULLETIN: VOL. 75, NO. 1, 1977.

FISHERY BULLETIN: VOL. 75, NO. 1

Eldridge et al.3). So far as we know, there is no
similar study, exposing fish just prior to spawning,
for any oil component.

Benzene was selected for most of our studies on
herring because of its relatively high proportion in
the water-soluble fraction of crude oil and refined
products (Anderson et al. 1974), high solubility in
water and relative toxicity (Benville and Korn
1974, footnote 4; Korn, Struhsaker, and Benville
1976). Monoaromatics were tested individually
rather than exposing fishes to the total oil or total
water-soluble fraction in order to more specifically
delineate physiological responses to a known toxic
component.

Initial research on Pacific herring adults, eggs,
and larvae was conducted with high (ppm level)
concentrations of benzene (Struhsaker et al. 1974;
Korn, Struhsaker, and Benville 1976). Because of
the high volatility of benzene, such concentrations
would probably occur only briefly after cata-
strophic incidents, such as tanker accidents and
well blowouts. Subsequently, we tested levels in
the low ppb (parts per billion) range as being more
representative of chronic exposures and poten-
tially more damaging over a long period to marine
populations.

In this study, ripe male and female herring were
exposed just prior to spawning to 100 nl/liter (ppb)
and 800 nl/liter (ppb) benzene for 48 h. The re-
labeled benzene and its metabolites were mea-
sured in the ovaries to determine uptake, ac-
cumulation, and depuration. Exposure effects on
behavior, the mortality of eggs in the gonads of
females, and rate of delayed mortality in embryos
at hatching and larvae through yolk absorption
were also recorded.

METHODS

Pacific herring were captured 4 December 1974
during the spawning season in San Francisco Bay
by a local bait dealer. The fish were captured with
a lampara net and wet-brailed from the net into
the vessel bait wells. The fish were transported
immediately in the bait vessel to the Tiburon
Laboratory dock and then transferred to 1,900-
liter tanks in the laboratory. Fish were "running
ripe" when captured. Because the purpose of these

3Eldridge, M. B., T. Echeverria, and J. W. Struhsaker.
Manuscr. in prep. The effect of benzene on the energetics of
Pacific herring (Clupea harengus pallasi) embryos and larvae.

4Benville, P., Jr., and S. Korn. Manuscr. in prep. The acute
toxicity of six mono-cyclic aroma tics to striped bass (Morone
saxatilis) and bay shrimp (Crago sp.).

experiments was to expose fish prior to spawning,
an acclimation period of only 24 h was allowed.
Previous experience with ripe herring has shown
that they usually spawn shortly after capture.

Fish were initially placed in circular tanks with
double sand-filtered, open flow seawater at
ambient conditions in the bay at the time. Initial
handling mortality was negligible. During the
experiment, conditions were as follows: salinity,
23.0-24.0%o; temperature, 10.0°-11.5°C; oxygen,
6.0-10.5 ppm. An ambient benzene concentration
was undetectable at the ppb level. Since herring
generally feed poorly when spawning, neither
exposed nor control fish were fed during the ex-
periment. The exposure treatments were as
follows:

Control: 0 nl/liter (ppb) benzene; open flow
system, no benzene exposure; approximately
100 fish (50 males, 50 females).

Exposed: 800 nl/liter (ppb) benzene, open flow
system, constant exposure for 48 h; ap-
proximately 100 fish (50 males, 50 females).

Exposed: 100 nl/liter (ppb) 14C-labeled benzene;
static system, declining exposure, 48 h; 25
females only; linear decrease in benzene
concentration to approximately 10% of initial
concentration remaining at end of 48 h.

All benzene exposures were terminated and
open flow reestablished in the 100 ppb static
exposure tank at the end of 48 h. The static ex-
posure of 14C-labeled benzene was to determine
the uptake, accumulation, and depuration of
benzene in the gonads of females. The open flow
constant exposure and control were primarily to
establish morphological and mortality effects on
the ovarian eggs and delayed effects on sub-
sequent larval development and mortality.

The behavior of fish was observed before
sampling. Subsamples of females were taken daily
for 6 days — 2 days during exposure and 4 days
after. Fish were removed randomly until 10
females were obtained from the control and 800
ppb exposure conditions. Five females were
removed daily from the static 100 ppb exposure.
Concentrations of benzene in the water of all tanks
were also measured daily.

Each female sampled was measured (standard
length), weighed (wet weight), and the ovaries
dissected out. The ovaries were also measured
(total length) and weighed (wet weight); the left
ovaries were examined microscopically, the right

STRUHSAKER: EFFECTS OF BENZENE ON SPAWNING HERRING

ovaries prepared for radiometric or gas
chromatograph analyses. Methods of preparation
for radiometric and chromatograph measure-
ments are described elsewhere (Benville and Korn
1974; Korn, Hirsch, and Struhsaker 1976, see
footnote 2). It should be emphasized that the
radiometric technique measures total radioactiv-
ity and concentrations calculated may include
metabolites of benzene as well as benzene itself.

Ovaries were examined under a dissecting
microscope for developmental stage [Hjort's stage
(Bowers and Holliday 1961)] and the presence of
opaque dead or dying eggs, and the gross ap-
pearance (color and degree of deliquescence) was
ranked. The maximum diameters of 10 eggs from
the ovary of each female were measured and the
eggs examined for abnormal development.

On day 3, after cessation of exposure, pieces of
clean plastic screening were placed around the
standpipe in the center of the 800 ppb and 100 ppb
exposure and control tanks to provide substrate
for spawned eggs. Males were placed with females
in the 100 ppb tank. After spawning occurred, the
screens were removed and eggs examined for
developmental stage and mortality. Pieces of
screen with 75 eggs on each (most in 4-cell stage)
were cut apart. Pieces of screen were selected with
a single layer of relatively separated eggs because
previous experience showed reduced survival in
dense egg clusters. Two pieces of screen with 75
eggs each were placed in each 8-liter rearing
container (total of 150 eggs). There were five rep-
licate containers for each treatment and control
(total of 15 containers). Temperature during
development was 11.0°-12.0°C, and salinity,
22.0%o. Other rearing conditions were as pre-
viously described (Struhsaker et al. 1974).
Hatching occurred 10 days after fertilization, and
percent survival at hatching was determined from
three replicate counts of swimming larvae in each
container and by counting the number of dead and
abnormal embryos left on the screen. The screens
were removed and surviving larvae fed the rotifer,
Brachionus plicatilis, through the remainder of
the experiment (past yolk absorption to larval day
7). Surviving larvae were counted and the percent
survival through yolk absorption determined from
the original egg number.

Data were analyzed, depending upon variables,
with the methods of analysis of variance and
covariance using University of California
Biomedical programs, BMD 01V, 02V, and 03V
(Dixon 1970).

RESULTS

No adult mortalities occurred during the 6 days
of the experiment. Stress behavior was noted in
exposed fish, particularly at the constant 800 ppb
exposure. Definite distress was observed by the
end of the first day, although oxygen levels were
above saturation. Milling was disrupted, fish were
gaping at the surface, and many exhibited dis-
equilibrium. Even after cessation of exposure,
stress behavior continued for the duration of the
experiment. Control fish may also have been
stressed by the capture conditions and the short
acclimation period, but they exhibited none of the
stress symptoms of exposed fish and milled
normally.

Although behavior was abnormal in exposed
fish, spawning occurred in the tanks. In fact, the
stress from benzene exposure appeared to pre-
maturely induce spawning. This is illustrated in
Table 1 by the percentage of exposed fish which
were spent (Stage VII) compared with control fish.
At the end of the 6-day experimental period, 73%
(100 ppb) and 70% (800 ppb) of the exposed fish
were spent, compared with only 25% of the con-
trols. The higher percentage of spent females in
the 100 ppb static treatment than in the 800 ppb
open flow treatment during the first 4 days may be
a result of additional stress imposed by static
conditions. At all treatments, most unspent
ovaries were ripe (Stage VI); only 7-10% were
immature (Stages III-V) (Table 1).

No changes in growth (as indicated by wet
weight and length) were expected in females over
the short experimental period. However, these
measurements were taken to determine the
similarity of fish between the treatments and to
adjust effect of size on the differences in weights of
ovaries between the treatments. Ovary length and
weight and egg diameters were measured to
determine if benzene uptake affected the growth
or resorption of ovaries or eggs and to determine
the ripeness or proximity to spawning. Data are
summarized in Table 2. Egg diameter did not
correlate with any other measurement variable.
Analysis of variance revealed no significant
difference (P>0.25) in egg diameter between 0 and
800 ppb benzene treatments. Since the size range
of females varied somewhat between the two
treatments (Table 2), analysis of covariance was
used to compare the weights of females and
ovaries between concentrations and days after
adjustment for the effect of lengths (Table 3). No

FISHERY BULLETIN: VOL 75, NO. I

Table l-

-Effects of benzene exposure on

ovaries and

eggs of Pacific herring.

Benzene

concentration

(nl/l; ppb)

No. of
ovaries

examined

Percent o

f eggs

in stage'

No. of

ripe ovaries

examined

Stages
dead <

lll-VI

Hours

lll-V
Immature

VI
Ripe

VII

Spent

>ggs

(Days)

No.

100

800

(2)

100

800

(3)

100

800

100

(4)

100

800

100

120

(5)

100

0-AII spent

—

800

100

0-AII spent

—

148

(6)

100

0-AII spent

—

800

100

0-AII spent

—

Totals

(6 days)

100

800

'Hjort's stage; Bowers and Holliday (1961).

TABLE 2. — Mean and range of female standard length, wet weight; ovary length and wet weight; and maximum egg
diameter for Pacific herring. Linear equation describes the regression of wet weights on lengths for both whole female fish
and left ovaries. Sample size = 59 females; 59 ovaries (spent females excluded).

Female

Standard length (X)
Benzene

concentration Range Mean

(ppb) (cm) (cm)

Ovary (Stages lll-VI)

Wet weight (Y)
Range

(g)

Total length (X)

Wet weight (/)

Max egg diameter

Mean

(g)

Range
(cm)

Mean
(cm)

Range

(g)

Mean

(g)

Range
(mm)

Mean
(mm)

16.8-22.4

19.3

76.8-239.6

136.8

7.7-11.5 10.4

6.7-30.8

18.2

1.20-1.50

1.30

800

16.4-21.5

18.7

75.3-189.6

120.3

7.5-14.3 9.3

6.3-26.5

13.6

1 20-1.56

1.30

Total

16.4-22.4

19.0

75.3-239.6

126 2

7.5-14.3 9.9

6.3-30.8

15.9

1.20-1.56

1.30

Regressions'

Y = -339 96

^24 98X

Y = -19.26 + 3.56X

800

Y = -267.50

• 20 89X

Y = -12.84+2.90X

'Tests of significance between slopes (to) and elevations (a) of regressions showed no significant difference (0.100<P<0.250) between
concentrations (Snedecor and Cochran 1967:432-436).

TABLE 3. — Analysis of covariance of wet weight on standard length of female, wet weight of ovary
on wet weight of female, and wet weight on total length of ovary for Pacific herring. Analysis of ripe
ovaries (Stage VI) only. Treatments: Concentrations (0 vs. 800 ppb); Days (1 to 4); 2x4 = 8 treat-
ment combinations x 5 observations per treatment combination = 40.

Analysis of dependent variable (wet wt female) after adjustment for covanate (standard length female)
Source of variation

F ratio'

Probability

Between concentrations (C)

(0 vs. 800 ppb)
Between days (D)
Interaction (CD)
Within cells

5.2508

675.2348

485.9035

6.721.2742

5.2508
2250783
161.9678
2168153

0.24
1.04
075

P>0250
P>0.250
P>0.250

NS2

Analysis of dependent variable (wet wt ovary) after adjustment for covanate (wet wt female)

Source of variation

Between concentrations (C)

(0 vs. 800 ppb)
Between days (D)
Interaction (CD)
Within cells

F ratio

Probability

0 6940

2.5351

19.4057

165.5181

06940
0 8450
64686
53393

0.13
0.16
1.21

P>0250
P>0.250
P~>0.250

NS
NS
NS

Analysis of dependent variable (wet wt ovary) after adjustment for covanate (total length ovary)

Source of variation df SS MS F ratio Probability

Between concentrations (C)

(0 vs 800 ppb)
Between days (D)
Interaction (CD)
Within cells

'F 0.05=4.16, df = 1,31;F 0.05=2.91, df=3,31.
2NS = not significant

04585

004

P>0 250

27.2532

9.0844

0.71

P>0.250

8.0860

2.6953

021

P>0 250

3982616

12.8471

STRl'HSAKKR: EFFECTS OF BENZENE ON SPAWNING HERRING

significant difference (P>0.25) between con-
centrations or days or interaction was found. Tests
between slopes (b) and elevations (a) of the re-
gression lines of weights on lengths of females and
weights on lengths of ovaries (Snedecor and
Cochran 1967:432-436) showed no significant
differences (P>0.10) between 0 and 800 ppb
concentrations (Table 2).

Microscopic examination of the ovaries,
however, revealed the presence of dead eggs in
ovaries of exposed fish by the second day of expo-
sure (Table 1). No dead eggs were found in control
fish until day 4, and then only a few (15-20 eggs) in
one female, the rest of the ovary appearing nor-
mal. Ovaries of exposed fish contained sig-
nificantly larger numbers of opaque dead eggs
(more than 10%) and were generally paler yellow
and deliquescent. By the end of 6 days, 67% (100
ppb) and 54% (800 ppb) of exposed females were
found with ovaries containing dead or dying eggs.

The uptake and depuration of benzene in
ovaries of females exposed to a static initial
concentration of 100 nl/liter (ppb) 14C-labeled
benzene is shown in Figure 1, together with data
determined from other larval studies for later
stages (Eldridge, Struhsaker, and Echeverria5).
Uptake was rapid, so that a maximum accumu-
lation (1.4 /u.l/g; ppm) was reached in 24 h. This
level was maintained through the 48-h exposure
period. After open flow was reestablished and
exposure ended, benzene and/or metabolites were
depurated until they reached an undetectable
level in 96 h. The figure shows that levels ac-
cumulated in ovarian eggs were higher and
sustained longer than in later egg and larval
stages from other experiments with comparable
exposure conditions.

Results of rearing experiments with eggs from
females exposed to 0 and 800 ppb unlabeled
benzene are summarized in Tables 4 and 5.
Survival was also reduced in eggs and larvae from
females exposed to an initial concentration of 100
ppb labeled benzene. However, results were
obscured by an additional variable. Eggs taken
from the static exposure tank were covered by
filamentous bacterial growth early in develop-
ment and many eggs died as a result. In the other
treatment with open flow and in controls, eggs did
not undergo this mortality due to epifloral growth.

i.o

Q- 0 8

^ 0 7

~ 06
oj

5 05

3 04
Cl
a.

O 03
O

E
o

f 0.2

Eggs In Ovary

0 6 12 18 24

Time (h)

sEldridge, M. B., J. W. Struhsaker, and T. Echeverria.
Manuscr. in prep. The uptake, accumulation and depuration of
14C-labeled benzene in embryos and larvae of Pacific herring
(Clupea harengus pallasi).

FIGURE 1. — Accumulation of 14C-labeled benzene in different
early Pacific herring developmental stages exposed to an initial
concentration of 100 nl/liter (ppb) in a static system. Concentra-
tions shown on y-axis were calculated from total radioactivity
and may include metabolites derived from benzene as well as
benzene. Spawned eggs were in a stage just prior to blastopore
closure; post yolk-sac larvae were fed the rotifer, Brachionus
plicatilis, containing high accumulated levels of labeled ben-
zene. ND = not detectable.

The 100 ppb treatment, therefore, was not in-
cluded in the analysis. Analysis of variance
showed survival at hatching and survival of lar-
vae through yolk absorption were significantly
less in exposed eggs (800 ppb) than in control eggs
(P<0.1; Table 5). Exposure to ppb benzene levels
for only 48 h reduced survival by about 43%
through yolk absorption to larval day 7 (Table 4).

DISCUSSION

When female herring were briefly exposed to
low levels of benzene for 48 h just prior to
spawning, a significant reduction occurred in
survival of eggs and resultant larvae from the
ovary through yolk absorption. It is probable that
further mortality would have occurred in later
larval stages if the experiments were continued.
When this result is compared with that from
exposing other life history stages after spawning
(Struhsaker et al. 1974; Eldridge et al. see footnote
5) where survival is not affected except at ppm
levels, it appears that the spawning female and
ovarian eggs are the most sensitive stages.

FISHERY BULLETIN: VOL. 75, NO. 1

TABLE 4. — Mean percent survival through hatching and yolk absorption of Pacific
herring larvae from eggs of benzene-exposed and control females.

Stage

Benzene

concentration

(nl/l; ppb)

Total
no. of
eggs

Mean

survival

(%)

95%

confidence

Interval

(%)

Mean

reduction

survival1

(%)

Embryos to hatching

Hatched larvae through
yolk absorption

800
0

800

750
750
750
750

92.9

666
76.7
34.4

91.5-94.3
64.1-69.1
74.5-78.9
32.0-36.8

-26.3
-43.3

1See Table 5 for test of significance.

TABLE 5. — One-way analysis of variance in survival of Pacific herring embryos to hatching and
larvae through yolk absorption (larval day 7). Ripe females exposed prior to spawning. Five
replicate containers per treatment; 150 eggs/container. ( Arcsin transformation applied to percent
survival data.)

Percent survival to hatching

Source of variation

F ratio

Probability

Between concentrations

0 vs. 800 ppb
Within groups

Total

1 .3442

0.0843
1 .4285

06721

0 0070

95.6098-

P<0.01

Percent survival through yolk absorption

Source of variation

F ratio

Probability

Between concentrations

0 vs. 800 ppb
Within groups

Total

12
14

0.8053

0.1599
0.9652

0.4026

0.0133

30.2147*

P<0.05

Although male herring were not studied in de-
tail here, their behavior was severely disrupted, as
in the females. Testes of mature, spawning her-
ring have been found to contain higher levels of
cholesterol (a lipid) during spawning than at other
times in their adult life (Blaxter and Holliday
1963), and it is possible the lipid-soluble benzene
may accumulate to high levels in testes of ripe
males. Effects on males and their spermatozoa, as
well as effects on females, may have contributed to
reduction in survival of fertilized eggs through
yolk absorption in these experiments.

Reference to Figure 1 shows that the maximum
accumulation of labeled benzene in ovarian eggs
was greater than in later egg and larval stages as
measured in other experiments. Accumulation in
ovarian eggs of exposed females was approxi-
mately twice that in eggs exposed just after
spawning and prior to blastopore closure and
about six times that in embryos exposed just after
yolk-sac absorption. Accumulation for the first 48
h of water column exposure in these stages ap-
pears to correlate with the yolk volume of the eggs
and larvae, decreasing as yolk is utilized, as would
be expected with lipid-soluble benzene. However,
the decreased accumulation may also relate to the
development of enzymes enabling later stages to
metabolize benzene and subsequently depurate
more rapidly. After being fed Brachionus

plicatilis, which accumulate high levels of benzene
(Echeverria6), the fish larvae rapidly accumulated
benzene from their food (Figure 1). Other studies
of accumulation in tissues of adult herring (Korn
et al. see footnote 2) show that only one site, the
gall bladder with bile, accumulates higher con-
centrations than ovarian eggs (30 times and 14
times initial concentration, respectively).

I have noted previously (Struhsaker et al. 1974)
that the percentage survival of eggs through
hatching is significantly less (approximately 25%
less;P<0.01) in Pacific herring eggs collected from
San Francisco Bay than in those from Tomales
Bay. Although other environmental differences
may be involved, this reduction in hatching suc-
cess may well relate to the effects of accumulated
pollutants in the gonads of spawning fish in the
relatively more polluted San Francisco Bay wa-
ters and warrants further study.

Estimating that the reduction in survival of
eggs through yolk absorption of spawning exposed
females is at least 43%, the effect on Pacific her-
ring populations exposed to only one toxic
component of petroleum could be significant.
Considering that the total water-soluble fraction
contains many other toxic aromatics, it is possible

"Echeverria, T. Manuscr. in prep. Uptake and depuration of
14C benzene in the rotifer, Brachionus plicatilus.

STRUHSAKER: EFFECTS OF BENZENE ON SPAWNING HERRING

that long-term chronic exposures to low levels
may be decreasing population survival in polluted
areas. In addition, chlorinated hydrocarbons in
pesticides may also be accumulating in the
gonadal lipids and interacting with petroleum
hydrocarbons producing even more deleterious
effects. More studies of the effects of these
components on spawning fish are clearly needed. If
fishes prove generally to be the most sensitive to
accumulated oil components during their spawn-
ing season, fisheries management decisions
should take into consideration their protection
from damaging levels, particularly at spawning
time.

ACKNOWLEDGMENTS

I thank the staff of the Physiology Program,
SWFC Tiburon Laboratory, for assisting me in
these experiments. I am grateful to Norman
Abramson and Vance E. McClure for reviewing
the manuscript and for making suggestions. Dale
Straughan, Institute of Marine and Coastal
Studies, University of Southern California, also
reviewed the manuscript and made several
improvements.

LITERATURE CITED

ANDERSON, J. W., J. M. NEFF, B. A. COX, H. E. TATEM, AND
G. M. HIGHTOWER.

1974. Characteristics of dispersions and water-soluble
extracts of crude and refined oils and their toxicity to
estuarine crustaceans and fish. Mar. Biol. (Berl.)
27:75-88.
BENVILLE, P. E., JR.. AND S. KORN.

1974. A simple apparatus for metering volatile liquids into
water. J. Fish. Res. Board Can. 31:367-368.
BLAXTER, J. H. S., AND F. G. T. HOLLIDAY.

1963. The behavior and physiology of herring and other
clupeids. Adv. Mar. Biol. 1:261-393.

BOWERS, A. B., AND F. G. T. HOLLIDAY.

1961. Histological changes in the gonad associated with
the reproductive cycle of the herring (Clupea harengus L.).
Dep. Agric. Fish. Scotl., Mar. Res. 1961(5), 16 p.
DIXON, W. J. (editorl

1970. Biomedical computer programs. Univ. Calif.
Press, Berkeley, 600 p.
EVANS, D. R., AND S. D. RICE.

1974. Effects of oil on marine ecosystems: A review for
administrators and policy makers. Fish. Bull., U.S.
72:625-638.

KORN, S., N. HIRSCH, AND J. W. STRUHSAKER.

1976. Uptake, distribution, and depuration of 14C-benzene
in northern anchovy, Engraulis mordax, and striped bass,
Morone saxatilis. Fish. Bull., U.S. 74:545-551.
KORN, S., J. W. STRUHSAKER, AND P. BENVILLE, JR.

1976. Effects of benzene on growth, fat content, and caloric
content of striped bass, Morone saxatilis. Fish. Bull.,
U.S. 74:694-698.
KUHNHOLD, W. W.

1969. Der Einfluss wasserloslicher Bestandteile von
Roholen und Rohblfraktionen auf die Entwicklung von
Heringsbrut. [Engl, abstr.] Ber. Dtsch. Wiss. Komm.
Meeresforsch., Neue Folge 20:165-171.
1972. The influence of crude oils on fish fry. In M. Ruivo
(editor), Marine pollution and sea life, p. 315-318.
Fishing News (Books) Ltd., Surrey, Engl.
LEE, R. F., R. SAUERHEBER, AND G. H. DOBBS.

1972. Uptake, metabolism and discharge of polycyclic
aromatic hydrocarbons by marine fish. Mar. Biol. (Berl.)
17:201-208.
NEFF, J. M.

1975. Accumulation and release of petroleum-derived
aromatic hydrocarbons by marine animals. Symposium
on chemistry, occurrence, and measurement of polynuc-
lear aromatic hydrocarbons, p. 839-849. Div. Pet.
Chem., Inc., Am. Chem. Soc. Chicago Meeting, 1975.

SNEDECOR, G. W., AND W. G. COCHRAN.

1967. Statistical methods. 6th ed. Iowa State Univ.
Press, Ames, 593 p.
STRUHSAKER, J. W., M. B. ELDRIDGE, AND T. ECHEVERRIA.
1974. Effects of benzene (a water-soluble component of
crude oil) on eggs and larvae of Pacific herring and north-
ern anchovy. In F. J. Vernberg and W. B. Vernberg
(editors), Pollution and physiology of marine organisms,
p. 253-284. Academic Press Inc., N.Y.

BIOLOGY OF THE REX SOLE,
GLYPTOCEPHALUS ZACHIRUS, IN WATERS OFF OREGON

Michael J. Hosie1 and Howard F. Horton2

ABSTRACT

Data are presented on the life history and population dynamics of rex sole, Glyptocephalus zaehirus
Lockington, collected from Oregon waters between September 1969 and October 1973. Length-weight
relationships vary little between sexes or with time of year. Otolith annuli form primarily from
January through May and were used for age determination. Age and length are highly correlated
(r = 0.9945 for males and 0.9864 for females), with females growing faster and living longer than
males. Estimates of total instantaneous mortality rate (Z) appear less variable when calculated by the
catch-curve method (mean Z of 0.64 for males and 0.51 for females), than by the Jackson method. Age at
50% maturity occurs at 1 6 cm ( about 3 yr ) for males and at 24 cm (about 5 yr ) for females. Spawning off
northern Oregon occurs from January through June, with a peak in March-April. Fecundity is
correlated (r = 0.9620) with length offish. There were 15 recaptures (0.59% ) from 2,537 fish tagged off
northern Oregon during March and June 1970. Maximum movement of recaptured fish was only 53.9
km, but the low recovery precludes definite conclusions. Twenty loci were detected by starch-gel
electrophoretic analysis using rex sole muscle tissue. Of these, three loci were polymorphic, but showed
no discernible variation between collections from northern, central, and southern Oregon in April
1973.

Investigation into the life history of rex sole,
Glyptocephalus zaehirus Lockington, by the Ore-
gon Department of Fish and Wildlife provided new
information on this species. The broad objective
was to develop knowledge of the biology and
population dynamics of rex sole found off the
Oregon coast which would enhance management
of this species.

Specific objectives were to: 1) determine the
length-weight and age-length relationships; 2)
estimate the total instantaneous mortality rate by
two independent methods; 3) determine rela-
tionships of maturity and fecundity with length
and age, and with the spawning season; and 4)
determine if rex sole off Oregon are composed of
separate stocks3 which undergo predictable
movements.

The rex sole is a slender, thin flatfish belonging
to the family Pleuronectidae (Starks 1918; Nor-
man 1934), the right-eyed flounders. Of the three
species of Glyptocephalus , rex sole is the only one
reported in the eastern Pacific Ocean (Pertseva-
Ostroumova 1961). Geographically distributed

'Oregon Department of Fish and Wildlife, Marine Field
Laboratory, P.O. Box 5430, Charleston, OR 97420.

2Department of Fisheries and Wildlife, Oregon State Uni-
versity, Corvallis, OR 97331.

3The rex sole spawning in a particular marine location (or
portion of it) at a particular season, and which do not interbreed
to a substantial degree with any group spawning in a different
place, or in the same place at a different season (modified from
Ricker 1972).

from southern California to the Bering Sea (Miller
and Lea 1972), it is found bathymetrically to 730
m (Alverson et al. 1964). Rex sole is important in
the commercial trawl fishery from California
northward through British Columbia. In 1972, rex
sole was the fifth most important flatfish in weight
(1.54 million kg [3.4 million pounds]) in the
domestic northeastern Pacific trawl food fishery.
Glyptocephalus zaehirus is also important in the
domestic trawl fishery for animal food (Best 1961;
Niska 1969), although this fishery has declined in
recent years. On the continental shelf off the
northern three-fourths of the Oregon coast, rex
sole was third in biomass4 and first in numbers of
all flatfish caught with an 89-mm (3.5-inch) mesh
trawl.

There is little published information on the
biology of rex sole. Villadolid (1927) and Frey
(1971) reported briefly on the time of spawning,
size and age at maturity, and food habits for
specimens captured off California. Hart (1973)
summarized the life history of rex sole off Canada
and suggested that the lack of information re-
sulted in doubtful deductions. An aging study was
conducted on rex sole by Villadolid (1927) who
used scales. Domenowske (1966) used otoliths,

Manuscript accepted August 1976.
FISHERY BULLETIN: VOL. 75. NO. 1. 1977.

4Demory, R. L., and J. G. Robinson. 1973. Resource surveys on
the continental shelf of Oregon. Fish Comm. Oreg.t Commer.
Fish. Res. Dev. Act Prog. Rep., July 1, 1972 to June 30, 1973, 19
p. (Unpubl. manuscr.).

FISHERY BULLETIN: VOL. 75, NO. 1

scales, and interopercles for aging rex sole; by
comparing the age-length relationships, he
concluded otoliths were the most readable
structure. Vanderploeg (1973) conducted food
habit studies on rex sole collected off Oregon.
Porter (1964) described the larvae of rex sole, and
Waldron (1972) and Richardson (1973) reported on
distribution and abundance of rex sole larvae.
Tsuyuki et al. (1965) conducted a general starch-
gel electrophoresis study on the muscle proteins
and hemoglobin of 50 species of North Pacific fish
and found that rex sole differed from 10 other
pleuronectids tested. Benthic distribution of rex
sole was investigated by numerous workers4
(Alverson et al. 1964; Day and Pearcy 1968;
Demory 1971; Alton 1972). Limited tagging
studies (Manzer 1952; Harry 1956) were con-
ducted to determine movements of rex sole, but no
tagged fish were recaptured.

METHODS

Rex sole were collected by otter trawl off Oregon
from the Columbia River south to Cape Blanco at
depths of 18-200 m during September 1969-73.
Most data were obtained from rex sole captured
incidentally to a study of pink shrimp, Pandalus
jordani, distribution during 1969-70. 5 Rex sole
were also obtained from commercial trawl land-
ings at Astoria, Oreg., in 1970 and 1973; at
Charleston and Brookings, Oreg., in 1973; and
from research vessel catches during the 1971-73
Fish Commission of Oregon (FCO) groundfish
surveys.4 6 All specimens were frozen until time of
examination.

Rex sole were sexed by examination of gonads,
measured for total length (TL) to the nearest
centimeter, and weighed to the nearest gram. The
left otolith was removed for aging studies, stored
in a 50:50 solution of glycerin and water, and read
using reflected light on a dark background ( Powles
and Kennedy 1967).

The length-weight relationship, by calendar
quarters, of rex sole collected off central and
northern Oregon in 1969-72 was determined by
the least squares method using the logarithmic

5Lukas, G., and M. J. Hosie. 1973. Investigation of the
abundance and benthic distribution of pink shrimp, Pandalus
jordani, off the northern Oregon coast. Fish Comm. Oreg.,
Commer. Fish. Res. Dev. Act, Final Rep., July 1, 1969 to June 30,
1970, 45 p. (Unpubl. manuscr.).

6Demory, R.L. 1974. Resource surveys on the continental shelf
of Oregon. Fish Comm. Oreg., Commer. Fish. Res. Dev. Act Prog.
Rep., July 1, 1973 to June 30, 1974, 6 p. (Unpubl. manuscr).

form of the equation W =aLb , where W is weight in
grams, L is length in centimeters, and a and b are
constants.

Estimates of the lineal growth of rex sole were
obtained from the age-length relationship of fish
collected off northern Oregon in September-
October 1969 and September 1971. A mean total
length (TL) at each age was determined from these
data and expressed mathematically in terms of the
von Bertalanffy growth equation (Ricker 1958;
Ketchen and Forrester 1966).

To obtain the calculated growth parameters, we
used ages 1.5-10.5 yr for males and 1.5-12.5 yr for
females.

Estimates of the instantaneous total mortality
rate (Z) were made using age group data obtained
from FCO groundfish cruises off northern Oregon
in 1971 and 1973 and off central Oregon in 1972.
Two methods, a catch curve (Ricker 1958) and the
Jackson technique (Jackson 1939), were used for
the analyses.

To determine maturity stages, gonads were
examined according to the procedures described
by Hagerman (1952), Scott (1954), and Powles
(1965). Definitions used for maturity stages are
listed in Table 1.

Fecundity was determined from 13 fish collected
in February 1970 and measured to the nearest
millimeter (TL). Both ovaries were removed from

TABLE 1. — Description of reproductive phases of rex sole gonads
used in this study.

Sex

Maturity
stage

Description

Females Immature (A): Ovaries very small (<40 mm TL), whitish in color,
semitransparent, and gelatinous. No eggs dis-
cernible to the naked eye.
Mature (B): Ripening. Ovaries enlarging, becoming reddish-
orange colored and granular in consistency, full of
developing eggs that can be recognized by direct
observation.

(C): Ripe. Ovaries full of mostly reddish-orange colored
granular eggs, although a few transparent ova are
present. Ova can be extruded from the fish by using
considerable pressure.

(D): Spawning Ovaries full of entirely translucent eggs
which will run with slight pressure.

(E): Spent. Ovaries flaccid, usually empty although
occasionally a few eggs will remain. Ovarian
membrane very transparent and saclike.

(F): Recovering. Ovaries filling with fluid, and reddish-
orange in color. No ova detectable to the naked
eye.
Males Immature (A): Testes very small (<3 mm TL), translucent in color
and not extending into the abdominal cavity.
Mature (B): Ripening Testes enlarged, extending posteriorly
into abdominal cavity, light brown to cream colored,
but retain sperm under pressure.

(C): Ripe and/or spawning. Testes full and cream
colored. Sperm will run under no or only slight
pressure.

(D): Spent-recovering. Testes shrunken and trans-
parent or dark brown in color.

HOSIE and HORTON: BIOLOGY OF REX SOLE

each fish and stored in 10% Formalin.7 Estimates
of fecundity were obtained gravimetrically,
following the method described by Harry (1959).

To obtain fish for tagging, short tows of about 15
min were made in March and June 1970 off
northern Oregon near the mouth of the Columbia
River. Any rex sole caught were held for 15-60 min
in a tank containing running seawater. Fish in
good condition were tagged and released. Petersen
disc (vinyl) tags, 16 mm in diameter, were at-
tached by a stainless steel pin inserted through
the musculature about Vz inch below the midbase
of the dorsal fin. Fishermen were advised of the
tagging program, and a $0.75 reward was offered
by the FCO for each tagged rex sole returned.

Electrophoresis was used to investigate stock
identification of rex sole. A preliminary electro-
phoretic examination was conducted using muscle
tissue of 145 rex sole collected in April 1973 in
three nearly equal samples taken off northern,
central, and southern Oregon. Tissue extraction
and starch gel electrophoresis procedures followed
the methods of Johnson et al. (1972). Tests were
conducted for polymorphisms in muscle protein
and the five enzyme systems: aspartate
aminotransferase (AAT) A-I and A-II; lactic
dehydrogenase (LDH); peptidase A-I and A-II;
phosphoglucomutase (PGM); and tetrazolium
oxidase (TO).

RESULTS AND DISCUSSION

Length-Weight Relationships

Length and weight were closely correlated, with

7Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

the derived coefficient of determination (r2) vary-
ing from 0.9902 to 0.9988 for males and from
0.9872 to 0.9966 for females (Table 2). These
coefficients of determination varied little by
season, possibly because of the extended spawning
period (Villadolid 1927) in the first half of the year.
Based on data in Table 2, we calculated mean
weights by season at representative lengths. For
both sexes weight increase was greatest in the
third quarter, average in the second quarter, and
slowest in the first and fourth quarters (Table 3).
Among mature fish, about 30 cm TL and larger,
females generally were slightly heavier than
males of the same length (Figure 1). A total of 950
males and 1,121 females were included in the
length-weight data analyzed.

Age and Growth

Validity of the Aging Technique

Opaque or hyaline zones occur on the margin of
rex sole otoliths. These zones mark the respective
periods of rapid or slow growth. Examination of
265 otoliths from rex sole <27 cm TL collected off
northern Oregon from September 1969 through
July 1970 revealed that hyaline edges were first
observed in September (Figure 2). No hyaline
edges were present the previous June or July. In
the fall the percentage of otoliths with a hyaline
zone on their edge began to increase. By January
the majority of otoliths had a hyaline zone on their
edge. The percentage rapidly increased and
peaked in March when 92.3% had hyaline zone
margins. Conversely, opaque zones on edges were
at their lowest in March, gradually increasing
until June or July when all otoliths had opaque
edges.

TABLE 2. — Length-weight relationship (log10 W = log10a + b logL) by quarterly period for male and
female rex sole collected off central and northern Oregon, 1969-72. '

Period
and sex

Number
of fish

Constant
log a

Constant
b

Standard
deviation

Correlation
coefficient

Coefficient of
determination

January-March:
Male

119

-3.1447

3.5551

0.1437

0.9972

0.9944

Female

-3.0978

3.5095

0.1587

0.9936

0.9872

Both

187

-3.1248

3.5258

0.1539

0.9932

0.9864

April-June:
Male

386

-2.8398

3.3557

0.1501

0.9994

0.9988

Female

356

-2.9398

3.4345

0.1488

0.9980

0.9960

Both

742

-2.8903

3.3914

0.1567

0.9984

0.9968

July-September:
Male

350

-3.0884

3.5598

0.1461

0.9982

09964

Female

621

-2.9886

3.5112

0.1661

0.9983

0.9966

Both

971

-3.0631

3.5553

0.1788

0.9988

0.9976

October-December:

Male

-2.9823

3.4423

0.1269

0.9951

0.9902

Female

-2.9795

3.4423

0.1599

0.9972

0.9944

Both

171

-2.9500

3.4252

0.1562

0.9973

0.9946

'Regression analysis conducted on 1 1- to 36-cm males and 1 1- to 51 -cm females.

FISHERY BULLETIN: VOL 75, NO. 1

TABLE 3. — Computed mean weight per quarter at selected
lengths of male and female rex sole, using regression formulas
from Table 2.

Sex

Total
length
(cm)

Computed mean weight (g) per quarter1
I II III IV

Male

Female

15
25
35
15
25
35
45

221

210

506

220

231

547

256

271

655

215

231

514

'I = Jan-Mar.; II = Apr-June; III = July-Sept.; IV = Oct -Dec

HOOr

KX>0

900

o»800

£ 700

^ 600

o 500

z 400

<
Id
2 300

• MALES (N=950)
O FEMALES (N=II2I)

^oo

•cP

200
I00

.CP

d?"

_l_

10 15 20 25 30 35
TOTAL LENGTH (Cm)

40 45 50

FIGURE 1. — Length-weight relationship for male and female rex
sole collected off central and northern Oregon, 1969-72. Body
weights obtained from an average of quarterly mean values.

From these observations, we concluded that the
hyaline margin is deposited on otoliths during
each winter and spring for all sizes of rex sole.
Thus, these hyaline zones are interpreted as an-
nuli with a year's growth occurring between
successive hyaline margins. These results are
similar to those of Villadolid (1927) who found
northern California rex sole formed a scale an-
nulus in March through May.

Age-Length Relationship

After 3.5 yr of age, females were consistently
longer than males at a given age. Females also
attained an older age and longer length. Statistics
for both males and females followed the von
Bertalanffy growth curve, as a good fit was ob-
tained for most age groups (Figure 3, Table 4).

I00r

80-

~ 70

w 60

>-
o
z 50

uj 40
or

(13)

(20)

(18)

30
20

10-

(93)

(28)

(32)

S 0 N D
1969

(12)

(13)

(20) (16)

MONTH

M A M J J A
1970

FIGURE 2. — Percent frequency of hyaline edges found on otoliths
of 265 rex sole (<27 cm TL) collected off northern Oregon,
September 1969-July 1970. Numbers in parentheses represent
sample size.

40 r

"-*

_1
<

30
20

MALES

I, =33.43

( N = 257 )

-0.1778 (t-0.8551)

0 1749 (t -0 5667)1

6 8 10 12

age (yr)

FIGURE 3. — Age-length relationship for male and female rex
sole collected off northern Oregon, September-October 1969 and
September 1971.

The calculated length at infinity (Loo) of 33.43
cm for males was close to the computed mean
value of 29.33 cm (Table 4). For females theL^ of

HOSIE and HORTON: BIOLOGY OF REX SOLE

TABLE 4. — Computed mean length at age and mean length at age estimated by von
Bertalanffy growth equation for 45 unsexed, 189 male, and 212 female rex sole collected off
northern Oregon in September-October 1969 and September 1971.

Age'
(yr)

No.

1.5

345

2.5

3.5

4.5

5.5

6.5

7.5

8.5

9.5

10.5

11.5

12.5

13.5

14.5

15.5

16.5

17.5

18.5

Male

Computed mean Estimated mean
length (cm) length2 (cm)

9.20
12.61
17 00
19.52
21 66
24.55
2539
2582
27.37
28.90
29.33
27.00

9.44
13.36
16.65
19.39
21 69
23.62
25.22
26.57
27.69
28 63
2942
30.07

345

Female

Computed mean Estimated mean
length (cm) length2 (cm)

920
12.71
16.64
20.45
24.95
25.64
26.33
28.05
3037
31.03
33.35
3245
33.75
33.50
37.00
47.00

0.00
47.30

891
13.44
17.25
2045
23.14
25.39
27.29
28 88
30.21
31 34
32.28
33.07

33 73

34 29
34.76

'These fall-caught fish were assumed to be about one-half way through the growing season, based upon
otolith readings.

2Von Bertalanffy growth equations were based on 1- to 10-yr-old males (La = 33.43 cm, K
-0 8551 yr), and 1- to 12-yr-old females (Lx = 37.21 cm, K = 0.1747, (0 = -0.5667 yr)
3Sexes were not separated for age 1 fish (45 specimens)

= 0.1778, tn

37.21 cm fit observed data through age 15.5, but
was far below the maximum computed mean TL of
47.30 cm. The apparent discrepancy does not in-
validate the data because Knight (1968) noted
that Lx is not the maximum obtainable length,
but rather a mathematical tool needed in compu-
tations for the von Bertalanffy growth equation.
This is exemplified by our collection of a 23-yr-old
( ± 1 yr), 59-cm female rex sole off northern Oregon
in February 1970, which we consider as about the
maximum length and age of rex sole. Hart (1973)
reported a 24-yr-old rex sole was collected off
British Columbia, but no length was given.

Mortality Rate

Estimates of the total instantaneous mortality
rate (Z) derived from data in Table 5 and using the
catch curve method varied from 0.53 to 0.70 for
males and from 0.44 to 0.55 for females (Table 6).
In this analysis the natural logarithm of the
numbers of males and females caught at each age
was plotted against the respective age class
(Figures 4, 5). The total mortality rate was the
best fitted slope on the right side of the catch curve,
determined by linear regression using ages rang-
ing maximally from 6 to 16 yr (Table 5).

Estimates of Z using the Jackson method
ranged from 0.43 to 0.61 for males and from 0.20 to
0.52 for females (Table 6). In this method annual
survival rate (S) is:

TABLE 5. — Numbers of rex sole per age group caught during
groundfish surveys off northern Oregon in 1971 and 1973 and
central Oregon in 1972.

Age

Number males

Number females

(yr)

1971

1972

1973

1971

1972

1973

116

142

102

124

270

290

337

353

207

514

244

663

387

329

732

613

375

278

881

418

501

1,217

380

412

432

400

560

570

215

274

382

366

465

596

320

106

582

108

201

123

138

283

247

219

Total

2,093

2,358

2,781

3,149

3,184

4,291

TABLE 6. — Estimates of the total instantaneous mortality rate
(Z) of rex sole collected off northern Oregon in September 1971
and 1973 and off central Oregon in September 1972.

Age of

Catch curve

Jackson method

Year

maximum

Ages

estimates of

and sex

numbers

utilized

1971:

Male

8-16

0.70

0.43

Female

7-16

0.44

0.20

1972:

Male

6-13

0.53

0.44

Female

6-16

0.55

0.31

1973:

Male

7-13

0.68

0.61

Female

7-14

0.54

0.52

Mean:1

Male

0.64

0.49

Female

0.51

0.34

'Based on simple average of Z's for the 3 yr.

FISHERY BULLETIN: VOL. 75, NO. 1

8
6
4
2

- 8

»-
x

<
o

CD o

8-
6-

4
2r

N = I833
r =0.9215

1971

1972

_l I I I I I I I I l_

1973

• N = I926
r =0.9558

_i i i i i i i i i

8 12

AGE

FIGURE 4. — Catch curves of male rex sole collected off Oregon in
September 1971, 1972, and 1973.

<
o

in
a.

1971

N = 2297
r =0 9135

j i i i i i i i '

1972

1973

FIGURE 5. — Catch curves of female rex sole collected off Oregon
in September 1971, 1972, and 1973.

S =

Nt + Ns + ... + Nr
Ne + Nl + ... + Nr-l

where N is the number of fish of age group r
caught. Annual mortality rate is 1 - S and the
corresponding instantaneous rate of total mortal-
ity is obtained from the expressions = e z, where e
and Z are derived from Ricker (1958).

The catch curve method probably gives more
reliable estimates of Z than those obtained using
the Jackson method. In the Jackson method the
larger samples of younger fish strongly affect the
estimates, with the older age groups weighted
less. Thus, the Jackson method substantially
underestimates the mean Z for the entire right
limb of the catch curve.

Reproduction

Size at Maturity

Some males were mature at 13 cm while no
females reached maturity until 19 cm (Figure 6).

30
20

</> 0

fe 50

iu 40

| 30

— MATURE

-o IMMATURE

A LENGTH AT 50% MATURITY

Q LENGTH AT 100% MATURITY

VUV^.

10 14 18 22 26 30 34 38 42 46 50 54 58 62
TOTAL LENGTH (Cm)

FIGURE 6. — Size composition of immature and mature rex sole,
by sex, collected off northern Oregon, September 1969-July
1970.

About 50% of the males were mature at 16 cm, and
all were mature at 21 cm. For females, 50% were
mature at 24 cm and 100% were mature at 30 cm.
Lengths at 50% and 100% maturity correspond to

HOME and IIORTON: BIOLOGY OF REX SOLE

about ages 3 and 5 for males and 5 and 9 for
females (Table 4).

The only maturity data on rex sole available
from other areas is that of Villadolid (1927). He
found that both males and females off San
Francisco, Calif., were fully mature at age 4,
which corresponded to about 21.8 cm for males and
22.8 cm for females. Possibly rex sole mature
earlier in the southern portion of their range.

Spawning

Duration of the spawning period was from
January through June, with a peak in March-
April (Figure 7). Although samples were not
obtained during August and December, the
percentage offish in each reproductive phase gives
a good indication of the spawning time.

The 6-mo spawning period we found is longer
than the January through April spawning re-
ported by Villadolid ( 1927) for rex sole collected off
central California in 1925 and 1926. Paul Reed
(FCO, pers. commun.) found a prolonged spawning
from January through August for 3,189 rex sole
collected off northern California in 1949-54 and

100

(20) (77) (16) (64) (60) (37) (84) (33) (55) (50)

RIPENING

_□_

2 ioor

u.
50

RIPE AND SPAWNING

I00r (—1 r^

SPENT AND RECOVERY

nil

SONDJFMAMJJA
1969 1970

MONTH

FIGURE 7. — Annual cycle of reproduction in 496 rex sole (274
males and 222 females) collected off northern Oregon, Sep-
tember 1969-July 1970. The number in each monthly sample is
shown in parentheses.

1962-63. This suggests the duration of rex sole
spawning varies by area and year.

Fecundity

Examination of 13 mature females ranging
from 240 to 590 mm TL yielded fecundity esti-
mates of 3,900 and 238,100 ova, respectively. The
numbers of ova generally increased with size of
the female. In 11 of 13 fish, the right ovary con-
tained more ova than the left ( 100 to 12,700 more).
A linear regression fitted to the fecundity-length
data gave a correlation coefficient of 0.9620 (Fig-
ure 8). The formula for the regression line was
F = 5.3797 x 10"7L422667, where F is fecundity in
number of ova and L is fish TL in millimeters.

300

200 300 400 500
TOTAL LENGTH (mm)

600

FIGURE 8. — Fecundity-length relationship for 13 rex sole col-
lected off northern Oregon, February 1970.

Stock Identification
Tagging Experiment

A total of 2,537 rex sole were tagged and re-
leased off the northern Oregon coast in April (200)
and June 1970 (2,337). There were 15 recaptures
(0.59% recovery) by July 1974, all from the June
1970 tagging (Table 7). Maximum movement was
53.9 km, and 788 days was the longest time at
liberty. There was little change in the depth range
occupied by recaptured fish, which were released
in 42-154 m and recovered by trawls in 51-101 m.

These results suggest only limited movement by
rex sole. However, tag returns were too few to
justify definite conclusions. This low recovery is
similar to reports of rex sole tagged off British
Columbia (Manzer 1952 [90 tagged]) and Oregon
(Harry 1956 [19 tagged]) from which no fish were
recovered.

FISHERY BULLETIN: VOL 75, NO. 1

TABLE 7. — Release and recovery data on 2,537 rex sole tagged off
northern Oregon, April and June 1970.

Date

Number Number Percent
tagged recovered recovery

Distance

traveled

(km)

Days at
liberty

April 1970
June 1970

200
2,337

0
15

000
0.64

0.0

1.5
17.1

0.0

3.7
23.0
14.1

2.2

8.0
14.3

0.9

38.9

539

unknown

39
523

0.0

189

240

278

279

294

346

364

374

450

788

Total

2.537

0.59

The low returns possibly were caused by rex sole
not surviving the tagging process. Manzer (1952)
reported rex sole reacted badly to capture and
tagging. Most tagged rex sole released at the ocean
surface did not immediately descend. Instead,
unlike most other flatfish species, they curled into
a semicircle and moved across the water surface in
a skipping motion. This peculiar reaction might
have resulted in a high initial tagging mortality
from predation. It may also indicate a stress
condition from which fish did not recover.

Starch-Gel Electrophoretic Analysis

There were 20 loci detected in the muscle tissue
of 145 rex sole. Of these loci 13 were enzymes and 7
were muscle proteins (Table 8). Only three of the
loci (15%) were polymorphic.

The polymorphism was found in only three of
the eight systems studied or examined. AAT
staining occurred in two anodal regions (A-I and
A-II). Zone II was the only polymorphic region,
having A, B, C, and D alleles (Figure 9, Table 9).
The enzyme peptidase also had two anodal re-

ORIGIN

O OBSERVED

■i NOT OBSERVED

□

CD
CD

o □

CD
CD

□

1 1 1 1 1

ZONE I
(POLYMORPHIC)

ZONE n
(MONOMORPHIC)

AA AB BB BC CC CD DD AD AC BD
AAT PHENOTYPES

FIGURE 9. — Diagrammatic representation of aspartate
aminotransferase (AAT) phenotypes in starch gel from 145 rex
sole collected off Oregon, April 1973.

TABLE 9. — Frequencies of aspartate aminotransferase (AAT)
phenotypes in 145 rex sole collected off Astoria, Charleston, and
Brookings, Oreg., in April 1973.

Item

Astoria

Charleston

Brookings

Sample size

Date

5, 9 April

30 April

8 April

AAT phenotypes:

Frequency of alleles:

0.28

0.30

0.31

0.47

0.42

0.43

0.23

0.26

0.24

0.02

gions. Only zone II was polymorphic, with A and B
alleles (Figure 10, Table 10). A third enzyme,
PGM, was polymorphic, having only one locus
which had A1, A, and B alleles (Figure 11, Table
11).

No discernible variation in the frequency or
kinds of phenotypes found was observed between
rex sole collections from off Astoria (northern),

TABLE 8. — Results of electrophoretic tests of muscle tissue samples from 145 rex
sole collected off Oregon, April 1973.

No. of

Proposed

no.

Type of

bands in

no. of

of alleles

per

alleles

Phenotypic

Protein1

starch gel

loci

locus

found

variation

AAT A-I

—

Monomorphic

AAT A-II

A,B,C,D

Polymorphic

LDH

—

Monomorphic

Peptidase A-I

—

Monomorphic

Peptidase A-II

A.B

Polymorphic

PGM

A'.A.B

Polymorphic

—

Monomorphic

Muscle proteins2

—

Monomorphic

1AAT (aspartate aminotransferase); LDH (lactate dehydrogenase); PGM (phospho-
glucomutase); TO (tetrazolium oxidase).

2Analysis of muscle proteins was nonspecific, with 6 anodal ( + ) bands and 1 cathodal ( -) band
found.

HOSIF and HORTON: BIOLOGY OF REX SOLE

FIGURE 10. — Diagrammatic representation of peptidase
phenotypes in starch gel from 137 rex sole collected off Oregon,
April 1973.

TABLE 10. — Frequencies of peptidase anodal zone II phenotypes
in 137 rex sole collected off Astoria, Charleston, and Brookings,
Oreg., in April 1973.

Item

Astoria

Charleston

Brookings

Sample size1

Date

5, 9 April

30 April

8 April

Peptidase phenotypes:

Frequency of alleles:

0.50

0.43

0.55

0.50

0.57

0.45

'An additional two rex sole from the Astoria sample and six fish from the
Brookings sample did not develop distinct patterns and hence are not included.

Charleston (central), or Brookings (southern)
Oregon (Tables 9-11). These data are insufficient
to warrant extended speculation. However, they
suggest that geographic selection or variation in
rex sole off Oregon, if any, may not revolve around
the genetic system included in the eight systems
tested. Other alternatives, such as testing ad-
ditional genetic systems or possible use of hel-
minth parasites as biological tags, should be
investigated to provide a more extensive evalua-
tion of the population structure of rex sole off
Oregon as a possible adjunct to effective man-
agement decisions.

ACKNOWLEDGMENTS

Financial support was provided by the Fish
Commission of Oregon (now Oregon Department
of Fish and Wildlife [ODFW]). James Meehan,
Gerald Lukas, Bill Barss, Edwin Niska, Jack
Robinson, Robert Demory, and Brent Forsberg (all
ODFW) helped collect and tag rex sole. Paul Reed

UJ +

-1 1

_l
_l
<

uj a

_i
_l

li-

1 7DNF T

(MONOMORPHIC)

F-

> A

t-
<

ZONE n
(POLYMORPHIC)

A
A

ui B

□ □

F-

_l
UJ

ORIGIN

1 1

AB BB

PEPTIDASE

PHENOTYPES

ORIGIN

□

A'A AA AB

PGM PHENOTYPES

FIGURE ll. — Diagrammatic representation of phospho-
glucomutase (PGM) phenotypes in starch gel from 145 rex sole
collected off Oregon, April 1973.

TABLE 11. — Frequencies of phosphoglucomutase (PGM)
phenotypes in 145 rex sole collected off Astoria, Charleston, and
Brookings, Oreg., in April 1973.

Item

Astoria

Charleston

Brookings

Sample size

Date

5. 9 April

30 April

8 April

PGM phenotypes:

A'A

Frequency of alleles:

000

0.00

0.01

0.98

099

0.99

0.02

0.01

0.00

(ODFW) provided spawning data on northern
California rex sole. Allyn Johnson (National
Marine Fisheries Service) conducted the elec-
trophoretic analysis. The assistance of Rudy
Lovvold of the MV Sunrise, and Thomas Oswald
and Olaf Rockness of the RV Commando is ap-
preciated. W. G. Pearcy (Oregon State Universi-
ty), S. J. Westrheim (Canada Department of the
Environment), and Robert Loeffel (ODFW)
criticized the manuscript.

LITERATURE CITED

Alton, M. S.

1972. Characteristics of the demersal fish fauna inhabiting
the outer continental shelf and slope off the northern
Oregon coast. In A. T. Pruter and D. L. Alverson (editors),
The Columbia River estuary and adjacent ocean waters, p.
583-634. Univ. Wash. Press, Seattle.
ALVERSON, D. L., A. T. PRUTER, AND L. L. RONHOLT.

1964. A study of demersal fishes and fisheries of the

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northeastern Pacific Ocean. H. R. MacMillan Lectures in
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BEST, E. A.

1961. The California animal food fishery 1958-1960. Pac.
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DAY, D. S., AND W. G. PEARCY.

1968. Species associations and benthic fishes on the con-
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DEMORY, R. L.

1971. Depth distribution of some small flatfishes off the
northern Oregon-southern Washington coast. Fish
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DOMENOWSKE, R. S.

1966. A comparison of age estimation techniques applied to
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Washington, Seattle, 102 p.
FREY, H. W.

1971. California's living marine resources and their utili-
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HAGERMAN, F. B.

1952. The biology of the Dover sole, Microstomas pacificus
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HARRY, G. Y. III.

1956. Analysis and history of the Oregon otter-trawl fishery.
Ph.D. Thesis, Univ. Washington, Seattle, 328 p.

1959. Time of spawning, length at maturity, and fecundity
of the English, petrale, and Dover soles (Parophrys vet-
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spectively). Fish Comm. Oreg., Res. Briefs 7:5-13.

Hart, j. L.

1973. Pacific fishes of Canada. Fish. Res. Board Can., Bull.
180, 740 p.

Jackson, c. h. n.

1939. The analysis of an animal population. J. Anim. Ecol.
8:238-246.

Johnson, A. G., F. M. Utter, and H. O. Hodgins.

1972. Electrophoretic investigation of the family Scor-
paenidae. Fish. Bull., U.S. 70:403-414.

Ketchen, k. S., and C. R. Forrester.

1966. Population dynamics of the petrale sole, Eopsetta
jordani, in waters off western Canada. Fish. Res. Board
Can., Bull. 153, 195 p.

Knight, w.

1968. Asymtotic growth: an example of nonsense dis-
guised as mathematics. J. Fish. Res. Board Can.
25:1303-1307.

MANZER, J. I.

1952. Notes on dispersion and growth of some British Co-
lumbia bottom fishes. J. Fish. Res. Board Can. 8:374-377.

Miller, D. J., and R. N. Lea.

1972. Guide to the coastal marine fishes of California.
Calif. Dep. Fish Game, Fish Bull. 157, 235 p.
NlSKA, E. L.

1969. The Oregon trawl fishery for mink food, 1958-
65. Pac. Mar. Fish. Comm., Bull. 7:90-101.

Norman, J. R.

1934. A systematic monograph of the flatfishes

(Heterosomata). Vol. 1. Psettodidae, Bothidae, Pleuronec-
tidae. Br. Mus. (Nat. Hist.), Lond., 459 p.
PERTSEVA-OSTROUMOVA, T. A.

1961. The reproduction and development of far-eastern
flounders. Akad. Nauk. USSR, Inst. Okeanol., 484 p.
(Transl. Fish. Res. Board Can. Transl. 856.)

Porter, P.

1964. Notes on fecundity, spawning and early life history
of petrale sole (Eopsetta jordani) with descriptions of
flatfish larvae collected in the Pacific Ocean off Humboldt
Bay. California. M.S. Thesis, Humboldt State Coll., Ar-
eata, Calif, 98 p.

POWLES, P. M.

1965. Life history and ecology of American plaice (Hip-
poglossoides platessoides F.) in the Magdalen Shallows. J.
Fish. Res. Board Can. 22:565-598.

POWLES, P. M., AND V. S. KENNEDY.

1967. Age determination of Nova Scotian greysole, Glyp-
tocephalus cynoglossus L., from otoliths. Int. Comm.
Northwest Atl. Fish., Res. Bull. 4:91-100.
RICHARDSON, S. L.

1973. Abundance and distribution of larval fishes in waters
off Oregon, May-October 1969, with special emphasis on
the northern anchovy, Engraulis mordax. Fish. Bull., U.S.
71:697-711.
RICKER, W. E.

1958. Handbook of computations for biological statistics of
fish populations. Fish. Res. Board Can., Bull. 119, 300 p.

1972. Hereditary and environmental factors affecting cer-
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SCOTT, D. M.

1954. A comparative study of the yellowtail flounder from
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STARKS, E. C.

1918. The flatfishes of California. Calif. Fish Game 4:161-
179.
TSUYUKI, H, E. ROBERTS, AND W. E. VANSTONE.

1965. Comparative zone electropherograms of muscle
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VANDERPLOEG, H. A.

1973. The dynamics of 65Zn in benthic fishes and their prey
off Oregon. Ph.D. Thesis, Oregon State Univ., Corvallis,
104 p.

VILLADOLID, D. V.

1927. The flatfishes ( Heterosomata) of the Pacific coast of the
United States. Ph.D. Thesis, Stanford Univ., Palo Alto,
332 p.
WALDRON, K. D.

1972. Fish larvae collected from the northeastern Pacific
Ocean and Puget Sound during April and May 1967. U.S.
Dep. Commer., NOAA Tech. Rep. NMFS SSRF-663,
16 p.

ABUNDANCE AND POTENTIAL YIELD OF THE ROUND HERRING,

ETRUMEUS TERES, AND ASPECTS OF ITS EARLY LIFE HISTORY

IN THE EASTERN GULF OF MEXICO1

Edward D. Houde2

ABSTRACT

Eggs and larvae of the round herring, Etrumeus teres, were surveyed from plankton collections made in
the eastern Gulf of Mexico from 1971 to 1974 to determine adult stock size, spawning areas, and
spawning seasons and to study aspects of its early life history. Spawning occurred from mid-October
through May where depths ranged from 30 to 200 m, surface temperatures from 18.4° to 26.9°C, and
surface salinities from 34.5 to 36.5°/oo. A major spawning area was present 150 km from Tampa Bay
between lat. 27°00' and 28°00'N and long. 083°30' and 084°30'W. Mean relative fecundity of 8 adult
females was 296.5 ova per gram and the sex ratio of 71 adults was 1:1. The development time of eggs
from spawning to hatching was approximately 2.0 days at 22°C. Three methods were used to determine
adult biomass. The most probable annual estimates of biomass were approximately 700,000 metric
tons in 1971-72 and 130,000 metric tons in 1972-73. The best estimates of the range of potential annual
yields to a fishery were from 50,000 to 250,000 tons. Abundance and mortality rates of larvae were
estimated in each year. It is probable that more than 99.4% mortality occurred between spawning and
the 15.5-mm larval stage during 31 days in 1971-72 and more than 98.3% mortality occurred for the
same period in 1972-73.

Round herring, Etrumeus teres (DeKay), is one of
several clupeid fishes that are abundant in conti-
nental shelf waters of the eastern Gulf of Mexico.
Distribution and abundance of this species was
determined, based on egg and larvae surveys, as
part of a program to investigate abundance and
fishery potential for sardinelike fishes in the east-
ern Gulf. It is generally believed that several
species of underexploited clupeid fishes from this
area could provide significant catches (Bullis and
Thompson 1967; Bullis and Carpenter 1968; Wise
1972) that would supplement yields of the heavily
exploited Gulf menhaden, Breuoortia patronus.
The egg and larvae surveys were carried out in 17
cruises from 1971 to 1974. Preliminary reports on
clupeid abundance, based on these surveys, have
been published (Houde 1973a, 1974) and overall
results of the surveys were recently summarized
(Houde 1976; Houde et al. 1976; Houde and Chitty
1976).

There are eight apparently discrete populations
of Etrumeus in the world oceans. Whitehead
(1963) has placed all of the forms in the single
species E. teres. Recorded populations occur in the

Contribution from Rosenstiel School of Marine and Atmo-
spheric Science, University of Miami, Miami, Fla.

2Division of Biology and Living Resources, Rosenstiel School
of Marine and Atmospheric Science, University of Miami, 4600
Rickenbacker Causeway, Miami, FL 33149.

western Atlantic from Cape Cod into the Gulf of
Mexico, in the eastern North Pacific from the Gulf
of California to north of Los Angeles, in the central
North Pacific near Hawaii, in the Indo-Pacific off
the south and west coasts of Australia, in the
western North Pacific off the coasts of Japan, in
the western Indian Ocean off the east coast of
South Africa, in the Red Sea, and near the Gala-
pagos Islands in the Eastern Pacific.

Eggs and larvae of E. teres have been described
from some areas where they occur (Blackburn
1941; Uchida et al. 1958; Mito 1961; Houde and
Fore 1973; O'Toole and King 1974; Watson and
Leis 1974). Ito (1968) examined fecundity and
maturity of round herring from the Sea of Japan.
Spawning by Hawaiian round herring recently
was discussed by Watson and Leis (1974). Dis-
tribution and abundance of round herring eggs
and larvae were reported in the Gulf of California
(Moser et al. 1974; De la Campa de Guzman and
Ortiz Jimenez 1975) and in the northern Gulf of
Mexico by Fore (1971). Khromov (1969) found
Etrumeus larvae to be common in plankton
catches during a winter survey of the eastern Gulf
of Mexico.

Round herring are fished commercially off
Japan and South Africa. A catch of approximately
26,000 metric tons was made by South Africa in
1973 (Food and Agriculture Organization 1974;

Manuscript accepted August 1976.
FISHERY BULLETIN: VOL.75, NO. 1, 1977.

O'Toole and King 1974), and the Japanese catch
was 40,400 metric tons in that year (Food and
Agriculture Organization 1974). The species is not
fished at present in the Gulf of Mexico. Salnikov
(1969) reported that round herring was abundant
in the northeastern Gulf of Mexico, and Harvey
Bullis (pers. commun.) stated that it was plentiful
in the eastern Gulf, based on acoustic traces and
trawl catches made by National Marine Fisheries
Service research vessels. Our initial surveys of
eggs and larvae indicated that it might be abun-
dant in the eastern Gulf (Houde 1973a), and Fore
(1971) reported round herring eggs and larvae to
be abundant in the northern Gulf of Mexico. In the
absence of a commercial fishery, catch and effort
statistics, and other data on abundance, I have
estimated the adult biomass in the eastern Gulf
from the abundance of eggs that were spawned
annually. This fishery-independent technique of
biomass estimation can provide preliminary
knowledge of fishery potential (Ahlstrom 1968)
and is considered to be a useful biomass estimat-
ing procedure (Saville 1964; Smith and
Richardson in press).

METHODS

Survey Area and Times

Seventeen plankton surveys were made in the
eastern Gulf of Mexico between lat. 24°45' and
30°00'N (Figure 1) in 1971-74 (Table 1). Most
sampling stations were located on the broad conti-
nental shelf, where depths ranged from 10 to 200
m, but a few stations were over the continental
slope where depths were greater. Potential sam-
pling stations were on transects running parallel
to lines of latitude; transects were spaced at 15-
nautical-mile (27.8-km) intervals. Stations were
located at 15-mile (27.8-km) intervals on each
transect, except for those stations beyond the
200-m depth contour, which were placed at 30-
mile (55.6-km) intervals (Figure 1). Not all sta-
tions were sampled on each cruise (Table 1). Other
details of survey planning and design have been
reported elsewhere (Rinkel 1974; Houde et al.
1976; Houde and Chitty 1976).

Beginning with cruise IS 7205 (Table 1), sam-
pling was restricted to stations on alternate tran-
sects. The three stations nearest to shore (at
27.8-km intervals) were sampled on each of the
designated transects but only stations at 30-mile
(55.6-km) intervals were sampled offshore. A few

FISHERY BULLETIN: VOL. 75, NO. 1

FIGURE 1.— Area emcompassed by the 1971-74 eastern Gulf of
Mexico ichthyoplankton surveys. Plus symbols ( + ) represent
stations that were sampled during the survey. The 10-, 30-,
50-, and 200-m depth contours are indicated.

additional stations were added on 1974 cruises in
areas where depth was less than 10 m; no round
herring eggs or larvae occurred at these stations
and they were not important with regard to
spawning by this species, but they were important
in determining spawning and distribution of other
Gulf clupeids.

Plankton Sampling

A paired 61-cm Bongo net plankton sampler was
used on all cruises except cruise GE 7101, in which
a 1-m ICITA [International Cooperative Investi-
gations of the Tropical Atlantic (Navy)] plankton
net with 505-^m mesh was towed. Meshes on the
Bongo sampler were 505 /xm and 333 fxm.
Ichthyoplankton was sorted from the 505-^tm
mesh net and plankton volumes were determined
from the 333-/u,m mesh net catch (Houde and
Chitty 1976). Net tows were double oblique from
within 5 m of bottom to surface or from 200-m
depth to surface at deep stations. Nets were towed
at approximately 3.0 knots (1.5 m/s) in 1971, but
towing speed was reduced on later cruises and
averaged 2.3 knots (1.2 m/s) (Table 2). Stations
were sampled whenever the ship occupied them;
thus, tows were made during either daylight or
darkness, depending on the time of arrival at a
station.

Prior to cruise GE 7208, all tows consisted of

HOUDE: ABUNDANCE AND POTENTIAL YIELD OE ROUND HERRING

TABLE 1 . — Summarized data on cruises to the eastern Gulf of Mexico, 197 1 -74, to estimate abundance of round herring eggs and larvae.
(GE = RV Gerda, 8C = RV Dan Braman, TI = RV Tursiops, 8B = RV Bellows, IS = RV Columbus Iselin, CL = RV Calcnus.)

Number

of
stations

Positive
stations

Mean egg abundance under 10 m2

Mean larvae abundance under 10 m2

Cruise

Dates

for eggs'

for larvae2

All stations

Positive stations

All stations

Positive stations

GE 71013

1-8 Feb. 1971

39.37

196.88

7.34

16.30

8C 7113

TI 7114

7-18 May 1971

123

0.21

12 88

300

1580

GE 7117

26 June-4 July 1971

0.00

—

000

—

8C 7120

TI 7121

7-25 Aug. 1971

146

0.00

—

0.00

—

TI 7131

8B 7132

GE 7127

7-16 Nov. 1971

41.41

187.73

4.18

14.20

8B 7201

GE 7202

1-11 Feb. 1972

151.20

604.81

20.29

49.97

GE 7208

1-10 May 1972

1.38

22.11

0.28

4.44

GE 7210

12-18 June 1972

0.00

—

0.00

—

IS 7205

9-17 Sept. 1972

0.00

—

0.00

—

IS 7209

8-16 Nov. 1972

0.83

8.30

1.61

40.28

IS 7303

19-27 Jan. 1973

23.77

101.04

19.12

48.76

IS 7308

9-17 May 1973

2.48

6072

229

37.41

IS 7311

27 June-6 July 1973

0.00

—

0.00

—

IS 7313

3-13 Aug. 1973

0.00

—

0.00

—

IS 7320

6-14 Nov. 1973

4.11

26 22

111

1 1 32

CL 7405"

28 Feb.-9 Mar. 1974

0.00

—

000

—

CL7412

1-9 May 1974

0.49

21.50

3.98

175.07

'Positive station is a station at which round herring eggs were collected.

2Positive station is a station at which round herring larvae were collected.

3An ICITA, 1-m plankton net was used on this cruise. On all other cruises a 61 -cm Bongo net was used.

4No stations in offshore areas were sampled, accounting for the failure to collect round herring eggs or larvae on this i

TABLE 2. — Summary of plankton tow characteristics for 17 ichthyoplankton cruises to the eastern Gulf of Mexico. The
61-cm Bongo net sampler was used on all cruises except GE 7101 in which a 1-m ICITA net was used.

Standard error

Mean

Standard error

Mean volume

Standard error of

Number

Mean volume

towing

filtered per

volume filtered

filtered

volume filtered

speed

towing speed

unit depth

per unit depth

Cruises

stations

(m3)

(m/s)

(m3/m)

GE7101

8C7113& TI 7114

GE 7117

8C 7120 & TI 7121

8B7132&TI 7131

GE 7202 & 8B 7201

GE 7208

GE 7210

IS 7205

IS 7209

IS 7303

IS 7308

IS 731 1

IS 7313

IS 7320

CL 7405

CL7412

358

335 <55 m
deep

124 >55 m
deep

675.25

160.17

104.39

231 .93

30 29

7.27

0.92

11.80

1.44

1.17

1.18

0.03

0.01

49.69

3.60

11.04

2.37

11.58

0.11

0.57

0.07

wire release at 50 m/min to desired depth and
retrieval at 20 m/min. In later cruises, two types of
tow were used, a shallow-water tow at stations less
than 55 m deep and the usual 50 m/min release-20
m/min retrieval tow at deeper stations (Table 2).
The shallow-water tow was of 5-min duration; it
consisted of 1 min for wire release and 4 min for
wire retrieval. The objective at shallow stations
was to filter 100 m3 of water. This objective was
met, but the volume of water filtered per unit of
depth fished by the net was increased significantly
at the shallow stations relative to deeper stations

(Table 2). This discrepancy in type of tow was
considered to be more desirable than the alterna-
tive situation, which existed in 1971, when as lit-
tle as 25 m3 of water were filtered at some of the
shallowest stations. Tows at stations deeper than
55 m filtered between 100 and 400 m3.

A stopwatch was used to monitor each tow and
the wire angle was measured at the end of each
minute of a tow. A time-depth recorder gave a
record of tow characteristics. Volume filtered was
determined from a flowmeter in the mouth of the
505-yu.m mesh net.

FISHERY BULLETIN: VOL. 75, NO. 1

Plankton Samples

All samples were preserved immediately in 10%
seawater Formalin3 buffered with marble chips.
Samples were transferred to 5% buffered Forma-
lin after they had been stored in the laboratory for
1 mo. Houde and Chitty (1976) have discussed
methods used to determine plankton volumes. All
fish eggs and larvae were sorted from each 505-/xm
mesh net plankton sample under a dissecting mi-
croscope for later identification and enumeration.

Eggs and larvae of round herring are distinctive
and easily identified (Houde and Fore 1973).
Round herring eggs from each station were enu-
merated; larvae were enumerated and measured
with an ocular micrometer in a dissecting micro-
scope.

Temperatures and Salinities

Temperature and salinity profiles of the water
column at each station were obtained on all
cruises.4 Usually a mechanical bathythermo-
graph cast was made to describe the vertical tem-
perature profile. This was followed by a hydrocast
consisting of from two to seven 1.7-liter Niskin
bottles with reversing thermometers. Samples for
salinity were brought to Rosenstiel School of
Marine and Atmospheric Science for analysis. On
cruises IS 7308 and IS 7320 a salinity-
temperature depth unit was used in place of the
Niskin bottles to obtain temperature and salinity
data. Round herring egg and larva data were
examined in relation to temperatures and
salinities at stations where they were collected.

Determining Egg and Larvae Abundance

Catches of round herring eggs and larvae at
each station were standardized to give abundance
in numbers under 10 m2 of sea surface:

cj2j

(1)

where n, = the number of individuals (eggs or lar-
vae) at station j under 10 m2 of sea
surface

'Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

••Temperature and salinity data for these cruises can be re-
trieved from the MAFLA file at the National Oceanographic
Data Center, Washington, D.C.

c = the catch of eggs or larvae at station^'
Zj = the depth of tow (in meters) at station/
Vj = the volume filtered by the net (in cubic
meters) at station j.

Both total larval abundance under 10 m2 and lar-
val abundance in each 1.0-mm length class under
10 m2 were determined.

Numbers of eggs or larvae also were estimated
in the area represented by each station. These
areas were determined by the polygons described
by the perpendicular bisectors of lines from the
station in question to adjacent stations (Sette and
Ahlstrom 1948):

CjZj

(2)

where p • = the estimated total number of eggs or
larvae in the area represented by sta-
tion j
Cj, Zj, and Vj are defined in Equation (1)
Aj = the area (in square meters) rep-
resented by station j .

Total larvae and larvae by 1.0-mm length classes
were estimated for each station area. Most sta-
tions represented areas ranging from 0.75 to 3.15
x 109 m2.

The estimated total number of eggs and larvae,
as well as larvae by 1.0-mm length classes, was
estimated for the entire area represented by each
cruise:

P, = I

(3)

7 = 1

where P, = the cruise estimate (i.e., the total
number of eggs or larvae estimated in
the area represented by cruise i)
k = the number of stations sampled dur-
ing cruise i
Pj is defined by Equation (2).

Variance estimates on the abundance of eggs
were obtained for each cruise using a combination
of methods outlined by Cushing (1957) and Taft
(1960). Only stations at which round herring eggs
had been collected at least once during the 1971-74
survey period were included in obtaining these
estimates. Other stations were considered to be
outside the area of spawning, because round her-
ring eggs were never collected there. These usu-
ally were the three stations on each transect that

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING

were located closest to the coast (Figure 1). An
estimate of the variance in egg abundance under a
square meter of sea surface (sy ) was obtained from
the log10 ((CjZjVvj) + 0.1 egg catch at each station
during a cruise (Cushing 1957). The log10 variance
estimate so obtained was backtransformed to ob-
tain the untransformed estimate of variance. The
variance estimate for a cruise was calculated
using the estimator given by Taft (1960) that as-
sumes random sampling. It is:

7 = 1

A2 <t*

(4)

where SP. = variance estimate on the abundance

ri.

of eggs spawned during the period
represented by cruise i

D, = the number of days represented by
cruise i, defined as the days included
in the cruise plus one-half the days
since the previous cruise and one-
half the days to the next cruise
(Sette and Ahlstrom 1948). When a
cruise took place shortly after the
assumed date of the beginning of the
round herring spawning period (15
October) or near the end of the
spawning season (31 May), the
number of days from the inclusive
cruise days to the beginning or end
of the season was used in estimating
D,

Ay = the area (m2) represented by thejth
station in the ith cruise

dy = the duration (days) of the egg stage
from spawning until hatching. The
best estimate of du for round herring
is 2.0 days, based on observed egg
stages in catches during the surveys
and this value was used in all abun-
dance and variance calculations

sfj = the variance estimate for the
number of eggs present under 1 m2 of
sea surface for cruise i

k, = the number of stations included in
the variance estimate for cruise i.

Sampling was not random in the eastern Gulf
surveys. Also, egg catches were not normally or
log-normally distributed, nor did the distribution
of catches fit contagious distributions like the
negative binomial. Thus, the variance estimates
that I have obtained are not the best estimates, but

they may be reasonable approximations (Saville
1964) for variance in the area represented by the
cruises. Variation in spawning that occurs over
time (i.e., day to day variation) has not been ac-
counted for, which is the usual situation in
ichthyoplankton abundance surveys (Saville
1964).

An estimate of the abundance of eggs spawned
over the entire spawning season is:

Pa - 1

P,D,

(5)

i = \

where Pa = the total number of eggs spawned in
an annual spawning season
r = the number of cruises upon which the
estimate of annual spawning is based
Pi, D,, and d, are defined in Equation (4).

An estimate of variance on the number of eggs
spawned annually was obtained, assuming that
sampling was random using the formula given by
Taft (1960):

= Isl

(6)

i = l

where Sp

the variance estimate on the number
of eggs spawned annually
r is defined in Equation (5)
Sp is defined in Equation (4).

This variance estimate, like that for individual
cruise abundance estimates, is not entirely satis-
factory because the assumptions of random sam-
pling and normally distributed catches do not hold.
Also, as in the cruise variance estimates (Equa-
tion (4)), it was not possible to obtain an estimate
of variance in abundance due to day to day varia-
bility, thus leaving variation in time unaccounted.
Taft has shown that this can be a large source of
error and that annual spawning estimates will not
be more precise than individual cruise estimates
when variation in time is not considered.

Biomass Estimating Procedure

An estimate of adult biomass of a fish stock can
be obtained if the annual spawning (number of
eggs), sex ratio, and relative fecundity (eggs pro-
duced per gram adult female per year) are known
(Saville 1964; Ahlstrom 1968). Biomass of adults
is:

FISHERY BULLETIN: VOL. 75, NO. 1

Fr ■ K

(7)

where B = biomass of adults in the stock

Fr = mean relative fecundity of females

(eggs produced per gram female per

year)
K = the proportion of adults that are

females
Pa is defined in Equation (5).

Estimates ofPa, Fr, and if were obtained for round
herring in the Gulf of Mexico.

An estimate of K was derived from examination
of 71 gonads of adult round herring trawled from
the Gulf of Mexico by the National Marine
Fisheries Service. The estimate of Fr also was ob-
tained from these specimens. Fecundity was esti-
mated by the gravimetric method (Holden and
Raitt 1974). Modes of yolked oocytes were as-
sumed to be spawned during an annual spawning
cycle. This assumption was supported by the pres-
ence of only a single mode of unyolked oocytes in
six females collected during months when no
spawned eggs were collected in plankton tows.
Fecundity was estimated in a sample of eight
near-ripe females. Procedures used to estimate
round herring fecundity are like those outlined for
scaled sardine, Harengula jaguana, by Martinez
and Houde (1975).

Three techniques were used to estimate adult
biomass. All give estimates of annual spawning
(Pa ) that are based on the same egg catches, stan-
dardized per unit area of sea surface. Thus, the
three estimates of biomass for each spawning sea-
son are not independent; but, because each
technique has unique assumptions, the spawning
estimates are different, and it was useful to calcu-
late biomass by each procedure for comparison
purposes. The three techniques are outlined by
Sette and Ahlstrom (1948), Simpson (1959), and
Saville(1956, 1964).

The method first used by Sette and Ahlstrom
(1948) and subsequently by Ahlstrom (1954,
1959a) is based on obtaining an estimate of annual
spawning by the techniques that I have outlined in
Equations (2), (3), (5), and (7). It assumes that the
abundance of eggs at a station is equal over the
entire area represented by that station. Moreover,
it assumes that egg abundance at the time of col-
lection is the same on each day of the cruise period
and also for one-half the days since the preceding
cruise, or since the beginning date of the spawning

season plus one-half the days until the next cruise
or the number of days until the end of the spawn-
ing season.

Simpson's ( 1959) method was modified to obtain
round herring annual spawning estimates. He ob-
tained his estimates of spawning during each
cruise by summing areas within contours of egg
abundance. I used Equation (3) to obtain cruise
estimates. The annual spawning estimate (Pa)
was obtained by plotting the daily spawning esti-
mate for each cruise (PJdi) against the middate of
the cruise (Simpson 1959). The area under the
resulting polygon was obtained by planimeter and
was equated to annual spawning. Because Equa-
tion (3) was used to obtain cruise spawning esti-
mates, Sette and Ahlstrom's (1948) and Simpson's
(1959) methods give results that converge, the two
annual spawning estimates differing only by some
number of eggs spawned near the beginning and
near the end of the spawning season. The Sette
and Ahlstrom technique will always give a some-
what larger estimate of annual spawning for
species like round herring that have a well-defined
spawning season, but identical estimates will re-
sult for species that spawn year round.

The third method (Saville 1956, 1964) assumes
that spawning follows some known distribution
during the season. Spawning is approximately
normally distributed throughout the season for
many fishes. Thus, cruises that fall within the
spawning season represent part of the area under
the normal curve. If the peak spawning date is
known (even approximately) each cruise can be
equated to some percentage of the area under a
standard normal curve. Then each cruise spawn-
ing estimate (P, ) can be used to obtain an annual
spawning estimate (Pa):

P,tt
x, d,

(8)

where x, = the proportion of the area under the
normal curve represented by cruise i
t, = the number of days included in cruise i
dj = the duration (days) of the egg stage
during cruise i.

Saville (1956, 1964) did not discuss use of the
technique if more than a single cruise is included
in the spawning season, but because each cruise
can provide an independent estimate of annual
spawning, it was possible to get as many as three
estimates of round herring annual egg production
within a spawning season.

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING

Potential Yield to a Fishery

Alverson and Pereyra (1969) and Gulland
(1971, 1972) have proposed that an estimate of
potential yield for an unfished stock can be ob-
tained if the virgin biomass and natural mortality
coefficient are known. The estimator is:

XMB0

(9)

where Cmax = the maximum sustainable yield

X = a constant, assumed to be 0.5 (Gul-
land 1971).
M = the natural mortality coefficient. It
is equal to Z, the total mortality
coefficient, in an unfished stock.
B0 = the virgin biomass. My biomass es-
timates of round herring are esti-
mates of B0 because there is no sig-
nificant fishing at this time.

No estimates of M are available for round her-
ring. It seems probable that it must lie in the range
0.4-1.0, based on literature on other relatively
short-lived tropical and warm temperate clupeid
stocks (Beverton 1963; Schaaf and Huntsman
1972; Dryfoos et al. 1973) and from the empirical
relationship of M to life span given by Tanaka
(1960). Assuming M is between 0.4 and 1.0, a
range of potential yields to a fishery can be pre-
dicted. I used this approach for round herring.

Larval Abundance and Mortality

As a first step in determining survival rates of
round herring larvae for comparisons among
years and to determine abundance of larvae by
length classes, larval abundance was estimated
for each 1-mm length class:

*«ZaX^-4

(10)

;=i

7 = 1

where Pal = the annual estimate of total larvae in
a length class /; this is the estimate if
no correction is made for night-day
variation in catches

Cji — the catch of larvae in length class / at
station,;' on cruise i

Zj = the depth of tow (in meters) at station
j on cruise i

Vj = the volume filtered (in cubic meters)
at station j on cruise i

Aj = the area (in square meters) rep-
resented by station j on cruise i
k = the number of stations sampled dur-
ing cruise i
Di = the number of days represented by
cruise i (for details, see definition
under Equation (4))
r = the number of cruises upon which the
estimate is based.

Larval abundance estimates are subject to er-
rors due to escapement of small larvae through the
meshes and due to avoidance of the gear by larger
larvae (Smith and Richardson in press). Avoid-
ance usually is greater during daylight than at
night. Some of the avoidance error can be cor-
rected if the differential between night and day
catches of larvae in each length class is evaluated.
Catches of round herring larvae were examined
from each station for 1971-73 cruises. The ratios of
the sum of larvae estimated under 10 m2 of sea
surface caught at night stations to the sum of
larvae estimated under 10 m2 of sea surface
caught at day stations were determined for each
1-mm length class. These ratios were then used to
derive functions that corrected the day-caught
larval abundance estimates. Thus, abundance of
larvae in each 1-mm length class at stations oc-
cupied during daylight was corrected by a factor R :

cilzi

p* =-7T*

(11)

where P.

- the number of larvae in length class /
in the area represented by station j
R = the factor by which the number of
larvae in length class / at station j
should be multiplied to correct for
night-day variation. It equals 1.0 for
stations sampled at night.
Cji,Zj, Vj, and Aj are defined in Equation (10).

R is greater than 1.0 if avoidance is more pro-
nounced during daylight hours. The corrected sta-
tion catches (from Equation (11)) were substituted
into Equation (10) for larvae caught at stations
occupied during daylight. Corrected larvae abun-
dance estimates (Pa/) were then obtained.

Larval mortality rates can be determined and
expressed in terms of age if the growth rate of
larvae is known or if a model of growth during the
larval stage can be used to describe growth
adequately. Smith and Richardson (in press)

FISHERY BULLETIN: VOL. 75, NO. 1

recently have discussed the problem of obtaining
crude mortality rates of larval fishes. A range of
possible mortality estimates for round herring egg
and larvae stages has been obtained which is use-
ful for year to year comparisons and for compari-
son with larval mortality estimates that have
been published on other species. Growth rates of
round herring larvae are unknown and could not
be determined from the data. But, from my experi-
ence in laboratory culture of clupeid larvae, an
exponential model describes growth reasonably
well during the larval stage. Ahlstrom (1954) and
Nakai and Hattori (1962) assumed that exponen-
tial growth was valid in determining survival
rates of California sardine, Sardinops caeruleus,
and Japanese sardine, S. melanosticta, larvae.
From laboratory rearing experiments it is evident
that mean daily growth increments (6) of clupeid
larvae range from 0.3 to 1.0 mm (Houde 1973b),
the increments depending on such factors as
temperature and food concentration. Using this
basic information, the probable mortality rates of
round herring larvae from hatching until 16.0 mm
SL (standard length) were estimated for the
1971-72 and 1972-73 spawning seasons.

Using a computer program several variables
were considered and then the instantaneous mor-
tality coefficient was calculated for larvae based
on predetermined combinations of values of the
variables. The following procedure was used:

1) For each designated mean daily growth incre-
ment (b), an instantaneous growth coefficient
(g) is calculated.

t =

L, L0

(12)

where t = the time in days to grow fromL0 toL, at
a mean daily growth increment b
Lt = the maximum length of larvae consi-
dered to adhere to the exponential
growth model (usually 20.0 mm SL)
L0 = the minimum length of larvae to be
considered in calculating the instan-
taneous growth coefficient (g). (This
value was 4.1 mm SL for round her-
ring.)

lo&X, - log,L0

S = :

(13)

value of b that is submitted to the pro-
gram.

2) The annual spawning estimate {Pa ) for a given
spawning season and the larval abundance es-
timates by 1-mm length classes, corrected for
night-day variation (Pa!) are entered.

3) The duration (in days) of each class from 2)
above is determined:

a) The egg: Duration is arbitrarily assigned,
based on knowledge of developmental
stages in plankton collections or from
laboratory rearing experiments. For round
herring in the eastern Gulf of Mexico it is
2.0 days.

b) Nonfully vulnerable length classes: Dura-
tion is arbitrarily assigned, usually by
submitting a range of possible values in the
program. Larvae in these length classes are
underrepresented in catches because of es-
capement through the meshes, and are not
considered in subsequent mortality estima-
tion.

c) Fully vulnerable length classes.

\ogeLB - log,L;
g

(14)

where g = the instantaneous growth coefficient.
A different value ofg results from each

where Dt = duration of the class (in days)

LB = upper boundary of length of a size

class
LA = lower boundary of length of a size

class
g is defined in Equation (13).
4) The mean age of each class is then estimated:

a) The egg: Mean age is arbitrarily assigned.
(It is one-half the assigned duration.)

b) Nonfully vulnerable length classes: Mean
age is assigned. It equals duration of the egg
stage plus one-half the duration of nonfully
vulnerable length classes.

c) The mean age of fully vulnerable length
classes.

TA = duration of the egg stage + duration
of nonfully vulnerable length classes
\ogeLb - log.Xa

+ _BL_h 6^ (15)

where Lb = the midpoint of the length class under
consideration
La = the smallest length larva considered

to be fully vulnerable to the gear
g is defined in Equation (13).

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING

5) Abundance estimates for each class are cor-
rected for duration. This is necessary to esti-
mate the number present at mean age in that
class. If exponential growth holds, the number
of larvae in each successive age group will have
been underestimated before the duration cor-
rection was made, because the time spent by
larvae in successive length classes is decreas-
ing. The correction is made by dividing the
abundance estimates of each class (including
the egg stage) from step 2 above by their dura-
tions, given in step 3.

6) The instantaneous mortality coefficient is then
calculated for each combination of mean daily
growth increment, assigned egg stage dura-
tion, and assigned nonfully vulnerable larvae
duration. It is estimated from the exponential
regression of night-day-corrected and
duration-corrected abundances on mean age
and is fitted for all age-classes that were
adequately represented in the data, excluding
nonfully vulnerable larvae. For round herring
the regression was fit for age-classes including
the egg stage and larvae ranging from 4.1 to
16.0 mm SL.

N, = N0 exp( -Zt)

(16)

where Z = the instantaneous coefficient of rate of
decline in catch. It is the instantaneous
mortality coefficient if factors such as
gear avoidance are not significant con-
tributors to the decline in catch as lar-
vae grow older
Nt = the number of eggs or larvae at time t
N0 — they-axis intercept; it is an estimate of
abundance at time 0 (i.e., the number
of eggs that was spawned)
t = the time (in days) from spawning.

7) Mortality with respect to length also is esti-
mated in the exponential regression of night-
day-corrected abundance on length. Only fully
vulnerable length classes were used in this cal-
culation. For round herring, larvae from 4.1 to
16.0 mm SL were included in the analysis.

NL = NA exp(-ZL)

(17)

where Z = the instantaneous coefficient of rate of
decline in catch. It is the instantaneous
mortality coefficient per millimeter of
standard length if factors such as gear

avoidance do not contribute sig-
nificantly to decline in catch as larvae
grow.

Nl = the number of larvae of length L

NA = they-axis intercept
L = the standard length (millimeters) of
larvae.

RESULTS

Occurrence of Eggs and Larvae

Eggs and larvae of round herring were collected
on cruises from November to May (Table 1), and
were most common in January and February.
They did not occur in cruises from June through
September, indicating that there is no spawning
during summer in the eastern Gulf of Mexico.
Most eggs and larvae were collected on the outer
continental shelf (Figure 2) where depths ranged
from 30 to 200 m. Eggs occurred on only two occa-
sions at stations less than 30 m deep and on a
single occasion at a station deeper than 200 m
(Figure 2), although relatively little sampling ef-
fort was made at stations beyond the 200-m depth
contour. Occurrences of larvae were more wide-
spread (Figure 2), as expected due to dispersal by
water currents, but most occurrences remained
within the 30- to 200-m depth zone. The observed
distribution suggests that most of the adult popu-
lation is found on the outer shelf, at least during
the spawning season. A major spawning center is
located between long. 082°30' and 084°30'W and
lat. 27°00' and 28°00'N (Figures 2-6). The location
is about 150 km from Tampa Bay in a west by
southwest direction. This is the same general area
where round herring adults were trawled in
exploratory fishing surveys (Anonymous 1958;
Salnikov 1969). There is evidence that a second
minor spawning center is found between long.
082°00' and 083°30' W and lat. 24°45' and 25°30'N.
This location is just north of the Dry Tortugas
Islands.

The cruise means for numbers of round herring
eggs under 10 m2 ranged from 0.00 to 151.20 for
the 17 cruises in the survey (Table 1). Considering
only positive stations (i.e., stations where round
herring eggs were collected on a cruise), cruise
means ranged from 8.30 to 604.81 under 10 m2 of
sea surface (Table 1). Catches at individual sta-
tions frequently ranged from 11 to 1,000 under 10
m2 but exceeded 1,000 on only three occasions
during the 17 cruises (Figures 3-6). Round herring

FISHERY BULLETIN: VOL. 75, NO. 1

tarts

'•-•.."• JM

•-- ***-'

Etrumeus tarts
LARVAE

86*

84*

82*

FIGURE 2. — A.) Stations in the survey area where eggs of
round herring were collected at least once during 1971-74.
Stations where eggs did not occur are indicated by dots.
B). Stations in the survey area where larvae of round herring
were collected at least once during 1971-74. Stations where
larvae did not occur are indicated by dots.

egg abundances for each cruise at all stations, as
well as summaries for other clupeid species, have
recently been reported (Houde et al. 1976).

Cruise means for round herring larvae ranged
from 0.00 to 20.29 under 10 m2 (Table 1). At posi-
tive stations the cruise means for larvae ranged
from 4.44 to 175.07 under 10 m2 (Table 1), but the
latter value was based on a single positive station
for cruise CL 7412. Excluding that cruise, the
highest mean larval abundance under 10 m2 at
positive stations was 49.97. No stations had more
than 1,000 larvae under 10 m2 during the 17
cruises. Tabulated station data on catches and

abundance of round herring, and other clupeid
larvae, have been published (Houde et al. 1976).

The survey area did not encompass the entire
spawning area of round herring in the eastern
Gulf. Eggs were collected at stations located farth-
est offshore on some cruises (Figures 3-6) but
abundance was less at stations deeper than 200 m
than at shallower stations. I believe that most of
the spawning area and spawning population was
included in the survey area, and that my egg
abundance estimates suffer only small biases be-
cause of failure to sample a part of the population.

There was no apparent difference in the inten-
sity of round herring spawning at stations be-
tween 30 and 50 m deep compared with stations
deeper than 50 m. The log10 mean abundance es-
timates of eggs under 10 m2 of sea surface for all
positive stations =£50 m and for those >50 m were
calculated from pooled data of all cruises that had
round herring eggs. The «50 ra logio mean was
1.6351 (n = 25, Sj = 0.1609); the >50 m log10 mean
was 1.5585 (n = 32, S; = 0.1209). These means did
not differ significantly (f-test;P>0.50). However,
the area between the 30- and 50-m depth contours
was less than that included between the 50- and
200-m contours. The total area between the 30-
and 200-m depth contours was considered to be the
spawning area; 40.1% of the area is in the 30- to
50-m zone while 59.9% is between 50 and 200 m.
Thus, the total abundance of eggs in the area
where depths exceeded 50 m probably was greater
than abundance in shallower areas. The 50-m
depth contour divides the shelf area in the eastern
Gulf into approximate halves. For eight cruises in
which sampling effort was distributed nearly
equally to include potential spawning area in
water =£50 m and >50 m (cruises 8C 71 13-TI 7114,
8B 7132-TI 7131-GE7127, 8B 7201-GE 7202, GE
7208, IS 7209, IS 7303, IS 7308, and IS 7320), the
summed totals of egg abundance from the areas
represented by stations on these cruises were
compared with respect to the 50-m depth contour.
A total abundance of 11.92 x 1011 eggs was esti-
mated for stations =£50 m; total abundance was
16.73 x 1011 at deeper stations. If these egg abun-
dance estimates reflect relative adult abundance,
then 41.6% of the adult population was located in
depths =£50 m and 58.4% was distributed at depths
>50 m. The total abundance of eggs, and appar-
ently of adult round herring, is directly propor-
tional to the surface area of the two depth zones.
Some small fraction of the spawning population
inhabited depths greater than those sampled in

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING

GE 7101

Ltrkus teres egos
February 1971

(£7101

I ; 6 TERES LARVAE
FEBRUARY 1971

50m-

•

• i* + +

' 4

+
4

. 4-

Number under IOm2
4 0

• <l

• i-io

• n-ioo

• 101 - IOOO
© >IOO0

86°

84'

8C 7113 S Tl 71114

etrumeus teres eggs

May 1971

30°

r ■ — r— ■ t ■

4 4 4 + + V \

50m-.

+ * + * * V-j \

*-»++++ + + V \
+\ +44 + 41 ««.
+ '"# 4 4 4 + + / W)
4*44*44/ Y

28e

+ + 4*.+ 4 4 + >J7 \

+ t ♦ V, + * n^ \

4 4 4 V + 4 + \ i

+ + + \+ + +\r? <J \
• + ♦ V + + * XSa ^* \

•+ 4 4- 1 + 4 4- 4 ^£
+ + *.»+ +4-4 \
+ + +\ + 4- 4 + \ L
+ + +\ + + + + 4 ^w /^

26°

Number under IOm2

• <l

• I-IO

• 11-100

• ioi-iooo

44 4; 444-*-+ 1^ /<
+ + {► + + + 4+ G±~7

+ +' + + + + >r

' '

84*

6E 7127, TI 7131 & 8B 7132
Etrumeus teres eggs

November 1971

30°

1 ■ - T

+ *■ * + + V.

50m-*

+ + ♦■ ♦ r \^/f

•

^ + * + + + ^l

•gV + + 4- + + I

*■ •• 4- + + t /

28°

«■•«©• * 4 SJ/

* • Ml • + 4 •,{

V -

* 4 • + \ • 4 f \

♦ t + t i t * * ^t

• ° 1

i.'b°

Number under 10m2

♦ 0

\ /

• <l

;

• I-IO

• 11-100

• IOI-IOOO

r' + +

.v'-^

30"

50m-

28*

■

i:6-

?4°

1 Number under IOm2

• 0

1 • "

• I-IO

• 11-100

• 101 - IOOO
© XOOO

•

.£:

4
•

+
4
+

4
4
4

4 +

z~-"^

84'

8C 7113 S TI 7111

f.truheus teres larvae

Nay 1971

1 M^,^

i i

30°

50m-.

f + + + 4 V

+ 4 4++ \-
*-.+ +4-4+4 V

4\ 4+44+ I

• fc 4 + + 4 + /

• •+444+/

28°

4 \ J(V^

4 • *« • 4 4 Sj^

• ••""* + 4 4 <,£
•••\++»\

+>•+•* 4 4 4 \ _

•••4 44+^M

4- 4- +'.+ + + + f

• 4 4\4 +4 4-

+ 4 +',• 4 + +

+ •+*«++ + +

Lb"

1 Number under IOm2
4 0

• I-IO

• 11-100

• IOI-IOOO

+ + +i 4 4- +4
+ + ,4 -»- 4 4
4 +J • + 4 +

+ +

<*--''

* 84°

GE 7127, TI 7131 & 8B 7132

Etrumeus teres larvae

November 1971

1 r—

30°

4 + * + + V

50m«

* +"*■"*■■*■ V-«

•

#.+ + * + ♦ 1

+#•+++- /

28°

v -

• ♦ • • y tt » yj

1 Number under IOm2

: ?■

• l-IO

T. [•

• 11-100

• 101 - IOOO

' ' * +

j*!*^

■ 1

FIGURE 3. — Distribution and abundance of round herring eggs and larvae. Catches are standardized
to numbers under 10 m2 of sea surface. A, B: Cruise GE 7101, February 1971. C, D: Cruise 8C 7113-
TI 7114, May 1971. E, F: Cruise GE 7127-TI 7131-8B 7132, November 1971.

FISHERY BULLETIN: VOL. 75, NO. 1

8B 7201 ft GE 7202

Etrumeus teres eggs

February 1972

SB 7201 & GE 7202

Etrumeus teres larvae

February 1972

— l —

1 M, _^-^

-1 T

30"

50m«

*■

* •

+ + + \^-

*-
\ + ■*■ + J

28"

• 0 \

26"

Number under 10m2
♦ 0

• <l

• 1 - 10

+ + *

+■

• 11-100

• 101-1000

+ + k.

♦

_«,-,.--

GE 7208

Etrumeus teres eggs

Hay 1972

30°

50m-. ^

26*

\ f^

V -

+ + +

+ 1 + * \ K»

+ +

+ + 'i + *- «^

+ \ + +

2fo°

Number under 10m2

+ 0
• <l

+ +■ j + +

+ \ y

• 1 - 10

• 11-100

• 101 - 1000

•; • -

,*H~*-'^

30°

50m«

•
• •

•

'• * *

28"

• \

26°

Number under 10m2
♦ 0

•\

>> fl

• 1 - 10

+ • w

• 11-100

• 101-1000

* * •*..

♦

.*•»--'

84"

GE7233

Etrumeus teres larvae

May 1972

30°

30m--,

i r

28"

(?\A

V -

+ ♦ +

X ♦ . ,/

* \ * *\tf

• <))

f +

+ 1 -t- +

2fo°

Number under 10m2

+ 0

• <\

• ♦ ! + *

* \ y

• 1 - 10

• 11-100

• 101 - 1000

• ; + *

.>--"

IS 7209

Etrumeus teres eggs

November 1972

30°

30m- .^

' ' f

***** \ \

*■ N« + * * + / Vy

28°

• \ * * * -/^ \

♦-

+ • * \ ♦ + * st€

♦ *\ *> + * V. J"

2b"

Number under 10m2

t 0

f +■ ! + * *" * V 0

• 1 - 10

• 11-100

• 101 - 1000

IS 7209
Etrumeus teres larvae

November 1972

• I - 10

• 11-100

• 101 - 1000
© >I000

FIGURE 4.— Distribution and abundance of round herring eggs and larvae. Catches are standardized
to numbers under 10 m2 of sea surface. A, B: Cruise 8B 7201-GE 7202, February 1972. C, D: Cruise
GE 7208, May 1972. E, F: Cruise IS 7209, November 1972.

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING

IS 7303

Etrumeus teres eggs

January 1973

IS 75)3

Etrumeus teres larvae

January 1973

JO'

26* ■

u*-^

50m-.

• \ * ' ' ' 1

■

• \ * • • \j-

*■ *■ * \ • * • wL

Number under

10m2

+ 0

+ • : • ♦ +

E /'

• 1 - 10

• n-ioo

• IOI-IOOO

•; • •

80°

50m-.. \_

• • • • V

• \ * * * /

• \ • • • <-/*y-

\ -

♦ • »'•-., • • - l/

• • \ + + ♦ \j-

+ • * \ • ♦ > Tc.

Number under 10m-

• * <-\ * ♦ ♦

+ 0

• • ': • * *

* \ y

• 1-10

• 11-100

• 101 - 1000

• •: •

.-<"'-''

i . _i_

IS 7308

Etrumeus teres eggs

Hay 1973

64"

IS 7308

Etrumeus teres larvae

May 1973

30°

50m-.,

-t-

28*

*■ * *-\ +■ + +

2b"

Number under 10m2

+ 0

* * ; +■ +- +

♦ \ y

• 1 - 10

• n-ioo

• 101 - 1000

*j * *

...*■*--'

30°

1 1 ■ ■ r-

50m'-. \~»
• * + * + * /

26°

• \ + - • ♦[ft.

* * \ + * *\l

* +■ \ *■ + * »x

26"

Number under 10m2

* . .,.+ .

♦ 0

. ': .

^9 /

• 1 - 10

• 11-100

• IOI-IOOO

*l * *

.-«--"'

1 '

■ «

IS 7320

Etruheus teres eggs

November 1973

84"

IS 7320

Etruheus teres larvae

November 1973

1 —

V&A" \

+ t + + \

50m..

• + + + V

+ \ • *■ + ♦ /

■

+ ♦ \ • + + *

0")

* + + 1 + + +

Number under 10m2

♦ 0

♦ • ! +

+ -+■

* \ y

• 1-10

• 11-100

• IOI-IOOO

+ tj

.'•"'-''

Number under

10m2

•

1 -10

•

11-100

•

101 - 1000

•-

>I000

86"

FIGURE 5. — Distribution and abundance of round herring eggs and larvae. Catches are standardized to
numbers under 10 m2 of sea surface. A, B: Cruise IS 7303, January 1973. C, D: Cruise IS 7308, May
1973. E, F: Cruise IS 7320, November 1973.

FISHERY BULLETIN: VOL. 75, NO. 1

a 7112

Etrikeus teres eggs

a 7112

Etrueus teres LARVAE

May 1971

— — r- r

50m-

X ' * • * *~\

\ -

\ * * *\|T

. <A

A + *

Number under 10m2

t 0

• • i( Q

• 1-10

• 11-100

• 101-1000

_.'*--''

k^-^

><~^ \

u^^'tX \

50m-.

\ . . :N\ \

\ ••••) 1)

V ' * w \ "

• '"■■•. •♦*•'/ \

V*\r 0 ' )

Y.\*\ J

Number under 10m2

♦ 0

• ' *^ _J

• 1 - 10

• II-IOO

• 101-1000

! . ■ ..'»■-''

FIGURE 6. — Distribution and abundance of round herring eggs and larvae on cruise CL 7412, May
1974. Catches are standardized to numbers under 10 m2 of sea surface.

our survey and the relative abundance of adults in
water >50 m deep may be higher than the esti-
mated 58.4%. Because the intensity of spawning
was the same in depths, =£50 and >50 m, adults
apparently are not more abundant per unit of sea
surface in deeper water but their greater abun-
dance reflects the larger area of habitat suitable
for round herring where shelf waters are >50 m
deep.

Temperature and Salinity Relationships

Round herring eggs were collected when surface
temperatures ranged from 18.4° to 26.9°C. They
occurred at surface salinities of 34. 50-36. 50°/oo.
Because no vertically stratified tows of the Bongo
sampler were made, the percentage of eggs or lar-
vae that occurred in surface waters is unknown.
Surface temperatures from November to May
were 0°-3°C higher than those at 50 m when verti-
cal sections along transects at three latitudes were
examined for each cruise in which round herring
eggs or larvae were collected. Surface salinities
differed by less than 0.5°/oo from those at 50-m
depth, except on cruise IS 7320 when surface
salinities ranged from 0.6 to 1.0%o less than those
at 50 m. It is reasonable to believe that surface
temperatures and salinities are representative of
conditions where pelagic eggs were incubated and
where larvae were found. Salinity may not be an
important factor affecting spawning since the
range of surface salinities at which eggs were col-
lected nearly encompasses the entire range of

salinities found in offshore waters of the eastern
Gulf. Larvae =£5.0 mm SL are from 0 to about 6
days old. They occurred where surface tempera-
tures ranged from 20.5° to 26.9°C and surface
salinities from 34.10 to 36.80%o.

The percentage cumulative frequency distri-
butions (Figure 7) of stations where eggs or
=s5.0-mm larvae occurred in relation to tempera-
ture and salinity were examined. For eggs, 82.5%
of the occurrences were between 21° and 26°C sur-
face temperature, while 87.2% of the =s5.0-mm
larvae occurrences were in that temperature
range. Only 10.5% of the egg occurrences were at
stations where surface temperatures exceeded
26°C and only 6.4% of the =£5.0-mm larvae occur-
rences were at such stations. The distribution of
egg occurrences in relation to temperature was
similar in the 1971-72 and 1972-73 spawning sea-
sons. In 1971-72, 78.3% of the eggs occurred at
stations where surface temperatures were less
than 25°C; in 1972-73, 79.0% of the occurrences
were at temperatures below 25°C. Comparable
data were not available for the 1973-74 spawning
season.

More than 50% of round herring eggs and
=s5.0-mm larvae were collected at stations where
surface salinity exceeded 36.00%o (Figure 7). For
eggs, considering all years' data, 79.7% of the oc-
currences were at surface salinities from 35.50 to
36.50%o; for «5.0-mm larvae, 80.0% of the occur-
rences were in that salinity range. In 1971-72,
88.0% of the egg occurrences were at stations with
surface salinities from 35.50 to 36.50%o; in 1972-

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING

TEMPERATURE

SALINITY

FIGURE 7. — Percent cumulative frequency dis-
tribution of 1971-74 stations where round her-
ring eggs occurred in relation to surface tem-
peratures (A) and to surface salinity (C), and
=£5.0-mm SL larvae occurred in relation
to surface temperature (B) and surface salinity
(D).

100

70-

60-

50-

>- 40
U

" 50

^ 100

3 9°

* 80

£ 70
Q.

60 -

50-

40-

Etrumeus teres
eggs

Etrumeus teres
larvae -5mm

-T 1 r-

Etrumeus teres
larvae '5mm

100

'-•')

t'i
50
40

SO
20

IB I

20.1*- 22 r-

24 1*-

26 r-

3401-

21 0' 23 0*

25 0-

27 0'

34 25

TEMPERATURE

CLASS CO

34 51- 35 01- 35 51- 3601-

34 75 35 25 35 75 36 25

SALINITY CLASS (%.)

36 51-
36 75

73, 94.7% of the egg occurrences were in that salin-
ity range. There were seven egg occurrences at
less than 35.50%o surface salinity on cruise IS
7320 (November 1973). This cruise influenced the
cumulative frequency distribution of egg occur-
rences in relation to salinity (Figure 7) over all
years. Data for the entire 1973-74 spawning sea-
son were not available to compare occurrence of
eggs in relation to salinity with 1971-72 and
1972-73 data; but, the frequency distribution ap-
parently would have been shifted to lower
salinities in that year, reflecting low surface
salinities that prevailed in the eastern Gulf in fall
1973.

Egg and Larvae Abundance in
Relation to Zooplankton

There was no apparent relationship between
zooplankton volumes and round herring egg or
larvae abundance. Zooplankton volumes (cubic
centimeters/1,000 m3 strained) were determined
at each station for cruises in 1972 through 1974.
Round herring egg abundance and larvae abun-
dance were examined in relation to zooplankton
volume for stations included in those cruises but
the correlations were not significant.

Fecundity and Maturity

A total of 71 adult round herring was examined,

of which 39 were males and 32 were females.
Based on this sample, the sex ratio did not differ
significantly from 1:1 (x2 = 0.69; 0.25<P<0.50).
Sixty-five specimens, from 93 to 165 mm SL, were
collected in the Gulf of Mexico in August and
November 1974. The 59 specimens more than 100
mm SL were maturing or near ripe. Six additional
females, from 157 to 160 mm SL, that were col-
lected in June 1973 off the east coast of Florida
(lat. 30°20'N) were examined. Those six specimens
were spent, the ovaries containing only small,
clear, nucleated oocytes.

Ripening females usually have two modes of
yolked oocytes (but occasionally only one), which
apparently are both spawned during a single
spawning season. Planktonic eggs were collected
only from November through May. The spawning
season extends from approximately 15 October to
31 May in the eastern Gulf of Mexico.

The fecundities of eight near-ripe females, 130-
165 mm SL, were estimated, based on yolked oo-
cytes present in ovaries (Table 3). Fecundities
ranged from 7,446 to 19,699 and increased with
size of the females. Relative fecundity (ova per
gram body weight) ranged from 150 to 428 ova/g,
the mean being 296.5 ova/g (S* = 33.7 ova/g).
There was no apparent relationship between rela-
tive fecundity and either length or weight of
females. The mean relative fecundity estimate,
296.5 ova/g, was used in subsequent adult biomass
determinations. If all yolked oocytes were not

FISHERY BULLETIN: VOL. 75, NO. 1

TABLE 3. — Fecundity estimates and related data from eight female round herring collected in

the Gulf of Mexico, November 1974.

Ovary

Standard

Ovary

Gonad

sample

Number

Relative

length

Weight

weight

index1

weight

ova in

Fecundity

fecundity

Specimen

(mm)

(g)

(%)

(g)

sample

(ova)

(ova/g)

165

55.60

1.13

2.03

0.030

523

19,699

354

138

34.82

0.36

1.03

0.025

709

10,210

293

152

44.41

0.41

0.92

0.025

454

7,446

168

149

40.65

1.10

2.71

0.035

553

17,380

428

161

55.20

0.60

1.09

0.020

276

8,280

150

143

37.97

0.43

1.13

0.025

781

13,433

354

130

29.62

0.65

2.19

0.035

535

9,936

335

144

37.28

0.33

0.89

0.025

818

10.798

290

'Gonad index is the ratio of ovary weight to weight of the female, expressed as a percentage.

spawned in a spawning season, the estimate of
relative fecundity is too high and biomass esti-
mates are low. Because no modes of yolked oocytes
remained in ovaries of spent females from the
June collection, I believe that yolked oocytes were
spawned and that biomass estimates were not
biased by this possible source of error.

Ito ( 1968) estimated mean fecundity of Japanese
round herring to be 9,212 ova. His estimates were
based only on the most advanced mode of yolked
oocytes, although two modes usually were present.
Ito's estimates are lower than the estimated
fecundities of Gulf of Mexico round herring. Also,
the diameters of near-ripe ova that he reported
averaged 1.4 mm which is greater than that for
spawned eggs in the Gulf of Mexico which average
only 1.29 mm in diameter (Houde and Fore 1973).
Diameters of ovarian ova reported by Ito (1968)
are not in accord with those reported for pelagic
eggs of Japanese round herring by Uchida et al.
(1958), who gave the diameter as 1.25 mm. The
length at first maturity, which Ito observed to be
approximately 170 mm SL in Japanese specimens,
exceeded that of my specimens by about 70 mm.

Time Until Hatching

Duration of the egg stage from spawning until
hatching was estimated indirectly from the oc-
currence of three distinct embryonic stages during
cruise IS 7303, at stations where surface tempera-
tures were 21°-22°C. Spawning by round herring
takes place at night, and early embryonic stages
were collected only between midnight and 0400
e.s.t. Two other distinct embryonic stages were
collected during those hours, one of which was a
full-term embryo that was about to hatch. I as-
sumed 2200 e.s.t. to be the peak spawning time.
The time from spawning to hatching is approxi-
mately 2.1 days at 21°-22°C. Watson and Leis
(1974) reported that Hawaiian round herring eggs

incubated approximately 2 days when surface
temperatures were in the range 23°-25°C.

The value of 2.0 days was used for hatching time
in subsequent abundance estimation procedures
(Equations (4), (5), and (8)). It probably over-
estimates duration for cruises during fall and
spring, but it is a good estimate for the winter
season when most spawning occurs. Over-
estimating duration would result in an under-
estimate of daily spawning and an underestimate
of adult biomass. Because there were no data on
duration of the egg stage for fall and spring
cruises, I chose to accept a possible small bias of
underestimating round herring biomass. O'Toole
and King (1974) incubated South African round
herring eggs at 11°-20.5°C. The eggs had been
collected in plankton tows when surface tempera-
ture was 16.5°C. They estimated that round her-
ring eggs hatched in 135 h at 11°C and 36 h at
20.5°C. They assumed that the blastodermal cap
stage eggs, with which they began experiments,
were only 4-6 h old. Gulf of Mexico round herring
probably do not spawn at the low temperatures
that O'Toole and King observed in South African
waters. Temperatures as low as 16.5°C during the
spawning season in the Gulf of Mexico occurred
only at depths of 150 m and greater, on the outer
edge of the continental shelf. Also, the rate of
development of Gulf of Mexico eggs at tempera-
tures above 20°C apparently is slower than that of
South African eggs.

Cruise Egg Abundances

The estimated abundances of round herring
eggs present in areas represented by each cruise
are given in Table 4. Egg abundances, including
all developmental stages, ranged from 0.24 to
209.31 x 1010 for cruises during the spawning
season. No round herring eggs (or larvae) were
collected on cruise CL 7405. That cruise was made

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING

TABLE 4. — Abundance estimates of round herring eggs for each
cruise. Estimates were obtained using Equations (2) and (3), and
are not corrected for duration of the egg stage.

Area represented

Cruise

by the cruise
(m2 x 109)

Positive area1

egg abundanc

Cruise

(m2 x 109)

(eggs x 1010

GE 7101

25.79

13.69

6.08

8C 7113

Tl 7114

120.48

21.80

0.24

GE 7117

101.10

0.00

000

8C 71 20

Tl 7121

189 43

0.00

GE 7127

8B 7132

Tl 7131

72.99

21.58

25.26

8B 7201

GE 7202

148.85

78.43

209.31

GE 7208

124.88

15.79

1.51

GE 7210

48.43

0.00

IS 7205

104.59

0.00

IS 7209

149.80

17.79

1.37

IS 7303

149.80

78.19

3849

IS 7308

151.42

10.52

4.04

IS 7311

156.50

0.00

IS 7313

153.18

000

0.00

IS 7320

153.89

31.34

6.33

CL 74052

52.00

0.00

CL7412

91.33

2.91

0.62

' Positive area is defined as the area representing stations where either eggs
or larvae of round herring were collected.

2No stations on this cruise were located far enough offshore for round herring
egg or larvae to have been collected.

during the spawning season, but because only
nearshore stations were sampled, the round her-
ring spawning area was not included in the cruise
area. Abundance estimates in Table 4 are based on
Equations (2) and (3). Cruise abundance estimates
for eggs were used to estimate adult biomass in
following sections.

Adjusting Cruise Egg Abundance Estimates

The cruise egg abundance estimates were ad-
justed for cruises GE 7127-TI 7131-8B 7132 and
GE 7208. On these two cruises only a part of the
round herring spawning area was sampled (Fig-
ures 3, 4). For cruise GE 7127-TI 7131-8B 7132
only 0.655 of the potential round herring spawn-
ing area was included, and for GE 7208 only 0.839

of the area was included. Abundance estimates for
each of those cruises were adjusted by dividing the
cruise egg abundance estimates (Table 4) by their
respective area factors (0.655 or 0.839). Adjusted
cruise egg abundance estimates are: (GE 7127-TI
7131-8B 7132)— 38.56 x 1010; (GE 7208)— 1.80 x
1010. The effect of adjusting egg abundance for
these cruises had a minor effect on biomass esti-
mation. Biomasses based on the adjusted and un-
adjusted egg abundance estimates were calculated
and are compared in subsequent sections.

Annual Spawning and Biomass Estimates

Method I

The cruise abundance estimates (Table 4) were
adjusted for duration of the egg stage by dividing
each estimate by 2.0 days, the estimated time from
spawning until hatching, to give estimates of daily
spawning during each cruise (Table 5). Daily
spawning estimates for each cruise were then ex-
panded by Sette and Ahlstrom's (1948) method to a
representative number of days (Dt defined in
Equation (4)) in the spawning season of 15 Octo-
ber to 31 May (Table 5). Variance estimates on
cruise and annual egg abundance were then ob-
tained (Equations (4) and (6)). Finally, the esti-
mated adult biomass was calculated (Equation
(7)) (Table 5).

Estimates of biomass were obtained for 1971-72
and 1972-73 when sampling was carried out over
the entire spawning seasons. Estimated biomass
was 717,815 metric tons in 1971-72 but only
131,136 metric tons in 1972-73 (Table 5). The var-
iance estimates are relatively low, but because
only three cruises were made within the round
herring spawning season and no estimates of day
to day variation in spawning are available, there
is a large source of unaccounted variation. The

TABLE 5. — Annual spawning and biomass estimates for round herring from the eastern Gulf of Mexico during the
1971-72 and 1972-73 spawning seasons. Estimates are based on the Sette and Ahlstrom's (1948) technique.

Spawning
season

Cruise

Daily spawning

estimate
(eggs x 1011)

Days

represented

by cruise

Eggs spawned during

cruise period

(x 1011)

Variance estimates

on spawned eggs

(x 1024)

Adult biomass
(metric tons)

1971-72

GE 7127
Tl 7131

8B 7132

1.928

71.0

136.888

10.245

8B 7201

GE 7202

10.466

88.0

921 .008

206.576

GE 7208

0.090

70.0

6.300

3.717

Annual total

229

1,064.196

220.538

717,815

1972-73

IS 7209

0.069

64.5

4.451

1.787

IS 7303

1.925

91.0

175.175

34.470

IS 7308

0.202

73.5

14.847

4.100

Annual total

229

194.473

40.357

131,136

FISHERY BULLETIN: VOL. 75, NO. 1

number of days representing each cruise is large
and spawning almost certainly was not uniform
within each cruise period. This may account for
the more than fivefold difference in biomass esti-
mated during the 2 yr. On the other hand it is
possible that biomass did differ greatly between
the 2 yr. This is especially possible because the
eastern Gulf may be an open-ended system with
regard to round herring habitat. Round herring
eggs and larvae were abundant in the north-
central Gulf (Fore 1971) indicating that a large
adult population is present there. If a single popu-
lation of round herring inhabits the Gulf, the part
found in the eastern Gulf might vary from year to
year.

The area adjustments that had been made for
two 1971-72 cruises, to account for part of the
spawning area not being sampled, affected the
biomass estimate in that spawning season. With-
out adjustments the biomass estimate was
685,273 metric tons rather than 717,815 metric
tons. The effect of adjustment was to raise the
estimate by more than 32,500 metric tons. This is
only a 4.7% increase in estimated biomass.

It is unlikely that round herring biomass is as
great as 1 million metric tons in the eastern Gulf of
Mexico, but it probably is considerably in excess of
100,000 metric tons. Confidence limits, at the 0.95
probability level, based on the annual spawning
variance estimates (Table 5) placed the probable
range of round herring biomass between 517,470
and 918,160 metric tons in 1971-72 and between
45,430 and 216,840 metric tons in 1972-73.

Method II

The daily spawning estimates for each of the
three cruises during 1971-72 and 1972-73 were
plotted against their cruise middates (Figure 8).
Areas under the resulting polygons were deter-
mined and were equated to annual spawning (Ta-
ble 6). This method is like that outlined by
Simpson (1959). Biomasses were calculated using
Equation (7).

Biomass estimates were 698,045 metric tons in
1971-72 and 130,995 metric tons in 1972-73 (Table
6). These estimates are similar to those obtained
by Method I.

Method III

If spawning follows a normal distribution dur-
ing the period 15 October to 31 May, then each

15 Oct l5Nov l5Dec l5Jan l5Feb l5Mar l5Apr l5May
CRUISE MIDDATE

FIGURE 8. — Round herring egg abundance estimates in the
eastern Gulf of Mexico based on three cruises in 1971-72 and
1972-73. Each symbol represents the estimated daily spawning
at the middate of a cruise. The area enclosed by the polygons is
an estimate of the total spawning by round herring during each
of the seasons.

TABLE 6. — Annual spawning and biomass estimates for round
herring from the eastern Gulf of Mexico during 1971-72 and
1972-73 spawning seasons. Estimates are based on the method
described by Simpson ( 1959).

Adult

Daily spawning

Annual spawning

biomass

Spawning

estimate

(metric

season

Cruise

(eggs x 1011)

tons)

1971-72

1972-73

GE7127

Tl 7131

8B 7132

1 928

8B 7201

GE 7202

10.466

GE 7208

0.090

IS 7209

0.069

IS 7303

1.925

IS 7308

0.202

1 .034.852

194.200

698,045

130.995

cruise within that 229-day period can be rep-
resented as some proportion of the area under a
normal curve with standard deviation of 38.17
days. Saville (1956, 1964) discussed use of the
technique for a single cruise near the peak of the
spawning season, but I have applied it (Equation
(8)) to eight representative cruises during four
round herring spawning seasons (Table 7). The
observed variation within a season on annual
spawning and biomass estimates is great. Al-
though spawning is heaviest near the middle of
the spawning season (Figure 8), it probably does
not follow the normal distribution closely. It seems
that in most years spawning intensity increases
rapidly to near peak level during late November
and then gradually decreases during spring
months. Deviations from normality would cause
large estimating errors, especially for cruises that

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING

TABLE 7. — Annual spawning and biomass estimates for round herring from the eastern Gulf of Mexico during
1970-71 through 1973-74 spawning seasons. Estimates are based on the method of partitioning the spawning
season into component parts of the normal curve ( Saville 1956). The spawning season is assumed to be 229 days in
length, ranging from 15 October to 31 May.

Proportion

Daily spawning

Days

Annual spawning

Adult biomass

Spawning

of area under

estimate

included

estimate

season

Cruise

normal curve

(eggs x 10")

in cruise

(eggs x 10")

(metric tons)

1970-71

8C7113

Tl 7114

0.0057

0.012

25.270

17,046

1971-72

GE 7127
Tl 7131

8B 7132

0.0081

1.928

2,618.258

1,766,110

8B 7201

GE 7202

0.1153

10.466

998.436

673,481

GE 7208

0.0072

0.090

125.310

84,526

Mean

1 ,247.335

841 ,373

1972-73

IS 7209

0.0072

0.069

85.592

57,735

IS 7303

0.0857

1.925

202.109

136,330

IS 7308

0.0041

0.202

443.798

299,358

Mean

243.833

164,474

1973-74

IS 7320

0.0067

0.316

425.198

286,81 1

were not made near the middle of the spawning
season.

Mean biomass estimates for the 1971-72 and
1972-73 seasons were 841,373 and 164,474 metric
tons, respectively (Table 7). These estimates do
not differ much from those obtained by Methods I
and II (Tables 5, 6). Also, it is interesting to note
that the midwinter estimates in the 1971-72
(673,481 metric tons) and 1972-73 ( 136,330 metric
tons) seasons, each based on a single cruise, gave
estimates of round herring biomass nearly identi-
cal to those obtained by Methods I and II. A single
cruise in January or February, with a subsequent
biomass estimate by Method III, seems to be as
good for obtaining estimates of round herring
biomass as three cruises spaced over the entire
spawning season. Multiple cruises within the
November through February peak spawning
period would, of course, be the best approach to
gain precision in estimating biomass of this
species from spawning surveys.

The annual spawning estimates, based on
Method III from the eight cruises (Table 7), are
log-normally distributed and an estimate of the
mean biomass present from 1970 to 1974, with
confidence limits at the 0.95-probability level, was
calculated based on the eight log10 egg abundance
estimates. Geometric mean annual spawning es-
timate for 1970-74 was 2,685.11 x 1010 and the
confidence limits are: P( 792.08 x 1010 ^ Pa =s
9,103.32 x 1010) = 0.95. Expressed in terms of
biomass, the geometric mean was 181,120 metric
tons with confidence limits, P(53,429 *£ B «=
614,052) = 0.95. If the arithmetic mean of the
eight biomass estimates is considered a valid es-
timate of mean biomass, its value is 415,175 met-

ric tons. A reasonable conclusion is that round
herring biomass in the eastern Gulf is less than 1
million metric tons but probably greater than
100,000 metric tons.

Concentration of Biomass

The largest positive areas (i.e., areas where
either round herring eggs or larvae were collected)
occurred in cruises 8B 7201-GE 7202 and IS 7303
when more than 78 x 109 m2 were in that category.
This is nearly equivalent to the 76.5 x 109 m2 in
the survey area between 30- and 200-m depths
that was determined by planimeter. The biomass
of adult round herring is primarily located in the
30- to 200-m depth zone. If the confidence limits on
biomass, based on Method I, are considered then
biomass per unit area of sea surface must have
been between 67.6 and 120.0 kg/hectare in 1971-
72 and between 5.9 and 28.3 kg/hectare in
1972-73.

Potential Yield to a Fishery

Using Equation (9), the potential yield to a
fishery, Cmax, can be estimated, based on the range
of biomass estimates that is available. Although
the natural mortality coefficient, M, is not known,
it probably lies between 0.50 and 1.00 for round
herring in the eastern Gulf of Mexico. The esti-
mated values of Cmax if Af equals 0.50, 0.75, or 1.00
are given in Table 8.

Potential yield estimates range from 32,749 to
420,687 metric tons (Table 8). The best estimates
almost certainly lie midway between the ex-
tremes, so that 50,000-250,000 metric tons are in

FISHERY BULLETIN: VOL. 75, NO. 1

TABLE 8. — Range of potential yield estimates for eastern Gulf of
Mexico round herring, based on biomass estimates by three
methods. Yields are predicted at three possible values of M, the
natural mortality coefficient. Biomass estimates were obtained
from values in Tables 5-7.

TABLE 9. — Abundance estimates of round herring larvae for
each cruise. Estimates include larvae in all size classes and
were obtained using Equations (2) and (3).

Biomass estimating

method and
spawning season

Biomass Estimated potential annual

estimate yields (metric tons) for

(metric given values of M

tons) M = 0.5 M = 0.75 M = 1.0

I 1971-72 717,815

I 1972-73 131,136

I Mean of 1971-72

and 1972-73 424,476

II 1971-72 698,045
II 1972-73 130,995

II Mean of 1971-72

and 1972-73 414,520

III 1971-72 mean 841,373

III 1972-73 mean 164,474
III 1971-72 cruises

8B 7201 and

GE 7202 673,481
III 1972-73 cruise

IS 7303 136,330
III 1 970-74 geometric

mean of 8 estimates 1 81 , 1 20
III 1970-74 arithmetic

mean of 8 estimates 415,175

179,454
32,784

269,181
49,176

358,908
65,568

106,119 159,179 212,238

174,511 261,767 349,022

32,749 49,123 65,498

103,630 155,445 207,260

210,343 315,515 420,687

41,118 61,678 82,237

168,370 252,555 336,740

34,082 51,124 68,165

45,280 67,920 90,560

103,794 155,691 207,588

the range that I believe represents the mean po-
tential annual yield of the stock. This is equiva-
lent to a potential harvestable yield of 6.5-32.7
kg/hectare in the 76.5 x 109 m2 of round herring
habitat in the eastern Gulf. If stock size fluctuates
greatly from year to year then the harvestable
yield also may vary. As Alverson (1971) has
pointed out, the biological potential yield is not
necessarily the realizable yield. The realizable
yield will depend upon the availability of the stock
and its vulnerability to fishing gear. Neither of
these factors has been evaluated for eastern Gulf
round herring. It is possible that large year to year
fluctuations in round herring biomass do occur, as
suggested by the great differences in 1971-72 and
1972-73 biomass estimates. Such variation could
reflect year class fluctuations or yearly changes in
distribution of parts of the stock between the
north-central and eastern Gulf. Although they are
abundant, there is no reason to believe that round
herring in the eastern Gulf constitute a stock as
large as the Gulf menhaden stock in the north-
central Gulf of Mexico, which produces a mean
annual yield of more than 550,000 metric tons.

Larval Abundance Estimates

Larvae occurrence and abundance varied sea-
sonally in the same manner as eggs (Table 9). The
range of larvae abundances for positive cruises,
including larvae in all length classes, was 0.47-
31.95 x 1010. In subsequent estimates of larval

Cruise

Area

represented

by the cruise

(m2 x 109)

Positive area'
(m2 x 109)

Cruise larvae

abundance

(larvae x 1010)

GE 7101
8C7113

Tl 7114
GE7117
8C 7120

Tl 7121
GE 7127

Tl 7131

8B7132
8B 7201

GE 7202
GE 7208
GE 7210
IS 7205
IS 7209
IS 7303
IS 7308
IS 7311
IS 7313
IS 7320
CL 74052
CL 7412

25.79

120.48
101.10

189.43

72.99

148.85

124.88

48.43

104.59

149.80

151.42

156.50

153.18

153.89

52.00

91.33

13.69

21.80
0.00

0.00

21.58

78.43

15.79

0.00

17.79

78.19

10.52

0.00

31.34

0.00

2.91

2.58

3.60
0.00

0.00

2.92

26.55
0.47
0.00
0.00
2.70

31.95
3.99
0.00
0.00
1.71
0.00
5.09

1 Positive area is defined as the area representing stations where either eggs
or larvae of round herring were collected.

2No stations on this cruise were located far enough offshore for round herring
eggs or larvae to have been collected.

abundance by length classes and in mortality es-
timation procedures, larval abundance by each
1-mm length class was adjusted for cruises GE
7127-TI 7131-8B 7132 and GE 7208 to account for
only part of the potential round herring spawning
area having been sampled. The adjustment factors
were 0.655 and 0.839, the same factors that were
used to adjust egg abundance for those cruises.

Larvae that were collected ranged from 2.1 to
30.0 mm SL during the survey. Length frequen-
cies of larvae in the 2.1-20.0 mm SL range are
illustrated in Figure 9. Larvae >20.0 mm were
rarely collected during the survey. Frequencies for
each length class in Figure 9 are given as esti-
mated abundance during each cruise (Equation
(3)). No area adjustments have been made in Fig-
ure 9 for the two cruises that did not cover the
entire spawning area. Round herring larvae <4.0
mm SL usually were in poor condition, with
curved or deformed bodies, and their measure-
ments are underestimates of true length. O'Toole
and King (1974) hatched eggs that they had col-
lected and reported that preserved, newly hatched
round herring larvae were 3.75-4.00 mm long. The
4.1- to 5.0-mm SL length class was the most abun-
dant class in my survey (Figure 9). I assumed that
this length class was fully vulnerable to the sam-
pling gear, although some escapement may have
occurred for larvae of this size.

The ratios of night-caught to day-caught larvae

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING

48
44
40
36
32
28
24
20
16
12
8
4

28
24
20
16
12
6
4

28
24

20
16
12

8
4

.rfTTh-i-^

8C7II3 - TI 7114

On-

~L-TK

GE7I27 - TI 7131
-8B7I32

887201-GE 7202

m.^.n

_Q_

GE 7208

TlD

IS 7209

IS7303

"h-TT-T-i-n

h, ,rh

r~i

,rnx^

IS 7320

CL 7412

tLu

2.1- 4 1- 6.1- 8.1- 10.1- 12.1- 14.1- 161- 181-
30 50 70 90 110 13 0 15 0 17.0 19 0
STANDARD LENGTH CLASSES (mm)

FIGURE 9. — Length-frequency distributions of round herring
larvae for 1971-74 cruises to the eastern Gulf of Mexico. Fre-
quencies are expressed as estimated abundance of larvae in each
length class within the area represented by the cruise.

by length classes were examined over all cruises
and they indicated that considerable net avoid-
ance was occurring in the day relative to that
occurring at night. The data were plotted by 2-mm
length classes (Figure 10), and functions were
fitted to allow estimation of the night-caught to
day-caught ratio for larvae in any length class.
The ratio increased rapidly for larvae of 4.0-13.0
mm, but then decreased from a factor of more than
3.0 to about 1.0 when larvae had grown to 18.0 mm.
Two power functions were fitted: for larvae 2.1-
14.0 mm SL the function was R = 0.3041 X° '9115,
where R is the ratio of night-caught to day-
caught larvae andX is standard length of larvae;
for 12.1- to 20.0-mm SL larvae the function was
R = 44,521.54 X"37298. Larva catches made at
daytime stations were adjusted by R (Equation
(ID). Exponential functions or a single poly-
nomial could have been used in place of the power
functions to describe the relationship, but the
power functions provided reasonably good fits to
the data and were acceptable for correction pur-
poses. No adjustments were made for larvae <4.0
mm or > 18.0 mm because there was no observable
difference in night or day catches for larvae of
those lengths.

The round herring larvae night to day catch
ratios are unusual with respect to the observed

: 3 50

<2 50

<0 50-

Y- 0.3046X09"5

Y- 44521. 54X

7.0 9.0 110 130 150

MIOPOINT OF LENGTH CLASS (mm)

17 0 19 0

FIGURE 10. — Night to day ratios of sums of catches, standardized
to numbers under 10 m2 of sea surface, for round herring larvae
collected in 1971-73 in the eastern Gulf of Mexico. The ratios
were calculated for larvae within each 2-mm length class from
2.1 to 20.0 mm SL. Fitted power functions describe the relation-
ships for larvae from 2.1 to 13.0 mm SL and for larvae from
13.1 to 20.0 mm SL. Larval abundance estimates for each length
class at stations occupied during daylight were corrected by the
appropriate ratio factor for each length class to account for
daytime avoidance.

FISHERY BULLETIN: VOL. 75, NO. 1

decrease in the ratio for larvae >13.0 mm. The
ratio increased in other studies on clupeoid larvae
throughout the size range of larvae that were col-
lected (Ahlstrom 1954, 1959b; Lenarz 1973; Mat-
suura in press), and this is true for other species of
clupeid larvae that I have studied in the Gulf of
Mexico. The return of the ratio toward unity after
round herring larvae reached 13.0 mm must indi-
cate that larvae 13.0-18.0 mm became as good at
avoiding the gear at night as during the day. The
alternative explanation, which seems unlikely, is
that larger larvae lost the potential to avoid the
gear during daylight. Daylight is only one factor
that could allow larvae to avoid the gear and ad-
justment of catches to account for it can only par-
tially correct for avoidance losses. The correction
was made, however, in an attempt to get the best
estimate possible for round herring lar-
val mortality during the 1971-72 and 1972-73
seasons.

Larval abundance estimates, corrected for day-
time avoidance, were determined by 1-mm length
classes for the 1971-72 and 1972-73 seasons (Fig-
ure 11) (Equation (10)). Except for larvae in the
4.1- to 5.0-mm length class, which were twice as
abundant in 1972-73, total abundance of larvae
was similar in the two seasons. The greater abun-
dance of 4.1- to 5.0-mm larvae in 1972-73 could
have reflected the reduction in towing speed from
the previous season. Escapement of small larvae
through the meshes may have been more impor-
tant in 1971-72 when towing speed averaged
about 0.7 knot faster.

Abundance of round herring larvae decreased
exponentially as lengths increased during each
season (Figure 11). Fitted exponential functions
for 5.1- to 16.0-mm larvae in 1971-72 and 4.1- to
16.0-mm larvae in 1972-73 provided estimates of
the instantaneous mortality coefficients per mil-
limeter increase in length (Figure 11). The
coefficients were Z = 0.2269 in 1971-72 andZ =
0.3647 in 1972-73. These correspond to percentage
losses per millimeter increase in length of 20.3%
in 1971-72 and 30.5% in 1972-73. Confidence in-
tervals at the 0.95 probability level were Z =
0.2269 ± 0.0930 in 1971-72 and Z = 0.3647 ±
0.1179 in 1972-73. The null hypothesis of no
difference in mortality coefficients between years
was accepted at the a = 0.05 probability level
U-test; 0.05<P<0.10), but the t value was close to
the rejection region suggesting that mortality
may have been higher in 1972-73 than in 1971-72.

The mortality coefficients that I obtained are

s- 10
b

~ 0

S'20

0 no

01 100

S 90

<
I 80

3 70

30 -

NL-(2.2799« IOl5)e°22G9L
(r2- 7718)

life

■(5 8721 « IO'*)e"

fa**

tf>T>

2 ,. »|. 4|. si- 6i- 7|- Bh 91- HI- 13 1- 151- 17 1- 19 1- 21. t- 23 1- 23 I- 271- 29 1-
3 0 40 30 60 70 8090(0 0 120 14 0 160 18 0 20 0 22.0 24 0 26 0 28 0 30 0

LENGTH CLASS (mm)

FIGURE ll. — Length-frequency distributions of annual larval
abundance estimates of round herring larvae collected in the
eastern Gulf of Mexico. Frequencies in each 1-mm length class
are expressed as estimated annual abundance and have been
corrected for daytime avoidance. Fitted exponential functions
provide estimates of the instantaneous coefficient of decline in
abundance by length, 1971-72 and 1972-73.

similar to those reported by Lenarz (1973) from
several years of data on Pacific sardine and north-
ern anchovy, Engraulis mordax. He reported a
range of instantaneous coefficients of 0.15-0.33,
averaging 0.22 for Pacific sardine, that correspond
to a 20% loss per millimeter of growth. For an-
chovy his instantaneous coefficients ranged from
0.32 to 0.46, averaging 0.39, a mean decrease of
32% per millimeter of growth. Matsuura (in press)
has measured the rate of decline in catches of
Brazilian sardine, Sardinella brasiliensis, obtain-
ing an instantaneous coefficient of 0.4962, corre-
sponding to a 39% decrease in catch per millimeter
of growth. Most of the decline in catch of larger
round herring larvae presumably was due to lar-
val mortality but gear avoidance also must be
important. For this reason mortality curves were
fitted only for larvae 16.0 mm or less in length.
Catches of larger larvae were sporadic and possi-
bly greatly influenced by gear avoidance.

Larval mortality is best expressed as a function
of age. If it is assumed that growth of round her-
ring larvae is exponential from the post yolk-sac

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING

stage to 20.0 mm SL, then the instantaneous mor-
tality coefficients, based on mean estimated ages
of larvae, can be calculated using Equations (12)-
(16). No information on growth rates of round her-
ring larvae was available, but mean daily
growth increments of other Gulf of Mexico clupeid
species have been determined in laboratory rear-
ing experiments and they range from 0.3 to 1.0
mm (Richards and Palko 1969; Saksena et al.
1972; Houde 1973b; Houde and Swanson 1975).
Growth rates in those experiments exceeded 0.7
mm/day only when temperature was above 26°C.
Mean daily growth of round herring larvae proba-
bly is between 0.3 and 0.7 mm. Duration of the egg
stage from spawning until hatching is about 2.0
days. The duration of nonfully vulnerable length
classes was estimated from a knowledge of growth
rate and development times of other clupeid
species that have been reared in the laboratory.
Larvae of yellowfin menhaden, Brevoortia smithi,
did not begin to grow in length until nearly 4 days
after hatching at 26°C (Houde and Swanson 1975)
when they were about 4.5 mm SL; larvae of
Harengula jaguana did not grow significantly
until they were nearly 3 days old and 4.5 mm SL at
26°-28°C (Houde et al. 1974). The exponential
growth phase was assumed to begin in the 4.1- to
5.0-mm length class for round herring. The non-
fully vulnerable length classes of 2.1-5.0 mm in
1971-72 were assigned durations that varied from
4.0 to 7.0 days; the nonfully vulnerable 2.1- to
4.0-mm length classes in 1972-73 were assigned
durations of 1.5-3.0 days. Various combinations of
mean daily growth increments and durations of
nonfully vulnerable length classes were entered

into the program to estimate mortality in relation
to age of larvae (Equations (12)-(16)) for 1971-72
and 1972-73. Examples, for one combination of
values of the variables in 1971-72 and one combi-
nation in 1972-73, are provided in Table 10 and
Figure 12.

Given mean daily growth increments of 0.3-0.7
mm (corresponding to instantaneous growth
coefficients of 0.0299-0.0698) and the most proba-
ble durations of nonfully vulnerable length clas-
ses, the probable range of instantaneous mortality
coefficients was 0.0866-0.1739 in 1971-72 and
0.0835-0.1719 in 1972-73 (Table 11). In terms of
daily mortality the 1971-72 probable estimates
ranged from 8.3 to 16.0%; in 1972-73 they ranged
from 8.0 to 15.8% . Although the estimated range is
great, it is nearly the same for the two seasons.
Varying duration of the nonfully vulnerable
length classes had only minor effects on mortality
rate estimation (Table 11), but varying the growth
rate had important effects.

The values ofiV0, they-axis intercepts, provide
yet another series of estimates of annual spawn-
ing, because they estimate the numbers of eggs
present at time zero. The intercept values are gen-
erally lower than spawning estimates by the other
methods and are not considered to be good esti-
mates of spawning. It seems that the exponential
model of loss fits the decrease in larval abundances
reasonable well, but that a greater than expected
mortality occurs between egg and fully vulnerable
larval length classes. Figure 12 illustrates this
possibility. If only larval mortality had been con-
sidered, rather than total mortality from egg to
16.0-mm larvae, the instantaneous coefficients

TABLE 10. — Two examples of data treated to obtain class durations and mean ages of round herring larvae from the eastern Gulf of
Mexico. Abundance estimates are then corrected for duration, and the duration-corrected abundances were subsequently regressed on
mean ages to obtain mortality rates (Table 11). Data are from 1971-72 and 1972-73 egg and larvae abundance estimates that were pre-
viously corrected for daytime avoidance. In these examples the mean daily growth increment (b) was set at 0.50. The nonfully vulner-
able length classes were 2.1-5.0 mm in 1971-72 with duration of 6 days, and 2.1-4.0 mm in 1972-73 with duration of 2.5 days. Calculat-
ing procedures are given in Equations (12)-(16). The regressions for these data are given in Figure 12.

1971-72

1972-73

Mean

Duration-corrected

Mean

Duration-corrected

Abundance

Duration

age

abundance

Abundance

Duration

age

abundance

Class

(no. x 10")

(days)

(no. x 1011)

Class

(no. x 10")

(days)

(no. x 10")

Eggs

2,128.39

2.00

1.00

1,064.20

Eggs

388.94

2.00

1.00

194.47

2.1-5.0

72.90

6.00

5.00

12.15

2.1-4.0

43.89

2.50

3.25

17.56

5.1-6.0

61.96

3.26

9.52

19.00

4.1-5.0

117.78

3.98

6.37

29.58

6.1-7.0

38.96

2.76

12.87

14.11

5.1-6.0

55.29

3.26

10.39

16.95

7.1-8.0

31.70

2.39

15.74

13.24

6.1-7.0

69.81

2.76

13.75

25 28

8.1-9.0

35.92

2.11

18.25

16.99

7.1-8.0

35.42

2.39

16.62

14.79

9.1-10.0

46.88

1.89

20.48

24.77

8.1-9.0

34.55

2.11

19.13

16.34

10.1-11.0

22.29

1.71

22.49

13.02

9.1-10.0

17.08

1.89

21.36

9.02

11 1-12.0

11.60

1.56

24.32

7.41

10.1-11.0

7.44

1.71

23.37

4.34

12.1-13.0

26.81

1.44

25.99

18.63

11.1-12.0

22.99

1.56

25.20

14.70

13.1-14.0

12.25

1.33

27.53

9.19

12.1-13.0

6.67

1.44

26.87

4.63

14.1-15.0

989

1.24

28.97

7.97

13.1-14.0

4.79

1.33

28.41

3.59

15.1-16 0

3.31

1.16

30.31

2.85

14.1-15.0

0.74

1.24

29.85

0.59

15.1-16.0

4.36

1.16

31.19

3.76

FISHERY BULLETIN: VOL. 75, NO. 1

1000-

500 -

r-100

(jj 50
o
z
<

Q
Z

>" 10

<r
cc

o 5
o

<
q:

0.5

Etrumeus teres survival
• - 1971 - 1972
x • 1972- 1973

1971-1972

Nt-(23l.455x I0")e"0l3l7t

1972-1973 S "«*

Nt- (125.123 xlo")e"0,286t >

■ i

2 4 6 6 10 12 14 16 16 20 24 28
ESTIMATED MEAN AGE (DAYS)

FIGURE 12. — Estimated abundance of egg and larval stages of
round herring in the eastern Gulf of Mexico in 1971-72 and
1972-73. Abundance is expressed as a function of estimated age.
Fitted exponential functions give estimates of the instantaneous
rates of decline in abundance for eggs and larvae up to 31 days
of age. The two symbols enclosed in circles represent nonfully
vulnerable length classes and were not included in the re-
gression estimates of instantaneous decline.

would have been lower. In 1971-72, Z = 0.0563 for
fully vulnerable larval stages and Z = 0.1123 for
those stages in 1972-73. The results suggest that
egg and nonfully vulnerable larvae mortality
were higher in 1971-72 than in 1972-73. Mortality
of vulnerable larval stages appears to have been
higher in 1972-73 when the population declined by
10. 6% /day as opposed to 1971-72 when it declined
only 5.5%/day. The higher mortality rate of
larvae in 1972-73 also was apparent in the mor-

tality estimates based on larval lengths (Fig-
ure 11).

High mortality of eggs or newly hatched larvae
may be characteristic of many clupeids, including
round herring. Smith (1973) recently reported
that Pacific sardine eggs experience high mortal-
ity, the instantaneous rate being Z = 0.31 during
that stage. Pilchard, Sardina pilchardus, eggs
undergo high mortality during early embryonic
stages (Southward and Demir 1974) and embryos
ofClupeonella delicatula suffered high mortality,
especially under unfavorable temperature re-
gimes (Pinus 1974).

The best probable estimates of mortality from
the egg to 16.0-mm larval size are near the middle
of the ranges given in Table 11, at instantaneous
growth rates of 0.0498. In 1971-72, Z = 0.1317 is
the most probable estimate while Z = 0.1286
seems most probable in 1972-73. These estimates
correspond to average daily losses of 12.3% in
1971-72 and 12.1% in 1972-73. Estimates of the
instantaneous mortality coefficients based on the
two examples given in Table 10 and Figure 12
coincide with what I believe may be the best esti-
mates of mortality. Confidence limits, at the 0.95
probability level, were placed on the instantane-
ous mortality coefficients derived from these
examples. They were wide, ranging from Z =
0.0635-0.1999 in 1971-72 andZ = 0.0823-0.1749
in 1972-73. The coefficients Z = 0.1317 in 1971-72
and Z = 0.1286 in 1972-73 did not differ sig-
nificantly between years U-test; P>0.50).

The estimates of mortality rates could be too
high if avoidance by larvae was increasing sig-
nificantly as they grew, reducing their probability
of capture. If growth was not exponential, but
linear, during the larval phase, then the mortality
estimates may be too low, because duration-
corrected abundances gave relatively high values
to older larvae that presumably were growing
through length classes at an increasing rate.

Because of the difficulty in ageing eggs or larvae
of marine fishes, few estimates of mortality rates
in relation to age have been reported. Ahlstrom
(1954) reported that about one Pacific sardine
larva survived to 21.25 mm/100,000 eggs spawned
during the first 40-45 days of life, which corre-
sponds to an instantaneous daily loss rate of 0.16-
0.17. Japanese sardine was investigated by
Nakai and Hattori (1962). They reported survival
from egg to the 15.0 mm stage as 0.10% in 54 days,
corresponding to an instantaneous rate of Z =
0.1279. This rate is nearly identical to that which

HOUDE; ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING

TABLE 11. — Summary of mortality estimates for round herring larvae from the eastern Gulf of Mexico, 1971-72 and 1972-73. Estimates
were obtained from the exponential regression of egg and larvae abundances on mean age. Instantaneous growth and mortality
coefficients were calculated for various possible combinations of mean daily growth increment and duration of the nonfully vulnerable
larval stages. Egg stage duration was assumed to be 2.0 days. Nonfully vulnerable larval stages were 2.1-5.0 mm SL in 1971-72 and
2.1-4.0 mm SL in 1972-73. Explanation of the estimating method is given in Equations (12)-(16).

Season

Mean daily

growth increment

(mm)

Instantaneous
growth coefficient

(g)

Nonfully vulnerable

larvae duration

(days)

Instantaneous

mortality coefficient

(2)

/-axis
intercept, Na
(no. x 10")

Daily mortality

rate,

1 - exp(-Z)

1971-72

1972-73

0.3

0.0299

4.0

0.0866

103.25

0.0830

0.3

0.0299

5.0

0.0866

112.07

0.0830

0.3

0.0299

6.0

0.0866

121.40

0.0830

0.3

0.0299

7.0

0.0866

131.21

0.0829

0.5

0.0498

4.0

0.1331

186.35

0.1246

0.5

0.0498

5.0

0.1325

208.29

0.1241

0.5

0.0498

6.0

0.1317

231.46

0.1234

0.5

0.0498

7.0

0.1307

255.74

0.1225

0.7

0.0698

4.0

0.1739

285.65

0.1596

0.7

0.0698

5.0

0.1718

324.45

0.1579

0.7

0.0698

6.0

0.1693

364.72

0.1558

0.7

0.0698

7.0

0.1665

406.00

0.1534

0.3

0.0299

1.5

0.0842

71.56

0.0808

0.3

0.0299

2.0

0.0840

73.89

0.0805

0.3

0.0299

2.5

0.0837

76.26

0.0803

0.3

0.0299

3.0

0.0835

78.68

0.0801

0.5

0.0498

1.5

0.1303

114.55

0.1222

0.5

0.0498

2.0

0.1295

119.80

0.1214

0.5

0.0498

2.5

0.1286

125.12

0.1207

0.5

0.0498

3.0

0.1278

130.52

0.1200

0.7

0.0698

1.5

0.1719

160.03

0.1580

0.7

0.0698

2.0

0.1702

168.78

0.1565

0.7

0.0698

2.5

0.1683

177.58

0.1549

0.7

0.0698

3.0

0.1665

186.39

0.1533

is most probable for round herring larvae. Hard-
ing and Talbot (1973) and Bannister et al. (1974)
reviewed the results of several years' investiga-
tions on plaice, Pleuronectes platessa. They found
that instantaneous mortality coefficients varied
from only 0.0209 to 0.0685 from egg stage 1 to
larval stage 4 during the long larval life of more
than 150 days. Mortality of haddock eggs and lar-
vae was reported by Saville (1956), who gave a
series of estimates that ranged from 4 to 16%/day
(Z = 0.04-0.17) during a 4-yr survey of egg
and larvae abundance at Faroe. Jack mackerel,
Trachurus symmetricus, larvae have a high rate of
mortality (Lenarz 1973), losses ranging from 57 to
67% per millimeter of growth. Farris (1961) re-
ported mortality of jack mackerel larvae in rela-
tion to age. The instantaneous mortality rate, cal-
culated from his data, was 0.23 during the first 30
days of life. Mortality of Japanese mackerel,
Scomber japonicus, larvae was very high
(Watanabe 1970), 99.95% mortality having occur-
red between the egg and 15-mm larval stage in
about 23 days. This corresponds to an instantane-
ous rate of Z — 0.3295. Round herring larval mor-
tality rates apparently are similar to those of other
clupeoids from temperate or subtropical marine
waters (Ahlstrom 1954; Nakai and Hattori 1962;
Lenarz 1973). On average they are slightly higher

than those reported for haddock (Saville 1956).
Round herring larvae have mortality rates that
are much higher than those reported for North
Sea plaice larvae and lower than those reported
for jack mackerel or Japanese mackerel larvae.

If any period can be considered critical in the
early life of round herring, it must occur between
the time that eggs are spawned and when larvae
reach 5.5 mm long. Greatest losses occurred at
that time in 1971-72 and 1972-73 (Figure 12).
Abundance estimates declined by more than 92%
between the egg and 5.5-mm larvae in 1971-72. A
decline of more than 78% in abundance was esti-
mated between egg and 5.5-mm larvae in 1972-73
(Table 12, Figure 12). For larvae longer than 5.5
mm mortality decreased, the decrease in rate
being especially great in 1971-72.

The number of survivors and percentage survi-
val of round herring larvae at various stages were
estimated (Table 12) from the number of spawned
eggs obtained by Method I and the information on
growth and mortality that is summarized in Table
1 1 . The Method I spawning estimate was assumed
to be a better estimate of initial number of eggs
than they- intercept estimates in Table 11. There
was an apparent high mortality between spawn-
ing and hatching which exceeded 75% in 1971-72
(Table 12). The larval populations were reduced by

FISHERY BULLETIN: VOL. 75. NO. 1

TABLE 12. — Estimated numbers and percentages of survivors of round herring larvae at hatching, 5.5 mm SL and 15.5 mm SL in
1971-72 and 1972-73. Estimates are made for three possible growth rates (see Table 11). Duration of the nonfully vulnerable larval
stages was set at 6.0 days for 2.1-5.0 mm larvae in 1971-72 and 2.5 days for 2.1-4.0 mm larvae in 1972-73. The number of spawned
eggs in each year was based on estimates by Method I (Table 5). Predicted numbers at hatching, 5.5 mm and 15.5 mm are calculated
from exponential functions based on Table 11 data.

Season

Instantaneous

growth

coefficient

(a)

Number of

spawned eggs

(x 1011)

Instantaneous

mortality

coefficient

(Z)

Number
hatching
(x 10")

% mortality
to hatching'

Number of

5.5-mm larvae

(x 10")

% mortality
to 5.5 mm

15.5

(

umber of
-mm larvae
x 10")

% mortality
to 15.5 mm

1971-72
1972-73

0.0299

0.0498
0.0698

0.0299
0.0498
0.1683

1 ,064.20
1,064.20
1 ,064.20

194.47
194.47
194.47

0.0866

0.1317
0 1693
0.0837
0.1286
0.1683

102.09
177.86
259.96

64.51

96.74

126.83

90.3
83.3
75.6

66.8
50.3
34.8

48.77

66.06
78.40

23.00
32.89
41.00

95.4
93.8
92.6

88.2
83.1
78.9

2.43
4.27
6.35

1.26
2.27
3.37

99.8
99.6
99.4

99.3
98.8
983

'Hatching assumed to occur at 2.0 days.

more than 99.4% at 15.5 mm in 1971-72 and by
more than 98.3% in 1972-73. The 15.5-mm stage
would be attained at about 31 days if the instan-
taneous growth coefficient was 0.0498 (equal
0.5-mm mean daily growth increment). At that
growth rate, approximately 4 larvae/1,000 eggs
spawned in 1971-72 and 12 larvae/1,000 eggs
spawned in 1972-73 would have survived to 15.5
mm and 1 mo of age.

SUMMARY

1) Surveys of eggs and larvae were used to inves-
tigate spawning, to determine adult stock size,
and to study aspects of the early life history of
round herring in the eastern Gulf of Mexico during
1971-74.

2) Spawning takes place from mid-October
to the end of May between the 30- and 200-m
depth contours. About 60% of the total spawning
occurred at depths greater than 50 m. Most spawn-
ing apparently occurred during January and
February.

3) Eggs occurred when surface temperatures
ranged from 18.4° to 26.9°C, and surface salinities
from 34.5 to 36.5%o. Larvae =s5.0 mm SL were
collected when surface temperatures were from
20.5° to 26.9°C, and surface salinities from 34.1 to
36.8%o. Of the eggs 82.5% and of the ^5.0-mm
larvae 87.5% were collected when surface temper-
atures were from 21° to 26°C. More than 50% of the
eggs and =£5.0-mm larvae were collected where
surface salinity exceeded 36.0%o.

4) There is a major spawning area between lat.
27°00' and 28°00'N and long. 083°30' and
084°30'W. The center of the area is located about
150 km west by southwest of Tampa Bay in depths
of 50-200 m.

5) The fecundity of eight round herring females
130-165 mm SL ranged from 7,446 to 19,699.

Mean relative fecundity was 296.5 ova/g (S~ =
33.7). Gonads of round herring collected from Au-
gust to November were ripening or near ripe.
Those collected in June were spent. The sex ratio
of 71 round herring adults did not differ sig-
nificantly from 1:1.

6) The time from spawning to hatching, based on
observations of development stages in planktonic
eggs, was about 2.0 days at 22°C.

7) Adult biomass was determined by three
methods from data on estimated annual spawn-
ing. The Sette and Ahlstrom's (1948) and
Simpson's (1959) techniques gave estimates that
ranged from 130,000 to 715,000 metric tons in
1971-72 and 1972-73. The geometric mean of eight
individual estimates by Saville's (1956) method
was 181,200 metric tons, the arithmetic mean
being 415,175 metric tons. But, the best estimates
by Saville's method were from two individual
cruises in midwinter. These were 673,481 metric
tons in 1971-72 and 136,330 metric tons in 1972-
73. Those estimates were nearly the same as esti-
mates obtained by the other two methods. Spawn-
ing biomass apparently was higher in 1971-72
than in 1972-73.

8) The estimated concentration of biomass be-
tween the 30- and 200-m depth contours, based on
the stock size estimates, was from 67.6 to 120.0
kg/hectare in 1971-72 and from 5.9 to 28.3 kg/hec-
tare in 1972-73.

9) The annual potential yield of round herring to
a fishery, if instantaneous natural mortality
coefficients lie in the range 0.5-1.0, ranged from
32,750 to 420,700 metric tons. The most probable
mean annual potential yield estimates are in the
range 50,000 to 250,000 metric tons. This is equiv-
alent to 6.5-32.5 kg/hectare in the 30- to 200-m
depth zone.

10) Total abundance of larvae was estimated in
1971-72 and 1972-73. The 4.1- to 5.0-mm length

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING

class was nearly twice as abundant in 1972-73 as
in 1971-72. Other length classes were somewhat
more abundant in 1971-72 catches.

11) Mortality rates of larvae were estimated by
length and for estimated ages. For lengths, the
instantaneous coefficients of decline in catches
wereZ = 0.2269 in 1971-72 and Z = 0.3647 in
1972-73, corresponding to 20.3 and 30.5% losses
per millimeter of growth. For ages, a range of
estimates of daily mortality, based on varying
growth rates and nonfully vulnerable larva stage
durations, was obtained. The most probable daily
mortality estimates were Z = 0.1317 in 1971-72
and Z = 0.1286 in 1972-73, corresponding to per-
centage losses of 12.3 and 12.1% on a daily basis.

12) It is probable that more than 99.4% mortal-
ity from eggs to 15.5-mm larvae occurred in 1971-
72, and that more than 98.3% mortality occurred
during that period in 1972-73. About 4 larvae/
1,000 eggs spawned survived to 31 days and 15.5
mm in 1971-72, while about 12 larvae/1,000 eggs
survived to that stage in 1972-73.

ACKNOWLEDGMENTS

This project was initiated as part of cooperative
efforts to investigate biological and physical pro-
cesses in the eastern Gulf of Mexico. Assistance
was provided by many people and agencies. Par-
ticular thanks go to Murice Rinkel of the State
University System of Florida, Institute of
Oceanography, for his help in coordinating
EGMEX and Western Florida Continental Shelf
cruises, as well as reduction of physical oceano-
graphic data. The 1971 plankton surveys were
coordinated with the National Marine Fisheries
Service MARMAP program in the eastern Gulf of
Mexico and special acknowledgments go to the
following personnel: Ed Hyman, Larry Ogren,
William J. Richards, Charles Roithmayr, and
Stuart Smith. My students and technical person-
nel deserve thanks for long hours spent at sea and
tedious hours sorting and enumerating; among
these are Steven Berkeley, Alfred Cardet, Reuben
Charles, Ann and Nicholas Chitty, Lise Dowd,
John Klinovsky, Walter Stepien, A. Keith
Taniguchi, and Gregg Waugh. Harvey Bullis and
Paul E. Smith of the National Marine Fisheries
Service criticized earlier drafts of this paper, and I
thank them for the suggestions and ideas that
they provided.

This research was sponsored by NOAA Office of

Sea Grant, Department of Commerce, under
Grant 04-3-158-27 to the University of Miami.

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REPRODUCTIVE BIOLOGY OF THE FEMALE DEEP-SEA RED CRAB,
GERYON QUINQUEDENS, FROM THE CHESAPEAKE BIGHT1 2

Paul A. Haefner, Jr.3

ABSTRACT

Collections of the deep-sea red crab, Geryon quinquedens, were made at depths from 270 to 1,300 m in
the vicinity of Norfolk Canyon in the northwest Atlantic Ocean in November 1974, September 1975,
and January 1976. The gross morphology and histology of ovary development are described. The size
range in which relative growth of the abdomen changes is associated with maturation of the vulvae,
copulation and insemination, gonad development, and egg extrusion. Females become sexually mature
within the intermolt size range 65-75 mm carapace length (80-91 mm carapace width). Most intermolt
females s*76 mm carapace length show signs of copulation and insemination, and their ovaries are in
intermediate to advanced stages of development. Few females <75 mm are ovigerous.

Historically the red crab, Geryon quinquedens
Smith, has been seldom utilized commercially
(Schroeder 1959; McRae 1961). Explorations have
established that red crabs can readily be captured
by pot or trap fishing in many regions along the
eastern United States. The commercial potential
of this crab has spurred investigations of the
general biology and distribution (Le Loeuff et al.
1974; Haefner and Musick 1974; Wigley et al.
1975; Gray4; Dias and Machado5; Ganz and
Herrmann6) as well as technological and economic
aspects of harvesting and processing (Meade and
Gray 1973; Holmsen and McAllister 1974).

The present study was prompted by recognition
that biological data on sexual maturity are re-
quired for proper management of red crab stocks.
This paper presents data on collections from
Chesapeake Bight and deals with various aspects
of reproductive biology of the female crab: ovary
development, size composition of catch, size of

'Research cruises supported by National Science Foundation
Grant GA-37561, J. A. Musick, principal investigator, and by the
University of Virginia Institutional Grant Program for P. A. H.
participation.

Contribution No. 777, Virginia Institute of Marine Science,
Gloucester Point, VA 23062.

'Virginia Institute of Marine Science, Gloucester Point, VA
23062.

"Gray, G. W., Jr. 1969. Investigation of the basic life history of
the red crab (Geryon quinquedens). R.I. Div. Conserv. P.L. 88-
309, Proj. 3-46-R Completion Rep., 36 p.

5Dias, C. A., and J. S. Machado. 1974. Preliminary report on
the distribution and relative abundance of deep-sea red crab
(Geryon sp.) off Angola. Sci. Pap. No. 26, 12 p. In Scientific papers
presented to the second session of the International Commission
for the Southeast Atlantic Fisheries (Madrid, December 1973).
Publ. Mimeogr. M. E. Bioceanol. Pescas, Angola 12, 75 p.

6Ganz, A. R., and J. F. Herrmann. 1975. Investigations into
the southern New England red crab fishery. R.I. Dep. Nat.
Resour. Div. Fish. Wildl. Mar. Fish. Sect., 78 p.

ovigerous individuals, abdomen width-carapace
length relationship, development of vulvae, and
evidence of copulation and insemination.

METHODS

Red crabs were collected at depths from 270 to
1,300 m in Norfolk Canyon and vicinity (lat.
36°32'-37°10'N; long. 74°10'-74°46'W) in Novem-
ber 1974 (RV James M. Gilliss 74-04), September

1975 (RV James M. Gilliss 75-08), and January

1976 (RV James M. Gilliss 76-01). Based on the
recommendations of Gray (see footnote 4), all
female crabs were measured for short carapace
length (CL, distance from the diastema between
the rostral teeth to the posterior edge of the
carapace, along the midline); width of the fifth
abdominal segment was recorded for 190 crabs.
Carapace length may be converted into carapace
width (CW) by using the equation CW = 11.04 +
1.06CL, r = 0.98, based on measurements of 268
female crabs.

Pleopods and vulvae were examined to deter-
mine if mating and egg extrusion had occurred.
Eggs or egg remnants or their absence on
pleopods, variations in the size, shape and physi-
cal condition of vulvae, and the relative size of
seminal receptacles were noted. Selected samples
of the spermathecal fluid were withdrawn directly
from incisions in the receptacle and examined mi-
croscopically for presence of sperm or spermato-
phores.

Ovaries were initially classified to relative size
following the scheme used for the rock crab,
Cancer irroratus (Haefner 1976). The scheme for

Manuscript accepted June 1976.

FISHERY BULLETIN: VOL. 75, NO. 1, 1977.

FISHERY BULLETIN: VOL. 75, NO. 1

red crabs was quantified by measuring ovary
volume and deriving gonad indices (Giese and
Pearse 1974) for the various stages. Certain ovar-
ian samples were selected on the basis of relative
size and color and treated in the following manner.
Displacement of ovaries was measured by placing
the entire, excised ovary in volumetrically
graduated tubes containing a known quantity of
seawater. Ovary volume (V0 in milliliters) was
used to compute a gonad index: G, = (Ovary
weight)/* Total body weight) x 100, where weights
in grams were calculated as follows Ovary weight
= 1.025 V0, assuming ovarian specific gravity
equals that of seawater. Total body weight was
derived from the following relationship based on
measurements of 142 females: log body weight =
-3.134 + 2.8833 log length, r = 0.968.

Portions of the ovaries were then preserved in
Davidson's fixative for histological processing and
in Gilson's fluid (Bagenal and Braum 1971) for
measurement of ova size.

Histological sections were stained in
haematoxylin and eosin and mounted in Per-
mount.7 Descriptions of developmental stages
were made from the resultant slides.

Samples in Gilson's fluid were shaken to release
ova which were then observed with a dissecting

'Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

microscope. The diameters of 20 spherical ova
from each sample were measured with a cali-
brated ocular micrometer. Misshapen ova were
not considered. Similarly, 20 extruded eggs from
11 ovigerous crabs were removed and measured
(length and width). A mean diameter was com-
puted for each crab.

RESULTS AND DISCUSSION

The Ovary

The following account of the gross morphology
and histology of the red crab ovary is based on
examination of the gross anatomy of 255 crabs and
on histological preparations from 34 crabs.

The ovary is an H-shaped organ located dorsally
just beneath the carapace (Figure 1). Two horns
extend anterolateral^ from either side of the
gastric mill and lie dorsal to the hepatopancreas.
At the posterolateral borders of the gastric mill,
near the origin of the posterior mandibular muscle
bundles, the anterior horns are joined by a
commissure. Two posterior horns, which lie ven-
tral to the heart, extend posteriorly on either side
of the intestine. The seminal receptacles arise
from the midlateral border of the posterior horns
and open externally through gonopores (vulvae)
on thoracic sternite VI, immediately adjacent to
sternite V.

FIGURE 1. — Dorsal dissection of
female Geryon quinquedens. Heart
and medial portion of branchial
chamber removed. Anterior (aov),
posterior (pov) and commissure (cov)
of ovary, gastric mill (g), gill (br),
intestine (i), hepatopancreas (hp),
seminal receptacle (sr), midgut caeca
(mc).

HAEFNER: REPRODUCTIVE BIOLOGY OFGERYONQUINQUEDENS

Very Early Development

In very early development (Table 1 ), the ovary is
small ( <0.2 ml in volume; horn width 0.5 mm) and
colorless. A central lumen is not apparent from
gross morphological examination, although the
precursor of one is indicated in Figure 2. Lobation
is not obvious in this stage. The bulk of the organ
consists of fibrous connective tissue, apparently
stratified, and blood sinuses (Figure 2A). The
outer connective tissue wall of the ovary is not
readily distinguishable from the inner connective
tissue. Various cell types are present. Most cells
contain one oval nucleus (7.2 fim long) while other
larger, less numerous cells have a large round
nucleus (7.2 /xm in diameter). Ova diameters are
small (40-172 /xm) and confined to germinative
areas or strands. In some instances, it is difficult to
free the ova from the surrounding tissue even after
treatment in Gilson's fluid. The germinal zone
consists of columnar cells with (12 /xm) elongate
nuclei (Figure 2B).

throughout the ovary. Cells in an early stage of
oogenesis, recognizable by vacuolate nuclei (Fig-
ure 3B), are small (14-53 /urn) compared with the
more advanced ova (74-278 /xm) characterized by
more compact nuclei and the presence of
cytoplasmic yolk granules (Figure 3C, D). They
are surrounded by a single layer of follicular cells
(Figure 3D) which are spindle shaped with an
elongate nucleus (72 /xm).

Intermediate Stage

As the ovary progresses to the intermediate
stage of development, accumulating yolk, it
gradually occupies more space (G, = 1.4-2.7) in the
visceral cavity and changes color (Table 1). The
ovarian architecture is little changed from that of
earlier stages; connective tissue is confined to the
margin of the ovary and to the interstices between
the now obvious lobes. Germinative zones are
present. Ova are larger (1 12-537 /xm) than those in
earlier stages.

Early Development

White, ivory, light gray, or light yellow ovaries
which are small (0.2-2.0 ml volume, 2-6 mm horn
width) may exhibit histological development in
advance of the previous stage. Most of the organ is
filled with ova in various early stages of de-
velopment (Figure 3A). Connective tissue is still
prevalent around the margin, penetrating the
ovary in numerous locations to form small lobes
which are not readily visible from a gross mor-
phological aspect.

The germinal zone is well defined and branches

Mature Stages

A fully mature ovary nearly obscures the
hepatopancreas in dorsal view. Only a small por-
tion of the hepatopancreas and the slightly coiled
midgut caecae are visible between the ovary and
branchial chamber (Figure 1). The high gonad
indices (>2. 7) attest to the large volume (8-32 ml)
of the organ at these stages of development. The
color remains variable but is generally darker
than that of earlier stages as reddish and brownish
hues become evident (Table 1).

The predominant histological feature in a

TABLE 1. — Descriptive stages of Geryon quinquedens ovary: color variation, horn size, volume, gonad index, and ova diameter.

Stage of
ovary

Color of ovary

Horn width range (mm)
n Ant. Post.

Ovary volume (ml)
n X Range

Gonad index

Ova diamet
n X

er (nm)

development

Range

Very early

Colorless, white, ivory

0.5-2.2

0.5-1.3

<0.2

0.1-0.2

0.29

0.09-0.88

102

49-172

Early

White, ivory, light gray,
light yellow

2-6

1.1

0.2-2

0.75

0.19-1.75

168

74-278

Intermediate

Ivory, white, light yellow,
yellow, yellowish
orange, light brownish
orange

8-15

6-10

5.2

4.5-7

205

1.45-2.73

289

112-537

Advanced

Yellow, yellowish orange,
brownish orange,
reddish brown,
brownish purple

16-23

6-12

13.4

8-12

4.24

2.74-6.02

508

298-666

Mature

Yellowish orange, orange,
brownish orange,
brownish purple

20-32

10-18

28.9

21-32

8.22

6.00-11.85

611

484-788

Redeveloping

Ivory, yellowish orange,
light brownish orange,
reddish brown, reddish
orange, brownish purple

8-20

5-7

9.0

2.5-21

2.67

1.04-7.25

347

148-671

FISHERY BULLETIN: VOL. 75, NO. 1

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FIGURE 2. — Ovary of Geryon quinquedens in very early development stage. A. 25 x . Fibrous connective tissue (f)
predominates. Germinal strand (g) and lumen (1) precursors are present. B. Enlargement (400x) of germinal
strand region showing columnar cells.

FIGURE 3.— Ovary of Geryon quinquedens in early development stage. A. 25 x . Ova in various stages of development are shown radiating
from germinal zone (g). Fibrous connective tissue (f ) evident. B. High magnification (400x ) emphasizing vacuolar nucleate cells in early
stages of oogenesis. C. Follicular development (125x) in early stage ovary. Yolk granules evident in larger ova. D. High magnification
(400x ) showing yolk granular consistency of cytoplasm in developing ova.

HAEFNER: REPRODUCTIVE BIOLOGY OFGERYONQUINQUEDENS

FISHERY BULLETIN: VOL. 75, NO. 1

mature ovary, usually brownish orange to brown-
ish purple, is the concentration of large ova
(484-788 /u.m) containing large yolk granules
which make sectioning difficult. The size range of
these ova overlaps the mean diameter range of
extruded eggs (638-817 fim).

The ovary is subdivided into lobes and possesses
a central hollow shaft or lumen as described for
Callinectes sapidus by Cronin (1942) and for
Portunus sanguinolentus by Ryan (1967). An
irregular matrix of compact germinal tissue,
surrounded by less compact zones of large ova,
borders the lumen.

Redeveloping Ovaries

The presence of developing ova in germinal
zones of ovaries suggests that oogenesis continues
after ovulation. Such redevelopment is indicated
by the range of ovarian developmental stages
observed in crabs known to have ovulated. Ovaries
from seven ovigerous crabs with egg remnants
resembled the early to advanced stages described
above. Mean values and ranges of horn width,
ovary volume, and gonad index reflect the wide
variety of stages of redevelopment (Table 1).

In ovaries from nine ovigerous crabs and seven
females with egg remnants on the pleopods,
germinative zones were clearly evident (Figure
4 A) but the ovary was less compact than that of the
mature or ripe ovary as the interstices were filled
with connective tissue (Figure 4B). The ova were
more variable in size within a given developmen-
tal stage. Relatively large ova (388 jitm) can be
found in an early stage ovary while unusually
small ova (168 /xm) are numerous in an advanced
ovary.

Incidence of Ovarian Development

A relationship exists between size of female and
ovarian development (Figure 5). Eighty-eight
percent of all crabs =£75 mm CL (91 mm CW)
possessed ovaries in early stages of development;
90% of the females >75 mm were in intermediate
to advanced stages of ovarian development. Early
developmental stages can occur in large crabs,
particularly after recent ovulation. This is evident
from the distribution of ovigerous crabs and those
with egg remnants on the pleopods. Such ovaries,
in redevelopment stages, can recede to early
developmental stages.

Size at Sexual Maturity

Hartnoll (1969) regarded a crab as mature
"when it enters the intermolt during which it is
first able to copulate successfully." It is generally
accepted that in brachyurans maturity in some
females cannot be determined from the condition
of the gonads because development and ovulation
often occur a considerable time after mating.

In the case of red crabs, several criteria were
examined in an effort to define the size (age) at
which females mature. These included the size
distribution of ovigerous and nonovigerous fe-
males, the incidence of physical indicators of copu-
lation, and changes in the features of the vulvae
and abdomen.

Ovigerous Females

The size-frequency distribution of 755 females
captured in November 1974, September 1975, and
January 1976 reveals the incidence of ovigerous
individuals and those with egg remnants on the
pleopods (Figure 6). In November and September,
27.3% and 15.7%, respectively, of females 3=71 mm
CL (97 mm CW) were ovigerous; 9.0% of females
2*71 mm in September carried egg remnants. In
January, 25.5% of females 2=71 mm CL were
berried; two of these showed some evidence of egg
hatching. Most (94%) of the ovigerous individuals
and those with egg remnants were between 71 and
1 13 mm CL (97-131 mm CW); only four crabs were
smaller.

Physical Evidence of Copulation

In numerous species of crabs, recent copulation
by the female is indicated by the presence of a
hardened mass of spermatozoa and associated
secretions protruding from the vulvae (Hartnoll
1969). This so-called sperm plug does not occur in
Geryon quinquedens .

The exoskeletons of red crabs that have not
recently molted are blackened or discolored in
abraded or damaged areas and are usually in-
fested with lepadid barnacles Trilasmis sp. The
association of lepadids and discoloration serves as
an indicator of a time lapse since the last molt,
although the exact length of time cannot presently
be determined. It was reasoned that abrasion and
damage of vulval margins due to copulation would
result in similar discoloration. This was verified

HAEFNER: REPRODUCTIVE BIOLOGY OFGERYON QUINQUEDENS

■

•4k

3» ■

FIGURE 4. — Redeveloping ovary of Geryon quinquedens from ovigerous crab. A. 25 x . Germinative zone (g) and
developing ova are evident. B. Higher magnification (125x) showing prevalence of fibrous connective tissue (f)
among various sizes of developing ova.

FIGURE 5.— Distribution of female
Geryon quinquedens according to size
(carapace length) and stage of ovarian
development. November 1974 and
September 1975 samples pooled.
Black areas indicate ovigerous crabs
and those with egg remnants on
pleopods.

VERY EARLY

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FISHERY BULLETIN: VOL. 75, NO. 1

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, "1 , ,

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SHORT CARAPACE LENGTH (mm)

OVIGEROUS

NOVEMBER 1974

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SEPTEMBER 1975

OVIGEROUS
EGG REMNANTS

1 1-1— I 1 ' T

n , n , n

JANUARY 1976

OVIGEROUS

Un.

fl H

J~L| S N^332

N--2I5

30 40 50 60 70 80 90 100 110 120

SHORT CARAPACE LENGTH (mm)

FIGURE 6.— Size-frequency distribution of female Greyon quinquedens captured in November 1974 (a), September 1975 (b), and
January 1976 (c). Ovigerous individuals are indicated in black; those with egg remnants on pleopods by horizontal stripes.

by examining the spermathecal contents of 67
crabs with discolored vulvae (14 with extruded
eggs, egg remnants, or damaged pleopods and 53
with clean, intact pleopods). Eleven (79%) of the
recently ovulated females (78-103 mm CD and 47
(89%) females with clean pleopods (45-105 mm
CD contained sperm (Figure 7). Twenty-one crabs
(50-75 mm CD with immature vulvae were
similarly examined; none had sperm in the
spermathecae. Another 17 crabs (50-72 mm CL)

with immature vulvae were not examined for the
presence of sperm because the spermathecae were
undeveloped; only the tubular vagina was present
between the ovary and gonopore.

Blackened vulval margins may be used as a
criterion to indicate that copulation of the female
crab has occurred, if other obvious signs (eggs or
remnants) are absent. The 89% incidence among
nonovigerous females supports this contention.
The 79% incidence among ovulated females is low,

HAEFNER: REPRODUCTIVE BIOLOGY OFGERYON QUINQUEDENS

FIGURE 7. — Isolated sperm from spermatheca of 83-mm CL
Geryon quinquedens. Nonmobile processes extend from nuclear
region surrounding a central, refringent structure, most likely
the acrosome (Brown 1966). Interference microscopy, 1300x.

but expected. None of these crabs had swollen or
turgid spermathecae of the type shown in Figure
1. In most cases, only residual quantities of semi-
nal secretions were present in the receptacles,
indicating that most of the deposit had been used
in past ovulation(s) or absorbed.

The presence of discolored vulval margins
among large crabs suggested that they may pro-
vide a physical criterion for copulation, similar to
those demonstrated for other brachyurans ( Veillet
1945; Butler 1960; Hartnoll 1969). Vulval mar-
gins of 93.5% of the females 2=70 mm CL examined
(n = 328) were blackened (Figure 8). All females
<70 mm CL had vulvae with intact margins. Not
included in Figure 8 are an unusually small
inseminated female (47 mm CL) and the ovigerous
64-mm CL specimen included in Figure 6b.

One crab (47 mm CL) with small (1.2 mm long),
but open, mature-type vulva was sperm positive.
This unusually small crab had obviously mated
but the vulval margins were not blackened. It is
physically possible for a female this small to mate
with a male of similar size. I have observed
morphologically functional pleopods, with penis
inserted in the first pair, on male crabs as small as
38 mm CL. The size at which males become
physiologically mature is not known, but it must
be relatively small.

Change in Vulvae

Although variable in form, vulvae of G.
quinquedens undergo a recognizable growth and
development pattern which parallels growth in
body size and ovarian development. Six types are
recognized (Figure 9). The first form vulvae (a) are
slitlike and tightly closed. The observed size range
appears to be related to crab length (Table 2).
Form (b) vulvae are recurved, closed, and slightly
larger than the longest form (a) vulvae. Forms (c)
and (d), irregularly shaped and partially open,
range from a size comparable to the largest vulvae
of type (a) to that of type (e). Unusually large (d)
vulvae (2.6 mm) were observed in a 78-mm CL
crab. Form (e) vulvae are oval, gaping, and appear
to immediately precede the mature vulva. Form
(f) is the enlarged (2.4-3.9 mm), gaping, and usu-
ally blackened vulvae of the larger, mated crabs.

TABLE 2. — Incidence of vulval type and size range in relation to
carapace length of female Geryon quinquedens.

Type

Carapace length
(mm)

Vulval length range
n (mm)

20-33

0.2-0.3

57-66

0.6-0.9

56-60

no data

61-74

0.7-1.2

50-60

0.5-0.8

61-74

0.8-1.5

61-72

0.7-1.3

2.6

47-60

0.6-1.2

61-72

0.8-1.2

3.0

70-103

2.4-3.9

Change in Abdomen Width

The abdomen width (Y) to carapace length (X)
relationship is allometric and is transformed to a
straight line by the equation:

log Y = -0.875 +1.321 logX, n = 251; r = 0.990

The relationship changes in the 60- to 75-mm
CL range (Figure 10) so linear regressions were
calculated separately for crabs with mature (f)
vulvae:

FIGURE 8.— Size-frequency dis-
tribution of female Geryon quin-
quedens with immature gonopores
(white) and with discolored gonopore
margins (black). November 1974,
September 1975, and January 1976
collections pooled.

■ BLACKENED VULVAL MARGINS
O IMMATURE VULVAE

50 60 70 80

SHORT CARAPACE LENGTH (mm)

00 MO 120

FISHERY BULLETIN: VOL. 75, NO. 1

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FIGURE 9. — Structural variation in vulvae of female Geryon quinquedens. Portions of thoracic sternites V, VI, VII
illustrated, a. First form, slitlike, from 20-mm CL crab. b. Recurved, closed, 66 mm CL. c and d. Irregular shape, partially
open, 74-mm and 71-mm CL crabs, respectively, e. Oval, gaping, 68 mm CL. f. Oval, enlarged, with blackened margins, 90
mm CL.

100

HAEFNER: REPRODUCTIVE BIOLOGY OFGERYON QUINQUEDENS

Y = -8.286 + 0.662X, n = 160; r - 0.943

and those with immature vulvae:

Y = -8.512 + 0.64LY, n = 91; r = 0.971.

The size range in which relative growth of the
fifth abdominal segment changes is clearly as-
sociated with the maturation of the vulvae,
copulation and insemination, gonad development,
and extrusion of eggs. Females become sexually
mature within the intermolt size range 65-75 mm
CL (80-91 mm CW). Most intermolt females 3=76
mm CL show signs of copulation and insemina-
tion, and their ovaries are in intermediate to
advanced stages of development. Few females <75
mm CL are ovigerous.

ACKNOWLEDGMENTS

I am indebted to the following personnel at
Virginia Institute of Marine Science who con-

tributed their expertise to the project: F. A.
Perkins, photomicrography; Patsy Berry, micro-
technique and photography; Peggy Peoples and
Kay Stubblefield, art work; W. A. Van Engel,
manuscript review; and those associated with the
canyon cruises.

LITERATURE CITED

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water, p. 166-198. IBP (Int. Biol. Programme) Handb. 3.
BROWN, G. G.

1966. Ultrastructural studies of sperm morphology and
sperm-egg interaction in the decapod Callinectes
sapidus. J. Ultrastruct. Res. 14:425-440.
BUTLER, T. H.

1960. Maturity and breeding of the Pacific edible crab,
Cancer magister Dana. J. Fish. Res. Board Can. 17:641-
646.
CRONIN, L. E.

1942. A histological study of the development of the ovary
and accessory reproductive organs of the blue crab,
Callinectes sapidus Rathbun. M.S. Thesis, Univ.
Maryland, College Park, 37 p.

I-

_)
<
z

Q
CD

70-1

60-

50-

40-

30-

20-

10-

• MATURE VULVAE
o IMMATURE VULVAE

Y - -8.29 + 0.662 x, N--I60

—r-

100

120

SHORT CARAPACE LENGTH (mm)

FIGURE 10.— Relationship of width of fifth abdominal segment to short carapace length for Geryon quinquedens with mature (dots)

and immature vulvae (circles).

101

FISHERY BULLETIN: VOL. 75, NO. 1

GIESE, A. C, AND J. S. PEARSE.

1974. Introduction: General principles. In A. C. Giese
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HAEFNER, P. A., JR.

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HAEFNER, P. A., JR., AND J. A. MUSICK.

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HARTNOLL, R. G.

1969. Mating in the Brachyura. Crustaceana 16:161-
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HOLMSEN, A. A., AND H. MCALLISTER.

1974. Technological and economic aspects of red crab
harvesting and processing. Univ. R.I. Mar. Tech. Rep.
28, 35 p.

LE LOEUFF, P., A. INTES, AND J. C. LE GUEN.

1974. Note sur les premiers essais de capture du crabe

profond Geryon quinquedens en Cote d'lvoire. Doc. Sci.
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MCRAE, E. D.

1961. Red crab explorations off the northeastern coast of
the United States. Commer. Fish. Rev. 23(5):5-10.
MEADE, T. L., AND G. W. GRAY, JR.

1973. The red crab. Univ. R.I. Mar. Tech. Rep. 11, 21 p.
RYAN, E. P.

1967. Structure and function of the reproductive system of
the crab Portunus sanguinolentus (Herbst) (Brachyura:
Portunidae). II. The female system. Mar. Biol. Assoc.
India Symp. Ser. 2(II):522-544.
SCHROEDER, W. C.

1959. The lobster, Homarus americanus, and the red crab,
Geryon quinquedens, in the offshore waters of the Western
Atlantic. Deep-Sea Res. 5:266-282.
VEILLET, A.

1945. Recherches sur le parasitisme des crabes et des
galathees par les rhizocephales et les epicarides. Ann.
Inst. Oceanogr. Monaco 22:193-341.
WIGLEY, R. L., R. B. THEROUX, AND H. E. MURRAY.

1975. Deep-sea red crab, Geryon quinquedens, survey off
northeastern United States. Mar. Fish. Rev. 37(8):1-21.

102

COMPARISONS OF CATCHES OF FISHES IN GILL NETS IN

RELATION TO WEBBING MATERIAL, TIME OF DAY, AND

WATER DEPTH IN ST. ANDREW BAY, FLORIDA

Paul J. Pristas and Lee Trent1

ABSTRACT

Monofilament and multifilament gill nets were fished simultaneously in shallow- (0.7-1.1 m), mid-
(2.2-2.6 m), and deep- (5.2-5.6 m) water zones for 40 days between 19 September and 29 December 1972,
in lower St. Andrew Bay, Fla. Each net was 33.3 m long, had stretched mesh of 9.5 cm, extended from
water surface to bottom, and was anchored in position. Nets were checked at sunrise and sunset.
Fifty-two species of fishes and one hybrid from 30 families were caught. The 12 most abundant species
composed 92^ of the total number (4,066) caught. Catch comparisons between 1 ) webbing materials, 2)
times of day, and 3) water depths were made from data on catches of the 12 most abundant species.
Catches in monofilament webbing were greater than those in multifilament webbing for 8 of the 12
species. Greater catches were made at night for all 12 species. Catches of eight species were highest in
the deep-water zone, but catches of the remaining four species were highest in the shallow-water zone.
Monofilament nets were damaged least, and percent damage decreased as depth zones increased.

The National Marine Fisheries Service (NMFS)
began collecting a variety of fishes from coastal
and offshore waters throughout the United States
in 1972 for heavy-metal analyses. Each coastal
laboratory of NMFS was responsible for the fish
collections in their respective geographic area,
and we at the Panama City Laboratory were to
collect relatively large numbers of about 15
species. We decided that set gill nets would be our
most effective sampling gear but could find no
published information on their effectiveness in
Gulf of Mexico estuaries in relation to various
efficiency factors such as twine size, mesh size, and
location and time of day to set the nets.

The literature did reveal that gill nets are
among the most important types of fishing gear
used in Florida. Over 34.6 million pounds of
finfish, valued at over $4.7 million to the
fishermen, were caught with gill and trammel
nets on the west coast of Florida in 1971 (National
Marine Fisheries Service 1974). Set gill nets, the
type used in this study, are not commercially used
to any extent in Florida estuaries except for spot-
ted seatrout, Cynoscion nebulosus, and even in
this fishery the nets are left in the water for only
about 2 h (Siebenaler 1955). Information about the
efficiency of set gill nets in the gulf was limited to

'Southeast Fisheries Center Panama City Laboratory, Na-
tional Marine Fisheries Service, NOAA, P.O. Box 4218, Panama
City, FL 32401.

comparisons of catches of king mackerel,
Scomberomorus cavalla, and Spanish mackerel, S.
maculatus, between monofilament and multi-
filament gill nets (Mihara et al. 1971).

We decided to capture the fishes needed for the
heavy-metal survey in such a way that informa-
tion could be generated on the efficiency of gill nets
in our area. The objectives of this study were: 1) to
compare gill net catches in an estuarine system in
relation to webbing materials, times of day, and
depth zones; and 2) to estimate net damage in
relation to webbing materials and depth zones.

STUDY AREA AND METHODS

The St. Andrew Bay system, located between
long. 85°23' and 85°53'W and lat. 30°00' and
30°20'N along the northwest Florida coast, covers
about 280 km2 (McNulty et al. 1972). Physical,
hydrological, and sedimentological characteris-
tics of the bay system have been presented by
Hopkins (1966), Ichiye and Jones (1961), and
Waller (1961). Tidal fluctuations in the bay aver-
age about 0.4 m (National Ocean Survey 1971).

The study area was located 0.6 km northwest of
the western entrance into St. Andrew Bay. Depths
at the net locations at mean low tide were 0.7-1.1
m (shallow), 2.2-2.6 m (mid), and 5.2-5.6 m (deep).
During the study, surface temperatures and
salinities ranged from 11.4° to 27.0°C and 25.3 to
34.6%o, respectively (determined with a

Manuscript accepted August 1976.
FISHERY BULLETIN: VOL. 75, NO. 1, 1977.

103

FISHERY BULLETIN: VOL. 75, NO. 1

Beckman2 RS5-3 salinometer), and turbidities
ranged from 0.2 to 2.8 Formazin turbidity units
(determined with a Hach turbidimeter). Substrate
was similar to the sand regime (greater than 80%
sand) described by Waller (1961). Submergent
vegetation was dense in the shallow zone, less
dense in the mid zone, and sparse in the deep zone
and consisted primarily of turtle grass, Thalassia
testudinum; shoal grass, Diplanthera wrightii;
and manatee grass, Syringodium filiforme. At
least 70 species of fishes and sharks were caught
by gill nets in 1973 in the immediate vicinity of the
study area (May et al. 1976; Pristas and Trent3).

The gill nets were constructed of either #208
monofilament webbing (transparent; 0.52-mm
strand diameter) or #220 multifilament webbing
(white; 0.64-mm strand diameter). The 9.5-cm
(3%-inch) stretched mesh webbing was hung on
the half basis (two lengths of stretched mesh to one
length of float line) with the floats spaced 1.5 m
apart. The nets were 33.3 m long and either 1.5,
3.0, or 6.1 m deep. Nets were held in position by
bridle lines attached to anchors.

One monofilament and one multifilament gill
net were set in each depth zone and were about 50
m apart. The webbing types were randomly as-
signed to the two net locations each time the nets
were set. The nets were fished during eight periods
from 19 September to 29 December 1972 (Table 1)
and were set and pulled within ±1 h of sunset
during each period. Nets were fished in a random
order and removal of fish from the nets required
from 1 to 3 h. Night catches were removed from the
nets between 1 h before to 2 h after sunrise, and
day catches were removed within ± 1 h of sunset;
consequently, day and night fishing intervals
overlapped slightly.

Wilcoxon's signed rank test, a nonparametric
procedure, was used statistically to compare catch
per net between day and night and between
monofilament and multifilament samples. For
these comparisons the number of fish of a species
caught in a single net, categorized by webbing
type, depth zone, and day or night was used.

Tukey's if -procedure was used statistically to
compare catch per net between depth zones. For
this procedure, the number of fish of a species
caught per net per 24-h period was transformed

2Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

3Pristas, P. J., and L. Trent. 1976. Seasonal abundance, size,
and sex ratio of fishes caught with gill nets in St. Andrew Bay,
Florida. (Unpubl. manuscr.)

(log10 number caught + 1) prior to running the
comparisons. Comparisons within each webbing
type and time of day were not made because of
insufficient data. Both testing procedures are
described by Steel and Torrie (1960).

In our comparisons between depth zones a
question arose as to whether the catches should be
adjusted for the unequal amounts of webbing
fished among depths, i.e., the 1.5-m nets had half
and a fourth as much webbing as the 3.0- and
6.1-m nets, respectively. We did not adjust values,
because we were interested in the number of fish
passing over an area of bay bottom per unit time
(i.e., the depth at which the most fish could be
caught) rather than the number of fish passing
through a unit volume of water per unit time. On
this basis we did not need to adjust catches among
depths, because each net blocked the same
horizontal distance of the water column.

Intermittently, the nets were inspected for
damage. Damaged areas never exceeded 8% of the
total net area before the netting was repaired or
replaced.

RESULTS

During the study, 4,066 fish representing 30
families, 52 species, and 1 hybrid were caught. We
decided that catches of only the 12 most abundant
species provided sufficient data for comparison.
These 12 species composed 92% of the total catch
(Table 1). Of the 12 species, 4 (bluefish, Pomato-
mus saltatrix; Spanish mackerel, Scomberomorus
maculatus; Atlantic croaker, Micropogon un-
dulatus; striped mullet, Mugil cephalus) are
considered important locally as recreational and
food fishes. The other eight species were: Gulf
menhaden, Brevoortia patronus; sea catfish, Arius
felis; yellowfin menhaden, B. smithi; little tunny,
Euthynnus alletteratus; Atlantic sharpnose shark,
Rhizoprionodon terraenovae; gafftopsail catfish,
Bagre marinus; hybrid menhaden, Brevoortia
patronus x B. smithi (Reintjes 1969); and pinfish,
Lagodon rhomboides.

Comparisons Between Webbing Materials

Differences in catch per net between webbing
materials varied in relation to species, time of day,
and depth zone. Combined (times of day and
depths) mean catches in monofilament webbing
were significantly greater than those in mul-
tifilament webbing for Gulf menhaden, bluefish,

104

PRISTAS and TRENT: CATCHES OF FISHES IN GILL NETS

TABLE 1.-

—Catches (nun

iber cat

lght per

24-h p

leriod) <

)f the 1

2 most <

ibunda

nt species in St

;. Andre

w Bay, F

la., 1972.

Date

c
8

X>
(0

CD
T3

c ra

«§

c —

ro ro

</> t/t
CJ <D

~ tn
ro c

r- ®

c <5

c 2

_ro o

o-c

CD
■D
CO

T3»

c/5

n
co

c
S.

Total
number
caught

20 Sept.

7
7

0
0

6 Oct.

1 Nov.

102

184

261

147

202

314

361

140

108

289

131

233

140

148

373

136

264

150

1 Dec.

Total

1,521

400

268

260

252

236

201

180

176

3,738

Spanish mackerel, Atlantic croaker, and striped
mullet (Table 2). When catches of each of these five
species were analyzed separately by time of day
and depth, those differences which were sig-
nificant showed greater catches again in the
monofilament webbing. These results for Spanish
mackerel are similar to those reported by Mihara
et al. (1971), who found monofilament webbing
more efficient than multifilament webbing on
Spanish mackerel.

Significant differences between webbing
materials were not found for combined mean
catches of the remaining seven species, but were
found for catches of four of these species (sea
catfish, Atlantic sharpnose shark, gafftopsail
catfish, and pinfish) during the night at one or
more depths. Catches of sea catfish were sig-
nificantly greater in multifilament webbing at
middepth. Catches of Atlantic sharpnose sharks
were significantly greater in monofilament in the

deep zone, and in multifilament in the mid zone.
Significantly more gafftopsail catfish were caught
in multifilament webbing in the mid zone as were
pinfish in multifilament webbing in the mid zone,
and in monofilament in the shallow zone.

Comparisons Between Times of Day

Combined (webbing types and depths) mean
catches of all 12 species were significantly greater
at night than during the day (Table 3). When
catches were analyzed separately by webbing
materials and depths, the significant differences
again revealed that more fish of each species were
caught at night.

Comparisons Between Depth Zones

Catches of 10 of the 12 species were significantly
different among depths (Table 4). Of the ten, Gulf

105

FISHERY BULLETIN: VOL. 75, NO. 1

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106

PRISTAS and TRENT: CATCHES OF FISHES IN GILL NETS

TABLE 4. — Statistical comparisons between catches from
low- (S), mid- (M), and deep- (D) water depth zones.

shal-

Species

Depth, mean catch, and
significance lines'

Error
df

Gulf menhaden

Sea catfish

Bluefish

Yellowfin menhaden

Little tunny

Atlantic sharpnose shark

Spanish mackerel

Atlantic croaker

Garftopsail catfish

Hybrid menhaden

Striped mullet

Pinfish

1.6

6.0

13.5

1.0

1.5

2.3

0.3

1.5

2.2

2.6

2.7

5.5

0.2

2.5

3.3

0.9

2.3

3.1

0.5

1.1

1.4

0.3

0.5

3.5

0.0

0.6
M

2.4

1.9

2.2

2.9

0.0

0.1

4.3

0.1

1.0

213

246

195

123
111
198
123
168
36
54
102

1 Any two means not underscored by the same line were significantly different
at the 5% level.

menhaden, little tunny, Atlantic sharpnose shark,
Spanish mackerel, and gafftopsail catfish were
caught in greater numbers as depth increased, and
sea catfish were caught in greatest numbers in the
deep zone. Conversely, catches decreased with
increasing depth for bluefish, Atlantic croaker,
striped mullet, and pinfish.

Net Damage

Monofilament nets were damaged less than
multifilament nets in each depth zone fished. In
terms of the amount of surface area damaged,
shallow nets received the least and deep nets the
greatest (Table 5). When corrected to percent of
total webbing damage in nets at each zone, shal-

TABLE 5. — Average daily net damage in square meters and
percent of total net area in relation to depth of net and to webbing
material.

Depth of net

Monofilament

Multifilament

(m)

Percent

1.5

0.11

0.21

0.16

0.33

3.0

0.16

0.23

6.1

0.31

0.15

0.44

0.22

Average of

three nets

0.25

0.16

0.34

0.24

low nets received the greatest proportion of
damage. Blue crab, Callinectes sapidus, caused
damage to both webbing types. Multifilament
webbing was damaged the most, possibly because
87% of all blue crabs taken were caught in multi-
filament webbing.

SUMMARY AND DISCUSSION

In this study, catch per net was higher with
monofilament than with multifilament gill nets;
over 58% of the 12 most abundant species and over
71% of the 4 most abundant food and recreational
fishes (bluefish, Spanish mackerel, Atlantic
croaker, and striped mullet) were caught in mono-
filament nets.

Catch per net was much greater at night than
during the day; about 93% of the 12 most abundant
species and about 82% of the 4 most abundant food
fishes were taken at night.

Total catches of the 12 most abundant species
were 816 (22%), 1,063 (28%), and 1,859 (50%) fish
in the shallow, mid, and deep zones, respectively.

For evaluation where the amount of webbing
could be an important cost factor, total catches in
each depth zone were converted to catches per unit
surface area of webbing by dividing total catches
for the shallow, mid, and deep zones by one, two,
and four, respectively. Catches per unit area of
webbing for the 12 species combined were 816
(45%), 531 (29%), and 465 (26%) fish for the
shallow, mid, and deep zones. For the four most
abundant species of food fishes unadjusted catches
per unit area of net were 407 (56%), 196 (27%), and
126 (17%), and adjusted catches per unit area of
net were 407 (76%), 98 (18%), and 32 (6%) fish for
the shallow, mid, and deep zones. Thus, on either
basis, fishing in the shallow zone was the most
productive.

Other factors of importance in this study in
terms of overall efficiency included net damage,
ease of fishing, cost, and storage of webbing. Daily
average net damage was 0.16% for monofilament
and 0.24% for multifilament webbing. Fish could
be removed faster and fewer crabs were caught in
monofilament nets. Monofilament nets tangled
less and were set and retrieved faster than multi-
filament nets. Disadvantages of monofilament
compared to multifilament nets were: greater cost
per pound (almost double); more storage room
required; and greater difficulty of repairing the
webbing owing to the requirement of double knots
to prevent slippage.

107

ACKNOWLEDGMENTS

We express sincere appreciation to John Ham-
ley of the University of Toronto and Edwin A.
Joyce, Jr. and his staff of the Florida Department
of Natural Resources for their time in reviewing
this manuscript and for their beneficial comments.
We are deeply grateful to Dennis Anderson and
Maxwell Miller for their assistance in the field
during this study.

LITERATURE CITED

HOPKINS, T. L.

1966. The plankton of the St. Andrew Bay system, Flori-
da. Publ. Inst. Mar. Sci., Univ. Tex. 11:12-64.
ICHIYE, T, AND M. L. JONES.

1961. On the hydrography of the St. Andrew Bay system,
Florida. Limnol. Oceanogr. 6:302-311.
MAY, N., L. TRENT, AND P. J. PRISTAS.

1976. Relation offish catches in gill nets to frontal periods.
Fish. Bull., U.S. 74:449-453.
MCNULTY, J. K., W. N. LINDALL, JR., AND J. E. SYKES.

1972. Cooperative Gulf of Mexico estuarine inventory and
study, Florida: Phase I, area description. U.S. Dep.
Commer., NOAA Tech. Rep. NMFS CIRC-368, 126 p.

FISHERY BULLETIN: VOL. 75, NO. 1

MIHARA, T., A. BRITO, J. RAMIREZ, AND J. V. SALAZAR.

1971. La pesca experimental con filete de ahorque en el
Golfo de Paria. Proyecto Invest. Desarrollo Pesq. Venez.,
Inf. Tec. 23, 15 p.

NATIONAL MARINE FISHERIES SERVICE.

1975. Fishery statistics of the United States 1971. U.S.
Dep. Commer., NOAA, Natl. Mar. Fish. Serv. Stat. Dig.
65, 424 p.

NATIONAL OCEAN SURVEY.

1971. Tide tables, high and low water predictions 1972,
east coast of North and South America including Green-
land. U.S. Dep. Commer., Natl. Ocean Surv., 290 p.

REINTJES, J. W.

1969. Synopsis of biological data on the Atlantic menha-
den, Brevoortia tyrannus. U.S. Fish Wildl. Serv., Circ.
320, 30 p.

SIEBENALER, J. B.

1955. Commercial fishing gear and fishing methods in
Florida. Fla. State Board Conserv., Univ. Miami Mar.
Lab., Tech. Ser. 13, 45 p.

STEEL, R. G. D., AND J. H. TORRIE.

1960. Principles and procedures of statistics with special
reference to the biological sciences. McGraw-Hill, N.Y.,
481 p.

Waller, R. a.

1961. Ostracods of the St. Andrew Bay system. M.S.
Thesis. Florida State Univ., Tallah., 46 p.

108

AGE DETERMINATION, REPRODUCTION, AND POPULATION DYNAMICS
OF THE ATLANTIC CROAKER, MICROPOGONIAS UNDULATUS12

Michael L. White and Mark E. Chittenden, Jr.3

ABSTRACT

A validated scale method of age determination is described for the Atlantic croaker, Micropogonias
undulatus. Two age-classes were usually observed, but only one was abundant. Mean total lengths
were 155-165 mm at age I and 270-280 mm at age II based on three methods of growth estimation. Fish
matured near the end of their first year of life when they were about 140-170 mm total length.
Spawning occurred from at least September through March but there was a distinct peak about
October. Somatic weight-length relationships varied monthly, and changes appeared to be associated
with maturation and spawning. Somatic weight reached a maximum in June, and the minimum was
observed in March. Maximum somatic weight loss (24%) occurred in March, but no data were obtained
from December through February. In estuaries, age 0 croaker apparently occupied soft-substrate
habitat and older fish occurred near oyster reefs. Life spans were only 1 or 2 yr, and the total annual
mortality rate was 96%. The above life history pattern appears similar for croaker found throughout
the Carolinian Province. Contrasts are presented to illustrate differences in the life histories and
population dynamics of croaker found north and south of Cape Hatteras, N.C. A parallel is drawn with
apparently similar changes in the American shad, A/osa sapidissima, and the suggestion is made that
changes in the population dynamics of species that traverse the Cape Hatteras area may represent a
general phenomenon.

The Atlantic croaker, Micropogonias undulatus
(Linnaeus), ranges in the western Atlantic from
the Gulf of Maine to Argentina (Chao 1976). It is
potentially a very important protein source be-
cause it is one of the most abundant inshore fishes
of the northern Gulf of Mexico (Gunter 1938, 1945;
Moore et al. 1970; Franks et al. 1972) and the
Atlantic Ocean off the southeastern United States
(Haven 1957; Bearden 1964; Anderson 1968).

Much work has been done on this species.
However, many aspects of its life history and
population dynamics are not clear; because no
reliable method of age determination exists, and
reproduction has not been studied intensively. A
few early workers, including Welsh and Breder
(1924) and Wallace (1940), attempted to age
croaker using scales; but criteria for marks were
not described and methods were not validated.
More recent workers, in general, have not at-
tempted to use hard parts to determine croaker
age and growth. The scale method is difficult to
apply to croaker (Joseph 1972), and this may be
related to its migratory habits and extended

'Based on a thesis submitted by the senior author in partial
fulfillment of the requirements for the MS degree, Texas A&M
University.

technical article TA 12419 from the Texas Agricultural
Experiment Station.

department of Wildlife and Fisheries Sciences, Texas A&M
University, College Station, TX 77843.

spawning season (Suttkus 1955). Only Wallace
(1940) studied reproduction using a large series of
gonads. However, he worked north of Cape
Hatteras, N.C. The life history of croaker found
north of Cape Hatteras seems quite different from
that of individuals in the Carolinian Province.
Studies of reproduction in croaker found south of
Cape Hatteras have been based on few fish
(Gunter 1945; Bearden 1964) or fish less than 200
mm long (Hansen 1969).

This paper describes a validated method of age
determination for croaker, their weight-length
and girth-length relationships, habitat segrega-
tion between age-groups, spawning seasonality,
somatic weight variation, growth, maximum size,
life span, and total annual mortality rates. Final-
ly, it contrasts the life histories of croaker found
north and south of Cape Hatteras. Geographically,
statements made herein apply to the Carolinian
Province and/or more northerly waters. With
modifications, particularly ones due to calendar
differences in seasons, our findings may also apply
in the southern hemisphere; but further work is
needed there.

MATERIALS AND METHODS

Collections were made from commercial shrimp
trawlers during 1974 in the Gulf of Mexico off

Manuscript accepted June 1976.

FISHERY BULLETIN: VOL. 75, NO. 1, 1977.

109

FISHERY BULLETIN: VOL. 75, NO. 1

Freeport-Galveston and Port Aransas, Tex., and
Cameron, La. Fish were also collected by trawling
in Palacios, Galveston, and Matagorda bays, Tex.,
and Calcasieu Lake, La. Additional fish, herein-
after termed reef fish, were captured by angling
with dead shrimp bait (about 25 mm long) near an
oyster bar in Galveston Bay. Collection months
are indicated in Figure 1.

A sample was taken from each trawl catch by
shoveling into a 25-liter container small portions
of the catch from various areas of the deck.
Unusually large fish were arbitrarily selected to
obtain older fish to develop an ageing technique.
Total length was measured on each croaker. Total
and gonad weights and girth at the origin of the
dorsal fin were determined for fish over a broad
size range during each sampling period. Scales
below the lateral line posterior to the pectoral fin
were removed from 1,123 fish, were pressed on
plastic slides, and were examined using a scale
projector. Scales were examined from small
numbers of croaker collected off Mississippi and
Fort Pierce, Fla., and in Chesapeake Bay, Va., to
judge whether or not the method of age deter-
mination proposed herein is valid throughout
their range in the Carolinian Province and more
northerly waters. The size and appearance of the
gonads of more than 1,700 fish were examined,
and ovaries were classified following Nikolsky
(1963) as summarized by Bagenal and Braum
(1971) except that the immature and resting
stages were combined.

The regressions of somatic, gonad, and total
weights, and girth on total length were computed
to express the best linear or quadratic fit using the
Statistical Analysis System (Service 1972). Sex
data were pooled to compute total weight-length,
somatic weight-length, and girth-length re-
gressions, because F tests (Ostle 1963:204)
indicated that pooled regression lines were
appropriate.

each sex began by late August, increased greatly
during September, reached a peak in October,
declined greatly by November, and was at the
latter level in March. Similarly, the coefficients of
determination (r2) of the regression lines (Table 1)
show that gonad weight variation in each sex was
increasingly associated with length until October
and then greatly declined. Therefore, it appears
that peak spawning occurred in October. Fish
captured in the Gulf and by the reef were in all
stages of development during September, as were
trawl-caught bay fish in October (Figure 3).
Therefore, spawning apparently began at least by
late September, and some individuals finished or
had nearly finished spawning then. Most spawn-
ing occurred during October in agreement with
the gonad weight-length analyses, because most
fish captured in the Gulf were still immature in
September. Most fish captured near the reef and in
the Gulf were ripe or spent during October and
November. Specimens captured in the Gulf during
late March were in a resting stage or nearly spent,
so that spawning is apparently completed by late
March except by a few individuals.

Croaker started to mature at about 140-170 mm
total length. Extrapolated x -intercepts or inflec-
tion points of the regressions of gonad weight on
total length occur in that size range for each sex
(Figure 2). Developing fish as small as 136 mm
were observed.

Many aspects of croaker spawning appear
similar throughout the Carolinian Province. The
prolonged spawning period suggested by our data
is consistent with frequently reported collections
offish about 25-40 mm long from October to June
(many references including Suttkus 1955; Bear-
den 1964; Hansen 1969; Parker 1971; Swingle
1971; Christmas and Waller 1973; Hoese 1973).
The apparent peak of spawning after September
agrees with Pearson ( 1929), Hildebrand and Cable

SPAWNING

Spawning occurred over a protracted period
extending at least from September to late March,
but there was a distinct peak about October. The
regressions of gonad weight on length were not
significant during May, June, or July for either
sex. The mean gonad weight in this period was
0.10 g, and its 95% confidence limits were 0.09-
0.11 g. The regressions of gonad weight on length
(Figure 2) indicate that gonad development in

TABLE 1. — Analyses for the regressions of gonad weight (Y) in
grams on total length (X ) in millimeters for each sex and month.
All regressions were significant at a = 0.0001.

Sample

Sex Month

size

Equation

Males August

0.46

Y =

0 389 • 0 004X

September

108

0.68

Y =

-4.737 + 0.033X

October

0.73

Y =

-8.804 + 0.055X

November

0.32

Y =

-2.782 + 0.01 8X

March

0.43

Y =

-3.785 + 0.021 X

Females August

0.47

Y =

-0.426 + 0.004X

September

286

0.63

Y =

-11.920 + 0.080X

October

154

0.67

Y =

-27.135 + 0.177X

November

0.28

Y =

-15.570 + 0.097X

March

0.32

Y =

-13.359 + 0.077X

110

WHITE and CHITTENDEN: AGE DETERMINATION OK ATLANTIC CROAKER

S 5-
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100

150 200 250

TOTAL LENGTH (MM)

300

350

FIGURE 1. — Length frequencies of Atlantic croaker in each area each month. Frequencies are moving averages of three.

Ill

FISHERY BULLETIN: VOL. 75, NO. 1

September

GULF

BAY

REEF

September

TOTAL LENGTH (MM)

FIGURE 2. — Gonad weight-length regressions for Atlantic
croaker by sex and month. The length of each line shows the
observed size range.

(1930), Suttkus (1955), and Bearden (1964); and
size at maturity agrees with Pearson (1929),
Bearden (1964), Hansen (1969), and Hoese (1973).
The general similarity of croaker reproduction
suggests that 15 October, which approximates the
time of peak spawning, would be appropriate as a
defined hatching date in warm-temperate waters.

100

" 50

> 3

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-f=t-

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100

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12 3 4 5

GONAD CONDITION

100-1

N n = 55

100-

50-

100

50-

12 3 4 5

FIGURE 3. — Gonad condition of Atlantic croaker by months and
areas. The ordinate represents percent of the sample. Gonad
conditions on the abscissa are: (1) immature or resting, (2)
maturation, (3) maturity, (4) reproduction, and (5) spent.

SOMATIC WEIGHT VARIATION

Somatic weight-length relationships varied
monthly, and these changes appeared to be as-
sociated with maturation and spawning. Peak
somatic weight occurred during June except in
fish smaller than about 140 mm. Somatic weights
predicted by the regression equations for other
months (Table 2) were compared with predicted
weights in June (Figure 4). The somatic weight of
individuals smaller than about 140 mm increased
from May to at least September. Fish about 140-
160 mm showed progressive somatic weight loss
from June to September-October. The smallest
fish greater than 160 mm, in general, showed the
greatest somatic weight loss (or smallest gain);

TABLE 2. — Analyses for the regressions of somatic weight (7) in
grams on total length (X) in millimeters for each month. All
regressions were significant at a = 0.0001.

Month

Sample
size

Equation

May

120

099

June

686

0.99

August

299

0.99

September

501

0.97

October

265

0.98

November

162

0.91

March

0.99

Y = 39.5303 - 0.8538X + 0.0057X2

Y = 71.1692 - 1.3371X + 0.0076X2

Y = 120.4035 - 1.9159X + 0.0092X2

Y = 158.951 1 - 2.3706X + 0.01 03X2

Y = 148.7089 - 2.201 6X + 0.0097X2

Y = 73.4739 - 1 2980X + 0 0072X2
y = 132.7087 -1.8537X + 0.0080X2

and somatic weight loss, in general, seemed to
progressively increase from June to September-
October. Somatic weight loss during the fall in fish
larger than 140 mm was greatest in September-

112

WHITE and CHITTENDEN: AGE DETERMINATION OF ATLANTIC CROAKER

30 ■
25 -
20 -
15 -
10 ■
5

5 -

10 -

z
uu

a. 15

UJ
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25 H
+ 30
35 -
40 -
45-

May

March

Novemb

September
August

August

September

200
TOTAL LENGTH (MM I

—I
300

FIGURE 4. — Monthly somatic weight changes in Atlantic
croaker. Percentage changes are in comparison to somatic
weights in June. The lengths of the curves represent observed
size ranges.

October just prior to the time of peak spawning.
However, greatest somatic weight loss was ob-
served in March when individuals of 170-250 mm
had lost 20-24% of the June weight. The ob-
served somatic weight-length relationships and
apparent weight changes in November may be
anomalous. Absolute somatic weight decreased in
fish smaller than 140 mm, but the percentage
weight loss in fish greater than 160 mm was about
5%. Croaker mature at about 140-160 mm, and
most fish were small and immature in November.
These smaller fish may have just begun to mature
for spawning, and their inclusion in the data may
have biased the observed pattern in November.
This interpretation is supported by the regression
coefficients of X and X2 which were markedly
smaller during November than during other
months in the August-March period (Table 2).

Somatic weight changes have not been reported
for croaker. Additional data, especially from the
post-peak spawning period December to February,
are needed to fully understand their annual cycle
of somatic weight change. Possibly, the percen-
tage of somatic weight loss may be greater in late
fall and winter than we observed in March.

AGE DETERMINATION AND GROWTH

General Basis for the Method of
Age Determination

Scale marks similar to annuli were distin-
guished by standard criteria, especially cutting
over and differential spacing of circuli. Croaker
appear to form two marks on their scales each year
except that no mark is formed during their first
winter. Some fish form no mark during their first
year if 1 5 October is defined as the hatching date of
croaker. Even-numbered marks (cold-period
marks) form from about December to March, and
odd-numbered marks (warm-period marks) form
from about May to November. Fish that do not
form a mark in their first year would not have
mark numbering that corresponds to the typical
odd and even system. Cold-period marks were
most distinct and were used as "year" marks,
although they represent 1-1 V2 yr of growth.
Recognition of the first cold-period mark is the
basis for this method. Subsequent marks, espe-
cially cold-period marks, seem to be easily
identified.

Age determination was validated by: 1) es-
tablishing the time of year when each mark forms,
2) establishing age through analysis of length
frequencies, and 3) showing that modes of back-
calculated and observed lengths at each age agree
with age determination by length frequencies.

Repeated reading suggests this method of age
determination is consistent. We found 91%
agreement between the first reading of scales from
200 fish (112 age 0 and 88 age I) and a second
reading 3 mo later.

We have suggested 15 October as a defined
hatching date for croaker. Definition of a hatching
date is essential in age and growth studies, so that
year classes and age groups can be referenced. In
the northern hemisphere 1 January is a standard
defined hatching date. That date is convenient and
has biological reality, especially for species that
spawn in the spring and summer of one year. In
more northerly waters, furthermore, growth
seasons tend to be short; and spawning tends to be
restricted in time and often occurs about when the
annulus forms. Croaker of the Carolinian Pro-
vince, in contrast, have a long, possibly year-
round, growing season; and their spawning
"season" is so long that it takes place over much of
two calendar years. Therefore, it seems more
convenient and biologically sound to select their

113

FISHERY BULLETIN: VOL. 75, NO. 1

peak spawning period as a denned hatching date
upon which year class and age group terminology
is based. Using an October hatching date, the year
class would pertain to the fall calendar year and
would include any fish of that spawning cycle
hatched in the following winter and spring. A
virtual annulus would be designated as of October.

Characteristics of Scale Markings
Used to Determine Age

The first mark is typically a more or less in-
distinct mark formed in warm periods. It is
characterized by cutting over in the lateral field,
but it has little or no differential spacing of circuli
before and after the mark (Figure 5a). This mark
is often difficult to distinguish after the heavier
second mark is formed. The typical second mark is
formed in cold periods. It is the most diagnostic
feature for age determination in croaker, and its
recognition is the basis for our method. This mark
is characterized by heavy cutting over of circuli
and differential spacing of circuli in the lateral
field (Figure 5b). Generally, circuli are closely
spaced before the second mark and more widely
spaced after it. When the first mark is absent or
difficult to see, the typical second mark is readily
distinguished. The third mark is typically formed
in warm periods and is similar to the first mark
(Figure 5c). We examined only six fish whose
scales had the fourth mark, and its criteria may
need modification. However, the fourth mark
apparently forms in cold periods and apparently,
resembles the second mark in having heavy cut-
ting over and differential spacing of circuli (Figure
5c).

Croaker from a broad geographical range
seemingly can be aged by the method proposed,
although further work is needed to establish this.
Scales offish from Mississippi, Fort Pierce (Figure
6a), and Chesapeake Bay (Figure 6b, c) showed
markings similar to those on scales from Texas
fish. Croaker scales from Florida generally had
more or less indistinct cutting over and seemed

FIGURE 5. — Top. Scale from a 190-mm croaker showing mark 1.
This fish was approaching age I when it was captured off Texas in
September. The axis depicted shows how measurements were
made to determine when each mark formed. Middle. Scale from a
255-mm croaker showing marks 1 and 2. This fish was ap-
proaching age II when it was captured off Texas in August.
Bottom. Scale from a 310-mm croaker showing marks 2,3, and 4.
This was an age 11+ fish captured off Texas in March.

114

WHITE and CHITTENDEN: AGE DETERMINATION OF ATLANTIC CROAKER

difficult to read, possibly because the fish were
collected in tropical waters of southern Florida
where temperature changes are not as extreme as
further north. Only six fish from Texas had scales
with four marks. In contrast, scales from some
Chesapeake Bay fish had six marks (Figure
6c). Croaker that live in the Carolinian Province
south of Cape Hatteras live only 1 or 2 yr (see
General Discussion) and, therefore, tend to have
comparatively few marks on their scales. These
fish might be easier to age than croaker that live
north of Cape Hatteras. The latter fish apparently
survive longer and, therefore, probably tend to
have more marks on their scales.

Times of Mark Formation

The time when each annuluslike mark formed
was determined by plotting for each month the
distance from the scale margin to the last mark.
Distance was measured across the lateral field of
the scale (Figure 5a). Croaker generally form two
marks per year except during their first year.
Scales with no marks had the smallest distance
between the scale margin and focus in May (Fig-
ure 7). The radius increased from May to October
as scales grew during that period. Therefore,
apparently no mark is formed during the first
winter; and some croakers form no mark during
the first year of life if 15 October is defined as their
hatching date. Scales with one mark had the mark
closest to the scale edge in warmer months. In
March the mark was far removed from the scale
margin, suggesting that the first mark normally
forms in warm months. Apparently this mark
formed on some fish throughout the period May to
at least October. The increment between the scale
margin and the first (or third) mark did not in-
crease with time, but the reason for this is not
clear. Scales with two marks showed the second
mark closest to the scale margin in March. The
increment between this mark and the scale edge
increased until June and then remained nearly
constant through November. Therefore, the sec-
ond mark apparently forms during the colder

FIGURE 6. — Top. Scale from a 305-mm croaker showing marks 1,
2, 3, and 4. This was an age 11+ fish when it was captured off
Florida in March. Middle. Scale from a 293-mm croaker showing
marks 1 and 2. This fish was approaching age II when it was
captured in Chesapeake Bay in July. Bottom. Scale from a
508-mm croaker showing marks 1, 2, 3, 4, 5, and 6. This fish was
approaching age IV when it was captured in Chesapeake Bay
during July.

115

NO MARKS

FISHERY BULLETIN: VOL. 75, NO. 1
MARK 1 MARK 2 MARK 3 MARK 4

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20 40 60 20 40 20 40 20 40

DISTANCE (MM X 42)

FIGURE 7. — Distance from scale margin
to the last mark or to the focus if no
marks were present.

months. Scales with three marks showed the third
mark being formed throughout the warm months,
the only period when scales with only three marks
were available. Scales with four marks were
observed only during March. The increment on
these scales suggests that the fourth mark was
formed during winter or spring. However, further
data are needed to establish this.

Our findings on times of mark formation agree
with Haven's (1954) suggestion that croaker form
one fall and one winter mark each year in
Chesapeake Bay and with Richards' (1973)
computer-simulated findings that the related
black drum, Pogonias cromis, forms one mark a
year until maturity and two marks a year
thereafter.

116

WHITE and CHITTENDEN: AGE DETERMINATION OF ATLANTIC CROAKER

Age Determination and Growth by
the Length-Frequency Method

Our length-frequency distributions suggest two
croaker year classes occurred off Texas. One age
group greatly predominated in the length fre-
quencies of trawl-caught fish from the bay and
Gulf during June (Figure 1). The size range of that
age group was primarily about 100-150 mm in the
bay and about 120-160 mm in the Gulf. Young-of-
the-year first appear in Texas bays about
November and increase in size from about 10-50
mm during January to 30-85 mm in March, 40-100
mm during May, and 70-130 mm in June (Gunter
1945; Parker 1971; Gallaway and Strawn 1974).
Therefore, the fish we captured by trawling during
June must be young-of-the-year. These young-of-
the-year fish grew to about 1 10-170 mm in August,
120-175 mm in September, and 140-180 mm in
October when they reached age I. Similar sizes in
October have been recorded by Gunter (1945),
Parker (1971), and Gallaway and Strawn (1974).
The fish that became age I in October were about
130-190 mm in November, and fish captured in
March were about 165-220 mm. The large fish
caught in June by angling near the oyster reef
were about 190-270 mm and apparently were
survivors of the year class that became age I on the
preceding 15 October. These age 1+ fish were
about 200-310 mm in September when they
approached age II. This agrees with Gunter's
(1945) size estimates for age II croakers off
Texas.

With minor differences, length frequencies
reported throughout the Carolinian Province by
many workers, including Hildebrand and Cable
(1930), Gunter (1945), Suttkus (1955), Bearden
(1964), Hansen (1969), Christmas and Waller
(1973), Hoese (1973), and Gallaway and Strawn
(1974), show growth and age composition similar
to our findings. Growth north of Cape Hatteras
seems similar to that in the Carolinian Province.
Haven (1957) presented monthly length fre-
quencies of fish he considered young-of-the-year.
His fish ranged from about 150 to 220 mm in
September, but the mode was about 175-180 mm.

Agreement of Observed and Back-Calculated
Lengths with Length-Frequencies

Observed sizes at ages 0, I, and II agree closely
with ages determined by length frequencies
(Figure 8). Only age 0 fish were captured in May

and age I fish in July, so that graphs are not
presented for these months. The frequencies show
overlap in size between the various ages each
month. This is to be expected, especially in a
species having a prolonged spawning season, and
makes it impossible to use the length-frequency
method to assign age confidently where sizes at
age overlap. The observed lengths of age 0 fish in
September were primarily 130-170 mm (mean =
151 mm), but they ranged from about 110 to 220
mm. This age group was about 140-220 mm (mean
= 158 mm) during October when they became age
I and about 130-220 mm (mean = 172 mm) during
November. The observed lengths of age I fish in
September were about 200-340 mm with the mean
being 253 mm. This age group was about 190-360
mm (mean = 274 mm) in October when they
became age II.

Lengths back-calculated to cold-period marks
reasonably agree with the sizes at age I estimated
by length frequencies in October (Figure 9).
However, cold-period marks apparently begin to
form generally after October; so that the back-
calculated lengths should be larger than the
observed lengths in October. The similarity
suggests Lee's phenomenon, possibly due to
selective mortality favoring survival of smaller
croaker. Back-calculated lengths were somewhat
smaller than the sizes at age 1+ in March, as
would be expected. Back-calculated lengths from
age 1+ fish were primarily 110-210 mm at age I
with a mean length of 165 mm. In agreement,
back-calculated lengths from six age 11+ fish had a
mean of 181 mm at age I and 270 mm at age II. The
body-scale regression equation used to back-
calculate length was:

Y = 2.6000 + 4.6389Z - 0.0122X2

where Y represents total length in millimeters,
andX represents the scale radius (millimeters x
42). The sample size was 1,123, and the total
length range was 90-360 mm. About 88% of the
variation in total length was associated with
variation in scale radius.

Growth estimates based upon the length-
frequency method and from observed and back-
calculated estimates using the scale method show
very close agreement. Mean lengths in October
were about 155-165 mm at age I and 270-280 mm
at age II depending upon how age was determined.
The wide back-calculated and observed size
ranges found at age may be due to the long

117

FISHERY BULLETIN: VOL. 75, NO. 1

3—1

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300

350

FIGURE 8. — Length compositions comparing observed ages with ages determined by the length-frequency method. Frequen-
cies are moving averages of three.

118

WHITE and CHITTENDEN: AGE DETERMINATION OF ATLANTIC CROAKER

Age I + Fish Captured in March.
Age Determined by L/F Method.

-i — i— i — i — i—i — i — i — i "T "i i VT^-p i ^i i i — r

> IR-i Back Calculated Length at Age I.
o

-c Age I Fish Captured in October,
Age Determined by L/F Method.

t — i — i — r
70 100

— i — r

160

130

TOTAL LENGTH (MM

l — l — I — T
190 220

— I — I — I — i
250 280

FIGURE 9.— Back-calculated length frequencies at age I and
length frequencies (L/F) of age I fish in October and age 1+ fish in
March. Frequencies are moving averages of three.

spawning season and/or prolonged time span when
the cold-period mark may form.

HABITAT SEGREGATION
BETWEEN AGE GROUPS

A portion of all croaker age groups apparently
utilized bays as feeding grounds during the
warmer months, but age I and older fish seemed to
occupy different habitat than young-of-the-year.
Croaker captured by angling near the oyster reef
from June to August were about 200-270 mm in
length (Figure 1) and seemed common there. In
contrast, trawl-caught bay fish were generally
much smaller than 200 mm. Reef and trawl-
caught bay individuals were then about age 1 +
and age 0, respectively. Many other workers,
including Reid (1955), Perret (1966), Nelson
(1969), Hansen (1969), Parker (1971), Hoese
(1973), and Gallaway and Strawn (1974), have
also captured few individuals greater than 200
mm by trawling in bays, but they captured
many small specimens like we did. Therefore,
although capture by angling may have selected
larger fish near the reef, the two age-groups seem
to segregate by habitat: young-of-the-year occupy
soft substrates, and age I and older fish occur near
oyster reefs (and similar hard substrates?). This
agrees with Harden Jones' (1968) generalization
that the feeding grounds of adult fishes are sepa-
rate from their spawning grounds and nurseries.

Age I and older fish seemed to remain near oys-
ter reefs until they migrated to sea to spawn. Fish
caught near oyster reefs were much larger than
those caught by trawling in the Gulf or bays until
September-October (Figure 1). Specimens larger
than 191 mm were not collected in the Gulf until
September, which is about when spawning begins
in the northern Gulf (Gunter 1945; Suttkus 1955;
present study). Simmons and Hoese (1959)
captured fish less than 175 mm long throughout
the summer as they migrated to the Gulf, but
these workers captured fish similar in size to our
reef fish only during September.

The larger young-of-the-year began moving to
sea by late spring or early summer. Trawl-caught
fish in the bay were smaller than those in the Gulf
during June (Figure 1) when modal length for
young-of-the-year was about 120 mm in the bay
and about 140 mm in the Gulf. The difference in
size between young-of-the-year in the bay and
Gulf agrees with Gunter (1945), Haven (1957),
and Reid and Hoese (1958) who found a size
gradient in estuaries, the smallest young-of-the-
year being farthest up the estuary. Haven (1957)
and Hoese et al. (1968) suggested that the gradient
was due to gradual seaward dispersal of the
largestyoung, and Parker (1971) and Franks etal.
(1972) suggested that young-of-the-year began
moving to sea at about 85-100 mm long. Evidently
the Gulf becomes a very important nursery by
midspring or early summer, because young
croaker compose about 24-29% by number of the
fishes found on the white shrimp grounds of the
Gulf then (Miller 1965, table 3; Chittenden and
McEachran 1976).

MAXIMUM SIZE AND AGE, LIFE
SPAN, AND MORTALITY RATE

Croaker in the Carolinian Province are typi-
cally small and have a short life span and high
mortality rate. Most fish we collected were less
than 200 mm long and the largest was 357 mm.
The largest croaker observed in warm-temperate
waters generally have been less than 300 mm
(many workers including Hildebrand and Cable
1930; Reid 1955; Bearden 1964; Miller 1965; Nel-
son 1969; Hansen 1969; Parker 1971; Hoese 1973),
although some workers captured fish as large as
330-380 mm (Pearson 1929; Gunter 1945; Suttkus
1955; Franks et al. 1972; Christmas and Waller
1973). Rivas and Roithmayr (1970) found a 668
mm specimen, but this is exceptional.

119

FISHERY BULLETIN: VOL. 75, NO. 1

Our length frequencies suggest that two year
classes occurred, but only one was abundant. This
agrees with other reported length frequencies
from warm-temperate waters (see references cited
in section on Age Determination and Growth by
the Length-Frequency Method). Therefore, the
typical croaker life span in warm-temperate water
appears to be only 1 or 2 yr. Age 11+ fish captured
in March were the oldest fish we examined in
agreement with other estimated maximum ages
from the Carolinian Province (Gunter 1945;
Suttkus 1955; Bearden 1964; Hoese 1973). Fish
associated with oyster reefs are larger and a year
older than trawl-caught bay or Gulf fish during
the summer. However, the abundance of these age
I croaker must be small compared with the
abundance of age 0 croaker, because the geograph-
ical area occupied by oyster reefs is comparatively
small.

Croaker have a high total annual mortality rate
as their short life span requires. We found only six
age 11+ fish in 1,123 aged. Greatest mixing of
age-groups probably coincides with fall spawning
in the Gulf. We observed 1 1 age I + and 250 age 0+
fish in random samples from trawl catches made
25-27 September 1974, so that the observed total
annual mortality rate was about 96% assuming
negative exponential survivorship. This must
approximate the total annual mortality rate
throughout the Carolinian Province because
maximum sizes and ages, length frequencies, and
life spans appear similar throughout this area.
The observed total annual mortality rate agrees
closely with the theoretical total annual mortality
rate. Following the reasoning of Royce (1972:238)
the negative exponential survivorship relation S
= Nt/N0 = e~Zt can be solved for an approximate
instantaneous total mortality rate over the entire
life span which can be used to estimate average
annual total mortality rates. A species with a life
span of 1 or 2 yr would have a theoretical
approximate total annual mortality rate of 90-
100%.

TOTAL WEIGHT-LENGTH AND
GIRTH-LENGTH RELATIONSHIPS

The regression of total weight in grams (Y) on
total length in millimeters (X) was expressed by
the equation:

log10 Y = -5.26 + 3.15 log10 X.

This relationship was based on a sample size of
2,081 fish in the length range 90-360 mm. About
98% of the variation in log10 total weight was
associated with variation in log10 total length. The
arithmetic mean log10 X was 2.21056, and
arithmetic mean log10 Y was 1.71546.

The regression of girth in millimeters (Y) on
total length (X) in millimeters was expressed by
the linear equation:

Y = -11.84 + 0.71X.

This relationship was based on a sample size of
2,081 fish in the length range 90-360 mm. The
arithmetic mean girth was 108.07 mm. About 94%
of the variation in girth was associated with
variation in total length.

GENERAL DISCUSSION

Many aspects of the life history of Atlantic
croaker in the Carolinian Province appear dif-
ferent than those of fish found in cold-temperate
waters north of Cape Hatteras except that the
growth rates appear similar. In general, our data
and the literature agree that in warm-temperate
waters: 1) peak spawning occurs about October
but the spawning season is long and lasts from
about September to at least March, 2) maturity is
reached at about 140-180 mm long as the fish
approach age I, 3) maximum size is about 300-350
mm and most fish are so small (about 200 mm or
less in length) that they do not support commercial
food fisheries, 4) the life span is about 1-2 yr and
maximum age is typically about 2 yr, 5) most fish
live only to about age I, and 6) total annual mor-
tality rate is about 95%. In contrast, fish living
north of Cape Hatteras generally:
1) Have a spawning season (July or August-
December?) that starts earlier and may end
earlier (Welsh and Breder 1924; Hildebrand
and Schroeder 1928; Wallace 1940; Pearson
1941; Massmann and Pacheco 1960).
However, the time when spawning ends is
not certain. Haven (1957) captured many
young 20-30 mm TL from February to April,
but their significance is not clear; they could
represent late-winter spawning or, perhaps,
fall spawning with little or no overwinter
growth. Peak spawning seemingly occurs no
later than midfall, because all the adult fish
that Wallace (1940) examined had spent or

120

WHITE and CHITTENDEN: AGE DETERMINATION OF ATLANTIC CROAKER

recovering gonads in late November and
thereafter.

2) Reach maturity when greater than 200 mm
long as they approach at least age II (Welsh
and Breder 1924; Wallace 1940; Haven
1954).

3) Have a maximum size of about 500 mm
(Hildebrand and Schroeder 1928; Gunter
1950) and large average size so that they
have supported important commercial food
fisheries (Gunter 1950; Haven 1957; Joseph
1972).

Maturity is reached about 1 yr later in cold-
temperate waters and typical sizes are much
larger, although growth rates appear similar.
Therefore, the typical maximum age is probably
about 2-4 yr north of Cape Hatteras. If so, the
total annual mortality rate must be lower north
of Cape Hatteras. Assuming negative exponential
survivorship, the theoretical approximate total
annual mortality rates would be 90, 78, and 68%
for life spans of 2, 3, and 4 yr, respectively.

The existence of an abrupt change at Cape
Hatteras in the life histories and population
dynamics of species whose ranges traverse this
area has apparently not been recognized, par-
ticularly as a possible general phenomenon;
although Cape Hatteras has long been recognized
as a significant zoogeographic boundary [see
Briggs' (1974) review]. Gunter (1950) noted dif-
ferences in the sizes and some aspects of the life
histories of certain fishes of the Gulf of Mexico and
mid-Atlantic coast of the United States. However,
he gave no consideration to the possibility that an
abrupt change might occur near Cape Hatteras.
Although the Cape Hatteras connection has not
been recognized, the pelagic, anadromous
American shad, Alosa sapidissima, also shows
changes in life history there that are similar to
those herein documented for croaker. Runs of shad
native to streams north of Cape Hatteras consist
primarily of somewhat older fish (ages IV- VII and
older) and include many repeater spawners in
contrast to the younger fish (ages IV- VI) and the
complete or virtual absence of repeat spawners
south of Cape Hatteras (for pertinent literature
see Walburg and Nichols 1967; Chittenden 1975).
La Pointe (1958) reported similar growth rates in
shad native to streams throughout their range.
Therefore, the geographic differences in age
compositions should result in differences in life
spans, ages at maturity, maximum ages,

maximum and average sizes, and mortality rates
as in croaker.

The life histories and population dynamics of
two species with different life styles but primarily
coastal habit have been shown to change abruptly
at Cape Hatteras. This may represent a general
phenomenon as Gunter (1950) apparently ob-
served. However, similar comparisons are
necessary in other species, especially noncoastal
forms, to see how far the inference extends.

The reason for the geographical differences in
population dynamics is not clear. However, shad
exhibit great somatic weight loss (about 25-55%
depending upon sex and size) associated with
migration and spawning (Leggett 1972; Chitten-
den 1976). Leggett (1972) suggested that the low
frequency of repeat spawning shad in southern
streams might be due to increased use of body
reserves during spawning migrations that occur
at higher average temperatures. Croaker also
show somatic weight loss associated with mat-
uration and spawning, although we did not ob-
serve weight loss comparable to that in shad.
However, we had no data for the post-peak
spawning period December-February when
weight loss may have been greater. It is pertinent
here that Chittenden has observed many
emaciated spot, Leiostomus xanthurus, in the Gulf
of Mexico during January, which is about when
this species spawns. The observed differences in
population dynamics north and south of Cape
Hatteras may be largely the result of different
temperature regimes that affect age at mat-
uration, spawning-associated somatic weight loss,
and the magnitude of a subsequent post-spawning
mortality.

ACKNOWLEDGMENTS

For assistance with field collections we are
indebted to R. Clindaniel, C. H. Stephens, G.
Graham, J. Surovik, M. Carlisle, and to Captains
R. Foreman, R. Foreman, Jr., J. Torres, H. For-
rester, and M. Forrester. C. E. Bryan and W. Cody
of the Texas Parks and Wildlife Department made
collections offish from the Gulf in November. S. M.
Lidell directed us to large croakers near the reef. J.
Merriner and J. Musick of the Virginia Institute of
Marine Science loaned scales from Chesapeake
Bay. J. McEachran, W. Neill, R. Noble, L. Ringer,
R. Stickney, K. Strawn, and M. VanDenAvyle of
Texas A&M University reviewed the manuscript
and L. Ringer programmed certain statistical

121

FISHERY BULLETIN: VOL. 75, NO. 1

analyses. Financial support was provided, in part,
by the Texas Agricultural Experiment Station
and the Office of Sea Grant, NO A A.

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1964. Distribution and abundance of Atlantic croaker,

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1974. Marine zoogeography. McGraw-Hill, N.Y., 475 p.
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1976. Aspects of the systematics, morphology, life history
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1975. Dynamics of American shad, Alosa sapidissima, runs
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1976. Weight loss, mortality, feeding, and duration of res-
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CHITTENDEN, M. E., JR., AND J. D. MCEACHRAN.

1976. Composition, ecology, and dynamics of demersal fish
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1968. Fish migration. Edward Arnold Publ., Lond., 325 p.

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1958. Age and growth of the American shad, from three
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1967. Biology and management of the American shad and
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123

COASTAL AND OCEANIC FISH LARVAE IN
AN AREA OF UPWELLING OFF YAQUINA BAY, OREGON

Sally L. Richardson and William G. Pearcy1

ABSTRACT

A 1%-yr survey of planktonic fish larvae collected from 2 to 111 km off the mid-Oregon coast in
1971-72 yielded 287 samples which contained 23,578 individuals in 90 taxonomic groups, 78 identified
at the species level.

Two distinct faunal assemblages were found: a "coastal" assemblage 2 to 28 km offshore and an
"offshore" assemblage 37 to 111 km from shore. The coastal group was dominated by Osmeridae,
Parophrys vetulus, Isopsetta isolepis, and Microgadus proximus. The offshore group was dominated by
Sebastes spp., Stenobrachius leucopsarus, Tarletonbeania crenularis, Lyopsetta exilis, and Engraulis
mordax. Peak abundance in both assemblages occurred between February and July when >9(Wc of all
larvae were taken. Larval distribution patterns in each assemblage were similar in 1971 and 1972, but
larval abundance was greater in 1971 than 1972.

Ninety-nine percent of the larvae in 53 taxa designated as coastal and 96% of the larvae in 31 taxa
designated as offshore were taken 2 to 28 km or 37 to 111 km offshore respectively. This separation of
coastal and offshore larvae may be explained, in part, by adult spawning locations and current
circulation patterns.

The species of larvae present in the coastal assemblage were similar to those in Yaquina Bay, but
dominant species were quite different. The coastal zone is an important spawning area for P. vetulus,
which utilizes Yaquina Bay estuary as a nursery during part of its early life.

In this paper, distribution patterns, seasonality,
species composition, dominance, and relative
abundance of larval fishes in an upwelling area off
Yaquina Bay, Oreg., are described. Included are
the most comprehensive time series of data yet
available on larval fishes in the northeast Pacific
Ocean north of California, data on the greatest
number of distinct larval taxa yet reported for this
area, and the first quantitative information on
coastal and offshore assemblages of larval fishes
off the northwest coast of the United States.

Larval fish distributions are discussed in rela-
tion to current circulation patterns and spawning
location of adults. Results are compared with
Pearcy and Myers' (1974) study of larval fishes of
Yaquina Bay. The data on fish larvae are com-
pared with data on zooplankton (Peterson and
Miller 1975, footnote 2), shrimp larvae (Rothlis-
berg 1975), and crab larvae (Lough 1975) collected
at the same time and location. Distribution
patterns of larval fishes off the mid-Oregon coast

'School of Oceanography, Oregon State University, Corvallis,
OR 97331.

2Peterson, W. T., and C. B. Miller. 1976. Zooplankton along the
continental shelf off Newport, Oreg., 1969-72: distribution,
abundance, seasonal cycle and year to year variations. Oreg.
State Univ. Sea Grant Coll. Prog. Publ. ORESU-T-76-002, 111 p.

are discussed in relation to a broader geographic
area in the northeast Pacific.

PREVIOUS STUDIES IN
THE NORTHEAST PACIFIC

This review includes only studies of a general
survey nature conducted in ocean waters from
northern California to the Gulf of Alaska,
excluding the Aleutian Chain and Bering Sea.
Studies in sounds, bays, and estuaries are not
considered.

Prior to 1972, data on ichthyoplankton in the
northeast Pacific were sparse and essentially
nonquantitative because of the gear used —
Isaacs-Kidd Midwater Trawls and Northern Pa-
cific area (NORPAC) nets (Motoda et al. 1957).
Surveys were designed primarily for biomass
estimates of pelagic invertebrates and fishes. The
ancillary data on fish larvae, often not identified to
species, were usually presented in the form of
appendix tables [Aron3 for northern Washington

Manuscript accepted September 1976.
FISHERY BULLETIN: VOL. 75, NO. 1, 1977.

3Aron, W. 1958. Preliminary report of midwater trawling
studies in the Pacific Ocean. Univ. Wash. Dep. Oceanogr. Tech.
Rep. 58, 64 p.

125

to southwest Alaska; Aron4 for southern Califor-
nia to southwest Alaska; Pearcy5 for Oregon;
Porter (1964) for northern California (flatfish
only); LeBrasseur6,7 for the northeast Pacific; Day
(1971) for Washington to British Columbia]. Two
additional reports (Aron 1959; LeBrasseur8)
briefly mentioned larval fishes in the text.

More recent reports have been based on surveys
designed specifically to sample ichthyoplankton
using meter nets and bongo nets [Waldron (1972)
off Oregon, Washington, and British Columbia in
April-May 1967; Richardson (1973) off Oregon
from May to October 1969; Naplin et al.9 off
Washington and British Columbia in October-
November 1971; Dunn and Naplin10 off Alaska in
April-May 1972; Pearcy and Myers (1974) off
Yaquina Bay from June 1969 to June 1970].
Results were quantitative and more refined
species lists were provided. However most of these
studies were restricted in seasonal coverage to
periods of less than 1 yr. Pearcy and Myers (1974)
presented a year-long data set but listed only
yearly mean abundances. Discussion of larval
distribution patterns in all these papers was
limited. Waldron (1972) arbitrarily divided his
data into two groups located inshore or offshore of
the 914-m contour and discussed larval abun-
dances in each region. Pearcy and Myers (1974)
discussed horizontal variations in larval dis-
tributions with respect to larvae that occurred
offshore and those that occurred in Yaquina Bay.
Vertical distribution and day-night differences
have not been discussed, although Richardson
(1973) compared deep (to 200 m) and shallow
(upper 20 m) tows.

4Aron, W. 1960. The distribution of animals in the eastern
north Pacific and its relationship to physical and chemical
conditions. Univ. Wash. Dep. Oceanogr. Tech. Rep. 63, Ref.
60-55, 65 p. + 156 append.

5Pearcy, W. G. 1962. Species composition and distribution of
marine nekton in the Pacific Ocean off Oregon. Oreg. State
Univ., Dep. Oceanogr., A.E.C. Prog. Rep. 1, Ref. 62-8, 14 p.

6LeBrasseur, R. J. 1964. Data record: a preliminary checklist
of some marine plankton from the northeastern Pacific Ocean.
Fish. Res. Board Can., Manuscr. Rep. Ser. (Oceanogr. Limnol.)
174, 14 p.

7LeBrasseur, R. 1970. Larval fish species collected in zoo-
plankton samples from the northeastern Pacific Ocean 1956-
1959. Fish. Res. Board Can. Tech. Rep. 175, 47 p.

8LeBrasseur, R. J. 1965. Seasonal and annual variations of net
zooplankton at Ocean Station P, 1956-1964. Fish. Res. Board
Can., Manuscr. Rep. Ser. (Oceanogr. Limnol.) 202, 162 p.

9Naplin, N.A., J. R. Dunn, and K. Niggol. 1973. Fish eggs,
larvae and juveniles collected from the northeast Pacific Ocean,
October-November 1971. NOAA-NMFS Northwest Fish. Cent.,
MARMAP Surv. I, Rep. 10, 39 p. + 121 tables.

10Dunn, J. R., and N. A. Naplin. 1974. Fish eggs and larvae
collected from waters adjacent to Kodiak Island, Alaska, during
April and May 1972. NOAA-NMFS, Northwest Fish. Cent.,
MARMAP Surv. I, Rep. 12, 61 p.

FISHERY BULLETIN: VOL. 75, NO. 1

MATERIALS AND METHODS

Most data came from samples taken at 12
stations, located 2 to 111 km offshore along an
east-west transect (lat. 44°39.1'N) off Newport,
Oreg., just north of Yaquina Bay (Figure 1). The
transect extended over the continental shelf and
slope; depths ranged from 20 to 2,850 m. Samples
were taken every month from January 1971 to
August 1972 except in January and February
1972, although not every station was sampled

46'

45'

44'

43«

42'

WASH

93 74 56 37 18 6 / mfxa/PORT
III 65 46 28 9 2rS

BROOKINGS
1 CALIF.

I26c

125*

I24e

123°

FIGURE 1. — Location of the major bongo net sampling stations
(circles) along an east-west transect (lat. 44°39.1'N) off Yaquina
Bay, Oreg., and a 24-h station (square) occupied in May 1972.
Numbers are kilometers from the coast.

126

RICHARDSON and I'EARCY: COASTAL ANDOCEANIC FISH LARVAE

every month (Table 1). Of the 287 station oc-
cupancies, 219 were made during daylight, 50 at
night, and 18 at dusk or dawn. In addition, a series
of replicate tows was made on 28-30 June 1971,
which included two daytime and two nighttime
hauls at stations 2, 6, and 9 and one daytime and
one nighttime haul at stations 46, 56, 65, and 74.

Samples were collected with a 70-cm (mouth
diameter) bongo net without a closing mechanism.
The bongos had two cylindrical-conical nets of
0.571-mm mesh Nitex11 which were 4.6 m long
and had a filtering area to mouth area ratio of
about 10:1. Tsurumi-Seiki Kosakusho (TSK)
flowmeters were positioned off center in the mouth
of each net. A 40-kg multiplane kite-otter depres-
sor (Colton 1959) was attached to the cable be-
neath the bongos which produced a 2:1 wire out to
depth fished ratio. A time-depth recorder
(bathykymograph) was attached to the cable
above the bongos to record depth and path of tow.

The net was towed along depth contours parallel
to the coast at a vessel speed of 2-3 knots. Tows
were made obliquely through the water column in
equal stepped intervals from the bottom or 150 m
to the surface. Tow times ranged from 8 to 39 min
and were usually between 10 and 30 min. Volume
of water filtered ranged from 283 to 1,411 m3 and
was usually between 500 and 1,000 m3.

At each station a bathythermograph (BT) cast
was made to the bottom or 140 m, a surface bucket

"Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

temperature was recorded, and surface and deep
(bottom or 140 m) salinity samples were taken.

Plankton samples were preserved at sea in 10%
buffered Formalin. One sample from each bongo
pair ( 287 samples) was sorted for fish larvae except
for the replicate series where both samples of each
pair (7 of the 287 samples plus 33 additional
samples) were sorted. All fish larvae were re-
moved from each sample and were stored in 5%
buffered Formalin. Larvae were identified to the
lowest possible taxonomic group, enumerated, and
measured (standard length). Numbers of larvae
from each sample were standardized to number
under 10 m2 of sea surface. This standardized
number was used in all analyses unless indicated
otherwise.

In addition to the above samples, a 24-h station
was occupied 18 km offshore at a location 46 km
north of the Newport transect at lat. 45°04.0'N
(Figure 1 ) on 30-31 May 1972. Water depth ranged
from 158 to 164 m. Four depth strata (0-10, 11-50,
51-100, and 101-150 m) were sampled. Tows were
designed to filter approximately the same volume
of water in each stratum (x = 912 m3 ± 142). The
nonclosing bongo gear was lowered rapidly to the
maximum depth of the zone to be sampled, towed
obliquely through the depth zone in equally
spaced steps, and then retrieved quickly to
minimize contamination. Two tows were made in
each depth stratum in daylight and again at night,
which yielded 32 ( 16 pairs) samples. All fish larvae
were sorted, identified, and enumerated. Numbers

TABLE 1. — Summary of 287 station occupancies made on an east-west transect (lat.
44°39.1'N) off Yaquina Bay, Oreg., 1971-72.

Station (km from coast)
28 37 46 56

111

Month

Bottom depth (m)
142 330

220

340

1.060

1,300

2,850

1971:

Jan.

Feb

—

Mar.

—

Apr.

—

May

June

July

Aug.

Sept

Oct.

Nov.

Dec.

—

1972:

Jan.

Feb.

Mar.

Apr.

—

May

June

July

Aug.

127

FISHERY BULLETIN: VOL. 75, NO. 1

of larvae from each of these samples were stan-
dardized to numbers per 1,000 m3 of water filtered.

TAXONOMIC PROBLEMS

The 287 samples yielded 23,578 fish larvae in 27
families and 1 order (Table 2). To date 90
taxonomic groups have been identified, 78 at the
species level, although 17 of these, primarily in
the Cottidae and Stichaeidae, are still only
numbered "larval types"12 which are considered to
be identified at the level of distinct species. These
larval types have not yet been named because
large specimens needed for positive identification
were absent from the collections. This is the
greatest number of species recorded from a larval
fish study in the northeast Pacific which reflects,
in part, refinements in larval fish identification as
well as the intensity of the sampling effort which
yielded many complete developmental series.
Many of these larvae, particularly the coastal
forms, have not yet been described in detail in the
literature.

While identification of many of the abundant
larvae, particularly the pleuronectids and
myctophids, has been accomplished with cer-
tainty, a few major taxonomic problems remain,
most notably with the osmerids and the scor-
paenids, primarily Sebastes spp. We have not yet
been able to identify the larval osmerids ( <30 mm)
to species, of which there are five possibilities:
Allosmerus elongatus, Hypomesus pretiosus,
Spirinchus starksi, Spirinchus thaleichthys, and
Thaleichthys pacificus. Available descriptions
(Morris13; Yap-Chiongco 1941; DeLacy and
Batts14; Dryfoos 1965; Moulton 1970) are in-
adequate to distinguish all five species. We have
not even established "larval types" below the
family level.

No attempt was made to separate Sebastes spp.,
another problem group, into "larval types"
(species or species groups) although a few distinct
kinds appeared to be present. Samples from Ore-
gon waters may contain some 35 species and

12The term larval type used in this paper refers to a particular
kind of larva which may be distinguished from other larvae on
the basis of larval characters but which has not yet been named.
The term does not necessarily denote identification to the species
level and is not intended to have any taxonomic implications.

13Morris, R. Some notes on the early life history of the night
surf smelt, Spirinchus starski (Fisk) 1913. Unpubl. manuscr.,
37 p.

14DeLacy, A. C, and B. S. Batts. 1963. A search for racial
characteristics in the Columbia River smelt. Res. Fish., Fish.
Res. Inst. Univ. Wash. Contrib. 147:30-32.

identification of the larvae is difficult (Moser 1967,
1972; Moser et al. in press).

One other problem group is the Cyclopteridae.
Based on its broad distribution pattern, our
Cyclopteridae spp. 1 probably represents a
multispecies group, perhaps Liparis spp., but we
have not yet been able to subdivide it on the basis
of larval characters.

These identification problems impose limita-
tions on analysis of ichthyoplankton data. Caution
must be exercised in interpretation of results
when multispecies groups constitute a major
proportion of larvae taken, such as Sebastes spp.
and osmerids off Oregon.

SAMPLING VARIABILITY

A series of replicate oblique tows (four day and
four night samples at stations 2, 6, 9; two day and
two night samples at stations 46, 56, 65, 74) made
in June 1971 was examined to assess sampling
variability. Species composition of day and night
tows at a station was similar, based on common
larvae collected and their relative rank abun-
dance. Total larvae in night catches exceeded
those in day catches at all stations except 65 and
74 (Figure 2). Large day-night differences oc-
curred at stations 6 and 9. This was primarily due
to increased catches of large (>23 mm) osmerid
larvae at night (Figure 3), which presumably
avoided the net by day or were deeper, although 76
to 87% of the water column was sampled in
daytime. Even so, osmerids were the most
abundant larvae captured in all samples from
these two stations. At station 2, the increased
night catches were due to an increase in the
numbers of large larvae (including osmerids), as
well as an increase in the number of species
captured (7-10 in daytime vs. 13-14 at night). Both
Isopsetta isolepsis (most >16.5 mm) and Micro-
gadus proximus (most >29 mm), species com-
mon at stations 6 and 9 during day and night,
were collected only at night at station 2. At sta-
tions 46 and 56, night catches yielded increased
numbers of Engraulis mordax (4-10 mm) and
Stenobrachius leucopsarus (4-15 mm) while night
catches of Sebastes spp. (3-9 mm) were half the
daytime numbers (3-12 mm). At station 65, E.
mordax (6-10 mm) was again more abundant in
night tows while Stenobrachius leucopsarus was
much less abundant at night, composing only 10
and 34% of the numbers of larvae in the two night-
time tows (6-13 mm) but 61 and 54% in the two

128

RICHARDSON and PEARCY: COASTAL AND OCEANIC FISH LARVAE

TABLE 2. — Species composition1 and abundance2 offish larvae taken 2 to 111 km off of Yaquina Bay, Oreg., from January 1971 to

August 1972.

Taxa

Total
standardized abundance2

Coastal Offshore

Taxa

Total

standardized abundance2

Coastal

Offshore

1.17

1.55

1.75

13.27

1.48

0.87

28.43

1.16

3.14

15.85

34.09

79.70

4.45

27.04

6.75

32.47

3.35

0.32

0.70

33.81

37 80

1.03

1.37

1.12

0.77

5.53

1.04

6.56

1.09

0.70

71.17

15.60

258.50

2.31

60.30

1.80

2.59

7.53

57.19

4.80

0.64

7.09

1.57

18.27

113.81

2.70

259

1,157.90

12.53

1.31

96.54

475.23

8.24

81.74

1,479.59

37.62

187.40

1.72

308.12

1.13

16.84

17.22

47.71

49.09

11,474.46

10,868.04

Clupeidae:

+ Clupea harengus pallasi (c)
Engraulidae:

+ - Engraulis mordax (o)
Osmeridae:

+ - Undetermined spp. (c)
Bathylagidae:

- Bathylagus milleri (o)

- Bathylagus ochotensis (o)

- Bathylagus pacificus (o)
Melanostomiatidae:

- Tactostoma macropus (o)
Chauliodontidae:

- Chaulidous macouni (o)
Paralepididae:

- Lestidiops ringens (o)
Myctophidae:

+ - Lampanyctus regalis (o)

- ?Loweina rara3 (o)

- Protomyctophum crockeri (o)

+ - Protomyctophum thompsoni (o)
+ - Stenobrachlus leucopsarus (o)
+ - Tarletonbeania crenulahs (o)

- Undetermined spp. (o)
Gadidae:

+ - Microgadus proximus (c)
Ophidiidae:

- Brosmophycis marginata (o)

- Ophidiidae sp. 1 (o)
Scorpaenidae:

+ - Sebastes spp. (o)

+ - Sebastolobus spp. (o)
Hexagrammidae:

+ - Hexagrammos spp. (o)

+ - Ophlodon elongatus (c)
Anoplopomatidae:

+ - Anoplopoma fimbria (o)
Cottidae:

Artedius sp. 1 (c)
Artedius sp. 2 (c)
Chitonotus pugetensis (c)
Cottus asper (c)
Enophrys bison (c)
Hemilepidotus hemilepidotus (c-o)
Hemilepidotus spinosus (c-o)
Icelinus sp. 1 (c)
Leptocottus armatus (c-o) •
Nautichthys oculofasciatus (c)
Oligocottus sp. 1 (c)
Paricelinus hopliticus (c)
Psychrolutes-hke sp. 1 (o)
Radulinus asprellus (c)
Rhamphocottus richardsoni (c)
Scorpaenichthys marmoratus (c)
Cottidae sp. 1C (c)
Cottidae sp. 12 (c)
Cottidae sp. 19 (c)
Cottidae sp. 20 (c)
Undetermined spp. (c)

Agonidae:

+
+
+
+ -
+ -
+ -
+ -
+ -
+
+
+

64.19

+ Agonopsis emmelane (c)
+ - Bathyagonus spp. (c-o)

13.39

1,000.70

+ Occella verrucosa (c)
+ Odontopyxis trispinosa (c)

5.749.53

13.65

+ Pallasina barbata (c)
+ Stellerina xyosterna (c)

2.90

+ Zeneretmus latifrons (c)

131.46

+ Agonidae sp. 6 (c)

34.18

Cyclopteridae:
+ Lipans pulchellus (c)

2.05

+ - Cyclopteridae spp. 1 (c-o)
+ Cyclopteridae sp. 3 (c)

29.47

+ - Undetermined spp. (c)
Bathymasteridae:

5.78

+ - Ronquilus jordani (c)
Blennioids:

0.82

37.04

+ Undetermined spp. (c)

1.15

Clinidae:

34.03

+ Gibbonsia Imontereyensis (c)

9.97

173.77

Stichaeidae:

45.30

3,648.00

+ Anoplarchus sp. 1 (c)

2.29

635.20

+ Chirolophis sp. 1 (c)

7.24

+ Lyconectes aleutensis (c)
+ Lumpenus sagitta (c)

580.28

5.44

+ Plectobranchus evides (c)
+ Stichaeidae sp. 1 (c)

2.86

+ - Stichaeidae sp. 2 (c)

1.32

+ Stichaeidae sp. 4 (c)
Ptilichthyidae:

180.66

3,967.82

+ Ptilichthys goodei (c)

0.60

19.21

Pholidae:
+ Apodichthys flavidus (c)

0.44

2.94

+ Pholis spp. (c)

53.44

1.24

Icosteidae:

- Icosteus aenigmaticus (o)

0.93

7.34

Ammodytidae:
+ Ammodytes hexapterus (c)

189.26

7.94

Gobiidae:

139.96

+ Clevelandia ios (c)

7.55

Centrolophidae:

145.43

- Ichichthys lockingtoni (o)

60.65

6.63

Bothidae:

13.13

6.44

- Citharichthys sordidus (o)

69.04

29.78

+ Citharichthys stigmaeus (c)

54.46

1.94

+ - Citharichthys spp.4 (o)

18.60

5.50

Pleuronectidae:

0.77

- Atheresthes stomias (o)

3.15

+ - Embassichthys bathybius (o)

0.79

- Eopsetta jordani (o)

2.21

+ - Glyptocephalus zachirus (o)

58.45

9.19

+ - Hippoglossoides elassodon (c-o)

0.77

+ - Isopsetta isolepis (c)

21.84

+ - Lepidopsetta bilineata (c)

5.94

+ - Lyopsetta exilis (o)

42.70

+ - Microstomus pacificus (o)

0.33

+ - Parophrys vetulus (c)

1.12

+ - Platichthys stellatus (c)

21.55

+ - Psettichthys melanostictus (c)
Unidentified larvae
Fragments

1 General distribution patterns are given for each taxon:

+ = taken 2 to 28 km offshore

- = taken 37 to 1 1 1 km offshore

c = coastal type ( >80% of all larvae taken 2 to 28 km from coast)

o = offshore type ( >80% of all larvae taken 37 to 1 1 1 km from coast)
c-o = neither c or o type (<80% of all larvae taken in either coastal or offshore area).
2The sum of the standardized numbers (number under 10 m2 sea surface) of larvae from each sample in the coastal (2-28 km) and offshore (37-111) km
assemblages (139 and 148 samples, respectively),
identification based on one partly mutilated specimen.
4Specimens too small to identify to species.

129

FISHERY BULLETIN: VOL. 75, NO. 1

lO.OOOr-

<
>

rr
<

Ll_

o
cr

UJ
QQ

_l
<

1000

DAY

• NIGHT
O DAY

100

(§>

2 6 9

46 56
STATIONS

FIGURE 2. — Day and night catches offish larvae on transect off
Yaquina Bay, Oreg., June 1971.

daytime tows (4-16 mm). Decreased larval abun-
dances at night at station 74 were due mainly to
reduced numbers of S. leucopsarus (5-13 mm at
night, 5-16 mm in day). Thus avoidance of the net
by large larvae in daytime seemed to account for
much of the day-night variation at the coastal sta-
tions 2, 6, and 9. Differences at the offshore
stations may have been due to patchiness of small
larvae.

Variability among repeated samples was
examined at the three inshore stations where four
day and four night replicate samples were taken at
each station. Coefficients of dispersion were
calculated for total larvae, osmerids, and total
larvae minus osmerids (Table 3). Values were
close to 1.0 for total larvae minus osmerids at

200 r-

100

900 1-

800
700

Ll.

600

500

4 00

•

300-

200-

100-

20 30

STANDARD LENGTH (mm)

FIGURE 3. — Day and night length frequencies of osmerid larvae
collected at 6 and 9 km off Yaquina Bay, Oreg., June 1971.
Numbers of larvae were combined for both nets from four day
and four night hauls.

stations 6 and 9 and for total larvae at station 2
where osmerids were not abundant suggesting
that larvae were randomly distributed. Coeffi-
cients were large, however, for total larvae and for
osmerids at 6 and 9 where smelt larvae were
abundant, except at night at station 9. These
large coefficients of dispersion indicate high con-
tagion, possibly caused by schooling behavior of
large osmerid larvae.

TABLE 3. — Coefficients of dispersion (s2/x) for total larvae,
osmerids, and total larvae minus osmerids in replicate tow series
made in June 1971 on the transect (lat. 44°39.1'N) off Yaquina
Bay, Oreg.

Station 2
Day Night

Station 6

Station 9

Item

Day

Night

Day Night

Total larvae
Osmendae
Total larvae
minus Osmendae

0.49 0.97

12.44

16.40

0.81

11.96
12.81

3.18

11.56 0.57
14.49 0.82

0.81 1.23

VERTICAL DISTRIBUTION

One attempt was made to study the vertical
distribution patterns of larvae in the coastal zone
18 km offshore north of the Newport transect
(Figure 1). Thirty-two samples were taken within
four depth strata (0-10, 11-50, 51-100, and 101-150

130

RICHARDSON andPEARCY: COASTAL AND OCEANIC FISH LARVAE

m) during a 24-h period in May 1972. Essentially,
the entire water column was sampled. The volume
of water filtered by each type of tow was about the
same and the number of day and night tows in
each stratum was equal. Because the nets had no
opening-closing device, samples from all but the 0-
to 10-m stratum were contaminated with catches
from overlying waters. However, the maximum
tow time spent outside the desired stratum was
20% for the deepest tows and was usually <10%
for the intermediate depths. Therefore, no cor-
rection factor was applied to the data.

The greatest number of larvae and taxa was
taken near the surface both day and night (Table
4). The 51- to 100-m stratum yielded the fewest
larvae and taxa while the 11- to 50- and 101- to
150-m strata were intermediate. More larvae were
taken at night, primarily in the 0- to 10-m stratum
where avoidance during the day would be expected
to be greatest. Mean larval length in this stratum
was much greater at night which also indicated
daytime avoidance by large larvae in surface
waters. Mean larval length was also high in the
101- to 150-m stratum day and night, primarily
because of the abundance of large osmerids there.

Of the 22 taxa taken, those represented by more
than 10 larvae were examined for trends in dis-
tribution (Table 4). Clupea harengus pallasi
(25-31 mm, x 28), Ammodytes hexapterus (17-37
mm,x33), and Ronquilus jordani (6-21 mm,f 13)
were concentrated in the upper 10 m at night and
were completely absent in daytime collections
from all depths. They exhibited strong daytime
avoidance, indicated by night/day ratios. Large
Sebastes spp. larvae (9-11 mm, x 10) were only
taken at night and perhaps avoided by day,
whereas small larvae (3-4 mm, x 4) were taken
both day and night in the upper two strata.
Stenobrachius leucopsarus (5-11 mm, x 8) and

Isopsetta isolepis (14-23 mm, x 20) occurred
predominantly in the upper two strata but showed
no evidence of daytime avoidance. Mean larval
lengths were about the same by day and night.

Of the remaining taxa, Radulinus asprellus
(9-15 mm, x 12) appeared to occur throughout the
water column in similar numbers and lengths
during both day and night. Cyclopteridae spp. 1
(4-8 mm,* 5) occurred mainly near the surface in
daytime but only in the 51- to 100-m stratum at
night, possibly a result of patchiness or con-
tamination of the deeper hauled net in the surface
stratum. Only osmerids occurred primarily near
the bottom (101-150 m), by day and night. Some
were taken near the surface at night which may
indicate vertical migration by some individuals or
avoidance by day. Preliminary examination of
specimens did not reveal the surface- and bottom-
occurring osrrierid larvae to be different species.
Mean lengths for deep- and surface-caught os-
merids were about the same, 21 and 23 mm.

ASSEMBLAGES

Two separate assemblages of fish larvae were
distinguished, using a similarity coefficient ma-
trix based on Sander's (1960) dominance-affinity
index (J lowest percent of all larvae in common
between two stations). In 1971 a coastal as-
semblage occurred at stations 2 to 28 km offshore,
which was distinct from another assemblage
occurring at stations farther offshore (Figure 4). A
similar pattern was found in 1972 during the 6 mo
for which data were available. In 1971, the mean
affinity value among stations 2, 6, 9, 18, and 28
was 65.81 and among stations 46, 56, 65, 74, 93,
and 111 it was 60.61. In 1972, the mean affinity
values for these same sets of stations were 43.21
and 56.61, respectively. Sebastes spp. were

TABLE 4. — Number/l,000m3, number of taxa, and mean length offish larvae by day, night, and depth strata taken
during a 24-h period 18 km off the mid-Oregon coast (lat. 45°04.0'N) in May 1972. N/D = night to day ratio. Each
number is the sum of four replicate samples.

CO CO
-C CD

Q.
Q.
CO

CO
T3

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Depth
strata

CD CD
CD =

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3 Q.

CO
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CD

O CO

CO
2
CD

CO 3
C $

CD «

<D T-

5 £

=: cd

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§■9.

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O <D

cog

Q.
CO

S
o

No.

taxa

Mean
length

taken
D N

(mm)

(m)

D N

0-10

0 46

9 3

7 1

14 0

0 29

0 22

31 8

78 131

13 21

11-50

0 1

0 4

3 5

3 0

0 0

12 12

24 30

15 15

51-100

0 2

0 0

3 2

0 8

0 0

0 1

1 1

6 14

11 12

101-150

0 1

0 0

2 5

0 0

0 1

3 2

27 25

20 20

Total

0 50

9 7

15 13

17 8

0 29

0 24

47 23

16 135 200

15 20

N D

0.86

0 78

3.00

0.87

0 47

049

0.73

1.48

131

FISHERY BULLETIN: VOL. 75, NO. 1

1971

1972

1 2

III

70 12

67 87

59 18

50 66

28 40

2 51

3 10

0 84

1 49

0 84

0 73

6 1

92 31

83 84

50 85

2365

2 99

4 09

164

2 16

1 67

2 35

87 90

49 64

26 44

317

4 09

1 70

2 13

1 77

1 72

45 69

29 64

6 86

671

4 29

4 94

4 09

2 88

47 79

28 65

30 19

26 II

24 04

22 28

21 39

32 42

29 04

24 10

1976

17 79

15 94

69 92

4844

36 46

34 96

32 45

67 43

55 II

55 00

53 27

6031

62 48

61 90

94 06

86 56

90 87

III

| > 70 00

15000-6999 [33000-4999 D<30 00

FIGURE 4. — Station to station similarity-coefficient matrices for 1971 and 1972 data on larval fishes based on Sander's (1960)
dominance affinity index. All taxa except Sebastes spp. were included in the analysis.

excluded from the analysis to minimize masking
effects that might have arisen because of the
multispecies nature of the group. Since osmerids
were known to be essentially coastal forms, they
were not excluded.

Peaks in larval abundances were associated
with the location of these two assemblages with an
apparent transitional zone of low larval abun-
dance between them (Figure 5). In both 1971 and
1972 abundance was relatively high inshore,
dropped to a low at 28 km, and then increased
seaward.

Larval taxa were determined to be associated
with the coastal or offshore zone on the basis of
whether 80% or more of all larvae were taken at
stations 2 to 28 (coastal = C) or stations 37 to 111
(offshore = O). Using these criteria, 84 of the 90
taxa (93%) could be designated as coastal or
offshore (Table 2). Fifty-three taxa in 16 families
and 1 order were coastal. Of these, 49 were
identified to species, 3 to family, and 1 to order.
Ninety-nine percent of all larvae in these 53 taxa
were taken in the coastal zone 2 to 28 km offshore.
Thirty-one taxa in 15 families were offshore. Of
these, 26 were identified to species, 4 to genus, and
1 to family. Ninety-six percent of all larvae in
these 31 taxa were taken 37 to 111 km offshore.

Only six taxa could not be designated as coastal
or offshore. This was probably due in part to rarity,

e.g., Hippoglossoides elassodon (total standard-
ized number = 5.29; 51% were C and 49% were
0),Bathyagonus spp. (3.30; 47% C and 53% O), and
to multispecies groups, e.g., Cyclopteridae spp. 1
(30% C and 70% O) and Bathyagonus spp. In-
terestingly, 96% of all Sebastes spp. larvae were
taken in the offshore area. Leptocottus armatus
was primarily coastal since 77% of all larvae were
taken there. Only one sample outside the coastal
area (Station 37, in February 1971) contained L.
armatus larvae, but they were present in moder-
ate numbers. Hemilepidotus hemilepidotus (67% C
and 33% O) and//, spinosus {IWc C and 30% O)
distributions are more difficult to explain.
Hemilepidotus spinosus larvae in the coastal area
were smaller (4-9 mm, x 5.3) than those farther
offshore (6-12 mm, x 8.9) as were//, hemilepidotus
(4-6 mm,x 5.2 in the coastal area and 8-11 mm, x
9.3 offshore). Hemilepidotus spinosus larvae are
sometimes abundant (>600 larvae/15 min tow) in
the neuston (upper 15 cm of the water column),
particularly at night (Richardson unpubl. data).
These data suggest that larvae which are as-
sociated with surface waters may undergo some
kind of offshore transport which does not affect
nonneustonic species.

Modes of reproduction differ considerably
between those species designated as coastal and
those designated as offshore. Of the 53 coastal taxa

132

RI< II I ARDSON and PE ARCY: COASTAL AND OCEANIC FISH LARVAE

440f

400

360

320

280-

240-

200-

160

120-

K 80
<

O 40h

-z.

1971

mm FEB -MAR -APR

I 1 MAY -JUN-JUL

C—l AUG-SEP-OCT-NOV-DEC

i ti fa .

2 6 9

28 37 46 56 65

FIGURE 5.— Mean standardized
abundance offish larvae by station in
1971 and 1972.

200
160
120-

1 — TT

1972

■■ MAR -APR
CZ) MAY -JUN-JUL

\lA

2 6 9

(Table 2), 87% presumably come from demersal
eggs (Breder and Rosen 1966) including all the
osmerids, cottids, agonids, cyclopterids, and
blennioids as well as Clupea harengus pallasi,
Ophiodon elongatus, Ronquilus jordani, Am-
modytes hexapterus, andClevelandia ios. The eggs
of Microgadus proximus are unknown but may
also be demersal, as are those of M. tomcod in the
Atlantic. Those not derived from demersal eggs,
i.e., the six coastal flatfishes, come from small (~1
mm or less in diameter) planktonic eggs. Of the 31
offshore taxa, 81% presumably come from plank-
tonic eggs. Eggs of the bathylagids, myctophids,
bothids, and Engraulis mordax are probably all
relatively small (~1 mm or less) whereas those of
Chauliodus macouni, Anoplopoma fimbria, Icos-
teus aenigmaticus, Atheresthes stomias, Embas-
sichthys bathybius, Glyptocephalus zachirus, and
Microstomas paciftcus are large, usually >2 mm.
Eggs of Tactostoma macropus, Icichthys locking-

is 28 37 46 56 65
STATIONS

III

toni, Eopsetta jordani, and Lyopsetta exilis are in-
termediate in size. Eggs of Sebastolobus spp., also
of intermediate size, occur in floating masses
rather than individually (Pearcy 1962). Larvae of
the live-bearers Brosmophycis marginata,
Sebastes spp., and possibly Ophidiidae sp. 1 are
extruded. Of the offshore taxa, only Hexagrammos
spp. and perhaps Psychrolutes-like sp. 1 come from
demersal eggs.

Coastal Assemblage

One hundred thirty-nine samples were taken in
the coastal assemblage, five at night, four at dusk
or dawn, and the rest during daylight. All but four
samples contained larvae, yielding 16,197
specimens or a standardized total [^ (number of
larvae under 10 m2 sea surface in each sample)] of
11,474.

133

FISHERY BULLETIN: VOL. 75, NO. 1

Species Composition and Dominance

Seventy-three taxa assigned to 19 families and 1
order were taken in the coastal samples (Table 2).
Of these, 62 were identified to species including
unnamed numbered larval types considered to be
distinct species, 7 to genus, 3 to family, and 1 to
order. Margalef's (1958) formula for diversity (D
= S — 1/ln N, where S = number of species, N =
total number of individuals), which provides a
measure of species richness, yielded a value of 7.43
for the coastal assemblage, which was higher than
that for the offshore assemblage.

Dominant taxa within the coastal assemblage
were determined by a ranking method (Biological
Index = BI) modified from Fager (1957), which
takes into account both abundance and frequency
of occurrence. By this method, the most abundant
species in each sample is given five points, the next
four, etc. Scores for each taxon are summed for all
positive samples and divided by the total number
of samples taken. The top 13 coastal dominants15
(Table 5) accounted for 91.8% of the total larvae
captured within 28 km of the coast over the entire
sampling period. These same 13 taxa were also the
13 most abundant, although not always in the
same order as dominance.

Osmerids were overwhelmingly the most
dominant taxonomic group making up 50% of the
total larval catch. They were the most abundant
and most frequently taken larvae in the coastal
assemblage. Parophrys vetulus and Isopsetta
isolepis were also important in terms of abun-
dance. These three taxa, together with fourth

ranked Microgadus proximus, composed 78% of all
larvae taken.

Seasonality

Obvious trends in seasonality were apparent
from the 1971 data, which included samples from
every month (Figure 6). Ninety-three percent of
all larvae were taken during the 6-mo period from
February through July. Two abundance peaks
occurred within that period, one in February-
March (24% of all larvae) before upwelling, and
one in May-July (68% of all larvae) during the
upwelling season. Larval abundance decreased
greatly in August and remained low through
December. Mean number of larvae under 10 m2
was 142 in February-March, 202 in May-July, and

e
o

<
>

q:
<

400

2-28 km

Offshore

300

200

100

—

ll. .1 ■ 1

J F

M 1 A M '

J ij i a 1 S ' 0 ' N 'D '

37-111 km

Offshore

Im!

J I A i S '0 'N' D

fWi

1971

15Data on distribution and abundance of all 90 taxa will be
available in an Oregon State University Sea Grant College
Program Technical Report by the senior author in 1976-77.

FIGURE 6. — Mean standardized abundance of fish larvae by
cruise in 1 97 1 i n the coastal assemblage ( stations 2 to 28) and the
offshore assemblage (stations 37 to 111).

TABLE 5. — Coastal dominants based on all larvae collected 2 to 28 km offshore in 1971 and 1972.
[BI = Biological Index modified from Fager (1957)].

Taxa

Rank

order

abundance

Total
standardized
abundance1

% of

total

abundance

Positive

tows out

of 139

Total
standardized
abundance1
Positive tows

'The sum of the standardized numbers (number under 10 m2 sea surface) of larvae from each sample.

Months of
occurrence

1. Osmeridae

2 49

5,749.53

50.1

63.88

l-VIII, X-XII

2. Parophrys vetulus

1.41

1,479.59

12.9

24.66

l-VI, IX-XII

3. Isopsetta isolepis

1.39

1,157.90

10.1

16.31

l-VIII, X

4. Microgadus proximus

0.97

580.28

5.1

9.36

ll-VIII

5. Sebastes spp.

0.77

180.66

1.6

3.17

l-XII

6. Psettichthys

melanostictus

0.71

308.12

2.7

5.60

l-XI

7. Artedius sp. 1

0.50

189.26

1.6

2.87

l-VIII

8. Platichthys

stellatus

0.39

187.40

1.6

6.25

lll-VI, IX

9. Lyopsetta exilis

0.34

96.54

0.8

2.35

lll-VIII

10. Artedius sp. 2

0.32

139.96

1.2

2.92

l-VIII

1 1 . Ammodytes hexapterus

0.31

258.50

2.2

11.75

ll-V

12. Hemilepidotus

spinosus

0.29

69.04

0.6

3.34

Mil

13. Cottus asper

0 24

145.43

1.3

6.61

lll-VII

134

RICHARDSON and PEARCY: COASTAL ANDOCEANIC FISH LARVAE

13 during August-December. Since samples were
taken only during 6 mo in 1972 and larval
abundances were greatly reduced, trends in
seasonality could not be assessed.

In 1971, 42 taxa were taken in the February-
March period and 46 taxa were taken from May to
July. Of these, 10 occurred only during the winter
period, 14 occurred only in the spring, and 32 were
taken in both periods. Dominant taxa (with BI>1)
in the February-March period were P. vetulus (BI
= 4.09), Ammodytes hexapterus (BI = 1.76), /.
isolepis (BI = 1.73), and Osmeridae (BI = 1.51).
Together they made up 70% of the total larvae.
Parophrys vetulus alone accounted for 44%.
Dominant taxa from May to July 1971 were
Osmeridae (BI = 4.12), /. isolepis (BI = 2.21), M.
proximus (BI = 2.03), and Lyopsetta exilis (BI =
1.07). Together they made up 90% of the total
number of larvae in those months. Osmerids
accounted for 71% of the total in that period.

Thus the two abundance peaks in 1971 were not
made up of completely different species. Some
were common to both (Table 6). Some species
occurred in the plankton collections during only a
few months. For example, Platichthys stellatus
larvae occurred over a restricted period of time
(Table 6), small larvae were taken only during a
few months mainly in spring, and they trans-
formed and settled out at a small size ( ~8 to 9 mm).
Hemilepidotus spinosus and A. hexapterus also
were taken during a short-time period, primarily
in winter. Larger A. hexapterus larvae avoid
plankton nets and may have been present for a

longer period than the data suggested. On the
other hand, some species, such as Parophrys vetu-
lus andPsettichthys melanostictus, occurred over a
longtime period because of protracted spawning
seasons and relatively long planktonic life (Table
6). Parophrys vetulus spawned primarily from
January through March. Increases in larval
lengths indicated that spawning stopped and
larvae had settled out by July. Spawning began
again in September and continued at least
through December. Small larvae of Psettichthys
melanostictus were taken in most months except
July, August, and December. An increase in
modal length occurred from June through August
and again from September through November.

Other species showed trends in seasonal oc-
currence somewhere between the two extremes.
Isopsetta isolepis apparently spawned from
February through May. Modal lengths increased
in successive months and large larvae were no
longer available to our gear by August. Micro-
gadus proximus also appeared to spawn from
February through June and the larvae were not
caught after August. Lyopsetta exilis apparently
spawned from March through June and larvae
were absent in collections from September
through February. Artedius sp. 1 and Artedius sp.
2 were taken over an 8-mo period and small larvae
occurred almost every month. Cottus asper was
taken from February through July, but larval
lengths showed no trends by month. Although
taxonomic problems exist with the osmerids, two
groups (possibly two species) were apparent from

TABLE 6. — Ranges and modal lengths (mm) for dominant fish larvae in the coastal assemblage (stations 2-28) in 1971. Asterisks
indicate month in which average abundance per cruise was greatest. Parentheses are used where more than one modal peak occurred.

Taxa

Jan.

Feb.

Mar.

Apr.

May

June

July

Aug.

Sept

Oct.

Nov.

Dec.

1 A. Osmeridae (group 1)

5-6-10

6-11-21

15-19-24*

6-12

5-8-25

1B. Osmeridae (group 2)

4-6-1 1

5-15-32

7-25-35*

1 °* (§7 )"36 5-29-37

2. Parophrys vetulus

2-3-9

2-4-18*

3-8-21

«-G§)-18

5-8-22

14-21

2-3-6

2-10-17

3-5-14

2-5-14

3. Isopsetta isolepis

2-4-6

3-7-16

3-9-17

3-13-21*

6-16-21

10-11-19

4. Microgadus
proximus

3-3-5

3-4-9

3-7-19

4-7-19

3-6-33*

6-16-24

14-(f°)-31

5 Sebastes spp.

3-4-4*

3-3-4

3-4-4

4-4-7

3-4-5

4-4-9

3-(43)^

3-3-14

6. Psettichthys
melanostictus

2-3-4

3-13-23*

5-6-23

8-11-21

14-22

4-(54)-8

2-9-13

3-11-26

1. Artedius sp. 1

2-3

2-3-4*

3-(io)-10

3-3-5

5
2-6-9*

4-10-19*

4-5-6*
4-5-8*

4-(5>9

3-6-13

4-7-12

4-6-12

3-P?>11

8. Platichthys

stellatus

9. Lyopsetta exilis
10 Artedius sp. 2

1 1 . Ammodytes

hexapterus

12. Hemilepidotus

spinosus

13. Cottus asper

2-3

5-5-8
0

2-4-6

4-4-9

4-5-6
5

\ /

3-4

4-4-7

14-19

0
0

3-7-9*
4-5-1 1
3-6-13

11-12

0
6-9-9

5-7-9

5-10-21*

3-3-13

0
5-6

0
9-11-21
6-7-10

0
6-7-9

0
11-19
3-4-9

0
0

3
0
0

0
0

0
0
0

0
0

0
0
0

0
0

0
0
0

0
0

135

FISHERY BULLETIN: VOL. 75, NO. 1

length-frequency data (Table 6). Two distinct
length modes occurred in March, which suggested
the presence of both a winter-spawned and a
spring-spawned group.

Distribution Trends

Peak abundances for dominant species within
the coastal assemblage generally occurred at
stations 6 and 9 (Figure 7) for those larvae that
were most abundant before the usual months of
upwelling (e.g., P. vetulus, Ammodytes hexap-
terus) and also for those most abundant during the
upwelling season (e.g., Osmeridae, /. isolepis, M.
proximus). Abundance usually decreased toward
the coast and farther offshore. However, on two

winter cruises, osmerids were most abundant at
the 2-km station. A few species, such as C. asper,
were always most abundant at the 2-km station,
and numbers decreased with distance from shore.
Cottus asper is known to spawn in Yaquina Bay
where it is the third most abundant larval species
(Pearcy and Myers 1974). It is found in greatest
numbers in the upper part of the Bay, and its
occurrence offshore probably is a result of tidal
flushing.

Year to Year Variation

The mean standardized number of larvae per
station during the winter and spring-summer
periods was considerably higher in 1971 than in

Parophrys vetulus

175
150
125
100
75
50
25
100
75
50
25
50
25
25
25
25
0

FEB

MAR

_l_l_

APR

MAY

JUN

~m — l — l — I — l — I — I — I 1-

2 69 18 28 37 46 56 65 74 93

STATIONS

JUL

Ammodytes hexapterus

10
80
70
60
50
40
30
20
10
10
10
10
10
0

i-r-T 1 1 1 1 1 1 [-

.11 .

FEB

MAR

APR

MAY

JUN

~rn — I — I — I — l — I I I T

269 18 28 37 46 56 65 74 93

STATIONS

JUL

Cottus asper

— m — i — I — i — i — i — i r

FEB

MAR A

APR

MAY

JUN

JUL

n — i — i — i — i : i r~

18 28 37 46 56 65 74 93

STATIONS

OSMERIDAE

Microqadus proximus

Isopsetta isolepis

400

350

150

100

650

600

400

350

300

250

200

150

100

150

100

tt — I — I — I — I — i — I — I r
O

FEB

Jl^

MAR

APR

MAY

JUN

JUL

TTT T l T — l — l — l — I 1 1—

269 18 28 37 46 56 65 74 93 III
STATIONS

10
30
20

10
40

50
20

10
20

10
0

III 1 1 1 1 1

1 ' 'FEB '

.1.

MAR -

APR

■

MAY

■ 1

JUN -

" ill

JUL -
ii 1 1

2 69 18 28 37 46 56 65 74 93 III

STATIONS

25
50
25
25
125
100
75
50
25
50
25
25
0

i'l 1 1 1 1 1

1 ' 'FEB'

MAR -

i _

APR

MAY ~

.1 .

JUN -

TTT 1 1 1 I

JUL
II 1 1

269 18 28 37 46 56 65 74 93
STATIONS

FIGURE 7. — Distribution patterns offish larvae in the coastal assemblage (stations 2 to 28) during months of peak abundance in 1971.

Abundances are monthly means.

136

RICHARDSON and PEARCY: COASTAL AND OCEANIC FISH LARVAE

1972, sometimes by an order of magnitude (Figure
5). These differences are exemplified further by
the mean standardized number of larvae per tow
(Table 7).

In March- April, five of the six dominant (BI 5* l)
taxa were more abundant in 1971 than 1972 (Ta-
ble 7). The exception was Sebastes spp., which was
6.5 times more abundant in 1972 based on mean
standardized number per tow. The greatest de-
crease occurred for P. vetulus, which was 24.9
times more abundant in 1971. The low numbers of
P. vetulus in 1972 may have been partly due to an
early spawning; small larvae were taken as early
as September and October 1971 (Table 6) and
many larvae may have settled out by the March-
April 1972 period. Or 1972 may have been a year
of reduced larval survival for P. vetulus. Am-
modytes hexapterus was also more abundant in
1971 with 12.2 times more larvae being taken
than in 1972. Dominance shifted fromP. vetulus in

1971 to the Osmeridae in 1972 even though os-
merids were less abundant in 1972 than 1971. The
number of taxa taken was similar each year
although the species richness value was higher in

1972 (Table 7).

During the May-July period, the five dominant
taxa were all more abundant in 1971 than in 1972
(Table 7). The largest decline occurred in M.
proximus where 13.5 times more larvae were
taken in 1971. Osmerids were 10.6 times more
abundant in 1971. Their decline in numbers had a
major impact on overall abundance in 1972. In
1971, an average of 143 osmerids were taken per
tow and they contributed 71% to the total larval
abundance. While still the dominant taxon in
May-July 1972, they were less abundant and
made up 57% of the total. Considerably fewer
taxonomic groups were taken in 1972. This may
have been a result of fewer samples taken and a
corresponding reduction in numbers of rare taxa.

TABLE 7. — Comparison of data on larval fishes collected off Oregon in 1971 and 1972.
[BI = Biological Index modified from Fager (1957)].

Taxa

(dominants

listed separately)

No. samples

1971

1972

1971

1972

1971

1972

4.25

31.13

1.25

1.85

1.63

12.17

3.16

1.68

16.83

1.38

1.25

5.59

2.12

2.00

11.41

8.50

1.39

0.33

2.13

—

39.69

12.72

—

117.14

34.82

4.12

3.33

143.23

13.51

2.21

1.88

23.10

2.85

2.03

12.59

0.93

1.07

2.31

0.37

1.03

2.04

0.86

—

18.99

5.02

—

202.14

23.55

3.97

4.32

26.05

29.12

2.53

1.20

8.48

1.90

1.34

2.94

0.54

1.30

0.48

0.93

—

6.43

1.41

Mean no./10 m2

1971/1972

% total abundance
1971 1972

Species richness
(D =S - 1/ln N)

1971

1972

March-April 2-28 km 12 22

Parophrys vetulus
Isopsetta isolepis
Ammodytes

hexapterus
Microgadus proximus
Osmeridae
Sebastes spp.
All other species

Total (41 in 1971;
48 in 1972)

May-July 2-28 km 34 20

Osmeridae
Isopsetta isolepis
Microgadus proximus
Lyopsetta exilis
Artedius sp. 1
All other species
Total (46 in 1971;

24 in 1972)

March-April 37-111 km
Sebastes spp.
Stenobrachius

leucopsarus
Tarletonbeania

crenularis
Hemilepidotus

spinosus
All other species

Total (16 in 1971;
16 in 1972)

May-July 37-111 km 38 28

Stenobrachius

leucopsarus
Sebastes spp.
Lyopsetta exilis
Tarletonbeania

crenularis
Engraulis mordax
All other species

Total (32 in 1971;

25 in 1972)

44.40

33.80

24.90
3.85

12.20
2.64
1.34
0.16
3.12

3.36

10.60
8.10

13.54
6.24
2.37
3.78

8.59

0.89

4.46

5.44

0.52
4.56

1.31

26.6

4.0

10.4

10.1

14.4

4.4

4.8

6.8

9.7

27.2

0.3

6.8

33.9

40.7

00.1

100.0

70.8

57.4

11.4

12.1

6.2

4.0

1.1

1.6

1.0

3.6

9.4

21.3

99.9

100.0

58.7

85.9

19 1

5.6

6.6

1.6

1.1

2.7

14.5

4.2

100.0

100 0

3.10

2.82

76.78

15.11

5.08

43.8

19.6

3.08

3.50

56.50

22.55

2.51

32.2

29.3

1.96

10.99

4.78

2.30

6.3

2.3

1.47

1.11

9.56

4.84

1.98

5.4

6.3

2.00

4.68

28.06

0.17

2.7

36.4

—

16.79

4.74

3.54

9.6

6.2

5.24

6.41

4.94

3.30

2.52

248

3.66

3.35

— 175.30

76.98

2.27

100.0

100.1

137

FISHERY BULLETIN: VOL. 75, NO. 1

The species richness value in 1972 (Table 7) was
lower than in 1971, indicating that fewer species
were present.

Offshore Assemblage

During the sampling period, 148 samples were
taken (45 at night, 14 at dusk or dawn, 89 in
daylight) in the offshore assemblage. The 141
positive samples yielded 7,381 larvae or a
standardized total [2 (number of larvae under 10
m2 sea surface in each sample)] of 10,868.

Species Composition and Dominance

Fifty-two taxa in 21 families were taken in the
offshore samples (Table 2). Of these, 43 were
identified to species, 6 to genus, and 3 to family.
The species richness value, based on Margalef's
(1958) formula for diversity, was 5.73 for the
offshore assemblage, which was lower than the
value of 7.43 for the coastal assemblage.

The top 10 dominant (BI) taxa (see footnote 15)
in the offshore assemblage accounted for 94.3% of
the total number of larvae in this assemblage
(Table 8). Nine of these 10 taxa also were among
the 10 most abundant although in different order,
with Microstomas pacificus (total standardized
abundance 81.74) replacing Hemilepidotus
spinosus.

The two major dominants were Sebastes spp.
and Stenobrachius leucopsarus, which together
accounted for 70% of all larvae taken offshore.
Tarletonbeania crenularis and Lyopsetta exilis
were also dominant in the offshore assemblage in
terms of overall abundance and frequency of
occurrence. Fifth ranked Engraulis mordax oc-
curred in concentrations (standardized numbers
per positive tow) equivalent to Sebastes spp. and
Stenobrachius leucopsarus (Table 8) although it

was less frequently taken. The top six dominant
taxa composed 91% of the total larval abundance
compared with 13 taxa contributing that per-
centage in the coastal area.

Seasonality

In 1971, 94% of all larvae were taken between
February and July, as in the coastal area, and 83%
were taken during the 3-mo period from May to
July (Figure 6). The winter (February-March)
peak of abundance noted in the coastal area was
absent offshore. Larval abundance decreased in
August and remained low for the rest of the year.
The minor increase in numbers in October was
solely due to small Citharichthys (probably
sordidus) larvae 37 to 46 km offshore. Since only 5
mo of data were available for the offshore as-
semblage in 1972, seasonal trends could not be
assessed.

Dominant taxa (BI>1) within the May-July
peak abundance period in 1971 were essentially
the same as those (Table 8) for the entire lVfe-yr
sampling period. These wereS. leucopsarus (BI =
3.10), Sebastes spp. (BI = 3.08), L. exilis (BI =
1.96), andT. crenularis (BI = 1.47). Together they
made up 88% of the total larvae taken in that
spring-summer period.

As in the coastal zone, some taxa had restricted
spawning periods and their larvae were present in
the plankton for a relatively short time, e.g., E.
mordax and L. exilis (Table 9). Both species
showed distinct growth trends. Hemilepidotus
spinosus was also present during a short period
although the larvae in the offshore zone were
usually larger than those in the coastal area (Ta-
ble 6). Glyptocephalus zachirus was taken as small
larvae only in April to June indicating a rather
restricted spawning period, but large larvae were
present through September. The larvae grow

Table 8.

-Offshore dominants based on all larvae collected 37 to 111 km offshore in 1971 and 1972.
[BI = Biological Index modified from Fager (1957)].

Rank
order

Total

%of

Positive

Total

standardized

total

tows out

abundance1

Months of

Taxa

abundance

abundance1

abundance

of 148

Positive tows

occurrence

1 . Sebastes spp.

3 24

3,967.82

36.5

112

35.43

l-XII

2 Stenobrachius leucopsarus

2.28

3,648 00

33.6

41.93

l-X

3. Tarletonbeania crenularis

1.27

635.20

5.8

9.92

ll-X, XII

4. Lyopsetta exilis

0.73

475.23

4.4

11.59

V-VIII

5 Engraulis mordax

0.67

1 ,000.70

9.2

40.03

VI-VIII

6. Protomyctophum thompsoni

0.67

173.77

1.6

3.34

lll-XII

7. Cyclopteridae spp. 1

0.51

79.70

0.7

2.10

ll-IX

8. Glyptocephalus zachirus

0.26

113 81

1.0

4.21

lll-IX

9. Hemilepidotus spinosus

0.22

29.78

0.3

3.26

ll-IV

10. Bathylagus ochotensis

0.19

131.46

1.2

4.24

lll-VIII

1The sum of the standardized numbers (number under 10 m2 sea surface) of larvae from each sample

138

RICHARDSON and PEARC Y: COASTAL AND OCEANIC FISH LARVAE

TABLE 9. — Ranges and modal lengths (mm) for dominant fish larvae in the offshore assemblage (stations 37 to 111) in 1971. Asterisks
indicate month in which average abundance per cruise was greatest. Parentheses are used where more than one modal peak occurred.

Tax a

Feb

Mar.

Apr.

May

June

July

Aug.

Sept.

Oct

Nov.

Dec.

1 Sebastes spp.

3-5-5

3 4-9

6-7-7

3-4-8*

3-4-20

3-4-14

3-3-8

3-14

2-3-14

3-5-5

2 Stenobrachius leucopsarus

4-5-5

4-5-7

4-6-6

3-7-17

4-7-18*

4-9-15

5-(8J-16

7-13-14

9-10-15

3. Tarletonbeania crenularis

7-11

5-11-15

11-15

8-12-16

4-8-20*

3-(ft"

5-8-17

9-10-15

4-11

9-10

4. Lyopsetta exilis

3-5-17'

4-14-19

5-14-21

15-(^)-22

5. Engraulis mordax

4-5-16'

4-10-25

6. Protomyctophum thompsoni

3-(g)-13

6-13-18*

5-11-16

11-13

8-12-17

5-14-16

5-14-18

5-14

7. Cyclopteridae spp. 1

8 Glyptocephalus zachirus

9 Hemilepidotus spinosus

4-5-5*
0
6*

7-10-10

8-8-9

5-20
4-8-20*

5-(lf>22

5-11

4-54

11
45
0

6-14-14
32
0

15-19
67
0

0
0
0

1 0. Bathylagus ochotensis

5-6-20

4-11-30*

15-24

13-22

quite large (>40 mm) before metamorphosis and
have an extended pelagic life (Pearcy et al. 1977).
Some taxa were taken throughout most of the year
and showed no strong evidence for a definite
spawning period, e.g., the multispecies group
Sebastes spp., T. crenularis, and Protomyctophum
thompsoni (Table 9). Intermediate to these were
species which occurred over a rather long period
but did show some indication of seasonality based
on larval lengths, e.g., Stenobrachius leucopsarus
and Bathylagus ochotensis. Cyclopteridae spp. 1
was taken over a long time period from February
through September. No trends in growth were
evident probably because it is a multispecies
group.

Distribution Trends

Peak abundances occurred 46 to 65 km offshore
for some species, e.g., L. exilis, G. zachirus, and
some Sebastes spp. (Figure 8). Spawning pre-
sumably took place near the outer shelf-upper
slope region where depths were —200-300 m.
Sebastes spp. also had an abundance peak further
offshore, possibly the result of offshore drift of
larvae.

A more oceanic distribution was characteristic
of larvae of mesopelagic fishes such as the myc-
tophids Stenobrachius leucopsarus, T. crenularis,
and P. thompsoni (Figure 8). Peak abundances
occurred at the 74- to 111-km stations with a
decline in abundance toward the coast, although a
few myctophid larvae were taken over the shelf at
18 to 28 km offshore.

Larvae of E. mordax occurred in large numbers
(147/under 10 m2) only once in 1971, at the 65-km
station in July. In 1972, peak abundance also
occurred in July but at 74, 93, and 111 km offshore
(236, 297, and 124/under 10 m2, respectively).

These peaks may be associated with spawning in
the relatively warm waters of the Columbia River
plume (Richardson 1973).

Year to Year Variation

In March-April, no major differences in
abundance or species richness occurred between
1971 and 1972 (Figure 5, Table 7). The dominant
taxa were reasonably similar, although there was
some decline in abundance in S. leucopsarus and
T. crenularis and some increase in Sebastes spp.
and Hemilepidotus spinosus in 1972.

In the May-July period, however, mean larval
abundance was higher in 1971 (Figure 5, Table 7).
Four of the five dominant taxa were more abun-
dant in 1971. A major decline occurred in S.
leucopsarus catches in 1972. A major increase in
abundance occurred inEngraulis mordax in 1972;
six times more larvae were taken than in 1971.
This may have been due to increased sampling in
Columbia River plume water (Richardson 1973).
Species richness values were similar in both years.

DISCUSSION

Coastal and Offshore Larval
Fish Distributions

There was a marked inshore-offshore separa-
tion of larval fish assemblages. Little overlap in
distribution occurred between coastal and offshore
larvae. Most (99%) larvae designated as coastal
were collected within 28 km of shore and most
(96%) larvae designated as offshore were found
beyond 28 km. The 28-km station consistently had
low larval abundances (Figure 5) and appeared to
be a transitional zone between coastal and
offshore waters. The biomass of fishes, shrimps,

139

Lyopsetta exilis

10
10
10

40
50

20
10

40
50

20
10
10
0

1 ' ' 1 1 1 1

FEB

MAR

■ A.PR

MAY
... 1 .

JUN
.1 i .

■

. JUL

1 — ttT t i

r-f-

r+-

-f-

-H

269 18 28 37 46 56 65 74 93
STATIONS

Stenobrachius leucopsarus

50r—

50 —

200 —

150-

100-

50-

350 —

300-

250-

200-

150-

100-

50-

200 —

150-

100-

50-

0 —

m 1 1 1 1 1 T

FEB .

MAR

APR

MAY

JUN

JUL

-m — I — I — I — l — l — T — T T

269 18 28 37 46 56 65 74 93
STATIONS

Glyptocephalus zachirus

E D
5 5

FEB

MAR

APR.

MAY

1 . 1

JUN

I.I.

JUL
Ml i l

i 1 l

-H

10
15
10
10
30
20
10
30
20
10
50
40
30
20
10
0

STATIONS

Tarletonbeama crenularis

FEB

MAR

j__L

APR

MAY

JUN

JUL

tti — i — i — i — T — i — T '

269 18 28 37 46 56 65 74
STATIONS

FISHERY BULLETIN: VOL. 75, NO. 1

Sebastes spp

150

100

0
350

300

250

200

150

100
50

'feb1 ' : ' ,

II 1 1

la-

MAR ,

1 1

APR

. Ill

—

MAY
... ... 1

1 1 1 1 1

JUN

1 1

1 ■

JUL
1 T 1 I I I I I I T

2 69 18 28 37 46 56 65 74
STATIONS

Protomyctophum thompsoni

<
>

'FEB' '

- MAR

■

1 1

APR

MAY

■

JUN

■ .

1 1

JUL

ii i i

-f-

I i

, — H

STATlONS

FIGURE 8. — Distribution patterns offish larvae in the offshore assemblage (stations 37 to 111) during months of peak abundance in

1971. Abundances are monthly means.

and cephalopods caught in plankton nets and
mid-water trawls was also low at this station
compared with offshore stations (Pearcy 1976).
Interestingly, this region is located over midshelf
where water depth is about 95 m rather than at the
shelf break.

Explanations for this observed phenomenon are
severalfold. Certainly peak concentrations of
coastal and offshore larvae are related in part to
the spawning location of adults. Most larvae that
are taken in plankton collections are small, have
not been in the water column for an extended
period of time, and thus occur near the area in
which they were spawned. Possibly few adult fish
spawn near 28 km offshore although data to
substantiate this are not available.

Circulation patterns also help to explain the
observed larval distributions. General seasonal
trends of currents over the continental shelf,
shoreward of the California Current, have been
described by Smith et al. (1971), Wyatt et al.

(1972), Huyer (1974), Smith (1974), Huyer et al.
(1975), and others. The predominant currents,
those of greatest velocity, are alongshore. In
winter, October through February, when winds
are predominantly from the southwest, the main
flow is northward (Davidson Current) at all
depths, with an onshore drift component at the
surface. A strong alongshore flow occurs within 28
km of the coast. In summer, May through August,
winds are predominantly from the northwest and
the main current flow is southward, with an
offshore drift component at the surface. South-
ward flow is greatest in a coastal jet located 15 to
20 km offshore. In spring, deeper water (bottom
third of the water column) flows south but at a
slower speed than the surface water (upper third of
the water column). In summer, this deeper water
flows northward. There is also a shoreward drift
component in these deeper and intermediate
waters which produces upwelling, a process which
taken place mainly within 10 to 20 km of the coast.

140

RICHARDSON and PEARCY: COASTAL AND OCEANIC FISH LARVAE

Spring (March, April) and fall (September) are
usually periods of transition with variable winds
and currents. Since the predominant currents
are north-south (perhaps 10 times stronger
than east-west), transport of larvae is also pre-
dominantly north-south rather than inshore-
offshore. Thus, the greatest concentrations of
larvae spawned in the coastal and offshore areas
would be retained along zones parallel to the coast.
Perhaps the strong north or south flow (coastal jet)
reported to occur around 15 to 28 km offshore
serves as some kind of barrier to inshore or
offshore transport of larvae. The presence of an
actual persistent front in this region, which would
help explain the faunal break at 28 km, has not
been demonstrated. The strongest front that has
been observed in this region is associated with
Columbia River Plume water, which flows south
off Oregon in summer. However, its position is not
stable and it is not present off Oregon in winter.
The presence of a surface front around 28 km
offshore has been demonstrated during upwelling
when upward sloping isopycnals break the sur-
face. This occurs only during upwelling, usually in
summer.

The extent of north-south transport is unknown.
However, evidence suggests that shoreward of 11
km, because of current reversals, the mean north-
south current velocity (alongshore flow) may be
approximately zero over the summer (Huyer 1974;
Huyer et al. 1975) and possibly also over the
winter (Huyer pers. commun.). Thus, at least in
the coastal zone, circulation patterns may explain
maintenance of larvae in specific areas with re-
spect to north-south as well as inshore-offshore. If
this apparent retention of coastal larvae in the
coastal area is persistent with respect to north-
south and east-west transport, it would seem that
other factors, most notably food, may be more
critical to early survival than transport away from
favorable areas (Hjort 1926). We have no evidence
that predators of fish eggs and larvae are con-
centrated at the 28-km station (Pearcy 1976).

Comparison of Coastal Larvae
With Yaquina Bay Larvae

Similarities exist between the species com-
position of fish larvae in the coastal area and in
Yaquina Bay (Pearcy and Myers 1974). The cot-
tids and the pleuronectids were the most speciose
families in both areas (not considering the po-
tential number of Sebastes spp.). Families in the

Bay not represented offshore were Gobiesocidae,
Gasterosteidae, and Syngnathidae. Families from
the coastal region not represented in the Bay were
Myctophidae, Anoplopomatidae, Bathymas-
teridae, and Clinidae.

Larval distributions described by Pearcy and
Myers (1974) as "bay" or "offshore" are generally
supported by the present study. Major differences
in dominant taxa were found between the Bay
fauna and the coastal assemblage in this paper.
The two most abundant Bay species, which ac-
counted for 90% of all larvae, were either not
taken in the coastal assemblage, i.e.,Lepidogobius
lepidus, or were relatively uncommon, i.e., Clupea
harengus pallasi. The only goby taken in the
coastal assemblage was Clevelandia ios, which
was designated Gobiidae type 1 from the Bay. Two
of the three taxa listed by Pearcy and Myers ( 1974)
as "bay only" types, Lumpenus sagitta and
Anoplarchus spp., were taken in the coastal
assemblage. The most abundant larvae in the
coastal assemblage, Osmeridae, Parophrys
vetulus, Isopsetta isolepis, and Microgadus proxi-
mus, did not contribute significantly to the larval
fish fauna of Yaquina Bay.

Seasonal patterns of larval abundance were
similar in both areas with the peak occurring
February to June in the Bay and February to July
in the coastal area. The egg abundance peak of
July to October in the Bay, which was primarily
attributed to northern anchovy, Engraulis
mordax, corresponds somewhat with the peak
abundance of anchovy larvae offshore in this
study. The eggs may have been spawned in the
Bay or carried into the Bay from coastal areas.
Whichever is the case, the fact that anchovy lar-
vae were not abundant in the Bay indicates de-
velopment there was unsuccessful. Additional
evidence for the lack of developmental success of
anchovy eggs and larvae in northern estuarine
areas was given by Blackburn (1973). Anchovy
eggs were taken in plankton collections in Puget
Sound from May through August during a year-
long survey. Larvae were never captured in V2-m
plankton nets (0.5-mm mesh), but a few anchovy
larvae (presumably large) and juveniles were
captured in larger tow nets (3 x 6 m mouth
diameter, 6-mm mesh cod end and 1 x 2 m mouth
diameter, 3-mm mesh cod end). In another year-
long study in the Columbia River estuary (Misi-
tano 1977), only large (22-55 mm) anchovy larvae
were taken in low numbers from October through
March. Similarly, anchovy larvae were rare in

141

FISHERY BULLETIN: VOL. 75. NO. 1

Humboldt Bay (Eldridge and Bryan 1972). Data
from this study and Richardson (1973; unpubl.
data) provide evidence that at least off Oregon
major anchovy spawning occurs and early de-
velopment is successful offshore beyond 28 km
rather than in coastal areas.

Pearcy and Myers (1974) reported Yaquina Bay
was an important spawning area only for Clupea
harengus pallasi and numerous cottids, gobies,
and stichaeids. It was, however, an important
nursery area for juvenile Parophrys vetulus,
Hypomesus pretiosus, Platichthys stellatus,
Citharichthys stigmaeus, and embiotocids. The
present study has shown that the coastal area 2 to
28 km offshore is important as a spawning area for
P. stellatus and Parophrys vetulus which utilize
Yaquina Bay estuary during part of their early
life.

Comparison With
Other Planktonic Components

Results from studies on zooplankton (Peterson
and Miller 1975, see footnote 2), pink shrimp,
Pandalus jordani, larvae (Rothlisberg 1975), and
crab larvae (Lough 1975) off Oregon indicate that
trends in seasonality and inshore-offshore dis-
tribution do not always correspond with those
found for fish larvae. These planktonic compo-
nents were all studied from the same sets of
samples (70- and 20-cm bongos, 0.571- and
0.233-mm mesh nets, collected from June 1969 to
August 1972 off Newport).

Seasonal abundance peaks of certain compo-
nents of the meroplankton, i.e., larvae of shrimp,
crabs, and fishes, appear to be similar but do not
correspond as well with those of zooplankton.
Total zooplankton (predominantly copepods)
abundance in the coastal zone is high in summer
during upwelling, with peaks usually in late June
and July, and low in winter (November-January).
A secondary winter-spring peak may develop
around February-April, but it is an order of
magnitude lower than the summer peak. Larvae
of the pink shrimp first occur in March and are in
the plankton through June. Larvae of most species
of crabs occur between February and July with
peak abundances in May and June, although a few
species are present all year; lowest abundances
are in December and January. Fish larvae are
most abundant between February and July. Those
larvae that are present during the summer

zooplankton peaks tend to be of advanced de-
velopmental stages. Since the 0.233-mm mesh
used for zooplankton did not adequately sample
smaller animals such as copepod nauplii, it may be
that peak abundances of such potential food items
actually coincide with larval abundance peaks.

Inshore-offshore distribution trends appear to
differ among the various planktonic constituents
with crab larvae being most similar to fish larvae.
Total zooplankton abundance, which is influenced
mainly by copepods, is consistently greatest (often
by an order of magnitude) in both summer and
winter at the 2-km station, grades to lows at 18
km; and according to Cross (1964), copepod
abundances continue to decrease farther from
shore. However, within the coastal zone (2-18 km)
abundance of individual species may not follow
that pattern, e.g., some may be more abundant
offshore of 2 km. Larvae of the pink shrimp first
occur (March) within 37 km of shore with greatest
concentrations at 9 to 28 km. Later (April-May)
the larvae are much more widely dispersed, oc-
curring from 2 to 111 km; abundance peaks may
occur coastally at 9 km as well as offshore at 93
km. Later in the season (June) when they are
ready to settle, peak abundances occur around 28
to 46 km offshore, apparently over favorable
settling areas. Larvae of most species of crabs
which are coastal forms as adults occur within 18
km of the coast. Highest densities are at 2 and 6
km with a dramatic decrease between 9 and 18
km. Larvae of slope species occur primarily in the
offshore area beyond 28 km. These distributions
are similar to the coastal and offshore distribu-
tions of larval fishes. However, larvae of a few crab
species which are coastal as adults are found at all
stations from 2 to 1 1 1 km and are abundant in the
coastal area as well as offshore. Larvae of at least
one of these species, Cancer oregonensis, have
been found in great abundance ( — 11 liters of
megalopa in one 15-min night surface tow) in the
neuston 65 km offshore (Richardson unpubl. data).
This type of distribution is similar to that found for
larvae of the fish Hemilepidotus spinosus, which
are also neustonic. This apparent offshore
transport of larvae spawned in the coastal zone
inside 28 km suggests that those which spend at
least part of their early life in surface waters may
be subjected to different dispersal mechanisms
than those which do not occur in the neuston.
Offshore flow of surface waters occurs during the
upwelling season, providing a mechanism of
transport.

142

RICHARDSON and PEARCY: COASTAL AND OCEANIC FISH LARVAE

Comparison to the Northeast Pacific

Direct comparisons between results from this
study and most previous reports on larval fishes in
the northeast Pacific with respect to species
composition, seasonality, and inshore-offshore
distribution patterns are difficult to make for
several reasons. Cruise tracks differed with re-
spect to distance of stations from shore and
proximity of stations to each other. Duration of
sampling effort and types of gear used were not the
same. Aron's (see footnote 4) data came from
mid-water trawl samples taken on long oceanic
cruise tracks between southern California and
southwest Alaska from July through October.
LeBrasseur's (see footnote 7) report was based on
mid-water trawl and NORPAC net collections
taken in the northeast Pacific at a broad array of
stations from 1956 to 1959. Waldron's (1972)
results, excluding Puget Sound, came from meter
net collections made in a grid pattern with
transects on each degree of latitude between 42°
and 51° (Oregon to British Columbia) and stations
extending from the 55-m isobath to 550 km
offshore. His samples covered only a 1-mo period
in April and May. Naplin et al. (see footnote 8)
reported on samples collected with 60-cm bongos
along three widely spaced transects off
Washington and British Columbia in October and
November. Richardson's (1973) data came from
70-cm bongo, meter net, and mid-water trawl
samples collected off Oregon at a wide array of
stations from May to October. However, some
trends are evident.

The most abundant, most dominant, and most
frequently taken taxa in the above mentioned
studies (which included few or no samples from
nearshore areas) were myctophids, mainly
Stenobrachius leucopsarus, Tarletonbeania
crenularis, and sometimes Protomyctophum
thompsoni (andDiaphus theta in southern areas),
and scorpaenids, mainly Sebastes spp. (particu-
larly over shelf and slope areas). This is similar to
the offshore assemblage in this study. Richardson
(1973) also found Engraulis mordax to be im-
portant as it was in our offshore assemblage.
Those studies which included samples from shelf
areas showed increased importance of pleuronec-
tid larvae, e.g., Isopsetta isolepis, Parophrys
vetulus, Platichthys stellatus, and Psettichthys
melanostictus (Waldron 1972). None of the above
studies included intensive sampling in the
nearshore zone (e.g., within 9 km of the coast) to

allow detailed comparison with our coastal
assemblage. However, Aron (1959) stated that
large numbers ofcapelin,Ma//otas uillosus, larvae
were taken in northerly inshore waters. Also,
osmerids and Ammodytes hexapterus were among
the 10 most abundant larvae taken in Waldron's
(1972) samples. Richardson (1973) showed that
osmerid larvae were taken in moderate numbers
at nearshore stations although they were not top
dominants when all samples were combined. More
recent samples from 12 transects 2 to 56 km off
Oregon (Laroche and Richardson16) have shown
that osmerids, Parophrys vetulus, I. isolepis,
Microgadus proximus, and some cottids are
dominant in the coastal waters from the Columbia
River to Cape Blanco in spring months, which is
similar to our coastal assemblage.

The only available information on seasonality
based on one or more years of data was presented
by LeBrasseur (see footnote 7). The greatest
number of larvae per sample (1.0) was taken in the
March-May quarter, with 0.3 in June- August, 0.1
in September-November, and 0.05 in December-
February. The May-October data discussed by
Richardson (1973) showed an abundance peak in
May in 1-m net samples and a peak in July- August
in bongo and mid-water trawl samples with low
abundances after August. The data of Naplin et al.
(see footnote 9) showed low abundances (except for
myctophids) and low numbers of species in
October-November. These trends are similar to
those found in this study.

No previous studies have demonstrated actual
coastal and offshore assemblages of fish larvae
although mention has been made of a break in
species composition, abundance, and frequency of
occurrence between shelf and oceanic areas. Aron
(1959) stated that, in oceanic regions, the larvae of
inshore fishes disappeared and myctophid larvae
became common. LeBrasseur (see footnote 7)
indicated larvae were taken in 5% of the samples
within 100 miles of the coast but in only 1% of the
samples from farther offshore. Waldron (1972)
reported a greater number of larvae were taken
inside the 914-m isobath than beyond it. More
recent data (Laroche and Richardson see footnote
16) have shown that coastal and offshore as-
semblages offish larvae, similar to those described
in this paper for the mid-Oregon coast, occur along

16Laroche, J. L., and S. L. Richardson. Spring patterns of larval
fish distributions from the Columbia River to Cape Blanco,
Oregon, 1972-1975, with emphasis on English sole, Parophrys
vetulus. Manuscr.

143

FISHERY BULLETIN: VOL. 75, NO. 1

the entire Oregon coast from the Columbia River
to Cape Blanco at least in spring (March-April).
Thus it seems likely that similar species com-
position, seasonality, and inshore-offshore as-
semblages of larval fishes may occur over a much
broader shelf-slope area in the northeast Pacific.

ACKNOWLEDGMENTS

We thank the many people who helped with
collecting, sorting, identifying, enumerating,
measuring, and data reduction. R. Gregory Lough
and Peter Rothlisberg were responsible for col-
lecting most of the samples. Elbert H. Ahlstrom,
James Blackburn, Carl Bond, Jean Dunn, Joanne
Laroche, April McLean, H. Geoffrey Moser, Karl
Niggol, Sharon Roe, Elaine Sandknop, and
Kenneth Waldron have all helped at one time or
another with larval fish identifications. Wayne
Laroche provided names for our agonid larval
types. James Rybock did the preliminary analysis
of the vertical distribution data for a class project.
Michael Richardson gave much advice on data
analysis and offered many helpful comments.
Jane Huyer provided information on physical
oceanography off the Oregon coast. This research
was supported by NOAA (U.S. Department of
Commerce) Sea Grant Institutional Grant No.
04-6-158-44004. Ship operations support was
provided by the National Science Foundation.

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RICHARDSON and PEARCY: COASTAL AND OCEANIC FISH LARVAE

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145

BIOLOGY OF OFFSHORE HAKE, MERLUCCIUS ALBIDUS,

IN THE GULF OF MEXICO1

Bennie A. Rohr and Elmer J. Gutherz2

ABSTRACT

Biological data of the offshore hake, Merluccius albidus, in the Gulf of Mexico are presented and
compared with those of other species of Merluccius . The species has been found from Georges Bank to
Rio de Janeiro, Brazil, in 192 to 1 , 1 70 m. In the Gulf of Mexico it occurs in greatest abundance in the De
Soto Canyon area in depths of 350 to 1,000 m.

Merluccius albidus are segregated by size and sex on the continental slope with juveniles, males, and
young females found in depths less than 550 m and large, mature females found in depths exceeding
550 m. Mature males were smaller than females and grew at a reduced rate following the onset of
sexual maturity.

Males and young females were found on the upper slope and older mature females found on the lower
slope. Spawning appeared to take place on or near the bottom in 330 to 550 m. Spawning in the southern
latitudes appears to occur from late spring to early fall and may be more protracted at the southern
limits of its range. Eggs and the earliest larval stages have been described only for M. albidus from New
England.

Merluccius albidus are opportunistic feeders preying primarily on fishes, squid, and crustaceans.
Fishes make up about 75% of their diet, with species of Merlucciidae and Myctophidae consumed most
frequently. Prey species exhibited diel movement, but the similarity between day and night catch rates
of M. albidus suggests that offshore hake do not move far off the bottom in pursuit of prey.

Density estimates suggested a small population of M. albidus in the northern Gulf of Mexico.
Merluccius albidus stocks in 370 to 730 m on the De Soto Canyon slope north of Tampa, Fla., are
estimated to be a minimum of 3.3 x 106 kg.

Species of the genus Merluccius are distributed
worldwide in temperate and tropical waters but
are exploited primarily in temperate seas. Aspects
of their biology, distribution, and utilization have
been reported by numerous authors (Hickling
1927, 1933; Bigelow and Schroeder 1953, 1955;
Graham 1956; Fritz 1960; Lozano Cabo 1965;
Marak 1967; Botha 1969, 1971; Grinols and
Tillman 1970; and Nelson and Larkins 1970).
Northern Gulf of Mexico Merluccius are consid-
ered to be divergent forms of M. albidus (Karnella
1973). Several of the above authors have com-
mented on the similarity in life history patterns of
various species of Merluccius. Offshore hake, M.
albidus, display some of these same patterns,
indicating that aspects of their life histories are
similar to those documented for other species.

Biological data concerning M. albidus are
sparse. Those reported in this paper are limited
primarily to the Gulf of Mexico. This study is a

'Contribution No. 453, Southeast Fisheries Center, Pas-
cagoula Laboratory.

2Southeast Fisheries Center Pascagoula Laboratory, National
Marine Fisheries Service, NOAA, P.O. Drawer 1207, Pascagou-
la, MS 39567.

Manuscript accepted June 1976.

FISHERY BULLETIN: VOL. 75, NO. 1, 1977.

composite of published accounts, data acquired
during resource assessment, gear evaluation and
general exploratory cruises, and results of
biological studies conducted by personnel of the
Southeast Fisheries Center Pascagoula Labora-
tory, National Marine Fisheries Service (NMFS),
NOAA.

MATERIAL AND METHODS

Specimens were collected with a variety of bot-
tom trawls (Table 1) equipped with mud rollers,
loop chain, floats, and usually a tickler chain. The
larger trawls (38 to 60 m headrope) were fished
with wooden bracket doors and ground cables
whereas the smaller trawls (12 and 22 m head-
rope) utilized wooden chain doors. Mesh size on the
larger trawls was 7.6 cm in the wings and body, 5.1
cm in the throat, and 4.5 cm in the cod end; smaller
trawls had 5.1-cm mesh throughout with 3.8 cm in
the cod end. In October 1971, a 22-m trawl with a
1.3-cm inner liner was used to collect juvenile M.
albidus. Rough bottom areas were fished with a
12-m flat or semiballoon trawl and smooth areas
with larger trawls (22 to 68 m).

147

FISHERY BULLETIN: VOL. 75, NO. 1

TABLE 1. — Trawling gear used by the RV Oregon II during slope
fishery surveys in the Gulf of Mexico and Caribbean Sea from
June 1969 through September 1973.

TABLE 2. — Gonad classification code — modified from Nikolsky

(1963).

Trawl size

(headrope length)

(m) (feet)

Door size
(length x width)
(m) (feet)

Type of door

12
22
38

125

130

150

191

204

224

2.4 x 1.03
3 x 1.12
3 x 1.22

3 x 1.22

3 x 1 .22

3 x 1.22

8 x 3.33
10 x 3.67
10 x 4

10x4

10 x 4

10x4

10 x 4

Wooden chain
Wooden chain
Iron bound wooden

bracket
Iron bound wooden

bracket

Specimens were measured at sea to the nearest
millimeter standard length (SL). Additional
specimens were frozen for processing ashore, and
were measured in standard, fork, and total lengths
(SL, FL, and TL) for computation of a conversion
curve and were also processed for length-weight
relationship, gonad maturation, and stomach
content data. Gonad maturation stages were
classified by a scheme modified from that by
Nikolsky (1963) and are listed in Table 2. Ovaries
were weighed to the nearest 0.1 g. Otoliths re-
moved from selected specimens (one specimen per
centimeter SL) were prepared and evaluated
following Jensen (1965). Morphometric and
meristic measurements were taken as defined by
Ginsburg (1954).

Age-class lines were computed using techniques
described by Harding (1949) and Cassie ( 1954) and
compared with ages determined from length-
frequency data.

Weights were recorded to the nearest ounce on
specimens larger than 200 mm SL and to the
nearest 0.1 g on smaller fish. The method of least
squares using the log transformation of the gen-
eral equation W = aLb was used to compute the
length-weight equations for males, females, and
sexes combined.

The sample design for RV Oregon II cruise 27
allowed for equal effort per stratum regardless of
stratum size, because distributional patterns and
abundance levels of M. albidus were undefined.
The sample area (Figure 1) on the De Soto Canyon
slope north of Tampa, Fla., was divided into four
90-m depth strata ranging from 370 to 730 m.
Each stratum was then further subdivided into 2.5
x 15 nautical mile sample sites (12,874 hectares
per site). The entire sampling area of 84 sites

U-1

Female:
F-2

F-3

F-4

F-5

F-6

Male:
M-2

M-3

M-4

M-5
M-6

Gonads undeveloped, vestigial tubes, sex determination impossible
by gross examination

Immature gonads, sex determinable by gross examination, gonads
very small, uninflated

Developing gonads, small yellow or white with no eggs visible to the
naked eye

Maturing gonads, filled with opaque yellow to yellowish-orange eggs
detectable by the naked eye

Ripe gonads, ovaries with translucent yellowish-white to whitish-
green eggs easily expelled from the genital opening by lateral pres-
sure on the gonads

Spent gonads, ovaries collapsed and bloodshot with some eggs being
reabsorbed

Immature gonads, sex determinable by gross examination, testes

very small, uninflated

Developing gonads, inflated to the same degree as those of F-3

females and white or whitish-pink in color

Maturing gonads, inflated to same degree as those of F-4 females and

milky white without free running milt

Ripe gonads, fully developed with free running white milt

Spent gonads, collapsed and bloodshot

totaled 1,081,416 hectares. Five sample sites were
randomly selected within each 90-m depth
stratum from a number table; however, only four
sites were sampled in stratum 4 due to a mal-
function of the trawl. No special consideration in
site selection was given to latitude.

Each sample site was fished with a 40-m trawl
(Table 1) for 5 h at 3 knots with a 2.5:1 scope ratio
(i.e., 2.5 m of wire out for each meter of depth).
Drag distance was variable because of changes in
the surface and bottom currents. Area swept in
hectares per drag was computed by measuring the
distance between the starting and ending point of
each tow and multiplying by a conversion factor.
An XBT (expendable bathythermograph) probe
was dropped at the start and finish of each station.

Standing stock estimates were computed using
an "area-swept" method. This method is computed
as follows:

SS, = (Pwi)(Ai)

(1)

where SS, = standing stock estimate in the ith

area

Pwi — average population expressed as

kilograms per hectare in the ith area

A, = total bottom area within the ith

area.

SStot = S ss,

; = 1

where SSt , = total standing stock estimate

'tot

expressed as kilograms

148

ROHR and GUTHERZ: BIOLOGY OF MERLUCCIUS ALB1DUS
8T 87

86°

FIGURE 1.— Northeastern section of the Gulf of Mexico showing stations on De Soto Canyon slope north of Tampa, Fla., made during the
June 1971 finfish survey and the Mississippi Delta slope; insert of entire Gulf of Mexico identifying all stations between 1950 and 1971
where the catch rate of Merluccius albidus exceeded 14 kg/h.

SSt = the computed standing stock
estimates for each area.

Confidence intervals were calculated using the
weighted pooled variance method described by
Snedecor and Cochran (1967):

S~ / w? s,2/n,

'tot

(2)

where Si == standard error of the mean

not

xtot = mean density (kilograms/hectare)

weighted by area
wt = weighting factor based on sample

size, i.e., wt = nJN
st2 = variance of density estimate for ith

stratum.

The weighted pooled variance was used to re-
duce the variation associated with different sam-
ple sizes within each stratum.

DISTRIBUTION AND ABUNDANCE

The range of M. albidus in the western Atlantic
extends from lat. 41°N off Georges Bank (Bigelow
and Schroeder 1955) to the Orinoco Delta and
possibly to the vicinity of Rio de Janeiro (Cervigon
1966). Bigelow and Schroeder (1955) reported a
depth range of 92 to 1,170 m for M. albidus on the
New England slope with approximately 75% of the
population residing in depths of 185 to 550 m.
Merluccius albidus are seldom caught by com-
mercial hake fishermen in New England (Fritz

149

FISHERY BULLETIN: VOL. 75, NO. 1

1960), suggesting a low population level, unavail-
ability to the fleet, or lack of recognition by the
fishermen. However, mixed commercial con-
centrations of M. albidus and M. bilinearis were
found south of Hudson Canyon on the edge of the
shelf by the RV Albatross III (Edwards et al. 1962)
and on Georges Bank by West German stern
trawlers (Mombeck 1971).

Exploratory fishing data from the Pascagoula
data files showed that M. albidus composed 25% of
the total finfish available to trawl gear between
350 and 1,000 m on the Mississippi slope and 60%
between 450 and 730 m on the west Florida-De
Soto Canyon slope. Several large catches con-
taining individual fish weighing in excess of 0.45
kg have been made by NMFS vessels.

In the Gulf of Mexico, M. albidus have been
taken at depths of 142 to 1,100 m. Between 1950
and 1971, NMFS vessels caught M. albidus at 73%
of all trawl stations in depths of 182 to 1,100 m.

Relative apparent abundance of M. albidus in
the Gulf of Mexico was established by computing
catch rates based on historical fishing records.
Highest concentrations occurred in the northern
Gulf between Tampa, Fla., and the Mississippi
Delta. Prior to the M. albidus assessment cruise in
June 1971, catch rates of 14 kg/h (31 pounds/h) or
greater occurred at only 37 Gulf of Mexico stations
(Figure 1) of which 78% had catch rates less than
50 kg/h. These stations are primarily in the
northeast quadrant of the Gulf of Mexico in depths
of 370 to 930 m (Figure 1). Maximum catch rates
recorded for this period in the Gulf of Mexico are as
follows: north Gulf, De Soto Canyon, 640 m, 161
kg/h; east Gulf, off Tampa, 490 m, 284 kg/h; west
Gulf, east of Brownsville, Tex., 430 m, 31 kg/h;
south Gulf, east of Veracruz, Mexico, 540 m, 22
kg/h; and north of Campeche Bank, 550 m, 20
kg/h.

Nineteen 5-h trawling stations were completed
on the De Soto Canyon slope in June 197 1 to obtain
biological data and estimate the size of the M.
albidus population. Catch rates varied from 5.7 to
144.0 kg/h in depths of 370 to 730 m and averaged
38.7 kg/h (Figure 1).

Highest catch rates of M. albidus after June
1971 were 12.5 kg/h in 440 m on the western slope
of De Soto Canyon, 15.5 kg/h in 550 m south of Dry
Tortugas, and 58.5 kg/h in 420 m on the De Soto
Canyon east slope. These catch rates may be arti-
ficially low, as the trawls used were not rigged
specifically for catching M. albidus. Abundance in
the western and southern Gulf of Mexico is

unknown due to the considerable area of un-
trawlable bottom off Texas, western Louisiana,
and in the Gulf of Campeche.

Merluccius albidus were caught at depths of 200
to 795 m in the Caribbean Sea including the insu-
lar slopes of the Antilles. During a 1970 trawl
survey on the Caribbean slope between Belize and
Aruba, it was taken most frequently at depths of
450 to 630 m north of Aruba. Caribbean trawling
records give no indication of any significant
concentrations of M. albidus. However, Cervigon
(1964) reported that M. albidus may be of
economic importance off Venezuela in depths
greater than 370 m.

RELATION OF DEPTH TO SIZE AND SEX

Studies have shown that size increases with
bottom depth in various species of hake (Grinols
and Tillman 1970). Rohr (1972) showed that M.
albidus segregates by size and sex on the conti-
nental slope in the Gulf of Mexico (Figures 2, 3).
Juveniles of both sexes, young adult females, and
adult males inhabit the upper slope (depths <550
m) while larger, mature females are concentrated
on the lower slope (depths >550 m). This pattern is
clearly demonstrated when plotting the male-
female ratio vs. depth (Figure 3).

A similar distributional pattern of M. albidus
was reported on the Honduran-Panamanian slope
by Bullis and Struhsaker (1970) and observed by
the senior author on both the western and south-
ern Caribbean slopes from Belize to Aruba.

W. i.o-

S 0.5-

640
METERS

FIGURE 2. — Average weight of individual Merluccius albidus vs.
depth for 487 trawl stations in the Gulf of Mexico.

150

ROHR and GUTHERZ: BIOLOGY OF MERLUCCWS ALBIDUS

2 2.0-

460 550

METERS

FIGURE 3. — Ratio of male to female Merluccius albidus de-
creases with increasing depth.

=- 1.0-

DE6REES CENTIGRADE

FIGURE 4. — Average weight of individual Merluccius albidus vs.
bottom temperature for 278 trawl stations in the Gulf of Mexico.

An increase in size of M. albidus with increasing
depths and decreasing temperature was observed
in the present study (Figures 2, 4; Table 3).

REPRODUCTION

Fecundity data of M. albidus were not collected;
however, a partially spent 680-mm SL female
taken on the De Soto Canyon slope in August 1970
yielded an estimated 340,000 greenish-white eggs
weighing 340 g. Advanced eggs in the ovaries of M.
productus ranged from 80,000 in small, 350 mm
SL, to 496,000 in large, 690 mm SL, specimens
(MacGregor 1966). Since the estimated number of
eggs in the specimen of M. albidus is somewhat

similar to that of M. productus, the fecundity of the
two species may be similar.

A spawning period extending from late spring to
early autumn is hypothesized forM. albidus in the
Gulf of Mexico and Caribbean Sea. Ripe fish were
observed as early as May and as late as October.
Running ripe males and females were taken
together in September 1973 on the Mississippi
Delta and De Soto Canyon slope (Table 4).
Females caught in February were in an advanced
resting stage, i.e., gonad maturation stage 4.
Spawning occurs in New England from April to
July (Colton and Marak3). Some species of Mer-
luccius spawn throughout much of the year,
although most have a short spawning period
varying in time for individual species (Grinols and
Tillman 1970).

Gonad maturation data suggest that spawning
occurs near the bottom in depths of 330 to 550 m.
Limited numbers of ripe fish were taken during
cruises which surveyed both the upper and lower

3Colton, J. B., Jr., and R. R. Marak. 1969. Guide for identifying
the common planktonic fish eggs and larvae of continental shelf
waters, Cape Sable to Block Island. Biol. Lab., Woods Hole,
Mass. Lab. Ref. 69-9, 15 Sept. 1969.

TABLE 4. — Date, area, and depth at which ripe Merluccius
albidus have been collected in the Gulf of Mexico.

Depth

Date

Area

(m)

Females

June 1970

Gulf of Campeche

360-730

Aug. 1974

Central north Campeche Bank slope

570-550

Aug.,

Sept. 1970

De Soto Canyon

380-770

June 1971

East De Soto Canyon and west Florida

slope

370-730

Oct. 1971

East Mississippi Delta slope and west De

Soto Canyon slope

550-730

May 1973

Mississippi Delta-west De Soto Canyon

slope

460

May 1973

Dry Tortugas slope

372

Sept. 1973

Mississippi Delta-west De Soto Canyon

slope

330-460

Males

Aug. 1970

Dry Tortugas slope

550

Aug. 1970

West Florida slope oft Tampa, Fla.

275

Aug. 1970

East De Soto Canyon slope

390

May 1973

Mississippi Delta-west De Soto Canyon

slope

357

May 1973

Dry Tortugas slope

350-550

Sept. 1973

Mississippi Delta-west De Soto Canyon

slope

330-460

TABLE 3. — Range and mean fishing depths, bottom temperatures, lengths, and weights of Mer-
luccius albidus sampled on the De Soto Canyon slope north of Tampa, Fla., in June 1971.

Depth (m)

Temperature (°C)

Number

fish
sampled

Standard length (mm)

Weight (g)

Stratum

Range

Range X

1
2
3
4

370-459
460-549
550-639
640-730

409
500
577
686

9.3-1 1 .0
7.8- 9.6
5.6- 8.5
5.6- 6.7

10.1
8.3
6.9
6.3

497
494
488
392

47-455
215-520
268-562
313-575

234
299
389
424

1- 985 158

42-1 ,550 360
265-1,960 624
315-2,070 818

151

FISHERY BULLETIN: VOL. 75, NO. 1

slopes. Ripe males were not found at depths grea-
ter than 550 m (Figures 5, 6, 7). Since few ripe fish
were caught by bottom trawls, it is possible that
spawning occurs at some distance above the
bottom. First time spawners appear to move down
slope to spawn whereas the older maturing
females (spawning for their second or more times)
were found lower on the slope and moved up the
slope into the spawning area.

Few spent males or females were taken during
this study. Spent females may move down the
slope from the spawning area to recover and then
gradually move back up the slope to enter a rest-
ing stage. Alternatively, after spawning they
might immediately move onto the upper slope in
depths of 180 to 360 m to feed and recover, and
finally move back into depths greater than 360 m
to enter the resting stage.

obzflm

□

MALES
FEMALES
JUVENILES
N=636

280

370

460 550
METERS

640

730

FIGURE 5. — Distribution of male, female, and juvenile Merluc-
cius albidus by depth on the east Mississippi Delta and west De
Soto Canyon slope in October 1971.

MALES
N=89

20-

10-
0

g 50 H

£ 40

10
0

STAGES 2-3

^
^

1 I i
STAGE 4

*"1 ■

10
0

30-

10
0

FEMALES
N=389
STAGES 2-3

STAGE 5

|\wy ^ y ■.■. «j

STAGE 6

pr^p^

280

460 640

METERS

280

460 640

METERS

FIGURE 6. — Gonad maturation stages of Merluccius albidus by
depth on the west Florida-De Soto Canyon slope in June 1971.

152

20-

10-
0

MALES N=II0

STAGES 2-3

rr-rv NSN^fSSS)-

FEMALES N=I33

40-
30-

STAGES 2-3

20-

10-

S^^ ,

STAGE 4

280

460 640

METERS

280

460 640

METERS

FIGURE 7. — Gonad maturation stages of Merluccius albidus by
depth on the east Mississippi Delta and west De Soto Canyon
slopes in October 1971.

European, Argentinean, and Pacific hake are
reported to feed ravenously after spawning. If M.
albidus follows this pattern, it would probably
move up to the shelf edge following spawning, as a
richer supply of food is available in this area.
Additional deepwater samples are needed before
this hypothesis can be tested.

Spawning males and females were found to-
gether at depths of 330 to 460 m but only one spent
male and female were caught in the same tow.

Merluccius albidus may spawn later in the
Caribbean than in the Gulf of Mexico. In
November 1970, 11 of 21 females collected off
Aruba in 604 m were in spawning condition. Spent
females were also found in November 1970 in
depths of 550 to 730 m off Colombia. The depth
distribution of females in the Caribbean appears
to be similar to that in the Gulf of Mexico; but data
are very limited. Only one male was collected from
the Caribbean.

Merluccius albidus are also distributed on the
slope in relation to gonad maturation stages.
Eighty-eight percent of the juveniles occurred in
370 to 460 m. They were observed at other times
and at other geographic sites in the Gulf of Mexico
and Caribbean Sea, but always on the upper slope
between 180 and 460 m. It is possible that the
distribution of juveniles seen in October is similar
to their overall distributional pattern.

The distribution of gonad stages of male and
female M . albidus on the Mississippi Delta and De
Soto Canyon slopes in 1971 are shown in Figures 6
and 7. Males were found primarily on the upper

ROHR and GUTHERZ: BIOLOGY OF MERLUCCIUS ALBIDUS

slope ( 280 to 550 m) during both June and October.
Only 1.3% of all males taken were caught in
depths exceeding 550 m, with 613 m being the
maximum depth at which males were taken.
Females were found throughout the depth ranges
surveyed (Figures 5, 6, 7).

Location of M. albidus on the slope appeared to
be dependent on gonad maturation stage and size
of individuals. In 1971, stage 4 males dominated at
all depths where males were collected except in
280 to 370 m; neither ripe (stage 5) nor spent
(stage 6) males were taken (Figures 6, 7). In 1973,
the data showed a predominance of stage 4 males
though a few ripe and spent males were found
(Table 5). Males, regardless of maturation stage,
were always taken in depths less than 550 m. The
predominance of stage 4 male M. albidus in the
autumn of 1971 and 1973 (Figure 7, Table 5)
suggests that stage 4 is an advanced resting stage,
with these fish not spawning until the following
spring. The stage 4 males were probably in the
spawning cycle in the spring of 1971 and 1973
(Figure 6, Table 5) and would have spawned some
time during the summer based on a spring-
summer spawning period for M. albidus.

Female M. albidus of all sizes and maturation
stages were found throughout the depth range
surveyed. Young females mixed with males and
juveniles on the upper slope, but larger females
predominated on the lower slope. Lower slope
females, larger than 250 mm SL, caught in the
autumn were in the gonad resting stage and would
not spawn until spring or summer. Females in
stages 2-4 were most frequently caught as they
were in the prespawning and/or resting stages.
The paucity of ripe or spent females caught in
trawls is evident from Figures 6 and 7 and Table 5.
The few ripe and spent females (stages 5, 6) caught
in 1973 (Table 5) were partially a result of the
depths at which fishing operations were con-
ducted, as few stations exceeded 600 m. Ripe and
spent female M. albidus were found lower on the
slope than were stages 2-4.

Eggs and early larval stages (first 84 h) of M.
albidus off Martha's Vineyard (New England)
were described by Marak (1967), but larvae larger
than 4 mm SL are unreported. Egg and early lar-
val development of M. albidus in the Gulf of
Mexico and the tropical Atlantic may be similar to
that off New England, although hatching may be
more rapid in warmer latitudes than the 6 to 8
days reported by Marak (1967). Larvae reared by
Marak (1967) ranged in length at hatching from
3.05 to 3.75 mm, averaging 3.5 mm and were rel-
atively undeveloped. The yolk was small and was
rapidly assimilated after hatching, thereby neces-
sitating early initiation of feeding.

FOOD HABITS

All hake species are opportunistic feeders
(Grinols and Tillman 1970). In the Gulf of Mexico,
M . albidus feed on a large variety of items found on
and off the bottom (Table 6).

A feeding pattern based on adaptive zones of
prey species (i.e., epipelagic, mesopelagic, and
benthic) suggests that hake feed primarily on ben-
thic and mesopelagic organisms (Table 7). The
lack of a day-night differential in bottom trawl
catch rates (Table 8) suggests that M. albidus feed
on or near the bottom since a differential would be
expected if M. albidus moved well off the bottom to
feed.

