.<**: °7% *^TCS 0« * Fishery Bulletin in 3 National Oceanic ar d Atmospheric Administration • National Marine Fisheries Service APR 'i S r 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) \t 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 B 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 k I h = l Nhyh'- Nyst2 +1^ /! = ! (Nh 1) + (Nh - N) (Nh - nh) N m (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 18 0.7 2.9 08 1.5 0.6 0.1 2.1 '0.0 04 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 36 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 48 3.9 3.4 6.6 3.0 05 Flounders: Yellowtail 12.0 11.8 8.7 79 11.9 11.1 12.3 137 7.6 26.8 2.6 1.2 Winter flounder 2.4 3.1 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 45 1.9 29 1.7 1.9 1.3 2.9 2.4 2.9 Other groundfish: Angler 4.4 7.0 49 6.7 1.9 1.2 2.5 28 1.5 9.8 2.9 1.0 Ocean pout 0.7 0.4 0.3 1.1 0.6 0.5 0.3 0.3 0.1 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 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 08 0.3 0.5 0.2 0.3 4.7 0.3 0.1 White hake 12 04 0.6 1.2 1.3 1.4 0.6 0.5 0.4 0.4 01 0 1 Other 0.1 0.1 0.1 '0.0 0.3 '0.0 0.1 0.1 0.3 '0.0 '0.0 0.0 Principal pelagics: Herring 0.2 '0.0 0.5 1.8 05 0.1 '0.0 '0.0 '0.0 '0.0 0.0 00 Mackerel '0.0 "0.0 '0.0 '0.0 1.0 0.2 3.9 '0.0 0.1 '0.0 '0.0 '0.0 Other pelagics and other fish: Butlerfish 26 6.0 4.5 1.5 22 4.0 6.5 1.1 58 2.4 63 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 32 Other2 01 1.9 2.0 0.7 1.7 1.3 4.1 5.1 4,1 3.1 5.3 52 Squid Short-finned squid (3) 40.1 "0.1 «0.1 05 07 0 1 0.3 03 0.6 0 1 02 Long-finned squid (3) «1.2 "16 "22 2.0 122 181 3.6 5.4 67 167 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 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 0.9 0.9 0.4 Witch 1.0 0.5 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 1.1 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 0.9 0.2 0.1 '0.0 0.1 '0.0 0.4 0.2 '0.0 Sculpins 3.4 1.8 3.3 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 2.2 3.5 2.0 Other 0.5 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 0.2 '0.0 0.3 0.1 '0.0 '0.0 Mackerel '0.0 0.0 0.1 0.1 0.2 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 0.5 0.5 0.4 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 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 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 26 2.0 26 2.4 3.0 63 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 05 0.5 Pollock 8.6 7.8 3.6 2.4 2.9 5.4 13.1 3.6 5.5 84 5.9 62 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 36 23 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 52 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 16 0.1 0.2 0.3 0.1 '0.0 "0.0 0.1 0.6 '0.0 '0.0 '0.0 Mackerel '0.0 0.0 0.0 '0.0 00 '0.0 '0.0 '0.0 '0.0 '0.0 '00 '00 Other pelagics and other fish: Spiny dogfish 58.2 10.6 11.8 4.0 78 22.8 98 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 02 Squid: Short-finned squid (3) '•"0.0 "0.2 "0.4 0.1 0.1 0.1 0.3 0.5 0.2 06 1.2 Long-finned squid (3) "0.0 '•40.0 "0.1 '0.0 '0.0 '0.0 '0.0 '0.0 '0.0 '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. 10 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 11 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 0.0 0 1.7 0.8 -53 Haddock 0.0 0.0 0 3.7 20.0 -99 Silver hake 0.9 0.2 -78 62 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 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 +7 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 0.2 20.0 -99 Mackerel 0.1 0.0 -100 20.0 20.0 +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 +4 Cusk 0.3 0.2 -33 1.6 1.6 0 Ocean pout 1.2 0.2 -83 20.0 0.1 +474 Sculpins 2.8 2.7 -4 0.2 0.2 0 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 20.0 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 20.0 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. 12 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 50 4.4 5.1 46 6.4 2.9 Haddock 8.1 5.8 38 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 18 Yellowtail 4.8 5.6 5.2 42 29 79 16 1.0 Other flounder 4.6 5.4 5.1 5.1 3.5 4.3 4.2 3.5 Herring 0.3 0.1 0.1 '0.0 0.3 0.1 '0.0 '0.0 Mackerel 03 02 1.1 '0.0 '0.0 0.1 '0.0 '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 03 0.3 0.4 Long-finned squid 2.8 5.1 6.8 22 2.1 4.6 76 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 80 3.6 Haddock 31.6 31.2 229 10.5 10.2 7.4 4.7 5.1 3.1 2.8 42 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 22 2.4 29 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 5.6 5.3 3.6 98 2.1 12 Other flounder 88 6.1 6.7 92 4.6 5.6 5.8 63 4.0 5.1 4.8 4.0 Herring 1.0 0.1 0.5 1.2 0.4 0.1 0.1 0.1 03 0.1 '0.0 0.1 Mackerel '0.0 '0.0 0.1 0.1 0.4 0.2 1.4 0.1 0.1 0.2 0.1 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 "0.1 0.2 0.4 0.1 0.3 0.4 0.3 0.4 05 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. 13 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. 14 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) F Redfish 1964-75 16 (Mayo26) 0.4 Other flounders 1964-69 25 0.7 Other flounders 1970-75 20 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 26-30, 36-40 5Z 5-30, 36-40 5-30, 36-40 Haddock 5Ze 13-25 13-25 Redfish 18, 22, 26-30, 36-40 1-30,36-40 Silver hake 5Y 26-30, 36-40 26-30, 36-40 5Ze 13-25 13-25 5Zw-6 61-76, 1-12 1-12 Red hake 5Ze 13-25 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 13-25 5Zw 5-12 5-12 6 69-76, 1-4 1-4 Other flounders 61-76, 1-30, 36-40 1-30. 36-40 Herring 5Y 26-30, 36-40 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 15 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: 5Y 39.954 0.31 44.545 0.44 5Z 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: 5Y 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 6 67.795 0.95 39.969 076 Other flounders 10.897 0.18 11.134 0.17 Herring: 5Y 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. 16 CLARK and BROWN: CHANGES IN BIOMASS OF FINFISHES AND SQUIDS 46 613 X \ LINEAR . RETRANSFORMED 1963 64 73 1974 V^ 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 8 ^ ~- (\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 1.00 121.231 >1.00 Other flounders 13.016 0.22 14.293 0.25 Herring: 5Y 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 18 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 V *"--. ____ ... ^,- .. - 1,000 i , 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. 19 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. 20 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. 21 / 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. 23 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. 24 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, 25 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 26 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. 27 FISHERY BULLETIN: VOL. 75. NO. 1 5 U LU O X «/» z o ►- z < EASTWARD TRANSPORT 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, 28 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 3 4 5 6 7 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 + 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. 29 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 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 _^ s z o 12 sj *^ CD o - 10 X o No. of R«cruitt 7 _ 130 O < H U O at 3 Qr- 6 A Ekman Tramporl— — ^ ^ / \ ' 90 at o I in A '*"' "*\ 1 1 / 1 \ ■ 60 a. Z < lu \ at i / 1 1 i-*ti ' O 2 - 1 v / 30 at CO t i n r^i < * 4> 3 \l h — * \ i i/t z n * 70 Y EAR CIA ss 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. 30 NELSON ET AL : LARVAL TRANSPORT OF BREVOORTIA TYR ANNUS o z < > > 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. 31 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 *i Jan. -Mar 0.789 0.001 0.789 0.298 62.2 lat. 35°N, long. 75°W Chesapeake Bay *6 July-Sept. -0.216 — 0.825 0.271 68.0 discharge Zonal Ekman transport *3 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 *5 Jan. -Feb. -0 177 — 0.914 0.181 83.6 Delaware Bay entrance Zonal Ekman transport x2 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. x2 *3 *4 *5 *6 *, 0.789 0.645 0.644 -0.333 0.032 X, 0.589 0.701 -0.580 -0.068 x, 0.868 -0.403 0.174 ** -0.510 0.213 *5 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 32 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- 33 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. x UJ 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 X, X2 *3 X4 *5 x6 1955 1.95 70 74 272 152 2.4 9 1956 1.94 64 107 307 271 1.0 30 1957 0.69 12 13 83 34 3.4 29 1958 3.64 94 124 141 169 0.6 9 1959 0.56 7 13 126 82 1.5 24 1960 0.71 40 42 121 78 1.6 11 1961 0.89 30 33 155 129 1.6 22 1962 0.54 27 63 149 79 1.4 17 1963 0.40 3 70 206 158 -0.3 9 1964 0.66 14 43 120 127 2.0 16 1965 0.96 11 32 96 35 1.8 7 1966 2.04 26 55 125 104 1.3 7 1967 0.61 4 21 98 63 1.8 8 1968 1.03 60 96 161 97 0.0 23 1969 1.82 92 76 317 212 0.4 16 1970 0.94 39 47 185 156 0.2 28 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 34 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- 35 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. 36 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 37 FISHERY BULLETIN: VOL. 75, NO. 1 o z O 7 PACIFIC SARDINE 2 9 39 ! i 3? 40 v\ ' 33> .--'43 \35 34 u: 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 38 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 39 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 LITERATURE CITED BAKUN, a. 1973. Coastal upwelling indices west coast of North Ameri- ca, 1946-71. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-671, 103 p. 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. BUMPUS, D. F. 1973. A description of the circulation on the Continental Shelf of the east coast of the United States. Prog. Oceanogr. 6:111-157. CARRUTHERS, J. N. 1938. Fluctuations in the herrings of the East Anglian autumn fishery, the yield of the Ostend spent herring fishery, and the haddock of the North Sea — in the light of relevant wind conditions. Rapp. P.-V. Reun. Cons. Perm. Int. Explor. Mer 107(3): 10-15. Clark, c. W. 1974. Possible effects of schooling on the dynamics of exploited fish populations. J. Cons. 36:7-14. Clark, F. n., and J. C. Marr. 1955. Population dynamics of the Pacific sardine. Calif. Coop. Oceanic Fish. Invest. Prog. Rep. July 1953-March 1955, p. 11-48. CUSHING, D. H. 1969. The fluctuation of year-classes and the regulation of fisheries. FiskeriDir. Skr. Ser. HavUnders. 15:368-379. 1971. The dependence of recruitment on parent stock in different groups of fishes. J. Cons. 33:340-362. 1974. The natural regulation of fish populations. In F. R. Harden Jones (editor), Sea fisheries research, p. 399-412. John Wiley and Sons, N.Y. harrison, w., j. j. norcross, n. a. pore, and e. m. Stanley. 1967. Circulation of shelf waters off Chesapeake Bight. Surface and bottom drift of Continental Shelf waters between Cape Henlopen, Delaware, and Cape Hatteras, North Carolina June 1963-December 1964. U.S. Dep. Commer., ESSA Prof. Pap. 3, 82 p. henry, k. a. 1971. Atlantic menhaden (Brevoortia tyrannus) resource and fishery — analysis of decline. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-642, 32 p. HIGHAM, J. H., AND W. R. NICHOLSON. 1964. Sexual maturation and spawning of Atlantic menhaden. U.S. Fish. Wildl. Serv., Fish. Bull. 63:255-271. June, F. C, and J. L. Chamberlin. 1959. The role of the estuary in the life history and biology of Atlantic menhaden. Proc. Gulf Caribb. Fish. Inst., 11th Annu. Sess., p. 41-45. KENDALL, A. W., JR., AND J. W. REINTJES. 1975. Geographic and hydrographic distribution of Atlantic menhaden eggs and larvae along the middle Atlantic coast from RV Dolphin cruises, 1965-66. Fish. Bull., U.S. 73:317-335. LEWIS, R. M. 1965. The effect of minimum temperature on the survival of larval Atlantic menhaden, Brevoortia tyrannus. Trans. Am. Fish. Soc. 94:409-412. 40 NELSON ETAL.: LARVAL TRANSPORT OF BREVOORTIATYRANNUS MARQUARDT, D. W. 1963. An algorithm for least-squares estimation of non- linear parameters. J. Soc. Ind. Appl. Math. 11:431-441. MASSMANN, W. H., J. J. NORCROSS, AND E. B. JOSEPH. 1962. Atlantic menhaden larvae in Virginia coastal waters. Chesapeake Sci. 3:42-45. MATTHIESSEN, G. C. 1974. Rome Point Investigations, Quarterly Progress Rept. Sept. - Nov., 1973. Marine Research Inc., East Wareham, Mass. Mimeo. Data Rep., lip. McHUGH, J. L. 1969. Comparison of Pacific sardine and Atlantic menhaden fisheries. FiskeriDir. Skr. Ser. HavUnders 15:356-367. MURPHY, G. I. 1967. Vital statistics of the Pacific sardine (Sardinops caerulea) and the population consequences. Ecology 48:731-736. PERMUTTER, A. 1939. Section I. An ecological survey of young fish and eggs identified from tow-net collections. In A biological survey of the salt waters of Long Island, 1938, Part II, p. 11-71, N.Y. Conserv. Dep., Suppl. 28th Annu Rep., 1938, Salt- water Surv. 15. RADOVICH, J. 1962. Effects of sardine spawning stock size and environ- ment on year-class production. Calif. Fish Game 48:123- 140. REINTJES, J. W. 1961. Menhaden eggs and larvae from MV Theodore N. Gill cruises, South Atlantic coast of the United States, 1953- 54. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 393, 7 p. 1968. Development and oceanic distribution of larval menhaden. In Report of the Bureau of Commercial Fisheries Biological Laboratory, Beaufort, N.C., p. 9-11. U.S. Fish Wildl. Serv., Circ. 287. 1969. Synopsis of biological data on the Atlantic menhaden, Brevoortia tyrannus. U.S. Fish Wildl. Serv., Circ. 320, 30 P- REINTJES, J. W., AND A. L. PACHECO. 1966. The relationship of menhaden to estuaries. In R. F. Smith, A. H. Swartz, and W. H. Massmann (editors), A symposium on estuarine fisheries, p. 50-58. Am. Fish. Soc. Spec. Publ. 3. RICKER, W. E. 1954. Stock and recruitment. J. Fish. Res. Board Can. 11:559-623. SCHAAF, W. E. 1972. Dynamics of Atlantic menhaden. Brevoortia tyrannus, population inferred from statistics of the purse-seine fishery: 1955-1969. Ph.D. Thesis, Univ. Michigan, Ann Arbor, 42 p. (Diss. Abstr. Int. 33:5153B.) In press. Fish population models: Potential and actual links to ecological models. Proceedings of a symposium "Ecological modeling in a resource management framework." Resour. of the Future, Inc., Wash., D.C. SCHAAF, W. E., AND G. R. HUNTSMAN. 1972. Effects of fishing on Atlantic menhaden stock: 1955- 1969. Trans. Am. Fish. Soc. 101:290-297. SETTE, O. E. 1943. Biology of the Atlantic mackerel (Scomber scombrus) of North America. Part I: Early life history, including the growth, drift, and mortality of the egg and larval popu- lations. U.S. Fish Wildl. Serv., Fish Bull. 50:149-237. SISSENWINE, M. P. 1974. Variability in recruitment and equilibrium catch of the southern New England yellowtail flounder fishery. J. Cons. 36:15-26. STEFANSSON, U., L. P. ATKINSON, AND D. F. BUMPUS. 1971. Hydrographic properties and circulation of the North Carolina shelf and slope waters. Deep-Sea Res. 18:383- 420. U.S. Department of Commerce. 1973. Surface water temperature and density- Atlantic coast North and South America. U.S. Dep. Commer.. NOAA, Natl. Ocean. Surv. Publ. 31-1, 109 p. WALFORD, L. A. 1938. Effects of currents on distribution and survival of the eggs and larvae of the haddock (Melanogrammus aeglefinus) on Georges Bank. U.S. Bur. Fish. Bull. 49:1- 73. 41 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. 43 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 44 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 45 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. % 24 0 10 10 80 10 9 0 0 d) 100 5 0 40 60 2 0 0 800 9 40 49 11 8 0 0 48 0 10 0 90 10 9 0 0 (2) 100 5 0 20 80 1 1 100 800 10 10 60 30 7 1 14 72 0 10 20 70 10 9 0 0 (3) 100 5 20 40 40 2 2 100 800 9 0 56 44 6 6 100 96 0 10 0 70 30 7 1 14 (4) 100 5 20 20 60 1 1 100 800 10 10 57 33 6 6 100 120 0 10 10 40 50 5 0 0 (5) 100 5 0 0 100 0-AII spent — — 800 9 0 0 100 0-AII spent — — 148 0 10 0 60 40 6 0 0 (6) 100 5 0 0 100 0-AII spent — — 800 10 0 0 100 0-AII spent — — Totals 0 60 7 68 25 36 1 3 (6 days) 100 30 7 20 73 6 4 67 800 57 10 20 70 24 13 54 '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) 0 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' 0 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 (0.1000250 P>0.250 P>0.250 NS2 NS NS 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 df SS MS F ratio Probability 1 3 3 31 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 1 04585 04585 004 P>0 250 NS 3 27.2532 9.0844 0.71 P>0.250 NS 3 8.0860 2.6953 021 P>0 250 NS 31 3982616 12.8471 46 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 09 Q- 0 8 Cl ^ 0 7 3. ~ 06 oj 6 5 05 o 0) to 3 04 Cl a. O 03 O E o f 0.2 Q. 3 c (V CD Eggs In Ovary 0 6 12 18 24 48 Time (h) 72 96 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. 47 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 0 800 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 df SS MS F ratio Probability Between concentrations 0 vs. 800 ppb Within groups Total 12 14 1 .3442 0.0843 1 .4285 06721 0 0070 95.6098- P<0.01 Percent survival through yolk absorption Source of variation df SS MS F ratio Probability Between concentrations 0 vs. 800 ppb Within groups Total 2 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. 48 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. 49 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.). 51 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. 52 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 68 -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 95 -2.9823 3.4423 0.1269 0.9951 0.9902 Female 76 -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. 53 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 11 67 221 11 64 210 506 13 71 220 13 73 231 547 13 77 256 14 83 271 655 12 68 215 12 68 231 514 'I = Jan-Mar.; II = Apr-June; III = July-Sept.; IV = Oct -Dec HOOr KX>0 900 o»800 £ 700 ^ 600 o 500 O m z 400 < Id 2 300 • MALES (N=950) O FEMALES (N=II2I) ^oo •cP 200 I00 d? .CP d?" Jp _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 90 80- ~ 70 w 60 >- o z 50 LU 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 30 20 I 10 "-* 0 I H z UJ _l 50 _1 < 40 30 20 10 0 MALES I, =33.43 ( N = 257 ) [h -0.1778 (t-0.8551) 0 1749 (t -0 5667)1 6 8 10 12 age (yr) 14 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 54 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 13 3.5 36 4.5 29 5.5 15 6.5 17 7.5 23 8.5 23 9.5 16 10.5 10 11.5 6 12.5 1 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 No 345 7 33 11 19 14 9 17 24 28 20 14 4 2 6 1 0 3 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 2 7 14 11 0 19 26 3 50 68 75 59 70 116 4 67 142 45 102 124 56 5 270 290 337 353 207 514 6 244 663 387 329 732 613 7 375 278 881 418 501 1,217 8 380 412 432 400 560 570 9 215 274 382 366 465 596 10 320 45 106 582 108 201 11 67 123 42 138 283 94 12 76 24 72 247 32 219 13 5 14 11 69 57 30 14 10 2 0 50 10 26 15 5 7 0 20 10 0 16 2 2 0 7 3 9 18 9 3 0 21 4 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 estimates of and sex numbers utilized Z Z 1971: Male 8 8-16 0.70 0.43 Female 10 7-16 0.44 0.20 1972: Male 6 6-13 0.53 0.44 Female 6 6-16 0.55 0.31 1973: Male 7 7-13 0.68 0.61 Female 7 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. 55 FISHERY BULLETIN: VOL. 75, NO. 1 8 6 4 2 0 c - 8 »- x < o cr UJ CD o 3 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 16 20 FIGURE 4. — Catch curves of male rex sole collected off Oregon in September 1971, 1972, and 1973. I < o in a. UJ m 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 10 I 0 u_ fe 50 cr iu 40 CD 5 | 30 20 10 — 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 56 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 50 (20) (77) (16) (64) (60) (37) (84) (33) (55) (50) RIPENING _□_ 2 ioor UJ =3 o UJ a. u. 50 o UJ RIPE AND SPAWNING n n XL I00r (—1 r^ 50 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. 57 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 4 4 5 18 40 189 240 278 279 294 346 364 374 450 788 Total 2.537 15 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 CD CD - CD a CD o □ CD CD CD CD CD 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 52 43 50 Date 5, 9 April 30 April 8 April AAT phenotypes: AA 3 8 6 AB 18 3 10 BB 9 10 11 BC 12 12 9 CC 3 2 3 CD 1 0 0 DD 0 0 0 AD 1 1 0 AC 4 6 9 BD 1 1 2 Frequency of alleles: A 0.28 0.30 0.31 B 0.47 0.42 0.43 C 0.23 0.26 0.24 D 0.02 0.02 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 Proposed no. Type of bands in no. of of alleles per alleles Phenotypic Protein1 starch gel loci locus found variation AAT A-I 1 1 — Monomorphic AAT A-II 4 4 A,B,C,D Polymorphic LDH 1 1 — Monomorphic Peptidase A-I 1 1 — Monomorphic Peptidase A-II 2 2 A.B Polymorphic PGM 3 3 A'.A.B Polymorphic TO 1 1 — Monomorphic Muscle proteins2 7 7 1 — 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. 58 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 50 43 44 Date 5, 9 April 30 April 8 April Peptidase phenotypes: AA 10 10 13 AB 30 17 22 BB 10 16 9 Frequency of alleles: A 0.50 0.43 0.55 B 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 + UJ + -1 1 i _l UJ _l _l < uj a _i _l < li- Cl u. z 1 7DNF T o o (MONOMORPHIC) z F- o o F- 0. O UJ -, O. > A t- < n CD ZONE n (POLYMORPHIC) UJ > A A ui B □ □ F- B or < _l UJ ORIGIN i 1 1 ac AA AB BB PEPTIDASE PHENOTYPES ORIGIN □ - CD CD CD 1 I C3 1 CD l A'A AA AB PGM PHENOTYPES BB 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 52 43 50 Date 5. 9 April 30 April 8 April PGM phenotypes: A'A 0 0 1 AA 51 42 49 AB 0 1 0 BB 1 0 0 Frequency of alleles: A1 000 0.00 0.01 A 0.98 099 0.99 B 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 59 FISHERY BULLETIN: VOL. 75, NO. 1 northeastern Pacific Ocean. H. R. MacMillan Lectures in Fisheries, Univ. B.C., 190 p. BEST, E. A. 1961. The California animal food fishery 1958-1960. Pac. Mar. Fish. Comm., Bull. 5:5-15. DAY, D. S., AND W. G. PEARCY. 1968. Species associations and benthic fishes on the con- tinental shelf and slope off Oregon. J. Fish. Res. Board Can. 25:2665-2675. 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. DOMENOWSKE, R. S. 1966. A comparison of age estimation techniques applied to rex sole, Glyptocephalus zachirus. M.S. Thesis, Univ. Washington, Seattle, 102 p. FREY, H. W. 1971. California's living marine resources and their utili- zation. Calif. Dep. Fish Game, Sacramento, 148 p. HAGERMAN, F. B. 1952. The biology of the Dover sole, Microstomas pacificus (Lockington). Calif. Dep. Fish Game, Fish Bull. 85, 48 p. 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- ulus, Eopsetta jordani, and Microstomas pacificus, re- 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- tain salmonid populations. In R. C. Simon and P. A. Lar- kin (editors), The stock concept in Pacific salmon, p. 19- 160. H. R. MacMillan Lectures in Fisheries, Univ. B.C. SCOTT, D. M. 1954. A comparative study of the yellowtail flounder from three Atlantic fishing areas. J. Fish Res. Board Can. 11:171-197. 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 myogens and blood hemoglobins of marine and freshwater vertebrates and their application to biochemical sys- tematics. J. Fish. Res. Board Can. 22:203-213. 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. 60 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. 61 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 T" 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 62 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 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 20 4 9 39.37 196.88 7.34 16.30 8C 7113 TI 7114 7-18 May 1971 123 2 24 0.21 12 88 300 1580 GE 7117 26 June-4 July 1971 27 0 0 0.00 — 000 — 8C 7120 TI 7121 7-25 Aug. 1971 146 0 0 0.00 — 0.00 — TI 7131 8B 7132 GE 7127 7-16 Nov. 1971 66 15 20 41.41 187.73 4.18 14.20 8B 7201 GE 7202 1-11 Feb. 1972 30 8 13 151.20 604.81 20.29 49.97 GE 7208 1-10 May 1972 30 2 2 1.38 22.11 0.28 4.44 GE 7210 12-18 June 1972 13 0 0 0.00 — 0.00 — IS 7205 9-17 Sept. 1972 34 0 0 0.00 — 0.00 — IS 7209 8-16 Nov. 1972 50 5 2 0.83 8.30 1.61 40.28 IS 7303 19-27 Jan. 1973 51 12 20 23.77 101.04 19.12 48.76 IS 7308 9-17 May 1973 49 2 3 2.48 6072 229 37.41 IS 7311 27 June-6 July 1973 51 0 0 0.00 — 0.00 — IS 7313 3-13 Aug. 1973 50 0 0 0.00 — 0.00 — IS 7320 6-14 Nov. 1973 51 8 5 4.11 26 22 111 1 1 32 CL 7405" 28 Feb.-9 Mar. 1974 36 0 0 0.00 — 000 — CL7412 1-9 May 1974 44 1 1 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 of towing of filtered per volume filtered of filtered volume filtered speed towing speed unit depth per unit depth Cruises stations (m3) (m3) (m/s) (m/s) (m3/m) (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 20 358 335 <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 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. 63 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: n. cj2j 10 (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): Pj CjZj Aj (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 64 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 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 70 HOUDE: ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING GE 7101 Ltrkus teres egos February 1971 (£7101 I ; 6 TERES LARVAE FEBRUARY 1971 1 i \ 50m- \ 4 1 • • i* + + ' 4 + 4 . 4- Number under IOm2 4 0 • IOO0 1 86° 84' 8C 7113 S Tl 71114 etrumeus teres eggs May 1971 30° i 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? r © xooo ' ' 1 84* 6E 7127, TI 7131 & 8B 7132 Etrumeus teres eggs November 1971 30° 1 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, \ / • I000 30" 50m- u^ \ 28* ■ M o\ i:6- ?4° 1 Number under IOm2 • 0 1 • " • I-IO • 11-100 • 101 - IOOO © XOOO 1 • l_ .£: 4 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 + + + •+*«++ + + 4- o\ Lb" 1 Number under IOm2 4 0 • I-IO • 11-100 • IOI-IOOO + + +i 4 4- +4 + + ,4 -»- 4 4 4 +J • + 4 + + + <*--'' © >I000 I * 84° GE 7127, TI 7131 & 8B 7132 Etrumeus teres larvae November 1971 1 r— 30° \ 4 4 + * + + V 50m« * +"*■"*■■*■ V-« • #.+ + * + ♦ 1 4 +#•+++- / 28° v - • ♦ • • y tt » yj o\ 1 Number under IOm2 : ?