Merluccius albidus apparently feed at about the
same rate throughout the day except near dawn
(0500-0700, Table 9). The higher incidence of food
in the stomach during daylight hours corresponds
to the time when the mesopelagic fauna are closer
to the bottom. This hypothesis is reinforced as 81%
of the myctophids were found in stomachs from
fish caught during daylight hours (0700-1800),
and in only 1% of the stomachs from fish caught at
dusk (1800-2000). The mesopelagic fauna leaves
the bottom at dusk and moves higher in the water
column, thus becoming unavailable as prey to the
hake. Stomachs from specimens caught at night

TABLE 5. — Maturation stages in Gulf of Mexico Merluccius albidus for May and September
1973 listed as percentage of occurrence.

May

September

Mississippi Delta-west

De Soto Canyon slope

344-730 m

Dry Tortugas slope
353-595 m

Mississippi Delta-west
De Soto Ci

anyon slope
330-503 m

Gonad
state

Females
N = 1 ,069

Males
N =59

Females
N =323

Males
N =525

Females
N = 2,083

Males
N = 1 ,430

2-3

43.3

6.8

96.6

6.5

65.3

7.2

55.7

88.1

2.2

66.1

32.5

79.0

0.4

5.1

1.2

20.4

1.6

12.1

0.6

0.0

7.0

0.6

1.7

Total

100.0

100 0

100.0

153

FISHERY BULLETIN: VOL. 75, NO. 1

TABLE 6. — General systematic list of prey species identified from
the stomachs of 649 Merluccius albidus. List is arranged al-
phabetically.

TABLE 7. — Types of identified prey, according to the adaptive life
zone they inhabit, from the stomachs of 649 Merluccius albidus.

FISHES
Apogonidae

Epigonus pandionus

Synagrops sp.

Synagrops bella

Synagrops spinosa
Argentinidae

Argentina striata
Ariommidae

Ariomma sp.

Ariomma bondi
Bathyclupeidae

Bathyclupea sp.
Brotulidae

Dicrolene intronigra

Monomitopus agassizi
Carangidae

Trachurus lathami
Chauliodontidae

Chauliodus sloani
Chlorophthalmidae

Chlorophthalmus agassizi
Clupeidae

Etrumeus teres
Evermanellidae

Evermanella sp.
Gempylidae

Nesiarchus nasustus

Scombrolabrax heterolepis
Gonostomatidae

Gonostoma sp.

Gonostoma elongatum

Mauroluccius mulleri

Polymetme corythaeoia

Triplophos hemingi

Yarella blackfordi
Macrouridae

Bathygadus macrops

Coelorhynchus carminatus

Coryphaenoides colon

Gadomus arcuatus

Gadomus longifilis

Hymenocephalus italicus

Malacocephalus sp.

Nezumia sp.

Nezumia aequalis
Malacosteidae
Melanostomatidae
Merlucciidae

Merluccius albidus

Steindachneria argentea
Myctophidae

Lampadema luninosa

Neoscopelus macrolepidotus

Nomeidae

Cubiceps sp.

Psenes sp.
Percophididae

Bembrops sp.

Bembrops gobioides
Polymixidae

Polymixia lowei
Squalidae

Etmopterus schultzi
Sternoptychidae
Stomiatidae
Trichiuridae
Unidentified fishes
MOLLUSKS
Limpets

Fissularidae
Squids

///ex sp.

///ex illecebrosus

Oregoniateuthis springeri

Pholidotheuthis adami
Unidentified squids
CRUSTACEANS
Caridea
Euphausiacea
Euryonidae

Steromastis sculpta
Glyphocrangonidae

Glyphocrangon sp.

Glyphocrangon alispina
Nematocarcinidae

Nematocarcinus sp.
Oplophridae

Notostomus sp.
Pandalidae

Plesionika acanthonotus
Pasiphaeidae

Pasiphaea sp.
Penaeidae

Aristeus antillensis

Benthysicymus sp.

Hymenopenaeus sp.

Hymenopenaeus debilis

Hymenopenaeus robustus

Parapenaeus sp

Penaeopsis megalops
Unidentified crustaceans
Unidentified shrimps
UROCHORDATA
Pyrosomidae

Pyrosoma sp.

Adaptive
zone

Taxa

Fre-
quency

Percent

total

frequency

Epipelagic

Carangidae and Clupeidae

1.4

Subtotal

1.4

Mesopelagic

Myctophidae

16.5

Miscellaneous fishes

3.9

Squids

18.7

Euphausiacea

2.0

Miscellaneous Crustacea

0.8

Pyrosomidae

0.2

Subtotal

214

42.1

Benthic

Steindachneria argentea

142

28.0

Apogonidae

4.1

Ariommidae

3.3

Macrouridae

3.3

Merluccius albidus

2.4

Trichiuridae

2.2

Miscellaneous fishes

5.9

Penaeopsis megalops

4.1

Penaeidae

1.4

Miscellaneous crustaceans

1.4

Mollusks

0.4

Subtotal

287

56.5

Grand total

508

100.0

TABLE 8. — Catch rates of Merluccius albidus and trawl effort by
time of day on the slope in the Gulf of Mexico during May 1973.

Item

Twilight

Day 0500-0659 Night

0700-1759 1800-1959 2000-0459

Average no. of fish/hour
Hours fished

15.2

60.75

13.6
34.00

14.5
54.00

TABLE 9. — Frequency of Merluccius albidus stomachs contain-
ing food, from the Gulf of Mexico in 330 to 730 m during May and
September 1973, in 4-h intervals.

Time of

No. fish

Number stomachs

Percent frequency

day

sampled

containing

food

stomachs with food

0000-0300

566

9.9

0400-0700

1,121

5.4

0800-1100

679

12.4

1200-1500

724

8.8

1600-1900

963

117

12.1

2000-2300

1,315

131
513

10.0

Total

5,368

9.6

contained primarily members of the resident
benthic community.

This feeding behavior is in contrast to that
described for other species of Merluccius. Initia-
tion of feeding after sunset has been suggested for
M. productus (Alton and Nelson 1970) and for all
hake (Hickling 1927).

Most offshore hake caught during the survey
regurgitated due to changes in hydrostatic pres-
sure with only 8.2% (651 of 7,944) of those stom-
achs examined containing food. Fishes composed
the major portion of the diet of M. albidus, followed
by squid and crustaceans (Table 7). Fishes were
exclusively present in about 75% of the stomachs

examined and either singularly or together with
crustaceans and squid in about 80% of these
stomachs. Twenty-nine percent of the fishes eaten
were mesopelagic and 69% were benthic.

Thirty-two identifiable prey species from M.
albidus stomachs are listed in Table 6 by familial
groups. Steindachneria argentea (Merlucciidae)
was found most frequently, followed by species of
Myctophidae (Table 7). About 2% of the specimens
examined had been feeding on juvenile M . albidus
indicating some degree of cannibalism.

Benthic penaeid and caridean shrimp were the
dominant crustaceans found in stomachs of M.
albidus. Penaeopsis megalops was the dominant

154

ROHR and GUTHERZ: BIOLOGY OF MERLVCCIUS ALBIDUS

penaeid shrimp and suggests selective feeding by
M. albidus. Stomachs of M. albidus contained a
higher frequency of P. megalops than Hymen-
openaeus robustus even at those stations where//.
robustus was more abundant. Abundance of these
two species was based on the catch rates when they
were taken together. This preference may indicate
a feeding migration to depths of greater abun-
dance of P. megalops.

Merluccius albidus are active predators with
type and size of prey varying as follows: juveniles
(90 to 149 mm SL) contained primarily shrimp 29
to 45 mm TL with a few fragments of fishes and
squid; maturing adults (150 to 299 mm SL)
contained a variety of fishes 100 to 240 mm TL,
with one 320-mm TL trichiurid, crustaceans 40 to
130 mm TL, and squid 38 to 160 mm ML (mantle
length); adults (larger than 300 mm SL) contained
primarily Stomiatoidei fishes 100 to 240 mm TL,
macrourids 150 to 255 mm TL, trichiurids up to
500 mm TL, caridean shrimp 49 to 80 mm TL, and
squid 70 to 170 mm ML.

AGE AND GROWTH

Otoliths have been used successfully to estimate
ages of several species of Merluccius. Annual
growth patterns for M '. productus were defined and
used to establish age composition (Nelson and
Larkins 1970). Botha (1969) used otoliths to es-
tablish the growth rates of both M. capensis andM.
paradoxus and concluded that zonation and
composition of the otoliths from various species of
Merluccius were similar.

Otoliths of M. albidus have well-defined opaque
and hyaline zones which increase in number with
size and age of the fish. However, an analysis of the
complex banding pattern in 206 pairs of otoliths
from juveniles (7 to 14 cm TL) was impossible,
because all bands were not defined and slow
growth rings (hyaline bands) did not agree with
age estimates based on length frequencies. Simi-
lar difficulties were encountered in the analysis of
otoliths from 56 males (15 to 34 cm TL) and 171
females (15 to 54 cm TL).

The tentative age structure presented for Gulf of
Mexico M . albidus was based on length frequency
data (Figure 8, Table 10). Harding-Cassie age-
class lines were computed (Harding 1949; Cassie
1954) based on the lengths of 1,839 males and
2,852 females taken in October 1971 and Sep-
tember 1973. Calculated mean lengths were very
similar to those shown on Table 10 for both male

12 -i

MALES

N = l,839

FEMALES

N=2,852

20 30 40 50

STANDARD LENGTH (cm)

FIGURE 8. — Length frequency and modal size for ages 0 to 5 for
Merluccius albidus from the east Mississippi Delta and west De
Soto Canyon slope October 1971 and September 1973.

TABLE 10. — Tentative ages with midpoint of modal size groups of
northern Gulf of Mexico Merluccius albidus.

Males

Females

Age (yr)

10.5

11.8

10.5

11.8

21.5

24.0

20.5

22.9

26.5

29.6

31.5

34.1

29.5

32.9

36.5

40.6

40.5

45.1

44.5

49.5

and female M. albidus. Longevity of M. albidus is
unknown, but Botha (1971) reported that Cape
hake live at least 11 yr. Juvenile male and female
M. albidus are about the same size, but males are
slightly larger than females at age 1. However,
females are significantly larger by age 2 with
difference becoming more evident as the fish
becomes older (Figures 8, 9; Table 10). The largest
male caught during this study was 404 mm SL and
0.6 kg while the largest female was 680 mm SL
and 4 . 1 kg. The growth rate until age 1 was similar
in both sexes. Thereafter, males which mature
earlier use a proportion of their available energy
to produce sexual products which may result in
their reduced growth and smaller size. Because
females mature later, they direct more of their
energy toward growth for a longer period of time
resulting in their larger size.

Female M . albidus between ages 4 and 5 grow at
a rate about equal to that reported for female M.
productus (Nelson and Larkins 1970; Table 11).

155

FISHERY BULLETIN: VOL. 75, NO. 1

90
80
70

OB
OS

I 60

S 50

I 40
30

II. ■<rUcciis

1 " ■•««* I (Fro. I

lotbo 1971 )
M. ppfodoims

M. ■•rlictln

M- blllMoris (llgelow I Schroadar 1953)

M. olbidts (Present study)

Mol«s

Ftnalts

1 2 3 4 5 6 7 8 9 10 11
AGE (years)

FIGURE 9. — Comparative growth rates for five species of Atlan-
tic Merluccius: M. merluccius, M. capensis, and M. paradoxus
from various authors after Botha (1971, fig. 17), M. bilinearis
from Bigelow and Schroeder (1953), and M. albidus (present
study).

TABLE ll. — Comparative length in centimeters by age for
Merluccius albidus, M. capensis, M. paradoxus, and M. pro-
ductus .

Age

M. albidus'1

M capensis-'

M. paradoxus2

M. productus3

(yr)

Male

Female

Male

Female

Male

Female

Male

Female

29.6

34.1

32.9

40.6

27.6

31.0 '

31.3

32.6

45.1

38.1

40.0

39.4

41.7

46.5

45.7

49.5

47.3

48.5

45.4

49.8

49.5

50.8

55.3

56.5

49.7

57.3

52.8

53.9

62.1

63.9

52.9

63.3

54.4

56.4

68.0

70.9

68.9

55.4

58.7

73.1

77.5

73.9

56.1

59.7

77.5

83.6

78.3

56.6

60.7

81.4

89.3

82.2

61.2

61 5

1 Data from Table 1 0 of present study.

Calculated lengths from Botha (1971).

Calculated lengths (Nelson and Larkins 1970); Dark (1975) gives similar
calculated lengths for M. productus including estimates for 1 , 2, and 3 yr fish as
16.6, 26.2, and 41.1 FL.

Growth rates of male and female M. productus
(Dark 1975) indicate that growth is rapid during
the first 3 yr but then slows perceptibly. Gulf of
Mexico M. albidus are larger than M . productus at
age 2. However, the growth rates of 3- to 5-yr-old
female M. albidus and M. productus appear
similar. Growth rates of males of these species do
not appear to be similar. Merluccius albidus from

the Gulf of Mexico appear to grow faster than M.
bilinearis (Figure 9).

A small number of female M. albidus were
collected in February 1970 below the head of De
Soto Canyon in depths of 550 to 730 m. These fish
ranged from 21 to 59 cm SL and showed modal
peaks at 36, 40, and 44 cm SL which were similar
to the peaks shown in Figure 8. Females collected
on the De Soto Canyon slope in June 1971 at
depths of 550 to 730 m showed modal peaks at 38,
42, and 45 cm SL.

Length frequency data imply that males rarely
live longer than 3 yr whereas a large number of
females live at least 5 yr (Figures 8, 9; Tables 10,
11). However, longevity in other species of Mer-
luccius is reported as upwards of 13 yr for females
and 1 1 yr for males. Additional sampling lower on
the slope throughout the year may generate a
broader data base from which additional age-
classes could be defined bringing longevity of M .
albidus in closer agreement to other species of
Merluccius. Figure 8 suggests a high mortality
rate for 2- to 3-yr-old males residing higher on the
slope which probably increases their accessibility
to predators. Botha (1971) showed that male M.
paradoxus do not live as long as females and stated
that males over 7 yr of age are extremely rare.

A length-weight curve for males and females
was computed from 1,920 specimens from the Gulf
of Mexico (Figure 10). Rate of weight increase was
similar in both sexes up to about 18 cm SL, af-
ter which the rate of increase for males became
greater possibly because males develop mature
gonads earlier.

STANDING STOCK OF M. ALBIDUS
IN THE GULF OF MEXICO

The standing stock estimate and confidence
interval for each stratum and for all strata are
listed in Table 12. Maximum density per drag in
June 1971 was 11 kg/hectare, mean density 3 kg/
hectare, and minimum density 0.45 kg/hectare.

Since trawl efficiency or catchability coefficient
(q) is unknown for offshore hake, a q of 1 was used
in the calculations thereby minimizing the
standing stock estimate. Catchability of any trawl
is somewhat dependent on several biological,
physiological, and adaptive characteristics of the
species sought which must be considered in as-
signing a value to q . Other species of hake come off
the bottom to feed and M. productus forms large
schools about 9 m off the bottom (Nelson and

156

ROHR and GUTHERZ: BIOLOGY OF MERLUCCWS ALB1DUS

— MALES

3.0

w 3.83 x 10*1 31" /
n 411 r .993

— FEMALES

w6.44.1oV0"

n 1,368 r .993

2.0

■••■ GENERAL FORMULA

.. •». 3.100 /

w-5.71 i 10 L /

n=1.920 r= .996

1.0

/
/
/
/
/

J — -— *r , i.i,

(

100 200 300 400 500 600 70

STANDARD LENGTH [millimeters)

FIGURE 10. — Length-weight relationship of Merluccius albidus
from the Gulf of Mexico.

Larkins 1970). If such behavior is characteristic of
M. albidus, then it may be necessary to use both
mid-water trawls and higher-opening fish trawls,
coupled with more tows of a shorter duration.
More short tows will allow greater coverage of the
grounds and dampen inherent variability in, the
catch rates. This will enable us to develop more
realistic population estimates.

Distribution and abundance ofM. albidus on the
De Soto Canyon grounds north of Tampa show
that the largest segment of the stock was located
in stratum 2 (Figure 11, Table 12). Numbers offish
were highest in stratum 1 (49%) but they only
represented 22% of the population biomass. Most
commercial-sized (greater than 0.45 kg) M. al-
bidus were caught in strata 3 and 4 (Figure 11).

Commercial potential for this species is con-
sidered to be low, particularly when compared to

BIOMASS

STRATUM 3
550-639 m

STRATUM 4
640-729 ffl

FIGURE ll. — Number and biomass of Merluccius albidus by
90-m depth strata on De Soto Canyon slope north of Tampa, Fla.,
June 1971.

landings of presently exploited hake species.
Landings of various species of Merluccius in 1965
were in excess of 9.1 x 109 kg (Grinols and Tillman
1970) yet our standing stock estimate is only
slightly more than 3.4 x 106 kg and our highest
recorded catch was only 284 kg/h.

Additional effort must be expended in order to
classify the life history and to test the hypothesis
discussed in this paper. Population estimates
must be more realistic and delineation of the
grounds occupied by this species more precise.
Merluccius albidus are known to occur from
Georges Bank to off the northeastern coast of
South America; however, presently little is known
concerning its population, life history, or com-
mercial potential.

ACKNOWLEDGMENTS

Richard B. Roe, NMFS, NOAA, Wash., D.C.,
assisted in developing the computer program to
calculate the length-weight equations. D. Nolf,
Rijksuniversiteit Gent, Belgium, supplied the

TABLE 12. — Standing stock estimates of both weights and numbers for Merluccius albidus on the De Soto Canyon slope north of Tampa,
Fla.; estimates are based on 19 5-h tows made in June 1971 using a 40-m fish trawl with 3-m bracket doors.

Number Area Total

Stratum Depth Area of sampled catch

number (m) (hectares) samples (hectares) (kg)

Biomass Number of

Mean Biomass Percent estimate2 individuals Percent

density1 (kg x 106) biomass (kg x 106) x 106 individuals

370-459

327,410

326.2

716

2.19

0.72

0.26-1.20

5.27

460-549

310,400

318.2

1.424

4.48

1.39

0-2.87

3.70

550-639

247,618

294.0

883

3.00

0.75

0.51-0.99

1.21

640-730

195,788

253.6

576

2.27
3.02

0.44
3.30

13
100

0.27-0.63
2.15-4.47

0.61

Total

1,081,216

1,192.0

3,599

10.79

100

'Values in kilograms per hectare.
Confidence interval = 90%.

157

FISHERY BULLETIN: VOL. 75, NO. 1

samples of eastern Atlantic M. merluccius oto-
liths, examined the Gulf of Mexico M. albidus
otoliths, and provided copies of his plates of
otoliths of both Atlantic and Pacific species of
Merluccius (unpublished monograph on Gadidae
otoliths). David M. Cupka, South Carolina Wild-
life and Marine Resource Department, Charles-
ton, S.C., kindly identified the squids commonly
found in M. albidus stomachs. D. M. Cohen kindly
reviewed the manuscript.

LITERATURE CITED

Alton, M., and M. O. Nelson.

1970. Food of Pacific hake, Merluccius productus,
Washington and northern Oregon waters. In Pacific
hake, p. 35-42. U.S. Fish Wildl. Serv., Circ. 332.

BIGELOW, H. B., AND W. C. SCHROEDER.

1953. Fishes of the Gulf of Maine. U.S. Fish Wildl. Serv.,
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1818, and of the blue whiting Gadus (Micromesistius)
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BOTHA, L.

1969. The growth of the Cape hake, Merluccius capen-
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BULLIS, H. R., JR., AND P. J. STRUHSAKER.

1970. Fish fauna of the western Caribbean upper
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CASSIE, R. M.

1954. Some uses of probability paper in the analysis of size
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CERVIGON, M. F.

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Cultura Cientifica, Caracas, Venez., 436 p.

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Fritz, r. l.

I960. A review of the Atlantic coast whiting fishery.
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GINSBURG, I.

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Harding, j. p.

1949. The use of probability paper for the graphical
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HlCKLING, C. F.

1927. The natural history of the hake. Parts I and
II. Fish. Invest. Minist. Agric. Fish. Food (G.B.), Ser. II,
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determination and the growth rate. Fish. Invest. Minist.
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1965. A standard terminology and notation for otolith
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KARNELLA, C.

1973. The systematic status of Merluccius in the tropical
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MARAK, R. R.

1967. Eggs and early larval stages of the offshore hake,
Merluccius albidus. Trans. Am. Fish. Soc. 96:227-228.
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1966. Fecundity in the Pacific hake, Merluccius productus,
(Ayres). Calif. Fish Game 52:111-116.

MOMBECK, F.

1971. Notes on the distinction of Northwest Atlantic
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Northwest Atl. Fish., Res. Bull. 8:87-89.

NELSON, M. O., AND H. A. LARKINS.

1970. Distribution and biology of the Pacific hake: A
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NIKOLSKY, G. V.

1963. The ecology of fishes. (Translated from Russ. by L.
Birrett). Academic Press, N.Y., 336 p.
ROHR, B. A.

1972. Size and sex segregation of offshore hake, Merluc-
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158

BEHAVIOR OF CALIFORNIA GRAY WHALE, ESCHRICHTWS ROBUSTUS,
IN SOUTHERN BAJA CALIFORNIA, MEXICO

Kenneth S. Norms,1 Robert M. Goodman,2 Bernardo Villa-Ramirez,3 and Larry Hobbs1

ABSTRACT

Mother-young pairs of the California gray whale, Eschrichtius robustus, have been studied by a variety
of means, including direct observation in calving lagoons from shore and ship, from aircraft, and by
attachment of jettisonable instrument packages to calves. Instrumented whale pairs were tracked
inside the lagoon, and one pair was followed for 63 h as the animals left Magdalena Bay and moved
southward along the Baja California coast 213 km at a traverse rate of 3.4 km/h.

Mother-young pairs far back in the calving lagoon were found to move toward the deepest nearby
water available on the outgoing tide, returning again after low water had passed. Aerial behavior
consisted of breaching and spying out. In a breach the leaping animal rose two-thirds or more of its
length from the water, falling back on its side. In our observations breaching seemed associated with
the presence of males. Spying out was much more leisurely and often seemed to involve an animal with
its flukes on the bottom, forcing its head out of the water. Contact between mothers and calves was very
common; the calf often slid over the body of the mother and was lifted by the mother in conditions of
stress. Floating whales seemed to be supported by inflated lungs which spread the loose rib cage apart
producing a very flat cross-sectional profile. The spout was of seawater and it is speculated that part of
its volume comes from water entering the nostrils as they open. Whales were observed grubbing in the
bottom both in and out of calving lagoons, but feeding was not definitely confirmed. Mating was
concentrated at lagoon mouths but some sexual behavior was noted inside lagoons. Female whales
were found to be aggressive when their calves were disturbed, thrashing sideways with flukes at
intruders, or attempting to hit a vessel with the flat of the flukes. Resonant clicks and loud broad band
claps were recorded from calves as they were released to their mothers.

Pacific Mexican lagoons frequented by calving and
breeding California gray whales, Eschrichtius
robustus (Lilljeborg), are easily accessible by road
and ship. Even so, information regarding the
behavior of adults and young in these lagoons
remains fragmentary. This paper describes be-
havior studies performed in January-February
1974 and 1975. Several methods were used.
Observations of undisturbed whales were made
from shipboard and skiff. Behavior was noted
during capture sequences of nine young whales.
Aircraft surveys were made. A set of sequential
observations, principally of mother-young pairs,
was made from a large dune (Colina Coyote) set on
the edge of a major nursery channel. Finally,
behavior of mother-young pairs was observed
during radio tracking sequences on three animals.
Data on diving depths and profiles, and water
temperature, were also gathered during these
tracks.

'Department of Biology, University of California, Santa Cruz,
CA 95064.

2Franklin Institute Research Laboratory, Philadelphia, Pa.
3Universidad Nacional de Mexico, Mexico City D. F., Mexico.

Manuscript accepted May 1976.

FISHERY BULLETIN: VOL. 75, NO. 1, 1977.

Captain Scammon's initial forays into Laguna
Ojo de Liebre (Scammon's Lagoon) to capture
whales resulted in the first record of the California
gray whale from these lagoons, though the nature
of his work certainly imposed disturbances that
masked much behavior. Little was added for
nearly a hundred years. Initial population counts
were begun for the entire eastern Pacific popula-
tion by Hubbs (1959), extended by Gilmore and
Ewing (1954), Gilmore (1960a, b), Hubbs and
Hubbs (1967), and Rice and Wolman (1971) and
finally by Henderson (1972) and Gard (1974).
Gilmore et al. (1967) added information about
calving along the Sonora coast.

These studies revealed information regarding
distribution of age-classes in the calving lagoons
and features of behavior such as respiration,
diving, swimming speeds, and aerial behavior.

Other studies have touched on several aspects of
gray whale life. Huey (1928) and Wyrick (1954)
gave field descriptions of behavior. Acoustic
studies in Laguna Ojo de Liebre have been made
by Eberhardt and Evans (1962), Poulter (1968),
and Spencer (1973), while more general studies of
mother-calf behavior have been made by Walker

159

FISHERY BULLETIN: VOL. 75, NO. 1

(1962) and Eberhardt and Norris (1964). Studies
by White and Mathews (1956) and Spencer (1973)
have given some information about physiological
functions of the whales.

Henderson (1972) has reviewed historical data
on the eastern Pacific gray whale fishery and
speculated about previous distributions of num-
bers in the breeding population.

The capture of the suckling gray whale calf,
Gigi, and her subsequent captivity and release
revealed several new aspects of young gray whale
behavioral and physiological biology. The various
studies performed on Gigi were collated and edited
by Evans (1974a).

Rice and Wolman ( 197 1 ) have summarized data
from all parts of the migratory path and their
studies of 316 whales captured off San Francisco
provide the best information on reproductive cy-
cles and what might be called the migrant
procession. They described the sequence occupied
by various age and sex classes in the migratory
column (see also Sund et al. 1974 and Leather-
wood 1974).

The study reported here will draw from these
works and add further information on feeding on
southern grounds, mating, aggression, mother-
calf relations, aerial behavior, respiration, and
tidally related movement.

MATERIALS AND METHODS

During 1974, capture and tracking exercises
were carried out using the 45-foot swordfish boat
Louson under the direction of Captain Tim
Houshar. In 1975, captures were performed from
the Orion (Captain Peter Zimmerman) and
tracking performed on the Scripps Institution RV
Dolphin, a 95-foot motor vessel.

Tracks were performed using Ocean Applied
Research (OAR) tracking radios, model PT-219,
equipped with lithium batteries that generate a
pulsed 50-ms/s signal each time the antenna rose
above the surface.4 Because the whip antenna had
been broken on one radio when a young whale
rubbed against the capture vessel during 1973
work, a flexible antenna equipped with a spring
base was substituted in 1974. This minimized such
antenna damage. Signals were processed with an
OAR automatic radio direction finder and plotted
on a strip chart recorder. In 1974, a multichannel

••Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

sensing and digital recorder system developed by
the Biotechnology Laboratory of the Franklin
Institute, Philadelphia, Pa., was used to record
water depth (pressure) and water temperature.

In 1975 a pressure recorder (TSK depth recor-
der, 0-1,000 m model) was used to record
maximum dive depth.

Harnesses used in both years consisted of a
stretchable nylon fabric harness, reinforced at
appropriate points with heavy nylon straps. This
material was fastened to a curved aluminum back
plate which was protected beneath with neoprene
sheeting to minimize abrasion to the animal (see
fig. 3, Norris and Gentry 1974). Instruments and
the tracking radio were mounted on the plate. A
syntactic polyurethane foam float was molded to
fit over these and painted bright yellow to aid
visual sighting. This float provided about 0.5 kg of
positive buoyancy to float the harness after jet-
tisoning.

Release was achieved by two means. First,
soluble machined magnesium bolts were used to
give timed release of up to 6 days duration. One
release during the 1975 expedition used a crystal
timed explosive bolt system backed up by a soluble
magnesium nut. The timing circuitry, which used
a serially charged capacitor bank, released early
because of a faulty magnetic switch.

The 25-m sand hill of Colina Coyote provides a
fine site for observation of undisturbed whales.
From it an observer can see a stretch of channel
approximately 5 km long. Often animals within
the area could be identified individually by scars
and marks. Details of behavior such as spying out,
respiration, and other features were observed
(Figure 1).

This dune appears to be just north of the south-
ern limit of most whale movement in the Boca
Soledad area. A moderate number of animals
passed the dune and swam a kilometer or so south
toward the north end of Devil's Bend, a narrow
winding channel flanked by tidal flats that ul-
timately connects to upper Magdalena Bay. Dur-
ing our observation period, we sighted no whales
swimming into the narrow channel itself.

The channel in front of Colina Coyote is ap-
proximately 1,200 m wide, is bordered on both
sides by tidal flats of variable width, and has a
central channel of rather uniform depth, varying
from about 8 to 10 m. Various landmarks were
named by our observation team to permit easy
notation and reference and are noted in the inset of
Figure 1. A camp was established behind a small

160

NORRIS ET AL : BEHAVIOR OF CALIFORNIA GRAY WHALE

FIGURE 1. — Chart of the capture and study areas in Magdalena Bay area of Baja California Sur, Mexico. Calves were captured in the
channel off Puerto Lopez Mateos, at Colina Coyote, and at Puerto San Carlos. Inset map shows area around Colina Coyote, where most
observation was done, with names of topographic features given by the study team.

sand hill nearby to prevent undue disturbance of
whales in the adjacent channel and to allow easy
access to the top of the dune.

A standard assemblage of telephoto-equipped
still and moving picture cameras, a spotting scope,

binoculars, and watches was used in recording.
Nighttime observations were assisted by use of a
Zoomar image intensifying night vision scope.

Watches were kept with two observers each and
daily observation of tidally related movements

161

FISHERY BULLETIN: VOL. 75, NO. 1

and other features were made. Observations of
aerial behavior, sound, respiration, and the re-
lationship between mother-calf pairs were made.
The sound recording system consisted of an At-
lantic Research Corporation LC 32 hydrophone,
with a response of ±4.0 dB over 0.1-100 kHz, a
Hewlett-Packard 466A amplifier, and a Uher 4400
Report Stereo tape recorder with an upper flat
frequency response of approximately 20 kHz at 7.5
ips. Signals recorded above 20 kHz are, at best,
nonquantitative indications of energy at these
levels and may also be instrumental in nature
(i.e., the result of ringing in one or more parts of
the system).

Counts of whales and their distribution were
made both from shipboard and from aircraft.

RESULTS

Tracking Studies

Tracking experiments were designed for a
maximum of 6 days and were intended primarily
to test logistic systems and instrumentation for
longer tracks. Nonetheless, examination of the
data provides some insights into behavior in and
out of the calving lagoons. Two animals were
equipped with radio packs and the depth/
temperature tape recorder units in the 1974 test
series. (Details of the data system are in prep-
aration and will be reported elsewhere.) The first
whale calf (a 5.6-m total length male) was caught
in Bahia Grande south of Lopez Mateos on 31
January 1974. During capture, its mother re-
peatedly rose beneath the captive which slid to
either side off the rising body of the larger animal.
The adult made no attempt to entangle the re-
straining line, nor was there any aggression noted
toward the collecting vessel, which sometimes
approached within approximately 15 m of the
struggling pair. The animal, restrained by a single
head noose that had cinched tight anterior to the
pectoral fins, proved to be extremely strong and
required 25 min of concerted effort by eight men to
beach it. The harness was attached and the animal
was quickly returned to the mother who patrolled
in the nearby channel. This pair stayed in the
lagoon for approximately 4 days. They first moved
northward toward Lopez Mateos and then turned
and swam southward through Bahia Grande, past
Colina Coyote, and into the narrowing channel
area north of Devil's Bend. They, however, did not
enter this narrow (approximately 50 m wide)

channel. Aboard the tracking vessel, we noted
that the animals were effectively in a cul-de-sac,
and that they would probably have to move
northward to leave the lagoon via Boca Soledad.
The vessel was therefore moved northward and
moored near the fishing village of Lopez Mateos.
During the night, the whale pair swam from Dev-
il's Bend to Lopez Mateos (22 km) and passed the
anchored vessel, stopping at a moderate-sized bay
just inside Boca Soledad. The next day the animals
returned downchannel past the vessel disap-
pearing into the region of Bahia Grande where
radio contact was lost. It was correctly assumed
that they would not pass through Devil's Bend, but
instead would remain in these southern channels.
The collecting crew then caught a young female
whale and instrumented it. This calf and its
mother immediately moved northward out of the
lagoon, through Boca Soledad, and began an ocean
traverse southward just offshore of the barrier
dunes. The crew was able to follow the pair by
shipboard direction finder over the intervening
dunes of Isla Magdalena for approximately 33 km
south of Boca Soledad when contact was finally
lost. That night the first cow and calf again came
upchannel and passed the anchored vessel at
Lopez Mateos moving toward the entrance at Boca
Soledad. It is surmised that somewhere in this
region the calfs harness cast loose, since a con-
tinuous signal was intermittently received. Only
when the vessel moved into the Boca itself, clear of
intervening sand hills, was the signal reacquired
fully. Directional signals indicated that it was
located approximately in the middle of the Boca,
and probably washing back and forth with each
tide change. It was later recovered on the beach 3
km north of the Boca, its instruments intact and
operating.

For the 1975 tracking study a 5.3-m male calf
was captured directly in front of Puerto San Carlos
in upper Magdalena Bay, stranded on the beach
south of the main pier, harnessed and released
there. When released at 1105 h on 5 February,
mother and calf reunited quickly and began mov-
ing rapidly toward the main part of Magdalena
Bay. The pair skirted along the 20-m contour of
the main bay until deeper water at the bay en-
trance (along Punta Redondo at the north tip of
Santa Margarita Island) was reached at 0200 h, 6
February. The pair went directly into deep water
past the point, out at least to the 100-m contour
before curving back toward shore again at 0600 h.
The depth recorder on the calf later showed that

162

NORRIS ET Al. BEHAVIOR OF CALIFORNIA GRAY WHALE

the animals dove to or near the bottom during this
traverse (maximum recorded depth 110 ±10 m).
The impression given by the track at this point is
that the animals were navigating to some extent
by diving to the bottom and when the water
deepened they turned for shallower inshore water.
This is similar to the findings of Evans (1974b) for
the instrumented whale Gigi released off San
Diego which also dove to near the bottom and
reached a maximum depth of 170 m.

Once near shore they skirted Punta Tosco at the
southern tip of Santa Margarita Island, moving
directly up the Rehusa Channel to a point off the
middle of Isla Cresciente in quite shallow water at
1400 h. The animals remained there for 2 h and
stayed almost constantly at the surface. Much
rolling and throwing of pectoral flippers and flukes
could be seen. We speculate that this interlude
could have included a nursing sequence following
the concerted swimming effort immediately after
capture (Figure 2). After milling in the general
area of Isla Cresciente at 0900 h, the pair began to
move southward again, staying close inshore. At
0200 h the following night, the radio signal
changed from the intermittent signal typical of a
swimming and periodically surfacing animal to a
constant signal, indicative of harness release. The
harness was retrieved successfully at 0930 h. The

track had covered 213 km in 63 h, for a traverse
rate of 3.4 km/h, or 1.8 knots (2.1 knots excluding
20 ± h of quiescence) and had travelled 159 km
southeast directly past the last calving lagoon on
the Baja California coast.

One may speculate why the two instrumented
animals that left the calving lagoon went south
rather than in the expected northerly direction.
The normal path at the beginning of northerly
movement is not known. First, it seems possible
that initial movement from the lagoon may in-
corporate some milling or nondirectional
movement before migration begins. Second, the
driving force which motivates and directs the
northern migration may be involved. Is it
hormonally stimulated, and timed by parturition
and nursing? If so, what is the equivalent change
in the male and how are these hypothetically
related hormonal events related to path direction
as well as to initiation of the migration itself? That
is, does an animal have a general southward
tendency of movement at one period that changes
to north before normal migration back to Arctic
latitudes? Third, could the attachment of in-
struments produce an initial direction aberration
in path? In view of our observations of instru-
mented mother-young behavior within the lagoon
itself, this appears unlikely, but further study of

3 4

Time (minutes)

_JU_

I
0

J_JL

I
2

I I

3 4

Time (minutes)

i
5

i
6

FIGURE 2.— Respiratory patterns of (a) a quiescent and (b) a swimming calf. The record in (a) was recorded off Isla Cresciente at the
entrance to Almejas Bay, Baja California Sur, Mexico. This is the southernmost calving lagoon on the peninsula. The mother-calf pair
lay at or near the surface in shallow water for 2 h. The repeated bouts of surface activity may represent nursing sequences. Each spike
represents a radio transmission from the calf. These transmissions were given every second when the antenna broke the surface, and
indicate an average of 16 s/min surface time. Amplitude of spikes varies with transmission efficiency. Time is in minutes. The record in
(b) is for the same pair during normal swimming and indicates an average surface time of 3 s/min.

163

the initial southerly movement of both non-
instrumented and instrumented animals appears
in order.

Observation Studies

Behavior of Instrumented Animal — 1974

The depth record of the lagoon track of the male
calf showed patterns quite different from those we
have come to expect from cetaceans during radio
tracking. The most striking difference was long
periods (up to 3 h) when the calf apparently was at
or very near the surface. Although instrumenta-
tion circuitry functioned properly in pre- and
post-track tests, we prefer to wait for replicate
tests to check the validity of these curious ob-
servations before reporting the results in greater
detail.

FISHERY BULLETIN: VOL. 75, NO. 1
Tidal and Water Depth Relations

Whales observed from Colina Coyote responded
to the changing tide every day. Each time the high
tide turned and while it was still high, many
mother-calf pairs swam slowly northward into the
extensive deeper water of Bahia Grande.
Sometimes well before the tide was very low most
animals would be gone from in front of Colina
Coyote, with most stragglers travelling in the
deepest water available (see Figure 3). The return
movement began in similar fashion with the
beginning of flood tide. The variation in arrival
was so great that some animals did not appear
until approximately high tide. Casual observa-
tions in channels in upper Magdalena Bay suggest
that similar behavior may occur there, though in
the deeper and broader waters of that open bay
some whales were present throughout the tidal

Caleta
Calloway*:0

Punta - '
Nichols

y I 234

2 34

HIGH

TIDE
LEVEL

LOW

TIME RELATIVE TO
TIDAL CYCLE (HR)

12 3 4

12 34

12 3 4

2 34

Playa

. P^JJf^Kii

12 34

^3yg?»yjf?S3

2 34

■| 2 34

g^frgra

12 3 4

Colina Coyote

FIGURE 3.— Tidally related movements of adult gray whales in the calving lagoon at Colina Coyote, Baja California Sur, Mexico.
Sketch map of waterways in front of Colina Coyote observation post showing tidally related movements of adult California gray whales.
Data were acquired visually and recorded on a base map without the grid marks, as tracks against time. The grid was superimposed and
an enumeration of sightings per square made for the time period involved. Animals entered or left on the turning tide, thus low tide (1)
shows a concentration of animals in Canal Dohl, but also some deep in the Canal Central. The latter represent animals that entered the
area soon after the change to incoming tide. Bars for high to 2 h after high tide (3) and 2 h after high to mid-low tide (4) reveal first a high
concentration of animals coming up channel toward Bahia Grande and passing Colina Coyote, and finally a few stragglers making this
passage before low tide. Animals seen in the period from medium rising to high tide (2) represent the more or less static population of
animals that milled slowly in the channels in front of Colina Coyote before tidally related movement began.

164

NORRIS ET AL : BEHAVIOR OF CALIFORNIA GRAY WHALE

cycle regardless of tide. Probably such behavior is
an important means of avoiding stranding in the
complicated shallower channels of calving la-
goons.

Whales seldom leave the fairly deep channels,
even at the highest tides. Much travel occurs along
the channel edges but the animals seldom venture
over tidal flats or sand bars, even those covered
with 2 or 3 m of water. Occasionally, whales will
venture over the edges of such flats when avoiding
other whales or a pursuing vessel. The usual
reaction to pursuit, however, is to seek deep water.
An exception was produced by what we suppose
were the pursuits of female whales by males.
These chases, often involving three animals,
sometimes went into water so shallow that the
whales were nearly stranded. Very narrow
channels are, however, avoided; we seldom saw
whales traverse areas narrower than 130-140 m in
width. Because the channel south of Colina Coyote
in Devil's Bend is both narrow and sinuous and
because we never saw whales there, we suspect it
is not used and thus whales in Magdalena Bay are
a separate group from those off Colina Coyote that
use the Boca Soledad entrance to the sea.

Aerial Behavior

A controversy has long existed over the func-
tions of the various kinds of aerial behavior
exhibited by the gray whale (see, for example,
Gilmore 1961, 1969; Walker 1962).

In our observations breaching is very different
behavior from the much more leisurely spying out
behavior (see also Walker 1962), and the two occur
in quite different contexts. We use the term
breaching to indicate a partial leap, often until
two-thirds or more of the animal is free of the
water, usually terminating with a rolling turn
that causes the animal to reenter backward or on
its side with a large splash that can often be seen
for several miles. Breaches usually occur in
sequences, often of three, and usually with de-
creasing vigor through the sequence. Gilmore
(1961) reported seeing 11 breaches in a single
sequence. A breach is vigorous, even violent
behavior. We have watched many breaches and
cannot report any being made by a cow with a calf,
though Gilmore (1961) reported that mothers and
calves sometimes breach. Instead, they seem to be
made predominantly by rapidly moving animals
that may be males or females in the company of
males. It seems possible to us that such leaps

represent sexually related displays, perhaps not
unlike the breaches of such forms as humpback
and male killer whales.

We have seen breaching most commonly at sea
or in the seaward parts of lagoons where mating
was common, although it was seen on three
separate occasions in the deepest part of the Boca
Soledad in front of Colina Coyote. On these oc-
casions, it was performed by a swift-swimming
unaccompanied animal that entered and caused
some chases and agitation among the otherwise
placid mother-calf pairs. Because of this creation
of agitation among the nursing females, and
because of its relatively small size, we suspect that
it was a male.

In sharp contrast, a spy out is a leisurely event
in which the animal raises its head slowly out of
the water, often nearly to or slightly beyond the
level of the eyes, and then slips back into the water
as gravity causes it to fall slowly out of
equilibrium. In shallow water, we believe spy outs
are performed by an animal with its tail pressed
against the bottom, and that flexing of the back
forces the head out. Cows with calves often spy out,
though single animals also exhibit the behavior.
At Colina Coyote, spying out most often occurred
in a rather tightly circumscribed sector at the edge
of the channel from the middle of Isla Pierce north
past Cabo Forment, Canal Segundo, and Isla
Central, though it was seen occasionally in the
middle of Canal Central (Figure 4). Soundings in
this area showed a rather uniform depth of 8 to
10 m.

The eyes of the animals spying out were often
below the waterline, and hence aerial vision was
not always involved. Further, spying out was
observed at night off Cabo Forment by use of a
night vision scope. The observation occurred on a
clear moonlit night. It is our strong impression
that this kind of spy out is not related to viewing
surrounding terrain or objects in air but is usually
performed by nearly quiescent animals that may
simply be making comfort or postural movements.
We could not determine if it had any relation to
nursing though we did see calves circling spying
adults which suggests that nursing was not
necessarily involved since the teats of the mothers
were at least 6 m below the surface. The reverse
behavior was occasionally seen, especially in
Bahia Grande, in which an animal extended its
tail into the air for a few seconds before subsiding
back into the water, as if its snout was resting in
the bottom mud.

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FISHERY BULLETIN: VOL. 75, NO. 1

FIGURE 4.— Distribution of spy outs
by adults and calves as noted from
the Colina Coyote observation
station.

Individual spy outs sometimes extend for rather
long periods, another evidence that the animal is
touching bottom at the time most of them occur.
Nineteen examples ranged from 4 to 17 s duration
with a mean of 7.6 s. In the longest, the animal
rose from the water above the eyes, subsided until
only the tip of its snout showed, and rose again to
about the angle of the gape before slipping back
again.

Occasionally spy outs occur in deeper water
where a whale cannot be expected to touch and
then the whale subsides very rapidly, just as
would be expected of an unsupported animal in
water.

Some spy outs do seem to involve aerial vision as
has been suggested by Gilmore (1961). When an
adult whale and calf are pursued, the adult may
sometimes stop her flight and spy out. In one such
case, the animal rose slowly and we could see its
eyes. After such a spy out, the whale pair typically
resumed avoidance behavior.

Of 52 spy outs recorded at Colina Coyote, 3
involved water coming from the corners of the
whale's mouth. In two cases, off Cabo Forment, the
released water was muddy. In one case, while the
observer watched through a telescope, the whale
rose with muddy water cascading out of the corner
of its mouth. A similar instance was noted at
Punta Tosco at the entrance to Almejas Bay in
which an animal rose near the observer in a drift-
ing skiff, its back toward the boat. As it rose, clear
water gushed a foot out from the head from both
lower mouth corners (Figure 5).

Thigmotaxis

One of the most striking behavioral attributes of

mother-young pairs is nearly constant bodily
contact in resting or passively floating animals.
The contact seems to be solicited by both partners
since the young often swims over the mother and is
lifted as she raises head, body, or tail under the
baby. Babies may slide over the mother from her
head to her tail stock. In the course of such contact,
the baby may roll onto its side or back, throwing
its pectorals into the air. Lifting by the mother
may force the baby calf out of the water even in a
relatively quiescent pair.

In frightened animals, the lifting continues on a
more violent scale as this excerpt from field notes
(Norris) shows. "February 2, 1974. 1300: Bahia
Grande. A calf was noosed and the line cinched
tight around the pectorals. The calf was ac-
companied by a large barnacle-encrusted whale
and shortly by another adult. They were the most
violent consorts we had yet encountered, thrash-
ing their tails and rolling over, repeatedly sup-
porting the baby partly out of water. An attempt
was then made to place a head net over the calf by
inching the vessel's plank over the thrashing trio.
Suddenly one flailed sideways sending a sheet of
water over the bow. The head net was successfully
placed and line slacked off, all three animals
moving 50 m or so from the bow. Then one adult
heaved its body into an incredibly powerful thrash
of the tail, calf on top, causing the young animal to
fly completely free of the water. Both head ret and
noose flew free."

On 1 February 1974 a young whale was cap-
tured and shortly after it was netted, the ac-
companying adult disappeared. Because we did
not want the young animal to lose its parent al-
together we released it as soon as it could be

166

NORRIS ET AL.: BEHAVIOR OK CALIFORNIA GRAY WHALE

FIGURE 5.— An adult gray whale spy-
ing out at the Rehusa Channel adjacent
to Punta Tosco, Baja California Sur,
Mexico. Note clear water gushing from
both posterior mouth corners.

brought alongside, but it refused to leave the
vessel. In fact, it pressed itself up against the hull,
sometimes sliding under the stem or taking up
station alongside the overboard discharge from
the main engine. Every attempt to push it away
with oars or brooms failed until the ship was
finally backed in an arc away from the animal,
leaving it following in our wake. Shortly, to our
considerable relief, the adult was seen surfacing
alongside the young animal. This thigmotactic
behavior is strikingly reminiscent of that reported
by Norris et al. (1974) for a humpback whale,
Megaptera novaeangliae, baby in which a released
young also refused to leave the side of the collec-
tion ship.

From time to time mothers with calves are
engaged in rather violent chases with other adults
which we speculate to be males. We observed one
such chase near Lopez Mateos about 3 km inside
Boca Soledad. These chases can be violent with
much rolling and thrashing and long high speed
sequences in open water, fast enough that the
animals produce bow waves of some size. In one
such chase we observed a baby racing along
attempting to keep station with three adults. The
next day in the same area a lone baby, perhaps the
same animal, was noted partially stranded. This
baby, apparently completely unharmed, swam
ashore until its belly touched the sloping sand of
the beach. We launched it repeatedly back into

deep water without avail. It circled back into the
shallows despite all our attempts and did so in
both directions (and because it circled in both
directions we did not feel it had a middle or inner
ear orientation problem). Our impression was that
the baby was seeking contact and thus stranding.

Buoyancy and Respiration

Passively floating or slowly moving adults in
the calm lagoon areas allowed close inspection of
some of the mechanics of respiration and of the
formation of the blow or spout (see Kooyman et al.
1975). In such adults, breaths were sometimes
taken with a few inches of the back exposed or with
just the nostrils protruding. The area anterior to
the nostrils swells before air is released, and
adults often seemed to straighten or arch the back
slightly causing a slight upward movement of the
head prior to expiration. This did not always occur
as sometimes an animal seemed simply to rise
slightly prior to a blow and to subside after it.

Sometimes when a wholly quiescent whale
blew, it raised its head slightly with the breath
and slid backwards slightly just after it. In such
quiet animals there seemed to be some internal
mechanism by which the animal trimmed its
buoyancy. It sometimes sank slightly after a
breath or seemed to bounce slightly, rising a few
inches to a new resting level.

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FISHERY BULLETIN: VOL. 75. NO. 1

Some breaths were released underwater both in
the lagoons and out, and by both adults and young,
usually causing a strong boil.

The gray whale spout is obviously double if
viewed in front or behind the whale and may
appear single from the side. It varies from a low
"mushy spout" in breezy conditions to a fairly
slender column perhaps as much as 2.5 m high in
very calm air.

The spout is dense throughout its height from its
initial exit point at the animal's nostrils to the top
of the blow, and one can occasionally see the col-
umn of rushing air "tear" at the surrounding
seawater entraining it into the blow as a ragged
sheet. Most times the blow seemed to start just as
the animal's nostrils rose to the surface and such
adjacent seawater was obviously a considerable
part of the blow. Occasionally, however, a floating
animal did not sink down before a blow and a spout
was sometimes not produced. It is our impression
that in the calving lagoon most or all of the spout
involved either water entrained in the column of
rushing air from the sides as the animal's nostrils
broke water or from a small amount of water
pooled on nostrils, or perhaps more likely from the
seawater that had entered the uppermost part of
the nostrils just prior to the blow. Condensation is
clearly an important part of the blow of whales
breathing into cold air, as in more polar latitudes,
but was not in our observations within calving
lagoons. Neither whales that did not submerge
between blows nor stranded calves spouted.

While spouts were taller and more evident in
calm morning air, they were present throughout
the day and at sea. Our impression is that visibil-
ity is affected by such changing conditions but that

the mechanism of spout production in this latitude
(25°N) remains the same. That is to say, wind may
shorten the spout and make it harder to see but
most respirations at sea produce spouts regardless
of time of day.

Baby whales during swimming tend to toss their
heads upwards when they blow, unlike adults, and
as a result respiration breaks the smooth course of
their swimming. This movement is extreme
enough that one can sometimes see their lower
jaws rise free of the water during respiration.
Adults always seem to remain more deeply
submerged with eyes and lower jaws well below
the surface during spouting.

Patterns of respiration are quite different in
mothers and young. One young animal observed
moving slowly with an adult took 88 breaths/h
while the attending adult took 58 breaths/h (Fig-
ure 6).

During what we suspect might be nursing
sequences by an instrumented calf, surface times
were considerably longer than otherwise, av-
eraging 16 s/min as opposed to 3 s/min in travel-
ling young.

During steady swimming the respiratory pat-
tern becomes more regular, generally with a
sequence of closely spaced blows followed by a
longer period of apnea, with this sequence re-
peated over and over (Figure 2) (see also Wyrick
1954).

Often, adult whales were encountered floating
absolutely passively in the calving lagoon. The
back from about the nostrils to the base of the tail
was often exposed. In such instances we were
impressed by the very broad curve of the exposed
back, as if the chest of the animal had a huge

Mother
Calf

10 15 20

Time (minutes)

FIGURE 6. — Respiratory patterns of a California gray whale mother and calf pair swimming slowly off Colina Coyote, Baja California
Sur, Mexico. Adult respirations equal 58/h; calf 88/h. Note that while initial respirations of a breathing sequence were sometimes
simultaneous indicating surfacing together, often the calf surfaced first while the adult swam out of sight below the calf.

168

NORRIS ET AL.: BEHAVIOR OF CALIFORNIA GRAY WHALE

diameter. This broad abdomen narrowed im-
mediately to the tail which seemed to be of normal
diameter. In rapidly swimming animals the back
often seemed much less broad. Our supposition is
that in the passively floating animals the loose
articulation of the rib cage allows the buoyant
lungs to press the ribs outward, flattening the
floating animal.

Feeding

Uncertainty exists with regard to the amount of
feeding gray whales perform outside the Arctic
feeding ground and especially in or near the calv-
ing lagoons. Both Gilmore (1969) and Rice and
Wolman (1971) emphasized that nearly all
migratory whales that have been examined had
empty stomachs, while a few contained small
quantities of gastropod opercula, wood,
polychaetes, sand and gravel, ascidians, and
hydroids. Matthews (1932) reported observations
of gray whales feeding on shoals of Pleuroncodes
planiceps, an anomuran swimming crab, or "red
crab," off Magdalena Bay. Even so, Gilmore
(1969:15) stated "one authoritative opinion holds
that gray whales enter lagoons primarily to feed.
The whales allegedly plow the lagoon bottoms in
long furrows, exhausting first one section then
another of the rich beds of eel grass and inver-
tebrates. This opinion also asserts that the whale's
high, vertical thrust of its head out of water — long
considered a visual 'spy-hop' — is gravity swal-
lowing, necessitated by his non-protrusible
tongue."

Our observation of a whale spying out with mud
cascading from the corners of his mouth at Colina
Coyote is difficult to interpret (Figure 5). Surely
the animal had grubbed in the bottom mud, but
this does not assure that feeding had occurred.
Nonetheless, at times we saw patches of muddy
water around whales that were diving and spying
out, indicating that much bottom grubbing was
not isolated and perhaps common.

A more convincing observation was made by our
flight observation team of Thomas Dohl and John
Hall. They reported seeing 20 whales in shallow
greenish water 75-300 m off the beach between
Boca Animas and Boca Santa Domingo. Six of
these animals were travelling slowly leaving
muddy trails behind them. The trails were solid
spreading wakes of muddy water and some of them
were curved. They saw one whale surface and blow
while continuing to trail such a wake, probably

indicating that muddy water was issuing from its
mouth. Their strong impression was of whales
grubbing in the bottom producing the trails as
they swam along. Once again we cannot be sure
that these animals were feeding, but it is fair to
say that probably with reasonable frequency
whales in or near calving lagoons grub in the bot-
tom mud or sand and take at least some of it into
their mouths. Perhaps it is "pseudo feeding" as
Gilmore (1969) suggested, but it is also possible
that limited feeding does occur in or near the
calving lagoons.

Population Segregation

We can confirm the long standing observation
(Gilmore 1961) that at lagoons population
segregation of a marked sort takes place. Mother
whales with newborn young are indeed confined
largely to inland waters within the lagoon sys-
tems. Single animals are rather uncommon there.
Aggregations of whales without calves are com-
mon at or near entrances and in the nearby
offshore waters. A considerable percentage of
these animals is found in groups of two to six
animals and much rolling, fluking, throwing of the
pectorals, and bodily contact can be seen. Occa-
sionally a protruded penis was noted as a whale
rolled on its back and more often the perineal
sheath of the male could be seen in such cir-
cumstances. Groups at bay mouths typically
contained many moderate size animals, which we
estimated at 10-12 m long. It seems probable that
both yearling, juvenile, or young adults of both
sexes and older males were involved.

All whales found south of the southernmost
calving lagoon at Almejas Bay seem to represent
this mixed group of males, yearlings, or non-
parturient animals. The large group of animals
seen around Cabo Falso and Cape San Lucas was
of this type with no small young of the year being
noted.

Aggressive Behavior

Gray whale aggression has been the subject of
some controversy. Hand whalers reported ag-
gression toward whale boats from animals har-
pooned in the lagoons (Scammon 1874). Later,
some research workers have had boats damaged in
encounters with whales. Nonetheless, suspicions
existed that these encounters were due to the
thrashings of a very large innocuous beast in

169

FISHERY BULLETIN: VOL. 75, NO. 1

shallow water. Gilmore (1969), for one, reported
no aggression from unprovoked whales during his
work in the calving lagoons. We can lay these
suspicions to rest. Female gray whales separated
from their young are apt, indeed, to be vigorously
aggressive. But like Gilmore, we have never seen
aggression from unprovoked whales. Two exam-
ples from our field notes will suffice.

During capture the female stays in close at-
tendance with the young, often placing herself
between the baby and the shore line party. She
sometimes pressed against the young, literally
yanking the line from line handlers. These
thrashings increased in intensity as the baby
neared the shelf and it is our opinion that the
mother was very dangerous at this time. We have
always taken care to work with the baby 20 m or so
into shallow water where the mother could not
come. She patrolled the shelf edge at this time in
water just deep enough to allow her passage and
she even partially stranded herself. When the
baby was taken into very shallow water or far over
a flat, the mother sometimes wandered away. We
presume this to indicate a loss of effective acoustic
communication.

During one capture a line handler allowed
himself to come within a few meters of the shelf
beyond which the mother patrolled. She reared up,
swung her flukes laterally just at the water's edge,
with sufficient force that a sheet of water was sent
over the entire work party. The blow missed the
nearby line handler by a couple of meters but none
of us doubted that it would have done serious in-
jury if it had hit him.

On another capture, a young animal was
stranded and the scientific party had worked on
harnessing the animal for perhaps 20 min when
the mother wandered away. The collection vessel
had been given the task of keeping the mother
close to the shore party by maneuvering around
her. The ship was standing by 1 km to the south
and about 0.5 km off the channel edge during
stranding and then moved up to within about 100
m of the shore party to herd the mother whale
while we harnessed the calf. The adult disap-
peared below the surface for about 45 s and came
up under the stern of the vessel, hitting the hull so
hard that the vessel was lifted up about a meter
and heeled over 25°-30° to starboard. The whale's
tail swung up in the air astern, with the broadside
of the flukes toward the ship and approximately 2
m of the tail extended above water. The captain
put the ship full speed ahead at about 12 knots and

attempted to elude the whale. The whale followed
below the vessel and three times rose to hit it,
swinging her flukes up above water astern even
though in full chase. The vessel ran in broad cir-
cles and finally swung over fairly shallow water,
and at the same time threw seal bombs into the
water (firecrackers used to disperse sea lions from
fishing nets). The whale moved away at this point,
after a chase of 5 to 7 min. The ship was largely
undamaged except for a slightly bent propeller
blade. The captain felt that the fast maneuvering
prevented serious damage to the vessel.

Phonation

Evidence has been accumulating in recent years
that the gray whale produces a number of different
sound signals, including grunts, pulses, clicks,
moans, bubble-release sounds, knocks, and rasp-
ing pulses. These sound records have been re-
viewed by Poulter (1968) and by Fish et al. (1974),
and the latter workers recorded the sound of the
yearling captive gray whale Gigi. These authors
suggest that the metallic pulses recorded from
Gigi may have been associated with the internal
flow of air bubbles, since no air was released dur-
ing the sound emission. They also reported click
trains released by feeding gray whales, which
consisted of clicks with principal energy from 2 to
6 kHz and duration of 1.0-2.0 ms, with a click
repetition rate of 9.5 to 36.0/s. Similar click trains
have been recorded by us in the channel near
Lopez Mateos. In addition, we can directly attri-
bute two kinds of sounds in whale calves since both
were heard or recorded directly from these ani-
mals as they lay partially out of water; these were
repeated low pulses and a very loud bang or in-
tense click.

Low resonant pulses, which were not recorded,
were emitted by a stranded calf on 27 January
1973 during harnessing. Each was a second or less
in duration, emitted each 2-3 s, and concurrent
with such emission one could see slight movement
of the animal's body surface behind the head on
the lateral body surfaces. No air was released
during emission. This young animal was emitting
pulses when reintroduced to the bay. The mother
had wandered off some 300 m down channel by
this time and as the baby swam across channel,
the mother was seen to throw her flukes twice and
then swim directly toward the distant baby. As
they met, the mother slashed the water rather
violently with her flukes, circled the baby and the

170

NORRIS ET AL.: BEHAVIOR OF CALIFORNIA GRAY WHALE

pair swam off together. Because of the distance
involved at reentry of the calf and the rapid
reunion, we assume acoustic communication was
involved, perhaps the pulses mentioned above.

The sharp clicks were made by two male calves,
on 2 and 5 February 1975, as they lay stranded at
Puerto San Carlos, upper Magdalena Bay. Prior to
click production the blowholes were pursed, giving
the impression the animal was about to blow, but
it did not, and no air was released. Instead it tossed
its head slightly upward causing the slightly
opened jaws to clap closed quickly (movement of
the throat also seemed involved), at which point
the click was produced. These signals were very
intense and could be heard for long distances
underwater; Bartley Gordon, who recorded the
sounds for us, could hear them very clearly at least
500 m from the stranded animal. In each case, as
the calf was released, clicks were heard before the
mother and calf rejoined. Low pulses or grunts
were also recorded from one animal.

In the 5 February release, the mother whale
swam approximately 500 m southwest of the point
at which the young was released. The baby swam
resolutely down channel and the mother was
noted taking up a collision course. Until the
moment of contact sharp clicks were recorded, and
then, as the whales met in a flurry of lunges
partway out of water, the clicks ceased altogether.

These clicks vary from those recorded by Fish et
al. (1974) in that we noted no long trains of closely
spaced clicks, but instead sporadic signals given at
a maximum rate of 2/s, but more often alone. The
signals we recorded seemed to be of much higher
intensity and of much broader band character
than those noted by Fish and his colleagues.
Further, their duration was about 0.25 s as op-
posed to 1-2 ms. In the sound spectrogram shown
in Figure 7, a very intense broad band signal is
portrayed, perhaps of frequency range extending
well above the flat response band of our in-
strumental system (0.1-20 kHz). One wonders if
these clicks bear any relation to the "earth-
quaking" reported by Ray and Schevill (1974).

ACKNOWLEDGMENTS

Work such as this requires many hands and
many minds. We cannot thank everyone who
participated but special thanks are due to our
hardworking and skillful field teams who helped

KHz

3*i

*~ *m*

■*

' J?^ ^

aJQfc^fjC.l

I 23456789 10

Time (ir '/P0 sec)

FIGURE 7. — Intense broad band "clack" emitted by a stranded
gray whale calf at Puerto San Carlos, Baja California Sur,
Mexico, on 5 February 1975. Effective analyzing filter band
width is 45 Hz. Due to the limits of the recording system (about
1-20 kHz flat response) the signal recorded above 20 kHz indi-
cates only some energy in that region, not its amount.

to capture, harness, and track the whales. We
thank Captains Tim Houshar, Robert Newbegin,
Peter Zimmerman, and their crews; Thomas Dohl,
Paul Sebesta, Richard Pierce, Roger Gentry, Jose
Castello, Phyllis Norris, Candace Calloway
Hobbs, Sigmund Rich, Bartley Gordon, Jerry
Kooyman and his associates, and James Knipe
and his associates.

We were helped with many logistical and official
details ashore by Senor S. Serrano of the cannery
at Lopez Mateos, Felix Armas Ortiz, Port Captain
of Puerto San Carlos, and Carlos Martinez
Toscano, ofConasupo, San Carlos, deserve special
mention. Our work would have been very difficult
without their assistance.

Our support for which we are grateful has come
from grants from the Janss Foundation, the
National Aeronautics and Space Administration,
the U.S. Marine Mammal Commission, and the
National Oceanographic and Atmosphere Ad-
ministration, the National Geographic Society,
and by provision of ship support through the
Scripps Institution of Oceanography, La Jolla.

Frank Brocato has helped us with advice and
equipment for capture and handling the calf
whales.

George Rees of the American Embassy, Mexico
City, gave endless help in liaison with the Mexi-
can government.

To all these people and organizations, our
thanks.

171

FISHERY BULLETIN: VOL. 75, NO. 1

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1956. Hunting the heartbeat of a whale. Natl. Geogr.
Mag. 110:49-64.
WYRICK, R. F.

1954. Observations on the movements of the Pacific gray
whale, Eschrichtius glaucus (Cope). J. Mammal.
35:596-598.

172

DISTRIBUTION AND DURATION OF PELAGIC LIFE OF LARVAE

OF DOVER SOLE, M1CR0ST0MUS PACIFICUS; REX SOLE,

GLYPTOCEPHALUS ZACHIRUS; AND PETRALE SOLE,

EOPSETTAJORDANI, IN WATERS OFF OREGON

William G. Pearcy,1 Michael J. Hosie,2 and Sally L. Richardson1

ABSTRACT

Dover and rex sole larvae attain an exceptionally large size and have a long pelagic life. Dover sole
larvae (9-65 mm standard length) were collected in mid-water trawls and plankton nets during all
months of the year. Judging from growth of larvae and occurrence in bottom trawls of recently
metamorphosed juveniles, Dover sole are pelagic during their first year of life. Large larvae (50-65 mm
standard length) are probably pelagic for over a year and few apparently are recruited to benthic
populations. Dover sole larvae were most common in oceanic waters beyond the continental slope and
in the upper 50 m of the water column.

The rex sole larvae captured were 5-89 mm long. Average size and stage of development of larvae
increased from March through February, and juveniles were common on the bottom during winter on
the outer shelf. Thus the pelagic phase usually lasts about a year. Both rex and Dover sole may utilize
the outer continental shelf-upper slope region for a nursery during early benthic life.

Petrale sole larvae (10-22 mm standard length) were rare. They were collected only from March to
June and appear to have a pelagic life of about 6 mo. Age-group Ojuveniles, uncommon in bottom trawl
collections, were only captured on the inner continental shelf in the fall.

Dover sole, Microstomus pacificus; petrale sole,
Eopsetta jordani; and rex sole, Glyptocephalus
zachirus, are commercially important flatfishes of
the northeastern Pacific. They ranked first, third,
and fourth respectively in 1973 Oregon flatfish
landings (Bruneau et al.3). Despite the abundance
of Dover, rex, and petrale sole in bottom trawl
catches, their larvae are not common in plankton
or mid-water trawl collections (Table 1; Ahlstrom
and Moser 1975).

Dover sole apparently spawn in specific sites in
offshore waters deeper than 400 m (Hagerman
1952; Demory4). Rex sole, which do not appear to
have specific spawning sites, spawn between the
100- and 300-m depth contours (Hosie5). Petrale
sole are known to spawn in fairly well-defined
locations in deep water (Ketchen and Forrester
1966; Alderdice and Forrester 1971). The rarity of
Dover and rex sole larvae may be partially due to

'School of Oceanography, Oregon State University, Corvallis,
OR 97331.

2Oregon Department of Fish and Wildlife, Charleston, OR
97420.

3Bruneau, C, J. M. Meehan, and J. Robinson. 1974. Ground-
fish and shrimp investigations. Annu. Rep. 1973, Fish. Comm.
Oreg., 25 p.

"Demory, R. L. 1975. The Dover sole. Oreg. Dep. Fish. Wildl.
Inf. Rep. 75-4, 4 p.

5Hosie, M. J. 1976. The rex sole. Oreg. Dep. Fish. Wildl. Inf.
Rep. 76-2, 5 p.

Manuscript accepted September 1976.
FISHERY BULLETIN: VOL. 75. NO. 1, 1977.

their reproductive strategy of producing relatively
low numbers of large eggs (Table 2). Although
development time to hatching is unknown, it is
probably long for both Dover sole and rex sole.
Petrale sole, on the other hand, produces smaller
eggs in greater numbers; yet petrale larvae are
perplexingly rare (Table 1). The incidence of lar-
val capture of these three species certainly does
not reflect their abundance as adults.

Larvae of two of these pleuronectids are unusual
because they attain a large size. The genera
Microstomus and Glyptocephalus both have giant
larvae. Metamorphosis of Microstomus kitt andM.
pacificus larvae takes place at lengths over 30 mm
(Norman 1934; Hagerman 1952), and M . pacificus
larvae 50 to 60 mm long have been collected ( Table
1; Ahlstrom and Moser 1975). We are not aware of
published reports on the size at metamorphosis of
Glyptocephalus zachirus larvae although
Ahlstrom and Moser (1975) stated that it is not
unusual to collect larvae that are 50 to 60 mm SL.
Metamorphosis in the congeneric G. cynoglossus
and G. stelleri occurs at 40 to 60 mm in length
(Pertseva-Ostroumova 1961; Okiyama 1963).

Because they attain a large size, Dover and rex
sole larvae presumably have long pelagic lives.
Hence they may be susceptible to dispersal and
drift by currents for many months, a factor that

173

FISHERY BULLETIN: VOL. 75, NO. 1

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TABLE 2. — Egg diameter and fecundity of Dover, rex, and petrale

sole.1

Species

Egg diameter

No. eggs/female

Dover sole
Rex sole
Petrale sole

2.04-2.57 mm
1.98-2.34 mm
1.21-1.25 mm

51,900 at 42.5 cm
265,800 at 57.5 cm
34,191 at 36 cm
238,144 at 59 cm
400,000 at 42 cm
1 ,200,000 at 57 cm

1 Data from Hagerman 1 952; Harry 1 959; Alderdice and Forrester 1971; Hart
1 973; Hosie 1 975; Ahlstrom and Moser 1 975; JR. Dunn and N. A. Naplin pers.
commun.

may affect survival and subsequent year-class
strengths of these species which are known to be
variable (Demory and Hosie6).

COLLECTIONS

We examined the catches of 593 bongo net tows
and over 2,200 Isaacs-Kidd Midwater Trawls
taken off Oregon to provide information on the
distribution, dispersal, and length of larval life of
these three species. The bongo nets had 70-cm
mouth diameters with 0.57 1-mm mesh nets. Tows
were made obliquely through the water column
from the bottom or 150 m to the surface at a speed
of 2-3 knots. Two data sets were examined. One set
consisted of 287 samples collected on an east- west
transect off Newport, Oreg., at stations 2, 6, 9, 18,
28, 37, 46, 56, 65, 74, 93, and 111 km from the coast
(Figure 1). Samples were taken every month from
January 1971 to August 1972 except January and
February 1972. The other set consisted of 306
samples collected along 12 transects between the
Columbia River and Cape Blanco, Oreg., with
stations located 2, 9, 18, 28, 37, 46, and 56 km from
the coast. Samples were taken in March and April
1972 and 1973, and March 1974 and 1975. Not all
stations were sampled on each cruise.

Isaacs-Kidd Midwater Trawl collections were
made with trawls having a mouth width of 1.8, 2.4,
and 3.1 m, a 5-mm (bar measure) mesh, and a
0.5-m diameter cod end of 0.571-mm mesh at
stations 28, 46, 84, and 120 km offshore (Figure 1).
Stations from 158 to 306 km offshore (at 37-km
intervals) were sampled less frequently. Tows
were mainly taken along four transect lines
perpendicular to the coast (Figure 1) during

6Demory, R. L., and M. J. Hosie. 1975. Resource surveys on the
continental shelf of Oregon. Fish Comm. Oreg., Annu. Rep. July
1, 1974 to June 30, 1975, 9 p.

174

PEARCY ET AL.: DISTRIBUTION AND DURATION OF PELAGIC LIFE OF LARVAE

1 1 1

1 \ H*.

J DV WASH.

A A A A A A

A A- A V~^C5"=^^

( )astoria' _

46°

A IKMT

I I

• BONGO-IGRiD)

o BONGO ISEASONAL)

^ • »..

» 80NG0 (GRIDS SEASONAL)

• • • • y • •/'"

A A A A A A

) 1

A A/ A ) NFWPORT

o o o • a • » * ooaiPL, wruK '

/ J

1 OREG.

"1 if i

15°

Stage III:

44°

A A A A A A

J ii i

A A 4 Ob

/ £

\ vcape Blanco

43°

Stage Ilia:

\ \i i -ii.i

Stage Illb:

( K\ KILOMETERS

-A A A A A A

1 1 1

o \ ■

^ \BR00KINGS
A A A V~.--

\ V-l CALIF.

42°

128° 127° 126° 125° 124° 123°

FIGURE 1. — Location of sampling stations off Oregon.

1961-69. These tows were generally oblique from
200 m (depth permitting) to the surface at a speed
of 5-6 knots. A series of opening-closing mid-water
trawl collections (Pearcy et al. in press) was also
made 100-150 km off Newport within the upper
1,000 m during 1971-74. Considering all the
collections, all seasons were sampled about
equally.

Benthic fishes were sampled with a 3-m beam
trawl (with 13-mm stretch mesh) on nine cruises
during all seasons over the continental shelf off
central Oregon (115 collections) and with a 5-m
otter trawl on monthly cruises from January 1971
to August 1973, 7 to 11 km off Newport.

LARVAL STAGES

Standard length (SL) of larvae was measured to
the nearest millimeter. Larvae were assigned to
an arbitrary developmental stage depending
primarily on position of the left eye:

Stage I: Larvae symmetrical. Left eye has
not yet begun to migrate.

Stage II: From time left eye has begun to
migrate to time it is on middorsal
ridge of head. The eye is considered

Stage IV:

to be on the middorsal ridge when a
line extended forward from the
dorsal fin transects any part of the
eyeball for Dover and petrale sole,
or when such a line transects the
middle of the eyeball and the
eyeball itself is directed upward for
rex sole.

Left eye is on middorsal ridge as
defined under Stage II. For Dover
sole, this stage was divided into two
parts on the basis of pigment
pattern, which appeared to corre-
late reasonably well with eye
migration.

Five or six dorsal and four or five
ventral horizontally elongated
streaks of pigment along the cen-
tral body musculature.
Dorsal and ventral pigmentation
streaks along the central body
musculature joined to form con-
tinuous lines.

Left eye fully on the right side of
head, so that a line extended for-
ward from the dorsal fin does not
transect any part of the eyeball.

In Dover sole, the left eye begins to migrate as
notochord flexion begins, and the caudal fin is
completely formed by the time the eye reaches the
middorsal ridge.7 In rex sole, however, the caudal
fin forms completely while the eyes remain
symmetrical. Limited evidence suggests petrale
may be like Dover sole in this respect.

GROWTH AND DEVELOPMENT

The number and length of larvae assigned to
developmental stages (Table 3) shows that each
stage often included a wide range of sizes. Most of
the Dover sole captured were stage I in bongo nets,
and metamorphosing stage Ilia larvae in mid-
water trawls. Only a few larvae 30-40 mm SL were
captured, resulting in a bimodal size-frequency
distribution. This may be a sampling artifact due
to the unavailability of intermediate-sized larvae
to our sampling methods, or it may be caused by
rapid growth between stages Ilia and Illb. A

7 We found one abnormal Dover sole larva, a 43-mm SL tailless
fish collected 125 miles off Newport, Oreg., in February 1964.
This lack of caudal fin condition has also been reported for post-
metamorphosed Dover sole (Demory 1972a).

175

FISHERY BULLETIN: VOL. 75, NO. 1

TABLE 3. — The number and lengths of Microstomas pacificus, Glyptocephalus zachirus, and Eop-
setta jordani larvae in assigned developmental stages, I to IV. Numbers in parentheses denote
catches in bongo nets, excluding grid tows; numbers without parentheses are mid-water trawl
catches.

Standard
length

(mm)

M. pacificus

G zachirus

E. jordani

Ilia

1Mb

4-5
6-7
8-9
10-11
12-13
14-15
16-17
18-19
20-21
22-23
24-25
26-27
28-29
30-31
32-33
34-35
36-37
38-39
40-41
42-43
44-45
46-47
48-49
50-51
52-53
54-55
56-57
58-59
60-61
62-63
64-65
66-67
68-69
70-71
72-73
74-75
89

Totals

(7)
(38)

(10) 2

(4) 13(2)

10(6)

8(4)

2(1)

6
20

55(1)
90
72

79(1)
45
25

16(1)
11

4
6
11
12
5
5
3
4

(5)

(28)
(41)
(5)
(2)
(2)
(4)
(1)
(1)

(2)
(2)

(2)

(3)

8 (1)

7 (1)
9

13 (1)

14 (1)

8 (1)
7
6
4
6
7
3
1
3
2

12
12

8(1)

(59) 36(13)431(13) 48

4
6

5 1 1

10 3

9 5

3(1) 2 5

5 1 3

10 1 3

7 2

1 (1
2 1

4
2

1
131(104)93(3) 12 20

34(1) 1

progression of increasing size with later de-
velopmental stages is apparent from stages I
through Ilia, but little growth in length is evident
between stage Hlb and IV. Larvae over 40-50 mm
SL included both partially metamorphosed indi-
viduals with the left eye on the dorsal ridge
and little pigmentation on the right side, and fully
transformed individuals with heavy pigmenta-
tion on the eyed side. The largest larva was a
partially metamorphosed individual of 65 mm.

Most rex sole larvae were classified as pre-
metamorphosed stage I. This stage included a
surprising length range, from 4 to 69 mm. Most of
the growth in length apparently occurs during
stage I before the left eye begins to migrate. The
median length of stage IV larvae was actually
shorter than that of stage II or III, suggesting
reduction in length during metamorphosis. The
largest larva was 89 mm (see Richardson 1973),
apparently a record for any species of Glyp-
tocephalus.

Petrale larvae occupied a small length range
compared with Dover and rex sole larvae. Most of
the larvae were stage III. Larvae smaller than 10
mm were never taken.

SEASONALITY, GROWTH, AND
LENGTH OF LARVAL LIFE

The relative abundance of the stages of Dover
sole larvae collected during different months in
bongo nets and mid-water trawls is illustrated in
Figure 2. Stage I larvae were the predominant
stage in the bongo net catches from March to July;
stage II larvae were most common during the
summer (bongos) and fall (mid-water trawls),
suggesting a progression of larval stages from
spring to fall. The continuation of this trend is not
apparent from the catches of stage Ilia larvae, the
most abundant developmental stage during all
months in mid-water trawl catches. Stage IV were
most common during fall and winter months.

176

PEARCY ET AL.: DISTRIBUTION AND DURATION OF PELAGIC LIFE OF LARVAE

BONGOS

IOOi-
50-

100

0
100

n r

Mil.

i r

"i 1

-i 1 r

i i r

IHa

I-
co

x
<

L_
O

Ld
0_

i
M

I
A

"T"

n = 0 0 7 9 29 29 2 I 000 0

100

MID-WATER TRAWL

JFMAMJJAS0ND
n= 30 48 19 17 15 68 204 36 35 13 39 46

FIGURE 2.— The relative abundance of each stage of Dover sole
larvae in bongo transect and mid-water trawl collections during
all months.

Dover sole are known to spawn off Oregon
primarily in winter, November through March
(Hagerman 1952; Harry 1959), when stage III and
IV larvae were present. It appears that Dover sole
larvae are pelagic for at least a year. The large
proportion of stage Ilia larvae during all months is
puzzling, since relatively few of this stage would
be expected during the winter and early spring if
the larval period lasts a year or less.

Interpretation of growth and length of larval life
is facilitated by the length-frequency data in
Table 4. A trend for increasing average size of
larvae is evident from April of one year to March of
the next year for larvae <30 mm SL. This suggests
growth only to at least 20-30 mm during the first
year of life, and a pelagic life that lasts at least a
year. No growth trends are apparent for large
larvae, which were present all months of the year.
Our interpretation of these data is that larvae
begin to settle out at 30-50 mm and metamorphose
after about 1 yr. Juvenile Dover sole of 40 mm
have been captured in bottom trawls in February
off Oregon. Possibly few 30- to 40-mm larvae were
available to our gear because they were close to
the sea floor. Larger larvae (>50 mm) may then
represent a residual pelagic population that has
not had an opportunity to begin benthic life,
perhaps because they resided in water too deep
during the period of settlement of most larvae.
Information on the size and seasonal occurrence of
juvenile Dover sole on the bottom, discussed in a
later section, supports these contentions. Such an
extended period of pelagic life after 1 yr suggests
that Dover sole larvae may delay metamorphosis
and settlement to the bottom if favorable condi-
tions are not present, a phenomenon known for
some benthic invertebrate larvae (Wilson 1968)
but to our knowledge not for any fishes.

Mearns and Gammon8 also reported Dover sole
larvae year-around in waters off southern
California with peak numbers in July. They
showed a distinct growth trend from about 5-9 mm
SL in April to 35-50 mm in October, suggesting
that larvae may attain a size of 50 mm or larger
during the first year of life. Ahlstrom and Moser
(1975) collected Dover sole larvae chiefly during
April through July off California.

The trends for rex sole are more readily in-
terpretable than those for Dover sole. Rex sole
were also captured in every month, but a progres-
sion of stages was obvious through the year (Fig-
ure 3). All larvae collected in March, April, and
May were stage I, and all were stage IV by the
following February. Since rex sole spawn off Ore-
gon from January to June (Hosie 1975), pelagic
life apparently lasts about a year. The presence of
stage IV larvae in November and December and

8Mearns, A. J., and R. Gammon. A preliminary note on multi-
ple recruitment of Dover sole populations {Microstomas pacif-
icus) off Southern California. Unpubl. manuscr., 7 p. Southern
California Coastal Water Research Project, 1500 East Imperial
Highway, El Segundo, CA 90245.

177

FISHERY BULLETIN: VOL. 75, NO. 1

TABLE 4. — Length-frequency distributions of Microstomas pacificus larvae collected during vari-
ous months. Numbers in parentheses denote larvae caught in bongo nets; numbers without
parentheses denote larvae caught in mid-water trawls.

Standard
length
(mm)

Apr.

May

June

July

Aug.

Sept.

Oct.

Nov.

Dec.

Jan.

Feb.

Mar.

4-5

(2)

(3)

6-7

(7)

(23

(5)

(3)

8-9

(3)

(7)

10-11

10(4)

6(1)

12-13

9(6)

14-15

15(4)

33(1)

16-17

4(1)

18-19

20-21

1(1)

22-23

24-25

26-27

4(1)

28-29

30-31

32-33

34-35

36-37

38-39

40-41

42-43

44-45

46-47

48-49

50-51

52-53

54-55

56-57

58-59

60-61

62-63

their absence in the spring suggest that some
larvae may settle out in less than a year. Con-
versely, the presence of large larvae (>50 mm)
during June, shortly after the end of spawning
season (Table 5), suggests that some larvae may be
pelagic for over a year, like some Dover sole lar-
vae. Powles and Kohler (1970) believed that G.
cynoglossus larvae in the North Atlantic are also
pelagic for the first year of life.

Petrale sole larvae were only found during 4
mo, March-June (Figure 4). No distinct progres-
sion of stages was apparent, though stage I lar-
vae were only collected in March and April and
stage IV only in June. Petrale sole spawn in winter
and early spring, November to April in the
northeastern Pacific (Harry 1959; Porter 1964;
Alderdice and Forrester 1971), so our limited data
indicate an egg and larval period of about 6 mo.

INSHORE-OFFSHORE AND
NORTH-SOUTH DISTRIBUTION

Both Dover and rex sole larvae were widely
distributed offshore. All three species of flounders
are considered to have "offshore" larvae by
Richardson and Pearcy (1977).

Bongo nets collected Dover sole larvae at all but

the 6-km station (Table 6), although the larvae
were most frequent and abundant at the offshore
stations (56-111 km), where 84.8% of all larvae
were taken. Peak abundance occurred at the
111-km station. Rex sole were taken at all stations
but were more abundant offshore (46-111 km)
where 80.5% of all larvae occurred. Peak
abundance was at 46 km. One specimen of petrale
sole was taken 56 km offshore.

Largest mid-water trawl catches of Dover sole
larvae were usually made in oceanic waters more
than 46 km offshore along all four station lines
(Table 7). Some larvae were taken as far as 550 km
offshore. Rex sole larvae were most common at the
28- to 83-km stations over the outer shelf and
slope, but were also captured farther offshore. The
farthest offshore a rex sole larva was collected was
195 km. Petrale sole larvae were collected from 2
to 120 km from the coast. About half the petrale
larvae were caught 83-120 km offshore.

Lengths of larvae at varying distances from the
coast provide clues to inshore-offshore dispersal.
In the bongo net transect data, Dover sole larvae
< 11 mm were collected at all stations except 6 km,
but the greatest numbers of small larvae were at
the 93- and 111-km stations. Larger larvae (11-26
mm) occurred only at stations 56 to 111 km

178

PEARCY ET AL.: DISTRIBUTION AND DURATION OF PELAGIC LIFE OF LARVAE

M
9

UJ
CD

O IOOi— I

Eumt

i T i — r-

i — i — i — i — n — i

A M J J
12 59 25 I

A
2

"i 1 1 r

0 N D J
0 0 0 0

MID-WATER TRAWL

h- °

lj 100

uj 50

100

0
100

JUul

i — i

fl f

"i 1

50-

"i — r

i r

Oil

MAMJJAS0NDJF
n = 0 5 19 50 67 51 18 16 5 8 12 5

FIGURE 3. — The relative abundance of each stage of rex sole
larvae in bongo transect and mid-water trawl collections during
all months.

offshore. Similarly, rex sole larvae <11 mm were
taken at all stations but greatest numbers oc-
curred at the 46-km station. All but 2 of the 29 rex
sole larvae 2=11 mm (11-67 mm) were taken at
stations 37 to 111 km offshore. These trends
suggest that larvae >11 mm of both species are
most common in waters beyond the continental
shelf In the bongo net grid samples, Dover and rex
sole larvae, which were mostly smaller than 10
mm SL, were widely distributed. They were taken
at all distances 2 to 56 km from the coast, but
always in low numbers. Mean numbers per 10 m2
sea surface were less than 0.30 for Dover sole lar-
vae and 0.70 for rex sole larvae.

100

<s>

IOO

1—

u_
o

100

i r

ail

1
F

1
M

1
A

-r-T-

M J

1
A

1
S

l
0

n = 0

20 II

FIGURE 4. — The relative abundance of each stage of petrale sole
larvae in bongo transect and mid-water trawl collections during
all months.

No obvious trend of increasing mean size of
large Dover or rex sole larvae with distance
offshore was apparent from mid-water trawl
collections. However, the eight rex sole larvae <30
mm SL in mid-water trawl collections were all
captured between 9 and 83 km offshore.

In mid-water trawl samples, the ratio of Dover
larvae =£30 mm to those larvae >30 mm during
the summer (May-September) was 15:1 and 6:1 at
stations inshore and offshore of 83 km, respec-
tively. This indicates a preponderance of "small-
er" larvae over the shelf and slope, probably a re-
sult of spawning the previous winter. During
winter (October-April) these ratios were 1:2
inshore and 2:1 offshore of 83 km, reflecting a
greater proportion of large larvae during the win-
ter especially over the shelf and slope where they
will settle.

North-south trends were not as obvious. In the
bongo grid samples, Dover sole larvae were taken
on 9 of the 12 lines with the mean number
per 10 m2 on each line always less than 0.26. Rex
sole larvae were taken on all 12 lines. Mean
number per 10 m2 on each line ranged from 0.24 to
1.26 with the greatest numbers occurring over
Heceta Bank. One petrale sole larva was taken 37
km offshore just north of Cape Blanco. In the
mid-water trawl samples the mean catch per tow
of Dover sole was about the same along the three
northern station lines, and was about twice as

179

FISHERY BULLETIN: VOL. 75, NO. 1

TABLE 5. — Length-frequency distributions of Glyptocephalus zachirus larvae collected during
various months. Numbers in parentheses denote larvae caught in bongo nets; numbers without
parentheses denote larvae caught in mid-water trawls.

Standard

Length

(mm)

Apr

May

June

July

Aug.

Sept.

Oct.

Nov.

Dec.

Jan.

Feb. Mar

4-5

(4)

6-7

(3)

(20)

(2)

(3)

8-9

(6)

(28)

(3)

(5)

10-11

(1)

(2)

(1)

12-13

(2)

14-15

16-17

(1)

(2)

18-19

1(1)

20-21

1(1)

22-23

24-25

2(2)

26-27

1(2)

28-29

30-31

2(2)

32-33

2(1)

34-35

1(1)

36-37

38-39

1(1)

40-41

5(1)

42-43

2(1)

44-45

(3)

2(1)

46-47

48-49

1(1)

50-51

52-53

54-55

3(1)

56-57

58-59

60-61

62-63

64-65

66-67

1(1)

68-69

70-71

72-73

74-75

TABLE 6. — Catches of Dover sole and rex sole larvae from bongo net collections taken on the transect off Newport,
Oreg., from January 1971 to August 1972. Numbers of larvae in each sample were standardized to number under 10
m2 sea surface.

Item

Station
28

(kilometers from <
37 46

:oast)

111

No. tows

Frequency of Dover
Mean no. Dover/10 m2

0.07

0
0

2
0.09

1
0.03

0.11

1
0.08

0.16

3
0.34

2
0.51

4
0.38

0.95

7
1.75

Frequency of rex
Mean no. rex/10 m2

2
0.03

0 05

4
0.23

4
0 15

3
0.21

3
0.25

2 27

4
0.69

3
0.52

5
0.55

3
0.32

3
0.51

TABLE 7. — Catches of Dover sole and rex sole larvae at various distances from shore. The data
are from mid-water trawl collections taken during all seasons of the year, 1961-67, along four
transect lines (Figure 1).

Distance offshore (kilometers)

Item

120

158-306

Columbia River:

No. tows

No. Dover (no/tow)

1(0.50)

3(0.20)

4(0.22)

2(0.12)

3(0.25)

5(0.55)

No. rex (no./tow)

0(0)

1(0.07)

3(0.17)

1(0.06)

0(0)

1(0.11)

Newport:

No. tows

No. Dover (no./tow)

0(0)

1 (0.02)

3(0.05)

11(0.18)

40(0.64)

17(0.31)

No. rex (no./tow)

0(0)

11(0.21)

24(0.42)

32(0.52)

9(0.14)

8(0.15)

Coos Bay:

No. tows

No. Dover (no./tow)

2(0.13)

6(0.40)

6(0.42)

1(0.17)

4(0.27)

No. rex (no./tow)

7(0.47)

4(0.27)

7(0.50)

0(0)

1(0.07)

Brookings:

No. tows

No. Dover (no./tow)

0(0)

10(0.83)

2(0.25)

22(059)

No. rex (no./tow)

3(0 43)

6(0 75)

9(0.75)

5(0.42)

2(0.25)

7(0.19)

180

PEARCY ET AL.: DISTRIBUTION AND DURATION OF PELAGIC LIFE OF LARVAE

high off Brookings, Oreg. Mean abundance of rex
sole larvae was lowest off the Columbia River
(Table 7).

Certainly the distribution of these larvae is
related to both alongshore and inshore-offshore
currents over the continental shelf and slope as
well as to spawning location of adults. The
predominant flow throughout the year off Oregon
is alongshore, yet current reversals occur ( south in
summer, north in winter) and subsurface counter-
currents are present (Huyer et al. 1975). There is
additional transport of surface waters offshore in
summer, and inshore in winter (Wyatt et al. 1972).
Perhaps these interacting current systems serve
to maintain the majority of these larvae within
areas favorable for settling, even though they
have extended pelagic lives and the continental
margin off Oregon is narrow.

VERTICAL DISTRIBUTION

Information was obtained on vertical distribu-
tion of Dover sole larvae from a series of opening-
closing mid-water trawl collections from the upper
1,000 m, 120 km off Newport. There, water depth
was about 2,800 m. All but two larvae were found
in the upper 600 m, revealing that this species
may occupy a broad depth range (Table 8), nearly
as extensive as the bathymetric range of adult
Dover sole (Alton 1972). Larvae were most
abundant (196 larvae/105 m3) in the upper 50 rh.
Convincing evidence for diel vertical migration
was absent, although the vertical distribution of
larvae during the July 1971 cruise appeared to be
shallower by night than by day. Rae (1953)
concluded that Microstomas kitt larvae exhibited
diel vertical migration of 10-20 m into near-

TABLE 8. — Average catches (number/105 m3 water filtered) of
Microstomas pacificus larvae in an opening-closing mid-water
trawl during one cruise in July 1971 and five cruises July 1971-
September 1974, 120 km off the central Oregon coast; water
depth was 2,800 m. D = day, N = night.

Total

numbers

No. per

105 m3

Depth

July 1971

1971

-74

July

1971

1971-74

(m)

0-50

188

196

50-100

127

100-150

156

150-200

200-300

300-400

400-500

500-600

600-700

700-800

800-900

900-1 ,000

surface waters at night. Such a shallow migration
would not be detectable from our samples.

BENTHIC JUVENILES

The season and depth of occurrence of the
smallest benthic juveniles are important indi-
cators of the lengths of the pelagic phase of these
fishes. Hagerman (1952) reported that young
Dover sole become demersal between 50 and 55
mm total length (TL). Mearns and Gammon (see
footnote 8) caught juvenile Dover sole of 45-75 mm
SL during both mid-autumn and early spring off
southern California, suggesting two major periods
of recruitment. Demory (1971, see footnote 4, and
pers. commun.) caught the largest numbers of
small juvenile Dover sole (40-70 mm TL) in
February in bottom trawls between 130 and 183 m
depth off northern Oregon. According to Demory,
these fish, which were 1 yr of age, subsequently
move into shallow water in the summer. Though
not common, we have taken Dover sole of 40-50
mm SL in the winter in beam trawl collections on
the outer shelf off central Oregon. These results
indicate that Dover sole off Oregon usually
complete metamorphosis and take up a benthic
life on the outer continental shelf after about 1 yr,
when they are less than 50 mm long. Larger larvae
are probably older than a year and have delayed
complete transformation to the benthic juvenile
form. These large, "holdover" larvae may con-
tribute little to the juvenile and subsequent adult
age-groups, based on Demory's (1972b for
methods, pers. commun.) observation of two cir-
culi patterns in the scales of small juvenile Dover
sole. These were: a dominant pattern with 6-9
circuli, and another rarer pattern with 20 or more
circuli. Thus fish with the larger number of circuli
probably represent our large larvae, which be-
come benthic well after 1 yr.

Juvenile rex sole, 40-60 mm SL, were common
in our beam trawl collections on the outer edge of
the continental shelf ( 150-200 m depth) during the
winter months off central Oregon. We also col-
lected 22 G. zachirus larvae of 46-60 mm TL (stage
III) in an otter trawl at 230-260 m depth off Coos
Bay, Oreg., in September. We do not know if these
rex sole larvae were benthonic before meta-
morphosis was completed or if they were living
pelagically when caught by the trawl. From these
data, we surmise that rex sole settle to the bottom
mainly on the outer continental shelf during the
winter when they are about 1 yr old. It is possible

181

FISHERY BULLETIN: VOL. 75, NO. 1

that they use this area as a nursery during early
benthic life as has been suggested for G. cyno-
glossus on the east coast (Powles and Kohler 1970;
Markle 1975). Rex sole smaller than and larger
than 180 mm TL have broadly overlapping depth
ranges off Oregon (Demory 1971), unlike G.
cynoglossus which occupies distinct depth zones as
juveniles and adults (Powles and Kohler 1970).

Juvenile E. jordani were uncommon in bottom
trawls. Only two small individuals (65 and 83 mm
SL) were found in 115 beam trawl collections. We
found only 28 small petrale sole (62-107 mm TL),
collected in October and November at 64-82 m
depth, from extensive otter trawl collections off
Newport in 1972. Examination of otoliths indi-
cated these petrale sole were all in their first year
of growth. This suggests that metamorphosis of
this species occurs during the fall of their first year
when they settle to the bottom of the inner con-
tinental shelf off Oregon. Our findings are cor-
roborated by those of other researchers. In British
Columbia waters, Ketchen and Forrester (1966)
found a few 0-age petrale sole only at depths of
18-90 m between May and August. From exten-
sive otter trawl collections off northern California
Gregory and Jow (1976) reported 17 petrale sole
(60-100 mm TL) in September and October be-
tween 28 and 73 m.

ACKNOWLEDGMENTS

We thank R. L. Demory who reviewed the
manuscript and provided important information
on the early life of Dover sole, E. M. Burreson who
conducted the otter trawl sampling off Newport,
and N. A. Naplin and J. R. Dunn for data on
diameters of rex sole eggs. This research was
sponsored by NOAA Office of Sea Grant, No. 04-
5-158-2.

LITERATURE CITED

AHLSTOM, E. H., AND H. G. MOSER.

1975. Distributional atlas of fish larvae in the California
Current region: Flatfishes, 1955 through 1960. Calif.
Coop. Fish. Invest., Atlas 23, 207 p.

Alderdice, d. f., and C. R. Forrester.

1971. Effects of salinity and temperature on embryonic
development of the petrale sole (Eopsetta jordani). J.
Fish. Res. Board Can. 28:727-744.

ALTON, M. S.

1972. Characteristics of the demersal fish fauna inhabit-
ing the outer continental shelf and slope off the northern
Oregon coast. In A. T. Pruter and D. L. Alverson
(editors), The Columbia River estuary and adjacent ocean
waters, p. 583-634. Univ. Wash. Press, Seattle.

DEMORY, R. L.

1971. Depth distribution of some small flatfishes off the

northern Oregon-southern Washington coast. Fish.

Comm. Oreg. Res. Rep. 3:44-48.
1972a. Tailless Dover sole from off the Oregon

coast. Calif. Fish Game 58:147-148.
1972b. Scales as a means of aging Dover sole (Microstomus

pacificus). J. Fish. Res. Board Can. 29:1647-1650.

Gregory, p. a., and T. Jow.

1976. The validity of otoliths as indicators of age of petrale
sole from California. Calif. Fish Game 62:132-140.
HAGERMAN, F. B.

1952. The biology of the Dover sole, Microstomus pacificus
(Lockington). Calif. Dep. Fish Game, Fish Bull. 85, 48 p.
HARRY, G. Y., JR.

1959. Time of spawning, length at maturity, and fecundity
of the English, petrale, and dover soles (Parophrys vet-
ulus, Eopsetta jordani, and Microstomus pacificus, re-
spectively). Fish Comm. Oreg., Res. Briefs 7(1):5-13.

Hart, J. L.

1973. Pacific fishes of Canada. Fish Res. Board Can.,
Bull. 180, 740 p.
HOSIE, M. J.

1975. Biology of the rex sole, Glyptocephalus zachirus
Lockington, in waters off Oregon. M.S. Thesis. Oregon
State Univ., Corvallis, 43 p.
HUYER, A. R., R. D. PILLSBURY, AND R. L. SMITH.

1975. Seasonal variation of the alongshore velocity field
over the continental shelf off Oregon. Limnol. Oceanogr.
20:90-95.
KETCHEN, K. S., AND C. R. FORRESTER.

1966. Population dynamics of the petrale sole, Eopsetta
jordani, in waters off western Canada. Fish. Res. Board
Can., Bull. 153, 195 p.
MARKLE, D. F.

1975. Young witch flounder, Glyptocephalus cynoglossus,
on the slope off Virginia. J. Fish. Res. Board Can.
32:1447-1450.
NORMAN, J. R.

1934. A systematic monograph of the flatfishes
(Heterosomata). Vol. I. Psettodidae, Bothidae,
Pleuronectidae. Br. Mus. Nat. Hist., 459 p.
OKIYAMA, M.

1963. Larvae and young of the witch flounder, Glyp-
tocephalus stelleri (Schmidt) at metamorphosis
stages. Bull. Jap. Sea Reg. Fish. Lab. 11:101-108.

PEARCY, W. G., E. KRYGIER, R. MESECAR, AND F. RAMSEY.
In press. Vertical distribution and migration of oceanic
micronekton off Oregon. Deep-Sea Res.
PERTSEVA-OSTROUMOVA, T. A.

1961. The reproduction and development of far eastern
flounders. Izd. Akad. Nauk SSSR, Mosk. 483 p. (Trans-
lated from Russ.). Fish. Res. Board Can. Transl. 856,
1003 p.
PORTER, P.

1964. Notes on fecundity spawning, and early life history
of Petrale sole (Eopsetta jordani), with descriptions of
flatfish larvae collected in the Pacific Ocean off Humboldt
Bay, California. M.S. Thesis, Humboldt State Coll.,
Areata, Calif. 98 p.

POWLES, P. M., AND A. C. KOHLER.

1970. Depth distributions of various stages of witch
flounder (Glyptocephalus cynoglossus) off Nova Scotia and
in the Gulf of St. Lawrence. J. Fish. Res. Board Can.
27:2053-2062.

182

PEARCY ET AL.: DISTRIBUTION AND DURATION OF PELAGIC LIFE OF LARVAE

RAE, B. B.

1953. The occurrence of lemon sole larvae in the Scottish
plankton collections of 1929, 1930, and 1931. Scott.
Home Dep. Mar. Res. 1953(1), 36 p.
RICHARDSON, S. L.

1977. Coastal and oceanic fish larvae in an area of up-
welling off Yaquina Bay, Oregon. Fish. Bull., U.S.
75:125-145.

WALDRON, K. D.

1972. Fish larvae collected from the northeastern Pacific
Ocean and Puget Sound during April and May
1967. U.S. Dep. Commer., NOAA Tech. Rep. NMFS
SSRF-663, 16 p.

WILSON, D. P.

1968. Some aspects of the development of eggs and larvae
of Sabellaria aleveolata (L.). J. Mar. Biol. Assoc. U.K.
48:367-386.

WYATT, B., W. V. BURT, AND J. G. PATTULLO.

1972. Surface currents off Oregon as determined from drift
bottle returns. J. Phys. Oceanogr. 2:286-293.

183

SELECTIVITY OF GILL NETS ON ESTUARINE AND
COASTAL FISHES FROM ST. ANDREW BAY, FLORIDA

Lee Trent and Paul J. Pristas1

ABSTRACT

Eleven gill nets, each of a different mesh size, were fished 126 days from 4 April to 29 December 1973 in
St. Andrew Bay, Fla. Of the estuarine and coastal fishes that were caught, 22 were in numbers
sufficient to evaluate the relation between length offish and mesh size. Mean length increased with an
increase in mesh size for 20 species. Ten species — gulf menhaden, Brevoortia patronus; spot, Leios-
tomus xanthurus; sea catfish, Arius felis; pinfish, Lagodon rhomboides; Atlantic croaker, Micropogon
undulatus; blue runner, Caranx crysos; pigfish, Orthopristis chrysoptera; bluefish, Pomatomus sal-
tatrix; Spanish mackerel, Scomberomorus maculatus; yellowfin menhaden, B. smithi — were caught in
sufficient numbers to apply and evaluate the normal probability model to define gill net selectivity.
One or more of the three assumptions — normality of selectivity curve, linearity of mean length-mesh
size relation, and constancy of standard deviation between mesh sizes — inherent in the model was
violated by the data for each species to which the model was applied except Atlantic croaker and blue
runner. Useful information was provided, however, in relation to evaluating mesh-size regulations and
for determining mesh sizes for increasing capture efficiencies in gill net fisheries.

Rarely will a particular type of fishing gear cap-
ture all sizes of a species of fish with equal prob-
ability. Gill nets are selective in that, for a par-
ticular species and mesh size, fish are retained
with high probability at certain lengths and with
decreasing probability for larger and smaller
individuals. Most streamlined fish without pro-
jecting spines, teeth, or opercular bones are caught
in gill nets by becoming tightly wedged or en-
meshed in the webbing. To describe selectivity for
these streamlined fishes, a smooth unimodal curve
with capture probabilities descending to zero is
suggested by several workers (Regier and Robson
1966). Fish species that are not streamlined, or
that have stiff projecting appendages or spines,
are frequently caught entangled in the webbing
rather than, or in addition to, becoming wedged in
the meshes. For these species skewed or multi-
modal curves are usually necessary to describe
capture probabilities (Hamley and Regier 1973).
An understanding of the selection properties of
gill nets is necessary to evaluate catch statistics,
alter catch per unit effort, and regulate the sizes of
caught fish. Most methods of estimating re-
cruitment, growth, sex ratio, and survival of a fish
species require samples that are representative of
the population in respect to size of individuals.

'Southeast Fisheries Center Panama City Laboratory, Na-
tional Marine Fisheries Service, NOAA, P.O. Box 4218, Panama
City, FL 32401.

Only if size selectivity of the fishing gear is known
can the catch statistics be adjusted and used to
provide correct estimates of the parameters of
interest (Cucin and Regier 1966). Alternatively,
an understanding of how selectivity depends on
the characteristics of the gear may be used to de-
sign a series of gear to yield samples of known
characteristics over a specified size range (Regier
and Robson 1966). A knowledge of the size selec-
tive properties of the gear permits recommen-
dations of mesh sizes to maximize (increase cap-
ture efficiency) or minimize (protect from harvest)
the catch on certain sizes and species.

Published information is not available on the
lengths of fish caught in particular mesh sizes of
gill nets for estuarine and coastal fishes inhabit-
ing the Gulf of Mexico except for a meager amount
on two species. Klima (1959) reported length-
frequency distributions of Spanish mackerel,
Scomberomorus maculatus, that were caught in
7.9- and 9.0-cm stretched-mesh gill nets. Modal
lengths of those were 37 and 43 cm, respectively.
Tabb (1960) reported a length-frequency dis-
tribution of spotted seatrout, Cynoscion
nebulosus, that were caught in 8.0-cm stretched-
mesh gill nets. Modal length of the distribution
was 33.5 cm.

Mesh sizes of gill nets most frequently used to
capture various species of fish in the commercial
gill net fishery in Florida were reported by
Siebenaler (1955).

Manuscript accepted August 1976.
FISHERY BULLETIN: VOL. 75, NO. 1, 1977.

185

FISHERY BULLETIN: VOL. 75, NO. 1

The objectives of this study for each species
caught in sufficient abundance were: 1) to show
the relations between mesh size and the mean
length and standard deviation in length offish, 2)
to define gill net selectivity by applying the nor-
mal probability model, 3) to evaluate the applica-
bility of this model for defining selectivity, and 4)
to discuss uses of the derived information.

STUDY AREA

The study area was in the St. Andrew Bay sys-
tem located in northwest Florida along the Gulf of
Mexico. This bay system, compared to most other
northern gulf estuarine systems, is deep, has high
salinities, low freshwater inflows, large areas of
submerged marine grasses, low turbidities, high
percentages of sand in the substrate, and has fish
and crustacean faunas typical of both coastal and
estuarine areas (Ichiye and Jones 1961; Hopkins
1966; Brusher and Ogren 1976; May et al. 1976;
and Pristas and Trent 1977). The diurnal range of
the tide in the St. Andrew Bay system is about
0.5 m.

ASSUMPTIONS

The relation between the mesh size of gill nets
and the size of captured fish can be determined by
setting a series of gill nets that vary only in respect
to mesh size if certain precautions are taken and
certain assumptions are valid. Fishing effort must
be equal among mesh sizes, i.e., assume all fish of a
given length are equally likely to encounter all
nets. This means damage to each net must remain
low or about equal among mesh sizes, and net
locations are equal in respect to the probability of
a net catching a particular fish. We must assume
that no "gear saturation" occurs, i.e., the number
of fish already entangled in the net in no way
influences subsequent behavior of other fish and
the net, and that no "spill-over" occurs, i.e., large
fish do not lead along the nets until they encounter
a large enough mesh in which perhaps to become
enmeshed or entangled (Regier and Robson 1966).
We must further assume that loss offish from the
nets through predation is not dependent on mesh
size or the size of fish.

GEAR AND METHODS

Eleven gill nets, each of a different mesh size,
were fished for 126 days from 4 April to 29 De-
cember 1973 at a location about 400-1,000 m

northwest of Courtney Point in St. Andrew Bay.
From 4 April through 20 September, the nets were
set every 14th day and fished for 72 consecutive
hours. From 20 September, the nets were fished
continuously until 13 December. The nets were set
again on 26 December and fished for 72 h. Nets
were anchored about 50 m apart parallel to each
other, perpendicular to shore, and in water depths
of 2.2 to 2.6 m (mean low tide). Nets were ran-
domized among net location each time the nets
were set. During the continuous fishing in the
autumn, the nets were randomized among lo-
cations twice during each 2-wk period. Net dam-
age to each net was maintained below 10% of the
total surface area.

Increments of mesh sizes in the series of fished
nets were small, so that widely overlapping ranges
offish lengths would result. Mesh sizes used in this
study were chosen to catch the more abundant
species frequenting the St. Andrew Bay area
(Pristas and Trent 1977). Stretched-mesh sizes
ranged from 6.35 cm (2.5 inches) to 12.70 cm (5.0
inches) in 0.63-cm (0.25-inch) increments.

The nets were 33.3 m long and 3.3 m deep. They
were made of #208 clear monofilament (0.33 mm
diameter, filament break strength about 26.4 kg)
nylon webbing. The webbing was hung to the float
and leadlines on the half basis (two lengths of
stretched webbing to one length of float or lead-
line, i.e., a hanging coefficient of 0.5).

Fish were removed from the nets between 1 h
before and 2 h after sunrise and occasionally
between sunset and 1 h after. The total numbers of
each species, including damaged specimens, were
counted. Lengths of undamaged specimens were
measured to the nearest 0.5 cm. Fork length (tip of
snout to fork of tail) was measured for those fishes
having forked tails and total length (tip of snout
horizontally to extremity of the caudal fin) was
measured for Atlantic croaker, Micropogon
undulatus, and sharks.

Length-frequency distributions of the catch by
species and mesh size, based on the number offish
that were measured, were adjusted to represent
the number of fish that were caught (those mea-
sured plus those damaged), so that the number
making up each distribution represented catch per
unit effort for each net.

MODEL FOR
DETERMINING SELECTIVITY

Basic mathematical models, or modifications of

186

TRENT and PRISTAS: SELECTIVITY OF GILL NETS

basic models, for describing selectivity of gill nets
were proposed by Baranov (as described by
McCombie and Fry 1960), Olsen (1959), McCom-
bie and Fry (1960), Gulland and Harding (1961),
Ishida (1962), Holt (1963), Regier and Robson
(1966), Hamley (1972), and Hamley and Regier
(1973). Ten methods of describing selectivity were
used by the above authors. Except for the DeLury
method described by Hamley (1972), the
mathematics and details of application of these
methods were discussed by Regier and Robson
(1966).

A comprehensive review of gill net selectivity
was presented by Hamley (1975). All basic models,
applications and shortcomings of these models,
and the variety of factors (thickness, materials,
and color of net twine, hanging of net, and methods
of fishing) that must be considered in determining
selectivity were discussed.

The method proposed by Holt (1963) was used to
evaluate selectivity on species that were caught in
this study. Holt assumed that: 1) the selectivity
curve would take the form of a normal frequency
distribution; 2) the efficiencies of two nets with
different mesh sizes would be similar for fish of
their respective mean lengths; and 3 ) the standard
deviations of the distributions for two different
mesh sizes would be equal. The equations for
evaluating the above assumptions and for de-
scribing selectivity have been given by Holt
(1963), Regier and Robson (1966), and Hamley
(1975).

If Holt's three asssumptions are analyzed and
deemed acceptable, points of the selectivity curve
for mesh size m, can be computed by

5<; =exp[-^,/'-7<)2]

2s,

where /,- = length offish in length stratum j
7, = mean selection length
s, = standard deviation of the selectivity

curve
ny = number of fish of length /, caught in
net m, .

Then nJs^ can be used to estimate abundance of
fish for each /; and therefore, the length-frequency
distribution in the fished population can be es-
timated from the length-frequency distribution
obtained from fishing a particular mesh size on the
population.

An additional assumption is necessary if

catches from a series of nets with different mesh
sizes are combined and used to estimate the
length-frequency distribution of the fished
population. The assumption is that the selectivity
curves for all meshes have the same shape (each s,
is an estimate of a commons) and amplitude (each
net fishes with equal efficiency on the length at
which the net is maximally efficient). This as-
sumption was questioned by Ricker (1947), Ishida
(1964), Regier and Robson (1966), and Hamley
(1972). The assumption can be tested only if the
length-frequency distribution of the fished
population is known. Hamley and Regier (1973)
tested this assumption on walleye, Stizostedion
vitreum vitreum, which were tagged prior to being
recaptured with gill nets, and found that the
shapes and amplitudes of their selectivity curves
changed with mesh size. This assumption could
not be tested in our study.

Information derived from a selectivity study has
various uses depending upon the validity of the
mathematical model used to describe selectivity
and on the accuracy and precision required. The
model can be useful for some purposes even if all
the assumptions are not met or even if the model is
not the most accurate and precise one for describ-
ing the empirical data.

The objective of most selectivity studies has
been to determine the most appropriate model for
describing gill net selectivity for a single species of
fish (Regier and Robson 1966). In this study we
have attempted to provide as much information as
possible about gill net selectivity on 22 species. To
10 of these we applied a single mathematical
model and either accepted or rejected the model in
relation to each of several potential applications.
By accepting the model we do not infer that it is
the most accurate or precise model but that the
approximation to the data is sufficiently close and
accurate to be useful.

NUMBERS AND MEAN LENGTHS OF
FISHES SELECTED FOR ANALYSES

Of the 76 species that were caught in the study
area during 1973 (May et al. 1976; Pristas and
Trent2), 22 species had catches exceeding 100
specimens. Of the 22 species, 15 were commer-
cially important in gill net fisheries in one or more
states along the south Atlantic and Gulf of Mexico

2Pristas, P. J., and L. Trent. 1976. Seasonal abundance, size,
and sex ratio of fishes caught with gill nets in St. Andrew Bay,
Florida. (Unpubl. manuscr.)

187

FISHERY BULLETIN: VOL. 75, NO. 1

coasts (National Marine Fisheries Service 1974).
Number caught in,), number measured (nmi),
mean length (SI,), and standard deviation (Ss,) of

mean length for each of the 22 species by mesh size
are shown in Table 1.

The assumption that mean lengths of fish that

TABLE 1. — Number offish caught (n, I, number measured (nm, ), mean length in centimeters (SI, ),and standard deviation of length (Ss, )

by stretched mesh size (m,) and species.

m; in centimeters and (inches)

Species

6.3

7.0

7.6

8.9

10.2

10.8

11 4

12.1

12.7

(2.5)

(2 75)

(3.0)

(3.25)

(3.5)

(3.75)

(4.0)

(4.25)

(4.5)

(4.75)

(5.0)

"/•

726

897

1,339

845

411

nm.

696

830

1.062

787

342

Slj

17.4

19.7

21.3

22.1

22.9

23.7

22.7

23.3

26.0

21.0

22.0

Ss,

1.0

1.4

1.1

1.3

2.4

3.2

0.7

1.3

1.5

r>i

1.830

1,054

172

nrrij

1,511

942

162

Slj

19.2

20.3

21.6

23.3

23.4

—

18.5

22.7

—

Ss,

0.8

1.0

1.3

2.1

—

0.3

—

314

393

463

344

303

229

154

nm/

236

323

394

283

258

205

202

136

Slj

24.8

26.2

27.8

29.4

30.7

32.1

32.7

33.9

33.5

33.3

Ss,

3.4

2.8

2.6

2.7

3.1

3.0

3.3

3.5

4.1

4.6

3.7

1,272

617

343

112

nm,

1,230

581

315

108

Sli

16.5

16.6

16.9

17.3

16.6

15.8

15.9

17.6

16.6

18.0

17.0

Ss,

1.3

1.8

2.1

2.7

2.6

2.3

1.4

2.0

1.6

0.0

731

741

479

134

182

nm.

450

602

378

107

155

Slj

22.6

24.5

26.1

28.5

29.6

31.2

32.5

35.0

32.7

25.0

24.5

Ss,

1.3

1.6

1.8

1.6

2.4

2.5

3.2

2.7

5.6

—

11.4

439

468

500

140

nm.

392

429

477

122

SI,

21.1

22.4

24.5

26.6

29.5

32.5

36.3

37.4

326

29.7

27.2

Ss,

1.4

1.7

2.1

3.0

4.2

4.3

4.4

3.4

8.4

9.2

11.2

617

359

127

nm.

597

346

124

Sli

18.1

19.5

21.0

21.8

22.5

24.5

20.0

—

17.5

—

Ssj

0.7

1.0

0.9

1.3

1.8

—

0.7

—

0.7

—

148

247

287

164

nm.

138

236

279

148

SI,

30.1

31.9

33.4

36.3

38.7

39.1

41.4

38.9

40.6

35.6

31.0

Ss,

3.8

3.5

3.9

3.4

4.0

3.7

7.1

5.9

110

4.4

146

109

145

133

101

nm.

126

130

108

Si,

33.4

34.5

36.0

38.1

39.7

42.2

44.5

45.7

47.4

44.6

49.1

Ssj

4.9

4.7

4.8

4.9

5.0

4.9

4.2

4.3

7.9

9.1

7.4

100

224

191

170

nrrij

204

182

161

Sli

23.0

24.3

24.4

25.5

25.8

26.5

26.4

26.6

28.5

28.4

31.0

Ss,

4.9

0.8

1.2

1.3

1.1

1.2

1.0

1.7

1.5

—

nm;

Si,

39.7

43.3

45.1

40.4

41.8

40.2

39.9

41.7

42.9

43.8

44.6

Ss,

3.2

1.7

5.3

5.7

6.5

5.0

4.3

3.9

3.4

4.1

nm,

Sli

30.3

32.7

36.3

38.6

43.7

45.5

47.8

50.7

54.0

57.0

36.5

Ssj

2.7

4.1

3.1

3.6

4.3

3.8

7.2

—

nm.

16.2

18.5

19.0

19.9

29.1

33.8

31.3

228

37.2

41.8

—

Ssi

0.9

3.0

1.0

5.9

9.3

3.6

5.6

2.6

10.3

—

nm/

Sli

42.3

51.2

44.6

58.3

60.5

57.4

59.0

588

54.6

57.3

Ss,

17.8

12.6

15.8

7.3

1.7

1.8

4.0

3.8

2.4

10.9

8.0

nm;

Sli

50.4

59.1

61.5

60.0

636

65.8

62.6

72.4

72.6

72.1

74.8

Ss,

4.1

14.6

10.1

12.2

11.6

13.1

11.9

10.4

6.0

13.3

9.8

nm,

sl,

15.0

15.6

15.7

16.5

17.7

17.0

—

19.2

—

15.5

Ss;

1.2

1.1

1.8

2.8

—

Gulf menhaden.'
Brevoortia patronus

Spot,1

Leiostomus xanthurus

Sea catfish,
Anus fells

Pinfish,

Lagodon rhomboides

Atlantic croaker,1
Micropogon undulalus

Blue runner,1
Caranx crysos

Pigfish,1

Orthopristis chrysoptera

Bluefish,1
Pomatomus saltratrix

Spanish mackerel,1
Scomberomorus maculalus

Yellowfm menhaden,
Brevoortia smith.

Gafftopsail catfish,
Bagre marinus

Spotted seatrout,1
Cynoscion nebulosus

Crevalle jack,1
Caranx hippos

Little tunny,
Euthynnus alletteratus

Atlantic sharpnose shark,
Rhizopnonodon terraenovae

Atlantic bumper,
Chloroscombrus chrysurus

188

TRENT and PRISTAS: SELECTIVITY OF GILL NETS
TABLE 1.— Continued.

in centimeters and (inches)

6.3

7.6

8.2

8.9

9.5

10.2

10.8

11.4

12.1

12.7

Species

(25)

(2.75)

(3.0)

(325)

(3.5)

(3.75)

(4.0)

(4.25)

(4.5)

(4.75)

(50)

Florida pompano,1

Tachmotus carolinus

nrrii

Slj

—

222

18.9

19.1

21.0

23.4

25.3

27.6

29.8

31.4

32.4

Ssj

—

3.9

1.7

1.5

4.2

3.0

2.4

2.1

3.9

Inshore lizardfish,

Synodus loetens

nrrij

Sli

36.1

386

396

39.5

33.5

—

35.0

26.0

31.2

33.5

38.0

Ss,

2.5

3.0

5.8

—

2.5

—

Gulf flounder.'

Paralichthys albigutta

nrrij

SI,

248

30.0

25.1

24.5

289

28.3

30.9

30.2

32.3

33.9

36.4

Ssj

8.3

—

3.3

—

6.1

3.7

4.7

3.3

3.1

4.2

3.8

Bonnethead shark,

Sphyrna tiburo

nm.

Sli

—

90.0

—

81.8

86.1

89.7

89.1

86.4

84.5

902

89.7

Ss;

—

13.1

—

11.3

17.0

144

10.6

12.8

15.1

7.7

10.0

Ladyfish,'

Elops saurus

nrrij

SI,

35.1

42.3

42.8

46.5

41.8

36.5

26.5

47.7

32.8

31.3

38.2

Ssj

4.7

5.0

4.4

6.4

2.2

—

8.1

11.8

7.9

Sand seatrout.1

Cynoscion arenarius

nrrij

SI,

29.7

32.1

33.5

35.2

31.3

20.0

24.2

—

54.0

26.0

Ss,

2.9

1.4

5.1

2.5

6.8

—

1.8

—

'Caught commercially in gill nets (National Marine Fisheries Service 1974).

are caught in gill nets increase with an increase in
mesh size seemed probable at least over part of the
range of mesh sizes, for 20 of the 22 species (Figure
1). The two species that did not show a definite
increase in mean length with an increase in mesh
size were little tunny, Euthynnus alletteratus, and
bonnethead shark, Sphyrna tiburo. Of the 22
species, none was caught (in numbers where
nrrii > 9) in every mesh size. The relation of an
increase in mean length for 20 species (little tunny
and bonnethead shark excluded) with an increase
in mesh size did not hold throughout the range of
mesh sizes for gulf menhaden, Brevoortia pat-
ronus; sea catfish, Arius felis; pinfish, Lagodon
rhomboides; blue runner, Caranx crysos; bluefish,
Pomatomus saltatrix; gafftopsail catfish, Bagre
marinus; crevalle jack, Caranx hippos; Atlantic
sharpnose shark, Rhizoprionodon terraenovae;
and yellowfin menhaden, Brevoortia smithi. The
primary reason for low catches in some mesh sizes
and for length not increasing progressively with
increasing mesh size was that the length ranges in
the fished populations of many species were not
great enough to provide the sizes offish that many
of the mesh sizes would efficiently capture. The
two species not showing the expected relation
usually were entangled or enmeshed in the
webbing in an abnormal manner. Most of the little
tunny that were caught were too large to deter-
mine mean length-mesh size relations in the mesh

•

•
•

•

• •

GULF MENHADEN -

2
o

z
<

21
19
17

48
44
40
16

42
34
26

60
5/
44

64
60

16
15
32
28

40
58

36
36
34
32

90
88
U
84

40
36

34
32
3C

•
•
•

•
•
•
• SPOTTED SEATROUT

23
21

- •

•
•
•

SPOT-

•
•

•

• • * *

* CREVALLE JACK

33
29
25

•

•
•
•

•

SEA CATFISH -

17
16

•

• PINFISH -

' ' . V

• LITTLE TUNNY

•

•
•
•

ATLANTIC CROAKER

32
28

_ 24

•
•

. * "ATLANTIC SHARPNOSE -
SHARK

I 37

•

•
•
•

•
•

• •

•

BLUE RUNNER '

5 33
3 29

• •
- • ATLANTIC BUMPER "

z 25
5 21

•
•
•
•
•

* FLORIDA POMPANO

21
19

•

•
•

•

PIGFISH

•
•

- • INSHORE LIZARDFISH-

40
36

•

•
•
•

•
• • •

•

BLUEFISH

• _

•
•
GULF FLOUNDER *

48
44

•

•
•
•

•
•

SPANISH MACKEREL -

40
36
32

BONNETHEAD SHARK

• •

. • •

• VELL0WFIN
MENHADEN

28
26
24

• •

* LADYflSH

44
42
40

GAFFTOPSAIL CATFISH. *

•
• •
• •

•

SAND SEATROUT -

t . , . i — , — i 1 1 1

76 89 10 2 114 12/
STRETCHED MESH (CM)

63 76 89 102 114 12 7
STRETCHED MESH (CM)

FIGURE 1.— Mean lengths of fishes caught in gill nets of various

mesh sizes.

189

FISHERY BULLETIN: VOL. 75, NO. 1

sizes used and were usually caught entangled by
their snout and caudal fin; they were rarely
wedged in the meshes. Bonnethead sharks were
almost always caught in meshes that had been cut
(probably by the sharks) and with their teeth
entangled in adjacent meshes; because of these
circumstances we did not expect a correlation
between the size of shark and mesh size.

Based on the data requirements of Holt's
method, only the 10 most abundant species (Table
1) were selected to evaluate one or more of the
three assumptions — normality of selection curve,
linearity of mean length-mesh size relation, and
constancy of standard deviation between mesh
sizes — required for Holt's model. For these species,
length-frequency distributions for those mesh
sizes where n(>50 are shown in Appendix Tables
1-3. These distributions are provided as the basis
for our evaluation of selectivity and for applying
other mathematical models to the data if other
investigators so desire.

SPECIES CAUGHT IN
GREATEST ABUNDANCE

Normality of Selection Curves

Natural logarithms of the ratios (lnR, + 1(/) of
numbers offish of length /, caught in meshes m( + 1
and rm were plotted against lengths of fishes to test
normality of the selection curves. Least squares
regression equations were computed, and the
intercepts (a) and slopes (b) of these equations are
shown in Table 2.

Best fits of the points to the straight lines were
obtained for spot, Leiostomus xanthurus; pigfish,
Orthopristis chrysoptera; Atlantic croaker; and
blue runner. The mean values of svx [standard
deviation of Y (ratio) for fixedX (length) in linear
regression analysis (Steel and Torrie I960)] were
lowest for these four species and ranged from 0.211
to 0.319 (Table 2). Slight curvilinearity appeared,
however, in the data for the 7.0/6.3 and 7.6/7.0 cm

TABLE 2. — Coefficients of, and estimates from, least squares regression equations of lnR +1 ■ on
length by species and mesh-size pair, and k values by species.

Stretched-mesh

Calculated mean

Standard deviation

size (cm)

selection length

of selection

Species

(mi)

a b

Sy.x

(// in cm)

curve (sj)

Gulf

6.3

17.52

menhaden

7.0/6.3
7.0

-27.87 1.51

0.512

19.27

1.08

7.6/7.0

-25.75 1.25

0.669

1.17

21.02

8.2/7.6

-20.27 0.90

0.259

1.38

8.2

2278

8.9/8.2

-17.28 0.73

0.146

1.55

8.9

24.53

9.5/8.9

-29.41 1.20

0.303

1.23

9.5

26.28

Mean Sy x =

0.377 k

= 2.759

Spot

6.3

19.20

7.0/6.3

-32.27 1.60

0.337

1.10

7.0

21 12

7.6/7.0

-34.28 1.55

0.302

1.11

7.6

23.05

Mean sv x =

0.319 k

3.024

Sea

6.3

2252

catfish

7.0/6.3
7.0

- 9.62 0.38

0.917

24.77

2.36

7.6/7.0

- 6.45 0.24

0.840

3.01

7.6

27.03

8.2/7.6

8.64 029

0.042

2.71

8.2

29.28

8.9/8.2

- 8.09 0.26

0.354

2.91

8.9

31.53

9.5/8.9

-10.40 0.32

0 202

2.66

9.5

33.78

10.2/9.5

- 5.65 0.17

0260

3.73

10.2

36.03

10.8/10.2

- 6.62 0.18

0.151

3.55

10.8

38.28

Means/X =

0.395 k

= 3.546

Pinfish

6.3

19.03

7.0/6.3

- 3.30 0.16

0.607

3.40

7.0

20.94

7.6/7.0

- 2.76 0 13

0.281

3.86

7.6

22.84

Mean Sy x =

0.444 k

2.997

190

TRENT and PRISTAS: SELECTIVITY OF GILL NETS

TABLE 2.— Continued.

Stretched-mesh
size (cm)

Calculated mean

selection length

ffj in cm)

Standard deviation
of selection

Species

sy.x

curve (si)

Atlantic

6.3

22.40

croaker

7.0/6.3
7.0

-23.48

1.00

0.296

24.64

1.50

7.6/7.0

-18.58

0.72

0.312

1.76

7.6

26.88

8.2/7.6

-41.74

1.50

0.335

1.22

29.12

Mean

sy.x =

0.314

= 3.527

Blue

6.3

20 94

runner

7.0/6.3
7.0

16.18

0.74

0.153

23.03

1.69

7.6/7.0

-22.80

0.97

0.541

1.49

7.6

25.12

8.2/7.6

-18.84

0.70

0.186

1.71

8.2

27.22

Mean

sy.x =

0.293

= 3.297

Pigfish

6.3

18.09

7.0/6.3

-33.77

1.78

0.305

1.01

7.0

19.90

7.6/7.0

-46.96

2.26

0.117

0.89

7.6

21.71

Mean

sy.x =

0211

= 2.849

Bluefish

6.3

28.54

7.0/6.3

- 2.94

0.11

0.198

5.39

7.0

31.39

7.6/7.0

- 7.27

0.22

0.582

3.59

7.6

34.25

8.2/7.6

- 7.94

0.21

0.312

3.58

8.2

37.10

8.9/8.2

- 9.81

0.24

0.422

3.35

8.9

39.96

Mean

sy.x

0.378

= 4.495

Spanish

6.3

30 84

mackerel

7.0/6.3
7.0

- 3.25

0.09

0.404

33.92

5.54

7.6/7.0

- 1.89

0.06

0.673

7.60

7.6

37.00

8.2/7.6

- 4.01

0.11

0.316

5.45

8.2

40.09

8.9/8.2

- 1.36

0.03

0.586

9.71

8.9

43.17

9.5/8.9

- 5.61

0.13.

0.436

4.96

9.5

46.26

Mean

sy.x

0.483

= 4.856

Yellowfin

8.2

24.58

menhaden

8.9/8.2
8.9

-16.13

0.67

0.427

26.47

1.73

9.5/8.9

- 8.32

0.31

0.228

2.50

9.5

28.36

10.2/9.5

-13.00

0.49

0.335

2.06

10.2

30.25

Mean

Sy.x =

0.330

2 978

mesh-size pairs for blue runner and in the 7.6/7.0
cm mesh-size pair for Atlantic croaker. Spot,
pigfish, and Atlantic croaker were almost always
caught wedged tightly in the meshes of gill nets.
Blue runner were also usually caught in this
manner. Occasionally, however, blue runner were
caught by the dorsal antrorse spine which hooks
over one or more bars of the mesh or meshes. If the
spine were not present, these fish could pass
through the meshes. Blue runner caught in this
manner probably contributed greatly to the
variation about regression.

Acceptable fits of the data, at least for most
mesh-size pairs, were obtained for gulf and

yellowfin menhaden. The normal curve, although
acceptable, did not appear to be the most ap-
propriate model to describe selectivity for gulf and
yellowfin menhaden because of observed cur-
vilinearity. Values of syx were smallest for gulf
menhaden in the mesh-size pairs (8.2/7.6, 8.9/8.2
cm; Table 2) that did not exhibit strong cur-
vilinearity. Gulf and yellowfin menhaden were
usually caught tightly wedged in the meshes at or
near maximum girth, but occasionally the larger
individuals taken from a particular mesh size
were caught loosely in a mesh by the opercle or
preopercle. The slight positive skews observed in
the length-frequency distributions (Appendix

191

FISHERY BULLETIN: VOL. 75. NO. 1

Tables 1, 2) for two of the smallest mesh sizes for
gulf menhaden and all mesh sizes for yellowfin
menhaden probably resulted from fish that were
caught by the opercles. This in turn probably
accounts for the curvilinearity of the data ob-
served for the two species of menhadens. A cubic
exponential equation such as that proposed by
Olsen ( 1959) might more accurately and precisely
define selectivity for gulf and yellowfin menhaden
over part of the length range of the selectivity
curve.

The normal curve also provided acceptable
approximations to the data for sea catfish and
bluefish, although refinements in data collection
procedures, indicating how each fish was caught,
are needed to evaluate more accurately the model.
Sea catfish are frequently caught entangled by the
pectoral and dorsal spines, and bluefish are
frequently caught enmeshed or entangled by their
teeth, maxillaries, preopercles, and opercles.

The normal curve did not provide acceptable
approximations to the data for pinfish and Spanish
mackerel. Pinfish were usually caught dorsally by
the dorsal antrorse spine and ventrally between a
point perpendicular to the antrorse spine and the
posterior end of the anal fin. With the fish and
webbing interacting in this fashion, the probabil-
ity of a given size of pinfish being caught was
probably about equal in a small range of mesh
sizes. The girth of a Spanish mackerel increases
gradually from its snout to the anterior point of its
second dorsal fin. Most individuals are caught
wedged in the mesh at any point between just
behind the opercle and the point of maximum
girth. The point of retention, therefore, is de-
pendent upon the mesh size within a small range
of mesh sizes. Also, many are entangled by the
teeth, maxillaries, and occasionally by the tail.

Attempts to suggest models which might better
define selectivity for sea catfish, bluefish, pinfish,
and Spanish mackerel were not made in this
study, because the position at which each fish was
wedged in the net and — for those fish not wedged
in the net — the position at which each fish was
entangled was not recorded, and additional
catches of bluefish and Spanish mackerel were
needed. Holt (1963) suggested that, for species
that are caught at two or more distinct positions
along their body, selectivity could be defined by
regarding the selection curve as the algebraic sum
of two or more normal selection curves, or by
fitting an empirical curve such as the cubic ex-
ponential. Hamley and Regier (1973) found that

the selectivity curve for walleyes was bimodal;
they resolved this curve into two unimodal
components representing fish that were caught by
wedging and entangling.

Mean Length-Mesh Size Relation

The second assumption of Holt's method is that
mean length of captured fish is proportional to
mesh size. To test this assumption, -2a/b was
plotted against the sum of mesh sizes (m,- + 1 + m,)
for each mesh-size pair (data from Table 2) and for
the seven species for which data for at least three
mesh-size pairs were available (Figure 2). Mean
selection length {alb or /,) in relation to mesh size
can also be determined from Figure 2 using the
bottom and right-hand scales. Data for Spanish
mackerel were plotted even though the assump-
tion of normality (previous section) for this species
was rejected. The straight lines in Figure 2 were
fitted through the origin by the least squares
method and the slopes (k) of these lines are given
in Table 2. With£ determined, the mean selection
length (/,-) for any mesh size is determined by /, =
m,k.

Best fits of the data were obtained for Atlantic
croaker, blue runner, and yellowfin menhaden,
and acceptable fits were obtained for gulf menha-
den and sea catfish. More data are required,
however, to determine the degree of fit for the
remaining five species (bluefish, Spanish mac-
kerel, and the three species not shown in Figure 2).
Although the degree of fit cannot be evaluated for
the five species, information presented in Figure 2
or Table 2 can be used to provide rough estimates
of mean selection length in relation to mesh size
for bluefish, pinfish, spot, pigfish, and Spanish
mackerel. Much of the deviation about the re-
gression for bluefish (and possibly sea catfish)
probably resulted from fitting the line through the
origin (Figure 2). Apparently the mesh size-mean
length relation is not linear throughout a range of
mesh sizes between 0 and 8.6 cm for bluefish. A
more reasonable approximation of the mean
length-mesh size relation for bluefish might result
by fitting a regular linear regression equation (Y
= a + bX rather than Y = bX) to the points in
Figure 2. For pinfish, spot, and pigfish, rough
approximations of the mean length-mesh size
relations can be obtained using the k value (Table
2 ) even though each k was based on only two points
and the origin. Variability about regression was
great for Spanish mackerel but this information

192

TRENT and PRISTAS SELECTIVITY OF GILL NETS

mi+l + mi
13.3 14.6 15.9 17.1 18.4 19.7 20.9

SPANISH MACKEREL

YELLOWFIN MENHADEN - 30.0

25.0

25.0
50.0

6.7 7.3 7.9 8.6 9.2 9.8 10.5
STRECHED MESH (CM)

FIGURE 2. — Regression of -2a/b on the sum of mesh sizes (m( + 1
+ mi ) and estimates of mean selection length by mesh size for
seven species of fishes.

was the best available to estimate the mean
length-mesh size relation.

Standard Deviation-Mesh Size Relation

The third assumption of Holt's method is that
the standard deviations of length between mesh
sizes estimate a common standard deviation.
Standard deviations for the selectivity curves are
shown in Table 2 by species and mesh-size pair.
Standard deviations tended to: increase with an
increase in mesh size for gulf menhaden, sea
catfish, and Spanish mackerel; decrease with an
increase in mesh size for bluefish; and show no
apparent trend in relation to mesh size for Atlan-

tic croaker, blue runner, and yellowfin menhaden.
Although only two estimates were available for
each species, standard deviations appeared simi-
lar between mesh-size pairs for spot and pigfish
and increased with an increase in mesh size for
pinfish.

Standard deviations were much smaller for the
species that were usually wedged in the meshes
(gulf menhaden, spot, Atlantic croaker, blue
runner, pigfish, and yellowfin menhaden) than for
those species that were frequently entangled in
the meshes or caught at different girths along the
body (sea catfish, pinfish, bluefish, and Spanish
mackerel).

SPECIES CAUGHT IN
LESSER ABUNDANCE

Twelve other species were caught in sufficient
numbers to warrant general comments (Table 1,
Figure 1). Florida pompano, Trachinotus caro-
linus; spotted seatrout; inshore lizardfish, Syn-
odus foetens; ladyfish, Elops saurus; and sand
seatrout, Cynoscion arenarius, usually were
enmeshed in the webbing near their maximum
girth, although the latter four species sometimes
were entangled by their teeth; gulf flounder, Par-
alichthys albigutta, usually were enmeshed just
behind the opercle; crevalle jack and Atlantic
bumper, Chloroscombrus chrysurus, usually were
enmeshed but frequently were restricted by the
antrorse spine as described for blue runner;
gafftopsail catfish usually were enmeshed in the
larger mesh sizes but often were entangled by
pectoral and dorsal spines in the smaller mesh
sizes; little tunny and Atlantic sharpnose and
bonnethead sharks usually were entangled in the
webbing by their teeth and fins. In general, the
magnitude of the standard deviations reflects the
amount of entanglement. Standard deviations
were lowest for those species normally caught
wedged in the meshes and highest for those that
were frequently caught entangled (Table 1).

Three of the above-mentioned species — spotted
seatrout, Florida pompano, and sand seatrout —
are important in the gill net fisheries along the
Gulf of Mexico. Although selectivity was not
evaluated for these species, owing to insufficient
data, estimates of the mean length-mesh size
relation can be made from the data in Figure 1.
The mean length plotted in Figure 1 would un-
biasedly estimate this relation only if equal
numbers of fish of each length class and species

193

FISHERY BULLETIN: VOL. 75, NO. 1

were available in the fished population — an
assumption that is not valid. Based on the low
standard deviations in length for each mesh size
(Table 1), however, it appears that a particular
mesh size would efficiently capture any of these
three species only over narrow length ranges.
When this situation exists, only a small amount of
bias in the mean length-mesh size relation results
from using the estimates derived by plotting the
empirical data.

DISCUSSION

Information presented in this paper can be used
in fisheries management and research, and by
commercial fishermen, in the following ways. We
categorized the uses into two types: mesh-size
regulations and capture efficiency.

Mesh-Size Regulations

Mesh-size regulations in a fishery should serve
specific purposes. These regulations can be useful
in controlling the size of captured individuals for
some species but not others, depending upon the
range in lengths of fish that a given mesh size
captures with high efficiency. For species where
the regulation can be useful (as indicated by low
values oiSs, ors,), the objective of the regulation is
usually to protect from harvest individuals of a
species below a certain length without decreasing
efficiency in the commercial gill net fishery.
Determination of the smallest mesh size that can
be fished is critical for the fish population and for
the fishermen. If the mesh size is too small, a
significant portion of the small individuals which
are to be protected will be caught. If the mesh size
is too large, the fishermen will possibly be pre-
vented from using a mesh size which would result
in high capture efficiency on legal-sized fish in the
population. Information presented in Tables 1 and
2 and Figures 1 and 2 can be used, with various
degrees of reliability, to evaluate the usefulness of
mesh-size regulations and, for some of the 22
species, to estimate the mesh size which would
best fulfill the above stated objective.

At least small amounts of gill net selectivity
information were provided on 15 species (Table 1)
of fish that were caught and sold by commercial
fishermen along the south Atlantic and Gulf of
Mexico. The probability that the size composition
of the populations for some of these species will
eventually be controlled, partially by mesh-size

regulations, is high. Of the 15 species, the sizes of
individuals caught by gill nets can be controlled,
possibly to a degree required for management
purposes, by mesh-size regulations, except for
bluefish and Spanish mackerel, based on the
available data. The degree of control, and the ef-
fect that a particular regulation would have on
capture efficiency for legal-sized fish in the fishery,
can be estimated from values of Ss, or sr

Assuming that a mesh-size regulation is de-
sirable to manage a particular fishery, the steps in
estimating the "optimum" mesh size are as follows
for two examples — Atlantic croaker and Florida
pompano. These two species were selected as
examples because, for croaker, data were
sufficient to derive selectivity curves and, for
pompano, we had insufficient data to derive the
curves.

1. Based on management objectives, determine
the maximum length (L) offish which you want to
protect from harvest ( minimum length offish to be
harvested) and the percent of catch allowed below
this length. We arbitrarily selected a length of 20
cm, and <2.5% as the maximum percent allowable
of fish below 20 cm, for each species.

2. For Atlantic croaker, the slope (k) for the
equation relating mesh size (m,) and mean selec-
tion length (/,), and a weighted mean of the s,
estimates of the selectivity curves (Table 2) were
used to determine an estimate of the required
mesh size. The calculations follow:

A. determine s = /£(«, + nl + l)s,2/^,n, = 1.56

B. determine the minimum mesh size (mm;)
mm, = (L + 2s)lk = (20 cm + 3.1D/3.527 =
6.5 cm.

Based on the above, one would expect about 2.5%
of the total catch to be composed of Atlantic
croaker under 20 cm total length by a gill net
having a stretched-mesh size of 6.5 cm.

3. For Florida pompano, appropriate equations
to determine /, and s, are not available, because
selection curves could not be determined. These
values can be estimated, however, if we assume
that the empirical means and standard deviations
(SI, and Ss,; Table 1) are reasonable estimates of /;
and s,. Estimates of the mean length-mesh size
relation and standard deviations based on the
above assumption would probably yield reason-
able and useful approximations for Florida
pompano, because: A) the length range within
which the pompano were caught efficiently in a

194

TRENT and PRISTAS: SELECTIVITY OF GILL NETS

particular mesh size was narrow; B) they rarely
became entangled in the webbing; and C) a wide
range of sizes was available in the fished popula-
tion (Table 1 ). Based on the above assumption, the
equations are:

A.Ss
B. mm.

= v Infis^ln, =3.12

based on data where n,>9 and
= (L + 2Ss)/Sk ---- (20 cm + 6.24V2.517
= 10.4 cm

where Sk = the slope of the least squares regres-
sion line fitted through the origin to the points
shown in Figure 1 for Florida pompano. Thus,
2.57c of the catch of pompano in gill nets with mesh
size of 10.4 cm can be expected to be below 20 cm in
length.

Capture Efficiency

Several factors should be considered in the
selection of mesh sizes for maximizing the ef-
ficiency of capture. Efficiency of capture is defined,
or measured by, the dollar return per unit of effort
in a gill net fishery. In a gill net fishery the more
important factors include: 1) whether individuals
of a single species or a group of species are sought;
2) the regulations (mesh size, minimum size limit,
etc.) that exist in the fishery; 3) how the gill net is
to be fished (anchored, drift, run-around, etc.); 4)
values of the species sought and values of
various-sized individuals in the fished popula-
tions; 5) information on the life history of each
species sought, especially the mean length of each
age class, the variation in year-class strength
between years, and the length-weight relation; 6)
the ability, in terms of cost, to use nets with more
than one mesh size; and 7) the most efficient mesh
sizes for capturing various lengths of fish in the
fished population. For this discussion the only
factor to be considered is the determination of
efficient mesh sizes.

For the 15 species of fish of commercial im-
portance shown in Table 1, the efficiency of cap-
turing a particular length group with maximum
efficiency is highly dependent on mesh size for all
except bluefish and Spanish mackerel. The range
in lengths offish that a particular mesh size would
capture with high efficiency can be estimated from
values of s, or Sst given in Tables 1 and 2. The
equations,

I sl,

m, =-orm, = —

similar to those in the previous section, and with
the same reservations regarding the accuracy of
the estimates, can be used to estimate the most
efficient mesh sizes for capturing various lengths
offish. A discussion of this type of application in a
particular fishery was given by Trent and Hassler
(1968).

Limitations on Uses

Selectivity information derived for the 10
species in this study as shown in Figure 1 should
be used cautiously, if at all, in adjusting length-
frequency distributions. The assumption that the
shapes and amplitudes of the selectivity curves
are the same for a species could not be tested, but is
probably not valid (Hamley and Regier 1973).
Further, for all species except Atlantic croaker
and blue runner to which we have applied Holt's
method, one or more of the three assumptions were
invalid, or questionable, or sufficient data were
not available to evaluate the assumptions.

Several other factors, not investigated in this
study, should be considered when applying our
results to estimate mesh sizes for controlling
capture efficiency or in adjusting length-
frequency distributions of the catch. Selection is
dependent to some extent on factors other than
mesh size. We used set gill nets, all of which were
constructed in the same manner from one type of
webbing material. Fishing often occurs with gill
nets by encircling the schools or by blocking an
area and scaring the fish into the net, or waiting
until falling tides force the fish from the blocked
area. When fishing is conducted in these ways,
many individuals are often caught loosely wedged
( Garrod 1961 ) or loosely entangled in the net; most
of these fish, if set gill nets had been used, would
have eventually escaped. Selection (size of cap-
tured individuals, or efficiency of capture, or both)
is also dependent on other factors: natural or
synthetic webbing (Washington 1973); color of
webbing (Jester 1973); twine size (Hansen 1974);
and the hanging coefficient (Hamley 1975).

LITERATURE CITED

BRUSHER, H. A., AND L. H. OGREN.

1976. Distribution, abundance, and size of penaeid
shrimps in the St. Andrew Bay system, Florida. Fish.
Bull., U.S. 74:158-166.
CUCIN, D., AND H. A. REGIER.

1966. Dynamics and exploitation of lake whitefish in
southern Georgian Bay. J. Fish. Res. Board Can.
23:221-274.

195

FISHERY BULLETIN: VOL. 75, NO. 1

GARROD, D. J.

1961. The selection characteristics of nylon gill nets for
Tilapia esculenta Graham. J. Cons. 26:191-203.
GULLAND, J. A., AND D. HARDING.

1961. The selection of Clarias mossambicus (Peters) by
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HAMLEY, J. M.

1972. Use of the DeLury method to estimate gillnet
selectivity. J. Fish. Res. Board Can. 29:1636-1638.

1975. Review of gillnet selectivity. J. Fish. Res. Board
Can. 32:1943-1969.
HAMLEY, J. M., AND H. A. REGIER.

1973. Direct estimates of gillnet selectivity to walleye
iStizostedion vitreum vitreum). J. Fish. Res. Board Can.
30:817-830.

HANSEN, R. G.

1974. Effect of different filament diameters on the selec-
tive action of monofilament gill nets. Trans. Am. Fish.
Soc. 103:386-387.

HOLT, S. J.

1963. A method for determining gear selectivity and its
application. Int. Comm. Northwest Atl. Fish. Spec.
Publ. 5:106-115.

HOPKINS, T. L.

1966. The plankton of the St. Andrew Bay system,
Florida. Publ. Inst. Mar. Sci. Univ. Tex. 11:12-64.
ICHIYE, T, AND M. L. JONES.

1961. On the hydrography of the St. Andrew Bay system,
Florida. Limnol. Oceanogr. 6:302-311.

ISHIDA, T.

1962. On the gill-net mesh selectivity curve. Bull.
Hokkaido Reg. Fish. Res. Lab. 25:20-25. (Translated from
Jap. Fish. Res. Board Can., Transl. Ser. 1338.)

1964. On the gill-net mesh selectivity curve. II. [In Jap.,
Engl, summ.] Bull. Hokkaido Reg. Fish. Res. Lab. 29:1-9.

JESTER, D. B.

1973. Variations in catchability of fishes with color of
gillnets. Trans. Am. Fish. Soc. 102:109-115.
KLIMA, E. F.

1959. Aspects of the biology and the fishery for Spanish
mackerel, Scomberomorus maculatus (Mitchill), of
southern Florida. Fla. Board Conserv. Mar. Lab. Tech.
Ser. 27, 39 p.

May, N., L. Trent, and P. J. Pristas.

1976. Relation of fish catches in gill nets to frontal
periods. Fish. Bull., U.S. 74:449-452.

MCCOMBIE, A. M., AND F. E. J. FRY.

1960. Selectivity of gill nets for lake whitefish Coregonus
clupeaformis. Trans. Am. Fish. Soc. 89:176-184.

National Marine Fisheries Service.

1974. Fishery statistics of the United States 1971. U.S.
Dep. Commer., Natl. Mar. Fish. Serv., Stat. Dig. 65, 424 p.
OLSEN, S.

1959. Mesh selection in herring gill nets. J. Fish. Res.
Board Can. 16:339-349.

PRISTAS, P. J., AND L. TRENT.

1977. Comparisons of catches of fishes in gill nets in rela-
tion to webbing material, time of day, and water depth in
St. Andrew Bay, Florida. Fish. Bull., U.S. 75:103-
108.

REGIER, H. A., AND D. S. ROBSON.

1966. Selectivity of gill nets, especially to lake
whitefish. J. Fish. Res. Board Can. 23:423-454.
RICKER, W. E.

1947. Mortality rates in some little-exploited populations
of fresh-water fishes. Trans. Am. Fish. Soc. 77:114-128.
SlEBENALER, J. B.

1955. Commercial fishing gear and fishing methods in
Florida. Fla. Board Conserv. Mar. Lab. Tech. Ser. 13,
45 p.

Steel, R. G. d., and J. H. Torrie.

1960. Principles and procedures of statistics with special
reference to the biological sciences. McGraw-Hill, N.Y.,
481 p.

TABB, D. C.

1960. The spotted seatrout fishery of the Indian River
area, Florida. Fla. Board Conserv. Mar. Lab. Tech. Ser.
33, 18 p.

Trent, L., and W. W. Hassler.

1968. Gill net selection, migration, size and age compo-
sition, sex ratio, harvest efficiency, and management of
striped bass in the Roanoke River, North Carolina.
Chesapeake Sci. 9:217-232.

Washington, p.

1973. Comparison of salmon catches in mono- and multi-
filament gill nets. Mar. Fish. Rev. 35(81:13-17.

APPENDIX TABLE 1. — Length-frequency distributions by mesh size for Gulf menhaden, spot,

pinfish, and pigfish.

Length
midpoint

Stretched mesh

size in centimeters and (inches)

6.3

7.0

7.6

8.9

9.5

6.3

7.0

7.6

(cm)

(2.5)

(2.75)

(3.0)

(3.25)

(3.5)

(3.75)

(2.5)

(2.75)

(3.0)

Gulf menhaden

—ni) -

Spot

14.0

1.0

14.5

1.0

15.0

4.2

15.5

7.3

16.0

60.5

1.1

1.3

1.1

16.5

86.6

3.2

3.6

17.0

201.3

19.5

2.5

2.1

1.1

17.0

17.5

134.5

43.2

2.1

44.8

18.0

110.6

76.7

1.3

1.1

187.7

4.5

18.5

43.8

87.5

3.8

1.1

288.2

15.7

1.1

19.0

35.5

121.0

21.4

1.1

2.4

491.7

81.7

1.1

195

17.7

127.5

41.6

2.1

2.4

370.6

149.9

2.1

20.0

11.5

128.6

114.7

9.7

3.6

256.8

277.5

10.6

20.5

10.4

• 85.4

163.9

24.7

7.2

1.1

105.4

211.5

17.0

21.0

84.3

273.6

92.3

13.2

1.1

41.2

176.8

27.6

21.5

44.3

249.6

148.2

34.9

2.2

18.2

839

30.8

22.0

32.4

230.7

189.0

66.1

4.4

4.8

33.6

43.5

22.5

25.9

128.6

168.6

66.1

5.6

11.2

21.2

23.0

6.5

64.3

97.7

63.7

8.9

6.7

9.6

196

TRENT and PRISTAS SELECTIVITY OF GILL NETS

APPENDIX TABLE 1.— Continued.

Length

Stretched mesh

size in centimeters and (inches)

midpoint

6.3

7.0

7.6

8.2

6.3

7.0

7.6

(cm)

(25)

(2.75)

(30)

(3.25)

(3.5)

(3.75)

(2.5)

(275)

(3.0)

Gulf menhaden

"II

Spot

23.5

5.4

26.5

52.6

62.5

15.6

1.1

4.2

24.0

1.1

5.0

268

32.4

25.6

3.2

24.5

2.2

8.8

16.1

26.4

11.1

25.0

5.4

14.4

10.0

25.5

1.1

2.1

8.4

10.0

26.0

1.1

2.4

26.5

1.3

2.4

1.1

27.0

1.2

27.5

1.2

Pinfish

Pigfish

8.0

1.1

9.0

1.1

9.5

1.1

10.0

1.1

11.0

1.0

1.1

1.0

11.5

3.1

4.2

1.1

12.0

7.2

4.2

1.1

12.5

2.1

3.2

1.1

1.0

13.0

5.2

4.2

6.5

4.3

13.5

23.8

12.7

5.4

1.0

2.1

14.0

43.4

21.2

10.9

1.0

4.3

14.5

51.7

18.0

20.7

8.3

4.3

1.0

15.0

91.0

63.7

21.8

9.3

5.4

15.5

90 0

51.0

28.3

11.4

10.7

1.0

16.0

139.6

82.8

33.8

7.2

7.5

3.1

16.5

194.4

48.8

39.2

13.5

8.6

12.4

1.0

17.0

264.7

70.1

37.0

10.4

7.5

66.1

3.1

17.5

167.5

52.0

35.9

12.4

6.4

109.6

6.2

18.0

124.1

59.5

29.4

11.4

3.2

186.0

24.9

3.1

18.5

30.0

38.2

6.5

6.2

6.4

132.3

42.5

1.0

19.0

238

45.7

5.4

1.0

4.3

71.3

70.6

19.5

2.1

24.4

22.9

2.1

24.8

71.6

4.1

20.0

4.1

6.4

9.8

3.1

1.1

8.3

58.1

8.2

20.5

3.1

1.1

9.8

2.1

1.0

46.7

23.6

21.0

2.1

9.8

1.0

2.1

24.9

39.9

21.5

2.2

2.1

6.2

24.6

22.0

1.1

2.1

10.2

22.5

1.1

1.0

9.2

23.0

2.2

2.1

2.0

23.5

2.1

1.0

24.0

•

1.1

26.0

1.0

26.5

1.0

29.0

1.0

APPENDIX

Table 2.

— Length-frequency distributions

by mesh

size for

sea catfish

and

yellowfin menhaden.

Length

Stretched mesh

size in centimeters and (inches)

midpoint

6.3

7.6

8.2

8.9

9.5

10.2

10.8

11.4

(cm)

(2.5)

(2.75)

(3.0)

(3.25)

(3.5)

(3.75)

(4.0)

(4.25)

(4.5)

n„

'/ —

ea catfish

14.0

1.3

16.5

2.6

1.1

2.2

1.1

19.0

2.6

1.2

1.1

1.2

21.5

75.8

8.5

2.4

1.2

2.4

1.1

1.2

24.0

127.7

171.5

52.9

10.9

3.6

2.2

5.7

1.1

2.4

26.5

57.2

130.2

182.1

78.0

18.8

5.5

2.2

1.2

29.0

19.9

43.8

162.1

136.5

119.8

36.9

15.9

6.7

1.2

31.5

17.3

26.9

44.8

85.2

110.4

97.1

77.0

36.4

6.0

34.0

5.4

8.4

14.1

20.6

38.7

59.3

89.5

55.8

26.0

365

2.6

3.6

1.2

12.0

5.8

21.3

30.6

36.4

22.4

39.0

1.3

2.4

2.2

3.4

11.4

3.5

41.5

1.1

1.2

44.0

1.2

1.1

46.5

1.2

54.0

1.2

Yellowfin menhaden

22.0

6.4

23.5

39.4

25.3

8.3

4.2

25.0

38.3

114.2

92.4

37.9

26.5

14.9

72.5

72.3

92.9

28.0

1.1

12.1

17.8

31.7

29.5

2.1

31.0

1.1

197

FISHERY BULLETIN: VOL. 75. NO. 1

APPENDIX TABLE 3.

-Length-frequency distribution by mesh size for Atlantic croaker, bluefish, Spanish mackerel, and blue

runner.

Length

midpoint

Stretched mesh

size in centimeters and (inches)

Length
midpoint

6.3

Stretched mesr
7.0

size in
7.6

centimeters and (inches)
8 2 8.9

6.3

7.0

7.6

8.2

8.9

9.5

(cm)

(2.5)

(2.75)

(3.0)

(3.25)

(3.5)

(3.75)

(cm)

(2.5)

(2.75)

(3.0)

(3.25)

(3.5)

(3.75)

Atlantic

Blue

(7;; --

:roaker

runner

19.0

1.6

16.5

1.1

19.5

1.6

1.2

1.3

17.5

4.5

1.1

20.0

16.2

1.2

18.0

4.5

1.1

20.5

37.5

2.5

18.5

6.7

21.0

61.7

4.9

1.3

19.0

13.4

2.2

1.0

21.5

56.8

1.3

19.5

23.5

5.4

22.0

125.0

17.2

20.0

63.8

16.4

2.1

22.5

94.2

44.4

5.1

20.5

65.0

13.1

23.0

116.9

70.2

5.1

21.0

82.9

50.2

5.2

23.5

66.6

81.3

19.0

1.3

21.5

42.6

58.9

4.2

1.1

1.2

24.0

78.0

104.7

31.7

22.0

48.2

74.2

16.8

1.1

24.5

27.6

104.7

36.7

0.6

1.2

22.5

29.1

796

31.4

2.2

25.0

27.6

80.1

58.3

0.6

1.2

23.0

23.5

58.9

69.2

4.6

25.5

9.7

64.1

57.0

2.3

1.2

23.5

19.0

36.0

72.3

5.7

1.1

26.0

3.2

48.0

60.8

4.3

1.2

24.0

3.4

30.5

639

9.2

26.5

3.2

35.7

53.2

4.9

7.0

24.5

4.5

12.0

54.5

5.7

27.0

1.6

29.6

45.6

12.7

14.1

25.0

2.2

7.6

44.0

20.7

1.2

27.5

16.0

25.3

17.4

12.9

25.5

6.5

18.9

14.9

10.1

28.0

1.6

16.0

22.8

25.2

15.3

1.3

26.0

9.8

51.4

21.8

11.3

28.5

4.9

20.3

13.0

14.1

2.5

26.5

1.1

23.1

12.6

7.5

29.0

1.2

10.1

20.3

15.3

1.3

27.0

1.1

12.6

9.2

7.5

29.5

2.5

13.9

10.1

18.8

6.4

27.5

11.5

8.0

1.2

30.0

1.3

4.1

12.9

6.4

28.0

3.1

1.1

30.5

1.2

2.5

3.2

15.3

5.1

28.5

4.2

31.0

2.5

4.6

5.9

7.6

29.0

1.0

1.2

31.5

3.8

11.7

10.2

29.5

1.1

32.0

2.5

3.8

3.5

3.8

30.0

2.1

1.1

1.2

32.5

1.3

10.6

8.9

30.5

1.0

2.3

1.2

33.0

1.7

7.0

5.1

31.0

4.6

7.5

33.5

2.3

1.3

31.5

1.0

1.1

3.8

1.1

34.0

3.5

2.5

32.0

6.9

3.8

2.2

34.5

1.2

32.5

1.1

1.2

35.0

1.3

3.5

2.5

33.0

2.3

6.3

1.1

35.5

1.2

33.5

1.1

36.5

2.5

34.0

1.1

1.2

3.3

Bluefish

34.5

1.0

2.2

24.0

12.8

1.0

35.0

1.2

4.5

26.5

23.5

24.1

3.0

1.0

36.0

1.1

2.5

4.5

29 0

51.5

75.4

68.0

15.4

1.0

3.0

36 5

4.5

31.5

31.0

61.7

53.4

15.4

3.0

4.0

37.0

2.1

2.5

4.5
22
3.3
2.2

34.0

10.8

36.6

78.3

26.6

7.2

4.1

37.5

36.5

10.7

30.2

52.4

45.5

10.3

13.8

38.0

39.0

6.5

6.2

21.6

41.0

24.8

32.8

38.5

1.0

41.5

1.1

10.4

9.0

12.1

17.5

21.1

39.0

1 .1

44.0

1.0

6.6

4,1

11.6

39.5

1.1

3.3

46.5

1.1

1.0

4.0

40.0
40.5

1.0

2.5

5.6
1.1

Spanish mackerel

41.0

1.1

26.5

4.6

3.6

1.2

42.0

1.1

29.0

42.9

21.6

12.2

2.4

42.5

1.1

31.5

37.1

21.6

22.3

13.6

2.4

1.1

44.5

1.1

34.0

12.7

16.8

39.0

21.0

15.0

2.2

36.5

20.7

13.2

30.2

38.2

18.9

7.5

39.0

13.8

20.4

16.6

14.8

25.2

21.4

41.5

7.0

7.2

12.2

22.2

11.2

17.1

44.0

2.4

3.6

2.2

13.6

13.8

13.9

46.5

3.6

1.2

6.6

3.6

7.5

9.7

49.0

1.2

2.2

1.2

2.4

4.3

51.5

2.4

1.1

54.0

1.1

1.2

1.1

56.5

1.1

59.0

1.2

1.1

198

LONG-TERM CADMIUM STRESS IN THE CUNNER,
TAUTOGOLABRUS ADSPERSUS

J. R. MacInnes, F. P. Thurberg, R. A. Greig, and E. Gould1

ABSTRACT

The cunner, Tautogolabrus adspersus, was exposed for 30 and 60 days to 0.05 or 0.10 ppm Cd as
cadmium chloride. The mean gill-tissue respiratory rates exhibited by the control fish and those
exposed to 0.05 and 0.10 ppm Cd were 972, 736, and 665 /u.1 Oj/h-g dry weight, respectively, after 30
days and 1,036, 702, and 587 ijl\ Ch/h- g, respectively, after 60 days. Changes were also observed in the
activities of two liver enzymes, aspartate aminotransferase (depression) and glucose-6-phosphate
dehydrogenase (induction). Results are compared with those from other metal -exposure studies with
cunners and other teleosts.

In recent years cadmium has become the subject of
numerous investigations to determine its toxicity
to various marine animals. These studies have
progressed from short-term exposures to deter-
mine the concentrations that cause death (Eisler
1971; National Oceanic and Atmospheric Ad-
ministration 1974; Westernhagen and Dethlefsen
1975), to long-term exposure studies to measure
physiological change caused by very low levels
(parts per billion, ppb) of cadmium (Eisler 1974;
Calabrese et al. 1975; Dawson et al. in press;
Gould in press; Thurberg et al. in press). Such
long-term physiological stress can lower an
animal's capacity to adapt to and survive in its
natural environment.

In a recent collaborative study, a common coast-
al fish, the cunner, Tautogolabrus adspersus, was
exposed to cadmium for 96 h and examined for
changes in respiration, osmoregulation, cadmium
uptake, histopathology, enzyme chemistry, and
immune response (National Oceanic and At-
mospheric Administration 1974). In the present
study, cunners were exposed to cadmium for up to
60 days so that the effects of both exposure regimes
might be compared. Parameters selected for study
were gill-tissue oxygen consumption, liver en-
zyme activity, and cadmium uptake by various
tissues.

Respiratory activity, a good indicator of the
general condition of a fish, has been related to
stress caused by such environmental variables as
temperature (MacLeod and Pessah 1973), salinity

'Middle Atlantic Coastal Fisheries Center Milford Labora-
tory, National Marine Fisheries Service, NOAA, Milford, CT
06460.

Manuscript accepted September 1976.
FISHERY BULLETIN: VOL. 75, NO. 1, 1977.

(Olson and Harrel 1973), and heavy-metal pol-
lutants (Calabrese et al. 1975). Gill-tissue res-
piration correlates well with whole-animal res-
piration, particularly the standard or inactive rate
of oxygen consumption ( Vernberg 1956; Thurberg
et al. 1975). Thurberg and Dawson (1974) found
that a 96-h exposure to 3 ppm Cd caused a de-
pression in the cunner's rate of gill-tissue oxygen
consumption. The present study examines the
oxygen-consumption rates in excised gill tissue of
cunners exposed to lower cadmium concentrations
for much longer periods of time.

Because the fish were small, biochemical testing
was restricted to the relatively large liver tissue
mass. Two enzymes were selected for assay: a key
enzyme of nitrogen metabolism that had been
tested in the earlier, short-term exposure of
cunners to high levels of cadmium (Gould and
Karolus 1974), and a magnesium-linked enzyme
whose activity in winter flounder, Pseudopleuro-
nectes americanus, tissues is affected by the fish's
exposure to sublethal levels of cadmium (Gould in
press). The first enzyme, aspartate amino-
transferase (E.C.3.6.1.L; AAT), is linked to the
production of animal energy (Gould et al. 1976),
and in cunners exposed to 24 ppm Cd for 96 h,
activity in the liver dropped to 40% of control
activity (Gould and Karolus 1974). The second
enzyme tested, glucose-6-phosphate dehydrogen-
ase (E.C.I. 1.1.49; G6PdH), is the first step in a
glycolytic pathway that produces metabolites for
reductive biosyntheses, and is found in abnor-
mally high amounts in tissues having the high
metabolic rates that often accompany stress
(Weber 1963).

Besides the respiratory and enzyme studies,

199

FISHERY BULLETIN: VOL. 75, NO. 1

chemical analyses were performed to determine
the cadmium uptake of certain tissues.

METHODS AND MATERIALS

Cunners for this study were trap-collected in
Long Island Sound near Milford, Conn., during the
summer of 1974 and held in the laboratory for 1 to
2 wk in flowing, sand-filtered seawater prior to
cadmium exposure. They were fed Purina Trout
Chow2 throughout the holding and exposure
periods. Beginning in August and ending in
October 1974, the cunners were exposed in aer-
ated, 285-liter fiber glass tanks filled to 228 liters
with sand-filtered seawater (24±2%o salinity,
22±2°C) by a proportional-dilution apparatus
(Mount and Brungs 1967). This diluter controlled
the intermittent delivery of toxicant-containing
water to each tank throughout the exposure period
at a flow rate of 1.5 liters every 2.5 min. This flow
rate provided approximately four complete ex-
changes of water daily in each tank. Cadmium was
added as CdCb ■21/2H20 at concentrations of 0.05
and 0.10 ppm Cd. Background level of cadmium in
the seawater was less than 0.001 ppm. Four tanks
were used per concentration and control, with 15
fish in each tank, for a total of 60 fish per test level.
The fish averaged 55.7 g in weight (range, 32.5-
96.9 g) and 157 mm total length (range, 133-185
mm). After 30- and 60-day exposure periods, fish
were removed for testing.

For oxygen-consumption measurements, two
gills were dissected from each fish and placed in a
15-ml Warburg-type flask containing 5 ml water
from the corresponding experimental tank. Oxy-
gen consumption was monitored over a 4-h period
at 20°C in a Gilson Differential Respirometer with
a shaking speed of 80 cycles/min. Rates of oxygen
uptake were calculated as microliters of oxygen
consumed per hour per gram dry weight gill tissue
(/a1 02/hg), including the gill arch, corrected to
microliters of dry gas at standard temperature and
pressure.

Liver tissue was taken for enzyme testing. Pools
comprising liver samples from two fish were
placed in small plastic pouches from which air was
subsequently excluded, then sealed and stored
frozen at -29°C. No more than 2 wk elapsed
between the end of the exposure period and test-
ing, as both AAT and G6PdH have been found to

lose some activity after a month's frozen storage of
whole liver tissue. For testing, each liver sample
was homogenized 1:9, wt/vol, with iced, doubly
glass-distilled water in a small, conical-tip glass
homogenizer containing 25-/xm glass powder to
facilitate grinding. Centrifugation was at 17,000 g
and 4°C for 45 min. The supernatant fractions
were removed with Pasteur pipettes, diluted 1:1.5
with the iced water, vol/vol, and recentrifuged
under the same conditions. The resulting
supernates served as the 4% liver preparations.
Protein determinations were made by the biuret
method (Gornal et al. 1949), with modifications by
Layne (1957), using a crystallized bovine serum
albumin standard. The coupled spectrophotomet-
ric assay for AAT was the same as that used in the
acute, short-term exposure of cunners to cadmium
described by Gould and Karolus (1974). For
G6PdH, both assay medium and spectro-
photometric procedures have also been described
elsewhere (Gould in press). Unit of activity was
micromoles NADH oxidized (AAT) or NADP
reduced (G6PdH) per minute per milligram
protein.

Gill, muscle, and liver tissues were analyzed for
cadmium uptake using the method described by
Greig et al. (1975), in which the samples were
wet-ashed with concentrated HNO3, taken up in
10% HNO3, and analyzed directly by atomic
absorption spectrophotometry. Values were
calculated on a wet-weight basis.

RESULTS AND DISCUSSION

Mortality and Respiration

Table 1 shows the actual and adjusted mortality
data after 30- and 60-day exposures. Mortality
data for the exposed fish were corrected for natural
mortality of the controls by using Abbott's formula
(Finney 1971), and can be interpreted as wholly
attributable to cadmium stress. Clearly, exposure
to low levels of cadmium increased the incidence of
mortality, more so at 0.1 ppm than at 0.05 ppm.

TABLE 1. — Actual and adjusted percent mortality of cadmium-
exposed cunner, Tautogolabrus adspersus.

2Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

Exposure
concentration

Mortality (%)

30 days

days

(ppm Cd)

Actual

Adjusted'

Actual

Adjusted'

0.00
0.05

0 1 0

3.3 (2)2
10.0(6)
15.0(9)

6.9
12.1

7.5 ( 5)
18.3(10)
37.4 (20)

11.7
32 3

'Adjustments made by Abbott's formula (Finney 1971).
2Number dead out of 60 fish.

200

MacINNES ET AL.: LONG-TERM CADMIUM STRESS IN THE CUNNER

TABLE 2. — Gill-tissue oxygen consumption rates of cadmium-exposed cunner,

Tautogolabrus adspersus.

Exposure

concentration

(ppm Cd)

30 days:

0.00

0.05

0.10
60 days:

0.00

0.05

0.10

Number
of
fish

Oxygen consumption rates'
X SE Range

Level of
significance2

972

101

754-1,436

736

530- 926

665

420- 967

1,036

788-1,324

702

612- 831

587

472- 810

>■ 005 "I
NS J

]
]

P 0.01
NS

'Microliters O; per hour per gram dry weight.
2Students f-test.

P- 0.025

P<0.005

Gill-tissue oxygen consumption was sig-
nificantly reduced after both 30- and 60-day
exposures to 0.05 and 0.10 ppm Cd (Table 2), a
result similar to that reported by Thurberg and
Dawson (1974) in cunners exposed to 3 ppm Cd for
96 h. The depression was more pronounced at the
end of the 60-day than at the end of the 30-day
exposure. In another chronic exposure study,
Dawson et al. (in press) found that gills of juvenile
striped bass, Morone saxatilis, exposed to 0.5, 2.5,
or 5.0 ppb Cd for 30 and 90 days, consumed sig-
nificantly less oxygen than did the controls. The
concentrations used were less than one-tenth of
those used in the present study, but they still
produced significant respiratory changes. The
results reported here are also supported by a study
using the winter flounder (Calabrese et al. 1975),
in which fish exposed to 5 or 10 ppb Cd for 60 days
showed significantly reduced oxygen consumption
rates.

Exposure to silver also depresses cunner gill-
tissue respiration (Thurberg and Collier in press).
There is some evidence, however, that other met-
als affect fish respiration differently. Cunners
exposed to 5 or 10 ppb mercury (as HgCh) for 30
and 60 days had significantly elevated respiration
rates after 30 days, but normal respiration after 60
days (unpubl. data). Similarly opposite effects of

the two metals, mercury and cadmium, were
reported for the winter flounder in 60-day expo-
sure studies (Calabrese et al. 1975); i.e., mercury
elevated the oxygen consumption rate, whereas
cadmium lowered it.

Enzyme Activity

In the liver of cunners exposed for 30 days to 0.1
ppm cadmium as chloride, AAT activity was
significantly lower (P<0.02) than in control fish
(Table 3). The drop in activity, about 20%, cor-
roborates the effect of cadmium on liver AAT
observed in cunners exposed for 4 days to high
concentrations (24 ppm Cd) of this metal salt
(Gould and Karolus 1974). As is the case with all
aminotransferases, pyridoxal phosphate is an
absolute requirement for activity. Because the
biosynthesis of this essential cofactor requires a
divalent metal cation (Meister 1955), and because
cadmium affects enzymes requiring or reacting
with divalent metal cations (Gould in press), it
seems probable that cadmium's inhibitory effect
on AAT activity is at the point of pyridoxal
phosphate synthesis.

Liver G6PdH in cunners exposed for 30 days to
0.05 ppm Cd was significantly higher (P<0.05)
than in controls (Table 3), and at 0.1 ppm the

TABLE 3. — Aspartate aminotransferase and glucose-6-phosphate dehydrogenase in
the liver of cunner, Tautogolabrus adspersus, exposed for 30 days to cadmium
chloride.

Exposure

concentration

(ppm Cd)

No. of

sample

pools

Enzyme activity'

Level of

Range

significance2

AAT:

0.00

233

194-281

0.05

217

160-254

P<0.02

0.10

181

154-234

G6PdH:

0.00
0.05

6
6

75
123

11
22

54- 91

78-149

P<U05 "I p<0001
P<0.01 J r uuu

0.10

169

148-224

'Unit of activity =

micromoles NADH oxidized (AAT;

i or NADP reduced (G6PdH) per minute per

milligram protein.
2Students f-test.

201

FISHERY BULLETIN: VOL. 75, NO. 1

increase was very highly significant (P<0.001).
This observation points to elevated pentose shunt
activity in the livers of exposed fish. We construe
this to be a compensatory mechanism, providing
metabolites for increased rates of biosyntheses, to
enable impaired biochemical systems to maintain
near-normal function. Similar inductive response
after sublethal metal challenge has been observed
in other teleosts, such as the winter flounder:
elevated levels of two metalloenzymes in the kid-
ney and hematopoietic tissue after 60 days' ex-
posure to 0.01 ppm Cd (Gould in press), and ele-
vated levels of ornithine decarboxylase, another
pyridoxal phosphate enzyme, in the liver and
kidney after intravenous injection of methyl-
mercury, following an initial drop in activity
(Manen et al.3).

Chemical Uptake

Gill, muscle, and liver tissues from each expo-
sure group were analyzed for cadmium uptake. In
contrast to the marked cadmium uptake in tissues
of cunners exposed for 96 h to cadmium at levels up
to 48 ppm (Greig et al. 1974), nearly all the sam-
ples from these 30- and 60-day exposures to both
0.05 and 0.1 ppm Cd, as well as controls, were
below the limits of detection (ca. 2 ppm, wet wt) for
the sample size and procedure used.

CONCLUSIONS

In summary, long-term exposures of the cunner
to 0.1 ppm Cd caused increased mortality, de-
pressed gill-tissue oxygen consumption, and
lowered transaminase and elevated pentose shunt
activity in the liver.

The toxicity of cadmium to marine animals is
influenced, however, by such environmental
variables as temperature, salinity, pH, dissolved
oxygen (Gardner and Yevich 1969; Vernberg and
Vernberg 1972), and chemical form (Gould et al.
1976). Moreover, toxicity of cadmium varies with
different species: Westernhagen et al. (1974) and
Westernhagen et al. (1975) found that low salini-
ties enhance the toxicity of cadmium to the de-
veloping eggs of herring, Clupea harengus, and
needlefish, Belone belone, but Westernhagen and

3Manen, C. A., B. Schmidt-Nielsen, and D. H. Russell. 1976.
Alterations of polyamine synthesis in liver and kidney of winter
flounder in response to methylmercury. Unpubl. manuscr. Univ.
Ariz. Med. Cent., Dep. Pharmacol., Tucson, and The Mt. Desert
Island Mar. Biol. Lab., Salsbury Cove, Maine.

Dethlefsen (1975) reported no such enhancement
using flounder, Pleuronectes flesus, eggs, possibly
because of the differences in the capacity of the egg
membranes to bind cadmium ions. The nature and
degree of cadmium's toxicity may well change
under different laboratory or field conditions.

ACKNOWLEDGMENT

We thank Rita S. Riccio for her critical reading
and typing of this manuscript.

LITERATURE CITED

CALABRESE, A., F. P. THURBERG, M. A. DAWSON, AND D. R.
WENZLOFF.

1975. Sublethal physiological stress induced by cadmium
and mercury in the winter flounder, Pseudopleuronectes
americanus. In J. H. Koeman and J. J. T. W. A. Strik
(editors), Sublethal effects of toxic chemicals on aquatic
animals, p. 15-21. Elsevier Publ. Co., Amst.

Dawson, M. a., e. Gould, F. p. Thurberg, and a.

CALABRESE.

In press. Physiological response of juvenile striped bass,
Morone saxatilis, to low levels of cadmium and mer-
cury. Chesapeake Sci.
EISLER, R.

1971. Cadmium poisoning in Fundulus heteroclitus
(Pisces: Cyprinodontidae) and other marine organ-
isms. J. Fish. Res. Board Can. 28:1225-1234.
1974. Radiocadmium exchange with seawater by Fun-
dulus heteroclitus (L.) (Pisces: Cyprinodontidae). J.
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1971. Probit analysis. 3d ed. Cambridge Univ. Press,
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203

MATURATION AND INDUCED SPAWNING OF
CAPTIVE PACIFIC MACKEREL, SCOMBER JAPONICUS

Roderick Leong1

ABSTRACT

Pacific mackerel, Scomber japonicus, became sexually mature under laboratory conditions and were
induced to spawn with hormone injections. Fish caught before the major spawning season became
mature under the natural photoperiod and under artificial photoperiods of 4 h light 20 h dark, 8 h light
16 h dark, and 16 h light 8 h dark. Mackerel caught near the end of the spawning season redeveloped
their gonads more rapidly at 18°C than at 15°C or ambient temperature. A 16°C-14 h light 10 h dark
environment was effective in maintaining mackerel in spawning condition beyond the normal spawn-
ing season. Any of three combinations of hormones induced spawning: gonadotropin from ground
salmon pituitary followed 24 h later by gonadotropin from pregnant mare serum; human chorionic
gonadotropin followed 24 h later by gonadotropin from pregnant mare serum; and salmon pituitary
plus human chorionic gonadotropin followed 24 h later by salmon pituitary plus human chorionic
gonadotropin plus gonadotropin from pregnant mare serum. The hormones did not induce spawning
when used individually. A procedure for routine spawning of Pacific mackerel is described.

Laboratory studies of the biology of pelagic fish
larvae are often limited by the uncertainty of
collecting eggs at sea. An alternative to collecting
eggs at sea is the maturation and spawning offish
in the laboratory. This objective was met for the
northern anchovy, Engraulis mordax (Leong
1971). Another species whose larvae are under
study at the Southwest Fisheries Center is the
Pacific mackerel, Scomber japonicus Houttuyn,
but the eggs are not available off the southern
California coast during most of the year. To in-
crease the availability of mackerel eggs for ex-
perimental work, I began a study designed to
develop procedures for routinely spawning
mackerel on demand throughout the year. My
approach was to first find a suitable photoperiod-
temperature environment which would encourage
maturation and to subsequently induce spawning
with gonadotropic agents. This report contains
observations on the maturation of mackerel under
different photoperiod-temperature conditions in
the laboratory; results of exploratory tests with
hormones to induce spawning; and a description of
a procedure currently used to spawn mackerel.

I followed the maturation of mackerel under
four photoperiods (4 h light 20 h dark, 8L16D,
16L8D, and ambient day length) and three
temperatures (15°C, 18°C, and ambient 12.8° to

Southwest Fisheries Center, National Marine Fisheries
Service, NOAA, La Jolla, CA 92038.

Manuscript accepted September 1976.
FISHERY BULLETIN: VOL. 75, NO. 1, 1977.

19°C). I also examined the effectiveness of a 16°C-
14L10D environment for maintaining mackerel in
spawning condition after the normal spawning
season. The hormones tested for the induction of
spawning were gonadotropin from ground salmon
pituitary, human chorionic gonadotropin, and
gonadotropin from pregnant mare serum. The
importance of the photoperiod-temperature en-
vironment in regulating maturation in fish and
the use of gonadotropins for inducing spawning
are well known from the early review of Pickford
and Atz (1957), but observations on marine
pelagic species are still limited. These are the first
observations on the maturation and spawning of a
scombrid fish under laboratory conditions.

METHODS

Maturation of Mackerel Under
Four Photoperiods

Knaggs and Parrish (1973) examined the
ovaries of mackerel from the commercial catch
and concluded that S. japonicus can spawn from
March through October but that the majority
spawn from April through August. Kramer
(1960), using sea-caught larvae as criteria,
concluded that spawning occurs from late April or
early May to August.

The fish used in these experiments were caught
off the southern California coast by hook and line

205

FISHERY BULLETIN: VOL. 75. NO. 1

between 1 February and 7 March 1973. The dates
of capture were 1 to 2 mo in advance of the major
spawning season. The fish ranged from 325 to 340
mm fork length; most fish of this size are capable of
spawning (Knaggs and Parrish 1973). During the
period of collection, the fish were held under
continuous incandescent lighting and a tempera-
ture of 19°C. These were arbitrary holding condi-
tions.

On 14 March, 1 wk after the last fish was
captured, the mackerel were divided into four
groups and placed in three indoor plastic swim-
ming pools (4.6 m in diameter, 1 m water depth)
and one outdoor pool ( 7.3 m in diameter, 1 m water
depth). Each of the three indoor pools was enclosed
in a separate room lined with black opaque
polyethylene film. A 200-W incandescent bulb, 1.2
m above the water surface, illuminated each in-
door pool during the artificial day. A timer-
controlled rheostat gradually lit and dimmed the
bulb over 30 min to avoid startling the fish. The
length of day was considered as the time of full
illumination. Two 3-W lamps, 1 m above the water
surface, burned continuously and provided low-
level illumination during the dark period. The
light intensity was about 215 lx at the brightest
spot on the surface during the day and less than
5.4 lx at night. The outdoor pool was shielded from
direct sunlight by an opaque plastic canopy 1.2 m
above the water surface but the sides were open
and the fish received a natural photoperiod.

Temperature control was achieved with a
commercial temperature regulator and mixing
valve unit which automatically adjusted the
inflow of chilled (10°C) and heated (20°C) seawater
to maintain a desired pool temperature. For this
series of observations the temperature was set at
19° ± 0.5°C for all tanks. I chose this temperature
because captive mackerel had spawned at this
temperature during a preliminary study. The flow
rates were 32 liters/min for the indoor tanks and
50 liters/min for the outdoor tank. Each tank also
had a recirculating pump of 250 liters/min
capacity.

Each of the experimental groups contained 50
fish. Commencing on 17 March, the three groups of
fish in the indoor tanks were maintained on
photoperiods of 4L20D, 8L16D, and 16L8D, re-
spectively. The group of fish in the outdoor tank
remained under the natural photoperiod where
the time between sunrise and sunset was 12 h.
Biopsy samples of the gonads were taken prior to
the photoperiodic change and again a month later

to note the change in maturation. The biopsies
were taken by inserting the tip of a glass pipette
(1.2 mm in diameter) through the genital pore of a
fish anesthetized in 7 ppm quinaldine and remov-
ing a small piece of gonad by mild suction. The
technique, a modification of that used by Stevens
( 1966), did not appear to cause permanent damage
to the fish. All ovarian samples were examined
with a dissecting microscope and the diameter of
the largest eggs measured to the nearest 0.1 mm.
No effort was made to categorize the males except
to note if milt was obtained. Six females were
biopsied at the start of the trial and two from each
treatment at the end.

An egg strainer was positioned at the outflow of
each tank and inspected daily to detect spon-
taneous spawning. The strainer, a 1 x 1 x 0.2 m
wooden frame with 202-^tm mesh netting
stretched across the bottom, was partially im-
mersed in a water bath to prevent desiccation of
eggs. The mackerel were fed daily with either
freshly thawed frozen anchovies or ground squid.
Occasionally, Oregon moist chow was mixed in
with the ground squid as a supplement. The
estimated daily ration was 49c of body weight.

Maturation of Mackerel Under Ambient,
15°C, and 18°C Temperatures

Mackerel judged to be in or near postspawning
condition were collected between 23 August and
28 September 1973. The fish ranged from 330 to
370 mm fork length and were kept indoors at
18°C-14L10D during the period of collection. The
mackerel were subsequently divided into three
groups of 50 fish each and placed in two of the
indoor pools and in the outdoor pool already de-
scribed. Beginning on 3 October, the two groups of
indoor fish were kept at 15°C and 18°C, respec-
tively. The fish in the outdoor tank received
seawater at ambient temperature (19°C at the
outset) which fluctuated with ocean conditions at
the intake. The intake was located at the end of the
pier at the Scripps Institution of Oceanography,
La Jolla. The photoperiods were 14L10D for both
indoor groups and natural for the outdoor group.
Six females were biopsied at the start of the trial
for ova measurements. Several fish from each
group were biopsied at various intervals af-
terwards until March 1974 to observe changes in
ovarian development. I attempted to obtain eggs
from at least two females per group with every
round of sampling.

206

LEONG: MATURATION AND SPAWNING OF SCOMBER JAPONICUS

Test of a 16°C-14L10D Environment

for Maintaining Mackerel

in Spawning Condition

After the Normal Spawning Season

The group of 50 fish that was held outdoors
under ambient conditions began to spawn
spontaneously at the end of April 1974. On 7 July,
while some spawning was still in progress, 25 fish
were transferred indoors to a tank with ambient
temperature (19°C) seawater and photoperiod of
14L10D. On 8 July, the temperature was lowered
to 16°C and the fish were kept at that temperature
for 9 mo. Biopsies were taken at the time of trans-
fer and in each succeeding month to determine if
at least one female was in spawning condition.
During each sampling, fish were catheterized
until a female with 0.7-mm diameter eggs was
found. Females with eggs of this size are func-
tionally mature, i.e., can be spawned with hor-
mone injections.

Testing of Hormones for Induction
of Spawning

The agents tested for the induction of spawning
were gonadotropin from ground chinook salmon,
Oncorhynchus tshawytscha, pituitary (SP),
human chorionic gonadotropin (HCG), and gonad-

otropin from pregnant mare serum (PMS). The
agents were applied individually and in combina-
tion, as indicated in Table 1.

The salmon pituitaries were collected, pre-
served, and prepared as described by Haydock
( 197 1). The carrier for all injections was saline and
the injection volume 0.1 ml. The injections were
applied intramuscularly near the base of the dor-
sal fin with a 24-gauge needle on a 0.5-ml syringe.

The mean weight of the fish was 0.9 kg (range
0.8 to 1.1 kg). Dosages were not adjusted for dif-
ferences in fish weight, and one male and one
female were injected for each treatment. The fish
had become sexually mature in the laboratory and
were among those used in the photoperiodic ex-
periment. The injection trials were carried out
during June through August which is also the
time of spawning in nature.

Fish were biopsied beforehand and only males
with generous amounts of milt and females with
0.7-mm diameter eggs were injected (preliminary
testing indicated that the eggs had to be close to
0.7 mm in diameter before the hormones would
stimulate a noticeable response). The injected pair
was isolated in a small swimming pool (3 m in
diameter, 0.5 m water depth) with water tempera-
ture at 17°C and a flow rate of 2.5 liters/min. An
egg strainer was placed at the outflow to detect
spawning. Biopsies and general observation were

TABLE 1 — Results of tests with gonadotropin from ground salmon pituitary (SP), human chorionic gonadotropin (HCG),
and gonadotropin from pregnant mare serum (PMS) for induction of spawning in Scomber japonicus .

After 24 h2

After 40 h

•S

■0

-0
B

Hormones and dosages

-0

M
CD

-0

Results of striDDino4

First

injection

Second injection1

Egg

diameter3
(mm)

■5

3
>
O

ra
0.
V)

CD
LL

Egg

diameter
(mm)

O
O

3
>
O

E
0

Number
eggs

Number

Hormone

Dosage

Hormone

Dosage

live larvae

1 mg

—

0.8

1.1

<500

<10

5 mg

—

0.8

1.1

—

10 mg

—

1.1

—

15 mg

—

1.1

<500

<10

25 mg

—

0.9

1.1

—

HCG

12.5 IU

—

0.8

1.1

<500

<10

HCG

25 IU

—

0.8

1.1

<500

<10

HCG

50 IU

—

0.9

1.1

—

HCG

125 IU

1.1

—

HCG

250 IU

1.1

<500

<10

HCG

500 IU

—

1.1

<500

<10

PMS

300 IU

0.8

—

PMS

750 IU

1.1

<500

<10

PMS

1,000 IU

0.8

1.1

5,000

<10

1 mg

PMS

100 IU

0.9

1.1

50,000

10,000

HCG

12.5 IU

PMS

100 IU

0.8

1.1

30,000

10,000

1 mg

0.9

1.1

80,000

30,000

HCG

12.5 IU

HCG

+
PMS

12.5 IU

200 IU

'Second injection given 24 h after first injection.

2Time measured after first injection.

3Egg diameter was 0.7 mm before first injection.

"Stripping was attempted on live fish with ovulated eggs. Stripping was attempted even if a fish spawned because the eggs were unfertilized.

207

FISHERY BULLETIN: VOL. 75, NO. 1

taken at 24 and 40 h after injection to note the
effects of the hormones. If ovulation or spawning
had occurred, stripping was attempted and the
eggs fertilized by the dry method (Davis 1961).

RESULTS

Maturation of Mackerel Under
Four Photoperiods

The female mackerel caught before the spawn-
ing season became mature in the laboratory under
the three constant photoperiods (4L20D, 8L16D,
and 16L8D) and under ambient light conditions.
At the start of the experiment (17 March) the
diameter of the largest eggs sampled from the six
females ranged from 0.4 to 0.6 mm. Thus, the
females were not fully mature but two of the males
sampled already had milt and may have been
capable of spawning. Recently spawned eggs
appeared in the egg strainer of the 16L8D tank on
17 April, 1 mo after the beginning of the ex-
periment. Catheterization of two females from
each treatment showed that all treatments
contained females with 0.7-mm diameter eggs
indicating sexual maturity. None of the treat-
ments appeared to inhibit maturation. The results
indicated that female mackerel in prespawning
condition will become sexually mature in the
laboratory under a wide range of photoperiods at
19°C.

The dates of initial spawning showed no relation
to the length of day. Spawning was detected in the
4L20D tank on 25 April and in the outdoor tank on
1 May 1973. In the outdoor tank, the time between
sunrise and sunset had lengthened from 12 h at
the start of the trial to 13V2 h on 1 May. Spawning
was never detected in the 8L16D tank although it
contained functionally mature males and females.

The mackerel spawned during the dark period
but the exact time is not known. Watanabe (1970)
stated that mackerel spawn between 2000 and
2400 h in nature. Spawning occurred three or four
times a week in the outdoor pool and two or three
times a week in the indoor pools from May to
mid-June. The frequency of spawning then de-
creased and was rare by mid-July when observa-
tions ended.

Although the fish spawned spontaneously, the
predictability of spawning and the viability of
eggs were not satisfactory. The number of eggs
collected per day was usually less than 3,000,
although one collection was over 50,000. The

percentage of viable eggs seldom exceeded 10%
and was often zero. The spontaneously spawned
eggs were translucent and of the proper size, 1.1
mm in diameter, but most were not fertilized.

Observations ended in mid-July because the fish
began to feed poorly and started to die. An ac-
companying symptom of failing health was the
malformation of jaws in about half of the fish.
Afflicted fish swam with their jaws constantly
agape and were unable to bite on food items. The
condition may have been partly due to the high
water temperature as some fish recovered when
transferred to a tank with 15°C seawater. Thus,
while the mackerel became fully mature at 19°C a
prolonged exposure may be detrimental.

Maturation of Mackerel at Ambient,
15°C, and 18°C Temperatures

Mackerel captured near the end of the spawning
season redeveloped their ovaries more rapidly at
18°C than at 15°C or ambient temperature (Figure
1). Three of the females sampled at the start of the
trial, 3 October, had eggs 0.7 mm in diameter
while three others had eggs 0.2 mm in diameter.
This difference in egg size can be expected near the
end of the spawning season as some females stop
spawning and begin resorption of ovaries earlier
than others. In November, one female from the
18°C treatment still had eggs 0.7 mm in diameter
but four other fish from that treatment and five
from each of the other two treatments could not be
sexed because of immaturity of the gonads. Below
a certain stage of maturity gonads are too small to
remove tissue for biopsy. Biopsies were still
difficult to perform in January and samples were
obtained from less than half of the fish. The
females that did provide samples had eggs
measuring 0.3 to 0.4 mm in diameter. Biopsies
were more successful in February; the females
from the 15°C and ambient temperature groups
still had eggs measuring 0.3 to 0.4 mm in diameter
but two females from the 18°C group had eggs of
0.5 and 0.6 mm in diameter, respectively. Two of
the three females sampled from the 18°C group on
20 March had eggs of 0.7 mm in diameter and one
was spawned with hormone injections. The
spawning date was about 5V2 mo after the start of
the trial. On 20 March, the females from the 15°C
and ambient temperature groups did not as yet
have eggs exceeding 0.5 mm in diameter. Ob-
servations ended shortly after for the 15° and 18°C

208

LEONG: MATURATION AND SPAWNING OF SCOMBER JAPONICUS

20°

Z, 18°

FIGURE 1. — Development of eggs in
female Scomber japonicus under three
temperature conditions. Upper panel,
weekly ambient temperature ranges
and medians. Lower panel, diameter of
the largest eggs in individual females
under 18°C, 15°C, and ambient
temperatures. Shaded area, numbers of
individuals which could not be sexed
due to immaturity. Closed circles
represent egg diameters in initial
sample, open circles at 18°C, squares at
15°C, and triangles at ambient
temperature. Arrow indicates when
group under ambient conditions
spawned naturally.

16'

uj 14"

12'

t!
k

i 5

J-I

2 5

r i

_1 1 1 L.

_t_

E°6t

E0.4fh

2
<

5 0.2^-

CD
C&

o
o

IMMATURE

NATURAL
SPAWNING

3 10
OCT.

groups because of a water system failure and total
loss of fish indoors.

The fish in the outdoor tank survived and began
to spawn spontaneously on 30 April, nearly 6 wk
after the induced spawning. The end of April is
also the approximate time that the natural
population begins to spawn off the southern
California coast (Kramer 1960). The temperatures .
in the outdoor tank were very similar to the
temperatures at Scripps Pier, which can be
considered indicative of surface coastal conditions
off southern California (Radovich 1961). Thus the
mackerel in the outdoor tank should have received
temperatures which were like the temperatures
found in the southern California spawning
grounds and the similar time of initial spawning
may be expected. However, it should be pointed
out that mackerel in the wild can migrate over
long distances (Roedel 1952) and the average
temperature cycle they undergo in nature is not
precisely known.

The temperature in the outdoor pool at the time
of initial spawning was 16°C which is a favorable
temperature for mackerel spawning in nature.
Kramer (1960), utilizing data from the California
Cooperative Oceanic Fisheries Investigations
surveys, found mackerel larvae occurring at
temperatures (taken at 10 m) ranging from 10.3°C
to 26.8°C with more than 68% of all occurrences
between 14.0° and 17.9°C. Watanabe (1970), using
Japanese data, found early stage mackerel eggs

17 24 31 7 14 21 28 5 12 19 26 2 9 16 23 30 6 13 20 27 6 13 20 27 3 10 17 24 I
NOV. DEC. JAN FEB. MAR. APR. MAY

DAY

occurring between temperatures (taken at the
surface) of 13° and 23°C with the mode of positive
stations between 16° and 19°C.

Test of a 16°C-14L10D Environment

for Maintaining Mackerel

in Spawning Condition

After the Normal Spawning Season

The group of 25 fish that was placed under a
16°C-14L10D environment contained functionally
mature individuals at the start of the trial, 7 July.
Monthly biopsies indicated that at least one
female in the group was sexually mature from
July 1974 through March 1975. The months of
sampling included December, January, and
February when the maturity indices of mackerel
are at the lowest levels (Knaggs and Parrish
1973). No more than three females were
catheterized in any month before one with 0.7-mm
diameter eggs was found. The eggs in the other
females ranged from 0.2 to 0.6 mm in diameter. I
am not certain if the ripe females remained
sexually mature continuously or if they resorbed
and subsequently redeveloped their ovaries.

Effectiveness of Hormones for the
Induction of Spawning

All injections of ground salmon pituitary (SP)
from 1 to 25 mg stimulated hydration and ovula-

209

FISHERY BULLETIN: VOL. 75, NO. 1

tion but the females did not spawn spontaneously
nor could they be satisfactorily stripped (Table 1).
The females ovulated within 24 h in the 10- and
15-mg trials and between 24 and 40 h in the 1-, 5-,
and 25-mg trials. Ovulated eggs were catheterized
from live fish in the 1- and 15-mg trials and from
dead fish in the 5-, 10-, and 25-mg trials. The live
females in the 1- and 15-mg trials were stripped as
soon as ovulation was detected but the fish re-
leased only small numbers of eggs even with
heavy stripping pressure. Attempted fertilization
resulted in less than 10 larvae in both trials. The
stripped eggs were translucent, measured 1.1 mm
in diameter, and appeared normal but nearly all
were not viable.

The females that received 5, 10, 15, and 25 mg of
SP died within 40 h after injection. The female
that received 1 mg was intentionally killed at 72 h
for dissection. All of the females including the one
that received only 1 mg of SP had severely dis-
tended abdomens. Subsequent dissection revealed
that the distension was due to extremely enlarged
ovaries. The ovaries contained many ovulated
eggs which were not extruded and the females
were apparently egg bound. I did not see any plugs
or clots which impeded the flow of eggs.

All injections of SP, 1 to 25 mg, to male mackerel
facilitated the stripping of milt. The milt in the
catheter samples before injection was thick and
only small amounts could be expressed. The in-
jections of SP brought about a thinning of the milt
and made stripping easier. None of the males
injected with SP died.

All injections of human chorionic gonadotropin
(HCG), 12.5 to 500 IU, stimulated hydration and
ovulation but the females could not be easily
stripped of eggs. Ovulation occurred within 24 h in
the 125-, 250-, and 500-IU trials and between 24
and 40 h in the 12. 5-, 25-, and 50-IU trials. None of
the females that were alive when ovulation was
detected could be stripped of more than 500 eggs.
The number of larvae produced was negligible in
all trials. All of the females that received 50 or
more IU of HCG died within 40 h after injection.
The females that received 12.5 or 25 IU of HCG
were purposely killed at 72 h. As with SP, all of the
females had severely distended abdomens and
enlarged ovaries. All dosages of HCG facilitated
the stripping of milt without killing the male.

The results of trials with pregnant mare serum
( PMS) were variable. In the 1 ,000-IU trial the eggs
increased in size from 0.7 to 0.8 mm in diameter in
24 h and were ovulated by 40 h. More than 5,000

eggs were stripped at 40 h but most of the eggs
were cloudy, had collapsed perivitelline mem-
branes, and were apparently overripe. However, a
few eggs were viable and a small number hatched
following fertilization. In the 750-IU trial, ovu-
lation was detected at 24 h but the eggs already
had collapsed perivitelline membranes and were
overripe. The eggs in the 300-IU trial grew to 0.8
mm within 24 h but did not show further im-
provement at 40 h. None of the females injected
with PMS had severely distended abdomens and
none were dead by 40 h after injection. At all levels
tested, PMS made the stripping of milt easier and
did not kill the injected male.

The three combinations of hormones tested were
all successful in stimulating hydration, ovulation,
and spontaneous release of eggs. The first injec-
tion, 1 mg SP, of the SP-PMS trial promoted egg
growth from 0.7 to 0.9 mm in diameter in 24 h. The
second injection of 100 IU PMS 24 h later appeared
to stimulate the release of eggs as 50,000 eggs
were found in the egg strainer at 40 h. The eggs
were translucent, measured 1.1 mm in diameter,
and appeared to be of good quality but were un-
fertilized. However, the female extruded another
50,000 eggs when stripped at 40 h and these were
artificially fertilized with milt from the injected
male. About half of the eggs showed signs of
cleavage and approximately 10,000 larvae
hatched. The larvae appeared normal when
compared with the larval descriptions of Kramer
(1960) and Watanabe (1970). Some of the larvae
later developed into juveniles which grew to more
than 100 mm total length.

The other two combinations (12.5 IU HCG ini-
tially and 100 IU PMS 24 h later; 1 mg SP + 12.5
IU HCG initially and 1 mg SP + 12.5 IU HCG +
200 IU PMS 24 h later) produced similar results.
The initial injection produced egg growth to 0.8 or
0.9 mm and spawning occurred after the second
injection but the spawned eggs were unfertilized.
The fish were then stripped and the eggs arti-
ficially fertilized. Many of these hatched and
produced thousands of viable larvae. All of the
females became bruised from the handling during
stripping, and died a few days after spawning.

RECOMMENDED PROCEDURE

A procedure for spawning mackerel has been
developed from the foregoing observations and the
method has been used since March 1975 to
routinely produce viable eggs. The 16°C-14L10D

210

LEONG: MATURATION AND SPAWNING OF SCOMBER JAPONICUS

environment is used to ripen and maintain
spawnable stocks of fish in the laboratory and
hormone injections are used to induce spawning. I
use 1 mg SP + 12.5 IU HCG for the first injection
followed by 1 mg SP + 12.5 IU HCG + 200 IU PMS
24 h later to spawn females and a 5-mg SP injec-
tion for spawning males. I inject two males to
insure an adequate supply of milt. The procedure
is essentially the same as described in the Methods
section. The egg strainer is checked regularly
beginning at 12 h after the second injection to the
female and the female is examined whenever eggs
are detected. The female is stripped if she releases
eggs easily and the eggs are extruded into a dry
finger bowl for fertilization. The male is stripped
and the milt collected with a spoon held below the
genital pore. The milt is washed into the finger
bowl with a little seawater and the contents
swirled gently for 3 min. The eggs are then placed
in an incubation tank for further development and
hatching. To date, induction of spawning has been
successful 26 times in 36 attempts, each spawning
producing 6,000 or more viable eggs, and success-
ful spawning has been induced during every
month of the year.

ACKNOWLEDGMENT

I thank John Hunter, Southwest Fisheries
Center, National Marine Fisheries Service,
NOAA, for his many useful suggestions in the
preparation of this paper.

LITERATURE CITED

DAVIS, H. S.

1961. Culture and diseases of game fishes. Univ. Calif.
Press, Berkeley, 332 p.
HAYDOCK, I.

1971. Gonad maturation and hormone-induced spawning of
the Gulf croaker, Bairdiella icistia. Fish. Bull., U.S.
69:157-180.
KNAGGS, E. H., AND R. H. PARRISH.

1973. Maturation and growth of Pacific mackerel, Scomber
japonicus Houttuyn. Calif. Fish Game 59:114-120.
KRAMER, D.

1960. Development of eggs and larvae of Pacific mackerel
and distribution and abundance of larvae 1952-56. U.S.
Fish Wildl. Serv., Fish. Bull. 60:393-438.

LEONG, R.

1971. Induced spawning of the northern anchovy, Engraulis
mordax Girard. Fish. Bull., U.S. 69:357-360.
PICKFORD, G. E., AND J. W. ATZ.

1957. The physiology of the pituitary gland of fishes. N.Y.
Zool. Soc, 613 p.
RADOVICH, J.

1961. Relationships of some marine organisms of the
northeast Pacific to water temperatures particularly
during 1957 through 1959. Calif. Fish Game, Fish Bull.
112, 62 p.

ROEDEL, P. M.

1952. A racial study of the Pacific mackerel, Pneuma-
tophorus diego. Calif. Fish Game, Fish Bull. 84, 53 p.
STEVENS, R. E.

1966. Hormone-induced spawning of striped bass for re-
servoir stocking. Prog. Fish-Cult. 28:19-28.
WATANABE, T.

1970. Morphology and ecology of early stages of life in
Japanese common mackerel, Scomber japonicus
Houttuyn, with special reference to fluctuation of popu-
lation. [In Engl, and Jap.] Bull. Tokai Reg. Fish. Res. Lab.
62, 283 p.

211

NOTES

INCORPORATING SOAK TIME INTO

MEASUREMENT OF FISHING EFFORT IN

TRAP FISHERIES

While it is recognized that soak time (number of
days a trap is allowed to fish before it is retrieved)
is an important fishing strategy decision for the
individual fisherman, there is surprisingly scarce
information on the subject. Little data is available
on the relationship between catch and soak time.
Similarly, the implications of variable soak times
have not been widely discussed.

This paper develops a model to determine the
profit-maximizing soak time for an individual
fisherman in the Florida spiny lobster, Panulirus
argus, fishery. This establishes the relative im-
portance of soak time as one of the components of
fishing effort in trap fisheries and leads to
suggestions for incorporating soak time into the
traditional measurement of trap days to more
accurately reflect fishing effort in trap fisheries.

Profit-Maximizing Soak Time

Catch per trap day was regressed on soak time
with the data collected by Robinson and Dimitriou
(1963). The best statistical fit using ordinary least
squares is in the form of Equation (1) (Figure 1).

C = <L (i)

D SP

where C = catch per trap haul

D = days fished for the sample
S = soak time in days
a = 2.94, ia = 5.40
0 = 0.90, in = 11.25

year: 1963
n = 25
R2 = 0.86.

Since the number of days fished (D) in this field
experiment was synonymous with the soak time
(D = S), then:

C = aS{

(2)

Taking the first and second derivatives of Equa-
tion (2) with respect to the soak time:

dC (1 - /8) a
dS ~

> 0

(3)

d2C (P2 - P) a

dS'<

S<l+/3>

< 0.

(4)

Equations (3) and (4) imply the catch per trap haul
increases at a decreasing rate with respect to the
soak time (Figure 2). This relationship seems

C
D

FIGURE 1. — Catch per day with respect to the soak time.

FIGURE 2. — Catch per haul with respect to the soak time.

213

reasonable for traps that attract fish because they
are baited, or because the trap acts as a refuge, or
some combination of both reasons. This rela-
tionship has been observed by Thomas (1973) in
the Maine (American lobster, Homarus
americanus) fishery and by Warner (pers.
commun.) and Simmons (pers. commun.) for
Florida Keys and Bahama spiny lobster trap
fishing. The distinction would be that the catch
curve for traps that are highly dependent on bait-
ing would presumably be relatively steeper than
for less bait-dependent traps reflecting the rela-
tive attracting power of the bait during the initial
soak time.

In both cases it is expected that the total catch
per trap haul would peak and perhaps even de-
crease with very long soak times either because of
mortality in the trap (starvation, cannibalism,
predation) or escapement. Therefore, while it is
recognized that the catch per trap haul with re-
spect to the soak time is probably sigmoidal
shaped, the negatively sloped portion that would
be associated with long soak times is excluded
from the model on the assumption it is not within
the range of normal commercial fishing strategies.

The number of times each trap is hauled in a
given time period (e.g., 1 mo) is the number of days
in the time period divided by the soak time (in
days). The total catch for the given fishing period
would be the catch per trap haul Equation (2)
times the number of times each trap is hauled
(D/S) times the number of traps (T).

= Ls

1-/3)

aPT

(5)

where L = total catch in the fishing period
T = number of traps fished
D = number of days in the fishing period
S = soak time in days.

FIGURE 3. — Total catch in the fishing period with respect to the

soak time.

respect to the soak time (Figure 3). This is because
a longer soak time increases the catch per trap
haul but decreases the number of hauls possible in
the fishing period.

Holding the number of traps constant is a highly
restrictive condition. The advantage of increasing
the soak time would be to permit the individual
fisherman to operate more traps. The most rea-
sonable constraint measurement for fishing capa-
bilities is a maximum number of hauls in a fishing
period.

It is assumed an individual vessel can make a
constant (maximum) number of hauls during the
fishing period. This maximum is predicated on
characteristics of the vessel, number in the crew,
distance traps are set from port, depth of water,
and weather conditions.

» #

H =K

(8)
(9)

Taking the first and second derivatives of Equa-
tion (5) with respect to the soak time:

-paDT

S<l+/3>

< 0

d*L _ ()8 + ff2) aDT

ds2 ' s«+jb>

> o.

(6)

(7)

Equations (6) and (7) imply that, holding the
number of traps constant, the total catch for the
fishing period decreases at a decreasing rate with

where H = total number of trap hauls in P days
K = maximum number of trap hauls in P
days.

Substituting Equation (9) into Equation (8) and
rearranging:

T =

(10)

Substituting Equation (10) into Equation (5)
results in a total catch equation where both the
soak time and number of traps vary in combi-

214

nations that always result in the maximum
number of possible hauls.

L =

(m)-

aKS

(1-/3)

(11)

Taking the first and second derivatives of Equa-
tion (11) with respect to the soak time:

dL= (1 - j8) aK

dS SO

d2L __ (/32 - j8) aK

dS'-

S'i^>

< 0.

(12)

(13)

Equations (12) and (13) imply that, holding the
number of total hauls constant, the total catch
increases at a decreasing rate with respect to the
soak time (Figure 4). This is because a longer soak
time decreases the catch per trap day but increases
the number of traps that can be fished.

The fisherman/entrepreneur is not interested in
maximizing the catch per trap day, the catch per
trap haul, or the total catch. He presumably wants
to maximize the net economic return (profit) from
fishing which is the difference between the total
revenue and total cost of his fishing activities. The
total revenue is equal to the ex-vessel price times
the catch. In the case of an individual fisherman, it
can normally be assumed that the price is constant
over all catch ranges. This is because the catch of

FIGURE 4. — Total catch in the fishing period with respect to the
soak time, given combinations of soak time and number of traps
that always result in the maximum number of hauls.

an individual fisherman is relatively small
compared with total landings in the fishery and
will, therefore, not have a significant influence on
the prevailing ex-vessel prices.

TR = pL

(14)

where TR = total revenue

p = ex-vessel fish price (per pound round
weight).

Total fishing costs are comprised of fixed in-
vestment costs, trap hauling costs, and trap costs:

TC = IK

HK + ST

(15)

where TC = total fishing costs

fixed costs (e.g., vessel depreciation,

insurance, routine maintenance) on

equipment capable of K hauls in D

days

costs of K hauls

costs of traps

unit cost (depreciated value and

maintenance cost) of a trap for the

fishing period {D days).

Trap hauling costs are treated as a constant in
the model because the number of hauls is held
constant. It is recognized that trap hauling costs
are dependent on factors such as fishing depth and
the distance traps are set from port as well as the
number of trap hauls. This model assumes these
factors are relatively constant. In the case of
Florida spiny lobster fishing, this may not be too
unreasonable an assumption because fishermen
customarily fish the same area for considerable
periods of time. When the assumption does not
hold, neither does the assumption about a con-
stant maximum number of hauls.

Since the model is an analysis of changes in soak
time and traps fished, the constant costs in the
model (IK andHK) play minor roles. It is assumed
that with the profit-maximizing soak time and
number of traps that total revenue will be greater
than total costs. If total costs were greater than
total revenue for all soak times and number of
traps fished, then presumably fishermen would
stop fishing to avoid incurring continuous losses.
Profit (77) is defined as total revenue (Equation
(14)) minus total costs (Equation (15)):

7T = pL

IK - HK - 8T.

(16)
215

Substituting Equations (10) and (11) into Equa-
tion (16):

n = p\aKS«-^-IK - HK - 8^. (17)

Taking the first and second derivatives of Equa-
tion (17) with respect to the soak time:

dir _ (1 - (3) paK _SK>Q
dS SP D <

d27T _((32 - p) paK

dS''

S<l + /3>

< 0.

(18)

(19)

The profit-maximizing soak time can be deter-
mined by setting Equation (18) equal to zero and
solving for S (Figure 5):

>•-£

- j8) paP\
8 J

(20)

XK + "k

Estimated life span of a trap: 1.5 seasons or 12

mo
8 = depreciated value of a trap forD days use (1

mo)
8 = 630
p = 38.30
D = 30
a = 2.94
j8 = 0.90
S„ = 6.52 (as estimated by Equation (20)).

The theoretically profit-maximizing soak time
compares favorably with the average soak time of
6-7 days in 1962 (October-December) observed by
Robinson and Dimitriou in the commercial
fishery. This favorable comparison should be
interpreted with reservations. First, Equation (1)
was estimated from a small sample (25 observa-
tions). Second, the model is sensitive to trap costs
and the method of calculating these costs is rather
crude. The life span of traps varies significantly.
Furthermore, maintenance costs involve remov-
ing underwater growth (traps fish better when
they are clean) and onshore storage costs that vary
considerably at different locations.

Influence of Relative Abundance on
Soak Time and Catch per Trap Day

The catch per trap day may not reflect declining
relative abundance (decreasing a in the model). As
the exploitable stock declines so will the profit-
maximizing soak time (Equation (20)). This re-
duces the number of traps each vessel can operate
(given a maximum number of hauls) but increases
the catch per trap day relative to what would have
prevailed with the originally longer soak time.
The net result is that as a declines the catch per
trap day will remain constant. This can be seen by
substituting Equation (20) into Equation (1).

FIGURE 5. — Total revenue, total cost, and profit with respect to
the soak time, given combinations of soak time and number of
traps that always result in the maximum number of hauls.

L_
TD

|l - fl) paD] y]

The parameters prevailing in 1962 were:

Purchase price of a trap: $6.00

Maintenance cost of a trap over its life span:

(0.25)(cost) = $1.50
Total cost of a trap: $7.50

(1 - 0) PD

(21)

Equation (21) and Table 1 indicate that the
measured catch per trap day will not vary with
changes in the exploitable stock when the soak
time also adjusts to the exploitable stock.

216

TABLE 1. — Catch per trap day that would be recorded with a
declining stock (decreasing a) with constant (column 6) and
variable (column 8) soak times.

^d=-t

UTD

2.94
2.44
1.94
1.44

0.90
0.90
0.90
0.90

0.383
0.383
0.383
0.383

0.63
0.63
0.63
0.63

6.52
6.52
6.52
6.52

0.54
0.45
0.36
0.27

652
5.24
4.07
2.94

0.55
0.55
0.55
0.55

Adjustment of Trap Days to Include Soak Time
as a Measurement of Fishing Effort

"Trap days" is customarily the recorded
measurement of fishing effort. This index may not
accurately reflect relative fishing effort because it
only records two components of fishing effort,
number of traps and number of days fished. The
frequency with which traps are hauled (soak time)
is not reflected. Therefore, trap days is an accurate
measurement of effort only as long as soak time
remains constant. According to the determinants
of the profit-maximizing soak time, a constant
soak time seems unlikely.

One method to adjust trap days to more accu-
rately reflect fishing effort would be according to
the relationship between the number of traps and
the soak time that will achieve the same total
catch. Taking the total differential of Equation (5)
and setting it equal to zero:

&(dS) + $k(dT) = 0

(22)

-/3aDTS"(/3+1) (dS) + aDS1* (dT) = 0 (23)

dT = BT
dS S

(24)

where T = number of traps

4 = numeraire soak time
x = prevailing soak time
T* = adjusted number of traps
D = fishing days
T*D = adjusted number of trap days.

When the prevailing soak time (x) differs sig-
nificantly from the base soak time (4), the in-
tegration of the interval can be more accurately
estimated by:

= t ± y —

S=4

T*D = T ± Z^ D

(28)

(29)

S=4

v BT
where x>4=>2,^q<^

S=4 ^

v PT

x < 4 => 2, q > °-

S=4 °

Utilizing Equations (28) and (29) and 1962
parameters, Table 2 indicates how the number of
traps, trap days, adjusted traps, and adjusted trap
days would compare with alternative soak times.
The interpretation of Table 2 is that the ad-
justed number of traps (column 5) reflects the
relative fishing power of a trap at different soak
times. Utilizing a 4-day soak time as a base, a trap
hauled every day has 2.75 the fishing power of a
trap hauled every 4 days. In the other direction, a
trap hauled every 7 days has 0.54 the fishing
power of a trap hauled every 4 days.

Equation (24) represents the relationship
between soak time and number of traps that will
result in the same total catch. This relationship
can be utilized to weight trap days according to
soak time. The first step is to choose a base soak
time (e.g., S = 4). When the soak time is 4 days,
then the number of "adjusted traps" is equal to the
number of traps and the number of "adjusted trap
days" is equal to the number of trap days.

T* =T - j4X^- (dS) (25)

T* = T + BT (In 4 - lnjc) (26)

T*D = [T + BT (In 4 - In x)] D (27)

TABLE 2. — Traps, trap days, adjusted traps, adjusted trap days
according to alternative soak times (base: S = 4).

No.

traps
(T)

Fishing
days
(D)

Trap
days
(TD)

Soak
time
(S)

Adjusted
no. traps

Adjusted no.

trap days

(T'D)

2.75

82.5

1.85

55.5

1.30

39.0

1.00

30.0

0.82

24.6

0.67

20.1

0.54

16.2

Adjustment of Catch Per Trap Day
to a Standardized Soak Time

Once the catch per trap day has been empiri-
cally estimated with respect to the soak time

217

(Equation (1)), then Equation (1) can be used to
easily estimate the catch per trap day that would
prevail at a standardized soak time. Comparing
catch per trap day at a standardized soak time will
provide a more accurate measurement of relative
abundance. The relative fishing power of a trap as
estimated by Equation (1) yields the same results
as the computations of adjusted traps in Table 2,
column 5.

Conclusions

When the soak time is variable in trap fisheries,
trap days may not be an accurate index of fishing
effort. Furthermore, there is evidence that as the
exploitable stock declines the profit-maximizing
soak time declines, which can result in a measured
catch per trap day that will not reflect the declin-
ing relative abundance. It is possible to adjust trap
days or catch per trap day according to the soak
time to more accurately reflect fishing effort (catch
per unit of effort). The calibration of this ad-
justment requires data on the relationship be-
tween the catch and soak time. It is recommended
that in the future soak time be documented to
facilitate this calibration.

Acknowledgments

Data collected by R. E. Warner, University of
Florida Cooperative Extension Service, Key West,
on trap fishing in the Florida Keys and D.
Simmons, Southeast Fisheries Center, National
Marine Fisheries Service, NOAA, on Bahama trap
fishing were helpful. D. Simmons also provided
review and recommendations in developing the
model.

Literature Cited
Robinson, R. K., and D. E. Dimitriou.

1963. The status of the Florida spiny lobster fishery, 1962-
63. Fla. State Board Conserv. Tech. Ser. 42, 30 p.

Thomas, j. C.

1973. An analysis of the commercial lobster (Homarus
americanus) fishery along the coast of Maine, August
1966 through December 1970. U.S. Dep. Coramer., NOAA
Tech. Rep. NMFS SSRF-667, 57 p.

C. Bruce Austin

Department of Economics, School of Business
and Division of Biology and Living Resources
Rosenstiel School of Marine and Atmospheric Science
University of Miami, FL 33149

SPECIES COMPOSITION AND

RELATIVE ABUNDANCE OF

LARVAL AND POST-LARVAL FISHES IN

THE COLUMBIA RIVER ESTUARY, 1973

Few ichthyoplankton surveys of northern Pacific
coast estuaries exist: Waldron (1972) and
Blackburn (1973) surveyed larvae in northern
Puget Sound; Eldridge and Bryan (1972) con-
ducted a 1-yr survey in Humboldt Bay, Calif;
Pearcy and Myers (1974) conducted an 11-yr sur-
vey in Yaquina Bay, Oreg. No data on
ichthyoplankton are available for the Columbia
River estuary.

In 1973, the National Marine Fisheries Service
conducted a survey of zooplankton in the Colum-
bia River estuary to study productivity and
seasonal variation of zooplankton populations.
The survey also captured larval and post-larval
fishes. This paper reports species composition, size
range, and seasonal and horizontal occurrence of
larval and post-larval fishes within the Columbia
River estuary. Substrate was provided for egg
deposition as an additional technique to deter-
mine if spawning was occurring in the estuary.
Such investigations are valuable to assessing the
importance of the estuary as a spawning and
nursery ground.

Methods

Seven stations from the Columbia River's
mouth to Tongue Point upstream 29 km were
sampled once a month with a 0.5-m plankton net
January to December 1973 (Figure 1). A single
station was sampled monthly from March to

FIGURE 1. — Columbia River estuary, showing location of sampl-
ing stations.

218

December 1973 with a 0.9-m Isaacs-Kidd Midwa-
ter Trawl. Stations were located in channel areas
where depths ranged from 12 to 26 m, with the
exception of station 5 which had a maximum depth
of 4.8 m.

A Coast Guard utility boat (12.3 m long) con-
verted for research was used to sample stations
during daylight at high tide. The 0.5-m net with
0.24-mm mesh was towed for 9 min at each station
bottom to surface using a 3-stepped oblique tow (3
min at each level). Volume of water strained was
estimated by a centrally located TSK1 flowmeter.
The 0.9-m trawl was towed once a month for 15
min at station 2 March through December 1973.
The trawl was towed in a 3-stepped oblique man-
ner (5 min at each level), surface to bottom.

Samples were preserved immediately on board
the vessel with 10% Formalin in seawater. In the
laboratory larvae were measured using a dissect-

1 Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

ing microscope having a micrometer eyepiece.
Measurements refer to standard lengths mea-
sured from snout tip to notochord tip; after for-
mation of the caudal fin, to the end of the hypural
plate. Salinities and temperatures were recorded
on the bottom and at the surface at each station
with a Beckman model RS5-3 induction
salinometer.

Evergreen boughs were provided as spawning
substrate January through July. A small trap
constructed of hardware cloth was attached to the
boughs to capture and identify fishes depositing
eggs. The device was operated with a hand winch
mounted on a pier near station 3 and examined
three times per week.

Results and Discussion
Species Composition

Larvae, postlarvae, and juvenile fishes from 13
families were captured during this investigation

TABLE 1. — Checklist of larval, post-larval, and juvenile fishes captured with a 0.5-m plankton net and a 0.9-m Isaacs-Kidd

Midwater Trawl during 1973.

Station

Size range

Total

Month

Family, scientific, and common names

captured

(mm)

number

collected

Clupeidae:

Clupea harengus pallasi. Pacific herring

1, 2,

4,6

10-40

Mar., May, June

Alosa sapidissima, American shad

Aug.

Engraulidae:

Engraulis mordax, northern anchovy

1. 2,

22-68

Jan., Mar., Oct., Nov.

Osmeridae:

•

Spirinchus thaleichthys, longfin smelt

1,2,

4, 5, 6, 7

6-64

1,959

Jan., June, Oct. -Dec.

Thaleichthys pacificus, eulachon

1,2,

4, 5, 6, 7

5-8

558

Feb. -May

Allosmerus elongatus, whitebait smelt

1. 2,

45-58

Oct. -Jan.

Hypomesus pretiosus, surf smelt

1, 2

36-53

Jan-Mar

Undetermined spp.

10-30

Dec. -Mar.

Gadidae:

Microgadus proximus, Pacific tomcod

1,2,

5-61

Mar., June, July

Stichaeidae:

Lumpenus sagitta, snake prickleback

2, 4

13-16

Jan. -Feb.

Pholidae:

Pholis ornata, saddleback gunnel

18-20

Mar.

Ammodytidae:

Ammodytes hexapterus, Pacific sand lance

1, 2

10-16

Mar-Apr.

Scorpaenidae:

Sebastes melanops, black rockfish

55-67

July

Seoasfes spp.

1. 3

Jan.

Hexagrammldae:

Ophiodon elongatus, lingcod

9,12

Feb. -Mar.

Hexagragrammos sp.

6,10

Jan. -Feb.

Cottidae:

Leptocottus armatus. Pacific staghorn sculpin

1. 2,

6-13

Jan. -Mar., May-Sept.

Enophrys bison, buffalo sculpin

5, 8

Feb.

Cottus asper, prickly sculpin

1. 2,

4,5, 7

6-12

204

Apr-June

Hemilepidotus spinosus, brown Irish lord

Mar.

Oligocottus maculosus, tidepool sculpin

4-8

Jan.

Undetermined spp.

6-15

Jan. -Feb., June

Agonidae:

Stellerina xyosterna, pricklebreast poacher

7-9

Feb. -Apr.

Cyclopterldae:

Liparis rutteri, ringtail snailfish

12-32

Jan., Mar-Apr.

Liparis puchellus, showy snailfish

June

Undetermined spp.

1, 2

Jan-Mar.

Pleuronectidae:

Psettichthys melanostictus, sand sole

28-34

June

Parophrys vetulus, English sole

1, 2,

4-21

Jan-Apr., Dec

Isopsetta isolepis, butter sole

1,2,

4-7

Jan. -Apr.

219

(Table 1). A total of 2,152 larvae and postlarvae
were taken in 84 tows with the 0.5-m net and 784
postlarvae and juveniles were captured in 10 tows
with the 0.9-m trawl.

Early stages of 22 species were taken with the
0.5-m net. The catch was dominated numerically
by the Osmeridae which accounted for 89% of the
total. Spirinchus thaleichthys were the most
numerous — composing 67% of the total catch.
Thaleichthys pacificus represented 19% of the
total. Cottus asper made up 7% of the total and
each of the remaining individual species ac-
counted for less than 1%.

Twelve species were captured with the trawl at
Station 2. Spirinchus thaleichthys, 22-64 mm,
composed 92% of the catch. Post-larval Hypomesus
pretiosus, Allosmerus elongatus, and juvenile
Engraulis mordax represented the majority of the
remaining total. The trawl captured three species
not taken with the 0.5-m net: Ophiodon elongatus,
Hemilepidotus hemilepidotus, and Alosa
sapidissima.

Species composition of ichthyoplankton in the
Columbia River estuary differed from that found
in other northwest estuaries. Waldron (1972) and
Blackburn (1973) found larval Gadidae dominated
catches in Puget Sound. In Humboldt Bay, El-
dridge and Bryan (1972) reported 82% of the total
catch was Clupea harengus pallasi and
Lepidogobius lepidus. In Yaquina Bay, Pearcy and
Myers (1974) reported this combination of species
was 90% of the catch. Clupea h. pallasi in the
Columbia River estuary composed less than 1% of
the total and no L. lepidus were captured.

Seasonal Abundance

Larval and post-larval fishes were most
abundant January through May. During the
summer no larval or post-larval stages were taken
at any of the seven stations. Similar findings were
reported in Humboldt Bay (Eldridge and Bryan
1972) and in Yaquina Bay (Pearcy and Myers
1974).

Abundance estimates are based on average
monthly catches at all stations with the 0.5-m net
(Figure 2). A peak of 1.1/m3 occurred in March,
primarily the result of an influx of newly hatched
Spirinchus thaleichthys. A maximum average
catch of 1.5/m3 occurred in May, the result of an
increased number of Thaleichthys pacificus and
Cottus asper. Maximum catch during the year was
4.0/m3 and occurred at station 2 in May. The

1.5

5 1.0

5 0.5
til

1 1

JAN

FEB

i
MAR

i
APR

MAY

1 i i i i 1

JUN JUL AUG SEP OCT NOV DEC

FIGURE 2. — Seasonal density of ichthyoplankton at seven loca-
tions in the Columbia River estuary during 1973. These results
show average catch at seven stations with the 0.5-m plankton
net.

composition was entirely S. thaleichthys, T.
pacificus, and C. asper.

Juveniles were the only stage captured with the
trawl from summer through fall. Those captured
were: Microgadus proximus (60-61 mm), Sebastes
melanops (55-67 mm), Alosa sapidissima (44 mm),
Leptocottus armatus (11-13 mm), Allosmerus
elongatus (49-58 mm), Engraulis mordax (45-68
mm), and Spirinchus thaleichthys (45-64 mm).

Horizontal Variation

The greatest variety of species was captured at
stations nearer the mouth where salinities were
higher. Large variations in tides and river flow
combine to create a fluctuating horizontal saline
intrusion; salinity is dissipated upstream and
station 7, except during reduced river flow in the
fall, is essentially fresh water (Haertel and Os-
terberg 1967 and Misitano 1974). The reduction in
salinity upstream was reflected by a correspond-
ing decrease in the variety of species (Figure 3). At
station 1 there were 22 identifiable species and at
stations 5 and 7 three species: S. thaleichthys, T.
pacificus, and C. asper. Stations 5, 6, and 7, which
exhibited similarly reduced salinities, accounted
for 47.8% of the total larvae captured in the es-
tuary with the 0.5-m net. This high percentage is
due to the influx of the two species of osmerid
larvae entering the estuary during the first part of
the year.

220

</>

a.
(/>
u.
O

(T
UJ

m
2
3
Z

^D-

20-

15-

10-
5-

| I

...

3 4 5 6 7

SAMPLING STATIONS

FIGURE 3. — Number of species of larval, post-larval, and
juvenile fishes collected at each station in the Columbia River
estuary during 1973.

Spawning on Provided Substrate

Evergreen boughs placed in the water attracted
two species to deposit eggs, Clupea harengus
pallasi and unidentified snailfish (Cyclopteridae).
Thirty-three ripe adult C. h. pallasi, 163 mm
average length, were trapped 10 April through 17
July confirming identification of the eggs. Light
spawning was first observed on the boughs 10
April; moderate deposition 1-3 July. Ova were
viable, eyed eggs were observed.

Adult snailfish began entering the trap 13
February. Eggs were deposited on boughs 12 and
26 February. Eggs were viable and emergent
larvae were observed. Fifteen gravid adults were
captured 13 February through 3 March. This
snailfish has some characteristics in common with
Liparis rutteri, which is also present in the es-
tuary. The unknown snailfish has been closely
examined and is now considered to be an unde-
scribed species by Carl Bond at Oregon State
University, Corvallis, Oreg.

Gravid adults of two species of Cottidae were
captured by trapping. Ripe Leptocottus armatus
were taken 18 February and 19 March but no
spawning was observed. Jones (1962) found egg
survival for this species optimum at 10-15% in-
dicating a probably spawning population in the
Columbia River estuary. Ripe Cottus asper were
trapped 26 March, 4 and 9 April. This cottid's
newly hatched larvae, as described by Stein
(1972), was the third most abundant species in the
estuarine ichthyoplankton. Krejsa (1967) noted

that coastal populations of this cottid migrate
downstream to spawn in brackish water. The
capture of ripe adults and large numbers of newly
hatched larvae verifies spawning of C. asper in the
estuary.

Utilization of the Estuary

Data obtained from this investigation indicated
four species, Clupea harengus pallasi, Cottus
asper, Leptocottus armatus, and a new species of
snailfish, utilized the Columbia River estuary for
spawning in 1973. The greatest number of species
was captured near the mouth suggesting most
species are oceanic in origin.

Spirinchus thaleichthys, the most numerous
species, was captured at all stations. This
anadromous osmerid was reported by Hart (1973)
to spawn in streams near the sea. The presence of
newly hatched larvae, as described by Dryfoos
(1965), confirms the presence of a spawning
population in the lower Columbia system. The
capture of early stages almost the year round
indicates a major importance of the estuary to this
species.

Thaleichthys pacificus is also an anadromous
osmerid in the Columbia River. Some mainstream
spawning occurs, but the majority of the run
spawns in the Cowlitz River, a tributary 109 km
upstream (Smith and Saalfeld 1955). Although
large numbers of larvae were captured February
to May, they were yolk bearing stages, 6-8 mm,
indicating a downstream drift through the estuary
to the ocean soon after hatching. Similar findings
were reported by Larkin and Ricker (1964).

No evidence of estuarine spawning by
pleuronectids was indicated. Although the upper
estuary is a nursery for juvenile Platichthys
stellatus (Haertel and Osterberg 1967), no larvae
or postlarvae of this species were captured. Pearcy
and Myers (1974) captured only three larvae in 11
yr in Yaquina Bay, indicating entry into the es-
tuary is accomplished after metamorphosis.
Parophrys vetulus were captured at two size
ranges: 4-6 mm and 20-21 mm. Information from
other estuaries (Pearcy and Myers 1974; Misitano
1976) indicates young P. vetulus enter estuarine
nurseries after completion of metamorphosis.

Isopsetta isolepis utilizes the Columbia River
estuary as a nursery. The National Marine
Fisheries Service conducted a bottom trawling
survey in the estuary from March 1973 to June
1974 (J. T. Durkin pers. commun.). Parophrys

221

vetulus, 85-165 mm, and /. isolepis, 95-155 mm,
were commonly captured. Isopsetta isolepis, 4-7
mm, were captured with 0.5-m plankton net. No
later stages were taken. Richardson (1973) took
this species (12-22 mm) off Oregon close to shore.
Entry into the estuary probably occurs as
metamorphosed juveniles.

Several types of sampling equipment should be
utilized in future studies to capture early stages
near bottom, on tide flats, in embayments, and
during darkness. This preliminary investigation
indicated little spawning occurred in this west
coast estuary; most species captured were
spawned in the ocean, or were anadromous species
that spawned upstream and drifted into the es-
tuary. Results of this investigation and bottom
trawling by other researchers indicated this
estuary is utilized primarily as a nursery grounds
by the post-larval and juvenile stages of several
species.

Acknowledgments

I express my gratitude to Kenneth Waldron and
Jean Dunn of the Northwest Fisheries Center who
assisted in the identification of larvae. I thank
Nick Zorich whose skillful operation of the vessel
and assistance with sampling were indispensable.

Literature Cited

BLACKBURN, J. E.

1973. A survey of the abundance, distribution, and factors
affecting distribution of ichthyoplankton in Skagit
Bay. M.S. Thesis, Univ. Washington, Seattle, 136 p.
DRYFOOS, R. L.

1965. The life history and ecology of the longfin smelt in
Lake Washington. Ph.D. Thesis, Univ. Washington,
Seattle, 242 p.
ELDRIDGE, M. B., AND C. F. BRYAN.

1972. Larval fish survey of Humboldt Bay, California.
U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-665,

8 p.
HAERTEL, L., and C. Osterberg.

1967. Ecology of zooplankton, benthos and fishes in the
Columbia River estuary. Ecology 48:459-472.

Hart, J. L.

1973. Pacific fishes of Canada. Fish. Res. Board Can.,
Bull. 180, 740 p.

JONES, A. C.

1962. The biology of the euryhaline fish Leptocottus ar-
matus armatus Girard (Cottidae). Univ. Calif. Publ.
Zool. 67, 368 p.
KREJSA, R. J.

1967. The systematics of the prickly sculpin, Cottus asper
Richardson, a polytypic species. Part II. Studies on the
life history, with especial reference to migration. Pac.
Sci. 21:414-422.

LARKIN, P. A., AND W. E. RlCKER (editors).

1964. Canada's Pacific marine fisheries, past performance
and future prospects. In Inventory of the natural re-
sources of British Columbia, p. 194-268.
MISITANO, D. A.

1974. Zooplankton, water temperature, and salinities in
the Columbia River estuary December 1971 through De-
cember 1972. U.S. Dep. Commer., Natl. Oceanic Atmos.
Admin., Natl. Mar. Fish. Serv., Data Rep. 92,
31 p.

1976. Size and stage of development of larval English sole,
Parophrys vetulus, at time of entry into Humboldt
Bay. Calif. Fish Game 62:93-98.

Pearcy, W. G., and S. S. Myers.

1974. Larval fishes of Yaquina Bay, Oregon: A nursery
ground for marine fishes? Fish. Bull., U.S. 72:201-213.

Richardson, S. L.

1973. Abundance and distribution of larval fishes in wa-
ters off Oregon, May-October 1969, with special emphasis
on the northern anchovy, Engraulis mordax. Fish. Bull.,
U.S. 71:697-711.

Smith, W. E., and R. W. Saalfeld.

1955. Studies on Columbia River smelt Thaleichthys pa-
cificus. Wash. Dep. Fish. Res. Pap. l(3):3-26.
Stein, R.

1972. Identification of some Pacific cottids. M.S. Thesis,
California State Univ., Humboldt, Areata, 41 p.

waldron, K. D.

1972. Fish larvae collected from the northeastern Pacific
Ocean and Puget Sound during April and May
1967. U.S. Dep. Commer., NOAA Tech. Rep. NMFS
SSRF-663, 16 p.

David A. Misitano

Northwest Fisheries Center
National Marine Fisheries Service, NOAA
2725 Montlake Boulevard East
Seattle, WA 98112

1X1 -iz£

A NOTE ON: "VELOCITY AND
TRANSPORT OF THE ANTILLES CURRENT
NORTHEAST OF THE BAHAMA ISLANDS"

Interest of fishery scientists in the Antilles Cur-
rent east of the Bahama Islands stems from a
generally accepted hypothesis that it served as a
conveyor of larvae of large pelagic fishes north-
ward into the Gulf Stream system. Larvae of
billfishes (Istiophoridae) were captured in
plankton tows east of the Bahamas during the first
MARMAP Operational Test Phase (OPT-I) cruise
in July- August 1972. l These captures clearly

•Richards, W. J., J. W. Jossi, and T. W. McKenney. Interim
report on the distribution and abundance of tuna and billfish
larvae collected during MARMAP Operational Test Phase
cruises I and II, 1972-1973. MARMAP Contrib. 16. Unpubl.
manuscr., 15 p.

222

show that adult billfishes had been in the area
shortly before the sampling occurred, but the
implication of the transport of the larvae north-
ward by the Antilles Current is not so clear. We
have reason to doubt the existence of the strong,
steady, broad surface flow to the northwest which
has been assumed to be characteristic of the An-
tilles Current east of the northern Bahamas.

In a recent analysis of six occupations of Stan-
dard Section A-7 (Figure 1) by U.S. Coast Guard
cutters, Ingham (1975) did not find a strong,
steady, broad surface flow attributed to the Antil-
les Current (Wiist 1924; Boisvert 1967). In a study
of directly measured values of the transport of the
Gulf Stream between the Florida Straits and Cape
Hatteras, Knauss (1969) noted that the transport
increases at a rate of about 7%/100 km, from
33 x 106 m3/s in the Florida Straits, to 63 x 106 m3/s
off Cape Hatteras. Increases of this magnitude
were also evident in earlier transport mea-
surements for the Florida Straits (Wiist 1924;
Montgomery 1941) and Cape Hatteras (Iselin
1936). Exactly how this increase takes place has
not been determined. Wiist (1924) and Iselin
(1936) felt that the Antilles Current makes a
significant addition (12xl06 m3/s) to the Gulf
Stream just north of the Bahama Islands, but
Stommel (1965) felt that this value for the con-
tribution of the Antilles Current was question-

82 80 78 76 74 72° W

\\) / STANDARD SECTION A7

W/g) ISLANDS *~ ANTILLES

I Ift I

±^L

36° N

- 26

able. It should be noted that Wiist's (1924) trans-
port to the northwest was approximately balanced
by two countercurrents on each side of the current
moving to the southeast.

The geostrophic velocities and volume trans-
ports (Table 1 ) obtained by Ingham ( 1975) indicate
that the previous estimate (Wiist 1924) of the
transport of the Antilles Current is too large and
that a better estimate of the mean northward
transport is on the order of 8.6xl06 m3/s. The
difference in reference levels between Ingham
(1,000 decibars) and Wiist (800 decibars) does not
account for this discrepancy since Wiist's shal-
lower reference level would result in less transport
than Ingham, not more. In the six transects
measured by Ingham only one showed a net
transport large enough to account for the above
mentioned increase in the Gulf Stream. In ad-
dition, the net transport through the section was
highly variable, showing values of 3.4 and
6.4 xlO6 m3/s southward in two of the transects.
Ingham (1975) suggested that some mechanism
other than the Antilles Current may account for
the increase in the Gulf Stream and that the
contribution of local wind-driven (Ekman)
transport be considered as a possibility, since the
mean direction of the winds in the vicinity would
produce a northward or northwestward drift.

In order to determine this northward transport
contribution by locally wind-driven currents,
quarterly averages (January-March, April-June,
etc.) of Ekman transport values for 1946-73 were
obtained from the Pacific Environmental Group,
National Marine Fisheries Service, NOAA for
three locations northeast of the Bahama Islands,
along lat. 27°N at long. 78°W, 75°W, and 72°W
(Figure 1). These values were calculated from the
mean monthly atmospheric pressure field using
the method described by Bakun (1973) to deter-
mine the mean monthly wind stress on the ocean
surface and the resulting Ekman transport. The
quarterly mean meridional Ekman transports,
per unit length, for each position were averaged to
give a mean transport value for a hypothetical

TABLE l.— Transports across Coast Guard Standard Section A-7
as reported by Ingham (1975).

FIGURE 1. — Position of Coast Guard Standard Section A-7 in
relationship to surrounding currents and land masses.

Date of transect

Transport (106 m3/s) and direction

29-30 Jan. 1967

16.0 North

26-28 June 1967

30.4 North

24-25 June 1968

3.4 South

9-11 Dec. 1969

3.9 North

29 Sept.- 1 Oct. 1970

6.4 South

17-19 Nov. 1970

1 1 .4 North

223

transect along lat. 27°N. This value was then
multiplied by the length of the transect to give a
net quarterly meridional transport through the
transect. The hypothetical transect extends
eastward from the Bahama Islands, 668 km, to the
same longitude as the eastern end of Standard
Section A-7 (about long. 70°12'W). Thus it crosses
the same portion of the Antilles Current as that
cut by Standard Section A-7, but about 180 km
upstream of it. Therefore, meridional Ekman
transports computed for the transect along lat.
27°N can be compared with measured geostrophic
transports through A-7. Although the effects of
lateral boundaries were not considered, the piling
up of water against the Bahama Banks would
result in a southeastward geostrophic flow,
further substantiating the result of this report.

The results of these computations, for this
hypothetical transect, show a large range of net
quarterly meridional Ekman transport values,
from 60xl03 m3/s northward to 20xl03 m3/s
southward with an overall mean of net transports,
over 28 yr, of 15±2xl03 m3/s northward (the
range gives the limits of the 95% confidence level)
and an SD of 11 x 103 m3/s. When the 28 yr of net
meridional transports were averaged by quarters,
there was the appearance of distinct seasonality,
with the lowest average value in the first quarter
(January- March) amounting to 7±4xl03 m3/s
northward with an SD of 12xl03 m3/s. The
transport increased in the second (April-June) and
third (July-September) quarters to 15±3 and
17 ±2 x 103 m3/s northward with respective SD's of
9 and 6xl03 m3/s. The fourth quarter (October-
December) had the highest value of 23±4xl03
m3/s northward, with an SD of 12 x 103 m3/s. These
values for the Ekman transport are three orders of
magnitude too small to account for the transport
increase in the Gulf Stream. Thus locally induced
Ekman drift can be ruled out as a significant
contributor.

There still is a possibility that an Antilles
Current could account for the observed increase in
transport of the Gulf Stream. If a strong, narrow
band of the current hugged the eastern edge of the
Bahama Banks and joined the Gulf Stream before
it crossed Standard Section A-7 (Figure 1), it
would have escaped detection in Ingham's (1975)
analysis. The existence of such an intense current
would contradict Knauss' (1969) observation that
the transport increase in the Gulf Stream takes
place gradually from the Florida Straits to Cape
Hatteras, with no large increase in transport

(>2xl06 m3/s) south of lat. 32°N and the sugges-
tion by Worthington (in press) and Sturges (1968)
that the increase in transport of the Gulf Stream
takes place over its entire length and at all levels.
Nevertheless a study in preparation by R. Yager
(pers. commun.) using direct transport measure-
ments appears to show a narrow (80 km), intense
(12xl06 m3/s) current to the northwest hugging
the east side of the Bahama Banks.

A measure of the significance of Ekman
transport in moving the larvae of pelagic fishes
northward to the Gulf Stream can be obtained by
deriving a rough estimate of the average speed of
neutrally buoyant objects in the wind-driven
layer. For this the average northward transport is
divided by the area of the cross-section through
which the flow is occurring (depth of layer x
length of section). Using the familiar empirical
relationship,

D =

7.6W
Vsin<£>

(Defant 1961 Vol. 1:422),

where D is the depth of the wind-influenced layer,
W is the wind speed (here the median wind speed,
5.5 m/s shown for lat. 25°-30°N, long. 70°-75°W in
the U.S. Naval Oceanographic Office atlas 1963),
and 0 is the latitude, we obtain an estimate of the
average depth of the wind-influenced layer to be
about 60 m. From the depth (60 m), the length of
the section (668 km), and the net transport
computed earlier (15±2xl03 m3/s), we obtain an
estimate of the average northward velocity of
larvae to be 0.04 cm/s. It is apparent that this
velocity, which translates to 0.03 km/day, is
considerably smaller than the geostrophic veloci-
ties through lat. 28°35'N reported by Ingham
(1975) which generally ranged from 5 to 40 cm/s
either northward or southward.

The vertical distribution of ichthyoplankton
could have a considerable effect on their transport
by wind-driven currents; however, their vertical
distribution is not well known. If, in order to ob-
tain a maximum possible velocity, we assume that
the larvae remain in the upper meter or so of the
wind-driven layer instead of spending time at
various depths throughout it, then their wind-
driven drift speed would be considerably greater
than the 0.04 cm/s average. Using the relationship

Vsinc^

(Defant 1961 Vol. 1:418),

224

which relates surface current speed (V0) to wind
speed (W) in terms oflatitude ((/>) and an empirical
constant (A = 10 2), we obtain an estimate of aver-
age wind-driven surface current velocity of 5.7
cm/s northward.

In light of the velocity estimates, it is apparent
that locally wind-driven currents are significant
for the northward transport of pelagic larvae east
of the northern Bahamas only if the larvae spend
most of their time near the sea surface. If, instead,
they are scattered throughout the upper layer or
undergo diurnal vertical migration, their
northward progress will be much slower.

Another possible pathway of larval transport
which should be considered, however, is the near-
shore band of strong flow mentioned by R. Yager
(pers. commun.). If such a band exists as a regular,
steady feature of the current field east of the
Bahama Banks, then it would be particularly
informative to conduct seasonal ichthyoplankton
surveys on a scale appropriate to determine the
relative abundance of pelagic larvae in and near
the current band.

Literature Cited

BAKUN, A.

1973. Coastal upwelling indices, west coast of North

America, 1946-71. U.S. Dep. Commer., NOAATech. Rep.

NMFS SSRF-671, 103 p.
BOISVERT, W. W.

1967. Major currents in the North and South Atlantic
Oceans between 64°N and 60°S. U.S. Nav. Oceanogr. Off.,
Tech. Rep. TR-193, 92 p.

DEFANT, A.

1961. Physical oceanography, Vol. I. Pergamon Press, N.Y.,
729 p.

Ingham, M. C.

1975. Velocity and transport of the Antilles Current north-
east of the Bahama Islands. Fish. Bull., U.S. 73:626-632.
ISELIN, C. O.

1936. A study of the circulation of the western North Atlan-
tic. Pap. Phys. Oceanogr. Meteor. 4(4), 101 p.
KNAUSS, J. A.

1969. A note on the transport of the Gulf Stream. Deep-Sea
Res. 16 (Suppl.):117-123.
MONTGOMERY, R. B.

1941. Transport of the Florida Current off Habana. J. Mar.
Res. 4:198-220.
STOMMEL, H.

1965. The Gulf Stream — A physical and dynamical descrip-
tion. Univ. Calif. Press, Berkeley, and Cambridge Univ.
Press, Lond., 248 p.
STURGES, W.

1968. Flux of water types in the Gulf Stream. [Abstr.] Trans.
Am. Geophys. Union 49:198.

U.S. NAVAL OCEANOGRAPHIC OFFICE.

1963. Oceanographic atlas of the North Atlantic Ocean,

Section IV Sea and Swell. U.S. Nav. Oceanogr. Off, Publ.

700, 227 p.
WORTHINGTON, L. V.

In press. On the North Atlantic circulation. John Hopkins

Univ. Press.
WUST, G.

1924. Florida-Und Antillestrom. Verbffentlichungen des

Instituts fur Meereskunde an der Universitat Berlin. A.

Geographisch-naturwissenschaftlicke Reiche. Heft 12, 48

P-

JOHN T. GUNN

Merton C. Ingham

Atlantic Environmental Group

National Marine Fisheries Service, NOAA

Narragansett, RI 02882

SALINITY ACCLIMATION IN
THE SOFT-SHELL CLAM, MYA ARENARIA

A steady increase in sewage pollution followed by
the closing of many productive shellfish growing
areas has seriously affected the harvesting of the
soft-shell clam, Mya arenaria, in the State of
Maine. In areas where a large percentage of the
population derives its income from harvesting
soft-shell clams, these closings have caused severe
economic hardships. Beginning in the mid-1950's
the Maine Department of Marine Resources (then
Maine Department of Sea and Shore Fisheries)
accelerated research on clam depuration in an
attempt to salvage moderately polluted clams of
70-700 most probable number of Escherichia coli
bacteria per 100 g. Based upon the design and
development of a pilot process (Goggins et al.
1964) five commercial depuration plants have
been established. The first of these (Seafair, Inc.1),
in Phippsburg, Maine, utilized clams dug from
Parker Head, Maine. During routine operation of
this plant, it was apparent that exposure of clams
to certain salinity and temperature conditions
increased the time required for depuration.

Former investigators have revealed that
pumping activity and associated shell and ciliary
movements are affected when bivalves other than
soft-shell clams are immersed in water of a dif-
ferent salinity from that to which they are ac-
customed (Wells et al. 1940; Medcof 1944;
Loosanoff2). In this paper, salinities lower than

1 Reference to a commercial enterprise does not imply en-
dorsement by the National Marine Fisheries Service, NOAA.

2Loosanoff, V. L. 1952. Behavior of oysters in water of low
salinities. Conv. Address Proc. Natl. Shellfish. Assoc., Atlantic
City.

225

the accustomed are called "dilutions," those above,
"concentrations." The literature shows that the
effects of dilution upon Mya arenaria are most
noticeable when reduced to the stress point. The
stress point for Massachusetts clams is ap-
proximately 15°/oo (Matthiessen 1960), 22-24°/oo
for Medomac River, Maine, clams (Welch and
Lewis3) and 5%o for Chesapeake Bay clams
(Schubel4).

Pumping activity and associated feeding and
ciliary movements of many bivalves are also
known to be directly affected by temperature
changes (Nelson 1923; Gray 1924; Galtsoff 1928;
Hopkins 1931, 1933; Elsey 1936; Loosanoff 1939,
1950, 1958; Harrigan 1956; Goggins et al. 1964;
Feng5).

To our knowledge, only Loosanoff (see footnote
2) and Welch and Lewis (see footnote 3) have
attempted to relate changes in bivalve behavior to
changes in both salinity and temperature.

This investigation was undertaken to establish
the relationship of temperature to acclimation
time when Mya is immersed into dilutions and
concentrations of seawater. The results are
applicable to many real situations where Mya are
harvested from an area with one set of en-
vironmental conditions and subjected to accli-
mation and depuration in an area of another.

Materials and Methods

Salinity Control Apparatus

The constant flow apparatus used in the follow-
ing experiments was similar in principle to that
used by Loosanoff and Smith (1950). The complete
system consists of freshwater and saltwater
constant head reservoirs and nine adjustable head
units, four regulating the freshwater flow and five
the seawater flow. Water from each adjustable
head or pair of heads flowed through plastic tubing
into the bottom of a large mixing tube and then
into the test tank. In this manner, ambient salin-
ity and four dilutions could be maintained
simultaneously. Temperature differences be-

3 Welch, W. R., and R. D. Lewis. 1965. Shell movements ofMya
arenaria. Unpubl. manuscr., [U.S.] Bur. Commer. Fish. Biol.
Lab., West Boothbay Harbor, Maine.

"Schubel, J. 1973. Report on the Maryland State Department
of Health and Mental Hygiene cooperative study to determine
cause and extent of high bacteria counts found in Mya arenaria
in 1973. Md. Dep. Health Ment. Hyg., 57 p.

5Feng, S. Y. 1963. Activity of the hard clam Mercenaria mer-
cenaria. Talk at Rutgers, the State University of New Jersey and
NAS Meeting July (Furfari 1966).

tween the freshwater and saltwater constant head
reservoirs were eliminated by the installation of a
temperature equalizer functioning on the heat
exchanger principle.

Experimental Design

Clams were dug by commercial clam diggers
(under Department of Marine Resources super-
vision) from moderately polluted clam flats at
Parker Head, Maine, and transported to the
laboratory shortly thereafter. Broken clams and
clams under 50 mm were discarded, and the
remaining clams were thoroughly washed and
held in flowing control salinities until shell liquor
salinities were the same as control salinities. The
experimental temperatures desired were obtained
over a 10-mo period using the natural range of
ambient seawater temperature available. Ap-
proximately 1 bushel of clams was used in each set
of dilution and concentration experiments testing
salinity acclimation rates at ambient water
temperature. Clams were acclimated to control
salinities of 30.54-31.80%o (dilution experiments)
and 16. 26-17. 14%o (concentration experiments)
and then roughly divided into five groups; one
group remained in the control salinity and the
other four groups were immersed into tanks set at
other dilutions and concentrations of seawater.

Changes in shell liquor salinity were chosen as
the criteria for the measurement of acclimation
because shell liquor was easily obtained from each
group of six clams by inserting a knife into the
region of the foot opening and draining the con-
tents into a paper cup. Five milliliters of this total
and a sample of tank water were analyzed for
salinity by the Knudsen Method. Acclimation had
occurred when shell liquor salinities were the
same as tank salinities. The oxygen content of the
water flowing into and out of each test tank was
measured by the Azide Modification of the
Iodometric Method (American Public Health
Association 1967). We attempted to regulate the
flow rate in each tank at approximately 1,000-
1,100 ml/min. All temperature measurements
were made with a calibrated glass thermometer.
Measurements of salinity, temperature, and flow
rate were recorded as the mean±l SE. Appropri-
ate curves were fit where necessary.

Results
The dissolved oxygen content of the water used

226

in dilution and concentration experiments varied
between 5.91 and 12.58 mg/liter depending
largely upon the ambient range of temperature
and salinity conditions encountered (Table 1). It is
evident in Table 1 that no significant differences
exist between flow rates at the beginning and end
of a given group of experiments.

The results of one typical set of dilution and
concentration experiments are presented in Fig-
ure 1. A comparison of this set of experiments
reveals that Mya acclimates faster to high salinity
from 17%o than to 17%o from high salinity.
Similar observations were noted for all ambient
temperature ranges used. The approximate
number of hours required to acclimate to each
dilution from the control was recorded for each

TABLE 1. — Parameters recorded during dilution (D) and concen-
tration (C) experiments with Mya arenaria at ambient tempera-
ture ranges.

Experiment

2.9°-3.2cC:
D

6.4°-6.9cC:
D

10.0°-10.7°C:
D

15.4°-16.3°C:
D

Tank
salinity

(°/oo)

Water
temp

Row rate (ml/min)
eginning End

'31.36 +
27.371
22.48 ±
16.88i
11.49i

31.16±
27.41 1
22.071
1 16.58i
11.58!

'31.80!
27.16!
22.35!
16.93!
11.91 !

31.43!
28.04!
22.65!
'17.14!
11.89!

'30.54!
27.15!
21.66!
16.82 =
11.71 d
31.18!
28.09:
21.82:

'16.26:
12.04:

'31.01:
27.55:
22.53:

16 95:
12.05:

30.89:
27 57:
22 95:

'17.11:
11.78:

0.04
008
0.04
0.05
0.06

0.06
0.10
0.04
0.03

:0.12

:0.15
:0.17
0.07

:0.08
:0.13

:0.05
:0.06
:0.12
:0.07
:0.03

:0.06
:0.11
:0.08
:0.06
:0.03
:0.07
:0.03
:0.07
:0.11
:0.32

:0.07
t0.15
t0.11
t0.06
£0.04

t0.09
t0.07
!0.14
!0.09
!0.03

2.910.2 1,1321 94 1,184±104

3.2i0.2 1,170i106 1.1561115

6.910.3 1.152i 71 1,1561 45

6.410.2 1,100i 66 1,064i 70

10.0±0.2 1, 1091122 1,111 ±112

10.7±0.1 1,068i123 1,084i123

16.310.1 938± 75 980i 62

15.410.1 1,028i 79 957 1 78

>■ 26

X 24

-I

1 22
CO

o: 20
o

=> 18
o

^ 16

_l
-> 14

£"

A. -A-

■-M-;

31.80 -~ 27.16

31.80 -*■ 2235

31.80 — »• 16,93

V v V

■«•«, 31.80 — «■ 11.84

132

• 26

■ 22

20
18
16

14
12

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140
TIME IN HOURS

CONCENTRATION

— '10
150

? 2S

_ 26

i 24

< 22
CO

ol 20

i0L

17.14 ». 3142

3?
30
28
26
24
22
20

- ie

£rr

"■^-v-.

1714

■*

• 14

q, ■ 12

1 ' '

'Control.

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75

TIME IN HOURS

FIGURE 1. — Shell liquor salinity acclimation rates for Mya
arenaria in dilutions and concentrations at 6.4°-6.9°C (lines
fitted by eye).

ambient tempreature range used, plotted for each
dilution in Figure 2, and the appropriate curve
was fit. Hence at 8°C in Figure 2, 95 h are required
for Mya to acclimate to 1 1.49-12. 05°/oo salinity
from the control, 45 h to 16.82-16.95%o from the
control, 15 h to 21.66-22.53°/oo from the control,
and 10 h to 27.15-27.55°/oo from the control. In
Figure 2, a geometric relationship exists between
temperature and acclimation time after immer-
sion into various dilutions. The approximate time
required to acclimate to each concentration from
the control, at each ambient temperature range,
was recorded in Table 2. Tested at 95% confidence
intervals (±2 SE), Table 2 reveals that no sig-
nificant differences exist between the mean
numbers of hours required to acclimate to each
concentration experiment at all temperature
ranges combined. Table 2 also reveals that no
significant differences exist between the mean

227

TABLE 2. — The relationship between temperature and the
approximate number of hours required for Mya arenaria to
acclimate to three concentrations from a control salinity of
16.26-17. 14°/oo.

2 4 6 8 10 12 14
TEMPERATURE , °C

FIGURE 2. — The relationship between temperature and time re-
quired to acclimate Mya arenaria from the control salinity
(30.54-31.80°/oo) to the following dilutions: (A) 11.49-12.05°/oo;
(B) 16.82-16.95%o; (C) 21.66-22.53°/oo; (D) 27.15-27.55°/oo.

acclimation time (±2 SE) for all concentration
experiments combined at each temperature range.

Discussion

A constant flow apparatus is ideally suited to
shellfish studies. Continuous exchange of water
assures a rapid elimination of metabolic waste
products and more closely resembles natural
conditions than does a standing water system

Temp

Control

30.89-31 .43°/oo

27.41 -28.09°/oo

21 82-22 95" oo

X±SE

3.2

about 10 h

about 7 h

9.0±1.0h

6.4

about 20 h

about 7 h

about 5 h

10.7±4.7h

10.7

about 8 h

about 5 h

about 4 h

5.7±1.2 h

15.4

about 8 h

about 6 h

7.3 ±0.7 h

X±SE

11. 5 ±2.9 h

7.5±1.0 h

5.5 ±0.6 h

(Loosanoff and Smith 1950; Loosanoff see foot-
note 2).

Van Dam (1935) observed that oxygen utiliza-
tion in Mya is independent of oxygen concentra-
tion down to about 2 cm3/liter (2.8 mg/liter). There
is therefore no reason to believe that the varia-
tions in dissolved oxygen encountered in these
experiments altered the pumping activity of Mya.

In these studies, the exclusive use of adult Mya
is consistent with Matthiessen's (1960) observa-
tion that adult and juvenile Mya have different
tolerance levels to low salinity conditions.

The phenomenon of faster acclimation to
concentrations than dilutions has not been
previously reported for Mya. Loosanoff (see foot-
note 2), however, reported that oysters moved
from 10%o into 20-25%o returned to normal
pumping very quickly.

The relationship of pumping activity to shellfish
depuration has been well documented (Furfari
1966). When shellfish are subjected to suitable
salinity and temperature conditions, high pump-
ing activity is maintained and efficient depuration
results.

Furfari (1966) reported that pumping activity is
reduced for a time when shellfish are subjected to
salinity other than that to which they are ac-
customed in the harvest area. During this time,
our data suggest that Mya periodically "samples"
the water conditions and acclimates to them
gradually. The length of time required is related to
the magnitude of the dilution. Welch and Lewis
(see footnote 3) have observed that this "sampling"
behavior is performed by opening the siphons very
slightly and then gently closing them, very little
water having passed through the clam in the
process.

Our studies indicate that water temperature
directly influences the rate at which salinity
acclimation occurs. The results are consistent
with Harrigan (1956) who observed that the
pumping rate of Mya increased up to a tempera-
ture of 16°-20°C and Goggins et al. (1964) who

228

observed that Mya activity (measured by physical
criteria: extension of siphon, response to tactile
stimuli) increased in direct proportion to an in-
crease in temperature. Other investigators have
reported that Mya arenaria pumps as effectively at
all temperatures (Belding 1930; Marston 1931;
Arcisz and Kelly 1955). If this were true in our
studies, Mya would be expected to acclimate to a
dilution as quickly at 3°C as at 16°C. Clearly, in
the case of Parker Head clams, our findings do not
agree with these authors.

In the case of Seafair, Inc., it is apparent that
depuration took longer because the Parker Head
clams first had to acclimate to unaccustomed
salinity before they could actively pump and
cleanse themselves. Low water temperature
would, of course, tend to lengthen this acclimation
period. Our findings are consistent with Furfari's
(1966) statements, "Time taken by shellfish to
acclimate to the stress of a change in salinity, is
time lost in depuration."

In addition to establishing the time required for
Mya to acclimate to dilutions at ambient tem-
perature ranges, this study demonstrates the need
for appraising the response of clams from the
harvest area to the environmental conditions
existing at the depuration site. Acclimation times
recorded in this paper are specific for Parker Head
clams. Mya dug from other locations may respond
differently.

Acknowledgments

We extend our appreciation to Philip L. Goggins
and John W. Hurst, Jr. for their advice and as-
sistance in various aspects of this research, and to
James A. Rollins for photographic services.

This research was conducted by the Maine
Department of Marine Resources Research
Laboratory, West Boothbay Harbor, Maine, in
cooperation with the U.S. Public Health Service,
under Contract No. 86-64-78.

Literature Cited

AMERICAN PUBLIC HEALTH ASSOCIATION.

1967. Standard methods for the examination of water and
waste-water. Am. Public Health Assoc. Inc., N. Y., 769 p.
ARCSIZ, W., AND C. B. KELLY.

1955. Self-purification of the soft clam Mya arenaria. Pub-
lic Health Rep. 70:605-614.
BELDING, D. L.

1930. The soft-shelled clam fishery of Massachusetts.
Commonw. Mass. Dep. Conserv. Mar. Fish. Ser. 1, 65 p.

ELSEY, C. R.

1936. The feeding rate of the Pacific oyster. Biol. Board
Can., Prog. Rep. Pac. Biol. Stn. Pac. Fish. Exp. Stn. 27:6-7.
FURFARI, S. A.

1966. Depuration plant design. U.S. Dep. Health, Educ.
Welfare Publ., 119 p.
GALTSOFF, P. S.

1928. The effect of temperature on the mechanical activity
of the gills of the oyster (Ostrea virginica Gm.). J. Gen.
Physiol. 11:415-431.
GOGGINS, P. L., J. W. HURST, AND P. B. MOONEY.

1964. Laboratory studies on shellfish purification. In
Soft clam depuration studies, p. 19-35. Maine Dep. Sea
Shore Fish., Augusta.

Gray, j.

1924. The mechanism of ciliary movement. III. — The ef-
fect of temperature. Proc. R. Soc. Lond., Ser. B 95:6-15.
HARRIGAN, R. E.

1956. The effect of temperature on the pumping rate of the
soft-shelled clam, Mya arenaria. M.S. Thesis, Colum-
bian Coll., George Washington Univ., 54 p.
HOPKINS, A. E.

1931. Temperature and the shell movements in oysters.

U.S. Bur. Fish., Bull. 47:1-14.
1933. Experiments on the feeding behavior of the oyster,
Ostrea gigas. J. Exp. Zool. 64:469-494.
LOOSANOFF, V. L.

1939. Effect of temperature upon shell movements of
clams Venus mercenaria (L.). Biol. Bull. (Woods Hole)
76:171-182.

1950. Rate of water pumping and shell movements of oys-
ters in relation to temperature. Anat. Rec. 108:620.
1958. Some aspects of behavior of oysters at different
temperatures. Biol. Bull. (Woods Hole) 114:57-70.
LOOSANOFF, V. L., AND P. B. SMITH.

1950. Apparatus for maintaining several streams of water
of different constant salinities. Ecology 31:473-474.
MARSTON, A. T.

1931. Preliminary experiments on the effect of tempera-
ture upon the ingestion of bacteria by the clam (Mya
arenaria). Mar. Fish. Ser. 4, Boston, Commonw. Mass.,
Dep. Conserv., Div. Fish Game, Mar. Fish. Sect., 5 p.
MATTHIESSEN, G. C.

1960. Observations on the ecology of the soft clam, Mya
arenaria, in a salt pond. Limnol. Oceanogr. 5:291-300.
MEDCOF, J. C.

1944. How relaying and transferring at different seasons
affects the fatness of oysters. Fish. Res. Board Can.,
Prog. Rep. Atl. Coast Stn. 35:11-14.
NELSON, T. C.

1923. On the feeding habits of the oyster. Proc. Soc. Exp.
Biol. Med. 21:90-91.
VAN DAM, L.

1935. On the utilization of oxygen by Mya arenaria. J.
Exp. Biol. 12:86-94.
WELLS, G. P., E C. LEDINGHAM, AND M. GREGORY.

1940. Physiological effects of a hypotonic environ-
ment. J. Exp. Biol. 17:378-385.

EDWIN P. CREASER, JR.

David A. Clifford

Maine Department of Marine Resources

Research Laboratory

West Boothbay Harbor, ME 04575

229

PHOTOGRAPHIC METHOD FOR MEASURING

SPACING AND DENSITY WITHIN

PELAGIC FISH SCHOOLS AT SEA

Few measurements exist of the spacing and den-
sity of fish within schools in the sea (Radakov
1973) although these characters have been well-
studied in the laboratory (Breder 1954; Keen-
leyside 1955; Dambach 1963; Williams 1964; John
1964; Cullen et al. 1965; Hunter 1966; van Olst
and Hunter 1970; Symons 1971). The density and
spacing of fish within schools under natural
conditions must be known if realistic fish
abundance estimates are to be made from sonar
survey data (Hewitt et al. 1976). This note de-
scribes a camera system that photographed fish
schools at sea and a method used for estimating
the density and interfish spacing from the
photographs.

The camera system1 consisted of an anodized
aluminum casing which housed a spring-driven
advance 35-mm camera, strobe light, and electri-
cal components. The system was made watertight
by creating a vacuum which sealed the acrylic
lenses to the casing. Attached to the casing were a
depth release with expendable chain ballast,
floats, and a signal flag (Figure 1).

Upon immersion, the camera assumed an
upright position, closing a mercury switch and
starting an electric timer which activated the
camera shutter and strobe light simultaneously.
The system took 14 photographs per drop at set
intervals of 24 or 48 s while sinking at a rate of 10

'Designed by Daniel M. Brown, Scripps Institution of
Oceanography (SIO) from an idea of John D. Isaacs, SIO.
Blueprints are available at the Marine Sciences Development
Shop, SIO.

FLAG-FLOAT UNIT

CAMERA HOUSING

--•-PLASTIC FLAGS
— CHEMICAL GLOW LIGHT

10' ALUMINUM POLE

-ALUMINUM TRAWL
FLOATS

-STAINLESS STEEL
PIPE

-20' -3/8"

POLYPROPYLENE ROPE

-3/8" STAINLESS STEEL
-CAMERA SHACKLE

— VACUUM VALVE
-STROBE

-24" x I" NYLON WEBBING

DEPTH RELEASE

SOLUBLE RELEASE

-I" THICK NYLON WEBBING

BALLAST

29 LINKS - 1/2" ANCHOR
CHAIN (.3276 lb/ link )

FIGURE 1. — (A) The Isaacs-Brown free vehicle drop camera.
(B) A lateral view of the upper camera housing. Once the
camera was upright, the mercury switch closed and the electric
timer discharged every 24 or 48 s which caused the solenoid to
contract bringing the depressor arm down on the shutter re-
lease. The strobe light fired simultaneously and the film was
advanced automatically. (C) The wiring diagram for the cam-
era system.

FOAM PADDING

SHUTTER
RELEASE"

STROBE
LEAD

ACRYLIC
LENS

LATERAL VIEW OF UPPER
CAMERA HOUSING

MERCURY SWITCH
MICRO-SWITCH
AS 408 A-l

~~UjuuuU

dormeyer

B24-755 A-l

10 2
°9 o 3'

12 V

II PIN SOCKET
MICROTRONICS
DIGILAY 275-IA

-o-f^J SWITCH

I ALCO DPDT
MST 205

2500 MFD
25V dc

H'l'k

22 5 V

DROP CAMERA WIRING

230

m/min. At a preset depth, the ballast was released
and the system returned to the surface.

Fish lengths were measured from photographic
enlargements with an x-y coordinate reader and
only those fish enclosed by a circle of 6 to 10 cm in
diameter, drawn centered on the photograph, were
counted in order to reduce computer processing
time and peripheral photographic distortion.
Repeated measurements of a photograph indi-
cated a mean error in individual body length of
3.49r and a maximum error of less than 9.0% for
any individual.

To estimate the distances from the camera to the
fish it was assumed that all the fish were of the
same size, were all oriented perpendicularly to the
camera lens, and thus the differences in fish image
size were dependent only on the distance from the
camera. The distance between any fish and the
camera was determined by calculating the ratio of
the standard fish size to the 35-mm negative
image size and substituting this value into the
underwater calibration equation of the camera
(Figure 2). The mean standard length of 12. 0 cm (s
= 1.9 cm) for anchovy in southern California
waters (Mais 1974) was used as the standard fish
size.

E
E
m
ro

—

/ X

l /

/•

/ i i

i i i

\ \

10 20 30 40

DISTANCE FROM THE CAMERA (m)

FIGURE 2. — The calibration curve for the Isaacs-Brown free
vehicle drop camera. This camera system was calibrated under
water by photographing objects of known sizes at fixed distances
and the ratio of the real object to negative image size (y) was
plotted against distance from the camera ix). The equation for
the line is.v = 19.56*. The distance to a fish was then determined
by calculating the ratio of the standard fish size (12 cm) to the
35-mm negative image size of that fish.

A computer program calculated the lengths of
the fish and produced a cumulative percent dis-
tribution of their sizes. One would expect the
number offish with small image sizes to increase
with distance from the camera lens, but analysis
revealed that a distance existed in most photo-
graphs at which the numbers of smaller fish failed
to increase presumably because the more distant
fish were not resolved owing to overlap, water
clarity, and loss of lighting. An arbitrary limit was
established at that image size by noting a change
in slope on the graph of the cumulative percent
distribution offish lengths (Figure 3) and all fish
smaller than the limit were not considered.

After establishing the minimum fish image size
to be included in the program, a three-dimensional
model of the photograph was constructed by
calculating a third coordinate, z, based on fish
image size and by adjusting thex and y coordinates
for distance from the camera. The midpoint of each
fish was then determined and a mean distance to
the nearest neighbor was calculated by compari-
son with the midpoints of all the fish. The density
of the school was computed by dividing the num-

LIMIT

40 30 20 10 0

F ISH LENGTH (digitizer units)

FIGURE 3. — The cumulative percent of length frequencies (in
arbitrary units) for the fish measured in photograph 10 (Figure
4). Graphs of this form were made for each photograph analyzed
in order to determine the distance beyond which all fish images
were not resolved. The limit was made arbitrarily at the first
apparent decrease in slope of the distribution.

231

ber of fish by the volume of the truncated cone
between the planes of the largest and smallest fish
image.

In September 1974, 14 camera drops were made
in the Santa Barbara Channel on anchovy schools
located by sonar. Observation of camera drops
revealed that the slow sinking rate and Vi.ooo-s
strobe flash did not disturb the fish. A space of
about 4 m in diameter opened up in the school
below the system as the camera descended. The
increase in the school density caused by formation
of the open space in the school was not detected in
my analysis.

Anchovy schools appeared on 16 of the 230
photographs taken. For the 10 photographs in
which the fish seemed to be perpendicular to the
camera, the mean density of the school was 114.8
fish/m3 where s = 99.1 fish/m3 and the mean of the
mean distance to the nearest neighbor was 1.2
body lengths with s = 0.3 body length (Figure 4,
Table 1).

Photographs 6-10 were of the same school taken
over a 10-min period. Excluding photograph 7, in
which the fish appeared to be reacting to the cam-
era or a predator and are more compact, the den-
sities calculated for this school were 60, 56, 51, and
55 fish/m3 with a mean distance to the nearest
neighbor of 1 .27, 1 .28, 1 .63, and 1 .42 body lengths,
respectively.

The interfish distances estimated for the schools
photographed in this field study are, in general,
larger than those reported in laboratory studies.
This suggests that the small tanks used in these
studies have caused fish to form more compact
schools than they typically do under natural
conditions.

The camera and these techniques could be of
considerable value in determining the density and
species composition of pelagic fish schools for

TABLE 1 . — Parameters of schooling compaction generated by the
computer program for the 10 photographs in Figure 4.

Mean distance (body lengths) to

Photo number

Fish/m3

the nearest neighbor

100

1 24

174

0.84

1.38

1.35

366

0.79

1.27

158

0.86

1.28

1.63

1.42

Mean

115

1.20

Standard

deviation

0.28

sonar surveys. They should also be of value in the
study of the behavior of schooling fish. School
densities are known to change during feeding,
predatory attack, and under diminished light
intensity (Shaw 1970; Radakov 1973). Using the
drop camera, it may now be possible to study the
behavior of schools in the sea since interfish
distance is as yet the best characteristic to mea-
sure changes in schooling tendencies.

Acknowledgments

I thank Daniel M. Brown of the Scripps Institu-
tion of Oceanography for instructing me in the use
of the camera; the California Department of Fish
and Game for providing time on the vessel Alaska
and the assistance of its crew; John Ford for as-
sisting with the camera calibration; John Hunter,
Paul Smith, and Roger Hewitt of the National
Marine Fisheries Service for helping in various
ways; and Evelyn Shaw and Charles Breder for
reviewing the manuscript.

Literature Cited
Breder, C. M., Jr.

1954. Equations descriptive of fish schools and other
animal aggregations. Ecology 35:361-370.

Cullen, J. M., E. Shaw, and H. A. Baldwin.

1965. Methods for measuring the three-dimensional
structure offish schools. Anim. Behav. 13:534-543.

DAMBACH, M.

1963. Vergleichende Untersuchungen uber das
Schwarmverhalten von Tilapia-Jungfischen (Cichlidae,
Teleostei). Z. Tierpsychol. 20:267-296.

Hewitt, R. P., P. E. Smith, and J. C. brown.

1976. Development and use of sonar mapping for pelagic
stock assessment in the California Current area. Fish.
Bull., U.S. 74:281-300.
HUNTER, J. R.

1966. Procedure for analysis of schooling behavior. J.
Fish. Res. Board Can. 23:547-562.

John, K. R.

1964. Illumination, vision, and schooling of Astyanax
mexicanus (Fillipi). J. Fish. Res. Board Can. 21:1453-
1473.

KEENLEYSIDE, M. H. A.

1955. Some aspects of the schooling behavior of
fish. Behavior 8:183-248.

Mais, K. F.

1974. Pelagic fish surveys in the California Current. Calif.
Dep. Fish Game, Fish Bull. 162, 79 p.

Radakov, D. V.

1973. Schooling in the ecology offish. Translated by H.
Mills, John Wiley and Sons, N.Y., 173 p.
SHAW, E.

1970. Schooling in fishes: critique and review. In L. R.
Aronson, D. S. Lehrman, J. S. Rosenblatt, and E. Tobach
(editors), Development and evolution of behavior, p. 452-
480. W. H. Freeman, San Franc.

232

FIGURE 4.— Anchovy schools photographed in the Santa Barbara Channel with the Isaacs-Brown free vehicle
drop camera during September 1974. Estimated fish density (fish/m3) in each photograph, left to right, top row
100, 174, second row 78, 50, third row 366, 60, fourth row 158, 56, fifth row 51, 55.

233

SYMONS, p. e. k.

1971. Estimating distances between fish schooling in an
aquarium. J. Fish. Res. Board Can. 28:1805-1806.
VAN OLST, J. C, AND J. R. HUNTER.

1970. Some aspects of the organization of fish schools. J.
Fish. Res. Board Can. 27:1225-1238.
WILLIAMS, G. C.

1964. Measurement of consociation among fishes and
comments on the evolution of schooling. Publ. Mus.
Mich. State Univ., Biol. Ser. 2:349-384.

John Graves

Southwest Fisheries Center

National Marine Fisheries Service, NOAA

La Jolla, CA 92038

FEEDING BY ALASKA WHITEFISH,

COREGONUS NELSONI,

DURING THE SPAWNING RUN

It seems to be generally agreed that most
coregonids feed but little, if at all, during their
prespawning run and only minimally until
spawning has taken place (Wagler 1927; Hart
1930, 1931; Birrer and Schweizer 1936; Van Oos-
ten and Deason 1939; Slack et al. 1957; Qadri
1961; A. H. Townsend and Ray Baxter, Alaska
Department of Fish and Game, pers. commun.).
Coregonids are, however, known to feed, at least to
some extent, during the spawning period, but we
have not found any published indications of
whether such feeding is pre- or post-spawning of
the individual fish. Until the individual fish has at
least begun to spawn, feeding is at a very low level
(Wagler 1927; Hart 1930, 1931; Birrer and
Schweizer 1936; Jacobsen 1974). Subsequent to
spawning, feeding intensity increases greatly,
apparently compensating for the loss of condition
due to spawning. Coregonid and other fish eggs are
often an important food item at this time (Bajkov
1930; Jacobsen 1974). The few eggs taken by
presumed prespawners are probably ingested
incidentally to normal respiratory movements
rather than by deliberate feeding (Hart 1930).

The purpose of the present paper is to document
an instance of active feeding by a coregonid species
during the prespawning run.

The least cisco, Coregonus sardinella, and
Alaska whitefish (Coregonus nelsoni = C.
clupeaformis complex of McPhail and Lindsey
1970) of the rivers of interior Alaska exhibit
highly concentrated spawning runs. In the
Chatanika River, near Fairbanks, these fishes

begin their upstream movement in late June and
early July. The larger fish begin their migration
first, moving upstream in a seemingly rather
indefinite fashion across the Minto Flats. As the
summer progresses, the fish congregate in the
lower reaches of the river east of the Minto Flats.
In the middle to latter part of September, there is a
concentrated upstream movement of virtually the
entire adult population. This is a journey of ap-
proximately 150 km to the spawning areas and is
accomplished in a period of 2 to 4 wk (Kepler1;
Townsend and Kepler2).

On 2 October 1975, we collected 25 ( 10 males, 15
females) Alaska whitefish and 23 least cisco in the
Chatanika River near Fairbanks, Alaska. The fish
were seined at two locations, one approximately
6.6 river km below the Elliott Highway bridge ( lat.
65°4.5'N, long. 147°45.6'W), the other 3.1 km
farther downstream (lat. 65°3.7'N, long.
147°47.3'W) between 1000 and 1200 h. Water
depths were 0-2.5 m; water temperature was
1.5°C. These locations are within the major
spawning area of the least cisco in the Chatanika
River. A few Alaska whitefish also spawn in this
part of the river, but their major breeding grounds
lie some 15-25 km farther upstream. All the least
cisco were fully ripe and running eggs or milt. The
Alaska whitefish were all mature but not quite
fully ripe. Most of the eggs of the females were still
in fairly firm skeins. We estimated that these fish
would not have spawned for another 2 wk.

The stomachs of all the fish were removed after
return to the laboratory in the evening and stored
in 10% Formalin3 and the contents analyzed dur-
ing the following 2 wk. Egg counts of each stomach
were made by counting the eggs in each of two
1-ml samples, then estimating the total by
comparison with the total volume of eggs in the
stomach.

The stomachs of all least cisco were much re-
duced in size. Except for one containing six fish
eggs and another with five unidentified seeds, all
were empty. By contrast, the stomachs of all the

'Kepler, P. P. 1973. Population studies of northern pike
and whitefish in the Minto Flats complex with emphasis on the
Chatanika River. Alaska Dep. Fish Game, Fed. Aid Fish
Restoration, Annu. Prog. Rep. Proj. F-9-5, Job G-II- J. 14, 23 p.

2Townsend, A. H., and P. P. Kepler. 1974. Population
studies of northern pike and whitefish in the Minto Flats com-
plex with emphasis on the Chatanika River. Alaska Dep. Fish
Game, Fed. Aid Fish Restoration, Annu. Prog. Rep. Proj. F-9-6,
Job G-II-J. 15, 21 p.

3Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

234

Alaska whitefish were more or less distended and
crammed with eggs, almost all of them least cisco
eggs. A few larger eggs in the stomachs were
probably those of the Alaska whitefish.

Volume of eggs per stomach ranged between 1.5
and 42.4 ml (x = 19.96 ml). Numbers of eggs per
stomach ranged between 200 and 7,842 (jc =
3,574). Other items, present only in insignificant
amounts, included Diptera, Tendepedidae,
Trichoptera, Hydracarina, unidentified insect
parts, a tree bud, and a small slimy sculpin, Cottus
cognatus.

As indicated previously, extensive life history
studies of this species conducted by the Alaska
Department of Fish and Game have shown that
prespawners do not feed. Presumably, then, the
phenomenon reported here is of rare occurrence.
However, if the entire Alaska whitefish popula-
tion of the Chatanika River, estimated at 7,000 to
8,000 fish (see footnotes 1, 2) should engage in this
activity, then it might constitute a major source of
egg mortality for the least cisco population. Since
both species are important components of the sport
fishery resources of the Chatanika River, the
matter is worth further investigation.

The samples reported upon here were collected
as part of a study of the environmental effects of
the Trans-Alaska Pipeline crossing of the
Chatanika River. This study is conducted jointly
by the Division of Life Sciences, University of
Alaska, Fairbanks, Alaska, and the Arctic En-
vironmental Research Laboratory, Environmen-
tal Protection Agency, Fairbanks, and is sup-
ported by the Environmental Protection Agency.

Literature Cited

BAJKOV, A.

1930. A study of the whitefish (Coregonus clupeaformis) in

Manitoban lakes. Contrib. Can. Biol. Fish., New Ser.

5:441-455.
BIRRER, A., AND W. SCHWEIZER.

1936. Der Edelfisch des Vierwaldstatter Sees Coregonus

Wartmanni nobilis, Fatio. Ein Beitrag zur Kenntnis der

Coregonen in den Schweizer Seen. Arch. Hydrobiol.

29:617-663.
HART. J. L.

1930. The spawning and early life history of the whitefish,
Coregonus clupeaformis (Mitehill), in the Bay of Quinte,
Ontario. Contrib. Can. Biol. Fish., New Ser. 6:165-214.

1931. The food of the whitefish, Coregonus clupeaformis
(Mitehill) in Ontario waters, with a note on the para-
sites. Contrib. Can. Biol. Fish., New Ser. 6:445-454.

JACOBSEN, O. J.

1974. Feeding habits of the population of whitefish
(Coregonus lavaretus (L.)) in Haugatjern — a eutrophic
Norwegian Lake. Norw. J. Zool. 22:295-318.

MCPHA1L, J. D., AND C. C. LlNDSEY.

1970. Freshwater fishes of northwestern Canada and
Alaska. Fish. Res. Board Can. Bull. 173, 381 p.
QADRI, S. U.

1961. Food and distribution of lake whitefish in Lac la
Ronge, Saskatchewan. Trans. Am. Fish. Soc. 90:303-
307.
SLACK, H. D., F. W.K. GERVERS, AND J. D. HAMILTON.

1957. The biology of the powan. Stud. Lock Lomond
1:113-127.
VAN OOSTEN, J., AND H. J. DEASON.

1939. The age, growth, and feeding habits of the whitefish,
Coregonus clupeaformis (Mitehill) of Lake Champlain.
Trans. Am. Fish. Soc. 68:152-162.
WAGLER, E.

1927. Die Blaufelchen des Bodensees {Coregonus
wartmanni Bloch). Int. Rev. Gesamten Hydrobiol.
Hydrogr. 18:129-230.

JAMES E. MORROW

Division of Life Sciences
University of Alaska
Fairbanks, AK 99701

ELDOR W. SCHALLOCK

Arctic Environmental Research Laboratory
Environmental Protection Agency
Fairbanks, AK 99701

GLENN E. BERGTOLD

Division of Life Sciences
University of Alaska
Fairbanks, AK 99701

EGG MORTALITIES IN WILD POPULATIONS

OF THE DUNGENESS CRAB IN

CENTRAL AND NORTHERN CALIFORNIA1

A recent study (Fisher and Wickham 1976) of
eggs from wild populations of the Dungeness crab,
Cancer magister, collected in the 1974-75 season
showed that epibiotic fouling and egg mortalities
occurred more heavily in the Drakes Bay region of
central California than in the other California
regions sampled (Pacifica, Point Reyes, Bodega
Bay, Russian River, Gualala, Fort Bragg, and
Eureka). The paper suggested that nutrients from
San Francisco Bay were carried northward by the
Davidson Current (the prevalent coastal current
during the winter months) causing an increase in
epibiotic fouling which restricted gaseous ex-
change across the egg membrane and increased
egg mortalities.

^his work is a result of research sponsored by NOAA Office of
Sea Grant, U.S. Department of Commerce, under Grant No. 04 5
158-20 NOAA. This work is also supported by California State
Legislature Funds for Aquaculture.

235

In the laboratory it has been shown (Fisher
1976) that increased phosphate and nitrate levels
in the seawater did, in fact, increase the number of
epibiotic filaments and concurrently the number
of egg mortalities. Conversely, chemotherapeutic
and antibiotic treatment reduced filamentous
growth and egg mortalities. It was also shown that
both the number of filaments and the number of
egg mortalities decreased exponentially with
increasing depth into the egg masses (to a depth of
9 mm).

This study is similar to the original field study
(Fisher and Wickham 1976) with modifications
based on the information gained in the laboratory.
All samples were collected from the same position
on the egg masses to discount probable errors due
to mortality variations within each egg mass.
Only samples with eyespot development and no
signs of hatching were used, restricting the var-
iation in developmental states to approximately 2
wk. Mortality estimates were made from both the
peripheral eggs of a sample and the total sample to
determine the in situ significance of the peripheral
mortalities reported for the laboratory conditions
(Fisher 1976).

Procedures

The crab eggs were sampled between 26 De-
cember 1975 and 27 January 1976 from four
regions: Pacifica, Drakes Bay, Russian River, and
Eureka. Relative to the mouth of San Francisco
Bay, Pacifica is slightly south, Drakes Bay
slightly north, Russian River 80 km north, and
Eureka 400 km north. Samplers in each area were
supplied with curved forceps, vials partially filled
with 10% Formalin2 in seawater, and a data sheet
for recording date, depth, and Loran reading for
each sample collected. As ovigerous females were
captured, small clusters of eggs were removed
about 1-2 cm from the posterior tip of the abdomen
along the midventral line with the curved forceps
and placed in the vials of preservative.

After arrival at Bodega Marine Laboratory, the
samples were examined under a dissecting
microscope for the presence of eyespots. The
samples were discarded if eyespots were lacking or
if embryos were beginning to hatch. Laboratory
observations have shown the time from eyespot
appearance to the time of hatch to be about 2 wk

while the entire external incubation period is
about 2 mo.

Ten setae were randomly selected from the
remaining samples (Pacifica, 27; Drakes Bay, 17;
Russian River, 21; Eureka, 23). The first 25 eggs
on the distal ends of these setae were examined
under the dissecting microscope for mortalities.
This provided a peripheral mortality estimate.
Percentage peripheral mortalities were calculated
from the average mortalities for each region.

The 10 setae from each sample were returned to
the sample vials and transferred to a second in-
vestigator. Ten to fifteen setae were then ran-
domly selected and an overall mortality estimate
was obtained by counting all the live and dead
eggs in this subsample (approximately 1,500
eggs). Percentage overall mortalities were cal-
culated for each sample and then averaged for
each region.

Results

Drakes Bay samples had the highest mor-
talities, while those from the Russian River and
Eureka had the lowest. The peripheral and overall
mortality estimates were consistent for all regions
except for Drakes Bay where peripheral mor-
talities averaged 39.4% and overall mortalities
averaged 27.6% (Table 1). A Student's t statistic
for the means of two samples showed all regions
except Eureka and the Russian River to be sig-
nificantly different (P<0.05) from all other reg-
ions using both peripheral and overall mortalities.
By the same analysis, the peripheral and overall
mortalities within each region were statistically
similar (P>0.1).

TABLE 1. — Average Dungeness crab egg mortalities for each re-
gion sampled. The first 25 eggs on the distal end of 10 setae from
each sample were examined.

No.
samples

Mortalities

Region

Peripheral Overall

Pacifica
Drakes Bay
Russian River
Eureka

17
21
23

14.6 ± 2.0 17.4 ± 18

39.4 ± 5.4 27.6 ± 5.0

8.1 ± 1.0 9.7 ± 1.4

9.1 ± 1.6 11.5 ± 1.6

2Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

Discussion

These results agree with the original study
completed during the 1974-75 season. High
numbers of egg mortalities were found in the
Drakes Bay region and low numbers in samples
from the Eureka and the Russian River regions.

236

The lower mortalities from the adjacent Pacifica
and Russian River regions confirm the suggestion
of the original study that the heavy mortalities
were substantially confined to the Drakes Bay
region. This is consistent with the suggestion that
the northerly Davidson Current may be sweeping
harmful effluent from San Francisco Bay into
Drakes Bay. The intermediate mortality levels of
the Pacifica region could simply be a result of
proximity while the Russian River region might
remain relatively unaffected due to blockage and
dispersion caused by the Point Reyes land mass
and to dilution of the harmful effluent.

The similarity between the peripheral and
overall mortalities found for the Pacifica, Russian
River, and Eureka regions show a constant
mortality distribution throughout the egg masses
in these areas. The Drakes Bay region, however,
showed considerably higher peripheral mor-
talities (39.4%) compared with the overall mor-
talities (27.6% ■). It is surmised that the peripheral
mortalities are the primary difference between
the high number of mortalities found in Drakes
Bay and the lower numbers in other regions. This
parallels the distribution of mortalities caused by
epibiotic fouling in the laboratory (Fisher 1976)
which were found to decrease with increased depth
into the egg mass and further supports the
proposition that epibiotic fouling contributes to
egg mortalities in the Dungeness crab population
of Drakes Bay.

There are several similarities between this egg
disease and that of the blue crab, Callinectes
sapidus, caused by the fungus, Lagenidium cal-
linectes (Couch 1942; Sandoz et al. 1944). Both
conditions are geographically selective, cause
peripheral mortalities, cause greater damage on
older egg masses, and coincide with increased
nemertean worm populations (Rogers-Talbert
1948; Fisher and Wickham 1976). It is interesting
to note that some epibiotic microorganisms were
also observed on the blue crab eggs (Rogers-
Talbert 1948). These similarities may indicate a
common factor such as environmental stress or
physiological impairment of the eggs that
supercedes the importance of the respective
etiological agents.

It is difficult to ascertain the effect of the
Dungeness crab egg mortalities in Drakes Bay on
the recruitment of the commercially important
adult stages. Specific production data for Drakes
Bay and migration patterns for the species are un-
known. Although no attempts have been made to

bear out the suggestion, Rogers-Talbert (1948) felt
that 25% mortality found on the blue crab eggs
could not be regarded as a factor in (adult) popu-
lation fluctuations. Recently, larval stages of the
Dungeness crab have also been found susceptible
to epibiotic microbial infestation in the laboratory
(Fisher and Nelson3) although no field data are
available. It can at least be speculated that the
combined losses of egg and larval stages have
decreased the adult population of Dungeness crabs
in Drakes Bay. This decrease is reflected by the
collapse of the fishery in central California since
1960 while northern California production, al-
though fluctuating, has been maintained (Orcutt
et al. 1975).

Acknowledgments

We thank Harold Ames, Tom Burke, Earl
Carpenter, Bill Genochio, Tony Anello, Willie
Ancona, Tom Estes, and Charles Fagg for their
sampling efforts and Richard Nelson for his
technical assistance.

Literature Cited

COUCH, J. N.

1942. A new fungus on crab eggs. J. Elisha Mitchell Sci.
Soc. 58(2):158-162.
FISHER, W. S.

In press. Laboratory studies on the relationships of
epibiotic fouling and mortalities of the eggs of the
Dungeness crab {Cancer magister). J. Fish. Res. Board
Can.
FISHER, W. S., AND D. E. WICKHAM.

1976. Mortalities and epibiotic fouling of eggs from wild
populations of the Dungeness crab, Cancer magis-
ter. Fish. Bull., U.S. 74:201-207.

Orcutt, H. G., R. N. Tasto, and p. w. wild.

1975. Dungeness crab research program. Calif. Dep.
Fish Game Mar. Resour. Adm. Rep. 75-8, 35 p.

Rogers-Talbert, r.

1948. The fungus Lagenidium callinectes Couch ( 1942) on
eggs of the blue crab in Chesapeake Bay. Biol. Bull.
(Woods Hole) 95:214-228.

Sandoz, M. D., R. Rogers, and C. L. Newcombe.

1944. Fungus infection of eggs of the blue crab Callinectes
sapidus Rathbun. Science (Wash., D.C.) 99:124-125.

3Fisher, W. S., and R. T. Nelson. Therapeutic treatment for
epibiotic fouling on Dungeness crab {Cancer magister) larvae
reared in the laboratory. Submitted for publication.

william s. fisher
Daniel e. wickham

University of California
Bodega Marine Laboratory
Bodega Bay, CA 94923

237

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Contents-continued

Notes

AUSTIN, C. BRUCE. Incorporating soak time into measurement of fishing effort in
trap fisheries 213

MISITANO, DAVID A. Species composition and relative abundance of larval and
post-larval fishes in the Columbia River estuary, 1973 218

GUNN, JOHN T., and MERTON C. INGHAM. A note on: "Velocity and transport
of the Antilles Current northeast of the Bahama Islands" 222

CREASER, EDWIN P., JR., and DAVID A. CLIFFORD. Salinity acclimation in the
soft-shell clam, Mya arenaria 225

GRAVES, JOHN. Photographic method for measuring spacing and density within

pelagic fish schools at sea 230 "

MORROW, JAMES E., ELDOR W. SCHALLOCK, and GLENN E. BERGTOLD.
Feeding by Alaska whitefish, Coregonus nelsoni, during the spawning run 234

FISHER, WILLIAM S., and DANIEL E. WICKHAM. Egg mortalities in wild pop-
ulations of the Dungeness crab in central and northern California 235

•sir GPO 79&O09

FISHERY WASTE EFFLUENTS: A SUGGESTED SYSTEM FOR
DETERMINING AND CALCULATING POLLUTANT PARAMETERS

Jeff Collins and Richard D. Tenney1

ABSTRACT

An improved and simplified system to test for pollutants in shrimp waste effluents is presented. In
addition, two methods were developed to calculate both protein and oil and grease content. The first
method is based on establishing empirical regressions of protein or oil and grease on total residue. The
second and preferred method, a simultaneous equation, is independent of these correlations but
dependent on the total residue and chemical oxygen demand (COD) of the waste effluent obtained
through routine analyses. The COD value was found to depend upon the amount of potassium di-
chromate remaining at the completion of the 2-h reflux period. The dichromate can vary from 0 to 6.25
meq excess and between 2 and 5 meq, the COD will vary 4.2% . A table of factors is given to correct the
COD to 3.5 meq excess. Coefficients of COD were determined on a number of preparations of protein
and oil and grease from shrimp waste effluent and from fish and shellfish. These coefficients (1.338 mg
COD/mg protein and 2.678 mg COD/mg oil and grease) were required for the simultaneous equation.
The simple analytical tests and mathematical treatment used in this system would be less expensive
to the industry and would result in a more accurate and comprehensive evaluation of the waste load
than currently obtainable by methods specified in the monitoring regulations.

An improved testing program for fishery waste ef-
fluents has been suggested (Collins and Tenney
1976) in which the total residue (TR) and the
chemical oxygen demand of the filterable residue
(CODfr) were to be determined by analysis and
used to calculate other parameters from equations
previously established for a particular plant and
process. It was also suggested that the protein and
oil and grease (O&G) content could probably be
calculated from COD and TR data to give more
accurate values than by direct analyses.

The purpose of this study was to test the validity
of such a testing-calculating system on waste ef-
fluents from a shrimp plant in Kodiak, Alaska. A
further purpose was to derive equations whereby
O&G and protein could be calculated from COD
and TR data.

EXPERIMENTAL

Grab samples were taken at specific times dur-
ing the shrimp production periods to obtain a
range in values that would be useful for subse-
quent mathematical treatment. Waste effluents
were taken from the underflow of a Bauer Hydra-

sieve2 (1 mm, 0.04 inch) in a plant processing
shrimp with combined Model A and PCA peelers.
The methods of analysis and the method of cal-
culating data are similar to those reported previ-
ously (Collins and Tenney 1976). The test for
filterable residue (FR) was modified, however, to
give sufficient filtrate (900 ml) for duplicate
macro-Kjeldahl, COD, FR, and ash analyses.
About 1,000-ml effluent, after settling 30 min,
was decanted through a plug of glass wool in a
powder funnel positioned over a 600-ml coarse
sintered glass funnel containing GF/A glass filter
paper and Vi inch of dry base-acid-water washed
ASTM standard Ottawa sand (C-190). The suction
flask was evacuated briefly several times during
filtration and clamped off to prevent plugging of
the filter and evaporation. We have found that use
of continuous evacuation causes rapid plugging of
the glass filter paper and, additionally, could
cause considerable errors through evaporation.

As will be discussed later, the precision of the
residue and ash analyses is particularly impor-
tant. Consequently, considerable attention was
given these analyses to obtain good precision as
well as convenience in conducting the analyses.
The major steps of the procedure follow:

'Northwest and Alaska Fisheries Center, National Marine
Fisheries Service, NOAA, P.O. Box 1638, Kodiak, AK 99615.

Manuscript accepted October 1976.
FISHERY BULLETIN: VOL. 75, NO. 2. 1977.

2Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

253

FISHERY BULLETIN: VOL. 75, NO. 2

1. Heat 100-ml Pyrex beakers at 500°C for 1 h, air
cool for 1 h, and weigh. Prior to use, new
beakers should be equilibrated to ashing condi-
tions.

2. Accurately weigh about an 80-ml sample of
effluent into the dry beaker. Dry overnight at
103°C in a forced draft oven and weigh after 1 h
of air cooling.

3. Calculate TR in milligrams/liter. (Note: this
system, of course, gives TR in milligrams/1,000
g, but we follow the convention and express it
in milligrams/liter.)

4. Heat beaker and dried sample at 500°C for 2 h,
air cool 1 h, and weigh as before.

5. Calculate ash from the initial weight of
sample, express as milligrams/liter as in step 3.

RESULTS

In general, these effluent samples were tested
for COD, residue, ash, O&G, and protein. The data
in Table 1 are averages of duplicate analyses, ex-
cept O&G which is in triplicate. The data should
not be considered representative of the effluent
from this plant because of the specific way of tak-
ing these grab samples. Comparisons in relative
data, however, can be made. For example, the
COD of the filterable residue (CODFR) was slightly
over one-half of the total COD (CODTR) and the
filterable residue (FR) was 64% of the total residue
(TR) on an ash-free basis. The TR contained 17%
ash, but most of the ash was found in the FR frac-
tion (92%) leaving only 8% in the nonfilterable
residue (NFR) fraction.

The relationship between COD and ash-free
residue is plotted in Figure 1 and that for O&G

2800 ■

2 400 •

2000

o
z
<

q 1600 •

I
u

200-

800 ■

4 00

CODTR = 1.41 TRK

CODFR = 1.39 FR(

CODNFR= 1.69 NFRK + 10

400 800 1200 1600 2000

RESIDUE , mg/l

FIGURE 1. — Relationship between the COD and the concentra-
tion of the ash-free residue in waste effluents from a plant using
both Model A and PCA peelers and fresh water.

and protein versus ash-free residue is given in Fig-
ure 2. The coefficients of correlation were 0.99 and
0.97 for the COD regressions on TRK and FRK,
respectively. The F-test for linearity at the 95%
level of significance was 0.015 for the TRK line and

TABLE 1. — Analyses of screened shrimp waste effluents from a plant using both Model A and PCA
mechanical peelers. [All values in milligrams/liter.]

Sample

Chemical

oxygen demand

Residue

Ash

Protein (6.25N)

Oil and grease
TR

number

1,517

672

1,420

946

304

291

831

522

185

2,839

1,280

2,328

1,441

325

310

1.319

859

486

2,190

1.016

1,911

1,146

264

241

1,215

785

276

2,182

1,413

1.897

1,400

308

288

1,281

947

258

1,824

1,139

1,567

1,146

261

242

1,056

790

203

1,917

1,210

1,602

1,182

242

220

1,075

806

230

2,039

1,393

1.833

1,418

324

298

1,212

944

229

1,771

964

1,532

1,061

280

256

1,037

744

195

2,481

1,565

2,137

1.522

378

332

1,425

1,072

302

1.969

1,066

1.750

1,197

321

284

1,175

835

204

1,666

883

1.460

965

247

224

1.025

703

186

1,829

1.046

1,573

1,093

286

263

1,116

794

175

2.041

1,156

1,822

1,310

352

328

1,188

863

233

1,522

883

1,351

946

256

228

925

644

148

Mean

1,985

1,120

1,727

1,198

296

272

1,134

808

236

361

240

280

193

158

136

254

COLLINS iind TENNEY: SYSTEM FOR DETERMINING POLLUTANT PARAMETERS

1400

1200

E
Z

^ 1000

800

o°

PROTE IN = 0 74 TRK + 103

400

200

L/.

1200

1400 1600

TRK. mg/1

1800

FIGURE 2. — Relationship between the concentration of protein
or oil and grease and the concentration of the ash-free total
residue in waste effluents from a plant using both Model A
and PCA peelers and fresh water.

product process, our testing-calculating system
would proceed as follows: Determine TR and ash
and substitute the difference into Equation ( 1 1
and solve for CODtr. Using the mean values for
TR and ash of Table 1 gives 1,431 mg/liter TRK.
Substitution into Equation (1) gives 1,990 mg
CODTR/liter which nearly agrees with the
mean analytical COD value. Similarly, the
other recommended routine test for COD of the fil-
trate (CODFR) gives a mean value from Table 1 of
1,120 mg/liter which, when substituted into Equa-
tion (2), gives 925 mg/liter for FRK, in agreement
with the difference between FR and ash, i.e., FR -
ash = 926 mg/liter. The NFR or CODNFR are ob-
tained by difference, e.g., TRK - FRK = NFRK. In
order to calculate protein and O&G, the TRK can
be substituted into Equations (4) and (5). A rough
estimate of O&G content can also be obtained by
dividing the COD by 9 which is the average for the
ratio of COD to the weight of O&G. The ratio actu-
ally varies from about 8 to 10 and inversely with
the COD. The ratio and equations only have appli-
cation to this plant and processing conditions. For
other processing conditions or plants, the baseline
data and equations should be determined in the
same manner.

CALCULATION OF O&G AND

PROTEIN USING
A SIMULTANEOUS EQUATION

0.068 for FRk- The regression lines and equations
found in Figures 1 and 2 include a correction for
ash content in the residue, i.e., TR - ash = TRK.
These equations, obtained by the method of least
squares, are as follows:

CODTR

= 1.41 TRK -

(1)

CODFR

= 1.39 FRK -

166

(2)

CODNFR

= 1.69 NFRK

+ 10

(3)

Protein

= 0.74 TRK +

103

(4)

O&G

= 0.20 TRK -

(5)

In our previous paper we suggested that back-
ground data for a particular plant should be deter-
mined [Equations (1), (2), and (3)] so that the other
parameters could be calculated from routine tests
for TR and CODFR. Since usage of salt and sea-
water in plants tends to vary, we now also suggest
that an ash analysis be done to eliminate varia-
bility in the total residue. Once background data
have been established for a particular plant or

In this section we will derive a simultaneous
equation that can be used as a substitute for direct
analysis so that O&G and protein can be calcu-
lated by using routine data on CODFR, TR, and
ash. The equation is based on the assumption that
the sum of the COD of each component in the ef-
fluent equals the total COD, i.e., COD (x, +
x2 . . . x„) = total COD; and that the sum of the
weights of each constituent having an effect on
COD equals the total residue minus ash, i.e.,
Residue (x, + x2 ■ ■ ■ xn) = Total residue - ash.

To develop the simultaneous equation, coeffi-
cients must first be determined that relate COD
to the two major constituents of a fishery waste
(protein and O&G). In addition, the residue-ash
relation needs defining.

COD in Relation to Protein and O&G

To establish a relationship between COD and
pollutants, we prepared samples of protein and

255

FISHERY BULLETIN: VOL. 75, NO. 2

O&G and determined their COD equivalent by
direct analysis.

To prepare protein a sample of muscle was
washed with water and centrifuged to remove the
blood and other small nitrogen components, then
washed with 2-propanol (IPA) to remove part of
the water. The sample was blended and refluxed
twice with IPA followed by filtration, washing,
and refluxing with petroleum ether (PE) and over-
night drying at 103°C. These oil free, white, odor-
less protein samples were analyzed for nitrogen
by the standard macro-Kjeldahl method (Horwitz
1965:273) and for COD. The COD factor was cal-
culated on a 100% protein basis.

To obtain O&G, the sample of fish or shellfish
was briefly rinsed with water and IPA; then, using
a high speed blender and anhydrous conditions
(MgS04), the O&G was extracted, cold, with IPA
and PE. For waste effluent, O&G was obtained by
the analytical method used previously (Collins
1976). By either method, after weighing the dry
O&G and diluting to volume with PE an aliquot of
the final solution equivalent to 8-10 mg O&G was
evaporated in the COD flask, oven-dried for 0.5 h,
and used for COD determination. Since PE has a
residue significantly affecting COD, freshly dis-
tilled PE was used throughout the tests.

The COD equivalent was determined on a num-
ber of different preparations of O&G and protein
from fish and shellfish muscle and from shrimp
waste effluent. The average values of from 5 to 30
replicate COD analyses for each material are
given in Table 2.

The COD coefficients for protein are in reason-
able agreement and are probably independent of

TABLE 2. — The COD coefficient of several preparations of oil and
grease (O&G) and protein from fish and shellfish and from
shrimp waste effluent.

Starting material

Black cod, frozen
Pollock, frozen
Snow crab, frozen
Pink salmon, fresh

Pink shrimp, fresh

Pink shrimp, canned

Shrimp waste effluent

Mean
SD

COD of 1.0 mg/ liter of

O&G

Protein

1.328

2.631

2.795

1.326

2.818

1.345

2.710

1.349

2.505

1.270

1.328

2.757

1.414

2.584

1.350

2.518

2.736

2.788

2.618

2.678

1.338

0.112

0.037

species or product form. The theoretical COD coef-
ficient of protein was calculated using amino acid
percentage composition data for snow crab re-
ported by Krzeczkowski and Stone (1974). The
theoretical figure of 1.285 mg COD/mg protein
was in close agreement with our experimental
figure of 1.338. The coefficients for O&G, however,
are quite different and are presumably caused by
errors in the COD method, differences in species,
product, and perhaps slight differences in the
method of extracting. There are, of course, known
differences in the lipid composition of these
species, especially the C-20 and C-22 polyunsatu-
rated fatty acids. The chain length and configura-
tion of the lipids would have a positive effect on
the COD coefficient. For example, some theoreti-
cal coefficients are: acetic acid (C2) 1.066, pro-
pionic (C3) 1.514, myristic (C14) 2.807, melissic
(C30) 3.115, lecithin (C44H8809NP) 2.458, and tri-
stearin (C57H110O6) 2.934. Recognizing the wide
variations possible, the empirically derived coef-
ficient of 2.678 seems reasonable.

These coefficients are used along with the con-
centration of protein and O&G to give the COD,
i.e., (1.338 mg COD/mg protein)mg protein +
(2.678 mg COD/mg 0&G)mg O&G = CODTR and
assumes that the total COD is the sum of the
COD of these two major constituents. To check the
validity of this equation the coefficients were mul-
tiplied by the predicted values for protein and
O&G [obtained from TRK data and Equations (4)
and (5)] and the resulting mean of the sums of the
products (2,155 mg COD/liter) was found to be
1.083 times greater than the mean predicted
value for CODTR (1,990 mg COD/liter) obtained
from TRK data and Equation (1). Although diffi-
cult to prove or demonstrate, we believe that the
lower analytical values for COD in a sample of
waste effluent are caused by the unequal and com-
peting oxidation of protein and O&G. As is well
known, O&G reacts slowly and especially if the
dichromate concentration has been reduced from
reacting with the more easily oxidized protein.
Minor constituents such as nonprotein nitrogen
and carbohydrates would contribute to COD in a
ratio different from the protein coefficient. Re-
gardless, if the simultaneous equation is to be
developed, the inequality must be adjusted by
increasing the COD value to equal the sum of the
COD of protein plus O&G, i.e.,

1.338 protein + 2.678 O&G = 1.083 CODTR. (6)

256

COLLINS and TENNEY: SYSTEM FOR DETERMINING POLLUTANT PARAMETERS

COD Reaction

The oxidation reaction in the COD method fol-
lows the usual chemical reaction laws, i.e., the
completeness of the reaction is dependent upon
the concentration of the reactants (potassium di-
chromate and waste). The method uses 25 ml
0.25N or 6.25 meq K2Cr207 in the reaction flask
and 50 ml of effluent. If the effluent is relative-
ly strong, most of the dichromate will be ex-
pended in the reaction which results in an
incomplete reaction and a lower COD value
than if the waste were weak, i.e., having a
larger excess of dichromate at the completion
of the reaction. Moore and Walker (1956) rec-
ommended that the size of sample should be
selected so that not more than 50^ of the
potassium dichromate is used up during the
oxidation. To illustrate the relationship be-
tween COD and amount of dichromate re-
maining (the excess) at the end of the 2-h
reflux period, data from six protein prepara-
tions were combined and plotted in Figure 3.
The equation of the regression line was then
used to calculate correction factors so that if
the COD were determined at an excess di-
chromate level above or below an arbitrary
point of 3.5 meq, the value can be corrected
to its value at 3.5 meq. These correction fac-
tors are listed in Table 3. To correct COD

TABLE 3. — Multiplication factors to correct COD to 3.5 meq
dichromate excess.

1.400

ta-
il.

z
o

o °oo

cP o ^o

~®°o% Po°o o

Y= 0 138 log X + I.26S

2 I M S

POTASSIUM DICHROMATE meq excess

FIGURE 3. — Relationhship between the protein coefficient and
the amount of dichromate remaining at the end of the 2-h
reflux period.

Excess

dichromate

Multiplication

dichromate

Multiplication

(meq)

factor

(meq)

factor

2.0

1.026

3.6

0.999

2.1

1.024

3.7

0.998

2.2

1.021

3.8

0.996

2.3

1.019

3.9

0.995

2.4

1.017

4.0

0.994

2.5

1.015

4.1

0.993

2.6

1.014

4.2

0.992

2.7

1.012

4.3

0.991

2.8

1.010

4.4

0.990

2.9

1.009

4.5

0989

3.0

1.007

4.6

0.988

3.1

1.005

4.7

0.987

3.2

1.004

4.8

0.986

3.3

1.002

4.9

0.985

3.4

1.001

5.0

0.984

3.5

1.000

values, determine the excess dichromate
(titration value times normality) and multiply
the corresponding factor from Table 2 by the
COD determined in the usual way.

Since titration (Jirka and Carter 1975),
sample, or reaction errors occur at either end
of the curve, we suggest that COD values are
valid only between 2 and 5 meq excess. All
data for the protein coefficients were deter-
mined by obtaining from 10 to 30 COD values
at different addition levels (5 to 30 mg pro-
tein/50 ml) and plotting the regression line.
The coefficient was obtained by substituting
the logarithm of 3.5 meq excess into the equa-
tion for the regression and solving for COD.
In addition, all COD data in Table 1 were cor-
rected to 3.5 meq excess dichromate.

Residue-Ash Correction

The major components of the total residue that
contribute to COD are protein and O&G. In addi-
tion, various salts and dirt contribute to TR and
possibly to COD. Unfortunately, there is no con-
venient method to measure these minor constitu-
ents so we estimate them by determining ash and
then subtract to give a corrected value for TR.
Since the weight of ash obtained after 500°C dry-
ing is less than its corresponding weight when
dried at 103°C, the TRK value (TR - ash) is accord-
ingly greater than it should be. Therefore, the TRK
was reduced as follows: To eliminate variability in
individual values, the O&G and protein values
were predicted using Equations (4) and (5) for the
regression lines in Figure 2 and TRK data. The
sum of the weight of protein plus O&G was found
to be about 37c smaller than TRK, i.e.,

257

FISHERY BULLETIN: VOL. 75, NO. 2

protein + O&G = 0.969 TRK.

(7)

This equation corrects the TRK so that it equals
the sum of the protein and O&G, and is convenient
to use in this form in the simultaneous equation.
The constant, 0.969, is the result of increasing the
analytical value for ash by 15.2% and represents,
in part, the difference in weight of ash between
drying at 500°C and 103°C.

Simultaneous Equation

In the preceding discussion we have shown the
two parts of the simultaneous equation: the first
showing the sum of the COD from protein and
from O&G to be equal to an adjusted total COD,
and the second showing the sum of the weights of
protein and O&G to be equal to the total residue
minus the ash content and corrected for the differ-
ence in weight caused by drying at 500°C or 103°C.
Equations (6) and (7) are combined in the follow-
ing so that a simple calculation can serve as a
substitute for the difficult direct analyses for pro-
tein and O&G:

(8)

X + Y = 0.969 TRK
1.338X + 2.678Y = 1.083 CODTR

where: X = protein in milligrams/liter
Y = O&G in milligrams/liter.

This equation should have general application to
fishery waste effluents provided: 1) TRK and
CODTR are known or can be derived, and 2) the
constant used to increase the value for CODTR has
general application. If our assumption is correct
that the COD is low because of the incomplete and
competitive oxidation of protein and O&G, the
constant would apply to any fishery waste having
a similar relative amount of protein and O&G, i.e.,
about 5:1, respectively.

The mean TR and ash data from Table 1 are
used to illustrate the use of this equation: From
Table 1, TR -- ash = 1,431 mg/liter and when
substituted into Equation (1) gives a value of
1,990 mg/liter for CODTR. These values, when sub-
stituted into the equation and solved forX and Y,
give,

X + Y = 0.969(1,431)
1.338X + 2.678y = 1.083(1,990)

where: X — 1,163 mg protein/liter
y = 224 mg O&G/liter.

The calculated values are 29 mg higher for protein
and 12 mg lower for oil than the mean analytical
values of Table 1 (1,134 and 236, respectively).
The differences between data obtained by the
direct analysis for protein and O&G and the two
methods of calculation are compared in Table 4.
A negative or positive sign indicates whether the
calculated value is less or more than the analyti-
cal value.

The analytical values of sample numbers 1,2,3,
and 12 for protein and 2 for O&G are obviously in
error and although these values were included in
the mean values in Table 1, they were omitted
from the regression lines and equations of Figure
2. The comparative data indicate that the calcu-
lated values are in reasonable agreement with
analytical values. Since a regression line deter-
mined by the method of least squares is by defini-
tion the best fit of empirical data containing
normal errors in precision and accuracy, and since
protein and O&G are less accurate analyses than
TRK or COD, it follows that a value for O&G cal-
culated from the simultaneous equation or from
the equation of the regression line should be more
correct than an individually determined value.
The data of Equations (4) and (5) in Table 4 are
merely a measure of the fit of each value to the
regression line. The data of Equation (8), however,
are independent of protein and O&G but depen-
dent upon COD and TR data.

If the simultaneous equation is used to calculate
O&G, TRK and CODTR are required for the equa-
tion and can be obtained through analysis and
calculation, respectively. Alternatively, O&G or

TABLE 4. — Comparison by difference of protein and O&G data
obtained by analysis or by calculation.

Sample
no

Protein mg/litei

O&G mg/liter

Analysis

Eq. (4)

Eq. (8)

Analysis

Eq. (5)

Eq. (8)

831

+ 98

+ 104

185

-24

-39

1,319

+266

+ 265

486

-147

-129

1,215

+ 107

+ 206

276

-9

-101

1,281

-2

+33

258

-2

-32

1.056

+ 13

-1

203

-4

1,075

+34

230

-20

1,212

+ 8

+63

229

+ 11

-42

1.037

-8

-44

195

-7

+25

1,425

-20

-24

302

-12

1,175

-15

+ 1

204

+20

1,025

-24

-22

186

-5

-13

1,116

-61

-102

175

+20

+59

1.188

+ 3

233

-1

-6

925

-12

-35

148

+23

258

COLLINS and TKNNKV: SYSTEM FOR DETERMINING POLLUTANT PARAMETERS

protein can be calculated from the regression of
O&G and protein on TRK. For practical reasons,
we prefer using the simultaneous equation be-
cause establishing the base data would be difficult
at the plant level in that both protein and O&G
should be determined and correlated with COD
and TRK to establish the accuracy of the analyst.
Occasionally, wild values might occur in analy-
ses but the average of the standard deviations
between duplicate analyses for TRK, FRK, CODTR,
and CODFR in this paper was 6.1, 3.6, 14.4, and
10.1 mg/liter, respectively. Using the 6 mg/liter
TRK figure the predicted value for COD from
1,431 ± 12 mg TRK is 1,990 ± 17 mg COD from
Equation (1). Based on this interval of two stan-
dard deviations, protein and O&G values obtained
by the simultaneous equation could vary as
follows:

TRK

CODTR

Protein

O&G

1,419

1,973

1,153

222

1,431

1,990

1,163

224

1,443

2,007

1,172

226

RECOMMENDATION

We recommend that this simplified testing-
calculating system be used by the fishing industry
provided proper regulatory approval is obtained.
The following background data will be required:

1. Determine the regression of CODTR and
CODFR on TRK and FRK and calculate the
equations [i.e., Equations (1), (2), (3)]. Use
grab samples (about 10) to give a good spread
of data.

2. For protein and O&G, either a regression or a
simultaneous equation can be used.

(A) Obtain O&G and protein data on the
same samples as above and determine
the equation of the regressions of protein
and O&G on TRK [i.e., Equations (4)
and (5)].

(B) Determine the ratio or weight of protein
to weight of O&G on several samples
and if between 4.6 and 5.9, the constant
(1.083) in Equation (8) is assumed

valid. If not, the constant must be re-
calculated in order that the CODTR
equals the sum of COD from protein and
O&G [see discussion for Equation (6)|.
(C) The O&G coefficient should be deter-
mined on fishery waste effluents in
which the oil may give a significantly
different value than 2.678.

The routine application of this system would be
as follows:

1. Determine CODFR, TR, and ash by direct
analysis.

2. Subtract ash from TR to give TRK.

3. Substitute into Equations (1) and (2) and solve
for CODTR and FRK.

4. Obtain CODNFR and NFRK by difference or by
Equation (3).

5. Obtain protein and O&G from Equations (4),
(5), or (8).

Thus, three simple and accurate tests give
reportable data on nine parameters which more
completely describe the pollutant load released to
the environment than those currently in use.

LITERATURE CITED

Collins, j.

1976. Oil and grease: A proposed analytical method for
fishery waste effluents. Fish. Bull., U.S. 74:681-683.

Collins, j., and r. d. tenney.

1976. Fishery waste effluents: A method to determine rela-
tionships between chemical oxygen demand and residue.
Fish. Bull., U.S. 74:725-731.
HORWITZ, W. (editor).

1965. Official methods of analysis of the Association of Offi-
cial Agricultural Chemists. 10th ed. Assoc. Off. Agric.
Chem., Wash., D.C., 957 p.
JIRKA, A. M., AND M. J. CARTER.

1975. Micro semi-automated analysis of surface and waste-
waters for chemical oxygen demand. Anal. Chem. 47:
1397-1402.

krzeczkowski, r. a., and f. e. Stone.

1974. Amino acid, fatty acid and proximate composition of
snow crab iChionoecetes bairdi). J. Food Sci. 39:386-388.
MOORE, W. A., AND W. W. WALKER.

1956. Determination of low chemical oxygen demands of
surface waters by dichromate oxidation. Anal. Chem. 28:
164-167.

259

AMERICAN SOLENOCERID SHRIMPS OF THE GENERA

HYMENOPENAEUS, HALIP0R01DES, PLEOTICUS,

HADROPENAEUS NEW GENUS, AND MESOPENAEUS NEW GENUS

Isabel Perez Farfante1

ABSTRACT

Twelve American species, one from Hawaii, are assigned to five genera: five to Hymenopenaeus, one
to Haliporoides , two to Pleoticus, three to Hadropenaeus, and one to Mesopenaeus; the latter two
genera are described herein. Each of the genera is defined and the relationships among them are
discussed. The species are described in detail mostly on the bases of collections made in the western
Atlantic and eastern Pacific during cruises of 29 exploratory vessels. For each species a diagnosis,
illustrations, references, disposition of types, locality records, and geographic as well as bathymetric
ranges are provided. The affinities of each species are indicated, and variations of several morpho-
logical and morphometric characters are analyzed. Keys for the identification of all taxa are given.
Photophores were discovered in Hadropenaeus affinis, here recognized as a distinct species, and
Mesopenaeus tropicalis. The spermatophores of three, Pleoticus robustus, P. muelleri, and M. tropicalis
(those of the latter previously unknown), are described and their mode of attachment to the females
is discussed. The range of Hymenopenaeus debilis was found to extend south of the Gulf of Mexico,
through the Caribbean to Guyana, and that of H. aphoticus to include the Caribbean. Pleoticus
muelleri is now known to occur north of the state of Rio de Janeiro, off Espfrito Santo, and Hadro-
penaeus affinis is newly reported from the southeast Atlantic coast of the United States, where it
ranges as far north as Cape Lookout, N.C.

This work is part of a continuing study of the
systematics and distribution of the American
members of the superfamily Penaeoidea. Exten-
sive collections made during cruises of 26 explora-
tory vessels provided excellent series of specimens
from the western Atlantic. In contrast, the
material available from the tropical and sub-
tropical eastern Pacific (including that obtained
during cruises of three exploratory vessels) is
rather meager and these waters still remain
appallingly unexplored, particularly beyond the
100-m contour. Few benthic collections from the
latter region have been deposited in American
institutions since the expeditions of the Albatross
in 1889 and 1891. The only major ones are those
resulting from the explorations sponsored by the
Allan Hancock Foundation and Scripps Institu-
tion of Oceanography among which no member of
the genera investigated in the present project has
been found.

The only species treated here from waters not
adjacent to the American continent is one which

'Systematics Laboratory, National Marine Fisheries Service,
NOAA, National Museum of Natural History, Washington, DC
20560.

Manuscript accepted November 1976.
FISHERY BULLETIN: VOL. 75, NO. 2, 1977.

ranges throughout the Indo-West Pacific, reach-
ing Hawaii. This shrimp is included because it is
the third member of a new genus, the other two
being found off American shores. Inasmuch as the
Hawaiian population of the species has not been
adequately described and because numerous
specimens from the area are available to me, a
detailed account of its morphology is presented.

The five genera treated in this paper, together
with Solenocera and Haliporus, constitute the
family Solenoceridae, a group that has been pre-
viously considered one of the four subfamilies of
Penaeidae. I am of the opinion that because of the
basic differences among these four suprageneric
groups they should be elevated to the category of
families, i.e., Aristeidae, Solenoceridae, Penaei-
dae, and Sicyoniidae, as has been defended by
Perez Farfante (in press). The western Atlantic
species of Solenocera (the other genus of Soleno-
ceridae which is present in the region, in addition
to four of those discussed here) were recently
monographed by Perez Farfante and Bullis
(1973).

In the diagnoses of the genera and descriptions
of the 12 species discussed here, many morpho-
logical characters have been studied in order to
base relationships at generic and specific levels.

261

FISHERY BULLETIN: VOL. 75, NO. 2

For each taxon a synonymy, bibliographic refer-
ences (selected for the genera, and complete for
the species), location of type-specimens, descrip-
tions, and distributional data are given, as are
variations for some species. Detailed accounts of
the spermatophores (both as attached to the fe-
males and as they appear when removed from the
terminal ampullae of the males) of three species
are also presented. These are the only species for
which spermatophore-bearing females were
secured.

Bate (1881) was the first to describe species of
the generic complex treated here, assigning all
except one — which was assigned to Solenocera
Lucas (1849) — in a new genus, Haliporus. A year
later, Smith (1882) proposed the genus Hymeno-
penaeus for another new species belonging to that
complex. Subsequently, Bate (1888) expanded his
preliminary descriptions of Haliporus and corre-
sponding species, and pointed out that the one he
had placed in Solenocera, together with two
others, should be relegated to a new genus,
Philonicus. After his manuscript was in press, he
discovered that the latter name was preoccupied
and changed it to Pleoticus in the Introduction.
Bouvier ( 1906b) presented a revision of the genus
Haliporus in which he recognized 19 species, most
of which had been described after Bate's last
contribution (1888). He separated them into three
groups on the basis of the relative length of the
posterior two pairs of pereopods, the relative
diameter of the proximal part of the respective
carpi, and the consistency of the integument. He
failed to recognize other important supraspecific
differences which led him to group together
species which are not closely related. Burkenroad
(1936) disagreed with Bouvier's arrangement
and, as a result of an extensive investigation,
recognized two genera, Haliporus and Hymeno-
penaeus. Several other generic names have been
proposed and later synonymized with Hymeno-
penaeus, a clear indication of the taxonomic diffi-
culties presented by this complex.

The genus Hymenopenaeus was defined by
Burkenroad (1936) as those "Solenocerinae with-
out podobranchs behind VIII; with well-developed
prosartema and only a single pair of lateral telson
spines in adult stages, and with cylindrical
filiform antennular flagella." Within it, he recog-
nized four separate groups based on the presence
or absence of branchiostegal or pterygostomian
spines and the arrangement of the epigastric and
rostral teeth.

An examination of Atlantic, eastern Pacific,
and Hawaiian species, supplemented by material
from the Indo-West Pacific region, convinces me
that, in addition to the arrangement of the mid-
dorsal teeth on the carapace, the following charac-
ters are more reliable than the branchiostegal and
pterygostomian spines in ascertaining inter-
relationships of the species previously included in
Hymenopenaeus: shape of the antennular flagella
and rostrum, proportions of the carapace, number
and comparative size of the articles of the man-
dibular palp, presence or absence of certain
carinae on the carapace, relative dimensions of
the posterior two pairs of pereopods, location of the
distolateral spine (terminal or subterminal) of the
lateral ramus of the uropod, structure of the
petasma, and degree of development of the arthro-
branchia on somite VII.

A comparative study based on the characters
cited above indicates that the species under con-
sideration should be assigned to five genera:
Hymenopenaeus , Pleoticus, and Haliporoides —
which had been erected previously — and Hadro-
penaeus and Mesopenaeus — which are proposed
here.

Diagnoses of the four groups established by
Burkenroad (1936) within Hymenopenaeus to-
gether with the conclusions resulting from my
revision of this species-complex follow.

Group I. This division contained the western
Atlantic H. muelleri and H. tropicalis, and the
Indo-West Pacific (Red Sea) H. steindachneri. As
pointed out by Burkenroad, these species share
the arrangement of the epigastric and rostral
teeth, which are separated by regularly decreas-
ing intervals anteriorly, and the absence of
branchiostegal and pterygostomian spines; to
these characters may be added the presence of
orbital spines and the lack of distinct branchio-
cardiac carinae. Several different features occur
in tropicalis which I consider to be of sufficient
importance to justify a separate genus, for which
I propose the name Mesopenaeus. Moreover, the
western Atlantic robustus, which was placed in
Group II by Burkenroad, shares basic characters
with muelleri and steindachneri; consequently,
the three are grouped herein under the available
generic name Pleoticus Bate (1888).

Group II. The species assigned to this group
were characterized by possessing branchiostegal
but lacking pterygostomian spines and, like those
of Group I, exhibit epigastric and rostral teeth
separated by regularly decreasing intervals.

262

PEREZ FAREANTE: AMERICAN SOLENOCERID SHRIMPS

Burkenroad subdivided the group into two sec-
tions: section 1, with orbital spines, to which only
H. robustus was assigned, and section 2, without
orbital spines, to which the western Atlantic H.
modestus and the Indo-West Pacific H. lucasii
were referred. As stated above, the former species
is here transferred to the genus Pleoticus, and
the latter two, together with the amphi-Atlantic
H. affinis (which Burkenroad considered as "very
doubtfully distinct" from//, modestus), are placed
in the genus Hadropenaeus.

Group III. This group comprised the species
with pterygostomian but lacking branchiostegal
spines, and with the epigastric tooth separated
from the rostral teeth by a long interval. The east-
ern Pacific//, diomedeae and the Indo-West Pacif-
ic H. sibogae and H. triarthrus were included, but
these three species are referred here to the genus
Haliporoides Stebbing 1914.

Group IV. This assemblage contained those
species that are armed with branchiostegal
spines, and have the epigastric and first rostral
teeth separated from the remaining rostral teeth
by a conspicuous interval. It was subdivided into
two sections characterized by the presence or
absence of pterygostomian spines. In section 1,
Burkenroad cited Hymenopenaeus laevis, found
on both sides of the Atlantic and in the Indo-West
Pacific, and H. doris and H. nereus of the Ameri-
can Pacific; in section 2, he included the Atlantic
H. aphoticus and H. debilis and the Indo-West
Pacific//, aequalis, H. obliquirostris, H. neptunus,
and H. propinquus. Since the publication of Bur-
kenroad's work, one species, the Indo-West Pacific
H. sewelli, has been added to section 1, and three
have been added to section 2: one from the eastern
Atlantic, H. chacei, and two from the Indo-West
Pacific, H. fattahi, and H. halli. These species
are included in Hymenopenaeus as restricted
here, and their separation into two sections is
recognized.

Burkenroad also discussed under Hymeno-
penaeus the two following Indo-West Pacific
species: Haliporus villosus Alcock and Anderson
1894 (syntype illustrated in Alcock and Anderson
1896), and Haliporus taprobanensis Alcock and
Anderson 1899 (holotype illustrated in Alcock
1899b). He indicated that the former perhaps
would merit being placed in an independent
group, and pointed out that although the latter
shares several characters with members of Group
III, it differs from them in other basic features.
Our knowledge of//, villosus prior to Kensley's

(1968) study was limited to the brief description
by Alcock and Anderson (1894) and their illustra-
tion published in 1896 (plate 26, figure 1). The
lack of detail in the figure of the telson, exhibiting
no movable spines, was probably responsible for
Burkenroad's assigning this shrimp to the genus
Hymenopenaeus. Kensley presented a detailed
description and several illustrations which dem-
onstrate that this species exhibits two basic fea-
tures characteristic of the genus Haliporus (as
restricted by Burkenroad 1936): in addition to the
podobranchia on the second maxilliped, another,
small one is present on the third maxilliped, and
the telson is armed with movable spines situated
anterior to the fixed pair. My examination of two
specimens of//, taprobanensis has shown that the
same characters are present in them; thus, in
respect to these two features, both this species and
H. villosus are more closely allied to the members
of Haliporus than to those assigned to Hymeno-
penaeus. It should be pointed out, however, that
H. villosus and H. taprobanensis differ from Hali-
porus curvirostris Bate 1881, the type-species, in
several characters (e.g., shape of rostrum, number
of podobranchiae posterior to the second maxilli-
ped, carinae present on the carapace) which seem
to me to be of supraspecific significance. Conse-
quently, I believe that a study of adequate mate-
rial might demonstrate that they should be rele-
gated to separate monotypic genera.

Although the illustration of the entire animal
of//, villosus by Alcock and Anderson (1896) and
that by Kensley (1968) leave little doubt that both
correspond to the same species, the specimens
available to the former authors were densely
covered by setae, as they explicitly stated, where-
as that studied by Kensley as well as the speci-
mens examined by me are glabrous. The mate-
rial available to Alcock and Anderson was from
the Laccadive Sea, off southwest India; Kensley's
specimen was caught off southwest of South
Africa, and the two at my disposal were collected
off eastern Madagascar.

All five genera (together with Haliporus and
Solenocera) are believed to have arisen from a
common solenoceroid ancestor, some of the char-
acters of which are presented in the accompany-
ing dendrogram. In the latter only the newly
acquired characters or those modified or lost in
each lineage are indicated. As shown in the
dendrogram, one of the lines arising from the
solenoceroid ancestor led to Haliporus, apparently
not only the most primitive solenocerid, but

263

FISHERY BULLETIN: VOL. 75, NO. 2

CHARACTERISTICS INVOLVED IN THE EVOLUTION OF SOLENOCERIDAE
(See text for explanation)

Hadropenaeus

Antennular flagella usually sub-
cylindrical, occasionally ven-
tral one depressed

Fifth pereopod flagelliform and
considerably longer than fourth

Petasma with ventral costa free
from heavily sclerotized termi-
nal part of ventrolateral lobule

Haliportndes

Integument firm

Epigastric tooth separated from rostral

teeth
Posthepatic carina absent
Fourth and fifth pereopods relatively

stout proximally, moderately long

Mesopen aeus

Antennular flagella dissimilar,

dorsal subcylindrical , ventral

depressed
Fourth and fifth pereopods stout

proximally, fifth moderately

longer than fourth
Petasma with ventral costa fused

to flexible terminal part of

ventrolateral lobule

Carapace proportionately short
Rostrum deep, with ventral margin

convex
Submarginal carina absent

Hymenopenaeus

Integument thin, flexible

Epigastric and first rostral teeth widely

separated from remaining rostral teeth
Posthepatic carina present
Fourth and fifth pereopods flagelliform,

very long

Solenocera

Antennular flagella strongly flattened,
ventral pair forming trough, four
together constituting respiratory
siphon

Petasma with dorsolateral lobule
bearing terminal process

Lateral ramus of uropod lacking
distolateral spine

Pleoticus

Submarginal carina sharp

Petasma with ventral costa free from
flexible terminal part of ventro-
lateral lobule

Petasma with distal part of ventral costa
fused to adjacent flexible portion of
ventrolateral lobule

Branchiocardiac carina lacking

Fourth and fifth pereopods rather stout

proximally, fifth moderately longer

than fourth

Telson with single pair of fixed

lateral spines only
Podobranchia on second maxilliped only

Solenoceroid ancestor-

Haliporus

Telson with pairs of movable spines

anterior to fixed pair
Podobranchia on at least second and

third maxillipeds

Carapace elongate

Rostrum low

Epigastric and rostral teeth separated by

intervals regularly decreasing anteriorly
Postorbital spine present

Branchiocardiac and submarginal carinae present
Lateral ramus of uropod bearing distolateral

spine
Antennular flagella similar, subcylindrical
Podobranchiae on appendages posterior to

second maxilliped
Petasma lacking terminal process

according to Burkenroad (1963b) "the Recent
Peneid which seems in several respects the near-
est of these to the stem-form of the relatively
primitive suborder Dendrobranchiata." A second
line gave rise to Hymenopenaeus and Haliporoi-
des, and a third lineage is believed to have been
ancestral to two stocks, one of which terminated
in Pleoticus and from the other evolved Hadro-

penaeus, Mesopenaeus, and Solenocera; the latter
appears to be the most specialized of all seven
genera.

The members of Solenoceridae, in general, oc-
cupy deep water beyond the continental and in-
sular shelves; however, most of the species of
Solenocera as well as Pleoticus muelleri are re-
stricted to shallow water. Mesopenaeus tropicalis

264

PEREZ KARFANTE: AMERICAN SOLKNOCKRID SHRIMPS

is found both on the shelves, at a minimum depth
of 30 m, and on the slopes to about 500 m.

Material

Abbreviations of the repositories of the speci-
mens examined during this study follow:

AMNH American Museum of Natural His-

tory, New York, N.Y.

BMNH British Museum (Natural History),

London.

IOUSP Instituto Oceanografico, Universi-

dad de Sao Paulo, Sao Paulo.

MCIP Ministerio de Comercio e Industrias,

Panama.

MCZ Museum of Comparative Zoology,

Harvard University, Cambridge,
Mass.

MP Museum National d'Histoire Natu-

relle, Paris.

RMNH Rijksmuseum van Natuurlijke His-

toire, Leiden, Netherlands.

TAMU Texas A&M University, College Sta-

tion, Tex.

UMML Rosenstiel School of Marine and At-

mospheric Sciences, University of
Miami, Fla.

UNC-IMS University of North Carolina - Insti-
tute of Marine Sciences, Morehead
City, N.C.

USNM National Museum of Natural His-

tory, Smithsonian Institution,
Washington, D.C.

YPM Peabody Museum of Natural His-

tory, Yale University, New
Haven, Conn.

Presentation of Data

The measurement of carapace length (cl) is the
linear distance between the orbital margin and
the midposterior margin of the carapace, and that
of total length (tl) is the distance between the
apex of the rostrum and the posterior end of the
telson. The scales accompanying the illustrations
are in millimeters. Figures 1 and 2 depict many
characters used in the descriptions. For the ter-
minology employed in the accounts of the sperma-
tophores, see Perez Farfante (1975).

Key to Genera of Solenoceridae

1. Telson with pairs of movable lateral

spines anterior to fixed pair; podo-
branchia on at least second and third

maxillipeds Haliporus

Telson with single pair of fixed lateral
spines only; podobranchia restricted to
second maxilliped 2

2. Dorsal and ventral antennular flagella

lamellate; lateral ramus of uropod lack-
ing distolateral spine Solenocera

Dorsal antennular fiagellum subcylin-
drical, ventral subcylindrical or flat-
tened; lateral ramus of uropod armed
with distolateral spine 3

tubercle

postrostral carina

epigastric tooth

rostral teeth.

adrostral carina

orbital spine
postorbltal spine

orbito-antennal sulcus- ^>antennal spine

hepatic spine

-^branchiostegal spine

pterygostomian spine

submargmal carina
FIGURE 1. — Diagrammatic lateral view of cephalothorax showing terms used in descriptions of solenocerid shrimps.

265

3. Ventral antennular flagellum conspicu-

ously depressed, orbital spine pres-
ent Mesopenaeus

Ventral antennular flagellum subcylin-
drical, occasionally depressed, if so or-
bital spine lacking 4

4. Epigastric tooth separated from first

rostral by interval not conspicuously
smaller or greater than that between

first and second rostral teeth 5

Epigastric or epigastric and first rostral
teeth separated from remaining teeth
by relatively long interval 6

5. Rostrum low, with ventral margin

straight or concave; submarginal ca-
rina present Plcoticus

Rostrum deep, with ventral margin pro-
nouncedly convex; submarginal carina
absent Madropenaeus

6. Epigastric and first rostral teeth sepa-

rated from remaining ones by long in-
terval; suprahepatic spine absent ....

Hymenopenaeus

Epigastric tooth separated from rostral
teeth by long interval; suprahepatic
spine present Ualiporoides

Hymenopenaeus Smith 1882

Haliporus Bate 1881:185 [part, excluding Hali-
porus curvirostris Bate 1881]. Bate 1888:284
[part]. Faxon 1893:213 [part]; 1895:189 [part].
Alcock 1901:22 [part]. Bouvier 1906b: 1 [part];
1908:78 [part]. A. Milne Edwards and Bouvier
1909:206 [part], de Man 1911:31 [part]. Fowler
1912:542 [part].

Hymenopenaeus Smith 1882:91 [type-species by
monotypy, Hymenopenaeus debilis Smith 1882.
Gender, masculine. Placed on the Official List
of Generic Names in Zoology as Name No. 1816,
International Commission on Zoological No-
menclature (1969), Opinion 864]. Smith 1885:
179 [part]. Burkenroad 1936:102 [part]. Kubo
1949:212 [part]. Holthuis 1962:108. Inter-
national Commission on Zoological Nomen-
clature 1969:139. Roberts and Pequegnat 1970:
29 [part].

Diagnosis. -Body slender, carapace elongate,
integument thin, flexible. Rostrum variable in

FISHERY BULLETIN: VOL. 75, NO. 2
lateral process-
mesial
process

ventrolateral
lobule

dorsolate ra I
lobule

vent romed la n
lobule

ventral costa

cincinnul i

dorsomedian

lobule

FIGURE 2. — Left half of petasma (dorsal view) of Hymeno-
penaeus debilis showing terms used in descriptions.

length, reaching between distal 0.25 of first anten-
nular article and end of peduncle; ventral margin
straight; usually armed only with dorsal teeth,
occasionally also with ventral teeth; epigastric
and first rostral teeth separated from remaining
teeth by relatively long interval. Orbital spine
absent; postorbital, antennal, hepatic, and
branchiostegal spines present; pterygostomian
spine present or absent. Cervical sulcus deep,
long, extending to, but not across, middorsum of
carapace; hepatic sulcus well marked; branchio-
cardiac carina sharp, accompanying sulcus deep;
posthepatic and submarginal carinae present. Ab-
domen carinate dorsally at least along posterior
three somites. Prosartema moderately long, flex-
ible. Telson with pair of conspicuous fixed, lateral
spines. Antennular flagella similar, filiform, and
longer than carapace. Mandibular palp two-
jointed, articles relatively narrow, distal one
much shorter than basal, and tapering to blunt
apex. First maxilla with unsegmented palp
(endite of basis), gently narrowing to rounded
apex. Fourth and fifth pereopods extremely long
and flagelliform. First pereopod with spine on

266

PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMI'S

basis and usually on ischium. Exopods on all max-
illipeds and pereopods. Lateral ramus of uropod
armed with distolateral spine, reaching distal
margin of lamella (terminal spine). In males,
petasma with distal part of ventral costa fused to
flexible flap of ventrolateral lobule; distal end of
rib of dorsolateral lobule elevated above adjacent
area and not projecting beyond distal margin;
ventromedian lobule usually produced in con-
spicuous processes distally; endopod of second
pleopod bearing appendices masculina and in-
terna, and with basal sclerite produced distally
into elongate, ventrolateral ("posterior") spur.
Thelycum of open type, lacking enclosed seminal
receptacle. Pleurobranchia present on somites IX
to XIV; rudimentary arthrobranchia on somite
VII, and anterior and posterior arthrobranchiae
on somites VIII to XIII. Podobranchia present on
second maxilliped, and epipod on second maxilli-
ped (and on first if proximal exite of coxa consid-
ered an epipod) through fourth pereopod.

List of species-Following are the species listed
in each of the two sections proposed by Burken-
road (1936), a division with which I am in full
agreement-
Section 1. Pterygostomian spine present.
Atlantic, Indo-West Pacific: Hymenopenaeus
laeuis (Bate 1881). Indo-West Pacific: Hy-
menopenaeus sewelli Ramadan 1938. East-
ern Pacific: Hymenopenaeus doris (Faxon
1893); Hymenopenaeus nereus (Faxon 1893).

Section 2. Pterygostomian spine absent.
Atlantic: Hymenopenaeus aphoticus Burken-
road 1936; Hymenopenaeus debilis Smith
1882; Hymenopenaeus chacei Crosnier and
Forest 1969. Indo-West Pacific: Hymeno-
penaeus aequalis (Bate 1881); Hymenope-
naeus fattahi Ramadan 1938; Hymenope-
naeus halli Bruce 1966; Hymenopenaeus
neptunus (Bate 1888); Hymenopenaeus obli-
quirostris (Bate 1881); Hymenopenaeus pro-
pinquus (de Man 1907).

Affinities. -The members of the genus Hymeno-
penaeus differ from those of the closely related
Haliporoides, Pleoticus, Hadropenaeus n. gen.,
and Mesopenaeus n. gen., in having a more slen-
der body; a thin, flexible, almost membranous in-
tegument; the epigastric and first rostral teeth
separated from the remaining teeth by an interval
longer than the spaces between the more anterior

teeth; and in possessing a posthepatic carina.
They also differ from those of the other genera
in having a slender mandibular palp in which the
distal article is much shorter than the basal; ex-
tremely long and flagelliform fourth and fifth
pairs of pereopods, and in certain features of the
petasma: the terminal part of the ventrolateral
lobule forms a flap to which the ventral costa is
fused, the rib of the dorsolateral lobule is elevated
distally from the surrounding area, and the
ventromedian lobule is produced distally into con-
spicuous processes.