■ • l-IO \ T. [• • 11-100 • 101 - IOOO ' ' * + j*!*^ © >I000 ■ 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. 71 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 \ - o\ 26" Number under 10m2 ♦ 0 • I000 GE 7208 Etrumeus teres eggs Hay 1972 30° 50m-. ^ \ + / 26* \ f^ V - + + + + 1 + * \ K» o\ + + + + 'i + *- «^ + \ + + 2fo° Number under 10m2 + 0 • I000 | 30° \ 50m« • • • • '• * * 28" + • \ + o\ 26° Number under 10m2 ♦ 0 •\ - >> fl • 1 - 10 + • w + + • 11-100 • 101-1000 * * •*.. ♦ +- .*•»--' © >I000 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 • ; + * .>--" © >I000 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 © >I000 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. 72 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- I000 1 80° 50m-.. \_ • • • • V • \ * * * / • \ • • • <-/*y- \ - ♦ • »'•-., • • - l/ • • \ + + ♦ \j- Tc. Number under 10m- • * <-\ * ♦ ♦ + 0 • • ': • * * * \ y • 1-10 • 11-100 • 101 - 1000 • •: • .-<"'-'' © >I000 i i . _i_ IS 7308 Etrumeus teres eggs Hay 1973 64" IS 7308 Etrumeus teres larvae May 1973 30° 50m-., -t- \ 28* + o\ *■ * *-\ +■ + + 2b" Number under 10m2 + 0 * * ; +■ +- + ♦ \ y • 1 - 10 • n-ioo • 101 - 1000 *j * * ...*■*--' © >I000 30° 1 1 ■ ■ r- 50m'-. \~» • * + * + * / \ 26° • \ + - • ♦[ft. V * * \ + * *\l o\ * +■ \ *■ + * »x 26" Number under 10m2 * . .,.+ . ♦ 0 . ': . ^9 / • 1 - 10 • 11-100 • IOI-IOOO *l * * .-«--"' © >I000 1 ' ■ « IS 7320 Etruheus teres eggs November 1973 84" IS 7320 Etruheus teres larvae November 1973 1 1 — V&A" \ + t + + \ 50m.. • + + + V + + \ • *■ + ♦ / ■ \ + ♦ \ • + + * 0") * + + 1 + + + + Number under 10m2 ♦ 0 ♦ • ! + + -+■ * \ y • 1-10 • 11-100 • IOI-IOOO + tj + .'•"'-'' © >I000 1 Number under 10m2 + 0 • 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. 73 FISHERY BULLETIN: VOL. 75, NO. 1 a 7112 Etrikeus teres eggs a 7112 Etrueus teres LARVAE May 1971 \ — — r- r \ 50m- X ' * • * *~\ - \ - \ * * *\|T . I000 k^-^ ><~^ \ * u^^'tX \ 50m-. \ . . :N\ \ \ ••••) 1) - V ' * w \ " • '"■■•. •♦*•'/ \ V*\r 0 ' ) Y.\*\ J Number under 10m2 ♦ 0 • ' *^ _J • 1 - 10 • II-IOO • 101-1000 ! . ■ ..'»■-'' © >I000 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- 74 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 90 80 70- 60- 50- >- 40 U " 50 ^ 100 X 3 9° * 80 £ 70 Q. 60 - 50- 40- 30 20 10 Etrumeus teres eggs Etrumeus teres larvae -5mm -T 1 r- Etrumeus teres larvae '5mm 100 '-•') 80 70 t'i 50 40 SO 20 10 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; 0.2520.0 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 80 HOUDE: ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING 48 44 40 36 32 28 24 20 16 12 8 4 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 D 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 50 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. 81 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; 0.05T> 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 82 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) (days) (no. x 1011) Class (no. x 10") (days) (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 83 FISHERY BULLETIN: VOL. 75, NO. 1 1000- 500 - r-100 b X (jj 50 o z < Q Z m < a UJ >" 10 UJ x< ■ i _L 2 4 6 6 10 12 14 16 16 20 24 28 ESTIMATED MEAN AGE (DAYS) 32 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 84 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 85 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 N 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 86 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. LITERATURE CITED AHLSTROM, 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. 1959a. Distribution and abundance of eggs of the Pacific sardine, 1952-1956. U.S. Fish Wildl. Serv., Fish. Bull. 60:185-213. 1959b. Vertical distribution of pelagic fish eggs and larvae off California and Baja California. U.S. Fish Wildl. Serv., Fish. Bull. 60:107-146. 1968. An evaluation of the fishery resources available to California fishermen. In The future of the fishing indus- try of the United States, p. 65-80. Univ. Wash., Publ. Fish., New Ser. 4. ALVERSON, D. L. 1971. Manual of methods for fisheries resource survey and appraisal. Part I. Survey and charting of fisheries re- sources. FAO, Fish. Tech. Pap. 102, 80 p. ALVERSON, D. L., AND W. T. PEREYRA. 1969. Demersal fish explorations in the northeastern Pacific Ocean — an evaluation of exploratory fishing methods and analytical approaches to stock size and yield forecasts. J. Fish. Res. Board Can. 26:1985-2001. Anonymous. 1958. Gulf exploratory fishery program. Commer. Fish. Rev. 20(7):29-32. BANNISTER, R. C. A., D. HARDING, AND S. J. LOCKWOOD. 1974. Larval mortality and subsequent year-class strength in the plaice (Pleuronectes platessa L.l. In J. H. S. Blaxter (editor), The early life history of fish, p. 21- 37. Springer- Verlag, N.Y. BEVERTON, R. J. H. 1963. Maturation, growth and mortality of clupeid and engraulid stocks in relation to fishing. Rapp. P.- V. Reun. Cons. Perm. Int. Explor. Mer 154:44-67. BLACKBURN, M. 1941. The economic biology of some Australian clupeoid fish. Aust. Counc. Sci. Ind. Res. Bull. 138, 135 p. BULLIS, H. R., JR., AND J. S. CARPENTER. 1968. Latent fishery resources of the central West Atlantic region. In The future of the fishing industry of the Unit- ed States, p. 61-64. Univ. Wash., Publ. Fish., New Ser. 4. BULLIS, H. R., JR., AND J. R. THOMPSON. 1967. Progress in exploratory fishing and gear research in region 2 fiscal year 1966. U.S. Fish Wildl. Serv., Circ. 265, 14 p. CUSHING, D. H. 1957. The number of pilchards in the Channel. Fish. In- vest. Minist. Agric. Fish Food (G.B.), Ser. II, 21(5), 27 p. De la Campa de Guzman, S., and J. M. Ortiz Jiminez. 1975. Distribucion y abundancia de larvas de peces en el Golfo de California durante abril-mayo de 1973, con espe- cial referenda a sardina monterrey y japonesa. Inst. Nac. Pesca. INP/SC:11, 25 p. Dryfoos, R. L., R. P. Cheek, and R. L. Kroger. 1973. Preliminary analyses of Atlantic menhaden, Bre- voortia tyrannus, migrations, population structure, 87 FISHERY BULLETIN: VOL. 75, NO. 1 survival and exploitation rates, and availability as indi- cated from tag returns. Fish. Bull., U.S. 71:719-734. FARRIS, D. A. 1961. Abundance and distribution of eggs and larvae and survival of larvae of jack mackerel (Trachurus symmet- ricus). U.S. Fish Wildl. Serv., Fish. Bull. 61:247-279. FOOD AND AGRICULTURE ORGANIZATION. 1974. Catches and landings, 1973. FAO, Yearb. Fish. Stat. 36, 590 p. Fore, p. l. 1971. The distribution of the eggs and larvae of the round herring, Etrumeus teres, in the northern Gulf of Mexico. (Abstr.) Assoc. Southeast. Biol. Bull. 18:34. GULLAND, J. A. 1971. The fish resources of the ocean. Fishing News (Books) Ltd., Surrey, Engl., 255 p. 1972. The scientific input to fishery management deci- sions. In Progress in fishery and food science, p. 23-28. Univ. Wash., Publ. Fish., New Ser. 5. Harding, D., and J. W. Talbot. 1973. Recent studies on the eggs and larvae of the plaice (Pleuronectes platessa L.) in the Southern Bight. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 164:261-269. HOLDEN, M. J., AND D. F. S. RAITT. 1974. Manual of fisheries science. Part 2. Methods of re- source investigation and their application. FAO, Fish. Tech. Pap. 115, 214 p. HOUDE, E. D. 1973a. Estimating abundance of sardine-like fishes from egg and larval surveys, eastern Gulf of Mexico: prelimi- nary report. Proc. Gulf Caribb. Fish. Inst., 25th Annu. Sess., p. 68-78. 1973b. Some recent advances and unsolved problems in the culture of marine fish larvae. Proc. World Maricult. Soc. 3:83-112. 1974. Research on eggs and larvae of fishes in the eastern Gulf of Mexico. In R. E. Smith (editor), Proceedings of marine environmental implications of offshore drilling in the eastern Gulf of Mexico, p. 187-204. State Univ. Syst. Fla., Inst. Oceanogr., St. Petersburg. 1976. Abundance and potential for fisheries development of some sardine-like fishes in the eastern Gulf of Mexico. Proc. Gulf Caribb. Fish. Inst., 28th Annu. Sess., p. 73-82. HOUDE, E. D., S. A. BERKELEY, J. J. KLINOVSKY, AND C. E. DO WD. 1976. Ichthyoplankton survey data report. Summary of egg and larvae data used to determine abundance of clupeid fishes in the eastern Gulf of Mexico. Univ. Miami Sea Grant Tech. Bull. 32, 193 p. HOUDE, E. D., AND N. CHITTY. 1976. Seasonal abundance and distribution of zoo- plankton, fish eggs and fish larvae in the eastern Gulf of Mexico, 1972-74. U.S. Dep. Commer., NOAA Tech. Rep. NMFSSSRF-701, 18 p. HOUDE, E. D., AND P. L. FORE. 1973. Guide to identity of eggs and larvae of some Gulf of Mexico clupeid fishes. Fla. Dep. Nat. Resour., Mar. Res. Lab., Leafl. Ser. 4(23), 14 p. HOUDE, E. D., W. J. RICHARDS, AND V. P. SAKSENA. 1974. Description of eggs and larvae of scaled sardine, Harengula jaguana. Fish. Bull., U.S. 72:1106-1122. HOUDE, E. D., AND L. J. SW ANSON, JR. 1975. Description of eggs and larvae of yellowfin menha- den, Brevoortia smithi. Fish. Bull., U.S. 73:660-673. ITO, S. 1968. Observations on the ovarian ova of the round her- ring, Etrumeus micropus (Temminck et Schlegel). Bull. Jap. Sea Reg. Fish. Res. Lab. 19:11-17. KHROMOV, N. S. 1969. Distribution of plankton in the Gulf of Mexico and some aspects of its seasonal dynamics. In A. S. Bogdanov (editor), Soviet-Cuban fishery research, p. 36-56. VNIRO, TsRI, 1965. (Translated from Russ. by Isr. Program Sci. Transl., available U.S. Dep. Commer., Clgh. Fed. Sci. Tech. Inf., as TT 69-59016.) LENARZ, W. H. 1973. Dependence of catch rates on size of fish larvae. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 164:270-275. Martinez, S., and E. D. houde. 1975. Fecundity, sexual maturation, and spawning of scaled sardine (Harengula jaguana Poey). Bull. Mar. Sci. 25:35-45. Matsuura, Y. In press. A study of the life history of Brazilian sardine, Sardinella brasiliensis . IV. Distribution and abundance of sardine larvae. Bol. Inst. Oceanogr. (Sao Paulo). MITO, S. 1961. Pelagic fish eggs from Japanese waters — I. Clupeina, Chanina, Stomiatina, Myctophida, Anguillida, Belonida and Syngnathida. [In Jap., Engl, summ.] Sci. Bull. Fac. Agric, Kyushu Univ. 18:285-310. MOSER, H. G., E. H. AHLSTROM, D. KRAMER, AND E. G. STE- VENS. 1974. Distribution and abundance of fish eggs and larvae in the Gulf of California. Calif. Coop. Oceanic Fish. In- vest. Rep. 17:112-128. NAKAI, Z., AND S. HATTORI. 1962. Quantitative distribution of eggs and larvae of the Japanese sardine by year, 1949 through 1951. Bull. Tokai Reg. Fish. Res. Lab. 9:23-60. O'TOOLE, M. J., AND D. P. F. KING. 1974. Early development of the round herring, Etrumeus teres (de Kay) from the South East Atlantic. Vie Milieu, Ser. A, 24:443-452. PINUS, G. N. 1974. Some factors influencing early survival and abun- dance of Clupeonella in the Sea of Azov. In J. H. S. Blaxter (editor), The early life history of fish, p. 81-86. Springer- Verlag, N.Y. RICHARDS, W. J., AND B. J. PALKO. 1969. Methods used to rear the thread herring, Opis- thonema oglinum, from fertilized eggs. Trans. Am. Fish. Soc. 98:527-529. RINKEL, M. O. 1974. Western Florida continental shelf program. In R. E. Smith (editor), Proceedings of marine environmental implications of offshore drilling in the eastern Gulf of Mexico, p. 97-126. State Univ. Syst. Fla., Inst. Oceanogr., St. Petersburg. SAKSENA, V. P., C. STEINMETZ, JR., AND E. D. HOUDE. 1972. Effects of temperature on growth and survival of laboratory-reared larvae of the scaled sardine, Harengula pensacolae Goode and Bean. Trans. Am. Fish. Soc. 101:691-695. SALNIKOV, N. E. 1969. Fishery research in the Gulf of Mexico and the Caribbean Sea. In A. S. Bogdanov (editor), Soviet- Cuban fishery research, p. 78-171. VNIRO TsRI, 1965. (Translated from Russ. by Isr. Program Sci. Transl., 88 HOUDE: ABUNDANCE AND POTENTIAL YIELD OF ROUND HERRING available U.S. Dep. Commer., Clgh. Fed. Sci. Tech. Inf., as TT 69-59016.) Saville, A. 1956. Eggs and larvae of haddock {Gadus aeglefinus L.) at Faroe. Scott. Home Dep. Mar. Res. 1956(4), 27 p. 1964. Estimation of the abundance of a fish stock from egg and larval surveys. Rapp. P.-V. Reun. Cons. Perm. Int. Explor. Mer 155:165-170. SCHAAF, W. E., AND G. R. HUNTSMAN. 1972. Effects of fishing on the Atlantic menhaden stock: 1955-1969. Trans. Am. Fish. Soc. 101:290-297. SETTE, O. E., AND E. H. AHLSTROM. 1948. Estimations of abundance of the eggs of the Pacific pilchard (Sardinops caerulea) off southern California dur- ing 1940 and 1941. J. Mar. Res. 7:511-542. SIMPSON, A. C. 1959. The spawning of the plaice (Pleuronectes platessa) in the North Sea. Fish. Invest. Minist. Agric. Fish. Food (G.B.), Ser. II, 22(7), 111 p. Smith, p. e. 1973. The mortality and dispersal of sardine eggs and lar- vae. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 164:282- 292. Smith, p. e., and S. Richardson (editors). In press. Manual of methods for fisheries resource survey and appraisal. Part 4. Standard techniques for pelagic fish egg and larvae survey. FAO, Rome. Southward, a. j., and n. demir. 1974. Seasonal changes in dimensions and viability of the developing eggs of the Cornish pilchard (Sardina pilchar- dus Walbaum) off Plymouth. In J. H. S. Blaxter (editor), The early life history of fish, p. 53-68. Springer- Verlag, N.Y. TAFT, B. A. 1960. A statistical study of the estimation of abundance of sardine (Sardinops caerulea) eggs. Limnol. Oceanogr. 5:245-264. TANAKA, S. 1960. Studies on the dynamics and the management offish populations. Bull. Tokai Reg. Fish. Res. Lab. 28:1- 200. UCHIDA, K., S. IMAI, S. MITO, S. FUJITA, M. UENO, Y. SHOJIMA, T. SENTA, M. TAHUKU, AND U. DOTU. 1958. Studies on the eggs, larvae and juvenile of Japanese fishes. Series I. [In Jap.] 2d Lab. Fish. Biol., Fish. Dep., Fac. Agric, Kyushu Univ., 89 p. WATANABE, T. 1970. Morphology and ecology of early stages of life in Japanese common mackerel, Scomber japonicus Hout- tuyn, with special reference to fluctuation of popula- tion. Bull. Tokai Reg. Fish. Res. Lab. 62:1-283. Watson, W., and J. M. leis. 1974. Ichthyoplankton of Kaneohe Bay, Hawaii. Univ. Hawaii, UNIHI-Sea Grant Publ. TR-75-01, 178 p. WHITEHEAD, P. J. P. 1963. A revision of the recent round herrings (Pisces: Dus- sumieriidae). Bull. Br. Mus. (Nat. Hist.) Zool. 10:305- 380. WISE, J. P. 1972. U.S. fisheries: A view of their status & poten- tial. Mar. Fish. Rev. 34(7-8):9-19. 89 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. 91 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). 92 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 n X Range Range Very early Colorless, white, ivory 7 0.5-2.2 0.5-1.3 8 <0.2 0.1-0.2 8 0.29 0.09-0.88 3 102 49-172 Early White, ivory, light gray, light yellow 12 2-6 2-6 15 1.1 0.2-2 15 0.75 0.19-1.75 10 168 74-278 Intermediate Ivory, white, light yellow, yellow, yellowish orange, light brownish orange 7 8-15 6-10 12 5.2 4.5-7 12 205 1.45-2.73 10 289 112-537 Advanced Yellow, yellowish orange, brownish orange, reddish brown, brownish purple 4 16-23 6-12 6 13.4 8-12 6 4.24 2.74-6.02 6 508 298-666 Mature Yellowish orange, orange, brownish orange, brownish purple 12 20-32 10-18 10 28.9 21-32 11 8.22 6.00-11.85 9 611 484-788 Redeveloping Ivory, yellowish orange, light brownish orange, reddish brown, reddish orange, brownish purple 6 8-20 5-7 14 9.0 2.5-21 14 2.67 1.04-7.25 16 347 148-671 93 FISHERY BULLETIN: VOL. 75, NO. 1 f ! ■ v ■ life -■ M «* ' IS © #»y* *. €> .# * I 4. $5 ^=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 96 HAEFNER: REPRODUCTIVE BIOLOGY OFGERYON QUINQUEDENS MM ■ •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. 97 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 n^l nfJl t*\ hr^lrnn D ,-D , n r— i FISHERY BULLETIN: VOL. 75, NO. 1 EARLY ^ r, nBp U ■ 30 40 q n ,- jliui^ INTERMEDIATE , "1 , , 5-1 N = 50 -0— P^r-^r^jlfrh 5, N=22 MATURE SHORT CARAPACE LENGTH (mm) 10 OVIGEROUS NOVEMBER 1974 n^Hrn h^V^ N=208 p n , n , < > Q Z o cr LU CD 15 10 SEPTEMBER 1975 tL 20 15 10 5 0 OVIGEROUS EGG REMNANTS H 1 1-1— I 1 ' T n , n , n JANUARY 1976 OVIGEROUS Un. u ^M 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, 98 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) a 4 20-33 4 0.2-0.3 10 57-66 10 0.6-0.9 b 5 56-60 0 no data 15 61-74 8 0.7-1.2 c 9 50-60 5 0.5-0.8 17 61-74 13 0.8-1.5 d 8 61-72 6 0.7-1.3 1 78 1 2.6 e 3 47-60 3 0.6-1.2 9 61-72 7 0.8-1.2 f 1 45 1 3.0 51 70-103 12 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 99 FISHERY BULLETIN: VOL. 75, NO. 1 Wm I 3. *&S--2^ .^€ ... / Si**** •v-. ~ns^ *'**>, VI- "*--. O.I6mm 0.65mm 'V -^ 0.65 mm ^§& *!» /v* •sjlt ■-W 5 "-**** 0.65mm i*5*****.-**.; % m < *} > ■"• " . w -*««<*>*"'' 065mm rx-ff' '" ^ji.T. ..■■■■ Jkh^'-' ■•■'"■"A *'«~., •^-j- ->**■' .-— " 1.33mm 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 BAGENAL, T. B., and E. braum. 1971. Eggs and early life history. In W. E. Ricker (editor), Methods for assessment offish production in fresh 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. Q I- 2 s O UJ (0 £ C CD IE o .c V) S m c CD T3 c ra Is 11 CD > c «§ c — ro ro t/t CJ - IX Q. o Q >- x Q X co X "D C CO CO o CO c\i co *r r-. 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CD CD 2- t> X >- X •^■T-Tt'^-'^- COOOCOO N indcM->ci:- m di d <5 NSTtCOO Tt c\i ■•- c\i in CM o m o I ciriN ' ' i- CD coscDino CM i- >- i- CM CM t O CM d d d d d i- in s coco cm oo o m co i- in co i- in cm p p CM d^-dddwd O CO CO CO CM O CO oi Wi-doi do o o o o 1 I in O 1 1 in o d d o o 1 1 CM o 1 1 h~ d CM CD CM i- CM CO •" in CO o CM 1 CO CD CM O i- CM o o o co CD I o h- in d d O o d d o O 1 o d d 0) r~ .,_ CO p o ,_ CO 1 f~ o co CM d CO *T CM d '" ■* 1 CO d T-' CD CD t ^ •q; co CD CM o o o ■* d d N in d <6 c\i CD CD o d CM CM i- CM CO i- in CO o in in CO in CO CD CD in en CD CD t- CO T— T_ C0 CO CM o ,_ CO ,_ *■ ,_ y- co in d d o o d d '- o o o d d 00 o CO ,- CM CD CD CD CO CO CO CM d ro CM CD •* d 1^ CM CM <» 1- I- i_l -* *jw — a* ^r *— CO CD CO CD > _J < 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 s M D 1.6 6.0 s 13.5 M D 1.0 1.5 2.3 D M s 0.3 1.5 2.2 M s D 2.6 2.7 5.5 S M D 0.2 2.5 3.3 S M D 0.9 2.3 3.1 S M D 0.5 1.1 1.4 D M S 0.3 0.5 3.5 S M D 0.0 0.6 M 2.4 s D 1.9 2.2 2.9 D M S 0.0 0.1 4.3 D M S 0.1 09 1.0 213 246 195 69 123 111 198 123 168 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) m2 Percent m2 Percent 1.5 0.11 0.21 0.16 0.33 3.0 0.16 0.16 0.23 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 r2 Equation Males August 67 0.46 Y = 0 389 • 0 004X September 108 0.68 Y = -4.737 + 0.033X October 64 0.73 Y = -8.804 + 0.055X November 46 0.32 Y = -2.782 + 0.01 8X March 35 0.43 Y = -3.785 + 0.021 X Females August 92 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 69 0.28 Y = -15.570 + 0.097X March 41 0.32 Y = -13.359 + 0.077X 110 WHITE and CHITTENDEN: AGE DETERMINATION OK ATLANTIC CROAKER I S 5- < 20 - BAY GULF REEF BAY GULF REEF _^£&- -cc r\ Ar^ 20 - BAY 30 - GULF 5 - REEF BAY GULF > o z HI D O uj K 0C CO U. D a 13 5 - REEF — L. 10 - BAY GULF 5 - REEF ^ ^ ^ ft LU 00 BAY 10- a. LU 5 — CO GULF REEF f- r\ r\ /V\ ^n /~\ 10 - O 5^ BAY <— ^ «-> ^- o GULF O 5- Q r-> ^^^—^^ REEF W y-1^ i s. s\ f\ /\ /S e- cc UJ CO 5- BAY f\ <-\ r\ *~~i GULF > ^-^ ^ Q i^. n REEF ^_ T — . 60 1^ 100 T 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 I " 50 > > 3 O -> z O a 3 < n = 60 Lj < 50 100 -rr l -f=t- n = 120 I 1 I I 100 -r^ ^ n = 448 50 100 1 50 n = 378 100 50 O 50- z t^JS 12 3 4 5 50 n=150 L 100 n = 187 iu 100 50 - -rf^l 3=^^, n = 137 100 ^ n 50- | v^V ^|^ 12 3 4 5 GONAD CONDITION 100-1 50 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 93 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 0 I < 5 - 10 - z uu a. 15 UJ Q. 20 25 H + 30 35 - 40 - 45- 50 May March Novemb September August August September 50 200 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 I o cc < 15n 5- J^T-i /\ i — i—n 20 40 15-, $ 5-l 15^ Z 5- ■h — r— i — r ■^iai i i i — r~i — i T-i — i — i -r~T — i — i A^ r — i — i — i > o z LJJ o LU CL I5n 5- 15n t — i — r t — I r-i — r— i ' i ' i — i — i T-1-! 1 1 Vm £ 15". CD 2 5^ o o cc LU cd I5n § 5-> t — i — n — r~-i T"""! 1 1 -\ — r ir i inln i T— I 1 1 t-^i — i — i — i — i r I11! I ^-T-. 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 5 I o < 10- 5 — 5 80 40 — > l- LU u D D O < 2 — 15 — 5 — LU CO 5 — I- 15 — CL LU OO 5 — cc 2 — LU CO o 2 — o o LU CO > O 2 10 — 5 — 2 — 10 — Age II+ Observed ■"^ *- --^- Age I + Observed - ^ „S Sss. r-. *. Aged By L/F ri-, , I + II + ? ^-~x Q^ ^-^ ,-> ^^-. Age I Observed n » «■ n n Age 0 Observed Age I Observed Age 0 Observed m am r-irs /-vr\ ■■ \r^,-i r-^ Aged By L/F •«--* Age I Observed _£ a. Q £\_ Age 0 Observed ~V\ Aged By L/F fl /— ^s. r-, A. Age II Observed — - Age I Observed s^> rW. m Age II Observed Age I Observed a ^^ ^^ _ca_ oa ^ Aged By L/F II 70 100 T 150 fca IR-i Back Calculated Length at Age I. o -c Age I Fish Captured in October, Age Determined by L/F Method. 5- 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. LITERATURE CITED Anderson, W. W. 1968. Fishes taken during shrimp trawling along the south Atlantic coast of the United States, 1931-35. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 570, 60 p. BAGENAL, T. B., AND E. BRAUM. 1971. Eggs and early life history. In W. E. Ricker (editor), Methods of assessment offish production in fresh waters, p. 166-198. IBP (Int. Biol. Programme) Handb. 3. Blackwell Sci. Publ., Oxf. BEARDEN, C. M. 1964. Distribution and abundance of Atlantic croaker, Micropogon undulatus, in South Carolina. Contrib. Bears Bluff Lab. 40, 23 p. BRIGGS, J. C. 1974. Marine zoogeography. McGraw-Hill, N.Y., 475 p. CHAO, L. N. 1976. Aspects of the systematics, morphology, life history and feeding of western Atlantic Sciaenidae (Pisces: Perciformes). Ph.D. Thesis, College of William and Mary, Williamsburg, 342 p. CHITTENDEN, M. E., JR. 1975. Dynamics of American shad, Alosa sapidissima, runs in the Delaware River. Fish. Bull., U.S. 73:487-494. 1976. Weight loss, mortality, feeding, and duration of res- idence of adult American shad, Alosa sapidissima, in fresh water. Fish. Bull., U.S. 74:151-157. CHITTENDEN, M. E., JR., AND J. D. MCEACHRAN. 1976. Composition, ecology, and dynamics of demersal fish communities on the northwestern Gulf of Mexico con- tinental shelf, with a similar synopsis for the entire Gulf. Sea Grant Publ. No. TAMU-SG-76-208, 104 p. Christmas, J. Y., and R. S. Waller. 1973. Estuarine vertebrates, Mississippi. In J. Y. Christmas (editor), Cooperative Gulf of Mexico estuarine inventory and study, Mississippi, p. 320-434. Gulf Coast Res. Lab. Franks, J. S., J. Y. Christmas, W. L. Siler, R. Combs, R. Waller, and C. Burns. 1972. A study of the nektonic and benthic faunas of the shallow Gulf of Mexico off the state of Mississippi as re- lated to some physical, chemical and geologic factors. Gulf Res. Rep. 4:1-148. GALLAWAY, B. J., AND K. STRAWN. 1974. Seasonal abundance and distribution of marine fishes at a hot-water discharge in Galveston Bay, Texas. Con- trib. Mar. Sci. Univ. Tex. 18:71-137. GUNTER, G. 1938. Seasonal variations in abundance of certain estuarine and marine fishes in Louisiana, with particular reference to life histories. Ecol. Monogr. 8:313-346. 1945. Studies on marine fishes of Texas. Publ. Inst. Mar. Sci. Univ. Tex. 1:1-190. 1950. Correlation between temperature of water and size of marine fishes on the Atlantic and Gulf coasts of the United States. Copeia 1950:298-304. HANSEN, D. J. 1969. Food, growth, migration, reproduction, and abun- dance of pinfish, Lagodon rhomboides, and Atlantic croaker, Micropogon undulatus, near Pensacola, Florida, 1963-65. U.S. Fish Wildl. Serv., Fish. Bull. 68:135-146. HARDEN JONES, F. R. 1968. Fish migration. Edward Arnold Publ., Lond., 325 p. Haven, D. S. 1954. Croakers. Va. Comm. Fish. 54th and 55th Annu. Rep. 1952-1953, p. 49-53. 1957. Distribution, growth, and availability of juvenile croaker, Micropogon undulatus, in Virginia. Ecology 38:88-97. HlLDEBRAND, S. F., AND L. E. CABLE. 1930. Development and life history of fourteen teleostean fishes at Beaufort, N.C. Bull. U.S. Bur. Fish. 46:384-488. HlLDEBRAND, S. F., AND W. C. SCHROEDER. 1928. Fishes of Chesapeake Bay. Bull. U.S. Bur. Fish. 43:1-366. HOESE, H. D. 1973. A trawl study of nearshore fishes and invertebrates of the Georgia coast. Contrib. Mar. Sci. Univ. Tex. 17:63-98. HOESE, H. D., B. J. COPELAND, F. N. MOSELY, AND E. D. LANE. 1968. Fauna of the Aransas Pass Inlet, Texas. III. Diel and seasonal variations in trawlable organisms of the adja- cent area. Tex. J. Sci. 20:33-60. Joseph, E. B. 1972. The status of the sciaenid stocks of the middle Atlantic coast. Chesapeake Sci. 13:87-100. LAPOINTE, D. F. 1958. Age and growth of the American shad, from three Atlantic coast rivers. Trans. Am. Fish. Soc. 87:139-150. LEGGETT, W. C. 1972. Weight loss in American shad (Alosa sapidissima, Wilson) during the freshwater migration. Trans. Am. Fish. Soc. 101:549-552. MASSMAN, w. h., and a. l. pacheco. 1960. Disappearance of young Atlantic croakers from the York River, Virginia. Trans. Am. Fish. Soc. 89:154-159. MILLER, J. M. 1965. A trawl study of the shallow Gulf fishes near Port Aransas, Texas. Publ. Inst. Mar. Sci. Univ. Tex. 10:80-107. Moore, d., H. a. Brusher, and L. Trent. 1970. Relative abundance, seasonal distribution, and species composition of demersal fishes off Louisiana and Texas, 1962-1964. Contrib. Mar. Sci. Univ. Tex. 15:45-70. NELSON, W. R. 1969. Studies on the croaker, Micropogon undulatus Linnaeus, and the spot, Leiostomus xanthurus Lacepede, in Mobile Bay, Alabama. M.S. Thesis, Univ. Alabama, University, 85 p. NIKOLSKY, G. V. 1963. The ecology of fishes. Academic Press, N.Y., 352 p. OSTLE, B. 1963. Statistics in research. 2d ed. Iowa State Univ. Press, Ames, 585 p. PARKER, J. C. 1971. The biology of the spot, Leiostomus xanthurus Lacepede, and Atlantic croaker, Micropogon undulatus (Linnaeus), in two Gulf of Mexico nursery areas. Sea Grant Publ. TAMU-SG. 71-210, 182 p. Pearson, j. C. 1929. Natural history and conservation of the redfish and other commercial Sciaenids on the Texas coast. Bull. U.S. Bur. Fish. 44:129-214. 1941. The young of some marine fishes taken in lower 122 WHITE and CHITTENDEN: AGE DETERMINATION OF ATLANTIC CROAKER Chesapeake Bay, Virginia, with special reference to the grey sea trout, Cynoscion regalis (Bloch). U.S. Fish Wildl. Serv., Fish. Bull. 50:79-102. PERRET, W. S. 1966. Occurrence, abundance, and size distribution of fishes and crustaceans collected with otter trawl in Vermilion Bay, Louisiana. M.S. Thesis, Univ. Southwest. La., Lafayette, 64 p. REID, G. K., JR. 1955. A summer study of the biology and ecology of East Bay, Texas. Part I. Introduction, description of area, methods, some aspects of the fish community, the in- vertebrate fauna. Tex. J. Sci. 7:316-343. REID, G. K., AND H. D. HOESE. 1958. Size distribution of fishes in a Texas estuary. Copeia 1958:225-231. RICHARDS, C. E. 1973. Age, growth and distribution of the black drum (Pogonias cromis) in Virginia. Trans. Am. Fish. Soc. 102:584-590. RIVAS, L. R., AND C. M. ROITHMAYR. 1970. An unusually large Atlantic croaker, Micropogon undulatus, from the northern Gulf of Mexico. Copeia 1970:771-772. ROYCE, W. F. 1972. Introduction to the fishery sciences. Academic Press, N.Y., 351 p. SERVICE, J. 1972. A user's guide to the statistical analysis system. N.C. State Univ., Raleigh, 260 p. Simmons, E. G., and H. D. Hoese. 1959. Studies on the hydrography and fish migrations of Cedar Bayou, a natural tidal inlet on the central Texas coast. Publ. Inst. Mar. Sci. Univ. Tex. 6:56-80. SUTTKUS, R. D. 1955. Seasonal movements and growth of the Atlantic croaker (Micropogon undulatus ) along the east Louisiana coast. Proc. Gulf Caribb. Fish. Inst., Annu. Sess. 7:151-158. Swingle, H. a. 1971. Biology of Alabama estuarine areas — cooperative Gulf of Mexico estuarine inventory. Ala. Mar. Res. Bull. 5, 123 p. Walburg, C. H., and P. R. Nichols. 1967. Biology and management of the American shad and status of the fisheries, Atlantic coast of the United States, 1960. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 550, 105 p. WALLACE, D. H. 1940. Sexual development of the croaker, Micropogon undulatus, and distribution of the early stages in Chesapeake Bay. Trans. Am. Fish. Soc. 70:475-482. WELSH, W. W., AND C. M. BREDER, JR. 1924. Contributions to life histories of Sciaenidae of the eastern United States coast. Bull. U.S. Bur. Fish. 39:141-201. 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. 2 6 9 18 Station (km from coast) 28 37 46 56 65 74 93 111 Month 20 46 59 85 95 Bottom depth (m) 142 330 220 340 1.060 1,300 2,850 1971: Jan. 2 2 2 2 Feb 2 2 2 2 — 2 — 2 — 1 1 1 Mar. 2 2 2 2 1 2 — 2 1 2 2 2 Apr. — — 1 1 1 1 1 1 — 1 1 — May 3 3 3 3 3 3 3 3 2 2 2 2 June 2 2 2 2 2 2 2 2 2 2 2 2 July 2 2 2 2 1 1 1 1 1 1 1 1 Aug. 2 2 2 2 2 2 2 2 2 2 2 1 Sept 1 1 1 1 1 1 1 1 1 1 1 1 Oct. 1 1 1 1 1 1 1 1 1 1 1 1 Nov. 1 1 1 1 1 1 1 1 1 1 1 1 Dec. 1 1 1 1 1 1 1 1 1 1 — — 1972: Jan. Feb. Mar. 3 2 3 3 3 3 3 3 2 2 2 2 Apr. 2 1 2 2 1 1 1 1 — — — — May 1 1 1 1 1 1 1 1 1 1 1 1 June 2 2 2 2 2 2 2 2 2 2 2 2 July 1 1 1 1 1 1 1 1 1 1 1 1 Aug. 1 1 1 1 1 127 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 0 1.55 1.75 13.27 0 1.48 0 0.87 0 28.43 0 1.16 0 3.14 0 15.85 0 34.09 79.70 4.45 0 27.04 6.75 32.47 3.35 0.32 0 0.70 0 33.81 0 37 80 0 1.03 0 1.37 0 1.12 0 0.77 0 5.53 1.04 6.56 0 1.09 0 0.70 0 71.17 0 0 15.60 258.50 0 2.31 0 0 60.30 0 1.80 2.59 0 7.53 57.19 0 4.80 0.64 7.09 0 1.57 18.27 113.81 2.70 259 1,157.90 12.53 1.31 0 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 0 + 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) 0 2.90 + Zeneretmus latifrons (c) 0 131.46 + Agonidae sp. 6 (c) 0 34.18 Cyclopteridae: + Lipans pulchellus (c) 0 2.05 + - Cyclopteridae spp. 1 (c-o) + Cyclopteridae sp. 3 (c) 0 29.47 + - Undetermined spp. (c) Bathymasteridae: 0 5.78 + - Ronquilus jordani (c) Blennioids: 0.82 37.04 + Undetermined spp. (c) 0 1.15 Clinidae: 0 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) 0 7.24 + Lyconectes aleutensis (c) + Lumpenus sagitta (c) 580.28 5.44 + Plectobranchus evides (c) + Stichaeidae sp. 1 (c) 0 2.86 + - Stichaeidae sp. 2 (c) 0 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 0 + Clevelandia ios (c) 7.55 0 Centrolophidae: 145.43 0 - 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 0 - Atheresthes stomias (o) 3.15 0 + - Embassichthys bathybius (o) 0.79 0 - Eopsetta jordani (o) 0 2.21 + - Glyptocephalus zachirus (o) 58.45 9.19 + - Hippoglossoides elassodon (c-o) 0.77 0 + - Isopsetta isolepis (c) 21.84 0 + - Lepidopsetta bilineata (c) 5.94 0 + - Lyopsetta exilis (o) 42.70 0 + - Microstomus pacificus (o) 0.33 0 + - Parophrys vetulus (c) 1.12 0 + - Platichthys stellatus (c) 21.55 0 + - 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- E o < > rr < Ll_ o cr UJ QQ _l < 1000 DAY • NIGHT O DAY 100 t o § o (§> <8 10 8 2 6 9 46 56 STATIONS 65 74 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- % < _i 800 700 Ll. o 600 o rr 00 500 o o 4 00 • 1 300- 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 O) c s CO CO -C CD Q. Q. CO CO IB CO T3 to <0 3 Depth strata co CD CD CD = a.™ 3 Q. CO T3 *i_ CD E CO O CO 11 CO 2 CD CO 3 C $ CD « 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- O 200- 160 120- > K 80 < O 40h -z. 0 1971 mm FEB -MAR -APR I 1 MAY -JUN-JUL C—l AUG-SEP-OCT-NOV-DEC tl 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 74 93 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 74 93 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: < o 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* 0 0 0 0 0 0 6-12 6 5-8-25 1B. Osmeridae (group 2) 0 0 4-6-1 1 0 5-15-32 7-25-35* 1 °* (§7 )"36 5-29-37 0 0 0 0 2. Parophrys vetulus 2-3-9 2-4-18* 3-8-21 «-G§)-18 5-8-22 14-21 0 0 2-3-6 2-10-17 3-5-14 2-5-14 3. Isopsetta isolepis 0 2-4-6 3-7-16 3-9-17 3-13-21* 6-16-21 10-11-19 0 0 2 0 0 4. Microgadus proximus 0 3-3-5 3-4-9 3-7-19 4-7-19 3-6-33* 6-16-24 14-(f°)-31 0 0 0 0 5 Sebastes spp. 3-4-4* 3-3-4 3-4-4 4-4-7 3-4-5 4-4-9 16 3-(43)^ 3-3-14 0 9 6 6. Psettichthys melanostictus 3 2-3-4 5 5 3-13-23* 5-6-23 8-11-21 14-22 4-(54)-8 2-9-13 3-11-26 0 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 0 0 0 0 8. Platichthys stellatus 9. Lyopsetta exilis 10 Artedius sp. 2 1 1 . Ammodytes hexapterus 12. Hemilepidotus spinosus 13. Cottus asper 0 0 2-3 0 5-5-8 0 0 0 2-4-6 4-4-9 4-5-6 5 \ / 3-4 4-4-7 8 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 0 5-6 0 9-11-21 6-7-10 0 0 6-7-9 0 11-19 3-4-9 0 0 0 3 0 0 0 0 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 II 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 50 50 50 400 350 150 100 50 650 600 400 350 300 250 200 150 100 50 150 100 50 0 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 15 10 30 20 10 30 20 10 40 50 20 10 20 10 0 III 1 1 1 1 1 1 ' 'FEB ' .1. MAR - 1. APR u ■ MAY ■ 1 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' L. MAR - i _ APR 1 MAY ~ Li . - .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 BI 1971 1972 1971 1972 1971 1972 4.25 <1 31.13 1.25 1.85 1.63 12.17 3.16 1.68 <1 16.83 1.38 1.25 <1 5.59 2.12 <1 2.00 11.41 8.50 <1 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 <1 12.59 0.93 1.07 <1 2.31 0.37 <1 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 <1 2.94 0.54 <1 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) 16 20 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 <1 10.99 4.78 2.30 6.3 2.3 1.47 1.11 9.56 4.84 1.98 5.4 6.3 <1 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 of standardized total tows out abundance1 Months of Taxa BI abundance abundance1 abundance of 148 Positive tows occurrence 1 . Sebastes spp. 3 24 1 3,967.82 36.5 112 35.43 l-XII 2 Stenobrachius leucopsarus 2.28 2 3,648 00 33.6 87 41.93 l-X 3. Tarletonbeania crenularis 1.27 4 635.20 5.8 64 9.92 ll-X, XII 4. Lyopsetta exilis 0.73 5 475.23 4.4 41 11.59 V-VIII 5 Engraulis mordax 0.67 3 1 ,000.70 9.2 25 40.03 VI-VIII 6. Protomyctophum thompsoni 0.67 6 173.77 1.6 52 3.34 lll-XII 7. Cyclopteridae spp. 1 0.51 10 79.70 0.7 38 2.10 ll-IX 8. Glyptocephalus zachirus 0.26 8 113 81 1.0 27 4.21 lll-IX 9. Hemilepidotus spinosus 0.22 13 29.78 0.3 12 3.26 ll-IV 10. Bathylagus ochotensis 0.19 7 131.46 1.2 31 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 0 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 0 0 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 0 9-10 4. Lyopsetta exilis 0 0 0 3-5-17' 4-14-19 5-14-21 15-(^)-22 0 0 0 0 5. Engraulis mordax 0 0 0 0 9 4-5-16' 4-10-25 0 0 0 0 6. Protomyctophum thompsoni 0 3-(g)-13 0 6-13-18* 5-11-16 11-13 8-12-17 5-14-16 5-14-18 8 5-14 7. Cyclopteridae spp. 1 8 Glyptocephalus zachirus 9 Hemilepidotus spinosus 4-5-5* 0 6* 9 0 7-10-10 14 8-8-9 0 5-20 4-8-20* 0 5-(lf>22 5-11 4-54 0 11 45 0 6-14-14 32 0 15-19 67 0 0 0 0 0 0 0 0 0 0 1 0. Bathylagus ochotensis 0 5-6-20 9 4-11-30* 15-24 13-22 0 0 0 0 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 . .1 1. 1 1 JUN .1 i . 1. ■ . JUL 1 — ttT t i -^ r-f- r+- -f- -H 269 18 28 37 46 56 65 74 93 STATIONS Stenobrachius leucopsarus 50r— 50 — 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 0 FEB MAR APR. MAY 1 . 1 1 1 JUN 1 I.I. JUL Ml i l i i 1 l 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 J JUN JUL tti — i — i — i — T — i — T ' 269 18 28 37 46 56 65 74 STATIONS 93 FISHERY BULLETIN: VOL. 75, NO. 1 Sebastes spp 50 50 150 100 50 0 350 300 250 200 150 100 50 50 50 0 'feb1 ' : ' , II 1 1 la- MAR , 1 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 L^ 2 69 18 28 37 46 56 65 74 STATIONS Protomyctophum thompsoni 10 < > cr o 'FEB' ' - MAR ■ 1 1 1 APR MAY ■ 1 1 JUN ■ . 1 1 1 1 JUL ii i i -f- I i l , — H 5- 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. LITERATURE CITED ARON, W. 1959. Midwater trawling studies in the North Paci- fic. Limnol. Oceanogr. 4:409-418. 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. BREDER, C. M., JR., AND D. E. ROSEN. 1966. Modes of reproduction in fishes. Natural History Press, Garden City, N.Y., 941 p. COLTON, J. B., JR. 1959. The multiplane kite-otter as a depressor for high- speed plankton samplers. J. Cons. 25:29-35. CROSS, F. A. 1964. Seasonal and geographical distribution of pelagic copepods in Oregon coastal waters. M.S. Thesis, Oregon State Univ., Corvallis, 73 p. DAY, D. S. 1971. Macrozooplankton and small nekton in the coastal waters off Vancouver Island (Canada) and Washington, spring and fall of 1963. U.S. Dep. Commer., Natl. Mar. Fish. Serv., Spec. Sci. Rep. Fish. 619, 94 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- FAGER, E. W. 1957. Determination and analysis of recurrent groups. Ecology 38:586-595. HJORT, J. 1926. Fluctuations in the year classes of important food fishes. J. Cons. 1:5-38. HUYER, A. 1974. Observations of the coastal upwelling region off Oregon during 1972. Ph.D. Thesis, Oregon State Univ., Corvallis, 149 p. 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. LOUGH, R. G. 1975. Dynamics of crab larvae (Anomura, Brachyura) off the central Oregon coast, 1969-1971. Ph.D. Thesis, Oregon State Univ., Corvallis, 299 p. MARGALEF, R. 1958. Information theory in ecology. Gen. Syst. 3:36-71. MISITANO, D. A. 1977. Species composition and relative abundance of lar- val and post-larval fishes in the Columbia River estuary, 1973. Fish. Bull., U.S. 75:218-222. 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. MOSER, H. G., E. H. AHLSTROM, AND E. M. SANDKNOP. In press. Guide to the identification of scorpionfish larvae (family Scorpaenidae) in the eastern Pacific with com- parative notes on species of Sebastes and Helicolenus from other oceans. U.S. Dep. Commer., NOAA Tech. Rep. NMFS Circ. MOTODA, S., M. ANRAKU, AND T. MINODA. 1957. Experiments on the performance of plankton samplings with net. Bull. Fac. Fish., Hokkaido Univ. 8:1-22. MOULTON, L. L. 1970. The 1970 longfin smelt spawning run in Lake Washington with notes on egg development and changes in the population since 1964. M.S. Thesis, Univ. Washington, Seattle, 84 p. PEARCY, W. G. 1962. Egg masses and early developmental stages of the scorpaenid fish, Sebastolobus . J. Fish. Res. Board Can. 19:1169-1173. 1976. Seasonal and inshore-offshore variations in the standing stocks of micronekton and macrozooplankton off Oregon. Fish. Bull., U.S. 74:70-80. PEARCY, W. G., M. HOSIE, AND S. L. RICHARDSON. 1977. Distribution and duration of pelagic life of larvae of Dover sole, Microstomas pacificus; rex sole, Glypto- cephalus zachirus; and petrale sole, Eopsetta jordani, in waters off Oregon. Fish. Bull., U.S. 75:173-183. 144 RICHARDSON and PEARCY: COASTAL AND OCEANIC FISH LARVAE 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. 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. 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. 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. ROTHLISBERG, P. C. 1975. Larval ecology of Pandalus jordani Rathbun. Ph.D. Thesis, Oregon State Univ., Corvallis, 104 p. Sanders, H. L. I960. Benthic studies in Buzzards Bay. III. The structure of the soft-bottom community. Limnol. Oceanogr. 5:138-153. Smith, R. L. 1974. A description of current, wind, and sea level vari- ations during coastal upwelling off the Oregon coast, July-August 1972. J. Geophys. Res. 79:435-443. Smith, r. l., C. N. K. Mooers, and D. B. Enfield. 1971. Mesoscale studies of the physical oceanography in two coastal upwelling regions: Oregon and Peru. In J. D. Costlow, Jr. (editor), Fertility of the sea, Vol. 2, p. 513-535. Gordon and Breach, N.Y. 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. WYATT, B., W. V. BURT, AND J. B. PATTULLO. 1972. Surface currents off Oregon as determined from drift bottle returns. J. Phys. Oceanogr. 2:286-293. YAP-CHIONGCO, J. V. 1941. Hypomesus pretiosus: its development and early life history. Ph.D. Thesis, Univ. Washington, Seattle, 123 p. 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 40 46 58 62 68 40 71 125 130 150 191 204 224 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 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 10 x 4 Wooden chain Wooden chain Iron bound wooden bracket Iron bound wooden bracket Iron bound wooden bracket Iron bound wooden bracket 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 X Range X Range X 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. 30 10 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 E £ 40 30 20 10 0 ^ STAGES 2-3 i! ^ ^ ^ 1 I i STAGE 4 i sf *"1 ■ o 10 0 30- 20 10 0 10 0 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)- "T T FEMALES N=I33 40- 30- ^ STAGES 2-3 20- 10- k 0 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 4 55.7 88.1 2.2 66.1 32.5 79.0 5 0.4 5.1 1.2 20.4 1.6 12.1 6 0.6 0.0 0.0 7.0 0.6 1.7 Total 100.0 100.0 100 0 100.0 100.0 100.0 153 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 7 1.4 Subtotal 7 1.4 Mesopelagic Myctophidae 84 16.5 Miscellaneous fishes 20 3.9 Squids 95 18.7 Euphausiacea 10 2.0 Miscellaneous Crustacea 4 0.8 Pyrosomidae 1 0.2 Subtotal 214 42.1 Benthic Steindachneria argentea 142 28.0 Apogonidae 21 4.1 Ariommidae 17 3.3 Macrouridae 17 3.3 Merluccius albidus 12 2.4 Trichiuridae 11 2.2 Miscellaneous fishes 30 5.9 Penaeopsis megalops 21 4.1 Penaeidae 7 1.4 Miscellaneous crustaceans 7 1.4 Mollusks 2 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 56 9.9 0400-0700 1,121 61 5.4 0800-1100 679 84 12.4 1200-1500 724 64 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) SL TL SL TL 0 10.5 11.8 10.5 11.8 1 21.5 24.0 20.5 22.9 2 26.5 29.6 31.5 34.1 3 29.5 32.9 36.5 40.6 4 40.5 45.1 5 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 20 10 0 II. ■ co E E CD CM CO (D "tf CO 0") CM *- CM CD t- nn no CO N "» ■* CM ID CO O CO CM 3 O O) CO CM ooo* O CO CO If) O CO co" A Q. o (1) n CO V i 0 . CD cn o> in n r m CO J> CO o> °2 o> "cn ko2 ~; ° " — co 0 s ro *£ mo. D> co O) o z z o 5 o 3 0 r o 0_ co co c d) -S ;oc5 ro -^ = ro _l _1 w CO CO r- E E^cm O CO ^ CO CO CO k |<- go! o E °o E co t cm "r CD in CO CO CO in c r- c cn c= Is- E >" E , ~ ■D O CO c <2c§ o O) c o m a; ra ■6 CO CD Q. CD DC O) o CO 0) 0 Q c ra Q. O c ra o ra 0. JC tr o CO CO 0. < rr < 2 o a. "> CD , o ;_ . O.C0 CD LJ- ■ z cZ co ■ "s « Z O Q) CD xi cr o JK CD U- JO . o C7> r; O) O CD CO in q> o> o Orf g to e8 2 0 (0 J= ra — j? E o — C TJ c ex 0 1.1 CO -D o ^ 2 cd' S <" N O) C O) - CD "° JI a « uS; CO i- 0 _. o o 0 O) Q. Ol .2 5 "8 £ ra . ra - <" T c 0 id r^ a *^ F o> ^ '- i- -r- rr cm Or r + °> O •-"< ■ >- 3 Q. ■ <0 CD -7 > 0 CO *- 2> > ^ CO - CO . to co 9 - 2i5 (j n < LI 1 Z Q. - ~ " ' CD rr 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 0 ) 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 IV IV IV 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) 1 6 20 55(1) 90 72 79(1) 45 25 16(1) 11 7 1 3 1 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 1) 1 1 1 3 1 1 1 12 12 8(1) 2 (59) 36(13)431(13) 48 53 4 6 3 4 5 1 1 10 3 9 5 3(1) 2 5 5 1 3 10 1 3 7 2 8 9 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- 0 100 50 0 100 50 0 n r Mil. i r "i 1 -i 1 r u i i r IHa UJ < I- co x < UJ L_ O Ld o Ld 0_ M i M i J I A i 0 "T" N D 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 (D (2) (3) 6-7 (7) (23 (5) (3) 8-9 (3) (7) 2 10-11 1 (D 10(4) 6(1) 1 12-13 1 9(6) 19 1 14-15 1 2 15(4) 33(1) 6 4 1 1 16-17 1 13 59 4(1) 3 4 5 1 2 18-19 1 1 3 35 4 6 2 10 5 2 4 20-21 1(1) 2 3 21 6 9 3 10 8 4 9 3 22-23 10 6 4 2 4 3 4 9 3 24-25 1 1 5 1 1 1 6 1 6 2 26-27 1 3 1 1 2 1 1 1 4(1) 28-29 1 1 1 1 1 5 1 30-31 2 1 1 2 1 1 32-33 1 34-35 1 1 36-37 2 1 38-39 1 1 1 1 40-41 1 1 1 42-43 1 3 44-45 1 1 1 1 46-47 1 2 1 2 1 1 48-49 1 1 1 1 1 1 1 1 50-51 3 1 1 1 5 3 1 1 52-53 1 2 3 1 2 2 4 3 54-55 1 1 2 2 1 1 1 1 56-57 1 2 1 1 2 2 1 58-59 1 2 60-61 1 1 3 1 1 1 1 1 62-63 1 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 CO O IOOi— I < UJ 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 t F o MID-WATER TRAWL 50 U. O h- ° lj 100 o or uj 50 0. 0 100 50 0 100 JUul i i — i m fl f "i 1 50- 0 12 "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 50 UJ 0 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 (D (4) 6-7 (3) (20) (2) (3) 8-9 (6) (28) (3) (5) 10-11 (1) (2) (1) 12-13 1 (2) 14-15 (D d) 16-17 (1) (1) (2) 18-19 1 1(1) 1 20-21 1 1 1(1) 1 22-23 2 1 24-25 1 1 2(2) 1 26-27 1(2) 2 28-29 1 2 30-31 1 2 2(2) 3 32-33 1 3 2 2(1) 34-35 1(1) 4 2 36-37 3 4 2 38-39 1 1(1) 5 4 1 1 40-41 3 1 5 5(1) 2 1 1 42-43 1 2(1) 6 1 2 2 44-45 2 (3) 2(1) 3 1 1 46-47 2 4 4 48-49 1 1(1) 6 1 1 1 50-51 2 5 5 1 3 3 52-53 1 4 4 4 1 2 4 1 54-55 3(1) 1 1 1 2 4 56-57 1 1 3 2 1 1 2 58-59 3 4 3 2 2 3 60-61 2 1 4 3 1 62-63 3 2 2 2 64-65 2 1 4 2 1 66-67 1(1) 68-69 3 1 70-71 3 1 72-73 1 1 1 74-75 1 89 1 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 2 6 9 18 Station 28 (kilometers from < 37 46 :oast) 56 65 74 93 111 No. tows 29 27 30 30 23 25 21 25 18 21 20 18 Frequency of Dover Mean no. Dover/10 m2 2 0.07 0 0 2 0.09 1 0.03 2 0.11 1 0.08 2 0.16 3 0.34 2 0.51 4 0.38 6 0.95 7 1.75 Frequency of rex Mean no. rex/10 m2 2 0.03 2 0 05 4 0.23 4 0 15 3 0.21 3 0.25 5 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 9 28 46 83 120 158-306 Columbia River: No. tows 2 15 18 16 12 9 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 2 53 57 61 62 54 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 0 15 15 14 6 15 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 7 8 12 12 8 37 No. Dover (no./tow) 0(0) 0(0) 10(0.83) 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) D N D N D N D N 0-50 27 15 53 29 188 196 15 4 50-100 6 11 14 13 20 127 6 2 100-150 21 1 21 1 156 5 11 <1 150-200 2 5 4 5 8 52 2 2 200-300 3 1 12 16 6 5 2 4 300-400 0 0 23 9 0 0 2 1 400-500 17 0 31 4 24 0 4 1 500-600 4 0 11 0 7 0 3 0 600-700 0 0 0 0 0 0 0 0 700-800 0 0 0 0 0 0 0 0 800-900 0 0 0 0 0 0 0 0 900-1 ,000 0 0 0 2 0 0 0 2 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. 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. RICHARDSON, S. L., AND W. G. PEARCY. 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 82 8.9 95 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 99 14 10 3 9 16 nm. 696 830 1.062 787 342 89 14 8 2 6 10 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 1.1 1.3 14 2.4 3.2 0.7 1.3 1.5 r>i 1.830 1,054 172 27 10 0 1 2 0 0 0 nrrij 1,511 942 162 27 7 0 1 2 0 0 0 Slj 19.2 20.3 21.6 23.3 23.4 — 18.5 22.7 — — — Ss, 08 0.8 1.0 1.3 2.1 — — 0.3 — — — ni 314 393 463 344 303 229 229 154 66 47 37 nm/ 236 323 394 283 258 205 202 136 56 43 33 Slj 24.8 26.2 27.8 29.4 30.7 32.1 32.7 33.9 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 n. 1,272 617 343 112 88 8 17 14 8 2 2 nm, 1,230 581 315 108 82 7 15 13 8 2 2 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 0.0 ni 731 741 479 134 182 70 24 7 3 1 3 nm. 450 602 378 107 155 55 23 7 3 1 3 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 ni 439 468 500 140 77 47 58 32 13 4 4 nm. 392 429 477 122 62 46 52 31 12 4 3 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 ni 617 359 127 36 3 1 2 0 0 2 0 nm. 597 346 124 36 3 1 2 0 0 2 0 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 — n. 148 247 287 164 69 95 46 25 8 11 4 nm. 138 236 279 148 67 91 46 22 7 11 4 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 3.8 3.5 3.9 3.4 4.0 3.7 7.1 5.9 110 4.4 "i 146 109 145 133 101 81 41 27 17 8 5 nm. 126 91 130 108 81 76 38 26 15 5 5 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 n. 2 4 28 100 224 191 170 49 10 12 1 nrrij 2 3 28 94 204 182 161 44 10 12 1 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 1.1 1.2 1.0 1.7 1.5 — ni 2 5 10 14 15 12 7 24 41 50 85 nm; 2 5 10 14 15 12 5 24 41 50 81 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 5.7 6.5 5.0 4.3 3.9 3.4 4.1 ni 77 66 32 26 14 13 11 3 1 1 1 nm, 70 59 28 22 12 13 11 3 1 1 1 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 3.6 4.3 3.8 7.2 — — — n. 64 28 26 17 10 12 18 8 26 23 1 nm. 63 27 26 17 10 12 18 8 26 23 0 S} 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 68 3.6 5.6 2.6 10.3 — ni 24 8 25 30 6 6 6 16 23 12 26 nm/ 24 8 25 29 5 6 4 15 23 10 26 Sli 42.3 51.2 44.6 58.3 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 ni 6 15 19 18 15 17 21 15 7 9 7 nm; 6 11 18 18 14 16 20 14 7 9 7 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 n. 61 64 17 2 3 1 0 0 2 0 1 nm, 61 63 17 2 3 1 0 0 2 0 1 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 18 — — — 46 — — 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. m, in centimeters and (inches) 6.3 70 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 "/ 0 2 7 11 14 20 19 18 19 20 18 Tachmotus carolinus nrrii 0 2 7 10 13 20 19 18 19 20 18 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 39 2.4 29 2.1 3.9 Inshore lizardfish, "i 60 41 11 4 4 0 3 1 4 1 1 Synodus loetens nrrij 51 36 11 4 3 0 3 1 4 1 1 Sli 36.1 386 396 39.5 33.5 — 35.0 26.0 31.2 33.5 38.0 Ss, 29 2.5 3.0 25 5.8 — 60 — 2.5 — — Gulf flounder.' ni 3 1 4 1 9 8 16 8 23 25 28 Paralichthys albigutta nrrij 3 1 4 1 8 8 14 8 23 23 28 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, n. 0 3 0 3 10 14 20 11 15 22 29 Sphyrna tiburo nm. 0 3 0 3 10 14 20 11 15 22 28 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,' "i 49 21 17 4 6 1 1 3 4 4 2 Elops saurus nrrij 36 19 14 2 6 1 1 2 3 3 2 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 39 Sand seatrout.1 Hi 63 14 14 2 3 1 3 0 0 1 1 Cynoscion arenarius nrrij 49 12 14 2 3 1 2 0 0 1 1 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 23 • • • • • • • GULF MENHADEN - 2 o I o z UJ z < UJ 21 19 17 48 44 40 16 32 42 34 26 lb 60 5/ 44 n 68 64 60 16 15 32 28 24 20 40 58 36 36 34 32 90 88 U 84 40 36 34 32 3C • • • • • • • SPOTTED SEATROUT 23 21 - • • • • SPOT- 19 • • • • • * * * CREVALLE JACK 33 29 25 • • • • • SEA CATFISH - 17 16 • • • • • PINFISH - ' ' . V • LITTLE TUNNY • • • • • • • ATLANTIC CROAKER 32 28 _ 24 5 • • . * "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 32 • _ • • 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 63 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 76 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 K> a b 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 82 29.12 Mean sy.x = 0.314 k = 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 k = 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 k = 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 k = 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 k = 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 k 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 nylon gill nets. J. Cons. 26:215-222. 