Remarks.-ln the widely utilized work of Kubo
(1949) several statements are made which should
be discussed. Kubo based his description of the
genus Hymenopenaeus primarily on two species
found in Japanese waters [H. lucasii (Bate 1881)
and H. aequalis (Bate 1888)], which led him to
make erroneous generalizations. First, he consid-
ered the presence of two, instead of one, arthro-
branchiae on somite VII as a character typical of
Solenocera, and in his key to the genera of the
subfamily Solenocerinae utilized this character to
distinguish it from other genera in the subfamily.
In at least one species {Pleoticus robustus, pre-
viously included in Hymenopenaeus) , of a genus
other than Solenocera, however, I find that there
are two arthrobranchiae on somite VII. Secondly,
Kubo noted that the petasma in "Hymenopenaeus"
possessed spinules along the distal margin; actu-
ally, in some species they are absent. Finally, in
the section "Arrangement of branchiae" Kubo indi-
cated the restriction of podobranchia to somite VIII
(on second maxilliped) in the members of the sub-
family Solenocerinae, and in his table 6D he noted
the presence of only one podobranchia in Hymeno-
penaeus and Parahaliporus (=Haliporoides).
In the key to the genera of the subfamily, how-
ever, he utilized the occurrence of a rudimentary
podobranchia on somites IX and X as the only
feature to distinguish Hymenopenaeus from Hali-
porus and Parahaliporus. He used this feature in
the key although in the following description of
the genus Hymenopenaeus, he stated that in the
specimens of H. lucasii and H. aequalis at his
disposal, the epipods of none of the thoracic ap-
pendages behind the second maxilliped are fur-
nished with podobranchia. It thus seems that in
the key the line corresponding to Hymenopenaeus
and the line corresponding to Parahaliporus and
Haliporus were transposed; however, podobran-
chiae are present behind somite VIII in Haliporus

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FISHERY BULLETIN: VOL. 75, NO. 2

(at least on the third maxilliped and as far as the
third pereopod) but not in Parahaliporus.

Key to Species of Hymenopenaeus
in American Waters

1. Pterygostomian spine present (section 1) . .2
Pterygostomian spine absent (section 2) . . .4

2. Scaphocerite, at most, barely over-

reaching antennular peduncle. Ros-
trum, in adult, falling short of distal end
of first article of antennular peduncle.
Females with pyramidal, median protu-
berance on sternite XIV projecting ven-
trally. Males with ventromedian lobule
of petasma bearing two or three small
triangular processes distomesially ....

H. laevis

Scaphocerite overreaching antennular
peduncle by, at least, 0.25 of its own
length. Rostrum, in adult, surpassing
distal end of first antennular article 3

3. Females lacking median protuberance

on sternite XIV. Males with petasma
bearing subrectangular distomesial
process projecting at right angle to
mesial margin, and armed with long

spines H. nereus

Females with subpyramidal median pro-
tuberance on sternite XIV projecting
anteroventrally. Males unknown . Ji. doris

4. Eye with cornea hemispherical and dis-

posed such that imaginary line extend-
ing from mesial tubercle parallel to
basal margin of ocular peduncle inter-
sects lateral border of latter far prox-
imal to proximolateral extremity of

cornea H. aphoticus

Eye with cornea subreniform and dis-
posed such that line extending from
mesial tubercle parallel to basal margin
of ocular peduncle intersects postero-
lateral extremity of cornea H. debilis

Hymenopenaeus debilis Smith 1882

Figures 2, 3, 4B, 5-9

Hymenopenaeus debilis Smith 1882:91, pi. 15, fig.
6-11, pi. 16, fig. 1-3 [syntypes: 1 9, SE of Savan-

nah Beach, Ga., 31°57'00"N, 78°18'35"W, 333
fm (609 m), 12 July 1880, Blake stn 317. 1 9,
MCZ 3270, SE of Cape Fear, N.C., 33°19'00"N,
76°12'30"W, 457 fm (836 m), 14 July 1880, Blake
stn 323. 1 9,USNM4920,EofCapeFear,N.C,
33°42'15"N, 76°00'50"W, 464 fm (849 m), 14
July 1880, Blake stn 326]. Smith 1887:687, pi.
16, fig. 7. Burkenroad 1936:111, fig. 63-64.
Yokoya 1941:52. Anderson and Lindner 1945:
289. Harvey 1952:352. Ramadan 1952:9, fig. 22-
23. Springer and Bullis 1956:7. Holthuis 1962:
108. Boschi 1964:38. Bullis and Thompson
1965:5. Zariquiey Alvarez 1968:47, fig. 24b.
Crosnier and Forest 1969:545. International
Commission on Zoological Nomenclature 1969:
139. Roberts and Pequegnat 1970:31. Pequeg-
nat and Roberts 1971:8. Crosnier and Forest
1973:269, fig. 85 c-d, 87b, 89a.

Haliporus debilis. Faxon 1896:163. Bouvier
1905a:980; 1906a:253; 1906b:3; 1908:83, pi. 1,
fig. 6, pi. 14, fig. 9-18. A. Milne Edwards and
Bouvier 1909:206, pi. 2, fig. 8. de Man 1911:7.
Fowler 1912:543. Boone 1927:78. Maurin 1961:
530; 1968:484. Vilela 1970:122.

Haliporus debilis var. africanus Bouvier 1908:83
[syntypes: 4 6 3 9 , MP, off Mazaghan, 33°46'N,
9°02'W, 1,319 m, 14 June 1883, Talisman
stn 21].

Material

UNITED STATES— New Jersey: 1 9, USNM, Hudson
Canyon, 550-600 m, 17 August 1972, Gosnold stn 123. 1 8,
USNM, off Barnegat Inlet, 768 m, 3 August 1884, Albatross stn
2187. 1 8 , USNM, N of Little Egg Inlet, 984 m, 19 August 1884,
Albatross stn 2201. North Carolina: 6 8 6 9, UNC-IMS, E of
Cape Fear, 495-490 m, 29 July 1970,Eastward 19 stn 14954. 1 9
syntype, USNM 4920, E of Cape Fear, 849 m, 14 July 1880,
Blake stn 326. 1 9 syntype, MCZ 3270, SE of Cape Fear, 836 m,
14 July 1880, Blake stn 323. 5^49, USNM, SE of Cape Fear,
744 m, 6 May 1886, Albatross stn 2676. Georgia: 1 9 , USNM,
off St Catherines I, 814 m, 25 June 1961, Atlantis stn A-266-2.
Florida: 4 9 , USNM, NE of Cape Kennedy, 922 m, 3 May 1886,
Albatross stn 2660. 6 8 , USNM, NE of Cape Kennedy, 931 m, 3
May 1886, Albatross stn 2659. 3 9 , USNM, SE of Key West, 558-
514 m, 29 August 1967, Gerda stn 861. 1 9, USNM, off St
Petersburg, 465 m, 29 September 1951, Oregon stn 489. 1 9,
USNM, off Destin, 512 m, 14 March 1885, Albatross stn 2397.
1 8 1 9, TAMU, off Santa Rosa I, 565 m, 4 August 1968, Ala-
minos stn 68A7-10A. 1 9, TAMU, off Gulf Beach, 1,061 m,
7 August 1968, Alaminos stn 68A7-13A. Alabama: 2 9,
USNM, off Orange Beach, 585 m, 13 August 1970, Oregon II stn
11146. 1 8 5 9, USNM, S of Mobile Bay, 366 m, 18 December
1962, Oregon stn 4151. Louisiana: 1 8 1 9, USNM, E of Missis-
sippi Delta, 439-448 m, 17 July 1960, Oregon stn 2825. 1 9,
USNM, E of Southeast Pass, Mississippi Delta, 626 m, 1 1 Febru-
ary 1885, Albatross stn 2376. 3 9 , TAMU, off Garden I Bay, Mis-

268

PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMPS

sissippi Delta, 476 m, 15 October 1969, Alaminos stn 69A13-40.
1 o* 7 9, USNM, E of Mississippi Delta, 457 m, 10 June 1959,
Silver Bay stn 1203. 1 6 1 9, MCZ, SE of Mississippi Delta, 587
m, 1878, B/a&e stn 47. 28 6 121 9 HOjuv and larvae, YPM,S of
Grand Terre Is, 302 m, 26 March 1936, Atlantis stn 2381. 1 9 ,
YPM, S of Grand Isle, 356 m [in Atlantis log 300 fm, 549 m], 23
March 1937, Atlantis stn 2831. 6 6 11 9, USNM, SW of Ship
Shoal Lighthouse, 549 m, 23 February 1964, Oregon stn 4709.
Texas: 1 9, TAMU, off Port Aransas, 476 m, 19-20 November
1968, Alaminos stn 68A13-22. 2 9, USNM, off Padre I, 585-658
m, 20 July-6 August 1969, Western Gulf stn 35. 19, USNM, off
Padre I, 501 m, 21 March 1969, Oregon II stn 10456.

MEXICO— Tamaulipas: 1 9, TAMU, SW of Matamoros,
713 m [according to label], 12 November 1968, Alaminos stn
68A13-3. 1 9, TAMU, SW of Matamoros, 878 m, 12 November
1968, Alaminos stn 68A13-1. Quintana Roo: 2 9 , USNM, off
Cabo Catoche, 585 m, 13 August 1970, Oregon II stn 11146.

BAHAMA ISLANDS— 1 9 , RMNH, NW of Matanilla Reef,
662-702 m, 18 July 1965, Gerda stn 671. 2 6 5 9 , RMNH, NW of
Great Stirrup Cay, 733-897 m, 4 July 1963, Gerda stn 190. 1 8,
USNM, off Dog Rocks, Cay Sal Bank, 618 m, 22 June 1967,
Gerda stn 815.

GREATER ANTILLES— 1 6 4 9 , USNM, N of Puerto
Rico, 732-658 m, 30 January 1933, Johnson-Smithsonian Deep-

SeaExp.,stnl. 1 9 , USNM, N of Puerto Rico, 476 m, 4 February
1933, Johnson-Smithsonian Deep-Sea Exp., stn 23. 1 6, USNM,
N of Puerto Rico, 512 m, 4 February 1933, Johnson-Smithsonian
Deep-Sea Exp., stn 24. 19, RMNH, SW of Navassa I, Jamaica
Channel, 1,034 m, 2 July 1970, Pillsbury stn 1187.

LESSER ANTILLES— 1(5 5 9, USNM, SW of Sombrero I,
664-704 m, 23 July 1969, Pillsbury stn 989. 1 6 2 9, USNM, off
Dog I, 688 m, 6 December 1969, Oregon II stn 10834. 1 9,
USNM, W of Dog I, 658 m, 10 December 1969, Oregon II stn
10847. 5 9 , USNM, W of Saba Bank, 786 m, 3 December 1969,
Oregonll stn 10833. 1 6 3 9 , USNM, E of Standfast Pt, Antigua,
786-1,125 m, 18 July 1969, Pillsbury stn 954. 2 9, USNM,
Guadeloupe Passage, 738-832 m, 17 July \969,Pillsbury stn 946.
1 9 , USNM, off Point du Nord, Marie Galante I, 704-732 m,
12 July 1969, Pillsbury stn 919. 3 6 14 9, USNM, E of
Capesterre, Guadeloupe I, 549-686 m, 14 July 1969, Pillsbury
stn 923. 8 9, USNM, off Dominica I, 808 m, 5 March 1966,
Oregon stn 5930. 2 9 , USNM, off Dominica I, 607 m, 4 March
1966, Oregon stn 5927. 2 6 3 9 , USNM, off Vieux Fort, St Lucia,
417-589 m, 9 July 1969, Pillsbury stn 904. 2 6, USNM, NE of
Soufriere, St Vincent, 576-842 m, 6 July 1969, Pillsbury stn 881.

BELIZE— 2 J49, YPM, N of Glover Reef, 885 m, 20 March
1925, Pawnee.

NICARAGUA— 5 5 , USNM, off Punta de Perlas, 613 m, 22
November 1968, Oregon II stn 10207.

FIGURE 3. — Hymenopenaeus debilis, 8 8.5 mm cl, south of
Grand Terre Islands, La. Lateral view.

269

FISHERY BULLETIN: VOL. 75, NO. 2

PANAMA— 1 2 , RMNH, Golfo de los Mosquitos, 664-681 m,
21 July 1966, Pillsbury stn 447.

COLOMBIA— 1 9 , USNM, Golfo del Darien, 731 m, 28 May
1964, Oregon stn 4902.

VENEZUELA— 1 9, USNM, E of San Juan de los Cayos,
421 m, 9 October 1963, Oregon stn 4439.

GUYANA— 1 9, USNM, N of Fort York, 1,373-1,446 m,
15 July 1968, Pillsbury stn 689.

AZORES ISLANDS— 1 9, MP, between Pico and Sao
Jorge, 1,257 m, 15 August 1883, Talisman stn 139.

MOROCCO — 4 d39 syntypes of Haliporus debilis var.
africanus Bouvier, MP, off Mazaghan, 1,319 m, 14 June 1883,
Talisman stn 21. 1 6 9 9 , MP, off Cap Cantin, 1,590 m, 17 June
1883, Talisman stn 33.

Description-Body slender, integument thin,

flexible and glabrous (Figure 3). Rostrum straight

or slightly to strongly upturned, moderately long,

reaching as far as distal end of second antennular

article, its length not greater than 0.55 that of

carapace, low and with dorsal and ventral mar-

8-11
gins straight. Rostral plus epigastric teeth Q.4

9-10
(usually ~~2 , only 3% lacking ventral teeth);

epigastric tooth located at about 0.4 cl from orbital
margin, first rostral tooth (largest of all) at about
0.3 cl, and third above orbital margin; ventral
teeth variously arranged, either closely grouped
together or rather broadly spaced. Adrostral ca-
rina low and sharp, extending from orbital margin
almost to apex of rostrum; orbital margin project-
ing anteroventrally in narrow shelf. Postrostral
carina strong to just caudal to cervical sulcus,
weak posteriorly, and followed by minute dorsal
tubercle very near margin of carapace. Lateral

spines on carapace slender and sharp: postorbital
spine situated directly posterior to antennal and
almost as long as branchiostegal; latter (largest of
all) continuous with short, sharp basal carina;
pterygostomian spine absent. Cervical carina
sharp, cervical sulcus deep, extending to, but not
crossing, postrostral carina, its dorsal extremity
located at 0.55 cl from orbital margin, or slightly
more posteriorly; hepatic sulcus with two ventral
convexities, extending from below hepatic spine
to anterior end of branchiocardiac sulcus; weak
posthepatic carina extending posteriorly from
junction of latter sulci. Branchiocardiac carina
strong, accompanying sulcus moderately deep;
submarginal carina slender, extending along
entire length of branchiostegite.

Eye (Figure 4B) with basal article produced
mesially into small scale. Cornea broad, its great-
est diameter approximately twice that of base of
ocular peduncle (1.6-2.1, x 1.95; N = 32), and pro-
portion of diameter to carapace length varying
between 15.5 and 23.0, x 19.7. Cornea subreni-
form, with proximal margin oblique, slanting
posterolaterally; an imaginary line drawn paral-
lel to base of short ocular peduncle at level of its
mesial tubercle intersects cornea.

Antennular peduncle length equivalent to
about 0.55 that of carapace; prosartema short, not
quite reaching distomesial margin of cornea, fall-
ing short of distal margin of first antennular arti-
cle, but its long distal setae overlapping base of
second article; stylocerite rather short, its length
about 0.6 of distance between its proximal extrem-

FlGURE 4. — Eyes. A, Hymenopenaeus laevis, 9 21 mm cl, off Martha's Vineyard, Mass. B, Hymenopenaeus
debilis, 6 10.5 mm cl, northwest of Great Stirrup Cay, Bahama Islands. C, Hymenopenaeus aphoticus, V 18mmcl,
northwest of Penfnsula de la Guajira, Colombia.

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PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMPS

FIGURE 5. — Hymenopenaeus debilis, 9 19.5 mm cl, off Cape Kennedy, Fla. A, Mandible. B, First maxilla. C, Second maxilla.
D, First maxilliped. E, Second maxilliped. f, Rudimentary arthrobranchia. f1, Enlargement of /"(all from left side).

ity and mesial base of distolateral spine; latter
long, slender, and sharp. Antennular flagella very
long and considerably unequal in length, ventral
2.15 and dorsal 7.5 times carapace length in
shrimp 7 mm cl, and 1.7 and 5.5 times, respec-
tively, in shrimp 10 mm cl. Scaphocerite over-
reaching antennular peduncle by as much as 0.25
of its own length; lateral rib ending in slender
spine, falling short to slightly surpassing distal
margin of lamella. Antennal flagellum incom-
plete in all specimens examined; however, in one
individual about 35 mm tl, antennal length 155
mm, thus not less than 4.4 times total length of
shrimp.

Mandibular palp (Figure 5A ) reaching to about
level of distal 0.2 of carpocerite; proximal article

2.4 times as long as wide; distal article consider-
ably shorter and narrower than proximal, and
tapering to blunt tip. First and second maxillae,
and first and second maxillipeds as illustrated
(Figure 5B-E, virtually identical throughout
genus); somite VII bearing rudimentary arthro-
branchia at base of first maxilliped ( Figure bDf-p-).
Third maxilliped overreaching antennular pedun-
cle by length of dactyl and propodus; length of
dactyl about 0.7 that of propodus.

First pereopod, stoutest of five, reaching distal
end of carpocerite or surpassing it by as much as
length of dactyl. Second pereopod overreaching
antennular peduncle by at least half length of
dactyl or by entire propodus. Third pereopod ex-
ceeding antennular peduncle by length of dactyl,

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FISHERY BULLETIN: VOL. 75, NO. 2

propodus, and as much as 0.4 that of carpus.
Fourth pereopod reaching beyond antennular pe-
duncle by length of last three podomeres. Fifth
pereopod exceeding antennular peduncle by
length of last three podomeres or by latter and
as much as 0.1 length of merus. Pereopods increas-
ing in length from first to fifth. First pereopod
with rather inconspicuous spine on basis, and
either slender spine or no spine on ischium; second
pereopod with small spine on basis. In female,
coxa of third pereopod produced into large sub-
trapezoidal plate directed mesially, and bearing
minute anteromesial spine in juveniles. In both
sexes spine present on anteromesial corner of coxa
of fifth pereopod, considerably stronger in males
than in females, spine minute in latter and borne
on rounded coxal plate.

Abdomen with middorsal carina from fourth
through sixth somites, posterodorsal margin of
fourth and fifth with short median incision; sixth
somite about 1.8 times as long as high, bearing
small, sharp spine at posterior end of carina, and
pair of minute spines posteroventrally. Telson
with rather shallow median sulcus practically dis-
appearing before reaching level of base of lateral
spines; sulcus flanked by ridges, blunt anteriorly,
sharp and slender posteriorly; terminal portion
length 5-6 times basal width; lateral spines length
1.5-2.0 times basal width of terminal portion.
Mesial ramus of uropod falling short of apex of
telson or slightly overreaching it; lateral ramus

overreaching mesial ramus by as much as 0.25 of
its own length, and armed with slender, disto-
lateral spine, reaching as far as contiguous
margin of ramus.

Petasma (Figures 2, 6A, B) with row of cincin-
nuli (hooklike structures along mesial margin of
median lobes of petasma that serve to interlock
its two halves) occupying only proximal 0.3 of
median line, and entire terminal margin armed
with spines; ventromedian lobule deeply cleft dis-
tally forming two elongate processes: mesial one
subspatulate and armed with rather conspicuous
spines mesially and minute ones distolaterally;
lateral process subelliptical, raised inwardly in
elongate prominence, and produced proximally in
small auricular process lacking spinules; distal
flap of ventrolateral lobule extending only to
basal portion of lateral process, and turned
strongly outward; ventral costa forming low prom-
inence at base of, and imperceptibly merging
with, flap.

Appendix masculina (Figure 6C, D) elevated in
sharp mesial ridge and with proximal part pro-
duced laterally into rounded, flattened lobe; distal
part narrowing and bearing lateral row of setae
terminating in apical tuft of longer ones. Appen-
dix interna elongate ovate, extending almost as
far as appendix masculina, and also armed with
apical tuft of setae. Ventrolateral spur of basal
sclerite long, its length 0.7-0.8 that of appendix
masculina.

FIGURE 6. — Hymenopenaeus debilis, 6 13 mm cl, off Cape Kennedy, Fla. A, Petasma, dorsolateral view of left half.
B, Ventral view. C, Right appendices masculina and interna, dorsolateral view. D, Ventral view.

272

PEREZ EARFANTE: AMERICAN SOLENOCERID SHRIMPS

FIGURE 7. — Hymenopenaeus debilis, 9 15.5 mm cl, Dominica
Island, Lesser Antilles. Thelycum, ventral view.

Thelycum (Figure 7) with median protuberance
on sternite XIV pyriform, strongly produced
anteriorly into acute, freely projecting apical
portion overlapping, and closely appressed to,
sternite XIII; latter bearing paired subtriangular
elevations with bases raised in horizontal ridges
flanking tip of protuberance on sternite XIV;
anterior part of sternite XIII with setose trans-
verse prominence; sternite XII bearing pair of
large, setose, posterolateral horns reaching or
slightly surpassing midlength of sternite XIII.

Photophores.-Six present on sternum: pair in
elevated posterior margin of sternite XIII, just
mesial to coxae of fourth pereopods; pair between
second pleopods; single one between bases of
fourth pereopods, and another between bases of
fifth pleopods. Details of their structure given by
Burkenroad (1936).

Co/or.-Bouvier (1908) on the basis of a water
color illustration made at the moment of capture
stated that the color is "d'un rouge-orange presque
uniform." Burkenroad (1936) described fresh
material as "transparent, speckled with minute
scarlet chromatophores which were concentrated

at the bases of the pleopods and uropods and at the
tip of the telson. The ocular peduncle at the base of
the cornea, the mouthparts, and the tip of the
second maxillipede were scarlet. The stomach was
red, the pleonic gut and nerve-cord orange; the
gastric gland brownish, the ovary creamy (as seen
through the overlying tissues). The eyes were
reddish brown."

Maximum size-Males, 55 mm tl; females, 78 mm
tl (Bouvier 1908). Largest specimens examined by
me: males 15.5 mm cl, 52 mm tl; females, 19.5 mm
cl, 75 mm tl.

Geographic and bathymetric ranges-Western
Atlantic: from Hudson Canyon, New Jersey
(39°55'N, 70°31'W) through the Gulf of Mexico
and Caribbean Sea to Guyana (08°14'N, 57°38'W).
Eastern Atlantic: Azores Islands and northwest
Africa — from Cap Spartel, Morocco, to Cape
Verde Islands, including Canary Islands (Figure
8). It has been found at depths (Figure 9) between
300 and 2,163 m (latter in Bouvier 1908).

Affinities -Hymenopenaeus debilis closely resem-
bles H. aphoticus, but differs from it in that the
rostrum is usually armed with ventral teeth (only
3% of the specimens examined by me lack such
teeth), and the sternum bears six photophores
which are absent in H. aphoticus. The cornea is
subreniform, and it is disposed such that its prox-
imal margin is oblique to the basal margin of the
ocular peduncle and an imaginary line extending
from the medial tubercle parallel to the basal
margin of the peduncle crosses its proximolateral
extremity. The cornea (actually the entire eye) of
H. debilis is also much larger than that of H.
aphoticus: its maximum diameter about twice
that of the basal margin of the peduncle, and the
proportion of the diameter to the carapace length
ranges from 15.5 to 22.0, averaging 19.7. Fur-
thermore, in males of H. debilis the petasma
exhibits larger distal processes than does that of
H. aphoticus, but the lateral one is produced
proximally in an auricle which is small and
unarmed, and the proximomesial spinules on the
free margin of the mesial process are only slightly
longer than the remaining ones instead of consid-
erably so as in//, aphoticus. Finally, the length of
the ventrolateral spur borne by the sclerite at the
base of the appendices masculina and interna is
equivalent to 0.50-0.75 that of the appendix
masculina. The thelyca of the two species are

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FISHERY BULLETIN: VOL. 75, NO. 2

FIGURE 8. — Ranges of Hymenopenaeus aphoticus and Hymenopenaeus debilis based on published records and specimens personally

examined.

Depth (meters)

1000

2000

3000

4000

5000

Hymenopenaeus debilis
Hymenopenaeus aphoticus
Hymenopenaeus laevis
Hymenopenaeus doris
Hymenopenaeus neveus
Haliporoides diomedeae
Pleotiaus vobustus
Pleotious muetleri
Hadropenaeus affinis
Hadropenaeus modes tus
Hadropenaeus luaasii
Mesopenaeus tropiaalis
274

FIGURE 9. — Bathymetric ranges of species of Hymenopenaeus, Hali-
poroides, Pleoticus, Hadropenaeus, and Mesopenaeus found in
American waters.

PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMPS

similar but the median protuberance of sternite
XIV tends to be broader in H. debilis than in H.
aphoticus.

According to Burkenroad (1936), in this species
the proportion of the maximum diameter of the eye
to carapace length is even greater than that given
above, ranging between 19.3 and 26.9, x 22.3. My
measurements of specimens studied by Burken-
road resulted in proportions not exceeding 23.0.
This could be due to a slight reduction of the
cornea caused by the preservatives, or the cornea
is now deformed in the specimens with larger
corneae examined by me.

Very similar to H. debilis is H. chacei which is
known only from off West Africa. According to
Crosnier and Forest (1969, 1973), these two
species differ in that in H. chacei the ventral
border of the rostrum is unarmed (actually, as
stated above, 39c of the individuals of//, debilis
examined by me lack such teeth), and no photo-
phores are present. The cornea of H. chacei is
narrower than that of//, debilis, in the former the
ratio of the greatest diameter to the carapace
length ranges from 13.2 to 16.0 (x 15.0), and it is
disposed such that its proximolateral extremity
lies slightly distal to the level of the medial
tubercle.

A careful study of the western Atlantic speci-
mens in which the rostrum is ventrally unarmed
has left no doubt in my mind that they are H.
debilis. Hymenopenaeus chacei, which typically
lacks teeth on the ventral margin of the rostrum,
is not represented in the extensive collections
from the western Atlantic examined by me.

I have found that in males of//, debilis the dis-
position of both the mesial and lateral processes of
the petasma varies from slightly to rather

strongly inclined mesially, the former illustrated
herein (Figure 6A, B), and the latter, illustrated
by Crosnier and Forest ( 1973, plate 85, figure c-d,
a male from Morocco). This variation is not associ-
ated with the size of the animal, and occurs
throughout the entire range of the species in the
western Atlantic. Males in which the processes
are only slightly inclined mesially resemble those
of//, chacei in which, according to Crosnier and
Forest (1973), the roughly angular portion of the
lateral process is typically directed forward. The
males of the two species can still be distinguished
by the size and armature of the auricular process
of the petasma, which in H. debilis is very small
and unarmed but relatively large in//, chacei and
provided with marginal spinules (Crosnier and
Forest 1969:546, figure 2).

Remarks. -The coordinates of the Talisman sta-
tions, cruise of 1883, where the material exam-
ined by me was collected, are given herein accord-
ing to the data presented by Crosnier and Forest
(1973).

The disposition of the third syntype, from south-
east of Savannah Beach, Ga., caught at Blake
stn 317 is unknown.

Hymenopenaeus aphoticus Burkenroad 1936

Figures 4C, 8-12

Hymenopenaeus aphoticus Burkenroad 1936:112,
fig. 62, 65, 66, 67 [holotype: 9 , YPM 4556; type-
locality: Turks Is Passage, 1,646-1,728 m,
21°15'40"N, 71°17'06"W, Pawnee stn 54].
Yokoya 1941:52. Crosnier and Forest 1969:547.

FIGURE 10. — Hymenopenaeus aphoticus. 9 18 mm cl, northwest of Peninsula de la Guajira, Colombia. Cephalothorax, lateral view.

275

FISHERY BULLETIN: VOL. 75, NO. 2

Roberts and Pequegnat 1970:31, fig. 3-1D.
Pequegnat and Roberts 1971:8. Crosnier and
Forest 1973:253, fig. 85e-f, 87c, 88b, 89c.

Material

UNITED STATES— Florida: 5 6 3 9, RMNH-UMML,
SW of Marquesas Keys, 1,373-1,428 m, 1 December 1964, Gerda
stn 449. 2 d , USNM, SW of Marquesas Keys, 948-969 m,
29 August 1967, Gerda stn 858. 2 6 , TAMU, NW of Dry Tortu-
gas, 3,256 m, 29-30 July 1968, Alaminos stn 68A7-4E. 1 6,
TAMU, SW of Cape San Bias, 1,097 m, 1 August 1968, Alaminos
stn68A7-7B. Alabama: 1 6, USNM, off Mobile Bay, 2,160 m,
3 March 1885, Albatross stn 2383. Texas: 1 9, TAMU, off
Padre I, 1,399 m, 7 August 1969, Alaminos stn 69A11-7.

MEXICO— Tamaulipas: 1 9, USNM, off Boca de San
Rafael, 1,668 m, 24 January 1970, Oregonll stn 10881. Vera-
cruz: 1 6 3 9, TAMU, NE of Tuxpan, 1,326 m, 24 August 1969,
Alaminos stn 69A11-83. 1 6, TAMU, Bahia de Campeche,
2,122 m, 16 August 1969, Alaminos stn 69A11-44.

BAHAMA ISLANDS— 1 6 paratype, YPM 4557, Tongue
of the Ocean, "Wire 7000 feet" [2,134 m], 2 March 1927,Pou;nee
stn 11. 6 holotype 1 9 paratype, YPM 4556, Turks I Passage,
1,646-1,728 m, 12 March 1927, Pawnee stn 54.

JAMAICA— 1 9, USNM, W of South Negril Point, 1,591-
1,829 m, 8 July 1970, Pillsbury stn 1238.

EASTERN CARIBBEAN— 1 6 6 9, USNM, S of I Aves,
1,249 m, 27 January 1884, Albatross stn 2117.

COLOMBIA— 10 d69, USNM, NW of Peninsula de la
Guajira, 1,500 m, 27 July 1966, Pillsbury stn 454. 3 9, USNM,
off Peninsula de la Guajira, 2,500 m, 27 July 1966, Pillsbury
stn 455.

Description. -Rostrum (Figure 10) slightly to
rather strongly upturned, reaching as far as distal
margin of second antennular article, its length
about 0.45 that of carapace, and with both margins
almost straight. Rostral plus epigastric teeth 7-8,
sharp; epigastric tooth located at about 0.4 cl from
orbital margin, first tooth (largest of all) at about
0.25, and second with apex at level of orbital
margin; ventral teeth absent. Adrostral carina
low and sharp, extending from orbital margin
almost to apex of rostrum; orbital margin project-
ing anteroventrally in narrow shelf. Postrostral
carina strong to just caudal to cervical sulcus,
from there weak or indistinct porteriorly, and fol-
lowed by minute tubercle located close to margin
of carapace. Spines on lateral surface of carapace
slender and sharp: postorbital spine situated
directly posterior to antennal, and branchio-
stegal, largest of all, continuous with short, sharp
carina; pterygostomian spine absent. Cervical
sulcus deep, extending to, but not crossing, post-
rostral carina, its dorsal extremity placed at about
0.54 cl (or slightly farther anteriorly) from orbital
margin; hepatic sulcus biconvex ventrally, run-
ning from base of hepatic spine to ventral end of

branchiocardiac sulcus; weak posthepatic carina
extending posteriorly from junction of latter sulci.
Branchiocardiac sulcus long, accompanying ca-
rina strong. Submarginal carina slender.

Eye (Figure AC) with basal article produced
mesially into small scale. Cornea comparatively
narrow, its greatest diameter approximately 1.5
times that of base of ocular peduncle (1.25-1.75,
x 1.55; N = 20), and proportion of diameter to
carapace length varying between 10.0 and 12.5,
x 11.1. Cornea hemispherical, with proximal
margin subperpendicular to longitudinal axis of
elongate ocular peduncle; an imaginary line
drawn parallel to base of ocular peduncle at level
of its mesial tubercle intersects lateral border far
proximal to cornea.

Antennular peduncle length equivalent to
about 0.5 that of carapace; prosartema short, ex-
tending only as far as distomesial margin of cor-
nea, falling short of distal margin of first anten-
nular article, but with long distal setae reaching
base of second antennular article; stylocerite
moderately long, extending 0.60-0.65 of distance
between its proximal extremity and mesial base of
distolateral spine; latter rather long, slender, and
sharp. Antennular flagella long and unequal in
length, ventral one 2.25 times as long as carapace
in shrimp 17.5 mm cl; dorsal flagellum longer
than ventral, unfortunately incomplete in all
specimens examined. Scaphocerite length approx-
imately 3.65 times maximum width, overreaching
antennular peduncle by as much as 0.3 of its own
length; lateral rib ending in slender spine extend-
ing to, or slightly surpassing, distal margin of
lamella. Antennal flagellum long, at least 6.8
times total length of shrimp: male with total
length of 45 mm bearing incomplete flagellum
300 mm long. Mandibular palp, maxillae and first
two maxillipeds similar to those inH. debilis (see
Figure 5). Third maxilliped overreaching anten-
nular peduncle by length of dactyl and propodus
or by their lengths plus 0.1 that of carpus; length
of dactyl about 0.7 that of propodus.

First pereopod, stoutest of five, reaching about
distal end of carpocerite. Second pereopod over-
reaching antennular peduncle by, at least, tip of
dactyl, or by as much as length of propodus. Third
pereopod exceeding antennular peduncle by
length of propodus and, at most, 0.4 that of carpus.
Fourth pereopod overreaching antennular pedun-
cle by length of distal three podomeres. Fifth
pereopod exceeding antennular peduncle by
length of distal three podomeres, or by length of

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PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMPS

FIGURE ll. — Hymenopenaeus aphoticus, 6 14.5 mm cl, south of Isla Aves, eastern Caribbean. A, Petasma (extended), dorsolateral
view. B, Ventral view. C, Right appendices masculina and interna, dorsolateral view. D, Ventromesial view.

those podomeres and as much as 0.15 length of
merus. Pereopods increasing in length from first
to fifth. First pereopod with rather inconspicuous
spine on basis, and long slender spine on ischium;
second pereopod with small spine on basis. In
female, coxa of third pereopod produced into sub-
trapezoidal plate, latter broadest mesially, dis-
posed almost at right angle to podomere, and bear-
ing minute anteromesial tooth in juvenile. In both
sexes, tooth present on anteromesial angle of coxa
of fifth pereopod, considerably stronger in male
than in female, in latter tooth minute and borne
on rounded coxal plate.

Abdomen with middorsal carina from fourth
through sixth somites, posterodorsal margin of
fourth and fifth with short median incision; sixth
somite about 1.8 times as long as high, bearing
small, sharp spine at posterior end of carina and
pair of minute spines posteroventrally. Telson
with rather shallow median sulcus extending
posteriorly to level of base of lateral spines, and
flanked by well-developed ridges; terminal por-
tion length 5-6 times its basal width; lateral
spines length 1.4-1.7 times basal width of termi-
nal portion. Mesial ramus of uropod falling short
of, or slightly overreaching, apex of telson; lateral
ramus overreaching mesial ramus by as much as
0.25 of its own length, and armed with small,
slender distolateral spine, falling slightly short of,

or barely overreaching, contiguous margin of
ramus.

Petasma (Figure 11A, B) with row of cincinnuli
occupying proximal 0.4 of median line, and entire
terminal margin armed with spines; ventro-
median lobule distally cleft forming two moder-
ately long processes: mesial one subtrapezoidal
and armed with conspicuous spines mesially and
minute ones distolaterally, lateral process sub-
elliptical, raised inwardly in strong prominence,
and produced proximally in rather large auricular
process armed with marginal spinules; distal flap
of ventrolateral lobule free, extending as far dis-
tally as lateral process, and only slightly turned
outward; ventral costa forming low prominence
at, and imperceptibly merging with, base of
flap.

Appendix masculina (Figure 11C, D) strongly
elevated along mesial portion and with proximal
part produced laterally into rounded, flattened
lobe; distal part narrowing and bearing lateral
row of setae continuous with apical tuft of long
setae. Appendix interna elongate-ovate, extend-
ing slightly farther distally than appendix mas-
culina, and armed with apical tuft of setae.
Ventrolateral spur short, its length not greater
than 0.5 that of appendix masculina.

Thelycum (Figure 12) similar to that of H.
debilis (see above).

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FISHERY BULLETIN: VOL. 75, NO. 2

FIGURE 12. — Hymenopenaeus aphoticus, 9 18.5 mm cl, south of
Isla Aves, eastern Caribbean. Thelycum, ventral view.

Maximum size-Males: 18 mm cl; females: 19.5
mm cl.

Geographic and bathymetric ranges-Western
Atlantic: southwest Florida (23°56'N, 82°13'W),
throughout the Gulf of Mexico, and the Caribbean
Sea (12°55'N, 72°04'W). Eastern Atlantic (ac-
cording to Crosnier and Forest 1973): south of the
Azores Islands and off Morocco (Figure 8). It
occurs at depths between about 950 m and 3,256 m
(Figure 9).

Affinities. -Hymenopenaeus aphoticus is closely
allied to H. debilis, but may be readily distin-
guished from it by the lack of teeth on the ventral
margin of the rostrum, the absence of photo-
phores, and the shape and disposition of the cor-
nea (see above). In males of H. aphoticus, the
petasma exhibits smaller distal processes than
does that of//, debilis, and the auricle of the disto-
lateral process is larger and armed with marginal
spinules; also the proximomesial spinules on the
free margin of the mesial process are considerably
longer than the remaining ones, instead of only
slightly longer as in H.debilis. Furthermore, in
H. aphoticus the length of the ventrolateral spur
at the base of the appendices masculina and
interna is equivalent to only 0.5 that of the appen-
dix masculina. Although the petasmata of the two

species are different, the thelyca are markedly
similar: the only detectable distinction is that the
median protuberance on sternite XIV tends to be
narrower in H. aphoticus than in H. debilis.

Remarks.-ln examining a lot of seven specimens
of//, aphoticus obtained at Albatross stn 2117,
Roberts and Pequegnat (1970) misread the num-
ber on the accompanying label. They stated that
in the Smithsonian Institution there is a lot of
H. aphoticus taken by the Albatross at "Stn 2217,
1889" in the western Atlantic. Actually, the num-
ber on the label is 2117 for which the coordinates
are 15°24'40"N, 63°31'30"W (south of Isla Aves in
the eastern Caribbean, visited by the Albatross in
1884) instead of 2217, an 1889 station situated at
39°47'20"N, 69°34'15"W, which is off New Jersey.
Because the authors thought the lot had been
obtained at the latter locality, they stated that the
species ranges as far north as 39°47' (actually it
has not been recorded from off the Atlantic coast of
the United States). The misreading of the label
also caused them to be unaware of the Caribbean
record for H. aphoticus and to state that "It may
eventually be found in the Caribbean also."

Hymenopenaeus laevis (Bate 1881)

Figures 4 A, 9, 13-16

Haliporus laevis Bate 1881:185 [syntypes: 2 9,
BMNH; type-locality: SW of Sierra Leone (W of
Cameroon), 2°25'N, 20°01'W, 2,500 fm (4,573
m), Challenger stn 104]. Bate 1888:289, pi. 42,
fig. 2. Bouvier 1906b:3; 1908:80. de Man 1911:7.
Estampador 1937:494.

Hymenopenaeus microps Smith 1884:413, pi. 10,
fig. 1 [syntypes: 1 9, USNM 7148, E of Georges
Bank, Mass., 41°13'00"N, 60°00'50"W, 906 fm
(1,657 m), Albatross stn 2076; 1 9 oral append-
ages, YPM 4559, off New Jersey, 38°50'00"N,
69°23'30"W, 1,731 fm (3,166 m), Albatross stn
2037]. Smith 1886:189; 1887:688, pi. 16, fig. 8.
Wood-Mason 1891:277. Wood-Mason and Al-
cock 1891:188.

Haliporus microps. Alcock and Anderson 1894:
146. Alcock 1901:25. Bouvier 1906a:255; 1906b:
3; 1908:80. de Man 1911:7. Fowler 1912:543.

Hymenopeneus microps. Alcock 1899a:30.

Haliporus androgynus Bouvier 1906a:253 [syn-
types: 1 9 , MP, between "Dakar et la Praya,"
(off Mauritania), 16°38'N, 20°44'W, 3,200 m,
Talisman stn 105. 1 9, MP, between "Dakar et

278

PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMPS

la Praya," (off Senegal), 15°48'N, 20°23'W,
3,655 m, Talisman stn 106]. Bouvier 1906b:3;
1908:80. de Man 1911:7.

Haliporus sp. Lenz and Strunck 1914:300, fig. 2.

Hymenopenaeus laevis. Burkenroad 1936:106;
1938:61. Anderson and Lindner 1945:289.Cros-
nier and Forest 1973:253, fig. 82a, 83b.

Material

UNITED STATES— Massachusetts: 1 9 syntype of H.
microps Smith, USNM 7148, E of Georges Bank, 1,657 m,
4 September 1883, Albatross stn 2076. 1 9, USNM, SE of
Martha's Vineyard, 2,844 m, 30 July 1883, Albatross stn 2042.
New Jersey: 1 9, USNM, off Atlantic City (Hudson Can-
yon), 1,977 m, 9 August 1885, Albatross stn 2550. 1 9 [oral
appendages] syntype of//, microps Smith, YPM 4559, 3,166 m,
18 July 1883, Albatross stn 2037. Virginia: 4 9 , USNM, 1 9 ,
AMNH, E of Delmarva Peninsula, 4,792 m, 29 August 1885,
Albatross stn 2566. North Carolina: 1 9 1 9, USNM, NE of
Kitty Hawk, 4,708 m, 8 September 1884, Albatross stn 2224.

BERMUDA ISLANDS— 1 3, YPM, N of Bermuda Is,
"10000 feet wire" [3,048 m], 20 April 1927, Pawnee stn 58.
1 9, YPM, N of Bermuda Is, "8000 feet wire" [2,438 m],
21 April 1927, Pawnee stn 59.

BAHAMA ISLANDS— 1 6 2 9, YPM. Turks I Passage,
"8000 feet wire" [2,438 m], 11 April 1927, Pawnee stn 52. 2 9,
YPM, Turks I Passage, "6500 feet wire" [1,981 m], 13 April
1927, Pawnee stn 56.

MAURITANIA— 1 9 syntype of H. androgynus Bouvier,
MP, between "Dakar et la Praya" [off Mauritania], 3,200 m,
18 July 1883, Talisman stn 105.

SENEGAL — 1 9 syntype of//, androgynus Bouvier, MP,
between "Dakar et la Praya" [off Senegal], 3,655 m, 19 July
1883, Talisman stn 106.

CAMEROON— 2 9 syntypes, BMNH, "south-west of
Sierra Leone," 2°25'N, 20°1'W [W of Cameroon], 4,573 m,
23 August 1873, Challenger stn 104.

PHILIPPINE ISLANDS— 1 9, BMNH, off Manila, 1,920
m, 13 November 1874, Challenger stn 205.

Description. -Rostrum (Figure 13) short, its
length about 0.2 that of carapace, falling short of
distal margin of first antennular article, horizon-
tal or slightly upturned, tapering to very sharp
tip, and with ventral margin slightly sinuous.

Rostral plus epigastric teeth 7-9, sharp; epigastric
tooth situated at about 0.4 cl from orbital margin,
first rostral tooth (largest of all) at approximately
0.3, and third opposite to, or slightly forward of,
orbital margin. Adrostral carina low and sharp,
extending from orbital margin almost to apex of
rostrum; orbital margin projecting antero-
ventrally in narrow shelf. Postrostral carina well
defined to near posterior margin of carapace,
followed by small tubercle. Pterygostomian spine
small; postorbital (situated directly posterior to
relatively small antennal spine), branchiostegal,
and pterygostomian spines continuous with sharp
basal carina. Cervical carina sharp, notched dor-
sal to hepatic spine; cervical sulcus deep, extend-
ing to, but not crossing postrostral carina, its
dorsal extremity located at or slightly posterior
to midlength of carapace; hepatic carina blunt,
its accompanying sulcus deep; additional short
carina lying dorsal and parallel to posterior part
of hepatic sulcus; posthepatic carina long, run-
ning almost to posterior margin of carapace;
branchiocardiac carina also long, virtually reach-
ing posterior margin of carapace; short sulcus ex-
tending posterodorsally from near posterior end
of branchiocardiac carina; submarginal carina
well defined, extending along entire length of
branchiostegite.

Eye (Figure 4A) with basal article produced
mesially into barely distinct scale; ocular pedun-
cle long; cornea comparatively narrow, its great-
est diameter about 1.4 times that of base of ocular
peduncle, its proximal margin only slightly slant-
ing posterolateral^.

Antennular peduncle length equivalent to
about 0.55 that of carapace; prosartema short, ex-
tending only as far as distomesial margin of
cornea, falling considerably short of distal margin
of first antennular article; stylocerite short, ex-
tending only 0.4-0.5 of distance between its prox-

FIGURE 13. — Hymenopenaeus laevis, 8 12.5 mm cl, Turks Island Passage, Bahama Islands. Cephalothorax, lateral view.

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FISHERY BULLETIN: VOL. 75. NO. 2

imal extremity and mesial base of distolateral
spine; latter long, slender, and sharp. Antennular
flagella incomplete in all specimens examined by
me, according to Bate ( 1888) "about two-thirds the
length of the animal." Scaphocerite reaching as
far as antennular peduncle or barely overreaching
it; lateral rib ending in slender spine falling
slightly short of, or slightly overreaching, distal
margin. Antennal flagellum broken in specimens
examined by me, according to Bate ( 1888) "rather
longer than the animal." Mandibular palp reach-
ing to about distal 0.25 of carpocerite. Third max-
illiped overreaching antennular peduncle by
length of dactyl and propodus; length of dactyl
about 0.75 that of propodus.

First pereopod extending to about distal end of
carpocerite. Second pereopod reaching distal end
of antennular peduncle, or exceeding it by as
much as length of dactyl. Third pereopod surpass-
ing antennular peduncle by length of dactyl, pro-
podus, and at least 0.25 that of carpus. Fourth
pereopod exceeding antennular peduncle by
length of dactyl, propodus, and 0.4-0.5 that of
carpus. Fifth pereopod overreaching antennular
peduncle by length of dactyl, propodus, and 0.75-
0.80 that of carpus. Pereopods increasing in
length from first to fifth. First pereopod with
minute spine on basis, and small one on ischium;
second pereopod with small spine on basis. Coxal

plate of third pereopod in females broadening
mesially and produced posteriorly into setose,
rounded lobe. Tooth present on anteromesial
corner of coxa of fifth pereopod in both sexes,
strong and blunt in males, minute, and borne by
rounded coxal plate in females.

Abdomen with middorsal carina from fourth
through sixth somites, posterodorsal margin of
fourth and fifth with short median incision, some-
times bearing minute spine at base; sixth somite
about twice as long as high, armed with small,
sharp spine at posterior end of carina and pair of
posteroventral spines. Telson with median sulcus
deep anteriorly, increasingly shallower poste-
riorly to level of base of lateral spines, flanked by
paired ridges, blunt anteriorly, sharp posteriorly;
length of terminal portion about 5 times its basal
width; spines moderately long, 1.20-1.35 basal
width of terminal portion. Mesial ramus of uropod
falling short of apex of telson, or overreaching it
by no more than 0.1 of its length; lateral ramus
exceeding mesial ramus by as much as 0.2 of its
own length, and armed with small, terminal,
distolateral spine.

Petasma (Figure 14A, B) with row of cincinnuli
occupying about proximal 0.5 of median line, its
entire terminal margin lacking spines; ventro-
median lobule bearing two, rarely three, small,
triangular processes distomesially, and short,

FIGURE 14. — Hymenopenaeus laevis, i 15 mm cl, Turks Island Passage, Bahama Islands. A, Petasma, dorsolateral view of left half.
B, Ventrolateral view. C, Right appendices masculina and interna, dorsolateral view. D, Ventromesial view.

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PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMPS

rigid, transversely elliptical process disto-
laterally; distal part of ventrolateral lobule
roughly elliptical and strongly trending toward
ventromedian lobule; ventral costa broad proxi-
mally, considerably narrower distally and, in
young, ending in minute marginal spine project-
ing from base of elliptical part of ventrolateral
lobule.

Appendix masculina (Figure 14C, D) with prox-
imal part produced laterally into rounded lobe
bearing row of long setae on distal margin con-
tinuous with row extending along midventral line
of narrow distal portion; latter armed with apical
tuft of long setae; appendix interna abruptly
narrowing from rounded base and bearing apical
tuft of long setae; ventrolateral spur with distal
part subovate, bearing longitudinal submarginal
rib on dorsal surface.

Thelycum (Figure 15) with median protuber-
ance on sternite XIV setose, pyramidal, and with
triangular base, its apical portion produced into
short ventrally directed projection; median la-
mella projecting vertically from posterior margin
of sternite XIII, flat, its distal margin slightly to
deeply emarginate (emargination angular or
curved), lateral margins straight or slightly
concave; posterior part of sternite XII bearing
paired, setose horns overreaching midlength of
sternite XIII.

Maximum size. -Males: 15 mm cl; females: 22 mm
cl.

Geographic and bathymetric ranges. -Western
Atlantic: from off Georges Bank, Mass.
(41°13'00"N, 60°00'50"W), to the Bahamas
(21°20'15"N, 71°13'20"W), including the Ber-
mudas (Figure 16). Eastern Atlantic: from west of
Mauritania to off Equatorial Guinea (Bate 1888).
Indo-West Pacific: in the Arabian Sea (Laccadive
Sea, Wood-Mason and Alcock 1891), the Bay of
Bengal (off Andaman Islands, Wood-Mason 1891;
Alcock 1901), and the Philippines (Bate 1888). If
the record oVHaliporus sp." by Lenz and Strunck
( 1914) is actually one for this species, its range off
west Africa reaches farther south, at least to off
Liberia <0°39'N, 18°57'W). This shrimp has been
found at depths between 1,657 and 4,792 m
(Figure 9). Its habitat together with its small size
are most probably responsible for the few collec-
tions available.

Affinities -Hymenopenaeus laevis is closely allied

FIGURE 15. — Hymenopenaeus laevis, 2 17 mm cl, Turks Island
Passage, Bahama Islands. Thelycum, ventral view.

to the American Pacific H. doris and H. nereus,
and to the Indo-West Pacific//, sewelli. These four
species form the compact section 2 of Burken-
road's group IV. They are the only members of the
genus which possess both branchiostegal and
pterygostomian spines.

Females of//, laevis differ strikingly from those
of//, nereus in the structure of the thelycum. In
those of//, nereus, the median lamella of sternite
XIII is directed anteriorly, and has arched or sin-
uous lateral margins converging basally. Further-
more, in H. nereus the median lamella is flanked
by paired, caudally inclined processes, which are
lacking in H. laevis, and sternite XIV is raised in
a median longitudinal ridge, very different from
the strong pyramidal prominence present in
the latter. This shrimp, in turn, can be separated
readily from H. doris by the median lamella of

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FISHERY BULLETIN: VOL. 75, NO. 2

FIGURE 16. — Ranges of Hymenopenaeus laevis and Hadropenaeus lucasii based on published records and specimens

personally examined.

sternite XIII which in the latter is concave ante-
riorly, has a usually convex, never emarginate,
distal margin. The median lamella also is flanked
by paired ridges which are triangular in cross
section and as high as the lamella. Furthermore,
in//, doris, sternite XIV bears a median protuber-
ance which is strongly produced in an elongate
projection lying quite close to the lamella.

Males of//, laevis differ markedly from those of
H. nereus in that the petasma of the latter bears a
single, large, mesial process distally which, more-
over, is subrectangular, directed perpendicular to
the main axis of the petasma, and armed with long
spines; in addition, the lateral process is directed
distomesially instead of extending transversely,
and is strongly curved outward. Finally, the distal
part of the ventrolateral lobule of the petasma is
acuminate instead of subelliptical, and is only
slightly inclined toward the ventromedian lobule.

As previously indicated by Burkenroad (1936)
and Crosnier and Forest (1973), females of this

species exhibit considerable variation in the
shape and size of the median lamella on sternite

XIII. Extending ventrally, it may be short or long,
reaching between midheight and slightly beyond
the apex of the median protuberance on sternite

XIV. In the young, the lamella is truncate, and in
the adult it ranges from shallow to deeply
emarginate distally, forming a fork with the pro-
jections varying from rather broadly triangular
to spinelike.

In the young male, as stated above, the petasma
bears a minute subdistal spine at the free margin
of the costa, and the more mesial of the two distal
projections of the ventromedian lobule is at best
only slightly developed.

Remarks. -Burkenroad (1936) presented a de-
tailed account of the external morphology and an
enlightened analysis of the taxonomic status of
this species; as a result, he placed two well-known
scientific names, H. microps and H. androgynus,

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PEREZ FARFANTK: AMERICAN SOLENOCERID SHRIMPS

in the synonymy of//, laeuis. In this same contri-
bution, Burkenroad mentioned a "minute denticle
of variable size" posterior to the epigastric tooth,
and suggested that it is "probably the remains of
the larval anterior dorsal organ." In that location,
however, I have observed nothing more than an
extremely slight elevation of the postrostral
carina, and that only in two specimens. Had this
feature not been mentioned by Burkenroad, I
should have overlooked it, and, after observing it,
I believe it to be insignificant.

Bouvier (1906b) described Haliporus andro-
gynus on the basis of two specimens which bear, in
addition to a fully developed thelycum, both
petasma and appendices masculinae. Burkenroad
(1936) stated that the simultaneous presence of
the female and male external genitalia in these
specimens probably represents an abnormality.
Recently, Crosnier and Forest (1973) indicated
that this combination of secondary sexual charac-
ters could represent an expression of protandric
hermaphroditism, as reported by Heegaard ( 1967 )
in Solenocera membranacea (Risso 1816). They
added that in a rather large number of penaeids
the maximum size of males corresponds to the
minimum size of females. It should be noted, how-
ever, that Burkenroad (1936) cited a female of
H. laevis, also examined by me, with a carapace
length of 8 mm, which is about half the length of
the largest known male, 15 mm cl.

In the two syntypes of H. androgynus, which
have a carapace length of about 20 mm, the petas-
mata are shorter than in other males of equal
size, and exhibit and armature with these juvenile
features. In one of the specimens, the mesial pro-
jection is extremely small, whereas the lateral
projection and the distolateral process are well
developed; in the other, the mesial projection is
distinct, the lateral one very small, the disto-

lateral process is well developed, and a subdistal
spine is present on the free margin of the ventral
costa.

Hymenopenaeus doris (Faxon 1893)

Figures 9, 17, ISA, 19-20

Haliporus doris Faxon 1893:214 [syntypes: 4 2,
MCZ 4648, off Cabo Velas Costa Rica, 10°14'N,
96°28'W, 2,232 fm (4,082 m), 8 April 1891,
Albatross stn 3414. 1 2, USNM 21182, S of
Punta Maldonado, Guerrero, Mexico, 14°46'N,
98°40'W, 1,879 fm (3,437 m), 10 April 1891,
Albatross stn 3415]. Faxon 1895:191, pi. 49,
fig. 1-lc. Bouvier 1906b:3; 1908:80. de Man
1911:7

Hymenopenaeus doris. Burkenroad 1936:104;
1938:60. Crosnier and Forest 1973:256, fig. 83d.

Aliporus doris. del Solar C. 1972:4.

Material

MEXICO— Territorio de Baja California: 1 9, USNM,
off Punta Chivato, Golfo de California, 1,567 m, 20 March 1889,
Albatross stn 3009. 1 2 , AMNH, 54 km off Punta Arena,
mouth of Golfo de California, 914 m, 29 April 1936, Temple-
ton Crocker Expedition stn 159 T-3 [station data from Beebe
1937].

COSTA RICA— 4 2 syntypes, MCZ 4648, off Cabo Velas,
4,082 m, 8 April 1891, Albatross stn 3414. 1 9, USNM, off
Cabo Velas, 4,082 m, 8 April 1891, Albatross stn 3414.

Description. -Rostrum (Figure 17) relatively
short, its length about 0.2 that of carapace, reach-
ing between base and midlength of second anten-
nular article, upturned, tapering to sharp tip, and
with ventral margin straight. Rostral plus epi-
gastric teeth 7-8, sharp; epigastric tooth situated
about 0.4 cl from orbital margin, first rostral tooth
(largest of all) at approximately 0.3, and base of

FIGURE 17. — Hymenopenaeus doris. syntype S 32.5 mm cl, off Cabo Velas, Costa Rica. Cephalothorax, lateral view.

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FISHERY BULLETIN: VOL. 75, NO. 2

third in line with orbital margin. Adrostral carina
low and sharp, extending from orbital margin
almost to apex of rostrum; orbital margin project-
ing in narrow shelf. Postrostral carina strong to
near posterior margin of carapace, followed by
small tubercle. Pterygostomian spine slender and
sharp like other lateral spines on carapace; post-
orb'tal (situated directly posterior to antennal),
pterygostomian, and branchiostegal spines with
sharp basal carina, that continuous with branchi-
ostegal spine merging with hepatic carina. Cer-
vical carina strong, extending to, but not crossing,
postrostral carina, its dorsal extremity located
immediately posterior to midlength of carapace;
hepatic carina blunt, its accompanying sulcus
deep; additional short carina lying dorsal and
parallel to posterior part of hepatic sulcus; post-
hepatic carina long, running from posterior
extremity of hepatic sulcus to posterior margin
of carapace; branchiocardiac carina also long,
reaching posterior margin of carapace; short
sulcus extending posterodorsally from near pos-
terior end of branchiocardiac carina; submarginal
carina well defined, extending along entire length
of branchiostegite.

Eye as illustrated (Figure 18A).

Antennular peduncle length equivalent to
about 0.4 that of carapace; prosartema extending
to distal margin of eye, but falling short of distal
end of first antennular article; stylocerite short,
extending 0.5 of distance between its proximal
extremity and mesial base of distolateral spine;
latter rather long, slender, and sharp. Antennular
flagella incomplete in specimens examined.

FIGURE 18. — Eyes. A, Hymenopenaeus doris, syntype 9 32.5
mm cl, off Cabo Velas, Costa Rica. B, Hymenopenaeus nereus,
syntype 9 21.5 mm cl, south of Cabo Blanco, Costa Rica.

Scaphocerite overreaching antennular peduncle
by 0.25 of its own length; lateral rib ending in
slender spine, extending to distal margin of
lamella. Antennal flagellum broken in specimens
studied. Mandibular palp reaching distal 0.2 of
carpocerite; proximal article about 2.5 times as
long as wide; distal article considerably shorter
and narrower than proximal, and tapering to
blunt tip. First maxilliped with single rudi-
mentary arthrobranchia at base. Third maxilli-
ped reaching beyond antennular peduncle by
dactyl and almost entire length of propodus;
length of dactyl about 0.65 that of propodus.

First pereopod extending to distal end of carpo-
cerite. Second pereopod overreaching antennular
peduncle by length of propodus. Third pereopod
exceeding antennular peduncle by length of pro-
podus and about 0.33 that of carpus. Fourth pereo-
pod overreaching antennular peduncle by dactyl,
propodus, and almost entire length of carpus.
Fifth pereopod reaching beyond antennular pe-
duncle by length of distal three podomeres. Pereo-
pods increasing in length from first to fifth. First
pereopod with rather inconspicuous spine on
basis, and slender spine on ischium; second pereo-
pod with minute spine on basis. In female, coxa of
third pereopod produced into large, subtrapezoidal
plate, broadest mesially, and disposed almost at
right angle to podomere; coxa of fifth pereopod
armed with minute anteromesial tooth.

Abdomen with middorsal keel from fourth
through sixth somites, and strong longitudinal
rib along lateral surface of fourth and fifth
somites; posterodorsal margin of latter two
somites with short median incision; sixth somite
very elongate, 2.5 times as long as high, bearing
small, sharp spine at posterior end of keel and
pair of minute posteroventral spines. Telson with
broad median sulcus deep anteriorly, quite shal-
low posteriorly, and flanked by low, sharp ridges;
terminal portion length 5-6 times basal width;
lateral spines short, their length about 1.5 times
basal width of terminal portion. In only specimen
with complete uropod, mesial ramus falling short
of apex of telson; lateral ramus overreaching
mesial ramus by 0.2 of its own length, and armed
with small, terminal, distolateral spine.

Petasma unknown; males not recorded.

Thelycum (Figure 19A, B) with median protu-
berance on sternite XIV subpyramidal, with sub-
triangular base and apical portion strongly
produced into elongate, acute projection directed
ventrally or anteroventrally, and lying quite near

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FIGURE 19. — Hymenopenaeus doris, syntype 9 32.5 mm cl, off Cabo Velas, Costa Rica. A, Thelycum, ventral view.
B, syntype 2 32 mm cl, same locality, thelycum, ventrolateral view (setae omitted).

median lamella of sternite XIII; lamella, project-
ing vertically, heavily sclerotized, excavate ante-
riorly, with distal margin truncate or convex; pair
of high ridges (triangular in cross section)
flanking and posteriorly overlapping median
lamella; posterior part of sternite XII bearing
paired short, blunt horns covered by long setae.

Maximum size. -Females: 33.5 mm cl.

Geographic and bathymetric ranges. -Eastern
Pacific: from off Punta Chivato (27°09'N,
111°42'W), Gulf of California, to Isla del Coco,
Costa Rica (Figure 20), at depths between 549 and
4,082 m (Figure 9). Burkenroad (1938) cited the
depth, 300 fm (549 m), at which one juvenile speci-
men was taken from the Arcturus off Isla del Coco,
but did not give the coordinates of the locality.
Beebe ( 1926), however, indicated that the various
hauls from the Arcturus in the area were made
slightly south of Isla del Coco, and cited the
following coordinates: 4°30'N, 87°00'W.

Affinities -Hymenopenaeus doris is closely allied
to H. nereus, the only other member of the genus
known from the American Pacific. Females of the

two species -can be distinguished readily by thely-
cal features: in//, doris a strong median protuber-
ance is present on sternite XIV, and the lamella
on the posterior margin of sternite XIII is disposed
vertically, is deeply excavate anteriorly, and its
distal margin is truncate or convex; in H. nereus
only a median longitudinal rib is present on ster-
nite XIV, and the lamella on XIII is inclined
anteriorly, is flattened, and its distal margin is
concave. Finally, in//, doris the lamella is flanked
by high ridges whereas in H. nereus these are
replaced by flattened, scalelike processes directed
caudally.

Remarks-Only nine specimens of H. doris are
known. Seven, five of which are syntypes, were
collected by the Albatross (1891); one of these (not
designated by Faxon as part of the type-series)
was taken with four syntypes at Albatross stn
3414, and the seventh was caught in the Gulf of
California at Albatross stn 3009. Two additional
specimens were cited by Burkenroad (1938), a
juvenile female from the mouth of the Gulf of
California, and another juvenile from off Isla del
Coco (Costa Rica) taken by the Arcturus in 300 fm
(549 m).

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FISHERY BULLETIN: VOL. 75. NO. 2

# H. don's

o H. nereus

• H. diomedeae

FIGURE 20. — Ranges of Hymenopenaeus doris, Hymenopenaeus nereus, and Haliporoides diomedeae based on published records and

specimens personally examined.

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Hymenopenaeus nereus (Faxon 1893)
Figures 9, 18B, 20-23

Haliporus nereus Faxon 1893:213 [syntypes: 1 9,
MCZ 4645, S of Cabo Blanco, Costa Rica, 5°30'N,
86°45'W, 1,067 fm (1,952 m), 27 February 1891,
Albatross stn 3366. 1 9 , USNM 21177, S of Mor-
ro de Puercos, Panama, 7°06'15"N, 80°34'00"W,
695 fm (1,271 m), 23 February 1891, Albatross
stn 3353. 2 9, USNM 21178, off Pen de Azuero,
Panama, 6°21'N, 80°41'W, 1,793 fm (3,279 m),
7 March 1891, Albatross stn 3382. 1 6 2 9,
USNM 21180, NW of Is Galapagos, Ecuador,
2°34'N, 92°06'W, 1,360 fm (2,487 m), 5 April
1891, Albatross stn 3413. 2 9, MCZ 4646, NW
of Punta Galera, Ecuador, 1°07'N, 80°21'W,
1,573 fm (2,877 m), 23 March 1891, Albatross
stn 3398. 1 6, MCZ 4647, NW of Punta Galera,
Ecuador, 1°07'N, 81°04'W, 1,740 fm (3,182 m),
24 March 1891, Albatross stn 3399. 2 9 , USNM
21179, E of Is Galapagos, Ecuador, 00°36'S,
86°46'W, 1,322 fm (2,418 m), 27 March 1891,
Albatross stn 3400. 1 9 , Is Galapagos, Ecuador,
00°04'00"S, 90°24'30"W, 885 fm (1,619 m),
3 April 1891, Albatross stn 3407]. Faxon 1895:
189, pi. 48, fig. 1-ld. Bouvier 1906b:3; 1908:80.
de Man 1911:7.

Hymenopenaeus nereus. Burkenroad 1936:104;
1938:60. Ramadan 1938:60. Crosnier and For-
est 1973:256, fig. 83c.

Materm/.-Syntypes, which are the only material
ever recorded; 1 9 collected at Albatross stn 3407
has not been located.

Description -Rostrum (Figure 21) relatively short,
its length about 0.3 that of carapace, reaching
about midlength of second antennular article,

horizontal or slightly upturned, tapering to sharp
tip, and with dorsal and ventral margins straight.
Rostral plus epigastric teeth 8; epigastric tooth
situated at about 0.4 cl from orbital margin, first
rostral (largest of all) at approximately 0.3, and
base of third opposite to orbital margin. Adrostral
carina low, sharp, extending from orbital margin
almost to apex of rostrum; orbital margin project-
ing anteroventrally in narrow shelf. Postrostral
carina strong to near posterior margin of cara-
pace, followed by small tubercle. Pterygostomian
spine slender and sharp, like other lateral spines
on carapace; postorbital (located directly posterior
to antennal), pterygostomian, and branchiostegal
continuous with sharp basal carina, that continu-
ous with branchiostegal merging with sharp
hepatic carina. Cervical carina strong; sulcus
extending to, but not crossing, postrostral carina,
its dorsal extremity located immediately posterior
to midlength of carapace; hepatic carina sharp,
its accompanying sulcus deep; additional short
carina lying dorsal and parallel to hepatic sulcus;
posthepatic carina long, running almost to pos-
terior margin of carapace; branchiocardiac carina
also long, extending nearly to posterior margin of
carapace; short sulcus extending posterodorsally
from near posterior end of branchiocardiac; sub-
marginal carina well defined, running along
entire length of branchiostegite.

Eye as illustrated (Figure 18B).

Antennular peduncle length equivalent to
about 0.4 that of carapace; prosartema broad,
reaching distal margin of eye, but falling short
of distal margin of first antennular article; stylo-
cerite short, extending 0.45-0.50 of distance
between its proximal extremity and mesial base
of distolateral spine; latter rather long and sharp;
second antennular article with transverse row of
sharp spines near distal margin; antennular fla-

FlGURE 21. — Hymenopenaeus nereus, syntype 2 23.5 mm cl, northwest of Islas Galapagos. Cephalothorax, lateral view.

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FISHERY BULLETIN: VOL. 75, NO. 2

gella incomplete in specimens examined; how-
ever, in Faxon's (1895) illustration both subequal,
about 1.25 times as long as carapace. Scaphocerite
overreaching antennular peduncle by as much as
0.3 of its own length, with lateral rib ending in
sharp, slender spine reaching, or overreaching,
distal margin of lamella. Mandibular palp extend-
ing to distal 0.3 of carpocerite; proximal article
about 2.6 times as long as wide. Third maxilliped
reaching beyond antennular peduncle by length
of dactyl and about 0.5 that of propodus;
length of dactyl about 0.65 that of propodus.

First pereopod extending to distal end of carpo-
cerite or overreaching it by 0.5 length of dactyl.
Second pereopod exceeding antennular peduncle
by length of propodus or by latter and 0.15 that of
carpus. Third pereopod overreaching antennular
peduncle by propodus and about 0.5 length of
carpus. Fourth pereopod surpassing antennular
peduncle by dactyl, propodus, and almost entire
length of carpus. Fifth pereopod exceeding anten-
nular peduncle by length of distal three podo-
meres. Pereopods increasing in length from first
to fifth. First pereopod with rather inconspicuous
spine on basis, and long slender spine on ischium;
second pereopod with minute spine on basis. In

female, coxa of third pereopod produced into large
plate disposed at right angle to podomere, its
anteromesial margin bearing blunt, strong tooth.
Coxa of fourth pereopod produced in short, prom-
inent plate armed with numerous strong setae. In
both sexes, tooth present on anteromesial angle of
coxa of fifth pereopod, tooth considerably stronger
in males than in females, in latter minute and
borne on rounded coxal plate.

Abdomen with middorsal keel from fourth
through sixth somites, and strong longitudinal
rib along lateral surface of fourth and fifth so-
mites; posterodorsal margin of latter somites with
shallow median incision; sixth somite very elon-
gate, 2.25 times as long as high, bearing small
sharp spine at posterior end of keel and pair of
minute posteroventral spines. Telson with broad
median sulcus, deep anteriorly, quite shallow
posteriorly, and flanked by low sharp ridges; ter-
minal portion length about 5 times basal width;
lateral spines short, their length 1.5-1.6 times
basal width of terminal portion of telson; mesial
ramus of uropod falling short, or slightly over-
reaching, apex of telson; lateral ramus exceeding
mesial ramus by 0.15-0.20 of its own length, and
armed with acute, terminal, distolateral spine.

FIGURE 22.— Hymenopenaeus nereus, syntype cJ 15.5 mm cl, northwest of Punta Galera, Ecuador. A, Petasma (partly bent laterally),
dorsal view of right half. B, Ventrolateral view. C, Right appendices masculina and interna, dorsal view. D, Ventromesial view.

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PEREZ FARKANTE: AMERICAN SOLENOCERID SHRIMPS

Petasma (Figure 22A, B) with row of cincinnuli
occupying proximal 0.35 of median line; ventro-
median lobule bearing two processes distally;
mesial one (disposed almost at right angle to
lobule) subrectangular, and armed with few long
spines, distolateral one (directed at about 45
degrees to lobule) unarmed, and produced prox-
imolaterally in small auricular process; distal flap
of ventrolateral lobule acuminate, large, extend-
ing as far as lateral process, and almost straight
rather than conspicuously inclined; ventral costa
projecting in strong rounded prominence at base
of flap.

Appendix masculina (Figure 22C, D) with prox-
imal part produced into rounded lobe; distal part
extremely narrow and bearing lateral row of short
setae continuous with apical tuft of longer setae.
Appendix interna abruptly narrowing, setting off
distal part from rounded proximal part. Ventro-
lateral spur short, roughly semicircular in outline
distally.

Thelycum (Figure 23) with median, longitudi-
nal ridge on sternite XIV; lamella at posterior
margin of sternite XIII rather flat, directed
anteriorly, with distal (cephalic) margin slightly
to deeply concave, and lateral margins convex
basally, straight or concave distally; lamella
flanked by pair of flattened, subtriangular to
rounded processes directed caudally; posterior
margin of sternite XII bearing paired, setose,
long horns, reaching almost midlength of sternite
XIII.

Maximum size-Males: 18 mm cl; females: 27 mm
cl.

Geographic and bathymetric ranges . -From south
of Cabo Blanco (5°30'N, 86°45'W), Costa Rica,
to northwest of Punta Galera and Islas Galapagos
(00°36'S, 86°46'W), Ecuador (Figure 20). It has
been found at depths between 1,271 and 3,279 m
(Figure 9).

Affinities. -Hymenopenaeus nereus and H. doris
are very similar in external morphology. How-
ever, the external genitalia allow a ready separa-
tion of these two species as well as both from the
closely related H. laeuis and H. sewelli. Females
ofH. nereus are unique among the four species in
possessing a longitudinal ridge, instead of a large
protuberance, on sternite XIV; furthermore, the
median lamella of sternite XIII is directed an-
teriorly, its lateral margins tend to converge
proximally (posteriorly), and the lamella is

FIGURE 23.— Hymenopenaeus nereus, syntype 9 21.5 mm cl,
south of Cabo Blanco, Costa Rica. Thelycum, ventral view.

flanked by a pair of processes which are flattened
and directed caudally. In the other species, these
processes are lacking or, if present, are directed
anteroventrally. Males of H. nereus differ from
those of//, laevis in that the petasma of the latter
bears two, occasionally three, small, triangular
projections on the distomesial margin of the
ventromedian lobule instead of a single, sub-
rectangular process bearing spines distally. More-
over, the lateral process is small and extends
transversely rather than being directed disto-
mesially, and the distal part of the ventrolateral
lobule is broadly semicircular and strongly in-
clined toward the ventromedian lobule.

Haliporotdes Stebbing 1914

Peneopsis. Faxon 1893:212; 1895:185.

Faxonia Bouvier 1905a:981 [part, excluding type-
species, Penaeopsis ocularis Faxon 1895 =
Pleoticus robustus (Smith 1885)].

Haliporus. Bouvier 1906b: 1 [part]; 1908:78 [part],
de Man 1911:31 [part]. Caiman 1925:9.

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FISHERY BULLETIN: VOL. 75, NO. 2

Haliporoides Stebbing 1914:20 [type-species, by
monotypy, Haliporoides triarthrus Stebbing
1914. Gender, masculine]. Caiman 1925:9.

Hymenopenaeus. Burkenroad 1936:102 [part].

Parahaliporus Kubo 1949:207.

Hymenopenaeus (Haliporoides). Barnard 1950:
619.

Diagnosis. -Body moderately robust, carapace
elongate, integument firm. Rostrum relatively
long, extending at least to, often beyond, second
antennular article, ventral margin straight or
concave; armed with dorsal and, frequently, with
ventral teeth; epigastric tooth separated from
rostral teeth by interval noticeably longer than
spaces between latter. Orbital and branchiostegal
spines absent; postorbital, antennal, ptery-
gostomian, hepatic, and suprahepatic spines
present. Cervical sulcus deep, long, extending to,
but not across, middorsum of carapace; hepatic
sulcus long, turning anteroventrally from almost
horizontal posterior part and reaching base of
pterygostomian spine; orbital-antennal and
branchiocardiac carinae and sulci well marked;
submarginal carina sharp. Abdomen carinate
dorsally at least along three posterior somites.
Telson with pair of fixed, lateral spines. Prosar-
tema moderately long, broad, and flexible. Anten-
nular flagella similar, subcylindrical and long,
not less than 3 times carapace length. Mandibular
palp three jointed (occasionally two jointed in
H. triarthrus, Ivanov and Hassan 1976), proximal
article short and narrow, intermediate one larger,
scalene-triangular in shape, and distal article
considerably shorter and narrower than preced-
ing one and tapering to blunt apex. First maxilla
with unsegmented palp, gently narrowing to
rounded apex. Fourth and fifth pereopods rela-
tively stout proximally, fifth not much longer
than fourth. First pereopod with or without spine
on basis. Exopods (quite small) on all maxillipeds
and pereopods. Lateral ramus of uropod armed
with subterminal, distolateral spine. In males,
petasma with distal part of ventral costa fused to
flexible flap of ventrolateral lobule; distal portion
of rib of dorsolateral lobule not elevated above,
but at level of adjacent area, and not projecting
beyond distal margin; ventromedian lobule lack-
ing paired processes distally; endopod of second
pleopod bearing appendices masculina and in-
terna, its basal sclerite produced into very short,
toothlike, ventrolateral spur. Thelycum of open
type. Pleurobranchia present on somites IX to

290

XIV; single, rather conspicuous arthrobranchia
on somite VII, and anterior and posterior arthro-
branchiae on somites VIII to XIII. Podobranchia
present on second maxilliped, and epipod on
second maxilliped (and on first if proximal exite
of coxa considered an epipod) through fourth
pereopod.

List of species .-Eastern Pacific: Haliporoides
diomedeae (Faxon 1893). Indo-West Pacific: Hali-
poroides sibogae (de Man 1907); Haliporoides
triarthrus Stebbing 1914.

Affinities. -The members of Haliporoides can be
distinguished readily from those belonging to
other related genera by the following features:
the epigastric tooth is separated from the series
of rostral teeth by an interval conspicuously
longer than the spaces between the latter; the
presence of a suprahepatic spine and an orbito-
antennal sulcus which, although shallow, is
clearly distinct; the spine of the lateral ramus
of the uropod which is subterminal. Also, the
arthrobranchia on somite VII is well developed
instead of being rudimentary and, in males, the
basal sclerite of the second pleopod is produced
into a very short, toothlike, rather than foliaceous,
ventrolateral spur.

In addition to the characters cited above,
Haliporoides, in contrast to Hymenopenaeus ,
possesses a thick, rigid integument, and lacks a
branchiostegal spine and a posthepatic carina; it
also possesses a petasma in which the ventro-
median lobule is not produced distally into con-
spicuous processes, and the rib of the dorsolateral
lobule is flush with the surrounding area. Finally,
Haliporoides may be separated from Pleoticus-
which it resembles in its general mien and in the
shape of the rostrum — not only by the characters
cited, but also by possessing a sharp branchio-
cardiac carina and deep branchiocardiac sulcus as
well as by the petasma, in which the ventral costa
is fused to the terminal part of the ventrolateral
lobule. The above clearly indicates that Hali-
poroides is the most distinct of the genera treated
here, except perhaps for Mesopenaeus.

Haliporoides diomedeae (Faxon 1893)
Figures 9, 20, 24-28

Peneopsis diomedeae Faxon 1893:212 [syntypes:
3 9, USNM 21175, off Golfo de Panama,
7°31'30"N, 79°14'00"W, 458 fm (838 m), 8 March

PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMPS

1891, Albatross stn 3384. 1 6 1 ?, USNM
21176, SW of Golfo de Panama, 7°30'36"N,
78°39'00"W, 730 fm (1,335 m), 11 March 1891,
Albatross stn 3395. 2 8 1 9 , MCZ 4644, SE of
Golfo de Panama, 7°21'N, 79°35'W, 511 fm
(935 m), 10 March 1891, Albatross stn 3394.
3 9 , off Punta Mala, Panama, 7°15'N, 79°36'W,
1,020 fm (1,866 m), 10 March 1891, Albatross
stn 3393. 2 9, off Punta Mariato, Panama,
7°06'15"N, 80°34'00"W, 695 fm (1,271 m),
23 February 1891, Albatross stn 3353. 1 6,
USNM 21 174, S of Peninsula de Azuero, 6°30'N,
81°44'W, 555 fm (1,015 m), 24 February 1891,
Albatross stn 3358]. Faxon 1895:185, pi. G.

Faxonia diomedeae. Bouvier 1905a:981.

Haliporus diomedeus. Bouvier 1906b:4; 1908:80.

Haliporus diomedeae. de Man 1911:7.

Hymenopenaeus diomedeae. Burkenroad 1936:
104. Hancock and Henriquez 1968:445. Idyll
1969:641. Chirichigno Fonseca 1970:13, fig. 18.
del Solar C. et al. 1970:18. Arana Espina and
Cristi V. 1971:25. Illanes B. andZiiniga C. 1972:
3, pi. 1-2.

Hymenopenaeus diomedaea. Bahamonde 1963:3

(unnumbered).
Vernacular names; gamba roja (Peru); gamba,

camaron de mar, camaron de profundidad

(Chile).

Material

PANAMA— 2 V , MCIP, 32 km SE of Punta Mala, Peninsula
de Azuero, 823-1,006 m, 1973, Canopus. 3 9 syntypes, USNM
21175, off Golfo de Panama, 458 fm (838 m), 8 March 1891,
Albatross stn 3384. 1 6 1 9 syntypes, USNM 21176, SW of
Golfo de Panama, 730 fm (1,335 m), 11 March 1891, Albatross
stn 3395. 2 6 1 9 syntypes, MCZ 4644, SE of Golfo de Panama,
511 fm (935 m), 10 March 1891, Albatross stn 3394. 1 6 syn-
type, USNM 21174, S of Peninsula de Azuero, 555 fm (1,015 m),
24 February 1891, Albatross stn 3358.

PERU— 1 9 , USNM, off Casitas, Tumbes, 550 m, 16 Decem-
ber 1968, Kaiyo Maru. 58 d 56 9, USNM, W of I Macabi', 607-
735 m, 5 September 1966, Anton Bruun stn 754.

CHILE— 4 9, USNM, off Paposo, Antofagasta, 950 m,
16 August 1966, Anton Bruun stn 714. 8 6 13 9, USNM, off
Bahia Pichidangui, Coquimbo, 960 m, 12 August 1966, Anton
Bruun stn 703. 1 6 1 9 , USNM, Valparaiso, 10 February 1956,
John Manning. 14 6 17 9, USNM, off Punta Topocalma,
Colchagua, 750-730 m, 5 August 1966, Anton Bruun stn 687.

FIGURE 2A.—Haliporoides diomedeae, 9 37.5 mm cl, off Bahi'a Pichidangui, Coquimbo, Chile. Lateral view.

291

FISHERY BULLETIN: VOL. 75, NO. 2

Description. -Body rather robust (Figure 24), in-
tegument firm and glabrous. Rostrum straight or
gently sinuous with upturned tip, moderately
long, at most slightly overreaching antennular
peduncle, its length 0.45-0.60 that of carapace.
Rostral plus epigastric teeth 3-6 (mode 5; N =
100); epigastric tooth situated at about 0.3 length
of carapace from orbital margin, first rostral at
level of, or immediately posterior to, orbital
margin. Adrostral carina strong, extending from
orbital margin almost to apex of rostrum; post-
rostral carina very strong to near posterior
margin of carapace, there merging with inconspic-
uous dorsal tubercle. Antennal, pterygostomian,
postorbital, and hepatic spines long, slender, and
sharp; both antennal and postorbital spines
(latter situated directly posterior to antennal)
continuous with short, blunt, basal carina; basally
broad suprahepatic spine (occasionally accom-
panied by smaller dorsal one) present, giving rise
to deep notch dorsal to hepatic spine; orbito-
antennal sulcus shallow, but clearly distinct;
cervical carina sharp, cervical sulcus deep, ex-
tending to, but not crossing, postrostral carina, its
dorsal extremity located almost 0.45 length of
carapace from orbital margin; hepatic sulcus
deep, hepatic carina sharp anteriorly and turning
anteroventrally to base of pterygostomian spine;
both hepatic carina and sulcus almost indistinct
posteriorly, to anteroventral end of branchio-
cardiac sulcus. Branchiocardiac carina long,
sinuous, and sharp, accompanying sulcus deep
and broad; submarginal carina long, extending
from base of pterygostomian spine to posterior
margin of carapace.

Eye (Figure 25) with basal article produced
distomesially into pubescent, relatively short
scale; ocular peduncle short, bearing rather small
mesial tubercle; cornea subreniform, greatest
diameter about 2 times that of base of ocular
peduncle, strongly slanting posterolaterally.

Antennular peduncle length equivalent to
about 0.5 that of carapace; prosartema broad and
short, extending only to distomesial extremity of
ocular peduncle; stylocerite extending about 0.6
of distance between its proximal extremity and
mesial base of distolateral spine; latter moder-
ately long, slender, and sharp. Antennular fla-
gella long, although incomplete in all specimens
examined, in shrimp 32.5 mm cl, broken dorsal
flagellum 118 mm long, thus 3.65 times as long
as carapace. Scaphocerite overreaching anten-
nular peduncle by about 0.2 of its own length;

FIGURE 25. — Haliporoid.es diomedeae, 2 44.5 mm cl, off Punta
Topocalma, Colchagua, Chile. Eye.

lateral rib ending in rather slender spine, falling
short of distal margin of lamella. Antennal fla-
gellum broken in specimens examined, according
to Illanes and Ziiniga (1972) "longer than total
length of body."

Mandibular palp (Figure 26A ) extending as far
as basal 0.4 length of carpocerite; proximal article
scalene-triangular, about 2.65 times as long as
wide; distal article considerably shorter and
narrower than proximal, and tapering to blunt
tip. First and second maxillae as illustrated
(Figure 26B, C); somite VII bearing single con-
spicuous arthrobranchia at base of first maxilli-
ped (Figure 26De-e1). Third maxilliped reaching
beyond antennular peduncle by tip or by length
of dactyl in males and by as much as dactyl and
0.5 length of propodus in females; dactyl with
acute tip in females, clublike in males, its length
0.90-0.95 that of propodus.

First pereopod reaching between base and
distal end of carpocerite in males, and almost to
distal end of carpocerite or overreaching it by as
much as length of dactyl in females. Second pereo-
pod extending, at most, to midlength of second
antennular article in males, and as far as distal
end of third article in females. Third pereopod
reaching distal end of third antennular article
or overreaching it by not more than length of
dactyl in males, and by entire propodus plus 0.15
length of carpus in large females. Fourth pereo-
pod exceeding antennular peduncle by, at most,
length of dactyl in males, and by dactyl or by
entire propodus in females. Fifth pereopod over-
reaching antennular peduncle by as much as
length of dactyl and 0.8 that of propodus in males,
and by distal two podomeres plus 0.15-0.25 length

292

PEREZ EARFANTE: AMERICAN SOLENOCERII) SHRIMPS

A-D.

FIGURE 26.— Haliporoides diomedeae, 9 45.5 mm cl, Valparaiso, Chile. A, Mandible. S, First maxilla. C, Second maxilla. D, First

maxilliped. e, Arthrobranchia. e\ Enlargement of e (all from left sidel.

of carpus in females. Pereopods increasing in
length from first to fifth; third and fourth extend-
ing distally for about same distance. First pereo-
pod with spine on basis and ischium, and one
movable distal spine and one or two fixed proximal
ones on merus; basis of second pereopod lacking
spine. In females, coxal plate of third pereopod
directed and broadening mesially, strongly con-
vex posteriorly. In both sexes, anteromesial spine
present on coxae of third through fifth pereopods;
in females, spine on third long, slender, and
situated anterodorsally to coxal plate, and spines
on fourth and fifth small and sharp; in males,
spines on third and fourth pereopods small and
sharp, but spine on fifth large, flattened, curved
laterally.

Abdomen with middorsal keel from fourth
through sixth somites and strong, sharp spine at
posterior end of keel on each; sixth somite short,
about 1.25 times as long as high, bearing postero-
ventral spines. Telson with broad median sulcus
deep anteriorly, shallower posteriorly, ending at
level of base of lateral spines, and flanked by
well-defined ridges; terminal portion length 4-5

times basal width, spines short, 1.0-1.65 times
basal width of terminal portion. Mesial ramus of
uropod reaching apex of telson or overreaching it
by about 0.15 of its own length; lateral ramus,
in turn, overreaching mesial by almost 0.2 of its
own length, armed with rather strong, sub-
terminal, distolateral spine. Third through fifth
pleopods in males bearing strong dorsomesial
ridge, that of third bearing distally strong sub-
rectangular tooth with minute tooth at its base;
ridge on fourth ending in also large, subtriangular
tooth; last three pleopods in females with barely
marked dorsomesial ridge.

Petasma (Figure 27 'A, B) with row of cincinnuli
occupying only proximal 0.3 of median line; ter-
minal part of ventromedian lobule abruptly
broadening distally with terminal margin serrate
laterally; rib of dorsolateral lobule broad prox-
imally, its distal extremity reaching, but not
overreaching, margin of adjacent membranous
portion; distal part of ventrolateral lobule free,
forming roughly subelliptical flap diverging from
ventromedian lobule; ventral costa broad prox-
imally, tapering along margin of flap.

293

FISHERY BULLETIN: VOL. 75, NO. 2

FIGURE 27 .—Haliporoides diomedeae, 6 34.5 mm cl, off Bahi'a Pichidangui, Coquimbo, Chile. A, Petasma, dorsal view (partly bent
laterally). B, Ventral view of left half. C, Right appendices masculina and interna, dorsal view. D, Ventromesial view.

Appendix masculina (Figure 27C, D) short,
length about 1.5 times maximum width, pro-
duced laterally into broad semicircular lobe, ven-
trally excavated and bearing patch of long setae
along entire distal margin. Appendix interna
falling short of distal margin of appendix mas-
culina, and armed with thickly set setae along
entire distal margin; distolateral spur very short
and obtuse.

Thelycum ( Figure 28 ) with no ridge or protuber-
ance on sternite XIV, latter smoothly convex or
low subconical, often bearing minute central
tubercle; posterior part of sternite XIII armed
with strong median, acute to blunt subconical
protuberance directed anteriorly and studded
with numerous setae on anterior half; posterior
margin of sternite XII lacking horns.

Co/or.-Overall pink with red and orange patches
and bands, both longitudinal and transverse. For
detailed account of coloration see Illanes B. and
Zuhiga C. (1972).

Maximum size-Males: 50 mm cl; females: 57 mm
cl (in material examined by me).

Geographic and bathymetric ranges.-Off Penin-
sula de Azuero, Panama (Figure 20) to Talca-
huano, Chile (36°40'S), in depths between 240

294

(Illanes B. and Zuhiga C. 1972) and 1,866 m (Fig-
ure 9). Information on the geographic and bathy-
metric distributions of this species, as well as of its
other two congeners in the American Pacific, is
extremely meager.

Affinities. -Haliporoides diomedeae is the only
member of the genus occurring in American
waters and may thus be readily distinguished
from the other solenocerids in the region by
generic characters. Its two congeners, the Indo-
West Pacific H. sibogae and H. triarthrus, differ
from it in possessing an arcuate, ventrally toothed
rostrum, and in lacking meral spines on the first
pair of pereopods, as well as in petasmal and thely-
cal features. In both of them, the ventromedian
lobule of the petasma is neither expanded distally
nor serrate along its terminal margin, and the
thelycum exhibits a midridge on sternite XIII
instead of a subconical, median protuberance.

Remarks-Studies of this species are extremely
few, and almost entirely restricted to its external
morphology. The most recent contribution is one
by Illanes B. and Zuhiga C. (1972), who presented
many fine observations on numerous features.
Previously, Arana Espina and Cristi V. (1971)
had determined the relations between the follow-
ing parameters: carapace length, total length,

PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMPS

whole weight, and abdominal weight (cl/tl, cl/ww,
cl/aw, tl/ww, tl/aw). They found statistically sig-
nificant differences between males and females in
all relations with the exception of carapace
length/total length.

Economic importance. -At present this species is
not taken commercially. However, dense concen-
trations have been located in various areas within
its range. Off the west coast of America three
deepwater shrimps — Solenocera agassizii Faxon
1893; Solenocera florea Burkenroad 1938, and
Heterocarpus reedi Bahamonde 1955 — are uti-
lized; consequently, it is to be expected that H.
diomedeae, a species larger than those mentioned
above, eventually will be exploited.

Pleoticus Bate 1888

Philonicus Bate 1888:273 [part, excluding Phi-
lonicus lucasii (Bate 1881) = Hadropenaeus
lucasii, and Philonicus pectinatus Bate 1888 =
Solenocera pectinata]. [Type-species, by

FIGURE 28.— Haliporoides diomedeae, 9 44.5 mm cl, off Punta
Topocalma, Colchagua, Chile. Thelycum, ventral view.

subsequent designation of Fowler 1912:543,
Philonicus mulleri Bate 1888]. Preoccupied by
Philonicus Loew 1849:144 (Diptera).

Pleoticus Bate 1888:xii [partj. [Replacement name
for Philonicus Bate. Type-species, Philonicus
mulleri Bate 1888. Gender, masculine].

Faxonia Bouvier 1905a:981 [part, excluding
Faxonia diomedeae (Faxon 1893)]. [Type-
species, by subsequent designation of Fowler
1912:543, Penaeopsis ocularis Faxon 1895 =
Pleoticus robustus (Smith 1885)].

Parartemesia Bouvier 1905b:747 [part, excluding
Parartemesia tropicalis Bouvier 1905b = Meso-
penaeus tropicalis (Bouvier 1905b)]. [Type-
species, by subsequent designation of Fowler
1912:543, Parartemesia carinata Bouvier 1905b
= Pleoticus muelleri (Bate 1888)].

Haliporus. Bouvier 1906b: 1 [part]; 1908:78 [part].
A. Milne Edwards and Bouvier 1909:206 [part],
de Man 1911:31 [part]. Fowler 1912:542 [part].

Hymenopenaeus. Smith 1885:179 [part]. Burken-
road 1936:102 [part]. Kubo 1949:212 [part].
Roberts and Pequegnat 1970:29 [part].

Diagnosis-Body robust, carapace elongate, integ-
ument thick, firm. Rostrum moderately long,
reaching midlength of second antennular article
or slightly overreaching peduncle; ventral margin
straight -to concave; armed only with dorsal teeth;
epigastric tooth and first rostral separated by
interval equal to, or only slightly greater than,
that between first and second rostral teeth.
Orbital, postorbital, antennal, and hepatic spines
present; pterygostomian spine absent; branchio-
stegal spine present or absent. Cervical sulcus
deep, long, extending to, but not across, mid-
dorsum of carapace; hepatic sulcus well marked;
posthepatic and branchiocardiac carina lacking;
branchiocardiac sulcus usually absent; sub-
marginal carina sharp; posthepatic carina absent.
Abdomen carinate dorsally at least along pos-
terior three somites. Telson with pair of conspic-
uous, fixed lateral spines. Prosartema long or
moderately long, flexible. Antennular flagella
similar, subcylindrical, and longer than carapace.
Mandibular palp two jointed, articles broad, distal
one as long, or almost as long, as basal, tapering
to blunt apex. First maxilla with unsegmented
palp, gently narrowing to rounded apex. Fourth
and fifth pereopods rather stout proximally, fifth
moderately longer than fourth. First pereopod
with spine on basis and ischium. Exopods on all
maxillipeds and pereopods. Lateral ramus of

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FISHERY BULLETIN: VOL. 75, NO. 2

uropod armed with terminal, distolateral spine.
In males, petasma with ventral costa free from
distally flexible terminal part of ventrolateral
lobule; ventromedian lobule not expanded dis-
tally. Endopod of second pleopod bearing appen-
dices masculina and interna, and with basal
sclerite produced distally into elongate ventro-
lateral spur. Thelycum of open type, lacking
enclosed seminal receptacle. Pleurobranchia pres-
ent on somites IX to XIV; one or two rudimentary
arthrobranchiae on somite VII; and anterior and
posterior arthrobranchiae on somites VIII to XIII.
Podobranchia present on second maxilliped, and
epipod on second maxilliped (and on first if prox-
imal exite of coxa considered an epipod) through
fourth pereopod.

List of species. -Western Atlantic: Pleoticus ro-
bustus (Smith 1885); Pleoticus muelleri (Bate
1888). Red Sea: Pleoticus steindachneri (Balss
1914).

Affinities. -The members of Pleoticus resemble
those of Hymenopenaeus and Haliporoides in the
character of the rostrum and general form of the
carapace; however, in Pleoticus the epigastric
tooth is separated from the first rostral by an
interval which is equal to, or only slightly greater
than, that between the first and second rostral
teeth; an orbital spine is present as it only is in
the more distantly related Mesopenaeus; the
branchiocardiac carina is absent; and the branch-
iocardiac sulcus is usually absent. Furthermore,
the mandibular palp is two jointed unlike the
usually three jointed one of Haliporoides but like
that of Hymenopenaeus; however, in contrast to
the palp of the latter, that of Pleoticus is broad and
its distal article is as long as, or longer than, the
basal. Finally, in the petasma of Pleoticus the
distal extremity of the ventral costa is free from
the ventrolateral lobule instead of being fused
to it.

Pleoticus agrees with Hadropenaeus in the
arrangement of the epigastric and rostral series
of teeth, the lack of branchiocardiac and post-
hepatic carinae, the absence of pterygostomian
spines, as well as in having the distal extremity
of the ventral costa of the petasma free from the
adjacent part of the ventrolateral lobule. The
considerably more elongate carapace, the low and
longer rostrum, and the presence of strong sub-
marginal carina, and orbital spine separate the
former from the latter.

The similarities cited above indicate ihatPleoti-
cus occupies a position somewhat intermediate
between the more primitive Hymenopenaeus and
Haliporoides, on one hand, and Hadropenaeus on
the other.

The genus Pleoticus is less homogeneous than
the other genera treated here. In P. robustus and
P. muelleri the branchiocardiac sulcus is abent or
indistinct whereas in P. steindachneri it is
distinctly marked; the branchiostegal spine, while
present in P. robustus and P. muelleri, is lacking
in P. steindachneri. Whereas in the petasma of
P. robustus and P. steindachneri the row of cincin-
nuli occupies almost the entire median line, and
the ventromedian lobule is distally membranous
and entire, in that of P. muelleri the row ofcincin-
nuli is limited to the proximal 0.4 of the median
line, and the ventromedian lobule is heavily scle-
rotized distally and bears strong projections. In
spite of these differences, it seems to me that the
many features shared by these species justify
their being grouped within a single genus. I have
not examined specimens of P. steindachneri, but
the descriptions and illustrations of Balss (1914,
1915) indicate that this shrimp is more closely
related to P. robustus and P. muelleri than to
members of other genera.

Key to the Species of Pleoticus in
the western Atlantic

1. Body entirely pubescent. Prosartema not
overreaching distal margin of first
antennular article. Branchiostegal
spine present. Females with paired,
triangular projections near anterior
margin of sternite XIV, and strong
median ridge on sternite XIII. Males
with petasma cincinnulate along en-
tire median line, its ventromedian

lobule entire distally P. robustus

Body almost entirely polished. Prosar-
tema considerably overreaching distal
margin of first antennular article.
Branchiostegal spine absent. Females
lacking triangular projections on ster-
nite XIV, bearing strong, median pro-
jection on sternite XIII. Males with
petasma cincinnulate along proximal
0.4 of median line, its ventromedian
lobule produced in two projections ....
P. muelleri

296

PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMPS

Pleoticus robustus (Smith 1885)
Figures 9, 29-36

Hymenopenaeus robustus Smith 1885:180 [syn-
types: 2 6 19, USNM 6907; 2 6 5 9 (1 9 in
original lot = Penaeopsis serrata Bate 1881),
USNM 6908; type-locality: 11°43'00"N,
69°09'30"W, 208 fm (380 m), S of Curacao, Alba-
tross stn 2125]. Burkenroad 1936:118. Ander-
son and Lindner 1945:288. U.S. Fish and Wild-
life Service 1948:2. Springer 1951a:80; 1951b:
6. Springer and Bullis 1952:11. Popovici and
Angelescu 1954:509. Springer and Bullis 1954:
3. Voss 1955:9, fig. 6. Bullis 1956:1 [not Fig. 1 =
Aristeus antillensis A. Milne Edwards and Bou-
vier 1909]. Springer and Bullis 1956:8. Clifford
1956:438. Guest 1956:7. Lindner 1957:87.
Anderson 1958:1, fig. 6. U.S. Fish and Wildlife
Service 1958:1, fig. 1-6. Bullis and Thompson
1959a:35; 1959b:l. Hutton et al. 1959:7. Eldred
and Hutton 1960:91, fig. 12. Cummins and Riv-
ers 1962:19. Bullis and Cummins 1963:9.
Davant 1963:21, fig. 19-20. Boschi 1964:38.
Hutton 1964:439. Bullis and Thompson 1965:5.
Holthuis and Rosa 1965:1. Pericchi Lopez 1965:
24. Joyce and Eldred 1966:24. Kutkuhn 1966:
21. Christmas and Gunter 1967:1442. Thomp-
son 1967:1454. Idyll 1969:638. Klima 1969:1.

Roe 1969:161, fig. 1. Anderson and Bullis 1970:
112. Perez Farfante 1970:13, fig. 3F-H. Roberts
and Pequegnat 1970:30, fig. 3-1B-C. Anderson
and Lindner 1971:313, fig. 1-7. Garcia Pinto
1971:5. Pequegnat and Roberts 1971:8. Garcia
del Barco 1972:172.

Peneopsis ocularis Faxon 1895:187.

Faxonia ocularis. Bouvier 1905a:981.

Haliporus robustus. Bouvier 1906b:4; 1908:8.
A. Milne Edwards and Bouvier 1909:210, fig.
29-37, pi. 1, fig. 14-15, pi. 2, fig. 1-7. de Man
1911:7. Lenz and Strunck 1914:303. Burken-
road 1934:69.

Parapenaeus paradoxus Boone 1927:79 [part].

Hymenopeneus robustus. Burkenroad 1963a:173.

Royal red shrimp. Bates 1957:9, figures. Bullis
and Rathjen 1959:1. Anonymous 1977:2.

Vernacular names: royal red shrimp (United
States), camaron rojo gigante (Mexico), caraa-
ron real rojo (Cuba), langostino rojo (Vene-
zuela).

Material

UNITED STATES— Massachusetts: 2 6 2 9,
USNM, S of Martha's Vineyard, 320 m, 28 January 1960,
Delaware stn 39. 19, USNM, off Georges Bank, 20 July 1955,
Delaware. North Carolina: HI?, USNM, NE of Cape
Lookout, 348-384 m, 13 November 1956, Combat stn 171.
6 2, USNM, off Cape Lookout, 366 m, 22 June 1957, Combat

FIGURE 29.— Pleoticus robustus, 6 31 mm cl, east of Peninsula Valiente, Panama. Lateral view.

297

FISHERY BULLETIN: VOL. 75, NO. 2

stn 410. 5 6 5 2, USNM, SE of Cape Fear, 402 m, 29 January
1972, Oregon II stn 11746. South Carolina: 16 19, USNM,
off Port Royal Sound, 366 m, 23 January 1972, Oregon II stn
11734. Florida: 3 6, USNM, off St Augustine, 384-393 m,
9 February 1965, Oregon stn 5231. 1 6 3 9 , USNM, off St Aug-
ustine, 344-338 m, 1 May 1956, Pelican stn 41. 3 2 , USNM, off St
Augustine, 316-329 m, 2 May 1956, Pelican stn 46. 1 6 22 2,
USNM, off St Augustine, 324-333 m, 3 February 1962, Silver Bay
stn 3725. 28 6 30 9, USNM, off Flagler Beach, 384 m,
16 November 1964, Oregon stn 5107. 1 6 2 9, USNM, off
Coronada Beach, 348 m, 10 February 1965, Oregon stn 5241.
9 6 6 9, USNM, off Oak Hill, 402-430 m, 11 February 1965,
Oregon stn 5247. 4 2, USNM, off Cape Kennedy, 338 m,
27 January 1962, Silver Bay stn 3714. 5 6 6 2, USNM, off
Cocoa Beach, 329 m, 11 March 1956,Pelican stn 13. 11 c? 15 9,
RMNH, E of Hutchinsons I, 324 m, 16 July 1965, Gerda stn 654.
11 <J 13 9, UMML, off St Lucie Inlet, 366-375 m, 21 May 1968,
Gerda stn 998. 15 <J 14 2, USNM, SE of St Lucie Inlet, 287-
262 m, 16 July 1965, Gerda stn 655. 2 6, USNM, E ofCarysfort
Reef, 549 m, 23 July 1957, Combat stn 444. 16 19, USNM,
off Islamorada, 457-476 m, 18 July 1955, Oregon stn 1351.

3 6 2 2, USNM, off Double Headed Shot Cays, 558-514 m,
29 August 1967, Gerda stn 861. 1 2, UMML, S of Marquesas
Keys, 512 m, 2 February 1968, Gerda stn 970. 9 2, USNM,
SW of Marquesas Keys, 402-267 m, 2 February 1968, Gerda
stn 969. 6 6 4 2 , USNM, SW of Marquesas Keys, 437-320 m,
2 February 1968, Gerda stn 968. 1 9 , UMML, S of Dry Tortugas,
622 m, 28 April 1969, Gerda stn 1099. 2 <J 3 9 , UMML, S of Dry
Tortugas, 459-494 m, 28 April 1969, Gerda stn 1098. 26 6 27 2 ,
USNM, SW of Dry Tortugas, 348 m, 13 April 1954, Oregon
stn 1005. 5 6 8 9, USNM, SW of Dry Tortugas, 402 m,
15 June 1956, Oregon stn 1539. 1 6, USNM, NW of Dry Tortu-
gas, 311-366 m, 7 July 1955, Oregon stn 1321. 2 6 2 2 , USNM,
S of St George I, 366 m, 21 August 1970, Oregon II stn 11180.

2 6 2 2 , USNM, S of Santa Rosa I, 439 m, 28 August 1970,
Oregon II stn 11189. 1 2, USNM, S of Santa Rosa I, 527 m,

4 February 1970, Oregon II stn 10899. 9 6 6 2 , USNM, off Gulf
Beach, 576-622 m, 28 April 1951, Oregon stn 319. Alabama (all
from off Mobile Bay): 4 9, USNM, 549 m, 10 August 1970,
Oregon II stn 11137. 1 2 , USNM, 594 m, 10 August 1970, Ore-
gonll stn 11 139. 2 6 2 2 , USNM, 433 m, 22 June 1969, Oregonll
stn 10640. 1 6 4 2, USNM, 366 m, 18 December 1962, Oregon
stn 4151. 8 2 juv, YPM, 219-238 m, 24 March 1935, Atlantis
stn 2377. 3 2, USNM, 512 m, 10 July 1952, Oregon stn 597.
Louisiana: 1 6, AMNH, E of Mississippi Delta, 384 m,
11 February 1885, Albatross stn 2377. 1 6, USNM, E of Mis-
sissippi Delta, 357 m, 1 September 1970, Oregon II stn 11202.
4 i , USNM, E of Mississippi Delta, 549 m, 23 October 1962,
Oregon stn 4005. 14 6 9 2 , USNM, E of Mississippi Delta,
357 m, 23 September 1950, Oregon stn 126. 7 6 10 2, USNM,
E of Mississippi Delta, 402 m, 22 April 1951, Oregon stn 307.

3 (517 9, USNM, E of Mississippi Delta, 402 m, 25 August 1962,
Oregon stn 3733. 1 S , YPM, E of Mississippi Delta, 302 m,
26 March 1935, Atlantis stn 2381. 3 6, USNM, off Atchafalaya
Bay, 402 m, 11 November 1951, Oregon stn 501. Texas: 2 6
3 9, USNM, SSE of Galveston, 366 m, 18 November 1951,
Oregon stn 503. 3 6 4 9 2 juv, USNM, E of St Joseph I,
503 m, 6 May 1956, Oregon stn 1506. 1 6, USNM, off Corpus
Christi, 640-732 m, 16 April 1952, Oregon stn 543. 1 6 2 9,
USNM, off Padre I, 549 m, 23 January 1964, Oregon stn 4637.
1 6 juv, USNM, off Port Isabel, 640 m, 6 August 1969,
Western Gulf stn 38. 1 9 , USNM, off Brownsville, 457 m,
6 August 1969, Western Gulf stn 39.

MEXICO— Tamaulipas: 1 6 1 9, USNM, off Las Lava-

deros, 558 m, 2 June 1970, Oregon II stn 10953. 2 9, USNM,
off Las Lavaderos, 677 m, 2 June 1970, Oregon II stn 10954.
Veracruz: 2 6 2 9 , USNM, N of Punta Roca Partida, 357 m,

5 June 1970, Oregon II stn 10959. ldlS, USNM, NE of Punta
Roca Partida, 613 m, 5 June 1970, Oregon II stn 10960.
Tabasco: 1 9 , USNM, NW of Laguna del Carmen, 430 m,

6 June 1970, Oregon II stn 10963. 1 9, USNM, N of Punta
Frontera, 613 m, 9 June 1970, Oregon II stn 10984.

HAITI— 14 6 7 9, USNM, off Cape-Haitien, 640 m, 12
February 1963, Silver Bay stn 5142.

DOMINICAN REPUBLIC— 1 6 1 9, USNM, E of Puerto
Plata, 732-640 m, 15 October 1963, Silver Bay stn 5168.

LESSER ANTILLES— 4 2 , USNM, off Dog I, 628 m,
6 December 1969, Oregon II stn 10835. 2 2, USNM, off Dog I,
688 m, 6 December 1969, Oregonll stn 10834. 7 6 6 2 , USNM,
NE of Saba I, 649-668 m, 18 May 1967, Oregon stn 6696.
4 6 5 2, USNM, E of Sint Eustatius, 642 m, 8 December 1969,
Oregon II stn 10840. 2 6 6 9, USNM, E of St Christopher,
644 m, 8 December 1969, Oregon II stn 10841. 34 <5 31 2,
USNM, off St Christopher, 640-676 m, 20 May 1967, Oregon
stn 6701. 2 2, USNM, E of Capesterre, Guadeloupe, 466-640 m,
16 July 1969, Pillsbury stn 936. 2 6 7 2 syntypes, USNM
6907, S of Curagao, 380 m, 18 February 1884, Albatross stn 2125.
2 6 5 2 syntypes, USNM 6908, S of Curacao, 380 m,

18 February 1884, Albatross stn 2125. 1 2, USNM, NW of
Aruba, 622 m, 26 November 1970, Oregon II stn 11307.

WESTERN CARIBBEAN— 2 6 19, USNM, W of
Rosalind Bank, 366 m, 7 June 1962, Oregon stn 3627. 2 6 1 9,
USNM, NE of Cayos Hobbies, 521 m, 25 October 1970, Oregon II
stn 11220. 3 9, USNM, W of Rosalind Bank, 457 m,
24 August 1957, Oregon stn 1889. 32 6 26 2, UMML, W of
Quita Sueho Bank, 450-576 m, 31 January 1971, Pillsbury stn
1355. 5 6 2 9, USNM, W of Quita Sueho Bank, 439-457 m,
21 May 1962, Oregon stn 3565. 1 2 , USNM, SW of I de Provi-
dencia, 549 m, 13 September 1957, Oregon stn 1927. 1 6 2 9,
USNM, W of I de San Andres, 549 m, 27 October 1970, Oregon II
stn 11225. 1 2, USNM, W of Cayos de Albuquerque, 585 m,

27 October 1970, Oregon II stn 11226. 1 2, USNM, W of Cayos
de Albuquerque, 192 m, 7 February 1967, Oregon stn 6444.

MEXICO— Quintana Roo: 1 6 5 2, USNM, off I de Cozu-
mel, 412-457 m, 16 March 1968, Pillsbury stn 602.

BELIZE— 8 6 2 9, YPM, off Glover Reef, 669 m,
29 April 1925, Pawnee. 4 6 6 9, USNM, off Stann Creek,
457-732 m, 10 June 1962, Oregon stn 3635. 2 6 3 2, USNM,
off Jonathan Point, 348 m, 9 June 1962, Oregon stn 3643.

NICARAGUA— 2 6 2 9, USNM, NE of Islas del Mai'z,
549-585 m, 23 May 1962, Oregon stn 3576.

PANAMA— 8 <J 14 9, USNM, E of Peninsula Valiente,
512 m, 25 May 1962, Oregon stn 3583. 6 cJ 9 2 , USNM, Golfo de
los Mosquitos, 549 m, 31 May 1962, Oregon stn 3600. 1 6 3 9,
USNM, Golfo de los Mosquitos, 732 m, 31 May 1962, Oregon
stn 3601. 2 9, USNM, NE of Belen, 439 m, 30 May 1962,
Oregon stn 3592. 1 juv, USNM, off Punta Manzanillo, 421 m,

19 October 1965, Oregon stn 5740. 1 6, USNM, 5 July 1972,
Canopus.

COLOMBIA— 1 9, USNM, off Punta Broquelles, 732 m,

28 May 1964, Oregon stn 4902. 3d3?, USNM, N of Islas de
San Bernardo, 549 m, 6 November 1970, Oregon II stn 11244.
7d8 9, USNM, off Puerto Colombia, 366 m, 2 December 1968,
Oregon II stn 10260. 4 9, USNM, W of Santa Marta, 631 m,
9 November 1970, Oregon II stn 11250. 1 6 1 9, USNM, W of
Ri'ohacha, 567-531 m, 30 July 1968, Pillsbury stn 781. 6d39,
UMML, W of Cabo de la Vela, 408-576 m, 29 July 1968, Pillsbury
stn 776. 3d7 9, USNM, W of Cabo de la Vela, 366 m,

298

PEREZ FARFANTE AMERICAN SOI.ENOCERII) SHRIMPS

2 June 1964, Oregon stn 4922. 21 c5 15 9, USNM, Wof Cabo de
la Vela, 439-448 m, 2 June 1964, Oregon stn 4923. 3 6 2 9,
USNM, off Cabo de la Vela, 485 m, 9 October 1965, Oregon
stn 5689.

VENEZUELA— 8 9 , USNM, E of Peninsula de Paraguana,
421 m, 27 September 1963, Oregon stn 4406. 4 9, USNM, off
Penfnsula de Paraguana, 457 m, 4 October 1963, Oregon stn
4419. 4 9, USNM, NE of San Juan de los Cayos, 384-607 m,
26 July 1968, Pillsbury stn 753. 3 6 9 9, USNM, off Peninsula
de Araya, 402 m, 20 October 1963, Oregon stn 4477. 2 6 9 9,
USNM, NE of Islas Los Testigos, 366-439 m, 24 September 1964,
Oregon stn 5037. 10 6 11 9, USNM, NE of Islas Los Testigos,
388-457 m, 23 September 1958, Oregon stn 2353. 5 6 6 9,
USNM, NE of Punta Araguapiche, 366 m, 3 November 1957,
Oregon stn 1981. 3 6 3 9, USNM, NE of Punta Araguapiche,
457 m, 3 November 1957, Oregon stn 1982.

GUYANA— 1 6, USNM, off Waini Beach, 137 m, 4 Novem-
ber 1957, Oregon stn 1993.

Description.- Body robust, integument thick, and
entirely covered by densely set, short setae (Fig-
ure 29). Rostrum almost reaching or slightly
overreaching distal end of antennular peduncle,
nearly horizontal and straight in large adults,
somewhat shorter, elevated, and broadly convex
dorsally almost to tip in young; tip saber or spear
shaped, 0.2-0.3 rostrum length, longest in adult.
Rostral plus epigastric teeth 10-12 (mode 11;
N = 200); teeth regularly closer from epigastric
to ultimate; epigastric tooth located almost at
level of dorsal extremity of cervical sulcus and
fourth rostral tooth near level of orbital margin.
Adrostral carina slender, extending from orbital
margin almost to apex of rostrum; postrostral
carina strong, long, almost reaching posterior
margin of carapace; small tubercle present behind
postrostral carina; antennal carina short but
prominent. Orbital spine short, broad basally;
postorbital spine slender, rather short, located
posterodorsal to base of antennal spine; latter
longest of lateral spines on carapace; branchio-
stegal spine moderately long; hepatic spine
relatively short; pterygostomian spine lacking.
Cervical sulcus sinuous, deep, ending lateral to
postrostral carina at about midlength of carapace;
cervical carina sharp. Hepatic sulcus almost hori-
zontal posteriorly, merging with depressed area
ventral to hepatic spine, from there inclining
anteroventrally, and ending in pit below branchio-
stegal spine; hepatic carina accompanying
anterior portion of sulcus sharp and prominent;
branchiocardiac carina indistinct or barely per-
ceptible; submarginal carina well marked, sub-
parallel to free ventral margin of carapace.

Eye (Figure 30E) with basal article produced
distomesially into pubescent, broad scale, bearing

spinelike distal projection; ocular peduncle short,
cornea broad, greatest diameter slightly more
than twice that of base of ocular peduncle, its
proximal margin strongly slanting postero-
lateral^.

Antennular peduncle length equivalent to
about 0.6 that of carapace; prosartema ending
slightly proximal to distal margin of first article;
stylocerite extending only to about 0.45 of
distance between its proximal extremity and
mesial base of distolateral spine, produced
distally into short, rather blunt spine; distolateral
spine slender and moderately long, sensibly over-
reaching distal margin of article. Antennular
flagella (Figure 30A ) rather broad proximally,
subfiliform distally, markedly unequal in length,
but both long, and increasing proportionately in
length with age: dorsal flagellum about 1.4 times
carapace length and ventral about 1.2 times cara-
pace length, in shrimp 8.5 mm cl, and 3.5 and 2
times carapace length, respectively, in shrimp
32 mm cl (flagella incomplete in all larger animals
examined). Dorsal flagellum with distal half of
proximal portion bearing longitudinal row of
combs of long setae on slightly concave ventral
surface (Figure 30D) and stiff short setae on
remaining surfaces; stiff setae increasingly sparse
toward tip of flagellum. Ventral flagellum exhibit-
ing strong sexual dimorphism: in mature male,
proximal portion resembling bottle brush, with
mesial surface flattened and bearing longitudinal
band of stiff, dense setae with apices directed
proximally (Figure SOB); lateral surface armed
with numerous, simple setae directed distally
(Figure 30C); dorsal and ventral surfaces bearing
flexible, plumose setae, most thickly set in comb-
like clusters. In females, ventral flagellum with
proximal portion covered by long flexible setae.

Scaphocerite exceeding antennular peduncle by
as much as 0.2 of its own length; lateral rib ending
in slender spine, falling short of distal margin
of lamella. Antennal flagellum long, as much as
5 times total length of shrimp. Mandibular palp
(Figure 31A) relatively short, extending to about
distal extremity of ischiocerite, proximal article
1.25 times as long as wide; distal article only
slightly longer and narrower than proximal one,
tapering to blunt tip. Maxillae and first and
second maxillipeds as figured (Figure 31B-E).
Two rudimentary arthrobranchiae on somite VII,
near base of coxa of first maxilliped (Figure
3lDg-gl), both anterior and posterior arthro-
branchiae on somite VIII, and podobranchia on

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FISHERY BULLETIN: VOL. 75. NO. 2

FIGURE 30.—Pleoticus robustus, 6 28 mm cl, south of Dry Tortugas, Fla. A, Antennular flagella. S, Mesial view of proximal part of
ventral flagellum. C, Lateral view of same. D, Ventrolateral view of proximal portion (distal half) of dorsal flagellum. E, Eye, 9 34
mm cl, same locality.

corresponding second maxilliped; pleurobranchia,
and anterior and posterior arthrobranchiae on
somite IX (Figure 31E, F), pleurobranchiae
present through somite XIV, and both arthro-
branchiae through XIII. Third maxilliped exceed-
ing antennular peduncle by at least 0.5 length of
dactyl, or by dactyl and about 0.2 length of
propodus.

First pereopod reaching between base and distal
end of carpocerite. Second pereopod overreaching
carpocerite by at least 0.5 length of dactyl, but
by as much as entire propodus and 0.1 length of
carpus. Third pereopod surpassing antennular

peduncle by length of dactyl or by length of
propodus and 0.2 that of carpus. Fourth pereopod
extending to distal end of carpocerite or over-
reaching it by length of dactyl and 0.5 that of
propodus. Fifth pereopod exceeding antennular
peduncle by at least 0.5 length of dactyl or by
length of dactyl and 0.4 that of propodus. Order of
pereopods in terms of their maximal anterior ex-
tensions: first, second, fourth, third, and fifth.
First pereopod with moderately long, sharp spine
at distomesial extremity of basis and ischium, and
midlength of merus. In female, coxa of third pereo-
pod expanded into thick, roughly trapezoidal plate,

300

1'KKKX 1 •WKKAXTK AMERICAN SOI.ENt H'EKII) SHRIMPS

FIGURE 3\.—Pleoticus robustus, 2 56 mm cl, off Dog Island, Lesser Antilles. A, Mandible. B, First maxilla. C, Second maxilla, c,
Endite of basipodite. c1, Enlargement of c, ventral view, c2, Dorsal view. D, First maxilliped. g. Rudimentary arthrobranchiae. g1,
Enlargement of g. E, Second maxilliped and proximal portion of third. F, Somites VIII and IX with proximal portions of second and
third maxillipeds, showing attachments of gills.

raised in strong, densely setose prominence on
ventral surface. Coxa of fifth pereopod in male
bearing blunt spine on anteromesial margin; in
female, coxa produced into setose, short plate.
Abdomen with middorsal carina from third

through sixth somites, carina rounded on third,
sharp and high from fourth posteriorly; sixth
somite with small spine at posterior end of carina
and paired, posteroventral spines. Telson with
median sulcus rather shallow, short, occupying

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FISHERY BULLETIN: VOL. 75, NO. 2

about 0.35 length of telson, flanked by low
carinae, latter becoming sharp posteriorly, reach-
ing base of lateral spines; length of spine 1.1
to 1.5 times width of terminal portion at base;
terminal portion length 3 to 4 times basal width.
Mesial ramus of uropod overreaching apex of
telson by about 0.2 of its length; lateral ramus,
in turn, overreaching mesial by as much as 0.25
of its own length, and bearing minute, terminal,
distolateral spine.

Petasma (Figure 32A, B) cincinnulate along
entire median line, with distal margin spinulous;
midrib of dorsolateral lobule broadest proximally,
and ending distally in narrow, sometimes sinuous
tip; ventrolateral lobule almost entirely sclero-
tized, but produced distally into rather flexible,
elongate flap, strongly inclined toward median
lobe; ventral costa with free terminal part curved
dorsally and armed with minute spines on distal
margin.

Appendix masculina (Figure 32C, D) elongate,
deeply excavate ventromesially for reception of
appendix interna, broad proximal part raised in
longitudinal, lateral rib extending to base of
narrower distal part; strong dorsal thickness
along distal part curving around terminal margin,
there bearing tuft of rigid setae. Appendix interna
considerably shorter than appendix masculina
and consisting of short bulbous basal portion

and elongate, narrow but thick distal portion.
Ventrolateral spur abruptly narrowing slightly
distal to midlength, becoming fingerlike.

Thelycum (Figure 33A) microscopically setose-
punctate (Figure 335), with paired subtriangular
projections on anteriormost part of sternite XIV,
usually inclined anteriorly, overlapping posterior
margin of sternite XIII; posterior part of sternite
XIV strongly bulging, often bearing midlongitu-
dinal groove. Median plate of sternite XIII de-
limited anteriorly by paired deep depressions, and
armed with strong anteromedian rib; sternite XII
with central elevation, and paired, transverse
marginal ridges overlapping sternite XIII.

Color-Both coloration, as previously indicated
by various authors, and color pattern are very
variable. Burkenroad (1936) described fresh,
though dead, juveniles, caught in the waters off
Alabama, as follows: "Eyes deep reddish-brown
with greenish reflections; gastric gland grayish-
brown with light yellow-green flecks, stomach
red; body pale orange-red, with a band of deeper
salmon on the posterior part of each pleonic
tergum; an iridescent blue-green area on the
dorsum of each pleonic segment and of the telson."
Springer (1951b) indicated that shrimp taken in
the northern Gulf of Mexico were "brick red as
they come from the water." Anderson and Bullis

FIGURE 32.— Pleoticus robustus, 6 32 mm cl, east of Peninsula Valiente, Panama. A, Petasma, dorsolateral view of left half.
B, Ventrolateral view (extended). C, Right appendices masculina and interna, lateral view. D, Mesial view.

302

PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMPS

0.5

FIGURE 33. — Pleoticus robustus, syntype 2 49 mm cl, south of
Curasao. A, Thelycum, ventral view. B, 2 61 mm cl, west of
Riohacha, Colombia. Portion of sternite XIV showing seta-
bearing depressions.

(1970) found that in animals observed from a
submarine the "Color varied from grayish pink to
red — similar to color observed on trawl-caught
specimens." A diel color change was pointed out
by Bullis (1956), who stated "nighttime catches
are typically bright red, while catches landed
during daylight hours are a light pink." Recently,
Garcia del Barco (1972) has confirmed this cir-
cadian variation.

My examination of large quantities of freshly
collected animals during a 1969 cruise of the

Oregon II in the Caribbean (Puerto Rico to
Antigua) corroborated earlier observations of the
great variation in this character, and disclosed
the existence of many color patterns. The overall
body color ranges from off white through pink
and salmon to deep red, and the color pattern
may consist of a few bright lines — mostly on var-
ious carinae — or even an abundance of strong
markings. Opaque white and, particularly,
reddish with white markings individuals were
very common, whereas salmon ones, apparently
similar in color to those shrimps from the northern
Gulf of Mexico described by Burkenroad, were
infrequent.

Descriptions of three color phases observed
follow:

Pink-red phase: Body pink, marked with red
and white. Gastric region intense pink; rostrum
brilliant red with tip paler; anterior rostral teeth
with bases red and apices light, but teeth posterior
to orbital margin with brilliant deep red apices;
small white patch in area between orbital, post-
orbital, and antennal spines; cardiac region light
red; anteroventral border as well as antennal and
cervical carinae and contiguous spines deep red;
longitudinal opaque white stripe tapering from
anteroventral margin (dorsal to branchiostegal
spine) to depressed area below hepatic spine,
from there broadening abruptly along entire
cervical sulcus, then tapering again to about
level of third pereopod, there forming narrow,
short stripe, continuing along posterior margin
of carapace then recurving anteriorly, parallel
to ventral margin, to level of base of second maxil-
liped, ending there in elongate white patch; deep
red stripe inserted between arms of pink one.
Abdomen light pink anteriorly, increasingly
deep pink posteriorly, turning red on sixth somite;
first five somites with posterior margin of tergum
bordered by transverse red band, and posterior
margin of pleuron with white band continuing
anteriorly onto ventral margin; middorsal carina
as well as posterior and ventrolateral margins
of sixth somite brilliant red. Telson light red,
with carinae, lateral margins, and transverse
band proximal to terminal portion deep red. Basal
podomere of uropod pink with lateral margin red;
lateral ramus intense pink except for deep red
tip; mesial ramus with pink proximal portion
followed by white transverse band and latter, in
turn, by red marking covering distal portion ex-
cept for white mesial patch. Antennular peduncle
light red, but apex of stylocerite and distolateral

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FISHERY BULLETIN: VOL. 75, NO. 2

spine brilliant red, and prosartema pink; flagella
red proximally fading to pink distally. Antenna
pink. Third maxilliped and pereopods with coxa
and basis white, remaining podomeres reddish.
Pleopods with basis white but bearing pink
semicircular, lateral patch; exopods white proxi-
mally, with red and pink transverse bands on
midportion, and white distal patch; endopods
white with pink band at midlength. Eye with
peduncle white, and separated from cornea by
two lines, proximal pink and distal red; basal
article pink.

Salmon phase: Carapace anterior to cervical
sulcus deep salmon, cardiac region, and ground
color of abdomen pale salmon; rostrum (except
for white tip) and branchiostegite bright reddish
orange, that on branchiostegite sharply delimited
dorsally along hepatic sulcus and branchiocardiac
carina; apices of rostral teeth and spines, as well
as postrostral and cervical carinae deep orange-
red; bases of teeth and spines, and cervical sulcus
opaque white. Tergum of first through fifth ab-
dominal somites with posterior, transverse band
of reddish orange, band broad on middorsal por-
tion, tapering ventrally to base of pleuron, from
there extending along posterior margin and onto
ventral margin; middorsal carina as well as pos-
terior and ventrolateral margins of sixth somite
deep reddish orange. Telson with ground color
deep salmon, except for yellowish white basal
portion; lateral portion of margins and paired
carinae bright orange-red, giving rise on each
side to angle with vertex on spine. Pereopods
with coxa and basis white, and remaining podo-
meres salmon with longitudinal orange-red strip.
Pleopods yellowish, but basis with roughly semi-
circular lateral white patch subtended by bright
reddish orange stripe on lateral margin. Uropod
mostly salmon; lateral ramus with distalmost
portion bright red and mesial ramus with tip
white.

Opaque white phase: Ground color opaque
white with very pale salmon suffusion, more
intense on rostrum; however, tip of rostrum, teeth
and adrostral carina corneous; cardiac region
grayish white, and entire branchiostegite milky
white; branchiostegal and hepatic spines as well
as cervical and postrostral carinae orange-red;
longitudinal streak of orange-red extending
posteriorly from dorsal end of cervical carina
well beyond midlength of carapace. Pleura of first
five abdominal somites with milky white U-
shaped band following contour of margin; mid-

dorsal carina and posterior and ventrolateral
margins of sixth somite orange-red. Telson almost
white with median sulcus orange-red. Lateral
ramus of uropod with oblique, milky white stripe
at base of distal fourth, and subtended distally
by intense salmon colored band and this, in turn,
by white tip; mesial ramus with large, proximo-
mesial, suboval, milky white patch bounded
laterally by salmon band, and with distalmost
portion milky white. Antennular peduncle deep
salmon proximally, becoming pink distally;
prosartema, antennular flagella, and antenna
pink. Third maxilliped and pereopods with coxa
and basis white, and remaining podomeres white
with very light pink suffusion. Pleopods pinkish
white bearing milky white, semicircular, lateral
patch. Ocular peduncle white, and bearing
orange-red stripe along border with cornea.

Maximum size.-The largest male examined by me
has a carapace length of 42 mm, about 173 mm tl,
and the largest female, 61.5 mm cl, about 219 mm
tl; however, Klima (1969), in his work on length-
weight relation, recorded larger specimens of both
sexes, a male within the range of 180-184 mm tl
and a female within 225-229 mm tl.

The sizes at which maturation occurs were de-
termined by Anderson and Lindner ( 1971) to be at
about 125 mm tl in males and about 155 mm tl
in females.

Geographic and bathymetric ranges. -Pleoticus
robustus ranges (Figure 34) from immediately
south of Martha's Vineyard, Mass. (40°00'15"N,
70°54'00"W), through the Gulf of Mexico, and the
Caribbean to French Guiana (07°05'N, 52°47'W),
occurring on the upper continental slope at depths
between about 180 and 730 m (Figure 9). It has
been found only occasionally north of Cape Hat-
teras, and seems to be scarce off the Guianas.
Inasmuch as this species has not been reported
from Brazilian waters, French Guiana is cited
here as the southernmost limit of the species on
the basis of samples taken during the Oregon
cruises off northeastern South America. The
southern range of the species given by Bullis and
Cummins (1963) was based on the same collec-
tions; consequently their statement that the royal
red reaches Brazil should be understood to mean
that it extends to about the border between
French Guiana and Brazil.

The highest concentrations of P. robustus — off
the northeast coast of Florida and in the north-

304

PEREZ EAREANTE: AMERICAN SOLENOCERID SHRIMPS

FIGURE 34.— Ranges of Pleoticus muelleri, Pleoticus robustus, and Mesopenaeus tropicalis based on published

records and specimens personally examined.

305

FISHERY BULLETIN: VOL. 75, NO. 2

eastern part of the Gulf of Mexico — occur at
depths between 250 and 475 m. The species is
scarce in less than 256 m, and not abundant at
depths greater than 500 m. If the data are correct,
the male found in 137 m off Guyana at Oregon stn
1993 represents an extremely rare occurrence of
the shrimp in waters shallower than 180 m, as
does the presence of the species at 70 m (at Oregon
stn 2669, 18°31'N, 66°47.5'W, north of Puerto
Rico), reported by Bullis and Thompson ( 1965). Al-
though Roberts and Pequegnat (1970) stated that
this shrimp has been found at depths as great as
500 fm (915 m), there is no precise record of its
presence below 400 fm (732 m). Their statement
seems to have been based on a catch from the
Alaminos, in 289-472 fm (529-863 m); however,
their remaining records, as well as those of all
others, suggest that the specimens obtained in
that haul were caught in the shallower part of
the depth range cited.

Throughout the Caribbean and northeastern
South America, the royal red shrimp seems to be
rather sparsely distributed; various explorations
by the Oregon and Oregon II in the region have
indicated a dense concentration only off Cabo de
la Vela, Colombia.

Affinities -Pleoticus robustus can be separated
from P. muelleri, the only other western Atlantic
representative of the genus, by the following char-
acteristics: the densely pubescent body, the
relatively short prosartema, which does not over-
reach the distal margin of the first antennular
article, the presence of a branchiostegal spine,
the lack of an orbital spine, and the disposition
of the submarginal carina which is subparallel to
the free border of the carapace along its entire
length. The external genitalia of the two species
are also quite different: whereas in the petasma
of P. robustus the row of cincinnuli occupies the
entire median line, the ventromedian lobule is
flexible and entire distally, and the ventral costa
is plain, in P. muelleri the row of cincinnuli
extends only along the proximal 0.4 of the median
line, the ventromedian lobule is produced distally
in cornified oval and hooklike projections, and the
distal part of the ventral costa bears a flange along
the inner border. Also, the thelycum of P.
robustus exhibits a pair of anterior triangular
projections on the flexible anterior part of sternite
XIV, and a median ridge on sternite XIII, whereas
that of P. muelleri bears nothing more than
a pair of minute tubercles on the heavily

sclerotized anterior part of sternite XIV, and a
strong median projection on sternite XIII.

Spermatophore. -Compound spermatophore (as
attached to female) consisting of broad, dorso-
ventrally depressed geminate body, with con-
spicuous transverse fold at about midlength, and
bearing anterolateral wings; also provided with
sculptured lateral flaps, and produced postero-
lateral^ in short flanges (Figure 35).

Ventral and lateral walls of each spermato-
phore (Figure 36A) thick, opaque, fusing im-
perceptibly, their anterior margins broad and
perpendicular to medial line. Spermatophore lack-
ing anterior lobe, deeply concave at base of wing,
there bearing conspicuous constriction; trans-
verse angular fold present at about midlength,
followed by depressed caudal half. Dorsomesial
wall (Figure 36C) largely translucent, with glob-
ular anterior evagination (Figure 36B) markedly
expanding lumen of sperm sac; posterior part of
latter attenuated caudally by close proximity of
opposing walls. Flap broad anteriorly and merg-

FlGURE 35. — Pleoticus robustus, compound spermatophore
attached to female, 9 44 mm cl, west of Quita Sueho Bank,
western Caribbean (setae omitted).

306

PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMPS

A-C l

FIGURE 36. — Pleoticus robustus, 6 37 mm cl, east of St Lucie Inlet, Fla. A, Left spermatophore dissected from terminal ampulla,
ventrolateral view. B, Lateral view. C, Dorsal view. D, 6 38 mm cl, off St Augustine, Fla. Distal portion of left spermatophore
(wing extended).

ing insensibly with lateral base of flange. Wing
(Figure 36D) heavy, opaque, with broad base
forming rounded lobe continuous with lateral
wall, and tapering to short, blunt tip. Flange
short, broadly subelliptical. Dorsal plate nearly
triangular, anteriorly fitting snugly into deep
groove of dorsomesial wall.

Compound spermatophore applied to female
with anterior margin lying approximately at
posterior margin of gonophores, and sperm
masses — protruding through dorsomesial walls
(apparently torn by forced release of those masses
during mating) — lodged in paired concavities of
sternite XIII. Bases of the wings attached to
sternite XIII, their distal parts resting on
same sternite, and on ventral articular mem-
branes of fourth pereopods. Lateral flaps affixed
to sternite XIV, and just posterior to transverse

folds of sacs, geminate body sloping caudo-
dorsally over bulge of sternite XIV; adjoining
flanges resting on posterior thoracic ridge. Wings
and lateral flaps lie under (dorsal) setose coxae of
fourth and fifth pereopods, respectively, which
also aid in securing compound spermatophore
on female. Dorsal plates, subjacent (dorsally)
to caudal part of sacs, directly anchored to sternite
XIV, thus helping to hold spermatophore in place.
The exceedingly large spermatophores of this
shrimp appear to become attached to the female
more firmly than those of many other penaeids
with open type thelyca. This statement is based
on the observation that females with attached
spermatophores are frequently found in collec-
tions, whereas in other species with open type
thelycum such females are rarely encountered.
Most of the compound spermatophores that I have

307

FISHERY BULLETIN: VOL. 75. NO. 2

detached from impregnated females are practi-
cally empty. This suggests that the sperm are
released with the entire spermatophore present,
i.e., that the spermatophore is not torn or split
leaving the sperm masses with the paired wings
flanking them on the female while the geminate
body and adjoining flanges fall away, as seems to
occur in some members of the subgenus Lito-
penaeus, genus Penaeus.

Reproduction-Anderson and Lindner (1971) re-
ported that on the St. Augustine Grounds, P.
robustus probably spawns throughout the year,
with a peak between January and May. Recruit-
ment begins when the shrimp are approaching
1 yr of age and are less than 100 mm tl; maturity
is reached in about 3 yr. Most shrimp on the
grounds are mature, and the life span appears to
be no less than 5 yr.

The larvae of P. robustus are unknown. Bur-
kenroad (1936) identified as "juveniles" the only
postlarvae of the species ever recorded, specimens
that I have examined. Curiously, Anderson and
Lindner (1971) found neither larval nor postlarval
stages in a large number of plankton samples
collected over an extensive area seaward of the
St. Augustine Grounds. They stated that only a
single larva was considered as possibly belonging
to "Hymenopenaeus."

Ecological notes.-ln the northestern Gulf of
Mexico and off the southeastern coast of the
United States, this shrimp has been found within
a temperature range of 5°-15°C, and is commer-
cially abundant betwen 9° and 12°C (Bullis 1956;
Bullis and Cummins 1963). The preference of P.
robustus for this range of temperature was re-
vealed by the observations of Bullis and
Cummins, who stated that within 1 or 2 days
after two incursions of cold bottom water off the
northeast coast of Florida, shrimp moved inshore
to waters 75 m shallower than those where they
had been observed previously. Later, Roe (1969)
reported that the maximum densities of this
shrimp is in water temperatures of 9° to 10°C.

Commercial concentrations of royal red have
been reported (Bullis 1956; Bullis and Rathjen
1959; Roe 1969) to occur on the following types
of bottoms: blue-black terrigenous silt and silty
sand off the Mississippi River Delta; whitish,
gritty, calcareous mud off Tortugas; and basically
similar sand or silty sand (called "green mud" by
the fishermen) off the northeast coast of Florida.

308

Anderson and Bullis (1970) presented direct
observations of this shrimp made from the sub-
marine Aluminaut off Daytona Beach, Fla., at a
depth of 459 m. They stated that "The bottom
was remarkably free from obstructions and con-
sisted of a grayish, loosely constituted sediment
that readily clouded the water at the least dis-
turbance. It was formed into a myriad of shallow
depressions and mounds, pitted with holes. . . .
Bottom photographs had previously indicated
that royal-red shrimp stayed on the sea-floor sur-
face, but we saw numerous shallow furrows (1 to
3 feet long) in the bottom in which royal-red
shrimp were partly buried. They apparently do
not burrow as deeply or completely as do brown
and pink shrimp. We believe the shrimp plow into
the bottom in search of food rather than pro-
tection, and that this feeding activity produces
the grooves or furrows."

Remarks-Smith (1885) cited 14 males and 4 fe-
males in USNM lots 6907 and 6908. My examina-
tion of this material has shown that the first lot
consists of 2 males and 7 females, but the second
lot includes 2 males and 5 females of "Hymeno-
penaeus" robustus and 1 female of Penaeopsis
serrata (Bate 1881). Consequently Smith's state-
ment is in error since there are only 4 males and,
furthermore, the total number of females (includ-
ing that of the latter species) must have been
either 13 or 12 if one of them is missing from the
lots. In the original description of the species,
Smith stated that the proximal portion of the
ventral antennular flagellum "is densely hairy in
the male"; however, the marked difference that
occurs between the pubescence of the flagellum in
the male and the female has not been cited in
subsequent morphological studies of the shrimp.
Here, for the first time, detailed accounts of the
setation of the ventral flagellum in both sexes
are presented.

The petasma of P. robustus has been described
previously by various investigators. Smith (1885)
gave the first brief account. Later, A. Milne Ed-
wards and Bouvier (1909) described and illus-
trated it in more detail; however, the two figures
presented by them include several inaccuracies
which were pointed out by Burkenroad (1936). In
the same publication, the latter gave an accurate
description of this structure. More recently,
Roberts and Pequegnat (1970) presented observa-
tions as well as a sketch of the petasma, and
Anderson and Lindner (1971) have provided the

PKRKZ KAKKANTK AMKKK \\\ Sol K\( )( KK1I) SHRIMPS

most complete illustration available. The account
of the petasma herein, utilizing Kubo's (1949)
terminology, is given in order that comparisons
of this species with others treated in this work
may readily be made.

Economic importance. -Pleoticus robustus is the
only deep-water penaeoid in the western Atlantic
that is now commercially exploited.

This large wide ranging shrimp has been found
in commercial quantities only in three areas off
the coast of the United States:

1. off northeast Florida on the St. Augustine

Grounds

2. south to southwest of Dry Tortugas Islands

3. southeast of the Mississippi River Delta to

off Tampa Bay.

The commercial potential of the species was re-
ported by Springer (1951b) and Springer and
Bullis (1952) on the basis of its abundance off
the Mississippi Delta. Subsequent explorations in
the northern and northeastern Gulf of Mexico
confirmed previous findings, and disclosed the
concentration off the Dry Tortugas (Springer and
Bullis 1954; Bullis 1956). Later, Bullis and Rath-
jen (1959) investigated the density of the popula-
tions off the southeast Atlantic coast of the United
States and indicated the high potential of the St.
Augustine Grounds, the exploitation of which
began in 1962 (Cummins and Rivers 1962). The
grounds in the northeastern Gulf of Mexico re-
mained unexploited until this decade, when fish-
ing was initiated. Total landings of royal red
shrimp in 1976 (Anonymous 1977) amounted to
167,000 pounds (75,751 kg), heads-off, caught
almost entirely off northwest Florida.

Pleoticus muelleri (Bate 1888)

Figures 9, 34, 37-42

Philonicus mulleri Bate 1888:275, pi. 39, fig. 1-2
[syntypes: 5 6 25 9 , BMNH, off Montevideo,
Uruguay, 35°02'S, 55°15'W, 13 fm (24 m),
25 February 1876, Challenger stn 321]. Fowler
1912:543.

Pleoticus mulleri. Bate 1888:939. Berg 1898:38.
Fesquet 1933:6, fig. 1-4, pi. 1-8; 1936:61. Barat-
tini and Ureta 1960:49.

Parartemesia carinata Bouvier 1905b: 748 [syn-
types: 1 6 3 9 , MP 59, off mouth Rio de la Plata,

35°42'S, 56°20'W, 44 fm (80 m), Hassler. 1 9,
Rio de la Plata, Montevideo, 7 fm (13 m),
Hassler].

Haliporus carinatus. Bouvier 1906b:4.

Haliporus mulleri. Bouvier 1908:80. A. Milne
Edwards and Bouvier 1909:214, fig. 38-44, pi. 2,
fig. 9-10. Pesta 1915:102.

Hymenopenaeus mulleri. Burkenroad 1936:103.
Fesquet 1941:64. Rioja 1941:200, fig. 13, 17;
1942:659, fig. 20, 21, 30, 31. Anderson and
Lindner 1945:288. Lopez 1954:46. Popovici and
Angelescu 1954:505. Lindner 1957:4. Ange-
lescu and Boschi 1960:1, fig. 4, 10-16, pi. 1, 2, 5,
6. Eldred and Hutton 1960:91 . Boschi and Ange-
lescu 1962:1, fig. 1-17, pi. 1, 2. Boschi 1963:5,
fig. 4. Mistakidis and Neiva 1964:471. da Silva
1965:4. Tremel and Mistakidis 1965:2. Mista-
kidis 1965:1. Neiva and Mistakidis 1966:4, fig.
4a, b. Mistakidis and Neiva 1966:434. Idyll
1969:642. Perez Farfante 1970:13, fig. 3I-K.
Iwai 1973:44.

Hymenopendeus mulleri. Carcelles 1947:4, pi. 1,
fig. 2.

Hymenopenaeus muelleri. Boschi 1964:38. Holt-
huis and Rosa 1965:1. Boschi 1966:452. Boschi
and Mistakidis 1966:1. Boschi and Scelzo
1969a:3; 1969b:152, pi. 1. Boschi 1970:65;
1974:3. Scelzo and Boschi 1975:193. Boschi and
Scelzo 1976:1. Boschi 1976:63.

Camarao barbado. Tremel et al. 1964:8.

Vernacular names: langostino, langostin (Uru-
guay, Argentina), camarao de Santana, lagos-
tinho da Argentina, camarao vermelho, ca-
marao barbado, camarao ferro (Brazil).

Material

BRAZIL— Espi'rito Santo: 2 9, USNM, off Praia de San-
tana, June 1962, G. de Souza Neiva. Rio de Janeiro: 2 9,
USNM, off Macae, 23 m. Superintendencia do Desenvolvimento
da Pesca, Segao de Pesquisas. 9 9 , USNM, Ilha dos Franceses,
Cabo Frio, 50 m, 17 October 1975, Staff Institute de Pesquisas da
Marinha, Estacao de Biologia Marinha. 4 9 , YPM, off Rio de
Janeiro, May 1934, M. W. Feingold. 1 9, USNM, off Ilha Grande,
23 m, 8 December 1961, Calypso stn 115. 3 9 , USNM, off Bai'a da
Ilha Grande, 36 m, 9 December 1961, Calypso stn 122. Sao
Paulo: 3 6, USNM, Ubatuba, 15 m, 10 April 1972, J. de Abreu.
1 65 9,MP,SofIlhadeSaoSebastia6,25m,llDecemberl961,
Calypso stn 135. 15 5 9 9, USNM, Bai'a de Santos, 6 September
1964, G. Vazzoler. 4 6 3 9, USNM, Bai'a de Santos, 29 Septem-
ber 1964, G. Vazzoler. 3 6 3 9 , USNM, Bai'a de Santos, 1 October
1962, G. de Souza Neiva. 3 6 5 9 , USNM, Farol de Moela, San-
tos, 9 September 1964, G. Vazzoler. Parana: 1 9, USNM, off
Paranagua, Ex. H. Jakobi. Santa Catarina: 37 6 47 9, MP,
off Ensenada de Tijucas, 18 m, 16 December 1961, Calypso stn
149. 5 9, USNM, Armacao de Piedade, 19 November 1965,

309

FISHERY BULLETIN: VOL. 75. NO. 2

E. Tremel. Rio Grande do Sul: 16 6 14 9, MP-USNM, off
Barra Casino, 21m, 1 8 December 1961, Ca/ypso stn 153. 1 6 1 9,
USNM, Xui', 19 m, 8 January 1962, Calypso stn 183.

URUGUAY— 8 <5 9 9, MP-USNM, off Punta del Palmar,
Rocha, 20-22 m, 21 December 1961, Calypso stn 156. 26 6 35 9,
MP, off Punta del Este, 57 m, 21 December 1961, Calypso stn 157.
1 :*, MP, N of La Paloma, 33 m, 21 December 1961, Calypso stn
158. 34 6 63 9, MP-USNM, N of Cabo Santa Maria, 25 m,
8 January 1962, Calypso stn 182. 26 6 48 9, MP-USNM, off
Laguna Rocha, 30 m, 22 December 1961, Calypso stn 161.

7 8 7 9 , MP, off Punta Negra, 18 m, 27 December 1961, Calypso
stn 167. 1 3 3 9, MP, off Maldonado, 115 m, 21 December 1961,
Calypso stn 160. 1 6 5 9 , ANSP, Bahia Maldonado, W. H. Rush.

8 cJ 15 9 syntypes ofPhilonicus miilleri, BMNH, off Montevideo,
13 fm (24 m), 25 February 1876, Challenger stn 321.

ARGENTINA — 1 6 3 9 syntypes of Parartemesia carinata
Bouvier, MP 49, mouth of Rio de la Plata, 44 fm (80 m), Hassler.
13 cJ 11 9, YPM, "Buenos Aires," 15 June 1936. 2 9, USNM,
Mar del Plata, 15 December 1922, H. M. Smith. 2 6 2 9 , UMML,
Mar del Plata, January 1959 Ex. E. Boschi. 2 9, Quequen,
7 January 1924, G. Haedo. 1 9. USNM, Puerto Madryn,
Chubut, Ex. Museo Argentino de Ciencias Naturales. 1 6 2 9,
Rawson, Chubut, November 1963, E. Boschi.

Description-Body robust, integument thick, pol-
ished except for dorsally pubescent rostrum,
narrow bands of setae flanking middorsal carina
of sixth abdominal somite, and similar bands
along borders of median and lateral sulci of telson;
also broad bands of longer setae flanking paired
longitudinal ridges of mesial ramus of uropod.
Rostrum horizontal (Figure 37), straight, rather
short, not reaching beyond distal 0.3 length of
second antennular article, with dorsal margin
slightly convex, and ventral margin almost
straight, occasionally with apical concavity. Ros-
tral plus epigastric teeth 7-13 (mode 9; N = 200),
epigastric tooth separated from first rostral by
interval similar to that between first and second,
epigastric tooth located at level of dorsal ex-
tremity of cervical sulcus and usually fourth tooth
at level of orbital margin. Adrostral carina

slender, extending from orbital margin to base of
ultimate tooth; postrostral carina strong, long,
almost reaching posterior margin of carapace,
where flanked by paired depressions. Orbital
spine short; broad postorbital, antennal, and
hepatic spines moderately long and sharp; ptery-
gostomian and branchiostegal spines lacking.
Cervical sulcus only slightly sinuous, deep, with
dorsal extremity situated relatively far from
postrostral carina; cervical carina sharp. Hepatic
sulcus nearly horizontal from posterior end to
depression below hepatic spine, there turning
anteroventrally and reaching to pterygostomian
region; hepatic carina accompanying anterior
part of sulcus sharp; branchiocardiac carina
lacking; submarginal carina well marked, hori-
zontal posteriorly, turning anteroventrally at
about midlength of carapace and then continuing
close to free ventral margin of carapace almost
to pterygostomian region.

Eye (Figure 38) with basal article produced
distomesially into pubescent, broad scale; ocular
peduncle short; cornea broad, greatest diameter
slightly less than 2 times that of base of ocular
peduncle, its proximal margin moderately slant-
ing posterolaterally.

Antennular peduncle length equivalent to
about 0.6 that of carapace; prosartema long,
reaching distal 0.4 of second antennular article;
stylocerite spiculiform distally, moderately long,
its length about 0.65 of distance between its
proximal extremity and mesial base of disto-
lateral spine; latter sharp and long. Dorsal
flagellum filiform, ventral flagellum broad
proximally, tapering distally, and bearing mar-
ginal (lateral and mesial) patches of long setae
proximally, latter continuous with single row
distally; in shrimp 24 mm cl, ratio of length of

FIGURE 37. — Pleoticus muelleri, 9 27.5 mm cl, off Laguna Rocha, Uruguay. Cephalothorax, lateral view.

310

PEREZ FARFANTE: AMERICAN SOLENOCERII) SHRIMPS

FIGURE 38.— Pleoticus muelleri, 9 33 mm cl, north of Cabo
Santa Maria, Uruguay. Eye.

dorsal and ventral flagella to that of carapace 2.90
and 2.25 respectively and in shrimp 30 mm cl,
2.5 and 2.0. Scaphocerite exceeding antennular
peduncle by 0.2 to 0.3 its own length; lateral rib
ending in long spine falling short of distal margin
of lamella; antennal fiagellum almost 3 times
total length of shrimp. Third maxilliped reaching
almost to distal margin of third antennular article
or surpassing it by as much as 0.5 length of dactyl.
First pereopod reaching between proximal 0.3
and distal margin of carpocerite. Second pereopod
overreaching antennular peduncle by almost
length of dactyl or by entire propodus. Third pere-
opod surpassing antennular peduncle by at least
length of dactyl and, at most, by propodus and
0.15 length of carpus. Fourth pereopod exceeding
carpocerite by as much as entire length of dactyl.
Fifth pereopod, longest of all appendages, exceed-
ing antennular peduncle by length of dactyl and
0. 15 or 0.20 length of propodus. Order of pereopods
in terms of their maximal anterior extensions:
first, fourth, second, third, and fifth. First pereo-
pod with spine at midlength of mesial border of
basis very long and sharp, and spine on ischium
sharp, but smaller than that on basis; second
pereopod with setose, squamiform tubercle on
distoventral border of coxa, and with long sharp
spine on basis. In females, coxa of fifth pereopod
produced as rounded, posteromesially directed
plate, terminating in tooth anteriorly, plate hing-
ing on horn of posterior plate of sternite XIV; coxa
of fourth pereopod narrow, thick, with two

rounded mesial projections, base of posterior one
hinging on anterior horn of median plate of
sternite XIII; coxa of third pereopod produced
mesially in subtrapezoidal plate provided with
long mesial setae overlapping those of opposite
plate, coxa bearing gonopore on dorsomesial sur-
face. In males, coxa of fifth pereopod with large
tooth on anterior margin.

Abdomen with middorsal carina along entire
length, carina low and rounded from first to third
somites (imperceptible in young), and keellike
posteriorly; posterodorsal margins of third
through fifth somites with median incision; sixth
bearing small, sharp spine at posterior end of
carina, and small posteroventral spines. Telson
with median sulcus moderately deep anteriorly,
posteriorly bearing median elevation merging
into convex terminal portion; lateral spines mod-
erately long; length of terminal portion about 4
times width at base. Mesial ramus of uropod sur-
passing apex of telson by 0.15-0.25 of its own
length; lateral ramus slightly overreaching
mesial ramus and bearing small, terminal disto-
lateral spine.

Petasma (Figure 39A, B) cincinnulate along
proximal 0.4 of median line; distal part of ventro-
median lobule cornified, forming plate bearing
terminal subqval projection and lateral spurlike
projection; much of lateral lobe heavily sclero-
tized, overlapping ventral costa, and with shallow
lateral emargination marking base of distal por-
tion; latter flexible, subelliptical, directed toward,
and partly covered (dorsally) by, ventromedian
lobule; ventral costa bearing membranous flap,
broadening distally and terminating in paired
unequal convexities; free terminal part of costa
forming dorsally directed, strongly curved, sharp
projection.

Appendix masculina (Figure 39C, D) elongate,
with heavily sclerotized dorsolateral portion and
flexible, subelliptical mesial portion. Appendix
interna spatulate, embracing ventromesial mar-
gin of appendix masculina proximally, and bear-
ing distolateral tuft of rigid, long setae. Basal
sclerite with deep distolateral groove along base
of sharp dorsal ridge; ventrolateral spur relatively
short.

Thelycum (Figure 40) microscopically setose-
punctate, with posterior plate on sternite XIV
often divided by median longitudinal groove,
and bearing lateral elevations terminating anter-
iorly in small knob; short anterior part of sternite
XIV heavily sclerotized, forming slightly convex,

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FISHERY BULLETIN: VOL. 75, NO. 2

FIGURE 39.—Pleoticus muelleri, 8 20 mm cl, off Laguna Rocha, Uruguay. A, Petasma, dorsal view. B, Ventrolateral view of left half.

C, Right appendices masculina and interna, lateral view. D, Mesial view.

FIGURE 40.— Pleoticus muelleri, 9 43 mm cl, off Praia de San-
tana, Espi'rito Santo, Brazil. Thelycum, ventral view.

paired plates, each bearing pair of minute tuber-
cles. Median plate of sternite XIII elevated lat-
erally in ribs ending anteriorly in blunt horns,
and armed with strong, blunt, setose median pro-
jection; latter flanked anteriorly by setose pro-
tuberances borne on articular membranes of
fourth pereopods; sternite XII markedly convex,
its strong transverse marginal ridge with deep
median depression and blunt, lateral, posteriorly
directed horns.

Co/or.-Pale yellow or yellowish red to tomato red
(Boschi and Angelescu 1962); reddish orange of
various shades in different areas of the body
(Boschi 1963); wine-red in young from 50 mm tl
through adulthood (Iwai 1973).

Maximum size. -Males: 37.5 mm cl; females:
58 mm cl.

Geographic and bathymetric ranges.-From off
Praia de Santana, about 20°S, 40°W, Espi'rito
Santo (data on label accompanying two specimens
collected by Getulio de Souza Neiva), south to
the northwestern portion of the Golfo de San Jorge,
Comodoro Rivadavia (Figure 34). It occurs most

312

PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMPS

abundantly in littoral waters at depths between
2 and 20-30 m (Figure 9), and rarely as deep as
80-100 m (Angelescu and Boschi 1960; Boschi and
Scelzo 1969a), and from near the shoreline to
0.5 km offshore, occasionally as far as 56 km
(Angelescu and Boschi 1960). This species was
reported by Iwai (1973) to range north to 21°36'S,
the first record north of Ilha Santana, 22°25'S,
Rio de Janeiro, where da Silva ( 1965) had reported
a fishery for this shrimp. The specimens taken at
Praia de Santana, Espfrito Santo, about 178 km
north of the locality where Iwai recorded the
species, have confirmed the presence of H.
muelleri beyond the state of Rio de Janeiro. The
southernmost limit of the species given above is
based on Boschi and Scelzo ( 1969a), who identified
a number of large specimens caught in the Golfo
de San Jorge at a depth of 80 m.

Affinities -Pleoticus muelleri has its closest affini-
ties with its Atlantic congener P. robustus, but
it may be readily separated from it by its almost
entirely glabrous body, long prosartema, which
may overreach the midlength of the second anten-
nular article, the absence of branchiostegal spines
and the presence of orbital spines. Also it may
be distinguished by the disposition of the sub-
marginal carina, the posterior part of which is
horizontal and situated far from the free ventral
border of the carapace, instead of extending sub-
parallel to that border as it does in all other species
of this generic complex. The external genitalia of
the two are also markedly different, as pointed out
under P. robustus. In the petasma of P. muelleri
the ventromedian lobule is cornified distally,
terminates in a rounded to ovate platelike pro-
jection which bears at its base a spurlike projec-
tion, and the ventral costa is produced into a
dorsally directed hook. The thelycum, in turn,
exhibits paired short plates on the anterior part
of sternite XIV, each bearing a pair of minute
knobs, and also an exceedingly strong projection
on the median plate of sternite XIII.

Spermatophore. -Compound spermatophore (Fig-
ure 41) consisting of broad geminate body with
angular hump at about midlength, and bearing
small pair of wings anterolaterally; also provided
with large, highly sculptured midlateral flaps,
and pair of broad, posterolateral flanges. Thick,
opaque ventral wall of each spermatophore (Fig-
ure 42A) truncate, lacking anterior lobe, broad-
ened and swollen at about midlength forming

hump; area posterior to hump dorsally depressed,
and strengthened by longitudinal ridge. Lateral
wall mostly thick, concave, and insensibly con-
tinuous with wing anteriorly, merging with
broad, subrectangular flap, and posteriorly bear-
ing prominent longitudinal ridge parallel to that
of ventral wall. Dorsomesial wall largely trans-
lucent, but heavily sclerotized and opaque mesi-
ally forming axial part of complex armature (Fig-
ure 42C). Latter bearing three transverse ribs:
1) anterior, forming arc, with one arm (ventral)
strengthening ventral hump and another running
across dorsomesial wall, then ending in foliaceous
process; 2) intermediate, close to former, very
strong, tonguelike, and deeply excavated; 3) pos-
terior, forming shelf projecting inside lumen of
sperm sac from dorsomesial wall. Wing short,
broad, and flexible except for posterior thickening
running along its entire length. Anterior part of
flap broad, subrectangular, elevated in marginal

FIGURE 41. — Pleoticus muelleri. Compound spermatophore
attached to female, $ 37 mm cl, Rawson, Chubut, Argentina
(setae omitted).

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FISHERY BULLETIN: VOL. 75, NO. 2

FIGURE 42.—Pleoticus muelleri, 6 37 mm cl, off Buenos Aires Province, Argentina. A, Right spermatophore dissected from terminal
ampulla, ventrolateral view. B, Dorsomesial view. C, Left spermatophore dislodged from female, V 59 mm cl, Puerto Madryn, Chubut,
Argentina.

ridge continuous with hump; posterior part
narrow, extending as flexible band joining flange.
Flange short, with broad mesial base and sinuous
lateral margin. Dorsal plate (Figure 42B) large,
extending almost from anterior extremity of
spermatophore to base of flange, and irregular in
contour.

Compound spermatophore applied to thelycum
much as it is in P. robustus. Anterior extremity
of geminate body lying opposite female gono-
pores, with wings attached to ventral articular
membranes of third pereopods. Ventral walls
fused mesially while lateral walls diverge dor-
sally becoming affixed to sternite XIII, their
lateral margins embracing mesial prominences
of dorsal articular membranes of fourth pereo-
pods. Strong humplike prominences projecting
ventrally from sternite XIV, latter serving as
place of attachment for broad anterior parts of
flaps as well as for intimately fused dorsal plates.
From humplike prominences, compound sperma-
tophore sloping posterodorsally, and held in
position by paired flanges affixed to ventral artic-
ular membranes of fifth pereopods.

The sperm is freed from each sac through an
anterior rupture of dorsomesial wall, close to
corresponding gonopores. The gelatinous sub-
stance which accompanies the sperm within the
sperm sac may be observed covering the gono-
pores in Figure 41. Spermatophore-bearing fe-
males are not infrequent in collections; it seems
that the spermatophores in this species as in P.
robustus, which are also exceedingly large,
become firmly anchored to the thelycum. Accord-
ing to Angelescu and Boschi (1960), the spermato-
phores in recently caught impregnated females
are light green.

Postembryonic stages. -Boschi and Scelzo (1969a)
prepared illustrated keys for the identification of
larvae of the three more common Penaeidea in the
waters off Argentina. These keys include diag-
noses of protozoeae, mysis, and postlarvae of
P. muelleri based both on specimens caught in
plankton samples and others reared in the lab-
oratory. Later, Scelzo and Boschi ( 1975) presented
the results of their successful rearing of this
shrimp from eggs spawned in the laboratory to

314

I'KKKZ FARFANTE: AMERICAN SOI.ENOCERII) SMRIMi'S

juveniles of an average total length of 21.3 mm.
They stated that spawning generally took place
the night following the capture of mature females,
and eggs hatched between 12 and 24 h (according
to the temperature) after being released. The
young passed through 6 nauplii, 3 protozoeae,
3 mysis, and an undetermined number of post-
larvae before becoming juveniles. The larval
development was completed in 19-23 days at
19.0°-23.5°C and juveniles reached 21.3 mm
(average) in 81 days after hatching. In more
recent experiments, Boschi and Scelzo (1976)
found that, at 24°C, P. muelleri attained an
average of 61 mm tl and 2.7 g in 180 days after
hatching. The studies mentioned above are the
only ones that have been made on the develop-
ment of any of the 12 species treated here.

Remarks-Much of our knowledge of the morphol-
ogy of this species is due to the study of Angelescu
and Boschi (1960) and their subsequent contribu-
tion (Boschi and Angelescu 1962). These authors
presented detailed accounts of the external and
internal anatomy, and included outlines and a
brief description of the "green" spermatophores
on the female. In addition, they calculated the
rate of growth of the species in Argentinian wa-
ters, studied the development of the testis and
ovaries, and determined that the spawning season
there extends from December to February (i.e.,
through the summer months). Furthermore, they
found that it feeds on organic detritus as well as
on small animals, such as sergestids and poly-
chaetes, and plants.

Ecological notes. -Pleoticus muelleri is the only
species of the genus which frequents shallow
littoral waters; it even invades seawater channels
and rias like those in the vicinity of Bahia Blanca,
Buenos Aires, where, according to Boschi (1963),
the "langostino" is trapped in weirs by the fisher-
men. Furthermore, this shrimp not only inhabits
such shallow waters, but occurs in sufficient abun-
dance to support commercial exploitation in
many areas.

This species completes its entire life cycle in the
sea but, as stated above, may frequent inshore
waters of high salinity. It occupies tropical and
subtropical waters off Brazil, where surface tem-
peratures are as high as 25°-27°C during the
warm months of the year, and 16°-17°C during
the cold ones; farther south, off Argentina, it oc-
curs in temperate waters where surface tempera-

tures range between 10° and 23°C during the
summer, and 5° and 10°C during the winter
(Boschi 1964).

This shrimp lives on mud and sand bottoms.

Economic importance. -Pleoticus muelleri is taken
commercially from Ilha Santana, Rio de Janeiro,
to Punta Clara, Chubut. Significant catches, how-
ever, are made only from Santa Catarina to Punta
Clara, and the largest fisheries are in Argentinian
waters (Boschi 1964), between Punta Rasa (prov-
ince of Buenos Aires) and Punta Clara, i.e.,
between 41° and 44°S. This species constitutes
the largest percentage of the shrimp landings
(which also include Artemesia longinaris Bate
1888) in Argentina.

Hadropenaeus New Genus

Hymenopenaeus. Smith 1885:179 [part]. Burken-
road 1936:102 [part]. Kubo 1949:212 [part].

Philonicus Bate 1888:273 [part].

Pleoticus Bate 1888:xii [part].

Haliporus. Bouvier 1906b:l [part]; 1908:78 [part].
A. Milne Edwards and Bouvier 1909:206 [part],
de Man 1911:31 [part].

Diagnosis-Body stout, carapace proportionately
short, integument moderately thick, firm. Ros-
trum short, not overreaching distal margin of
first antennular article, deep, ventral margin
pronouncedly convex; armed only with dorsal
teeth; epigastric tooth and first rostral separated
by interval equal to, or only slightly greater than,
that between first and second rostral teeth. Or-
bital and pterygostomian spines absent; post-
orbital, antennal, hepatic, and branchiostegal
spines present. Cervical sulcus long, almost
reaching middorsum of carapace; hepatic sulcus
deep; branchiocardiac sulcus and carina absent,
posthepatic and submarginal carinae absent.
Abdomen carinate dorsally from third through
sixth somites. Telson with pair of conspicuous,
fixed, lateral spines. Prosartema long, flexible.
Antennular flagella longer than carapace, usually
subcylindrical, ventral flagellum occasionally
depressed. Mandibular palp two jointed, articles
moderately broad, distal one as long as or slightly
shorter than basal, and tapering to blunt apex.
First maxilla with unsegmented palp (endite of
basis) gently narrowing to rounded apex. Fifth
pereopod subflagelliform and considerably longer
than fourth. First pereopod with spine on basis,

315

FISHERY BULLETIN: VOL. 75. NO. 2

ischium, and merus. Exopods on all maxillipeds
and pereopods. Lateral ramus of uropod armed
with distolateral spine reaching distal margin of
lamella (terminal spine). In males, petasma with
ventral costa free from heavily sclerotized, plate-
like terminal part of ventrolateral lobule; ventro-
median lobule broadly expanded distally. Endo-
pod of second pereopod bearing appendices
masculina and interna, and with basal sclerite
produced distally into elongate ventrolateral
spur. Thelycum of open type, not enclosing
seminal receptacle. Pleurobranchia on somites
IX to XIV; single rudimentary arthrobranchia on
VII, and anterior and posterior arthrobranchiae
on somites VIII to XIII; podobranchia on second
maxilliped, and epipod on second maxilliped (and
on first if proximal exite of coxa considered an
epipod) through fourth pereopod.

Hadropenaeus is an extremely homogeneous
genus, the three known species being quite
similar.

Type-species. -Hymenopenaeus modestus Smith
1885.

Etymology. -From the Greek hadros, stout, in com-
bination with the generic name Penaeus, allud-
ing to the comparatively short and thick
carapace.

Gercofer.-Masculine.

List o/"spedes.-Amphi-Atlantic: Hadropenaeus af-
finis (Bouvier 1906b). Western Atlantic: Hadro-
penaeus modestus (Smith 1885). Indo-West
Pacific: Hadropenaeus lucasii (Bate 1881).

Affinities. -The members of Hadropenaeus resem-
ble those of Pleoticus (as here defined) in having
the epigastric tooth separated from the first ros-
tral by an interval equal to, or only slightly
greater than, that between the first and second
rostral teeth, in lacking both branchiocardiac and
posthepatic carinae, and in possessing a petasma
in which the ventral costa is free from the plate-
like, terminal part of the ventrolateral lobule.
However, Hadropenaeus differs from Pleoticus
(as well as from the other closely related genera
except Mesopenaeus) in the proportionately
higher carapace, in the shape of the rostrum
which is short, deep, and possesses a strongly
convex ventral margin, and in lacking sub-
marginal carinae.

316

The members of this genus are closely allied to
those of Mesopenaeus. They share a stout appear-
ance, short, deep rostrum in which the ventral
margin is convex, similar arrangement of the
epigastric and rostral teeth, and they lack
branchiocardiac sulci and carinae. Furthermore,
the ventral flagellum, which is typically flattened
in Mesopenaeus, is occasionally depressed in one
species of Hadropenaeus; the depressed flagellum
seemingly represents the first step in a process
of specialization which progressed through the
flattened ventral flagellum in Mesopenaeus, and
culminated in the two lamellate flagella (both
ventral and dorsal) in Solenocera. Hadropenaeus,
in contrast to Mesopenaeus, lacks submarginal
carinae and orbital spines; it possesses branchio-
stegal spines and, most significantly, exhibits a
petasma in which the ventral costa is free from
the terminal part of the ventrolateral lobule.

Key to Species of Hadropenaeus

1. Rostrum lacking conspicuous carina dor-

sal to adrostral one. Thelycum with
median protuberance on sternite XIV
high, projecting ventrally as far as
posterior convexities of sternite XIII;
latter with median ridge bearing large
tooth anteriorly. Petasma with ventro-
median lobule produced into disto-
lateral projection 2

Rostrum with conspicuous carina dorsal
to adrostral one. Thelycum with me-
dian protuberance on sternite XIV
low, not projecting ventrally as far as
posterior convexities of sternite XIII;
latter with median, keellike ridge
lacking tooth anteriorly. Petasma
with ventromedian lobule not pro-
duced into distolateral projection ....
H. lucasii

2. Scaphocerite reaching distal end of an-

tennular peduncle or overreaching it
by not more than 0.1 of its own length.
Prosartema extending only to disto-
mesial extremity of first antennular
article. Thelycum with median pro-
tuberance on sternite XIV projecting
ventrally, and tooth of median keel of
sternite XIII directed anteriorly. Pe-
tasma with distomesial projection of

PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMPS

ventromedian lobule directed mesially

H. affinis

Scaphocerite overreaching antennular
peduncle by about 0.25 of its own
length. Prosartema conspicuously
overreaching distomesial margin of
first antennular article. Thelycum
with median protuberance on sternite
XIV projecting anteriorly, and tooth
of median keel of sternite XIII directed
ventrally or posteriorly. Petasma with
distomesial projection of ventro-
median lobule directed distally

H. modestus

Hadropenaeus affinis (Bouvier 1906)
Figures 9, 43, 44A, 45-49

Haliporus modestus Bouvier 1905a:980. [Not
Hymenopenaeus modestus Smith 1885.]

Haliporus affinis Bouvier 1906b:4 [syntypes:
1 S 2 9,4 6 4 9,2 6 2 9, MP; type-locality: off
Cape Verde Is, 16°53'N, 25°10'W, 410-460 m,
29 July 1883, Talisman stn 116. Unrecorded
number of syntypes from off Cape Verde Is,
"100 m" from uncited Talisman station. 1 6,
MCZ 7196, off Barbados, 188 m, 5 March 1879,
Blake stn 273, 13°03'05"N, 59°36'18"W].
Bouvier 1908:80. A. Milne Edwards and
Bouvier 1909:209. de Man 1911:7.

Hymenopenaeus affinis. Burkenroad 1936:104.
Crosnier and Forest 1973:258, fig. 82b, 84, 94d.

Hymenopenaeus modestus. Bullis and Thompson
1965:5 [part]. [Not Hymenopenaeus modestus
Smith 1885.]

Material

UNITED STATES— North Carolina: 2 9, UNC-IMS, SE
of Cape Lookout, 229 m, 8 June 1949, Albatross III stn 21-4.
3 6 14 2, USNM, E of Port Fisher, 366 m, 15 November 1956,
Combat stn 177. 2 6 1 9, UNC-IMS, about 111 km SE of Cape
Fear, 412-369 m, 23 June 1956, Pelican stn 75. South Caro-
lina: 2 2 , USNM, E of Cape I, 366 m, 20 April 1957, Combat stn
288. Florida: 1 9, USNM, off Hobe Sound, 302-285 m,
21 May 1968, Gerda stn 997. 1 2 , USNM, off Boca Raton, 366 m,
29 March 1956, Pelican stn 17. 1 6, USNM, SE of Key Largo,
185 m, 22 January 1965, Gerda stn 452. 1 <5, USNM, off Mara-
thon, 201 m, 21 June 1967, Gerda stn 813. 1 6, USNM, S of Pine
Is, 293-302 m, 25 February 1969, Gerda stn 1029. 2 9, USNM,
NW of Double Headed Shot Cays, 223 m, 29 August 1967, Gerda
stn 864. 1 6, USNM, NW of Charlotte Harbor, 366 m,
21 August 1970, Oregon II stn 11180.

BAHAMA ISLANDS— 1 3, RMNH, NW of Matanilla
Reef, 549-567 m, 1 July 1963, Gerda stn 179. 1 6, USNM, NW

of Matanilla Reef, 466-417 m, 30 September 1967, Gerda stn 935.

1 9, USNM, NW of Matanilla Reef, 421 m, 3 February 1957,
Combat stn 238. 1 9 , USNM, N of Matanilla Reef, 393 m,
3 February 1957, Combat stn 237. 2 6, RMNH, W of Bimini Is,
452-474 m, 30 January 1964, Gerda stn 234. 3 2 , USNM, SW of
Bimini Is, 403-421 m, 30 January 1964, Gerda stn 233. 5 2,
RMNH, off Gun Cay, 439-421 m, 29/30 January 1964, Gerda stn
232. 1 6, USNM, SW of Gun Cay, 312-348 m, 30 March 1964,
Gerda stn 274. 1 6 1 2, USNM, Santaren Channel, 384-366 m,
6 November 1960, Silver Bay stn 2468. 1 2 , USNM, Santaren
Channel, 412-220 m, 22 June 1967, Gerda stn 820. 1 9, USNM.

5 of Great Inagua, 311 m, 13 December 1969, Oregon II stn
10849.

PUERTO RICO— 3 2, USNM, Mona Passage, 366 m,
17 October 1963, Silver Bay stn 5190.

HAITI— 1 9 juv, USNM, W of Anse d'Hainault, [?] 77 m,

2 July 1970, Pillsbury stn 1186.

LESSER ANTILLES— 1 6, USNM, E of Riviere Pilote,
Martinique I, 170-214 m, 9 July 1969, Pillsbury stn 907.
1 6, USNM, SE of Georgetown, St Vincent I, 165-201 m,

6 July 1969, Pillsbury stn 874. 1 6 syntype + 1 6, MCZ 7196,
off South Point, Barbados, 188 m, 5 March l879,Blake stn 273.

WESTERN CARIBBEAN— 2 <J 4 9, USNM, Arrowsmith
Bank, 311-146 m, 28 January 1968, Gerda stn 954. 1 9 , USNM,
Arrowsmith Bank, 307-192 m, 28 January 1968, Gerda stn 951.
1 6, UMML, Arrowsmith Bank, 252-293 m, 14 March 1968,
Pillsbury stn 591. 2 6 2 2, USNM, Arrowsmith Bank, 155-
205 m, 15 March 1968, Pillsbury stn 598. 1 6, USNM, W of
I de Providencia, 289-274 m, 4 February 1967, Oregon stn 6423.

MEXICO— Quintana Roo: 1 6 juv, UMML, SE of Isla
Mujeres, 241-320 m, 10 September 1967, Gerda stn 893. 1 2,
UMML, SE of Isla Mujeres, 210-366 m, 23 August 1970, Gerda
stn 1286. 3 2, USNM, off Puerto de Morelos, 165-168 m,
10 September 1967, Gerda stn 899.

PANAMA— 1 2 , USNM, off Caribbean coast of Panama,
274 m, 5 July 1972, Canopus.

PORTUGAL— Cape Verde Is:lcJ29,4d49,2d29
syntypes, MP, 410-460 m, 29 July 1963, Talisman stn 116.

Description. -Body stout (Figure 43), integument
moderately thick, firm. Carapace with restricted
pubescent areas, setae dense and long at base of
rostrum, on pterygostomian region, and in patch
extending from orbital margin to epigastric tooth;
minute, sparsely set setae on dorsum and hepatic
region. Abdomen polished, almost entirely naked
except for setae on posterior part of dorsal keel;
telson and mesial ramus of uropod rather densely
pubescent. Rostrum short, its length 0.20-0.25
that of carapace, falling short of distal margin of
first antennular article, almost horizontal, with
dorsal margin straight and ventral margin
strongly convex, with subapical concavity giving
rise to saber-shaped tip; latter almost 0.4 length
of rostrum. Rostral plus epigastric teeth 5-7 (mode
6; N = 60), base of third rostral tooth at
level of orbital margin. Adrostral carina extend-
ing from orbital margin to ultimate tooth; more
dorsal barely perceptible carina extending from
second to ultimate rostral tooth; postrostral

317

FISHERY BULLETIN: VOL. 75. NO. 2

;g» g s. ^..g

FIGURE 43. — Hadropenaeus affinis, 9 21.5 mm cl, Mona Passage, off Puerto Rico. Lateral view (third pereopod slightly raised).

carina ending immediately posterior to cervical
sulcus. Orbital margin produced anteriorly into
ventrally inclined, short shelf. Postorbital spine,
longest of four lateral spines on carapace, located
dorsal to base of small antennal spine; branchio-
stegal and hepatic spines sharp. Cervical sulcus
deep, ending dorsally just posterior to midlength
of carapace, and close to postrostral carina;
cervical carina sharp; hepatic sulcus sub-
horizontal posteriorly, inclined anteroventrally
from depressed area below hepatic spine to pit
below branchiostegal spine.

Eye (Figure 44 A) with basal article produced
distomesially into pubescent, elongate scale;
ocular peduncle moderately long, bearing minute
tubercle; cornea broad, greatest diameter 1.5-1.9
times that of base of ocular peduncle, strongly
slanting posterolaterally.

Antennular peduncle length equivalent to 0.65
that of carapace; prosartema falling short, or
barely reaching, distomesial margin of first
article; stylocerite length about 0.65 of distance
between lateral base of first article and base of

318

distolateral spine, terminating in sharp spine;
distolateral spine very slender and long, conspic-
uously surpassing proximal margin of second
article. Antennular flagella long, length of dorsal
fiagellum 2.2 and 1.9 times carapace length in
shrimp 8 and 23 mm cl, respectively; ventral
shorter and broader than dorsal, gently tapering
distally, and armed with marginal rows of long
plumose setae. Scaphocerite extending to distal
margin of antennular peduncle or exceeding it by
less than 0.1 of its own length; lateral rib ending
in slender spine, reaching to or very slightly
beyond distal margin of lamella. Antennal fia-
gellum long, although incomplete in all specimens
examined, longest observed by me 3 times total
length of shrimp. Mandibular palp (Figure 45A)
moderately broad, distal article slightly shorter
than basal. First maxilliped as illustrated (Fig-
ure 455); rudimentary arthrobranchia of corre-
sponding somite VII situated near its base (Figure
45c-cM. Third maxilliped exceeding antennular
peduncle by length of dactyl and half or as much
as entire length of propodus.

PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMPS

FIGURE 44. — Eyes. A, Hadropenaeus affinis, 9 21 mm cl, southeast of Cape Lookout, N.C. B, Hadropenaeus modes-
tus, 6 11 mm cl, southwest of Dry Tortugas, Fla. C, Hadropenaeus lucasii, 2 18 mm cl, Pailolo Channel, Hawaiian
Islands.

First pereopod, stoutest of all, reaching at least
basal 0.65 length of carpocerite, and, at most,
exceeding it by tip of dactyl. Second pereopod
moderately stout, extending to distal end of carpo-
cerite or exceeding it by as much as entire pro-
podus. Third pereopod surpassing antennular
peduncle by length of dactyl or by entire propodus.
Fourth pereopod exceeding antennular peduncle
by dactyl and 0.2-0.6 length of propodus; length of
dactyl about 0.4 that of propodus; length of carpus
about 1.25 times that of merus. Fifth pereopod
slender and long, overreaching antennular pe-
duncle at least by length of dactyl and propodus,
or by as much as their length and almost 0.3
length of carpus. Order of pereopods in terms of
their maximal anterior extensions: first, second,
fourth, third (occasionally third, fourth), and
fifth. First pereopod with very long, slender spine
on basis, small spine on distomesial margin of
ischium, and small one near midlength of mesial
margin of merus. Second pereopod with long spine
on basis. Coxa of fourth and fifth pereopods in
males armed with anterior spine. Coxa of fifth
pereopod in females produced mesially into short
plate bearing sharp spine anteromesially.

Abdomen with middorsal keel from fourth
through sixth somites; low rounded carina some-
times present on third; posterodorsal margin of
third, fourth, and fifth somites with median in-
cision; sixth somite bearing sharp spine at pos-

±l^cA

FIGURE 45. — Hadropenaeus affinis, 9 21.5 mm cl, southeast of
Cape Lookout, N.C. A, Mandible. B, First maxilliped. c, Arthro-
branchia. c\ Enlargement of c (all from left side).

319

FISHERY BULLETIN: VOL 75, NO 2

terior end of keel, and minute spine at postero-
ventral angles. Telson (Figure 46A) pubescent
except for median sulcus and terminal portion;
sulcus deep anteriorly, increasingly shallow pos-
teriorly, ending before reaching lateral spines;
spines long, their length 1.6-1.9 basal width of
terminal portion; latter long, length 3.5-4.5 times
basal width; mesial ramus of uropod barely over-
reaching apex of telson, or exceeding it by about
0.15 of its own length; lateral ramus distinctly
surpassing mesial, and armed with small, disto-
lateral spine, projecting beyond contiguous distal
margin of ramus.

Petasma (Figure 47 A, B) cincinnulate along
proximal 0.65 of median line; broad distal part
of ventromedian lobule strongly produced into
elongate, distally directed distomesial projection,
and short distolateral projection; entire terminal
margin of lobule spinulous; distal part of ventro-
lateral lobule heavily sclerotized, forming plate,
with border adjacent to ventral costa bearing

FIGURE 46.— Telsons. A, Hadropenaeus affinis, 9 20 mm cl,
southwest of Bimini Islands, Great Bahama Bank. B, Hadro-
penaeus modestus, 9 19 mm cl, west of Isla de Providencia,
western Caribbean.

320

emargination delimiting basal part from subovate
terminal part; latter strongly inclined toward,
and partially covered by, ventromedian lobule,
and armed with minute spinules along ventral
margin; ventral costa with distal part free from
contiguous plate, bent outward and bearing spin-
ules on distalmost margin.

Appendix masculina (Figure 47 C,D) with prox-
imal part broad, strongly produced mesially into
thickened lobe, and bearing long setae along
lateral margin; distal part narrow, strongly
turned laterally, with apical portion armed with
tuft of long setae; appendix interna shorter than
appendix masculina, narrow, sinuous, and bear-
ing apical tuft of long setae. Ventrolateral spur
large, subelliptical to paddlelike.

Thelycum (Figure 48A, B) with median protu-
berance on sternite XIV subconical, its apical por-
tion directed anteriorly or ventrally and produced
into spinelike projection; protuberance situated
distinctly posterior to prominent, setose, paired
convexities of posteriormost part of sternite XIII;
longitudinal median keel on sternite XIII pro-
duced anteriorly into anteriorly directed blunt
tooth, its cephalic margin concave, its posterior
margin convex.

Photophores.-Paired photophores situated on
posterolateral margins of sternites X through
XIII just mesial to coxae of first four pairs of
pereopods.

Color-Color notes made by Lipke B. Holthuis
(pers. commun.) on a male caught southeast of
Georgetown, St. Vincent Island, at Pillsbury
stn 874, state that the shrimp was "uniformly
red, with darker bands parallel to the posterior
margins of the abdominal terga."

The following description is based upon a
freshly caught specimen observed by me during
a 1969 cruise of Oregon II, south of Great Inagua
Island, Bahamas. Body translucent pinkish or-
ange, with gnathal appendages, and pereopods
reddish orange. Carapace with milky white sub-
triangular patch lying immediately dorsal to
hepatic spine, its broad base abutting cervical
sulcus; small, middorsal, diamond shaped mark-
ing (formed by white lines) just posterior to mid-
length of carapace; anterolateral sides of marking
continuing posterolateral^ in dorsalmost arm of
transverse, strongly sinuous, opaque white, nar-
row band; ventral arm of U-shaped dorsal portion
of band extending anteriorly to cervical sulcus,

I'KKKZ KARFANTK AMKKH'AN SOI.KNI )< 'KR1I) SHRIMPS

FIGURE 47. — Hadropenaeus affinis, 6 16 mm cl, about 11 km southeast of Cape Fear, N.C. A, Petasma (partly bent laterally)
dorsal view of right half. B, Ventral view. C, Right appendices masculina and interna, dorsal view. D, Ventromesial view.

there turning caudad reaching posterior end of
hepatic sulcus; middorsal patch of white specks
extending from posterior sides of diamond to pos-
terior margin of carapace. First five abdominal

somites with reddish orange band along posterior
margin of tergum, band broader dorsally, taper-
ing posterovehtrally to level of articular knob,
then extending anteroventrally to about mid-

FlGURE 48. — Hadropenaeus affinis, 9 19 mm cl, east of Cape Island. S.C. A, Thelycum, ventral view. B,

Ventrolateral view.

321

FISHERY BULLETIN: VOL. 75, NO. 2

length of ventral margin of pleuron and from
there anteriorly to ventral angle of latter.

Maximum size-Males: 15 mm cl, about 66 mm tl;
females: 23 mm cl, about 82 mm tl.

Geographic and bathymetric ranges. -In the
western Atlantic: from off Cape Lookout, N.C.
(34°15'N, 75°58'W), southward to the Straits of
Florida, in the northeastern part of the Gulf of
Mexico (northwest of Charlotte Harbor, Fla.), and
throughout the Caribbean. In the eastern Atlan-
tic: off Cape Verde Islands (Figure 49). This spe-
cies has been found at depths between 165 and
570 m (Figure 9), with one dubious record from
Haiti at 77 m.

Affinities. -Hadropenaeus affinis, which is amphi-
Atlantic, and H. modestus, found only in the
western Atlantic, are closely allied, but can be
distinguished by the characters presented in
Table 1.

Burkenroad (1936), for unexplained reasons,

expressed doubt that H . affinis is different from
H. modestus, an opinion apparently shared by
Bullis and Thompson (1965) who recognized only
H. modestus in their western Atlantic collections.
I have examined part of their material and found
that it also includes H. affinis. On the basis of
the original description of H. modestus (Smith
1885), Bouvier (1906b) distinguished H. affinis
from the former species by six features. I have
found that two of them are diagnostic: the relative
length of the scaphocerite, and the ratio length
of dactyl/length of propodus of the fourth pereopod
(see Table 1). The number of rostral teeth is not
7 in H. modestus as Smith indicated, but 6 in all
specimens I have examined, the number usually
possessed by H. affinis. The relative length of
the antennular flagella, which Bouvier indicated
was greater in H. affinis, varies within a given
length of carapace, and may be the same in ani-
mals of the two species, e.g., 1.9 times carapace
length in shrimp 23 mm cl. The carpus of the
fourth pereopod is longer than the merus in both
species, and not shorter in H. modestus, as Bou-

TT^

o H. affinis
. H. modestus

FIGURE 49. — Ranges of Hadropenaeus affinis and Hadropenaeus modestus based on published records and specimens personally

examined.

322

I'EREZ KARKANTK: AMKRK'AN SOI.KNOCKRII) SHRIMPS

TABLE 1. — Characteristics distinguishing Hadropenaeus affinis from H. modestus.

Feature

H. affinis

H modestus

Scaphocerite
Prosartema
Fourth pereopod

Coxa of fifth pereopod in

females
Terminal portion of telson
Telsonic spines

Telsonic pubescence

Petasma

Thelycum

Reaching distal end of antennular peduncle or surpassing it

by less than 0.10 of its own length

Extending only to distomesial extremity of first antennular

article

Extending farther anteriorly than third pereopod; surpassing

antennular peduncle by as much as length of dactyl and that

of propodus; length of dactyl less than 0.5 that of propodus

Bearing strong anteromesial spine

Long, length 3.5-4.5 its basal width

Long, length more than 1.5 basal width of terminal portion of
telson

Extensive, lacking on terminal portion

Ventromedian lobule with distomesial projection directed
mesially; distal part of dorsolateral lobule subelliptical

Protuberance of sternite XIV mammiform, with apical part
directed ventrally; median keel of sternite XIII produced into
anteriorly directed blunt tooth

Surpassing antennular peduncle by as much as 0.25 of its
own length

Conspicuously overreaching distomesial extremity of first
antennular article

Not extending so far anteriorly as third pereopod. reaching at
most distal end of first antennular article; length of dactyl
greater than 0.5 that of propodus

Lacking anteromesial spine in adult, occasionally with in-
conspicuous one in juvenile
Short, length 2.5-3.3 its basal width

Short, length not more than basal width of terminal portion of
telson

Limited to paired rows flanking median sulcus and lateral
margins

Ventromedian lobule with distomesial projection directed
distally; distal portion of dorsolateral lobule subrectangular

Protuberance of sternite XIV subovate, with apical part di-
rected anteriorly; median keel of sternite XIII produced into
ventrally or posteriorly directed blunt tooth

vier calculated from Smith's erroneous data.
Finally, the lateral ramus of the uropod is similar
in shape in the two species, its distal part truncate
and turning gently proximomesially. The descrip-
tions of both the petasma and the thelycum of
H. affinis presented by A. Milne Edwards and
Bouvier (1909), together with the two diagnostic
characters mentioned above, adequately diagnose
the species.

Specimens from various localities in the west-
ern Atlantic exhibit differences in the shape of
coxal spine of the fifth pereopod which varies
from nearly blunt to sharply acute. Also in the
sculpture of the thelycum, the apical portion of
the protuberance on sternite XIV may be directed
anteriorly or ventrally. The observed variations,
however, intergrade and, furthermore, in some
specimens the shape of the spine and the direction
of the protuberance are identical to those ex-
hibited by the syntypic material.

Remarks -The numerous records cited above are
the first from the western Atlantic since Bouvier
(1906b) cited a syntypic male from off Barbados
(Blake stn 273) in the original description of the
species, and A. Milne Edwards and Bouvier ( 1909)
recorded an additional juvenile male, which had
been taken with the syntype.

The presence of photophores on the thoracic
sternites of this species is revealed here for the
first time. The photophores were observed in a
recently caught specimen obtained from the Ore-
gon II, south of Great Inagua, Bahamas; they are
similar to those described by Burkenroad (1936)
in Hymenopenaeus debilis.

Hadropenaeus modestus (Smith 1885)
Figures 9, 44B, 46B, 49-52

Hymenopenaeus modestus Smith 1885:183 [holo-
type: 9 USNM 7267; type-locality: off Bethany
Beach, Del., 38°31'N, 73°21'W, 156 fm (285 m),
Fish Hawk stn 1047]. Burkenroad 1936:104.
Bullis and Thompson 1965:5 [part]. Crosnier
and Forest 1973:259.

Haliporus modestus. Bouvier 1905a:980; 1906b:4;
1908:80. A. Milne Edwards and Bouvier 1909:
209. de Man 1911:7. Fowler 1912:543.

Material

UNITED STATES— Delaware: 2 holotype, USNM 7267,
off Bethany Beach, 285 m, 10 October 1881, Fish Hawk stn
1047. North Carolina: 1 6, USNM, SE of Cape Lookout,
348-384 m, 13 November 1956, Combat stn 171. 1 3, USNM,
SE of Cape Lookout, 329 m, 1 February 1972, Oregon II stn
11762. 1 6 2 9, USNM, SE of Cape Fear, 187-190 m,
29 February 1960, Silver Bay stn 1693. Georgia: 1 2, USNM,
off Ossabaw, 238 m, 21 January 1972, Oregon II stn 11720.
Florida: 1 6, USNM, off Melbourne Beach, 329 m, 31 January
1957, Combat stn 226. 1 2 , USNM, off Hobe Sound, 302-285 m,

21 May 1968, Gerda stn 997. 1 2, AMNH, 21 km E of Boynton.
320-266 m, 17 May 1948, Burey. 1 9, RMNH, off Miami, 418 m,
27/28 August 1962, Gerda stn 53. 19, RMNH, E of Old Rhodes
Key, 146 m, 25 September 1964, Gerda stn 427. 2 2 , USNM, off
Elliott Key, 194-187 m, 25 August 1967, Gerda stn 857. 1 9,
UMML, NE of Key Largo, 265-275 m, 24 January 1964, Gerda
stn 229. 3 6 3 9, USNM, SE of Key Largo, 185 m.

22 January 1965, Gerda stn 452. 1 2, RMNH, SW of Marquesas
Keys, 188-199 m, 28 November 1964, Gerda stn 432. 1 6,
USNM, SW of Marquesas Keys, 177-229 m, 26 April 1969,
Gerda stn 1087. 1 S, UMML, S of Dry Tortugas Is, [?] 68 m,
12 April 1965, Gerda stn 564. 1 I , USNM, SW of Dry Tortugas,
348 m, 13 April 1954, Oregon stn 1005. 1 part of carapace,

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FISHERY BULLETIN: VOL. 75, NO. 2

USNM, NW of Charlotte Harbor, 274 m, 22 August 1970,
Oregon II stn 11181.

BAHAMAS— 2 9, RMNH, W of Gun Cay I, 458-531 m,

30 January 1964, Gerda stn 242. 1 9 , RMNH, N of Double
Headed Shot Cays, 443 m, 27 January 1965, Gerda stn 483.

LESSER ANTILLES— 3 d 1 9, USNM, E of The Grena-
dines, 357-658 m, 4 July 1969, Pillsbury stn 861.

WESTERN CARIBBEAN— 1 ?, USNM, W of Old Provi-
dence I, 549 m, 12 September 1957, Oregon stn 1918.

PANAMA— 1 9 , USNM, Golfo de los Mosquitos, 274-293 m,

31 May 1962, Oregon stn 3597.

VENEZUELA— 1 $ , USNM, E of Peninsula de Paraguana,
366 m, 4 October 1963, Oregon stn 4421. 1 6, USNM, off San
Juan de los Cayos, 384 m, 9 October 1963, Oregon stn 4440.

TRINIDAD - TOBAGO— 2 <?, USNM, NW of Tobago,
146 m, 2 July 1969, Pillsbury stn 848.

BRAZIL— Alagoas: 1 6, BMNH, off Barra Grande,
10 September 1873, Challenger stn 122-122C.

Description-Carapace (Figure 50) finely pubes-
cent; setae dense and long on base of rostrum,
gastric, and epigastric regions; small setae on
cardiac region, and minute ones sparsely set on
hepatic and branchial regions; abdomen polished,
and almost entirely naked except for setae on
posterodorsal keel; pubescence of telson as in
Figure 46B. Rostrum short, its length 0.25-0.30
that of carapace, reaching little beyond midlength
of first antennular article, almost horizontal,
with dorsal margin straight and ventral margin
strongly convex but with subapical concavity
giving rise to saber shaped tip; latter 0.3-0.4
length of rostrum. Rostral plus epigastric teeth 6,
apex of third rostral tooth or fourth tooth at level
of orbital margin. Adrostral carina extending
from orbital margin to ultimate tooth; postrostral
carina ending immediately behind cervical sul-
cus. Orbital margin produced anteriorly in ven-
trally inclined short shelf. Postorbital spine,
longest of four lateral spines on carapace, situated

dorsal to base of small antennal spine; branchio-
stegal and hepatic spines sharp. Cervical sulcus
deep, ending dorsally just posterior to midlength
of carapace at base of postrostral carina; cervical
carina sharp; hepatic sulcus almost horizontal
posteriorly, inclined anteroventrally from de-
pressed area below hepatic spine to pit below
branchiostegal spine.

Eye as illustrated (Figure 445).

Antennular peduncle length equivalent to
about 0.65 that of carapace; prosartema long, con-
spicuously overreaching distomesial margin of
first article; stylocerite length about 0.65 of dis-
tance between lateral base of first article and base
of distolateral spine; latter slender and long; fia-
gella long, length of dorsal fiagellum 1.9 cl in
shrimp 23 mm cl, proximal portion of fiagellum
slightly broader than subfiliform distal portion;
ventral fiagellum slightly shorter and broader
than dorsal, gently tapering distally, and bearing
long, marginal plumose setae. Scaphocerite over-
reaching antennular peduncle by as much as 0.2
of its own length, gently tapering from base to
narrow distal portion; lateral rib ending in long,
slender spine, barely or conspicuously over-
reaching distal margin of lamella. Antennal fia-
gellum long, at least 3 times total length of
shrimp. Mandibular palp with distal article
slightly shorter than basal and almost reaching
or barely overreaching distal margin of carpo-
cerite. Third maxilliped surpassing antennular
peduncle by length of dactyl and 0.2-0.5 length
of propodus.

First pereopod stout, reaching between mid-
length and distal end of carpocerite. Second pereo-
pod moderately stout, extending almost to distal
end of carpocerite or overreaching it by not more

FIGURE 50. — Hadropenaeus modestus, 19 mm cl, west of Isla de Providencia, western Caribbean. Cephalothorax, lateral view.

324

PEREZ FARFANTE AMERICAN SOLENOCERID SHRIMPS

than 0.5 length of dactyl. Third pereopod rather
slender, exceeding antennular peduncle by tip or
by entire length of dactyl. Fourth pereopod very
slender, shorter than third, surpassing carpo-
cerite by tip or by entire length of dactyl; length
of dactyl 0.65-0.75 that of propodus; length of
carpus about 1.1 times that of merus. Fifth pereo-
pod very slender and long, overreaching anten-
nular peduncle at least by length of dactyl and
propodus, and at most by their length and 0.2
length of carpus. Order of pereopods in terms of
their maximal anterior extensions; first, second,
fourth, third, and fifth. First pereopod with very
long, slender spine on basis, small spine on disto-
mesial margin of ischium, and rather minute one
near midlength of mesial margin of merus. Second
pereopod with long spine on basis. Coxa of fourth
and fifth pereopods in males armed with anterior
spine. Coxa of fifth pereopod in females mesially
produced into short plate, lacking spine on antero-
mesial margin; minute spine present in young.

Abdomen with high, sharp, median keel from
fourth through sixth somites, low, rounded carina
sometimes present on third; posterodorsal margin

of third, fourth, and fifth somites with median
incision; sixth somite bearing sharp spine at
posterior end of keel, and minute spine on postero-
ventral angles. Telson (Figure 46B) with median
sulcus deep anteriorly, disappearing well anterior
to terminal portion; fixed lateral spines relatively
short, their length 0.7-0.8 basal width of terminal
portion; latter broad, length 2.5-3.3 times basal
width; mesial ramus of uropod overreaching apex
of telson by as much as 0.2 of its own length;
lateral ramus conspicuously surpassing mesial,
and armed with small distolateral spine, slightly
projecting beyond contiguous distal margin of
ramus.

Petasma (Figure 51A, B) cincinnulate along
proximal 0.6 of median line; broad distal part of
ventromedian lobule strongly produced into elon-
gate, distally directed distomesial projection,
and short distolateral projection, and with ter-
minal margin spinulous; distal part of ventro-
lateral lobule heavily sclerotized, forming plate
with border undulate adjacent to ventral costa,
its terminal portion subrectangular, strongly
inclined toward, and partially covered by, ventro-

FIGURE 51.— Hadropenaeus modestus, 6 16.5 mm cl, southeast of Cape Fear, N.C. A, Petasma (partly bent laterally), dorsal view of
right half. B, Ventral view. C, Right appendices masculina and interna, dorsal view. D, Ventromesial view.

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FISHERY BULLETIN: VOL. 75, NO. 2

FIGURE 52. — Hadropenaeus modestus, holotype i 8 mm cl, off Bethany Beach, Del. A, Thelycum, ventral view. B,

Ventrolateral view.

median lobule; ventral costa with distal part free
from contiguous plate, bent outward and bearing
minute spinules on distalmost margin.

Appendix masculina and appendix interna
together with ventrolateral spur (Figure 51C, D)
similar to those of//, affinis (see above).

Thelycum (Figure 52A, B) with median protu-
berance on sternite XIV pyriform or subovate,
its apical portion directed anteriorly, and lying
between prominent, setose, paired convexities of
posteriormost part of sternite XIII; longitudinal,
high, median keel on sternite XIII produced
anteriorly into ventrally or posteroventrally
directed blunt tooth, with anterior margin
straight or convex and posterior margin concave.

Maximum size. -Females: 19.5 mm cl; males:
17.5 mm cl.

Geographic and bathymetric ranges.-Off Dela-
ware Bay (38°31'N, 73°21'W), to the Straits of
Florida, and in the Gulf of Mexico, northwest of
Charlotte Harbor, Fla.; also from the Bahamas,
throughout the Caribbean to off Barra Grande
(about 9°10'S, 34°52'W), Brazil (Figure 49). This
species has been recorded at a depth range of
about 150-550 m (Figure 9).

326

Affinities. -Hadropenaeus modestus may be read-
ily distinguished from its close relative H. affinis
by the characters included in Table 1.

Remarks.-! have examined the holotype of H.
modestus and found that, contrary to the data
presented by Smith (1885), it possesses 6 rostral
teeth (including epigastric), not 7, and that the
merus of the fourth pereopod is only 6.5 mm long,
not 7.5 mm. Therefore the carpus, which is 7.2 mm
long, is not shorter than the merus, but about
1.1 times the length of the latter. These incorrect
statements led Bouvier (1906b) to point out dif-
ferences in the rostral armature and relative
length of the carpus between H. modestus and
H. affinis which do not exist.

Hadropenaeus modestus is newly reported here
in the Caribbean and the Atlantic off northeast
South America. The locality record from off Barra
Grande, Brazil, is based on a single male taken
during the voyage of the Challenger (1873-76).
On the label accompanying this specimen is
"Barra Grande, Brazil, Challenger." Although
there are several towns in Brazil bearing the
name Barra Grande, the locality referred to
above must be that in the State of Alagoas,
because according to Tizard et al. ( 1885), the white
cliffs of Barra Grande could be seen from Chal-

PEREZ FARFANTE: AMERICAN SOLENOCERII) SHRIMPS

lenger stn 122, 122A, 122B, and 122C, which are
between 9°5' and 9°10'S. This specimen has not
been recorded in the literature previously —
probably because it is a juvenile, not readily
identifiable.

Hadropenaeus lucasii (Bate 1881)

Figures 9, 16, 44C, 53-55

Solenocera lucasii Bate 1881:185 [holotype: 9,
BMNH, off Kai Is, south of New Guinea,
5°49'15"S, 132°14'15"E, 140 fm (256 m), 26 Sep-
tember 1874, Challenger stn 192]. [Not Soleno-
cera lucasii. Miers 1884:15. Rathbun 1906:904,
pi. 20, fig. 9.]

Philonicus lucasii. Bate 1888:277, pi. 42, fig. 4.
? Thomson 1904:254.

Pleoticus lucasii. Bate 1888:939.

Haliporus modestus. Rathbun 1906:905, pi. 20,
fig. 4. [Not Hymenopenaeus [Hadropenaeus]
modestus Smith 1885.]

Haliporus lucasi. Bouvier 1908:80.

IHaliporus malhaensis Borradaile 1910:258, fig. 2
[type not extant; type-locality: off Saya de
Malha, Indian Ocean, 145 fm (265 m)]. de Man
1911:7.

Haliporus lucasii. de Man 1911:7.

Hymenopenaeus lucasii. Burkenroad 1936:104.
Anderson and Lindner 1945:289. Kubo 1949:
213, fig. 8 B\ 20 Q, 27 K-N, 66 O, P, 72 C, 1, 80 H,
91, 92 A, C.

^.Hymenopenaeus lucassi. Ramadan 1938:57.

Hymenopenaeus lucasi. Crosnier and Forest 1973:
256, fig. 83a.

Material

HAWAII— 6 6 5 9, USNM, Pailolo Channel, 271-223 m,
23 July 1902, Albatross stn 4101. 1 6 1 9, USNM, Pailolo
Channel, 223-241 m, 23 July 1902, Albatross stn 4102. 1 9,
USNM, Pailolo Channel, 241-258 m, 23 July 1902, Albatross
stn 4103. 1 V, USNM, N coast of Maui 1, 369-402 m, 21 July 1902,
Albatross stn 4081. 3 6 10 9, USNM, NW coast of Maui I,
214 m, 16 November 1968, Townsend Cromwell stn 40-43.
4 9, USNM, NW coast of Maui I, 218 m, 17 November 1968,
Townsend Cromwell stn 40-48. 4 6 12 9, USNM, NW coast of
Maui I, 218 m, 17 November 1968, Townsend Cromwell stn 40-
49. 1 6 12 9, USNM, NW coast of Maui I, 216-232 m, 28 April
1968, Townsend Cromwell stn 36-11. 1 6 16 9, USNM, Kaiwi
Channel, 177-183 m, 5 May 1968, Townsend Cromwell stn 36-26.
3 9 , USNM, S coast of Oahu I, 538-470 m, 6 May 1902, Albatross
stn 3920. 2 9, USNM, N coast of Oahu I, 176-201 m, 12 July
1972, Townsend Cromwell stn 59-3. 2 6, USNM, NW coast of
Oahu I, 395-459 m, 25 July 1902, Albatross stn 4121. HIS,
USNM, vicinity of Laysan I, 271-298 m, 16 May 1902, Albatross
stn 3938. 1 6, USNM, vicinity of Laysan I, 364-177 m, 19 May
1902, Albatross stn 3947.

NEW GUINEA— 1 9 holotype, BMNH, off Kai Is, 256 m,
26 September 1874, Challenger stn 192.

REPUBLIC OF MALDIVES— 1 9, BMNH, off Maldive
Is, 256-293 m, 4 April 1934, The John Murray Expedition stn 153.

MADAGASCAR— 1 6, USNM, NW of Baie du Currier,
350-360 m, 15 September 1972, A. Crosnier.

Description. -Carapace (Figure 53) with restricted
pubescent areas: setae dense and long at base of
rostrum, on pterygostomian region, and in patch
extending from orbital margin to epigastric tooth.
Abdomen polished and naked; telson with rows of
minute setae flanking median sulcus and lateral
margins; mesial ramus of uropod sparsely pubes-
cent. Rostrum short, its length 0.30-0.35 that of
carapace, reaching to, or almost to, distal margin
of first antennular article, horizontal, with dorsal
margin straight and ventral margin strongly

FIGURE 53. — Hadropenaeus lucasii, 9 18.5 mm cl, northwest coast of Maui, Hawaiian Islands. Cephalothorax, lateral view.

327

FISHERY BULLETIN: VOL. 75, NO. 2

convex; tip about 0.2 length of rostrum. Rostral
plus epigastric teeth 6-8 (mode 7; percentage
distribution: 6-13.3, 7-83.3, 8-3.3; N = 60); third
rostral tooth usually situated at level of orbital
margin. Adrostral carina extending from orbital
margin to base of ultimate tooth, and shorter,
more dorsal, conspicuous carina extending from
second rostral tooth to penultimate; postrostral
carina ending immediately behind cervical sul-
cus. Orbital margin produced anteriorly into
ventrally inclined, short shelf. Postorbital spine,
longest of four lateral spines on carapace, usually
more slender than middorsal teeth on carapace,
and located dorsal to base of small antennal spine;
branchiostegal and hepatic spines sharp. Cervical
sulcus deep, ending dorsally just anterior to mid-
length of carapace, near postrostral carina; cer-
vical carina sharp; hepatic sulcus subhorizontal
posteriorly, originating almost at level of dorsal
extremity of cervical sulcus, shallow and inclined
anteroventrally from depressed area below he-
patic spine to pit below branchiostegal spine.

Eye as illustrated (Figure 44C).

Antennular peduncle length equivalent to 0.65
that of carapace; prosartema long, conspicuously
overreaching distomesial margin of first article;
stylocerite length about 0.65 of distance between

its proximal extremity and mesial base of disto-
lateral spine; latter very slender and long, con-
siderably surpassing proximal margin of second
article. Antennular flagella long and considerably
unequal in length, dorsal 1.85 times carapace
length and ventral 1.30 in shrimp 12.5 mm cl,
and 1.35 and 0.90, respectively, in shrimp 27 mm
cl; dorsal flagellum subcylindrical, ventral sub-
cylindrical to depressed. Scaphocerite reaching to
distal margin of antennular peduncle or over-
reaching it by as much as 0.15 of its own length;
lateral rib ending in spine reaching to, or slightly
beyond, distal margin of lamella. Antennal flagel-
lum long, although incomplete in all specimens,
longest observed 3 times total length of shrimp.
Mandibular palp with article as long as or slightly
shorter than basal, reaching between midlength
and distal 0.35 of carpocerite. Third maxilliped
reaching to midlength of third antennular article
or overreaching it by as much as 0.5 length of
propodus; length of dactyl 0.75 that of propodus.
First pereopod, stoutest of five, reaching be-
tween midlength and distal 0.15 of carpocerite.
Second pereopod extending to distal end of carpo-
cerite or overreaching it by as much as entire
length of dactyl. Third pereopod overreaching
antennular peduncle by 0.5 length of dactyl or by

FIGURE 54.— Hadropenaeus lucasii, 6 13 mm cl, Pailolo Channel, Hawaiian Islands. A, Petasma (partly bent laterally), dorsal view
of right half. B, Ventral view. C, Right appendices masculina and interna, dorsolateral view. D, Ventromesial view.

328

PEREZ EARFANTE: AMERICAN SOLENOCERID SHRIMI'S

as much as entire propodus. Fourth pereopod
exceeding carpocerite by almost length of dactyl
and sometimes by as much as length of dactyl
and 0.15 that of propodus. Fifth pereopod reaching
beyond antennular peduncle by length of dactyl
and 0.6 to entire length of propodus. Order of
pereopods in terms of their maximal anterior
extensions: first, second, fourth, third, and fifth.
First pereopod bearing very long spine on disto-
mesial extremity of basis, long one on that of
ischium, and relatively small spine almost at mid-
length of merus. Second pereopod with long spine
on basis. In female, coxa of third pereopod pro-
duced mesially into rather short densely setose
plate; coxa of fourth pereopod bearing narrow
plate. In both sexes, coxa of fourth and fifth pereo-
pods bearing conspicuous anterior spine.

Abdomen with strong middorsal carina from
third through sixth somites, carina rounded on
third, forming keel from fourth posteriorly;
posterodorsal margin of third, fourth, and fifth
with long median incision; sixth somite length
about 1.3 times maximum height, bearing sharp
spine at posterior end of keel and minute spines
at posteroventral angles. Telson with median
sulcus deep anteriorly, progressively shallower
posteriorly, disappearing just before reaching
base of lateral spines; terminal portion length
3.3-4.0 times basal width; lateral spines short,
1-1.4 times basal width of terminal portion.
Mesial ramus of uropod reaching to, or slightly
surpassing, apex of telson; lateral ramus over-
reaching mesial by as much as 0.2 of its own
length, and armed with minute distolateral spine,
reaching distal margin of ramus.

Petasma (Figure 54A, B) cincinnulate along
proximal 0.70 of median line; broad distal part
of ventromedian lobule produced into blunt, disto-
mesial projection, its lateral part turned strongly
inward; entire terminal margin of lobule spinu-
lous; distal part of ventrolateral lobule heavily
sclerotized, forming plate, border adjacent to
ventral costa bearing emargination delimiting
basal part from short, broadly subelliptical ter-
minal part; latter inclined toward, and partially
covered by, ventromedian lobule, and armed with
spinules along entire distal margin; ventral costa
with distal part free from, and falling short of,
contiguous plate, its distal margin bearing very
minute spinules.

Appendix masculina (Figure 54C, D) with prox-
imal part broad, produced mesially into thickened
lobe, and bearing long setae along lateral margin;

distal part narrow, directed strongly laterally,
and bearing apical tuft of long setae. Appendix
interna shorter than appendix masculina, nar-
row, and lacking setae. Ventrolateral spur large,
paddlelike.

Thelycum (Figure 55) with median protuber-
ance on sternite XIV roughly elliptical, low,
markedly less elevated than prominent setose,
paired convexities of sternite XIII; median ridge
of latter long, lacking tooth, sometimes ending
in small knob at one or both extremities.

Maximum size-Female (holotype), 25.5 mm cl,
100 mm tl; male, 18.5 mm cl, 72.5 mm tl (Kubo
1949). Largest male examined by me, 14 mm cl,
about 64 mm tl.

Geographic and bathymetric ranges-Madagascar
(off northwest coast) through the Indo-West Pacif-
ic to Hawaii (Figure 16), in depths between 180
and 500 m (Figure 9). The few records available
are from scattered localities.

FIGURE 55.— Hadropenaeus lucasii, ? 19.5 mm cl, Pailolo
Channel, Hawaiian Islands. Thelycum, ventral view.

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FISHERY BULLETIN: VOL. 75, NO. 2

Affinities. -Hadropenaeus lucasii is closely allied
to its two Atlantic congeners, H. affinis and H.
modestus, but it may be distinguished from them
by the possession of a conspicuous carina on the
rostrum dorsal to the adrostral carina, and by
certain petasmal and thelycal features. In H.
lucasii the ventromedian lobule of the petasma is
not produced into a distolateral projection; in-
stead, its lateral portion is turned strongly
inward; the distal plate of the ventrolateral lobule
bears spinules along the entire terminal margin
and is produced in a blunt, ventral projection; in
addition, the ventral costa falls conspicuously
short of the distalmost part of the adjacent plate.
The thelycum, in turn, is characterized by a
median protuberance on sternite XIV, which does
not project ventrally so far as the posterior convex-
ities of sternite XIII, and the latter bears a low
median ridge which is not produced anteriorly in
a large tooth. Furthermore, in females of H.
lucasii, the coxae of the fourth pair of pereopods
bear a conspicuous anteromesial spine which is
lacking in the other two species.

Hadropenaeus lucasii exhibits some morpho-
logical variations which are undoubtedly taxo-
nomically insignificant because extremes of
variations occur in animals from the same region
and even from the same locality. Among them
are the relative extension of the scaphocerite,
gnathal and thoracic appendages, the total
number of rostral teeth as well as the number
situated on the carapace. The evidence at hand,
however, indicates that the ventral antennular
flagellum and some features of the petasma differ
regionally. The ventral antennular flagellum is
somewhat depressed in the holotype from New
Guinea, in Japanese specimens (Kubo 1949) and
in two specimens from Madagascar examined by
me, and subcylindrical in individuals from Indo-
nesia (de Man 1911) as well as in all those avail-
able from Hawaii. In addition, the distomesial
projections of the ventromedian lobules of the
petasma are larger in specimens from Japan than
in males from Madagascar and Hawaii. Whereas
the shape of the flagellum exhibits definite varia-
tions which seem to be regionally restricted, the
differences in the petasma are limited to degree
of development and are perhaps insignificant.
Except for the collection from Hawaii, available
material is extremely meager; consequently, the
variations that I have noted are pointed out, with
the conviction that definite conclusions as to their
taxonomic value must await examination of ade-

quate collections from various areas throughout
the Indo-West Pacific.

I have examined the female from the Maldive
Islands, Indian Ocean, that Ramadan (1938) iden-
tified as H. lucasii. This specimen differs from
other specimens of the latter species in the follow-
ing features: the rostral and epigastric teeth are
slenderer — not much stronger than the post-
orbital spine — and inclined more anteriorly; the
anteromesial spine on the coxa of the fifth pereo-
pod is longer and more slender; and the median
protuberance on sternite XIV is smaller and sur-
rounded by a shallow depression. Crosnier and
Forest (1973), who presented an illustration of
the thelycum of the specimen (plate 85, figure a),
suggested that the slight differences between the
thelycum of the latter and that of the type of H.
lucasii could be due to the difference in size of
the animals, the type being 90 mm long (23.5 mm
cl) and Ramadan's specimen 70 mm. As these
authors indicated, Ramadan's specimen exhibits
6 middorsal teeth (rostral plus epigastric), 3 of
which are located on the carapace; this number
and arrangement of teeth occurs infrequently in
members of H. lucasii, but has been observed in
several specimens by both Rathbun (1906) and
me. Crosnier and Forest suggested further that
because of the number and arrangement of the
middorsal teeth and the relative size of those
behind the rostrum (which are not much stronger
than the postorbital spine), Ramadan's specimen
might be referable to Borradaile's (1910) Hali-
porus malhaensis. This species was described from
Saya de Malha, Indian Ocean, and its identity is
still uncertain, primarily because the holotype,
the only specimen on which the description was
based, is no longer extant (Ramadan 1938). The
features pointed out above suggest that the
shrimp from the Maldive Islands might belong to
a species other than H. lucasii, but an under-
standing of its systematic position must await
more material from the Indian Ocean.

Both Burkenroad (1936) and Ramadan (1938)
were inclined to think that H. malhaensis was
identical with H. lucasii, and placed the former
name in the synonymy of the latter preceded by a
question mark. Previously, de Man (1911) had
indicated that he would have identified them as
one species, except for Borradaile's statement that
in H. malhaensis neither the fourth nor the fifth
pereopod is "particularly slender." De Man also
called attention to the fact that in Borradaile's
illustration the propodi of the fourth and fifth

330

l'KRKZ KARKANTK: AMERICAN SOLENOCKRII) SHRIMI'S

pereopods are missing. Kubo (1949) considered
that H. malhaensis and H. lucasii are distinct
species; he stated that his specimens of//, lucasii
cannot be referred to H. malhaensis because in
the latter there are 3 teeth on the carapace, the
scaphocerite does not overreach the antennular
peduncle, and the dorsal antennular fiagellum is
not longer than the ventral which also lacks
"rather long setae" on the dorsal and ventral bor-
ders. Actually, the first two features are not typi-
cal of H. malhaensis but occur in H. lucasii, in
which, as stated above, 3 teeth may be present on
the carapace, and the scaphocerite, which usually
overreaches the antennular peduncle, extends
only to the distal end of the peduncle in some
individuals. Features of the antennular fiagella
of H. malhaensis cited by Kubo could be due to
the fact that the dorsal fiagellum was incomplete
in the type, as it often is in preserved specimens,
or to omissions of the artist. The two species dis-
cussed seem to me to be quite similar, and if there
is doubt in my mind as to the status of//, malhaen-
sis, it is mainly because of Borradaile's statement
that the fourth and fifth pereopods are not "par-
ticularly slender." The species exhibits most of
the features of Hadropenaeus: stout body, thick
carapace, short rostrum with ventral margin con-
vex, middorsal teeth on the carapace separated by
regularly decreasing intervals, lack of branchio-
cardiac carina and sulcus, and relative length of
the last two pereopods having "fourth leg rather
longer and fifth considerably longer than the
third." These features of Hadropenaeus combined
with a fifth pereopod that is not very slender, how-
ever, are unique. Perhaps the question of the
identity of Borradaile's species will be resolved
when large collections of solenocerids from the
Indian Ocean are studied. Meanwhile, I am
inclined, tentatively, to assign H. malhaensis to
the synonymy of H. lucasii.

Mesopenaeus New Genus

Parartemesia Bouvier 1905b:747 [part, excluding

Parartemesia carinata Bouvier 1905b = Pleoti-

cus muelleri (Bate 1888)].
Haliporus. Bouvier 1906b:l [part]; 1908:78[part].

A. Milne Edwards and Bouvier 1909:206 [part].
Hymenopenaeus. Burkenroad 1936:102 [part].

Roberts and Pequegnat 1970:29 [part].

Diagnosis- Body stout, carapace proportionately
short; integument thick, firm. Rostrum short,

reaching approximately to base of second anten-
nular article; deep, with ventral margin pro-
nouncedly convex, and armed only with dorsal
teeth; epigastric tooth and first rostral separated
by interval similar to that between first and sec-
ond rostra] teeth. Orbital, postorbital, antennal,
and hepatic spines present; pterygostomian and
branchiostegal spines absent. Cervical sulcus
long, almost reaching middorsum of carapace;
hepatic sulcus deep; branchiocardiac carina and
sulcus, posthepatic, and submarginal carinae
lacking. Abdomen carinate dorsally from third
through sixth somites. Telson with pair of con-
spicuous, fixed lateral spines. Prosartema long,
flexible. Antennular flagella not much longer
than carapace and dissimilar: dorsal fiagellum
subcylindrical and slender, ventral one conspicu-
ously depressed. Mandibular palp two jointed,
articles broad, distal one almost as long as basal
and tapering to blunt apex. First maxilla with
unsegmented palp (endite of basis) gently narrow-
ing to rounded apex. Fourth and fifth pereopods
rather stout proximally, fifth moderately longer
than fourth. First pereopod with spine on basis
and ischium. Exopods on all maxillipeds and per-
eopods. Lateral ramus of uropod armed with disto-
lateral spine reaching distal margin of lamella
(terminal). In males, petasma with ventral costa
not projecting free distally, there bearing flexible
flap; distal portion of rib of dorsolateral lobule
projecting beyond margin of adjacent area; endo-
pod of second pleopod bearing appendices mascu-
lina and interna, and with basal sclerite produced
distally into long ventrolateral spur. Thelycum of
open type, lacking enclosed seminal receptacle.
Pleurobranchia on somites IX to XIV; single,
rudimentary arthrobranchia on VII, and anterior
and posterior arthrobranchiae on somites VIII to
XIII; podobranchia on second maxilliped, and epi-
pod on second maxilliped (and on first if proximal
exite of coxa considered an epipod) through fourth
pereopod.

Type-species.-Parartemesia tropicalis Bouvier
1905b.

Etymology. -The generic name is derived from the
Greek mesos, something in between, in combina-
tion with the generic name Penaeus, alluding to
the fact that the dorsal antennular fiagellum is
subcylindrical and filiform, as in Pleoticus, Hali-
poroides and Hymenopenaeus, and the ventral
one flattened, much as in Solenocera.

331

FISHERY BULLETIN: VOL. 75, NO. 2

Gender-Masculine.

List of species. -This genus includes only one spe-
cies: the western Atlantic Mesopenaeus tropi-
calis (Bouvier 1905b).

Affinities. -Mesopenaeus resembles Solenocera in
possessing a flattened ventral flagellum, but in
the former this appendage is neither so flattened
and broad nor is it channeled as it is in the latter.
It shares with its more closely allied genera —
Hymenopenaeus , Haliporoides, Pleoticus, and
Hadropenaeus — a subcylindrical dorsal flagellum,
and a similar armature of the lateral ramus of
the uropod, the lateral rib of which ends in a well-
defined spine. The stout body, deep rostrum with
the ventral margin pronouncedly convex, ar-
rangement of the epigastric and rostral teeth,
and absence of both branchiocardiac sulcus and
carina place Mesopenaeus closer to Hadropenaeus
than to the other genera. Mesopenaeus differs
from Hadropenaeus, however, in that the ventral
flagellum is invariably depressed, whereas in the
latter it is almost always subcylindrical (in occa-
sional individuals of//, lucasii the ventral flagel-
lum is depressed). In Mesopenaeus orbital and
branchiostegal spines are present, and the thely-
cum exhibits paired anterior protuberances on
sternite XIV which are present elsewhere among
the solenocerids only in the members of the
nominal genus. Finally, in Mesopenaeus the ven-
tral costa of the petasma is fused to the flexible
terminal part of the ventrolateral lobule, whereas
in Hadropenaeus the ventral costa is distally free
from the sclerotized terminal part of the lobule.

Mesopenaeus tropkalis (Bouvier 1905)

Figures 9, 34, 56-63

Parartemesia tropicalis Bouvier 1905b:748 "mer
des Antilles" in 80-175 fm ( 146-329 m). [No type
designated.]

Haliporus tropicalis. Bouvier 1906b:4; 1908:80.
A. Milne Edwards and Bouvier 1909:217, fig.
45-54, pi. 3, fig. 1-19 Llectotype 9, MCZ 7199;
type-locality: "Blake: Florida Bank, lat. N. 26°
31', long. 0. 85° 03', 119 brasses." Paralectotype
9, MP, off Barbados, 13°04'12"N, 59°36'45"W,
76 fm (139 m), 5 March 1879, Blake stn 2721.
de Man 1911:7.

Hymenopenaeus tropicalis. Burkenroad 1936:103.
Springer and Bullis 1956:8. Boschi 1964:38.

332

Bullis and Thompson 1965:5. Williams 1965:15,
fig. 5-7. Cerame-Vivas and Gray 1966:263.
Mistakidis and Neiva 1966:434. Roberts and
Pequegnat 1970:29. Pequegnat and Roberts
1971:8. Iwai 1973:44, fig. 13.

Solenocera weymouthi Lindner and Anderson
1941:181, fig. la-e [holotype 9, USNM 79357;
type-locality: off Orange Beach, Ala., 29°28'N,
87°30'W, 46 fm (84 m), Pelican stn 137-2,
1 March 1939; allotype 6, USNM 79359, 23 km
S of Dry Tortugas, 110 m, 5 August 1932, Anton
Dohrn stn 74-32; paratype 6, USNM 79358,
locality as in holotype; 71 6 78 9 , USNM 23420,
between Cape Hatteras and Cape Lookout,
N.C., 34°35'30"N, 75°45'30"W, 32 fm (59 m),
18 October 1885, Albatross stn 2605]. Ander-
son and Lindner 1945:286.

Hypenepenaeus tropicalis. Mistakidis 1965:9.

Material

UNITED STATES— North Carolina: 2 6 1 9,UNC-IMS,
NE of Cape Lookout, 90-110 m, 27 April 1965, Eastward stn
1087. 71 6 78 9 (paratypes Solenocera weymouthi), USNM
23420, NE of Cape Lookout, 59 m, 18 October 1885, Albatross
stn 2605. 1 9, USNM, SE of Cape Lookout, 82 m, 21 June 1957,
Combat stn 406. 1 6 1 9 , UNC-IMS, SE of Cape Lookout, 229 m,
8 June 1949, Albatross III stn 21-4. 8 8 8 9 , USNM, SE of Cape
Lookout, 154 m, 8 June 1949, Albatross III. 2 6 4 9, UNC-IMS,
E of Cape Fear, 100 m, 27 April 1965, Eastward stn 1089. 1 6,
UNC-IMS, SE of Cape Fear, 140-145 m, 27 April 1965, Eastward
stn 1086. 2 6 2 9, USNM, SE of Cape Fear, 183 m,
29 January 1972, Oregon II stn 11747. 3 6 5 9, USNM, off
Cape Fear, 190-187 m, 29 February 1960, Silver Bay stn 1694.
1 6 8 9, USNM, SE of Cape Fear, 187-190 m, 29 February 1960,
Silver Bay stn 1693. South Carolina: 1 9, USNM, off Cape I,
183 m, 28 January 1972, Oregon II stn 11743. 1 9, USNM,
E of Bull Bay, 181 m, 5 January 1885, Albatross stn 2313. 2 9,
USNM, E of Bull Bay, 155 m, 5 December 1960, Silver Bay
stn 2535. 1 9, USNM, off Santa Helena Sound, 83 m,
28 April 1966, Oregon stn 6073. Georgia: 4 9, USNM, off
Savannah, 68-91 m, 14 December 1961, Silver Bay stn 3658.
18 2 9, USNM, off Savannah, 73 m, 12 March 1956, Bowers
stn 54. 19, USNM, off Savannah Beach, 73 m, 26 April 1966,
Oregon stn 6062. 1 6, USNM, off Catherines Sound, 37 m,
13 March 1940, Pelican stn 195-10. Florida: 1 V, USNM, off
Fernandina, 179 m, 18 January 1972, Oregon II stn 11699.
1 6 9 9, USNM, off St Augustine, 75 m, 24 April 1966, Oregon
stn 6044. 1 8 3 9, USNM, off St Augustine, 40 m, 5 September
1962, Silver Bay stn 4340. 1 9, USNM, off Matanzas Inlet,
183 m, 18 November 1965, Oregon stn 5741. 1 9, USNM, off
Matanzas Inlet, 64-87 m, 7 October 1962, Silver Bay stn 4451.
1 9, USNM, off Ponce de Leon Inlet, 73-97 m, 5 October 1962,
Silver Bay stn 4420. 18 19, USNM, off Edgewater, 51-37 m,
24 August 1965, Oregon stn 5603. 1 9, USNM, off Cape
Kennedy, 70 m, 16 January 1966, Oregon stn 5860. 1 9 , USNM,
off Melbourne Beach, 73 m, 14 July 1961, Silver Bay stn 3279.
1 9, UMML, NE of St Lucie Inlet, 38-42 m, 21 May 1968,
Gerda stn 1002. 1 6, UMML, SE of St Lucie Inlet, 60-62 m,
21 May 1968, Gerda stn 1001. 1 9, RMNH, E of Miami, 119 m,

PEREZ I'AKKANTE: AMERICAN SOLENOCERII) SIIKIMI'S

16 April 1965, Gerda stn 622. 3 9, RMNH, off Elliott Key,
82-77 m, 15 April 1965, Gerda stn 610. 2 9, USNM, off Old
Rhodes Key, 91 m, 10 November 1961, Silver Bay stn 3524.
2 ' 3 i , USNM, off Key Largo, 86-79 m, 10 July 1967, Gerda
stn 834. 1 (J 2 9, RMNH, off Key Largo, 86-95 m, 14 September
1965, Gerda stn 752. 1 6 2 9, RMNH, off Key Largo, 92-97 m,
14 September 1965, Gerda stn 751. 1 9 , UMML, off Key Largo,
108-88 m, 26 January 1966, Gerda stn 767. 2 9, RMNH, off
Key Largo, 146 m, 26 January 1966, Gerda stn 770 . 1 9 , USNM
+ 4 8 2 9, RMNH, off Key Largo, 99-91 m, 10 July 1967, Gerda
stn 833. 4 8 2 9, RMNH, SE of Key Largo, 95 m, 15 April 1965,
Gerda stn 602. H 1 9, USNM, off Key Largo, 102 m, 9 April
1886, Albatross stn 2639. 1 9, USNM, Hawk Channel, 110 m,
27 October 1960, Silver Bay stn 2391. 1 6 9 9, USNM, Hawk
Channel, 128 m, 27 October 1960, Silver Bay stn 2392. 1 6 1 9,
USNM, SE of Key West, 93-106 m, 25 February 1969, Gerda
stn 1024. 2 6 2 9, USNM, SE of Key West, 135-146 m,
25 February 1969, Gerda stn 1028. 2 tJ, USNM, off Key West,
179 m, 14 February 1902, Fish Hawk stn 7279. 1 6, USNM,
SW of Marquesas Keys, 196-210 m, 26 April 1969, Gerda stn
1084. 1 6, USNM, SW of Marquesas Keys, 201-210 m, 26 April
1969, Gerda stn 1085. 2 9, USNM, SW of Marquesas Keys,
(depth not given), 12 December 1962, Oregon stn 4142. 2 6 2 9 ,
USNM, Sof Dry Tortugas,366 m, 10 July 1965, Oregon stn 1330.
1 d, USNM, S of Dry Tortugas, 229-274 m, 28 April 1969, Gerda
stn 1095. i (allotype S. weymouthi), USNM 79359, 23 km S of
Dry Tortugas, 110 m, 5 August 1932, Anton Dohrn stn 74-32.

1 d, USNM, SW of Dry Tortugas, 348 m, 13 April 1954, Oregon
stn 1005. 1 9, USNM, SW of Dry Tortugas, 183 m,
6 August 1963, Oregon stn 4370. 1 6 21 9 , USNM, NW of Dry
Tortugas, 298 m, 19 April 1954, Oregon stn 1026. 9 lectotype,
MCZ 7199, Florida Bank, 218 m, Blake. 4 6 19, USNM, off
St Petersburg, 106 m, 18 March 1954, Oregon stn 938. 2 9,
USNM, W of Clearwater, 146 m, 11 March 1956, Oregon stn 920.

6 6 12 9, USNM, off Apalachicola Bay, 88 m, 10 March 1954,
Oregon stn 917. 2 6 7 9, USNM, S of St Vincent I, 64 m,

7 March 1954, Oregon stn 896. 1 8, USNM, off Panama City,
101-130 m, 26 July 1957, Silver Bay stn 100. 4J39, USNM,
off Choctawhatchee Bay, 91 m, 21 March 1954, Oregon stn 944.

2 J . USNM, off Gulf Beach, 165 m, 1 March 1955, Oregon stn
1254. Alabama: 9 (holotypeS. weymouthi), USNM 79357, off
Orange Beach, 84 m, 1 March 1939, Pelican stn 137-2. 1 cS (para-
type S. weymouthi), USNM 79358, same locality as holotype.

MEXICO— Quintana Roo: 2 6 18 9, USNM, NE of Cape
Catoche, 183 m, 22 January 1967, Oregon stn 6399.

BAHAMA ISLANDS— 1 c5 3 9, USNM, NE of Little
Bahama Bank, 183 m, 25 October 1961, Silver Bay stn 3466.
1 i , RMNH, Northwest Providence Channel, 278-329 m,

3 March 1965, Gerda stn 526. 1 6 4 9 , RMNH, off Great Isaac I,
311-329 m. 2 March 1965, Gerda stn 509. 1 6, USNM, off Dog
Rocks, Cay Sal Bank, 618 m, 22 June 1967, Gerda stn 815.
1 2, USNM, off Great Inagua, 183-137 m, 5 November 1961,
Silver Bay stn 3502. 1 6 1 9, USNM, S of Great Inagua, 311 m,
13 December 1969, Oregon II stn 10849. 1 6 4 9, USNM, S of
Great Inagua, 311 m, 13 December 1969, Oregon II stn 10850.

CUBA— 2 $, USNM, N of Las Villas, 461 m, 15 December
1969, Oregon II stn 10860.

DOMINICAN REPUBLIC— 1 8 1 9, USNM, off Cabo
Engario, 201 m, 17 October 1963, Silver Bay stn 5188.

PUERTO RICO— 2 6 2 9, USNM, Mona Passage, 366 m,

17 October 1963, Silver Bay stn 5190.

LESSER ANTILLES— 2 9, USNM, Dominica Passage,
640 m, 1 December 1969, Oregon II stn 10825. 1 9 , USNM, off
Barbados, 91-366 m, J. B. Lewis. 1 9 paralectotype, MP, off
Barbados, 139 m, 5 March 1878, Blake stn 272.

WESTERN CARIBBEAN— 18 6 12 9, USNM, Arrow-
smith Bank, 311-146 m, 28 January 1968, Gerda stn 954.
H 5 9, USNM, Arrowsmith Bank, 252-293 m, 14 March 1968,
Pillsbury stn 591. 1 6 2 9, USNM, Arrowsmith Bank, (depth
not given), 15 November 1968, Pillsbury stn 598. 1 i, UMML,
Arrowsmith Bank, 115-190 m, 23 August 1970, Gerda stn 1286.

1 d 1 9, USNM, Arrowsmith Bank, 307-192 m, 28 January 1968,
Gerda stn 951. 1 6, USNM, Arrowsmith Bank, 225-437 m,
21 August 1970, Gerda stn 1275. 1 9, USNM, NE of Banco
Gorda, 265-274 m, 6 June 1962, Oregon stn 3622. 2 9, UMML,
NW of Quita Sueno Bank, 296-375 m, 31 January 1971, Pills-
bury stn 1356. 1 d 1 9, USNM, W of Quita Sueno Bank,
201-207 m, 12 February 1967, Oregon stn 6460. 22 d 24 9,
USNM, W of Isla de Providencia, 289-274 m, 4 February 1967,
Oregon stn 6423. 1 6 5 9, USNM, SW of Isla de San Andres,
201-219 m, 4 February 1967, Oregon stn 6424. 18 d 20 9,
USNM, W of Isla de San Andres, 139 m, 6 February 1967, Oregon
stn 6434. 6 d 10 9 , USNM, W of Cayos de Albuquerque, 192 m,
7 February 1967, Oregon stn 6444.

BELIZE— 1 d 3 9, USNM, W of Lighthouse Reef, 329-274 m,
24 January 1966, Oregon stn 6404. 1 9, USNM, W of Light-
house Reef, 262 m, 23 January 1967, Oregon stn 6403. 6 d 7 9 ,
USNM, W of Lighthouse Reef, 183 m, 24 January 1967, Oregon
stn 6405.

NICARAGUA— 1 9, USNM, NE of Puerto Cabezas, 183-
219 m, 21 May 1962, Oregon stn 3568. 1 9 , USNM, NE of Puerto
Cabezas, 274-293 m, 21 May 1962, Oregon stn 3566. 11 d 23 9,
USNM, 190 m, off La Barra de Ri'o Grande, 5 February 1967,
Oregon stn 6426. 7 d 3 9 , USNM, off La Barra de Ri'o Grande,
176-110 m, 5 February 1967, Oregon stn 6427. 18 d 10 9,
USNM, NE of Islas del Mai'z, 119 m, 5 February 1967, Oregon
stn 6432. 23 d 18 9, USNM, NE of Islas del Mai'z, 192-198 m,
7 February 1967, Oregon stn 6448. 5 9 , USNM, NE of Islas del
Mai'z, 198-201 m, 7 February 1967, Oregon stn 6447.

PANAMA— 1 d.'USNM, off Code del Norte, 137 m,
29 May 1962, Oregon stn 3587.

VENEZUELA— 2 6 19, USNM, off Golfo de Venezuela,
201 m, 26 September 1963, Oregon stn 4398. 1 9, USNM, off
Puerto Cumarebo, 161-187 m, 27 July 1968, Pillsbury stn 757.

2 6 3 9 , USNM, E of Pen de Paraguana, 915 m, 4 October 1963,
Oregon stn 4416. 1 6, USNM, off La Guaira, 97 m, 13 October
1963, Oregon stn 4459. 1 8 1 9, USNM, off La Guaira, 97 m,
13 October 1963, Oregon stn 4461. 2 6, UMML, W of I La Tor-
tuga, 68-60 m, 22 July 1968, Pillsbury stn 734. 26 6 11 9,
USNM, off Cabo Cordera, 60-73 m, 22 July 1968, Pillsbury
stn 737. 6 6 3 9, USNM, NE of Islas Los Testigos, 585-439 m,
24 September 1964, Oregon stn 5039. 2 9 , USNM, NE of Islas
Los Testigos, 128-119 m, 24 September 1964, Oregon stn 5040.

BRAZIL— Amapa: HI 9, USNM, mouths of the Amazon
River, 229 m, 17 November 1957, Oregon stn 2080. Maranhao:
1 9, USNM, off Sao Luis, 183 m, 9 March 1963, Oregon stn
4225. Sao Paulo: HI!, IOUSP, SSE of I de Sao Sebastiao,
156-152 m, 3 July 1971, Prof. W. Besnard stn 1471. 4 6 2 9,
USNM-MP, SE of Quemado Grande I, 97-100 m, 11 December
1961, Calypso stn 138.

Description-Body robust (Figure 56), integument
firm, mostly glabrous, but carapace with rather
long densely set setae on rostrum above adrostral
carina; patch of minute setae extending from
orbital margin to base of epigastric tooth; and
elongate patch of sparsely set setae below hepatic
sulcus.

333

FISHERY BULLETIN: VOL. 75. NO. 2

Lr"

1 I

FIGURE 56. — Mesopenaeus tropicalis, 2 23.5 mm cl, east of Cayosde Albuquerque, western Caribbean. Lateral view.

Rostrum rather short, its length not exceeding
0.4 that of carapace, reaching, at most, base of
second antennular article, straight or slightly
tilted upward, moderately high, its ventral mar-
gin strongly convex, often with subapical concav-
ity giving rise to saber shaped tip. Rostral plus
epigastric teeth 7-10, mode 8 (percentage distribu-
tion in North America: 7-2, 8-60, 9-36, 10-2,
N = 100; percentage distribution in South
America: 7-4, 8-80, 9-15, 10-1, N = 100); teeth
long and sharp; usually third rostral tooth, some-
times second, at level of orbital margin. Adrostral
carina sharp, extending from orbital margin to
ultimate tooth; postrostral carina low, short, ex-
tending only to level of cervical sulcus. Orbital
spine with broad base, short but sharp; postorbital
spine longest of lateral spines on carapace; anten-
nal spine moderately long, and hepatic spine
about same length. Cervical sulcus deep, gently
sinuous, extending almost to, but not crossing,
postrostral carina, ending at about 0.55 cl; hepatic
sulcus almost horizontal posteriorly, turning
anteroventrally in broad arc below hepatic spine,

334

and nearly reaching anterior margin of carapace.

Eye (Figure 57) with basal article produced
distomesially into densely pubescent, elongate,
narrow scale; ocular peduncle short; cornea rather
broad, greatest diameter about 1.8 times that of
base of ocular peduncle, its proximal margin
strongly slanting posterolateral^.

Mandibular palp (Figure 58A ) broad, distal
article almost as long as proximal, and armed
with unique distomesial series of hooks. First
maxilliped as illustrated (Figure 585); rudimen-
tary arthrobranchia on articular membrane (Fig-
ure 58BC-C1). Antennular peduncle length about
0.6 cl; prosartema long, reaching as far as mid-
length of second antennular article; stylocerite
long, spiculiform distally, its length about 0.7 of
distance between its base and that of distolateral
spine; latter rather long, very slender, and sharp.
Ventral antennular flagellum typically de-
pressed, slightly shorter than subcylindrical
dorsal flagellum. Flagella longer in North Amer-
ican than in West Indian, Central American, and
South American populations (Figure 59). Ratio of

PEREZ FARFANTE: AMERICAN SOLENOCERII) SHRIMPS

length of dorsal flagellum to length of carapace in
North American shrimp ranging from about 1.15
in 10-mm cl individuals to about 0.95 in 23-mm cl
shrimp. In Bahamian and southern populations,
ratio decreasing from about 0.95 in shrimp 10 mm
cl to about 0.6 in shrimp 24 mm cl. Scaphocerite
not reaching distal margin of antennular pedun-
cle or exceeding it by as much as 0.1 of its own
length; lateral rib ending distally in long spine,
usually extending to level of distal margin of
lamella; antennal flagellum at least 3.5 times
total length of shrimp: 1 10-mm tl female with
flagellum 385 mm long (measurements taken by
me of specimen caught south of Great Inagua,
Bahama Islands, in 311 m, at Oregon II stn
10849). Third maxilliped usually exceeding an-
tennular peduncle by length of dactyl, occasion-
ally surpassing it by length of dactyl and as much
as 0.2 that of propodus; length of dactyl about
0.75 that of propodus.

First pereopod, stoutest of five, reaching at most
distal end of carpocerite. Second pereopod sur-
passing carpocerite by length of dactyl or by entire
length of propodus. Third pereopod exceeding an-
tennular peduncle by 0.6 to entire length of pro-
podus. Fourth pereopod overreaching carpocerite
by 0.5 or more length of dactyl. Fifth pereopod,
longest of five, exceeding antennular peduncle by
length of dactyl or by latter and as much as 0.2
length of propodus. Order of pereopods in terms
of their maximal anterior extensions: first and
fourth, second, third and fifth. First pereopod
with long, strongly pointed spines on basis and
ischium; second pereopod with long sharp spine

FIGURE 57. — Mesopenaeus tropicalis, ? 25 mm cl, off Key Largo,

Fla. Eye.

FIGURE 58. — Mesopenaeus tropicalis, 2 20 mm cl, west of Light
House Reef, Belize. A, Mandible. B, First maxilliped. c, Arthro-
branchia. c\ Enlargement of c (all from left sidel.

on basis. In female, coxa of third pereopod pro-
duced into plate extending mesially, then
uniquely folded ventrolaterally; coxa of fourth
pereopod produced in strong plate resembling
head of bird, "beak" consisting of long, sharp
spiniform projection directed posteriorly, entire
plate curving around lateral horn on plate of
sternite XIII; coxa of fifth pereopod bearing short
plate produced anteromesially in blunt projection.
In male, coxa of fourth pereopod with short plate
bearing small anterior tooth; fifth pereopod with
large subtriangular tooth on anterior margin.

Abdomen with sharp, high, middorsal carina
from third to sixth somites; low, rounded, some-
times barely perceptible carina on second somite
in larger specimens; posterodorsal margin of third
through fifth somites with median incision; sixth
somite with small, sharp spine at posterior end
of carina, and pair of small spines postero-
ventrally. Telson with median sulcus deep an-
teriorly and penetrated posteriorly by longitud-

335

FISHERY BULLETIN: VOL 75, NO. 2

o
■o

North
South

America
America

(N = 105)
(N= 127)

-VA

o o

oo (

OO 88 3°0 O

oo o ooo :
go oo oo c
oo

O yg 000 CD OO

ooo ceo o o

22 23 24 25 26 27 28

carapace length (mm)

FIGURE 59. — Mesopenaeus tropicalis. Relationship between length of dorsal antennular flagellum and carapace length.

inal elevation merging with convex terminal
portion; latter moderately long, its length 4-5
times basal width; lateral spines short, 0.9-1.4
times basal width of terminal portion; mesial
ramus of uropod reaching tip of telson or over-
reaching it by no more than 0.1 of its own length;
lateral ramus surpassing mesial ramus by 0.1-0.2
of its own length, and bearing small, terminal,
distolateral spine.

Petasma (Figure 60A, B) cincinnulate along
proximal 0.7 of median line and with terminal
margin lacking spinules, often minutely rugose
across ventromedian lobule; distal portion of
ventromedian lobule thick, flexible, folded, its
mesial portion strongly excavate ventrally, and
overlying its shorter lateral portion; latter pro-
duced laterally into process resembling bird head
in silhouette, dorsolateral lobule with heavy rib
curved in hooklike terminal portion lying against
ventral surface of process; inner surface of dorso-
lateral lobule studded with minute setae mesially
and bearing proximolateral row of long setae;
corresponding, but shorter, row of long setae on
outer surface. Ventral costa reaching distally as
far as, or slightly overreaching, row of cincinnuli,
trending dorsally, and bearing flexible sub-
rectangular, marginal flap, extending horizon-
tally almost perpendicular to costa.

Appendix masculina (Figure 60C, D) very elon-
gate, convex dorsally, deeply channeled ventrally,
its proximal part produced laterally into rounded,
ventrally turned lobe; distal part tapering, its tip
twisted mesiad, mesial surface deeply concave,

and armed with densely set, relatively long setae
on proximolateral border, short setae on borders
of concavity, and tuft of long setae apically.
Appendix interna almost as long as appendix mas-
culina, broad, subelliptical, bearing lateral rib,
abutting corresponding border of appendix mas-
culina, and armed with tuft of long setae on disto-
lateral border, and very short setae on mesial
border. Basal sclerite obliquely crossed by heavy
ridge separating deep proximal concavity from
anterior depressed area, and with its ventro-
lateral spur proximally rounded and strongly
attenuate distally.

Thelycum (Figure 61) with paired short, blunt,
cushionlike protuberances on flexible anterior
part of sternite XIV, contiguous to ventrally
raised, heavily sclerotized posterior shield; free
border of shield sharp or thickened, and varying
from slightly concave to produced into antero-
median, minute spine. Median plate of sternite
XIII divided by median longitudinal incision into
paired rounded to subrectangular lobes overhang-
ing sternite XIV, each bearing blunt horn antero-
lateral^. Sternite XII with paired blunt, distally
flattened projections overhanging sternite XIII.

Photophores- Observations by me on freshly col-
lected specimens demonstrated that this species,
like H. affinis and H. debilis, bears photophores,
which are arranged as follows: one adjacent to the
base of the podobranchia of both the third maxilli-
ped and fourth pereopod, and a pair on the an-
terior part of the sternum from the second through

336

PEREZ FARFANTE AMERICAN SOI.KN(K'KRII) SHRIMPS

the sixth abdominal somites, immediately poste-
rior to the transverse ridge of the preceding seg-
ment. The seven pairs of photophores consist of a
yellow conical portion and a red lens.

Color-Body translucent salmon with obliquely
vertical, deep yellow stripes, and milky white
patches of various sizes on carapace. Rostrum
yellow from second rostral tooth to apex, epi-
gastric and first rostral teeth salmon. Carapace
with three anterior stripes resembling chevron:
anteriormost short, arched, extending from near
base of orbital spine posterodorsally to below first
rostral tooth; second extending almost from base
of postorbital spine to posterior base of epigastric
tooth; third posteriorly flanking cervical sulcus,
and broadening on middorsum, forming diamond-
shaped mark. Additional posterior stripe on cara-
pace narrow on middorsum, broadening rapidly
anteroventrally, and then narrowing again, form-
ing band along dorsal part of branchiostegite.
White patches on carapace very conspicuous:
anterior one subcircular, situated on depression
below hepatic spine; second oblong, lying ventral
to hepatic sulcus; posteriormost ovate and large,

almost covering entire branchiostegite. First
abdominal somite with yellow spot immediately
anterior to posterolateral hinge, remaining five
somites with broad, uniformly wide yellow stripe
extending from anterior half of middorsum
posteroventrally to lateral hinge, except stripe on
sixth reaching posteroventral extremity of pleu-
ron; sixth somite also with short posterodorsal
yellow stripe extending from dorsum to lateral
base of telson; midventral part of pleura of an-
terior five somites with deep salmon spot, sixth
somite with deep salmon patch on anteroventral
part of pleuron. Telson salmon, with median
sulcus yellow; uropodal rami bearing broad trans-
verse band across midlength. Antennulae and
antennae deep salmon, darker on basicerite of
antenna and on adjacent anteroventral portion
of carapace. Thoracic sternites, first and second
maxillipeds, and proximal podomeres (including
merus) of third maxilliped and pereopods pale
salmon; distal podomeres deep salmon except for
narrow milky white longitudinal band. Basis of
pleopods deep salmon preaxially with lateral part
milky white; endopods and exopods whitish with
orange line along midlength; ventral surface of

FIGURE 60. — Mesopenaeus tropicalis, 2 17.5 mm cl, east of Cayos de Albuquerque, western Caribbean. A, Petasma, dorsal view. B,
Ventral view. C, Right appendices masculina and interna, dorsal view. D, Ventromesial view.

337

FISHERY BULLETIN: VOL. 75, NO. 2

FIGURE 61. — Mesopenaeus tropicalis, 9 25.5 mm cl, east of
Cayos de Albuquerque, western Caribbean. Thelycum, ventral

abdomen with orange transverse rib at posterior
margin of sternites, interrupting overall trans-
lucent salmon.

Although the color pattern described is altered
with the expansion and contraction of the chro-
matophores, this basic arrangement of colors was
usually recognizable in all specimens examined
by me. However, according to Iwai (1973), this
species exhibits an overall red in Brazilian waters.

Maximum size.-Males: 20.5 mm cl; females:
28 mm cl.

Geographic and bathymetric ranges-Northeast of
Cape Lookout, N.C. (34°43'N, 76°40'W), to the
Straits of Florida, and into the Gulf of Mexico to
Alabama. Also off the Bahamas, through the
Caribbean, and along the Atlantic coast of South
America as far as Rio Grande do Sul (Figure 34).
The record from Rio Grande do Sul (34°00'S) is
from Iwai (1973). This species occurs at depths
between 30 and 915 m (Figure 9), thus from rel-

atively shallow waters (where it is infrequent) on
the continental shelf to the upper zone of the
continental slope. This bathymetric range is not
peculiar to M. tropicalis, but is also exhibited by
various other penaeoids. The single record of the
shrimp from northeast of Cape Catoche, and its
apparent absence in the Gulf of Mexico from Mis-
sissippi to northern Yucatan, suggest inadequate
sampling in the region. Its presence on the con-
tinental slope, even if only in the shallower zone,
where no barriers prevent its dispersion, also
favors this conclusion.

According to the limited data at my disposal, in
the warm temperate waters of North America this
species tends to remain on the continental shelf,
where 85% of the samples examined by me were
caught; in contrast, off the Bahamas and to the
south, it seems to be more abundant off the shelf
edge, where 76% of the samples were taken. In
neither region do the animals appear to exhibit a
seasonal migration, moving from warmer waters
of the shelf to greater depth in late fall and
returning in the spring.

Affinities .-Mesopenaeus tropicalis, ths sole mem-
ber of the genus, differs strikingly from the other
solenocerids occurring in the western Atlantic in
possessing antennular fiagella which are dis-
similar in shape, the dorsal one subcylindrical
and the ventral depressed.

Variations in the relative length of the anten-
nular fiagella were pointed out by Lindner and
Anderson (1941). I have confirmed their observa-
tions and, in addition, have found that the range
of variations in North American populations is
different from that in populations occurring from
the Bahamas to Brazil, the former having longer
fiagella than the latter. Noteworthy is the paral-
lelism that exists in the relative length of the
antennular fiagella between Mesopenaeus tropi-
calis and two closely related allopatric species of
the genus Solenocera. Like the northern popula-
tion of M. tropicalis, S. vioscai, a North American
species, possesses longer fiagella than does S.
acuminata, which occurs from the Bahamas to
Brazil (Perez Farfante and Bullis 1973). A similar
tendency was observed by Perez Farfante and
Bullis in S. atlantidis, the northern populations
of which tend to have longer fiagella than do those
from the Bahamas southward. The thelycum of
M. tropicalis also exhibits considerable variation,
even within a single population, the shield of
sternite XIV varying from flat with the anterior

338

PEREZ FARFANTE: AMERICAN SOLENOCERII) SHRIMPS

margin bladelike, to deeply excavated on the
median portion, and with the anterior margin
elevated in a strong ridge; in addition, this margin
ranges from bearing a minute anteromedian spine
to being concave. Furthermore, the anterolateral
protuberances of sternite XIII may be low or
rather strongly raised.

Spermatophore. -Compound spermatophore con-
sisting of slender, laterally compressed geminate
body continuous with broad anterior lobes, bear-
ing lateral wings, and produced posterolateral^
in relatively narrow flanges (Figure 62).

Thick opaque ventral wall and lateral wall of
each spermatophore (Figure 63A) extending
anteriorly forming ventral portion of anterior
lobe; lateral wall, opaque anteriorly, translucent
posteriorly, bearing fleshy wing; dorsomesial wall
(Figure 63B) mostly translucent but thickened
mesially, continuous with dorsomesial portion of
anterior lobe, and extending posteromesially
beyond fundus of sac, there joining flange, and
giving rise to pocketlike caudal projection. Ante-
rior lobe forming obliquely truncate collar opening
laterally and through posterior slit, with ventro-
lateral surface subrectangular, and dorsomesial
surface elongate trapezoidal, broadest laterally.
Wing flexible (lacking heavily sclerotized support-
ing structures), bearing rounded lobe anteriorly.
Flange extending from about midlength of sac
around posterolateral margin, bearing anteriorly
cornified, reniform projection, and produced lat-
erally in roughly semicircular flap. Spermato-
phore supported by strong C-shaped armature, its
mesial part fused to dorsomesial wall and its
anterior arm extending across and supporting
ventral wall, with lateral extremity forked: ante-
rior branch forming foliaceous process, directed
dorsally, facing posterior slit of anterior lobe;
posterior branch spirally twisted and located just
cephalic to reniform projection of flange. Dorsal
plate elongate ovate, extending from base of wing
to posterior margin of flange.

Compound spermatophore attached to female
with anterior lobes on sternite XII, their elongate
lateral openings lying close to gonopores; angles
formed by anterior lobes and wings embracing
posterior corners of coxal plates of third pereopods;
wings extending laterally, attached to sternite
XIII, pressing against marginal ridge of XII. Pos-
terior part of geminate body affixed by dorsal
plates to shieldlike posterior plate of sternite XIV,
elevated (ventrally) well above level of anterior

FIGURE 62. — Mesopenaeus tropicalis. Compound spermatophore
attached to female, 5 19.5 mm cl. off Gulf Beach, Fla. (setae
omitted).

lobes, thus geminate body directed antero-
dorsally. Posterior parts of flanges sloping
posterodorsally, lateral parts attached to sternite
XIV, and reniform projections lying near coxae of
fourth pereopods. Finally, foliaceous processes
meeting on middorsal line, whereas spirally
turned branches of C-shaped armature (diverging
from bases of foliaceous processes) projecting
laterally.

I have observed sperm masses protruding from
the sperm sacs into the cavity of the respective
anterior lobe, from which the sperm must be dis-
persed into the surrounding water adjacent to
the female gonopores. A complete compound sper-
matophore detached by me from an impregnated
female was found to lack sperm masses, suggest-
ing that the sperm had been freed while the intact
spermatophore was still anchored to the animal;
furthermore, there was no trace of such masses on

339

FISHERY BULLETIN: VOL. 75. NO. 2

FIGURE 63.— Mesopenaeus tropicalis, 6 19 mm cl, south of Great Inagua, Bahama Islands. A,
Left spermatophore dissected from terminal ampulla (wing slightly displaced), ventrolateral
view. B, Dorsomesial view (dorsal plate removed).

the thelycum. Unlike the release of the sperm
masses in certain members of the subgenus Lito-
penaeus (genus Penaeus) the sperm appears to be
liberated in M. tropicalis without a rupture of
the spermatophore.

Three females with spermatophores attached
were examined by me. The smallest of these speci-
mens, 12 mm cl, was caught off Savannah, Ga.,
at Silver Bay stn 3658. The other two were 19.5
mm cl, and one was taken south of St Vincent
Island at Oregon stn 896 and the other off Gulf
Beach at Oregon stn 1254, both localities off
northwestern Florida.

Remarks.-ln his original brief diagnosis oiParar-
temesia tropicalis, Bouvier ( 1905b) stated that the
species is from the "mer des Antilles," where it
had been collected between 80 and 175 fm (146
and 320 m), during a cruise of the Blake; he cited
neither the number of specimens he had examined
nor the locality where they had been found. Later,
he (1906b) mentioned the same shrimp (including
it among the species of the genus Haliporus
found in the tropical subtropical Atlantic) as
occurring in the "Antilles." However, A. Milne
Edwards and Bouvier ( 1909) — in a rather detailed
account of various morphological features of the
female of the species, including the thelycum —

referred to the same specimen (17.5 mm cl, about
74 mm tl), as the "type," and added the following
information: "Habitat, . . . — Blake: Florida Bank,
lat. N. 26° 31', long. O. 85° 03', 119 brasses.— Le
type femelle decrit plus haut." Furthermore, on
plate 3, eight figures are explicitly identified as
parts of the "type." A. Milne Edwards and Bouvier
also recorded and illustrated a smaller female,
"25 a 30 mm de longeur" (5.5 mm cl, about
27 mm tl), from Barbados taken in 76 fm (139 m)
which, according to a label dated 1907, in
Bouvier's handwriting, is a "cotype juvenile,"
evidently thus designated during the course of the
investigations published 2 yr later. The minimum
depth of the bathymetric range (80-175 fm) origin-
ally given for the species is only slightly greater
than that at which the small female was collected,
but the maximum depth is considerably deeper
than that reported for the larger female, suggest-
ing that the authors had examined additional
specimens. Of the material first studied by
Bouvier, these two females are the only specimens
of this species known to have been taken during
cruises of the Blake and, furthermore, the small
one was identified by Bouvier on a piece of paper
accompanying the specimen in the bottle as Parar-
temesia tropicalis, i.e., within the genus pro-
posed in 1905. Consequently, I am convinced that

340

I'KKKZ FAKFANTE: AMERICAN SOLENOCERID SHRIMPS

these two specimens are part of the syntypic
series. Inasmuch as the larger female was treated
as the type by A. Milne Edwards and Bouvier,
I am furthering the latter authors' intent by desig-
nating it the lectotype of Parartemesia tropicalis
[=Mesopenaeus tropicalis], and the small female
is, therefore, a paralectotype.

The type-locality of H. tropicalis is uncertain.
A. Milne Edwards and Bouvier (1909) copied the
coordinates of Blake stn 50 from the label enclosed
in the jar with the specimen; I have examined this
label and confirmed their data. However, the
locality corresponding to those coordinates is
beyond the 1,500-fm (2,744-m) contour, and thus
considerably deeper than the greatest depths
otherwise recorded for this shrimp, a species that
penetrates only the shallower portion of the upper
slope. Prior to the publication of A. Milne Edwards
and Bouvier, the coordinates and depth of Blake
stn 50 were recorded, in a serial list of Blake sta-
tions (Anonymous 1879), as follows: 26°31'N,
85°53'W, 119 fm (218 m). Later, S. Smith (1889)
quoted the latter data, noting that "The position
or depth must be wrong as there are 1700 fm
(3109 m) there, perhaps 28°31'." S. Smith's
suggestion concerning the latitude was perhaps
based on that of the three previous Blake stations,
which were 28°42'00"N, 28°47'30"N, and
28°51'30"N; however, these are at longitudes
greater than 88°W, situated off the Delta of the
Mississippi River, and thus far from Florida. The
confusion regarding the location of station 50 is
even greater, because the name "Florida Bank"
is not found on American hydrographic charts,
although it can be deduced that A. Milne Edwards
and Bouvier referred to West Florida Shelf, the
edge of which lies just east of where, according to
the label, the specimen was obtained. It seems to
me that the type-locality of this species will
remain indeterminable.

Under the name Solenocera weymouthi, Lind-
ner and Anderson (1941) presented an excellent
description of M. tropicalis. Two of their state-
ments seem to be in need of modification: only the
ventral antennular flagellum is flattened (but not
canaliculate), the dorsal one being subflagelli-
form. The locality given for the allotype is in error.
W. L. Schmitt kindly allowed me to examine his
logbook of the collections made off the Dry Tortu-
gas in 1932, the time at which the specimen was
collected. His records show that "boat sta 74,"
the locality in question, corresponds to the Anton
Dohrn trawl haul made 14 miles (22.5 km) south

of the Dry Tortugas in 60 fm ( 110 m) on 5 August
1932. The data given by Lindner and Anderson
are those for Anton Dohrn station 71, made the
same day but, as they quoted, 19.5 miles (31.4 km)
south of the Dry Tortugas at 190-280 fm (347.5-
512 m).

ACKNOWLEDGMENTS

Special thanks are due Horton H. Hobbs, Jr., of
the Smithsonian Institution, for his suggestions,
and the interest demonstrated during this study.
I am grateful to Fenner A. Chace, Jr., Smith-
sonian Institution, for his aid in clarifying several
taxonomic problems and comments on the final
draft of the manuscript, which also benefited from
the suggestions of Raymond B. Manning of the
Smithsonian Institution and Austin B. Williams
of the Systematics Laboratory, National Marine
Fisheries Service, NOAA.

The illustrations, a necessary part of this work,
were prepared by Maria M. Dieguez, who once
again has applied her artistic talent and pains-
taking efforts to a better understanding of the
American penaeoids, a contribution which I fully
appreciate.

For placing at my disposal specimens in their
respective institutions or for donating material
to the Smithsonian Institution I am grateful to:
Enrique E. Boschi (Instituto de Biologi'a Marina,
Mar del Plata); Harvey R. Bullis, Jr. (Southeast
Fisheries Center, National Marine Fisheries
Service, NOAA, Miami); Alain Crosnier (Office de
la Recherche Scientifique et Technique Outre
Mer, Paris); Harold S. Feinberg (AMNH);
Anthony A. Fincham (BMNH); Jacques Forest
(MP); Willard D. Hartman (YPM); Lipke B. Holt-
huis (RMNH); Raymond W. Ingle (BMNH);
Motonaga Iwai (IOUSP); Leslie W. Knapp (Smith-
sonian Oceanographic Sorting Center); Herbert
W. Levi (MCZ); Linda H. Pequegnat (TAMU);
Solange C. de Saint-Brisson (Estagao de Biologia
Marinha, Arraial do Cabo, Rio de Janeiro); Paul
J. Struhsaker (Southwest Fisheries Center, Na-
tional Marine Fisheries Service, NOAA, Hono-
lulu); and Gilbert L. Voss (UMML).

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THOMSON, G. M.

1904. Class Crustacea. In F. W. Hutton (editor), Index
faunae Novae Zealandiae, p. 247-275. Dulau and Co.,
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TIZARD, T. H., H. N. MOSELEY, J. Y. BUCHANAN, AND
J. MURRAY.

1885. Narrative of the cruise of H.M.S. Challenger with
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Rep. Sci. Res. Voyage H.M.S. Challenger, 1873-76,
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1965. Algumas observacoes sobre a pesca do camarao no

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TREMEL, E., J. P. WISE, M. N. MlSTAKIDIS, AND S. JONSSON.

1964. Relatorio do projeto de pesca exploratoria na costa
de Santa Catarina Janeiro-Fevereiro, 1963. Setor
Pesq., Dep. Estadual Caca Pesca, Santa Catarina, Bras.
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1958. Survey of the United States shrimp industry,
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1948. The shrimp and the shrimp industry of the South
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VILELA, H.

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Rapp. P.-V. Reun. Cons. Int. Explor. Mer 159:119-125.

VOSS, G. L.

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WILLIAMS, A. B.

1965. Marine decapod crustaceans of the Carolinas.
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WOOD-MASON, J.

1891. Phylum Appendiculata. Branch Arthropoda. Class
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YOKOYA, Y.

1941. On the classification of penaeid shrimps by the
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510 p.

346

SMALL-SCALE MOVEMENTS OF ALBACORE, THUNNUS ALALUNGA, IN

RELATION TO OCEAN FEATURES AS INDICATED BY

ULTRASONIC TRACKING AND OCEANOGRAPHIC SAMPLING

R. Michael Laurs,1 Heeny S. H. Yuen,2 and James H. Johnson3

ABSTRACT

Studies with ultrasonic tracking techniques and oceanographic sampling demonstrated that
oceanographic conditions play an important role in the local concentrations and movements of
albacore, Thunnus alalunga, in U.S. coastal waters. Albacore show a tendency to congregate in the
vicinity of coastal upwelling fronts, presumably to feed. They move away from the immediate area
when upwelling ceases and the upwelling front is no longer present at the surface. The movements of
albacore also appear to be related to the distribution of sea surface temperature, with fish spending
little time in water with surface temperatures cooler than 15.0°C.

The average swimming speed for three fish tracked between 27.8 and 50 h was 1.6 knots (82.4 cm/sl
with each fish exhibiting slightly faster swimming speeds during hours of daylight than during hours
of darkness.

The albacore, Thunnus alalunga (Bonnaterre), is
widely distributed in the Pacific Ocean. The single
subpopulation which is found in the North Pacific
(Otsu 1960) supports important surface commer-
cial fisheries in coastal waters off North America
and Japan and subsurface fisheries in the central
temperate Pacific. The species is also highly prized
by U.S. recreational fishermen. Passive tagging
methods have been used to study large-scale mi-
gratory patterns of albacore in the North Pacific
(Ganssle and Clemens 1953; Otsu 1960; Clemens
1961, 1963; Otsu and Uchida 1963; Laurs and
Nishimoto4); however, information on small-scale
movements is scant.

In order to examine the small-scale movements
of schools of albacore and evaluate the effects that
oceanographic conditions may have on the local
concentrations and movements of albacore in
coastal waters off the United States, studies were
conducted with ultrasonic tracking techniques
and oceanographic sampling.

Tracking the movements of animals to which
ultrasonic transmitters have been attached is a
technique that has been developed over the past
two decades. This valuable technique has gained

'Southwest Fisheries Center, National Marine Fisheries
Service, NOAA, P.O. Box 271, La Jolla, CA 92038.

2Southwest Fisheries Center, National Marine Fisheries
Service, NOAA, P.O. Box 3830, Honolulu, HI 96812.

3Northwest and Alaska Fisheries Center, National Marine
Fisheries Service, NOAA, 2725 Montlake Blvd. East, Seattle,
WA 98112.

"Laurs, R. M., and R. N. Nishimoto. 1974. Joint NMFS-AFRF
albacore tagging study. SWFC Admin. Rep. LJ-74-47:63-81.

Manuscript accepted October 1976.
FISHERY BULLETIN: VOL. 75. NO. 2. 1977.

such wide application in recent studies of marine
fishes and Crustacea that it is more convenient to
cite a bibliographic source (Stasko 1975) than to
cite individual references.

METHODS

In the course of acoustic tracking studies,
environmental data commonly have been col-
lected for correlation with observed movements of
the animal. At times, small auxiliary craft have
been used for this purpose in support of the vessel
doing the tracking, but usually the collection of
environmental data has been done entirely from
aboard the tracking vessel, necessarily limiting
measurements to the ship's track. This study
represents a significant expansion of supportive
environmental data acquisition: for the first time
a major oceanographic research vessel and an
aircraft were coordinated with acoustic tracking
of fish. The ultrasonic tracking experiment in-
volved the use of the commercial albacore fishing
baitboat Linda on charter to the American
Fishermen's Research Foundation, the National
Marine Fisheries Service (NMFS) RV David Starr
Jordan, and a Coast Guard aircraft equipped with
sea surface temperature measuring equipment.

Capture, Handling, and Tagging
of Albacore

The capture of fish, tagging with ultrasonic

347

FISHERY BULLETIN: VOL. 75. NO. 2

transmitters, and tracking of the fish were done
aboard Linda by three NMFS scientists with
assistance from the crew of Linda. Albacore
ranging in size from 74 to 87 cm fork length with
estimated weights of 8.2 to 13.6 kg were caught on
hook and line baited with anchovy. The fish was
played an average of 5 min before being brought
on board by dip net. Without removing it from the
net, the fish to be tagged was placed on its side on a
plastic covered foam measuring pad on the deck
where it was measured to the nearest lower
centimeter and the transmitter was attached. A
wet burlap bag was placed over its head to keep
the fish calm. No anesthetic was used.

The ultrasonic transmitter was attached to the
back of the fish, immediately in front of the second
dorsal fin, with two sutures through the skin and
muscle tissue in that area. Upon completion of
tagging, fish were immediately replaced in the
water. Total elapsed time for fish out of water was
between 1 and IV2 min. Within 2 to 4 s after being
released, each tagged fish was observed righting
itself and actively swimming downward and out of
sight. One fish was tracked at a time. The three
fish tracked longer than 24 h were tagged in the
manner described above. Several fish tracked for
shorter periods early in the cruise were tagged by
inserting the transmitter into the stomach
through the mouth. This latter method was
abandoned when it appeared that acoustic signal
attenuation caused by internal implacement was
resulting in an inadequate receiving range.

Tracking Equipment

The transmitter tags and hydrophone used were
built by the Northwest and Alaska Fisheries
Center, Seattle, Wash. The tags were cylindrical
measuring 8.2 by 1.9 cm, weighing 67 g in air and
43 g in water, and emitted a 45 or 50 kHz signal at
a pulse rate of 120 pulses/min. Acoustic source
level of the tag was 63 dB (reference to 1 £ibar at 1
m in fresh water).

The hydrophone was a tuned 6-element array
(sensitivity - 69 dB, reference to 1 /xbar at 1 m)
with a beam width of 20° horizontally and 40°
vertically at the 3-dB point. This was attached to
the lower end of a 3-cm aluminum pipe, bracketed
to the starboard rail amidship of the tracking
vessel. A geared electric motor at the top of the
pipe rotated the hydrophone, which was remotely
controlled from the tracking station in the
wheelhouse. Signals picked up by the hydrophone

were fed into a Lawson VLF-15 superheterodyne
receiver.

Tracking Procedure

With the hydrophone remote-control unit
installed in the pilothouse of Linda alongside the
engine and steering controls and the receiver
placed about 2 m away, one person was able to
operate the tracking system and control the vessel
simultaneously. Directing the hydrophone for
maximum signal, the operator moved the vessel
on that heading until satisfied, on a basis of signal
strength, with his proximity to the fish. The
receiving range varied widely according to sea
state, but on the average Linda was kept an
estimated 500 m from the tagged fish. The fish
moved continuously and so, consequently, did the
vessel, but vessel speed of more than 2 knots was
seldom necessary to keep up with the fish. Position
of the tracking vessel was determined approx-
imately once an hour and was taken also to
represent the position of the fish at that time. Most
of the navigation for Linda was done by the
nearby David Starr Jordan , with a combination of
Loran, radar, and Omega systems.

Oceanographic Observations Made
From Ship

Detailed oceanographic observations were
made aboard David Starr Jordan in support of
the ultrasonic tracking experiments. These in-
cluded continuous monitoring of surface temper-
ature and salinity and measurements of sub-
surface temperature and salinity at selected
stations. Observations were also made to evaluate
biological factors of the marine environment.
These included continuous monitoring at the
surface and subsurface measurements at selected
stations of chlorophyll a by fluorometric tech-
niques (Holm-Hansen et al. 1965), measurements
of primary productivity by 14C methods (Owen
and Zeitzschel 1970), and estimates of the
standing stocks of potential albacore food organ-
isms.

The estimates of potential albacore forage were
derived from hauls made with a 1.8-m Isaacs-Kidd
midwater trawl (IKMT) lined with a 58-mm mesh.
The hauls were taken during hours of darkness

5Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

348

I.AUKS KT AL.: SMALL-SCALE MOVEMENTS OF ALBACORE

from the surface to a depth of approximately 175
m at a ship speed of about 5 knots. The volumes of
water strained were estimated from data obtained
by a TSK6 depth-distance recorder mounted in'the
mouth of the trawl. The Formalin-preserved
IKMT catches were sorted into several categories
of fishes, cephalopods, crustaceans, and other
animals, and the displacement volume of each of
these kinds of animals was measured and stan-
dardized in ml/1,000 m3 of water filtered for each
haul. The standardized values of 1) larval and
juvenile fishes, 2) epipelagic fishes, 3) cephalo-
pods, and 4) crustaceans were summed for each
haul and collectively regarded as potential alba-
core forage. Analysis of stomach contents of
albacore has shown that these categories of
organisms are important in the diet of albacore
(Pinkas et al. 1971) in this area.

Oceanographic Observations Made
by Aircraft

A Coast Guard aircraft equipped with a Barnes
PRT-5 infrared radiometer made measurements
of sea surface temperature for evaluation of the
small-scale features and changes in the distribu-
tion of sea surface temperature.

RESULTS AND DISCUSSION

Six albacore were tagged and tracked with
ultrasonic equipment for periods ranging
from about 2 to 50 h and distances ranging from
6.5 to 150.7 km (3.5 to 81.3 nmi). Results will be
presented for fish numbers 4, 5, and 6, which were
tracked for 27.8, 41.4, and 50.0 h, respectively.
There are too few data for discussion for fish
numbers 1, 2, and 3 because of the short periods
that the fish were tracked. A summary of the
tracking date and time, tagging location, distance
tracked, and fork length offish for fish numbers 4,
5, and 6 is given in Table 1.

Tagged fish rejoined untagged albacore after
being returned to the water, and tended to remain
in their company. Surface "boils" characteristic of
albacore were frequently sighted close by Linda,
and approximately 30 fish of the same general size
as fish tagged with ultrasonic transmitters were
caught by the crew while tracking was in
progress. Also, one tagged fish "lost" the previous
day was heard intermittently over a 4-h period

8-16-72

1445

8-17-72

1845

8-19-72

0715

8-20-72

2345

8-25-72

1000

8-27-72

1205

TABLE 1. — Summary of tracking date and time, fork length of
albacore, location of tagging, and distance tracked.

Fork Tagging location

No Date Time length Lat. Long. Distance

84 cm 36 49.8'N,122°19.1'W 41 6 nmi

(77.1 km)

87 cm 36"50.3'N,122'13.6 W 61 .4 nmi

(113.8 km)

85 cm 35°20.0'N, 12122 0'W 81 3 nmi

(150.7 km)

during the track that followed. We were able to
distinguish between the two fish because of
slightly different signals from the tags.

Speed of Albacore Movements

Swimming speeds for albacore were estimated
from straight-line calculations using position of
the tracking vessel. The average swimming speed,
based on the total distance and time that the fish
were tracked, for fish numbers 4, 5, and 6 was
about 1.6 knots (82 cm/s). Speeds calculated from
hourly ship positions for each fish ranged from 0.1
to 3.6 knots (5 to 185 cm/s). Table 2 shows the
percentage of time each fish spent at various
swimming speeds. There were day-night differ-
ences in the rate of movement, with fish exhibit-
ing faster swimming speeds during hours of
daylight (0500 to 1900 h) than during hours of
darkness. The average speed during daylight for
fish numbers 4 and 5 was 1.7 knots (88 cm/s) and
for number 6 was 2.1 knots (108 cm/s). The
average speed during nighttime for fish numbers

4 and 6 was 1.3 knots (67 cm/s) and for fish number

5 was 1.0 knot (51 cm/s). Table 3 gives a summary
of time, distance, and mean speeds.

Moonlight also appeared to influence the rate of
movement offish number 5. This fish, which had
been moving steadily at about 2.0 knots ( 103 cm/s)
for about 3 h after moonrise and following a course
about 20° west of the full moon, came to a near stop

TABLE 2. — Percent of time each albacore spent at various swim-
ming speeds.

Speed

Fish
no. 4

Fish
no. 5

Fish
no. 6

knots

cm/sec

Percent

GTsurumi Seiki Kosakusho Co., Ltd., Yokohama, Japan.

• 0.5

<26

0.5-0.9

26- 46

1.0-1.4

51- 72

1.5-1.9

77- 98

2.0-24

103-124

2.5-2.9

129-149

3.0-3.4

154-175

3.5

175

8.0

5.9

0.0

12.0

23.5

15.8

32.0

35.3

28.9

24.0

11.8

15.8

16.0

17.6

289

4.0

2.9

0.0

2.9

10.5

4.0

0.0

349

FISHERY BULLETIN: VOL. 75. NO. 2

TABLE 3. — Summary of duration and distance tracked and mean
speed of albacore tracked with ultrasonic transmitters.

Fish

Item

no. 4

no. 5

no. 6

Time tracked (h)

278

41.4

500

Distance tracked:

nmi

41.6

61.4

81 3

77.1

113.8

150.7

Mean speed:

knots

1.6

1.5

1.6

cms

bl/s1

0.98

0.88

0.96

Mean speed, day:2

knots

1.7

2 1

cms

108

bl/s'

1.05

1.01

1.27

Mean speed, night:3

knots

1.3

1.0

1.3

cm/s

bl/s'

0.80

0.59

0.79

'bl s body lengths per second.
20500-1900 h.
3 1900-0500 h.

15 16 17
TEMPERATURE °C

FIGURE 1. — Percent of time (hours) spent in waters of various
sea surface temperature by albacore numbers 4, 5, and 6.

for nearly an hour when the moon was suddenly
obscured by dense fog at about 0300 h.

The mean swimming speeds calculated from the
tracking experiment are close to estimates of
swimming speed derived from passive tagging
results. For example, based on data given in the
Japanese Fisheries Agency (1975) report, two
tagged albacore, which were released in the
western North Pacific and recovered in the
eastern North Pacific about 3V£ mo later, traveled
at 1.1 knots (57 cm/s), assuming they followed a
great circle route and were caught the day they
arrived at the recovery location. The mean
swimming speeds found in this study are slightly
less than twice the calculated minimum swim-
ming speed necessary for an 80-cm albacore to
maintain hydrostatic equilibrium (Dotson 1977).

Relationship of Albacore Movements to
Sea Surface Temperature

The movements of the fish tagged with ultra-
sonic transmitters appeared to be influenced by
the distribution of sea surface temperature.
Figure 1 shows the percentage of the time that fish
numbers 4, 5, and 6 spent in waters of various
surface temperatures. Fish number 6 spent no
time in water with surface temperatures less than
15.0°C although roughly 20<7r of the waters 5 nmi
distant on both sides of the path followed by the
fish were colder than 15.0°C. Fish number 4 was in
water which had surface temperatures colder
than 15.0°C 12.5% of the time, while 35% of the
waters 5 nmi distant on both sides of the path
followed by the fish was colder than 15.0°C. Fish
number 6 was in water with surface temperatures'

350

warmer than 17.0°C 229c of the time, which
coincided with the percentage of area with
temperatures greater than 17.0°C. Water with
temperature higher than 17.0°C was not available
to fish numbers 4 and 5.

These results indicate that the transmitter-
tagged fish spent very little time in water with
surface temperatures less than 15.0°C. This is
especially evident when charts showing the tracks
followed by the fish and the contoured field of sea
surface temperature observed by David Starr
Jordan at the time of tracking are examined.
Figures 2, 3, and 4 show tracks followed by fish
numbers 4, 5, and 6, respectively, and sea surface
temperature. In these figures, temperatures less
than 15.0°C, which are considered below the habi-
tat preference for albacore (Clemens 1961), are
shaded. Fish number 4 remained in the vicinity of
a band of water cooler than 15.0°C for nearly the
total time it was tracked, but did not appear to
enter it (Figure 2). Fish number 6 traveled on a
southerly course, in a corridor of warm water
which was sandwiched between two wedges of cool
water on 25 August, but did not enter the cool
water on either side except very briefly at the start
of tracking (Figure 4). When the fish passed to the
south of the cool water, where there was a large
area of water warmer than 15.0°C, the fish
changed its direction generally to a more south-
westerly course.

Relationship of Albacore Movements to
Upwelling Temperature Fronts

A well-developed temperature front occurs at
the boundary between cool, biologically rich

LAURS ET AL.: SMALL-SCALE MOVEMENTS OF ALBACORE

FIGURE 2. — Movements of albacore number 4 as indicated by
ultrasonic tracking and contoured field of sea surface tempera-
ture in degrees Celsius. Triangles on fish track indicate hourly
position. The time and date that tracking commenced is noted at
the starting location and shown above and below a slash mark,
respectively. The 0000 and 1200 h local time positions are also
indicated. Dots show where temperature observations were
made by David Starr Jordan. Temperatures below 15.0°C are
shaded.

FIGURE 4. — Movements of albacore number 6 as indicated by
ultrasonic tracking and contoured field of sea surface tempera-
ture in degrees Celsius. Triangles on fish track indicate hourly
position. The time and date that tracking commenced is noted at
the starting location and shown above and below a slash mark,
respectively. The 0000 and 1200 h local time positions are also
indicated. Dots show where temperature observations were
made by David Starr Jordan. Temperatures below 15.0°C are
shaded.

upwelled water and warmer, nonupwelled water
(Smith 1968). The effects that an upwelling front
may have on the movements of albacore were
indicated during the ultrasonic tagging experi-
ment. On 17 August, during tracking operations
for fish number 4, a relatively well-developed
upwelling surface temperature front was ob-

served in the northeast portion of the tracking
area. The upwelling was caused by brisk north-
erly winds which had been blowing for several
days. The remainder of the area surveyed has a
rather simple surface temperature distribution
mostly within the temperature range considered
as the habitat preference for albacore (Figure 2).

FIGLIRE 3. — Movements of albacore number 5 as
indicated by ultrasonic tracking and contoured
field of sea surface temperature in degrees Cel-
sius. Triangles on fish track indicate hourly posi-
tion. The time and date that tracking commenced
is noted at the starting location and shown above
and below a slash mark, respectively. The 0000
and 1200 h local time positions are also indicated.
Dots show where temperature observations were
made by David Starr Jordan.

SO' 20'

10' I22"00

351

FISHERY BULLETIN: VOL. 75, NO. 2

Infrared radiation temperature measurements
made during an overflight by the Coast Guard
aircraft on 16 August showed that the water on
the cold side of the front continued to decrease
toward shore to values below 13.0°C.

Fish number 4 traveled in about an 8 x 8 nmi
area on the warm side of the upwelling front and
in close proximity to it for nearly the total time
the fish was tracked. Subsequently, high winds
and rough seas made tracking difficult and the
signal from the fish was lost during hour 27 of
tracking.

Fish number 5 exhibited a much different
pattern of movement than did number 4 (compare
Figures 2 and 3). It moved many miles from the
location where it had been tagged, in a general
northwesterly direction, rather than remaining in
the local vicinity as fish number 4 had done.

Examination of oceanograhic data revealed
that marked changes in the distribution of sea
surface temperature had occurred between 17 and
19 August (compare Figures 2 and 3). Upwelling
had subsided, the upwelling temperature front
was no longer present on 19 August, and the
temperature over much of the area had increased
by about 1.5°C. The breakdown of the upwelling
front and warming was due to a slackening and
shifting of the winds to a westerly-southwesterly
direction which allowed a thin layer of warmer
offshore water to flow toward the coast.

It is presumed that the school offish with which
fish number 4 was traveling remained in the
vicinity of the upwelling front to feed in the highly
productive water associated with the upwelling.
Measurements of chlorophyll were high in the
tracking area and showed a very strong positive
gradient on the cold side of the upwelling front
(Figure 5). Measurements of 14C uptake indicated
a primary production rate integrated over the
euphotic zone (0 to 36 m) of 1 ,5 1 1 mg C/m2 per day.
The biomass of potential albacore food organisms
was also high, ranging from about 20 to 56
ml/1,000 m3 water strained, in midwater trawl
collections made at night in the nearby area
where tracking took place (Table 4).

Albacore were frequently seen boiling in the
area nearby the upwelling front by personnel
aboard Linda and David Starr Jordan. Also,
observers aboard the Coast Guard aircraft noted
about 25 to 30 commercial albacore jig boats
fishing immediately on the warm side of the front
in water warmer than 15.0°C. High biological
production in the area of the upwelling front was

qystf

FIGURE 5. — Movements of albacore number 4 as indicated by
ultrasonic tracking and the distribution of surface chlorophyll
in milligrams per cubic meter.

TABLE 4. — Summary of dates, times, positions, and estimates of
potential albacore forage, 1972.

Fish IKMT

no. no. Date

Time

Lat.
(N)

Long.

(Wj

Forage

biomass

(ml/1,000 m3)

15 Aug

2200-2240

36°50'

122°14'

28.8

16 Aug

2159-2238

36°47'

122°15'

36.2

17 Aug

2137-2215

36°55'

122°24'

56.2

18 Aug

0032-0111

36°53'

122°16'

51.5

18 Aug

0130-0210

36°52'

122°19'

30.4

18 Aug

0232-031 1

36°49'

122^22'

37.7

18 Aug

0352-0430

36°50'

122°11'

30.7

18 Aug

0516-0553

36°41 '

12219'

29.8

21 Aug

2116-2150

37136 '

122°50'

5.7

21 Aug

2236-2314

36°57'

122°59°

10.1

22 Aug

0032-0115

36°54'

122°38'

24.5

22 Aug

0152-0231

36 '48

122°30'

23.1

22 Aug

0302-0341

36°55'

122°25'

10.6

22 Aug

0412-0450

36°52'

122°17'

24.9

27 Aug

2119-2156

34 40

122°14'

5.8

27 Aug

2241-2320

34°48c

122°02'

8.0

28 Aug

0040-0122

34°53'

121*51'

5.9

28 Aug

0214-0251

35c07

121 °29'

10.1

28 Aug

0325-0402

35°15'

121 °26'

19.6

also indicated by large numbers of sea birds and
numerous sightings of marine mammals, includ-
ing blue whales and other whales.

It is possible that fish number 5 and the school it
was traveling with left the immediate area where
it had been tagged because food organisms were
no longer concentrated there due to the break-
down of the upwelling front. This explanation is
supported by the observation on 19 August of an
overall reduction in the concentration of surface

352

LAURS ET AL.: SMALL-SCALE MOVEMENTS OF ALBACORE

FIGURE 6. — Movements of albacore number 5 as
indicated by ultrasonic tracking and the dis-
tribution of surface chlorophyll in milligrams per
cubic meter.

chlorophyll a, as much as three to four times lower
in waters where upwelling had been taking place
on 17 August (Figure 6). Also, measurements of
14C uptake indicate that the rate of primary
production was about 33% lower, 1,014 mg C/m2
per day, than it had been when fish number 4 was
tracked. In addition, estimates of biomass of
potential albacore forage organisms taken in
midwater trawl hauls made during tracking
operations for fish number 5 were less, ranging
from about 6 to 25 ml/1,000 m3 of water filtered
(Table 4), than during tracking operations for fish
number 4. (Relatively low chlorophyll a values
(Figure 7) and albacore forage biomass values
(Table 4) were also observed during tracking
operations for fish number 6.)

While tracking information on only two fish
does not provide sufficient data from which to
make generalizations, the results suggest that 1)
albacore concentrate in the vicinity of upwelling
fronts, presumably to feed, and 2) albacore move
away from the immediate area when upwelling
ceases and the upwelling front is no longer present
at the surface. Pearcy and Keene (1974) discussed
the possibility of albacore congregating in the
region of upwelling fronts. The concentration of
albacore in the vicinity of upwelling fronts has
also been indicated by high catch rates made by
fishing and research vessels near upwelling fronts
(Pearcy and Mueller 1970; Panshin 1971; Laurs
1973).

Relationship of Albacore

Movements to Other Sea Surface

Temperature Fronts

During the tracking operations, it appeared
that fish numbers 5 and 6 tended to slow down

FIGURE 7. — Movements of albacore number 6 as indicated by
ultrasonic tracking and the distribution of surface chlorophyll
in milligrams per cubic meter.

when crossing temperature fronts where the tem-
peratures on both sides of the front were within
the favorable range for albacore. To examine this
more closely, mean speeds were estimated for
tagged fish when they were within a 5-nmi dis-
tance before crossing and after crossing the tem-
perature front and when crossing the front. A
sea surface temperature front was defined as a
change in surface temperature of 0.5°C or larger in
a nautical mile (0.003°C/m). The results are sum-
marized in Table 5 and show that for the three
cases examined, 1) the mean speed was slower
when crossing the front than it was before

353

FISHERY BULLETIN: VOL. 75, NO. 2

TABLE 5. — Mean speed crossing temperature front1 and mean speed within 5-nmi radius

before and after.

Item

Fish
no.

Date

Time

Total
(h)

Total distance
(nmi) (km)

Mean speed
(knots) (cm/s)

Before
At front
After

5
5
5

8/19

8/19-20

8/20

1330-1600
1600-0300
0300-0800

2.5

11.0
5.0

5.0
7.8
7.0

9.3

144
130

2.0

0.7
1 4

103
36
72

Before
At front
After

6
6
6

8/26

8/26
8 26-27

1700-1900
1900-2100
2100-0200

2.0
2.0
5.0

5.6

3.7
8.0

104
6.9

14.8

28
1.8
1.6

144
93
83

Before
At front
After

6
6
6

826
826
8/26

0800-1230
1230-1400
1400-1600

4.5
1.5
2.0

6.1
2.0
5.2

11.3
3.7
9.7

14
0.7

2.6

134

'A7"20.5 C. 1.0 nmi.

crossing the front in all three cases, and 2) the
mean speed was slower when crossing the front
than after crossing the front in two cases. These
data should be viewed with caution, however, be-
cause in two instances, daytime and nighttime
data were used together and some of the differ-
ences in speed may be due to variation associated
with time of day. The relationship did hold up well
in the single case when daytime data only were
used.

We think the changes in swimming behavior
observed at temperature fronts reflected percep-
tion and response to the increased temperature
gradient per se. In the case of the alteration in the
swimming pattern of fish number 5 as it encoun-
tered a temperature front at lat. 36°53'N, long.
122°27'W (Figure 3), there was no sharp gradient
in any of the other environmental parameters we
measured.

That tunas can perceive abrupt temperature
changes as small as 0.1°C has been demonstrated
by Steffel et al. (1976) for captive kawakawa,
Euthynnus affinis. Moreover, a mechanism has
recently been suggested (Neill et al. in press)
whereby tunas might be able to orient themselves
in temperature gradients much gentler than those
of our fronts, perhaps even as slight as
0.0001°C/m; this speculative mechanism invokes
the large thermal inertia of tunas as a device for
thermal "memory."

Movements of Albacore in Relation to
Vertical Thermal Structure

The availability of albacore in offshore waters
has been shown to be related to vertical thermal
structure (Laurs and Lynn7). However, no obvious

7Laurs, R. M., and R. J. Lynn. 1974. The offshore distribution
and availability of albacore during early-season and the
migration routes followed by albacore into North American
waters. SWFC Admin. Rep. LJ-74-47: 19-46.

354

relationship was observed in this study between
the movements of sonic-tagged albacore in coastal
waters and subsurface temperature structure.
This may be due to the complicated vertical
temperature structure that was observed in the
areas where fish were tracked and the lack of data
on the depth of the fish.

SUMMARY

Six albacore were tagged and tracked with
ultrasonic equipment for periods ranging from 2
to 50 h and distances ranging from 6.5 to 150.7 km
(3.5 to 81.3 nmi). The average swimming speed
for these fish tracked between 27.8 and 50.0 h was
1.6 knots (82 cm/s) with each fish exhibiting
slightly faster swimming speeds during the day
than during the night. The mean swimming
speeds observed during the tracking experiment
are similar to estimates of swimming speed
derived from passive tagging results and about
twice the calculated minimum swimming speed
necessary to maintain hydrostatic equilibrium.

The tracking experiment indicated that ocean-
ographic conditions may play an important role in
the local concentrations and movements of alba-
core in coastal waters. The movements of fish
appeared to be related to the distribution of sea
surface temperature, with transmitter-tagged
fish spending very little time in water with
surface temperatures less than 15.0°C. The results
also indicate that upwelling temperature fronts
may markedly influence the local concentration of
albacore, with albacore tending to concentrate in
the vicinity of upwelling fronts, presumably to
feed, and moving away from the immediate area
when upwelling ceases and the upwelling front is
no longer present at the surface. There was also
some indication that albacore tended to slow down
when crossing sea surface temperature fronts

LAI RSET \I. S.MALI. -SCALE \1< >\ TMI NTS OF ALBACORE

where the temperatures on both sides of the front
were within the optimal range for albacore.

Finally, the tracking experiment demonstrated
that acoustic tracking of albacore is feasible and
that it can be a useful tool in studies designed to
understand better the relationships between
albacore and the marine environment.

ACKNOWLEDGMENTS

We acknowledge the assistance provided in the
tracking operations by Michael Swiston, and
Scotty Hazelton and crew of Linda, the U.S. Coast
Guard, Pacific Area, for providing aircraft over-
flights, and James Squire for assistance in making
and processing the airborne radiometer tempera-
ture observations. We thank Charles Forster and
crew of the RV David Starr Jordan for the
cooperative support in making oceanographic
observations, and the American Fishermen's
Research Foundation for providing funds for the
charter of Linda. We also thank M. Blackburn, J.
J. Magnuson, W. H. Neill, and W. G. Pearcy for
critically reviewing the manuscript.

LITERATURE CITED

CLEMENS, H. B.

1961. The migration, age, and growth of Pacific albacore
(Thunnus germoK 1951-1958. Calif. Div. Fish Game,
Fish Bull. 115, 128 p.
1963. A model of albacore migration in the north Pacific
Ocean. FAO Fish. Rep. 6:1537-1548.
DOTSON, R. C.

1977. Minimum swimming speed of albacore, Thunnus
alalunga. Fish. Bull., U.S. 74:955-960.
GANSSLE, D., AND H. B. CLEMENS.

1953. California tagged albacore recovered off Japan.
Calif. Fish Game 39:443.
HOLM HANSEN. O., C. J. LORENZEN, R. W. HOLMES. AND J. D.
H. STRICKLAND.

1965. Flurometric determination of chlorophyll. J. Cons.
30:3-15.

Japanese fisheries Agency

1975. Report of tuna tagging for 1974. [In Jap. 1 Pelagic
Res. Sec, Far Seas Fish. Res. Lab. June, 18 p.
LAURS, R. M.

1973. Requirements of fishery scientists for processed
oceanographic information. Proc. WMO Tech. Conf.,
Tokyo, 2-7 Oct. 1972. WMO 346, Rep. 6, Vol. 1:95-111.

Neill. w. h., R. K. C. Chang, and a. e. dizon

In press. Magnitude and ecological implications of ther-
mal inertia in skipjack tuna, Katsuwonus pelamis (Lin-
naeus). Environ. Biol. Fish.
OTSU. T.

1960. Albacore migration and growth in the North Pacific
Ocean as estimated from tag recoveries. Pac. Sci.
14:257-266.
OTSU, T., AND R. N. UCHIDA.

1963. Model of the migration of albacore in the North
Pacific Ocean. U.S. Fish Wildl. Serv., Fish. Bull. 63:33-44.
OWEN. R. W., AND B. ZEITZSCHEL.

1970. Phytoplankton production: Seasonal change in the
oceanic eastern tropical Pacific. Mar. Biol. (Berl.) 7:32-
36.

PANSHIN, D. A.

1971. Albacore tuna catches in the northeast Pacific dur-
ing summer 1969 as related to selected ocean conditions.
Ph.D. Thesis, Oregon State Univ., 110 p.

Pearcy, w. g., and d. f. keene.

1974. Remote sensing of water color and sea surface tem-
peratures off the Oregon coast. Limnol. Oceanogr. 19:
573-583.

pearcy. w. G., and j. L. Mueller

1970. Upwelling, Columbia River plume and albacore
tuna. Proc. Sixth International Symposium on Remote
Sensing of Environment, p. 1101-1113. Univ. Mich., Ann
Arbor.

PINKAS. L.. M. S. OLIPHANT. AND I. L. K. IVERSON.

1971. Food habits of albacore, bluefin tuna, and bonito in
California waters. Calif. Dep. Fish Game, Fish Bull.
152, 105 p.

SMITH. R. L.

1968. Upwelling. Oceanogr. Mar. Biol. Annu. Rev.
6:11-46.
STASKO. A. B.

1975. Underwater biotelemetry, an annotated bibliog-
raphy. Fish. Mar. Serv. Res. Dev. Dir. Tech. Rep. (Can.)
534, 31 p.

STEFFEL. S., A. E. DIZON. J. J. MAGNUSON. AND W. H. NEILL

1976. Temperature discrimination by captive free-
swimming tuna, Euthynnus affinis. Trans. Am. Fish.
Soc. 105:588-591.

355

ANNUAL FLUCTUATIONS IN BIOMASS OF TAXONOMIC GROUPS OF
ZOOPLANKTON IN THE CALIFORNIA CURRENT, 1955-59

J. M. COLEBROOK1

ABSTRACT

Year-to-year fluctuations in the abundance of the zooplankton of the California Current region, from
1955 to 1959, have been studied. The abundance of zooplankton was measured in terms of the biomass
of each of 17 major taxonomic categories (generally Class or Order). Principal components analysis was
used to produce concise descriptions of the major elements of the fluctuations in the abundance of the
categories in each of 14 areal subdivisions of the survey area. Considerable coherence with respect to
annual changes was found both between the taxonomic categories and between the areas. The
principal common element in the fluctuations could be associated with a marked increase in the
temperature of the surface waters which occurred in 1957 and persisted through 1958 and 1959. A less
pronounced but still quite clear common element in the fluctuations could be associated with year-to-
year fluctuations in the amount of coastal upwelling in the area.

Since 1949, the regular surveys conducted by the
California Cooperative Oceanic Fisheries Inves-
tigation (CalCOFI) program have yielded infor-
mation about a variety of physical, chemical, and
biological parameters (see, e.g., Marine Research
Committee 1957). For the CalCOFI survey cruises
during January, April, July, and October for each
of the years from 1955 to 1959, samples of
zooplankton were analyzed to provide estimates of
the biomass for each major taxonomic category
within the zooplankton (Isaacs et al. 1969).

These data were generously made available to
the author by J. D. Isaacs to provide material for a
study of year-to-year changes in the abundance of
the major components of the zooplankton. As
stated by Isaacs et al. (1969), "Selection of the
years 1955 through 1959 for analysis of biomass
distribution was dictated by interest in the
occurrence and nature of patterns of seasonal and
annual variability among the functional groups of
zooplankton. During this time, yearly mean
temperatures above the thermocline shifted up-
ward from the relatively cold years of 1955 and
1956 to the relatively warm years of 1958 and
1959."

The object of the study described in this paper is
to describe the annual changes, from 1955 to 1959,
in the abundance of the zooplankton of the
CalCOFI survey area in as much detail as is

'Institute for Marine Environmental Research, Plymouth,
England.

available from the survey data in order to discover
whether observed changes can be associated with
environmental fluctuations.

MATERIAL

The details of the procedures for deriving
biomass estimates .have been described by Isaacs
et al. (1969), who also give the reasons for the
selection of the particular set of taxa (listed in
Table 1). It was their intention to provide

TABLE 1. — A list of the taxa from CalCOFI cruises for which
biomass estimates are available. They are listed in alphabetical
order and a code used in Figures 7 and 10 is given.

Taxa

Code

Taxa

Code

Amphipoda

AMPH

Larvacea

LARV

Chaetognatha

CHET

Medusae

MEDS

Cladocera

CLAD

Mysidacea

MYSD

Copepoda

COPD

Ostracoda

OSTR

Crustacea larvae

CRST

Pteropoda

PTER

Ctenophora

CTEN

Radiolana

RADL

Decapoda

DECP

Siphonophora

SIPH

Euphausiacea

EUPH

Thaliacea

THAL

Heteropoda

HETP

Manuscript accepted October 1976.
FISHERY BULLETIN: VOL. 75, NO. 2, 1977.

estimates of the "nutrient quality" of the standing
crop of zooplankton as well as an index of
"trophodynamic complexity." The categories were
chosen to represent the quality and quantity of
zooplankton as food for fish rather than as
indicators of variability of the zooplankton as
such.

The collection method for the standard
CalCOFI plankton samples has been described in

357

FISHERY BULLETIN: VOL. 75, NO. 2

detail by, e.g., Ahlstrom (1954) and Fleminger
( 1964). Very briefly, the net is 1 m in diameter at
the mouth and 5 m long, the filtering section
having a mesh size of about 0.5 mm. The net is
towed obliquely, from a ship traveling at a speed of
about 2 knots, from the surface down to a depth of
140 m and then returned to the surface. The
volume of water fitered varies from about 400 to
600 m3.

Charts of the distribution of biomass for each
taxon have been given by Isaacs et al. (1969) for
the April and October cruises, by Isaacs et al.
( 1971 ) for the January cruises, and by Fleminger
et al. ( 1974) for the July cruises. The station data
are held on a magnetic tape file at the Southwest
Fisheries Center, National Marine Fisheries
Service.

DATA PROCESSING METHODS

For the purposes of presenting summaries of
CalCOFI data in a compact form and to permit
some smoothing of the data by taking average
values, P. E. Smith's proposal for subdividing the
survey area into 23 zones was used in this study
(Figure 1 ). The extent of the survey and hence the
number of stations occupied varied from cruise to
cruise. The station patterns for the cruises
included in this study are given in Smith (1971),
and a summary showing the numbers of samples
in each zone is given in Table 2.

The biomass data are available as grams/1,000
m3 and estimated to two decimal places. The range
of estimates is from zero to over 5,000 g, and
within each taxon they are heavily positively
skewed.

The results presented here were expressed in
terms of relative changes in biomass in time and
space within each taxonomic category, and exten-
sive averaging was employed. It was decided,
therefore, to apply a logarithmic transformation
to the original estimates. Averages based on log
transformed values are weighted in favor of the
more numerous low values as opposed to arith-
metic means, the values of which may be
determined largely by small numbers of high
estimates.

In order to give zero a value on the transformed
scale it is normal to add 1 to the observation prior
to transformation. In this case, where the biomass
has been estimated to two decimal places, a
number of options is available, either 1.0, 0.1, or
0.01 can be added prior to transformation. Trials

' ' — ^ 1

o o

O O O O O O O OJO o oo f ' • ^ w

NORTHERN CALIFORNIA

1 INSHORE

2 OFFSHORE

3 SEAWARD

ooooooAoo /cfipE MENDOCINO
2 1 \

o o o

•••••(

9 O OoJ

o .

o o o = „

3 O O o\ n

40"

■> o o

o o o o o

o o o (k

CENTRAL CALIFORNIA
•4 INSHORE
»5 OFFSHORE
6 SEAWARD

o o o o o

rtJSiN FRANCISCO

O O O O J

4 r

■ • •

o o o o o

o o o o\

o . o

o o o o o

0 . o .}

INT CONCEPTION

. . o

\~i

SOUTHERN CALIFORNIA
•7 INSHORE
•8 OFFSHORE
•9 SEAWARD
10 EXTENDED

o A* \poj

7 A

\. [ SAN DIEGO

!S"

. . .

o <, o o o

"J ' >

BAJA CALIFORNIA
•II INSHORE

* 12 BAY

* 13 OFFSHORE

* 14 SEAWARD
15 EXTENDED

O o o
o o O

o o^o .

o o o

QfO

ii \ A

o oof J

:::

oi o o o o\ 1

/ l2 \ \ -

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SOUTH BAJA
•16 INSHORE
• 17 OFFSHORE
•18 SEAWARD
19 EXTENDED

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o o olo o o°\\pUNT4 >
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° °\7 °\°\6°\^, |

= 0

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o o o o e

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•20 INSHORE

• 21 OFFSHORE

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23 EXTENDED

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a e o o a

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25"

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i '

FIGURE 1. — A chart of the area of the CalCOFI survey showing
the grid of station positions on which were based the cruises
during the period 1955-59. Also shown is the subdivision of the
area into the standard zones used in this study. The well-
sampled zones for which annual means of biomass were calcu-
lated are marked with an asterisk (see Table 2).

involving the calculation of means for each zone
for each cruise for a subset of the taxonomic
categories indicated that adding 1.0 produced a
considerable loss of resolution for means corre-
sponding to less than 1 g/1,000 m3, and adding
0.01 produced a resolution of low means that ap-
peared to be greater than was warranted by the
accuracy of the data. Therefore throughout this
study a transformation of the form

Y = log10(10X + 1)

358

COI.EBROOK: FLUCTUATIONS IN BIOMASS OF ZOOPLANKTON

TABLE 2. — The numbers of samples collected during each of the January (Jn), April ( Ap), July (Jl), and October (Oc) CalCOFI cruises
for the years 1955-59 in each of the standard zones (see Figure 1). Annual totals are given in boldface and the grand total is printed in
italic.

1955

1956

1957

1 958

1 959

To-

Grand

Zone

tal

total

Central California:

Inshore

226

Offshore

186

Southern California:

Inshore

29 100

27 112

474

Offshore

769

Seaward

327

Baja California:

Inshore

237

Bay

265

Offshore

330

Seaward

312

South Baja:

Inshore

295

Offshore

283

Seaward

120

Cape:

Inshore

130

Offshore

113

has been employed. By this transformation,
means corresponding to greater than about 0.2
g/1,000 m3 are virtually on a logarithmic scale
while lower means show a progressive transition
to an arithmetic scale.

Quarterly means were calculated by averaging
the data for the stations in each zone and then
these were averaged to give annual values. For
those occasions when less than five stations were
occupied in any zone, the station data were
ignored and a quarterly mean was interpolated by
the following method:

1. For each taxonomic category the set of overall
zone means (the sum of all the observations
for all the cruises in each zone divided by the
total number of stations occupied in the zone)
was calculated. The set of overall quarterly
means (the sum of all the observations for all
the cruises in each quarter divided by the
number of stations in each quarter) was
calculated.

2. For each missing value the sum of the
remaining means for the other zones for the
cruise and the sum of the corresponding
overall zone means were calculated. The
latter was weighted by the ratio of the
relevant overall quarterly mean to the grand
mean and the missing value then calculated
as the product of the remaining zone means
for the cruise and the weighted sum of the
overall zone means.

From these quarterly means, annual means

were calculated for each taxon for each of a set of
regularly sampled zones (those marked with an
asterisk in Figure 1); and principal components
analysis was used to extract from these data the
main patterns of year-to-year change in biomass.
This is a technique of multivariate analysis (see,
e.g., Kendall 1957) which generates a sequence of
variables known as components with, in this case,
values for each year, which are the weighted sums
of the standardized data variables, in this case
sets of annual means of the taxonomic categories.
The sets of weighting factors, with values for each
taxonomic category, are the successive latent
vectors of the correlation matrix derived from the
original data, in this case the table of correlations
between the annual variations in abundance of all
possible pairs of taxonomic categories. The first
latent vector generates a component which has
the largest possible variance. The second vector
generates a component which has the largest
possible variance in relation to the residual
following the removal of the variability associated
with the first component, and so on. If the original
data are coherent to any extent, it is normal for
the first few components to account for a large
proportion of the variability of the original data
array.

GEOGRAPHICAL DISTRIBUTIONS

To provide some geographical background to
the study of year-to-year changes in biomass,
charts of the overall mean for each taxon in each
standard zone were prepared. In order to search

359

for possible relationships between the geograph-
ical distributions of the taxonomic categories,
these data were subjected to a principal compo-
nents analysis.

Figure 2 is a graph of the first latent vector
plotted against the second. The graph has a point
for each taxonomic category, and the disposition of
points represents in a spatial form the relation-
ships between the geographical distributions of
the taxonomic categories with respect to the first
two components which, in this case, account for
61% of the variability of the original geographical
distributions. The interrelationships are probably
best regarded in the form of a more or less circular
sequence; only the point for Medusae falls well off
the sequence.

Figure 3 shows charts of the first two compo-
nents. The first component shows a very clear
north to south, alongshore gradient; and the
second shows an equally clear inshore to offshore
gradient, indicating that the sequence of cate-
gories in Figure 2 runs from categories with
northern distributions (Siphonophora to Radio-
laria) to inshore distributions (Euphausiacea to
Cladocera) to southern and inshore distributions
(Larvacea to Mysidacea) to offshore distributions
(Heteropoda to Ostracoda). Figure 4 shows the

(ONSHORE) +0.5

CRST

-0.4-1- „CHET COPD

CLAD.

+ 0.3- -

LARV

DECP

MYSD
(SOUTH)
-04 -03 -02 -0.1

+ 0.2--

+ 0.I--

-+-

■+■

-+-

HETP
PTER

-0.2- -

(OFFSHORE) -04-L

EUPH

(NORTH)
RADL
+ 0.1 +0.2 +0.3 *

-+-

MEDS

1amph* ¥i

CTEN
THAL

SIPH

0 3- •

OSTR

FIGURE 2. — A plot of the first vector against the second vector
derived from a principal components analysis of the geographi-
cal distributions of the taxa. A key to the abbreviations of the
names of the categories is given in Table 1.

FIRST COMPONENT

FISHERY BULLETIN: VOL. 75, NO. 2

SECOND COMPONENT

FIGURE 3. — Charts of the first and second components derived
from a principal components analysis of the geographical dis-
tributions of the taxa.

distributions of the taxonomic categories ar-
ranged in this sequence. They are based on
averages of the transformed data, for each zone,
for each quarterly cruise for the period 1955-59,
excluding zones for which fewer than five stations
were occupied. These distributions show varia-
bility other than that involved in their relation-
ships with the first two components; nevertheless,
the north to inshore to south to offshore sequence
can be seen fairly clearly. Heteropods and
Pteropods are firmly placed in the sequence of
taxonomic categories in the vector plot in Figure
2. They have, however, fairly low values compared
with the other categories, and only parts of their
distributions conform with the south to offshore
transition indicated by their position in the vector
plot. The distribution of Medusae (Figure 4) can be
seen to include areas of relatively high biomass
both in the north and in the south, and clearly it
does not fit into the sequence of the other
categories.

It is obviously unrealistic to attempt to classify
the internally diverse taxonomic categories used
here in terms of geographical distribution types
such as Brinton (1962) found for Euphausiacea.
Brinton found that the alongshore axis of the
California Current in the CalCOFI survey area
was characterized by transitions from "subarctic"
species in the north to "transition" species in the
region between lat. 30° and 40°N to "equatorial"
species in the south. "Central" species occurred
offshore and some "boundary" species occurred
inshore in the area. McGowan (1971) has shown

360

COLEBROOK II UCTUATIONS IN BIOMASS OF ZOOPLANK I < >X

that these patterns are reflected generally in the
distribution of the plankton of the Pacific Ocean.
It may, nevertheless, he significant that the
pattern of distribution of the taxonomic categories
reflects both the alongshore and the inshore-
offshore transitions in the distribution of the
Euphausiacea.

YEAR-TO-YEAR FLUCTUATIONS
IN BIOMASS

Annual means of biomass were calculated, as
described above, for each taxonomic category
(Table 1) for each of the well-sampled standard
zones ( Figure 1 ) for each of the years 1955-59. Two
sets of principal components analyses were
carried out, firstly for each of the 14 standard

TABLE 3. — For each zone (a ) the percentage
ity of the original data accounted for by the
i b ) the number of taxa with positive first
imum = 17). The code names for the zones
Figures 6 and 9 are also given.

of the total variabil-
first component and
vector values (max-
used in Table 4 and

Zone

Code

Central California:

Inshore

CCALIN

Offshore

CCALOF

Southern California:

Inshore

SCALIN

Offshore

SCALOF

Seaward

SCALSW

Baja California:

Inshore

BCALIN

Bay

BCALBY

Offshore

BCALOF

Seaward

BCALSW

South Baja:

Inshore

SBAJIN

Offshore

SBAJOF

Seaward

SBAJSW

Cape:

Inshore

CAPEIN

Offshore

CAPEOF

zones on the annual fluctuations in biomass of
each taxonomic category and secondly for each
taxonomic category on the annual fluctuations in
abundance in each of the standard zones. The
same data are involved in both sets of analyses.

Graphs of the first principal components for
each of the zone analyses are given in Figure 5.
Table 3 shows that these components accounted
for between just under one-half and about three-
quarters of the total variability; it also shows that
all but a very few of the categories showed positive
relationships with the components. The graphs
show considerable similarity between the various
zones. These results indicate that a large element
of the year-to-year fluctuation in biomass is
common to all the zones and to a vast majority of
the taxonomic categories. Nearly all the zones
show a relatively high biomass (relative to a mean
of zero) in 1955 and 1956 and a low biomass in
1958 and 1959. The data for 1957 vary from zone
to zone, perhaps tending to be higher in the
northern and offshore zones and lower in some of
the southern and inshore zones.

A table was prepared of the corresponding
vectors with the taxonomic categories arranged,
by trial and error, to give the high positive terms
at the top, and the low positive and the few
negative terms at the bottom of the table. The
final ranking of categories and the vector values
are given in Table 4. This rank was compared with
the rank of taxa based on the relationships
between their geographical distributions (Figure
2) starting with the northern distributions, with
Siphonophora and Thaliacea, working round the
sequence and ignoring Medusae (also left out of
Table 4) to finish with Pteropoda and Ostracoda.

TABLE 4. — The first vectors of principal component analyses for each standard zone with the taxonomic categories ranked as described

in the text. Also the rank of the categories derived from Figure 2.

Taxa

z
—i
<
o
o

ll
O
_i
<
o
o

z
_i
<

o
en

ll
O
_j
<
o
co

co
_i
<

o
co

z
_i
<
o

>
m
_i
<

o
m

CO
CO

LL
O
— D
<

CO
CO

— 3

CO
CO

LU
Q.
<
O

LU
O-
<

Copepoda

0.28

0.30

0.31

0.36

029

0.29

0.30

0.34

0.30

031

0.27

0.30

Thaliacea

0.27

0.30

0.28

0.31

028

0.29

0.32

0.33

0.29

0.31

029

030

0.31

Amphipoda

0.27

0.28

0.30

0.32

0.31

0.27

0.28

0.31

0.33

0.28

0.22

0.29

0.28

Siphonophora

0.27

028

0.22

0.29

0.23

029

0.29

0.25

0.29

0.28

0.30

0.32

0.28

028

Radiolarla

0.28

0.27

0.30

0.29

0.31

028

0.28

0.30

028

0.23

0.28

0.20

-.02

0.00

Ctenophora

0.26

0.27

0.30

0.26

0.28

0.26

0.33

0.27

0.26

0.06

0.16

0.05

Decapoda

0.25

025

0.26

0.29

0.27

0.24

0.31

0.29

0.24

0.28

0.29

0.30

0.33

Euphausiacea

0.27

0.26

0.28

0.26

0.28

0.21

0.14

0.17

0.24

0.28

0.18

0.31

Chaetognatha

0.28

0.27

0.30

0.28

0.27

0.24

0.11

0.27

0.24

0.25

-.26

0.31

0.32

Crustacea larvae

0.25

0.06

0.30

0.27

0.22

0.25

0.24

0.17

-.09

0.25

0.31

-.25

029

0.11

Heteropoda

0.15

0.24

0.14

0.18

0.23

0.16

0.29

0.20

0.07

0.19

0.29

0.19

0.27

0.28

Larvacea

0.28

0.27

0.17

0.13

0.24

0.27

0.29

0.21

-.05

0.22

-.08

0.29

0.22

0.23

Ostracoda

0.22

0.26

-.01

0.26

0.23

0.12

0 18

0.23

0.13

018

0.11

-.21

0.21

0.24

Cladocera

0.12

0.19

-.03

0.01

0.03

-.23

0.03

-.25

0.06

0.23

0.17

0.11

0.09

-.08

Pteropoda

0.19

0.13

0.10

0.08

-.02

0.04

0.12

-.02

-.19

-.06

0.05

-.08

-.17

021

Mysldacea

0.15

0.17

-.28

0.09

-.15

0.08

0.11

-.12

-.27

0.26

0.14

-.33

0.29

0.16

361

FISHERY BULLETIN: VOL. 75. NO. 2

SIPHONOPHORA THALIACEA

CTENOPHORA

AMPHIPODA

FIGURE 4. — Charts of the geographical distribution of biomass for each of the taxa based on logarithmic means for
each standard zone (see Figure 1 ) for all the CalCOFI cruises for 1955-59. Contours are drawn at levels correspond-

The ranks are given in Table 4, and the value of
Spearman's rank correlation coefficient between
the two ranks is + 0.806 which is significant at the
0.19c level.

Figure 6 shows graphs of the first principal
components of the analyses for each taxonomic
category with the categories ranked in the same
order as in Table 4. All the northern and inshore
categories, down to Crustacea larvae in Figure 2,
show the same form of year-to-year fluctuations in
biomass as do the zones, with relatively high
biomass in 1955 and 1956 and low biomass in 1958
and 1959. The remaining categories show some

features of this pattern with only Cladocera
showing a negative relationship.

These results suggest that whatever influence
or influences are responsible for the fluctuations
in the plankton either have their origin in the
north of the survey area or have a greater effect on
those categories with northern patterns of distri-
bution. It is, at least, fairly safe to infer that there
is some commonality between the influences
which determine geographical distribution and
those which are responsible for the form of the
year-to-year changes in biomass.

The years from 1955 to 1959 were deliberately

362

COLEBROOK: FLUCTUATIONS IN BIOMASS OF ZOOPLANKTON

CHAETOGNATHA

CLADOCERA

LARVACEA

DECAPODA

ing to the mean + 1 SD, the mean, and the mean - 1 SD. The keys to the contour levels for each category give the arithmetic values, as
grams per 1,000 m3, corresponding to these levels.

chosen for the production of biomass data to cover
a period of marked change in physical conditions
and in the distribution of many species in the
CalCOFI area. The main features of these changes
have been described in the proceedings of a special
symposium (Sette and Isaacs 1960). The most
striking feature was a considerable warming of
the surface waters which started in the south in
1956 and spread through the area during 1957
(see, e.g., Longhurst 1967).

The general form of the change can be typified
by the variation in temperature in the top 50 m in
the southern California offshore area shown in

Figure 7. Favorite and McLain (1973) showed that
this is part of a widespread change in surface
temperature affecting almost the whole of the
North Pacific Ocean. The reasons for the change
are not yet completely clear. The initial warming
in 1957 appears to be associated with a reduction
in the flow of the California Current which
occurred between the late summer of 1957 and
midsummer 1958. As an index of the flow of the
California Current, Saur (1972) used the differ-
ence in sea level between Honolulu and San
Francisco. A plot of monthly means (with a linear
trend removed and adjusted to normal atmo-

363

C CAL OF . C CAL IN

FISHERY BULLETIN: VOL. 75, NO. 2
THAL AMPH SIPH

55 56 57 58 59 CApE QF CAPE IN

55 56 57 58 59 55 56 57 58 59
YEAR

FIGURE 5.— Graphs for each of the well-sampled CalCOFI zones
(see Figure 1) of the first principal component of the year-to-year
fluctuations in biomass of all the 17 taxa. Each graph is drawn
with a mean of zero and the vertical scale is in SD units.

55 56 57 58 59 55 56 57 58 59 55 56 57 58 59

55 56 57 58 59

YEAR

FIGURE 6. — Graphs for each taxon of the first principal compo-
nent of the year-to-year fluctuations in biomass for all the well-
sampled CalCOFI standard zones. A key to the abbreviations of
the names of the taxa is given in Table 1. They are in the same
order as in Table 4 (see text). Each graph has a mean of zero and
the vertical scale is in SD units.

spheric pressure) for 1955-59 is shown in Figure 7.
Differences greater than 58 cm are believed to
indicate a stronger than normal flow and differ-
ences less than 58 cm a less than normal flow. It
can be seen that the period of less than normal
flow in 1957-58 corresponds well with the timing
of the increase in temperature in the southern
California offshore zone. In the California Cur-
rent region, and indeed over most of the eastern
North Pacific, the increase in temperature per-
sisted through 1958 and 1959 while the sea level
differences indicate a normal or above average
flow during this time. The period of below normal
flow corresponds with El Nino off the coast of Peru

and perhaps with an anomalous weakening of the
trade winds of the southern hemisphere and a
concurrent reduction of equatorial upwelling
(Bjerknes 1966; Favorite and McLain 1973).

Wickett (1967) found a relationship between
the year-to-year changes in zooplankton volume
for the CalCOFI survey (Thrailkill 1963) and the
mean meridional Ekman transport (Fofonoff
1962) for January to August in the previous year
at lat. 50°N, long. 140°W (over 1,000 miles
upstream from the CalCOFI survey area) for the
years 1952-59. He suggested that a major cause of
variation in the abundance of zooplankton in the
California Current region is the change in the

364

COLEBROOK: FU'(Tl'ATIONS IN HIOMASS OK ZOOI'l.ANKTON

1955

1956

1957

1958

1959

<I5°
1 5°- 1 7°
>I7°

FIGURE 7. — Top) A contoured diagram
of monthly vertical temperature
profiles for the upper 50 m for the years
1955-59 for the southern California
offshore zone (see Figure 1). CalCOFI
survey data. Bottom) A graph of the dif-
ference in sea level between Honolulu
and San Francisco at monthly intervals
for the years 1955-59 ( plotted from Saur
1972).

proportion of the superficial wind-driven water
that is swept southward out of the North Pacific
subarctic circulation.

There seems little doubt that the change in
temperature in 1957 and its persistence through
1958 and 1959 is related to the relative reduction
in biomass of the zooplankton associated with the
first principal components of all zones and most of
the taxonomic categories. The data presented by
Wickett showed a marked reduction in southward
transport at lat. 50°N, long. 140°W during 1958
and 1959 and this, coupled with the reduction in
the flow of the California Current in 1957 and
1958 (Figure 7), would appear to support Wick-
ett's suggestion of a direct influence by water
movements. The relationship between the north
to south geographical gradient (Figure 3) and the
first principal components is also entirely con-
sistent with this hypothesis.

An examination of the remaining components
for each of the zones indicated the existence of a
second pattern of fluctuation common to most of
the zones. In Figure 8 are given graphs of a
component, other than the first, for each zone
selected to give the best approximation to a form
common to all the zones. In 8 of the 14 zones it is
the second component; in the remaining zones it is
either the third or the fourth component. Given
the quantity and the quality of the original data
and considering the large proportion of the
variability of the data associated with the first
components, the lack of consistency in the position

of the common pattern among the components is
perhaps not surprising. Figure 9 shows the same
for each taxonomic category; again the majority
are second components and only one, for Radio-
laria, is the fourth component. The main features
of the pattern are a low in 1957 and highs in 1956
and 1958; 1955 and 1959 tend to be low but their
positions vary somewhat within both the zones
and the taxonomic categories.

Coastal upwelling is a feature of the California
Current region, and Bakun (1973) has produced
estimates of relative fluctuations in upwelling at a
number of positions along the west coast of North
America. They are based on estimates of the
offshore component of the Ekman transport which
is in turn estimated from atmospheric pressure
fields.

Monthly means of the upwelling index for five
positions off the coast at latitude and longitude
36°N, 122°W; 33°N, 119°W; 30°N, 116°W; 27°N,
116CW; and 24°N, 113°W, for the period 1955-58
were extracted from Bakun's report. Uncertain-
ties about the differences in absolute terms
between the estimates at different positions
particularly off southern California, discussed by
Bakun, suggested that principal components
might provide a good method of summarizing the
data from this set of positions. For each calendar
month, analyses were carried out on the index
estimates for the five positions and the 5 yr.
Examination of the components showed that a
pattern common to the first 7 mo of the year was

365

FISHERY BULLETIN: VOL. 75. NO. 2

C CAL IN

AMPH

CHET

CLAD

COPD

S BAJ OF . S BAJ IN 55 56 57 58 59

55 56 57 58 59 55 56 57 58 59

YEAR

FIGURE 8. — Graphs, for each CalCOFI standard zone, of princi-
pal components of annual fluctuations in biomass. See text for
the method of selection of the components, see also the legend to
Figure 6.

-3u - y

THAL 55 56 57 58 59 55 56 57 58 59 55 56 57 58 59

55 56 57 58 59

YEAR

FIGURE 9. — Graphs, for each taxonomic group (Table 1), of prin-
cipal components of annual fluctuations in biomass. See text for
the method of selection of the components, see also the legend to
Figure 7.

present within the components, and graphs of
these are given in Figure 10. The pattern was
found as the first component in all the months
except March and April where it was found in the
second component. Graphs of the first components
for August to December are also given in Figure
10.

There is a marked similarity between the
pattern of year-to-year fluctuations in upwelling
as represented by the components for the first 7 mo
of each year and the fluctuations in biomass of the
zooplankton represented by the components
shown in Figures 8 and 9, and it is reasonable to
assume that some form of causal relationship is

involved. As with the first component in relation
to the temperature range, the precise mecha-
nisms involved cannot be inferred from the infor-
mation here. Upwelling has effects on the vertical
temperature structure and particularly on the
timing of the establishment of a clear thermo-
cline. It can also be expected to have a consider-
able influence on the supply of nutrients. It is
probable, therefore, that the effect on the zoo-
plankton is an indirect one through the influence
of vertical stability of the water column and the
supply of nutrients on primary production pro-
cesses. Peterson (1973) has established a relation-
ship between year-to-year variation in upwelling

366

COLEBROOK: FLUCTUATIONS IN BIOMASS OF ZOOPLANKTON

JAN

FEB

MAR

55 56 57 58 59 55 56 57 58 59 55 56 57 58 59

YEAR

FIGURE 10. — Graphs of principal components of upwelling index
for the CalCOFI survey area for each month for the years 1955-
59. See text and Bakun 1 19731.

off the coast of Oregon and the catch of the
Dungeness crab, Cancer magister, with a time lag
of about 18 mo. He attributed this to an increased
food supply in years with pronounced upwelling,
implying a relationship between upwelling and
plankton similar in sign to that found further
south in the California Current.

CONCLUSIONS

At least during the period 1955-59, a consider-
able proportion of the variability from year to year
in the biomass of zooplankton, as represented by
estimates for the taxa listed in Table 1, can be
associated with hydrographic events, variations
in the strength of the California Current, and
variations in the intensity of coastal upwelling.

The precise mechanisms involved are not clear,
but in relation to the California Current there is a
similarity in the relationships within the taxa
with respect to both geographical distribution and
annual fluctuations in abundance which suggests
that advection of stocks may be involved to a
considerable extent. The influence of upwelling on
primary production through effects on tempera-
ture stratification and the supply of nutrients
probably accounts for the relationship with the
zooplankton.

The only data that have been produced rou-
tinely from the whole series of CalCOFI cruises,
which relate to plankton other than fish eggs and
larvae, are in the form of displacement volumes of
unsorted samples (Smith 1971). The marked
coherence between the various taxonomic cate-
gories suggests that these data can be expected to
produce estimates of long-term variations which
indicate real changes in the abundance of the
zooplankton. Such data cannot, however, reflect
the geographical differentiation within the zoo-
plankton, and this imposes a limit, to the extent to
which they can be used, to provide the basis for the
examination of the influences of a complex of
environmental factors of the kind suggested by
this study as playing an important role in
determining the year-to-year fluctuations in the
plankton.

The taxonomic categories used in this study
were selected by Isaacs et al. (1969) to represent
the plankton as food for fish. I have used them to
represent fluctuations in the zooplankton as such
for the 1955-59 period.

For future studies the only definitive method of
selecting taxa to represent year-to-year changes
in the zooplankton is by trial and error: there are,
moreover, numerous possibilities, and the labor
involved would be prohibitive if some compromise
is not made. It is indicated above that there is a
tendency for taxa which have similar geograph-
ical distributions also to show similar year-to-
year fluctuations in abundance. As a first approxi-
mation, this fact might be used as a guide to the
selection of representative categories. It is implicit
that each selected category should be geographi-
cally homogeneous, and the set of categories should
cover the full range of geographical distributions.

It is probable that the species is the highest
taxon for which geographical homogeneity can be
assumed, and even here there may be some species
which have geographically differentiated races.
Isaacs et al. (1969) gave an estimate of about 550

367

FISHERY BULLETIN: VOL. 75, NO. 2

species found, or likely to be found, in the
zooplankton of the CalCOFI survey area. Allow-
ing for the fact that somewhere between one-half
and three-quarters of these species will probably
occur infrequently in samples, the labor involved
in routinely analyzing for this number of species is
very considerable. The geographical distributions
of species belonging to many of the major taxa
within the zooplankton have been studied and
published in the CalCOFI Atlas series which
could provide the basis for the selection of a
limited number of species which will represent the
range of geographical distributions in the survey
area and, hopefully, will provide a good represen-
tation of the range of year-to-year fluctuations in
abundance.

ACKNOWLEDGMENTS

My thanks are due to Brian Rothschild,
Director, Southwest Fisheries Center, National
Marine Fisheries Service, NOAA, for making
available to me the facilities of the La Jolla
Laboratory. I also thank J. D. Isaacs for furnish-
ing unpublished data. Nancy Wiley and Dorothy
Roll were of great assistance in the computations
involved in the study and John G. Wyllie helped
with some data problems. Finally I must thank
Paul E. Smith whose knowledge of the California
Current region and of the CalCOFI survey was
invaluable. My visit to the La Jolla Laboratory
was supported by the U.K. Natural Environment
Research Council.

LITERATURE CITED

AIILSTROM, E. H.

1954. Distribution and abundance of egg and larval popu-
lations of the Pacific sardine. U.S. Fish Wildl. Serv.,
Fish. Bull. 56:83-140.
BAKUN. A.

1973. Coastal upwelling indices, west coast of North
America, 1946-71. U.S. Dep. Commer., NOAA Tech.
Rep. NMFS SSRF-671, 103 p.
B.JERKNES, J.

1966. Survey of El Nino 1957-58 in its relation to tropical
Pacific meteorology. [In Engl, and Span] Inter- Am.
Trap. Tuna Comm. Bull. 12:25-86.
BRINTON, E.

1962. The distribution of Pacific euphausiids. Bull.
Scripps Inst. Oceanogr., Univ. Calif. 8:51-270.
FAVORITE, F., AND D. R. McLAIN.

1973. Coherence in transpacific movements of positive and

negative anomalies of sea surface temperature, 1953-

60. Nature (Lond.) 244:139-143.
FLEMINGER, A.

1964. Distributional atlas of calanoid copepods in the

California Current region, Part 1. Calif. Coop. Oceanic

Fish. Invest. Atlas 2, 313 p.
FLEMINGER. A., J. D. ISAACS. AND J. G. WYLLIE.

1974. Zooplankton biomass measurements from CalCOFI

Cruises of July 1955 to 1959 and remarks on comparison

with results from October, January and April cruises of

1955 to 1959. Calif. Coop. Oceanic Fish Invest. Atlas 21,

118 p.
FOFONOFF, N. P.

1962. Machine computations of mass transport in the
North Pacific Ocean. J. Fish. Res. Board Can. 19:1121-
1141.

ISAACS. J. D., A. FLEMINGER, AND J. K. MILLER.

1969. Distributional atlas of zooplankton biomass in the
California Current region: spring and fall 1955-1959.
Calif. Coop. Oceanic Fish. Invest. Atlas 10, 252 p.
1971. Distributional atlas of zooplankton biomass in the
California Current region: winter 1955-1959. Calif.
Coop. Oceanic Fish. Invest. Atlas 14, 122 p.
KENDALL, M. G.

1957. A course on multivariate analysis. Charles Griffin,
Lond., 136 p.
LONGHURST. A. R.

1967. The pelagic phase of Pleuroncodes planipes
Stimpson (Crustacea, Galatheidae) in the California Cur-
rent. Calif. Coop. Oceanic Fish. Invest. Rep. 11:142-154.
MCGOWAN. J. A.

1971. Oceanic biogeography of the Pacific. In B. M. Fun-
nel and W. R. Riedel (editors), The micropaleontology of
oceans, p. 3-74. Cambridge Univ. Press.

MARINE RESEARCH COMMITTEE.

1957. The marine research committee, 1947-55. Calif.
Coop. Oceanic Fish. Invest. Prog. Rep. 1953-1955, p. 7-9.

Peterson, W. T.

1973. Upwelling indices and annual catches of Dungeness
crab, Cancer magister, along the west coast of the United
States. Fish. Bull., U.S. 71:902-910.
SAUR, J. F. T.

1972. Monthly sea level differences between the Hawaiian
Islands and the California coast. Fish. Bull., U.S.
70:619-636.

SETTE, O. E., AND J. D. ISAACS (EDITORS).

1960. Part II. Symposium on the changing Pacific Ocean in
1957 and 1958. Calif. Coop. Oceanic Fish. Invest. Rep.
7:13-217.

Smith, p. e.

1971. Distributional atlas of zooplankton volume in the
California Current region, 1951 through 1966. Calif.
Coop. Oceanic Fish. Invest. Atlas 13, 144 p.
THRAILKILL, J. R.

1963. Zooplankton volumes off the Pacific coast.
1959. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 414,
77 p.

WICKETT, W. P.

1967. Ekman transport and zooplankton concentration in
the North Pacific Ocean. J. Fish. Res. Board Can.
24:581-594.

368

POPULATION BIOLOGY OF PACIFIC OCEAN PERCH, SEBASTES

ALUTUS, STOCKS IN THE WASHINGTON-QUEEN CHARLOTTE

SOUND REGION, AND THEIR RESPONSE TO FISHING1

Donald R. Gunderson2

ABSTRACT

Production and catch per unit effort of Pacific ocean perch, Sebastes alutus, stocks in the Washington-
Queen Charlotte Sound region have declined drastically in recent years, largely as a result of Soviet
and Japanese exploitation during 1966-69. In the region off Washington and southern Vancouver
Island, production declined from 39,000 metric tons in 1967 to 6,000 metric tons in 1969, and catch per
hour declined 45% during the same period. Pacific ocean perch are ovoviviparous, and so their
populations lack the resilience of highly fecund, oviparous groups such as the gadoids. Their ability to
maintain even current levels of abundance is uncertain.

Age composition, growth rates, and mortality rates were estimated for two separate stocks occupying
this region: one in Queen Charlotte Sound, B.C., and one occupying the area off northern Washington
and southern Vancouver Island. Instantaneous rate of natural mortality was estimated to lie between
0.1 and 0.2. Recruitment to the fishing grounds is not complete until age 16 and the proportion of each
age group vulnerable to fishing was estimated by stock for age groups 10 (0.31-0.35) through 15
(0.87-0.94).

Age at sexual maturity «o.5o' differed between stocks, ranging from 9 to 11 yr for females and 6 to 7
yr for males. Fecundity was determined for several females, and the fecundity-length and fecundity-
age relationships discussed. For a variety of reasons, all fecundity estimates were regarded as tenta-
tive, bearing a rather uncertain relationship to the number of larvae released.

The effects of fishing on stocks of Pacific ocean perch were examined through an approach similar to
the yield per recruit analysis that is commonly used in stock assessment, although the computer
program developed for this study enabled estimation of exploitable biomass and. population fecundity
as well as yield per recruit.

Compensatory mechanisms that would tend to restore population fecundity and recruitment to
preexploitation levels were discussed, and the limits of some of these mechanisms (density dependent
growth and earlier sexual maturation) were explored with the computer program mentioned previ-
ously. The results of this analysis suggested that past levels of exploitation went far beyond those levels
that could be sustained by Pacific ocean perch stocks on a long-term basis. It was coucluded that future
rates of exploitation should be regulated so that the annual catch never exceeds 10% of the mean stock
biomass on hand during the year.

Pacific ocean perch, Sebastes alutus (Gilbert), are
found throughout the northern Pacific, from
California to the Bering Sea, and as far southwest
as the Kurile Islands. Murphy (1968) has shown
that species with several reproductive age-groups
are well adapted to unpredictable levels of larval
mortality, and Pacific ocean perch seem to be a
prime example of this line of evolution. Twenty-
year-olds are common in this species, and there
are 10 or more reproductive age-groups of sig-
nificance. In the unexploited state, large standing

^ased on a dissertation submitted in partial fulfillment of the
requirements for the Ph.D. degree, University of Washington.

2Washington State Department of Fisheries, Fisheries Center,
University of Washington, Seattle; present address: Northwest
Fisheries Center, National Marine Fisheries Service, NOAA,
2725 Montlake Blvd. East, Seattle, WA 98112.

stocks of S. alutus accumulated, furnishing a sub-
stantial hedge against uncertain larval survival.
Quast (1972) estimated the original catchable
biomass of S. alutus off western North America to
be roughly 1,750,000 metric tons.

Commercial fishing for S. alutus was initiated
in 1946 by U.S. trawlers operating off central Ore-
gon (Alverson and Westrheim 1961). Develop-
ment proceeded slowly, but by 1955, United States
and Canadian vessels were harvesting S. alutus
from as far north as Queen Charlotte Sound, B.C.
Westrheim et al. (1972) have characterized the
North American trawl fishery for Pacific ocean
perch as undergoing a short development period
(1946-51) with low production, a longer period
(1953-60) of moderate production, and a short
period (1961-66) of increasing production. Since

Manuscript accepted November 1976.
FISHERY BULLETIN: VOL. 75, NO. 2, 1977.

369

FISHERY BULLETIN: VOL. 75, NO. 2

1966, Pacific ocean perch production has fallen
drastically in several areas fished by these North
American trawlers, largely because of excessive
catches by Japanese and Soviet fleets.

Japanese and Soviet trawl fisheries for Pacific
ocean perch began in the Bering Sea about 1960
and expanded southward into the eastern Gulf of
Alaska in 1963. The Soviet fleet operated
throughout the Queen Charlotte Sound-Oregon
region by 1965, and they were joined by Japanese
trawlers in 1966. Catches from the Oregon-Queen
Charlotte Sound region were quite high initially
(Figures 1 through 3), but the stocks were far too
limited to sustain these harvests. By 1969, S.
alutus stocks were severely depleted throughout
the Oregon- Vancouver Island region (Figures 1,
2). Production in the International North Pacific
Fisheries Commission (INPFC) Vancouver and
Columbia areas plummeted from 39,000 metric
tons in 1967 to 6,000 metric tons in 1969 (an 85%
decline), and catch per hour by North American
trawlers declined 45% during the same period
(Westrheim et al. 1972). Data on catch per unit
effort (CPUE) suggest that the exploitable
biomass of Pacific ocean perch in the Vancouver-

'56

'60

'65

'70

1 1 1 1 1 1 1

I I I I I

CPUE

/ \ US

\^_n -

_ 20

E
n
O

CATCH

JAPAN

U S.S R

° 10

U.S.

0.6

0.4

0.2 <->

Columbia region has changed little since 1969,
despite the fact that a series of relatively strong
year classes have recruited to the fishery.

Pacific ocean perch stocks in Queen Charlotte
Sound were affected less drastically by fishing
than those in the Oregon-Vancouver Island re-
gion. Biomass estimates and CPUE data (Wes-
trheim et al. 1972) indicated that S. alutus were
initially more abundant in the former area and
that they did not undergo such intensive exploita-
tion. During 1966-68, production declined 50%
while CPUE of Washington trawlers declined
36%. Fishing effort was reduced substantially
after March 1971, when most of Queen Charlotte
Sound was declared to be an exclusive Canadian
fishing zone. Bilateral agreements between
Canada and the United States allowed the tradi-
tional United States fishery for S. alutus to con-
tinue, but Japanese and Soviet fishing was prohib-
ited. Recent information, however, indicates that
in 1974, large catches of Queen Charlotte Sound
Pacific ocean perch were made by Japanese vessels

E
m
O

£ io

CPUE

CATCH

JAPAN
U.S.S.R

CANADA - U.S.

60 '65

YEAR

'70

0.8

0.6

0.4

0.2

FIGURE 1.— Catch and CPUE data for Pacific ocean perch in the
INPFC Columbia area (from Westrheim et al. 1972).

370

FIGURE 2.— Catch and CPUE data for Pacific ocean perch in the
INPFC Vancouver Area (from Westrheim et al. 1972).

GUNDERSON: POPULATION BIOLOGY OF SEBASTES ALUTUS
'56 '60 '65 '70

YEAR

FIGURE 3.— Catch and CPUE data for Pacific ocean perch in
Queen Charlotte Sound (from Westrheim et al. 1972).

operating outside the Canadian fishing zone
(Gunderson et al. 1977).

Both biomass and longevity have been drastic-
ally reduced for Pacific ocean perch throughout
the Washington-Queen Charlotte Sound region,
and it seems unlikely that the current situation
will be stable over the long term. The purpose of
this study is to outline the population biology of S.
alutus stocks in the Washington-Queen Charlotte
Sound area and to examine their immediate and
long-term response to different harvesting
strategies.

METHODS AND MATERIALS

Delineation of Stocks

Two stocks of S. alutus will be examined and
contrasted: one in Queen Charlotte Sound (QCS)
and one inhabiting the waters off northern
Washington and southern Vancouver Island

(WVI).

The QCS stock is contained wholly within
Queen Charlotte Sound. North of lat. 52°N, the
continental shelf off western Graham Island is
quite narrow and there is little available habitat
for S. alutus. Recent work by Westrheim3 has
shown that previously unexploited stocks exist in
Moresby Gully, an undersea canyon extending
into Hecate Strait, north of lat. 52°N. The Triangle
Islands form a definite southern limit for this
stock, since Pacific ocean perch catches im-
mediately south of these islands are almost neg-
ligible. Pacific Marine Fisheries Commission
(PMFC) statistical areas 5 A and 5B offer a con-
venient unit for studying this stock.

The northern limit of the WVI stock lies some-
where near the middle of Vancouver Island and,
for practical reasons, this was represented by the
northern boundary of PMFC area 3C (lat. 49°N).
Pacific ocean perch catches in PMFC area 3D have
been quite limited historically ( Figure 4), and dur-
ing 1966-72, only 13% of the Washington landings
in the INPFC Vancouver area came from there
(Table 1).

The southern limit of the WVI stock is more
difficult to establish. Since Pacific ocean perch
catches by Washington trawlers fall off sharply
south of PMFC area 3B-3C (lat. 47°20'N), this was
the boundary used throughout this study. This
boundary, as well as the others used in this report,
is in basic agreement with Snytko (1971), whose

3Westrheim, S. J. 1974 Echo-sounder and trawl survey of
Queen Charlotte Sound and southern Hecate Strait, 1971-73.
Fish. Res. Board Can. Manuscr. Rep. 1307, 43 p.

55'

50'

4 5'

40°

140° 130°

54°30 -/

[5C
•50""

CHARLOTTE % 2 M

52*00-

5A 5B2,804^

50° 30'

30 596"

VANCOUVER «9'oo'--

J6-3C 2,291
4 7° 30'

47-20

1,079

COLUMBIA

44*18'

2B 488

43°00 ^™

EUREKA |4

40°30'

I20°W

55*

50«

45°

40°

140°

130°

120°W

FIGURE 4. — Chart of the northeastern Pacific Ocean showing
INPFC and PMFC statistical areas used in this study. Mean
annual Pacific ocean perch catch (metric tons) during 1960-65
(heavy lettering) is shown for each PMFC Area.

371

FISHERY BULLETIN: VOL. 75, NO. 2

TABLE 1. — Catches (in metric tons) of Pacific ocean perch by
different components of the international trawl fleet, 1966-72.

United States

Washington

and Canada
3B-3D 5A-5B

All rv
3B-3D

ations

Year

3B-3C

3B-3D

5A-5B

1966

2,104

2,283

5.616

2,358

8,252

16.358

27,054

1967

701

783

5,341

805

5,745

17,746

26,741

1968

459

526

4,787

552

6,051

9,905

13,492

1969

462

573

4.992

583

6,628

4,513

12,951

1970

980

1,208

4.308

1,955

6,077

4,955

9,854

1971

638

718

2,925

1,155

4,165

4,138

4,867

1972

419

504

3.364

624

5,561

3,082

7,842

Total

5,763

6,595

31,333

8,032

42.479

60,697 102,801

research cruise data suggested that the two most
significant aggregations of S. alutus in the Van-
couver-Oregon region were found at lat. 48°-50°N
and lat. 46°-47°N. For all practical purposes then,
PMFC Statistical areas 3B and 3C offer a conve-
nient unit for studying the WVI stock.

Data Employed

Production records used in this study came from
the Washington State Department of Fisheries,
PMFC, INPFC, and from data furnished during
U.S.-U.S.S.R. scientific meetings.

Landings by Washington trawlers made up a
relatively small proportion of the total interna-
tional landings during the 1966-72 study period,
but the quality of their production records is such
that the CPUE data from this fleet offer the best
available index of stock abundance. During
1966-72, the Washington landings made up 30% of
the total international catch from Queen Char-
lotte Sound, and 11% of the catch from the INPFC
Vancouver area (Table 1). Washington trawlers
accounted for the bulk of the North American
landings in these areas, however, landing 74% of
the Pacific ocean perch caught in Queen Charlotte
Sound and 82% of those from the INPFC Van-
couver area during 1966-72.

Most of the data on age composition (as deter-
mined from otoliths), length composition, and
maturity were obtained by sampling the catches
landed by Washington trawlers and were collected
during 1967-72. Data from research vessel cruises
off Washington and Oregon were used to estimate
growth rates and fecundity-length relationships
for the WVI stock.