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 82 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 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 89 95 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 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 2.1 10.2 22.5 1.1 1.0 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 70 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) S 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 1.1 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 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 1.1 1.1 1.2 44.0 1.2 1.1 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 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 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 98 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 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 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 11 35.0 1.3 3.5 2.5 33.0 2.3 6.3 1.1 35.5 1.2 33.5 1.1 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 12 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 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 22 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 1.2 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 60 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 10 972 101 754-1,436 10 736 46 530- 926 12 665 57 420- 967 5 1,036 94 788-1,324 5 702 37 612- 831 5 587 62 472- 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 X SE Range significance2 AAT: 0.00 6 233 12 194-281 0.05 6 217 14 160-254 P<0.02 0.10 6 181 13 154-234 J G6PdH: 0.00 0.05 6 6 75 123 11 22 54- 91 78-149 : P -0 B CD CD > Hormones and dosages ra 3 X) -0 0> T3 CD M CD 00 3 -0 s -0 CD CD ra Results of striDDino4 First injection Second injection1 Egg diameter3 (mm) > o ■5 z 3 > O c ra 0. V) ra E LL CO E CD LL Egg diameter (mm) O O z 3 > O i ra Q. ra E 0 LL ra E o> LL Number eggs Number Hormone Dosage Hormone Dosage live larvae SP 1 mg — 0.8 X X 1.1 X X <500 <10 SP 5 mg — — 0.8 X X 1.1 X X — — SP 10 mg — 1.1 X X — — — SP 15 mg — — 1.1 X X X <500 <10 SP 25 mg — — 0.9 X X 1.1 X X — — HCG 12.5 IU — 0.8 X X 1.1 X X <500 <10 HCG 25 IU — — 0.8 X X 1.1 X X <500 <10 HCG 50 IU — — 0.9 X X 1.1 X X — — HCG 125 IU 1.1 X X — — — HCG 250 IU 1.1 X X X <500 <10 HCG 500 IU — — 1.1 X X X <500 <10 PMS 300 IU 0.8 X X 0.8 X X — — PMS 750 IU 1.1 X X X <500 <10 PMS 1,000 IU 0.8 X X 1.1 X X 5,000 <10 SP 1 mg PMS 100 IU 0.9 X X 1.1 X X 50,000 10,000 HCG 12.5 IU PMS 100 IU 0.8 X X 1.1 X X 30,000 10,000 SP 1 mg SP 1 mg 0.9 X X 1.1 X X 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° o Z, 18° UJ Z3 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_ _t_ E°6t E E0.4fh 2 < 5 0.2^- CD C& o o IMMATURE CO O D NATURAL SPAWNING I _L 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 = 0 (3) d2C (P2 - P) a dS'< S < 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: as -paDT S < 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 = P (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). lK 8T S 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 < 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 a a SI |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. 0 S ^d=-t UTD ij 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: dh &(dS) + $k(dT) = 0 as dT (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 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 (n Adjusted no. trap days (T'D) 30 30 1 2.75 82.5 30 30 2 1.85 55.5 30 30 3 1.30 39.0 30 30 4 1.00 30.0 30 30 5 0.82 24.6 30 30 6 0.67 20.1 30 30 7 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, 3. 4,6 10-40 15 Mar., May, June Alosa sapidissima, American shad 2 44 1 Aug. Engraulidae: Engraulis mordax, northern anchovy 1. 2, 3 22-68 21 Jan., Mar., Oct., Nov. Osmeridae: • Spirinchus thaleichthys, longfin smelt 1,2, 3. 4, 5, 6, 7 6-64 1,959 Jan., June, Oct. -Dec. Thaleichthys pacificus, eulachon 1,2, 3, 4, 5, 6, 7 5-8 558 Feb. -May Allosmerus elongatus, whitebait smelt 1. 2, 3, 4 45-58 27 Oct. -Jan. Hypomesus pretiosus, surf smelt 1, 2 36-53 27 Jan-Mar Undetermined spp. 1 10-30 34 Dec. -Mar. Gadidae: Microgadus proximus, Pacific tomcod 1,2, 3 5-61 4 Mar., June, July Stichaeidae: Lumpenus sagitta, snake prickleback 2, 4 13-16 5 Jan. -Feb. Pholidae: Pholis ornata, saddleback gunnel 1 18-20 4 Mar. Ammodytidae: Ammodytes hexapterus, Pacific sand lance 1, 2 10-16 12 Mar-Apr. Scorpaenidae: Sebastes melanops, black rockfish 3 55-67 3 July Seoasfes spp. 1. 3 5 3 Jan. Hexagrammldae: Ophiodon elongatus, lingcod 2 9,12 2 Feb. -Mar. Hexagragrammos sp. 1 6,10 2 Jan. -Feb. Cottidae: Leptocottus armatus. Pacific staghorn sculpin 1. 2, 3. 6 6-13 6 Jan. -Mar., May-Sept. Enophrys bison, buffalo sculpin 1 5, 8 2 Feb. Cottus asper, prickly sculpin 1. 2, 3, 4,5, 7 6-12 204 Apr-June Hemilepidotus spinosus, brown Irish lord 2 32 1 Mar. Oligocottus maculosus, tidepool sculpin 1 4-8 2 Jan. Undetermined spp. 1 6-15 3 Jan. -Feb., June Agonidae: Stellerina xyosterna, pricklebreast poacher 4 7-9 3 Feb. -Apr. Cyclopterldae: Liparis rutteri, ringtail snailfish 1 12-32 3 Jan., Mar-Apr. Liparis puchellus, showy snailfish 2 18 1 June Undetermined spp. 1, 2 3 2 Jan-Mar. Pleuronectidae: Psettichthys melanostictus, sand sole 1 28-34 3 June Parophrys vetulus, English sole 1, 2, 3, 4 4-21 22 Jan-Apr., Dec Isopsetta isolepis, butter sole 1,2, 3. 4 4-7 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 2 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 UJ o UJ 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 34 32 30 28 - 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 Vn 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 £" 10 r A. -A- ■-M-; 31.80 -~ 27.16 31.80 -*■ 2235 31.80 — »• 16,93 V v V ■«•«, 31.80 — «■ 11.84 132 30 28 • 26 24 ■ 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 _i < 22 CO ol 20 14 12 i0L 17.14 ». 3142 r I! f* I L 3? 30 28 26 24 22 20 - ie £rr "■^-v-. 1714 ■* 16 • 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 Control Control CO 30.89-31 .43°/oo 27.41 -28.09°/oo 21 82-22 95" oo X±SE 3.2 about 10 h 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 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. B 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 22 5 V H 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. UJ < < E E m ro O < UJ or — 80 - / 70 / X 6C 50 l / -: /• 3: - 2C i 0 n / 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- B 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 1 100 1 24 2 174 0.84 3 78 1.38 4 50 1.35 5 366 0.79 6 60 1.27 7 158 0.86 8 56 1.28 9 51 1.63 10 55 1.42 Mean 115 1.20 Standard deviation 99 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 27 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 INFORMATION FOR CONTRIBUTORS TO THE FISHERY BULLETIN Manuscripts submitted to the Fishery Bulletin will reach print faster if they conform to the following instructions. These are not absolute requirements, of course, but desiderata. CONTENT OF MANUSCRIPT The title page should give only the title of the paper, the author's name, his affiliation, and mailing address, including Zip code. The abstract should not exceed one double- spaced page. In the text, Fishery Bulletin style, for the most part, follows that of the Style Manual for Biologi- cal Journals. 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The sequence of the material should be: TITLE PAGE ABSTRACT TEXT LITERATURE CITED APPENDIX TEXT FOOTNOTES TABLES (Each table should be numbered with an arabic numeral and heading provided) LIST OF FIGURES (Entire figure legends) FIGURES (Each figure should be numbered with an arabic numeral; legends are desired) ADDITIONAL INFORMATION Send the ribbon copy and two duplicated or carbon copies of the manuscript to: Dr. Bruce B. Collette, Scientific Editor Fishery Bulletin National Marine Fisheries Service Systematics Laboratory National Museum of Natural History Washington, DC 20560 Fifty separates will be supplied to an author free of charge and 100 supplied to his organiza- tion. No covers will be supplied. 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 6 •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 < UJ q 1600 • > o < s UJ 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 TR FR TR FR TR FR TR FR 1 1,517 672 1,420 946 304 291 831 522 185 2 2,839 1,280 2,328 1,441 325 310 1.319 859 486 3 2,190 1.016 1,911 1,146 264 241 1,215 785 276 4 2,182 1,413 1.897 1,400 308 288 1,281 947 258 5 1,824 1,139 1,567 1,146 261 242 1,056 790 203 6 1,917 1,210 1,602 1,182 242 220 1,075 806 230 7 2,039 1,393 1.833 1,418 324 298 1,212 944 229 8 1,771 964 1,532 1,061 280 256 1,037 744 195 9 2,481 1,565 2,137 1.522 378 332 1,425 1,072 302 10 1.969 1,066 1.750 1,197 321 284 1,175 835 204 11 1,666 883 1.460 965 247 224 1.025 703 186 12 1,829 1.046 1,573 1,093 286 263 1,116 794 175 13 2.041 1,156 1,822 1,310 352 328 1,188 863 233 14 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 SD 361 240 280 193 41 38 158 136 83 254 COLLINS iind TENNEY: SYSTEM FOR DETERMINING POLLUTANT PARAMETERS 1400 1200 E Z O ^ 1000 800 O o° PROTE IN = 0 74 TRK + 103 /- < O b 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 - 28 (1) CODFR = 1.39 FRK - 166 (2) CODNFR = 1.69 NFRK + 10 (3) Protein = 0.74 TRK + 103 (4) O&G = 0.20 TRK - 62 (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 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 z UJ y ta- il. uj o (J z o o o - 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 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) 1 831 + 98 + 104 185 -24 -39 2 1,319 +266 + 265 486 -147 -129 3 1,215 + 107 + 206 276 -9 -101 4 1,281 -2 +33 258 -2 -32 5 1.056 + 13 -1 203 -4 +8 6 1,075 +34 +9 230 -20 +4 7 1,212 + 8 +63 229 + 11 -42 8 1.037 -8 -44 195 -7 +25 9 1,425 -20 -24 302 -12 +2 10 1,175 -15 + 1 204 +20 +5 11 1,025 -24 -22 186 -5 -13 12 1,116 -61 -102 175 +20 +59 13 1.188 + 3 +9 233 -1 -6 14 925 -12 -35 148 +9 +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 267 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. 270 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, 271 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 273 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 U 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 276 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). 277 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. 279 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. 280 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 281 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, 282 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. 283 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 284 PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMPS 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). 285 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. 286 PEREZ FARFANTE: AMERICAN SOLENOCERID SHRIMPS 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. 287 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. 288 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. 289 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 295 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 \ 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 0 o o O O O O O O O OJO o oo f ' • ^ w NORTHERN CALIFORNIA 1 INSHORE 2 OFFSHORE 3 SEAWARD 3 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 6 o o o o o 5 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 10 9 8 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 15 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 \ \ - 30' , . o SOUTH BAJA •16 INSHORE • 17 OFFSHORE •18 SEAWARD 19 EXTENDED 19 ' °I8° ' o o olo o o°\\pUNT4 > \ C EUGENIA / ° °\7 °\°\6°\^, | = 0 „ ooo , / r . . o o o o e ° ° °?C / ' CAPE •20 INSHORE • 21 OFFSHORE 22 SEAWARD 23 EXTENDED o c 23 o o o o o 22 a e o o a ° y, ° o o o o o o\oo\ (» \20V \f 25" . o ooo oooooooocAoool / 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- To- To- To- To- Grand Zone Jn Ap Jl Oc tal Jn Ap Jl Oc tal Jn Ap Jl Oc tal Jn Ap Jl Oc tal Jn Ap Jl Oc tal total Central California: Inshore 0 0 13 13 26 0 18 16 0 34 0 0 16 0 16 9 21 23 20 73 15 20 24 18 77 226 Offshore 0 0 9 6 15 0 9 18 0 27 0 0 10 0 10 2 21 20 17 60 12 14 30 18 74 186 Southern California: Inshore 20 17 27 22 86 21 22 29 27 99 0 25 26 26 77 18 27 26 29 100 29 28 28 27 112 474 Offshore 4 6 14 6 30 4 6 13 9 32 0 7 12 6 25 5 13 14 9 41 6 12 14 9 41 769 Seaward 3 17 20 6 46 5 13 26 6 55 0 17 23 17 57 11 21 27 17 76 11 30 29 17 87 327 Baja California: Inshore 12 12 13 12 50 12 12 14 0 38 8 13 12 13 46 12 13 11 13 49 13 14 13 14 54 237 Bay 12 13 14 11 50 11 12 15 0 38 12 15 16 14 57 10 16 14 16 56 15 16 17 16 64 265 Offshore 11 13 26 4 54 11 11 22 0 44 10 20 26 11 67 10 25 25 18 78 18 26 24 16 87 330 Seaward 4 12 24 5 45 6 16 20 0 42 2 16 19 13 50 10 30 23 18 81 18 29 29 18 94 312 South Baja: Inshore 16 15 16 14 61 13 13 14 0 40 16 15 17 17 65 15 16 17 17 65 17 11 19 17 64 295 Offshore 8 12 13 6 39 8 8 13 0 29 8 21 18 12 59 12 22 19 20 73 19 17 27 20 83 283 Seaward 3 2 2 3 10 1 2 2 0 5 1 12 13 13 39 3 15 6 7 31 8 7 12 8 35 120 Cape: Inshore 15 0 0 0 15 16 16 0 0 32 0 19 0 0 19 17 0 0 17 34 20 10 0 0 30 130 Offshore 1 0 0 0 1 1 10 0 0 11 0 22 0 0 22 10 0 0 24 34 31 14 0 0 45 113 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-- H -+- ■+■ -+- 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 a b Central California: Inshore CCALIN 74 17 Offshore CCALOF 71 17 Southern California: Inshore SCALIN 63 14 Offshore SCALOF 58 17 Seaward SCALSW 58 15 Baja California: Inshore BCALIN 70 15 Bay BCALBY 66 16 Offshore BCALOF 52 14 Seaward BCALSW 48 13 South Baja: Inshore SBAJIN 64 16 Offshore SBAJOF 56 16 Seaward SBAJSW 45 12 Cape: Inshore CAPEIN 54 15 Offshore CAPEOF 53 16 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 5 co _i < o co z _i < o CO > m _i < o m n. o _l < o CD 5 CO _l < o CO z < CO CO LL O — D < CO CO CO — 3 < CO CO z LU Q. < O LL O LU O- < o Copepoda 0.28 0.28 0.30 0.31 0.36 029 0.29 0.30 0.34 0.30 0.30 031 0.27 0.30 7 Thaliacea 0.27 0.27 0.30 0.28 0.31 028 0.29 0.32 0.33 0.29 0.31 029 030 0.31 2 Amphipoda 0.27 0.28 0.30 0.32 0.31 0.27 0.28 0.31 0.33 0.28 0.28 0.22 0.29 0.28 4 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 1 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 5 Ctenophora 0.26 0.27 0.30 0.26 0.28 0.26 0.26 0.26 0.33 0.27 0.26 0.06 0.16 0.05 3 Decapoda 0.25 025 0.26 0.29 0.29 0.27 0.24 0.31 0.29 0.24 0.28 0.29 0.30 0.33 12 Euphausiacea 0.27 0.26 0.28 0.26 0.26 0.28 0.21 0.14 0.17 0.24 0.28 0.18 0.18 0.31 6 Chaetognatha 0.28 0.27 0.30 0.28 0.28 0.27 0.24 0.11 0.27 0.24 0.25 -.26 0.31 0.32 9 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 8 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 14 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 11 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 16 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 10 Pteropoda 0.19 0.13 0.10 0.08 -.02 0.04 0.12 -.02 -.19 -.06 0.05 -.08 -.17 021 15 Mysldacea 0.15 0.17 -.28 0.09 -.15 0.08 0.11 -.12 -.27 0.26 0.14 -.33 0.29 0.16 13 361 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 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 30 - \^_n - _ 20 - E n O CATCH X JAPAN I U S.S R c ° 10 I U.S. 0 rm 0.6 0.4 0.2 <-> 56 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 56 60 65 70 20 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 ~r _L 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 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- 10 20- 10- 0- 20- 10 20- 10 20 - 10 20 10 0 20- 10- 0 20- 10- 0 20- 10 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 LA 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 D G> 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- 0- 20 10- 0- 20- 10 fc - «j 0 £ 20 10- 0 20 10 0 20 10 0 20- 10- 0 20 "-598 ,.rJ\ 1 Why, N = I225 frfii-L J "W . tk jfl tthCL J 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 42 41 g 40- 39 38- 37 .^-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 length observations length length observations length length observations length length 2 3 18.0 18.1 2 18.5 19.1 3 1 22.0 21.2 1 22.0 21.6 4 10 23.7 23 9 11 24.5 24.0 5 8 27.0 26.6 4 26.2 26.0 18 25.8 26.3 6 26.5 26.1 6 19 29.1 28.6 26 29.4 28.4 9 28 3 284 10 28.1 28.0 7 70 30.0 305 73 30.6 30.6 8 29.6 30.2 5 28.5 29.8 8 164 31.6 32.2 124 32.1 32.6 34 32.3 31.8 21 31.4 31.4 9 186 33.1 33.6 173 33.5 34.3 58 33.2 33.2 22 33.2 32.9 10 219 34.4 35.0 213 34.8 35.9 123 34.2 34.4 71 34.6 34.3 11 233 36.1 36.1 179 36.3 37.2 172 35.5 35.5 123 35.7 35.5 12 411 37.4 37.1 253 383 38.5 78 363 36.5 89 36.5 36.6 13 463 38.5 380 374 40.0 396 42 37.0 37.3 72 37.6 37.6 14 417 39.4 38.9 459 41.2 40.6 59 38.0 38.0 57 38.0 38.6 15 308 40.1 39.6 468 42.2 41.4 56 389 38.6 58 39.0 39.4 16 203 40.5 40.2 377 43.2 42.2 50 39.7 39.2 61 40.8 40.2 17 116 41.1 40.8 308 43.6 42.9 37 40.2 39.7 75 41.3 41.0 18 80 41 1 41.3 186 44.0 43.6 24 40.8 40.1 52 41.7 41.6 19 30 41.6 41.7 115 44.4 44.1 29 41.1 40.5 36 42.2 42.2 20 14 41.9 42.1 92 44.2 44.6 16 41.3 40.8 30 42.4 42.7 21 13 41.9 42.5 36 45.1 45.0 7 41.4 41.1 14 43.7 43.2 22 10 45.0 45.4 2 39.0 41.4 16 43.6 43.7 23 3 45.3 45.8 7 43.9 44.1 24 7 45.6 46.1 4 44.5 44.5 von Bertalanffy growth function parameters U 45.25 48.75 43.15 4847 K 0.1192 0.1135 0 1320 0.0908 to -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 20 20 10- 0 20 10 0 20- 10- 10 0 20 10 0 940 ^tflTTIrnv. rfTI 1 '.JTr-rrv^ r- t t dfccL" I I Jw 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 1 Tttttt-t-^— 532 _£fl L -J L 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: Uu u. 1.31 = V 15 16 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: Uu Uu 1.14 VM 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: U C, 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 M 10 11 12 13 14 15 16 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 0.63 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- • 04 1 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 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 30 13 5 19 6 1 7 1 3 1 2 2 15 237 30 10 6 5 1 1 2 240 26 7 4 3 1 227 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 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 4 9 5.0- 9.9 10 16 26 10.0-14.9 17 12 29 15.0-19.9 4 7 11 20.0-24.9 3 1 4 Total 39 40 79 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) / / / Sj — • Vancouver Is -Ore (Snylko, 197! ) & 8 ■ — Wash -Ore \ )hlS s,udy — a Queen Charlotte Sound J / y Q S s S s\s^ §200- ^**r ^ S" -* Q --' ^T^ «: aS ^^s -*' — -*"""^ '"' c -- *^ ^-"^"^ ^ ^ "6 *■*"* ^^— -"-"^ --' t; -"° -~- — — * ^*£r^ 3 iSf ioo- ^=^ r^^^^ --^1^^^^^ 0 1 1 1 1 1 1 1 1 35 36 37 39 40 Length (cm) 42 45 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 m. Popu Fecun- Hon biomass Yield dity fecundity Q=tc Mn A/0s0(=A/0) W0 KF\ °MJ1 -exp -W0F+M0)\ V0B0 FV0B0 m0 N0m0 M, V, s, = exp -{V0F+M0) A/0s, W, N.W, F , M 11 exp (V,F + M,)| V,8, FV,B, m, A/,m, M, V2 s2 = s,exp -{V,F t/W,) N0s N2W2 FV2B2 m2 N2m2 M, V3 s3 =s2exp -(V2F+M2) N0s Wi v3F +M311 'exP - "i — i — i — i — i — i — i — i — i — i — i — r 40 30 ... — 5% increase _ — 3% increase QCS 10 15 20 Age (years) 25 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 F 0.1 0.2 M = 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. LITERATURE CITED ALVERSON, D. L., AND S. J. WESTRHEIM. 1961. A review of the taxonomy and biology of the Pacific ocean perch and its fishery. Cons. Perm. Int. Explor. Mer Rapp. P.-V. Reun. 150:12-27. BAGENAL, T. B., AND E. BRAUM. 1968. Eggs and early life history. In W. E. Ricker (editor), Methods for assessment offish production in fresh waters, p. 159-181. IBP (Int. Biol. Programme) Handb. 3. CHIKUNI, S. 1975. Biological study on the population of the Pacific ocean perch in the North Pacific. Far Seas Fish. Res. Lab. Fish. Agency Japan, Bull. 12, 119 p. CUSHING, D. H. 1974. The possible density -dependence of larval mortality and adult mortality in fishes. In J. H. S. Blaxter (editor), The early life history of fish, p. 103-111. Springer- Verlag, N.Y. CUSHING, D. H., AND J. G. K. HARRIS. 1973. Stock and recruitment and the problem of density dependence. Cons. Int. Explor. Mer Rapp. P.-V. Reun. 164:142-155. FADEEV, N. S. 1968. Migrations of Pacific ocean perch. Izv. Tikhoo- kean. Nauchno-issled. Inst. Rybrv Khoz. Okeanogr. 65:170-177. (Transl. Fish. Res. Board Can. Transl. Ser. 1447.) FINNEY, D. J. 1971. Probit analysis; a statistical treatment of the sig- moid response curve. Cambridge Univ. Press, Engl., 333 P GULLAND, J. A. 1969. Manual of methods for fish stock assessment. Part I. Fish population analysis. FAO Man. Fish. Sci. 4, 154 p. GUNDERSON, D. R. 1971. Reproductive patterns of Pacific ocean perch (Sebas- todes alutus) off Washington and British Columbia and their relation to bathymetric distribution and seasonal abundance. J. Fish. Res. Board Can. 28:417-425. 1972. Evidence that Pacific ocean perch (Sebastes alutus) in Queen Charlotte Sound form aggregations that have different biological characteristics. J. Fish. Res. Board Can. 29:1061-1070. 1974. Availability, size composition, age composition, and growth characteristics of Pacific ocean perch i Sebastes alutus) off the northern Washington coast during 1967- 1972. J. Fish. Res. Board Can. 31:21-34. 1976. Population biology of Pacific ocean perch (Sebastes alutus) stocks in the Washington-Queen Charlotte Sound region, and their response to fishing. Ph.D. Thesis, Univ. Washington, Seattle, 153 p. GUNDERSON, D. R., S. J. WESTRHEIM, R. L. DEMORY, AND M. E. FRAIDENBURG. 1977. The status of Pacific ocean perch stocks off British Columbia, Washington, and Oregon in 1974. Environ. Can., Fish. Mar. Serv., Tech. Rep. 690, 63 p. HOLDEN, M. J. 1973. Are long-term sustainable fisheries for elasmo- branchs possible? Cons. Int. Explor. Mer Rapp. P.-V. Reun. 164:360-367. Jones, R. 1973. Density dependent regulation of the numbers of cod and haddock. Cons. Int. Explor. Mer Rapp. P.-V. Reun. 164:156-173. KETCHEN, K. S. 1956. Factors influencing the survival of the lemon sole (Parophrys vetulus) in Hecate Strait, British Colum- bia. J. Fish. Res. Board Can. 13:647-693. 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. LISOVENKO, L. A. 1956. Fecundity oiSebastodes alutus Gilbert in the Gulf of Alaska. Tr. Vses. Nauchno-issled. Inst. Morsk. Rybn. Khoz. Okeanogr. 58 (Izv. Tikhookean. Nauchno-issled. Inst. Rybn. Khoz. Okeanogr. 53):171-178. (Transl., 1968, In P. A. Moiseev (editor), Soviet fisheries investigations in the northeast Pacific, Part 4, p. 162-169, available U.S. Dep. Commer., Natl. Tech. Inf. Serv., Springfield, Va., as TT 67-51206.) LYUBIMOVA, T. G. 1963. Basic aspects of the biology and distribution of Pacific rockfish (Sebastodes alutus Gilbert) in the Gulf of Alaska. Tr. Vses. Nauchno-issled. Inst. Morsk. Rybn. Khoz. Okeanogr. 48 (Izv. Tikhookean. Nauchno-issled. Inst. Morsk. Rybn. Khoz. Okeanogr. 50):293-303. (Transl., 1968, In P. A. Moiseev (editor), Soviet fisheries investiga- tions in the northeast Pacific, Part 1, p. 308-318, available U.S. Dep. Commer., Natl. Tech. Inf. Serv., Springfield, Va., as TT 67-51203.) 1964. Biological characteristics of the school of Pacific rockfish (Sebastodes alutus G.) in the Gulf of Alaska. Tr. Vses. Nauchno-issled. Inst. Morsk. Rybn. Khoz. Okeanogr. 53 (Izv. Tikhookean. Nauchno-issled. Inst. Morsk. Rybn. Khoz. Okeanogr. 52): 213-221. (Transl., 1968, In P. A. Moiseev (editor), Soviet fisheries investiga- tions in the northeast Pacific, Part 3, p. 208-216, available 402 GUNDERSON: POPULATION BIOLOGY OF SEBASTES ALUTVS U.S. Dep. Commer., Natl. Tech. Inf. Serv., Springfield, Va., as TT 67-51205.) 1965. Main stages in the life cycle of the rockfish Sebas- todes alutus Gilbert in the Gulf of Alaska. Tr. Vses. Nauchno-issled. Inst. Morsk. Rybn. Khoz. Okeanogr. 58 (Izv. Tikhookean. Nauchno-issled. Inst. Morsk. Rybn. Khoz. Okeanogr. 531:95-120. (Transl., 1968, In P. A. Moiseev (editor), Soviet fisheries investigations in the northeast Pacific, Part 4, p. 85-111, available U.S. Dep. Commer., Natl. Tech. Inf. Serv., Springfield, Va., as TT 67-51206.) MAY, A. W. 1967. Fecundity of Atlantic cod. J. Fish. Res. Board Can. 24:1531-1551. MURPHY, G. I. 1968. Pattern in life history and the environment. Am. Nat. 102:391-403. PARAKETSOV, I. A. 1963. On the biology of Sebastodes alutus of the Bering Sea. Tr. Vses. Nauchno-issled. Inst. Morsk. Rybn. Khoz. Okeanogr. 48 (Izv. Tikhookean. Nauchno-issled. Inst. Morsk. Rybn. Khoz. Okeanogr. 50):305-312. (Transl., 1968,/rc P. A. Moiseev (editor), Soviet fisheries investiga- tions in the northeast Pacific, Part 1, p. 319-327, available U.S. Dep. Commer., Natl. Tech. Inf. Serv., Springfield, Va., as TT 67-51203.) PAUTOV, G. B. 1972. Some characteristic features of the biology of Pacific ocean perch (Sebastodes alutus Gilbert) in the Bering Sea. Izv. Tikhookean. Nauchno-issled. Inst. Rybn. Khoz. Okeanogr. 81:91-117. (Transl., 1973, Fish. Res. Board Can. Transl. Ser. 2828.) QUAST, J. C. 1972. Reduction in stocks of the Pacific ocean perch, an important demersal fish off Alaska. Trans. Am. Fish. Soc. 101:64-74. RAITT, D. F. S., AND W. B. HALL. 1967. On the fecundity of the redfish, Sebastes marinus (L.). J. Cons. 31:237-245. SNYTKO, V. A. 1971. Biology and peculiarities of distribution of Pacific ocean perch (Sebastodes alutus G.) in Vancouver-Oregon area. Izv. Tikhookean. Nauchno-issled. Inst. Rybn. Khoz. Okeanogr. 79:3-41. (Transl., 1973, Fish. Res. Board Can. Transl. Ser. 2805.) SNYTKO, V. A., AND L. A. BORETS. 1972. Some data on fecundity of ocean perch in Vancouver-Oregon region. Izv. Tikhookean. Nauchno- issled. Inst. Rybn. Khoz. Okeanogr. 81:249-252. (Transl., 1973, Fish. Res. Board Can. Transl. Ser. 2502.) TEMPLEMAN, W. 1963. Otter-trawl covered codend and alternative haul mesh-selection experiments on redfish, haddock, cod, American plaice, and witch flounder: girth measurements of haddock, cod, and redfish, and meshing of redfish in the Newfoundland area. In The selectivity of fishing gear, p. 201-217. Int. Comm. Northwest Atl. Fish. Spec. Publ. 5. TOMLINSON, P. K., AND N. J. ABRAMSON. 1961. Fitting a von Bertalanffy growth curve by least squares. Calif. Dep. Fish Game, Fish Bull. 116, 69 p. WESTRHEIM, S. J. 1958. On the biology of the Pacific ocean perch, Sebastodes alutus (Gilbert). M.S. Thesis, Univ. Washington, Seat- tle, 106 p. 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. WESTRHEIM, S. J., D. R. GUNDERSON, AND J. M. MEEHAN. 1972. On the status of Pacific ocean perch (Sebastes alutus) 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 insufficient calcification zones present, but not enumerable insufficient calcification zones present, but not enumerable zones present, but not enumerable insufficient calcification insufficient calcification zones present, but not enumerable insufficient calcification insufficient calcification zones present, but not enumerable insufficient calcification insufficient calcification enumerable zones present zones present, but not enumerable insufficient calcification zones present, but not enumerable enumerable zones present 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 29 24 59 Opercle — — 3 — — Otolith 10-18 15.2 34 24 71 Scale 8-15 11.2 32 16 59 Vertebral centrum 8-18 12.9 Canary rockfish 35 11 49 Anal pteryg- iophore 7-20 9.5 33 33 76 Opercle 4-18 7.8 31 10 48 Otolith 5-22 8.9 35 77 97 Scale 7-23 10.7 32 31 69 Vertebral centrum 5-18 8.9 Black rockfish 35 31 60 Anal pteryg- iophore 5-18 9.6 32 19 66 Op3rcle 5-18 92 28 39 75 Otolith 6-15 10.7 35 40 74 Scale 7-16 10.7 31 23 61 Vertebral centrum 6-18 10.3 35 14 54 407 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 N Yellowtail rockfish 42 80 26 60 14 53 89 Canary rockfish 37 73 36 70 15 39 91 Black rockfish 48 81 26 54 11 43 98 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 ANTERIOR 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 N Mean estimated age 37 71 91 14.0 21 57 91 14.7 21 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 ~n 1 1 II i r~ ■ i i i ■ i i 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 SE 95% conf. limits Estimate SE 95% conf. limits R2 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: c 28.00 28.41 (25.96-30.03) (26.37-30.45) b 0.18 0.17 (0.15-0.21) (0.14-0.20) 9 yellowtail rockfish: c 25.08 23.66 (23.05-27.12) (21.62-25.71) b 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) k 0.19 0.18 (0.17-0.21) (0.16-0.20) to 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) k 0.15 0.18 (0.12-0.17) (0.15-0.20) to 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) k 0.23 0.22 (0.21-0.26) (0.19-0.25) to -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) to -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 a • G • o 0 • c o " • o • 0 • o • o o • First reading 6 O.I8068 L = 27.9962A 40 • 8 « ° Second reading L = 28.4II8A°-17206 55 FEMALES 6 6 6 o . o o 0 50 - 45 - • o o • o • O • O o o • First reading 0.26386 L = 25.084IA ° Second reading 0.28150 L=23.6646A 40 o ] . 1 ' ' i 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. 60 - MALES * -aSoSo 6° o 8 40 « e • • • First reoding 20 9 9 o l,= 53.60[l-e-0J855l7('-°-68l0). o Second reading -O.I83965(t-0.542l)"| 1, =53.30 [l-e 0 60 FEMALES # , 9 o o * o o c. o o 40 9 6 9 o ? 9 0 First reading l,= 60.95[l-e-ai46062('-°-"67)] 20 o ■ ii, J 1 1 i 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 60 MALES 40 , g V V 9 . . . • 20 - • First reading 6 l, = 50.30[l-e-a2"85el,'a4622|] 0. 60 40 6 o Second reading 1,-52.03 [j.e-M'*»°<,.a4404J] FEMALES o o o 9 9 • o 9 ° ' ' * 0 » ' 9 ' 9 9 • First reading 20 - l1 = 57.83[l-e-0-l684l6,,-a7426'] 8 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 5 27.1 16) 27.6 10) — 30.0 (D 31.9(116) rockfish 10 42.3 (4) 41.0 (2) 42.9(15) 46.6(19) 43.0 (48) 15 46.6(18) 49.2 (7) 46.1 (17) 50.4 (8) 50.4 (6) 20 476 (8) — 53.0 (1) Canary 5 22.5 (1) 235 (1) 29.0 (8) 29.2 (26) 31 .9 ( 128) rockfish 10 38.5 (1) 44.7 (11) 48.0 (6) 46.8 (57) 15 49.2 (32) 52.4(12) 56.5 (7) 20 505 (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 ABRAMSON, N. J. 1965. Von Bertalanffy growth curve II, IBM 7094, UNI- VAC 1107, Fortran IV. Trans. Am. Fish. Soc. 94:195- 196. ALBRECHTSEN, K. 1968. A dyeing technique for otolith age reading. J. Cons. 32:278-280. ALVERSON, D. L., AND S. J. WESTRHEIM. 1961. A review of the taxonomy and biology of the Pacific ocean perch and its fishery. Cons. Perm. Int. Explor. Mer, Rapp. P.-V. 150:12-27. BLACKER, R. W. 1974. Recent advances in otolith studies. In F. R. Harden Jones (editor). Sea fisheries research, p. 67-90. John Wiley and Sons, N.Y. 1975. Stereoscan observations of a plaice otolith. J. Cons. 36:184-187. CHEN, L. 1971. Systematics, variation, distribution, and biology of rockfishes of the subgenus Sebastomus (Pisces, Scor- paenidae, Sebastes). Bull. Scripps Inst. Oceanogr. Univ. Calif. 18, 115 p. CHIKUNI, S. AND K. WAKABAYASHI. 1970. On the scale characters of the Pacific ocean perch in the Bering Sea — III. Objectivity and accuracy of age de- termination by scale reading. [In Jap., Engl, synop.] Bull. Far Seas Fish. Res. Lab. (Shimizu) 3:205- 214. CHRISTENSEN, J. M. 1964. Burning of otoliths, a technique for age determina- tion of soles and other fish. J. Cons. 29:73-81. 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- 72. J. Fish. Res. Board Can. 31:21-34. HUBBS, C. L., AND C. HUBBS. 1953. An improved graphical analysis and comparison of series of samples. Syst. Zool. 2:49-56, 92. 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. mentella Travin). I Engl, abstr.) Ber. Dtsch. wiss. 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 structure of their otoliths. In T. B. Bagenal (editor), The ageing of fish, p. 124-136. Unwin Brothers, Surrey, Engl. MILLER, D. J. 1961. Black rockfish. In California ocean fisheries re- sources to the year 1960, p. 37-38. Calif. Dep. Fish Game, Sacramento. MILLER, D. J., AND J. J. GEIBEL. 1973. Summary of blue rockfish and lingcod life histories; a reef ecology study; and giant kelp, Macrocystis pyrifera, experiments in Monterey Bay, California. Calif. Dep. Fish Game, Fish Bull. 158, 137 p. PATTEN, B. G. 1973. Biological information on copper rockfish in Puget Sound, Washington. Trans. Am. Fish. Soc. 102:412-416. PERLMUTTER, A., AND G. M. CLARKE. 1949. Age and growth of immature rosefish iSebastes marinus) in the Gulf of Maine and off western Nova Scotia. U.S. Fish Wildl. Serv., Fish. Bull. 51:207-228. PHILLIPS, J. B. 1964. Life history studies on ten species of rockfish (genus Sebastodes). Calif. Dep. Fish Game, Fish Bull. 126, 70 p. RICKER, W. E. 1975. Computation and interpretation of biological statis- tics offish populations. Fish. Res. Board Can., Bull. 191, 382 p. ROBSON, D. S., AND D. G. CHAPMAN. 1961. Catch curves and mortality rates. Trans. Am. Fish. Soc. 90:181-189. SANDEMAN, E. J. 1961. A contribution to the problem of the age determina- tion and growth-rate in Sebastes. Int. Comm. Northwest Atl. Fish., Spec. Publ. 3:276-284. SMITH, S. W. 1968. Otolith age reading by means of surface structure examination. J. Cons. 32:270-277. SNEDECOR, G. W., AND W. G. COCHRAN. 1967. Statistical methods. 6th ed. Iowa State Univ. Press, Ames, 593 p. TESCH, F. W. 1968. Age and growth. In W. E. Ricker (editor), Methods for assessment of fish production in fresh waters, p. 93- 123. IBP (Int. Biol. Programme) Handb. 3. TOMLINSON, P. K., AND N. J. ABRAMSON. 1961. Fitting a von Bertalanffy growth curve by least squares including tables of polynomials. Calif. Dep. Fish Game, Fish Bull. 116, 69 p. Van Oosten, J. 1929. Life history of the lake herring (Leuciethys artedi Le Sueur) of Lake Huron as revealed by its scales, with a critique of the scale method. U.S. Bur. Fish., Bull. 44: 265-428. Wales, J. H. 1952. Life history of the blue rockfish Sebastodes rnys- tinus. Calif. Fish Game 38:485-498. WESTRHEIM, S. J. 1973. Age determination and growth of Pacific ocean perch (Sebastes alutus ) in the northeast Pacific Ocean. J. Fish. Res. Board Can. 30:235-247. WESTRHEIM, S. J., AND W. R. HARLING. 1975. Age-length relationships for 26 scorpaenids in the northeast Pacific Ocean. Fish. Mar. Serv. (Can.), Res. Dev. Dir., Tech. Rep. 565, 12 p. WESTRHEIM, S. J., AND H. TSUYUKI. 1971. Taxonomy, distribution, and biology of the northern rockfish, Sebastes polyspinis. J. Fish. Res. Board Can. 28:1621-1627. 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 in 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 This report Sept. 1973 Marine Biological Laboratory, Mass. Kaneohe Bay, Hawaii Kaneohe Bay, Hawaii Hepsitia stipes Menidia Pranesus insularum 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 o ~a > 8 _2 -a CO C S CD _£ re cO - £ to C J3 S 'S. s ■— -J *-» • ? -S IB « O B fe c CD X J 3 o -o ?. 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CD "" >% X CD CO 'E -*= 2 c r 3 420 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 Beginning Initial school Location Date sunrise (h) of sunrise nautical twilight civil twilight formation Schools formed Lilipuna Pier 7 Oct. 1972 0625 0 -48 -23 -44 -33 HIMB lagoon 8 Oct 1 972 0624 0 47 22 34 24 23 Oct. 1972 0629 0 48 -22 -26 20 19 Nov. 1972 0644 0 -51 -24 -38 31 21 Nov 1972 0646 0 -51 -24 33 28 22 Nov 1972 0647 0 -51 24 40 33 12 Sept. 1973 0617 0 -48 21 -24 18 14 Sept 1973 0619 0 -48 -21 -23 21 Local time of Relative time Difference in time (minutes) between sunset and End of End of Initial school Complete Location Date sunset (h) of sunset nautical twilight civil twilight breakup school breakup HIMB lagoon 8 Oct 1972 1814 0 + 48 +22 + 26 22 Oct 1972 1804 0 + 48 -22 -16 — 13 Sept. 1973 1835 0 + 48 + 22 — •24 17 Sept. 1973 1832 0 •48 + 22 + 15 -21 18 Sept 1973 1932 0 •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 E 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 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 • • N DHB D \ 1 *• □ 1' □ D V • • 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 - — ^ i -■ " ^ *» * Buoyed Current V Meier @ -. / S lb; sjg :•.-. •* ■ .500 • .ISO D .115 O .061 0 . * » * * - 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 L 9 9 9 9 .■■■9T- 9 9 % 9 V 30' - 34"20 '^V J_ 50 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. c 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 1 2 3 4 5 6 7 (mm) 18 Feb. 18 Feb. 18 Feb. 18 Feb 21 Mar 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 -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) 25 24 24 22 22 24 25 Scallop producing area no yes no yes no yes yes Sediment size 8 9 10 11 12 13 14 (mm) 21 Mar. 21 Mar. 10 May 14 June 14 June ' 14 June 25 June 4 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) 28 23 26 23 21 29 37 Scallop producing area yes yes yes no no yes no Sediment size 15 16 17 18 19 20 21 22 (mm) 27 June 17 Aug 17 Aug. 17 Aug. 12 Sept. 12 Sept 23 Oct. 23 Oct >4 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) 18 22 23 19 21 20 21 26 Scallop producing area yes'' yes yes . no yes? yes 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 86 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 21 1 1 1 18 2 — — 1 — 92 135 6 1 3 2 25 1 1 1 — — — 1 54 32 1 1 12 5 25 15 200 1 — 2 2 75 57 171 1 1 2 1 1 5 6 - — 4 2 4 68 - — 10 1 5 — 1 — 3 — 2 4 — 12 2 11 4 — 2 1 5 3 1 27 1 1 19 4 — 2 73 — — 3 1 7 3 — 67 57 16 57 67 2 — 4 — 2 26 1 1 47 3 5 23 11 8 171 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 10 1 1 81 1 235 1 8 2 4 10 3 17 8 3 9 1 2 11 10 42 — 1 40 4 55 1 1 1 2 95 1 2 2 3 3 252 8 1 4 1 9 1 2 1 2 2 75 57 386 1 9 1 10 1 3 1 5 6 4 74 10 3 5 37 11 122 254 1 1 1 2 7 2 1 2 3 6 7 249 1 2 20 91 1 413 1 8 2 4 101 7 36 8 3 23 1 4 104 1 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 — 3 3 20 5 3 6 — — 1 14 4 2 1 1 — 1 — — 1 1 — 2 3 8 29 2 1 1 8 — 3 2 — 6 — — 7 1 1 3 19 1 9 1 — 6 8 7 — 76 15 25 2 — — — — 3 5 2 — 10 2 1 2 1 4 1 6 6 1 3 14 6 1 — 1 1 1 — 11 — 8 11 9 9 — 1 1 — 21 — 20 39 32 48 6 — 22 — 2 36 2 — — — 9 28 4 4 1 3 — 2 — 7 1 — 3 — 4 — 1 10 — — 1 3 1 8 3 1 4 6 4 30 36 1 2 7 1 5 1 28 7 1 — 18 50 6 145 19 — 5 7 1 — 1 2 — — — — — — — 4 1 1 — — — 1 — 20 120 281 149 534 312 135 105 478 115 215 81 178 129 69 421 995 718 411 309 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 2 1 960 1 Mustelus canis 8 33 440-972 13 15 5 Squatina dumenli 2 1 1,160 1 Ra/a eglanteria 20 135 136-580 7 127 1 Dasyatis americana 4 1 676 1 Gymnura micrura 4 1 415 1 Gymnothorax nigromarginatus saxicola 2 1 276 1 Synodus foetens 23 200 98-426 11 163 26 Trachmocephalus myops 6 8 170-216 1 2 5 Opsanus tau 2 1 246 1 Ponchthys porosissimus 6 8 146-210 8 Lophius amencanus 4 3 560-716 1 1 1 Urophycis regius 2 4 110-208 1 1 2 Centropristis ocyurus 4 7 112-172 6 1 C. striata 15 57 92-325 21 28 8 Diplectrum formosum 9 67 46-282 37 23 7 Pomatomus saltathx 3 1 138 1 Haemulon plumieri 6 1 230 1 Orthopnstis chrysopterus 14 47 116-216 36 6 5 Calamus senta 6 15 120-225 15 Lagodon rhomboides 4 10 87-122 10 Stenotomus aculeatus 22 101 90-256 64 27 10 Leiostomus xanthurus 4 90 144-188 1 86 3 Menticirrhus amencanus 2 2 1 70-262 2 M. saxatilis 5 10 190-280 1 8 1 Chaetodipterus faber 9 4 286-290 4 Hemipteronotus nov'acula 17 40 128-172 7 26 7 Pepnlus alepidotus 2 3 118-156 3 P. triacanthus 2 25 97-156 1 4 20 Scorpaena calcarata 15 24 64-142 1 23 Phonotus evolans 19 75 196-342 2 61 12 P. salmonicolor 6 1 186-222 1 P. scitulus 19 145 134-268 2 136 7 Ancylopsetta quadrocellata 28 19 1 70-290 19 Cithanchthys macrops 11 3 120-142 3 Etropus microstomus 3 1 158 1 Paralichthys albigutta 21 25 200-289 25 P. dentatus 42 81 153-370 81 P. lethostigma 14 4 210-500 4 Syacium papillosum 8 15 86-300 1 13 1 Aluterus schoepli 14 56 342-390 56 A. scriptus 3 12 90-222 1 5 6 Batistes capriscus 18 53 105-356 20 28 5 Monacanthus hispidus 14 59 92-222 23 20 16 Sphoeroides maculatus 21 198 68-268 77 94 26 Chilomycterus schoepfi 6 7 72-142 2 4 1 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 catches Taxa N = 14 W = 10 N = 14 N = 10 N = 48 N = 40 A/ = 8 COELENTERA Renillidae: Renilla reniformis 7 2 2 Actiniana (sea anemones) 14 20 8 10 Madreporana (corals) 20 4 5 ANNELIDA Aphroditidae: Aphrodita hastata 7 2 2 MOLLUSCA Arcidae: Area imbncata 7 2 2 A zebra 14 10 7 10 10 12 Anadara floridana 36 20 21 21 25 Noetia ponderosa 14 4 5 Mytilidae: Brachidontes modiolus 14 30 36 21 25 Pterndae: Pteria colymbus 14 10 6 15 Pectmidae: Aequipecten muscosus 10 2 2 Argopecten gibbus 93 100 71 80 85 100 13 Lyropecten nodosus 10 21 10 10 10 13 Pecten reveneli 21 30 21 30 25 28 13 Ostreidae: Ostrea permollis 7 20 6 7 Chamidae: Arcinella cornuta 43 40 79 30 50 55 25 Chama macerophylla 10 2 2 Crassatellidae: Eucrassatella speciosa 43 40 86 10 48 50 38 Cardiidae: Dinocardium robustum 7 10 14 20 13 13 13 Laevicardium multilineatum 21 10 21 10 17 15 25 Venendae: Chione intapurpurea 7 10 43 30 23 18 50 C. latilirata 29 20 64 40 40 35 63 Macrocallista maculata 57 20 43 20 38 43 13 M. nimbosa 10 2 2 Solemdae: Ensis directus 10 2 2 Tellinidae: Tellina magna 7 2 13 T. nitens 10 2 2 Solecurtidae: Solecurtus cumingianus 7 2 2 Trochidae: Calliostoma euglyptum 7 10 4 25 Turbimdae: Astraea phoebia 7 2 13 Turbo castanea 10 14 30 13 15 13 Architectonicidae: Architectonica nobilis 10 10 4 5 Cerithlldae: Cerithium litteratum Xenophondae: Xenophora conchyliophora 14 30 7 20 17 20 Strombidae: Strombus alatus 14 50 57 30 38 45 S. costatus 7 4 2 Cypraeidae: Cypraea cervus 14 4 5 Naticidae: Natica canrena 7 10 4 5 Polinices duplicates 36 20 50 20 33 35 25 P. duplicatus eggs 7 2 2 Sinum maculatum 7 10 7 20 10 12 Cassididae: Cassis madagascanensis 21 80 79 50 56 60 38 C. madagascariensis eggs 20 4 5 Cypraecassis testiculus 7 2 2 Phalium granulatum 21 20 36 20 25 25 25 P granulatum eggs 10 2 2 Cymatidae: Dislorsio clathrata 7 20 21 13 15 Tonnidae: Oocorys abyssorum Tonna galea 7 40 7 13 15 441 FISHERY BULLETIN: VOL. 75, NO. 2 Table 7.— Continued. Good scallop Poor scallop Mar-Apr. May-June July-Aug. Sept -Oct. Total catches catches Taxa N = 14 N = 10 N = 14 N = 10 N = 48 N = 40 N = 8 Ficidae: Ficus communis 7 20 14 10 12 Muricidae: Eupleura caudata 7 2 2 Murex dilectus 7 2 13 M. fulvescens 29 30 71 35 40 13 M. fulvescens eggs 14 4 5 Murex pomum 21 30 29 40 29 28 38 Thais haemastoma flondana 10 2 2 Melongenidae: Busycon canaliculatum 7 2 2 B. carica 20 7 20 10 10 13 B. contrarium 29 10 20 15 15 13 B. contrarium eggs 21 6 7 B spiratum 21 20 14 30 21 23 13 B spiratum eggs 14 4 5 Fasciolarndae: Fasciolaria lilium huntena 7 40 57 20 31 30 38 F. 1 huntena eggs 14 4 5 F tulipa 21 30 21 10 21 23 13 F. tulipa eggs 7 27 2 Pleuroploca gigantea 43 70 50 70 56 55 63 P. gigantea eggs 10 7 4 5 Olividae: Oliva sayana Ravenel 43 10 50 20 33 35 25 Cancellamdae: Cancellana reticulata 7 Conidae: Conus delessertii 7 30 14 13 15 Octopodidae: Octopus vulgaris 71 70 93 60 75 75 75 Loliginidae: Lolliguncula brevis 7 2 2 Loligo pealeii 71 50 93 60 71 70 75 ARTHROPODA Stomatopoda: Gonodactylus aerstedi 21 20 14 15 17 Penaeidae: Penaeus sp. 29 20 7 20 19 22 Sicyonia brevirostris 21 10 29 30 23 21 13 Scyllaridae: Scyllandes nodifer 7 20 10 8 10 Porcellandae: Porcellana sayana 14 4 5 Pagundae: Pagurus sp. 7 10 4 5 P. annulipes 60 64 40 40 40 38 P. pollicaris 40 64 40 35 35 38 Ranmidae: Ranilia muncata 14 7 6 7 Calappidae: Calappa angusta 7 10 4 5 C flammea 64 60 79 60 67 73 38 Hepatus epheliticus 43 70 64 70 60 65 38 Osachila sp 10 2 13 Portunidae: Ovalipes quadulpensis 21 6 7 0 ocellatus 21 30 36 10 25 25 25 Portunus gibbesii 57 40 36 30 42 45 25 P. spinimanus 7 30 8 10 Callmectes sapidus Arenaeus cribrarius 7 10 4 5 Cancridae: Cancer irroratus 7 2 2 Majidae: Libinia emerginata 36 50 36 40 40 43 25 Stenocionops furcata coelata 10 2 2 Parthenopidae: Parthenope serrata 14 4 5 P. pourtelesii 10 2 2 Xiphosura: Xiphosura polyphemus 43 50 50 10 40 40 38 ECHINODERMA Astropectinidae: Astropecten articulatus 100 90 93 80 92 93 88 Luididae: Luidia alternata 57 90 86 20 65 70 38 L clathrata 100 100 93 90 96 98 88 442 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 catches Taxa (V = 14 N = 10 N = 14 N = 10 N = 48 N = 40 N = 8 Gomastendae: Goniaster amencanus 7 40 7 13 13 13 Echmastendae: Echinaster brasiliensis 14 30 14 30 21 23 13 Asterndae: Astenas forbesi 7 30 8 10 Gorgonocephalidae: Gorgonocephalus arcticus 10 10 4 3 13 Amphiundae: Hemipholis elongata 79 70 64 60 69 73 50 Arbacndae: Arbacia punctulata 7 60 64 60 46 45 50 Toxopneustidae: Toxopneustes vanegatus 36 80 79 60 63 65 50 Scutellidae: Encope emargmata 64 50 71 30 56 60 38 Cucumariidae: Thyone bhareus 29 10 10 12 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. 1 85 0 71 Mar. 7 226 6 87 Apr 7 151 28 178 May 158 67 17 66 June 29 314 7 311 July 8 86 3 36 Aug 2 154 0 56 Sept. 7 89 0 43 Oct. 3 67 0 20 '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 72 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 42 Aug. 64.5 28-120 169 84.6 28-112 85 Sept. 83.1 35-136 113 87,0 51-134 44 Oct 622 23-124 101 896 23-124 22 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 45 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 1 8 10 62 39 5 4 5 2 Luidia clathrata: Average valve length — 4.3 33.9 1.9 43.7 24 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 39 6 9 14 1 1 443 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 N Dead shells Luidia clathrata Astropecten articulatus Mar 13 23 8 5 Apr. May June 8 2 8 19 19 22 5 1 1 4 2 2 July Aug. Sept. Oct. 7 11 4 1 106 220 134 290 2 3 1 2 6 3 8 55 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- leatus. Allen, D. M., and T. J. Costello. 1972. The calico scallop, Argopecten gibbus. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-656, 19 p. ANDERSON, W. W., J. E. MOORE, AND H. R. GORDY. 1 96 1 . Water temperature of the south Atlantic Coast of the United States, Theodore N. Gill Cruises 1-9, 1953-54. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 380, 206 p. Anonymous. 1962. Calico scallop explorations off North Carolina. M V Silver Bay Cruise 39. Commer. Fish. Rev. 24(8):38-39. 1969. Underwater research vehicle RUFAS makes de- but. Commer. Fish. Rev. 31(6):6. 1972. Data report for R/V Eastward cruise E-12-72, July 3-8, 1972. Duke Univ. Mar. Lab., Beaufort, N.C, 34 p. BLANTON, J. 1971. Exchange of Gulf Stream water with North Carolina shelf water in Onslow Bay during stratified conditions. Deep-Sea Res. 18:167-178. Bloom, S. A., J. L. Simon, and V. D. hunter. 1972. Animal-sediment relations and community analysis of a Florida estuary. Mar. Biol. (Berl.) 13:43-56. BRIGGS, J. C. 1974. Marine zoogeography. McGraw Hill Co., N.Y., 475 p. BULLIS, H. R„ JR., AND R. M. INGLE. 1959. A new fishery for scallops in western Florida. Proc. Gulf Caribb. Fish. Inst. 11th Annu. Sess., p. 75-78. BULLIS, H. R. , JR., AND J. R. THOMPSON. 1965. Collections by the exploratory fishing vessels Oregon, Silver Bay, Combat, and Pelican made during 1956 to 1960 in the southwestern North Atlantic. U.S. Fish Wildl. Serv.. Spec. Sci. Rep. Fish. 510, 130 p. BUMPUS, D. F. 1973. A description of the circulation on the continental shelf of the east coast of the United States. Prog. Oceanogr. 6:111-157. CARRIKER, M. R. 1959. The role of physical and biological factors in the culture of Crassostrea and Mercenaria in a salt-water pond. Ecol. Monogr. 29:219-266. CERAME-VIVAS, M. J., AND I. E. GRAY. 1966. The distributional pattern of benthic invertebrates of the continental shelf off North Carolina. Ecology 47:260-270. CHESTNUT, A. F. 1951. The oyster and other mollusks in North Carolina. In Harden F. Taylor (editor I, Survey of marine fisheries of North Carolina, p. 141-190. Univ. N.C. Press, Chapel Hill. CHESTNUT. A. F., AND H. S. DAVIS. 1975. Synopsis of marine fisheries. Sea Grant Publ. UNC-SG-75-12, Univ. North Carolina, 425 p. CUMMINS, R., JR. 1971. Calico scallops of the southeastern United States, 1959-69. U.S. Dep. Commer., Natl. Mar. Fish. Serv., Spec. Sci. Rep. Fish. 627, 22 p. Cummins, R., jr.. and j. b. rivers. 1970. Calico scallop fishery of southeastern U.S. A photo review of latest developments. Commer. Fish. Rev. 32(31:39-43. CUMMINS, R., JR., J. B. RIVERS. AND P. J. STRUHSAKER. 1962. Exploratory fishing off the coast of North Carolina. 445 FISHERY BULLETIN: VOL. 75, NO. 2 September 1959-July 1960. Commer. Fish. Rev. 24(l):l-9. DRUMMOND, s. b. 1969. Explorations for calico scallop, Pecten gibbus, in the area off Cape Kennedy, Florida, 1960-1966. U.S. Fish Wildl. Serv., Fish. Ind. Res. 5:85-101. FORBES, E. 1856. Map of the distribution of marine life. In A. K. Johnston, The physical atlas of natural phenomena. New ed. Edinb. and Lond. GRASSLE, J. F. 1967. Influence of environmental variations on species di- versity in benthic communities of the continental shelf and slope. Ph.D. Thesis, Duke Univ., Durham, N.C., 195 p. Gray, I. E., and M. J. Cerame-Vivas. 1963. The circulation of surface waters in Raleigh Bay, North Carolina. Limnol. Oceanogr. 8:330-337. Gray, I. E., M. E. Downey, and M. J. Cerame-Vivas. 1968. Sea-stars of North Carolina. U.S. Fish Wildl. Serv., Fish. Bull. 67:127-163. HULINGS, N. C. 1961. The barnacle and decapod fauna from the nearshore area of Panama City, Florida. Q. J. Fla. Acad. Sci. 24:215-222. HULINGS, N. C, AND D. W. HEMLAY. 1963.. An investigation of the feeding habits of two species of sea stars. Bull. Mar. Sci. Gulf Caribb. 13:354-359. HYMAN, L. H. 1955. The Invertebrates: Echinodermata. Vol. 4. McGraw-Hill Book Co., Inc., N.Y., 763 p. KIRBY-SMITH, W. W. 1970. Growth of the scallops, Argopecten irradians concen- tricus (Say) and Argopecten gibbus (Linne), as influenced by food and temperature. Ph.D. Thesis, Duke Univ., Durham, N.C., 127 p. LYLES, C. H. 1969. Fishery statistics of the United States 1967. U.S. Fish Wildl. Serv., Stat. Dig. 61, 490 p. MCEACHRAN, J. D., AND W. N. ESCHEMEYER. 1973. Range extensions of the scorpionfish, Scorpeaena isthmensis. Fla. Sci. 36:209-211. MCNULTY, J. K., R. C. WORK, AND H. B. MOORE. 1962. Some relationships between the infauna of the level bottom and the sediment in South Florida. Bull. Mar. Sci. Gulf Caribb. 12:322-332. MORGANS, J. F. C. 1956. Notes on the analysis of shallow-water soft sub- strata. J. Anim. Ecol. 25:367-387. Newton, J. G, O. H. Pilkey, and j. O. blanton. 1971. An oceanographic atlas of the Carolina Continental Margin. N.C. Board Sci. Technol., 57 p. Pearse, a. S., and L. G. Williams. 1951. The biota of the reefs off the Carolinas. J. Elisha Mitchell Sci. Soc. 67:133-161. Porter, H. j. 1971. The North Carolina scallop fishery - a bonanza to shell collectors? N.C. Shell Club Bull. 6:24-25. 1972a. Mollusks coincident with North Carolina's calico scallop fishery. Bull. Am. Malacol. Union, p. 32-33. 1972b. Shell collecting from stomachs of the sea-star genus Astropecten. N.Y. Shell Club Notes 180:2-4. PORTER, H. J., AND D. A. WOLFE. 1972. Mollusca from the North Carolina commercial fishing grounds for the calico scallop, Argopecten gibbus (Linne). J. Conchyliol. 109:91-109. RIVERS, J. B. 1962. A new scallop trawl for North Carolina. Commer. Fish. Rev. 24(5):11-14. ROE, R. B., R. CUMMINS, JR., AND H. R. BULLIS, JR. 1971. Calico scallop distribution, abundance, and yield off eastern Florida, 1967-1968. Fish. Bull., U.S. 69:399- 409. SANDERS, H. L. 1958. Benthic studies in Buzzards Bay. I. Animal- Sediment Relationships. Limnol. Oceanogr. 3:245-258. SCHUMACHER, J. D. 1974. A study of near-bottom currents in North Carolina coastal waters. Ph.D. Thesis, Univ. North Carolina, 134 p. SCHWARTZ, F. J. 1965. Inter-american migrations and systematics of the western Atlantic cownose ray, Rhinoptera bonasus. As- soc. Isl. Mar. Lab. Caribb. 6th Meet., Isla Margarita, Venez. 20-22 Jan. In press. An analysis of benthic and demersal fishes found commonly associated with various provinces and habitats off North Carolina. An oceanographic atlas of the North Carolina margin. Strickland, j. d. h., and T. R. parsons. 1968. A practical handbook of seawater analysis. Fish. Res. Board Can., Bull. 167, 311 p. STRUHSAKER, P. 1969. Demersal fish resources: Composition, distribution, and commercial potential of the continental shelf stocks off southeastern United States. U.S. Fish Wildl. Serv., Fish. Ind. Res. 4:261-300. TAYLOR, C. B., AND H. B. STEWART, JR. 1959. Summer upwelling along the east coast of Florida. J. Geophys. Res. 64:33-40. VERNBERG, F. J., AND W. B. VERNBERG. 1970. Lethal limits and the zoogeography of the faunal assemblages of coastal Carolina waters. Mar. Biol. (Berl.) 6:26-32. WALLER, T. R. 1969. The evolution of the Argopecten gibbus stock (Mol- lusca: Bivalvia), with emphasis on the tertiary and quar- ternary species of eastern North America. Paleontol. Soc. Mem. 3, 125 p. WEBB, N. B., AND F. B. THOMAS. 1968. A study of the quality of North Carolina scallops. An investigation of methods for the improvement of the qual- ity and yield of scallop meat during processing. N.C. Dep. Conserv. Dev., Spec. Sci. Rep. 16, 83 p. WEBSTER, F. 1961. A description of Gulf Stream meanders off Onslow Bay. Deep-Sea Res. 8:130-143. WELLS, H. W., AND I. E. GRAY. 1960. The seasonal occurrence of Mytilis edulis on the Carolina coast as a result of transport around Cape Hat- teras. Biol. Bull. (Woods Hole) 119:550-559. WELLS, H. W., M. J. WELLS, AND I. E. GRAY. 1961. Food of the sea-star Astropecten articulatus. Biol. Bull. (Woods Hole) 120:265-271. 1964. The calico scallop community in North Carolina. Bull. Mar. Sci. Gulf Caribb. 14:561-593. 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 DOTSON, R. C. 1977. Minimum swimming speed of albacore, Thunnus alalunga. Fish. Bull., U.S. 74:955-960. Japanese Fisheries agency. 