MIGRATIONS AND AVAILABILITY

General Features of the Life History
Extensive investigations into the life history of

S. alutus have been carried out in the Bering Sea
(Paraketsov 1963; Pautov 1972; Chikuni 1975),
Gulf of Alaska (Lyubimova 1963, 1964, 1965;
Fadeev 1968; Chikuni 1975), and in the Queen
Charlotte Sound-Oregon region (Alverson and
Westrheim 1961; Westrheim 1970, 1973, 1975;
Gunderson 1971, 1974; Snytko 1971). These
studies have shown that there are several basic
similarities in the life history and biology of
Pacific ocean perch throughout its range.

Age and growth analyses have shown that S.
alutus attain sexual maturity relatively late in
life (6-10 yr), grow slowly, and are long-lived. In
lightly fished stocks, S. alutus may reach an age of
30 yr (Alverson and Westrheim 1961; Paraketsov
1963).

Sebastes alutus is an ovoviviparous species,
with three distinct phases in its reproductive cy-
cle. These are: mating (when spermatozoa are
transferred from males to females), fertilization
(when the ova are actually fertilized), and spawn-
ing (when the larvae are released).

Well-defined bathymetric migrations occur in
all areas. Pacific ocean perch occupy relatively
shallow water during the summer feeding period,
then move to deep water during winter. The
depths inhabited seem to vary little throughout
the geographic range, despite significant differ-
ences in thermal conditions (Table 2). Mating oc-
curs shortly before or during migration from shal-
low water, but fertilization and embryo release do
not occur until the fish are in deep water.

The larvae of S. alutus are pelagic and do not
settle into a demersal existence until 2-3 yr old.
Juveniles and young adults are confined to the
shallowest portions of the adult bathymetric
range, so that size and age composition vary
widely at different depths.

Despite these common characteristics, there are
substantial geographic differences in life history
and migration patterns, even within the relatively
restricted region dealt with in this study. For this
reason, migration patterns, seasonal availability,
age composition, growth, age at maturity, and

TABLE 2. — Depth and temperature characteristics of Pacific
ocean perch habitat.

Depths of

maximum

abundance

(m)

Temperat
Range

jre (°C)

Area

Summer

Winter

Optimum

Vancouver-Oregon

(Snytko 1971)

200-300

350-450

4.0-9.5

6-8

Gulf of Alaska

(Lyubimova 1965)

1 80-250

250-420

2.5-6.5

3-5

Bering Sea

(Pautov 1972)

150-350

350-450

1.0-6.0

3-4

372

GUNDERSON: POPULATION BIOLOGY OF SEBASTES ALUTUS

fecundity must be discussed separately for the
QCS and WVI stocks.

Migrations and Availability Within
the Study Area

Availability of S. alutus fluctuates widely over
short periods of time. Short-term fluctuations in
availability were quite evident during a series of
2- to 3-wk research cruises off the Washington
coast (Gunderson 1974), and masked any long-
term changes in biomass that occurred during
1968-72.

For this reason, catch and CPUE data can be
used to study migration patterns and seasonal
availability only if they are based on a large quan-
tity of trawling effort, carried out more or less
continuously. The data from the Washington
trawl fleet seem well suited to this purpose, since
these trawlers spend a great deal of time searching
out and catching Pacific ocean perch. Sebastes
alutus is frequently the target species for this fleet,
and made up 29% of its total coastal landings dur-
ing 1967-71.

In this section, catch and effort data from the
Washington trawl fleet will be used to describe
migration patterns and seasonal trends in the
availability of S. alutus. Data on sex and length
composition of the catch will also be brought into
the analysis, since it is difficult to interpret trends
in availability without them.

Queen Charlotte Sound
Seasonal Patterns for the Region

The continental shelf is steep and untrawlable
seaward of 150 fm (274 m) in Queen Charlotte
Sound, so the fish in this area are inaccessible to
trawlers when they move into deep water
(January-April). Examination of gonads indicates
that spawning occurs in March (Gunderson 1971),
but there is no certainty as to where this occurs.
Few fish are caught during January-April, and
virtually all of these are males (Figure 5) that do
not participate in the spawning migration.

Males precede females in their return from win-
tering areas, and when the fishery first begins in
earnest (May), males constitute 68% of the catch.
The availability of females increases sharply after
May, and by July they dominate the catches.

During June- August, Pacific ocean perch are at
the shallowest point in their bathymetric cycle.
Catches are low during this period, and large
quantities offish 35 cm or smaller are landed (Fig-
ure 6).

Both catch and CPUE rise in September, and
although the mean depth of catch is about the
same as in July and August, there is a sharp in-
crease in the proportion offish larger than 35 cm in
the catch. Aggregations of large adults must sud-
denly become available during September, prob-
ably because mating activities are beginning.

QUEEN CHARLOTTE SOUND

WASHINGTON -VANCOUVER [S

| 500- J05-
i *

FIGURE 5. — Mean monthly catch, catch
per hour, mean depth of catch, and sex
ratio for the Washington trawl fleet dur-
ing 1967-71. Data for the QCS and WVI
stocks of Pacific ocean perch are pre-
sented separately.

Jon-Apr Moy Jun Jul Aug. Sep Oct Nov Dec Jon Feb Mor Apr May Jun Jul Aug Sep Od Now Dec

373

FISHERY BULLETIN: VOL. 75, NO. 2

20-

20-
10-

20-
10

20-

- 10

20
10
0

20-

10-
0

20-

10-
0

20-

20-
10
0

N.499I746) _^fj| | [^

N = I644(349)

!!4ifrrrffTTK.

"^mnrm^

!!!Utitt1T1 1 IT-i-^

N=3633(420)

^T^tTTTlh^

"^^fTfTlTlTk. .

^rfTTTTffJTK

^^mTrm^!1

N-- 2240(291)

N=2762 (376)

-^-rrTTTTrrrfTTTT-u ,

N=2I73(469)

^^rrrrrrnTn-h_

^-r-rfTTTT

N=3504(5I6)

TflfTlTK. .

N=280l(561

20 25 30 35 40 45 20 25 30 35 40 45 50

Length (cm) Length (cm)

FIGURE 6. — Size composition of 1967-71 Pacific ocean perch
catches from Queen Charlotte Sound, by month. Mean numbers
caught per hour during 1967-71 are shown in parentheses.

Previous work (Gunderson 1972) has shown that
these aggregations are faster growing, but only
slightly older, than the rest of the stock.

Pacific ocean perch move into progressively
deeper water during October-December, as they
return to deepwater spawning areas. Catch per
hour remains high during this period, but de-
teriorating weather conditions force a decline in
trawling effort and landings.

Because catch, CPUE, sex ratio, length compo-
sition, and age composition all varied with season,
the data from different time periods were treated
independently in much of the later analysis. The

time periods utilized were January-April, May,
June-August, and September-December.

Seasonal Patterns for Specific Grounds

The geographic distribution of the catch varied
from month to month (Figure 7) and there is a
possibility that between-ground variations in size
composition could contribute to the results shown
in Figure 6. Length and age composition data were
analyzed by fishing ground (Figure 8) to examine
this point further. To insure that the data used
were as typical as possible of the grounds in ques-
tion, only samples from characteristic fishing
depths were chosen for this analysis. The 1967-71
mean depth of catch was computed for each month
and ground in question, and only those samples
whose range was within 15 fm (27 m) of this mean
were analyzed.

The results (Figure 9) show that within a given
time period, length composition differed some-
what between grounds, but the differences showed
no consistent, predictable pattern. There was no
ground that could always be characterized as hav-
ing larger or smaller fish than the other grounds.
Size composition data for SE Corner, SW Corner,
and Triangle grounds, the three major fishing
grounds, showed only slight between-ground
heterogeneity within any given time period.

Washington-Vancouver Island

Unlike Queen Charlotte Sound where the con-
tinental shelf drops off abruptly past 150 fm (274
m), a wide range of depths can be fished off
Washington and Vancouver Island (Figure 5).
Trawlers can follow fish in this area into deep-
water spawning areas, and exploit them year
around. The year can be divided into a

10 30 50 70 90

Percent

10 30 10 30

10 30 10 30 10 30 50

Tnonqle

374

Toloh

rzzn

Jan-Mar

Apr May Jun

Jul

Aug Sep

Oct

Nov

Dec

FIGURE 7.— Distribution of 1967-71
Pacific ocean perch catch from Queen
Charlotte Sound by month and fishing
ground. Data on distribution by ground
were derived from the portion of the
catch for which fishermen interviews
were available. The Virgin Rocks-
Mexicana ground includes Virgin Rocks
and all grounds east of the Cape Scott
ground.

Gl'NDERSON: POPULATION BIOLOGY OK SKBASTKS AU'Tl'S

QUEEN
CHARLOTTE
SOUND

S. E. Corner - S.E. Edge

PACIFIC
OCEAN

Triangle Island

• " N /

128°

^o>

A-

■50 fathoms (9i m)
100 fathoms 083 m)
Fishing grounds

129°

FIGURE 8. — Major Pacific ocean perch fishing grounds in Queen Charlotte Sound, B.C.

November-May period when most of the fish are in
deepwater spawning areas, and a June-October
period when they are in shallow water. Mean
depth of catch is 140-180 fm (256-329 m) during
the November-May period, and 120-130 fm (219-
238 m) during June-October.

Seasonal variability in the biological composi-
tion of the catch is less significant than in Queen
Charlotte Sound, since the sex ratio is close to 50%
males all year. Data on the size composition of the
catch was quite limited during certain months,
but size composition generally seemed to depend

on the depths at which the fishery was operating.
The proportion of small fish (35 cm or smaller) in
the landings was highest during the shallow-
water fishery, and decreased during November-
May (Figure 10).

Considering the wide differences in the mag-
nitude of the landings between Washington-
Vancouver Island and Queen Charlotte Sound,
CPUE levels are surprisingly similar (Figure 5).
Results of research cruises have shown that the
availability of Pacific ocean perch varies widely in
the Washington- Vancouver Island region (Gun-

375

FISHERY BULLETIN: VOL. 75, NO. 2

April-May

June-Aug.

Sept.- Dec

Virgin |Q
Rocks IU

N=2378

FIGURE 9.— Size composition of 1966-72 Pacific ocean perch
catches in Queen Charlotte Sound, by fishing ground and season.

derson 1974), and fishermen probably restrict
their efforts to periods of high availability. If this
is the case, the relative levels of monthly catch
give the best index of stock availability. Peak
availability occurs during March-April (near the
time of embryo release) and in August-December
(near the mating period). This pattern of seasonal
availability agrees well with results from previous
studies of the WVI stock (Gunderson 1971; Snytko
1971).

AGE-LENGTH RELATIONSHIPS

Queen Charlotte Sound

The age-length relationship in any sample of
Pacific ocean perch from Queen Charlotte Sound is
influenced by the availability of large, fast-
growing fish, the depth at which the fish were
captured, and the proportion of the annual growth
completed. In order to examine the relative impor-
tance of these factors, analysis similar to that out-
lined by Gunderson (1974) was employed.

This involved fitting observed mean length at
age data to the von Bertalanffy growth model,

lt =L«(1 - exp-K(t - *0))

20
10-

0-
20-
10-

0-
20
10-

20-

fc -

«j 0

£ 20
10-

0
20
10

0
20-
10-

"-598 ,.rJ\ 1 Why,

N = I225

frfii-L

"W .

jfl

tthCL

SEP

Trrfl^

urn

OCT

"h-TUn

-^RTrrfrrH,

DEC

"■gy^mfflTTL ,

30 40

Length (cm)

.^TliTTr^636

N=I95

^rMh^^»

-AiWhuyrTW^--'

-^iihH^Th^-^

jf.

"U^-HtTU n"

-^flTh^fTr^"701

30 40 50

40
Length (cm)

FIGURE 10. — Size composition in 1967-71 Pacific ocean perch
catches from Washington-Vancouver Island, by month.

376

where lt = length of fish in centimeters at t years
Lx = theoretical asymptotic length
K = constant expressing the rate of ap-
proach to Lx
£0 = theoretical age at which I, = 0.

The least squares technique of Tomlinson and Ab-
ramson (1961) was employed to do this, and a
separate age-length relationship was computed
for each combination of fishing ground and season
(April-May, June-August, and September-
December) where adequate data were available.
All comparisons of the age-length relationship at
different grounds and seasons could then be made
by comparing fitted length at some common age
(age 15 in this case).

The results (Figure 11) show that the age-length
relation is more dependent on the availability of
fast-growing fish to bottom trawls than on any
other factor examined. The main line of evidence
supporting this is the close correspondence be-
tween changes in fitted length at age 15 (Figure
11) and seasonal changes in size composition (Fig-
ure 9), a situation that would be expected if both
depend on the availability of large, fast-growing

GUNDERSON: POPULATION BIOLOGY OF SEBASTES ALUTUS

43-1

g 40-

38-

.^-o

FEMALES ^o °

MALES

Apr-May ■
Jun-Aug -
Sep Dec -

NE
Corner

SE
Corner

SW
Corner

CaPe Triangle Vlrl3'n
Scott y Rocks

FIGURE 11. — Fitted length at age 15 for Pacific ocean perch in
Queen Charlotte Sound ( 1966-72), by fishing ground, season, and
sex.

fish. Both age-length and size composition data
indicate that aggregations of these fish are least
available during April and May, and that it is only
during September-December that they are fully
available on all fishing grounds. This general pat-
tern seemed to hold throughout Queen Charlotte
Sound, at least on the major fishing grounds. In
some instances, however, availability of large,
fast-growing fish was unusually high on a rela-
tively minor fishing ground. This seemed to be the
case at NE Corner during May and Cape Scott
during June- August (Figures 9, 11).

Sampling problems caused by disporportionate
fishing intensity in extremes of the bathymetric
range are usually insignificant compared with the
problems caused by differential availability. Re-
search cruises have shown that mean length at
age decreases as depth increases (S. J. Westrheim,
pers. commun.), so that fitted length at age 15
should either remain constant (if fishery shifts in
response to stock location) or decrease (if fishery
shift is independent of stock location) as the
fishery shifts to deeper water during September-
December (Figure 5). Instead, mean length at age
actually increases during September-December
(Figure 11) because this is the season when large,
fast-growing fish are most available.

Considering all sources of data on catch, CPUE,
and biological composition of the landings, it is
apparent that there is a significant increase in the
size of the exploitable population inhabiting
Queen Charlotte Sound during September-
December. Age-length data collected during

January-August consequently apply to only a
fraction of the known population in Queen Char-
lotte Sound. If it is assumed that all Pacific ocean
perch are fully vulnerable to fishing by fall, how-
ever, the September-December market sampling
data can be taken as representative of the exploit-
able segment of the QCS stock.

Consequently, 1967-71 age-length data from
September-December market samples were used
to estimate growth parameters for the QCS stock.
Queen Charlotte Sound was treated as a unit,
mean length at each age was determined by sex,
and the resulting data were fitted to the von Ber-
talanffy growth model. Both the original data and
fitted mean length at age are shown in Table 3.

Washington-Vancouver Island

Availability of Pacific ocean perch in this region
influences the age-length relationship, but in a
different manner than in Queen Charlotte Sound.
Results from research surveys off northern
Washington (Gunderson 1974) suggest that mean
length at age actually decreases with increasing
availability, rather than increasing. The highest
rates of catch in this region were obtained when
aggregations of large, old, slow-growing fish were
most available.

The WVI and QCS stocks also differ substan-
tially in the degree to which mean length at age
varies with depth. In contrast to Queen Charlotte
Sound, mean length at age has been shown to
decrease sharply as depth increases off Wash-
ington and Vancouver Island (Westrheim 1973;
Gunderson 1974). The decline is so sharp, in fact,
that Westrheim (1973) has suggested that there
are separate shallow and deepwater stocks in this
region.

It is clear, then, that both depth of fishing and
availability must be taken into consideration in
order to arrive at an age-length relationship that
characterizes the WVI stock. Research cruise data
obtained off the coast of northern Washington
(Gunderson 1974) are particularly well suited to
do this, since age-length relationships and avail-
ability were systematically observed throughout
the bathymetric range. Availability varied widely
during these cruises, and, as previously men-
tioned, this phenomenon masked any long-term
changes that occurred during 1968-72. Availabil-
ity was maximal during the July 1972 cruise,
however, and the results from that cruise were
used to represent growth in the WVI stock.

377

FISHERY BULLETIN: VOL. 75, NO. 2

TABLE 3. — Number of age-length observations, mean length (centimeters), and fitted length at each age for QCS and WVI stocks

of Pacific Ocean perch.

QCS stock

WVI stock

Males

Females

Males

Females

Number of

Mean

Fitted

Number of

Mean

Fitted

Number of

Mean

Fitted

Number of

Mean

Fitted

Age

observations

length

observations

length

observations

length

observations

length

18.0

18.1

18.5

19.1

22.0

21.2

22.0

21.6

23.7

23 9

24.5

24.0

27.0

26.6

26.2

26.0

25.8

26.3

26.5

26.1

29.1

28.6

29.4

28.4

28 3

284

28.1

28.0

30.0

305

30.6

29.6

30.2

28.5

29.8

164

31.6

32.2

124

32.1

32.6

32.3

31.8

31.4

186

33.1

33.6

173

33.5

34.3

33.2

32.9

219

34.4

35.0

213

34.8

35.9

123

34.2

34.4

34.6

34.3

233

36.1

179

36.3

37.2

172

35.5

123

35.7

35.5

411

37.4

37.1

253

383

38.5

363

36.5

36.6

463

38.5

380

374

40.0

396

37.0

37.3

37.6

417

39.4

38.9

459

41.2

40.6

38.0

38.6

308

40.1

39.6

468

42.2

41.4

389

38.6

39.0

39.4

203

40.5

40.2

377

43.2

42.2

39.7

39.2

40.8

40.2

116

41.1

40.8

308

43.6

42.9

40.2

39.7

41.3

41.0

41 1

41.3

186

44.0

43.6

40.8

40.1

41.7

41.6

41.7

115

44.4

44.1

41.1

40.5

42.2

41.9

42.1

44.2

44.6

41.3

40.8

42.4

42.7

41.9

42.5

45.1

45.0

41.4

41.1

43.7

43.2

45.0

45.4

39.0

41.4

43.6

43.7

45.3

45.8

43.9

44.1

45.6

46.1

44.5

von

Bertalanffy growth function parameters

45.25

48.75

43.15

4847

0.1192

0.1135

0 1320

0.0908

-2.4157

-1.7159

-2.1186

-3.5041

SEof

estimate

0.44

0.64

0.68

0.45

Data from the 120-, 160-, and 200-fm (219-, 293-,
and 366-m) sampling stations were combined by
weighting the mean length at each age by the
catch rate of Pacific ocean perch in that depth
stratum and arriving at an overall weighted mean
length for each age group (Table 3). The calcula-
tions were carried out separately for males and
females, and the resulting age-length data were
then fitted to the von Bertalanffy growth model
using the technique described previously.

The results (Table 3) suggest that fish off
Washington grow somewhat slower than those in
Queen Charlotte Sound. In order for the results
from the two stocks to be strictly comparable,
however, several research cruises should have
been made in Queen Charlotte Sound during
September-December. The age-length data from
those cruises where availability was maximal
could then have been weighted in proportion to the
catch rate for each depth stratum, as was done for
the WVI stock. If fishermen effectively "sample" in
proportion to abundance, however, the results
from commercial fisheries data should agree well
with those from research cruises.

FIGURE 12. — Changes in the size composition (sexes combined)
of Pacific ocean perch in commercial catches, 1956-73. N =
number of fish sampled.

ANNUAL CHANGES IN SIZE AND
AGE COMPOSITION

Size Composition

Queen Charlotte Sound

The Washington State Department of Fisheries
has obtained size composition data on landings
from Queen Charlotte Sound since 1956. Collec-
tion of such data was limited and sporadic prior to

QUEEN CHARLOTTE SOUND

WASHINGTON -VANCOUVER IS

378

GUNDERSON: POPULATION BIOLOGY OF SERASTES ALUTUS

1967, but a good series of data, taken over the
entire year, is available for each year during
1967-73.

Because a limited number of samples was avail-
able during 1956-66, it was frequently necessary
to pool data from adjacent years when examining
temporal trends in size composition. The results
(Figure 12) furnish the only available estimates of
the size composition of Pacific ocean perch in
1956-66 Washington trawl landings.

Collection of biological data was quite intensive
during 1967-73, and it was possible to make al-
lowances for the extensive seasonal changes in
length and sex composition that occur in Queen
Charlotte Sound. The Sound was treated as a
single geographic unit, but size composition was
determined separately for each of the four time
strata previously discussed (January-April, May,
June- August, and September-December). If few
landings were made in one of these strata, it was
combined with an adjacent stratum, and biological
data from the latter were used to represent it.
Table 4 shows the time strata used for each year's
catch data, the landings in each stratum, and the
amount of biological data collected.

Males and females differ in relative abundance
and size composition, so they were treated sepa-
rately. Mean weights of males and females in each
time stratum were obtained by employing the

TABLE 4. — Time strata used for analysis of 1966-73 size and
age composition data from Queen Charlotte Sound. Pacific
ocean perch catch by Washington trawlers (metric tons) and
amount of biological data collected in each stratum are also
shown.

Wash-

Number of

ington

Origin of

fish sam

pled for

Time

trawl

biological

Length-

Year

stratum

catch

data

sex

Age

1966

Sept -Dec.

2,723

Oct.-Dec.

3,517

1,419

1967

Mar-May

868

May

1,104

433

June-Aug.

2.817

June-Aug.

1.049

848

Sept-Dec.

1.656

Sept-Dec.

2,648

1,183

1968

Jan-Apr

220

Jan-Apr.

1,470

680

May

842

May

1.310

505

June-Aug.

1.870

June-Aug.

1,165

608

Sept -Dec.

1,855

Sept. -Nov

3,041

1,011

1969

Jan-May

687

May

648

298

June-Aug.

2,205

June-Aug

2,461

698

Sept-Dec.

2,099

Sept -Dec.

4.255

714

1970

Jan-May

546

Apr-May

2,435

498

June-Aug.

1,749

June-Aug

4,214

649

Sept-Dec.

2,014

Oct.-Dec.

3,996

497

1971

Apr. -Aug

1,446

May-Aug.

6.974

1,004

Sept -Dec

1,480

Sept-Dec

3,733

1,232

1972

Apr. -May

379

May

3,174

887

June-Aug.

1,568

June-Aug.

7,337

2,587

Sept-Dec

1,417

Sept. -Nov.

4,434

1,321

1973

Mar -Apr.

530

Apr.

2,940

942

May

244

May

1,201

398

June-Aug.

1,019

June-Aug

5,058

1,658

Sept-Dec.

472

Sept. -Nov.

2,303

803

length-weight relation (sexes combined) reported
by Westrheim and Thomson ( 1971 ), together with
the appropriate length frequencies in that
stratum. The number of males and females landed
in each stratum could then be estimated by divid-
ing total pounds landed by the mean weight offish
in that stratum. These values were combined with
size composition data to obtain the number offish
landed by time period, sex, and size group. Pooling
these data by year and expressing the results in
terms of percent frequency yielded the results
shown in Figure 12.

Substantial quantities of large Pacific ocean
perch were present in Queen Charlotte Sound dur-
ing 1956-58. Subsequent changes in size composi-
tion reflect changes caused by the commercial
fishery and by recruitment of two strong series of
year classes. The first series of year classes was
centered around the 1952 year class and included
the 1951-53 brood years (Westrheim et al. 1972).
The presence of this series first became apparent
in the 1960-63 landings, when the modal size was
35 cm — corresponding to an age of about 10 yr. The
1952 year class series caused the modal size to
move progressively toward the right during
1960-70 (as its members grew in length), but
seemed to have little influence on size composition
in subsequent years. This is probably the cumula-
tive result of large fishery removals during 1965-
69, when the 1952 year class would have been
13-17 yr old.

A second series of strong year classes, centered
around the 1961 and 1962 brood years (Westrheim
et al. 1972) first showed up in the 1970 landings,
when there was a secondary mode at 34 cm. This
series of year classes came to dominate the land-
ings during 1971-73, since the abundance of older
fish had been drastically reduced by commercial
fishing.

Washington-Vancouver Island

Size composition data from this region were
more limited than data from Queen Charlotte
Sound and it was never possible to analyze differ-
ent time strata separately. All size composition
data were summarized by year to produce the data
in Figure 12. Data from 1956 to 1965 were espe-
cially limited and size composition data from adja-
cent years frequently had to be combined. This
was done in such a manner that direct compari-
sons with Queen Charlotte Sound could be made.

Research surveys during 1965 (Westrheim

379

1970) suggested that the 1952 year class domi-
nated here, as well as in Queen Charlotte Sound,
and the results (Figure 12) tend to support this
conclusion. The modal size was 35 cm for the
1960-63 period, and this corresponds to an age of
about 10 yr. The 1966-67 size composition data
also reflect the presence of a strong 1952 year class
series, but is is not possible to follow the series past
1967. Extensive fisheries removals during 1966-
68 resulted in sharply attenuated right-hand
limbs for 1968-73 size composition curves, and the
1952 year class series was presumably swallowed
up in these removals.

As in Queen Charlotte Sound, the strong 1961-
62 year class series first showed up on the 1970
landings, when there was a mode at 35 cm. Be-
cause the biomass of older fish had been drastic-
ally reduced by the extensive fisheries removals of
1966-68, these year classes dominated the catches
in the first year they appeared and in each sub-
sequent year.

Age Composition

Queen Charlotte Sound

Age composition data for the Washington trawl
landings from Queen Charlotte Sound have been
collected since 1966. A series of data taken over
the entire year is available for each year during
1967-73.

The procedure used to estimate the age composi-
tion of the 1967-73 landings was identical to that
employed in the section on size composition. The
number of fish landed in each time stratum was
combined with the age-frequency data for that
stratum to estimate the number of fish landed by
age-group, sex, and time stratum. Pooling these
data by year and dividing by the total Washington
trawl effort expended in Queen Charlotte Sound
yielded annual estimates of the number caught
per hour, by age-group, and of percent age compo-
sition (Figure 13).

The 1952 year class series was centered around
age 13 in 1965 and was almost fully vulnerable to
fishing when the Queen Charlotte Sound fishery
began its dramatic expansion. The cumulative ef-
fects of the extensive removals of 1966-67 were
such that the 1951-53 year classes no longer domi-
nated the catches after 1967-68. The 1952 year
class series was exploited far more intensively
than preceding year classes, and by the time the
1951-53 year classes were 17-19 yr old, they were

FISHERY BULLETIN: VOL. 75, NO. 2

QUEEN CHARLOTTE SOUND WASHINGTON - VANCOUVER IS.

30-
20-

10-

1968

10-

0
20
10

0
20-
10-

10
0

20
10
0

940

^tflTTIrnv.

rfTI 1 '.JTr-rrv^

r- t t

dfccL"

I I

jJHfTTr^

i i

llTfTrn^-

9l7.,^1|TTirTT>^_.
1002 ^JrnTTTT--

-ffl

rrrlTh-^

588

^fjTir^T>7>p ,

373 . ^{TTT¥tt»^

rill 11 L^

568

H I r

^j-ITtttttw^

i i 1

Tttttt-t-^—

532

_£fl

-J

10 15 20

Age (years)

i i — i

5 10 15 20 25

Age tyeors)

FIGURE 13. — Changes in the age composition (sexes combined)
of Pacific ocean perch in commercial catches, 1967-73. The
number of fish caught per hour is shown for each year, and the
1952 and 1961 year classes have been indicated by shading.

less abundant than the relatively weak 1948-50
year classes had been at corresponding ages. This
can be seen by comparing the abundance of 17-19
yr olds in 1970 (45 fish caught per hour) with their
abundance in 1967 (118 fish caught per hour).

During 1970 and 1971, recruitment of the
strong 1961 and 1962 year classes to the fishery
restored the abundance of Pacific ocean perch to
1967 levels (Figure 13) and the number of fish
caught per hour continued to increase through
1973. The condition of the QCS stock in 1973 was
far from satisfactory, however, since it was made
up of much younger fish than those characterizing
even the 1967 stock.

Washington-Vancouver Island

No age composition data were available for
Pacific ocean perch catches from the WVI stock
until 1966, and it was not until 1967 that an
adequate series of age composition samples was
collected (Table 5). Age composition data on the
WVI catches were quite limited, so no attempt was
made to treat different time strata separately.

Age composition data for 1967-73 are remark-
ably similar to corresponding data from Queen
Charlotte Sound (Figure 13). The harvests of
1966-68 sharply reduced the biomass of the 1952

380

OUNDERSON: POPULATION BIOI.OCV OK SEBASTES ALUTUS

TABLE 5.— Number of Pacific
sampled for

ocean perch from the WVI stock
biological data.

Year Length-sex

Age

War

Length-sex Age

1966 581

1967 1,020

1968 912

1969 1,213

216
707
502
296

1970
1971
1972

1973

3,089 1,124
3,944 1 ,460
3,044 1,036
3,684 1.335

year class series, which would have ranged from
about 13 to 15 yr of age in 1966 and would have
been almost fully vulnerable to trawling. Re-
cruitment of the 1961 and 1962 year classes to the
fishery began to restore abundance (as indicated
by the number caught per fishing hour) to former
levels and, as of 1970, the WVI stock was on the
road to recovery. After 1970, however, the condi-
tion of the WVI stock followed an entirely different
course than the QCS stock.

Exploitation rates for the QCS stock were low
enough to allow an increase in abundance
(number caught per hour) during 1970-73 (Figure
13), as the 1960-61 year classes became fully
available to the fishery. Off Washington and
Southwest Vancouver Island, however, exploita-
tion rates remained at high levels during 1970-73,
and the 1961-62 year classes were cropped off as
soon as they recruited to the fishing grounds.
Abundance consequently declined during 1970-
73, opposite to the trend in Queen Charlotte
Sound. The abundance offish 15 yr and older was
reduced below even 1970 levels, and 10 to 13 yr-
old fish dominated the WVI stock as of 1973.

RECRUITMENT TO THE FISHERY

Consideration of the length-maximum girth
data presented by Westrheim and Nash (1971)
indicates that gear selection should begin at a
relatively small size. The internal (between-knot)
measure of the cod end mesh size commonly used
by Washington trawlers is about 3.25 inches (8.26
cm) and the smallest fish retained should have a
girth of 2 x 3.25 = 6.5 inches. This assumes that
escape is not facilitated by compressability on the
one hand and that the rigidity of the trawl meshes
does not hinder escape on the other. If these as-
sumptions are valid, and the girth at 50% reten-
tion is 6.5 inches, Westrheim and Nash's results
show that the 50% selection length should be 24.5
cm.

A 25.4-cm fish would be too small for market
acceptance, but previous comparisons of Pacific
ocean perch size composition in research catches
and commercial landings (Gunderson 1972) have

indicated that 50% of all 32- to 34-cm fish on the
grounds are retained by Washington trawlers.
Virtually all fish 36 cm and larger are retained by
the fishermen. Reference to the age-length infor-
mation in Table 3 shows that the length at 50%
retention corresponds to an age of about 8 or 9 yr,
and that all fish older than 11 yr would be re-
tained. Slight between-stock differences in reten-
tion would be expected, owing to differences in
growth rate.

Despite the fact that all fish older than age 10
are vulnerable to the fishing gear in use, and large
enough that almost all are retained for market
sales, age composition data from commercial
catches (Figure 13) and research surveys (Gun-
derson 1974) show that recruitment to the fishing
grounds is not complete until much later than age
10. On the assumption that the modal age of the
catch lies near the first year in which recruitment
is complete, these data would imply that full re-
cruitment could occur anywhere from age 1 1 to 14.

The high variability in modal size is caused by
year to year variation in availability, year class
strength, and fishing mortality, and one way to
reduce its significance is to deal with long-term
averages of relative abundance. In order to do this,
a relative abundance index (£/,) was calculated for
each age group using the 1967-73 age composition
data for the QCS and WVI stocks. This index was
calculated as:

1973

7 n = X9&\f /"

where Ul = the relative abundance of the iih age-
group and ( — J = the number of fish in the iih

age-group caught per hour. Percentage age com-
position during 1967-73 has been calculated from
these U, data and is shown by stock in Figure 14.

The results show that although the modal age in
both stocks is 11 yr, recruitment to the fishing
grounds is quite gradual. In fact, it is not until age
15 that the full force of fishing mortality seems to
be exerted on any given year class. Estimates of
the exact proportion of the fish in each age-group
that have recruited to the fishing grounds, and are
vulnerable to fishing, can be derived from U, val-
ues, starting with the relation:

C, = uVLN,

where C, = catch of fish in the ith age-group

381

FISHERY BULLETIN: VOL. 75. NO. 2

lOO-i

-Cl

10-

A WVI
• QCS

7.4l57-0.3465x

-[ — l — I — I — l — i — I — i — l — l — I — I I l I
10 15 20

Age

FIGURE 14. — Relative abundance of age groups 5-19 during
1967-73, for the QCS and WVI stocks of Pacific ocean perch.

u = exploitation rate

V, = proportion of population vulnerable
at age i

N( = total number of fish in the ith age-
group.

expressed as percent frequency
X = age in years.

The slope of this line (0.35) was used to repre-
sent Z for fully recruited age-groups. This was
then separated intoF and M by assuming a known
value for M.

Estimation of V, schedules began by assuming
that the vulnerability coefficient for 16 yr olds
(V16) was 1.0. Using the QCS data, and M = 0.12
for example:

1.31 =

1.0 exp -(0.23 V15 + 0.12)

By iteration, it was determined that V15 = 0.94
and this value was used to determine V14 from:

1.14

0.94 exp -(0.23 V14 + 0.12)

Again this was solved iteratively, giving V14 =
0.79. Proceeding backwards, the vulnerability
coefficients for Queen Charlotte Sound were esti-
mated for all age-groups 10 and older. The calcula-
tions could not be carried past age 10, since
younger age-groups may be subject to substantial
rates of discard by fishermen.

Estimates of the V, schedules for both the QCS
and WVI stocks are shown in Table 6. Calculations

Similarly, Ci+\ = uVl + 1Nl + i = «V(--iiV,exp -(V,
F + M) if we assume that V,- remains constant
throughout the year, and:

Ui+1 Ci+1 V,,iexp -iV,F + M)

This equation can be solved iteratively for V, if we
have estimates of F (fishing mortality). M (nat-
ural mortality), V;+1, and the ratio UJU,+i.

The estimates of Z (total instantaneous mortal-
ity) andF were derived directly from the data in
Figure 14. Trends in the relative abundance of
15-19 yr olds were quite similar in the QCS and
WVI stocks, and Z was estimated by fitting a
common regression line to the data for both stocks.
The resulting regression equation for 15-19 yr olds
was:

log Y - 7.4157 - 0.3456X,

where Y = relative abundance during 1967-73,
382

TABLE 6. — Proportion of Pacific ocean perch population vulner-
able to fishing, by age-group and stock.

Stock

QCS

0.12

0.32

0.45

0.53

0.62

0.79

0.94

1.00

0.15

0.30

0.43

0.52

0.61

0.78

0.94

1.00

Mean

0.31

0.44

0.53

0.62

0.79

0.94

1.00

WVI

0.12

0.36

0.53

064

069

0.75

0.87

1.00

0.15

0.34

0.51

0.63

0.75

0.87

1.00

Mean

0.35

0.52

0.64

0.69

0.75

0.87

1.00

were carried out for M — 0.15, F = 0.20 as well
as for M = 0.12, but this had little effect on the
estimates of vulnerability. The geometric means
of the vulnerability coefficients obtained by as-
suming different values of M have been plotted
graphically in Figure 15 and suggests that the
proportion recruited to the fishery is a linear func-
tion of age. There is no obvious reason why this
should be so, however, and no attempt was made
to fit a straight line (or lines) to these data, or to
extend the relationship to fish less than 10 yr old.
The geometric means of the V, estimates were
used directly in all later work.

Cl'NDKKSON POPULATION BIOLOO I >!■ SEBASTES M UTUS

I O-i

£ 08-

•

<C 0.2-

• OCS

A WVI

10 II 12 13

Age (years)

— i —
15

— i
16

FIGURE 15. — Estimated proportion of each age group recruited
to the fishing grounds, for the QCS and WVI stocks of Pacific
ocean perch.

MORTALITY

All estimates of Pacific ocean perch mortality
rates depend on a knowledge of the age structure
of the population. Virtually all fish caught die
from the effects of decompression, so that no suc-
cessful tagging studies have ever been carried out.

In this section, data on number caught per hour
by age-group were used to estimate the survival of
14- to 18-yr-old Pacific ocean perch in year n to
ages 15-19 in year n + 1, or to ages 16-20 in year
n + 2. These age-groups were chosen so as to strike
a balance between problems with incomplete
recruitment on the one hand and age determina-
tion problems on the other. Previous analysis has
suggested that recruitment is not complete until
age 16, about the same time that age determina-
tion becomes difficult (Table 7) and the ages
of some individuals are presumably underesti-
mated. No age-groups older than 20 should be
included in survival estimates, and restricting
mortality estimates to fully recruited age-groups
(16-19 yr olds) could result in underestimation of
survival rates. Inclusion of the incompletely re-

cruited 14 and 15 yr olds offset this to some degree
and had the additional benefit of basing the sur-
vival estimates on five age-groups rather than
three.

All survival estimates were expressed on an an-
nual basis (S ), and then used to estimate Z. On the
assumption that M is density independent and
thatF is a linear function of total hours trawled,
the model Z — qf + M, where q = proportion of
population caught by trawling 1 h and f = mean
annual number of hours trawled, was employed.
Linear regression ofZ on /yields estimates of q
and M where the model is appropriate.

Total international fishing effort (f) was esti-
mated by dividing the total international catch in
a given year by the corresponding CPUE for the
Washington trawl fleet (after Gulland 1969). The
value of/" was obtained by averaging f over the
years that each estimate of Z pertained to.

Queen Charlotte Sound

Calculation of total international fishing effort
is outlined in Table 8. The 1967-72 Soviet catch
data for the INPFC Charlotte area was taken from
unpublished analyses by T. A. Dark and N. B.
Parks. These data were derived from analysis of
fleet location and catch by quarter and give the
most detailed breakdown of the Soviet catch that
is currently available. Soviet catch estimates for
1965, 1966, 1972, and 1973, as well as all Japanese
and North American data for the years 1963-73,
were derived from Westrheim et al. (1972) and a
recent update of that report.

Estimates of Z are plotted against mean inter-
national fishing effort (Table 8) in Figure 16 and
the results indicate that the information collected
so far can provide only tentative estimates of M.
Pacific ocean perch vary widely in their availabil-
ity to on-bottom trawls and the CPUE indices used
in mortality estimation are consequently suscep-

TABLE 7. — Deviations of Canada's final otolith readings from those of United States, by age-group, for a collection of

Pacific ocean perch from Queen Charlotte Sound, June 1972. '

Deviations

from

Per-

Washington

Total

cent

+ 5

—

3.6

4.8

•3
+ 2
-1

1
2
1

—

2
5
8

2.4
6.0
9.5

10 4

—

70.2

-1

—

3.6

Total

10 4

100.1

'S. J. Westrheim and W. R. Harlmg. 1973. Report on the 1972 comparison of Pacific ocean perch otolith and scale interpretations.
Unpubl. manuscr., 24 p.

383

FISHERY BULLETIN: VOL. 75, NO. 2

TABLE 8. — Calculation of total international fishing effort for Pacific ocean
perch in Queen Charlotte Sound and the INPFC Vancouver area.

68-69

Total

0.8-

Washington

international

Catch (metric tons)

CPUE (metric
tons/hour)

effort
(Wash, hours)

Year

US-Can

Jap.

USSR.

Total

0 7-

Queen Charlotte Sound

1963

3,712

0.841

4,414

06-

1964

3,507

0.731

4,798

1965

4.889

7,000

11,889

1.040

1 1 ,432

05-

1966

8,254

few

18,800

27,054

1.132

23,899

1967

5.745

3,196

17.800

26.741

0.800

33,426

1968

6,051

5,614

1,827

13,492

0.722

18,687

1969

6,628

6,268

12,951

0.656

19,742

1970

6,077

3,775

9854

0.714

13,801

1971

4,165

702

few

4.867

0.670

7,264

1972

5,561

2,281

7,842

0.710

11,045

1973

3,626

958

0
Vancouver area

4,584

0.812

5,644

1966

2,358

few

14,000

16,358

0.640

25,559

1967

805

6,678

10,263

17,746

0.434

40,889

0 I

1968

552

4,751

4.602

9,905

0.247

40,101

1969

583

1,787

2,143

4,513

0.242

18,649

1970

1,955

2,186

814

4,955

0.298

16,628

1971

1,155

1,838

1,145

4,138

0.317

13,054

1972

624

1,580

878

3,082

0.312

9,878

-0 I

1973

344

2.989

490

3,823

0.228

16,768

tible to fluctuations that have no relation to abun-
dance. Fluctuations of this nature were responsi-
ble for much of the variability in Figure 16 and
resulted in negative mortality estimates for
1972-73. The low quality of the data on interna-
tional catch (especially U.S.S.R. data) also con-
tributed to this variability, however.

Linear regression was carried out for the data in
Figure 16, and the resulting estimates of M and q
were 0.065 and 0.00002, respectively. As expected,
correlation between Z and f was quite low (r =
0.30).

Washington-Vancouver Island

Calculation of international effort in the INPFC
Vancouver Area is outlined in Table 8. The data
sources used to estimate total international effort
are the same as for Queen Charlotte Sound.

Annual estimates ofZ are plotted against mean
international effort in Figure 17. Research cruises
off Washington (Gunderson 1974) have shown
that extreme fluctuations in the availability of
Pacific ocean perch occur here and that changes in
the age composition of the catch seem to be as-
sociated with them. As in Queen Charlotte Sound,
these changes in availability, together with the
low quality of the international effort data, gener-
ate a high degree of variability in the relation
between Z and/1 Correlation between these vari-
ables was higher than in Queen Charlotte Sound
(r = 0.49), however, and the data seemed to con-

-0 2

-03-

IOjOOO

20,000
Fishing effort (hrs)

30POO

FIGURE 16. — Relation between total instantaneous mortality
rate (Z) and fishing effort for the QCS stock of Pacific ocean
perch, based on data from the Washington trawl fleet.

ur-
06-

05-

1970-71

•

^^ 1967-68
* 1968-69

Mortality rate
O o

1971-72 s^
• *^

^^ 1972-73

02-

1-- 0 232 + 00001 7

0 1-
0-

• 1969-70

1 1 1 1

10,000 20,000 30,000

Fishing effort (hrs)

40,000

FIGURE 17. — Relation between total instantaneous mortality
rate (Z) and fishing effort for the WVI stock of Pacific ocean
perch, based on data from the Washington trawl fleet.

form more closely to the model proposed. Linear
regression analysis resulted in estimates of M =
0.232 and q = 0.00001 for the WVI stock.

384

(H'NI)KRSON POPULATION BIOLOGY OF SEBASTES ALUTUS

The estimate of M obtained for the WVI stock
agrees well with an estimate obtained by Chikuni
(1975). Chikuni used CPUE and age composition
data from the Japanese trawl fleet, and estimated
M to be 0.227 for Pacific ocean perch in the
Oregon-British Columbia region.

The general applicability of the Z - qf + M
model for both the QCS and WVI stocks was
encouraging and suggests that further collection
of data on mortality rates should give increasingly
more reliable estimates of M. At present, how-
ever, it probably is unwise to overemphasize the
between-stock differences found in natural mor-
tality. The results of the current study should be
regarded as somewhat tentative and serve mainly
to show that M in the Washington-Queen Char-
lotte Sound region lies in the range between 0.1
and 0.2.

SEXUAL MATURATION

Maturity Criteria Used

Seasonal changes in the gross morphology of
Pacific ocean perch gonads have previously been
used to describe the reproductive cycle in the
Washington-Queen Charlotte Sound region
(Gunderson 1971; Snytko 1971). This technique
was again employed in this study, and, during
1968-73, 9,548 mature fish were classified as to
maturity state using the criteria in Table 9.

Mating and insemination activities cause a re-
duction in the proportion of males whose gonads
are swollen with sperm (Stage 3), and seem to
occur during August-September in both the QCS
and WVI stocks (Table 10). About 3 mo pass before

TABLE 9. — Description of the stages used to describe Pacific
ocean perch maturity.

Maturity

Code Stage

Description of gonads

Males

Immature

Stringlike, translucent

Maturing

Strmglike, translucent brown or white

Resting

Ribbonlike. triangular in cross-section,
brown or white

Large white

Large and swollen, somewhat rounded in
cross-section, glistening white

Females

Immature

Ovary small and translucent

Maturing

Ovary small and yellow

Large yellow

Ovary firm, oocytes yellowish and opaque

Yolk cleared
(eggs fertilized)

Ovary not firm, eggs yellowish and translucent

Eyed embryos

Ovary not firm, eggs translucert with black dots

or larvae

or visible larvae

Spent

Ovary large and flaccid with a red, purple, or
dark gray color

Resting

Ovary firm, gray or pink, some with black blotches.

ovulation and fertilization of eggs occur, and this
is first detectable when females in maturity Stage
4 are encountered. Embryonic development be-
gins after fertilization and continues for about 2
mo before embryos are released.

The peak of the embryo-release period occurs
during March in the WVI stock (Table 10). Most of
the females examined in February were in the
"fertilized" stage (Stage 4), while most of those
examined during April were in the "resting" stage
(Stage 7). Few observations could be made for QCS
females during February-April, but the results
suggest that embryo release occurs near March.
The relatively high proportion of recently spent
fish (Stage 6) encountered during May suggests
that spawning occurs somewhat later in Queen
Charlotte Sound than it does off Washington and
southwest Vancouver Island.

Age and size at first maturity should be deter-
mined during the period when mature gonads are
most fully developed, near August-September for
males and near March for females. The central
problem in determining length or age at maturity
is the status of "maturing" fish (Table 9), and
further work was carried out to determine
whether or not these fish are sexually mature. Two
hundred sixteen fish covering a broad range of
lengths were selected, from the 1971-72 commer-
cial landings for this purpose. The length (cen-
timeters), sex, and weight (decigrams) of each fish
were determined, and the gonads classified as to
maturity state. The gonads were then removed
from the fish and weighed to the nearest 0.01 g.
The results ( Figure 18) were expressed in terms of
relative gonad weight (g), where

gonad weight (grams)
body weight (grams)

x 102

i.e.; gonad weight expressed as a percentage of
body weight.

Males

Between-season comparisons show that the re-
lative gonad weights of "maturing" males are vir-
tually the same during the mating season
(August-September) as they are during March,
when all male gonads are in a quiescent state.
These fish are obviously immature and seasonal
changes in their relative gonad weight contrast
sharply with those of adult fish. Fish classified as
"maturing" should therefore be grouped with

385

FISHERY BULLETIN: VOL. 75, NO. 2
TABLE 10. — Percentage of adult Pacific Ocean perch in each maturity stage, by stock, during 1968-73.

Item

Jan.

Feb.

Mar.

Apr.

May

June

July

Aug.

Sept.

Oct.

Nov.

Males:

QCS Stock

Total examined

231

339

659

486

279

328

407

430

340

Percent In each

maturity stage:

Stage 8

100

Stage 3

Total

100

Females:

Total examined

219

364

212

358

442

675

512

Percent in each

maturity stage:

Stage 3

100

Stage 4

Stage 5

Stage 6

Stage 7

Total

100

101

100

Males:

WVI Stock

Total examined

234

223

448

'183

151

102

225

Percent in each

maturity stage:

Stage 8

100

Stage 3

Total

Too

Females:

Total examined

1 1 01

197

213

537

'129

178

118

210

Percent in each

maturity stage:

Stage 3

100

Stage 4

Stage 5

Stage 6

Stage 7

Total

101

Too

1 All fish examined during this month came from research vessel catches.

08-

06-

0 2-

MARCH

FEMALES

AUG -NOV

08-

06-

02-

MALES

MARCH

molure
"maturing"

30 35 40 45 25 30

Length (cm)

FIGURE 18. — Seasonal changes in the relative gonad weight of
mature and "maturing" Pacific ocean perch by length group and
sex.

"immature" males in all analysis of length or age
at maturity.

There was considerable overlap in the relative
gonad weight of mature and "maturing" males
during March. Relative gonad weight of adult
males examined during the mating season in-
creased exponentially with size, however, so that
mature and immature fish were readily differen-
tiated for fish longer than about 32 cm. For smaller
fish, however, the relative size of the gonad was
not sufficient to determine whether or not a fish
was mature, and color had to be relied on to a large
degree. If the gonads were white rather than
brown, this was taken to indicate the presence of
developing sperm and the fish was classified as
mature. Whether or not these small males actu-
ally participate in mating remains an unanswered
question, however.

Because mature and "maturing" males were
most readily differentiated when mature fish had
white, swollen gonads, only data collected during
June-October were used to determine size and age
at maturity. The data in Table 10 show that sig-
nificant quantities of males with Stage 3 gonads
were found during this period.

386

GUNDERSON: POPULATION BIOLOGY OF SEBASTES AIMTUS
Females

Female gonads are difficult to weigh during the
embryo release period, since they are easily rup-
tured then. Furthermore, eggs and embryos can be
extruded with slight pressure on the body cavity
during this period, and it is possible that sig-
nificant quantities of these sex products are lost
when fish are compacted in the cod end of a trawl.
For these reasons, no data on gonad weight of
mature females were taken during March.

Between-season comparisons for "maturing"
females (Figure 18) show that their relative gonad
weights were virtually the same during August-
November as they were during the embryo release
period in March. This is conclusive evidence that
"maturing" fish are not sexually active, and they
were grouped with immature fish in all later
analysis.

Differentiation of "maturing" and mature fish
was less difficult for females than for males. It was
most difficult during July-November, when most
adult fish were in maturity Class 3 (Table 10), and
had gonads that were similar to "maturing"
gonads in color. There was also some overlap in the
relative gonad weights of mature and "maturing"
individuals of the same length during this period
(Figure 18).

During the embryo release period, or when
females were in the resting state, adult gonads
were readily differentiated from the small, yel-
lowish gonads of "maturing" fish. Consequently,
only maturity data collected during February-
June were used to examine the size and age at first
maturity for females.

Length and Age at Maturity

Data on maturity of Pacific ocean perch have
been gathered since 1968, during the course of
routine biological sampling of commercial
catches. In addition, some maturity data were
available from research cruises off the northern
Washington coast. The data for 1968-72 combined
were examined by stock to determine size and age
at maturity.

In most instances, age, length, and maturity
data were available for individual fish, and the
proportion of mature fish in each cell of an age-
length matrix could be calculated. This type of
analysis was carried out for both males and
females from Queen Charlotte Sound (Tables 11,

12) and for females off Washington and southwest
Vancouver Island (Table 13).

Only 213 age-length-maturity observations
were available for WVI males, too few to allow
direct analysis of maturation by age-groups.
Examination of the relation between length and
maturity was possible, however, as 551 length-
maturity observations were available.

Length-maturity relation

Tables 11 through 13 show the proportion of
mature fish in each cell of an age-length matrix.
The region in which 50-80% of the fish were ma-
ture is delineated by the isopleths drawn in these
tables and can be interpreted as a maturity re-
sponse surface. For all three sets of data, the
50-80% region occupied a narrow range of size
groups (3-5 cm) and a relatively wide range of
age-groups (5-6 yr). Hence it seems that matura-
tion of both male and female Pacific ocean perch
depends more on the size of a fish than its age.

Raw data on length versus proportion mature
were plotted for each area and sex (Figure 19) and
seemed to conform to a logistic equation (Finney
1971) of the form:

1 + exp

-(^H

where / = length in centimeters

Pi = proportion mature at length /
l0 50 = length where: Pt = 0.5 = maturation
length
cr = constant.

The length-maturity curves are quite steep in
the vicinity of P/ = 0.2-0.8 and maturation can be
regarded as knife-edged, taking place at lQ5Q. Be-
cause the above equation is symmetrical about
Z0 50, the area under the curve and to the left of /0.50
is equal to the area above the curve and to the
right of it. Hence, the errors introduced by assum-
ing knife-edged maturation at /0 50 tend to
balance.

By algebraic manipulation, the above equation
can be linearized to:

- (k - 0

0.50
cr

The equation was then in the formy = a + (31 and

387

FISHERY BULLETIN: VOL. 75, NO. 2

TABLE 11. — Proportion mature in each length and age-group, for female Pacific ocean perch from the QCS stock.

Cells with only one observation were not considered.

Length (cm)

16-

Proportion

mature by

length

Number
examined

49
Proportion
mature
by age
Number
examined

0.00

000

0.00

0.06

0.00

0.05

0.04

0.00

0.20

0.09

0.04

0.00

0.07

0.00

0.03

0.15

0.11

0.25

0.00

0.09

0.00
0.00

022
|0.56

0.48

| 0.32

0.56

0.27
0.28
0.92

0.30

000

1.00
0.83

1.00
1.00

0.29
0.44
0.68

0.64
0.56

0.67
0.57

1.00

0.67

0.64

J 083 L
0.83

0.75

0.82
1.00

1.00

0.88

0.74
0.95

1.00

0.89

1.00

0.90

1.00

0.95

1.00

0.95

0.88

0.97

1.00

0.93

0.99

1.00

1.00
1.00

1.00
1.00
1.00

0.00 0.00 0.03 0.13 0.25 0.37 0.64 0.81 0.96 0.97 0.95
1 4 35 75 152 143 139 77 116 135 108 110

TABLE 12. — Proportion mature in each length and age-group, for Pacific ocean perch males from the QCS stock.

Cells with only one observation were not considered.

Length (cm)

15 16 +

Proportion

mature by

Number

length

examined

0.33

0.14

0.00

0.10

0.33

0.61

0.75

0.91

113

0.94

166

0.99

150

0.98

157

0.99

167

1.00

202

1.00

207

1.00

224

1.00

149

1.00

45
Proportion
mature by
age
Number
examined

0.00

0.33

0.00

0.50

0.40

0.25

0.50
0.61

0.80

0.57

0.64

0 50 |

0.50

0.61
0.69

080
0.97

0.69
0.94

1.00

0.92

1.00

0.97

0.93

0.88

1.00

0.98

1.00

094

0.98

1.00

0.98

1.00

0.97

1.00

1.00
1.00

1.00
1.00
1.00
1.00

0.00 0.14 0 29 0 56 0.89 0 92 0 97 0 98 100 100 100 100
5 7 34 94 150 225 230 241 250 217 158 230

the data in Tables 1 1-13 could be used in weighted
linear regression of In [(1/P,) - 1] on/. The weights
used fory observations were 1/Var (y) = nPi (1 -

P/). Regression coefficients obtained were then
used to estimate /0.50 (_a//3) and cr (-1//3).

These estimates were made by sex for Pacific

388

GUNDERSON: POPULATION BIOLOGY OK SKHASTKS AU'TUS

TABLE 13. — Proportion mature in each length and age-group, for female Pacific ocean perch from the WVI
stock. Cells with only one observation were not considered.

Length (cm)

Proportion

mature by

length

Number
examined

49
Proportion
mature by
age
Number
examined

0.00

1.00

000

067

1.00

000

0.40
0.33
0.67
1.00
0.75

000
0.00
038

059
0.77
0 75

0.89
1.00

0.00
025

0.70
0.50
0.70

1.00
1.00

1.00

0.57
0.67

0.92
0.95
0.86
0.88
1.00
1.00

1.00
1.00
0.88
1.00
1.00
1.00
1.00
1.00

1 0 501
1.00
0.85
0.83
1.00
0.93
1.00
1.00
1.00
100
1.00

0.33 0.25 0.42 0.46 0.60 0.65 0.87 0.98 0.94
3 8 12 24 67 81 101 105 103

1.00
1.00
0.80
1.00
1.00
1.00
1.00
1.00
1.00

0.80
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00

0 98 1.00
98 219

0.00
0.00
0.00
0.00
0.00
0.33
0.44
0.65
0.79
0.87
0.97
0.97
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00

100

105

123

111

FIGURE 19.— Length-maturity relation for QCS and WVI stocks
of Pacific ocean perch, by sex.

ocean perch in the QCS and WVI stocks (Table 14).
Predicted curves for proportion mature at each
length have been calculated and are represented
by the solid lines (QCS stock) and dashed lines
(WVI stock) in Figure 19. These curves, and the
Z0.5o estimates they are based on, indicate that both

TABLE 14. — Estimated values of parameters for the equations
used to examine length and age at maturity for Pacific ocean
perch.

Males

Females

Item

QCS stock WVI stock

QCS stock

WVI stock

Length at Maturity

'o.50

304627 29.3782

36.2705

34.2335

1.2791 1.4170

1.2405

1 .3252

Var (/0 50)

00492 0.0809

00105

0.0316

2 statistic1

3.0067

9.9277

Age at Maturity

f0.50

7.5884

11.3775

9 2899

0.9799

1.1819

1.6132

Var (f0.50)

0.0543

0.0204

0.1068

Z statistic2

—

5.8533

<0.50

7.0 6.5

10.3

10.0

1For test of between-stock differences in /q 50
2For test of between-stock differences in tq 50

males and females mature at a much smaller size
off Washington and Southwest Vancouver Island
than they do in Queen Charlotte Sound.

In order to examine the significance of
between-area differences further, the variance of
/0 50 was approximated by using the delta method:

Var(/050) -Var "/)=^<Var

+ f^Var (/3) - 2 -^ Cov (a, /3).

This variance was estimated for each sex and
area considered ( Table 14) using information from

389

FISHERY BULLETIN: VOL. 75, NO. 2

the linear regression program previously
employed. If it is assumed that the estimates of
Z0.5o are normally distributed, then the quantity

«2
02

Vvar(£)+Var(!)

is distributed as Z and can be used to test the
hypothesis that there is no difference in l050 be-
tween areas. TheZ values obtained for both males
and females (Table 14) indicate that the observed
differences in length at maturity are highly sig-
nificant, since P(Z>3.0067) = 0.0013 and
P(Z>9.9277) « 0 under the hypothesis being
tested.

Age-maturity relation

Age at maturity was estimated by two methods.
The first series of estimates was developed by
using the logistic equation:

Pt =

1 + exp

C-^n)

where Pt = proportion mature at age t

*o.50 = age whenP, = 0.50 = age at maturity
cr = constant.

The parameters for this equation were estimated
in the same manner described in the length-
maturity section, through weighted linear regres-
sion analysis of the data in Tables 11-13. The re-
sulting estimates of £0.5o and cr are shown in Table
14, and the predicted relationships betweenP, and
t are shown by the solid lines (QCS stock) and
dashed lines (WVI stock) in Figure 20. The £0.5o
estimates obtained in this way are estimates of the
age when males mate for the first time and when
females release their first brood of embryos. TheZ
statistic shows that between-stock differences in
age at first brood release were statistically sig-
nificant, since P(Z>5. 8533) ~ 0.

A second series of estimates for the age at
maturity it'050) was obtained by utilizing the Z0.50
values obtained in the previous section, and von
Bertalanffy growth parameters from Table 3. The
equation used was:

390

FIGURE 20.— Age-maturity relation for QCS and WVI stocks
of Pacific ocean perch, by sex.

Resulting estimates for males (Table 14) are
probably quite accurate, since both l0 50 and the
age-length relations in Table 3 were based on data
collected during June-December (near the mating
season). The t'05Q estimates for females are biased,
however, since a significant amount of growth oc-
curs between the period when /0.5o was estimated
(February- June) and the period when the age-
length data were collected (July for the WVI stock,
September-December for the QCS). The bias is
relatively small for the WVI stock, but in Queen
Charlotte Sound most of the annual growth prob-
ably occurs during the intervening time period.
The £'0.50 value obtained for QCS females con-
sequently underestimates age at first brood re-
lease by almost a year.

The results from both methods used to estimate
age at maturity (Table 14) indicate that both
males and females mature at an earlier age off
Washington and southwest Vancouver Island
than they do in Queen Charlotte Sound. When
biases in t'050 are considered, it appears that WVI
females release their first brood when 9-10 yr old,
while those in Queen Charlotte Sound are 11 yr
old. Estimates of age at first mating for males were
not subject to the same bias as those for females
and can be taken directly from Table 14. These
results suggest that males first mate at age 6

GUNDKRSON POPULATION BIOLOGY OV SKUAS I IS Ml II S

in the WVI stock and age 7 in Queen Charlotte
Sound.

FECUNDITY

Methods Used in Fecundity Determination
Collection of Ovaries

Previous fecundity work on Sebastes has indi-
cated that the time of ovary collection must be
carefully controlled. Lisovenko (1965) determined
fecundity for two groups of Pacific ocean perch in
the Gulf of Alaska, the first consisting of 61 fish
collected prior to fertilization and the second of 29
fish with fertilized ova. He found that the esti-
mated fecundity of the first group was 1.5-2.0
times higher than that of the second, considering
females of comparable size. Lisovenko attributed
this difference to eggs bursting when females were
hauled to the surface, but accidental extrusion of
the fertilized eggs could also have beem impli-
cated. Pacific ocean perch containing fertilized
eggs can be made to extrude these eggs by slight
pressure on the body cavity and make poor speci-
mens for determination of fecundity.

If ovary samples are collected too far in advance
of fertilization, however, maturing oocytes that
will be fertilized in the fall are too small to be
differentiated from immature oocytes. The opti-
mal time to collect material for fecundity observa-
tions is therefore August-November, when imma-
ture and maturing oocytes can be differentiated,
but fertilization of ova has not yet occurred.

Collection dates and times for fecundity samples
used in this study are shown below:

Date Number

(1973) Location collected

22 Aug. Destruction Island, Wash. 14

26 Aug. Tillamook Head, Oreg. 27

19 Sept. S.E. Corner, Goose Island 40

All fish from Queen Charlotte Sound were taken
from the landings of a commercial trawler, while
those from the southern region were collected
aboard the U.S.S.R. research trawler Seskar. The
cruise objectives of the Seskar were such that only
limited quantities of Pacific ocean perch were
caught off Washington, and collections made off
the Oregon coast were used to supplement those
from the WVI stock.

Since between-area fecundity comparisons were
to be made, the attempt was made to collect
ovaries from Queen Charlotte Sound when the fish
were in the same stage of the reproductive cycle as
those off Washington and Oregon. Despite this,
gross examination of male gonads and data on
oocyte diameters (Gunderson 1976) indicated that
fish in the Queen Charlotte Sound collection were
not quite as advanced as those collected 1 mo ear-
lier off Washington and Oregon.

All ovaries collected were placed in modified
Gilson's solution (Bagenal and Braum 1968) to
harden the eggs and separate them from sur-
rounding ovarian tissue. After about 1 mo, ovar-
ian tissue was removed from the eggs and the fluid
was changed. After the samples had been
in Gilson's solution for a total of 3 mo, they
were removed and stored permanently in 10rr
ethyl alcohol.

Differentiation of Mature and Immature Oocytes

A series of ovaries was collected over the whole
range of the reproductive cycle so that the growth
progression of maturing oocytes could be followed.
All specimens were collected in the Washington-
Oregon region and their ovaries were placed in
Gilson's solution until- the oocytes separated from
ovarian tissue. Subsampling of the eggs in an
ovary was accomplished by the same technique
used to estimate fecundity (described below).

The size frequency for the eggs in a specimen
was obtained by systematically measuring
(nearest 0.01 mm) those eggs lying on transect
lines drawn on a Petri dish, until a desired sample
size had been attained. Many of the eggs were
elliptical or irregularly shaped and, in these cases,
the longest axis parallel to the counting scale was
selected for measurement. One specimen was in
the "embryo or eyed larvae" stage of maturity and,
in this particular instance, all eggs with embryos
were measured along the longitudinal axis of the
embryo.

The results (Figure 21 ) showed that there was a
significant overlap in the size of immature and
maturing oocytes during the period when fecun-
dity samples were collected. By October, the size of
maturing oocytes had increased substantially and
differentiation of maturing oocytes was
straightforward. Following fertilization of the
first brood, however, it appears that other groups
of oocytes begin to mature, so that several sizes of
eggs and embryos are present in ovaries that have

391

FISHERY BULLETIN: VOL. 75, NO. 2

1(76 5)

"Large Yellow" 8/24/73 N = 77l 4specimens

Large Yellow" 10/21/74 N = I495 4specimens

"Embryos" 3/7/74 N=379 Ispecimen

"Resting" 3/22/74 NM894 4 specimens

-i 1 1 1 1 1 1 1 1 1 1 1 1 1 1

2 03 04 05 06 07 08 09 10 II 12 13 14 15 16 17 18

Diameter (mm)

FIGURE 21. — Size composition of oocytes, ova, and larvae within
Pacific ocean perch ovaries at different stages of the reproductive
cycle. Maturity stage of the gonads these data were collected
from is shown above each size frequency curve. Numbers in
parentheses indicate the percentage of oocytes that are 0.15 mm
or smaller.

son 1974) indicate that most embryos are released
during a single spawning peak that lasts only 2 or
3 wk.

In view of the oocyte measurement results and
the fact that studies on the fecundity of Sebastes
marinus have suggested a strong element of fail-
ure in oocyte fertilization (Raitt and Hall 1967), it
seems that current estimates of fecundity must be
regarded as somewhat tentative. Complex
changes in fecundity probably occur after the first
brood of oocytes has been fertilized and detailed
morphological work will be required to determine
their significance.

For purposes of this study, fecundity was esti-
mated from the number of mature oocytes present
prior to fertilization. All oocytes less than 0.30 mm
in diameter were classified as immature on the
basis of preliminary comparisons of oocyte size
frequencies for juvenile and adult specimens. The
data in Figure 21 suggest that this cutoff point was
somewhat high, however, and that many of the
oocytes in the 0.25- to 0.30-mm size class eventu-
ally mature. Even if all oocytes that were in the
0.249- to 0.293-mm size class during the collection
period were actually maturing, the error gener-
ated by calling them immature would be less than
about 10%.

Counting the Oocytes

passed the fertilization stage. There was no single
dominant mode of mature eggs or larvae in any of
the fertilized specimens that were examined (Ta-
ble 15).

Despite the wide range of egg size and develop-
ment within fertilized specimens, most of their
progeny will probably hatch and be released at
about the same time. Field observations (Gunder-

TABLE 15. — Oocyte size frequencies for individual specimens of
"fertilized" Pacific ocean perch females.

Oocyte size
class (mm)

Number observed

Oocyte size
class (mm)

Number observed

0 159
0.159-0.203
0.204-0.248
0.249-0.293
0.294-0.338
0.339-0.383
0384-0.428
0.429-0.473
0.474-0.518
0.519-0.563
0.564-0.608
06090 653
0.654-0.698
0699-0.743
0.744-0.788

262

2
2

237

30
10
6
5
1
1
2

240

4
3

227

54
10

7
1

0.789-0.833
0.834-0.878
0879-0.923
0.924-0.968
0.969-1.013
1.014-1.058
1.059-1.103
1.104-1 148
1.149-1.193
1.194-1.238
1.239-1.283
1.284-1.328
1 .329-1 .373

Total

11
4
4
2
2
1

2
1
10
4
5
2
6
1

— 2 1 —
395 321 317 324

Fecundity was estimated through subsampling
by volume. The ovarian contents from each fish
were removed from the storage solution, passed
through a 1.17-mm screen to remove large parti-
cles of ovarian tissue that remained, and placed in
a large beaker; water was then added until 2,000
ml of oocytes and water had been obtained. The
mixture was stirred magnetically until all oocytes
were distributed throughout the water column
and a 5-ml subsample withdrawn with a pipette.
Care was taken to sample all parts of the water
column with the pipette. Four to six subsamples
were taken in this manner, the exact number de-
pending on the standard deviation of the first four
subsamples.

The oocytes in each subsample were then
counted, using a binocular microscope. Two or
three replicate counts of each subsample were
made by two different observers during the early
phases of the study. The number of replicate
counts was gradually reduced, however, as it be-
came clear that there was little variation between
them. Throughout the study, all counts for a given

392

GUNDKRSON: POPULATION BIOLOGY OF. SEBASTES Ml FUS

fish were partitioned between two different ob-
servers to balance out the effects of any bias.

The mean number of eggs per milliliter was
calculated for each of the 4-6 subsample means
from a given specimen and the coefficient of varia-
tion (CV = standard deviation/mean of subsample
counts) for these subsample means had the follow-
ing distribution:

Range of

Washington-

CV (%)

Oregon

QCS

Total

0.0- 4.9

5.0- 9.9

10.0-14.9

15.0-19.9

20.0-24.9

Total

For most specimens (81% ), the standard deviation
of the subsample means was within 15% of the
grand mean. The fecundity of each specimen was
estimated by using the formula: F = 2,000n,
where F = fecundity and n = mean number of
eggs per milliliter in the subsamples.

Results of Fecundity Study

May (1967) reviewed the results of fecundity
work on several species (cod, Gadus morhua; her-
ring, Clupea harengus pallasi; long rough dab,
Hippoglossoides platessoides), which showed that,
for most practical purposes, variation in fecundity
is adequately explained in terms of length alone.
Raitt and Hall ( 1967 ) came to the same conclusion
in their work on the Atlantic redfish, Sebastes
marinus, a species belonging to the same genus as
Pacific ocean perch. They carried out multiple re-
gression of log F and logL using weight or age as
second independent variables, and it was found
that inclusion of variates other than length did not
significantly reduce residual variation. As a re-
sult, the fecundity work in the current study was
directed primarily toward determining the rela-
tion between fecundity and length.

Fecundity data for Sebastes alutus seemed to fit
the relation F =aLb, where F = number of oocytes
in thousands, L = fork length in centimeters, and
a and b = constants.

The values of a and b were determined by trans-
forming this equation into: logF = logo + b log L
and using linear regression techniques to fit logF
- log L data to a straight line. Data from
Washington-Oregon and Queen Charlotte Sound

were treated separately, and the following results
were obtained:

Washington-Oregon
F = (0.19295 x io-9) L7-32506
Queen Charlotte Sound

F = (0.12240 X 10 6) £5.51258

Predicted fecundity at each length was calcu-
lated from these relationships, and is shown in
Figure 22. The significance of between-area dif-
ferences in the length-fecundity relation was
examined statistically, using the BMD 3R4V4
computer program for analysis of covariance. The
results of this analysis showed that between-area
differences in the fecundity-length relation are
statistically significant at the 95% level and that
they are due to differences in the intercepts of the
logF - logL regression lines (F = 5.85 with 1,76
df ) rather than to differences in their slope (F =
3.43 with 1,75 df).

Two workers (Westrheim 1958; Snytko 1971)
have previously examined the length-fecundity
relation for Pacific ocean perch off Washington-
Oregon, although neither carried out correspond-
ing studies for the Queen Charlotte Sound stock.
Westrheim's results were the first available and
were based on examination of 13 specimens. Wes-
trheim collected his fecundity samples during
September-November ( 1951 and 1952), estimated

4BMD 3RV. Regression with Analysis of Covariance. This is
an addition to the University of California BMD program series,
developed at the University of Washington Computer Center by
W. Farr.

'■: .

— ° Wash -Ore (Westrheim, 1958)

/
/
/

— • Vancouver Is -Ore (Snylko, 197! )

8 ■

— Wash -Ore \ )hlS s,udy

— a Queen Charlotte Sound J

s\s^

§200-

^**r

S" -*

--' ^T^

«:

aS ^^s

-*' — -*"""^ '"'

-- *^ ^-"^"^ ^

*■*"* ^^— -"-"^ --'

-"° -~- — — * ^*£r^

iSf ioo-

^=^

r^^^^ --^1^^^^^

1 1 1 1 1 1 1 1

39 40

Length (cm)

FIGURE 22.— Relation between fecundity and length for Pacific
ocean perch off Washington-Oregon (as determined by three
different workersl and in Queen Charlotte Sound.

393

FISHERY BULLETIN: VOL. 75, NO. 2

fecundity by a gravimetric method, and found that
his results could be represented by the relation:
F = (4.8556 x 10 15)^6.33454^ whereL = fork length
in millimeters.

Snytko's (1971) fecundity observations on 171
specimens were the most extensive made to date in
the Washington-Oregon region. Snytko collected
his fecundity samples during November-March
1967-68, in the "Vancouver-Oregon region" (lat.
40°-50°N). The ovaries were collected before
fertilization of the oocytes had occurred and
fecundity was determined gravimetrically by
counting the oocytes present in 0.5- to 1.0-g sub-
samples of the ovaries (Snytko and Borets 1972).
Snytko ( 1971) presented his data in terms of mean
fecundity at a given length and regression of log F
on logL indicates that they can be represented by
the relation: F = (0.13103 x 105)L49883y, where
L = length in centimeters.

Length-fecundity relationships for Pacific ocean
perch off Washington-Oregon, as predicted by
Westrheim (1958), Snytko (1971), and myself are
shown in Figure 22. There was substantial varia-
tion in the results obtained by different workers
and this is to be expected in view of the differences
in the timing of ovary collection, techniques used
to subsample and count oocytes, and the wide ex-
panse of time (1951-73) covered by the studies.
There is also a strong possibility that length-
fecundity differences exist between substocks
within the Washington-Oregon region and could
have contributed to these differences.

The variability in the results of different work-
ers reflects only the difficulties in estimating the
number of maturing oocytes a given fish will pro-
duce and leaves a larger question unanswered.
What we would really like to estimate is the
number of viable larvae that fish of a given length
or age will give birth to during the embryo-release
period, and yet we are totally ignorant of the rela-
tionship between the estimated number of matur-
ing oocytes and the number of larvae that will
result from them.

Preliminary estimates of the number of larvae
that will be released at each age can be made,
however, if it is assumed that all oocytes present
immediately after fertilization will develop into
viable larvae. It should be kept in mind that even
though this assumption is patently false, the re-
sulting estimates are still well-suited to be-
tween-area comparisons if oocyte-larval mortality
does not differ between areas.

It will be recalled that fecundity observations

394

applied to fish collected during August-
September, while estimates of mean length at
each age applied to the September-December
period for Queen Charlotte Sound and to July in
the case of the WVI stock. The estimate of the
number of larvae released during March of any
given year of life (Table 17) was consequently ob-
tained by combining the age-length and length-
fecundity relationships pertaining to the previous
July-December. For example, the estimated
number of larvae released by 11-yr-olds in Queen
Charlotte Sound was estimated from predicted
mean length at age 10 (Table 3), and the length-
fecundity relationship appropriate to that stock {F
= 0.12240 x 10-6L5-51258).

RESPONSE OF PACIFIC OCEAN
PERCH STOCKS TO FISHING

Methods Used to Examine the Effects
of Fishing

In the past, management recommendations for
Pacific ocean perch in the INPFC Vancouver area
have been developed by arriving at some estimate
of the fishing mortality (F) that the stock can with-
stand, then applying this value to the best avail-
able estimate of stock biomass to arrive at a quota.
Much discussion has consequently focused on
what levels of F can be sustained.

In this section, the effects of different levels of
fishing intensity on a hypothetical cohort of fish
will be examined, with an approach similar to the
yield per recruit analysis that is commonly used in
stock assessment. In contrast to conventional
yield per recruit analysis, however, I have at-
tempted to look at the costs involved in exerting
high levels of fishing intensity on a population, as
well as the benefits of increased yield. In particu-
lar, the decline in exploitable biomass (CPUE/g,
where q is the catchability coefficient) and popula-
tion fecundity that go hand in hand with increases
in yield have been evaluated quantitatively.

The basic computations used to accomplish this
are shown in Table 16. Data required included
age-specific schedules of instantaneous natural
mortality, vulnerability to fishing, mean weight,
and fecundity (Table 17). The mean weight
schedule represents average values for the entire
year, while the fecundity schedule applies to the
embryo release period at the beginning of the year.
Vulnerability and mortality were assumed to be
constant throughout the year.

GUNDERSON: POPULATION BIOLOGY OF SKBASTES ALVTUS

TABLE 16. — Example of computations used to estimate exploitable biomass, yield, and population fecundity for a hypothetical Pacific
ocean perch population based on No recruits. Input parameters needed are indicated by asterisks.

Mj' V,' N,

Natural Vulner- sj Number alive W, '

mortality ability Proportion alive at at beginning Mean

Age coefficient coefficient beginning of age / of age / weight

8, Mean biomass

Mean
exploitable

Popu
Fecun- Hon

biomass Yield dity fecundity

Q=tc

A/0s0(=A/0) W0 KF\ °MJ1 -exp -W0F+M0)\ V0B0

FV0B0 m0 N0m0

V, s, = exp -{V0F+M0) A/0s,

N.W,

F , M 11 exp (V,F + M,)| V,8, FV,B, m, A/,m,

V2 s2 = s,exp -{V,F t/W,) N0s

N2W2

FV2B2 m2 N2m2

V3 s3 =s2exp -(V2F+M2) N0s

Wi v3F +M311 'exP -<y3^-M3)l ^S3

2 WS/ = S'

FV383 m3 N3m3

Table 17.

— Vital statistics for females

from the QCS

and WVI

stocks

of Pacific ocean perch.

Proportion

Mean length

Mean weight1

Fecundity

vulnerable

Age

(cm)

(g)

(thousands)

to fishing2

WVI Stock

31.4

433

12.1

0.10

32.9

502

17.8

0.20

34.3

573

25.1

035

35.5

639

34.0

0.52

36.6

704

43.7

0.64

37.6

766

54.7

0.69

386

833

666

0.75

39.4

889

808

0.87

40.2

947

93 9

1.00

41.0

1,008

1088

1.00

41.6

1.056

125.7

1.00

42.2

1,105

139.8

1.00

42.7

1,147

155.2

1.00

43.2

1,190

169.2

1.00

43.7

1,234

184.3

1.00

44.1

1,270

200.5

1.00

44.5

1,307
QCS Stock

214.3

1.00

34.3

573

0.20

35.9

662

—

0.31

37.2

741

45.7

0.44

38.5

826

55.7

0.53

39.6

903

67.3

0.62

40.6

977

78.6

0.79

41.4

1,040

90.1

0.94

42.2

1.105

1004

1.00

42.9

1,164

111.5

1.00

43.6

1,225

122.1

1.00

44.1

1,270

133.5

1.00

44.6

1,316

142.2

1.00

45.0

1,354

151.3

1.00

45.4

1,392

158.9

1.00

45.8

1,431

166.9

1.00

46.1

1,461

175.2

1.00

'Estimated from the age-length data in Table 3 and Westrheim and
Thomson's (1971) all-B.C. length-weight relation for females: W = 0.0078571

3.16734

Vulnerability coefficients for 8- and 9-yr-olds were assigned arbitrarily. The
values used were more conservative than those predicted by extrapolation of
the straight line obtained for 10- to 16-yr-olds (0.20 for 8-yr-olds and 0 29 for
9-yr-olds).

Yield, exploitable biomass, and total fecundity
are calculated for each age group, then summed.
The results give the annual yield to the fishery,
annual production of larvae, and average exploit-

able biomass on hand during the year for an
equilibrium population of Pacific ocean perch.
This population is based on a constant number of
recruits (N0), with individual growth and mortal-
ity being determined by the input values of the
constants used to describe mortality, vulnerabil-
ity to fishing, and mean weight at each age.

A computer program5 was written to carry out
the calculations in Table 16 and offers a variety of
ways to evaluate the effects of different fishing
strategies on a stock. The basic calculations can be
carried out for any combination of instantaneous
rates of fishing mortality (F) and age of entry into
the fishery (t'p) that the user specifies.

The mesh size used when fishing for Pacific
ocean perch is dictated primarily by convenience,
since the incidence of "gilling" and entanglement
in the meshes is reduced sharply when using 3.0-
inch mesh (internal measure) in the cod end. This
was not found to be the case in mesh studies with
Atlantic redfish (Templeman 1963), where use of
smaller cod end mesh sizes simply "gilled" fish of a
smaller size. In the Pacific ocean perch stocks
examined in this paper, recruitment to the fishing
grounds is quite gradual and the fish that would
normally be "gilled" in a 3.0-inch cod end are
poorly represented on the grounds.

Pacific ocean perch offer a special case then,
where evaluation of the effects of different size or
age restrictions is of no practical interest for
fisheries management. Consequently, all analysis
in this section was focused on determining the
optimal intensity of fishing for the Pacific ocean

5D. Gunderson and J. Buss. 1976. Users guide to ASSESS:
Assessment of the effects of different fishing strategies on fish
populations (FORTRAN IV). Norfish Pap. NC09, 8 p.

395

FISHERY BULLETIN: VOL. 75. NO. 2

perch stocks being examined and the effects of
varying the age at entry into the fishery (t'p ) were
ignored.

In addition, the analysis was restricted to the
female portion of the stock. Over the long term, the
population will be far more sensitive to removals
of females and reduced population fecundity than
it will to removals of males, and the optimal har-
vest rate for females will determine the level of F
that should be applied to the stock as a whole.

The input data used to describe the QCS and
WVI stocks are shown in Table 17. The values
used for mean weight at age, vulnerability
coefficients, and fecundity at age were derived
from the information in Tables 3 and 6 and Figure
22. Natural mortality was assumed to be the same
for all age groups concerned and computations
were carried out for both M = 0.1 and M = 0.2.

Assessment of Immediate Response
to Fishing

Only a small fraction offish less than 8 yr old are
recruited to the fishing grounds and, for the pur-
poses of this study, it was assumed that recruit-
ment begins at age 9 (tp = 9). It is possible that
significant quantities of 9-yr-olds are discarded by
fishermen, however, making it difficult to esti-
mate their vulnerability coefficient from market
samples. For this reason, t„ = 10 was also consid-

ered, so that the sensitivity of the results to
changes in tp could be evaluated.

The results (Figure 23) showed that different
values of tp had very little effect on the relative
trends in yield, population fecundity, and exploit-
able biomass with increasing F. In fact, the rela-
tive levels of each followed almost identical trends
for both stocks and both values of tp considered.
However, the value of M used in the calculations
had a pronounced effect on the results.

In all cases examined, there was a sharp rise in
yield as F increased from 0.0 to 0.2, and a more
gradual increase for F-values greater than 0.2.
Relative levels of exploitable biomass and popula-
tion fecundity showed a reciprocal trend, decreas-
ing sharply as F increased from 0.0 to 0.2, then
declining more gradually for F greater than 0.2.

Relative changes in population fecundity were
almost identical to changes in exploitable bio-
mass, indicating that changes in CPUE can be
used directly to estimate the magnitude of
changes in population fecundity. During 1966-68,
then, population fecundity for stocks in the
Oregon-Queen Charlotte Sound region must have
declined in the same manner as CPUE and is cur-
rently only about 50% of what it was prior to in-
tensive fishing.

Preliminary examination of the data (Figure
23) shows that the most significant changes in
yield, exploitable biomass, and population fecun-

o 0.1

0.2 Q3 0.4 Q5 0J6 07

F (WVI,lp=IO)

0.2 0.3 0.4 0.5
F (0CS,tp=l0)

600-

400-

"5200'

■s

■J 200

I io

0.2 0.3 0.4 0.5 6.6 0.7
F (WVI,tp=9)

FIGURE 23.— Population fecundity (es-
timated number of larvae released an-
nually), exploitable biomass. and an-
nual yield for hypothetical populations
based on 1,000 recruits per year. Re-
sults are presented by stock, for two dif-
ferent ages at recruitment itp) and two
different levels of instantaneous
natural mortality (A/).

0.2 0.3 0.4 0.5
F (QCS, tp=9)

396

GUNDERSON: POPULATION BIOLOGY OF SEBASTES ALUTUS

TABLE 18. — Relative yield (Y/Ymax), population fecundity
V2/Emax), and exploitable biomass (B7B 'max ) atF = 0.1 and 0.2. l
The range of values obtained by taking tp = 9 or 10, for two
different stocks of Pacific ocean perch is presented.

= 0.1

F ■■

= 0.2

Item

M = 0.1

M = 0.2

M = 0.1

M = 0.2

W^max

0.62-0.64

0.45

0.84-0.85

0.67

£/£max

0.59-0.62

0.68-0.70

0.40-0.43

051-0.53

B IB max

0.60-0.61

0.68

0.40-041

050-0.51

1ymax = y'e'd wnen F = 0 .7; £max and S'max = population fe-
cundity and exploitable biomass when F = 0.0.

dity occurred when F = 0.1 andF = 0.2, and the
results for these two levels of fishing intensity
have been summarized in Table 18. All data were
presented in terms of the range of values obtained
when considering different stocks and tp values.
The ranges were always quite narrow, attesting to
the fact that consideration of different stocks and
tp values had little influence on the results.

The conclusions that can be drawn from Table
18 depend to a large degree on what is considered
to be the best estimate of M. If M = 0.1, the costs of
letting F reach 0.2 are quite high, since exploit-
able biomass and population fecundity would be
reduced to about 40% of their virgin stock levels.
From this consideration alone, it would seem ad-
visable to limit F to 0.1.

IfM = 0.2, however, the costs of letting F reach
0.2 are somewhat lower with exploitable biomass
and population fecundity declining to about 50% of
their level in the virgin stock. Limiting F to 0.1
would reduce the yield to only 45% of the level
attainable at F = 0.7, while population fecundity
and exploitable biomass would undergo reduc-
tions of about 30% from virgin stock levels.

On the basis of this analysis, then, there is a
reasonable possibility that if M = 0.2, the optimal
level of F could be as high as 0.2. From a biological
point of view, however, a central question still
remains unanswered, since we have not yet
evaluated the consequences of reducing popula-
tion fecundity. It is one thing to point out the
degree to which population fecundity will be re-
duced by various levels of fishing intensity and
quite another to determine the impact this reduc-
tion will have on future recruitment.

Effects of Fishing on
Future Recruitment

Variability in egg and larval survival is ex-
tremely high for marine teleosts. Larvae grow
rapidly during the planktonic phase and require

large quantities of food. For example, haddock
larvae initially grow at rates of about 12% per day,
increasing in weight by a factor of 105 during their
first year of life (Jones 1973). When food is not
plentiful, available supplies can be exhausted
rapidly, resulting in starvation and high rates of
density-dependent mortality. Even if larval mor-
tality is not directly due to starvation, density-
dependent mortality could easily result from slow
growth and prolonged exposure to predators
(Cushing 1974).

Density-independent mortality, such as that
suffered when eggs or larvae are swept into un-
favorable nursery areas, can also be quite vari-
able. Ketchen (1956) and Ketchen and Forrester
(1966) found that in the case of English sole and
petrale sole, mortality of this nature seems to ac-
count for a high proportion of the variability in
year class strength.

Marine fish have evolved three basic ways of
adapting their life history to cope with the highly
variable survival of their progeny: 1) iteroparity
(repeat spawning), 2) high fecundity, and 3) com-
plete elimination of the egg and/or larval stage
through ovoviviparity or viviparity. Murphy
( 1968) has shown that iteroparity is favored under
conditions of high variability in larval survival
and relatively constant adult mortality. This line
of evolution leads to the existence of a large
number of adult age-groups — a common situation
in marine fishes. With several adult age-groups in
the population, the size of the adult stock is buf-
fered somewhat against variations in the strength
of individual year classes.

High fecundity and elimination of the
planktonic phase offer two divergent means of cop-
ing with variable larval mortality and are typified
best by the gadoids on one hand and by elasmo-
branchs on the other. Atlantic cod commonly pro-
duce several million eggs per adult, and Cushing
and Harris (1973) have shown that the spawner-
recruit relation for this species is distinctly convex
or dome-shaped (curve a in Figure 24). This rela-
tionship implies that eggs are "overproduced" at
high parental stock densities, with attendant de-
clines in larval survival. At stock densities below
the replacement point (Pr), the high fecundity al-
lows for great resilience and rapid return to Pr.

The development of most elasmobranchs is
characterized by the elimination of the larval
stage found in the majority of teleosts and the
young are fully developed when born. Fecundity is
extremely low, with 2-108 young being produced

397

FISHERY BULLETIN: VOL. 75, NO. 2

Stock

FIGURE 24. — Relationship between parent stock and recruit-
ment for gadoids (a) and elasmobranchs (b).

per year (Holden 1973). Any compensatory re-
sponses to increase the number of recruits must
act through changes in growth (with attendant
changes in the age at maturity) or fecundity, and
are relatively sluggish. Holden (1973) has
suggested that the stock-recruitment relation for
most elasmobranchs is probably of the form of
curve b in Figure 24, departing little from the
bisector on either side of the replacement point.

By eliminating the free-living larval stage,
elasmobranchs have reduced the susceptibility of
adult stock size to environmental perturbations.
In the natural state, then, the compensatory
mechanisms that return the stock toPr do not need
to provide the same degree of resilience they do in
the gadoids. This lack of resilience makes the
elasmobranchs poorly adapted to harvests by man,
however, and they are quite susceptible to over-
fishing.

Pacific ocean perch are ovoviviparous, and, like
the elasmobranchs, they are probably much less
resilient to perturbations from P, than a highly
fecund, oviparous species like cod. It is important,
therefore, that population fecundity be kept quite
near the levels found in the virgin stock when the
adult stock was presumably near Pr. Any reduc-
tion in population fecundity from virgin stock
levels could easily result in reduced recruitment.

Some increases in the number of larvae released
could probably come through compensatory
growth, since the age at sexual maturity and level
of individual fecundity are both correlated
strongly with size. There must be some limits to
the degree of compensation this mechanism is
capable of, however, and this was explored quan-
titatively by using the model (Table 16) and com-
puter program described previously.

This analysis was begun by setting up four sets
of hypothetical populations ( one set for each stock )
and calculating the population fecundity under
different levels of fishing mortality. In the first
population, the "standard" age-length data in
Table 17 were used to describe individual growth
in each stock. In the second and third populations,
the mean lengths at each age were increased 3%
and 5% (Figure 25) to simulate compensatory
growth. In the fourth population, mean length at
each age was again increased 59£- above standard,
and it was also assumed that sexual maturation
occurred 1 yr earlier than in the other populations.
The latter assumption was justified by the fact
that a 5% increase in growth brought 8-yr-olds
from the WVI stock and 10-yr-olds from the QCS
stock up to the size at which sexual maturity oc-
curred in the standard population (Figure 25). The
last population was presumed to embody the
maximum possible degree of compensation in
population fecundity, since the projected increases
in mean length at age would be quite remarkable
in a species growing as slowly as S. alutus. The
assumption that the age at sexual maturity would
decline because of earlier attainment of a critical
maturation size is also tenuous, and only time will
tell if this actually occurs.

The age of recruitment was taken as age 8 for
the WVI stocks and age 10 for the QCS stocks, in

50-

40-

WVI

5% increase

"1- —3% increase

'V>

"i — i — i — i — i — i — i — i — i — i — i — r

... — 5% increase
_ — 3% increase

QCS

15 20

Age (years)

FIGURE 25. — Mean length at age for female Pacific ocean perch
in the WVI and QCS stocks, assuming standard growth, and two
different levels of compensatory increase in growth.

398

(il'NDKRSON: POPULATION KIOLOOV MF SEHASTES ALUTUS

TABLE 19.— Estimated

populations based on 1
growth and maturity.

population fecundity (millions of larvae released) for hypothetical
,000 recruits per year, under different levels of fishing mortality

Pacific ocean perch
and compensatory

WVI stock

Item

QCS stock

Item

0.0

F
0.1

0,2

0.0

0.1

0.2

= 0.1

Standard growth, mature at age 9

607

356

237

Standard growth, mature at age 1 1

703

437

302

3°o increase, mature at age 9

753

442

294

3% increase, mature at age 1 1

828

515

356

5% increase, mature at age 9

867

510

339

5% increase, mature at age 1 1

920

572

396

5°o increase, mature at age 8

884

527

357
M

5°o increase, mature at age 10
0.2

966

618

442

Standard growth, mature at age 9

256

174

130

Standard growth, mature at age 1 1

358

251

191

3°o increase, mature at age 9

318

216

162

3°o increase, mature at age 1 1

422

296

225

5°o increase, mature at age 9

366

249

187

5°o increase, mature at age 1 1

469

328

249

5% increase, mature at age 8

383

266

204

5°o increase, mature at age 10

515

375

296

order to accommodate the changes in age at
maturity. It was assumed that the length-weight
relationships, length-fecundity relationships, and
vulnerability coefficients characterizing the stan-
dard populations would apply to the other popula-
tions as well. All calculations have been carried
out for M = 0.1 and M = 0.2.

The results (Table 19) for standard growth when
F = 0 give the estimated population fecundity for
the virgin stock. In actual fact, biomass was re-
duced below virgin stock levels several years prior
to the time when the "standard" rates of growth
were estimated and some compensatory changes
could already have occurred. The population
fecundity in the "standard" population when F =
0 could consequently overestimate preexploita-
tion fecundity to some degree.

For both stocks considered, fishing mortalties
greater than F = 0.1 doom Pacific ocean perch to
lower levels of population fecundity than those
existing prior to exploitation. None of the popula-
tions examined were able to recover preexploita-
tion levels of population fecundity when F = 0.2,
even when mean length at age increased by 5%
and sexual maturation occurred a year earlier
than normal.

Even ifF is restricted to 0. 1, the ability to regain
virgin stock levels of fecundity varies sharply with
M. IfF = M = 0.1, the results for both stocks show
that even if growth increases by 59c and sexual
maturation occurs a year earlier than normal,
population fecundity will be 12-13% less than in
the virgin stock. If M = 0.2, the outlook is better,
since the stocks were able to recover 92-97% of the
preexploitation fecundity with a 5% increase in
growth.

The main point to be considered, however, is
that even when F = 0.1, Pacific ocean perch would
have to undergo significant compensatory changes

in growth to regain virgin stock levels of popula-
tion fecundity and would possibly have to mature
a full year earlier than normal. In this light, the
intensive fishing of the U.S.S.R. and Japanese
trawl fleets in the past has been quite remote from
the concept of long-term equilibrium yield.

In the case of the WVI stock, exploitation was
most intensive during 1967, and, depending on the
value of M used, 1967-68 estimates of F ( = Z - M)
would range from 0.36 to 0.46 (Figure 17). In al-
most every year since, the estimated value of F
would exceed 0.1, regardless of whether M = 0.1 or
0.2. The situation is less clear in the case of the
QCS stock, but mortality estimates based on the
age composition of the Washington trawl fleet
(Figure 16) indicate that F was between 0.66 and
0.76 during 1968-69 and exceeded 0.1 during
1969-72.

Drastic action will probably be required to re-
turn Pacific ocean perch to their former levels of
population fecundity, beginning perhaps with a
total ban on commercial fishing, such as that pro-
posed by Snytko (1971). Once this has been ac-
complished, harvest from both the QCS and WVI
stocks should be regulated so that the catch does
not exceed 0.1 (3, where /3 is the estimated stock
biomass.

SUMMARY

Pacific ocean perch are a dominant component of
the fauna of the North Pacific, attaining a wide
geographic distribution and high levels of popula-
tion density prior to exploitation. Intensive exploi-
tation by man created a sudden change in their
population biology, and one that they were poorly
adapted to cope with. Pacific ocean perch stocks
lack the resilience of highly fecund, oviparous
groups like the gadoids and their ability to main-

399

FISHERY BULLETIN: VOL. 75, NO. 2

tain even current levels of abundance is uncertain.

The biology and population dynamics of Pacific
ocean perch in the Washington-Queen Charlotte
Sound region were examined in detail, to gain
some insight into the effects of different fishing
strategies on this species. Two stocks were de-
lineated: one in Queen Charlotte Sound (QCS
stock) and one inhabiting the waters off northern
Washington and southern Vancouver Island ( WVI
stock).

Production in the region occupied by the WVI
stock plummeted from 39,000 metric tons in 1967
to 6,000 metric tons in 1969 (an 85% decline), and
catch per hour by North American trawlers de-
clined 45% during the same period. The QCS stock
was affected less drastically by fishing, since
biomass estimates and CPUE data indicated that
S. alutus were initially more abundant in the
former area and did not undergo such intensive
exploitation. During 1966-68, production declined
50%, while CPUE of Washington trawlers de-
clined 36%.

Changes in size and age composition of Pacific
ocean perch in the commercial landings were ex-
amined for the years 1967-73. Substantial quan-
tities of large S. alutus were present in Queen
Charlotte Sound during 1956-58 and subsequent
changes in size and age composition reflected the
changes caused by commercial fishing and re-
cruitment of two strong series of year classes. The
first series was centered around the 1952 year
class and included the 1951-53 brood years, while
the second series centered around the 1961 and
1962 brood years. Size composition data for the
WVI stock were too limited to be useful prior to
1961, but data for subsequent years suggested
that the same year classes that predominated in
Queen Charlotte Sound were also predominant in
landings from the WVI stock.

Fisheries exploitation has resulted in drastic
reductions in the abundance of the 1951-53 year
class series in both the QCS and WVI stocks and
the 1973 Washington trawl catches from these
stocks were dominated by 10- to 13-yr-old fish.

Growth rates were estimated from commercial
fisheries and research cruise data, taking perti-
nent features of the life history such as seasonal
and bathymetric variability in the age-length re-
lation into consideration. Parameters of the von
Bertalanffy growth model were estimated by sex
for both the QCS and WVI stocks.

Although fish older than age 10 are large
enough that almost all can be caught by conven-

tional trawling gear and retained for market
sales, age composition data from commercial
catches and research surveys showed that re-
cruitment to the fishing grounds is not complete
until much later than age 10. The proportion of
each age group vulnerable to fishing (V,) was es-
timated by employing a model that assumed that
natural mortality (M) and V, were constant
throughout the year. The results suggested that
recruitment to the fishing grounds differed some-
what between stocks, but that V, ranged from
0.31-0.35 during age 10 to 0.87-0.94 during age 15.
Estimation of V, could not be made for fish less
than 10 yr old, since these age groups may be
subject to substantial rates of discard by fisher-
men.

Any yield per recruit analysis of Pacific ocean
perch stocks must take these recruitment patterns
into consideration to be meaningful. Recruitment
to the fishing grounds is quite gradual, and many
age groups that could potentially be retained by
conventional mesh sizes are poorly represented on
the fishing grounds. Evaluation of the effects of
different size or age restrictions would be quite
misleading if this were not considered.

Age composition data (number caught per hour
by age-group) were used to estimate the survival
of 14- to 18-yr-old Pacific ocean perch in year n to
ages 15-19 in year n + 1, or to ages 16-20 in year n
+ 2. These survival estimates were then conver-
ted to total instantaneous mortality rates (Z) and
plotted against total international effort (/*) on the
assumption that they conform to the model: Z = qf
+ M, where M = instantaneous natural mortality
rate. The data seemed to fit this model in a general
way but there was a relatively low correlation
between Z and f (r = 0.3-0.5), due principally to
wide variability in the availability of Pacific ocean
perch to on-bottom trawls (totally unrelated to
variations in actual abundance) and to the low
quality of the data on international fishing effort.
Despite this, there was good agreement between
the estimates of M derived from this study (0.07
for the QCS stock and 0.23 for the WVI stock) and
results obtained in previous studies. It was
concluded that between-stock differences in natu-
ral mortality probably should not be overempha-
sized, and that the results of the mortality studies
served mainly to show that M in the Washington-
Queen Charlotte Sound region lies in the range
between 0.1 and 0.2.

Data on the proportion of sexually mature indi-
viduals in each age-length group were sum-

400

GUNDERSON: POPULATION BIOLOGY OF SEBASTKS MA 77 s

marized by stock and suggested that maturation of
both male and female Pacific ocean perch depends
more on the size of a fish than on its age. The
maturation length (where 509c of the fish in that
length group are sexually mature) showed statis-
tically significant differences between stocks, fish
from the WVI stock maturing at a smaller size
than those from the QCS stock. Males matured at
29.4 cm in the WVI stock and 30.5 cm in the QCS
stock, while corresponding values for females
were 34.2 and 36.3 cm.

Estimates of the age at sexual maturation indi-
cated that WVI females release their first brood
when 9-10 yr old, while those in Queen Charlotte
Sound are 11 yr old. The results for males suggest
that males from the WVI stock mate for the first
time when 6 yr old, while this occurs at age 7 in the
QCS stock.

Measurement of oocyte diameters from a series
of ovaries collected over the complete extent of the
reproductive cycle suggested that any estimates of
fecundity must be regarded as tentative, owing to
the uncertain significance of auxiliary modes of
oocytes. Incomplete fertilization of oocytes also
complicates the situation, and there is very little
known about the relation between the number of
developing oocytes and the number of viable lar-
vae that will result from them.

Length (L)-fecundity (F) data were summarized
by stock and were described by the relation: F =
aLb. Analysis of covariance showed that there
were significant between-area differences in the
length-fecundity relationship, females from Wash-
ington-Oregon being more fecund than Queen
Charlotte Sound females of comparable length.

The effect of fishing on stocks of Pacific ocean
perch was examined through an approach similar
to the yield per recruit analysis that is commonly
used in stock assessment. However, the model and
computer program developed for this study differ
from conventional methods in that they allow for
estimation of exploitable biomass and population
fecundity as well as yield per recruit. Data re-
quired included age-specific schedules of instan-
taneous natural mortality, vulnerability to
fishing, mean weight, and fecundity. Annual yield
to the fishery, annual production of larvae, and
average exploitable biomass on hand during the
year were then calculated for a population based
on a constant number of female recruits, assuming
different combinations of instantaneous fishing
mortality (F) and age of recruitment to the fishery
(tp).

The results showed that different levels of t,„ or
between-stock differences in the input parameters
had very little effect on the relative trends in yield,
population fecundity, and exploitable biomass
with increasing F. In all cases examined, there
was a sharp rise in yield as F increased from 0.0 to
0.2 and a more gradual increase for F-values
greater than 0.2. Relative levels of exploitable
biomass and population fecundity showed a recip-
rocal trend, decreasing sharply as F increased
from 0.0 to 0.2, and declining more gradually forF
greater than 0.2.

The value of M used in the calculations had a
pronounced effect on the results. If M = 0.1, the
costs of letting F reach 0.2 are quite high, since
exploitable biomass and population fecundity
would be reduced to about 407c of their virgin stock
levels. If M = 0.2, however, the costs of letting F
reach 0.2 are somewhat lower, with exploitable
biomass and population fecundity declining to
about 509^ of their level in the virgin stock.

This preliminary analysis provided some esti-
mates of the reductions in population fecundity
that could be expected under different levels of
fishing intensity, but gave no insight into the ef-
fects of this reduced fecundity on future recruit-
ment. As a result, the analysis was carried one
step further and it was assumed that, at reduced
levels of population density, all compensatory
changes in recruitment are mediated through in-
creases in growth. Attendant changes in fecundity
at age and age at sexual maturation would then
tend to increase the level of population fecundity
and recruitment, since both fecundity and mat-
uration are related to size.

Three hypothetical levels of compensatory
growth and sexual maturation were considered,
and none of these were effective in restoring
preexploitation levels of population fecundity
when F = 0.2. This was true even when mean
length at each age increased 57c and sexual mat-
uration occurred a year earlier than normal. Even
when F is restricted to 0.1, Pacific ocean perch
would have to undergo significant compensatory
changes in growth to restore population fecundity
to virgin stock levels, when the stock was presum-
ably near the replacement point (Pr) on the
spawner-recruit curve.

Since Pacific ocean perch stocks are poorly
adapted to extensive displacements from Pr, it was
suggested that drastic action will probably be re-
quired to return them to their former levels of
population fecundity, beginning perhaps with a

401

FISHERY BULLETIN: VOL. 75, NO. 2

ban on fishing. Once the stocks approach their
former levels of abundance, the harvest from both
the QCS and WVI stocks should be regulated so
that the catch does not exceed 0.1/3, where /3 is the
estimated stock biomass.

ACKNOWLEDGMENTS

This study was conducted in cooperation with
NOAA, National Marine Fisheries Service, under
Grant-in-Aid Project No. 1-75-R. I am grateful to
several members of the Washington Department
of Fisheries who helped with the collection and
processing of the data employed, notably Mark
Pedersen, James Beam, Wayne Gormely, Ruth
Mandapat, Sandra Oxford, and Dan Kimura.

Discussions with S. B. Mathews (University of
Washington) and S. J. Westrheim (Fisheries Re-
search Board of Canada) were particularly helpful
throughout the study and I thank both of them for
reviewing the manuscript.

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stocks off British Columbia, Washington, and Oregon in
1970. Fish. Res. Board Can. Tech. Rep. 326, 48 p.
WESTRHEIM, S. J., AND F. W. NASH.

1971. Length-girth relationship for Pacific ocean perch
(Sebastes alutus) collected off British Columbia in
1969. Fish. Res. Board Can. Tech. Rep. 251, 6 p.

WESTRHEIM, S. J., AND J. A. THOMSON.

1971. Weight-length relationship for Pacific ocean perch
(Sebastes alutus) collected off British Columbia in
1969. Fish. Res. Board Can. Tech. Rep. 237, 12 p.

403

ANALYSIS OF AGE DETERMINATION METHODS FOR

YELLOWTAIL ROCKFISH, CANARY ROCKFISH,

AND BLACK ROCKFISH OFF OREGON1

Lawrence D. Six2 and Howard F. Horton3

ABSTRACT

Age determination methods and their application are presented for yellowtail rockfish, Sebastes
flavidus; canary rockfish, S. pinniger; and black rockfish, S. melanops, collected off Oregon during
1972-75. Of 25 anatomical structures examined, those compared for consistency of readings were the
anal fin pterygiophore, opercle, otolith, scale, and vertebra. Various heating, staining, and micros-
copy techniques were applied to otoliths and scales with little success. The effect of deviation between
otolith readings on survival estimates and age-length relationships is discussed. Consistency of otolith
readings was generally superior to other structures for these three species. For yellowtail, canary, and
black rockfishes, respectively, 71, 76, and 76% of two independent otolith readings deviated by no more
than ±1 assumed annulus. Consistency of otolith readings for all three species decreased with age.
Even though age estimates were not completely consistent, Chapman-Robson and catch curve esti-
mates of survival, as well as age-length relationships, each derived from two readings of the same set
of otoliths, were not significantly different at the 95% level for the three species. Age-length relation-
ships are given for both male and female yellowtail, canary, and black rockfishes.

In 1973, yellowtail rockfish, Sebastes flavidus
(Ayres); canary rockfish, S. pinniger (Gill); and
black rockfish, S. melanops Girard, composed 41,
38, and 4%, respectively, of the total Oregon
commercial trawl catch of rockfishes consisting of
19 species (Oregon Department of Fish and
Wildlife4 unpubl. data). Because little is known of
the biology of these fishes, information on age,
length, and weight are needed for estimates of
mortality, growth, and ultimately sustainable
yield.

The investigation was based on analysis of
samples taken off Oregon from 1972 to 1975. The
overall objective was to determine if an acceptable
technique! s) could be developed for age determi-
nation of these species. Specific objectives were: 1)
to determine if counts of annuli on aging
structures can be reproduced consistently; and 2)
to determine if deviations between successive

'Supported by funds from the Oregon Department of Fish and
Wildlife. Technical Paper No. 4254, Oregon Agricultural
Experiment Station, Corvallis, OR 97331.

department of Fisheries and Wildlife, Oregon State Univer-
sity, Corvallis, OR 97331; present address: Pacific Marine
Fisheries Commission, 1400 SW. Fifth Avenue, Portland, OR
97201.

department of Fisheries and Wildlife, Oregon State Univer-
sity, Corvallis, OR 97331.

4Formerly known in part as the Fish Commission of Oregon.

Manuscript accepted October 1976.
FISHERY BULLETIN: VOL. 75, NO. 2. 1977.

counts of annuli significantly affect estimates of
survival and the age-length relationships.

Considerable effort has been expended on age
determination of commercially important species
of Sebastes in the North Atlantic. Perlmutter and
Clarke (1949) used scales to age juvenile redfish,
iS. marinus, but did not include older fish in the
study because of difficulty in discerning annuli.
Kelly and Wolf (1959) reported 100% agreement
between independent readings of redfish otoliths
with less than 10 annuli, but agreement between
readings for fish from 7 to 20 + yr was only 31%.
Sandeman (1961) used scales for juvenile redfish
( <5 yr), but found otoliths to be superior for older
fish.

In the North Pacific Ocean, the majority of
research relative to our study has been conducted
on the Pacific ocean perch, S. alutus. Alverson and
Westrheim (1961) reported readability of scales
for Pacific ocean perch was only fair, while
Chikuni and Wakabayashi (1970) were satisfied
with scales for the same species. Westrheim
(1973) subsequently found that agreement be-
tween readings of Pacific ocean perch otoliths
decreased from 100% for 0-zone otoliths to 26% for
19-zone otoliths. Phillips ( 1964) found both scales
and otoliths could be used for valid age estima-
tions for 10 species of California rockfish, includ-

405

FISHERY BULLETIN: VOL. 75, NO. 2

ing S. flavidus and S. pinniger, but used scales
because they were obtained with less effort. Miller
and Geibel (1973) preferred scales to otoliths for
blue rockfish, S. mystinus, off California because
scales allowed greater ease in back-calculation of
growth. Wales (1952), working on the same
species, reported that scales were easier to read
than otoliths. Chen (1971) found scales were
frequently regenerated on rockfish of the sub-
genus Sebastomus, so he used otoliths for age
determination.

Otoliths were used to age copper rockfish, S.
caurinus, in Puget Sound (Patten 1973) and
northern rockfish, S. polyspinis, in the Gulf of
Alaska ( Westrheim and Tsuyuki 1971 ). There are
no published reports on the life of S. melanops,
although Miller (1961) indicated that the ages of
several specimens were estimated. Westrheim
and Harling ( 1975) used otoliths to determine age-
length relationships for 26 scorpaenids in the
northeast Pacific.

TABLE 1. — Structures examined from yellowtail rockfish,
canary rockfish, and black rockfish with a description of their
suitability for age determination.

Structure

Description

Anal fin pterygiophore

Anal spine

Articular

Astenscus

Basipterygium

Ceratohyal

Cleithrum

Dentary

Epihyal

Hypurals

Interopercle

Lachrymal

Lapillus

Maxilla

Mesopterygoid

Neurocranial bones

Opercle

Pelvic fin rays

Postcleithrum

Premaxilla

Sagitta

Scale

Subopercle

Supracleithrum

Vertebral centrum

enumerable zones present

zones present, but not enumerable

insufficient calcification

zones present, but not enumerable

insufficient calcification

zones present, but not enumerable

insufficient calcification

zones present, but not enumerable

insufficient calcification

zones present, but not enumerable

insufficient calcification

enumerable zones present

zones present, but not enumerable

insufficient calcification

zones present, but not enumerable

enumerable zones present

insufficient calcification

zones present, but not enumerable

enumerable zones present

METHODS AND MATERIALS

Most fish used in this study were sampled
randomly from the commercial trawl landings in
Astoria and Coos Bay, Oreg., from 1972 to 1975.
Sex, length to the nearest centimeter, and weight
to the nearest gram were recorded, and one or both
saccular otoliths (sagittae) were extracted.
Twenty-five anatomical structures (Table 1),
including the anal fin pterygiophores (largest),
opercles, otoliths, scales, and several anterior
vertebrae were sampled from carcasses obtained
from fish processing plants in Newport, Oreg.,
from 1974 to 1975. Juvenile fish were collected on
research cruises on the Oregon continental shelf
from 1972 to 1974, and by scuba and hook-and-
line in Yaquina and Tillamook bays from 1973 to
1975.

Otoliths were stored in a 50:50 solution of
glycerine and water and read using reflected light
on a dark background utilizing a binocular
dissecting microscope at 10 x. Otolith sections 0.3
mm thick were obtained with a thin sectioning
machine after being embedded in polyester
casting resin. Scales were cleaned, dried, and
mounted between glass slides or impressed on
acetate cards and read using a scale projector with
a 48-mm objective. Other structures, including
opercles, pterygiophores, and vertebrae were
heated in a detergent-water solution at 50°C for 20
min to remove adhering tissue and air dried.

Opercles were examined with the naked eye and
pterygiophores and vertebrae were examined by
use of a binocular dissecting microscope at 10 x.

One year of the life of the fish was assumed to be
represented by an opaque zone followed by a
hyaline zone on otoliths (Kelly and Wolf 1959;
Westrheim 1973) as well as on opercles, pterygio-
phores, and vertebrae. A scale annulus was
defined as a zone of closely spaced circuli (check)
following a zone of widely spaced circuli (Van
Oosten 1929; Tesch 1968). True annuli are
represented by pronounced hyaline zones on
otoliths and bony structures and by pronounced
checks on scales. Indistinct zones or zones that are
split or discontinuous were considered accessory
(false) annuli. A zone that obviously interrupts
the periodicity of the pattern of zonation was
considered to be accessory unless it occurred in
many fish in the same sample.

Consistency of readings of aging structures was
measured by the ability of the reader to reproduce
successive, independent counts of annuli. To
insure independence there was a period of several
months between most otolith readings. When the
period was less than 2 wk, a five digit code number
was assigned to each structure to prevent possible
memorization of previous age estimations. Inde-
pendent readings of yellowtail rockfish otoliths
were made by two people, while those of canary
and black rockfishes were made by the same
person.

406

SIX and HORTON: ANALYSIS OF AGE DETERMINATION METHODS

Age composition data were described graphi-
cally by FISHPLOT, a computer plotting routine
based on the method of Hubbs and Hubbs (1953).
Survival estimates were obtained by the
Chapman-Robson (Robson and Chapman 1961)
and the catch curve (Ricker 1975) methods. The
age-length relationship of yellowtail rockfish was
described by the equation L - cAh, where L =
length (centimeters), A = estimated age (years),
and c and b are constants. The age-length
relationships for canary and black rockfish were
described by the von Bertalanffy growth-in-
length equation with the computer program BGC-
2 (Abramson 1965) using the method of least
squares weighted according to sample size (Tom-
linson and Abramson 1961).

A total of 71 young unsexed black rockfish,
mostly young-of-the-year, were used in the age-
length analysis. Their corresponding lengths
were applied to both males and females, with the
assumption that there were little or no sexual
differences in length at these younger ages. The
assumption was based on the fact that growth
curves for male and female Pacific ocean perch,
obtained by Westrheim (1973) for fish from
Oregon to British Columbia and by Gunderson
(1974) for Washington samples, were nearly
identical at ages less than 6 yr.

RESULTS AND DISCUSSION

Suitability of Structures for
Age Determination

Only 5 of 25 anatomical structures sampled
were suitable for estimation of age. These were
the anal fin pterygiophore, opercle, otolith, scale,
and vertebra. The criterion used to determine
suitability for aging was the presence of enumer-
able growth zones. Based on examination of a
limited sample, most structures did not satisfy
this criterion because: 1) they were not suf-
ficiently calcified to reveal distinct growth zones,
or 2) calcification was evident but growth zones
were not discernible (Table 1). The above five
structures were examined further to determine
whether successive, independent estimates of age
were consistent.

Consistency of Readings

Percent agreement between two independent
counts (readings) of assumed annuli by the same

person on anal fin pterygiophores, opercles,
otoliths, scales, and vertebral centra sampled
from the same yellowtail, canary, or black
rockfish is presented in Table 2. Exact agreement
±1 assumed annulus is also given. Agreement
was low for all structures and species except oto-
liths of canary rockfish. Agreement between oto-
lith readings for yellowtail and canary rockfishes
was superior to agreement between readings of
other structures, with 71 and 97% agreement ±1
assumed annulus, respectively. For the sample of
black rockfish, otoliths and opercles were equally
readable with 74 and 75% agreement ± 1 assumed
annulus, respectively.

Means of the two readings of the five structures
agreed fairly well for black rockfish, indicating
that counts of assumed annuli on the structures
were similar. Means were not similar for these
structures from yellowtail and canary rockfishes.

A number of samples of each structure were not
read due to crystallization and breakage of
otoliths, regeneration of scales, and poor calcifi-
cation of opercles and pterygiophores. Throughout
the entire study at least one of the two otoliths was
partially or completely crystallized in 23 of 1,116
(2.1%) yellowtail rockfish, 27 of 666 (4.1%) canary
rockfish, and 29 of 302 (9.6%) black rockfish.
There were more readable vertebral centra and
otoliths than any of the other structures. Many

TABLE 2. — Estimations of age, number of readable structures,
and percent agreement of two independent readings of five
structures sampled from 35 yellowtail rockfish, canary rockfish,
and black rockfish landed off Newport, Oreg., 1974-75.

Estimated age (yr)

No.

Agreement (%)

Structure

Min-max

Mean readable

Exact

±1 yr

Yellowtail rockfish

Anal pteryg-

iophore

9-18

125

Opercle

—

Otolith

10-18

15.2

Scale

8-15

11.2

Vertebral

centrum

8-18

12.9
Canary rockfish

Anal pteryg-

iophore

7-20

9.5

Opercle

4-18

7.8

Otolith

5-22

8.9

Scale

7-23

10.7

Vertebral

centrum

5-18

8.9
Black rockfish

Anal pteryg-

iophore

5-18

9.6

Op3rcle

5-18

Otolith

6-15

10.7

Scale

7-16

10.7

Vertebral

centrum

6-18

10.3

407

FISHERY BULLETIN: VOL. 75, NO. 2

opercles were not readable, especially those
sampled from yellowtail rockfish, where 32 of 35
could not be used for age determination.

Consistency of otolith and scale readings subse-
quently was compared in a larger sample. A chi-
square test for paired data corrected for continuity
revealed that exact agreement between otolith
readings was significantly greater than exact
agreement between scale readings for yellowtail
(P<0.05)5 and black (P<0.005) rockfishes (Table
3). No significant difference occurred between
readings of otoliths and scales for canary rockfish
(P>0.90). Percent agreement between first read-
ings of both structures for all three species was
low.

TABLE 3. — Percent agreement in estimates of age between first
and second readings of the same structure and between first
readings of different structures (otoliths and scales) sampled
from the same yellowtail rockfish, canary rockfish, or black
rockfish caught off Oregon, 1974-75.

I Frrsr reading
] Second reading

Within

structures

Between strut
Exact ±1

Otolith

Scale

;tures

Species

Exact

±1

Exact

±1

Yellowtail
rockfish

Canary
rockfish

Black
rockfish

In terms of consistency of readings, the otolith is
the best structure of those examined for age
determination of yellowtail, canary, and black
rockfishes; yet, even this method is questionable.
Deviations of readings of yellowtail rockfish
otoliths by two readers generally increased with
age of the fish (Figure 1). For canary rockfish
otoliths read twice by the same person, deviations
of readings initially increased and then stabilized
with increasing age (Figure 2). Deviations of
readings of black rockfish otoliths read twice by
the same person also increased with age of the fish
(Figure 3). The distribution of deviations is
skewed considerably in the positive direction,
indicating that the second reading was substan-
tially lower than the first. For our largest sample
of 322 yellowtail rockfish, 481 canary rockfish,
and 357 black rockfish, respectively, 71, 76, and
76% of the two readings deviated by no more than
±1 assumed annulus. In a study on Pacific ocean
perch by Westrheim (1973), 85% of two otolith
readings by different people deviated by no more

FIGURE l.— Age composition of 322 yellowtail rockfish obtained
by two independent readings of their otoliths; specimens were
collected from fish processing plants in Astoria and Coos Bay,
Oreg., 1973-74.

■ First reaemff
^ Stcond raodine

FIGURE 2. — Age composition of 353 canary rockfish obtained by
two independent readings of their otoliths; specimens were
collected from fish processing plants in Astoria and Coos Bay,
Oreg., 1974.

I First reading

J Second reading

Probability of a greater chi-square value.

408

FIGURE 3.— Age composition of 242 black rockfish obtained by
two independent readings of their otoliths; specimens were
collected from fish processing plants in Astoria and Coos Bay,
Oreg., 1974.

SIX and HORTON: ANALYSIS OF AGE DETERMINATION METHODS

than ±1 zone. Kelly and Wolf (1959) reported
59.7% agreement ±1 yr for otoliths of 7-20+ yr-
old redfish.

Several explanations exist for the observed
deviations between readings. Due to the presence
of split zones and the irregularity of the marginal
areas on older rockfish otoliths, different readings
may be obtained from different areas of the same
otolith. There are eight major marginal areas on
otoliths that can be used in age determination
(Figure 4); two or three generally give superior
results depending on the species in question.
However, these favored areas are not consistently
readable from one otolith to the next in any
sample. Therefore, there is no specific area that
can be used consistently on all the otoliths,
making it possible that two different areas could
be read on two independent readings of the same
otolith. Indeed a comparison of areas used by
readers A and B for yellowtail rockfish otoliths
showed that of the readings that disagreed, 71%
were made on different areas of the otolith,
whereas, of the readings that agreed, only 56%
were made on different areas.

Discrepancies in counts of annuli also are
probably a function of the difficulty in defining the
type of outer edge on otoliths. If an otolith had two
opaque zones, each followed by a hyaline zone,
plus an additional opaque zone on the outer edge,
then an age of 2 was assigned. If an additional

ANTERODORSAL

DORSAL

POSTERODORSAL

ANTEROVENTRAL

VENTRAL

POSTEROVENTRAL

POSTERIOR

FIGURE 4. — Drawing of the right otolith (sagittal from a 4-yr-old
black rockfish as seen under reflected light on a dark background
showing the marginal areas used in age determination (O-
opaque zone; H-hyaline zone).

hyaline zone existed on the edge of the above
otolith, then an age of 3 was assigned. But since
the zones on the outer edge of older rockfish are
indistinct because of slow growth at older ages, it
is conceivable that discrepancies of 1 yr could exist
between independent readings of the same area of
a particular otolith.

A third cause of discrepant counts is that entire
samples of otoliths were often exceptionally
opaque, or, conversely, transparent, possibly due
to the storage medium and/or length of storage.
Annuli on otoliths such as these are difficult to
distinguish.

Because one could question the use of only two
readings to assess the consistency of otolith
readings, a sample of 198 yellowtail rockfish
otoliths was read independently three times with
a week between readings. A chi-square test for
independent data corrected for continuity indi-
cated no significant differences among the three
agreement statistics (P>0.75). In this case,
consistency of readings was not changed by the
addition of a third reading.

Validity of the Otolith Method

Until the data needed for validation can be
collected, it is assumed for the purposes of this
study that one opaque and one hyaline zone are
laid down each year on otoliths of rockfishes in
Oregon. Van Oosten (1929) and Graham (1956)
listed methods used to provide indirect evidence of
the validity of age readings of scales and other
structures. The commonly applied methods are
observation of a dominant year class over a period
of years, and analysis of seasonal changes of the
margin of some anatomical structure. Westrheim
(1973) was able to follow the yearly progression of
a dominant year class of Sebastes alutus for a
period of several years and also demonstrated, by
examination of the marginal zones on the otolith,
that the hyaline zone is formed annually on
juvenile fish. Kelly and Wolf ( 1959) found that one
opaque and one hyaline zone are laid down each
year on otoliths of young S. marinus.

Unfortunately, similar tests could not be con-
ducted in this study owing to the absence of any
obviously dominant year classes in the fish
sampled and to the inadequate samples of young
fish from a sufficient number of months through-
out the year to permit demonstration of the
seasonal changes in the margin of the otolith.
Otoliths from older rockfish are not suitable for

409

FISHERY BULLETIN: VOL. 75, NO. 2

this method, because zones on the outer edge are
narrow and therefore difficult to distinguish until
late in the growing season. Moreover, because of
the irregular growth of otoliths of older rockfish,
different marginal areas provide different results.

Otolith Sections

Results indicate that consistency of otolith
readings is superior to that of scales or other
structures for the three species of rockfishes
studied, but agreement of otolith readings still
may be unsatisfactory. Otoliths were sectioned to
try to improve consistency of readings. Blacker
( 1974) noted that annuli are laid down only on the
proximal (internal) surface of the otolith during
later years in the life of fishes such as sole, Solea
solea; plaice, Pleuronectes platessa; turbot, Scoph-
thalmus maximus; redfish, Sebastes sp.; and horse
mackerel, Trachurus trachurus. These annuli are
not seen when the distal surface of the otolith is
used for age determination and the investigator
underestimates the age of the fish.

Exact agreement between readings of whole
and sectioned otoliths of canary rockfish (37 vs.
219c ) differed by 16 percentage points (Table 4). A
chi-square test for paired data corrected for
continuity revealed that there was a significant
difference between the two (P<0.025). Percent
agreement between first readings of whole and
sectioned otoliths was low with a value of 51% ±1
assumed annulus. The similarity of the mean
estimated ages indicates that the phenomenon
reported by Blacker (1974) probably does not
occur in canary rockfish otoliths. Ages were not
substantially underestimated by reading the
distal surface of the whole otolith.

Sectioning did not improve consistency of
readings of canary rockfish otoliths. Moreover, it
is not possible to follow specific annuli completely
around the sectioned otolith to determine if an
assumed annulus is split. Whole otoliths allow the

TABLE 4. — Percent agreement between first and second read-
ings of whole otoliths and between first and second readings
of sectioned otoliths, and percent agreement between first
readings of whole and sectioned otoliths of canary rockfish
caught off Oregon, 1974.

reader a choice of marginal areas to read, whereas
sections do not.

Additional treatments were applied to otoliths
and scales with little success (Table 5).

TABLE 5. — Treatments applied to otoliths and scales of yellow-
tail, canary, and black rockfishes captured off Oregon during
1972-75.

Treatment

Description

Result

Otoliths

Baking

Lawler and McRae
(1961)

Resolution not improved

Burning

Christensen (1964)

Difficult to obtain con-
sistent effect

Scanning electron

Liew (1974),

Impracticable to view en-

microscopy

Blacker (1975)

tire otolith in detail

Surface microscopy

Smith (1968)

Zones indistinct

Alizarin red S staining

In 1% KOH to obtain
purple color

Stain not readily absorbed

Methyl violet stain

Albrechtsen (1968)

Stain absorbed, but zones
indistinct

Silver nitrate stain

1% aqueous solution
Scales

Stain not absorbed

Polarized light

Kosswig (1971)

Zones near focus indistinct

microscopy

Agreement

Within technique
Whole Sectioned

Between techniques
(Whole vs. sectioned)

Exact

±1

Mean estimated age

71
91
14.0

21
57
91
14.7

51
91

Effect of Deviations of Otolith Readings
on Biological Information

Age Composition

The frequencies of two independent readings of
yellowtail rockfish otoliths made by different
readers generally correspond for ages 9-15 (Figure
1). Correspondence is lower for younger and older
age-groups. The two distributions are approxi-
mately normal with means of 12.2 and 12.8 yr,
respectively. Figure 5 graphically demonstrates
that the means are not significantly different
because the 95% confidence intervals for the
means overlap. For the two distributions, the
standard deviations are similar and the ranges
are equal, but the minimum and maximum values
disagree by 1 yr (Figure 3).

Frequencies of age readings for canary rockfish
derived from two independent readings by the
same person correspond over most of the ranges of
ages (Figure 2). Greatest discrepancies occurred
at ages 11, 14, and 20. Again the distributions are
approximately normal with means of 13.6 and
14.2 yr for first and second readings, respectively.
The means are not significantly different at the
95% level (Figure 5). The standard deviations are
similar, while the maximum ages disagree by 2 yr.

Otolith reading frequencies for two indepen-
dent readings by the same person for black
rockfish correspond closely for ages 9-12. There is
less agreement for other ages (Figure 3). The

410

SIX and HORTON: ANALYSIS OF AC.K DETERMINATION MIIIK IDS

S tlavidus

READER I

READER 2
S pirtmg»r

READER I

READER 2

S mtlonops

READER I

READER 2

1 1

1 II

■ i

i ■

— t-n

13 18

ESTIMATED AGE (yr)

FIGURE 5. — Mean (vertical line), range (horizontal line),
standard deviation of the mean (white bar), and 95% confidence
intervals about the mean (black bar) for two otolith age readings
of yellowtail rockfish, canary rockfish, and black rockfish landed
in Oregon, 1973-74.

distributions are approximately normal with
means of 11.1 and 10.2 yr, respectively, for first
and second readings. Figure 3 shows the means to
be significantly different at the 959c level. The
standard deviations of the two distributions differ
more for this species than for yellowtail and
canary rockfishes. Ranges of the two distributions
are similar (Figure 5).

Survival

Estimates of survival obtained by two methods
generally correspond for all species and readings,
although Chapman-Robson estimates were con-
sistently lower than catch curve estimates (Table
6). At the 957c level none of the paired estimates
from the two readings were significantly different,
as shown by the overlap of confidence intervals.
Differences between survival estimates calcu-
lated from readings of the same otoliths were
greatest for yellowtail rockfish and smallest for
canary rockfish by either the catch curve or the

Chapman-Robson method; yet, on the average,
differences between catch curve estimates for the
two readings were greater than those obtained by
the Chapman-Robson method (Table 6). The
differences between catch curve estimates were
0.11, 0.015, and 0.093 for yellowtail, canary, and
black rockfishes, respectively, while differences
between Chapman-Robson estimates were 0.051,
0.031, and 0.051, respectively.

Age-Length Relationship

The age-length relationships derived from two
otolith readings for yellowtail rockfish were
described by the equation L = cAh (Figure 6).
Fitted lengths-at-age for the first reading were
slightly higher than those for the second reading,
but 959c confidence limits of the estimates of
constants c and b overlap considerably for the first
and second readings (Table 7). Little or no overlap
of confidence limits for constants c and b exists for
males and females for either the first or second
readings (Table 7), indicating a significant differ-
ence between the age-length relationships by sex
for yellowtail rockfish. Age-length data for yellow-
tail rockfish were initially applied to the von
Bertalanffy growth-in-length equation, but were
not well described by this equation due to the
lack of young fish in the samples.6

Age-length relationships for male canary rock-
fish based on two independent readings are nearly
identical (Figure 7). Growth curves for females
are similar (Figure 7), but discrepancies exist at
older ages where fitted lengths for the first
reading were higher than those for the second.

6The von Bertalanffy equations derived from two readings of
yellowtail rockfish otoliths were:

Males— Reading 1: lt = 47.96[1 - exp( -0.16(^ + 4.01))]
Reading 2: I, = 46.34 [1 - exp( -0.27U - 1.03))]
Females— Reading 1: /, = 55.47 [1 - exp( -0.14(^ + 3.19))]
Reading 2: /,= 53.81 [1 - exp( -0.19U - 0.24))].

TABLE 6. — Survival estimates based on two independent readings of the otoliths of yellowtail rockfish, canary rockfish,

and black rockfish landed in Oregon, 1973-74.

Chapman

Robson

Catch curve

Species

Estimate

95% conf. limits

Estimate

95% conf. limits

Ages used

Yellowtail rockfish:

Reading 1

0.54

0.04

0.46-0.61

0.60

0.04

0.49-0.70

0.95

14-18

Reading 2

0.59

0.03

0.52-0.65

0.71

0.05

0.59-0.82

0.90

14-18

Canary rockfish:

Reading 1

0.67

0.03

0.62-072

0.73

0.04

0.65-0.80

0.86

15-23

Reading 2

0.70

0.02

0.65-0.75

0.74

0.04

0.66-0.82

0.85

15-23

Black rockfish:

Reading 1

0.60

0.03

0.54-0.66

067

0.02

0.62-0.72

0.98

12-17

Reading 2

0.55

0.04

0.47-0.63

0.58

0.03

0.52-0.64

0.97

12-17

411

FISHERY BULLETIN: VOL. 75, NO. 2

TABLE 7. — Estimates of parameters describing the age-length
relationship for yellowtail rockfish, canary rockfish, and black
rockfish based on two independent readings of their otoliths.
The 95% confidence limits for the estimates are in parentheses.
Parameters First reading Second reading

6 yellowtail rocktish:

28.00

28.41

(25.96-30.03)

(26.37-30.45)

0.18

0.17

(0.15-0.21)

(0.14-0.20)

9 yellowtail rockfish:

25.08

23.66

(23.05-27.12)

(21.62-25.71)

0.26

0.29

(0.23-0.30)

(0.25-0.32)

6 canary rockfish:

"*-«

53.60

53.30

(52.38-54.82)

(52.14-54.46)

0.19

0.18

(0.17-0.21)

(0.16-0.20)

0.68

0.54

(0.39-0.97)

(0.25-0.83)

9 canary rockfish:

(.«

60.95

57.43

(58.09-63.81)

(55.90-58.96)

0.15

0.18

(0.12-0.17)

(0.15-0.20)

0.54

0.90

(-0.03-1.11)

(0.49-1 .30)

6 black rockfish:

Loo

50.30

52.03

(49.07-51.53)

(50.48-53.58)

0.23

0.22

(0.21-0.26)

(0.19-0.25)

-0.46

-0.44

(-0.65)-(-0.28)

(-0.62M-0.26)

9 black rockfish:

<-*

57.83

58.78

(55.30-60.36)

(56.43-61.13)

0.17

0.18

(0.14-0.19)

(0.15-0.20)

-0.74

-0.56

(-0.99M-0.49)

(-0.77M-0.35)

This difference exists because the first reading
was generally lower than the second, and read-
ability decreased with age. Interval estimates of
the von Bertalanffy constants Lx, k, and t0 for first
and second readings for males are comparable
(Table 7). Greater differences occur between
estimates of the parameters for first and second
readings for females, although interval estimates
still overlap. For males and females for the first
reading, there is no overlap of interval estimates
for Lx, slight overlap for k, and considerable
overlap for t0 (Table 7). Similarly, for males and
females for the second reading, there is no overlap
of interval estimates for Lx, and considerable
overlap of interval estimates for k and t0. This
indicates that differences in growth exist.

Growth curves for male black rockfish derived
from two otolith readings are similar (Figure 8),
although discrepancies existed between fitted
lengths at older ages. The same is true for the age-
length relationship for females (Figure 8). Inter-
val estimates of all three von Bertalanffy con-

45 -

MALES

•
G

•

• c o "
• o

• 0

• o

• o
o

• First reading

O.I8068
L = 27.9962A

•

8
«

° Second reading

L = 28.4II8A°-17206

FEMALES

6
6
6
o
. o
o

•

o
o

•

•
O

• First reading

0.26386
L = 25.084IA

° Second reading

0.28150
L=23.6646A

] . 1

1 . i X 1 1 1 1 1

5 7 9 II 13 15 17 19 21

ESTIMATED AGE (yr)

FIGURE 6 — Age-length relationships for yellowtail rockfish
derived from two independent readings of their otoliths collected
from Oregon samples, 1973-74.

MALES

-aSoSo 6°
o 8

•

• First reoding

9
9
o

l,= 53.60[l-e-0J855l7('-°-68l0).

o Second reading

-O.I83965(t-0.542l)"|
1, =53.30 [l-e

FEMALES

# , 9 o o * o o c. o o

9
6

First reading

l,= 60.95[l-e-ai46062('-°-"67)]

■ ii,

o Second reading

c-,^^r, -O.I77790(i-0.8960}"|

Ii = 57.43[l-e

1 1 1 1 1 1 1 l . 1 J _L 1 1

0 2 4 6 8 10 12 14 16 18 20 22 24

ESTIMATED AGE (yr)

FIGURE 7. — Age-length relationships for canary rockfish de-
rived from two independent readings of their otoliths collected
from Oregon samples, 1972 and 1974.

stants overlap considerably (Table 7), indicating
no significant differences between growth curves
obtained from the two readings. For males and
females for the first reading, there is no overlap of
interval estimates for Lx and k, and considerable
overlap for to. For males and females for the
second reading, there is no overlap of interval

412

SIX and MORTON: ANALYSIS OF ACE DETERMINATION METHODS

E
I

MALES

, g V V 9 . . .

•

- • First reading
6 l, = 50.30[l-e-a2"85el,'a4622|]

0.
60

o Second reading

1,-52.03 [j.e-M'*»°<,.a4404J]

FEMALES o o o 9 9 •
o 9 ° ' ' *

0 » '

9 '
9
9

• First reading

l1 = 57.83[l-e-0-l684l6,,-a7426']

o Second reading

, .o 7o T, -0.178094(1.0.5585)1
1, = 58.78 |J-e J

2 4 6 8 10 12 14 16 18 20 22

ESTIMATED AGE (yr)

FIGURE 8. — Age-length relationships for black rockfish derived
from two independent readings of their otoliths collected from
Oregon samples, 1973-75.

estimates for L„, slight overlap for k, and
considerable overlap for tQ. As was found for
yellowtail and canary rockfishes, sexual differ-
ences in growth of black rockfish are apparent.

Further support of the otolith method may be
evidenced by a comparison of mean lengths-at-age
obtained in this study with those of other
investigators. Phillips ( 1964) and Westrheim and
Harling (1975) reported mean lengths similar to
those obtained in this study for yellowtail rockfish
(Table 8). A similar correspondence of canary
rockfish lengths does not exist, where an increase
of values from north to south is noted. This
analysis is limited by small sample sizes and could
further be complicated by geographical differ-
ences in growth reported to exist for other species
of rockfishes in the Northeast Pacific (Westrheim
and Harling 1975).

In summary, the observed deviations between
otolith readings produced slightly different esti-
mates of survival and of age-length relationships,
although these differences were not statistically
significant. The otolith method is the most
reliable of those analyzed and we believe, with
some reservations, that it can be used reliably for
management purposes. The reader should be
cautioned that contrary to the results of the
statistical test, some of the survival estimates
appear to be substantially different (Table 6).
Possibly a Type II error exists (Snedecor and
Cochran 1967), i.e., the statistical test shows no
significant difference when, in fact, one exists. We
believe that, for the most part, the observed
deviations between readings are minor; moreover,
with the collaboration of two or more trained
readers, consistency of age determinations can be
improved.

Further studies establishing the validity of the
technique are warranted. This may be made
possible by analysis of the marginal growth of the
otoliths of juvenile rockfish. By providing evi-
dence that an opaque and an adjacent hyaline
zone truly constitute an annulus, accuracy of
otolith age determinations will be ensured.

ACKNOWLEDGMENTS

We thank the following individuals and organi-
zations for their willing and generous support:
personnel of the Oregon Department of Fish and
Wildlife provided financial support, advice, and
samples — especially J. M. Meehan, J. G. Robin-
son, and R. L. Demory. Ruth Mandapat and
Sandra Oxford, Washington Department of Fish-
eries, provided some of the age determinations of
yellowtail rockfish; and Alfred Soeldner, Oregon
State University, helped with electron micros-
copy. R. G. Peterson, D. G. Chapman, and S. J.
Westrheim provided statistical advice; N. J.

TABLE 8.— Mean length (centimeters) at selected ages of yellowtail rockfish and canary
rockfish from British Columbia, Oregon, and California. Numbers of fish are shown in
parentheses.

British Columbia
(Westrheim and Harling 1975)

Oregon
(This study — reading 1 )

California
(Phillips 1964)

Species

Age

Male

Female

Male

Female

Sexes combined

Yellowtail

27.1

16)

27.6

10)

—

30.0

31.9(116)

rockfish

42.3

(4)

41.0

(2)

42.9(15)

46.6(19)

43.0

(48)

46.6(18)

49.2

(7)

46.1 (17)

50.4

(8)

50.4

(6)

476

(8)

—

53.0

(1)

Canary

22.5

(1)

235

(1)

29.0 (8)

29.2 (26)

31 .9 (

128)

rockfish

38.5

(1)

44.7 (11)

48.0

(6)

46.8

(57)

49.2 (32)

52.4(12)

56.5

(7)

505

(1)

51.0 (2)

56.0

(6)

413

FISHERY BULLETIN: VOL. 75. NO 2

Abramson supplied the von Bertalanffy computer
program, BGC-2; and J. K. Andreasen provided
the graphical program FISHPLOT.

LITERATURE CITED

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1965. Von Bertalanffy growth curve II, IBM 7094, UNI-
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196.
ALBRECHTSEN, K.

1968. A dyeing technique for otolith age reading. J.
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ALVERSON, D. L., AND S. J. WESTRHEIM.

1961. A review of the taxonomy and biology of the Pacific
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BLACKER, R. W.

1974. Recent advances in otolith studies. In F. R. Harden
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1975. Stereoscan observations of a plaice otolith. J.
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CHEN, L.

1971. Systematics, variation, distribution, and biology of
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CHIKUNI, S. AND K. WAKABAYASHI.

1970. On the scale characters of the Pacific ocean perch in
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termination by scale reading. [In Jap., Engl,
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214.

CHRISTENSEN, J. M.

1964. Burning of otoliths, a technique for age determina-
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Graham, M.

1956. Sea fisheries; their investigation in the United
Kingdom. Edward Arnold, Lond., 466 p.
GUNDERSON, D. R.

1974. Availability, size composition, age composition, and
growth characteristics of Pacific ocean perch (Sebastes
alutus) off the northern Washington coast during 1967-
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HUBBS, C. L., AND C. HUBBS.

1953. An improved graphical analysis and comparison of
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KELLY, G. F., AND R. S. WOLF.

1959. Age and growth of the redfish iSebastes marinus) in
the Gulf of Maine. U.S. Fish Wildl. Serv., Fish. Bull.
60:1-31.
KOSSWIG, K.

1971. Polarisationsoptische Untersuchungen an den
Schuppen des Rotbarsches iSebastes marinus L. und S.
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Komm. Meeresforsch. 22:219-225.

LAWLER, G. H., AND G. P. McRae.

1961. A method for preparing glycerin-stored otoliths for
age determination. J. Fish. Res. Board Can. 18:47-50.
LIEW, P. K. L.

1974. Age determination of American eels based on the
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ageing of fish, p. 124-136. Unwin Brothers, Surrey, Engl.

MILLER, D. J.

1961. Black rockfish. In California ocean fisheries re-
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Game, Sacramento.
MILLER, D. J., AND J. J. GEIBEL.

1973. Summary of blue rockfish and lingcod life histories;
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1973. Biological information on copper rockfish in Puget
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1964. Life history studies on ten species of rockfish (genus
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1975. Computation and interpretation of biological statis-
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ROBSON, D. S., AND D. G. CHAPMAN.

1961. Catch curves and mortality rates. Trans. Am.
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1961. A contribution to the problem of the age determina-
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1968. Otolith age reading by means of surface structure
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1967. Statistical methods. 6th ed. Iowa State Univ.
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TESCH, F. W.

1968. Age and growth. In W. E. Ricker (editor), Methods
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TOMLINSON, P. K., AND N. J. ABRAMSON.

1961. Fitting a von Bertalanffy growth curve by least
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Van Oosten, J.

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414

PREDATOR-PREY INTERACTIONS IN SCHOOLING FISHES

DURING PERIODS OF TWILIGHT: A STUDY OF THE

SILVERSIDE PRANESUS INSULARUM IN HAWAII1

Peter F. Major2

ABSTRACT

Observations of free living and captive silversides were made in Kaneohe Bay, Hawaii, in October and
November 1972 and September 1973. The silversides demonstrated changes in schooling behavior
associated with changes in light levels during the periods of twilight. During morning twilight,
individual silversides formed schools, which in some areas moved from deep water to shallow water
over reefs. All silversides remained in large inactive schools in shallow water or along the edge of
channels throughout the day. During evening twilight, schools left the reef and/or broke up, with
individual silversides spreading out to feed near the surface. Predation upon the silversides, as
evidenced by their jumping behavior, was most intense during the twilight periods as schools formed
and broke up. Captive silversides, when not in the presence of predators, tended to increase their
interfish distance when in diurnal schools. The formation and breakup of schools of these silversides
appear to be very similar to behavioral patterns of related and unrelated species offish in many parts of
the world. The formation and break up of silverside schools appear to be related to the threat of
predation, the availability of the silverside's food, and the visual sensitivity and thresholds of both the
silversides and their predators.

Daily twilight or crepuscular periods are critical
ones with respect to predator-prey interactions
between many species of fishes, at least in tropical
regions of the world. Hobson 1 1968, 1972), Collette
and Talbot (1972), and Domm and Domm (1973)
demonstrated the importance of twilight periods
on behavioral changes in reef fishes. Hobson
( 1968, 1972, 1974) suggested that such transitions
in behavior are shaped by the threat of predation.
Predation pressure is also clearly a factor in the
evolution of schooling behavior in prey species
(Breder 1959, 1967; Hobson 1968; Shaw 1970;
Radakov 1973). Most reef fishes hide from their
predators amongst the interstices of the coral reef.
Many surface and open water prey species lack
such hiding places and appear to form schools as a
means of cover seeking (Williams 1964, 1966), the
school serving as a mobile biological refugium
especially during daylight hours. During evening
twilight periods many such schools break up with
individuals spreading out to feed. During morning

'Hawaii Institute of Marine Biology Contribution No. 509.
From a thesis submitted in partial fulfillment of the require-
ments for the degree of Doctor of Philosophy. University of
California, Santa Cruz.

2Center for Coastal Marine Studies, University of California,
Santa Cruz, C A 95064; present address: Department of Biolog-
ical Sciences, Simon Fraser Universitv, Burnabv, B.C.. Canada
V5A 1S6.

twilight periods individuals once again form
schools (Hobson 1968, 1972, 1973; Hobson and
Chess 1973).

Vision has been shown to be important in the
maintenance of schools ( Woodhead 1966; Hunter
1968; Shaw 1970; Radakov 1973). In addition,
Munz and McFarland (1973) indicated that the
behavioral changes of tropical marine fishes
during periods of twilight are due to shifts in the
visual sensitivity of these fishes with changes in
light levels.

The objectives of this study were to determine if
schools of the Hawaiian silverside, the iao,
Pranesus insularum, broke up and reformed in
response to light levels occuring during twilight,
and to determine how the activity of predators of
this species of silverside was related to this
behavior.

Study Sites

Field observations were made at two locations
within Kaneohe Bay, along the island of Oahu in
the Hawaiian chain. These sites were a 10,000 m2
area of flat reef (water depth ^2 m at high tide )
immediately adjacent to the east side of Lilipuna
Pier (Dock), and a 2,500 m2 area near the central
portion of a dredged out (to a depth of 2-3 m)

Manuscript accepted October 1976.
FISHERY BULLETIN: VOL. 75. NO. 2. 1977

415

FISHERY BULLETIN: VOL. 75, NO. 2

"lagoon" adjacent to the Hawaii Institute of
Marine Biology (HIMB) on Coconut Island. The
northern edge of the reef adjacent to Lilipuna Pier
drops abruptly into a 3- to 10-m deep channel,
while the southern side is adjacent to the shore.

The reef and channel area near Lilipuna Pier
are open to the effects of wind and waves within
Kaneohe Bay throughout the year. Occasionally,
the winds abate or shift and the bay's surface
becomes calm and glassy. The observations
reported here could only be made at such times
when the estimated wind velocity was less than
2.6 m/s (5 knots). At night near the end of the pier
a fixed low intensity incandescent light bulb casts
an arc of light out over a small area in the channel.
Observations were not made within the area
encompassing this arc of light. The waters in the
HIMB lagoon are usually calm or only slightly
rippled, being protected by a vegetation covered
coral rubble peninsula on its normally windward
side and thicker, higher, vegetation on its island
or leeward side.

Kaneohe Bay is rimmed at approximately 1.6
km inland by mountains that rise to 762-960 m.
Throughout each day, dense clouds usually form
along these mountains, occluding the sun during
the late afternoon. This often results in twilight
conditions occurring earlier than would normally
be predicted for the bay's position of latitude and
longitude.

METHODS

The prey species of fish observed in this study
was P. insularum, approximately 20-60 mm SL
and approximately 0.03-2.45 g wet weight. Obser-
vations of the silverside's behavior were made
during calm periods in October (7 days) and
November (3 days) 1972 and September (5 days)
1973. All observations were made visually from a
height of 0-3 m above the surface of the water. The
morning observations commenced approximately
115 min prior to the time of sunrise. The evening
observation period terminated about 60 min after
the time of sunset.

The only attribute monitored quantitatively
during the course of the observations was the
jumping escape behavior of the silversides in
response to attacking predatory fishes. Enumerat-
ing the jumps became a shorthand method of
quantifying the number of predatory attacks in
the calm areas studied because jumping was

observed to be the primary means of escaping
predators once an attack occurred. Pranesus
insularum was the only prey species observed to
jump in the above areas during the periods of this
study. The success of predators at capturing prey
during the attacks was not determined. Hobson
(1968) used a similar method to quantify the
number of times leaping predatory cabrilla,
Mycteroperca rosacea, attacked flatiron herring,
Harengula thrissina, in the Gulf of California.

During periods of darkness or reduced light,
when visual observations under existing light
were not possible, jumping by schools of prey could
be heard within the areas studied by careful
listening; this could only be done when there was
no wind and the surface of the water was calm.
The time at which schools broke up or reformed
during twilight was estimated by listening to
changes in the sound of jumps made by multiple
and single prey close by, or with a flashlight beam
which was quickly turned on and off in one spot, or
swept rapidly across the surface of the water from
above, and/or held underwater within 0.3 m of the
surface. Whether the silversides were schooling or
spread out could be readily determined when the
fish were illuminated by the beam of light.

Light measurements were made above the
surface of the water with a photometer ( Weston
Ranger 9 universal exposure meter).3 Readings
taken with this photometer were compared with
those made with a Gossen foot-candle meter and a
Spectra-Combi 5000 Model photometer (Photo
Research, Burbank, Calif.). The readings ob-
tained during twilight periods were comparable to
those given by Brown (1952).

The observations and events reported here are
related to the time of sunrise, sunset, and the
periods of morning and evening civil and nautical
twilight. The two periods of twilight are defined by
the angular distance of the sun below the horizon,
0° to -6° for civil twilight, and -6° to -12° for
nautical twilight. Fish respond directly to the
amount and type of light present, which is
influenced by astronomical as well as local
environmental conditions. However, the use of
these terms and that of the corresponding angular
distance of the sun below the horizon is of
immense value when comparing the observations
of many investigators working in different loca-

•'Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

416

MAJOR: PREDATOR PREY INTERACTIONS IN FISHES

tions at different times of the year and under
different environmental conditions.

BEHAVIOR OF
FREE-LIVING SILVERSIDES

Between sunrise and sunset each day hundreds
to thousands of individual silversides could be
observed in large, often elongated, schools along
Lilipuna Pier and other structures over shallow
reefs, along the edge of reefs, and in quiet pro-
tected waters such as the HIMB Lagoon. At times
the silversides remained in the shadow of struc-
tures or overhanging vegetation, rarely venturing
into sunlit water. The schools were located just
under the surface of the water, with individuals
often forming single or multitiered layers. The
schools as a whole were largely stationary and in-
active except for the occasional individual that
darted out from and immediately returned to a
school. These individuals appeared to be feeding,
snapping at objects which I could not see when
they left the school. While in the large inactive
schools, individuals about one-half to two body
lengths apart were randomly oriented to one an-
other. However, upon the approach of a predator
or potential predator, or when attacked, the indi-
viduals rapidly became polarized, often less than a
body length apart as the school maneuvered about
the predator) s) in well coordinated patterns.

When a predator slowly approached a school of
silversides it frequently penetrated into the
school. However, as the predator moved into and
through a school, the silversides split into two or
more smaller groups which passed around to the
sides of the predator to reunite behind and along
the path just traversed by the predator. This
maneuver resulted in the formation of a void or
halo of clear water around the entire predator as it
moved through the school. This halo was esti-
mated to average about one to two predator body
lengths in width in any direction from the
predator. Similar behavior has been reported and
illustrated by Breder (1959), Nursall (1973), and
Radakov (1973). When a predator actually at-
tacked, it usually dashed at high speed toward an
individual in or near a school or into a segment of a
school. When attacked, individuals in the imme-
diate area of the predator jumped out of the water
as they radiated out and away from the path of the
predator. In a larger school, silversides at increas-

ingly greater distances from the attacking pred-
ator jumped less, the jump(s) grading into evasive
swimming; and in some instances, little or no
initial response was made by individuals some
distance from the predator.

As jumping silversides reentered the water they
realigned with other silversides that had jumped
or evaded by swimming. At the same time there
was a general, though somewhat belated, move-
ment of individuals around into the wake of the
rapidly moving predator. When an attack was
prolonged, as when a predator chased an indi-
vidual or small group of silversides, a large school
often formed a number of smaller schools, which
occasionally coalesced later. Frequently, jumping
and/or evading individuals or segments of the
attacked school joined with one or more other
schools which were usually nearby but unaffected
by the predator(s).

When a predator, such as a barracuda, attacked
from a horizontal direction, the silversides usu-
ally had a strong lateral component to their
jumps. Such jumps usually occurred at a shallow
angle just above the surface and less than 45° to
the surface. When attacked from directly below,
initial jumps tended to have a somewhat more
vertical than horizontal component, being greater
than 45° to the water's surface. Distances covered
during single horizontal jumps were not mea-
sured, but may have been as great as 5-10 times an
individual's body length; several meters were
spanned during a series of jumps.

When more than one predator simultaneously
approached or attacked a school of silversides,
evasive maneuvering and jumping became con-
fused. The more rapidly increased numbers of
predators approached or attacked, the more
"disorganized" the silverside's evasive response
appeared to become.

In Kaneohe Bay the most common diurnal
predators observed attacking and chasing silver-
sides were barracuda, Sphyraena barracuda; blue
jack, Caranx melampygus; leatherjacket, Scom-
beroides lysan; and lizardfish, Saurida gracilis.
Needlefish, Tylosurus sp., were also observed near
silverside schools, but attacks were not seen.
During the day, and particularly during the
evening twilight period, the jack, Caranx ig-
nobilis, may also have been a predator. This jack
readily attacked silversides in field and cement
enclosures. Recently ingested silversides were
occasionally found in the stomach contents of

417

FISHERY BULLETIN: VOL. 75, NO. 2

young scalloped hammerhead shark, Sphyrna
lewini (45-90 cm TL), caught by gill net at night in
the channels of Kaneohe Bay.

Solitary barracuda and needlefish slowly
cruised along just under the surface of the water
when they were near schools of silversides. When
stalking, they usually remained relatively mo-
tionless as they drifted or used slow caudal fin
undulations to scull along the surface. The
barracuda attacked by quickly dashing, usually
horizontally, a short distance towards an indi-
vidual or school of silversides.

Individuals or schools of jacks and leather-
jackets usually swam near the bottom in the
lagoon or at some midwater depth in the deeper
channels near Lilipuna Pier. Individuals of these
species slowly approached or rapidly attacked the
silversides, usually at an angle of about 45° to the
surface. They immediately retreated towards the
bottom after their approach or attack.

Lizardfish are cryptically colored, solitary ben-
thic "sit and wait" predators. When a school of
silversides swam over a lizardfish, it usually
dashed at an angle nearly perpendicular to the
surface, or at an angle greater than about 45° to
the surface as it approached the silversides.

Because the silversides were located just under
the surface of the water, the attacks by their
predators could usually be detected in one or both
of two ways. The momentum of a rapidly moving
predator often carried it clear out of the water
during an attack. This was particularly evident
during attacks made in a vertical direction. If the
predator turned as it approached the surface, its
body and/or caudal fin usually created a boil of
water at the surface, which often erupted with a
popping sound into a splash or spray of water. If it
was calm, a boil of water often left a small area of
residual foam bubbles as concentric circles moved
out across the water. When chases occurred along
or near the surface, the predators often left a wake
of disturbed water and froth to mark its path of
pursuit.

In the Lilipuna Pier area an infrequent diurnal
aerial predator was also observed. One to four
common noddies, Anous stolidus pileatus, re-
mained near or on the pier and flew to the areas of
jumping silversides and attempted to catch them
while the fish were still at the surface. Noddies
were more successful at catching silversides when
predatory fish attacked and then chased the
silversides along the surface.

BEHAVIOR OF
CAPTIVE SILVERSIDES

Over 100 h of observations of captive silversides
in net enclosures (3mx3mx3m deep to 6. 1 m x
6.1 m x 2 m deep) in the lagoon in Kaneohe Bay
and in a circular cement tank ( 9 m in diameter and
3 m deep with an underwater viewing window)
were made during day and night periods. Within
several days after introduction into the enclosures
that lacked predators, the individuals in the
schools of silversides slowly increased their
interfish distances from less than one or two body
lengths (as seen in the field) up to distances of 5-10
body lengths or more. Although the individuals
were often randomly aligned with respect to each
other, they did not lose their polarity to one
another when a school moved. Individuals occa-
sionally fed during the day, much as they did
when free in the field. However, they did not dash
out towards an object and immediately return to a
school. When one or more predators, such as jacks
or barracuda, were introduced into an enclosure
the schools tightened as interfish distances be-
tween silversides decreased to less than one to two
body lengths. Individuals continued to dart out
from the relatively stationary and motionless
schools, much as they did in the field. If attacks or
approaches were not initiated by a predator, the
schools loosened as interfish distances increased
once again. These distances were not as great as
they had been prior to the introduction of the
predator(s). Feeding continued until approaches
or attacks occurred. When approached, schools
split and formed a halo around the predator as
they moved to the rear of the predator to reform a
school again. When attacked, individuals jumped
out of the water and across the surface, away from
the predator. The behavior of individuals and
schools of silversides in the enclosures was much
the same as that observed in the field, as described
above.

During evening twilight periods, interfish dis-
tances increased as individuals in the schools
spread out across the surface. During the twilight
period, I could see the prey silhouetted against the
evening sky, but not the predators against the
bottom. As darkness increased, it rapidly became
impossible to see the silversides as well, although
the boils of water and splashes made by an
attacking predator and the return of jumping prey
into the water could be heard. During morning

418

MA.inK PREDATOR-PREY INTERACTH )\S I \ FISHES

twilight, interfish distances decreased as polar-
ized schools once again formed and moved in
coordinated patterns as they did in the field.

Silverside Jumping Activity Patterns

Morning Twilight

In the Lilipuna Pier area prior to nautical
twilight, I could hear jumping silversides and the
"pop" associated with attacking predators strik-
ing the water's surface approximately 20 min
after the observation periods had commenced and
95 min prior to sunrise (Figure 1). These jumps
were made primarily by individual fish in close
proximity to the pier in the channel near the edge
of the reef. Jumping occurred later by increas-
ingly larger numbers of individuals in schools at
the easternmost end of the observation area.
Jumps occurred initially near the edge of the reef,
moved toward, then turned northwest parallel to
and along the shore, finally spreading out over the
reef and toward the pier. These attacks by
predators and jumps of silversides sequentially
traced three sides of the perimeter of a rectangle
defining the east, south, and west boundaries of
the observed area near the pier. Attacks and
jumps in shallow water over the reef pre-
dominated after the beginning of nautical twi-
light, and by sunrise all attacks and jumping
occurred within a few meters of the pier. Peak
activity in shallow reef and deep channel water
was recorded just after the beginning of civil
twilight and steadily decreased to midday levels
(Figure 1).

The only predators observed to attack the
silversides over the reef in the early morning were
lizardfish. Blue jacks and barracuda were ob-
served in the channel and occasionally over the

reef near sunrise and during the late morning.

In the lagoon area, jumps in the central deeper
area of the lagoon were initially recorded 45 to 50
min before sunrise (Figure 1). As twilight pro-
gressed, jumping was eventually seen in narrow
bands of shallow water along the sides of the
lagoon, but occurred infrequently. Barracuda and
jacks were the principal early morning predators,
although lizardfish were also observed attacking
the silversides. Since the shallows were relatively
small in area, most of the silversides were
concentrated over the central deeper water of the
lagoon. A period of increased jumping activity did
not occur in the lagoon during twilight as it did
near the pier.

Light meter readings of 0.096-0.402 foot candle
(Table 1) were made in 1973 during the time ( 18-
24 min before sunrise, i.e., the time of civil
twilight) when silversides were in the process of
forming schools, especially in the lagoon area.
Initial schooling became noticeable (individuals
moving closer together, becoming more cohesive
and polarized when swimming as they did during
the day) in 1972 and 1973 as early as 44-23 min
before sunrise and was completed as late as 33-18
min before sunrise (Table 2). Silversides then
remained in schools throughout the day.

In summary, during the morning, predator
attacks and silverside jumping could not be
detected until 95 min before sunrise at the pier
and 50 min before sunrise in the lagoon. Deep-
water attacks were initially noted for individual
silversides, but subsequently increased numbers
of jumps were recorded in shallower water for
increasingly larger schools, especially near the
pier. During the time peak jumping occurred (30-
10 min before sunrise), silversides were forming
cohesive polarized schools (44-18 min before
sunrise, mean 29.4 min).

Table i

, — Light levels

(light meter readings

foot

candle) and the

hreakup £

ind formation

of schools of silversides.

Type of

Author Location Species

Light levels

No
read

of
mgs

activity

Mean Range

Remarks

Breakup
of schools

Formation
of schools

Steven 1959 West Indies

Shaw 1961

This report
Sept. 1973

Marine Biological
Laboratory, Mass.

Kaneohe Bay,

Hawaii
Kaneohe Bay,

Hawaii

Hepsitia
stipes

Menidia

Pranesus
insularum

0.06 0.07-0.05 2 Fish in aquariums indoor with windows and door

closed, no artificial light. Watched until

nightfall.
0.12 0.35-0.03 14 Experimental; gradual reduction of light until

school began dispersing. Used neutral density

filters.
0.21 0.402-0.035 3 Field, during evening twilight.

0.18 0.402-0.096 4 Field, during morning twilight.

'One-way analysis of variance (ANOVA) of all light meter readings (P = 0.57).

419

FISHERY BULLETIN: VOL. 75, NO. 2

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420

MAJOR PREDATOR PREY INTERACTIONS IN FISHES

TABLE 2. — Comparison of .school formation and breakup mPranesus insularum with twilight phenomena recorded near Lilipuna Pier

and HIMB lagoon, Kaneohe Bay, Hawaii.1
(Mean school formation = -29.4 min (before sunrise), mean school breakup = +19.1 min (after sunrise).]

Local time of

Relative time

Difference in time (mini

jtes) between sunrise anc

Beginning

Initial school

Location

Date

sunrise (h)

of sunrise

nautical twilight

civil twilight

formation

Schools formed

Lilipuna Pier

7 Oct. 1972

0625

-48

-23

-44

-33

HIMB lagoon

8 Oct 1 972

0624

23 Oct. 1972

0629

-22

-26

19 Nov. 1972

0644

-51

-24

-38

21 Nov 1972

0646

-51

-24

22 Nov 1972

0647

-51

12 Sept. 1973

0617

-48

-24

14 Sept 1973

0619

-48

-21

-23

Local time of

Relative time

Difference in time (minutes) between sunset and

End of

Initial school

Complete

Location

Date

sunset (h)

of sunset

nautical twilight

civil twilight

breakup

school breakup

HIMB lagoon

8 Oct 1972

1814

+ 48

+22

+ 26

22 Oct 1972

1804

+ 48

-22

-16

—

13 Sept. 1973

1835

+ 48

+ 22

—

•24

17 Sept. 1973

1832

•48

+ 22

+ 15

-21

18 Sept 1973

1932

•48

+ 21

-14

+ 18

'One-way ANOVA comparison of times of starting to school/schooling and starting to break up/complete breakup (P - 0.004)

Midday (1000- 1 500 H, Local Time)

In the pier area accurate counts of jumps made
by the silversides during the time between 1000
and 1500 h local time were usually difficult to
make due to waves caused by wind and nearby
vessel activity.

Figure 1 presents the data collected during
representative midday periods near the pier when
interference was minimal. Generally, the silver-
sides formed large elongated schools (hundreds to
thousands of individuals) under or near the pier.
The schools were largely inactive except when
predators or potential predators such as barra-
cuda, lizardfish, jacks, and needlefish, approached
or attacked. When the tide level was low, the
schools condensed and moved into deeper water
near or under the end of the pier.

In the lagoon area at HIMB, the behavior and
distribution of silversides was much the same
during midday as it was near the pier (Figure 1).
Small schools of silversides were strung out along
the sides of the channel. Large schools of hundreds
to thousands of fish were relatively inactive and
concentrated over deeper water in the center of
the lagoon. Barracuda and jacks were the most
frequent predators, but lizardfish and leather-
jackets were occasionally active in the lagoon.

Evening Twi light

As sunset approached, predator-prey activity
increased in frequency in the pier area (Figure 1).

Peak activity occurred between sunset and the
end of the period of civil twilight and then declined
rapidly to stop just after the end of the nautical
twilight period. The silversides moved off the reef
along, but in the direction opposite to, the path
taken during the morning twilight movement
onto and across the reef. Attacks and jumping
occurred near the pier, then out over the reef,
moved eastward along and parallel to shore,
finally northward to the edge of the reef at the
easternmost end of the observation area. As
darkness increased, attacks and jumping grad-
ually diminished in frequency and intensity
(fewer individuals in smaller and fewer schools
jumped).

In the lagoon area midday jumping activity in
shallow and deep water continued until just after
sunset, then stopped abruptly (Figure 1). The low
number of jumps in deep water in the late
afternoon and evening in the lagoon contrasts
sharply with the frequency of jumps in the earl}'
morning (Figure 1). This difference may be
related to the low levels of incident light striking
the surface of the lagoon in the afternoon and
evening due to the vegetation and the mountains
and clouds to the northwest obscuring the sun. In
the morning the lack of high vegetation and
mountains nearby to the northeast resulted in
light striking the lagoon's surface so that the
silverside were presumably visible to their pred-
ators.

Light meter readings of 0.035-0.402 foot candle
(Table 1) were made during the time (20-24 min

421

FISHERY BULLETIN: VOL. 75, NO. 2

after sunset, i.e., during civil twilight) silverside
schools were breaking up, the individuals spread-
ing out just under the surface of the water. In 1972
and 1973 schools began to break up (increased
interfish distances became noticeable) between 14
and 16 min after sunset and were spread out by 18-
26 min after sunset (Table 2).

In summary, with the approach of dusk,
predator attacks and silverside jumping increased
in frequency and intensity to peak during the
period of civil twilight, shortly after sunset, near
the pier. In the lagoon there was no peak activity;
the last attacks and jumps were recorded imme-
diately after sunset. Peak jumping near the pier
was recorded 5-15 min after sunset, just before the
time the silverside schools were observed to break
up becoming less polarized and cohesive (14-26
min after sunset, mean 19.1). In the lagoon,
however, attacks stopped before the prey schools
spread out; this may have been due to the shadows
and increased darkness caused by heavy vegeta-
tion along the northwest side of the lagoon.

Silverside Behavior: Conclusions

The temporal pattern of predatory attacks and
silverside jumping relative to sunrise was the
mirror image of that relative to sunset, at least for
the Lilipuna Pier area (Figures 1, 2). For each of
the four environmental situations studied, Figure
2 simplifies and graphically presents (at 50-min
intervals) the mean frequency of silverside jumps
illustrated in Figure 1. Midday (1000-1500 h)
jumps were combined and were not divided into
50-min intervals. Statistical comparisons (analy-
sis of variance, P=£0.05) of the jumping data for
sunrise ( -50 to +50 min), midday, and sunset
(-50 to +50 min) for each of the four situations
indicated that, at least for the shallow-water reef
area near Lilipuna Pier, the frequencies of jumps
at sunrise and sunset were similar and differed
from the number during midday.

The mean time of school formation occurred just
prior to the beginning of civil twilight in the
morning, and the mean time of the breakup of
schools occurred just before the end of civil
twilight in the evening. Peak predator activity
occurred just after schools formed (mean time) in
the morning and just prior to their breakup (mean
time) in the evening. The data presented indicate
that related events (e.g., school formation versus
breakup) occurred in the study sites significantly

S 200

3
O

W Pier -Shallow

INTERVALS OF OBSERVATION (minutes relative 10 sunrise or sunset)

FIGURE 2. — Mean frequency of Pranesus insularum jumps for
nine 50-min intervals (except midday). Based on data also pre-
sented in Figure 1.

earlier (about 5-15 min) in the evening, relative to
sunset compared with the morning events, rela-
tive to sunrise (Table 2). This discrepancy may be
due to the shadow effect of the clouds and
mountains near Kaneohe Bay, which produce
evening twilight conditions 5-15 min earlier than
predicted, as discussed above. The relatively low
frequency of deepwater attacks near the pier in
the evening indicated that by the time silversides
had moved off the reef and/or spread out, it may
have been too dark for predators to see individual
silversides. In the morning, the lack of mountains
and vegetation and increasing light levels re-
sulted in sufficient light being available for
predators to see their prey.

Observations of free-living and particularly
captive silversides, as well as my observations of
other schooling prey species (striped mullet,
Mugil cephalus, and Hawaiian anchovy, Stole-
phorus purpureus) in Hawaii, indicate that
predation is of prime importance in shaping the
behavioral patterns of prey species. When held
captive in the absence of predators for days or
weeks, individual prey in schools increased their
interfish distances and appeared to feed more
actively than they did in the field. When predators
were present, interfish distances within captive
schools were similar to interfish distances be-
tween individuals in the field. During the day,
schooling behavior appears to serve a protective
function for individuals, reducing the number of

422

MAJOR: PREDATOR-PREY INTERACTIONS IN FISHES

attacks made by predatory fish. This protective
function has also been observed for other school-
ing prey species (Radakov 1958, 1973; Neill and
Cullen 1974). The chance that a predator has of
singling out a specific individual silverside are
greatly reduced if schools are formed. This
appears to be especially true when the prey are
polarized towards one another and move close
together through coordinated maneuvers. In the
field, when predators were not in the immediate
vicinity of silverside schools, individual silver-
sides became relatively motionless and randomly
oriented towards one another, darting out from
schools presumably to feed. When individual
silversides presumably became exposed and/or
appeared to be accessible to one or more nearby
predators, the predators approached or attacked.
If the predator's approach was slow, the individual
silversides became polarized, the school maneu-
vering evasively. If a predator's approach was
sudden or rapid, individual silversides jumped out
of the water one or more times to evade. Both
schooling and jumping presumably decrease the
time a predator had to align itself with a specific
individual prey. In addition, a jumping silverside
often landed in the midst of its own, or that of
another nearby, school, presumably disappearing
from the predator's field of vision and/or path of
swimming. The formation of large schools com-
posed of many hundreds or thousands of indi-
viduals, especially a number of such schools
relatively close to one another, appeared to
increase an individual silverside's chance of
escape when jumping.

The movement of silversides into the shallow
water over reefs, and their location near and
under Lilipuna Pier and heavy overhanging
vegetation and along the sides of the lagoon, may
be additional means, besides schooling, of reduc-
ing predation. In the shallow water near the pier,
the most common vertical attacking predators
were lizardfish. In deeper water in the lagoon and
near the pier, jacks and leatherjackets also
attacked vertically. Horizontal stalking and at-
tacking predators, such as barracuda and needle-
fish, occurred in both deep and shallow water. The
depth of water over the reefs may have been less
than sufficient for some of the vertical attacking
species to maneuver and approach schools of
silversides undetected. The occurrence of silver-
sides near structures and along the sides of the
lagoon may have also limited the maneuver-

ability and avenues of approach for all species of
predators.

DISCUSSION

The interactions between silversides and their
predators in relation to solar phenomena are
almost identical in pattern and time to those given
by Hobson (1968, 1972) for the interactions of
Hurengula thrissina and their predator Mycter-
operca rosacea in the Gulf of California. Hobson
and Chess's (1973) study of the arrival and
departure of Pranesus pinguis to and from reefs at
Majuro Atoll in the Marshall Islands also showed
school movement related to specific times during
twilight. However, only a few predatory attacks
were observed at Majuro Atoll. Comparisons of
lunar and tidal changes during the studies in
Kaneohe Bay and Majuro Atoll and Baja Califor-
nia seem to indicate a relatively minor influence
on the crepuscular behavior of schools.

Hobson (1968, 1972, 1973), Collette and Talbot
(1972), and Domm and Domm (1973) have
demonstrated that there is relatively little activ-
ity amongst most coral reef fishes during a specific
segment of the twilight period. In the morning,
nocturnally active reef fish leave the open water
column to hide in the coral reef approximately 30
min before sunrise (Hobson 1972). Diurnal species
do not reoccupy the water column until approx-
imately 12-16 min prior to sunrise. It is exactly
between the above times, the "quiet period," as
defined by Hobson (1972), that peak surface
predator-prey activity and school formation takes
place in Kaneohe Bay, just as it does in the Gulf of
California (Hobson 1968, 1972), and possibly
Majuro Atoll (Hobson and Chess 1973). The
pattern is reversed during evening twilight
(Hobson 1972). Diurnal reef species evacuate the
water column approximately 6-22 min after
sunset. Nocturnal species then reoccupy the water
column about 14-34 min after sunset. Again,
surface predator-prey interactions peak and
schools break up in Kaneohe Bay during the time
that would be comparable with the evening quiet
period in other parts of the world.

The combined observations of reef fishes in the
Virgin Islands (Collette and Talbot 1972), the
Great Barrier Reef, Australia (Domm and Domm
1973), Hawaii (Hobson 1972), and the Gulf of
California (Hobson 1968) indicate nearly identi-
cal time relationships of behavioral events during

423

FISHERY BULLETIN: VOL. 75. NO. 2

the twilight transitional periods. This would be
the predicted relationship since fish respond to
specific intensities and spectral composition of
light (Munz and McFarland 1973). The intensity
and spectral composition of incident light at
specific times relative to sunrise or sunset are
identical each day, although they vary with time
and season and with latitude. The amount of cloud
cover and/or high mountainous terrain nearby, as
in Kaneohe Bay and Kona, Hawaii (Hobson 1972)
or Baja California (Hobson 1968), may shift the
activity patterns to later in the morning, or earlier
in the evening (i.e., shift the time relative to
sunrise and/or sunset at which specific light levels
occur). However, the basic relationships between
behavior and twilight periods appear to hold.

Light meter readings recorded during the
formation and break up of Hawaiian silverside
schools are compared with those recorded for two
other species of siversides in Table 1. The
readings for all three species are not significantly
different. Such light levels occur naturally when
the sun is between -5° and —9° below the horizon
during the periods of evening or morning twilight
(Brown 1952). These data and the field observa-
tions reported here are also comparable to the
light levels and the sun angles calculated from the
data presented by Pavlov (1962) for another
silverside, Atherina mochon pontica. Pavlov found
that peak predator success occurred at light levels
of approximately 0.01-108 foot candles corre-
sponding to sun angles of - 9° to + 1 ° to the horizon
(Brown 1952) (i.e., centered during the period of
civil twilight).

These comparisons indicate that related species
of silversides, which live in widely separate parts
of the world, have similar visual thresholds and,
perhaps, sensitivity. Munz and McFarland (1973)
provided a synopsis of research, which has shown
that many related species demonstrate a consid-
erable diversity in their visual sensitivity. How-
ever, species, whether related or not, which occur
in similar environments, appear to have similar
thresholds and sensitivity. These relationships
indicate that the above silverside species from
various locations in the world may have very
similar behavioral patterns and/or live in very
similar physical and biological environments.

When light levels decrease in the evening,
visual thresholds may be reached, making coordi-
nated schooling movements impossible, or at least
more difficult for the silversides. These thresholds

may be reached at the time when cone vision shifts
to rod vision (the Purkinje shift), neither cone nor
rod vision being fully efficient (Munz and McFar-
land 1973). As school formation breaks down or
increases, the silversides appear to be the most
vulnerable to predatory attack. This vulnerability
may be due to reduced visual sensitivity, leading
to an inability to see their predators below them
against a dark bottom or deep water (Hobson
1966, 1968) and react in time to avoid and escape
from them (Dill 1972, 1974a, b). In addition, such
prey may be unable to simultaneously interact
with conspecifics, and look out for predators at a
distance at low light levels.

Predators are presumably able to see their prey
at a horizontal angle or silhouetted against the
twilight sky for a short period of time before their
lower visual threshold is reached in the evening
(Hobson 1966, 1968). Munz and McFarland ( 1973)
indicated that increased visual sensitivity in
predators, which provides sufficient resolution for
the detection of prey in motion during twilight,
may be a result of having relatively larger, but
fewer, cones in their retinas compared with those
found in diurnal fishes. This factor is critical since
predators must align themselves and be able to
predict where their prey will be during the mouth
opening phase of their strike (Nyberg 1971).

Weighing against the hypothesis that the
schools of silversides break up and reform as a
result of changes in visual sensitivity, are a
number of observations made of captives held in
the field enclosures in the absence of predators.
When held for weeks at a time, these silversides
did not completely lose their cohesion and
polarity, indicating that there may be a strong
genetic component to their schooling behavior.
This genetic component may result in the silver-
sides remaining within a short distance of one
another at all times. The silversides appear to be
adapted to feeding at night as well as in the day
(McMahon 1975). If they can feed at night, the
silverside are probably able to detect the presence
of conspecifics, either using visual and/or lateral
line cues. The ability to detect conspecifics would
be particularly beneficial as individuals would not
become so widely scattered during the night that
polarized schools could not easily reform during
morning twilight. In addition, the observation
that captive silversides held in large enclosures in
the field in the absence of predators did not all
spread out to look continuously for food indicates

424

MAJOR: PRKDATOR-PREY INTERACTIONS IN FISHES

that there may be a biological (circadian) rhythm
related to school formation and breakup and the
availability of specific food resources. Thus, the
breakup of schools may reflect a preemptory
predilection of individual silversides to spread out
and feed rather than remain within the safety of
compact polarized schools. Concurrently, pred-
ators are rapidly losing their ability to distinguish
individual silversides in the fading light, but their
presence remains a threat.

During the morning the process is reversed as
light levels increase with predators becoming
increasingly active and presumably more success-
ful at capturing silversides. It is during relatively
short daily time spans within the periods of twi-
light that the silversides become particularly
vulnerable to certain predators. It is at these
times that the silversides are passing to or from a
period of feeding to a period of relative quiescence.
In some areas, exposure to predators may be
increased because the transition involves the
movement from one location to another. The
timing of such movements and the behavioral
changes that occur within schools appear to be
related to the threat of predation, the availability
of food and the visual sensitivity and thresholds of
both the silversides and their predators.

ACKNOWLEDGMENTS

I thank Edmund S. Hobson, Kenneth S. Norris,
John S. Pearse, Mary E. Silver, and an anonymous
reviewer for editorial advice. M. Gadsden of
Aberdeen University provided information con-
cerning twilight phenomena. My wife, Elaine A.
Major, typed and helped edit various drafts of the
manuscript. The figures were drafted by D.
Heinsohn of the University of California at Santa
Cruz, and the Audio Visual staff of Simon Fraser
University in Canada. I am particularly indebted
to the Edwin F. Pauley Fund for providing
financial assistance.

LITERATURE CITED

Breder, C. m., Jr.

1959. Studies on social groupings in fishes. Bull. Am.

Mus. Nat. Hist. 117:393-482.
1967. On the survival value of fish schools. Zoologica

(N.Y.) 52:25-40.

Brown, d. r. e.

1952. Natural illumination charts. U.S. Navy Bur. Ships
Project NS 714-100, Rep. No. 374-1. Wash., D.C.
COLLETTE, B. B., AND F. H. TALBOT.

1972. Activity patterns of coral reef fishes with emphasis

on nocturnal-diurnal changeover. In B. B. Collette and
S. A. Earle (editors), Results oftheTektite program: Ecol-
ogy of coral reef fishes, p. 98-124. Bull. Los Ang. Cty.
Mus. Nat. Hist. Sci. 14.
DILL, L. M.

1972. Visual mechanism determining flight distance in
zebra danios iBrachydanio rerio Pisces). Nat. New Biol.
236:30-32.

1974a. The escape response of the zebra danio

iBrachydanio rerio) I. The stimulus for escape. Anim.

Behav. 22:711-722.
1974b. The escape response of the zebra danio

(Brachydanio rerio) II. The effect of experience. Anim.

Behav. 22:723-730.
DOMM, S. B., AND A. J. DO.MM.

1973. The sequence of appearance at dawn and disappear-
ance at dusk of some coral reef fishes. Pac. Sci. 27:128-
135.

Hobson, E. S.

1966. Visual orientation and feeding in seals and sea lions.

Nature (Lond.) 210:326-327.
1968. Predatory behavior of some shore fishes in the Gulf

of California. U.S. Fish Wildl. Serv., Bur. Sport Fish.

Wildl., Rep. 73, 92 p.

1972. Activity of Hawaiian reef fishes during the evening
and morning transitions between daylight and darkness.
Fish. Bull., U.S. 70:715-740.

1973. Diel feeding migrations in tropical reef fishes. Hel-
golander wiss. Meeresunters. 24:361-370.

1974. Feeding relationships of teleostean fishes on coral
reefs in Kona, Hawaii. Fish. Bull, U.S. 72:915-1031.

Hobson, E. S., and J. R. Chess.

1973. Feeding oriented movements of the atherinid fish
Pranesus pinguis at Majuro Atoll, Marshall Islands. Fish.
Bull., U.S. 71:777-786.
HUNTER, J. R.

1968. Effects of light on schooling and feeding of jack
mackerel, Trachurus symmetricus. J. Fish. Res. Board
Can. 25:393-407.
MC'MAHON, J. J.

1975. Estimation of selected production for iao, Pranesus
insularum insularum, in Kaneohe Bay, Oahu. M.S.
Thesis, Univ. Hawaii, 83 p.

MUNZ, F. W., AND W. N. MCFARLAND.

1973. The significance of spectral position in the rhodop-
sins of tropical marine fishes. Vision Res. 13:1829-1874.

NEILL, S. R. ST. J., AND J. M. CULLEN.

1974. Experiments on whether schooling by their prey af-
fects the hunting behaviour of cephalopods and fish pred-
ators. J. Zool. (Lond.) 172:549-569.

NURSALL. J. R.

1973. Some behavioral interactions of spottail shiners
[Notropis hudsonius), yellow perch iPerca ftavescens), and
northern pike (Esox lucius). J. Fish. Res. Board Can.
30:1161-1178.
NYBERG, D. W.

1971. Prey capture in the largemouth bass. Am. Midi.
Nat. 86:128-144.

Pavlov, D. S.

1962. On the availability of the young ofAtherina mochon
pontica Eichw. for Smaris smaris L. under different condi-
tions of illumination. [In Russ., Engl, summ.] Zool. Zh.
41:948-950.

425

FISHERY BULLETIN: VOL. 75, NO. 2

RADAKOV, D. V.

1958. Adaptive value of the schooling behavior of young

pollock [Pollachius virens (L.)]. [In Russ.] Vopr. Ikhtiol.

11:69-74.
1973. Schooling in the ecology of fish. (Translated from

Russ. by Israel Program Sci. Transl. Publ.) John Wiley

and Sons, N.Y., 173 p.

Shaw, E.

1961. Minimal light intensity and the dispersal of school-
ing fish. Bull. Inst. Oceanogr., Monaco 1213, 8 p.

1970. Schooling in fishes: critique and review. InL.A.E.
Tobach, D. S. Lehrman, and J. S. Rosenblatt (editors),
Development and evolution of behavior, p. 452-480. W.
H. Freeman and Co., San Franc.

Steven, d. m.

1959. Studies on the shoaling behaviour of fish. I. Re-
sponses of two species to changes of illumination and to
olfactory stimuli. J. Exp. Biol. 36:261-280.
WILLIAMS, G. C.

1964. Measurement of consociation among fishes and
comments on the evolution of schooling. Publ. Mus.
Mich. State Univ., Biol. Ser. 2:351-383.

1966. Adaptation and natural selection: A critique of some
current evolutionary thought. Princeton Univ. Press,
Princeton, 307 p.
WOODHEAD, P. M. J.

1966. The behaviour of fish in relation to light in the
sea. Oceanogr. Mar. Biol. Annu. Rev. 4:337-403.

426

FISHES, MACROINVERTEBRATES, AND

THEIR ECOLOGICAL INTERRELATIONSHIPS WITH

A CALICO SCALLOP BED OFF NORTH CAROLINA

Frank J. Schwartz and Hugh J. Porter1

ABSTRACT

A 1972 study documented the fishery, fish and macroin vertebrate faunas, possible predators, and the
ecological interrelationships of the offshore North Carolina calico scallop, Argopecten gibbus, bed(s).
Environmental data of water temperature, salinities, chlorophyll a, water current direction, sediment
grain size, and organic composition were obtained aboard commercial and chartered research vessels.
Water temperatures progressed seasonally from 12° to 26° C while bottom salinities varied between 31
and 37"/ooyet were not radically different from the surrounding habitats. Chlorophyll a data suggested a
fairly stable but low plankton fauna over the bed(s) except for June and late October. Little or no
differences in bottom type within or without the bed(s) were noted on the basis of sediment particle size,
grain size, skewness, or sorting coefficients. Scallops grew faster in the experimental bed than in the
commercial bed but little could be found to account for their differences in size. Some 111 species of
fishes were captured over the bed(s). Of a vast moving fish fauna, 33 species dominated the catches. Of
46 species with food in their stomachs, 20.4% feed on scallops with only 9 species considered scallop
predators. Bothids, soleids, rajids, labrids, dasyatids, and myliobatids were not active scallop pred-
ators. Halichoeres eaudalis appeared in October when the fishery collapsed economically. Of 12
species of echinoderms, the sea stars Luidia clathrata and Astropecten articulatus were active scallop
predators. While less abundant, 21 additional invertebrates were also suspected predators. Luidia
clathrata and A. articulatus abundance on the beds remained high throughout the season; however,
abundance off the beds was somewhat lower. No one factor has yet been found that made the North
Carolina calico scallop beds unique, why they existed, or were productive in 1972.

Three commercial species of scallops occur in
North Carolina: the Atlantic deepwater scallop,
Placopecten magellanicus (Gmelin), the shallower
offshore calico scallop, Argopecten gibbus (Linne),
and the inshore bay scallop, A rgopeeten irradians
(Lamarck). The offshore calico scallop fishery,
while yielding varying quantities of harvestable
scallops (Table 1), has alternately experienced
good and bad years of production (Lyles 1969;
Cummins 1971; Chestnut and Davis 1975). The
disappearance of calico scallops from an area,
whether off North Carolina, Florida, or elsewhere,
is common knowledge (Bullis and Ingle 1959; Hu-
lings 1961; Anonymous 1962; Kirby-Smith 1970;
Roe et al. 1971; Porter and Wolfe 1972). Off North
Carolina the causes of scallop fluctuations and
production have been attributed to mortalities,
migration, poor larval transport from elsewhere,
introduction of scallop shucking and eviscerating
machines, or overfishing (Webb and Thomas 1968;
Lyles 1969; Cummins and Rivers 1970; Kirby-

TABLE 1. — North Carolina calico scallop production, 1959-75. '
[No production 1962-64, 1968-69, and 1974-75.]

Meats

Value

Year

(pounds)

(dollars)

Gear

1959

6.572

2.629

Dredge

1960

111.726

44,691

Trawl

1961

22,427

8,971

Trawl

1965

871,100

244,709

Trawl

1966

1,856.760

368,685

Trawl

1967

1,388,606

308,843

Trawl

1970

1 ,574,087

498.570

Trawl

1971

1 ,285,304

432,025

Trawl

1972

1,050,320

492.899

Trawl

1973

556,315

353.757

Trawl

'Data supplied by the National Marine Fisheries Service Statistical Office.
Beaufort, N.C., and Chestnut and Davis 1975.

Smith 1970; Cummins 1971; Allen and Costello
1972). This report documents the fish and mac-
roinvertebrate faunas, possible predators, and
their ecological interrelationships with the scallop
bed(s) that supported the 1972 fishery.

NORTH CAROLINA
CALICO SCALLOP FISHERY

'Institute of Marine Sciences, University of North Carolina,
Morehead City, NC 28557.

Manuscript accepted November 1976.
FISHERY BULLETIN: VOL. 75, NO. 2, 1977.

While A. gibbus occurs in the western North
Atlantic from the northern side of the Greater
Antilles and throughout the Gulf of Mexico to

427

FISHERY BULLETIN: VOL. 75, NO. 2

Bermuda and possibly Delaware Bay (Waller
1969; Allen and Costello 1972), only three areas
produce calico scallops of commercially harvest-
able quantities: North Carolina, Cape Canaveral
off eastern Florida, and the Gulf of Mexico off
Apalachicola Bay, Fla. (Drummond 1969; Cum-
mins 1971; E. Willis pers. commun.). Throughout
its range it has been found in depths of 2-370 m
(Waller 1969). Off North Carolina, calico scallops
occur at open water depths of 13-94 m (Cummins
et al. 1962; Bullis and Thompson 1965; Porter
1971, 1972a; Allen and Costello 1972).

Until recently, North Carolina calico scallops
were hand shucked by shore-based operations
(Cummins 1971). In 1970, two shucking machines
(Webb and Thomas 1968) were introduced in
North Carolina and by 1975 there were eight. The
present North Carolina and Florida fisheries pre-
fer this shucking method rather than utilizing
offshore vessels equipped with machine shuckers,
as was briefly used off Florida (Allen and Costello
1972). Generally, commercial fishing is considered
feasible when 20 bushels (in shell) are caught per
hour with shell diameter of at least 40 mm
(Drummond 1969). Meat size to be acceptable to
hand shucking should be 190 meats/kg or 90
meats/pound (Cummins 1971). Machine processed
meats can be as small as 495 meats/kg (225
meats/pound).

Off North Carolina, the high cost of hand shuck-
ing and the early lack of knowledge concerning a
possible calico scallop fishery delayed its develop-
ment (Chestnut 1951). The fishery seems to have

begun in 1959 and has since been described by
Cummins et al. (1962), Cummins (1971), Porter
(1971, 1972a), and Porter and Wolfe (1972). At
first scallop dredges were used to harvest calico
scallops. Today, otter trawls are the gear used by
the commercial fishery (Rivers 1962). Short tows
of 10-15 min often land 60 or more bushels, with
an average day's catch being 800-1,500 bushels
of shell stock.

STUDY AREA

Cummins et al. ( 1962) characterized the princi-
pal North Carolina calico scallop grounds as an
elliptical shaped bed 16 km long near Cape Look-
out, with several lesser beds located in 19-37 m
depths northeast and southeast of the Cape. The
major North Carolina calico scallop fishery in
1971 was located southeast of Cape Lookout; a
small bed southeast of the Cape was also fished
briefly in September of that year. Exploratory ef-
forts in 1972 by the commercial fleet and the RV
Dan Moore on the beds southwest of New River
and northeast of Cape Lookout (Figure 1) failed to
locate commercial quantities of calico scallops.
The only beds that supported the 1972 fleet of 13
vessels from February to October were located
16-24 km south of Beaufort, N.C., producing some
1 million pounds of meats (Table 2).

The 1972 study area consisted of the above beds
located at lat. 33°35'N between long. 76°35' and
76°55'W (Figure 2). Depths were 20-25 m and most
sampling occurred inside the 28-m contour.

10 jo

lOMitlll

78°00

428

77°00

FIGURE l.— North Carolina calico scal-
lop fishing grounds. Dots refer to areas
of poor catch by commercial fishermen
during the 1972 season. Dashed lines
indicate exploratory trips by one or
more trawlers. Solid line refers to the
area contained in Figure 2. Dotted line
indicates 20-fathom (36.6-m) contour.

SCH WART/ AND PORTER: FISHES. MACROINVERTEBRATES OFF NORTH CAROLINA

TABLE 2.— North Carolina calico scallop production, 1972. '
(No production in November and December]

Value

Month

Pounds

($)

Month

Pounds

($)

Jan.

2.800

1,624

July

68,768

46,763

Feb

24,064

9.626

Aug.

43.624

35.772

Mar.

184,688

72.028

Sept.

33,008

29,047

Apr.

280.800

101.087

Oct.

544

478

May

228.400

93.644

Total

1 .050,320

492.899

June

183,624

102.830

'Data supplied by the National Marine Fisheries Service Statistical Office.
Beaufort. N.C.. and Chestnut and Davis 1975.

METHODS

Sampling Vessels

Two types of vessels were used to sample the
offshore North Carolina calico scallop beds. Com-
mercial fishing vessels, from which most of the
samples were obtained, were the 25-m MV Ensign,
a side trawler of Gloucester design and the 15-m
MV Seven Brothers, a double rigged shrimper de-
sign. Research vessels include the RV Beveridge, a
17-m shrimp trawler which was chartered
monthly to collect additional samples or to main-
tain anchored equipment, and the Duke Univer-
sity 33-m RV Eastward, a side trawler of Glouces-
ter design. One bottom observational cruise was
accomplished by using RUFAS (Anonymous 1969)
aboard NOAA RV George M. Bowers. Two addi-
tional samples, 23 April and 27 June, were also
obtained while returning from other Eastward
projects.

All commercial or chartered vessels towed one
or two 10-12 m scallop trawls (Rivers 1962) which
were modified to have heavily weighted foot lines
and heavy-duty chaff gear on the cod end. The
trawl on theBeveridge was rigged the same as that
of the commercial vessels except that the foot line
was the standard weighted loop chain design pre-
ceded by a light tickler chain. Mesh size of all
trawls was the standard flat shrimp type. Sam-
pling tow interval varied on the commercial ves-
sels by season as a function of scallop abundance.
Beveridge or Eastward tows were kept to 15 min.
Sample tow distances, by commercial vessels, var-
ied Va-V-z km, whereas Beveridge and Eastward
tows were Va km. No effort, by type of vessel, was
made to sample with or against the current.

Environmental Data

Salinities were determined from the water sam-
ple by using a direct reading American Optical
Corp.2 refractiometer.

Chlorophyll a was determined spec-
trophotometrically for 19 stations (Figure 2) fol-
lowing the methods of Strickland and Parsons
< 1968) and expressed as milligrams per cubic me-
ter.

A Braincon 381 current meter was anchored and
buoyed at the northwestern edge of the commer-
cial grounds. Excessive fouling during much of the
sample year by hydroids, sponges, and tunicates
prevented precise long-term bottom current data
being recorded at the surface of the bed. After
rebouying the meter to record currents 30 cm
above the bed, current data obtained over a 26-day
period, mid-August to mid-September, indicated a
northeastward current drift component
(Schumacker 1974).

Sediment samples taken by Peterson (Bev-
eridge) and Shipek (Eastward) grabs (Figure 3)
were frozen until grain size and organic determi-
nations could be made. Pretreatment for grain-
size analysis included washing each sample in a
large volume of fresh water and then decanting
after all sediment had settled. Washing was done
to reduce weighing errors induced by salt crystals.
Following decanting, sediments were oven dried
at 85°C and separated into sediment sizes by a U.S.
Standard Sieve Series and mechanical sieve
shaker. All samples were in the shaker for at least
2 h. Analysis of data followed Morgans (1956).

Percent organic material was determined from
1 to 2 g unwashed subsamples which had been
oven dried for 48 h at 85°C. The amount of organics
was assumed to be the difference in sample
weights before and after firing at 500°C for 2 h.
This followed a technique used in the Marine Sed-
iments Laboratories of Oregon State University
(J. Paul Dauphin pers. commun.).

An attempt was made to develop a fast method
for percent organic determinations of marine sed-
iments through the manufacturer's suggested use
of a Coleman Model 33 Carbon-Hydrogen
Analyzer, rented from the Duke University
Marine Laboratory. Comparison of data, by statis-
tical means, showed no correlation between
analyzer and ovenfired organic values from
offshore marine sediments.

Water temperatures were obtained with a mer-
cury thermometer immersed in bottom water ob-
tained by a 3.1-liter Kemmerer sampler.

2Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

429

FISHERY BULLETIN: VOL. 75, NO. 2

• •

DHB

1 *•

□ 1'

□

• •

KILOMETERS

34°30'

. 20'

10'

77°00'

50'

40'

30'

FIGURE 2. — North Carolina calico scallop fishing grounds. Dots refer to known locations of good catches by commercial trawlers. Open
squares refer to known locations of good catch by RV Beveridge. Letters refer to chlorophyll a sampling stations. For location of enclosed
area off North Carolina coast see Figure 1.

Fishes

Fishes of at least 100 mm standard length were
tagged using 12-mm Peterson disk tags held in
place (in the middorsolateral musculature) by
Monel pins. Fish lengths, except for skates and
stingrays where wing width was used, were ex-
pressed for each species and specimen as standard
length. Once tagged, release was immediate over
the original collecting site. The ship's loran was
used to pinpoint the release site. Other biological
data were taken on those additional fishes that
had not been too badly damaged by the fishery or

scallop catches. Notations of other fishes not cap-
tured, such as flyingfishes, completed the field
data.

Fish samples from commercial catches and des-
tined for stomach content analyses were kept on
ice because of the danger of Formalin contamina-
tion of the scallop catch and the cramped ship
quarters prevented carrying extra gear afield.
Similar fish sampled aboard research vessels were
preserved in 209r Formalin. In the laboratory, the
entire digestive tract was removed, contents iden-
tified, and noted whether the food items were in
the stomach or intestine. Positive identification of

430

SCHWARTZ AND PORTER: FISHES. MACKOINVERTEHRATES OFF NORTH CAROLINA

- — ^

-■

" ^

*» * Buoyed Current

Meier

/ S lb;

sjg :•.-.

•*

■

.500

•

.ISO

.115

.061

* »

- 34'30'

34*00'

FIGURE 3. — Twenty-two sediment sample stations. Dominant
grain size is indicated by station. Broken lines enclose the com-
mercial area, an area fished by the calico scallop fishery.

the food items to species was possible in most
cases.

Scallops

Scallops were sampled from two areas — one
general and one specific. The general area, here-
after referred to as the commercial area, included
wherever the scallop fishery was operating (Fig-
ures 1-4). Scallop tissue samples from this area
were taken, when possible, once a week; shell
length measurements and other appropriate scal-
lop data were taken more frequently. Tissue,
gonad and/or spawning condition data will be cov-
ered in a paper by Porter and Schwartz (in prep.).

The specific area, hereafter referred to as the
experimental area, was an area just northwest of
the commercial area. This area was sampled
monthly by the Beveridge and was marked from
June to September 1972 by a large red buoy; this
buoy further served to support the Braincon cur-
rent meter (Figure 3). The seabed interval be-
tween this area and the commercial area to the
south contained no scallops, which suggested that
this area was a small separate bed. Only briefly
during the latter part of the commercial scallop

season was the experimental area worked by the
1972 fishery.

Sea Stars

Data were accumulated on seasonal distribu-
tion of the sea stars present on the scallop beds,
their size, and relative abundance. Sea star size is
here defined as the radius of a sea star through its
longest arm.

About 20 Astropecten articulatus and about 20
Luidia clathrata were examined weekly, when
available, for stomach contents. Luidia alternata,
Goniaster americanus, and Echinaster brasiliensis
stomachs were also examined, when available.
Stomach analysis examinations which also de-
lineated associated organisms were similar to
those of Porter (1972b) and will be reported on
elsewhere.

Associated Macroinvertebrates

Unculled bushels of scallops, as caught by the
trawlers, were examined periodically by the field
investigator to note other associated organisms,
amount of shell material, and signs of dead or
dying scallops. Counts were made of each or-
ganism and the amount, of dead shell or trash. A
log was also kept of all macroinvertebrate species
seen during each cruise.

ENVIRONMENTAL OBSERVATIONS

Bottom water temperatures exhibited a natural
progression from about 12°C in February to a high
near 26°C in September. These were within the
range 9.9°-33°C noted by Waller ( 1969). Vernberg
and Vernberg ( 1970), in laboratory experiments of
North Carolina calico scallops, found none sur-
vived after 48 h exposure to water of 10°C.

Bottom salinities throughout the bed, as evi-
denced during the shifting seasonal fishing effort
(Figure 4), remained fairly constant at 35%o (range
31-37%o, Figure 5). This agreed with observations
of others for scallop grounds elsewhere (Anderson
et al. 1961; Hulings 1961; Grassle 1967; Pequeg-
nat and Pequegnat3).

Kirby-Smith (1970) and Allen and Costello
(1972) suggested that upwelling in the vicinity of

3Pequegnat, W. E., and L. H. Pequegnat. 1968. Ecological
aspects of marine fouling in the northeastern Gulf of Mexico.
Texas A&M Univ. Dep. Oceanogr. Proj. 286-F, Ref. 68-22T, 80 p.

431

FIGURE 4. — Areas fished by commercial
fishery during the 1972 season. Loca-
tions taken from ship's log.

FISHERY BULLETIN: VOL. 75, NO. 2
1

V •

/"K

......... March

April

O May
©©©©©© June
July

^——_ ■ "" August

■ •■■■■• Stpttmb«r

9
9

.■■■9T-
9

%
9

30'

- 34"20

'^V

76"40

FIGURE 5. — Environmental data col-
lected from the calico scallop grounds.
Each data point for water and salinity
indicates individual date sampled. Let-
ters on chlorophyll graph refer to sta-
tion sampled that date, see Figure 2 for
locations.

28
26
24
22
20
IS
16
14
12

1.6
L4

1.2
1.0
.8
.6
.4
.2
0

-\ 1 1 1 r

TEMPERATURE

CHIOROPHYU

°/
'oo

39
36
34
32
30

F.b

II 21 31
Mar I

Apr

• II 24
Aug l

S«P

7 17 27

Ocl I

Cape Lookout (Taylor and Stewart 1959; Wells
and Gray 1960; Gaul et al.4) may produce high
plankton concentrations and that these concen-

trations may occur where scallop abundance is
greatest. Chlorophyll a analyses during 1972
(Anonymous5) suggested that a fairly stable but

"Gaul, R. D., R. E. Boykin, and D.E. Letzring. 1966. Northeast
Gulf of Mexico hydrographicsurvev data collected in 1965. Texas
A&M Univ. Dep. Oceanogr. Proj. 286-D, Ref. 66-8T, 202 p.

^Anonymous. 1972. Data report for R/V Eastward cruise
E-12-72, July 3-8, 1972. Duke Univ. Mar. Lab., Beaufort, N.C.,
34 p.

432

SCHWARTZ AND PORTER FISHES. MACROINVERTEBRATES OFF NORTH CAROLINA

low plankton fauna existed over the scallop beds,
except during June and late October, when indica-
tions of a late spring and early fall bloom occurred
(Figure 5).

Twenty-two sediment samples were taken dur-
ing the 1972 study (Figure 3). Of these, seven were
deliberately taken in areas where no scallops were
collected by the fishery (Table 3). As the sediments
were taken immediately after a trawl tow, they

may not be representative of the same bottom cov-
ered during the tow. No discernible differences
were found between sediments from scallop pro-
ducing and nonproducing areas (Table 3, Figure
2).

Newton et al. (1971, Sediment Distribution
Chart No. 2) characterized the area which was
later encompassed by the 1972 commercial scallop
fishery (Figures 3, 4) as consisting of two sediment

TABLE 3. — Sediment size analyses, data listed as percent per sample, sediment sorting coefficients, skewness, for
scallops sampled in 1972 from producing and nonproducing areas off North Carolina.

Sediment sample station and sample date

Sediment size

(mm)

18 Feb.

18 Feb

21 Mar

21 Mar.

-4

0.572

0.701 1.031

0.102

0.072

0.406

0.0027

2-4

1 734

0.381 0.626

0.165

18235

0362

0381

00068

1-2

8289

1.530 2 715

0.573

22 831

0.651

0.964

00139

0.5-1

32299

2.325 3903

2.090

25053

1.505

2.224

0.0303

0.250-0.5

40 606

3898 5.842

34 711

19.814

13.576

12 670

0.1443

0 125-0 250

13.847 14 748 14,649

49834

7782

81.622

40.021

0.2982

0 063-0.125

1.826 69 186 64 396

9836

3 431

0.001

40.096

04646

•0.063

0826

7.231 6837

2 688

2.855

2.211

3239

0 0392

Median particle size1

1.17

3 37 3 32

222

0.35

2.42

280

3.02

Median particle size (mm)

0.44

009 0.09

0.21

077

0.17

0.14

0.12

Sediment sorting coef1

0.675

0.365 0485

0.555

1.100

0.300

0635

0.685

Sediment skewness'

-0.045

0015 -0105

-0035

-0.020

0.035

-0.155

Percent organic

2.027

1.080

0844

2 118

0884

0 790

1.394

Latitude N

34 22'

34 24

34 24'

34 26.5

34=27'

34 "24'

34=24

Longitude W

76 44

76=42'

76 39'

76=45'

76 44

76 41

76=42.5'

Depth (m)

Scallop producing area

yes

Sediment size

(mm)

21 Mar.

10 May

14 June

14 June '

14 June

25 June

0 0019

0.0313

8026

3640

0491

0012

0.064

2-4

0.0196

0.0347

0.341

8.118

3855

1.088

0.339

0.074

1-2

0 0595

0.0643

1.062

8.102

7.438

3.318

1.084

0.890

0.5-1

0.2356

0.2678

2.769

19.210

19.475

9.113

5.071

3936

0.250-0.5

0.5574

0.4873

11.619

2623

2.810

44.895

27.046

30 632

0 125-0 250

0.1132

00854

44.095

28.842

40 369

6.080

61.209

62.931

0.063-0.125

0 0096

0.0207

31.974

13.432

16.683

30 813

5218

1.231

<0.063

0 0032

0.0085

8.139

1 1 .647

5.730

4201

0022

0.242

Median particle size1

1.33

1.22

2.78

2.13

2.32

1.80

2.27

1.23

Median particle size (mm)

0.39

0.42

0.14

0.22

0.18

0.28

0.20

0.41

Sediment sorting coef

0525

0.645

0.650

1 465

1.215

1.060

0505

0.480

Sediment skewness1

-0 085

-0.145

0.070

-0.615

-0.605

0.500

-0.095

-0.090

Percent organic

2.176

2.461

ND2

1.638

0885

0.763

0.840

Latitude N

34 = 19.5'

34 235

3421

34=27

34 27.5'

34185

34=34

Longitude W

76 41

76 43.5

76c41.5'

76°44

76=45

76 42

76 32.7'

Depth (m)

Scallop producing area

yes

Sediment size

(mm)

27 June 17 Aug

17 Aug.

12 Sept.

12 Sept

23 Oct.

23 Oct

1.082

0.021

0.044

0 000

0.049

0.000

0.665

0.243

2-4

1.016

0.437

0.146

0.234

0.363

0.001

0.480

0.446

1-2

1.472

1.556

0.756

0.603

1.043

0.007

1.386

1.162

0.5-1

2573

3.345

2.472

2646

2.103

0.026

2.515

2.821

0.250-0.5

5.800

24 389

6.758

8376

6.175

0.209

6.451

11.387

0.125-0.250

14.705

58 881

20 293

23028

62 728

0638

20.518

46.534

0.063-0.125

66.049

9525

62 619

59 094

26885

0097

62 462

35 038

<0.063

7.304

1.847

6.912

6.019

0.654

0022

5.523

2.370

Median particle size1

3.35

2.36

3.32

3.26

2.65

2.38

3.27

2.72

Median particle size (mm)

009

0.19

0.10

0 10

0.15

0.19

0.10

0.15

Sediment sorting coef1

0.425

0485

0.500

0.555

0.465

0.380

0.505

0.585

Sediment skewness1

-0.055

-0.075

-0.100

-0.135

0065

0.020

-0.095

0.090

Percent organic

0.967

1.151

0.866

1.037

0 593

1.251

1.021

1.119

Latitude N

34=26.3

34 "26'

34°23 5

34=29.5'

34°27'

34=29'

34 27

34=21

Longitude W

76 '43'

76°43'

76=41 '

76°41.5'

76 42.5

76=54'

76 42'

76=38.5'

Depth (m)

Scallop producing area

yes''

yes

. no

yes?

yes

'See Morgans (1956) for definition
2Not determined

433

FISHERY BULLETIN: VOL. 75, NO. 2

types, most of the bed being "fine sand - grey"
while areas of its western edge were "shell hash -
often brown - many types of organic contributors."
The latter was typical of our sediment sample 14.
The area from which sediment sample 20 was
taken was characterized as "Coarse sand - very
shelly - iron stained"; the experimental area
northwest of the main scallop producing area was
characterized as "fine sand - iron stained - less
than 25% shell material." Median grain size
analyses of our data agreed with Newton et al.

(1971) in that parts of the western edge of the
calico scallop bed had coarser sediments than
other areas encompassed by the main bed (Figure
3); however, no differences were found between
the main scalloping area, the experimental area
north of the bed, and stations 14 and 20.

Sanders (1958) and Bloom et al. (1972)
suggested that optimal sediment conditions for
filter feeders were a fine (about 0.18 mm) and a
well-sorted, but positively skewed, grain size. Me-
dian sediment sizes found within the 1972 North
Carolina calico scallop bed averaged below San-
ders' 0.18 mm optimal size for filter feeders. Sub-
sequent to this study, plotting the location of the
1973 calico scallop fishery off the North Carolina
coast on the Newton et al. (1971) sediment chart,
revealed that the 1973 fishery was in an area not of
fine sand but very coarse shelly sand. This has
been further corroborated by personal observa-
tions aboard vessels in the fishery. These data may
support the contention of McNulty et al. (1962)
that other factors besides grain size are important
to the well being of filter feeders.

Sorting coefficient values for most sediment
samples ranged from 0.300 to 0.685 (Table 3, a
condition considered well sorted), although two
samples located northwest of the main fishery had
relatively high sorting coefficients (1.100 to
1.465). Sediments in these same two samples were
also strongly skewed ( -0.615 and 0.500, Table 3).
While sorting coefficient values agreed with the
conclusions of Sanders (1958) and Bloom et al.
(1972), the sediment skewness data did not. Most
of the data was only slightly skewed (-0.155 to
0.090) and not strongly positively skewed as they
suggested.

Commercial fishermen reported that there were
numerous rough areas, including a small low
ledge, outside the commercial area which caused
great damage to their nets. Porter and Wolfe

(1972) described the North Carolina scallop
grounds as consisting of sand, shell fragments,

and occasionally large pieces of trent marl and
coquina. Porter and Wolfe (1972) and Pearse and
Williams (1951) described a small bed southwest
of New River which was surrounded by bottom
containing large heads of lobe star coral, Sol-
enastrea hyades (Dana). During 1972, large mas-
ses of trent marl were not infrequently brought up
in the scallop nets by the commercial fishermen.
Ledgelike outcroppings of marl (?) and large heads
of the lobe star coral outside the commercial area
were observed in 1972 while aboard the George M.
Bowers through use of its remote underwater tele-
vision sled RUFAS. While such marl outcrops and
coral heads are not uncommon throughout the
southern North Carolinian coastal area, known
calico scallop beds do not seem to be dependent
upon their presence.

CALICO SCALLOP GROWTH

Length measurements were taken on 5,180 scal-
lops during the sampling period (Table 4). Scallop
(865) mean growth in the experimental area was
faster than that from the commercial area (Table
4); size increase over a 7-mo sampling period was
17.8 mm or 2.5 mm/mo. Comparable growth data
obtained from 4,315 scallops landed by the com-
mercial fishery over the 9-mo sampling period
were 8.7 mm or 1.1 mm/mo; their sizes ranged
from 35 to 65 mm with no live small scallops being
noted. The difference in rate of growth was proba-
bly related to the original smaller size of the ex-
perimental area scallops, which ranged from 28 to
57 mm in length (Table 4). Allen and Costello
(1972), reviewing the calico scallop literature,
noted growth data of 4.0 mm/mo for scallops hav-
ing mean sizes of 13.9 to 37.8 mm and 0.3 mm/mo
for scallops having mean sizes of 75 to 80 mm.

As mentioned above, the scallops from the ex-

TABLE 4. — Lengths (millimeters) of calico scallops collected
monthly from the experimental bed north of the main bed and
commercial catch, 1972.

Experimental

bed

Commercial catch

Average
lengtn

Size

Sample

Average

Size

Sample

Month

range

size

length

range

size

Feb.

35.5

28-44

100

47.3

40-54

545

Mar.

37.4

30-47

150

46.3

37-55

510

Apr.

—

47.3

35-56

617

May

49.8

43-55

47.8

41-62

276

June

44.8

33-54

152

50.7

39-70

1,100

July

—

47.6

35-61

450

Aug.

45.0

39-57

127

50.8

36-59

400

Sept.

53.3

44-64

150

54.2

48-65

316

Oct.

50.5

42-57

100

55.0

43-65

101

Average li

sngth

increase

17.8

8.7

434

SCHWARTZ AND PORTER: FISHES, MACROINVERTEBRATES OFF NORTH CAROLINA

perimental area were consistently smaller than
those from the commercial area (Table 4). Median
sediment size and texture analyses data from the
two areas were virtually identical (Table 3). There
was some indication that organic values in the
experimental area may be slightly higher than
those from the commercial area (Table 3). Car-
riker ( 1959) noted that growth of Mercenaria mer-
cenaria was faster in his low organic areas than in
areas with higher organic percentages. This was
the opposite of our findings.

Apparently the growth of the calico scallop is
not related to chlorophyll a content for we noted
primarily little difference between chlorophyll a
content, regardless of sampling area (Figure 5).

FISHES OF
THE CALICO SCALLOP BED

Some 4,461 fishes belonging to 49 families and
111 species were collected during the 51 cruises
between 9 January and 23 October 1972. One ad-
ditional species, Scorpaena isthmensis, was added
to the faunal list during exploratory trips in 1971
and 1973. Pelagic, demersal, and benthic families
and species were represented in the catches (Table
5). Of the total fishes landed (4,392) as part of the
1972 scallop catches, 985 were tagged and re-
leased to note movements, 1,655 were analyzed for
food content, and 1,752 specimens were merely
observed and identified. Most of the 112 species
encountered were sporadic components of the scal-
lop bed either as they passed north-to-south or
east-to-west, depending on the season of the year.

Of the 112 species of fishes associated with the
calico scallop bed, 94 or 84.0% can be considered
Caribbean in their main distribution and abun-
dance, while 7 (6.2%) were Virginian forms that
had moved seasonally south of the Cape Hatteras
barrier. Eleven species (9.8%) were those whose
distribution ranges extended naturally over a
broad north-south geographic area and could not
be considered northern or southern faunal compo-
nents. Controversy still exists whether that por-
tion of the shelf off North Carolina is simply a part
of an overall north-south temperate Virginia
Province faunal region (Forbes 1856) or an area
divided into a nearshore Virginia and offshore
Gulf Stream influenced Carolinian Province
(Gray and Cerame-Vivas 1963; Wells et al. 1964;
Cerame-Vivas and Gray 1966; Gray et al. 1968;
Bumpus 1973; Briggs 1974). Struhsaker (1969)
and Schwartz (in press) have shown this area to be

rich in fishes with an overall 70:30 ratio of south-
ern to northern fishes, a condition far richer than
that of the northern Gulf of Mexico, contrary to the
findings of Briggs (1974).

Some 33 species dominated the 1972 catches, of
which 21 species accounted for 77.1% of the fishes
handled: Stenotomus aculeatus (413 specimens),
Synodus foetens (386), Paralichthys dentatus
(303), Diplectrum for mosum (254), Raja eglanteria
(252), Orthopristes chrysopterus (249), Prionotus
scitulus (196), Monacanthus hispidus (174), Cen-
tropristes striata (122), Batistes capriscus (120),
Prionotus evolans (116), Hemipteronotus novacula
(104), Leiostomus xanthurus (104), Mustelus canis
(95), Lagodon rhomboides (91), Aluterus schoepfi
(85), Paralichthys albigutta (77), Etrumeus teres
(75), Urophycis regius (74), Syacium papillosum
(73), and A ncylopsetta quadrocellata (71).

A few species, notably Raja eglanteria, Centro-
pristes striata, Ancylopsetta quadrocellata, and
Paralichthys dentatus, seemed to occupy the beds
throughout the year (Table 5). The loss of such
species as Prionotus evolans, Orthopristes chrysop-
terus, and Aluterus schoepfi from the beds was
evident as they moved shoreward during the
summer months. Mustelus canis and Urophycis
regius were winter components of the fauna prior
to their movement northward or seaward away
from the encroaching higher summer water tem-
peratures. Others, such as Diplectrum formosum,
Mullus auratus, and Aluterus scriptus occurred
during or appeared late in the summer, apparent-
ly transported by meanders of the Gulf Stream
(Webster 1961; Roe et al. 1971) from the south
when water conditions met their usual tropical
temperature requirements for existence. Rhinop-
tera bonasus was a good sample of a north-south
transient in April and August as the schools
moved past the area to other grounds (Schwartz
1965). Halieutichthys was an example of an
offshore species apparently moving into shallower
water with occasional incursions (Blanton 1971) of
deep ocean water onto the shelf. As expected, bot-
tom fishes of the families Bothidae, Soleidae, Trig-
lidae, and hard shell crushers of the Balistidae and
Tetraodontidae predominated (Table 5). The most
exciting captures were Letharchus velifer, Ser-
raniculus pumilio, Prionotus ophryas, and Scor-
paena isthmensis, as their capture represented
sizeable northward range extensions. McEachran
and Eschmeyer (1973) have also recently noted
the northward extension of S. isthmensis.

Nineteen species were tagged for movement

435

FISHERY BULLETIN: VOL 75, NO. 2

TABLE 5. — A list of fish species encountered during the various calico
T = tagged; F = food analysis; A= additional

Jan -Feb- March April May June

Species 1971 ~T F A~ ~T F A "t F A~ ~T F A "t F~~

Carcharhinus obscurus — — — — — — 1 — — — — — — 1 —

Mustelus canis 6 3 20 21 7— 14 23 1 — — ____

Rhizopnnodon terraenovae — — — — — — — — — — — — — — —

Squalus acanlhias — — 2 — — — — — — — — — — — —

Squatina dumerili — — — — — — 1 1 — — — — — — —

Fthinobatos lentiginosus — — — — — — — — — — — — — — —

Narcme brasihensis — — — — — — — — — — — — — — —

Raja eglanteria — 1 11 30 114 12 9 8 2 14 — — 12 1 —

Dasyatis amencana — — — — — — 5 1 1 — — — 1 — —

D. centroura — — — — — — — — — — — — — — —

Gymnura micrura — — — 1 — — 2 1 — — — — — — —

Myliobatis freminvillei — — — — — — — — 1 — — — — — —

Rhinoptera bonasus — — — — — — — — — — — — — — —

Manta birostris — — — — — — — — — — — — — — —

Gymnothorax nigromarginatus

saxicola — — — — — — — — — — — — — — —

Conger oceanicus — — — — — — — — 1 — — — — — —

Letharchus velifer — — — — — — — — — — — — — — —

Ophichthus ocellatus — — — — — — — — — — — — — — —

Etrumeus teres — — — — — 60 — — — — — 15 — — —

Anchoa hepsetus — — — — — — — — 57 — — — — — —

Synodus foetens — 1 13 6 75 70 — — 16 9 47 10— 2 —

S. poeyi — — — — — — — — — — — — — — —

Trachinocephalus myops 4 — — — — — — — — — — — — — 1 —

Opsanus tau — — — — — — — — — — — — — — —

Ponchthys porosissimus — — — — 3 — — — — — 1 — — — —

Gobiesox slrumosus — — — — — — — — — — — — — — —

Lophius amencanus — — — — 2 — — 1 — — — — — — —

Antennarius ocellatus — — — — — — — — — — — — — — —

A. scaber 1 — — — — — — — — — — — — — — —

Halieutichthys aculeatus — — — — — — — — — — — — — — —

Ogcocephalus sp. — — — — — — — — — — — — — — —

Urophycis earli — — — — — — — — 3 — — — — — —

U. regius 1 — 12— — 54 2 3 12— — — — — —

Rissola margmata — — — — — — — — 10 — — — — — —

Fistularia tabacaria 1 — — — — — — — — — — — — — — —

Hippocampus erectus — — — — — — — — — — — — — — —

Syngnathus springer! 3 — — 2 — — — — — — — — — — — —

Centropnstes ocyurus — — 15 — — — — — — 1 2 — 5 — —

C philadelphicus — — — — — — — — — — — — — — —

C striatus 11 — 2 2 — — — 10 7 214 5— 11 6 —

Diplectrum formosum 3 — — — — — — — — — 3 1 — 11 52 —

Serranus phoebe — — — — — — — — — — —

S. subligarius — — — — — — — — — — —

Serraniculus pumilio — — — — — — — — — — —

Rypticus maculatus — — — — — — — — — — —

Pristigenys alta 1 — — — — — — — — — — —

Pomatomus saltatrix — 1 1 — — — — — — — —

Caranx fusus — — — — — — — — — — —

Decapterus punctatus — — — — — — — — — — —

Lut/anus vivanus — — — — — — — — — — —

Haemulon aurolmeatus — — — — — — — — — — —

H plumieri — — — — — — — — — — —

Orthopristis chrysopterus 7 23 1 5 2 4 11 151 16 21

Archosargus probatocephalus — — — — — — — — — 1 —

Calamus ba/onado — — — — — — — — 1 — —

C. leucosteus

Lagodon rhomboides — 10 75— — — — — 5 — — — —

Spansoma radians — — — — — — — — — — — — —

Stenotomus aculeatus 5 13 3 20 16 11 12 171 10 45 — 4

Cynoscion nebulosus — — — — — — — — — — — — —

C. regalis — — 6 — — — — — — —

Parequetus sp. 3 — — — — — — — — — — — — —

Lanmus tasciatus — — — — —

Leiostomus xanthurus — 3 1 o

Menticirrhus americanus — 2 3 2

/M. saxatilis — 26417571 — —

Micropogon undulatus — — — — — — —

Mullus auratus 1 —

Chaetodlpterus faber — — — 1 3 1 —

Chromis enchrysurus —

Halichoeres bivittatus 2 — — — — — — — — — — —

H. caudalis 1 — — —

Hemipteronotus novacula 17 — — — — 3 3 1 1 — — 4 5 611

Astroscopus y-graecum — — — — — — — — —

Tnchurus lepturus —

Euthynnus alletteratus — —

436

SCHWARTZ AM) PORTKR FISHES, MACROINVERTEBRATKS OFF NORTH CAROLINA

scallop cruises aboard commercial, research, and chartered vessels.
species encountered but not examined or tagged.

July

August

September

October

1972 total

Species

Total
1972

Carcharhinus obscurus
Mustelus canis
Rhizopnnodon terraenovae
Squalus acanthias
Squalina dumerili
Rhinobatos lentiginosus
Narcine brasiliensis
Ra/a eglanteria
Dasyatis amencana
D centroura
Gymnura micrura
Myliobatis Ireminvillei
Rhinoptera bonasus
Mania birostris
Gymnothorax nigromargmatus

saxicola
Conger oceanicus
Letharchus velifer
Ophichthus ocellatus
Etrumeus teres
Anchoa hepsetus
Synodus loetens
S poeyi

Trachinocephalus myops
Opsanus tau
Ponchthys porosissimus
Gobiesox strumosus
Lophius americanus
Antennanus ocellatus
A. scaber

Halieutichthys aculeatus
Ogcocephalus sp.
Urophycis earli
U. reglus

Rissola margmata
Fistulana tabacaria
Hippocampus erectus
Syngnathus spnngen
Centropristes ocyurus
C. philadelphicus
C striatus

Diplectrum formosum
Serranus phoebe
S subligarius
Serraniculus pumilio
Rypticus maculatus
Pnstigenys alta
Pomatomus saltatnx
Caranx fusus
Decapterus punctatus
Lut/anus vivanus
Haemulon aurolineatus
H. pkimien

Orthopnstis chrysopterus
Archosargus probatocephalus
Calamus ba/onado
C. leucosteus
Lagodon rhomboides
Spansoma radians
Stenotomus aculeatus
Cynoscion nebulosus
C regalis
Parequetus sp.
Lanmus fasciatus
Leiostomus xanthurus
Menticirrhus americanus
M- saxatilis

Micropogon undulatus
Mullus auratus
Chaetodipterus faber
Chromis enchrysurus
Halichoeres bivittatus
H. caudalis

Hemipteronotus novacula
Astroscopus y-graecum
Tnchurus lepturus
Euthynnus alletteratus

1
41

1
33

1
18

2 — —

1 —

92 135

6 1

1 1 — — —

5 25

15 200

1 —

171

2
1

5
6

- — 4
2 4 68

- — 10

5 — 1

— 3 —

2 4 — 12

2 11 4 —

1
5
3
1
27
1
1

4 —

73 —

— 3
1

7 3

— 67

57
16

57
67

2 —

4 —

2
26

1
47

171
1
1
1

2
7
1
1
2
3
6
4

176

1 2 11

1 — —

1 —

4 15
10

1 5

2 42

1
30

77 101

— — 2 —

— 85 — 1

1 90
— — 2 2

— — — — — 3 9 10

— 1

1
1

81
1
235
1
8
2
4

10
3

17
8
3
9
1

2 11

10 42

— 1

95
1
2
2
3
3
252
8
1

4
1
9
1

1
2
2

386

3
1

5
6
4

74
10

122

254
1
1
1
2
7
2
1
2
3
6
7

249

413
1
8
2
4

101
7
36
8
3
23
1

104

1
1

437

FISHERY BULLETIN: VOL. 75, NO. 2

Table 5. — Continued.

Species

Jan -Feb

March

April

May

June

1971

Pepnlus alepidotus
P. triacanthus
Scorpaena brasiliensis
S. calcarata
Bellator militaris
Pnonotus evolans
P. ophryas
P. roseus
P. scitulus
P. salmonicolor
P. tnbulus

Ancylopsetta quadrocellata
Bothus sp.

Citharichthys macrops
Cyclopsetta fimbriata
Etropus microstomus
E. nmosus

Paralichthys albigutta
P. dentatus
P. lethosligma
P. squamilentus
Scophthalmus aquosus
Syacium papillosum
Gymnachirus melas
Trinectes maculatus
Alutera schoepfi
A. scriptus
Balistes capnscus
Monacanlhus hispidus
Lactophrys quadncornis
Sphoeroides dorsalis
S. maculatus
S. spenglen

Chilomycterus antillarum
C schoepfi

Subtotal
Total

—

15
25

—

3
5

—

10
2

2
1

14
6

—

1
1

—

3
1

8
3

—

145

—

7
1

—

— — — — 4 1 1 — — — 1 —
20 120 281 149 534 312 135 105 478 115 215 81

178 129

421

995

718

411

309

studies. Of those tagged, Paralichthys dentatus
(184 specimens), Monacanthus hispidus (107),
Raja eglanteria (92), Stenotomus aculeatus (77),
Balistes capriscus (66), Centropristes striata (57),
Mustelus canis (41), Ancylopsetta quadrocellata
(40), Aluterus scriptus (35), and Paralichthys
lethostigma (35) accounted for 74.3%. Of the 985
fishes tagged, 17 (1.7% ) were recaptured involving
11 species: Centropristes striata, Balistes capris-
cus, Aluterus schoepfi, Centropristes ocyurus,
Calamus bajonado, Monacanthus hispidus,
Paralichthys albigutta, P. dentatus, Rhinoptera
bonasus, Raja eglanteria, and Stenotomus acule-
atus. Paralichthys dentatus and Balistes capris-
cus accounted for 6 and 2 of the recaptures respec-
tively, while all others were single recaptures.
Most recaptures were returned from near their
release point on the bed. The longest period at
liberty was 8 days. This, in the light of the intense
fishing of the 13 boats that composed the 1972 fleet
and the few recaptures, suggested that the fish
population over the scallop bed was large, con-
stantly moving, and subject to constant recruit-
ment from elsewhere.

Stomach analysis of 1,655 of the 33 most fre-
quently encountered fishes (Table 6) revealed that
the stomachs of most of the fishes over the bed
usually contained food even though all samples
were made only during daylight hours; 89.4% had
scallops or other food as part of the stomach con-
tents. Sphoeroides maculatus, Stenotomus acu-
leatus, Diplectrum formosum, Orthopristes
chrysopterus, Monacanthus hispidus, Balistes
capriscus, Centropristes striata, Mustelus canis,
and Sy nodus foetens (in descending order of
species whose stomachs contained scallops) were
found to be scallop predators (Table 6). Small as
well as large individuals of these species had parts
or whole scallops in their stomachs and digestive
tracts (Table 6). These species fed either by crack-
ing the scallop shell with their beaklike jaws
(Balistes, Sphoeroides) or by finding dying or
cracked (possibly a result of the fishing activity)
individuals (Stenotomus, Diplectrum, Ortho-
pristes). It was surprising that bottom feeders of
the families Bothidae (Paralichthys albigutta, P.
lethostigma), Soleidae (Trinectes maculatus),
Rajidae (Raja eglanteria), Labridae (Hemip-

438

SCHWARTZ AND PORTER: FISHES, MACROINVERTEBRATES OFF NORTH CAROLINA

Species

July August September October 1972 total

~T F A ~T F A ~T F A T F A "f F A~ 1972

~Z Z Z Z Z Z Z Z Z Z Z Z Z- 3 _ 3

___________ _ 3 25 3 31

1 3__ 3__ 1 1 _ _ 1 10 24 8 42

3 7 — 3 12 5 — 7 1 1 8 4 16 75 25 116

__ — — — 1 — — 3_____ 4 4

— 16 — — 19 1 — 2 5 — — 7 5 145 46 196

— — — — — 8 — — 3 — — — — 145 46

— — — — — — — — 1 _ — — — — 4 4

9 2 — 6 3 1 1 1 4 — — — 40 19 12 71

— — — — — 1 — — 1 — — 1 — — 4 4

— — — — 1 10 — — 4 — — — 6 3 25 34

— — — — — — — — 1 — — 1 1— 2 3

— — — — — — — — — — — — — 1 1 2

— — — — — — — — — — — — — — 1 1

_ _ _ 10 3 1 3 — 5 2 — 3 33 25 19 77

24 4 — 17 1 — 11 2 1 6 6 3 184 81 38 303

— • — — 1 — — 5 — — 1— 3 35 4 17 56
___________ 1 — — 1 1

1_ _________ — 1_ 2 3

1 1 — 1 4 33 — — 3 — — 1 19 15 39 73

_ _ -,____ — — — — — — _ 1 1

___________ 1 — — 1 1

3 — — 12 26 2 6 14 — 3 8 — 27 56 2 85

35 11 — — 1 1 — — — — — — 35 12 1 48

8 4 — 10 5 — 6 1 — — — — 66 53 1 120

34 13 — 28 32 5 7 — 1 2 — — 107 59 8 174

_ _ i__ ________ _ 2 2

— — 2 — — 1 — — — — — 2 — — 5 5

— 1 — — 18 1 — 6 8 — 4 — 6 198 87 291
________ -,_____ 1 1

___ — — — — — — — — — — — 1 1

— — — — 1 — — 1 — — — 3 1 7 4 12

136 108 17 137 223 219 51 169 161 64 52 201 985 1,655 1,752

261 579 381 317 4,392 4,392

Grand total 4,461

Peprilus alepidotus
P. tnacanthus
Scorpaena brasiliensis
S calcarala
Bellator militaris
Pnonotus evolans
P. ophryas
P. roseus
P. scitulus
P. salmonicolor
P. tribulus

Ancylopsetta quadrocellata
Bothus sp.

Citharichthys macrops
Cyclopsetta fimbriata
Etropus microslomus
E. rimosus

Paralichthys albigutta
P. dentatus
P. lethostigma
P. squamilentus
Scophthalmus aquosus
Syacium papillosum
Gymnachirus melas
Tnnectes maculatus
Alutera schoepfi
A scnptus
Balistes capnscus
Monacanthus hispldus
Lactophrys quadncornis
Sphoeroides dorsalis
S. maculatus
S spenglen

Chilomycterus antlllarum
C. schoepfi

Subtotal

Total

teronotus novacula), and other Balistidae
(Aluterus schoepfi) were not active scallop preda-
tors.

Our observations agree with Roe et al. (1971),
who noted that Sphoeroides is an active predator
of calico scallops. While Dasyatis centroura is a
possible predator (Struhsaker 1969) neither it, the
dasyatids D. americana and Gymnura micrura,
nor the myliobatid, Rhinoptera bonasus, fed on
scallops.

MACROINVERTEBRATE
ASSOCIATES AND PREDATORS

Field observations yielded 60 species of mac-
romolluscs, 25 crustaceans, 12 echinoderms, 4
coelenterates, and 1 annelid as associates of the
bed (Table 7). These species, their numbers, and
abundances varied by season throughout the bed.
Species found in 50 or more percent of the samples
which may be considered the macroinvertebrates
common to the beds were: Eucrassatella speciosa,
Arcinella cornuta, Cassis madagascariensis,

Pleuroploca gigantea, Octopus vulgaris, Loligo
pealei, Calappa falmmea, Hepatus epheliticus, As-
tropecten articulatus, Luidia alternata, L. clath-
rata, Hemipholis elongata, Toxopneustes variega-
tus, and Encope emarginata.

Luidia clathrata and Astropecten articulatus oc-
curred abundantly throughout the bed during all
seasons and were predators of scallops (Table 7).
The following were found less abundantly and
were suspected predators of calico scallops: As-
terias forbesii, Busycon carica, B. contrarium, B.
spiratum, Fasciolaria hunteria, F. tulipa, Loligo
pealei, Murex fulvescens, M.pomum, Octopus vul-
garis, Pleuroploca gigantea, Polinices duplicatus,
Strombus alatus, Arenaeus cribrarius, Calappa
flammea, Hepatus epheliticus, Libinia emar-
ginata, Ovalipes quadulpensis, and Portunus
spinimanus.

The most common sea stars on the 1972 calico
scallop grounds were Astropecten articulatus,
Luidia alternata, and L. clathrata. Goniaster
americanus, Echinaster brasiliensis, Asterias for-
besi, and Gorgonocephalus arcticus were noted in
lesser numbers (Table 7). Identifications were

439

FISHERY BULLETIN: VOL. 75, NO. 2

TABLE 6.— Analysis of 1,655 stomach contents from 46 species of fishes captured on the scallop
grounds during commercial operations between February and October 1972.

Cruises
occurred in

Specimens
examined

Size

Number eating

Species

range

Scallops

Other food

Empty

Carcharhinus obscurus

960

Mustelus canis

440-972

Squatina dumenli

1,160

Ra/a eglanteria

135

136-580

127

Dasyatis americana

676

Gymnura micrura

415

Gymnothorax nigromarginatus

saxicola

276

Synodus foetens

200

98-426

163

Trachmocephalus myops

170-216

Opsanus tau

246

Ponchthys porosissimus

146-210

Lophius amencanus

560-716

Urophycis regius

110-208

Centropristis ocyurus

112-172

C. striata

92-325

Diplectrum formosum

46-282

Pomatomus saltathx

138

Haemulon plumieri

230

Orthopnstis chrysopterus

116-216

Calamus senta

120-225

Lagodon rhomboides

87-122

Stenotomus aculeatus

101

90-256

Leiostomus xanthurus

144-188

Menticirrhus amencanus

1 70-262

M. saxatilis

190-280

Chaetodipterus faber

286-290

Hemipteronotus nov'acula

128-172

Pepnlus alepidotus

118-156

P. triacanthus

97-156

Scorpaena calcarata

64-142

Phonotus evolans

196-342

P. salmonicolor

186-222

P. scitulus

145

134-268

136

Ancylopsetta quadrocellata

1 70-290

Cithanchthys macrops

120-142

Etropus microstomus

158

Paralichthys albigutta

200-289

P. dentatus

153-370

P. lethostigma

210-500

Syacium papillosum

86-300

Aluterus schoepli

342-390

A. scriptus

90-222

Batistes capriscus

105-356

Monacanthus hispidus

92-222

Sphoeroides maculatus

198

68-268

Chilomycterus schoepfi

72-142

Total, number

337

1,143

175

percent

20.4

69.0

10.6

based upon Gray et al. (1968) and Downey (pers.
commun.).

Roe et al. (1971) suggested that Asterias forbesi
may be a major predator on the calico scallops of
the Cape Canaveral grounds. The low total per-
cent of its occurrence on the 1972 North Carolina
calico scallop grounds (Table 7) precludes this as-
sumption for the 1972 fishery. Stomachs of A. for-
besi were not examined because it everts its
stomach when feeding (Hyman 1955:369). Hyman
(1955) made no mention of the feeding habits of
sea stars belonging to the Goniasteridae, Echinas-
teridae, or the Gorgonocephalidae. Stomachs of
species belonging to these families (Goniaster
americanus, Echinaster brasiliensis, and Gor-
gonocephalus arcticus) contained no recognizable

material. What they were feeding upon is not
known but, in light of their small numbers on the
scallop beds and the lack of scallops in their
stomachs, it is assumed that they were not sig-
nificant scallop predators on the 1972 bed.

Luidia alternate: frequented the calico scallop
bed yet was not as common as eitherL. elathrata or
Astropecten articulatus (Table 7). Stomach con-
tents yielded no calico scallops. Several specimens
were found in the field feeding upon smaller A.
articulatus. One large living specimen, held in an
experimental tank under controlled environmen-
tal conditions with living calico scallops, showed
no interest in the scallops but was seen feeding
upon A. articulatus and L. elathrata. It did at-
tempt unsuccessfully to feed on a Asterias forbesi

440

SCHWARTZ AND I'ORTK.R KISHKS. M ACROINVFRTFBRATFS OFF NORTH CAROLINA

TABLE 7. — Macroinvertebrate fauna of offshore calico sea

Hop beds in 1972 by season and

areas of good and

poor catches. N =

= number of

samples.

data listed as

percent of TV.

Good scallop

Poor scallop

Mar-Apr.

May-June

July-Aug.

Sept. -Oct.

Total

catches

Taxa

N = 14

W = 10

N = 14

N = 10

N = 48

N = 40

A/ = 8

COELENTERA

Renillidae:

Renilla reniformis

Actiniana (sea anemones)

Madreporana (corals)

ANNELIDA

Aphroditidae:

Aphrodita hastata

MOLLUSCA

Arcidae:

Area imbncata

A zebra

Anadara floridana

Noetia ponderosa

Mytilidae:

Brachidontes modiolus

Pterndae:

Pteria colymbus

Pectmidae:

Aequipecten muscosus

Argopecten gibbus

100

Lyropecten nodosus

Pecten reveneli

Ostreidae:

Ostrea permollis

Chamidae:

Arcinella cornuta

Chama macerophylla

Crassatellidae:

Eucrassatella speciosa

Cardiidae:

Dinocardium robustum

Laevicardium multilineatum

Venendae:

Chione intapurpurea

C. latilirata

Macrocallista maculata

M. nimbosa

Solemdae:

Ensis directus

Tellinidae:

Tellina magna

T. nitens

Solecurtidae:

Solecurtus cumingianus

Trochidae:

Calliostoma euglyptum

Turbimdae:

Astraea phoebia

Turbo castanea

Architectonicidae:

Architectonica nobilis

Cerithlldae:

Cerithium litteratum

Xenophondae:

Xenophora conchyliophora

Strombidae:

Strombus alatus

S. costatus

Cypraeidae:

Cypraea cervus

Naticidae:

Natica canrena

Polinices duplicates

P. duplicatus eggs

Sinum maculatum

Cassididae:

Cassis madagascanensis

C. madagascariensis eggs

Cypraecassis testiculus

Phalium granulatum

P granulatum eggs

Cymatidae:

Dislorsio clathrata

Tonnidae:

Oocorys abyssorum

Tonna galea

441

FISHERY BULLETIN: VOL. 75, NO. 2

Table 7.— Continued.

Good scallop

Poor scallop

Mar-Apr.

May-June

July-Aug.

Sept -Oct.

Total

catches

Taxa

N = 14

N = 10

N = 14

N = 10

N = 48

N = 40

N = 8

Ficidae:

Ficus communis

Muricidae:

Eupleura caudata

Murex dilectus

M. fulvescens

M. fulvescens eggs

Murex pomum

Thais haemastoma flondana

Melongenidae:

Busycon canaliculatum

B. carica

B. contrarium

B. contrarium eggs

B spiratum

B spiratum eggs

Fasciolarndae:

Fasciolaria lilium huntena

F. 1 huntena eggs

F tulipa

F. tulipa eggs

Pleuroploca gigantea

P. gigantea eggs

Olividae:

Oliva sayana Ravenel

Cancellamdae:

Cancellana reticulata

Conidae:

Conus delessertii

Octopodidae:

Octopus vulgaris

Loliginidae:

Lolliguncula brevis

Loligo pealeii

ARTHROPODA

Stomatopoda:

Gonodactylus aerstedi

Penaeidae:

Penaeus sp.

Sicyonia brevirostris

Scyllaridae:

Scyllandes nodifer

Porcellandae:

Porcellana sayana

Pagundae:

Pagurus sp.

P. annulipes

P. pollicaris

Ranmidae:

Ranilia muncata

Calappidae:

Calappa angusta

C flammea

Hepatus epheliticus

Osachila sp

Portunidae:

Ovalipes quadulpensis

0 ocellatus

Portunus gibbesii

P. spinimanus

Callmectes sapidus

Arenaeus cribrarius

Cancridae:

Cancer irroratus

Majidae:

Libinia emerginata

Stenocionops furcata coelata

Parthenopidae:

Parthenope serrata

P. pourtelesii

Xiphosura:

Xiphosura polyphemus

ECHINODERMA

Astropectinidae:

Astropecten articulatus

100

Luididae:

Luidia alternata

L clathrata

100

442

SCHWARTZ AND PORTER: FISHES. MACROINVERTEBRATES OFF NORTH CAROLINA
Table 7.— Continued.

Good scallop

Poor scallop

Mar -Apr

May-June

July-Aug

Sept -Oct

Total

catches

Taxa

(V = 14

N = 10

N = 14

N = 10

N = 48

N = 40

N = 8

Gomastendae:

Goniaster amencanus

Echmastendae:

Echinaster brasiliensis

Asterndae:

Astenas forbesi

Gorgonocephalidae:

Gorgonocephalus arcticus

Amphiundae:

Hemipholis elongata

Arbacndae:

Arbacia punctulata

Toxopneustidae:

Toxopneustes vanegatus

Scutellidae:

Encope emargmata

Cucumariidae:

Thyone bhareus

and was noted to have killed a large Strombus
alatus. Hyman (1955:369) pointed out that species
of Luidia eat mainly other echinoderms. At this
time, we do not consider L. alternata a calico scal-
lop predator.

Luidia clathrata was a predator of calico scal-
lops (Table 8). Between March and June we found
small numbers of scallop valves (ranging from 0.9
to 11.6 and 21.1 to 45.3 mm) in L. clathrata
stomachs (Table 9). Maximum predation took
place (April) just as calico scallop spawning began.
Why large scallops (21-45 mm lengths) were fed on
only in March and April is not known. The data
does indicate that numbers of Luidia (Table 10)
large enough (110 to 160 mm?) to swallow the
available scallops (28 to 70 mm length) were more
available during March through June. Prelimi-
nary observations on L. clathrata kept in the
laboratory indicated that they will feed readily on
calico scallops, digestion occurring within 24 h.
Hulings and Hemlay (1963) found L. clathrata to
engulf sediments and utilize whatever was avail-
able as food.

Wells et al. (1961) suggested that A. articulatus
was a nonselective feeder, while Porter (1972b)

TABLE 9. — Average number of calico scallop valves found per
month in stomach samples of sea stars A stropecten articulatus
and Luidia clathrata sampled in 1972 on the producing calico
scallop beds off North Carolina.

Astropecten articulatus
No./lOO No. stomachs

Luidia clathrata

No/100

No. stomachs

Month

stomachs'

examined

stomachs'

examined

Feb.

Mar.

226

Apr

151

178

May

158

June

314

311

July

Aug

154

Sept.

Oct.

'Approximate number.

TABLE 10. — Monthly lengths (millimeters) for sea stars cap-
tured on the calico scallop beds in 1972.

Astropecten articulatus

Luidia clathrata

Month

Average

arm

length

Size
range

Sample
size

Average
arm Size
length range

Sample
size

Feb.

61.6

34-101

109

92.7 46-142

Mar.

63.3

24-111

433

95.6 58-155

134

Apr

60.0

18-124

176

91.2 27-166

227

May

58 9

35-122

125

88.2 40-140

110

June

61.1

25-134

497

88 8 50-160

315

July

64.8

28-103

112

89.6 61-122

Aug.

64.5

28-120

169

84.6 28-112

Sept.

83.1

35-136

113

87,0 51-134

Oct

622

23-124

101

896 23-124

TABLE 8. — Lengths (millimeters) of calico scallop valves removed from stomachs of sea stars A stropecten articulatus
and Luidia clathrata collected on the calico scallop beds during the 1972 catch season.

Sea star

Feb.

Mar

Apr.

May

June

July

Aug.

Sept.

Oct.

Astropecten articulatus:

Average valve length

1.8

2.4

1.9

2.3

3.0

2.9

2.3

2.9

Size range

1.8

1.6-3.8

0.7-4.3

0.9-3.6

0.7-6.4

23-36

1.4-2.6

1 7-2.6

3.3-5.6

Number valves found

Luidia clathrata:

Average valve length

—

4.3
33.9

1.9

43.7

3.3

21.1

4.2

—

Size range

—

2.4-11.6
30.0-40.4

09-69
41 .0-45.3

1.4-3.5

10-6 4
21 1

4.2-4.2

Number valves found

—

5
8

443

FISHERY BULLETIN: VOL. 75, NO. 2

showed that large numbers of recently set calico
scallops may be eaten by A. articulatus and that
though continued examination of their stomach
contents, knowledge may be gained concerning
when and where calico scallop setting takes place.
During May and June 1972, numerous small scal-
lop valves appeared in the stomachs of this sea star
(Table 10). Valve numbers/100 stomachs were not
nearly as many as the 3,000/100 stomachs re-
ported by Porter ( 1972a) for June 1971. It is infer-
red from this that the 1972 scallop set on the sam-
pled grounds was relatively small. Note that
numbers of dead scallop shells increased from July
through October when the fishery collapsed ( Table
11). Also, the presence of L. clathrata decreased
while A. articulatus presence increased during the
March to October period (Table 11).

Stomach content data (Table 10) suggested that
if there were scallop spawnings following the ini-
tial May spawning as we have theorized, then the
set from these and the May spawnings either did
not survive after June or the setting occurred in an
area not covered by the sampling. Stomach
analysis data of sea stars continues to be worked
up and evaluated.

TABLE ll. — Average monthly numbers of dead shells and sea
stars per bushel catch (TV) occurring on the calico scallop beds in
1972.

Month

Dead
shells

Luidia
clathrata

Astropecten
articulatus

Mar

Apr.
May
June

8
2
8

19
19
22

1
1

4
2
2

July
Aug.
Sept.
Oct.

106
220
134
290

1
2

DISCUSSION

We had expected to find that the calico scallop
bed(s) that sustained the 1972 North Carolina
fishery to have been distinct in either physical,
chemical, or biological features. Instead, few dif-
ferences were found which could be pinpointed as
factors that made the bed(s) more unique than the
surrounding shelf areas. We noted that bottom
texture within and without the beds studied were
nearly identical (Table 3). Likewise, no extremes
of water temperatures, salinities, or phytoplank-
ton population (as measured by chlorophyll a
levels) seemed to exist in 1972. While the fish and

invertebrate faunas were diverse and speciose,
they too were little different from that noted from
the nearby reefs or areas (Pearse and Williams
1951; Wells et al. 1964; Cerame-Vivas and Gray
1966). Seasonal shifts in the fishes and inverte-
brates inhabiting the bed(s) occurred but these
were directly related to seasonal water tempera-
tures, salinities, or their natural migrating
movements (Tables 5, 7). Most populations of
fishes apparently moved over the bed(s) con-
stantly, some 24 species (of 33 most abundant) feed
on scallops. Of the macroinvertebrates, 3 species of
sea stars and 19 other macroinvertebrates were
predators. Whether the fishes and sea stars or
other macroinvertebrate predators, which were
definite predators of calico scallops, were attracted
to the area because of the scallops or the activities
of the fishery, which created available food in the
form of broken scallops, remains unresolved. One
interesting correlation was noted in that the
painted wrasse, Halichoeres caudalis, appeared
over the bed, in September and October, as in-
creased numbers of dead scallops occurred just
prior to the demise of the 1972 fishery on 28 Oc-
tober. This relationship has also been noted for the
Cape Canaveral calico scallop beds of Florida
(George Miller pers. commun.).

While we document the fish and macroinverte-
brate faunas and the ecology of a North Carolina
bed(s) that sustained the 1972 fishery, we are still
at a loss as to what creates the vacillations of
scallop availability in a bed or why one bed pre-
vails over another during any one or succeeding
years. Note that while the experimental bed was
fished and did possess scallops throughout 1972, it
as well as the commercial bed failed to support
scallops in the years 1973 through 1976. We can-
not ultimately conclude that the 1972 bed and
fishery collapsed as a sole result of overfishing but
that the levels of scallops available after 28 Oc-
tober could not economically support the fleet.
Sampling the planktonic stages of calico scallops
may resolve the repopulation aspects of the beds
for we still do not know whether we are simply at
the northern edge of its range, which may be de-
pendent on larval drift and recruitment from more
southern areas, or are dealing with a population
dependent upon native larvae for repopulation.
Additional field observations of the shelf water
mass movements and how they affect the survival,
growth, and existance of scallops needs refinement
while laboratory experiments which vary a
number of ecological parameters will hopefully

444

SCHWARTZ AND PORTER: FISHES. MACROINVERTEBRATES OFF NORTH CAROLINA

resolve what permits a calico scallop bed to exist. LITERATURE CITED

ACKNOWLEDGMENTS

Many contributed to the success and completion
of this study which was supported as Grant 456 of
the North Carolina Board of Science and Technol-
ogy. Foremost was the hard-working, dependable,
and conscientious Eugene Pond who served as our
field assistant and who contributed to all facets of
the projects far beyond the call of duty. These
efforts extended over many long hours enduring
the calm and not so calm Atlantic Ocean. The
wholehearted support and assistance by members
of the fishing fleet and their shore based represen-
tatives did much to make the project a success.
Notable among these were: C. Willis and crew of
the Ensign and C. Davis of Davis Fish Co.,
Beaufort, N.C.; W. Ipock and crew of the Seven
Brothers; the captain and crew of MV Ken Pat of
Styron's Seafood Company, Beaufort; and O. Ful-
ford of Harkers Island, N.C.

Cruises aboard the Eastward were as parts of
programs of F. Schwartz and W. Woods, Institute
of Marine Sciences, Morehead City. R. Barber, J.
Newton, G. Newton, and G. Kelly, Duke Marine
Lab., were most helpful during these cruises.
Work aboard the chartered Beveridge was made
possible with the assistance of J. Willis, J.
Costlow, and N. Hill. Student assistants during
various cruises were W. Link, D. Pettipas, S. Bor-
tone, and T. Herbert. Laboratory assistants were
D. Willis, V. Ebron, D. Oakley, A. Midgett, M.
Bortone, and R. Baldree. K. West prepared the
computer analyses.

The late Harry Davis, Atlantic Estuarine
Fisheries Center, National Marine Fisheries Ser-
vice (NMFS), NOAA, Beaufort, supplied data for
Table 2. M. Downy, U.S. National Museum,
Washington, D.C., assisted with several starfish
determinations. J. Lewis was instrumental in
handling procurement and supplies. R. Baldree
and B. Bright typed the final report. G. Miller,
Southeast Fisheries Center, NMFS, NOAA,
Miami, Fla., contributed helpful comments on
Halichoeres. R. Cummins and S. B. Drummond
and the crew of the George M. Bowers provided
space for one of us (HJP) to participate during the
RUFAS survey of some of the North Carolina scal-
lop beds.

In galley: we anticipate Rick Dawson's revision
of Stenotomus and list our S. caprinus as S. acu-
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1973. A description of the circulation on the continental
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1959. The role of physical and biological factors in the

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1951. The oyster and other mollusks in North Carolina.
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1969. Demersal fish resources: Composition, distribution,
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446

NOTES

ENERGY FOR MIGRATION IN
ALBACORE, THUNNUS ALALUNGA

The relations between immigrants and residents
of a specific fishing ground can likely be evaluated
from examination of the relative fat content of
individuals from a time sequenced sampling of the
fishery. These kinds of information are not yet
estimable for pelagic populations.

The problem of energy availability and utiliza-
tion in migrations offish is a perplexing one. Mi-
grations are energetically quite expensive unless
a fish is passively carried by currents. Recently
recorded migrations of two tagged albacore,
Thunnus alalunga (Bonnaterre), across the
Pacific Ocean indicate that they traveled an aver-
age of 48 km/day (Japanese Fisheries Agency
1975). As these fish were approximately 80 cm
long on release, the average migration speed was
about 0.65 body lengths/s (55.6 cm/s). This is well
within the range of observed swimming speeds for
this species. These albacore were reported to have

traveled from lat. 35°44'N, long. 171°37'E (Figure
1, point E) to lat. 47°00'N, long. 125°30'W (Figure
1, point F), a distance of 5,239 km in 110 days. The
caloric equivalent, in grams of fat,1 utilized by
these two fish at the estimated rate of travel of
about 55 cm/s would be about 1,450 g or 14.5% of
their expected weight at the onset of migration.
Although great amounts of feed would not be
necessary for this migration given the 1 kcal/g
average available caloric content for forage (Sharp
and Francis 1976), the albacore has been reported
to have up to 18.2% fat in the edible flesh portions
(Sidwell et al. 1974). Muscle tissue constitutes
58.2% of the total body weight of albacore (Dotson
unpubl. data) which means up to 10.6% body
weight in fat has been observed, a value approach-
ing that necessary to provide the caloric energy for
these migrations.

There is little doubt that albacore do not mi-
grate directly, that feeding does occur, and that
the fish probably do grow in overall length and

*9.4 kcal/g fat.

160° 170° 180" 170° 160°

EAST - LONGITUDE - WEST

150°

140°

130°

FIGURE 1. — A great circle plotting chart is shown and the quantity and location of albacore samples is indicated by the numerals. A
length-mass equation was developed for the 477 albacore caught west of long. 130°W during June 1974. The numbers 14 and 37 near
San Diego represent the samples collected in July and September 1975, respectively. Using ▲ as the origin the letters A and B along the
line represent the distances which a 63-cm albacore could swim utilizing 404 g of fat at A, its minimum speed; B, the observed
diurnal-nocturnal activity level. Points C and D on the same line represent the distance that the 65-cm fish with the greatest observed
mass deficit (999 g) could have traveled utilizing the energy of this quantity of fat at the two respective activity levels described above.
Points E and F are the release and recapture positions of two albacore tagged by Japanese researchers. The minimum temperature
habitat limit of albacore (14.5°C) is depicted by a dashed line. The great circle route does not differ markedly from this boundary but
likely represents a conservative estimate of the total distance traveled between points E and F.

447

mass during the migratory period. What appears
to be an important question is whether or not the
migrations of albacore and other tunas are extra
demanding, meaning sufficient short-term energy
is required to induce fat store utilization even
though feeding is still accomplished. Too often the
concepts of growth and fat deposition are inte-
grated such that it is considered unlikely that
morphological growth can take place during fat
store utilization. Certainly from observations of
adolescent growth in mammals it is obvious that
there is no necessary dichotomy here. The two
processes require separate biochemical pathways
and are very likely separated temporally, well
within the standard day.

In a preliminary effort to examine the question
of fat utilization, the length-mass relationship of
albacore collected offshore preceding their ap-
pearance in the onshore eastern Pacific surface
fishery has been compared with fish freshly ar-
rived in this fishery, and with fish which have
presumably been grazing and reconditioning for
the postsummer exodus from the onshore area.
Calculations from these data support the
hypothesis that fat stores are utilized for migra-
tion energy.

We hope that these calculations and subsequent
inferences will stimulate further research into the
considerable problem of highly variable length-
mass information and its potential use in studies
of migratory fishes.

Observations

In June 1974, 477 albacore 463 to 794 mm long
were captured in the area between long. 130° to
140°W and lat. 30° to 40°N (Figure 1). A curve was
fitted by regression to the length-mass data from
these fish resulting in the equation ( Dotson 1977),

M = 4.514 x 10 5L28746

(1)

where M is the mass in grams and L the fork
length in millimeters. Measured values fell
within 250 g of the regression line.

Mass and length measurements were made on
14 albacore (600 to 657 mm FL, mean 631) col-
lected during July and 37 fish (516 to 851 mm FL)
collected during September 1975, in a region 110
km south of San Diego, Calif. ( Figure 1). The mass
of September-caught albacore was not different
from those estimated by the length-mass regres-
sion curve. The mass of July-caught albacore,

however, averaged 404 g below those estimated by
regression (range: 172 g greater to 999 g less).
Analysis of body densities indicated that the mass
deficit of the albacore caught in July was probably
due to fat loss, or simply stated, as a fish of a given
length gets lighter its density increases (Dotson
1977).

The albacore fishery near the coast commenced
in July 1975. The albacore in this fishery are
known to migrate from the offshore region (Laurs
and Lynn in press), and it is assumed, therefore,
that the mass ( fat) deficit was utilized as an energy
source during migration to the coast.

Calculations and Inferences

Using the observed mass deficits observed in the
July 1975 sample, it is possible to estimate the
migration path length assuming 1) little or no
growth occurs during the migration, and 2) the fat
utilized is the only energy source during migra-
tion.

Based upon studies of swimming energetics of
tunas, Sharp and Francis (1976) estimated the
relation between swimming speed (V) in cen-
timeters per second, fork length ( / ) in centimeters,
and the swimming caloric expenditure per unit
time (Cs) in kilocalories per hour. The basic equa-
tion for this relation, in calories utilized per hour,
is as follows:

Cs = 8.7 x 10-8 (I)2 (V)3 Cd.

(2)

The coefficient of drag {Cd) is estimated using the
relation (Sharp and Francis 1976)

Cd = 0.262 exp [-(4.805 x 10 6)Re] (3)

where Re (Reynolds number) = IV I v (at#es=6.8 x
105, Cd = 0.01), v is the kinematic viscosity of
seawater, approximated by the value 0.01.

Sharp and Francis (1976) also estimated the
metabolic maintenance energy (Cm) (i.e. stasis
energy requirements) for tunas to be 1 g cal/g per
h. The metabolic weight (Wmet) is approximated
by the relation

Wmet = (M,)n *

(4)

met - UH/-)

Cm = Wmet x 10 3 kcal/g per h (5)

where Mf is the mass of the fish in grams.

Assuming that the mean mass deficit of 404 g of

448

the albacore caught in July was fat loss and given
that fat yields about 9.4 kcal/g, less ~159f due to
the cost of fat mobilization (SDA), leaving about
8.0 kcal/g, the caloric value of the fat loss is 3,272
kcal. The mean length of the albacore in the July
sample was 63 cm with a computed mass for the
offshore region (from Equation (1)) of 5,030 g. As
this would be the weight at the initial stage, it
seems appropriate to use as the mass for the calcu-
lations the equivalent of one-half of the observed
loss in mass (202 g) subtracted from the computed
initial mass to give a value of 4,828 g. Using these
equations, the rate of caloric expenditure per hour
was estimated for a 63-cm albacore swimming at
54 cm/s which is the estimated minimum speed a
63-cm albacore can swim and maintain hydrostat-
ic equilibrium, V100 (Magnuson 1970; Dotson
1977). Where C, plus Cm is equal to the total caloric
expenditure (Ctotai' during migration, then:

^ total ^s "• ^m

= 2.78 kcal/h
= 3.67 kcal/h.

0.89 kcal/h

(6)

The caloric equivalent of the fat divided by the
hourly caloric utilization rate, Ctotai, Equation (6)
yields the number of hours that swimming at 54
cm/s could be sustained utilizing this energy
source alone and is estimated to be

3,272 kcal
3.67 kcal/h

892 h or -37 days.

The speed and time multiplied together yield the
linear distance traveled during this period. This
was calculated to be 1,730 km (935 nmi).

Based upon sonic tracking experiments, the av-
erage swimming speeds of three albacore 84, 85,
and 87 cm in length have been observed to be 95
cm/s during the day and 62 cm/s at night (Laurs
et al. 1977). The minimum swimming speed for
hydrostatic equilibrium of these fish (V100) is esti-
mated to be about 42 cm/s (Dotson 1977). Assum-
ing the ratio of observed speed (V0) to minimum
speed ( V100 ) to be relatively constant over the size
range, then diurnal and nocturnal speeds can be
estimated where V0/V100 = 42 cm/s = 2.260 is the
multiplier for daylight speeds and (62 cm/s)/(42
cm/s) = 1.575 is the multiplier for night speeds.
The result of this estimation is that the daylight
and nighttime speeds for a 63-cm albacore are 122
and 80 cm/s, respectively. Assuming equal time
spent at each speed, about 6.08 kcalm are utilized.

If the tracking observations are representative of
migratory swimming speed, and therefore caloric
expenditures, then the fat energy would have been
utilized in a period of nearly 22 days and the linear
distance traveled would be about 1,960 km (1,060
nmi).

From the nearshore area of capture, the
maximum linear distance traveled using the av-
erage fat loss of a 63-cm albacore is indicated by
points A and B in Figure 1. The two values indi-
cated represent a) 37 days at a minimum speed of
54 cm/s, and b) the estimated diurnal rates of 80
and 122 cm/s for equal portions of 22 days. The
interesting result is that both the distances are
within the area where the offshore samples with
the greater length-mass relationship were col-
lected and compared with the onshore material.

The maximum observed mass difference from
the offshore mean of an albacore caught inshore is
999 g or 189c of its body weight for a 65-cm fish
(Dotson 1977). Assuming the total weight differ-
ence to be fat, at its calculated minimum speed of
54 cm/s, this albacore could have traveled 4,200
km (2,270 nmi) over a period of 90 days utilizing
only this fat as an energy source. This would place
the fish well out in the mid-Pacific, as shown by
point C in Figure 1. Swimming at the estimated
day and night speeds of 122 and 80 cm/s for equal
parts of the day this fish could travel 4,680 km
(2,520 nmi) in 54 days (Figure 1, point D).

These observations, calculations, and hypoth-
eses should indicate some of the potential effects
which can be examined in the future, given broad-
scale sampling and interest in the migrations of
tunas. Fat content is an important indicator of the
calories available for migration and/or spawning
in fish of sufficient maturity. The importance of
immigrants to population assessment in managed
fisheries is obvious. Certainly, spawning success
and behavior is dependent upon the available
caloric stores. For tunas where migration and
grazing up to spawning condition may be competi-
tive processes, a thorough examination of the fat
level cycles may offer insights into both periodic-
ity and location of the potential spawners. This is
an area of minimal understanding in tunas to
date. Considering the importance of these pro-
cesses in the life cycles of tunas, it seems that a
certain amount of importance should be placed
upon obtaining comprehensive data from several
behavioral categories of tunas where inferences
could be made about the relation of fat stores and
behavior.

449

Literature Cited

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1977. Minimum swimming speed of albacore, Thunnus
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Gary D. Sharp

Inter-American Tropical Tuna Commission
La Jolla, CA 92038

RONALD C. DOTSON

Southwest Fisheries Center

National Marine Fisheries Service, NOAA

P.O. Box 271, La Jolla, CA 92038

UNDERWATER SOUNDS FROM RIBBON SEAL,
PHOCA (HISTRIOPHOCA) FASCIATA1

Intense downward frequency "sweeps" and broad-
band "puffing" sounds were recorded underwater
in the presence of ribbon seal, Phoca (His-
triophoca) fasciata Zimmerman 1783. The record-
ings were made in the waters off Savoonga, St.
Lawrence Island, Alaska, on 16, 17, 18, and 23
May 1967.

The seals were encountered in the final ice of the
spring made up of windrows of small to moderate
floes mixed with brash ice, and with stretches of up

to 1 km of open water between. On this ice typi-
cally occur adults and pups of a variety of other
pinniped species (Phoca largha, Erignathus bar-
batus,Pusa hispida, andOdobenus rosmarus), but
during the spring of 1967 there was a preponder-
ance of Histriophoca in this area. This is reflected
in the records of the pinniped harvest for this area
(Alaska Department of Fish and Game) which
show that Histriophoca usually composes less
than 2% of the catch, but in 1967 it made up 60% of
the harvest and most of the Histriophoca were
caught during the last half of May. The 1967
underwater recordings showed similar differ-
ences, contrasting sharply with previous years
when Erignathus dominated the underwater
sound ambient (Ray et al. 1969).

Relatively little is known of the behavior of His-
triophoca (cf. Scheffer 1958; King 1964). Breeding
assemblages occur on ice that rarely approaches
shore (Burns 1970) and other social behavior may
mostly occur in the water.

Instruments and Methods

Underwater sounds were recorded with a
Chesapeake Instrument Corp.2 hydrophone sys-
tem and a Nagra III B tape recorder whose com-
bined response was 50 Hz to 18 kHz ( ±2 dB, deci-
bels). The sounds were studied by means of a Kay
Elemetrics 7029A spectrographic analyzer and
time sequences were measured by a Tektronix 565
oscilloscope.

To make the recordings, appropriate His-
triophoca habitat in the sea ice was located with
the aid of Eskimo hunters, and their skin boat was
allowed to drift with the ice while the hydrophone
was in the water. Only a few of these seals were
seen as we approached, and they always sub-
merged and were difficult to find again. However,
some of their underwater sweep sounds were loud
enough to be audible in air, implying that these
seals were not far away.

Taped sequences of 5 to 8 min duration were
analyzed from each of nine locations over 4 days of
field study. Higher level underwater sounds, pre-
sumably from nearby seals, were analyzed and
compared with background lower level sounds.
Sounds from distant animals were not used for
detailed analysis.

As is usually the case with underwater record-

contribution No. 3753 from the Woods Hole Oceanographic
Institution.

2Reference to manufacturers does not imply endorsement by
the National Marine Fisheries Service, NOAA.

450

ings, the attribution of these sounds to His-
triophoca is circumstantial since they are under-
water sounds from animals out of sight below the
surface. These sounds are unlike sounds attrib-
uted to any of the other animals known to inhabit
the area: gray whales (Asa-Dorian and Perkins
1967; Cummings et al. 1968; Fish et al. 1974),
walrus (Schevill et al. 1966; Ray and Watkins
1975), and the ringed seal and spotted seal
(Schevill et al. 1963; Stirling 1973; Ray pers. obs.).
The bearded seal, Erignathus barbatus, was seen
at times in low numbers during May 1967; some of
the recordings have a background that we recog-
nize as from Erignathus, but we eliminate it be-
cause: 1) the Histriophoca sounds are very differ-
ent from the Erignathus sounds heard at this
season (Ray et al. 1969); 2) in previous years when
only Erignathus was nearby, none of the His-
triophoca sounds was heard; 3) Histriophoca
sounds were heard in the presence of these seals
whether Erignathus were audible or not; and 4)
none of these sounds were heard unless His-
triophoca were observed in the area.

The recordings were made in a variety of ice
conditions and ice is known to produce sounds
underwater (Schevill 1966; Watkins and Ray pers.
obs. ). The seal sounds did not vary with the ice and
did not match the kinds of sound we associate with

ice.

Underwater Sounds
Two types of underwater sounds were heard in
5-

the presence of Histriophoca: a relatively intense
prolonged downward sweep in frequency and a
broadband puffing sound. These calls were heard
sporadically, with no obvious pattern to repeated
sounds nor to any answering calls. Nearby seals
could be heard at least once in 2 min and often
there were enough seals in audible range so that
when calling was most frequent we recorded 3 to 5
calls in 10 s. Since the seals were out of sight and
probably underwater during the recordings, we
could not correlate the sounds with behavior.

The sweep sound (Figure 1) varied in frequency
from 7 to 0.1 kHz in downward sweeps of 2 to 5 kHz
each. Of the 120 sweep sounds measured, all but
one could be separated into three length categories
(Figure 2), each with somewhat different starting
and ending fundamental frequencies:

Short sweeps, 1 s or less, sweeping from 2000-1750 Hz

to 300 Hz.
Medium sweeps, 1.3 to 1.8 s, sweeping from 5300-2000 Hz

to 100 Hz.
Long sweeps, 4 to 4.7 s, sweeping from 7100-3500 Hz

to 2000 Hz.

Short sweeps were common in the background
ambient sound, but only a few were heard from
nearby seals (16 measured). Midlength sweeps
were the ones most often heard from local seals (84
measured), and some of these began with a short
segment of sound at constant frequency for the
first 0.1 to 0.2 s before beginning the downward
frequency sweep (Figure 1). The long sweeps were
not particularly abundant but were conspicuous

$ 3

Seconds

FIGURE 1. — The midlength sweep sound of Histriophoca often has a short portion of constant frequency before it begins to sweep
downward in frequency. Analyzing filter bandwidth was 45 Hz. Analyses of short and long sweeps (not figured separately) were
generally similar in character to the midlength sweep.

451

SECONDS

FIGURE 2. — Lengths of 120 sweep sounds from Histriophoca
separate all but one (at 2.75 s) into three categories.

(19 measured) because of the higher frequency
ending. Harmonics (up to 6 or more) were consis-
tently present in the spectrographic analyses of
even low-level sweep sounds, and appear to be a
result of the pulsed character of the seal sounds
(Watkins 1967).

Since we never knew the distance to calling
seals, we did not have accurate acoustic source
levels for these sounds. Some sweeps overloaded
the recording system at the usual gain settings
and therefore were received at levels estimated in
excess of 40 dB (re 1 volt/dyne cm2). Assuming a
60-65 dB source level at 1 m and spherical spread-
ing losses, these very loud sounds were sometimes
from animals that were only 15 to 20 m from the
hydrophone. Sounds of each type and length cate-
gory were heard from distant as well as nearby
seals so that none of these sounds were character-
istic of a particular seal.

A second type of underwater sound which we
associate with Histriophoca was a broadband

puffing sound with frequencies below 5 kHz and
lasting a little less than 1 s (Figure 3). This was
somewhat reminiscent of some seal respiratory
sounds, but it was not audible in air and we could
not correlate them with respiratory activity. The
puff sounds were 20 to 25 dB lower level than the
sweeps.

Discussion

The downward sweeping frequency and pulsed
quality of the sounds is characteristic of many
underwater calls of other seals: Erignathus bar-
batus (Ray et al. 1969), Leptonychotes weddelli
(Ray 1967; Schevill and Watkins 1965, 1971),
Pagophilus groenlandica (Watkins and Schevill in
prep.), Pusa hispida (Stirling 1973), Arcto-
cephalus philippii (Norris and Watkins 1971).
Coincident with spring reproductive activities,
most of these pinnipeds produce striking under-
water acoustic signals and greatly increase their
calling. Ovulation normally occurs from mid-
April to mid-May in Histriophoca and adult males
remain sexually potent through early June
(Burns3). Analogy to these other pinnipeds
suggests similar social functions for the under-
water sounds of Histriophoca, in reproductive
and/or territorial behavior.

3Burns, J. J. 1969. Seal biology and harvest. Marine Mammal
Investigations. Fed. Aid Completion Rep., Alaska Dep. Fish
Game 10:1-25.

FIGURE 3,

Seconds

-The "puffing" sound of Histriophoca is not related to any respiratory activity but is an underwater sound with broadband
characteristics that are quite variable. Analyzing filter was 45 Hz.

452

Acknowledgments

The field work was sponsored by a grant to The
Johns Hopkins University from the Arctic Insti-
tute of North America under contractural agree-
ments with the Office of Naval Research. Field
recording equipment was supplied by the National
Science Foundation, Office of Polar Programs.
Help in the field was given by D. 0. Lavallee of
New York City and Winfred James of Gambell,
Alaska. Teresa Bray and Karen E. Moore assisted
in acoustic analyses and manuscript preparation,
which has been supported by contract N00014-
74-C0262 NR 083-004, with the Oceanic Biology
Program of the Office of Naval Research. We
thank F. H. Fay, John J. Burns, and William E.
Schevill for their critical reading of the manu-
script.

Literature Cited

ASA-DORIAN, P. V., AND P. J. PERKINS.

1967. The controversial production of sound by the
California gray whale, Eschrichtius gibbosus. Nor.
Hvalfangst-Tid. 56:74-77.

BURNS, J. J.

1970. Remarks on the distribution and natural history of
pagophilic pinnipeds in the Bering and Chukchi seas. J.
Mammal. 51:445-454.

CUMMINGS, W. C, P. O. THOMPSON, AND R. COOK.

1968. Underwater sounds of migrating gray whales, Es-
chrichtius glaucus (Cope). J. Acoust. Soc. Am. 44:1278-
1281.

FISH, J. F., J. L. SUMICH, AND G. L. LlNGLE.

1974. Sounds produced by the gray whale, Eschrichtius
robustus. Mar. Fish. Rev. 36(4):38-45.

KING, J. E.

1964. Seals of the world. Br. Mus. (Nat. Hist.), Lond.,
154 p.

NORRIS, K. S., AND W. A. WATKINS.

1971. Underwater sounds of Arctocephalus philippii, the
Juan Fernandez fur seal. Antarct. Res. Ser. 18:169-171.

Ray, C.

1967. Social behavior and acoustics of the Weddell seal.
Antarctic J., U.S. 2:105-106.
RAY, G. C, AND W. A. WATKINS.

1975. Social function of underwater sounds in the walrus
Odobenus rosmarus. In K. Ronald and A. W. Mansfield
(editors), Biology of the seal, p. 524-526. Rapp. P.-V.
Reun. Cons. Int. Explor. Mer. 169.

RAY, C, W. A. WATKINS, AND J. J. BURNS.

1969. The underwater song oiErignathus (bearded seal).
Zoologica (N.Y.) 54:79-83, phonograph disc.

SCHEFFER, V. B.

1958. Seals, sea lions, and walruses; a review of the Pin-
nipedia. Stanford Univ. Press, Stanford, 179 p.
SCHEVILL, W. E.

1966. Classification of natural sounds in the underwater
ambient. J. Underwater Acoust. 16:339-340.

Schevill, w. E., and w. A. Watkins.

1965. Underwater calls of Leptonychotes (Weddell seal).
Zoologica i N.Y.) 50:45-46.

1971. Directionality of the sound beam in Leptonychotes
weddelli (Mammalia: Pinnipedia). Antarct. Res. Ser.
18:163-168.

Schevill, w. E., W. A. Watkins, and C. ray.

1963. Underwater sounds of pinnipeds. Science (Wash.,
D.C.) 141:50-53.

1966. Analysis of underwater Odobenus calls with re-
marks on the development and function of the pharyngeal
pouches. Zoologica (N.Y.) 51:103-106, phonograph disc.

STIRLING, I.

1973. Vocalization in the ringed seal (Phoca hispida). J.
Fish. Res. Board Can. 30:1592-1594.
WATKINS, W. A.

1967. The harmonic interval: fact or artifact in spectral
analysis of pulse trains. In W. N. Tavolga (editor),
Marine Bio-Acoustics, Vol. 2, p. 15-42. Pergamon Press,
Oxf.

WILLIAM A. WATKINS

G. CARLETON RAY

Woods Hole Oceanographic Institution
Woods Hole, MA 02543

Department of Pathobiology
The Johns Hopkins University
615 North Wolfe Street
Baltimore, MD 21205

OBSERVATIONS ON FEEDING, GROWTH,

LOCOMOTOR BEHAVIOR, AND BUOYANCY OF

A PELAGIC STROMATEOID FISH,

ICICHTHYS LOCK1NGTONI

Stromateoid fishes (Order Perciformes) occur in
either coastal or oceanic regions of the sea. In-
habitants of the latter region are generally rare
and sporadic in occurrence, especially as adults.
Many of the oceanic species have particular adap-
tations for pelagic existence (Horn 1975) and their
frequent association with floating objects, espe-
cially coelenterates (scyphomedusae and
siphonophores), is well documented (e.g., Man-
sueti 1963; Haedrich 1967; Bone and Brook 1973;
Horn 1975).

The live capture and successful laboratory
maintenance of a juvenile Icichthys lockingtoni
Jordan and Gilbert (family Centrolophidae), an
oceanic fish of the North Pacific, provided the first
opportunity to record the feeding, growth, and
locomotor behavior of this pelagic stromateoid
and, upon the death of the fish, to measure its
buoyancy and lipid content (as a factor in
buoyancy). In this paper, the laboratory rearing
and maintenance of oceanic stromateoids are
briefly reviewed, and the adaptive strategy of/.

453

lockingtoni for locomotion and buoyancy in the
open ocean is compared with that of another
pelagic centrolophid, Schedophilus meduso-
phagus Cocco.

Materials and Methods

One /. lockingtoni was captured during an
open-water skin and scuba diving operation con-
ducted from the RV Nautilus in the San Pedro
Channel (lat. 33°30'N, long. 118°30'W) off south-
ern California on 24 October 1974. The fish was
approached by a scuba diver at a depth of 1 1 m as it
swam slowly beneath a scyphozoan medusa (ten-
tatively identified as a member of the family
Pelagiidae) approximately 30 cm in bell diameter.
The specimen was captured in a 1-liter jar, placed
in a container filled with aerated seawater aboard
the ship and transported to the laboratory at
California State University, Fullerton, where it
was placed in a 95-liter Instant Ocean1 Tank. Ap-
proximately 6 h lapsed between time of capture
and placement of the fish in the laboratory tank.
Sea temperature at the depth of capture was 15°C
and the temperature of the seawater in the tank
when the fish was introduced was 13°C. Tempera-
ture of the seawater in the tank during the
maintenance period ranged from 8.8°C to 22.2°C (x
± 1 SD = 14.9 ± 2.2°C) and the salinity from
35.0%« to 37.5%« (35.7 ± 2.3%o).

The fish began feeding regularly on 7 November
1974 and was fed daily (except for 8 days, irregu-
larly spaced, when feeding was not possible) by
hand with measured amounts of frozen brine
shrimp (90% water content). The fish took the food
at the surface so that it was possible to keep an
accurate record of the amount of food it ingested.
The daily diet of frozen brine shrimp ranged in
weight from 1.2 to 8 g (0.4 -1.4 g dry wt/100 g live
wt fish). The feeding rate was based on the amount
the fish would consume immediately. Weight and
standard length (SL) of the specimen were re-
corded on 7 November and at irregular intervals
throughout the maintenance period by removing
the fish in a tray from the tank and placing it on a
platform balance beside a metric rule. The weigh-
ing and measuring procedure required that the
fish be out of water a maximum of 15 s. The con-
version of food into fish flesh was obtained by di-

1 Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

viding the food intake (dry wt) by the gain in
weight of the fish (wet wt) (Hastings and Dickie
1972).

Locomotor behavior was recorded from periodic
observations and from analysis of an 8-mm cine
film made of the fish swimming in the tank.

Buoyancy of the specimen was measured im-
mediately after its death (7 April 1975) by weigh-
ing it in air and in water of known temperature
and salinity. Results were expressed as the per-
cent of the weight in air that the fish weighed in
seawater.

After the buoyancy determination the specimen
was frozen and later thawed for lipid analysis.
Total lipids of the spine, skull, viscera, and flesh
(all other tissues) were extracted with
chloroform-methanol (2:1, vol/vol) and expressed
for each of the four body parts as the percent of
total body lipid and as the percent of dry weight of
that body part.

Results

The specimen of /. lockingtoni became con-
ditioned within 1 wk of capture to take food di-
rectly from the hand. Chunks of frozen brine
shrimp offered at the surface were quickly ap-
proached and usually taken in a single bite.
Throughout the maintenance period, the fish occa-
sionally swam upside down, apparently a normal
mode of swimming, and sometimes fed in this posi-
tion. The fish also bit at other available objects in
the tank, including human fingers at feeding time,
grasping them and then rolling and twisting its
body as if to tear free the objects. Vision appeared
to be the primary sense used in locating food.

The specimen measured 105 mm SL at the time
of capture. On 7 November, when the fish began to
feed regularly and the record of food intake and
growth was begun, the fish weighed 30.6 g and was
115 mm SL (Table 1). The specimen lived 165 days,
until 7 April 1975, when the temperature of the
tank increased unexpectedly to 26°C apparently
causing death. At death, the fish weighed 54.5 g
(78.1% increase over its 7 November weight) and
had grown to 168 mm SL (46.1% increase). Its
weight peaked on 5 February at 64.6 g then de-
clined to the final value.

During the 151-day period (7 November-7 Ap-
ril), 65.7 g (dry wt) of frozen brine shrimp were
ingested by the fish (Table 1). Based on this intake
and the weight gain recorded (23.9 g wet wt), the
overall conversion factor was 2.7. For the 90-day

454

TABLE 1. — Size, food intake, and food conversion, at cumulative
intervals, of Icichthys lockingtoni maintained in the laboratory
over a 151 -day period.

Conversion

Fish

Food

factor

length

weight

intake'

(food intake

Date

(mm SL)

(g wet wt)

(g dry wt)

fish w'gam)

7 Nov. 1974

115

30.6

—

22 Nov 1974

120

33.8

3.8

14 Dec 1974

125

365

11.7

2.0

4 Jan 1975

135

43.2

21.2

1.7

5 Feb. 1975

—

64.6

389

1.1

7 Apr 1975

168

54.5

65.7

2.7

'Based on 90% water content.

period ending on 5 February when the fish's
weight reached a maximum, /. lockingtoni in-
gested 38.9 g of food (dry wt) and gained 34.0 g ( wet
wt) for a food conversion of 1.1.

The fish swam slowly and continuously most of
the time but infrequently hovered in one position.
The short ( 12.6% SL, 168 mm SL), fanlike pectoral
fins were the primary propulsive elements when
the fish cruised slowly in the tank. Each pectoral
fin was flapped in a semirotary manner, alter-
nately to the opposing fin, at approximately 1
stroke/s. At short-term increased speeds, the pec-
toral fins were held against the body and thrust
obtained by sinuous movements of the posterior
trunk and caudal region. The small (6.5% SL, 168
mm SL) pelvic fins were actively used during
swimming especially in braking and turning. As
mentioned, the fish was adept at swimming for
short distances upside down and at other attitudes
about its longitudinal axis.

The weight of the fish in seawater (20°C, 33%o)
immediately after death was 0.36 g or 0.66% of its
weight in air (slight negative buoyancy).

Lipids constituted 4.9% of the dry weight of the
spine, 10.6% of the skull, 17.0% of the viscera, and
4.4% of the flesh. Spine lipids made up 2.2% of the
total body lipids, skull lipids 2.9%, visceral lipids
35.3%, and flesh lipids 59.6%.

Discussion

The stromateoid characteristic of associating
with pelagic coelenterates as juveniles is particu-
larly well developed in/, lockingtoni. Many of the
small ( <200 mm SL) specimens captured have
been taken with medusae (Fitch 1949; Haedrich
1966; Fitch and Lavenberg 1968). The locomotor
behavior and feeding behavior of Icichthys re-
corded in this report are traits well suited for liv-
ing with medusae. The ability to swim at various
attitudes about the longitudinal axis and to hover
and maneuver using the paired fins would be ad-

vantageous in moving among and avoiding the
stinging tentacles of medusae. The grasping of
large objects followed by a rolling and twisting of
the body appears to be a feeding pattern especially
appropriate for tearing chunks from the tentacles
and other tissues of coelenterates. Haedrich (1966)
reported that the stomachs of Icichthys often con-
tain siphonophore remains. A feeding behavior
also consisting of grasping objects and twisting
the body has been observed (R. L. Haedrich pers.
commun.) in two other pelagic centrolophids,
Hyperoglyphe perciforma (Mitchill) and
Schedophilus medusophagus.

The food conversion values for Icichthys of 2.7
for the 151-day period and 1.1 for the initial 90-day
period are comparable to or, in the latter case,
more efficient than average total conversions
(1.75-2.7) reported by Phillips (1972:19) for brook
trout and brown trout fed a variety of diets at
temperatures ranging from 8.3° to 15.6°C. The
feeding rates of 0.4-1.4% for /. lockingtoni were
lower than those of 2-3% at which maximum con-
version occurred in channel catfish (Tiemeier et al.
1969). Useful comparisons between different ex-
periments and different species are limited since a
variety of physical and biological factors influence
energy requirements and conversion efficiencies
and since food conversions, as calculated here, are
less meaningful and often different from caloric
conversions (Phillips 1972). The most important
result of the present study, however, is that the
conversion efficiency of/, lockingtoni did change,
generally declining with age of the fish (see be-
low).

Limited success has been achieved in maintain-
ing pelagic stromateoids in the laboratory. Maul
(1964) recorded rapid growth in two species of cen-
trolophids Schedophilus (= Mupus) maculatus
and Schedophilus ( = Mupus ) ovalis, fed on a diet of
shrimp in a large (700-liter) aquarium. The former
species increased in weight from 7 to 95 g in 61
days, andS. ovalis increased in length from 100 to
198 mm SL over the same period. R. L. Haedrich
(pers. commun.) has kept two other centrolophids,
S. medusophagus and Hyperoglyphe perciforma,
for 2- to 3-mo periods in small (40- to 100-liter)
tanks at Woods Hole Oceanographic Institution.
D. Gruber at the Southwest Fisheries Center in La
Jolla has hatched and reared a series of larvae of/.
lockingtoni (E. H. Ahlstrom pers. commun.). One
larva that hatched on 12 June 1975 at a notochord
length of 3 mm grew to 90 mm SL by 30 August
1975 (80 days).

455

The rare and sporadic live capture of
stromateoids prevents the development of appro-
priate procedures for long-term maintenance. To
date, maintenance trials indicate (pers. obs.; R. L.
Haedrich pers. commun.) that the fishes will grow
rapidly for short periods but then lose interest in
feeding and gradually decline in health, especially
as the adult stage is reached when pelagic
stromateoids generally change their mode of life
and occupy greater depths. The initial growth and
high conversion efficiency followed by the reduced
growth and lowered efficiency of/, lockingtoni are
consistent with these observations.

The apparent adaptive strategy for pelagic exis-
tence of juvenile/, lockingtoni involving locomotor
behavior, buoyancy, and lipid content parallels
that described (Bone and Brook 1973) for juvenile
(85-200 mm SL) Schedophilus medusophagus
from the North Atlantic. There is no swim bladder
in either species in this size range, the lipid con-
tent of both is low and both species are slightly
negatively buoyant (weight in water 0.35-0.53% of
weight in air for S. medusophagus). In each case,
the pectoral fins are important in generating both
thrust and lift.

The two species also appear to undergo similar
changes in mode of life as the adult stage (about
>200 mm SL) is reached and the fishes become
independent of floating objects and occupy greater
depths in the water column. Data, particularly on
adultS. medusophagus, indicate that certain den-
sity reducing mechanisms (increase in lipid and
water content, decrease in dense tissues, i.e., mus-
cle and bone) are more prominent than in the
juvenile stage. Horn (1975) found that a large (285
mm SL) specimen of S. medusophagus was neut-
rally buoyant, swam in a slow, near-anguilliform
manner and had relatively small pectoral fins of
minor importance in generating thrust and lift.
Lipid content in the same specimen was relatively
high, especially in the bones (spine 23% and skull
21% lipid by dry wt) (Lee et al. 1975).

Data are yet insufficient on adult/, lockingtoni
to fully demonstrate parallel strategies in the two
species. The relative length of the paired fins of
Icichthys, however, decrease with age (Haedrich
1966) at a rate and magnitude similar to that in S.
medusophagus. In addition, the muscles of large
(270 mm SL) Icichthys are soft and loosely packed
as in Schedophilus. Data on buoyancy and lipid
content of adult /. lockingtoni are needed to test
the hypothesis.

Acknowledgments

Special recognition is due Wayne S. White who
dexterously captured the/, lockingtoni and helped
identify the medusa with which the fish was as-
sociated. I thank Charles F. Phleger for determin-
ing the lipid content and the captain and crew of
the RV Nautilus for facilitating a safe open-water
diving operation.

Literature Cited
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1973. On Schedophilus medusophagus (Pisces:
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FITCH, J. E.

1949. Some unusual occurrences of fish on the Pacific
Coast. Calif. Fish Game 35:41-49.
FITCH, J. E., AND R. J. LAVENBERG.

1968. Deep-water teleostean fishes of California. Univ.
Calif. Press, Berkeley, 155 p.
HAEDRICH, R. L.

1966. The stromateoid fish genus Icichthys: notes and a
new species. Vidensk. Medd. Dan. Naturhist. Foren.
129:199-213.

1967. The stromateoid fishes: systematics and a classifica-
tion. Bull. Mus. Comp. Zool. Harv. Univ. 135:31-139.

Hastings, W. H., and l. M. Dickie.

1972. Feed formulation and evaluation. In J. E. Halver
(editor), Fish nutrition, p. 327-374. Academic Press, NY.

Horn, m. h.

1975. Swim-bladder state and structure in relation to be-
havior and mode of life in stromateoid fishes. Fish. Bull.,
U.S. 73:95-109.

Lee, R. F., C. f. phleger, and M. H. Horn.

1975. Composition of oil in fish bones: possible function in
neutral buoyancy. Comp. Biochem. Physiol. 50B:13-16.
MANSUETI, R.

1963. Symbiotic behavior between small fishes and jel-
lyfishes, with new data on that between the stromateid,
Peprilus alepidotus, and the scyphomedusa, Chrysaora
quinquecirrha. Copeia 1963:40-80.

MAUL, G. E.

1964. Observations on young live Mupus maculatus
(Gunther) and Mupus ovalis (Valenciennes). Copeia
1964:93-97.

Phillips, A. M., Jr.

1972. Calorie and energy requirement. In J. E. Halver
(editor), Fish nutrition, p. 1-28. Academic Press, N.Y.
TIEMEIER, O. W., C. W. DEYOE, A. D. DAYTON, AND J. B. SHRA-
BLE.

1969. Rations containing four protein sources compared at
two protein levels and two feeding rates with fingerling
channel catfish. Prog. Fish Cult. 31:79-89.

MICHAEL H. HORN

Department of Biology
California State University
Fullerton, CA 92634

456

BODY SIZE AND LEARNED AVOIDANCE AS

FACTORS AFFECTING PREDATION ON COHO

SALMON, ONCORHYNCHUS KISUTCH, FRY BY

TORRENT SCULPIN, COTTUS RHOTHEUS

Wild coho salmon juveniles, Oncorhynchus
kisutch, in Washington streams range in fork
length (FL) from about 30 mm at the time of
emergence from the gravel to 120 mm on migra-
tion to the sea. Predation by sculpins, Cottus spp.,
is limited to the smaller salmon; few salmon >45
mm FL have been recovered from the stomachs of
sculpins (Patten 1962, 1971a, 1972). Yet, sculpins
are capable of eating hatchery reared fall chinook
salmon, O. tshawytscha, of 60 mm FL (Patten
1971a). Apparently, the reason sculpins do not
normally prey on wild coho salmon >45 mm FL is
not entirely dependent on the relative sizes of prey
and predator.

The present study is on the ability of torrent
sculpin, C. rhotheus, to prey on coho salmon >45
mm FL, as well as the predator avoidance be-
havior of coho salmon to torrent sculpins in stream
aquaria adjacent to the Cedar River near
Ravensdale, Wash., during 1965 and 1966. One
experiment indicates the absolute size of coho
salmon that can be caught, subdued, and swal-
lowed by a torrent sculpin of a given length. The
other suggests that coho salmon previously ex-
posed to torrent sculpins become less susceptible
to these predators in future interactions.

Facilities and Procedures

Two related studies — one on predator-prey size
relations and the other on the learned predator
avoidance ability of coho salmon prey — were con-
ducted in stream and holding aquaria that re-
ceived water from the Cedar River. The two
stream aquaria were 2.4 m long, 0.6 m wide, and
0.6 m high; water depth ranged from 2 to 18 cm.
The eight holding aquaria were 34 cm wide, 41 cm
long, and 36 cm high; water depth was 18 cm (a
more complete description of the experimental
facilities is given by Patten 1971b).

Water was gravity fed from a low level dam on
the Cedar River to a head box through a flume and
then to the aquaria. Each aquarium received a
continuous supply of clear water; temperatures in
the morning during the study ranged from 4.4° to
12°C.

Torrent sculpins were collected by electro-
fishing in Soos Creek, King County, Wash., and

coho salmon were seined in upper Rock Creek of
the Cedar River drainage. It was assumed that
the state of hunger of all torrent sculpins was
similar, that the coho salmon had little experience
with fish predators, and that this experience was
similar for all subjects. The assumption for the
coho salmon was probably valid because the only
other common species of fish at the seining site
was the shorthead sculpin, C. confusus — a rela-
tively nonpredaceous species of fish (unpubl.
studies of author). Furthermore, the few individu-
als of the shorthead sculpin observed were small.
The effect of predator-prey length relations on
predation was determined from 23 tests where six
coho salmon of a given length group were avail-
able to four torrent sculpins of a given length
group (Table 1) for 4 days. The test procedure was
to collect torrent sculpins the first day and place
them in a holding aquarium without food; on the
second day, coho salmon were collected and six
individuals within 5 mm of a given length were
placed in a holding aquarium; on the third day,
four torrent sculpins within 5 mm of a given
length were introduced into the holding aquarium
containing the coho salmon; 4 days later, the
number of coho salmon eaten was recorded and the
experimental fish were discarded. The largest
available size group of torrent sculpins used was
120 mm total length (TL).

TABLE 1. — Results of 23 tests where six coho salmon of a length
group were subjected to predation by four torrent sculpins of a
length group. Predation on one or more coho salmon is denoted
by P and no predation by N.

Total length
of

Fork le

ngth of salmon (mm)

sculpin (mm)

100

120

The ability of coho salmon to learn to evade
predation was tested by comparing the relative
survival of naive coho salmon ( those which had not
been exposed to torrent sculpin predators) with
coho salmon conditioned to predation by the tor-
rent sculpin. Coho salmon were conditioned by
placing 20 individuals into a stream aquarium
with eight torrent sculpins. Some of those that had
survived a 48-h association with torrent sculpins

457

were maintained in holding aquaria without tor-
rent sculpins for 24 h before being subjected to
predation in test conditions. Two types of test
groups, each consisting of 20 coho salmon (per
stream aquarium), were used. In the naive group,
all coho salmon were naive; in the naive and con-
ditioned group, 10 naive and 10 conditioned fish
were tested together.

The procedure for testing naive coho salmon was
to collect torrent sculpins and place them in hold-
ing aquaria without food; on the second day, coho
salmon were collected and 20 individuals, 37 to 42
mm FL, were placed in each stream aquarium; on
the third day, 10 torrent sculpins, 83 to 127 mm
TL, where lengths averaged about 100 mm per
test group, were transferred from the holding
aquarium to each stream aquarium. Forty-eight
hours later, the surviving coho salmon were
counted and experimental fish were discarded.

The procedure for testing the naive and con-
ditioned group of coho salmon was similar to the
foregoing test procedure except that on the second
day, 10 naive coho salmon were collected and
placed in each stream aquarium with 10 con-
ditioned coho salmon. The tip of a ventral fin of the
conditioned coho salmon was clipped at the time
they were introduced into the stream aquarium to
allow them to be recognized at the end of the test.
Thus, if there was an adverse effect from clipping,
it would be on the group with the greater expected
survival. Eight replicate tests were made on each
of the two conditions.

Length Relation

The experimental procedure placed the coho
salmon in close proximity to torrent sculpins for a
prolonged period to enhance the possibility of pre-
dation. Torrent sculpins responded to this oppor-
tunity by preying on larger coho salmon than has
been observed in nature (Table 1). The maximum
size of coho salmon a torrent sculpin is capable of
preying upon is probably limited by the physical
size of a coho salmon that a torrent sculpin can
catch, subdue, and swallow. While the swimming
ability is probably greater for larger coho salmon,
this may not be too important because predation
by torrent sculpins is accomplished by ambush
rather than by pursuit. Torrent sculpins under
natural conditions rarely eat coho salmon 40 to 80
mm FL, indicating that some factor of coho salmon
behavior must decrease their susceptibility .to
predation.

Predator Avoidance Response

The average survival of the naive group consist-
ing only of naive fish was 45.5%; within the naive
and conditioned group, consisting of conditioned
and naive coho salmon tested together, the naive
fish had a 71% survival, and the conditioned coho
salmon had a 75% survival. Cumulative chi-
square tests of homogeneity showed no significant
differences within the naive test group or within
the naive and conditioned group (Table 2). TheZ
test showed no significant difference between the
conditioned and naive coho salmon that were
tested together (ZP0 05 = + 0. 53 < 1.645). There was,
however, a significant difference between the
group consisting of naive coho salmon only and the
group consisting of naive plus conditioned coho
salmon (ZPom = +5.29>1.645).

Mortalities of coho salmon were significantly
reduced by conditioning; also, naive fish tested
with conditioned fish behaved as conditioned fish.
The results of these tests are probably due to rapid
conditioning of the coho salmon and a transferable
predator avoidance reaction. Rapid conditioning
was evident because conditioning of fish to a
stimulus other than predators is usually ac-
complished only after many trials. Conditioning
coho salmon to evade predation by exposing them
to torrent sculpins probably reinforces a strong
innate avoidance behavior. In another case, rapid
conditioning of sockeye salmon, O. nerka, to evade
predation by rainbow trout, Salmo gairdneri, has
been demonstrated by Ginetz and Larkin (1976).
Experiments by Russians have shown that certain
fishes, including the chum salmon, O. keta, in-
creased their ability to evade predation after a 2-
to 4-day training period with predators (Kanid'yev
et al. 1970).

TABLE 2. — Comparative survival of two groups of coho salmon
that were exposed to predation by the torrent sculpin. One group
consisted of naive fish only and the other consisted of naive and
conditioned coho salmon combined. The initial number of coho
salmon per group per stream aquarium was 20.

group

Naive and

nditioned group

Naive

Conditioned

No of

No. of

fish

Survivors

fish

Survivors

fish

Survivors

458

A transferable predator avoidance reaction may
account for the conditioned and naive coho salmon
acting as a homogeneous group in the present
study. Conditioned coho salmon had learned to
avoid torrent sculpins through some unknown
mechanism. Apparently the naive fish behaved as
conditioned individuals through visual clues re-
sulting in mimicry. O'Connell (1960) noted
mimicry in sardines in a conditioned response ex-
periment where unconditioned replacement fish
performed in unison with the school of conditioned
fish from the first trial. Kanid'yev et al. (1970)
indicated that the consensus of Russian workers
was that sight played the main role in developing
the predator avoidance reaction and that rein-
forcement is maximal for fish that are observers.

Sculpins commonly cohabit streams with and
prey on young salmon. Growth of salmon to a size
too large for sculpins to successfully prey on effec-
tively removes them from this predator predation.
The maximum size of coho salmon that a torrent
sculpin can catch and eat in laboratory conditions
is much larger than those that are normally
preyed upon in nature. This indicates that al-
though growth is effective in limiting torrent
sculpin predation on coho salmon, other factors
are equally important. Among salmon, the coho
has a well-developed innate predator avoidance
response (Patten 1975). The response apparently
can be reinforced by experience with fish predators
and this conditioning probably increases their
early survival in streams.

Acknowledgments

I thank J. R. Heath and other personnel of the
City of Seattle Water Department who granted me
use of the flume site within a secured area.

Literature Cited

GlNETZ, R. M., AND P. A. LARKIN.

1976. Factors affecting rainbow trout (Salmo gairdneri)
predation on migrant fry of sockeye salmon (Oncorhyn-
chus nerka). J. Fish. Res. Board Can. 33:19-24.
KANID'YEV, A. N., G. M. KOSTYUNIN, AND S. A. SALMIN.

1970. Hatchery propagation of the pink and chum salmons
as a means of increasing the salmon stocks of Sakha-
lin. Vop. Ikhtiol. 10:360-373. (Transl. J. Ichthyol. 10:
249-259.)

O'Connell, c. p.

I960. Use of fish school for conditioned response experi-
ments. Anim. Behav. 8:225-227.
PATTEN, B. G.

1962. Cottid predation upon salmon fry in a Washington
stream. Trans. Am. Fish. Soc. 91:427-429.

1971a. Predation by sculpins on fall chinook salmon, On-
corhynchus tshawytscha, fry of hatchery origin. U.S.
Dep. Commer., Natl. Mar. Fish. Serv., Spec. Sci. Rep. Fish.
621, 14 p.

1971b. Increased predation by the torrent sculpin, Cottus
rhotheus, on coho salmon fry, Oncorhynchus kisutch, dur-
ing moonlight nights. J. Fish. Res. Board Can. 28:1352-
1354.

1972. Predation, particularly by sculpins, on salmon fry in
fresh waters of Washington. U.S. Dep. Commer., Natl.
Mar. Fish. Serv., Data Rep. 71, 21 p.

1975. Comparative vulnerability of fry of Pacific salmon
and steelhead trout to predation by torrent sculpin in
stream aquaria. Fish. Bull., U.S. 73:931-934.

Benjamin G. Patten

Northwest and Alaska Fisheries Center
National Marine Fisheries Service, NOAA
2725 Montlake Boulevard East
Seattle, WA 98112

DESCRIPTION OF MEGALOPA OF

SNOW CRAB, CHIONOECETES BAIRDI

(MAJIDAE, SUBFAMILY OREGONIINAE)

Chionoecetes bairdi Rathbun, a brachyuran crab,
occurs on the continental shelf from Puget Sound
in Washington State, northward into the Bering
Sea, and westward along the Aleutian Islands.
The species has been taken as deep as 474 m
(Garth 1958), but adults commonly occur at depths
less than 190 m. Chionoecetes bairdi may be quite
abundant in inshore areas throughout its range
and has become an important subsistence and
commercial species because of its large size and
accessibility. It supports an extensive fishery in
the Bering Sea and Gulf of Alaska for three
nations — the United States, the Soviet Union, and
Japan.

The range of C. bairdi overlaps that of three
other species of Chionoecetes: C. tanneri Rathbun,
C. angulatus Rathbun, and C. opilio (O. Fab-
ricius). Chionoecetes tanneri ranges from Mexico
north to the State of Washington, and commonly
occurs between 370 and 1,630 m on the outer
slopes of the continental shelf (Garth 1958).
Chionoecetes angulatus occurs throughout the
range of C. bairdi, but C. angulatus occurs on the
lower slopes of the shelf edge between 730 and
2,980 m (Garth 1958). Chionoecetes opilio occurs
only in the Bering Sea, and its distribution is often
sympatric with C. bairdi. Two other species of
Chionoecetes occur in the western Pacific Ocean,

459

C. japonicus (Rathbun) and C. opilio elongatus
Rathbun.

Since C. bairdi has become commercially impor-
tant, its biology and distribution are receiving
more attention. Descriptions of the larvae for C.
bairdi and C. opilio are important because both
are taken commercially and their distribution
overlaps. Haynes (1973) described prezoeae and
stage I zoeae of C. bairdi (and C. opilio), but stage
II zoeae and megalopa have not been described.

In this paper we describe megalopa of C. bairdi
and compare them with megalopa of C. opilio
(Motoh 1973) and C. opilio elongatus (Kurata
1963b) — the only other Chionoecetes species for
which the megalopal stages have been described.

There seems to be some lack of consistency in
the literature concerning the singular and plural
of the megalopal stage. The original singular was
called megalops, because of the large and promi-
nent eyes. Many authors (e.g., Kurata 1963a, b;
Makarov 1967; Motoh 1973) have changed this to
megalopa for both singular and plural. Others
(e.g., Hart 1960; Poole 1966) have latinized
megalopa in the plural to megalopae. In this man-
uscript both singular and plural of the megalopal
stage will be referred to as megalopa since this is
more widely accepted.

Methods and Materials

About 50 larvae1 of C. bairdi were taken from
Fish Bay near Sitka, Alaska, at lat. 57°22'N, long.
135°33'W on 14 April 1971. They were caught
with 70-cm-diameter nylon bongo nets towed 8 to
9 m below the surface; mesh sizes of the nets were
0.505 and 0.333 mm. The larvae were held in a
3-liter aquarium supplied with continuous-
flowing filtered seawater. The aquarium was
transferred from the research vessel to the
laboratory on 19 April. The water temperature
fluctuated between 8° and 10°C on the vessel and
6.3° and 6.9°C in the laboratory. The C. bairdi
larvae fed upon other zooplankton caught during
the same tow until that food was gone. By then, it
appeared all the larvae were at the megalopal
stage, and we began feeding them finely chopped
herring. Some megalopa were preserved on 19
April in 59c formaldehyde and seawater. Their

'The specimens preserved 14 April were lost and could not be
examined to determine their stage of development. We believe
that they were stage II zoeae or megalopa or a combination of
both.

identification as C. bairdi was confirmed by rais-
ing the remaining megalopa to the juvenile stage
(maximum carapace width 13.9 mm) and compar-
ing them with the juvenile morphology described
by Garth (1958).

Megalopal larvae identical morphologically to
those we had raised were collected in a vertical
plankton haul on 21 May 1973, at the entrance to
Resurrection Bay south of Seward, Alaska, at lat.
59°48'N, long. 149°30'W. These specimens were
dissected and used as the basis for our illustrations
of morphology, appendage setation, and other
characteristics.

Illustrations (Figure 1) were prepared with the
aid of a camera lucida. An ocular micrometer was
used to measure body dimensions of nine of the
preserved specimens. The measurements were 1)
carapace length (two measurements had to be
taken because the rostral tip was often
damaged — straight-line distance from rostral tip
to posterior median margin of carapace and
straight-line distance from the notch between
rostral and preorbital spine to posterior median
margin of carapace); and 2) carapace width
(straight-line distance between widest part of
carapace).

To compare our description of megalopal larvae
of C. bairdi with descriptions of megalopa of other
species in the genus, we used our collections from
the Chukchi Sea and descriptions by Motoh ( 1973)
for C. opilio and descriptions by Kurata (1963b)
for C. opilio elongatus.

Description of Megalopa

Carapace length 3.12 to 3.48 mm (mean 3.30
mm) inclusive of rostrum and 2.60 to 2.80 mm
(mean 2.73 mm) from rostral notch. Carapace
width 1.80 to 2.12 mm (mean 1.97 mm).

Carapace triangular shaped and bears seven
major processes (Figure la-c). Anterior rostral re-
gion bears three sharp spines, two preorbital and
one rostral. Rostral spine three times length of
preorbital spines (measuring from rostral notch)
and points ventrally. Frontal and rostral region
slightly depressed. Pair of anterolateral spines
separated by thin median ridge. Pair of cardiac
dorsolateral spines sweep slightly posteriorly.
Minute but conspicuous lateral spines occur in
region of pterygostomial-branchial ridge. Small
ridge along posterolateral margin of carapace
bears a wartlike protuberance medially, directly
above proximal end of abdomen. Eyes stalked.

460

FIGURE 1. — Megalopa oCChionoecetes bairdi; antennule and antenna from right side of specimen (a) dorsal view of entire specimen;
(b) lateral view of carapace; (c) lateral view of entire specimen; (d) antennule; (e) antenna.

ANTENNULE (Figure Id)— Three-segmented
peduncle has terminal pair of segmented rami.
Smaller ramus has two segments. Distal segment
has four setae, proximal shorter segment naked.
Second terminal ramus has four segments.
Number of setae per segment, beginning distally,
5, 3, 10, and 0.

ANTENNA (Figure le)— Antenna has eight
segments. Setation formula is 4, 0, 2, 4, 0, 3, 2, and
1. Setae located on distal ends of segments.

MANDIBLE (Figure 2a)— Mandibular palp has
three segments. Distal segment has about 10
setae; middle and proximal segments naked.

MAXILLULE (Figure 2b)— Endopodite has one
hook-shaped segment with two terminal setae.
Basipodite has 20-23 coarse plumose setae.
Smaller coxopodite has 13-16 coarse plumose
setae.

MAXILLA (Figure 2c)— Exopodite (scaphag-
nathite) outer margin lined with 38 plumose
setae. One endite naked and ends in a point. Two
endites heavily bifurcated. Lobes of basal endite

distally bear 10 and 8 plumose setae, respectively,
and lobes of coxal (proximal) endite bear 6 and 10
plumose setae.

FIRST MAXILLIPED (Figure 2d)— Epipodite
has eight long hairs. Exopodite is two segmented
with six heavily plumose setae; setation formula is
5 and 1. Broad endopodite has three spines on
distal end. Basal endite bilobed with 22-29
plumose setae on larger lobe and 11-14 plumose
setae on smaller.

SECOND MAXILLIPED (Figure 2e)—
Epipodite has three hairs. Exopodite has two seg-
ments with five heavily plumose setae on distal
segment. Endopodite has four segments; setation
formula 9, 4, 1, and 1.

THIRD MAXILLIPED (Figure 2f)— Epipodite
well developed with several nonplumose hairs.
Exopodite two segmented with five terminal setae.
Endopodite has five large segments with numer-
ous spines on all segments; setation formula 8,
15-17, 8-10, 8, and 30-34.

PEREIOPODS (Figures la, 2g)— Pereiopods

461

1.0 mm

FIGURE 2. — Mouthparts from right side of megalopa ofChionoecetes bairdi (a) mandible; (b) maxillule; (c) maxilla; (d) first maxilliped;
(e) second maxilliped; (f) third maxilliped; (g) ventral view of sternum and pleopod attachment; (h) ventral view of telson and uropods;
(i) lateral view of abdomen.

closely resemble those of adult. Coxopodite and
basipodite spines, one each, located ventrally on
chelipeds and ambulatory legs except for fourth
leg. First ambulatory leg spines especially long.
Cheliped and third ambulatory leg spines minute.
Dactylopodites of ambulatory legs one, two, and
three have conspicuous spine projecting from tip.

ABDOMEN AND TELSON (Figure 2h, i)—
Abdomen six segmented. Sixth segment and tel-
son small. No spines present. Segments two
through five have long setae on dorsal surface.

PLEOPODS (Figure 2i)— Pleopods present on
abdominal segments two through five. A single-
segmented endopodite (not shown in figure) arises
from proximal segments of each pleopod. Endo-
podites have four hooked setae on distal end of first
three pairs of pleopods and three hooked setae on
distal end of last pair of pleopods. Exopodites of
pleopods two and three have variable numbers of
plumose setae, 15 through 18. Exopodites of
pleopods four and five have 17 and 15 plumose
setae, respectively.

UROPODS (Figure 2h)— Uropods two seg-
mented and have seven plumose hairs arising
from each distal segment.

How to Distinguish Megalopa of

Chionoecetes bairdi, C. opilio,

and C. opilio elongatiis

Megalopa of C. bairdi are similar to megalopa
of C. opilio and C. opilio elongatus in major
carapace spination and size. The characteristics
which separate these species can be determined
without dissection. The four most useful charac-
teristics are: 1) C. bairdi has a minute lateral
spine in the region of the pterygostomial-
branchial ridge while the others do not (see
Kurata 1963b; Motoh 1973); 2) C. bairdi has a
more pronounced ridge along the posterior margin
of the carapace than C. opilio and C. opilio elon-
gatus (Kurata 1963b; Motoh 1973); 3) the rostral
spine of C. bairdi is three times the length of the
preorbital spines, whereas the rostral spine on C.

462

opilio is 1.5 to 2.0 times the length of the preorbi-
tals (from our samples from Chukchi Sea); and on
C. opilio elongatus all three spines are nearly the
same length (Kurata 1963b); 4) C. bairdi has a
rudimentary spine immediately posterior to each
eye; in C. opilio and C. opilio elongatus this spine,
though still minute, is quite conspicuous.

Key to Megalopa of Some Common
Brachyuran genera of the Northwest

The following key is to provide a means of iden-
tification of some common Brachyura megalopa of
the northwest to the generic level. As only charac-
teristics which can be determined without dissec-
tion have been used, the key should be used for
preliminary sorting. The present state of knowl-
edge of these megalopa comes from six sources
(i.e., Hart 1960; Kurata 1963a, b; Poole 1966;
Makarov 1967; Motoh 1973). Key modified after
Makarov (1967).

A. Carapace bears dorsal spines

B. Posterior part of carapace bears one

spine Hyas; Oregonia; Cancer

B'. Posterior part of carapace bears two

spines Chionoecetes

A'. Carapace bears no dorsal spines

B. Angles of posterior margin of abdom-
inal somite 5 reach beyond somite 6

Telmessus

B'. Angles of posterior margin of abdom-
inal somite 5 reach to middle of
somite 6 Erimacrus

Acknowledgments

Funding in partial support of this project was
made available through U.S. Department of
Commerce (NOAA) contract no. 03-5-022-56 to
H. M. Feder, Institute of Marine Science, Univer-
sity of Alaska, Fairbanks.

The authors thank the following people: George
Mueller, Curator of Marine Collections, Univer-
sity of Alaska, gave guidance with the drawings;
H. M. Feder and Evan Haynes, National Marine
Fisheries Service, NOAA, reviewed the manu-
script; R. T. Cooney, Institute of Marine Science,
University of Alaska, Fairbanks, loaned the
Chionoecetes bairdi larvae collected 21 May 1973;
and Bruce Wing, National Marine Fisheries Ser-
vice, NOAA, supplied the Chionoecetes opilio
megalopa from the Chukchi Sea.

Literature Cited
Garth, j. S.

1958. Brachyura of the Pacific coast of America.

Oxyrhyncha. Allan Hancock Pac. Exped. 21(2), 854 p.
HART, J. F. L.

1960. The larval development of British Columbia

Brachyura. II. Majidae, subfamily Oregoniinae. Can. J.

Zool. 38:539-546.

Haynes, E.

1973. Descriptions of prezoeae and stage I zoeae of
Chionoecetes bairdi and C. opilio. (Oxyrhyncha,
Oregoniinae). Fish. Bull., U.S. 71:769-775.
KURATA, H.

1963a. Larvae of Decapoda Crustacea of Hokkaido. 1.
Atelecyclidae (Atelecyclinae). [In Jap., Engl,
summ.] Bull. Hokkaido Reg. Rish. Res. Lab. 27:13-24.

1963b. Larvae of Decapoda Crustacea of Hokkaido. 2.
Majidae (Pisinae). [In Jap., Engl, summ.] Bull. Hok-
kaido Reg. Fish. Res. Lab. 27:25-31. (Fish. Res. Board
Can., Transl. Ser. 1124.)

Makarov, r. r.

1967. Larvae of the shrimps and crabs of the West
Kamtschatkan Shelf and their distribution. Translated
from Russian by B. Haigh. Natl. Lending Libr. Sci.
Technol., Boston Spa, Engl., 199 p.
MOTOH, H.

1973. Laboratory-reared zoeae and megalopae of zuwai
crab from the Sea of Japan. Bull. Jap. Soc. Sci. Fish.
39:1223-1230.
POOLE, R. L.

1966. A description of laboratory-reared zoeae of Cancer
magister Dana, and megalopae taken under natural con-
ditions (Decapoda, Brachyura). Crustaceana 11:83-97.

Stephen C. Jewett

Institute of Marine Science
University of Alaska
Fairbanks, AK 99701

RICHARD E. HAIGHT

Northwest and Alaska Fisheries Center Auke Bay Laboratory
National Marine Fisheries Service, NOAA
P.O. Box 155, Auke Bay, AK 99821

463

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Fishery Bulletin

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Marine Biological Laboraw,

UHRARY

">V

of the Southern

NOV 141977

Vol. 75, No. 3 July 1977

Woods S.

SISSENWINE, MICHAEL P. A compartmentalized simulation mode

New England yellowtail flounder, Limanda ferruginea, fishery 465

OWERS, JAMES E. Income estimates and reasonable returns in Alaska's salmon

fisheries 483

HOUDE, EDWARD D. Abundance and potential yield of the Atlantic thread herring,

Opisthonema oglinum, and aspects of its early life history in the eastern Gulf

of Mexico 493

McDERMOTT-EHRLICH, D. J., M. J. SHERWOOD, T. C. HEESEN, D. R. YOUNG,

and A. J. MEARNS. Chlorinated hydrocarbons in Dover sole, Microstomas pacif-

icus: Local migrations and fin erosion 513

SCIARROTTA, TERRY C, and DONALD R. NELSON. Diel behavior of the blue

shark, Prionace glauca, near Santa Catalina Island, California 519

LAURENCE, GEOFFREY C. A bioenergetic model for the analysis of feeding and

survival potential of winter flounder, Pseudopleuronectes americanus, larvae

during the period from hatching to metamorphosis 529

LAROCHE, WAYNE A. Description of larval and early juvenile vermilion snapper,

Rhomboplites aurorubens 547

PATTEN, BENJAMIN G. Short-term thermal resistance of zoeae of 10 species of

crabs from Puget Sound, Washington 555

RAFAIL, SAMIR Z. A simplification for the study offish populations by capture data. 561
LUNDSTROM, RONALD C. Identification of fish species by thin-layer poly-

acrylamide gel isoelectric focusing 571

SCURA, EDWARD D., and CHARLES W. JERDE. Various species of phytoplankton

as food for larval northern anchovy, Engraulis mordax, and relative nutritional

value of the dinoflagellates Gymnodinium splendens and Gonyaulax polyedra . . 577
OLLA, BORI L., and CAROL SAMET. Courtship and spawning behavior of the

tautog, Tautoga onitis (Pisces: Labridae), under laboratory conditions 585

ARTHUR, DAVID K. Distribution, size, and abundance of microcopepods in the

California Current system and their possible influence on survival of marine

teleost larvae 601

HOUDE, EDWARD D. Abundance and potential yield of the scaled sardine, Haren-

gula jaguana, and aspects of its early life history in the eastern Gulf of Mexico . 613

(Continued on back cover)

Seattle, Washington

U.S. DEPARTMENT OF COMMERCE

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NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION

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Fishery Bulletin

EDITOR

Dr. Bruce B. Collette

Scientific Editor, Fishery Bulletin

National Marine Fisheries Service

Systematics Laboratory

National Museum of Natural History

Washington, DC 20560

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National Marine Fisheries Service

Dr. William H. Bayliff

Inter-American Tropical Tuna Commission

Dr. Roger F. Cressey, Jr.
U.S. National Museum

Mr. John E. Fitch

California Department of Fish and Game

Dr. William W. Fox, Jr.
National Marine Fisheries Service

Dr. Marvin D. Grosslein
National Marine Fisheries Service

Dr. Edward D. Houde
University of Miami

Dr. Merton C. Ingham

National Marine Fisheries Service

Dr. Reuben Lasker

National Marine Fisheries Service

Dr. Sally L. Richardson
Oregon State University

Dr. Paul J. Struhsaker

National Marine Fisheries Service

Dr. Austin Williams

National Marine Fisheries Service

Kiyoshi G. Fukano, Managing Editor

The Fishery Bulletin is published quarterly by Scientific Publications Staff, National Marine Fisheries Service, NOAA, Room 450,
1 107 NE 45th Street, Seattle, WA 98105. Controlled circulation postage paid at Tacoma, Wash.

The Secretary of Commerce has determined that the publication of this periodical is necessary in the transaction of the public
business required by law of this Department Use of funds for printing of this periodical has been approved by the Director of the
Office of Management and Budget through 31 December 1978.

Fishery Bulletin

CONTENTS

Vol. 75, No. 3 July 1977

SISSENWINE, MICHAEL P. A compartmentalized simulation model of the Southern

New England yellowtail flounder, Limanda ferruginea, fishery 465

OWERS, JAMES E. Income estimates and reasonable returns in Alaska's salmon
fisheries 483

HOUDE, EDWARD D. Abundance and potential yield of the Atlantic thread herring,
Opisthonema oglinum, and aspects of its early life history in the eastern Gulf
of Mexico 493

McDERMOTT-EHRLICH, D. J., M. J. SHERWOOD, T. C. HEESEN, D. R. YOUNG,
and A. J. MEARNS. Chlorinated hydrocarbons in Dover sole, Microstomas pacif-
icus: Local migrations and fin erosion 513

SCIARROTTA, TERRY C, and DONALD R. NELSON. Diel behavior of the blue

shark, Prionace glauca, near Santa Catalina Island, California 519

LAURENCE, GEOFFREY C. A bioenergetic model for the analysis of feeding and
survival potential of winter flounder, Pseudopleuronectes americanus, larvae
during the period from hatching to metamorphosis 529

LAROCHE, WAYNE A. Description of larval and early juvenile vermilion snapper,
Rhomboplites aurorubens 547

PATTEN, BENJAMIN G. Short-term thermal resistance of zoeae of 10 species of
crabs from Puget Sound, Washington 555

RAFAIL, SAMIR Z. A simplification for the study offish populations by capture data. 561

LUNDSTROM, RONALD C. Identification of fish species by thin-layer poly-
acrylamide gel isoelectric focusing 571

SCURA, EDWARD D., and CHARLES W. JERDE. Various species of phytoplankton
as food for larval northern anchovy, Engraulis mordax, and relative nutritional
value of the dinoflagellates Gymnodinium splendens and Gonyaulax polyedra . . 577

OLLA, BORI L., and CAROL SAMET. Courtship and spawning behavior of the

tautog, Tautoga onitis (Pisces: Labridae), under laboratory conditions 585

ARTHUR, DAVID K. Distribution, size, and abundance of microcopepods in the
California Current system and their possible influence on survival of marine
teleost larvae 601

HOUDE, EDWARD D. Abundance and potential yield of the scaled sardine, Haren-
gula jaguana, and aspects of its early life history in the eastern Gulf of Mexico . 613

(Continued on next page)

Seattle, Washington

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Contents-continued

Notes

PERRIN, WILLIAM F., RUTH B. MILLER, and PRISCILLA A. SLOAN. Reproduc-
tive parameters of the offshore spotted dolphin, a geographical form of Stenella
attenuata, in the eastern tropical Pacific, 1973-75 629

KORN, SID, NINA HIRSCH, and JEANNETTE W. STRUHSAKER. The uptake,
distribution, and depuration of 14C benzene and 14C toluene in Pacific herring,
Clupea harengus pallasi 633

FOLTZ, JEFFREY W., and CARROLL R. NORDEN. Food habits and feeding chro-
nology of rainbow smelt, Osmerus mordax, in Lake Michigan 637

LOESCH, JOSEPH G. Useable meat yields in the Virginia surf clam fishery 640

HALL, ALICE S., FUAD M. TEENY, and ERICH J. GAUGLITZ, JR. Mercury
in fish and shellfish of the northeast Pacific. III. Spiny dogfish, Squalus acanthias . 642

PEARSE, JOHN S., DANIEL P. COSTA, MARC B. YELLIN, and CATHERINE R.
AGEGIAN. Localized mass mortality of red sea urchin, Strongylocentrotus fran-
ciscanus, near Santa Cruz, California 645

RENSEL, JOHN E., and EARL F. PRENTICE. First record of a second mating
and spawning of the spot prawn, Pandalus platyceros, in captivity 648

DIZON, ANDREW E. Effect of dissolved oxygen concentration and salinity on
swimming speed of two species of tunas 649

HALL, JOHN D. A nonlethal lavage device for sampling stomach contents of small
marine mammals 653

Vol. 75, No. 2 was published on 13 June 1977.

A COMPARTMENTALIZED SIMULATION MODEL OF THE SOUTHERN NEW
ENGLAND YELLOWTAIL FLOUNDER, LIMANDA FERRUGINEA, FISHERY

Michael P. Sissenwine1

ABSTRACT

A compartmentalized simulation model of the Southern New England yellowtail flounder, Limanda
ferruginea, fishery was developed. The population was divided into 10 age-groups, each of which was
subdivided into 7 size categories. The model simulated discard mortality as well as natural mortality
and fishing mortality. Fishing and discard mortality rates depended on the level of fishing and on
gear and market selection factors. Both linear and density independent stock-recruitment functions
were considered. Seasonal variations in growth and exploitation were incorporated into the model. The
influence of fluctuation in temperature on recruitment and growth was also simulated. The model
using a linear stock-recruitment function accounted for 85.5% of the variability in the yield of the
fishery for 1943-65; with a density independent stock-recruitment function, the model explained
83.2% of the variability in yield for the same period.

The linear stock-recruitment model was used to investigate the response of the fishery to alternative
fishing strategies. Substantial increases in the past yield of the fishery were indicated by the model
when fishing effort was concentrated during the second half of the year and when fishing effort
and discard mortality were reduced.

This paper describes a compartmentalized sim-
ulation model of the Southern New England
yellowtail flounder, Limanda ferruginea (Storer),
population. There is evidence that production of
the Southern New England yellowtail flounder
population is influenced by environmental tem-
perature (Sissenwine 1974). The model is in-
tended to demonstrate the feasibility of predicting
catch under fluctuating environmental conditions
based on the rate of exploitation. The model
shares many of the characteristics of Walters'
(1969) "generalized computer simulation model,"
which incorporates growth, fishing and natural
mortality, and a stock-recruitment relationship,
and also incorporates several additional features.
These features include 1) temperature dependent
growth and recruitment, 2) growth and fishing
mortality rates which vary seasonally, and 3) age-
groups subdivided into size categories.

More than 600 thousand metric tons of yellow-
tail flounder valued at over $120 million have
been landed in Southern New England and
New York since the onset of fishing in the late

Graduate School of Oceanography, University of Rhode
Island, Kingston, RI 02881; present address: Northeast Fish-
eries Center, National Marine Fisheries Service, NOAA, Woods
Hole, MA 02543.

1930's. The magnitude of the fishery has stimu-
lated numerous quantitative investigations.
Royce et al. (1959), Lux (1964, 1969a), Brown and
Hennemuth,2 Brown,3 and Parrack4 reported
catch and fishing effort data for each of the three
major fishing grounds (Lux 1963) since 1943.
Until recently, most of the catch has been from
the Southern New England ground. Catch and
fishing effort data were used by Sissenwine (1974)
to estimate the annual recruitment and equilib-
rium catch produced by the Southern New
England ground for 1944-65. The equilibrium
catch and recruitment were shown to be highly
correlated with the atmospheric temperature
record at Block Island, R.I. Lux and Nichy (1969)
determined the growth rate of the yellowtail
flounder. Lux (1969b) and Pitt (1971) calculated
the length-weight and length-fecundity func-
tions of the species, respectively. Mortality rates
of the yellowtail flounder were estimated by Lux

Manuscript accepted January 1977.
FISHERY BULLETIN: VOL. 75, NO. 3, 1977.

2Brown, B. E., and R. C. Hennemuth. 1971. Assessment of
the yellowtail flounder fishery in Subarea 5. Int. Comm. North-
west Atl. Fish., Res. Doc. 71/14, Ser. No. 2599, 57 p.

3Brown, B. E. 1972. Current status of the yellowtail flounder
fishery in ICNAF Subarea 5 - January, 1972. Int. Comm. North-
west Atl. Fish., Res. Doc. 72/23, Ser. No. 2174, 18 p.

4Parrack, M. L. 1973. Current status of the yellowtail flounder
fishery in ICNAF Subarea 5. Int. Comm. Northwest Atl. Fish.,
Res. Doc. 73/104, Ser. No. 3067, 3 p.

465

FISHERY BULLETIN: VOL. 75, NO. 3

(1969a), Brown and Hennemuth (see footnote 2),
and Penttila and Brown.5

Some of the research cited above is recorded
only in unpublished documents. Any information
extracted from these reports must be considered
as preliminary. Accordingly, the work reported in
this paper was primarily based on the published
literature.

Catch data used in this paper include both
domestic and foreign landings of yellowtail
flounder but exclude the industrial catch. All
effort data are expressed in standard days fished
as defined by Lux (1964).

DESCRIPTION OF
THE MODEL STRUCTURE

A diagram representing the compartments and
activities of the system is shown in Figure 1. Since
yellowtail flounder greater than 10 yr of age are
seldom encountered, fish were divided into 10 age-
groups. Certainly, the length of individuals
within each age-group is not uniform. Therefore,
each age-group was subdivided into seven size
categories in which all fish were assumed to be
of a uniform length. The number of size categories
was limited to seven in order to minimize com-
puter cost. The level (number of fich) of each of
the 70 age-size compartments is denoted by Nltj
where i indicates the age-group and j the size
category. Another attribute of each compartment
is its mean length, denoted by L,7 with i and j
defined in the same manner.

The yield of the fishery in weight (Yw) and
number offish ( Yn) landed annually are attributes
of the yield compartment. Total fecundity of the
population during each spawning season is Pe
(number of eggs in the egg compartment).

The important activities affecting the system
are: 1) fishing which results in a continuous trans-
fer of fish from age-size compartments to the
yield compartment and results in some non-
productive mortality (discard mortality) since not
all fish captured are actually landed (Brown and
Hennemuth see footnote 2); 2) natural mortality
which results in a continuous decay of each age-
size compartment and loss offish from the system;
3) aging which results in a discrete advancement

RECRUITMENT

N|0

Lio,

•

N
10

N,0

Lio,

5Penttila, J. A., and B. E. Brown. 1972. Total mortality rates
for two groups of yellowtail flounder estimates from survey
cruise data from ICNAF Subarea 5. Int. Comm. Northwest Atl.
Fish., Res. Doc. 72/22, Ser. No. 2713, 14 p.

DISCRETE DURING MAY OF YEAR
CONTIN UOUS

FIGURE 1. — Compartments representing a fish population.
Three dots (...) indicate additional compartments. The age-
group is indicated by i and the size category by j. N,,, is the
number of fish in thejth size category of age-group i, and L,,, is
the mean length of the fish of the same compartment. Each com-
partment (only shown for (i,j)) undergoes continuous loss due to
fishing, discard, and natural mortality. Losses due to fishing
mortality are added to the yield compartment. At the beginning
(or end) of each year, aging occurs, advancing each compart-
ment to the next higher age-group, retaining the same value of
j. Recruitment to age-group 1 also occurs at the beginning of
each year as a function of the previous year's egg production.
Spawning occurs during May of each year (only shown for (i,j))
with egg production a function of the number and size of fish in
each compartment.

offish to the next higher age-group (retaining the
same value of j) at the beginning of each year;
4) spawning which is the discrete production of
eggs (Pe) during May (Bigelow and Schroeder
1953) of each year; 5) recruitment which is
represented as the discrete addition of individuals
to the youngest age-group of the model at the
beginning of each year according to the magni-
tude of Pe during the previous year; and 6)
growth which results in a continuous increase
in Ltj.

The dynamic system briefly described above
was simulated by a FORTRAN program using
finite difference approximation. Details of each
activity regulating the system are presented
below. The variables used in the model are defined
in Table 1.

Fishing, Discard, and
Natural Mortality

Each age-size compartment is subject to mor-
tality at a rate proportional to the number of
fish of the compartment; that is,

466

SISSENWINE: COMPARTMENTALIZED SIMULATION MODEL

TABLE 1. — List of variables of yellowtail flounder, Limanda
ferruginea, model.

Variable

Description

Yn
Yw
Pe

w
Fe

Z
D
F
M
G
f
t

T
k
Tr

Number of fish in size category y of age-group /

Length of fish in size category/ of age-group /

Yield of fishery in number of fish

Yield of fishery in weight of fish

Annual egg production of stock

Weight of fish as function of length

Fecundity of fish as function of length

Instantaneous total mortality rate

Instantaneous discard mortality rate

Instantaneous fishing mortality rate (excluding discard mortality)

Instantaneous natural mortality rate

Instantaneous gear mortality rate (G F • D)

Instantaneous rate of fishing

Time

Relative gear effectiveness as function of length

Probability of landing a captured fish as function of length

Probability of a fish being mature as function of length

Index of temperature

Growth rate coefficient of von Bertalanffy equation

Recruitment-temperature factor as function of temperature

Growth-temperature factor as function of temperature

Annual recruitment to age 1

diNjj)
dt

= -(F + D + M) • Ntj

(1)

where F, D, and M are the instantaneous fishing,
discard, and natural mortality rates, respectively,
and t is time in years. Total mortality of fish
greater than 10 yr old was assumed. Very few
fish reach this advanced age. Lux (1964) reported
that fish discarded at sea suffered a high mortality
rate. In the model, all discarded fish were assumed
lost. The yield rate, in number offish and biomass,
contributed by each compartment is

d(Yn)
dt

= F ■ N

(2)

and

d(Yw)
dt

= F ■ N

i,j

W(LU)

ij'

(3)

where W(L) is a function relating the weight of
a fish to its length. This function assumes the
usual form,

W(L) = Cl • V

(4)

The letter c with a numerical subscript is used
throughout the paper to denote constants. The
total yield rate is obtained by summing d(Yn)ldt
and d(Yw)/dt for all age-size compartments.

The mortality rate inflicted by fishermen
(F + D) on the yellowtail flounder population is

assumed to be proportional to the instantaneous
annual rate of fishing if) for fish which are fully
vulnerable. This mortality is called the gear
mortality (G),

G =F +D =q ■ f

(5)

where q is the catchability coefficient. The num-
ber of days fished annually is determined exter-
nally to the model and acts as a driving variable.
Natural mortality was assumed to decrease with
age until maturation and then remain constant
through the rest of the life span.

In order to approximate the seasonality of
fishing, the instantaneous rate of fishing is esti-
mated by multiplying the total number of days
fished annually by quarterly effort adjustment
factors (c3, c4, c5, andc6) where the average value
of these factors is 1.

Yellowtail flounder first become available to
trawl gear on the Southern New England ground
in about 1 yr (Brown and Hennemuth see footnote
2), but they are not captured commercially until
they have grown to the minimum size retained
by the fishermen's nets, Lgmin. Some fish continue
to escape the nets because of their small size until
they have grown to the length at which the gear
obtains its maximum effectiveness, L

gmax-

It is

assumed that the relative effectiveness of the gear
from fish with a length between Lgmin and Lgmax
can be calculated by linear interpolation. Accord-
ingly, the relative effectiveness of the gear, Plt
is defined as follows:

(Li L/gm[n)/(Ligmax

for Lgmin =s L ^ L

0 for L < Lgmin

1 for L > Lgmax

J-'grnin'
gmax

(6)

where L is the length for which Pj is applied.

Since not all of the fish captured are large
enough to be marketed (for economic and techno-
logical reasons), the probability of landing a cap-
tured fish (P2) as a function of its length must
be calculated. Let Lmmin be the minimum length
landed by the fishermen and Lmmax be the length
at which all fish are landed. Note that the deter-
mination of the marketability of each fish is made
by the fishermen on the decks of their vessels.
Therefore, a gradual transition from total un-
acceptability to total acceptability as L increases
is expected. Again applying linear interpolation,

467

FISHERY BULLETIN: VOL. 75, NO. 3

(L - L,

T!min''^mma)i

^mmin

for Lmmin *£ L

"mmax

OforL

*^ ^mmin

1 forL

■^ "mmax'

(7)

Using Equations (5), (6), and (7); G, F, and D
are calculated as follows for fish of any length:

G=q ■ f
F=q f

D =q ■ f ■ P, ■ (1 - P2).

(8)

(9)

(10)

Since G, F, and D vary with L and f, they are
time dependent functions.

Aging

The aging process of yellowtail flounder is
simulated by advancing individuals of each age-
size compartment to the next higher age-group
within the same size category.

Growth

The mechanism used in the model to simulate
growth was based on the von Bertalanffy growth
function. The von Bertalanffy function can be
expressed in many forms, but the following is
most applicable to this study:

*-» ~ J->m + U'O Lm)

-kt

(11)

where Lm is the maximum length obtained by the
fish of the population, L0 is the length of a fish at
the beginning of a time interval of duration t, k
is the growth rate coefficient that applies during
the interval, and L is the length obtained by the
end of the interval. The derivative of Equation
(11) is identical to the growth equation deduced
by von Bertalanffy (1938).

A single value of Lm is usually assumed for an
entire population. In the model, differences in the
mean length of size categories are maintained by
assigning a unique maximum value to L for each
size category (Lml, Lm2, . . ., Lml). Fish are distrib-
uted among the size categories in the following
manner. AssumeL^ is a normally distributed ran-
dom variable with mean Lm4 and standard devia-
tion sm. For Glt G2) . . ., G7, the portion of the
population in each size category respectively (in
the absence of fishing), the range of values of Lm
included in each size category can be determined
from a standard normal table. The mean value of

Lm for the jth size category (L„y) is obtained by
integrating the product of the normal density
function and the random variable Lm over the
range of values of Lm included in the size category
and then dividing the result by Gj.

Taylor (1962) showed that k of the von Berta-
lanffy function was related to water temperature
for a number of species, and there is evidence
(which is discussed later in this paper) that this
is also true for the Southern New England
yellowtail flounder. The influence of temperature
on k is simulated by adjusting k by a multipli-
cative growth-temperature factor, Tg, defined as

Tg = \+c

l-i

(T - T)

(12)

where T is an index of temperature and f is the
average value of the index over the total period
for which data are available. T is an exogenous
variable of the model.

Different values of k (kx, k2) were necessary to
describe the growth of yellowtail flounder less
than and greater than 2 yr old (Lux and Nichy
1969). Seasonal variations of growth were incor-
porated into the model by multiplicative quarterly
growth factors Kx, K2, Ks, K4 (with an average
value of 1.0). The length of age-size compartment
i,j after an interval of time t is calculated accord-
ing to Equation (11) using the length of the com-
partment at the beginning of the interval L„y,
and k as follows:

where n indicates the quarter of the year
indicates age less than or greater than 2 j

(13)
and a

yr.

Spawning

Spawning occurs during May or at 0.4 of each
year. The fecundity-length function of the yellow-
tail flounder was assumed to be of the usual form,

Fe(L)

(14)

where Fe is the egg production of a mature female
fish of length L. Not all fish mature at the same
age or length. Royce et al. (1959) found that
maturation was more closely associated with
length than age. A relationship of the following
form, expressing the probability of a fish of specific
length being mature (P4) was assumed.

468

SISSENWINE: COMPARTMENTALIZED SIMULATION MODEL

P. =

f y3 for 0 « P3 ■■= c9 + c10L = ; 1
0 for P,

1 for P,

< 0
> 1.

(15)

Equation (15) assumes maturation is a linear
function of length in the transition zone between
the length below which the entire population is
immature and the length above which the entire
population is mature. Assuming that the propor-
tion of females in the population is constant, c11;
then the egg production of each age-size com-
partment is the product of Njj, Fe (LIJ),P4, andcn.
The total egg production of the population (Pe) is
obtained by summing over all age-size compart-
ments.

Recruitment

The possibilities that recruitment is a linear
function of egg production and that recruitment
is independent of egg production, under average
environmental conditions, were considered. There
is evidence (Sissenwine 1974) that recruitment
of the Southern New England yellowtail flounder
is also related to temperature. In fact, most of the
variability in estimated recruitment for 1944-65
was explained by anomalies in air temperature,
ignoring egg production. In order to simulate the
influence of temperature, a recruitment tempera-
ture factor (Tr) was defined as follows:

Tr = 1 + c

(T - T).

(16)

The number of recruitments as affected by tem-
perature is calculated by multiplying the level of
recruitment expected at average temperature
conditions by T ',..

The total recruitment (R) of a year class (at
age 1) is calculated by

-13

Cl3

Tr.

(18)

The parameter c13 has a different value in each
equation. Equation (17) is applicable when re-
cruitment is linearly related to Pe for average tem-
perature conditions. Equation (18) is applicable
when recruitment is independent of Pe. Equations
(17) and (18) will be referred to as the linear and
density independent recruitment functions, re-

spectively. The model described in this paper
incorporating either Equation (17) or (18) will be
referred to as the linear or density independent
models, respectively. Recruits are assigned to size
categories of age-group 1 by multiplying R by
the appropriate value of Gr

Parameter Estimation

Estimates of the parameters of the model were
taken from the literature or based on published
or unpublished data sources. The parameter val-
ues used in all the simulations reported in this
paper (unless otherwise stated) are shown in
Table 2 along with citations of the source of the
estimate. Special attention is given below to the
estimation of some parameters and initial condi-
tions. These estimates of parameters and initial
conditions required some subjectivity.

The natural mortality rate of the yellowtail
flounder has yet to be precisely estimated. Lux
( 1969a) estimated that the upper limit on natural
mortality of adult yellowtail flounder is 0.20.
Beverton and Holt (1957) estimated the natural
mortality of a similar species (North Sea plaice)
as 0.10. Values of instantaneous natural mortal-
ity of 0.10 and 0.20 have been used in the litera-
ture in the past, An instantaneous natural mor-
tality rate of 0.10 was assumed for age-groups
3 and older fish in the model. Instantaneous nat-
ural mortality rates of 0.4 and 0.2 were applied
to age-groups 1 and 2, respectively. Based on a
generalized simulation model, Walters (1969)
concluded that natural mortality rates, especially
in older fish, could vary widely without affecting
harvesting strategies.

Brown and Hennemuth (see footnote 2) reported
the size-group structure of fish captured and
landed by yellowtail flounder fishermen during
1963. According to these data, few fish less than

250 mm).

(17) 250 mm long were captured (L

gm\i\

The modal value of Brown and Hennemuth's
capture curve is about 330 mm. The modal value
usually coincides closely with the length of com-
plete functional recruitment. Therefore, gear
efficiency was assumed to reach its maximum at
this length (Lgmax = 330 mm). All yellowtail
flounder less than 300 mm long were discarded
at sea (Lmmin = 300 mm) and almost all fish cap-
tured of greater than 350 mm were landed (Lmmax
= 350 mm). Of course, market conditions will
change with time and there are now reports of
some fish less than 300 mm being landed.

469

FISHERY BULLETIN: VOL. 75, NO. 3

TABLE 2.— Value of each parameter used to yield best results with yellowtail flounder model. The parentheses indicate values used for
the model in which recruitment is independent of spawning stock. Lmi for i = 1,2,. . ., 7 are given in Table 3.

Parameter

Value

Description

Source

0.233 x 10"°

3.233

1.26

0.37

0.87

1.49

-6

0.725 x10

4.69

-1.821

C10

0.00707

C11

0.50

C12

-0.68 (-0.89)
—6

C13

5.8 x 10 fi
(60.0 x 10

C14

-0.466
1.68 x 10 "4

i-gmm

250.0 mm

Lg max

330.0 mm

i-mmin

300.0 mm

4/7? max

350.0 mm

10.175°C

0.05

0.10

C33

0.20

0.30

0.20

0.10

0.05

33.9 mm

0.56

0.285

0.0

2.0

0.40

0.20

M/, / = 3, 1C

0.10

From weight-length function (Equation (4))

First quarter seasonal effort factor

Second quarter seasonal effort factor

Third quarter seasonal effort factor

Fourth quarter seasonal effort factor

From fecundity-length function (Equation (14))

From proportion mature-length function (Equation (15))

Proportion of females

Slope of recruitment-temperature factor

Slope of stock-recruitment function

Slope of growth-temperature factor
Catchability coefficient
Minimum size retained by net
Size of maximum net retention
Minimum size at which fish are marketed
Size at which all fish are marketed
Mean temperature
Proportion entering size-class 1
Proportion entering size-class 2
Proportion entering size-class 3
Proportion entering size-class 4
Proportion entering size-class 5
Proportion entering size-class 6
Proportion entering size-class 7
Standard deviation of Lm
Growth rate for fish less than 2 yr
Growth rate for fish greater than 2 yr
First quarter seasonal growth factor
Second quarter seasonal growth factor
Third quarter seasonal growth factor
Fourth quarter seasonal growth factor
Natural mortality of age-group 1
Natural mortality of age-group 2
Natural mortality of age-group 3

Lux (1969b)

Based on quarterly average effort data for 26 to 50 gross ton
vessel reported by Lux (1964)

Pitt (1971) for fish from Grand Bank

Based on percent mature data from Royce et al. (1959)

Data on 9,268 fish provided by Northeast Fisheries Center
From recruitment estimates (Sissenwine 1974), see text
Fitted to catch data with the model, see text

From annual growth estimates (Sissenwine 1975), see text
Sissenwine (1974)

From length composition of catch for 1963, see text

National Weather Service data, Block Island

Arbitrary

Data on 9,268 fish provided by Northeast Fisheries Center
\ See text

I Based on length by quarter estimates (Lux and Nichy 1 969). see
text

> See text

The annual average air temperature at Block
Island was used as an index of temperature on the
Southern New England ground because there are
no water temperature records of adequate length
(1944 to present). Block Island is located on the
southwest edge of the Southern New England
ground.

Taylor et al. (1957) concluded that air tempera-
ture data are a rough index of the general level
of surface water temperature. Colton (1968)
reported that trends in offshore water masses
paralleled trends in surface water temperature at
Boothbay Harbor, Maine. Lauzier (1965) used
trends in air temperature from 1875 to 1905 as an
index of the water temperature of the Gulf of
Maine. Templeman (1965) concluded that air
temperature at St. John's, Newfoundland, and
water temperature at Cape Spear for 1952-62
agreed extremely well.

A record of the bottom water temperature at
Lurcher Lightship off Nova Scotia (Lauzier and
Hull6) was collected from 1951 to 1969. The water

depth was about 100 m. The correlation between
the average annual bottom water temperature at
Lurcher Lightship and the average annual air
temperature at Block Island is 0.78. The correla-
tion between the annual average air temperature
at Block Island and the annual average surface
water temperature at Woods Hole, Mass., for
data reported by Chase (1967) is 0.87 during the
period 1956-66. The correlation between monthly
averages of water temperature at Woods Hole and
air temperature at Block Island for this 132-mo
time series is 0.98. Therefore, Block Island air
temperature record was used as an index of water
temperature on the Southern New England
ground.

The annual equilibrium catch of a fishery is the
level of catch that results in no change in the
biomass of the nominal stock (stock suitable for

6Lauzier, L. M., and J. H. Hull. 1969. Coastal station data
temperature along the Canadian Atlantic coast 1921-1969.
Fish. Res. Board Can., Tech. Rep. No. 150, 5 p.