1975. Report of tuna tagging for 1974. [In Jap.] Pelagic Res. Sect., Far Seas Fish. Res. Lab., 18 p. LAURS, R. M., AND R. J. LYNN. In press. 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. LAURS, R. M., H. S. H. YUEN, AND J. H. JOHNSON. 1977. Small-scale movements of albacore, Thunnus alalunga, in relation to ocean features as indicated by ultrasonic tracking and oceanographic sampling. Fish. Bull., U.S. 75: MAGNUSON, J. J. 1970. Hydrostatic equilibrium of Euthynnus affinis, a pelagic teleost without a gas bladder. Copeia 1970:56-85. SHARP, G. D., AND R. C. FRANCIS. 1976. An energetics model for the exploited yellowfin tuna, Thunnus albacares, population in the eastern Pacific Ocean. Fish. Bull., U.S. 74:36-51. SIDWELL, V. D„ P. R. FONCANNON, N. S. MOORE, AND J. C. BONNET. 1974. Composition of the edible portion of raw (fresh or frozen) crustaceans, finfish, and mollusks. 1. Protein, fat, moisture, ash, carbohydrate, energy value, and cholesterol. Mar. Fish. Rev. 36(3):21-35. 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 4- $ 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 1 55 24 19 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. 4- r 2- 0 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 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 12 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 Bone, Q., and C. E. R. brook. 1973. On Schedophilus medusophagus (Pisces: Stromateoidei). J. Mar. Biol. Assoc. U.K. 53:753-761. 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) 40 50 60 70 80 90 100 60 _ P N - - - - 80 P P P N - - - 80 - P N - - - - 100 - - P P N - - 100 - - P N - - - 100 - - - N - - - 120 - - P P P N N 120 - - - - N N N 120 - - - - P - - 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 CO nditioned group Naive Naive Conditioned No of No. of No. of fish Survivors fish Survivors fish Survivors 20 6 10 7 10 9 20 12 10 9 10 10 20 12 10 6 10 6 20 7 10 7 10 9 20 8 10 5 10 8 20 10 10 7 10 6 20 12 10 9 10 7 20 6 10 7 10 5 458 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 1 1 1 1 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 INFORMATION FOR CONTRIBUTORS TO THE FISHERY BULLETIN Manuscripts submitted to the Fishery Bulletin will reach print faster if they conform to the following instructions. These are not absolute requirements, of course, but desiderata. CONTENT OF MANUSCRIPT The title page should give only the title of the paper, the author's name, his affiliation, and mailing address, including Zip code. The abstract should not exceed one double- spaced page. In the text, Fishery Bulletin style, for the most part, follows that of the Style Manual for Biologi- cal Journals. 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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 Juanita M. Kreps, Secretary NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION Richard A. Frank, 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, 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 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 mailingl. Cost per single issue — $2.95. 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. 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. 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 i Lio, i • . N 10 j V j ': N,0 7 Lio, 7 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 m Yn Yw Pe w Fe Z D F M G f t P1 P2 pa 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 ij (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: Pi (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 g: "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 Pi 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 12 (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 R -13 Pe or R 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 C1 0.233 x 10"° C2 3.233 C3 1.26 C4 0.37 C5 0.87 C6 1.49 -6 C7 0.725 x10 C8 4.69 C9 -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 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 o 15 - 10 CO 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. 30 £ 25 a; E 20 CO o o 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, 25 o C3=I26,C4 = 037, C5 = 0 88, C6 = I 49 ± _L ± 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. 30 £ 25 o I 20 en ■o c o in o en Q -z. < 10 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 30 in c o 25 - e 20 in T3 c a in o CO o Q < 15 10 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. c4 c5 C6 Percentage change in yield c3 1943 1944 1943-65 1.26 0.37 0.88 1.49 — — — 1.00 1.00 1.00 1.00 -6.7 -4.5 + 3.6 4.00 0.0 0.0 0.0 -20.7 -14.3 -40.6 0.0 4.00 0.0 0.0 -24.0 - 16.8 -0.6 0.0 0.0 4.0 0.0 -9.4 -9.3 + 92.8 0.0 0.0 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 30 to S 25 E 20 o CO o 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 e to C o o CO z a 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 30 § 25 E c o l/> 3 O CO Q 20 15 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 O 1 a UJ a. w z o a: H UJ £ v> 13 Z o z 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 (C) per 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 68 Kodiak 5.947 4,805 430 — 37,902 .33 91 4,685 .019 368 Chignik 2,541 10,213 .420 — 66,307 18 95 2,007 .045 80 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 85 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 — 32 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 — 77 Bristol Bay 1,248 1,021 — — 1,758 — .78 473 — 803 Power troll: Statewide 5,290 3,580 .272 2 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 of gross Net less interest income from permits earnings 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 53 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 14 $5,292 356 395 Prince Wm Sound 10 3,780 202 238 Cook Inlet 10 3,780 '37 68 Kodiak 12 4,536 258 368 Chignik 12 4,536 76 80 Peninsula-Aleutians 12 4,536 2111 111 Drift gill net: Southeastern 22 8,316 362 453 Prince Wm Sound 19 7,182 '281 511 Cook Inlet 9 3,402 327 545 Peninsula-Aleutians 13 4,914 147 155 Bristol Bay 11 4,158 1,252 1,669 Set gill net: Yakutat 17 6,426 '83 150 Prince Wm Sound 9 3,402 21 32 Cook Inlet 15 5,670 '377 686 Kodiak 12 4,536 '101 183 Peninsula-Aleutians 14 5,292 54 77 Bristol Bay 9 3,402 '442 803 Power troll: Statewide 23 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 41 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 19 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 68 202 368 72 80 '111 111 294 453 2281 511 2300 545 101 155 1,001 1,669 283 150 218 32 2377 686 2101 183 62 77 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 Of operator equal to gear operator equal to 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 '395 395 Prince Wm Sound 202 214 178 238 Cook Inlet 237 41 237 68 Kodiak 258 313 202 368 Chignik 76 '80 72 80 Peninsula-Aleutians '111 '111 1111 111 Drift gill net: Southeastern 362 M53 294 453 Prince Wm Sound 2281 2281 2281 511 Cook Inlet 327 2300 2300 545 Peninsula-Aleutians 147 132 101 155 Bristol Bay 1,252 918 1,001 1,669 Set gill net: Yakutat 283 283 283 150 Prince Wm Sound 21 19 218 32 Cook Inlet 2377 2377 2377 686 Kodiak 2101 2101 2101 183 Peninsula-Aleutians 54 242 62 77 Bristol Bay 2442 2442 2442 803 Power troll: Statewide 1492 2492 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 20 7-18 May 1971 123 26 June-4 July 1971 27 7-25 Aug. 1971 146 7-16 Nov. 1971 66 1-11 Feb. 1972 30 1-10 May 1972 30 12-18 June 1972 13 9-17 Sept. 1972 34 8-16 Nov. 1972 50 19-27 Jan. 1973 51 9-17 May 1973 49 27 June-6 July 1973 51 3-13 Aug. 1973 50 6-14 Nov. 1973 51 28 Feb-9 Mar. 1974 36 1-9 May 1974 44 13 4 0 4 2 0 0 0 4 12 0 0 0 10 47 13 11 0.00 28.42 0.85 0.72 0.00 0 0.00 14 7.98 10 2.11 4 0.00 0 0.00 0 0.00 21 60.53 19 28.28 10 0.00 0 0.00 5 0.00 22 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' 26' 1 0 m A\_. © © ©©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 30 1 ■ " 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 o\ + + +'.+ + 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 • I00Q, ' i GE 7117 Opistmonema oglinum eggs June - Jul* 1971 I 1 T w 1S> \ 50 in-.. \ ( - + + v-t + t #«\)7 \ - .*♦*.. ».\ Number under 10m2 * 0 '. ^ /■ • «l ; • 1 - 10 • n-ioo • 101-1000 ' ♦ ♦ + © >I000 1 8C 7120 8 TI 7121 Opisthonema oglinum eggs August 1971 30° + + ~T 4 1 1 / 4 4 4 4 \^f*<^' \ 4 + + 4 t + ♦ 450 r "■"*-. \w* 4 + 4 4 4- \ V 4 + 4 + 4 \ / + A 4 + + 4 / 28° - + + + 4 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# ^^ o\ 4 M *■*+ 4* f 4 ) k!6° Number under I0m 2 +■ -•- +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 1 r— \ 50m.. \ I : * * *H • • «»Sj / V - ...*•• »»\r7 o\ * • «'.* • • • +^ Number under I0m? t 0 '• B 1 • IOOO 84° 8C 7120 i TI 7121 Opisthonema oglinum larvae August 1971 - 4- 4- + 4 ^ + + 4 4 4I iw*^^ \ 4 4 4 + 4 + 4 +50 mH 4 + 4 + -* *S + ) 4 4 4 4 t 4 A + + + + / - 4 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- + • o\ NumDer 4 0 under 10m2 + + + + +J + ++00 • 1-10 • 11-100 • 101-1000 4- +4--*+#4-» + + ++;+•+ + «---' © >I000 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 30 28 GE 7208 Opisthoneha oglinuh eggs May 1972 26' 1 \^~SIS> 50m-., + \ 4 4 # / 4 4 + +• \ + + *c o + 4 + • -f Number under 10m2 4 0 4- ■*- 1 + 4- - T| /' • I-IO • 11-100 • 101-1000 +1 + +■ .■^""'^ © >I000 1 1 28° - GE 7208 Opisthoneha oglinum larvae Hay 1972 l)^J^> - 50m-. , \ \ t \ + • • / + + + o\ +■ + + \ • • Number under 10m2 + 0 • * ; • + • x. y • I-IO • 11-100 *-j • • • 101-1000 o,^.-^ ® >I000 I 1 I 82° 80° 86° 84° 82° 80° GE 7210 Opisthoneha oglinum eggs June 1972 30' 28' 86° GE 7210 Opisthoneha oglinuh larvae June 1972 T \ 50m-, \ 4 "\ 4 • \<* y • \-» 4 + ^i 4 4 ' ° 1 Number under 10m2 4 0 • I000 1 J -t- ...XT-' 30' 28' T W^ 50m-., - \ - \ • *\ft o\ \ 0 • Number under 10m2 •f C • 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 — - T w \s^* \ 50m-.^ \ + ♦ • • / - 4- \ + + * */^ \ ♦ *\ ♦♦ A 0"] + 'i + + 4 ♦- f-v 4 4 4 Number under 10m2 + 0 • I000 1 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° - i i w . \. 50m-., ♦ *■ * * * V \ + • - * 1 " * \ + * + */I000 i i 30° 50m-., + I r ♦ * •V f ♦ ♦ • \, s, • • ♦ ♦ / \ 28° * + t \ + • • IfJ o\ ♦ \ • • • \ti - A • • • 2b" Number under 10m2 * 0 • I000 .. 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 /• • IOOO . i 1 i 30 I 1 T 0^^#^^ \ • * * • V 50m-., \- *-, ♦■ * ♦ ♦ \. ♦ «- "i * ♦ + • / «■ \ + ♦ • •[ A. V - • » \ • ••><; ♦ - \ • • • o\ - »\ *© ► © \ Number under torn2 - t . *\ •< + 0 + t- J ♦ • • • s /' • 1 - 10 • 11-100 *' ♦ • • 101-1000 ! • ' ..- © >I000 1 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 V 28° + + \ + + • •( (V. + + \ + + • *.<* + + \ + + + \ o\ 4 +■ 1 + + + + 4- + +■ • 4- 26° Number under 10m2 + 0 + 4- ', + *■ * • ^P ft • 1 - 10 • 11-100 • 101 - 1000 + .' + +■ -■-^ © >I000 ' i .. _ _ 80* 499 FISHERY BULLETIN: VOL. 75, NO. 3 CL 7105 opisthoneha ogl1nuh larvae February - March 1974 24' Number under 10m2 + 0 • I000 CL 7112 0p1sthonema oglinum eggs May 1974 82° 80" CL 7412 opisthoneha oglinum larvae Hay 1974 26° - 26" 24' 1 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 \ • • .-^^ © >IOOO 1 — ' ' 1 \s^r ' ' * N \ 50»-., \ * . • • -A \ \ *■ * * * / vb - \ ♦ ♦ * '/ewi \ " ♦N, ♦ • #nr \ \-\ o) •\ . • 0^ I Number under 10m2 + 0 • I000 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 u 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 ( r 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 48.43 104.59 149.80 149.80 151.42 156.50 153.18 153.89 52.00 91.33 0.00 55.81 48.73 26.26 0.00 0.00 65.98 38.93 11.16 0.00 0.00 54.09 53.21 21.75 0.00 6.70 47.89 0.00 34.25 0.86 1.37 0.00 0.00 11.93 1.02 0.00 0.00 0.00 91.66 44.26 0.00 0.00 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 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 0.00 8B7201 and GE7202 14885 0.00 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 0.00 IS7303 149.80 0.00 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 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 X tS 3 < « 15.0 < Q O 12.5 I- H X g 100 < H r B 2 b- O 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 - 60 40 - 20 Z o 111 o |80 < Q Z CD < 160 O UJ t- < X 140 120 100 80 60 40 20 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 Duration-corrected Abundance Duration Mean age abundance Abundance Duration Mean age abundance Stage (no. x 10") (days) (days) (no. x 10") Stage (no. x 10") (days) (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, 9 Nonfully vulnerable larvae duration (days) Instantaneous mortality coefficient, Z /-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 09 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 60 0.2211 948.51 01983 0.8 00797 6.0 0.2442 1,149.53 0.2167 09 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 b < Q z 3 CD < Q 111 o LU cc cc o CJ I z l- < cc 3 Q 10 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. g Number of spawned eggs (x 10") Instantaneous mortality coefficient. Z 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. LITERATURE CITED AHLSTROM, 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. 1959. Vertical distribution of pelagic fish eggs and larvae off California and Baja California. U.S. Fish Wildl. Serv., Fish. Bull. 60:107-146. 1968. An evaluation of the fishery resources available to California fishermen. In The future of the fishing indus- try of the United States, p. 65-80. Univ. Wash. Publ. Fish., New Ser. 4. ALVERSON, D. L., AND W. T. PEREYRA. 1969. Demersal fish explorations in the northeastern Pacific Ocean — an evaluation of exploratory fishing methods and analytical approaches to stock size and yield forecasts. J. Fish. Res. Board Can. 26:1985-2001. BANNISTER, R. C. A., D. HARDING, AND S. J. LOCKWOOD. 1974. Larval mortality and subsequent year-class 510 HOUDE: ABUNDANCE AND POTENTIAL YIELD OF THREAD HERRING strength in the plaice (Pleuronectes platessa L.). In J. H. S. Blaxter (editor), The early life history offish, p. 21-37. Springer- Verlag, N.Y. BERRY, F. H., AND I. BARRETT. 1963. Gillraker analysis and speciation in the thread her- ring genus Opisthonema. Inter-Am. Trop. Tuna Comm., Bull. 7:113-153. BULLIS, H. R., JR., AND J. S. CARPENTER. 1968. Latent fishery resources of the central West Atlantic region. In The future of the fishing industry of the Unit- ed States, p. 61-64. Univ. Wash. Publ. Fish., New Ser. 4. BULLIS, H. R., JR., AND J. R. THOMPSON. 1967. Progress in exploratory fishing and gear research in Region 2 fiscal year 1966. U.S. Fish Wildl. Serv., Circ. 265, 14 p. BUTLER, J. A. 1961. Development of a thread-herring fishery in the Gulf of Mexico. Commer. Fish. Rev. 23(9):12-17. CUSHING, D. H. 1957. The number of pilchards in the Channel. Fish. In- vest. Minist. Agric. Fish. Food (G.B.), Ser. II, 21(5), 27 p. FARRIS, D. A. 1961. Abundance and distribution of eggs and larvae and survival of larvae of jack mackerel (Trachurus symmet- rica). U.S. Fish Wildl. Serv., Fish. Bull. 61:247-279. FOOD AND AGRICULTURE ORGANIZATION. 1975. Catches and landings, 1974. FAO Yearb. Fish. Stat. 38, 378 p. FUSS, C. M., JR. 1968. The new thread herring fishery in eastern Gulf of Mexico. Commer. Fish. Rev. 30(6):36-41. Fuss, C. M., Jr., J. A. Kelly, jr., and k. w. Prest, jr. 1969. Gulf thread herring: aspects of the developing fishery and biological research. Proc. Gulf Caribb. Fish. Inst. 21:111-125. GULLAND, J. A. (editor). 1971, The fish resources of the ocean. Fishing News (Books) Ltd., Surrey, Engl., 255 p. GULLAND, J. A. 1972. The scientific input to fishery management deci- sions. In Progress in fishing and food science, p. 23-28. Univ. Wash. Publ. Fish., New Ser. 5. HILDEBRAND, S. F. 1963. Family Clupeidae. In H. B. Bigelow (editor), Fishes of the western North Atlantic. Part Three, p. 257- 454. Mem. Sears Found. Mar. Res. Yale Univ. 1. HOUDE, E. D. 1973a. Estimating abundance of sardine-like fishes from egg and larval surveys, eastern Gulf of Mexico: prelimi- nary report. Gulf Caribb. Fish. Inst. Proc. 25th Annu. Sess., p. 68-78. 1973b. Some recent advances and unsolved problems in the culture of marine fish larvae. World Maricult. Soc. Proc. 3:83-112. 1977a. Abundance and potential yield of the round her- ring, Etrumeus teres, and aspects of its early life history in the eastern Gulf of Mexico. Fish. Bull., U.S. 75:61-89. 1977b. Abundance and potential yield of the scaled sar- dine, Harengula jaguana, and aspects of its early life history in the eastern Gulf of Mexico. Fish. Bull., U.S. 75: 613-628. HOUDE, E. D., S. A. BERKELEY, J. J. KLINOVSKY, AND C. E. DOWD. 1976. Ichthyoplankton survey data report. Summary of egg and larvae data used to determine abundance of clupeid fishes in the eastern Gulf of Mexico. Univ. Miami Sea Grant Tech. Bull. 32, 193 p. HOUDE, E. D., AND N. CHITTY. 1976. Seasonal abundance and distribution of zoo- plankton, fish eggs, and fish larvae in the eastern Gulf of Mexico, 1972-74. U.S. Dep. Commer., NOAA Tech. Rep. NMFSSSRF-701, 18 p. HOUDE, E. D., AND P. L. FORE. 1973. Guide to identity of eggs and larvae of some Gulf of Mexico clupeid fishes. Fla. Dep. Nat. Resour., Mar. Res. Lab., Lean. Ser. 4(23), 14 p. HOUDE, E. D., W. J. RICHARDS, AND V. P. SAKSENA. 1974. Description of eggs and larvae of scaled sardine, Harengula jaguana. Fish. Bull., U.S. 72:1106-1122. HOUDE, E. D., AND L. J. SWANSON, JR. 1975. Description of eggs and larvae of yellowfin menha- den, Brevoortia smithi. Fish. Bull., U.S. 73:660-673. JOHNSON, L. E. 1974. Florida landings, annual summary 1973. U.S. Dep. Commer., Natl. Mar. Fish. Serv., Curr. Fish. Stat. 6419, 18 p. KINNEAR, B. S., AND C. M. FUSS, JR. 1971. Thread herring distribution off Florida's west coast. Commer. Fish. Rev. 33(7-8):27-39. KLIMA, E. F. 1971. Distribution of some coastal pelagic fishes in the western Atlantic. Commer. Fish. Rev. 33(6):21-34. LENARZ, W. H. 1973. Dependence of catch rates on size of fish larvae. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 164:270- 275. MARTINEZ, S. 1972. Fecundity, sexual maturation and spawning of scaled sardine (Harengula pensacolae). M.S. Thesis, Univ. Miami, Coral Gables, 51 p. MATSURA, Y. In press. A study of the life history of Brazilian sardine, Sardinella brasiliensis . IV. Distribution and abundance of sardine larvae. Bol. Inst. Oceanogr. (Sao Paulo). NAKAI, Z., AND S. HATTORI. 1962. Quantitative distribution of eggs and larvae of the Japanese sardine by year, 1949 through 1951. Bull. Tokai Reg. Fish. Res. Lab. 9:23-60. PRISTAS, P. J., AND R. P. CHEEK. 1973. Atlantic thread herring (Opisthonema oglinum) - movements and population size inferred from tag returns. Fish. Bull., U.S. 71:297-301. REINTJES, J. W., AND F. C. JUNE. 1961. A challenge to the fish meal and oil industry in the Gulf of Mexico. Proc. Gulf Caribb. Fish. Inst. 13th Annu. Sess., p. 62-66. RICHARDS, W. J., R. V. MILLER, AND E. D. HOUDE. 1974. Egg and larval development of the Atlantic thread herring, Opisthonema oglinum. Fish. Bull., U.S. 72:1123-1136. RICHARDS, W. J., AND B. J. PALKO. 1969. Methods used to rear the thread herring, Opis- thonema oglinum, from fertilized eggs. Trans. Am. Fish. Soc. 98:527-529. RINKEL, M. O. 1974. Western Florida continental shelf program. In R. E. Smith (editor), Proceedings of marine environmental implications of offshore drilling in the eastern Gulf of Mexico, p. 97-126. State Univ. Syst. Fla., Inst. Oceanogr., St. Petersburg, Fla. 511 FISHERY BULLETIN: VOL. 75, NO. 3 SAKSENA, V. P., AND E. D. HOUDE. 1972. Effect of food level on the growth and survival of laboratory-reared larvae of bay anchovy (Anchoa mitch- illi Valenciennes) and scaled sardine (Harengula pen- sacolae Goode and Bean). J. Exp. Mar. Biol. Ecol. 8:249- 258. SAKSENA, V. P., C. STEINMETZ, JR., AND E. D. HOUDE. 1972. Effects of temperature on growth and survival of laboratory-reared larvae of the scaled sardine, Harengula pensacolae Goode and Bean. Trans. Am. Fish. Soc. 101:691-695. SAVILLE, a. 1964. Estimation of the abundance of a fish stock from egg and larval surveys. Rapp. P.-V. Reun. Cons. Perm. Int. Explor. Mer 155:164-170. SETTE, 0. E., AND E. H. AHLSTROM. 1948. Estimations of abundance of the eggs of the Pacific pilchard (Sardinops caerulea) off southern California dur- ing 1940 and 1941. J. Mar. Res. 7:511-42. SIMPSON, A. C. 1959. The spawning of the plaice (Pleuronectes platessa) in the North Sea. Fish. Invest. Minist. Agric. Fish. Food (G.B.), Ser. II, 22(7), 111 p. SMITH, P. E., AND S. L. RICHARDSON (editors). In press. Manual of methods for fisheries resource survey and appraisal. Part 4. Standard techniques for pelagic fish egg and larvae survey. FAO, Rome. TAFT, B. A. 1960. A statistical study of the estimation of abundance of sardine (Sardinops caerulea) eggs. Limnol. Oceanogr. 5:245-264. WATANABE, T. 1970. Morphology and ecology of early stages of life in Japanese common mackerel, Scomber japonicus Hout- tuyn, with special reference to fluctuation of popula- tion. Bull. Tokai Reg. Fish. Res. Lab. 62:1-283. 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 n Median Range n Median Range Palos Verdes: 5 Winter 3 18 15 -29 2 7.0 2.0-12 7 Winter 2 36 29 -44 3 1.8 1.3- 2.3 1 Spring 2 26 18 -34 1 25 — 2 Spring 2 20 16 -24 3 5.0 4.3- 5,3 3 Spring 3 13 7.2-45 2 11 9.6-13 4 Spring 1 16 — 1 14 — 6 Summer 3 15 80-29 3 11 8.8-13 Orange County: 8 Spring 4 31 19 -75 1 7.6 — 10 Fall 6 7.6 4.2-57 2 1.0 0.3- 17 11 Fall 1 19 — 2 1.2 0.3- 2 2 9 Fall 3 4.2 0.9- 6 1 3 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 n Median Range n Median Range Palos Verdes: 5 Winter 3 2.6 1.8-3.6 2 1.2 0.6-1.9 7 Winter 2 3.8 3.4-1.3 3 0.3 02-0.5 1 Spring 2 2.0 1 7-2.2 1 2.6 — 2 Spring 2 2.4 1.5-3.4 3 0.5 0.4-0.6 3 Spring 3 1.0 . 0.8-3 0 2 1.4 1.4-1 5 4 Spring 1 2.1 — 1 1.6 — 6 Summer 3 1.5 0.6-3.3 3 1.0 0.8-2.6 Orange County: 8 Spring 4 3.0 2.1-6.6 1 09 — 10 Fall 6 3.4 1.3-5.2 2 4.0 1.8-6.2 11 Fall 1 1.6 — 2 0.3 03 9 Fall 3 09 0.9-1.1 3 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 1 3/3 1.8 M 7.0 1040-1740 ? 2 3/11 2.3 F 8.5 0910-1740 ? 3 3/17 2.3 ? 6.4 1105-1730 beginning 4 3/30 2.0 M 11.6 1125-2300 yes 5 4/7 2.6 M 8.4 1145-2010 yes 6 4/15 2.0 F 16.1 1155-0400 yes 7 4/29 1.8 F 18.0 1200-0600 yes 8 5/6 2.0 M 21.9 1010-0805 yes 9 5/20 2.0 F 19.6 1 1 55-0730 yes 10 6/3 2.2 M 16.3 1615-0830 yes 11 6/14 2.3 M 4.8 1145-1630 ? 12 6/24 2.3 M 14.8 1445-0530 no 13 9/13 2.0 F 13.4 1305-0230 no 14 10/7 2.0 F 18.8 1215-0700 no 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 *>» © twilight 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 *>» © twilight • nig III 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 s\ "----—-.. ._.---- - —-■■' '--. Isfrimus X vt SANTA CATALINA ISLAND N^ 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 24 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- ken Havet 1966(1): 1-15. 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. 10. 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, Heterodontus francisci: effect of light intensity. Bull. South. Calif. Acad. Sci. 74:20-26. 527 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. Rev. 27(12):1-21. Nelson, D. R., and R. H. Johnson. 1970. Diel activity rhythms in the nocturnal, bottom- dwelling sharks, Heterodontus francisci, and Cephaloscyl- lium ventriosum. Copeia 1970:732-739. 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- metry system for the study of shark behavior at sea- with 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- lantic, 1972-1975. J. Mar. Biol. Assoc. U.K. 56:929- 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 10,0.0 LOG IflRVHl DRY HEIGHT ^"^ • • 5 MEEK LflRVRE 25.0- • 20. 0- •/ y/^ 15.0- 10.0- 5.0- / -0.1l3p\ r = 2.6\l-« 1 0 0 t MEEK LflRVRE 1 1 1 ~\ 0.0- —* — 0 0 I 1 T ..__._ , r 0.0 6.8 13.6 20.4 27.2 34.0 40.8 47.6 PREY CONCENTRATION 54.4 61.2 68.0 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 of mortality (cal/liter) out of 500 survival1 coefficient 20.50 171 49 0.022 6.80 19 49 0.069 3.40 13 42 0.091 0.68 5 15 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) or 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) a 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: K, 01 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 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 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 3 1.0 « . 0 K IS 3 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 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 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 LITERATURE CITED ANRAKU, M. 1964. Some technical problems encountered in quanti- tative studies of grazing and predation by marine plank- tonic copepods. J. Oceanogr. Soc. Jap. 20:221-231. BAJKOV, A. D. 1936. How to estimate the daily food consumption of fish under natural conditions. Trans. Am. Fish. Soc. 65: 288-289. BEAMISH, F. W. H., AND L. M. DICKIE. 1967. Metabolism and biological production in fish. In S. D. Gerking (editor), The biological basis of freshwater fish production, p. 215-242. John Wiley and Sons, N.Y. 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. 1969. Development: eggs and larvae. In W. S. Hoar and D. J. Randall (editors), Fish physiology, Vol. 3, p. 178-252. Academic Press, N.Y. BRAUM, E. 1967. The survival of fish larvae with reference to their feeding behavior and the food supply. In S. D. Gerking (editor), The biological basis of freshwater fish production, p. 113-131. John Wiley and Sons, N.Y. BRODY, S. 1945. Bioenergetics and growth. Rheinhold Co., N.Y., 1023 p. CHIBA, K. 1961. The basic study on the production of fish seedling under possible control. I. The effect of food in quality and quantity on the survival and growth of the common carp fry. [In Jap., Engl, abstr.] Bull. Freshwater Res. Lab., Fish Agency, Tokyo 11(1):105-129. CONOVER, R. J. 1960. The feeding behavior and respiration of some marine planktonic Crustacea. Biol. Bull. (Woods Hole) 119:399-415. CUSHING, D. H, AND J. G. K. HARRIS. 1973. Stock and recruitment and the problem of density dependence. Rapp. P.-V. Reun. Cons. Int. Explor. Mer 164:142-155. DAVIES, P. M. C. 1964. The energy relations of Carassius auratus L. — I. Food input and energy extraction efficiency at two ex- perimental temperatures. Comp. Biochem. Physiol. 12:67-79. DETWYLER, R., AND E. D. HOUDE. 1970. Food selection by laboratory-reared larvae of the scaled sardine Harengula pensacolae (Pisces, Clupeidae) and the bay anchovy Anchoa mitchilli (Pisces, Engrauli- dae). Mar. Biol. (Berl.) 7:214-222. DRAPER, N. R„ AND H. SMITH. 1966. Applied regression analysis. John Wiley and Sons, N.Y., 407 p. EDWARDS, R. R. C, D. M. FINLAYSON, AND J. H. STEELE. 1969. The ecology of O-group plaice and common dabs in Loche Ewe. II. Experimental studies of metabolism. J. Exp. Mar. Biol. Ecol. 3:1-17. FRAME, D. W. 1973. Conversion efficiency and survival of young winter flounder (Pseudopleuronectes americanus) under experi- mental conditions. Trans. Am. Fish. Soc. 102:614-617. 544 LAURENCE: BIOKNERGETIC MODE!. FOR WINTER KLOUNDER LARVAE FRY, F. E. J. 1947. Effects of the environment on animal activity. Univ. Toronto Stud., Biol. Ser. 55, Publ. Ont. Fish. Res. Lab. 68, 62 p. Gaudy, R. 1974. Feeding four species of pelagic copepods under ex- perimental conditions. Mar. Biol. (Berl.) 25:125-141. HARGRAVE, B. T., AND G. H. GEEN. 1970. Effects of copepod grazing on two natural phyto- plankton populations. J. Fish. Res. Board Can. 27: 1395-1403. Heinle, D. R., and D. a. Flemer. 1975. Carbon requirements of a population of the estua- rine copepod Eurytemora affinis. Mar. Biol. (Berl.) 31: 235-247. HOUDE, E. D. 1973. Some recent advances and unsolved problems in the culture of marine fish larvae. Proc. World Maricult. Soc. 3:83-112. 1975. Effects of stocking density and food density on sur- vival, growth and yield of laboratory-reared larvae of sea bream Archosargus rhomboidalis (L.) (Sparidae). J. Fish Biol. 7:115-127. IVLEV, V. S. 1939a. Energy balance of the growing larva of Silurus glanis. Dokl. (C. R.) Akad. Nauk SSSR, Nov. Ser. 25: 87-89. 1939b. The effect of starvation on energy transformation during the growth of fish. Dokl. (C. R.) Akad. Nauk SSSR, Nov. Ser. 25:90-92. 1939c. (Energy balance in the carp.) [In Russ., Engl. summ.] Zool. Zh. 18:303-318. 1961a. Experimental ecology of the feeding of fishes. Yale Univ. Press, New Haven, 302 p. 1961b. On the utilization of food by plankton-eating fishes. [In Russ.] Tr. Sevastop. Biol. Stn. Im. A. D. Kovalenskogo Akad. Nauk SSSR 14:188-201. (Fish. Res. Board Can., Transl. Ser. 447, 17 p.) KRAMER, D., AND J. R. ZWEIFEL. 1970. Growth of anchovy larvae (Engraulis mordax Girard) in the laboratory as influenced by temperature. Calif. Coop. Oceanic Fish. Invest. Rep. 14:84-87. LASKER, R. 1962. Efficiency and rate of yolk utilization by developing embryos and larvae of the Pacific sardine, Sardinops caerulea (Girard). J. Fish. Res. Board Can. 19:867-875. LAURENCE, G. C. 1969. The energy expenditure of largemouth bass larvae iMieropterus salmoides) during yolk absorption. Trans. Am. Fish. Soc. 98:398-405. 1971a. Digestion rate of larval largemouth bass. N.Y. Fish Game J. 18:52-56. 1971b. Feeding and bioenergetics of largemouth bass lar- vae (Micropterus salmoides). Ph.D. Thesis, Cornell Univ., Ithaca, 139 p. 1973. Influence of temperature on energy utilization of embryonic and prolarval tautog, Tautoga onitis. J. Fish. Res. Board Can. 30:435-442. 1974. Growth and survival of haddock Melanogrammus aeglefinus larvae in relation to planktonic prey concentra- tion. J. Fish. Res. Board Can. 31:1415-1419. 1975. Laboratory growth and metabolism of the winter flounder Pseudopleuronectes americanus from hatching through metamorphosis at three temperatures. Mar. Biol. (Berl.) 32:223-229. 1976. Caloric values of some North Atlantic calanoid copepods. Fish. Bull., U.S. 74:218-220. LISIVNENKO, L. N. 1961. (Plankton and feeding of larvae of the Baltic her- ring in the Riga Guld.) [In Russ.] Tr. Nauchno-issled. Inst. Ryb. Khoz. Soveta Nar. Khoz. Lat. SSR [LatvNIRO] 3:105-108. NISHIKAWA, Y. 1975. Feeding of larval and juvenile skipjack tuna in relation to the development of their stomachs. [In Jap., Engl, abstr.] Bull. Far Seas Fish. Res. Lab. (Shimizu) 12:221-236. 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. PALOHEIMO, J. E., AND L. M. DICKIE. 1966a. Food and growth of fishes. II. Effects of food and temperature on the relation between metabolism and body weight. J. Fish. Res. Board Can. 23:869-908. 1966b. Food and growth of fishes. III. Relations among food, body size, and growth efficiency. J. Fish. Res. Board Can. 23:1209-1248. PANDIAN, T. J. 1967. Intake, digestion, absorption, and conversion of food in the fishes Megalops cyprinodes and Ophiocephalus striatus. Mar. Biol. (Berl.) 1:16-32. PARKER, R. R., AND P. A. LARKIN. 1959. A concept of growth in fishes. J. Fish. Res. Board Can. 16:721-745. POWERS, J. E. 1974. Competition for food: An evaluation of Ivlev's model. Trans. Am. Fish. Soc. 103:772-776. RILEY, J. D. 1966. Marine fish culture in Britain. VII. Plaice (Pleuro- nectes platessa L.) post-larval feeding on A rtemia salina L. nauplii and the effects of varying feeding levels. J. Cons. 30:204-221. ROSENTHAL, H., AND G. HEMPEL. 1970. Experimental studies in feeding and food require- ments of herring larvae iClupea harengus L.). In J. H. Steele (editor), Marine food chains, p. 344-364. Univ. Calif. Press, Berkeley. SAKSENA, V. P., AND E. D. HOUDE. 1972. Effect of food level on the growth and survival of laboratory-reared larvae of bay anchovy (Anchoa mit- chilli Valenciennes) and scaled sardine (Harengula pen- sacolae Goode and Bean). J. Exp. Mar. Biol. Ecol. 8: 249-258. SCHUMANN, G O. 1965. Some aspects of behavior in clupeid larvae. Calif. Coop. Oceanic Fish. Invest. Rep. 10:71-78. SHELBOURNE, J. E. 1965. Rearing marine fish for commercial purposes. Calif. Coop. Oceanic Fish. Invest. Rep. 10:53-63. SHIROTA, A. 1970. Studies on the mouth size of fish larvae. [In Jap., Engl, abstr.] Bull. Jap. Soc. Sci. Fish. 36:353-368. SMIGIELSKI, A. S. 1975. Hormonal-induced ovulation of the winter flounder, 545 FISHERY BULLETIN: VOL. 75. NO. 3 Pseudopleuronectes americanus. Fish. Bull., U.S. 73: 431-438. SM1GIELSKI, A. S., AND C. R. ARNOLD. 1972. Separating and incubating winter flounder eggs. Prog. Fish-Cult. 34:113. SOROKIN, YU. I., AND D. A. PANOV. 1965. Balance of consumption and expenditure of food by larvae of bream at different stages of development. Dokl. Biol. Sci. 165:797-799. Steel, R. G. C, and J. H. Torrie. I960. Principles and procedures of statistics with special reference to the biological sciences. McGraw-Hill, N.Y., 481 p. STEPIEN, W. P. 1974. Feeding of laboratory-reared larvae of sea bream Archosargus rhomboidalis (Linnaeus): Sparidae. M.S. Thesis, Univ. Miami, Miami, Fla., 81 p. Swift, R. W., and C. E. French. 1954. Energy metabolism and nutrition. Scarecrow Presss, Wash., D.C., 264 p. SYSOEVA, T. K., AND A. A. Degterva. 1965. The relation between the feeding of cod larvae and pelagic fry and the distribution and abundance of their principle food organisms. Int. Comm. Northwest Atl. Fish., Spec. Publ. 6:411-416. UMBREIT, W. W., R. H. BURRIS, AND J. F. STAUFFER. 1964. Manometric techniques. Burgess Publ. Co., Minneap., 305 p. Ware, D. M. 1975. Growth, metabolism, and optimal swimming speed of a pelagic fish. J. Fish. Res. Board Can. 32:33-41. WARREN, C. E., AND G. E. DAVIS. 1967. Laboratory studies on the feeding, bioenergetics, and growth offish. In S. D. Gerking (editor), The biolog- ical basis of freshwater fish production, p. 175-214. John Wiley and Sons, N.Y. WINBERG, G. G. 1956. Rate of metabolism and food requirements of fishes. [In Russ.] Nauch. Tr. Belorussk. Gos. Univ. Imeni V. I. Lenina, Minsk, 253 p. (Fish. Res. Board Can., Trans. Ser. 194, 239 p.) WYATT, T. 1972. Some effects of food density on the growth and behaviour of plaice larvae. Mar. Biol. (Berl.) 14:210- 216. 1973. The biology of Oikopleura dioica and Fritillaria borealis in the Southern Bight. Mar. Biol. (Berl.) 22: 137-158. ZAIKA, V. E., AND N. A. OSTROVSKAYA. 1972. Indicators of the availability of food to fish larvae. I. The presence of food in the intestines as an indicator of feeding conditions. [In Russ.] Vopr. Ikhtiol. 72:109-119. (Transl. in J. Ichthyol. 12:94-103.) 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 SL 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 V straight 4.13 VI straight 4.67 8 7 VIII straight 4.80 8 8 IX I 8 5 flexed 4.80 9 8 XI 12 I I 7 5 straight 4.80 9 8 X 13 I I 8 5 flexed 4.87 9 8 X 13 I I 8 5 flexed 4.93 9 8 X 13 I I 8 5 flexed 4.93 9 8 X 13 I I 8 5 straight 5.07 9 8 VIII 15 I I 8 5 flexed 5.07 9 8 X 13 I I 8 5 flexed 5.07 9 8 IX 14 1 I 8 5 flexed 5.07 9 8 IX 14 I I 8 5 flexed 5.13 9 8 XI 12 I I 8 5 flexed 5.27 9 8 X 13 I I 8 5 flexed 5.40 9 8 X 13 I I 9 5 flexed 5.46 9 8 XI 12 I I 9 5 flexed 5.46 9 8 X 13 I I 9 5 flexed 6.06 9 8 X 13 I I 9 5 flexed 6.13 9 8 XI 12 I I 9 5 flexed 6.26 9 8 XI 12 I 9 5 flexed 6.33 9 8 XI 12 I I 9 5 flexed 6.40 9 8 XI 12 I I 9 5 flexed 6.53 9 8 XI 12 I I 9 5 flexed 6.53 9 8 XI 12 I 9 5 flexed 6.53 9 8 XI 12 I 9 5 flexed 6.93 9 8 XI 12 I 9 16 5 flexed 7.80 9 8 XI — I 9 16 5 flexed 8.26 9 8 XII 11 II I 8 16 5 flexed 8.60 9 8 XI 12 II I 8 17 5 flexed 8.66 9 8 XII 11 II I 8 17 5 flexed 9.00 9 8 XI 12 II I 8 17 5 flexed 10.00 9 8 XI 12 II I 8 17 5 flexed 10.53 9 8 XII 11 I I 8 17 5 flexed 10.80 9 8 XII 11 II I 8 17 5 flexed 10.93 9 8 XI 12 II I 8 18 5 flexed 11.20 9 8 XII 11 II I 8 17 5 flexed 14.20 9 8 XII 11 I I . 8 17 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 y range (mm) X y N b a Sy.x r Head length 4.00-14.20 6.64 2.62 37 0.326 0.454 0.217 0.988 Body depth 4.00-14.20 6.64 2.28 37 0 285 0.388 0.198 0.986 Snout to anus 4.00-14.20 6.64 4.01 37 0.672 -0.450 0.185 0.995 Eye diameter 4.00-14.20 6.73 0.91 35 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 SL 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 Anderson, w. D., Jr. 1967. Field guide to the snappers (Lutjanidae) of the west- ern Atlantic. U.S. Fish Wildl. Serv., Circ. 252, 14 p. 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. Publ. 6, 149 p. BOHLKE, J. E., AND C. C. G. CHAPLIN. 1968. Fishes of the Bahamas and adjacent tropical waters. Livingston Publ. Co., Wynnewood, Pa., 771 p. FAHAY, M. P. 1975. An annotated list of larval and juvenile fishes cap- tured with surface-towed meter net in the south Atlantic bight during four RV Dolphin cruises between May 1967 and February 1968. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-685, 39 p. FOURMANOIR, P. 1973. Notes ichthyologiques(V). Cah. O.R.S.T.O.M. Ser. Oceanogr. 11:33-39. 553 FISHERY BULLETIN: VOL. 75, NO. 3 HEEMSTRA, P. C. 1974. On the identity of certain eastern Pacific and Carib- bean post-larval fishes (Perciformes) described by Henry Fowler. Proc. Acad. Nat. Sci. Phila. 126:21-26. HILDEBRAND, S. F. 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 24 26 28 30 32 34 36 38 Percentaae Anomuran: Bering hermit crab, 20 6/20 2 60 53 30 80 '55 47 0 0 — — — Pagurus bennganus 60 7/28 55 73 37 10 0 — — — 120 50 30 0 17 0 — — — 240 65 37 3 0 0 — — — Granular hermit crab, 20 6/25 3 90 92 30 — 87 83 70 0 0 — — Pagurus granosimanus 60 6/27 — 93 80 77 0 0 — — 120 7/2 — 90 90 53 0 0 — — 240 — 90 83 23 0 0 — — Hairy hermit crab, 20 6/5 3 80 93 10-30 — 80 80 53 10 7 0 — Pagurus hirsutiusculus 60 6/13 — 100 77 85 37 0 0 — 120 6/23 — 100 80 80 30 0 — — 240 — 80 83 65 7 0 0 — Porcelain crab. 20 6/23 3 40 83 10-30 — 45 30 0 0 — — — Petrolislhes enomerus 60 6/25 — 70 50 0 0 — — — 120 7/2 — 100 0 0 0 — — — 240 — 80 0 0 0 — — — Brachyuran: Black clawed crab, 20 6/16 3 100 89 40 100 98 90 95 63 13 0 — Lophopanopeus bellus 60 6/23 100 98 98 85 5 3 — — 120 9/16 90 100 98 75 8 0 — — 240 80 98 83 55 0 3 — — Dungeness crab, 20 6/7 4 60 93 50 100 90 80 78 14 0 — — Cancer magister 60 6/9 100 94 74 18 6 0 — — 120 6/28 100 96 90 0 0 0 — — 240 2/29/72 100 94 62 2 0 0 — — Graceful crab, 20 7/16 2 60 95 40 88 90 90 88 23 0 — — Cancer gracilis 60 7/18 93 90 90 25 0 0 — — 120 90 83 93 3 0 0 — — 240 93 85 80 0 0 0 — — Kelp crab, 20 9/2 2 80 100 40 — 100 100 100 90 10 0 — Pugettia producta 60 10/15 — 98 100 98 88 0 0 — 120 — 98 90 93 13 0 0 — 240 — 95 95 30 0 0 0 — Messmate crab, 20 7/30 2 80 95 40 90 83 85 83 25 0 — — Pinmxa littoralis 60 8/4 95 98 88 60 3 0 — — 120 83 85 95 30 0 0 — — 240 93 93 63 13 0 0 — — Mud flat crab, 20 6/13 5 130 98 20-50 — 100 100 100 92 52 0 0 Hemigrapsus oregonensis 60 6/18 — 97 98 96 94 54 10 — 120 7/2 — 100 100 100 100 46 0 — 240 7/8 8 28 — 100 90 100 98 48 0 '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 Af (/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) C 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 af 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: ak = (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 = 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 ak (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 or 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 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 Rk A'k Mk = Bk a constant B-kTk - F'k (5.5) and or A'k2 = Bk2Tk2 - 2BkTkF'k + F^2 (5.6) and (£>A' of Equation (5.4) .becomes <7* = 4>A' + [Rk - Mk][Tk(2ai - 1) + TViU " «i» " ^Tk + l] - \oge(C/f)'k 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) Qk 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 = 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 + 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 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 Qk f + 0/ (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 Qk ^ log,(C//-U + Zp !<*>/■ (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 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 k N/co fk mortality a'h exp(^) a* Nk0Fkak Period 1 qk = 2 x 106 M'k = 0.001 0003 Rk = 0.450 1 1,000,000 1,000 0.447 1 5636 1 26085 2,522 2 1 ,563,600 3,000 0.007 0443 1.5575 1.25847 11,807 3 2,435,307 2,000 0005 0.445 1 5605 1 25955 12.269 4 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 1 5.894,992 40,000 0.100 -0.098 0.90666 0.95245 449,175 2 5,344,753 20,000 0.060 -0.058 0.94365 0.97155 207,708 3 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: K n 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'/\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 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 f = -500 qk = -0.0009/- 500 = 1.8 x 10"6. .'.A'/\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 Qk -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\ a; ak = 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 K -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'/\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 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" «s tu S>~ £~1 i t~X 2: s s 1— I ^3 *"* 2 OS J O M3 i— H O UJ o H X »*i t-< E3 ►J © cw M g S O r W J§ fa < 5* Q w O o 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 W W H Q 3 O fa Z W tW W < u 2 o CJ M OS 3 O w Cm 1 _! js a w o S M < o en z O < £x3 <*S » M ►J E-t 8S u >< § w »5 H JxJ W < X X 3 M Q O 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 8S 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- D u 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 i, "U 42 54 18 24 30 36 DISTANCE TO CATHODE (mm) 60 66 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 65 65 7 28 182 X G splendens 162 54 48 9 43 18.2 X G splendens 162 70 53 16 31 2 (8.0) 18.2 G. splendens 180 70 33 16 51 185 X D. brightwellii 164 59 0 0 100 19.6 X D brightwellii 164 46 0 0 100 3 (8.0) 17.0 G splendens 240 67 67 16 17 17.0 X C affinis 127 chains 59 0 0 100 17.0 X C affinis 127 chains 80 0 0 100 170 X T decipiens 154 73 0 0 100 17.0 X T decipiens 205 69 0 0 100 4 (8.0) 17.1 G splendens 195 60 55 7 38 16 9 X L. danicus 197 chains 75 0 0 100 16.9 X L. danicus 780 chains 57 2 0 98 5 (8.0) 174 G. splendens 208 62 34 10 56 17.7 P- trochoideum 56 65 67 22 11 17.7 P. trochoideum 97 54 65 7 28 177 P. trochoideum 210 46 50 26 24 177 Chlamydomonas sp. 211 46 0 0 100 17.7 P. micans 201 38 45 21 34 6 (8.0) 18.2 G splendens 193 26 58 23 19 18.2 G polyedra 102 58 78 7 15 18.2 G. polyedra 60 48 60 10 30 17.7 Dunaliella sp. 303 67 0 0 100 177 Dunaliella sp 242 31 0 0 100 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 sx Gymnodinium splendens 3.3 100 5.0 11 33.3 4.24 0359 0039 3.4 100 5.0 15 44.1 4.87 0.671 0.048 2.2 100 1.0 5 22.7 4.30 0.480 0.061 2.5 100 1.0 12 48.0 4.73 0.677 0.047 3.1 100 0.1 13 41 9 4.46 0.355 0.046 39 100 0.1 6 15.4 3.57 0314 0.046 28 100 0.0 9 32.1 4.23 0485 0.042 3.6 100 Gonyaulax polyedra 0.0 8 22.2 4.03 0.413 0.056 3.3 100 50 5 152 4.02 0 403 0.065 3.9 100 50 14 35.9 4.82 0.710 0.059 3.8 100 1.0 5 13.2 4.54 0.796 0.077 3.7 100 1.0 7 18.9 4.41 0.219 0057 2.8 100 0.1 1 3.6 3.7 — (') 29 100 0.1 1 3.5 4.0 — n 3.5 100 00 1 2.9 3.0 — o 3.9 100 0.0 0 0.0 — — — 42 0 5.0 8 19.1 4.51 0.669 0.050 2.3 0 5.0 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 50 - • _, 40 i 3 30 if) • > ^L1zo2j^J23 - A • • 5 u 20 cr UJ a. 1 • • 10 0 1 1 1 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— • «- • • • • 55 • A % • E • £ I ■ — 5.0 • X • • t- • • || • 3 4.5 • ♦ y = 0.08 X + 4-2j ■ • • » • • Q « cr • o 1 § 40M • t • < 9 • h- » • • , • ► 3,5 r-» m • 3.0 • 1 i 1 i i 2 3 MICROZOOPLANKTON / ml S.0 55 < a z , 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 - 3.5 - 1.8 - 2.9 - 3.3 - 2.4 - 3.9 3.3 - 3.9 38 - 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 P 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 1 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 98 78 - 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 + 6 11 No. of 5 0 Difference 1 11 P 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. LITERATURE CITED ATZ, J. W. 1964. Intersexuality in fishes. In C. N. Armstrong and A. J. Marshall (editors), Intersexuality in vertebrates in- cluding man, p. 145-232. Academic Press, Lond. BIGELOW, H. B., AND W. C. SCHROEDER. 1953. Fishes of the Gulf of Maine. U.S. Fish Wildl. Serv., Fish. Bull. 53, 577 p. Bridges, D. w., and M. p. Fahay. 1968. Sexual dichromatism in the tautog, Tautoga onitis (Linnaeus), with an observation of possible courtship be- havior. Trans. Am. Fish. Soc. 97:208-209. BRIGGS, P. T. In press. Tautog ( Tautoga onitis) at artificial reefs in New York waters. N.Y. Fish Game J. CHENOWETH, S. 1963. Spawning and fecundity of the tautog, Tautoga onitis. M.S. Thesis, Univ. Rhode Island, Kingston, 60 p. CHOAT, J. H. 1969. Studies on the biology of labroid fishes ( Labridae and Scaridae) at Heron Island, Great Barrier Reef. Ph.D. Thesis, Univ. Queensland, Queensland, 294 p. Cooper, R. A. 1965. Life history of the tautog, Tautoga onitis (Lin- naeus). Ph.D. Thesis, Univ. Rhode Island, Kingston, 153 p. 1966. Migration and population estimation of the tautog, Tautoga onitis (Linnaeus), from Rhode Island. Trans. Am. Fish. Soc. 95:239-247. 1967. Age and growth of the tautog, Tautoga onitis (Lin- naeus), from Rhode Island. Trans. Am. Fish. Soc. 96:134-142. CROKER, R. A. 1965. Planktonic fish eggs and larvae of Sandy Hook es- tuary. Chesapeake Sci. 6:92-95. DE VLAMING, V. L. 1974. Environmental and endocrine control of teleost re- 598 OLLA and SAMET: COURTSHIP AND SPAWNING BEHAVIOR OE TAUTOG production. In C. B. Schreck (editor), Control of sex in fishes, p. 13-83. Va. Polytech. Inst. State Univ., Blacksburg. Dixon, W. J., and A. M. Mood. 1946. The statistical sign test. J. Am. Stat. Assoc. 41:557-566. HOBSON, E. S. 1965. Diurnal-nocturnal activity of some inshore fishes in the Gulf of California. Copeia 1965:291-302. KUNTZ, A., AND L. RADCLIFFE. 1917. Notes on the embryology and larval development of twelve teleostean fishes. Bull. U.S. Bur. Fish. 35:87- 134. MOYER, J. T., AND J. W. SHEPARD. 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 Sound. In Oceanography of Long Island Sound, p. 95- 124. Bull. Bingham Oceanogr. Collect., Yale Univ. 17(1). ROBERTSON, D. R., AND J. H. CHOAT. 1974. Protogynous hermaphroditism and social systems in labrid fish. Proc. 2d Int. Symp. Coral Reefs 1:217-225. ROEDE, M. J. 1972. Color as related to size, sex, and behavior in seven Caribbean labrid fish species (genera Thalassoma, Halichoeres and Hemipteronotus). Stud. Fauna Curasao Other Caribb. Isl. 42(138), 264 p. TUKEV, J. W. 1959. A quick, compact, two-sample test to Duckworth's specifications. Technometrics 1:31-48. WHEATLAND, S. B. 1956. Pelagic eggs and larvae. In Oceanography of Long Island Sound, 1952-1954, p. 234-314. Bull. Bingham Oceanogr. Collect., Yale Univ. 15. WICKLUND, R. I. 1970. Observations on the spawning of the cunner in wa- ters of northern New Jersey. Chesapeake Sci. 11:137. WILLIAMS, G. C. 1967. Identification and seasonal size changes of eggs of the labrid fishes, Tautogolabrus adspersus and Tautoga onitis, of Long Island Sound. Copeia 1967:452-453. YOUNGBLUTH, M. J. 1968. Aspects of the ecology and ethology of the cleaning fish, Labroides phthirophagus Randall. Z. Tierpsychol. 25:915-932. 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 7.6 143 143 612 Truncated net 17.5 76 56 239 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°- 1 W 1 ' I - . • • . ( •■%•- Inner boundary of • • V Mecynocera \\ . ' '/r San Froncisco — — \ Ct>Njs\\\. • \Pt. Conception ^ \«: ' ' A.^an Diego _ i 1 1 1 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- co U- o UJ > I- < _l 3 Z> O 80 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) 56 120 143 Usual number retained/ liter 2.884 0.095 0.058 IUU A A CLARKE-BUMPUS -& ~~° ~~ " / O O MICROPLANKTON ~ ° / 60 h / / U_ / / o / / 55 / / / / UJ / / > 40 / J \- i r < i / _i 0/ ID // 2 / / J 3 20 / / / / A / o / / / / / / / / — i^r / 0 *--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 CO ■z. 80 o h- < r- co 60 Ll_ O III > 40 h- < _J Z> o 20 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. J .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 UJ z < H UJ cr Zj cr UJ cr UJ CD < to z> u. o X H cr < O -1.00 — -2.00 0 • THIS REPORT BEERS and STEWART - ^ •\ 1967 - \ o •\ 1 1 1 1 1 1 1 \o 1 1 1 1 J 1 1 0 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 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 if < Q z 5 9 2- J I l I i I i i_ 50 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 9 1.0056 0.3343 Nearshore 11 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 20 1 0 064 23.05 0.00 0.00 8C7113 TI7114 7-18 May 1971 123 2 12 0.78 64.66 6.73 51.52 GE7117 26 Juried July 1971 27 2 0 1.67 19.95 0.00 0.00 8C7120 TI7121 7-25 Aug. 1971 146 8 8 0.83 28 09 0.21 4.37 TI7131 8B7132 GE7127 7-16 Nov. 1971 66 0 0 0.00 0.00 — 8B7201 GE7202 1-11 Feb. 1972 30 0 0 0.00 — 0.00 — GE7208 1-10 May 1972 30 1 4 1.68 76.21 1.24 11.57 GE7210 12-18 June 1972 13 3 3 35.31 146.94 5.97 2278 IS7205 9-17 Sept. 1972 34 0 2 000 — 0.16 4.70 IS7209 8-16 Nov. 1972 50 0 0 0.00 — 0.00 — IS7303 19-27 Jan. 1973 51 0 1 000 — 0.01 0.26 IS7308 9-17 May 1973 49 8 14 14.38 154.16 9.26 38 34 IS7311 27 June-6 July 1973 51 8 6 31.59 174.14 0.59 5.51 IS7313 3-13 Aug. 1973 50 9 11 67.49 747.09 10 86 50 26 IS7320 6-14 Nov. 1973 51 0 0 0.00 — 0.00 — CL7405 28 Feb.-9 Mar. 1974 36 0 4 0.00 — 0.39 4.06 CL7412 1 -9 May 1 974 44 20 23 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 /f Number under 10m2 + 0 • I000 + +■+; + *++* •? /j + + !+ + + + - 9 C&^-rfr * *■; * + + + >^ 8C 7120 8 TI 7121 Harengula jaguana eggs August 1971 - + + +■ T 1 J + 4 4 4- ■t- ^-s^*^^ \ \ + 4 4 4- + 4 + 450 n-t 4 4 4 + 4 +\ + \ fc^ 4 + 4 4 4. 4A+4 + 4-+/ Y - 4 4 + 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 2 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 • • ^-^ © >IOOO i 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 + \ /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 • 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 D August 1971 30' - * *■ • • ^ 4 4 + + *\ X^^ \ \ 4 4 + 4 *■ 4 + 450m-t \^f \ 4 + + 4 t +\ * \ Vy 4 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+ + + *IOOO 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 A Iay 1972 30» 50m-. % \ 28° * '", ♦ + • / ♦ * * * \ * ' "C + + + + 1 ♦ t ^ , <}"] 2b° Number under 10m2 t 0 • IO0O *'. * * Jkfr*** GE 7208 Harengula jaguana LARVAE Nay 1972 1 30m-. t + ■•.+ +•/ y i- + * '-. *■ * °o \ /y.V 0) Number under 10m2 • 0 • 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 • I000 : + • \ A D June 1972 30° 50m- 28° \ + + \r \ \ + • V J. iib* Number under 10m2 t 0 • I000 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 l* • * »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-'^ © >I000 ' ' IS 7308 Harengula jaguana larvae Ray 1973 \ * • • #v \ 50m-. - + * ♦ '\ ♦ ♦ • \r V - + 4 \ t + • \ 0*\ • '. 4 ( a * 4 -*■',* + Number under 10m2 ♦ 0 • I000 1 ' 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 • I000 ' 30" * * * • x \ 50m-. ^ V- \ - 28° * + 4 V, + * ♦ \i~ * - \ * • • w i»b° Number under 10m2 * * *- 4* * • * 'L t 0 - '; * +■ «■ • \ I' • 1 - 10 • 11-100 • 101-1000 fl . • \yl ® >I000 IS 7315 Harengula jaguana eggs IS 7313 Harengula jaguana larvae E August 1973 30° • * + * x \ 50m-., V^ \ + * * - > 4 + \ 4 4 4 • / - 28° » \ + * *GKva + * ♦ \ 4 • + \f + 4 \ 4 4 • \ ^ o\ 4 + \ + + 4 TC Number under 10m2 4 4 t\ 4 4 + V t 0 fl • I000 1 — 1 1 F August 1973 30° • ■ •V 50m-., \^- "\ + * * 9 \ 4 + \ 4 4 * • / - 28° 4 \ 4 -»■ • •/rK. 4 4 4*\ 4 4 4 \J + + \ + + • \ o\ » 4 \ * . 4 • Lb° Number under 10m2 4 4 4'., 4 4 4 0 4 4 I 4 4 4 f> • 1 - 10 • 11-100 • 101 - 1000 4! 4 • „*H"> *>r © >I000 ' 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 • IO0O 30° — 1 — j «^ • • •V Mm.., • • • • • \ 28" & ^ i \:: •\^ } 2b" Number under 10m2 t 0 • 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 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 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 0.00 8B7201 and GE7202 148.85 0.00 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 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 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 20 15 0 ^ a. U UJ I >■ CD 5 - uj 5 30 20 10 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 K < 4.0 h- I O D < U >-30 < Q o 1- R . 