470

SISSENWINE: COMPARTMENTALIZED SIMl I.ATION MODEL

landing). The equilibrium catch is the sum of
recruitment and growth (of the individual fish of
the nominal stock) minus loss due to natural mor-
tality. Based on this relationship using earlier
estimates of equilibrium catch and recruitment
(Sissenwine 1974) and assuming annual natural
mortality of 0.1, Sissenwine (1975) estimated the
average annual weight gain per fish of the South-
ern New England yellowtail flounder fishery for
1944-65. These estimates ranged from 72 to 331
g/fish per year and are significantly correlated
(Kendall rank correlation coefficient (t) of —0.60)
with annual average air temperature at Block
Island. Estimates of k of the von Bertalanffy func-
tion derived from growth increments of age-
classes for 1962-71 were also significantly cor-
related (r = -0.42) with temperature at Block
Island. Thus, the model was designed to simulate
the effect of temperature on growth.

The instantaneous growth rate of a fish is
related to k by the following equation:

dw
dt

kctc2 {Lm — L) L

(19)

The proportion of yellowtail flounder recruits
entering each size category of age-group 1 was
assumed as follows: Gl = G7 = 0.05, G2 = G6 =
0.10, G3 = G5 = 0.20, and G4 == 0.30.

Lux and Nichy (1969) reported a value of 500
mm for parameter L,„ of the von Bertalanffy
growth function for the yellowtail flounder. They
selected this value since it was the maximum
length observed. The model described in this
paper requires values of Lm for each of the seven
size categories. Considering the magnitude of s„,
(33.9 mm, see Table 2) a value of 500 mm for Lm4
may yield fish far in excess of the maximum
length observed. Therefore, a more conservative
value was used: Lm4 = 480 mm.

The probability density function of Lm was used
to calculate values of Lmi for i = 1, 2, 3, 5, 6, 7.
The range of values of Lm represented by each size
category (Zu to Z2l) was calculated based on G,
and the normal density table and found to be as in
Table 3. The mean value of Lm for each size cate-
gory equals the integral of Lm times its density
function divided by the integral of the density
function (results also shown in Table 3).

Equation (19) was derived by substituting Equa-
tion (11) into Equation (4) and differentiating
with respect to t. For the values of k, c1; c2, and Lm
reported by Lux (1969b) and Lux and Nichy
(1969), dwldt is 143, 172, 182, and 163 g/yr for a
length of 250, 300, 350, and 400 mm, respectively.
Most of the fish in the catch are within this range
of length. Therefore, only a minor proportion of
the estimated range in annual growth per fish can
be accounted for by changes in size composition of
the stock. Thus, within the constraints of the
model described here (c1; c2, Lm do not vary with
time), k must be nearly proportional to the rate
of weight gain.

During the period 1944-65 there were 4 yr in
which the estimated average annual air tempera-
ture was greater than 11°C and 7 yr in which it
was less than 10°C. For the four warmer years,
temperature averaged 11.2°C and growth per fish
averaged 88 g. For the seven colder years, tem-
perature averaged 9.5°C and growth 222 g.
Assuming k proportional to annual average
weight gain per year, c14 was estimated as
-0.466 by solving:

{1 + c14(lL2 - f)}l
{l + c14(9.5 - T)} = 88/222.

TABLE 3. — Range and mean for Lm, the maximum length pa-
rameter of the von Bertalanffy growth function, representing
each of the size categories of the yellowtail flounder model.

Size Range of Lm Mean of Lm
category (mm) (mm)

0.0-425.1
425.1-^45.4
445.4-467.2
467.2-4928

410.9
436 3
457.0
480 0

492.8-514.6
514.6-534.9
534.9-x

503.0
523.6
549.1

Lux and Nichy (1969) estimated the growth rate
coefficient (k of the von Bertalanffy growth func-
tion) for yellowtail flounder older than 2 yr of age
as 0.335. For the period during which Lux and
Nichy collected their data, the average annual
temperature at Block Island was about 9.8°C. This
temperature results in a growth-temperature
factor (Tg) of 1.175. Lux and Nichy's estimate
was divided by Tg resulting in an estimate of k2 =
0.285. An estimate of kx (=0.56) was determined
using the model so that fish would grow to a
realistic length by age 2.

The seasonal nature of yellowtail flounder
growth was exhibited when the average lengths
of age-groups were determined quarterly (Lux
and Nichy 1969). In general, the mean size of
an age-group changes little from the first to the
second quarter. Thus, most growth apparently
occurs during the second half of the year. In order

471

FISHERY BULLETIN: VOL. 75, NO. 3

to simulate this phenomenon, the following
quarterly growth adjustment factors were used:
K, = K2 = 0.0 and K3 = K4 = 2.0.

Estimation of c12 of the recruitment-tempera-
ture factor (TV, Equation (16)) depends on the form
of the recruitment relationship that is assumed.
The parameter c12 was estimated for both the
linear and density independent recruitment func-
tions (Equations (17) and (18)) using estimates
of annual recruitment reported by Sissenwine
(1974). During 1949-53, recruitment averaged
6.82 million fish (recruits to the stock of market-
able fish, about 3 yr and older) with a spawning
stock size proportioned to an average relative
abundance of 1.4 tons/day and an average annual
temperature of 11.08°C. On the other hand, for
1960-63, recruitment averaged 49.7 million fish
with a relative abundance and annual average
temperature of 2.9 tons/day and 9.65°C, respec-
tively.

For the density independent recruitment func-
tion, fluctuations in recruitment result directly
from fluctuations in Tg. An increase in recruit-
ment and in Tg by a factor of 7.3 while the tem-
perature anomaly changes from 0.905 to -0.525
provides an estimate of c12 = -0.89 by solving the
following expression:

7.3{l + c12(0.905)} = 1 + c12(-0.525).

If egg production is assumed proportional to stock
size or relative abundance, then for the linear
recruitment function, the increase in recruitment
by a factor of 7.3 would reflect an increase in
spawning stock size by a factor of 2.05 (=2.9/1.4)
and an increase of Tg by a factor of 3.56 (=7.3/
2.05). Therefore, solving the following expression:

3.56{l + c12(0.905)} = 1 + c12( -0.525)

C12 = -0.68 for the linear recruitment function.

Since little is known about the survival of
yellowtail flounder eggs and their eventual re-
cruitment to age-group 1, c13 of the recruitment
function was estimated by fitting the model to
data (see Verification). The parameter c13 was
estimated as 5.8 x 106 (fish per egg) for the linear
recruitment model and as 60.0 x 106 (fish) for the
density independent recruitment model.

Both estimates appear realistic as indicated by
the following discussion. The average recruitment
to the stock of marketable fish reported by Sissen-
wine (1974) was 22.8 x 106 fish. Assuming an

instantaneous natural mortality of 0.4 for age-
group 1 and a natural mortality of 0.2 with a total
gear mortality of 0.5 (F + D) for age-group 2,
recruitment to age-group 1 may be crudely esti-
mated by multiplying recruitment to the market-
able stock by 3.0. Thus, average annual recruit-
ment to age-group 1 could be estimated as 68.4
x 10G fish which is similar to the estimate of c13
for the density independent model. For the linear
recruitment model, c13 is the proportion of eggs
that survive to be recruited to age-group 1 under
average temperature conditions. Using the aver-
age catch per effort for 1943-66 ([/ = 2.5 x 106
g/day), the sex ratio (c11 = 0.5), the catchability
coefficient (q = 1.68 x 10~4), and an estimate of
average weight and fecundity (of females) of the
nominal stock (W = 451 g, Fe = 700,000 eggs),
c13 could be crudely estimated as 5.9 x 10~6 using
c13 = (R ■ W ■ q)/(Uc11 ■ Fe). For the winter
flounder, Pseudopleuronectes americanus, Saila's
(1961) work indicated about 18 recruits to age-
group 1 per million eggs (actually reported 18
recruits/100,000 hatched eggs assuming 10%
hatching success). The value used here is some-
what lower, but the fecundity of the yellowtail
flounder is higher than for the winter flounder.

In order to avoid the possibility of recruitment
becoming negative for extremely high tempera-
tures, the additional constraint that recruitment
never falls below 5 million fish was incorporated
into the model.

The initial length and number of individuals of
each age-size compartment had to be specified
prior to simulating the fishery. Royce et al. (1959)
reported the mean length of age-groups 2-6 for
the first quarter of 1943. These values were
assumed as the initial length of size category 4
of the appropriate age-groups. For the initial
lengths of the other age-groups, reasonable but
arbitrary values were selected. The average ini-
tial size of each age-group is listed in Table 4. The
lengths of size categories 1, 2, 3, 5, 6, and 7 were
determined by multiplying the length of size
category 4 by 0.856, 0.908, 0.950, 1.050, 1.092,
and 1.144, respectively. These factors correspond
to the ratio of the maximum length of each size
category to the maximum length of size category
4.

The onset of the collection of fishing effort data
was 1943; therefore, the model was used to simu-
late the fishery from that date. The relative abun-
dance of the yellowtail flounder during the first
quarter of 1943 was 5,742 fish/day (Royce et al.

472

SISSENWINE: COMPARTMENTALIZED SIMULATION MODEL

TABLE 4. — Initial (1 January 1943) mean total length in milli-
meters of each age-group for yellowtail flounder model. The
lengths of age-groups 2-6 were reported by Royce et al. ( 1959).

Age-group

Mean length (mm)

Age-group Mean length (mm)

160
271
324
353
372

401
425
440
450
460

1959). Dividing this by q, the mean population
size during this quarter was estimated as 34.2 x
106 fish. Because there is little growth and, there-
fore, little recruitment during the first quarter
(since fish are recruited as they grow to the size
vulnerable to fishing gear), the population was
assumed to undergo exponential decay during this
time interval. The effort expended during the
first quarter of 1943 was 2,038 days (Royce et al.
1959), resulting in a total maturity Z = 1.47
(Z = M + qf where /"is the rate of fishery in days
per year). Accordingly, the size of the landable
stock at the beginning of 1943 was estimated as
about 41.1 x 106 fish (using Equation 1.38 of
Ricker (1975) modified for an interval of one-
quarter of a year).

Royce et al. (1959) also reported the age compo-
sition for the first quarter of 1943. The catch pri-
marily comprised fish greater than 3 yr of age.
The number offish captured per day for age-group
3 and older is shown in Table 5. Based on the

TABLE 5. — Catch per day and relative abundance adjusted for
fishing vulnerability of age-group 3 and older yellowtail flounder
for the first quarter of 1943. These age-groups represented 95%
of the catch.

Adjusted
Age-group Catch/day relative abundance

1,793

1.596

1,008

504

476

3.984

1,995

1,061

504

476

length composition assumed for each age-group
and Equation (9), the relative level of fishing
mortality suffered by fish of age 3, 4, 5, and older
was calculated as 0.45, 0.80, 0.95, and 1.00, re-
spectively. By dividing the catch per day of each
age-group by the appropriate factor, the relative
abundance adjusted for fishing vulnerability was
obtained (also Table 5). These values represent
the relative abundance of each age-group in the
population. Using Table 5,

N5.
Ne.
N7.
N8.

N10.

0.55 7V4
0.48 2V5,
0.50 N6
0.50 7V7
0.50 N8.
0.50 JV9.

0.280 2V3.
0.130 2V3.
0.065 N3
0.033 N3_
0.016 N3_
0.008 N3m

where the subscript . indicates the summation over
all size categories, and the survival of fish older
than 7 yr was assumed to be 0.50. The size of the
marketable population was estimated by sum-
ming N, times the relative fishing vulnerability
of age-group i. This expression was set equal to
41.1 x 106 fish and solved for N3_ (=32.0 x 106
fish). Estimates of initial conditions for other
age-groups were obtained using the equations in
this paragraph. Age-group 2 was assumed to be
twice age-group 3 as indicated by a natural mor-
tality of 0.2 and a discard mortality of about 0.5.
Based on a natural mortality of 0.40 age-group 1
was assumed to be 1.5 times age-group 2. The
initial conditions of each age-group for the begin-
ning of 1943 based on the above discussion are
shown in Table 6. The population was distributed
among the size categories according to the appro-
priate values of G,.

TABLE 6. — Initial size of each age-group of yellowtail flounder
population assumed at the beginning of 1943.

Age-group Number in thousands Age-group Number in thousands

95,000
64,000
32,000
16,000
8,800

6
7
8
9
10

4,200

2,100

1.100

530

260

Nd = 0.50 JV,

VERIFICATION

The primary mode of verification of the model
was to compare predicted annual levels of catch
with published values. Lux's (1969a) record of
catch and fishing effort for 1943-66 is in conflict
for several years with data reported by Brown and
Hennemuth (see footnote 2) in an unpublished
form. These conflicts are minor, except for the
1966 catch where the difference is about 40%.
Since this year is at the end of the published record
and could easily be ignored, 1943-65 were initially
used for verification. After c13 was fit to the data,
the model was then compared with data through
1972.

Before comparing the model with the published
data, it was necessary to select a time step or

473

FISHERY BULLETIN: VOL. 75, NO. 3

integration interval that would not result in un-
reasonable numerical errors being propagated
through many years of simulated time. This was
done by increasing the time step until the simu-
lation results converged. With an integration
interval of 0.005 yr, the results converged suffi-
ciently so that a numerical error of less than 57c
is expected after 23 yr of simulation (the length of
the data record used for verification). This level
of error was considered acceptable in light of the
precision of all the data upon which this work
was based. It was noted that each decrease in
the time step was accompanied by an increase in
the simulated catch; therefore, the predictions
yielded by the computer simulations are probably
slightly lower than would have resulted from an
exact solution of the model.

The average length of age-groups 2-5 according
to the model for 1943-66, 1957-62, and 1962-71,
and the average length of these age-groups as
reported by Lux and Nichy ( 1969), and of the catch
for 1962-71 are compared in Table 7. Age-groups
2-5 were considered because they were most
abundant in available samples; and, therefore,
their means have smaller standard errors than
less abundant age-groups.

Most of the fish measured by Lux and Nichy
were collected during 1957-62. Model results for
this period compare favorably as expected since
the model was designed to simulate the situation
reported by Lux and Nichy. The average simu-
lated lengths for 1943-66 are generally lower
than for the 1957-62 design period since the
design period had a lower temperature (favorable
to growth) than the longer time interval.

The model tends to overestimate growth for
1962-71. The mean length of fish of a particular
age-group collected from the catch for 1962-71 is
lower than is predicted by Lux and Nichy's growth
function. This situation cannot be explained as an
effect of temperature. As has been the practice
throughout this work, the model was designed

TABLE 7. — Average length (millimeters) of yellowtail flounder
age-groups 2-5 according to the model for 1943-66, 1957-62, and
1962-71 according to Lux and Nichy (1969), and for samples
from the commercial catch collected January-March 1962-71
(data provided by Northeast Fisheries Center).

Age-

Model

Catch samples

Lux and

group

1943-66

1957-62

1962-71

Nichy

275

290

323

306

266

303

338

365

342

338

351

367

397

365

378

385

416

387

404

in accordance with the published literature;
therefore, some apparent overestimation of
growth in later years of the simulations is in-
evitable. This situation makes application of the
model less satisfactory for recent years, but part
of the effect of overestimating growth would be
compensated for by a shift in age-group structure
of the catch. If the model slightly overestimates
growth, there is a tendency to catch younger fish;
and, therefore, the effect of overestimating growth
is partially offset.

The simulated size-category structure of cap-
tured (landed and discarded) fish for 1943-65 is
compared with unpublished data for 1963 as re-
ported by Brown and Hennemuth (see footnote 2)
in Figures 2 and 3. Clearly, it would have been

OBSERVED O
SIMULATED •

300

350 375

LENGTH , mm

400

FIGURE 2.— Simulated (1943-651 and observed (unpublished
data for 1963 as reported by Brown and Hennemuth (see footnote
2)) size-category structure of catch ( including discards) of yellow-
tail flounder.

OBSERVED O
SIMULATED •

300 325

LENGTH, mm

FIGURE 3.— Simulated (1943-65) and observed (unpublished
data for 1963 as reported by Brown and Hennemuth (see footnote
2)) size-category structure of discards as percentage of catch
(including discards) for yellowtail flounder.

474

SISSK.WV1NE: COMPARTMENTALIZED SIMULATION MODEL

better to compare the 1963 simulated size-
category structure with these data, but, because
of a programming oversight, this information
was not available. The comparisons in Figures 2
and 3 are generally favorable and indicate that
the assumed linear relationships (Equations (6)
and (7)) describing the relative effectiveness of
the fishing gear and the marketability of fish as
a function of length were adequate. The model
indicates that 39.5% of the fish captured by fisher-
men for 1943-65 were discarded. The average
weights of landed and discarded fish based on
Figures 2 and 3 are 455 and 249 g, respectively.
The parameter c13 of the recruitment function
(Equations (17) and (18)) was estimated by run-
ning the model for several values of this param-
eter and selecting the value that explained the
greatest proportion of variation in observed yield.
Of the values considered, c13 equal to 60.0 x 106
and 5.8 x 10 6 for the density independent and
linear recruitment models were most successful
in explaining variation in yield. Since only a finite
number of values of c13 were considered, the val-
ues selected are probably not the "best least
squares" estimates, but the results (Table 8) indi-
cate that the model is not very sensitive to 5-10%
fluctuations in this parameter. As noted earlier,
these values appear realistic.

TABLE 8. — Percent of variation in yield explained by the yellow-
tail flounder model with various values of c\3 for 1943-65.

Linear

Density

independent

Stock

-recruitment

stock-recruitment

C13

(%)

C13

(%)

5.4 ■ 10

-6

73.6

55.0 K 106

81.3

5.6 ■ 10

-b

82.0

57.5 ■ 106

82.6

5.7 ■ 10

-b

84.5

60.0 ■ 106

83.2

5.8-10

-b

85.5

62.5 ■ 10|j

83.0

6.0 x 10

82.3

65.0 ■ 106
70.0 x 106

82.1
78.1

The model using linear or density independent
recruitment explained 85.5 and 83.2% of the vari-
ation in yield from 1943-65, respectively. In addi-
tion to catch and effort data reported by Lux
(1969a), catch data through 1972 and effort data
through 1971 were available (at the time when
this research was in progress) for the Southern
New England ground (Brown and Hennemuth
see footnote 2; Brown see footnote 3; and Par-
rack see footnote 4). Both the linear and den-
sity independent stock-recruitment models were
run for 1943-72 (assuming that the level of effort
was unchanged from 1971 to 1972), and the

results were compared with the available data in
Figures 4 and 5. Both models seem to simulate
catch as well since 1965 (although yield is sub-
stantially underestimated for 1969 and 1970) in
spite of the fact that they were developed indepen-
dently of the later data and that growth is appar-
ently somewhat overestimated toward the end of
the simulation. Since errors for any particular

E 20

c
o
u>

- 10

Q
<

• PREDICTED
▲ UNPUBLISHED
O PUBLISHED

1945

1950

1955

I960

1965

1970

FIGLTRE 4. — Landings of Southern New England yellowtail
flounder as reported in published and unpublished reports and
predicted by the model with linear recruitment function (Equa-
tion (17)1.

£ 25

z
<

• PREDICTED
A UNPUBLISHED
O PUBLISHED

Ol L

1945

1950

1955

I960

1965

1970

FIGURE 5.— Landings of Southern New England yellowtail
flounder as reported in published and unpublished reports and
predicted by the model with a density independent recruitment
function (Equation (18)).

475

FISHERY BULLETIN: VOL. 75, NO. 3

year are propagated through the simulation, it is
surprising that the model seems to recover after
occasional substantial deviations from the ob-
served yield.

Sissenwine (1974) explained most of the vari-
ability in recruitment of the Southern New
England ground even though the size of the
spawning stock was ignored. This earlier work
noted that spawning stock size may have an im-
portant effect on recruitment, but the effect might
be obscured by environmental noise. The work
reported here demonstrates that models incor-
porating either linear or density independent
recruitment explain most past variability in catch
of the fishery. Nevertheless, the model incorporat-
ing recruitment linearly dependent on spawning
stock size is preferable for the following reasons:

1. While the linear model only explained 2.2%
more variation than the density independent
model, it did explain 13% of the density in-
dependent model's residual variation with no
increase in number of parameters.

2. While the density independent model is more
simplistic mathematically, a direct linear
relationship between stock size and recruit-
ment is a more basic biological relationship.
Obviously, recruitment cannot be independent
of spawning stock size over its entire range.
The density independent situation can only
exist as a special case of a more complex non-
linear stock-recruitment relationship.

3. It seems unrealistic for recruitment to be un-
affected by size of spawning stock when stock
size varies by a factor of 3.

4. The linear stock-recruitment model is a more
conservative management tool than the den-
sity independent model. Management prac-
tices designed to prevent a dangerous reduc-
tion in stock size of a population regulated by
a linear stock-recruitment relationship will
also prevent a reduction in stock size of a pop-
ulation regulated by a density dependent
stock-recruitment relationship.

No attempt was made to use the Ricker (1954,
1958) stock-recruitment function or other non-
linear functions because the results obtained
using the linear and density independent func-
tions (Equations (17) and (18)) indicated that most
likely these more complicated functions would not
significantly increase the accuracy of the model.
When using the linear model where the Ricker

function (for example) is more appropriate, the
linear model is expected to be accurate at low
population levels but overestimates recruitment
(and catch) at higher population levels. The re-
verse situation is expected when the density in-
dependent model is used where a Ricker function
is more appropriate. In neither case was the more
complex Ricker function indicated.

Based on the above discussion, the linear stock-
recruitment function ( Equation (17)) seemed most
appropriate over the observed range of population
size. Therefore, only the linear model is used in
the remainder of this paper.

The linear stock-recruitment model was run for
1943-65 without temperature dependent growth
(c14 = 0.0), without temperature dependent re-
cruitment (c12 = 0.0), and without temperature
dependent growth or recruitment (c12 = c14 = 0.0).
None of these situations explained a significant
portion of variation in catch. This fact does not
constitute rigorous evidence that incorporation of
Tg and Tr into the model is necessary to explain
most of the variability in catch because no attempt
was made to tune the model for the temperature
independent cases. Earlier work by Sissenwine
(1974, 1975) demonstrated the influence of tem-
perature on the fishery and supports the incor-
poration of Tg and Tr into the model.

APPLICATIONS

The effects of several alternative fishing strat-
egies were examined using the model. These ex-
amples deal with some aspects of the model which
are not common components of other fishery mod-
els (such as discard mortality, temperature de-
pendence, and seasonal growth and fishing rate).

The impact of discarding at sea fish shorter than
300 mm was evaluated by running the model with
the assumption that the minimum size retained
by a net equaled this value. The results for Lgmin
= 300 mm are compared with the model results as
described earlier (Lgmin = 250 mm) in Figure 6.
Landings in excess of 30,000 metric tons are not
shown because these have not been observed dur-
ing the history of the fishery; thus simulations
indicating these high values are extrapolative in
nature. These higher simulated landings result
because the model assumes a linear stock-
recruitment relationship at all stock sizes, while
in reality the relationship probably becomes
density dependent as stock size becomes large.
By eliminating discard mortality of fish shorter

476

SISSENWINE: COMPARTMENTALIZED SIMULATION MODEL
30

1965

FIGURE 6. — Simulated landings of yellowtail flounder with

-'gmm

= 250 mm and 300 mm. Landings greater than 30,000

metric tons are not shown.

than 300 mm, these fish have a higher probability
of surviving until they are recruited and spawn.
The result was from a 207c to a severalfold in-
crease in landings.

Using the Beverton and Holt yield per recruit
(YPR) function, Brown and Hennemuth (see foot-
note 2) found less than a 40% increase in yield
by delaying the age at first capture from 1.75 yr
(or 245 mm) to 2.5 yr (or 302 mm) for F less than
1.1. This was the highest simulated fishing mor-
tality rate during 1943-65. The substantially
greater increase in yield from the simulation
reported in Figure 6 results from increased re-
cruitment which is not considered in the Beverton
and Holt YPR function.

The benefit of increasing mesh size to eliminate
discard mortality is clearly demonstrated (for the
linear recruitment model), but this analysis ig-
nores financial and technological difficulties
which may be involved (Gates and Norton 1974).

The effect of the seasonality of fishing mortality
was explored by varying seasonal effort adjust-
ment factors (c3, c4, c5, and c6). Situations where
effort was applied uniformly throughout the year
and where all effort was applied during a single
quarter were considered. These cases are com-
pared with the results reported earlier (c^ = 1.26,

o C3=I26,C4 = 037, C5 = 0 88, C6 = I 49

1945

1950

1955

I960

1965

FIGURE 7. — Simulated landings of yellowtail flounder with fish-
ing effort applied uniformly and with c3-c6 as assumed for
1943-65.

£ 25
o

I 20

en
■o

c
o
in

-z.
<

5 -

O C3 = 1.26, C4 =0 37, C5
• C3 =4 0, C4 = C5 = C6 = 0
AC4 =4 0, C3 = C5 = C6 =0

965

FIGURE 8. — Simulated landings of yellowtail flounder with all
fishing effort in the first or second quarter of the year and with
c3-c6 as assumed to have occurred for 1943-65.

c4 = 0.37, c5 = 0.88, and c6 = 1.49) in Figures 7-9
and Table 9.

The simulations reported in Figures 7-9 indi-
cated that the seasonal aspect of the expenditure
of effort and resulting fishing mortality could

477

FISHERY BULLETIN: VOL. 75, NO. 3

c
o

25 -

e 20

in
T3
c
a
in

Q
<

5 -

O C3 = 1.26, C4 = 0.37,

C5 =0.88, C6= I 49
• C5=40,C3=C, = C6 =0
A C6 = 40,C3 = C4=C5=0

1945

1950

1955

I960

1965

FIGURE 9. — Simulated landings of yellowtail flounder with all
fishing effort in the third or fourth quarter of the year and with
c3-ce as assumed to have occurred for 1943-65.

TABLE 9. — Comparison of simulated catches of yellowtail floun-
der with various values of the seasonal effort factors (03, C4, C5,
C6>- Percentage changes in yield are relative to the simulated
yield with C3, C4, c.5, and cq as in the first line of the table.

Percentage change

in yield

1943

1944

1943-65

1.26

0.37

0.88

1.49

—

1.00

-6.7

-4.5

+ 3.6

4.00

0.0

-20.7

-14.3

-40.6

0.0

4.00

0.0

-24.0

- 16.8

-0.6

0.0

4.0

0.0

-9.4

-9.3

+ 92.8

0.0

4.0

+36.4

+21.0

+22.6

have a very significant impact on the yield of the
fishery. There was little change in yield indicated
when fishing mortality was assumed uniform
throughout the year. The simulations showed that
yield of the simulated fishery would have been
reduced if all fishing mortality occurred during
the first quarter of the year. If all fishing mortality
were applied during the second quarter, yield of
the fishery would have been lower during the
first few years of the simulation, but little differ-
ence in total yield is indicated over 23 yr. The
expenditure of effort during the third quarter also
tended to reduce the early catch, but in the long
run appeared to result in the highest yield. By
restricting fishing mortality to the fourth quarter
of the year, some initial increase in catch was
indicated and long-term yield was also increased.

These results reflect the facts that spawning
occurs during the second quarter and growth of
fish is limited to the third and fourth quarters of
the year according to the model. Clearly, to obtain
a short-term gain in yield, it is most advantageous
to harvest at or near the end of the growing season
(Table 9). Long-term gains were obtained when
egg production was optimized by harvesting just
after spawning (third quarter). By concentrating
effort during the fourth quarter, an increase in
yield was indicated for all years of the simulation.
Fishing during the first quarter appears to be
particularly detrimental because it crops fish just
prior to spawning.

The seasonal pattern of effort exhibited by the
fishery in the past includes intense fishing during
the first quarter and the fourth quarter of the
year. Apparently these balance, resulting in
yields similar to the case where fishing is uniform
through the year. In recent years, the annual
catch quota for the United States (established by
the International Commission for the Northwest
Atlantic Fisheries (ICNAF)) was divided equally
among the four quarters. The result is that fishing
mortality was probably distributed nearly uni-
formly through the year. There may be some ad-
vantage to increasing the portion of the annual
quota captured during the second half of the year.
It is important to note that the long-term gains
obtained by concentrating fishing just after the
spawning season will not be realized if recruit-
ment is independent of spawning stock size ( Equa-
tion (18)).

Several experiments were conducted with the
model in order to determine to what degree the
yield of the fishery could be stabilized or increased
by regulating the annual expenditure of effort
and ultimately F. For a fishery in which recruit-
ment is linearly related to stock size, in the long
run it is advantageous to reduce fishing effort
(and mortality) in order to increase egg produc-
tion. Therefore, the fishery was simulated with
effort at 80% of observed values (Figure 10). The
short-term decrease in yield was rather minor.
Considerable long-term advantage was predicted;
but even with a reduced level of effort, the simu-
lated fishery declined during the late 1940's and
early 1950's. However, the recovery when condi-
tions became favorable was more rapid at the
lower level of effort for this particular case.

The Beverton and Holt YPR equation (Brown
and Hennemuth see footnote 2) indicates less than
a 5% increase in catch with a 20% decrease in

478

SISSK.WVINK COMPAKTMF.NTAI.IZKI) SIMULATION MODi L

S 25

E 20

Q
<

OBSERVED EFFORT

80% OF OBSERVED

EFFORT

1945

1950

1955

I960

1965

FIGURE 10. — Simulated landings of yellowtail flounder with
observed level of fishing effort and with 80% of the observed
level.

fishing mortality (for 0.6 =£ F =s 1.5 and age at

first capture between 1.75 and 3.0). Therefore,
most of the increase in yield indicated in Figure 10
must result from improved recruitment at lower
levels of F.

Since recruitment and growth appear related to
temperature, the possibility of using this environ-
mental variable to predict an appropriate level
of effort was considered. The model is such that
growth and recruitment are proportional to Tg
and Tr, respectively. Therefore, the following
relationship between fishing effort and Tg and Tr
was utilized:

fi=cl5- {(TPi-i+OVi-J.

(20)

Effort for year i was based on the growth-
temperature factor for the year i — 1 since Equa-
tion (20) is of little value unless effort can be set
in advance. The recruitment-temperature factor
from 2 yr prior (i - 2) was used since recruitment
lags spawning by about 2 yr. A 3-yr lag could have
been used. Tg and Tr could have been weighted in
Equation (20) since the latter is usually more
important in determining equilibrium yield, but
this would have introduced another parameter.
Initially, c15 was estimated as 1,870 days of

fishing, which yields about the average level of
effort for 1943-65 when Tg and Tr equal 1. A
value higher and lower than 1,870 days was also
considered. Simulated catches for each value of c15
are shown in Figures 11-12, and the simulated
catch per unit of effort is shown in Figure 13.

For 1943-65, c15 = 2,200 days resulted in a
decrease in relative abundance while Ci5 = 1,540
days permitted the relative abundance to in-
crease. The value of c15 (1,870 days) corresponding
to the average effort during 1943-65 best stabi-
lized the relative abundance of the fishery, but
was only slightly more effective than the volun-
tary actions of the fishermen who probably re-
sponded to fluctuations in fishing success (U). It
appears that a function even more sensitive to
temperature than Equation (20) is required to
better stabilize the population. Since Tr is more
sensitive to temperature than Tg, weighting of
these factors (in favor of the former) might result
in a function more effective in maintaining the
population size during the early 1950's. Never-
theless, the yield of the simulated fishery (with
the linear recruitment function) could have been
substantially increased if fishing effort were reg-
ulated by a simple function such as Equation (20)
with c15 considerably less than 1,870 days.

c
o

z
<

1945

I960

FIGURE 11. — Simulated landings of yellowtail flounder with ob-
served effort and with effort set by Equation (20) using c15 =
2,200 or 1,540.

479

FISHERY BULLETIN: VOL. 75, NO. 3

§ 25

</)
T>

c
o
l/>

3
O

O OBSERVED EFFORT
• C,5 = 1870

1945

1950

1955

I960

1965

FIGURE 12. — Simulated landings of yellowtail flounder with ob-
served effort and with effort by Equation (20) using c15 =
1,870.

6.0

O OBSERVED LANDINGS PER DAY

• C,5 = 1540

A C,5 ■ 1870

-A C15 = 2200

£
v>

4.0

_L.

1945

1950

1955

1960

1965

FIGURE 13. — Observed catch of yellowtail flounder per day of
fishing and simulated catch per day with effort set by Equation
(20) using c15 = 1,540, 1,870, or 2,200.

At present, annual catch quotas for the South-
ern New England yellowtail flounder stock are
based on a prerecruit index (Brown and Henne-

480

muth 1971). The index is calculated from the catch
of 1-yr-old fish in an autumn bottom trawl survey
(Grosslein 1969). Thus the major source of vari-
ability in production resulting from the influence
of temperature on recruitment is accounted for in
current stock assessments. This model should not
be considered as an alternate method of manage-
ment of the fishery on a year to year basis without
further verification and refinement.

Walters (1969) developed a yield optimization
procedure for his generalized fish simulator using
the steepest ascent method. The development of
an optimization procedure for the model reported
in this paper would be more difficult because this
model is driven by two exogenous factors, temper-
ature and the rate of fishing, while Walters's
model is only driven by fishing mortality. This
model is generally more complex than Walters's
model and much more expensive to run. There-
fore, the development of an optimization proce-
dure is beyond the scope of the present work.

DISCUSSION

A complex compartmentalized simulation
model of the Southern New England yellowtail
flounder fishery has been described, verified
against catch statistics, and used to examine
methods of increasing yield. The relationships
and parameters upon which the model was based
do not appear to be unreasonable since most vari-
ability was explained. Nevertheless, in retrospect,
some consideration of alternate approaches to
estimating parameters and of modifications of the
model is appropriate. It is important to remember
that there may be numerous other models or
parameter values equally as successful at explain-
ing variation in catch as the one proposed here.

An average maximum length (Lm4) for the sim-
ulated population of 480 mm was assumed. This
value was used in order to assure that few fish
would exceed 500 mm in length. When fishing
pressure was applied to the simulated population,
its average maximum length was suppressed. For
some years, the average length of the older age-
groups converged to about 460 mm. Since the
growth rate coefficients (kt) of adult fish were
based on Lux and Nichy's (1969) work where a
maximum length of 500 mm was assumed, the
model tends to underestimate the length of older
fish. In order to compensate for this effect, the
growth rate coefficient of fish younger than 2 yr
of age was overestimated. The result was that

SISSENWINE: COMPARTMENTALIZED SIMULATION MODEL

the mean size of younger fish was higher than
observed while the converse applied to older fish.
The differences were generally small. The sizes
of the most abundant fish in the catch (age-groups
3 and 4) were well simulated. While the model
adequately simulates growth, more precise re-
sults might have been obtained by assuming an
average maximum size in excess of 500 mm. The
result, with fishing, would be an average max-
imum size near the value assumed by Lux and
Nichy ( 1969). Thus the assumed value of k2 would
have been more appropriate.

The parameters of c12 and c14 specify the tem-
perature dependence of the model. Estimates of
these parameters were based on Sissenwine's
(1974, 1975) calculations of recruitment and
average growth per fish for 1944-65. No attempt
was made to improve these estimates by tuning
them to the model. While Figures 4 and 5 indicate
the adequacy of the model and its parameters,
these figures also reveal that catch was generally
overestimated during warm years and under-
estimated during cold years. This implies that
the fishery was probably more sensitive to tem-
perature than indicated by estimates of c 12 and c14.
Rather minor adjustment of these parameters
would probably account for much of the remaining
unexplained variation in catch. On the other
hand, since tuning in effect reduces the residual
degree of freedom and, more subjectively, reduces
confidence in the model, no attempt was made to
improve the initial estimates of c12 and cu.

Adult female yellowtail flounder are generally
longer than males of the same age. The model does
not distinguish between sexes. To do so would
require doubling the central processing time
required to run the model. Fishing pressure would
tend to shift the sex ratio in favor of males because
of this size difference. Since the sex ratio (cu = 0.5)
was estimated for the exploited population, the
influence of fishing was incorporated into the
model through the estimation of this parameter.
Variations in cu resulting from changes in level
of fishing were not simulated.

Since females are larger than males, the total
fecundity of the population is underestimated
when based on the mean size of the age-size com-
partments. This bias is probably compensated for
by overestimating mean recruitment per egg (c13).
Thus, expansion of the model to segregate fish
according to sex should not affect the results re-
ported here, although some revision of cJ3 would
be required.

In recent years, several changes have occurred
in the Southern New England yellowtail flounder
fishery that were not reflected in the model.
During the late 1960's, more active industrial and
distant water fisheries (using small mesh nets)
for the yellowtail flounder developed. The fish-
eries statistics used in this report do not include
the catch of the industrial fishery which in a few
years equaled 20r/r of the total yield. Estimates
of the catch of the distant water fishery are in-
cluded and the fishing effort of the distant water
fleet is estimated by assuming that the catch per
unit effort was the same as for the domestic fish-
ery. Since 1971, the fishery has been regulated by
quotas set by ICNAF. During the 1970's, landings
of yellowtail flounder within ICNAF Subarea 6
(south of the Southern New England ground
which is within ICNAF Subarea 5) have in-
creased. The relationship between the fisheries in
these two areas is unknown (Brown see footnote 3;
Parrack see footnote 4). These recent changes
necessitate several modifications of the model
before it can be used to simulate the present
fishery.

The work reported here indicates the potential
for predicting future trends of certain well-studied
fisheries in which the role of a specific environ-
mental variation can be described. Two important
limitations of this approach are demonstrated.
Firstly, model parameters may change with time;
thus it is important to keep the model up-to-date.
This does not imply that the model should be regu-
larly tuned to assure that it successfully predicts
each additional year of data but rather that
parameters be updated as evidence of change in
the fishery becomes available. Secondly, numer-
ous fundamentally different models may be
nearly as successful in simulating a specific sys-
tem. Therefore, it is dangerous to limit considera-
tion to a single model or regulatory mechanism.

ACKNOWLEDGMENTS

I thank Saul B. Saila for his support throughout
this work. Numerous valuable constructive com-
ments on the manuscript were provided by Brad-
ford Brown, Judith Brennan, and Richard Henne-
muth. Ilene Sissenwine edited and proofread the
typescript. Part of this work was completed in
partial fulfillment of the requirements for the
degree of Doctor of Philosophy at the University
of Rhode Island and was sponsored by the Office
of Sea Grant, NOAA, U.S. Department of Com-

481

FISHERY BULLETIN: VOL. 75, NO. 3

merce, through a grant awarded to the University
of Rhode Island. The University of Rhode Island's
Computer Laboratory provided processing time
and facilities. The Northeast Fisheries Center,
National Marine Fisheries Service, NOAA, gen-
erously provided some of the unpublished data
prior to my employment by that agency.

LITERATURE CITED

BERTALANFFY, L. von.

1938. A quantitative theory of organic growth. (Inquiries
on growth laws. II). Human Biol. 10:181-213.

Beverton, R. J. H., and S. J. Holt.

1957. On the dynamics of exploited fish populations. Fish.

Invest. Minist. Agric. Fish. Food (G. B.), Ser. II, 19, 533 p.
BIGELOW, H. B., AND W. C. SCHROEDER.

1953. Fishes of the Gulf of Maine. U.S. Fish Wildl. Serv.,

Fish. Bull. 53, 577 p.

Brown, B. E., and R. C. Hennemuth.

1971. Prediction of yellowtail flounder population size
from prerecruit catches. Redbook Int. Comm. Northwest
Atl. Fish. Part 111:221-228.
CHASE, J.

1967. Recent trends of temperature along the New
England coast. Redbook Int. Comm. Northwest Atl.
Fish. Part IV:37-41.

COLTON, J. B., JR.

1968. A comparison of current and long-term tempera-
tures of Continental shelf waters, Nova Scotia to Long
Island. Int. Comm. Northwest Atl. Fish., Res. Bull. 5:
110-129.

Gates, m. G, and V. J. Norton.

1974. The benefits of fisheries regulation: A case study of
the New England yellowtail flounder fishery. Univ. R.I.
Mar. Tech. Rep. 21, 35 p.
GROSSLEIN, M. D.

1969. Groundfish survey program of BCF Woods Hole.
Commer. Fish. Rev. 31(8-9):22-30.

LAUZIER, L. M.

1965. Long-term temperature variations in the Scotian

Shelf area. Int. Comm. Northwest Atl. Fish., Spec. Publ.

6:807-816.
LUX, F. E.

1963. Identification of New England yellowtail flounder
groups. U.S. Fish Wildl. Serv., Fish. Bull. 63:1-10.

1964. Landings, fishing effort, and apparent abundance in
the yellowtail flounder fishery. Int. Comm. Northwest
Atl. Fish., Res. Bull. 1:5-21.

1969a. Landings per unit effort, age composition, and total

mortality of yellowtail flounder, Limanda ferruginea

(Storer), off New England. Int. Comm. Northwest Atl.

Fish., Res. Bull. 6:47-52.
1969b. Length- weight relationships of six New England

flatfishes. Trans. Am. Fish. Soc. 98:617-621.
LUX, F. E., AND F. E. NICHY.

1969. Growth of yellowtail flounder, Limanda ferruginea

(Storer), on three New England fishing grounds. Int.

Comm. Northwest Atl. Fish., Res. Bull. 6:5-25.
PITT, T. K.

1971. Fecundity of the yellowtail (Limanda ferruginea)

from the Grand Bank, Newfoundland. J. Fish. Res.

Board Can. 28:456-457.
RICKER, W. E.

1954. Stock and recruitment. J. Fish. Res. Board Can.

11:559-623.

1958. Handbook of computations for biological statistics
of fish populations. Fish. Res. Board Can. Bull. 119,
300 p.

1975. Computation and interpretation of biological statis-
tics offish populations. Fish. Res. Board Can. Bull. 191,
382 p.
ROYCE, W. F., R. J. BULLER, AND E. O. PREMETZ.

1959. Decline of the yellowtail flounder (Limanda ferru-
ginea) off New England. U.S. Fish Wildl. Serv., Fish.
Bull. 59:169-267.

SAILA, S. B.

1962. The contribution of estuaries to the offshore winter

flounder fishery in Rhode Island. Gulf Caribb. Fish.

Inst, Proc. 14th Annu. Sess., p. 95-109.
SISSENWINE, M. P.

1974. Variability in recruitment and equilibrium catch
of the Southern New England yellowtail flounder fishery.
J. Cons. 36:15-26.

1975. Some aspects of the population dynamics of the
Southern New England yellowtail flounder (Limanda
ferruginea) fishery. Ph.D. Thesis, Univ. Rhode Island,
Kingston. University Microfilm, Ann Arbor, Mich. Order
No. 76-4980.

TAYLOR, C. C.

1962. Growth equations with metabolic parameters.
J. Cons. 27:270-286.
TAYLOR, C. C, H. B. BIGELOW, AND H. G. GRAHAM.

1957. Climatic trends and the distribution of marine
animals in New England. U.S. Fish Wildl. Serv., Fish.
Bull. 57:293-345.
TEMPLEMAN, W.

1965. Anomalies of sea temperature at Station 27 off Cape
Spear and of air temperature at Torbay-St. John's. Int.
Comm. Northwest Atl. Fish., Spec. Publ. 6:795-806.
WALTERS, C. J.

1969. A generalized computer simulation model for fish
population studies. Trans. Am. Fish. Soc. 98:505-512.

482

INCOME ESTIMATES AND REASONABLE RETURNS IN
ALASKA'S SALMON FISHERIES1

James E. Owers2

ABSTRACT

Earnings in some fisheries may fall to a level that is unacceptable from the viewpoint of public policy.
Using the Alaska salmon fisheries as an example, this paper examines a method for establishing the
number of operating units that will provide a reasonable economic return in a fishery. Estimates are
provided of the rates of return that can be expected with various numbers of operating units. Three
criteria are then developed to determine a reasonable rate of return. These criteria include: 1) a
comparison with wages in a similar industry in an equal time period, 2) a comparison with total annual
incomes from all sources with total incomes of workers in other occupations, and 3) an estimate
provided by fishermen themselves. These three different measures indicate an optimum number of
operating units within a fairly narrow range. In some fisheries it appears that substantial reductions in
the number of fishing units will not be sufficient to raise incomes to an "acceptable" level. This raises
questions about the allocation of valuable fishery resources among various user groups.

During the last two decades economists have de-
veloped a general theory of a common property
fishery under conditions of open access. The sa-
lient implications of that theory are that: 1) there
is a danger that the resource will be fished beyond
maximum sustained yield, 2) the resource will not
be harvested with maximum economic efficiency,
and 3) there will be a misallocation of productive
factors between the fishing sector and other sec-
tors of the economy (Crutchfield and Pontecorvo
1969). Empirical research has shown that there
may be a fourth consequence of open access that is
not adequately dealt with in the theoretical litera-
ture. This is the fact that earnings of fishermen
under conditions of open access may fall below a
level that is acceptable from the viewpoint of pub-
lic policy (Sinclair 1960; Owers 1974; Huq3;
Smith4). The public interest arises from the fact
that poor earnings have been responsible for creat-
ing sanitation, health, safety, and other hazards;
that programs providing government assistance
for fishermen are becoming increasingly expen-
sive; and that in many cases commercial users can

'The opinions and conclusions set forth in this paper are not
those of the Commercial Fisheries Entry Commission nor the
State of Alaska.

2Cornell Law School, Myron Taylor Hall, Ithaca, NY 14853.

3Huq, A. M. 1971. A study of the economic impact of changes in
the harvesting labor force in the Maine lobster fishery. U.S. Dep.
Commer., NOAA, Natl. Mar. Fish. Serv., contract 14-17-007-
1121, Wash., D.C., 34 p.

"Smith, F. S. 1974. 1972 commercial fishermen survey. Dep.
Agric. Econ., Oreg. State Univ., Corvallis, 7 p.

no longer afford to pay their share of management
costs. The cause of the problem appears to be the
very low opportunity costs of fishermen who have
only an avocational interest in fishing or else have
little mobility and limited access to alternative
employment.

Data collected by interview and from landing
records indicate that 44% of the purse seiners, 15%
of the drift gill netters, and 60% of the set gill
netters in Alaska showed a net loss in 1973 (Smith
et al.5). In the same year, the average net return to
the more than 6,400 gear operators who partici-
pated in those salmon fisheries which now have
limited entry was about $1,600 per gear operator.

Recognition of the recurring problems created
by low earnings in many of the state's fisheries led
Alaska to pass the first comprehensive limited
entry law in the United States in 1973. The law
directs an independent commission to stabilize or
reduce the number of legal units of gear that can
be fished in those fisheries where economic or
biological conditions require it. Specifically the
law states the following must be considered in
establishing an economically sound number of
entry permits: "The number of entry permits
sufficient to maintain an economically healthy
fishery that will result in a reasonable average

5Smith, F. S., D. Liao, J. Martin, and P. Adelman. 1975.
Profitability analysis for Alaska fishing businesses. Dep. Agric.
Econ. Oreg. State Univ., Corvallis, 13 p.

Manuscript accepted May 1976.

FISHERY BULLETIN: VOL. 75, NO. 3, 1977.

483

FISHERY BULLETIN: VOL. 75, NO.3

rate of economic return to the fisherman par-
ticipating in that fishery considering time fished
and necessary investments in vessels and gear . . .
(Anonymous 1973a)." As used in the law and this
discussion, a "fishery" refers to a specific combina-
tion of species, gear type, and management dis-
trict. Figure 1 shows the salmon management dis-
tricts in the state. An entry permit entitles the
holder to operate a legal unit of gear in a fishery.

In 1974 entry was limited in the power troll
fishery and all salmon net fisheries, with the ex-
ception of those in the Arctic, Yukon, and Kus-
kokwim management districts. This paper
examines a procedure that can be used to evaluate
the gear cutbacks that may be required to achieve
"reasonable" earnings in these fisheries. Because
the limited entry law seeks to achieve a balance
among social objectives, biological management,
and economics, the reductions suggested here,
which consider only possible economic objectives,
are not necessarily those which the law would
require.

A detailed discussion of sample size, methodol-
ogy, and other factors affecting the validity of data
used can be obtained from several of the references
cited at the end of the article. Further elaboration
is not provided in the text, other than to briefly
describe the data used and its source. It should be
further recognized that it is not the purpose of this
paper to present a rigorous mathematical defini-
tion of a problem, but rather to point out its gen-
eral magnitude and direction.

ESTIMATING EXPECTED RETURNS IN
THE SALMON FISHERIES

Several equations were used to estimate returns
salmon fishermen might receive with various
numbers of operating units in the fisheries. All the
equations are presented below, followed by a more
detailed description of the variables. Table 1
summarizes the input data used in the equations.
To estimate gross returns per operating unit in
each fishery, the following equation was used:

G =

T • (1 + S)
P ■ E

(1)

where G is the gross return per fishing unit in the
particular fishery; T is the total exvessel revenue
paid to all fishermen in that particular fishery; S is
the percent of revenue paid as bonus payments to
fishermen; P is the percent of entry permits actu-
ally used in a particular fishery; and£ is the total
number of entry permits outstanding.

To estimate net returns per entry permit holder,
exclusive of opportunity costs of capital, the fol-
lowing equation was used:

A^G-ffJ-C

(2)

where N1 is net return not including the oppor-
tunity cost of capital; L is the percent of total

ARCTIC YUKON KUSKOKWIM

FIGURE 1. — Alaska salmon management
areas.

ALEUTIAN ISLANDS

484

OWERS: INCOME ESTIMATES AND RETURNS IN SALMON FISHERIES

TABLE 1. — Input data used to generate estimates of fishermen's incomes by fishery.

Fraction of

Estimated

Total

Crew

Net

gross return

fraction

Earnings

Bonus

No. of

exvessel

Costs

share (L)

earnings

Market

earned in

of permits

from

payments

entry

revenue

Ifraction

from other

value of

other

actually

nonfishing

(S)

permits

(T) in

operating

of 7

fisheries

investment

fisheries

(P)

sources

[fraction

issued

Fishery

thousands'

unit2

paid]2

(XV

(02

(F)2

fished3

(O)"

of 7]2

(E)

Purse seme:

Southeast

$9,750

$10,279

0.500

$7,390

$91,212

0.46

0.87

$4,155

0.196

395

Prince Wm Sound

4,385

5,804

.450

2,128

39,592

.31

.89

3,016

—

238

Cook Inlet

467

4,506

.510

2,607

33,657

.37

.61

4,343

.004

Kodiak

5.947

4,805

430

—

37,902

.33

4,685

.019

368

Chignik

2,541

10,213

.420

—

66,307

2,007

.045

Peninsula-

Aleutians

1,603

1,627

.340

8,703

51,473

.74

.78

4,061

—

111

Drift gill net:

Southeast

4,404

4,381

.072

2,583

27,254

.12

.74

4,012

.092

453

Prince Wm Sound

3,063

4,436

.058

879

15,642

.23

.79

1,906

.024

511

Cook Inlet

2,235

2,744

.176

589

15,254

.17

.67

2,501

.029

545

Peninsula-

Aleutians

1,526

3,780

.092

1,171

23,428

.22

.83

1,925

—

155

Bristol Bay

13,933

1,879

.380

—

1 1 ,548

.12

3,378

—

1,669

Set gill net:

Yakutat

476

52,930

—

58,223

—

.82

1,632

—

150

Prince Wm Sound

119

52,930

—

58,223

—

.68

3,540

—

Cook Inlet

1,508

2,930

—

8,223

—

.71

3,874

002

686

Kodiak

459

2,590

—

8,139

—

.83

1,511

.050

183

Peninsula-

Aleutians

226

1,485

—

4,317

—

.48

318

—

Bristol Bay

1,248

1,021

—

1,758

—

.78

473

—

803

Power troll:

Statewide

5,290

3,580

.272

33,002

.36

.88

3,439

.026

895

1 Computed from landing records of the Alaska Department of Fish and Game for the years 1 969-73 Adjusted by Wholesale Price Index using 1 973 as a base year,
information gathered from a cost survey of Alaskan fishermen (Source: Owers 1974).

3Computed from landing records and license files of the Alaska Department of Fish and Game for the years 1969-72.

■•Information gathered from a random sample of gear license holders. Reported from Internal Revenue Service in confidential format that did not reveal individual
identities.
5No reliable data. Data from Cook Inlet used as an approximation.

exvessel revenue paid to crewmembers, exclusive
of the entry permit holder; and C is expenses per
vessel.

To estimate net returns to the entry permit hold-
er, including the opportunity cost of capital, the
following equation was used:

N2 = Nt - A • B • I ■ (1 - F) - 2 ■ JVX ■ B (3)

where N2 is the net return less opportunity capital
costs; A is a constant term used to deflate the
average value of investment; B is a constant used
for the opportunity cost of capital; / is the average
total value of investment per operating unit in the
fishery as estimated by fishermen; and F is the
percent of income received in other fisheries.

Finally, to estimate the entry permit holder's
total annual income from all sources, the following
equation was used:

Y = N, + X + O

(4)

where Y is total annual income; X is net earnings
from other fisheries; and O is income earned from
employment other than commercial fishing.

All these equations provide an estimate of the
average rate of return per entry permit holder or
operating unit in a particular fishery. Analysis of
fish landings indicates that a large number of
fishermen participate only a short period out of the
total fishing time available. A study of returns in
Alaska's fisheries shows there is evidence that the
time an operator spends fishing is correlated with
profit (Smith et al. see footnote 5). Therefore, the
average rate of return discussed here is assumed
to be the potential earnings of a fisherman who
participates during the entire season in that par-
ticular fishery but, it is still likely that there will
be some concentration of landings by top pro-
ducers.

A further simplifying assumption in these equa-
tions is that the resource will be harvested at the
same level of output with all the various numbers
of operating units considered. Preliminary esti-
mates provided by management biologists of the
Alaska Department of Fish and Game indicate
that the magnitude of cutbacks described in this
paper would not affect the ability of the salmon
fishing fleet to harvest at the maximum sustain-
able yield level (Jackman et al. 1973).

485

FISHERY BULLETIN: VOL. 75, NO.3

Base Period for Determining
Total Exvessel Revenue

In the salmon fisheries total revenue fluctuates
widely from year to year depending upon the size
of the salmon runs and the price paid fishermen. In
the analysis, the 5-yr period from 1969 to 1973 was
used as the base period for determining the total
revenue produced by the state's salmon fisheries.
This period was used because it appears to be the
most recent, reasonably representative period for
which good data exist. The total catch value was
adjusted for each year by the wholesale price index
using 1973 as a base year.

It was assumed in estimating the total revenue
produced by each fishery that regulatory decisions
would seek to maintain an historical allocation
among gear types. If a reduction in the size of the
southeast drift gill net fleet were to occur, for
example, it is assumed that no attempt would be
made to reduce the percentage of the total catch
available to this fishery. It was also assumed that
gear reductions in one fishery would not be made
without considering the effect on catches by other
fisheries utilizing the same stock. For example, a
large reduction in the Cook Inlet drift gill net
fishery could lead to increased catches in the set
gill net fishery if it is not reduced in some reason-
able proportion.

Fixed and Variable Costs

Fishing costs include such standard items as
fuel, food, repairs, moorage, administrative costs,
and so forth. Average costs in each fishery were
collected by means of a survey in spring 1974
(Owers 1974). For vessels fishing in several
fisheries, costs were prorated among each fishery
based upon the length of time fished and percent of
total earnings received. Other items were specif-
ically allocated, such as gear repairs.

Because there is presently so much excess
capacity in the harvesting segment of the Alaska
salmon fishery, it was assumed that the total cost
of harvesting the resource was a linear function of
the number of boats in the fishery. This logic is
used in Equations (2), (3), and (4). While this
might appear to be inconsistent with economic
theory because fish production would be increased
for each operating unit without increasing any
factor of production, in reality it is likely that costs
would decrease even faster than the number of
operating units leaving the fishery. This is be-

cause overcrowding in the salmon fisheries in-
volves frequent delays in setting nets and tangled
gear, and forces operators to travel long distances
to make all openings. Should substantial reduc-
tions take place in a fishery, consideration of in-
creasing costs per boat would be necessary.

Depreciation has been standardized for all ves-
sels to a 30-yr straight line writeoff with no sal-
vage value. Depreciation for set net sites is
standardized with a 10-yr writeoff since most
equipment includes small skiffs and outboard
motors with a shorter useful life span.

Labor Costs

Labor costs in the fisheries are determined by a
share system and fluctuate directly in proportion
to gross earnings. Crew shares are ordinarily
computed before bonus payments are made to the
boat operator. In the analysis, it was assumed that
the entire bonus was kept by the entry permit
holder, which is the logic used in Equation (2).
Labor costs, as used here, do not include a return to
the entry permit holder's own labor.

Capital Costs

The opportunity cost of capital is assumed to be
10% and is the constant value used in Equation
(3). The estimated market value of each operating
unit was used in determining capital investment
in the fishing business. Average market values of
vessels, equipment, and fishing gear were derived
for each fishery by survey. It was found in surveys
conducted by the British Columbia License Con-
trol Program that the true market value of vessels
averaged about 84% of the estimated value
supplied by fishermen (Campbell6). In this
analysis it was assumed that the market value of
investment was 85% of the value estimated by
fishermen in the survey. This is the constant value
used in Equation (3) to deflate the estimated value
of investment.

In addition to vessels and gear, the capital in-
vestment in the freely transferable entry permit
was included in estimating total capital costs.
Theoretically the permit value might be calcu-
lated by discounting future cash flows or some

6Campbell, B. A. 1973. A review of the development of the
buy-back program and its impact on the salmon fishery. Fish.
Serv., Vancouver, B.C., 54 p.

486

OWERS: INCOME ESTIMATES AND RETURNS IN SALMON FISHERIES

other method of determining future benefits. The
problem with this approach is that it involves
making implicit assumptions about the worth of
the operator's own contribution of labor and man-
agement and deducting this as an expense. As an
approximation of permit value, it was assumed
that the permit value would equal 2 years' net
earnings for those remaining in the fishery, but
further research is needed to determine actual
values and the relationship between price and
productivity. A preliminary survey of permit val-
ues after 6 mo of limited entry indicates permits
may not be worth as much as the values used here
(Anonymous 1975). Using the above relationship
in Equation (3), however, the permit value will
increase as the number of permits is reduced and
capital costs per boat will rise.

Outside Earnings

Outside earnings come principally from two
sources: earnings in other fisheries and earnings
from nonfishing employment. Information on av-
erage earnings from outside employment for a
randomly selected sample of gear operators who
fished in 1971 and 1972 was provided by the Inter-
nal Revenue Service in a format which did not
disclose individual identities (Anonymous7).

Data on earnings from other fisheries were ex-
trapolated from fish price data, landing statistics,
and by survey. It was assumed in the analysis that
outside earnings in other fisheries would not be
affected by limited entry and would remain con-
stant, except in those instances where other
fisheries produced a net loss. In those cases it was
assumed that a fisherman would break even in
other fisheries and the value of net earnings from
other fisheries would be zero.

No data have been collected to determine how
much gear operators may have earned as crew-
members in other fisheries, but it is not likely that
this is a substantial amount since a fisherman
responsible for a vessel in one fishery is most likely
the operator in other fisheries as well. No reliable
data has been collected on incomes of spouses,
investment earnings, transfer payments, and pen-
sions, so no estimates were included.

Fraction of Permits Issued
That Are Used

Because there is no requirement that a fisher-
man use his entry permit every fishing season, it
can be expected that not all outstanding permits
will be fished.

In the analysis, the fraction of gear licenses sold
to gear licenses fished during the period from 1969
to 1972 was taken as the fraction of entry permits
that would be used. It will be important to monitor
actual rates of participation from year to year to
establish more meaningful figures.

Examples of Estimates

Using the equations and input data discussed
above, tables similar to that shown in Table 2 for
the southeast Alaska purse seine fishery were
prepared for all those salmon fisheries which had
entry limited in 1974. In each fishery, returns
were first calculated using the present number of
entry permits issued in that fishery. Returns were
then calculated for a hypothetical reduction in the
number of outstanding permits by 5% increments
of the total number issued. No calculations were
prepared for greater than a 45% reduction in per-
mits because many of the assumptions discussed
above would probably no longer prove correct.
Table 3 shows the four estimates of returns with
the present number of entry permits in each of the
fisheries considered.

OPERATING UNITS NECESSARY TO
ACHIEVE REASONABLE RETURNS

Once expected returns with various numbers of

TABLE 2. — Expected returns in the southeast purse seine fishery
with the present number of entry permits and reductions in the
number by 5% increments. No estimates have been made for
greater than a 45% reduction in the number of entry permits.
Similar data was prepared for all those fisheries which had entry
limited in 1974.

'Anonymous. 1975. Data collection and analysis necessary to
limit entry in Alaska's salmon fisheries. U.S. Dep. Commer.,
NOAA, Natl. Mar. Fish. Serv., contract 03-4-208-262, Juneau,
75 p.

Number

Expected

Net earnings

Total annual

gross

Net

less interest

income from

permits

earnings

at 10%

all sources

395

$33,933

$ 9,468

$ 3,388

$21,013

375

35,719

10,507

4,219

22,052

356

37,703

11.662

5,143

23,207

336

39,921

12,953

6.175

24,498

316

42,416

14,405

7,337

25,950

296

45,244

16,050

8,653

27,595

277

48,475

17,931

10,158

29,476

257

52,204

20,101

1 1 ,894

31,646

237

56,555

22,632

13,919

34,177

217

61,696

25,624

16,313

37,169

487

FISHERY BULLETIN: VOL. 75, NO.3

TABLE 3. — Estimated earnings per operating unit by fishery with the present number of entry permits.

Fishery

Net return per entry Net return per entry

permit holder with no permit holder with Total annual income

Gross allowance for opportunity capital from all sources per

return capital costs cost of 10% entry permit holder

Purse seine:

Southeastern

Prince Wm Sound

Cook Inlet

Kodiak

Chignik

Peninsula-Aleutians
Drift gill net:

Southeastern

Prince Wm Sound

Cook Inlet

Peninsula-Aleutians

Bristol Bay
Set gill net:

Yakutat

Prince Wm Sound

Cook Inlet

Kodiak

Peninsula-Aleutians

Bristol Bay
Power troll:

Statewide

$33,933

$9,468

$3,388

$21,013

20,702

5,582

2,143

10,726

1 1 ,303

1,056

-958

8,006

18,096

5,655

2,365

10,340

34,939

10,683

3,925

12,690

18,515

10,593

7,337

23,357

14,346

9.019

5,177

15,614

7,770

2,894

1,291

5,679

6,298

2,477

905

5,567

1 1 ,862

6,990

4,039

10,086

9,821

4,210

2,504

7,588

3.870

940

2,572

5,469

2,539

1,332

6,079

3,102

172

-561

4,046

3,173

583

-225

2,094

6,115

4,630

3,337

4,948

1,993

972

628

1,445

6,820

1,432

-650

4,873

operating units have been estimated, it is possible
to compare these figures with similar data from
other sectors of the economy. This provides some
indication of the magnitude of cutbacks in fleet
size that may be necessary to achieve similar earn-
ings in the fisheries.

Comparison With Wages
Earned in a Similar Industry

As a minimum, the average rate of return
should be sufficient to cover all normal operating
expenses, labor costs besides those of the operator,
depreciation, and a minimum return on invest-
ment of about 10%. An amount less than this indi-
cates that the average return to the operator's
labor is actually zero or less than zero. As Table 3
shows, with the present number of operating
units, returns in the Cook Inlet and Kodiak set net
fisheries, the Cook Inlet purse seine fishery, and
the power troll fishery are not adequate. In these
four fisheries, returns under this assumption were
negative.

It is reasonable to expect, however, that the
fisheries should provide some wage for the
operator's physical labor and ability to work with
mechanical equipment under hazardous working
conditions. The contract construction industry is
similar to the fisheries in this respect, as well as
the fact that work is highly seasonal and charac-
terized by long periods of unemployment. The
comparison used here assumes that a fisherman
should earn a wage equal to that of a worker in the

contract construction industry during the time he
is actually fishing.

The time spent in each fishery was derived by an
examination of the dates of fish landings. The
number of weeks shown in Table 3 represents the
typical maximum length of the season between
1969 and 1972. It is recognized that not all boats
fish every opening in a season, but these figures
also make no allowance for the time spent prepar-
ing vessels and gear, travelling to the fishing
grounds prior to the season, or time spent storing
and repairing gear at the close of the season. For
this reason the figures are probably somewhat
conservative. Prior to the construction boom
created by the Alaska pipeline, the 1973 average
weekly earnings of workers in the contract con-
struction industry in Alaska was $378 per week
(Anonymous 1973b). Table 4 shows the average
wage earned in the construction industry in a
period of time equal to the length of the fishing
season. This is compared with the number of
operating units that would provide an equal rate
of return to the fisherman; which can then be com-
pared to the number of operating units now
licensed.

None of the large set net fisheries or the power
troll fishery are capable of earning a comparable
rate of return with even a 45% reduction of entry
permits. The southeast and peninsula drift gill net
fisheries would require some reduction and the
other drift gill net fisheries including Bristol Bay,
Cook Inlet, and Prince William Sound would re-
quire substantial reductions. The purse seine

488

OWERS: INCOME ESTIMATES AND RETURNS IN SALMON FISHERIES

TABLE 4. — Number of permits required to produce reasonable returns assuming earnings from fishery
considered are equal to wages paid in an equal time period in contract construction. The average wage in
contract construction in 1973 was $378 per week.

Average wage paid in

No. of permits

Length of fishing

equal time period in

that would provide

Present no

Fishery

season (weeks)

contract construction

an equal return

of permits

Purse seine:

Southeastern

$5,292

356

395

Prince Wm Sound

3,780

202

238

Cook Inlet

3,780

'37

Kodiak

4,536

258

368

Chignik

4,536

Peninsula-Aleutians

4,536

2111

111

Drift gill net:

Southeastern

8,316

362

453

Prince Wm Sound

7,182

'281

511

Cook Inlet

3,402

327

545

Peninsula-Aleutians

4,914

147

155

Bristol Bay

4,158

1,252

1,669

Set gill net:

Yakutat

6,426

'83

150

Prince Wm Sound

3,402

Cook Inlet

5,670

'377

686

Kodiak

4,536

'101

183

Peninsula-Aleutians

5,292

Bristol Bay

3,402

'442

803

Power troll:

Statewide

8,692

'492

895

'Reasonable returns cannot be achieved with a 45% reduction in entry permits.
Reasonable returns can be achieved with the present number of entry permits

fisheries, with the exception of Cook Inlet, are
capable of providing a comparable rate of return
with either the present maximum number or a
modest reduction.

Comparison With Total Annual Earnings
of Nonfarm Workers

An equally important objective of limited entry
may be to bring the total income of fishermen up to
levels comparable to the average earned by all
workers in Alaska. It has been tacitly accepted
that earnings in the fisheries, particularly in
areas where few other employment opportunities
exist, can be lower than in other segments of the
State's economy. The continuation of this policy in
the future probably makes little sense. As Alas-
ka's economy develops, a more reasonable ap-
proach is to provide vocational training to resi-
dents of the State in areas of traditionally high
unemployment so they can find employment in
other sectors of the economy. If this approach is not
adopted, it can be expected that job openings in the
future will continue to be filled by trained persons
from outside the State. In achieving increased in-
comes from the fisheries it should also be pointed
out that a reduction in entry permits under the
Alaska law will be achieved through a voluntary
buy back of permits and vessels spread over as
many as 10 yr. Thus, older persons in the fisheries
that would have trouble finding other employment

need not be displaced. Furthermore, a person who
voluntarily sells to a buy-back program will re-
ceive a cash settlement that will ease the transi-
tion period.

A comparison can be made with the average
incomes earned in other employment in Alaska.
Estimates of total income include income from
other fisheries and nonfishing employment. Be-
cause of the seasonal nature of salmon fishing, it is
anticipated that many permit holders will con-
tinue to seek other employment when it is avail-
able.

Statistics collected by the Alaska Department of
Labor show that average nonagricultural wage
and salary earnings in 1973 were $l,006/mo, or
$12,072/yr (Anonymous 1973b). Table 5 compares
the number of operating units in each fishery that
would be required to provide fishermen with a
level of earnings equal to the state average. It is
assumed that any increase in earnings will come
from the particular fishery being examined.

With the exception of the small Prince William
Sound set net fishery, none of the set net fisheries,
the Cook Inlet and Prince William Sound drift gill
net fisheries, or the power troll fishery could pro-
vide this level of income with even a 45% reduction
of entry permits. The purse seine fisheries, with
the exception of Cook Inlet, and the southeastern
and peninsula drift gill net fisheries would provide
a reasonable income with either the present
number of operating units or a modest reduction.

489

FISHERY BULLETIN: VOL. 75, NO.3

TABLE 5. — Number of permits required to produce reasonable
returns assuming the total annual income from all sources of
fishermen is equal to the average earnings of nonfarm wage and
salaried workers in Alaska in 1973. Nonfarm wage and salaried
workers earned $12,072 in 1973.

Fishery

No. of permits required

to provide total annual

income of $12,072

Present no
of permits

Purse seine:

Southeastern

1395

Prince Wm Sound

'214

Cook Inlet

Kodiak

313

Chignik

180

Peninsula-Aleutians

'111

Drift gill net:

Southeastern

'453

Prince Wm Sound

2281

Cook Inlet

2300

Peninsula-Aleutians

132

Bristol Bay

918

Set gill net:

Yakutat

283

Prince Wm Sound

Cook Inlet

2377

Kodiak

2101

Peninsula-Aleutians

242

Bristol Bay

2442

Power troll:

Statewide

2492

395
238

68
368

80
111

453
511
545
155
1,669

150
32

686

183
77

803

895

'Reasonable returns can be achieved with the present number of entry
permits.

Reasonable returns cannot be achieved with a 45% reduction in entry
permits.

Comparison With Estimates Provided
by Fishermen

In addition to the two measures discussed so far,
as part of a survey fishermen were asked to esti-
mate what they needed to gross from fishing in a
particular year in order to earn a reasonable re-
turn (Owers 1974). In Table 6 the mean value of
responses for each fishery is shown with the cor-
responding number of entry permits that would
yield an equal level of gross earnings.

In the power troll fishery, all the set gill net
fisheries with the exception of the Alaska Penin-
sula, the drift gill net fisheries in Prince William
Sound and Cook Inlet, and the Cook Inlet purse
seine fishery, it would not be possible to earn a
level of earnings considered reasonable by fisher-
men with even a 45% reduction in entry permits.

Several other fisheries would need some reduc-
tion in the amount of gear. The purse seine
fisheries in southeastern, Chignik, and the Alaska
Peninsula appear capable of earning a reasonable
return with either the present number of entry
permits or a slight reduction.

SUMMARY BY FISHERY OF
THE COMPARISONS USED

TABLE 6. — Number of permits required to produce reasonable
returns assuming expected gross earnings equal necessary gross
earnings as estimated by fishermen.

No. of permits

required to
provide equal Present
level of no of

Fishery (thousands) earnings permits

Reasonable gross

return estimated

by fishermen

(thousands)

Purse seine:

Southeastern

Prince Wm Sound

Cook Inlet

Kodiak

Chignik

Peninsula-Aleutians
Drift gill net:

Southeastern

Prince Wm Sound

Cook Inlet

Peninsula-Aleutians

Bristol Bay
Set gill net:

Yakutat

Prince Wm Sound

Cook Inlet

Kodiak

Peninsula-Aleutians

Bristol Bay
Power troll:

Statewide

$31.9
26.9
24.2
32.8
39.5
12.2

22.6
19.6
14.5
17.9
16.4

14.9

14.9
14.9
11.1
7.8
12.4

15.3

'395

395

178

238

237

202

368

'111

111

294

453

2281

511

2300

545

101

155

1,001

1,669

283

150

218

2377

686

2101

183

2442

803

2492

895

'Reasonable returns can be achieved with the present number of entry
permits.

Reasonable returns cannot be achieved with a 45% reduction in entry
permits.

parisons used provide an estimate of the optimum
number of entry permits that falls within a fairly
narrow range. The following summarizes the
economic performance by type of fishery.

Purse Seine

Purse seining in general appears to be the most
economically viable of the four types of salmon
gear fished. This is due in part to the fact that
purse seiners are used in a variety of fisheries,
which allows overhead expenses to be spread, and
minimizes risks in any one fishery. As can be seen
in Table 1, this is particularly true of the purse
seine fisheries in the Alaska Peninsula and south-
eastern Alaska where a substantial percentage of
gross earnings comes from other fisheries. The
Prince William Sound and Kodiak purse seine
fisheries could justify a modest reduction, al-
though income levels would be only slightly re-
duced with the present maximum number. The
Cook Inlet purse seine fishery, which is restricted
to a hand purse seine fishery, does not appear able
to provide a reasonable return with the present
number of entry permits under any of the criteria.

Drift Gill Net

It will be noticed in Table 7 that the three com-
490

Unlike the purse seine fishery, the typical vessel

OWERS: INCOME ESTIMATES AND RETURNS IN SALMON FISHERIES

TABLE 7. — Number of entry permits required to produce reasonable earnings — summary of three

measures.

Return to gear

Total

annual income

operator equal to

gear operator equal

Reasonable

Present

average wage in

annual

income of noni

:arm

earnings estimated
by fishermen

no of

Fishery

contract construction

wage and salaried workers

permits

Purse seine:

Southeastern

356

'395

395

Prince Wm Sound

202

214

178

238

Cook Inlet

237

Kodiak

258

313

202

368

Chignik

'80

Peninsula-Aleutians

'111

1111

111

Drift gill net:

Southeastern

362

M53

294

453

Prince Wm Sound

2281

511

Cook Inlet

327

2300

545

Peninsula-Aleutians

147

132

101

155

Bristol Bay

1,252

918

1,001

1,669

Set gill net:

Yakutat

283

150

Prince Wm Sound

218

Cook Inlet

2377

686

Kodiak

2101

183

Peninsula-Aleutians

242

Bristol Bay

2442

803

Power troll:

Statewide

1492

2492

895

'Reasonable returns can be achieved with the present number of entry permits.
Reasonable returns cannot be achieved with a 45% reduction in entry permits.

used in the drift gill net fisheries is not generally
used in other fisheries besides salmon. In the
southeast drift gill net fishery the present level of
income appears adequate. All measures indicate
that the Prince William Sound and the Cook Inlet
drift gill net fisheries require a reduction in the
number of entry permits. With a 45% reduction,
total income and a reasonable gross income as
estimated by fishermen cannot be achieved.

The Alaska Peninsula drift gill net fishery
would require a reduction under all three mea-
sures examined, although substantial reductions
are not required.

The Bristol Bay drift net fishery would also re-
quire a gear reduction under all of the criteria
examined.

Set Gill Net

Returns in all of the set net fisheries are ex-
tremely low. The Kodiak and Cook Inlet set net
fisheries cannot provide a rate of return sufficient
to cover operating and capital costs. All the mea-
sures discussed indicate a 45% reduction or more.
The other set net fisheries in the State would re-
quire substantial reductions in the number of
entry permits.

Other data collected indicate that the set net
fisheries have a rapid rate of license turnover from
year to year, a high percentage of casual fishermen
who participate only a few weeks out of the season,

and many fishermen with low income dependence
on commercial fishing (Owers 1975).

Power Troll

Returns in the power troll fishery appear in-
adequate to cover any of the measures discussed
with a 45% reduction in permits. The fishery again
cannot provide a rate of return sufficient to cover
all expenses.

The power troll fishery is similar to the set net
fisheries in that there is a large license turnover
from year to year, and fishermen show relatively
little dependence on commercial fishing for a
source of income.

CONCLUSION

In many salmon fisheries it appears that re-
stricting or reducing the number of operating
units will enable earnings to rise to levels compar-
able to that earned in other sectors of Alaska's
economy. This is probably not a practical objective
in other fisheries, however, particularly the set
net fisheries and the power troll fishery. This does
not imply that limited entry is not necessary in
these fisheries. Limited entry is still a desirable
policy for management reasons and the fact that
reducing or stabilizing the number of operating
units in other fisheries in the same area could

491

FISHERY BULLETIN: VOL. 75, NO.3

result in increased catches by these fisheries if
they are not limited.

Rather, the problem that must be faced is one of
resource allocation. If a commercial fishery cannot
be made a viable economic enterprise, the public
interest to be served by allowing it to exist at all
must be carefully examined. This is particularly
relevant in such areas as Cook Inlet and south-
eastern Alaska where sport fishing is in many
cases in direct competition with the commercial
fisheries for a share of the resource. The fisheries
are a valuable asset that belong to all the people of
a state and allocation decisions must be made with
this in mind.

LITERATURE CITED

ANONYMOUS.

1973a. Session laws of Alaska, Chapter 79. State of Alaska,
Juneau, 13 p.

1973b. Statistical quarterly, 4th quarter 1973. Alaska Dep.

Labor, Juneau, 38 p.
1975. Entry permit price survey. Commer. Fish. Entry

Comm., Juneau, 8 p.

CRUTCHFIELD, J. A., AND G. PONTECORVO.

1969. The Pacific salmon fishery: A study of irrational con-
servation. Johns Hopkins Press, Baltimore, 220 p.

JACKMAN, D. S., A. ADASIAK, R. A. RICKEY, R. F. LlSTOWSKI,

J. Brakel, and R. L. Schubert.

1973. A limited entry program for Alaska's fisheries. State
of Alaska, Juneau, 345 p.

OWERS, J. E.

1974. Costs and earnings of Alaskan fishing vessels — an
economic survey. Commer. Fish. Entry Comm., Juneau,
40 p.

1975. An empirical study of limited entry in Alaska's
salmon fisheries. Mar. Fish. Rev. 37(7):22-25.

Sinclair, S.

1960. License limitation — British Columbia: A method of
economic fisheries management. Dep. Fish., Ottawa,
256 p.

492

ABUNDANCE AND POTENTIAL YIELD OF THE ATLANTIC THREAD

HERRING, OPISTHONEMA OGLINUM, AND ASPECTS OF

ITS EARLY LIFE HISTORY IN THE EASTERN GULF OF MEXICO1

Edward D. Houde2

ABSTRACT

Eggs and larvae of the Atlantic thread herring, Opisthonema oglinum, were collected in plankton
surveys from 1971 to 1974 in the eastern Gulf of Mexico to determine spawning seasons, spawning
areas, adult biomass, and potential yield to a fishery. Aspects of the early life history also were studied.
Spawning occurred from February to September, but mostly from April through August, when surface
temperatures were 22.5° to 30.3°C and surface salinities ranged from 32.4 to 36.8%o. Most spawning
took place from the coastline out to the 30-m depth contour, and virtually all spawning occurred where
depths were less than 50 m. The area of heaviest spawning was between latitudes 26°00'N and 28°00'N.
The most reliable estimates of adult biomass were approximately 110,000 metric tons in 1971 and
370,000 metric tons in 1973. The most probable estimates of potential annual yield range from 60,300
to 120,600 metric tons. Based on the best larval mortality estimates, more than 99% mortality occurred
from time of spawning until 19 days and 15.5 mm standard length in 1973, and approximately 98%
mortality occurred for the same period in 1971.

The Atlantic thread herring, Opisthonema og-
linum (Lesueur), is an underexploited clupeid fish
that occurs widely in the western Atlantic from
southern Brazil to the Gulf of Maine (Berry and
Barrett 1963), but is mainly tropical and sub-
tropical in its distribution (Hildebrand 1963). It is
a coastal species that seldom occurs in depths
greater than 90 m and is most abundant in depths
less than 35 m (Klima 1971 ). In the Gulf of Mexico
it is abundant and its fishery potential has been
recognized for many years (Butler 1961; Reintjes
and June 1961; Bullis and Carpenter 1968; Fusset
al. 1969; Houde 1973a). The total western Atlantic
thread herring catch was 12,016 metric tons in
1974 (Food and Agriculture Organization 1975), of
which 2,434 metric tons were landed by the United
States. Some thread herring are landed as inci-
dental catches by both Atlantic and Gulf of Mexico
menhaden fleets (Klima 1971). Catch statistics
are poor for thread herring in the Gulf of Mexico,
but only 435 tons were reported in 1973 (Johnson
1974). However, 5,000 tons were landed from the
eastern Gulf during a 4-mo period in 1967 when a
preliminary attempt was made to establish a di-
rected fishery. Based on school sightings and catch

'This is a contribution from the Rosenstiel School of Marine
and Atmospheric Science, University of Miami, Miami, Fla.

2Division of Biology and Living Resources, Rosenstiel School
of Marine and Atmospheric Science, University of Miami, 4600
Rickenbacker Causeway, Miami, FL 33149.

rates by commercial purse seiners, Bullis and
Thompson ( 1 967 ) roughly estimated that the total
Gulf of Mexico thread herring stock might be 1 x
106 tons.

Eggs and larvae of thread herring have been
described (Richards et al. 1974) and the species
has been successfully reared from egg to juvenile
under laboratory conditions (Richards and Palko
1969). There was no information on thread her-
ring eggs or larvae from the eastern Gulf prior to
my research. Kinnear and Fuss (1971) reported
seasonal north-south migrations and distribution
of thread herring in the eastern Gulf of Mexico,
while Fuss et al. (1969) presented data on age,
growth, maturity, and food habits of that stock.
Fecundity of thread herring in the eastern Gulf
was determined by Prest3 and by Martinez (1972)
for fish collected on the Florida Atlantic coast.

The objective of this research was to obtain a
fishery-independent estimate of the abundance
and potential yield to fisheries of thread herring in
the eastern Gulf of Mexico based on annual sur-
veys of eggs and larvae during 1971 to 1974. In
addition, information was obtained on spawning
seasons and areas, as well as on aspects of their
early life history in the eastern Gulf.

Manuscript accepted November 1976.
FISHERY BULLETIN: VOL. 75, NO. 3, 1977.

3Prest, K. W., Jr. 1971. Fundamentals of sexual maturation,
spawning, and fecundity of thread herring (Opisthonema og-
linum) in the eastern Gulf of Mexico. Unpubl. manuscr., Natl.
Mar. Fish. Serv., NOAA, St. Petersburg Beach, Fla.

493

FISHERY BULLETIN: VOL. 75. NO. 3

METHODS

Adult biomass was determined from estimates
of annual abundance of spawning products, a
knowledge of the mean relative fecundity of
thread herring, and an assumed sex ratio of 1:1
(Saville 1964; Ahlstrom 1968). Methods to deter-
mine thread herring egg and larval abundance,
distribution, adult biomass, potential yield to a
fishery, and mortality during egg and larval
stages were analogous to methods reported in de-
tail for round herring (Houde 1977a). Other de-
tails of survey design and planning also have been
published (Rinkel 1974; Houde and Chitty 1976;
Houde et al. 1976). Temperature and salinity data,
as well as some egg and larvae data, from these
surveys are stored in the National Oceanographic
Data Center, Washington, D.C., under the
MAFLA file.

The survey area was located on the broad conti-
nental shelf off western Florida in the eastern Gulf
of Mexico, between lat. 24°45'N and 30°00'N (Fig-
ure 1). In 17 cruises (Table 1) from 1971 to 1974,
plankton was collected with a 61 -cm bongo net
sampler fitted with 505- and 333-fMm mesh nets.
Most stations were over water depths from 10 to
200 m, except in 1974 when some stations as shal-
low as 5 m were added to the sampling plan. These
shallow stations were added to determine if thread
herring and scaled sardine, Harengula jaguana,
spawning increased significantly nearshore where
there had been no previous sampling. Thread her-

k-^-^

30'

28'

26°

24'

200m

86°

84°

82°

80°

FIGURE l.— Area encompassed by the 1971-74 eastern Gulf of
Mexico ichthyoplankton surveys. Plus symbols ( + ) represent
stations that were sampled during the survey. The 10-, 30-, 50-,
and 200-m depth contours are indicated.

ring eggs and larvae were identified using descrip-
tions by Houde and Fore (1973) and by Richards et
al. (1974).

Egg and larval abundances at stations in the
cruise area, over the time period represented by a
cruise, and on an annual basis, were estimated
using techniques similar to those outlined by Sette
and Ahlstrom (1948), reviewed by Saville (1964),
and most recently discussed by Smith and

TABLE 1. — Summarized data on cruises to the eastern Gulf of Mexico, 1971-74, to estimate abundance of thread herring eggs and
larvae. GE = RV Gerda, 8C = RV Dan Braman, TI = Tursiops, 8B = RV Bellows, IS = RV Columbus Iselin, CL = RV Calanus.

Cruise

Dates

Number

of
stations

Positive
stations
for eggs1

Positive

stations

for larvae2

Mean egg abundance under 1 0 m2 Mean larvae abundance under 1 0 m2
All stations Positive stations All stations Positive stations

GE71013
8C7113

TI7114
GE7117
8C7120

TI7121
TI7131

8B7132

GE7127
8B7201

GE7202
GE7208
GE7210
IS7205
IS7209
IS7303
IS7308
IS7311
IS7313
IS7320
CL7405
CL7412

1-8 Feb. 1971

7-18 May 1971

123

26 June-4 July 1971

7-25 Aug. 1971

146

7-16 Nov. 1971

1-11 Feb. 1972

1-10 May 1972

12-18 June 1972

9-17 Sept. 1972

8-16 Nov. 1972

19-27 Jan. 1973

9-17 May 1973

27 June-6 July 1973

3-13 Aug. 1973

6-14 Nov. 1973

28 Feb-9 Mar. 1974

1-9 May 1974

0
4
2
0
0
0
4

12
0
0
0

47
13

0.00

28.42
0.85

0.72

0.00

7.98

2.11

0.00

60.53

28.28

0.00

13.98

276.82
14.39

42.46

75.92
17.09

999.46
137.98

75.53

0.00

27.67
17.48

11.02

0.00

52.63
51.87

79.91

0.00

—

13.61

36.08

172.28

228.36

1.04

13.78

0.00

—

0.00

—

34.73

101.19

68.74

229.37

6.10

40.24

0.00

—

0.31

2.43

30.80

57.56

'Positive station is a station at which thread herring eggs were collected.

2Positive station is a station at which thread herring larvae were collected.

3An IOTA 1-m plankton net was used on this cruise. On all other cruises a 61 -cm bongo net was used.

494

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF THREAD HERRING

Richardson (in press). Variance estimates on
cruise and on annual egg abundance estimates
were calculated by methods used by Cushing
(1957) and Taft (1960). Houde (1977a) has given
detailed procedures, including estimating for-
mulae, that were used to obtain abundance esti-
mates of clupeid eggs and larvae in eastern Gulf of
Mexico surveys.

Two methods were used to estimate adult
biomass, based on two different procedures for de-
termining annual spawning by thread herring.
The first procedure is that given by Sette and
Ahlstrom (1948). The estimate of annual spawn-
ing depends on integrating station and cruise es-
timates over area and time. The second procedure
is based on a modification of Simpson's (1959)
method in which annual spawning is estimated by
plotting the daily spawning estimates for each
cruise against the middate of the cruise and then
determining the area under the resulting polygon
by planimetry.

Potential Yield to a Fishery

Houde (1977a) used the estimator suggested by
Alverson and Pereyra (1969) and Gulland (1971,
1972) to predict potential yield of round herring in
the eastern Gulf. The same procedure was used for
thread herring. The estimating formula is Cmax =
XMB0 where X is assumed to equal 0.5, M is the
natural mortality coefficient, and Bo is the virgin
biomass. My biomass estimates are estimates ofB0
since the thread herring stock is virtually
unfished in the eastern Gulf. Because no estimate
of M exists for thread herring, the potential an-
nual yield was predicted using a range of probable
values of the mortality coefficient.

Larval Abundance and Mortality

Mortality estimates were determined for larvae
by length and by estimated ages. The exponential
decrease in abundance of 1-mm length classes was
used to calculate mortality coefficients to describe
the decline in catches by length. Growth was as-
sumed to be exponential during the larval phase.
Based on this assumption and information on
laboratory growth rates for thread herring larvae,
ages of larvae in 1-mm length classes were esti-
mated. Mortality coefficients were then estimated
from the decline in abundance of larvae in relation
to estimated age. Houde (1977a) gave estimating
formulae and discussed the rationale for his pro-

cedures, which are similar to those used previ-
ously by Ahlstrom (1954) and Nakai and Hattori
(1962).

RESULTS AND DISCUSSION

Occurrence of Eggs and Larvae

Thread herring eggs occurred in 8 of the 17
cruises from 1971 to 1974, and larvae occurred
during 11 of the cruises (Table 1). Eggs were col-
lected on cruises from May through August, al-
though significant spawning may have occurred
during April when no cruises were scheduled.
Some larvae were collected as early as March and
as late as September, but they were most abun-
dant from May through August. No eggs or larvae
were collected from September through January.
Fuss et al. (1969) reported ripe or nearly ripe adult
thread herring from the eastern Gulf in March
through August. My data support their finding
that thread herring spawning is confined to spring
and summer in this area.

Most spawning takes place within 50 km of
shore on the inner continental shelf in depths <30
m, and virtually all spawning occurs within 100
km of shore at depths <50 m (Figure 2). A single
instance of egg occurrence beyond the 50-m depth
contour was recorded (Figure 2). Spawning was
most intense between lat. 26°00'N and 28°00'N,
the area from just south of Fort Myers to Tampa
Bay, Fla. This is the area where an attempt was
made to establish a commercial fishery for thread
herring in the 1960's (Fuss 1968; Fuss et al. 1969).
Kinnear and Fuss (1971) found that thread her-
ring that were concentrated near Fort Myers (lat.
26°00'N) in winter migrated north during warmer
months. My egg distribution data suggest that a
large part of the thread herring population re-
mains within the Fort Myers-Tampa Bay area
throughout the year.

Larval distribution was more widespread than
that of eggs, presumably due to dispersal by water
currents, but was generally similar to egg dis-
tribution (Figure 2). Most larvae were collected
where water depths were <50 m and only six oc-
currences were recorded where depths were >50 m
(Figures 2-6).

Thread herring eggs and larvae were relatively
common in eastern Gulf ichthyoplankton. A total
of 4,236 thread herring eggs were collected during
the 17 cruises, 1.39% of the 304,507 total fish eggs

495

FISHERY BULLETIN: VOL. 75, NO. 3

30* -

28'

26'

30'

26'

1 0 m A\_<i^; ;_.-©_<
30m.-/_" © ©©©'©'
50 m-., V;---. • • • 0,

• "*v • •- ® ® ®'-0-

•\ •-,••©,
200m.. . \ ® >. © © ©©I

•\ • G^© ©,©•;© J

• \ • •', • -X© ©\©[i

•, © Sk; © \© 0©V
'. . . '© ©">© ©\
.'■••. \ .'"0©Yy ~

\. . . '© ©'© ©\J „ vr

• '•,•■• \- 0'©
'; • © •'«• ©•© 0 '
• ; • • -\© ©;© 0 ©•■•
■ • • ■ \ © © • • &

_ . , . • '© • • •' 0 0 © © ©0©

Opisthonama oglinum \ _ j ; T

LARVAE . \. . .; . © © © ©;©

V,--._ ■ ,©•-:' 0 ©_;.-' b,~.

86*

84"

82"

FIGURE 2. — Top. Stations in the survey area where eggs of
thread herring were collected at least once during 1971-74.
Stations where eggs did not occur are indicated by dots. Bottom.
Stations in the survey area where larvae of thread herring were
collected at least once during 1971-74. Stations where larvae did
not occur are indicated by dots.

sorted from 867 samples. Number of thread her-
ring larvae totalled 11,255, 7.87% of the 143,004
total larvae collected throughout the survey.
Thread herring eggs constituted 13.20% of the
total clupeid eggs collected, and thread herring
larvae constituted 39.69% of the clupeid larvae.
Mean abundances of thread herring eggs under
10 m2 of sea surface ranged from 0.00 to 60.53 for
the 17 cruises (Table 1). At positive stations,
cruise means ranged from 14.39 to 999.46 under
10 m2. Most egg abundances at individual stations
were <100 under 10 m2 of sea surface, but abun-

dances ranged from 101 to 1,000 under 10 m2 on
eight occasions and > 1,000 under 10 m2 on four
occasions (Figures 3-6).

Thread herring larvae mean abundances for the
17 cruises ranged from 0.00 to 172.28 under
10 m2 of sea surface (Table 1). At positive stations,
mean cruise abundances ranged from 2.43 to
229.37 under 10 m2. Larval abundances exceeded
1 ,000 under 10 m2 on three occasions ( Figures 3- 6)
and frequently were in the range of 101 to 1,000
under 10 m2. Detailed summaries of station and
cruise data for both larvae and eggs of thread
herring were recently published (Houde et al.
1976).

Spawning intensity appeared to vary within the
observed spawning area. The logio mean egg
abundance under 10 m2 for positive stations from
all cruises was 1.3837 at stations =£30 m deep but
was only 1.2750 at stations >30 m. The means did
not differ significantly U-test, P>0.50). But, the
surface area encompassed by the ^30-m depth
zone was 76.03 x 109m2 as opposed to only 30.69 x
109 m2 in the 30- to 50-m depth zone, beyond which
virtually no spawning was observed (Figure 2).
Most eggs were spawned where depth was <30 m.

There was no evidence that spawning intensity
increased nearer to the coast than measured by
our usual survey stations, based on cruise CL7412
(Figure 6, Table 1), when 12 nearshore stations
were added to the usual stations. Thread herring
eggs were collected at three of the nearshore sta-
tions and at seven of the regular, more offshore
stations (Figure 6) on that cruise. The log10 mean
catch under 10 m2 was higher at the offshore sta-
tions, but due to the small number of stations it did
not differ significantly (P>0.10) from the near-
shore stations' mean:

A^o. of stations
with thread
Stations herring eggs Log10 x Log10 S*

Regular 7 1.5272 0.5064

Nearshore 3 0.5525 0.3101

tca]c = 1.69 *0.05C2,8) = 2.306

Temperature and Salinity Relations

Thread herring eggs were collected where sur-
face temperatures ranged from 22.5° to 30.3°C and
surface salinities from 32.4 to 36.8%<>. From May to
September temperatures from surface to 15 m
were nearly homothermous, but temperatures at
the 30-m depth often differed from the surface by

496

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF THREAD HERRING

8C 7113 * TI 7111

Opisthonema oglinum eggs

May 1971

8C 7113 < TI 7111

Opisthonema oglinum labvae

May 1071

■ " 7 1 /
4 4 + + 4 V

50m-.

4 4 4 4 • \.

\+ ♦• + + + + V
+\+ + + + # \

+ \ 0 *■*■■* * 1
4- \ ****** (

* * *t + + * */

* ♦ i\* * 0 \C

4 + 4- * + + • \

+ + + +. + 4 • \ -»

f + + f + + + Vl

+ + +'.+ + 4 * ^C

+ 4 *>\+ 0+4 1

+ + t\+ + + + V

+ + +\ + + + + + ^

+ ++: + +. + 0#
+ + V + + • + +
■*•+,'• * ■ •

z***"

Number under 10m2
+ 0

• «l

• 1 - 10

• 11-100

• 101 - 1000

® >IOO0

30"

" T-

T ■ 1 7

♦ * * * • V V

SOm-.

+ + f + • v. \
■■.,♦ * + + + • v \

+ **+ + +••/ ffl)

• • • • Y

28°

♦ • *+ • • • * / \

+ ++>» + #• \e \

+ ++\+»#\ /NX.

* + + 4, • • • \_. C J A

+ + ♦ v • • • >lL v/ )

♦ + +\+ « • 0 \

+ 4- +\+ + • 0 V I
* + *\* • + + •^^ ft

i-b"

Number under IOm?
♦ 0

• <l

• 1 - 10

• 11-100

• 101-1000

' i

GE 7117

Opistmonema oglinum eggs

June - Jul* 1971

1 T

1S> \

50 in-..

\ (

+ + v-t + t #«\)7

\ -

.*♦*.. ».\

♦ +♦',•++ + +>

Number under 10m2

* 0

^ /■

• «l

;

• 1 - 10

• n-ioo

• 101-1000

' ♦ ♦ +

8C 7120 8 TI 7121

Opisthonema oglinum eggs

August 1971

30°

+ +

1 1 /

4 4

\^f*<^' \

+ +

+ ♦

450 r

"■"*-. \w*

+ 4

4- \ V

+ 4

4 \ /
+ A 4 + + 4 /

28°

- +

+ +

t 4-4 4', 4 4- + + Hfi\-

4 4 4"^ + + + >J/

4- 44- + >,44- + ^

4-44 4y4 4+\
4- 4 4-4^ 4 # • \^
4-4 4- f 4 4 4 ^J
4- 4- 44-4U-44# ^^

4 M *■*+ 4* f 4 )

k!6°

Number under

I0m

+■ -•- +A 4- 4-4 4 \^
4-4-+->«+4-4 + + *

4 4- 44+', 4-4++ +

•
•
•

l-IO

n-ioo
ioi - IOOC

+ + l*-4-++ + +
+ 4 + 4,' + + 4 4

4- + W ■+ + + £|

~0,**'

>I000

84'

GE 7117

Opisthonema oglinum larvae

June - July 1971

80*

1 r—

50m..

\ I

* * *H • • «»Sj /

V -

...*•• »»\r7

* • «'.* • • • +^

Number under I0m?

t 0

'•

B 1

• <l

;

• l-IO

;

• n-ioo

• IOI - 1000

• • * *

..•*'-''

84°

8C 7120 i TI 7121

Opisthonema oglinum larvae

August 1971

- 4- 4-

4 ^

+ +

4 4I

iw*^^ \

4 4

4 +

+50 mH

4 +

+ -*

*S + )

4 4

4 t

4 A + + + + /

- 4 4

4 4

+ + +*,+ + •# */ft-

+■ *" *\ 4 • • Sj )

4 4- 4 + +% 4 + * \f
+ + +++ *»\
+ + • 4> -li + 4> • V j-
4 + + f 4 + « yj,

*■ 4- + + +'i+ + +# ^C

+ + +■*+ 4 + • \

+ + +»• • + + Sfc

+ + +'>,• + 4- + •

NumDer
4 0

under

10m2

+ + + + +J + ++00

• 1-10

• 11-100

• 101-1000

4- +4--*+#4-»
+ + ++;+•+ +

«---'

FIGURE 3. — Distribution and abundance of thread herring eggs and larvae. Catches are standardized to
numbers under 10 m2 of sea surface A, B. Cruise 8C7113-TI7114, May 1971. C, D. Cruise GE7117,
June-July 1971. E, F. Cruise 8C7120-TI7121, August 1971.

497

FISHERY BULLETIN: VOL. 75, NO. 3

GE 7208

Opisthoneha oglinuh eggs

May 1972

26'

\^~SIS>

50m-.,

\ 4 4 # /

4 4 +

+• \ + + *c

+ 4

+ • -f

Number under 10m2

4 0

4- ■*- 1 + 4-

- T|

• I-IO

• 11-100

• 101-1000

+1 + +■

.■^""'^

1 1

28° -

GE 7208

Opisthoneha oglinum larvae

Hay 1972

l)^J^>

50m-. ,

\ + • • /

+ + +

+■ +

+ \ • •

Number under 10m2

+ 0

• * ; • +

• x. y

• I-IO

• 11-100

*-j • •

• 101-1000

o,^.-^

® >I000

I 1

82°

80°

86°

84°

82°

80°

GE 7210

Opisthoneha oglinum eggs

June 1972

30'

28'

86°

GE 7210

Opisthoneha oglinuh larvae

June 1972

50m-,

4
"\ 4

• \<*

y • \-»
4 + ^i

4 4

' ° 1

Number under 10m2
4 0

• <l

• i-io

• ii-ioo

• ioi-iooo

J -t-

...XT-'

30'

28'

50m-.,

\ -

\ • *\ft

\ 0 •

Number under 10m2

•f C

• <l

; -f

•

« /'

• I-IO

• 11-100

• IOI-IOOO

•

m-^

® >I000

' I

82°

80°

84° 82°

IS 7205

Opisthonema oglinuh larvae

Septehber 1972

80°

FIGURE 4. — Distribution and abundance of thread
herring eggs and larvae. Catches are standardized to
numbers under 10 m2 of sea surface. A, B. Cruise
GE7208, May 1972. C, D. Cruise GE7210, June 1972.
E. Cruise IS7205, September 1972. No eggs were
collected on this cruise.

26'

"1 — -

\s^* \

50m-.^

\ + ♦ • • /

4- \ + + * */^

♦ *\ ♦♦ A

0"]

+ 'i + + 4
♦- f-v 4 4

Number under 10m2

+ 0
• <l

* :♦

4 4

• <? u

• I-IO

• 11-100

• IOI-IOOO

; +

•

,«---

® >I000

86°

82°

498

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF THREAD HERRING

IS 7308
Opisthonema oglinum eggs

Hay 1973

IS 7308

Opisthonema 06linum larvae

May 1973

30° -

28° -

50m-.,

♦

*■ * * * V

\ + • - * 1

* \ + * + */<S-

\ -

* ♦ \ + • + v

* * \ + ♦ «■

Number under 10m2

+ 0
• <l

* * I *

* \ y

• 1 - 10

• n-ioo

• 101 -tooo

+' ♦■

•

.■*--■"

30°

50m-.,

I r

♦ * •V

f ♦ ♦ • \,

s, • • ♦ ♦ /

28°

+ t \ + • • IfJ

♦ \ • • • \ti

- A • • •

2b"

Number under 10m2

* 0

• <l

♦ ♦ • •

•

■I /

• 1 - 10

• 11-100

• 101 - 1000

*l • •

tv—-^

.. i. i

IS 7311

Opisthonema oglinum eggs

June - July 1973

84° 82°

IS 7311

Opisthonema oglinum larvae

June - July 1973

80°

28°

26'

24'

T 1 r

\^^^ S

• * ► * V.

50m-., \^^

N * • - • \-

* *■ \ ♦ +*-•/

* \ * • • *Kv>

\ -

+■ f +■ \ ♦ * + \f

* * \ ••®\rr

' <))

* \ t » • v(

Number under 10m2

*■ *• *■ *-\ -*-+ +

+ 0

Sa /•

• <l

+ + ; * + *

# T (.A

• 1 - 10

• 11-100

• 101-1000

►,' • •

..<*-■'

1 i

I 1

0^^#^^ \

• * * • V

50m-., \-

*-, ♦■ * ♦ ♦ \.

♦ «- "i * ♦ + • /

«■ \ + ♦ • •[ A.

V -

• » \ • ••><;

♦ - \ • • •

- »\ *©

► © \

Number under torn2

- t . *\ •<

+ 0

+ t- J ♦

• • •

s /'

• 1 - 10

• 11-100

*' ♦

•

• 101-1000

! • '

..-

84°

82°

84°

IS 7313
Opisthonema oglinum larvae

82*

80°

FIGURE 5. — Distribution and abundance of thread
herring eggs and larvae. Catches are standardized to
numbers under 10 m2 of sea surface. A, B. Cruise
IS7308, May 1973. C, D. Cruise IS7311, June-July
1973. E. Cruise IS7313, August 1973. No eggs were
collected on this cruise.

August 1973

30°

50m-,,,

+■

+ • »v

+ +■ • • V
*, + ■+■*■• 1

28°

+ \ + + • •( (V.

+ + \ + + • *.<*

+ + \ + + + \

4 +■ 1 + + +
+ 4- + +■ •

26°

Number under 10m2

+ 0

+ 4- ', +

*■ *

•

^P ft

• 1 - 10

• 11-100

• 101 - 1000

+ .' +

+■

-■-^

.. _ _

80*

499

FISHERY BULLETIN: VOL. 75, NO. 3

CL 7105

opisthoneha ogl1nuh larvae

February - March 1974

24'

Number under

10m2

•

1 - 10

•

11-100

•

101 - 1000

>I000

CL 7112

0p1sthonema oglinum eggs

May 1974

82° 80"

CL 7412

opisthoneha oglinum larvae

Hay 1974

26° -

26"

24'

1 1 r

fs^^^ ' * S \

. . ,\ y

50m-.

•N . • • • ri \

• ' •• W)

\ ' * * *K\« \ "

• \ *■ * #^c \

V-V o\

Number under 10m2

♦ 0

'» ^^j /*

• I - 10

• 11-100

• 101-1000

\ • • .-^^

— ' ' 1

\s^r

' ' * N \

50»-.,

\ *

. • • -A \

*■ * * * / vb

\ ♦ ♦ * '/ewi \ "

♦N, ♦ • #nr \

\-\ o)

•\ . • 0^ I

Number under 10m2

+ 0
• <l

^- A

• i - 10

• 11-100

• 101-1000

• • • ^^/

i i

86°

82°

80°

84°

82°

FIGURE 6. — Distribution and abundance of thread herring eggs and larvae. Catches are standardized to numbers
under 10 m2 of sea surface. A. Cruise CL7405, February-March 1974. No eggs were collected on this cruise. B, C.
Cruise CL7412, May 1974.

2° to 3°C, with a maximum difference of 5°C ob-
served. At the 50-m depth, temperatures differed
from the surface by as much as 9°C, but usually by
3° to 5°C. Because most spawning takes place at
depths less than 30 m, it is unlikely that spawning
and surface temperatures differed by more than
2°C. Salinity did not differ by more than l%o from
surface to the 50-m depth, except in 1973, when
surface salinities over wide areas during summer
were depressed (Anonymous 1975)4 due to Missis-

"Anonymous. 1975. Compilation and summation of historical
and existing physical oceanographic data from the eastern Gulf
of Mexico. State Univ. Syst. Fla., Inst. Oceanogr., St. Petersburg,
Fla. Final Rep. to U.S. Bur. Land Manage., Contract No.
08550-CT4-16, 97 p., 10 app.

sippi River runoff some months earlier. In 1973
salinity differences as great as 4%o between sur-
face and 50 m were observed in areas where some
thread herring spawning occurred. Small larvae
(s=5.0 mm standard length [SL]), <5 days old, were
collected where surface temperatures were 18.5°
to 30.9°C and salinities were 27.3 to 36.9%o. The
ranges were greater for larvae than for eggs.

Based on combined 1971-74 data, most thread
herring eggs and $5.0-mm larvae were collected
at surface temperatures from 25.1° to 30.0°C (Fig-
ure 7). All stations with eggs and more than 98% of
the stations with s=5.0-mm larvae had surface
temperatures above 22°C. More than 74% of the

500

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF THREAD HERRING

3 20

^100

s
3 9°

z 80

a 70 -

a.
60 -

50 ■

40 -
30

TEMPERATURE

Opisthonema oglinum
eggs

SALINITY

O oglinum
eggs

VH 1 1 t--f — I 1 1 1 1 1 t 1 1^ — • — • — I — ' — I — ' — I — I — !■

C oglinum
larvae - 5 mm

ie i-

19 (

C? oglinum
larvae 4 5mm

• .«\

210'
TEMPERATURE CLASS CO

2701- 2801- 2901- 30 01- 3101- 32 01- 3301- 34 01- 35 01- 36.01-
2750 2B50 2950 30 50 3150 32 50 3350 34 50 35 50 36 50
SALINITY CLASS (V..)

FIGURE 7.— Percent cumulative fre-
quency distribution of 1971-74 stations
where thread herring eggs occurred in
relation to surface temperatures (A)
and to surface salinities (C), and *£5.0-
mm SL larvae occurred in relation to
surface temperatures (B) and surface
salinities (D).

stations with eggs and 68% with =£5.0-mm larvae
occurred where salinity ranged from 35.0 to
36.5%o. Spawning rarely occurred at surface
salinities <33%o.

Egg and Larval Abundance in
Relation to Zooplankton

There was no clear relationship between abun-
dance of thread herring eggs or larvae and zoo-
plankton volume at stations for 12 cruises in
1972-74. Houde and Chitty (1976) determined
that mean zooplankton volume from the 333-^tm
mesh bongo net was 153.4 cm3/l,000 m3 in that
period. Egg abundances showed no relationship to
zooplankton volumes; larvae did appear to be most
abundant at stations where zooplankton volumes
exceeded 153.4 cm3/ 1,000 m3. But, zero catches or
low catches of larvae also were common where
zooplankton volumes were high. The lack of sig-
nificant correlation between larval abundance
and zooplankton volume was not surprising be-
cause the 333-ju.m mesh does not sample zoo-
plankton of the size eaten by small thread herring
larvae.

Relative Fecundity

The mean relative fecundity of thread herring
females is 594.0 ova/g (S* = 29.4 ova/g), calculated
from Martinez's ( 1972) weight and fecundity data
that he obtained from nine females of 53.8 to 109.4
g. There was no apparent relationship between

relative fecundity and either length or weight of
the nine thread herring used in this analysis. The
mean relative fecundity value was used in all sub-
sequent biomass estimate calculations. Because
mean relative fecundity with its 0.95 confidence
limits is x — 594 ± 68, the maximum biomass
estimating error attributable to the relative
fecundity estimate is about ±11%.

Time Until Hatching

Thread herring eggs apparently hatch in <24 h
at temperatures of 25° to 30°C, where most spawn-
ing takes place in the eastern Gulf. The evidence is
indirect because no living thread herring eggs
were available for incubation experiments. Eggs
did not occur in more than one stage of develop-
ment from any single sample during these sur-
veys. Newly fertilized eggs were collected only at
night, mostly from 2200 to 0200; and full-term
embryos were found only during the afternoon
from 1400 to 1800. I assigned a mean estimated
hatching time for eggs as 0.84 days (20 h) from the
evidence that was available. Thread herring eggs
were rarely caught at stations sampled between
the hours of 1600 and 2100, presumably because
they had already hatched. Thus, abundance of
thread herring eggs spawned during each cruise
was underestimated. Annual spawning estimates,
as well as variances, were corrected for egg stage
duration (equations 4, 5; Houde 1977a) and cor-
rected estimates were subsequently used to calcu-
late biomasses.

501

FISHERY BULLETIN: VOL. 75, NO. 3

Cruise Egg Abundance

The estimated abundance of thread herring
eggs in the area represented by each cruise is
given in Table 2. For cruises in which eggs oc-
curred, abundances ranged from 0.86 to 91.66 x
1010 eggs. The Table 2 estimates, which represent
abundance of eggs present on a day during a
cruise, were corrected for egg stage duration and
then expanded to represent the number of days
encompassed by the cruise period (Sette and
Ahlstrom 1948; Houde 1977a).

TABLE 2. — Abundance estimates of thread herring eggs for each
cruise. Estimates were obtained using Equations (2) and (3)
(Houde 1977a) and are not corrected for duration of the egg
stage.

Cruise

Area represented

by the cruise

(m2 x 109)

Positive area1
(m2 x 109)

Cruise egg

abundance

(eggs x 10'°)

GE7101
8C7113 and

TI7114
G7117
8C7120 and

TI7121
GE7127, 8B7132

andTI7131
8B7201 and

GE7202
GE7208
GE7210
IS7205
IS7209
IS7303
IS7308
IS7311
IS7313
IS7320
CL7405
CL7412

25.79

120.48
101.10

189.43

72.99

148.85

124.88

48.43

104.59

149.80

151.42

156.50

153.18

153.89

52.00

91.33

0.00

55.81
48.73

26.26

0.00

65.98

38.93

11.16

0.00

54.09

53.21

21.75

0.00

6.70

47.89

0.00

34.25
0.86

1.37

0.00

11.93

1.02

0.00

91.66

44.26

0.00

12.77

1 Positive area is defined as the area representing stations where either eggs
or larvae of thread herring were collected.

Adjusting Cruise Egg
Abundance Estimates

Because the entire potential spawning area was
not sampled on cruises GE7117, 8C7120-TI7121,
GE7208, and GE7210 (Figures 3, 4), an area ad-
justment factor was applied to correct the egg
abundance estimates in Table 2. The area adjust-
ment factor was equal to the fraction of the poten-
tial spawning area that was sampled on a given
cruise. For cruise GE7117 it was 0.404; for
8C7120-TI7121, 0.746; for GE7208, 0.746; and for
GE7210, 0.753. The abundance estimate for each
of those cruises (Table 2) was corrected by dividing
it by its area adjustment factor. Corrected abun-
dance estimates are: GE7117— 2.12 x 1010;
8C7120-TI7121— 1.83 x 1010; GE7208— 15.98 x

1010 GE7210— 1.36 x 1010.

Annual Spawning and Biomass Estimates
Method I

Estimates of total annual spawning by thread
herring in the eastern Gulf ranged from 140.528 x

1011 eggs in 1972 to 1,105.932 x 1011 eggs in 1973
(Table 3). Estimated adult biomasses were
110,024 metric tons in 1971, 47,316 metric tons in
1972, and 372,367 metric tons in 1973 (Table 3).
The 1972 estimate is unreliable because a cruise
that was scheduled during the peak of the spawn-
ing season was terminated before completion, due
to a hurricane. The actual biomass in 1972 prob-
ably is much higher than the estimate. Consider-

TABLE 3. — Annual spawning and biomass estimates for thread herring from the eastern Gulf of Mexico during
1971, 1972, and 1973 spawning seasons. Estimates are based on the Sette and Ahlstrom (1948) technique. The
1972 estimate is unreliable because a hurricane curtailed survey cruise GE7210 during the peak of the spawning
season. Details of the estimating procedure are given in Houde (1977a).

Year

Cruise

Daily spawning

estimate
(eggs x 1011)

Days

represented

by cruise

Eggs spawned during

cruise period

(x 10")

Variance estimates

on spawned eggs

(x 1024)

Adult biomass
(metric tons)

1971

GE7101
8C7113

0.000

51.5

0.000

—

TI7114

4.111

74.5

306.283

20.429

GE7117

0.255

44.5

1 1 .365

8.549

8C7120

TI7121

0.220

41.5

9.124

1.556

Annual total

326.772

30.534

110,024

1972

8B7201

GE7202

0.000

50.0

0.000

—

GE7208

1.919

65.0

124.706

47.060

GE7210

0.163

97.0

15.822

25.507

Annual total

140.528

72.567

47,316

1973

IS7303

0.000

46.5

0.000

—

IS7308

1 1 .004

79.5

874.802

49.839

IS731 1

5.313

43.5

231.130

20.284

IS7313

0.000

42.5

0.000

—

Annual total

1,105.932

70.123

372,367

502

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF THREAD HERRING

ing only 1971 and 1973 estimates of egg abun-
dance and their respective variances, the 0.95
confidence intervals on thread herring biomass
during those years ranged from 72,814 to 428,758
metric tons.

The area adjustments that corrected egg abun-
dance estimates for four 1971 and 1972 cruises had
a relatively minor effect on biomass estimates in
those years. Corrected estimates, presented in
Table 3, exceeded uncorrected estimates by 3,060
metric tons in 1971 and by 11,946 metric tons in
1972.

Method II

An estimate of annual spawning also was ob-
tained by a modification of Simpson's (1959)
method (Houde 1977a). Biomasses of adult thread
herring were then estimated (Table 4); they were
108,139 metric tons in 1971, 45,048 metric tons in
1972, and 325,803 metric tons in 1973.

Most Probable Biomass

If the 1972 estimates are not considered, the
most likely adult thread herring biomass in the
eastern Gulf during 1971-73 was between 100,000
and 400,000 metric tons. Yearly fluctuations in
thread herring biomass may be significant in the
eastern Gulf of Mexico but the size of such fluctua-
tions could not be determined. Severe red tides,
which are common in the area, and hurricanes are
just two phenomena occurring during summer

months that might affect annual recruitment,
causing significant year-class fluctuations. But,
during the years of this study it seems unlikely
that the stock of adult thread herring exceeded
430,000 metric tons and it probably was less than
that amount. These estimates represent only a
part of the Gulf of Mexico thread herring popula-
tion. Large sotcks exist in the northern and west-
ern Gulf that are not included in the estimates.
Also, juvenile thread herring biomass is not in-
cluded and it may constitute a significant part of
the population that could be harvested by a
fishery.

Concentration of Biomass

If thread herring adults were evenly distributed
from the coastline to the 50-m depth contour in
1971 and 1973, an area of 106.7 x 105 ha, the
concentration of biomass would be in the range of
6.8 to 40.2 kg/ha, based on adult biomass esti-
mates and the 0.95 confidence interval on those
estimates. The estimated thread herring biomass
concentration is less than that for round herring
(Houde 1977a) which ranged from 14.1 to 102.3
kg/ha. Round herring occur in a smaller area of
the eastern Gulf than thread herring; the round
herring being mostly confined to the 30- to 200-m
depth zone which is 76.5 x 105 ha. Thread herring,
although less concentrated, are highly visible be-
cause of surface schooling behavior and also are
presumably more accessible to a potential fishery
because they are found nearer to the coast in shal-
lower water.

TABLE 4. — Annual spawning and biomass estimates for thread
herring from the eastern Gulf of Mexico during 1971, 1972, and
1973. Estimates are based on the method described by Simpson
(1959). The 1972 estimate is unreliable because a hurricane cur-
tailed survey cruise GE7210 during the peak of the spawning
season.

Year

1971

1972

1973

Cruise

Daily spawning

estimate
(eggs x 10")

Annual spawning

estimate

(eggs x 10")

GE7101

0.000

8C7113

TI7114

4.111

GE7117

0.255

8C7120

TI7121

0.220

8B7201

GE7202

0.000

GE7208

1.919

GE7210

0.163

IS7303

0.000

IS7308

1 1 .004

IS7311

5.313

IS7313

0.000

321.172

133.793

967.636

Adult biomass
(metric tons)

108,139

45,048

325,803

Potential Yield to a Fishery

Estimates of annual potential yield of adult
thread herring from the eastern Gulf range from
27,506 to 186,184 metric tons (Table 5). Estimates
were obtained from Cmax = XMB0 where M, the
natural mortality coefficient, was assigned three

TABLE 5. — Range of potential yield estimates for eastern Gulf of
Mexico thread herring, based on biomass estimates in 1971 and
1973 by the Sette and Ahlstrom (1948) method. Yields are pre-
dicted at three possible values of M, the natural mortality coef-
ficient. Biomass estimates were obtained from values in Table 3.

Year

Biomass

estimate

(metric

tons)

Estimated potential annual yields
(metric tons) for given values of M

M=0.5

M=0.75

M = 1.0

1971
1973

Mean of 1971
and 1973

110,024
372,367

241,196

27,506
93,092

60,299

41,259
139.638

90,448

55,012
186,184

120,598

503

FISHERY BULLETIN: VOL. 75, NO. 3

values (0.5, 0.75, and 1.00) within the probable
range for thread herring. Based on the mean of
1971 and 1973 biomass estimates, potential yield
ranged from 60,300 to 120,600 metric tons. It is
likely that the sustainable yield of adult stock was
in that range during 1971-73. Assuming thread
herring are evenly distributed within the 106.7 x
105 ha spawning area, then probable harvestable
yields of adult thread herring range from 5.6 to
11.3 kg/ha. Yield could be supplemented by some
additional catch of juveniles.

The eastern Gulf thread herring stock appar-
ently is not as large as the menhaden stock in the
north-central Gulf. But, a potential harvest, based
on 1971-73 biomass levels, of about 100,000 met-
ric tons substantiates the belief that thread her-
ring are a significant resource in the eastern Gulf
that could provide raw material for the fishmeal
industry. Because large fluctuations in thread
herring year-class strength may occur, yield in
some years could be considerably higher than that
predicted based on 1971-73 abundance. The po-
tential for thread herring harvest is higher in the
eastern Gulf of Mexico than that estimated along
the Atlantic coast by Pristas and Cheek (1973).

Larval Abundance

Larval abundance varied seasonally with peak
abundance in spring and summer months (Table

TABLE 6. — Abundance estimates of thread herring larvae for
each cruise. Estimates include larvae in all size classes and were
obtained using Equations (2) and (3) (Houde 1977a).

Area represented

Cruise larvae

by the cruise
(m2 x 109)

Positive area1

abundance2

Cruise

(m2 > 109)

(larvae * 10'°)

GE7101

25.79

0.00

8C7113 and

TI7114

120.48

5581

33.34

GE7117

101.10

48.73

17.67

8C7120 and

TI7121

189.43

26.26

2087

GE7127, TI7131,

and 8B7132

72.99

0.00

8B7201 and

GE7202

14885

0.00

GE7208

124.88

65.98

20.36

GE7210

48.43

38.93

83.43

IS7205

104.59

11.16

1.09

IS7209

149.80

0.00

IS7303

149.80

0.00

IS7308

151.42

54.09

52.58

IS7311

156.50

53.21

107.57

IS7313

153.18

21 75

9.34

IS7320

153.89

0.00

CL7405

52.00

6.70

0.16

CL7412

91.33

47 89

28.13

1 Positive area is defined as the area representing stations where either eggs
or larvae of thread herring were collected.

2Values are not adjusted for cruises that did not encompass the entire area,
nor have estimates been corrected to account for gear avoidance by larvae at
stations sampled in daylight.

6). Abundance estimates for cruises in which
thread herring larvae were collected ranged from
0.16 to 107.57 x 1010 larvae in the survey area.
Thread herring larvae were collected in small
numbers on three cruises in which no eggs were
taken (Table 1). Cruises IS7205 and IS7313 were
made in late summer when eggs, if present, must
have been rare. Larvae collected in early March,
during cruise CL7405, occurred only in the south-
ernmost part of the survey area (Figure 6). They
occurred at five stations on that cruise but abun-
dances were only 0.6 to 4.4 under 10 m2. The pres-
ence of larvae indicated that some spawning
began as early as February and that it continued
as late as September.

The seasonal nature of thread herring larvae
abundance can be observed in plotted length-
frequency distributions for each cruise in which
larvae were collected (Figure 8). Larvae were rep-
resented in length classes up to 23.0 mm SL, but
specimens longer than 15.0 mm were uncommon.
The smallest length classes (1.1-3.0 mm) repre-
sent larvae in poor condition or that were distorted
from net capture and preservation, because re-
cently hatched thread herring larvae are 3.8 to 4.0
mm SL (Richards et al. 1974).

Fewer larvae were collected at stations sampled
during the day than at night, indicating that gear
avoidance was relatively great during daylight,
particularly by larger larvae. The ratio of night
catches to day catches increased rapidly when
summed catches under 10 m2 over all cruises were
plotted for each 1-mm length class (Figure 9). No
larvae longer than 17.0 mm were collected during
daylight. An exponential function R =
0.3470e° 2492X was fitted to the plotted data for lar-
vae up to 17.0 mm (Figure 9), where/? is the ratio
of night-caught to day-caught larvae and X is
standard length. It provided the correction factor
R (Houde 1977a), by which daytime catches were
adjusted to obtain abundance estimates of larvae
by 1-mm length classes in each station area on a
cruise. The correction for under-sampling during
daylight probably did not completely account for
gear avoidance by larvae (Smith and Richardson
in press), but it helped to provide a better estimate
of larval abundance for subsequent estimation of
survival rates. The observed increase in ratio of
night- to day-caught thread herring larvae
throughout the larval period seems typical of
clupeid larvae ( Ahlstrom 1954, 1959; Lenarz 1973;
Matsuura in press). But, observations on round

504

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF THREAD HERRING

70 -
60 -
30 -
40 -
30 "
20 -
10 -

8C 7113- TI7II4

h-r>-^.

90
60
70
60
50

IS 7205

IS7308

1 I-

2 0

3.1- 5.1-
4.0 6.0

71- 3 1- 15 1- ' 171- ' 19.1- ' 2I.I-' II- 3.1- 5.1- 7.1- 9.1- II. I- 13.1- 15.1- 17.1- 19.1- 21.1-

8.0 10 0 12 0 14.0 16 0 18 0 200 22 0 2 0 4 0 6.0 80 10 0 12 0 14 0 160 18.0 20.0 22 0

STANOARD LENGTH CLASSES (mm)

FIGURE 8.— Length- frequency distributions of thread herring larvae for 1971-74 cruises to the eastern Gulf of
Mexico. Frequencies are expressed as estimated abundance of larvae in each length class within the area
represented by the cruise. No adjustments for abundance have been made for cruises that did not cover the entire
area where thread herring larvae might occur.

505

FISHERY BULLETIN: VOL. 75, NO. 3

$20 0

t- 17.5

« 15.0

O 12.5

I-

g 100

H
r
B

b-
O

I-
<

7.5

5 0

2 5

I 0

R • 0.3470e^

,-•

"f""f I L.

J 1 I L_

1.5 2.5 3.5 4.5 5.5 6.5 8.5 10.5 12.5 4.5 16.5

MIDPOINT OF LENGTH CLASS (mm)

FIGURE 9.— Night to day ratios of sums of catches, standardized
to numbers under 10 m2 of sea surface, for thread herring larvae
collected in 1971-74 in the eastern Gulf of Mexico. The ratios
were calculated for larvae within each 1-mm length class from
1.1 to 17.0 mm SL. A fitted exponential regression describes the
relationship. Larval abundance estimates for each length class
at stations occupied during daylight were corrected by the ap-
propriate ratio factor for each length class to account for daytime
avoidance.

herring larvae (Houde 1977a) showed relative in-
creases in night catches until larvae were 13.0
mm; then the ratio declined to unity for larger
larvae. In scaled sardine larvae (Houde 1977b),
the ratio increased throughout the larval size
range, but the relative increase in night catches
was slight compared to thread herring.

Annual estimates of larval abundance by 1-mm
length classes were calculated for 1971 and 1973
(Figure 10), after the data had been corrected for
daytime avoidance. Abundance of larvae was
slightly higher in 1973 than in 1971. The abun-
dance of 3.0- to 7.0-mm larvae accounted for the
difference between the two years (Figure 10). Lar-
vae longer than 17.0 mm were more abundant in
1973 than in 1971.

Abundance of larvae decreased exponentially in
both years as lengths increased (Figure 10). Expo-
nential functions were fitted to data in the 4.1- to
19.0-mm length classes in 1971 and to the 5.1- to
20.0-mm length classes in 1973 (Figure 10), giving
estimates of the instantaneous decline in abun-
dance of thread herring larvae per millimeter in-
crease in length. The instantaneous coefficients
estimate larval mortality rates if gear avoidance

140

120

IOO

80 -

40 -

Z o

111

o |80

<
Q

< 160

t-
<
X 140

120

100

1971

I MS (13.7572 x IO,3)e03545L

r* ■..)..»..li.*..r.ii.Y'* ■.r,»,,r«,t,,i «,r.»iri.F.T.«.r

,,w;p3

- ■ * ■ ' i «

1973

I ^_NL- (17.9238 xlOl3)e03942L

AS"

I.I- 2.1-3.1- 4.1- 6.1- 8 1- 10 1- 12.1- 14.1- 16 1 18 1- 20.1- 22 1-
2 0 3040 50 7,0 90 110 130 15 0 170 19 0 21.0 23 0

LENGTH-CLASS (mm)

FIGURE 10. — Length- frequency distribution of annual larval
abundance estimates for thread herring larvae collected in the
eastern Gulf of Mexico, 1971 and 1973. Frequencies in each
1-mm length class are expressed as estimated annual abundance
and have been corrected for daytime avoidance. Fitted exponen-
tial functions provide estimates of the instantaneous coefficient
of decline in abundance by length.

is not too great over the length ranges in the
analysis. Coefficients wereZ = 0.3545 in 1971 and
Z = 0.3942 in 1973. The corresponding percentage

506

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF THREAD HERRING

losses per millimeter increase in length are 29.9%
in 1971 and 32.6% in 1973. Confidence limits on Z
at the 0.95 probability level were Z ± 0.0816 in
1971 and Z ± 0.1385 in 1973. The mortality
coefficients did not differ significantly between
years tf-test; P>0.50).

Mortality coefficients for round herring larvae
per millimeter increase in length were Z = 0.2269
in 1971-72 and Z = 0.3647 in 1972-73 in the east-
ern Gulf of Mexico (Houde 1977a). Larval mortal-
ity of scaled sardines in 1973 was Z = 0.3829
(Houde 1977b), which is nearly identical to that
for thread herring. Lenarz (1973) reported ranges
of instantaneous coefficients for abundance at
length data to be 0.15 to 0.33 for Pacific sardine,
Sardinops caeruleus, and from 0.32 to 0.46 for
northern anchovy, Engraulis mordax, larvae. The
Pacific sardine coefficients were lower than those
for thread herring, but the anchovy coefficients
were similar to thread herring coefficients. Ma-
tsuura (in press) obtained a high instantaneous
coefficient of Z = 0.4962 for Brazilian sardine,
Sardinella brasiliensis, which is higher than any
values observed for Gulf of Mexico clupeid larvae.

To obtain estimates of larval mortality relative
to age rather than length, an exponential growth
model was used to estimate age at length for
thread herring larvae, given various mean daily
growth increments during the larval stage. Mean
daily growth increments of eastern Gulf clupeid
larvae probably range from 0.3 to 1.0 mm based on
laboratory rearing experiments for some species
(Richards and Palko 1969; Saksena and Houde

1972; Saksena et al. 1972; Houde 1973b; Houde
and Swanson 1975). At temperatures above 26°C,
healthy larvae grew, on average, more than 0.5
mm/day. Duration of the egg stage for thread her-
ring is about 0.84 days. The duration of nonfully
vulnerable length classes also was estimated be-
fore mean age of each fully vulnerable 1-mm
length class was calculated. Nonfully vulnerable
length classes were 1.1 to 4.0 mm in 1971 and 1.1
to 5.0 mm in 1973. The duration of these stages in
thread herring probably is from 1.0 to 3.0 days and
4.0 to 6.0 days, respectively, based on evidence
from laboratory rearing of similar clupeid larvae
(Houde et al. 1974; Houde and Swanson 1975).
Eastern Gulf clupeid larvae quickly attain 4.0 mm
length during the first day after hatching, but
show no further growth in length until the fourth
day after hatching. No direct observations of stage
duration for thread herring larvae 5.0 mm or less
in length were available from laboratory experi-
ments but their growth pattern during this stage
probably does not differ from that of other
clupeids. Stage durations of nonfully vulnerable
length classes were assigned based on observa-
tions of the other species. Methods and details of
the mortality estimating procedure were given by
Houde (1977a).

Two examples of duration-corrected abundance
data assuming exponential growth of fully vul-
nerable larval length classes up to 19.0 mm in
1971 and 20.0 mm in 1973 are given in Table 7. In
these examples, the mean daily growth increment
was assumed to be 0.8 mm. Sets of such abundance

TABLE 7. — Two examples of data from 1971 and 1973 used to obtain stage duration, mean age, and duration-corrected abundance of
thread herring eggs and larvae. Duration-corrected abundances were subsequently regressed on mean ages to obtain mortality rates
(Table 8). Abundance estimates in the second column of the Table were previously corrected for daytime avoidance. In these examples,
the mean daily growth increment (6) was set at 0.80 mm. The nonfully vulnerable size classes were 1.1 to 4.0 mm in 1971 and 1.1 to
5.0 mm in 1973. Calculating procedures were given in Houde (1977a), Equations (12) to (16). Regressions for these data are presented
in Figure 18.

Duration-corrected

Abundance

Duration

Mean age

abundance

Abundance

Duration

Mean age

abundance

Stage

(no. x 10")

(days)

(no. x 10")

Stage

(no. x 10")

(days)

(no. x 10")

1971

1973

Eggs

274.49

0.84

0.42

326.77

Eggs

921.24

0.84

0.42

1,105.93

1.1- 4.0 mm

31.65

1.00

1.34

31.65

1.1- 5.0 mm

313.69

4.00

2.84

78.42

4.1- 5.0

117.33

2.49

3.01

47.14

5.1- 6.0

163.32

2.04

5.79

80.13

5.1- 6.0

83.72

2.04

5.52

41.08

6.1- 7.0

15418

1.73

7.88

89.33

6.1- 7.0

66.38

1.73

7.62

38.46

7.1- 8.0

109.80

1.50

968

73.35

7.1- 8.0

108.92

1.50

9.41

72.77

8.1- 9.0

94.93

1.32

11.25

71.84

8.1- 9.0

102.14

1.32

10.98

77.30

9.1-10.0

75.86

1.18

1264

64.14

9.1-10.0

66.52

1.18

12.38

5624

10.1-11.0

49.55

1.07

13.90

46.28

10.1-11.0

55.47

1.07

13.63

51.81

11.1-12.0

31.82

098

15.04

32.55

11.1-12.0

53.74

0.98

14.77

54.96

12.1-13.0

888

0.90

16.08

9.87

12.1-13.0

19:29

0.90

1582

21.44

131-14.0

4.53

0.83

17.05

5.44

13.1-14.0

12 68

0.83

16.79

15.21

14.1-15.0

4.24

0.78

17.94

5.46

14.1-15.0

22.51

0.78

17.68

2901

15.1-16.0

1.56

0.73

18 78

2.15

15.1-16.0

7.16

0.73

18.52

9.86

16 1-17.0

5.59

0.68

19.57

8.20

16.1-17.0

6.38

0.68

19.30

9.35

17.1-18.0

5.24

0.64

20.30

8.15

17.1-18.0

0.17

0.64

20.04

0.26

18.1-19.0

4.60

0.61

21.00

7.55

18.1-19.0

0.31

0.61

20.74

0.51

19.1-200

1.44

0.58

21.66

2.49

507

FISHERY BULLETIN: VOL. 75, NO. 3

estimates, assigning other mean daily growth in-
crements and other durations for nonfully vulner-
able larvae, were generated. Duration-corrected
abundances (Table 7) were then regressed on es-
timated mean ages, the resulting regression
coefficients from the fitted exponential functions
being estimates of the instantaneous mortality
coefficients (Z ) for age in days.

Examples of probable thread herring larval
mortality estimates in 1971 and 1973 for a range
of possible mean daily growth increments and for
two probable stage durations of nonfully vulnera-
ble larvae are given in Table 8. The ranges of
probable larval mortality rates were similar in the
two years. The probable instantaneous mortality
coefficients ranged from 0.1371 to 0.2575 in 1971,
corresponding to daily mortality rates of 12.8 to
22.7%. In 1973 the estimates of instantaneous
mortality coefficients ranged from 0.1691 to
0.3050, which correspond to daily rates of 15.6 to
26.3% . The effect of varying the assumed duration
of nonfully vulnerable stages had a relatively
minor effect on mortality rate estimation com-
pared with varying growth rates (Table 8).

The y-axis intercepts (N0) of the exponential
regressions used to obtain mortality estimates
(Table 8) also estimate annual spawning by thread
herring. The range of estimates in Table 8 encom-
passes the estimate obtained for 1971 and 1973 by

the Sette and Ahlstrom (1948) or Simpson (1959)
techniques (Tables 3, 4). At a mean daily growth
increment of 0.8 mm, a probable value based on
laboratory growth data, the annual spawning es-
timates from the y-axis intercepts (Table 8) are
similar to those obtained by the other methods
(Tables 3, 4).

I believe that the best estimates of larval mor-
tality were generated from abundance and age
data in Table 7. These data indicated that daily
mortality of thread herring larvae was approxi-
mately 20% in both 1971 and 1973. Instantaneous
mortality coefficients for conditions in Table 7
wereZ = 0.2124 in 1971 andZ = 0.2564 in 1973,
which correspond to daily mortality rates of 19.1
and 22.6% (Table 8). Regressions from which those
instantaneous mortality coefficients were derived
are given in Figure 11. Confidence intervals onZ
at the 0.95 probability level ranged from 0.0990 to
0.3258 in 1971 and from 0.1993 to 0.3224 in 1973.
The instantaneous coefficients were not tested to
determine if they differed significantly between
1971 and 1973 because variances of the estimates
were not homogeneous (Sg = 0.0028 in 1971, Sf =
0.0007 in 1973), but the overlapping confidence in-
tervals indicated that they did not differ sig-
nificantly.

Regressions of duration-corrected abundance on
estimated mean age (Figure 11) suggested that

TABLE 8. — Summary of mortality estimates for thread herring larvae from the eastern Gulf of Mexico, 1971 and 1973. Estimates were
obtained from the exponential regression of egg and larvae abundances on mean age. Instantaneous growth and mortality coefficients
were calculated for various possible combinations of mean daily growth increment and duration of the nonfully vulnerable larval stages.
Egg stage duration was assumed to be 0.84 days. Nonfully vulnerable larval stages were 1.1 to 4.0 mm SL in 1971 and 1.1 to 5.0 mm SL
in 1973. Explanation of the estimating method is given in Equations (12) to (16) of Houde (1977a).

Year

Mean daily

growth increment,

b (mm)

Instantaneous

growth coefficient,

Nonfully vulnerable

larvae duration

(days)

Instantaneous
mortality coefficient,

/-axis intercept,
(no. x 1011)

Daily mortality

rate,
1 - exp(-Z)

1971

1973

0.5

0.0498

1.0

0.1403

219.43

0.1309

0.6

00598

1.0

0 1650

258 43

0.1521

0.7

00698

1.0

0.1890

297.83

0.1722

0.8

0.0797

1.0

0.2124

337.80

0.1913

0.9

0.0897

1.0

0.2352

378.36

0.2096

1.0

0.0997

1.0

0.2575

419.59

0.2270

0.5

0.0498

3.0

0.1371

266.31

0.1281

0.6

00598

3.0

0.1601

321.57

0.1479

0.7

00698

3.0

0 1820

378.83

0.1664

0.8

0.0797

3.0

0.2030

437.93

0.1837

0.9

0.0897

3.0

0.2230

498 64

0.1999

1.0

0.0997

3.0

0.2421

560.70

0.2150

0.5

00498

4.0

0.1733

466.83

0.1591

0.6

0.0598

4.0

0.2024

588 96

0.1832

0.7

00698

4.0

0.2301

722.16

0.2056

0.8

0.0797

4.0

0.2564

86578

0.2262

00897

4.0

0.2814

1.019.02

0.2453

1.0

0.0997

4.0

03050

1,180.73

0.2629

0.5

0.0498

6.0

0.1691

590.12

0.1556

0.6

00598

6.0

0.1961

761.18

0.1780

0.7

0.0698

0.2211

948.51

01983

0.8

00797

6.0

0.2442

1,149.53

0.2167

00897

6.0

02656

1,361.12

0.2333

1.0

0.0997

6.0

0.2853

1.580.16

02482

508

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF THREAD HERRING

1000

~I00

3
CD

111

cc
cc

CJ
I

l-
<
cc

3
Q

I -

0 I

1973
Nt- (865.78 x 10 "le025"'

1971
N,- (337.80x10 ")e°2l24t

Opisthonema oglinum survival
• • 1971
- -197 3

6 8 10 12 14 16

ESTIMATED MEAN AGE (DAYS)

18 20 22

FIGURE 11. — Estimated abundance of egg and larval stages of
thread herring in the eastern Gulf of Mexico in 1971 and 1973.
Abundance is expressed as a function of estimated age. Fitted
exponential functions give estimates of the instantaneous rates
of decline in abundance for eggs and larvae up to 21 days of age.
The two symbols enclosed in circles represent nonfully vulner-
able length classes and were not included in the regression of
instantaneous decline.

abundance of young larvae was underestimated in
each year. If this is true, then mortality estimates
(Table 8) are too low. Also, if growth was not expo-
nential, but linear, then abundance of larvae in

older age-classes was overestimated and mortality
rates of thread herring larvae would be greater
than estimates from the regression coefficients
(Table 8).

Houde ( 1 977a) estimated instantaneous mortal-
ity coefficients from abundance at age data for
round herring larvae to be Z = 0.1317 in 1971-72
and Z = 0.1286 in 1972-73. These estimates are
lower than the most probable rates for thread her-
ring larvae. The estimated mortality coefficient (Z
= 0.2835) for scaled sardine larvae in 1973 was
similar to those for thread herring (Houde 1977b).
The thread herring instantaneous mortality
coefficients for abundance at age data were similar
to those for Pacific sardine (Z = 0.16-0.17)
(Ahlstrom 1954), jack mackerel (Z = 0.23)(Farris
1961), and Japanese mackerel (Z = 0.3295)
(Watanabe 1970), but higher than those reported
for Japanese sardine (Z = 0.1279) (Nakai and Hat-
tori 1961 ) or plaice (Z = 0.0209 to 0.0685) (Bannis-
ter et al. 1974).

Estimated numbers and percentage survival of
thread herring at hatching, 5.5 mm SL, and 15.5
mm SL were calculated given three possible in-
stantaneous growth rates, corresponding to mean
daily growth increments of 0.6, 0.8, and 1.0 mm
(Table 9). The estimating procedure used
parameters from the exponential functions de-
scribing decline in numbers by age (Table 8) and
the age-at-length data assuming exponential
growth (examples in Table 7). The estimated
number of spawned eggs, from Table 3, varied by
more than a factor of three between 1971 and
1973, yet the estimated number of survivors when
larvae begin to transform to juveniles (15.5 mm
SL) (Richards et al. 1974) was not much different
between years (Table 9). Percentage survival from
spawned egg to that stage did vary between 1971
and 1973; an estimated mortality of >99c7c oc-
curred in 1973, but mortality was approximately

TABLE 9. — Estimated numbers and percentages of survivors of thread herring at hatching, 5.5 mm SL, and 15.5 mm SL in 1971 and
1973. Estimates are made at three possible growth rates (see Table 8). Duration of the nonfully vulnerable larval stages was set at 1.0
days for 1.1 to 4.0 mm larvae in 1971 and at 4.0 days for 1.1 to 5.0 mm larvae in 1973. The number of spawned eggs in each year was
based on the estimates in Table 3. Predicted numbers at hatching, 5.5 mm, and 15.5 mm are calculated from exponential functions
based on Table 8 data.

Year

Instantaneous

growth

coefficient.

Number of

spawned eggs

(x 10")

Instantaneous

mortality

coefficient.

Number
hatching
(x 10")

Percent

mortality'

to hatching

Number of

5.5-mm larvae

(x 10")

Percent

mortality
to 5.5 mm

Number of

1 5.5-mm larvae

(x 10")

Percent

mortality

to 15.5 mm

1971
1973

0.0598
0.0797
00997

00598
0.0797
0.0997

326.77
326.77
326.77

1,105.93
1.105.93
1,105.93

0.1650
0.2124
0.2575
0.2024
0.2564
0.3050

224.98
282 60
337.98

496.88
698.02
913.87

31.2
13.5

551
36 9
17.4

84.85
104.59
122.22

171.35

196.19
213.98

74.0
68.0
62.6

84.5
82.3
80.7

4.86
6.61
8.42

5.14
7.02
9.00

98.5
980
97.4

995
99.4
99.2

'Hatching assumed to occur at 0.84 days.

509

FISHERY BULLETIN: VOL. 75, NO. 3

98% in 1971. Estimated percentage mortalities
from spawning to hatching (Table 9) were lower
for thread herring than those estimated previ-
ously for round herring (35 to 90% ) from the east-
ern Gulf (Houde 1977a). They also were lower
than those (>85%) estimated for scaled sardines
(Houde 1977a) in 1973. The 5.5 mm SL stage rep-
resents postyolk-sac thread herring larvae that
had succeeded in starting to feed; percentage mor-
tality to that stage was estimated to range from
62.6 to 84.5% (Table 9).

The 15.5-mm stage would be attained at 18.5 to
19.0 days if the instantaneous growth coefficient
was 0.0797 (equals 0.80-mm mean daily growth
increment) (Table 7). At that growth rate 20
larvae/ 1,000 spawned eggs would have survived
to 15.5 mm SL in 1971, but only 6 larvae/1,000
eggs would have survived to 15.5 mm in 1973
(Table 9). The expected number of thread herring
survivors at 15.5 mm/1,000 spawned eggs was
similar to that estimated for round herring from
the eastern Gulf (Houde 1977a), but greater than
the number estimated for scaled sardines (Houde
1977b).

SUMMARY

5. Estimates of annual potential yield to a
fishery, based on 1971 and 1973 biomass esti-
mates, ranged from 27,500 to 186,200 metric tons
of adult thread herring. The potential yield, based
on the mean of 1971 and 1973 biomass estimates,
was between 60,300 and 120,600 metric tons.

6. Larval abundance was greater in 1973 than
in 1971. Mortality rates for larval thread herring
were estimated by length and for estimated ages.
For lengths, the instantaneous coefficients of de-
cline in catches wereZ = 0.3545 in 1971 andZ =
0.3942 in 1973, corresponding to 29.9 and 32.6%
losses per millimeter of growth. For age, the most
probable daily mortality estimates were Z =
0.2124 in 1971 and Z = 0.2564 in 1973, which
correspond to daily loss rates of 19.1 and 22.6%.

7. It is probable that >99% mortality occurred
between spawning and the 15.5-mm stage in 1973,
and that approximately 98% mortality occurred in
1971. About 20 larvae/1,000 spawned eggs were
estimated to have survived to 18.5 to 19.0 days
after hatching and 15.5 mm SL in 1971, but only 6
larvae/ 1,000 eggs were estimated to have sur-
vived to that stage in 1973.

ACKNOWLEDGMENTS

1. Spawning by thread herring in the eastern
Gulf of Mexico occurred from February to Sep-
tember, based on catches of larvae from March
through September and eggs from May through
August. Most spawning took place from April to
August in depths <30m, within 50 km of the coast.
Spawning was most intense between lat. 26°00'N
and 28°00'N (Fort Myers to Tampa Bay, Fla.).

2. Eggs were collected when surface tempera-
tures ranged from 22.5° to 30.3°C and when sur-
face salinities were 32.4 to 36.8%o. Larvae ^=5.0
mm SL were collected at surface temperatures
from 18.5° to 30.9°C and at surface salinities from
27.3 to 36.9%o. Most eggs and =£5.0-mm larvae
were taken when surface temperature exceeded
25°C and when surface salinity was above 35.0%o.

3. Estimates of adult biomass ranged from
108,000 to 372,000 metric tons in 1971 and 1973.
The 0.95 confidence intervals on 1971 and 1973
estimates range from 72,800 to 428,800 metric
tons.

4. The estimated concentration of adult thread
herring biomass from the coast to the 50-m depth
contour was in the range of 6.8 to 40.2 kg/ha. The
total area in which thread herring occurred was
106.7 x 105 ha.

People and agencies that were acknowledged for
their support of this project by Houde (1977a) are
thanked once again. Harvey Bullis reviewed an
early draft of the paper. This research was spon-
sored by NOAA Office of Sea Grant, U.S. Depart-
ment of Commerce, under Grant 04-3-158-27 to
the University of Miami.

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WATANABE, T.

512

CHLORINATED HYDROCARBONS IN DOVER SOLE,
MICROSTOMUS PACIFICUS: LOCAL MIGRATIONS AND FIN EROSION

D. J. McDermott-Ehrlich,1 M. J. Sherwood,2 T. C. Heesen,2 D. R. Young,2 and A. J. Mearns2

ABSTRACT

Dover sole, Microstomas pacificus, with and without fin erosion were collected from the municipal
wastewater discharge sites of Los Angeles and Orange counties. While there was a significant differ-
ence between the total DDT levels in muscle tissue of the unaffected fish from the two regions, there
was no significant regional difference between the muscle DDT levels in the diseased fish. This is
consistent with the proposed hypothesis that the Orange County diseased fish had originated at the
Los Angeles County discharge site. Comparisons of chlorinated hydrocarbon levels in diseased and
unaffected Dover sole from the Palos Verdes discharge site of Los Angeles County indicate: 1 ) DDT
levels were significantly higher (P<0.05) in Dover sole with fin erosion, and 2) polychlorinated
biphenyl levels were higher at the 90% confidence level (P<0.10) in diseased Dover sole.

In recent years, fin erosion diseases have been
observed in several species of marine fishes col-
lected from areas contaminated by industrial or
municipal waste such as the Duwamish River es-
tuary, Wash. ( Wellings et al. 1976), the New York
Bight (Mahoney et al. 1973; Murchelano 1975),
and major municipal wastewater discharge sites
in the Southern California Bight (Mearns and
Sherwood 1974). In southern California, the dis-
ease is most prevalent in the Dover sole, Micro-
stomas pacificus Lockington, a marine flatfish.

Dover sole with fin erosion occur most fre-
quently near the Palos Verdes discharge site of
the Joint Water Pollution Control Plant ( JWPCP)
submarine outfalls of the County Sanitation Dis-
tricts of Los Angeles County. During the period
1972-76, 39% of the 20,854 Dover sole collected
in 268 samples off Palos Verdes had fin erosion.
Only 3.5% of 894 individuals collected in Santa
Monica Bay to the north (109 samples), 2.0% of
5,354 individuals collected in south San Pedro
Bay to the south (138 samples), and 0.67% of 889
individuals collected off Dana Point farther south
(77 samples) were affected with the disease.

The JWPCP outfalls are the dominant source of
DDT residues (total DDT) and most trace metals
introduced via municipal wastewaters to the
Southern California Bight (Galloway 1972;
Young et al. 1973; Young et al. 1976b). Although

'Southern California Coastal Water Research Project; present
address: Lockheed Center for Marine Research, P.O. Box 398,
Avila, CA 93424.

2Southern California Coastal Water Research Project, 1500
East Imperial Highway, El Segundo, CA 90245.

in 1974 Orange County's discharge of poly-
chlorinated biphenyl (PCB) was twice that of any
other discharger (Young et al. 1976a), the sedi-
ments off the Palos Verdes Peninsula, as a result
of past discharges, have the highest levels of total
PCB and total DDT found in marine sediments of
the Bight (Young et al. 1976a, b).

The Dover sole is one of the most abundant
and most frequently encountered species in trawl
catches taken in the vicinity of the southern Cal-
ifornia submarine municipal wastewater outfalls
(Southern California Coastal Water Research
Project 1973). In southern California, as in north-
ern California where it is the focus of a major
bottom fishery (Hagerman 1952), Dover sole
undergo seasonal onshore-offshore migrations
(Mearns and Sherwood 1974). Individuals move
offshore in the winter and onshore in the summer
and have been collected off southern California at
depths generally greater than 25 m.

In May and August 1972, trawl catches taken
in the vicinity of the Orange County outfall sys-
tem in south San Pedro Bay contained higher
numbers of Dover sole with fin erosion than did
previous catches (6 of 684 individuals and 34 of
611 individuals, respectively). This increase was
associated with a large influx of Dover sole into
the area. Only 273 individuals had been collected
in February 1972. Orange County trawls were
taken at a standard set of eight stations with the
same gear and vessel combination. Only larger
individuals (generally >120 mm standard length,
SL) were affected with the disease; this contrasted
with the situation off Palos Verdes, where Dover

Manuscript accepted February 1977.
Fishery Bulletin: VOL. 75, NO. 3, 1977.

513

FISHERY BULLETIN: VOL. 75, NO. 3

sole <120 mm SL also had eroded fins. These ob-
servations suggested that Dover sole with fin
erosion caught in the vicinity of the Orange
County outfall could have migrated from the
Palos Verdes shelf (Mearns and Sherwood 1974).
Since the increase had occurred 13 mo after the
depth of discharge off Orange County had been
changed from 20 to 60 m, within the range of the
Dover sole, one objective of this study was to test
the hypothesis that the diseased fish collected off
Orange County had migrated from the Palos
Verdes region and that the disease did not orig-
inate in the Orange County area. Since collections
on the Palos Verdes shelf contained the highest
percentage of Dover sole with fin erosion and the
shelf was also the site of highest bottom sediment
contamination by total DDT, we attempted to use
this contamination as a tag of exposure to the
JWPCP discharge area. Reported values for the
biological half-life of DDT compounds in fish gen-
erally range from about 1 to 5 mo (Buhler et al.
1969; Grzenda et al. 1970; Hansen and Wilson
1970; Macek et al. 1970). Since the Orange County
discharge site is about 35 km to the south of the
JWPCP discharge area, it is possible that move-
ment over this distance could occur before a sig-
nificant fraction of the accumulated DDT residues
had been depleted.

In Dover sole, external signs of the disease were
restricted to the fins. The noninflammatory na-
ture of the lesions and the absence of any demon-
strable organisms associated with the lesions, as
determined by histological examination, suggest
that the disease is not the result of an infectious
process (Klontz and Bendele3). If chemical agents
are involved, then it is possible that concentra-
tions of these agents in tissues might reflect their
involvement in disease development. A second ob-
jective of this study was to explore the role of
chlorinated hydrocarbons in the fin erosion dis-
ease by determining if there were differences
between the levels of total DDT and total PCB
in muscle tissue of Dover sole with and without
eroded fins.

SAMPLING AND ANALYSIS

Fish analyzed in this study were subsamples of
collections made during routine trawl monitoring

surveys by the County Sanitation Districts of Los
Angeles and Orange counties. During 1974, up to
four trawl series were conducted off the Palos
Verdes Peninsula and Orange County (Figure 1).
The trawls off Orange County were conducted
with a Marinovich semiballoon otter trawl with a
7.6-m (25-ft) headrope and a 1.3-cm (0.5-in)
stretch mesh cod end liner. Hauls off Palos Verdes
were made with a net of identical dimensions but
of heavier construction and otter boards.4 The
nets were towed at a speed of 1.3 m/s (2.5 knots)
and remained in contact with the ocean floor for
10 min. When the net was brought aboard ship,
specimens of Dover sole, with eroded fins (dis-
eased) and without eroded fins (unaffected), were
removed, bagged, labeled, and immediately
frozen. The frozen samples were returned to the
laboratory and placed in freezers.

ORANGE
COUNTY

DEPTHS IN METERS

FIGURE 1. — Stations off Palos Verdes and Orange County at
which Dover sole were collected.

The following numbers of Dover sole were ob-
tained from each of the 1974 quarterly trawl
series: winter (December 1973-February 1974),
10 from off Palos Verdes; spring (March-May
1974), 15 from off Palos Verdes and 5 from off
Orange County; summer (June-August 1974), 6
from off Palos Verdes; and fall (September-
November 1974), 17 from off Orange County.

The mean and the standard error of the stan-
dard lengths for the Palos Verdes samples with
(n = 16) and without (n = 15) eroded fins were

3Klontz, G. W., and R. A. Bendele. 1973. Histopathological
analysis of fin erosion in southern California marine fishes.
South. Calif. Coastal Water Res. Proj., Rep. TM 203.

4This net was constructed for the Coastal Water Project by
J. Willis, Morro Bay, Calif.

514

McDERMOTT EHRLIC'H ET A I, Clll.l >KINA TKI ) 1 1 YI)R< X AKI'.i >NS IN IHIVKR SOI.K

174 ± 3 mm and 193 ± 6 mm, respectively; the
respective body weights were 78 ± 5 g and 115 ±
11 g. Measurements for the diseased (n = 14) and
unaffected (n = 8) Orange County specimens
were 195 ± 4 mm and 182 ± 7 mm SL, 119 ± 8 g
and 98 ± 10 g, respectively. These fish were gen-
erally 3 to 4 yr old, though some were younger and
some older. The mean standard lengths of several
age-classes of over 425 southern California Dover
sole collected at coastal locations by small otter
trawl were as follows: age-class I, 70 mm; II,
140 mm; III, 170 mm; IV, 190 mm; V, 220 mm
(Mearns and Harris5).

Muscle tissue subsamples were excised from
each of the specimens when they were semi-
thawed. The dissections were performed on
cleaned Teflon6 sheets, using carbon steel imple-
ments. The tissue samples were placed in glass
containers, which had been heated overnight in
a kiln at 538°C (1,000°F). The samples were then
frozen until chemical analyses were performed.

Levels of total DDT and total PCB were mea-
sured in the samples using electron-capture gas
chromatography (Young et al. 1976b). The com-
ponents were identified by retention time; values
were derived by comparing the peak heights of the
samples with the peak heights of standards.

RESULTS AND DISCUSSION

Migration Hypothesis

The hypothesis that the diseased Dover sole
collected off Orange County had migrated from
the Palos Verdes shelf was tested by measuring
the levels of total DDT and total PCB in muscle
tissue from specimens with and without eroded
fin tips from both locations. To discount possible
seasonal variability, all results obtained for each
disease category at an individual station were
combined on a quarterly basis. To discount possi-
ble station variability, only data from those sta-
tions for which both diseased and unaffected
specimens had been analyzed were used. For com-
parison, we used the median total DDT and total
PCB concentrations for diseased and unaffected
fish. Tables 1 and 2 present the results for total
DDT and total PCB, respectively.

TABLE l, — Median concentrations (milligrams per kilogram
wet weight) of total DDT in muscle tissue of Dover sole, with
and without eroded fins, collected off Palos Verdes Peninsula
and Orange County, 1974 quarterly trawl series.

Diseased

Unaffected

Location

(with eroded fins)

(without eroded fins)

Station

Quarter

Median

Range

Median

Range

Palos

Verdes:

Winter

15 -29

7.0

2.0-12

Winter

29 -44

1.8

1.3- 2.3

Spring

18 -34

—

Spring

16 -24

5.0

4.3- 5,3

Spring

7.2-45

9.6-13

Spring

—

Summer

80-29

8.8-13

Orange

County:

Spring

19 -75

7.6

—

Fall

7.6

4.2-57

1.0

0.3- 17

Fall

—

1.2

0.3- 2 2

Fall

4.2

0.9- 6 1

0.4

0.4- 0.5

TABLE 2. — Median concentrations (milligrams per kilogram
wet weight) of total PCB in muscle tissue of Dover sole, with
and without eroded fins, collected off Palos Verdes Peninsula
and Orange County, 1974 quarterly trawl series.

Diseased

Unaffected

Location

(with eroded fins)

(without eroded fins)

Station

Quarter

Median

Range

Median

Range

Palos

Verdes:

Winter

2.6

1.8-3.6

1.2

0.6-1.9

Winter

3.8

3.4-1.3

0.3

02-0.5

Spring

2.0

1 7-2.2

2.6

—

Spring

2.4

1.5-3.4

0.5

0.4-0.6

Spring

1.0

. 0.8-3 0

1.4

1.4-1 5

Spring

2.1

—

1.6

—

Summer

1.5

0.6-3.3

1.0

0.8-2.6

Orange

County:

Spring

3.0

2.1-6.6

—

Fall

3.4

1.3-5.2

4.0

1.8-6.2

Fall

1.6

—

0.3

Fall

0.9-1.1

0.3

0.2-0.3

5Mearns, A. J., and L. H. Harris. 1975. Age, length, and weight
relationships in southern California populations of Dover sole.
South. Calif. Coastal Water Res. Proj., Rep. TM 219.

6Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

Using the Mann- Whitney Latest, we found no
significant difference (P>0.20) between total
DDT concentrations in the muscle tissue of dis-
eased fish from the Orange County and Palos
Verdes regions. The overall median total DDT
concentrations were 13 and 18 mg/kg wet weight,
respectively. In contrast, there was a significant
difference (P<0.05) between total DDT levels in
the unaffected fish from the two regions (over-
all medians of 1.1 and 11 mg/kg wet weight,
respectively).

In this study, the overall median values ob-
tained for total DDT levels in diseased Dover
sole from both areas and in the unaffected fish
from Palos Verdes were 10 or more times greater
than the overall median value obtained for the
unaffected Orange County specimens. McDermott
and Heesen (1975) had previously found that the

515

FISHERY BULLETIN: VOL. 75, NO. 3

median level of total DDT in muscle tissue from
Dover sole collected off Palos Verdes was about
10 times greater than the median level observed
for the Orange County specimens (McDermott
and Heesen7).

These results support the hypothesis that the
Dover sole with fin erosion collected off Orange
County came from the Palos Verdes population.
They also suggest that levels of DDT in tissues
may be used as a tag when investigating local
migrations of fish from or across a known point
source of DDT.

There were no significant differences (P>0.20)
between the total PCB levels in unaffected Dover
sole from Orange County and Palos Verdes, nor
between the total PCB levels in diseased fish from
the two areas. The overall median total PCB con-
centrations in muscle tissue of unaffected fish
from Orange County and Palos Verdes were 0.6
and 1.2 mg/kg wet weight, respectively; from dis-
eased specimens, 2.3 and 2.1 mg/kg wet weight,
respectively.

Association of Chlorinated Hydrocarbons
with Fin Erosion

Since the diseased fish at Orange County appear
to have originated from Palos Verdes and the
Palos Verdes area is the primary site of total DDT
and total PCB sediment contamination, only the
results obtained for total chlorinated hydrocarbon
measurements in diseased and unaffected Dover
sole collected from Palos Verdes were utilized to
test for the association of chlorinated hydro-
carbons with fin erosion. Using the Mann-
Whitney 17-test we found that the DDT levels in
diseased Palos Verdes Dover sole were signifi-
cantly greater (P<0.05) than the DDT levels
measured in unaffected Palos Verdes specimens.
The overall median values for diseased and un-
affected Dover sole were 18 and 11 mg/kg wet
weight, respectively.

Differences in the levels of total PCB in the
muscle tissue of diseased and unaffected Dover
sole were significant only at the 90% confidence
level (P<0.10). Thus there was a tendency for
the total PCB levels to be higher in the diseased

fish. The median values for the diseased and un-
affected groups were 2.1 and 1.2 mg/kg wet
weight, respectively.

These results indicate that there is a significant
association between high levels of total DDT and
fin erosion, and a possible association between
high levels of total PCB and fin erosion in Dover
sole collected off Palos Verdes.

There are several possible reasons for these
associations. DDT and PCB in combination with
each other and/or other constituents present in
this region (such as hydrogen sulfide, high levels
of trace metals, or abrasive materials) could be
involved in the development of the disease. Alter-
natively, chlorinated hydrocarbon uptake could
be enhanced in diseased fish; hence the higher
levels might be the result of the disease rather
than a cause. A third possibility is that the fish
with fin erosion have been present on the Palos
Verdes shelf longer than the unaffected fish and
have been exposed to the chlorinated hydro-
carbons for a longer period of time. These possible
explanations are presently under investigation.

It is interesting to note that while the Palos
Verdes municipal wastewater discharges of DDT
significantly decreased from greater than 20
metric tons in 1971 to 2 metric tons in 1974
(Young et al. 1975), the levels of DDT in the Dover
sole have remained unchanged (McDermott and
Heesen see footnote 7). Similarly, the level of DDT
in the surface sediments off the Palos Verdes
Peninsula remained relatively constant over the
3-yr period, 1971-73 (Young et al. 1975; Young et
al. 1976b). The situation for PCB is similar. The
discharge of PCB decreased from greater than
19 metric tons in 1972 to 5 metric tons in 1974
(Young et al. 1976a) and the levels of PCB in the
Dover sole remained unchanged (McDermott et
al. 1976). Unfortunately, reliable historical data
for PCB's in the Palos Verdes surface sediments
are not available. The overall prevalence of fin
erosion in Dover sole also remained relatively
constant over the same time period (Sherwood
and Mearns8). These findings point to the poten-
tially significant role that the sediments may
have in the uptake of chlorinated hydrocarbons
and in the development of fin erosion in Dover
sole.

'McDermott, D. J., and T. C. Heesen. 1975. DDT and PCB
in Dover sole around outfalls. In Coastal water research project
annual report, p. 117-121. South. Calif. Coastal Water Res.
Proj., El Segundo.

"Sherwood, M. J., and A. J. Mearns. 1975. Sampling diseased
fish populations. In Coastal water research project annual
report, p. 27-32. South. Calif. Coastal Water Res. Proj., El
Segundo.

516

Mc-DERMOTT-EHRLICH ET AL.: CHLORINATED HYDROCARBONS IN DOVER SOLE

SUMMARY

1. Levels of DDT in Dover sole with fin erosion
collected off Palos Verdes and Orange County
were not significantly different. This is con-
sistent with the hypothesis that the Orange
County diseased fish migrated from the Palos
Verdes region and that the disease did not
originate at Orange County.

2. A dominant point source discharge of a con-
taminant, such as the municipal wastewater
discharge of DDT compounds off Palos Verdes,
may provide a useful tag when investigating
the migration offish from or across that point
source.

3. Dover sole with fin erosion from Palos Verdes
have significantly higher levels of total DDT
(P<0.05) than Dover sole without the disease
from the same region.

4. There is a tendency for Dover sole with fin
erosion from Palos Verdes to have higher
levels of PCB (P<0.10) than Dover sole with-
out the disease from the same region.

ACKNOWLEDGMENTS

We thank Douglas Hotchkiss and the field staff
of the County Sanitation Districts of Los Angeles
County for their cooperation in this work. We also
appreciate the efforts of M. James Allen, Elliot
Berkiheiser, Edward Motola, Ileana Szpila,
Harold Stubbs, and Robert Voglin of this Project.
This work was supported in part by Grants
R801152 and R801153 from the Environmental
Protection Agency. Contribution no. 84 of the
Southern California Coastal Water Research
Project.

LITERATURE CITED

BUHLER, D. R., M. E. RASMUSSON, AND W. E. SHANKS.

1969. Chronic oral DDT toxicity in juvenile coho and
chinook salmon. Toxicol. Appl. Pharmacol. 14:535-555.

Galloway, J. N.

1972. Man's alteration of the natural geochemical cycle of
selected trace metals. Ph.D. Thesis, Univ. California,
San Diego, 143 p.

Grzenda, A. R., D. F. Paris, and w. J. Taylor.

1970. The uptake, metabolism, and elimination of chlori-
nated residues by goldfish {Carassius auratus) fed a 14C-

DDT contaminated diet. Trans. Am. Fish. Soc. 99:
385-396.
HAGERMAN, F. B.

1952. The biology of the Dover sole, Microstomas pacificus
(Lockington). Calif. Dep. Fish Game, Fish Bull. 85, 48 p.
HANSEN, D. J., AND A. J. WILSON, JR.

1970. Residues in fish, wildlife and estuaries. Significance
of DDT residues from the estuary near Pensacola, Fla.
Pestic. Monit. J. 4:51-56.
MACEK, K. J., C. R. RODGERS, D. L. STALLING, AND S. KORN.
1970. The uptake, distribution and elimination of dietary
14C-DDT and 14C-dieldrin in rainbow trout. Trans. Am.
Fish. Soc. 99:689-695.
MAHONEY, J. B., F. H. MIDLIGE, AND D. G. DEUEL.

1973. A fin rot disease of marine and euryhaline fishes in
the New York Bight. Trans. Am. Fish. Soc. 102:
596-605.

MCDERMOTT, D. J., D. R. YOUNG, AND T. C. HEESEN.

1976. PCB contamination of southern California marine
organisms. In Proceedings of the National Conference
on Polychlorinated Biphenyls, 19-21 Nov. 1975, Chicago,
p. 209-217. EPA Rep. 560/6-75-004.

MEARNS, A. J., AND M. SHERWOOD.

1974. Environmental aspects of fin erosion and tumors in
southern California Dover sole. Trans. Am Fish. Soc.
103:799-810.

MURCHELANO, R. A.

1975. The histopathology of fin rot disease in winter
flounder from the New York Bight. J. Wildl. Dis. 11:
263-268.

Southern California Coastal Water research
Project.

1973. The ecology of the Southern California Bight:

Implications for water quality management. South.

Calif. Coastal Water Res. Proj., El Segundo, TR 104, 531 p.

WELLINGS, S. R., C. E. ALPERS, B. B. MCCAIN, AND B. S.

MILLER.

1976. Fin erosion disease of starry flounder (Platichthys
stellatus) and English sole (Parophrys uetulus) in the
estuary of the Duwamish River, Seattle, Washington.
J. Fish Res. Board Can. 33:2577-2586.

YOUNG, D. R., D. J. MCDERMOTT, AND T. C. HEESEN.

1976a. Marine inputs of polychorinated biphenyls off
southern California. In Proceedings of the National
Conference on Polychlorinated Biphenyls, 19-21 Nov.
1975, Chicago, p. 199-208. EPA Rep. 560/6-75-004.
1976b. DDT in sediments and organisms around southern
California outfalls. J. Water Pollut. Control Fed. 48:
1919-1928.
YOUNG, D. R., D. J. MCDERMOTT, T. C. HEESEN, AND D. A.
HOTCHKISS.

1975. DDT residues in bottom sediments, crabs, and
flatfishes off southern California submarine outfalls.
Calif. Water Pollut. Control Assoc. Bull. 12:62-66.
YOUNG, D. R., C. S. YOUNG, AND G. E. HLAVKA.

1973. Sources of trace metals from highly-urbanized
southern California to the adjacent marine ecosystem.
In Cycling and control of metals, p. 21-39. U.S. Environ.
Prot. Agency, Natl. Environ. Res. Cent., Cincinnati, Ohio.

517

DIEL BEHAVIOR OF THE BLUE SHARK, PRIONACE GLAUCA,
NEAR SANTA CATALINA ISLAND, CALIFORNIA1

Terry C. Sciarrotta2 and Donald R. Nelson3

ABSTRACT

The diel activity levels and movements of the blue shark, Prionace glauca, were studied in the natural
environment using ultrasonic telemetry. Two initial sharks were tagged with single-channel trans-
mitters equipped with depth sensors. Twelve sharks were tagged with multichannel transmitters with
various combinations of sensors to measure depth, swimming speed, swimming direction, and temper-
ature. From March to early June, the sharks made an evening-twilight migration from their
epipelagic daytime habitat to the shallower waters bordering the island. From late June to October, the
sharks remained offshore throughout the day and night. This change in movement pattern is suggested
to be in response to a seasonal shift in location of prey. The telemetry data indicated that the blue shark
is basically nocturnal, showing highest activity in the early evening and lowest activity in the early
daylight morning. Measured parameters increasing at night included 1) rate of horizontal movement,
2) swimming speed, 3) variability in depth, and 4) variability in swimming direction. The sharks
usually remained within a relatively narrow range of water temperatures.

This paper describes a study in which the diel
activities of an epipelagic shark were monitored
remotely in the natural environment. Multichan-
nel ultrasonic transmitters were used to telemeter
certain behavioral and environmental parameters
of free-ranging blue sharks, Prionace glauca (Lin-
naeus). The primary objective was to track the
sharks continuously throughout the day-night
cycle to determine diel patterns of activity and
movement.

Prior to the initiation of this study, surprisingly
little had been published on the behavior of the
blue shark, one of the most abundant large pred-
ators in warm temperate seas. Bigelow and
Schroeder (1948) summarized what was then
known about the biology of the species. Suda
(1953) studied embryonic development, size re-
lationsips, and sex ratios as related to distribution
in the north tropical and subtropical Pacific.
Strasburg (1958) investigated the distribution,
abundance, capture depths, reproduction, and food
habits of pelagic sharks, including the blue shark,
in the central Pacific. Miscellaneous data on blue

'Adapted in part from the Masters Thesis of the senior author,
Sciarrotta.

department of Biology, California State University, Long
Beach, Calif.; present address: Southern California Edison,
Water Quality Biology Group, 2244 Walnut Grove Ave., Rose-
mead, CA 91770.

department of Biology, California State University, Long
Beach, CA 90840.

Manuscript accepted February 1977.
FISHERY BULLETIN: VOL. 75, NO 3, 1977.

sharks have been reported from the Atlantic
( Aasen 1966), the Canadian Atlantic (Templeman
1963), and the Gulf of Alaska (LeBrasseur 1964).
A study of the blue shark off southern California,
still largely unpublished, was conducted by Bane
(1968).

More recently, the blue sharks off southwest
England have received investigation in regard to
age determination, reproduction, diet, and migra-
tion (Stevens 1973, 1974, 1975, 1976; Clarke and
Stevens 1974). Casey, Stillwell, and Pratt at Nar-
ragansett, R.I. have gathered considerable infor-
mation on the biology of sharks of that area, in-
cluding data on migrations, food habits, and
reproduction of blue sharks (Weeks 1974; Casey
1976; Stevens 1976). Tag returns from these
studies have documented some long-range, long-
term movements by blue sharks in the Atlantic.
Several similar movements have also occurred in
the Pacific (Bane 1968; D. R. Nelson, unpubl.
data — see Discussion). Short-term movements,
however, such as related to the diel cycle, have not
been described for the blue shark.

Observations relating to the diel patterns of
sharks have been mentioned by several authors
(Springer 1963; Limbaugh 1963; Randall 1967;
Hobson 1968), but specific quantitative studies
have been few. Nelson and Johnson (1970) found
that the horn shark, Heterodontus francisci, and
the swell shark, Cephaloscyllium ventriosum,
exhibited distinctly nocturnal activity patterns

519

FISHERY BULLETIN: VOL. 75, NO. 3

under laboratory and field conditions. In sub-
sequent work with the horn shark, Finstad and
Nelson (1975) measured the effect of light inten-
sity on releasing activity onset, both in the natural
environment and in the laboratory under artificial
twilight transitions. For a colony of captive bon-
nethead shark, Sphyrna tiburo, under semi-
natural conditions, Myrberg and Gruber (1974)
reported a late-afternoon peak in patrolling speed,
suggesting a diurnal activity rhythm.

Using ultrasonic telemetry, Standora (1972) es-
tablished a basically nocturnal pattern of activity
and a limited home range for the Pacific angel
shark, Squatina californica. His multichannel
transmitters were a similar, but earlier version of
those used in the present study. Carey and Lawson
(1973) tracked a free-ranging dusky shark, Car-
charhinus obscurus, in order to study body tem-
perature regulation. They used a two-channel,
frequency-shifting transmitter that measured
both surface and deep body temperatures. Thorson
( 1971) monitored long-term movements of the bull
shark, C. leucas, with relatively long-life, sensor-
less pingers and automatic-recording receivers at
several locations. Using this technique in conjunc-
tion with conventional tagging, he showed that
bull sharks move via the San Juan River from the
Caribbean Sea to Lake Nicaragua.

The present paucity of behavioral information
on active, wide-ranging sharks, especially pelagic
species, is undoubtedly due in part to the difficulty
of studying them by direct observation. Ultrasonic
telemetry now offers one promising avenue of ap-
proach to this problem. This paper reports on an
initial study using this technique to investigate
diel patterns of behavior in a wide-ranging pelagic
shark.

METHODS

The present study is based on 14 individual
telemetry trackings conducted between 3 March
and 7 October 1972 (Table 1). Each tracking was
initiated in the pelagic environment of the San
Pedro Channel approximately 6 to 7 km north of
the Isthmus, Santa Catalina Island, Calif. The
blue shark was well suited for this telemetry study
because of its moderately large size, high abun-
dance for most of the year, and attractability to
bait. The abundance and/or attractability of blue
sharks in the offshore baiting area was low only
during the months of January and February, the
sharks being easily obtainable the rest of the year.

TABLE 1. — Summary of tracking data for 14 telemetered blue

sharks.

Track-

Esti-

Tracking

Evening

ing

Date

mated

duration

Tracking

shoreward

no.

(1972)

TL(m)

Sex

(h)

period

movement

3/3

1.8

7.0

1040-1740

3/11

2.3

8.5

0910-1740

3/17

2.3

6.4

1105-1730

beginning

3/30

2.0

11.6

1125-2300

yes

4/7

2.6

8.4

1145-2010

yes

4/15

2.0

16.1

1155-0400

yes

4/29

1.8

18.0

1200-0600

yes

5/6

2.0

21.9

1010-0805

yes

5/20

2.0

19.6

1 1 55-0730

yes

6/3

2.2

16.3

1615-0830

yes

6/14

2.3

4.8

1145-1630

6/24

2.3

14.8

1445-0530

9/13

2.0

13.4

1305-0230

10/7

2.0

18.8

1215-0700

The estimated range in total lengths of blue
sharks telemetered was 1.8 to 2.6 m; for those
otherwise observed, 1.2 to 3.0 m.

Telemetry System

The ultrasonic telemetry system used in the
present study has been described in detail by
Standora (1972), Ferrel et al. (1974), and Nelson
( 1974). The transmitters were of the oil-filled type,
about 15 to 18 cm long, 3.5 cm in diameter, and
emitted 10-ms pulses (tone bursts) at 40 kHz. The
units were set for a life of several days, and a
maximum range of 3 km (average conditions) to 5
km (ideal conditions). Data were encoded as pulse
rate (pulse interval) which varied with the value
of resistive sensors. The first two trackings
utilized single-channel transmitters incorporat-
ing depth sensors. The remaining 12 trackings
were performed with multichannel units (rapid-
multiplexing type) with various combinations of
sensors to measure depth, swimming speed,
swimming direction, and temperature.

Two commercial tunable ultrasonic receivers
were used. For continuous monitoring of rela-
tively clear, nearby signals, the Smith-Root
Ta-254 receiver (25-80 kHz) was employed using
an omnidirectional hydrophone on a 25-m cable.
The more sensitive, narrow-band DuKane model
N15A235 receiver (30-45 kHz) with its staff-
mounted directional hydrophone was used for
directional tracking and for reception of weaker
signals.

4 Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

520

SCIARROTTA and NELSON: DIEL BEHAVIOR OF BLUE SHARK

Application, Tracking, and Recovery

The sharks to be tagged were attracted with bait
to the 7-m tracking boat. Cut Pacific mackerel,
Scomber japonicus, in two bait cannisters, was
suspended at depths of about 5 and 15 m. Since
drifting of the boat established the odor corridor
necessary for shark attraction, the time needed for
attraction decreased as the wind (and drift rate)
increased. The time necessary to attract the first
blue shark ranged from 10 min to 4 h and the mean
was 1.5 h.

Whenever a choice was possible, a larger indi-
vidual shark was selected for tagging in order to
lessen the possible effect of the transmitter on its
behavior. The shark to be tagged was enticed to
the surface next to the boat using a short baited
line, then harpoon tagged in the middorsal region
anterior to the first dorsal fin. The sex of the shark
was noted and its total length estimated (Table 1).
An attempt was made to prevent the shark from
actually taking the bait, as this might have
influenced subsequent feeding motivation.

The transmitter was attached to the shark by a
stainless steel dart (Floy FH 69) thrust beneath
the skin with a hand-held applicator pole. The
transmitter package included a syntactic foam
float and a magnesium breakaway link which cor-
roded through in a roughly predictable time, al-
lowing the unit to float to the surface for recovery.

The tracking procedure involved continuous
monitoring of the signal from the drifting boat
using the omnidirectional hydrophone. As the
signal became weak, its direction was determined
with the directional hydrophone, and the boat was
then moved closer to the shark. Distance to the
shark was estimated primarily from approximate
signal strength and by triangulation from suc-
cessive positions of the moving boat. To minimize
the effect of the boat on the shark's behavior, an
effort was made to maintain a distance of at least
200 m between the boat and the shark.

Ultrasonic tracking in the study area at times
presented certain problems. Noise from crusta-
ceans, echo-locating cetaceans, ship traffic, wave
action, hydrophone turbulence, and bottom echoes
could be picked up by the receivers, and if of high
enough level, would mask the data pulses. Signal
reception was also affected when the shark went
below the thermocline (reflection) or was swim-
ming very near the surface (wave shielding,
bubble attenuation, downward ray refraction).
These factors at times caused signal losses that

could be counteracted only by lowering the hydro-
phone to a depth of about 10 or 15 m.

Data Recording and Reduction

Approximately once per half-hour, a 30-s data
sequence was recorded on magnetic tape and the
estimated position of the shark plotted. The
omnidirectional hydrophone was preferred for
recording purposes whenever the signal was
sufficiently strong. It was less convenient to use
the directional hydrophone for recording long data
sequences because of the difficulty of maintaining
continuous accurate aim, thus resulting in greater
signal-strength variability.

Decoding of the single-channel depth data re-
quired only a stopwatch and calibration graph.
Ten pulse intervals were timed and converted to a
depth value. For the multichannel data, the tape
recordings were converted into paper oscillograms
on which the pulse intervals were measured man-
ually. For analysis, the mean value for three clear
8-channel sequences were graphed for each half-
hour recording period.

RESULTS

The telemetered blue sharks were generally
most active at night, with highest activity in the
early evening and lowest activity in the early day-
light morning. While some activity occurred
throughout the diel cycle, the mean recorded val-
ues for all trackings were greater at night for 1)
rate of horizontal movement, 2) swimming speed,
3) variability in depth, and 4) variability in
swimming direction. Experienced tracking per-
sonnel were also able to detect by ear subtle
changes in the multiplexed pulse intervals. Al-
though not quantified, the trackers received the
distinct impression that these changes occurred
more often at night — thus further supporting a
nocturnal activity maximum.

Horizontal Movement —
Island-Oriented Migration

The most striking behavior demonstrated by the
present study was a seasonal, evening-twilight
migration from the epipelagic offshore habitat to
the shallower waters bordering the island. Be-
tween late March and early June, each of the
seven sharks tracked made this movement to-

521

FISHERY BULLETIN: VOL. 75, NO. 3

FIGURE 1. — Positions of seven blue sharks tracked from late
March through early June 1972. Note that all day positions are
offshore from the island, while the majority of night positions are
nearshore, often in relatively shallow water.

wards the island shoreline. Examples of trackings
of this type are shown in Figures 1 and 2.

These sharks remained offshore in the general
vicinity of the tagging during the daylight hours.
Approximately at dusk, the sharks initiated a rel-
atively straight-line course towards the island. It
is difficult to place precise times on when the
sharks began this move, but it appeared to be from
about 1.6 h before to 1.3 h after sunset, with a
mean slightly after sunset. During the shoreward
movement, the sharks swam at depths varying
from near the surface to over 90 m. Once near the
island, the sharks usually moved in an easterly
direction parallel to the shoreline. Several hours
before sunrise, there was a directed movement
away from the island back to the offshore envi-
ronment. The closest estimated nighttime ap-
proaches to the island for these individuals aver-
aged 1,100 m (range, 200-4,000), corresponding to
water depth averaging 115 m (range, 80-380).

Although three preliminary trackings in early
and mid-March ended prior to nightfall, the last of
these appeared to show the beginnings of a shore-
ward movement prior to transmitter release. One
tracking in mid-June ended prematurely prior to
dusk. From late June until early October, the
three sharks successfully tracked remained off-
shore throughout the day and night over bottom
depths of 500 m or more (Figures 3, 4).

Rate of Horizontal Movement

Rate of movement was calculated for each shark
from its half-hourly estimated positions such as

522

shown in Figures 2 and 4. The mean values for all
sharks tracked (Figure 5) showed an increase in
rate of movement at sunset which continued
through most of the night. The mean rate of
movement for the daytime was 1.2 km/h (range,
0.3-7.0); for the nighttime, 1.8 km/h (range, 0.4-
4.0).

Swimming Speed

There was a definite increase in telemetered
instantaneous swimming speed at night (Figure
5). However, no abrupt increase in speed occurred
at the dusk transition, as might be expected in
view of the rate of movement increase at that time.
Swimming speed peaked a few hours after sunset
and remained comparatively high until a few
hours before sunrise. The artifactual burst of
speed immediately after tag application was short
lived, even in those sharks that did not promptly
return to the bait cannister.

Although the maximum speed capability of the
sensor was 5 km/h, this speed was not often
reached during the half-hourly data recording
periods, which suggests speeds in excess of 5 km/h
seldom occurred. The mean swimming speed for
the daytime was 1.3 km/h, for the nighttime 2.8
km/h, while the range for both covered the entire
sensor range.

Increases in swimming speed were often as-
sociated with brief dives during the same record-
ing session (Figures 2, 4). In seven of the eight
trackings in which both speed and depth were
telemetered, and where tracking extended at least
into dusk, the highest mean speeds occurred at
relatively great depths (means: 4.8 km/h, 69 m)
while the lowest speeds occurred at much shal-
lower depths (means: 0.5 km/h, 20 m). This
suggests that some factor in deeper water stimu-
lated this speed increase, possibly presence of food.

Swimming Direction

Figure 5 shows clearly the relationship between
swimming speed and rate of movement through-
out the diel cycle. As expected, swimming speeds
had the higher values, as the two measures would
have been equal only in cases where the shark
swam in a straight line for the entire 30-min in-
terval between position determinations. During
daylight hours both rates were moderately close,
suggesting that the sharks made gradual changes
in swimming direction rather than abrupt

SCIARROTTA and NELSON: DIEL BEHAVIOR OF BLUE SHARK

0 *>»

0 night

0 2000
m«t»r l

StOft

-5°0 - T

~~~~~ T"~"

100 meters . \

^~« .-■ --■ f>v-- i~— :-"

Isthmus Cove

SANTA

CATALINA ISLAND

9° ..)

o *>»

0 ' 2(

m«t#f»

100 meters

l'frrj^ .Ovt;

SANTA

CATALINA ISLAND

TIME OF DAY

18 20

TIME OF DAY

FIGURE 2. — Data from two individual trackings of blue sharks typical of the late March to early June period. Top, shark positions at
approximately 0.5-h intervals. Bottom, telemetered sensor data. Note the characteristic evening-twilight migration towards the
island, the initial plunge occurring immediately after transmitter application, and the close correlation between temperature and
depth. Depths in excess of 110 m (the sensor limit) are indicated by x x.

changes. During the dusk transition, rate of
movement most closely matched swimming speed,
indicating the greatest consistency in swimming

direction. In timing, this coincides with the rela-
tively oriented shoreward migrations of from late
March to early June. The greatest disparity be-

523

FISHERY BULLETIN: VOL. 75. NO. 3

O dor

C twilight

• mghi

• cu »

o
%°o

• ° •

-t*-

FIGURE 3.— Positions of three blue sharks tracked from late
June to early October 1972. Note that both day and night posi-
tions are well offshore over relatively great depths.

tween rate of movement and swimming speed was
during the early evening, evidence that much of
the swimming then was variable in direction — a
possible indication of searching for and/or pursu-
ing prey. Beginning in the early morning and con-
tinuing through dawn, the differences between
the two rates lessened.

A compass sensor for direct measurement of in-
stantaneous swimming direction (azimuth) was
incorporated during only one successful tracking.
The compass data from this tracking (Figure 4)
show that the greatest number of multiple-
direction recordings (i.e., during single-recording
periods) occurred at night, suggesting that vari-
ability of swimming direction is generally greater
at night. During one nighttime recording, a
change of at least 360° coupled with a speed
change of 1 to 5 km/h was noted during one 15-s
period.

variability in depth. During four trackings, the
sharks may have been close to the bottom when in
the relatively shallow water near the island.

The first hour of depth data were excluded from
Figure 6 because of what appears to be an initial
plunge induced by tagging trauma. As shown in
Figure 7, the data also suggest that this initial
effect decreased or disappeared within 1.5 h after
tagging. About half of the sharks tagged exhib-
ited this "abnormal" plunge (to a mean depth of at
least 95 m) within 0.5 h of being tagged. The others
apparently did not — possibly a result of the tag
dart penetrating in a less sensitive spot. Of the
first nine sharks tagged, six were seen to return to
the bait cannister within seconds after transmit-
ter application — suggesting little, if any, tagging
trauma. Two of these six sharks, however, still
made a deep dive by the next recording session.

Temperature

Blue sharks in the study area appeared to prefer
a relatively narrow range of water temperatures.
Overall, the telemetered sharks were found in a
temperature range of 8.5° to 17.5°C, but occurred
in the much narrower range of 14.0° to 16.0°C for
73% of the time. Seasonality of diel depth/tem-
perature selectivity was not apparent from either
the temperature or depth data. As expected, the
telemetered depth and temperature data usually
corresponded quite well, i.e., an increase in depth
accompanied by a decrease in temperature (Fig-
ures 2, 4). Individuals were most often seen
swimming at the surface during the cooler
months, but rarely during either the coldest or
warmest months, a behavior that may have been
influenced by surface temperatures.

Vertical Movement

DISCUSSION

Figure 6 illustrates the mean depths teleme-
tered from all sharks with transmitters equipped
with depth sensors. The sharks were within a
depth range of 18 to 42 m for 92% of the time; they
appeared to equal or exceed 100 m only during
3.9% of the readings (excluding initial plunges).
The apparent tendency was a slight increase in
mean depth at night. The mean daytime depth was
30 m; at night 40 m. Individual tracking graphs
show that the sharks covered the entire depth
range of the sensors (0-110 m) during both day
and night, but that at night there were more verti-
cal excursions from shallow to deep, i.e., greater

It is not surprising that the blue shark appears
more active at night than during the day. Car-
charhinids in general are considered by Randall
(1967) to be nocturnal. In addition, most sharks
studied quantitatively in this regard have proven
to be basically nocturnal, the bonnethead shark
studied by Myrberg and Gruber (1974) being a
possible exception. Like other nocturnal sharks,
however, blue sharks certainly feed diurnally at
times, and it is common knowledge that they read-
ily respond to opportunistic feeding stimuli (e.g.,
bait) during the day. There have also been obser-
vations of blue sharks feeding naturally during

524

SCIARROTTA and NELSON: DIEL BEHAVIOR OF HI. IK SHARK

O <*°r

1 twilight

• n.tjhl

0 2000
rMftri

start

-.500 m i*_

100 meters

"----—-..

._.---- - —-■■'

'--.

Isfrimus

X vt

SANTA

CATALINA ISLAND

O dai

O twilight

*\9\

• night

0 2000
meter i

~5°0„

t^T

100 meters...

.„,.. ...--- ••-

'"--..

Isthmus Cove

SANTA

CATALINA ISLAND

"i — i r

18 20 22

TIME OF DAY

8 «H

PuJr=

zSHc
< o-|z

10-

So *-

X XXX

Jtxx X

t — i — i — i — i — i — i — i — i — i — i i i i i i r-

12 14 16 18 20 22 24 02 04

TIME OF DAY

1 1

FIGURE 4. — Data from two individual trackings of blue sharks typical of the late June to early October period. Top, shark positions at
approximately 0.5-h intervals. Bottom, telemetered sensor data. Note the absence of shoreward movement, the increased swimming
speed and depth at night (left), and the greater frequency of sudden direction change, i.e., multiple-direction recordings, at night I right ).

the day, e.g., on blacksmith, Chromis punctipinnis
(R. R. Given pers. commun.; D. R. Nelson unpubl.
data) and on northern anchovy, Engraulis mordax
(T. C. Sciarrotta unpubl. data).

The large size of the blue shark's eye suggests
adaptation to low light, as in general, nocturnal
fishes have relatively large eyes. However, large
eyes are also associated with moderately deep

525

FISHERY BULLETIN: VOL. 75, NO. 3

times of fog applicodon

\ /. / »-x r \ — ~m * \

\/\ / " V /\\

X \ ,* f~~x „x «•/

fiATE OF MOVEMENT

"I 1 1 T~

i — r — i — r-

TIME OF DAY

— i 1 1 1 — i r

02 04 06

FIGURE 5. — Comparison of mean rate of movement (all sharks)
and telemetered swimming speed (sharks with speed sensors) for
blue sharks. Note the increase in both parameters at night, the
greater values for swimming speeds (as expected), the close simi-
larity during times corresponding to shoreward movements (rel-
atively straight swimming), and the large disparity in early
evening (relatively nonstraight swimming).

20 22

TIME OF DAY

FIGURE 6.— Mean depths of all blue sharks tracked with trans-
mitters having depth sensors. The first hour of each tracking is
deleted because of the initial plunge in response to tag applica-
tion. Note the generally greater depths at night.

habitat (mesopelagic), but since the blue shark's
habitat appears relatively shallow (epipelagic),
the large eye would seem best suited to visual
hunting at night.

It is known that cephalopods and small pelagic
fishes form a major part of the diet of blue sharks
(Strasburg 1958; Stevens 1973; Tricas 1977). The
observed seasonal differences in diel movement
patterns (Figures 1, 3) may reflect differences in
type or location of prey. Fishery landings of mar-
ket squid, Loligo opalescens, were high during
February to June 1972, but low from July to De-
cember (Pinkas 1974), thereby indicating the in-
shore presence of spawning congregations (Frey

TIME AFTER APPLICATION (hr)

FIGURE 7. — Mean depths of blue sharks for the first 3 h of each
tracking. Upper curve, all 12 sharks carrying transmitters with
depth sensors. Lower curve, seven sharks judged to have made
an "abnormal" plunge in response to the trauma of tag applica-
tion. Note that the initial depth response appears to have sub-
sided by the recording session 1.5 h after application.

1971), which are susceptible to commercial
fishermen using night-lighting techniques. Cou-
steau and Cousteau (1970) described blue sharks
gorging themselves on spawning squid that were
light-attracted to the surface near their vessel.

The evening-twilight onshore movements
which occurred during March to early June may
be due to the nearshore abundance of squid and a
possibly reduced availability of prey offshore.
Conversely, the offshore pattern from late June to
October may be a result of reduced squid popula-
tion nearshore, but increased populations of jack
mackerel, Trachurus symmetricus, and anchovy
offshore. The limited stomach-content data col-
lected during this study support this hypothesis.

In regard to depth/temperature preferences, the
results of Strasburg (1958) are somewhat different
from those of the present study. His longline
catches of blue sharks at equivalent latitudes were
from depths of 53 to 93 m (45%), 93 to 143 m (30%),
and 123 to 166 m (25%). The blue sharks tracked
in the present study appeared to exceed 93 m only
about 5.1% of the time (excluding initial plunges).
It is conceivable, however, that Strasburg's per-
centages may have been influenced by the sharks
being attracted deeper than normal by the sloping
odor corridors from baits on the gradually sinking
longlines. That blue sharks on occasion go even
deeper than Strasburg's deepest hooks was noted
by Pethon (1970) who reported captures in Norwe-

526

SCIAKROTTA and NELSON: DIKL BEHAVIOR OK BLUE SHARK

gian waters from depths as great as 370 m. Davies
and Bradley (1972) observed individuals at depths
between 100 and 275 m during a descent in the
submersible Deepstar 4000. A large school of
northern anchovy was also observed in this depth
range and a predator-prey relationship was sug-
gested, although the possibility of the sharks
following the descending submersible could not be
eliminated.

In regard to temperature, Strasburg (1958) re-
corded 99^ of his catches over the range of 7° to
20°C, with 67% between 10° and 15°C. Thus,
temperature alone may not be reason for the ap-
parent absence of blue sharks from the offshore
study area during January and February 1972
when the surface temperature was about 13 °C.

The navigational mechanism employed by the
sharks during their island-oriented migration is
unknown. Traditional explanations for such fish
movements include sun-compass orientation, vi-
sual landmark recognition, and orientations to
chemical or thermal gradients. None of these
mechanisms seem plausible in view of the con-
stancy of the pelagic environment, depths usually
occupied during the movement, and the relative
darkness in which the movements often occurred.
Orientation to magnetic or electric fields is one
possibility that must be considered in view of the
recent findings of Kalmijn (1971, 1973) dem-
onstrating magnetic/electric responses in sharks
of adequate sensitivity for such a mechanism.
Another possibility is orientation by passive
acoustic means to the sounds of the island
shoreline, in a manner similar to that suggested
by Evans (1971) for dolphins.

The diel inshore-offshore migration shown by
this study must also be considered in view of the
much longer range movements exhibited by blue
sharks. Individuals off California are known to
segregate by sex, and seasonal changes in sex
ratios imply seasonal north-south migration,
perhaps in response to water temperature (John-
son 1974; Bane 1968; Tricas 1977). Tagged indi-
viduals have exhibited some very long-range
movements. One blue shark tagged by Bane off
Newport Beach, Calif, in July 1967 was recovered
in December of the same year about 1 ,300 km west
of Nicaragua. Another tagged by D. R. Nelson
(unpubl. data) off San Diego, Calif, in October
1966 was recovered in October 1969 about 1,800
km west of the Galapagos Islands, a distance of
4,000 km from its tagging site. This shark was
captured only 8 days short of a full 3 yr at liberty

and, therefore, did not appear to be participating
in any seasonal north-south migration. Both of
the above sharks were recovered by Japanese
fishing vessels, presumably longlining in rela-
tively deep, cool water.

ACKNOWLEDGMENTS

We sincerely thank the many persons who con-
tributed to this study, especially E. Standora (ini-
tial development and testing of telemetry system),
H. Carter and D. Ferrel (circuit design), and J.
Hall (assistance during trackings at sea). We also
acknowledge the Office of Naval Research for
financial support, through contract N00014-68-
C-0318, under project NR-104-062, for the pro-
gram of shark research of which this study is a
part.

LITERATURE CITED

aasen, o.

1966. Blahaien, Prionace glauca (Linnaeus), 1758. Fis-
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Bane, G. W.

1968. The great blue shark. Calif. Curr. 1:3-4.
BIGELOW, H. B., AND W. C. SCHROEDER

1948. Sharks. In J.Tee-Van.C.Breder.S. F. Hildebrand,
A. E. Parr, and W. C. Schroeder (editors), Fishes of the
western North Atlantic, Part one, p. 59-546. Mem. Sears
Found. Mar. Res., Yale Univ. 1.
CAREY, F. G., AND K. D. LAWSON.

1973. Temperature regulation in free-swimming bluefin
tuna. Comp. Biochem. Physiol. 44A:375-392.

CASEY, J. G.

1976. Migrations and abundance of sharks along the At-
lantic coast. In W. Seaman, Jr. (editor), Sharks and man
— a perspective, p. 13-14. Fla. Sea Grant Program, Rep.
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CLARKE, M. R., AND J. D. STEVENS.

1974. Cephalopods, blue sharks and migration. J. Mar.
Biol. Assoc. U.K. 54:949-957.

COUSTEAU, J. Y., AND P. COUSTEAU.

1970. The shark: splendid savage of the sea. Doubleday
and Co., Garden City, N. Y., 277 p.

DAVIES, I. E., AND R. P. BRADLEY.

1972. Deep observations of anchovy and blue sharks from
Deepstar 4000. Fish. Bull., U.S. 70:510-511.
EVANS, W. E.

1971. Orientation behavior of delphinids: Radio telemetric
studies. Ann. N.Y. Acad. Sci. 188:142-160.

Ferrel, d. w., d. r. Nelson, T. C. Sciarrotta, e. a. Stan-
dora, and H. C. Carter.

1974. A multichannel ultrasonic biotelemetry system for
monitoring marine animal behavior at sea. ISA (In-
strum. Soc. Am.) Trans. 13:120-131.

Finstad, w. O., and d. r. Nelson.

1975. Circadian activity rhythm in the horn shark,
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South. Calif. Acad. Sci. 74:20-26.

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FISHERY BULLETIN: VOL. 75, NO. 3

FREY, H. W. (editor).

1971. California's living marine resources and their utili-
zation. Calif. Dep. Fish Game, 148 p.
HOBSON, E. S.

1968. Predatory behavior of some shore fishes in the Gulf
of California. U.S. Fish Wildl. Serv., Res. Rep. 73, 92 p.
JOHNSON, C. S.

1974. Countermeasures to shark attack. In G. V.
Pickwell and W. E. Evans (editors), Handbook of danger-
ous animals for field personnel, p. 123-141. Nav. Under-
sea Cent. Rep. NUC TP 324.
KALMIJN, A. J.

1971. The electric sense of sharks and rays. J. Exp. Biol.
55:371-383.

1973. Electro-orientation in sharks and rays: theory and
experimental evidence. Scripps Inst. Oceanogr. Rep.
SIO 73-39, 22 p.

LEBRASSEUR, R. J.

1964. Stomach contents of blue sharks (Prionace glauca
L. ) taken in the Gulf of Alaska. J. Fish. Res. Board Can.
21:861-862.
LIMBAUGH, C.

1963. Field notes on sharks. In P. W. Gilbert (editor),
Sharks and survival, p. 63-94. D. C. Heath and Co.,
Boston.
MYRBERG, A. A., JR., AND S. H. GRUBER.

1974. The behavior of the bonnethead shark, Sphryna tib-
uro. Copeia 1974:358-374.

Nelson, d. r.

1974. Ultrasonic telemetry of shark behavior. Nav. Res.
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Nelson, D. R., and R. H. Johnson.

1970. Diel activity rhythms in the nocturnal, bottom-
dwelling sharks, Heterodontus francisci, and Cephaloscyl-
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PETHON, P.

1970. Occurrence of the great blue shark, Prionace glauca,
in Norwegian waters. Rhizocrinus l(3):l-5.
PINKAS, L.

1974. California marine fish landings for 1972. Calif.
Dep. Fish Game, Fish Bull. 161, 53 p.

Randall, j. e.

1967. Food habits of reef fishes of the West Indies. Stud.
Trop. Oceanogr. (Miami) 5:665-847.
SCIARROTTA, T. C.

1 974 . A telemetric study of the behavior of the blue shark,

Prionace glauca, near Santa Catalina Island, California.
M.S. Thesis, California State Univ., Long Beach, 138 p.

SPRINGER, S.

1963. Field observations on large sharks of the Florida-
Caribbean region. In P. W. Gilbert (editor), Sharks and
survival, p. 95-114. D. C. Heath and Co., Boston.

STANDORA, E. A.

1972. Development of a multichannel, ultrasonic tele-
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a preliminary study on the Pacific angel shark, Squatina
californica. M.S. Thesis, California State Univ., Long
Beach, 143 p.

STEVENS, J. D.

1973. Stomach contents of the blue shark {Prionace glauca
L.) off south-west England. J. Mar. Biol. Assoc. U.K.
53:357-361.

1974. The occurrence and significance of tooth cuts on the
blue shark {Prionace glauca L.) from British waters. J.
Mar. Biol. Assoc. U.K. 54:373-378.

1975. Vertebral rings as a means of age determination in
the blue shark {Prionace glauca L.) J. Mar. Biol. Assoc.
U.K. 55:657-665.

1976. First results of shark tagging in the North-east At-
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937.

STRASBURG, D. W.

1959. Distribution, abundance, and habits of pelagic
sharks in the central Pacific Ocean. U.S. Fish Wildl.
Serv., Fish. Bull. 58:335-361.
SUDA, A.

1953. Ecological study on the blue shark {Prionace glauca
Linne). (Translated from Jap.). South Seas Area Fish.
Res. Lab. Rep. 26(1):1-11.
TEMPLEMAN, W.

1963. Distribution of sharks in the Canadian Atlantic
(with special reference to Newfoundland waters). Fish.
Res. Board Can., Bull. 140, 77 p.
THORSON, T. B.

1971. Movement of bull sharks, Carcharinus leucas, be-
tween Caribbean Sea and Lake Nicaragua demonstrated
by tagging. Copeia 1971:336-338.
TRICAS, T. C.

1977. Food habits, movements, and seasonal abundance of
the blue shark, Prionace glauca (Carcharhinidae), in
southern California waters. M.S. Thesis, California
State Univ., Long Beach, 76 p.

WEEKS, A.

1974. Shark! NOAA 4(1):8-13.

528

A BIOENERGETIC MODEL FOR THE ANALYSIS OF

FEEDING AND SURVIVAL POTENTIAL OF WINTER FLOUNDER,

PSEUDOPLEURONECTES AMERICANUS, LARVAE DURING

THE PERIOD FROM HATCHING TO METAMORPHOSIS

Geoffrey C. Laurence1

ABSTRACT

A bioenergetic model was developed which simulated effects of temperature, prey density, and larval
size on ability of winter flounder, Pseudopleuronectes americanus, larvae to obtain food energy to
provide for experimentally determined growth and metabolism. Larval feeding at constant tempera-
ture and as a function of prey concentration was exponential and more sharply asymptotic in younger
fish than in those near metamorphosis. Specific growth rates were exponentially related to prey
concentrations and ranged from 5.72 to 8. 70% /day at survival prey concentrations of 3.7 to 21.7 cal/
liter. Daily required feeding time was directly related to prey availability. Critical plankton densities
below which larvae did not have enough time during the day to obtain adequate food for growth
and metabolism varied with age and ranged from 2.1 to 5.7 cal/liter. Simulated physiological energy
utilization and required caloric food intake were inversely related to prey concentration and varied
with larval stage of development. Food requirements expressed as numbers of copepod nauplii
consumed per day ranged from 19 for first feeding larvae to 235 for metamorphosed juveniles.
Predicted gross growth efficiencies were directly related to prey concentration and increased with
age from 5 to 33%. All indications pointed to a "critical period" of larval survival during the period
of exogenous feeding initiation and immediately after.

One of the important problems in fishery research
and management is identifying and understand-
ing the functional mechanisms of the stock-
recruitment relationship. It is becoming more
apparent that focusing attention on studies of
mortality in the early life stages, particularly
the larval stage, may help in this understanding.
Mortality rates are usually the highest and most
variable from year to year during the early life
stages. Because of this, even small changes in
mortality during this period can produce a mag-
nified effect on the eventual numbers of recruits
to sport or commercial fisheries.

Other than predation, the most important prob-
able factors influencing larval mortality are food
and feeding relationships and the influence of en-
vironmental parameters on these processes. The
acquisition of the required food ration by fish
larvae is of prime importance in survival and
successful development. Without the proper quan-
tity and quality of food, larvae will be adversely

'Northeast Fisheries Center Narragansett Laboratory, Na-
tional Marine Fisheries Service, NOAA, Narragansett, RI
02882.

Manuscript accepted December 1976.
FISHERY BULLETIN: VOL. 75. NO. 3, 1977.

affected and survival will be influenced. Bio-
energetic relationships have been studied exten-
sively for adult fishes, and the works of Ivlev
(1939a, b, c), Winburg (1956), Paloheimo and
Dickie (1966a, b), and Warren and Davis (1967)
are among the most complete. However, the use
of energy resources in physiological mechanisms
and the relationships of feeding, growth, and sur-
vival in the early life stages of fishes have only
recently been studied (Ivlev 1961a, b; Lasker
1962; Laurence 1969, 1973).

It is the object of this research to examine the
effects of food and feeding on winter flounder,
Pseudopleuronectes americanus, survival from
the period of hatching to metamorphosis and to
develop a model of these critical processes. The
model includes the forcing variables of tempera-
ture, prey density, and larval size or age and their
effects on the ability of winter flounder larvae to
successfully acquire energy rations necessary for
experimentally determined growth and metabolic
parameters. The energy rations are quantified as
to caloric value of ration, numbers of specific prey
organisms consumed, time for required intake,
and metabolic parameters dealing with conver-
sion into fish flesh.

529

FISHERY BULLETIN: VOL. 75, NO. 3

MATERIALS AND METHODS

Adult winter flounder were captured by trawl
net from Narragansett Bay, R.I., and maintained
in 1,900-liter experimental aquaria. Embryos
were obtained by allowing the fish to ripen nat-
urally under optimum temperature and photo-
period conditions or causing ovulation with
hormones according to the techniques of Smigiel-
ski (1975). Embryos were incubated with methods
developed at the Narragansett Laboratory (Smi-
gielski and Arnold 1972).

All experiments and rearing were done at 8°C
during these studies since this temperature is the
approximate mean temperature for the entire per-
iod from hatching to metamorphosis for winter
flounder in the Narragansett Bay area. Stock cul-
tures of larvae were reared in series of black 64-
liter experimental aquaria. The aquaria were
placed in an environmental room or in water
baths where the temperatures were maintained
by program recorders controlling heating and
cooling coils. All experimental aquaria were aer-
ated with air stones and were semiclosed systems
with a portion of the seawater being replenished
every 1 or 2 days. Illumination was controlled by
timers which provided a 12:12 day-night photo-
period corresponding to the mean photoperiod
during the normal winter flounder spawning
time.

Zooplankton fed during all experiments consist-
ed mainly of the nauplii, copepodites, and adults
of the copepods Acartia clausi, Centropages hama-
tus, and a few Temora longicornis and Euryte mora
affinis collected from the Narragansett Bay area
with 0.5-m plankton nets fitted with 64- and 116-
)u.m mesh. Collections were sieved through 200- or
500-yu.m mesh strainers, depending on the size of
larvae to be fed. Plankton densities in experi-
mental aquaria were monitored by taking two to
four 5-ml aliquots from the aquaria and counting
the number of plankters under a dissecting
microscope.

The relationship between larval size (body dry
weight) and stomach contents was studied from
hatching to metamorphosis. Larvae were reared
in a 64-liter black aquarium and were fed high
prey concentrations of 13.6-20.5 cal/liter or ap-
proximately 2 or 3 nauplii/ml. Samples of 25
larvae were taken each week until metamor-
phosis for stomach analyses and dry body weight
determinations.

Experiments determining the influence of prey

concentration on daily feeding intensity expressed
as stomach contents were conducted at 0.68, 3.41,
6.80, 20.5, 34.1, and 47.8 cal/liter (corresponding
to 0.1, 0.5, 1.0, 3.0, 5.0, and 7.0 nauplii/ml). Larvae
aged 2, 5, and 7 wk after hatching were used.
Approximately 25 larvae were placed in all black
4-liter aquaria containing the desired prey densi-
ties. The larvae were allowed to feed for 1 day's
photoperiod (12 h) after which they were pipetted
onto a 100-/u.m mesh screen and allowed to suffo-
cate to prevent regurgitation of food before being
preserved in 5% Formalin.2 Ten larvae from each
prey concentration were used for stomach analy-
ses and 10 were used for mean dry body weight
determinations. Stomach analyses were done
with a dissecting microscope. Larval stomachs
and intestines were teased apart with fine needles,
and contents were identified to genus and species
if possible.

Digestion rate measured by gut clearance time
of larval winter flounder at 8°C was determined
by feeding dyed zooplankton according to the tech-
niques of Laurence (1971a). Transparency of the
larvae permitted visual observation of dyed
plankters in stomachs of living larvae. To deter-
mine the evacuation time of the stomach and
intestine under active feeding conditions, larvae
feeding on dyed plankters at concentrations of
1 or 2 nauplii/ml were removed and placed in
duplicate aquaria with similar concentrations of
nondyed plankton, and the gut clearance times of
the dyed plankters from individual larvae were
recorded.

Experiments determining the influence of tem-
perature on growth of winter flounder larvae were
conducted in 38-liter experimental aquaria. Feed-
ing, monitoring, and sampling techniques and
results for these experiments are described in
detail by Laurence (1975).

The influence of planktonic prey concentration
on growth and survival at 8°C from the period
hatching to metamorphosis was studied at prey
concentrations of 0.068, 0.68, 3.41, 6.80, and 20.5
cal/liter, corresponding approximately to 0.01,
0.1, 0.5, 1.0, and 3.0 nauplii/ml. Larvae were
stocked at an initial density of 500 per aquarium;
methods for maintaining prey concentrations,
sampling, and determining growth and survival
rates are described in detail by Laurence (1974).

Standard manometer equipment (Warburg res-

2Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

530

LAURENCE: BIOENERGETIC MODEL FOR WINTER FLOUNDER LARVAE

pirometers) and techniques (Umbreit et al. 1964)
were used to measure oxygen consumption for
metabolic determinations in relation to tempera-
ture and larval size. A description of the specific
methods and results has been reported earlier
(Laurence 1975).

All combustions for caloric determinations of
larval winter flounder tissue were done in tripli-
cate in a Parr 1241 automatic adiobatic calori-
meter adapted for a microbomb. Caloric values for
copepod prey species and methodology for these
determinations are reported by Laurence (1976).

All statistical analyses used in this research are
described in Steel and Torrie (1960) and Draper
and Smith (1966). Modeling and analyses were
done in the FORTRAN IV language on an IBM
370 computer.

EXPERIMENTAL RESULTS

Food Consumed and Relationship
to Larval Size

Numerical analysis of stomach contents is not
very meaningful in itself. It can, however, be
useful in conjunction with the measurement of
other parameters. An estimation of the dry weight
and caloric value of food consumed per larval
dry weight was needed as part of the overall bio-
energetic model. Stomach analysis by enumerat-
ing copepods in larvae fed high concentrations
(2 or 3 nauplii/ml) combined with information on
dry weights and caloric values of the copepods
provided this. Mean dry weights for the copepod
species and life stage were taken from the litera-
ture (Conover 1960; Anraku 1964; Hargrave and
Geen 1970; Gaudy 1974). Caloric values were
determined in our laboratory (Laurence 1976).
The average composite values used for the cope-
pods in this study were 1.3 /u-g dry weight for
nauplii, 15.4 fig dry weight for older stages, and
5,251 cal/g dry weight for all copepod tissue. Mul-
tiplying the numbers of plankton species and life
stage per stomach by the average dry weight val-
ues for each plankter type and summing yielded
the mean dry weight of the stomach contents.
Results of these analyses along with nauplii to
older stage ratios of copepods consumed and calor-
ic value per stomach are shown in Table 1. The
regression relationship of the logarithms of larval
dry body weight and larval stomach contents
weight was positively linear (Figure 1) and sig-
nificantly correlated (R = 0.87, P = 0.01).

TABLE 1. — Mean numbers, weights, and caloric values of cope-
pods consumed by larval winter flounder of different sizes. Each
sample consists of 25 larvae.

Mean larval

dry wt

(Mg)

Mean no. of

copepods per

stomach

Naupllus to

older stage

ratio

Mean dry wt

per stomach

(M9)

Calorie

per
stomach

10.4

2.0

1:0

2.6

0.0137

14.3

1.0

1:0

1.3

0.0068

21.5

2.1

1:0

2.7

0.0142

29.4

5.4

1:0

7.0

0.0368

51.1

3.3

29:1

6.0

0 0315

81.2

32.3

12:1

41.9

0.2205

226.8

2.9

12:1

6.9

0.0362

396.6

4.7

3:4

43.8

0.2300

444.2

33.5

22:1

57.7

0.3030

513.9

8.4

1:2

89.9

0.4720

667.6

3.0

1:2

32.1

0.1686

LflRVSL DRY HEIGHT <UG>
10,0.0

LOG IflRVHl DRY HEIGHT <UG)

FIGURE 1. — The regression relationship of larval dry body
weight to larval stomach contents weight for winter flounder
at 8°C.

Prey Density and Intensity
of Feeding

The relationship between intensity of feeding
and concentration of prey is important in deter-
mining food intake. Ivlev (1961b) has analyzed
this relationship and expressed it by the following
function:

4L = oc{R - r)
dp

where r = size of a unit ration for a unit time

R = maximum size of the ration during the
same unit time at the upper limiting
level of food concentration beyond
which ration size does not increase

531

FISHERY BULLETIN: VOL. 75, NO. 3

a = coefficient of proportionality
p = plankton concentration.

After integration, the function becomes:

r = R (1 - e~aP).

Use of this relationship in analyzing winter
flounder feeding as influenced by prey densities of
0.68-47.8 cal/liter, or 0.1-7.0 nauplii/ml, yielded
some interesting results (Figure 2). Feeding was
reasonably constant in the youngest fish with an
asymptote being reached quickly at the lower prey
concentrations. Five-week-old larvae displayed a
rather classic form of the Ivlev curve with food
intake increasing with prey density, reaching a
maximum at approximately 6.8 cal/liter or 1.0

nauplius/ml, and then remaining quite stable.
The oldest larvae, prior to metamorphosis, showed
an increasing food intake through the whole
range of plankton densities1, right up to 47.8
cal/liter or 7.0 nauplii/ml. In general, there
appeared to be an increasing of the upper limiting
level of food concentration and a decreasing of the
coefficient of proportionality (a) with increasing
larval age.

Digestion Rate

Winter flounder larvae were known to be con-
tinuous, visual daylight feeders from prior re-
search. Preliminary attempts at establishing
digestion rates and unpublished results of night
feeding experiments showed that larvae at-

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FIGURE 2.-

532

-The relationship between planktonic prey concentration and feeding intensity expressed as stomach ration for different

aged winter flounder larvae at 8°C.

LAURENCE: BIOENERGETIC MODEL FOR WINTER FLOUNDER LARVAE

tempted to feed constantly under daylight condi-
tions and ceased feeding entirely during darkness.
Evacuation rates of the gut while larvae were
actively feeding were recorded at 8°C for estimates
of digestion rates. Results of 10 individual larvae
showed a mean, active digestion time of 6.6 h with
a range of 5.1-8.4 h.

Effects of Prey Density on
Growth and Survival

The effects of five prey densities from 0.068 to
20.5 cal/liter (approximately 0.01-3.0 nauplii/ml)
on growth and survival of winter flounder larvae
from hatching to metamorphosis at 8°C were
examined. Larval survival did not exceed 2 wk at
the lower two densities of 0.01 and 0.1 nauplius/
ml. Growth expressed as dry weight against time
at the three survival densities (3.4, 6.8, and 20.5
cal/liter) was similar (Figure 3), as indicated by
the confidence intervals about the slopes of the
descriptive regression equations (Table 2). Spe-

J 100. 0

20 5 CA L/l

3 4 C A I / 1

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
NEEKS AFTER YOLK ABSORPTION

8.0 9.0

FIGURE 3.— Growth of winter flounder larvae at 8°C and at
three different planktonic prey densities.

TABLE 2. — Regression equations and statistical parameters of
winter flounder dry weight growth vs. time at 8°C and different
planktonic prey densities.

Corre-

Planktonic

Growth

Confidence

lation

concentration

regression

interval

coeffi-

(cal/liter)

equation

about slope

cient

20.5

log Y = 0.849 + 0.269X

0.212-0.326

098

680

log/ =0.830 +0.272X

0.234-0.311

0.99

3.41

log Y = 0.990 + 0.208X

0.141-0.275

0.97

0.68

No survival to

metamorphosis

0.068

No survival to

metamorphosis

cific growth rates on a daily basis increased with
plankton concentration and were experimentally
observed to be 8.62%/day for 3.0 nauplii/ml,
7.68%/day for 1.0 nauplius/ml, and 5.72%/day for
0.5 nauplius/ml.

Plankton density influenced survival more sig-
nificantly than growth. Specific mortality coeffi-
cients calculated by the methods of Laurence
(1974), which correct for the number of experi-
mental removals for growth measurements, dem-
onstrated a direct relationship with lower mor-
tality rates at each higher plankton density (Table
3). Plots of predicted specific mortality coefficients
through the range of plankton densities from 0.68
to 20.5 cal/liter based on the above results yielded
an exponential relationship (Figure 4).

TABLE 3. — Daily mortality coefficients of winter flounder at8°C
as influenced by planktonic prey density.

Corrected

Planktonic

number of

Days

Specific

concentration

survivors

mortality

(cal/liter)

out of 500

survival1

coefficient

20.50

171

0.022

6.80

0.069

3.40

0.091

0.68

0.307

'No calculable survival at the lowest plankton density of 0.068 cal/liter.

0.0 1.5 3.0

7.5 9.0 10.5 12.0 13.5 15.0 19.5 19.0 19.5 7 1.0
PLANKTON CONCENTRATION tCAL/LHRE)

FIGURE 4. — Daily mortality coefficients of winter flounder at
8°C from the period hatching to metamorphosis as influenced
by prey density.

Metabolic Rate

Laurence (1975) expressed metabolism of
winter flounder from hatching through meta-
morphosis in terms of oxygen consumption.
Regression relationships of mean hourly oxygen

533

consumption in microliters from hatching
through and beyond metamorphosis on dry body
weight were nonlinear and fitted best by a third-
degree polynomial (Figure 5 from Laurence 1975).
A third-degree polynomial was statistically most
significant, as indicated by analysis of variance
(F = 13.2 for cubic term, 7.4 for quadratic term,
and 9.5 for linear term) over the weight range
studied (10-4,000 /xg). However, in this research
the size range for larvae was 10-1,000 /xg, and
only the predicted data from the first ascending
leg of the polynomial at 8°C were used in the
computations.

2-C 02 -0 451 ♦ 6 0 » id'w - IJ « ld*W2+ 15 .lO^W5

5*C 0, = 0601 ♦ 33 x 10 W-l 7x 10 W »2 5 i 10 W

'^.-> c . ,^»,„>

DRY WEIGHT (ug)

FIGURE 5. — Regression of mean hourly oxygen consumption on
dry weight of winter flounder larvae and juveniles at three
temperatures. Circled data points indicate metamorphosed
juveniles. Results at 8°C used in these studies. (From Laurence
1975.)

FISHERY BULLETIN: VOL. 75, NO. 3

BIOENERGETIC MODEL

A general model for the transformation of food
to fish flesh and the energy relationships involved
has been discussed in detail by Winburg (1956)
and Warren and Davis ( 1967). The basic relation-
ship can be expressed as:

Q+ =Q +Q' +Q

(1)

where Q + = energy of food consumed

Q* = energy of waste products in feces and

urine
Q' = energy of growth
Q_ = energy of metabolism.

Since a portion of the energy value of food is
lost in the feces and urine and not utilized or
assimilated, Winburg (1956) proposed the follow-
ing "balanced equation":

Q+ -Q* =Q' +Q_

(2)

bQ+ =Q' +Q_

(3)

where b = the coefficient of utilization or, in
Brody's (1945) terminology, the physiological
useful ration. Equation (3) analyzes the conver-
sion of food energy inside the fish (physiological).
However, influences of the environment on food
consumption and utilization must also be consid-
ered. Many modifications based on my experimen-
tal results and additions of methods of other
researchers have been incorporated into a model
suitable for a broader analysis of the bioenergetics
of winter flounder larvae. The following para-
graphs present a detailed description of the
methods used to derive this model.

Ivlev (1961b) formulated a model founded on
the basic bioenergetic equation (Equation (3)) for
the utilization of food by plankton-eating fishes.
The relationship is:

0.7Q+ = Q' + Q

(4)

The coefficient of utilization (b) is assumed to
be 0.7, based on information provided by Ware
(1975) who reviewed the most recent thinking of
the efficiency of food conversion. During the
course of a day, a larval fish will be active in
daylight (while feeding) and relatively passive the
remainder of the time (usually at night). It can
be assumed that the intensity of metabolism dur-

534

LAURENCE: BIOENERGETIC MODEL FOR WINTER FLOUNDER LARVAE

ing rest is represented by the standard metabolic
rate (Qs) and active metabolism by the active rate
(Q). Thus, if it is assumed that a fish actively feeds
for a given number (a) of hours, the total daily
expenditure of energy for metabolism can be de-
fined as:

Q_ =a(Q -Qs) + 24QS. (5)

The basic Equation (4) can then be rewritten as:

0.7Q + = Q' + a(Q - Qs) + 24Qs. (6)

Also, the energy of food consumed (Q + ) can be
equal to the sum of the hourly rations, r (see Prey
Density and Intensity of Feeding), or Q + = ar, and
thus:

Q+ = aR(l - e~aP).

(7)

Solving Equations (6) and (7) simultaneously by
equating the Q:

Q' + a(Q - Qs) + 24Q,
0.7

is obtained. Thus:

aR(l - e~aP) (8)

Q' + 24QS

0.7i?(l - e~«p) - (Q -Qs

(9)

Deriving the value of a, a number of different
parameters can be computed. They are: 1) critical
plankton density below which growth, metab-
olism and subsequent survival would be adversely
affected, 2) food intake, 3) energy expenditure,
4) nonassimilated energy, 5) growth efficiency,
6) percent body weight eaten, and 7) the number
of a given plankton species and life stages eaten
per day. The following is a step by step explana-
tion of the modifications used to compute these
parameters at 8°C for larval dry weight from 10
to 1,000 ixg (corresponding to the time period
hatching to metamorphosis), for plankton concen-
trations from 0.5 to 21.7 cal/liter (approximately
0.1-3.0 nauplii/ml), and for growth, metabolic
and digestion rates observed in laboratory exper-
iments at 8°C.

1. Stomach contents weight in micrograms of
planktonic prey eaten by a given size larva was
computed from the regression equation presented
in Figure 1.

2. The stomach contents weight per hour, or
weight of food consumed per hour, was calculated
from a modification of Bajkov's (1936) digestion
equation. The modified equation is:

ST
H

(10)

where F = weight of food consumed per hour

S = average weight of food in the stomach

at the time of sacrifice
T = feeding time in hours
H = number of hours necessary for food to
be evacuated from the stomach at a
given temperature = 6.6 h at 8°C for
actively feeding winter flounder
larvae.

Unpublished experiments indicated that winter
flounder larvae fed only in daylight hours. There-
fore, it was assumed that T was equal to 12.0 h
in these experiments, or the approximate number
of mean daylight hours in the period mid-Feb-
ruary to mid-April, when winter flounder spawn.
Also, F was considered to represent the maximum
ration of a larva, or R (Prey Density and Intensity
of Feeding section, Equations (7)-(9)).

3. R was converted to a caloric value by multi-
plying by 0.0052519 cal, or the average caloric
value/microgram of the copepod species inhabit-
ing Narragansett Bay and serving as potential
prey for winter flounder (Laurence 1976).

4. The coefficient of proportionality (a) in Equa-
tion (9) was found to change linearly in a negative
manner with increasing larval size (see Prey Den-
sity and Intensity of Feeding) and was correspond-
ingly adjusted.

5. The growth increment, Q', was computed by
multiplying the weight of a larva by the specific
growth rate at 8°C for the specified plankton den-
sity (see Effects of Prey Density on Growth and
Survival). This was converted to calories by mul-
tiplying by 0.0050026, or the caloric value for
winter flounder tissue as determined in labora-
tory combustion experiments with a bomb calo-
rimeter.

6. Metabolism for a larva of given weight was
calculated from the regression equations for
oxygen consumption and weight (Laurence 1975;
Figure 5) and converted to calories by multiplying
by 0.005 which represents the caloric equivalent
of 1 ix\ of oxygen for the full range of respiratory
quotients associated with the utilization of fats,

535

FISHERY BULLETIN: VOL. 75, NO. 3

carbohydrates, and proteins (Swift and French
1954). Active metabolism (Q) was derived by
multiplying standard metabolism (Qs) measured
in the oxygen consumption experiments by 2.5.
Fry (1947) showed that the active metabolism in
small fishes was about twice the standard rate.
More recently, however, Ware (1975) demon-
strated in a re-analysis of Ivlev's (1961b) data
that active metabolism calculated for a variety of
growth rates and feeding densities could vary
between 2 and 3 times the standard rate. Recog-
nizing that active metabolism is a dynamic factor,
it is not unrealistic to assume a multiplier of 2.5
times standard metabolism for an estimate of
active metabolism.

7. The number of hours (a) a larva of given
weight needed to feed to attain a given growth
rate at a given temperature and plankton concen-
tration was computed from Equation (9).

8. Since winter flounder larvae were observed
in experiments to be visual feeders, the plankton
densities for each weight which predicted 12.0 h
feeding time (a) were identified. These were con-
sidered critical densities because feeding times
longer than this were ecologically impossible due
to unsuitable photoperiod.

9. Food intake in calories was computed from
Equation (7).

10. Metabolism or energy expenditure was com-
puted from Equation (5).

11. Nonassimilated energy was computed by

f 19. D-

o.o too.o too. o loo.o too.o soo.o (oo.o roo.o 100.0 900. 0 1000. 0 uoo.o

OH* WIGHT (UG)

FIGURE 6. — Number of daily feeding hours required by winter
flounder larvae to obtain energy for calculated growth and
metabolism as influenced by larval dry weight and planktonic
prey concentration at 8°C. Numbers for each simulated line
indicate prey concentration in calories per liter.

536

subtracting the energies of growth (Q') and me-
tabolism {Q (from the energy of food intake (Q + ).
12. Gross growth efficiency was calculated from
the formula:

where K1 = gross growth efficiency and Q ' and Q +
are as previously defined.

13. The percent body weight eaten per day was
calculated by dividing the caloric value of food
intake (Q+ ) by the caloric value of the given body
weight.

14. The number of naupliar or adult copepods
consumed per day at the given parameters was
calculated by dividing the caloric value of the
food intake (Q + ) by the previously defined aver-
age caloric value for nauplii or adults.

MODEL SIMULATION RESULTS

Daily Feeding Time and
Critical Prey Densities

The number of daily feeding hours required to
meet growth and metabolism (a, Equation (9)) in
relation to larval dry weight and at plankton den-
sities which allowed feeding at some time within
the limits of the 12-h day length simulated by the
model is plotted in Figure 6. Feeding time at all
plankton densities was initially high for the
younger, smaller fish which later decreased before
increasing again to a peak around 500 /xg dry
weight, or when metamorphosis starts to take
place. A gradual decrease occurred during the
metamorphosis period (500-1,000 /xg larval dry
weight). As was expected, required daily feeding
times decreased with increasing prey density.

The critical, minimal prey densities below
which longer than 12 h would have been required
to obtain energy to meet growth and metabolism
over the range of weights showed the highest
critical densities during the period corresponding
to first feeding with a decrease to a minimum
shortly after (10-75 fxg larval dry weight, Figure
7). An increase was then noted until the beginning
of metamorphosis (500 /xg) after which the critical
prey density gradually decreased to complete
metamorphosis (1,000 /xg). The range of critical,
minimum densities for the whole period was from
2.1 to 5.7 cal/liter, or approximately 0.3 to 0.8
nauplius/ml.

LAURKNVK BIOENERGETIC MOIiEI. KOR WINTKR FLOUNDER LARVAE

y ».o

0.0 100.0 200.0 300.0 400.0 SOO.O 600. 0 700.0 800.0 900.0 1000.0 1100.0
DRY HEIGHT <UG>

FIGURE 7. — Critical, minimum prey densities, below which feed-
ing longer than the available photoperiod would permit to obtain
energy for calculated growth and metabolic processes, over the
weights range from hatching to metamorphosis for winter
flounder at 8°C.

0.0 100.0 200.0 300.0 100.0 500.0 600.0 700.0 800.0 300.0 1000.0 1100.0
DRY UEIGHT <PG>

FIGURE 9. — Nonassimilated energy of winter flounder larvae
at 8°C over the range of dry body weight from hatching to
metamorphosis and at different planktonic prey concentrations.
Numbers for each simulation indicate prey concentration in
calories per liter; 6.7-21.7 cal/liter simulations are in ascending
order from top to bottom.

Physiological Energy Utilization

Predicted daily metabolic energy utilized by
winter flounder larvae from hatching to metamor-
phosis (Q_, Equation (5)) showed a decrease
shortly following hatching which later increased
until initiation of metamorphosis when there was
a leveling off (Figure 8). Energy expended was
substantially higher at the lower prey concentra-

0.0 100.0 300.0 SOO.O 400.0 900.0 SOO.O 700.0 000.0 900.0 1000.0 1100.0
DRY UEIGHT IUG>

FIGURE 8. — Metabolic energy utilized by winter flounder larvae
at 8°C over the range of dry body weight from hatching to meta-
morphosis and at different plankton concentrations. Numbers
for each simulated line indicate prey concentration in calories
per liter.

tions with the differences minimized with increas-
ing concentration. Predicted daily unassimilated
energy, or energy not utilized in physiological
processes and lost to the larval system, followed
a similar trend to metabolic energy (Figure 9). In
general, the ratio of nonassimilated to metabolic
energy overall factor combinations was approx-
imately 1:2.

Required Food Ration and
Growth Efficiency

Predicted daily caloric food requirements (Fig-
ure 10, Equation (7)) after an initial decrease
following first feeding (10-30 fig dry weight) in-
creased until the beginning of metamorphosis
(500 fig), after which the rate of increase slowed
until complete metamorphosis (1,000 fig). Food
requirements were greater at lower prey concen-
trations with decreasing differences at higher
concentrations. Conversion of caloric values of
daily food requirements by division by mean ca-
loric values of the copepod life stages per unit
weight showed the numbers of nauplii or older
stages necessary for consumption (Figure 11).
Actual feeding experiments demonstrated that
larvae do not prey entirely on one particular
copepod life stage. The stages they consume are
more a function of larval and copepod size.
Smaller larvae initiate feeding on nauplii and
gradually eat increasingly greater percentages of

537

FISHERY BULLETIN: VOL. 75, NO. 3

0.0 100.0 200.0 300.0 100.0 500.0 600.0 700.0 800.0 300.0 1000.0 1100.0
0RY HEIGHT c)JG>

FIGURE 10. — Daily food requirements of winter flounder larvae
at 8°C over the range of dry weight from hatching to metamor-
phosis and at different planktonic prey concentrations. Numbers
for each simulation indicate prey concentration in calories per
liter; 6.7-21.7 simulations are in ascending order from top
to bottom.

v «0.0

. 1 1 1 1 1 1 1 '

0.0 100.0 200.0 300.0 100.0 500.0 600.0 700.0 800.0 300.0 1000.0
DRr HEIGHT ipG>

FIGURE 12. — Regression relationships of percentages of nauplii
and older stage copepods eaten by winter flounder larvae of
different sizes at 8°C.

B.O

1.0 «

. 0 K

0.0 lOO.O 700.0 100.0 000.0 500.0 600.0 700.0 100.0 300.0 1000.0 1100. 0 1700.0
DRY HEIGHT (JJG)

FIGURE ll. — Predicted number of nauplii or older stage cope-
pods required for daily consumption by winter flounder larvae
at 8°C over the range of dry body weights from hatching to
metamorphosis and at different planktonic prey concentrations.
Numbers for each simulation indicate prey concentration in
calories per liter; 6.7-21.7 simulations are in ascending order
from top to bottom.

older stage copepods as larval size increases
(Figure 12).

The percentage of body weight consumed per
day index (Figure 13) demonstrated sharply de-
creasing values during the first weeks of life (10-
75 fig), after which values remained fairly stable
until metamorphosis. More food was consumed
per body weight at lower plankton densities. The
differences became minimal with increasing
plankton density.

Predicted gross growth efficiencies increased
sharply from first feeding until a dry body weight
of 100 fig, after which they continued to increase
but at a decelerated rate (Figure 14). Efficiencies
were lower at lower plankton concentrations, and
the differences became smaller as plankton con-
centration increased.

DISCUSSION

A majority of the prior research has dealt with
instantaneous estimates of larval food needs
(Chiba 1961; Braum 1967) rather than a descrip-
tive relationship over the range of larval sizes
from hatching to metamorphosis. Larval winter
flounder exhibited a linear increase in food con-
sumption, as indicated by stomach contents with
increasing size (Figure 1). A linear relationship
was also reported for larval largemouth bass,
Micropterus salmoides (Laurence 1971b). Stepien
(1974) observed an exponential increase for the
larvae of sea bream, Archosargus rhombodalis, at
much higher temperatures (23°-29°C) than the
8°C studied for winter flounder in this research.

The amount of food a larval fish consumes dur-
ing a day depends on the size of the fish and den-
sity of the prey organisms available (Ivlev 1961a,
b). This is especially evident for winter flounder
larvae for which the traditional Ivlev relationship
changes with age or size (see Prey Density and
Intensity of Feeding, Figure 2). Smaller, younger
larvae reached maximum ration (R, Equation (7))

538

LAURENCE: moENERUETIC MODEL FOR WINTKK FLOUNDER LARVAE

«.oo

J. 75

3.50-

3.15

3.00

t. 75

t. SO

t.li

s.oo-

1.75-
1.50-
1.25-

1.00-
0.75-
0.50
0. ZS
0.00

0.0 100.0 200.0 300.0 400.0 500.0 600.0 700.0 BOO. 0 300.0 1000.0 1100.0
DRY UEIGHT (US)

FIGURE 13. — Index of body weight consumed per day by winter
flounder larvae at 8°C over the range of dry weights from hatch-
ing to metamorphosis and at different planktonic prey concen-
trations. Numbers for each simulation indicate prey concentra-
tion in calories per liter; 6.7-21.7 simulations are in ascending
order from top to bottom.

71.7

:. 3C-

_^<^^~^"'

^<^ — ^>^— ^"^-"

/— ^^^^2^^^ • '

C.J0-

^^^^^^-

0. 10-

0.00-

0.0 100.0 200.0 300.0 HOO.O 500.0 600.0 700.0 300.0 300.0 1000.0 1100.0
DRY UEIGHT (UG>

FIGURE 14. — Gross growth efficiencies of winter flounder larvae
at 8°C over the dry body weights from hatching to metamor-
phosis and at different plankton concentrations. Numbers for
each simulation indicate prey concentration in calories per liter.

at lower prey densities, while larger, older larvae
approached maximum feeding ration at increas-
ingly higher densities. The higher coefficient of
proportionality (a, Equation (7)) values for the
smaller larvae suggests that they have an easier
time capturing their maximum ration. In fact,
they reach their maximum ration at lower prey
densities because their stomach capacity is very
small and limited, while large larvae with greater
stomach volumes can take advantage of higher
plankton densities. From the standpoint of suc-
cessful captures to obtain the maximum ration,

smaller, younger larvae are actually much less
efficient than larger.

This size effect on feeding ration over a range
of prey densities has not been specifically exam-
ined for fish larvae before. Powers (1974) theoret-
ically evaluated tha Ivlev relationship with
laboratory feeding data for an amphipod, Aniso-
gammarus confervicolus. He examined changing
coefficients of proportionality (a) at constant
maximum ration. The results showed that the
asymptote is approached more quickly at higher
a's, similar to the results noted in this research.
Powers did not analyze maximum feeding ration
as a function of animal size at changing a's. He
did, however, state that animal size would prob-
ably have an effect since larger animals are better
predators than smaller ones.

The initial sharp reduction in feeding times pre-
dicted by the model following hatching until a dry
weight of 75 /ug (Figure 6) was undoubtedly due
to the increased ability of growing winter flounder
larvae to capture prey. This is supported by Schu-
mann (1965), who reported that larvae of Pacific
sardine, Sardinops sagax, which were initially
successful at feeding increased their searching
ability and the probability of capturing a sub-
sequent prey. The increase in predicted feeding
times from 75- to 500-^g size was due to the
exponential increase in metabolic rate for pre-
metamorphosed larvae (Laurence 1975). The re-
duction in predicted feeding time from the initia-
tion of metamorphosis until its completion
(500-1,000 fMg) was related to the decrease in
absolute metabolism due to behavioral changes
of metamorphosing winter flounder (Laurence
1975) and their greatly increased efficiency at
capturing prey, which required less energy expen-
diture. The decrease in predicted feeding time
with increase in prey concentration was due to
the increased chance of prey encounter and cap-
ture. Zaika and Ostrovskaya (1972) also con-
firmed this for Baltic smelt and Pacific herring,
Clupea harengus pallasi, larvae when they theo-
retically showed that the time spent searching for
food decreased exponentially with an increase in
food concentration.

Most larval fish have been reported as visual
feeders (Houde 1973) and require daytime light
intensities for optimum feeding (Blaxter 1969).
In view of this, it is surprising that little research
has been done on the relationship of feeding pa-
rameters and available time for feeding. Ivlev
(1961b) combining field and laboratory data for

539

FISHERY BULLETIN: VOL. 75, NO. 3

Atlantic herring, C. harengus, from the Gulf of
Finland reported that, at observed plankton con-
centrations in the field, the calculated time of
feeding was 15 h. This coincided exactly with the
length of day. Laurence (1971a), working with
the stipulation of a 14-h feeding period for large-
mouth bass larvae, found that prey concentrations
of7.0cal/liter (400 organisms/liter) were limiting.
The results of this research show that simulated
critical prey densities, below which winter floun-
der larvae do not have enough daylight hours for
feeding to meet growth and metabolic energy
requirements, actually vary with age and stage
of development (Figure 7). The critical densities
range from a high of 5.7 (0.8 nauplius/ml) to a
low of 2.1 cal/liter (0.3 nauplius/ml) when feeding
behavior has been established but before growth
and metabolic demands are high. Critical density
then increases until initiation of metamorphosis
when it remains fairly constant around 4.5 cal/
liter (0.6 nauplius/ml). Results such as these have
not been quantitatively reported in the literature
before. Most previous laboratory studies for a
variety of species delineate constant critical prey
densities for the larval period usually in the range
0.1-1.0 organism/ml (Kramer and Zweifel 1970;
O'Connell and Raymond 1970; Saksena and
Houde 1972; Laurence 1974; Houde 1975), al-
though Rosenthal and Hempel (1970) reported
that prey densities for optimum feeding (not crit-
ical densities) for larval Atlantic herring were
higher for younger than older larvae.

The critical prey densities for larval survival of
approximately 0.5 organism/ml noted in this and
the other cited laboratory research are somewhat
disparate with densities described from field data.
Lisivnenko ( 1961 ) noted that larval Baltic herring
were much less abundant in years when prey
abundance was <0.01 organism/ml. Sysoeva and
Degtereva (1965) reported that the minimum
abundance of Calanus finmarchicus, when the
intensity of feeding of cod, Gadus morhua, larvae
decreased, was from 0.01 to 0.005/ml and that a
concentration of 0.02/ml provided sufficient food
for survival. It is my opinion that the results re-
ported for laboratory studies may be more accu-
rate than the field study data presented thus far.
The laboratory studies represent highly con-
trolled experiments with accurate counts of prey
organisms. On the other hand, the field studies
give estimates of prey abundance which represent
average densities over linear or oblique sampling
distances. Planktonic prey organisms have conta-

gious distributions and larvae may well be associ-
ated with "patches" of prey that are more densely
concentrated than indicated by plankton net tows
(Wyatt 1973). Many larval fish researchers feel
that density dependent mechanisms control
larval survival (Cushing and Harris 1973), and
the concept of contagious distributions in which
larvae and prey are associated in "clumps" that
may or may not be associated and occupying the
same area is one of the most logical ways to ex-
plain the fluctuations noted for natural larval
mortality. Also, field zooplankton sampling de-
signs rarely use nets with mesh smaller than
200 /xm. Most of the significant food organisms
utilized by larval fishes especially in the early
stages are <200 /xm in smallest dimension (Houde
1973) and would be lost in field sample estimates.
Use of the plankton pump may prove to be more
accurate in locating patches of zooplankton and
sampling the size organisms that larval fish con-
sume. Recently, Heinle and Flemmer (1975),
using a moving plankton pump, reported concen-
trations of nauplii of Eurytemora affinis in the
Chesapeake Bay area as high as 2.8/ml with con-
centrations of 1.0-1.8/ml not at all uncommon.
These concentrations are more than adequate for
good growth and survival of winter flounder lar-
vae and many other larval species.
. The initial, predicted decrease in metabolic
energy expended (Figure 8) during the period of
feeding initiation and shortly after ( 10-30 /xg dry
weight) is undoubtedly explained by the increased
feeding success with experience by first feeding
larvae. First feeding individuals have a lower
success ratio of captures and have to expend more
energy in searching for prey than older and more
accomplished feeders. This success or fail period
is critical to eventual survival and is relatively
short in duration for winter flounder, occurring
during the first 8 days after feeding begins at
8°C. The increase in metabolic energy expended
from 30- to 500-/xg dry weight after successful
feeding establishment is due to normal increases
in energy demand for all processes with rapid
increases in size usually seen in larval fishes. The
leveling off of metabolic energy demand during
the metamorphosis period (500-1,000 /xg dry
weight) may be unique to flatfishes due to marked
morphological and behavioral changes (Laurence
1975) and increased predatory efficiency requir-
ing less energy expenditure.

The decrease in metabolic energy expenditure
with increasing prey concentration is logically

540

LAURENCE: BIOENEROET1C MODEL FOR WINTER FLOUNDER LARVAE

explained by the increased chance of successful
feeding at higher plankton concentrations and
concurrent decrease in energy expended to obtain
prey. Warren and Davis (1967) concurred with
this type relationship, stating that the density
of food determines an animal's energy cost in
obtaining the food. Decreasing metabolism with
increasing food concentration is contrary to re-
ported laboratory studies using fish older than
the larval stages. Paloheimo and Dickie (1966a)
and Beamish and Dickie (1967), examining data
from other researchers, concluded that higher
average metabolic rates result at higher feeding
rates. However, it may be presumptuous to as-
sume this type relationship for fish larvae. Most
older, nonplanktivorous feeding fishes, such as
those referred to in the above citations, are satia-
tion or periodic feeders. In fact, most of the experi-
mental data cited above were for restricted daily
diets at different levels. Larval fish, like the win-
ter flounder, are active continuous feeders and
the assumption in this model was continuous feed-
ing at maintained prey densities. Older fish have
more body reserves and can exist on maintenance
rations to which they can adjust metabolically in
contrast to larval fish which must feed continu-
ously and are committed to growth or else die.
In fact, the concept of maintenance probably is
not relevant to larval fish feeding and energetics.
So, it seems logical that fish larvae feeding con-
tinuously and committed to relatively high
growth rates would optimize growth by reduced
metabolic expenditure which would result from
the increased contact and efficiency of capture at
higher prey densities and resultant feeding levels.
The research of Wyatt (1972) with plaice larvae
tends to further support this concept. He noted
that activity, which he attributed to food search-
ing, decreased with increasing prey concen-
tration.

The trends of nonassimilated energy over the
range of weights and plankton concentrations in
this research are similar to those for metabolic
energy expenditure and food consumption (Fig-
ure 9). This is not surprising due to the inter-
relationships of these factors. The decrease in
nonassimilated energy with increasing weight
(10-30 /jig) for first feeding larvae is apparently
due to their initial inefficient digestion which
improves with morphological development. Vi-
sual examination of food in the anterior portions
of the digestive tracts of young larvae during the
digestion rate studies indicated relatively intact

nauplii. This has been observed for other larval
fish species. Rosenthal and Hempel (1970) noted
that the efficiency of digestion in Atlantic herring
fed Artemla nauplii was very low compared with
older larvae. Morphological development of the
alimentary tract during the larval stage was
studied by Nishikawa (1975) who noted an in-
crease in stomach size and extension of the diges-
tive tract as a whole in relation to increasing
standard length. He postulated that these mor-
phological developments cause a rapid increase
in the function of the organs during the larval
period. The subsequent increase in nonassimi-
lated energy with size of winter flounder larvae
is merely proportional to the increased ration.

Daily food requirements of winter flounder lar-
vae were initially higher for the period associated
with first feeding (10-30 /xg, first 2-3 wk after
hatching, Figure 10). These short-term higher
requirements were due to the inefficient manner
in which newly feeding larvae captured prey and
the associated, higher energy expenditure. Re-
searchers have reported that young fish larvae
are much less adept and successful at capturing
prey than older larvae. Braum (1967) showed that
freshwater whitefish larvae, Coregonus wart-
manni, increased their successful captures from
3 to 21% during the first 16 days of feeding. Schu-
mann (1965) noted an obvious increase in profi-
ciency at capturing food with increased age of
Pacific sardine larvae. The reasons for increased
success with age are increased visual perception
of food organisms and increased locomotor abili-
ties with advancing development (Blaxter 1965;
Rosenthal and Hempel 1970). The subsequent in-
crease in required ration with larval size was
the result of normal increased energy demand
of growth and metabolism associated with larger
sized larvae. An interesting fact is the decrease
in rate of food requirement noted in metamorphos-
ing larvae (500-1,000 fj.g). This may be associated
with the previously mentioned decrease in routine
metabolic rate peculiar to flatfish larvae and in-
creased efficiency of prey capture during the meta-
morphosis period. Riley's (1966) results for an-
other flatfish, the plaice, Pleuronectes platessa,
substantiate this observation. He noted declin-
ing ingestion rates and rations during meta-
morphosis.

Conversion of the caloric values of daily food
required into numbers of nauplii or older stages
consumed (Figure 11) showed, of course, the same
trends for food required. This conversion does,

541

FISHERY BULLETIN: VOL. 75, NO. 3

however, give a different perspective in that it
shows the actual numbers of organisms that win-
ter flounder larvae require on a daily basis. The
differences in numbers between nauplii and older
stages reflect the differences in sizes providing
equivalent caloric intake. Also, winter flounder
larvae did not feed entirely on nauplii, but
changed in part to larger stage copepods as they
grew older. Size selection of prey by larval fishes
has been shown to be a factor of mouth size which
increases with increased larval size (Shelbourne
1965; Blaxter 1969; Detwyler and Houde 1970;
Shirota 1970). The numbers of nauplii consumed
per day ranged from 19 to 235 over the range
of sizes and plankton densities. These values are
similar to requirements for other larval species
(Chiba 1961; Braum 1967; Rosenthal and Hempel
1970), although temperature, larval species and
size, and food organisms can account for variable
results.

Decrease in percent food eaten per day with
body weight (Figure 13) is in accordance with re-
sults of other researchers and was due to the rel-
ative decrease in the rate of food intake compared
with the growth rate with larval development.
Pandian (1967) observed decreases in percent
eaten per day with increases in body size of Mega-
lops cyprinoides and Ophiocephalus striatus, as
did Laurence (1971b) for larval largemouth bass
and Stepien (1974) for larval sea bream.

The percentages of body weight consumed per
day predicted in this research were high from over
300% at the smallest larval sizes and lowest prey
concentration to 27-31% at the higher prey con-
centrations and largest larval sizes. Percent body
weight eaten per day is typically much greater
for larval and juvenile fishes as compared with
adults since there is a much higher energy
demand for growth purposes (Winburg 1956).
Stepien (1974), in the only other known compar-
able research on marine larvae, also reported high
percentages. His results for sea bream at 29°C
were from 222.4% for 2-day hatched larvae to 79%
for 7-day-old larvae. Sorokin and Panov (1965)
reported 40-60% body weight eaten per day by
larval freshwater bream.

The gross growth efficiencies recorded in this
research increased rapidly with size for the small-
est larvae (10-75 /u.g) and then increased at a
decelerated rate for the remainder of the larval
period to metamorphosis (Figure 14). Increased
gross growth efficiency at greater body weights
observed in my experiments is contrary to the re-

sults of research with older fishes. Parker and Lar-
kin (1959) stated that within any growth stanza
the gross efficiency must decline with increasing
size, as a greater portion of the food must be used
in maintenance. This may not be true for larval
fishes, as their development is so rapid that a
large portion of the energy derived from food in-
take is used in growth. It is my opinion that larval
fishes could not exist on a maintenance ration.
Rapid growth is a definite prerequisite for success-
ful survival in the environment of larval fishes,
and they must either consume food at high levels
with resultant rapid growth or die. The ability
of larvae to increase their feeding efficiency with
increased size could also contribute to greater
growth efficiency.

Divergent opinions have been expressed by re-
searchers concerning the relationship between
growth efficiency and feeding level or prey concen-
tration. Paloheimo and Dickie (1966b) stated that
growth efficiency declined with increasing ration.
Warren and Davis (1967) showed that growth
efficiency increased to two-thirds the maximum
feeding level and then decreased. Finally, Davies
(1964) demonstrated that efficiency of digestion
and absorption of food by goldfish, Carassius
auratus, was improved by increasing food input
over a given weight range. He postulated that
secretion of digestive fluids was stimulated by the
effects of increased food. In all cases the studies
and analyses were done with adult fishes. Winter
flounder larvae increased their gross growth effi-
ciencies with increased plankton density similar
to Davies' results. However, the causative mech-
anism was most likely the increased efficiency of
prey capture with increased prey encounter at
higher densities with resultant metabolic savings
for growth rather than increased secretion of
digestive fluids. Growth efficiency is most likely
a dynamic factor not subject to generalizations
and dependent on life stage, type of feeding strat-
egy, or prey type.

The range of values of growth efficiency for
larval winter flounder on this research were from
5 to 33%, depending on larval size and plankton
concentration. These values are similar to those
for other young fishes (Ivlev 1939a; Sorokin and
Panov 1965; Edwards et al. 1969; Laurence 1971a;
Frame 1973; Stepien 1974).

The above discussions have revealed that there
are interrelationships between the bioenergetic
parameters simulated by the model and that the
whole system works in a circular pathway to

542

LAURENCE: BIOENERGETIC MODEL FOR WINTER FLOUNDER LARVAE

maintain an energy balance in the larva's body.
Energy expended at a given temperature pro-
motes growth and results in a metabolism that
produces activity, which in turn acts on the plank-
tonic prey to provide an assimilated food intake
that supplies energy for metabolism and growth.
The whole process at a given temperature is in
turn influenced by the size or age of larvae and
the planktonic prey concentration. A good exam-
ple which depicts the effect of larval age or size
on these interrelationships and one which points
to a definite "critical period" shortly after hatch-
ing around the period of feeding initiation is
shown in Figure 15. In this figure the caloric ex-
penditures for the important bioenergetic param-
eters over the range of weights from 10 to 50 /Ltg
are summed for all plankton concentrations. A
definite divergence of energy away from growth
to metabolism and nonassimilation with a result-
ant increased food requirement is shown during
early life (10-30 tig). This period coincides with
first feeding and is the time when larvae need
to grow at a fast rate because of their small size,
fragility, and vulnerability to predators. This
identified "critical period" is caused by a number
of factors and interrelationships including: 1) de-
velopmental factors of which reduced visual per-
ception and locomotor (swimming) abilities in

0.060-

FOOO CONSUMPTION

METABOLISM

4 ON ASS IM I I A T ION

20.0 30.0

DRV WEIGHT <UG>

FIGURE 15. — Caloric energy expenditure for the major bio-
energetic parameters of winter flounder larvae summed for all
prey concentrations over the range of dry weights from 10 to
50 /xg at 8°C.

young larvae prevent efficient prey capture com-
pared with older and better developed larvae;

2) less efficient conversion of food to flesh because
of higher metabolic expenditure associated with
more searching due to less efficient prey capture;

3) less efficient digestion in young larvae causing
a smaller fraction of the food to be assimilated
and be available for potential growth. As the lar-
vae grow larger and older, especially during the
metamorphosis period (50-1,000 /xg), they
become more efficient at converting food to
growth. The slopes of the lines connecting the
simulated values of the important bioenergetic
components summed for all prey concentrations
over the weight range of hatching to metamor-
phosis in Figure 16 show that the rate of growth
accelerates more rapidly towards food consump-
tion rate than metabolic and nonassimilation
rates with increasing larval size after the critical
period.

In addition to the critical period, plankton den-
sity is an important determinant of larval survi-
val and, of course, interacts crucially during the
critical period. The overall influence of prey den-
sity is shown in Figure 17 where the caloric expen-
ditures of the important bioenergetic parameters
simulated by the model are summed over all
weights at each plankton concentration. It can
easily be seen that low prey densities strongly
affect the dispensation of energy available from
food consumption in comparison with high densi-
ties. A greater portion of the energy intake is
utilized for metabolism and is not assimilated

0.0 100.0 200.0 300.0 »00. 0 500.0 600.0 700.0 800.0 300.0 1000.0 1100.0
DRY UCIGMT <yG>

FIGURE 16. — Caloric energy expenditure for the major bio-
energetic parameters of winter flounder larvae smiimed for all
prey concentrations over the range of dry weights from hatching
to metamorphosis at 8°C.

543

1.000

0.900-

o.aoo

o.soo

g °-S0°

0.100

0. 300

0. 100

fOO 0 COMSUMP1IOM

Minmiii"

0.7 3.7 8.7 S.7 12.7 15.7 18.7 21.7
PLRNKTON CONCENTRATION (CHL/LITRE>

FIGURE 17.— Caloric energy expenditure for the major bio-
energetic parameters at 8°C of winter flounder larvae summed
for all dry weights from hatching to metamorphosis at different
planktonic prey concentrations.

than is used for growth at lower prey densities.
Also, the food requirements are higher at the
lower densities which causes problems because
food is harder to obtain at lower densities.

In conclusion, these experimental studies and -
model simulations demonstrate that there is
strong evidence for a "critical period" of mortality
in the larval stage of winter flounder and that
planktonic prey density is one of the most impor-
tant factors affecting survival during the larval
stage. Additionally, the bioenergetic model devel-
oped presents a means to assess other trophic
interactions in the marine, planktonic commun-
ity. Larval fish are planktonic carnivores and the
food requirements predicted by the model in com-
bination with biomass estimates of larvae and
prey and survival estimates of larvae can be used
to predict the impact of larval grazing on their
prey. This type of research is currently being pur-
sued in continuing studies.

ACKNOWLEDGMENTS

I am grateful to B. Burns, K. Dorsey, T. Hala-
vik, and A. Smigielski for their help with labora-
tory experiments and data analyses. Thanks also
go to B. Brown, J. Colton, R. Hennemuth, E.
Scura, and K. Sherman for their critical review of
the manuscript.

FISHERY BULLETIN: VOL. 75. NO. 3

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1965. Balance of consumption and expenditure of food by
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1974. Feeding of laboratory-reared larvae of sea bream

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546

DESCRIPTION OF LARVAL AND EARLY JUVENILE
VERMILION SNAPPER, RHOMBOPLITES AURORUBENS1

Wayne A. Laroche2

ABSTRACT

Larval and early juvenile development of vermilion snapper, Rhomboplites aurorubens, family Lut-
janidae, is described and illustrated. Identification and description are based upon morphology, pig-
mentation, and meristics of 27 larval and 11 early juvenile specimens ranging from 4.0 to 14.2 mm
standard length. All specimens were collected 65 km east of Sapelo Island, Ga., lat. 31°30'N, long.
80°30'W on 10 August 1972.

Larval and early juvenile vermilion snapper,
Rhomboplites aurorubens (Cuvier), family Lut-
janidae, are described from 27 larval and 11 small
juvenile specimens collected at a station located
approximately 65 km east of Sapelo Island, Ga.,
lat. 31°30'N, long. 80°30'W on 10 August 1972
(depth 22 m, surface temperature 26.7°C).

The genus Rhomboplites is monotypic and oc-
curs only in the western Atlantic, from North
Carolina and Bermuda to Rio de Janeiro, Brazil,
including the Gulf of Mexico (Jordan and Ever-
mann 1898; Hildebrand and Schroeder 1928; Hil-
debrand 1941; Anderson 1967; Bohlke and Chap-
lin 1968). Walker (1950) and Munro et al. (1973)
reported R. aurorubens with mature ovaries dur-
ing the cooler months, but Munro et al. (1973)
suggested that some lutjanids may spawn
throughout the year. I was unable to find any
descriptions of lutjanid larvae. Small juveniles of
the genera Lutjanus (Starck 1971; Heemstra
1974; Fahay 1975) and Symphysanodon (Four-
manoir 1973) have been illustrated.

METHODS

All specimens were collected by personnel
aboard the U.S. National Marine Fisheries Ser-
vice RV Delaware II. Ichthyoplankton was col-
lected with a 60-cm diameter, 0.505-mm mesh,
bongo net towed obliquely at 1.1 km/h (0.6 knot)
from 20 m to the surface.

'Contribution No. 77 from the Ira C. Darling Center, Univer-
sity of Maine, Walpole, ME 04573. Supported in part by National
Marine Fisheries Service Contract No. 03-3-043-12 to the Ira C.
Darling Center of the University of Maine, Orono.

2School of Oceanography, Oregon State University, Corvallis,
OR 97331.

The specimens were stored in 3-5% buffered
Formalin3 after being removed from the sample
(fixed in 10% buffered Formalin). Specimens were
lightly stained with alizarin to facilitate measur-
ing and counting body parts. One specimen (10.8
mm) was cleared and stained using the technique
of Taylor (1967).

Illustrations were prepared using a camera
lucida. Measurements were taken on the left side
with an ocular micrometer. Measurements in-
clude:

Standard length (SL) — distance from tip of snout
to posterior tip of notochord (before hypural
formation) and tip of snout to posterior margin
of hypurals (after hypural formation posterior
to notochord tip).

Head length — distance (horizontal) from tip of
snout to cleithrum.

Snout to anus — distance from tip of snout to pos-
terior margin of anal opening.

Body depth — vertical distance between dorsal and
ventral surfaces, to the ventral tip of the clei-
thrum.

Eye diameter — maximum diameter of eye.

Spine and fin ray lengths — distance from point of
entry of spine or ray into flesh to distal tip.

IDENTIFICATION

Identification of the series was based on counts
of small juvenile specimens which had 24 myo-
meres; 7 branchiostegal rays; XII, 11 dorsal fin

3Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

Manuscript accepted January 1977.
FISHERY BULLETIN: VOL. 75, NO. 3, 1977.

547

FISHERY BULLETIN: VOL. 75, NO. 3

spines and rays; III, 8 anal fin spines and rays;
17-18 pectoral fin rays; I, 5 pelvic fin spine and
rays; 9 + 8 principal caudal fin rays. Taxa listed by
Bailey et al. (1970) were checked for the counts
listed above. Only R. aurorubens was found to
have the above counts (Jordan and Evermann
1898; Hildebrand and Schroeder 1928; Anderson
1967; Bbhlke and Chaplin 1968; Miller and
Jorgenson 1973) among fishes inhabiting western
North Atlantic waters less than 200 m deep. Lar-
vae were linked to the juvenile specimens by
similarities of morphology and pigmentation.

Future identifications of small larvae based
upon this paper should be made with care since
larvae of other lutjanids have not been described.

DESCRIPTION OF LARVAE AND
JUVENILES

Only large larval and small juvenile stages are
described since egg, yolk-sac, and small post
yolk-sac stages were not available. Larvae are
defined as all forms between yolk-sac absorption
and differentiation of the adult complements of
spines and soft rays in the fins. Transformation
from larva to juvenile is gradually completed be-
tween 8.3 and 10.9 mm.

Pigmentation

Head pigmentation increases through the lar-
val period (Figures 1, 2) with the smallest larva
(4.0 mm) showing least pigmentation (Figure 1A).
Head pigmentation includes a large stellate
melanophore centered over the posterior portion of
the midbrain and another on the ventral surface
anterior to the tips of the cleithra (Figures 1, 2).
The large dorsal melanophore is present on all
larval and juvenile specimens except one which
has a melanophore over each hemisphere of the
midbrain on either side of the point where the
central melanophore would be expected. A small
area of internal pigmentation is also present ven-
tral to the juncture of the midbrain and hindbrain.
As the larvae increase in size, smaller stellate
melanophores develop on each hemisphere of the
midbrain anterior to the large central
melanophore.

By 4.8 mm, a melanophore appears posterior to
the dorsal tip of the opercle and 2 or 3
melanophores appear on the body beneath the
opercle anterior to the cleithrum. Additional
melanophores are added to the area of internal

548

pigmentation ventral to the juncture of midbrain
and hindbrain (Figure IB).

There is a gradual increase of pigmentation over
the forebrain and midbrain until melanophores
form a cap of pigment over those structures (Fig-
ure 2B, C). From 15 to 20 melanophores per fore-
brain hemisphere and from 60 to 80 melanophores
per midbrain hemisphere make up the cap in
larger juvenile specimens (>10.0 mm). Three to
five small melanophores appear at 9.0 mm scat-
tered along the dorsal surface of the snout. On
juveniles >10.0 mm, 8-12 small melanophores
are scattered on the anterior portions of upper and
lower lips.

Preanal body pigmentation includes dense
peritoneal pigment which spreads ventrally in
bands along the dorsolateral surface of the
coelomic wall. The banding results from varia-
tions in size and spacing of discrete melanophores.
Peritoneal pigmentation appears less distinct on
largest juveniles due to an increase in overlying
musculature. A pronounced melanophore occurs
on the ventral surface anterior to the anus on all
specimens <5.1 mm, and occasionally on those
5.1-6.3 mm, but is absent on individuals >6.3
mm.

A large stellate melanophore is present (on all
specimens examined) internally on myomere 15,
16, or 17 above the posterior end of the anal fin
near the ventral body margin (Figures 1A, B;
2A-C). Three to seven smaller melanophores de-
velop anteroventrally to this spot along the bases
of anal fin rays, appearing first on 4.7-mm larvae
and occurring on all larger specimens (Figures 1C,
2). Posterior to the large internal melanophore,
1-4 melanophores occur on the ventral margin of
specimens <7.0 mm. The number of melanophores
present in this region is variable, tending to in-
crease in number with body length, specimens
>7.0 mm having 5-12.

A small melanophore appears on larvae 5.1-5.4
mm along the dorsal margin of myomere 21 or 22.
Specimens >5.4 mm have 5-9 melanophores on
the dorsal margin of the caudal peduncle (Figure
2B, C). At 4.9 mm, an internal melanophore ap-
pears dorsal to the point of notochord flexure and is
present in all larger specimens examined (Figure
2A-C). An additional melanophore appeared an-
terior to this melanophore in two specimens, 8.7
and 10.5 mm long. Specimens with all principal
caudal rays developed have 1-6 melanophores
near the bases of the rays, usually on the lower 8
principal rays (Figure 2).

LAROCHE: DESCRIPTION OF VERMILION SNAPPER

FIGURE 1.— Developmental stages of Rhomboplites aurorubens: A. 4.0-mm larva; B. 4.7-mm larva; C. 4.7-mm

larva, ventral view; D. 4.7-mm larva, dorsal view.

549

FISHERY BULLETIN: VOL. 75, NO. 3

FIGURE 2.— Developmental stages of Rhomboplites aurorubens: A. 5.1-mm larva; B. 6.9-mm larva; C. 14. 2-mm juvenile.

550

LAROCHE: DESCRIPTION OF VERMILION SNAPPER

Fin Formation

Dorsal and pelvic fin formation begins by 4.0
mm (Figure 1A). Other fin development initiates
in the following sequence: caudal, anal, and pec-
toral. The pelvic fins are first to complete de-
velopment, while the dorsal fin is last.

Dorsal Fin

The anterior five dorsal spines are present on
the smallest larva (4.0 mm) with an undifferen-
tiated fin fold continuing to the caudal region
(Figure 1A). The fin develops from anterior to pos-
terior. At 4.8 mm, the adult number of dorsal fin
elements appears with the posterior 1-3 spinous
dorsal elements represented by soft rays.

Development of the dorsal fin occurs rapidly be-
tween 4.0 and 4.8 mm. After the adult number of
fin-ray elements (23) appears, development to-
wards the final adult dorsal fin complement (XII,
11) proceeds slowly as spines form from soft rays
immediately posterior to the posteriormost spine.
Dorsal spine development is similar to that de-
scribed by Mansueti (1958) for anal spine de-
velopment in Roccus saxatilis.

The dorsal fin is the last fin to attain the adult
complement of spines and rays. Attainment of full
dorsal fin complement between 8.3 and 10.9 mm
marks the division between larval and juvenile
stages.

The fourth dorsal spine is longest in adult
Rhomboplites aurorubens (Jordan and Evermann
1898). The second dorsal spine is longest in all
specimens of my series except the largest juvenile
(14.2 mm) in which the third spine is longest (Fig-
ure 2C). The longest dorsal spine is longer than the
longest dorsal soft ray throughout the series.

Dorsal spines are V-shaped in cross section,
with the V open posteriorly. The two posterior
edges are serrated nearly to the tip, which is sharp
and oval in cross section. On larger spines the
anterior edge is sometimes serrate for a short dis-
tance above the base (Figures IB, 2B, C). Speci-
mens between 4.8 and 9.0 mm have 29-40 serra-
tions along each posterior edge of the second dorsal
spine; larger specimens have 42-45 serrations.

Pelvic Fins

Pelvic fin spines and fin folds compose the pelvic
fins of the4.0-mm larva (Figure 1A). The pelvic fin
attains the adult complement of I spine and 5 rays

between 4.7 and 4.8 mm. The pelvic spine is long
and serrate, extending slightly beyond the anus
(24% SL) at its longest (about time of dorsal fin
completion). Small specimens have spines which
are V-shaped in cross section with serrations
along all three edges. Specimens >4.5 mm have a
double row of serrations along the leading edge of
the spines creating an almost trapezoidal appear-
ance in cross section (Figure 2).

Caudal Fin

The adult caudal fin has 17 principal and 19-21
procurrent rays (Miller and Jorgenson 1973).
Principal rays are divided into two groups with 9
rays above and 8 rays below the midline of the
body.

Notochord flexure occurs between 4.8 and 4.9
mm (Table 1). Flexure probably results in a slight
decrease in standard length because the angle of
the flexed notochord shortens the horizontal dis-
tance from snout tip to end of notochord. As a
result of flexure and individual variation in rate of
development, larvae of equal length may be at
various stages of development (Table 1).

The caudal fin starts to form at the beginning of
notochord flexure, about 4.7 mm. Fifteen or six-
teen principal rays form simultaneously, slightly
below and ventral to the posteroventral margin of
the notochord. As the notochord flexes, these rays
become elevated into the terminal position. The
remaining rays are added dorsally and ventrally
until the adult principal ray number is attained at
about 4.8 mm (Figures IB, 2A).

Anal Fin

The adult fin ray complement for vermilion
snappers is III spines and 8 soft rays. Initial anal
fin formation occurs at 4.7 mm. Embryonic fin rays
(actinotrichia) are visible on 4.8-mm larvae. True
soft rays (lepidotrichia) begin to form by 4.9 mm.
The fin ray count remains II, 8 until about 5.4 mm
and then becomes II, 9 (Table 1). The posterior-
most ray forms last. The adult complement (III, 8)
appears at about 8.3 mm as the anteriormost soft
ray transforms into a spine. Each spine becomes
serrate along its posterior edge, larger spines hav-
ing a few serrations along the base of the anterior
edge. The second anal spine is longest throughout
the series studied, but in adults the third spine is
longer.

551

FISHERY BULLETIN: VOL. 75, NO. 3

TABLE 1. — Development ofmeristic characters of larval and small juvenile vermilion snapper,

Rhomboplites aurorubens.

Principal

caudal fin rays

Dorsal fin

Anal fin

Pectoral

Pelvic fin

Notochord

(mm)

Upper

Lower

Spines

Rays Spines Rays

fin rays Spines Rays

flexure

4.00

straight

4.13

straight

4.67

VIII

straight

4.80

I 8

flexed

4.80

12 I

I 7

straight

4.80

13 I

I 8

flexed

4.87

13 I

I 8

flexed

4.93

13 I

I 8

flexed

4.93

13 I

I 8

straight

5.07

VIII

15 I

I 8

flexed

5.07

13 I

I 8

flexed

5.07

14 1

I 8

flexed

5.07

14 I

I 8

flexed

5.13

12 I

I 8

flexed

5.27

13 I

I 8

flexed

5.40

13 I

I 9

flexed

5.46

12 I

I 9

flexed

5.46

13 I

I 9

flexed

6.06

13 I

I 9

flexed

6.13

12 I

I 9

flexed

6.26

I 9

flexed

6.33

12 I

I 9

flexed

6.40

12 I

I 9

flexed

6.53

12 I

I 9

flexed

6.53

I 9

flexed

6.53

I 9

flexed

6.93

I 9

flexed

7.80

—

I 9

flexed

8.26

XII

11 II

I 8

flexed

8.60

12 II

I 8

flexed

8.66

XII

11 II

I 8

flexed

9.00

12 II

I 8

flexed

10.00

12 II

I 8

flexed

10.53

XII

11 I

I 8

flexed

10.80

XII

11 II

I 8

flexed

10.93

12 II

I 8

flexed

11.20

XII

11 II

I 8

flexed

14.20

XII

11 I

I . 8

I 5

flexed

Pectoral Fins

The pectoral fins are the last to begin develop-
ment, embryonic rays becoming visible at about
4.9 mm. Ray formation proceeds from dorsal to
ventral. True rays begin to form at about 6.9 mm,
the adult complement, 17-18 rays, appearing by
8.6 mm.

Pectoral fin rays were frayed and broken on
many specimens (including the specimen in Fig-
ure 2C). Longest pectoral fin rays without obvious
damage were 11.9-15.0% SL, having no obvious
within range correlation with standard length.

Head

All larvae have one small spine projecting from
the posterodorsal portion of the operculum. This
spine is very small and difficult to locate on small
specimens (Figures 1, 2).

The preopercle is armed with two rows of spines.
The smaller spines are located proximally along

552

the margin of the preopercular crest, and the
larger spines occur distally along the preopercular
margin (Figures 1, 2). Both preopercular crest and
preopercular margin have an upper (ascending)
and lower (horizontal) margin which form approx-
imately right angles.

Specimens <5.0 mm have 2 or 3 spines along the
lower margin and 1 spine on the upper margin of
the preopercular crest. Larger specimens have 3 or
4 spines along the lower and 1 or 2 spines along the
upper margins (Figures 1, 2). Spines increase in
size towards the angle of the preopercular crest.

Three spines are present along the lower margin
of the preopercular margin on specimens <4.0
mm, 4 spines on specimens 4.0-5.4 mm, 5 spines
on specimens 5.4-9.0 mm, and 6 or 7 spines on
specimens >9.0 mm. These spines increase in size
towards the angle of the margin, larger spines
being serrated on juvenile specimens. A large,
stout, and serrate spine occurs at the preopercular
angle in all specimens. Length of the angle spine
was 6.5% SL on the smallest larva (4.0 mm). All

LAROCHE: DESCRIPTION OF VERMILION SNAPPER

other specimens <8.0 mm had angle spines which
were 10.1-14.6% SL, averaging 12.6%. Specimens
>8.0 mm had angle spines which were 7.0-13.1%
SL, averaging 9.7%. The largest juvenile (14.2
mm) had the smallest spine within this group
(7.0%). One spine occurred on the upper margin of
the preopercular margin of all specimens
examined, with a smaller spine occasionally oc-
curring between it and the angle spine (Figure
2B).

The posttemporal has 1 or 2 sharp spines pro-
jecting posterodorsally; the supracleithrum, 2-5
similar spines; the number of spines increasing
with growth (Figures 1, 2). The supraocular crest
has 2-7 serrations which increase in number with
growth. A sharp projection which appears to be the
anterior tip of the lachrymal bone projects an-
teriorly and slightly ventrally from each side of
the snout on all specimens.

The eye is nearly circular and has a ventral cleft
(Figures 1, 2).

Conical teeth are present on premaxillary and
dentary of all specimens; vomerine and palatine
teeth, on 14.2-mm specimen.

Body Growth

Measurements of body parts is presented in
Table 2. The growth of various body parts as re-
lated to standard length is described by linear
regression analysis using Bartlett's three-group
method for Model II regression (Sokal and Rohlf
1969). Statistics for regressions of head length,
depth of body, snout to anus distance, and eye
diameter versus standard length are presented in
Table 3. Correlation coefficients are greater than
0.97 for all relationships.

TABLE 3. — Statistics describing regressions of body measure-
ments versus standard length for larval and small juvenile ver-
milion snapper, Rhomboplites aurorubens. The x variable is
standard length in all cases.1

Variable

Size

range (mm)

a Sy.x r

Head length

4.00-14.20

6.64

2.62

0.326

0.454 0.217 0.988

Body depth

4.00-14.20

6.64

2.28

0 285

0.388 0.198 0.986

Snout to anus

4.00-14.20

6.64

4.01

0.672

-0.450 0.185 0.995

Eye diameter

4.00-14.20

6.73

0.91

0.110

0.170 0.090 0.978

'x = mean value of x, y = mean value of y, N = number of specimens
examined, b = rate of increase of y with respect to x, a = regression line
intercept, Sy x = standard deviation from the regression, r = correlation
coefficient.

TABLE 2. — Measurements of body parts for larval and juvenile
vermilion snapper, Rhomboplites aurorubens, in millimeters.

Head

Snout to

Eye

length

anus

Depth

diameter

4.00

1.53

2.00

1.32

0.52

4.13

1.69

2.23

1.42

0.60

4.67

1.90

2.67

1.65

0.62

480

1.92

2.53

1.65

0.68

4.80

2.13

2.93

1.85

0.75

4.80

1.92

2.80

1.82

0.68

4.87

2.03

2.73

1.75

0.70

4.93

2.20

2.97

1.88

0.75

4.93

1.87

2.93

1.88

0.70

5.07

2.11

293

1.82

0.72

5.07

2.13

2.93

1.84

0.72

5.07

2.26

3.13

1.82

—

5.07

2.00

2.87

1.85

0.70

5.13

2.13

3.00

1.88

0.72

5.27

2.21

3.20

1.85

—

5.40

2.26

3.20

200

0.75

5.46

2,21

3.27

1.92

0.78

5.46

2.24

3.20

2.08

0.80

6.06

2.52

3.60

2.08

0.85

6.13

2.55

3.53

2.18

0.85

6.26

2.52

3.73

2.30

0.90

6.33

2.65

3.77

2.20

0.90

6.40

255

3.87

2.28

0.91

6.53

2.83

4.00

2.38

0.92

6.53

2.68

4.13

2.20

0.90

6.53

265

4.00

2.50

0.88

693

2.78

4.33

2.40

0.95

7.80

3.12

5.06

2.60

1.05

8.26

3.27

5.33

2.67

1.12

8.60

3.07

5.27

293

1.15

8.66

3.33

5.47

2.93

1.12

9.00

3.40

5.60

2.93

1.12

10.00

3.53

6.13

320

1.30

10.53

3.73

6.73

3.47

1.35

10.93

4.00

6.73

3.47

1.35

11.20

3.93

7.00

3.53

1.40

14.20

4.93

8.46

4.00

1.48

ACKNOWLEDGMENTS

I thank John B. Colton, Jr., National Marine
Fisheries Service, for specimens; and Sally L.
Richardson and Joanne L. Laroche, Oregon State
University, and Hugh H. DeWitt and Bernard J.
McAlice, University of Maine, for constructive
criticisms.

LITERATURE CITED

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BAILEY, R. M., J. E. FITCH, E. S. HERALD, E. A. LACHNER, C. C.
LINDSEY, C. R. ROBINS, AND W. B. SCOTT.

1970. A list of common and scientific names of fishes from
the United States and Canada. Am. Fish. Soc, Spec.
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BOHLKE, J. E., AND C. C. G. CHAPLIN.

1968. Fishes of the Bahamas and adjacent tropical waters.
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FAHAY, M. P.

1975. An annotated list of larval and juvenile fishes cap-
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and February 1968. U.S. Dep. Commer., NOAA Tech.
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FOURMANOIR, P.

1973. Notes ichthyologiques(V). Cah. O.R.S.T.O.M. Ser.
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FISHERY BULLETIN: VOL. 75, NO. 3

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1974. On the identity of certain eastern Pacific and Carib-
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1941. An annotated list of salt and brackish water fishes,
with a new name for a menhaden, found in North Carolina
since the publication of "The Fishes of North Carolina" by
Hugh M. Smith in 1907. Copeia 1941:220-232.
HILDEBRAND, S. F., AND W. C. SCHROEDER.

1928. Fishes of Chesapeake Bay. U.S. Bur. Fish., Bull.
43(1), 366 p.
JORDAN, D. S., AND B. W. EVERMANN.

1898. The fishes of North and Middle America: A descrip-
tive catalogue of the species offish-like vertebrates found
in the waters of North America, north of the Isthmus of
Panama. Part II. Bull. U.S. Mus. 47:1241-2183.
MANSUETI, R.

1958. The development of anal spines and soft-rays in
young striped bass, Roccus saxatilis. Md. Dep. Res.
Educ, Chesapeake Biol. Lab. Contrib. 113, 12 p.
MILLER, G. L., AND S. C. JORGENSON.

1973. Meristic characters of some marine fishes of the

western Atlantic Ocean. U.S. Fish Wildl. Serv., Fish.
Bull. 71:301-312.
MUNRO, J. L., V. C. GAUT, R. THOMPSON, AND P. H. REESON.
1973. The spawning seasons of Caribbean reef fishes. J.
Fish. Biol. 5:69-84.

SOKAL, R. R., AND F. J. ROHLF.

1969. Biometry. The principles and practice of statistics in
biological research. W. H. Freeman and Co., San Franc,
776 p.

STARCK, W. A., II.

1971. Biology of the gray snapper, Lutjanus griseus (Lin-
naeus), in the Florida Keys. In W. A. Starck, II and R. E.
Schroeder, Investigations on the gray snapper, Lut-
janus griseus, p. 11-150. Stud. Trop. Oceanogr. (Miami)
10.

TAYLOR, W. R.

1967. An enzyme method of clearing and staining small
vertebrates. Proc. U.S. Natl. Mus. 122(3596), 17 p.

WALKER, E. T.

1950. Spawning records of fishes seldom reported from
North Carolina waters. Copeia 1950:319.

554

SHORT-TERM THERMAL RESISTANCE OF ZOEAE OF
10 SPECIES OF CRABS FROM PUGET SOUND, WASHINGTON

Benjamin G. Patten1

ABSTRACT

Zoeae of 10 crab species were subjected to tests that simulated thermal stress associated with steam-
powered electric stations. Shortly after hatching, the unfed zoeae were subjected to conditions
simulating passage through heat exchangers (held at elevated test temperatures for 20 min with an
abrupt increase and decrease from ambient) or mixing with thermal plumes (held at test temperature 1
to 4 h with temperatures gradually rising and decreasing from ambient). All species used in tests were
hatched from February to November and were naturally acclimated to ambient conditions of the
littoral zone. Observations were made on the point in temperature that zoeae became torpid in heat
exchanger tests and on the TL50 (maximum temperature-time that 50% or more of the subjects
survived 48 h after testing).

In the heat exchanger tests, the most sensitive species, the Bering hermit crab, Pagurus beringanus,
and the porcelain crab, Petrolisthes eriomerus , did not become torpid at 24°C; their torpid point and
their TL50 were at 26°C. The economically important Dungeness crab, Cancer magister, did not become
torpid at 28°C; its TL50 was at 30°C. The TL50 of other species ranged from 30° to 34°C.

The TL50 of zoeae given the thermal plume test ranged from 26° to 34°C for a 1-h exposure and 24° to
32°C for a 2- to 4-h exposure.

Thermal conditions in heat exchangers are postulated to be more critical to the survival of zoea than
mixing with thermal plumes. The maximum temperature that should be permitted in heat exchangers
to protect the most sensitive species studied is 24°C for the Puget Sound area.

Thermal resistance of marine organisms should
be understood before seawater in a specific area is
used for industrial cooling. In the State of
Washington, for example, nuclear power plants
are being planned for construction by municipali-
ties and industries. These plants require large
quantities of seawater to cool condensers of the
steam turbine system; their waste hot water
would be discharged back into the environment,
along with toxic chemicals (Becker and
Thatcher2). Organisms entrained into steam
electric stations would be subjected to mechanical
injury (Marcy 1973) from passage through such a
system. Studies are needed to fully evaluate the
impact of entrainment and the discharge of
altered waste water on the associated life;
temperature effects are considered here.

Some information is available on the thermal
maximums and optimums of two species of Puget

Northwest and Alaska Fisheries Center, National Marine
Fisheries Service, NOAA, 2725 Montlake Boulevard East,
Seattle, WA 98112.

2Becker, C. D., and T. O. Thatcher (compilers). 1973.
Toxicity of power plant chemicals to aquatic life.
Battelle Pac. Northwest Lab., Richland, Wash., WASH-
1249, U.S. AEC, misc. pagination.

Sound crabs (Todd and Dehnel 1960; Reed 1969;
Prentice 1971; Mayer34). These studies show the
effects of long-term temperature increases but do
not depict situations related to industrial use of
seawater for cooling. Experiments reported here
were designed to simulate the stress that zoeae
would be exposed to in passing through heat
exchangers of steam electric stations and in
mixing with thermal plumes of the waste water
released into the environment.

This study is one of a series describing the
thermal resistance of selected species of plank-
tonic organisms. The time-temperature combina-
tions used are considered a measure of thermal
resistance (Fry 1971) because they are probably
beyond the environmental tolerance of the species
used. This paper describes the elevated tem-
peratures that cause immediate and imminent

Manuscript accepted January 1977.
FISHERY BULLETIN: VOL. 75, NO. 3, 1977.

3Mayer, D. L. 1973. Thermal tolerance of Cancer ma-
gister eggs. In Q. J. Stober and E. O. Salo (editors),
Ecological studies of the proposed Kicket Island nuclear
power site, p. 412-419. Univ. Wash., Coll. Fish., FRI-UW-
7304.

4Mayer, D. L. 1973. Response of Dungeness crab in a
thermal gradient. In Q. J. Stober and E. O. Salo
(editors), Ecological studies of the proposed Kicket Island
nuclear power site, p. 420-429. Univ. Wash., Coll. Fish.,
FRI-UW-7304.

555

FISHERY BULLETIN: VOL. 75, NO. 3

death and stress to the zoeae of four species of
anomuran and six species of brachyuran crabs
acclimatized to natural ambient conditions. These
crabs constitute some of the more important types
in the littoral zone and include species important
in sport and commercial fisheries. Testing was
done at the National Marine Fisheries Service
facility at Mukilteo, Wash., from May to October
1971 and in February 1972.

MATERIALS AND METHODS

Ovigerous crabs were collected from the mid-
Puget Sound areas of Possession Sound, Poverty
Bay, and at Alki Point. Graceful crab, Cancer
gracilis, Dungeness crab, C. magister, and kelp
crab, Pugettia producta, were collected subti dally;
other species were taken on beaches during low
tides. The messmate crab, Pinnixa littoralis, was
collected inside horse clam, Tresus capax, that
had been excavated. Most of the experimental
species were ovigerous in May and June; the mud
flat crab, Hemigrapsus oregonensis, black clawed
crab, Lophopanopeus bellus, and porcelain crab,
Petrolisthes eriomerus , had ovigerous individuals
to August. Pugettia producta were ovigerous July
to November.

Ovigerous crabs and pre- and posttest zoeae
were held in aquaria receiving running seawater-
of temperatures ranging from 8.2° to 23.5°C (Table
1); salinity ranged from 24.1 to 28.3%o; and
dissolved oxygen ranged from 5.6 to 9.0 ppm.
Laboratory water was sometimes 3°C higher than
ambient temperatures at the surface in the
afternoon on sunny days in July and August
because of heating of the water supply pipe. Other

TABLE 1. — Temperature of Mukilteo, Wash., laboratory sea-
water summarized by 10-day periods in 1972.

Water temperature (°C)

Average

Month

Low

High

Range

May

9.3

10.0

8.2-10.7

9.9

10.4

9.1-11.1

9.5

11.4

8.8-127

June

10.4

12.2

100-13.3

10.4

12.7

97-14.3

10.8

13.5

10.4-14.3

July

11.0

13.1

10.4-14.0

12.3

16.4

11 3-18.2

August

12.9

16.4

11.3-18.2

16.6

20.7

13.5-23.5

15.7

18.6

13.0-23.0

September

13.2

14.9

126-15.6

12.9

15.5

12.5-16.8

13.7

15.9

12.5-16.8

than this, the ambient water temperatures of the
Mukilteo area were similar to that expected of
central Puget Sound locations (Wennekens 1959).

Test facilities consisted of floating holding
boxes for test groups of zoeae and 5 Jiter battery
jars for maintaining water baths of a controlled
temperature. Holding boxes were 2.5 cm3, with
two screened sides having 0.110-mm apertures,
attached to Styrofoam5 for floatation. Battery jars
received 3 liters of seawater immediately before
testing. Temperatures were maintained within
±0.5°C of the test temperatures during experi-
ments. Continuous aeration insured mixing and
oxygenation.

Zoeae generally hatched within a week after
their parents were collected, but some parents
were held a month before hatching occurred.
When the zoeae hatched (hatching of all ova of a
parent occurred within about 12 h), 10 were
counted into each of the holding boxes within 24 h
of hatching and remained there, unfed, to the
termination of an experiment. Zoeae used as
controls were held at the temperature of labora-
tory water, and others were given two types of
thermal tests.

To simulate passage through heat exchangers,
holding boxes containing 10 zoeae were removed
from water of ambient temperature and placed
directly into battery jars having water of an
elevated temperature ranging from 24° to 38°C by
2°C increments (Table 2). The zoeae remained at
the elevated temperature for 20 min and were
then placed into water of ambient temperature.
Actual temperature change within the holding
boxes was delayed. On the average, the increase
from ambient to midway to the test level occurred
in 5 s. Temperatures were within 1°C of the test
level in 2 min. Decreases from test temperatures
to ambient occurred in about IV2 min. Activity of
zoeae was noted before, during, and after testing.

To simulate conditions encountered in thermal
plumes, zoeae in holding boxes were placed in
water of ambient temperature in the battery jar.
The temperature of the water was then elevated to
a test temperature ranging from 24° to 36°C by 2°C
increments (Table 2) over a 30-min period.
Specific groups of zoeae were held at specific test
temperatures for durations of 1, 2, or 4 h. After
this, the temperature was gradually decreased to
ambient level over a 20-min period, and the

5Reference to trade name does not imply endorsement by
the National Marine Fisheries Service, NOAA.

556

PATTEN: SHORT-TERM THERMAL RESISTANCE OF CRAB ZOEAE

TABLE 2. — Percentage survival of first stage zoeae 48 h after testing of 10 species of crabs subjected to a range of temperatures at four
durations (percentages are from combined data of two or more tests). Increases to and decreases from a test temperature were rapid for
the 20-min test (heat exchanger test) and gradual for the longer durations of exposure (thermal plume test).

Minutes held

Date at

Control

No.

Survival at
different water temDeratui

•es ( C)

at test
temperature

end of
test

No. Of

parents

No. Percent
zoeae survival

zoeae

tested

Species

Percentaae

Anomuran:

Bering hermit crab,

6/20

60 53

'55

—

Pagurus bennganus

7/28

—

120

—

240

—

Granular hermit crab,

6/25

90 92

—

Pagurus granosimanus

6/27

—

120

7/2

—

240

—

Hairy hermit crab,

6/5

80 93

10-30

—

Pagurus hirsutiusculus

6/13

—

100

—

120

6/23

—

100

—

240

—

Porcelain crab.

6/23

40 83

10-30

—

Petrolislhes enomerus

6/25

—

120

7/2

—

100

—

240

—

Brachyuran:

Black clawed crab,

6/16

100 89

100

—

Lophopanopeus bellus

6/23

100

—

120

9/16

100

—

240

—

Dungeness crab,

6/7

60 93

100

—

Cancer magister

6/9

100

—

120

6/28

100

—

240

2/29/72

100

—

Graceful crab,

7/16

60 95

—

Cancer gracilis

7/18

—

120

—

240

—

Kelp crab,

9/2

80 100

—

100

—

Pugettia producta

10/15

—

100

—

120

—

240

—

Messmate crab,

7/30

80 95

—

Pinmxa littoralis

8/4

—

120

—

240

—

Mud flat crab,

6/13

130 98

20-50

—

100

Hemigrapsus oregonensis

6/18

—

120

7/2

—

100

—

240

7/8
8 28

—

100

'Italic denotes the TL50.

holding boxes containing zoeae were replaced in
aquaria with running seawater.

The numbers of replicate tests made at a
temperature for a test varied because of numbers
of ovigerous crabs available and numbers of zoeae
resulting from a hatching. The offspring from at
least two parent crabs of a species were used
(Table 2). Some species were tested at intervals
over a 2- to 3-mo period to indicate seasonal
acclimation effects. One test for C. magister was
made in 1972; all other species were tested in
1971. Percentage survival of a species of crab for a
given duration and temperature is the combined
survival of two to five tests made for a species
(Table 2).

Observations were made on the levels of

activity, point of torpor, and the TL50 (maximum
temperature-time combination survived by 507c
or more of subjects 48 h after testing) to evaluate
the effects of experimental conditions. A 48-h
posttest observation duration was deemed appro-
priate for these tests as the zoeae were not fed and
could have been affected by starvation although
they readily survived to 72 h.

TEMPERATURE EFFECTS

Temperature-time combinations for a type of
test that was critical to the survival of the zoeae of
a species were indicated by survival of the controls
and by experimental conditions affecting activity
and survival of the test subjects.

557

FISHERY BULLETIN: VOL. 75, NO. 3

Zoeae used as controls had survival rates
ranging from 53 to 100% (Table 2). Guidelines set
in the American Public Health Association (1971)
state that losses of greater than 10% of control
subjects invalidate an experiment. Control zoeae
of the Bering hermit crab, Pagurus beringanus,
with a survival of 53%, L. bellus with a survival of
89%, and Petrolisthes eriomerus, with a survival
of 83% fall below this standard. Although the
TL50's are invalid for these species, the point of
torpor is valid as it demonstrates an immediate
condition the zoeae lapse into with a given
temperature stress.

Activity and survival of a species of zoeae de-
creased with increasing temperature and dura-
tion at an elevated test temperature (Table 2).
In heat exchanger tests, zoeae experienced a rapid
temperature change and were initially hyper-
active, probably as a result of thermal shock
(Kinne 1964). With time, zoeae at a temperature
4°C below the TL50 appeared normal. Those at
2°C below TL50 had reduced activity and had
difficulty maintaining themselves off the bottom.
Subjects placed in water at the TL50 temperature
and above were initially hyperactive, but in 2 to
7 min became torpid and sank to the bottom. Heat
exchanger test temperatures producing torpor
were 26°C for Pagurus beringanus and Petro-
listhes eriomerus and 30°C for most other test
species; the maximum was 32°C for L. bellus,
Pugettia producta, and H. oregonensis. After the
zoeae were returned to ambient conditions, those
tested at the TL50 temperature had not become
active after 20 min.

Zoeae subjected to the heat exchanger tests
generally had high survival to the point of the
TL50 (Table 2). Thereafter, mortalities were
complete at 2° to 4°C higher except in the case of
the hairy hermit crab, Pagurus hirsutiusculus,
where all died at 6°C above the TL50. The minimal
TL50 was at 28° and 30°C for most other crabs; it
was at 32°C for Pugettia producta and L. bellus
(Table 2). The most tolerant species was H.
oregonensis with a TL50 at 34°C.

Zoeae subjected to the thermal plume tests had
lower TL50's than those given the heat exchanger
tests (Table 2). The TL50 of zoeae given the 60-min
test was similar to or 2°C lower than those given
the 20-min heat exchanger test; TL50's were at
progressively lower temperatures for the 120- and
240-min tests. Mortalities were complete at 2°
to 4°C above the TL50. The least tolerant species
were the Cancer crabs (Table 2) with TL50's at

28°C for the 60- and 240-min tests. TL50's were
generally at 30°C for the other crabs for the three
time durations they were tested. The species with
the highest tolerance was H. oregonensis with a
TL50 at 34°C for the 60-min test and at 32°C for the
120- and 240-min tests.

DISCUSSION

The situation postulated to be most critical to
the survival of the planktonic zoeae is their
passage through heat exchangers; zoeae will be
entrained into heat exchanger systems but those
encountering thermal plumes will probably only
be exposed to lowering temperatures (Coutant
1970) at the periphery where turbulence occurs.

The maximum temperature limit that should
occur in heat exchangers is best described as the
one causing no adverse effects to the least
resistant species — to be consistent with the
protection of all species tested. Conditions that
could be overtly recognized as affecting the
survival of the zoeae were the degree of stress
causing torpor and the TL50. While the TL50
directly relates to death, torpor indicates a
condition that could indirectly cause death.
Torpid zoeae would have their feeding interrupted
and they would not be able to evade predators
until they recovered. Selective predation on zoeae
subjected to a stress below that causing torpor
could also be a factor of survival at sublethal
temperature-time combinations. In fish, for ex-
ample, Coutant (1973) experimentally observed
that rainbow trout, Salmo gairdneri, predators
selectively preyed on juvenile rainbow trout and
chinook salmon, Oncorhynchus tshawytscha , that
had been exposed to shock temperature treat-
ments of durations below that required for the
prey to lose equilibrium.

The maximum temperature that had no observ-
able effect on the species studied was 24°C, as this
was the greatest stress that did not cause Pagurus
beringanus and Petrolisthes eriomerus to become
torpid. The maximum for other species should be
no greater than 28°C for Cancer and up to 30° to
32°C for the most resistant species.

A properly sited steam electric station should
not discharge hot waste water in quantities or at
locations where thermal plumes would retain
their integrity over periods of 1 to 4 h. This could
be a problem if Puget Sound waters were
intensively used for cooling. TL50's for the zoea
subjected to the 1- to 4-h thermal plume test

558

PATTEN S1IORT-TKRM THERMAL RESISTANCE OF CRAB ZOEAE

ranged from 28° to 32°C, except that H. orego-
nensis had a TL50 of 34°C for the 1-h test.

The maximum temperature increase in a steam
electric station that will not cause mortality to the
species studied can be estimated from the sea-
water temperature in Puget Sound and the
maximum temperatures tolerated by zoeae. Sur-
face temperatures of Puget Sound range from
about 10°C in the spring when most zoeae hatch to
15°C or more in some locations in the summer
(Wennekens 1959). Temperatures in heat ex-
changers can be increased 14°C in the spring and
9°C in the summer without causing direct or
indirect mortalities to the least resistant species.
Synergistic effects from the release of toxic
chemicals and from mechanical damage may act
to lower the thermal maximums tolerated.

Knowledge of the temperature tolerance of the
zoeae studied provides a partial input into the
assessment of the impact of a steam electric
station using Puget Sound waters for cooling.
Zoeae are generally a minor component of
zooplankton within the depths of Puget Sound
that would be subject to entrainment (Hebard
1956; Patten unpubl. data). Also, the volume of
water entrained by a steam electric station would
be small in comparison to that of Puget Sound.
Therefore, if all entrained zoeae were destroyed in
a steam electric station, the proportion lost may be
of minor concern on the population level. Losses of
zoeae from high temperature conditions may be
more serious if a series of steam electric stations
used Puget Sound waters for cooling. In this case,
some conservation measures should be con-
sidered.

ACKNOWLEDGMENTS

I thank Eugene Collias of the University of
Washington Department of Oceanography for
providing me with water quality data from Elliot
Point, Wash. I also thank Warren Ames, Donovan
Craddock, and George Slusser of the National
Marine Fisheries Service for assisting me.

LITERATURE CITED

American public Health association, American
water Works association, and water Pollution
Control Federation.

1971. Standard methods for the examination of water and
wastewater. 13th ed. Am. Public Health Assoc,
Wash., D.C., 874 p.
COUTANT, C. C.

1970. Entrainment in cooling water: Steps toward pre-
dictability. Proc. 50th Annu. Conf. West. Assoc. State
Game Fish Comm., Victoria, B.C., July 13-16, 1970,
p. 90-105.

1973. Effect of thermal shock on vulnerability of juvenile
salmonids to predation. J. Fish. Res. Board Can. 30:
965-973.
FRY, F. E. J.

1971. The effect of environmental factors on the
physiology of fish. In W. S. Hoar and D. J. Randall
(editors), Fish physiology, Vol. 6, p. 1-98. Academic Press,
N.Y.

Hebard, J. F.

1956. The seasonal variation of zooplankton in Puget
Sound. M.S. Thesis, Univ. Washington, Seattle, 64 p.
KLNNE, O.

1964. Animals in aquatic environments: crustaceans.
In D. B. Dill, E. F. Adolph, and C. G. Wilber (editors),
Handbook of physiology, Sect. 4, Adaptations to the
environment, p. 669-682. Waverly Press, Inc.,
Baltimore.
MARCY, B. C, JR.

1973. Vulnerability and survival of young Connecticut
River fish entrained at a nuclear power plant. J. Fish.
Res. Board Can. 30:1195-1203.

prentice, E. f.

1971. Respiration and thermal tolerance of the Dungeness
crab. Cancer magister. M.S. Thesis, Western Washing-
ton State Coll., Bellingham, 47 p.

Reed, p. h.

1969. Culture methods and effects of temperature and
salinity on survival and growth of Dungeness crab
[Cancer magister) larvae in the laboratory. J. Fish Res.
Board Can. 26:389-397.
TODD. M.-E., AND P. A. DEHNEL.

1960. Effect of temperature and salinity on heat tolerance
in two grapsoid crabs, Hemigrapsus nudis and Hemigrap-
sus oregonensis. Biol. Bull. (Woods Hole) 118:150-172.
WENNEKENS, M. P.

1959. Marine environment and macro-benthos of the
waters of Puget Sound, San Juan Archipelago, southern
Georgia Strait, and Strait of Juan de Fuca. Ph.D. Thesis,
Univ. Washington, Seattle, 298 p.

559

A SIMPLIFICATION FOR THE STUDY OF
FISH POPULATIONS BY CAPTURE DATA

Samir Z. Rafaii.1

ABSTRACT

Expressions given by Rafaii for estimating catchability are modified here to eliminate iteration,
for better accuracy, and a large economy in calculations and time. The evaluation of catchability
allows the estimation of other important parameters with the useful assumption of their variabilities
according to seasons and recognized sections of a population.

The evaluation of some parameters offish popula-
tions from capture data began at the start of the
century (Edser 1908; Heincke 1913; Baranov
1918). Beverton and Holt ( 1957) derived an equa-
tion in two forms (equations (14.19) and (14.86))
for the estimation of catchability and natural
mortality from catch and effort data for a whole
series of years assuming identical survival rates
and catchabilities for all ages in a given year,
fishing effort varies from year to year, and neg-
ligible recruitment and migrations.

Paloheimo ( 1961 ) modified the iteration method
by Beverton and Holt (1957) to a simpler one
without iteration using the relationship (1 — e l)/i
» e-o.5i where i is the instantaneous total mor-
tality.

Allen (1966) described three methods for esti-
mating a population and one for recruitment by
using data on annual age composition, number
caught, effort to take a known part of the catch
assuming a constant recruitment rate all over a
year, equal catchability for the different age
groups, and available comparisons between ex-
ploited and unexploited populations with equal
natural mortality. Allen (1968) described a
simplification of his method for computing re-
cruitment rates.

Among the investigators who studied the vari-
ability of parameters offish populations, Gulland
(1964) described variations in catchability as
cyclical, long-term trends due to amount of fishing
and changes in abundance, diurnal changes due
to feeding and light, temperature like severe

'Ministry of Agriculture and National Resources, Port Har-
court, Nigeria; present address: College of Science and Technol-
ogy, P. M. B. 5080, Port Harcourt, Nigeria.

winters, and sex. Paloheimo and Kohler (1968)
concluded from their analysis of a cod population
that catchability and natural mortality showed
variations associated with age and years. Walker
(1970) gave evidence of increased natural mortal-
ity with age due to senescence for cod.

Rafaii (1974) recognized the probable great
variability of parameters offish populations and
derived expressions for the evaluation of catch-
ability, fishing mortality, natural mortality, and
recruitment assuming their variability from one
season to another and their constancy during the
seasons as well as their variation from a recog-
nized section of a population to another like age-
groups and different sexes. His equations for the
evaluation of catchability as the first parameter
to be estimated require a number of iterations
which may be relatively very large if recruit-
ments exceed the sum of natural and fishing mor-
talities. Therefore, a computer is needed for
accurate calculations and this is a disadvantage.

The present treatment transforms the equa-
tions given by Rafaii (1974) to estimate catch-
ability into forms that dispense with iterations
and yield more accurate estimates.

SAMPLING PROCEDURE

A fish population with a certain initial size is
distributed on a constant area and subjected to
a sequence of sampling surveys which can be
grouped into a number of groups. Each group of
surveys must contain at least three sampling
surveys. The parameters of the population are
assumed to vary among the groups of surveys and
remain constant within each group which repre-
sents a season with constant properties. The
entire fishing fleet may be considered as sampling

Manuscript accepted November 1976.
FISHERY BULLETIN: VOL. 75, NO. 3, 1977.

561

FISHERY BULLETIN: VOL. 75, NO. 3

vessels whose catch data are to be collected
adequately.

If the fleet is large, a part of the fleet is appointed
as sampling vessels while the effective fishing
effort of unappointed vessels should be estimated.
The sampling surveys should follow one another
with no intervening time periods within a group
of surveys. The durations of the surveys may vary
from one survey to another or kept constant if
the total fishing effort varys from survey to
survey. The total effort exerted on the population
should vary from one survey to another.

ASSUMPTIONS

1 . A fish population has a constant area of distri-
bution and a constant uniform distribution of
fishing relative to fish concentration so that the
instantaneous fishing mortality is proportional to
fishing effort.

2. The population is subjected to a sequence of
n sampling surveys grouped into M groups repre-
senting M seasons with constant population
parameters. The duration of the &th survey is
denoted by Tk. The catchability or percentage of
available fish captured by a standard unit of fish-
ing effort during the kth survey is denoted by qk.

3. The commercial and sampling vessels exert
a constant fishing effort per unit time during the
&th survey denoted by fkc and fks respectively,
so that the efforts exerted become

noted by N0. The number of fish present at the
start of the £th survey is Nk0 while the number of
fish present at the end of the kih survey or the
start of the (£ + l)th survey is A^,^ + 110.

6. The instantaneous natural mortality rate per
unit time during the Mh survey is Mk. The instan-
taneous natural mortality during the £th survey
is

Mh ■ Ty = Mi.

(1.8)

7. The instantaneous recruitment rate per unit
time during the kth survey relative to the number
of fish present is Rk- The number offish present
at the end of the kih survey or the start of the
(k + l)th survey when recruitment is acting solely
is

(/t + l>0

Nk0 ■ exp(Rk ■ Tk)
Nk0 ■ exp(R'k),

that is.

Rb Ty — R'y

(1.9)

(1.10)

where R'k denotes the instantaneous recruitment
rate during the /eth survey.

8. The instantaneous rate of change offish abun-
dance per unit time during the kth survey relative
to the number of fish present is "Ay" which is
the "instantaneous abundance coefficient" so
that

fks ' Tk = f'ks

(1.1)

fkc ' Tk = f'kc

(1.2)

N(/t + l>o - A^0

■ exp{Ak

■ Tk

fks + fkc = fk

(1.3)

= Nk0

■ exp(A^).

fks + f'kc = fk

(1.4)

where f'kK, f'kc, and f'k represent the total fishing
effort exerted by the sampling, commercial ves-
sels, and the whole fleet, respectively, during the
£th survey.

4. The instantaneous fishing mortalities per
unit time by the sampling, commercial, and total
fleet in the Mh survey are denoted by Fks, Fkc,
and Fk, respectively. The instantaneous fishing
mortalities during the £th survey (F'ks, F'kc> and
F'h ) are evaluated as

Fks ■ Tk --- Fy[s ---- qk ■ flu

Fkc ■ Tk = Fkc = Qk ' fkc
Fk ■ Tk = F'k = qk ■ f'k.

(1.5)
(1.6)

(1.7)

5. The fish population has an initial size de-
562

(1.11)

In other words, Ak • Tk = A'k and A'k denotes the
instantaneous change of abundance during the
Mh survey.

According to previous assumptions we have

A'k ---- R'k - Mk' - F^ ---- (Rk - Mk - Fk)Tk (1.12)

and

N.*n>o = Nko ■ exp(A^)

= Nk0 ■ exp(Rk - Mk' ~ F^). (1.13)

9. If the sampling surveys (&- 1), k, and (k + 1)
belong to the same season,

#*-i == Rk = Rk + \ = Rj (1.14)

Mk-i --= Mk = Mk + 1 --= Mk (1.15)

RAFAIL: STUDY OF FISH POPULATION BY CAPTURE DATA

and

Qk-i = Qk = Qk>\ = Qk

(1.16)

where Rk, Mk, and qk are constant parameters
per unit time during the (£-l)th, /? th, and
(ft + l)th sampling surveys which should belong
to the same season.

Rk - Mk = Bk (a constant). (1.17)

10. If Tk = Tk-i = Tk+ i and similar to Equations
(1.8), (1.10), and according to (1.17), we get

MkTk ---- M'k, RkTk ---- Rk\ and BkTk -= B'k (1.18)

where M'k,R'k, andB*. represent the instantaneous
rates of natural mortality, recruitment, and the
difference between them during single surveys
(not per unit time) belonging to the same season
when the durations of the surveys are made equal.

11. The number of fish captured by the sam-
pling, commercial, and the total fleet during the
/?th survey are denoted by Cks, Ckc, and Ck,
respectively.

12. The catch per unit efforts during the Mh
survey obtained from sampling, commercial, and
total fleet are respectively

(C/f')ks, (C/f)kc, and(C/f>*

where fis primed (f ) according to previous nota-
tions to designate exerted effort during a whole
sampling survey and not per unit time.

13. The following expressions are used to obtain
simpler mathematical equations:

(explA*) - l)lA'k = ak (1.19)

a*2/a*-i ' ak + 1 = a'k (1.20)

(C/f)k2KC/f )*_! • {Clf)k+l = (Clf)'k. (1.21)

A MODIFICATION FOR

THE EXPRESSION ESTIMATING

CATCHABILITY

Rafail (1974) developed an estimate for qk ac-
cording to his equation (4.16) briefly as follows
when the whole fleet is engaged for sampling:

Ck = N0 ■ exp

,k \ .

C?,4

Fk ■ ak (2.1)

and

Ck+1 ■■-- N0 ■ exp(^V A/)- F{+i ■ ak+l (2.2)

k i i

cr =exp,A^ m-z

a* + i F'k + \

F'k

(2.3)

and

Ck ak F'k

= exp(A^_!) • ■ -^— (2.4)

Ck-\

a*-i Fk_i

and

Ct2

Ck-\ ' Ck+\

.2 F'2

exp(Aj;_i) _

exp(A^) a*_i • ak + 1 F'k^ ■ Fk + 1

(2.5)

According to Equations (1.7) and (1.16) we get

Qk2 ■ f'k2

F'k-i ■ F'k+i Qk2 ' f'k-i " fk+i
f'k2

As we have

fk-i ' fk+i
exp(A'k-i)

(2.6)

exp(A^_! - A'k) and

exp(A^)
according to Equation (1.12), we get

exp(A;_! - A'k) = exp((Rk-i - M*_i - *V-i)7*_i
- (Rk - Mk -Fk)Tk).

Again according to Equations (1.14) and (1.15),
as well as (1.7) and (1.16), we get

exp(A*_! - Ak) =exp(Rk - Mk)(Tk^ - Tk)

- qkif'k-i ~ /*)> '2-7)

From Equations ( 1 .20), (2.5), (2.6), and (2.7) we get

r Ck2r - exp{iRk- Mk)(Tk-X - Tk)

f'2

~ Qk^f'k-l ~ f'kU ' a'k ' ~FT~ ~£t •
' fk-1 Ik+1

Rearranging and according to assumption 12 we
get

(Clf')k2

tc/Dk-i ■ (C/f)k+1

exp^R,- M^Tk-i- TS

- Wk-i ~ /*))' «*•

563

FISHERY BULLETIN: VOL. 75, NO. 3

Using Equation (1.21), the above equation is
transformed to

loge(ak) + (Rk ~ MkMT^ - Tk) - \oge(C/f)'k

Qk ~ f'k-i - f'k

(2.8)

If sampling surveys are arranged to have equal
durations (or Tk-X = Tk = Tk + l), then Equation
(2.8) reduces to

Qk =

\oge(a'k) - \oge(C/f)'k
f'k-i ~ f'k

(2.9)

Equations (2.8) and (2.9) will be modified if a
part of the commercial fleet is engaged with the
sampling surveys so that (Clf)'k will be replaced
by (C/fi'ks, so that the last expression will be evalu-
ated from the catch per unit effort of the sampling
vessels '\Clf')ks of assumption 12," while all other
items will remain the same.

Again it is important to note that the data of
three successive surveys should be used to obtain
a single q-estimate because in case of unsucces-
sive data the fraction exp(A'k_i)/exp(A'k) of Equa-
tion (2.5) will be biased and Equations (2.8) and
(2.9) will not hold good.

Equations (2.8) and (2.9) can be used to estimate
qi, by a number of iterations which is large when
fish abundance is increasing and much fewer- with
decreasing abundance (Rafail 1974).

The modification of Equations (2.8) and (2.9) is
based on the fact that ak shown by Equation (1.19)
can be evaluated as a function of A'k. Paloheimo
(1961) gave the following approximation:

= (l - exp(-A'))/A' - exp(-0.5A'). (3.1)

Rafail (1974) has shown that when the instan-
taneous rate of change offish abundance is nega-
tive, then ak of Equation (1.19) can be represented
as in Equation (3.1). In fact ak is more precisely
expressed as

a*=exp(a,A; +a2A'k2+ a3A'k3) (3.2)

where a1; a^, and a3 denote certain constants. A
simpler and sufficient precise expression for ak is
fitted here as

ak « exp(±0.5A* + 0.04A*2).

(3.3)

Table 1 shows a comparison between the values
564

TABLE 1. — A comparison between a^-values calculated accord-
ing to the exact Equations (1.19) and (3.3).

a =

x = ±0.54'

a =

exp(^')

(exp(A') - 1)/>4'

+ 0.04/4'2

exp(x)

-0.02

09802

0.9901

-0.01

0.9900

-0.10

0.9048

0.9516

-0.0496

0.9516

-0.20

0 8187

0.9063

-0.0984

0.9063

-0.50

0.6065

0.7869

-0.2400

07866

-1.00

03679

06321

-0.4600

0.6313

-2.00

0.1353

0.4323

-0.8400

0.4317

-2.25

0.1054

0.3976

-0.9225

03975

-2.50

0.0821

0.3672

-1.00

0.3679

-2.65

00707

0.3507

-1.0441

0.3520

-2.75

00639

0.3404

- 1 0725

0.3421

-3.00

0.0498

0.3167

-1.14

0.3198

0.02

1.0202

1.0100

0.010016

1.0107

0.10

1.1053

1 0530

0.05040

1.0517

0.20

1 2215

1.1075

0.10160

1.1070

0.50

1.6486

1 .2972

0.26000

1 .2968

1.00

27184

1.7184

0.54000

1.7160

2.00

7.3890

3.1945

1.16000

3.1900

2.25

9.4877

3.7723

1 .32750

3.7716

2.50

12.1828

4.4731

1 .50000

4.4817

2.65

14.1544

4 9639

1.60590

4.9823

2.75

15.6428

5 3246

1.67750

5.3521

300

20.087

6 3623

1 .86000

6.4237

of ak calculated by the exact Equation (1.19)
and those calculated by Equation (3.3).

Table 1 shows that Equation (3.3) can be used
to calculate ak with a maximum error less than
1% when A' lies between ±3.00, i.e., an error
which is practically negligible. Again, the smaller
the value of A' the smaller is the error so that
when A' lies between ±2.5, the error is less than
0.29c, and Equation (3.3) can be considered as a
highly precise expression in that range which is
always encountered in fisheries studies. Equation
(3.3) can be used to evaluate a'k given by Equation
(1.20) as

(explc^A^ + tyU2))'

expioCiA'k-i + a2A'k2-i) ■ expta^Afc + i + «2-A* + i)

and

log, a^ = al{2A'k - A^_j -- A'k + 1)

+ a2(2A'k2 - Ai2-! - AklO- (4.1)

According to Equations (1.12), (1.14), (1.15), and
(1.16) we get

A'k ---- [Rk - Mk)Tk - F'k

(4.2)

2AL - Ai

*-l

= 2Tk (Rk - Mk )_- 2Fk'

- 7Vj (Rk - Mk) + F'k-i
_Tk + l_(Rk - Mk) + F'k + 1

= {Rk-Mk)(2Tk-Tk.1-Tk+1)

- 2F'k + Fk-i + Fk\,

RAFAIL: STUDY OF FISH POPULATION BY CAPTURE DATA

2A'k -Ak-i- AJ+i = (Rk - Mk )(2Tk -Tk^- Tk + l )

- QkWk " f'k . - /Z + i>.<4.3)

0.5(f*

*-l

f'k + ]

(5.3)

Denoting

a2(2A*2 -A*2, -A'klx)

(4.4)

of Equation (4.1) by (f>A' .

Equations (4.3) and (4.4) can be used to evaluate
logt, a'k given by Equation (4.1) as

logea^ = ax(Rk - Mk)(2Tk - Tk.x - Tk + l)

- a.q^n - fk-l - fk+l) + M'. (4.5)

Equation (4.5) can be inserted in Equation (2.8)
to have another expression for q~k as follows:

Equation (3.3) shows that o^ is estimated at 0.04
so that <J)A ' becomes according to Equation (4.4) as

c/>A' = 0.04(2A^2 - A'^ - A'klx). (5.4)

The correction term 4>A ' given in Equation (5.4)
can be put in another form by the inspection of
the term A' shown by Equation (4.2)

A'k = (Rk - Mk)Tk - Fk.

The parameters Rk and Mk are supposed to be
constant during any group of sampling surveys
according to assumption 9, and Equation (1.17)
we have

Qk^f'k-i ~ fk)

4>A' + «i(«* " Mk)(2Tk - Tk-X - Tk+1)

- aAqk(2£k - f'k-i -fk+i)

+ (Rk - Mk)(Tk-X -Tk)- loge(C/f)'k

A'k

Mk = Bk a constant
B-kTk - F'k

(5.5)

and

A'k2 = Bk2Tk2 - 2BkTkF'k + F^2 (5.6)
and (£>A' of Equation (5.4) .becomes

<7*<A-i ~ f'k + 2aifk ~ «i/*-i ~ «i/**i>
= 4>A' + [Rk - Mk][Tk(2ai - 1)

+ TViU " «i» " ^Tk + l] - \oge(C/f)'k <t>A' = 0.04(Rk - Mk)2(2Tk2 - Tk*x - Tk*x)

- 0.08(Rk - Mk)(2F'kTk - F'k.xTk.x - F'k+1Tk+1)
or + 0.04(2F'k2 - F'k2-X - F^ ). (5.7)

cbA' + [Rk- MJ\\Tk(2ax - 1) 4- Tk-tl - a,) - a.T k^}~ \oge(C/f)'k
A(2ax - 1) + Aid - ^) - a,n + 1

(5.1)

According to Equation (3.3) we find that 0.5 is
a very good estimate for ax which can be inserted
in Equation (5.1) to obtain

Qk =

<bA' + 0.5(Rk - Mk)(Tk-x ~ ?W - \oge(Clf)'k

0.5( A

£-1

/*+l)

(5.2)

If sampling surveys are carried out during
equal time intervals, i.e., Tk-\ = Tk = Tk + \, Equa-
tion (5.2) becomes

If Tk = Tk-\ = Tk + x and according to Equation
1.18) we have

MkTk = Mk and RkTk = R'k

.'.</>A' = -0.08iR'k- M'k)(2F'k- F'k + 1 - F'k+l)
+ 0.04(2F*2 - F'fcx - Fkli). (5.8)

If Equation (3.2) is used to evaluate ak.

a'k-

(expto^A* + a2A*2 + o^A*3))2

ex\o{axA'k~i + o^Ak2! + a^Ak3^ ■ expi^A'k + x + a2A'k2+l + <VU3-i)

565

FISHERY BULLETIN: VOL. 75, NO. 3

and

log, a* '- ax(2A'k - A'k-i - A* + 1)

+ a2(2Ak2 - A£x - A*2+1)
+ a3(2A'k3 - Af-i -AkW.

Following Equations (4.1) to (5.1) steps, we get
an expression for q~k similar to Equation ( 5 . 1 ) with
4>A' as

M'= a2(2Af - Ak2-! - Ai2+1)

+ a3(2A'k3 - Ak3-i - A£x ). (5.9)

ESTIMATION OF CATCHABILITY

Denoting all terms of the numerators of Equa-
tions (5.1), (5.2), and (5.3) with the exception of
\oge(Clf)'k by "p" and their denominator by 4>F;
the equations become

(Jk

\ogiAC/fVh + p

<t>f

(6.1

Equating p to zero, a first estimate for qk is ob-
tained which is used together with catch data to
estimate A', Rk, Mk, and 4>A' so that p can be
estimated and used to obtain the required esti-
mate for qk as well as other parameters.

If p has a negative sign, this means that the
first estimate for q^ was higher than the true value
and p/4>f is the correction to be subtracted to ob-
tain the improved estimate and the reverse holds
good as will be shown by the solved example.
Equation (6.1) is therefore betterly transformed to

<t>f

(6.2)

Solved examples showed that one single correc-
tion is sufficient to obtain precise estimates for

qk for populations with increasing or decreasing
abundance which is a great advantage.

If a number of equations like (6.2) are available,
they may be combined in a single expression as

^ log,(C//-U

!<*>/■

(6.3)

EXAMPLE

Detailed informations are required to use the
equations given above for estimating correctly the
catchability as dividing sampling surveys into
groups coinciding with seasons having more or
less constant population parameters like periods
with high, low, or nil recruitment, migration,
natural mortality, and catchability.

As published data reviewed by the author
lacked such information, it was decided to treat
the hypothetical example given by Rafail (1974)
so as to demonstrate the advantage of the above
modified equations. Table 2 shows a part of 1974
example containing periods I and III with increas-
ing and decreasing abundance, respectively.

Computations for Period I

A) Surveys 1, 2, and 3

\oge(Clf)'k = lo&( 1.001 18) = 0.00116
(bf= 0.5(1,000-2,000) = -500
qk = -0.00116/-500 = 2.320 x 10 K.

Above ^-estimate is used to evaluate A', (Rk -
Mk), and <t>A ' using the relations:

F'k --= qkfk,Nk0 --= catch/F^
exp{Ap = Nk + 1/Nk
Rk-Mk= Ai + FJ

A'=Ri- Mkxx - Fi .

TABLE 2. — A hypothetical example showing sampling periods I and III with increasing and

decreasing abundance.

Period and

Initial

Abundance

survey

abundance

Effort

Total

coefficient

Catch

N/co

mortality

a'h

exp(^)

Nk0Fkak

Period 1

qk = 2 x 106

M'k = 0.001
0003

Rk = 0.450

1,000,000

1,000

0.447

1 5636

1 26085

2,522

1 ,563,600

3,000

0.007

0443

1.5575

1.25847

11,807

2,435,307

2,000

0005

0.445

1 5605

1 25955

12.269

3,800,297

4,000

0.009

0.441

1.5543

1 25692

38,212

Period III

Q|(=2x 10 6

Mk = 0.020

Rk = 0.002

5.894,992

40,000

0.100

-0.098

0.90666

0.95245

449,175

5,344,753

20,000

0.060

-0.058

0.94365

0.97155

207,708

5,043,576

10,000

0.040

-0.038

0.96271

0.98132

98,985

566

RAFAIL: STUDY OF FISH POPULATION BY CAPTURE DATA

where R'k - M*xx is the mean of available values.
All the above relations are correct except the
relation N^ = catch/F*. which is an approxima-
tion of Nk0 = catch/FA' ■ a* . Ifthe computations
show that the calculated (R - M)-values are close
to each other, then the approximate expression
for Nko is satisfactory to obtain accurate estimates
for qk. Significantly different (R - M)-values may
also lead to accurate estimates for qk. However, it
may be necessary to use A'k to estimate a* to ob-
tain improved estimates for A/*0-values_to arrive
at a better estimate for A'k and (R - M)-
values. The rest of the computations for period I
are:

Nk0

= CIF'

exp(Ai) Ak Rk - Mk Ak

1 2.32 x 10"3 1,087,070 1.56503 0.44789 0.45021 0.44818

2 6.96 x 10"3 1,696,408 1.55869 0.44378 0.45072 0.44354

3 4.64 x 10~3. 2,644,181 0.4505xx 0.44586

According to Equation (5.4) we get

A? = 0.1967277, A '? = 0.2008653,

A 'i= 0.1987911
<$>A' = 0.04(0.393455-0.399656)
= 0.04(-0.0062) = -0.000248
M'/\<l>f\ = -0.000248/500 = -0.496 x 10"6

qk = (2.320-0.496)10~6 = 1.824 x 10"6.

According to Equation (5.8) we can calculate &A '
by another way as

<t>A'

= -0.08(0.4505)(13.92-2.32-4.64)(10 3)

+ 0.04(96.88-5.38-21. 53X10 6)
= (-0.2508 + 0. 0028)(10"3) = -0.248(10-3)

That is, the two methods gave the same results.

B) Surveys 2, 3, and 4

\oge(C/f)'k = 0.0009
<t>f = -500
qk = -0.0009/- 500 = 1.8 x 10"6.

.'.<t>A'/\<i>f\ = 0.000191/500 = 0.382 x lO"6
qk = (1.8 + 0.382H0-6
= 2.182 x 10-6.

The arithmetic mean for qk from the four surveys is

(1.824 + 2. 182)(10-6)/2 = 4.006 x 10"6/2

= 2.003 x 10"6.

Equation (6.3) can be used to estimate qk in one
step as

-0.00116 + 0.00090 -0.000248 + 0.000191
-1,000 1,000

0.002060 0.000057 0.002003

1,000 1,000
2.003 x 10"6.

1,000

Period I has four sampling surveys and only two
estimates for q can be obtained as the data of only
three successive surveys are used to get a single
g-estimate as explained above.

Computations for Period III

\oge{Clf)'k = -0.03012

tf = 1/2(40,000-10,000) = 15,000

-0.03012 onnQ v in_6

g*= 15,000 =2QQ8x 106-

The following computations are obtained ac-
cording to the last estimate of catchability

K Nk0 = CIFk (R'k-Mk\

= C/Fjflk

1 5,592,318 0.00214 -0.08322 0.9595 5,828,366

2 5,172,012 -0.00788 -0.04306 0.9786 5,285,113

3 4,929,531 -0.00290xx -0.02298 0.9887 4,985,871

(Ri - Mk)a

-0.01763

-0.09819

-0.01811

-0.05803

-0.01787xx

-0.03795

The following estimates are obtained by above
steps

R'k - M'k™ = 0.44782

A2 = 0.44242, A^ =
A4 = 0.44062
4>A' = 0.04(0.3946628
= 0.000191

0.44422,

0.3898815)

Above estimates show a recognizable variability
for the first estimated (R'k - M'k\ parameters; so
the calculations are proceeded to obtain the next
(R'k - M'k)2 -estimates which are in fact highly
accurate if compared with the original values in
Table 2.

Using the so-called the less accurate A[ -esti-
mates to calculate <}>A'; we get

567

FISHERY BULLETIN: VOL. 75, NO. 3

</,A' = 0.04(0.0037080-0.0074535)
= -0.00015
(f)A'/\(j)f\ = -0.00015/15,000= -0.00001/1,000
= -0.01 x 10"6
qk = (2.008-0.010)10 6 = 1.998 x 10"6.

Using the more accurate A± -estimates we get

(l)A' = 0.04(0.00673496-0.01108147)
= -0.000174
<t>A'/\4>f\= -0.000174/15,000= -0.011 x 10"6
qk = (2.008-0.01D10-6 = 1.997 x 10"6.

Using Equation (5.8) and the more accurate
(R'k - M/;)-estimates, we get a similar result as

<t>A' = -0.08< -0.01787)1 -0.02008)
+ 0.04( -0.0036289)
= -0.0000287-0.0001451 = -0.000174.

The above example shows that the so-called less
accurate estimates gave equivalent results to the
more accurate estimates. However, in situations
with variable (R'k M'k (-values it will be pref-
erable to compare their results with those to be
obtained with the more accurate values.

DISCUSSION

Rafail (1974) showed the great advantages of
his method for the estimation of some important
parameters of fish populations like catchability,
fishing mortality, natural mortality, and recruit-
ment from catch data. He also showed that a
similar analysis of data of tagged fish can allow
the estimation of other important parameters like
migrations and at the same time may correct the
estimates of parameters of untagged fish that
may be biased by unexpected recruitments and
migrations.

The modifications presented here for expres-
sions used to estimate catchability cause a great
simplification, shortening of calculations and
more accurate results. Rafail (1974) gave in his
table 4 a summary of results of HP-20 computer
programme for iteration of period I with increas-
ing abundance. The results of the computer
showed that after 16 iterations with a precision
at six decimals and 22 iterations with a precision
at nine decimals; q was estimated at 1.92 x 10-6
and 1.83 x 10 6, respectively. The corresponding
estimate by the present modified expressions was
1.824 x 10 6 by a single step. This simplification

allowed the estimation of q from the next series of
sampling surveys of period I (2, 3, and 4) so that
an overall estimate of 2.003 x 10 6 becomes avail-
able which is highly accurate as the original value
is 2 x 10'6.

As far as period III with decreasing abundance
is concerned, we find that 1974-expressions gave
after three iterations 1.98 x 10 6 while the new
expressions gave after one step 1.998 x 10-6 or
1.997 x 10"6 for q compared with an original
value of 2 x 10~6.

It is, therefore, concluded that the present modi-
fied expressions allow better accuracy and large
economy in calculations and time during estimat-
ing q as compared with 1974-expressions. This
greater accuracy of q will allow better estimates
for other parameters. It appears what is a logic
conclusion that the larger number of surveys, the
larger will be the number of available g-estimates
allowing a more accurate evaluation for catch-
ability and other parameters.

SUMMARY

Modifications are presented here for expres-
sions given by Rafail (1974) for estimating catch-
ability to evaluate fishing and natural mortalities,
recruitment, and migration assuming seasonal
and subpopulation variability and the constancy
of the parameters within the seasons. These modi-
fications depend on the relation

(exp(A^) - l)IA'k = exp(±0.5A* + 0.04A*2)

where A'k denotes the instantaneous rate of
change offish abundance during the kth sampling
period. The above expression is an extension of
Paloheimo (1961) expression and gave a maxi-
mum error less than 1% when A ' lies between
±3.0 and smaller errors at smaller values of A
so that the errors are less than 0.2^ when A'
lies between ±2.5. This expression can be consid-
ered as highly accurate in the range that is always
encountered in fisheries studies.

The modified expressions allow a large economy
in calculations and time and a better accuracy
for the estimation of catchability.

LITERATURE CITED

ALLEN, K. R.

1966. Some methods for estimating exploited populations.
J. Fish. Res. Board Can. 23:1553-1574.

568

RAFAIL: STUDY OF FISH POPULATION BY CAPTURE DATA

1968. Simplification of a method of computing recruitment
rates. J. Fish. Res. Board Can. 25:2701-2702.

BARANOV, F. I.

1918. On the question of the biological basis of fisheries.
[In Russ.] Izv. Nauchny. Issled. Ikhtiol. Inst., Izv. Otd.
Rybovod. Nauchnopromysl. Issled. 1( 1 ):81— 128.

BEVERTON, R. J. H., AND S. J. HOLT.

1957. On the dynamics of exploited fish populations.
Fish Invest. Minist. Agric. Fish. Food (G.B.), Ser. II, 19,
533 p.

EDSER, T.

1908. Note on the number of plaice at each length, in
certain samples from the southern part of the North Sea,
1906. J. R. Stat. Soc. 71:686-690.

GULLAND, J. A.

1964. Catch per unit effort as a measure of abundance.
Rapp. P.- V. Reun. Cons. Perm. Int. Explor. Mer 155:8- 14.

HEINCKE, F.

1913. Investigations on the plaice. General report. 1. The
plaice fishery and protective regulations. First part.
Rapp. P.-V. Reun. Cons. Perm. Explor. Mer 17A, 153 p.
PALOHEIMO, J. E.

1961. Studies on estimation of mortalities. I. Comparison
of a method described by Beverton and Holt and a new
linear formula. J. Fish. Res. Board Can. 18:645-662.
PALOHEIMO, J. E., AND A. C. KOHLER.

1968. Analysis of the southern Gulf of St. Lawrence cod
population. J. Fish. Res. Board Can. 25:555-578.
RAFAIL, S. Z.

1974. Study of fish populations by capture data and the
value of tagging experiments. Stud. Rev. Gen. Fish.
Counc. Mediterr. 54:1-27.
GREER-WALKER, M.

1970. Growth and development of the skeletal muscle
fibres of the cod (Gadus morhua L.). J. Cons. 33:
228-244.

569

IDENTIFICATION OF FISH SPECIES BY THIN-LAYER
POLYACRYLAMIDE GEL ISOELECTRIC FOCUSING

Ronald C. Lundstrom*

ABSTRACT

Conventional electrophoretic techniques for the identification offish species are limited in the resolu-
tion and reproducibility needed for the reliable identification of fish species. This paper describes
the potential of a high resolution protein separation technique, thin-layer polyacrylamide gel
isoelectric focusing (IEF), as a new means of identifying fish species. Sarcoplasmic protein patterns
are shown for 11 species of commercially important New England fishes under both low resolution
(pH 3.5-10 gradient) and high resolution ipH 3.5-5 gradient) conditions. The reproducibility of
the protein patterns and pH gradients from day to day is also shown. The inherent high resolution
and excellent reproducibility of IEF should allow the positive identification offish species without
the costly procedure of maintaining a supply of known species for use as standards.

Many different electrophoretic techniques have
been used for the identification of fish species.
Protein extracts from several species of fishes
were first compared using moving boundary
electrophoresis (Connell 1953). Differences in the
electrophoretic protein patterns between species
formed a "fingerprint" for each. In an effort to
obtain higher resolution and reproducibility of
the protein patterns, starch gel zone electro-
phoresis was applied as a method for diffentiating
fish species (Thomson 1960). Subsequent attempts
to further improve species identification tech-
niques centered on the investigation of new sta-
bilizing media. The use of polyacrylamide gels
(Payne 1963; Cowie 1968) and agar gels (Hill et al.
1966) resulted in shortened analysis times,
increased resolution, and easier handling and
storage of gels. A rapid identification technique
based on cellulose acetate electrophoresis (Lane
et al. 1966) has found widespread use in quality
control.

Each of these electrophoretic techniques (except
moving boundary electrophoresis) is still in
common use and has contributed much towards
eliminating problems of species substitution.
Unfortunately, each of these techniques is subject
to one or more limitations that lessen its effective-
ness as a routine species identification test. Varia-
tions in stabilizing media composition, sample
application technique, separation time, applied

•Northeast Fisheries Center Gloucester Laboratory, National
Marine Fisheries Service, NOAA, Emerson Avenue, Gloucester,
MA 01930.

Manuscript accepted February 1977
FISHERY BULLETIN: VOL."75. NO. 3. 1977.

voltage or current, and the technician's skill
indicated the need for simultaneously running
known species along with unknown samples to
obtain a reliable identification. Collaborative
studies of the two most widely used species identi-
fication procedures, disc electrophoresis (Thomson
1967) and cellulose acetate electrophoresis (Lear-
son 1969, 1970), showed. that reproducibility of
specific protein patterns from analysis to analysis
was a major problem.

This paper describes the potential of a high
resolution protein separation technique, thin-
layer polyacrylamide gel isoelectric focusing
(IEF), as a new means of identifying fish species.
IEF is an equilibrium technique in which proteins
are separated according to their isoelectric points
in a reproducible natural pH gradient. The pH
gradient is formed in the gel by the electrolysis
of amphoteric buffer substances called carrier
ampholytes. Protein molecules migrate in the
electric field along the pH gradient until they
reach the pH equal to their isoelectric point. Here
the protein has a net charge of zero, and no further
migration can take place. The proteins become
concentrated into very sharp bands and molecules
whose isoelectric points differ by 0.07 pH units
(pH 3.5-10 gradient) or 0.02 pH units (pH 3.5-5
gradient) may be resolved.

PROCEDURE

Isolation of Sarcoplasmic Proteins

Fresh iced fish was obtained from various Glou-

571

FISHERY BULLETIN: VOL. 75, NO. 3

cester fish processors. Four specimens of each
species were examined except for cod and haddock
where 15 individuals each were examined. All
fish were held on ice from purchase to filleting.
Fillets were held at 8°C until extraction of sarco-
plasmic proteins.

Sarcoplasmic protein extracts were prepared by
blending 100 g of muscle tissue with 200 ml of
distilled water in a 500-ml Waring2 blender jar.
A Teflon baffle shaped to fit the inside contour
of the blender jar about 1 cm below the water
level was used to prevent the incorporation of
air bubbles during the blending operation. The
distilled water, blender jar, and baffle were chilled
to 8°C prior to use to prevent protein denaturation
from heat generated during blending. The result-
ing mixture was centrifuged at 1,400 g for 30 min
at 4°C in an International PR-2 Refrigerated
Centrifuge. The resulting supernatant was used
for analysis without any further purification.

Preparation of Polyacrylamide Gel Slab

The polyacrylamide gel slab was chemically
polymerized between a glass plate and an acrylic
template. The glass plate and acrylic template
were separated by a 0.75-mm acrylic spacer that
extended around three sides leaving the top open.
The template had embedded teeth that formed
sample wells in the gel surface. The gel slabs used
in these experiments were 175 mm x 90 mm x
0.75 mm and contained 12 sample wells, each
capable of holding up to 5 ju.1.

A 4% (wt/vol) polyacrylamide gel containing
2% (wt/vol) carrier ampholytes was prepared as
follows:

Into a 25-ml Erlenmeyer flask was pipetted

8.2 ml distilled water

3.0 ml 50% (vol/vol) glycerol (final concentra-
tion 10% [vol/vol])

3.0 ml 20% (wt/vol) acrylamide (final concen-
tration 4% [wt/vol]) plus 0.8% (wt/vol)
bisacrylamide (final concentration 0.16%
[wt/vol])

5.0 /u.1 tetramethylethylenediamine (final
concentration 0.03% [wt/vol | )

0.75 ml 40% (wt/vol) ampholine of appro-
priate pH range (final concentration 2%
I wt/vol |).

2Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

This solution was degassed under vacuum for
4 min. Polymerization was started with the addi-
tion of 50 fx\ 10% (wt/vol) ammonium persulfate
(final concentration 0.03% [wt/vol]). After a final
degassing under vacuum for one more minute,
the solution was immediately pipetted into the
gel mold. The top of the gel solution was layered
with water to form an even surface. Polymeriza-
tion was complete in 20 min at room temperature.
The open top of the gel mold was then sealed with
masking tape, and the whole assembly was placed
in a refrigerator (8°C) overnight before use. A
supply of gel slabs may be prepared and stored
for 2 wk in this manner. After the gel had polymer-
ized, the template and spacer were removed leav-
ing the gel adhering to the glass plate.

Electrofocusing Procedure

Electrofocusing was carried out using a Medical
Research Apparatus Slab Electrofocusing Appa-
ratus, Model M-150. The gel slab was placed on
the cooling platform and cooled to -2°C prior to
sample application. To insure good thermal con-
tact, a layer of light paraffin oil was used between
the glass plate and the cooling platform. After
the gel slab had cooled, 5 /x\ of the protein extract
was pipetted into a sample well with a micro-
pipette. Up to 12 samples may be compared in a
single gel slab. Felt strips soaked in 1M NaOH
(catholyte) and 1M H3P04 (anolyte) were applied
to the edges of the gel to provide electrical contact
with the platinum wire electrodes. A power supply
was connected to the electrodes, and power was
applied until equilibrium focusing was attained.
Both constant-power and constant-voltage power
supplies were used in these experiments. In iso-
electric focusing, a power supply capable of
delivering constant power is preferred. Using a
constant power of 10 W, equilibrium focusing
was complete in 1.5-2.0 h. Using constant
voltage, the voltage must be manually increased
to compensate for increased resistance through
the gel as the pH gradient forms. Separation times
are longer (5-6 h) and resolution suffers due to
joule heating within the gel. With either type of
power supply, equilibrium focusing is attained
and the reproducibility of the protein patterns
is not affected. After electrofocusing is complete,
the pH gradient may be measured as a check on
reproducibility or to determine the isoelectric
points of the separated proteins. The plate is
warmed to room temperature and the pH gradient

572

LUNDSTROM IDENTIFICATION OF FISH SPECIES

is measured using a 3-mm diameter Ingold micro-
combination surface pH electrode and Corning
Model 101 digital pH meter. The electrode was
calibrated with standard pH buffer solutions at
room temperature.

The protein patterns were stained with Coo-
massie Blue R-250 and destained in \Q'7e ethanol-
109? acetic acid (Righetti and Drysdale 1974).
After destaining, the gels may be air dried and
stored indefinitely.

RESULTS AND DISCUSSION

Figure 1 shows typical protein patterns for
11 species of commercially important New En-
gland fishes. The pH gradient in this gel runs
from pH 3.5 at the top (anode) to pH 10.0 at the
bottom (cathode). The pattern for each species
appeared to be unique and demonstrated resolu-
tion not normally attained by conventional
electrophoretic techniques. Closely related spe-
cies such as cod and haddock or red hake and
white hake show similarities in overall patterns,
but enough differences are present to permit a
positive identification.

Due to the large number of protein bands re-
solved in the pH 3.5-10.0 gradient, many of which
have the same isoelectric point, it is sometimes
advantageous to look at only a small portion of
the pattern under increased resolution. Figure 2
shows the same 11 species compared in a pH 3.5-
5.0 gradient. The resolution is much greater and
identification is not complicated by the presence
of as many proteins with the same isoelectric point
from species to species.

Figures 3 and 4 illustrate the reproducibility of
the protein patterns through a time interval. The
proteins in Figure 3 were focused in 2.5 h using
a constant power of 10W. The proteins in Figure 4
were focused in 5.5 h using a constant-voltage
power supply. The voltage was manually in-
creased from 100 V to 300 V in hourly 100-V
intervals. The voltage was then held constant at
300 V for 3.5 h. The proteins in both plates have
been focused to equilibrium, and the pattern for
each species is reproducible.

The protein patterns one obtains in isoelectric
focusing are dependent on the pH gradient formed
in the gel. Commercially prepared carrier ampho-
lytes form pH gradients that remain stable and
reproducible during the time necessary for the
complete equilibrium focusing of sarcoplasmic

proteins. Figure 5 shows the pH gradients formed
in the previous two figures. The pH gradient curve
labeled "A" corresponds to the plate in Figure 3,
and the one labeled "B" corresponds to the plate
in Figure 4. The slightly lower position of pH
gradient A is also seen by the displacement of
the patterns in Figure 3 toward the lower end of
the gel (cathode). This slight shift of the pH
gradient, however, was not enough to affect the
reproducibility of the protein patterns.

Isoelectric focusing offers several advantages
over electrophoretic techniques for the identifica-
tion offish species. Isoelectric focusing is an equi-
librium technique where the proteins are limited
in how far they can travel by the pH gradient.
Since proteins have a net charge of zero at their
isoelectric point, no migration beyond that point
can take place. Diffusion of the isoelectric proteins
is prevented by the electric field. During the
course of a normal electrofocusing experiment,
as long as the pH gradient remains stable, the
protein patterns will not vary. In contrast, protein
patterns from conventional electrophoretic tech-
niques are time dependent and may suffer loss
of resolution due to diffusion.

Another advantage of isoelectric focusing over
conventional electrophoretic techniques is the
ease of sample application. Samples were applied
directly from micropipettes into molded sample
wells. Samples may also be applied as a drop or
streak on the gel surface or by placing a small
rectangle of filter paper saturated with the sample
directly on the gel. The position of sample appli-
cation may be at any point on the gel slab. While
some of these sample application techniques may
be common to other electrophoretic procedures,
only in IEF may these techniques be used inter-
changeably without affecting the protein pat-
terns. This versatility is an important asset.
Dilute extracts (e.g., when the amount of muscle
tissue available is unavoidably small) may be
applied in a large volume to obtain a protein
pattern comparable to that obtained with a small
volume of a concentrated extract (e.g., a drip fluid
sample from a recently frozen fish). Large sample
volumes may also be applied so that minor com-
ponents may be detected and compared between
species. The ability to vary the position of sample
application without affecting the protein pattern
eliminates one more possibility for human error.
Sample application technique in conventional
electrophoretic methods affects the protein pat-
tern. Samples must be carefully applied as a thin

573

FISHERY BULLETIN: VOL. 75, NO. 3

jt^^^ttmm-- •mmmm^^m* aMNlMlMMlM

as as"

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i t~X

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FIGURE 1. — Sarcoplasmic protein patterns from 11 species of fishes focused in a pH 3.5-10 gradient. The species are from left to right:
winter flounder, Pseudopleuronectes americanus; American plaice, Hippoglossoides platessoides; gray sole, Glyptocephalus cyno-
glossus; yellowtail, Limanda ferruginea; ocean perch, Sebastes marinus; cusk, Brosme brosme; whiting, Merluccius bilinearis; red
hake, Urophycis chuss; white hake, Urophycis tenuis; haddock, Melanogrammus aeglefinus; and cod, Gadus morhua.

0£ 05
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FIGURE 2. — Sarcoplasmic protein patterns from 11 species of fishes focused in a pH 3.5-5 gradient. The species arrangement is
the same as shown in Figure 1. Note that the bands separated in Figure 2 correspond to the bands shown in the upper portion of
the gel in Figure 1.

574

l.L'NDSTKOM IDENTIFICATION OF FISH SPE( IKS

FlOl'RE 3. — Sarcoplasmic protein patterns
from seven species of fishes focused in a pH
3.5-5 gradient under constant power condi-
tions. The species are from left to right:
winter flounder, Pseudopleuronectes ameri-
canus; American plaice, Hippoglossoides
platessoides; gray sole, Glyptocephalus
cynoglossus; yellowtail, Lunanda ferru-
ginea; ocean perch, Sebastes marinus; cusk,
Brosme brosme; and whiting, Merluccius
bilinearis.

>« &i

> J

a X

«!3

O <

< «

w as

O 01

_3 H
S

FIGURE 4. — Sacroplasmic protein patterns
from seven species of fishes focused in a pH
3.5-5 gradient under constant voltage con-
ditions. The species arrangement is the
same as shown in Figure 3. Figures 3 and 4
illustrate the reproducibility of the protein
patterns for seven species of fishes on two
successive days.

cj as

w m
a q

3 M

c <
m

uj or
O a-

zone at a particular position to obtain a satisfac-
tory separation. Isoelectric focusing is actually
less demanding in experimental technique when
compared to electrophoresis, yet still offers in-
creased resolution and reproducibility.

Due to the limited number of individuals and
species studied, additional work is underway to
increase the reliability and potential of IEF as a
species identification test. Additional species will
be compared. Their protein patterns will be added
to a library of standard IEF protein patterns.

Additional individuals from each species will be
tested for variations in protein patterns due to
size, sex, season, or geographical origin. Varia-
tions in some minor components of the protein
patterns for some species after frozen storage have
been observed. Work is planned to examine this
in greater detail. The use of commercially pre-
pared polyacrylamide gel slabs will reduce varia-
tions in stabilizing media composition and elim-
inate gel preparation time. These ready prepared
gels used with a high-voltage constant-power

575

FISHERY BULLETIN: VOL. 75, NO. 3

h S
CvJ

18 24 30 36

DISTANCE TO CATHODE (mm)

FIGURE 5. — Reproducibility of pH gradients. Measurements of
pH were taken after focusing the gels shown in Figures 3 and 4.
The pH gradient A corresponds to the pH measurements taken
from the gel in Figure 3. The pH gradient B corresponds to the
pH measurements taken from the gel in Figure 4. (The pH
gradients do not match exactly because the platinum electrodes
were not placed with the same relative sample well to cathode
distance. The only effect this has on the protein patterns is to
shift them either up or down. Relative distances between the
various proteins in the pattern remain essentially the same.)
The similarity of these two pH gradients may be correlated with
the reproducibility of the protein banding patterns shown in
Figures 3 and 4.

power supply should produce high quality sarco-
plasmic protein patterns in 1.0-1.5 h. New protein
staining methods have been investigated that
allow staining of the protein patterns in 15-30
min with no destaining required. Using these im-
provements, samples may be identified in less
than 2 h.

CONCLUSIONS

Thin-layer polyacrylamide gel isoelectric focus-
ing has been shown to be a promising technique
for the identification offish species. The inherent
high resolution of this method allows the produc-
tion of characteristic protein patterns of a quality
not normally attained by conventional electro-
phoretic techniques. The excellent reproducibility
of this technique should allow the positive identi-
fication of fish species without maintaining a
supply of known species for use as standards.

Investigations utilizing commercially prepared
gel slabs, high-voltage constant-power power
supplies, and rapid staining techniques promise
to produce an extremely reliable procedure for
the routine identification of fish species.

ACKNOWLEDGMENT

I thank James Drysdale and Wendy Otavsky
of Tufts University Medical School, Boston, Mass.,
for their valuable assistance in the early stages
of this work.

LITERATURE CITED

CONNELL, J. J.

1953. Studies on the proteins of fish skeletal muscle.
Electrophoretic analysis of low ionic strength extracts of
several species of fish. Biochem. J. 55:378-388.

COWIE, W. P.

1968. Identification offish species by thin-slab polyacryla-
mide gel electrophoresis of the muscle myogens. J. Sci.
Food Agric. 19:226-229.

HILL, W. S., R. J. LEARSON, AND J. P. LANE.

1966. Identification of fish species by agar gel electro-
phoresis. J. Assoc. Off. Anal. Chem. 49:1245-1247.

Lane, j. P., W. S. Hill, and R. J. Learson.

1966. Identification of species in raw processed fishery
products by means of cellulose polyacetate strip electro-
phoresis. Commer. Fish. Rev. 28(3):10-13.

Learson, R. J.

1969. Collaborative study of a rapid electrophoretic
method for fish species identification. J. Assoc. Off.
Anal. Chem. 52:703-707.

1970. Collaborative study of a rapid electrophoretic
method for fish species identification. II. Authentic fish
standards. J. Assoc. Off. Anal. Chem. 53:7-9.

Payne, W. R., Jr.

1963. Protein typing of fish, pork, and beef by disc
electrophoresis. J. Assoc. Off. Anal. Chem. 46:1003-
1005.
RIGHETTI, P. G., AND J. W. DRYSDALE.

1974. Isoelectric focusing in gels. J. Chromatogr. 98:
271-321.
THOMPSON, R. R.

1960. Species identification by starch gel zone electro-
phoresis of protein extracts. I. Fish. J. Assoc. Off.
Anal. Chem. 43:763-764.

1967. Disk electrophoresis method for the identification of
fish species. J. Assoc. Off. Anal. Chem. 50:282-285.

576

VARIOUS SPECIES OF PHYTOPLANKTON AS FOOD FOR LARVAL

NORTHERN ANCHOVY, ENGRAULIS MORDAX, AND RELATIVE

NUTRITIONAL VALUE OF THE DINOFLAGELLATES

GYMNODINIUM SPLENDENS AND GONYAULAX POLYEDRA

Edward D. Scura1 and Charles W. Jerde2

ABSTRACT

First feeding northern anchovy larvae were presented with a variety of phytoplankters common to
coastal waters of southern California to determine which species are acceptable as food. Most of
the larvae ate the four species of dinofiagellates tested in feeding experiments but did not feed on
diatoms or small flagellates. Larval rearing experiments were conducted to compare the nutritional
value of Gymnodinium splendens and Gonyaulax polyedra, two species of dinofiagellates readily
eaten by anchovy larvae and known to predominate in the chlorphyll maximum layers off the
southern California coast. Gymnodinium splendens was a nutritional food for the first 10 days of
larval life, but Gonyaulax polyedra was judged to be inadequate. Supplementing the G. polyedra
diet with microzooplankton increased larval survival comparable to survival on a microzooplankton
diet alone. When the Gymnodinium splendens diet was supplemented with microzooplankton,
the larvae grew faster but survival did not increase. Results are discussed in relation to studies on
larval survival in the Southern California Bight during 1974 and 1975.

The strength of a year class offish may depend on
availability of food organisms during the early
larval stages (May 1974). Consequently, there
have been attempts to assess the abundance of
planktonic organisms in larval feeding areas as
a step towards predicting year class success (Shel-
bourne 1957; Bainbridge and Forsyth 1971;
Lasker 1975, in press). For this approach to be suc-
cessful, additional information is also necessary
concerning: 1) selection of prey by the fish larvae,

2) concentration and size of food organisms nec-
essary to initiate feeding by the fish larvae,

3) nutritional value of the food that the larvae
select, and 4) temporal and spatial distribution of
the food organisms in the feeding area.

The northern anchovy, Engraulis mordax,
larva has been studied in the laboratory and many
criteria for successful feeding have been deter-
mined (Lasker et al. 1970; O'Connell and Ray-
mond 1970; Hunter 1972, 1976; Hunter and
Thomas 1974). Results of these studies indicate
that first feeding anchovy larvae require small
particles (<100 /xm in smallest dimension) at

'Southwest Fisheries Center, National Marine Fisheries
Service, NOAA, P.O. Box 271, La Jolla, CA 92038.

2San Diego Mesa College, 7250 Mesa College Drive, San
Diego, CA 92111.

relatively high densities to initiate feeding and
to insure moderate survival. O'Connell and Ray-
mond ( 1970) found in laboratory experiments that
anchovy larvae reared in seawater containing
1 copepod nauplius/ml or less experienced heavy
mortalities during the sixth and seventh days
after hatching. To date such a high concentration
has not been found in the nearshore region of the
California Current (Beers and Stewart 1967,
1969). However, the possibility does exist that
anchovy larvae could survive on some of the larger
phytoplankters during early stages of develop-
ment (Hunter and Thomas 1974). Lasker et al.
(1970) found that anchovy larvae would feed and
grow to a length of 5 to 6 mm in the laboratory
on a diet of the naked dinoflagellate, Gymno-
dinium splendens. With this in mind, Lasker
(1975) used laboratory-spawned anchovy larvae
to test for feeding activity in seawater pumped
from the surface and chlorophyll maximum layer
in the nearshore region of the Southern California
Bight. Lasker found that during March and April
1974 there were sufficient numbers of G. splen-
dens (>20 organisms/ml) in the chlorophyll max-
imum layer for initiation of feeding by anchovy
larvae. During 1974 and 1975, Lasker (in press)
monitored the plankton distribution off the south-
ern California coast in an effort to establish a

Manuscript accepted February 1977.
FISHERY BULLETIN: VOL. 75, NO. 3, 1977.

577

FISHERY BULLETIN: VOL. 75, NO. 3

relationship between oceanographic conditions
and larval anchovy food organisms. In 1975 he
found that G. splendens was replaced as the dom-
inant organism in the chlorophyll maximum layer
by the armored dinoflagellate, Gonyaulax poly-
edra, and later by a variety of small diatoms. In
an effort to assess effects that this succession
might have on survival of anchovy larvae, we
have conducted feeding experiments with some of
the phytoplankters common in the Southern Cal-
ifornia Bight to determine which species are ac-
ceptable as food by anchovy larvae. In addition,
we have examined the relative nutritional value
of Gymnodinium splendens and Gonyaulax
polyedra.

METHODS AND MATERIALS

Phytoplankton Cultures

The phytoplankters chosen for feeding experi-
ments are common to southern California coastal
waters, and most were major components of the
chlorophyll maximum layers during 1974 and
1975 (Lasker in press). Also, they were of an appro-
priate size for ingestion by first feeding anchovy
larvae (Table 1). Axenic cultures of the selected
phytoplankters were supplied by James Jordan
of the Food Chain Research Group at Scripps
Institution of Oceanography. Culture techniques
were described by Thomas et al. (1973).

TABLE 1. — Average dimensions of phytoplankters offered as
food to first feeding anchovy larvae.

BACILLARIOPHYCEAE:

Ditylum bnghtwellii (25 ■ 150/xm, single cells)
Chaetoceros affinis (4/xm wide in chains to 200^m)
Thalassiosira decipiens (8 x '\0fim, single cells)
Leptocylindrus danicus (5jim wide in chains to 75^m)
DINOPHYCEAE: CHLOROPHYCEAE:

Gymnodinium splendens (51 /xm) Chlamydomonas sp. (10/xm)

Gonyaulax polyedra (40/xm) Dunaliella sp. (6/xm)

Prorocentrum micans (27 x 38/xm)
Pendinium Irochoideum (20/xm)

Feeding Experiments

To determine which phytoplankters are preyed
upon by anchovy larvae, feeding experiments
were conducted using methods similar to those of
Lasker (1975). Cylindrical 8-liter battery jars,
wrapped with dull black cardboard, were filled
with approximately 5 liters of filtered seawater
(filter pore size, 5 ttm) and inoculated from a
dense culture of the phytoplankton to be tested.

The densities were determined by counting or-
ganisms in 1-ml alilquots in a Sedgwick- Rafter3
counting chamber and/or with a Coulter Counter
Model Ta, and the size was measured with an
ocular micrometer. Experiments were conducted
at temperatures ranging from 16.9° to 19.6°C, and
the test jars were illuminated from above with a
bank of four 40-W fluorescent lamps. Light inten-
sity at the surface of the test jars was approxi-
mately 2,400 lx. Because anchovy larvae readily
feed on Gymnodinium splendens (Lasker 1975),
at least one container in each series of experi-
ments contained only this food organism as a con-
trol to test the feeding ability of each batch of
larvae.

Diatoms were maintained in suspemsion dur-
ing the feeding trials by a gentle stream of bubbled
air in each test jar. To evaluate the effect of such
agitation on the ability of larvae to feed, experi-
ments were conducted with and without bubbled
air using G. splendens as food. Little effect on
feeding ability could be detected (Table 2, Trial 1).

Anchovy eggs were obtained from adult ancho-
vies maintained in spawning condition at the
Southwest Fisheries Center Laboratory. Spawn-
ing techniques were described by Leong (1971).
Anchovy eggs and larvae were allowed to develop
in 1-liter jars (100 eggs/jar) containing filtered
seawater (filter pore size, 5 /xm). First feeding
larvae (2.5 days after hatching at 17°C) were
placed in the experimental containers with the
test organism for approximately 8 h before being
siphoned from the containers and quickly im-
mobilized on a membrane filter (pore size, 8 /urn)
by vacuum filtration. This technique helped to
prevent the larvae from defecating (Lasker 1975).
The larvae remained somewhat transparent after
air drying so that the presence of food in the gut
could be determined by microscopic examination
of the intact animal.

Larval Rearing Experiments

Anchovy larvae were reared for 10 days in 10-
liter circular containers immersed in a tempera-
ture-controlled bath in an air-conditioned room
(Lasker et al. 1970). The containers were filled
with membrane filtered seawater (pore size,
0.45 /xm), the salinity was33.4°/oo,and the temper-
ature was maintained at 16.0° ± 1.1°C. Lighting

3Mention of trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

578

SCURA and JKRDE: PHYTOI'LANKTON AS FOOD FOR LARVAL ANCHOVY

TABLE 2. — Laboratory feeding experiments showing the percentage of anchovy larvae that fed on: 1 ) diatoms — Ditylum brightwellii,
Chaetoceros affinis, Thalassiosira decipiens, and Leptocylindrus danicus; 2) dinoflagellates — Gymnodinium splendens, Gonyaulax
polyedra, Prorocentrum micans, and Peridimum trochoideum; and 3) flagellates — Chlamydomonas sp. and Dunaliella sp.

Feeding

Concentration of

Number of

Feeding by anchovy larvae

trial no

% of larvae

% of larvae with

% of larvae

(duration

Temp

Air-

food particles

larvae per

with Va to

<8 particles

with empty

in hours)

(°C)

stone

Food organism

(organisms/ml)

experiment

full gut

in gut

gut

1 (7.25)

18.2

G splendens

162

182

G splendens

162

18.2

G splendens

162

2 (8.0)

18.2

G. splendens

180

185

D. brightwellii

164

100

19.6

D brightwellii

164

100

3 (8.0)

17.0

G splendens

240

17.0

C affinis

127 chains

100

17.0

C affinis

127 chains

100

170

T decipiens

154

100

17.0

T decipiens

205

100

4 (8.0)

17.1

G splendens

195

16 9

L. danicus

197 chains

100

16.9

L. danicus

780 chains

5 (8.0)

174

G. splendens

208

17.7

P- trochoideum

17.7

P. trochoideum

177

P. trochoideum

210

177

Chlamydomonas sp.

211

100

17.7

P. micans

201

6 (8.0)

18.2

G splendens

193

18.2

G polyedra

102

18.2

G. polyedra

17.7

Dunaliella sp.

303

100

177

Dunaliella sp

242

100

was provided for 14 h/day by 40- W fluorescent
lamps as described earlier.

Eight rearing containers were inoculated with
G. splendens and eight with Gonyaulax polyedra
at a concentration of 100 organisms/ml. As a sup-
plement to these food organisms, some containers
were also stocked with a combination culture of
the rotifer, Brachionus plicatilis, and the harpac-
ticoid copepod, Tisbe holothuriae, with final

concentrations of 0.0, 0.1, 1.0, and 5.0 organisms/
ml (Table 3). Duplicate experiments were run
simultaneously for all treatments including two
containers without dinoflagellates but stocked
with B. plicatilis and T. holothuriae, at a concen-
tration of 5 organisms/ml.

The relative proportions of B. plicatilis and
T. holothuriae (hereafter also referred to as micro-
zooplankton) in the larval rearing containers

TABLE 3. — Survival and growth of anchovy larvae reared for 10 days on different diet regimes.

Stocking density

of larvae on day 0

(no. 'liter)

Concentration
of dmoflagellate
(organisms/ml)

Concentration of

microzooplankton

(organisms/ml)

Surv

ival

Standard

length (mm)

Average weight
(mg)

Number

Percent

Mean

Gymnodinium splendens

3.3

100

5.0

33.3

4.24

0359

0039

3.4

100

5.0

44.1

4.87

0.671

0.048

2.2

100

1.0

22.7

4.30

0.480

0.061

2.5

100

1.0

48.0

4.73

0.677

0.047

3.1

100

0.1

41 9

4.46

0.355

0.046

100

0.1

15.4

3.57

0314

0.046

100

0.0

32.1

4.23

0485

0.042

3.6

100
Gonyaulax polyedra

0.0

22.2

4.03

0.413

0.056

3.3

100

152

4.02

0 403

0.065

3.9

100

35.9

4.82

0.710

0.059

3.8

100

1.0

13.2

4.54

0.796

0.077

3.7

100

1.0

18.9

4.41

0.219

0057

2.8

100

0.1

3.6

3.7

—

(')

100

0.1

3.5

4.0

—

3.5

100

2.9

3.0

—

3.9

100

0.0

—

5.0

19.1

4.51

0.669

0.050

2.3

5.0

0.0

—

'Sample too small to weigh

579

FISHERY BULLETIN: VOL. 75. NO 3

varied during the course of the experiment. Ini-
tially, approximately 907c of the microzoo-
plankters in the containers were T. holothuriae,
but by the end of the rearing experiment, B.plica-
tilis was the dominant organism (97%). We were
unable to determine if the anchovy larvae were
selectively feeding on the copepods because the
combination culture of microzooplankton which
was used to stock the larval rearing containers
also experienced a similar succession in species
dominance during the experimental period.

Brachionus plicatilis and T. holothuriae were
cultured together in the same vessel using tech-
niques described by Hunter (1976). The cultures
were filtered through 105- tun screening to remove
the largest organisms before inoculating the
larval rearing containers. Microscopic examina-
tion of the filtrate revealed a predominance of
small rotifers and copepod nauplii.

Fifty anchovy eggs were added to each container
the day after spawning and the appropriate dino-
flagellate was also introduced at this time. Hatch-
ing occurred on the next day, which corresponds
to day 0 of the experiment. The number of dead
embryos on the container bottom was counted at
this time and the percentage hatch was calcu-
lated. On day 2, most of the yolk sac was absorbed,
the eyes were pigmented, and the larvae initiated
feeding. At this time, the microzooplankton were
added. The experiments were terminated on day
10; standard lengths were measured for each
animal; average dry weight for larvae in each
container was determined; and the percent sur-
vival in each container was calculated.

Each larval rearing container was sampled
daily to monitor the concentration of food organ-
isms. Because Gymnodinium splendens and
Gonyaulax polyedra tend to form patches, 1-ml
samples were taken from three different locations
in the tank outside of a patch; the numbers were
averaged and an appropriate amount of a dense
dinoflagellate culture was added daily to main-
tain a concentration of 100 organisms/ml. The
density of B. plicatilis and T. holothuriae was
maintained in a like manner except that the vol-
ume sampled was larger (from 10- to 100-ml sam-
ples/container, depending on the stock density of
microzooplankton). Also, we were careful to sam-
ple a few centimeters away from the container
surfaces because T. holothuriae copepodids
and adults are thigmotactic. We stocked the rear-
ing containers with nauplii (which are less
thigmotactic than the older stages). However,

during the course of the experiments, surviving
T. holothuriae developed beyond the naupliar
stages and tended to settle out on container sur-
faces becoming less available to anchovy larvae.
These stages were not included in our counts.

RESULTS
Feeding Experiments

A total of 518 larvae were presented with four
species of diatoms (Table 2). Only one larva fed on
diatoms. This single individual ate a narrow (5 x
50-75 /um) chain-forming diatom, Leptoeylindrus
danicus.

Most larvae fed on the dinoflagellates Gymno-
dinium splendens, Gonyaulax polyedra, Proro-
centrum micans, and Peridinium trochoideum.
There was no apparent preference by larvae for
a particular species of dinoflagellate. Between 72
and 89' \ of the larvae tested fed on P. trochoideum
(20 /xm), which are as small as the smallest sized
particles known to be ingested by first feeding
anchovy larvae (Arthur 1976). Peridinium trocho-
ideum is a darkly pigmented dinoflagellate. Per-
haps this characteristic makes it more visible to
the larvae than other particles of a similar size.
Lasker (1975) concluded that first feeding an-
chovy larvae required a particle greater than
40 (iim to fill their gut in 8 h.

Anchovy larvae did not feed on the smallest
prey used in the feeding experiments, the flagel-
lates Chlamydomonas sp. ( 10 /urn) and Dunaliella
sp. (6 /xm).

Larval Rearing Experiments

Growth and survival of anchovy larvae reared
for 10 days on different diet regimes are shown in
Table 3. The survival rate of larvae reared on the
Gymnodinium splendens diet was higher than on
the Gonyaulax polyedra diet. The relationship be-
tween larval survival and supplementation of the
dinoflagellate diet with microzooplankton was de-
scribed with linear regressions (Figure 1). The
survival of larvae reared in seawater containing
100 Gymnodinium splendens/ml did not signif-
icantly increase (t for the slope of the regression
= 0.1, P<0.20) when microzooplankton were
added to their diet as a supplement (Figure 1).
Supplementation of the Gonyaulax polyedra diet
with microzooplankton did result in a significant
increase (t for the slope of the regression = 3.24,

580

SCURA and JERDE: PHYTOPLANKTON AS FOOD FOR LARVAL ANCHOVY

•

_, 40

3 30
if)

•
>

^L1zo2j^J23 -

•
•

u 20
cr

•

1 1

2 3

MICROZOOPLANKTON / ml

2 3

MICROZOOPLANKTON / ml

FIGURE 1. — Percent survival of Engraulis mordax at 10 days in
relation to supplementation of a dinoflagellate diet with micro-
zooplankton. A) Gymnodinium splendens diet. B) Gonyaulax
polyedra diet.

P<0.025) in larval survival. Larvae reared on a
G. polyedra diet required at least 1 microzoo-
plankton/ml in order to have survival rates that
were comparable to larvae reared on a diet of
Gymnodinium splendens. These results were
comparable to the survival rates recorded by
O'Connell and Raymond (1970) for anchovy larvae
fed copepod nauplii at various concentrations.
They found that larvae did not survive for 12 days
in containers with less than 1 nauplius/ml.

Although anchovy larvae grow slowly during
the first several days of feeding, a slight but sig-
nificant increase (t = 2.67, P<0.05) in standard
length occurred in larvae fed G. splendens when
their diets were supplemented with microzoo-
plankton (Figure 2), but no differences in dry
weight were detected. Larvae fed Gonyaulax
polyedra also appeared to increase in standard
length when their diets were supplemented (Fig-
ure 2), but because the increase was slight and
the number of data points was small due to the
low survival rates on this diet, no significant in-
crease was detected (t = 1.50, P>0.20).

Survival was low in larvae fed only 5 micro-
zooplankters/ml without any dinoflagellates (Ta-
ble 3). One container had no survivors and the
other had 19.9% survival. Theilacker and
McMaster (1971) found that larval anchovies that
were fed only rotifers (B. plicatilis) had a lower

6.0

1—

•

«-

•

•
•
•

•

■

— 5.0

•

3 4.5

•

♦

y = 0.08 X + 4-2j ■

•
•

•

o 1

§ 40M

•

h- » •

•

►

3,5 r-»

•

3.0

•

i 1

2 3

MICROZOOPLANKTON / ml

S.0

, 0.09 X + 4.18

2 3

MICROZOOPLANKTON /ml

FIGURE 2. — Standard lengths of Engraulis mordax at 10 days
in relation to supplementation of a dinoflagellate diet with
microzooplankton. A) Gymnodinium splendens diet. B) Gonyau-
lax polyedra diet.

rate of survival than those fed Gymnodinium
splendens and B. plicatilis in combination. They
related this finding to the low feeding success of
larvae on the larger sized rotifers during the first
few days of feeding. Also, Houde (1973) believes
that survival of fish larvae is increased when
blooms of phytoplankton are maintained in rear-
ing containers to "condition" the water (presum-
ably by removing metabolites).

DISCUSSION

Anchovy larvae apear to select their prey and
it seems as if size is not the only criterion for
selection. Larvae did not feed on any of the four
species of diatoms tested in this study. The most
obvious explanation is that spines and other proc-
esses on the diatoms either discouraged the larvae
from striking or prevented them from swallowing.
On the other hand, most larvae fed on all species
of dinoflagellates tested. Visibility might also
play an important role in prey selection since the
darkly pigmented dinoflagellate, P. trochoideum,

581

FISHERY BULLETIN: VOL. 75. NO. 3

was heavily preyed upon by anchovy larvae even
though P. trochoideum are as small as the small-
est particles detected by Arthur ( 1976) in the guts
of larval anchovies.

It appears that prey differ in their nutritional
value to anchovy larvae. Gymnodinium splendens
and Gonyaulax polyedra are readily eaten by an-
chovy larvae, but G. polyedra was an inadequate
food. Only 1 larva of the 74 that were reared on
an exclusive diet of G. polyedra survived for
10 days. Larvae reared on a diet of G. polyedra
supplemented with microzooplankton had sur-
vival rates that increased relative to the degree
of supplementation. Although certain species of
Gonyaulax are known to be toxic, it seems un-
likely that this was a cause of mortality in our
experiments because survival was good when lar-
vae were fed G. polyedra supplemented with 5
microzooplankters/ml.

We offer two possible explanations for the dif-
ference in the nutritional value of the two dino-
flagellates: 1) G. polyedra is about 10 /xm smaller
in diameter than G. splendens. Therefore, on the
basis of volume alone, G. splendens could have
twice as many calories as Gonyaulax polyedra,
because the volume increases as the cube of the
radius in a sphere. 2) G. polyedra is armored while
Gymnodinium splendens is not, and, therefore,
G. splendens is presumably more, digestible by
anchovy larvae which have an undifferentiated
gut during the early stages of their development.
Lasker et al. ( 1970) found that the armored dino-
flagellate, Prorocentrum micans (27 x 38 /xm),
did not sustain life in first feeding anchovy larvae
but again, this organism is smaller than G.
splendens.

Lasker (1975) concluded that the nearshore
area of the Southern California Bight was a good
feeding ground for first feeding anchovy larvae
during the spring of 1974 because of the high
concentrations of G. splendens found in the chloro-
phyll maximum layer. In this study, the survival
of anchovy larvae fed 100 G. splendens/m\ was
acceptable, and it did not differ from that of larvae
fed a G. splendens diet supplemented with micro-
zooplankton at concentrations up to 5 organisms/
ml. Although larvae grew slightly faster when
given the microzooplankton, these results still
indicate that a larva could survive until an age
of 10 days without the high concentrations of
micronauplii that O'Connell and Raymond ( 1970)
found to be necessary. If anchovy larvae survive
to a size of 5 to 6 mm on G. splendens, their feeding

582

efficiency would be higher than smaller larvae
(Hunter 1972), and because of their larger size,
the volume of water that larvae could search for
food would also be increased. These factors would
reduce the concentration of microzooplankton
necessary for survival (Vlymen in press).

During several sampling periods in 1975,
Lasker (in press) found that the chlorophyll maxi-
mum layer in the nearshore region of the South-
ern California Bight was dominated by Gonyaulax
polyedra or a variety of small diatoms. Our work
indicates that during the time periods when
these phytoplankters predominated, feeding con-
ditions for post yolk-sac anchovy larvae would
be less suitable than when G. splendens was
abundant.

ACKNOWLEDGMENTS

We thank James Alexander and Geoffrey Lewis
for their technical assistance and Charles Bary
for culturing the phytoplankton. Thanks also go
to Reuben Lasker and John Hunter for reviewing
the manuscript. This research was supported by
a grant to Reuben Lasker from the Brookhaven
National Laboratory.

LITERATURE CITED

ARTHUR, D. K.

1976. Food and feeding of larvae of three fishes occurring
in the California Current, Sardinops sagax, Engraulis
mordax, and Trachurus symmetricus. Fish. Bull., U.S.
74:517-530.

Bainbridge, v., and D. C. T. Forsyth.

1971. The feeding of herring larvae in the Clyde. Rapp.
P.-V. Reun. Cons. Int. Explor. Mer 160:104-113.

Beers, J. R., and G. L. Stewart.

1967. Micro-zooplankton in the euphotic zone at five loca-
tions across the California Current. J. Fish. Res. Board
Can. 24:2053-2068.
1 969. Micro-zooplankton and its abundance relative to the
larger zooplankton and other seston components. Mar.
Biol. (Berl.) 4:182-189.
HOUDE, E. D.

1973. Some recent advances and unsolved problems in the
culture of marine fish larvae. Proc. World Maricult. Soc.
3:83-112.

Hunter, j. r.

1972. Swimming and feeding behavior of larval anchovy
Engraulis mordax. Fish. Bull., U.S. 70:821-838.

1976. Culture and growth of northern anchovy, Engraulis
mordax, larvae. Fish. Bull., U.S. 74:81-88.

Hunter, j. r., and G. L. Thomas.

1974. Effect of prey distribution and density on the search-
ing and feeding behaviour of larval anchovy Engraulis
mordax Girard. In J. H. S. Blaxter (editor). The early
life history offish, p. 559-574. Springer-Verlag, Berl.

SCURA andJERDE PHYTOPLANKTON AS FOOD FOR LARVAL ANCHOVY

LASKER, R.

1975. Field criteria for survival of anchovy larvae: The
relation between inshore chlorophyll maximum layers
and successful first feeding. Fish. Bull., U.S. 73:
453-462.

In press. The relation between oceanographic conditions
and larval anchovy food in the California Current: Identi-
fication of factors contributing to recruitment failure.
Proceedings of the Joint Oceanographic Assembly, Edin-
burgh, Scotl., Sept. 1976.
LASKER, R., H. M. FEDER, G. H. THEILACKER, AND R. C. MAY.

1970. Feeding, growth, and survival of Engraulis mordax
larvae reared in the laboratory. Mar. Biol. (Berl.) 5:
345-353.

LEONG, R.

1971. Induced spawning of the northern anchovy, En-
graulis mordax Girard. Fish. Bull, U.S. 69:357-360.

May, R. C.

1974. Larval mortality in marine fishes and the critical
period concept. In J. H. S. Blaxter (editorl, The early life
history offish, p. 3-19. Springer- Verlag, Berl.

O'CONNELL, C. P., AND L. P. RAYMOND.

1970. The effect of food density on survival and growth of
early post yolk-sac larvae of the northern anchovy (En-
graulis mordax Girard I in the laboratory. J. Exp. Mar.
Biol. Ecol. 5:187-197.

SHELBOURNE, J. E.

1957. The feeding and condition of plaice larvae in good

and bad plankton patches. J. Mar. Biol. Assoc. U.K.

36:539-552.
THEILACKER, G. H., AND M. F. MCMASTER.

1971. Mass culture of the rotifer Brachwnus plicatilis and
its evaluation as a food for larval anchovies. Mar. Biol.
(Berl.) 10:183-188.

Thomas, w. h.. a. N. dodson, and C. a. Linden.

1973. Optimum light and temperature requirements for
Gymnodinium splendens, a larval fish food organism.
Fish. Bull., U.S. 71:599-601.
VLYMEN, W. J.

In press. A mathematical model of the relationship be-
tween larval anchovy (E. mordax) growth, prey micro-
distribution, and larval behavior. J. Fish. Ecol.

583

COURTSHIP AND SPAWNING BEHAVIOR OF

THE TAUTOG, TAUTOGA ONITIS (PISCES: LABRIDAE),

UNDER LABORATORY CONDITIONS1

Bori L. Oli.a and Carol Samet2

ABSTRACT

Courtship and spawning behavior of the tautog, Tautoga onitis, were observed under controlled
laboratory conditions. Two separate groups of tautog, consisting of two males and one female, were
each studied over an entire spawning season. The larger male of each group was dominant over the
other two animals. This dominance was expressed during the spawning season by intensified aggres-
sion towards the subordinate male. The dominant male of each group, once reaching seasonal reproduc-
tive readiness, was the primary spawning partner of the female. Prior to the onset of spawning, a rapid
approach of the dominant, formerly a component of an aggressive chase, functioned as a courtship
behavior directed at the female. Each day the female exhibited dynamic and transient shading changes
which became maximally developed as the time of each spawning approached in the afternoon. Actual
gamete release, which took place each day following 6 to 8 h of courtship, occurred as the dominant
male and the female moved upwards in synchrony and spawned near or at the surface. The significance
of courtship and spawning in tautog is discussed and compared with reproductive behavior in other
labrids.

The tautog, Tautoga onitis, a member of the fam-
ily Labridae, occurs along the coastal regions of
North America, ranging from South Carolina to
Nova Scotia (Bigelow and Schroeder 1953). As
with labrids in general, the fish are found as-
sociated with shelter or cover, a habit primarily
related to the animals' requiring protection espe-
cially during nighttime, when they are quiescent
(Olla et al. 1974).

According to previously published accounts,
tautog are long-lived, reaching a maximum age of
at least 34 yr (Cooper 1965) and becoming sexually
mature at 3 to4yrofage(Chenoweth 1963; Cooper
1965; Briggs in press). The adults move offshore in
the late fall to overwinter, a pattern established in
field studies off Rhode Island (Cooper 1966) and off
Long Island, N.Y. (Olla et al. 1974; Briggs in
press). In contrast to the adults, the young remain
inshore, spending the winter in a torpid condition
(Olla et al. 1974).

Although a portion of the adult population re-
mains offshore throughout the year in deep water
( e.g., sports divers report finding tautog at offshore
shipwrecks throughout the year), the remainder of

•This work was supported in part by a grant from the U.S.
Energy Research and Development Administration, No. E (49-7 )
3045.

2Middle Atlantic Coastal Fisheries Center, National Marine
Fisheries Service, NOAA, Highlands, NJ 07732.

Manuscript accepted January 1977.
FISHERY BULLETIN: VOL. 75. NO 3. 1977

the population moves inshore in late spring. Peak
spawning activity occurs primarily in May and
June (Chenoweth 1963; Cooper 1966).

From May through October adults are com-
monly found, especially in the midportion of their
range, wherever there is appropriate cover and
food supply. They are frequently seen by divers
and are easily disturbed by such intrusions. The
fish's reaction to divers may account for the fact
that spawning in the natural environment has not
been described. Spawning has also not been de-
scribed under laboratory conditions. Until now the
only mention of any components of a possible
courtship repertoire has been by Bridges and
Fahay (1968). These authors introduced a ripe
male and female into a small laboratory aquarium
in early June and observed transient changes in
the pigmentation pattern of the female, assumed
to reflect a reproductive predisposition. However,
no actual gamete release was seen.

Courtship and spawning behavior in labrids has
been observed in a number of species both under
natural and laboratory conditions. Both paired
and aggregate spawning occurs within the family.
Species which have been observed to be primarily
pair spawners include Crenilabrus melops (Potts
1974); Halichoeres bivittatus, H. garnoti, H.
maculipinna, and H. radiatus (Randall and Ran-
dall 1963); Labroides dimidiatus (Robertson and

585

FISHERY BULLETIN: VOL. 75, NO. 3

Choat 1974); and L. phthirophagus (Youngbluth
1968). Pair spawning has also been described in
Cirrhilabrus temminckii (Moyer and Shepard
1975), although the authors do not discount the
possibility that group spawnings may occur as
well in this species.

Species in which only group spawnings have
been documented include Thalassoma lucasanum
(Hobson 1965); T. hardwicki (Robertson and
Choat 1974); and the cunner, Tautogolabrus
adspersus, a coresident of the tautog (Wicklund
1970).

At least two labrid species have each been
shown to possess both modes of gamete release.
The bluehead, Thalassoma bifasciatum, was first
seen to exhibit the dual spawning behavior under
natural conditions by Randall and Randall (1963).
Robertson and Choat (1974) observed similar be-
haviors in T. lunare. Both T. bifasciatum (Rein-
both 1967) and T. lunare (Choat 1969) are pro-
togynous hermaphrodites, a condition ". . . in
which the individual functions first as a female,
and later in life as a male" (Atz 1964). Although
protogynous hermaphroditism is rather wide-
spread in labrids (at least 30 species mentioned by
Robertson and Choat 1974), until now only the two
species mentioned above have been identified as
possessing both modes of spawning.

Our aim in this work was to examine and de-
scribe the various components comprising court-
ship and spawning of the tautog. The studies were
performed on adults which were held under
laboratory conditions in a large aquarium.

MATERIALS AND METHODS

Two studies, spanning the 2-yr period of 1975
and 1976, were conducted on two different groups
of adult tautog, with each group consisting of two
males and a female. The fish were collected during
late summer and early fall at Fire Island, N.Y., at
temperatures ranging from 19° to 24°C. Scuba
divers, using hand-held nets, were readily able to
capture the fish at night when they are normally
quiescent. The animals were easily identifiable
with respect to their gender by the sexually di-
morphic mandible, which is more pronounced in
males (Cooper 1967).

The studies were conducted in a 121-kl, ellipti-
cally shaped aquarium, 10.6 x 4.5 x 3.0 m, located
in a temperature-controlled room in which
natural diurnal changes in light intensity were

586

simulated (Olla et al. 1967). Layers of sand (0.6-
0.8 mm) and gravel (2-5 mm), 0.6 m deep, pro-
vided a natural substrate for the fish. Beneath the
gravel, seawater flowed through a network of
pipes on the floor of the aquarium from a series of
external filters containing sand, gravel, and oys-
ter shells, and which provided continuous circula-
tion and filtration. Water quality in the aquarium,
operated primarily as a semiclosed system, was
also maintained by addition of seawater from
Sandy Hook Bay. The pH averaged 7.5, salinity
averaged 24.0%o, and dissolved oxygen averaged
7.5 ppm.

It had been previously determined that in the
natural environment a shelter area is a physical
requirement of tautog, particularly during their
nighttime quiescence. Shelter was, therefore, pro-
vided in the form of a triangular-shaped structure
consisting of three clay drainage tiles (30.5 x 60.9
cm) cemented together. The shelter was placed
approximately 3 m from one end of the aquarium
in proximity to viewing windows. Clumps of live
blue mussel, Mytilus edulis (5-17 kg), a major
component of the tautog's diet (Olla et al. 1974),
were introduced periodically to insure a continual
food supply which allowed the fish to feed ad
libitum. The mussels were placed 4 m from the
shelter and constituted a more or less fixed feeding
area.

Diurnal changes in light intensity from morn-
ing to evening civil twilight were simulated by
banks of fluorescent lights mounted on the walls
above the aquarium and controlled by a series of
timers (Olla et al. 1967). A low level of night il-
lumination, 0.75 lx was provided by incandescent
bulbs, programmed to come on before the last row
of fluorescent lights was extinguished.

Aquarium Conditions During
Animals' Residency

Study 1

One male [51.5 cm TL (total length)] and one
female (50.0 cm TL) were introduced into the
aquarium on 20 September 1974, with a second
male (59.0 cm TL) introduced 7 days later. From
this point, the animals were kept in the aquarium
for a total of 244 days. The fish were initially held
at 19.1°C ( +0.8°; - 1.6°C) for 50 days. The animals
were then the subjects of a long-term study deal-
ing with the effects of temperature on activity and
social behavior (Olla in prep.). Beginning at light

OLLA and SAMET: COURTSHIP AND SPAWNING BEHAVIOR OK TAUTOG

onset 51 days after the three fish were placed in
the aquarium, the water temperature was in-
creased during a 9-day period (mean rate 0.04°C/
h) and held for 11 days at 28.7°C ( + 0.2°; -0.1°C).
The temperature was then decreased over an
8-day period (mean rate 0.05°C/h) and held for 165
days from 14 December 1974 to 28 May 1975 at
18.7°C ( + 1.1°; -0.8°C).

During the first 10 days of the animals' resi-
dency, the photoperiod was decreased from 13.18 h
to 12.25 h and then held constant through 22 Feb-
ruary 1975. Beginning on 23 February 1975 the
light schedule was set to conform with the natural,
increasing photoperiod. The interval from 14 De-
cember 1974 to 16 January 1975 comprised the
baseline nonreproductive period for Study 1. Ob-
servations on courtship behavior first began on 11
April 1975.

Study 2

Two males (54.0 cm TL and 55.3 cm TL) and one
female (47.0 cm TL) were introduced into the
aquarium on 28 August 1975 and kept in the
aquarium for a total of 225 days. They were ini-
tially held at 21.3°C ( + 1.9°; -1.5°C) for 80 days.
The animals were then the subjects of a long-term
study dealing with the effects of temperature on
activity and social behavior (Olla in prep.). Begin-
ning at light onset of the 81st day of the animals'
residency, the water temperature was gradually
raised over a 9-day period (mean rate 0.04°C/h),
held for 11 days at 28.7°C (+0.2°; -0.4°C), de-
creased during 8 days (mean rate 0.04°C/h), and
then held for 115 days from 14 December 1975 to 8
April 1976 at 20.2°C (±0.7°C).

During the first 22 days of the animals' resi-
dency, the photoperiod was decreased from 14.23 h
to 12.32 h and then held constant through 2 March
1976. Beginning on 3 March 1976 the light
schedule was set to conform with the natural, in-
creasing photoperiod. The interval from 14 De-
cember 1975 to 15 January 1976 comprised the
baseline nonreproductive period for Study 2. Ob-
servations on courtship behavior first began on 29
January 1976.

Observation Schedule

Hourly observations made on the fish during the
light period of each study consisted of 15-min read-
ings. During each, the following measures of be-
havior (described in Results) for each fish were

recorded for 50 counts in sequence at 18-s inter-
vals: 1) number of aggressive interactions be-
tween fish and identity of aggressive and submis-
sive individuals, and 2) number of courtship
interactions and identity of participants. Qual-
itative aspects of behavior were also recorded dur-
ing each reading.

During the nonreproductive period, 12 hourly
observations (0700-1800 EST) were made daily in
4-day periods with intervals up to 3 days between
periods. A total of 28 observation days ( 336 h ) were
made in the nonreproductive period of Study 1 and
20 days (240 h) in Study 2. During the reproduc-
tive period 8 hourly observations (0800-1500
EST) were made daily. In Study 1 these were
taken in 2-day periods, with intervals up to 5 days
between periods, while in Study 2 there were
4-day observation periods with intervals of up to 3
days between each. During the reproductive
period a total of 15 observation days ( 120 h) were
made in Study 1, and 13 days (104 h) in Study
2.

To compare differences in aggressive interac-
tions prior to and during spawning, we selected 1 1
typical days of observations during the nonre-
productive and reproductive periods of each study.
Data based on the hourly, means (0800-1500 EST)
from these days are presented in tabular form in
the Results.

Once we discovered that gamete release oc-
curred in the afternoon on a daily basis and we had
become acquainted with the reproductive reper-
toire of the animals, we could predict approxi-
mately when daily spawnings would occur. There-
fore, in addition to the readings mentioned above,
we also began to observe the fish at least 60 min
and some days up to 150 min prior to and including
each spawning. In Study 1 approximately 35 h and
in Study 2, 25 h of observations were made prior to
spawnings. During 11 typical spawning days, data
collected in this fashion enabled us to determine
quantitatively: 1) if there were any changes in
aggression throughout the day as the spawning
time approached, and 2) how close (temporally) to
the spawnings, changes in courtship behavior
were manifested.

Throughout each study and particularly prior to
each spawning, observations were made with the
use of a tape recorder. In addition, periodic motion
pictures taken throughout the spawning period
allowed us to analyze and interpret behavioral
components and sequences both in slow motion
and at stop frame.

587

FISHERY BULLETIN: VOL. 75. NO. 3

RESULTS

Interactions Prior to Spawning Season

Prior to the onset of spawning in each study,
there had developed a clear dominance hierarchy
based on size, with the largest fish of each group, a
male, being dominant over a smaller male and
still smaller female. In turn, the smaller male was
dominant over the female. Prior to the reproduc-
tive season, the majority of interactions among the
three fish consisted of aggressive behavior. During
various hours of the day the aggression, initiated
particularly by the dominant male, served in part
to limit the access of the subordinate male and
female to different areas of the tank, such as the
feeding area and shelter site (Olla in prep.).

Aggression was manifested at varying levels of
intensity with the more intense involving the pur-
suit of a fleeing subordinate by a dominant, which
we termed a chase. Prior to such an encounter a
dominant often rapidly approached (swam to-
wards) a subordinate. The subsequent chase could
last as long as 30 to 45 s, with the fish swimming
the length of the tank and at speeds reaching 100
to 150 cm/s. The most intense but rarest encounter
involved a chase accompanied by the dominant
biting a subordinate on any area of its body, which
we termed nipping.

Aggressive encounters could also be quite sub-
tle, with a subordinate exhibiting a change in its
location, either vertically or horizontally, to a new
position 0.5 to 1.0 m away, which we termed dis-
placement. The behavior of a dominant causing
this response often did not appear to differ from its
forward swimming motion. Displacement of a
subordinate occurred either as a dominant ap-
proached or simply turned towards it, as much as a
full tank length away (10.6 m). Then there were
instances in which a similar action of a dominant
did not elicit any response by a subordinate. This
variation in response by a subordinate was due to
our not being able to assign an observable cause
with regard to the actions of the dominant. We
could only infer, through a subordinate's behavior,
the generation of an aggressive intention signal
by the dominant male.

Aggression by the dominant also caused a sub-
ordinate to assume a posture which we interpreted
to be submissive, which involved the subordinate
tilting its dorsal surface towards the dominant at
an angle ranging from 5° to 90°. Frequently, when
a subordinate was swimming about the tank and

588

approaching an area in which the dominant was
present, it would show the submissive posture as it
bypassed and clearly avoided the dominant. The
distance at which this would occur varied, ranging
from 1.0 to 3.0 m.

Onset of Reproductive Period and
Courtship Behavior

The most obvious manifestation of the approach
of reproduction was the change in aggression di-
rected toward the female by the dominant male.
Beginning in early April 1975 (Study 1 ) and in late
January 1976 (Study 2), a rapid approach of the
male, which had previously represented the initi-
ation of a chase, became functionally transformed
into a component of the courtship repertoire. Now
when the male approached, when within 5 to 10
cm, he veered off to one side or the other. The
female was neither displaced nor showed any
change in posture. We defined these acts of the
male as rushes to distinguish them from ap-
proaches which formerly caused displacements
and were aggressive. Rushes were directed at the
female whether she was active or resting. At times
as the male veered off, the magnitude of the water
displacement from the force of the caudal thrusts
was great enough to stir the adjacent sand and
cause the female to be moved several centimeters.
Rushes were observed approximately 2 wk (Study
1) and 7 wk (Study 2) prior to the first spawning.

The female, previously limited in her access to
different areas of the tank, now was more mobile
and concurrently began to show changes in her
behavior towards the dominant. Sometimes im-
mediately after the male's rush, the female fol-
lowed him at a distance of approximately 0.5 to
1.0 m. The duration of the following behavior was
usually short, lasting no more than 2 to 5 s. If the
male did not initiate another rush, one of the pair
simply swam away.

Another change in the female's behavior to-
wards the dominant male was her resting in areas
in which the dominant was resting. While in
Study 2 this generally occurred along the walls of
the tank or in the feeding area, in Study 1 it often
focused around the shelter. On occasion when the
dominant male was resting inside the shelter, the
female often settled at the base of the structure, or
sometimes actually entered and came to rest
alongside the male within the same tube or in a
different one.

While the female of Study 1 appeared to play a

OLLA and SAMET: COURTSHIP AND SPAWNING BKHAVIOR OF TAUTOG

rather passive role in stimulating the dominant
male's attention (except when she simultaneously
entered the shelter with him), the female of Study
2 was behaviorally much more conspicuous in at-
tracting the attention of both males, particularly
as they fed. On several occasions the female not
only ingested mussels from the same small pile on
which a male was feeding, but even wrested a
clump of mussels from a male's mouth. This be-
havior was readily tolerated by both males.

In contrast to the termination of aggressive in-
teractions between the dominant male and the
female during this early prespawning period, the
aggression of the dominant towards the subordi-
nate male began to increase both in frequency and
in intensity. In Study 1, aggressive acts by the
dominant toward the subordinate rose from an
average of 2.4/h during the nonreproductive
period to 16.0/h in the week prior to the first
spawning. In Study 2 aggressive acts rose from an
average of 2.6/h during the nonreproductive
period to 6.3/h in the week prior to spawning. Once
daily spawning began in both studies, intermale
aggression remained consistently high and was
significantly greater during the entire reproduc-
tive period than during the nonreproductive
period (Ps=0.05; end count test; Tukey 1959;
Table 1).

The heightened intensity of aggression was
reflected by the increased duration of a chase,
which commonly lasted as long as 60 to 90 s with
the two fish covering anywhere from 1 to 3 circuits
around the tank. In both Studies 1 and 2, the other
obvious factor reflecting this heightened aggres-
sion was that the dominant began nipping and
biting the subordinate during chases. As a result,
each subordinate male in Studies 1 and 2 bore
numerous wounds on all areas of its body.

One further piece of evidence of the increased
aggression of the dominant male in each study was
that the subordinate male now spent the majority
of time confined to either end of the aquarium,
sculling in place along the wall between middepth
and the surface. These locations appeared to be the
ones which elicited least aggression by the domi-
nant male.

Along with behavioral changes, external
changes in the appearance of the female were also
occurring with the onset of the reproductive
period. Enlargement of the gonads increased the
girth of the female, resulting in a more rotund
appearance. At the same time, we also noted
minor changes in the female's pigmentation.

TABLE 1. — Comparison of aggressions by dominant male toward
subordinate male Tautoga onitis for 11 days during nonrepro-
ductive and reproductive (spawning) periods of Studies 1 and 2.
Data are presented as a mean of 8 h/day ( 0800-1500 EST) during
nonreproduction and reproduction.

Study 1

Study 2

No. aggressions per

No.

aggressions per

hourly observation

End

hourly observation

End

per day (x)

count

per day (x)

count

Nonreproductive period:

1.5

1 _

3.0

—

2.8

2.3

3.5

1.8

2.9

3.3

2.4

3.9

3.3

3.9

0.9

—

1.4

1.9

2.3

1.1

2.3

2.0

1.8

Reproductive period:

14.2

2 +

10.8

22.4

10.6

10.2

10.0

9.9

7.6

8.4

12.9

10.2

14.6

7.0

12.4

8.8

20.1

3.5

23.5

3.6

26.4

7.1

26.5

Total end count

= 18

Total end count

= 22

sO.05

Ps005

1 - = Values for aggression during nonreproduction smaller than smallest
reproduction value.

2+ = Values for agression during reproduction greater than greatest non-
reproduction value.

While prior to this period she was generally a solid
dark gray, now there was a mottled white, vertical
bar or stripe down the middle of each side of the
body, which we termed a "saddle." At this time,
the saddle was in an early stage of development
(Figure la) of what was to be a progression of
significant shading changes taking place prior to
and during each daily spawning (see below for
further explanation). In addition, a pale,
grayish-white patch developed in the inter- and
supraorbital areas of the female, giving the ap-
pearance of eyebrows. The first observations of the
female's saddle were made on 11 April 1975 in
Study 1 and 29 January 1976 in Study 2.

Unlike the female, the dominant male's appear-
ance prior to and during spawning was altered
very little. The only discernible shading changes
of the dominant males of both studies were the
development of a light gray shading covering the
entire head and opercula, and the transient ap-
pearance of faint white rays (approximately 2-4
cm long) extending outwards from the orbits of the
eyes. Additionally, it appeared that the ventral
portion of the maxilla and the entire mandible
became a lighter, almost white, shade, with the
exception of the dark pores of the mandibular lat-
eral line canals. Otherwise the male's shading re-

589

FISHERY BULLETIN: VOL. 75, NO. 3

FIGURE 1, — Development of daily shading changes associated with spawning in female Tautoga onitis: a) earliest stage of white
saddle development; b) increased size of the saddle and first, faint appearance of caudal banding as it occurs in the afternoon; c) final
reproductive shading with tail-up posturing exhibited prior to spawning.

590

OLLA and SAMET: COURTSHIP AND SPAWNING BEHAVIOR OF TAUTOG

mained unchanged, with the trunk being a dark
gray. Occasionally in Study 2, we noticed tran-
sient shading changes on the dominant male that
were most apparent during aggression or court-
ship. In these cases the length of the male's mid-
section became a much lighter gray than the
darker, dorsal area of its body. This was not a
persistent change and lasted perhaps 1 or 2 min.

Development of Pair Formation

On 4 April 1975 in Study 1 (approximately 2 wk
prior to the first spawning), it was apparent that
there was in progress a transition from nonsexual
to sexual (courtship) activities between the dom-
inant male and female. We interpreted this to be
the development of pair formation, at least within
the context of the social situation and the un-
natural laboratory condition.

In this same 2-wk period prior to the first spawn-
ing, the dominant's aggression directed at the
subordinate male not only persisted but also
began to increase and apparently served to inhibit
(suppress) the subordinate's motivation to either
court the female (i.e., by rushing her) and/or par-
ticipate eventually in any of the spawning ac-
tivities as long as the dominant was present. Since
our observations in Study 1 began after courtship
was under way, we were unable to ascertain the
initial responses of the subordinate male toward
the female, e.g., whether or not this male had
originally shown any receptivity to the female (or
vice versa) or attempted to court her.

In contrast to Study 1, the development of pair
formation between the dominant male and female
in Study 2 was slightly altered at first by the
participation of the subordinate male. The domi-
nant male had initiated rushes at the female as
early as 29 January 1976 (7 wk prior to the first
spawning), but then on 23 February 1976, the
subordinate began to rush her periodically. In the
4-wk observation period (23 February- 18 March
1976) immediately prior to the first spawning, the
rushes by the dominant continued, averaging
8.8/day (range of 3-22/day), and while the rushes
by the subordinate also occurred, they were lower
in frequency, averaging 1.4/day (range of 0-5/
day).

The events during the first and subsequent
spawnings of Study 2 offered some preliminary
evidence that, while gamete release was not con-
tingent upon an established pair formation, this
type of social interaction ultimately prevailed, at

least under laboratory conditions. On the date of
the first spawning, 19 March 1976, the female
mated not with the dominant, but with the subor-
dinate male. Although the dominant initiated
some of the final courtship behavior that normally
led to gamete release (see results below), and up to
a point, had continued to attack the subordinate,
eventually the dominant withdrew from all ac-
tivities, remained inside the shelter, and did not
interfere as the subordinate briefly rushed and
then released gametes with the female (details
described below). This type of pattern in which the
dominant initiated prespawning behavior, but
then withdrew and "allowed" the subordinate
final access to the female for spawning persisted
for 4 days through 22 March 1976.

On 23 March the dominant began taking a more
active and sustained role in the final reproductive
behavior. Because of this and the fact that his
aggression towards the subordinate had been in-
creasing, it appeared that the dominant might be
the sole mate of the female. However, just as the
dominant and female were about to spawn, the
subordinate male rapidly approached the pair and
simultaneously released his gametes with theirs.
This pattern in which the dominant initiated and
completed the spawning activities with the
female, but still had not sufficiently inhibited a
simultaneous spawning release by the subordi-
nate male persisted for 7 days through 29 March
1976.

It was not until 30 March, 11 days after the first
gamete release, that the spawning was completed
exclusively by the dominant male and the female.
Throughout the remainder of the study, the
female mated exclusively with the dominant
male.

Daily Reproductive Behavior

All spawnings that were observed during both
Studies 1 and 2 occurred between 1330 and 1600
(EST) with the exception of one at 1015 (EST) in
Study 1. The first spawning of Study 1 was on 21
April with 36 subsequent spawnings observed
(1-3/day), and in Study 2 the first spawning oc-
curred on 19 March 1976 with 22 subsequent
spawnings (1-2/day).

Throughout the morning of a typical day when
spawning was to occur, the dominant male was
generally active, swimming about the tank, feed-
ing, and intermittently rushing the female. Ag-
gression towards the subordinate male usually oc-

591

FISHERY BULLETIN: VOL. 75, NO. 3

curred right up until and after each spawning. The
subordinate male continued to be restricted in its
movements by the heightened aggression directed
towards it and remained almost exclusively at
either end of the tank, usually in midwater. The
female, besides showing a minimal change in
shading (i.e., early saddling, Figure la), as well as
an occasional responsiveness to the dominant, also
engaged in activities not directly related to spawn-
ing, such as feeding, swimming (with no apparent
interactions with the other animals), and resting.

While the female either briefly followed after
and/or rested near the dominant or exhibited no
response to the rushes prior to this period, as the
morning progressed she responded with progres-
sive shading changes of varying magnitude. For
example, within several seconds after a vigorous
rush by the dominant male, the saddle oftentimes
increased in depth and width. On some occasions
the saddle took on a pale yellowish hue. The an-
terior half of the dorsal fin became a mottled
white, ending at the same posterior border as the
saddle. In addition, faint, white vertical stripes
became evident on the caudal areas of the body,
originating at the posterior edge of the saddle and
extending just past the caudal peduncle (Figure
lb), similar to that described by Bridges and
Fahay (1968). The pattern could vary, with these
stripes modified into a kind of" checkerboard.
Along with this shading, the female often erected
her dorsal fin very briefly (1-2 s) immediately
following a rush.

Unless spawning was imminent, i.e., occuring
within 15 to 30 min, these shading changes in the
morning were retrogressive. A particular pattern
might not last for more than 10 to 20 s or, at the
longest, several minutes, followed by fading, with
only a thin saddle persisting.

During the afternoon as the time of spawning
approached (30-60 min prior to spawning), the
dominant male became more responsive to the
female, as evidenced by the increased intensity of
the rushes. As these continued the female began to
erect the dorsal fin for progressively longer
periods, anywhere from 5 to 15 s. During fin erec-
tion the total area of white spanning the saddle
and the dorsal fin was now maximized and, we
believe, served to increase the female's conspicu-
ousness.

In this same period she began to swim at times
only with the pectorals and also intermittently
began to flex the caudal fin upward. When caudal
flexion first began, it usually followed a rush and

592

was accomplished by a series of small lifts in which
the female raised the caudal fin progressively
higher.

The responsiveness of both the male and female
was at its peak for the 15 min prior to spawning.
While the number of rushes during each of the
15-min hourly observations throughout the day
averaged 1.2 (Study 1) and 3.3 (Study 2), the
number of rushes in this 15-min period preceding
a spawning increased to an average of 6.4 (Study
1) and 9.4 (Study 2). Aggression by the dominant
towards the subordinate male was not sig-
nificantly different between morning and after-
noon for Study 1 (P>0.05), but increased sig-
nificantly in the afternoon of Study 2 (P^0.05;
sign test; Dixon and Mood 1946; Table 2).

During the 15-min period prior to spawning, the
saddle of the female was almost maximally de-
veloped, appearing whiter than it had been earlier
in the day, and extending fully down the abdomen.
The caudal checkerboard or striped pattern was
now much more clearly defined. In addition the
vent began to dilate.

The behavior of the female also began to change.
She was now more active, and often swam by using
only the pectoral fins. When the male moved
rapidly towards her in a rush, she often erected the
dorsal fin and flexed the caudal fin before the male
had reached her rather than afterwards. The du-
ration of the upward caudal flexion continued to
increase. Accompanying the caudal flexion was
the forward tilting of the body at about a 20° to 30°
angle, serving to expose maximally the dilated
vent.

TABLE 2. — Sign test comparing mean number of agressions per
hourly observation by dominant male towards the subordinate
male Tautoga onitis during the morning (0800-1100 EST) and
the afternoon (1200-1500 EST) on 11 spawning days of Studies 1
and 2.

Study

Study 2

Date

0800-

1200-

Sign

Date

0800-

1200-

Sign

1975

1100

1500

test

19 76

1100

1500

test

4/28

17.0

11.5

3/24

10.2

11.2

4/29

24.2

20.5

3/25

8.0

13.2

4/30

4.5

16.0

3/29

5.8

14.2

5/1

8.8

11.0

3/30

6.8

8.5

5/2

7.5

9.2

3/31

9.2

16.5

5/5

7.2

13.2

4/1

12.5

16.8

5/6

8.2

5.8

4/2

8.2

16.5

5/12

4/5

14.5

25.8

5/13

4.0

3.0

4/6

15.5

31.5

5/19

2.5

4.8

4/7

21.2

31.5

5/20

3.8

10.5

4/8

16.0

37.0

No. of +

No. of

Difference

0.05

sO.05

OLLA and SAMET: COURTSHIP AND SPAWNING BEHAVIOR OF TAUTOG

Beginning anywhere from 2 to 5 min before
spawning, the female began swimming back and
forth along the length of the tank close to the sand
using only the pectoral fins, a behavior we defined
as a run. A run was usually accompanied by a full
and constant erection of the dorsal fin and the final
shading development in which all of the white
areas of her body (i.e., the saddle, caudal stripes or
white portions of the checkerboard pattern, the
"eyebrows," and the anterior half of the dorsal fin)
were almost totally blanched, sometimes colored
with a yellowish hue. Then, as a run was either
beginning or in progress, the caudal fin was rigidly
flexed upward one final time (Figure lc), exposing
the maximally dilated vent, while at the same
time the head was tilted downward. The female's
swimming in this position seemed awkward, re-
sulting in her moving with a characteristic wobble
or wiggle. The female made one or two runs alone
which apparently served to heighten the attention
of the dominant male, for he would break off other
activities (e.g., chasing the subordinate male,
swimming randomly about the tank) to usually
rush her first and then to follow her (Figure 2a).

As the female continued on the runs, the male
tended to swim more in a parallel alignment with
her. Eventually he swam just slightly behind with

his head moving closer to the female's operculum
or midsection, 30 to 40 cm away from her ( Figure
2b). Then suddently, while increasing her speed by
changing from pectoral swimming to caudal
thrusts, the female swam rapidly toward the sur-
face, with the male immediately accelerating in a
similar manner to keep apace with her i Figure 2c).
The angle of their ascent was anywhere from 40°
to 70°. When the fish were less than a meter from
the surface and while still swimming rapidly, they
turned their bodies so that their ventral areas
faced toward each other. On those occasions when
the fish's movements were perfectly coordinated,
the pectorals of the male appeared to be embracing
the female (Figure 2d). With the animals in con-
tact, they arched their bodies into U-shapes and
released gametes either before reaching the sur-
face or as they broke the surface (Figure 2e). Then
the pair separated and swam downwards (Figure
2f ), with the female coming to rest on the sand
where the male usually rushed her 2 or 3 times
within 5 to 10 s following the spawning. After a
spawning, the female's shading usually regressed
to just a thin saddle within a few minutes.

The spawning as we have described it appeared
to comprise the prevalent mode of gamete release.
However, there occurred slight variations in the

FIGURE 2. — Final sequence of behaviors leading to spawning in Tautoga onitis: a) male approaches female; b) they swim parallel with
female slightly ahead; c) male and female move upwards in the water column; d) the pair orient to each other in a ventral-to-ventral
alignment; e) with bodies flexed the pair release gametes as they break the water surface; f )the fish separate and move downwards.

593

FISHERY BULLETIN: VOL. 75, NO. 3

behavior which still resulted in gamete release.
For example, as the female was moving to the
surface, rather than orienting the ventral area of
her body toward the male, she bent her body into
the U-shape with the result that her dorsal side
faced the ventral side of the male. Gamete release
still occurred as the fish flexed their bodies into
U-shapes. The origin of this variation was usually
due to the fact that while moving upward the
female was swimming too rapidly to assume the
proper alignment for the ventral-to-ventral re-
lease with the male.

A critical factor for maximizing fertilization
was the breaking of the water surface at the time
of release. As the fish moved upwards, churned the
water, and swam downwards again, currents were
created which mixed the "cloud" of gametes to-
gether. From visual observations and motion pic-
ture analysis, this occurred whether there was
ventral-to-ventral or ventral-to-dorsal alignment
of the pair. We would assume, however, that the
most efficient method for fertilization involved the
ventral-to-ventral alignment.

While runs were always performed prior to
spawning, on some days there were as few as 2
runs prior to a spawning, while on other days there
were as many as 11. Similarly, the duration of a
series of runs varied from 30 to 180 s.

Runs were not always performed in succession.
Particularly in Study 1, many times after complet-
ing one run, the pair began circling around each
other in midwater. In some cases they followed
each other, head to tail, along the perimeter of an
imaginary circle. In other cases, as the male swam
around the female, she either remained sculling in
a fixed position or pivoted about her vertical axis,
obviously orienting to the moving male. The total
number of separate circling bouts during a run
sequence ranged from 2 to 10 with a duration of
each ranging from 2 to 40 s.

Occasionally at the end of a run, the pair began
to swim upwards, as if to spawn. Typically, at the
onset of this, the female began the transition from
pectoral swimming to caudal thrusts. Moving
rapidly upwards with the male alongside, the
female broke away from him short of the surface
and swam downwards to the sand without releas-
ing gametes. This behavior sometimes did not
occur at all while in other cases it occurred as
many as six times prior to a spawning.

The continuity or fluidity of the run sequences
appeared to be a critical factor serving to syn-
chronize the fish for final release of gametes. Lack

594

of mutual stimulatory behaviors or even slightly
inappropriate behavior by one of the mates during
a run, in general, were sufficient causes for a tem-
porary breakoff of the entire sequence. During a
breakoff the female's shading often regressed
somewhat and she came to rest on the sand or even
returned to the shelter for a few seconds.

One of the specific causes for these breakoffs was
due to the fact that the dominant male, instead of
maintaining his attention toward the female,
chased or displaced the subordinate male which
had either ( actively) moved too close to the pair or
(passively) happened to be in areas where the pre-
spawning behavior was being carried out.

Other reasons for the breakoffs were inappro-
priate stimuli initiated usually by the male during
the run sequence. In Study 1, if the male contacted
the female during a run along the sand or as she
ascended to spawn rather than at the apex of the
pathway, the female often turned away from the
male. Conversely, premature contact behavior by
the male in Study 2 was an appropriate stimulus
to his mate and in fact was frequently exhib-
ited during the run sequence as well as during
spawning.

Other cases in which the female initiated a
breakoff from a run occurred if the male assumed
an atypical position relative to hers. In Study 1,
the female usually swam between the wall and the
male and slightly ahead of him. Occasionally if the
male assumed the position closest to the wall dur-
ing a run (i.e., the female was now closer to the
center of the tank) or if the male swam ahead of
her, the female broke away. Since the male some-
times "corrected" his position relative to hers and
hence the female did not break away, it appeared
that each animal had become conditioned to a
rather stereotyped set of behavioral patterns and
positions which facilitated bringing the spawning
to completion.

Reproductive Behavior of
the Subordinate Male

In both studies each subordinate male had
achieved gonadal maturation and was able to
complete spawning with the female under a lim-
ited set of conditions. In each case, the reproduc-
tive behavior occurred only when the subordinate
was not behaviorally inhibited by the dominant
male. In Study 1, the first spawning by the subor-
dinate male and the female occurred later in the
spawning season, on the very day (29 May 1975)

OLLA and SAMET: COURTSHIP AND SPAWNING BEHAVIOR OF TAUTOG

that the dominant male was dying (unknown
causes). This latter animal was obviously in a
weakened condition and did not participate or in-
terfere with the reproductive activities during his
last day of survival. In Study 2, as described above,
the subordinate male initiated courtship and
spawning with the female at the onset of the re-
productive season and continued until the aggres-
sion by the dominant literally suppressed all of his
normal behavior.

The behavior exhibited by each subordinate
male immediately prior to and during spawning
was essentially comparable to that of the domi-
nant, except that it was less stereotyped. Some-
times during a run the subordinate male weaved
from one side of the female to the other; and in
other cases he actually swam ahead of her on the
first and second runs. Gradually as the male came
to align himself more with her position, the male
initiated flank contact, and positioned his body
slightly above hers.

In both studies, once this continuous contact by
the subordinate male was maintained, the runs, as
discrete behavioral patterns, were no longer dis-
cernible. Generally the pair swam in a meander-
ing, zig-zag pattern in midwater, and eventually
circled approximately 0.5 to 1.0 m below the sur-
face. During this behavior, it always appeared
that the male was herding the female. Generally,
because the pair was now so close to the surface,
the final movement upwards covered only a short
distance.

The subordinate male of Study 1 was last ob-
served to spawn with the female on 25 July 1975,
comprising an estimated total of 57 spawning days
for this pair. Conversely, the subordinate male of
Study 2 completed only 4 days of exclusive paired
spawning with the female before the dominant
male took an active role in the reproductive
activities.

DISCUSSION

It is well known that light and temperature play
a role via the neuroendocrine system in both ini-
tiating and synchronizing reproduction in fish (see
review and discussion by de Vlaming 1974). How-
ever, spawning occurred in the laboratory even
though the fish previously had been exposed to an
unnatural photoperiod and temperature. Temper-
atures were, in fact, at high, stressful levels. It is
possible that the endocrinological events as-

sociated with gonadal recrudescence may have
been initiated 8 to 10 mo or more before the fish
were captured. The photoperiod in the laboratory
was eventually lengthened and regulated to keep
apace of the natural changes beginning 16 days
(Study 2) to 56 days (Study 1) before the first
spawning. Temperatures of 18° to 20°C, well
within levels at which eggs have been found in
nature (Perlmutter 1939; Williams 1967), were
maintained 93 days (Study 2 ) to 126 days ( Study 1 )
prior to the onset of spawning.

Previously published field observations indicate
that tautog spawn sometime between May and
June in the waters of New York (Olla et al. 1974;
Briggs in press) and Rhode Island (Chenoweth
1963; Cooper 1966), with June being the principal
spawning month in Massachusetts waters (Kuntz
and Radcliffe 1917; Bigelow and Schroeder 1953).
These spawning dates are supported by data based
on collections of eggs and larvae from Sandy Hook
Bay estuary (Croker 1965) and are further ex-
tended through mid-August based on similar col-
lections from Long Island Sound (Wheatland
1956; Richards 1959).

That the fish spawned earlier in the laboratory
than they would have in nature supports the sup-
position that the final synchrony may depend on
proximal environmental cues. While the gonadal
recrudescence may have been initiated by events
occurring in nature prior to capture, final syn-
chronization may have been caused by the
changes in temperature and the advancing photo-
period. Because the study was not designed to
examine such questions, assignable causes of the
spawning occurrence must be conjectural.
Nevertheless, whatever the causative environ-
mental events, the animals did achieve reproduc-
tive synchrony.

To date there are no specific descriptions of
spawning behavior in the tautog. In a laboratory
study on tautog in June 1967, Bridges and Fahay
(1968) reported that during a 10-day period, a ripe
female and male both underwent a shading
change between 1500 and 1630 and exhibited be-
havior which the authors described as possible
courtship. Our observations concur with these au-
thors with respect to the daily afternoon shading
alteration of the female. However, their descrip-
tions of the behavior suggested aggressive in-
teractions between the two animals and thus the
male's shading more likely reflected an animal
involved in aggression rather than courtship. The
female and male's behavior further suggest that

595

FISHERY BULLETIN: VOL. 75, NO. 3

either the animals were not in complete reproduc-
tive synchrony or the confines of the aquarium
may have produced behavioral artifacts.

In our studies, pair spawning, with the domi-
nant male tautog being the exclusive partner of
the female, was the prevalent mode of reproduc-
tive activity. However, in Study 2 when spawning
began, the female spawned first with the subordi-
nate male, then both males, and finally only with
the dominant. This transition period, we surmise,
may have been caused by either or both of the
following: 1) due to the small difference in size
(1.3 cm) between the males, dominance may not
have been sufficiently defined initially to inhibit
the subordinate, and 2) the final phase of seasonal
reproductive readiness of the dominant was
slightly behind that of the subordinate. Once the
dominant reached an appropriate level of sexual
maturation, pair spawning involving only the
dominant male and the female occurred exclu-
sively for the remainder of the study.

Pair spawning again proved to be the mode of
gamete release in our laboratory facility when a
single male was in the presence of two gravid
females (Olla and Samet unpubl. data). In July
1976 these two females (approximately 48 and 58
cm) were introduced into the aquarium where the
dominant male from Study 2 was still residing.
During intermittent observations of the fish, pair
spawning occurred five times with the smaller
female, although both females were rushed and
exhibited a high degree of attention towards the
male.

While we have never seen tautog spawning
under natural conditions, it is reasonable to as-
sume from our observations that pair spawning
may play a leading role in the reproductive reper-
toire of this species. However, we reserve judg-
ment as to whether this is the only pattern of
gamete release, especially because of the occur-
rence in Labridae of both paired and aggregate
spawnings within a single species, e.g., Thalas-
soma bifasciatum (Randall and Randall 1963) and
T. lunare (Robertson and Choat 1974), both of
which are protogynous hermaphrodites (Reinboth
1967 and Choat 1969, respectively).

Another factor contributing to our reserve in
assigning only one pattern of reproduction to
tautog is that during recent preliminary field
studies, Olla and Bejda (in prep.) found sexually
mature young tautog, both males and females,
which were of a much smaller size and younger
age than has previously been reported

596

(Chenoweth 1963; Cooper 1966; Briggs in press).
In addition, these young fish did not show sexual
dimorphism of the mandible (Cooper 1967), a
characteristic trait which was conspicuous in the
subjects used in our studies. One explanation for
the absence of the mandibular dimorphism in
these young fish might be that this trait occurs in
older, larger fish. Although we do now know yet
whether the young animals participate in spawn-
ing, the other possibility is that these fish may
represent a different sexual stage than that of the
older fish of our study. It is even possible, as re-
mote as it seems, that hermaphroditism may be
present. The question is raised here because we
know nothing of the behavior or gonadal develop-
ment of these young fish and because hermaphro-
ditism, in the form of protogeny, has been found in
a number of labrids (e.g., 30 species according to
Robertson and Choat 1974).

While it appeared that pair formation did take
place within the laboratory, whether or not a true
pair bonding between mates occurs in nature is
still unanswered. It is possible that in their
natural environment, other male tautog in the
vicinity of a pair could conceivably participate at
the moment of spawning. However, in these cir-
cumstances it is also quite possible that the ex-
treme aggression of a dominant, courting male
would cause other subordinate males to remain
sexually passive or to move away and seek a
female partner elsewhere. The hypothesis that
within a given locale a dominance hierarchy
among males determines which male becomes
sexually active is supported by a field experiment
on Thalassoma bifasciatum by Reinboth (1973).
Additionally, it is quite possible in a natural envi-
ronment that a female might spawn each day with
a different male.

On the other hand, if true pair formation solely
between one male and a female is possible, the
selective advantage here is obvious, inasmuch as
1) it would not be necessary for an animal to ex-
pend energy finding a mate each day, and 2) to
sustain its dominance (and pairing with a female)
the male must continue to be a highly successful
competitor. When the motivation to spawn wanes,
males capable of becoming sufficiently dominant
over others would have priority to act as mates.

Of all the sensory stimuli that could potentially
come into play during tautog courtship, visual
cues arising from the female appeared to be the
most conspicuous. First, the swollen, gravid ab-
domen of the female, which as Youngbluth (1968)

OLLA and SAMET: COURTSHIP AND SPAWNING BEHAVIOR OF TAUTOG

studying the cleaning wrasse, Labroides
phthirophagus, and Potts (1974) studying the
corkwing wrasse, Crenilabrus melops, suggested,
may have served as one of the first important vi-
sual cues to the male. In addition, the development
of the female tautog's saddle, even in its most
rudimentary state 2 to 7 wk before the first spawn-
ing of each study could have played an important
role in identifying the reproductive state of the
female. More specifically, the daily transient
changes in the saddling would have served to iden-
tify the readiness of the female to spawn right up
to the moment of spawning.

The existence and development of reproductive
shading patterns in the female tautog is in distinct
contrast with the situation found in other labrids
in which the conspicuous or bright appearance,
when present, is usually found in males (see Roede
1972, for review and discussion). Substantiation of
the female tautog's spawning pattern was made
during an observation with scuba at approxi-
mately 1500 (EST) on 26 May 1976 near the Fire
Island Coast Guard Station. An adult, gravid
female (approximately 45-50 cm) with a well-
developed saddle was observed swimming in mid-
water along with a dark gray male (A. D. Martin
pers. commun.). (Turbidity and the fact that the
pair moved away from the diver prevented any
further observations.)

Another major difference between tautog and
other labrids regarding coloring or shading is that
the shading change of the female was a dynamic,
transient process each day. This kind of shading
change in tautog falls within the category of
physiological color changes discussed by Roede
(1972), which reflect rapid alterations in shading
and which are also reversible processes. Con-
versely, the descriptions of color patterns in other
labrids all appear to reflect morphological color
changes, which develop only gradually within
each individual and particularly within discrete
life phases or stages.

In concert with these shading changes were ac-
tions of the female that apparently served to en-
hance or facilitate the male's perception of these
visual stimuli. For example, the final sustained
erection of the female's dorsal fin further enlarged
the white area of the saddle. Lifting of the female's
caudal fin, occurring when the saddle and caudal
pattern were maximally developed, was mani-
fested in the final moment before spawning. This
lift, coupled with the female's swimming near the
male in such a fashion as to expose the dilating

vent, provided another stimulus towards which
the male could orient.

Visual shading cues arising from the dominant
male appeared to be minimal except perhaps for
the lightening of its face and lips. These features
may have provided a stimulus to the female indi-
cating the male's motivation to court and spawn,
particularly during rushes directed at the female's
head. The stimulus value of the male's white lips
during courtship displays in Crenilabrus melops
has also been suggested by Potts (1974).

The obvious visual cues of the male, arising
from its rapid approach during a rush, were quite
likely a primary source of stimulation to the
female. It is also possible that there was a second-
ary, lateral-line stimulation, created by the force
of the water currents as the male rushed by and
which may have enhanced the overall response of
the female. Other potential stimuli arising from
either of the mates may have been chemosensory
in origin. We have no basis at this point to conjec-
ture whether or not the animals released and/or
perceived any chemical products (i.e., phero-
mones), which may have functioned to facilitate
reproduction.

An important indicator of the approaching onset
of the reproductive season was the change in be-
havior of the dominant male towards the female. It
gradually ceased being aggressive to the female,
initiated courtship rushes, and permitted her un-
restricted access to any area of the tank. This
behavioral transition from aggressive to courtship
activities is very similar to that observed in Cren-
ilabrus melops (Potts 1974). In this species, which
pair spawn at a nest site, the nesting male is ag-
gressive to both males and females at the onset of
the reproductive period. Eventually, however, in-
stead of approaching a female to chase or bite her,
the male performs an exaggerated courtship,
swimming around the female which apparently
stimulates her to approach the male and his nest.

As with many other species, each of the court-
ship activities of the tautog seem to serve one
major purpose, which was the gradual excitation
and synchronization of the partners prior to the
spawning each day. In the extended period before
the very first spawning of the season, the domi-
nant male appeared to assume the more physically
active role in the early courtship, primarily by
rushing the female. While the female did occa-
sionally follow after or rest near him, she did not
perform any obvious (ritualized) activities.
Nevertheless, even the slight shading changes in

597

FISHERY BULLETIN: VOL. 75, NO. 3

her saddle during a rush may have functioned as a
type of response, communicating to the male her
receptivity and possibly her altering physiological

state.

Once the first and subsequent daily spawnings
began, it appeared that the female now set the
tempo for synchronizing the events leading to
spawning. The first "signal" that spawning was
imminent occurred when the female's caudal
stripe or checkerboard pattern was consistently
maintained, followed by a further broadening and
blanching of her saddle. Then, once her pectoral
swimming, the tail lift, and head-down behaviors
were sustained, the female initiated the final
courtship behavior (i.e., runs). Even though the
male synchronized his movements with hers, the
pace and completion of the runs and upward
spawning motion were contingent on the female's
actions.

The separate behavioral components of the
courtship and spawning repertoire in the tautog
reflect both similarities and differences when
compared with other labrid groups. In the clean-
ing wrasse, Labroides phthirophagus, pair forma-
tion and courtship precede spawning by at least a
week or more (Youngbluth 1968). During this
time the male repeatedly performs rapid ap-
proaches ("passes") towards the side of the female
which she tolerates; however, the male's action in
this case is generally also accompanied by a body
quivering. In some species the only vigorous ap-
proaches by males toward females are described as
chases, such as in the four Halichoeres species
observed by Randall and Randall (1963); the cun-
ner, Tautogolabrus adspersus (Wicklund 1970);
Thalassoma bifasciatum (Randall and Randall
1963); and T. lunare (Robertson and Choat 1974).
In Cirrhilabrus temminckii the male performs a
single rushing action similar to the tautog, but
this only occurs immediately prior to the upward
darting for gamete release (Moyer and Shepard
1975).

In many of the species described above, the
males also perform ritualized swimming patterns
or displays to attract the females. These have been
described as circling, looping, fluttering, dancing,
or simply courtship swimming. The responses of
females among the various species can vary from a
simple approach such as in T. bifasciatum (Rein-
both 1973) to an over, reciprocal response such as
"sigmoid posturing" and "dancing" as in L.
phthirophagus (Youngbluth 1968), or a lateral ap-
proach to the male in which the swollen flank and

genital papilla are presented as in Crenilabrus
melops (Potts 1974).

With the exception of C. melops which spawn on
the sand in a nest, all of the other species men-
tioned above and tautog share a common mode of
swimming or darting rapidly upwards to spawn.
Body bending (only by the male of a pair) in T.
bifasciatum has been observed by Reinboth ( 1973)
as well as the brief alignment of the pair's genital
openings.

ACKNOWLEDGMENTS

We thank Anne L. Studholme, Allen J. Bejda,
and A. Dale Martin for their valuable assistance
throughout all phases of the study. Illustrations of
the spawning act, taken from motion picture films,
were expertly done by Carol Gene Schleifer. We
also thank Myron Silverman for his assistance in
photographing the fish.

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1975. Notes on the spawning behavior of the wrasse, Cir-
rhilabrus temminckii. Jap. J. Ichthyol. 22:40-42.
OLLA, B. L., A. J. BEJDA, AND A. D. MARTIN.

1974. Daily activity, movements, feeding, and seasonal
occurrence in the tautog, Tautoga onitis. Fish Bull., U.S.
72:27-35.
OLLA, B. L., W. W. MARCHION1, AND H. M. KATZ.

1967. A large experimental aquarium system for marine
pelagic fishes. Trans. Am. Fish. Soc. 96:143-150.
PERLMUTTER, A.

1939. Section I. An ecological survey of young fish and eggs
identified from tow-net collections. In A biological sur-
vey of the salt waters of Long Island, 1938, Part II, p.
11-71. N.Y. State Conserv. Dep., Suppl. 28th Annu. Rep.,
1938, Salt-water Surv. 15.
POTTS, G. W.

1974. The colouration and its behavioural significance in
the corkwing wrasse, Crenilabrus melops. J. Mar. Biol.
Assoc. U.K. 54:925-938.

Randall, J. E., and H. A. Randall.

1 963. The spawning and early development of the Atlantic
parrot fish, Sparisoma rubripinne, with notes on other
scarid and labrid fishes. Zoologica (N.Y.) 48:49-60.

REINBOTH, R.

1967. Biandric teleost species. Gen. Comp. Endocrinol.
9:486 (Abstr. 146).

1973. Dualistic reproductive behavior in the protogynous
wrasse Thalassoma bifasciatum and some observations
on its day-night changeover. Helgolander wiss.
Meeresunters. 24:174-191.

RICHARDS, S. W.

1959. Pelagic fish eggs and larvae of Long Island
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ROBERTSON, D. R., AND J. H. CHOAT.

1974. Protogynous hermaphroditism and social systems in
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ROEDE, M. J.

1972. Color as related to size, sex, and behavior in seven
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1959. A quick, compact, two-sample test to Duckworth's
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1956. Pelagic eggs and larvae. In Oceanography of Long
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1970. Observations on the spawning of the cunner in wa-
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1967. Identification and seasonal size changes of eggs of
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599

DISTRIBUTION, SIZE, AND ABUNDANCE OF MICROCOPEPODS

IN THE CALIFORNIA CURRENT SYSTEM AND THEIR POSSIBLE

INFLUENCE ON SURVIVAL OF MARINE TELEOST LARVAE1

David K. Arthur2

ABSTRACT

The California Current system can be divided into onshore and offshore faunal zones by a copepod
indicator species, Mecynocera clausii. Near the outer edge of the onshore zone copepod nauplii densities
were higher than usual. There were about 3 times as many microcopepodids and 12 times as many
nauplii on the average throughout the onshore as in the offshore zone. Feeding habits of larvae of
sardines, anchovies, and jack mackerel may be adapted to the usual naupliar and copepodid concen-
trations of the zone in which they were spawned. The usual concentration of 56- /um and wider nauplii
in the onshore zone was about 3/liter with 17/liter the highest observed which indicates that for
nauplii of all sizes there were usually about 36/liter and with the highest density of 195/liter. These
concentrations are lower than has usually been reported to be required for rearing larval fish in
laboratories. Numbers of nauplii decreased exponentially with increasing size but a naupliar biomass
maximum was found to occur at about the 70 /xm width. Nauplii of this size are ingested at first
feeding by Pacific sardine, northern anchovy, and jack mackerel larvae. It is suggested that larval
feeding habits of these fish have evolved to utilize this important food resource at their first feeding.

Copepods form the bulk of most zooplankton hauls
from the sea and are important because they are
the main convertors of phytoplankton into food
suitable for higher organisms (Marshall 1973).
Copepods are especially important as food for
planktonic larvae of pelagic marine teleosts. Food
of the larvae of commercially important marine
fishes has been widely reported as being primarily
eggs, nauplii, and copepodid stages of small cope-
pods. Yokota et al. (1961) found that food occur-
ring in the feeding larvae of all the 57 species
taken in their primarily coastal samples was
almost entirely small copepods, especially nauplii.
Duka and Gordina (1973) investigated the food of
larvae of 26 species of teleosts from the Medi-
terranean and adjacent areas of the Atlantic and
reported that copepod nauplii composed 90% of
all items eaten by small larvae (2.3 to 5.0 mm).
Stomach content analyses of fish larvae are also
corroborated by population dynamic studies of
plankton organisms. Fish ( 1936) noted that in the
Gulf of Maine a small copepod, genus Pseudo-
calanus, suffers a much higher predation rate

■Based on a portion of a dissertation submitted in partial
satisfaction of the requirements for the Ph.D. degree at the
University of California, Scripps Institution of Oceanography.

2Senior Research Associate, National Academy of Science,
Southwest Fisheries Center, National Marine Fisheries Service,
NOAA, P.O. Box 271, La Jolla, CA 92038.

Manuscript accepted January 1977.
FISHERY BULLETIN: VOL. 75, NO. 3, 1977.

during the naupliar stages than does Calanus
finmarchicus whose eggs (140 /xm wide) and nau-
plii are too large to be. ingested by many fish
larvae.

When it became apparent that the population
of Pacific sardine, Sardinops sagax, was in
serious decline, a research program [later to
become known as CalCOFI (California Coopera-
tive Oceanic Fisheries Investigations)] was initi-
ated in 1949 to investigate the ecology of this
important fish. One part of this investigation was
a study of the food and food resources of sardine
larvae and consisted of two main objectives:
1) determine what the larvae eat, and 2) to study
the abundance and distribution of these food
items. The ultimate purpose was to determine if
feeding conditions, especially for the first feeding
larvae, could be a contributing factor to the sar-
dine's decline, as was proposed by Hjort (1914)
to explain poor year class survival of fishes in
general.

The identifiable food of first feeding sardine
larvae was primarily copepod nauplii ranging
from 25 to 80 fxm but mostly about 70 /xm wide
(Arthur 1976). Nauplii of this size are produced
only by small species of copepods, roughly less
than 1.5 mm long. The assemblage of these small
copepods is composed of many species. Several
genera have often been recorded as being abun-

601

FISHERY BULLETIN: VOL. 75, NO. 3

dant in the plankton as well as in the intestinal
contents of larval fishes. Among these are the
cyclopoid genus Oithona, (especially O. similis),
and the calanoid genera Pseudocalanus and
Paracalanus. Oithona similis, whose first stage
nauplius is 70 /um wide (Oberg 1906) and can,
therefore, be ingested by sardine larvae, composed
over 50^ of the cyclopoid fauna in 37 of the 42
samples off Oregon through Baja California
examined by Olson (1949). Because of the large
number of species, many of whose developmental
stages had not been described, no attempt was
made in this study to identify eggs, nauplii, and
copepodid stages to species.

This report deals with size, abundance, and dis-
tribution of naupliar and copepodid stages of
copepods captured with relatively fine meshed
plankton samplers in and near the California
Current. These small species of copepods will be
referred to as microcopepods, and all postnaupliar
stages, including adults, as copepodids. The term
nauplii will include true nauplii and metanauplii.

SAMPLING METHODS

tember 1950 and from 130 m on cruises from No-
vember 1950 to July 1952.

After a study had been made of the food ingested
by ocean-caught sardine larvae, it became obvious
that very small copepod nauplii are critical in the
ecology of these larvae. Therefore, after August
1951 a plankton sampler of much finer mesh was
used. This sampler was essentially a medium
Epstein net (Sverdrup et al. 1942:379) with a
mouth opening 17.5 cm in diameter, connected by
a canvas collar to a filtering cone constructed of
#20 bolting silk (76 /um in unused condition). This
sampler was hauled vertically from a depth of
50 m and was called the "truncated net."

These three plankton samplers were used be-
tween May 1949 and September 1954. Pertinent
statistics are compared as follows:

Mouth

Mesh

aperture size

diameter

(pm)

No. of

Sampler

(cm)

New

Used

samples

Clarke-Bumpus

12.5

203

120

185

Microplankton

7.6

143

612

Truncated net

17.5

239

1.036

The need for a study of the small crustacean
plankton was anticipated early in the CalCOFI
program. The 1-m net with its relatively coarse
mesh (505 fxm) was considered adequate for
sampling sardine eggs and large copepods and
euphausiids, but most small copepods and nauplii
pass through this size mesh. Starting in May 1949,
a Clarke-Bumpus sampler (Clarke and Bumpus
1940) equipped with a #8 mesh bolting silk net,
(203 /urn in unused condition) was used routinely
at stations in the central and upper southern
California areas. It was towed obliquely from a
depth of 70 m, filtering about 5 m3 of water.

The Clarke-Bumpus sampler was abandoned
after March 1950 in favor of the "high-speed
sampler" (California Academy of Sciences et al.
1950) which was modified by having a mouth
diameter of 7.6 cm, the same as the main fuselage
of this device, rather than being tapered to a
narrower opening as in the original high-speed
sampler. It was equipped with a 143-^m wire
filter and was towed on the same wire as the meter
net and was used because the record it made of
depth versus volume of water filtered could be
used to analyze the meter net track as well as
its own. This modified version was called the
"microplankton sampler." It was towed obliquely
from a depth of 70 m during March 1950-Sep-

602

Because of expansion when wet, and the un-
raveling of threads when used, the aperture size
of used wet silk nets is considerably smaller than
new dry ones. The above "used" values were ob-
tained by measuring aperture sizes, when sub-
merged in water in the laboratory, of nets being
used in the collections. Even with the smallest
aperture size used (56 jam) many nauplii and
copepodids must have escaped. Beers and Stewart
(1967) reported that a significant quantity of
copepods pass through a 35-jiim mesh. Most food
particles of sardine, anchovy, and jack mackerel
larvae, however, are wider than 56 pun (Arthur
1976.)

COUNTING METHOD

The plankton samples were examined in a plas-
tic chamber measuring 60 mm by 70 mm, the
floor of which was lined every 5 mm to form a grid.
Its total fluid capacity is approximately 50 ml
with a water depth of about 12 mm. In practice,
the fluid volume in the chamber measured less
than half of this. If the amount of material in the
sample was not too great, the entire sample was
counted. Most samples taken with the Clarke-
Bumpus and truncated nets contained so much
material that subsampling was necessary. This

ARTIU'K DISTRIBUTION AND AHI'NDAM 'K OK Ml( 'RO( 'OI'KPODS

was accomplished by first measuring the total
fluid volume of the sample, then stirring it vigor-
ously to disperse the material, then drawing off
a convenient amount for examination, and finally
measuring the remainder in order to determine
what percentage the subsample was of the orig-
inal sample.

FAUNAL AREAS IN THE
CALCOFI SECTOR

Although the primary purpose of the micro-
plankton program was a quantitative appraisal
of the microcopepod fauna, a few prominent cope-
pod species were routinely recorded. One of these,
Mecynocera clausii, proved useful as an indicator
organism allowing the CalCOFI sector to be
roughly divided into two plankton faunal areas,
onshore and offshore.

Mecynocera is a monotypic genus. It can readily
be distinguished from other copepods by its excep-
tionally long first antennae (Mori 1964). Its small
size (about 1 mm) places it within the micro-
copepod range. These attributes make it conve-
nient and useful as an indicator of conditions
affecting the microcopepod fauna. Mecynocera
clausii has been reported near the surface
throughout tropical areas of the oceans, as well
as in temperate areas such as the Mediterranean.
In the CalCOFI area its presence may be consid-
ered as indicating the more tropical offshore and
southern waters.

A typical distribution of M. clausii off southern
California and off northern and central Baja Cal-
ifornia is illustrated by data for February 1951
(Figure 1). Mecynocera is characteristic of off-
shore water whereas the occurrence of plutei of
benthic echinoderms may indicate coastal water.
The two boundaries tend to interdigitate, which
must imply alternating tongues of warm offshore
water penetrating toward the coast and jets of
cold onshore water moving out to sea. The 15°C
isotherm supports this interpretation.

Submergence of the water of the California Cur-
rent under the offshore subtropical water may be
indicated at stations where Mecynocera and
plutei were taken together. This would result if
the net in its 130-m deep track caught Mecynocera
near the surface and plutei at some depth where
the submerging water had carried them.

The shoreward boundary of Mecynocera, as
determined by the various cruises, is presented
in Figure 2. In general, the average boundary is

•35°

-30°

120°
_i_

• '

FIGURE 1. — Distribution of Mecynocera clausii and pluteus
larvae during CalCOFI cruise for February 1951 off California
and Baja California.

found about 400 km offshore in the San Francisco
area and inclines toward the coast farther south.
In the northern Baja California area it may im-
pinge upon the shoreline, but it becomes erratic
in the turbulent Punta Eugenia area.

ZONE OF COPEPOD
NAUPLII MAXIMUM

For a given cruise, if each line is examined and
the station which contained the greatest concen-
tration of nauplii is circled and the circled stations
for the various lines are connected, one obtains a
line of maximum copepod nauplii concentrations.
Figure 3 presents a typical distribution of copepod
nauplii and their maximum zone in the Channel
Island area. Two stations have been circled for the
line extending offshore from San Diego. It is com-
mon to find a high local concentration at stations
near the coast and a second high offshore particu-
larly in the area north of Point Conception. Had
the station pattern extended closer to the beach,
higher concentrations of nauplii probably would
have been encountered there. During a 5-mo

603

130°

120°

110°

40'

30°

20°-

W 1 '

- . •

• . ( •■%•- Inner boundary of
• • V Mecynocera

\\ . ' '/r San Froncisco

—

— \

Ct>Njs\\\. • \Pt. Conception
^ \«: ' ' A.^an Diego

40°

-30°

130°

120°

110°

FIGURE 2. — Inner boundary of Mecynocera for individual
CalCOFI cruises from June 1949 to July 1951 off California and
Baja California.

study of plankton off La Jolla, Beers and Stewart
(1970), using 35-/um mesh nets, found that for
the three stations located 1.4, 4.6, and 12.1 km
from shore, naupliar densities averaged 63/liter,
33/liter, and 26/liter, respectively.

The zone of maximum nauplii seems to be asso-
ciated with the Mecynocera boundary, which is
also indicated in Figure 3. The station of maxi-
mum nauplii for a line usually occurs one to three
stations onshore of this boundary.

As may be seen in Figure 3, there appears to be
an association between the zone of maximum
nauplii and the tongue of relatively cold water
(13° and 14° isotherms) extending south of
Point Conception. This cold tongue probably is
nutrient rich water upwelled north of Point
Conception. Shoreward from this zone lies the
counterclockwise gyre of the Southern California
Bight, extending from Point Conception to north-
ern Baja California. Allen (1939) stated that his
most offshore station, located 120 km from the
coast, which is in the general vicinity of the
nauplii maximum, was consistently the richest
station for microcrustacea. Berner (1959) noted
that stations where he found anchovy larvae to

125°

FISHERY BULLETIN: VOL. 75, NO. 3
120° 115°

30'

028

.019

1 Point Conception

\0|

. V.098 •

■039 /

""'■'•. 031
'•., .'o34\

. '-A85 : : •C.0I4

026 >}SQ

.033 ~

?,255 •.

■;-. °UJ W ©

000 / •• XI9?

.001 pQ.
,031 I . : .185

■ooo .• . I :050-

:ooo V. •••;•. ••. /

003 • \ .035--

000 - Number of nauplii (wider than 143pm) per liter

0 -Nauplii maximum

Inner boundary of Mecynocera

Outer boundary of plutei

- Isotherms at 10 meters

30°

125°

120°

115°

FIGURE 3. — Distribution of copepod nauplii (wider than 143 /xm)
and their relation to some other biological and physical
variables during June 1950.

130°

120°

110°

40'

30'

20°

-v^-Copepod nauplii
maximum

San Francisco

Pt. Conception

San Diego

40°

20°

130°

120°

no*

FIGURE 4.— Copepod nauplii maxima for individual CalCOFI
cruises from June 1949 to July 1951.

be feeding were in the area of the copepod nauplii
maximum as described by Arthur (1956).

604

ARTHUR: DISTRIBUTION AND ABUNDANCE OF MICROCOPEPODS

In the San Francisco area, where two maxima
are commonly found, the outer one is usually
about 115 to 400 km offshore (Figure 4). The
maximum zone is consistently found seaward from
the Channel Islands, about 100 to 320 km off the
mainland shore. Occasionally nauplii-rich sta-
tions are found inside the islands. The average
nauplii maximum approaches the coast south of
San Diego, and is adjacent to the shoreline in
northern Baja California, probably a result of up-
welling along the coast. From Punta Eugenia
south, this zone becomes irregular, as does the
Mecynocera boundary.

QUANTITATIVE DISTRIBUTION OF

MICROCOPEPODIDS AND NAUPLII

IN THE CALCOFI AREA

On examining the values obtained in this pro-
gram, it is apparent that there are very wide
ranges in densities. Values for microcopepodids
range from 0.003 to 7.886/liter. Nauplii were
sampled in numbers ranging from 0 to 17.280/
liter. Frequency distributions are highly skewed
toward the lower densities. To overcome this prob-
lem, the data are presented as logarithms to nor-
malize the frequency distributions.

The method used for comparing data is the
ogive, or cumulative frequency curve. The ogive
is useful to depict what percentage of the samples
from an area contains any particular concentra-
tion of copepodids or their nauplii. Furthermore,
in considering concentrations of any two areas,
the value of the 50 percentile concentrations can
be quickly read off and compared. The 50 percen-
tile value in this particular type of distribution
lies very near the mode and so may be considered
to closely represent the most common value of
concentration for a given area.

Ogives for nauplii and microcopepodids as sam-
pled by all Clarke-Bumpus and all microplankton
samples in both the onshore zone and offshore
zone are presented in Figure 5. Because of the
large mesh size of the nets used, most nauplii
escaped which resulted in more copepodids than
nauplii being caught. The truncated net (56-/xm
mesh) caught more nauplii than copepodids. Very
few samples were taken in the offshore zone with
the truncated net and so it cannot be compared
with the other two samplers in this manner. Dif-
ferences in the ratios of onshore zone to offshore
zone for the 50 percentile values are as follows:

• • MICROPLANKTON

o o CLARKE-BUMPUS

100

z
o

H
<

I-

U-

I-
<

Z>
O

60-

40-

20-

" NAUPLII
OFFSHORE ZONE

^MICROCOPEPODIDS
/—ONSHORE ZONE

/microcopepodids
offshore zone

0
0.001.003 .010 .032 .100 .316 1.000 3.162 10.000

UNCORRECTED CONCENTRATIONS (Number/ liter)

FIGURE 5. — Ogives for abundance of nauplii and micro-
copepodids in offshore and onshore zones as sampled with the
Clarke-Bumpus (120-/L/.m mesh) and microplankton samplers
(143- fim mesh).

Sampler Microcopepodids Nauplii

Clarke-Bumpus 3.17:1 12.58:1

Microplankton 2.57:1 11.22:1

There are about two and one-half to three times
as many copepodids in the onshore zone as there
are in the offshore zone. There are, however, about
12 times as many nauplii in the former as in the
latter. There are about four times as many nauplii
per copepodid in the onshore zone as in the off-
shore zone. This is probably a result of the in-
creased fecundity of copepods living in the richer
phytoplankton owing to upwelling in the onshore
zone.

CORRECTING FOR CALIBRATION
ERRORS AND ESCAPEMENT

The ogive was useful to correct errors of the
various samplers used in this survey. Figure 6
presents the ogives obtained for microcopepodids
by all samples taken in the onshore zone with the
three different samplers. Of the three samplers,
the Clarke-Bumpus was the most accurately cali-
brated for volume and so the other two samplers
were corrected to it. Such a correction can be made

605

FISHERY BULLETIN: VOL. 75, NO. 3

0.001 003 .010 .032 .100 .316 1.000 3.162 10.000
CONCENTRATIONS (Number/ liter)

FIGURE 6. — Ogives for abundance of microcopepodids in the
onshore zone as sampled by the three samplers.

by measuring their 50 percentile differences and
adding this value to all the points along their
respective curves. This correction assumes that
all net meshes used retained copepodids in equal
percentages. This is not entirely correct as Beers
and Stewart ( 1967) reported that some copepodids
can escape even a 35-^tm mesh.

Having corrected the volume errors of the three
devices (or, at least, made them comparable in
value), we can now roughly correct for the amount
of escapement by nauplii through the three differ-
ent mesh sizes. Figure 7 presents ogives for nau-
plii in the onshore zone as sampled by the three
devices, the numbers of which have been corrected
for volume strained by values obtained by the
50 percentile differences in Figure 6. These ogives
are based upon the same amount of water filtered,
thus their differences are due to differential
escapement of nauplii. By comparing the 50 per-
centile values in Figure 7, the following approxi-
mation of the size distribution of the naupliar
population in the onshore zone is obtained:

Sampler
Truncated net
Clarke-Bumpus
Microplankton

606

Mesh opening

(fjun)

120

143

Usual number
retained/ liter

2.884

0.095

0.058

IUU

A A CLARKE-BUMPUS

-& ~~° ~~ " /

O O MICROPLANKTON <r

SAMPLER /

P /

^ 80

• • TRUNCATED / /

NET / /

/ /

/ J

H-

i 4

<f> ~

° /

h / /

/ /

/ /
/ /

/ /

> 40

/ J

i r

i /

/ / J

3 20

/ / /
/ A /

o / /
/ / /
/ / /

— i^r /

*--cr- /

•i — « — • — *r~ i i

1 1

.001 .003 .010 .032 .100 .316 1.00 3.16210.000
CONCENTRATION OF NAUPLII ( Number/ liter)

FIGURE 7. — Ogives for nauplii of all sizes retained by each of
the three samplers in the onshore zone corrected for volume
filtered.

A plankton net hauled from some depth to the
surface may pass through a wide range of plank-
ton concentrations but its catch will represent
only the average of these conditions and will not
reveal rich but thin strata that might exist. The
above concentrations, therefore, probably under-
estimate somewhat the highest concentrations
found in the usual water column.

When the ogives for the three samplers are cor-
rected to the Clarke-Bumpus for volume and to
the truncated net for escapement, by their 50
percentile differences (Figure 8), they are similar
over the mid-60% of their ranges. It is interesting
that the three curves for nauplii are so similar
when it is considered that two of them represent,
primarily, the small percentage contributed by
larger nauplii. This implies that the various sizes
of nauplii have essentially the same type of distri-
bution and with the same degree of patchiness.

The slope of an ogive is determined by the de-
gree of dispersion within the samples. If the dis-
tribution of an organism is so homogeneous that
all the observations should fall in one interval,
then the resultant ogive would be a vertical line.
With wider ranges of densities the ogive will slope
less abruptly. By comparing slopes of the two sets
of ogives in Figure 8, it can be seen that the cope-
podid stages are more uniformly distributed than
are nauplii.

ARTHUR DISTRIBUTION AND ABUNDANCE OF MICROCOI'KI'MDS

100

A A CLARKE-BUMPUS

O O MICR0PLANKT0N

TRUNCATED NET

■z.

Ll_

III

Microcopepodids

FIGURE 8. — Comparison of ogives for
abundance of nauplii and micro-
copepodids for all sizes retained by each
of the three samplers in the onshore
zone corrected for volume and escape-
ment.

.001 .003 .010 .032 .100 .316 1.000 3.162 10.00 31.622 100.00
CONCENTRATIONS (Number/ liter)

DISCUSSION

Microcopepod Size and Feeding Habits
of Three Larval Fishes

Feeding habits of larvae of Pacific sardine,
Sardinops sagax; northern anchovy, Engraulis
mordax; and jack mackerel, Trachurus symmetri-
ca, as reported by Arthur ( 1976), may have been
associated with spawning distribution of the adult
fish as well as with the distribution of micro-
copepods and nauplii during the years of this
program. Jack mackerel spawned mainly in the
offshore zone, as can be determined by comparing
the Mecynocera boundary with the distribution
of jack mackerel larvae (Anonymous 1953:36).
Jack mackerel larvae first start to feed when
3.0 mm long and ingest mostly 60- to 70-/um wide
(total range 50 to 200 /xm) copepod nauplii. How-
ever, when they have grown to 3.5 mm their food
is primarily about 125-/xm wide copepodid stages
of small copepod species and when 9.0 mm long
they eat 250- to 450-/u,m wide copepodids of larger
species. The quick change from nauplii to cope-
podids, which is facilitated by their relatively

large mouths, may be related to the low nauplii/
copepodid ratio of the offshore zone.

Most anchovy larvae were caught inside the
Mecynocera boundary (Anonymous 1953:34). The
more omnivorous 3.0-mm long first feeding an-
chovy larvae select food from the 25 to 100 /xm
range with little preference for any size within
this range. Food size increases to 125 /xm when
larvae are about 4.0 mm after which, though there
is some increase, food size does not increase iso-
metrically with the increase in length of larvae.
This curious slow increase in food size appears to
be common to early larval stages of the genus
Engraulis, as can be observed in food-size/larval-
length graphs for Japanese anchovy, E. japonica
(Yokota et al. 1961), Argentine anchovy, E. an-
choita (Ciechomski 1967), Peruvian anchovy,
E. ringens (Rojas de Mendiola 1974), and can be
calculated for northern anchovy, E. mordax, from
data presented by Berner (1959) and Arthur
(1976). This lack of selecting for the largest in-
gestible food size may be related to the high
nauplii/copepodid ratio of the inshore zone and
may also account for the importance of copepod
eggs in the diets of anchovy larvae as reported
by the above authors except Yokota et al. (1961).

607

FISHERY BULLETIN: VOL. 75. NO. 3

Sardines spawn near the Mecynocera boundary,
inshore of the jack mackerel and mostly offshore
of anchovy (Anonymous 1953:22), but, also, more
southerly of the other two. Sardine larvae combine
some feeding characteristics of jack mackerel and
anchovy larvae. Food particle size of sardine lar-
vae increases isometrically with length of larvae
as in jack mackerel but is smaller for unit larval
length and is composed more of copepod eggs and
nauplii as in anchovy larvae.

Microcopepod Densities Influence
Larval Fish Survival

Other investigations in the CalCOFI area, and
in similar latitudes in Japanese waters, helped
to approximate the biomass spectrum of the
naupliar population. Beers and Stewart (1967)
estimated numbers of various microzooplankton
at five locations across the California Current.
Samples were taken by pumping water through
several sizes of niters from depths ranging from
the surface to 105 m. Their values for copepod
nauplii, averaged and integrated, are compared
with the values reported herein as follows:

Q +2.00

z
<

H
UJ

UJ
CD

u.
o

X
H

cr
<

-1.00 —

-2.00

•

THIS REPORT
BEERS and STEWART

- ^

•\

1967

\ o

•\

1 1 1

1 1

1 1 1 1 J 1 1

50 100

MESH SIZE (jjm)

150

FIGURE 9. — Logarithms of the usual densities of various sizes
of nauplii in relation to mesh size. The line is a least square
fit to all data points combined from the equation N = -0.0188w
+ 1.3370.

Nauplii/

Mesh size liter Logrithm

Total no., all sizes 22.078 1.3440

Retained by 35 fim 3.878 0.5886

Retained by 56 /xm 2.884 0.4600

Retained by 103 /xm 0.198 -0.7033

Retained by 120 /*m 0.095 -1.0223

Retained by 143 /xm 0.058 -1.2366

Source
Beers and Stewart
Beers and Stewart
This report
Beers and Stewart
This report
This report

Beers and Stewart

N = -0.01976u; + 1.31857

r = 0.9994, r

This report

2 -

0.9988.

N = -0.02029u> + 1.5577
r = 0.9900, r2 = 0.9801.

(2)

(3)

Logarithms of the above, plotted in Figure 9,
are highly correlated with mesh size for the two
individual sets of data as well as when they are
combined. The line in Figure 9 is a least square
fit to all data points combined and is expressed as:

N = -0.0188u; + 1.3370
(intercept at size 0)

(1)

where N is concentration of nauplii (number per
liter) and w is mesh aperture size. The correlation
coefficient, r, is 0.9931 and the coefficient of de-
termination, r2, implies that 98.62% of the varia-
tion of naupliar concentrations can be explained
by mesh size alone.

Least square fits for the two individual sets of
data are as follows:

The microcopepod assemblage in onshore water
off the southern California-northern Baja Cali-
fornia coast is strikingly similar to that in coastal
waters at the same latitudes on the other side of
the Pacific. Yokota et al. (1961) measured widths
and lengths of 8,839 copepod nauplii and 1,389
copepodids from 666 samples captured in 1-liter
containers from an area off the southeast coast
of Kyushu over a 2-yr period. Average widths and
lengths of nauplii were 67.7 and 156.1 /xm, respec-
tively, with a length to width ratio of 2.306.
Assuming a cylindrical form, the average Kyushu
nauplius has a volume of about 562,000 /j.m3
which differs by only about 10% from the
510,000 tim3 volume of the average La Jolla nau-
plius (Beers and Stewart 1970). Concentrations
ranged from 0 to 524 nauplii/liter (only two
samples were greater than 100/liter) with an

608

ARTHUR: DISTRIBUTION AND ABUNDANCE OF MICROCOPEPODS

average of 13.27/liter. Size distribution as calcu-
lated from the data of Yokota et al. (1961) is:

Width of nauplii

All sizes

>50 pm

>100 pm

>150 fim

>200 fxm

Average number/ liter
13.27
3.87
0.53
0.10
0.05

In comparing the Kyushu to the California area
it appears that there are fewer very small nauplii
but about twice as many larger nauplii. These
differences may result from the Kyushu samples
being taken at the surface whereas the California
samples were collected at varying depths.

Usual densities of total nauplii and copepodids
of all sizes calculated from the several investiga-
tions discussed herein are as follows:

Nauplii/ Copepodids/

liter

36.12

1.41

13.27

2.10

22.08

36.35

34.33

4.17

Source
This report, Equation (3)
Averaged from Yokota et al. 1961
Averaged from Beers and Stewart 1967
Averaged from Beers and Stewart 1970

The calculated number of nauplii of all sizes
from this report appears to be somewhat high
which may result from being derived by extrap-
olating from Equation (3). The average number
of copepodids found by Beers and Stewart (1967)
appeared to be much higher than the other inves-
tigations and may be a result of sampling an un-
usually rich but short-lived condition (all samples
were taken during a 7-day period). Numbers of
nauplii and copepodids of Beers and Stewart
(1970) should be somewhat higher than the av-
erage for coastal areas because they were taken
very close to the beach. In general, the usual den-
sities in onshore areas at these latitudes (30°-
35°N) is about 1.5 to 4 copepodids/liter and about
13 to 30 nauplii/liter. These densities are similar
to those found by Allen ( 1939) who, while studying
phytoplankton off California by trapping 5-liter
samples, found that the combined densities of
nauplii and copepodids ranged from 10 to 30/liter.
Copepod nauplii average about 20-30/liter in
Japanese coastal waters and 10 or less/liter in
the warm offshore Kuroshio (Honjo et al.3'4).

These densities are considerably lower than
those usually reported to be required to support
growth of marine teleost larvae in the laboratory
as is illustrated by a few examples. O'Connell
and Raymond (1970) found poor survival of an-
chovy larvae in densities of nauplii and copepodids
of less than 4,000/liter. Hunter (in press) used
100,000 Gymnodinuml liter combined with 8,000
to 115,000 rotifers/liter to grow early anchovy
larvae. Houde (1975) found best survival of larval
sea bream, Archosargus rhomboidalis, was on
50- to 100-pm wide nauplii and copepodids in
densities of 1,500-3,000/liter, but 10% survived
at 100/liter at low larval stock densities. In coastal
and offshore areas even the highest densities of
nauplii reported do not equal those used in most
laboratory rearing experiments. The highest con-
centration of larger than 56-/xm nauplii I encoun-
tered was 17.28/liter which indicates that, calcu-
lating from Equation (1), for nauplii of all sizes
there were about 195/liter. Highest concentra-
tions reported by others are 524/liter (Yokota
et al. 1961), 180/liter (Beers and Stewart 1970),
and 134/liter (Allen 1939).

Gallagher and Burdick (1970) calculated that
the mean distance R, between a particle and its
nearest neighbor in a random three-dimensional
array can be computed from R = 0.553960p ',
where p is their mean density in space. At concen-
trations of 25 nauplii/liter the distance from the
mouth of a fish larva to the nearest nauplius is
on the average about 18.9 mm, whereas at 200
nauplii/liter this distance is 9.5 mm.

Concentrations approaching laboratory re-
quirements are encountered in localized condi-
tions, i.e., Schnack (1974) caught nauplii with a
55-pm net in numbers up to 917/liter in a shallow
fjord off the western Baltic. Lasker (1975) found
the dinoflagellate, Gymnodinum splendens, in
the ocean in high enough densities (20,000-
40,000/liter) to support life of early laboratory-
spawned anchovies. These densities were depen-
dent on stable oceanic conditions which were
quickly dispersed by a storm.

The reason for the disparity between the ob-
served naupliar densities in the ocean and the

3Honjo, K., T. Kidechi, and H. Suzuki. 1959. On the food
distribution and survival of post larval iwashi-I-Distribution
of food organisms, the food of the anchovy and ecologically
related species along the southwestern Pacific coast of Honshu,

Sept.-Nov. 1958. Reports on the major coastal fish investiga-
tions, and the investigations for forecasting of oceanographic
conditions and fisheries (Preliminary Report), February 1959,
7 p. Engl, transl. by S. Hayashi.

"Honjo, K., T. Kitachi, and M. Kudo. 1957. Food of the post-
larvae of iwashi. Reports of the major coastal fish investigations
for 1956 (Preliminary Report) November 1957, 5 p. Engl, transl.
by S. Hayashi.

609

FISHERY BULLETIN: VOL. 75, NO 3

densities required for larval survival in the
laboratory may be that present microplankton
sampling techniques do not detect small but dense
aggregations of nauplii which, however, can be
found by fish larvae. It, also, may be that present
rearing techniques do not approximate oceanic
conditions sufficiently to permit assaying of
actual prey concentrations required to allow sig-
nificant larval survival. Blaxter (1965) reported
that the condition factor of herring larvae living
in the ocean is worse than that of larvae which
died presumably of starvation in the laboratory.
This may attest to greater ability of larvae to
survive poor rations in the usual oceanic environ-
ment than in the laboratory.

Maximum of Naupliar Biomass Spectrum

The abundance of copepod nauplii decreases
exponentially with increasing size of individuals
(Figure 9), whereas the volume of an individual
nauplius increases exponentially with increasing
size (roughly by the cube of width). When the
naupliar size range is divided into 10-/xm wide
size classes and the average volume per nauplius
is multiplied by numbers of individuals per class
(calculated from the equation for combined data,
Figure 9) it is seen that the naupliar biomass
is at a maximum at about the 70 yum width
(Figure 10) even though there are many more
nauplii of smaller sizes.

Figure 10 includes, also, the food-particle size
range at first feeding of larvae of Pacific sardine,

RANGE OF FOOD WIDTH AT FIRST FEEDING

• SARDINE

• OVERLAP

ANCHOVY

JACK
MACKEREL

= o

< Q
z 5

9 2-

J I l I i I i i_

J I I I l_

100 150

WIDTH OF NAUPLII ( jim )

200

FIGURE 10. — Biomass spectrum of naupliar size range compared
with food size at first feeding of the larvae of three fishes in
the California Current system.

610

northern anchovy, and jack mackerel (Arthur
1976). It is interesting to note that these ranges
overlap at the 50- to 80-/xm width range which
brackets the naupliar biomass spectrum maxi-
mum. This suggests that larval feeding habits of
these three fishes have evolved to take advantage
of this important food resource at first feeding.

ACKNOWLEDGMENTS

I express my appreciation to Martin W. John-
son, Reuben Lasker, and Paul E. Smith for their
helpful comments and criticisms during the prep-
aration of the manuscript.

LITERATURE CITED

Allen, w. e.

1939. Micro-copepoda in marine phytoplankton catches.
Science (Wash., D.C.) 89:532-533.

ANONYMOUS.

1953. California Cooperative Oceanic Fisheries Investiga-
tions. Progress report, 1 July 1952 to 30 June 1953.
Calif. Dep. Fish Game, Mar. Res. Comm., 44 p.

Arthur, D. k.

1956. The particulate food and the food resources of the
larvae of three pelagic fishes, especially the Pacific sar-
dine, Sardinops caerulea (Girard). Ph.D. Thesis, Univ.
Calif., Scripps Inst. Oceanogr., La Jolla, 231 p.

1976. Food and feeding of larvae of three fishes occurring
in the California Current, Sardinops sagax, Engraulis
mordax, and Trachurus symmetricus. Fish. Bull., U.S.
74:517-530.

Beers, J. R., and G. L. Stewart.

1967. Micro-zooplankton in the euphotic zone at five
locations across the California Current. J. Fish. Res.
Board Can. 24:2053-2068.

1970. Numerical abundance and estimated biomass of
microzooplankton. In J. D. H. Strickland (editor), The
ecology of the plankton off La Jolla, California, in the
period April through September, 1967, p. 67-87. Bull.
Scripps Inst. Oceanogr., Univ. Calif. 17.
BERNER, L., JR.

1959. The food of the larvae of the northern anchovy,
Engraulis mordax. [In Engl, and Span.] Inter-Am. Trop.
Tuna Comm., Bull. 4:1-22.

Blaxter, J. H. s.

1965. The feeding of herring larvae and their ecology in
relation to feeding. Calif. Coop. Oceanic Fish. Invest.
Rep. 10:79-88.

California academy of Sciences and Others.

1950. California Cooperative Sardine Research Program.
Progress report 1950. Calif. Dep. Nat. Resour., Mar.
Res. Comm., 54 p.
CIECHOMSKI, J. D. DE.

1967. Investigations of food and feeding habits of larvae
and juveniles of the Argentine anchovy Engraulis an-
choita. Calif. Coop. Oceanic Fish. Invest. Rep. 11:72-81.
CLARKE, G. L., AND D. F. BUMPUS.

1940. The plankton sampler-an instrument for quantita-

AKTHl'K DISTKIHl'TION AND ABUNDANCK OK MH'KOCOI'KI'ODS

tive plankton investigations. Limnol. Soc. Am. Spec.
Bull. 5:1-8.
DUKA, L. A.. AND A. D. GORDINA.

1973. Abundance of ichthyoplankton and feeding of fish
larvae in the Western Mediterranean and adjacent areas
of the Atlantic Ocean. Hydrobiol. J. 9(21:54-59.
FISH, C. J.

1936. The biology of Pseudocalanus minutus in the Gulf
of Maine and Bay of Fundy. Biol. Bull. (Woods Hole)
70:193-216.
GALLAGHER, B. S., AND J. E. BURDICK.

1970. Mean separation of organisms in three dimensions.
Ecology 51:538-540.

HJORT, J.

1914. Fluctuations in the great fisheries of northern
Europe, viewed in the light of biological research.
Rapp. P.-V. Reun. Cons. Perm. Int. Explor. Mer 20:
1-228.

HOUDE, E. D.

1975. Effects of stocking density and food density on
survival, growth and yield of laboratory-reared larvae
of sea bream, Archosargus rhomboidales (L.) (Sparidae).
J. Fish Biol. 7:115-127.

HUNTER, J. R.

In press. Behavior and survival of northern anchovy
Engraulis mordax, larvae. Calif. Coop. Oceanic Fish.
Invest. Rep. 19.
LASKER, R.

1975. Field criteria for survival of anchovy larvae: The
relation between inshore chlorophyll maximum layers
and successful first feeding. Fish. Bull., U.S. 73:
453-462.

Marshall, S. M.

1973. Respiration and feeding of copepods. Adv. Mar.
Biol. 11:57-120.

MORI, T.

1964. The pelagic copepoda from the neighboring waters
of Japan. The Soyo Company, Inc., Tokyo, 150 p.
OBERG, M.

1906. Die metamorphose der Plankton-copepoden der
Dieler Bucht. Wiss. Meeresunters. Dtsch. Meere, in
Kiel, abut. Kiel. 9:37-103.
O'CONNELL, C. P., AND L. P. RAYMOND.

1970. The effect of food density on survival and growth
of early post yolk-sac larvae of the northern anchovy
(Engraulis mordax Girard) in the laboratory. J. Exp.
Mar. Biol. Ecol. 5:187-197.

Olson, j. b.

1949. The pelagic cyclopoid copepods of the coastal waters
of Oregon, California and Lower California. Ph.D.
Thesis, Univ. California, Los Ang., 208 p.
ROJAS DE MENDIOLA, B.

1974. Food of the larval anchoveta Engraulis ringens J.
In J. H. S. Blaxter (editor), The early life history offish,
p. 277-285. Springer- Verlag, Berl.

SCHNACK, D.

1974. On the biology of herring larvae in the Schlei Fjord,
Western Baltic. Rapp. P.-V. Reun. Cons. Int. Explor.
Mer 166:114-123.
SVERDRUP, H. U„ M. W. JOHNSON, AND R. H. FLEMING.

1942. The oceans, their physics, chemistry, and general
biology. Prentice-Hall, Inc.. N.Y., 1087 p.
YOKOTA, T., M. TORIYAMA, F. KANAI, AND S. NOMURA.

1961. Studies on the feeding habit of fishes. [In Jap.,
Engl, summ] Rep. Nankai Reg. Fish. Res. Lab. 14, 234 p.

611

ABUNDANCE AND POTENTIAL YIELD OF THE SCALED SARDINE,

HARENGVLA JAGUANA, AND ASPECTS OF

ITS EARLY LIFE HISTORY IN THE EASTERN GULF OF MEXICO1

Edward D. Houde2

ABSTRACT

Eggs and larvae of the scaled sardine, Harengulajaguana, were collected in 1971-74 from the eastern
Gulf of Mexico to determine spawning seasons, spawning areas, adult biomass, and fisheries potential.
Aspects of the early life history of the species also were studied. Spawning occurred from January to
September, but was most intense from May to August, when surface temperatures ranged from 20.8° to
30.7°C and surface salinities were 29.9 to 36.9%o. All spawning occurred between the coast and the
30-m depth contour, mostly within 50 km of the coast. The biomass of scaled sardines, based on annual
spawning estimates, apparently increased from 1971 to 1973, the mean estimate for the 3 yr being
184,527 metric tons. Potential yield estimates, based on the 3-yr mean biomass, ranged from 46,000 to
92,000 metric tons. Larval abundance and mortality rates were estimated from 1973 data. More than
99. 9^ mortality occurred between time of spawning and attainment of 15.5 mm standard length at
20 days of age. Comparisons were made of scaled sardine distribution, abundance, potential yield, and
larval mortality with those of other eastern Gulf clupeids.

Scaled sardine, Harengulajaguana Po-ey, is abun-
dant in coastal waters of the western Atlantic
from New Jersey to Santos, Brazil, including
the Gulf of Mexico (Berry 1964). It is common
from Florida to Brazil (Rivas 1963), but there are
no large-scale directed fisheries for the species.
Klima (1971) reported it to be an abundant,
surface-schooling species that is usually found
within the 20-fathom curve in the northeastern
Gulf of Mexico. It is one of the most common
species in Gulf Coast estuaries (Gunter 1945;
Springer and Woodburn 1960; Roessler 1970).
Because of its abundance, it is an important latent
fishery resource in the Gulf of Mexico and Carib-
bean region (Reintjes and June 1961; Bullis and
Thompson 1970; Klima 1971). Small catches of
Harengula spp. totalling 2,189 metric tons in 1974
presently are landed by Cuba, Brazil, and the
Dominican Republic (Food and Agriculture Or-
ganization 1975). No reported catches are made
by the United States, but a small amount, prob-
ably less than 500 tons annually, is landed in
Florida for bait in commecial and recreational
fishing.

Some aspects of the biology of scaled sardines
are known. Low (1973) discussed the species and
its occurrence in Biscayne Bay, Fla., including
food habits and juvenile growth rates. Fecundity,
size at maturity, and spawning were reported by
Martinez and Houde (1975). Roessler (1970) dis-
cussed growth, recruitment, and the relationship
of environmental factors to scaled sardine abun-
dance in an Everglades estuary, and Springer
and Woodburn (1960) discussed its ecology in
Tampa Bay. Eggs and larvae have been described
by Matsuura (1972), Houde and Fore (1973),
Houde et al. (1974), and Gorbunova and Zvyagina
(1975).

Objectives of this study were to estimate scaled
sardine biomass and fishery potential in the east-
ern Gulf of Mexico from the distribution and abun-
dance of its eggs and larvae. Information on the
early life history also was obtained. Similar
studies on round herring, Etrumeus teres, and
thread herring, Opisthonema oglinum, were re-
cently published (Houde 1976, 1977a, b).

METHODS

'This is a contribution from the Rosenstiel School of Marine
and Atmospheric Science, University of Miami, Miami, Fla.

2Di vision of Biology and Living Resources, Rosenstiel School
of Marine and Atmospheric Science, University of Miami,
4600 Rickenbacker Causeway, Miami, FL 33149.

Methods to determine scaled sardine biomass
and fisheries potential are the same as those used
for round herring and thread herring (Houde
1977a, b). Collecting methods were described
(Houde 1977a), and summarized station data from

Manuscript accepted November 1976.
FISHERY BULLETIN: VOL. 75, NO. 3, 1977.

613

FISHERY BULLETIN: VOL. 75, NO. 3

the 17 ichthyoplankton cruises have been pub-
lished (Houde and Chitty 1976; Houde et al. 1976).
The survey area and its potential sampling sta-
tions were illustrated in figure 1 of Houde (1977a,
b). Analytical and statistical procedures are based
on those discussed by Saville (1964), Ahlstrom
(1968), and Smith and Richardson (in press).

RESULTS AND DISCUSSION

Occurrence of Eggs and Larvae

A total of 19,183 scaled sardine eggs and 3,828
larvae were collected during the 17 cruises, in
which 867 stations were sampled. Scaled sardines
composed 59.8% of all clupeid eggs collected and
their larvae composed 13.2% of all clupeid larvae.
Scaled sardine eggs made up 6.39c of the total
fish eggs from the 867 stations and their larvae
constituted 2.7% of the total larval fish catch.

Scaled sardine eggs or larvae were collected on
cruises from January through September, but
they were most abundant from May through
August (Table 1). Stations where they occurred
are given in Figure 1. Distribution and abundance
of eggs and larvae are illustrated for the May
through August cruises (Figures 2-5). Spawning
from January to March probably is confined to
the southernmost parts of the survey area, since
eggs and larvae were collected only at stations
south of lat. 26°N on cruises during those months.

No eggs were collected where depths exceeded
30 m (Figure 1). Larval distributions were similar
to those for eggs, except for a single anomalous
occurrence of larvae at a station on the 200-m
depth contour (Figures 1, 3). On cruises CL7405
and CL7412 several stations nearer to shore (of
only 4-10 m depth) than any on previous cruises
were sampled (Figure 5). On cruise CL7412, when
intense spawning was taking place, catches of
eggs at the nearshore stations exceeded catches
at the regular stations. Mean egg abundance
under 10 m2 at positive stations was 1.85 times
greater at the nearshore stations than at the reg-
ular stations ( 158.93 compared with 85.75). Log10
transformed means were tested in a /-test.

No. of stations

with scaled

Stations

sardine eggs

Log10 mean LogU) Sj

Regular

1.0056 0.3343

Nearshore

1.8118 0.1913

^calc

2.15*

^0.05(2)18 =2.10

Differences were significant (P<0.05). Failure
to sample nearshore stations on earlier cruises
probably resulted in an underestimate of scaled
sardine spawning and also an underestimate of
adult biomass if egg distribution during cruise
CL7412 was representative of earlier cruises.

The observed egg and larvae distributions indi-
cate that most adults are located where depth

TABLE 1. — Summarized data on cruises to the eastern Gulf of Mexico, 1971-74, to estimate abundance of scaled sardine eggs and
larvae. GE = RV Gerda, 8C = RV Dan Braman, TI = RV Tursiops, 8B = RV Bellows, IS = RV Columbus Iselin, CL = RV Calanus.

Number
of

Positive

^tatinn^

Positive

Mean egg abi.

indance under 10 m2

Mean larvae

abundance under 10 m2

Cruise

Dates

stations

for eggs'

for larvae2

All stations

Positive stations

All stations

Positive stations

GE71013

1-8 Feb. 1971

064

23.05

0.00

8C7113

TI7114

7-18 May 1971

123

0.78

64.66

6.73

51.52

GE7117

26 Juried July 1971

1.67

19.95

0.00

8C7120

TI7121

7-25 Aug. 1971

146

0.83

28 09

0.21

4.37

TI7131

8B7132

GE7127

7-16 Nov. 1971

0.00

—

8B7201

GE7202

1-11 Feb. 1972

0.00

—

0.00

—

GE7208

1-10 May 1972

1.68

76.21

1.24

11.57

GE7210

12-18 June 1972

35.31

146.94

5.97

2278

IS7205

9-17 Sept. 1972

000

—

0.16

4.70

IS7209

8-16 Nov. 1972

0.00

—

0.00

—

IS7303

19-27 Jan. 1973

000

—

0.01

0.26

IS7308

9-17 May 1973

14.38

154.16

9.26

38 34

IS7311

27 June-6 July 1973

31.59

174.14

0.59

5.51

IS7313

3-13 Aug. 1973

67.49

747.09

10 86

50 26

IS7320

6-14 Nov. 1973

0.00

—

0.00

—

CL7405

28 Feb.-9 Mar. 1974

0.00

—

0.39

4.06

CL7412

1 -9 May 1 974

50.29

125 82

14.45

2879

'Positive station is a station at which scaled sardine eggs were collected.

2Positive station is a station at which scaled sardine larvae were collected.

3An ICITA 1-m plankton net was used on this cruise. On all other cruises a 61 -cm bongo net was used.

614

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF SCALED SARDINE

FIGURE 1 . — Top. Stations in the survey area where eggs of scaled
sardines were collected at least once during 1971-74. Stations
where eggs did not occur are indicated by dots. Bottom. Stations
in the survey area where larvae of scaled sardines were collected
at least once during 1971-74. Stations where larvae did not
occur are indicated by dots.

is <20 m and that nearly all are found within
the 30-m depth contour. Spawning adults are con-
fined to a band within 85 km of the coast. Klima
(1971) reported that scaled sardines in the Gulf
of Mexico usually are found within the 20-fathom
curve (36.5 m), but he noted occasional occurrence
over depths as great as 165 fathoms (302 m).
Brazilian scaled sardines also spawned near the
coast, within 18.5 km of shore where water depth
was <65 m (Matsuura 1972).

There were no areas in the eastern Gulf where
consistently high egg or larval catches occurred
that would suggest great concentrations of adults.

Consistent catches of eggs and larvae between
lat. 24 45'N to 25°45'N and long. 81°30'W to
82°30'W, as well as just north of Tampa Bay be-
tween lat. 28°00'N to 28°30'N and long. 82°45'W
to 83°15'W did indicate that scaled sardines
usually were abundant in those areas.

Mean egg abundances for the 17 cruises ranged
from 0.00 to 67.49 under 10 m2 of sea surface
(Table 1). Considering only positive stations,
means ranged from 19.95 to 747.09 under 10 m2
(Table 1). Abundances of eggs at stations rarely
exceeded 100 under 10 m2 of sea surface during
1971 and 1972, but frequently were between 100
and 1,000 under 10 m2 during 1973 and 1974 (Fig-
ures 2-5). Only once, in August 1973, did abun-
dance of eggs exceed 1,000 under 10 m2 ( Figure 4).

Cruise means for scaled sardine larval abun-
dances ranged from 0.00 to 14.45 under 10 m2
when all stations were considered, and from 0.26
to 51.52 under 10 m2 at positive stations (Table 1 ).
At positive stations larval abundances usually
ranged from 11 to 100 under 10 m2, and exceeded
100 under 10 m2 at only eight stations during
1971-74 (Figures 2-5).

Most scaled sardine eggs and larvae were found
nearer to shore than those of either thread herring
or round herring (Houde 1977a, b). However,
there was considerable overlap in areas and sea-
sons of occurrence of thread herring and scaled
sardine spawning. Eggs and larvae of scaled sar-
dines and round herring did not occur together
because round herring did not spawn in water
shallower than 30 m, and most spawning by that
species occurred during winter.

Temperature and Salinity Relations

Scaled sardine eggs were collected at surface
temperatures from 20.8° to 30.7°C and at surface
salinities from 29.92 to 36.88%<>. Larvae ^5 mm
standard length (SL), 5 days or less in age, were
taken at surface temperatures from 18.4° to 30.5°C
and surface salinities of 27.27 to 36.88%<>. Vertical
sections showing temperature and salinity pro-
files for cruises during the scaled sardine spawn-
ing season indicated that surface temperatures
differed from those at 10 m by a maximum of only
1°C, but that a maximum difference of 4°C could
occur at 30 m. The difference between the surface
and the 30-m depth usually did not exceed 2°C.
Salinity differences between the surface and 10 m
were always <0.5%o and never exceeded 1.5%o

615

FISHERY BULLETIN: VOL 75. NO. 3

8C 7113 S Tl 7111)

Harengula jaguana eggs

Iay 1571

8C 7113 S TI 7111

Harengula jaguana larvae

May 1171

+ + 4 + *■ s. V

50m-

* *+■*-+ v_- \

*'•+ + + + + + V \

+\ 4 4 4 + 4 \ K^

+ -H++-+++- / Vn)

+ * + +■*- + #/ Y

+ i /f?\ft V

+ + +•*■* + + >j y \

+ 44+) 4 + 4 »<* \

* + * \* f * \J7 <J A

+ +. + <f. + 4- + ^ V/ f

* + ♦'.+ ++ + 1^X1

*-++»+ 4 4 4 |

+ ♦ +\+ + + + V^ J-

+ 4 4\ + 4 + + 4 ^> /f

Number under 10m2
+ 0

• <l

• l-IO

• ii-ioo

• 101 - 1000
© >I000

+ +■+; + *++* •? /j

+ + !+ + + + - 9 C&^-rfr

* *■; * + + + >^

8C 7120 8 TI 7121

Harengula jaguana eggs

August 1971

- + +

+■

T 1 J

+ 4

■t-

^-s^*^^ \ \

+ 4

450

n-t

4 4

+\ + \ fc^

4 +

4A+4 + 4-+/ Y

- 4 4

4 + 4\ 4- + 4- + HAu V

4- 4- 4".f 4 + + \Iy \
4 +■ + + -k + +• tr \
++4++«»\ r\ ^

4- 4 4 4 i. 4- 4- • V-- £^ J \

+ 4- ♦» y + +■ + Y[ ^-/ |

4 + + 4 4 U- 4 + 4- \Z.

4 4- +-\ + 4 4 4- *) 1
4 + 4-\+ 4-4-4 V |-

Number

under

10m

4 0

♦*++*+++++ ^y j?

+ 4 44 4|4+44 + •! / j

• l-IO

• 11-100

• 101-1000

4 4+44 + •+ V$~s-*T
4 4 4 4-J 4- 4 4 • ^"^A^
+ 4 +_t • • ^-^

50m-.

4 • + 4 #V V

* + * + • V-j \

"'•.+ 4 4 4 4 * V \
4\ + 4 4 4 • I *fc.
4 4, + 4 4- + % J 9S)

**+• + ++•/ Y

+ \ /<Sa \
4- 4 4'+ 4 4-4- >J/ \
4- + 4- 4v + +• +■ \r \

4 ■»- 4 f + + • rt v f

4- 4- 4- Vf 4 + + ^T
4- 4- +\4- + 4- • \

Number under 10m2
4 0

• <l

• i-io

• 11-100

• 101 - 1000
© >I000

4 4- +-'.+ 4-4 4 V^ J-

4 4- +\(+ 4- 4- 4- « ^V Jf

+ 4 4l44+4# X (j

+ + + •*■++•*■* ^ ^r+lf

* +; + 4 + + ^Vj^A

8C 7120 « TI 7121
Harengula jaguana larvae

August 1971

30'

- * *■ •

• ^

4 4 +

+ *\

X^^ \ \

4 4 +

*■ 4 +

450m-t

\^f \

4 + +

4 t

+\ * \ Vy

4 4

t4,+ 44+/ Y

28°

- ♦ 4 4

4 t

T ♦ V, 4 + 1- + -H A. \

+ + +'t + + + \j y \

4 +■ ♦■ 4 4> 4 ♦ t ir \

* ' * *• * * * \ /\ ^

4 4 + 4- +, + 4 4 \-» y \ \

*" + + V+#+\J* ^4 |
+ f 4+4'r4+ + + *<L
♦•4+1+ 4-4-+ 1

* * *\* * * * V. J"

4 4 +\+ + + + + ^^ y^

i:b"

Number under

10m2

+ + 4+4|444-»-+ T? /i

• l-IO

• 11-100

• I01-I00C

4 + ■+■ +J + 4 4 • ^iy/
+ 4 A- + # • tnZ~'^

FIGURE 2. — Distribution and abundance of scaled sardine eggs and larvae. Catches are standardized to
numbers under 10 m2 of sea surface. A, B. Cruise 8C7113-TI71 14, May 1971. C, D. Cruise 8C7120-TI7121,
August 1971.

between the surface and 30 m. The buoyant eggs
and pelagic larvae probably developed at tempera-
tures and salinities similar to those at the sea
surface.

Relatively few eggs or s=5.0-mm larvae occurred
where surface temperature was <24.0°C over the
1971-74 period (Figure 6). For eggs, 82.3% of the
station occurrences were at surface temperatures
above 24°C; for larvae, 71.0% occurred above 24°C.
Although spawning occurred over a wide salinity
range, 71.0% of the stations with eggs had salini-
ties that exceeded 35.0%..; 62.3% of the stations
with s=5.0-mm larvae had salinities above 35.0%.,.

Matsuura (1972) collected eggs and larvae of
Brazilian scaled sardine at temperatures and
salinities within the ranges observed for eggs

and larvae in the eastern Gulf. Spawning occurred
at temperatures and salinities similar to those
recorded for thread herring (Houde 1977b). Scaled
sardine eggs and larvae were found over slightly
wider ranges of temperature and salinity than
were thread herring, reflecting the slightly longer
spawning season of scaled sardines in the eastern
Gulf and their tendency to be most abundant
nearer to the coast where temperatures and salini-
ties varied most.

Egg and Larval Abundance in
Relation to Zooplankton

There was no apparent relationship between
either egg or larval abundance at stations and

616

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF SCALED SARDINE

GE 7238
Harengula jaguana eggs

Iay 1972

30»

50m-. %

28°

* '", ♦ + • /

♦ *

* * \ * ' "C

+ + + 1 ♦ t ^

, <}"]

2b°

Number under 10m2
t 0
• <l

• l-IO

• 11-100

• 101-1000
© >IO0O

*'. * *

Jkfr***

GE 7208

Harengula jaguana LARVAE

Nay 1972

30m-.

+ ■•.+ +•/ y

i- + * '-. *■ * °o \

/y.V 0)

Number under 10m2

• 0

• <l

• l-IO

• 11-100

• 101-1000
© >I000

*! * • ^TrV/

GE 7210

Harengula jaguana eggs

June 1972

GE 7210
Harengula jaguana larvae

50m-

r 1 t

+ V^ a. \
'"-. + • i/ \

Y.Vfc ^ )

Number under 10m2
t 0

• <l

• l-IO

• 11-100

• 101-1000
© >I000

: + • \ A

June 1972

30°

50m-

28°

\ + + \r \

\ + • V J.

iib*

Number under 10m2

t 0
• <l

: * • \ fl

• l-IO

• 11-100

• 101-1000

FIGURE 3. — Distribution and abundance of scaled sardine eggs and larvae. Catches are standardized to
numbers under 10 m2 of sea surface. A, B. Cruise GE7208, May 1972. C, D. Cruise GE7210, June 1972.

volume of zooplankton collected in the 333-/um
mesh bongo net in 1972-74. Mean zooplankton
volume was 153.4 cm3/l,000 m3 in 1972-74
(Houde and Chitty 1976). Highest abundances of
scaled sardine eggs and larvae occurred where
zooplankton volumes exceeded 153.4 cm3/l,000 m3
but correlations between zooplankton volume and
scaled sardine egg or larval abundance were not
significant. Because the 333-^tm mesh did not
collect small copepod nauplii, a major food offish
larvae, and because zooplankton was not identi-
fied, significant correlations between larvae and
zooplankton were unlikely. The relatively high
catches of eggs at stations with high zooplankton
volumes may have reflected the ability of scaled
sardine adults to concentrate in rich zooplankton

areas, rather than indicating that eggs were
spawned where food would be abundant for larvae.

Relative Fecundity and
Size at Maturity

Mean relative fecundity of scaled sardines is
528.0 ova/g (Sj = 26.5 ova/g), based on data from
22 females collected near Miami, Fla., by Mar-
tinez and Houde (1975). They found that two
modal groups of ova ripened during the spawning
season and that both modes apparently were
spawned. The relative fecundity estimate here dif-
fers slightly from their reported value because
they estimated it for female weights minus ovary
weights. To determine stock biomass, the best

617

FISHERY BULLETIN: VOL. 75, NO. 3

IS 7308

Harengula jaguana eggs

Nay 1973

• * »V V

50m-

•S-'.'.'J \

* V ''*>&) \ "

* * ' 4 * • HV

+ *\ * + + "L h

Number under 10m2

4 0

+ 4 j ♦ * • • \ h

• 1 - 10

• 11-100

• 101 - 1000

+: 4 • "^*/

1 . JMfr-'^

' '

IS 7308

Harengula jaguana larvae

Ray 1973

* • • #v

50m-.

+ * ♦ '\ ♦ ♦ • \r

V -

+ 4 \ t + • \

0*\

• '. 4 ( a

* 4 -*■',* +

Number under 10m2

♦ 0

• <l

<• ': •

•

• X (a

• 1 - 10

• 11-100

• 101-1000

*] *

•

.*■-''

® >I000

84°

IS 7311

Harengula jaguana eggs

June - July 1973

IS 7311
Harengula jaguana larvae
June - July 1973

^^^-> \

4 . »\

50m--. V-

■-. . ... V

4 4 \ . * * • /

* \ * *• ♦ •/^v«

\ -

f + *■'*,**■♦ »r

* .'',.»»'>

<0)

. * 4 . + * •

# \

Number under 10m2

+ + + *',**■

4 0

• <l

♦ '; ♦

• • •

? /'

• 1 - 10

• 11-100

• 101-1000

'; *

•

«.-^^

30"

* * * • x \

50m-. ^ V- \

28°

* + 4 V, + * ♦ \i~

* - \ * • • w

i»b°

Number under 10m2

* * *- 4* * • * 'L

t 0

- '; * +■ «■ • \

• 1 - 10

• 11-100

• 101-1000

fl . • \yl

® >I000

IS 7315
Harengula jaguana eggs

IS 7313
Harengula jaguana larvae

August 1973

30°

• * + * x \

50m-., V^
\ + * * - >

4 + \ 4 4 4 • /

28°

» \ + * *GKva
+ * ♦ \ 4 • + \f

+ 4 \ 4 4 • \ ^

4 + \ + + 4 TC

Number under 10m2

4 4 t\ 4 4 + V

t 0

• <l

4 + 1 4 4 4 4 1

• 1 - 10

• 11-100

• 101-1000

4,' 4 •

; - • ,*°»%

--*

?4°

® >I000

— 1 1

August 1973

30°

• ■ •V

50m-., \^-
"\ + * * 9 \
4 + \ 4 4 * • /

28°

4 \ 4 -»■ • •/rK.

4 4 4*\ 4 4 4 \J
+ + \ + + • \

» 4 \ * . 4

•

Lb°

Number under 10m2

4 4 4'., 4 4

4 0

4 4 I 4

4 4

• 1 - 10

• 11-100

• 101 - 1000

4! 4

•

„*H">

*>r

FIGURE 4. — Distribution and abundance of scaled sardine eggs and larvae. Catches are standardized to
numbers under 10 m2 of sea surface. A, B. Cruise IS7308, May 1973. C, D. Cruise IS7311, June- July 1973.
E, F. Cruise IS7313, August 1973.

618

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF SCALED SARDINE

CL 7«2

Harengula jaguana eggs

Mat 1971

CL 7H12
Harenguia jaguana larvae

30'

50m-

1 —

• ' •• /

T ■ -7

28'

*■ \

\ * * ••V

*■ \ * * •■

k ° 1

2b°

Number under 10m2

* 0

• <l

• »«\ L

* 1 - 10

• 11-100

• •• ^^7

• 101 - 1000

-*w--^

® >IO0O

30°

— 1 — j

«^

• • •V

Mm..,

• • • • • \

28"

& ^ i

\::

•\^ }

2b"

Number under 10m2

t 0

• <l

• • • • \ u

• 1 -10

• 11-100

• 101 - 1000

• • • ^^/

® >I000

FIGURE 5. — Distribution and abundance of scaled sardine eggs and larvae. Catches are standardized to
numbers under 10 m2 of sea surface. A, B. Cruise CL7412, May 1974.

TEMPERATURE

SALINITY

FIGURE 6.— Percent cumulative fre-
quency distribution of 197 1-74 stations
where scaled sardine eggs occurred in
relation to surface temperatures (A)
and to surface salinities (C), and §5.0-
mm SL larvae occurred in relation to
surface temperatures (B) and surface
salinities (D).

24 1- 26 1- 26 1-

230 250 270 29 0

TEMPERATURE CLASS CO

28 01 29 01- 30 01- 3101- 32 01- 33 01- 34 01- 35 01- 36 01-

28 50 29 50 30 50 3150 32 50 33 50 34 50 35 50 36 50

SALINITY CLASS (VM>

relative fecundity estimate is for total weight,
including ovary and the estimate given here is
based on that criterion. Because relative fecun-
dity did not differ significantly among females
from 8.5 to 16.3 cm SL (14.8 to 98.4 g) (Martinez
and Houde 1975), the mean value was used in
calculating biomass estimates. Mean relative
fecundity with 0.95 confidence limits is 528.0 ±
55.1 ova/g. It seems unlikely that biomass esti-
mating errors greater than ±10% could be attrib-
utable to errors in fecundity estimates.

Cruise Egg Abundance

The estimated abundances of scaled sardine

eggs, before correction for egg stage duration,
within the areas represented by each of the cruises
range from 0.00 to 103.39 x 1010 (Table 2). The
Table 2 estimates, which represent the number of
eggs present on a day during a cruise, were cor-
rected for egg stage duration and then expanded
to represent the number of days encompassed by
the cruise period (Sette and Ahlstrom 1948;
Houde 1977a), before they were used in the bio-
mass estimating procedure.

Time Until Hatching

Egg stage duration is less than 24 h for scaled
sardines when temperatures are above 24°C.

619

FISHERY BULLETIN: VOL. 75, NO. 3

TABLE 2. — Abundance estimates of scaled sardine eggs for each
cruise. Estimates were obtained using equations (2) and (3)
(Houde 1977a) and are not corrected for duration of the egg
stage.

Cruise

Area represented

by the cruise

(m2 x 109)

Positive area1
(m2 x 109)

Cruise
egg abundance
(eggs x 10'°)

GE7101
8C7113and

TI7114
GE7117
8C7120and

TI7121
GE7127, 8B7132

andTI7l31
8B7201 and

GE7202
GE7208
GE7210
IS7205
IS7209
IS7303
IS7308
IS7311
IS7313
IS7320
CL7405
CL7412

25.79

120.48
101.10

189 43

72.99

148.85

124.88

48.43

104.59

149 80

14980

151.42

156.50

153.18

153 89

52 00

91.33

0.77

18.32
7.93

13.41

0.00

27.56

15.60

4.88

0.00

3.05

43.38

25.43

40.79

0.00

5.84

43.45

0.18

0.94
1.69

1.57

0.00

0.00
2.51

17.10
0.00
0.00
0.00

21.77

49 44

10339

0.00

45.93

' Positive area is defined as the area representing stations where either eggs
or larvae of scaled sardines were collected.

Newly fertilized eggs were collected only at night
in the Gulf of Mexico surveys and only advanced
embryos usually were present from midday to late
afternoon. Similar observations were made for
scaled sardine eggs collected near Miami and used
in laboratory rearing experiments (Houde and
Palko 1970; Houde et al. 1974). The estimated
peak spawning time is 2200 h.

Egg abundance was underestimated on most
cruises because hatching time was less than 1 day.
All cruise abundances were adjusted by dividing
them by the estimated mean egg stage duration
(Table 3) before annual spawning estimates were
made.

Adjusting Cruise Egg Abundance
Estimates for Area

Some cruises did not completely cover the area
within the 30-m depth contour of the eastern Gulf
where scaled sardines spawned. Egg abundance
estimates for those cruises were adjusted by divid-
ing the cruise abundance estimate (Table 2) by

TABLE 3. — Assigned egg stage durations of scaled sardine eggs
for each cruise in which they occurred, 1971-73.

Cruise

Egg stage duration
(days)

Egg stage duration
Cruise (days)

GE7101

1.17

GE7208

0.84

8C7113

GE7210

0.80

TI7114

0.84

IS7308

0.84

GE7117

0.80

IS7311

080

8C7120

IS7313

0.80

TI7121

0.80

an adjustment factor, the proportion of the spawn-
ing area represented by the cruise. Egg abundance
estimates were adjusted for cruises GE7117,
8C7120-TI7121, GE7208, and GE7210. Area ad-
justment factors were: GE71 17— 0.394; 8C7120-
TI7121— 0.746; GE7208— 0.644; and GE7210—
0.574. Cruise IS7205, in which scaled sardine
larvae but no eggs were taken, also did not
encompass the entire spawning area. Larval
abundance estimates were adjusted for that cruise
by its area factor, 0.750. Cruise egg abundance
estimates from Table 2, after adjustment, were:
GE7117— 4.29 x 1010; 8C7120-TI7121— 2.10 x
1010; GE7208— 3.90 x 1010; and GE7210— 29.79
x 1010.

Annual Spawning and Biomass Estimates
Method I

Estimates of total annual spawning by scaled
sardines were obtained after egg stage duration
and area factor corrections had been made on
daily spawning estimates using the Sette and
Ahlstrom ( 1948) method and procedures described
by Houde (1977a). They were: 44.106 x 1011 eggs
in 1971, 391.357 x 1011 eggs in 1972, and
1,025.834 x 1011 eggs in 1973 (Table 4). No esti-
mate was obtained in 1974 because the entire
season was not surveyed, but the abundance of
eggs from cruise CL7412 (Table 2) suggested that
annual spawning was high in that year.

Estimated biomasses increased from 16,708
metric tons in 1971 to 148,255 metric tons in 1972,
and to 388,610 metric tons in 1973 (Table 4).
Variance estimates for each year's spawning
(Table 4) were used to place 0.95 confidence inter-
vals on biomass estimates. These ranged from 0 to
56,210 metric tons in 1971, 0 to 327,130 metric
tons in 1972, and 300,965 to 476,271 metric tons
in 1973. The mean of the three annual biomass
estimates was 184,527 metric tons. The 1972
estimate may be unreliable because of poor area
coverage and curtailment of cruise GE7210 due
to a hurricane, but the low 1971 estimate probably
is accurate because area coverage was good on
cruises during the peak spawning period.

A severe red tide in 1971 occurred during spring
and summer along the Florida coast of the Gulf of
Mexico (Steidinger and Ingle 1972), and it may
have caused a high mortality of adult scaled sar-
dines. Dead scaled sardines were observed in red
tide areas during cruise GE7 1 17. It is also possible

620

HOUDE: ABUNDANCE AND POTENTIAL YIELD OE SCALED SARDINE

TABLE 4. — Annual spawning and biomass estimates for scaled sardines from the eastern Gulf of Mexico during
1971, 1972, and 1973 spawning seasons. Estimates are based on theSette and Ahlstrom (1948) technique. Details
of the estimating procedure are given in Houde (1977a).

Year

Cruise

Daily spawning

estimate
(eggs ■ 10")

Days

represented

by cruise

Eggs spawned during

cruise period

(x 10")

Variance estimates

on spawned eggs

(x 1024)

Adult biomass
(metric tons)

1971

GE7101
8C7113

0.015

51.5

0.773

0.134

TI7114

0 112

74.5

8.344

1.950

GE7117

0.541

44.5

24.074

22.959

8C7120

TI7121

0.263

41 .5

10.915

2.121

Annual total

44 106

27.164

16,708

1972

8B7201

GE7202

0.000

50.0

0.000

—

GE7208

0468

65 0

30.420

22.664

GE7210

3.721

97.0

360.937

534.743

Annual total

391.357

557.407

148,255

1973

IS7303

0 000

63.5

0.000

—

IS7308

2.613

79.5

207.734

56 388

IS7311

6.180

43.5

268 830

42829

IS7313

12.924

42.5

549.270

34.628

Annual total

1.025 834

133.845

388,610

that few adult scaled sardines were killed, but
that they did not spawn during red tides or that
spawned eggs experienced high mortality. Failure
to spawn or unusual egg mortality could have
caused biomass to be underestimated in that year.
Effects on biomass estimates of area adjust-
ments for the four cruises that did not completely
cover the scaled sardine spawning area were im-
portant. Unadjusted biomass in 1971 was only
10,100 metric tons, 60.5% of the adjusted esti-
mate; in 1972 it was 85,964 metric tons, 58.0%
of the adjusted estimate.

Method II

Biomass estimates, using Simpson's (1959)
method in a modified form (Houde 1977a), were
calculated (Table 5). Mean biomass estimated for
the 3 yr was 146,595 metric tons.

Most Probable Biomass

Scaled sardines as small as 8.0 cm SL are ma-
ture (Martinez and Houde 1975), and estimates
of adult biomass from egg and larvae surveys
probably include most of the stock, juvenile
weights being relatively insignificant. Biomass
estimates ranged from 16,000 to nearly 400,000
metric tons and stock apparently increased from
1971 to 1973. The evidence from cruise CL7412
indicated that spawning increased nearer to shore
than measured at regular survey stations. This
suggests that biomasses were underestimated,
perhaps by as much as 30%. If so, then biomass
may have ranged from 23,000 to 571,000 metric
tons during 1971-73, the mean being 265,000

TABLE 5. — Annual spawning and biomass estimates for scaled
sardines from the eastern Gulf of Mexico during 1971, 1972,
and 1973. Estimates are based on the method described by
Simpson (1959).

Year

Cruise

Daily spawning Annual spawning

estimate estimate Adult biomass

(eggs x 10") (eggs x 10") (metric tons)

1971

1972

1973

GE7101

0015

8C7113

TI7114

0.1 12

GE7117

0.541

8C7120

TI7121

0.263

8B7201

GE7202

0.000

GE7208

0.468

GE7210

3.721

IS7303

0.000

IS7308

2.613

IS731 1

6.180

IS7313

12.924

42.981

1 6,282

245 940 93.168

872000 330,334

metric tons. Despite variability in estimates, it
is clear that the eastern Gulf scaled sardine
stock was less than 700,000 metric tons between
1971 and 1973, and it apparently was less than
100,000 metric tons in 1971.

Comparison of Scaled Sardine Biomass
With That of Other Clupeids

Biomass of scaled sardines in the eastern Gulf
of Mexico is similar to that reported for round
herring and thread herring (Houde 1977a, b).
Mean biomass of round herring was estimated to
be approximately 400,000 metric tons, mostly
distributed between the 30- and 200-m depth
contours, while thread herring mean biomass was
about 250,000 metric tons, much of it occurring
in the same areas as scaled sardine, although

621

FISHERY BULLETIN: VOL. 75. NO. 3

many thread herring also occurred farther off-
shore (Houde 1977b). In aggregate the three spe-
cies totalled approximately 850,000 metric tons.
The menhaden (Breuoortia spp.) resource appar-
ently is small in the survey area, since relatively
few eggs and larvae were collected (Houde et al.
1976). No estimate of Spanish sardine {Sardinella
spp.) biomass was obtained, but its eggs and lar-
vae were abundant (Houde et al. 1976). Its bio-
mass may be as great as that for thread herring,
i.e., 250,000 metric tons. If true, then aggregate
adult biomass of unfished clupeids exceeds 1 mil-
lion metric tons. The contention that large poten-
tial fisheries exist in the eastern Gulf of Mexico
is supported by the estimated biomasses. How-
ever, none of the individual species appears to
represent a resource as large as that of Gulf men-
haden, B. patronus, which presently yields about
500,000 metric tons annually to the northern Gulf
fishery.

TABLE 6. — Range of potential yield estimates for eastern Gulf of
Mexico scaled sardines, based on biomass estimates in 1971,
1972, and 1973 by the Sette and Ahlstrom ( 1948) method. Yields
are predicted at three possible values of M, the natural mor-
tality coefficient. Biomass estimates were obtained from values
in Table 4.

Biomass

estimate

(metric

tons)

Estimated potential annual yields

(metric tons) for given

values of M

Year

M=0 50

M=0.75

M = 1.0

1971

16,708

4,177

6,266

8.354

1972

148,255

37,064

55,596

74,128

1973

388.610

97,153

145,729

194.305

Mean of

3yr

184.527

46,132

69,198

92.264

194,305 metric tons (Table 6). Based on mean bio-
mass estimates for 1971-73, potential yield was
between 46,132 and 92,264 metric tons. If scaled
sardines were evenly distributed over the
60 x 109 m2 where they occur in the eastern Gulf,
harvestable annual yield, based on 1971-73
mean biomass, is 7.7 to 15.4 kg/ha.

Concentration of Biomass

Scaled sardine eggs and larvae occurred in most
of the 76 x 109 m2 area between the coast and
30-m depth contour, except for approximately 15
to 20 x 109 m2 in the northeastern part of the
survey area (Figure 1-). During the spawning
season, adult scaled sardines were assumed to
occur in 60 x 109 m2 of the eastern Gulf. Concen-
tration of biomass, assuming an even distribution,
based on the annual biomass estimates from
Method I (Table 4) and their 0.95 confidence limits
were: 1971, 0 to 9.4 kg/ha; 1972, 0 to 54.5 kg/ha;
and 1973, 50.2 to 79.4 kg/ha. Mean biomass con-
centrations were: 1971, 2.8 kg/ha; 1972, 24.7 kg/
ha; and 1973, 64.8 kg/ha. Estimated scaled sar-
dine biomasses under a hectare of sea surface are
similar to those of thread herring but less than
those of round herring (Houde 1977a, b).

Potential Yield to a Fishery

Estimates of annual yield varied greatly from
year to year, reflecting the biomass fluctuations
(Table 6). The estimator Cmax = XMBQ was used
to predict potential maximum sustainable yield
(Alverson and Pereyra 1969; Gulland 1971, 1972).
X is assumed to equal 0.5 and B0 is the virgin
biomass. M, the natural mortality coefficient,
was allowed to vary from 0.5 to 1.0, values that
are probable for scaled sardines. The range of
potential yields over the 3-yr period was 4,177 to

Comparison of Potential Yield With
That of Other Clupeids

Potential yield of scaled sardines is slightly less
than that estimated for thread herring and less
than that for round herring (Houde 1977a, b).
Using mean annual biomass estimates by Method
I, and the value 1.0 for M, potential maximum
sustainable yields are: scaled sardines — 92,264
metric tons; thread herring — 120,598 metric tons;
and round herring — 212,238 metric tons. Total
potential for the three species is 425,100 metric
tons. If Spanish sardines are as abundant as
thread herring, they could contribute another
120,000 metric tons raising the aggregate poten-
tial yield to 545,100 metric tons.

Potential yields were estimated for adult stock.
If a significant biomass of harvestable juveniles
is present, they could contribute to the yield. For
scaled sardines, and probably round herring
(Houde 1977a), small size at first maturity makes
it unlikely that a significant, unestimated juve-
nile biomass is present, but the large size at first
maturity of thread herring (Prest3) and Spanish
sardines (Varea Rivero 1967) indicates that a
significant unestimated biomass of juveniles may
be present.

3Prest, K. W., Jr. 1971. Fundamentals of sexual maturation,
spawning, and fecundity of thread herring {Opisthonema
oglinum ) in the eastern Gulf of Mexico. Unpubl. manuscr., Natl.
Mar. Fish. Serv., NOAA, St. Petersburg Beach, Fla.

622

HOUDE: ABUNDANCE AND POTENTIAL YIELD OK SCALED SARDINE

Larval Abundance

Larval abundance varied annually and season-
ally (Table 7; Figure 7); the greatest abundances
being observed in 1973 and 1974 cruises. Abun-
dance estimates for cruises in which larvae oc-
curred, ranged from 0.20 to 16.63 x 101(' larvae.
Estimated annual abundances of larvae were low
in 1971 and 1972, but increased in 1973 (Figure 8).
No annual estimates were available for 1974, but
the great abundance of larvae from cruise CL7412
(Figure 7) suggests that more larvae were present
in that year than in any previous year. The in-
creases in larval abundance between 1971 and
1974 are further evidence that spawning intensity
increased during the period.

Some scaled sardines as long as 30 mm SL were
collected but few larvae longer than 20 mm were
taken, and only larvae from 1.1 to 20.0 mm are
included in the length-frequency distributions.
Most larvae of 1.1 to 3.0 mm were distorted from
collection and preservation. Scaled sardine larvae
are 2.4 mm at hatching, but within 15 h their
length increases to more than 4.0 mm, mostly
due to straightening of the body axis rather than
true growth (Houde et al. 1974). The most abun-
dant larvae were 2.1 to 4.0 mm in 1972-74, but
were larger in 1971 (Figure 7) when towing speed
was faster (Houde 1977a) and mesh escapement
by small larvae may have been greater.

The ratio of night-caught to day-caught scaled
sardine larvae increased slowly as larvae in-
creased in length. No larvae longer than 18.0 mm
were sampled during daylight hours. An exponen-
tial model R = 0.7999e° 0550X was fitted to the data
(Figure 9), where R is the ratio of night-caught
to day-caught larvae and X is standard length.
It provided the correction factor R, by which day-
time catches were adjusted to obtain abundance
estimates of larvae by 2-mm length classes in
each station area (equation 11, Houde 1977a).

An exponential decrease in abundance of larvae
was observed in 1973 (Figure 8) and the larval
mortality rate was estimated from these data.
Larvae longer than 3.0 mm were assumed to be
fully vulnerable to the sampling gear. Abun-
dances (Figure 8) were previously corrected for
daytime avoidance. An exponential function was
fitted to the data, and the instantaneous rate of
decline in abundance per millimeter increase in
length was estimated for larvae from 3.1 to
20.0 mm SL. The instantaneous coefficient, Z =
0.3829, is a measure of larval mortality, if gear

TABLE 7. — Abundance estimates of scaled sardine larvae for
each cruise. Estimates include larvae in all size classes and
were obtained using equations (2) and (3) (Houde 1977a).

Area represented

Cruise larvae

by the cruise

Positive area'

abundance2

Cruise

(m2 ■ 109)

(m2 x 109)

(larvae x 10'°)

GE7101

25.79

0.77

0.00

8C7113 and

TI7114

120 48

18.32

8.11

GE7117

101.10

7.93

0.00

8C7l20and

TI7121

189.43

13.41

0.39

GE7127. TI7131

and 8B7132

72 99

0.00

8B7201 and

GE7202

148.85

0.00

GE7208

124.88

27.56

1.85

GE7210

48.43

15.60

2.89

IS7205

104.59

4.88

0.17

IS7209

149.80

0.00

IS7303

149.80

3.05

0.01

IS7308

151.42

43.38

14.02

IS7311

156.50

25.43

0.92

IS7313

153.18

40.79

16.63

IS7320

153 89

0.00

CL7405

52.00

5.84

0.20

CL7412

91.33

43.45

13.19

'Positive area is defined as the area representing stations where either
eggs or larvae of scaled sardines were collected

2Values are not adjusted for cruises that did not encompass the
entire area, nor have estimates been corrected to account for gear
avoidance by larvae at stations sampled in daylight.

avoidance was not too great for larval length
classes in the analysis. The 0.95 confidence limits
on Z are Z ± 0.0833. The. observed coefficient
corresponds to a 31.8% decrease in larval abun-
dance per millimeter increase in length. Although
mortality was not estimated for 1972 larvae, the
high estimated abundance of larvae longer than
10 mm (Figure 8) indicates that survival may
have been relatively good in that year.

Mortality relative to age of larvae was deter-
mined assuming an exponential model of growth
for scaled sardine larvae, based on evidence from
laboratory rearing experiments. Mean daily
growth increments of scaled sardine larvae reared
at temperatures above 26°C exceeded 0.5 mm, and
frequently were in the range of 0.7 to 1.0 mm
(Houde and Palko 1970; Saksena and Houde 1972;
Saksena et al. 1972). Methods to estimate age at
length and mortality have been reported (Houde
1977a).

Mean egg stage duration for scaled sardine is
about 0.81 day. In 1973 the nonfully vulnerable
length classes were 1.1 to 3.0 mm. Duration of
that larval stage is from 1.0 to 3.0 days based on
laboratory experiments (Saksena and Houde
1972; Houde et al. 1974).

An example of duration-corrected abundance
data at estimated mean ages for eggs and larvae
up to 20.0 mm in 1973 is given in Table 8. In this
example the mean daily growth increment was

623

FISHERY BULLETIN: VOL 75. NO. 3

^
a.
U

>■

5 -

uj 5
<n

Q. 2

cr
<

O
" 2

z
3
CO

25-

15 -

. r

t i **r-*

8C 7II3-TI7I14

tbu

8C7I20-TI7I2I

, t- .rVrrri ,n

GE 7208

r— I ""i f l

GE72IO

ru^K

IS7205

i ■ i I I

IS 7303

476

IS7308

38 3

IS 7311

IS73I3

68 7

□

35 2

V'*"!' * I » I * I ' I r I ' T

^--. . 1 1 r-

CL7405

70 2

CL74I2

, i , rTh-frvi

I.I- 3 1- 5.1- 71- 9.1- III- 13.1- 15.1- 17.1" 19.1- I.I- 3.1- 5.1" 7.1- 9.1- III- 13.1- 15.1- 17 1- 19.1-

2.0 40 60 80 100 12 0 14.0 16 0 18 0 20 0 20 40 60 8.0 100 12.0 140 16 0 180 20 0

STANDARD LENGTH CLASSES (mm)

FIGURE 7. — Length- frequency distributions of scaled sardine larvae for 1971-74 cruises to the eastern Gulf of
Mexico. Frequencies are expressed as estimated abundance of larvae in each length class within the area repre-
sented by the cruise. No adjustments for abundance have been made for cruises that did not cover the entire area
where scaled sardine larvae might occur.

624

HOUDE: ABUNDANCE AND POTENTIAL YIELD OF SCALED SARDINE

10 -

~ 10

u o

< 50

<
o40

I-
<
2

u>30

1971

l~~1

1972

-Jl3-

,,,,■,,,,,,■,,,,,.,,,,,.,,,,,.,,,,,.,,,,,. , ■ , ■ , ■ , ■ , , T

1973

NL- (134.8070 x I0")e° 3829L

l.l- 2.1-3.1- 4.1-
2.0 30 4 0 5.0

6.1- 8.1- 10.1-
7.0 9.0 1 1.0

LENGTH-CLASS (mm)

i • I
12.1- 14.1-
130 150

16.1-
17.0

18.1-
19.0

FIGURE 8. — Length-frequency distribution of annual larval
abundance estimates for scaled sardine larvae collected in the
eastern Gulf of Mexico, 1971-73. Frequencies in each 1-mm
length class are expressed as estimated annual abundance and
have been corrected for daytime avoidance. A fitted exponential
function for 1973 data provides an estimate of the instantaneous
coefficient of decline in abundance by length.

set at 0.8 mm and nonfully vulnerable larval stage
duration was 1.0 day. I believe that those values
are the best estimates for scaled sardine larvae,
but other values also were assigned from which
both mean ages and duration-corrected abun-
dances were generated. Duration-corrected abun-
dances (Table 8) were regressed on mean ages in
an exponential regression to estimate the instan-
taneous mortality coefficient (Z) for age in days.
Mortality coefficients were calculated for var-
ious combinations of mean daily growth incre-
ments and durations of the nonfully vulnerable
larval stage for 1973 data (Table 9). Possible
values of the mortality coefficient, Z, range from
0.1822 to 0.3471, which correspond to daily per-
centage losses of 16.7 to 29.3%. For data from
Table 8, where mean daily growth increment was
0.8 mm and nonfully vulnerable larval stage

4.0

>-30

R . 0.7999e° °"°*

j20

^\ -""'

• \ --

_, _ — "*

£i.o

- - ' ' •

•

■

1 1

i i i i i i i i i i

4.0 6.0 8.0 10.0 12 0 14 0 16.0

MIDPOINT OF LENGTH CLASS (mm)

18.0

FIGURE 9. — Night to day ratios of sums of catches, standardized
to numbers under 10 m2 of sea surface, for scaled sardine larvae
collected in 1971-74 in the eastern Gulf of Mexico. The ratios
were calculated for larvae within each 2-mm length class from
1.1 to 19.0 mm SL. A fitted exponential regression describes the
relationship. Larval abundance estimates for each length class
at stations occupied during daylight were corrected by the appro-
priate ratio factor for each length class to account for daytime
avoidance.

TABLE 8. — An example of data from 1973 used to obtain stage
duration, mean age, and duration-corrected abundance of scaled
sardine eggs and larvae. Duration-corrected abundances were
subsequently regressed on mean ages to obtain mortality rates
(Table 9). Abundance estimates in the second column of the
Table were previously corrected for daytime avoidance. In this
example, the mean daily growth increment (o) was set at 0.80.
The nonfully vulnerable size classes were 1.1 to 3.0 mm. Calcu-
lating procedures were given in Houde (1977a), equations (12)
to (16). The regression for these data is presented as Figure 10.

Duration-corrected

Abundance

Duration

Mean age

abundance

Stage

(no. - 10")

(days)

(no. - 10")

Eggs

827.54

0.81

0.41

1,025.83

1.1- 3.0 mm

43.27

1.00

1.33

43.27

3.1- 4.0

46.63

2.89

3.21

16.14

4.1- 5.0

45.49

2.25

6.06

20 23

5.1- 6.0

14.71

1.84

8.33

7.99

6.1- 7.0

13.20

1.56

10.22

8.47

7.1- 8.0

7.25

1.35

11.84

5.36

8.1- 9.0

4.52

1.19

13.26

3.79

9.1-100

1.45

1.07

14.52

1.35

10.1-11.0

0.84

0.97

15.66

087

11.1-12.0

1.65

088

16.69

1.87

12.1-13.0

1.24

0.81

17.63

1.52

13.1-14.0

0.83

0.75

18.50

1.11

14.1-15.0

1.56

0.70

19.31

2.23

15.1-16.0

0.61

0.66

20.07

0.93

16.1-17 0

0.05

0.62

20.78

0.09

17.1-18.0

0.39

0.58

21.44

0.68

18 1-19.0

0.00

0.55

22.07

—

19.1-20.0

0.04

0.52

22.67

0.07

duration was 1.0 day, the estimated mortality
coefficient isZ = 0.2835, corresponding to a 24.7' <
daily loss rate (Figure 10). The most probable
scaled sardine mortality estimate for abundance
at age data, Z = 0.2835 ± 0.0754 at the 0.95
confidence level, is similar to those for thread

625

FISHERY BULLETIN: VOL. 75, NO. 3

TABLE 9. — Summary of mortality estimates for scaled sardine larvae from the eastern Gulf of Mexico, 1973. Estimates were obtained
from the exponential regression of egg and larvae abundances on mean age. Instantaneous growth and mortality coefficients were
calculated for various possible combinations of mean daily growth increment and duration of the nonfully vulnerable larval stages.
Egg stage duration was assigned the value 0.81 days. Nonfully vulnerable larval lengths were 1.1 to 3.0 mm SL. Explanation of
the estimating method is given in equations (12) to (16) of Houde (1977a).

Mean daily

growth increment, b

(mm)

Instantaneous

growth coefficient,

Nonfully vulnerable

larvae duration

(days)

Instantaneous
mortality coefficient,

V-axis intercept.

A/o

(no. • 10")

Daily mortality rate,
1 - exp(-Z)

0.5

0.0552

1.0

0.1842

97.32

0.1683

0.6

0.0662

1.0

02179

1 16.45

0.1958

0.7

0.0772

1.0

02509

136.44

0 2220

0.8

0.0883

1.0

02835

157 36

0.2469

0.9

0 0993

1.0

03156

179.28

02706

1.0

0.1103

1.0

0.3471

202.26

0 2933

0.5

0.0552

3.0

0.1822

131.23

0.1665

0.6

00662

3.0

0.2146

164.36

0.1932

0.7

0.0772

3.0

0.2461

200.90

0.2182

0.8

0.0883

3.0

0.2767

240.98

0.2417

0.9

0.0993

3.0

0.3065

284 66

0.2640

1.0

0.1103

3.0

0.3353

332.06

0.2849

herring (Z = 0.2124 in 1971 and Z = 0.2564 in
1973), but higher than those for round herring:
Z = 0.1317 in 1971-72 andZ = 0.1286 in 1972-73
(Houde 1977a, b).

The y-axis intercepts (7V0) of the regressions
in Table 9 also estimate the number of eggs
spawned in 1973. Their values are lower than
those calculated by the Sette and Ahlstrom ( 1948)
method for 1973 (Table 4), which is considered
the best estimate of annual spawning. A higher
than expected mortality rate of eggs or nonfully
vulnerable larvae may have caused the discrep-
ancy (Figure 10). Larval mortality, considering
only fully vulnerable stages, may be lower than
that for the entire egg-larval stage. For data from
Table 8 and Figure 10, the mortality coefficient
for fully vulnerable 3.1- to 20.0-mm larvae is
Z --= 0.2458, a daily loss rate of 21.8%.

The numbers of probable survivors at hatching,
5.5 mm, and 15.5 mm were estimated in 1973
for three instantaneous growth rates that likely
encompass the true rate for scaled sardine larvae
(Table 10). Initial egg abundance was the 1973
estimate from Table 4. The estimated number
alive at each stage was calculated from the param-
eters of the exponential functions (Table 9) and
from the estimated age in days at each stage
(Table 8).

Mortality was high during the egg and larval
stages. An apparent mortality of 85 to 91% oc-
curred between spawning and hatching (Table
10). Less than 2% survived to 5.5 mm, when larvae
would have been feeding for 2 days at 26° to 28°C
(Houde et al. 1974). More than 99.9% mortality
had occurred by 15.5 mm, when larvae were be-
ginning to transform to juveniles. At the most
probable growth rate, g = 0.0883, only 5 larvae/

IOOO

_•

Harengula jaguana

survival

1973

IOO

® \

z
<

CD
<

Nt = (l57 36xlO")e"028i5t

•

• >

Q 10
UJ

O
UJ
K

cc
o

• ^v

z
o
1-
<
cc

\ •
\ •
\ •

O 1

' '

i i i i i i i.i.

6 8 10 12 14 16

ESTIMATED MEAN AGE (DAYS)

20 22

FIGURE 10. — Estimated abundance of egg and larval stages of
scaled sardines in the eastern Gulf of Mexico in 1973. Abundance
is expressed as a function of estimated age. A fitted exponential
function gives an estimate of the instantaneous rate of decline
in abundance for eggs and larvae up to 23 days of age. The
symbol enclosed in the circle represents the nonfully vulnerable
1.1- to 3.0-mm length classes and was not included in the regres-
sion estimate of instantaneous decline.

10,000 spawned eggs were estimated to have sur-
vived to 15.5 mm and 20 days of age in 1973.

626

HOUDE ABUNDANCE AND POTENTIAL YIELD OE SCALED SARDINE

TABLE 10. — Estimated numbers and percentages of survivors of scaled sardines at hatching, 5.5 mm SL, and 15.5 mm SL in 1973.
Estimates are made at three possible growth rates (see Table 9). Duration of the nonfully vulnerable larval stage was set at 1.0 day
for 1.1 to 3.0 mm larvae. The number of spawned eggs was based on the estimate in Table 4. Predicted numbers at hatching, 5.5 mm,
and 15.5 mm are calculated from exponential functions based on Table 9 data.

Instantaneous

growth

coefficient.

Number of

spawned

eggs

(■10")

Instantaneous

mortality

coefficient,

Number
hatching
(-10")

Percent

mortality'

to hatching

Number of

5.5-mm larvae

(x10")

Percent

mortality

to 5.5 mm

Number of

1 5.5-mm larvae

(x10")

Percent

mortality to

15.5 mm

0.0662
00883
0 1103

1,025.83
1,025 83
1,025.83

0.2179
02835
0 3471

97.61
125.07
152 69

90.5
87.8
85 1

11.82
14.83
1763

98.8
986
98.3

0.39
0.53
068

99 96

99 95
99 93

'Hatching assumed to occur at 0.81 day.

Estimated survival of scaled sardines at hatch-
ing and 5.5 mm was lower than that for thread
herring or round herring (Houde 1977a, b). In
1973 scaled sardines apparently experienced high
mortality during embryonic and young larval
stages, which quickly reduced the initial number
of eggs to relatively few larvae. Thread herring
and scaled sardine mortality rates may be similar
for larvae in the fully vulnerable length classes.
Round herring larvae had a lower estimated mor-
tality rate than either scaled sardines or thread
herring. But, the probable slower growth rate of
round herring larvae at cooler temperatures
(Houde 1977a) caused estimated numbers at
15.5 mm to be only 40 to 120 survivors/10,000
spawned eggs, which was comparable with the
thread herring estimate of 60 to 200 survivors/
10,000 eggs, but higher than the 5 survivors/
10,000 eggs estimated for scaled sardines.

SUMMARY

1. Scaled sardines spawned from January to
September in the eastern Gulf of Mexico, with
most spawning occurring during spring and sum-
mer. They spawned in waters <30 m deep, mostly
within 50 km of the coast.

2. Eggs were collected where surface tempera-
tures ranged from 20.8° to 30.7°C and surface
salinities were 29.9 to 36.9%<». Larvae «5.0 mm SL
were collected at surface temperatures from 18.4°
to 30.5°C and at surface salinities of 27.3 to 36.9%o.
Most eggs and =£5.0-mm larvae occurred where
surface temperature exceeded 24°C and surface
salinity was above 35%<>.

3. Estimates of annual spawning increased in
each year, 1971-73. Biomass estimates increased
from 16,000 to 390,000 metric tons during
those years. The mean biomass estimate for the
3-yr period was 184,527 metric tons. Concentra-
tions of adult biomass between the coast and the
30-m depth contour were: 1971—2.8 kg/ha;
1972—24.7 kg/ha; 1973—64.8 kg/ha.

4. Estimated annual potential yields to a fishery
were: 1971—4,177 to 8,354 metric tons; 1972-
37,064 to 74,128 metric tons; 1973—97,153 to
194,305 metric tons. Potential yield, based on the
3-yr mean biomass estimate, was between 46,132
and 92,264 metric tons, or 7.7 to 15.4 kg/ha.

5. Larvae were more abundant in 1973 than
in 1971 or 1972. Larval mortality, relative to
length and to estimated ages, was estimated for
1973 data. For length, the instantaneous coeffi-
cient was Z = 0.3829, corresponding to a 31.8%
decrease in larval abundance per millimeter in-
crease in length. For age, the most probable esti-
mate is Z = 0.2835, which corresponds to a
24.1% daily loss rate.

6. It is probable that more than 99.99<- mortality
occurred between spawning and the 15.5-mm
stage in 1973. Only 5 larvae/ 10,000 spawned eggs
were estimated to have survived to 15.5 mm at
20 days of age in that year.

ACKNOWLEDGMENTS

People and agencies that were acknowledged
for their support of this project by Houde (1977a)
are thanked once again. Harvey Bullis reviewed
an early draft of the paper. This research was
sponsored by NOAA Office of Sea Grant, Depart-
ment of Commerce, under Grant 04-3-158-27 to
the University of Miami.

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1976. Abundance and potential for fisheries development
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1970. Laboratory rearing of the clupeid fish Harengula
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1972. Egg development of scaled sardine Harengula pen-
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SPRINGER, V. G., AND K. D. WOODBURN.

1960. An ecological study of the fishes of the Tampa Bay
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STEIDINGER, K. A., AND R. M. INGLE.

1972. Observations on the 1971 summer red tide in Tampa
Bay, Florida. Environment. Lett. 3:271-278.
VAREA RIVERO, J. A.

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628

NOTES

REPRODUCTIVE PARAMETERS OF THE
OFFSHORE SPOTTED DOLPHIN,

A GEOGRAPHICAL FORM OF
STENELLA ATTENUATA, IN THE

EASTERN TROPICAL PACIFIC, 1973-75

Perrin et al. (1976) presented estimates of repro-
ductive parameters of the offshore population of
Stenella attenuate in the eastern Pacific based on
data collected in 1968-73, inclusive. The sample
included 3,527 specimens. Only the 1973 sample
(2,036) was putatively cross-sectional with re-
spect to age and sex structures of the kill; in ear-
lier years, adult females were selected for exami-
nation. The purpose of this paper is to present
analyses of samples collected in uniform fashion
in 1973, 1974, and 1975, updating the prior report
and providing a uniformly developed, albeit short,
time series of annual estimates.

Methods and Materials

The data and specimens were collected by
NMFS biological technicians aboard commercial
tuna vessels. Data collection procedures were the
same as described by Perrin et al. (1976). Data on
S. attenuata were collected on 24 cruises in 1973,
33 in 1974, and 32 in 1975.

The total sample includes 6,243 specimens,
6,168 from precisely known localities (Figure 1).
Because of the seasonal nature of the fishery, the
sample is heavily biased toward the first half of
the calendar year with practically no coverage of
the summer months (Table 1).

Laboratory procedures were the same as re-
ported by Perrin et al. (1976), but the analytical
methods differed slightly. In calculating gross
annual reproductive rate (proportion female x
proportion of total females which are reproductive

FIGURE 1. — Sample of the offshore spot-
ted dolphin, Stenella attenuata, col-
lected in 1973-75, by 5° squares.

629

TABLE 1. — The sample of the offshore spotted dolphin, Stenella
attenuata, by sex, year, and month, 1973-75. Date of capture was
not available for 18 of the total 6,243 specimens collected.

1973

1974

1975

Total

Month

;

Jan.

267 326

239

300

395

442

901

1,068

Feb.

200 231

428

532

249

312

877

1.075

Mar.

137 210

133

153

336

435

Apr.

41 46

135

183

211

271

May

85 156

124

193

June

56 69

122

125

July

0 0

Aug.

0 0

Sept

0 0

Oct.

5 16

Nov

72 103

124

190

Dec.

8 9

Totals

871 1,166

841

1,022

1,047

1,278

2.759

3.466

2,037

1 ,863

2,325

6,225

x annual pregnancy rate), Perrin et al. (1976)
estimated the proportion of adult females which
were reproductive from coloration phase data,
based on a subsample of data on percentage
mature in the various coloration phases
("mottled" and "fused-adult"). In the present
study, a much larger sample of complete reproduc-
tive data was available; therefore, the proportion
of total females which were reproductive was
estimated directly from that sample. Specimens
for which ovarian data were lacking or incomplete
were allocated to mature or immature categories
based on a length criterion. Average length at
attainment of sexual maturity was estimated as
that length (177 cm) at which the number of
shorter but mature specimens in the sample
equals the number of longer but immature
specimens.

Results and Discussion

Calving Cycle and Pregnancy Rate

The calving cycle, for purposes of analyzing
field data, can be divided into three phases: 1)
pregnancy, 2) lactation, and 3) "resting" (a catch-

all phase for animals neither pregnant nor lactat-
ing, which includes females truly resting, i.e., not
ovulating because of being between cycles, those
which have just ovulated but have not become
pregnant, some with extremely small embryos
missed in dissection, those which recently
aborted, and those which have prematurely termi-
nated lactation due to death of the suckling calf).

We estimated the length of the cycle (and preg-
nancy rate) in two ways: 1) based on the reproduc-
tive structure of the sample of adult females, i.e.,
based on the assumption that the samples are not
biased with respect to reproductive phase, and
that the proportion of a sample of mature females
in a particular phase is directly proportional to
the relative length of that phase, using the pre-
viously estimated (Perrin et al. 1976) length of
gestation (11.5 mo) as a time calibration, and 2)
based on the estimate of length of gestation and
a largely independent estimate of length of
lactation.

The first estimate was based on data for 1,876
females classified as pregnant, lactating, preg-
nant and lactating, "resting," or postreproductive
(Table 2). The "resting" females were further
subdivided into those with and without a corpus
luteum. As discussed above, some proportion of
those with a corpus luteum can be assumed to
represent females not truly resting (with a corpus
luteum of infertile ovulation). In the total sample
of 3,443 females, 61 were simultaneously preg-
nant and lactating (6.1% of the lactating females).
Minor differences between the numbers in Table 2
and in table 8 of Perrin et al. (1976) reflect in-
crease of the 1973 sample by eight specimens and
reexamination and reevaluation of the materials.

Subtraction of the postreproductive females
from the aggregate of mature females of deter-
mined reproductive condition and allocation of
the females both pregnant and lactating to both

TABLE 2. — Reproductive condition of 3,469 female offshore spotted dolphins, Stenella attenuata,

collected 1973-75.

1973

1974

1975

1973-75
No.

pooled

Condition

No.

Sexually immature

522

45.0

465

45 9

580

45.7

1,567

45.5

Sexually mature:

Condition undetermined

5.0

5.9

191

15.0

309

9.0

Pregnant only

232

20.0

122

12.1

119

9.4

473

13.7

Pregnant and lactating

1.4

2.3

1.7

1.8

Lactating only

226

19.5

256

25.3

264

208

746

21.7

"Resting"

With corpus luteum

2.9

3.2

2.2

2.7

Without corpus luteum

5.7

4.7

5.0

178

5.2

Postreproductive

0.6

0.2

0.4

Totals

1.161

100.0

1,012

100 0

1,270

100.0

3,443

100.0

630

categories provides estimates of the proportions
of reproductive females in the three phases of the
cycle and, comparing the proportions, of the rela-
tive lengths of the phases. Estimated average
length of the phases and the total cycle can then
be calculated for each 1-yr sample and for the
pooled samples, based on the relative lengths of
the phases and on the estimated gestation period
of 11.5 mo (Method 1 in Table 3). The estimates of
average length of cycle thus derived trend from
27.3 mo in 1973 to 42.3 mo in 1975, due to increase
in the estimated length of lactation from 11.2 mo
to 23.3 mo.

Annual pregnancy rate under Method 1 (also in
Table 3 ) is calculated as proportion of reproductive
females pregnant divided by the length of gesta-
tion (0.958 yr). The reciprocal of annual preg-
nancy rate is the estimate of average calving
interval.

In the second method of calculating length of
calving cycle, we estimated length of lactation
by assuming that a suckling calf existed in the
samples for each lactating female. Under this
assumption, the length at which the cumulative
frequency of calves in a sample equals the number
of lactating females should be the average length
at weaning (from which, using the length-age
equations published by Perrin et al. (1976), the
average age at weaning can be calculated). If the
length of lactation increases, the average length

TABLE 3. — Estimates of lengths of reproductive phases, preg-
nancy rate, and calving interval under two methods of estimat-
ing length of calving cycle (see text) of the offshore spotted
dolphin, Stenella attenuata, 1973-75.

Item

1973 1974

1975

1973-75
pooled

Sample size (no.)
Pregnancy (mo)
Lactation (mo):
Method 1

Method 2 (Hyp. II)
"Resting (Method 1)
Sum of phases:
Method 1
Months
Years
Method 2
Months
Years
Annual pregnancy rate
(APR):
Method 1
Method 2
Calving interval
(1/APR):
Method 1
Years
Months
Method 2
Years
Months

574
11.5

481
11.5

497
11.5

11.2 219 23.3

11.2 12.4 12.1

4.6 6.4 7.5

27.3
2.28

0.452
0.472

2.21
26.5

2 12
25.4

39.8
3.32

28.5
238

0314
0459

3.18
38.2

2.18
262

42.3
3.53

28.2

235

0 296
0.461

3.38
40.5

2.17
260

1,552
11.5

17.4
11.9

5.9

348
2.90

28.0
2.33

0.359
0463

279
33.4

2.16
259

at weaning estimated by this method should in-
crease concomitantly. The calculated length at
weaning did not increase sharply between years
(Table 4). Under Hypothesis II of Perrin et al.
( 1976 1 of the rate of deposition of dentinal growth
layers (two in first year and one per year there-
after— the most likely alternative), the estimated
length of lactation ranges from 11.2 mo in 1973
to 12.4 mo in 1974. To arrive at estimates of the
total length of the calving cycle under Method 2,
we used the estimate of time spent in the "resting"
phase under Method 1 for 1973 (the year for which
the two estimates of length of lactation coincide
exactly) or 4.6 mo, for each of the three annual
estimates. This estimate is based on the assump-
tions under Method 1 but must suffice as a first
approximation. In estimating pregnancy rate (as
reciprocal of calving interval) — Table 3 — over-
lapping cycles were taken into consideration by
adjusting the effective length of lactation down-
ward by a factor equal to the percentage of lactat-
ing females also pregnant.

The 1973 estimate of length of lactation (and
length of cycle, pregnancy rate, and calving inter-
val) is very close to that obtained by Method 1
above (11.2 mo), but the two sets of estimates
diverge sharply thereafter. The first method could
be invalid and cause diverging estimates if 1 )
lactating females (and their nursing calves) were
overrepresented in the samples for 1974 and 1975
or, conversely, 2) either (or both) pregnant or
"resting" females were underrepresented. The
first situation could obtain if lactating females
and their accompanying calves are more likely to
be captured and killed in the net because of lim-
ited endurance and ability to escape of the calf,
certainly less than those of adults, and the
strength of the mother-calf bond. The second
method could yield erroneous estimates if 1 ) nurs-
ing calves were overrepresented in the samples or,

TABLE 4.— Estimates of length of lactation in the offshore
spotted dolphin, Stenella attenuata, based on the cumulative
calf length /lactating females method (see text) 1973-75.

Lactating

females1

(no.)

Length2
(cm)

Length of lactation

Sample

Under hypothesis

Growth I II III
layers (mo) (mo) (mo)

1973
1974
1975
1973-75
pooled

259
301
376

936

1358
138.5
1382

137.8

1.86
2.03
2.01

1.98

11.2
12.2

12.1

11.9

11.2
12.4

12.1

11.9

11.2

122
12.1

11.9

'Includes mature females (s177 cm) without lactation data prorated to
lactating and nonlactatinq based on proportions in sample with lactation data.
2Length at which cumulative number of calves = number of lactating females.

631

conversely, 2) lactating females were under-
represented. Ongoing analyses of data for the
spotted dolphin, S. attenuata (J. E. Powers pers.
commun.), indicate that small calves are probably
overrepresented in small single-set samples. In
addition, the absence of sharp change in length
of calves at weaning as estimated by the
cumulative-calves method speaks against the
alternative explanation of development between
the years of differential bias against calves and
lactating females. The balance of evidence favors
the first alternative above, that of progressive
overrepresentation of both nursing calves and
lactating females as the average number of
animals encircled has increased and the average
number killed per net haul has decreased1 accen-
tuating the factor of differential stamina.

Gross Annual Reproduction

Estimates of gross annual reproductive rates
can be calculated based on the two methods of
estimating pregnancy rate (Table 5). It must be
noted that if, as discussed above, small calves are
overrepresented in small samples (which make up
most of the aggregate sample), then pregnancy
rate (and, therefore, gross annual reproductive
rate) under Method 1 are underestimated to an
unknown, but probably small, degree. This factor,
of course, would also cause overestimation of the
proportion of the total sample female and the pro-

'Staff, Porpoise/Tuna Interaction Program, Oceanic Fisheries
Resources Division. 1975. Progress of research on porpoise mor-
tality incidental to tuna purse-seine fishing for fiscal year 1975.
SWFC Admin. Rep., Natl. Mar. Fish. Serv., La Jolla, Calif.,
LJ-75-68, 98 p. (Unpubl. rep.)

portion of total females which are reproductive,
causing a countering overestimation of gross
annual reproduction of unknown, but again prob-
ably small, size.

Standard errors are attached to the various
estimates where sample size sslOO, under the
assumption that the binomial distribution tends
to normality in large samples (Bailey 1959),
allowing calculation of the standard error as:

p(l — p)/n

where p = proportion (estimate of parameter)
n — sample size.

Although gross annual reproductive rate as
calculated in Table 5 is a product of three esti-
mates, it can be calculated directly from the total
sample (number of females pregnant ■*■ total
number of males and females), to yield the same
estimate and allowing estimation of the variance
by the above method. The total sample size was
adjusted downward by a factor equal to the propor-
tion of mature females in unknown reproductive
condition. The effect on the variance by the con-
stant used to adjust the pregnancy rate to an
annual rate was ignored, because the constant
(11.5 mo gestation -^ 12 mo, or 0.958) is close
to unity.

The estimates of pregnancy rate (and gross
annual reproductive rate) for 1973 and 1974 based
on structure of the samples (Method 1) are sig-
nificantly different from each other (using ±2 SE
as an approximation of a 959c confidence interval),
and the estimate for 1975, although not statis-
tically different from that for 1974, continues the
trend. The estimates based on independent esti-

TABLE 5. — Calculation of estimates of gross annual reproductive rate of offshore spotted dolphin, Stenella attenu-
ata, for 1973-75, using two alternative estimates of pregnancy rate (see text). Standard error follows estimate
(see text).

A x

x C

Proportion
female

Proportion of

females
reproductive

Annual pregnancy rate

Gross annual rep
Method 1

iroductive rate

Year

Method 1

Method 2

1971

0.546

1972

(86)
0.465 ± 0.023

1973

0.572 ± 0.011

0.544 ± 0.015

(455)
0.452 ± 0.021

0.472 ± 0.021

0.141 ± 0.008

0.147 ± 0008

1974

(2,037)
0.548 ± 0.012

(1,161)
0.535 ± 0.016

(574)
0.314 ± 0.021

(574)
0.459 £ 0.023

(2,036)
0.092 £ 0.007

(1.934)
0.135 £ 0.008

1975

(1,863)
0.559 ± 0.010

(1,012)
0.542 ± 0.014

(481)
0.296 ± 0.020

(481)
0.461 ± 0.022

(1,860)
0.087 ± 0.006

(1.750)
0.140 £ 0.007

1973-75

(2,321)
0.560 £ 0 006

(1.270)
0.541 ± 0.008

(523)
0.359 ± 0.012

(523)
0.463 ± 0.012

(2,321)
0 109 £ 0004

(2,001)
0.140 £ 0.004

(6,221)

(3,443)

(1,578)

(6.243)

(5,685)

632

mates of lengths of gestation and lactation also
trend downward, but the year-to-year differences
are not statistically significant. As discussed
above, the balance of evidence favors the (rela-
tively nonvarying) estimates based on Method 2.

Although adequate data for estimating sex
ratio and proportion of total females which were
reproductive in 1971 and 1972, using the methods
employed here, or for estimating pregnancy rate
using Method 2, are not available because of
selection of adult females for dissection, the
estimates of pregnancy rate (using Method 1) for
those two years are included in Table 5. The
sample for 1971 is too small to allow direct statis-
tical comparison with the estimates for later
years, but the 1972 estimate is not significantly
different from the estimates for 1973, reinforcing
the suggestion that a major shift in population
structure or (more likely) in degree of representa-
tiveness of the kill or the sample occurred in 1974.

In summary, the balance of evidence indicates
that, in management of the dolphin/tuna situa-
tion, changes in the structure of the dolphin kill,
per se, should not be taken to necessarily mean
that parallel changes in reproductive rates have
occurred. The changes more likely represent
sampling artifacts caused by changes in the fish-
ing and dolphin rescue operations.

Literature Cited

Bailey, N. T. J.

1959. Statistical methods in biology. English Univ.
Press, Ltd., Lond., 200 p.
PERRIN, W. F., J. M. COE, AND J. R. ZWEIFEL.

1976. Growth and reproduction of the spotted porpoise,
Stenella attenuata, in the offshore eastern tropical Pacific.
Fish. Bull., U.S. 74:229-269.

WILLIAM F. PERRIN
RUTH B. MILLER

priscilla A. Sloan

Southwest Fisheries Center

National Marine Fisheries Service, NO A A

La Jolla, CA 92038

THE UPTAKE, DISTRIBUTION, AND

DEPURATION OF 14C BENZENE AND

,4C TOLUENE IN PACIFIC HERRING,

CLUPEA HARENGUS PALLAS I

This note is a sequel to Korn et al. (1976), where
uptake, distribution, and depuration of 14C ben-
zene were examined in striped bass, Morone
saxatilis, and northern anchovy, Engraulis mor-
dax. Like benzene, toluene is a prevalent, water-
soluble, and toxic monoaromatic component of
petroleum and associated products. According to
Anderson et al. ( 1974a), toluene is second only to
benzene as the most abundant aromatic oil com-
ponent in the water-soluble extracts of southern
Louisiana and Kuwait crude oils (6.75-3.36 \s\l
liter benzine; 4.13-3.62 /u,l/liter toluene, respec-
tively).

Although levels of the volatile aromatics are
thought to be low in areas subject to chronic oil
exposure, few actual measurements have been
made. Further, if fish can accumulate benzene and
if energy is required to metabolize, detoxify, and
depurate these aromatics, long-term physiological
and population effects are possible.

In this study, a comparison of the uptake, dis-
tribution, and depuration of 14C benzene and 14C
toluene, at a low sublethal concentration [100
parts per billion (ppb)], was undertaken to deter-
mine which of these prevalent aromatics may pose
the greatest problem. It was hypothesized that,
although toluene is less soluble in seawater (An-
derson et al. 1974a), it may be more toxic and
exhibit greater accumulation levels and persis-
tence. Our previous work with striped bass and
northern anchovy indicated other tissues that
should be examined, such as kidney, pyloric caeca,
gonad, and intestine, and in the present compari-
son, residues in the additional tissues were mea-
sured. Pacific herring, Clupea harengus pallasi,
were selected as test animals because of their im-
portance as estuarine and nearshore forage fish for
many important recreational and commercial
species, including striped bass and chinook salm-
on.

Methods

Pacific herring were obtained from a San Fran-
cisco Bay bait dealer and were transported di-
rectly to the Tiburon Laboratory dock. The fish
were acclimated under test conditions for at least 2

633

wk in 2,000-liter tanks. Fish were not in spawning
condition.

In each of two separate studies, 10 fish were
placed into each of six 660-liter fiber glass tanks
and further acclimated for 1 wk before exposure.
Salinity and temperature were 24%o and 9°-ll°C,
respectively, during the acclimation and test
periods. In the first study, fish were exposed to 100
nl/liter (ppb) 14C benzene (4.2 dpm/ng specific ac-
tivity). In the second study, fish were exposed to
100 nl/liter (ppb) 14C toluene (3.2 dpm/ng specific
activity). In both studies, one of the six tanks was a
control, with no exposure. Exposures were static
(single dose with delining concentration) for 48 h,
preceded and followed by a continuous water flow
of 2 liters/min.

Water samples for radiometric aromatic anal-
yses were taken from all tanks at 0, 6, 24, and 48 h
after initial dosage. Gallbladder, intestine, pyloric
caeca, gill, brain, liver, muscle, kidney, and imma-
ture male and female gonad tissues were sampled
for radiometric analyses at 6 h, then daily for 7
days.

Methods of exposure and radiometric analyses
are identical to Korn et al. (1976), except that the
tissues from fish exposed to toluene were digested
at 50°C for 24 h.

Since accumulation levels in the gallbladder
were based solely on radiometric analysis of the
14C present and could include metabolites of the
monoaromatics as well as unchanged benzene or
toluene, an additional study was made to interpret
the residue. Two groups of fish, with six fish per
tank, were exposed to 100 nl/liter 14C benzene (1
tank), and 100 nl/liter 14C toluene (1 tank) for 48
h. Exposure was the same as in the above experi-
ments. At the end of the 2-day exposure, the gall
bladders were removed, weighed, and extracted
with 0.2 ml trifluorotrichloroethane-Freon.1 The
extracts were analyzed for benzene and toluene by
gas chromatography (Benville and Korn 1974).
Efficiency of extraction was not determined and
therefore the gas chromatography analyses were
more qualitative than quantitative.

Results and Discussion

There were no mortalities in either exposed or
control fish. Unlike herring exposed during
spawning condition (Struhsaker 1977), no abnor-

mal behavior was noted, thus immature herring
appear less sensitive to exposures than mature
herring in spawning condition.

The concentration of benzene and toluene in
seawater in all tanks declined linearly (Y — a +
bX where Y = concentration in microliters per
liter, a = initial concentration in microliters per
liter, b = rate of decline in microliter per liter per
hour, and X = time in hours), during the 48-h
static exposure, as follows:

Item
Total no. samples
a (Y-intercept)
b
Percentage of initial

concentration remaining:
24 h
48 h

Benzene

20
0.094997
0.0006075

85
69

Toluene

20
0.09195
0.0007587

80
60

'Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

The equation for decline in benzene and toluene is
probably a function of the volume of seawater. In
earlier studies, at smaller volumes, decline was
exponential over the 48-h static exposure. At the
volume in these experiments it was linear, but
probably would have been exponential over a
longer time period. The rate of decline appears to
decrease with increasing volume.

In all herring tissues, toluene accumulated to
higher levels than did benzene (Table 1), despite
the faster loss of toluene compared with benzene
from the test solution. Certain trends were com-
mon to both aromatic components. The tissue
exhibiting the highest accumulation was the
gallbladder (3.1 nl/g benzene, 34 nl/g toluene,
maximum level). The lowest level of maximum
accumulation was found in the immature gonad
(0.24 nl/g benzene, 0.44 nl/g toluene). Pyloric
caeca and intestine contained varying amounts of
bile and therefore had a wide range of 14C activity
and a resulting wide variance in calculated con-
centrations.

Benzene was accumulated up to 31 times the
initial water concentration (gallbladder) and tol-
uene reached 340 times the initial water concen-
tration (gallbladder).

In most tissues, and for most components,
maximum accumulation levels were reached
rapidly. Within 24 h, maximum residues were ob-
tained in all tissues except the gallbladder and
pyloric caeca. Toluene accumulated to the
maximum level (0.25 days) before benzene peaked
( 1-2 days) in all tissues except the gallbladder and
intestine.

634

TABLE 1. — Residues of benzene and toluene and/or metabolites (mean nl/g±SE) accumulated during and after a 48-h
exposure to 100 nl/liter (ppb) 14C benzene or 100 nl/liter (ppb) 14C toluene in the tissues of Clupea harengus pallasi.
Number of samples in parentheses.

Time (days) from start of exposure'

Tissue and

Uptake

Depuration

compound

0.25 (6 h)

2 3 4 5

Gallbladder:
Benzene

Toluene

Intestine:
Benzene

Toluene

Pyloric caeca:
Benzene

Toluene

Gill:

Benzene

Toluene

Brain:
Benzene

Toluene

Liver:
Benzene

Toluene

Muscle:
Benzene

Toluene

Kidney:
Benzene

Toluene

Gonad:
Benzene

Toluene

0.37±0.075 2.1-0 71 3.1 ±0.48

(4) (5) (5)
4.6±3.4 30 ±11 27±15

(5) (5) (5)

2.7+1.5

(3)

34±17

(5)

0.83±0.78 0.42±0.28 0.61 ±0.55 0.16

(4) (5) (5) (1)
3.9±2 4 2.3±2.1 2.1 ±1.7 0.70±0.7

(5) (4) (5) (5)

0.56±0.30 0.92±0.79 0.60±0.14 0.61

(3) (4) (4) (1)

19±9.0 1.7±095 0.24-0.49 6.0 ±4.9

(5) (5) (3) (2)

— 2 0.087 0081

(D (1)

0.09±0.014 0092±0013 0 .1 1 ±0.025 0.13±070

(2) (3) (2) (3)

0 058 ±0 34 0 63 ±0 38 0 64 ±0 38 0 095 ±0 039 — 0 056 — —

(5) (5) (5) (3) (1)

3 6±3 6 1.8±0.32 2.4±1.4 0.77 ±0.46 0.23 ±0.94 0.13±0.03 0.11 ±0.037 0.16±0.081

(5)

(4)

0068

(1)

0.51 ±0.12 0.61 ±0.33 0.73±0.46 0 073

(5) (5) (5) (2)

1.8 ±0.58 1 2 ±1.2 1.0±0.96 0.20±0 12

(5) (5) (5) (5)

0.742:0.11 075±014 0.62±0.052 0 59

(5) (5) (5) (2)

2.1 ±0.19 2.0±0.28 1.5±0.18 0.13±0.073

(5) (5) (5) (3)

0.45 ±0.070 0.53 ±0.096 0.50 ±0.067 —

(5) (5) (4)

1.5±044 1.4±0.44 1.2±0.13 0.36±0.15 0.23±005

(5)

(4)

0.41 ±0 22 0.63±0.36 0.44±0.33 0 035

(5) (5) (4) (1)

1.3 ±0.80 0 52±0.28 0.66±0.71 0.33

(5) (5) (5) (2)

0.32±0.066 0.32±0.066 0.40±0 .12 —

(5) (5) (5)

13±0 50 1.1 ±0.40 0.75 ±0.33 0 18±0099

(5) (5) (5) (4)

0.15±0.021 0.24±0.062 0.21 ±0.10 —

(5) (5) (5)

0.43 ±0.24 0.44±0.21 0.44 ±0.28 0 16

(5) (5) (4) (1)

0 066

(1)

'Exposure terminated after 2 days; then fish remained in flowing seawater for 5 days
2 — = nondetectable levels

Residues were depurated rapidly, with most tis-
sues having nondetectable amounts after 3-4 days
(1-2 days after termination of exposure). The
gallbladder, intestine, and pyloric caeca retained
residues through the duration of the study (7
days).

In the experiment in which gas chromato-
graphic analyses were performed on the gallblad-
der, no detectable benzene (<0.1 nl/g) was mea-
sured. Gas chromatography analysis resulted in
only 0.56-1.5 nl/g toluene. This indicates that
most or all of the radioactivity measured by liquid
scintillation in the gallbladders offish exposed to
benzene is not the parent compound, but one or
more metabolites. Fish exposed to toluene had a
small amount of the parent compound as opposed

to metabolites (1.5 nl/g toluene maximum, com-
pared with 27 nl/g expected [Table 1]).

The above result and the occurrence of delayed
depuration in the gallbladder, intestine, and
pyloric caeca supports the contention that benzene
and toluene are metabolized in the liver, stored in
the gallbladder, then passed into the intestine and
are excreted with the feces. This agrees with
Roubal et al. (in press) who found high levels of
benzene metabolites in the liver and gallbladder of
salmon which had previously received in-
traperitoneal benzene injections. This also agrees
with our previous results with benzene in other
fishes (Korn et al. 1976), results of Neff (1975), and
with work by Lee et al. (1972) who demonstrated
metabolism of polycyclic aromatics in the liver

635

and subsequent storage in the gallbladder.
Studies with polycyclic aromatics (naphthalene,
benzpyrene) by other investigators (Lee et al.
1972; Anderson et al. 1974b; Neff 1975; Roubal et
al. in press) indicate higher accumulation levels
and slower depuration than we have found with
benzene and toluene. However, different species
are involved, and these higher aromatics are also
less prevalent in the water-soluble extract of crude
oil.

The results of this study are generally consis-
tent with our previous work exposing striped bass
and northern anchovy to 14C benzene at the same
initial concentration and exposure period (100 nl/
liter for 48 h; Korn et al. 1976), except for the
considerably higher accumulation in the anchovy
than in the other species. This is probably primar-
ily a result of the higher stress, activity level, and
scale and mucus loss in anchovy while in captivity.

The gonads sampled in this study were imma-
ture and showed low accumulation levels. In
another study exposing mature spawning herring
to 100 nl/liter benzene for 48 h (Struhsaker 1977),
higher accumulation occurred in the ovary, with
associated deleterious effects on the ripe ovarian
eggs and on development of larvae subsequent to
exposure of the parental females.

Of the two components studied here, toluene
would appear to be potentially a greater problem
to fish. Toluene could be rapidly accumulated to
high levels in fish after even a brief contact during
an oil spill. Since toluene is one of the more preva-
lent water-soluble oil components, further re-
search on the effects and uptake of this component
are indicated. Further, chronic exposures are
probably of more importance to the survival offish
populations than are spills, and studies of long-
term exposure to chronic concentrations should be
made.

Finally, the probability that benzene and tolu-
ene are rapidly metabolized or converted to
metabolites (possibly phenol, which is also highly
toxic) leads to the need for metabolite research.
Uptake studies with phenolic metabolites would
be of interest, as would be the determination of
uptake over extended time intervals.

Acknowledgments

We acknowledge the considerable assistance of
other members of the Physiology Investigation,
Tiburon Laboratory, particularly Pete Benville

for the gas chromatography analysis. We also
thank Stanley Rice, Northwest and Alaska
Fisheries Center, Auke Bay Laboratory, and Jerry
M. Neff of Texas A&M University for their critical
reviews of the manuscript.

Literature Cited
Anderson, J. W., J. M. Neff, B. A. Cox, H. E. Tatem, and G.

M. HlGHTOWER.

1974a. Characteristics of dispersions and water-soluble
extracts of crude and refined oils and their toxicity to
estuarine crustaceans and fish. Mar. Biol. (Berl.)
27:75-88.

1974b. The effects of oil on estuarine animals: toxicity,
uptake and depuration, respiration. In F. S. Vernberg
and W. B. Vernberg (editors), Pollution and physiology of
marine organisms, p. 285-310. Academic Press, N.Y.

Benville, p. E., Jr., and S. korn.

1974. A simple apparatus for metering volatile liquids into
water. J. Fish. Res. Board Can. 31:367-368.

Korn, S., N. Hirsch, and J. W. Struhsaker.

1976. Uptake, distribution, and depuration of 14C-benzene
in northern anchovy, Engraulis mordax, and striped bass,
Morone saxatilis. Fish. Bull., U.S. 74:545-551.

Lee, R. F., R. Sauerheber, and G. H. Dobbs.

1972. Uptake, metabolism, and discharge of polycyclic
aromatic hydrocarbons by marine fish. Mar. Biol. (Berl.)
17:201-208.
NEFF, J. M.

1975. Accumulation and release of petroleum-derived
aromatic hydrocarbons by marine animals. In Proceed-
ings, Symposium on Chemistry, Occurrence, and Mea-
surement of Polynuclear Aromatic Hydrocarbons. Am.
Chem. Soc, Chicago, 24-29 Aug. 1975, p. 839-849.

Roubal, W. T., T. K. Collier, and D. C. Malins.

In press. Accumulation and metabolism of carbon-14
labeled benzene, naphthalene, and anthracene by young
coho salmon (Oncorhynchus kisutch). Arch. Environ.
Contam. Toxicol.

Struhsaker, J. W.

1977. Effects of benzene (a toxic component of petroleum)
on spawning Pacific herring, Clupea harengus pallasi.
Fish. Bull, U.S. 75:43-49.

Sid Korn

Northwest and Alaska Fisheries Center Auke Bay Laboratory
National Marine Fisheries Service, NOAA
P.O. Box 155, Auke Bay, AK 99821

NINA HIRSCH
JEANNETTE W. STRUHSAKER

Southwest Fisheries Center Tiburon Laboratory
National Marine Fisheries Service, NOAA
3150 Paradise Drive
Tiburon, CA 94920

636

FOOD HABITS AND FEEDING CHRONOLOGY

OF RAINBOW SMELT, OSMERUS MORDAX,

IN LAKE MICHIGAN'

Rainbow smelt, Osmerus mordax Mitchill, in
Lake Michigan originated from a planting in
Crystal Lake, Mich., in 1912 (Van Oosten 1937).
Since its introduction in Lake Michigan, the smelt
has become abundant, serving as forage for larger,
predatory species (Wright 1968; Harney and Nor-
den 1972) and sustaining a small seasonal sport
and commercial fishery. There has been consider-
able controversy regarding the smelt's role as a
piscivore. Food studies of smelt in Saginaw Bay,
Lake Huron (Gordon 1961) and Lake Erie (Price
1963) have shown that smelt consumes fishes, but
not the alewife, Alosa pseudoharengus . Recently,
a fall collection of smelt revealed that it consumes
young-of-the-year alewives (O'Gorman 1974).

The food habits of Lake Michigan smelt have
not been studied on a seasonal basis and little
information exists concerning its food habits dur-
ing the winter months. Also, feeding chronology
has never been considered. The purpose of this
study was to examine food habits of smelt during 6
mo representing all four seasons and to consider
feeding chronology during two representative
months.

Materials and Methods

Rainbow smelt were collected along the western
shore of Lake Michigan by gillnetting or trawling
on six dates between March 1973 and June
1974 (Table 1). Gill nets were placed on the bottom
overnight and 45-min trawl hauls performed at
4-h intervals over a 24-h period. Gill nets were set
and retrieved at 4- to 6-h intervals over a 24-h
period on 13 October 1973 in order to examine
feeding chronology. Smelt were collected at differ-
ent depths during the course of the study because
of their seasonal inshore-offshore movements.
Fish were frozen shortly after capture.

Feeding chronology was examined on 23 March
and 13 October 1973. Stomachs of smelt used in
this portion of the study were dissected out and the
contents removed. Fish and stomach contents
were dried for 48 h at 60°C and weighed to the

TABLE 1. — Dates, locations, depths, and methods of capture of
Lake Michigan smelt examined in this study.

Collection

Location

Depth

Method of

date

(off shore from)

(m)

capture1

20 Feb 1974

Algoma, Wis

Gill net

23 Mar. 1973

Two Rivers, Wis

Bottom trawl2

21 May 1974

Milwaukee, Wis

Gill net

18 June 1974

Milwaukee, Wis

Gill net

15 Aug 1974

Milwaukee, Wis

Gill net

13 Oct 1973

Port Washington, Wis.

Gill net2

'This research was supported hy the University of Wisconsin
Sea Grant Program. Contribution No. 154, Center for Great
Lakes Studies, University of Wisconsin-Milwaukee, Milwaukee,

Wis.

'All collections made on the bottom
2Feeding chronology examined

nearest milligram. Dried stomach contents were
expressed as a percentage of dry body weight. The
significance of time of day on the amount of food in
stomachs was ascertained with analysis of var-
iance (ANOVA). Means and the ANOVA were
calculated from arcsine transformed data (Sokal
and Rohlf 1969). A chi-square contingency test
was used to ascertain the significance of time of
day on the occurrence of empty stomachs. Sig-
nificance testing was performed at the 0.05 error
level.

Separate smelt were examined for food habits.
These fish were measured to the nearest millime-
ter in length. Stomachs were removed, contents of
each stomach were placed in a Petri dish with
water, and the organisms enumerated. Food
habits were defined in terms of percentage num-
bers and percent dry weight of stomach contents
(Wells and Beeton 1963). Dry weight indices used
were fish, 176; Mysis, 3; Pontoporeia, 1; fingernail
clam, 1; Tendipedidae, 0.4; and Cladocera-
Copepoda, 0.003 (Morsell and Norden 1968).

Results

Stomachs of 515 smelt were examined. Food of
smelt included Mysis; Pontoporeia; alewives
(young-of-the-year and yearlings); and to a lesser
extent, fingernail clams; Tendipedidae pupae;
cladocerans; and copepods (Table 2, 3). A marked
increase in piscivorous food habits was observed in
smelt longer than 180 mm. For this reason, smelt
were divided into two size groups.

Smelt shorter than 180 mm consumed primarily
Mysis during October, February, and March (Ta-
ble 2). Smelt were found in shallower water during
May, June, and August and their stomachs con-
tained yearling alewives, Pontoporeia, and Ten-
dipedidae. Pontoporeia were consumed most fre-
quently during August, when they represented
35% dry weight of the diet. Tendipeds represented
25, 6, and 2 percentage numbers of the diet during
May, June, and August, respectively. However,

637

TABLE 2. — Food habits of Lake Michigan smelt shorter than 180 mm total length. Upper values for food
organisms represent dry weight and values in parentheses are the percentage numbers.

i„Dr3n» ann Food organisms

range of

No of

% of

Copepoda

Collection

lengths

stomachs

Ponto-

Fingernail

Tendi-

and

date

(mm)

examined

empty

Mysis

poreia

Alewife

clam

pedidae

Cladocera

20 Feb. 1974

147
90-1 79

(95)

(3)

—

1
(2)

—

23 Mar. 1973

138
94-179

100

(100)

—

21 May 1974

162

—

109-179

(73)

(1)

(25)

18 June 1974

160

—

140-179

(12)

(1)

(6)

(82)

15 Aug 1973

157

120-175

(26)

(61)

(1)

(9)

(2)

13 Oct 1973

158
115-179

87
(88)

(9)

10
(1)

(2)

—

Total

154

417

(66)

(12)

(<1)

(2)

(6)

(14)

TABLE 3. — Food habits of Lake Michigan smelt 180 mm total
length and longer. Upper values for food organisms represent
percent dry weight and values in parentheses are the percentage
numbers.

Average

and
range of No. of % of
Collection lengths stomachs stomachs
date (mm) examined empty

Food organisms

z _

Mysis

Ponto-
poreia

Alewife

Finger-
nail
clam

LU ~

Z 01
O iii

<-> i

20 Feb. 1974 210

—

1 ■?
o £

180-251
23 Mar, 1973 206

(93)
95

(5)
5

(2)

180-246

(86)

(14)

21 May 1974 199

—

181-238
18 June 1974 206

(78)
1

(22)
99

196-232
15 Aug. 1973 201

(33)
93

(66)

1 82-225
13 Oct. 1973 201

(82)
12

(16)
1

181-248
Total 204

(75)

(14)
2

(9)
57

(2)

FIGL
lecte

(75)

(8)

(17)

(<1)

these numbers never exceeded 1% dry weight of
the diet. Alewives were consumed most frequently
during the June collection when yearlings com-
posed 58% dry weight of the diet. Small alewives
constituted 30 and 10% dry weight of the diet
during August and October, respectively.

Food eaten by smelt 180 mm and longer con-
sisted principally of small alewives and Mysis, but
included small numbers of Pontoporeia and occa-
sionally fingernail clams (Table 3). Yearling ale-
wives represented 94 and 99% dry weight of the
diet during the May and June collections, respec-
tively.

Smelt examined for feeding periodicity aver-
aged 158 mm total length. Weight of stomach con-
tents differed statistically over the 24-h period
during the October collection (F = 9.99, P^O.001,
df = 5, 82). Stomachs contained the most food
(1.5% body weight) at 2430 h and decreased to
0.2% by 0400 h (Figure 1). In addition, the occur-

2.0-

1.5-

\^5

1.0-

0.5-

i 1

-49/15

1200

1600

2000

2400

0400

0800

TIME OF DAY

1. — Feeding periodicity of Lake Michigan smelt col-
lected on 13-14 October 1973. Dry weights of stomach contents
are expressed as a percentage of dry body weight. Vertical lines
represent ±2 SE of the mean and the horizontal black bar the
hours of darkness. The number of empty stomachs and number of
stomachs examined are given near each average.

rence of empty stomachs was dependent upon time
of day (x2 = 31.51, P^O.001, df = 5). Only 1 out of
45 stomachs was empty in the collections between
1600 and 2430 h. In contrast, 23 out of 43 stomachs
were empty between 0400 and 1200 h (Figure 1).
The March collection showed no significant differ-
ences in weight of stomach contents over a 24-h
period.

Discussion

Smelt examined in this study were piscivorous,
consuming young-of-the-year and yearling ale-
wives. Food habit studies of smelt in Saginaw Bay,
Lake Huron (Gordon 1961) and Lake Erie (Price
1963) have shown that smelt consume fishes, but
not alewives. Smith (1970) hypothesized that dif-

638

ferences in their depth distributions could explain
failure to demonstrate predation of smelt upon
alewives. Recently, smelt collected from northern
Lake Michigan during the fall were reported to
contain large numbers of young-of-the-year ale-
wives in their stomachs (O'Gorman 1974). Smelt
examined in this study consumed alewives not
only during the fall, but also during February,
May, June, and August. This study and O'Gor-
man's confirm the smelt's role as a predator of
alewives in Lake Michigan. The high frequency of
small alewives and Mysis in the diet of smelt
suggests a preference for larger food items.

Increased piscivority with size is well known
among predatory fishes. Lake Erie smelt longer
than 126 mm consumed more fishes than smaller
specimens (Price 1963). In this study, smelt 180
mm and longer consumed about three times more
fish than the smaller individuals (grand averages
of 57 and 239c, respectively). According to O'Gor-
man (1974), the smallest smelt which had con-
sumed a fish was 143 mm total length. In the
present study, the smallest smelt which had con-
sumed an alewife was 157 mm.

Seasonal differences in food habits reflect
changes in depth distribution of smelt and annual
changes in abundance of prey. Smelt in Gull Lake,
Mich., consumed primarily copepods and cladoce-
ran during early winter but from May to August,
dipterans were their principal food (Burbidge
1969). Similarly, smelt examined in this study
consumed Tendipedidae only during May, June,
and August, when the flies were abundant. In
Lake Superior, smelt longer than 125 mm con-
sumed mostly Mysis except during May and June,
when copepods ranked first (Anderson and Smith
1971). Likewise, smelt examined in our study
showed a change in food habits from winter to
spring but, in this case, from Mysis to yearling
alewives. Following littoral spawning during
April, smelt were captured in shallower water
where Mysis is not abundant. Schools of small
alewives occupying this zone provided an alterna-
tive food.

Smelt examined during October fed after dusk
and ceased feeding during the night. Mysis rep-
resented 879c dry weight of the diet during the
October collection. This in conjunction with the
known fact that Mysis undergoes a nocturnal ver-
tical migration (Beeton 1960) suggests that their
feeding was associated with the migration, and
consequent availability of the smelt's principal
food organism. Feeding of young-of-the-year sock-

eye salmon, Oncorhynchus nerka, has been re-
lated to diel vertical movements of zooplankton
(Narver 1970). A statistically significant feeding
periodicity was not demonstrated during the
March collection. However, this could be due to
reduced feeding intensity as evidenced by very
small amounts of food present in their stomachs
(e.g., 0.17c body weight).

Literature Cited

ANDERSON, E. D., AND L. L. SMITH, JR.

1971. A synoptic study of food habits of 30 fish species from
western Lake Superior. Univ. Minn. Agric. Exp. Stn.
Tech. Bull. 279:36-49.

BEETON, A. M.

1960. The vertical migration of Mysis relicta in lakes
Huron and Michigan. J. Fish. Res. Board Can. 17:517-
539.

Burbidge, R. C.

1969. Age, growth, length-weight relationship, sex ratio,
and food habits of American smelt, Osmerus mordax
(Mitchill), from Gull Lake, Michigan. Trans. Am. Fish.
Soc. 98:631-640.

GORDON, W. G.

1961. Food of the American smelt in Saginaw Bay, Lake
Huron. Trans. Am. Fish. Soc. 90:439-443.

HARNEY, M. A., AND C. R. NORDEN.

1972. Food habits of the coho salmon, Oncorhynchus
kisutch, in Lake Michigan. Trans. Wis. Acad. Sci. Arts
Lett. 60:79-85.

MORSELL, J. W„ AND C. R. NORDEN.

1968. Food habits of the alewife, Alosa pseudoharengus
(Wilson), in Lake Michigan. Proc. 11th Conf. Great
Lakes Res., p. 96-102.

Narver, D. W.

1970. Diel vertical movements and feeding of underyear-
ling sockeye salmon and the limnetic zooplankton in
Babine Lake, British Columbia. J. Fish. Res. Board Can.
27:281-316.

O'GORMAN, R.

1974. Predation by rainbow smelt {Osmerus mordax) on
young-of-the-year alewives [Alosa pseudoharen-
gus). Prog. Fish. Cult. 36:223-224.
PRICE, J. W.

1963. Study of the food habits of some Lake Erie
fish. Bull. Ohio Biol. Surv., New Ser. 2(1), 89 p.
SOKAL, R. R., AND F. J. ROHLF.

1969. Biometry: The principles and practice of statistics in
biological research. W. H. Freeman and Co.. San Franc,
776 p.

Smith. S. H.

1970. Species interactions of the alewife in the Great
Lakes. Trans. Am. Fish. Soc. 99:754-765.

VAN OOSTEN, J.

1937. The dispersal of smelt, Osmerus mordax (Mitchill),
in the Great Lakes region. Trans. Am. Fish. Soc.
66:160-171.
WELLS, L., AND A. M. BEETON.

1963. Food of the bloater, Coregonus hoyi, in Lake Michi-
gan. Trans. Am. Fish. Soc. 92:245-255.

639

Wright, K. J.

1968. Feeding habits of immature lake trout (Salvelinus
namaycush) in the Michigan waters of Lake Michi-
gan. M.S. Thesis, Michigan State Univ., East Lansing,
42 p.

JEFFREY W. FOLTZ

Department of Zoology

University of Wisconsin-Milwaukee

Present address: Environmental, Population and

Organismic Biology, University of Colorado

Boulder, CO 80309

Carroll R. Norden

Department of Zoology

University of Wisconsin-Milwaukee

Milwaukee, WI 53201

USEABLE MEAT YIELDS IN
THE VIRGINIA SURF CLAM FISHERY1

The weight of surf clam meat landed in Virginia is
estimated by the National Marine Fisheries Ser-
vice, Division of Statistics and Market News
(DSMN) by multiplying bushels landed by a con-
stant of 17 lb (7.71 kg) of total meat per bushel.
However, total meat weight includes the viscera, a
portion of clam not utilized by the industry. Here-
in is an analysis of the yield of useable surf clam
meat weight per bushel and seasonal variability
in meat weight relative to seawater temperature
for Virginia stocks.

lished by National Oceanic and Atmospheric Ad-
ministration (NOAA), Oceanographic Surveys
Branch, exhibited seasonal trends which were cor-
related to changes in useable meat yield per
bushel. Although these temperatures are not in
situ measurements, they are a convenient
covariate of meat yield.

The relationship of MMUWB to MMST was es-
timated by Model II regression analysis since both
variables were subject to sampling error. The
choice of a particular Model II analysis relative to
the source of the variability (measurement errors,
inherent variability, or both) is a somewhat unset-
tled subject recently discussed by Moran (1971),
Ricker ( 1973, 1975) and Jolicoeur ( 1975). No such
theoretical considerations were used in the pre-
sent analyses. Four models were employed to de-
rive "predictive" equations from the 1974 data:
Ricker's (1973) geometric mean analysis (GM re-
gression); Wald's (1940) and Bartlett's (1949)
arithmetic mean analysis (termed AM regression
by Ricker); and principal axis analysis (although
it is recognized that variables do not truly have
a bivariate normal association). Empirically, the
adequacy of the models in predicting the observed
1975 annual mean useable meat weight per
bushel (AMUWB) from the MMST in 1975 was
assessed by a randomized block (two-way)
analysis of variance in which the predicted and
observed MMUWB were the experimental units
replicated by months. MMST was recorded to
0.1°C, MMUWB to 0.01 lb.

Methods

Results and Discussion

Monthly mean useable meat weight per bushel
( MMUWB) was estimated from 181 daily landings
totaling 167,564 bushels in 1974, and 160 daily
landings totaling 270,170 bushels in 1975. The
surf clams were harvested from Virginia stocks in
the region offshore of Cape Henry and south to
about False Cape.

Meat weight landings reported by DSMN are in
pounds, for conformity useable meat weight esti-
mates are also cited in pounds.

Monthly mean seawater temperature (MMST)
was estimated from daily surface water tempera-
tures recorded at Kiptopeke Beach, Va. (lat.
37°10.0'N, long. 75°59.3'W), about 13 n.mi. north
of Cape Henry. These data, collected and pub-

'Contribution No. 801, Virginia Institute of Marine Science,
Gloucester Point, Va.

The MMUWB of surf clams ranged from 10.8 to
14.0 lb in 1974, and from 10.6 to 14.5 lb in 1975
(Table 1). AMUWB, 12.5 lb in 1974 and 12.6 lb in
1975, were nearly identical (P>0.80). There was a
cyclical increase in the MMUWB from the minima
in winter months to maxima in July and August
1974 and in July 1975. The correlation coefficients
(r) for MMUWB and MMST were 0.64 and 0.79 in
1974 and 1975, respectively; r = 0.71 for the
pooled data.

The sinusoidal trend in MMUWB is probably
related to maturation and subsequent spawning.
Ropes ( 1968) reported a major spawning period in
summer and a minor period in fall in New Jersey
waters, but the time and duration of surf clam
spawning in Virginia waters has not been re-
ported. If increasing MMUWB is indicative of
maturation, the data imply that most spawning by

640

TABLE 1. — Number of bushels of surf clams processed, mean
weight tpoundsi of useable meats per bushel, and mean surface
seawater temperature at Kiptopeke Beach by months in 1974
and 1975.

Number of
bushels

Mean useable
meat bushel

Mean seawater
temperature ( C)

Month

1974

1975

1974

1975

1974

1975

Jan. 19.736 18,225

Feb. 11.791 18,489

Mar. 13.450 8,237

Apr 14,415 23.725

May 19.020 39,130

June 12,981 30.049

July 8.328 19.488

Aug. 10.140 23,930

Sept. 14.430 23.038

Oct. 14,558 29,136

Nov 13,388 8,407

Dec 15,327 28,316

Total 167,564 270,170
Annual mean yield bushel

11.7

123
12.3
13.3
138
13.9
140
14.0
12.0
114
10.8
10.8

1252

10.6
11.3
12.7

13.2
12 9
137
14.5
13.7
13.2
12.4
11 8
111

12 59

6.7

12.2

176

21.7

248

250

229

16.2

122

5.9

5.7

6.7

17.1

22.5

24.6

266

232

19.5

14.0

Virginia surf clams is from about May or June
through August. Loesch2 reported a size range of 2
to 18 mm for young-of-the-year surf clams in early
October 1974 and estimated their age ranged from
1 to 4.5 mo. Thus, spawning in 1974 occurred from
at least June through early September.

The regression of MMUWB on MMST for the
1974 data by the four models resulted in the fol-
lowing equations:

Wald's AM regression: W = 10.1 + 0.102 C

Bartlett's AM regression: W = 11.0 + 0.101 C

flicker's GM regression: W = 10.0 + 0.168 C

Principal axis: W = 10.9 + 0.108 C

where W = MMUWB; C = MMST (degrees Cel-
sius); and the first and second values are the inter-
cept and regression coefficients, respectively.

Predicted MMUWB values in 1975 and their
respective AMUWB are presented in Table 2.
Analysis of variance (Table 3) indicated a sig-
nificant difference among the predicted and ob-
served AMUWB values (P<0.001). The Student-
Newman-Keuls multiple range test indicated that
the only significantly different AMUWB was that
associated with the predicted MMUWB estimates
derived from Wald's AM regression. Thus, the
other three regression models predicted the
AMUWB with equally acceptable precision.

The total useable meat yield obtained from the
270,170 bushels of surf clams processed in 1975
was 3,425,654 lb (1,554 metric tons). The sum of
the products of MMUWB and monthly landings

2Loesch, J. G. 1975. Inventory of surf clams in nearshore wat-
ers from Cape Henlopen to the False Cape area. Final Rep.
03-4-043-357, U.S. Dept. Commerc, Natl. Mar. Fish. Serv.,
State-Fed. Fish. Manage. Prog.

TABLE 2. — Mean monthly useable meat weight (pounds) per
bushel for Virginia surf clams in 1975 estimates by four regres-
sion models.

Month

AM
(Wald)

AM
(Bartlett)

GM
(Ricker)

Principal
axis

Jan
Feb.
Mar.
Apr.
May
June
July
Aug.
Sept
Oct.
Nov.
Dec

Annual mean
yield bushel

10.7
10.7
10.8
11 1
11 8
124
126
12.8
12.5
12.1
11.5
10.9

11.65

11.6
11.6
11.7
12.0

12.7
133
13.5
137
13.4
130
12.4
118

12.55

11 1

11.6

129

138

14.1

14 5

139

13.3

124

113

12.57

11.5
115
11.6
12 0
12.8
133
13.6
13.8
13.4
130
12.4
117

12.55

TABLE 3. — Randomized block analysis of variance of the 1975
observed and predicted mean monthly useable meat weight
(pounds) per bushel replicated by months.

Source of
variation

Degree
freedom

Sum of
squares

Mean
square

Critical
ratio (F)

Months

Among models
Within models
Total

50 96
7.97
684

65.77

4.63
1.99
0.155

1283-

•P- 0.001

for all three acceptable models estimated the total
useable meat yield with an error =£0.5%. For all
practical purposes the estimate could have been
made by using the 1974 AMUWB of 12.5 lb. Total
useable meat estimated with this constant was in
error by only 1.4%. However, because of seasonal
changes in body weight, monthly total useable
meat yields should be derived from the MMUWB
predicted by one of the acceptable regression equa-
tions.

The observed AMUWB for the pooled data of
1974 and 1975 is 12.55 lb and can be used if only
annual estimates of useable surf clam meat yields
for Virginia stocks are desired. If a substantial
change in seasonal harvesting occurred, e.g., a
closed season, one of the acceptable regression
equations should be used until a new AMUWB
constant is estimated.

Barker and Merrill (1967) reported losses of 11
to 20^ in body weight with the removal of the
viscera from New Jersey surf clams. However,
they sampled in May and November when the
gonadal portion of the viscera is not near its
maximum weight. The present data indicate that
the reported DSMN yearly landing weights, based
on 17 lb of meats per bushel, must be reduced by
26^ to more accurately ascertain the weight of
Virginia surf clam meats actually shipped to mar-
ket.

641

Acknowledgments

I am indebted to Ned Doughty, owner and op-
erator of the C&D Seafood Company, Oyster, Va.,
who made available his daily surf clam landing
and meat yield data for 1974 and 1975. Also, I
acknowledge the aid of Charles R. Muirhead,
Chief, Oceanographic Surveys Branch, NOAA,
who supplied the monthly mean seawater temper-
ature data for Kiptopeke Beach, Va., prior to its
publication.

Literature Cited

BARKER, A. M., AND A. S. MERRILL.

1967. Total solids and length-weight relationship of the
surf clam, Spisula solidissima. Proc. Natl. Shellfish. As-
soc. 57:90-94.

Bartlett, M. S.

1949. Fitting a straight line when both variables are sub-
ject to error. Biometrics 5:207-212.
JOLICOEUR, P.

1975. Linear regressions in fishery research: Some com-
ments. J. Fish. Res. Board Can. 31:1491-1494.
MORAN, P. A. P.

1971. Estimating structural and functional relation-
ships. J. Multivariate Anal. 1:232-255.
RICKER, W. E.

1973. Linear regressions in fishery research. J. Fish.

Res. Board Can. 30:409-434.
1975. A note concerning Professor Jolicoeur's comments.
J. Fish. Res. Board Can. 32:1494-1498.
ROPES, J. W.

1968. Reproductive cycle of the surf clam, Spisula solidis-
sima, in offshore New Jersey. Biol. Bull. (Woods Hole)
135:349-365.

WALD, A.

1940. The fitting of straight lines if both variables are
subject to error. Ann. Math. Stat. 11:284-300.

JOSEPH G. LOESCH

Virginia Institute of Marine Science
Gloucester Point, VA 23062

MERCURY IN FISH AND SHELLFISH OF

THE NORTHEAST PACIFIC.

III. SPINY DOGFISH, SQUALUS ACANTHIAS

The spiny dogfish, Squalus acanthias Linnaeus, is
a small shark that is abundant in the northeast
Pacific and has been utilized both as a food fish and
as a source of industrial fishery products. This
species was heavily harvested in the 1940's for the
high vitamin A content in the liver oil until the
population was significantly reduced (Alverson

and Stansby 1963). The declining resource, along
with the availability and low cost of synthetic vi-
tamin A, led to the collapse of the fishery in the
early 1950's. Since that time the dogfish popula-
tion has significantly increased, but the low
economic value of the species precluded develop-
ment of any substantial fishery.

Another limiting factor in commercial handling
of dogfish is its rather rapid deterioration. Stansby
et al. (1968) found that rancidity, not bacterial
spoilage, was the principal factor limiting the ice-
storage life of dogfish. If dogfish are properly iced
and handled quickly, off flavors due to rancidity
and the breakdown products of urea are
minimized, and they can be used as food.

Recently there has been a renewed interest in
commercial exploitation of this species in Puget
Sound, primarily because of the export demand
and increased price for frozen dogfish fillets and
bellyflaps in Europe. In 1975 only 0.43 million lb of
dogfish were landed in the State of Washington for
both food and reduction purposes, in contrast to 4.9
million lb landed during 1976 in Puget Sound
ports1 and processed for export to Great Britain
and West Germany. As a result of the current
interest in the use of Puget Sound dogfish as food
and the mercury levels in relation to import regu-
lations of various countries, this investigation was
undertaken to determine the mercury levels in
dogfish from inland waters of the State of
Washington. This report summarizes our findings.

Materials and Methods

The specimens were obtained from commercial
gill net and longline catches through the coopera-
tion of the industry and the State of Washington
Department of Fisheries. They were collected from
the Strait of Georgia near Blaine, Wash. (Figure
1), and from five locations in Puget Sound: Port
Townsend, Port Susan, Seabeck (Hood Canal),
Seattle (Elliott Bay), and Tacoma (Tacoma Nar-
rows to Carr Inlet). Date and location of capture,
round weight, length, and sex were recorded for
each fish. Commercial buyers had established a
minimum acceptable length of 32 in (81.3 cm) for
food processing; therefore, the size distribution of
most samples reflected this market practice rather
than the normal range of lengths in the dogfish
population.

'Preliminary landings data. State of Washington Department
of Fisheries.

642

FIGURE l. — General points of collection of spiny dogfish in Puget
Sound and the Strait of Georgia.

Analytical samples were prepared at this
laboratory and consisted of the skinned and de-
boned edible muscle tissue from both fillets and
bellyflaps. Since the bellyflaps are marketed as a
separate product, they were removed and
analyzed separately. Each sample was ground and
thoroughly mixed prior to subsampling for
analysis.

Total mercury was determined by the U.S. Food
and Drug Administration's Vanadium Pentoxide

Method (Munns 1972), which uses a nitric-sulfuric
acid digestion with vanadium pentoxide as a
catalyst. Final determination was by flameless
atomic absorption spectroscopy with results stated
in parts per million (ppm) of mercury on a wet-
weight basis. All samples were subjected to single
analysis, and those exceeding 0.40 ppm were re-
peated. Differences between replicates did not ex-
ceed 0.05 ppm. A standard fish sample was
analyzed routinely as an internal control.

Results and Discussion

A total of 141 dogfish (127 females, 14 males)
were analyzed for mercury content. Mean mercury
levels in specimens from each area (Table 1) were
at or above the action level of 0.50 ppm set by the
U.S. Food and Drug Administration (FDA)
(Schmidt 1974). Specimens taken from the west
side of Puget Sound (Port Townsend and Seabeck)
contained lower levels of mercury than did those
taken from the east side of Puget Sound ( including
Blaine). The mercury levels appeared to increase
from north to south on each side of the Sound. This
phenomenon may be due to the absence of industry
at points of collection on the west side of the Sound
and an increase of industrial activity from north to
south along the east side of the Sound; however,
these observations on the effect of catch area may
not be representative of the total Puget Sound
dogfish population.

The mean mercury level for the 127 female
dogfish fillets was 0.92 ppm, which is almost twice
the FDA action level. The mercury level in 91
females (729c) exceeded 0.50 ppm and 48 (387c)
exceeded 1.0 ppm. Regression analysis showed a
positive correlation between mercury content of

TABLE 1. — Mercury concentration in spiny dogfish from the State of Washington.

No. of

fish

Weight (g)

Length
Range

cm)
Mean

Mercury (ppm)

Fillets

Bellyflaps

No. of

fish

Range

Mean

■0 5 ppm
No.

No o
fish

Range

Mean

>0.5
No

ppm

Location

Range

Mean

Females

Port Townsend

2,190-4,160

3,194

85-102

939

0.16-1.28

0.50

40.9

0.14-1.18

0.41

25.0

Seabeck

2,465^.915

3,372

86-106

935

0 34-1.43

0.63

58.3

0 29-1.30

0.57

583

Blame

2.360-5,065

3,469

86-106

946

0 20-1.38

0.71

75.0

0 17-1.27

062

75.0

Port Susan

1,340-4,560

3,033

70-106

896

0.09-2.28

0.89

625

0 17-1.95

1.02

86.3

Seattle

5,230-7,930

6,706

105-117

1099

0.82-1.94

1.16

100 0

—

Tacoma

700-6,630

3.862

60-113

952

0.43-2.58

1.41

969

038-2.24

1.25

969

127

700-7,930

3,608

60-117

942

127

0.09-2.58

Males

0.92

71.6

107

0 14-2.24

0.85

72.9

Port Susan

1,445-2,645

1,864

75-87

79.4

0.21-0 98

0.64

85.7

0.49-0.95

072

50.0

Seattle

2.025-3,400

2,626

85-93

890

1 16-1.61

1.38

100 0

—

Tacoma

1,240-2.180

1,728

68-84

77.3

0.94-1 27

1.15

100 0

0.92-1.24

1.08

100 0

1.240-3,400

2,052

68-93

81.7

0.21-1.61

096

92.8

0.49-1 24

093

80.0

643

the fillets and fish weight for the 127 females ( Fig-
ure 2). The weight of individual fish was evenly
distributed in each of the area samples with the
exception of the small sample of eight fish from
Seattle. Although these were the largest fish col-
lected, they contained less mercury than smaller
fish from other areas. The Seattle sample does not
appear to be adequate in number and may not be
representative of the population. In all areas, ex-
cept Seattle, the correlation coefficients were sig-
nificant for the relationship of mercury content to
weight (Table 2). The correlations between mer-
cury content and fish length were significant but
slightly lower in four of the five groups showing

2.5
E 2.0

>- 1.5
rr

0.5

+
++ + +
-

+ ^^4- ++ ++ +

+
+

2000 4000 6000
WEIGHT (GRAMS)

8000

FIGURE 2. — Relationship between weight and mercury concen-
tration in female dogfish fillets.

TABLE 2. — Correlation coefficients (r) and significance level (a)
of mercury content to the weight and length of female spiny
dogfish fillets from the State of Washington.

No. of

Weight vs

mercury

Length vs

mercury

Location

fish

Port

Townsend

0.645

0.01

0.507

0.05

Seabeck

0 648

0.05

0616

0.05

Blame

0 768

0.001

0.756

0.001

Port Susan

0 699

0.001

0643

0001

Seattle

0 501

NS1

-0.414

Tacoma

0.601

0.001

0.648

0.001

127

0.576

0.001

0.530

0.001

1Not significant

positive coefficients. We expected a more sig-
nificant correlation with length, since the weight
of the females varied as to whether or not they
were pregnant and the length of gestation. Childs
et al. (1973) stated that mercury is not concen-
trated in the fetuses in situ; therefore, the mercury
level in the flesh of the female is presumably un-
affected by pregnancy.

The bellyflaps of 107 female and 5 male dogfish
were analyzed (Table 1 ). Bellyflaps of the fish from
Seattle and 10 small females from Port Susan
were not analyzed. The bellyflaps contained
slightly less mercury than the corresponding
fillets; however, the percentage exceeding the ac-
tion level (739?-) was not significantly different
from that for fillets.

The limited data on mercury levels in male
dogfish (Table 1) indicated that essentially all
male dogfish over the minimum commercial size
(81.3 cm) would exceed the FDA action level. Of
the 14 males analyzed, 13 (939r ) exceeded the ac-
tion level. The mean weight of the males (2,052 g)
was less than the mean weight of the females
(3,608 g), yet the mean mercury level was higher
(0.96 ppm for males and 0.92 ppm for females).
This difference may be attributed to the fact that
males are smaller than females of the same age
(Jensen 1966). Our findings agree with those of
Forrester et al. (1972) on the mercury levels in
male and female spiny dogfish from inland waters
of British Columbia.

A study by Childs and Gaffke (1973) included 88
dogfish taken off the Oregon coast and showed a
similar correlation of mercury level to weight and
length but a lower mean level of 0.602 ppm mer-
cury in all muscle samples. This suggests that
dogfish taken from the Pacific Ocean off the Ore-
gon coast may contain less mercury than the popu-
lation sampled in this study of the inland waters of
Washington. Tagging studies by Kauffman ( 1955)
and Holland ( 1957) indicated that offshore dogfish
populations may be highly migratory. Jensen
(1966) noted that the nature of the dogfish's sea-
sonal migration in offshore coastal waters was not
clearly understood. Alverson and Stansby (1963)
stated that the dogfish within Puget Sound show
less tendency to migrate and that Puget Sound
stocks are apparently somewhat independent
from the coastal and offshore stocks. They further
stated that some movement of dogfish may occur
between ocean areas and Puget Sound. The mer-
cury levels found in our study are most probably
those of a population indigenous to Puget Sound.

Acknowledgments

We thank Raymond Buckley, James Beam, and
Mark Pederson of the Marine Fish Program of the
State of Washington Department of Fisheries for
obtaining most of the specimens used in this
study.

644

Literature Cited

ALVERSON, D. L., AND M. E. STANSBY.

1963. The spiny dogfish (Squalus acanthias) in the north-
eastern Pacific. U.S. Fish Wildl. Serv., Spec. Sci. Rep.
Fish. 447, 25 p.
CHILDS, E. A., AND J. N. GAFFKE.

1973. Mercury content of Oregon groundfish. Fish. Bull.,
U.S. 71:713-717.
CHILDS, E. A., J. N. GAFFKE, AND D. L. CRAWFORD.

1973. Exposure of dogfish shark feti to mercury. Bull.
Environ. Contam. Toxicol. 9:276-280.

FORRESTER, C. R., K. S. KETCHEN, AND C. C. WONG.

1972. Mercury content of spiny dogfish (Squalus acan-
thias) in the Strait of Georgia, British Columbia. J. Fish.
Res. Board Can. 29:1487-1490.
HOLLAND, G. A.

1957. Migration and growth of the dogfish shark, Squalus
acanthias (Linnaeus), of the eastern North Pacific. Wash.
Dep. Fish., Fish. Res. Pap. 2(11:43-59.
JENSEN, A. C.

1966. Life history of the spiny dogfish. U.S. Fish Wildl.
Serv., Fish. Bull. 65:527-554.
KAUFFMAN, D. E.

1955. Noteworthy recoveries of tagged dogfish. Wash.
Dep. Fish., Fish. Res. Pap. l(3):39-40.
MUNNS, R. K.

1972. Mercury in fish by cold vapor AA using sulfuric-
nitric acid/V205 digestion. Food Drug Admin. Inf. Bull.
1500, 8 p.
SCHMIDT, A. M.

1974. Action level for mercury in fish and shellfish. Fed.
Regist. 39(236), Part 11:42738-42740.

STANSBY, M. E., G. KUDO, AND A. HALL.

1968. Chemical spoilage pattern of grayfish. Food
Technol. 22:765-768.

ALICE S. HALL

FUAD M. TEENY

ERICH J. GAUGLITZ, JR.

Northwest and Alaska Fisheries Center
National Marine Fisheries Service, NOAA
2725 Montlake Boulevard East
Seattle, WA 98112

LOCALIZED MASS MORTALITY

OF RED SEA URCHIN,

STRONGYLOCENTROTUS FRANC1SCANUS,

NEAR SANTA CRUZ, CALIFORNIA

Johnson (1971) reported on the occurrence of a
mass mortality of red sea urchin, Strongylocen-
trotus franciseanus (Stimpson 1857) off Point
Loma, San Diego, in the summer of 1970, and she
detailed the symptoms of the diseased sea urchins.
Large areas of the test, particularly of the inter-
ambulacra, were denuded of spines and epidermis.

These denuded areas were chalky white with
green blotches and often were bordered by a ring of
swollen tissue. The test plates of the denuded area
were layered and a middle "red-friable" layer with
disorganized cellular structure replaced the nor-
mal plate tissue and ossicle. In some cases, lesions
broke through the denuded tests and these appar-
ently led to the animals' death. The internal or-
gans appeared to be normal. Johnson (1971) was
unable to determine the cause of these symptoms,
but she suggested that a microorganism, perhaps
a fungus, might be responsible.

The area affected in the 1970 mass mortality off
Point Loma was limited to a few hectares (Johnson
1971). It was first noted in May 1970, when the
center of the area was littered with dying sea ur-
chins while the perimeter had fewer diseased
animals with only small patches of denuded tests.
The affected area did not spread, and by the middle
of summer, many of the surviving urchins were
regenerating spines. Diseased animals with par-
tially denuded tests were difficult to find in
November 1970.

We report here two other localized mass mor-
talities of S. franciseanus in central California,
which seem to be similar to the one documented by
Johnson (1971). One was found in 3-5 m of water
off the southeast side of Ano Nuevo Island (lat.
37°06'25"N, long. 122°19'30"W). It was first ob-
served on 18 July 1976, and revisited on 31 July
1976. Diseased animals with drooping spines and
partially denuded tests were found scattered
among healthy-appearing individuals. They did
not seem to be clumped or segregated, although
most diseased animals were in the open while
healthy-appearing animals tended to be under
ledges or in crevices. Diseased animals did not
hold onto the rocks as normal animals usually do,
and they were picked up easily by divers. Empty
tests of recently dead animals littered portions of
the bottom. Red sea urchins were the only animals
noted to be affected at the Ano Nuevo Island site.
Other areas of similar depth to the south and
northwest of Ano Nuevo Island supported numer-
ous healthy-appearing red sea urchins and none
with denuded tests.

The diseased animals collected from Ano Nuevo
Island were very similar to those described by
Johnson (1971) (Figure 1). Portions of the test
were denuded of spines while the remainder of the
test was covered with normal-appearing spines.
The affected test plates were layered with a thin
greenish surface layer, a red-friable middle layer

645

FIGURE 1. — Four diseased Strongylocentrotus franciscanus col-
lected on 31 July 1976 from 3-5 m depth off Ano Nuevo Island,
Calif. Each animal is about 10 cm in diameter. Note the large
portion of test denuded of spines in each animal.

and a nearly normal white inner layer (the "cal-
lus" layer, see Pearse and Pearse (1975) for de-
scription of the layers of the test plates and
methods for examining them). Portions of the
inner layer of the affected area were discolored
reddish brown, however, often with a rather
blotchy appearance. Clorox1 cleaned and thin-
ground preparations of the plates showed that
middle layer of the diseased plates had lost much
of its trabecular structure and there were large
spaces between the middle layer and the inner
layer. In the most diseased plates, the inner layer
could be separated easily from the middle layer of
the plates. The ambulacral system with the water
vascular canals, ampullae, and radial nerve were
all discolored reddish brown under the diseased
portions of the test and much of these tissues were
speckled with dark reddish-brown flakes, prob-
ably clumped coelomocytes. The internal organs
in other portions of the diseased animals appeared
normal.

'Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

The symptoms noted in the diseased animals at
Aho Nuevo Island in 1976 seemed identical to
those described for diseased animals found at
Point Loma in 1970 by Johnson ( 1971 ). Such simi-
larity suggests that the same disease organism
may be involved in these mass mortalities. Alter-
natively, the symptoms could reflect a general re-
sponse to localized infections or disruptions of the
test from a variety of physical, chemical, or biolog-
ical agents. As Johnson (1971) cautioned, careful
microbiological work needs to be done before the
causative agent( s) of these mass mortalities can be
identified.

The Aho Nuevo Island site of the mass mortality
was revisited on 24 September 1976. Sea urchins
were scarce compared with the earlier visit and
most were nestled in crevices. Only one animal
was found with symptoms of the disease; it had a
narrow strip down one interambulacrum which
was denuded of spines. However, when this ani-
mal was examined in the laboratory, it was found
that a large portion of the diseased interambu-
lacrum and adjacent ambulacrum was covered
with short regenerating spines, and the ambulac-
rum was concave and grossly deformed. Six other
normal-appearing animals were brought into the
laboratory and two of these had small areas on the
test with regenerating spines. From these obser-
vations, it appeared that the mass mortality had
ceased and some of the animals survived and re-
generated their lost spines.

The second mass mortality of S. franciscanus we
found in 1976 occurred at 4-6 m depth off the east
side of Point Santa Cruz (lat. 36°57'05"N, long.
122°01'30"W); this area was described by Matti-
sonetal. ( 1977). Animals looking "sick" and losing
spines were seen in the area in early June (A. L.
Shanks, J. D. Trent pers. commun.). We did quan-
titative studies at fixed stations off Point Santa
Cruz on 28-30 June 1976 and again on 10-11
September 1976. Although we found no animals
with denuded tests at our study stations, there was
a notable decrease in the number of animals pres-
ent compared with the counts made in the previ-
ous two summers (Figure 2). The number of ani-
mals at the seaward edge of the kelp forest main-
tained densities of about 55-65/10 m2 during the
summers of 1974 and 1975. Fifty and one hundred
meters seaward of the kelp forest, lower densities
of 20-30 animals/ 10 m2 occurred on the barren-
appearing rocks. In the summer of 1976, we found
only about 20 animals/10 m2 at the edge of the
kelp forest and about 1-2/10 m2 50 and 100 m

646

80-

50-

40-

30-

20-

Station 2

Seaward edge of kelp

J S J S
1974 1975

J S
1976

Strongylocentrotus froncisconus

Station 3
50 m seaward
of kelp

J S
1974

J S
1975

J s
1976

Station 4
100 m seaward
of kelp

J S
1974

J S
1975

J S
1976

FIGURE 2. — Densities of Strongylocentrotus franciscanus at
three fixed stations off Point Santa Cruz as estimated in June
and September 1974, 1975, and 1976. Each station encompassed
an area of 2,500 m2 and the density estimates are based on counts
from 12 randomly selected 10 m2 quadrats. Station 1 was located
50 m inshore from Station 2 within the kelp forest and always
contained very low densities of sea urchins, <1/10 m2. Figure
shows mean number of animals per 10 m2 and the standard er-
ror of the mean. The arrows indicate the period of the mass
mortality.

offshore. This represents a decrease of about 60%
of the dense population of animals at the kelp
forest edge and about 95% of the animals farther
offshore. The area of each study station was about
2,500 m2. In absolute terms, the decrease in
number of animals within the study station at the
edge of the kelp forest was about 9,000 animals,
while in each of the two study stations 50 and 100
m farther offshore, about 5,500 animals were lost.

About 10% of the animals remaining in our
Point Santa Cruz study site in June 1976 had large
conspicuous portions of the test covered with
regenerating spines only 1-5 mm long, contrast-
ing noticeably with the surrounding normal-
appearing areas. Since we did not detect any ab-
normalities in January 1976, the mass mortality
probably followed its full course in less than 6 mo,
as did the one described by Johnson (1971), and
probably the one we observed at Ario Nuevo
Island.

During August-October 1976 we (M. B. Y. and
C. R. A.) surveyed the 35-km coastline between
Point Santa Cruz and Aho Nuevo Island at 2-km
intervals. Most of the kelp forests along this
coastline have dense populations of S. francis-
canus along their seaward edge, similar to condi-
tions found at Point Santa Cruz before 1976. No
evidence of mass mortality of these populations of
sea urchins was found, either as large numbers of

dying animals or unusually low numbers of ani-
mals. However, diseased animals with partially
denuded tests were found occasionally all along
the coastline with estimated incidences of 1 in
1,000 animals. These observations suggest that
potential outbreaks of localized mass mortalities
could occur in many places under suitable condi-
tions.

The mass mortality of S. fransicanus at Point
Loma in 1970 and those at Aho Nuevo Island and
Point Santa Cruz in 1976 were all relatively small
and localized in both space and time. Moreover, all
the animals in the populations were not killed.
Rather, within less than 6 mo low numbers of
normal and healthy-appearing animals were
present and there was little trace of the mass
mortalities — no piles of empty tests remained.
Small localized mass mortalities might occur in
other areas and not be noticed or reported. If they
do, such mass mortalities could be important in
regulating the distributions and densities of sea
urchin populations. Moreover, since a major por-
tion of the recruitment of juveniles of S. francis-
canus occurs under adult animals (Tegner and
Dayton 1977), near complete mass mortalities,
such as that in our study stations 50 and 100 m
seaward of the kelp forest off Point Santa Cruz,
could have long lasting effects. Such a source of
mortality could have practical importance both as
means of minimizing overgrazing of kelp by sea
urchins (North and Pearse 1971) and as a threat to
the developing sea urchin fishery in California
(Kato 1972).

Acknowledgments

We appreciate discussions and critical readings
of the manuscript by V. A. Gerard, A. H. Hines,
and V. B. Pearse. We are grateful to R. Buchsbaum
for the photograph used in Figure 1 . This work was
supported by NOAA Office of Sea Grant, U.S. De-
partment of Commerce, under Grant No. 04-6-
1584402 and the Marine Mammal Commission,
Contract No. MMCAC029.

Literature Cited

JOHNSON, P. T.

1971. Studies on diseased urchins from Point Loma. Kelp
Habitat Improvement Project, Annual Report, 1970-
1971, p. 82-90. Calif. Inst. Technol., Pasadena.

KATO, S.

1972. Sea urchins: A new fishery develops in California.
Mar. Fish. Rev. 34(9-10):23-30.

647

MATTISON, J. E., J. D. TRENT, A. L. SHANKS, T. B. AKIN, AND
J. S. PEARSE.

1977. Movement and feeding activity of red sea urchins
{Strongylocentrotus franciscanus) adjacent to a kelp
forest. Mar. Biol. (Berl.l 39:25-30.
NORTH, W. J., AND J. S. PEARSE.

1970. Sea urchin population explosion in southern
California coastal waters. Science (Wash., D.C.)
167:209.
PEARSE, J. S., AND V. B. PEARSE.

1975. Growth zones in the echinoid skeleton. Am. Zool.
15:731-753.
TEGNER, M. J., AND P. K. DAYTON.

1977. Sea urchin recruitment patterns and implications
of the commercial fishery. Science (Wash., D.C.) 196:
324-326.

JOHN S. PEARSE

Daniel P. Costa

Marc b. Yellin

Catherine R. Agegian

Center for Coastal Marine Studies
University of California, Santa Cruz
Santa Cruz, CA 95064

FIRST RECORD OF A SECOND MATING
AND SPAWNING OF THE SPOT PRAWN,
PANDALUS PLATYCEROS, IN CAPTIVITY

The spot prawn, Pandalus platyceros Brandt, is
the largest species of the family Pandalidae. It
supports a minor fishery within its range of San
Diego to the Bering Strait, Korea, and Japan in
depths to 532 m (Butler 1964). The prawn is being
studied at the National Marine Fisheries Service
(NMFS) Aquaculture Research Station, Manches-
ter, Wash., as a possible companion crop to Pacific
salmon reared in floating net pens (Mahnken
1975; Prentice 1975). One phase of this work is to
investigate the reproductive potential of the
prawn in captivity.

The prawn is a protandric hermaphrodite, i.e.,
an individual matures first as a male (at age
1.5 yr), breeds one or more times as a male, passes
through a transitional phase (at age 2.5 yr), and
becomes a functional female (at age 3.5 yr) (Butler
1964). In studies of natural populations in south-
ern British Columbia, Butler (1964) found that
few if any females breed more than once and
suggested that the females die soon after spawn-
ing.

At the Aquaculture Research Station, prawn
culture and breeding experiments have been car-
ried out since 1973. The matings reported in this
study were made with laboratory-cultured males

and captured, wild females. The females were cap-
tured in ovigerous condition in 1974 from Hood
Canal, Wash., and their eggs hatched in the
laboratory during February and March 1975.
Therefore, we know these females have spawned
at least once, and since their prior history is un-
known, there is the possibility that some or all
may have spawned more than once.

The spawned females (103) were held from
March to August at the Aquaculture Research
Station in floating net pens or in benthic cages 10
m beneath floating net pens containing salmon.
The postspawning survival was 100% through
August 1975 for both groups. All prawns in the net
pens were maintained on a diet of frozen clam
meat, Panope generosa, and salmon mortalities.
The benthic cage group did not receive any sup-
plemental food.

In August varying densities of spawned females
and cultured males (Table 1) were placed either in
three net pens, eight laboratory tanks, or in a
benthic cage. The net pens were constructed of
18-mm mesh (stretch measure) knotless nylon
with 6.8 m2 of substrate per pen available to the
prawns. The top of each pen was covered with
black plastic sheeting. Each laboratory tank had
0.24 m2 of available substrate. All water entering
the tanks was sand filtered and not recycled. The
single benthic cage was constructed of vinyl-
coated wire mesh (9.0-mm stretched measure) and
had 2.6 m2 of substrate available to the prawns.
All test groups were fed the clam-salmon diet
with the exception of those in the benthic cage
which received no supplemental food. A continu-
ous low-level mortality was observed among the
females from August to early October 1975 which
reduced their survival to 39.8%.

Survival of the female prawns was not depen-
dent upon stocking density; however, survival was
significantly greater in the benthic cage and
laboratory tanks than in the net pens (Table 1).

TABLE 1. — Survival (percent in parentheses) and second spawn-
ing of female Pandalus platyceros in three seawater systems.

Container
type

No of prawns
per container

Female

Male

Density

of
prawns'

Survival of

previously

spawned

females

Survivors

spawning

a second

time

Benthic cage

(9 m deep)

Net pen 1

Net pen 2

Net pen 3

Laboratory

tanks2

'Prawns per square meter of available substrate
2A total of eight laboratory tanks.

5
29
24
29

5
56
43
89

3.8

12.5

9.9

17.4

16.7

4 (80 0)

12(44.8)

6 (25.0)

6 (20.7)

12(75.0)

3 (75.0)
10(84.6)

4 (66.7)

5 (83.3)

12(100 0)

648

Females held in the bottom cage or in the labora-
tory tanks were subject to less ambient light, more
stable temperatures, and water below the photo-
synthetic zone. The laboratory water system
utilizes water pumped from an area 2 m above the
sea floor, thereby approximating the water avail-
able to the bottom caged prawns. Previous work
has shown that juvenile and yearling prawns are
sensitive to rapidly fluctuating water tempera-
ture, light, and plankton blooms (Rensel and
Prentice1).

A second spawning was recorded for 85.4% of the
surviving females. The average carapace length of
these spawners was 39.2 mm (SD = 1.31). Eggs
developed normally, producing viable larvae, but
the fecundity was low, ranging from 10 to 1,000
eggs. The fecundity of wild bred stocks is 2.000-
5,000 eggs per female. The reduced fecundity in
the female prawns spawning for the second time
may be due to nutritional or environmental fac-
tors. However, in some instances the female
prawns were observed actively removing eggs
from their own abdomens, using the second
pereiopod. In other cases, we observed egg losses
during the holding period due to abrasion on the
nets and tanks.

Multiple breeding and spawning are common in
other families of caridean shrimps, but among the
Pandalidae only P. montagui Leach in the north-
eastern Atlantic Ocean has been known to spawn
for two consecutive years (Allen 1963). This study
shows that female spot prawns can also success-
fully breed, spawn, and hatch eggs for a second
time. This is important to both the aquaculturist
and the field biologist. If multiple breeding also
takes place in wild populations, then estimates of
year-class recruitment based on single spawning
populations are in error.

Literature Cited

ALLEN, J. A.

1963. Observations on the biology of Pandalus montagui
[Crustacea: Decapoda]. J. Mar. Biol. Assoc. U.K.
43:665-682.

BUTLER, T. H.

1964. Growth, reproduction, and distribution of pandalid
shrimps in British Columbia. J. Fish. Res. Board Can.
21:1403-1452.

MAHNKKN, C. V. W.

1975. Status of commercial net-pen farming of Pacific

salmon in Puget Sound. Proc. 6th Annu. Meet.

World Maricult. Soc, p. 285-298.
PRENTICE, E. F.

1975. Spot prawn culture: status and potential. In C. W.

Nyegaard (editor), Proceedings of a Seminar on Shellfish

Farming in Puget Sound, Oct. 7, 1975, Poulsbo, Wash., p.

1-11. Wash. State Univ., Coll. Agric, Coop. Ext. Serv.,

Pullman.

John E. Rensel
earl f. Prentice

Northwest and Alaska Fisheries Center
National Marine Fisheries Service, NOAA
2725 Montlake Boulevard East
Seattle, WA 98112

EFFECT OF DISSOLVED

OXYGEN CONCENTRATION AND

SALINITY ON SWIMMING SPEED OF

TWO SPECIES OF TUNAS

Studies on captive skipjack tuna, Katsuwonus
pelamis, have determined three physiological
parameters that may operate to delimit oceanic
distribution of this fish. If 1) a lower temperature
limit of 18°C, 2) a size-dependent upper tempera-
ture limit, and 3) a lower oxygen limit of 5 ppm are
mapped onto the temperature and oxygen levels of
the central Pacific area, the resulting model is
consistent with many of the peculiar features of
the geographical distribution of the skipjack tuna
(Barkley et al.1). In particular, the exclusion of
adult skipjack tuna from warm, oxygen-poor wa-
ters of the eastern tropical Pacific Ocean is
explained.

But the physiological parameters used in the
model were either speculative — upper tempera-
ture limits — or based upon acute and stressful
experimental conditions — lower oxygen and tem-
perature limits. Gooding and Neill2 determined
the lower oxygen limit by introducing tunas into a
small tank (1.8 x 2.4 x 0.6 m oval) containing

'Rensel, J. E., and E. F. Prentice. A comparison of growth and
survival of cultured spot prawns, Pandalus platyeeros Brandt, at
two salmon farming sites in Puget Sound. Unpubl. Manuscr.,
25 p. Northwest and Alaska Fish. Cent., Natl. Mar. Fish. Serv.,
NOAA, Seattle. Wash.

'Barkley, R. A., W. H. Neill, and R. M. Gooding. Skipjack tuna
habitat based on temperature and oxygen requirements.
Manusc. in prep. Southwest Fish. Cent. Honolulu Lab., Natl.
Mar. Fish. Serv., NOAA, Honolulu, HI 96812. (Material pre-
sented at 26th Tuna Conference, Lake Arrowhead, Calif., 29
Sept.-l Oct. 1975.)

2Gooding, R. M., and W. H. Neill. Respiration rates and reac-
tions to low oxygen concentrations in skipjack tuna. Katsuwonus
pelamis. Manusc. in prep. Southwest Fish. Cent. Honolulu Lab.,
Natl. Mar. Fish. Serv.. NOAA, Honolulu, HI 96812.

649

seawater at a given level of oxygen saturation.
Swimming speed and survival time were mea-
sured. They found that survival time and swim-
ming speed were independent of oxygen levels in
excess of 4 ppm; below 4 ppm survival time was
directly and swimming speed inversely propor-
tional to dissolved oxygen amounts. So apparently
4 ppm is close to the incipient lower lethal limit for
skipjack tuna under the given experimental con-
ditions. For modeling distribution limits, Barkley
et al. (see footnote 1) used a more conservative
figure of 5 ppm.

However, a physiological limit of 4 or 5 ppm is
not necessarily a behavioral limit; if the limit is
approached slowly under natural and otherwise
unstressful conditions, can a fish adaptively re-
spond? Whitmore et al. (1960) found that coho
salmon, Oncorhynchus kisutch, avoided water of
lowered oxygen levels yet which produced no res-
piratory distress. In contrast, kawakawa, Eu-
thynnus affinis, a species closely related to skip-
jack tuna, tolerated 2-ppm water for short periods
in order to get food (Chang and Dizon3).

In the present experiment, I tested the re-
sponses of free-swimming tunas — both skipjack
tuna and yellowfin tuna, Thunnus albacares —
encountering slowly changing oxygen levels. The
rate of change was comparable with that which a
tuna might encounter in nature. Yellowfin tuna
were tested for comparison because they are
abundant in the same areas of the eastern tropical
Pacific avoided by large skipjack tuna. Finally,
salinity fronts have been suggested as a factor
determining distribution, so responses to decreas-
ing salinity levels were also examined.

Materials and Methods

Eight skipjack tuna and three yellowfin tuna
were tested with decreasing oxygen levels, and
three skipjack tuna, and one yellowfin tuna were
tested with decreasing salinity levels. Fish were
chosen from stocks at the Kewalo Research Facil-
ity of the Southwest Fisheries Center, National
Marine Fisheries Service, NOAA, Honolulu,
Hawaii. Tuna stocks for this experiment were kept
in outdoor tanks (7.3 m diameter x 1.2 m deep)
until used; they were then removed by angling

3Chang, R. K. C, and A. E. Dizon. Low oxygen levels as
barriers to voluntary movements of tunas. Manusc. in prep.
Southwest Fish. Cent. Honolulu Lab., Natl. Mar. Fish. Serv.,
NOAA, Honolulu, HI 96812. (Material presented at 26th Tuna
Conference, Lake Arrowhead, Calif., 29 Sept.-l Oct. 1975.)

with a barbless hook and transferred to the swim
chamber in a plastic bag partially filled with wa-
ter. This is a good transfer technique since fish on
occasion have fed immediately after transfer.

The responses of tunas to decreasing oxygen and
salinity levels were examined in a tank system
consisting of a swim chamber equipped with
photocells for monitoring and recording fish be-
havior. (For details see Dizon et al. 1977.) The
swim chamber was a 6.1 m diameter x 0.61 m deep
fiber glass tank fitted with a concentric inner wall
so the fish was constrained to swim in a 0.75-m
channel around the periphery. Six laps equaled
100 m. Water (24°C) was introduced and removed
from the swim channel through two pairs of con-
centric rings of polyvinyl chloride pipe. Entering
(or exiting) water divided equally into two inflow
(or outflow) pipes, each flowing countercurrent to
the other to provide minimum oxygen or salinity
asymmetry and horizontal transport of water
within the swim channel. Water was recirculated
through an outside circuit at 1,136 liters/min to
insure thorough mixing of any introduced new
water. New seawater was added to the tank at
38 liters/min.

Oxygen was reduced in the tank by replacing
the 38 liters/min new seawater with 38 liters/min
anoxic seawater obtained at our well head before
aeration and introduced into the intake of the
1,136 liters/min recirculation pump. Oxygen de-
creased approximately exponentially within the
swim chamber — 0.06 ppm/min after 30 min and
0.03 ppm/min after 60 min. Salinity levels in the
swim chamber were reduced by introducing aer-
ated freshwater (38 liters/min) into the pump in-
take. Salinity decreased exponentially — 0.07%o/
min after 30 min and 0.03%o/min after 60 min.

Passage of the fish was sensed at four photocell
stations (six photocells/station) at 90° intervals
around the periphery of the swim channel. Infor-
mation from the photocells was translated into
swimming speed (minutes per lap), direction
(clockwise or counterclockwise), and frequency of
reversals or swimming direction by digital logic
equipment and printed on adding machine tape.

Procedures were quite simple; tuna (starved for
1 day) were moved into the tank and allowed 100
min to habituate; swimming speeds were continu-
ously recorded to provide baseline data to compare
with behavior during periods of changing oxygen
or salinity. After 100 min, a test was started and
behavior was recorded as salinity or oxygen de-
creased. Oxygen and salinity levels were allowed

650

to reach 2 ppm and 29%n, respectively. After reach-
ing these levels (about 200 min), test water was
shut down and normal seawater restored. The fol-
lowing morning fish were removed, weighed, and
measured, and survivors were returned to holding
tanks. Oxygen and salinity levels were monitored
by oxygen meter and salinograph; samples were
taken periodically for laboratory analysis to verify
the instruments.

Results and Discussion

Behavioral responses to decreasing levels of sa-
linity were unremarkable; Table 1 summarizes
results from three skipjack tuna and one yellowfin
tuna. No consistent swimming speed changes
were observed during periods when salinity de-
creased from about 34%n to 29%o. Although sample
size is small, these tunas did not make any dra-
matic response to salinity changes of magnitudes
expected within their normal habitat.

Figure 1 illustrates typical results from tunas
encountering slowly changing oxygen concentra-
tion. At or about 4 ppm, skipjack tuna (Figure la)
demonstrated an abrupt increase in swimming
speed. In most fish tested, speed increased to over 2
lengths/s. Yellowfin tuna, in contrast, showed no
alteration in swimming speed as oxygen levels
decreased (Figure lb).

Figure 2 summarizes the oxygen experiment
observations from eight skipjack tuna and three
yellowfin tuna. Individual points plotted are me-
dian swimming speeds for the eight skipjack tuna
grouped by: 1) before treatment and 2) 1-ppm dis-
solved oxygen intervals both decreasing and in-
creasing, i.e., 6-5, 5-4, 4-3, 3-2, and 2-3, 3-4, 4-5,
5-6. Number of swimming speeds sampled ranged
from under 5 to over 100 depending on the number
of laps swum during each interval. Heavy line
connects the grand median of each interval. Simi-

TABLE 1. — Effect of decreasing salinity on mean swimming
speed in tunas.

DISSOLVED OXYGEN

Item

(length/s)

Skipiack tuna 1 (38.3 cm,

925 g)

Before salinity change

2.10

0.40

During salinity change

1.82

0.40

Skipjack tuna 2 (37.7 cm,

882 g)

Before salinity change

2.03

026

During salinity change

2.37

0.19

Skipjack tuna 3 (42.0 cm,

1.352 g)

Before salinity change

1.21

007

During salinity change

1 16

0.06

Yellowfin tuna 1 (45.3 cm

1.491 g)

Before salinity change

1 54

030

During salinity change

1.81

026

C5
Z
UJ

SKIPJACK TUNA

1.0

YELLOWFIN TUNA

o
en
(/>

0 50 100 150 200 250 300 350 400

ELAPSED TIME (MINUTES)

FIGURE 1. — Effect of dissolved oxygen level on swim speed in
two species of tunas. Swim speeds are median values sampled for
10-min periods.

lar data for each yellowfin tuna (decreasing oxy-
gen intervals only) are included for comparison.

Not all of the skipjack tuna survived the treat-
ment; three of the eight died when oxygen levels
dropped below about 2.5 ppm. Survival times for
skipjack tuna under conditions of low oxygen are
as follows: in excess of 240 min at 4 ppm, 59 min at
3 ppm, and 18 min at 2 ppm ( Gooding and Neill see
footnote 2). My data are consistent with this
resistance-time distribution, and both studies
support the Barkley et al. (see footnote 1)
hypothesis that there does exist a low oxygen level
that limits the observed oceanic distribution of
skipjack tuna.

Yellowfin tuna are not apparently stressed dur-
ing the exposures to the low oxygen water
employed. In separate tests done after the expo-
sures to decreasing oxygen, two additional yel-
lowfin tuna survived and made no overt locomo-
tory changes when introduced directly into water

651

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3.0
2.8
2.6
24
2 2
2.0
1.8

S 1.6

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1.0-

• DECREASING OXYGEN
a INCREASING OXYGEN

YF-C

YF-B

BEFORE
TEST

5.5 4.5 3.5
DISSOLVED OXYGEN LEVEL (ppm)

2.5

FIGURE 2. — Summary of data from the oxygen experiment ob-
servations from eight skipjack tuna and three yellowfin tuna.
Dots — decreasing oxygen levels, median swim speeds grouped
by 1-ppm intervals and "before" test observations. Open trian-
gles — increasing oxygen levels, median swim speeds grouped by
1-ppm intervals. Solid line — grand median for eight skipjack
tuna. Broken lines — medians for each of the three yellowfin
tuna, decreasing oxygen levels only.

containing 1.4 and 1.6 ppm oxygen. They survived
a 200-min exposure and a 100-min recovery
period. By way of contrast, brook trout, Salvelinus
fontinalis, LD50'sfor 1.5 ppm and 1.4 ppm were 300
and 100 min, respectively (Shepard 1955). The
brook trout and the yellowfin tuna were swim-
ming at about the same speeds, 1.0-1.5 lengths/s.
Although conditions of the two experiments are in
no way similar, these data do imply that yellowfin
tuna are at least as low oxygen tolerant as brook
trout. The higher energy requirements (larger
fish, warmer water) of yellowfin tuna allow this
conclusion. Perhaps if oxygen levels dropped low
enough in my tank (1.4 ppm is about the lowest
that could be achieved), an increase in speed simi-
lar to that in skipjack tuna would have been ob-
served.

Increased swimming speed should function
either to remove the fish from suboptimal areas (if

coupled with some directive stimuli) or to provide
more water to the gills — tunas are ram ven-
tilators. Within the skipjack tuna habitat, water
deficient in oxygen is found within and below the
thermocline (Barkley et al. see footnote 1). Ap-
propriate behavior would be to swim up and out of
the low-oxygen water. Even without a change in
direction, angle of attack of pectoral fins, or body
attitude, increased swimming speed alone will
cause a tuna to rise due to increased lift ( Magnu-
son 1973).

Faster swimming speeds do not seem to be a
response to increase ram ventilation (open mouth
swimming). Increased flow over the gills providing
more oxygen delivery is offset by increased res-
piratory demands imposed by faster swimming.
Under conditions of saturated seawater (7.2 mg
02/liter), 15% head loss along the respiratory flow
path (Brown and Muir 1970), a conservative oxy-
gen utilization factor of 75% (Stevens 1972), and a
1 cm2 mouth gape (Brown and Muir 1970), oxygen
is delivered to the gills at the rate represented by
the middle broken line (Figure 3). This, of course,
also increases as swimming speed increases. Res-
piratory demand (solid black line) and oxygen de-
livery intersect at two points: the lower is at the
minimum swimming speed that can still furnish
sufficient oxygen for an animal in an almost basal
state and the upper is a point at which exponen-
tially increasing respiratory demand again ex-
ceeds linearly increasing oxygen delivery.

The latter would seem to be maximum sus-
tained swimming speed; anaerobic metabolism
would be necessary at speeds above. However,
neither function (anaerobic or aerobic) may be cor-
rectly extrapolated to the faster swimming speeds.
Respiratory demand might well be less at higher
speeds if swimming efficiency increases.

Yet, if dissolved oxygen concentration drops to 4
ppm, increase in swimming speed is an inefficient
way to make up the deficit (lower broken line).
But, increase gape to 2 cm2 (I am assuming for
argument's sake that this doubles ventilation vol-
ume) restores the amount of oxygen delivered
(upper broken line). In summary, I suspect that
increased swimming speed of skipjack tuna en-
countering oxygen-deficient water is not due to
ram ventilation needs but rather is a behavioral
response to remove an animal from a suboptimal
area. Considering the relative expense of faster
swimming in terms of oxygen needs, the modest
increases in swimming speeds observed are prob-
ably very adaptive in that they should cause a

652

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FIGURE 3. — Respiratory demand (Gooding and Neill see foot-
note 2 1 versus respiratory supply ( Brown and Muir 1970; Stevens
1972) as a function of swimming speed in a 40-cm, 1.4-kg skip-
jack tuna. Respiratory demand increases geometrically while
respiratory supply increases arithmetically with increasing
swimming speed. When oxygen concentration decreases it is
more efficient to increase ram ventilation by increasing gape
rather than simply swimming faster.

fairly rapid rise in the water column at a relatively
low energetic cost. Yellowfin tuna, in contrast, are
just not stressed at the levels of saturation
employed in our experiments. Yellowfin tuna
should be able to occur in the anoxic water in or
below the thermocline and since in the eastern
central Pacific Ocean anoxic, cool waters are as
inhospitable as the upper too warm waters, skip-
jack tuna may find no suitable habitat.

Literature Cited

BROWN, C. E., AND B. S. MUIR.

1970. Analysis of ram ventilation offish gills with applica-
tion to skipjack tuna \Katsuwonus pelamis). J. Fish.
Res. Board Can. 27:1637-1652.
DIZON, A. E., W. H. NEILL, AND J. J. MAGNUSON.

1977. Rapid temperature compensation of volitional
swimming speeds and lethal temperatures in tropical
tunas (Scombridae). Environ. Biol. Fish. 2:83-92.
MAGNUSON, J. J.

1973. Comparative study of adaptations for continuous
swimming and hydrostatic equilibrium of scombroid and
xiphoid fishes. Fish. Bull., U.S. 71:337-356.
SHEPARD, M. P.

1955. Resistance and tolerance of young speckled trout
iSalvelinus fontinalis) to oxygen lack, with special refer-

ence to low oxygen acclimation. J. Fish. Res. Board Can.
12:387-446.

Stevens, e. D.

1972. Some aspects of gas exchange in tuna. J. Exp. Biol.
56:809-823.

Whitmore, C. M., C. E. Warren, and p. Doudoroff.

I960. Avoidance reactions of salmonid and centrarchid
fishes to low oxygen concentrations. Trans. Am. Fish.
Soc. 89:17-26.

ANDREW E. DIZON

Southwest Fisheries Center Honolulu Laboratory
National Marine Fisheries Service, NOAA
P.O. Box 3830. Honolulu, HI 96812

A NONLETHAL LAVAGE DEVICE FOR

SAMPLING STOMACH CONTENTS OF

SMALL MARINE MAMMALS

Historically, the only expedient and successful
method for determining the species upon which
marine mammals feed has been to kill the animal,
remove its stomach, and examine the contents in
the laboratory (e.g., Wilke and Nicholson 1958;
Tautsumi et al. 1961; Shomura and Hida 1965;
Fiscus and Baines 1966; Fitch and Brownell 1968;
Imler and Sarber 1947). This method, however,
does not always work. For example, when actively
feeding marine mammals are harpooned or shot,
they sometimes regurgitate most or all of their
food. While regurgitation by live captured marine
mammals is possible, it does not appear to be a
significant problem. Of the last 10 cetaceans that I
have captured alive and later released unharmed,
none has regurgitated during the capturing, hand-
ling, or releasing process. Although some re-
searchers have reported on stomach samples from
stranded marine mammals (e.g., Houck 1961;
Fitch and Brownell 1968), these samples may not
be representative of feeding habits of active
healthy organisms.

Passage of the Marine Mammal Act in 1972 has
made it necessary to develop techniques beside
killing if we are to continue certain types of
marine mammal research. A useful tool for deter-
mining feeding habits of delphinids and certain
small pinnipeds would be a portable stomach
pump device capable of being used in the field. To
be effective, this device must be capable of remov-
ing small identifiable bits of food such as otoliths,
scales, preopercular bones, squid beaks, or other

653

skeletal elements from the stomach of a pinniped,
or forestomach of a small cetacean. I do not con-
sider it essential to be able to remove whole fish or
squid from marine mammal stomachs, as several
recent or current marine mammal food habit
studies have successfully utilized the above-
mentioned skeletal elements for prey species iden-
tification (Fitch and Brownell 1968; Evans 1975;
Burns and Lowry 1976).

Soft tissue digestion in pinnipeds and small
cetaceans is normally quite rapid, thus it is possi-
ble to remove partially digested skeletal elements
from the stomachs of live animals a few hours
after the animal has eaten; and yet, because such
elements as otoliths, preopercular bones, and
squid beaks tend to resist this rapid digestion,
they are still available for removal several hours
after being consumed. In this paper I report on
development and testing of a lavage designed to
sample marine mammal stomach contents with-
out killing the animal.

the entubation tube was modified by sealing the
distal end (stomach end) with a machined Nylon
plug, opening a side suction port (8.9 cm long by
1.25 cm wide) in the side of the tube 5 cm back from
the Nylon plug, and removing the inflation cuff to
allow passage of the irrigating solution into the
stomach opposite the suction port. The assembled
unit is detailed in Figures 1 and 2. The completed
unit was tested in the laboratory using a 2-liter
beaker in place of a marine mammal stomach.

Marine mammals were first tested at the Naval
Undersea Center and Sea World, Inc. in San Die-
go, Calif., in December 1975. A total of five ani-
mals were lavaged, including two California sea
lions, Zalophus californianus, two Pacific white
sided porpoise, Langenorhynchus obliquidens,
and one bottlenose porpoise, Tursiops truncatus.
Animal weights ranged from 70 kg for the small-
estZ. californianus to 210 kg for the T. truncatus.
All animals except a 100-kgZ. californianus had
fasted for at least 24 h prior to being lavaged. The

Methods

Several design criteria were considered essen-
tial. The lavage unit had to be effective in remov-
ing skeletal elements, simple to operate, portable,
and capable of being used without injuring the
animal. Discussions with persons who had
pumped human stomachs or were familiar with
the characteristics of marine mammal digestive
tract anatomy resulted in the decision to utilize a
water-driven aspirator to create suction. A 30-mm
outside diameter by 1.0-m long Rousch Equine1
endotracheal tube was modified for use as the irri-
gation and content removal device. These two
pieces were coupled to a machined Plexiglas
stomach content collection chamber with short
sections of clear vinyl tubing. A ball valve was
attached to the aspirator for vacuum control. The
completed unit utilized normal city water pres-
sure (35-50 psi) delivered through a 12-mm
diameter rubber hose to the ball valve as driving
source for the aspirator. A small hand pump was
connected to the irrigation port on the side of the
entubation tube so that warm (25°-35°C) water
could be pumped into the animal's stomach to
create a slurry which could be easily removed by
light suction. To facilitate removal of this slurry,

FIGURE 1. — Schematic of lavage device. Entubation tube (a),
Nylon end plug (b), side suction port (c), irrigation port (d),
irrigating solution hand pump (e), stomach content collection
chamber (f).

'Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

FIGURE 2. — Oblique view of the aspirator (a) and control valve
(b) attached to the top of the collecting chamber of lavage device.

654

100-kg sea lion had been fed 5 kg of surf smelt,
Hypomesus pretiosus, 3 h prior to being lavaged.

Successful lavage required two procedures: 1)
restraint of the animal and 2) entubation, irriga-
tion, and suction. Restraint varied greatly depend-
ing on whether a pinniped or cetacean was to be
lavaged. Delphinids are generally easy to re-
strain. The procedure many investigators have
used with success utilizes a canvas sling and
U-shaped pipe frame to hold the animal (Ridgway
1972). Normally the use of a sling is sufficient
restraint, however A. B. Irvine (pers. commun.)
has also used a wooden step ladder covered with
closed cell foam padding and padded straps to re-
strain large or especially aggressive delphinids.
This latter procedure requires that the animal be
gently lowered onto the padded ladder and then
immobilized with the padded straps. Pinnipeds
are more difficult to restrain in the field than del-
phinids. Squeeze cages (Ridgway 1972) are gen-
erally effective, but are normally too cumbersome
and heavy to use at sea. During the lavage test in
San Diego, the squeeze cage was used with suc-
cess, though considerable care was taken to avoid
being severely bitten. Use of the padded wooden
ladder and straps as a restraining technique for
pinnipeds in the field appears reasonable but
needs testing.

With the animal successfully restrained, we
proceeded with entubation after lubricating the
entubation tube with a jelly lubricant. The
plugged end of the tube was gently pushed down
the animal's esophagus. After completing the en-
tubation I waited a few moments to make sure the
animal was breathing normally. If the animal
gagged or abnormal respiration was evident, I
quickly but gently removed the tube. If respiration
was normal, I connected the content collection
chamber and irrigation solution hose and pumped
about 300 ml of warm water into the stomach.
Warm water was used to avoid thermal shock to
the stomach. I then opened the vacuum control
valve and applied suction to the stomach. As suc-
tion began to remove the stomach content slurry,
more irrigating solution was pumped into the
stomach. In this manner a 2- to 3-liter food sample
was collected in a period of about 5 min. When I
felt I had collected sufficient material for test pur-
poses, I shut off the suction, ceased pumping ir-
rigating solution, and gently removed the stomach
tube. The stomach contents were filtered from the
slurry using a small hand vacuum pump and then
preserved in 70% alcohol.

Results

Using the above procedure otoliths, muscle
myomeres, skeletal bones, and scales were col-
lected from all five marine mammals. The animals
tested were returned to their tanks unharmed and
were doing well several days later.

Discussion

Using the equipment described and associated
procedure it was possible to remove almost all of
the diluted stomach slurry by suction; and by
rotating the tube while suctioning, it was possible
to vacuum the rugae of the stomach in order to
collect otoliths and squid beaks which tend to ac-
cumulate in these folds. J. E. Fitch of the Califor-
nia Department of Fish and Game has used fish
otoliths as a means to identify prey species on a
routine basis. With experience it is possible to
correlate size of otoliths and approximate sizes
and weights of the intact fish. The Alaska De-
partment of Fish and Game is presently establish-
ing such an otolith reference collection, allowing
not only identification of otoliths but also estima-
tion of intact prey length and weight (L. F. Lowry
pers. commun.).

The limiting factor in the use of this device ap-
pears to be the ability of the capture personnel to
restrain specimens. Pinnipeds over 150 kg are
probably too large to be effectively restrained
mechanically, and are therefore very difficult or
impossible to entubate. Cetaceans, perhaps as
large as 500 kg, can be effectively entubated and
lavaged since these animals are generally much
more easily restrained out of water than the pin-
nipedia. In addition, certain pinnipeds, e.g., Erig-
nathus barbatus,Phoca hispida,P.fasciata, feed to
a greater or lesser degree on soft-bodied crusta-
ceans, and these prey organisms would probably
be effectively destroyed by suction and passage
through the entubation tube (L. F. Lowry pers.
commun.).

I have made no mention of the use of chemo-
restraining techniques because I feel that these
methods are still unsuited for general use in the
field, especially with cetaceans. With proper
supervision, they have proven effective for re-
straining captive pinnipeds. In August 1972, I
used a chemorestraining solution of Ketamine-
Atropine onZ. californianus in the field. Although
dosages were at the level recommended by marine
mammal research veterinarians, I found the drugs

655

to be too slow acting to be generally effective for
stopping highly mobile pinniped species before
they could reach the sea. Two major drawbacks to
chemorestraints in a field situation are judging
animals' size adequately for effective dose deter-
mination, and the time required for the animal to
recover sufficiently to be able to swim unassisted
and maintain pace with the herd or pod from
which it was captured. Should future work develop
either drugs or techniques which allow safe and
semi-instantaneous chemorestraint of any marine
mammal species, then these drugs or techniques
would be extremely useful when used in connec-
tion with the stomach pump. Until such drugs are
available, I believe physical restraint is indicated
during the lavage procedure.

Acknowledgments

I am indebted to S. H. Ridgway and the person-
nel at the Naval Undersea Center for their pa-
tience and cooperation, and to Lanny Cornell and
his staff at Sea World, Inc. for their cooperation
during testing of this lavage device. I thank L. F.
Lowry of the Alaska Department of Fish and
Game and A. B. Irvine of the U.S. Fish and
Wildlife Service for their comments concerning
restraint and use of this technique. I also thank
Larry Hobbs and Mike Honing of University of
California Santa Cruz and Steve Leatherwood of
the Naval Undersea Center for assisting me dur-
ing tests of the lavage. Thanks also to S. B. Stone of
Marine General Hospital, K. S. Norris, T. P. Dohl,
and R. W. Pierce of University of California Santa
Cruz for their comments concerning design of the
equipment. K. S. Norris, J. S. Leatherwood, W. E.
Evans, T. P. Dohl, and Robert Hoffman reviewed
the manuscript. This work was supported by con-
tract number MM4AC013 from the U.S. Marine
Mammal Commission.

Literature Cited

BURNS, J. J., AND L. F. LOWRY.

1976. Trophic relationships among ice inhabiting phocid
seals. In Environmental assessment of the Alaskan con-
tinental shelf, Vol. 1. Marine mammals. Principal inves-
tigators' reports for the year ending March 1976, p. 303-
332. U.S. Dep. Commer., Environ. Res. Lab., Boulder.
EVANS, W. E.

1975. Distribution, differentiation of populations and
other aspects of the natural history of Delphinus delphis
Linneaus in the north eastern Pacific. Ph.D. Thesis.,
Univ. California, Los Ang., 144 p.
FISCUS, C. H., AND G. A. BAINES.

1966. Food and feeding behavior of Steller and California
sea lions. J. Mammal. 47:195-200.
FITCH, J. E., AND R. L. BROWNELL, JR.

1968. Fish otoliths in cetacean stomachs and their impor-
tance in interpreting feeding habits. J. Fish. Res. Board
Can. 25:2561-2574.
HOUCK, W. J.

1961. Notes on the Pacific striped porpoise. J. Mammal.
42:107.
IMLER, R. H., AND H. R. SARBER.

1974. Harbor seals and sea lions in Alaska. U.S. Fish
Wildl. Serv., Spec. Sci. Rep. 28, 23 p.
RIDGWAY, S. H.

1972. Homeostasis in the aquatic environment. In S. H.
Ridgway (editor), Mammals of the sea: biology and
medicine, p. 590-747. Charles C. Thomas, Springfield,
111.
SHOMURA, R. S., AND T. S. HIDA.

1965. Stomach contents of a dolphin caught in Hawaiian
waters. J. Mammal. 46:500-501.
TSUTSUMI, T., Z. KAMIMURA, AND K. MIZUE.

1961. Studies on the little toothed whales in the West Sea
Areas of Kyusyu — V. About the food of the little toothed
whales. [In Jap., Engl, abstr.] Bull. Fac. Fish.
Nagasaki Univ. 11:19-28.
WILKE, F„ AND A. J. NICHOLSON.

1958. Food of porpoises in waters off Japan. J. Mammal.
39:441-443.

JOHN D. HALL

U.S. Fish and Wildlife Service

Office of Biological Services - Coastal Ecosystems

800 A Street- Suite 110

Anchorage, AK 99501

656

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Fishery Bulletin

CONTENTS

Vol. 75, No. 4 October 1977

CHAO, LABBISH N., and JOHN A. MUSICK. Life history, feeding habits, and
functional morphology of juvenile sciaenid fishes in the York River estuary, Vir-
ginia 657

JONES, ALBERT C, and ALEXANDER DRAGOVICH. The United States shrimp

fishery off northeastern South America (1972-74) 703

PETERSON, WILLIAM T., and CHARLES B. MILLER. Seasonal cycle of zooplank-
ton abundance and species composition along the central Oregon coast 717

PERRIN, WILLIAM F., DAVID B. HOLTS, and RUTH B. MILLER. Growth and
reproduction of the eastern spinner dolphin, a geographical form of Stenella lon-
girostris in the eastern tropical Pacific 725

CARLINE, ROBERT F. Production by three populations of wild brook trout with

emphasis on influence of recruitment rates 751

SECKEL, GUNTER R., and MARIAN Y. Y. YONG. Koko Head, Oahu, sea-surface
temperatures and salinities, 1956-73, and Christmas Island sea-surface tempera-
tures, 1954-73 767

DeWITT, HUGH H. A new genus and species of eelpout (Pisces, Zoarcidae) from the

Gulf of Mexico 789

LAURS, R. MICHAEL, and RONALD J. LYNN. Seasonal migration of North Pacific
albacore, Thunnus alalunga, into North American coastal waters: Distribution,
relative abundance, and association with Transition Zone waters 795

SMITH, RONAL W., and FRANKLIN C. DAIBER. Biology of the summer flounder,
Paralichthys dentatus, in Delaware Bay 823

JOHNS, D. MICHAEL, and WILLIAM H. LANG. Larval development of the spider

crab, Libinia emarginata (Majidae) 831

ROSENBLATT, RICHARD H., and JOHN L. BUTLER. The ribbonfish genus Des-

modema, with the description of a new species (Pisces, Trachipteridae) 843

INGHAM, MERTON C, STEVEN K. COOK, and KEITH A. HAUSKNECHT. Oxy-
cline characteristics and skipjack tuna distribution in the southeastern tropical
Atlantic 857

Notes

KRYGIER, EARL E., and WILLIAM G. PEARCY. The source of cobalt-60 and migra-
tions of albacore off the west coast of North America 867

PHINNEY, DUANE E. Length-width-weight relationships for mature male snow

crab, Chionocoetes bairdi 870

(Continued on next page)

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Contents-continued

FINE, MICHAEL L., HOWARD E. WINN, LINDA JOEST, and PAUL J. PERKINS.

Temporal aspects of calling behavior in the oyster toadfish, Opsanus tau 871

WEINSTEIN, MICHAEL P., and KENNETH L. HECK, JR. Biology and host-parasite

relationships of Cymothoa excisa (Isopoda, Cymothiodae) with three species of

snappers (Lutjanidae) on the Caribbean coast of Panama 875

HOWELL, W. HUNTTING, and DAVID H. KESLER. Fecundity of the southern New

England stock of yellowtail flounder, Limanda ferruginea 877

GREEN, JOHN H., and LOUIS J. RONSIVALLI. "Mock fish" method for studying

microbial inhibiting agents 880

GOLDBERG, STEPHEN R., and WILLIAM C. TICKNOR, JR. Reproductive cycle of

the pink surfperch, Zalembius rosaceus (Embiotocidae) 882

HARRELL, LEE W. Gallbladder lesions in cultured Pacific salmon 884

BOEHLERT, GEORGE W. Timing of the surface-to-benthic migration in juvenile

rockfish, Sebastes diploproa, off southern California 887

INDEX, VOLUME 75 891

Vol. 75, No. 3 was published on 27 October 1977.

LIFE HISTORY, FEEDING HABITS, AND FUNCTIONAL

MORPHOLOGY OF JUVENILE SCIAENID FISHES

IN THE YORK RIVER ESTUARY, VIRGINIA1 2

Labbish N. Chao3 and John A. Musick4

ABSTRACT

Four abundant sciaenid fishes, Cynoscion regalis, Bairdiella chrysoura, Micropogonias undulatus, and
Leiostomus xanthurus, use the York River, Va., as a nursery ground and as an adult seasonal feeding
ground. In addition, six species of sciaenids, Menticirrhus saxatilis, M. americanus , Sciaenops ocellata,
Cynoscion nebulosus, Pogonias cromis, and Larimus fasciatus, are present in the estuary occasionally.
Yearling C. regalis were first caught in April and young-of-the-year in July or August. Yearling B.
chrysoura were first caught in March or April and young-of-the-year in July or August. Juvenile
Micropogonias undulatus and Leiostomus xanthurus maybe present in the York River all year-round.
Young-of-the-year L. xanthurus were first caught in April and M. undulatus were first caught in
August. Small M . undulatus ( <20 mm TL) were caught from August to June, which may indicate a
prolonged spawning season (or a late spawning stock). Emigration to the ocean was found in all the four
species during late fall or early winter. Water temperature and dissolved oxygen seemed to be the most
important factors in the spatial and temporal distributions of these four species in the York River.
Mouth position, dentition, gill rakers, digestive tract, pores and barbels, nares, and body shape of six
sciaenid species, Larimus fasciatus, C. regalis, B. chrysoura, M. undulatus, Menticirrhus saxatilis, and
Leiostomus xanthurus, were found to be important in locating and ingesting prey in the water column.
Stomach contents indicated that the food partitioning of these six species was closely correlated with
the species and their prey habitat. Larimus fasciatus, C. regalis, andB. chrysoura fed mainly above the
bottom, whereas Micropogonias undulatus, Menticirrhus saxatilis, and L. xanthurus fed on epifauna,
infauna, or both. Juvenile sciaenids are able to coexist in the same area because of differences in spatial
and temporal distribution, relative abundance, and food habits.

Sciaenid fishes are among the most important in-
shore bottom fishery resources of the Atlantic and
Gulf of Mexico coasts of the United States (Roith-
mayr 1965; Joseph 1972; Gutherz et al. 1975).
Sciaenid fishes usually use the estuary as a nur-
sery ground and seasonal feeding ground. Among
the 14 species of sciaenids recorded from
Chesapeake Bay proper (Musick 1972), young-of-
the-year of 10 species were caught in the York
River system during this study. Leiostomus
xanthurus, Micropogonias undulatus, Bairdiella
chrysoura, and Cynoscion regalis were the most
abundant species. Menticirrhus saxatilis, M.
americanus, Sciaenops ocellata, C. nebulosus,

lA portion of a dissertation submitted to the School of Marine
Science, College of William and Mary, Williamsburg, Va., in
partial fulfillment of the requirements for the degree of Doctor of
Philosophy in Marine Science, by the first author, May 1976.

Contribution No. 816, Virginia Institute of Marine Science,
Gloucester Point, Va.

3Ichthyology Unit, Vertebrate Zoology Division, National
Museum of Natural Sciences, Ottawa, Ontario, Canada K1A
0M8.

■•Virginia Institute of Marine Science, Gloucester Point. VA
23062.

Manuscript accepted April 1977.

FISHERY BULLETIN: VOL. 75, NO. 4. 1977.

Pogonias cromis, and Larimus fasciatus were
caught only occasionally.

Juvenile sciaenids, except the Atlantic croaker,
Micropogonias undulatus, usually entered the
York River in late spring and left in late fall.
During this period, sciaenid fishes dominated bot-
tom trawl catches in the York River (Colvocores-
ses 1975; Markle 1976). By yearly average, they
composed more than 50^ of the total catch by
weight and 18 to 289c by number of individuals.
The purpose of this study is to describe the coexis-
tence of the four most abundant juvenile sciaenids
in the York River system, Va., based upon relative
abundance, temporal and spatial distribution,
length frequency, apparent movements, and feed-
ing habits. Morphological structures related to
feeding habits and habitats were also studied.
Specimens of the banded drum, Larimus fasciatus,
and the northern kingfish, Menticirrhus saxatilis,
were included to show the range of variability in
the feeding habits of juvenile sciaenids. Bottom
trawl surveys conducted by the Virginia Institute
of Marine Science (VIMS) from January 1972 to

657

December 1974 provided the data for analyses of
distribution and food habits. An analysis of fish
community structure based on this data has been
reported by Colvocoresses (1975).

The York River and its major tributaries
(Pamunkey and Mattaponi rivers) represent an
estuarine system which is relatively well known
biologically and is relatively undisturbed (Boesch
1971). The general trend of geomorphology, hy-
drography (salinity, dissolved oxygen, and tem-
perature), ecology, and alteration by man of the
area were described by McHugh (1967), Boesch
(1971), and Brehmer.5

MATERIALS AND METHODS

Survey Programs

Seven longitudinal strata (A, B, C, D, E, F, and
G) and three cross-sectional substrata (north
shoal, channel, and south shoal) within each
stratum were sampled monthly (Figure 1). Shoal
hauls were usually in water <4 m and channel
hauls in water >5 m deep. Randomly numbered
square grids (540 m on a side) were assigned as
trawl stations. In the lower 16 km (10 miles) of the
York River, strata A, B, C, and D were sampled
from March 1972 to December 1974. The upper
part of the York River was sampled from January
1972 to March 1974, but the random method was
not used until June 1972 and strata E, F, and G
were not designated until January 1973. Before
the random sampling program, fixed sampling
stations in the channel were assigned at 8-km
(5-mi) intervals from the mouth of the York River
(mile zero) up to 45 km (mile 28, also see Haven
1957; Markle 1976). Data from fixed station sam-
ples (January-May 1972) were combined within
the strata for analyses. Lower portions of the Mat-
taponi and Pamunkey rivers (strata: M and P)
were sampled after January 1973. Three sub-
strata (1, 2, and 3) were set at 8-km (5-mi) inter-
vals for the lower 24 km (15 mi) upstream from
their confluence with the York River (about 45 km
from the York River mouth). Each sampling
stratum was divided into station grids, each
measuring 540 m on a side; four to six grid stations
were sampled randomly from each stratum
monthly.

FISHERY BULLETIN: VOL. 75, NO. 4

Gear

Bottom trawl tows were against the current, of
5-min duration on the bottom with a 4.9-m ( 16-ft)
semiballoon otter trawl (7-m rope, 1.9-cm bar
mesh, 0.63-cm bar mesh cod end liner), 7-m bridle,
and 0.6-m weighted otter doors at a speed of ap-
proximately 90 m/min. Nine stations were sam-
pled monthly with beach seines along the shores of
lower parts (strata A-D) of the York River (Figure
1) and three replicate hauls were made with a
15.25-m (50-ft) bag seine (1.8 m deep with a square
bag, 0.64-cm bar mesh in the wing and 0.48-cm bar
mesh in the bag). Thirteen beach seine stations
were selected along the shores of the upper part of
the York River (strata E-G, Figure 1). These sta-
tions were only sampled from July to October in
1972 and 1973 with a 30.5-m (100-ft) bag seine.
Beach seine data were used only for length fre-
quency analysis in the present study. Hy-
drographic (salinity, temperature, and dissolved
oxygen) data were collected from both surface and
bottom water.

Sampling Procedure

All fishes were identified, counted, and weighed
in the field or laboratory. Total length (TL), mea-
sured from snout to the posterior tip of the caudal
fin (on the midline), was taken to the nearest mil-
limeter. All individuals of each species were mea-
sured from each trawl haul. For very large
catches, at least 25 individuals were subsampled.
Specimens were randomly selected for stomach
analyses and preserved in 109c Formalin;6
stomachs were dissected out and transferred to
409c isopropanol or 109c ethanol. Stomach con-
tents were identified to the lowest practical taxon
and frequency of occurrence of each item was re-
corded.

The standard methods of Hubbs and Lagler
(1964) were used for all counts and measurements,
if applicable. Upper and lower jaw lengths were
measured from tips of the premaxilla and dentary,
respectively, to the symphysis at the posterior
corner of the mouth gape. Digestive tracts were
removed from the fish. The intestine was
straightened and measured from its junction with
the stomach to the anus. Osteological observations

5Brehmer, M. L. 1970. Biological and chemical studies of Vir-
ginia's estuaries. Unpubl. manuscr., 120 p. Va. Inst. Mar. Sci.,
Gloucester Point.

6Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

658

CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCIAENIDFISHES

77° 00

76° 40'

STRATA: a,b,c,d,e,f,g,m,p.

SUBSTRATA: north shoal
south shoal
channel ;•_'.:

M-l, M-2.M-3

P-I.P-2.P-3

BEACH SEINE STATION

37?
40'

76°]40'

FIGURE 1. — The trawl strata, substrata, and beach seine stations in the York River estuary, Va. Strata: A-G, M, and P. Substrata:
north shoal, channel, and south shoal. Substrata in Mattaponi River expressed as M-l, M-2, and M-3, in Pamunkey River as P-l, P-2,
and P-3. River distances from the mouth of York River (0 km) are indicated in kilometers.

were made on cleared and stained specimens, ac-
cording to the methodology of Taylor (1967).

The nomenclature used for the study fishes fol-
lows Chao (in press). Micropogonias must replace
Micropogon because the generic name Micropogon
was preoccupied by Boie (1826 in Aves). The
specific name chrysoura is used instead of chrys-
ura for Bairdiella because the spelling chrysourus
was used by the original author (Lacepede
1803:166).

RESULTS AND DISCUSSION

Hydrographic Description

Water depth, temperature, salinity, and dis-
solved oxygen were measured with each sample
and are listed in the appendix section of Chao
(1976). The benthic environment was of particular

importance to the present study. Mean values for
bottom temperature, salinity, and dissolved oxy-
gen in each stratum from May 1972 to August
1973 are summarized in Figure 2, to show sea-
sonal patterns in the York River estuary.

Temperature

The bottom water temperature of the York
River (Figure 2) was lowest in January and high-
est in July (1973) or August (1972). The gradual
increase of temperature from April to June and
the decrease from October to December are most
important to migratory fishes in the York River
(Markle 1976). In winter months (December-
February), the bottom temperature of the upper
portion of the York River was lower than that of
the lower portion. No apparent differences in
temperature were found among the shoal and the

659

FISHERY BULLETIN: VOL. 75, NO. 4

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the bottom temperature
(°C — solid line), salinity
(%o — dashed line), and dissol-
ved oxygen (milligrams/
liter — dotted line) in the York
River estuary from May 1972
to August 1973. Strata: A-G
in York River and P in
Pamunkey River. Substrata:
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nel and S = south shoal.

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660

CHAO and MUSICK. LIFE HISTORY OF JUVENILE SCIAENID FISHES

channel stations. In spring months (March-May),
bottom temperatures increased rapidly, and the
upper portion of the York River had slightly
higher temperatures than the lower portion. The
shoal stations also showed a slightly higher mean
bottom temperature than the channel stations. In
summer months (June-August), the bottom
temperature of the upper portion of the river was
higher than the lower portion. The shoal stations
also showed a higher mean bottom temperature
than the channel stations. In fall months
(September-November), bottom temperature de-
creased rapidly. The upper portion of the river had
slightly higher temperatures than the lower por-
tion in the early fall (September-October). In
early winter (December), bottom water tempera-
ture was slightly higher in the lower portion of the
river (Figure 2). No apparent differences were
found among the shoal and channel stations.

Dissolved Oxygen

Dissolved oxygen in the York River (Figure 2)
was generally lower in warmer months (May-
October) and higher in colder months
(November- April). In the warmer months, dis-
solved oxygen was lowest at the deeper channel
stations. There was no apparent difference be-
tween the upper and lower portions of the York
River. In colder months, dissolved oxygen was
slightly higher in the upper portion of the river
and no apparent difference was found among shoal
and channel stations.

Salinity

Salinity decreased toward the upper portion of
the York River (Figure 2). Lower salinities usu-
ally were found in spring ( March-May) and winter
(December-February). The extremely low
salinities of June to August 1972, were caused by
hurricane Agnes (Anderson et al. 1973). Salinity
at channel stations was usually higher than at
shoal stations, especially in the lower portion of
the river from March to June.

Temporal and Spatial Distributions

Young sciaenids are among the most abundant
migratory finfishes in the York River (Massmann
1962; Colvocoresses 1975; Markle 1976). Tem-
poral and spatial distributions of juveniles of the
four most abundant sciaenids, Cynoscion regalis,

Bairdiella chrysoura, Micropogonias undulatus,
and Leiostomus xanthurus, are compared (Figures
3-5) to determine ecological partitioning during
their estuarine life. The relative abundance of
each species is expressed by the geometric mean,
logio (x + 1), of the individual catches per tow
within the substrata, where x is the mean number
of individuals per tow. Four months (July, Oc-
tober, January, and April) were selected to repre-
sent the seasonal abundances from different parts
of the York River (Figure 3). Monthly mean
catches per tow by river distance (stratum) and
depth (substratum) were compared (Figures 3-5).
Fishes caught in the Mattaponi and Pamunkey
rivers were compared only by river distance (Fig-
ure 4).

In July 1972 and 1973, all four species of
juvenile sciaenids were present in all parts of the
estuary except the upper part ( Figures 3-5). Rela-
tive abundance varied among species (Figure 3).
Bairdiella chrysoura was more abundant in the
lower and middle part of the river, while C. regalis
and M. undulatus were more abundant in the
upper part of the river (Figure 5). Leiostomus
xanthurus was ubiquitous. Micropogonias un-
dulatus gradually declined in abundance up-
stream in both the Mattaponi and Paumkey rivers
(Figures 4, 5). Leiostomus xanthurus catches were
quite variable in the Pamunkey River. This may
have been caused by the contagious distribution of
this species. Sciaenids were more abundant in
shoal stations (Figure 3) than channel stations,
especially in July 1972. Colvocoresses (1975) and
Markle ( 1976) noted a general decline in the mean
number of species and individuals of fishes caught
per month in the summer from channel stations.
This may be attributed to a reduction in the dis-
solved oxygen concentration, usually below 5 mg/1
at the bottom of the channel (Markle 1976;
Brehmer see footnote 5), and was apparently the
case in the present study (Figure 2). Catches of C.
regalis did not decline in channel stations, but this
species is the best adapted for pelagic life of the
four species studied (see "Correlation of Feeding
Structures and Food Habits" section), and may
have been captured in midwater where dissolved
oxygen values did not decline.

In October (1972, 1973) juveniles of all four
species of sciaenids were present in all parts of the
estuary (Figure 3) and all reached their highest
total abundance (Markle 1976). Cynoscion regalis
was more abundant in the lower parts of the York
River; B. chrysoura and L. xanthurus were more

661

FISHERY BULLETIN: VOL. 75. NO. 4

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662

CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCIAENID FISHES
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FIGURE 3. — Seasonal abundance of four juvenile sciaenids with depth and distance upstream in the York
River. Mean numerical catch per tow of each substratum expressed as log (x + 1). Strata: A-G; substrata: N
= north shoal, Ch = channel, and S = south shoal.

663

FISHERY BULLETIN: VOL. 75, NO. 4

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Cynoscion regain J Micropogon undulatus

Bairdiella chysoura frS] Leiostomus xanthurus

FIGURE 4. — Seasonal abundance of four juvenile sciaenids in the
Mattaponi and Pamunkey rivers. Mean numerical catch per tow
of each substratum expressed as log (x +1). Strata: M = Matta-
poni River, P = Pamunkey River. Substrata: 1, 2, and 3 desig-
nated by river distance upstream.

abundant in the middle part of the river. Micro-
pogonias undulatus was more abundant in the
upper part of the river, and especially in the Mat-
taponi and Pamunkey rivers (Figures 4, 5). Mean
catch per tow increased up the estuary. Depth
distribution of these four species of sciaenids indi-
cated that they were more abundant in the chan-
nel stations (Figure 3). The relative abundance at
south shoal stations was higher than at north
shoal stations. The area was larger and the sam-
pling depth was greater in the south shoal than
the north shoal area (Colvocresses 1975; Chao
1976). Also, the average size of young sciaenids,
especially the young-of-the-year groups, was
larger in the channel than in the shoal stations
(see section on "Distribution and Size"). Larger
size juvenile sciaenids might use deeper areas to
seek food and shelter.

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FIGURE 5. — Seasonal mean abundance of four juvenile sciaenids along the salinity gradient (strata) in the York River estuary. Grand
mean numerical catch of four juvenile sciaenids per tow of stratum expressed as log (x + 1). Strata: A-G in York River, M = Mattaponi
River, P= Pamunkey River. Grand means of January and April represent the average of 3 yr. (1972 to 1974).

664

CHAOand MUSICK: LIFE HISTORY OF JUVENILE SCIAENID FISHES

In January 1972-74, the numbers of individual
sciaenid fishes were considerably reduced, except
for M. undulatus (Figures 3, 5). Cynoscion regalis,
B. chrysoura, and L. xanthurus were caught only
occasionally. During the winter months, resident
fish species were more abundant than transients,
especially in the upper tributaries of the York
River (Markle 1976). Micropogonias undulatus
was the most abundant sciaenid fish in the middle
part of the York River (Figure 5). Depth distribu-
tion in January 1973 (Figure 3), indicated that
most fish were caught in the channel. Bottom
temperatures of the channel stations were higher
than shoal stations (Figure 2), which might have
been the major factor causing the concentration of
young sciaenids in the channel.

In April 1972-74, C. regalis, M. undulatus, and
L. xanthurus were caught (Figures 3, 5). Cyno-
scion regalis was absent in 1973 (Figure 3) but
sparse in 1972 and 1974 (Figure 5). Micropogonias
undulatus was more abundant in the upper part of
the river and L. xanthurus was more abundant in
the lower reaches (Figures 4, 5), apparently be-
cause the young-of-the-year L. xanthurus had just
entered the estuary (see section on "Distribution
and Size"). Depth distribution of these two species
(Figure 3) showed that they were more abundant
in shoal areas, especially M. undulatus. Bairdiella
chrysoura was completely absent.

Life History and Size

Length-frequency distributions (Figures 6-19)
indicate that juvenile Leiostomus xanthurus,
Bairdiella chrysoura, Cynoscion regalis, and Mi-
cropogonias undulatus enter the York River con-
secutively from April on, and all but M. undulatus
leave the York River by December. Seasonal size
distributions of these four species in the York
River will be discussed individually and compared
with studies from other areas. Modes I and II in
Figures 6 and 10 and the following discussions
represent young-of-the-year (mode I) and year-
lings (or older fishes, mode II), respectively, except
in M. undulatus and Figure 16, where modes I and
II represent young-of-the-year and mode III the
yearlings (or older fishes).

Leiostomus xanthurus Lacepede — Spot

EARLY LIFE HISTORY IN THE YORK
RIVER. — Young-of-the-year spot, entered the

trawl and beach seine catches in early April and
most left by December (Figure 6, mode I). A few
smaller fish stayed in the estuary over winter.
Yearling spot usually entered the study area from
March to May and left the area in September ( Fig-
ure 6, mode II). The intermediate mode (between
modes I and II) on Figure 6, April and May 1972,
was not found in the 1973 and 1974 samples. This
may indicate late spawning in the previous year
(1971). The length frequencies of young spot from
May to July during 1972-74 were pooled and
grouped by river strata (Figure 7). Young-of-the-
year spot moved up to the confluence of the
Pamunkey and Mattaponi rivers (Figure 1); most
yearling spot stayed in the lower parts of the York
River. During the same periods, no differences
were found between the length frequency dis-
tributions in shoal and channel stations (Figure 8)
of either young-of-the-year or yearling spot.

Spot caught in the beach seine (Figure 8) were
obviously smaller than those taken by trawls. Spot
was the most abundant sciaenid in the beach seine
zone (depth <1.5 m) for collections with the
15.25-m and 30.5-m seines. The length frequency
distribution of spot caught by beach seine was
typically unimodal; mostly young-of-the-year
(Figure 9). Some smaller yearlings were taken
occasionally (Figure 9, 1974, mode II) and indi-
viduals >135 mm TL were captured only with the
30.5-m seine (Figure 9, August and September
1972).

In summary, young-of-the-year spot entered the
York River in April and used the estuary as a
nursery ground. In December, most spot left
though some smaller fish stayed in the estuary
through the winter, joining the yearlings as they
returned to the river in the next spring. The year-
lings left the estuary after an extended feeding
period from March to October.

OTHER STUDIES.— Selected length frequency
data for spot along the Atlantic and Gulf of Mexico
coasts of the United States are summarized (Table
1 ) for comparison with the present study. Hilde-
brand and Schroeder (1928) and Pacheco (1957,
1962a) reported length frequency of spot from the
present study area (York River and Chesapeake
Bay). Across all areas (Table 1), young-of-the-year
spot (Group 0 on Table 1) enter the estuarine nur-
sery grounds during the first half of the year. They
may enter estuaries as early as January (Table 1;
Hildebrand and Cable 1930; Springer and Wood-
burn 1960; Sundararaj 1960). Spot first enter the

665

FISHERY BULLETIN: VOL. 75, NO. 4

TOTAL LENGTHin

10 30 50 70 90 110 130 150 170 190 210 230 250
TOTAL LENGTH (mm)

estuary in February along the Atlantic coast of
Georgia (Music 1974) and the Gulf of Mexico coast
of Florida (Townsend 1956), Louisiana (Dunham
1972), and Texas (Parker 1971). In South Carolina
(Dawson 1958; Shealy et al. 1974), North Carolina

2.5
1.5
0.5-
2.5-

1.5-
0.5-
2.5
1.5
0.5
2.5
1.5
0.5
2.5
1.5-
0.5
2.5
1.5-
0.5-
2.5
1.5
0.5
2.5
1.5-
0.5
2.5
1.5-
0.5-
2.5
1.5
0.5
2.5
1.5
0.5
2.5
1.5
0.5

1974

NO SAMPLE

i — n

JU □_

-i — i — i — i — i — i — i — i — r-^i — i — i — i — i — i — i — i — i — i — i — i — ' — i — ' — i
10 30 50 70 90 110 130 150 170 190 210 230 250

TOTAL LENGTH (mm)

FIGURE 6. — Monthly length-frequency distributions of juvenile
spot, Leiostomus xanthurus, from York River, 1972-74. Mode I,
young-of-the-year; mode II, yearlings. Frequencies expressed as
log (x + 1) at 5-mm increments. Only the lower portion of river
(strata A-D) is represented in 1974.

-I- — i 1 1 1 1 — r — I 1 1 1 1 1 — i r — i 1 — i 1 1 r — r-h 1 r

10 30 50 70 90 110 130 150 170 190 210 230 250

TOTAL LENGTH(mm)

FIGURE 7. — Length-frequency distributions of spot, Leiostomus
xanthurus, by river distance (strata) upstream in the York River
estuary. Pooled total, May to July 1972-74. Strata: A-G in York
River, M = Mattaponi River, P = Pamunkey River. Frequencies
expressed as log (x + 1) at 5-mm increments.

(Hildebrand and Cable 1930), and the lower
Chesapeake Bay (Hildebrand and Schroeder 1928

666

CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCIAENID FISHES

TABLE 1.—

■Growth of spot, Leiostomus xanthurus, :

from different estuarine areas along U.S. Atlantic and Gulf of Mexico

coasts.

Author

Thomas 1971

Young 1953

Hildebrand ai

Pacheco 1957

Chao 1976

Schroeder 1928

Locality

Lower Chesapeake Bay

Delaware River, Del

Chesapeake

Bay, Md

Chesapeake

Bay

and York Ri

ver, Va

York River.

Va.

Period

June 1968-Sept 1970

May-Oct 1951

Prior to 1928

May 1955-Feb. 1956

Jan. 1972-Dec 1974

Gear'

16-ft Tand S

75 x 4 ft Haul S

P and 30-ft T

16-ft Tand S

Source

Table 68

Tables 4 and 5

Table on p. 273

Table 3

Fig 6 (present study)

Length (mm)

Total length

Age-group2

January

75-149

155-255

95-175

February

1 50-275

70-140

March

15-19

90-160

April

20-24

15-65

95-185

May

16-60

15-74

155-174

80-105

1 30-225

20-95

95-225

June

19.2

26-80

20-99

115-174

115-(140)

(145)-210

25-105

140-235

July

30- 80

90-140

(26-130)

40-124

135-209

115-(150)

(155)-230

35-155

155-235

August

45-100

110-165

86-90

65-149

125-(180)

(200)-245

55-(175)

(160)-250

September

120-170

86-106

94-170

190-209

135-(185)

(190)-260

70-185

230

October

125-175

(71-155)

100-184

190-299

135-(235)

80-(195)

(170)-240

November

75-184

165-(205)

80-185

(160)-240

December

75-119

155-185

220-240

75-190

Author

Hildebrand and

Shealy et al.

1974

Music 1974

Townsend 1956

Springer and

Cable 1930

Woodburn 1960

Locality

Beaufort, NO

South Carolina

Georgia

Alligator Harbor, Fla.

Tampa Bay,

Fla

Period

Prior to 1 93C

Feb. 1973-Jan. 1974

Oct. 1970-Sept. 1973

Mar. 1955-1

May 1956

Jan-Dec 1958

Gear'

PI and T

20-ftT

40-ftT. 12-ft S, 300-ft G

150- and 600-ft S

T, 80-ft S, and Pu

Source

Tables 7 and 8

Table 27

Fig. 10

Table I

Table 1 3

Length (mm)

Total length

Standard length

Age-group2

January

4-21

82-195

88-207

80-250

13-31

February

3-27

91-200

83-142

10-35

85-225

10-34

95-159

13-49

March

10-39

93-200

113-182

10-40

95-225

15-54

105-175

10-73

April

7.5-54

84-214

18-52

107-162

15-75

95-280

20-74

105-184

19-79

May

11-94

97-215

23-82

88-147

30-100

120-260

20-89

125-189

25-85

June

29-119

122-198

33-(132)

40-130

135-270

60-89

145-164

31-103

July

43-127

1 30-228

23-(152)

45-(170)

(170)-280

60-99

145-159

48-118

August

67-139

140-219

48-117

153-157

45-(175)

(175)-280

75-99

165-169

49-103

September

81-153

155-234

73-132

148-152

65-150

150-265

100-109

52-82

October

92-170

175-269

78-127

80-150

150-250

70-124

145-169

52-97

November

90-188

190-264

78-127

75-115

120-250

85-129

67-91

December

1.5-9.2

84-188

83-147

168-192

65-95

100-260

76-109

Author

Nelson 1969

Parker 1971

Pearson 1929

Sundararaj

1960

Dunham 1972

Locality

Mobile Bay. ,

Ma.

Galveston Bay, Tex.

Sabine River

to Rio

Lake Pontchartram, La

Louisiana coast

Grande, Tex.

Period

May 1963-Ap

>r. 1964

Jan. 1963-Dec. 1965

Mar 1926-May 1927

July 1953-May 1955

July 1969 -June 1972

Gear'

16-ft T

4.0-m T

Tr, T, S, and G

T, Tr, S, and R

16-ft T

Source

Table 9

Table 2

Table 31

Fig. 17

Fig. 21

Length (mm)

Total length

Age-group2

January

75-160

60-170

15-25

90-165

100-170

February

90-125

70-180

15-40

115-165

10-80

110-170

March

90-180

10-30

60-190

10-75

140-230

20-100

110-170

April

45-70

90-165

10-70

90-160

10-90

120-250

30-100

140-255

40-110

May

45-(125)

(130)-171

30-100

110-190

40-120

130-250

45-120

(120)-240

50-125

June

50-140

170-180

30-110

140-190

70-(150)

(150)-230

55-145

150-255

50-155

July

55-145

200

30-140

170

80-140

150-230

40-160

165-250

20-155

August

80-135

30-150

170-180

110-(220)

230-270

85-(180)

(180)-215

70-160

September

30-160

110-(240)

250-260

95-(150)

(150)-210

90-170

110-210

October

95-(190)

50-160

110-(170)

(170)-260

90-150

170-190

120-160

November

95-165

60-150

130-190

200-250

110-(170)

(170)-205

100-180

December

90-175

200

70-180

130-190

200-250

135-165

70-180

'Gear: G, gill net; P, pound net; PI, plankton net; Pu. push net; R, rotenone; S, seine; T, trawl; Tr, trammel net.

2Age-group: 0 represents smallest group of young-of-the-year first taken from January on, other fishes (including overwintering young-of-the-year) are included in
age-group I. Parentheses indicate that the boundary of age-group 0 and I is indistinguishable.

and the present study), young-of-the-year spot
first entered the estuary in April (Table 1). In
upper Chesapeake Bay (Young 1953) and Dela-
ware River (Thomas 1971 ), young-of-the-year spot
probably do not appear until May (Table 1). The
smallest young-of-the-year spot from trawl
catches are about 15 to 20 mm TL in all areas
which indicates that the young-of-the-year spot in

northern areas enter the estuary later than in
southern areas. When spot first enter estuaries,
gear selectivity (Table 1) affects the size ranges of
spot captured; beach seines usually catch only the
small specimens (Young 1953; Figure 9), but
pound nets (Pacheco 1957) and large otter trawls
(Music 1974) usually catch larger fishes. Offshore
movements of spot during the winter season are

667

FISHERY BULLETIN: VOL. 75, NO. 4

BEACH SEINE

N-1574

FIGURE 8.— Length-frequency dis-
tributions of spot, Leiostomus xan-
thurus, by depth of York River. Pooled
total, May to July 1972-74. Frequen-
cies expressed as log (x + 1) at 5-mm
increments.

2.5-
1.5-
0.5-

N^5239

~^~1 n r-

110

130

150

170

190 210

230

250

TOTAL LENGTH imm)

2.5
5-

05-
2.5
1.5-
0.5-
2.5
I
0.5-
2.5

0.5
2.5

I 5
0.5
2.5

1972

1.5-

H-\7

0.5-

,__r^T_n_,

2.5-

1.5-

N=6

0.5-

. en

2.5
1.5
0 5-
2 5
1.5-
0.5
2.5
1.5
0.5
2 5
i 5
0.5
2.5-
1.5
0 5H
2 5
1.5
0.5
2.5
l 5
0.5
2.5-
1.5
0.5

90 MO 130 150
TOTAL LENGTH ( mm]

170 190 210 230 250

1973

10 30 50 70 90 NO 130 150 170 190 210 230 250
TOTAL LENGTH (mm)

evident in all areas studied because spot are com-
pletely absent or in low abundance in inshore
catches. Yearling or older spot (Table 1, group I)
usually leave the estuary after September and do
not return until spring of the next year. Some

2.5-.
1.5-
0.5
2.5
1.5-
0.5
2.5
1.5
0.5
2.5
I 5
0.5
2.5
b
0.5
2.5
1.5;
0.5-
2.5
1.5
0.5
2.5
1.5
0 5

1974

^H^l^

NO SAMPLE

_Dn_

-i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i i i
10 30 50 70 90 110 130 150 170 190 210 230 250

TOTAL LENGTH (mm)

FIGURE 9. — Monthly length-frequency distributions of spot,
Leiostomus xanthurus, from the beach seine catches of York
River, 1972-74. Frequencies expressed as log (x + 1) at 5-mm
increments.

young-of-the-year spot over-winter in the estuary
(Figure 6; Table 1). Tagged spot (Pacheco 1962b)
have moved from Chesapeake Bay south to an
area west of Diamond Shoals, N.C. Similarly, a
spot tagged and released from Delaware Bay in
October 1930 was recovered south of Ocracoke In-
let, N.C, in December 1930 (Pearson 1932). Thus,
spot from these areas may have a common coastal
feeding or spawning ground during the winter,
although Struhsaker (1969) reported a winter
offshore movement of spot into deeper water
(lower-shelf habitat off South Carolina). These
offshore spot may be a mixture of northern and
southern populations or just southern residents.
The late fall or early winter spawning time of spot
may be the same in both Atlantic and Gulf of

668

(II AOandMUSICK: LIFE HISTORY OF JUVENILE SCIAENII) FISHES

Mexico waters (Welsh and Breder 19231. Later
spawning by a northern component of the popula-
tion is evidenced from the length ranges of post-
larvae and juvenile spot (Table 1).

( ynoscion regain (Bloch and Schneider) —
Weakfish

EARLY LIFE HISTORY IN YORK
RIVER. — Young-of-the-year weakfish first en-
tered trawl catches in July or August and virtu-
ally left the estuary in the winter (Figure 10, mode
I). Yearling weakfish returned to the river in April
or May and left in September or October (Figure
10, mode II). Larger weakfish (2 yr or older) were
caught only sporadically during this study be-
cause of gear avoidance. The length mode of small
weakfish in August showed a rapid increase (Fig-
ure 10). This increase may be due to the recruit-
ment of yearlings or an earlier spawned group of
young-of-the-year. Length frequencies for
weakfish ( <250 mm TL) caught from August to
October 1972-74, were pooled to compare dis-
tribution by size in the York River and its
tributaries (Figure 11). Smaller fishes were more
abundant in the Pamunkey and Mattaponi rivers
than in the York River proper. Yearling weakfish
also showed a movement upriver ( Figure 11). This
suggests that young weakfish entered the low sa-
linity nursery ground (upper portion of the York
River) and then moved downriver as they grew.
Pooled length frequency distributions revealed an
apparent difference between shoal and channel
areas of the York River (Figure 12). Yearling
weakfish (or larger ones) were proportionally
more abundant in the channel. The 15.25-m beach
seine catches contained no weakfish, but occasion-
ally the 30.5-m seine caught some young-of-the-
year weakfish in the summer.

OTHER STUDIES.— Major populations of
weakfish are confined to the Atlantic coast of the
United States from New York to Georgia. Existing
data indicate young-of-the-year weakfish enter es-
tuarine or coastal catches from May to July ( Table
2). The smallest sizes of the weakfish in the
catches differ with area and may be due to gear
and/or time of sampling. Small fishes with less size
variation (about 5 mm) were taken over a longer
period of time in southern areas than northern
areas (Table 2 ). Young-of-the-year weakfish do not
occur in catches during winter months in northern
coastal areas or estuaries (Perlmutter 1956;

Massmann et al. 1958; Thomas 1971; Markle
1976). Year-round catches of weakfishes from
North Carolina (Hildebrand and Cable 1934) and
Georgia (Mahood 19741 were from sounds and
short coastal rivers. Most of the studies suggest
the age-group 0 on Table 2 was a combination of
young-of-the-year and yearlings. No distinct mode
could be identified for young-of-the-year from
these studies. This may be due to the multiple
spawning (Merriner 1973, 1976) and/or the re-
cruitment of the young-of-the-year from different
spawning populations.

The reproductive biology of weakfish is better
known than other sciaenid fishes studied here.
Welsh and Breder (1923) described the eggs and
development of weakfish and noted that Delaware
Bay was a spawning ground for weakfish. Mer-
riner (1973) indicated that weakfish have an ex-
tended spawning season in North Carolina
(March- August) and are characterized by high
fecundity and possible multiple spawning by some
females. Pearson (1941) took plankton tows in
lower Chesapeake Bay from May to August in
1929 and 1930 and reported greater densities of
weakfish larvae (1.5-17 mm TL) in subsurface
tows (average 67/tow) than in surface tows (aver-
age 13/tow). The density of planktonic weakfish
decreased at those stations within Chesapeake
Bay, compared with sites near the bay mouth.
Harmic ( 1958) reported that newly hatched larval
weakfishes averaged 1.8 mm TL. Soon after hatch-
ing, the larvae became demersal and were dis-
persed into the nursery areas of Delaware Bay by
means of the "salt wedge." The smallest weak-
fishes taken in the bottom trawl were 6 to 10 mm
TL (Hildebrand and Cable 1934). The young-of-
the-year weakfish in York River are probably
progeny from adults spawning near the mouth of
Chesapeake Bay. Weakfish tagged and released in
lower Chesapeake Bay (Nesbit 1954) were later
recovered to the north in New York and New Jer-
sey, and southward in North Carolina. Nesbit
(1954), Perlmutter et al. (1956), and Harmic
(1958) cited the presence of a northern spawning
population in New York and northern New Jersey
waters and a southern spawning population from
New Jersey to North Carolina. Seguin (1960)
found that morphometric and meristic variation of
weakfish exists along the middle Atlantic coast
and suggested that three possible population seg-
ments may exist: a New York group, a Delaware
and lower Chesapeake group, and a North
Carolina group. Joseph (1972) questioned the

669

FISHERY BULLETIN: VOL. 75, NO. 4

2.5

D 15;
0.5-
2.5

N 1.5
0.5-|
2.5

0 1.5
0.5
2.5-

S !.5:
0 5:
2.5

A 1.5
0.5-
2.5

j 1.5

- 0.5-

+ 2.5

— J 1.5

g 0.5

2.5

M 1.5

0.5

2.5

a i.sq

0.5
2.5

M 1.5
0.5
2.5

F 1.5
0.5
2.5

J 1.5
0.5

1972

N = 19

n n n f^-^-n ■-■ ■-■

jzO-

N = 2I8

n— n n-,

i^l

_E3 CX-

N = 230

r^-.

N = I75

N = I93

N = 2I

_□ n i — i

_n d~J □_

N = 74

N = I6

N = 0

N = I2

~i — i — i — i — i — i — i — i — i — i — i — r I rT1 -i — p-( — i — i — P— i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — r — i
20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400

TOTAL LENGTH (mm ]

2.5n

D 1.5
0.5
2.5

N 1.5-
0.5
2.5-

0 1.5
0.5
2.5-

S 1.5
0.5
2.5

A 1.5
0.5-
2.5-

J 1.5
0.5-
2.5-

J 1.5-
0.5
2.5

M 1.5-
0.5:
2.5

A 1.5
0.5
2.5

M 1.5
0.5
2.5

F 1.5
0.5
2.5

J 1.5
0.5

1973

N= 8

n n— n

N=I5

N = 295

NU460

_□_

N=243

n n-^~, □_

N= 13

r^-H n

N = 34

N = 38

i— n

n n

N = 0

N = 2

N = 0

20 30 50 70 90 110 130 150 170 190 210 230 250 270 290 310 330 350 370 390 410 430 450

TOTAL LENGTH (mn

670

NO SAMPLE

zEb-

CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCIAENID FISHES

253 1974
D 1.5-

°-5: a^ a a

2.5-

1.5;

0.5-

2.5-

1.5-
0.51

2.5-
l.5:

0.5:

2.5-
1.5-

0.5:

2.5-

l.5:

0.5:

2.5-

l.5:

0.5-

2.5-

1.5-

0.5 :

2.5-

1.5;

0.5-

2.5;

1.5-

0.5:

2.5-

l.5:

0.5-

2.5-
1.5-
0.5 :

N = 87

N = 2II

NMO

NO SAMPLE

N=I8

n i

N=4

N = 0

-i — i —
20

60 80

100 120 140 160 180 200 220 240 260 280 300 320 340 360
TOTAL LENGTH (mm)

FIGURE 10. — Monthly length-frequency distributions of weakfish, Cynoscion regalis, from York
River, 1972-74. Mode I, young-of-the-year; mode II, yearlings. Frequencies expressed as log (.r +
1) at 5-mm increments. Only the lower portion of river (strata A-D) is represented in 1974.

FIGURE 11.— Length-frequency dis-
tributions of weakfish, Cynoscion re-
galis, by river distance (strata) up-
stream of the York River estuary.
Pooled total, August to October 1972-
74. Strata: A-G in York River, M =
Mattaponi River, P = Pamunkey River.
Frequencies expressed as log (x + 1) at
5-mm increments.

2.5

P 1.5
0.5
2.5

M I .5
0.5
2.5

G 1.5
0.5
2.5

F 1.5
0.5
2.5-

E 1.5
0.5
2.5

D 1.5
0.5-
2.5-

B 1.5-
0.5-

Il^n tzzQ.

r-i

TOTAL LENGTH (mm)

671

FISHERY BULLETIN: VOL. 75, NO. 4

TOTAL LENGTH (mm)

FIGURE 12. — Length-frequency distributions of weakfish, Cynoscion regalis, by depth of York River. Pooled
total, August to October, 1972-74. Frequencies expressed as log (j: + 1) at 5-mm increments.

TABLE 2. — Growth of weakfish, Cynoscion regalis, from different estuarine areas along

U.S. Atlantic coast.

Author

Thomas 1971

Pearson 1941

Chao 1976

Locality

Delaware River, Del.

Lower Chesapeake Bay

York River,

Va.

Period

1969

1929-30

Jan. 1972-Dec

Gear1

Tand S

PI and P

16-ftT

Source

Table 4

Fig. 23

Fig. 10 (present study)

Length (mm)

Total length

Age group2

January

120-205

February

130-315

March

April

130-250

65-175

May

1 55-330

June

5-70

140-385

July

15-125

20-(150)

20-55

105-305

August

15-(185)

30-(160)

10-(95)

100-370

September

70-(185)

(130)- 180

70-(110)

115-300

October

40-(175)

35-(135)

140-325

November

65-(140)

140-205

December

95-(170)

Author

Hildebrand and

Shealy et al.

1974

Mahood 1974

Cable 1 934

Locality

Beaufort, N.C

South Carolina coast

Georgia Coast

Period

Feb. 1973-Jan. 1974

Oct. 1970-Sept. 1973

Gear'

PI, P, and T

20-ft T

40-ftT

Source

Table 4

Table 32

Table 7

Length (mm)

Total length

Age group2

January

75-204

138-327

68-438

February

105-274

68-388

March

90-230

155

83-358

April

80-284

118-188

78-408

May

4-9

1 25-224

48-358

June

4-44

95-279

23-47

13-(128)

(133)-328

July

4-(39)

40-379

23-(52)

(53)- 187

18-(173)

(178)-363

August

4-(64)

65-369

23-(72)

(73)- 182

23-(203)

(208)-323

September

10-(79)

80-314

23-(67)

(68)-208

18-(213)

(218)-388

October

45-(94)

100-329

28-(72)

(73)-228

28-(223)

(228J-313

November

45-(99) (

100)-329

68-72

78-702

48-(233)

(238J-348

December

85-(94)

(95)-299

88-92

108-197

53-(233)

(238)-348

'Gear: P, pound net; PI, plankton net; S, seine; T, trawl.

2Age-group: 0 represents smallest groups of young-of-the-year taken from January on, other fishes (including
overwintering young-of-the-year) are included in age-group I. Parentheses indicate that the boundary of
age-groups 0 and I is indistinguishable.

division of weakfish into northern and southern
stocks and did not consider the decline of weakfish
in Chesapeake Bay to be a result of the trawl
fisheries in the shallow coastal waters and bays of
North Carolina. He indicated Chesapeake Bay as
a major spawning area and nursery ground, but
also cited failure to obtain one weakfish larva/tow
in extensive VIMS ichthyoplankton studies dur-

ing 1959-63. However, weakfish eggs and larvae
were reported from Chesapeake Bay by Hilde-
brand and Schroeder (1928) and Pearson (1941).
Massmann (1963) implied that Chesapeake Bay
weakfish are from southern spawning populations
or stocks. Therefore, the question remains
whether lower Chesapeake Bay and nearshore
waters are a major spawning ground for weakfish

672

CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCIAENID FISHES

(Merriner 1976). Pearson (1932) described the
winter trawl fishery off North Carolina and cited
higher total catches of weakfish from area B
(southwest of Cape Hatteras) than from area A
(northeast of Cape Hatteras) in deeper waters. It is
possible that most young-of-the-year and larger
weakfish that leave the York River move south-
ward to their wintering ground off Cape Hatteras.
In spring, weakfish disperse from the wintering
ground. Some fish move north and spawning may
occur from late spring to summer along the coast
from North Carolina to New York.

Buirdiella chrysoura (Lacepede) — Silver Perch

EARLY LIFE HISTORY IN THE YORK
RIVER. — Silver perch were present from April to
December and were most abundant from August
to October (Figure 13). Total catches were reduced
in 1973 and 1974. Young-of-the-year silver perch
first entered the catches in July and most silver
perch left the river in November. Yearlings may
enter the river as early as April and most left the
river in November. There were no silver perch

taken from January to March during the present
study (1972-74). Pooled length frequencies from
August to October, 1972 to 1974, indicated that
silver perch were most concentrated in the lower
part of the York River (Figure 14) and larger
specimens tended to stay in the channel (Figure
15). The 30.5-m beach seine caught young-of-the-
year occasionally but the 15.25-m seine rarely
caught any silver perch.

OTHER STUDIES.— Silver perch occur along
the U.S. coast from New York to Texas. The sea-
sonal distribution pattern is similar in all Atlantic
coastal states (Table 3). Young-of-the-year silver
perch were first caught in bottom trawls during
June or July. Size of the smallest young-of-the-
year silver perch during a given month decreases
as latitude of the nursery ground increases on the
Atlantic coast and west coast of Florida (Table 3).
Silver perch are present almost all year round
south of Chesapeake Bay (Table 3), which may be
due to the higher salinity or temperature of those
study areas. The embryonic development of silver
perch from Beaufort, N.C., was described by Kuntz

TABLE 3. — Growth of silver perch, Bairdiella chrysoura, from different estuarine. areas
along U.S. Atlantic and Gulf of Mexico coasts.

Author

Thomas 1971

Chao 1976

Hildebrand and Cable 1930

Locality

Delaware River. Del

York River, \

/a.

Beaufort, N.C.

Period

1969

Jan. 1972-Dec 1974

Spring 1926-Summer 1927

Gear1

16 ft T

PI and T

Source

Table 28

Fig. 13 (present study)

Tables 5 and 6

Length (mm)

Total length

Age-group2

January

74-204

February

90-209

March

98-204

April

93-195

May

85-200

1-6

85-204

June

5-20

145-185

1-38

110-210

July

5-65

20-60

120-190

9-76

105-224

August

45-100

15-85

100-205

20-92

130-204

September

70-120

65-135

160-210

45-122

135-189

October

65-130

60-135

160-220

73-115

145-224

November

70-155

210

68-143

150-229

December

73-110

78-124

Author

Shealy et al.

1974

Springer anc

Reid 1954

Woodburn 196(

Locality

South Carolina coast

Tampa Bay,

Fla.

Cedar Key,

Fla

Period

Feb. 1973-Jan. 1974

Oct. 1957-Dec 1958

June 1950-May 1951

Gear1

20 ft T

T, S, and Pi

15 ft T, S, and Pu

Source

Table 42

Fig. 12

Fig. 10

Length (mm)

Total length

Standard length

Age-group2

January

18-(72)

93-182

55-60

February

88-137

52-76

March

98-172

67-73

65-95

April

73-182

May

113-152

13-25

5-40

84-110

June

123-132

16-52

15-50

July

33-87

128-192

16-70

20-70

August

58-107

143-172

16-82

5-80

September

73-132

138-177

25-85

10-82

October

78-(187)

28-91

40-95

November

98-(172)

19-97

50-70

December

98-(182)

46-106

^ear: PI, plankton net; Pu. puchnet; S, seine; T, trawl.

2Age-group: 0 represents smallest group of young-of-the-year first taken from January on. other fishes
(including overwintering young-of-the-year) are included in age-group I Parentheses indicate that the boundary
of age-groups 0 and I is indistinguishable.

673

2.5-

D 1.5-

0.5-

2.5-
N 1.5-
0.5

2.5

0 1.5-
0.5
2.5

S 1.5
0.5-
2.5-

A 1.5-
0.5-
2.5-

J 1.5
0.5
2.5-

J 1.5-
0.5-
2.5-

M I -5
0.5
2.5

A 1.5

0.5

1972

FISHERY BULLETIN: VOL. 75. NO. 4

N = 2

r~i

r-i

i~i

~\ i

N = 273

N--370

N = 368

^bL.

N=304

N=5

l~l

N = 28

r-\ n

N=0

"i 1 1 r

— i r

190

~i 1 r-

110

130

150

170

TOTAL LENGTH (mm)

210

230 250

FIGURE 13.— Monthly length-
frequency distributions of silver
perch, Bairdiella chrysoura, from
York River, 1972-73. Frequen-
cies expressed as log (x + 1) at
5-mm increments.

674

2.5-
1.5-

0.5-
2.5-
I .5-
0.5-
2.5-
1.5-
0.5-
2.5-
1.5
0.5
2.5

1.5
0.5
2.5
1.5
0.5
2.5

1.5
0.5

1973

r^l

ii ii

10 30 50

N = 3

N=3I

r~i

N=I5I

N = 96

N = 58

N^9

N=0

1 ■-! 1 1 1 1 T 1 ' 1 1 1 1 ' 1 1 ' 1 !

70 90 110 130 150 170 190 210 230 250

TOTAL LENGTH (mm)

CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCIAENID FISHES

FIGURE 14.— Length-frequency dis-
tributions of silver perch, Bairdiella
chrysoura, by river distance (strata) up-
stream of the York River estuary.
Pooled total, August to October 1972-
74. Strata: A-G in York River, M =
Mattaponi River, P = Pamunkey River.
Frequencies expressed as log (x + 1) at
5-mm increments.

A +B
Slrolo

2.5

1.5

0.5
2.5
1.5
0.5-
2-5
1.5
0.5
2 5-
1.5
0.5
2.5-
1.5-
0.5-
2.5
1.5
0.5
2.5
1.5
0.5-

N = 2l

l~l

-nn

,r^np-^

i~i

i~i i~i

rn i ^

10 30 50

TOTAL LENGTH [inn

FIGURE 15.— Length-frequency dis-
tributions of silver perch, Bairdiella
chrysoura, by depth of York River.
Pooled total, August to October 1972-
74. Frequencies expressed as log (x + 1)
at 5-mm increments.

70 90 110

TOTAL LENGTH (mm)

(1914). Welsh and Breder (1923) made further ob-
servations from material obtained at Atlantic
City, N.J. Jannke (1971) described larval silver
perch from the Everglades National Park, Fla.,
and showed that larvae of 2 to 3 mm "notochord"
length were present all year round. Hildebrand
and Schroeder (1928) reported ripe fish of both
sexes in Chesapeake Bay (24 m deep, off
Chrisfield, Md.) as early as 16 May. This suggests
that silver perch may spawn in the deeper waters
of lower Chesapeake Bay and nearshore waters in
late spring and early summer. Because of its rela-
tively small size, commercial landings of silver
perch are relatively small. Silver perch move
oceanward and probably to the south of
Chesapeake Bay in winter. Large numbers cap-
tured by commercial haul seines between Virginia
Beach, Va., and Kitty Hawk, N.C., have been ob-
served in fall (J. A. Musick, pers. obs.).

Micropogonias undulatus (Linnaeus) — Atlantic Croaker

EARLY LIFE HISTORY IN YORK RIVER.—
Young-of-the-year croaker first entered the trawl
and beach seine catches in August and stayed in
the York River throughout the winter (Figure 16,
mode I). They left the estuary between August and
September of the following year as yearlings (Fig-
ure 16, mode III). Large croaker (more than 1.5 yr
old) were caught only sporadically in this study
due to gear avoidance, but they were present from
February to September. There were apparently
two to three length groups (modes) of young-of-
the-year croaker in September 1972-74. Mode II
was different from mode I and mode III of 1972 and
1974 (Figure 16). The former group did not stay in
the York River over winter, but entered the es-
tuary as early as May (Figure 16, mode II). Most of
this group left in November 1972-74.

675

FISHERY BULLETIN: VOL. 75, NO. 4

2.5

D 1.5
0.5-
2.5

N 1.5
0.5
2.5;

0 1.5;
0.5-
2.5

S 1.5
0.5-
2.5;

A 1.5-

0.5-

__ 2.5-

+ j i-5-

0.5

o 2.5

J 1.5
0.5-

1974

Cn_

2.5

M 1.5
0.5
2.5

A 1.5
0.5-
2.5

M I 5"
0.5-
2.5

F 1.5
0 5
2 5-

J '.5
0.5-

r-. rs

-dJ

NO SAMPLE

r"-i

60 100 120 140 160
TOTAL LENGTH (mm)

1973

180 200 220 240

90 HO .30 150 '70 190

TOTA^ LENGTH n

Size may be a determining factor for migration
of young croakers from the York River. From 1972
to 1974, length frequencies (Figure 16) indicated
that very few young-of-the-year croakers >130

10 30 50 70 90 110 130 150 170 190 210 230 250
TOTAL LENGTH (mm )

FIGURE 16.— Monthly length-frequency distributions of croaker,
Mieropogonias undulatus, from York River, 1972-74. Modes I and
II, young-of-the-year; mode III, yearling. Frequencies expressed as
log (x + 1) at 5-mm increments. Only the lower portion of river
(strata A-D) is represented in 1974.

mm TL stayed in the York River during the winter
months. Young-of-the-year croakers were present
in the York River in large numbers all year round
except during the summer months (June-
August). Young croakers showed slower growth
rates over winter (Figure 16). Those entering the
estuary between September and November were
the main strength of the year class ( modes I and III
of Figure 16). Whether they represent progeny
from a different spawning population compared
with the earlier group (mode II of Figure 16) is
unknown at present.

Length frequencies of croakers taken between
September and November 1972-74 were pooled to
compare distribution by size in the York River
(Figure 17). The size composition indicated that
smaller fish were caught in the upper part of the
York River and saline portions of the Mattaponi
and Pamunkey rivers. Larger fish were propor-
tionally more abundant in the lower part of the
river. Larger fish also constituted a larger portion
of the croaker catch in. the channel than in the
shoal area (Figure 18). The 30.5-m beach seine

676

CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCIAENID FISHES

TOTAL LENGTH (mm)

FIGURE 17. — Length-frequency distributions of croaker, Micro-
pogonias undulatus, by river distance (strata) upstream of the
York River estuary. Pooled total, September to November
1972-74. Strata: A-G in York River, M = Mattaponi River, P =
Pamunkey River. Frequencies expressed as log (x + 1) at 5-mm
increments.

(Figure 19) caught yearlings exclusively. The
15.25-m seine caught almost no croakers.

In summary, young-of-the-year croaker entered
the estuary in May and from August on. The ear-
lier group entered in May and left the estuary in
November, as did older year classes. The later
group (August-November) stayed in the estuary
until the summer months of the following year.
Young croaker moved to the upper part of the York
River and the saline portions of major tributaries
after first entry, then moved down the York River
into more saline waters as they grew. Smaller
fishes ( <130 mm TL) stayed in the river through-
out the winter.

OTHER STUDIES.— Croakers occur from the
Gulf of Maine to Argentina, along the coasts of the
Atlantic and Gulf of Mexico. Length-frequency
distributions exist for different areas of the United
States [see Wallace (1940) and Haven (1957) for

the lower Chesapeake Bay and York River (Table
4)]. Studies usually show that small croakers
(10-20 mm TL) are present in the estuary during
all except the summer months (June-August).
Croakers seemingly have a long spawning season
since small individuals (<20 mm TL) are present
from September to May in different estuarine
areas (Table 4). Some croakers may be very small
( <15 mm TL) in spring because of slow growth of
fish spawned late in winter, or because they were
spawned in spring. Such a group was also found in
the present study (Figure 16, mode II) but not in
previous Chesapeake Bay studies. Croakers from
Maryland and Virginia tagged by Haven (1959)
showed springtime movement of croakers up the
estuaries and up Chesapeake Bay, and oceanward
and southerly in fall (some recoveries were from
off the North Carolina coast). Pearson (1932) re-
ported a high percentage of croakers in the catches
of the commercial trawl fishery during November
(88%) and December (76%) from the fishing
grounds off the North Carolina coast. Hildebrand
and Cable (1930) implied that croaker spawning
probably began in August in Chesapeake Bay and
northward, in September at Beaufort (North

2.5-j
1.5-
0.5
2.5
l.5:
0.5
2.5
1.5-
0.5
2.5
1.5-
0.5:
2.5
1.5
0.5-

N=0

N = l?

20 40 60 80 100 120 140 160 180 200 220 240
TOTAL LENGTH (mm)

FIGURE 19. — Length-frequency distributions of croaker, Micro-
pogonias undulatus, from beach seine catches of York River,
May to September 1972. Frequencies expressed as log (x + 1) at
5-mm increments.

FIGURE 18.— Length-frequency dis-
tributions of croaker, Micropogonias
undulatus, by depth of York River.
Pooled total, September to November
1972-74. Frequencies expressed as log
(x + 1) at 5-mm increments.

2.0-

i.o-
o.o-

n r-H

90 110 130 150

TOTAL LENGTH (mm)

170 190 210 230 250

677

FISHERY BULLETIN: VOL. 75, NO. 4

TABLE 4. — Growth of croaker, Micropogonias undulatus, from different estuarine areas along U.S. Atlantic and Gulf of Mexico coasts.

Author

Thomas 1971

Haven 1957

Chao 1976

Hildebrand

Shealy et al.

1974

and Cable 1 930

Locality

Delaware River, Del.

York River, '

Va.

York River, Va.

Beaufort, N.C

South Carolina coast

Period

June 1968-Dec. 1970

Oct. 1952-July 1<

Jan. 1972-Dec 1974

Spring 1926-

Feb. 1973-J.

an 1974

Summer 1927

Gear'

16-ftT

30-ft T

1 6-ft T and S

T and PI

20-ft T

Source

Table 70

Fig. 7

Fig. 16 (present study)

Tables 9 & 10

Table 22

Length (mm)

Total length

Age-group2

January

15-(85)

(95)-105

20-120

3-24

25-269

18-97

108-297

February

10-60

45)- 100

20-155

3-29

40-294

28-82

113-187

March

10-(70)

(70)-120
70-100

20-175

2-24

40-294

13-102

123-173

April

10-(65)

25-120

25-19

100-259

18-(132)

138-192

May

25-(90)

70-140

20-30

(20J-240

8-25

195-239

28-112

June

40-(120)

(120)-155

20-70

(60J-245

31-284

33-142

July

75-145

(135)-175

30-(110)

(80)-250

43-234

28-(182)

August

N.S.

N.S

30-(90)

(70)-240

66-289

53-177

September

N.S.

10-(100)

(70)-195

2-9

80-279

78-182

October

135-140

10-(40)

(40)-85

10-(1 10)

(100)-250

2-50

98-294

68-182

November

15-(60)

(60)-115

15-100

(60)-250

1 .5-66

85-284

43-153

December

20-50

10-(60)

(60)-120

20-110

165-175

2.5-69

85-259

48-163

183-197

Author

Hoese 1973

Hansen 1969

Suttkus 1955

Parker 1971

Locality

Georgia coast

Pensacola, F

:la.

Lake Pontchartrain

Galveston Bay, Tex.

and Louisiana coast

Period

Aug. 1956-Aug.

Aug. 1963-Dec. 1965

July 1953-Oc

t 1954

Jan. 1963-Dec 1

Gear'

30- and 40-ft

5-mT

T and S

4.9-m T

Source

Fig. 12

Fig. 2

Table 1

Fig. 21

Length (mm)

Total length

Age-group2

January

10-80

120-130

15-20

45-95

10-79

120-189

10-(80)

90-200

February

20-80

20-25

40-95

10-89

130-179

10-(90)

(90)-250

March

20-80

110-120

15-35

75-85

20-119

120-259

10-(90)

(100)-250

April

40-100

N.S.

20-129

130-339

10-(120)

(130)-250

May

20-110

20-(75)

(60)-135

30-139

140-319

10-(130)

(130)-240

June

50-140

200-210

30-(95)

(90)- 150

30-139

140-329

40-(140)

(156)-250

July

60-140

35-(90)

(90)- 145

50-159

160-380

30-(150)

(160)-230

August

90-160

190-200

35-(110)

(100)- 150

80-169

170-319

60-160

170-250

September

60-150

40-(90)

(90)- 150

80-169

170-319

60-(170)

(170)- 190

October

100-180

45-(110)

(110)-150

90-189

(170)-349

10-40

60-220

November

50-105

20-59

130-309

10-(60)

60-210

December

10-95

10-79

120-299

10-(70)

70-230

'Gear: PI, plankton net; S. seine; T. trawl.

2Age-group: 0 represents smallest group of young-of-the-year first taken from
age-group I. Parentheses indicate that the boundary of age-groups 0 and I is

January on, other fishes (including overwintering young-of-the-year) are included in
indistinguishable. N.S.; no sample.

Carolina), and in October in Texas. Arnoldi et al.
(1973) "tagged" young-of-the-year croakers (9-48
mm TL). Their successful recaptures indicated
that individual croaker remained in the particular
marsh for only 1 to 4 mo, which was much shorter
than the total length of time croaker were ob-
served in the marsh (October- June). Thus, they
also suggested that several croaker "populations"
may utilize coastal marsh as nursery ground dur-
ing the course of the year. White and Chittenden
(1977) indicated that some croakers in the Gulf of
Mexico may lack the first (overwinter) ring on the
scales. This suggests that some croakers may
spawn in the spring in the Gulf of Mexico.

Massmann and Pacheco (1960) reported the dis-
appearance of young croakers from the York
River, but their conclusion may have been in error
because of selectivity of their fishing gear. Haven's
( 1957) length frequencies for croakers during 1952
and 1953 differ from those presented by
Massmann and Pacheco (1960) for the same years.
No fish <100 mm TL were reported by Massmann
and Pacheco ( 1960), but their gear was a net with

%-in (about 1.9-cm) mesh, whereas Haven (1957)
used V4-in (about 0.6-cm) mesh. Joseph (1972) at-
tributed the decline of croaker in the commercial
catches of the middle Atlantic coast to climatic
trends. Present data support his hypothesis. The
apparent increase in juvenile croakers in 1973 and
1974 was probably due to warmer winter months.
Mean bottom temperatures of the York River
channel were about 3.6°C and 3.2°C in January
and February, respectively, from 1967 to 1971
(Markle 1976). It was 6.7°C for January and 6.3°C
for February in 1973 and 1974 ( Figure 2). The year
class strength of croaker in the York River was
dependent on the success of the late young-of-the-
year group (Figure 16, mode I), which stayed in the
estuary through the winter. Historical York River
trawl data show mass mortalities of young-of-
the-year croaker during some cold winters (VIMS,
Ichthyology Department, unpubl. data).

Feeding Mechanisms

The Sciaenidae have the widest spectrum of

678

CHAOandMUSICK: LIFE HISTORY OF JUVENILE SCI AENID FISHES

feeding niches of any fish family in the
Chesapeake Bay. The four most abundant species,
Cynoscion regalis, Bairdiella chrysoura, Micro-
pogonias undulatus, and Leiostomus xanthurus,
are most abundant in the estuary from late spring
to fall, especially young-of-the-year and yearlings
(see previous sections). Under these conditions,
food resources may be limiting and division of
feeding niches may have evolved in order to reduce
competitive exclusion among the dominant
species. Fishes that are closely related and show
feeding niche segregation also often show mor-
phological differentiation in the feeding ap-
paratus (Keast and Webb 1966; Davis 1967; Keast
1970; Davis and Birdsong 1973; Emery 1973). This
section of the paper examines the morphology of
the feeding apparatus in Larimus faseiatus, C.

regalis, B. chrysoura, M. undulatus, Menticirrhus
saxatilis, and Leiostomus xanthurus to test the
hypothesis that adaptations to feeding niche divi-
sion have evolved among those six species.

Characters important in feeding were examined
including mouth position and size, dentition,
number of gill rakers, and intestine length. These
directly affect the size and kind of food ingested
and digested. Other accessory characters
examined were the pore and barbel system on the
snout and/or lower jaw, the nares, and body shape.

Mouth Position

Mouth position and size of the opening limit the
size of prey and habitats in which a predator can
effectively capture prey. These characters were

FIGURE 20. — Mouth position and opening in juveniles of six species of sciaenids: A, A', a, a', Larimus fasciatus; B, B', b, b', Cynoscion
regalis; C, C ', c, c ', Bairdiella chrysoura; D, D ', d, d ', Micropogonias undulatus; E, E ', e, e '. Menticirrhus saxatilis; F, F', f, f ', Leiostomus
xanthurus. A-F, mouth closed. A '-F' mouth wide open. Front view of mouth openings ( lower case letters) in corresponding positions.

679

FISHERY BULLETIN: VOL. 75, NO 4

studied from freshly caught and preserved speci-
mens. Larimus fasciatus has the most oblique
mouth (Figure 20 A) with the lower jaw projecting
strongly in front of the nonprotrusible upper jaw.
The maxilla (Figure 21A) is under the lateral
margin of the rostral fold and its anterior end is
firmly attached to the premaxilla and skull (der-
methmoid). As the mouth opens, the distal ends of
the premaxilla and maxillae push forward as the
lower jaw is lowered (Figure 20A'). The mouth
opens widely. Cynoscion regalis has a large
oblique mouth with the tip of the lower jaw project-
ing in front of the nonprotusible upper jaw ( Figure
20B). The anterior end of the maxilla is firmly
attached to the premaxilla and articulates with
the dermethmoid (Figure 21B). As the mouth is
opened, the posterior end of the premaxilla and the
lower jaw move forward (Figure 20B'). The mouth
opens widely. Bairdiella chrysoura has a similar
mechanism of jaw movement (Figure 20C), but

the mouth is only slightly oblique with the lower
jaw about equal in length to the upper jaw (Fig-
ures 20C, 21C). Micropogonias undulatus has an
inferior mouth with the tip of the lower jaw en-
closed by the protrusible upper jaw (Figure 20D).
The anterior end of the maxilla is loosely attached
to the premaxilla (Figure 21D). As the mouth is
opened, the entire premaxilla and the lower jaw
move anteroventrally (Figure 20D'). The mouth
opens widely. Menticirrhus saxatilis and Leiosto-
mus xanthurus have a similar mechanism of jaw
movement but their upper jaws seem more pro-
trusible (Figures 20E', F'; 21E, F). Their gape is
small. In M. saxatilis, the mouth is inferior and the
lower jaw is enclosed by the upper jaw (Figure
20E). Leiostomus xanthurus also has a small in-
ferior mouth (Figure 20F) with a small gape.

The mouth position indicates that Larimus fas-
ciatus, C. regalis, and B. chrysoura are pelagic
feeders (Figure 20A-C) and that Micropogonias

ETHMOID REGION
DENTARY

PREMAXILLA
MAXILLA

FIGURE 21. — Jaw bones involved in mouth opening in juveniles of six species of sciaenids: A. Larimus fasciatus; B. Cynoscion regalis; C.
Bairdiella chrysoura; D. Micropogonias undulatus; E. Menticirrhus saxatilis; F. Leiostomus xanthurus.

680

CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCI AENID FISHES

undulatus, Menticirrhus saxatilis, and Leiostomus
xanthurus feed on the bottom (Figure 20D-F). The
relative length of the premaxilla and dentary
bones decreases and the height of the anterior
dorsal process of the premaxilla increases from
fishes adapted to feed in "midwater" to those
adapted to feed on the bottom (Figure 21). This
trend is also evident in the relative mouth size and
angle (Figure 21 A-F). An index number (Table 5),
the length of the upper jaw multiplied by the
length of the lower jaw then divided by head
length, decreases through the series of species to-
wards a bottom feeding habit.

Bottom feeders, M. undulatus, L. xanthurus,
and Menticirrhus saxatilis, have protrusible pre-
maxillae (Figures 20D-F', 21D-F). This can be
advantageous in getting the mouth opening close
to food that is to be sucked in from the bottom
(Alexander 1967). Midwater feeders, Larimus fas-
ciatus, C. regalis, and B. chrysoura, lack the pro-
trusibility of the premaxillae (Figures 20A-C;
21A-C); C. regalis andB. chrysoura may compen-
sate for this with faster swimming speed. Gero
(1952) and Nyberg (1971) have discussed this as-
pect in detail. Larimus fasciatus differs from other
sciaenids studied here. It may swim around with
its mouth open using its gill rakers as a filter
similar to that of Engraulis (Gunther 1962).

Dentition

Teeth on the premaxilla and dentary are impor-
tant in capturing prey whereas the pharyngeal
teeth are used for grinding and/or transporting
food to the esophagus. Members of the genus
Cynoscion usually have a pair of enlarged canine
teeth at the tip of the upper jaw (Figures 21B,
22B). Other teeth are conical and present on nar-
row bands of the premaxilla and dentary. The tips
of the upper and lower jaws are broad and have
several rows of teeth which decrease in number to
a single prominent row on the narrower posterior

portion of the jaws. Small teeth also develop inside
the larger row of upper jaw teeth and outside the
lower jaw teeth. Bairdiella chrysoura has a nar-
row band of teeth similar to C. regalis but lacks
large canine teeth at the tip of the upper jaw (Fig-
ure 22C). Micropogonias undulatus, Leiostomus
xanthurus, and Menticirrhus saxatilis have vil-
liform teeth set in broad bands on the premaxillae
and dentaries, and also lack canine teeth (Figure
22D-F). The teeth on the outer row of the pre-
maxillae and inner row of the dentaries are
slightly enlarged. Larimus fasciatus is unique in
having only one or two rows of small teeth on both
jaws (Figure 22A).

Pharyngeal teeth are generally conical in sci-
aenids (Figure 23). The lower pharyngeal teeth
form a pair of separate narrow tooth patches and
are situated on the most medial pairs of cerato-
branchial bones. The upper pharyngeal teeth
occur mainly as two pairs of patches on the two
most medial pairs of epibranchial bones. The
pharyngeal plates are relatively small and narrow
in L. fasciatus and C. regalis compared with the
other sciaenids examined (Figure 23 A, B). The
pharyngeal teeth of L. fasciatus and C. regalis are
sharp, conical, and directed backward, but in B.
chrysoura the pharyngeal teeth are blunt and the
median ones are enlarged (Figure 23C). Micro-
pogonias undulatus has much stronger and more
enlarged pharyngeal teeth along the median rows
(Figure 23D). Menticirrhus saxatilis has fine and
sharp pharyngeal teeth (Figure 23E). Leiostomus
xanthurus develops molariform teeth medially on
the pharyngeal plates (Figure 23F). These sequen-
tial morphological differences in pharyngeal teeth
reflect the feeding niche differentiation from mid-
water to benthic.

Gill Rakers

Gill rakers on the branchial arches of fishes are
important in protecting the delicate gill filaments

TABLE 5.— Relative size of mouth and eye diameter in juveniles of six species of sciaenids from the York

River.

(mm)

Head length
(mm)

Index of mouth size'

Eye diameter in

% of SL

Species

Range

Larimus fasciatus

55.3-107

18.7-36.3

3.17-5.90

4.634

0 957

7.38- 9.84

8602

0.672

Cynoscion regalis
Bairdiella chrysoura

35.2- 75.3

12.7-29.6

1 .93-3.54

2.827

0.518

8.20-11.45

9.55

0 782

38.4- 77.5

14.3-27.4

1.76-3.08

2.494

0.431

827-10.82

9407

0.677

Micropogonias undulatus

35.5-116

12.1-39.3

1.20-2.41

1.686

0.325

6.45- 9.46

7850

0.837

Menticirrhus saxatilis

29.2- 99.6

9.3-29.0

0.50-1.37

0.957

0.264

6.03- 8.56

7.043

0644

Leiostomus xanthurus

47.4-146

18.0-41.3

0.77-2.64

1.472

0.477

7.05-11.11

9 139

0.889

1 1ndex of mouth size = (upper jaw length x lower jaw length)/head length.

681

FISHERY BULLETIN: VOL. 75, NO. 4

PREMAXILLARY TEETH

DENTARY TEETH

FIGURE 22. — Dentition of right premaxilla and dentary in juveniles of six species of sciaenids: A. Larimus fasciatus; B. Cynoscion
regalis; C. Bairdiella chrysoura D. Micropogonias undulatus; E. Menticirrhus saxatilis; F. Leiostomus xanthurus. Posterior end toward
the middle of the figure.

from abrasion by ingested materials and may also
be adapted to particular food and feeding habits.
In sciaenids, the gill rakers reflect feeding niche
by their numbers, size, and shape. They are found
on the dorsolateral surface of the branchial arch
( Figure 24 ) and along its inner surface. The lateral
gill rakers are well developed only on the first gill
arch and the inner (or medial) gill rakers occur
only as tubercles on all five gill arches. Only the

rakers on the first gill arch are discussed here.

Menticirrhus saxatilis and C. regalis have the
fewest gill rakers (Table 6). Bairdiella chrysoura
and Micropogonias undulatus have an inter-
mediate number and L. xanthurus and Larimus
fasciatus have the most gill rakers. Numbers of
inner gill rakers (Table 6) follow a similar se-
quence. The relative size of the gill rakers and
their morphology differ among species ( Figure 24).

682

CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCIAENID FISHES

UPPER PHARYNGEAL TEETH

LOWER PHARYNGEAL TEETH

FIGURE 23. — Portions of left pharyngeal teeth in juveniles of six species of sciaenids: A. Larimus fasciatus; B. Cynoscion regalis; C.
Bairdiella chrysoura; D. Micropogonias undulatus; E. Menticirrhus saxatilis; F. Leiostomus xanthurus. Posterior end toward the
middle of the figure.

TABLE 6. — Total number of lateral and inner gill rakers in juveniles of six species of sciaenids from the York River.

Species

(size in mm SL)

17 18

Menticirrhus saxatilis

12.04

(29.2-99.6)

—

[30]

[6.73]

Cynoscion regalis

13 13

17.19

(35.2-75.3)

—

[27]

[11.40]

Micropogonias undulatus

—

22 55

(35.5-116)

[30]

[15.73]

Bairdiella chrysoura

24.27

(38.4-75.3)

[20]

[15.70]

29 30

Leiostomus xanthurus

4 7

3229

(47.4-148)

6 2]

[44]

[27.18]

Larimus fasciatus

38.00

(55.3-107)

[21]

[21.041

Ml medial gill rakers.

Larimus fasciatus has the longest and the most
closely spaced gill rakers (Figure 24 A). Each raker
has many minute spicules scattered on it (Figure
24a). Cynoscion regalis and B. chrysoura have
moderately long gill rakers compared with the
length of the gill filaments (Figure 24B, C).
Numerous minute spicules are also present on
each raker, especially the basal portion (Figure
24b, c). Micropogonias undulatus has relatively

shorter gill rakers (Figure 24D) with seemingly
strong serrations limited to the basal half of the
raker (Figure 24d). The relative lengths of the
lateral gill rakers in Menticirrhus saxatilis and
Leiostomus xanthurus are the shortest (Figure
24E, F) and lack strong spicules (Figure 24e, f).
Leiostomus xanthurus has only slightly denticu-
late gill rakers and M. saxatilis has smooth gill
rakers.

683

FISHERY BULLETIN: VOL. 75, NO. 4

FIGURE 24. — First right gill arch in juveniles of six species of sciaenids: A, a, a ', Larimus fasciatus; B, b, b ', Cynoscion regalis; C, c, c ',
Bairdiella chrysoura; D, d, d', Micropogonias undulatus; E, e, e', Menticirrhus saxatilis; F, f, f, Leiostomus xanthurus . a-f, lateral
view at the corner, a'-f, medial view at the corner.

684

CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCI AENID FISHES

The inner gill rakers are knoblike, sometimes
with spicules or teeth on their distal ends (Figure
24a '-f'). Cynoscion regalis, Micropogonias un-
dulatus, and Menticirrhus saxatilis have broad,
short inner gill rakers, with the height not longer
than the width of the base. Cynoscion regalis and
Micropogonias undulatus have prominent
spicules at the distal ends of their inner gill rakers
(Figure 24b', d'). Menticirrhus saxatilis lacks
spicules on its inner gill rakers (Figure 24e').
Larimus fasciatus, B. chrysoura, and Leiostomus
xanthurus have long inner gill rakers, with the
height longer than the width of the base. Larimus
fasciatus and B. chrysoura have prominent
spicules at the distal ends of their inner gill rakers
(Figure 24b', c'). Leiostomus xanthurus has mi-
nute spicules on its inner gill rakers (Figure 24f).
Furthermore, in Larimus fasciatus a small inner
gill raker is often present in between the larger
inner gill rakers (Figure 24a'). This is rather
common among western Atlantic sciaenids (Chao
in press).

The lateral and inner gill rakers on the second to
fifth gill arches are similar in size and structure to
the inner gill rakers on the first gill arch. The gill
arches of these six species also differ in the relative
lengths of the epibranchial (upper) arm and
ceratobranchial (lower) arm (Figure 24). Leio-
stomus xanthurus has the shortest upper arm and
M. saxatilis has the shortest lower arm. The num-
bers and size of the gill rakers indicate that mid-
water feeders have lateral rakers longer than
those of bottom feeders. The relative lengths of
inner rakers are longer in fishes with higher num-
bers of lateral rakers, e.g., Larimus fasciatus and
Leiostomus xanthurus (Figure 24a', f; Table 6).
Although Micropogonias undulatus has the
strongest spicules on the lateral gill rakers (Fig-
ure 24d), the midwater feeders usually have better
developed spicules on the lateral rakers than the
bottom feeders (Figure 24). Higher numbers of
rakers (both inner and lateral) are associated with
filter feeding.

Digestive Tract

The digestive tract of sciaenids includes four
parts: esophagus, stomach, pyloric caeca, and in-
testine. The intestine usually has two loops (Fig-
ure 25), except that of C. regalis which is a straight
tube from stomach to anus (Figure 25B). The rela-
tive position and size of the stomach and intestine
vary with the amount of food present. The num-

bers of pyloric caeca and the relative length of the
intestine may be correlated with feeding habits
(Suyehiro 1942). The relative length of the intes-
tine of these six species of sciaenid fishes (Table 7)
may be grouped into three general categories.
Cynoscion regalis has the shortest intestine, less
than half the standard length. Bairdiella
chrysoura has an intermediate intestine length.
Micropogonias undulatus, Menticirrhus saxatilis,
Larimus fasciatus, and Leiostomus xanthurus
have long intestines. The numbers of pyloric caeca
(Table 8) in these six sciaenid fishes show a similar
trend. Cynoscion regalis has the fewest pyloric
caeca, four or five. Bairdiella chrysoura and M.
saxatilis usually have 6 or 7, and Micropogonias
undulatus and L. xanthurus have 7 to 10 pyloric
caeca. Larimus fasciatus has the most, 10 or 11.
Larimus fasciatus and Leiostomus xanthurus
have both a longer intestine and more pyloric
caeca, but Larimus fasciatus is a midwater feeder
and Leiostomus xanthurus is a bottom feeder.
They both consume large numbers of small crusta-
ceans (see "Food Specialization" section). Cynos-
cion regalis has the shortest intestine and the
fewest pyloric caeca. Its diet is mainly composed of
large crustaceans and fishes. Thus, the relative
lengths of the intestine and the numbers of pyloric
caeca in these sciaenids may be correlated with
the size of the food rather than the feeding position
in the water column.

TABLE 7. — Relative length of intestine in juveniles of six species
of sciaenids from the York River.

Intestine length in % of SL

Species

SL (mm) Range

Cynoscion regalis
Bairdiella chrysoura
Micropogonias undulatus
Menticirrhus saxatilis
Larimus fasciatus
Leiostomus xanthurus

35.2-152 35.5-49.6 40.24 3.07 36

30.0-151 46 1-64 1 55.34 5.92 30

35.5-145 52.3-88.6 65.57 6.56 39

29.2-91.2 56.6-88.2 76.06 6.67 26

35.3-99.8 73.1-97.7 83.87 9.08 14

47.4-166 736-97.8 84.69 6.95 30

TABLE 8. — Number of pyloric caeca in juveniles of six species of
sciaenids from the York River.

Species

(size in mm SL)

456789 10 11 N x

Cynoscion regalis

(35.2-82.4)
Bairdiella chrysoura

(30.0-75.3)
Menticirrhus saxatilis

8
11

20 1
19

34
29
30

4.41
6.76
6.63

(29.2-996)
Micropogonias undulatus

(35.5-116)
Leiostomus xanthurus

1 25
6 13

11
8

37
28

8.27
8.14

(47.4-148)
Larimus fasciatus

6 15

10.4

(55.3-107)

685

FISHERY BULLETIN: VOL. 75, NO. 4

*••'• ••

PYLORIC
CAECA

STOMACH

INTESTINE

FIGURE 25. — Ventral view of the digestive tract in juveniles of six species of scaienids: A. Larimus fasciatus; B. Cynoscion regalis; C.
Bairdiella chrysoura; D. Micropogomas undulatus; E. Menticirrhus saxatilis; F. Leiostomus xanthurus.

Pores and Barbels

The pores on the snout and the tip of the lower
jaw, and mental barbels in fishes are sense organs
probably involved in touch, taste, or both. The
number and arrangement of the pores and barbels
in sciaenid fishes are closely related to their feed-
ing habitats (Chao 1976). These six species of sci-
aenid fishes show a gradual increase in the
number and size of pores from upper water column
feeders to lower water column and bottom feeders
(Figure 26). Larimus fasciatus has five marginal

pores on the snout and four minute pores at the tip
of the underside of the lower jaw (Figure 26A, a).
Cynoscion regalis has only two marginal pores on
the snout and no pores or barbels on the lower jaw
(Figure 26B, b). Bairdiella chrysoura has five
marginal and five upper pores on the snout, and
six mental pores at the tip of the lower jaw (Figure
26C, c). Leiostomus xanthurus has five marginal
and five upper pores on the snout, and five mental
pores at the tip of the lower jaw (Figure 26F, f).
Micropogonias undulatus also has five marginal
and five upper pores on the snout, and five mental

686

CHAO and MUS1CK: l.IFE HISTORY OF JUVENILE SCIAENID FISHES

tfVft

E
\

All A #>J\sA <£.[[&

F
\ /

0 0 0 0

FIGURE 26. — Anterior view of snout (captial letters) and ventral view of lower jaw (lower case letters) in juveniles of six species of
sciaenids: A, a, Larimus fasciatus; B, b, Cynoscion regalis: C, c.Bairdiella chrysoura; D, d, Micropogonias undulatus; E, e, Menticirrhus
saxatilis: F, f, Lewstomus xanthurus.

pores plus six minute barbels at the tip of the lower
jaw (Figure 26D, d). Menticirrhus saxatilis has five
marginal pores and three upper pores on the
snout, and four mental pores and a short, rigid
barbel at the tip of the lower jaw (Figure 26E, e).
An apical pore is also present on the barbel of M.
saxatilis. The anterior margin of the snout (rostral
fold) in Larimus fasciatus and C. regalis is com-
plete without notches (Figure 26A, B). Bairdiella
chrysoura and Leiostomus xanthurus have a
slightly indented rostral fold (Figure 26C, F), al-
though the former has a terminal mouth and the
latter has an inferior mouth (Figure 26c, f). Both
M. saxatilis and Micropogonias undulatus have
deeply notched rostral folds (Figure 26D, E), corre-
lated with their inferior mouth positions. The
mental pores of Larimus fasciatus (Figure 26a) are
the smallest of these sciaenids. The barbels of M.
undulatus and Menticirrhus saxatilis may differ
in function as well as in number, because the
single barbel of M. saxatilis has a pore at the tip,
whereas barbels of Micropogonias undulatus do
not (Figure 26d, e>. The numbers and size of pores
increase from species to species as the feeding
niche tends toward the bottom; barbels are present
only in the bottom feeders.

Nares

Sciaenid fishes have two pairs of closely set nos-
trils. The anterior one is usually round; the pos-
terior one is oval and elongate (Figure 27). A flap

of skin is sometimes also present along the poste-
rior margin of the anterior nostril in bottom feed-
ing species. The nasal cavity is generally oval
shaped with a cluster of olfactory laminae forming
a nasal rosette anteriorly. Larimus fasciatus has
the shortest nasal cavity from anterior to posterior
nostril (Figure 27A), and Leiostomus xanthurus
has the longest (Figure 27F). The shape of the
nasal rosettes and olfactory laminae are similar in
these six species of sciaenid fishes. The mean
number of laminae (averaging both sides per
specimen and rounding upwards) differs among
these species (Table 9) and is variable within a
species. The numbers of laminae are 11 to 14 in
Larimus fasciatus; 12 to 22 in C. regalis; 12 to 25 in
B. chrysoura; 10 to 31 in M. undulatus; 11 to 22 in
Menticirrhus saxatilis; and 16 to 30 in Leiostomus
xanthurus. Larimus fasciatus, C. regalis, and B.
chrysoura average fewer laminae than Micro-
pogonias undulatus, L. xanthurus, and Men-
ticirrhus saxatilis (Table 9). Within a species, the
number of nasal laminae seems higher in larger
specimens. The maximum number of nasal
laminae tends to be greater in bottom feeding
fishes.

Other Morphological Characters

Differences in body shape, mouth structure, food
specialization, and habitat preferences of fishes
may act to restrict interspecific competition
within a fauna (Keast and Webb 1966). The six
species of sciaenid fishes discussed here show a

687

FISHERY BULLETIN: VOL. 75, NO. 4

FIGURE 27.— Right olfactory rosette
and nasal cavity in juveniles of six
species of sciaenids: A. Larimus fas-
ciatus; B. Cynoscion regalis; C. Bair-
diella chrysoura; D. Micropogonias un-
dulatus; E. Menticirrhus saxatilis; F.
Leiostomus xanthurus. Dotted circles
represent nostrils, the anterior nostril
to the right.

TABLE 9. — Number of laminae in olfactory rosettes in juveniles of six species of sciaenids from the York River.

Species

(size in mm SL)

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 N

Larimus fasciatus

(55.3-107)
Cynoscion regalis

(35.2-86.4)
Bairdiella chrysoura

(30.0-75.3)
Micropogonias undulatus

(35.5-116)
Menticirrhus saxatilis

(29.2-99.6)
Leiostomus xanthurus

(47.4-148)

3 5 2 5 15 12.6

16647512112 36 15.9

222846263— — 1 — 1 37 16.8

11— — 33433 — 21232 — 2111 134 19.5

1— — 166336321 32 17.3

12443276 — 151— — 1 37 21.7

correlation between body shape and feeding
habitat (Figure 28). Young Larimus fasciatus are
oblong, relatively deep, and have a compressed
body and a double truncate tail (Figure 28 A).
These features, in combination with a strong
oblique mouth and large eyes (Figure 20A, A'; Table
5), indicate that L. fasciatus is a moderate swim-
mer that feeds in the upper water column by sight.

Young C. regalis have a more fusiform and com-
pressed body, and a long pointed tail (Figure 28B).
These features, in combination with a large
lique mouth and relatively large eyes (Figure 20B,
20B, B'; Table 5), indicate that C. regalis is a fast
swimmer that feeds in the upper to middle water
column by sight. Young B. chrysoura have an ob-
long and compressed body, and a broad and

688

CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCIAENID FISHES

FIGURE 28. — Body shape and cross sections in juveniles of six species of sciaenids: A. Larimus fasciatus; B.
Cynoscion regalis; C. Bairdiella chrysoura; D. Micropogonias undulatus: E. Menticirrhus saxatilis; F. Leiostomus
xanthurus.

689

FISHERY BULLETIN: VOL. 75, NO. 4

slightly rounded to truncate tail (Figure 28C).
These features, together with its terminal mouth
and relatively large eyes (Figure 20C, C; Table 5),
indicate that B. chrysoura is a moderately fast
swimmer that feeds in the middle water column by
sight. Young Micropogonias undulatus have an
elongate and less compressed body and a long
pointed tail (Figure 28D). These features, com-
bined with an inferior mouth with barbels and
relatively smaller eyes (Figure 20D, D'; Table 5),
indicate that M. undulatus is a moderately fast
swimmer that feeds in the lower water column by
sight, olfaction, and touch. Young Leiostomus
xanthurus have a rather short and deep body, and
a broad and truncate tail (Figure 28F). These fea-
tures, combined with an inferior mouth and large
eyes (Figure 20F, F'; Table 5), indicate that L.
xanthurus is a slow swimmer that feeds in the
lower water column by sight and olfaction. Young
Menticirrhus saxatilis have an elongate, round,
and narrow body, and a relatively pointed tail
(Figure 28E). These features, combined with an
inferior mouth with a pored-barbel (Figure 26e)
and relatively smaller eyes (Figure 20E, E '; Table
5), indicate that M. saxatilis is a slow swimmer
that feeds in the lower water column by olfaction
and touch.

The cross sections of these young sciaenid fishes
(Figure 28) also reflect their habitat. Larimus fas-
ciatus, C. regalis, and B. chrysoura are compressed
and have relatively narrow ventral surfaces (Fig-
ure 28A-C) in comparison to Micropogonias un-
dulatus, Leiostomus xanthurus, and Menticirrhus
saxatilis (Figure 27D-F). Some of these mor-
phological characters, such as the shape of the
tails and the size of the eyes, vary ontogenetically.
Generally, most juvenile sciaenids have pointed
tails and relatively larger eyes than adults.

Food Specialization

The food habits of young sciaenids have been
studied by numerous authors and the information
reported by them is scattered and presented in
different ways. Some of this work has been sum-
marized for comparison with the present study
(Tables 10-14). Only those studies having some
sort of quantitative analysis were chosen for the
comparison. Different authors have used different
taxonomic categories to analyze their informa-
tion. The classification of the food items in the
present study has been modified from Darnell
(1961) and Qasim (1972). Six major food groups

were employed more or less according to their ver-
tical occurrence in the water column, from the
upper water column to the bottom. They were
fishes, macrozooplankton, microzooplankton,
epibenthos, infauna, and other organic matter.
Within each food group, several items were listed
and the generic and specific names of the primary
prey species in the study area were indicated.
Boundaries for these six food groups are not
definite because some prey taxa move vertically in
the water column and some taxa may also include
both pelagic and benthic species. Generalized
terms used by many authors such as shrimps, an-
nelids, mollusks, crabs, etc., were placed under
respective food groups for the convenience of com-
parison. Food habits of each species were com-
pared with previous studies from different geo-
graphic areas and seasons. Food items were listed
in different categories for each species. Under each
listed item, there were cases where more than a
single food taxon was listed by the original au-
thors. Then, the one that had the highest fre-
quency (by occurrence, volume, or weight) was
chosen to represent that item.

All fish specimens used for stomach analyses in
this study were randomly selected from specimens
collected in June to November (1972 to 1974). Dur-
ing this period, these sciaenids reach their
maximum abundance and degree of sympatry. All
specimens were young-of-the-year or yearlings.

Larimus fasciatus

Stomachs of 12 L. fasciatus (14-125 mm TL)
were examined. All stomachs contained crusta-
ceans, exclusively: Neomysis americana in seven
stomachs, Cumacea in five, Amphipoda (mostly
Gammarus spp.) in four, and calanoid copepoda
(mostly Acartia tonsa) in two. Most of these prey
species were of small size.

Published information on the food habits of L.
fasciatus was scarce. Welsh and Breder (1923) re-
ported on food of fourL. fasciatus (50-110 mm SL)
from Mississippi and Texas. Only two stomachs
had food, one with a post-larval clupeoid and the
other with "schizopodous forms" (crustacean re-
mains).

Cynoscion regalis

Stomachs of 36 C. regalis (67-183 mm TL) were
examined (Table 10). They fed mostly on Anchoa
mitchilli and N. americana. Anchoa mitchilli was
very abundant in the same area as C. regalis in the

690

CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCIAENID FISHES

TABLE 10. — Stomach contents of weakfish, Cynoscion regalis, from different estuarine areas along U.S. Atlantic coast.

Author

Chao 1976
York River, Va.

Welsh and Breder 1 923

Mernner 1975

Locality

Acushnet River,

Cape Charles.

Winyah Bay,

Fernandina,

Pan.lico Sound and

Mass.

Va.

S.C.

Fla.

Morehead City, N.C

Period

June

-Aug. 1973

Sept

1882

Sept. 1916

July 1915

Mar

1920

June 1967-Jan 1970

Source

Original

p. 159

p. 160

p. 161

p 161

Table 1

Number of specimens

105

2,159

Empty stomachs

1.342

Length ol specimens

70-183 n

7-11 cm SL

43-1 1.5 cm SL

2.8-6.2 cm SL

5-17

cm SL

135-481 mm SL

Quantitative method

% of

occurrence

% of volume

% of % of

occur- volume

rence

Fishes:

Anchoa mitchilh

72.2

58.1 15.6

Others and remains

8.3

48.0

2.0

15.7 74.0

Macrozooplankton :

Mysidace

2.8

Neomysis americana

639

31.0 0.9

Isopoda

Decapoda (shrimps)

47.0

0.5

0.1

Others and remains

91.0

1.5 1.2

Microzooplankton:

Copepoda

3.5

Epibenthos:

Polychaeta

0.5

Amphipoda

3.0

0.1

Others and remains

1.5

Unidentified remains

4.0

968 8.2

Author

Thomas 1971

Stickney et al. 1975
Savannah River and

Locality

Delaware River, Del

Ossabaw Sound, Ga.

Period

June 1969

July 1969

Aug 1969

Sept.

1969

Oct

1969

May 1972- July 1973

Source

Table 20

Table 1

Number of specimens

120

Empty stomachs

Length of specimens

11-76

mm TL

5-123

mm TL

15-180 mmTL

20-180 mmTL

61-180

mm TL

30-169 mm SL

Quantitative method

% Of I

Dccurrence

% of occurrence

°o of occurrence

Fishes

'7.0

'14.9

'16.0

133.3

'34.8

Anchoa mitchilli

1.4

2.1

1.1

3.3

4.5

2.5

Others and remains

2.8

7.4

13.8

12.5

30.3

31.7

Macrozooplankton:

Mysidace

74.6

59.6

65.8

66.7

0.8

Neomysis americana

55.0

Isopoda

4.3

2.1

1.7

2.5

Decapoda (shrimps)

2.1

3.2

6.7

10.6

2.5

Others and remains

Microzooplankton:

Copepoda

19.7

4.3

2.1

3.3

5.0

Calanoid

2.5

Others and remains

9.9

4.3

1.1

0.8

1.5

Epibenthos:

Neris succmea

15.0

Amphipoda

2.5

Gammarus sp.

58.5

28.3

28.8

1.7

Others and remains

9.2

Unidentified remains

2.5

'All fishes combined

same months (Colvocoresses 1975; Markle 1976).
Fishes and planktonic crustaceans were the major
food items of C. regalis (Table 10). A shift of food
habits with growth was noted by Thomas (1971),
Merriner (1975), and Stickney et al. (1975). The
smaller weakfish fed more on mysid shrimp and
the larger weakfish fed more on fishes.

and fishes (Table 11). Smaller specimens ( <40 mm
SL) fed mostly on copepods but as they grew they
fed more onN. americanus, amphipods, and other
larger crustaceans. Fishes became more impor-
tant food items for specimens over 70 mm SL
(Thomas 1971; Carr and Adams 1973; Stickney et
al. 1975).

Bci irdiella chrysou ra

Stomachs of 68 B. chrysoura (57-190 mm TL)
were examined (Table 11). They fed mainly onN.
americanus and A. mitchilli. In other areas,
juvenile B. chrysoura fed mainly on crustaceans

Micropogonias undulatus

Stomachs of 69 M. undulatus (65-199 mm TL)
were examined (Table 12). They showed as wide a
variety of prey items as have previous studies from
other geographic areas (Table 12). Polychaetes

691

FISHERY BULLETIN: VOL. 75, NO. 4

TABLE ll. — Stomach contents of silver perch, Bairdiella chrysoura, from different estuarine areas along U.S.

Atlantic and Gulf of Mexico coasts.

Author
Locality
Period
Source

Chao 1976
York River, Va.
June-Aug. 1973
Original

Thomas 1971
Delaware River, Del.
Aug.-Oct. 1969
Table 46

Number of specimens
Empty stomachs
Length of specimens
Quantitative method

57-153 mm TL

% of occurrence

99
9
5-130 mm TL
% of occurrence

Fishes

'12.1

Anchoa mitchilli

5.1

3.0

Others and remains

20.7

8.1

Macrozooplankton:

Mysidace

1.7

89.9

Neomysis americana

74.1

Isopoda

1.7

1.0

Decapoda (shrimp)

10.3

17.2

Others and remains

1.7

Epibenthos:

Annelida (polychaete)

3.5

Neris succinea

3.5

Cumacea

1.7

Amphipoda

1.7

15.2

Gammarus sp.

3.5

62.6

Crabs

3.0

Others and remains

1.7

Infauna (bivalve and Nematoda)

Unidentified remains

6.9

2.0

Author

Stickney et al.

1975

Reid,

1954

Locality

Savannah River and

Cedar Key, Fla.

Ossabaw Sound, Ga.

Period

May 1972-July

1973

June 1950-May

Source

Table 1

Table 5

Number of specimens
Empty stomachs
Length of specimens
Quantitative method

161
48
30-149 mm TL
% of occurrence

45 6

0 0

25-99 mm SL 100-130 mm SL
% of occurrence

Fishes:

Anchoa mitchilli

Others and remains
Macrozooplankton:

Mysidace

Neomysis americana

Isopoda

Decapoda (shrimp)

Others and remains
Microzooplankton

Copepoda

Others and remains
Epibenthos:

Annelida (polychaete)

Neris succinea

Amphipoda

Gammarus sp.

Crabs
Others and remains
Unidentified remains

2.7
6.6

0.6
25.1
1.1
5.5
8.2

3.9
2.2

0.6
8.2
2.2
6.0
8.2
0.6

4.4

73.3
4.4

4.0

2.2
33.3

6.6

16.6

33.3
666

16.6
16.6

'All fishes combined.

and crustaceans were the main food items of the
juvenile M. undulatus in the study area. Juvenile
M. undulatus fed on a large variety of inverte-
brates and sometimes fishes (Table 12). Stickney
et al. (1975) indicated that smaller specimens
( <100 mm SL) depend extensively on harpacticoid
copepods, which are mainly bottom dwellers. As
the fish grow, they become more generalized feed-
ers (Parker 1971). Geographic variation in food
habits of juvenile M. undulatus (Table 12) proba-
bly is attributable to availability of prey species in
the area.

Menticirrhus saxatilis

Stomachs of 20 M. saxatilis (36.5-118 mm TL)
were examined. All contained crustaceans and

Welsh and Breder 1923
Cape Charles, Va.
Sept. 1916
p 174-175

21
0
6-8.2 cm TL
% of occurrence

5
87

2
5

Carr and Adams 1973
Crystal River, Fla.

Oct. 1970-Aug. 1971
Estimate from Fig. 9

195
43
5-130 mm TL
% of occurrence

31.2

51.6

7.3
9.2

polychaetes were also important in their diet. The
occurrence of organic detritus was also frequent
suggesting that M. saxatilis is a bottom feeder.
The literature also indicates that juvenile M.
saxatilis feed mainly on crustaceans and
polychaetes (Table 13). Welsh and Breder (1923)
indicated that M. saxatilis fed mainly on rela-
tively large crustaceans.

Leiostotnus xanthurus

Stomachs of 77 L. xanthurus (73-205 mm TL)
were examined. Although they showed a wide va-
riety of food species, the major part of the food was
benthic. Pectinaria gouldii, a burrowing
polychaete, was a major food item in the diet of L.
xanthurus in the study area. Stickney et al. (1975)

692

CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCI AENID FISHES

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693

FISHERY BULLETIN: VOL. 75, NO. 4

TABLE 13. — Stomach contents of northern kingfish, Menticir-
rhus saxatilis, from different estuarine areas along U.S. Atlantic
coast.

Author

Chao 1976

Welsh and Breder 1 923

Locality

York River, Va.

Cape May,

Falmouth,

N.J.

Mass

Period

Mar.
Dec.

1972-
1974

Aug. 1916

Aug. 1892

Source

Origi

nal

p. 194

Number of specimens

Empty stomachs

Length of specimens

37-118

1.9-7.2

2.4-7.4

cm SL

Quantitative methods

%of

occurrence

% of vol.

Macrozooplankton:

Neomysis americana

35.0

Isopoda

5.0

Decapoda (shrimp)

9.0

42.0

Crangon septemspinosa

5.0

Palaemonetes

10.0

Insecta

5.0

Others and remains

70.0

9.0

42.0

Microzooplankton:

Copepoda

5.0

Calanoid

5.0

Epibenthos:

Polychaetes

70.0

19.0

Glycindae solitaha

10.0

Spionids

15.0

Amphipoda

35.0

30.0

Gammarus sp.

15.0

Others and remains

40.0

Unidentified remains

and organic matters

50.0

26.0

16.0

found that harpacticoid copepods were the main
food for juvenile L. xanthurus and that seasonal
variations in diet were slight. Organic detritus
and unidentified remains were also common in
stomachs (Table 14).

Food Partition

To compare the feeding habits of the juveniles of
the six sciaenid species, a chart (Figure 29) has
been prepared for the six food groups defined pre-
viously. The main food group of Larimus fasciatus
was mostly planktonic and the primary food
species was Neomysis americana. Cynoscion re-
galis and B. chrysoura fed mainly on fishes and
macrozooplankton; the primary food species were
Anchoa mite hi Hi and N. americana, respectively.
Micropogonias undulatus fed on a wide variety of
food including all six food groups, with the domin-
ant food organisms being N. americana and Nereis
succinea. Menticirrhus saxatilis fed mainly on
macrozooplankton and epibenthos, with the pri-
mary food organisms being N. americana and
polychaetes. Leiostomus xanthurus fed on a wide
variety of food including five food groups. The
dominant food organisms were Pectinaria gouldii
and other polychaetes.

Neomysis americana was very abundant and
available to all species of sciaenids in the study

area. This shrimp migrates vertically in response
to change in ambient light (Herman 1962).
Neomysis americana is negatively phototactic. In
shallow turbid water (as in the study area) during
daylight it might concentrate near the bottom in
the darkest sector of the vertical light gradient
(Stickney et al. 1975). Because of the abundance
and availability of N. americana, the other prey
items should provide a better indication of feeding
specialization. As has been repeatedly shown (Ta-
bles 10-14), most fishes were sufficiently oppor-
tunistic in their food habits to take advantage of
extremely abundant prey species. All the fishes in
the present study were sampled by bottom trawl
during the daytime. Therefore, both prey and pred-
ators probably were dwelling close to the bottom.
Polychaetes were a major food resource for the
bottom feeders (Tables 12-14), Micropogonias un-
dulatus, L. xanthurus, and Menticirrhus saxatilis.
But Micropogonias undulatus fed more on the
"crawling" species of worms (Table 12) such as
Nereis and Nephthys (Barnes 1968) and L. xan-
thurus fed more on "tubiculous" or "burrowing"
species of worms (Table 14), such as Pectinaria and
Amphitrite. This is contradictory to the findings of
Roelofs ( 1954) and Stickney et al. (1975). Observa-
tions of the feeding behavior of these two species in
aquarium generally agreed with Roelofs (1954).
But L. xanthurus seemed to "dive" into the bottom
sand much more often than M. undulatus, and the
depth of the dives by L. xanthurus was not shal-
lower than M. undulatus as stated by Roelofs
(1954).

Correlation of Feeding Structures
and Food Habits

Larimus fasciatus and C. regalis have oblique
mouths (Figure 20A, B) and their upper jaws are
slightly or not protrusible (Figure 21A, B). These
features allow them to feed anteriorly and dorsally
to the longitudinal axis of their bodies along their
swimming course. Their mouths open as the lower
jaws drop anteroventrally and the distal ends of
the premaxillae move forward (Figure 20A', B').
The mouth openings of L. fasciatus and C. regalis
are relatively larger than in the other species
studied (Table 5). The anterior views of their
mouths (Figure 20a, a', b, b') show that the upper
jaws (premaxillae) are longer or equal to the lower
jaws (dentaries). Although both of them feed "an-
terodorsally" and pelagically, they did show dif-
ferences in diet (Figure 29). The following mor-

694

CHAO and MUSICK: LIFE HISTORY OF Jl'VKNILES(TAKNID FISHES

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695

FISH

Anchoa milchilli

MACROZOOPLANKTON
Neomysis omericona

MICROZOOPLANKTON
Copepodo

EPIBENTHOS
Nereis succineo
ft Amphipodo

IN FA UN A
Pectmoria gouldn

ft Nemotoda

UNIDENTIFIED REMAINS a
ORGANIC MATTERS

TOTAL LENGTH (mm)
NUMBER OF STOMACHS

76.5

8.2

k V \ \ \ \ \ \ ',

■

24.1 20.3

^^^ k\\\\\\\\l

K\\\\\\\H

74-126
12

Larimus

foscialus

FISHERY BULLETIN: VOL. 75, NO. 4

rioo

14.1 10.0

75.0

70.0

61.0

41.7

o 0 8.6

■

SSm

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»

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riOO
50

1 8 8

23.5

i^^ ^

70- 183
34

57-153
58

56-199
64

37-118
20

73-202
73

Cynosaon Bairdiella Micropogon

regols chrysoura undulafus

Menhcirrhus Leiostomus
saxatil/s xonthurus

<r
ir

Z>
O

o
o

FIGURE 29. — Frequencies of occurence of various categories of food groups in stomachs of juveniles of six species of sciaenids from the

York River and lower Chesapeake Bay estuary.

phological characters are correlated with the
dietary differences. The premaxillary and dentary
teeth of both species are sharp and set in narrow
ridges or bands (Figure 22 A, B). Cynoscion regalis
has much larger teeth than L. fasciatus , especially
a pair of large canines at the tip of upper jaw in C.
regalis. These large sharp teeth are adaptations
for grasping larger swimming prey. Both species
have small sharp pharyngeal teeth (Figure 23 A,
B). The arrangement and size of the gill rakers
(Figure 24A, B) in L. fasciatus are much denser
and longer than those of C. regalis. These differ-
ences reflect the food contents in the stomachs of L.
fasciatus, which consisted of small crustaceans
collected by filtering. The stomach contents of C.
regalis consisted of large crustaceans and fishes
(Table 10). Larimus fasciatus has a much longer
two-looped intestine than the straight intestine of
C. regalis (Figure 25A, B; Table 7). The number of
pyloric caeca in L. fasciatus (10 or 11) is also

higher than in C. regalis (4 or 5). These mor-
phological differences are probably correlated
with the size of food ingested. The cephalic pore
systems of C. regalis and L. fasciatus are not well
developed. Cynoscion regalis has only two mar-
ginal pores on the snout (Figure 26B) whereas L.
fasciatus has five minute marginal pores on the
snout and four pores on the underside of the lower
jaw (Figure 26 A). In addition, the more fusiform
C. regalis (Figure 28B) is adapted for fast swim-
ming and active predation. The robust, and pre-
sumably slower moving, L. fasciatus (Figure 28A)
shows adaptations characteristic of a plankton
grazing type of feeding.

Bairdiella chrysoura has a slightly oblique ter-
minal mouth (Figure 20C) and a slightly protrusi-
ble upper jaw (Figure 20C). These features allow
the fish to feed directly in front of its body axis
along its swimming course. Its mouth opens as the
lower jaw drops anteroventrally and the premaxil-

696

CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCI AENID FISHES

lae move forward (Figure 20C). The relative size
of the mouth opening in B. chrysoura (Table 5) is
similar to C. regalis. The anterior view of its
mouth opening shows equal upper and lower jaws
(Figure 20c, c'). Although B. chrysoura feeds an-
teriorly, a pelagic feeder, its stomach contents are
similar to those of C. regalis (Figure 29), except for
a smaller proportion of fishes. The jaw teeth of B.
chrysoura are strong, conical, and arranged in
narrow bands, but canines are absent at the tip of
the premaxilla (Figure 22C). Its pharyngeal teeth
are relatively stronger and blunter than in C. re-
galis (Figure 23B, C), especially along the median
rows. Gill rakers of B. chrysoura are intermediate
between L. fasciatus and C. regalis in number
(Table 6) and length (Figure 24A-C). The intes-
tine of B. chrysoura has two loops and its relative
length and number of pyloric caeca (6-8) are also
intermediate between L. fasciatus and C. regalis
(Figure 25C; Tables 7, 8). These intermediate fea-
tures reflect the intermediate feeding habits of B.
chrysoura (Figure 29). In addition, the body shape
of B. chrysoura is oblong (Figure 28C) and not
fusiform as in C. regalis, thus resulting in slower
swimming and less efficiency in capturing fishes,
as reflected in the diet. The relatively well-
developed cephalic pore systems of B. chrysoura
(Figure 26C), three upper and five marginal pores
on the snout and six mental pores on the tip of the
lower jaw, also may indicate that B. chrysoura
depends more on "taste" feeding lower in the water
column than L. fasciatus and C. regalis.

Micropogonias undulatus, Leiostomus xan-
thurus, and Menticirrhus saxatilis have inferior
mouths (Figure 20D-F) and rather protrusible
premaxillae (Figure 21D-F). These features en-
able them to feed anteriorly and ventrally to their
body axis along their swimming courses. Their
mouths open as the lower jaws drop ventrally
backward and the premaxillae protrude antero-
ventrally (Figure 20D-F'). Their mouths are rel-
atively smaller than those of the pelagic feeders
described previously (Table 5). The anterior views
of their mouths ( Figure 20d, d ', e, e ', f, f ' ) show that
the upper jaws (premaxillae) are shorter or equal
to the lower jaws (dentaries). Although they all
feed anteroventrally and benthically, there are
differences in their feeding habits (Figure 29).
These differences are reflected in the structural
differences in the feeding apparatus and feeding
behavior among them. The jaw teeth of M. sax-
atilis, Micropogonias undulatus , and L. xanthur-
us are all set in bands and the outer row of teeth on

the upper jaws and an inner row of teeth on the
lower jaws are slightly enlarged (Figure 22D-F).
The pharyngeal teeth of M. undulatus and Men-
ticirrhus saxatilis are conical (Figure 23D, E) and
the median rows are larger and blunt. Leiostomus
xanthurus has smaller pharyngeal teeth and the
median ones are molariform (Figure 23F). The gill
rakers of these three bottom feeding sciaenids dif-
fer in number (Table 6) and size (Figure 24D-F).
Menticirrhus saxatilis has the fewest and shortest
gill rakers among them. Micropogonias undulatus
has fewer but longer gill rakers than L. xanthurus.
The inner gill rakers of L. xanthurus are longest
(Figure 24f) and most numerous (Table 6). This is
reflected in the larger numbers of small crusta-
ceans (e.g., copepods) ingested by L. xanthurus
(Table 14). The relative length of intestines (Table
7) and their in situ position (Figure 25D — F) are
similar among these benthic feeders. The average
relative intestinal length of M. undulatus and
Menticirrhus saxatilis is slightly shorter than in
L. xanthurus (Table 7). The numbers of pyloric
caeca of these bottom feeders are similar ( Table 8).
The cephalic pore and barbel system differ among
Micropogonias undulatus , L. xanthurus, and Men-
ticirrhus saxatilis. They all have five upper and
five marginal pores on the tip of snout (Figure
26D-F). Micropogonias undulatus and Menticir-
rhus saxatilis also have a deeply notched rostral
fold. Ventrally, Micropogonias undulatus has five
pores and six miniature barbels (Figure 26d);
Menticirrhus saxatilis has four pores and a short
rigid barbel with an apical pore (Figure 26e); L.
xanthurus has five pores and no barbel (Figure
26f). Menticirrhus saxatilis also has the most pro-
nounced snout and most elongate and rounded
body form (Figure 28E). Leiostomus xanthurus
has the least pronounced snout and shortest and
deepest body form (Figure 28F). Micropogonias
undulatus is intermediate in snout and body form
between Menticirrhus saxatilis and L. xanthurus.
The length of snout and body form reflect the
feeding habits of these three species. Food habits
(Figure 29) indicate that M. saxatilis and Micro-
pogonias undulatus feed on the substrate, on the
epifauna, more than they feed "into" the substrate
on the infauna. Leiostomus xanthurus feeds more
on the infauna. The long projecting snout seems to
be an obstacle for fishes with an inferior mouth to
forage into the bottom for food. Roelofs' (1954)
observations on feeding behavior of M. undulatus
and L. xanthurus in aquaria with sandy bottoms
were repeated during the present study. Juveniles

697

FISHERY BULLETIN: VOL. 75, NO. 4

of both species foraged into the bottom sand often,
especially when the substrate was freshly dug
from the beach. Foraging tapered off gradually,
especially in M. undulatus, apparently as the food
in the substrate decreased. Brine shrimp, Ar-
temia, were fed to these two species in the
aquarium. Both M. undulatus and L. xanthurus
were able to feed on brine shrimp just below the
water surface. Micropogonias undulatus fed on
the surface shrimp in an oblique to vertical posi-
tion. To feed on brine shrimp close to the surface,
L. xanthurus occasionally maneuvered in an
oblique upside-down position, with the dorsal fin
pointing toward the bottom to overcome the in-
ferior position of its mouth.

Other accessory organs of feeding, such as the
nares and eyes, also reflect the feeding habits of
young sciaenid fishes. The numbers of nasal
laminae of the six species (Table 9) overlap, partly
due to ontogenetic changes; the absolute numbers
of nasal laminae increase as the fishes grow
larger. Generally, the bottom feeders, M. un-
dulatus and L. xanthurus, have more nasal
laminae than Larimus fasciatus, C. regalis, and B.
chrysoura (Table 9). Menticirrhus saxatilis has
relatively fewer nasal laminae than other benthic
feeders, but it has a pored mental barbel on the
lower jaw. This suggests that M. saxatilis depends
more on touch for foraging than other benthic
feeders. The relative eye size of M. saxatilis is
smaller than in other sciaenid fishes studied here
(Table 5). Larger eyes were found among the
pelagic feeders, L. fasciatus, C. regalis, and B.
chrysoura (Table 5). Allometrically, the relative
eye size of all these sciaenid fishes is larger in
young specimens and smaller in adults. For
benthic feeders, decrease in relative eye size with
growth is faster than for the pelagic feeders. The
relative roles of olfaction, touch, and vision in
feeding in young sciaenids studied may be
hypothesized as follows. The benthic feeders, Mi-
cropogonias undulatus, L. xanthurus, and Men-
ticirrhus saxatilis, depend more on their senses of
smell or touch or both to locate their prey. The
pelagic feeders, Larimus fasciatus, C. regalis, and
B. chrysoura, depend more on sight to catch their
prey, especially C. regalis and B. chrysoura which
prey on Anchoa mitchilli, an active small anchovy.

Morphological differences in the feeding ap-
paratus, especially the mouth position, size, and
protrusibility, the form of teeth, and the gill raker
structure are limiting factors for the level of water
column and the size of the prey species which can

be eaten by the fish. The pelagic feeders, L. fas-
ciatus, C. regalis, and B. chrysoura, almost com-
pletely lack any sedentary benthos in their diets
(Figure 29). Even among the bottom feeders, Mi-
cropogonias undulatus feeds more on epibenthic
polychaete species (Table 12) and Leiostomus
xanthurus feeds more on burrowing polychaete
species (Table 14).

Morphological differences in the digestive tract,
the number of pyloric caeca, and the length of
intestine may be adaptations to more efficient use
of food. As is evident in Larimus fasciatus and
Leiostomus xanthurus, size of the food items is
important; Larimus fasciatus fed exclusively on
small crustaceans (small Mysidacea and Am-
phipoda), Leiostomus xanthurus fed mainly on
copepods (Table 14). Larimus fasciatus is mainly a
pelagic feeder and Leiostomus xanthurus is
mainly a benthic feeder. Both species have longer
intestines (Table 7) and more pyloric caeca (Table
8) than other species in their respective groups
(pelagic and benthic).

Svetovidov reported a similar relationship be-
tween the number of gill rakers and size of food
items in Caspian shads (Nikolsky 1963). However,
he also found more pyloric caeca in shad that fed
on fishes than in species that ate small crusta-
ceans, a relationship opposite to that found here.
In feeding, the role of gill rakers is in ingestion and
the role of the pyloric caeca is in digestion. Al-
though there are morphological and numerical
correlations among the ingestive apparatuses and
digestive organs, they are highly adaptive and
may be variable among fishes.

The so-called "selective feeding habits" of these
young sciaenids reported by many previous au-
thors (see citations of Tables 10-14) are not evi-
dent in the present study. Partitioning of food
among these young sciaenids depends more on the
habits of the prey species than on "selective pref-
erences" of the fishes. Juvenile sciaenids feed op-
portunistically in a limited depth range in the
water column, probably within or close to 2 m
above the bottom. Within this layer of the water
column, Larimus fasciatus, C. regalis, and B.
chrysoura feed in the upper portion of the water
column and M. undulatus, Leiostomus xanthurus,
and Menticirrhus saxatilis feed in the lower por-
tion of the water column to the bottom. Feeding
niche division and resulting dietary differences
among these species of sciaenids in the
Chesapeake estuary area are probably attribut-
able to differences in feeding behavior imposed

698

CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCIAENID FISHES

upon these species by adaptive morphological
limitations rather than to selective feeding per se.

CONCLUSION

In the Sciaenidae, a family of primarily coastal
marine fishes, many species utilize the same
coastal area as common nursery and seasonal
feeding grounds. In the York River estuarine sys-
tem, the coexistence of sciaenid fishes may be at-
tributed to: 1) Differences in their temporal and
spatial distributions. Juveniles of the four most
abundant sciaenid fishes entered the estuary at
different times of the year. Within a given period,
the highest catches of each species were usually in
different areas (upper and lower reaches) and
depths (beach zone, shoals, and channel) of the
York River system. Also, the size distributions of
each species were often separated temporally and
spatially. 2) Differences in their habitat adapta-
tions and food habits. The diverse morphological
features of these sciaenid fishes enable them to
utilize food resources from different levels (micro-
habitats) of the water column. Correlations of
feeding apparatus, digestive system, and food
habits are evident and result in niche division. 3)
The abundant food resources of the study area. At
times some prey organism (e.g., Neomysis
americanus) may be ubiquitous and very abun-
dant, providing food for several species of juvenile
sciaenids. Then food would not be a limiting re-
source and intrafamilial competition may not oc-
cur.

ACKNOWLEDGMENTS

We thank D. F. Boesch, B. B. Collette, G. C.
Grant, P. A. Haefner, Jr., and J. V. Merriner for
their helpful suggestions and critical review of
this manuscript. We also express our appreciation
to the following persons from VIMS: R. Bradley, J.
Gilley, and M. Williams for preparation of graphs;
Susan Barrick and her staff at the VIMS library;
William H. Kriete, Jr., James Colvocoresses,
Douglas F. Markle, Jerome E. Illowsky, and
James Green who helped in field work, including
trawling, collecting, and measuring fishes during
the study; Deborah A. Sprinkle and Julia F. Mil-
len who typed many drafts of this manuscript;
Joyce S. Davis who answered many questions
about different surveys; Genie Shaw who re-
trieved all the hydrographic data from the VIMS
computer data storage; and to our colleagues, K.

W. Able, J. Colvocoresses, D. F. Markle, J. D.
McEachran, L. P. Mercer, G. Sedberry, and C. A.
Wenner for allowing us to talk to them about sci-
aenids and for helpful suggestions.

Our special appreciation goes to Bruce B. Col-
lette, Systematics Laboratory, National Marine
Fisheries Service, NOAA, Washington, D.C., who
instigated this joint adventure a few years ago.

D. E. McAllister, National Museums of Canada,
reviewed the final draft of the manuscript and
offered helpful suggestions. J. McConnell and her
staff at the Word Processing Centre, National
Museums of Canada, typed the final draft.

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SUYEHIRO, Y.

1942. A study of the digestive system and feeding habits of
fish. Jap. J. Zool. 10:1-303.
TAYLOR, W. R.

1967. An enzyme method of clearing and staining small
vertebrates. Proc. U.S. Natl. Mus. 122(3596), 17 p.
THOMAS, D. L.

1971. The early life history and ecology of six species of
drum (Sciaenidae) in the lower Deleaware river, a brac-
kish tidal estuary. Ichthyol. Assoc. Bull. 3, 247 p.
TOWSEND, B. C.

1956. A study of the spot, Leiostomus xanthurus
Lacepede, in Alligator Harbor, Florida. M.S. Thesis,
Florida State Univ., Tallahassee, 43 p.

WALLACE, D. H.

1940. Sexual development of the croaker, Micropogon un-
dulatus, and distribution of the early stages in
Chesapeake Bay. Trans. Am. Fish. Soc. 70:475-482.
WELSH, W. W. AND C. M. BREDER. JR.

1923. Contributions to life histories of Sciaenidae of the

701

FISHERY BULLETIN: VOL. 75. NO. 4

Eastern United States Coast. Bull. U.S. Bur. Fish. YOUNG, R. H.

39:141-201. 1953. An investigation of the inshore population of the

WHITE, M.L., AND M. E. CHITTENDEN, JR. spot (Leiostomus xanthurus, Lacepede) with particular

1977. Age determination, reproduction, and population reference to seasonal growth and size distribution in

dynamics of the Atlantic croaker, Micropogonias un- Chesapeake Bay. M.S. Thesis, Univ. Maryland, College

dulatus. Fish. Bull., U.S. 75:109-123. Park, 34 p.

702

THE UNITED STATES SHRIMP FISHERY OFF
NORTHEASTERN SOUTH AMERICA (1972-74)1

Albert C. Jones and Alexander Dragovich2

ABSTRACT

The Guianas-Brazil shrimp fishery off the northeastern coast of South America is supported by four
principal species— pink-spotted shrimp, Penaeus brasiliensis; brown shrimp, P. subtilis; pink shrimp,
P. notialis; and white shrimp, P. schmitti. The areas off Guyana, Surinam, and western French Guiana
were dominated by pink-spotted shrimp; brown shrimp were most prevalent off eastern French Guiana
and Brazil, pink shrimp off Guyana, and white shrimp off Guyana, French Guiana, and Brazil, chiefly
in shallow waters.

U.S.-flag vessels landed 5.0 million pounds of shrimp during the second half of 1972, 13.6 million
pounds in 1973, and 9.0 million pounds in 1974. In 1973 and 1974 U.S.-flag vessels took 50% and 39% of
the total international landings. Mean annual catch rates for 1972, 1973, and 1974 were 20.0, 26.0, and
18.3 lb/h, respectively. Monthly catch rates peaked each year in March and April and declined
gradually thereafter. The catch rates off Brazil were higher than off the Guianas. Most fishing was
carried on at night and at depths of 21-35 fathoms.

Small shrimp appeared to be recruited to the fishery mainly in April and October and mainly off
French Guiana, Brazil, and Guyana.

An exponential surplus yield model estimated the maximum sustainable yield to be 28.7 million
pounds and a linear model estimated the maximum sustainable yield to be 27.1 million pounds.
Maximum observed yield was 27.3 million pounds (1973).

The shrimp resource off the northeastern coast of
South America (Figure 1) is the basis of a major
international fishery. This fishery consists of four
principal species — pink-spotted shrimp, Penaeus
brasiliensis; brown shrimp, P. subtilis; pink
shrimp, P. notialis; and white shrimp, P.
schmitti. Penaeus subtilis and P. notialis until
recently were known as P. aztecus subtilis and P.
duorarum notialis, respectively (Perez Farfante in
press). The earliest exploratory fishery survey of
the continental shelf off the northeastern coast of
South America was made in 1944 by Whiteleather
and Brown (1945). Commercial shrimp fishing by
U.S. vessels began in 1959 stimulated by
exploratory surveys made in 1957 and 1958 (Hig-
man 1959; Bullis and Thompson 1959). Thereafter
the fishery expanded rapidly and soon included
vessels of other nations. The history of the fishery
through 1959, and a description of the fishing
grounds, species, fishing fleets, and stock status, is
given by Naidu and Boerema (1972).

'Contribution No. 481 from the Southeast Fisheries Center,
Miami Laboratory, National Marine Fisheries Service, NOAA,
Miami, Fla.

2Southeast Fisheries Center Miami Laboratory, National
Marine Fisheries Service, NOAA, 75 Virginia Beach Drive,
Miami, FL 33149.

Manuscript accepted March 1977.

FISHERY BULLETIN: VOL. 75, NO. 4, 1977.

This report is based on data collected in 1972-74
from U.S.-flag vessels and from processing plants
under the terms of the bilateral United States-
Brazil Shrimp Agreement. This paper evaluates
and reviews the status of the fishery based on
analysis of these data. Information from process-
ing plant records before 1972 is also used.

The United States-Brazil Shrimp Agreement of
1972 dealt with conservation of shrimp resources
and operations of U.S. shrimp vessels off northern
Brazil (Allen 1973). The agreement stated that the
information on catch and effort, and biological
data relating to the shrimp fishery in that area, be
collected from U.S. vessels. Similar agreements
were effected between Brazil and Barbados,
Surinam, and Trinidad and Tobago.

SOURCES OF DATA AND METHODS

Catch data for U.S. vessels came from logbooks
and landing records for July 1972- December 1974
(Figure 2; Appendix Table 1). Logbook records
were submitted for approximately 509c of the
fishing trips, but this percentage varied monthly
from 10% at the beginning of data collection to
809c later in the period. Landing records were
submitted for all trips. Information on area of cap-

703

FISHERY BULLETIN: VOL. 75, NO. 4

10°-

KEY TO
SHADED AREA

OPEN
MAR1
NOV 30

OPEN

MAR1-

JUNE30

EAST 7a

GULLIES Ia

DROP-OFF
RIDGES

STEEPLES 81

FIGURE 1. — The Guianas-Brazil shrimping grounds. The chart shows the fishing zones and their common names. The United
States-Brazil Shrimp Agreement Area is shaded and the boundaries of the Area and the fishing seasons for U.S. vessels are shown in the
insert.

1,500,000-1

r700

1,000,000-

t/t

z
o

500,000-

A S O N D
1972

MAM

SONDJ FMAMJ
1973 1974

MONTH OF LANDING

O N

FIGURE 2. — Shrimp catches of U.S. vessels by month and area for the Guianas-Brazil fishery. Weights of heads-off shrimp are in
pounds and metric tons. Vertical lines represent the total U.S. landings reported by the processing plants and are reported by month
in which the landing was made. Vertical bars represent the "hail" or estimated catches of U.S. vessels submitting logbooks and are
reported by the month of capture. The shaded area of the vertical bar represents the proportion of the logged catches recorded from the
United States-Brazil Shrimp Agreement Area.

ture, fishing effort, catch, and species and size of
shrimp, were taken from logbooks and landing
records. The vessel captain made daily entries in
the logbook on fishing area (identified by 1°-

coastal zone and by water depth), fishing effort
(number of hauls and number of hours fishing, by
day and by night), estimated shrimp catch
(pounds, heads-off weight), and most abundant

704

JONES and DKACON ll'H UNITED STATES SHRIMP FISHERY

species, and commercial tail-weight. The retained
catch was reported; no estimate was made of the
discarded catch. Landing records for each fishing
trip included the total weight of shrimp in each
commercial weight category. The landings were
recorded in two categories: "mixed" shrimp (pink-
spotted, brown, and pink) and white shrimp. In our
treatment of the landing data, however, we com-
bined the landings of "mixed" and white shrimp.
Information on area of catch was not available in
the landing records. In addition, processing plants
reported total yearly landings of shrimp and aver-
age fleet sizes, including both U.S.- and other-flag
vessels.

We estimated total monthly areal catches by
adjusting the monthly catches reported by area in
logbooks for 1) catches unreported by area and 2)
landings unreported in logbooks. For example, the
total U.S. catch off northern Brazil (fishing zones
78-81) in April 1974 was estimated as follows:

A' x

B_
B'

C
C

where A

= estimated total catch in zones 78-81,

April 1974;
= catch reported in logbooks for zones

78-81, April 1974;
= total catch reported in logbooks, April

1974;
= total catch reported in logbooks by

fishing zone, April 1974;
= total landings reported in landing

records, April and May 1974;
= total catch reported in logbooks, April

and May 1974.

The ratio BIB ' adjusted A ' for the logbook catch
that was unreported by fishing zone and the ratio
CIC adjusted for the landings that were unre-
ported in logbooks. The second ratio used data for 2
mo, since catches made in a given month often
were landed in both that and the following month.
This method resulted in estimates of the total an-
nual catches by areas of capture which were
within 2% of the total reported annual landings.
The logbook sample was not random and the catch
off Brazil was probably overestimated, since more
vessels probably submitted information when
fishing off Brazil than when fishing off the
Guianas. However, there was no way to assess the
difference in completeness of reporting of vessels
fishing different areas. For this reason, estimates

of catches were not made for smaller subareas.

The size index was a weighted mean value cal-
culated by assigning the values 1, ... 9 to the
commercial tail-weight categories >50, . . . <15.

ANNUAL LANDINGS AND CATCHES

During the second half of 1972, total landings by
U.S. -flag vessels were 5.0 million pounds; in 1973
and 1974, they were 13.6 and 9.0 million pounds,
respectively (Table 1). Landings of U.S. vessels
were 50% and 39% of total international landings
in 1973 and 1974. Monthly catches (Table 2) vary
slightly from landings since they are estimated
values and because catches are often landed in
months subsequent to the month of capture.

To gain a perspective of the entire fishery, we
assembled the historical landings of U.S.- and for-
eign-flag vessels for 1960-74 (Table 3, Figure 3)
and the number of shrimp trawlers by country for
1961-74 (Table 4). There was a continuous in-
crease in landings from 1960 (3.9 million pounds)
through 1968 (27.3 million pounds). The landings
declined slightly in 1969 and 1970 to 27.1 and 27.0
million pounds, respectively. There was a sharp
decline in landings in 1971 andl972 (to 22 million
pounds). In 1973 the fishery. attained a maximum
catch of 27.3 million pounds. The following year
there was a decline in landings to 23.1 million
pounds.

Ninety percent of the landings from 1960
through 1974 were made in Guyana (46% ), French
Guiana (21%), Surinam (14%), and Trinidad
( 10% ). The remaining landings were made in Bar-
bados (6%), Brazil (3%), and Venezuela (1^ ). Na-
tional- and foreign-flag vessels landed in Bar-
bados, Trinidad, Guyana, Surinam, and French

TABLE 1. — Landings of shrimp in pounds, heads-off weight, re-
ported for U.S. vessels in the Guianas-Brazil shrimp fishery,
1972-74. This table is based on data submitted by processing
plants; monthly data for January- June 1972 were not available.

Month of

landing

1972

1973

1974

January

774,056

757,189

February

967,677

772.844

March

1,145,173

704.377

April

1,589.147

1,072.920

May

1 ,346,502

948.434

June

1.226,817

832,016

July

715.929

1.291,120

864.596

August

940,223

1 .362,976

813,548

September

777.443

1,049,902

548.299

October

888.829

1.147.035

617.972

November

747,252

824.470

523.404

December

889,776

844,284

520,493

Total

4,959.452

13,569,159

8,976,092

705

FISHERY BULLETIN: VOL. 75, NO 4

TABLE 2. — Estimated total catch of shrimp in pounds, heads-off weight, by area of capture for U.S. vessels in the
Guianas-Brazil shrimp fishery, 1972-74. Monthly data for January-June 1972 were not available.

1972

1973

1974

Month of

Zones

capture

69-77

78-81

Total

69-77

78-81

Total

69-77

78-81

Total

January

884,040

—

884,040

924,749

—

924,749

February

943,550

—

943,550

558,397

—

558,397

March

354,064

1,028,331

1,382,395

405,853

635,532

1.041,385

April

319,021

1,214,699

1,533,720

434,842

597,420

1,032,262

May

349,367

838,737

1,188,104

415,514

497,284

912,798

June

480,020

805,609

1 ,285,629

352,805

448,404

801,209

July

253,057

561,134

814,191

541,619

969,059

1,510,678

337,820

566,662

904,482

August

560,547

316,461

877,008

464,255

690,750

1,155.005

240,074

502,583

742,657

September

425,187

410,184

835,371

386,446

737,912

1,124,358

269,655

266.952

536,607

October

550,666

337,679

888,345

531,989

482,733

1,014,722

428,949

114,212

543,161

November

649,768

149,558

799,326

518,332

238,878

757,210

512,751

1 1 ,956

524,707

December

713,867

—

713,867

669,802

—

669.802

318,141

—

318,141

Total

3,153,092

1,775,016

4,928.108

6.442,505

7,006,708

13,449,213

5,199,550

3,641,005

8,840,555

TABLE 3. — Annual landings of shrimp for the Guianas-Brazil shrimp fishery,
1960-74. Figures are in thousands of pounds, heads-off weight. Figures in paren-
theses are estimated values. Data for 1960-69 are from Naiduand Boerema( 1972).

French

Year

Barbados

Trinidad

Venezuela

Guyana

Surinam

Guiana

Brazil

Total

1960

—

3,568

381

—

3,949

1961

—

3,942

447

—

4,389

1962

—

5,126

1,072

—

6,198

1963

319

—

6,040

1,387

2,789

—

10.535

1964

1,481

—

6,984

1,709

2,961

—

13,135

1965

1,891

—

8,048

2,223

3,960

—

16,122

1966

2,400

2,386

—

9,546

2,943

4,668

—

21 ,943

1967

2,179

3,392

—

9,036

2,536

7,279

—

24,422

1968

2,570

4,280

—

9,161

3,438

7,860

—

27,309

1969

2,069

4,469

—

10,469

3,477

6,577

27,135

1970

1,339

4,373

—

11,807

3,534

4,867

1,137

27,057

1971

3,346

—

9,642

3,083

4,559

1,349

21,979

1972

2,082

—

10,743

3,518

4.553

(1 ,500)

22,396

1973

462

1,514

1 2,454

1 2,000

3,949

5,442

(1,500)

27,321

1974

864

1,808

2NA

11,213

4,457

3,260

(1,500)

323,102

'Novoa, D. 1974. Pesqueria Venezolana en el area de las Guayanas durante 1973. Unpubl.
manuscr., 14 p. FAO Governmental Consultation on Shrimp Resources in the CICAR Area. FIR:
SR/74/NR-9.

2Not available.

3Does not include catch of 1 1 Cuban-flag trawlers.

Guiana; but only national-flag vessels operated in
Brazil and Venezuela. The variation in landings
between countries reflects mainly the differences
in the sizes of the fleets supplying the processing
plants in these countries (Table 3).

SPECIES COMPOSITION AND
DISTRIBUTION

Our discussion about the species caught and
their geographic distribution is based on data from
logbooks. Vessel captains recorded a single, most
abundant species to represent their daily catch;
however, if two or more species were present, they
recorded their catch as mixed. Single species were
recorded in 58% of the catch and mixed species in
42%. Since the four species of shrimps are easily

FIGURE 3.— Total landings of shrimp (heads off) for the
Guianas-Brazil fishery, 1960-74 and the number of vessels
operating each year. Data are from Tables 2 and 3.

706

JONKS and DRAGOVICH: UNITED STATES SHRIMP FISHERY

TABLE 4. — Number of shrimp trawlers for the Guianas-Brazil shrimp fishery, 1961-74. The
figures represent the average number of vessels fishing each year. Data for 1961-69 are from
Naidu and Boerema (1972).

French Guiana

(St. Lauren

Year

Barbados

Trinidad

Venezuela

Guyana

Surinam

& Cayenne

Brazil

Total

1961

—

100

1962

—

1963

—

147

1964

—

51 (20 t

—

187

1965

—

58(30 +

28)

—

203

1966

—

105

67 (28 +

39)

—

281

1967

—

113

89 (40 +

49)

—

342

1968

—

134

90(53 •

37)

—

362

1969

—

142

110(65 +

45)

403

1970

—

162

83 (37 +

46)

421

1971

—

160

60(18 +

42)

346

1972

—

175

60(17 +

43)

370

1973

'40

200

68(22 +

46)

443

1974

2NA

202

106

62(16 +

46)

3460

'In 1973, 80 Venezuela-flag trawlers operated for a 6-mo period.

2Not available.

3Does not include 1 1 Cuban-flag trawlers that fished with a mothership from March to December 1974.

distinguishable and there was no obvious bias in
reporting species, we considered the single species
to be representative of the entire daily catch, even
though this overestimates the more abundant
species. The composition of the catch for the entire
area, according to this method, consisted of brown
shrimp (70%), pink-spotted shrimp (23%), and
other shrimps (7%) (Figure 4).

The geographic distribution of the different
species of shrimps in the fishery is a subject of
continuing research, but certain patterns in areal
distribution were apparent (Figure 4). The areas
off Guyana, Surinam, and western French Guiana
(zones 69-75) were dominated by pink-spotted
shrimp. Brown shrimp were listed more fre-
quently off eastern French Guiana and Brazil
(zones 76-81); white shrimp off Guyana (zones
69-71) and French Guiana and Brazil (zones 77-
80); and pink shrimp off Guyana (zones 70-71).

We also examined the geographic distribution of
the U.S. -vessel catch of all species. In 1972, U.S.
vessels caught 36% of their catch in the Agree-
ment Area off Brazil and 64% off the Guianas. The
analogous catches for U.S. vessels in the Agree-
ment Area were 52% (1973) and 41% (1974) (Table
2). Fishing off the Guianas (zones 69-77) was
year-round. In the Agreement Area fishing by
U.S. vessels was allowed 1 March-30 November
(zones 78-80) and 1 March-30 June (zone 81).

Species composition of shrimp catches as re-
ported by Japanese vessels3 is in general agree-
ment with our observations. Japanese catches off

3Far Seas Fisheries Research Laboratory. 1971, 1972, 1973,
1974. South America north coast shrimp trawl fishing ground
charts, 1969, 1970, 1971, 1972, 1973. Unpubl. manuscr., Far
Seas Fish. Res. Lab., Shimizu.

AIL
ZONES

BROWN

PINK-SPOTTED

_i—

40 60

PERCENT

FIGURE 4. — Species composition by fishing zone of the shrimp
catches of U.S. vessels in the Guianas-Brazil fishery for the
period July 1972- December 1974. The data for this figure were
calculated as explained in the text from the fishermen's log-
books.

Guyana and Surinam had higher percentages of
"pink shrimp" (presumably mostly P. brasiliensis)
than off French Guiana and Brazil. There were
differences, however, between our data and the
Japanese reports. Overall, brown shrimp were less
prevalent in the Japanese catches than in the U.S.
catches. The Japanese catch from 1969 to 1973

707

FISHERY BULLETIN: VOL. 75, NO. 4

was reported as 20%-35% brown shrimp (presum-
ably P. subtilis) and 65%-80% pink shrimp (pre-
sumably mostly P. brasiliensis) (Far Seas
Fisheries Research Laboratory see footnote 3).

SIZE COMPOSITION

The data on temporal and spatial distribution of
sizes of shrimp provide information necessary for
management of fishery stocks (Rounsefell and
Everhart 1953). In particular, data on size reveal
information on progressive changes as an indi-
cator of rates of growth, population structure,
maturity stages, and potential use of habitat by
shrimp of different sizes, the latter being related to
spawning, recruitment, and migration.

In our study the more precise data came from
landing records, which we used to measure tem-
poral changes in size composition. Size data from
logbooks (less precise) were used to measure areal
differences in size composition.

The majority of shrimp in U.S. landings for the
entire period of 1972-74 were in the 26-30, 21-25,
16-20, and 11-15 tails-per-pound size categories
(Figure 5). The sizes of shrimp caught may repre-
sent a true picture of size availability, but in many
instances are also governed by factors which cause
fishermen to select certain sizes (e.g., market price
of shrimp, fuel price, feasibility of operation, and
physical condition of the boat).

In studying the temporal and, to a lesser extent,
the areal distribution of shrimp, we plotted from

n—

FISHING LOG REPORTS

, LANDING RfPORTS

ti-4-

36/40 31/35 35/30

SIZE CATEGORY

31/ 35 10/10 11/10

FIGURE 5. — Size composition of the shrimp catches of U.S. ves-
sels as reported in landing records and fishing log reports for the
period July 1972 to December 1974. The size categories given are
the number of heads-off shrimp per pound.

landing data the average size of shrimp for all
ports combined and for Cayenne, French Guiana,
only (Figure 6). The landings for all ports include
catches from the entire fishery, while Cayenne
landings reflect catches primarily off French
Guiana and northern Brazil. The shrimp landed at
Cayenne generally averaged slightly smaller than
the shrimp from all ports combined. The smallest
average size of shrimp, for both total landings and
Cayenne landings, were in April and October in
1972 and 1973. In 1974, when fishing success was
markedly lower than in 1973, small shrimp were
present in October, but the expected April peak of
small shrimp was less evident. Shrimp were larger
in December-January and in June-August of
each year.

Trends in average size of shrimp calculated from
the logbook data were similar to those of average
size calculated from the landing data (Figure 7).
This similarity suggested that the size data from
logbooks, although less precise, could also be used
to compare areas; the smallest shrimp occurred in
zones 69-70 and 77-81, and the largest in zones
71-76 (Figure 7). The magnitude of fluctuations in
average size calculated from the log data were less
than one size category unit, because the original
data reported by fishermen are averages.

At present we have no satisfactory explanation
for the greater prevalence of smaller shrimp off
French Guiana and Brazil than in other areas of
this fishery. We can offer some plausible hypoth-
eses. Cayenne landings consist primarily of small
brown shrimp caught off French Guiana and
northern Brazil. These shrimp are probably re-
cently recruited to the fishable population. Small

°0"^ JASON 0|J FMAMJ JASON OjJ FMAMJ J A S O N D|

1972 1973 1974

MONTH OF LANDING

FIGURE 6. — Distribution by month of the mean size index of
shrimp calculated from landing records of U.S. vessels at all
ports of the Guianas shrimp fishery (marked as total on the
graph) and at the Port of Cayenne, French Guiana. The size
index was calculated as described in the text.

708

JONES and DRAGOVICH: UNITED STATES SHRIMP FISHERY

6.0

Of 5.8'

™ 5.6-

5 5.4'

5.2

z
<

00-1-

A S O
1972

N D J J

M A M J J
1973

F M A M J j
1974

MONTH OF LANDING

6.0
5.8

o 56H

£ 5.4

0 5.2
Hi

7, 5.0-

Z
<

69 70

—f—
71

—1 1 1 1 1 1—

72 73 74 75 76 77
FISHING ZONE

—1 —
79

80 81

shrimp also are present off Guyana. The smaller
size of shrimp and higher catch rates in both areas,
as compared with the larger shrimp and lower
catch rates off Surinam, suggest that the East and
West Grounds represent the principal areas of re-
cruitment (Figure 1). Furthermore, the peaks of
small shrimp in March, April, and October may
indicate seasonal recruitment. Seasonal peaks in
spawning and recruitment are common in penaeid
shrimp populations, even where these activities
occur throughout the year (Cook and Lindner
1970; Costello and Allen 1970). To determine the
exact areas and chronology of recruitment for each
species off the Guianas and northern Brazil will
require additional research.

VARIATION IN CATCH RATES

Fishing success, or catch rate, provides a mea-
sure of the relative densities and availability of
shrimp to the fishing gear and to the skilled
fishermen. We examined the variations in catch
rate by year, month, area, depth, and time of day to
learn about the biology and ecology of the shrimp.

The average annual catch rates for U.S. vessels
were 20.0 lb/fishing hour (1972 half year), 26.0 lb
( 1973), and 18.3 lb ( 1974). To observe the monthly
differences in average catch rates off the Guianas

FIGURE 7. — Distribution by month and fishing zone of the
mean size index of shrimp calculated from fishing log reports of
U.S. vessels. The size index was calculated as described in the
text.

and off Brazil we plotted catch rates for each sta-
tistical zone (Figures 8 and 9). Fluctuations in
monthly catch rates followed a fairly regular pat-
tern, peaking each year in March and April and
then gradually declining during the remainder of
the year. There were smaller peaks in July and
August (Figure 8). Catch rates were consistently
higher off Brazil (zones 78-81) than off the
Guianas (zones 69-77). The highest catch rates
were recorded in zones 78-81, intermediate in
zones 75-77 and 69-71, and lowest in zones 72-74
(Figure 9).

Information on water depth without specific
knowledge of the type of sediment, chemical con-
tent of water masses, and information on water
temperature and speed and direction of the cur-
rent means little in ecological terms. But, in a
pragmatic sense, the statistics on shrimp catches
versus depth are important. In our study the dis-
tribution of shrimp catches varied with water

I «*-rr amnuai •■.!■*■- 1

tNNUll »¥l»

FIGURE 8. — Distribution by month of the mean catch rate of
shrimp for U.S. vessels fishing off the Guianas (zones 69-77) and
off Brazil f zones 78-81 ), July 1972 to December 1974. Catch rate
is expressed as pounds and kilograms of shrimp (heads-off
weight) per hour of fishing.

709

FISHERY BULLETIN: VOL. 75. NO. 4

WEIGHT (HEADS OFFI PER H<

Pounds

JUR

Kilo

<6.

■6.

grams

•

151-20-

3-91
— 1 1.3

4-136

0 25.1

•

>159

aw.

1972

1973

1974

jmurfilSE

■T| 01 i | tfrt |i

M»K 1 *PH

«ji

■

si i;

1 1 !

i I

...

IAK

M u

■ |-'

■- !

ft |l|

• •

•

• •

•

■

•

• •

•
•

•

• O

. .

= .

77
73

- •

•

• ■

•

• •

•

. .

•

• •

•

• •

•

• ■ • o

. o

■

•

• •

•

•r

•

- •

• •

• -

- •

•

FIGURE 9.— Distribution by month and
fishing zone of the mean catch rate of
shrimp for U.S. vessels fishing in the
Guianas-Brazil fishery, July 1972 to
December 1974. See Figure 1 for loca-
tion of fishing zones. Catch rate is ex-
pressed as pounds (and kilograms) of
shrimp (heads-off weight) per hour of
fishing.

depth. The average catch rates were: 35.4 lb/h
(0-5 fm), 25.0 lb/h (6-10 fm), 21.5 lb/h (11-15 fm),
20.5 lb/h (16-20 fm), 21.1 lb/h (21-25 fm), 20.7
lb/h (26-30 fm), 21.1 lb/h (31-35 fm), 23.2 lb/h
(36-40 fm), 22.7 lb/h (41-45 fm), and 24.5 lb/h
(46-60 fm). Off Guyana, Surinam, and French
Guiana (zones 69-77), average catches were lower
at the intermediate depths (16-35 fm) than in
shallower or deeper water (Figure 10). Off Brazil
the average catch did not vary with depth in zones
78 and 79, but in zones 80 and 81 average catches
were higher at the intermediate depths than in
shallower or deeper water.

We also examined the distribution of fishing
effort in relation to depth. Fishing effort was con-
centrated primarily in intermediate depths. Sixty
percent of the fishing effort reported in logbooks
occurred between 21 and 35 fm, 189c in <20 fm,
and 22% in >36 fm. Off Guyana, Surinam, and
French Guiana most fishing was between 16 and
30 fm; off Brazil, it was in deeper water (Figure
11). While the highest catch rates were usually in
the shallow and deep zones at the edge of the
fishing grounds, these areas supported only a
small percentage of the total fishing effort. Shal-
low and deep zones probably were fished only
when good catches could be made, whereas the
intermediate depths were fished during times of
both good and poor fishing.

The availability of shrimp to the fishermen in
relation to time of day varies for each area, species,
and time of the year. Most fishing for shrimp was
done at night, some during the day, and some on a

24-h/day basis (Figures 12 and 13). The time spent
fishing at night was three times that spent during
the day. White shrimp were caught primarily dur-
ing daylight hours off the Guianas and fishing in
the East Gullies (zone 79) was usually done during
the day. In the Drop-Off and Steeples (zones 80-
81), fishing on a 24-h/day basis made up nearly
half the total fishing time. The average catch rates
for the entire fishery were 29.6 lb/h (day fishing),
18.9 lb/h (night fishing), and 22.1 lb/h (day and
night fishing). The mean catch rates were higher
for day fishing than night in all zones and at all
depth intervals. We conclude that the usual
strategy is to fish at night, except for certain
species (e.g., white shrimp) or in certain areas
(e.g., East Gullies) where day fishing is more suc-
cessful. During periods of high catches, fishing is
usually carried out on a 24-h/day basis until a full
catch is made or until the fishermen are
exhausted.

APPRAISAL OF THE FISHERY

The fishery for shrimp in the Guianas-Brazil
area reached a historical maximum annual pro-
duction of 27.3 million pounds heads-off in 1973.
We used a surplus yield model to estimate the
maximum sustainable yield of the resource (Fox
1970). We also compared predicted annual equi-
librium yields with actual annual yields attained
to measure the expected variation from equilib-
rium conditions.

An exponential surplus yield model suggested

710

JONES and DRAGOVICH: UNITED STATES SHRIMP FISHERY

46 60

41 4S

36 40

26 30

16 20

— _

•

' ~- _

— — _

"**»

•

~- -^ _

•

~~~

—

•

-»,

•

■—

- _

•

"""

— -

•

•
•

•

•
•

•

•
•

•

•
•

•

~~ ■

•

—

"*•

•

"^ ^

•

....

75s

•

***

m&nP

**,

SORt

NAM

RENCt

•

\ O

GUIANA

EFFORT: HOURS X 100

>200 ^A 150-2O0

79\

O x O x • • •

\ " \

HAZH

\ o \ o \ •

\ o \ o \ • • • • ''., • \ • •

DEPTH IN FATHOMS

FIGURE 10. — Distribution by fishing zone and water depth of the fishing effort reported on logbooks by U.S. vessels in the Guianas-

Brazil fishery, July 1972 to December 1974.

that the maximum sustainable yield was 28.7
million pounds, which could be taken by 692 ves-
sels. This estimate was made from the relation-
ship between the logarithm of the annual catch
per vessel and average number of vessels (r =
0.80) for the years 1965-74. A linear surplus yield
model applied to the data for the same years
suggested that the maximum yield was 27.1 mil-
lion pounds, which could be taken by 531 vessels
(r = 0.82) (Figure 14).

The average number of vessels is the only index
of total effort available for the fishery before 1972.
The double-rigged Florida-type shrimp trawler
has been, almost without exception, the only type
vessel used in the fishery. Increases in fishing ef-

ficiency probably occurred as the length and
horsepower of the vessels increased (Jones and
Dragovich 1973), and as the addition of refrigera-
tion equipment permitted longer and farther
ranging fishing trips; but these changes were
minor in the 1965-74 period.

Before 1965 the increase in average annual
catch per vessel paralleled the increase in fleet size
(Table 5). The catch per vessel rose sharply be-
tween 1961 and 1962; from 1962 to 1965 the in-
crease continued but was less pronounced. Pre-
sumably, during these early years of the fishery,
the efficiency of the fleet increased as familiarity
was gained with the fishing grounds. The earlier
data, therefore, were not used in the model. After

711

FISHERY BULLETIN: VOL. 75, NO. 4

46 60

36 40

31-35

26 30

DEPTH IN FATHOMS

FIGURE 11. — Distribution by fishing zone and depth of the mean catch rate of shrimp for U.S. vessels fishing in the Guianas-Brazil
fishery, July 1972 to December 1974. Catch rate is expressed as pounds (and kilograms) of shrimp (heads-off weight) per hour of fishing.

1964, the decline in the average production per
vessel was consistent with the increase in the
number of vessels. The average annual production
per vessel declined from 79,000 lb of shrimp in
1965 to 50,000 lb in 1974; during this time the fleet
size increased from 203 vessels (1965) to 460 ves-
sels (1974).

The decline in annual catch per vessel suggests
that the average abundance of shrimp available to
the fishery has decreased as a result of fishing.
Total yields, however, are not depressed at present
levels of fishing effort. Apparently the productiv-
ity of the resource allows the present level of com-
mercial harvest and also sufficient recruitment to
the next generation.

Surplus yield models have been applied in
shrimp fishery analysis, though certain assump-
tions in their use are not completely valid, e.g.,
instantaneous recruitment, equilibrium condi-
tions, and behavior of the species and populations
as a single unit. Also, there is no evidence that the
abundance of shrimp recruits is dependent on the
abundance of the parent stock in this fishery.
Therefore, the prediction of maximum equilib-
rium yield by a surplus yield model, should be
interpreted with caution, especially when the
maximum is predicted to occur at fishing effort
levels beyond those observed.

The historical shrimp catches follow closely the
trends predicted by the surplus yield model (Fig-

712

JONES and DRAGOVICH: UNITED STATES SHRIMP FISHERY

CATCH l«bl BY TIME Of FISHING

EFFORT I"- 1 BY TIME OF FISHING

40 «0

PERCENT

EFFORT CM BY TIME OF FISHING

6-10

I I L_

40 60

PERCENT

DAY ONIY

NIGHT ONLY

DAY & NIGHT

FIGURE 13. — Distribution of fishing effort (expressed as
percentage of total) by time of day and water depth for U.S.
vessels in the Guianas-Brazil fishery, July 1972 to December
1974.

ure 14). From 1961 to 1968 the total production
from the fishery rose in proportion to the increase
in the number of fishing vessels. In 1969 and 1970
fishing effort increased, but production remained
constant at 27 million pounds. Fishing was re-
duced in 1971 and the catch, therefore, declined.
After 1971, catch and effort continued upwards at
rates similar to those in the early year's of the
fishery and a catch of 27 million pounds was again
attained in 1973. In 1974 the number of vessels

DAY ONLY
NIGHT ONLY
DAY & NIGHT

FIGURE 12.— Distribution of catch and
fishing effort (expressed as percentage
of total) by time of day and fishing zone
for U.S. vessels in the Guianas-Brazil
fishery, July 1972 to December 1974.

NUMBER OF VESSELS

FIGURE 14. — Relationship of the average annual landings per
vessel (A) and the total production of shrimp (B) to the total
estimated fishing effort (average number of vessels operating)
for the Guianas-Brazil shrimp fishery. The linear trend line
shown was fitted to the data for the years 1965-74; the estimated
production curve was derived from the line in A. The exponential
trend line was calculated as explained in the text but is not
shown in this figure.

remained high, but the catch declined to 23 mil-
lion pounds.

The variation of the annual catches from those
predicted by the model were 53% and 319c in 1961

713

FISHERY BULLETIN; VOL. 75, NO. 4

TABLE 5. — Average annual catch of shrimp (in pounds, heads-off weight) per vessel
by country. Data are derived from Tables 3 and 4.

French

Year

Barbados

Trinidad

Venezuela

Guyana

Surinam

Guiana

Brazil

Total

1961

—

65,700

11,175

—

43,890

1962

—

71,194

44,667

—

64,562

1963

—

67,865

55,480

84,515

—

71,667

1964

49,367

—

86,222

68,360

58,059

—

70,241

1965

78,792

—

83,833

88,920

68,276

—

79,419

1966

75,000

55.488

—

90,914

86,559

69,672

—

78,089

1967

68,094

58,483

—

79,965

50,720

81,787

—

71 ,409

1968

73,429

89,167

—

68,366

62,509

87,333

—

75,439

1969

57,472

70,937

—

73,725

68,176

59,791

74,000

67,333

1970

53,560

56,064

—

72,883

64,255

58,639

63,167

64,268

1971

—

55,767

—

60,263

68,511

75,983

64,238

63,523

1972

—

37,855

—

61 ,389

63,964

75,883

60,000

60,530

1973

77,000

36,048

61,350

60,000

62,683

80,029

62,500

61,673

1974

41,143

46,359

—

55,510

42.047

52,581

50,000

50,222

and 1962, respectively, but for 1963-74 they
ranged from 3% to 18%, averaging 8.5%. These
variations in catches are deviations about the
mean condition predicted by the model. The devia-
tions include the effects of dynamic environmental
conditions, but also include random variations
and the failure of the model to predict the effects of
fishing.

The Penaeus shrimp fishery operates mostly on
a single year class and year-to-year fluctuations in
shrimp populations are to be expected because of
the short life cycle of the species. Fluctuations in
the annual yield of shrimp are partly the result of
variations in spawning success and in survival of
young in the inshore nursery grounds, which are
generally subject to more extreme variations in
environmental conditions than the offshore
habitat of adult shrimp. An important manage-
ment problem for this shrimp fishery is to predict
and utilize annual fluctuations in the populations,
rather than to only predict an equilibrium yield at
a constant level of fishing effort. This will require
more detailed knowledge of growth, mortality,
and recruitment patterns of the shrimp and the
application of yield-per-recruit and stock-re-
cruitment models.

LITERATURE CITED

ALLEN, H. B.

1973. U.S. -Brazil shrimp conservation agreement — A
status report. Proc. Gulf Caribb. Fish. Inst. 25:23-25.

BULLIS, H. R., JR., AND J. R. THOMPSON.

1959. Shrimp exploration by the M/V Oregon along the
northeast coast of South America. Commer. Fish. Rev.
21(11):1-19.

Cook, H. L., and M. J. Lindner.

1970. Synopsis of biological data on the brown shrimp
Penaeus aztecus aztecus Ives, 1891. FAO Fish. Rep.
57:1471-1497.
COSTELLO, T. J., AND D. M. ALLEN.

1970. Synopsis of biological data on the pink shrimp
Penaeus duorarum duorarum Burkenroad, 1939. FAO
Fish. Rep. 57:1499-1537.
FOX, W. W., JR.

1970. An exponential surplus-yield model for optimizing
exploited fish populations. Trans. Am. Fish. Soc. 99:
80-88.
HIGMAN, J. B.

1959. Surinam fishery explorations, May 11-July 31,
1957. Commer. Fish. Rev. 21(9):8-15.
JONES, A. C, AND A. DRAGOVICH.

1973. Investigations and management of the Guianas
shrimp fishery under the U.S.-Brazil Agreement. Proc.
Gulf Caribb. Fish. Inst. 25:26-33.
NAIDU, K. S., AND L. K. BOEREMA.

1972. The high-sea shrimp resources off the Guyanas and
northern Brazil. FAO Fish. Circ. 141, 18 p.

Perez Farfante, I.

In press. FAO species identification sheets for fishery pur-
poses (shrimps). Central western Atlantic (Fishing Area
31). Food and Agriculture Organization of the United
Nations, Rome.
ROUNSEFELL, G. A., AND W. H. EVERHART.

1953. Fishery science: its methods and applications.
John Wiley and Sons, Inc., N.Y., 444 p.
WHITELEATHER, R. T., AND H. H. BROWN.

1945. An experimental fishery survey in Trinidad, Tobago
and British Guiana. Anglo-American Caribb. Comrn.,
U.S. Gov. Print. Off., 130 p.

714

JONES and DRAGOVICH: UNITED STATES SHRIMP FISHERY

APPENDIX TABLE l.— Catches by area and month for the Guianas-Brazil shrimp fishery reported by U.S. vessels.
Catches are reported by month in which capture was made; landings are reported by month in which trip was
completed.

1972

Item

July

Aug.

Sept.

Nov.

Dec.

Catches:

Zones 69-77:

No drags

501

2,433

2.301

2,740

3,269

3,473

No hours

2,950

12,705

12,815

14.809

18,580

19,666

Catch (pounds')

56,530

250,097

230,857

300,346

357,385

361,234

Catch/drag

112.8

102.8

100.3

109 6

109.3

104.0

Catch/hour

19.2

19.7

18.0

203

19.2

18.4

Zones 78-81 :

No. drags

909

1,184

1,643

1.537

737

No. hours

5,234

6.785

9,485

8,477

4,120

Catch (pounds')

125,351

141,194

222,71 1

184,178

82,260

Catch/drag

137.9

119.3

135.6

119.8

111.6

Catch/hour

23.9

20.8

23.5

21.7

20.0

Total:

No. drags

1,414

3,617

3,946

4,285

4,006

No. hours

8,205

19,490

22,310

23,334

22,700

Catch (pounds')

182,311

391,291

454,518

485,894

439,645

Catch/drag

128.9

108.2

115.2

113.4

109.7

Catch/hour

22.2

20.1

20.4

20.8

19.4

Landings (pounds')

715.929

940,223

777,443

888,829

747,252

889,776

Percent of landings

reported on fishing logs

6.1

34.8

56.5

52.6

57.2

53.1

1973

Item

Jan.

Feb.

Mar.

Apr.

May

June

Catches:

Zones 69-77:

No. drags

3,636

3,119

1.308

1,289

1,580

2.216

No. hours

20,522

16,996

6,804

7,154

8,692

12,677

Catch (pounds')

437,420

390,142

172.585

181,845

205,385

309,276

Catch/drag

120.3

125.1

131.9

141.1

130.0

139.6

Catch/hour

21.3

23.0

25.4

23.6

24.4

Zones 78-81 :

No. drags

2,366

3,511

3,024

3.208

No. hours

12,005

18,694

16,888

17,435

Catch (pounds')

501 .250

692,390

493,075

519.053

Catch/drag

211.8

197.2

163.0

161.8

Catch/hour

41.8

37.0

29.2

29.8

Total:

No drags

3,682

4,883

4,629

5,461

No. hours

18,857

26.022

25,726

30,334

Catch (pounds')

674,735

882,175

700,950

832,369

Catch/drag

183.2

180.7

151.4

152.4

Catch/hour

35.8

33.9

27.2

27.4

Landings (pounds')

774,056

967,677

1,145,173

1,589,147

1,346,502

1,226,817

Percent of landings

reported on fishing logs

47.9

53.2

35.2

58.6

56.2

62.1

1973

Item

July

Aug.

Sept.

Oct.

Nov.

Dec.

Catches:

Zones 69-77:

No. drags

2,450

2,007

1.675

2,144

2,422

3,249

No. hours

13,772

1 1 ,932

9,663

12.023

14,254

18.683

Catch (pounds')

329,048

251,585

192,636

249,005

237,945

332,835

Catch/drag

134 3

121.1

115.0

116.1

982

102.4

Catch/hour

23.9

21.1

19.9

20.7

16.7

17.8

Zones 78-81 :

No. drags

2,922

2,118

2,362

2.746

948

No. hours

16,920

11,814

13,323

9,612

5.683

Catch (pounds')

588.729

374,325

367,835

225,950

109,200

Catch/drag

201.5

176.7

155.7

129.4

1152

Catch/hour

34.8

31.7

27.6

23.5

19.2

Total:

No. drags

5,409

4,195

4,037

3.903

3.370

No. hours

30,914

23,746

22,986

21,723

19.937

Catch (pounds')

922,557

625,910

560,471

476.785

347.145

Catch/drag

170.6

149.2

1388

122.2

103.0

Catch/hour

29.8

26.4

24.4

21.9

17.4

Landings (pounds')

1,291,120

1,362,976

1,049,902

1.147.035

824,470

844.284

Percent of landings

reported on fishing logs

67.3

55.2

52.9

47.0

46.9

44.9

'Heads-off weight.

715

FISHERY BULLETIN: VOL. 75, NO. 4

APPENDIX TABLE 1.— Continued.

1974

Item

Jan.

Feb.

Mar.

Apr.

May

June

Catches:

Zones 69-77:

No drags

4,028

3,425

2,348

2,473

3.103

2,563

No. hours

22,242

19,319

12,167

12,471

15,962

14816

Catch (pounds1)

509,163

360,836

266,896

259,317

297,838

246,021

Catch/drag

126.4

105 3

113.7

104.9

96.0

Catch/hour

229

18.7

21.9

20.8

18.6

16.6

Zones 78-81 :

No. drags

3,145

2,845

3,039

?,531

No. hours

17,152

16.011

17.388

13,878

Catch (pounds1)

417,937

356,270

356,450

312,685

Catch/drag

132.9

125.2

117.3

123.5

Catch/ hour

24.4

22.2

20.5

22.5

Total:

No. drags

5,551

5,354

6,190

5,163

No. hours

29,649

28.712

33,696

29,203

Catch (pounds1)

691 ,463

624,907

664,083

571,941

Catch/drag

124.6

116.7

107.3

110.8

Catch/hour

23.3

21.8

19.7

19.6

Landings (pounds')

757,189

772,844

704,377

1,072.920

94,834

832,016

Percent of landings

reported on fishing logs

55.1

59.2

79.3

58.0

63.5

83.3

1974

Item

July

Aug.

Sept.

Oct.

Nov.

Dec.

Catches:

Zones 69-77:

No. drags

2,183

1,977

2,131

2,813

3.478

3,038

No. hours

13,059

1 1 ,599

12,156

16,936

20,658

18,482

Catch (pounds')

213,244

159,665

167,545

229,588

282,405

237,991

Catch/drag

97.7

80.8

78.6

81.6

81.2

78.3

Catch/hour

16.3

13.8

13.6

13.7

12.9

Zones 78-81 :

No. drags

2,975

3,063

1,959

873

No. hours

17,640

18,486

1 1 ,724

5,427

577

Catch (pounds')

375,697

334,250

165,865

61,130

6,585

Catch/drag

120.2

109.1

84.7

70.0

72.4

Catch/hour

20.3

18.1

14.1

11.3

11.4

Total:

No. drags

5,158

5,040

4,090

3.686

3,569

No hours

30,699

30,085

23,880

22,363

21,235

Catch (pounds')

571,961

494,915

333,410

290,718

288,990

Catch/drag

110.9

98.2

81.5

78.9

81.0

Catch/hour

18.6

16.4

14.0

13.0

13.6

Landings (pounds1)

864,569

813,548

548,299

617,972

523,404

520,493

Percent of landings

reported on fishing logs

59.9

66.8

66.4

58.4

47.8

62.4

'Heads-off weight.

716

SEASONAL CYCLE OF ZOOPLANKTON ABUNDANCE AND
SPECIES COMPOSITION ALONG THE CENTRAL OREGON COAST

William T. Peterson and Charles B. Miller1

ABSTRACT

Species composition of zooplankton collected during 3 yr of sampling close to the coast at Newport,
Oreg., varied with season. In all seasons the most abundant plankters were copepods. Dominant species
in summer were Pseudocalanus sp., Acartia clausii, A . longiremis, Calanus marshallae, and Oithona
similis. These are primarily coastal forms with northern affinities, and they were present all year.
Dominant species in winter were Paracalanus parvus and Ctenocalanus vanus, forms of southern
affinities. They tended to disappear completely in summer. These geographic affinities are in corre-
spondence with the source regions for surface waters that are implied by the direction of flow in the
different seasons. Abundances are about one order of magnitude higher in summer than in winter.
Copepod diversity is greater in winter than summer: the winter checklist contains 5 1 species, while the
summer list contains only 38 species.

An analysis of differences in the zooplankton of the three winter periods of the study shows 1969-70
to have had much greater dominance by southern forms and a larger variety of them than 1970-71 or
1971-72. This corresponds with differences in the wind patterns between the years. Winds in the
winter of 1969-70 were gentle and directly from the south, while the other winters had the more usual
southwesterly storms. Gentle winds directly from the south were more effective at moving sur-
face water northward alongshore than southwesterly storms, despite their lesser overall northerly
component.

The hydrography and pelagic ecology of the Pacific
Ocean very close to the Oregon coast are strongly
seasonal. Winter winds from the southwest, which
produce surface flow from the south and toward
shore, alternate with summer winds from the
north, which produce flow from the north and
away from shore, generating coastal upwelling.
These seasonal changes in the source of currents
flowing through the area cause changes in the
species of zooplankton that are present. In this
paper we describe this cycle of change in species
composition from a series of samples collected
along a transect normal to the coast at Newport,
Oreg., approximately every 2 wk from June 1969
through July 1972. In a previous paper (Peterson
and Miller 1975) we have used these data to make
a detailed comparison of the upwelling seasons of
the years 1969, 1970, and 1971 with emphasis
upon the differences between years. Here we con-
sider the entire annual cycle with emphasis upon
consistent aspects of the differences between sea-
sons. The discussion includes a consideration of
the differences between the three winters of the
study.

'School of Oceanography, Oregon State University, Corvallis,
OR 97331.

MATERIALS AND METHODS

Detailed description of collection and laboratory
procedures are given in Peterson and Miller ( 1975,
1976). Plankton samples were collected with a
240-/xm mesh net hauled obliquely from near the
bottom to the surface at stations 2, 5, 9, and 18 km
from the Oregon coast along a transect at lat.
44°40'N. The stations will be referred to as NH 1,
NH 3, NH 5, and NH 10, respectively, which stand
for Newport Hydrographic stations at 1, 3, 5, and
10 n.mi. from the shore. Water depths for the four
stations were 20, 46, 55, and 80 m. Surface tem-
perature and salinity measurements were made at
most stations, and a bathythermograph was usu-
ally lowered. A total of 213 samples from 56 dates
are included in the present analyses. Distribution
of samples among stations, exact dates, and com-
plete data for all samples can be found in Peterson
and Miller (1976).

There are important limitations on the zoo-
plankton data. We chose to express numerical
abundance as numbers of individuals per cubic
meter (no. m~3). Because our nets were towed
obliquely through the entire water column, the
quantitative abundance estimates are actually
abundances averaged over the water column. If an

Manuscript accepted April 1977.

FISHERY BULLETIN: VOL. 75, NO. 4. 1977.

717-

FISHERY BULLETIN: VOL. 75, NO. 4

animal is equally abundant at all depths, then
oblique tows will adequately estimate its abun-
dance. If an animal is restricted to a narrow sur-
face layer, then its abundance will be underesti-
mated by deeper tows relative to shallower ones.
Recent work by ourselves and Myers (1975) has
shown that highest zooplankton abundances are
found within the top 20 to 30 m of the water
column. Therefore, our oblique tows from depths
greater than about 30 m do underestimate zoo-
plankton abundances. This becomes a problem for
tows taken at stations farther from shore as the
water depth increases, because an increasing frac-
tion of the water column sampled contains few
animals. Therefore, abundance gradients should
not be considered to be real between stations NH 1
(water depth = 20 m) and NH 10 (water depth =
80 m) unless abundance differences are greater
than a factor of four.

Abundances are also underestimated for many
copepod taxa because the small copepodite stages
could easily pass through our 240-/u.m mesh net.
Copepodites of species of Pseudocalanus and Acar-
tia younger than stage III were seldom seen in our
samples. Probably only stages IV and V were sam-
pled quantitatively.

The data set gains its value from being a 3-yr
time series of samples collected in exactly the
same manner at the same stations. As such, these
are good baseline data to which future work can be
compared. Point estimates of abundance have lit-
tle meaning, but comparisons of abundances be-
tween seasons and years at a set of stations are
valid and meaningful.

RESULTS

Frequency of Occurrence of
Zooplankton Taxa

Copepods were the most frequently occurring
and the most abundant members of the zoo-
plankton community in the nearshore region off
Newport, Oreg. Fifty-eight species were seen in
our samples (Table 1). Thirty-eight species were
found in the summer samples and 5 1 species in the
winter samples. During our study, species from
the Subarctic, Transition, and Central Pacific
faunal groups (McGowan 1971) were taken.

The copepods in Table 1 can be grouped on the
basis of patterns of occurrence. Eight species occur
commonly during both winter and summer
months: Calanus marshallae , Paracalanus par-

TABLE 1. — A checklist of copepod species taken off Newport,
Oreg., in summer ( S) and winter ( W) months during the period of
the study.

[C = Common, occurrence in >50% of the samples taken, U =
Unusual, occurrence in <50% but >5 samples taken, R = Rare
occurrence <5 samples.]

Copepod species

Calanus marshallae

Metridia lucens2

C. tenulcomis

M. pacifica2

C. plumchrus

Lucicuiia flavicornis

C. cristatus

Candacia columbiae

Rhincalanus nasutus

C bipinnata

Eucalanus bungii

Immature Heterorhabdus

Mecynocera clausii

spp.

Paracalanus parvus

Pleuromamma borealis

Calocalanus styliremis

P. abdominalis

C. tenuis

Centropages abdominalis

C. sp

Epilabidocera amphitrites

Pseudocalanus sp.1

Acartia clausii

Microcalanus pusillus

A. longiremis

Clausocalanus masti-

A. tonsa

gophorus

A. danae

C furcatus

Eurytemora americana

C. arcuicornis

Tortanus discaudatus

C. jobei

Microsetella sp

C. pergens

Sapphirina sp.

C parapergens

Oithona similis

C. paululus

O. spinirostris

Ctenocalanus vanus

Oncaea tenella

Aetideus pacificus

O borealis

Immature Gaidius spp.

O conifera

Gaidius brevispinus

O mediterranea

Immature Gaetanus spp.

O. dentipes

Gaetanus simplex

O. subtilis

Paraeuchaeta japonica

O. media hymena

Racovitzanus antarcticas

Corycaeus anglicus

Scolecithricella minor

C. amazonicus

1 Pacific representatives of the genus Pseudocalanus are not adequately
described They are being studied by B. Frost.

2Two morphs of the genus Metridia were separated on the basis of the shape
of the prosome in lateral view. The M. pacifica type is more robust and has a
steeply sloping forehead. Detailed morphological analysis of the two types has
not been done.

vus, Psuedocalanus sp., Metridia lucens, Acartia
clausii, A. longiremis, Oithona similis, and O.
spinirostris. Seven species were found only during
the summer months and probably have northern
affinities: Aetideus pacificus, Gaidius imma-
tures, Gaetanus immatures, Racovitzanus ant-
arcticas s.l., Metridia pacifica, and Oncaea media
hymena. Eurytemora americana occurred very
rarely in the sample series, but it is a common
form in all of the local estuaries (Frolander et al.
1973). Only one species was common during the
summer and uncommon during the winter: Cen-
tropages abdominalis. This species has northern
affinities. A group of six species had the opposite
characteristic; that is, they were common during
the winter but uncommon or rare during the
summer: Calanus tenuicornis, Clausocalanus ar-
cuicornis, C. pergens, Ctenocalanus vanus s.l.,
Acartia tonsa, and Corycaeus anglicus. All of these
species are common in warmer water south of
Oregon.

The majority of the copepod species (43) were

718

PETERSON and MILLER: SEASONAL CYCLE OF ZOOPLANKTON ABUNDANCE

always uncommon or rare in our samples and
probably have unimportant roles in the commun-
ity. However, taxonomic study of these rare or
uncommon species is important because in many
cases their presence indicates the presence of a
particular water type or mixture of types. Most of
the species that are found off Newport only during
winter months have southern affinities (Central
Pacific waters). They are transported north along
the continental shelf by the Davidson Current and
are probably very near the extreme northerly
limit of their range. These species were Mecyno-
cera clausii, Calocalanus styliremis, C. tenuis,
Calocalanus sp., Clausocalanus mastigophorus , C.
furcatus, C. jobei, C. parapergens, C. paululus,
Acartia danae, Corycaeus amazonicus, Oncaea
dentipes, and O. subtilis. Other species that were
found only during winter months have northern
affinities and are usually found in deep water over
the continental slope. They were probably trans-
ported shoreward as a result of onshore winds.
These species were Calanus cristatus, Gaidius
brevispinus, Gaetanus simplex, Candacia colum-
biae, Heterorhabdus immatures, Pleuromamma
borealis, and P. abdominalis . The 16 species that
were rare or uncommon in both summer and
winter include representatives of both northern
and Central Pacific faunal groups.

Seasonal Cycle of
Total Zooplankton Abundance

The annual cycles of total zooplankton abun-
dance for stations NH 1, NH 3, NH 5, and NH 10
are shown in Figures 1, 2, and 3. Abundance is
high during the upwelling season and often re-
mains high during the autumn period of hydro-
graphic transition. Abundance is low during the
period from November through April. All four sta-
tions have this basic pattern, but there are impor-
tant changes with distance offshore. Table 2 gives
several indices of cycle amplitude. The amplitude

TABLE 2. — Some indices of the amplitude of the seasonal cycle of
zooplankton density off the Oregon coast. Median density esti-
mates for summer and winter seasons at the four stations on the
Newport, Oreg., transect, the ratio of median densities between
seasons, and the number of dates with densities >5,000 m .

I0:

Summer-

No. dates

Summer

Winter

winter

with density

Station

(May-Oct.)

(Nov. -Apr.)

ratio

>5,000m"3

NH1

4,350 m "3

850 m -3

5.1

NH3

2,250 m -3

800 m-3

2.8

NH5

1 .550 m -3

530 m-3

2.9

NH 10

1 ,000 m "3

365 m-3

2.7

o
<

io-

- I969

I I I I

i i

- I 970

•

N H 1

I97I

• I972

1 1 1

\
l\

* ^ — <

f \

•

» \

►

\ /

\ '

iiii

i i

CD
<

_l io2

JFMAMJJASOND

MONTHS

FIGURE 1. — Annual cycle of totaled zooplankton abundance 2
km from the Oregon coast at Newport (NH 1) during the 3-yr
study period.

10'
UJ

<
a

2 io3

CD
O io2

,'969' ' r~T~

1970

1971

1972

NH 3

. 4 . • • •,

J I I I I I I I I I L

_l JFMAMJJAS0ND

MONTHS

FIGURE 2. — Annual cycle of totaled zooplankton abundance 5
km from the Oregon coast at Newport (NH 3) during the 3-yr
study period.

of the cycle is greater inshore. First, there are
more dates at NH 1 and NH 3 with densities in
excess of 5,000 m 3 (an arbitrary value). Second,
the absolute difference between summer and
winter density decreases with distance from shore.
All of the decrease in the ratio of the densities in
the two seasons occurs between 2 and 5 km from
shore (NH 1 to NH 3).

There is a suggestion in the data for NH 1 (Fig-
ure 1) that the annual cycle of zooplankton abun-
dance is more complex than just a summer high

719

FISHERY BULLETIN: VOL. 75, NO. 4

10'

I0J

O 2

<
Q

CD io3
O

10'

■ 1969

• 1970

» 197 I

• 1972

' , A"\.

/ v?

\ ■

J L

J FMAMJ J ASO ND

~1 1 1 r~

■ 1969

• -- 1970

* 1971
•-•-1972

t I I L

J FMAMJ J ASO ND

MONTHS

FIGURE 3. — Annual cycle of totaled zooplankton abundance 9
and 18 km from the Oregon coast at Newport (NH 5 and NH 10)
during the 3-yr study period.

and a winter low. In addition to that basic cycle,
there are peaks in total abundance at NH 1 in each
year of the study in either February or March. The
25 February 1970 sample had high numbers of
copepod nauplii other than Calanus (1,840 m"3 =
27% of the total zooplankton). This indicates the
presence of an actively reproducing adult copepod
population. A diatom bloom was in progress at
that time as well. Our nets were clogged with the
diatom Thalassiosira. The 16 February 1971 peak
had high numbers of Pseudocalanus sp. (680 m~3
= 41% of the catch), Calanus marshallae (240 m-3
= 15%), and Calanus nauplii (192 m 3 = 12%).
The Pseudocalanus sp. population was almost
entirely stage I copepodites. These facts again in-
dicate actively reproducing adult copepod popula-
tions in late winter. In both of these years, abun-
dances decreased after the February peak to lower
values in March or April. In 1972 no samples were
collected in January or February. The 15 March
sample at NH 1 had high numbers of Pseudo-
calanus sp. (1,844 m~3 = 62%), Oithona similis
( 690 m ~3 = 23% ), and Acartia longiremis (265 m "3
= 9%). Half of the total catch were immature
Pseudocalanus sp. and half of the A. longiremis

were immature. Again, there is some evidence of a
late winter cycle of reproduction of the species of
copepods permanently resident in the nearshore
zone and dominant later in the year. There is evi-
dence of this late winter peak in copepod abun-
dance at NH 3 only in 1970, and it is not seen at all
in the data for NH 5 and NH 10.

The months of April and May are periods of
transition in the direction of the prevailing wind.
An atmospheric high pressure cell begins to form
over the North Pacific Ocean, and the winds begin
to blow from the north with greater frequency. In
all years of this study, heavy phytoplankton
blooms were observed at NH 1 during this period.
The blooms are probably associated with the re-
plenishment of nutrients within the photic zone by
the earliest brief episodes of upwelling. Dates with
dense blooms were 27 April 1970, 3 and 14 May
1971, 20 April 1972, and 22 May 1972. Zoo-
plankton abundances were low at these times.

Seasonal Cycle of
Relative Species Abundance

The seasonal cycle of relative abundance of the
most abundant species of copepods is shown in
Figure 4 for all four stations. The graphs for each
station represent cumulative percentage of the
total catch for the species as labelled. The result is
complex but deserves careful study because some
interesting patterns are present. The simplest
pattern is the sinusoidal annual cycle. This pat-
tern is in phase with the seasonal cycle of total
abundance. It can be concluded from comparison of
the zooplankton abundance plots (Figures 1, 2, 3)
and from the relative species abundance plot (Fig-
ure 4), that low numbers during winter months
are coincident with 1 ) a decrease in relative abun-
dance of the endemic copepod species and 2) an
increase in importance of warmwater species and
noncopepod taxa. In addition to copepods with
southern affinities, Oikopleura spp. and chaeto-
gnaths become important during the winter.

There is marked seasonality in the relative
abundance of each taxon. This will be discussed
station-by-station. At NH 1 Pseudocalanus sp.
were numerically important during the upwelling
season, usually through August. Acartia clausii
and A. longiremis were always important during
the autumn after the cessation of upwelling. Cen-
tropages abdominalis was never a major compo-
nent after August, with the exception of 1971.
Calanus marshallae copepodites and nauplii were

720

PETERSON and MILLER: SEASONAL CYCLE OF ZOOPLANKTON ABUNDANCE

I00r

ACARTIA CLAUSII

\CENTROPACES

A LONGIREMIS

CALANUS ' NAUPLII \pARACALANUS

FIGURE 4. — Seasonal cycle of relative abundance (percent of total catch) of the most abundant zooplankton species (all copepods) at
stations NH 1, NH 3, NH 5, and NH 10 along the Newport, Oreg., transect over the 3-yr study period. Centropages were C. abdominalis,
A. longiremis were Acartia longiremis , Calanus were C. marshallae, Paracalanus were P. parvus, and Oithona were O. similis.
Pseudocalanus sp. are represented by the white area at the bottom of each graph. All remaining zooplankton are represented by the
white area at the top of each graph.

most dominant during the spring. Paracalanus
parvus and Oithona similis have their highest rel-
ative abundance during the winter.

Different years were different at NH 1, as previ-
ously noted (Peterson and Miller 1975).
Pseudocalanus sp. had a much higher relative
abundance during the 1969 and 1971 upwelling
seasons than in 1970. During the 1970 upwelling
season, A. clausii and Pseudocalanus sp. shared
numerical dominance in many samples. Centro-
pages abdominalis was less important during the
1971 upwelling period than in earlier years. Acar-
tia longiremis was about equally dominant at var-
ious times during all three upwelling seasons.
Oithona similis was more important during the
summers of 1969 and 1971. Paracalanus parvus
was a significant fraction of the plankton over

broader time intervals in 1969 and 1970 than in
1971.

At NH 3 the most striking aspect of the annual
cycle compared with NH 1 is the greatly decreased
importance of Acartia clausii and generally in-
creased importance of A. longiremis and Calanus
marshallae. Acartia clausii made up a large frac-
tion of the catch only during October 1970. Acartia
longiremis and C. marshallae were major compo-
nents over broader intervals in 1970 and 1971 at
NH 3 than at NH 1. The annual cycle of Pseudo-
calanus sp. relative abundance at NH 3 was about
the same as for NH 1, except for two periods: July
of 1970 and 1971. During both times Pseudo-
calanus sp. was dominant at NH 1, whereas A.
longiremis was dominant at NH 3.

The NH 5 plot is similar to that for NH 3, par-

721

FISHERY BULLETIN: VOL. 75, NO. 4

ticularly between November 1969 and May 1970
and between January and July 1971. Similarly to
NH 3, the importance of A. clausii is greatly re-
duced and the importance of A. longiremis and C.
marshallae are increased relative to NH 1. The
NH 10 plot follows the NH 5 plot closely during
1970 and 1971 with one exception: in September
1970 A. clausii was a significant component at NH
5 but not at NH 10.

DISCUSSION

The annual cycle in the species composition of
the zooplankton community along the Oregon
coast must result from the annual cycle of the
nearshore circulation, which is well described by
Huyer et al. (1975). There is an exact correspon-
dence between the sources of currents implied by
the direction of flow in each season and the geo-
graphic affinities of the species occurring in the
water. In summer, when the net water transport is
to the south, species with northern affinities
dominate. In winter, when transport is northward,
species with southern affinities are mixed with the
indigenous fauna. Abundances are about an order
of magnitude higher in summer than winter, pre-
sumably because of production stimulated by
coastal upwelling. We term the summer domi-
nants "indigenous" both because they are present
throughout the year and because they are the
forms which reproduce and complete their life cy-
cles in the Oregon nearshore zone. None of these
forms is endemic, however, in that the distribu-
tions of all of them extend north around the rim of
the Gulf of Alaska and into the Bering Sea. New
studies now in progress are intended to describe
the distributions within the upwelling ecosystem
of the life cycle stages of the summer dominants,
and to explain the maintenance of their popula-
tions within the system of nearshore currents.

A similar interpretation of seasonal changes in
zooplankton species present off Oregon was of-
fered by Cross and Small ( 1967). They used Acar-
tia danae as an indicator of transport from the
south (following Frolander 1962), and Centro-
pages abdominalis (called C. mcmurrichi in their
paper) as an indicator of flow from the north. In the
present study A. danae was very infrequent, and a
variety of other species (Paracalanus parvus,
Ctenocalanus vanus, Clausocalanus pergens, etc.)
appear to be much better indicators of southern
sources. The studies were different in that the
earlier one sampled farther offshore, and it began

with the notion that A. danae would be an indi-
cator, rather than examining the fauna as a whole.
While there is a generally similar sequence each
year in the changes of the copepod species and
their abundance, there are also marked differ-
ences in these changes between years. These were
discussed for the upwelling season by Peterson
and Miller (1975). We would like to add to that a
brief evaluation of some differences between the
winters of our study. Temperature-salinity dia-
grams including all of the data collected at our
inshore stations during the months of October
through March are shown in Figure 5. The winter
of 1969-70 was warmer than the other winters.
Progressive vector diagrams of the winds in each
of the winter periods of our study are shown in
Figure 6. The winds during 1969-70 were differ-
ent from those of 1970-71 and 1971-72. During
the fall and winter months of 1969-70 there were

15 -

*° ° »«

1969-70

J I L

<
rr

LU
Q_

I 5

1970-71

°o°°
o

o o

orf>

8 o

% °

1971 -72

j i

J I I L.

25 30 35

SALINITY (%o)

FIGURE 5. — Temperature-salinity scatter diagrams combining
data from stations NH 1, NH 3, NH 5, and NH 10 along the
Newport, Oreg., transect for the winters of 1969-70, 1970-71,
and 1971-72 from October through March.

722

PETERSON and MILLER: SEASONAL CYCLE OF ZOOPLANKTON ABUNDANCE

SCALES: THOUSANDS
OF WIND -KILOMETERS

FIGURE 6.— Progressive vector diagrams for the wind at Newport, Oreg., for the winters of 1969-70, 1970-71, and 1971-72.

three intervals with winds from the east: most of
October, 23 November to 8 December, and 30 De-
cember to 12 January. The entire 6-mo period of
winter winds lacked the southwesterly storms
that are characteristic of most winters. The other
two winter wind patterns shown in Figure 6 are
more typical on the basis of comparisons to the
winters of later years (1972-73, 1973-74, 1974-
75).

Upwelling index data taken from Bakun (1973)
for the winters of our study are presented in Table
3. Negative values of the index indicate winds that
will produce shoreward convergence of surface
waters on the average over the month. Negative
values of the anomaly indicate greater-than-usual
shoreward convergence. Indices for winter 1969-
70 are quite different from those of the other two
winters. Onshore convergence was anomalously
high in 1969-70 and anomalously low in 1970-71
and 1971-72.

The zooplankton data (see Peterson and Miller
(1976) for detailed tabulations) indicate that the
northward flow of the Davidson Current probably
was much greater in 1969-70 than in the other
two years. A number of southern zooplankton
species had their greatest abundance during that

TABLE 3.— Monthly upwelling inde* values from Bakun (1973)
for midwinter period at lat. 45 °N, just north of the Newport,
Oreg., transect, during the years of our study.

20-yr

mean

index

for month

1969-70

1970-71

197

-72

Month

Index

Anomaly

Index

Anomaly

Index

Anomaly

Nov

-74

-53

+21

-54

+ 19

-40

+34

Dec.

-93

-157

-64

-106

-12

-27

*66

Jan.

-94

-98

-4

-32

+62

-19

+ 75

Feb.

-47

-71

-24

-16

+32

-103

-56

Total

-71

+ 101

-119

winter: Clausocalanus jobei, C.paululus, Oncaea
dentipes, and O. subtilis. All of the above 16
copepod species are indicators of water originating
south of at least Cape Mendocino, Calif. (Olsen
1949; Fleminger 1964, 1967; Frost and Fleminger
1968).

The physical implication of this set of biological
observations is that winter periods of gentle winds
directly from the south (Figure 6a) are much more
effective at moving water northward alongshore
than winter periods of violent southwesterly
storms (Figures 6b, c), even though the total
northward component of the winds during the
stormy winters might be much greater. This is in
agreement with the temperature results (Figure
5) and with the anomaly in the upwelling indices.

723

FISHERY BULLETIN: VOL. 75, NO. 4

Bakun (1973) pointed out that winters of extreme
shoreward convergence of wind-drifted surface
waters (negative index anomaly) should cause
the density structure to be depressed toward the
coast and should accelerate northward flow or de-
celerate southward flow. "Either situation would
favor an anomalous warm advection," according to
Bakun.

ACKNOWLEDGMENTS

The sampling program for this study was
started by Jefferson J. Gonor and William G.
Pearcy who graciously allowed us to participate.
R. Gregory Lough, Peter Rothlisberg, and others
helped with the sampling. William Gilbert pro-
vided the wind data and drafted Figure 4. The
manuscript was greatly improved by Lawrence F.
Small. The work was supported by NOAA, U.S.
Department of Commerce, Sea Grant Institu-
tional Grant No. 04-3-158-4.

LITERATURE CITED

Bakun, a.

1973. Coastal upwelling indices, west coast of North
America, 1946-71. U.S. Dep. Commer., NOAA Tech.
Rep. NMFS SSRF-671, 103 p.
CROSS, F. A., AND L. F. SMALL.

1967. Copepod indicators of surface water movements off
the Oregon coast. Limnol. Oceanogr. 12:60-72.
FLEMINGER, A.

1964. Distributional atlas of calanoid copepods in the
California Current region, Part I. Calif. Coop. Oceanic
Fish. Invest., Atlas 2, 313 p.

1967. Distributional atlas of calanoid copepods in the
California Current region, Part II. Calif. Coop. Oceanic
Fish. Invest., Atlas 7, 213 p.

FROLANDER, H. F.

1962. Quantitative estimations of temporal variations of
zooplankton off the coast of Washington and British Co-
lumbia. J. Fish. Res. Board Can. 19:657-675.
FROLANDER, H. F., C. B. MILLER, M. J. FLYNN, S. C. MYERS,
AND S. T. ZIMMERMAN.

1973. Seasonal cycles of abundance of zooplankton popula-
tions of Yaquina Bay, Oregon. Mar. Biol. (Berl.)
21:277-288.
FROST, B., AND A. FLEMINGER.

1968. A revision of the genus Clausocalanus (Copepoda:
Calanoida) with remarks on distributional patterns in
diagnostic characters. Bull. Scripps Inst. Oceanogr.
12:1-235.

HUYER, A., R. D. PILLSBURY, AND R. L. SMITH.

1975. Seasonal variation of the alongshore velocity field
over the continental shelf off Oregon. Limnol. Oceanogr.
20:90-95.
MCGOWAN, J. A.

1971. Oceanic biogeography of the Pacific. In B. M. Fun-
nell and W. R. Riedel (editors), The micropaleontology of
oceans, p. 3-74. Cambridge Univ. Press, Cambr.
MYERS, A.

1975. Vertical distribution of zooplankton in the Oregon
coastal zone during an upwelling event. M.S. Thesis,
Oregon State Univ., Corvallis, 60 p.
OLSEN, J. B.

1949. The pelagic cyclopoid copepods of the coastal waters
of Oregon, California and Lower California. Ph.D.
Thesis, Univ. California, Los Angeles, 208 p.
PETERSON, W. T., AND C. B. MILLER.

1975. Year-to-year variations in the planktology of the
Oregon upwelling zone. Fish. Bull., U.S. 73:642-653.

1976. Zooplankton along the continental shelf off New-
port, Oregon, 1969-1972: distribution, abundance, sea-
sonal cycle, and year-to-year variations. Oreg. State
Univ. Sea Grant Coll. Prog. Publ. ORESU-T-76-002,
111 p.

724

GROWTH AND REPRODUCTION OF THE EASTERN SPINNER DOLPHIN,

A GEOGRAPHICAL FORM OF STENELLA LONGIROSTRIS

IN THE EASTERN TROPICAL PACIFIC

William F. Perrin, David B. Holts, and Ruth B. Miller1

ABSTRACT

Estimates of life history parameters for use in assessing status of the population of the eastern spinner
dolphin and assessing impact of incidental mortality in the yellowfin tuna fishery are developed from
data on 2,675 specimens collected from 1968 to 1975. Average length at birth is 77.0 cm, gestation is
10.6 mo, average length at 1 yr is approximately 134 cm. Three alternative hypotheses of rate of
deposition of dentinal growth layers are: I) 1.5 layers/yr throughout life; II) 1.5 layers in the first year,
1/yr thereafter ( most favored hypothesis); and III) 1.5 layers until puberty (at 5.5 layers in females and
9 layers in males), and 1/yr thereafter. Males attain sexual maturity on the average at about 170 cm
(range 160-195) and 9-12 layers (6.0-11.5 yr), depending on the criterion of testis-epididymis weight
chosen. Average length at attainment of social maturity is unknown. Average length of adult males is
174-176 cm. Females on the average attain sexual maturity at 165 cm (5.5 layers or 3.7, 5.0, or 3.7 yr
under Hypotheses I, II, and III). Average length of sexually adult females is 171 cm (range 152-187).
Ovulation rate is 1/growth layer (1/0.67-1.00 yr) until about 10 ovarian corpora have been accumu-
lated, after which the rate declines. Approximately 1% of adult females are postreproductive. Best
estimates of annual pregnancy rate range from 0.450 (based on 1973 data) to 0.474 (based on 1974
data). The pooled estimate for all years' data is 0.461. The corresponding estimates of calving interval
(reciprocal of pregnancy rate) are 2.22 yr, 2.11 yr, and 2.17 yr, respectively. Pregnancy rate decreases
after age of about 12 layers (8.0, 11.5, or 10.2 yr) concomitant with increase in lactation rate. Overall
sex ratio is near parity, but there are about 6% more females than males in adults. Best estimates of
gross annual reproductive rate based on the 1973, 1974, and 1975 data are 0.099, 0.103, and 0.105,
respectively. The estimate based on pooled data for the 3 yr is 0.102. The estimates are compared with
estimates for the spotted dolphin, Stenella attenuata, and for other cetaceans.

This paper presents the results of a study of the life
history of the eastern spinner dolphin, a geograph-
ical form2 of Stenella longirostris (Gray 1828), in
the eastern tropical Pacific. The eastern spinner
dolphin accounted for the second-highest level of
incidental mortality in the purse seine fishery for
yellowfin tuna, Thunnus albacares, in the eastern
Pacific through 1975, after the offshore spotted
dolphin, a form of S. attenuata (Gray 1846) (Perrin
1969, 1975a; Perrin et al.3) The purpose of the

study was to develop estimates of life history
parameters for use in assessing the status of the
eastern spinner dolphin stock and the impact on
the stock of incidental mortality in the yellowfin
tuna fishery. Preliminary results of partially com-
pleted analyses reported here in full appeared in
Perrin et al.4

Very little previously published information is
available on growth and reproduction of the pan-
tropically distributed S. longirostris. Cadenat and
Doutre (1959) listed body weights and gonadal

'Southwest Fisheries Center, National Marine Fisheries Ser-
vice, NOAA, P.O. Box 271, La Jolla, CA 92038.

2Perrin (1975b) gave the eastern spinner dolphin subspecific
rank but stated that the nomenclature is not yet resolved, be-
cause the holotype of the species is from an unknown locality.
The term "geographical form" is used here as a substitute for the
more unwieldy "[Stenella longirostris] subspecies (unnamed)."
The term "dolphin" is used in conformance with the "list of
smaller cetaceans recognized" adopted by the Subcommittee on
Smaller Cetaceans, Scientific Committee, International Whal-
ing Commission (Anonymous 1975).

3Perrin, W. F., T. D. Smith, and G. T. Sakagawa. 1974. Status
of populations of spotted dolphin, Stenella attenuata, and spinner
dolphin, Stenella longirostris, in the eastern tropical Pacific.

Manuscript accepted February 1977.
FISHERY BULLETIN: VOL. 75, NO. 4, 1977.

Working Document for Meeting of Ad Hoc Consultants Group on
Small Cetaceans and Sirenians (Ad Hoc Group 2), Working
Party on Marine Mammals, Advisory Committee of Experts on
Marine Resources Research ( ACMRR) of the Food and Agricul-
ture Organization of the United Nations, La Jolla, Calif.. De-
cember 16-19, 1974. SWFC Admin. Rep. LJ-74-42, Natl. Mar.
Fish. Serv., NOAA, La Jolla, Calif., 22 p. (Unpubl. real

"Perrin, W. F., D. B. Holts, and R. B. Miller. 1975. Preliminary
estimates of some parameters of growth and reproduction of the
eastern spinner porpoise, Stenella longirostris subspecies.
SWFC Admin. Rep. LJ-75-66, Natl. Mar. Fish. Serv., NOAA, La
Jolla, Calif., 33 p. (Unpubl. rep.)

725

FISHERY BULLETIN: VOL. 75, NO. 4

data for two males (1,940 and 2,040 mm) and two
females (1,790 and 1,800 mm) from off Senegal in
the tropical Atlantic. Layne (1965) published
similar data for two males (1,845 and 1,910 mm)
and one female (1,965 mm) from Florida. Pilson
and Waller (1970) reported on an adult female of
S. microps [= S. longirostris] 176 cm long, from
the eastern Pacific. Harrison et al. (1972) pub-
lished detailed length, weight, and gonadal data
for 12 males (79 to 185 cm) and 21 females (86 to
188 cm) of S. longirostris from the eastern Pacific;
five males (150 to 182 cm) and two females (169
and 179 cm) of S. roseiventris [= S. longirostis]
from Hawaii; and nine specimens from the eastern
Pacific, eight males (165 to 178 cm), and one
female (171.5 cm) listed as "probably S. longiros-
tris." In their discussion of growth and reproduc-
tion, however, they did not differentiate between
S. longirostris and S. graffmani [ = S. attenuata], a
larger species that differs significantly from S.
longirostris in several features of life history
(compare results below with those for S. attenuata
in Perrin et al. (1976) and Kasuya et al. (1974)).

Several recent reports emanating from the
Southwest Fisheries Center, National Marine
Fisheries Service (NMFS), NOAA, have dealt
with the developmental components of various as-
pects of the life history of S. longirostris other than
reproduction. Perrin (1972) described the de-
velopment of the color pattern in eastern Pacific
forms of the species. Perrin and Roberts (1972)
analyzed changes in organ weights with size,
based on 14 specimens. Dailey and Perrin (1973)
described differences in parasite frequencies cor-
related with age in 19 specimens. Perrin (1975a, b)
described developmental variation in morphology
in the eastern Pacific and defined three geograph-
ical forms (subspecies), of differing adult size: the
less-than-2-m-long "eastern spinner," the subject
of this report; the slightly larger "whitebelly spin-
ner," found farther offshore; and the "Costa Rican
spinner," which is restricted to the coastal waters
of Central America and attains a total length of
well over 2 m.

This paper treats only the eastern spinner, the
form of S. longirostris most heavily involved in the
tuna fishery through 1975 in terms of numbers of
seine net sets and numbers killed (Perrin 1975a).
Some data for the whitebelly spinner are included
in certain of the analyses of the eastern spinner,
including those of length at birth and of brain
weight relative to body length, for reasons ex-
plained below. A preliminary report on the white-

726

belly form of S. longirostris appeared in Perrin et
al.5

METHODS AND MATERIALS

The Field Program

Nearly all of the data were collected by NMFS
scientific observers aboard commercial tuna ves-
sels. The data collection procedures were the same
as previously described for the spotted dolphin
(Perrin et al. 1976). Data on S. longirostris were
collected on 1 cruise in 1968, 4 in 1971, 12 in 1972,
21 in 1973, 33 in 1974, and 30 in 1975. Some
specimens were also collected in 1970 by personnel
of the Inter- American Tropical Tuna Commission
aboard chartered purse seiners.

The Sample

In 1971 and early 1972, when the observer pro-
gram was very limited, adult female specimens
were selected for dissection when available, and
the samples for those periods are, therefore, biased
with regard to the age and sex structures of the
kill. In 1968 and on cruises from October 1972 on,
no selection was practiced in determining which
animals were to be examined, and those samples
are assumed to be cross-sectional with respect to
the kill. Fetuses were not collected in 1968.

The sample of animals for which life history
data including at least, but not restricted to, sex
and body length includes 2,675 specimens, 2,663
from precisely known localities (Figure 1) and 12
from imprecisely known localities, from the east-
ern tropical Pacific between lat. 2 1 °N and 3 °S and
west to long. 117°W. Because of the seasonal na-
ture of the tuna fishery, the sample is heavily
biased toward the early months of the year, with
minimal coverage of the latter part of the year and
practically no specimens from the summer months
(Table 1). Length-frequency distributions by 5-cm
increments for males and females, including
fetuses, are presented by year and month in Fig-
ures 2 and 3.

5Perrin, W. F., D. B. Holts, and R. B. Miller. 1976. Preliminary
estimates of some parameters of growth and reproduction of the
whitebelly spinner dolphin, a geographical form ofStenella lon-
girostris, in the eastern tropical Pacific. Working document
submitted to Meeting of Subcommittee on Small Cetaceans, Sci-
entific Committee, International Whaling Commission, London,
7-8 June 1976. SWFC Admin. Rep. LJ-76-12, Natl. Mar. Fish.
Serv., NOAA, La Jolla, Calif., 36 p. (Unpubl. rep.)

PERRIN ET AL.: GROWTH AND REPRODUCTION OF THE EASTERN SPINNER DOLPHIN

104 128

Clipperton IS

Galapagos is r

J L_ "

Galapagos is ^r

■ 0°

130° 120° 110°

100° 90° 80°

30°

20°

10°

V 1

1 1

1 1 1 1 1

1975 (n=773)

20°
10°

Revil

agiged

3S IS 0

c <.

Chpp

■rton 1

110

257

Galapagos is ^

I i

f'36

" ,

130° 120° 110°

100° 90° 60°

Xf —

FIGURE 1.— Samples of Stenella longirostris collected 1968-75, by 5° square.

727

FISHERY BULLETIN: VOL. 75, NO. 4

TABLE 1. — The sample of eastern spinner dolphins used in the life history analysis, by year and month.

1968

1970

1971

19721

1973

1974

1975

All

years

Month2

Males Females

Males

Females

Males

Females

Males

Females

Males

Females

Males

Females

Males

Females

Total

Jan.

1 2

104

163

170

283

323

606

Feb.

135

128

230

209

453

439

892

Mar.

148

162

310

Apr.

52 55

177

178

355

May

June

July

Aug.

Oct.

Nov.

115

120

235

Dec.

Total

52 55

3 2

347

345

405

395

364

411

1,295

1,380

2,675

'In these years, adults were selected (except in Oct. 1972). Fetuses were not collected in 1968.
2No samples in September.

FIGURE 2.— Length-frequency dis-
tribution, by 5-cm increments, of col-
lected male eastern spinner dolphins by
year and month. Shaded squares are
fetuses. Hatched squares are small
fetuses of unknown sex (plotted with the
males). Sample sizes in parentheses.

NOV I97I (36)

- ,- a , n C-^

APR I968 (52)

-, ,r-H

JAN I970 (2)

JUL I970 (2)

JAN I97I (2)

FEB I97I (22)

DEC I97I (7)

JAN I972 (9)

r^ln

MAR 1972 (10)

l-H r-n-H

APR 1972 (28)

P^L

0 —

JAN 1974 (100)

MAR 1974 (28)

1974 (I)
P-

NOV

-M

H-rLjV1

-— i — —— l n —

I (41) J

1974 (3)

n p— i r-p

JAN 1975 (173)

FEB 1975 (73)

00 125 150 175 200

LENGTH (cm)

MAY

-P =■

■^1 .

JUL 1975 (18)

AUG 1975 (12)

P — ■=>-, 1

OCT 1975 (18)

-F3-

nrv^

NOV 1975 (13)

_a '-'

100 125 150

P— n-n

Laboratory Procedures

Most laboratory procedures were the same as
reported for the earlier study of the growth and
reproduction of the spotted dolphin (Perrin et al.

728

1976). The techniques used in sectioning and read-
ing, however, differed somewhat. Some of the ap-
proximately 2,500 teeth prepared (includes recuts,
multiple specimens, etc.) were sectioned with mul-
tiple cuts, using a high-speed diamond saw

PERRIN ET AL.: GROWTH AND REPRODUCTION OF THE EASTERN SPINNER DOLPHIN

FIGURE 3.— Length-frequency dis-
tributions, by 5-cm increments, of col-
lected female eastern spinner dolphins
by year and month. Shaded squares are
fetuses. Sample sizes in parentheses.

(Felker6 model 80BQ Hi-speed Precision Cut-off
Machine — 36,000 rpm) with a single blade, as for
S. attenuata (Perrin et al. 1976), but most were
sectioned with a single cut of tandem blades (yield-
ing a section of uniform 10/1,000-in thickness)
with a low speed saw (Isomet model 11-1180 low
speed saw — speed variable to 300 rpm). The latter
method yielded sections of more uniform thickness
and with fewer extraneous surface striations than
did the former. After cutting, sections were im-

6Reference to trade names does not imply endorsement of the
product by the National Marine Fisheries Service, NOAA.

mediately mounted under coverslips on micro-
scope slides in balsam, omitting the clearing step
used for the S. attenuata teeth. Our reading and
scoring methods also differed from those in the
earlier study. We found postnatal dentinal growth
to be much more consistent in S. longirostris than
in S. attenuata in pattern of deposition and in
readability. No teeth were encountered that did
not contain an open cavity, albeit in older speci-
mens a very small one, and a smaller proportion of
teeth from younger animals (<12 to 13 layers)
contained convoluted secondary dentine than in S.
attenuata. In the study of S. attenuata, growth

729

FISHERY BULLETIN: VOL. 75, NO. 4

layers were merely counted to the nearest half
layer. In view of the better readability of the S.
longirostris material, we felt that the approach
could be refined. We measured the thickness of
each growth layer on an image projected on a
16-cm diameter ground-glass screen attached to a
compound microscope using dial calipers accurate
to 0.1 mm. The total magnification on the screen
was approximately 263 diameters. The first two
layers inside the neonatal tooth were measured at
approximately the same point along the length for
each tooth, about halfway between the proximal
end of the neonatal tooth (point where neonatal
line meets outer surface) and the distal end of the
neonatal pulp cavity. Layers beyond the second
were measured at the place along the length of the
tooth where they were most clearly defined. In
converting measurements to layer units, non-
innermost layers beyond the first layer were
scored as full layer units regardless of thickness.
The first layer, second (when innermost), and sub-
sequent layers (when innermost) were treated dif-
ferently, as follows:

First Layer

Cumulative percent of 417 first layers measured
rapidly approaches an asymptote at approxi-
mately 0.20 mm (Figure 4). A first layer 0.20 mm
thick or thicker was therefore scored as a full layer
unit, and the thickness of a first layer <0.20 mm
thick was divided by 0.20 mm to yield a partial
layer unit.

Second Layer

In 361 teeth with three or more layers, the sec-
ond layer averaged 0. 145 mm thick with relatively
low variance (Figure 5). In teeth with two layers,
the second layer was scored as a full layer unit if
0.145 mm thick or thicker. An innermost second
layer <0.145 mm thick was scored as a partial
layer unit by division of the thickness by 0.145
mm.

Layers Beyond Second Layer

Full layers beyond the second layer averaged
more than 95% of the thickness of the next older,
adjacent layer, with considerable variation that
increased toward the center of the tooth (Figure 6).
We assumed, as a reasonable approximation, that
complete layers beyond the third are of about the

730

100 r

— 80 -

005

0.10 0.15 020 025

THICKNESS OF FIRST LAYER (mm)

030

FIGURE 4. — Cumulative percent of first growth layers in rela-
tion to thickness of layer in the teeth of 417 eastern spinner
dolphins showing asymptote of sigmoid curve at about 0.20 mm.

AVERAGE = 0 145 mm

008 012 0.16 020

THICKNESS OF SECOND LAYER (mm)

028

FIGURE 5. — Frequency distribution of thickness of second
growth layer in teeth of 361 eastern spinner dolphins.

same thickness as adjacent layers, and thickness
of the innermost layer in teeth with three or more
layers was scored as a proportion of the next older,
adjacent layer. Layer scores thus obtained were
added and rounded off to the nearest tenth of a
layer.

Brain weights were obtained from brains dis-
sected out of freshly thawed heads or whole car-
casses of specimens deep frozen at sea aboard
tunaboats, except for nine weights for S. attenuata
(two fetuses, two neonates, and four adults) ob-
tained from George A. Sacher (Argonne National
Laboratory, Argonne, 111., pers. commun.).

Testes were weighed with the epididymes at-
tached.

PERRIN ET AL.: GROWTH AND REPRODUCTION OF THE EASTERN SPINNER DOLPHIN
22r ioor

"i; 20

5 I 8

.2. 16

iii

04 -

(245)

^HHHHHHkfj^HHkn-

(23)

(44) (28)

(68)

183)

(212) (174) (109)

(2461(244)

J ! I I I 1

8 10

LAYER (no)

FIGURE 6. — Thickness of growth layers, beyond second post-
natal layer, in teeth of the eastern spinner dolphin as proportion
of thickness of next older, adjacent zone. Box is one SD on each
side of mean; vertical line is range; sample size in parentheses.

RESULTS
Growth

Length at Birth

The largest fetus encountered was 84 cm long.
The smallest free-swimming calf was 70 cm long.
Estimated average length at birth is 76.9 cm. The
estimate is based on a weighted linear regression
of percent postnatal on body length, for 3-cm
groupings, of 101 specimens (54 fetuses and 47
neonates) between 67 and 99 cm long (Figure 7)
collected in random samples. Because of the small
sizes of the available samples, 23 specimens of the
whitebelly form (11 neonates and 12 fetuses) and
23 specimens unidentified to geographical form
(16 neonates and 7 fetuses) were included. This is
justified because of the small difference in length
of adults of the two forms ( <5 cm — Perrin 1975a).
Such a difference could be expected to translate
into a probable error in the estimate of length at
birth, based on the present sample composition, of

• (9)

Y = 6083l X -4176
r = 0.970)

70 73 76 79 82 85 88

LENGTH (cm)

FIGURE 7. — Estimation of average length at birth, based on
weighted linear regression of percent postnatal on body length,
in 3-cm increments, for 101 specimens of Stenella longirostris (54
fetuses and 47 neonates) between 67 and 88 cm long.

<0.5 cm, less than that to be expected to be intro-
duced by reduction of the sample size (by 47'' I
through restriction to specimens known to be
eastern spinner dolphins. The estimate is rounded
off to 77 cm in analyses below.

This method of estimating average length at
birth assumes that pregnant females and calves
are 1) equally vulnerable to capture in the purse
seine, 2) equally likely to die once captured, and 3 )
equally represented in the sample of dead animals
measured. It also assumes equal rates of prenatal
and postnatal natural mortality and assumes that
the stresses imposed by pursuit and capture do not
cause premature births during the chase or in the
net. It was not possible to test these assumptions
although some evidence indicates that the last
may not be justified (see discussion below in The
Calving Cycle and Pregnancy Rate).

Length of Gestation and Fetal Growth

The usual method used to estimate length of
gestation is that of Laws ( 1959), in which progres-
sion of a mode in fetal lengths is followed through
the seasons. This method was used to estimate
length of gestation for the spotted dolphin (Perrin
et al. 1976). The method could not be applied to the
present samples of data for the eastern spinner
dolphin, however. Although breeding is perhaps
synchronous at some level (e.g., note peaks in the
length-frequency distributions for postnatal
males and females in February and April 1973,
and February 1974— Figures 2, 3), progression of

731

FISHERY BULLETIN: VOL. 75, NO. 4

100 r

^ GO

X
h-
tD

|5 40

Ave

lencjUi at birth

• I •

•

•
•

• 1

. 1

•

•
•

. •

•

••

•

•
• •

1 ! 1

10 20

JAN

10 20

FEB

1974

10 20

MAR

FIGURE 8. — Scatterplot of lengths of fetuses and neonates (open
dots) of the eastern spinner dolphin on day of capture,
January-March 1974.

fetal modes is not apparent in the data. For exam-
ple, in the large samples of fetuses collected in
January-March 1974 (Figure 8), a sharp mode at
60 to 75 cm in January is not apparent in Feb-
ruary, even as neonates, and the diffuse mode at
30 to 60 cm in February is not accounted for in the
January sample. A probable reason for these dis-
crepancies is the existence of area-related differ-
ences in the timing of calving peaks or in the
degree of synchrony of breeding. The tuna fleet,
our source of samples, moves around from month
to month. The January 1974 samples came for the
most part from more easterly, offshore localities
than did the February samples (Figure 9). In other
words, in 1974, calving in the more offshore region
may have been sharply synchronized, with a peak
in February-March, while in the more onshore
region, calving may have been spread over most of
the year. This hypothesis is reinforced by the data
for January- April 1975, when sizeable samples of
fetuses were collected in the more onshore region
during both January and February and smaller
samples through April (Figure 10) were from more
offshore (around Clipperton Island), northerly

125° 120° 115° 110" 105° 100° 95° 90° (

J5° 80°

i. ' i i i i

l u

•
t

J \ V

20°

Rtvillagigedo Is .

■

\s (0

^^ y-^ ■ ^—

IS0

%•

10°

Clipperton

• I

5°

•

n°

Galopogos Is tJo

30°

25°

20°

- 10°

-0°

125° 120° 115° 110° 105° 100° 95° 90° 85° 80

125° 120° 115° 110° 105° 100° 95° 90° 85° 80°

FIGURE 9. — Localities at which fetuses of the eastern spinner dolphin were collected in January (a) and February (b) 1974.

732

PERRIN ET AL.: GROWTH AND REPRODUCTION OF THE EASTERN SPINNER DOLPHIN

(Revillagigedos Islands), or southerly (near the
Equator, east of the Galapagos Islands) regions.
Even if only onshore samples are considered ( those
circled in Figure 10), there is no clear pattern of
progression of fetal length modes ( Figure 1 1 ). It is,
of course, possible that the size of the population
unit within which breeding is synchronous may be
smaller than suggested by the onshore-offshore
comparison. In any case, this complexity makes
impossible the use of Laws' method for estimating
gestation based on aggregated samples, and strat-
ification of the data to even smaller areas than
used above yields samples too small for meaning-
ful analysis. For these reasons, we attempted to
estimate length of gestation by two other, less

direct methods: a) on the basis of relative length at
birth compared with that of other, closely related
delphinids for which estimates of gestation period
exist, and b) on the basis of a recently discovered
empirical relationship between brain size
parameters and gestation in mammals.

ESTIMATE FROM COMPARISON WITH
OTHER DELPHINIDS BASED ON LENGTH AT
BIRTH. — Estimates of length of gestation derived
by comparable methods are available for four del-
phinids, sensu stricto (Table 2). There is a positive
correlation among these closely related forms be-
tween length of gestation and length at birth ( Fig-
ure 12). Extrapolation of this relationship to

130° 120° 110°

100° 90° 80°

130° 120° 110°

100° 90°

80°

30°

1 1 l l 1

JANUARY

JO°

30"

1 l 1

FEBRUARY

:<■

1975

20°

1975

-20°

Revil

ogiged

OS Is #

• «

^-"w-U tf <;

Revi

lagiged

os is m

b^ ^

iO,J

Chpp

erton 1

•
•

IG°

10°

Chpp

srlon 1

(

•

^i!

•

*^_

■

* /

0°

Galapagos Is. ^

1 i

Galapagos Is. ^

I i •

130° 120° 110°

100° 90° 80°

130° 120° 110°

100° 90°

80°

130° 120° 110°

100° 90° 80°

130° 120° 110°

100° 90°

,JP

1 1 1 l 1

MARCH

'■•'•

VJ>

APRIL

?.'

1975

20°

1975

20°

Revil

ogiged

• «

\^6 £ <;

Revil

agtged

3S Is «

• •

•

Clipperton Is _

• /

Clipperton Is m

10°

3°

0°

c°

0°

Galapagos is 9

l i

Galapagos Is W

I i 1

130° 120° 110°

100° 90° 80°

i30° 120° 110°

100° 90°

80°

FIGURE 10.— Localities at which fetuses of the eastern spinner dolphin were collected, January- April 1975.

733

FISHERY BULLETIN: VOL. 75, NO. 4

£ 40 -

Average length at birth

•

—

••

•

• •

•

• •

•
•

•

. '• :

i •

•
•

i i

1 1

l.2r

10 20

JAN

10 20

FES

10 20

MAR

31 10

APR

FIGURE 1 1. — Scatterplot of lengths of fetuses and neonates (open
dots) of the eastern spinner dolphin on day of capture, January-
April 1975 (specimens from localities circled in Figure 10).

TABLE 2. — Estimated average length at birth and length of
gestation in four delphinids. Data for Globicephala from Ser-
geant (1962), for Tursiops from Sergeant et al. (1973), for
Stenella coeruleoalba from Kasuya (1972), for S. attenuata from
Kasuya et al. (1974) (off Japan) and from Perrin et al. (1976)
(eastern Pacific). Common and scientific names follow Subcom-
mittee on Small Cetaceans, Scientific Committee, IWC
(Anonymous 1975).

Length at birth

Gestation

Species

(cm)

(mo)

Long-finned pilot whale

176.0

15.75

Globicephala melaena

(average of males

(15.5-16.0)

(Newfoundland)

and females)

Botttenose dolphin

100.0

12.0

Tursiops truncatus

(northeast Florida)

Striped dolphin

99.8

12.0

Stenella coeruleoalba

(off Japan)

Spotted dolphin

Stenella attenuata

a. (off Japan)

89.0

11.2

b. (eastern Pacific)

82.5

11.5

length at birth for S. longirostris of 77 cm yields a
deduced length of gestation of 10.74 mo (325 days).

ESTIMATE BASED ON GROWTH PARAM-
ETERS OF THE BRAIN.— Sacher and Staffeldt
(1974) recently demonstrated an empirical rela-
tionship between gestation time and brain weight
in placental mammals. This relationship explains
more of the wide variation in mammalian gesta-
tion times than do previous empirical approaches
involving body size parameters, such as cube root

c
o
E

§ I.I

0J
C7>

Log Y = 04586 LogX + 01659
(r = 0989)

G = 10 74 months

S ottenuato
(East Poc) •

J LL

"16 17 18 19 2 0 21 2.2

LOG ( length at birfh in cm )

FIGURE 12. — Relationship between log of length of gestation and
log of length at birth in four delphinid cetaceans, with extrapola-
tion to predicted length of gestation in the eastern spinner dol-
phin.

of weight at birth (Huggett and Widdas 1951) or
length at birth (as in-above -estimate). They de-
veloped a predictive equation based on linear mul-
tiple regression analysis:

log G = 0.274 log En + 0.144 log Ae
+ 0.173 log N + 1.853

where G = gestation time in days

En = neonatal brain weight in grams
Ag = "brain size advancement," or ratio of

neonatal to adult brain weight
N= litter size (1 in cetaceans).

Application of this equation to brain data for S.
longirostris (Figure 13 — neonatal brain weight =
231 g, adult brain weight = 465 g) yields an esti-
mate of gestation time of 286 days (9.45 mo). The
method has not yet been tested on a significant
number of delphinid species for which gestation
time has been more directly estimated,7 and we

7The estimates used by Sacher and Staffeldt of brain weight at
birth and adulthood for Tursiops are from Lilly (1967) and are
based on samples of unstated and probably sjnall size, a very
important consideration in light of the large individual variation
in these features (Figures 15, 16) and geographical variation in
overall size (Anonymous 1975). For example, eight Tursiops
brain weights summarized by Gihr and Pilleri (1969) averaged

734

PERRIN ET AL.: GROWTH AND REPRODUCTION OF THE EASTERN SPINNER DOLPHIN

600

S? 400

(X.

200

Ave In at birth

1
1

Attainment of adult cranium size

1
1
1
1
1
1
1

Adult ave = 465 g

1 o- <f

(n=3l,sd=908)

t Ljjf^C- Y = 4 3I9X- 1015
♦ t<tf«*"1vr (n = 22,r=0730)

♦' Ave brain weight at birth = 231 g

«'

1
1

' 1

L ,111

1 — ill i i i

110 130

BODY LENGTH (cm)

150

170

190

FIGURE 13. — Scatterplot of brain weight on body length for 77 specimens ofStenella longirostris
from the eastern Pacific. The sample of fetuses and neonates ( <100 cm) includes 1 1 eastern
spinner dolphins, 9 whitebelly spinner dolphins, and 9 specimens (mostly fetuses) unidentified to
race. Triangles are fetuses, open circles are sexually immature postnatal specimens, shaded
circles are sexually adult specimens ( by criteria explained in text below). Length at attainment of
adult cranium size based on data in Perrin ( 1975b). The linear regression to estimate brain
weight at birth is based on 22 near-term fetuses and neonates 63 to 88 cm long.

_ 600

§ 400

Ave In at birth
I

Attainment of adult cranium size

i * ?

i , ■

~ ■ Y = I0 259X -535 3
.* '.. ' (n = l5, r = 0.820)

i Ave brain weight at birth = 311 g

?? <f

o*
d-d1

<f%

Adult ave - 726 g
9 (n = 40d"+429,sd=64l)

130 150

BODY LENGTH (cm)

170

FIGURE 14. — Scatterplot of brain weight on body length for 133 eastern spinner dolphins from the offshore
eastern tropical Pacific. Triangles are fetuses, open circles are sexually adult specimens. Linear regression
to estimate brain weight at birth based on near-term fetuses and neonates, 73 to 91 cm long. Criteria for
sexual maturity and basis for length at attainment of adult cranium size from Perrin (1975b).

1,475 g, compared with the 1,600 g reported by Lilly based on an
unknown sample size. Twelve nonneonatal brain weights (prob-
ably including some of juveniles) published by Morgane and
Jacobs ( 1972 ) ranged from 1 ,260 to 1 ,950 g and averaged 1 ,536 g.
Thus, deviation of the estimate of Sacher and Staffeldt for Tur-
siops (396 days, or 13.08 mo) from the more directly obtained
estimate of 12 mo ( Sergeant et al. 1973 ), an overestimate of about
10%, is of unknown significance and probably reflects statistical
error as well as possibly deductive error.

therefore applied the equation to brain data for the
spotted dolphin, S. attenuate (Figure 14 —
neonatal brain weight = 3 1 1 g, adult brain weight
= 726 g). The estimate of gestation time obtained
is 304 days, or 10.03 mo, as compared with 11.5 mo
(rounded off) estimated by a more direct method

735

(Perrin et al. 1976). If it be assumed that some
factor in delphinid growth is unaccounted for in
the Sacher-Staffeldt model and that gestation
time for S. longirostris is underestimated to a
similar degree (11.5 mo minus 10.0 mo/ 11. 5 mo, or
13%), an adjusted Sacher-Staffeldt estimate of
10.54 mo is obtained.

The estimate based on length at birth ( 10.74 mo)
and the adjusted Sacher-Staffeldt estimate (10.54
mo) are close to each other, and a rounded off aver-
age of the two estimates, 10.6 mo, is used below in
the analyses of reproduction. Making the assump-
tion that fetal growth follows a pattern similar to
that in S. attenuata, i.e., that t0 in Laws' fetal
growth equation L = a(t - t0) is approximately the
same proportion of gestation time as in S. at-
tenuata, or 0.135 tg (Perrin et al. 1976), a fetal
growth curve can be estimated (Figure 15). The
slope of the linear portion of the curve is 8.367
cm/mo, as compared with 8.283 cm/mo estimated
for S. attenuata (Perrin et al. 1976).

Postnatal Growth

We found it impossible to estimate postnatal
growth rates by the usual method of following the
seasonal progression of length modes, for the
reasons discussed above. We deduced an estimate
of growth rate during the first 10 to 11 mo by
application of the equation, log Y = 0.99 \ogX -
1.33, expressing an inferred relationship in
toothed cetaceans between length at birth (X
above) and the difference (Y above) between the
growth rates during the linear phases of fetal and
early postnatal growth (Perrin et al. 1976). The
predicted difference based on length at birth of 77
cm is 3.60 cm/mo. Subtraction of this from the

80 -_ _ Average Jength_at birUi

FISHERY BULLETIN: VOL. 75. NO. 4

fetal linear growth (estimated above) of 8.37
cm/mo yields an estimate of average growth rate
during the first 10 to 11 mo after birth of 4.77
cm/mo. If this is taken as an estimate of average
growth rate during the first year, predicted length
at 1 yr is 134 cm. This method overestimates
length at 1 yr to some unknown, but slight extent,
as growth is only approximately linear in the first
year.

We examined the relationship between length
and number of postnatal dentinal growth layers in
the teeth for 183 males and 250 females (Figure
16). The occurrence in the samples of length-layer
data for relatively more females than males with
more than about 12 layers is accounted for by the
fact that the sample of males selected for tooth-
sectioning was stratified entirely by length,
whereas the sample of females was stratified by
length in juveniles and by number of ovarian cor-
pora in adults. All females with more than 10
ovarian corpora were included in the sample, in
addition to randomly selected, corpora-stratified
subsamples of females with <10 corpora.

We fit growth curves to the data (to single-layer
incremental means), using a two-cycle version of
the Laird growth model (see Perrin et al. 1976 for
discussion of the model). Juvenile males and
females were considered jointly. The fit was forced
through the origin (zero growth layers, and esti-
mated length at birth of 77 cm), and asymptotic
length (La,) was estimated as the average length of
animals with 13 or more layers (Loo for 12 males =
179.46 cm and for 60 females = 170.91 cm), fixing
the upper ends of the two curves of the second
cycle. The simultaneous iterative fitting proce-
dure arrived at 4.111 growth layers (rounded off to
4 below) as the age at which convergence of the
three curves (estimated onset of a secondary
growth spurt) yields the best fit (Figure 16). Esti-
mated length at this age is 156.85 cm. The Laird/
Gompertz model (Laird 1969) is

L(t) = L exp \±\ l-exp(

""'HI

FIGURE 15. — Estimated fetal growth curve for the eastern spin-
ner dolphin.

736

where L = length in centimeters
t = age

L = length at age zero

a = specific rate of exponential growth
a = rate of decay of exponential growth.

A form of the model generalized to the present
case of more than one cycle is

PERRIN ET AL.: GROWTH AND REPRODUCTION OF THE EASTERN SPINNER DOLPHIN

200 1-

o o o

19 20 21 22

GROWTH LAYERS (no.)

200

I
I-
C3

Q
O
00

• °^&1°

O O

OOP

o o o o

_ l*' o • _ a t

o o

-O— o-

OD CD

. °e"°o° ° o ° ; ° o °* °° ° ° °o °

% °o o 8 » 8 °

FEMALES

AVERAGE LENGTH AT BIRTH

GROWTH LAYERS (no)

FIGURE 16.— Scatterplot of body length on number of postnatal dentinal growth layers in 183 male ia> and 250 female (b) eastern
spinner dolphins. Circled dots are means for 0-1 layer, 1-2 layers, for 2-layer increments thereafter until 12 layers in males and 16 in
females and for ^12 layers and a 16 layers, respectively. The line is a two-cycle Laird fit to single-layer incremental means ( see text i.

737

L(0=L'exp K [l-exp(-a(*-0)]}

where L' = length (centimeters) at start of cycle
V = age (growth layers) at start of cycle.

The growth equation for juveniles of <4 growth
layers is

L = 77 exp Q^Qg [l - exp(-0.90980

The growth equation for males of >4 growth
layers is

FISHERY BULLETIN: VOL. 75, NO. 4

below in the various hypotheses of rate of accumu-
lation of layers.

It appears that, effectively, in terms of the data
yielded by the tooth readings, 1.5 layers are laid
down in the first year. One possible explanation
alternative to that of actual deposition of 1.5
layers/yr is that a single layer is laid down in the
first year, but that in some individuals ( about half)
there is a strongly developed subsidiary line
within the layer that makes the single layer ap-
pear like two layers, yielding an average of 1.5
layers. This explanation seems unlikely, however,
in view of the data on thickness of the first layer.

L = 156.85 exp

0.0507
0.3765

l-exp(-0.3765(f-4.11))

and for females

L = 156.85 exp yffff f1 " exP(-°-6354^ - 4-n))

The fits of the model to both males and females is
excellent, albeit slightly better for the females
about the point of convergence of the two curves
than for males.

The equations rearranged and reduced for es-
timating age from length are

6 and 9 < 157 cm

t = -1.099 ln(6.960 - 1.372 InL)

d>157cm

t = 4.113 - 2.656 ln(38.540 - 7.426 InL)

9>157cm

t = 4.113

1.574 ln(59.871 - 11.645 InL).

Note: These equations should not be used to esti-
mate age from actual length data except for
grouped samples of smaller animals (about 165 cm
or less in females and 170 cm in males), for which
growth rate is still large compared with individual
variation in length.

Estimated age in growth layers at 134 cm, the
predicted length at 1 yr derived above from ex-
trapolative comparison with other delphinids, is
1.57 layers. Since, as discussed above, the esti-
mate of 134 cm is likely to be a slight overestimate
due to some nonlinearity of growth during the first
year, the estimate of 1.57 layers is rounded down
(to the nearest half layer) to 1.5 layers for use

738

The "subsidiary line" hypothesis would predict a
subsidiary inflection or plateau in the cumulative
percent of first layers in relation to thickness, and
such is not apparent (Figure 4).

We found no correlation between thickness of
the innermost growth layer and month of capture
(Table 3). It is apparent from the data that the
layers are formed rapidly (very few relatively thin
innermost layers are seen) and probably through-
out the year in the population.

With no basis for direct calibration, we provi-
sionally use three alternative hypotheses of rate of
layer deposition (similar to those put forth for the
spotted dolphin, S. attenuata — Perrin et al. 1976)
in the age-based analyses below, namely:

I. One and one-half layers per year, or

TABLE 3. — Thickness of innermost growth layer in teeth of 331
eastern spinner dolphins, with 3-12 layers, by month of capture.

Thickness of innermost layer ■*■
thickness of next youngest layer

Sample size

Average

Minimum

Maximum

Month

(no.)

(%)

Jan.

90.1

100

Feb.

107

83.3

100

Mar.

88.3

100

Apr.

81.1

100

May

89.9

100

Aug.

98.0

100

Oct.

71.1

100

Nov.

83.6

100

Dec.

94.0

PERRIN ET AL.: GROWTH AND REPRODUCTION OF THE EASTERN SPINNER DOLPHIN

II. One and one-half layers in the first year
and one per year thereafter, or

III. One and one-half layers per year until pu-
berty (at about nine layers in males and five
to six layers in females) and one per year
thereafter.

There is a rapidly increasing body of evidence
(Perrin et al. 1976; Best 1976) that most del-
phinids accumulate growth layers at the rate of
1/yr, making Hypothesis II the most likely true of
the three, but some uncertainty still exists, espe-
cially for tropical forms. We therefore express the
conclusions of all age-based analyses below in
terms of the three hypotheses. Other, more com-
plex hypotheses can be suggested, but these three
in our view probably include the truth.

Reproduction

The Male

Spermatogenesis is histologically evident in
50% of (right) testes weighing 94 g or more (weight
of epididymis included) (Figure 17). A perhaps
better criterion of sexual maturity is presence of
sperm in the epididymis (Figure 18). Combined
testis-epididymis weight at which half the males
possess "some" or "copious" sperm in the epididy-
mis is approximately 150 g. Another epididymal
criterion can be defined, namely, the testis-
epididymis weight above which the proportion of
males having "copious" sperm in the epididymis
does not increase, in this case above 50% at about
400 g. The three testis-epididymis weight criteria
of 94 g (50% spermatogenic), 150 g (50% with

?. 100

I- 80

£ 60

100

40 -

o
o

C/5

y\\z\

•

(49, from
300-747

(3D

•

(15)

— Y=06I66 X - 8 II
(n = 6, r = 0977)

(18) y

• yS

' (18)

S Y50%

= 94q

(791129)/

>200

20 40 80 120 160

WEIGHT OF TESTIS + EPIDIDYMIS (g)

200

FIGURE 17. — Linear regression analysis of relationship between
proportion of males spermatogenic and testis-epididymis weight
in the eastern spinner dolphin. Sample sizes in parentheses.

100 200 300 400 500 600

WEIGHT OF TESTIS + EPIDIDYMIS (a)

700

FIGURE 18. — Presence of sperm in epididymis in relation to
testis-epididymis weight in the eastern spinner dolphin. Sample
sizes in parentheses.

sperm in epididymis), and 400 g (asymptotic
weight with respect to proportion with copious
sperm) are considered below in relation to body
length and age (in dentinal growth layers).

Testis-epididymis weight on the average in-
creases precipitously with body length between
160 and 170 cm (Figure 19), but is only weakly
correlated with body length beyond 175 cm. Males
of any length above 160 cm can be mature or im-
mature under each of the three criteria defined
above. The proportion of males mature under the
three criteria stabilizes at about 170 to 175, 175 to
180, and 180 to 185 cm body length, respectively
(Figure 20). The average length of adult males
under the three criteria ranges from 174 to 176 cm
(Table 4).

■5 600

400

-400? -

-ISO?

- 94, -

140 150 160 170
BODY LENGTH (cm)

i_± i

ieo

FIGURE 19.— Relationship between testis-epididymis weight
and body length in the eastern spinner dolphin. Circled dots are
sample means. Vertical bars are ranges. Sample sizes in
parentheses.

739

FISHERY BULLETIN: VOL. 75, NO. 4

100 T (51) (83) (89) (101) (134) (175) (80)

(37)

155

165 170 175 180

BODY LENGTH (cm)

185

195

FIGURE 20. — Proportion of males sexually mature in relation to
body length in the eastern spinner dolphin under three criteria of
testis-epididymis weight. Sample sizes in parentheses.

TABLE 4: — Body length of adult male eastern spinner dolphins
under three criteria of sexual maturity.

Weight of
testis and
epididymis

(g)

Sample
size
(no.)

Body length (cm)

Minimum

Maximum

Average

<94
&94

3150
3400

594

356

230

108
160
160
162

192
195
195
190

176.0
175.8
174.1

5.99
6.06
5.79

Testis-epididymis weight is more closely corre-
lated with age (in dentinal growth layers) than
with body length (Figure 21). The 94-g level is
reached on the average at about 9 growth layers
and attained by all males with more than 12
layers. The 150-g level is reached at about 10
layers on the average and by all males at about 13
layers. The 400-g level is reached on the average
at about 12 layers, but the oldest male examined
(16.5 layers) had a testis-epididymis weight of
only 333 g. Estimated average age in years at
sexual maturity under the three criteria and
under the three layer/year hypotheses ranges
from 6.0 to 11.5 yr (Table 5), with the most likely
estimates (Hypothesis II) 8.5 to 11.5 yr.

The question of age at attainment of social
maturity (sense of Best 1969) in the spinner dol-
phin must await studies of social structure and
breeding patterns. Other (larger) odontocetes,
such as the sperm whale, Physeter catodon, and
the long-finned pilot whale, Globicephala melae-
na, are known or thought to be polygynous, to
varying degrees, but the social structure of the
spinner dolphin is as yet unknown.

No systematic seasonal variation in testis
weight or condition was detected, although the
heavy bias in seasonal coverage of the sample pre-
cludes an adequate evaluation of this factor.

740

/ou

600

500

• •

400

300

200

•

100

• • % . .

— - •*•** »••• -•-

^. ,

. — '•

;■ ~- • ■

6 8 10 12 14

DENTINAL GROWTH LAYERS (no)

18 20

FIGURE 21. — Scatterplot of testis-epididymis weight on age (in
dentinal growth layers) for 106 eastern spinner dolphins.

TABLE 5. — Estimated average age in years at attainment of
sexual maturity in male eastern spinner dolphins under three
criteria of maturity and three growth layer hypotheses.
[See text for definition.]

Testis-epididymis
criterion

Age (years) under growth layer hypotheses

(9)

II III

94
150
400

6.0
6.7
8.0

8.5 6.0

9.5 7.0

11.5 9.0

The Female

ATTAINMENT OF SEXUAL MATURITY.—
The smallest sexually mature female in the pre-
sent sample was 152 cm long. The largest imma-
ture female was 182 cm long. One estimate of
average length at attainment of sexual maturity
is the length at which 50% of the females show
evidence of having ovulated, i.e. possess ovaries
with one or more scars (corpus luteum or corpus
albicans). This length in the present sample of
eastern spinner dolphins is estimated at 164.1 cm
(Figure 22).

The sigmoid curve in Figure 22 is slightly
asymmetrical, that is to say, there are more imma-
ture animals (91) above the 50%-mature length of
164.1 cm than there are mature animals below it
(62). At 165 cm, the numbers are 80 and 77, respec-
tively. This length, 165 cm, is used below to clas-
sify as sexually mature or immature specimens for
which ovarian data are lacking. The predicted
number of growth zones (from the growth equa-
tion) at this length is 5.5.

Average age at attainment of sexual maturity
can also be estimated directly from the smaller
sample of females for which teeth were sectioned
(n = 247). This analysis (Figure 23) estimates

PERRIN ET AL.: GROWTH AND REPRODUCTION OF THE EASTERN SPINNER DOLPHIN

100 r es) • ■" ioo

150 160 170

BODY LENGTH (cm)

FIGURE 22.— Estimation of body length at which 50% of female
eastern spinner dolphins show ovarian evidence of sexual matu-
rity (one or more scars). Fit to central portion of curve (solid line)
is linear regression. Dashed portions of curve fitted by eye. Sam-
ple sizes in parentheses.

average age at attainment of maturity at about 5.4
growth layers, in close agreement with the esti-
mate derived from the age/length equation. A
rounded-off average of 5.5 layers is used below.
Average age in years at attainment of maturity
under the three hypotheses of layer deposition
rate are 3.7, 5.0, and 3.7 yr, respectively, with the
second estimate being most probably correct.

Sexually adult females in the sample ranged
from 152 to 187 cm and averaged 171.2 cm in
length (Figure 24).

DISTRIBUTION OF CORPORA TO LEFT
AND RIGHT OVARIES.— As in all other odonto-
cetes so far studied, the left ovary predominates in
ovulation. As in the case of S. attenuata, the dis-
tribution between left and right side (Table 6) can
be accounted for by assuming that about 90 to 95%
of the females ovulate the first time from the left
ovary, and the remainder from the right, and that

6 7 8 9

AGE (growth layers)

FIGURE 23. — Relationship between proportion of females sexu-
ally mature and age, in dentinal growth layers, in the eastern
spinner dolphin. Fit is by eye.

200 1-

EASTERN
FEMALES
Ave. = 171.2cm
s.d. = 6.08cm
n = 560

145

155 165 175 185

BODY LENGTH (cm)

FIGURE 24.— Length-frequency distribution of 560 sexually
adult (possessing at least one ovarian corpus) female eastern
spinner dolphins.

741

FISHERY BULLETIN: VOL. 75, NO. 4

TABLE 6. — Location of corpora (corpora lutea and corpora al-
bicantia) in ovaries of 556 eastern spinner dolphins.

Sample
size
(no.)

Location of corpora

Corpora
(no.)

Left ovary
only

(%)

Right ovary
only
(%)

Both
ovaries

(%)

92.7

7.3

—

78.4

9.8

11.8

92.0

2.0

6.0

90.7

2.3

7.0

91.1

3.6

5.3

86.8

11.3

1.9

85.0

15.0

0.0

82.1

10.3

7.6

80.8

11.5

7.7

10-11

73.0

19.0

8.0

12-15

41.8

1.8

56.4

16-19

23.1

0.0

76.9

20-26

16.7

0.0

83.3

succeeding ovulations are from the same ovary
(left or right) about 90 to 95% of the time. When
about 10 corpora have accumulated, emphasis
shifts sharply to the opposite ovary.

OVULATION RATE.— The number of ovarian
corpora, including corpora lutea, ranged from 1 to
26 in 555 sexually adult females. The frequency
distribution (Figure 25) is very similar in shape to
that for S. attenuata (Perrin et al. 1976) with high-
est frequencies at 5 to 7 corpora and a sharp falloff
after about 10 corpora.

Size-frequency distribution of the various types
of corpora albicantia among the corpora-type
categories relative to total number of corpora were
the same in this sample as in the sample of S.
attenuata previously studied (Perrin et al. 1976)

60 r

(n = 555)

10 15 20 25 30

CORPORA IN OVARIES (no.)

FIGURE 25. — Frequency distribution of ovarian corpora count in
555 female eastern spinner dolphins.

leading us to believe that, for this species also,
corpora of ovulation persist throughout the life of
the animal, accumulating at Type 3.

Scatter in a plot of number of corpora on age in
growth layers is wide (Figure 26) but not as great
as encountered in a study of S. attenuata (Perrin et
al. 1976). Factors producing the scatter are 1)
error in reading growth layers, 2) individual vari-
ation in ovulation rate, and 3) change in ovulation
rate during the reproductive span. The teeth of S.
longirostris in this study had more clearly defined,
more easily readable growth layers than did those
of S. attenuata in the previous study, and this
probably accounts for the relatively less scatter for
the former, although less influence by either or
both of the other two factors cannot be ruled out.

Calculation of average ovulation rates from the
data in Figure 26 must take into account indi-
vidual variation in age at first ovulation. The data
were grouped into 2-layer intervals (all those with
12 or more layers were included in a single final
increment), and average reproductive age by in-
terval P calculated as

p
2

aibi

A =

£ 16

<
a.

o
a.

<
or
<
>
o

D|«'f| "I

10 II

17 18 19 20 21 22

GROWTH LAYERS (no.)

FIGURE 26. — Scatterplot of number of ovarian corpora on age, in
dentinal growth layers, in 1,972 female eastern spinner dol-
phins.

742

PERRIN ET AL.: GROWTH AND REPRODUCTION OF THE EASTERN SPINNER DOLPHIN

where a, = percent maturing in zth interval (per-
cent maturing in i minus percent
maturing in i - 1)

b, = average reproductive age in interval P

of females maturing in i

c, = percent mature in interval P.

Average reproductive age in the ith interval of
females maturing in i was set at 0.50 layer. A plot
of number of ovulations on average reproductive
age (Figure 27) shows linear increase, with a slope
of unity (one ovulation per layer), in number of
corpora until about 10 corpora have been accumu-
lated at about 10 layers of reproductive age (15.5
layers total age on the average) when the ovula-
tion rate apparently drops sharply. This is very
different from the results obtained in a similar
best-fit analysis for S. attenuata (Perrin et al.
1976), which indicated average ovulation rates of
about four during the first layer, two during the
second, and about one per layer thereafter. A
power fit to the data for S. longirostris (Figure 27)
shows much less variation in ovulation rate with
age. It appears that in the presently sampled popu-
lation of S. longirostris there is less multiple infer-
tile ovulation in very young mature females than
in the studied population of S. attenuata. This may
be an inherent difference or may reflect differen-
tial status of the two populations with respect to
exploitation. For example, females could on the
average become sexually mature at an earlier age

6 8 10 12

REPRODUCTIVE AGE (growth layers)

FIGURE 27.— Scatterplot of 2-layer means (last mean is for 12-16
layers) of average number of ovulations on average reproductive
age in growth layers in the eastern spinner dolphin. Regression
line is power fit. One-ovulation-per-layer line added. Sample
sizes in parentheses.

in an exploited population but be less fertile, in
terms of pregnancies per ovulation, than had they
become mature at greater age. Estimated ovula-
tion rates were higher in the studied eastern
Pacific population of S. attenuata than in a rela-
tively unexploited population of the same species
in Japanese waters (Perrin et at. 1976).

POSTREPRODUCTIVE FEMALES.— Four
adult females of 536 examined (=1.0%) showed
clear evidence of being postreproductive, or
"senile," by criteria of 1) being inactive, or "rest-
ing" (neither pregnant nor lactating); 2) having
high corpora count (2=10); 3) having small, with-
ered ovaries (weighing <3.5 g); 4) having no
developing follicles (largest follicle <1 mm in
diameter); and 5) having no Type 1 or 2 corpora
albicantia (terminology of Perrin et al. 1976), in-
dicating recent ovarian activity (Figure 28).

THE CALVING CYCLE AND PREGNANCY

RATE. — The calving cycle, for purposes of analyz-
ing the types of field data available, can be divided
into three phases: 1) pregnancy, 2) lactation, and
3) "resting" — a catch-all "phase" for animals
neither pregnant nor lactating, which includes

-I
o

UJ 4

o
or
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3 -

2 -

' ®

® ®

® ® «® ®

®
® ©

©@°

®%>

-v*

J. *■

1 / .

iii;

0 12 3 4 5 6 8

OVARIES WEIGHT (g)

FIGURE 28. — Scatterplot of diameter of largest follicle on com-
bined weight of ovaries for 73 adult female eastern spinner
dolphins classified as "resting" (not pregnant or lactating).
Specimens with corpora lutea or cystic follicles not included.
Number in circle is total number of corpora in ovaries (including
corpus luteum). Double circles are specimens with no Types 1 or
2 corpora albicantia indicating recent ovarian activity. Four
postreproductive females indicated with arrows.

743

FISHERY BULLETIN: VOL. 75, NO. 4

females truly resting, i.e., not ovulating because of
being between cycles, those which have just ovu-
lated but did not get pregnant, some with ex-
tremely small embryos missed in dissections,
those which have recently aborted, and those
which have prematurely terminated lactation due
to death of the suckling calf.

The gestation phase of the cycle was estimated
above, at 10.6 mo. We estimated average length of
lactation by two methods; 1) by assuming that the
proportion of a sample of mature females in a
particular reproductive phase is directly propor-
tional to the relative length of that phase in the
overall cycle, i.e., that the samples are not biased
with regard to reproductive phase (the length of
the "resting" phase was also estimated this way);
and 2) by assuming that a suckling calf exists for
each lactating female, and the samples are un-
biased with respect to suckling calves and lactat-
ing females, under which assumptions the length
at which the cumulative frequency of calves in a
sample equals the number of lactating females
should be the average length (and, from the
growth equation, age) at weaning. The first esti-
mate was based on data for 536 adult females
collected 1971-75, classified as pregnant, lacta-
ting, pregnant and lactating, "resting," or post-
reproductive (Table 7). The resting females were
further subdivided into those with and without a
corpus luteum. As discussed above, some propor-
tion of those with a corpus luteum can be assumed
to represent females not truly resting (with a cor-
pus luteum of infertile ovulation). Only three
females were simultaneously pregnant and lactat-
ing (1.44% of lactating females).

Subtraction of the postreproductive females and
allocation of the females both pregnant and lacta-
ting to both of the two categories provides esti-
mates of the proportions of the reproductive
females in the three phases of the cycle (Figure 29)
and of the relative lengths of the phases. Estima-
ted average length of the phases and the total cycle
can then be calculated for each 1-yr sample and for
the pooled samples, using the estimated gestation

CE
O
Q.

1971

1972

1973

1974

1975

71-75
pooled

(39)

(46)

(140)

(158)

(149)

(532)

FIGURE 29. — Proportions of 532 adult reproductive female east-
ern spinner dolphins in pregnant, lactating, and "resting" (not
pregnant or lactating) phases of cycle. Based on Table 4. Females
both lactating and pregnant alloted to both phases. Postre-
productive females excluded.

period of 10.6 mo (Method 1 in Table 8). The esti-
mates of average length of lactation thus derived
range from 13.1 to 29.7 mo (the possible causes of
this wide year-to-year variation in phase struc-
ture of the samples are discussed below in Gross
Annual Reproduction), with a pooled average of
17.5 mo.

The second method of estimating length of lac-
tation, the "cumulative calf length/lactating
females" method yielded estimates for six
single-month samples ranging from 7.7 to 16.0 mo
and for single-year samples from 9.4 59 10.6 mo
(Method 2 in Table 8). The pooled estimate for
1973-75 is 10.1 mo. The three yearly estimates
are consistent with each other and sharply lower
than the estimates yielded by the "proportion-in-
phase" method above (compare in Table 9). The
first method could be invalid and cause disparate
estimates if 1) lactating females (and their nurs-
ing calves) were overrepresented in the samples,
or conversely, 2) either (or both) pregnant or "rest-
ing" females were underrepresented. This situa-
tion could obtain if lactating females and their

TABLE 7. — Reproductive condition of 536 adult female eastern spinner dolphins collected 1971-75.

1971

1972

1973

1974

1975 1971-75 pooled

Condition

No.

°o

No.

33.3

30.4

20.6

37.3

32.9

165

30.8

59.0

43.5

58.9

46.6

49.7

275

51.3

0.7

1.2

0.7

8.7

2.1

3.1

2.0

7.7

17.4

17.0

9.9

14.8

13.6

0.7

1.9

0.7

100.0

141

100.0

161

100.0

149

100.0

536

100.0

Pregnant only

Lactating only

Pregnant and lactating

"Resting"
with corpus luteum
without corpus luteum

Postreproductive
Total

744

PERRIN ET AL.: GROWTH AND REPRODUCTION OF THE EASTERN SPINNER DOLPHIN

TABLE 8. — Estimated lengths of postreproductive phases, under two methods of es-
timating length of lactation, of the eastern spinner dolphin based on single-year sam-
ples, 1971-75, and on pooled samples for all years, with estimates of pregnancy rate and
calving interval based on lactation estimate 1.

Item

1971

1972

1973

1974

1975

Pooled

Sample size (no.)

140

158

149

532

Pregnancy (months)

10.6

Lactation (months):

Method 1

18.8

15.2

29.7

13.1

15.9

17.5

Method 2

(Hyp. II)

—

10.6

9.4

10.2

10.1 (1973-75)

"Resting" (Method 1)

2.6

9 1

9.5

3.6

5.3

5.5

Sum of phases:

Method 1

(months)

32.0

34.9

49.8

27.4

31.8

33.6

(years)

2.66

2.91

4.15

2.28

2.65

2.80

Method 2

(months)

—

26.7

25.5

26.3

26.2

(years)

—

2.23

2.13

2.19

2.18

Annual pregnancy rate (APR):

Method 1

0.375

0.344

0.243

0.444

0.380

0.360

Method 2

—

0.450

0.474

0.459

0.461

Calving Interval (1/APR):

Method 1

(years)

2.66

2.91

4.12

2.25

2.63

2.78

(months)

32.0

34.9

49.5

27.0

31.6

33.4

Method 2

(years)

—

2.22

2.11

2.18

2.17

(months)

—

26.6

25.3

26.2

26.1

TABLE 9.— Estimates of length of lactation in the eastern spinner dolphin based on the
"cumulative calf length/lactating females" method (see text), for 6 single-month samples
and for 1973-75 by year and pooled.

Lactatlng females1
(no.)

Length at which

cumulative number

of calves = number

of lactating females

(cm)

Length of lactation

(months, under

Hypotheses)

Sample

Layers

II and III

Feb. 1973

139

1.83

14.6

16.0

Mar. 1973

133

1.52

12.2

Jan. 1974

124

1.16

9.3

Feb. 1974

118

0.97

7.7

Jan. 1975

132

1.48

9.4

Feb. 1975

120

1.03

8.2

Year:

1973

128.5

1.33

10.6

1974

124.5

1.18

9.4

1975

127.0

1.27

10.2

Pooled

260

126.7

1.26

10.1

1 1ncludes mature females (5=165 cm) without lactation data prorated to lactating and nonlactatmg based on
proportions in sample with lactation data.

accompanying calves are more likely to be cap-
tured and killed in the net because of limitations
imposed on endurance of the mother by that of the
calf, certainly lower than adult endurance. The
second method could yield erroneous estimates if
1) nursing calves were overrepresented in the
samples, or, conversely, 2) lactating females were
underrepresented. Recent data for S. attenuata (J.
E. Powers pers. commun.) indicate that small
calves are probably overrepresented in small
single-set samples of that species. This may be
caused by the above-mentioned lesser stamina of
calves in the energetically stressful purse seine
chase, capture, and release sequence. The lesser
year-to-year variation in the estimates yielded by
Method 2 also supports the idea that these may be

better estimates. If neonates are overrepresented
in the samples, however, then the percent preg-
nant must be underestimated to some unknown,
but small, degree. In view of these considerations,
both the proportion-in-phase estimate and the
cumulative calf length/lactating female estimate
are used below as alternatives in estimating preg-
nancy rate, calving interval, and gross annual re-
production, and we conclude that the true length
of lactation in an unperturbed birth-to-weaning
period can be assumed to lie somewhere between
the estimates yielded by the two methods.

Annual pregnancy rate by Method 1 was calcu-
lated by division of the proportion pregnant (Fig-
ure 29) by the length of gestation 1 0.875 yr). The
reciprocal of annual pregnancy rate is the esti-

745

FISHERY BULLETIN: VOL. 75, NO. 4

mate of average calving interval. For the Method 2
estimates, calving interval was calculated by
summing the phases, taking into consideration
overlapping cycles by adjusting the effective
length of lactation downward by a factor equal to
the percentage of lactating females also pregnant.
Lacking an independent estimate of the length of
the "resting" phase, the Method 1 estimate for
1973-75 was used as a reasonable approximation
in the Method 2 calculations of length of cycle and
calving interval.

CHANGES IN REPRODUCTIVE RATES
WITH AGE. — Pregnancy rate in the sample de-
creases with age after about 12 layers (8.0, 11.5, or
10.2 yr, depending upon whether layer Hypothesis
I, II, or III is applied, respectively), while lactation
rate rises (Figure 30). Assuming that the samples
are representative of the population, this may
mean that 1) pregnancy rate decreases with age in
the individual, or 2) that older females belong to
older cohorts in which reproductive rates have
been lower than in younger cohorts since recruit-
ment to the breeding population. The former
seems most likely; it would appear that older
females have fewer calves and nurse them longer.
The same result was obtained for S. attenuata in
the eastern Pacific (Perrin et al. 1976).

Sex Ratios

Sex ratios are at or very near parity at birth and
overall in the samples (Table 10), but there were
slightly more females than males in adults in the
samples for each of the 3 yr 1973-75, a result
consistent with that encountered in S. attenuata
(Perrin et al. 1976) but less pronounced.

9 10 II 12 13 14 15 16 17 22
GROWTH LAYERS (no.)

FIGURE 30. — Change in reproductive rates with age in the east-
ern spinner dolphin. Sample sizes in parentheses.

Gross Annual Reproduction

Estimates of gross annual reproductive rates
can be made based on 1973-75 samples, the 3 yr
for which the samples are large and nonselected
with respect to age and sex structures (Table 11).
It must be noted that if, as discussed above, small
calves are overrepresented in small samples
(which make up most of the aggregate sample),
then the proportion of total females which are
reproductive and pregnancy rate (for Method 1)
are underestimated and the proportion of total
sample female is overestimated, all to an un-
known, but probably small, degree. Standard er-

TABLE 10. — Sex ratios in 126 fetuses and 2,261 neonatal-to-adult eastern spinner dolphins. Fetal samples

limited to fetuses longer than 15 cm.

Length
(cm)

Sample size
(no.)

Average

length

(cm)

Females

Males

Sex ratio

Stage

No.

(M^F)

Fetuses

>15

126

49.0

51.6

48.4

0.94

Neonates to adults

70-129

294

116.0

140

47.6

154

52.4

1.10

130-149

269

141.2

132

49.1

137

50.9

1.04

150-159

362

154.9

186

51.4

176

48.6

0.95

>160

(adult size)
1973

408

171.2

207

50.7

201

49.3

0.97

1974

439

171.3

226

51.5

213

48.5

0.94

1975

483

172.4

254

52.6

229

47.4

090

1973-75

pooled

1,330

171.7

687

51.7

643

48.3

0.94

Total:1

1973

688

—

342

49.7

346

50.3

1.01

1974

797

—

395

49.6

402

50.4

1.02

1975

776

—

411

53.0

365

47.0

0.89

1973-75

pooled

2,261

—

1,148

50.8

1,113

49.2

0.97

'Includes six specimens for which length data not available.

746

PERRIN ET AL.: GROWTH AND REPRODUCTION OF THE EASTERN SPINNER DOLPHIN

TABLE 11.— Calculation of estimates of gross annual reproductive rate of the eastern spinner dolphin, 1973-75.
Standard error follows estimate (see text). Sample sizes in parentheses.

B
Proportion
of females

Annual pregnancy rate

A ' B > C
Gross annual reproductive rate

Year

female

reproductive

Method 1

Method 2

Method 1

Method ?

1973

0.497 ±0.01 9

0.443 ±0.027

0.243 ±0.036

0.450 ±0.042

0.054 ±0.009

0.099 ±0 011

(690)

(343)

(140)

(690)

1974

0.496±0.018

0.438 ±0.025

0.444 ±0.040

0.474 ±0.042

0.096 ±0.010

0 103-0.011

(797)

(391)

(158)

(797)

(797,

1975

0.530^0.018

0.432 ±0.024

0.380 ±0.040

0.459 ±0.041

0087 ±0.010

0 105-0011

(776)

(410)

(149)

(776)

(776,

1973-75

0.508 ±0.011

0.437 ±0.01 5

0.360 ±0.028

0.461 ±0.024

0.080 ±0.006

0.1 02 ±0.006

pooled

(2,262)

(1,144)

(447)

(2,262)

rors (SE) are attached to the various estimates
where sample size 3^100, under the assumption
that the binomial distribution tends to normality
in large samples (Bailey 1959), allowing calcula-
tion of SE as:

SE = N/p(l-p)/n.

Although gross annual reproductive rate as cal-
culated in Table 11 is a product of three estimates,
it can be calculated directly from the total sample
(number of females pregnant -J- total number of
males and females), allowing estimation of the
variance by the above method. The effect on the
variance by the constant used to adjust the preg-
nancy rate to an annual rate was ignored because
the constant (11.5 mo gestation -j- 12 mo, or 0.958)
is close to unity.

The only statistically significant differences
among the estimates year-to-year (at a = 0.05) are
between the Method 1 estimates for 1973 and 1974
of annual pregnancy rate and, as a result of that,
gross annual reproductive rate. This sharp and
real shift cannot be accounted for by a time-
sampling effect, because seasonal coverage in the
2 yr was approximately the same. Prompted by the
knowledge that areal variation may exist in the
timing of calving peaks and/or in the degree of
breeding synchrony (see Length of Gestation and
Fetal Growth), we divided the data for each of the
years into three geographical strata: an "inside"
sample, an "outside" sample, and a "southern
sample" (Figure 31). More of the 1973 sample was
taken from the outside area than from the inside
area (108 versus 28), and the reverse was true in
1974 (46 versus 106). The southern samples, 5 in
1973 and 14 in 1974, were too small for analysis.
Comparison of the distribution of reproductive
condition in inside and outside samples in 1973
and 1974, however, reveals very small areal dif-
ferences compared with those between years (Ta-
ble 12). It must be concluded that the sharp in-

1 35° 130' 125' 120' IIS* IIP' 105' 100' 95' 90' 65* 80*

Rt*i!iogig*do II

OUTSIDE

135* 130° 125* 120" 115° 110° 105* 100* 95' 90' 85* 60«

FIGURE 31.— Areas used to stratify 1973-74 samples of distribu-
tion of reproductive condition in female eastern spinner dol-
phins.

TABLE 12. — Distribution of reproductive
stratified samples of sexually adult female
phins in 1973 and 1974.

condition in area-
eastern spinner dol-

Inside

Outside

Year

(n = 134)

(n = 154)

(n = 28)

(n = 108)

1973

14.3°o pregnant

19.4% pregnant

57.1% lactating

61 1% lactating

{n = 136)

3.6% pregnant and

0.0% pregnant and

lactating

25.0% "resting '

18.5% "resting'

0.0% postreproductive

0 9% postreproductive

{n = 106)

(r? = 46)

1974

38.7% pregnant

39 1% pregnant

48.1% lactating

50.0% lactating

{n = 152)

0 0% pregnant and

4.3% pregnant and

lactating

10.4% resting

6 5% resting

2.8% postreproductive

0.0% postreproductive

crease in percent pregnant and decrease in percent
lactating from 1973 to 1974 is not a seasonal or
areal effect. Several other possible explanations
exist, to wit:

747

FISHERY BULLETIN: VOL. 75, NO. 4

1 ) The samples were biased with respect to repro-
ductive structure of the population, in one or
both years or differently in the 2 yr.

2) The change was a real and normal event,
perhaps reflecting differential breeding rates
in single-year cohorts (the data suggest about a
3-yr cycle — see below — and the 1974 rates
were similar to those for 1971).

3) An anomalous increase in pregnancy rate oc-
curred from 1973 to 1974, perhaps related to
exploitation in the tuna fishery or to natural
variation in the pelagic environment.

The balance of evidence discussed above favors
the first alternative, suggesting that the Method 2
estimates of gross annual reproduction are the
more accurate of the two alternative sets of esti-
mates.

DISCUSSION

Comparison with the Spotted Dolphin

The estimated gross reproductive rates (Method
1) for the eastern spinner dolphin are lower than
those estimated for the offshore spotted dolphin by
Perrinetal. (1976), 10 to 11%, as opposed to 14%.
Three major points of difference between the data
for the two species contribute to this disparity.

1) A higher proportion of the spotted dolphins
were females (55.1% as opposed to 50.8% in the
present 1973-75 sample of eastern spinner
dolphins).

2) The proportion of total females which were re-
productive was higher for the spotted dolphin
(55.7% as opposed to 43.7% for the eastern
spinner dolphin).

3) There is apparently much less overlapping of
reproductive cycles in the eastern spinner dol-
phin than in the spotted dolphin in the eastern
Pacific. Only 1.4% of lactating females
examined were simultaneously pregnant, as
opposed to 9.6% in the spotted dolphin, a seven-
fold difference. At least part of this difference
may be inherent in the species; the rate in the
unexploited western Pacific population of spot-
ted dolphin is 5.1%(Kasuya et al. 1974), still
nearly four times greater than in the eastern
spinner dolphin.

In summary, the data suggest that there is an
inherent difference in reproductive capability be-

tween the spotted and spinner dolphins, but that
part of the total difference in present reproductive
rate may be related to differential exploitation.
Gross annual reproductive rate in the unexploited
western Pacific population of S. attenuata is esti-
mated at 0.094 (calculated from data in Kasuya et
al. 1974—0.57 female x 0.61 mature x 0.27 an-
nual pregnancy rate = 0.094/yr), as opposed to
0.144 in the exploited eastern Pacific population of
the same species, a possible example of difference
in rate correlated with differential exploitation.
Whereas the western Pacific population is thought
to be virtually unexploited and at its original size,
the eastern Pacific population is estimated to be at
62% of its original, preexploitation size (midpoint
estimate).8

Comparison with Other Cetaceans

The estimates of gross annual reproductive rate
for the eastern spinner dolphin lie at the lower end

8Report of the Workshop on Stock Assessment of Porpoises
Involved in the Eastern Pacific Yellowfin Tuna Fishery. SWFC
Admin. Rep. LJ-76-29, Natl. Mar. Fish. Serv., NOAA, La Jolla,
Calif, 109 p. (Unpubl. rep.)

TABLE 13. — Estimated gross annual reproductive rate of the
eastern spinner dolphin compared with estimated rates for other
cetaceans. Data for S. attenuata from Perrin et al. (1976) for
eastern Pacific and Kasuya et al. (1974) for western Pacific; for S.
coeruleoalba from Kasuya (1972), for Delphinus from
Danilevskiy and Tyutyunnikov (1968); for Globicephala from
Sergeant (1962); for Delphinapterus from Sergeant (1973); and
for Eschrichtius from Rice and Wolman (1971). Common and
scientific names follow Subcommittee on Small Cetaceans, Sci-
entific Committee, IWC (Anonymous 1975); alternative common
name in parentheses.

Exploited

Gross annual

(now or

reproductive

Species and locality

in past)

rate

Eastern spinner dolphin

(porpoise), Stenella

0.08

longirostris subsp.

Yes

(pooled 1973-75)

Spotted dolphin (porpoise),

S. attenuata

Eastern Pacific

Yes

0.14

Western Pacific

0.09

Striped dolphin (streaker

porpoise), S. coeruleoalba.

in western Pacific

Yes

0.11

Common dolphin (whitebelly

porpoise), Delphinus

delphis, in Black Sea

Yes

0.14

Long-finned pilot whale (pot-

head whale), Globicephala

melaena, in western North

Atlantic

Yes

0.10 to 0.13

White whale (beluga), Delphi-

napterus leucas, in western

Hudson Bay

Yes

0.12

Gray whale, Eschrichtius ro-

bustus, in eastern North

Pacific

Yes

0.13

748

PERRIN ET AL.: GROWTH AND REPRODUCTION OF THE EASTERN SPINNER DOLPHIN

of the range of estimates for other cetaceans (Table
13), with only the estimate for 1974 included in the
range. The estimated rates for populations
thought to have declined due to exploitation {S.
attenuata in the eastern Pacific — Perrin et al.
1976; D. delphis in the Black Sea — Danilevskiy
and Tyutyunnikov 1968; and Eschrichtius — Rice
and Wolman 1971) are very close to each other, at
13 or 14%.

ACKNOWLEDGMENTS

This study would not have been possible without
the generous cooperation and assistance of the
owners, masters, and crews of the tuna seiners A.
K. Strom, Anna Marie, Anne M, Antonina C,
Aquarius, Bernadette, Bettie M, Blue Pacific, Bold
Contender, Bold Venture, Cabrillo, Captain Vin-
cent Gann, Carol Virginia (now Carol S), City of
San Diego, Commodore, Connie Jean, Conquest,
Constitution, Conte Bianco, Denise Marie, Diana
C, Eastern Pacific, Eileen M, Elizabeth Anne, Elsie
A, Enterprise, Finisterre, Frances Ann, Gemini,
Gina Karen, Independence, Jacqueline A, Jac-
queline Marie, Jeanette C, Jeanine, J. M. Mar-
tinac, John F. Kennedy, Katherine Lisa, Kathleen,
Kerri M, Larry Roe, Lois Seauer, Lucky Strike,
Marco Polo, Margaret L., Marietta, Mary An-
toinette, Mary Elizabeth, Mermaid, Missouri,
Nautilus, Pacific Queen, Pan Pacific, Polaris,
Proud Heritage, Queen Mary, Quo Vadis, Rosa
Oliva, San Juan, Santa Rosa, Saratoga, Sea
Preme, Sea Quest, Sea Royal, South Pacific,
Trinidad, Venturous, Voyager, Westport, and
Willa G.

Scientists and technicians (in addition to two of
the authors, Perrin and Holts) who collected data
and specimens aboard the vessels include G.
Ahern, R. E. Amick, G. M. Armstrong, S. F. Baril,
A. D. Bates, R. E. Bourke, C. E. Bowlby, D. A.
Bratten, R. L. Charter, J. M. Coe, R. W. Cunning-
ham, J. D. Dohrman, R. C. Dotson, T. M. Duffy, W.
E. Evans, C. M. Fedde, M. L. Fitzsimmons, W. C.
Flerx, T. J. Foreman, R. K. Fountain, G. L. Fried-
richsen, R. S. Garvie, J. M. Greene, J. A. Halas, D.
P. Hoffman, R. Hoffmaster, R. E. Hundt, M. J.
Jacobson, J. E. Jurkovich, J. LaGrange, J. F.
Lambert, J. S. Leatherwood, K. P. LeVeille, R. E.
Loghry, R. W. McLain, R. L. McNeely, C. W.
Oliver, R. J. Olson, C. J. Orange, D. J. Otis, C. B.
Peters, J. W. Ploeger, A. Poshkus, C. W. Potter, S.
H. Powers, F. M. Ralston, S. B. Reiley, C. J. Ryan,
0. Seth, K. D. Sexton, T. B. Shay, W. W. Steel, J. H.

Thompson, P. A. Thompson, G. M. Treinen, D.
Twohig, W. H. Tyndall, G. L. Ulrich, L. S. Wade,
W. A. Walker, J. A. Young, D. B. Zantiny, and J. A.
Zwack.

R. L. Brownell, Jr., G. D. Fitzgerald, D. W. Rice,
W. A. Walker, and D. W. Waller contributed un-
published data. J. M. Coe assisted extensively
with many phases of the data collection, handling
and processing. J. R. Zweifel, A. L. Coan, J. E.
Gilbert, T. D. Smith, and N.K. Wiley provided
advice and assistance in data processing and
analysis. F. G. Alverson of Living Marine Re-
sources, Inc., provided invaluable liaison with the
tuna fleet. I. Barrett, J. E. Powers, W. W. Fox, J. T.
Everett, D. W. K. Au, R. L. Brownell, Jr., J. M.
Coe, and D. W. Rice read the manuscript. We
thank these persons and others not mentioned for
their help.

LITERATURE CITED

ANONYMOUS.

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Montreal, April 1-11, 1974. In E. D. Mitchell (editor),
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875-1242. J. Fish. Res. Board Can. 32.

BAILEY, N. T. J.

1959. Statistical methods in biology. English Univ.
Press, Ltd., Lond., 200 p.
BEST, P. B.

1969. The sperm whale (Physeter catodon) off the west
coast of South Africa. 3. Reproduction in the male. S.
Afr. Div. Sea Fish., Invest. Rep. 72, 20 p.

1976. Tetracycline marking and the rate of growth layer
formation in the teeth of a dolphin (Lagenorhynchus
obscurus). S. Afr. J. Sci. 72:216-218.

CADENAT, J.. AND M. DOUTRE.

1959. Notes sur les Delphinides ouest-africans.V. Sur un

Prodelphinus a long bee capture au large des cotes du

Senegal Prodelphinus longirostris (Gray) 1828. Bull.

Inst. Fondam. Afr. Noire, Ser. A, Sci. Nat. 31:787-792.
DAILEY, M. D., AND W. F. PERRIN.

1973. Helminth parasites of porpoises of the genus

Stenella in the eastern tropical Pacific, with descriptions

of two new species: Mastigonema stenellae gen. et sp. n.

(Nematoda: Spiruroidea) andZatophotrema pacificum sp.

n. (Trematoda: Digenea). Fish. Bull., U.S. 71:455-471.
DANILEVSKIY, N. N., AND V. P. TYUTYUNNIKOV.

1968. Present state of Black Sea dolphin described. [In
Russ.] RybnXhoz. (Fisheries) 44(ll):25-27.

GIHR, M., AND G. PILLERI.

1969. Hirn-Korpergewichts-Beziehungen bei Cetaceen.
In G. Pilleri (editor), Investigations on Cetacea, Vol. 1, p.
109-126. Brain Anat. Inst.. Univ. Berne, Berne, Switz.

HARRISON, R. J., R. L. BROWNELL, JR.. AND R. C. BOICE.

1972. Reproduction and gonadal appearances in some
odontocetes. In R. J. Harrison (editor). Functional
anatomy of marine mammals, Vol. 1, p. 361-429.
Academic Press, Lond.

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HUGGETT, A. ST. G., AND W. F. WlDDAS.

1951. The relationship between mammalian foetal weight
and conception age. J. Physiol. (Lond.) 114:306-317.

KASUYA, T.

1972. Growth and reproduction of Stenella caeruleoalba
based on the age determination by means of dentinal
growth layers. Sci. Rep. Whales Res. Inst. 24:57-79.

KASUYA, T., N. MIYAZAKI, AND W. H. DAWBIN.

1974. Growth and reproduction of Stenella attenuata in the
Pacific coast of Japan. Sci. Rep. Whales Res. Inst.
26:157-226.

LAIRD, A. K.

1969. The dynamics of growth. Research/Development
Aug. 1969:28-31.

LAWS, R. M.

1959. The foetal growth rates of whales with special refer-
ence to the fin whale, Balaenoptera physalus Linn. Dis-
covery Rep. 29:281-308.

LAYNE, J. N.

1965. Observations on marine mammals in Florida
waters. Bull. Fla. State Mus. Biol. Sci. 9:131-181.
LILLY, J. C.

1967. The mind of the dolphin. A non-human intelli-
gence. Doubleday and Co., Inc., Garden City, N.Y., 310

P-
MORGANE, P. J., AND M. S. JACOBS.

1972. Comparative anatomy of the cetacean nervous sys-
tem. In R. J. Harrison (editor), Functional anatomy of
marine mammals, Vol. 1, p. 117-244. Academic Press,
N.Y.
PERRIN, W. F.

1969. Using porpoise to catch tuna. World Fishing
18(6):42-45.

1972. Color patterns of spinner porpoises (Stenella cf. S.
longirostris) of the eastern Pacific and Hawaii, with com-

ments on delphinid pigmentation. Fish. Bull., U.S.

70:983-1003.
1975a. Distribution and differentiation of populations of

dolphins of the genus Stenella in the eastern tropical

Pacific. J. Fish. Res. Board Can. 32:1059-1067.
1975b. Variation of spotted and spinner porpoise (genus

Stenella) in the eastern Pacific and Hawaii. Bull.

Scripps Inst. Oceanogr. Univ. Calif. 21, 206 p.
PERRIN, W. F., AND E. L. ROBERTS.

1972. Organ weights of non-captive porpoise (Stenella
spp.). Bull. South. Calif. Acad. Sci. 71:19-32.

PERRIN, W. F., J. M. COE, AND J. R. ZWEIFEL.

1976. Growth and reproduction of the spotted porpoise,
Stenella attenuata, in the offshore eastern tropical Pa-
cific. Fish. Bull., U.S. 74:229-269.

Pilson, M. E. Q., and D. W. Waller.

1970. Composition of milk from spotted and spinner por-
poises. J. Mammal. 51:74-79.

RICE, D. W., AND A. A. WOLMAN.

1971. The life history and ecology of the gray whale (Es-
chrichtius robustus). Am. Soc. Mammal., Spec. Publ. 3,
142 p.

SACHER, G. A., AND E. F. STAFFELDT.

1974. Relation of gestation time to brain weight for pla-
cental mammals: Implications for the theory of vertebrate
growth. Am. Nat. 108:593-615.

Sergeant, d. e.

1962. The biology of the pilot or pothead whale Globice-
phala melaena (Traill I in Newfoundland waters. Fish.
Res. Board Can., Bull. 132, 84 p.

1973. Biology of white whales (Delphinapterus leucas) in
western Hudson Bay. J. Fish. Res. Board Can.
30:1065-1090.

Sergeant, d. e., d. k. Caldwell, and M. C. Caldwell.

1973. Age, growth, and maturity of bottlenosed dolphin
(Tursiops truncatus) from northeast Florida. J. Fish.
Res. Board Can. 30:1009-1011.

750

PRODUCTION BY THREE POPULATIONS OF

WILD BROOK TROUT WITH EMPHASIS ON

INFLUENCE OF RECRUITMENT RATES

Robert F. Carline1

ABSTRACT

Populations of wild brook trout, Salvelinus fontinalis, in three small ponds in northern Wisconsin
were studied for 4 yr to determine annual production with particular emphasis on influence of
recruitment rates. Recruitment included trout hatched in ponds and immigrants from adjacent
waters. Age-specific growth rates and densities of trout were estimated in spring and fall. Harvest
of trout was estimated through partial creel surveys.

Among populations annual production ranged from 26 to 331 kg/ha and was directly related
to recruitment rates. Production was most influenced by population biomass. Instantaneous growth
rates did not vary significantly within or among populations despite large differences in population
densities; hence, variations in production appeared unrelated to growth rates. Among populations,
yield of trout ranged from 25 to 72 kg/ha and fishing pressure ranged from 154 to 1,405 h/ha.
Proportion of annual production that was harvested was directly related to fishing pressure.

Production of fry during the first 9 mo of life may have been overestimated because mortality
rates from emergence to fall were assumed constant. Estimates of production of adult trout could
have been positively or negatively biased depending upon immigration patterns. Despite these
possible errors, it was clear that recruitment was the most important factor affecting production.

Estimation of fish production has gained wide-
spread acceptance because it provides some
measure of a system's capacity to support species
of interest (Gerking 1967). Production is defined
as the total elaboration of tissue by a population
during a specified time interval, regardless of the
fate of that tissue (Ivlev 1945). Unlike standing
crop estimates, production is a dynamic popula-
tion parameter that is useful in evaluating the
environmental performance of a fish population
(Le Cren 1972). Studies by Ricker and Foerster
(1948), Allen (1951), and Hunt (1971) are good
examples of how fish production has been related
to predation, the food supply, and habitat suit-
ability. While many studies have considered the
effects of standing crops, growth rates, and mor-
tality on production, the importance of recruit-
ment has not been well defined.

In northern Wisconsin, standing crops of wild
brook trout, Salvelinus fontinalis, in spring- fed
ponds vary greatly. Some ponds have filled-in
naturally and living space is limiting. In others,
living space appears to be adequate, but spawning

'Wisconsin Department of Natural Resources, Route 1,
Box 203, Waupaca, WI 54981; present address: Ohio Cooperative
Fishery Research Unit, Ohio State University, 1735 Neil
Avenue, Columbus, OH 43210.

Manuscript accepted April 1977.

FISHERY BULLETIN: VOL. 75, NO. 4, 1977.

areas are small or nonexistent and recruitment
seems to be limiting standing crops of trout. The
objective of this study was to determine annual
production by three populations of wild brook
trout with particular emphasis on the influence
of recruitment rates. Recruitment includes all
trout hatched in the ponds plus all immigrant
trout.

The ponds were chosen because they differed
greatly in areas available for spawning and
numbers of immigrating trout. Ponds were sim-
ilar in size and watershed characteristics, and
springs were the primary sources of water. Outlet
streams, which flowed into larger streams and/or
lakes, provided convenient sampling boundaries,
but did not impede movement of trout into or out
of the ponds. I estimated densities and growth
rates of trout every spring and fall from 1968-72
and conducted partial creel surveys during 3 yr
of the study to estimate trout yields.

DESCRIPTION OF STUDY AREA

The study ponds, situated in a terminal mo-
raine, are located within 7 km of each other in
Langlade County, north central Wisconsin. The
moraine is composed of glacial till ranging in size
from sand to large boulders. These permeable

751

FISHERY BULLETIN: VOL. 75, NO. 4

materials permit a relatively uninhibited flow of
ground water that is the main source of water
for all ponds. Hoglot and Clubhouse springs are
on state-owned land and Maxwell Springs is
privately owned. The ponds are located in wooded
lowlands and all three drain into trout streams
that are part of the Wolf River drainage, a major
Lake Michigan watershed.

The ponds are similar in size and have rel-
atively short exchange times due to large inflows
of ground water (Table 1). Because all ponds are
supplied by the same aquifer, concentrations of
common ions are similar. Bottom materials con-
sist mostly of marl and organic matter. About
10% of the shorelines in Maxwell and Hoglot
springs are composed of gravel with emerging
ground water and brook trout spawn in these
areas. Numbers of trout redds in Hoglot Springs
ranged from 85 to 105/ha of pond area, and in
Maxwell Springs redd densities ranged from 165
to 230/ha. Clubhouse Springs lacks gravel areas
with upwelling ground water and brook trout do
not spawn there.

Continual inflow of ground water and rapid
exchange times tend to moderate pond tempera-
tures and maintain relatively high concentrations
of dissolved oxygen. Ground water temperatures
typically range from 6° to 7°C and concentrations
of dissolved oxygen, from 8 to 9 ppm. Pond tem-
peratures in summer at depths of 15 cm rarely
exceed 16°C. Concentrations of dissolved oxygen
rarely fall below 5 ppm at any depth throughout
the year and they usually exceed 7 ppm. Ponds
are ice-covered from early November to late
March.

All ponds supported dense beds of aquatic vege-
tation. Chara vulgaris covered about 40% of the
bottom in Clubhouse Springs and 15% in Hoglot
Springs. Anacharis canadensis, the only common

TABLE 1. — Some physicochemical features of study ponds in
north central Wisconsin. Chemical measurements were taken
in April 1970.

Item

Clubhouse
Springs

Hoglot
Springs

Maxwell
Springs

Surface area (ha)

Mean depth (m)

Outlet discharge1 (m3/s)

Exchange time2 (days)

Specific conductance (umbolcm)

Total alkalinity (mg/l as CaCOs)

Calcium (mg/l)

Nitrate (mg/l-N)

Dissolved phosphorus (mg/l-P)

0.81

0.38

0.97

1.11

0.64

0.86

0.03

0.005

0.05

3.3

5.6

2.0

341

335

310

180

153

168

0.5

0.7

1.1

0.02

0.01

0.03

'Summer base flow.
2Pond volume/discharge.

plant in Maxwell Springs, extended over 50% of
the bottom.

Fish communities in the three ponds were sim-
ilar. Brook trout composed the major portion of
fish biomass. A small population of brown trout,
Salmo trutta, in Clubhouse Springs never ac-
counted for more than 10% of the total number
of trout. The white sucker, Catostomus commer-
soni; mottled sculpin, Cottus bairdi; Central
mudminnow, Umbra limi; and brook stickleback,
Culaea inconstans , were common in all ponds. The
brook stickleback was an important food source
for age 3 and older trout; however, benthic inver-
tebrates composed the major portion of the diet for
trout of all sizes.

METHODS

Trout populations were estimated in spring and
fall using Bailey's modification of the Petersen
mark and recapture method (Ricker 1975). Trout
were captured at night with electrofishing gear
and held overnight in screen cages. The following
day, fish were anesthetized, measured to the near-
est 2 mm (total length), weighed to the nearest
gram, given a temporary mark by clipping the
tip of the caudal fin, and released. A second
electrofishing run was made two or more days
later. Proportions of marked trout captured dur-
ing the second electrofishing sample were used
to calculate confidence limits for population esti-
mates (Adams 1951).

Age structures of trout populations were deter-
mined from length distributions of known age fish
and scale analyses. Fall fingerlings and spring
yearlings, determined from length-frequency
distributions, were permanently marked by fin
removal. Estimated numbers of trout in each
25-mm length group were placed in appropriate
age-groups based on relative proportions of known
age fish. The electrofishing gear was size selective.
Efficiency was lowest for smallest fish and in-
creased until fish size reached about 12 cm. Sep-
arate estimates for 25-mm length intervals
avoided bias due to size selectivity of electro-
fishing gear.

Maxwell outlet and Elton Creek, the stream
into which Clubhouse Springs flowed, were
sampled with electrofishing gear to obtain data
on growth rates of trout in outlet waters and on
movement of trout between ponds and adjoining
streams. A 1-km section of Elton Creek was
sampled five times from 1968 to 1971; Clubhouse

752

CARLINE: PRODUCTION BY WILD BROOK TROUT

outlet joined this section at its midpoint. Maxwell
outlet (200 m) was sampled in 1969 and 1972.
All trout were measured, about 25'7( were
weighed, and fall fingerlings and spring yearlings
were permanently marked by fin removal.

Sampling dates in ponds varied from year to
year. I estimated mean lengths and weights of
each cohort on 15 April and 15 September so that
growth rates from different years could be
compared. Mean weights of individuals in each
year class were determined graphically by
assuming constant instantaneous rates of growth.
By graphically estimating mean length, I as-
sumed length increased linearly between succes-
sive estimates. Most of the adjustments in length
or weight involved extrapolating over periods
<2 wk and size changes were usually <5%.

Year class biomass was estimated by multiply-
ing mean weights of individual trout by year class
density. Biomasses in spring and fall were
averaged to calculate mean biomass (B ). I followed
procedures suggested by Ricker ( 1975) to calculate
instantaneous rates of growth by weight (G), total
mortality (Z), natural mortality (M), and fishing
mortality (F). Production, the product of G and
B, was computed semiannually for each cohort.
Production by fingerling trout was calculated
from emergence (1 March) to time of spring
population estimate and from spring to fall.
A mean weight of 0.04 g was assigned to emergent
fry (Hunt 1966). I assumed that instantaneous
growth and mortality rates from emergence to
fall were constant. Mean annual biomass of each
cohort was calculated by weighting mean bio-
masses in the two intervals according to interval
lengths. Annual production was calculated by
summing production during the two intervals and
expressing the sum for 365-day periods.

Potential egg production for each population
was estimated from numbers of mature females
in fall and from a relationship between total
length of females and number of eggs. Fecundity
of trout was determined from 83 females that were
collected from two ponds in the same watershed
as the study ponds. Trout were collected in early
October, about 2 wk prior to spawning. Mature
ova could be easily distinguished from recruit-
ment eggs on the basis of size and color ( Vladykov
1956). Data on trout length, weight, and total
number of eggs were fitted to linear, curvilinear,
and logarithmic regression models. A linear
regression of total trout length and number of
eggs yielded the highest correlation coefficient.

At Clubhouse and Hoglot springs, densities of
some year classes increased during sampling
intervals because of immigration from outlets or
adjoining streams. Numbers of immigrants were
estimated by first calculating expected densities
at the end of sampling intervals by using mean,
age-specific mortality rates; expected densities
were then subtracted from actual densities. If the
expected number of trout at the end of an interval
was within 107( of the actual number or the
difference was negative (suggesting emigration),
it was assumed no immigration had occurred.
Age-specific mortality rates for trout in Club-
house and Hoglot springs were estimated from
permanently marked fish. For some age groups,
mortality rates could not be estimated because
of insufficient numbers of marked fish. In these
instances I used age-specific mortality rates of
the population in Maxwell Springs, where immi-
gration did not influence year class densities
(discussed later).

Harvest of trout from Clubhouse and Hoglot
springs was estimated from partial creel surveys
in 1969, 1970, and 1972. State-wide angling
regulations included a bag limit of 10 trout/day
and minimum length of 154 mm (6 in). Census
clerks worked five randomly.chosen days per week
during the entire fishing season, mid-May to mid-
September. Catch rates were estimated from data
collected during interviews of anglers, and fishing
pressure was calculated from instantaneous
counts of anglers (Lambou 1961). Harvest was
estimated monthly from the product of the hours
of fishing and numbers of trout caught per hour.
Harvested trout were measured, examined for
permanent marks, and scales were collected from
a sample of the catch. Harvest data from
Maxwell Springs were compiled by the owner and
others who fished the pond. Ages of harvested
trout from Clubhouse and Hoglot springs were
determined from scales and size distributions of
permanently marked fish. Ages of trout harvested
from Maxwell Springs were estimated from
comparisons of lengths of harvested trout with
lengths of known age fish in spring and fall.

RESULTS

Population Densities and Biomass

Electrofishing was the most efficient method of
collecting trout in these shallow ponds. Popula-
tion estimates derived from collections with trap

753

FISHERY BULLETIN: VOL. 75, NO. 4

nets and seines showed that collecting trout with
just electrofishing gear did not yield biased
estimates (Carline unpubl. data). Efficiency of the
electrofishing gear usually increased with trout
size (Table 2). Mean proportions of marked trout
captured during the second electrofishing sample
for age 0 to 3 fish were 0.18, 0.31, 0.35, and 0.39,
respectively. Recapture efficiencies were always
lowest for age 0 trout and values ranged from
0.05 to 0.30. For age 1 and older fish, precision
of estimates depended mostly upon sample size
and confidence limits for the oldest age groups
were generally broad because of their low densi-
ties (Table 2).

TABLE 2. — Examples of trout population estimates and 95%
confidence limits by age-groups. Data were collected in fall 1970.

Item

Clubhouse Springs:
Mean length (mm)
Proportion of marked

fish recaptured
Population estimate

(no./ha)
95% confidence limits

Maxwell Springs:
Mean length (mm)
Proportion of marked

fish recaptured
Population estimate

(no./ha)
95% confidence limits

0.30

386
234
782

0.05

175

0.40

363
279
466

147

0.43

2,195 1,572
1,183 1,408
3,944 1,778 1,003

211

0.41

124

182

0.53

909

845

274

0.50

220

0.34

433
367

507

287

0.22

28
17
56

Clubhouse Springs

The brook trout population in Clubhouse
Springs was the smallest of the three populations.
Because no spawning areas were present, this
population was entirely dependent upon immigra-
tion from downstream areas. Trout densities
usually declined from spring to fall and only age 0
trout appeared to immigrate in substantial
numbers oversummer (Figure 1). Total trout
numbers in 3 of 4 yr increased overwinter due
to immigration. Numbers of trout in spring
ranged from 390 to 1,750/ha and densities in fall
ranged from 390 to 840/ha. Age structure of the
population was at times atypical because young
age groups were less numerous than older ones,
owing to differential rates of immigration.

Changes in population biomass closely paral-
leled numerical changes. Biomass in spring
averaged 45 kg/ha and in fall 26 kg/ha (Table 3).
In all years, population biomass increased from
fall to spring, the period when immigration
appeared greatest.

APR OCT

1968

FIGURE 1. — Estimated numbers of brook trout in Clubhouse
Springs, 1968-72. Numbers designate age-groups and hatched
areas separate calendar years.

TABLE 3. — Estimated biomass (kilograms per hectare) by age-
group of brook trout in study ponds, 1968-72. Mean weights of
individuals in each age-group were multiplied by estimated
density of the age-group to calculate biomass.

Site and date

Total

Clubhouse Springs:

27 Mar. 1968

28 Aug. 1968
8 Apr. 1969

8 Sept. 1969 1.8

1 Apr. 1970

8 Sept. 1970 3.5

29 Apr. 1971

8 Sept. 1971 2.1

21 Apr. 1972
Hoglot Springs:

2 Apr. 1 968

26 Aug. 1968 6.8

8 Apr. 1969

8 Sept. 1969 15.9

13 Apr. 1970

8 Oct. 1970 16.9

28 Apr. 1971

21 Sept. 1971 7.0

2 May 1972
Maxwell Springs:

9 Apr. 1969

13 Oct. 1969 27.0

26 Mar. 1970

6 Oct. 1970 22.0

26 Apr. 1971

20 Sept. 1971 24.6

26 Apr. 1972

29 Sept. 1972 14.8

10.9

15.6

8.7

3.5

38.7

22.9

10.8

1.2

1.7

36.6

3.0

23.7

14.4

5.2

46.3

7.6

10.4

4.3

0.4

24.5

17.2

26.2

20.4

4.6

68.4

17.4

7.0

1.2

29.1

12.0

22.9

12.2

2.3

49.4

6.6

3.1

0.2

12.0

3.0

13.1

4.4

0.7

21.2

22.6

69.1

26.5

11.2

129.4

26.1

35.8

13.6

3.6

85.9

5.0

37.2

66.8

8.1

117.1

33.7

47.6

12.5

2.3

112.0

13.0

38.3

38.5

13.3

103.1

91.0

36.4

9.1

0.7

154.1

10.8

70.7

21.5

2.1

105.1

26.6

40.7

5.6

0.2

80.1

10.8

17.0

6.5

2.5

36.8

34.4

50.8

26.3

41.6

80.3

233.4

55.8

88.8

29.3

20.8

16.1

237.8

25.3

47.3

69.6

16.2

12.4

170.8

56.6

63.6

53.7

6.9

2.6

205.4

8.2

48.0

46.9

17.6

0.5

121.2

19.2

32.6

13.8

0.9

91.1

27.1

7.3

7.1

3.7

45.2

46.6

11.0

4.5

1.4

78.3

Hoglot Springs

Although some fingerlings were hatched in
Hoglot Springs, numbers of immigrating trout,
particularly age 1 fish, had the most impact on
population size. In 3 of 4 yr, densities of yearling
trout increased oversummer, and during the

754

CARLINE: PRODUCTION BY WILD BROOK TROUT

winter of 1968-69 fall 2-yr-olds increased by 50%
(Figure 2). Mean population densities were higher
in fall than in spring (4,480 vs. 3,200/ha) because
of recruitment by age 0 trout and age 1 trout.

Trout migrating into Hoglot Springs had a
marked effect on population biomass. Biomass
was highest in fall 1970 because of the large stock
of yearlings (91 kg/ha), most of which were recent
immigrants (Table 3). Little immigration oc-
curred oversummer in 1971 and overwinter in
1971-72. As a result, population biomass in spring
1972 reached its lowest level of the 4-yr period.

APR OCT

1970

APR OCT

1971

APR
1972

FIGURE 2. — Estimated numbers of brook trout in Hoglot
Springs, 1968-72. Numbers designate age-groups and hatched
areas separate calendar years.

Maxwell Springs

Except for 1972, Maxwell Springs supported
the largest of the three populations, and natural
reproduction accounted for nearly all recruitment.
Two experiments were conducted to evaluate the
extent of immigration from Maxwell outlet into
the pond. In June 1969 and April 1972, a total of
602 ages 0 and 1 trout were captured in the outlet
and marked. In subsequent surveys of the pond,
I examined over 4,000 trout, only 3 of which had
been marked in the outlet. Hence, I concluded
that trout reared in the outlet did not materially
affect recruitment in the pond.

From April 1969 to September 1972 trout densi-
ties in Maxwell Springs declined markedly (Fig-
ure 3). Spring densities steadily decreased from
7,300/ha in 1969 to 1,810/ha in 1972. Fall
populations followed a similar trend. This decline
was due in part to decreasing numbers of fall
fingerlings. Densities of age 0 trout ranged from
4,085/ha in October 1969 to 1,940/ha in Septem-
ber 1972. However, even the 1969 year class,
which was larger than the succeeding three year
classes, had to be smaller than the 1968 and 1967
year classes, based on their densities as ages 1
and 2 fish in April 1969 (Figure 3). I estimated
numbers of fall fingerling for the 1967 and 1968
year classes by using average mortality rates of
succeeding year classes. The 1967 year class was
estimated at 16,000/ha and the 1968 year class
at 8,300/ha. Thus, numbers of fall fingerlings had
steadily declined from 1967 to 1972 with one
exception, the 1971 year class.

The reduction in year class strength in Maxwell
Springs may have been related to the installation
of a weir in the pond outlet in 1968. The weir,
which was used to monitor discharge, was located
132 m downstream from the pond and it created

APR OCT

1969

FIGURE 3.— Estimated numbers of brook trout in Maxwell
Springs, 1969-72. Numbers designate age-groups and hatched
areas separate calendar years.

755

FISHERY BULLETIN: VOL. 75, NO. 4

an impoundment that extended to within 5 m of
the pond. The impounded area was heavily silted
by fall 1968 and I counted only four redds there.
The owner had reported that large numbers of
brook trout spawned in this area prior to weir
installation. In fall 1974, 1 yr after the weir had
been removed, I counted 34 redds and about half
the streambed was covered with silt. Since effects
of impoundment were still evident, this portion
of the outlet may have provided much more
spawning area than was evident in 1974. Possibly,
immigration was an important source of recruit-
ment prior to this study.

Population declines at Maxwell Springs were
accompanied by changes in age structure. In April
1969, density of age 3 and older trout was nearly
1,000/ha and they totaled 233 kg/ha, or 63% of
population biomass (Table 3). By September 1972,
density of age 3 and older trout was 22/ha and
biomass was about 6 kg/ha, the lowest in the 4-yr
period.

Mortality

Numbers of fall fingerlings in Hoglot and Max-
well springs represented from 0.2 to 1% of the
estimated number of eggs deposited the previous
fall. I sampled 52 redds in five different ponds
to assess preemergence mortality. Numbers of
eggs per redd ranged from about 30 to 220.
Percentage of live embryos in individual redds
ranged from 76 to 99 (mean = 89%); stage of
development of these embryos varied from eyed
egg to alevin. Due to additional mortality to
emergence, I used 80% of potential egg deposition
to estimate numbers of emerging fry. Although
highest mortality rates in both ponds occurred
during years of highest egg production, egg
production and fingerling mortality were not
significantly correlated (Table 4).

To estimate age-specific total mortality rates
of trout in Maxwell Springs, I assumed that
immigration was negligible. At Clubhouse and
Hoglot springs, where immigration was sub-
stantial, unmarked residents and immigrants
could not be separated; therefore, mortality rates
were calculated using only permanently marked
trout. Numbers of age 2 and older trout were
usually too small to allow estimation of mortality
rates.

Mean rates of oversummer mortality in Max-
well and Hoglot springs increased with age (Table
5). Overwinter mortality rates at Maxwell

TABLE 4. — Estimated egg production of brook trout populations
and densities of fall fingerlings. Egg deposition was estimated
from number of mature female trout in fall and the relationship
of fecundity (Y) and trout length in millimeters (X); Y = -588 +
6.14X. Instantaneous mortality rates (Z) were based on 80% of
egg production and were corrected for 182-day intervals.

Year

No.

No. fall

Pond

class

eggs/ha

fingerlings/ha

Z/182days

Hoglot Springs

1969

281 ,000

2,938

4.111

1970

276,000

2,481

3.681

1971

433,000

1,049

5.148

Mean

330,000

2,156

4.313

Maxwell Springs

1969

543,000

4,085

3.742

1970

550,000

2,195

4.384

1971

739,000

3,519

4.549

1972

212,000

1,945

3.800

Mean

511,000

2,936

4.119

Springs also increased with age, except that age 0
trout had higher mean mortality rates than did
age 1 trout. However, within years there was
considerable variability between age of fish and
mortality rates. In all ponds mean mortality rates
oversummer exceeded overwinter rates.

Immigration

Estimation of immigration rates at Clubhouse
and Hoglot springs were based on mortality rates
calculated from relatively small numbers of
permanently marked trout and from mean, age-
specific mortality rates of trout from Maxwell
Springs (Table 5). Although accuracy of these
estimates is suspect, they should be useful in
illustrating seasonal differences in immigration
and in assessing the effect of immigration on
recruitment.

At Clubhouse Springs most immigration oc-
curred overwinter and age 0 trout made up 55%
of all migrants (Table 6). Largest migrations into
Hoglot Springs occurred between April and
September when age 1 trout accounted for 73%
of all migrants. In both populations periods of
peak immigration coincided with highest popula-
tion densities. Immigration was the only source
of recruitment at Clubhouse Springs; at any one
time more than half the population consisted of
fish that had immigrated within the previous
6 mo. At Hoglot Springs percentages of recent
immigrants ranged from 8.2 to 54.9 (mean =
34%).

If estimates of trout migrating into Hoglot
Springs are reasonable, immigration accounted
for a major portion of total recruitment. The four
year classes produced in the pond from 1968 to
1971 amounted to 7,700 fall fingerlings/ha. About
3,800 of these fish survived to the following spring.

756

CARLINE: PRODUCTION BY WILD BROOK TROUT

TABLE 5. — Instantaneous total mortality rates for 182-day intervals. Mortality rates of trout in
Maxwell Springs were calculated from year class densities. Mortality rates of trout in Hoglot
and Clubhouse springs were calculated from permanently marked fish. Estimated numbers of
trout at the end of sampling intervals given in parentheses.

Interval

Maxwell Springs

Hoglot Springs
1 2

Clubhouse Springs

and year

Oversummer:

1968

2.254
(72)

1.238
(75)

1969

0 766

0.573

0.510

1.521

0.408

2.151

1.914

(1.691)

(1,368)

(233)

(109)

(110)

(7)

(13)

1970

0.448

0.373

0.850

1 492

0.725

1.080

1.489

(1.525)

(882)

(420)

(31)

(158)

(8)

(81)

1971

0 500

1.552

2.439

4.404

1 382

1.631

1 522

(442)

(264)

(62)

(3)

(33)

(20)

(65)

1972

0.681

(863)

0.670
(82)

1.185
(17)

1.532

(4)

Mean

0.599

0 792

1.246

2.237

1.192

1.742

1.541

Overwinter:

1968-69

0.175
(58)

0.804
(28)

1969-70

0.530

0282

0.306

0.826

1 085

1.312

1 662

(2.457)

(1.310)

(1.039)

(110)

(41)

(23)

(2)

1970-71

1.048

0.444

0.606

1.243

2.498

0.687

0.573

(664)

(931)

(450)

(106)

(2)

(74)

(39)

1971-72

0.659

0917

1 398

1.211

0.926

0 826

1.186

(1.549)

(147)

(49)

(14)

(1)

(12)

(15)

Mean

0.746

0 548

0.770

1 093

1 503

0.750

1.056

'Age at start of interval.

TABLE 6. — Estimated numbers of immigrant brook trout present by age-groups at the end of
sampling intervals. Summer intervals were from April to September and winter intervals from
September to the following April. Percent of population at the end of the interval composed
of recently immigrated trout given in parentheses.

Year and

Cli

ubhouse Springs

Hoglot Springs

interval

2 3

Sum

2 3

Sum

1968

Summer

346

0 0

346 (57)

207

42 0

249 ( 8)

Winter

147

277

65 14

503 (74)

802

659 34

1.495 (55)

1969

Summer

130

104

0 0

234 (60)

1,046

619 0

1.665 (32)

Winter

955

514

130 12

1.611 (92)

191

767

149 56

1.163 (36)

1970

Summer

387

102

0 0

489 (58)

3,205

417 0

3.622 (53)

Winter

451

215

46 6

718 (70)

773

0 0

773 (21)

1971

Summer

262

0 0

262 (55)

645

133 0

778 (27)

Winter

128

12 0

226 (57)

478

157

0 0

635 (41)

Sum

2,418

1,686

253 32

4,389

669

7.602

2,019 90

10,380

Percent

55.1

38.4

5.8 0.7

6.4

73.2

19.5 0.9

During this 4-yr period over 9,700 age 1 and older
trout immigrated into the pond, hence, migrants
accounted for about 70% of total recruitment of
yearling and older trout.

It is likely that trout migrating from Elton
Creek into Clubhouse Springs were smaller than
pond residents because: 1) trout in Elton Creek
grew more slowly than those in Clubhouse
Springs and 2) permanently marked trout in the
pond, i.e. residents, were larger than unmarked
trout, which were mostly recent immigrants.
From 1968 to 1970 fall fingerlings in Elton Creek
averaged 4.2 g and those in Clubhouse Springs
were 9.6 g. Fall yearlings in Elton Creek averaged
30 g and yearlings in the pond were 46 g. In spring

and fall, marked yearlings in Clubhouse Springs
were about 20% heavier than unmarked year-
lings. For age 2 trout in spring, marked trout
were 58% larger than unmarked ones. I made
similar comparisons for ages 1 and 2 trout in
Hoglot Springs; differences in sizes among
marked and unmarked trout were not consistent
and I concluded that migrants were similar in
size to pond residents.

Growth

Among populations, mean size attained by trout
of a given age was greatest in Clubhouse Springs
(Table 7). After the first full year of life trout in

757

FISHERY BULLETIN: VOL. 75, NO. 4

TABLE 7. — Estimated mean annual lengths (millimeters) and
weights (grams) of brook trout on 15 April and 15 September.
Data from Clubhouse and Hoglot springs were from 1968-71
and those from Maxwell Springs were from 1969-72.

Age

month

L W

Clubhouse Springs:
April

126

176 55

229 127

September

105

166

212 105

276 238

Hoglot Springs:
April

107

150 31

199 72

241 136

September

130

178 56

226 118

Maxwell Springs:
April

106

154 38

203 89

264 172

September

147

200 88

246 168

300 284

Clubhouse Springs were from 58 to 90% larger
than spring yearlings in Hoglot or Maxwell
springs. Although trout in Clubhouse Springs
maintained a size advantage over their counter-
parts in the other ponds after the first growing
season, age-specific instantaneous growth rates
for all populations were similar. I compared mean
age-specific growth rates for intervals of April to
September and September to April for ages 1-3
trout. There were no significant differences for
similar age trout among populations U-test
P>0.05). During summer instantaneous growth
rates of trout tended to be highest in Maxwell
Springs, but there were no consistent differences
during winter intervals.

Growth rates of fingerling trout were inversely
related to their density (number or weight) when
data from all populations were combined (Table
8). Density of yearling trout also had an effect
on growth of fingerlings; correlation coefficients
were highest when fingerling growth was related

to combined density of fingerlings and yearlings.
Effects of density on growth rates of age 1 and
older trout were inconsistent. When instan-
taneous growth rates were used as the dependent
variable and density in numbers or weight was
the independent variable, correlation coefficients
were consistently low (Table 8). When age-specific
growth was expressed as mean weight or length
in September or weight gain from April to Septem-
ber, correlation coefficients were consistently
high (Figure 4). The lack of correlation between
instantaneous growth rates and density may have
been due to underestimation of mean weights of
trout in fall, particularly in Clubhouse Springs.
Biases could have resulted from: 1) immigration
of trout smaller than pond residents, 2) differen-
tial exploitation of faster growing individuals in
a year class, and 3) errors in estimating year class
densities. The lack of correspondence between
instantaneous growth rates and other growth
parameters has been noted in other studies
(Eipper 1964).

Harvest

Fishing success and harvest of trout were in-
fluenced by trout densities and fishing pressure.
Maxwell Springs supported the largest trout
population in 1969 and 1970 and catch rates were
highest (Table 9). Among populations annual
catch rates were positively related to spring
densities of age 1 and older trout (r = 0.88;
P<0.01). There was a significant correlation be-
tween biomass of trout harvested (yield) and the

TABLE 8. — Linear correlation coefficients for growth and density of trout ages 0 to 3
in study ponds, (df = 10; *P<0.05, **P<0.01.)

Independent

Age-group of

Instantaneous

Mean length

Mean weight

Weight gain

variable

dependent variable

growth rates

on 15 Sept.

Apr-Sept.

Mean trout biomass

(kg/ha) of:

Age 0

-0.62*

-0.59

Age 1

-0.86"

-0.72*

Ages 0 and 1

-0.85**

-0.76"

Age 1

-0.08

0.38

-0.61*

-0.53

All ages

0.13

-0.66"

-0.72"

0.59*

Age 2

0.04

-0.81"

-0.79"

-0.62*

All ages

0.14

-0.72"

-0.68'

-0.48

Age 3

0.05

0.68*

0.64*

-0.58*

All ages

-0.07

-0.82"

-0.79"

-0.68*

Mean trout density

(no./ha) of:

Age 0

-0.78*

-0.84"

Age 1

-0.67*

-0.64*

Ages 0 and 1

-0.82"

-0.85"

Age 1

0.01

-0.57

-0.70*

-0.62

All ages

0.01

0.66*

-0.77"

0.63*

Age 2

006

-0.87"

-0.86"

-0.68*

All ages

0.17

-0.71**

-0.69'

0.46

Age 3

-0.09

-0.82"

-0.76"

-0.67*

All ages

-0.12

-0.81"

-0.80"

0.69'

758

CARLINE: PRODUCTION BY WILD BROOK TROUT

AGE 1

G CLUBHOUSE SPRINGS
A HOGLOT SPRINGS

□

O MAXWELL SPRINGS

"~^nq^

□

r = -066*

"W o

^^\ o

? 22
u

AGE 2

ann.

Si 20
in

z
o

LENGTH
65

A
AA

z
<

r = -072"

29 l

AGE 3

r = -0 82"

50 100 150

MEAN BIOMASS (kg/ ha)

200

250

FIGURE 4. — Relationships between mean biomass of all ages
of trout and mean lengths of ages 1,2, and 3 trout on 15 Septem-
ber. (*P<0.05; **P<0.01.)

TABLE 9. — Annual fishery statistics for brook trout populations
in study ponds.

Pond and
year

Fishing

pressure

(angler h/ha)

Total
harvest
(no./ha)

Catch

rate

(no./h)

Mean
size

(cm)

Yield
(kg/ha)

Clubhouse

Springs:
1969

1,069

580

0.55

21.8

68.4

1970

1,405

392

0.28

21 4

37.2

1972

809

298

0.37

20.3

27.4

Hoglot
Springs:
1969

835

926

1.11

18.3

54.6

1970

526

391

0.74

19.3

25.4

1972

401

218

0.54

18.8

13.5

Maxwell

Springs:
1969

189

334

1.77

27.2

71.8

1970

154

320

2.08

23.1

39.7

because the pond was privately owned and public-
access was restricted. The largest trout (up to
430 mm) were harvested from Maxwell Springs
which supported the greatest number of age 4
and older trout. In spring 1969 there were about
530 age 4 and older trout/ha in Maxwell Springs
and only 16/ha and 69/ha in Clubhouse and Hog-
lot springs, respectively.

Age 2 trout made up the major portion of the
harvest in Clubhouse and Hoglot springs (Figure
5). In both populations, proportions of age 2 and
older trout in the harvest were higher than their
proportions in the spring populations, suggesting
some size selection by anglers.

The fishery at Maxwell Springs differed signifi-
cantly from the public ponds in 1969 when age 5
and older trout dominated the catch (Figure 5).
Large numbers of age 5 trout were present in
spring 1969 and 58% were harvested that season.
The owner of Maxwell Springs reported that
harvest and fishing pressure in years prior to the
study were well below those of 1969 and 1970;

* 0

CLUBHOUSE SPRINGS

A A HARVEST

HOGLOT SPRINGS

.:.

2 3.

MAXWELL SPRINGS 1969

MAXWELL SPRINGS 1970

i \

/ \

; \

\ / ^

\l ^

' \ \

\ \

' \ \

1
1

\ A

\ N.

\ N

V ^

independent variables of fishing pressure and
trout biomass in spring (r = 0.88; P<0.05).
Fishing pressure was lowest at Maxwell Springs

FIGURE 5.— Age-frequency distributions of harvests and popula-
tions of legal-sized trout in spring. Data points for Clubhouse
and Hoglot springs are means of data from 1968 to 1970, and
1972.

759

FISHERY BULLETIN: VOL. 75, NO. 4

it is likely that the population had been lightly
exploited prior to 1969. Results of electrofishing
surveys apparently stimulated greater fishing
effort. Shape of the 1970 catch-frequency curve
resembled those of public ponds, except that sub-
stantial numbers of age 4 and older trout were
harvested.

Size selection by anglers at Maxwell Springs
was reflected in the relative rates of natural and
fishing mortality. For ages 2-5 trout, mean total
mortality rates from spring to fall increased with
age and were paralleled by fishing mortality (Fig-
ure 6). Natural mortality changed little with age
of fish. Differences between natural and fishing
mortality were greatest for age 5 trout and fish-
ing mortality accounted for 69% of their total
mortality.

3 20
o

1.0

2
to

i2 0.5

O TOTAL
▲ NATURAL
□ FISHING

171'-

- 1

AGE

FIGURE 6.— Instantaneous rates of total, fishing, and natural
mortality (spring to fall) of ages 2 to 5 trout at Maxwell Springs.
Data points are 2-yr means, 1969-70.

Production

Production was most influenced by numbers of
fingerlings hatched in ponds and numbers of
immigrants. Growth rates varied little among
populations, hence year class biomass had the
most effect on production. Among populations
annual production ranged from 26 kg/ha at
Clubhouse Springs to 331 kg/ha at Maxwell
Springs (Table 10).

Annual production in Clubhouse Springs was
dependent upon biomass of ages 1 and 2 trout.
Few fingerlings immigrated into the pond and

TABLE 10. — Production (kilograms per hectare) by age-group
of brook trout in study ponds. Production by age 0 trout during
fall to spring intervals covers the period from 1 March to end
of interval. Production by age 4 trout includes all older age-
groups. Total annual production was expressed in terms of
365 days.

Site and
interval

Annual
Total total

Clubhouse
Springs:

27 Mar. 1968

28 Aug. 1968
8 Apr. 1969
8 Sept. 1969

1 Apr. 1970
8 Sept. 1970

29 Apr. 1971
8 Sept. 1971

21 Apr. 1972
Hoglot
Springs:

2 Apr. 1968
21 Aug. 1968

8 Apr. 1969

8 Sept. 1969
1 3 Apr 1 970

8 Oct 1970
28 Apr. 1971
21 Sept. 1971

2 May 1972
Maxwell
Springs:

6 Apr. 1969
13 Oct. 1969
26 Mar. 1970

6 Oct. 1970
26 Apr. 1971
20 Sept. 1971
26 Apr. 1972

20.8

11.4

1.5

4.4

0.9

5.1

10.8

1.8

- 2.0

2.7

17.8

9.4

5.7

8.7

1.0

5.6

5.2

1.8

7.2

40.1

20.9

32.2

2.9

5.6

51.1

21.2

22.7

11.3

7.2

3.8

56.2

52.9

23.3

18.5

6.4

14.7

34.8

15.9

35.7

14.1

5.1

3.1

97.0

56.8

80.0

11.6

10.9

4.9

97.5

52.5

38.6

34.0

2.8

17.2

90.6

17.4

35.3

10.6

23.0

1.8

3.9
4.0
5.6
1.5
5.5
6.1
1.8
2.7

10.6
13.4
18.5
15.5
11.5
7.7
5.9
10.2

17.5
24
38.7
20.4
22.9
3.1

0.5

1.0
0.6
1.4
0.8

7.9
-0.3
4.6
2.7
3.0
1.4
0.6
1.3

37.0
1.7

12.2
8.6
6.1
1.2

36.6
9.9
23.4
1.9
36.8
21.3
13.6
11.7

111.8
31.1

118.1
40.5

146.9
48.7
92.9
33.9

288.3
30.2

239.5
83.0

172.3
39.7

45.3

25.8

54.1

25.9

141.4

156.4

187.9

125.4

331.2

297.2

211 4

'Age at end of interval.

they contributed only 109c of total annual
production. Highest annual production occurred
in 1970 when the population was bolstered by
high levels of immigration during winter 1969-70
and in summer 1970. Low biomass in spring and
below average rates of immigration in 1969 and
1971 resulted in low annual production.

At Hoglot Springs, annual production was most
affected by numbers of fingerlings hatched in the
pond and numbers of immigrants. Age 0 trout
accounted for nearly 32% of average annual pro-
duction. Annual production peaked in 1970 (Table
10) when large numbers of age 1 trout immigrated
oversummer and cohort biomass increased from
13 kg/ha in spring to 91 kg/ha in fall.

Annual production in Maxwell Springs was
related to the number of strong year classes
present and their subsequent biomasses. The
highest annual production was in 1969 when two
large age-groups were present (1968 and 1969
year classes), and there was a high biomass of
age 2 and older trout (Table 10). In 1971, the
year of lowest production, the only large age-
group was the fingerlings. In all years, production

760

CARLINE: PRODUCTION BY WILD BROOK TROUT

of age 0 trout was important; they averaged 449c
of the total.

Among populations the influence of age 0 trout
on total production was evident when production
by individual age-groups was considered in rela-
tion to their biomass (Figure 7). Age 0 trout had
a marked^ effect on the slope of the relationship
between B and P when all age-groups were com-
bined. The linearity of these relationships was
due to similarity in growth rates within and
among populations. If growth rates had declined
with increasing biomass, the relationship be-
tween B and P would have been curvilinear.

There was no single parameter that could
adequately describe levels of recruitment because
numbers of trout hatched within ponds and num-
bers of immigrants were different in each popula-
tion. If densities of fall fingerlings or spring
yearlings were used as indexes of recruitment,
mean annual production among populations and

□ CLUBHOUSE SPRINGS

A HOGLOT SPRINGS

~ 300-

O MAXWELL SPRINGS

»-

^ 200-

t±/

o 100-

3
Z

g/a

i 0J

100

200

MEAN BIOMASS OF ALL COHORTS (kg/ha)

tr
o
I
o
t_>
_l
<

3
Q

120 -i

100

p 40

°- 20

20 40 60

MEAN BIOMASS OF INDIVIDUAL COHORTS (kg/ha)

FIGURE 7. — Relationships between mean annual biomass and
annual production. Production and biomass of all cohorts are
combined in upper panel. In lower panel each point represents
a single cohort. Lines fitted by inspection.

recruitment were directly related (Figure 8).
Although age 0 trout made up a substantial
portion of total production in Hoglot and Maxwell
springs, production of just age 1 and older trout
was also related to recruitment.

The ratio of annual production to mean annual
biomass (PIB) has been called "turnover rate"
and "efficiency of production." The PIB ratio is,
in fact, the weighted mean growth rate of the
population. Population production is the sum of
G x B for each year class, hence, dividing total
production by the sum of year class biomasses
yields population growth rate, weighted according
to the biomass of each age-group.

Among populations annual PIB ratios for age 1
and older trout varied by more than 100^ (Table
11). The PIB ratio in 1969 at Clubhouse Springs
( 0.63) was probably underestimated. Growth rates

300

200

100

2 o

3
O

Q-

MAXWELL SPRINGS

HOGLOT SPRINGS

.— age I*

CLUBHOUSE SPRINGS

-age 0

300

200

'00

1250 2500

MEAN DENSITY OF SPRING YEARLINGS (No /ha)

MAXWELL SPRINGS

HOGLOT SPRINGS

CLUBHOUSE SPRINGS

age I*-

age 0-

1000 2000

MEAN DENSITY OF FALL FINGERLINGS (No ./ha)

3000

FIGURE 8. — Mean annual densities of spring yearlings and fall
fingerlings in relation to mean annual production of age 0 and
age 1 and older trout.

761

FISHERY BULLETIN: VOL. 75, NO. 4

TABLE 11. — Total annual production (P), mean biomass (B),
and PIB ratios for all age 1 and older brook trout.

Pond and year

(kg/ha)

PIB

Clubhouse Springs:
1968

43.4

39.0

1.11

1969

23.0

36.5

0.63

1970

45.7

363

1.26

1971

23.0

20.1

1.14

Hoglot Springs:
1968

89.3

103.1

0.87

1969

95.2

100.0

0.95

1970

110.0

118.2

093

1971

71.9

65.9

1.09

Maxwell Springs:
1969

206.9

1998

1.04

1970

173.6

162.2

1.07

1971

87.7

64.2

1.37

of individual age-groups during winter 1969-70
were well below average and age 1 trout lost
weight. This was the only period in which an
age-group in Clubhouse Springs had a negative
growth rate, and it was probably due to immigra-
tion of yearling trout smaller than pond residents.
Overwinter production in 1969-70 was 2 kg/ha;
production during other winter periods ranged
fromlO to 21 kg/ha.

PIB ratios for age 1 and older trout in Hoglot
and Maxwell springs tended to decline with
increasing biomass (Table 1 1 ), i.e., mean weighted
growth rates were inversely related to density.
As I have noted, age-specific, instantaneous
growth rates (G) were the only growth parameters
poorly correlated with density. Biased estimates
of G for individual year classes could have
obscured relationships with population density,
but did not markedly affect mean weighted
growth rates when all adult trout were combined.

DISCUSSION

Estimation of trout production in this study
required several assumptions and the data should
be interpreted accordingly. Major assumptions
were: 1) numbers of emergent fry were 80% of
total egg production, 2) growth and mortality
rates of age 0 trout were constant from emergence
to fall, and 3) production could be estimated from
the product of G and B when immigration
occurred.

Chapman (1967) suggested that production of
brown trout fry in Horokiwi Stream (Allen 1951)
could have been overestimated by fourfold due to
errors in estimating egg deposition and emer-
gence. 1 used fecundity data from two populations
of wild brook trout that were collected from ponds
in the same watershed as the study ponds.

Fecundity differences among populations were
probably not large since growth rates of the trout
were similar. I assumed that all eggs were
spawned because egg retention was insignificant
in other stream populations of wild brook trout
(Wydoski and Cooper 1966). In addition, I as-
sumed emergent fry represented 80% of total egg
production. Percentage of live embryos in indi-
vidual redds exceeded 80% in my study. Brasch
( 1949) studied brook trout reproduction in several
ponds; he found survival from egg to emergence
was 79%. In laboratory experiments, emergence
of brook trout fry exceeded 80% when the
substrate was composed of 5% or less sand and
concentrations of dissolved oxygen exceeded
7 ppm (Hausle 1973). Therefore, I do not believe
estimates of egg production or emergent fry
seriously biased production estimates.

The assumption of constant mortality rates
from emergence to fall represents potentially
large errors in production estimates for age 0
trout. Hunt (1966) found that instantaneous
mortality rates from emergence in February to
June were about 10 times greater than mortality
from June to September; he based mortality rates
on 90% emergence of fry. To assess the influence
of variable mortality rates, I calculated produc-
tion for the 1970 year class at Maxwell Springs
from emergence to October with different mortal-
ity schedules. If mortality were five times greater
during the first half of the interval than during
the second, production would have been 63 kg/ha,
and if mortality rates varied by tenfold, produc-
tion would have been 60 kg/ha. With a constant
mortality rate from emergence to October, esti-
mated production was 109 kg/ha. Thus, if there
was an initial high mortality of fry, production
of age 0 trout could have been overestimated by
50 to 60%, and annual production by all age-
groups would have been overestimated by 19%.

Assumptions that instantaneous growth rates
were constant from emergence to fall certainly
oversimplify growth history of fingerlings, but
overall effects of this assumption on production
estimates did not appear significant. Hunt (1966)
found large variations in monthly growth rates
of brook trout from emergence to October; growth
rates increased to a maximum in May and then
declined the rest of the year. Average monthly
growth rates from February through April were
not different than those from May to October
U-test P>0.05). These periods correspond to
periods for which I calculated production by age 0

762

CARLINE: PRODUCTION BY WILD BROOK TROUT

trout. If changes in growth rates of trout fry in
my study were similar to those in Lawrence
Creek, then assumptions of constant growth rates
are much less serious than those regarding
mortality rates.

To estimate production with the Ricker formula
(G x B) one assumes that no emigration or im-
migration occurred (Chapman 1967). Effects of
emigration on production are similar to those of
mortality. Recognition of emigration allows one
to demonstrate the fate of production, but does
not directly affect calculated values. Immigration,
however, can have serious effects upon production
estimates. The Ricker formula integrates two
simultaneous processes, growth and mortality.
Numbers offish are assumed to decrease exponen-
tially and their mean weights are assumed to
change in a similar fashion. When immigration
occurs and an age-group increases in number, the
Ricker formula treats this increase as an exponen-
tial one.

To assess the influence of immigration on pro-
duction, I simulated three different immigration
patterns in which year class density increased
from 1 ,400 trout/ha in April to 3,600/ha in October
(Figure 9). Curve B represents an exponential
increase in density, i.e., that assumed in the
Ricker formula. Production was calculated at
monthly intervals and the same growth rate was
used for each simulation. If all immigration had

4500

3500

2500

1500

500

A. 57

C 26

APRIL

JUNE

AUG

OCT

FIGURE 9.— Three hypothetical immigration patterns for a
single age-group. Production for each curve was calculated
monthly using the same instantaneous growth rate i G = 0.99, t
= 0.5 yr>. Total production for each curve is given next to letter
designation.

occurred in the first half of the interval (A),
estimation by the Ricker formula would have
underestimated production by 307c , and if trout
had immigrated in the latter half of the interval
(C), production would have been overestimated
by 549c. This increase in cohort size was similar
to that of age 1 trout in Hoglot Springs in 1970,
the largest increase that occurred in either Hoglot
or Clubhouse springs. Therefore, potential errors
in production estimates for other intervals would
have been less serious.

Recruitment, via immigration and spawning
within ponds, appeared to be the most important
factor influencing production. Even though pro-
duction by age 0 trout could have been over-
estimated, production by age 1 and older trout
was closely tied to recruitment rates. In other
studies, only a few attempts have been made to
link production to recruitment. Backiel and
Le Cren (1967) analyzed data from Lawrence
Creek (Hunt 1966) and Cultus Lake (Ricker and
Foerster 1948) and showed that production was
directly related to numbers of emerging fry.
Highest annual production of sockeye salmon,
Oncorhynchus nerka, in Lake Dal'neye occurred
in years of highest egg deposition (Krogius 1969 1.

In this study population biomass was deter-
mined by annual recruitment. Among popula-
tions, production was most influenced by trout
biomass because age-specific growth rates were
not significantly different. As a result, production
increased linearly with biomass. Hunt (1974)
found similar linear relationships for brook trout
in Lawrence Creek. Backiel and Le Cren (1967)
reviewed density effects on production and illus-
trated both linear and curvilinear associations
between production and biomass. Curvilinear
relationships resulted when growth rates were
severely depressed at high fish densities and in
all of these studies fish were stocked and move-
ment was restricted. I am not aware of any study
of wild fish populations in which inverse density-
dependent growth caused curvilinear relation-
ships between production and biomass. Rather,
in wild populations of salmonids, fish densities
appear to be maintained at levels that do not
result in seriously depressed growth rates and
production increases directly with biomass.

Standing crops of harvestable trout (age 1 and
older) in the three populations declined over a
year's time because total mortality exceeded
growth rates, even though immigration bolstered
density of some age-groups (Table 12). The actual

763

FISHERY BULLETIN: VOL. 75. NO. 4

TABLE 12. — Comparison of annual yield of brook trout with potential yield and biomass
loss to natural mortality. Data are for trout age 1 and older. All values are in kilograms
per hectare.

Pond and interval

Annual
biomass loss

(2)

Annual

production

(1 - 2)

Potential
yield

(3)

Actual
yield

[(1 + 2) - 3]

Biomass loss

to natural

mortality

Actual

potential

yield

(%)

Clubhouse Springs:
1970-71

31.0

49.7

80.7

68.4

12.3

Hoglot Springs:
1969-70

27.0

89.0

116 0

54.6

61.4

1970-71

8.8

114.5

1233

25.4

97.9

Maxwell Springs:
1969-70

87.9

200.3

288.2

71.8

216.4

1970-71

57.8

188.2

246.0

39.7

206.3

biomass loss includes both the change in standing
crops from one year to the next and the production
during that interval. In all three populations, the
actual annual loss in biomass exceeded average
standing crops. This loss in biomass may be
viewed as the potential yield (Table 12). Biomass
lost to natural mortality was calculated as the
difference between potential and actual yields.
Fate of potential yields appeared dependent upon
fishing pressure. In Clubhouse Springs fishing
pressure was highest (Table 9), and yield in 1970
was 859c of the potential. Only 16 and 25% of
potential yields were taken in Maxwell Springs,
where fishing pressure was lowest. The relatively
low level of exploitation in Maxwell Springs
resulted in substantial biomass losses to natural
mortality.

Estimates of fish production in lentic waters
have varied from less than 1 g/m2 to 64 g/m2,
but in most studies they were <20 g/m2 (Le Cren
1972). Highest reported values were for juvenile
sockeye salmon in Lake Dal'neye (Krogius 1969).
Production estimates for Maxwell Springs (21-
33 g/m2) are among the highest values currently
available. Even if contributions of age 0 trout in
Maxwell Springs are ignored, production esti-
mates still rank high (11-22 g/m2). Carline and
Brynildson (1977) suggested that high levels of
trout production in ponds similar to Maxwell
Springs were due to extensive littoral areas and
high standing crops of benthic organisms. While
prevailing food densities determine the level of
potential fish production, attainment of this poten-
tial level is dependent upon annual recruitment
of some minimum number offish.

In this study differences in spawning areas
among ponds were obvious and trout production
varied accordingly. In many instances quantity
and quality of spawning sites are unknown or
cannot be readily determined. Where recruitment
is limiting, fish production will be relatively low,

regardless of the water's general productivity.
If production is to be used as a measure of a
system's capacity to support species of interest,
recruitment of that species should be at or near
maximum levels.

ACKNOWLEDGMENTS

I am indebted to O. M. Brynildson and
R. L. Hunt for their guidance throughout the
study. K. Neirmeyer and H. Sheldon provided
much technical assistance. J. J. Magnuson made
many valuable suggestions during data analysis.
D. W. Coble and R. A. Stein ably reviewed earlier
manuscripts. This study was supported by the
Wisconsin Department of Natural Resources and
by funds from the Federal Aid in Fish Restoration
Act under Project F-83-R.

LITERATURE CITED

ADAMS, L.

1951. Confidence limits for the Petersen or Lincoln Index
used in animal population studies. J. Wildl. Manage.
15:13-19.
ALLEN, K. R.

1951. The Horokiwi stream, a study of a trout population.
N.Z. Mar. Dep. Fish. Bull. 10, 238 p.

Backiel, T., and E. D. Le Cren.

1967. Some density relationships for fish population
parameters. In S. D. Gerking (editor), The biological
basis of freshwater fish production, p. 261-293. Blackwell,
Oxf.
BRASCH, J.

1949. Notes on natural reproduction of the eastern brook
trout (S. fontinalis) with a preliminary report on several
experiments on the subject. Wis. Conserv. Dep., Div.
Fish. Biol., Invest. Rep. 653, 9 p.
CARLINE, R. F., AND O. M. BRYNILDSON.

In press. Effects of hydraulic dredging on the ecology of
native trout populations in Wisconsin spring ponds.
Wis. Dep. Nat. Resour. Tech. Bull.
CHAPMAN, D. W.

1967. Production in fish populations. In S. D. Gerking
(editor), The biological basis of freshwater fish produc-
tion, p. 3-29. Blackwell, Oxf.

764

CARLINE: PRODUCTION BY WILD BROOK TROUT

EIPPER, A. W.

1964. Growth, mortality rates, and standing crops of trout
in New York farm ponds. N.Y. Agric. Exp. Stn., Ithaca,
Mem. 388, 68 p.
GERKING, S. D.

1967. Introduction. In S. D. Gerkingl editor), The biolog-
ical basis of freshwater fish production, p. xi-xiv.
Blackwell, Oxf.
HAUSLE, D. A.

1973. Factors influencing embryonic survival and emer-
gence of brook trout iSalvelinus fontinalis). M.S. Thesis.
Univ. Wisconsin, Stevens Point, 67 p.

HUNT, R. L.

1966. Production and angler harvest of wild brook trout

in Lawrence Creek, Wisconsin. Wis. Conserv. Dep.

Tech. Bull. 35, 52 p.
1971. Responses of a brook trout population to habitat

development in Lawrence Creek. Wis. Dep. Nat. Resour.

Tech. Bull. 48, 35 p.

1974. Annual production by brook trout in Lawrence
Creek during eleven successive years. Wis. Dep. Nat.
Resour. Tech. Bull. 82, 29 p.

IVLEV, V. S.

1945. The biological productivity of waters. [In Russ.]
Ups. Sourem. Biol. 19:98-120. (Translated by W. E.
Ricker. 1966. J. Fish. Res. Board Can. 23:1727-1759.)

KROGIUS, F. V.

1969. Production of young sockeye salmon (Oncorkyncus
nerka KWalb.) in LakeDal'neye. [In Russ.l Vopr. Ikhtiol
9:1059-1076. (Transl. in Prob. Ichthyol
LAMBOU, V. W.

1961. Determination of fishing pressure from fishermen
or party counts with a discussion of sampling problems.
Southeast. Game Fish Comm. Proc. 15th Annu. Conf,
p. 380-401.
LE CREN, E. D.

1972. Fish production in freshwaters. Symp. Zool. Soc.
Lond. 29:115-133.
RICKER, W. E.

1975. Computation and interpretation of biological
statistics of fish populations. Fish. Res. Board Can.,
Bull. 191, 382 p.
RICKER, W. E„ AND R. E. FOERSTER.

1948. Computation of fish production. Bull. Bingham
Oceanogr. Collect, Yale Univ. 11:173-211.
VLADYKOV, V. D.

1956. Fecundity of wild speckled trout iSalvelinus fon-
tinalis) in Quebec lakes. J. Fish. Res. Board Can. 13:
799-841.
WYDOSKI, R. S., AND E. L. COOPER.

1966. Maturation and fecundity of brook trout from
infertile streams. J. Fish. Res. Board Can. 23:623-649.

765

KOKO HEAD, OAHU, SEA-SURFACE TEMPERATURES AND

SALINITIES, 1956-73, AND CHRISTMAS ISLAND

SEA-SURFACE TEMPERATURES, 1954-73

GUNTER R. SECKEL1 AND MARIAN Y. Y. YONG2

ABSTRACT

Sea-surface temperatures and salinities have been collected twice weekly at Koko Head, Oahu,
Hawaii, since 1956; and at Christmas Island in the central equatorial Pacific, sea-surface temperatures
have been collected daily since 1954. In 1971, Seckel and Yong used harmonic analysis as a curve-
fitting method to bring these observations, 1 yr at a time, through 1969, into a form useful for
descriptive and numerical applications. In this paper the analyses are updated through 1973 and
the method is used to describe the entire data series.

The data series have been separated into several scales of variability: long-term variability
(periodicities larger than 1 yr), short-term variability (12-mo and shorter periodicities), average
annual cycle (the 12-, 6-, 4-, and 3-mo periods), and the residual variability that characterizes
individual years (the short-term variability with the annual cycle removed). In contrast to the
Koko Head temperature where the annual cycle predominates, the interannual variability pre-
dominates, at times obscuring the annual cycle, in the Koko Head salinity and Christmas Island
temperature. The interannual change of the Koko Head salinity can be about three times, and that
of the Christmas Island temperature can be about four times the average annual variability. In the
average annual temperature and salinity cycles at Koko Head the amplitudes of the 6-, 4-, and
3-mo periods are small in relation to the 12-mo period. In the average annual temperature cycle
at Christmas Island, however, the amplitude of the 6-mo period is almost one-half that of the 12-mo
period. The residual variations exhibit changing amplitudes and periodicities at intervals of more
than 1 yr that resemble amplitude and frequency modulations.

Speculations are made about processes that contribute to the temperature and salinity variations.
It appears that in addition to the heat exchange across the sea surface, advection contributes
materially to the observed changes at Koko Head and Christmas Island.

Harmonic coefficients resulting from the analyses are listed in the appendices to facilitate repro-
duction of the data presented.

In an earlier paper, Seckel and Yong (1971) used
harmonic analysis as a curve-fitting method,
bringing rapidly into usable form regularly sam-
pled sea-surface temperatures and salinities.
Analyses were made of sea-surface temperature
and salinity obtained once or twice weekly from
1956 to 1969 at Koko Head, Oahu (lat. 21°16'N,
long. 157°41'W,), and of sea-surface temperature
obtained daily from 1954 to 1969 at Christmas
Island (lat. 1°51'N, long. 157°23'W). The tempera-
ture and salinity variations for each year were
then specified by sets of harmonic coefficients
and phase angles. Values calculated at 15-day
intervals from the resulting annual functions

'Southwest Fisheries Center Pacific Environmental Group,
National Marine Fisheries Service, NOAA, c/o Fleet Numerical
Weather Central, Monterey, CA 93940.

2Southwest Fisheries Center Honolulu Laboratory, National
Marine Fisheries Service, NOAA, P.O. Box 3830, Honolulu,
HI 96812.

were used in long-term analyses of the entire data
records. These analyses showed that interyear
differences in the Koko Head salinity and Christ-
mas Island temperature were larger than sea-
sonal changes.

The long-term changes in surface properties
reflect climatic scale ocean-atmosphere processes
and, in turn, affect these processes. The changes
in properties and processes affect life in the sea.
For example, the Koko Head salinity changes
indicate primarily changes in the advection pro-
duced by variations in ocean circulation (Seckel
1962). It was postulated that changes in circula-
tion also affect the concentration and, therefore,
the availability of skipjack tuna caught in Hawaii
(Seckel 1972).

The long-term changes in the Christmas Island
temperatures are linked with large-scale (at
least ocean-wide) ocean-atmosphere processes.
Bjerknes (1969) related anomalously high tern-

Manuscript accepted March 1977.

FISHERY BULLETIN: VOL. 75, NO. 4, 1977.

767^
9&?

FISHERY BULLETIN: VOL. 75, NO. 4

peratures and high precipitation at Canton Island
in the central equatorial Pacific with intensifi-
cation of the Hadley circulation and changes in
the "southern oscillation." Quinn (1974) related
an index of the southern oscillation (the difference
of atmospheric pressure between Easter Island
and Darwin, Australia) with El Nino phenomena
and abnormally high rainfall in the equatorial
Pacific. One of the latter is the failure of the Peru-
vian anchovy fishery. The large interyear dif-
ferences of equatorial sea-surface temperatures
undoubtedly affect the biota in as yet undescribed
ways.

It is of value, therefore, to bring the results
of monitoring into a form that is useful for fishery
applications. Toward this objective we have 1) up-
dated our previous Koko Head and Christmas
Island analyses through 1973; 2) analyzed the
long series (18 yr for Koko Head, 20 yr for Christ-
mas Island) and separated changes into long-term
variability, the annual cycle, and the short-term
variability that characterizes individual years;
and 3) speculated about the processes that affect
the changes evident in the data records.

THE 1970-73 UPDATE
Sampling and Processing

Koko Head, where bucket samples for tempera-
ture and salinity determinations were taken twice
weekly, is located at the exposed, eastern shore
of Oahu. At this location, cliffs extend into the
water, and temperature and salinity samples
have been found to be representative of offshore
conditions. At Christmas Island, bucket tempera-
tures were obtained daily near the plantation
village on the ocean side of the lagoon entrance.
Measurements were made during the morning at
each location.

The procedures used to derive the harmonic
coefficients for the 1970-73 observations were the
same as those described by Seckel and Yong
(1971). Fourier analysis was performed on the
residuals from a linear fit so that the temperatures
and salinities are expressed as a function of time,
t, by

S - K + bt + £ Cn cos co (nt — an).

(1)

n=\

where K =F(t0) + ^, to = 2?, and k isthe highest
z 7/

768

harmonic in the series. F(t0) is the first observed
value, A0 is the Fourier coefficient for n — 0,
Cn are the coefficients for n =£ 0, and txn are the
phase angles, b is the slope of the straight line
joining the first and last observations of the funda-
mental period, T.

The fundamental period for the Koko Head
analyses was 365 days. For the Christmas Island
analyses the fundamental periods were 120 which
for a full year followed in sequence with a 30-day
overlap from Julian day 1 to 20, 91 to 210, 181
to 300, and 271 to 390 extending 25 days into
the following year.

Results

Results of the analyses for the update years
are presented in the appendices. Coefficients and
phase angles for the Koko Head temperatures and
salinities are found in Appendix A, Tables 1 and 2.
Figures of the expected values computed from the
harmonic functions together with the observed
values for the Koko Head temperatures and salin-
ities are found in Appendix B, Figures 1 and 2.
The coefficients and phase angles for the Christ-
mas Island temperatures are found in Appendix C,
and the plotted functions together with the ob-
served values are found in Appendix D.

Standard errors of estimate for the fitted Koko
Head temperatures and salinities and Christmas
Island temperatures are listed in Appendix E,
Tables 1, 2, and 3, respectively.

Christmas Island Data Problems

Observer problems at Christmas Island caused
the sea temperature sampling to be interrupted
from May 1972 to April 1973. The data gap was
reduced by Hawaii Institute of Geophysics (HIG)
bucket temperatures obtained daily since Novem-
ber 1972 near the airport on the northeast shore
of the island. Although NMFS (National Marine
Fisheries Service) sampling resumed in April
1973, HIG data were used in our analysis for the
entire year. In our long-term analysis the remain-
ing data gap between May and November 1972
was closed by linear interpolation. Mean monthly
temperatures obtained from the two sampling
sites indicate that NMFS temperatures are on
average about 0.5°C lower than the HIG values
(Table 1). The HIG data have not been adjusted
to reflect this temperature difference.

The large scatter of data at Christmas Island

SECKEL and YONG: SEA-SURFACE TEMPERATURES AND SALINITIES

TABLE 1. — Mean monthly sea-surface temperature (°C),
Christmas Island: National Marine Fisheries Service station
(NMFS) and Hawaii Institute of Geophysics station (HIG).

Date

NMFS

HIG

1973

1974

May

June

July

August

September

October

November

December

January

February

March

April

May

June

Average

26.6

26.2

24.7

25.6

23.6

25.2

23.9

24.5

23.8

24.1

23.4

23.8

23.0

23.3

23.4

23.5

23.9

24.0

24.1

24.3

24.6

24.7

25.2

23.9

24.9

23.6

25.0

24.1

24.6

in comparison with that at Koko Head indicates
another data problem. The scatter probably is
caused by sampling of water in the shallow beach
area that is more sensitive to changes in the local
heating-cooling processes than the deep water of
an offshore site.

Finally, there are no systematically observed
sea-surface temperatures near Christmas Island
against which the shore measurements can be
calibrated. However, the monthly pamphlet Fish-
ing Information3 contains a temperature chart for
the equatorial Pacific. Contours near Christmas
Island are based on insufficient observations to
reproduce the temperature distribution reliably.
Therefore, the values from these charts, plotted
on the annual graphs of Appendix D, show large
variations in the difference between the Fishing
Information temperatures and Christmas Island
observations. On average the Fishing Information
values are 1.3°C higher than the midmonth ex-
pected values with differences ranging from -1.2°
to 4.1°C.

The discrepancy between the temperature sets,
in part, may be due to a tendency toward a warm
bias of merchant vessel temperature reports.
More probable, however, Christmas Island tem-
peratures, being measured in the morning, reflect
the effect of night cooling in shallow water that
would be in excess of the temperature decline
taking place in deeper, offshore water.

Despite the apparent discrepancies between the
beach and offshore temperatures, the data from
the shore sampling sites reflect climatic scale

Wishing Information. March 1970 through December 1973.
U.S. Dep. Commer., NOAA, Natl. Mar. Fish. Serv., Southwest
Fish. Cent., La Jolla, Calif.

anomalies. For example, both the Christmas
Island record (Seckel and Yong 1971) and the
Canton Island record (Bjerknes 1969) show the
equatorial cold anomaly of 1955-56, the warm
anomaly of 1957-58, and the anomalous biannual
temperature variations of 1963-67.

ANALYSES OF
LONG-TERM DATA RECORDS

In this section we present harmonic analysis
results of the entire data series and separately
display the long-term variability, the short-term
variability, the average annual cycle, and the
variability that characterizes individual years.

The entire data series is expressed by the
function

Sl = A + 2^ Cn cos oj (nt

OCn

(2)

n=l

where A gives the average value of the series,
k is the highest harmonic of the analysis, and
other symbols have the same meaning as given
for Equation (1).

Input values for these analyses were calculated
at 15-day intervals from the annual analyses
presented in this and our previous paper (Seckel
and Yong 1971). Analysis of the 1956-73 Koko
Head data was carried to the 72d harmonic and
of the 1954-73 Christmas Island data to the 80th
harmonic so that the shortest period resolved in
each series is 3 mo. Analyses were carried out
on the residuals from a linear fit as in the analyses
of the annual data sets. The harmonic and linear
coefficients for the long-term series are listed in
Tables 1, 2, and 3 of Appendix F.

The fitted curves resulting from these analyses
together with the input values are shown in
panels A of Figures 1, 2, and 3. Dominant in the
Koko Head temperature is the annual variation
without pronounced longer term trends other
than the rise of maximum and minimum tempera-
tures from 1966 to 1968. In contrast to the Koko
Head temperature curve, the salinity curve shows
longer term variations that are larger than the
seasonal variations. Also, during some years such
as in 1957, annual variation is not apparent. The
Christmas Island temperatures convey a similar
picture; interannual changes are larger than the
annual changes. Again, the latter may be ob-
scured or absent as during the years 1963-66 and
in 1973 when biannual changes dominated.

769

FISHERY BULLETIN: VOL. 75, NO. 4

LLl

1956 1957 1958 1959 I960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973

FIGURE 1. — Koko Head temperature, 1956-73: A. Fitted curve with a 3-mo resolution (n = 1-72). B. Long-term variation (n = 1-17).
C. Short-term variation (n = 18-72). D. Residual variation (n = 19-35, 37-53, 55-71).

The amplitudes (C„) of the long-term analyses
(Figure 4) confirm these qualitative impressions.
In the Koko Head temperature, the amplitude
of the annual sinusoid (18th harmonic) is dom-
inant and almost six times as large as the largest
amplitude of the long periods. In the Koko Head
salinity and Christmas Island temperature, on
the other hand, long periods have the largest
amplitudes. For the Koko Head salinity the
amplitude of the fourth harmonic is larger than
that of the annual sinusoid and for the Christmas
Island temperature the amplitude of the first
harmonic is almost twice that of the annual
sinusoid.

Long-Term Changes

When long-term changes are of interest, the
annual and shorter term variability can be
filtered by a variety of methods including the
commonly used 12-mo moving average method.
After harmonic analysis has been used as a curve-
fitting technique, however, it is simple to evaluate
only the terms in the harmonic function up to
but not including the annual sinusoid in order
to display long-term changes. Thus, in Equation
(2), the Koko Head temperatures and salinities
were evaluated for n = 1 to 17 and the Christmas
Island temperatures for n =1 to 19. The resulting

770

SECKEL and YONG: SEA-SURFACE TEMPERATURES AND SALINITIES

35 50

35 25

35.00

34 75

34 50

3525

35.00

34 75

t 3450

-0 50

0.25

0.00

-0.25

\ A/\.~^n/\/\ A~ /\

j\l\

r\ t

\/\ \/\

/Ya

AAA

/V- /"

\ A

\ rj V Vv^' \J w \jS \

vl/ v

J ^

VVV\

1 """ v~

' v V

^/ ^v

J\/

^ v

1956 1957

1958

1959

I960

1961 1962 1963 1964

1965

1966

1967

1966

1969

1970

1971

1972

1973

FIGURE 2.— Koko Head salinity, 1956-73: A. Fitted curve with a 3-mo resolution (n = 1-72). B. Long-term variation <n = 1-17).
C. Short-term variation (n = 18-72). D. Residual variation in = 19-35, 37-53, 55-71).

curves are shown in panels B of Figures 1, 2,
and 3.

In the Koko Head temperature little variation
due to the longer period harmonics is apparent
until 1960 when perturbations of 0.5° to 1°C
began. A rising temperature trend between 1966
and 1968 was followed by a decline to a pre-1960
temperature level. Both the Koko Head salinity
and Christmas Island temperatures show the
large perturbations previously noted. At Koko
Head a pronounced salinity decline began in 1966,
reaching almost 34.5%o in 1968 before rising
again to a range near 35%o. Times of high Christ-

mas Island temperatures stand out. A prominent
feature is the pronounced temperature decline
during 1973 from one of the highest values to the
coldest temperatures observed during the 20 yr
of our record.

Short-Term Changes

The short-term changes relative to the long-
term trends are another scale of interest that can
be obtained by subtracting the moving average
or the long-term values of the previous section
from the monthly observations. In our case, and

771

FISHERY BULLETIN: VOL. 75, NO. 4

1954 1955 1956 1957 1958 1959 I960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973

FIGURE 3. — Christmas Island temperature, 1954-73: A. Fitted curve with a 3-mo resolution (n = 1-80). B. Long-term variation
(n = 1-19). C. Short-term variation (n = 20-80). D. Residual variation (n = 21-39, 41-59, 61-79).

when variations of <3 mo need not be resolved,
it is simple to display short-term changes by
evaluating the higher harmonics in Equation (2)
beginning with the annual sinusoid (n = 18-72
for Koko Head, n = 20-80 for Christmas Island).
The resulting curves are shown in panels C of
Figures 1, 2, and 3.

The Koko Head temperature curve looks sim-
ilar to the initial harmonic fit (Figure 1A) because
the long-term changes are small in comparison
to the annual variations. In the case of the Koko
Head salinity and the Christmas Island tempera-
ture, the annual variations that during some

772

years were obscured by the long-term trends are
clearly apparent. At Koko Head low salinities
occur during spring and summer and high salini-
ties during fall and winter. At Christmas Island
high temperatures occur in late spring and low
temperatures in fall or winter.

Annual Sinusoid and Its Harmonics

Evaluation of the annual sinusoid and its har-
monics yields the mean annual variation. For
annual analyses the harmonics n =1,2, 3, and 4
have periods of 12, 6, 4, and 3 mo. For the 18-yr

SECKEL and YONG: SEA-SURFACE TEMPERATURES AND SALINITIES

I50| | | | | | | | | I I I I I I I I I I I M I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I

1 I i ! i r

• 0.30
UJ

I 020
□

0 10

.ll.hlil.ii

KOKO HEAD , OAHU

■IHilLillli.l-ihiiL-liiiliiillil

illl1_l.ll««Hl.llH.««..

i ,

0 10, ! | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |

008

J' 0.06

i i i i i i i i i i i i i i r

KOKO HEAD, OAHU

i °

0.02

■IIImM

■■iili.ill.HilliiLliiillllih-iiLi.ii.iiin.i.-i-

id cbc*i^K>cc>o's"^"-"C7icb»bif>croojed — oo^OT(TiQO©QdKf^^Ku>^^U)U>o^u^ioo^ir>^^^^^^^^^^^fOiofOiOfOfOroi<iK>fOioroiOfOiOfOi<ifO
— OKtfi^-fOioCMCsjcg

CM-
PERIOD IN MONTHS

1.00

oooo

?ogo
CVJ CO 10
CSJ —

qoflONOcoo

(O — oo — mcoo<T<J>fl-ou>cMcn<oioqf-iO'0 — o>t^inioc<jocr>t^ioioi<icM — ocncor-ioin<r<rioc\j ocricncocqf^ioioininwrotocjtvjcvj- ■ — oq

cbi^<Dir>^'fOoJcu — oopo>cricdcocbco>-^f^f^^u3co^u>u5ici^iniriiri

PERIOD IN MONTHS

FIGURE 4.— Absolute magnitude of amplitudes of the long-term harmonic functions for Koko Head temperatures, 1956-73; Koko

Head salinities, 1956-73; and Christmas Island temperatures, 1954-73.

Koko Head series, these periods are given by
n = 18, 36, 54, and 72; and for the 20-yr Christmas
Island series, they are given by n = 20, 40, 60,
and 80. The mean annual variations evaluated
from Equation (2) are shown in Figure 5 panels
A, B, and C.

The mean annual temperature range of 3°C at
Koko Head is about twice the long-term range.
In contrast, the mean annual salinity range is
0.2%o and only about 307c of the long-term range.
At Christmas Island the mean annual tempera-
ture range is 1°C and only one-quarter of the
long-term range.

At Koko Head the annual sinusoid, although
visibly modified, dominates the mean annual
changes. In both the temperature and the salinity,
the amplitude of the annual sinusoid is an order
of magnitude larger than that of the 6-, 4-, and
3-mo sinusoids (Figure 4). In the case of the tem-
perature, the interference pattern of the 6- and
4-mo sinusoids is such that during the first half
of the year the annual sinusoid is not visibly
affected. Constructive interference by these sinus-
oids depresses the annual sinusoid by about 0.2°C
in August, which causes first an increase by that
amount in October and then a decrease by the end

773

1.50

o 50-

tr.

-1.00

JAN

JUNE

MONTHS

JAN

.10 -

.05 -

E o

-05

! I ! 1 1

1 1 1 1 1 1 1 1 I i 1 1 1 I

JAN

JUNE

MONTHS

JAN

FISHERY BULLETIN: VOL. 75, NO. 4

150

1.00

i — i — i — i — i — i — r

-1.00

1.50 I — I — L.

JAN

i i i i

JUNE

JAN

MONTHS

FIGURE 5. — Mean annual variations: A. Koko Head temperatures (re = 18, 36, 54, 72). B. Koko Head salinities (re = 18, 36, 54, 72).

C. Christmas Island temperatures (re = 20, 40, 60, 80).

of the year. Consequently, the mean annual curve
reflects the temperature trends evident in indi-
vidual years in that warming lasts between 1 and
2 mo longer than cooling and the cooling rate
is higher than the warming rate.

Departures of the mean annual salinity varia-
tion from the annual sinusoid, evident in Fig-
ure 5B, are not significant.

In contrast to the Koko Head spectra, the ampli-
tude of the 6-mo sinusoid at Christmas Island
is large enough to produce a significant modifica-

tion of the annual sinusoid (Figure 5C). The abso-
lute amplitudes of the 12-, 6-, 4-, and 3-mo
sinusoids are 0.43°, 0.21°, 0.04°, and 0.003°C,
respectively. Thus, the mean annual temperature
variation at Christmas Island has the typical
interference pattern produced by a 12- and a 6-mo
sinusoid as illustrated in Figure 6. The residual
curve, namely the difference between the mean
annual curve and the annual sinusoid, is approx-
imately the 6-mo sinusoid.

Residual Variations

0.8

0.6

0.4

0.2

K
3

5 -0.2

-0.4

-0.6

-0.8

1 I

! 1 1

! 1

1 1

! -

\ i

/ ''~~\

\\
\ \

V i

\ \

•• ' 1

' J

/ ;

\ \ .-•"

1 I

''■■■ ' /"'

'•• \ *

\ / t

'■■ ' I

•••....V \

'■■ / /

v....,/

*■■ 1

k / /

/ /

V/ /

/ J

y \ /

^.y

1 1

JAN MAR MAY JULY SEPT NOV JAN MAR

MONTHS
FIGURE 6. — Interference patterns of sinusoids for mean annual
variation at Christmas Island. Solid line - n = 20, 40, 60, 80;
dashed line- annual sinusoid (n = 20); dotted line- remaining
variation (re =40, 60, 80).

774

The dominant feature in the short-term curves
(panel C of Figures 1, 2, 3) is the annual variation
superimposed upon which is the variability that
characterizes each year. This "residual" variabil-
ity is obtained by evaluating in Equation (2) the
short-term variability without the annual sinus-
oid and its harmonics (n = 19-35, 37-53, and
55-71 for Koko Head, and n = 21-39, 41-59, and
61-79 for Christmas Island). Residual variability
is shown in panel D of Figures 1, 2, and 3.

The residual curves are the interference pattern
produced by all the sinusoids used in the evalua-
tion. The irregular amplitudes and periodicities
occurring at intervals of more than 1 yr give an
impression of amplitude and frequency modula-
tions. For example, in the Koko Head salinity
curve, relatively large perturbations occur in
groups during 1959, 1964-65, 1967-68, 1969-70,
and 1972-73. In the Christmas Island residual
temperature curve, relatively large perturbations
during 1955-60 are followed by smaller pertur-
bations during 1960-65 and by larger perturba-

SECKEL and YONG: SEA-SURFACE TEMPERATURES AND SALINITIES

tions again during 1965-68. These modulations
are of a long-term nature but do not appear to
be related with the variations shown in panel B
of Figures 1, 2, and 3.

On the Separation of Variability
Into Various Time Scales

Although there are a number of curve-fitting
procedures such as were reviewed by Holloway
(1958), we have found Fourier analysis to be a
convenient method for the Koko Head and Christ-
mas Island time series. The filtering described
above is a byproduct of this method and serves
interpretive and descriptive purposes.

Although the moving average method is not
recommended for climatological time series,4 it
is commonly used. For this reason, curves ob-
tained by the moving average and the harmonic
analysis methods are compared in Figures 7 and 8.
The long-term as well as the residual curves of
the two procedures are similar though not identi-
cal. The amplitudes of the long-term variations
are larger in the curves derived by harmonic
analysis than in those derived by the moving
average method. This difference is to be expected
because, in contrast to the harmonic method,
input values in the moving average method are
weighted equally.

The examples in Figures 7 and 8 were chosen
because they illustrate limitations, in terms of
physical interpretations, of the filtering tech-
niques. A time series of the sea-surface tempera-
ture (salinity) is the signature of processes that
govern the observed changes. What information
about the governing processes, then, can be
inferred from the time series? For example, is
the observed change of temperature the result
of an anomaly in the local heat exchange across
the sea surface and advection produced by the
local wind driven current, or is this temperature
change a part of a larger scale change with the
local processes remaining normal? The examples
in panel B of Figures 7 and 8 exhibit variations
with an annual periodicity during 1957 in the
Koko Head salinity and during 1963, 1964, and
1965 in the Christmas Island temperature al-
though this periodicity is not apparent in panel
A of Figures 2 and 3. In these cases were annual

variations, such as produced by annually varying
processes, present or were they absent?

In the case of the moving average method, 2 yr
of data are required to provide the smoothed curve
for a single year. At Koko Head the normal mid-
year declines in salinity occurred during 1956
and 1958, affecting the shape of the smoothed
1957 curve. Consequently the residual curve
showed an annual variation during 1957 (Fig-
ure 7B). At Christmas Island (Figure 8B), the
residual temperature curve during 1964 also
exhibits an annual variation, a maximum in
spring and a minimum in fall, although no sea-
sonal trends were indicated during the adjacent
years (Figure 3A). In this case, was the normal
annual variation in temperature present but
obscured by the long-term trend?

In the harmonic analysis procedure the dom-
inant signal in the annual variation is produced
by the annual sinusoid. The amplitude of this
period is determined by all the data in the series
and contributes the same amount to the short-
term variations of every year shown in panel C
of Figures 1, 2, and 3. For example, a time series
could be synthesized by combining a long-term
variation with one that has an annual periodicity

1956

1957

1958

1959

"Climate change. Tech. Note 79, WMO-No. 195, Tp. 100.
Seer. World Meteorol. Organ., Geneva, Switz., 1966, 79 p.

FIGURE 7.— Koko Head salinity, 1956-59: A. Long-term varia-
tion produced by 12-mo moving average and by harmonic func-
tion (n = 1-17). B. Short-term variation (monthly input values
minus long-term values). Solid line — 12-mo moving average;
dashed line — harmonic function (/i = 1-17).

775

FISHERY BULLETIN: VOL. 75, NO. 4

Id
Q.

1 ! I I I I

I I ' ! I i

<r
a:

LlI

1962

FIGURE 8. — Christmas Island temperature, 1962-67: A. Long-term variation produced by 12-mo moving average and by
harmonic function (n = 1-19). B. Short-term variation (monthly input values minus long-term values). Solid line — 12-mo moving
average; dashed line — harmonic function (n = 1-19).

every second year. After harmonic analysis and
separating the hypothetical curve into a long-
term and a short-term variation, the latter would
exhibit an annual periodicity during every year.
Thus, the mathematical procedure cannot an-
swer the questions posed above. The procedures
illustrated in Figures 7 and 8 as well as other
procedures, separate the scales of variability but
there is no basis for inferring that the long-term
changes are related with, possibly, ocean-wide
processes and short-term changes with local proc-
esses. Only if the local processes are measured
is there a physical basis for the separation into
different scales of change.

Speculations About Temperature
and Salinity Variations

It is not the purpose of this paper, and the infor-
mation is not available, to investigate the causes
for the temperature and salinity variations that
have been described. Nevertheless, such an inves-
tigation would further an understanding of the
fishery environment as well as the ocean-atmo-
sphere linkages. It is useful, therefore, to specu-
late about the processes affecting changes in
surface properties.

In Hawaiian waters air-sea interaction pro-
cesses and advection appear to dominate the local

776

SECKEL and YONG: SEA-SURFACE TEMPERATURES AND SALINITIES

change of temperature and salinity ( Murphy et al.
1960; Seckel 1960, 1962). Advection is the product
of the surface temperature (salinity) gradient and
the component of the current normal to the
isotherm or salinity isopleth. Generally near
Hawaii the temperature increases and the salinity
decreases equatorward. Consequently, with a
northward component of flow, advection would in-
crease the temperature and decrease the salinity
at Koko Head.

The usual spring salinity decline at Koko Head
is best explained by advection. It is estimated that
at the latitude of Hawaii there is an excess of
evaporation over precipitation with the highest
excess occurring during spring and summer
(Seckel 1962). Thus, since the salinity is increas-
ing with depth, the only source of lower salinity
water lies south of the islands.

On average the orientation of isotherms is
northwest-southeast and that of salinity isopleth
is zonal. In this case only the meridional com-
ponent of flow causes salt advection, but both
meridional and zonal components of flow cause
heat advection. Consequently, meridional com-
ponents of flow causing salinity variations do not
necessarily produce temperature variations. Co-
incident changes of salinity and temperature
that appear to be advection related, tend to occur
during late winter and early spring when the
North Equatorial Current is weak. For example,
between days 60 and 110 of 1973 (Appendix B),
decreasing and increasing temperatures corre-
sponded with increasing and decreasing salini-
ties. Pronounced coincident temperature and
salinity variations occurred during the first half
of 1959 and are most evident in the residual
curves, panel D of Figures 1 and 2.

Coincident changes in temperature and salinity
during specific seasons are not necessarily associ-
ated in the longer term. From 1956 through 1959
when the long-term salinity variations were pro-
nounced, there was no long-term temperature
change (panel B of Figures 1, 2). Later, a strong
salinity decline lasting from 1966 to 1968 corre-
sponded with a temperature increase. Then, as the
salinity returned toward 35%o, the temperature
also returned to the pre-1965 values. The first
situation may mean that there were climatic
shifts in the general northwest-southeast direc-
tion, parallel to the isotherms, thus causing a
long-term change in the salinity but not in the
temperature. In the second situation the climatic

shift was first northward and then southward,
affecting both temperature and salinity.

White ( 1975) described secular changes in baro-
clinic transport and morphology of the North Pa-
cific subtropical gyre and indicated that during
the years of low maximum transport the south-
west portion of the gyre extended farther south
than during the years of large transport. Sim-
ilarly, it is possible that higher baroclinic flow
and tightening of the gyre near Hawaii will result
in lower salinity and a relaxation of flow will
result in higher salinity. The long-term changes
in the Koko Head salinity do not correspond with
the changes described by White and are only in
partial agreement with the supposition when
tested against Wyrtki's (1974) North Equatorial
Current index. The supposition, therefore, is in
error or, the local wind induced surface flow,
superimposed on the baroclinic flow, plays an
important part in the long-term salinity changes.

At Christmas Island, in addition to the heat
exchange and advection, the effect of wind-
induced equatorial divergence is a process affect-
ing the sea-surface temperature. Unfortunately,
meteorological observations suitable for the cal-
culation of heat exchange across the sea surface
were not made on the island. Estimates made by
Wyrtki (1966) and Seckel (1970) indicate the net
heat exchange across the sea surface near Christ-
mas Island to lie in the range of about 100 to
300 cal cm"2 day"1. Assuming that the heat is
distributed through a column of water 50 m deep,
this process can produce temperature changes
from about 0.6° to 1.8°C/mo. Temperature in-
creases within this range are observed (Fig-
ure 3A).

An important term in the net heat exchange is
the radiation from sun and sky that is affected
in the equatorial region of the central Pacific by
large variations in cloudiness (Bjerknes et al.
1969). The effect of such variability is most pro-
nounced in late fall and early winter (Seckel 1970,
figure 6). For example, the average net heat ex-
change near Christmas Island for November 1963
to January 1964 was calculated to be 177 cal cm-2
day"1, and for the same months 1 yr later, 274 cal
cm"2 day"1. The average calculated radiation
from sun and sky during the same periods was
372 cal cm2 day"1 and 440 cal cm "2 day"1 , respec-
tively, and accounted for 70^ of the interyear
difference in the net heat exchange. The Christ-
mas Island water temperature declined in the

777

FISHERY BULLETIN: VOL. 75, NO. 4

first and rose in the second of these years
(Figure 3A).

Heat gain across the sea surface cannot produce
a temperature decline and, therefore, other pro-
cesses must affect the temperature. One of these
processes is heat advection that, at the Equator,
is the product of the zonal current and the zonal
temperature gradient. A raft designed for under-
water biological observations was set out in Feb-
ruary 1964 near the Equator at about long. 150°W
and drifted westward 1,084 km (585 n.mi.) in
194 h (Gooding and Magnuson 1967) giving an
average speed of 155 cm s_1. A current with the
speed of the raft, given a zonal temperature gra-
dient of 0.5°C/10° of longitude, would produce a
temperature change of more than 1.8°C/mo. A
slower surface current, 30 cm s_1, was observed
on the Equator at long. 140°W during April 1958
(Knauss 1960). This current with the same zonal
temperature gradient as before would produce a
temperature decline of about 0.4°C/mo.

The South Equatorial Current indices pre-
sented by Wyrtki (1974) reflect large variability
in the zonal current such as cited above. Addition-
ally, monthly charts of sea-surface temperature
(Eber et al. 1968) show the zonal gradient at the
Equator to range from zero to >1°C/10° of longi-
tude. Advection, therefore, is expected to play a
large role in the temperature variations observed
at Christmas Island.

Near the Equator the wind field is a key element
in the evaporative heat loss, the cloudiness (affect-
ing the radiation flux across the sea surface), up-
welling, and in driving the equatorial currents.
Quinn's (1974) southern oscillation (SO) index is
related to the central South Pacific trade winds.
It is not surprising, therefore, to find coherence
in the changes of the SO index, Wyrtki's current
index, and the Christmas Island temperature.
Selecting the pronounced features of Figure 3B,
declining SO index values during 1956, 1963,
1965, 1968, and 1971-72 correspond with rising
temperatures. Increasing index values during
1964, 1966, and 1970 correspond with declining
temperatures. During the first series of years
South Equatorial Current speeds are declining
and during the second series they are increasing.

SUMMARY

In this paper we have used harmonic analysis
to make Koko Head temperature and salinity
time series and Christmas Island temperature

778

time series available for descriptive as well as
numerical applications.

Time series data can be treated by a number
of mathematical procedures in order to elicit
important information. Initially, however, the
presentation of the data in graphical form is most
useful. The graphs in the appendices indicate the
nature of the annual variations, and Figures 1,
2, and 3 indicate the nature of the long-term
variations.

Although spectral analysis is not the objective
of our work, the curve-fitting procedure further
serves the descriptive purposes in that it permits
separation of the time series into different scales
of variability (panels B, C, D of Figures 1, 2, 3).
For example, at Christmas Island the interannual
temperature variation is as much as four times
the average annual variation (Figures 3B, 5C).
Equivalent figures of Koko Head salinity show
that the interannual change can be about three
times as large as the average annual variation.

Results of our analyses are also useful in
numerical applications. Coefficients and phase
angles (Appendices A, C, F) rather than observed
values can be used for further calculations. In
this manner the sampling variability apparent
in the graphs of Appendices B and D is filtered
out and variations of undesired duration can be
omitted.

The separation of the time series into different
scales of variability is a mathematical procedure
and physical inferences must be made with
caution. For example, Figures 2C and 3C show
an annual cycle during every year although no
annual cycle was apparent during 1957 in Fig-
ure 2A or during 1963, 1964, and 1965 in Fig-
ure 3A. The procedure does not indicate whether
during these years the processes producing the
annual cycle were absent or whether they were
present but obscured by other processes. In
another example, a 12-mo and a 6-mo sinusoid
combine to reproduce the mean annual tempera-
ture cycle at Christmas Island. Again, the proce-
dure does not indicate whether there exists a pro-
cess affecting the temperature with a 6-mo
periodicity.

Available information indicates that advection
is an important process affecting the observed
temperature and salinity variations. At Christ-
mas Island large changes in the zonal component
of the South Equatorial Current appear to cause
large variations in advection. At Koko Head
changes in the North Equatorial Current (Wyrtki

SECKEL and YONG: SEA-SURFACE TEMPERATURES AND SALINITIES

1974) do not correlate with the salinity changes,
and variations in the meridional component of
flow appear to cause the seasonal and long-term
salinity changes.

On the basis of the long-term temperature curve
at Koko Head (Figure IB) one might conclude that
interannual changes in environmental processes
are unimportant. The Koko Head salinity curve
(Figure 2B) shows such an inference to be incor-
rect and illustrates the value of monitoring more
than one property at a location.

An understanding of the processes governing
the temperature and salinity changes is pertinent
to fishery management problems. Our specula-
tions about these processes illustrate that good
correlations between environmental properties
and biological concentrations do not necessarily
imply causal relationships. An example is the
good correlation between skipjack tuna captures
in the eastern Pacific yellowfin tuna regulatory
area and central equatorial Pacific temperatures
or the southern oscillation index, the skipjack
tuna catches lagging about 18 mo.5 Do these corre-
lations mean that temperatures in the central
equatorial Pacific determine larval survival and
year-class strength or do they mean that the cur-
rents affect the concentration and distribution of
skipjack tuna in the eastern Pacific with the tem-
perature variations being ancillary? These ques-
tions are important if environmental factors are to
be included in fishery population models.

ACKNOWLEDGMENTS

We thank A. Bakun, Pacific Environmental
Group, NMFS, for helpful discussions; T. P. Bar-
nett and W. C. Patzert, Scripps Institution of
Oceanography, and J. Hayes, Fleet Numerical
Weather Central, for reading the manuscript and
making many useful comments; and M. J. Vitou-
sek, Hawaii Institute of Geophysics, for making
Christmas Island temperatures available to us.

5Bi-monthly report, November-December 1974. Inter-Am.
Trop. Tuna Comm., La Jolla, Calif.

LITERATURE CITED

BJERKNES, J.

1969. Atmospheric teleconnections from the equatorial
Pacific. Mon. Weather Rev. 97(31:163-172.
BJERKNES, J„ L. J. ALLISON, E. R. KREINS. F. A. GODSHALL,
AND G. WARNECKE.

1969. Satellite mapping of the Pacific tropical cloudiness.
Bull. Am. Meteorol. Soc. 50:313-322.
EBER, L. E., J. F. T. SAUR, AND O. E. SETTE.

1968. Monthly mean charts, sea surface temperature,
North Pacific Ocean, 1949-62. U.S. Fish Wildl. Serv.,
Circ. 258, 168 charts.
Gooding, R. M., and J. J. magnuson.

1967. Ecological significance of a drifting object to pelagic
fishes. Pac. Sci. 21:486-497.
HOLLOWAY, J. L., JR.

1958. Smoothing and filtering of time series and space
fields. Adv. Geophys. 4:351-389.
KNAUSS, J. A.

1960. Measurements of the Cromwell Current. Deep-
Sea Res. 6:265-286.

Murphy, G. I., K. D. waldron, and G. R. seckel.

I960. The oceanographic situation in the vicinity of the
Hawaiian Islands during 1957 with comparisons with
other years. Calif. Coop. Oceanic Fish. Invest. Rep.
7:56-59.
QUINN, W. H.

1974. Monitoring and predicting El Nino invasions.
J. Appl. Meteorol. 13:825-830.

Seckel, G. R.

I960. Advection — a climatic character in the mid-Pacific.

Calif. Coop. Oceanic Fish. Invest. Rep. 7:60-65.
1962. Atlas of the oceanographic climate of the Hawaiian

Islands region. U.S. Fish Wildl. Serv., Fish. Bull. 61:

371-427.

1970. The Trade Wind Zone Oceanography Pilot Study,
Part VIII: Sea-level meteorological properties and heat
exchange processes, July 1963 to June 1956. U.S. Fish
Wildl. Serv., Spec. Sci. Rep. Fish. 612, 129 p.

1972. Hawaiian-caught skipjack tuna and their physical
environment. Fish. Bull., U.S. 70:763-787.
SECKEL, G. R., AND M. Y. Y. YONG.

1971. Harmonic functions for sea-surface temperatures
and salinities, Koko Head, Oahu, 1956-69, and sea-
surface temperatures, Christmas Island, 1954-69. Fish.
Bull., U.S. 69:181-214.

WHITE, W. B.

1975. Secular variability in the large-scale baroclinic
transport of the North Pacific from 1950-1970. J. Mar.
Res. 33:141-155.

WYRTKI, K.

1966. Seasonal variation of heat exchange and surface

temperature in the North Pacific Ocean. Hawaii Inst.

Geophys., Univ. Hawaii, HIG-66-3, 8 p.
1974. Equatorial Currents in the Pacific 1950 to 1970 and

their relations to the trade winds. J. Phys. Oceanogr.

4:372-380.

779

FISHERY BULLETIN: VOL. 75, NO. 4

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SECKEL and YONG: SEA-SURFACE TEMPERATURES AND SALINITIES

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781

FISHERY BULLETIN: VOL. 75, NO. 4

APPENDIX B

Sea-surface temperatures and salinities, Koko Head, Oahu, 1970-73: Fitted curves with observed
values for each year.

Note: Circled observations have not been used in the harmonic analysis.

*-*

?fi

111

1970

111

_>
1-

1971

1972

1973

40 80 120 160 200 240 280 320 360 400 0 40 80 120 160 200 240 280 320 360 400
DAYS DAYS

APPENDIX B FIGURE 1.— Sea-surface temperatures, Koko Head, 1970-73.

35.50

35 25

3500

34 75

34.50
35.50

3525

t 3500

34 75

34.50

1970

1971

1972

1973

40 80 120 160 200 240 280 320 360 400 0 40 80 120 160 200 240 280 320 360 400

DAYS DAYS

APPENDIX B FIGURE 2.— Sea-surface salinities, Koko Head, 1970-73.

782

SECKEL and YONG: SEA-SURFACE TEMPERATURES AND SALINITIES

APPENDIX C

^ Sea-surface temperatures, Christmas Island, 1970-73: Phase angles and coefficients for harmonic
functions for each quarter of the year.

Days 1 to 120 = First quarter,
91 to 210 = Second quarter.
181 to 300 = Third quarter,
271 to 390 = Fourth quarter, extending 25 days into new year,

S = K + bt+ 2, Cn cos co \nt - «„>,

co = ^ days K

t is the time in days beginning with the first day of each quarter.

PHASE ANGLES IN OA V S

N-VALUES

YEAR

QU.

19"

1971

1972

1973

1 2. 44

-6.13

-16.78

-23. 7 3

-2.18

6.9 1

1 *.58

-22. 31

1 7.61

7. 60

1 4. 33

".98

1 3. 05

-6.74

-22.04

-10.25

- 16. 75

26.25

29.57

9.s i

1(J. 38

26. 63

-22. 46

-18.15

-13.17

25.9:

1^.12

3.83

-9.01

1 8.72

". 88

-23.22

-19.97

23. 73

2' . ?1

- 14.62

-1 1 .07

-2^. 19

- 1 9. 3?

1 8. 78

-28. C 3

12. 39

-3. 95

-4. ''A

8. 41-

- 1 3. 99

-2.6"

-6.' 5

-2C ,C5

-7. 34

24. 95

-13. 18

3.2 1

1 1. 7b

- 16.66

25. 18

7. 99

-27.53

-29.51

- 1 4 . 94

-26. 1 A

1 2. «5

-22. *4

-7.77

-27.22

2 0 . C 6

4. 35

-1.33

21.18

1 "".69

-6.13

-If. 93

- 1 5. 60

2Q.25

23. 39

21.23

1 ° . 5 3

1.16

2 1 . 36

11.98

1 .52

24. 55

0.57

- 19 .27

28. 56

26. 13

9. 53

-4. 76

-15.17

26. 74

24 .63

2S. 96

21.19

12. ce

25.17

-8. 93

-2^.7"

-13.43

23. 99

- 1 8.26

7. 15

- 1 1 .40

-2". 1 1

-13.69

16.43

17.68

26.83

-28. 86

27.12

- 1 9. 7a

-21.2 1

13. C 1

AMPL I TUOES

N-VALUES

VEAP

QU.

197?

1971

1972

1973

26.8641

P .0 034

r. . "85 1

-0. 1 98 3

- ".."75 3

- i . 2552

-0.1641

'. .0452

- .C599

2ft. 8841

- : . o c 4 i

-(. .4763

r . 3681

o . 16 "9

' - . 0 8 24

-<~ .0936

- " . 1 r 1 1

-' . "466

2 5.7091

-r. -C49

-o . 4564

- 0.2126

".1819

-" . 075A

r . 1993

'" . ". 043

" . 16 64

24. 16 13

0. - 033

0 . 36 38

- C . 1039

-C. 1 390

-".0981

-, . 1 2 S 9

- - . '1722

- '.-893

23.91 e>5

0." 176

0. I«T1

u.CKc

0.1309

- 0 . 1 C 2 4

-C . "435

- . " ' JJ

. 1 "56

2 5.6f*'"Q

0 . C 0 8 3

-O. 5 38 9

-0.1219

-0. 1488

-0. 1"29

0 . " 5 1 6

o.r i 46

0.1975

26.31 06

-t . 0098

-C .5 171

0. 202 1

o .047?

".1281

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0. }G9 1

-0. 2 184

0.211'

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-•:•• 1 34 6

-0.r573

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0.0 133

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-C . ""632

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26.5641

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-0.1173

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- :. 1676

0. 1233

27. 3256

3. : 12'.

-0.291 A

-0.5543

0 .5779

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- .1923

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24.6561

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C. 243

783

FISHERY BULLETIN: VOL. 75, NO. 4

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784

SECKEL and YONG: SEA-SURFACE TEMPERATURES AND SALINITIES

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785

FISHERY BULLETIN: VOL. 75. NO. 4

APPENDIX E

APPENDIX E TABLE 1. — Standard error of estimate (°C) for each annual temperature function at
Koko Head, 1970-73, with harmonic analysis carried out in sequence to n = 1, 2, 3, . . . and 13.

n-values

Year

1970

0.41

0.32

0.30

0.29

0.28

0.26

0.25

0.24

0.23

022

0.22

1971

0.37

026

0.25

0.23

0.22

0.21

0.18

1972

0.35

0.29

0.28

0.26

0.23

0.22

022

0.22

0.21

1973

0.29

0.28

0.26

0.24

0.23

022

0.22

0.21

APPENDIX E TABLE 2. — Standard error of estimate (%o) for each annual salinity function at Koko
Head, 1970-73, with harmonic analysis carried out in sequence to n = 1, 2, 3, . . . and 13.

-values

Year

1970
1971
1972
1973

0.055
0.047
0.080
0.068

0.043
0.046
0.058
0.066

0 042
0.046
0.054
0.064

0.040
0.045
0047
0.059

0.031
0.044
0.044
0.052

0.030
0.042
0.043
0.051

0.029
0.040
0.043
0050

0.029
0.040
0.043
0.047

0.029
0.039
0.042
0.045

0.029
0.038
0041
0.040

0 029
0037
0.040
0.040

0.027
0037
0.040
0.039

0026
0 036
0.040
0.037

APPENDIX E TABLE 3.— Standard error of estimate <°C) for each quarterly temperature function at Christmas Island, 1970-73,

with harmonic analysis carried out in sequence to n = 1, 2, 3, . . . and 7.

Quarter

■values

Year

Quarter

n-values

Year

1970

0.35

0.32

0.31

0.25

0.23

0.22

1972

0.36

0.35

0.33

0.32

0.31

0.46

0.37

0.35

0.34

032

0.32

0.50

0.47

0.46

0.45

0.43

0.42

3 ?

Data sets incomplete or

missing

0.39

0.38

0.36

0.35

0.34

0.33

1971

0.30

0.28

0.27

0.26

1973

0.64

0.60

0.59

0.58

0.55

0.30

0.29

0.27

0.26

0.25

0.24

0.71

0.68

0.69

0.66

0.65

0.64

0.58

0.42

0.39

0.38

0.37

0.33

032

0.32

0.53

0.49

0.46

0.42

0.41

0.40

0.39

0.34

0.31

0.30

0.29

0.28

0.27

0.46

0.43

0.37

0.35

0.34

APPENDIX F

Harmonic coefficients for the long-term series. Coefficients for each harmonic term in the series

S = a

bt +A0 + 2j (An cos nwt + Bn sin ncot)

are given in the tables below. Harmonic analysis was performed on the residuals from a linear fit.

2tt

If t is in months, for the Koko Head series, oj = ofa > an^ the first month in January 1956; for the
Christmas Island series, oj =240 , and the first month is January 1954.

786

SECKEL and YONG: SEA-SURFACE TEMPERATURES AND SALINITIES

APPENDIX F TABLE 1.— Coefficients for Koko Head temperature, a = 23.7009, b = 0.0020.

0.5478

-0.1755

-0.1397

0.1131

0.0279

-00538

0 0263

0.0583

00782

00245

0.0174

00760

0.0642

0.0401

0.0905

0.0168

00439

0.0641

-0.2483

00055

0.1262

0 0126

-0.0035

-0.0263

0 0408

0.0211

0.0253

0 0235

0.0576

00279

-0.0428

00019

-0 0060

00497

-0.0114

0.0191

0.0134

0.0348

-00041

0.0258

0 0332

0 0042

-0.0024

0.0502

0.0274

0.0056

00239

0 0040

-0.0171

-0.0274

0.0377

-0.0436

0.0015

00116

-0.1030

0.0298

0.0257

0.0154

-0.0007

0 0068

0 0162

-0.0113

-0.0050

-0.0267

00202

0 0202

0.0231

00107

0.0145

-00234

0.0174

00117

-0 0067

Bn
0 0305

0 0887

0.2135

0.1425

0 0989

0.0023

0.0552

0.0418

0.0052

0 1329

0 0093

0 0696

0 0044

0.0437

-0.0274

0.0195

0 0056

-1.4540

0.0197

00262

00509

0.0531

0.0198

0 0676

0.0572

-0.0049

0.0035

0.0105

0.0409

-0.0313

0.0422

-0.0177

- 0.0767

-0.0058

0.0373

- 0.1468

-0.0175

00347

0.0226

00519

0.0306

0.0078

-0.0188

-0.0288

0.0258

0.0207

-0.0533

00105

00327

0.0151

-0.0145

00652

-0.0230

-0.0113

0.0283

-0.0074

0.0238

0.0050

0.0090

0 0188

-0.0138

0 0200

0.0272

-0.0316

-0.0222

0.0053

-0.0254

0.0177

-0.0083

0.0011

-0.0167

-0.0020

APPENDIX F TABLE 2.— Coefficients for Koko Head salinity, a = 35.0141, b = 0.0001.

-0 1228

0.0366

0.0685

-0.0653

An
-0.0894

0.0441

-0 0034

-0.0048

00165

0.0163

00286

-0.0017

0.0109

-0.0128

-0.0156

0.0024

0.0043

0 0093

0.0903

-0.0020

-0 0004

-0.0095

0 0032

-0.0127

0.0017

-0.0035

0 0020

-0.0101

-0.0034

0.0028

0.0020

0.0117

-0.0043

-0.0097

-0.0132

-00023

-0.0091

0.0094

-0.0067

-0.0039

-0.0057

0.0085

0.0070

0.0040

-0.0136

-0.0098

-0.0035

0.0041

0.0030

-0.0053

-00031

-0.0062

0 0070

00130

-0.0002

-0.0092

-0.0053

-0.0002

0.0064

0.0046

-0.0006

-0.0048

-0 0039

-0.0021

00013

-0.0008

-0.0063

0.0002

0.0014

0.0022

00089

-00016

00028

Bn
0 0206

0.0663

-0.0287

-0.0063

0.0174

-0.0532

0.0026

-0.0221

00006

-0.0372

-0 0034

-0.0095

-0.0047

0.0268

-0.0041

0.0007

-0.0199

0.0085

0 0034

-0.0099

-0.0050

-00075

-0.0012

-0.0108

0.0020

0.0058

0.0075

0.0131

0 0026

00109

0 0028

0 0088

0.0086

-0.0105

-0.0095

0.0021

0.0126

0.0043

0.0138

-00050

-0.0067

-0.0039

00158

-0.0005

-0.0121

-00124

0.0064

0.0125

0.0092

-0 0002

0.0028

0.0037

00001

0.0050

0.0003

00001

-0.0089

-0.0003

0.0000

0 0074

0.0108

-0.0071

-0.0070

0.0059

-0.0028

0.0028

0.0049

-0.0011

00007

0.0072

-0.0021

0.0015

APPENDIX F TABLE 3.— Coefficients for Christmas Island temperature, a = 26.1443, b = -0.0054.

1 5694

-0.2024

-0.3409

-0.1310

An
0.1924

0.3505

-0.1455

-0.4605

-0.1400

-0.2839

0.1658

-0.3162

0.0228

-0.2507

-0.0381

0.1309

0.2614

0.0088

-0.0257

0.0569

-0.4204

-0.0517

-0.0635

0.0676

0.0431

0.0179

0.0014

-0.0727

-0.0298

-0.0637

0.0295

-0.0316

-0.0583

-0.0133

0.0264

0.0040

0.0073

-0.0021

-0.0587

-0.0397

0.1025

-0.0243

-0.0049

0.0496

-0.0108

0.0176

0.0054

-0.0458

0.0351

-0.0144

00100

0.0321

0 0211

-0.0272

0.0145

-0.0076

00085

0.0031

-0.0410

0.0141

0.0369

-00001

0.0292

-00495

-0.0385

-00080

-0.0065

00232

-00204

0.0170

0.0134

00126

-0.0021

-0.0141

0.0203

-0.0178

-0.0085

0.0325

0.0144

0.0445

00022

-0.8028

-0.2146

-0.6457

-0.4963

-0.3942

-0.3880

0 1339

-0 1839

0.0969

-0.1253

0.1038

0.1556

-0.0039

00555

0.2400

0 1030

0.1198

-0.0589

0.1246

00883

0.0041

0.0403

-0.1501

-0.0233

0.0791

-0.0622

-0.0063

0.0252

0.0138

00456

0.0172

00133

-0.0420

-0.0357

0.0625

0.0097

0.0054

0.0347

-0.0026

-0 1791

-0.0090

00979

-0.0668

-0.0407

0.0247

0.0003

-0.0241

0.0154

-0.0151

00073

0 0230

0.0144

0.0196

-0.0277

-0.0250

0.0374

-0.0110

0.0054

00258

-0.0250

00336

-0.0219

-0.0223

-0.0124

-0.0314

0.0035

-0.0044

0.0041

0.0267

-0.0323

0.0071

-00183

-0.0084

0.0289

-0.0417

0.0431

-00055

00038

0.0022

787

A NEW GENUS AND SPECIES OF EELPOUT (PISCES,
ZOARCIDAE) FROM THE GULF OF MEXICO1

Hugh H. DeWitt2

ABSTRACT

Exechodontes daidaleus n.gen. and n.sp., captured at lat. 27°01 'N, long. 84°55 'Wat a depth of 503 m in
the Gulf of Mexico, is described and figured. Its characteristics include the presence of pelvic fins, the
absence of scales, teeth on the vomer but not on the palatines, the absence of enlarged canine teeth,
teeth on the lateral margin of the dentary and directed outward, grooves behind the upper and lower
lips interrupted at the symphyses, the absence of cephalic lateral-line pores, and a greatly reduced
lateral line. The new genus appears to be most closely related to the Hadropareinae of the western
North Pacific. A key to the genera of the Hadropareinae, including Exechodontes, is given.

During June of 1969 the Bureau of Commercial
Fisheries (now the National Marine Fisheries
Service) RV Oregon II was engaged in a survey of
shrimp abundance in relatively deep water (360-
900 m) in the eastern Gulf of Mexico. Among the
fishes captured is one small specimen of a zoarcid
which does not appear to belong in any of the
currently recognized genera of the family. More
surprising, it seems most similar to a group of
genera known only from the western North Pacific
Ocean.

Exechodontes n.gen.

Type-Species Exechodontes daidaleus n.sp.

Diagnosis. — A zoarcid with pelvic fins and lacking
scales, with vomerine teeth (two in type-species),
but without palatine teeth. No enlarged canine
teeth although a few anterior teeth in upper jaw
somewhat enlarged; teeth of lower jaw small, in
two distinct rows, the outer on the lateral and
anterior edge of the dentary such that the teeth
are directed outward and are visible when the
mouth is closed. Grooves behind upper and lower
lips interrupted at symphyses; upper lips not
greatly broadened posteriorly. Pores of lateral-
line canals absent on head and body; lateral line of
body greatly reduced, only a few neuromasts visi-
ble close behind head and base of pectoral fin.

■Contribution No. 96 from the Ira C. Darling Center for Re-
search, Teaching and Service, University of Maine at Orono,
Walpole, Maine.

2 Department of Oceanography, University of Maine at Orono,
Ira C. Darling Center, Walpole, ME 04573.

Manuscript accepted April 1977.

FISHERY BULLETIN: VOL. 75, NO. 4, 1977.

Head small and without prominent bulging cheek
musculature. Pelvic rays long, but only about dis-
tal one-fifth of their length bends to extend into
the visible fins, the proximal four-fifths lying hid-
den beneath skin of ventrum. Branchiostegal rays
six. Vertebrae with anterior and posterior halves
of equal size.

Discussion. — Using various keys to the genera of
Zoarcidae (Soldatov and Lindberg 1930; Norman
1966; Lindberg and Krasyukova 1975),
Exechodontes falls into a group of three genera
known only from the western North Pacific Ocean:
Hadropareia Shmidt (1904) andBilabria Schmidt
( 1936), both monotypic, and Davidijordania Popov
(1931) with five species. These three genera con-
stitute the subfamily Hadropareinae (Shmidt
1950), characterized by the absence of spines in
the posterior portion of the dorsal fin, the presence
of pelvic fins and the absence of crests on the chin
(Lindberg and Krasyukova 1975). Exechodontes
seems closest to Hadropareia in that it lacks scales
and palatine teeth. Hadropareia has, however,
distinct pores in the infraorbital lateral-line canal
(other pores have not been described or illus-
trated) and a few pores in the anterior portion of
the lateral line which extends posteriorly about
three-fourths the length of the body. In addition,
Hadropareia is described and figured as having
the cheek musculature enlarged such that each
cheek forms a prominent bulge (Soldatov and
Lindberg 1930). Davidijordania differs from
Exechodontes in having scales, palatine teeth and
the groove behind the upper lip complete across
the snout. Bilahria differs in having scales, pores

789

FISHERY BULLETIN: VOL. 75, NO 4

in both the cephalic lateral-line system and the
anterior part of the lateral line, and the lips of both
jaws expanded (Soldatov 1922; Schmidt 1936;
Shmidt 1950).

It is possible that the similarities described
above are not of real phyletic significance. A. P.
Andriyashev(pers. commun.) has pointed out that
the Hadropareinae and some other genera (e.g.,
Zoarces) have vertebral centra with the anterior
cone shorter than the posterior cone, i.e., the con-
striction of each amphicoelous centrum is shifted
anteriorly. He adds that the Lycodinae,
Lycogramminae, and Lycodapodidae have "sym-
metrical" centra with the constriction placed
midway in the length of each centrum. The centra
in Exechodontes are symmetrical, indicating that
relationships may not be with the Hadropareinae
(see Figure 3). I have, however, examined radio-
graphs of Macrozoarces americanus andLycenche-
lys verrilli and find that both have "asymmetrical"
centra, at least anteriorly. Further analysis of ver-
tebral characters seem indicated.

The following key should serve to separate the
four hadroparein genera.

KEY TO THE HADROPAREINAE

la. Cephalic lateral-line system without
pores; outer teeth of lower jaw placed
on anterior and lateral margins of
dentary and directed outward; scales

and palatine teeth absent

Exechodontes n. gen.

lb. Pores of cephalic lateral-line system
present on upper parts of head; no out-
wardly directed teeth on lower jaw;
scales and palatine teeth present or
absent 2

2a. Scales absent; musculature of cheek
enlarged, forming a prominent bulge
along margin of preopercle; palatine
teeth absent Hadropareia

2b. Scales present; cheek musculature
may be slightly swollen, but not form-
ing a prominent bulge; palatine teeth
present or absent 3

3a. Palatine teeth present; groove behind

upper lip continuous across snout ....

Davidijordania

3b. Palatine teeth absent; groove behind

upper lip interrupted at tip of snout. .

Bilabria

Discovery of a zoarcid in the Gulf of Mexico that
has its closest apparent affinities with a small
group of genera in the northwestern Pacific is of
zoogeographic interest. It is consistent with cur-
rent thoughts regarding the origin and relation-
ships of several faunal groups of the cooler North
Atlantic which also have affinities with the North
Pacific. The boreal North Pacific is considered a
dominant evolutionary center which provided
significant numbers of migrants that invaded the
Arctic and North Atlantic during the late Miocene
and late Pliocene epochs (Briggs 1974).

Discovery of Exechodontes might suggest that
there are a number of undescribed species of the
family inhabiting the slope waters of the Ameri-
can warm-temperate and tropical Atlantic. The
only previously known zoarcid from the Gulf of
Mexico is Lycenchelys bullisi Cohen which ap-
pears to be related to species found in the northern
Atlantic and Gulf of Panama (Cohen 1964).
Otherwise, the southernmost record for the family
in the western North Atlantic is that of Lycodes
brunneus Fowler from off the east coast of Florida
just north of the Bahama Islands (Fowler 1944). In
the eastern Atlantic, the family is known south to
about lat. 20 °N, where two species, probably both
misidentified, have been captured at depths be-
tween 1,000 and 1,500 m (Vaillant 1888). The
pelagic species Melanostigma atlanticum has been
recorded southward only to the waters off Virginia
(McAllister and Rees 1964). It is significant in the
present context that M. atlanticum is most closely
related to the western North Pacific M . orientate
rather than the eastern North Pacific M. pam-
melas (Tominaga 1971).

Name. — From the Greek exeches, projecting, and
odontos, teeth. The compound is a masculine
noun.

Exechodontes daiduleus n.sp.

Holotype. — 96.3 mm SL (standard length), col-
lected at Oregon II station 10632: 27°01'N,
84°55 ' W, about 120 n.mi. ESE of Tampa Bay, Fla.,
in 503 m (275 fm); 124-ft shrimp trawl, dragged on
the bottom, 18 June 1969. The specimen (Figure 1)
has been deposited in the National Museum of
Natural History, Washington, D.C., USNM
211797.

Description. — All measurements are given as

790

DEWITT: NEW GENUS AND SPECIES OF EELPOUT

FIGURE 1.— Lateral view of holotype of Exeehodontes daidaleus n.gen. and n.sp., USNM 211797, 96.3 mm SL.

thousandths of standard length unless otherwise
indicated.

Head relatively short, 143 of SL, slightly com-
pressed, its depth and width at cheeks, 78 and 69 of
SL. Snout slightly greater than diameter of eye, 39
of SL, very bluntly rounded in both dorsal and
lateral views. Nostrils 21 from tip of snout and eye,
36 apart, all of SL, placed at lateral edges of
slightly bulbous median part of snout. Eyes placed
high on head, but not bulging into dorsal profile,
their diameter 34 of SL, placed 38 of SL apart
(bony interorbit about 18 of SL). Postorbital part of
head 76 of SL. Gill slit moderate, extending ven-
trally almost to lower edge of base of pectoral fin.

Gape of mouth relatively short, maxilla extend-
ing posteriorly to below anterior edge of pupil,
length of upper jaw 57 of SL. Teeth all relatively
small; those of upper jaw in a single, irregularly
spaced row, a few teeth in anterior one third of jaw
somewhat enlarged, especially adjacent to sym-
physis. Teeth of lower jaw in two distinct rows;
inner row on dorsal edge of dentary, teeth some-
what irregularly spaced, none enlarged; outer row
on lateral and anterior edge of dentary such that
teeth are directed outward (most teeth in outer
row are missing; cavities in dentary indicate prob-
able tooth positions). Lower jaw included in upper,
leaving anterior teeth of upper jaw and outer row
of lower jaw visible when mouth is closed. Vomer
with two teeth (one missing, but a large tooth
cavity present); palatines edentulous. Gill rakers
of anterior series of first arch 0+0 + 12; those of
posterior series 0 + 0 + 11; all are short and blunt.
About nine small nubbins present in posterior
series of last arch. Pseudobranchiae absent.

Grooves behind lips of both jaws interrupted at
symphyses; upper jaw appears to be nonprotrac-
tile. Lips narrow, not expanded. No fleshy pro-
tuberances or crests present on lower jaw; no
cephalic lateral-line pores present anywhere on
head (Figures 1, 2). Oral valves present in both
jaws, that of lower jaw appearing double, one thin
and membranous, lying somewhat anterior and
overlying a more fleshy one. Tongue fleshy. Bran-
chiostegal rays six on both sides.

Body slender and compressed, its depth and
width 78 and 48 of SL; pectoral to pectoral distance
71 of SL. Lateral line not prominent; a single,
prominent, raised neuromast present on each side
just above and slightly anterior to upper end of gill
slit; a few similar organs (appearing as pale spots)
visible in a line curving downwards toward mid-
line behind pectoral fin. Skin delicate but firm on
the body. Scales absent. Vertebrae 19 + 78 = 97
(including urostylar vertebra). Vertebrae appear
in radiographs to be amphicoelous with anterior
and posterior cones of equal size (Figure 3).

%•■■

• r, • ■
. ■*' '

'•2- . i

)

'■J

• •' . / ' .

■Ir

:'f ■

/•.:•'■:•

FIGURE 2.— Ventral view of head of holotype of Exechodontes
daidaleus n.gen. and n.sp., USNM 211797, 96.3 mm SL. Missing
teeth in outer row of lower jaw outlined in dots to show presumed
position and size.

791

FISHERY BULLETIN: VOL. 75, NO. 4

FIGURE 3. — Holotype of Exechodontes daidaleus n.gen. and
n.sp.,USNM 211797. A. Left pelvic rays; the tips originally were
straight at about a right angle to main axis. B. Outlines of
selected vertebrae traced from a radiograph with the aid of a
camera lucida: a, vertebra no. 14; b. no. 20; c, no. 50; d, no. 80. The
lines equal 1 mm.

104 and 27 of SL, not reaching to above anus.
Pelvic fins with two rays, appearing as a pair of
small nipples below and slightly behind bases of
pectoral fins, their length about 6 of SL. The rays,
however, are much longer, 31 of SL, originating
anterior to the pectoral fins and lying for most of
their length horizontally beneath the skin with
only their distal ends bent sharply into the visible
nubbins (Figure 3).

Dorsal fin originates behind bases of pectoral
fins, above about middle of their length, 235 of SL
from tip of snout and 786 from base of caudal fin,
with 86 rays. Anal fin originates below base of
12th ray of dorsal fin 341 of SL from tip of snout,
683 of SL from base of caudal fin, and 215 of SL
from nipples of pelvic fins, with 79 rays. Caudal fin
38 of SL, with a total of about eight rays.

Color (in alcohol) very pale yellow-brown, al-
most white, with large, scattered brown
melanophores, especially over ventral two-thirds
of body which is therefore slightly darker than
upper one-third. Small to medium-sized (about 1-3
mm in diameter), irregularly shaped and placed
brown spots on upper half of body, rather widely
spaced (separated by at least their own diameter).
Cheeks and snout darker than body, with more
numerous melanophores; brown pigment present
in an arc around front of eyes; tip of snout brown.
Lower jaw with darker areas of larger and more
numerous melanophores. Darker pigment present
along bases of posterior parts of dorsal and anal
fins, and base of caudal fin. Pelvic nipples brown;
pectoral fins with brown pigment. Peritoneum
very dark brown, showing through belly as dark
blue-grey; viscera pale. Lining of mouth and
pharynx pale. Anus ringed with black.

Name. — From the Greek daidaleos, dappled or
spotted.

ACKNOWLEDGMENTS

Upper part of small intestine greatly enlarged,
about equal in volume to empty stomach. Two very
blunt, short and broad pyloric caeca just posterior
to thick and muscular pylorus. Gallbladder large
and transparent, lying between liver and enlarged
upper intestine. A pair of thin gonad chords ex-
tending from midway in length of body cavity al-
most to anus indicate holotype is a male.

Pectoral fins with 15 rays, rounded in outline
when rays spread, their length and width of base

I thank Harvey R. Bullis, then Director of the
Pascagoula Laboratory of the Bureau of Commer-
cial Fisheries, for the opportunity of joining the
Oregon II and for permitting me to retain selected
fishes from the cruise, including the new zoarcid. I
also thank the crew and scientists of the Oregon II
for their friendliness and cooperation, especially
Benjamin Rohr who kindly helped me identify and
preserve the collections. Daniel M. Cohen of the
National Marine Fisheries Service and Ernest A.
Lachner and Stanley H. Weitzman of the National

792

DEWITT: NEW GENUS AND SPECIES OF EELPOUT

Museum of Natural History very kindly permitted
me to examine zoarcid material from the western
North Pacific in their care, provided space and
facilities for work, and helped in obtaining litera-
ture on western Pacific zoarcids.

LITERATURE CITED

BRIGGS, J. C.

1974. Marine zoogeography. McGraw-Hill, N.Y., 475 p.

Cohen, D. M.

1964. Lycenchelys bullisi, a new eelpout from the Gulf of
Mexico. Proc. Biol. Soc. Wash. 77:113-118.
FOWLER, H. W.

1944. A new eelpout from the Gulf Stream off east Flori-
da. Fish Cult. 23:73-74.
LINDBERG, G. U., AND Z. V. KRASYUKOVA.

1975. Fishes of the Sea of Japan and the adjacent areas of
the Sea of Okhotsk and the Yellow Sea. [In Russ.] Akad.
Nauk. SSSR, Zool. Inst., Keys to the Fauna of the USSR
108, 442 p.

MCALLISTER, D. E., AND E. I. S. REES.

1964. A revision of the eelpout genus Melanostigma with a
new genus and with comments on Maynea. Natl. Mus.
Can. Bull. 199:85-110.
NORMAN, J. R.

1966. A draft synopsis of the orders, families and genera of

recent fishes and fish-like vertebrates. Br. Mus. iNat.
Hist.), Lond., 649 p.

Popov, a. m.

1931. On a new genus offish Davidijordania (Zoarcidae,
Pisces) in the Pacific Ocean. |In Russ.l Akad. Nauk.
SSSR, Dokl. 1931:210-215.

Schmidt, p. j.

1936. On the genera Davidojordama Popov and Bilabria
n. (Pisces, Zoarcidae). C.R. Acad. Sci. URSS 1:97-100.
SHMIDT, P. YU.

1904. Fishes of the eastern seas of the Russian Empire |In

Russ.l Izd. Russ. Geogr. Obshch, St.-Peterb., 466 p.
1950. Fishes of the Sea of Okhotsk. [In Russ] Akad.
Nauk. SSSR, Tr. Tikhookean. Kom. 6:1-392. (Translated
by Israel Program Sci. Transl., Jerusalem, 1965.)
SOLDATOV, V. K.

1922. On a new genus and three new species of Zoar-
cidae. Annu. Mus. Zool. Acad. Sci. Russ. 23:160-163.
SOLDATOV, V. K., AND G. J. LINDBERG.

1930. A review of the fishes of the seas of the far east. [In
Russ.] Izv. Tikhookean. Nauchn. Inst. Rybn. Khoz. 5,
576 p.
TOMINAGA, Y.

1971. Melanostigma orientate, a new species of zoarcid fish
from Sagami Bay and Suruga Bay, Japan. Jap. J.
Ichthyol. 18:151-156.
VAILLANT, L. L.

1888. Expeditions scientifiques du Travailleur et du
Talisman pendant les annees 1880, 1881, 1882, 1883.
Poissons. G. Masson, Paris, 406 p.

793

SEASONAL MIGRATION OF NORTH PACIFIC ALBACORE,

THUNNUS ALALUNGA, INTO NORTH AMERICAN COASTAL WATERS:

DISTRIBUTION, RELATIVE ABUNDANCE, AND ASSOCIATION

WITH TRANSITION ZONE WATERS

R. Michael Laursand Ronald J. Lynn1

ABSTRACT

In the spring months of 1972-74, fishery-oceanography surveys were conducted in the eastern North
Pacific which combined intensive oceanographic sampling by research vessels with concurrent fishing
effort for albacore by chartered commercial fishing vessels. The catches demonstrate an association of
albacore distribution with the Transition Zone and its boundaries. The relative abundance of albacore
was found to be high in the eastern sector of the Transition Zone or a period just prior to their movement
across the California Current and into the traditional nearshore fishing grounds. These centers of high
relative abundance of albacore are sometimes sufficient to support commercial fishing earlier and
farther offshore than the traditional fishing season. Variations in the pattern of migration occur in
apparent response to variations in the character and development of the Transition Zone and its frontal
structure. Analyses of albacore tagging and size frequency data provide evidence that the shoreward-
migrating albacore of the Pacific Northwest and California are independent groups.

The North Pacific albacore, Thunnus alalunga
(Bonnaterre), is a wide-ranging species which
spawns in the central subtropical Pacific, performs
transpacific migrations, and supports important
commercial fisheries in the western, central, and
eastern North Pacific. That marked variations in
distribution and relative abundance of albacore
occur in the eastern North Pacific is indicated by
major latitudinal shifts in the location of the U.S.
fishery off the west coast of North America (Laurs
et al. 1976). In order to evaluate factors which may
affect variations in distribution, relative abun-
dance, and migration patterns of albacore in the
eastern North Pacific, and to improve our under-
standing of the underlying factors affecting the
onset and subsequent development of the fishery,
early season surveys were conducted in offshore
waters of the North American Pacific coast in
1 972-74. 2 These surveys found that relative abun-
dance of albacore was high in the vicinity of
oceanic fronts of the Transition Zone waters in the
eastern North Pacific. Survey results also provide

'Southwest Fisheries Center, National Marine Fisheries Ser-
vice, NOAA, P.O. Box 271, La Jolla, CA 92038.

2These surveys were carried on cooperatively by the National
Marine Fisheries Service, Southwest Fisheries Center La Jolla
Laboratory, and the U.S. albacore fishing industry through the
American Fishermen's Research Foundation.

Manuscript accepted February 1977.
FISHERY BULLETIN: VOL. 75. NO. 4. 1977

the basis for a hypothesis concerning migration of
albacore into coastal waters off the west coast of
North America. During these surveys albacore
were taken in commercial concentrations farther
offshore than traditionally, and several weeks ear-
lier than the fishing season which usually com-
mences in mid-July.

BACKGROUND INFORMATION

Numerous exploratory albacore fishing and al-
bacore oceanographic surveys have been con-
ducted in the central and eastern North Pacific.
From surveys conducted during the 1950's, scien-
tists described seasonal variations in distribution
of albacore in the central and parts of the eastern
Pacific, and demonstrated the association of alba-
core with Transition Zone waters in the central
North Pacific (Shomura and Otsu 1956; Graham
1957; McGary et al. 1961 >. Flittner <1963, 1964)
reported on albacore trolling experiments con-
ducted from U.S. Navy picket vessels operating
approximately along long. 130° to 135°W, and pre-
sented a schematic model of albacore movement
off the Pacific coast (Flittner 1963). Neave and
Hanavan 1 1960) showed that the northern limit of
albacore catches made during high-seas salmon
gillnetting studies conducted between long. 125°
and 175°W was about lat. 45c to 47°N in July and

795

FISHERY BULLETIN: VOL. 74, NO. 4

lat. 45° to 50°N in August and September. Accord-
ing to Brock (1943), yachts sailing between
Hawaii and Oregon during June made albacore
catches between lat. 30° and 44°N in waters be-
tween long. 154° and 140°W.

Numerous exploratory fishing and oceano-
graphic surveys also have been conducted within a
few hundred miles of the coast to obtain informa-
tion on distribution, availability, and migration
patterns of albacore during early season in waters
off the Pacific Northwest (Powell 1950, 1957; Pow-
ell and Hildebrand 1950; Powell et al. 1952;
Schaefers 1953; Owen 1968; Meehan and Hreha
1969; Pearcy and Mueller 1970; and others), and
in waters off California (Graham 1959; Clemens
1961; Craig and Graham 1961; and others listed in
Clemens 1961 and Pinkas 1963). Johnson (1962),
Laurs et al. (1976), and others have discussed var-
iations in distribution and relative abundance of
albacore in waters off North America where the
U.S. fishery takes place. These studies have
shown: 1 ) the limits of where albacore are found; 2)
their general migration patterns; 3) the impor-
tance of environmental conditions and changes,
notably ocean temperature, in relation to the dis-
tribution and relative abundance of albacore; and
4) the considerable annual variation in location of
available concentrations of albacore.

In the present study early season albacore sur-
veys were planned to encompass a portion of the
eastern sector of the Transition Zone during a
period prior to the commencement of the near-
shore fishery. The primary objectives of these sur-
veys were:

1 1 To investigate the early season distribution
and abundance of albacore off the North
American Pacific coast.

2) To investigate the eastward migration path
of albacore entering the American west coast
fishery.

3) To determine if migrating albacore are as-
sociated with major offshore oceanographic
features, particularly the Transition Zone
and the ocean fronts that form its bound-
aries.

METHODS

The general work plan for each offshore survey
employed one National Marine Fisheries Service
(NMFS) research vessel (Townsend Cromwell in
1972 and David Starr Jordan in 1973 and 1974)

and a group of 5 to 12 commercial albacore fishing
vessels on charter to the American Fishermen's
Research Foundation ( AFRF). The research vessel
and chartered fishing vessels worked coopera-
tively to obtain estimates of distribution and rela-
tive abundance of albacore in the offshore area and
to make concurrent oceanographic measure-
ments. The research vessel collected physical,
chemical, and biological oceanographic data and
conducted supplementary fishing activities. The
fishing vessels conducted exploratory fishing, tag-
ged fish, and collected surface and subsurface
temperature data. The oceanographic findings
made on meridional transects were used in direct-
ing the exploratory fishing operations, particu-
larly at the onset of each survey. In several in-
stances, especially in 1973 and 1974, the findings
of large numbers offish were used to redirect the
research vessel to conduct detailed oceanographic
observations in the vicinity.

Operations Aboard Research Vessels

Three meridional oceanographic sections were
taken along long. 135°, 137°30', and 140°W be-
tween lat. 31° and 41°N in 1972 and 1973; in 1974
the middle section, portions of the section along
long. 135°W, and additional transects were taken
(Figure 1). Hydrographic stations were occupied
at 25- to 30-n.mi. intervals. Figure 2 shows station
positions occupied in 1973; Lynn and Laurs34
gave figures of the station positions for other
years. Observations included: 1) salinity-
temperature-depth profiles to 500 or 1 ,000 m using
an STD;5 2) Nansen bottle or command rosette
sampler6 bottle casts for collection of water sam-
ples for determination of dissolved oxygen,
chlorophyll, and salinity; 3) oblique zooplankton
net hauls and simultaneous surface hauls with
neuston plankton nets; and 4) at night stations,

3Lynn, R. J., and R. M. Laurs. 1972. Study of the offshore
distribution and availability of albacore and the migration
routes followed by albacore tuna into North American waters. In
Report of joint National Marine Fisheries Service- American
Fishermen's Research Foundation albacore studies conducted
during 1972, p. 10-44. (Unpubl. rep.)

4Lynn, R. J., and R. M. Laurs. 1973. Further examination of
the offshore distribution and availability of albacore and migra-
tion routes followed by albacore into North American waters. In
Report of joint National Marine Fisheries Service-American
Fishermen's Research Foundation albacore studies conducted
during 1973, p. 3-35. (Unpubl. rep.)

sPlessey model 9006 electronic salinity-temperature-depth
profiler. Use of a trade name does not imply endorsement by the
National Marine Fisheries Service, NOAA.

"General Oceanics, Inc.

796

LAURS and LYNN: SEASONAL MIGRATION OF THUNNUS ALALUNGA

150° 145° 140° 135° 130

48'

i — i — r

115°
48°

45"

40c

35c

30c

RESEARCH VESSEL
CRUISE TRACKS
MAY- JULY

1972
1973
1974

.-- f SAN DICGO

.^-J I ■

J I L

J L

150°

145° 140° 135° 130° 125° 120°

FIGURE 1. — Albacore research vessel cruise tracks for the 1972-74 offshore research surveys.

115°

oblique midwater trawl hauls using an Isaacs-
Kidd Midwater Trawl. Also, surface temperature,
salinity, and chlorophyll were recorded continu-
ously while underway.

Generally, 10 jiglines (five on Townsend Crom-
well cruise in 1972) were trolled for albacore on
transects between oceanographic stations during
daylight. In some regions that were not covered by
fishing vessels, trolling was carried on by the re-
search vessel exclusively throughout daylight. On
such fishing days, three or four expendable
bathythermograph (XBT) drops were made in ad-
dition to continuous monitoring of surface temp-
erature, salinity, and chlorophyll.

Operations Aboard Fishing Vessels

The AFRF charter vessels which took part in the
offshore surveys were jigboats, except for two
baitboats in 1973 which were outfitted to conduct

either live-bait fishing or jig fishing. Twelve
fishing vessels participated in the operations in
1972 and 1973 and five in 1974.

The fishing vessels sailed in groups of four from
San Diego, Calif., and Astoria, Oreg., at 15- to
20-day intervals during 1972 and 1973, and all
vessels sailed together from San Diego in 1974.
The vessels usually worked in pairs. A schematic
diagram of the cruise tracks for the 1972-74
offshore surveys is shown in Figure 3. Detailed
cruise tracks showing daily positions and loca-
tions of XBT stations for each fishing vessel or pair
of fishing vessels by 10-day period are given in
Lynn and Laurs7 (see footnotes 3 and 4).

7Lynn, R. J., and R. M. Laurs. 1974. Cooperative NMFS-AFRF
early season offshore studies conducted during 197 4. In Report of
joint National Marine Fisheries Service- American Fishermen's
Research Foundation albacore studies conducted during 1974, p.
3-18. Southwest Fish. Cent. Admin. Rep. LJ-74-47

797

FISHERY BULLETIN: VOL. 75, NO. 4

46'

150°

145°

i — i — i — | — i — r

45c

40<

35°

30°

25c

3ZI 18

SONIC TAGGING

AREA

21 20

J I L

J L

- , ^

J L

25°

150°

145° 140° 135° 130° 125° 120°

FIGURE 2.— Track and station positions for RV David Starr Jordan cruise 79, 9 June-6 July 1973.

115°

Standard commercial albacore fishing equip-
ment and regular commercial fishing methods
were used. Most of the jig vessels trolled 10 lines
and baitboats 6 or 8 lines when jig fishing. (Bait-
boats had better success when trolling than when
baitfishing. ) Daily records pertaining to fishing
operations were maintained aboard each vessel,
including number of fish caught, fork length of
most fish caught (except for two vessels in 1972),
positions where fishing was started and ended,
amount of fishing effort expended, and fishing
conditions and signs of fish. In addition, sea-
surface temperature, sea conditions, and surface
weather conditions were recorded. Half of the
fishing vessels chartered in 1972 and 1973, and all
in 1974, were equipped with an XBT system; gen-
erally one or two XBT probes were launched each

day. Sea-surface temperature measurements were
made using bucket thermometers.

EARLY SEASON DISTRIBUTION

AND RELATIVE ABUNDANCE OF

ALBACORE IN OFFSHORE WATERS

Distribution of Catches Made By
Charter Vessels

Nearly 27,000 albacore were caught by the
chartered fishing vessels during the three offshore
surveys (Table 1). In all three surveys, albacore
were taken in substantial numbers in an offshore
region between lat. 31° and 36°N from late May
through June. Catch rates were generally low or
zero in surrounding regions and during explorato-

798

LAURS and LYNN: SEASONAL MIGRATION OF THUNNUS ALALUNGA
150° 145° 140° 135°

48'

45c

i — i — i — r

i — i — r

I j *

~i — r

130°

125°

120°

115°

40=

AFRF CHARTER
FISHING VESSEL
CRUISE TRACKS

1972
1973
1974

48°

35'

30°

25°

J 1 L

J I L_L

150°

145°

J I L

J I i L

- 1 L.

"*0° 135° 130° 125° 120° 115

FIGURE 3.— American Fishermen's Research Foundation charter fishing vessel cruise tracks for the 1 972-74 offshore research

25°

surveys.

ry fishing before late May. Variations in distribu-
tion and relative abundance of albacore were ob-
served within and between surveys.

Differences Between Surveys

Plots of the charter vessel catches for each sur-
vey are given in Figures 4a-c. The catches rep-
resented in these and other plots have been stan-
dardized to the number of fish caught per 150

TABLE 1. — Albacore survey catches.

Year

Total catch by
charter vessels

Tagged and
released

Total catch by
research vessel

1972
1973
1974

Total

6,746
1 1 ,027

9,146
26,919

1,431
1,738
1,369
4,538

155
130
495

780

line-hours (averaged between pairs of vessels that
fished together for 1972 and 1973) and presented
graphically by proportionately increasing size of
dots.

In 1972 and 1973, relative abundance of alba-
core was high between lat. 32°and 35°N, long. 135°
and 140°W, and lat. 32° and 35°N, long. 135° and
143°W, respectively (Figure 4a-b). In both of these
years small or no catches were made in the region
between long. 135°W and inshore waters within
150 mi of the coast where fishing takes place dur-
ing the traditional albacore fishing season. In
1974 (Figure 4c), high catch rates were again
made offshore of long. 135°W, but over a larger
latitudinal range, lat. 31° to 36°N, and somewhat
more scattered than in the two preceding years.
Also, high catches were made at about lat. 33° to
36°N, long. 124° to 135°W in the region between

799

FISHERY BULLETIN: VOL. 75, NO. 4

48*

150°

145°

140° 135°

130°

125°

120° 115

48°

■ 1

I i 1 | i i

1 1 i [ i i

: i

1
•

1 \

LMAY 23-JULY 10, 1972

•
•

•

castor a

45°

X
X

•
•

•

CATCH/150 LINE HOURS

/ x No Catch
o L- «S

C BLANCO ' ^

• 6-50
\ • 51-100

•

£ 101-200

> C MENDOCINO

40°

m
o o X

X
o

•

•
o

•

• •

\ A 201-300 -

•

0 •

•

35°

•X

•

o .'

OXO

•
•

° <

•

• <->

• 1 —
IfT CONCEPT'ON

• °
x •

■
o

0
X

•

x x

•
X

o
X

^^ *f SAN OiEGO

X
X

c \ -

X X ° L

30°

X
X

X i
X

x X

X
X

oco

i ,

' ,— ' i '

150
48°

45=

45°

40°

35°

145°

140°

35°

MAY 10-JULY 16,1973

• X

ox*

x •

X O Q^fc* *

X O X

25°

125°

150°

800

LAURS and LYNN: SEASONAL MIGRATION OF THUNNUS ALALUNGA

150° 145° 140° 135" 130°

45° -

1 — r

40=

35°

30°

25'

MAY29-JUNE30, 1974

CATCH/150 LINE HOURS
x No Catch

' f

> *a

V A

J I I L-

25°

150° 145° 140° 135° 130° 125°

FIGURE 4. — Albacore catch per 150 line-hours by American Fishermen's Research Foundation charter vessels:
a. 23 May-10 July 1972; b. 10 May-16 July 1973; c. 29 May-30 June 1974.

the offshore area of high catches and inshore wa-
ters.

Differences Within Surveys

Representative information on spatial and tem-
poral variations in the distribution and relative
abundance of albacore in offshore waters during
May and June is given in Figure 5a-e. In the early
part of the 1973 survey, 10 to 30 May, four vessels
worked westward making only small scattered
catches between lat. 31° and 35°N, long. 142° and
145°W. In the second time period, 31 May to 9
June, the vessels returned through waters they
had scouted earlier and began making catches of
over 100 fish/day between lat. 32° and 34°N, long.
139° and 143°W. Good catches continued to be
made in the general area of lat. 33° to 35°N, long.
135° to 143°W for several weeks with charter ves-
sels landing up to 300 fish/day on many days. A
second group of four charter boats, which left San
Diego on 25 May, did not catch any fish until 4

June when they moved westward of long. 139°W
near lat. 33° to 35°N. On their return to San Diego
during mid- June, the first group of boats failed to
catch any fish east of long. 135°W despite favora-
ble ocean temperature conditions. Similarly, on
the return to San Diego near the end of June,
catches by the second group of charter boats drop-
ped off abruptly east of long. 135°W with only
small scattered or no catches made east of Fieber-
ling Guyot (long. 128°W). The four vessels survey-
ing the area north of lat. 38°N found generally
poor to moderate catches. (The region lat. 35° to
38°N was not covered by the fishing vessels.) This
sequence of catch charts shows that: 1 ) albacore
were apparently unavailable to jig fishing, except
for scattered catches, through May in a region
which subsequently was to prove very productive;
2) albacore became available to trolling gear in the
first week of June in a region which will be shown
later to be associated with the subtropic boundary
of the Transition Zone; 3) good catches persisted
within a block of 2° latitude by 7° longitude for

801

FISHERY BULLETIN: VOL. 75, NO. 4

125° 120° 115°

802

LAURS and LYNN: SEASONAL MIGRATION OF THUNNUS ALALUNGA

,50° 145° 140° 135° '30°

803

FISHERY BULLETIN: VOL. 75, NO. 4

40°

FIGURE 5. — Albacore catch per 150 line-hours by American Fishermen's Research Foundation charter vessels
and sea-surface temperature: a. 10-30 May 1973; b. 31 May-9 June 1973; c. 10-19 June 1973; d. 20-29 June 1973;
e. 30 June-16 July 1973.

over a 3-wk period in June, and 4) elsewhere
catches were substantially lower.

Catches Made By
Noncharter Commercial Fishing Vessels

Because of the fishing success of the chartered
fishing vessels, in the years following the first
survey (1972), noncharter commercial albacore
vessels have fished in the offshore region concur-
rently with the chartered fishing vessels and re-
search vessels. During June 1973 and June 1974 it
is estimated that, respectively, 25 to 30 and 50 to
60 albacore vessels fished across a large zone of
latitudes in the offshore regions (Jack Bowland
pers. commun.). Additional information on the
distribution and relative abundance of albacore is
provided by these catch data.

Figure 6a-e shows estimates of mean catch-
per-unit effort by 15-day period and 1° quadrangle
of latitude and longitude for May through July
1973, for those commercial albacore vessels from

804

which logbook records were available. [Logbook
records were standardized by methods given in
Laurs et al. (1976).]

As with the charter vessels, a center of high
relative abundance was found in the offshore re-
gion between lat. 33° and 35°N and long. 139° and
143°W. From mid-May through mid- June (Figure
6a, b) no catches were reported north of lat. 36°N
nor (with one exception) east of long. 134°W. In the
latter half of June (Figure 6c), a scattering of
catches was made in the intervening zone. The
distribution and relative abundance of albacore,
indicated by the charter and noncharter fishing
vessel catches, were similar. Catches by nonchar-
ter vessels were made over the same latitudinal
range and the same offshore to nearshore se-
quence was observed. The fishing success of the
noncharter vessels further demonstrates that
commercial concentrations of albacore were
available 4 to 6 wk earlier than the normal fishing
season in waters hundreds of miles offshore of the
area where the fishery has traditionally operated.

LAURS and LYNN: SEASONAL MIGRATION OF THUNNUS ALALUNGA

40'

J5'

30'

0 0 0

0 0 0 0
0 0 0 0 0 Oj

SNO 0 0 0 0 0

^S n^O 0 0

FIGURE 6. — Mean daily albacore cateh-per-unit effort
by 1° quadrangles for noncharter vessels for the period:
a. 16-30 May 1973; b. 1-15 June 1973; c. 16-30 June
1973; d. 1-15 July 1973; e. 16-31 July 1973.

805

FISHERY BULLETIN: VOL. 75. NO. 4

The last two charts in this series (Figure 6d, e,
through the end of July 1973) reveal subsequent
stages of albacore migration and commencement
of the nearshore fishery. The relative abundance
of albacore was high in nearshore waters by late
July. In comparison to recent years, the 1973
nearshore fishery started about 3 weeks late.

SIZE COMPOSITION OF FISH

TABLE 2. — Percentage size composition by number and by weight
for albacore catches made by American Fishermen's Research
Foundation charter vessels in the offshore area west of long.
130°W and south of lat. 38°N.

Year

<4 kg 4-8 kg >8 kg

1972
1973
1974

Percent by number
39 33 27
43 53 4
37 61 2

Percent by weight
18 33 49
25 65 10
22 73 5

'Estimated from length-weight relationship given by Clemens (1961).

Three size modal groups of fish were caught in
each year by the AFRF charter vessels; however,
the relative proportions of the size groups varied
among the years (Figure 7; Table 2). In 1972 about
equal proportions of each size modal group were
caught. In 1973 and 1974 the medium-size modal

AFRF CHARTER, 1972
TOTAL =6,428 ALBACORE

45 50 55 60 65 70 75

i i i i i i i i
85 90 95 100

FORK LENGTH IN CENTIMETERS

FIGURE
sus fork
surveys

806

i > i — i — i — i — i — i — i — i — i — i — i — i — i — i i i

z 3 4 5 6 7 8 9 10 12 14 16 18 20

WEIGHT IN KILOGRAMS

7. — Size composition by percent frequency of catch ver-
length for total catches of albacore from the research
in 1972-74.

group was predominant and the larger one nearly
absent.

THE MARINE ENVIRONMENT

Albacore were found mainly in Transition Zone
waters. Variations in distribution and relative
abundance between each of the surveys appeared
to be related to oceanographic conditions of the
Transition Zone. Transition Zone waters lie be-
tween the cool low salinity Pacific Subarctic wa-
ters to the north and the warm, saline Eastern
North Pacific Central waters to the south and have
temperatures and salinities that are characteris-
tic of a mixture of these two primary water masses
(Sverdrup et al. 1942; Christensen and Lee 1965).
Transition Zone waters are found in a band across
the North Pacific middle latitudes within the
North Pacific Current and are bounded by sharp
horizontal gradients in temperature and salinity
(McGary and Stroup 1956; Roden 1970, 1972,
1975). These bounding gradient regions are some-
times referred to as the Subtropic and Subarctic
fronts. The dynamic processes which produce and
maintain these gradients also enrich these waters
(McGary and Stroup 1956).

An oceanographic section of the vertical dis-
tribution of temperature and salinity was taken
along long. 137°30'W in June 1972, 1973, and
1974 (Figure 8). In 1972 and 1973, Subarctic wa-
ters were found north of lat. 35 °N and Central
waters south of lat. 31°30'N and 32 °N, respec-
tively. Boundaries of the Transition Zone between
these water masses were well developed and read-
ily identifiable. The Subarctic front was marked
by abrupt shoaling of the 33.8%o isohaline and
58°F (14.4°C) isotherm and a sharp horizontal
gradient in salinity extending from the surface to
greater than 175 m. The Subtropic front was de-
lineated by steep shoaling of the 34.2%o isohaline
and 62°F ( 16.7°C) isotherm and a sharp gradient in
salinity extending from the surface to greater

LAURS and LYNN: SEASONAL MIGRATION OF THUNNUS ALALUNGA

200

w 400
uj

i 600
I-
a.
ill

800
1000

31 30 29 28

1972

27 26 25

mm'

Along I37°30' W.

100 £

200

d300

3I°N

32°N

38°N

39°N

40°N

200 -

400

600

800

1000

3I°N

32°N

33°N

34°N

35°N 36°N

LATITUDE

37°N

38°N

1973

Along I37°30' W

39°N

40°N

200 <?;

300

4I°N

200

400

600

a.
a

800

1000

>4/0/?S? /J7°J(?' J*'

200

300

32°N

33°N

34°N

35°N 36°N

LATITUDE

38°N

39<>N

40°N

4I°N

FIGURE 8. — Vertical sections of temperature and salinity along long. 137°3G" W during June 1972, 1973, and 1974. Low salinity water
(<33.8%o) indicative of Subarctic water is hatched and crosshatched. High salinity water (>34.2%o) indicative of Central water is
shaded with a dot pattern. The 58° and 62°F isotherms are shown by heavy dashed lines.

than 150 m. A temperature gradient on the order
of 0.6°C in 13 km was often found to mark these
fronts at the sea surface. At other times, however,
seasonal heating in the surface layer eroded the
horizontal temperature gradient at the surface.
Mixing was evident in the Transition Zone in 1972
with low-salinity water penetrating southward
and some high-salinity water northward at inter-
mediate depths.

Oceanographic conditions were different in the
region of the Transition Zone in 1974 from those
which were observed in 1972 and 1973. In 1974,
boundaries of the Transition Zone were poorly de-

veloped and broken. Salinity gradients were dif-
fuse and changes in depth of the isotherms gradual
and variable in the regions of the Subarctic and
Subtropic fronts. The Subarctic front was virtu-
ally nonexistent and Transition Zone waters
graded gradually into Subarctic waters. The Sub-
tropic front was weak and spread between lat.
31°30' and 33°30'N. Saur8 found that the diffuse

8Saur, J. F. T. 1976. Anomalies of surface salinity and temper-
ature on the Honolulu-San Francisco route, June 1966-June
1975. NORPAX Highlights 4:2-4. (Unpubl. rep.)

807

FISHERY BULLETIN: VOL. 75. NO. 4

nature of the Transition Zone and its frontal
boundaries became evident late in 1973 and per-
sisted throughout 1974.

ALBACORE CATCHES IN
RELATION TO OCEANIC FRONTS

Graphical depictions of the frontal gradients
that form the boundaries of the Transition Zone9
and standardized albacore catches for June of each
of the three surveys are shown in Figure 9a-c. This
figure indicates that the catches were largely
made within the Transition Zone in all 3 yr. Dur-
ing June 1972 and 1973, productive centers of
fishing, indicating high relative abundance of al-
bacore, developed in the Transition Zone between
lat. 33° and 35°N and west of long. 135°W (Figure
9a, b). These centers persisted for several weeks

^he temperature and salinity fields measured by the research
vessel, augmented by the XBT data collected by the charter
fishing vessels, were analyzed to delineate the frontal gradients.

before fishing effort was ended. In these years, the
frontal structure was strongly developed and the
Transition Zone easily identifiable. During June
1974 when the frontal structure was poorly de-
veloped and water mass boundaries were less dis-
tinct, catches were distributed over a larger range
of latitude and longitude (Figure 9c). Overall
catches in 1974 were substantial but they were not
persistent in any area for more than a few days.
Thus, while albacore were still associated with
Transition Zone waters, the influence of extensive
lateral mixing between water masses and the dif-
fuse nature of the boundary frontal structure ap-
parently failed to concentrate fish in a given loca-
tion for periods of time as had apparently occurred
in the previous 2 yr.

While graphical depictions of frontal structure
outline the location of the boundaries associated
with Transition Zone water (Figure 9a-c), they do
not indicate the intensity of the gradients of the
frontal structure. The frontal structure has been
shown generally to have weak gradients during

48e

45°

150°

145°

140°

135°

130°

120°

115°

40°

35'

1 — I — I — T

-i — r

X *

. * •

30°

25'

j* ji

JNE 1-30, 1972

CATCH/150 LINE HOURS

x No Catch

C BLANCO

o 1-5
• 6-50

• 51-100

£ 101-200

C MENDOCINO

£ 201-300

(C\ SA*

— -'.

'. r

X X o

48°

45"

40°

35°

50*

25°

150°

14 5°

140°

135°

.20°

115°

FIGURE 9. — Albacore catch per 1 50 line-hours by American Fishermen's Research Foundation charter vessels
and locations offronts delineating Transition Zone waters during: a. 1-30 June 1972; b. 1-30 June 1973; c. 1-30
June 1974.

SOS

LAURS and LYNN: SEASONAL MIGRATION OF THUNNUS ALALUNGA

150° 145° 140° 135" 130°

125°

120°

48"

i — ! — r

~i — r

T T

15°
48°

45° -

40°

35°

30c

JUNE 1-30, 1973

r*si in a

CATCH/150 LINE HOURS

x No Catch
o 1-5

• 6-50

• 51-100
A 101-200

25=

150°

48°

40°

30°

25°

145°

"i — i — r

45c

40°

35°

25° l—
150°

JUNE 1-30, 1974

CATCH/150 LINE HOURS

x No Cotch

C BLANCO

o 1-5

• 6-50

• 51-100

£ 101-200

►C MENDOCINO

A 201-300

145°

140°

135°

125°

120°

115°

809

FISHERY BULLETIN: VOL. 75. NO. 4

June 1974; however, one localized area did have
sharp, abrupt gradients. The eastward protruding
tongue of Transition Zone water centered at lat.
35°30'N, long. 132°30°W had salinity gradients
comparable with those found in previous years.
Substantial catches of albacore persisted in this
one region for a week after which fishing effort was
terminated.

Further information on the distribution of alba-
core can be derived from the catches made by the
research vessels (Figure 10a-c).10 The research
vessels trolled for albacore along tracks that
crossed the oceanic fronts and expended fishing
effort in Central, Subarctic, and Transition Zone
waters. With few exceptions, they did not catch
albacore in Central or Subarctic waters. In 1972
and again in 1973, when a large meander de-

10Catches are expressed in number offish caught per 15 line-
hours in 1972 and 1973 and per 60 line-hours in 1974. These
numbers of line-hours approximate the amount of fishing effort
expended each day by the research vessels during respective
years.

veloped in the Subarctic front, albacore were
taken in the northward protrusion of Transition
Zone water (Figure 10a, b). Albacore often were
found close to the front. During each of the sur-
veys, catches were made by the research vessel as
the frontal gradients were being recorded by ship-
board instrumentation.

Analyses of variance were performed upon the
charter vessel catch data to test the hypothesis
that catch rates were dependent upon water mass
in the offshore area during June. For the 1972
survey, daily or twice daily XBT casts were
matched with the daily catch data. Because
specific isotherms were found to fall within very
different depth ranges from one water mass to
another, the dependence of catch rate upon classes
of depth ranges for these isotherms was tested.
Thus for this statistical test the water masses may
be defined as follows:

Water mass
Pacific Subarctic
Transition Zone

Isotherm
58°F (14.4°C)
58°F

Depth
<60 m
&60 m

48'

45c

150°

145°

140°

135°

130°

-h"

40°

35°

30'

-TP^

a r/v

T. CROMWELL

f ASTOBlA

) I..

j JUNE 4-23

, 1972

/ CATCH/ 15

LINE HOURS

C 8LANC0

No Catch

01-05

•

0.6-5

•

5.1-10

C MENDOCINO

•

10.1-20

•

20.1-30

pQ sa*

■ ■■

45=

40°

55°

51 °

25°

125°

150°

140°

135°

130°

120°

FIGURE 10. — Albacore catch per 15 line-hours by National Marine Fisheries Service research vessel and
location of fronts delineating Transition Zone waters during: a. 4-23 June 1972; b. 9 June-5 July 1973; c. 29
May-1 July 1974.

810

LAURS and LYNN: SEASONAL MIGRATION OF THUNNUS ALALUNGA
150° 145° 140° 135° 130°

48°

45'

1 — i — I r

48'

40'

35°

30°

25°

CATCH/ 15 LINE HOURS
No Catch
0.1-0.5
0.6-5
5.1-10

10.1-20

40°

30°

25°

150°

48'

-•

40'

35°

30'

R/V D S JORDAN

ASTORIA

MAY 29 -JULY I, 1974

CATCH/ 60 LINE HOURS
c 8l«ncc * No Cotch

•

-20

•

-40

MEM

•

-80

-120

- 40°

25°

150°

25°

115°

811

FISHERY BULLETIN: VOL. 75. NO. 4

Pacific Central

62°F (16.7°C)
62°F

s=90 m
>90 m

The data were transformed to logarithms in
order to standardize between-sample variance.
Results of the analysis of variance show that mean
catch in the Transition Zone, which was greatest,
is significantly different (P = 0.01) from those in
other water masses.

For the 1973 survey, both charter and nonchar-
ter vessel catches were available for test. The
fronts were assumed fixed for this time frame, as
shown in Figure 9b, and catches were assigned to a
water mass based upon reported geographic posi-
tion. Because no fishing effort was expended in
Central waters, except close to the Subtropic front
where catches are expected, an analysis of this
division could not be included. Both the charter
and noncharter vessel data revealed that mean
catches were significantly greater (P = 0.01) in the
Transition Zone than those in the Subarctic wa-
ters.

The poor development of the boundary fronts
between water masses during 1974 precludes a
definitive assignment of catch to water mass;
therefore, a test of the 1974 data was not consi-
dered.

Catches made by both the charter fishing ves-
sels and the research vessel during each of the
three surveys demonstrate that albacore are dis-
tributed within the Transition Zone and may be
absent (or unavailable) or nearly so in water
masses to the north and south during this phase of
their shoreward migration. Relative abundance is
high in offshore areas within the Transition Zone
waters and at times close to the oceanic fronts that
form the boundaries of Transition Zone waters.
Further, when the oceanic fronts are diffuse and
widely spread there is likely to be a corresponding
spread in the distribution of albacore and a dislo-
cation of the centers of high relative abundance.

MIGRATION PATTERN FROM
OFFSHORE TO NEARSHORE WATERS

We view the general pattern of seasonal migra-
tion of albacore into coastal waters where the U.S.
fishery traditionally takes place during summer-
fall as proceeding in three main stages: First, al-
bacore migrate eastward from central North
Pacific regions and form centers of high relative
abundance within the eastern sector of the Transi-
tion Zone waters 600 to 1,000 mi off the coast. This

development initially occurs in late May and
June, a time when seasonal warming has raised
the surface layer temperature of these waters to
values considered to be within the habitat prefer-
ence for albacore. These concentrations offish may
persist in offshore waters for several weeks. Next,
as nearshore waters warm in ensuing weeks, alba-
core migrate toward coastal regions. Fishing ef-
forts in the intervening zone usually produce only
scattered catches, thus suggesting that during the
shoreward migration the behavior of the fish is
such that they are not available to fishing gear
and/or that albacore may not be concentrated.
Then, usually by mid- July, concentrations of high
relative abundance are found near the coast, often
in the vicinity of oceanic fronts related to coastal
upwelling. Although variations may occur in this
general pattern, the main features of the migra-
tion tend to repeat each year. The stages of shore-
ward migration and initial development of the
albacore fishery can be seen in the two series of
charts showing nominal catch per unit effort for
1973 (Figures 5a-e, 6a-e).

The shoreward migration of albacore from the
central North Pacific into coastal waters appears
to continue through the summer months. Albacore
trolling experiments conducted from U.S. Navy
picket vessels operating approximately between
long. 130°and 135°W (Flittner 1963, 1964) showed
albacore to be available there throughout the
summer. Also, two albacore tagged by the
Japanese in the western Pacific (near lat. 35°N
and long. 171°E) in mid-June 1974 were recovered
in the U.S. fishery in September 1974 (Japanese
Fisheries Agency 1975).

Division in Migration Pattern

In order to examine migration of albacore from
offshore to nearshore waters, an albacore tagging
program was conducted during each of the offshore
surveys. Over 4,500 albacore were tagged and re-
leased (Table 1). Recoveries of tagged fish made
during the same season as released provide infor-
mation on migration of albacore into nearshore
waters (Figure lla-c). Most recoveries of tagged
fish made in 1972 offish tagged during early sea-
son 1972 in waters offshore of long. 130°W were
made in central-southern California waters and
only a few recoveries were made in Pacific North-
west waters (Figure 11a). A similar recovery pat-
tern was observed in 1973 (Figure lib). A con-
trasting recovery pattern was observed in 1974

812

LAURS and LYNN: SEASONAL MIGRATION OF THUNNUS ALALUNGA

150° !«5°

48° I — | — i — r

813

FISHERY BULLETIN: VOL. 75, NO. 4

150° 145°

48° | 1 1 1 1 1 —

45'

140°

4'. '

35°

30c

25'

i — l — I — r

_i i i i_

j I i i i

I 1 25°

150°

145°

140°

135°

130°

125°

120°

115°

FIGURE 11.— Recoveries made during the same season as release offish tagged during the early-season

surveys in: a. 1972; b. 1973; and c. 1974.

when almost all of the recoveries offish tagged in
1974 were made in waters off the Pacific North-
west (Figure lie).

Differences in recovery pattern cannot be ac-
counted for by geographic variations in fishing
effort and fish catch. In all 3 yr, 70% or more of the
fish caught during the commercial fishery was off
the Pacific Northwest. It appears, instead, that
differences in recovery patterns could be related to
the location where tagged fish were released. In
both 1972 and 1973, most of the tagging effort in
offshore waters was between lat. 33° and 34°N and
in 1974 it was farther north, between lat. 35° and
36°N. The different and divergent patterns appar-
ently are the result of the albacore following dif-
ferent and divergent migration routes toward the
nearshore waters. Tagging efforts of 1972 and
1973 and those of 1974 were apparently concen-
trated upon different branches of the migration.
The division in the migration pattern appears to
have occurred near lat. 35°N and must have occur-
red west of, and prior to, the appearance of the fish
in the survey region.

Support for this proposed division in the migra-
tion pattern of albacore is indicated by differences
in length-frequency distribution of albacore
caught in the commercial fishery off California
and north of California. Differences in size com-
position offish caught in 1972 in the two regions
(Figure 12 upper and lower) include: 1) the mode of
large-size fish was about 5 cm larger in fish caught
off California than in fish caught off the Pacific
Northwest; 2) the mode of the medium-size fish,
which formed the dominant size group in both
regions, was 1 to 2 cm larger in fish caught off
California than in fish caught off the Pacific
Northwest; and 3) occurrence of three modal size
groups taken in the fishery off California, but only
two off the Pacific Northwest, where the smallest
modal size group was absent. Examination of
size-frequency distributions for 1973 and 1974
yielded similar results.

The size composition of albacore caught west of
long. 130°W by charter vessels in 1972 (Figure 12
lower) was very similar to that for fish taken in the
commercial fishery off California (Figure 12 mid-

814

LAURS and LYNN: SEASONAL MIGRATION OF THUNNUS ALALUNGA

1972 Fishing Season

NORTH OF
LIFORNIA

l0r 1972 Fishing Season

CALIFORNIA

45 50 55 60 65 70 75 80 85

FORK LENGTH IN CENTIMETERS

FIGURE 12. — Size composition of albacore caught by U.S.
fishermen during 1972 north of California (upper), off California
(middle), and size composition of albacore caught during the
1972 National Marine Fisheries Service- American Fishermen's
Research Foundation offshore survey (lower).

(Figure 13) show that albacore initially appeared
offshore near the end of May and there was an
abrupt increase in relative abundance in the be-
ginning of June. A decline in relative abundance
was observed offshore after 19 June as centers of
abundance shifted to nearshore where there was
an increase in early July. Within these overall
trends, changes in each of the three modal size
groups can be followed. The mid-size modal group
(fork length centered about 67 to 69 cm), initially
dominated early offshore catches and then di-
minished in relative importance. It formed almost
the entire catch of the first nearshore catches and
continued to dominate nearshore catches into
July. The large-size modal group (fork length cen-
tered about 82 to 85 cm) showed similar trends: a
rise and fall in relative abundance offshore and
with a subsequent shift to nearshore, but lagging
behind the mid-size modal group by one 10-day
period. The small-size modal group (fork length
centered about 52 and 53 cm) was dominant
offshore after 10 June but made little appearance
in the nearshore region during the survey. This
size group subsequently entered the nearshore
fishery, however, as is evident from the size com-
position of the 1972 fishery off California (Figure
12 middle). An additional geographic division in

WEST OF I30°W

die) and hence different from the size composition
of fish taken in the commercial fishery north of
California ( Figure 12 upper). It appears, then, that
albacore caught in the offshore region of high rela-
tive abundance south of lat. 35°N in 1972 were a
part of the migration of fish that reached regions
off California.

We interpret the findings concerning offshore-
nearshore and north-south geographic variations
in size composition as supporting the hypotheses
1) that the fish which compose the fishery off
California are separate from those which make up
the fishery off the Pacific Northwest, and 2) that
these two groups offish follow different migration
routes into nearshore waters.

Movements of Albacore by Size Groups

The size composition data for the 1972 charter
vessel catch were stratified into offshore and near-
shore regions at long. 130°W and into one 8-day
and four 10-day time periods. Graphs of the strat-
ified data standardized by fishing effort for 1972

MAY 23- S^50
MAY 30 5 8

* 0

=.k

, <"S;

1406 L-H

(1 r", . i

I30°W
I

45 50 55 60 65 70 75 80 85 90 95 100

MAY 31- £
JUNE 9

JUNE 10- £
JUNE 19

45 50556O6S707580859095O0

EAST OF I30°W

[ NO CATCH )

(NO CATCH I

JUNE 20- £
JUNE 29 -

sk^^t^1^-

45 50 55 60 65 70 75 80 85 90 95 100

JUNE 30- g

july 9 ;

(NO EFFORT 1
(NO CATCH I

FORK LENGTH (cm)

,00 1 5552 L-H

45 505560 65 707580 85 9095-00

60 65 70 75 80 85 90 95 KJC

FORK LENGTH (cm)

FIGURE 13. — Size composition of albacore caught by American
Fishermen's Research Foundation charter vessels in 1972 by
time periods and east and west of long. 130CW.

815

FISHERY BULLETIN: VOL. 75. NO. 4

the offshore region, splitting the catch north and
south of lat. 35°N showed that the catches first
developed south of lat. 35°N and then moved
north. By the fourth period (20 to 29 June), the
small-size modal group composed almost the en-
tire catch south of lat. 35°N and offshore of long.
135°W.

Several conclusions are evident from these tem-
poral and areal changes in size composition. While
catches persisted for up to 4 wk within a 2° by 4°
quadrangle of latitude and longitude in the
offshore region, changing patterns of size composi-
tion suggest that albacore were moving through
the region within a period of 10 days or less and
that the size groups migrated somewhat indepen-
dently. The mid-size group, which composes the
major portion of the U.S. fishery, led other size
groups by 10 or more days. Also, the sequence of
compositional changes of each size group and the
geographic differences suggest that the migration
from the offshore region to the nearshore fishery
takes about 20 days or more; at least it did in 1972.

The 1972 catch data were chosen for examina-
tion of spatial and temporal changes in size com-
position because each of the size groups was well
represented in the survey catches and all phases of
the migration into the fishery are evident, includ-
ing commencement of the fishery, by the comple-
tion of the survey. In 1973 the fishery started late,
weeks after the survey, and in 1974 the patterns
were less distinct, apparently in response to weak
oceanic frontal conditions.

DISCUSSION

Association of Albacore Distribution
With Oceanic Frontal Regions

The commercial fisheries on North Pacific alba-
core and the migration of albacore among these
fisheries have frequently been associated with
oceanic frontal regions in the western Pacific
(Yamanakaetal. 1969; Uda 1973; other works), in
the central North Pacific (Shomura and Otsu
1956; McGary et al. 1961), and in coastal upwell-
ing regions (Pearcy and Mueller 1970; Panshin
1971; Laurs 1973; Laurs et al. 1977).

Results of our study provide evidence for the
continuity of the association of albacore distribu-
tion with the Transition Zone and frontal bound-
aries into the eastern North Pacific. Catches made
by the AFRF charter fishing vessels and the re-
search vessel during each of the three surveys

demonstrate that albacore are distributed mainly
within the Transition Zone and usually are absent
(or unavailable) in water masses to the north and
south. Furthermore, our work strengthens the
general concept that the distribution and relative
abundance of large, highly migratory fish may be
markedly influenced by oceanic frontal features.
Other studies usually have had to rely on mean
ocean conditions and/or statistically averaged
fishery data, whereas our fishery and oceano-
graphic data were collected concurrently during
several surveys, and the amounts of fishing effort,
fish catch, and oceanographic data were substan-
tial.

Relative Abundance of Albacore in the
Eastern Sector of the Transition Zone

We have found centers of high relative abun-
dance of albacore in June within the eastern sector
of the Transition Zone and often close to its frontal
boundaries. Annual and intra-annual areal varia-
tions in relative abundance of albacore were ob-
served and appeared to be related to development
of the frontal boundaries of the Transition Zone.
When the Subarctic and Subtropic fronts were
strongly developed, areas of high relative abun-
dance developed within relatively narrow bands
in the Transition Zone and persisted for several
weeks. When the Transition Zone was broader and
the fronts were poorly developed, centers of high
relative abundance were found over a larger area
within the Transition Zone and did not persist for
more than several days in any one location.

Based on scouting results from several research
surveys, it appears that the timing and the loca-
tion of fishing effort may be critical in locating
centers of high relative abundance of fish in the
eastern sector of the Transition Zone. In 1973,
charter vessels first found a center of high relative
abundance on 4 June near lat. 34°N, long. 140°W
in Transition Zone waters. For several weeks prior
to this finding, the AFRF charter vessels had made
only scattered catches while scouting in and about
this same area. Thus, it seems that the center of
high relative abundance appeared in a surge
within the first week of June. In 1955, an albacore
survey cruise by a single U.S. Bureau of Commer-
cial Fisheries (BCF) research vessel (Hugh M.
Smith) scouted this area in late May and early
June (Graham 1957). Seven longline sets and
trol ling conducted between lat. 4 1 ° and 28 °N along
long. 139°W resulted in only a single albacore

816

LAIRS iind LYNN SEASONAL MIGRATION OF THUNNUS ALALUNC I

being taken before the vessel departed the area on
5 June. The 1955 scouting effort may have been
too early by a matter of days to weeks to locate
substantial numbers offish. In 1957, a BCF fishery
research vessel (John R. Manning! scouted to the
north and east of this area in late June (Callaway
and McGary 1959). Small to modest catches of
albacore were made by trolling and in gill net sets
in and about the Transition Zone, but the area
which we have found to have a center of high
relative abundance was not scouted.

Extension in Space and Time of
U.S. Albacore Fishery

The cooperative NMFS-AFRF albacore re-
search surveys have demonstrated the feasibility
of extending the U.S. fishery for albacore in space
and time. Albacore were caught by chartered
fishing vessels in commercial concentrations con-
siderably farther offshore than where the albacore
fishery has traditionally taken place and up to 6
wk prior to the usual beginning of the fishing
season. Noncharter commercial albacore fishing
vessels, attracted to the early season offshore
fishery by the research survey findings, have
begun operating in this fishery in increasing
numbers.

While fishing results of the AFRF-chartered
and the nonchartered fishing vessels indicate that
commercial amounts offish can be caught earlier
and farther offshore than the usual fishing season,
additional experience is needed to examine the
variability of this extension of the fishery, espe-
cially in terms of timing and availability, in order
to judge properly whether it can provide a depend-
able contribution to the U.S. fishery. If in the
long-run the early season offshore fishery proves
viable, its development could be an important fac-
tor in reducing annual fluctuations in the catch of
albacore. According to Clemens (1962) large an-
nual fluctuations in catch are a prominent feature
of the U.S. albacore fishery. Stabilization of catch
among years could contribute significantly to the
proper utilization and ultimately to the effective
management of the resource.

The fishing success by charter and noncharter
albacore commercial fishing vessels in 1972-74 is
in contrast to an earlier attempt to establish com-
mercial fishing in waters offshore from where the
U.S. fishery has historically operated. According
to McGary et al. (1961), an unsuccessful gill net
and trolling effort was made in the summer of

1958 by a chartered commercial fishing vessel in
areas of the central North Pacific where albacore
were caught during research surveys conducted in
summers of 1955 and 1956. The failure to catch
albacore in amounts sufficient to support commer-
cial fishing may have been an accidental event
related to intense anomalous oceanic conditions
which occurred ocean-wide and affected numerous
fisheries in 1957-58 (Sette and Isaacs 1960).

Association of Shoreward Albacore

Migration With Transition Zone

and Possible Mechanisms

Shoreward Migration and Transition Zone

Based on association of albacore distribution
and relative abundance with the Transition Zone
and its frontal boundaries, we conclude that the
shoreward migration of albacore is linked to the
Transition Zone and that variations in the pattern
of migration occur in response to variations in the
character and development of the Transition Zone
and its frontal structure. When the Transition
Zone is narrow and its fronts are well developed, as
in 1972 and 1973, the migration pattern of the fish
is narrow and relatively well defined. In contrast,
when the Transition Zone is broad and its fronts
weakly formed, as in 1974, the migration pattern
offish is wide and less well defined.

There is also some suggestion that the strength
and continuity of the Transition Zone fronts in
offshore waters may affect the timing of arrival of
fish in nearshore waters. When the fronts are well
developed, fish appear to aggregate in their vicin-
ity, resulting in a tendency for the fish to remain in
offshore waters for periods of time that delay their
arrival in the nearshore fishing grounds. How-
ever, when the fronts are weak the fish appear to
move through offshore waters with less delay and
arrive earlier in nearshore waters. Initial showing
offish in nearshore waters during the years of the
surveys supports this speculation. The nearshore
commercial fishery and sport fishery off southern
California commenced several weeks later in 1972
and 1973 than in 1974.

Possible Mechanisms tor Association of
Albacore With the Transition Zone

The mechanisms responsible for the relation-
ship between albacore and the Transition Zone
and its frontal boundaries may result from a

817

FISHERY BULLETIN: VOL. 75. NO. 4

number of factors acting in an interrelated matrix
which impacts the fish both directly through
physiological means and indirectly through forage
availability. We postulate that the factors include,
but are probably not limited to: 1 ) habitat temper-
ature preference, 2) biological productivity, and 3 )
thermal gradients as they affect the albacore's
thermoregulation processes, and that these fac-
tors act in an interrelated way superimposed on
the innate drive of the fish to migrate across the
North Pacific Ocean.

HABITAT TEMPERATURE PREFERENCE.

— The distribution and relative abundance of al-
bacore are related to sea-surface temperature (Cle-
mens 1961; Johnson 1962; Panshin 1971; and
others). The habitat temperature preference for
albacore ranges from approximately 16° to 19°C

(Clemens 1961; Laveastu and Hela 1970). This
temperature range is found in the upper mixed
layer waters of the Transition Zone in spring.
Near-surface waters to the south of the Transition
Zone are generally warmer than this and those to
the north cooler.

The sequence of spring-summer warming of the
surface layer along a section between Honolulu
and San Francisco during 1972 is illustrated in
Figure 14. The Transition Zone boundaries iden-
tified by the abrupt changes in depth of isotherms
at intermediate depths fall between long. 130° and
140° W. The habitat temperature preference range
for albacore (16° to 19°C) is shown with shading. In
early and mid-spring (upper left) only the Central
waters have preferred temperatures and these
waters occur down to a considerable depth, almost
200 m. In subsequent time periods, a shallow sur-

APRIL 15-19. 1972

^HONOLULU-
2.000

NAUTICAL MILES -

1,500 1,000

SAN FRANCISCO^

500 0

MAY 27-31,1972

^HONOLULU -
2.000

NAUTICAL MILES-

1.500 1.000

SAN FRANCISCO-.

500 0

800

1.200

JUNE 24-28. 1972

VOYAGE 45

-HONOi

2.000 1.500

-NAUTICAL MILES
1.000

SAN FRANCISCO-

500 0

I45°W I40°W

LONGITUDE

30°W I25°W

JULY 22-26,1972
^HONOLULU—

NAUTICAL MILES -

1.500 1.000

VOYAGE 4 7
-SAN FRANCISCO^

LONGITUDE

FIGURE 14.— Vertical temperature sections on a transect from Honolulu to San Francisco during April to July 1972. The temperature

range between 16° and 19°C (60.8° and 66.2°F) is shaded.

818

LAURS and LYNN: SEASONAL MIGRATION OF THUNNUS ALALUNGA

face layer develops and warms to preferred temp-
eratures, initially in the Transition Zone and then
in more nearshore waters. It is near the end of May
and through June that the preferred temperature
range occurs in the Transition Zone and is gener-
ally restricted to depths <70 m. The depth limita-
tion of preferred waters greatly improves the vul-
nerability of albacore to surface trolling gear.

BIOLOGICAL PRODUCTIVITY.— Tagging
data show that migration of albacore from the west-
ern to the eastern North Pacific is active with an
average migration speed of 48 km/day for 78- and
80-cm fish (Japanese Fisheries Agency 1975). This
suggests that an albacore requires considerable
energy to complete the transpacific migration.
Sharp and Dotson (1977) calculated that the
caloric expenditure per hour for a swimming alba-
core 63 cm in fork length is 5.02 kcal/h. They also
speculated that fat stores may be an important
energy source utilized by albacore for migration.
Studies of the food habits of albacore caught dur-
ing the surveys11 show that albacore feed actively
in offshore waters during their shoreward migra-
tion. The composition of the food found in the
stomachs is different from that of fish caught in
inshore waters (Pinkas et al. 1971, Laurs and
Nishimoto MS12), but average volumes of food in
stomachs from the two regions are similar. There-
fore, availability of forage is likely to be an impor-
tant factor influencing the route of albacore mi-
gration.

There are three major oceanic habitats in the
North Pacific which are separated by pronounced
latitudinal faunal boundaries and steep latitudi-
nal gradients in standing stocks of phytoplankton
and zooplankton (McGowan and Williams 1973).
These species and biomass boundaries are coinci-
dent with the boundaries of the Pacific Subarctic,
Transition Zone, and Pacific Central waters
(Johnson and Brinton 1963). A northward increas-
ing step-cline occurs among the North Pacific
habitats in standing stocks of phytoplankton
(Venrick et al. 1973; McGowan and Williams
1973 ), zooplankton ( Reid 1962; McGowan and Wil-
liams 1973), and micronekton (Aron 1962), and in

"Laurs, R. M., and R. N. Nishimoto. 1973. Food habits of
albacore caught in offshore area. In Report of joint National
Marine Fisheries Service-American Fishermen's Research
Foundation albacore studies conducted during 1973, p. 36-40.
(Unpubl. rep.)

12Laurs, R. M., and R. N. Nishimoto. Food habits of albacore in
the eastern North Pacific. (Unpubl. manuscr.)

primary production ( Koblents-Mishke 1965).
Zooplankton and micronekton standing stock es-
timates made during the offshore albacore surveys
show similar results with values generally being
highest in Subarctic waters, intermediate in
Transition Zone waters, and lowest in Central
waters.

Since biological productivity is higher in Sub-
arctic waters than in Transition Zone or Central
waters, it would be most advantageous from the
standpoint of food availability for albacore to
confine their migration path to Subarctic waters.
However, during spring months the temperature
of the Subarctic waters is much lower than the
habitat preference for albacore. We conclude,
then, that the northern limit of the albacore mi-
gration route during spring is determined by
ocean temperature and that the limiting tempera-
ture is found near the northern boundary of the
Transition Zone. The temperature of the upper
layer of the Central waters is higher than the
habitat temperature preference for albacore, but
there are temperatures below the upper layer
which lie within the habitat temperature prefer-
ence for albacore. Thus, temperature could restrict
the distribution of albacore from the upper layer
but not at some depth interval below the upper
layer. We propose that while temperature may
play a role in determining the southern limit of the
albacore distribution and migration route, the
major factor is the abundance and availability of
forage organisms which drop off sharply near the
southern boundary of the Transition Zone.

OCEAN THERMAL GRADIENTS AND
THERMOREGULATION OF ALBACORE.—
Thermoregulation processes by albacore may be
an important factor in determining their associa-
tion with the Transition Zone and its frontal
boundaries. Thermoregulation is characteristic of
tunas and certain other fishes (Carey et al. 1971).
According to Neill ( 1976) for fishes as a group, the
only effective means of regulating body tempera-
ture is by behavioral regulation of the immediate
environmental temperature through locomotory
movements.

Computer simulation models developed by Neill
(1976) indicate that where environmental condi-
tions are characterized by large expanses of
isothermal or nearly isothermal water separated
by relatively narrow thermal discontinuities (e.g.,
oceanic frontal systems), fishes will be relatively
concentrated near the discontinuities.

819

FISHERY BULLETIN VOL. 75, NO. 4

Division in the Migration of Albacore
Into the American Fishery

Our study indicates that there is a division in
the migration pattern of albacore into the Ameri-
can fishery with fish which compose the fishery off
the Pacific Northwest and off California following
different routes. We believe that the "northern"
branch of the migration progresses as described by
Powell et al. (1952) who, during an exploratory
albacore fishing survey over a region off the Pacific
Northwest, found albacore along a warm-water
edge that develops seasonally 400 to 500 n.mi.
offshore of southern Oregon in late June and early
July. The warmwater edge was observed to prog-
ress northward and coastward in a bulge or
pouchlike pattern as seasonal warming of the sur-
face waters took place over the ensuing weeks. The
occurrence of albacore was found to follow the
progression of the warmwater zone shoreward and
northward along the coasts of Oregon and
Washington and by mid- August to waters off the
Queen Charlotte Islands, British Columbia. Pow-
ell et al. (1952) concluded that these findings, as
well as earlier observations, indicated that the
main barrier directly or indirectly influencing the
distribution of albacore throughout their northern
range is water temperature.

Clemens (1961) investigated the onset and
movements of the albacore fishery off California
and Baja California for the fishing seasons 1951
through 1953. From catch records he found that
albacore entered the coastal waters as far south as
200 n.mi. south of Guadalupe Island (lat. 29°N) in
some years and as far north as the San Juan Sea-
mount (lat. 33°N) in others. He also presented tag
recovery data which showed that albacore move
from Baja California or southern California in the
early season northward to central California as
the season progresses (however, only one recovery
of a tagged fish was made off northern California).
Clemens concluded that albacore entering the
American fishery initially migrate to Baja
California or southern California and that
longshore movement was the dominant mode of
their dispersal into coastal zones to the north. Al-
though he allowed that albacore may reach Ore-
gon and Washington waters by following the sea-
sonal bulge of warm offshore water as suggested
by Powell et al. ( 1952 ), Clemens stated that a large
part of the main body of albacore travel northward
up the coast to waters off the Pacific Northwest
from Baja California and southern California. No

evidence was given for this statement and our
newer findings do not support it. We concur that
northward longshore movement is important in
nearshore waters, but conclude that fish entering
waters off Baja California or southern California
do not migrate farther north than about San Fran-
cisco before leaving the American fishery.

Flittner (1963) presented a schematic diagram
of albacore movement off the Pacific coast based on
albacore catches made by U.S. Navy picket vessels
during 1960-62. The picket vessels, stationed 200
to 500 n.mi. offshore (no farther west than long.
135W) and spaced at latitudinal intervals of 300
n.mi., each trolled several jig lines from May
through October. Flittner said that albacore ap-
peared to congregate within an "optimum-
temperature" zone and seem to split into two mi-
gratory components. Early arrivals proceed to
southern feeding areas and late arrivals turn to
the northern area, each movement depending
upon the progression of seasonal warming.

Progression of seasonal warming continues to
appear to be an important factor affecting paths of
albacore migration. However, influence of the
Transition Zone development and the division of
migration pattern described here add considerable
complexity to earlier ideas. Our findings suggest
that events in offshore waters are important in
determining the distribution and relative abun-
dance of albacore in coastal waters.

Pacific Northwest and
California Groups of Fish

Based on offshore- nearshore and north-south
geographic variations in size composition of alba-
core we postulate that the group of fish which
compose the albacore fishery off California are
separate from those which make up the fishery off
the Pacific Northwest. Brock (1943) arrived at a
similar conclusion after comparing length-
frequency distributions of albacore landed in Sap
Pedro, Calif., and Astoria, Oreg. Brock found dif-
ferences in size composition and stated, "This
would argue that the schools offish off the Oregon
coast were not a part of the schools appearing off
the California coast, even though, as indicated
above, the two groups may have had a common
origin. . . The time of arrival of fish and their
abundance as shown by the monthly commercial
catch for the ports discussed here (San Pedro and
Astoria) make it seem likely that at least two
separate groups of schools invaded the coastal

820

LAURS and LYNN: SEASONAL MIGRATION OF THUNNUS ALALVNGA

area, one in the north off Oregon and the other in
the south off southern California."

Results of studies on the artificial radionuclide
60Co in albacore provide additional evidence that
the "northern" and "southern" groups of fish are
independent. Krygier and Pearcy (1977) found
that the peak activity levels of 60Co in albacore off
Oregon occurred a year earlier than the peak ac-
tivity levels seen by Hodge et al. (1973) off south-
ern California. According to Krygier and Pearcy,
the heaviest fallout input of 60Co into the North
Pacific occurred at about lat. 40°N. They specu-
lated that due to circulation in the North Pacific,
albacore which were associated with waters north
of lat. 35°N could have experienced high levels of
60Co up to a year before the tuna associated with
waters to the south. They concluded that, "Circu-
lation in the North Pacific and the latitudinal dif-
ferences in the location of the two portions of the
albacore population [as proposed by Laurs and
Lynn in this paper] appear to be a plausible expla-
nation for the difference of 1 yr in activity peaks
between albacore caught off Oregon by us and
those off southern and Baja California by Hodge et
al. (1973)." Thus, strong evidence from several
independent sources points toward two separate
groups of albacore following separate migration
paths.

ACKNOWLEDGMENTS

We thank the American Fishermen's Research
Foundation for their farsighted interest and their
support for albacore and oceanographic research
(particularly, in this regard, Robert Insinger and
John Bowland). We owe a debt of gratitude to the
captains and crews of the RV Townsend Cromwell
and David Starr Jordan, and the chartered fishing
vessels, and to the staff of the Albacore Fishery
Investigations whose loyal support and perserver-
ance made this work possible.

LITERATURE CITED

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1962. The distribution of animals in the eastern North
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BROCK, V. E.

1943. Contribution to the biology of the albacore (Germo
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Callaway, R. J., and J. w. McGary.

1959. Northeastern Pacific albacore survey. Part 2.

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Clemens, h. b.

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FLITTNER, G. A.

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Graham, J. J.

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1959. Northeastern Pacific albacore survey. Part 1.
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HODGE, V. F., T. R. FOLSOM, AND D. R. YOUNG.

1973. Retention of fall-out constituents in upper layers of
the Pacific Ocean as estimated from studies of a tuna
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environment, p. 263-276. Int. At. Energy Agency, Vienna.
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Res. Sect., Far Seas Fish. Res. Lab., June, 18 p.

JOHNSON, J. H.

1962. Sea temperatures and the availability of albacore off
the coasts of Oregon and Washington. Trans. Am. Fish.
Soc. 91:269-274.

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1963. Biological species, water masses and currents. In
M. N. Hill (editor), The Sea, Vol. 2, p. 381-414. John Wiley
and Sons, Inc.

KOBLENTS-MISHKE, O. I.

1965. Primary production in the Pacific. [In Russ.]
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5(2):104-116.)

KRYGIER, E. E., AND W. G. PEARCY.

1977. The source of cobalt-60 and migrations of albacore
off the west coast of North America. Fish. Bull., U.S.
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LAURS, R. M.

1973. Requirements of fishery scientists for processed
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gan. Tech. Conf., Tokyo, 2-7 Oct. 1972. WMO 346:95-111.

laurs. R. M., H. B. Clemens, and l. h. hreha.

1976. Nominal catch-per-unit effort of albacore, Thunnus
alalunga (Bonnaterre), caught by U.S. jig vessels during
1961-1970. Mar. Fish. Rev. 38(5):l-32.

821

FISHERY BULLETIN: VOL. 75, NO. 4

LAURS, R. M., H. S. H. YUEN, AND J. H. JOHNSON.

1977. Small-scale movements of albacore, Thunnus
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ultrasonic tracking and oceanographic sampling. Fish.
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LAVEASTU, T., AND I. HELA (editors).

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MCGARY, J. W., J. J. GRAHAM, AND T. OTSU.

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Coop. Oceanic Fish. Invest. Rep. 8:45-53.
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latitude waters, January-March 1954. U.S. Fish Wildl.
Serv., Spec. Sci. Rep. Fish. 180, 173 p.
MCGOWAN, J. A., AND P. M. WILLIAMS.

1973. Oceanic habitat differences in the North Pacific. J.
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1969. Oregon albacore tuna fishery statistics, 1961-
1967. Oreg. Fish Comm., Data Rep. Ser. 1, 143 p.

NEAVE, F., AND M. G. HANAVAN.

1960. Seasonal distribution of some epipelagic fishes in the
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233.
NEILL, W. H.

1976. Mechanisms of behavioral thermoregulation in
fishes. Report of Workshop on the Impact of Thermal
Power Plant Cooling Systems on Aquatic Environments.
Electric Power Res. Inst. Spec. Rep. 38:156-169.
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1968. Oceanographic conditions in the northeast Pacific
Ocean and their relation to the albacore fishery. U.S.
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1971. Albacore tuna catches in the northeast Pacific dur-
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PEARCY, W. G., AND J. L. MUELLER.

1970. Upwelling, Columbia River plume and albacore tu-
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PINKAS, L.

1963. Albacore scouting in the eastern North Pacific
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POWELL. D. E.

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POWELL, D. E., AND H. A. HlLDEBRAND.

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Far Seas Fish. Res. Lab. (Shimizu) 2:257-273.

822

BIOLOGY OF THE SUMMER FLOUNDER,
PARALICHTHYS DENTATUS, IN DELAWARE BAY'

Ronal W. Smith and Franklin C. Daiber2

ABSTRACT

Data on the age, growth, food habits, and racial characters of summer flounder, Paralichthys dentatus ,
from Delaware Bay were examined. Fish were present year-round, although 95% were taken from May
through September, and no mature fish were caught during the winter. Fish were aged from annuli on
the largest left otolith. The growth rate for males was described by L t +1 = 141.91 + 0.767(L,), and
for females Lt + j = 136.72 + 0.843(L(). The Delaware Bay commercial fishery in 1966 was primarily
supported by age-groups 2 through 5. The total length-weight relationship was described by, log weight
(grams) = log 0.404 x 10~5 + 3.151 log [total length (millimeters)], and the total length-standard
length relationship by, total length (millimeters) = 16.695 + 1.55[standard length (millimeters)]. Age
and sex made no significant difference in meristic character evaluation. The reported range of varia-
tion for some characters was extended: dorsal rays, 89-98; anal rays, 63-78; pectoral rays, 10-13;
vertebrae, 40-43; standard length/head length, 3.64-4.30; and head length/upper jaw length, 1 .54-2.26.

One objective of this study was to investigate the
age, growth, and food habits of summer flounder,
Paralichthys dentatus (Linnaeus), caught in Del-
aware Bay. Previous research on age and growth,
Eldridge (1962) and Poole (1961), disagreed and
additional study was needed.

A second objective was to determine the mag-
nitude of variation in meristic characters of sum-
mer flounder from Delaware Bay for comparison
with other geographic areas. Ginsburg (1952) re-
ported that summer flounder from Chesapeake
Bay and from Beaufort, N.C., might belong to two
distinct racial stocks on the basis of gill raker
frequency distributions. According to Poole
(1966), unpublished studies found no real differ-
ences between these populations, but he added
that analysis of racial data from Maryland, Vir-
ginia, and North Carolina areas suggested the
need for additional research.

Summer flounder are common from Cape Cod to
North Carolina and they have been reported from
Maine to Texas (Bigelow and Schroeder 1953;
Poole 1962). They normally inhabit coastal and
estuarine waters during the warmer months of the
year and move off on the continental shelf in 20 to
100 fm of water during the fall and winter

'Contribution No. 91, College of Marine Studies, University of
Delaware. Based on a thesis by Ronal W. Smith submitted to the
University of Delaware as part of the requirements for the M.S.
degree in Biological Sciences.

2College of Marine Studies, University of Delaware, Newark,
DE 19711.

Manuscript accepted March 1977.

FISHERY BULLETIN: VOL. 75, NO. 4. 1977.

(Bigelow and Schroeder 1953). Spawning occurs
during the fall and winter while the fish are mov-
ing offshore or at their wintering location, and
larvae and postlarvae drift and migrate inshore to
coastal and estuarine nursery areas (Smith 1973).

COLLECTION OF MATERIAL

Most fish examined were caught by a 9-m (30-ft)
otter trawl, 7.6-cm (3-in) stretch mesh in the body
and 5.1 cm (2 in) in the cod end, during monthly
fish survey trips in Delaware Bay. A total of 13
sectors were sampled during the period August
1966 through November 1971 (Figure 1), with a
minimum of 3 and a maximum of 12 sampled in
any 1-mo interval. Sectors sampled were selected
to cover a range of salinities and depths in Dela-
ware Bay. During the summer of 1968, three sec-
tors were sampled during the day and again that
night. Sampling at each station consisted of mak-
ing a Nansen cast within 2 m of the bottom for
temperature and a water sample, and trawling for
30 min. The mean tow length was 1.2 n.mi. Aver-
age water depth for each tow was determined by
eye from a recording fathometer trace. Some fish
were taken by beach seining, while others were
caught during miscellaneous trawling operations
through February 1973.

Stomachs for gut analysis were removed im-
mediately on fish capture and placed in 95% iso-
propyl alcohol.

The commercial summer flounder catch from

823

FISHERY BULLETIN: VOL. 75, NO. 4

39°20'

DELAWARE BAY
0_l_2_3

NAUTICAL MILES

7 5° 30' 7 6°20

3 8°50'

FIGURE 1. — Delaware Bay with sampling sectors shaded.

Delaware Bay was sampled on four occasions in
1966 by measuring all (1,060) fish caught by a
14-m trawler using both a 15-m (50- ft) otter trawl,
body — 7.6-cm (3-in) stretch mesh, cod end — 5.1 cm
(2 in), and a 16-m (52-ft) otter trawl, body— 10.2
cm (4 in), cod end — 7.6 cm (3 in). This vessel was
typical of the few commercial boats operating in
the bay then, and 1966 was the last year trawling
was permitted.

GENERAL OBSERVATIONS

Summer flounder seem to have a ubiquitous
range in Delaware Bay. They were caught in all
sectors sampled; and in water with temperatures
from 1.6° to 26.8°C, salinities from 10.6 to 31.8%o,
and depths from the shore to 25 m. Most (95% ) fish
were caught from May through September. A few
juvenile fish were taken in every winter month,
indicating that some juveniles move to deeper
parts of the estuary during the winter rather than
offshore. Poole (1966) suggested a similar
phenomenon for estuaries in North Carolina.

During the 5-yr survey, the yearly mean
number of summer flounder caught per nautical
mile of trawling (number offish caught per year
divided by the total length of tows containing

summer flounder) varied from 1.5 to 4.7, with no
significant trend. No real difference was apparent
in the number (34 day versus 29 night) of flounder
caught between day and night tows.

AGE AND GROWTH ANALYSIS

Otoliths were used for aging fish because they
were much easier to read than scales, and both
Poole (1961) and Eldridge (1962) found them suit-
able for aging. Left and right otoliths were
examined, and we found the radial length (dis-
tance from the center of the core to the anterior tip)
was different between left and right ones from the
same fish. This occurred because the center area or
core (Figure 2) was located more posteriorly in the
right otolith. We did not compare left and right
otoliths to see if the relationship between radial
length and the various annuli lengths were the
same for both.

Left otoliths were removed from all flounder
(either fresh or previously frozen) caught in

8
6

CORE

FIGURE 2. — Left otolith from an age-group 8 summer flounder,
total length 69 cm, with estimated age indicated against respec-
tive annuli (rule marking in millimeters).

824

SMITH and DAIBER: BIOLOGY OF SUMMER FLOUNDER

1966-68. Upon removal, they were cleaned in
water and stored dry. Prior to examination,
otoliths were soaked for 30 min in a 2c/c solution of
the plant enzyme, papain, according to the
technique of Pruter and Alverson ( 1962) for clean-
ing and clearing. Annuli were visible before soak-
ing and it is doubtful this clearing process helped.

For examination, otoliths were placed in distil-
led water in the wells of a Coor's3 black porcelain
spot plate. They were measured with an ocular
micrometer to the nearest 0. 1 mm for radial length
and annuli lengths with the concave surface up.
All otoliths were read twice, and those very
difficult to interpret a third time. Approximately
20% of the otoliths were discarded because of ir-
regular shape or indistinct annuli, leaving 319
used in the age analysis. Mean annuli lengths are
given in Table 1. No age-group 6 males were col-
lected in this study.

There was a linear relationship between total
length (TL in millimeters) and otolith radial
length in millimeters, and this relationship was
best described by:

Otolith radial length = 0.012(TL)

Correlation coefficient = 0.998
Standard error of estimate = 0.336

This equation applied to both sexes.

Fish length at time of annulus formation or
back-calculated length was calculated as de-
scribed in Rounsefell and Everhart (1953), and
these lengths for males and females are given in

3Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

Tables 2 and 3, respectively. No correction factor
was used in the calculation because: 1) the line
best representing the total length-otolith radial
length relationship had a zero origin and 2) correc-
tion factors obtained were not reasonable because
they gave the fish a negative length at time of
otolith formation. According to Rugh (1962), who
used Fundulus heteroclitus as an example of a
typical teleost, otoliths start to form in the first
quarter of development. Therefore, fish length at
time of otolith first formation could be considered
negligible when compared with fish length at 1 yr.

The observed 17 cm length at 1 yr as reported by
Eldridge (1962) is far above a 12 cm length we
back-calculated using the otolith core edge as the
first annulus. We assumed the first annulus was
located at the core edge (radial length from 1.1 to
1.5 mm) because typically the first well-defined
annulus away from the core (approximately 3.3
mm radial length, Table 1) was only present in
otoliths from fish larger than 27 cm, fish we be-
lieved too large to be in age-group 1 (fish 1 or 1 + yr
old). Supporting our belief is Eldridge's reported
length frequency at 1 yr and our subsequent cap-
ture (1973) of Delaware Bay flounder during
winter in the 15-20 cm size range. A few otoliths
we examined had faint rings at radial lengths of
2.0 to 2.6 mm, but we thought these represented a
false annulus. Probably these faint rings were
true first annuli and they were not observed in
most otoliths.

The primary reason for the difference between
our back-calculated fish lengths and those given
by Poole ( 1961 ) and Eldridge ( 1962), Tables 2 and
3, is the interpretation of age at the first annulus
used. Examination of Poole's calculated length at
1 yr plus his photographs of otoliths indicated he
considered the first well-defined annulus as being

TABLE 1. — Mean radial distance ± 1 standard deviation of annuli on otoliths from
summer flounder taken in Delaware Bay during 1966-68. (No suitable first annulus was
found.)

Age-

Number of
otoliths

Measured radial distance for successive annuli (mm)

group

Male:

3.3:5:0.3

3.2 ±0.3

4.2 ±0.3

3.2 ±0.3

4.2 ±0.3

4.9±0.2

3.2±0.2

4.2 ±0.2

4.9 ±0.3

5.4 ±0.3

3.0

4.3

4.8

5.6

6.1

6.4

Female:

3.4±0.2

3.4 ±0.2

4.6 ±0.3

3.3 ±0.3

4.6±0.3

5.5±0.3

3.3 ±0.3

4.6±0.4

5.4 ±0.4

6.0 ±0.4

3.4 ±0.1

4.7 ±0.2

5.6 ±0.3

6.4 ±0.4

7 1 ±0.4

3.2 ±0.1

4.3±06

5.3 ±0.5

6.2 ±0.4

7.1 ±0.7

7.9±0.8

3.2 ±0.3

4.3 ±0.5

5.1 ±0.4

5.7±0.5

6.3 ±0.6

6.8 ±0.6

7.2±0.6

825

FISHERY BULLETIN: VOL. 75, NO. 4

TABLE 2. — Mean back-calculated total length ± 1 standard deviation and annual
percent increase in mean total length for male summer flounder captured in Dela-
ware Bay during 1966-68. Included for comparison are mean back-calculated
lengths from other studies.

Age- Number

Back-calculated

lenqth at successive annuli (mm)

group of fish

2 44

277 £20

3 51

261 ±23

344±16

4 23

258 ±21

342±17

400±14

5 11

261 ±12

348±10

403 ± 9

445±11

7 1

242

347

388

452

493

517

Mean length

260

345

397

448

493

517

Annual % increase

24.6

13.'

I 11.4

9.1

4.6

Poole (1961)

251

326

387

427

Eldridge (1962)'

170

240

319

357

381

399

414

426

'Lengths given for Eldridge at the end of year 1 and 2 are estimates of the average observed
length frequency.

TABLE 3. — Mean back-calculated total length ± 1 standard deviation and annual percent increase in
mean total length for female summer flounder captured in Delaware Bay during 1966-68. Included for
comparison are mean back-calculated lengths from other studies.

Age-

Number
of fish

Back-calculated lenqth at successive annuli (mm)

group

301 ±21

280±19

383 ±21

279 ±25

389 ±24

465 ±25

289 ±20

399 ±24

470 ±22

526 ±22

273 ±23

379 ±33

450 ±21

512±22

568 ±25

252±12

332 ±48

412±34

484 ± 5

553±16

612±19

289 ±12

395 ±20

469 ± 6

521 ±12

575±18

624±14

661 ± 9

Mean length

280

380

453

511

565

618

661

Annual % increase

26.3

I 16.1

11.4

9.6

8.6

6.5

Poole (1961)

271

377

465

531

644

Eldridge (1962)'

170

240

377

424

471

518

566

613

657

'Lengths given for Eldridge at the end of year 1 and 2 are estimates of the average observed length frequency.

formed at the end of the first year. Eldridge de-
cided that Poole's calculated length at 1 yr seemed
too high when compared with observed length fre-
quencies, so he considered this first well-defined
annulus to be formed at first spawning, or at the
end of the flounder's third year. We considered the
first well-defined annulus to be formed at age 2.
Therefore, Poole's age 1 fish = our age 2 fish =
Eldridge's age 3 fish. Work by Richards (1970)
supported our age interpretation. He found sum-
mer flounder growth curves generated by analog
simulation only fit Poole's length data when
Poole's age-groups were shifted 1 yr forward, i.e.,
his age 1 fish were made age 2. Richards did not
examine Eldridge's age data.

Comparing Poole's (1961) lengths to ours after
adjustment for age interpretation, we find them
similar except for age 5 females. With age in-
terpretation adjustment, Eldridge's (1962)
lengths for males are smaller than ours except at
ages 2 and 3 when they are larger, and his lengths
for females are noticeable larger until age 5 when
they begin to agree quite well.

The length-frequency distribution of the 1966
commercial catch and the 1966-71 research catch

826

revealed that both were primarily composed of
age-groups 2 through 5. Figure 3, using the 1966
and 1968 research catch because lengths were by
sex, is representative of this distribution. This age
composition is similar to the age composition re-
ported by Poole (1961) for the sport fishery catch of
Great South Bay, N.Y., after adjustment is made
for age interpretation differences.

Equations representing growth rates from Wal-
ford's growth transformation (Rounsefell and
Everhart 1953) are:

for males Lt+1= 141.91 + 0.767 (Lt)

Correlation coefficient = 0.996
Standard error of estimate = 7.39

for females Lt+1= 136.72 + 0.843(L,)

Correlation coefficient = 0.998
Standard error of estimate = 6.20

where Lt +1 = fish length (millimeters) at time t
plus 1 yr
Lt = fish length (millimeters) at time t.

SMITH and DAIBER: BIOLOGY OF SUMMER FLOUNDER
5

x
<

FEMALE

tut

ID □_

i n

h. 5

<* 4 -

3 -

2 -

1 -

MALE

tin.

JZL

45 50 55

TOTAL LENGTH (CM)

FIGURE 3. — Total length-frequency distribution for 149 male and 202 female summer flounder caught in Delaware Bay in 1966 and

1968.

We found no significant difference in growth rates
between the sexes, although both Poole (1961) and
Eldridge (1962) did report a significant difference.
The growth rates probably are significantly differ-
ent, an indication of this being the large differ-
ence in predicted maximum lengths from Wal-
ford's growth transformation (62 cm for males and
88 cm for females), but our limited sample size in
older age-groups, particularly males, prevented
this difference from being significant. The percent
increase in annual length (Tables 2, 3) is similar
for both sexes until age 6, and then it begins to
decline more rapidly in males.

Our calculated growth rates underestimate
those actually observed. Bigelow and Schroeder
(1953) stated that the largest summer flounder for
which they could find a definite record weighed
11,793 g (26 lb), and the largest fish recorded in
sport fishing was 94 cm (37 in) long and weighed
9,072 g (20 lb). Using our predicted maximum
lengths and length-weight relationship (see next
section), we calculated that a male 62 cm (24.4 in)
would weigh 2,339 g (5.21 lb) and a female 88 cm
(34.7 in) would weigh 8,199 g (18.1 lb). Also our
predicted length of 14 cm at age 1 ( Y-axis intercept
from Walford's growth transformation) is 3 cm

smaller than the observed length given by El-
dridge (1962). The lack of samples from age-group
1 and above age-group 8 and the limited samples
in age-groups 6 through 8 might account for most
of this error. A small change in the female growth
rate would give a predicted maximum length of 98
cm, and then we have a fish weighing 11,793 g (26
lb). The growth rate offish in age-groups 2 through
5 may approximate the growth of the same age-
groups in the actual population.

LENGTH AND
WEIGHT RELATIONSHIPS

A linear relationship existed between total
length-standard length (Table 4), standard
length-head length, and head length-upper jaw
length. There were no significant differences in
these relationships when the sexes are consid-
ered separately. The slope (3.151) of the line rep-
resenting the total length-weight relationship
(Table 4) was not significantly different from that
(3.146) reported by Lux and Porter (1966) for
summer flounder caught in June off Mas-
sachusetts. They found no difference between the
slopes of the lines when sex was considered, but

827

FISHERY BULLETIN: VOL. 75, NO. 4

TABLE 4. — Calculated values for regression equations describ-
ing the total length (TL in millimeters)-weight (W in grams)
relationship and the total length (TL in millimetersl-standard
length (SL in millimeters) relationship for summer flounder
from Delaware Bay.

Number
of fish

Sex

Intercept

Correlation
Slope coefficient

Standard

error of

estimate

log

W = log intercept

+ slope (log TL)

'333

102

167

both
male
female

0.404 x 10 ~5
0.102 x 10 ~4
0.227 x 10-5

3.151 0.995
2.994 0.953
3.246 0.987

0.095
0.086
0.086

314

both

TL = intercept 4
16.695

slope (SL)
1.155 0.986

4.035

102

male

1 1 .044

1.173 0.994

3.531

168

female

18.861

1.150 0.998

4.351

'This includes 20 juveniles from North Carolina.

they stated that males were slightly heavier than
females on an equal length basis. We found no real
difference between the weights of equal sized
males and females in Delaware Bay, nor did El-
dridge (1962) for fish off Virginia. Twenty fish
from North Carolina were included in our total
length- weight relationship so we could have some
data points from fish in age-groups 0 and 1.

GONAD DEVELOPMENT

Summer flounder gonads were examined from
1966 to 1968 for size and the ovaries for the pres-
ence of eggs. Gonads were small and flaccid from
April through mid-August. From mid-August
through November, the gonads began to enlarge
or mature, and the ovaries contained eggs up to 0.4
mm in diameter. Murawski4 stated that the size of
mature eggs is 1.0 to 1.1 mm. There was never
more than one-third of any catch during the fall
with ripening gonads, and no mature fish were
caught from December through March. We con-
cluded that fish leave the bay as they ripen, sup-
porting reports that summer flounder spawn after
moving offshore during the winter. The smallest
male taken with ripening testes was 30.5 cm, and
the smallest female with ripening ovaries was 36
cm. These observations agree with those reported
by Eldridge (1962) who stated summer flounder
become sexually mature at age 3.

FOOD PREFERENCE

Stomachs from 131 flounder, ranging in size
from 31 to 72.5 cm, were examined under a dissect-

4Murawski, W. S. 1966. Fluke investigations. N.J. Fed. Aid
Proj. F-15-R-7 (Completion Rep. Job No. 3). N.J. Dep. Conserv.
Econ. Dev., 24 p.

ing microscope, and 57% of them contained food.
Food items found, listed in order of percent fre-
quency of occurrence were: sand shrimp (Crangon
septemspinosa , 4:19c ), weakfish ( Cy nose ion regalis,
339c ), mysid (Neomysis americana, 20%), anchovy
{Anchoa sp., 7%), squid (Loligo sp., 4%), silverside
(Menidia menidia, 1%), herring iAlosa sp., 1%),
hermit crab (Pagurus longicarpus , 1%), andisopod
(Olencira praegustator, 19c). On a volume basis
weakfish were first, sand shrimp second, and the
rest remained in the same order. Fish under 45 cm
fed predominantly on invertebrates, while larger
ones ate more fish. Poole ( 1964) found sand shrimp
the primary organism eaten by summer flounder
in Great South Bay, and that out of 10 fish species
eaten, the winter flounder, Pseudopleuronectes
americanus, was first by weight and the weakfish
next to last. These observations indicate that the
diet of summer flounder reflects local abundances
of prey species.

Flounder caught during the day had a greater
volume of food in their stomachs (x =5.1 ml) than
those caught at night (x =3.3 ml), but the differ-
ence was not significant according to £-tests.

RACIAL ANALYSIS

The following morphometric and meristic
characters were measured or counted on fish
caught in 1966: total, standard, head, and upper
jaw lengths; dorsal, anal, and pectoral fin rays; gill
rakers on the first arch; and vertebrae (Table 5).
All measurements and counts were made on the
left side for uniformity. The number of caudal fin
rays (17) and pyloric caeca (4) was constant so
counting of these characters stopped after 20 fish.
Woolcott et al. (1968) reported 18 caudal fin rays,
with the posteriormost dorsal ray being very small
and easily overlooked in unstained specimens. We
missed this 18th ray in our count.

Ranges of some meristic and morphometric
characters examined exceed those reported in the
literature (Table 5). Analysis of variance showed
no significant difference in the counts of the six
variable meristic characters due to age or sex.

Comparison by £-test of meristic character
counts on summer flounder sampled in Delaware
Bay, Chesapeake Bay, and North Carolina (Table
6) gave inconclusive results. There was no sig-
nificant difference between these areas for num-
bers of dorsal fin rays and vertebrae. Differences
based on gill raker counts by Woolcott et al. ( 1968)
might not be valid, because Deubler (1958) stated

828

SMITH and DAIBER: BIOLOGY OF SUMMER FLOUNDER

TABLE 5. — Meristic and morphometric data for summer flounder taken from Delaware
Bay in 1966, and ranges reported in the literature that were exceeded.

Number

Standard

Literature

Characters

of fish

Range

Mean

error

reported range

Meristic

Dorsal fin rays

194

80-98

88 92

0.20

'80-96

Anal fin rays

194

63-78

68.54

0.16

260-73

Pectoral fin rays

196

10-13

11.83

0.05

'11-13

Gill rakers:

Lower arch

196

14-19

16.31

0.08

Upper arch

196

4- 7

5.59

0.05

Vertebrae

195

40-43

41.34

0.04

M0-42

Morphometric:

Standard length/head l<

sngth

235

3.64- 4.30

3.96

001

2'4 3- 4

Head length/upper jaw length

235

1.54- 2.26

2.05

0005

22- 2.26

'Ginsburg (1952)

2Hildebrand and Schroeder (1928).

3Deubler (1958).

"Jordan and Evermann (1898)

TABLE 6. — A comparison of some summer flounder meristic characters between Delaware Bay ( present
study), Chesapeake Bay (Ginsburg 1952), and North Carolina [1 (Deubler 1958), 2 (Ginsburg 1952), and 3
(Woolcott et al. 1968)].

Dorsal fin rays

Anal fin

rays

Vertebrae

Gill rakers

Upper arch

Lower arch

Location

Mean

Delaware Bay

88.9

2.8

68 5

2.3

41.3

0.6

5.6

0.7

16.3

1.1

Chesapeake Bay

88.6

2.6

686

2.3

0.6

16.5

0.9

N.C. (1)

89.0

2.7

68.4

2.6

41.3

N.C. (2)

88.1

2.7

67.7

2.2

5.0

0.7

15.6

1.3

N.C. (3)

88.4

1.4

68.3

1.2

41.2

0.6

5.2

1.0

14.6

1.5

Anal fin

rays

Gill rakers

Upper arch

Lower arch

Del.

Ches. N.C

N.C.

Del.

Ches. I

M.C.

N.C.

Del.

Ches.

N.C.

Location

Bay

Bay (1)

(2)

(3)

Bay

(2)

(3)

Bay

(2)

(3)

Delaware Bay

•

••

Chesapeake Bay

N.C. (1)

N.C. (2)

•

*•

••

N.C. (3)

significant difference at 0.05 level,
significant difference at 0.01 level.

the definitive number of gill rakers is not usually
present until summer flounder are 18 mm stan-
dard length. Woolcott et al. used fish below this
length, and this could account for the significant
difference between their counts of lower arch gill
rakers and the counts by Ginsburg ( 1952), also for
fish from North Carolina.

Anal fin and gill raker data (Table 6) do suggest,
however, that summer flounder from North
Carolina belong to a population that is racially
different from the population containing
Chesapeake Bay and Delaware Bay flounder. This
supports Smith's (1973) observation that there is
mounting evidence for the existence of separate
populations of summer flounder based on: 1) dis-
tribution of eggs and larvae, 2) meristic differ-
ences, 3) tag returns, and 4) commercial flounder
landings. It is possible that separate populations
or stocks exist because summer flounder undergo

fairly rapid development, 74 to 94 h hatching time
(Smith 1973), and conditions affecting egg and
larval transport may minimize mixing between
geographic areas. This possibility is suggested by
Chang and Pacheco (1976) even though they
assumed a unit stock for their population evalua-
tion. There should be more research into the possi-
bility of multiple populations before final man-
agement recommendations are made.

ACKNOWLEDGMENTS

We thank George R. Abbe, Gary W. Schmelz,
Raymond C. Wockley, and the boat crew at the
Lewes Field Station for all their help in the field.
Special thanks go to Henry B. Tingey for help in
some statistical analyses; to Earl E. Deubler, Jr.,
of the University of North Carolina for donating
otoliths and data from small summer flounder;

829

FISHERY BULLETIN: VOL. 75, NO. 4

and to Victor A. Lotrich and Kent S. Price, Jr., for
reviewing this manuscript. This research was
supported by Dingell-Johnson funds made avail-
able by the former Delaware Game and Fish
Commission.

LITERATURE CITED

BIGELOW, H. B., AND W. C. SCHROEDER.

1953. Fishes of the Gulf of Maine. U.S. Fish Wildl.Serv.,
Fish. Bull. 53:1-577.
CHANG, S., AND A. L. PACHECO.

1976. An evaluation of the summer flounder population in
sub-area 5 and statistical area 6. Int. Comm. Northwest
Atl. Fish., Sel. Pap. 1:59-71.
DEUBLER, E. E.. JR.

1958. A comparative study of the postlarvae of three
flounders {Paralichthys) in North Carolina. Copeia
1958:112-116.
ELDRIDGE, P. J.

1962. Observations on the winter trawl fishery for summer
flounder, Paralichtys dentatus. M.S. Thesis, Coll. Wil-
liam and Mary, Williamsburg, Va., 55 p.
GlNSBURG, I.

1952. Flounders of the genus Paralichthys and related
genera in American waters. U.S. Fish Wildl. Serv, Fish.
Bull. 52:267-351.
HILDEBRAND, S. F., AND W. C. SCHROEDER.

1928. Fishes of Chesapeake Bay. Bull. U.S. Bur. Fish.
43:1-366.
JORDAN, D. S., AND B. W. EVERMANN.

1898. The fishes of North and Middle America: a descrip-
tive catalogue of the species offish-like vertebrates found
in the waters of North America, north of the Isthmus of
Panama. Part III. Bull. U.S. Natl. Mus. 47:2183a-3136.

LUX, F. E., AND L. R. PORTER, JR.

1966. Length-weight relation of the summer flounder
Paralichthys dentatus (Linnaeus). U.S. Fish Wildl.
Serv., Spec. Sci. Rep. Fish. 531, 5 p.

Poole, j. C.

1961. Age and growth of the fluke in Great South Bay and
their significance to the sport fishery. N. Y. Fish Game J.
8:1-18.

1962. The fluke population of Great South Bay in relation
to the sport fishery. N.Y. Fish Game J. 9:93-117.

1964. Feeding habits of the summer flounder in Great

South Bay. N.Y. Fish Game J. 11:28-34.
1966. A review of research concerning summer flounder
and needs for further study. N.Y. Fish Game J. 13:226-
231.
PRUTER, A. T., AND D. L. ALVERSON.

1962. Abundance, distribution, and growth of flounders in
the South-Eastern Chukchi Sea. J. Cons. 27:81-99.
RICHARDS, C. E.

1970. Analog simulation in fish population
studies. Analog/Hybrid Computer Educational Users
Group Trans. 2(7):203-206.
ROUNSEFELL, G. A., AND W. H. EVERHART.

1953. Fishery science: its methods and applications. John
Wiley and Sons, Inc., N.Y., 444 p.
RUGH, R.

1962. Experimental embryology. Techniques and proce-
dures. 3d ed. Burgess Publ. Co., Minneapolis, Minn.,
501 p.

Smith, W. G.

1973. The distribution of summer flounder, Paralichthys
dentatus, eggs and larvae on the continental shelf be-
tween Cape Cod and Cape Lookout, 1965-66. Fish. Bull.,
U.S. 71:527-548.
WOOLCOTT, W. S., C. BEIRNE, AND W. M. HALL, JR.

1968. Descriptive and comparative osteology of the young
of three species of flounders, genus Paralichthys. Chesa-
peake Sci. 9:109-120.

S30

LARVAL DEVELOPMENT OF THE SPIDER CRAB,
LIBINIA EMARGINATA (MAJIDAE)1

D. Michael Johns2 and William H. Lang3

ABSTRACT

Larval development of the spider crab, Libinia emarginata, consists of two zoeal stages and megalopa.
Laboratory-reared larvae (South Carolina and Rhode Island) are described and compared with
planktonic larvae from Narragansett Bay, R.I. No significant variations in morphology were found
between laboratory-cultured larvae and "wild" larvae from plankton catches; first stage zoea from
South Carolina were smaller than Rhode Island specimens. Using Artemia diets, the best percentage
survival in culture was found to be 20°C for Rhode Island larvae and 25°C for South Carolina larvae.
Zoeal stages show little difference from larvae of L. dubia; however, the megalopae of the two species
can be differentiated by the number of protuberances on the cardiac region of the carapace.

Larval stages have previously been described for a
number of species from the family Majidae (San-
difer and Van Engel 1971, 1972). For the genus
Libinia only two complete descriptions have been
published. Boschi and Scelzo (1968) described lar-
val stages of L. spinosa from Mar del Plata Harbor,
Argentina; and Sandifer and Van Engel (1971)
described the larval stages of L. dubia from
Chesapeake Bay. Larvae of L. erinacea have been
described by Yang (1967), but the results remain
unpublished. In all cases, the larval development
consists of two zoeal stages and a megalopa.

Adult Libinia emarginata Leach range from
Windsor, Nova Scotia, to the western Gulf of
Mexico and are found in nearshore waters down to
a depth of 29 m (Williams 1965). Although the
larvae of L. emarginata have not been formally
described, they have been successfully reared (J.
D. Costlow, pers. commun.). Grassle (1968)
studied heterogeneity of hemocyanins during on-
togeny, but no attempt was made to describe de-
velopment. In support of ongoing studies using
Libinia larvae at this laboratory, the present
study was undertaken to: 1) describe the larval
stages, 2) compare morphology of laboratory cul-
tured and field collected larvae, and 3) determine
successful temperature-salinity rearing parame-

•Contribution No. 176 from the Belle W. Baruch Institute for
Marine Biology and Coastal Research.

2United States Environmental Protection Agency, Environ-
mental Research Laboratory, South Ferry Road, Narrangansett,
R.I. 20882.

3Belle W. Baruch Institute for Marine Biology and Coastal
Research, University of South Carolina, Columbia, SC 29208.

ters and development times. Characteristics
which distinguish L. emarginata larvae from the
larvae of L. dubia and L. erinacea were also noted.

METHODS AND MATERIALS

Ovigerous females of L. emarginata were col-
lected off Charleston, S.C., during fall 1975 and
spring 1976, and in Narragansett Bay, R.I. , during
summer 1976. Females were isolated in chambers
at 25 °C (in South Carolina) or 20°-22°C (in Rhode
Island) and 30%o. After hatching, zoeae were iso-
lated into compartmentalized plastic boxes. Lar-
vae were fed day old Artemia every other day
following a change of water. Larvae reared at
salinities other than 30%o were brought to the
appropriate levels (15, 20, 40, or 45 %o) using in-
crement changes of 2.5%o every 30 min. Larvae
reared at temperatures other than hatching tem-
perature were brought to the test temperature
(15°, 20°, or 30°C) by placing larvae in environ-
mental chambers and allowing them to equili-
brate to these temperatures.

Field samples were obtained from surface
plankton tows collected in Narragansett Bay dur-
ing July and August 1976.

Drawings were made with the aid of camera
lucida using exuviae and larvae fixed in 10^ For-
malin.4 Carapace and total lengths were made
with an ocular micrometer. Dry weights were de-
termined with a Cahn Electrobalance on larvae

Manuscript accepted March 1977.

FISHERY BULLETIN: VOL. 75, NO. 4, 1977.

"•Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

831

FISHERY BULLETIN: VOL. 75, NO. 4.

that were dried in an 80°C oven for 24 h. The
weights for each stage were calculated from three
samples of five zoeae each.

One-way analysis of variance was computed on
carapace length measurements taken on larval
stages from South Carolina reared, Rhode Island
reared, and field samples. If significant differences
(at P = 0.05) were found within stages, a Scheffe
Posterior comparison was used to determine
where the differences lay (Nie et al. 1975).

The following abbreviations were used in all
descriptions: AN1 = antennule, AN2 = antenna,
MN = mandible, MAX1 = maxillule, MAX2 =
maxilla, MXP1 = first maxilliped, MXP2 = second
maxilliped, MXP3 = third maxilliped, PI to P5 =
pereopods 1 to 5, PL2 to PL6 = pleopods on abdom-
inal somites 2 to 6. Types of setae specified are as
described by Bookhout and Costlow (1974).

RESULTS

Development

Development times in both the South Carolina
and Rhode Island reared larvae vary with temper-
ature and salinity. In the South Carolina larvae,
optimal and most advanced development occurred
at 25°C and 30%o. At these conditions, the second
stage appeared at day 3, megalopa at day 6 and
first crab at day 14. In other conditions tested,
development did not continue past the megalopa
(Table 1).

In the Rhode Island reared larvae, complete de-
velopment occurred only at 20°C and 30%o with the
second zoeal stage appearing at day 5, megalopa at
day 8, and first crab at day 14. With other condi-

TABLE 1. — Time to various developmental stages (in days) for
the spider crab, Libinia emarginata, reared at various
temperature-salinity combinations in both South Carolina and
Rhode Island.

Rearing site

Temperature-
salinity
combination

No. of
larvae

Stage
Megalopa

1 st crab

South Carolina

15°C-30%«

(')

20°C-30%o

(')

25°C-15%.

(1)

25oC-20%«

25°C-30V

25°C-40%o

(')

25°C-45%o

30°C-30%o

(1)

Rhode Island

15°C-30%o

(2)

20°C-30%«

25°C-30%«

(')

tions tested, development was varied (Table 1).

South Carolina reared larvae tended to be
smaller than both Rhode Island reared and field
samples (Table 2). With statistical analysis, this
difference is significant in stage I (P<0.05) but
only between South Carolina reared and Rhode
Island reared. At no other stage were the size
variations found to be significant.

TABLE 2. — Comparison of carapace lengths for South Carolina
reared, Rhode Island reared, and field sample larvae of Libinia
emarginata.

South Carolina

Rhode Island

Field

Stage

Item

reared

samples

Zoea 1*

x (mm)

'0.75

10.78

0.775

SD (mm)

0.019

0.020

0.028

Zoea II

x (mm)

0.94

0.96

SD (mm)

0.02

0 038

0 035

Megalopa

x (mm)

1.16

1.21

1.20

SD (mm)

0.049

0064

0001

'All larvae had died prior to this stage.
2Second stage was not reached by day 15.

'Indicates significant differences within a stage by one-way analysis of var-
iance (P = 0.05).

1 Significant differences exist between the two means, according to Scheffe's
Posterior comparison.

Larval Description

Two zoeal stages and one megalopa were ob-
tained during the rearing period. Mandibles of the
zoea are without palps and have a complex trian-
gular biting surface. Since, in these stages, man-
dibles appear to have little diagnostic value and
are difficult to accurately portray, they have been
omitted from the following description.

Zoea 1

Size and weight — Average carapace length,
0.78 mm (range 0.76-0.80 mm), average total
length 2.19 mm (range 2.00-2.30 mm). Average
dry weight 0.0214 mg (range 0.0200-0.0224 mg).

Carapace (Figure 1A, B) with dorsal and rostral
spines; lateral spines absent. Dorsal spine long
and slightly curved posteriorly; rostral spine
nearly as long as antennule and slightly curved
inward. Carapace large and somewhat rounded; 7
small plumose setae along the ventrolateral mar-
gin of carapace. Eyes sessile.

Abdomen ( Figure 1C) with 5 somites; 6th somite
fused to telson. Somite 2 with small anteriorly
curved knobs on each side of lateral surface; so-
mites 3-5 with pair of small posterolateral spines.
Bifurcate telson; each furca bearing 1 spine. Inner

832

JOHNS and LANG: LARVAL DKVKLOPMKNT OF LIBIN1A EMARG1NATA

FIGURE 1. — Libima emarginata zoea I and II. (A) lateral view of stage I, (B) front view of stage I, (Cl dorsal view of
abdomen at stage I, <D) lateral view of stage II, (E) front view of stage II, (F) dorsal view of abdomen at stage II. All
unmarked scales =0.1 mm.

833

FISHERY BULLETIN: VOL. 75. NO. 4.

margin of telson fork bearing 6 spines of approxi-
mately the same length.

AN1 (Figure 2C) — Uniramous, unsegmented,
and conical with 2 long aesthetascs, 2 smaller aes-
thetascs, and one simple setae on the terminal
end.

AN2 (Figure 2D) — Protopodite long, ending in a
point with 2 rows of spinules distally, small en-
dopodite bud near base. Exopodite long, spinulose
distally; 2 small spines just subterminal, inner-
most spinulose.

MAX1 (Figure 2F) — Endopodite 2-segmented;
proximal segment with 1 long simple or sparsely
plumose seta, distal segment with 4 terminal
setae (2 plumose, 2 plumodenticulate) and 1 sub-
terminal plumose seta. Basal endite with 4
plumodenticulate cuspidate and 2 plumodenticu-
late terminal setae and 1 subterminal plumose

seta; smaller coxal endite with 5 plumose setae
and 2 simple setae.

MAX2 (Figure 2E)— Scaphognathite with 9
plumose marginal setae and a plumose apical tip.
Endopodite simple with 4 (rarely 5) terminal
plumodenticulate setae and 1 simple seta. Basal
endite slightly bilobed; 4-5 plumodenticulate
setae on distal lobe and 5 (rarely 4) plumodenticu-
late setae on proximal lobe. Coxal endite bilobed;
3-4 plumose setae on distal lobe and 4 plumose
setae on proximal lobe.

MXP1 (Figure 2A)— Exopodite with 4 long,
plumose natatory setae. Endopodite 5-segmented;
setation formulae (proximal to distal): 3, 2, 1, 2, 5.
Terminal segment with 5 setae (4 multidenticu-
late and 1 short, simple). Basiopodite with up to 9
setae.

MXP2 (Figure 2B)— Exopodite with 4 plumose

FIGURE 2. — Libinia emarginata. Appendages of stage I zoea. (A) first maxilliped, (B) second maxilliped, (C) antennule, (D)

antenna, (E) maxilla, (F) maxillule. All unmarked scales = 0.1 mm.

834

JOHNS and LANG: LARVAL DEVELOPMENT OF L1R1N1A EMARGINATA

natatory setae. Endopodite 2-segmented; terminal
segment with 4 setae (2 plumodenticulate and 2
simple). Basiopodite with 3 setae.

Zoea II

Size and weight — Average carapace length.
0.94 mm (range 0.89-0.98 mm), average total
length 2.69 mm (range 2.56-2.82 mm). Average
dry weight, 0.0654 mg (range 0.0613-0.0712 mg).

Carapace (Figure ID) same as for stage I. Dorsal
spine proportionately shorter and stouter than be-
fore. Ventrolateral margin now with 8-10 small
plumose setae. Eyes stalked.

Abdomen (Figure IF) with 6 somites. Somite 2
with small anteriorly curved knobs as before. So-
mites 2-5 with 2 pleopod buds ventrally. Telson as
in stage I.

AN1 (Figure 3C)— With 2 long, thick aes-

thetascs, 4 smaller aesthetascs, and 1-2 simple
setae or thin aesthetascs on terminal end.

AN2 (Figure 3D) — Protopodite same as before,
endopodite bud at least half length of protopodite.
Exopodite same as before.

MAX1 ( Figure 3F) — Endopodite same as before.
Basal endite with 8 terminal setae (5 denticulate
cuspidate and 3 plumodenticulate), and 2 subter-
minal plumose setae; coxal endite with 8 setae (5
plumose and 3 simple).

MAX2 ( Figure 3E)— Scaphognathite with 16 ( in
South Carolina reared) or 20 (in Rhode Island
reared and field samples) plumose marginal setae.
Endopodite with basal endite and coxal endite
same as in stage I.

MXP1 (Figure 3A)— Exopodite with 6 large
plumose natatory setae. Endopodite same as be-
fore. Basiopodite with up to 10 setae.

MXP2 (Figure 3B)— Exopodite with 6 large,

I-

FIGURE Z.—Libinia emarginata. Appendages of stage II zoea. (A) first maxilliped, <B> second maxilliped, (C> antennule, <D> antenna,

(E) maxilla, (F) maxillule. All unmarked scales = 0.1 mm.

835

plumose natatory setae. Endopodite and basiopo-
dite same as before.

MegaJopa

Size and weight — Average carapace length,
1.21 mm (range 1.16-1.28 mm), average total
length 2.14 mm (range 2.07-2.17 mm). Average
dry weight 0.205 mg i range 0.145-0.259 mg).

Carapace (Figure 4 A. B> without spines: short

FISHERY BULLETIN vol 75, NO I

rostrum tapers to blunt tip. Median Hue of
carapace depressed between eyes with 2 partially

connected protuberances along gastric region,
paired protuberances at cardiac region and slight
protuberance at posterior border. Lateral
carapace region with 3 paired protuberances, sur-
face somewhat expanded over posterolateral area.
Abdomen 'Figure 4B> with 6 somites plus tel-
son.

FIGURE A.—Libima emarginata megalopa. (A) dorsal view, (B) lateral view, (C) antenna, (D) antennule, (E> cheliped. (Ft pleopod. All

unmarked scales =0.1 mm.

836

JOHNS and LANG LARVAL DEVELOPMEN1 OF UBIN1A EMARQ1NATA

AN I i Figu re I 1 )) Pedunclei 3 tegmented;
basal segment bare, Becond and thud segment
with l shorl Beta each. Inner flagellum unseg-
mented with 3 terminal Bimple etae doi al
flagellum 2-segmented proximal segmenl with 5
aesthetascs; distal with 3 aesthetascs and I sub
terminal imple seta.

AN2 (Figure 1C) Peduncle 3-segmented.
Flagellum 4-segmented, with 2 distal segments
having 3 subterminal and 4 terminal simple setae,

respect i vel y.

M N I Figure 5A i Palp 3-segmented wit h 5 tei
minal setose 3etae

MAX1 (Figure 5B) — Endopodite unsegmented
witli 2-3 terminal simple setae. Basal endite with
14 processes (6 plumodenticulate cuspidate 6
plumodenticulate, 2 short multidenticulate) and
2-3 marginal plumose setae; coxa! endite with 3
plumodenticulate and 3 simple terminal setae and
4 subterminal plumose setae.

MAX2 (Figure 5C)- Scaphognathitewith31-33
< in South Carolina reared) or 33-35 'm Rhode Is-
land reared and field samples) plumose marginal
setae. Endopodite with 0-1 seta. Basal endite
bilobed; distal portion and proximal portion with
6-7 plumodenticulate or plumose setae each.
Coxal endite bilobed; distal portion with 3
plumose setae and proximal portion with 4
plumose and 1 simple setae.

MXP1 (Figure 5D)— Exopodite 2-segmented,
proximal segment with 1 plumose seta; distal
segment with 5 plumose and 1 simple setae. En-
dopodite unsegmented with 1-3 terminal setae.
Basal endite with 8-10 plumodenticulate setae;
coxal endite with 6 plumodenticulate and 1
plumose setae. Epipodite with 4 long simple
setae.

MXP2 (Figure 5E) — Exopodite 2-segmented;
distal segment with 5-6 long plumose setae. En-
dopodite 4-segmented; setation formulae (proxi-
mal to distal) 0, 1, 3, 6. Distal setae, 5 plumoden-
ticulate cuspidate, 1 simple.

MXP3 (Figure 5F)— Exopodite 2-segmented;
terminal segment with 3-4 long plumose and 2
small simple terminal setae. Endopodite
5-segmented; setation formulae (proximal to dis-
tal) 9-10, 7-8, 4, 6, 4, mostly plumodenticulate or
serrate plumose setae. Epipodite with 3 terminal
and 3 subterminal multidenticulate setae.

PI to P5 (Figure 4 A, E) — Moderately setose,
cheliped similar to adult form.

PL2 to PL6 (Figure 4F)— Exopodite
2-segmented; plumose natatory setae on distal

segment vanes from ll (PL2) to 8 (PL5). Endopo

dite small with 2 small books.
Zoeal Chromatophores

Libinia emarginata larvae are sparsely pig-
mented m freshly sacrificed specimen
Chromatophore color ranges from orange to a dark
brown-red, Distinctive pigment areas with little
individual variation include an orange spot at the
posterior dorsal spine base, a deep red area po te
rior to the eye base, a large distinctive red spot on
the posterolateral carapace region near the
carapace setae and red pigmentation of the man
dibles. The abdomen is pigmented in the central
ventral area of each segment juncture. Additional
pigment spots occur on I he carapace and append
ages but do riot appear consistent in location or
occurrence.

DISCUSSION

There is only a narrow range of temperature
salinity conditions at which the larvae succe
fully develop in the laboratory. With South
Carolina larvae, these conditions are 25 C and
30%o, while with Rhode Island larvae, maximum
development occurs at 20°C and 30%o. The differ
ence in these temperature possibly reflect-, the
influence- of latitudinal separation on larval de
velopment, however, until critical experiment
are undertaken, this cannot be confirmed (Vein
berg 1062; Vernberg and Costlow I960; Sastry
1970; Sastry and Vargo 1 977 1. The larvae develop
besl in temperatures that represent the mean
temperature during the larval season. Gravid L.
emarginata were collected from May to September
in South Carolina in coastal waters that bad a
mean water temperature near 25 C. In Rhode Is-
land, gravid crabs were collected from July to Au-
gust in bay and coastal waters that had a mean
water temperature near 20 C

The narrowness of successful rearing conditions
may reflect inadequate rearing variables such as
diet, substrate, water circulation, etc. (Rob<
1972; Sulkin 1975; Sulkm and Norman 1976), or
reflect the habitat of L. emarginata. With larvae
that develop entirely in bay or coastal wat<
I here fol lows a characteristic inability of larvae to
develop successfully over wide range- of tempera-
ture and salinity, while larvae from estuarine
waters usually develop in a much wider range of
temperatures and salinity. In the offshore

837

FISHERY BULLETIN: VOL. 75, NO. 4.

FIGURE 5. — Libinia emarginata. Appendages of megalopa. (A)
mandible, (B) maxillule, (C) maxilla, (D) first maxilliped, (E)
second maxilliped, (F) third maxilliped. All unmarked scales =
0.1 mm.

HUH

JOHNS and LANO LARVAL DEVELOPMENT OK L1BINIA EMARGINATA

spawner, Callinectes sapidus, for example, larvae
will complete early development only at 25°C and
31.1%o (Costlow and Bookhout 1959) while an es-
tuarine xanthid, Rhithropanopeus harrisii , com-
pletes development at temperatures of 20°, 25°,
and 30°C and salinities between 2.5 and 40%<>
(Costlow et al. 1966). Throughout this study, all
gravid females were collected in near coast bay or
open coastal waters >30%» salinity).

The duration of development within the genus
Libinia also varies. Boschi and Scelzo (1968) re-
ported that development for L. spinosa required
20-30 days (at 20°C) or an average of 8- 10 days per
stage. Libinia erinacea required 14 days (at 20°C)
or 9 days (at 25 C) to reach first crab stage (Yang
1967). Sandifer and Van Engel (1971) reported
that L. dubia needed only 9 days (at 25.5°-28.5°C)
for larval development. Libinia emarginata is in-
termediate with at least 14 days needed to reach
first crab stage. As pointed out by Sandifer and
Van Engel (1971), these differences in develop-
ment times may be explained, in part, by rearing
temperatures. For L. erinacea, total development
time is reduced by 5 days with a 5°C increase in
temperature. However, other factors must also
play a role in development for L. spinosa and L.
erinacea reared at the same temperature (20°C)
and given the same food source (Artemia) still
showed a 6- to 16-day difference in development
times.

The number of larval stages for L. emarginata is
typical for the family Majidae (Gurney 1942; Hart
1960). Larvae from the three sources examined
showed few differences. South Carolina larvae
tended to be slightly smaller than Rhode Island
and field samples (Table 2). Morphology of larvae
was virtually identical in all cases, except for the
scaphognathite setal number being consistently
lower in South Carolina larvae. In this case,
reared larvae appear to represent accurate
"mimics" of wild larvae, even to specific setal
types. However, it is unknown if this similarity
also pertains to physiological or behavioral
parameters.

In comparing larval descriptions of L. erinacea,
L. dubia, L. spinosa, and L. emarginata, we have
found that carapace setation and armature of the
abdominal somites are the most useful zoeal
characters (Table 3). Libinia erinacea and L.
spinosa may be distinguished by the presence of
lateral spines on abdominal somite 2, as opposed to
small knobs for L. dubia and L. emarginata.
Libinia spinosa may be differentiated from L.
erinacea by the lack of setation on the ventrolat-
eral margin of the carapace. The first zoea of L.
dubia and L. emarginata show no differences in
general morphology and setal numbers. The sec-
ond zoea of L. emarginata Usually has 10 setae on
the ventrolateral margin while L. dubia has 8
setae but as in stage I there appears to be no ready

TABLE 3. — Comparison of diagnostic characteristics for zoeal stages of Libinia erinacea, L. spinosa, L. dubia, and L. emarginata.

Species
and stage

Dorsal spine

Abdominal somites

Somite 2

Somites 3-5

Carapace setation

erinacea :1

Zoea I

Single, long, curved

Two lateral spines, one

Two medium spines, one

6 setae on ventrolateral

posteriorly, sometimes

on each side, pointing

margin

ending in short hook

posteriorly

Zoea II

Same as zoea I

Same as in zoea I, but

8 setae on ventrolateral

with pair of pleopod

margin

buds per somite

spinosa:2

Zoea I

Same as in L. erinacea

Same as in L erinacea

Two long spines, one on
each side, pointing
posteriorly

No setation on ventro-
lateral margin

Zoea II

Same as in L erinacea

Same as in zoea I, but
with pair of pleopod
buds per somite

No setation on ventro-
lateral margin

dubia:3

Zoea I

Single, fairly long.

Two small curved knobs,

Two small spines, one on

6-7 setae on ventro-

curved posteriorly

one on each side

each side, pointing
posteriorly

lateral margin

Zoea II

Same as zoea I

Same as in zoea I, but

Same as in zoea I. but

7-8 setae on ventro-

with pair of pleopod

lateral margin

buds per somite

emarginata

Zoea I

Single, long, slightly
curved posteriorly

Same as in L. dubia

7 setae on ventro-
lateral margin

Zoea II

Short and stout

Same as in L. dubia

Same as in L dubia

8- 1 0 setae on ventro-
lateral margin

'From Yang (1967).

2From Boschi and Scelzo (1968),

3From Sandifer and Van Engel (1971).

839

FISHERY BULLETIN: VOL. 75, NO. 4.

TABLE 4. — Average carapace lengths, total lengths and dry weights for the larval stages of Libinia
emarginata, L. dubia, L. erinacea, and L. spinosa.

Carapace length (mm)

Total length (mm)

Dry weight (mg)

Species

Zoea I Zoea II Megalopa Zoea I Zoea

Megalopa

Zoea I Zoea II Megalopa

L emarginata
L dubia'1
L erinacea2
L. spinosa3

0.78
0.81
088
080

0.94
0.97
1.03
096

1.21
1.16
1.24
1.30

2 19
2.35

2.30

269
2.78

2.80

2.14
2.11

3.10

'From Sandifer and Van Engel (1971)

2From Yang (1967).

3From Boschi and Scelzo (1968)

0.0214 0.0654

0.205

means to distinguish the species. Libinia dubia
zoea, as described by Sandifer and Van Engel
( 1971), are larger than L. emarginata zoea (Table
4), but statistical analysis of various samples
would be needed to determine if a consistent size
difference exists. Differences in setal types may
also occur, but these have not been described for L.
dubia. As with larvae of various species of Uca
(Hyman 1920), a rapid, reliable means to distin-
guish L. emarginata andL. dubia larvae to species
does not exist.

Megalopae of all four species, however, are dis-
tinguishable. Libinia spinosa has a distinct dorsal
spine which curves posteriorly (Boschi and Scelzo
1968) while the dorsal spine of L. erinacea is long
and upright (Yang 1967). Libinia dubia and L.
emarginata megalopae both lack a dorsal spine.
The median cardiac protuberance of the L. dubia
megalopa is single but is paired in L. emarginata .
This difference is relatively easy to observe, thus
unlike zoeal stages, L. dubia and L. emarginata
megalopae may be identified to species.

ACKNOWLEDGMENTS

We express our appreciation to Walter Schaffer
and the crew of the Carol El from Mt. Pleasant,
S.C., for assisting in collection of gravid crabs, and
to Austin Williams, National Marine Fisheries
Service Systematics Laboratory, NOAA, who
confirmed identification of several of the sponge
crabs. Also, we are indebted to Tom Bigford for
help in the maintenance and rearing of the larvae
in Rhode Island. DMJ was the recipient of the
Slocum-Lunz Predoctoral Fellowship in Marine
Biology during part of this study.

LITERATURE CITED

BOOKHOUT, C. G., AND J. D. COSTLOW, JR.

1974. Larval development oCPortunus spinicarpus reared
in the laboratory. Bull. Mar. Sci. 24:20-51.

Boschi, e. e., and m. a. Scelzo.

1968. Larval development of the spider crab Libinia

spinosa H. Milne Edwards, reared in the laboratory
(Brachyura, Majidae). Crustaceana, Suppl. 2:169-180.
COSTLOW, J. D., JR., AND C. G. BOOKHOUT.

1959. The larval development of Callinectes sapidus
Rathbun reared in the laboratory. Biol. Bull. (Woods
Hole) 116:373-396.

COSTLOW, J. D., JR., C. G. BOOKHOUT, AND R. MONROE.

1966. Studies on the larval development of the crab, Rhi-
thropanopeus harrisii (Gould). I. The effect of salinity and
temperature on larval development. Physiol. Zool.
39:81-100.
GRASSLE, J. P.

1968. Heterogeneity of hemocyanins in several species of
embryonic, larval, and adult crustaceans. Ph.D. Thesis,
Duke Univ., 218 p.
GURNEY, R.

1942. Larvae of decapod Crustacea. Ray Soc. Publ. 129,
Lond., 306 p.
HART, J. F. L.

1960. The larval development of British Columbia
Brachyura. II. Majidae, Subfamily Oregoniinae. Can. J.
Zool. 38:539-546.

Hyman, O. W.

1920. The development of Gelasimus after hatching. J.
Morphol. 33:485-525.

Nie, N. H., C. H. Hull, J. G. Jenkins, K. Steinbrenner, and
D. H. Bent.

1975. Statistical package for the social sciences. 2d ed.
McGraw-Hill Book Co., N.Y., 675 p.

Roberts, m. H.

1972. Culture techniques for decapod crustacean lar-
vae. In W. C. Smith and M. H. Chanley (editors), Cul-
ture of marine invertebrate animals, p. 209-220. Plenum
Press, N.Y.
Sandifer, P. A., and W. A. Van Engel.

1971. Larval development of the spider crab, Libinia
dubia H. Milne Edwards (Brachyura, Majidae, Pisinae),
reared in laboratory culture. Chesapeake Sci. 12:18-25.

1972. Larval stages of the spider crab, Anasimus latus
Rathbun, 1894 (Brachyura, Majidae, Inachinae) obtained
in the laboratory. Crustaceana 23:141-151.

SASTRY, A. N.

1970. Reproductive physiological variation in latitudi-
nally separated populations of the bay scallop, Aequipec-
ten irradians Lamarck. Biol. Bull. (Woods Hole)
138:56-65.

SASTRY, A. N., AND S. C. VARGO.

In press. Variations in the physiological responses of crus-
tacean larvae to temperature. In F. J. Vernberg, A.
Calabrese, F. Thurberg, and W. B. Vernberg (editors),
Physiological responses of marine biota to pollutants.
Academic Press, N.Y.

840

JOHNS and LANG I.ARVAI. DEVELOPMENT OF UIUS1A EMARGINATA

SULKIN, S. D.

1975. The significance of diet in the growth and develop-
ment of larvae of the blue crab, Callinectus sapidus
Rathbun, under laboratory conditions. J. Exp. Mar.
Biol. Ecol. 20:119-135.

SULKIN. S. D., AND K. NOKMAN.

1976. A comparison of two diets in the laboratory culture
of the zoeal stages of the brachyuran crabs Rhi-
thropanopeus harrisii and Neopanope sp. Helgol. wiss.
Meeresunters. 28:183-190.

VERNBERG , F. J.

1962. Comparative physiology: Latitudinal effects on
physiological properties of animal populations. Annu.
Rev. Physiol. 24:517-546.

VERNBERG, F. J , AND .J. D. COSTLOW, JR.

1966. Studies on the physiological variation between trop-
ical and temperate-zone fiddler crabs of the genus Uca. IV.
Oxygen consumption of larvae and young crabs reared in
the laboratory. Physiol. Zool. 39:36-52.

WILLIAMS, A. B.

1965. Marine decapod crustaceans of the Carolinas.
Fish Wildl. Serv., Fish. Bull. 65.1-298.

U.S.

YANG, W.

1967. A study of zoeal, megalopal and early crab stages of
some oxyrhynchous crabs iCrustacea: Decapoda). Ph.D.
Thesis, Univ. Miami, 459 p.

841

THE RIBBONFISH GENUS DESMODEMA, WITH THE DESCRIPTION
OF A NEW SPECIES (PISCES, TRACHIPTERIDAE)

Richard H. Rosenblatt1 and John L. Butler2

ABSTRACT

The genus Desmodema is unique within the Trachipteridae in that the upper caudal lobe, borne on the
second ural centrum, is not upturned, and the lower caudal lobe, borne on the first ural centrum in other
trachipterids, is absent, and in that there are seven dorsal pterygiophores before the first neural spine.
Desmodema lorum n.sp. can be distinguished from D. polystictum (Ogilby) on the basis of having more
vertebrae, fewer caudal rays, a longer tail, and the snout longer than the eye diameter. Desmodema
polystictum is probably circumtropical; D. lorum is restricted to the North Pacific Ocean. The species of
Desmodema have a distinctive prejuvenile phase characterized by polka dots on the sides, long pelvic
fins, a relatively short tail, and elongation of the first six dorsal rays. Metamorphosis is abrupt and
involves loss of the pelvic fins, elongated dorsal rays and polka dots, and a great lengthening of the tail.
It is suggested that metamorphosis accompanies movement to a deeper habitat. The elongated tail is
related to extension of the lateral-line sensory system. On the basis of joint possession of a dermal
tubercle and pore system and an abruptly constricted body, Desmodema and Zu are regarded as
related. Desmodema, but not Zu, agrees with Regalecus in the arrangement of the dorsal
pterygiophores.

The genus Desmodema was erected for the recep-
tion of Trachypterus jacksoniensis polystictus
Ogilby (Walters and Fitch 1960). Fitch ( 1964) sub-
sequently redescribed Desmodema polystictum,
mainly utilizing material from the northeast
Pacific, and placed Trachypterus misakiensis
Tanaka, 1908 and T. deltoideus Clark, 1938 in its
synonymy. Our interest arose from the observa-
tion that two recently collected specimens had
what appeared to be anomalously low vertebral
counts. This initiated the present study, which has
revealed the existence of two species, one of them
undescribed. In addition to distinguishing and de-
scribing the species, our material has allowed us to
amplify the generic description of Desmodema and
to detail some of the remarkable ontogenetic
changes undergone by its species.

MATERIALS AND METHODS

Specimens used in this study are housed in the
following institutions: California Academy of Sci-
ences (CAS), Department of Biology, University of
California, Los Angeles (UCLA), Natural History
Museum of Los Angeles County (LACM), and
Scripps Institution of Oceanography (SIO). In the

lScripps Institution of Oceanography, La Jolla, CA 92093.
2Southwest Fisheries Center, National Marine Fisheries Ser-
vice, NOAA, P.O. Box 271, La Jolla, CA 92038.

Manuscript accepted March 1977.

FISHERY BULLETIN: VOL. 75, NO. 4, 1977.

material list the first length measurement is the
snout-vent length (SV), the second the standard
length (SL). A single value indicates snout- vent
length of a broken specimen.

Because of the delicacy of the species, most of the
specimens were damaged in some way, and not all
counts and measurements were made on all
specimens. In particular, fin lengths represent
minimum measurements, since all fins seem to
have been broken to some degree. No specimen
appeared to have unbroken pelvic fins. Measure-
ments are self-explanatory and were taken with
flat-point dividers or dial calipers. Vertebral
counts were taken from radiographs or cleared
and stained material. Dorsal rays could be enum-
erated on only a few specimens.

RESULTS

Desmodema Walters and Fitch

Desmodema Walters and Fitch 1960. Type-species
Trachypterus jacksoniensis polystictus Ogilby
1897, by original designation.

Diagnosis. — A trachipterid with 4-10 caudal
rays, the caudal on the same axis as the caudal
peduncle, all caudal rays borne on terminal cen-
trum, no lower caudal lobe. Seven dorsal
pterygiophores before first neural spine. Body con-

843

FISHERY BULLETIN: VOL 75, NO. 4

stricted behind anus, tail exceedingly elongated in
juveniles and adults. Young with numerous dark
round spots. Skin of adults pierced by numerous
pores.

Description — Body strongly compressed later-
ally, postanal portion of body narrowing into a
whiplike tail in juveniles and adults (posterior
vertebrae about four times as long as 14th ver-
tebra). Posterior region of body of larvae and pre-
juveniles narrow, but not exceedingly elongate
(posterior vertebrae shorter than 14th vertebra).
Seven pterygiophores before first neural spine,
one or two pterygiophores between first and sec-
ond neural spines. First pterygiophore closely
applies to back of skull, no predorsal bones. An-
terior five or six dorsal rays elongated in larvae
and prejuveniles to form a dorsal pennant; these
rays completely lost in adults. Pelvics long and
fanlike in young, absent in adults. Caudal well
developed, of 4-10 unbranched rays, parallel to
axis of tail. Caudal rays all borne on last ural
centrum, no ventral caudal lobe (Figure 1).

Fin rays with a lateral row of small spines, these
weak or absent on posterior pelvic rays, middle
caudal rays, and pectoral rays. Each dorsal ray
anterior to elongated tail portion of body with a
single laterally directed stout spine on either side
of the base.

Lateral line ending at caudal base, lateral-line
scales with a pair of spines. Body otherwise scale-
less at all sizes (D. polystictum ), or young covered
with scales, each with a pair of longitudinal spin-
ous ridges (D. lorum). Skin of adults with cartilag-
inous tubercles, and pierced by numerous pores
(Walters 1963). No enlarged tubercles on ventral
midline.

FIGURE l.— Caudal skeleton of Desmodema polystictum, SIO
73-340. Camera lucida drawing at 25 x magnification. Only
bases of caudal rays shown. CR, caudal ray; Hy hypural; Ui,
first ural centrum; U2, second ural centrum and hypural.

844

Two nostrils in prejuveniles, the posterior just
before anterior margin of eye; posterior opening
obliterated in juveniles and adults. Nasal
epithelium without ridges or folds at all sizes.
Head bones cancellous and ridged. Mouth strongly
oblique. Teeth restricted to one to four in each
premaxilla and two enlarged, recurved fangs on
mandible, one on either side of symphysis. Gill
rakers (2-3) + (9-10) usually 3+ 9, fleshy, distally
expanded and leaflike. Rakers of upper limb with a
few teeth. Pseudobranch well developed. Gas
bladder present in smalljuveniles (to about30 mm
SV), rudimentary or absent in large juveniles and
adults.

Very young silvery, prejuveniles silvery with
profuse dark spotting, adults without spots.

Growth changes. — Although we have no mate-
rial smaller than 18.9 mm SV, it appears that
development from a silvery or transparent form
with a triangular outline with the head deepest,
into the polka-dotted, deep bodied prejuvenile is
gradual. The transition from prejuvenile to
juvenile is probably rapid and can fairly be termed
a metamorphosis. There is a large-size gap in our
material of D. polystictum (91-260 mm SV), but
our material of D. lorum includes the appropriate
size classes. The difference between the pre-
juvenile and the final body form can be seen in
Figure 5. The two specimens are almost identical
in snout-vent length. However, the upper speci-
men is essentially a miniature adult. The major
differences are in the change in the ventral profile,
elongation of the tail, increase in eye size, eruption
of lower jaw teeth, and loss of the spots, pelvic fins,
and posterior nostril. Juveniles, including our
largest (173 mm SV) have an elongate opening not
yet covered over by the skin at the position of the
pelvic fins, indicating that loss of the pelvics may
be rapid, and from the base.

Walters (1963) indicated that juveniles of D.
polystictum are scaled, but that adults are scale-
less, and have cartilaginous tubercles and a sub-
dermal canal system connected to the surface by
numerous pores. In our material of D. lorum an
18.5-mm SV silvery individual lacks both scales
and tubercles. An individual 36 mm SV is scaled,
but lacks tubercles, and in another (36.5 mm SV),
tubercles are present ventrally, and on the sides
behind the head. Our largest polka-dotted pre-
juvenile is 95 mm SV. The upper sides are scaled;
the remainder of the body is covered with tuber-
cles and the subcutaneous canal system. is well

ROSENBLATT and BUTLER: THE RIBBONFISH GENUS DESMODEMA

developed, with surface pores present. A juvenile
ofl04 mm SV has scales along the dorsal base, and
one of 131 mm SV lacks scales and has tubercles
and pores over the entire body.

Desmodema polystictum does not agree with D.
lorum in the course of development of the tuber-
cles and pore system. None of our specimens has
scales. Instead tubercles are developed in a speci-
men of 36 mm SV, and tubercles and pores are
present in an individual of 42 mm SV. Walters
(1963) was unaware of the existence of the two
species of Desmodema and his figure 1 was un-
doubtedly based on a juvenile of D. lorum.

In juveniles the first six dorsal rays are elon-
gated (broken in all our specimens). These rays,
which are borne on the pterygiophores before the
first neural spine, are lost, and in adults rep-
resented by a stiffening in the skin. The recurved,
fanglike lower jaw teeth first appear at a snout-
vent length of about 100 mm.

Life history and behavior. — We lack data from
closing nets, and thus have no precise information
on depth of capture of our material. Fitch and
Lavenberg (1968) inferred that Desmodema
"polystictum" lives "500 to 1,000 feet beneath the
sea's surface" and Walters (1963) predicated his
discussion of energetics on the assumption that
Desmodema is mesopelagic. Harrison and Palmer
(1968) speculated that Desmodema, which they
described as "chocolate brown," might live deeper
than its silvery relatives. Actually Desmodema is
silvery and turns brown in preservative.

The number of polka-dotted juveniles of D.
polystictum taken at or near the surface indicates
that they probably mainly occupy the euphotic
zone. The polka-dotted pattern would be maxi-
mally useful as protective coloration in the light-
dappled environment near the surface. However,
records (presumably juveniles) from stomachs of
Alepisaurus (Fourmanoir 1969) suggest a consid-
erable depth range. A number of juvenile D. lorum
have been taken from albacore, Thunnus
alalunga, stomachs, and others have been taken
by gear fished near the surface. We see no reason
to assume that the albacore had been feeding "far
beneath the surface" (Fitch 1964); however, Fitch
figured a metamorphosing juvenile of D. lorum
from an Alepisaurus taken on a longlineand listed
four other such specimens, again indicating a wide
depth range. Several of the metamorphosed
specimens of D. lorum were taken by open nets
fished to considerable depths. However, three of

the largest specimens were taken in purse seines,
indicating depths of capture of no more than 100
m. We have three adult D. polystictum: two were
taken in nets towed in the upper 500 m, and one
was taken in a purse seine.

Fitch's (1964) report on stomach contents pro-
vides equivocal evidence; Idiacanthus is a
mesopelagic vertical migrator, but Phronima
sedentaria occurs in the upper 300 m (Eric
Shulenberger, Scripps Institution of Oceanog-
raphy, pers. commun.1. There is thus no objective
evidence that either species of Desmodema lives
below 500 m (although the possibility is not
excluded). The species of Desmodema would seem
to be members of the deep epipelagic group as
defined by Parin (1968).

Keeping in mind the sketchy nature of the
available data on depth distribution, the following
hypothetical scheme is suggested for both species.
The silvery young have a gas bladder. The large
fins and the deep head and rapidly tapering body
suggest that they are feeble swimmers. They are
probably epipelagic. The polka-dotted pre-
juveniles probably occupy the euphotic zone. The
tail is short and anguilliform propulsive waves
could involve almost the entire body. The very
elongate, fanlike pelvic fins and dorsal pennant
indicate that swimming is normally slow and
probably involves undulations of the dorsal fin,
rather than the body.

With metamorphosis the dorsal pennant and
the pelvic fins are lost, the latter dropping off en-
tirely. The tail rapidly elongates at this time (see
Figure 5). The polka-dotted pattern is also lost, but
more gradually. The greatly elongated tail with
its associated dorsal rays would produce drag dur-
ing active swimming, but probably less so than in
Trachipterus, in which the posterior part of the
body is deeper. We propose that adult Desmodema
normally occupy the twilight zone of a few
hundred meters, where they hover, probably in a
head-up posture, maintaining position by undula-
tions of the dorsal fin. Rapid bursts of anguilliform
swimming would accompany prey capture or
predator avoidance. The tubercle and pore system
might act to maintain laminar flow during burst
swimming, as hypothesized by Bone ( 1972) for the
oilfish, Ruuettus.

The elongate tail of Desmodema can be related
to the hypothesized mode of life. The lateral line
runs the length of the tail, ending at the caudal.
The tail then serves the function of greatly extend-
ing the lateral line, and in effect provides an an-

845

FISHERY BULLETIN: VOL. 75, NO. 4

tenna for the reception of water displacement and
low frequency sound. In this connection it may be
pointed out that in the related Stylephorus chor-
datus the lateral line is continued onto the exceed-
ingly elongated caudal filament (R.H. Rosenblatt
pers. obs.). Stylephorus has tubular eyes directed
forward, and it is assumed that it maintains a
vertical posture in the water (Marshall 1971:44).
That elongate bodies in deep-sea and pelagic fishes
are related to a sensory function has been
suggested by Wynne-Edwards (1962:80).

Our presumption is that adult Desmodema
hover vertically, visually seeking prey silhouetted
against downwelling light. The lateral-line sys-
tem of the tail would be used to sense predators
approaching beneath the field of view of the eyes.
Undulations of dorsal fin would be used for
position-holding and the lateral body musculature
used for burst swimming for prey capture and pre-
dator avoidance.

This mode of life may predominate in the elon-
gate trachipteroids. Nishimura (1963) has infer-
red a similar life-style for Trachipterus ishikawai.
Adults of Zu cristatus have a long, thin tail, re-
miniscent of that of the species of Desmodema, and
Clarke and Haedrich (in Gaul and Clark 1968)
recorded the following observation: "A large
oarfish, Regalecus glesne, was sighted at about
210 meters. It was hanging vertically in the water,
head up, and appeared to be almost two meters in
length .... The dorsal fin was moving continu-
ously with wave-like motions progressing from
the head end to the tail end, very much like the fin
motions seen in file fish."

Distribution. — Desmodema poly stictum is prob-
ably circumtropical, and D. lorum appears to be
restricted to the northern Pacific (Figure 2). The
most obvious feature of the distributions is the
lack of sympatry. Desmodema polystictum is
broadly distributed in the tropical Pacific; the
northern and southernmost records for the species
are in areas influenced by warm currents. Des-
modema lorum on the other hand is mostly re-
stricted to the cooler waters of the North Pacific.
Twenty of the 21 eastern Pacific specimens were
taken north of lat. 28 °N, that is in areas north of
the 20 °C August surface isotherm and the 9°C
200-m isotherm. The single western Pacific cap-
ture (a metamorphosed juvenile) was in the area
where the temperature at 200 m is about 16°C.

The only area of possible sympatry indicated is
near Cape San Lucas, lower California, where

there are several records of D. polystictum and a
single record of D. lorum. Occurrence of the latter
that far south may be related to transport by the
California Current.

From Figure 2 it appears that both species of
Desmodema are especially common in the eastern
Pacific. The pattern of captures more likely
reflects effort. Many of the specimens of D. poly-
stictum have been taken incidentally by the purse
seine tuna fishery, wrhich is concentrated in the
eastern tropical Pacific. Similarly the predomi-
nantly eastern records for D. lorum probably
reflect the intensive collection effort in the region
of the California Current.

The presence of D. polystictum in the Atlantic
rests on the records of Leapley ( 1953) and Walters
(1963). G. Krefft, Instit fur Seefischeri, Hamburg,
has informed us that the RV Walter Her wig has
taken several specimens of Desmodema in the
central and southern Atlantic, but that the mate-
rial is not available for study at the present time.

Comparison and relationships. — Walters and
Fitch (1960) distinguished Desmodema from
Trachipterus primarily on the basis of the nature
of the caudal fin (parallel to the body axis), the
length of the gastric caecum (long), the absence of
sharp-tipped midventral tubercles, and the pre-
sence of scales in Desmodema. The last character
is not diagnostic, since our study indicates that D.
polystictum lacks scales at all sizes. The caudal
structure of Desmodema is unique in the Trachip-
teridae in that all of the caudal rays are borne on
the terminal centrum and the hypural of the first
ural centrum is ray less (Figure 1). Additionally, in
the species of Desmodema there are seven
pterygiophores before the first neural spine and
one or two between the first and second neural
spines, and in Zu and Trachipterus there is a
single pterygiophore before the first neural spine,
and nine between the first and second neural
spines.

Walters (1963) regarded Zu as the most
generalized and Desmodema as the most
specialized of the three trachipterid genera. De-
spite the specializations unique to Desmodema
and Zu respectively, present evidence indicates
that the two genera are more closely related to
each other than either is to Trachipterus . The
most important indicator of relationship if the
presence in both of the dermal tubercles in large
prejuveniles, and tubercles and a cutaneous pore
system in juveniles and adults. Dermal tubercles,

846

ROSENBLATT and BUTLER: THE RIBBONFISH GENUS DESMODEMA

FIGURE 2. — Distribution of the species of Desmodema.

pores, and subdermal canals have not previously
been reported for Zu cristatus. Instead the species
has been described as having deciduous cycloid
scales (Tortonese 1958; Walters and Fitch 1960;
Palmer 1961; Fitch 1964). However, none of our
specimens (8, 27.5-811 mm SL) has scales. Two
specimens of about 40 mm SL have the skin intact
and smooth, except for small tubercles on the
lower sides anteriorly, with no trace of scales. Two
specimens of 135 and 141 mm SL respectively

have the body studded with soft tubercles, with a
few interspersed pores; in a specimen of 210 mm
SL both tubercles and pores are well developed. In
the 811-mm SL adult the skin is superficially very
similar to that of Desmodema. Our 135-mm SL
specimen is from the Atlantic, so it does not appear
that we are dealing with a difference between At-
lantic and Pacific populations. We can only sur-
mise that the tubercles and pores of Zu have been
taken to represent scale pockets left behind by

847

FISHERY BULLETIN: VOL. 75, NO. 4

deciduous scales. The "modified cycloid scales"
mentioned by Harrisson and Palmer (1968) may
have been the dermal tubercles.

In addition to the tubercle and pore system, Zu
and Desmodema agree in two other specialized
characters: the body is constricted behind the vent
to form an elongated, slender tail, and there is a
distinctive prejuvenile which metamorphoses into
the juvenile phase.

In our interpretation, Trachipterus is the most
generalized trachipterid genus, with Desmodema
and Zu specialized in respect to the characters
given above. Desmodema is advanced with respect
to Zu in the loss of the lower caudal rays and great
elongation of the tail, and probably in the crowd-
ing of the pterygiophores before the first neural
spine. The significance of the difference in the
relationship of the anterior dorsal fin
pterygiophores between Trachipterus and Zu on
the one hand and Desmodema on the other is dif-
ficult to interpret. In Lophotus there is a single
rayless pterygiophore before the strongly
forward-curved first neural spine, then about 15
uncrowded pterygiophores in the wide interspace
between the first and second neural spines. The

figure of Regalecus given by Parker (1886) clearly
shows a condition much like that of Desmodema.
Although the caudal of Regalecus has been de-
scribed as lacking a ventral lobe, we find that two
caudal rays are associated with the terminal cen-
trum and four with the (ventral) hypural of the
first ural centrum.

Desmodema polystictum (Ogilby)

Figures 3, 4

Trachypterus jacksoniensis polystictus Ogilby
1897:649; Newcastle, New South Wales, Aus-
tralia; holotype, Australian Museum.

Trachypterus misakiensis Tanaka 1908:52, pi. IV,
fig. 2, "shores of Misaki" Japan; holotype, Zool.
Inst. University of Tokyo, No. 960. Herre and
Herald 1951:318, fig. 3; 6°26'N, 121°35'E.

Trachypterus deltoideus Clark 1938:180; Rurutu
Island, "Australs" (Tubuai Islands); holotype,
CAS 5532.

Desmodema polysticta. Walters 1963:260;
28°58'N, 88°18'W; Integumentary system.
Fitch 1964:230; in part, see synonymy of D.

FIGURE 3.— Adults of the species of Desmodema . Upper figure D. polystictum, SIO 68-333, 1,040 mm SL. Lower figure holotype of D.

lorum, USNM 216726, 1,098 mm SL.

848

ROSENBLATT and BUTLER: THE RIBBONFISH GENUS DESMODEMA

FIGURE 4.— Prejuveniles ofDesmodema. Upper figure D. lorum, LACM 30597-1, 87 mm SV, 188 mm SL. Lower figure D. polystictum,

SIO 75-55, 88 mm SV, 125 mm SL.

lorum. Fourmanoir 1969:36. Legand et al.
1972:383.
Trachipterus trachyurus, not of Poey. Leapley
1953:236; Fort Lauderdale, Fla.

Diagnosis. — A Desmodema with 71-74 total
vertebrae (18-20 precaudal and 37-42 before the
anus), 7-10 (usually 8) caudal rays, snout length
less than eye diameter, attenuate tail in juveniles
and adults (Figures 3, 7), and scales absent at all
sizes.

Description of adult (see also Tables 1-3). —
Ventral profile of body almost straight to anus,
then tapering to elongate tail. Dorsal profile rising
in a gentle curve to a point a little less than 1 head
length behind head, then tapering rapidly to a

point about IV2 head lengths behind anus, then
tapering more gradually along elongate tail sec-
tion. Tail long and straplike, postanal length al-
most two-thirds of standard length. Anus on vent-
ral midline.

Head 2.2-2.5 in snout- vent length, and about 1.3
in greatest body depth. Eye large, diameter
slightly greater than snout length. Ascending pro-
cesses of premaxillae extending back to a point
over posterior third of eye.

Dorsal origin over preopercle, preceded by a
thickening representing pterygiophores of first six
dorsal rays of juveniles. First fin rays short, suc-
ceeding rays becoming rapidly longer to about
point of maximum body depth, height of fin then
increasing more slowly, with longest rays slightly
before anus. Behind level of anus fin rays become

849

FISHERY BULLETIN: VOL. 75, NO. 4

TABLE 1. — Regression parameters for selected morphometric
characters in Desmodema; p = polystictum, 1 = lorum.

Characters

Species

Intercept

Slope

Correlation
coefficient

SV vs. SL'

40.7
54.8

0.30
0.19

0.97
0.97

11
8

HL2 vs. SV

-1.95
-1.02

0.29
0.28

0.95
0.98

15
15

Depth at pelvics
vs. SV

8.72
14.57

0.30
0.28

0.97
0.96

15
15

Greatest depth
vs. SV

P
1

6.93
10.66

0.35
0.35

0.97
0.97

15
14

Depth at anus
vs. SV

-0.39
5.16

0.20
0.20

0.92
0.97

Depth at caudal
base vs. HL

-0.13
0.65

0.02
0.03

0.95
0.78

11
8

Orbit diameter
vs. HL

0.05
0.09

0.40
0.36

0.97
0.98

Eye length
vs. HL

-0.52
-0.46

0.38
0.33

0.96
0.99

14
14

Snout vs. HL

-1.19

-1.50

0.38
042

0.99
0.93

15
15

Maxillary length
vs. HL

0.65
0.44

0.37
0.38

0.99
0.99

15
15

Maxillary width
vs. HL

-2.27
-2.81

0.34
0.34

0.96
0.96

15
15

Interorbit
vs. HL

0.31
-0.56

0.23
0.26

0.96
0.71

13
15

Pectoral-pelvic
origin vs. HL

4.10
8.07

0.25
0.23

0.97
0.75

Pectoral length
vs. HL

4.26
6.69

0.32
0.21

0.95
0.97

12
8

Longest dorsal
ray vs. HL

P
1

19.66
2.90

0.31
0.88

0.81
0.94

11
12

1SV = Snout vent length, SL
2HL = Head length.

Standard length.

Table 2.-

—Caudal and pectoral rays in Desmodema.

Species

Caudal rays
6 7 8 9

D. polystictum
D. lorum

Species

1
23

5 8 1
9 1

Total pectoral rays
24 25 26 27

7.9
5.8

D. polystictum
D. lorum

5 3 6 2
7 2 3

25.3
24.4

rapidly shorter, then fin margin even to caudal
base. Pelvics absent but with buried bases still
evident. Pectorals low, their bases almost horizon-
tal, outline pointed, tip probably extending almost
to lateral line when fin is intact.

Color in alcohol dark brown. Dorsal fin clear,
becoming dusky, then black along tail. Caudal
black. Pectoral clear. Iris dark, with a golden ring
around pupil. In life the fish is silvery with dark
red tones dorsally and on the head, and the fins
red, except that the dorsal rays along the tail ex-
tension are black.

Description of prejuvenile. — Ventral profile of
body sloping gradually down from tip of lower jaw
to pelvic, then tapering in a gentle curve back to
beginning of narrow tail section. Vent asymmetri-
cal, opening on left side. Dorsal profile of head
steep, but less so than in D. lorum of the same size.
In the 44-mm SV individual, the profile is almost
vertical to the dorsal origin, but in larger juveniles
the slope is gentler, and slightly rounded above
the eyes.

Dorsal profile of body curved from dorsal origin
to over opercle then tapering back to tail. Point of
maximum body depth just behind pelvic bases.
Tail extension thin, but relatively short; postanal
length about one-quarter of standard length. The
narrow part of the tail is characteristically curved
upward, so that caudal fin points up and forward.

Head length about 4 in snout-vent length, about
1.6 in greatest body depth. Eye diameter slightly
greater than snout length. Ascending processes of
premaxillae end over anterior third of eye. Dorsal
origin over middle of eye, first five or six dorsal
rays elongate, remainder of fin much as in adults.

Pelvic fins present, close together, origin level

TABLE 3. — Vertebral counts in Desmodema.

Precaudal

Species

20 21

O. polystictum

19.3

D. lorum

Preanal

22.8

Species 37

42 .

46 47

D. polystictum 1

—

38.5

D. lorum

3 5
Total

—

48.2

Species

. . . 106

107

108

109

110

D. polystictum

71.7

D. lorum

—

108.5

850

ROSENBLATT and BUTLER: THE RIBBONFISH GENUS DESMODEMA

with rear end of pectoral base. Orientation of fin
bases and shape of rays as described for D. lorum.
Pelvics frayed in all specimens, but reaching
beyond end of caudal in one and to caudal base in
another.

Color in alcohol pale, with a dusky area above
and behind head, extending over forehead and an-
terior to snout tip. Ventral parts of head dusky, a
dark streak below eye, running down behind
maxilla, a dusky streak along throat to pelvic
base. Body with conspicuous black spots which are
somewhat larger and more widely spaced poste-
riorly and above midline. No spots conspicuously
larger than others. A narrow dark streak on back
along dorsal base, running out to caudal base.
Probable life colors, based on two frozen speci-
mens, silver with black spots; iris silver and the
dorsal and caudal red; pectorals with pink tinge.
This coloration corresponds well with that of the
figure given by Tanaka (1908) except that the iris
is shown by him as green. Smaller individuals
differ (our smallest 32 mm SV) mainly in that the
body is less deep and the ventral profile nearly
straight, and there are no polka dots. The 37.5-mm
SV holotype of T. deltoideus was described as "uni-
form bright silvery." A 55-mm SL individual in
poor condition has traces of spots.

Remarks. — Leapley (1953) figured and de-
scribed a Florida specimen of D. polystictum under
the name Trachipterus trachyurus Poey 1861. The
identification was based on the presence of 76 dor-
sal rays in Leapley's specimen, Poey's specimen
having been reported to have 82 dorsal rays.

Leapley's photograph is of a Desmodema with a
large eye and a relatively deep tail, in agreement
with D. polystictum. No vertebral counts were
given, but Frank Schwartz (pers. commun.) has
supplied vertebral counts for Leapley's specimens,
as well as an additional individual from the west-
ern North Atlantic. Both have 18 precaudal ver-
tebrae, also in agreement with D. polystictum.

If Leapley's identification were correct, Poey's
name would be a senior synonym of Desmodema
polystictum (Ogilby 1897). However, three charac-
ters indicate that D. polystictum cannot be iden-
tified with T. trachyurus. These are number of
ventral rays (6 in trachyurus, 8 or 9 in polystic-
tum), pectoral rays (15, vs. 12-14), and coloration
(silvery with a midlateral yellow band vs. polka-
dotted). In addition, T. trachyurus was described
as having vertebral processes piercing the skin
(probably an artifact caused by postmortem dry-

ing) and lacking elongated anterior dorsal rays
(present in all juvenile trachipterids).

The supposed agreement in low number of dor-
sal rays is invalid, since Leapley's specimen was
broken far in advance of the caudal. Using his
value for body depth of his specimen (141 mm) we
estimate the actual length to have been between
1,400 and 1,500 mm. Poey's description does not
allow the identification of T. trachyurus with any
known trachipterid. Zu cristatus is excluded be-
cause juveniles of that form are strongly barred
and have peculiar fleshy abdominal lobes that are
unlikely to go unmentioned in a description.

The species of Trachipterus are not completely
understood, but juveniles of that genus have dark
markings, a dorsal pennant, and tubercles along
the venter.

Material examined. — Western and Central
Pacific: CAS SU 23783, Sagami Bay 1(72.8, 102.5);
CAS 5532, Rurutu, Tubuai Islands 1(37.5, 49.9),
holotype of Trachipterus deltiodeus. Eastern
Pacific: UCLA W58-103, 96 km southwest of Cabo
San Lucas, Baja California, tuna purse seine, 2(66,
91 and 88, 125); SIO 70-142, 19°50'N, 106°15'W,
tuna purse seine, 1(260); SIO 68-33, 19°53'N,
1 10°46 ' W, "5 x 5" nekton net towed at 5 knots, 800
m wire out, 1(333, 1,040); SIO 63-915, 16°01.5'N,
100°54'W, "5 x 5" nekton net, 0-200 m, 1(277,
785); SIO 76-167, 12°55'N, 90°54'W, tuna purse
seine, 1(111.5); SIO 76-294, 12°35'N, 92°15'W,
tuna purse seine, 1(84.9, 126.5); SIO 76-67,
12°15'N, 92°25'W, tuna purse seine, 1(42); UCLA
W67-135, 11°48'N,88°25'W, 1(60 SL); SIO 73-392,
11°18'N, 91°31'W, tuna purse seine, 1(91.5); SIO
75-139, 10°00'N, 119WW, midwater trawl, 0-50
m, 2(74.3, 100.5 and 90 SL); SIO 76-325, 10°24'N,
107°46'W, midwater trawl, 225 m wire out,
1(25.5); SIO 73-400, 08°41'N, 85°03'W, dipnetted
at surface, 1(82); SIO 64-397, 03°18.4'N,
101°54.3'W, stomach of Alepisaurus ferox 1(55.5);
SIO 63-299, 04°03'N, 80°46'W, meter net, 400 m
wire out, 1(23); SIO 75-590, 00°00.2'S,
119°17.0'W, meter net, 0-200 m, 1(28.0, 36.0); SIO
52-334, 02°47'S, 112°13'W, meter net, 0-250 m,
1(29, 40.5); SIO 73-340 "Eastern N. Pacific," tuna
purse seine, 1(296, 835).

Desmodema lorum n.sp.

Figures 3, 4, 5, 6
Desmodema polysticta, not of Ogilby. Fitch

851

FISHERY BULLETIN: VOL. 75, NO. 4

f s

■■sif

•> ■ ' ''

^ftS^Ni ^^^^

■■'.-

1)1

FIGURE 5. — Juvenile and prejuvenile of Desmodema lorum. Upper figure juvenile, LACM 35237-1, 103.7 SV, 412 mm SL. Lower figure

prejuvenile, LACM 30230-1, 95 mm SV, 198 mm SL.

FIGURE 6.— Holotype of Des-
modema lorum, USNM 216726.
Fins reconstructed.

852

ROSENBLATT and BUTLER: THE RIBBONKISH GENUS DESMODEMA

1964:321; in part, all but 10th, 12th, 13th of

listed specimens (fig. 2 is D. lorum, fig. 3 is D.

polystictum).
Desmodema polystictum, not of Ogilby. Berry and

Perkins 1966:668. Fitch and Lavenberg

1968:88. Miller and Lea 1972:87.
Desmodema polystictus, not of Ogilby. Radovich

1961:18.

Diagnosis. — A Desmodema with 106-111 total
vertebrae (21-25 precaudal and 46-50 before the
anus), 4-7 (usually 6) caudal rays, snout length
greater than eye diameter, an exceedingly long
attenuate tail in juveniles and adults (Figures 3,
7) and scales present in prejuveniles and small
juveniles.

Description of adult (see also Tables 1-3). —
Ventral profile of body almost straight, but with a
slight convexity back to anus, then tapering back
to elongate tail section. Dorsal profile rising
rapidly from snout tip to dorsal origin, then as-
cending more gently to maximum depth of body
about one-half to three-quarters of head length
behind head, then tapering back to tail. Tail ex-
ceedingly long and narrow, postanal length
three-quarters of standard length. Anus on ven-
tral midline.

Head length 3.2-3.8 in snout- vent length, 1.2-
1.3 in greatest body depth. Eye moderate, equal to
or (usually) shorter than snout. Ascending proces-
ses of premaxillae ending over or behind rear
margin of eye. Dorsal origin just behind preopercle
to over middle of opercle, preceded by a horny
process representing pterygiophores of first six
dorsal rays. First few dorsal rays short, succeeding
rays becoming longer, with maximum height of fin
over and posterior to anus. Fin height decreases
gradually along tail, probably as reconstructed in
Figure 6. Pelvics absent, but with buried bases
still evident. Pectorals low, their bases horizontal.
Pectoral pointed, but tip frayed and broken in all
specimens.

Color in alcohol tan. Dorsal fin clear, becoming
dusky, then black along tail. Caudal black. Pec-
torals clear. Iris dark with a golden ring around
pupil. In life, probably silvery with red tones dor-
sally and on the head, and with the fins red.

Description of prejuvenile. — Ventral profile
sloping down from tip of lower jaw to pelvics, then
tapering convexly back to vent, then tapering
more sharply to beginning of tail, then straight.

>
I

t 150 -

O
2

100 200 300 400 500 600 700 800 900 1000 1100 1200
STANDARD LENGTH (mm)

FIGURE 7. — The regression of snout-vent length on standard
length in Desmodema . Open circles D. polystictum , closed circles
D. lorum.

Usually a notch in outline at position of vent,
which is asymmetrical, opening on the left side.
Dorsal profile of head steep, almost vertical in
smaller specimens. Back curved, point of
maximum body depth just behind pelvic base.
Dorsal profile becomes straight along tail elonga-
tion. Tail long and thin, postanal length about
one-half of standard length.

Head length 3.8-4.2 in snout-vent length, 1.8-
2.2 in greatest body depth. Eye about equal to
snout length. Because of the steepness of the
forehead, the ascending processes of the premaxil-
lae end over the anterior third of the eye.

Dorsal origin over middle to posterior third of
eye. First five or six dorsal rays elongate, remain-
der of fin shaped much as in adult except that the
rays along the elongate tail are not as long. Pelvic
fins present, close together, origin under pectoral
base. Anteroposterior axes of pelvics parallel with
sides. Pelvics broken in all our material, but
reaching beyond anus in one specimen. Pelvic rays
flattened and bladelike basally, the first the
broadest, becoming filamentous distally. Minute
prickles along rays. Pectorals as in adults.

Color in alcohol tan, a darker area on back over
and behind head, extending down over forehead
onto snout. A variably developed dusky streak
from lower margin of orbit down behind maxilla. A
dusky streak along throat to pelvic bases. Spotting
somewhat variable but spots becoming larger and
more widely spaced posteriorly and above midline.
Three of five specimens with two noticeably larger

853

FISHERY BULLETIN: VOL. 75, NO. 4

spots on upper back on middle-third of body (see
Figure 4). A narrow dark streak on back at base of
dorsal, broadening on narrow part of tail. Indi-
viduals of about 35 mm SV differ in that the body
is not so deep, and there is little or no pigment.
Also the dorsal is relatively higher. Our smallest
specimen, 18.5 mm SV, has the back with a
straight taper behind the head, the ventral profile
more evenly tapering, and has scattered
melanophores on the head and over the viscera.
These probably represent the larval pigmenta-
tion.

Identification and remarks. — The characters
given in the generic and specific diagnoses serve to
distinguish D. lorum adequately from all known
trachipterids. In addition to the characters given
in the diagnoses, the two species of Desmodema
differ in number of dorsal rays. The single D.
lorum counted had 197 dorsal rays and three D.
polystictum had 120, 124, and 121, respectively.
Another feature is the height of the dorsal. Large
D. lorum have proportionately longer dorsal rays
than do D. polystictum of equivalent size (Figure 8,
Table 1). Prejuveniles of D. lorum can most easily
be distinguished from those of D. polystictum by
their deeper body, and more rounded anteroven-
tral contour (Figure 4).

E
E

>-
<

<r
o

li-
CO

30 40 50 60 70

HEAD LENGTH (mm)

FIGURE 8. — The regression of length of longest dorsal ray on
head length in Desmodema. Open circles D. polystictum, closed
circles D. lorum.

Although Ogilby did not illustrate the holotype
of Tnachypterus jacksoniensis polystictus, his de-
scription is sufficiently detailed to allow iden-
tification with considerable certainty. The polka-
dotted coloration and lack of lower caudal lobe are
diagnostic of Desmodema, and the dorsal ray
count of 126 indicates that our material has been
correctly assigned. The caudal count of seven or
eight rays also accords with our concept of D.
polystictum. Tanaka's ( 1908) excellent figure indi-
cates that Trachypterus misakiensis has properly
been synonymized with D. polystictum, and the
presence of eight caudal rays in the small holotype
of Trachipterus deltoideus dictates a similar
placement.

Etymology. — From the Latin lorum, a whip, in
reference to the elongate tail. Suggested common
name, whiptail ribbonfish.

Material examined.— Holotype: USNM 216726,
formerly SIO 62-434, a 1,098 mm SL (276 mm SV)
male, taken between 29°05'N, 126°37'W and
29°03'N, 126°42'W by RV John N. Cobb with a
Cobb Mk II trawl with 1,200 m wire out (esti-
mated fishing depth 400 m) between 1930 and
2110 h on 25 August 1962. (Original station
number 90.160, C6208, see Berry and Perkins
1966.) Paratypes: LACM 30217-1, 34°42'N,
121°20'W, spit up by Thunnus alalunga, 1(91.5,
167); LACM 9890-2, 34°25'N, 120°28'W, 15.2-m
midwater trawl, 8 fm, 1(97, 173); LACM 9982,
33°00'N, 118°03'W, IKMT, 2,743 m wire out,
1(131); SIO 76-335, 13 km west of Oceanside,
Calif., bait net, 1(95, 198); LACM 30597-1,
32°48'N, 118°16'W to 32°30'N, 118°30'W, IKMT,
1(87, 188); LACM 35237-1, 32°43'N, 118°57.5'W,
10-m midwater trawl, 1(103.7, 412); LACM
31678-1, San Clemente Island, Calif., off Pyramid
Head, 1(83); LACM 30998-1, 31°45'N,118°48'W to
31°44'N, 118WW, IKMT, 1,300 m, 1(93); SIO
63-375, 31°40.5'N, 122°03.5'W to 31°37.0'N,
122°04.3'W, Cobb Mk II trawl, 1,144 m wire out,
1(139.8, 580); SIO 63-429, 29°58.5'N, 120°07'W,
IKMT, 4,500 m wire out, 1(173); LACM 9726-8,
29°29'N, 118°35'W, IKMT, 2,134 m wire out,
1(92.5, 189); SIO 74-47, 28°10.2'N, 160°00.9'E,
IKMT, 0-1,000 m, 1(125, 364); UCLA W61-125, 64
km off Cabo Colnett, Baja California, 1(286),
LACM 31800-2, 129 km south of Cabo San Lucas,
Baja California, 1(283).

Additional material. — UCLA W55-320,

854

ROSENBLATT and BUTLER: THE RIBBONFISH GENUS DESMODEMA

33°39'N, 135°00'W, 1; SIO 75-588, 29°17'N,
116°59'W, 1(55); UCLA A343, 28°N, 132°W, 1;
UCLA W62-73, 32°10'N, 118°24'W, 1(53); SIO
75-589, 28°37.5'N, 118°18'W, 1(18.5); SIO 75-591,
33°34'N, 118°34'W, 1(89+ SL); LACM 31804, no
data, 1(132); SIO 64-96, 31°39'N, 117°51'W,
1(289); SIO 72-16, 27°22'N, 155°23'W, 1(19.8,
26.4).

ACKNOWLEDGMENTS

We thank William Eschmeyer (CAS), Robert
Lavenberg (LACM), and Boyd W. Walker (UCLA)
for permission to examine specimens under their
care. Gary L. Friedricksen turned three specimens
over to us. John Fitch supplied collection data for
certain specimens and read the manuscript.
Robert Lavenberg and John Fitch supplied the
original of the drawing of the holotype of D. lorum,
first published in Fitch and Lavenberg 1968.
Frank Schwartz, Institute of Marine Science,
University of North Carolina, supplied vertebral
counts of two Atlantic specimens of D. polystictum .

LITERATURE CITED

Berry, f. h., and H. C. Perkins.

1966. Survey of pelagic fishes of the California Current
area. U.S. Fish Wildl. Serv., Fish. Bull. 65:625-682.

Bone, Q.

1972. Buoyancy and hydrodynamic functions of integu-
ment in the castor oil fish. Ruvettus pretiosus (Pisces:
Gempylidae). Copeia 1972:78-87.
CLARK, H. W.

1938. The Templeton Crocker Expedition of 1934-35. Ad-
ditional new fishes. Proc. Calif. Acad. Sci., Ser. 4,
22:179-185.

Fitch, j. e.

1964. The ribbonfishes (Family Trachipteridae) of the
eastern Pacific Ocean, with a description of a new
species. Calif. Fish Game 50:228-240.

Fitch, J. E., and R. J. Lavenberg.

1968. Deep-water teleostean fishes of California. Univ.
Calif. Press, Berkeley, 155 p.

FOURMANOIR, P.

1969. Contenus stomacaux d'Alepisaurus (poissons) dans
le Sud-Ouest Pacifique. Cah. ORSTOM, Ser. Oceanogr.
7(4):51-60.

Gaul, R. d., and W. D. Clarke.

1968. Gulfview diving log. Gulf Res. Corp. Publ. 106,
37 p.

Harrisson, C. M. h., and G. palmer.

1968. On the neotype of Radi-icephalus elongatus Osorio
with remarks on its biology. Bull. Br. Mus. (Nat. Hist.)
Zool. 16:185-208.

herre, a. w., and e. s. herald.

1951. Noteworthy additions to the Philippine fish fauna
with descriptions of a new genus and species. Philipp. J.
Sci. 79:309-340.
LEAPLEY, W. T.

1953. First record of the ribbonfish, Trachipterus
trachyurus, from the mainland of North Ameri-
ca. Copeia 1953:236.
LEGAND, M., P. BOURRET, P. FOURMANOIR, R. GRANDPERRIN,
J. A. GUEREDRAT, A. MICHEL, P. RANCUREL, R. REPELIN,
AND C. ROGER.

1972. Relations trophiques et distributions verticales en
milieu pelagique dans l'Ocean Pacifique intertropi-
cal. Cah. ORSTOM, Ser. Oceanogr. 10:301-393.
MARSHALL, N. B.

1971. Explorations in the life of fishes. Harvard Univ.
Pres, Camb., 203 p.

MILLER, D. J., AND R. N. LEA.

1972. Guide to the coastal marine fishes of Califor-
nia. Calif. Dep. Fish Game, Fish Bull. 157, 235 p.

NISHIMURA, S.

1963. Observations on the dealfish, Trachipterus
ishikawai Jordan & Snyder, with descriptions of its para-
sites. Publ. Seto Mar. Biol. Lab. 11:75-99.
OGILBY, J. D.

1897. On a Trachypterus from New South Wales. Proc.
Linn. Soc. N.S.W. 3:646-659.

Palmer, G.

1961. The dealfishes (Trachipteridae) of the Mediterra-
nean and north-east Atlantic. Bull. Br. Mus. (Nat. Hist.)
Zool. 7:335-352.
PARIN, N. V.

1968. Ichthyofauna of the epipelagic zone. Akad. Nauk
SSSR Inst. Okeanol. Moskva. (Engl, transl., Israel Pro-
gram Sci. Transl., TT69-59020, 206 p.)
PARKER, T. J.

1886. Studies in New-Zealand ichthyology. I. On the
skeleton of Regalecus argenteus. Zool. Soc. Long., Trans.
12:5-33.
POEY, F.

1861. Memorias sobre la historia natural de la Isla de
Cuba, Apendice:415-427.
RADOVICH, J.

1961. Relationships of some marine organisms of the
northeast Pacific to water temperatures. Calif. Dep.
Fish Game, Fish Bull. 112, 62 p.

Tanaka, S.

1908. Notes on some Japanese fishes, with descriptions of
fourteen new species. J. Coll. Sci., Imp. Univ. Tokyo
23(7):l-54.
TORTONESE, E.

1958. Cattura di Trachypterus cristatus Bon. e note sui
Trachypteridae del Mare Ligure. Doriana 11:1-5.

Walters, v.

1963. The trachipterid integument and an hypothesis on
its hydrodynamic function. Copeia 1963:260-270.
WALTERS, V., AND J. E. FITCH.

1960. The families and genera of the lampridiform (Allot-
riognath) suborder Trachipteroidei. Calif. Fish Game
46:411-451.
WYNNE-EDWARDS, V. C.

1962. Animal dispersion in relation to social be-
haviour. Oliver and Boyd Ltd., Edinb., 653 p.

855

OXYCLINE CHARACTERISTICS AND SKIPJACK TUNA DISTRIBUTION
IN THE SOUTHEASTERN TROPICAL ATLANTIC

Merton C. Ingham,1 Steven K. Cook,1 and Keith a. Hausknecht*

ABSTRACT

A shallow layer of low oxygen concentration, containing minimum values frequently less than 1.0 ml/1
and a strong oxycline, was measured on two cooperative cruises in the southeastern tropical Atlantic
Ocean and found to be consistent with previous portrayals and hypotheses based on fragmentary data.
The low-oxygen layer was in the form of a thick wedge off the southwestern coast of Africa, extending
from about lat. 18° to 3° S. The oxycline overlying the low-oxygen layer was generally coincident with a
pycnocline and was found at depths of 20-50 m in most of the area surveyed, as revealed by the
topography of the 3.5 ml/1 iso-oxygen surface. It is believed that a shallow oxycline has a strong
influence on the distribution and availability of skipjack tuna schools. The hypothesis was tested by
overlaying school sighting positions on the 3.5 ml/1 topography. The association between sightings and
oxycline depth was further defined by developing a linear "equation" relating the two variables as
follows: s = 23.15 - 0.59z, where s is the number of school sightings, z is the depth of the 3.5 ml/1
surface, and 23.15 and 0.59 are constants. A similar correlation was attempted with school sightings
and habitat layer thickness, but the results were less systematic and convincing than the oxycline
correlation.

A shallow oxycline containing low values of dis-
solved oxygen concentration should serve as a
lower boundary of the environment habitable by
surface schooling tunas. In a study of the relation-
ship of thermocline depth to success of purse sein-
ing of tuna in the tropical Pacific, Green (1967)
stated that an oxycline approximately coincident
with the thermocline could play a major role in
restricting the fish to near surface waters. Work
on the oxygen requirements of captive skipjack
tuna in the Southwest Fisheries Center Honolulu
Laboratory3 by R. M. Gooding and W. H. Neill
indicated a 4-h TLm (median tolerance limit) be-
tween 2.4 and 2.8 ml 02 /l, and in experiments with
gradually declining oxygen concentrations an
alarm threshold was found near 3.5 ml/1. If we
regard the 3.5 ml/1 iso-oxygen surface to be the
"floor" of habitable environment of surface school-
ing tunas in tropical waters, then the topography
of this surface becomes significant in describing
their environment.

The shoaling of the oxycline, the floor of the
habitable environment, may serve not only to

•Northeast Fisheries Center Atlantic Environmental Group,
National Marine Fisheries Service, NOAA, Narragansett, RI
02882.

2Graduate School of Oceanography, University of Rhode Is-
land. Narrangansett, RI 02882.

3Neill, W. H. Unpubl. exp. data, Southwest Fish. Cen. Hon-
alulu Lab., Natl Mar. Fish, Serv., NOAA, pers coramun., 1974
and 1976.

Manuscript accepted February 1977.
FISHERY BULLETIN: VOL. 75, NO. 4, 1977.

crowd the skipjack tuna schools to the surface, but
also to influence the lateral distribution of the fish
schools through other ecological factors associated
with the shoaling. The oxycline is imbedded in the
thermocline, which is brought up to or near the sea
surface under conditions of upwelling which sea-
sonally occur off the southwestern coast of Africa.
Such conditions, when well developed, will lead to
the development of fronts, which tend to concen-
trate forage, and higher rates of primary and sec-
ondary productivity to sustain larger forage popu-
lations; both processes tending to concentrate
predators such as tunas, as described by
Blackburn (1965).

BACKGROUND INFORMATION ON

OXYGEN MINIMA IN
THE SOUTHEASTERN ATLANTIC

The oxygen minima in the Atlantic have been
studied since the early part of this century. These
studies have not, however, resulted in a definitive
explanation of the mechanisms of formation of
these low-oxygen layers. While many theories
have been proposed to explain the origin of these
layers, the mechanisms generally cited as being
most significant are either an extremely high
biochemical oxygen consumption or low rates of
oxygen replenishment by mixing processes. Some
recent papers have dealt with a synthesis of these

857

FISHERY BULLETIN: VOL. 75, NO. 4

processes in an attempt to give a more complete
explanation of the observed patterns (Wyrtki
1962; Bubnov 1966, 1972; Menzel and Ryther
1968).

Proponents of the first mechanism argue that an
oxygen minimum layer is formed as a result of
biochemical oxidation of organic matter that has
accumulated at intermediate depths due to
specific gravity relationships between seawater
and sinking detritus (Seiwell 1937; Miyake and
Saruhashi 1956). Those supporting the second
mechanism suggest that an oxygen minimum will
be formed at the relatively still boundary between
circulating water masses where replenishment of
oxygen will be minimal. This view was first ad-
vanced by Jacobsen in 1916 and was later sup-
ported by Dietrich and Wiist (Richards 1957).

More recent studies (Redfield 1942; Wyrtki
1962; Bubnov 1966, 1972; Menzel and Ryther
1968) have stressed the importance of advective
processes in the formation of oxygen minimum
surfaces. Redfield (1942) hypothesized that the
deep oxygen minimum of the Atlantic could be
formed by advection along isentropic surfaces of
water carrying a heavy load of organic detritus
and solutes from high latitude convergence areas.
Subsequent oxidation of the organic load forms a
minimum. Wyrtki (1962), Menzel and Ryther
(1968), and Bubnov (1966, 1972) considered high
oxygen consumption as necessary for initial for-
mation of low-oxygen water with advective and
mixing processes controlling its position and
movement. Wyrtki (1962) contended that oxida-
tion occurring in the layer of least advection re-
sults in formation of an oxygen minimum, which
can spread by mixing into other water masses.
Menzel and Ryther (1968) and Bubnov (1966,
1972) argued that oxygen depleted water will form
in specific areas due to high biochemical oxygen
consumption and that these waters are then
spread by advection and turbulent diffusion.

Bubnov (1972) stated that the main factors con-
trolling the formation of an oxygen minimum are
the rate of biochemical oxidation, the density
stratification of the water, and the supply of
oxygenated water to bottom layers. In the south-
eastern tropical Atlantic the presence of one or
more of these factors results in highly favorable
conditions for the formation of an oxygen
minimum. The coastal region off South- West Af-
rica has strong upwelling conditions which result
in high organic production and subsequent high
oxygen consumption (Hart and Currie 1960).

Though the coastal waters are weakly stratified in
comparison with the region of the Congo River
effluent, there is, nonetheless, a well-developed
pycnocline which inhibits downward-mixing of
highly oxygenated surface waters (Visser 1970;
Bubnov 1972). In addition, the deep waters of the
Angola Basin are somewhat lower in oxygen than
those of the western basin of the South Atlantic.
This reduces the amount of oxygen which will be
mixed into the upper layers by upwelling or turbu-
lent diffusion (Bubnov 1972). Taft (1963) and Vis-
ser (1970) suggested that the waters to the north of
lat. 20 °S off the coast of South- West Africa may be
isolated from the highly oxygenated deepwater
masses formed at high latitudes, thus inhibiting
the renewal of oxygen from this source.

Because of the favorable conditions for the for-
mation of low-oxygen water in the coastal region
of South- West Africa, it has been suggested that
this area is a source for much of the water that
forms the oxygen minimum surfaces in the South
Atlantic. Taft (1963) plotted the oxygen and salin-
ity distributions on surfaces of constant potential
specific volume anomaly for the South Atlantic.
On the 125, 100, and 80 cl/t surfaces (a-0 26.81,
27.07, and 27.49 g/1, respectively), the isopleths of
both oxygen and salinity are zonal at lat. 20°S.
The areas of lowest oxygen concentration are lo-
cated just north of lat. 20°S off the coast of
South- West Africa, strongly suggesting that this
region serves as a source area for low-oxygen
water which is then transported westward to form
the primary minimum at 300-600 m in the study
area).

In a study by Menzel and Ryther (1968), the
concentration of dissolved organic carbon in the
South Atlantic was found to be essentially con-
stant below 400-500 m while the oxygen content
varied. Based on this finding, they concluded that
oxygen concentrations in the minimum layer will
not be further reduced by in situ decomposition of
organic matter. They suggest that low-oxygen
water is formed off South- West Africa and is then
distributed horizontally along isentropic surfaces
to form the primary oxygen minimum layer.
Changes in the oxygen content occur by mixing
with water masses of higher oxygen content, re-
sulting in the increase of oxygen concentrations as
the water moves farther from its source.

Bubnov (1972) identified three areas off
South-West Africa where waters of very low oxy-
gen content are formed (see Figure 1): 1) the shelf
region to the south of lat. 17°S, 2) the coastal

858

INGHAM ET AL: OXYCLINE AND SKIPJACK TUNA DISTRIBUTION

region extending from long. 8°-10°E to the shelf,
and from lat. 7°-9°S to 17°-18°S, and 3) the region
of the quasi-stationary cyclonic gyre to the west of
long. 6°E.

In the shelf region south of lat. 17 °S, water with
extremely low-oxygen content ( <1 ml/1) forms in
the near-bottom layer (80-150 m) and spreads
northward and westward beneath the warmer,
less dense surface water by advection and turbu-
lent diffusion. This water forms the shallow
minimum layer that is characteristic of this re-
gion, extending westward to about long. 0° where
it loses its identity due to mixing.

10° S

10° w

FIGURE 1. — Diagram of geostrophic water circulation in the 0 to
100 m layer. 1) South equatorial countercurrent; 2) Angola Cur-
rent; 3) west (main) branch of Benguela Current; 4, 5, 6) north
branches of Benguela Current; 7) eddies in inner region of cy-
clonic gyre; 8) anticyclonic curl; 9) Benguela divergence; 10)
merging zone of Angola Current and north littoral branch of
Benguela Current. From Moroshkin et al. (1970).

The "eastern coastal region" and the region of
the cyclonic gyre are areas where low-oxygen
water Kl ml/1) forms at "intermediate" depths
(Bubnov 1972). These waters apparently are ad-
vected and mixed to the west, forming the primary
oxygen minimum in the eastern South Atlantic.
These observations provide further evidence to
support the hypothesis that the coastal waters off
Southwestern Africa are a source for much of the
low-oxygen water that forms the oxygen minima
in the South Atlantic.

RESULTS OF JISETA CRUISES

In 1968 the National Marine Fisheries Service,
then Bureau of Commercial Fisheries, joined with
the U.S. Coast Guard and the Missao de Estudos
Bioceanologicos e de Pescas de Angola in the Joint
Investigation of the Southeastern Tropical Atlan-
tic (JISETA); an oceanographic and biological in-
vestigation in the coastal waters of southwestern
Africa. Distribution of tunas and oceanographic
conditions from the Equator to lat. 18°S were in-
vestigated on cooperative cruises of the RV Un-
daunted, the USCGC Rockaway, and the RV Goa
during February through April and September
through December 1968.

Low-Oxygen Layer

Vertical sections of dissolved oxygen concentra-
tion developed from the JISETA data (Cook et al.
1974) characteristically showed a layer of low
oxygen concentration, including a minimum
which frequently was<1.0 ml/1 and occasionally
<0.5 ml/1 in concentration. The minimum values
were not well defined because of the means of
sampling employed: 1 cast of 10 Niskin bottles
spaced throughout the upper 1,000 m of the water
column at each station. However, the samples
were spaced well enough to portray the layer of
low concentration and the sharp oxycline which
formed its upper boundary.

The transects obtained in March 1968 (Figures
2, 3) showed a layer of oxygen concentration-^. 0
ml/1 of variable thickness (50-450 m) extending
from lat. 15° to 18°S in the upper 500 m of the
water column. In the southern portion of the area
the layer was thicker and nearer the sea surface.

In the October-November transects (Figures 4,
5) a thick layer of water containing<1.0 ml/1 dis-
solved oxygen was found to extend from lat. 17° to
7°S in the upper 600 m of the water column. Once
again the layer was thicker (up to 550 m) and
nearer the surface in the southern portion of the
area. In the northern portion it thinned to <100 m
and was detected at about 300-400 m depth at the
outer stations, about n.mi. (180 km) offshore.

The form of the layer of very low oxygen con-
centration (<1.0 ml/1) observed in October-
November 1 968 ( Figure 6 ) appears to be consistent
with Bubnov's (1972) contention that the source of
the layer is located in coastal waters between lat.
18° and 23 °S, from which it is advected northward
by the northern branches of the Benguela Cur-

859

10° s

15°-

FISHERY BULLETIN: VOL. 75, NO. 4

20'

FIGURE 2. — Locations of transects of dissolved oxygen concen-
tration conducted by Undaunted during 8-16 March 1968. From
Cook et al. 1974.

CL
Q

FIGURE 3. — One of the transects of dissolved oxygen concentra-
tion (milliliters per liter) produced from Undaunted data (8-16
March 1968). From Cook et al. 1974.

rent. The apparent divergence of the layer from
the coast shown in the onshore-offshore transects
north of lat. 9°S (Cook et al. 1974) also is consist-
ent with the general direction of flow given for the
extension of the current.

Although a subsurface oxygen minimum was
found throughout the area surveyed from lat. 18°S
to the Equator, the layer of very low oxygen con-
centrations (<1.0 ml/1) extended northward only
as far as lat. 7°-8°S. The increase in oxygen con-
centration northward from those latitudes is the
result of either westward turning of the northward
currents carrying the low oxygen concentrations
as suggested by Bubnov (1972) or increased mix-
ing rates attenuating the oxygen minimum.

Oxycline

Overlying the layer of low oxygen concentration
throughout its extent was an intense oxycline.
The range of concentrations in the oxycline usu-
ally was from 2.0 to 4.0 ml/1, but was found to be as
great as from 1.0 to 5.0 ml/1 in the southern por-
tion of the surveyed area. The oxycline thickness
ranged from about 40 m to 10 m, producing intense

860

vertical gradients when thinnest. The most in-
tense gradients were found on the shoreward ends
of the transects and in the southern portion of the
surveyed area.

The 3.5 ml/1 iso-surface was selected to portray
oxycline topography because it was found in the
upper oxycline throughout the area surveyed (lat.
18°S-Equator) and because this oxygen concen-
tration has been found to be significant in the
physiology and distribution of skipjack tuna in the
eastern tropical Pacific (Neill see footnote 3;
Barkley et al.4). The resulting topographies for
the February-April and October-November
periods (Figures 7, 8) were generally of low relief
and shallow (<50 m) except at the seaward end of
transects south of lat. 16° S in March and north of
lat. 2°-3°S in October- November. Two large areas
of shallow depths (<25 m) to the oxycline were
found in the October-November data field, from
lat. 10° to 16°S and from lat. 5° to 7°S. Due to the

"Barkley, R. A., W. H. Neill, and R. M. Gooding. 1977. Skipjack
tuna habitat based on temperature and oxygen requirements.
Unpubl. Manuscr. 12 p. Southwest Fish. Cen. Honolulu Lab.,
Natl. Mar. Fish. Serv., NOAA, P.O. Box 3830, Honolulu, HI
96812.

INGHAM ET AL: OXYCLINE AND SKIPJACK TUNA DISTRIBUTION

5°

0°-

5°S

10°-

I5«

20c

IO°E

15'

FIGURE 4. — Location of transects of dissolved oxygen concentra-
tion by Undaunted and Rockaway 15 October-21 November
1968. Derived from Cook et al. 1974.

relatively incomplete sampling grid in the
February- April period, little can be learned from
any attempts to compare the results of the two
periods.

Pycnocline

The density field of the upper waters off south-
western Africa is determined mostly by tempera-
ture, except in the area influenced by the effluent
of the Congo River (Bubnov 1972). Results of the
JISETA cruises support this contention, showing
a well-developed thermocline throughout the
area.

During the October-November period thermo-
cline gradients increased from south to north with
the most intense gradients found off the Congo
River. The sea-surface temperature ranged from
<17° C in the south (lat. 18° S) to >26° C near the
Equator. In the February-April period the ther-
mocline appeared to be more intense than during
the October-November period but generally con-

ui
o

FIGURE 5. — One of the transects of dissolved oxygen concentra-
tion (milliliter per liter) produced from Undaunted data (22-23
October 1968). From Cook et al. 1974.

ROCKAWAY

19-21 NOV 1968

V «5 a> o w

UNDAUNTED

21-29 OCT 1968
]_

ROCKAWAY

19-28 OCT 1966

FIGURE 6.— Synthetic transect of
oxygen concentration from Un-
daunted and Rockaway data col-
lected during 19 October-21
November 1968.

861

FISHERY BULLETIN: VOL. 75, NO. 4

5°N

- 5°S

5°E

20°

FIGURE 7. — Depth (meters) to the 3.5 ml/1 iso-oxygen surface
from Undaunted data, February-March 1968.

15°

5°N

0°

5°S

15°

20°

FIGURE 8.— Depth (meters) to the 3.5 ml/1 iso-oxygen surface
from Undaunted and Rocka way data, October-November 1968.

stant throughout the limited area surveyed. The
sea-surface temperature ranged from 22 °C in the
south (lat. 18°S) to 29°C in the north (lat. 2°N).

In order to portray the pycnocline topography
and minimize the differences in surface heating in
the two periods, an isopycnal surface found near
the bottom of the thermocline, the a, = 26.0 sur-
face, was chosen (Figures 9, 10). Comparison of the
vertical sections of density and oxygen from the
JISETA cruises (Cook et al. 1974) shows that the
26.0 iso-cr, surface parallels the oxycline and is
found in its lower levels. Therefore the topography
of the isopycnal surface also should reflect geo-
strophic circulation patterns in the lower oxycline.

During the October-November 1968 period the
26.0 g/1 topography (Figure 10) deepened near-
shore north of lat. 10°S, but was shallow and ir-
regular south of there. The topography north of
lat. 10°S indicates a general southward flow in the
upper layer from about lat. 4° to 10°S, correspond-
ing with the southward Angola Current described

by Moroshkin et al. (1970), but not extending as
far south as they portray it (Figure 1).

RELATIONSHIP BETWEEN

OXYCLINE DEPTH AND
SKIPJACK DISTRIBUTION

Variations in the thickness of the habitable en-
vironment of skipjack tuna, bounded beneath by
the oxycline, should strongly inflence the distribu-
tion and availability of surface schooling tunas. To
test this contention, the positions of sightings of
skipjack schools during the October-November
1968 cruise period were plotted on a map of oxy-
cline (3.5 ml/1) topography (Figure 11). A cursory
study of this plot reveals that the fish were gener-
ally sighted where the oxycline was <50 m deep,
and over 809c of the schools were seen where it was
<30 m deep.

An apparent relationship between school dis-
tribution or availability and oxycline depth can

862

INGHAM ET AL: OXYCLINE AND SKIPJACK TUNA DISTRIBUTION
5°E 10° 15°

5°N

100° I

O ' >l00c^>

—

I0°— ~~-_\

75_\

)

_ 75

75 N

/ 1

>50

y>5of

75^

50 J
<£5(

^50^

— 5°S

— I0<

20°

FIGURE 9.— Depth (meters) to the 26.0 g/1 at surface from Un-
daunted data, February-April 1968.

best be demonstrated with the data collected in
October-November, involving 49 sightings with
relevant oxygen data. After grouping the oxycline
depth measurements into 5-m classes and plotting
a sighting versus depth-frequency bar graph (Fig-
ure 12), it appears that a smooth inverse relation-
ship exists for depths >10 m. By assigning the
central value of each depth class to each sighting
in the class, a least squares linear "equation" can
be obtained for sighting frequency as a function of
oxycline depth in the form:

s = a + mz

(1)

where

s
z

= the number of sightings
= the depth of the 3.5 ml/1 surface
a and m = constants, in this case, equal to
23.15 and -0.59, respectively,
leading to

5°E

I5e

5°N

5°S

10'

I5C

20°

FIGURE 10.— Depth (meters) to the 26.0 g/1 a, surface from
Undaunted and Rockaway data, October-November 1968.

s = 23.15 - 0.59z

(2)

as the "equation." Note that the equation is
defined only over the range of depths from 1 1 to 40
m. At depths greater than this, school sightings
may be difficult to make and at depths less than
this the fish may avoid the thin habitable layer.

Although the relationship portrayed in the bar
graph appears to be nonlinear, the errors intro-
duced by interpolation between sampling bottle
depths and the arbitrary assignment of central
values to the frequency classes make any attempts
to obtain a best-fit, nonlinear "equation" unwar-
ranted. The linear relationship shown above is
about all the sophistication the data will bear,
particularly in view of the small number of fish
school sightings.

To further pursue the role of environmental
conditions in influencing the distribution of skip-
jack tuna, we considered the concept of habit layer

863

5°E

5°N

5°E

FISHERY BULLETIN: VOL. 75, NO. 4
10° 15°

20°

FIGURE ll. — Location of sightings of schools of skipjack tuna
during October-November 1968 plotted on the observed ocycline
(3.5 ml/1) topography.

FIGURE 13.— Location of sightings of schools of skipjack tuna
(dots) and habitat thickness i meters) from Undaunted and
Rockaway data, October-November 1968.

25 -i

X
C9

W 25 — |

20 —

§ 20-

15 —

I CD
<J ID

— 15-

fl-

10— i

Q. ' 10-

10s*

\'OQ

o
ir

5 —

O 5-1

m 0 - .

0-5

6-10

11-15

16-20

21-25

26-30

31-35

5 0-5 6-10 11-15

16-20

21-25

26-30

31-35

36-40

41-45 '

36-40

Z=DEPTH(m) TO OXYCLINE ( 3 5 ml / liter )
»o

FIGURE 12. — Relationship between skipjack school sightings
and oxycline depth from Undaunted and Rockaway data for
October- November 1968.

THICKNESS OF HABITABLE ENVIRONMENT (M)

FIGURE 14. — Relationship between skipjack school sightings
and habitat thickness from Undaunted and Rockaway data for
October-November 1968.

864

INGHAM ET AL: OXYCLINE AND SKIPJACK TUNA DISTRIBUTION

developed by Barkley et al. (see footnote 4). They
defined the habitat of adult skipjack to be bounded
above by the sea surface or 22°-26°C (for 9- to 4-kg
fish) and below by 18°C or 3.5 ml/1 oxygen concen-
tration, whichever is shallower. We plotted the
skipjack tuna school sightings on a horizontal
chart of habitat layer thickness ( using 24 °C ) for the
October-November cruise period (Figure 13). The
distribution of school sightings at various habitat
layer thicknesses (Figure 14) is considerably dif-
ferent from that at various oxycline depths. Many
points in the school sightings versus oxycline
depth plot (Figure 12) have shifted to shallower
classes in the school sighting versus habitat
thickness plot, including seven observations in
habitat thicknesses of 5 m or less. This shift is the
consequence of regarding the 18 °C isothermal
surface as the floor of the habitat when it is shal-
lower than the oxycline and assuming that it has a
constraining effect equal to that of the 3.5 ml/1
oxygen surface. The validity of this assumption is
unknown, but comparison of the two distributions
(Figures 11, 13) suggest that the 3.5 ml/1 oxygen
surface has a stronger effect on the skipjack tuna
than the 18°C isothermal surface.

The question of whether it is school distribution
or availability (to a fishing method) which has
been related to oxycline depth cannot be resolved
without an independent assessment of tuna school
distribution by a different method. The means
used to locate tuna schools is essentially that
employed by crews of purse seiners and live-bait
boats; a watch is maintained for bird activity
above feeding or "breezing" schools. This
technique reveals only those schools which are
available to seines or pole-and-line fishing
methods, hence it would be more accurate to con-
sider the factor portrayed in Equation (2) as avail-
ability rather than distribution. Those fish not
closely approaching the surface would not be de-
tected and would not be available to these harvest-
ing methods.

The pragmatic significance of the relationship
between skipjack tuna school availability and
oxycline depth lies in its use by fishermen and
fishery scientists, the former for more efficient
harvest strategy and the latter for more accurate
resource assessment. The coincidence of the oxy-
cline and thermocline should provide a very strong
lower barrier to downward excursions of tropical
tunas, perhaps even strong enough to prevent an
encircled school from escaping by sounding before

the seine is pursed. If this were true, the efficiency
of capture by purse seine would be greater in wa-
ters containing a shallow oxycline.

LITERATURE CITED

Blackburn, m.

1965. Oceanography and the ecology of tunas. Oceanogr.
Mar. Biol., Annu. Rev. 3:299-322.

BUBNOV, V. A.

1966. The distribution pattern of minimum oxygen con-
centrations in the Atlantic. Oceanology 6:193-201.
Translated from Okeanologiya 6:240-250.

1972. Structure and characteristics of the oxygen
minimum layer in the southeastern Atlantic. Oceanol-
ogy 12:193-201. Translated from Okeanologiya 12:225-
235.
COOK, S. K., J. F. HEBARD, M. C. INGHAM, E. C. SMITH, AND C.
A. DIAS.

1974. Oceanic conditions during the Joint Investigation of
the Southeastern Tropical Atlantic (JISETA) — February,
April, and September- December 1968. U.S. Dep. Com-
mer., Natl. Mar. Fish. Serv., Data Rep. 82, 358 p.

Green, R. E.

1967. Relationship of the thermocline to success of purse
seining for tuna. Trans. Am. Fish. Soc. 96:126-130.

Hart, T. J., and R. I. Currie.

1960. The Benguela Current. Discovery Rep. 31:123-298.
MENZEL, D. W., AND J. H. RYTHER.

1968. Organic carbon and the oxygen minimum in the
South Atlantic Ocean. Deep-Sea Res. 15:327-337.

MlYAKE, Y., AND K. SARUHASHI.

1956. On the vertical distribution of the dissolved oxygen
in the ocean. Deep-Sea Res. 3:242-247.

MOROSHKIN, K. V., V. A. BUBNOV, AND R. P. BULATOV.

1970. Water circulation in the eastern South Atlantic
Ocean. Oceanology 10:27-34. Translated from
Okeanologiya 10:38-47.

REDFIELD, A. C.

1942. The processes determining the concentration of oxy-
gen, phosphate and other organic derivates within the
depths of the Atlantic Ocean. Pap. Phys. Oceanogr.
Meteorol. 9(2), 22 p.

RICHARDS, F. A.

1957. Oxygen in the ocean. In J.W. Hedgpeth (editor),
Treatise on marine ecology and paleoecology, p. 185-238.
Geol. Soc. Am. Mem. 67(1).

SEIWELL, H. R.

1937. The minimum oxygen concentration in the western
basin of the North Atlantic. Pap. Phys. Oceanogr.
Meteoral. 5(3), 24 p.
TAFT, B. A.

1963. Distribution of salinity and dissolved oxygen on sur-
faces of uniform potential specific volume in the South
Atlantic, South Pacific, and Indian oceans. J. Mar. Res.
21:129-146.
VlSSER, G. A.

1970. The oxygen-minimum layer between the surface
and 1000 m in the north-eastern South Atlantic. S. Afr.,
Div. Sea Fish., Fish. Bull. 6:10-22.
WYRTKI, K.

1962. The oxygen minima in relation to ocean
circulation. Deep-Sea Res. 9:11-23.

865

NOTES

THE SOURCE OF COBALT-60 AND

MIGRATIONS OF ALBACORE OFF

THE WEST COAST OF NORTH AMERICA

Cobalt is an integral part of the vitamin B12 com-
plex and an important cofactor in enzyme systems
(Lowman et al. 1971; Reichle et al. 1970). It is,
therefore, an element whose cycle in oceanic
ecosystems is of interest. The artificial radionuc-
lide cobalt-60 (60Co) has been observed in the liv-
ers of albacore, (Thunnus alalunga Bonnaterre)
collected off the west coast of North America,
Washington to Baja California (Pearcy and Oster-
berg 1968; Hodge et al. 1973).

The albacore is a commercially important mi-
gratory species of tuna which normally inhabits
the epipelagic subtropical and transitional waters
of the Pacific, Atlantic, and Indian oceans. In the
North Pacific, albacore may undertake trans-
pacific migrations between Japan and the west
coast of America (Clemens 1961; Otsu and Uchida
1963; Clemens and Craig 1965).

While single-pass nuclear reactors were oper-
ated at Hanford, Wash., the Columbia River was
an important source of artificial radionuclides in
the Pacific Ocean off Oregon and Washington.
Some radionuclides, formed by neutron activation
of impurities in river water used to cool the reac-
tors, were transported via the Columbia out into
the ocean and were detectable in the plume water
far at sea (Osterberg et al. 1965). Cobalt-60 was
among the radionuclides carried by the Columbia
River effluent (Gross and Nelson 1966). Fallout
from nuclear detonations, however, was another
source of 60Co (Lowman and Ting 1973; Hodge et
al. 1973). Which of these sources was more sig-

nificant in contaminating tuna is not known. We
shall attempt to use the temporal and geographi-
cal variations in 60Co content of albacore livers to
estimate the relative importance of the two
sources and to provide information on migrations
of albacore.

Methods

During the period June-October of 1963
through 1969, over 200 albacore livers were re-
moved from fish (520-850 mm fork length, x =
640 mm) collected on surface jigs and preserved
aboard ships either by freezing or with Formalin.1
In the laboratory, livers were weighed, dried,
ashed (500° to 570°C), ground, and packed into
15-cm3 plastic counting tubes for radioanalysis.
Samples were counted for 100 min using a 12.7-
cm2 Nal (Tl) crystal detector with a 512 channel
pulse-height analyzer. See Pearcy and Osterberg
(1968) for additional details on collection and
analysis. Results are expressed in picocuries per
gram wet weight to be compatible with other pub-
lished results on cobalt in tuna livers.

Results and Discussion

Concentrations of 60Co in the livers of albacore
caught in three general regions along the west
coast of North America are shown in Figure 1 for
1964. Of all the years, 1963-69, this year provided
the most data for inter-regional and temporal
comparisons. Two general trends are evident:

■Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

~ I0r

O
V

0 1

001

N. Ore. a Wash.

S. Ore.

_i_

S. & Baja Calif.

J A S
MONTHS

FIGURE 1 — Cobalt-60 concentrations
(dots = actual observations, open
triangles = x values) from livers of al-
bacore captured off three west coast re-
gions during June-October 1964.

867

first, relatively high 60Co activities were seen off
the southern Oregon coast and somewhat lower
concentrations off northern Oregon and
Washington as well as off southern and Baja
California; second, 60Co concentrations decreased
with time during the summer-fall period. Data
from other years corroborated these trends.

Annual variations of 60Co in albacore off the
Oregon coast (dots and solid line in Figure 2) indi-
cate that 60Co concentrations increased from 1963
to 1964 then declined steadily until 1967, but in-
creased again in 1968.

There are two possible sources of 60Co for alba-
core in the northeastern Pacific. Until 1965, eight
Hanford reactors were a relatively constant source
of 60Co entering the Columbia River (Gross and
Nelson 1966). In 1965, however, a sequence of
shutdowns of individual reactors began (Foster
1972). The other possible source of this isotope is
fallout from atmospheric tests of nuclear weapons
which also varied in time, but according to a dif-
ferent pattern (Lowman and Ting 1973; Hodge et
al. 1973). Inputs of 60Co into the environment by
atmospheric tests that could directly effect the
activity levels in the North Pacific include over
100 U.S. and U.S.S.R. tests in 1961-62 and Lop
Nor, China, tests in 1964-65 (one test each year),

1966 (three tests), 1967 (two tests), and 1968 (one
test) (U.S. Environmental Protection Agency
1960-72).

The relatively constant input from the Hanford
plant fails to account for the low 60Co values ob-
served in albacore during 1963 nor the increased
values in 1964 (Figure 2). Other evidence indicat-
ing that Hanford was not the major 60Co source is
based on our knowledge of the migration of alba-
core into the Pacific Northwest fishery and their
subsequent movements. Albacore often first ap-
pear off the southern Oregon coast and move
northward and inshore as the summer progresses
(Powell et al. 1952; Keene 1974), sometimes along
the axis of the warm Columbia River plume wa-
ters (Pearcy 1973). Levels of 60Co did not increase
with residence time of albacore in Oregon waters
or proximity to the Columbia River in northern
Oregon (Figure 1), as would be expected if Hanford
was the main 60Co source.

These trends are opposite of those noted in alba-
core livers for 65Zn, a radionuclide that was known
to be associated with the Columbia River effluent,
but are similar to those of 54Mn, a radionuclide
associated with atmospheric fallout (Pearcy and
Osterberg 1968). We conclude, therefore, that
most of the 60Co we find in albacore livers was

FIGURE 2.— Concentration of 60Co in liv-
ers of albacore captured off Oregon and
Washington. Solid line indicates mean
values of our observations (dots); broken
line is a plot of 60Co levels off southern and
Baja California as presented by Hodge et
al. (1973). Also indicated is the number of
Hanford reactors in operation and the
number of nuclear atmospheric tests
(bars = pre-1963 non-Chinese testing af-
fecting the North Pacific and post- 1963
testing at Lop Nor, China) which occurred
during our study period.

o
U
O

No of
Reactors ^

— , , — -.-^

en o

O
Q.

0 0!

(110) Nuclear
Tests

110

105

100

• (3)

(I)

(2)

(I)

(2)

1961- ' 1963
1962

1964 ' 1965

1966 ' 1967
YEAR

1968 ' 1969

c_>

-z.

1970

868

derived from fallout, even off the coast of Oregon
where the influence of the Columbia River plume
should be the greatest.

Since radioactivity originating from fallout is
higher in the open ocean than in coastal waters
where upwelling occurs (Pillai et al. 1964; Folsom
and Young 1965; Gross et al. 1965), the spatial-
temporal trends evident in Figure 1 may be
explained by the residence time of albacore in
coastal waters. Highest levels of 60Co are expected
in oceanic waters off southern Oregon in June and
July; lower levels are expected later in the season
after albacore have migrated northward and
shoreward and have resided in coastal waters,
provided that the biological half-life of 60Co in
tuna livers is short enough. The decrease in 60Co
levels in albacore (Figure 1) is much more rapid
than would be expected from natural radioactive
decay of 5.26 yr. Biological turnover must be rapid
in order to produce a short effective half-life.

Hodge et al. (1973) related the levels of 60Co in
albacore to fallout deposition and found that
maximum uptake of 60Co by albacore lagged nuc-
lear atmospheric detonations by 1-2 yr. Annual
changes of 60Co concentrations observed off Ore-
gon (Figure 2) show a similar delayed response,
but the peak activity levels in albacore occurred a
year earlier than the peaks seen by Hodge et al.
( 1973) off southern California (dashed line, Figure
2). The main atmospheric input by nuclear deto-
nations occurred in 1961-62. Our main peak of
60Co in albacore occurred in 1964, and that re-
ported by Hodge et al. occurred in 1965, indicating
a delay of about 2 and 3 yr respectively after
testing before the uptake is observed in albacore.
This not only suggests that the source of 60Co in
albacore is from atmospheric fallout, but that the
availability of the radionuclide was different be-
tween the albacore caught off California and those
caught off Oregon, perhaps because of differences
in distributions and migratory patterns than
those described by Clemens (1961).

Laurs and Lynn (1977) presented data that
confirm this suggestion. Based on recapture of
tagged albacore and length-frequency distribu-
tions, they concluded that the albacore population
found off Oregon is different from that found off
southern and Baja California. They further
suggest that albacore which migrate into Oregon
waters may come from a portion of the offshore
population which is located north of the 35th
parallel, while those that move into the California
waters are located south of the 35th parallel.

The bomb detonations at Lop Nor (lat. 40°N)
gave the heaviest fallout input into the North
Pacific at about this latitude. Due to the circula-
tion in the North Pacific (Sverdrup et al. 1942), it
appears quite possible that albacore which were
associated with waters north of lat. 35°N may
have experienced high levels of 60Co up to a year
before the tuna associated with waters to the
south. Circulation in the North Pacific and the
latitudinal differences in the location of the two
portions of the albacore population appear to be a
plausible explanation for the difference of 1 yr in
activity peaks between albacore caught off Oregon
by us and those off southern and Baja California
by Hodge et al. (1973).

Acknowledgments

This research was supported by the U.S. Energy
Research and Development Administration (con-
tract E(45-l)-2227, task agreement 12), RLO-
2227-T12-69. We thank N. H. Cutshall, T. R.
Folsom, R. M. Laurs, and V. F. Hodge for their
comments on the manuscript.

Literature Cited
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1961. The migration, age, and growth of Pacific albacore
(Thunnus germo), 1951-1958. Calif. Dep. Fish Game,
Fish Bull. 115, 128 p.
CLEMENS, H. B., AND W. L. CRAIG.

1965. An analysis of California's albacore fishery. Calif.
Dep. Fish Game, Fish Bull. 128, 301 p.
FOLSOM, T. R., AND D. R. YOUNG.

1965. Silver-llOm and cobalt-60 in oceanic and coastal
organisms. Nature (Lond.) 206:803-806.

Foster, r. F.

1972. The history of Hanford and its contribution of
radionuclides to the Columbia River. In A. T. Pruter and
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adjacent ocean waters, p. 3-18. Univ. Wash. Press, Seat-
tle.

Gross, M. G., C. a. Barnes, and g. k. Riel.

1965. Radioactivity of the Columbia River effluent. Sci-
ence (Wash., D.C.) 149:1088-1090.

Gross, M. G., and J. L. nelson.

1966. Sediment movement on the continental shelf near
Washington and Oregon. Science (Wash., D.C.)
154:879-885.

Hodge, v. f., t. r. folsom, and D. R. Young.

1973. Retention of fall-out constituents in upper layers of
the Pacifiic Ocean as estimated from studies of a tuna
population. /^Radioactive contamination of the marine
environment, p. 263-276. Int. At. Energy Agency, Vienna.

KEENE, D. F.

1974. Tactics of Pacific Northwest albacore fisherman -
1968, 1969, 1970. Ph.D. Thesis, Oregon State Univ.,
Corvallis, 102 p.

869

LAURS, R. M., AND R. J. LYNN.

1977. Seasonal migration of North Pacific albacore,
Thunnus alalunga, into North American coastal waters:
Distribution, relative abundance, and association with
Transition Zone waters. Fish. Bull., U.S. 75:795-822.
LOWMAN, F. G., T. R. RICE, AND F. A. RICHARDS.

1971. Accumulation and redistribution of radionuclides by
marine organisms. In Radioactivity in the marine envi-
ronment, p. 161-199. Nat. Resour. Counc, Natl. Acad.
Sci., Wash., D.C.
LOWMAN, F. G., AND R. Y. TING.

1973. The state of cobalt in seawater and its uptake by
marine organisms and sediment. In Radioactive con-
tamination of the marine environment, p. 369-384. Int.
At. Energy Agency, Vienna.
OSTERBERG, C, N. CUTSHALL, AND J. CRONIN.

1965. Chromium-51 as a radioactive tracer of Columbia
River water at sea. Science (Wash., D.C.) 150:1585-
1587.
OTSU, T., AND R. N. UCHIDA.

1963. Model of migration of albacore in the North Pacific
Ocean. U.S. Fish Wildl. Serv., Fish. Bull. 63:33-44.

PEARCY, W. G

1973. Albacore oceanography off Oregon — 1970. Fish.
Bull., U.S. 71:489-504.
PEARCY, W. G., AND C. L. OSTERBERG.

1968. Zinc-65 and maganese-54 in albacore Thunnus
alalunga from the west coast of North America. Limnol.
Oceanogr. 13:490-498.
PILLAI, K. C, R. C. SMITH, AND T. R. FOLSOM.

1964. Plutonium in the marine environment. Nature
(Lond.) 203:568-571.

POWELL, D. E., D. L. ALVERSON, AND R. LIVINGSTONE, Jr.
1952. North Pacific albacore tuna exploration —
1950. U.S. Fish. Wildl. Serv., Fish. Leafl. 402, 56 p.
REICHLE, D. E., P. B. DUNAWAY, AND D. J. NELSON.

1970. Turnover and concentration of radionuclides in food
chains. Nuc. Saf. 11:43-55.
SVERDRUP, H. U., M. W. JOHNSON, AND R. H. FLEMING.

1942. The oceans, their physics, chemistry, and general
biology. Prentice-Hall, Inc., N.Y., 1087 p.
U.S. ENVIRONMENTAL PROTECTION AGENCY (previously
Public Health Service).

1960-72. Radiation data and reports, 1960 through
1972. (Mon. Rep.) U.S. Gov. Print. Off., Wash., D.C. 13
vol.

Earl E. Krygier
William G. Pearcy

School of Oceanography
Oregon State University
Corvallis, OR 97331

LENGTH-WIDTH-WEIGHT RELATIONSHIPS

FOR MATURE MALE SNOW CRAB,

CHIONOCOETES BAIRDI

Snow crabs have been exploited commercially in
Alaska since 1961 (Alaska Department of Fish

and Game 1975). Chionocoetes bairdi is the pre-
dominant species with C. opilio composing up to
25% of the catch from the Bering Sea. Landings
were small and intermittent in the early 1960's
but increased to about 3.2 million lb in 1968. Land-
ings expanded dramatically thereafter and ex-
ceeded 60 million lb in 1974, with an ex-vessel
value of more than $12 million.

Carapace width measurements have been col-
lected from the commercial snow crab catch by
biologists since the inception of the fishery; indi-
vidual weights, however, are not routinely col-
lected because the task is rather time-consuming.
The relationships between carapace width,
length, and body weight are of interest to
biologists and processors. The relationship be-
tween carapace length and width is of interest be-
cause the carapace shape is one of the diagnostic
characteristics to distinguish between C. bairdi
and C. opilio and hybrids of the two species (Kari-
nen and Hoopes 1971). The relationships between
carapace width and weight and carapace length
and weight have many uses. They are, for exam-
ple, indicators of condition, used to calculate
biomass, and used to estimate recovery of edible
meat from crabs of various sizes.

Materials and Methods

Carapace length and width and body weight
measurements were taken from 240 mature male
C. bairdi from commercial catches made south of
the Alaska Peninsula in the vicinity of the
Shumagin Islands in May 1975. Length and width
measurements were taken to the nearest millime-
ter with vernier calipers and weights were re-
corded to the nearest gram. Length was measured
from the posterior medial edge of the carapace to
the anterior medial point of the right orbit. The
rostrum was not included in the length measure-
ment because it often erodes when crabs are car-
ried in the live tank of fishing vessels. Width was
measured at the widest part of the carapace and
included the lateral branchial spine. Width
ranged from 128 to 185 mm, weights from 635 to
2,230 g, and lengths from 92 to 143 mm.

The basic linear regression formula W = a + bL
was used to express the relationship between
width (W) and length (L). Weight ( Wt) was related
to width and length by the power functions, log10
Wt = log10 a + b log10 W and log10 Wt = log10 a + b
log10 L. The constants a and b were determined
empirically.

870

Results

The length-width, length-weight, and width-
weight relationships are summarized in Table 1.
All relationships were characterized by very high
correlation coefficients. No relationships between
length, width, and weight have previously been
reported for C. bairdi.

male's internal state. Calling rate has been man-
ipulated experimentally (Winn 1967, 1972; Fish
1972; Fish and Offutt 1972), but no one has studied
the calling rate of undisturbed individual fish.
This note is a preliminary attempt to look at these
twin problems ( when and how fast toadfish call) by
recording the boatwhistles of individual males on
their nests.

TABLE 1. — Length- width, length- weight, and width- weight re-
lationships for mature male Chionocoetes bairdi.
ISample size was 240 animals for each relationship]

Relationship

Coefficient

Formula

Length -width
Length-weight
Width -weight

0.96
099
0.99

W =
log,0IW =

iog,0 wt =

3.584 + 1.268/.
-3.076 + 2.956 log, 0L
3.363 + 2.936 log10W

Literature Cited

Alaska Department of fish and Game.

1975. Alaska 1974 catch and production, commercial

fisheries statistics. Alaska Dep. Fish Game Stat. Leafl.

27, 49 p.
KARINEN, J. F., AND D. T. HOOPES.

1971. Occurrence of Tanner crabs ( Ch ionocoetes sp. ) in the

Bering Sea with characteristics intermediate between C.

bairdi and C. opilio. (Abstr.) Proc. Natl. Shellf. Assoc.

61:8-9.

DUANE E. PHINNEY

Alaska Department of Fish and Game

Kodiak, AK 99615

Present address: Washington Department of Fisheries

Olympia, WA 98504

Materials and Methods

Terra cotta drainage tiles were set out individu-
ally adjacent to the pilings of a dock at Solomons,
Md. Male toadfish which settled into three of the
tiles started calling, and the calls were moni-
tored between 9 and 15 June 1969. Because of
changing tapes and mechanical problems, the re-
cord was not continuous. The recording system
consisted of individual Clevite1 oyster (CH 15-J)
hydrophones with their own General Electric
Phono-Mic preamplifiers (UPX-003C) and a Preci-
sion Instrument Model 207 multichannel tape re-
corder. The gain was turned down so that only
boatwhistles from the fish in the tile adjacent to
the hydrophone would present a loud signal. The
tapes were transduced onto strip chart paper
(Bruel and Kjaer level recorder type 2305), and
segments equivalent to 6 min of real time were
continuously marked on the chart paper. The
number of boatwhistles in each segment was
counted.

Results

TEMPORAL ASPECTS OF CALLING BEHAVIOR
IN THE OYSTER TOADFISH, OPSANUS TAU

The oyster toadfish, Opsanus tau (Linnaeus), pro-
duces two calls: an agonistic grunt and a boatwhis-
tle associated with courtship (Fish 1954; Tavolga
1958, 1960; Gray and Winn 1961). The boatwhis-
tle is produced only by males on nests (Gray and
Winn 1961) and is endogenously driven as well as
influenced by calling of surrounding males (Winn
1964, 1967, 1972; Fish 1972). A toadfish, not hear-
ing other males, may still boatwhistle for long
periods and attract a female. Although toadfish
may be influenced to call by the calling of adjacent
males, one would assume the circadian patterning
of the boatwhistle to be influenced by photoperiod
and the fish's behavioral strategy relative to it.
Additionally, the rate of calling may be a key to a

The activity patterns for the three fish appear
aperiodic (Figure 1; Table 1). All of the animals
called both day and night ( 1 1 calling periods day, 9
night), and the total number of boatwhistles pro-
duced for day and night was similar (7,905 day,
6,202 night). Considering the data on a calls-per-
hour basis, since daylight hours exceed nighttime
in June, does not appreciably alter the results. The
fish averaged 41.3 boatwhistles/h during the day
and46.1/h at night from recordings covering 191.5
h of daylight and 134.5 h of darkness. Not only
were crepuscular peaks absent, but dawn and
dusk appeared irrelevant as cues for calling be-
havior. There are similarities between certain
periods in the data, such as the nights of 14 and 15
June for channel 2, but these similarities are a

1 Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

871

CHANNEL S

I I I I I I I I I I I 1 I I I I I I | I I I I I I

JUNE II JUNE It

I I I I I I I I I I I I I I I
JUNE 13

— Mt

1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1"

JUNE 13 JUNE 14

I I I I I I I I I I I I I I I I I I I | ^^^^^^
JUNEI3 JUNE M

'"Uw

1111 I I I I I

JUNE H)

J\H«

I I I I I I I 1 T I t I T I T I I I | n-^^^t^1

«0 -

to -

, , , A^^MW unrn

■ ■■MM

JUNE IS

I I I I I I I I I I I I I TTTTTIITTlfT

I I I I I I I I I I I
JUNE 14

J«fcUL

JUNE 19

a to t4 4

I i i TfvFAfAt r i . i i t r t i t ir l

It 10 H 4 II

FIGURE 1. — Temporal record of boatwhistle production for each of three toadfish. A missing baseline indicates gaps in the record, and

the horizontal line below the baseline indicates the period of darkness.

TABLE 1. — Number of boatwhistles produced during 24-h
periods by three toadfish.
[L is light, D is dark, and dash indicates no data.]

Channel 2

Channel 4

Channel 5

Date

June 9-10

849

951

10-11

890

1.838

2,315

1,103

11-12

2,435

848

13-14

364

14-15

354

355

719

650

—

206

—

Total

1,682

2,567

5,954

2,916

269

719

Periods called

Total D/total L

.53

0.49

2.67

minor feature of the record. Each of the fish pro-
duced different numbers of boatwhistles and exhi-
bited separate patterns of calling (Figures 1, 2;
Table 1) that were not obviously correlated with
each other. One fish (channel 4) boatwhistled
twice as much during the day as at night, while the
other two (channel 2 and 5, respectively) called 1.5
and 2.7 times more at night than during the day.
These ratios from Table 1 change to 2.24, 0.66, and
3.92, respectively when considered on a per-hour
basis.

In order to see how fast individual fish called, we
constructed histograms of the frequency of occur-

872

rence of number of boatwhistles in the 6-min seg-
ments (Figure 2). Even though the distributions
for day and night were statistically different
(Kolmogorov-Smirnoff test), they were combined
in each of these histograms. Since these day-night
differences have already been mentioned and were
inconsistent between fish (Table 1), it seemed
reasonable to present differences between the fish
rather than differences between day and night.

Data from the three channels were combined to
show the calling rate from all boatwhistles re-
corded in this study (Figure 3). It is obvious that
toadfish remain quiet for long periods (Figure 1).
For Figures 2 and 3, all quiet periods of 60 min or
longer were arbitrarily excluded. Still, zeros ac-
counted for close to 207c of all intervals measured
(Figure 3). From the cumulative percent curve
(Figure 3), it is striking how strongly the distribu-
tion is skewed toward the low end. Over 50% of the
intervals measured had «= 1 to 2 boatwhistles/min
(ca. 10 calls/6 min), and over 75% of the intervals
had =£4 to 5 boatwhistles/min. Only 10% of the
intervals contained calls emitted at a rate of 6 or
more per minute. Finally less than 17c of the in-
tervals contained calls emitted at a rate of 10 to
12/min. Although an animal may have called for

60 -

Channel 2

40 -

20 -

lll.ll

ll||||||||||.|,...|.| ... V

■ .li-.a.i..

-H

■ - • i

^"^T

Channel 4

Lll.llll|jJ.llilflJlLlll|lllllllllflb.iiLv^ ^

Channel 5

lll.li.ll. hill. ). ■■ .. ■■

u ~i i r i i 1 1 1 1

0 20 40 60 80

NUMBER OF BOATWHISTLES / 6-MIN UTE INTERVAL

FIGURE 2. — Histogram of frequency of occurrence (i.e.,
"number" on Y-axis) of number of boatwhistles in 6-min inter-
vals (X-axis) for each of three toadfish. Silent periods of an hour
or longer were excluded from the analysis.

many hours (Figure 1), the number of calls fluc-
tuated markedly. High rates of calling were often
strongly peaked, i.e., not maintained for long
periods.

Discussion

The only obvious feature of the data from this
study (Figure 1; Table 1) is its lack of patterning or
predictability. Clearly, the recordings indicate no
diel cycle. While they do not rule out the possibil-
ity of maximal or minimal periods of sound pro-
duction for a toadfish population (Breder 1968), it
appears unlikely that individuals would be syn-
chronized to any great degree. It is difficult to
reconcile these results with the periodicity of the
in-air respiration data of Schwartz and Robinson
(1963) and the impressions of Tavolga (1960) and
Schwartz and Robinson ( 1963) that the toadfish is
basically nocturnal. Squirrelfishes are active at
night, when they are least vocal (Winn et al. 1964;
Salmon 1967; Bright 1972; Bright and Sartori
1972), and likewise toadfish might not have a clear
vocalization rhythm, while maintaining rhythms
for respiration or other functions.

The rate of calling by fish in this study was low.

0 20 40 60 80

NUMBER OF BOATWHISTLES /6-MINUTE INTERVAL

FIGURE 3. — Histogram of frequency of occurrence (left axis) and
cumulative frequency of occurrence (right axis) of number of
boatwhistles in 6-min intervals combined for the three toadfish.
Silent periods of an hour or longer were excluded from the
analysis.

and individuals lapsed into silence for long
periods. This result verifies our experience from
playback studies (Winn 1967, 1972; Fish 1972;
Fish and Offutt 1972); fish were often silent, forc-
ing us to sample many tiles to find a male calling
rapidly enough for use in an experiment. For this
reason preplayback calling rates, equivalent to
control calling rates, were biased upward. From 68
experiments, each with sample sizes ranging be-
tween 11 and 16, Winn's (1972) preplayback data
(recalculated) show a mean of 22.41 ± 4.3 (1 SD)
boatwhistles/3 min, or an average of 7.5 calls/min.
In his initial playback experiments, Winn (1967)
increased the calling rate to an average of 11.46,
11.70, and 11.48 boatwhistles/min by playbacks of
18, 26, and 36 boatwhistles/min. Playbacks of 10
calls/min did not increase calling. Fish (1972)
found that with optimally spaced playbacks, he
could increase their rate to 14 to 16 sounds/min ( 1
call every 3.7 to 4.3 s). He called this pace the
maximum sustained calling rate. Fish's data com-
bined with Winn's indicate that when competing
with other males, the toadfish does not grade his
output uniformly, but follows more of a step func-
tion, i.e., his calling is either facilitated or not. In
one chance encounter Fish ( 1972) observed a male
calling 25 times/min as a female approached his
shelter.

Our fish called considerably below their
capabilities. However, calling rates of 11 and
12/min would suggest that the males were sexu-
ally receptive. It will take more work to establish
what is normal for the toadfish and what abiotic

873

and biological factors control motivation during
the season. An unspawned male and a once-
spawned male guarding eggs, might call at differ-
ent rates. Schwartz (1974) and Lowe (1975) have
indicated spawning peaks, which could be related
to calling motivation. Although calling decreases,
boatwhistles are still emitted after the assumed
mating season (Fine 1976) It is not possible to
accurately place the perud of 9-15 June 1969 in a
spawning peak or lull.

Density within a toadfish population will also
affect sound production since calling fish facilitate
each other. There could also be a tonic facilitation
(Schleidt 1973), so that fish hearing boatwhistles,
even if below the stimulatory rate, would be more
prone to call than would a solitary male. It is also
possible that some populations of toadfish could be
limited by shelter availability for male nesting. At
the dock at Solomons, where these recordings were
made, shelter was provided primarily by our tiles
placed along the dock pilings. Since the area was
largely clear of rocks, tin cans, and boards which
might provide shelter, the density of calling fish in
the experimental area was not high, and we might
not expect a great deal of facilitation.

Acknowledgments

This investigation was supported by the Office
of Naval Research through contract N000 14-68-
A-0215-0003 under project NR 083-165.

Literature Cited
Breder, C. M., Jr.

1968. Seasonal and diurnal occurrences offish sounds in a
small Florida Bay. Bull. Am. Mus. Nat. Hist. 138:327-
378.
BRIGHT, T. J.

1972. Bio-acoustic studies on reef organisms. In B. B.
Collette and S. A. Earle (editors), Results of the Tektite
program: Ecology of coral reef fishes, p. 45-69. Bull. Nat.
Hist. Mus. Los Ang. Cty. 14.
BRIGHT, T. J., AND J. D. SARTORI.

1972. Sound production by the reef fishes Holocentrus
coruscus, Holocentrus rufus, and Myripristis jacobus fam-
ily Holocentridae. Hydro-Lab J. 1:11-20.
FINE, M. L.

1976. Variation of natural and brain-stimulated sounds of
the oyster toadfish Opsanus tau L. Ph.D. Thesis, Univ.
Rhode Island, Kingston, 70 p.

Fish, J. F.

1972. The effect of sound playback on the toadfish. In
H.E. Winn and B. L. Olla (editors), Behavior of marine
animals: current perspectives in research. Vol. 2. Verte-
brates, p. 386-434. Plenum Press, N.Y.
FISH, J. F., AND G. C. OFFUTT.

1972. Hearing thresholds from toadfish, Opsanus tau,

measured in the laboratory and field. J. Acoust. Soc. Am.
51:1318-1321.
FISH, M. P.

1954. The character and significance of sound production
among fishes of the western North Atlantic. Bull. Bing-
ham. Oceanogr. Collect. Yale Univ. 14(3), 109 p.

Gray, G. a., and h. e. winn.

1961. Reproduction ecology and sound production of the
toadfish, Opsanus tau. Ecology 42:274-282.
LOWE, T. P.

1975. Reproductive ecology of oyster toadfish (Opsanus
tau) in Charlestown Pond, Rhode Island. Ph.D. Thesis,
Univ. Rhode Island, Kingston, 120 p.

Salmon, M.

1967. Acoustical behavior of the menpachi, Myripristis
berndti, in Hawaii. Pac. Sci. 21:364-381.
SCHLEIDT, W. M.

1973. Tonic communication: continual effects of discrete
signs in animal communication systems. J. Theor. Biol.
42:359-386.

SCHWARTZ, F. J.

1974. Movements of the oyster toadfish (Pisces: Ba-
trachoididae) about Solomons, Maryland. Chesapeake
Sci. 15:155-159.

Schwartz, F. j., and p. F. Robinson.

1963. Survival of exposed oyster toadfish and biological
clocks. Prog. Fish-Cult. 25:151-154.

TA VOLGA, W. N.

1958. Underwater sounds produced by two species of
toadfish, Opsanus tau and Opsanus beta. Bull. Mar. Sci.
8:278-284.
1960. Sound production and underwater communication
in fishes. In W. E. Lanyon and W. N. Tavolga (editors),
Animal sounds and communication, p. 93-136. Am.
Inst. Biol. Sci. Publ. 7.
WINN, H. E.

1964. The biological significance offish sounds. In W. N.
Tavolga (editor), Marine bio-acoustics, p. 213-231. Perg-
amon Press, N.Y.

1967. Vocal facilitation and the biological significance of
toadfish sounds. In W. N. Tavolga (editor), Marine bio-
acoustics. Vol. 2, p. 283-304. Pergamon Press, N.Y.
1972. Acoustic discrimination by the toadfish with com-
ments on signal systems. In H. E. Winn and B. L. Olla
(editors), Behavior of marine animals: current perspec-
tives in revol. 2. Vertebrates, p. 361-385. Plenum Press,
N.Y.
Winn, H. E., J. A. Marshall, and B. Hazlett

1964. Behavior, diel activities, and stimuli that elicit
sound production and reactions to sounds in the longspine
squirrelfish. Copeia 1964:413-425.

Michael L. Fine

Section of Neurobiology & Behavior
Cornell University
Ithaca, NY 14853

Howard E. Winn

Linda Joest

Paul J. Perkins

Graduate School of Oceanography
University of Rhode Island
Kingston, RI 02881

874

BIOLOGY AND HOST-PARASITE

RELATIONSHIPS OF CYMOTHOA EXCISA

(ISOPODA, CYMOTHOIDAE) WITH THREE

SPECIES OF SNAPPERS (LUTJANIDAE)
ON THE CARIBBEAN COAST OF PANAMA

Although parasitic isopods of the family Cymo-
thoidae have been described from both freshwater
and marine fishes, relatively little is known of
their biology and host-parasite relationships
(Morton 1974). Probably all species of cymothoids
are protandrous hermaphrodites, with the male
larvae settling out of the plankton onto the mouth,
body surface, body cavity, or gills of their host.
After a period of maturation, males of some species
become associated with the buccal cavity where
they undergo a sex change. Both broad and limited
host specificities have been described for members
of the Cymothoidae (Trilles 1964).

Here we comment on the biology and occurrence
of Cymothoa excisa Perty on three sympatric spe-
cies of Caribbean snappers: Lutjanus synagris
(Linnaeus), L. analis (Cuvier), and Ocyurus chry-
surus (Bloch). Host-parasite relationships and in-
festation rates are discussed and evidence is pro-
vided suggesting that this parasite does little, if
any, damage.

Methods and Materials

All specimens were collected along the Carib-
bean coast of the Republic of Panama and the
Canal Zone, near the Smithsonian Tropical Re-
search Institute's Galeta Marine Laboratory.
Samples were taken in sea grass habitats consist-
ing primarily of Thalassia testudinum, using a
4.9-m otter trawl with 1.3-cm bar mesh. Details of
the trawling program and site descriptions are
given in Heck (in press). All material was sorted in
the laboratory and subsequently preserved in 10%
Formalin.1

Fishes from which parasites had been removed
were wet weighed after blotting. Standard lengths
of fishes were measured to the nearest 0.5 mm, and
total lengths and widths of isopods were measured
to the nearest 0.01 mm, using dial calipers. Indi-
vidual isopods were sexed according to the pre-
sence of an appendix masculina on the second
pleopod (males) or from the development of ooste-
gites and presence of larvae (females). The Mon-

1 Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

talenti femininity index |F. I. = W/L x 100, where
W = width and L = length (Montalenti 1941)] was
used for the isopods as a measure of the degree of
transformation from male to female.

Fulton's coefficient of condition [K = W/L3,
where W = wet weight and L = standard length
(Ricker 1971 )] was used to assess the well-being of
fish in relation to the presence or absence of iso-
pods. Values of K were computed for 30 infested
and 30 isopod-free individuals in each of the three
species of snappers, L. synagris, L. analis, and O.
chrysurus. An arc-sin transformation was per-
formed on K values before statistical analyses
were carried out.

Results and Discussion

Cymothoa excisa was found to occur on 4.7%
(32/681) of the L. synagris, 10.5% (16/152) of the
L. analis, and 2.1% (11/527) of the O. chrysurus
collected. Adults of the two snapper genera exhibit
different habitat preferences: members of the
genus Lutjanus prefer near-bottom habitats with
ample cover, while O. chrysurus inhabits the
open-water column above coral reefs. Juveniles of
all three species are commonly associated with sea
grass beds, and it may be during this stage of their
life cycle that infestation occurs. This is suggested
by the occurrence of metamorphosed parasites in
very small fish (20-30 mm SL). In addition, a
linear relationship exists between lengths of the
isopod and those of its host (Figure 1), which
further suggests that fishes are infested early in
life with subsequent growth by both host and
parasite. Six male parasites differed significantly
from this relationship, however, and each of these
occurred jointly (or in triplicate) with a much
larger female. Previously, Bowman (1960) re-
ported that pairs of isopods (Lironeca puhi Bow-
man) were nearly always present in the gill cavity
of the moray eel Gymnothorax eurotus (Abbott). In
our specimens, pairs (or triplicates) were found in
only 6.8% of the parasitized fishes and during sort-
ing no free isopods were found which might have
escaped from the mouth cavity. Unless male
isopods were differentially lost during the trawl-
ing operations, it appears that the population biol-
ogy of cymothoid genera can be quite different.

Several other species of lutjanids collected
showed no indication of isopod infestation. For
example, none of the 53 Lutjanus griseus (Lin-
naeus) nor any of the 19 L. apodus (Walbaum)
contained C. excisa. Differences in habitat prefer-

875

E
E.

i
t—
:

w 10
<

• L. synagns

* O. chrysurus
o L analis

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140
FISH LENGTH (mm)

FIGURE 1. — Relationship between Cymothoa excisa and lutjanid
lengths. Least squares line was fit excluding the six points which
fall far below the cluster of other points. These six points repre-
sent males which occurred jointly with females.

ences may be responsible for the absence of cymo-
thoids on these species. It is also possible that
nonparasitized snapper species are cleaned of
parasites by cleaner fishes and decapod crusta-
ceans on nearby reefs.

All isopods were attached to the tongue and
oriented anteriorly with smaller males positioned
behind females. Some degeneration and possibly
some scar tissue were evident at the base of the
tongue, but not elsewhere in the mouth. The
mouth parts of C. excisa seem adapted for piercing
and sucking and Morton (1974) has postulated
that cymothoids are hemophages. As expected,
females of C. excisa are proportionately wider
than males, and the transition from male to
female appears to occur in the 13- to 19-mm size
range (Figure 2).

Bowman (1960) presented evidence that the
presence of a female suppresses feminity in cooc-
curring males, as expressed by the Montalenti in-
dex. We found just the opposite result: males oc-
curring jointly with females displayed a sig-
nificantly higher average femininity index than
males which occurred alone (Figure 2); U-test,
P<0.01). The reason for this difference is un-
known.

Because C. excisa filled so much of the mouth
cavity of infested snappers, it seemed, a priori,
that the presence of isopod parasites must inter-
fere with feeding. However, several crustacean

families, including Xanthidae {Micropanope sp.,
Pilumnus sp., Panopeus sp.), Porcellanidae (Pet-
rolisthes sp.), Squillidae (Squilla sp.), Penaeidae
(Penaeus sp.), and Alpheidae (Alpheus sp.), were
represented in the gut contents of the infested
snappers. Moreover, there were no significant dif-
ferences between coefficients of condition calcu-
lated for parasitized and unparasitized fish in any
of the three lutjanids (/-test, P = 0.01). Thus it
appears that any harmful effects due to the pre-
sence of parasites are not reflected in either the
ability to capture prey or in overall health, as
measured by K. It is possible, however, that the
presence of isopod parasites may lower fitness by
causing increased mortality during periods of
stress (Keys 1928), by reducing the reproductive
output of infested fish, or by decreasing the ability
of parasitized individuals to avoid predators. Al-
though the requisite data are lacking to test the
first two premises, we were able to test the latter
possibility indirectly using the following reason-
ing: If predation is not selective for parasitized
individuals, then a similar distribution would be
expected for each group. This was tested by assign-
ing both parasitized and nonparasitized individu-
als of all three species to 20-mm (SL) size classes
for all but the largest fish (excluded because of
small sample size). There was no significant dif-
ference between the two groups (x2 = 6.69, P =
0.05).

•

•
•

•

• •
•
• • •

o *

** * * * *?

*• *?
* *?

30
9e;

* * * *

* ^ ******* *

• * * *

*
*

2 4 6 8 10 12 14 16 18 2022 24 26
LENGTH (mm)

FIGURE 2. — Femininity index in Cymothoa excisa. Legend: *
male, • = female, o = male occurring jointly with female, *?
sex indeterminate.

876

On the basis of these results and the data previ-
ously presented, we consider C. excisa to be a rela-
tively benign parasite. This appears to be a gen-
eral characteristic of host-parasite relationships
between cymothoids and fishes, at least in un-
stressed situations (Keys 1928).

Acknowledgments

Specimens of C. excisa were kindly identified by
T. Bowman, U.S. National Museum of Natural
History (USNM), and have been deposited at the
USNM. C. M. Courtney, Marco Ecology Labora-
tory, Marco Island, Fla., sexed the parasites and
analyzed gut contents of parasitized fishes. D. T.
Logan and M. H. Baslow provided comments on
the manuscript.

Literature Cited
Bowman, T. E.

I960. Description and notes on the biology of Lironeca
puhi, n. sp. (Isopoda: Cymothoidae), parasite of the
Hawaiian moray eel, Gymnothorax eurostus (Abbott).
Crustaceana 1:84-91.

Heck, k. l., jr.

In press. Patterns of community organization and popula-
tion dynamics in tropical seagrass i Thalassia testudinum )
meadows. Mar. Biol. (Berl.).

Keys, a. b.

1928. Ectoparasites and vitality. Am. Nat. 62:279-282.
MONTALENTI, G.

1941. Studi sull' ermafroditismo dei Cimotoidi. - I. Eme-
tha audouinii (M. Edw.) e Anilocra physodes (L.). Pubbl.
Stn. Zool. Napoli 18:337-394.
MORTON, B.

1974. Host specificity and position on the host in Nerocila
phaeopleura Bleeker (Isopoda, Cymothoidae). Crusta-
ceana 26:143-148.
RICKER, W. E. (editor).

1971. Methods for assessment offish production in fresh
waters. 2d ed. IBP (Int. Biol. Programme) Handb. 3,
Blackwell Sci. Publ., Oxf. and Edinb., 348 p.
TRILLES, J. -P.

1964. Specificite parasitaire chez les Isopodes
Cymothoidae mediterraneens. Note preliminaire. Vie
Milieu 15:105-116.

MICHAEL P. WEINSTEIN

Lawler, Matusky and Skelly Engineers
Tappan, NY 10983

Kenneth L. heck, jr.

Academy of Natural Sciences of Philadelphia
Benedict Estuarine Research Laboratory
Benedict, MD 20612

FECUNDITY OF THE SOUTHERN NEW

ENGLAND STOCK OF YELLOWTAIL FLOUNDER,

LIMANDA FERRUGINEA

The yellowtail flounder, Limanda ferrunginea, is
an important commercial species to both the New
England and Canadian fishing industries. Accord-
ing to Royce et al. (1959) there are five relatively
distinct stocks of yellowtail flounder with little
migration occurring between them: southern New
England, Georges Bank, Cape Cod, Nova Scotian,
and Grand Bank stocks. Catches have recently
been declining. For example in the southern New
England and Cape Cod stocks (ICNAF (Interna-
tional Commission for the Northwest Atlantic
Fisheries) subarea 5Zw), the number of metric
tons landed per standard fishing day has declined
from 3.5 in 1970 to 1.5 in 1975; the total catch
declining from 24,103 to 5,460 metric tons over the
same period (Cain1).

Pitt (1971) has estimated the fecundity of the
Grand Bank stock (ICNAF Subareas 3L, 3N, 30)
but no other yellowtail flounder fecundity data
have been published. Fecundity may vary from
one stock of flatfish to another, e.g., plaice
(Simpson 1951), so we have analyzed the fecundity
of the southern New England stock of yellowtail
based on 50 fish, and compared these values with
the fecundity estimates of Pitt (1971).

Methods and Materials

Ovaries used for fecundity estimates were col-
lected on 9 and 12 April 1976 from fish landed by
commercial vessels at Point Judith, R.I. Fish were
randomly sampled from the combined catches of
several vessels, and therefore represented a ran-
dom sample of the southern New England popula-
tion. Only ripening ovaries, i.e., ovaries swollen
but eggs not fully developed in size (Scott 1954),
were used thus omitting fish that may have begun
to spawn. Fish were measured to the nearest cen-
timeter total length, and the ovary wet weight was
determined to the nearest 0.1 g. Ovaries were pre-
served in Gilson's fluid as modified by Simpson
(1951) and allowed to remain in this solution for
3-5 mo to facilitate ovarian tissue breakdown.
Otoliths, read independently by each of us, were
used to determine ages. The growth rings were
recognized according to Scott (1954) who also

•Cain, W. L. 1976. Yellowtail flounder tabulations for 1977
assessments. Int. Comm. Northwest Atl. Fish. Working Pap. No.
76/IV/49.

877

demonstrated the validity of the use of otoliths for
the age determination of yellowtail flounder.

Eggs were separated from the ovarian tissue by
washing with a gentle stream of water through a
series of four fine mesh screens (mesh sizes 1.52,
0.98, 0.51, 0.14 mm). After separation the eggs
were placed in a gallon jar and diluted with water
to 3,000 ml. Large samples were first divided using
a plankton splitter and only half of the sample
diluted. The lid of the gallon jar was modified to
hold a 1-ml Hensen-Stemple pipette which ex-
tended approximately 15 cm into the jar. The jar
was then inverted 10 times and the sample taken
before any settling of the eggs occurred. The sub-
sample was placed onto a gridded Petri dish and
the eggs counted with a dissecting microscope. A
minimum of three subsamples were counted for
each fish. The coefficient of variation was com-
puted and ranged from <1 to 18% (mean = 7.5%).
Fecundity \/as estimated by multiplying the mean
number of eggs from the subsamples by 3,000, or
6,000 if the sample had been split.

Results and Discussion

Linear regressions, correlation coefficients (r),
and coefficients of determination (r2) were com-
puted from data transformed to common
logarithms. These were:

F = 0.986L3858 (Figure 1!

r = 0.885, r2 = 0.784

(1)

and fecundity vs. age (t = 4.84, df = 47, PO.001).
Gonad weight, therefore, contributed most to the
variation in fecundity and would be the best
parameter to measure in estimating fecundity.
However, since the relationship between ovary
weight and fecundity varies seasonally, depend-
ing on the stage of development, this conclusion
may be valid only for prespawning fish.

In addition to the 50 pairs of ovaries collected by
us, we estimated the fecundity of 14 fish (lengths
29-46 cm, ages 2-6 yr) from the southern New
England stock collected in 1976 by the Northeast
Fisheries Center, National Marine Fisheries Ser-
vice, NOAA, Woods Hole, Mass. The regression
lines for fecundity vs. length and fecundity vs. age
for these fish were not significantly different
(P>0.25) from our regressions when compared

O 4

o
to

F = . 9857 L 3 95S HOWEL L B KESL ER
r - . 885

TOTAL LENGTH (cm)

F = 240,700A ! 294 (Figure 2) (2)

r = 0.812, r2 = 0.659

FIGURE 1. — Yellowtail fecundity plotted against length. Solid
line is the fitted curve for the southern New England population,
and the dashed line that of the Grand Bank population.

F = 62,150G0678 (Figure 3) (3)

r = 0.941, r2= 0.885

were F, L, A, and G are fecundity (106 eggs/
female), length (centimeters), age (years), and
gonad weight (grams), respectively. In all equa-
tions the slopes were significantly different from
zero (PO.001).

The coefficient of determination for Equation (3)
shows that 88.5% of the variation in fecundity was
related to gonad weight independent of both
length and age. This was more than the variation
related to length alone (78.4%, Equation (D) or
age alone (65.9% , Equation (2)). Furthermore, the
correlation coefficient for fecundity vs. gonad
weight was significantly higher than that for
fecundity vs. length (t = 3.85, df = 47, P <0.001),

5-i
CO

O 4-

r =812

F » 2O550 A '

PITT (1971)

"I
12

AGE (YR)

FIGURE 2. — Yellowtail fecundity plotted against age. Solid line
is the fitted curve for the southern New England population, and
the dashed line that of the Grand Bank population.

878

CO
CD
O 4

fe ■

F; 62,150 Gc
r = .941

0 - ii ii m i ii 1 1 1 n

|inii ii| i i i
0 50 100

i I i i i i i i i i i I t '
200 300

400

OVARY WEIGHT (g)

FIGURE 3. — Yellowtail fecundity plotted against ovary weight,
and the fitted curve for southern New England.

using an analysis of covariance (Snedecor and
Cochran 1967).

We compared our data with those of Pitt (1971)
for the Grand Bank stock (lengths 37-54 cm,
ages 5-12 yr) using analysis of covariance. The
slopes of fecundity vs. length and fecundity vs. age
regression lines were not significantly different
(P>0.25) (Figures 1, 2). This indicates that the
rate with which fecundity increased with both
length and age was not significantly different be-
tween the two populations. However, the inter-
cepts of the fecundity vs. length regressions were
significantly different (F = 8.67; df = 1, 94;
P<0.01), southern New England fish being more
fecund for a given length than Grand Bank fish
(Figure 1). In addition, the intercepts of the fecun-
dity vs. age regressions were significantly differ-
ent (F = 28.87; df = 1,92; P<<0.005) indicating
that southern New England fish were more fecund
for a given age (Figure 2).

There may be several reasons why fecundity is
higher at a given length and age in the southern
New England stock. Several authors including
Hodder (1965), Bagenal (1969), and Tyler and
Dunn (1976) have suggested that both nutrition
and temperature can affect egg production. Little
is known about the type and amount of food avail-
able to the two populations so no speculation can
be made about the possible nutritional effects on
fecundity in this species. Water temperatures in-
habited by the two stocks are different. Southern
New England yellowtail flounder inhabit waters
of 4.9-12.3°C (Royce et al. 1959), while Grand
Bank yellowtail flounder are found at tempera-
tures of -l°to 6.5°C (Pitt 1974). Pitt (1974) found
that the southern New England population grew
faster than the Grand Bank population, probably

due to these warmer temperatures. This acceler-
ated growth rate apparently results in earlier
maturation of the southern New England fish,
50% of the females being mature at 2-3 yr old and
32 cm long (Royce et al. 1959) as compared with
5-6 yr and 37 cm long for Grand Bank females
(Pitt 1970). Simpson (1951) found that faster
growing plaice were more fecund for a given age
and length. Likewise, Pitt (1964) found that in
American plaice of comparable ages, ovaries of
faster growing fish were larger than those of
slower growing individuals, and fecundity was
higher. If the ovaries of the faster growing south-
ern New England yellowtail flounder are larger at
comparable ages and lengths than those of Grand
Bank fish, we would expect southern New Eng-
land fish to be more fecund, as was the case. The
ecological implications of this higher fecundity are
unknown and require further study.

Acknowledgments

We thank Robert Livingstone and Judith Pent-
tila of the Northeast Fisheries Center, NMFS,
NOAA, Woods Hole, who generously provided us
with ovaries and ages of some yellowtail flounder.
Thanks go to T. K. Pitt who provided us with the
raw data necessary to compare the two stocks, and
to S-. B. Saila and W. H. Krueger of the University
of Rhode Island who critically read the manu-
script.

Literature Cited

BAGENAL, T. B.

1969. The relationship between food supply and fecundity
in brown trout Salmo trutta L. J. Fish Biol. 1:167-182.

HODDER, V. M.

1965. The possible effects of temperature on the fecundity
of Grand Bank haddock. Int. Comm. Northwest Atl. Spec.
Publ. 6:515-522.
PITT, T. K.

1964. Fecundity of the American plaice, Hippoglossoid.es
platessoid.es (Fabr.) from Grand Bank and Newfoundland
areas. J. Fish. Res. Board Can. 21:597-612.

1970. Distribution, abundance, and spawning of yellow-
tail flounder, Limanda ferrunginea, in the Newfoundland
area of the northwest Atlantic. J. Fish. Res. Board Can.
27:2261-2271.

1971. Fecundity of the yellowtail flounder [Limanda fer-
ruginea) from the Grand Bank, Newfoundland. J. Fish.
Res. Board Can. 31:1800-1802.

ROYCE, W. F., R. J. BULLER, AND E. D. PREMETZ.

1959. Decline of the yellowtail flounder Limanda ferrun-
ginea off New England. U.S. Fish Wildl. Serv., Fish.
Bull. 59:169-267.
SCOTT, D. M.

1954. A comparative study of the yellowtail flounder from

879

three Atlantic fishing areas. J. Fish. Res. Board Can.
11:171-197.

Simpson, a. C.

1951. The fecundity of the plaice. Fish. Invest. Minist.
Agric. Fish. Food (G.B.), Ser. II, 17(5), 27 p.

Snedecor, G. w., and w. G. Cochran.

1967. Statistical methods. 6th ed. Iowa State Univ.
Press, Ames, 593 p.
TYLER, A. V., AND R. S. DUNN.

1976. Ration, growth, and measures of somatic and organ
condition in relation to meal frequency in winter flounder,
Pseudopleuronectes americanus, with hypotheses regard-
ing population homeostasis. J. Fish. Res. Board Can.
33:63-75.

Department of Zoology
University of Rhode Island
Kingston, RI 02881

Division of Biological Sciences
University of Michigan
Ann Arbor, MI 48109

W. HUNTTING HOWELL

DAVID H. KESLER

structurally with cheesecloth was devised. The
mock fish allowed us to control: total number and
composition of the microbial flora; location of mi-
crobial contamination, e.g., surface or evenly dis-
persed throughout the sample; uniformity of dis-
tribution of microbes from sample to sample; size
and thickness of the samples; and the handling
history and physiological state of the samples.
This system permits the quantitative recovery of
the inoculated microbes by simply melting the
gelatin at 31°-32°C.

This note describes the application of mock fish
in studying the effects of disodium ethylenedi-
amine tetraacetate (EDTA, Fisher Scientific Co.1)
with or without an iodophor (Wyandotte Co.) con-
tained in ice for controlling microbial outgrowth of
a mixture of four Pseudomonas species. This pro-
cedure is not recommended as a means of predict-
ing the effectiveness of an inhibitor on a specific
species of fish. Its role is to screen inhibiting
agents for general effectiveness and to permit a
comparison among them.

"MOCK FISH" METHOD FOR STUDYING
MICROBIAL INHIBITING AGENTS

Materials and Methods

Mixture of Pseudomonas Species

In experiments intended to study the effects of
various agents or conditions on the microbial out-
growth in food products, it is desirable to approach
efficacy similar to those conditions of actual han-
dling and marketing. However, in experiments on
fishery products, when one wishes to find effects of
an agent or condition, the use of whole fish or fish
fillets adds variables to any experimental design
These undesired variables are: variations in the
total microbial population and in the composition
of the microbial flora from fish to fish; different
time intervals and other storage variations in the
handling history offish even from the same catch;
different fillet or sample thicknesses which will
affect the counts per gram ratio from sample to
sample; different physiological conditions, age,
wounds, etc., of the fish which might affect ex-
perimental comparisons; and possible presence of
inherent antibiotics in the substrate. The latter
variable does not permit a separation of the an-
tibiotic effects of the additives from the antibiotic
effects of the substrate.

In order to study what effects agents might ac-
tually have on specific microbial outgrowth in an
efficacious situation, a "mock fish," composed of
gelatin (containing nutrients) and supported

Four Pseudomonas species, previously isolated
from iced fish in our laboratory, were used in these
experiments. Each species of Pseudomonas was
grown in separate Eugon Broth (BBL) test tube
culture for 18 h at 20°C. Then 2 ml from each
culture were pooled and well mixed in a sterile test
tube to prepare an inoculum mixture. From this
mixture 1 ml was inoculated into 1 liter of melted
gelatin medium described below to give an esti-
mated 104 to 105 bacteria/ml of the final prepara-
tion.

Mock Fish Preparation

1 ) Cheesecloth discs were cut to size to fit inside
glass Petri dishes, and then they were cut in half.
The Petri dishes were then sterilized at 121°C for
15 min.

2) Ten milliliters of melted, inoculated 10%
gelatin and 1% Eugon Broth medium were pi-
petted into each sterile Petri dish. A sterile needle
was used to make sure that the cheesecloth disc
halves did not overlap during gelatin solidifica-

1 Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

880

tion. Once solidified, the gelatin in each plate was
cut in half with a sterile needle along the cheese-
cloth division, thus making two mock fish for use
in experimental procedures. The mock fish were
gently pried loose from the Petri dish with the aid
of a sterile spatula or large, blunt forceps and
placed into a beaker containing crushed ice. The
cheesecloth provides ample structural support to
the solidified gelatin.

Preparation of Crushed Ice

To minimize contamination, distilled water,
glassware, ice cube trays, and an ice cube crusher
were sterilized prior to use in the preparation of
solutions and crushed ice. Using distilled water to
minimize the presence of chlorine, minerals, etc.,
the following solutions were prepared: 1) 1%
EDTA; 2) 0.1% EDTA; 3) 1% EDTA plus 1%
CaCl2; 4) 0.1% EDTA plus 1% CaCl; and 5) 0.1%
EDTA plus 10 ppm of Accord (an iodophore man-
ufactured by BASF Wyandotte Corp., Wyandotte,
Mich.).

In order to demonstrate the applicability of this
mock fish method, we tested the effect of EDTA
embedded in ice on typical Pseudomonas species
found associated with iced fish. Interest in EDTA
for use as a microbial inhibitor has been cited by
Levin ( 1967), Winarino et al. (1971), and Maunder
et al.2 The addition of calcium ions was to interfere
with the chelating property of EDTA. The addition
of an iodophor was to observe for a possible greater
effect.

The control ice contained no added ingredients.
These solutions were poured into ice cube trays
and frozen. A hand operated individual ice cube
crusher was used to prepare crushed ice to fill
800-ml beakers. From 8 to 10 mock fish were
placed into each beaker containing crushed ice
and stored at 0°C for the duration of the experi-
ment.

Bacterial Assays

At each time interval (0, 1, 3, 6, and 11 days),
mock fish were removed from each beaker and
placed in a sterile plastic petri dish. The Petri
dishes were floated on a 31°-32°C water bath to
melt the gelatin. Aliquots of the melted, well-

2Maunder, D. T., W. P. Segner, C. F. Schmidt, and J. K. Boltz.
1966. Growth characteristics of Type E Clostridium botulinum
in the temperature range of 34 to 50°F. Annu. Rep. to U.S. At.
Energy Comm. (now ERDA), Contract No. ATI 11-1)1 183.

stirred gelatin were decimally diluted and plated
using Eugon Agar (BBL) with 0.1% yeast extract
(BBL) added. Plates were incubated at 20°C for 5
days prior to counting.

Results and Discussion

The results of the experiments are shown in
Figure 1 . The initial starting population was 4.5 x
104 pseudomonads/ml of gelatin medium. The re-
sulting growth patterns reflect the effect of agents
contained in the ice and melt water. By the 5th
day, melt water entirely surrounded the mock fish
in each beaker. By about the 10th day, the floating
ice composed one-half to one-third of the beaker
contents.

The mock fish held together throughout the ex-
periment with only occasional slivers, not sup-
ported by the cheesecloth, breaking off.

The mock fish method permits an evaluation of
the effects of microbial inhibiting additives, used
singly or in combination, to yield relatively accu-
rate results. Thus, the method may be used to
screen a wide variety of antibiotic systems before
going into efficacy studies. The value of the mock
fish system is that it not only permits a broad
screening of additives, but it also permits one to
determine, in efficacy studies, whether microbial
inhibition is due to additives alone or partly to
substrate antibiotic components such as certain
polypeptides (J. T. R. Nickerson pers. commun.). It
affords a method of controlling some variables
and/or allowing the study of effects upon specific
microorganisms. We have employed versions of

EDTA ■ Ethylenediominetetracetic acid
Co*" = Calcium ions

Control

-O
0.1% EDTA

0.1% EDTA

plus 10 ppm iodophore

_i i i i_

2 3 4 5 6

DAYS

7 8

FIGURE 1. — Survival of Pseudomonas spp. in mock fish.

881

mock fish before in irradiation studies in which we
either embedded the inoculum evenly throughout
the gelatin disc or smeared the same size inoculum
on one surface of the gelatin disc (Green and
Kaylor 1977). The method might be extended to
other applications where some detail or specific
effects are to be elucidated.

From Figure 1 it is obvious that 1% calcium ions
negate the effect of 0.1% EDTA and reduce the
effect of 1% EDTA. An improved effect is noticed
when 10 ppm iodophor is coupled with 0.1%
EDTA, and this was somewhat expected.

The implied conclusion is that 1% EDTA em-
bedded in ice, free of divalent ions, will reduce the
outgrowth ofPseudomonas spoilage organisms on
iced fish and that the inhibitory effect of 0.1%
EDTA combined with 10 ppm iodophor is even
greater. The expected results obtained with the
mock fish supports their reliability for the in-
tended use, but it is not suggested for use as a
substitute for efficacy tests. Therefore, conculsions
regarding the effectiveness of inhibitory additives
for any specific substrate must ultimately be de-
rived from conventional efficacy tests.

Literature Cited
Green, J. H., and J. D. kaylor.

1977. Variations in the microbial log reduction curves of
irradiated cod fillets, shrimp and their respective homo-
genates. Appl. Environ. Microbiol. 33:323-327.
LEVIN, R. E.

1967. The effectiveness of EDTA as a fish preserva-
tive. J. Milk Food Technol. 30:277-283.
WINARINO, F. G., C. R. STUMBO, AND K. M. HAYES.

1971. Effect of EDTA on the germination of and outgrowth
from spores of Clostridium botulinum 62-A. J. Food Sci.
36:781-785.

John H. Green

Northeast Fisheries Center Gloucester Laboratory
Present address: Department of Food Science
Cornell University
Ithaca, NY 14853

LOUIS J. RONSIVALLI

Northeast Fisheries Center Gloucester Laboratory
National Marine Fisheries Service, NOAA
P.O. Box 61
Gloucester, MA 01930

REPRODUCTIVE CYCLE OF

THE PINK SURFPERCH,

ZALEMBIUS ROSACEUS (EMBIOTOCIDAE)

Embiotocids received early attention from
biologists (e.g., Eigenmann 1892) partly because
of the viviparous mode of reproduction displayed
by fishes of this family. The pink surfperch,
Zalembius rosaceus (Jordan and Gilbert), is one of
the' lesser known members of this group. What is
most distinctive about Z. rosaceus as compared
with other embiotocids is the timing of the various
events of its annual reproductive cycle. The pur-
pose of this report is to describe this cycle.

Materials and Methods

Specimens were collected off the coast of south-
ern California at depths ranging from 27 to 33 m.
Samples were taken from Redondo Beach, Los
Angeles County, to San Clemente, Orange
County, Calif. Monthly collections were obtained
from May 1972 to September 1973 and January
and March 1977. Collections were made using
otter trawls from the Occidental College RV Van-
tuna and from the RV Fury II, operated by the
Orange County Board of Education. Specimens
from July, August, and September 1973 were pro-
vided by the Southern California Coastal Water
Research Project. Specimens were also examined
in the ichthyology collection of the Los Angeles
County Museum of Natural History.

The fish were preserved in 10% Formalin.1
Gonads were embedded in paraffin. Histological
sections were cut at 8 /jltti and stained with iron
hematoxylin followed by eosin counterstain.
Gonads were sectioned from the following num-
bers of females: January (7), February (4), March
( 11), April (6), May (5), June (10), July (1), August
(15), September (18); October (3); December (6);
and from 85 males, as shown in Table 1. Sectioned
material was collected in 1973 except that for
May, June, October, and December 1972.

Results and Discussion

The gonadal morphology and histology of Z.
rosaceus closely resembles that of the embiotocids
Cymatogaster aggregata as described by Eigen-

1 Reference to trade names does not imply endorsement by the
National Marine Fisheries Service, NOAA.

882

mann (1892), Turner (1938), and Wiebe (1968) and
Embiotoca jacksoni by Lagios (1965).

The seasonal testicular cycle is summarized in
Table 1. From August to November, testes are
regressed with the seminiferous tubules contain-
ing mainly spermatogonia and Sertoli cells. Tes-
ticular recrudescence (i.e., renewal of the germi-
nal epithelium to start a new cycle) was evident in
December. The testicular cycle was far advanced
in one December male whose testes contained
small clusters of sperm. The major period of sper-
miogenesis (sperm formation) occurred from
March through June (Table 1). Germinal
epithelium was exhausted or greatly reduced in
seminiferous tubules of regressing testes which
were first observed (Table 1) in June males. In
these testes, lumina are typically filled with com-
pact sperm cysts called spermatophores by Wiebe
(1968). Some breeding may conceivably continue
as late as July because residual sperm cysts
lingered into this month in the regressing testes of
three males. While the exact duration of the mat-
ing season is not known for Z. rosaceus, the tes-
ticular cycle seems to indicate that it encompasses
March-June.

Embryos were observed for the first time in
ovarian histological sections from 7 of 15 August
females. The gestation period appears to last
about 5-7 mo as one December and one January
female gave birth while in the otter trawl aboard
ship, and females that had recently given birth, as
well as several that were still gravid, were found
in the January and March 1977 samples. The 23
gravid females that were examined contained a
mean of 3.5 young (range 2-6). A sample of 26
near-term young that were removed from females
during this period averaged 34 mm SL.

There appear to be two trends in the timing of
the reproductive cycles of California embiotocids.
In the first, breeding occurs mainly during au-

tumn with the young being born in spring and
summer. This group includes Amphistichus
argenteus (Carlisle et al. 1960), Brachyistius fre-
natus (Feder et al. 1974), Damalichthys vacca
(Feder et al. 1974), E. jacksoni (Lagios 1965),
Hyperprosopon argenteum Rechnitzer and Lim-
baugh 1952), and H. ellipticum (Feder et al. 1974).
Young of D. vacca may appear as late as October
(Feder et al. 1974). In the second group, breeding
takes place during the summer with parturition
occurring the following spring and summer. This
group includes Amphigonopterus ( = Micrometrus)
aurora, Micrometrus minimus (Hubbs 1921), and
C.aggregata (Bane and Robinson 1970; Shaw etal.
1974).

The timing of the reproductive cycle of Z.
rosaceus with mating in the spring and parturi-
tion in the winter is a pattern clearly distinct from
that currently known for any other California em-
biotocid. The advantages of this type of cycle are
not clear at this time and further studies on the
biology of this species will be necessary.

Acknowledgments

We thank the following persons for aiding in the
collection of specimens: M. James Allen (Southern
California Coastal Water Research Project), John
S. Stephens (Occidental College), Mark Howe
(Orange County Board of Education, Marine
Laboratory), and Michael Hynes (Orange County
Sanitation District, Marine Laboratory). Camm
C. Swift allowed us to examine specimens from the
ichthyology collection of the Los Angeles County
Museum of Natural History. Portions of this paper
are from a Master of Science thesis submitted by
the junior author to the Department of Biology,
Whittier College, on May 1974. We thank A. War-
ren Hanson and Inez M. Hull for their help in the
preparation of this thesis.

TABLE 1. — Monthly samples otZalembius rosaceus showing per-
centage of males in various stages of the testicular cycle.

Spermio-

Partial

Total

Recru-

Month

genesis

regression

descence

Jan.

Feb.

Mar.

Apr.

100

May

100

June

July

100

Aug.

100

Sept

100

Oct.

100

Dec.

Literature Cited
Bane, G., and M. Robinson.

1970. Studies on the shiner perch, Cymatogaster ag-
gregate! Gibbons, in upper Newport Bay, Califor-
nia. Wasmann J. Biol. 28:259-268.

Carlisle, J. G, jr., J. w. Schott, and N. J. abramson.

I960. The barred surfperch (Amphistichus argenteus

Agassiz) in Southern California. Calif. Dep. Fish Game,

Fish Bull. 109, 79 p.
EIGENMANN, C. H.

1892. Cymatogaster aggregatus Gibbons, a contribution to

the ontogeny of viviparous fishes. Bull. U.S. Fish.

Comm. 12:401-478.

883

FEDER, H. M., C. H. TURNER, AND C. LlMBAUGH.

1974. Observations on fishes associated with kelp beds in
southern California. Calif. Dep. Fish Game, Fish Bull.
160, 144 p.
HUBBS, C. L.

1921. The ecology and life-history of Amphigonopterus au-
rora and other viviparous perches of California. Biol.
Bull. (Woods Hole) 40:181-209.
LAGIOS, M. D.

1965. Seasonal changes in the cytology of the
adenohypophysis, testes, and ovaries of the black
surfperch, Embiotoca jacksoni, a viviparous percomorph
fish. Gen. Comp. Endocrinol. 5:207-221.
RECHNITZER, A. B., AND C. LlMBAUGH.

1952. Breeding habits of Hyperprosopon argenteum, a vi-
viparous fish from California. Copeia 1952:41-42.

Shaw, E., J. Allen, and R. Stone.

1974. Notes on collection of shiner perch, Cymatogaster
aggregata in Bodega Harbor, California. Calif. Fish
Game 60:15-22.
TURNER, C. L.

1938. Histological and cytological changes in the ovary of
Cymatogaster aggregatus during gestation. J. Morphol.
62:351-373.
WIEBE, J. P.

1968. The reproductive cycle of the viviparous seaperch,
Cymatogaster aggregata Gibbons. Can. J. Zool.
46:1221-1234.

Stephen R. Goldberg
William C. Ticknor, Jr.

Department of Biology
Whittier College
Whittier, CA 90608

GALLBLADDER LESIONS IN
CULTURED PACIFIC SALMON

This note records observations on a previously un-
reported biliary lesion in the gallbladders of vari-
ous samples of coho, Oncorhynchus kisutch;
chinook, O. tshawytscha; and sockeye, O. nerka,
salmon cultured mainly in Puget Sound, Wash.,
during 1974-76. There were no obvious signs of
distress or physical debilitation in affected fish.
The gallbladders were enlarged and impacted
with an amorphous yellow or white material
which, in some instances, extended into the com-
mon bile duct (Figure 1).

Efforts to prove infectious origin were unsuc-
cessful. No bacteria were consistently isolated
from gallbladder or hepatic tissues and attempts
to demonstrate a viral agent on a chinook cell line
were negative. Possibilities of protozoan or hel-
minth parasitism were discounted after micro-

scopic examination of tissues, gallbladder, and in-
testinal contents.

Normal and impacted gallbladder, liver, and
kidney tissues were fixed in 10% buffered Forma-
lin1 and stained sections were prepared at North-
west and Alaska Fisheries Center (NWAFC),
NMFS, NOAA, Seattle, Wash. Excessive vacuola-
tion of the columnar epithelium was evident in
affected gallbladders (Figure 2). No lesions were
observed in either the livers or kidneys offish with
the gallbladder condition.

Preliminary studies (Table 1) indicate a pre-
dominance of an as yet uncharacterized
mucopolysaccharide material in impacted
gallbladders. Serum bilirubin, cholesterol, and
glucose concentrations of coho salmon with im-
pacted gallbladders were not different from those
found in normal fish.

TABLE 1. — Composition of material in impacted gallbladders in

coho salmon.

Material

Percentage

Solids (dry wl @ 105°C)

Ash

Nitrogen

Reducing sugar (ortho-toluidine method)

30.4
14.2

1.25
11.52

Case History

Impacted gallbladders were first observed in
May 1974, when 25 yearling coho salmon from
saltwater pens in southern Puget Sound were re-
ferred to the disease laboratory at NWAFC
Aquaculture Experiment Station near Manches-
ter, Wash., for diagnosis of an unrelated skin in-
fection (Table 2). The condition was detected in
four separate lots of coho and chinook salmon in
central Puget Sound during the summer growing
season of 1974. In July 1975, the lesion was seen in
a subsample of 250 chinook salmon smolts in a
private freshwater rearing pond in Oregon (Table
2). Several lots of salmon being held for husbandry
and disease research at the Aquaculture Experi-
ment Station have also been found to have this
condition.

Four thousand 0-age coho salmon smolts ( 18-20
g) reared on commercially prepared Oregon Moist
Pellets (OMP) were transferred to saltwater pens
at the Aquaculture Experiment Station in early
August 1976 where they continued to receive the
same ration. Smolts of the same stock (1,000) were

1 Reference to trade names does not imply endorsement of the
National Marine Fisheries Service, NOAA.

884

ApiipJJH^^*^^^^

FIGURE l. — Impacted material can be clearly seen in the gallbladder of affected coho salmon (upper fish). Normal gallbladder (lower

fish) is shown for comparison.

TABLE 2. — Occurrence of impacted gallbaldders in Pacific salmon subsampled from saltwater and freshwater rearing areas.

Date

Species

Age

Feed

No. of

fish
in lot

No. of

fish

examined

Percentage of

fish examined

with gallbladder

anomalies

Environment and site

May 1974

Coho

1 +

OMP'

—

100

Oct. 1974

Coho

1 +

OMP

100.000

100

Oct. 1974

Coho

1 +

OMP

100,000

100

Oct. 1974

Coho

1 +

OMP

100,000

165

Oct. 1974

Chinook

0 +

OMP

100,000

157

July 1975

Chinook

0 +

OMP

50,000

250

Aug. 1975

Sockeye

1 +

OMP

450

Sept 1975

Coho

1 +

OMP

250

160

Nov. 1975

Coho

1 +

OMP

164

Nov. 1975

Coho

1 +

Dry2

9,000

600

Dec. 1975

Chinook

2 +

OMP

Dec. 1975

Coho

2 +

OMP

Dec. 1975

Coho

Natural

Dec 1975

Coho

1 +

OMP

500

200

Jan. 1976

Coho

1 +

SC3

400

Jan. 1976

Coho

1 +

OMP

66,000

Oct. 1976

Coho

1 +

OMP

1,600

120

Oct. 1976

Coho

0 +

OMP

1,000

100

Oct. 1976

Coho

0 +

OMP

4,000

180

Aug.-Oct. 1976

Coho

1 +

Dry

100,000 +

114

Net pens: South Puget Sound

Net pen: Central Puget Sound

Freshwater holding pond: lower Columbia River

Net pen: Research fish, Manchester, Wash

Net pen: Research fish, Manchester

Net pen: Central Puget Sound

Cultured brood stock: Manchester

Cultured brook stock: Manchester

Mature fish returning from sea: Manchester

Freshwater station: Seattle, Wash

Freshwater station: Seattle

Net pen: Research fish, Manchester

Freshwater station: Seattle

Net pen: Research fish, Manchester

Net pen4: Central Puget Sound

'Oregon Moist Pellet — Commercial product.
2Commercial dry pelleted ration.

3Fish fed experimental OMP diet containing single cell protein.
4Pers. commun., D. Weaver, Domsea Farms, Gorst, Wash.

885

FIGURE 2. — Upper photo shows histopathologic features ( vacuolation) of the epithelium from an impacted gallbladder of
a small coho salmon cultured in saltwater. Lower photo shows normal epithelium of the gallbladder from a small wild
coho salmon collected in saltwater. Hematoxylin-eosin stain; x320.

886

held back for freshwater rearing. Approximately
38^ of the fish in saltwater were found to have the
gallbladder condition by mid-October. The condi-
tion did not develop in those remaining in fresh-
water.

In all cases observed thus far, affected fish were
young ( <2 yr) salmon that had been reared exclu-
sively on commercially prepared pellets. With the
exception of the occurrence in Oregon, all cases of
the abnormality have occurred in saltwater net
pens.

With dietary adjustments the condition is ap-
parently reversible. In an unrelated nutrition
study, 757c of the subsamples of one lot of 1,800
coho salmon that had been fed a ration of OMP for
several months had impacted gallbladders. These
test fish were divided into two lots. One group
(1,400) was fed a laboratory prepared moist pellet
diet and the remaining fish (400) were continued
on the commercial OMP diet. After 4 mo, subsam-
ples indicated that incidence of abnormal
gallbladders in fish on the laboratory diet had
been reduced to 5%. Incidence of the condition in
the test group maintained on the OMP diet re-
mained at 759c.

Discussion

I have found no published information relative
to gallbladder abnormalities in fishes. The
pathological features described for this condition
do not resemble any infectious disease currently
described for fishes and are more suggestive of a
toxic or nutritional disorder.

The biliary system is an integral part of the
digestive apparatus, playing an important role in
lipid digestion. It also provides a mechanism for
recycling certain metabolic byproducts of hepatic
origin through the digestive system. Many of
these metabolic byproducts are excretory wastes
while others can be salvaged for reuse by rediges-
tion. Studies as yet do not prove a major detrimen-
tal effect of this condition on the fish. Knowing the
importance of the biliary system, however, it is
inconceivable that it does not have an adverse
effect on the animals' nutritional status, particu-
larly in relation to systems dependent upon
adequate and diverse lipid supply.

Acknowledgments

I thank Kenneth Pierce; graduate student, Uni-
versity of Washington, Seattle; for preparing the

gallbladder specimens for histological examina-
tion.

Lee W. Harrell

Northwest and Alaska Fisheries Center
National Marine Fisheries Service, NOAA
2725 Montlake Boulevard East
Seattle. WA 98112

TIMING OF THE SURFACE-TOBENTHIC

MIGRATION IN JUVENILE ROCKFISH,

SEBASTES DIPLOPROA, OFF

SOUTHERN CALIFORNIA

Species of the genus Sebastes lead a pelagic exis-
tence as larvae, transforming to pelagic pre-
juveniles and finally benthic juvenile stages at
varying sizes (Moser 1967, 1972). Pelagic pre-
juveniles of some species often congregate under
drifting objects (Hitz 1961); off the coast of south-
ern California, Sebastes diploproa (Gilbert 1890)
is the dominant rockfish species found under drift-
ing kelp ( Mitchell and Hunter 1 970). Adults of this
species inhabit a bathymetric range of 91-578 m
and a latitudinal range from Alaska to Baja
California (Hart 1973). Little is known about the
movement of this rockfish from surface to benthic
waters. This paper provides information on the
disappearance from surface waters and the ap-
pearance in the benthic habitat based on seasonal
size distribution from the two habitats.

Materials and Methods

Surface prejuveniles were collected by dip net
off San Diego, Calif, (lat. 32°52'N, long.
117°30'W), from beneath drifting kelp (primarily
Macrocystis pyrifera) during 1975 and 1976.
Benthic juveniles were sampled in standard
10-min bottom trawls with a 7.6-m (25-ft) otter
trawl (12.7-mm stretch mesh cod end liner) in
1972 through 1976. Most trawls were made in and
around the Los Angeles Bight from Point Dume
(lat. 34WN, long. 118°48'W) to Dana Point (lat.
33°28 'N, long. 117°43'W) at depths from 92 to 183
m, although small S. diploproa were captured as
shallow as 46 m. This does not encompass the
entire adult bathymetric range, but younger
stages of Sebastes generally tend to occupy shal-
lower parts of the adult range (Kelly and Barker
1961; Moser 1967, 1972; Westrheim 1970). Only

887

those trawls containing one or more specimens of
S. diploproa were considered, a total of 96 trawls.

Results

Surface dip net collections consisted of 873 pre-
juveniles, the largest of which was 58.7 mm stan-
dard length (SL). A total of 2,418 benthicjuveniles
were taken in the trawl collections, with the fol-
lowing size breakdown: <30mm, 2; 30-39 mm, 84;
40-49 mm, 892; and 50-59 mm, 1,440. Few pre-
juveniles larger than 50 mm SL were captured in
surface collections (Figure 1); thus they appear to
settle out at a size under 50 mm. At this size
prejuveniles are about 1 yr old according to
laboratory growth measurements (unpublished
data) and the growth curve determined by Phillips
(1964); this is well within the range of published
values for other members of the genus. Age of
settlement has been estimated to be 6 mo for S.

~~**\ A,

CO 5

n
10
5

10
5

15
10
5

" r^ rp

DEC (43)

AW,

_2 8_S_

i r

r~~A

r~M f»./

rt.ri

I 1 rN

n A n r* /V*!

f I

■f^A

' 1 —

.r^Av^N

1M A »-<

.r~*Vi /Vs

NOV (35)

— I

OCT (53)

SEP (63)

AUG (84)

JUL (36)

JUN (50)

MAY (98)

APR (65)

AvfH

MAR (194)

M«

"f^-

FEB (64)

JAN (88)

I n 1 1 1 1 1 r

10 20 30 40 50

STANDARD LENGTH (mm)

FIGURE 1. — Monthly size distribution for surface prejuvenile
Sebastes diploproa from the combined dip net collections of
1975-76. Parenthetical numbers indicate numbers of fish col-
lected in that month.

umbrosus (Chen 1971), 4 or 5 mo for S. marinus
(Kelly and Barker 1961), and 6-12 mo for S.
alutus (Westrheim 1973; Carlson and Haight
1976).

Female S. diploproa are ovoviviparous, releas-
ing yolk sac larvae from February to July off
California (Phillips 1964). The abundance of
newly transformed prejuveniles (10-14 mm SL) in
August through December indicates that the prin-
cipal parturition season occurred in the latter part
of this interval (Figure 1). The presence of small
individuals in February and March, however, may
indicate that there were two principal parturition
seasons. Westrheim (1975) provided evidence for
two parturition seasons in 1973 off British Colum-
bia (July and October-December) and suggested
that this species might release larvae throughout
the year.

Surface prejuveniles in the correct size category
for settlement were present throughout the year
but their abundance was greatest in late spring to
early summer. The percentage of specimens larger
than 40 mm SL peaked in May and dropped off
rapidly thereafter (Figure 2), suggesting that
emigration from surface waters occurred primar-
ily in May and June. For comparison, seasonal
abundance of pelagic prejuveniles of three other
Sebastes species are shown (Figure 3). Emigration
from surface waters occurred in January to Feb-
ruary for S. rubrivinctus , May to June for S.
paucispinis , and July to August for S. serriceps.

Benthic juvenile S. diploproa occurred in a
highly clumped distribution (variance exceeded
mean number offish per trawl for all months with
more than one trawl). Since several months were
undersampled or lacked a sufficient number of
trawls, data were combined by 2-mo intervals
(Figure 4). Small benthicjuveniles first appeared
in July-August; abundance peaked in
November-December and tapered off thereafter.

JAN ' FEB ' MAR ' APR T MAY ' JUN ' JUL ' AUG ' SEP ' OCT ' NOV DEC

MONTH

FIGURE 2. — Percentage of surface prejuvenile Sebastes diplop-
roa >40 mm SL from the combined dip net collections of 1 975-76.

888

ioor

S; rubrivinctus
^ poucispims
S. semceps

FIGURE 3. — Monthly abundance of surface prejuveniles of
Sebastes rubrivinctus, S. paucispinis, and S. serriceps from the
combined dip net collections of 1975-76.

40r—

5*20

1-5

CD ~
<

JUL/AUG [ SEP/OCT | NOV/DEC 1 JAN/FEB | MAR/APR |MAY/JUN | JUL/AUG I
(3) (13) (29) (6) (12) (33) (3)

INTERVAL

FIGURE 4. — Bimonthly abundance ( number caught per trawl ) of
benthic juvenile Sebastes diploproa from trawl collections of
1972 through 1976. Circles represent abundance of all specimens
<50 mm; triangles, all <60 mm. Parenthetical numbers indicate
the number of trawls made per interval.

Discussion

Surface size distribution and abundance data
indicate that the bulk of emigration from the sur-
face occurred in late spring to early summer (Fig-
ures 1, 2), whereas appearance of benthic juveniles
began in midsummer and continued over a period
of several months (Figure 4). The temporal dis-
crepancy between disappearance from the surface

and peak benthic appearance suggests that mig-
rant juveniles may occupy an intermediate
habitat between emigration and settlement. Dur-
ing this period, the juveniles are probably in mid-
water, as shown for S. macdonaldi by Moser
(1972). Four specimens of S. diploproa have been
taken in two discrete-depth midwater trawls by
the RV Velero IV and are presently in the fish
collection of the Natural History Museum of Los
Angeles County (LACM). Three of these speci-
mens (43, 47, 48 mm SL) were captured in October
1970 at a depth of 250 m off San Clemente Island
(lat. 32°39'N, long. 118°11'W; LACM 36315-1);
the fourth specimen (43 mm SL) was taken in
December 1970 at a depth of 200 m off Santa
Catalina Island (lat. 33°21'N, long. 118°46'W;
LACM 36307-1). Both tows were taken between
0200 and 0430 (local time) over bottom depths of
1,915 and 1,280 m, respectively. Since these bot-
tom depths greatly exceed the bathymetric range
for S. diploproa, time may be spent in horizontal
movement to benthic habitat of suitable depth.
Early migrants may come from nearshore areas,
such as those sampled in the dip net collections,
whereas those appearing later in the year may
come from offshore prejuvenile populations; larval
Sebastes are known to be distributed hundreds of
kilometers offshore (Ahlstrom 1961).

Southern California is near the southern end of
the geographic range for S. diploproa (Phillips
1964); no information was available on the surface
prejuveniles of this species from the center or
northern parts of its range. Extension of the tim-
ing of emigration and subsequent appearance in
the benthic habitat is probably a direct result of
the long parturition season off California. Westr-
heim (1975) has shown that two parturition sea-
sons may occur per year off British Columbia and
has suggested that limited year-round spawning
may take place. In general, however, as one goes
further north, the principal parturition season is
progressively shorter and later; off Oregon, the
season is mid-May to June (Hitz 1962), June to
July off Washington ( DeLacy et al. 1964), and July
off British Columbia (Westrheim 1975). I would
expect surface prejuvenile year classes to be more
distinct in the north than shown in my data (Fig-
ure 1), and that timing of emigration from surface
waters would be more precise.

Acknowledgments

I thank M. J. Allen of the Southern California

889

Coastal Water Research Project for supplying the
compiled data on benthic trawled samples. H. G.
Moser and R. Lavenberg kindly provided informa-
tion on the midwater specimens. This work was
supported in part by the Hubbs-Sea World Re-
search Institute and by a Sigma Xi Grant-in- Aid of
Research.

Literature Cited

AHLSTROM. E. H.

1961. Distribution and relative abundance of rockfish
(Sebastodes spp.) larvae off California and Baja Califor-
nia. Rapp. P.-V. Reun. Cons. Perm. Int. Explor Mer
150:169-176.

CARLSON, H. R., AND R. E. HAIGHT.

1976. Juvenile life of Pacific ocean perch, Sebastes alutus ,
in coastal fiords of southeastern Alaska: Their environ-
ment, growth, food habits, and schooling be-
havior. Trans. Am. Fish. Soc. 105:191-201.

Chen, l.-C.

1971. Systematics, variation, distribution, and biology of
rockfishes of the subgenus Sebastomus (Pisces, Scor-
paenidae, Sebastes). Bull. Scripps Inst. Oceanogr. 18,
115 p.
DELACY, A. C, C. R. HITZ, AND R. L. DRYFOOS.

1964. Maturation, gestation, and birth of rockfish (Sebas-
todes) from Washington and adjacent waters. Wash.
Dep. Fish., Fish. Res. Pap. 2(3):51-67.

Hart, J. L.

1973. Pacific fishes of Canada. Fish. Res. Board Can.,

Bull. 180, 740 p.
HITZ, C. R.

1961. Occurrence of two species of juvenile rockfish in

Queen Charlotte Sound. J. Fish. Res. Board Can.

18:279-281.

1962. Seasons of birth of rockfish {Sebastodes spp.) in Ore-
gon coastal waters. Trans. Am. Fish. Soc. 91:231-233.
KELLY, G. F., AND A. M. BARKER.

1961. Vertical distribution of young redfish in the Gulf of
Maine. Rapp. P.-V. Reun. Cons. Perm. Int. Explor. Mer
150:220-233.
MITCHELL, C. T., AND J. R. HUNTER.

1970. Fishes associated with drifting kelp, Macrocystis
pyrifera, off the coast of southern California and northern
Baja California. Calif. Fish Game 56:288-297.
MOSER, H. G.

1967. Reproduction and development of Sebastodes
paucispinis and comparison with other rockfishes off
southern California. Copeia 1967:773-797.

1972. Development and geographic distribution of the
rockfish, Sebastes macdonaldi (Eigenmann and Beeson,
1893), family Scorpaenidae, off southern California and
Baja California. Fish. Bull., U.S. 70:941-958.

PHILLIPS, J. B.

1964. Life history studies on ten species of rockfish (genus
Sebastodes). Calif. Dep. Fish Game, Fish Bull. 126, 70 p.
WESTRHEIM, S. J.

1970. Survey of rockfishes, especially Pacific ocean perch,
in the northeast Pacific Ocean, 1963-1966. J. Fish. Res.
Board Can. 27:1781-1809.

1973. Age determination and growth of Pacific ocean perch
(Sebastes alutus) in the northeast Pacific Ocean. J. Fish.
Res. Board Can. 30:235-247.

1975. Reproduction, maturation, and identification of lar-
vae of some Sebastes (Scorpaenidae) species in the north-
east Pacific Ocean. J. Fish. Res. Board Can. 32:2399-2411.

George W. boehlert

Scripps Institution of Oceanography
University of California, San Diego
P.O. Box 109
La Jolla, CA 92093

890

INDEX

Fishery Bulletin Vol. 75, No. 1-4, 1977

Abralia trigonura

bioluminescence, intensity regulation of during coun-
tershading 242

Abraliopsis sp.

bioluminescence, intensity regulation of during coun-
tershading 243

"Abundance and potential yield of the Atlantic thread
herring, Opisthonema oglinum, and aspects of its early
life history in the eastern Gulf of Mexico," by Edward D.
Houde 493

"Abundance and potential yield of the round herring,
Etrumeus teres, and aspects of its early life history in the
eastern Gulf of Mexico," by Edward D. Houde 61

"Abundance and potential yield of the scaled sardine,
Harengulajaguana, and aspects of its early life history in
the eastern Gulf of Meixco," by Edward D. Houde .... 613

Acartia clausii

Oregon coast, central

seasonal cycle of abundance 717

Acartia longiremis
Oregon coast, central

seasonal cycle of abundance 717

Age determination

methods, analysis of for rockfish off Oregon

age composition 410

age-length relationship 411

consistency of readings 407

otolith method, validity 409

otolith sections 410

suitability of structures 407

survival 411

AGEGIAN, CATHERINE R.— see PEARSE et al.

Alaska
salmon

income estimates and reasonable returns 483

Albacore — see Tuna, albacore

"American solenocerid shrimps of the genera
Hymenopenaeus, Haliporoides, Pleoticus, Hadropenaeus
new genus, and Mesopenseus new genus," by Isabel Perez
Farfante 261

"Analysis of age determination methods for yellowtail
rockfish, canary rockfish, and black rockfish off Oregon,"
by Lawrence D. Six and Howard F. Horton 405

Anchovy, northern
larval
relative nutritional value of the dinoflagellates
Gymnodinium splendens and Gonyaulax polyedra 577

various species of phytoplankton as food for 577

"Annual fluctuations in biomass of taxonomic groups of
zooplankton in the California Current, 1955-59," by J. M.
Colebrook 357

Antilles Current
velocity and transport northeast of the Bahama Is-
lands 222

Argopecten gibbus — see Scallop, calico

ARTHUR, DAVID K., "Distibution, size, and abundance
of microcopepods in the California Current system and
their possible influence on survival of marine teleost
larvae" 601

Atlantic Ocean, southeastern tropical

oxycline characteristics 857

skipjack tuna distribution 857

AUSTIN, C. BRUCE, "Incorporating soak time into
measurement of fishing effort in trap fisheries" 213

Bahama Islands

Antilles Current, velocity and transport northeast of

Bairdiella chrysoura

York River estuary, Virginia
life history, feeding habits, and functional mor-
phology of juveniles

222

Baja California, Mexico
whale, gray
behavior of California

"Behavior of California gray whale, Eschrichtius robus-
tus, in southern Baja California, Mexico," by Kenneth S.
Norris, Robert M. Goodman, Bernardo Villa-Ramirez,
and Larry Hobbs

657

159

Benzene

herring, Pacific

effects on spawning

159

BERGTOLD, GLENN E.— see MORROW et al.

"(A) bioenergetic model for the analysis of feeding and
survival potential of winter flounder, Pseudopleuronectes

891

americanus, larvae during the period from
hatching to metamorphosis," by Geoffrey C. Laurence 529

"Biology and host-parasite relationships of Cymothoa
excisa (Isopoda, Cymothoidae) with three species of
snappers (Lutjanidae) on the Caribbean coast of
Panama," by Michael P. Weinstein and Kenneth L. Heck 875

"Biology of offshore hake, Merluccius albidus, in the Gulf

of Mexico," by Bennie A. Rohr and Elmer J. Gutherz 147

"Biology of rex sole, Glyptocephalus zachirus, in waters

off Oregon," by Michael J. Hosie and Howard F. Horton 5 1

"Biology of the summer flounder, Paralichthys dentatus,
in Delaware Bay," by Ronal W. Smith and Franklin C.
Daiber 823

Bioluminescence
animals, intensity regulation in midwater

Abralia trigonura 242

Abraliopsis sp 243

Crytopsaras couesi 247

Enoploteuthis sp 245

Heteroteuthis hawaiiensis 247

Octopoteuthis nielseni 246

Oplophorus gracilirostris 248

Pterygioteuthis microlampas 244

Pyroteuthis addolux 245

Biomass

finfish and squid
changes in, Gulf of Maine to Cape Hatteras, 1963-74 1

"Body size and learned avoidance as factors affecting
predation on coho salmon, Oncorhynchus kisutch, fry by
torrent sculpin, Cottus rhotheus," by Benjamin G. Patten 457

BOEHLERT, GEORGE W., "Timing of the surface-to-
benthic migration in juvenile rockfish, Sebastes diplop-
roa, off southern California" 887

Brazil

U.S. shrimp fishery off, 1972-74 703

Brevoortia tyrannus — see Menhaden, Atlantic

BROWN, BRADFORD E— see CLARK and BROWN

BUTLER, JOHN L.— see ROSENBLATT et al.

Cadmium
cunner, long-term stress in 199

Calanus marshallae
Oregon coast, central
seasonal cycle of abundance 717

California
blue shark

diel behavior near Santa Catalina Island 519

red sea urchin

localized mass mortality 645

California, central and northern
crab, Dungeness
egg mortalities in wild populations 235

California, southern
rockfish, juvenile

migration, timing of surface to benthic 887

California Current
microcopepods

distribution, size, and abundance 601

survival of marine telost larvae, influence on .... 601
zooplankton

biomass, annual fluctuations, 1955-59 357

Cancer magister — see Crab, Dungeness

Capture data
simplification for the study offish populations 561

Caribbean coast

snapper, host-parasite relationship with Cymothoa ex-
cisa 875

CARLINE, ROBERT F., "Production by three popula-
tions of wild brook trout with emphasis on influence of
recruitment rates" 751

"Changes in biomass of finfishes and squids from the Gulf
of Maine to Cape Hatteras, 1963-74, as determined from
research vessel survey data," by Stephen H. Clark and
Bradford E. Brown 1

CHAO, LABBISH N., and JOHN A. MUSICK, "Life his-
tory, feeding habits, and functional morphology of
juvenile sciaenid fishes in the York River estuary, Vir-
ginia"

Chesapeake Bight
crab, red
reproductive biology of female

657

Chionoecetes bairdi — see Crab, snow

CHITTENDEN, MARK E., Jr.

TENDEN

-see WHITE and CHIT-

"Chlorinated hydrocarbons in Dover sole, Microstomas
pacificus: Local migrations and fin erosion," by D. J.
McDermott-Ehrlich, M. J. Sherwood, T. C. Heeson, D. R.
Young, and A. J. Mearns 513

Christmas Island
sea-surface temperatures, 1954-73 767

Clam, soft-shell

salinity acclimation 225

Clam, surf
Virginia

useable meat yields 640

CLARK, STEPHEN H., and BRADFORD E. BROWN,
"Changes in biomass of finfishes and squids from the Gulf

892

of Maine to Cape Hatteras, 1963-74, as determined from
research vessel survey data" 1

CLIFFORD, DAVID A— seeCREASER and CLIFFORD

Clupea harengus pallasi — see Herring, Pacific

"Coastal and oceanic fish larvae in an area of upwelling
off Yaquina Bay, Oregon," by Sally L. Richardson and
William G. Pearcy 125

Cobalt-60
albacore, content in
source and migration estimates on west coast .... 867

COLEBROOK, J. M., "Annual fluctuations in biomass of
taxonomic groups of zooplankton in the California Cur-
rent, 1955-59" 357

COLLINS, JEFF, and RICHARD D. TENNEY, "Fishery
waste effluents: A suggested system for determining and
calculating pollutant parameters" 253

Columbia River

cobalt-60 content

contamination source for albacore off west coast 867

estuary, 1973
species composition and relative abundance of larval
and post-larval fishes 218

"Comparisons of catches of fishes in gill nets in relation to
webbing material, time of day, and water depth in St.
Andrew Bay, Florida," by Paul J. Pristas and Lee Trent 103

"(A) compartmentalized simulation model of the South-
ern New England yellowtail flounder, Limanda fer-
ruginea, fishery," by Michael P. Sissenwine 465

COOK, STEVEN K.— see INGHAM et al.

Cope pods

Oregon coast, central

seasonal cycle of abundance 717

Coregonus nelsoni — see Whitefish, Alaska

COSTA, DANIEL P.— see PEARSE et al.

Cottus rhotheus — see Sculpin, torrent

"Courtship and spawning behavior of the tautog,
Tautoga onitis (Pisces: Labridae), under laboratory con-
ditions," by Bori L. Olla and Carol Samet 585

Crab, Dungeness

California, central and northern

egg mortalities in wild populations 235

Crab, red

reproductive biology of female, Chesapeake Bight

abdomen width changes 99

copulation, physical evidence 96

ovarian development incidence 96

ovaries, redeveloping 96

ovary development 92

ovigerious females 96

size at sexual maturity 96

vulvae changes 99

Crab, snow

mature male, length-width-weight relationships . . . 870
megalopa description 459

Crab, spider
larval development

laboratory-reared and planktonic, described and
compared 831

Crabs

Puget Sound, Washington
zoeae, short-term thermal resistance of 10 species 555

CREASER, EDWIN P., Jr., and DAVID A. CLIFFORD,
"Salinity acclimation in the soft-shell clam, Mya
arenaria" 225

Croaker, Atlantic

age determination, reproduction, and population

dynamics

age determination growth 113

habitat segregation between age groups 119

size, maximum, and age, life span, and mortality

rate 119

somatic weight variation 112

spawning 110

total weight-length and girth-length relationships 120

Crytopsaras couesi

bioluminescence, intensity regulation of during coun-
tershading 247

Ctenocalanus vanus
Oregon coast, central

seasonal cycle of abundance 717

Cunner
cadmium, long-term stress

chemical uptake 202

enzyme activity 201

mortality and respiration 200

Cymothoa excisa

biology and occurrence on three species of snappers 875

Cynoscion nebulosus

York River estuary, Virginia
life history, feeding habits, and functional morphol-
ogy of juveniles 657

Cynoscion regalis

York River estuary, Virginia
life history, feeding habits, and functional morphol-
ogy of juveniles 657

DAIBER, FRANKLIN C— see SMITH and DAIBER

Delaware Bay
flounder, biology of summer

age, growth, food habits, and racial characters .

823
893

"Description of larval and early juvenile vermilion snap-
per, Rhomboplites aurorubens," by Wayne A. Laroche 547

"Description of megalopa of snow crab, Chionoecetes
bairdi (Majidae, subfamily Oregoniinae)," by Stephen C.
Jewett and Richard E. Haight 459

Desmodema — see Ribbonfish

DeWITT, HUGH H., "A new genus and species of eelpout
(Pisces, Zoarcideae) from the Gulf of Mexico" 789

"Diel behavior of the blue shark, Prionace glauca, near
Santa Catalina Island, California," by Terry C. Sciar-
rotta and Donald R. Nelson 519

Dinoflagellates
nutritional value of two species for larval northern
anchovy 577

"Distribution and duration of pelagic life of larvae of
Dover sole, Microstomas pacificus; rex sole, Glyptocepha-
lus zachirus; and petrale sole, Eopsettajordani, in waters
off Oregon," by William G. Pearcy, Michael J. Hosie, and
Sally L. Richardson 173

"Distribution size, and abundance of microcopepods in
the California Current system and their possible
influence on survival of marine teleost larvae," by David
K. Arthur 601

DIZON, ANDREW E., "Effect of dissolved oxygen con-
centration and salinity on swimming speed of two species
of tunas" 649

Dogfish, spiny

Pacific Ocean, northeast
mercury in 642

Dolphin, eastern spinner
Pacific Ocean, eastern tropical

growth and reproduction 725

Dolphin, spotted

Pacific Ocean, eastern tropical
gross annual reproductive rates compared with es-
timates for eastern spinner dolphin, 1973-75

reproductive parameters, 1973-75

725
629

DOTSON, RONALD C— see SHARP and DOTSON

DRAGOVICH,
DRAGOVICH

ALEXANDER— see JONES and

Eelpout
Gulf of Mexico

new genus and species described and figured

"Effect of dissolved oxygen concentration and salinity on
swimming speed of two species of tunas," by Andrew E.
Dizon

"Effects of benzene (a toxic component of petroleum) on

789

649

spawning Pacific herring, Clupea harengus pallasi," by
Jeanette W. Struhsaker 43

"Egg mortalities in wild populations of the Dungeness
crab in central and northern California," by William S.
Fisher and Daniel E. Wickham 235

"Energy for migration in albacore, Thunnus alalunga,"

by Gary D. Sharp and Ronald C. Dotson 447

Engraulis mordax — see Anchovy, northern

Enoploteuthis sp.

bioluminescence, intensity regulation of during coun-
tershading 245

Eopsetta jordani — see Sole, petrale

Eschrichtius robustus — see Whale, gray

Etrumeus teres — see Herring, round

Exechodontes daidaleus — see Eelpout

"Fecundity of the southern New England stock of yellow-
tail flounder, Limanda ferruginea," by W. Huntting
Howell and David H. Kesler 877

"Feeding by Alaska whitefish, Coregonus nelsoni, during
the spawning run," by James E. Morrow, Eldor W. Schal-
lock, and Glenn E. Bergtold 234

FINE, MICHAEL L., HOWARD E. WINN, LINDA
JOEST, and PAUL J. PERKINS, "Temporal aspects of
calling behavior in the oyster toadfish, Opsanus tau" . 871

Finfishes
Gulf of Maine to Cape Hatteras, 1963-74
biomass changes as determined from research vessel
survey data 1

"First record of a second mating and spawning of the spot
prawn, Pandalus platyceros, in captivity," by John E.
Rensel and Earl F. Prentice 648

Fish
identification

thin-layer polyacrylamide gel isoelectric focusing 571

"mock," for studying microbial inhibiting agents . . . 880

Fish larvae

coastal and oceanic off Yaquina Bay, Oregon

assemblage, coastal 133

assemblage, offshore 138

comparison of coastal and Yaquina Bay larvae . . . 141

comparison to northeast Pacific 143

comparison with other planktonic components . . . 142

distribution, coastal and offshore 139

distribution, vertical 130

sampling variability 128

taxonomic problems 128

Columbia River estuary, 1973

species composition and relative abundance 218

894

flounder, winter

analysis of feeding and survival potential, bio-
energetic model for 529

marine teleost, California Current

microcopepod influence on survival 601

menhaden, Atlantic

larval transport and year-class strength 23

Oregon, distribution and duration of pelagic life in
waters off

sole, Dover 173

sole, petrale 173

sole, rex 173

snapper, vermilion

description of 547

various species of phytoplankton as food for larval an-
chovy 577

Fish schools, pelagic
photographic method for measuring spacing and den-
sity within at sea 230

FISHER, WILLIAM S., and DANIEL E. WICKHAM,
"Egg mortality in wild populations of the Dungeness crab
in central and northern California" 235

Fisheries, trap

soak time, incorporating into measurement of fishing
effort 213

Fishery products
"mock fish," for studying microbial inhibiting agents 880

"Fishery waste effluents; A suggested system for deter-
mining and calculating pollutant parameters," by Jeff
Collins and Richard D. Tenney 253

Fishes

Columbia River estuary, 1973

species composition and relative abundance of larval

and post-larval 218

estuarine and coastal, St. Andrew Bay, Florida

gill net selectivity 185

gill net catches, St. Andrew Bay, Florida

depth zone comparison 105

net damage 107

time of day comparison 105

webbing material comparison 104

"Fishes, macroinvertebrates, and their ecological inter-
relationships with a calico scallop bed off North
Carolina," by Frank J. Schwartz and Hugh J. Porter . 427

Fishing effort
trap fisheries

soak time, incorporating into measurement 213

Flounder, summer

biology, Delaware Bay

age, growth, food habits, and racial characters

823

Flounder, winter
larvae

analysis of feeding and survival potential,
bioenergetic model for 529

Flounder, yellowtail
New England, southern

compartmentalized simulation model 465

fecundity 877

FOLTZ, JEFFREY W., and CARROLL R. NORDEN,
"Food habits and feeding chronology of rainbow smelt,
Osmerus mordax, in Lake Michigan" 637

"Food habits and feeding chronology of rainbow smelt,
Osmerus mordax, in Lake Michigan," by Jeffrey W. Foltz
and Carroll R. Norden 637

French Guiana
U.S. shrimp fishery off, 1972-74 703

"Gallbladder lesions in cultured Pacific salmon," by Lee

W. Harrell 884

GAUGLITZ, ERICH J., JR.— see HALL et al.

Geryon quinquedens — see Crab, red

Gill nets

St. Andrew Bay, Florida
comparison of fish catches in relation to webbing
material, time of day, and water depth 103

selectivity on estuarine and coastal fishes, St. Andrew

Bay, Florida

capture efficiency 195

curves, normality of selection 190

fishes, numbers and mean lengths of, selected for

analysis 187

gear and methods 186

mean length-mesh size relation 192

mesh-size regulations 194

model for determining selectivity 186

standard deviation-mesh size relation 193

use limitations 195

Glyptocephalus zachirus — see Sole, rex

GOLDBERG, STEPHEN R., and WILLIAM C.
TICKNOR, Jr., "Reproductive cycle of the pink
surfperch, Zalembius rosaceus" 882

Gonyaulax polyedra

nutritional value for larval northern anchovy 577

GOODMAN, ROBERT M.— see NORRIS et al.

GOULD, E.— see MacINNES et al.

GRAVES, JOHN, "Photographic method for measuring
spacing and density within pelagic fish schools at sea" 230

GREEN, JOHN H., and LOUIS J. RONSrVALLI, " 'Mock

fish' method for studying microbial inhibiting agents" 880

GREIG, R. A— see MacINNES et al.

"Growth and reproduction of the eastern spinner dol-
phin, a geographical form of Stenella longirostris in the

895

eastern tropical Pacific," by William F. Perrin, David B.
Holts, and Ruth B. Miller 725

Gulf of Mexico
eelpout

new genus and species described and figured 789

hake, offshore

biology 147

thread herring, Atlantic

abundance, potential yield, and early life history . 493

Gulf of Mexico, eastern
scaled sardine

spawning seasons, spawning areas, adult biomass,

and fisheries potential 613

GUNDERSON, DONALD R., "Population biology of
Pacific ocean perch, Sebastes alutus, stocks in the
Washington-Queen Charlotte Sound region, and their
response to fishing" 369

GUNN, JOHN T., and MERTON C. INGHAM, "A note
on: 'Velocity and transport of the Antilles Current
Northeast of the Bahama Islands'" 222

GUTHERZ, ELMER J— see ROHR and GUTHERZ

Guyana

U.S. shrimp fishery off, 1972-74 703

Gymnodinium splendens

nutritional value for larval northern anchovy 577

HAEFNER, PAUL A., Jr., "Reproductive biology of the
female deep-sea red crab, Geryon quinquedens, from the
Chesapeake Bight" 91

Hadropenaeus affinis

American solenocerid shrimp 317

Hadropenaeus lucasii

American solenocerid shrimp 327

Hadropenaeus modestus

American solenocerid shrimp 323

HAIGHT, RICHARD E.— see JEWETT and HAIGHT

Hake, offshore
biology in Gulf of Mexico

age and growth 155

depth related to size and sex 150

distribution and abundance 149

food habits 153

reproduction 151

standing stock 156

Haliporoides diomedeae

American solenocerid shrimp 290

HALL, ALICE S., FUAD M. TEENY, and ERICH J.
GAUGLITZ, JR., "Mercury in fish and shellfish of the
northeast Pacific. III. Spiny dogfish, Squalus acanthias" 642

896

HALL, JOHN D., "A nonlethal lavage device for sam-
pling stomach contents of small marine mammals" . . . 653

Harengula jaguana — see Sardine, scaled

HARRELL, LEE W., "Gallbladder lesions in cultured
Pacific salmon" 884

HAUSKNECHT, KEITH A— see INGHAM et al.

Hawaii

Koko Head, Oahu
sea-surface temperatures and salinities, 1956-
73 767

silverside, Hawaiian

predator-prey interactions in schools during twi-
light 415

HECK, KENNETH L., JR.— see WEINSTEIN and HECK

HEESEN, T. C— see McDERMOTT-EHRLICH et al.

Herring, Atlantic thread
Gulf of Mexico

abundance and potential yield 493

early life history 493

Herring, Pacific

benzene, effects on spawning 43

uptake, distribution, and depuration of 14C benzene

and 14C toluene in 633

with 14C benzene and 14C toluene

uptake, distribution, and depuration 633

Herring, round

abundance, potential yield, and early life history in

eastern Gulf of Mexico, 1971-74

biomass concentration 79

biomass estimating procedure 65

egg abundance 64, 76

egg and larvae abundance in relation to zooplankton 75

egg occurence 69

fecundity and maturity 75

hatching time 76

larval abundance 64, 80

larval abundance and mortality 67

larvae occurrence 69

plankton sampling 62

potential yield to a fishery 67, 79

spawning, annual, and biomass estimates 77

survey area and times 62

temperature and salinity 64, 74

Heteroteuthis hawaiiensis

bioluminescence, intensity regulation of during coun-
tershading 247

HIRSCH, NINA— see KORN et al.

HOBBS, LARRY— see NORRIS et al.

HOLTS, DAVID B— see PERRIN et al.

HORN, MICHAEL H., "Observations on feeding,

growth, locomotor behavior, and buoyancy of a pelagic

stromateoid fish, Icichthys lockingtoni" 453

HORTON, HOWARD F.— see HOSIE and HORTON

—see SIX and HORTON

HOSIE, MICHAEL J— see PEARCY et al.

and HOWARD F. HORTON, "Biology of the

rex sole, Glyptocephalus zachirus, in waters off Oregon" 51

HOUDE, EDWARD D., "Abundance and potential yield
of the Atlantic thread herring, Opisthonema oglinum,
and aspects of its early life history in the eastern Gulf of
Mexico" 493

, "Abundance and potential yield of the round

herring, Etrumeus teres, and aspects of its early life his-
tory in the eastern Gulf of Mexico" 61

, "Abundance and potential yield of the scaled

sardine, Harengula jaguana, and aspects of its early life
history in the eastern Gulf of Mexico" 613

HOWELL, W. HUNTTING, and DAVID H. KESLER,
"Fecundity of the southern New England stock of yellow-
tail flounder, Limanda ferruginea" 877

Hymenopenaeus aphoticus

American solenocerid shrimp 275

Hymenopenaeus debilis

American solenocerid shrimp 268

Hymenopenaeus doris

American solenocerid shrimp 283

Hymenopenaues laevis

American solenocerid shrimp 278

Hymenopenaeus nereus

American solenocerid shrimp 287

Icichthys lockingtoni

observations on feeding, growth, locomotor behavior,

and buoyancy 453

"Identification of fish species by thin-layer polyacryl-
amide gel isoelectric focusing," by Ronald C. Lund-
strom 571

IEF— see Isoelectric focusing

"Income estimates and reasonable returns in Alaska's
salmon fisheries," by James E. Owers 483

"Incorporating soak time into measurement of fishing
effort in trap fisheries," by C. Bruce Austin 213

INGHAM, MERTON C— see GUNN and INGHAM

—see NELSON et al.

, STEVEN K. COOK, and KEITH A.

HAUSKNECHT, "Oxycline characteristics and skipjack

tuna distribution in the southeastern tropical Atlantic" 857

"Intensity regulation of bioluminescence during coun-
tershading in living midwater animals," by Richard Ed-
ward Young and Clyde F. E. Roper 239

Isoelectric focusing
polyacrylamide gel

identification of fish species by thin layer

Isopod
Cymothoa excisa

biology and occurence on three species of snappers

571

875

JERDE, CHARLES W.— see SCURA and JERDE

JEWETT, STEPHEN C, and RICHARD E. HAIGHT,
"Description of megalopa of snow crab, Chionoecetes
bairdi (Majidae, subfamily Oregoniinae)" 459

JOEST, LINDA— see FINE et al.

JOHNS, D. MICHAEL, and WILLIAM H. LANG, "Lar-
val development of the spider crab, Libinia emarginata
(Majidae)" 831

JOHNSON, JAMES H.— see LAURS et al.

JONES, ALBERT C, and ALEXANDER DRAGOVICH,
"The United States shrimp fishery off northeastern
South America (1972-74)" 703

KESLER, DAVID H.— see HOWELL and KESLER

"Koko Head, Oahu, sea-surface temperatures and
salinities, 1956-73, and Christmas Island sea-surface
temperatures, 1954-73," by Gunter R. Seckel and Marian
Y. Y. Yong 767

KORN, SID, NINA HIRSCH, and JEANNETTE W.
STRUHSAKER, "The uptake, distribution, and depura-
tion of 14C benzene and 14C toluene in Pacific herring,
Clupea harengus pallasi" 633

KRYGIER, EARL E., and WILLIAM G. PEARCY, "The
source of cobalt-60 and migrations of albacore off the
west coast of North America" 867

Lake Michigan
rainbow smelt

food habits and feeding chronology 637

LANG, WILLIAM H.— see JOHNS and LANG

Larimus fasciatus

York River estuary, Virginia
life history, feeding habits, and functional morphol-
ogy of juveniles 657

897

LAROCHE, WAYNE A, "Description of larval and early
juvenile vermilion snapper, Rhomboplites aurorubens"

Larvae, fish — see Fish larvae

547

"Larval development of the spider crab, Libinia emar-
ginata (Majidae)," by D. Michael Johns and William H.
Lang 831

"Larval transport and year-class strength of Atlantic
menhaden, Brevoortia tyrannus," by Walter R. Nelson,
Merton C. Ingham, and William E. Schaaf 23

LAURENCE, GEOFFREY C, "A bioenergetic model for
the analysis of feeding and survival potential of winter
flounder, Pseudopleuronectes americanus, larvae during
the period from hatching to metamorphosis" 529

LAURS, R. MICHAEL, and RONALD J. LYNN, "Sea-
sonal migration of North Pacific albacore, Thunnus
alalunga, into North American coastal waters: Distribu-
tion, relative abundance, and association with Transi-
tion Zone waters" 795

HEENY S. H. YUEN, and JAMES H.

JOHNSON, "Small-scale movements of albacore, Thun-
nus alalunga, in relation to ocean features as indicated
by ultrasonic tracking and oceanographic sampling"

347

Leiostomus xanthurus

York River estuary, Virginia
life history, feeding habits,
phology of juveniles

and functional mor-

"Length-width-weight relationships for mature male
snow crab, Chionocoetes bairdi," by Duane E. Phinney

LEONG, RODERICK, "Maturation and induced spawn-
ing of captive Pacific mackerel, Scomber japonicus" . .

Libinia emarginata — see Crab, spider

"Life history, feeding habits, and functional morphology
of juvenile sciaenid fishes in the York River estuary,
Virginia," by Labbish N. Chao and John A. Musick . .

657

870

205

657

Limanda ferruginea — see Flounder, yellowtail

"Localized mass mortality of red sea urchin, Stron-
gylocentrotus franciscanus, near Santa Cruz, Califor-
nia," by John S. Pearse, Daniel P. Costa, Marc B. Yellin,
and Catherine R. Agegian 645

LOESCH, JOSEPH G., "Useable meat yields in the Vir-
ginia surf clam fishery" 640

"Long-term cadmium stress in the cunner, Tautogolab-
rus adspersus," by J. R. Maclnnes, F. P. Thurberg, R. A.
Greig, and E. Gould 199

Los Angeles

Dover sole, local migrations and fin erosion
chlorinated hydrocarbons in 513

LUNDSTROM, RONALD C, "Identification of fish
species by thin-layer polyacrylamide gel isoelectric
focusing" 571

LYNN, RONALD J.— see LAURS and LYNN

McDERMOTT-EHRLICH, D. J., M. J. SHERWOOD, T.
C. HEESEN, D. R. YOUNG, and A. J. MEARNS,
"Chlorinated hydrocarbons in Dover sole, Microstomus
pacificus: Local migrations and fin erosion" 513

MacINNES, J. R., F. P. THURBERG, R. A. GREIG, and
E. GOULD, "Long-term cadmium stress in the cunner,
Tautogolabrus adspersus" 199

Mackerel, Pacific
maturation and induced spawning of captive

hormones, test for induction of spawning 207, 209

photoperiods 205, 208

spawning condition, maintaining after normal

spawning season 207, 209

temperatures, ambient 206, 208

MAJOR, PETER F., "Predator-prey interactions in
schooling fishes during periods of twilight: A study of the
silverside Pranesus insularum in Hawaii" 415

Mammals, marine
small

nonlethal lavage device for sampling stomach con-
tents 653

"Maturation and induced spawning of capitve Pacific
mackerel, Scomber japonicus," by Roderick Leong ....

MEARNS, A. J— see McDERMOTT-EHRLICH et al.

205

Menhaden, Atlantic

larval transport and year-class strength

Ekman transport influence 30

fishery implications 38

physical oceanography of spawning region 26

recruit-environmental model 33

sardine, comparison with Pacific 37

spawner-recruit relation 28

spawning and larval distribution 24

Menticirrhus americanus

York River estuary, Virginia

life history, feeding habits, and functional morphol-
ogy of juveniles 657

Menticirrhus saxatilis

York River estuary, Virginia

life history, feeding habits, and functional morphol-
ogy of juveniles 657

"Mercury in fish and shellfish of the northeast Pacific. III.
Spiny dogfish, Squalus acanthias ," by Alice S. Hall, Faud
M. Teeny, and Erich J. Gauglitz, Jr 642

Merluccius albidus — see Hake, offshore

898

Mesopenaeus tropicalis

American solenocerid shrimp 332

Microbial outgrowth
"mock fish," for studying inhibiting microbial agents 880

Microcopepods
California Current

distribution, size, and abundance 601

survival of marine teleost larvae, influence on ... 601

Micropogonias undulatus

York River estuary, Virginia
life history, feeding habits, and functional morphol-
ogy of juveniles 657

Micropogonias undulatus — see also Croaker, Atlantic

Microstomus pacificus — see Sole, Dover

MILLER, CHARLES B— see PETERSON and MILLER

MILLER, RUTH B— see PERRIN et al.

MISITANO, DAVID A., "Species composition and rela-
tive abundance of larval and post-larval fishes in the
Columbia River estuary, 1973" 218

'"Mock fish' method for studying microbial inhibiting
agents," by John H. Green and Louis J. Ronsivalli . . . 880

MORROW, JAMES E., ELDOR W. SCHALLOCK, and
GLENN E. BERGTOLD, "Feeding by Alaska whitefish,
Coregonus nelsoni, during the spawning run" 234

Mortality
urchin, red sea

localized mass mortality near Santa Cruz, Califor-
nia 645

MUSICK, JOHN A.— see CHAO and MUSICK

Mya arenaria — see Clam, soft-shell

Narragansett Bay, Rhode Island
crab, planktonic spider

larval development

NELSON, DONALD R.— see SCIARROTTA and NEL-
SON

NELSON, WALTER R., MERTON C. INGHAM, and
WILLIAM E. SCHAFF, "Larval transport and year-class
strength of Atlantic menhaden, Brevoortia tyrannus" .

831

New England, Southern
flounder, yellowtail
compartmentalized simulation model 465

"(A) nonlethal lavage device for sampling stomach con-
tents of small marine mammals," by John D. Hall . . .

NORDEN, CARROLL R.— see FOLTZ and NORDEN

653

NORRIS, KENNETH S„ ROBERT M. GOODMAN,
BERNARDO VILLA-RAMIREZ, and LARRY HOBBS,

"Behavior of California gray whale, Eschrichtius robus-

tus, in southern Baja California, Mexico" 159

North America, west coast
albacore, cobalt-60 content in
source and migration estimates on west coast .... 867

North Carolina
scallop, calico

fishes, macroinvertebrates, and their interrelation-
ships with 427

"(A) note on: 'Velocity and transport of the Antilles Cur-
rent northeast of the Bahama Islands,'" by John T. Gunn
and Merton C. Ingham 222

Nuclear detonations
cobalt-60 content

contamination source for albacore off west coast 867

Oahu

Koko Head, Hawaii

sea-surface temperatures and salinities, 1956-73 . 767

"Observations on feeding, growth, locomotor behavior,
and buoyancy of a pelagic stromateoid fish, Icichthys
lockingtoni," by Michael H. Horn 453

Oceanographic sampling
albacore movements

small-scale in relation to ocean features 347

Octopoteuthis nielseni

bioluminescence, intensity regulation of during coun-
tershading 246

Oithona similis

Oregon coast, central

seasonal cycle of abundance 717

OLLA, BORI L., and CAROL SAMET, "Courtship and
spawning behavior of the tautog, Tautoga onitis, (Pisces:
Labridae), under laboratory conditions" 585

Oncorhynchus kisutch — see Salmon, coho

Opisthonema oglinum — see Herring, Atlantic thread

Oplophorus gracilirostris

bioluminescence, intensity regulation of during coun-
tershading 248

Opsanus tau — see Toadfish, oyster

Oregon

larvae, distribution and duration of pelagic life in wat-
ers off

sole, Dover 173

sole, petrale 173

sole, rex 173

899

rockfish
age determination methods, analysis
biology, 1969-73

Oregon coast, central
zooplankton

seasonal cycle of abundance and species composition

Osmerus mordax — see Smelt, rainbow

OWERS, JAMES E., "Income estimates and reasonable
returns in Alaska's salmon fisheries"

"Oxycline characteristics and skipjack tuna distribution
in the southeastern tropical Atlantic," by Merton C. In-
gham, Steven K. Cook, and Keith A. Hausknecht ....

405
51

717

483

857

Oxygen
Atlantic, southeastern tropical
oxycline characteristics and skipjack tuna distribu-
tion 857

Oxygen, dissolved

York River estuary, Virginia
mean values, May 1972-August 1973 659

Oxygen concentration, dissolved
tuna
swimming speed, effect on 649

Pacific Ocean, central equatorial
Christmas Island

sea-surface temperatures, 1954-73 767

Pacific Ocean, eastern tropical
dolphin, eastern spinner

growth and reproduction 725

dolphin, spotted
gross annual reproductive rates compared with es-
timates for eastern spinner dolphin, 1973-75 725

reproductive parameters, 1973-75 629

Pacific Ocean, North
albacore

seasonal migration into North American coastal
waters 795

Pacific Ocean, northeast
dogfish, spiny

mercury in 642

Panama
Caribbean coast

snapper, host-parasite relationship with Cymothoa
excisa 875

Pandalus platyceros — see Prawn, spot

Paracalanus parvus
Oregon coast, central

seasonal cycle of abundance 717

Paralichthys dentatus — see Flounder, summer

PATTEN, BENJAMIN G., "Body size and learned avoi-
dance as factors affecting predation on coho salmon, On-
corhynchus kisutch, fry by torrent sculpin, Cottus
rhotheus"

, "Short-term thermal resistance of zoeae of

457

555

10 species of crabs from Puget Sound, Washington" . . .
PEARCY, WILLIAM G.— see KRYGIER and PEARCY

—see RICHARDSON and PEARCY

, MICHAEL J. HOSIE, and SALLY L.

RICHARDSON, "Distribution and duration of pelagic
life of larvae of Dover sole, Microstomus pacificus; rex
sole, Glyptocephalus zachirus; and petrale sole, Eopsetta
jordani, in waters off Oregon" 173

PEARSE, JOHN S., DANIEL P. COSTA, MARC B.
YELLIN, and CATHERINE R. AGEGIAN, "Localized
mass mortality of red sea urchin, Strongylocentrotus
franciscanus, near Santa Cruz, California" 645

Perch, Pacific ocean

population biology in Washington-Queen Charlotte

Sound region

age composition 380

age-length relationships 376

fecundity 391

life history, general features 372

migrations and availability 373

mortality 383

recruitment to fishery 381

response to fishing 394

sexual maturation 385

size composition 378

stock delineation 371

PEREZ FARFANTE, ISABEL, "American solenocerid
shrimps of the genera Hymenopenaeus, Haliporoides,
Pleoticus, Hadropenaeus new genus, and Mesopenaeus
new genus" 261

PERKINS, PAUL J.— see FINE et al.

PERRIN, WILLIAM F., DAVID B. HOLTS, and RUTH
B. MILLER, "Growth and reproduction of the eastern
spinner dolphin, a geographical form of Stenella lon-
girostris in the eastern tropical Pacific" 725

, RUTH B. MILLER, and PRISCILLA A.

SLOAN, "Reproductive parameters of the offshore spot-
ted dolphin, a geographical form of Stenella attenuata, in
the eastern tropical Pacific, 1973-75" 629

PETERSON, WILLIAM T., and CHARLES B. MILLER,
"Seasonal cycle of zooplankton abundance and species
composition along the central Oregon coast" 717

PHINNEY, DUANE E., "Length- width- weight relation-
ships for mature male snow crab, Chionocoetes
bairdi" 870

Phoca (Histriophoca) fasciata — see Seal, ribbon

900

"Photographic method for measuring spacing and den-
sity within pelagic fish schools at sea," by John Graves 230

Phytoplankton

food for larval northern anchovy 577

Plankton — see Zooplankton

Pleoticus muelleri

American solenocerid shrimp 309

Pleoticus robustus

American solenocerid shrimp 297

Pogonias cromis
York River estuary
life history, feeding habits, and functional morphol-
ogy of juveniles 657

Pollution

14C benzene and 14C toluene in Pacific herring

uptake, distribution, and depuration 633

chlorinated hydrocarbons in Dover sole

local migrations and fin erosion 513

cobalt-60 content in albacore

source and migration estimates on west coast .... 867
fishery waste effluents

parameters, system for determining and calculating 253
Puget Sound, Washington

short-term thermal resistance of zoeae of 10 species

of crabs 555

Polyacrylamide gel
fish identification

thin-layer isoelectric focusing 571

"Population biology of Pacific ocean perch, Sebastes
alutus, stocks in the Washington-Queen Charlotte Sound
region, and their response to fishing," by Donald R. Gun-
derson 369

PORTER, HUGH J— see SCHWARTZ and PORTER

Pranesus insularum — see Silverside, Hawaiian

Prawn, spot

second mating and spawning in captivity, first record

of 648

"Predator-prey interactions in schooling fishes during
periods of twilight: A study of the silverside Pranesus
insularum in Hawaii," by Peter F. Major 415

PRENTICE, EARL F.— see RENSEL et al.

Prionace glauca — see Shark, blue

PRISTAS, PAUL J— see TRENT and PRIST AS

, and LEE TRENT, "Comparisons of catches

of fishes in gill nets in relation to webbing material, time

of day, and water depth in St. Andrew Bay, Florida" 103

"Production by three populations of wild brook trout with

emphasis on influence of recruitment rates," by Robert F.
Carline 751

Pseudocalanus sp.
central Oregon coast

seasonal cycle of abundance 717

Pseudomonas sp.

"mock fish" used for studying microbial outgrowth

of 880

Psuedopleuronectes americanus — see Flounder, winter

Pterygioteuthis microlampas

bioluminescence, intensity regulation of during coun-
tershading 244

Puget Sound, Washington
crabs, 10 species

short-term thermal resistance of zoeae 555

Pyroteuthis addolux

bioluminescence, intensity regulation of during coun-
tershading 245

Queen Charlotte Sound
perch, Pacific ocean

population biology and response to fishing 369

RAF AIL, SAMIR Z., "A simplification for the study of

fish populations by capture data" 561

RAY, G. CARLETON— see WATKINS and RAY

RENSEL, JOHN E., and EARL F. PRENTICE, "First
record of a second mating and spawning of the spot
prawn" 648

"Reproductive biology of the female deep-sea red crab,
Geryon quinquedens, from the Chesapeake Bight," by
Paul A. Haefner, Jr 91

"Reproductive cycle of the pink surfperch, Zalembius
rosaceus," by Stephen R. Goldberg and William C.
Ticknor, Jr 882

"Reproductive parameters of the offshore spotted dol-
phin, a geographical form of Stenella attenuata, in the
eastern tropical Pacific, 1973-75," by William F. Perrin,
Ruth B. Miller, and Priscilla A. Sloan 629

Rhode Island
spider crab, laboratory-reared

larval development 831

spider crab, planktonic

larval development 831

Rhomboplites aurorubens — see Snapper, vermilion

"(The) ribbonfish genus Desmodema, with the descrip-
tion of a new species (Pisces, Trachipteridae)," by
Ricahrd H. Rosenblatt and John L. Butler 843

901

RICHARDSON, SALLY L.— see PEARCY et al.

, and WILLIAM G. PEARCY, "Coastal and

oceanic fish larvae in an area of upwelling off Yaquina

Bay, Oregon" 125

Rockfish
California, southern

migration, timing of surface-to-benthic in juveniles 887

Rockfish, canary
Oregon

age determination methods, analysis 405

Rockfish, black
Oregon
age determination methods, analysis 405

Rockfish, yellowtail
Oregon

age determination methods, analysis 405

ROHR, BENNIE A., and ELMER J. GUTHERZ, "Biol-
ogy of offshore hake, Merluccius albidus, in the Gulf of
Mexico" 147

RONSIVALLI, LOUIS J.— see GREEN and RON-
SIVALLI

ROPER, CLYDE F. E.— see YOUNG and ROPER

ROSENBLATT, RICHARD H, and JOHN L. BUTLER,
"The ribbonfish genus Desmodema, with the description
of a new species (Pisces, Trachipteridae)" 843

St. Andrew Bay, Florida
gill net

selectivity on estuarine and coastal fishes 185

gill net fish catches

comparison of webbing materials, times of day, and

water depths 103

Salinity

Koko Head, Oahu, 1956-73 767

tuna

swimming speed, effect on 649

York River estuary, Virginia

means values, May 1972-August 1973 659

"Salinity acclimation in the soft-shell clam, Myaarenar-

ia," by Edwin P. Creaser, Jr. and David A. Clifford . . 225

Salmon
Alaska

income estimates and reasonable returns 483

Pacific, cultured

gallbladder lesions in 884

Salmon, coho

body size and learned avoidance as factors affecting
predation by torrent sculpin 457

Salvelinus fontinalis — see Trout, brook

SAMET, CAROL— see OLLA and SAMET

Santa Catalina Island, California
blue shark
diel behavior of 519

Santa Cruz, California
urchin, red sea
localized mass mortality 645

Sardine, scaled

Gulf of Mexico, eastern

abundance and potential yield 613

early life history 613

Scallop, calico
fishes, macroinvertebrates, and their interrelation-
ships with, off North Carolina

environmental data 429

environmental observations 431

fishery 427

growth 434

sampling vessels 429

SCHAFF, WILLIAM E.— see NELSON et al.

SCHALLOCK, ELDOR W.— see MORROW et al.

SCHWARTZ, FRANK J., and HUGH J. PORTER,
"Fishes, macroinvertebrates, and their ecological inter-
relationships with a calico scallop bed off North
Carolina" 427

Sciaenids

York River estuary, Virginia
life history, feeding habits, and functional morphol-
ogy of juveniles 657

Sciaenops ocellata

York River estuary, Virginia
life history, feeding habits, and functional morphol-
ogy of juveniles 657

SCIARROTTA, TERRY C, and DONALD R. NELSON,
"Diel behavior of the blue shark, Prionace glauca, near
Santa Catalina Island, California" 519

Scomber japonicus — see Mackerel, Pacific

Sculpin, torrent
predator on coho salmon fry 457

SCURA, EDWARD D., and CHARLES W. JERDE, "Var-
ious species of phytoplankton as food for larval northern
anchovy, Engraulis mordax, and relative nutritional
value of the dinoflagellates Gymnodinium splendens and
Gonyaulax polyedra" 577

Sea-surface temperature — see Temperature

Sea urchin, red
Santa Cruz, California

localized mass mortality 645

902

Seal, ribbon

underwater sounds from

450

Shrimp, brown
northeastern South America, 1972-74
U.S. fishery

Sebastes alutus — see Perch, Pacific ocean

Sebastes diploproa — see Rockfish

Sebastes flavidus — see Rockfish, yellowtail

Sebastes melanops — see Rockfish, black

Sebastes pinniger — see Rockfish, canary

"Seasonal cycle of zooplankton abundance and species
composition along the central Oregon coast," by William
T. Peterson and Charles B. Miller

"Seasonal migration of North Pacific albacore, Thunnus
alalunga, into North American coastal waters: Distribu-
tion, relative abundance, and association with Transi-
tion Zone waters," by Michael Laurs and Ronald J. Lynn

717

795

SECKEL, GUNTER R., and MARIAN Y. Y. YONG,
"Koko Head, Oahu, sea-surface temperatures and
salinities, 1956-73, and Christmas Island sea-surface
temperatures, 1954-73" 767

"Selectivity of gill nets on estuarine and coastal fishes
from St. Andrew Bay, Florida," by Lee Trent and Paul J.
Pristas 185

Shark, blue
Santa Catalina Island, California, near

diel behavior 519

SHARP, GARY D., and RONALD C. DOTSON, "Energy

for migration in albacore, Thunnus alalunga" 447

SHERWOOD, M. J.— see McDERMOTT-EHRLICH et al.

"Short-term thermal resistance of zoeae of 10 species of
crabs from Puget Sound, Washington," by Benjamin G.
Patten 555

Shrimp

northeastern South America, 1972-74

U.S. fishery 703

solenocerid, American

Hadropenaeus, key to species 316

Hadropenaeus affinis 317

Hadropenaeus lucasii 327

Hadropenaeus modestus 323

Haliporoides diomedeae 290

Hymenopenaeus, key to species 268

Hymenopenaeus aphoticus 275

Hymenopenaeus debUis 268

Hymenopenaeus doris 283

Hymenopenaeus laevis 278

Hymenopenaeus nereus 287

Mesopenaeus tropicalis 332

Pleoticus, key to species in western Atlantic 296

Pleoticus muelleri 309

Pleoticus robustus 297

Solenoceridae, key to genera 265

Shrimp, pink-spotted
northeastern South America, 1972-74
U.S. fishery

Silverside, Hawaiian

predator-prey interactions in schools during twilight

"(A) simplification for the study of fish populations by
capture data," by Samir Z. Rafail

SISSENWINE, MICHAEL P., "A compartmentalized
simulation model of the Southern New England yellow-
tail flounder, Limanda ferruginea, fishery"

SIX, LAWRENCE D., and HOWARD F. HORTON,
"Analysis of age determination methods for yellowtail
rockfish, canary rockfish, and black rockfish off Oregon"

SLOAN, PRISCILLA— see PERRIN et al.

"Small-scale movements of albacore, Thunnus alalunga,
in relation to ocean features as indicated by ultrasonic
tracking and oceanographic sampling," by R. Michael
Laurs, Heeny S. H. Yuen, and James H. Johnson ....

Smelt, rainbow
Lake Michigan
food habits and feeding

703

415

561

465

405

SMITH, RONAL W., and FRANKLIN C. DAIBER,
"Biology of the summer flounder, Paralichthys dentatus,
in Delaware Bay"

Snapper
Panama, Caribbean coast of

host-parasite relationship with Cymothoa excisa

347

637

823

875

Snapper, vermilion

larval and early juvenile, description of 547

Soak time
incorporating into measurement of fishing effort in
trap fisheries 213

Sole, Dover

chlorinated hydrocarbons in

local migrations and fin erosion 513

larvae, distribution and duration of pelagic life off

Oregon

collections 174

distribution, inshore-offshore and north-south .... 178

distribution, vertical 181

growth and development 175

juveniles, benthic 181

larval stages 175

seasonality, growth, and length of larval life 176

Sole, petrale
larvae, distribution and duration of pelagic life off
Oregon
collections

174

903

distribution, inshore-offshore and north-south .... 178

distribution, vertical 181

growth and development 175

juveniles, benthic 181

larval stages 175

seasonality, growth, and length of larval life 176

Sole, rex

biology in Oregon waters, 1969-73

age and growth 53

length-weight relationships 53

mortality rate 55

reproduction 56

stock identification 57

larvae, distribution and duration of pelagic life off

Oregon

collections 174

distribution, inshore-offshore and north-south .... 178

distribution, vertical 181

growth and development 175

juveniles, benthic 181

larval stages 175

seasonality, growth, and length of larval life 176

"(The) source of cobalt-60 and migrations of albacore off
the west coast of North America," by Earl E. Krygier and
William G. Pearcy 867

South America, northeastern
U.S. shrimp fishery off, 1972-74 703

South Carolina
crab, spider

larval development of laboratory-reared 831

Spawning

prawn, spot

second mating and spawning in captivity, first
record of 648

tautog
behavior under laboratory conditions 585

"Species composition and relative abundance of larval
and post-larval fishes in the Columbia River estuary,
1973," by David A. Misitano 218

Squalus acanthias — see Dogfish, spiny

Squids
Gulf of Maine to Cape Hatteras, 1963-74

biomass changes as determined from research vessel
survey data 1

SST — see Temperature

Stenella attenuata — see Dolphin, spotted

Stenella longirostris — see Dolphin, eastern spinner

Strongylocentrotus franciscanus — see Sea urchin, red

STRUHSAKER.JEANNETTEW., "Effects of benzene (a
toxic component of petroleum) on spawning Pacific herr-
ing, Clupea harengus pallasi" 43

904

— see also KORN et al.

Surfperch, pink
reproductive cycle 882

Surinam

U.S. shrimp fishery, 1972-74 703

Swimming speed
tuna

dissolved oxygen concentration and salinity, effect

of 649

Tautog

courtship and spawning behavior under laboratory
conditions 585

Tautoga onitis — see Tautog

Tautogolabrus adspersus — see Cunner

TEENY, FUAD M.— see HALL et al.

Temperature

bottom, York River estuary
mean values, May 1972-August 1973 659

crabs, 10 species

short-term thermal resistance of zoeae from Puget
Sound, Washington 555

sea-surface

Christmas Island, 1954-73 767

Koko Head, Oahu, 1956-73 767

"Temporal aspects of calling behavior in the oyster
toadfish, Opsanus tau," by Michael L. Fine, Howard E.
Winn, Linda Joest, and Paul J. Perkins 871

TENNEY, RICHARD D— see COLLINS and TENNEY

Thunnus alalunga — see Tuna, albacore

THURBERG, F. P.— see MacINNES et al.

TICKNOR, WILLIAM C, JR.— see GOLDBERG and
TICKNOR

"Timing of the surface-to-benthic migration in juvenile
rockfish, Sebastes diploproa, off southern California," by
George W. Boehlert 887

Toadfish, oyster
calling behavior, temporal aspects 871

Tracking, ultrasonic
albacore movements

small-scale in relation to ocean features 347

TRENT, LEE— see PRIST AS and TRENT

, and PAUL J. PRISTAS, "Selectivity of gill

nets on estuarine and coastal fishes from St. Andrew Bay,
Florida" 185

Trout, brook
wild
production by three populations with emphasis on
influence of recruitment rates 751

Tuna

swimming speed

dissolved oxygen concentration and salinity, effect

of 649

Tuna, albacore

cobalt-60 content

source and migration estimates on west coast .... 867

energy for migration 447

movements, small-scale related to ocean features

capture, handling, and tagging 347

oceanographic observations, aircraft 349

oceanographic observations, ship 348

sea surface temperature 350

speed 349

temperature fronts, upwelling 350

thermal structure, vertical 354

tracking equipment 348

tracking procedure 348

North American coastal waters
distribution, relative abundance, and association

with Transition Zone waters 795

Tuna, skipjack

southeastern tropical Atlantic
distribution, October-November 1968 857

"Underwater sounds from ribbon seal, Phoca (His-
triophoca) fasciata," by William A. Watkins and G.
Carleton Ray 450

"(The) United States shrimp fishery off northeastern
South America ( 1972-74)," by Albert C. Jones and Alex-
ander Dragovich 703

"(The) uptake, distribution, and depuration of 14C ben-
zene and 14C toluene in Pacific herring, Clupea harengus
pallasi," by Sid Korn, Nina Hirsch, and Jeannette W.
Struhsaker 633

"Useable meat yields in the Virginia surf clam fishery,"

by Joseph G. Loesch 640

"Various species of phytoplankton as food for larval
northern anchovy, Engraulis mordax, and relative nu-
tritional value of the dinofiagellates Gymnodinium
splendens and Gonyaulax polyedra," by Edward D. Scura
and Charles W. Jerde 577

Washington

crab

short-term thermal resistance of zoeae from Puget
Sound 555

perch, Pacific ocean

population biology and response to fishing 369

WATKINS, WILLIAM A., and G. CARLETON RAY,
"Underwater sounds from ribbon seal, Phoca (His-
triophoca) fasciata" 450

WEINSTEIN, MICHAEL P., and KENNETH L. HECK,
JR., "Biology and host-parasite relationships of
Cymothoa excisa (Isopoda, Cymothoidae) with three
species of snappers (Lutjanidae) on the Caribbean coast
of Panama" 875

Whale, gray

Baja Califonia, southern

behavior, aerial 165

behavior, aggressive 169

buoyancy and respiration 167

feeding 169

observation studies 164

phonation 170

population segregation 169

thigmotaxis 166

tracking studies 162

WHITE, MICHAEL L„ and MARK E. CHITTENDEN,
JR., "Age determination, reproduction, and population
dynamics of the Atlantic croaker, Micropogonias un-
dulatus" 109

Whitefish, Alaska
feeding during spawning run 234

WICKH AM, DANIEL E.— see FISHER and WICKHAM

WINN, HOWARD E.— see FINE et al.

Wisconsin, northern
trout, wild brook
production by three populations with emphasis on
influence of recruitment rates

751

Yaquina Bay, Oregon
fish larvae
coastal and oceanic in an upwelling area off

125

YELLIN, MARC B.— see PEARSE et al.

YONG, MARIAN Y. Y.— see SECKEL and YONG

VILLA-RAMIREZ, BERNARDO— see NORRIS et al.

Virginia

sciaenids, juvenile

life history, feeding habits, and functional morphol-
ogy in the York River estuary

surf clam
useable meat yields

657
640

York River estuary, Virginia
sciaenid fishes, juvenile

life history, feeding habits, and functional morphol-
ogy

YOUNG, D. R.— see McDERMOTT-EHRLICH et al.
YOUNG, RICHARD EDWARD, and CLYDE F. E.

657

905

ROPER, "Intensity regulation of bioluminescence dur-
ing countershading in living midwater animals" 239

YUEN, HEENY S. H.— see LAURS et al.

Zalembius rosaceus — see Surfperch, pink

Zoeae

Puget Sound, Washington
crabs, short-term thermal resistance of 555

Zooplankton

California Current, annual fluctuations in biomass,

1955-59

data processing methods 358

geographical distribution 359

year-to-year fluctuations 361

Oregon coast, central
seasonal cycle of abundance and species composi-
tion 717

906

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Contents-continued

FINE, MICHAEL L., HOWARD E. WINN, LINDA JOEST, and PAUL J. PERKINS.

Temporal aspects of calling behavior in the oyster toadfish, Opsanus tau 871

WEINSTEIN, MICHAEL P., and KENNETH L. HECK, JR. Biology and host-parasite

relationships of Cymothoa excisa (Isopoda, Cymothiodae) with three species of

snappers (Lutjanidae) on the Caribbean coast of Panama 875

HOWELL, W. HUNTTING, and DAVID H. KESLER. Fecundity of the southern New

England stock of yellowtail flounder, Limanda ferruginea 877

GREEN, JOHN H., and LOUIS J. RONSIVALLI. "Mock fish" method for studying

microbial inhibiting agents 880

GOLDBERG, STEPHEN R., and WILLIAM C. TICKNOR, JR. Reproductive cycle of

the pink surfperch, Zalembius rosaceus (Embiotocidae) 882

HARRELL, LEE W. Gallbladder lesions in cultured Pacific salmon 884

BOEHLERT, GEORGE W. Timing of the surface-to-benthic migration in juvenile

rockfish, Sebastes diploproa, off southern California 887

INDEX, VOLUME 75 891

ft GPO 796-009

MBL WHOI LIBRARY

H niilB 7

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