0.7999e° °"°* j20 - ^\ -""' IS • \ -- 3 < _, _ — "* (J £i.o (3 - - - ' ' • • Z o o 1 1 ■ 1 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) (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, 9 Nonfully vulnerable larvae duration (days) Instantaneous mortality coefficient, Z 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 b X ® \ UJ o z < D Z CD < Nt = (l57 36xlO")e"028i5t • • > Q 10 UJ 1- O UJ K cc o • ^v z o 1- < cc Q 1 \ • \ • \ • O 1 ' ' 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. g Number of spawned eggs (■10") Instantaneous mortality coefficient, Z 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. LITERATURE CITED AHLSTROM, E. h. 1968. An evaluation of the fishery resources available to California fishermen. In The future of the fishing indus- try of the United States, p. 65-80. Univ. Wash. Publ. Fish., New Ser. 4. ALVERSON, D. L., AND W. T. PEREYRA. 1969. Demersal fish explorations in the northeastern Pacific Ocean — an evaluation of exploratory fishing methods and analytical approaches to stock size and yield forecasts. J. Fish. Res. Board Can. 26:1985-2001. 627 FISHERY BULLETIN: VOL. 75, NO. 3 BERRY, F. H. 1964. Review and emendation of: Family Clupeidae by Samuel F. Hildebrand. Copeia 1964:720-730. BULLIS, H. R., JR., AND J. R. THOMPSON. 1970. Bureau of Commercial Fisheries exploratory fishing and gear research base, Pascagoula, Mississippi July 1, 1967 to June 30, 1969. U.S. Fish Wildl. Serv., Circ. 351, 29 p. Food and Agriculture Organization. 1975. Catches and landings, 1974. FAO Yearb. Fish. Stat. 38, 378 p. GORBUNOVA, N. N., AND O. A. ZVYAGINA. 1975. Eggs and larvae of the sardine Harengula pensa- colae Goode et Bean (Pisces, Clupeidae). [In Russ.]. Vopr. Ikhtiol. 15:922-926. GULLAND, J. A. (editor). 1971. The fish resources of the ocean. Fishing News (Books) Ltd., Surrey, 255 p. 1972. The scientific input to fishery management deci- sions. In Progress in fishing and food science, p. 23-28. Univ. Wash. Publ. Fish., New Ser. 5. GUNTER, G. 1945. Studies on marine fishes of Texas. Univ. Tex. Publ. Inst. Mar. Sci. 1:1-190. HOUDE, E. D. 1976. Abundance and potential for fisheries development of some sardine-like fishes in the eastern Gulf of Mexico. Proc. Gulf Caribb. Fish. Inst. 28:73-82. 1977a. Abundance and potential yield of the round her- ring, Etrumeus teres, and aspects of its early life history in the eastern Gulf of Mexico. Fish. Bull., U.S. 75:61-89. 1977b. Abundance and potential yield of the thread her- ring, Opisthonema oglinum, and aspects of its early life history in the eastern Gulf of Mexico. Fish. Bull., U.S. 75:493-512. HOUDE, E. D., S. A. BERKELEY, J. J. KLINOVSKY, AND C. E. DOWD. 1976. Ichthyoplankton survey data report. Summary of egg and larvae data used to determine abundance of clupeid fishes in the eastern Gulf of Mexico. Univ. Miami Sea Grant Tech. Bull. 32, 193 p. HOUDE, E. D., AND N. CHITTY. 1976. Seasonal abundance and distribution of zooplank- ton, fish eggs, and fish larvae in the eastern Gulf of Mex- ico, 1972-74. U.S. Dep. Commer., NOAA Tech. Rep. NMFS SSRF-701, 18 p. HOUDE, E. D., AND P. L. FORE. 1973. Guide to identity of eggs and larvae of some Gulf of Mexico clupeid fishes. Fla. Dep. Nat. Resour., Mar. Res. Lab., Leafl. Ser. 4(23), 14 p. HOUDE, E. D., AND B. J. PALKO. 1970. Laboratory rearing of the clupeid fish Harengula pensacolae from fertilized eggs. Mar. Biol. (Berl.) 5: 354-358. HOUDE, E. D., W. J. RICHARDS, AND V. P. SAKSENA. 1974. Description of eggs and larvae of scaled sardine, Harengula jaguana. Fish. Bull., U.S. 72:1106-1122. KLIMA, E. F. 1971. Distribution of some coastal pelagic fishes in the western Atlantic. Commer. Fish. Rev. 33(6):21-34. LOW, R. A., JR. 1973. Shoreline grassbed fishes in Biscayne Bay, Florida, with notes on the availability of clupeid fishes. M.S. Thesis, Univ. Miami, Coral Gables, 145 p. MARTINEZ, S., AND E. D. HOUDE. 1975. Fecundity, sexual maturation, and spawning of scaled sardine (Harengula jaguana Poey). Bull. Mar. Sci. 25:35-45. MATSUURA, Y. 1972. Egg development of scaled sardine Harengula pen- sacolae Goode & Bean (Pisces, Clupidae). Bol. Inst. Oceanogr. (Sao Paulo) 21:129-135. REINTJES, J. W., AND F. C. JUNE. 1961. A challenge to the fish meal and oil industry in the Gulf of Mexico. Proc. Gulf Caribb. Fish. Inst. 13:62-66. RIVAS, L. R. 1963. Genus Harengula Cuvier and Valenciennes 1847. Sardines. In Fishes of the western North Atlantic. Part Three, p. 386-396. Mem. Sears Found. Mar. Res. Yale Univ. 1. ROESSLER, M. A. 1970. Checklist of fishes in Buttonwood Canal, Everglades National Park, Florida, and observations on the seasonal occurrence and life histories of selected species. Bull. Mar. Sci. 20:860-893. SAKSENA, V. P., AND E. D. HOUDE. 1972. Effect of food level on the growth and survival of laboratory-reared larvae of bay anchovy (Anchoa mitchilli Valenciennes) and scaled sardine (Harengula pensacolae Goode and Bean). J. Exp. Mar. Biol. Ecol. 8:249-258. SAKSENA, V. P., C. STEINMETZ, JR., AND E. D. HOUDE. 1972. Effects of temperature on growth and survival of laboratory-reared larvae of the scaled sardine, Harengula pensacolae Goode and Bean. Trans. Am. Fish. Soc. 101:691-695. SAVILLE, A. 1964. Estimation of the abundance of a fish stock from egg and larval surveys. Rapp. P.-V. Reun. Cons. Perm. Int. Explor. Mer 155:164-170. SETTE, O. E., AND E. H. AHLSTROM. 1948. Estimations of abundance of the eggs of the Pacific pilchard (Sardinops caerulea) off southern California during 1940 and 1941. J. Mar. Res. 7:511-542. SIMPSON, A. C. 1959. The spawning of the plaice (Pleuronectes platessa) in the North Sea. Fish. Invest. Minist. Agric. Fish. Food (G.B.), Ser. II, 22(7), 111 p. Smith, P. E., and S. L. Richardson (editors). In press. Manual of methods for fisheries resource survey and appraisal. Part 4. Standard techniques for pelagic fish egg and larvae survey. FAO, Rome. SPRINGER, V. G., AND K. D. WOODBURN. 1960. An ecological study of the fishes of the Tampa Bay area. Fla. State Board Conserv. Mar. Lab., Prof. Pap. Ser. 1, 104 p. 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. 1967. Algunos aspectos sobre la distribucion y biologia de la sardina, Sardinella anchovia Val. (1847) del Golfo de Mexico. Cent. Invest. Pesq. Cuba, Trab. Ill Congr. Nac. Oceanogr., p. 36-59. 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 I jj ; Jan. 267 326 239 300 395 442 901 1,068 Feb. 200 231 428 532 249 312 877 1.075 Mar. 137 210 66 72 133 153 336 435 Apr. 41 46 35 42 135 183 211 271 May 85 156 5 2 34 35 124 193 June 56 69 36 9 30 47 122 125 July 0 0 0 0 6 12 6 12 Aug. 0 0 11 13 2 4 13 17 Sept 0 0 1 4 0 0 1 4 Oct. 5 16 0 0 31 51 36 67 Nov 72 103 20 48 32 39 124 190 Dec. 8 9 0 0 0 0 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. % No. % No. % % Sexually immature 522 45.0 465 45 9 580 45.7 1,567 45.5 Sexually mature: Condition undetermined 58 5.0 60 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 16 1.4 23 2.3 22 1.7 61 1.8 Lactating only 226 19.5 256 25.3 264 208 746 21.7 "Resting" With corpus luteum 34 2.9 32 3.2 28 2.2 94 2.7 Without corpus luteum 66 5.7 48 4.7 64 5.0 178 5.2 Postreproductive 7 0.6 6 0.6 2 0.2 15 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 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: SE V. 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 B C A x B x C Proportion female Proportion of females reproductive Annual pregnancy rate Gross annual rep Method 1 iroductive rate Year Method 1 Method 2 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) (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) 1 2 3 4 5 6 7 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) (5) (5) (5) (5) (5) (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) (5) (5) (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 85 Gill net 23 Mar. 1973 Two Rivers, Wis 74 Bottom trawl2 21 May 1974 Milwaukee, Wis 18 Gill net 18 June 1974 Milwaukee, Wis 18 Gill net 15 Aug 1974 Milwaukee, Wis 27 Gill net 13 Oct 1973 Port Washington, Wis. 37 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 stomachs Ponto- Fingernail Tendi- and date (mm) examined empty Mysis poreia Alewife clam pedidae Cladocera 20 Feb. 1974 147 90-1 79 79 42 98 (95) 1 (3) — 1 (2) — — 23 Mar. 1973 138 94-179 80 36 100 (100) — — — 21 May 1974 162 68 60 62 1 37 <1 1 — 109-179 (73) (1) (1) (1) (25) 18 June 1974 160 62 61 42 — 58 — <1 <1 140-179 (12) (1) (6) (82) 15 Aug 1973 157 40 1 30 35 30 5 <1 1 120-175 (26) (61) (1) (9) (2) (2) 13 Oct 1973 158 115-179 88 34 87 (88) 3 (9) 10 (1) <1 (2) — — Total 154 417 41 70 7 23 1 <1 <1 (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 21 43 39 1 60 — 1 ■? o £ 180-251 23 Mar, 1973 206 20 25 (93) 95 (5) 5 (2) 180-246 (86) (14) 21 May 1974 199 27 37 6 — 94 — 181-238 18 June 1974 206 10 60 (78) 1 (22) 99 196-232 15 Aug. 1973 201 8 12 (33) 93 6 (66) 1 1 82-225 13 Oct. 1973 201 12 42 (82) 12 (16) 1 87 1 181-248 Total 204 98 37 (75) 41 (14) 2 (9) 57 (2) 1 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- M5 \^5 - 1.0- - \ 0.5- ' \ i 1 1 3^ -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 56 84 12.2 176 21.7 248 250 229 16.2 122 68 5.9 5.7 6.7 98 17.1 22.5 24.6 266 232 19.5 14.0 76 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 11 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 11 4 44 59 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 f Range Mean >0.5 No ppm Location Range Mean % Females Port Townsend 22 2,190-4,160 3,194 85-102 939 22 0.16-1.28 0.50 9 40.9 20 0.14-1.18 0.41 5 25.0 Seabeck 12 2,465^.915 3,372 86-106 935 12 0 34-1.43 0.63 7 58.3 12 0 29-1.30 0.57 7 583 Blame 20 2.360-5,065 3,469 86-106 946 20 0 20-1.38 0.71 15 75.0 20 0 17-1.27 062 15 75.0 Port Susan 32 1,340-4,560 3,033 70-106 896 32 0.09-2.28 0.89 20 625 22 0 17-1.95 1.02 19 86.3 Seattle 8 5,230-7,930 6,706 105-117 1099 8 0.82-1.94 1.16 8 100 0 — — — — — Tacoma 33 700-6,630 3.862 60-113 952 33 0.43-2.58 1.41 32 969 33 038-2.24 1.25 32 969 1 127 700-7,930 3,608 60-117 942 127 0.09-2.58 Males 0.92 91 71.6 107 0 14-2.24 0.85 78 72.9 Port Susan 7 1,445-2,645 1,864 75-87 79.4 7 0.21-0 98 0.64 6 85.7 2 0.49-0.95 072 1 50.0 Seattle 4 2.025-3,400 2,626 85-93 890 4 1 16-1.61 1.38 4 100 0 — — — — — Tacoma 3 1,240-2.180 1,728 68-84 77.3 3 0.94-1 27 1.15 3 100 0 3 0.92-1.24 1.08 3 100 0 j 14 1.240-3,400 2,052 68-93 81.7 14 0.21-1.61 096 13 92.8 5 0.49-1 24 093 4 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 Q. >- 1.5 rr O 0.5 + ++ + + - + ^^4- ++ ++ + + + 0 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 r at r a Port Townsend 22 0.645 0.01 0.507 0.05 Seabeck 12 0 648 0.05 0616 0.05 Blame 20 0 768 0.001 0.756 0.001 Port Susan 32 0 699 0.001 0643 0001 Seattle 8 0 501 NS1 -0.414 NS Tacoma 33 0.601 0.001 0.648 0.001 j 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- ra 60 50- 40- 30- 20- 10 I' H Station 2 Seaward edge of kelp J S J S 1974 1975 J S 1976 Strongylocentrotus froncisconus I Station 3 50 m seaward of kelp J S 1974 J S 1975 J s 1976 I' 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 n X (length/s) SD Skipiack tuna 1 (38.3 cm, 925 g) Before salinity change 28 2.10 0.40 During salinity change 22 1.82 0.40 Skipjack tuna 2 (37.7 cm, 882 g) Before salinity change 44 2.03 026 During salinity change 12 2.37 0.19 Skipjack tuna 3 (42.0 cm, 1.352 g) Before salinity change 30 1.21 007 During salinity change 15 1 16 0.06 Yellowfin tuna 1 (45.3 cm 1.491 g) Before salinity change 39 1 54 030 During salinity change 31 1.81 026 C5 Z UJ SKIPJACK TUNA Id a. in 1.0 0L YELLOWFIN TUNA UJ o en (/> o 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 UJ m tn i Q. 34 3 2 3.0 2.8 2.6 24 2 2 2.0 1.8 S 1.6 4 1.2- 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 652 200 T 1.00 o uj 80 60 .40 IE £ 20 > UJ Q tr O D z < 5 UJ Q UJ O V X o 10 08 06 04 02 1 I ! 02 DELIVERY 4.0 ppm 2cm2 GAP Js 02 DELIVERY, 7.2 ppm >-^ Icm2 GAPE\^, ^- '^S^~~0i DEMAND s^ ^ S* 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 Ch 30 20 10 o 20 10- 0 30-| 20 10- ABCDEFGP MAY 1972 JO- 30- -i — i — i — i — l — i — r— i ' ABCDEFGP JUNE 1972 V„ :* - 1 1 1 1 1 1 1 1 0 ABCDEFGP JULY 1972 - 1 — i — I 1 1 1 1 — I ABCDEFGP AUGUST 1972 30 20 N,0] 0 Ch s10: iO-\ 20 10 - 0 20- 10- - 0 —f — I — I — I — I — I — I — I o ABCDEFGP SEPTEMBER 1972 "" i — i — i — i — i — i — i — i ° ABCDEFGP OCTOBER 1972 20 : -. I0" 0 20 10- — I — I — I — I — I — I — I — I o- ABC DE FGP NOVEMBER 1972 ~1 1 1 1 1 1 1 — i ABCDEFGP DECEMBER 1972 FIGURE 2.— Monthly means of 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: N = north shoal, Ch = chan- nel and S = south shoal. Ch - S - Ch x . 30 20 10- ~ I 1 1 I 1 ' 1 1 ABCDEFGP JANUARY 1973 30 20 10 V 10- " o 20 10- - 0 20- -1 1 — I 1 1 1 1 1 0 ABCDEFGP MAY 1973 ~1 — I — I 1 1 1 1 — I °' ABCDEFGP FEBUARY 1973 30"! 20 N— - 10- — i 1 1 1 1 1 1 1 0' ABCDEFGP JUNE 1973 30-i 20 10 10- - 0 ~i — i — i — i — i — i — i — I o- ABCDEFGP MARCH 1973 — I 1 1 — I — I 1 — ^ — I ABCDEFGP APRIL 1973 - 1 1 — I 1 — i 1 1 — i ABCDEFGP JULY 1973 30- .. " ■ 20 T^Z \ 10- \m ^ 80- 0- - 20- 10- "*•■* - I I I I I I I t ABC DEFGP AUGUST 1973 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 = 2.0- ♦ N S ' ° o -1 0.0 _ >:j p 1 j fl GRAND MEAN h L5" Ch § 0.5- a a r i BJb sJIb GRAND MEAN -2.0- S - io- o -" 0.0 — fi£JLpiJ_pj D ' E JULY 1972 ~^~~ r GRAND MEAN = 20- 1.0- N o o -1 0.0 ^ GRAND MEAN Chio C 1-5 3 0.5 4* lipJl.JL E ' F ' G GRAND MEAN - 2.0- s 2 i-o- o -J 0.0 — D ' E OCT. 1972 fp ■f GRAND MEAN n s 05: O 0.5 a n r ' i n GRAND MEAN Ch * 1.5- I 0.5- B ■n Q, ^ D _r JZL i — ?. — r GRAND MEAN x 1.0- S I " °, 0.0- n_ . ^ n l — c r D ' E JAN. 1973 □ — GRAND MEAN ^y- Cynoscion regalis J Micropogon undulatus Bairdiella chysoura rag] Leiostomus xanthurus 662 CHAO and MUSICK: LIFE HISTORY OF JUVENILE SCIAENID FISHES 2 0- N 2 ' °' o 0.0- JHL C "r D~ F ' G ' GRAND MEAN 1.5- Wll o 0.5- _Q NO SAMPLE i — I r F G GRAND MEAN ♦ 1.5 s - § 0.5- T n n _d D E APRIL 1973 GRAND MEAN - 20~ N 2 i.o- 3 0.0 — oJ] GRAND MEAN 2.0- Ch^ i.o- o.o- -P- rm _ _ ftDAMh f "^T-1" GRAND MEAN - 2.0- S 2 ,.o- IS o _ O 0.0- fcj i ra r J rn I £ D E JULY 1973 ill , rM . EJJ 1 ~ G GRAND MEAN N 2.5- x 1.5- o o 0.5- II B M ^ GRAND MEAN - 2.0- Chs I -o- o - -1 0.0— ^ 1 1 B0 ,-.i ^ p-i^rf GRAND MEAN --. 2.0- S 2 ,.o- 3 o.o- _E3_ P- ri Lp_ F*?^ C D E OCT. 1973 GRAND MEAN 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 ~ 20- x a 1-0- o _i 00— 3.0- x 2 0- 3 i.o- oo JULY 1973 _E3_ M-2 M-3 I -r-^. O P-2 P-3 ,^m OCT 1973 I I I M-2 M-3 mJ p-i P-2 P-3 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. cj - z: 0- o < -1 0.0-™- CJ ■= 2 0- >'£ i.o- _l CD Z> O -3 -1 0.0 to - 2 0- >-•£ i.o- -I o Z) o -i 0.0-"=- N '* , «' (-S io" O O O -1 0 0 ro -2 0- S- * - £»5 i.o- O jo.O- LiL _rD sH B at! JZL a n J ad n ,- i-i £L mm ai Jl n: □£] I Cynoscion regalis Bairdiella chysoura J Micropogon undulatus ■:'y.i Leiostomus xanthurus M M 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 NO SAMPLE 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 id 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 Total length Total length Total length Total length Age-group2 0 I 0 0 1 0 I 0 I 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 i 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 Total length Total length Total length Standard length Age-group2 0 1 0 1 0 1 0 1 0 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 Total length Total length Total length Total length Age-group2 0 I 0 I 0 I 0 1 0 I January 75-160 60-170 15-25 90-165 100-170 February 90-125 30 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- r1 N^5239 r- ~^~1 n r- n 10 30 50 70 90 110 130 150 170 190 210 230 250 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 NO SAMPLE Xn ki _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 x — 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 = 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 ] O 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 = 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 N 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 NO SAMPLE N=I8 n i N=4 N = 0 N = 0 N = 0 -i — i — 20 40 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 Total length Total length Age group2 0 0 I 0 I 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 Total length Total length Age group2 0 I 0 I 0 I 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 72 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 16 ft T PI and T Source Table 28 Fig. 13 (present study) Tables 5 and 6 Length (mm) Total length Total length Total length Age-group2 0 0 I 0 I 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 I 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 i 15 ft T, S, and Pu Source Table 42 Fig. 12 Fig. 10 Length (mm) Total length Standard length Standard length Age-group2 0 I 0 I 0 I January 18-(72) 93-182 67 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 n n i~i ~\ i 70 N = 273 N--370 N = 368 ^bL. N=304 N=5 l~l N = 28 m r-\ n N=0 "i 1 1 r — i r 190 ~i 1 r- 10 30 50 90 110 130 150 170 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 ni EL 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 n ,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 ZL 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 NO SAMPLE 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 Total length Total length Total length Total length Age-group2 0 I 0 I 0 I 0 I 0 I 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. N.S. 10-(100) (70)-195 2-9 80-279 78-182 October 20 135-140 10-(40) (40)-85 10-(1 10) (100)-250 2-50 98-294 68-182 November 25 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 T 5-mT T and S 4.9-m T Source Fig. 12 Fig. 2 Table 1 Fig. 21 Length (mm) Total length Total length Total length Total length Age-group2 0 I 0 I 0 I 0 I 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. 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 B B' 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 B mn 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. SL (mm) Head length (mm) Index of mouth size' Eye diameter in % of SL Species Range X SD N Range X SD N Larimus fasciatus 55.3-107 18.7-36.3 3.17-5.90 4.634 0 957 20 7.38- 9.84 8602 0.672 21 Cynoscion regalis Bairdiella chrysoura 35.2- 75.3 12.7-29.6 1 .93-3.54 2.827 0.518 22 8.20-11.45 9.55 0 782 2b 38.4- 77.5 14.3-27.4 1.76-3.08 2.494 0.431 17 827-10.82 9407 0.677 20 Micropogonias undulatus 35.5-116 12.1-39.3 1.20-2.41 1.686 0.325 30 6.45- 9.46 7850 0.837 JU Menticirrhus saxatilis 29.2- 99.6 9.3-29.0 0.50-1.37 0.957 0.264 30 6.03- 8.56 7.043 0644 30 Leiostomus xanthurus 47.4-146 18.0-41.3 0.77-2.64 1.472 0.477 30 7.05-11.11 9 139 0.889 4b 1 1ndex of mouth size = (upper jaw length x lower jaw length)/head length. 681 FISHERY BULLETIN: VOL. 75, NO. 4 PREMAXILLARY TEETH B D .0 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 B LOWER PHARYNGEAL TEETH vM h% 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) 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 A/ X Menticirrhus saxatilis 6 11 9 3 1 30 12.04 (29.2-99.6) [5 20 4 — ir [30] [6.73] Cynoscion regalis 1 8 13 13 2 37 17.19 (35.2-75.3) f — 4 10 8 2 21 [27] [11.40] Micropogonias undulatus 1 — 3 16 15 7 42 22 55 (35.5-116) [2 8 16 4] 1 [30] [15.73] Bairdiella chrysoura 2 3 13 14 33 24.27 (38.4-75.3) [1 2 5 6 6] [20] [15.70] 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 N X Leiostomus xanthurus 4 7 6 12 9 13 3 1 55 3229 (47.4-148) [1 1 4 9 7 14 6 2] [44] [27.18] Larimus fasciatus 5 9 5 2 1 22 38.00 (55.3-107) [1 1 5 7 4 2 1] [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 B f f 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 SD N 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 20 14 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 1 37 28 8.27 8.14 (47.4-148) Larimus fasciatus 9 6 15 10.4 (55.3-107) 685 FISHERY BULLETIN: VOL. 75, NO. 4 B *••'• •• 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 B 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 B 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 B 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 36 28 45 34 105 2,159 Empty stomachs 2 5 0 5 74 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 volume % of volume % 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 9 18 15.7 74.0 Macrozooplankton : Mysidace 2.8 Neomysis americana 639 31.0 0.9 Isopoda 05 6 Decapoda (shrimps) 47.0 0.5 46 0.1 Others and remains 91.0 83 18 1.5 1.2 Microzooplankton: Copepoda 3.5 2 Epibenthos: Polychaeta 0.5 05 Amphipoda 3.0 0.1 Others and remains 1.5 Unidentified remains 56 4.0 18 968 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 20 Table 20 Table 20 Table 20 Table 1 Number of specimens 71 94 94 120 66 120 Empty stomachs 10 11 10 18 12 35 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 % of occurrence % of occurrence % 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. 99 58.5 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 68 10 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 a 3J c— O S3 3 o -a c cS c JS c/j D M C o OJ c 'C M 3 C cu - 3 13 C 3 o CD cs o .2 c c o cj CO E O 7 w j CQ < E- m CO u => Hi C CO CO CO co > CO co co coO o a> a CO CD O) id *~ J? b>.o 3 CO »- CO CD O d CD— COI- C •9- CDuS P tfl— CO CM O 5 CD *- E O CO m o 6 co m m o CD oS co en Oinui ^t cb co cb o o o o o oS cb in CO CM i- CM CO SO 2^r co •t c o o "" CO co O o in o> co c o CO ,_ CO O C ~ CD CD S S ro "5 cr z o en tr *" £ CJ CD 9 l-~ CD 03 _: > 2 CD CD O m DDZh Tf CD eg _i CO E o CM cb CO Tt O) c^- . in o r- CO co CO i*- > a> CO lT t-~ CD O) > *• be re -6 -c o O > □> D_ < CO , c 8-5) mcoco CN OJ E E en mio co in CO C CO CD C E » (3 CO. I i! < _l cr d CD O Q-CO — fc rt f-.' in Cli o CM O 1-^ O CO in c\i o o o O CM oS CM CM r- in 00 in CO CD — CD o o co CO t- O) co -^t co *- cb co in •- cj> W co CO CD CNc0^1-CDC0l>-0>O)'-CO COCOCD [icboS'-cb •<»■'- r~-co cb in — ^ 10 — cm — E co CD q. o ■o o C N CO o a. E CD ^ O co co CO is-o P E Q ifl O a > qj O 52" CO ■g o CO c ra E a; TD C 10 CO CO £ - CO CO cog c o D CD TO Q. 'c •Q CO CO — "D T3 CO C !L' E S £ E 9-m cd e £ ?; E <0 -CD CD .§ O < O 0- Z g -D 3 CO CO "O 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 p. 194 Number of specimens 20 21 17 Empty stomachs 0 0 4 Length of specimens 37-118 1.9-7.2 2.4-7.4 cm SL cm SL Quantitative methods %of occurrence % of vol. % of vol. Macrozooplankton: Neomysis americana 35.0 Isopoda 5.0 Decapoda (shrimp) 9.0 42.0 Crangon septemspinosa 1 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 D cm c o C u 3 ■e c B H to 3 E p eg £ q DO < Si s 38co .O) ■- C*" © co :>-.o r="5.co CD jo to [X. 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CO •c E co E co 2 l66^<2O21l«0O E £ 3 CD E CO 0 CD ~ co a < o q. z o c 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 50 14.1 10.0 75.0 70.0 61.0 41.7 o 0 8.6 ■ SSm HI ^P" » ^ ^ .. ■ ■"■ K\\\\\\\N 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 UJ o O o o z UJ 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. LITERATURE CITED ALEXANDER, R. McN. 1967. The functions and mechanisms of the protrusible upper jaws of some acanthopterygian fish. J. Zool. (Lond.) 151:43-64. ANDERSON, M., W. J. DAVIS, M. P. LYNCH, AND J. R. SCHUBEL (compilers). 1973. Effect of hurricane Agnes on the environment and organisms of Chesapeake Bay. Va. Inst. Mar. Sci., Spec. Rep. Mar. Sci. Ocean Eng. 29, 172 p. ARNOLDI, D. C, W. H. HERKE, AND E. J. CLAIRAIN, JR. 1973. Estimate of growth rate and length of stay in a marsh nursery of juvenile Atlantic croaker, Micropogon undulatus (Linnaeus), "sandblasted" with fluorescent pigments. Gulf Caribb. Fish. Inst., Proc. 26th Annu. Sess., p. 158-172. Barnes, R. D. 1968. Invertebrate zoology. 2d ed. W. B. Saunders Co., Phila., 743 p. Boesch, d. F. 1 97 1 . Distribuion and structure of benthic communities in a gradient estuary. Ph.D. Thesis, College of William and Mary, Williamsburg, Va., 120 p. BOIE, B. F. 1826. Oder encyclopaedische Zeitung. Isis (Jena) 19:970-982. Carr, w. e. S., and C. a. Adams. 1973. Food habits of juvenile marine fishes occupying seagrass beds in the estuarine zone near Crystal River. Florida. Trans. Am. Fish. Soc. 102:511-540. CHAO, L. N. 1976. Aspects of systematics, morphology, life history and feeding of western Atlantic Sciaenidae (Pisces: Per- ciformes). Ph.D. Thesis, Coll. William and Mary, Wil- liamsburg, Va., 342 p. In press. A basis for classifying western Atlantic Sci- aenidae (Teleostei: Perciformes). U.S. Dep. Commer., NOAA Tech. Rep. NMFS Circ. COLVOCORESSES, J. 1975. Fish and major decapods: trawl analysis. Part II. In R. A. Jordan, R. W. Virnstein, J. E. Illowsky, and J. Colvocoresses. Yorktown power station ecological study. Phase II. Final technical report, p. 415-462. Va. Inst. Mar. Sci.. Spec. Sci. Rep. 76, 462 p. 699 FISHERY BULLETIN: VOL. 75, NO. 4 DARNELL, R. M. 1961. Trophic spectrum of an estuarine community, based on studies of Lake Pontchartrain, Louisiana. Ecology 42:533-568. DAVIS, W. P. 1967. Ecological interactions, comparative biology and evolutionary trends of thirteen pomadasyid fishes at Al- ligator Reef, Florida Keys. Ph.D. Thesis, Univ. Miami, Coral Gables, 127 p. DAVIS, W. P., AND R. S. BIRDSONG. 1973. Coral reef fishes which forage in the water column. A review of their morphology, behavior, ecology and evolutionary implications. Helgol. wiss. Meeresunters. 24:292-306. DAWSON, C. E. 1958. A study of the biology and life history of the spot, Leiostomus xanthurus Lacepede, with special reference to South Carolina. Contrib. Bears Bluff Lab. 28, 48 p. DUNHAM, F. 1972. A study of commercially important estuarine- dependent industrial fishes. La. Wildl. Fish. Comm., Tech. Bull. 4, 63 p. EMERY, A. R. 1973. Comparative ecology and functional osteology of fourteen species of damselfish (Pisces: Pomacentridae) at Alligator Reef, Florida Keys. Bull. Mar. Sci. 23:649- 770. GERO, D. R. 1952. The hydrodynamic aspects of fish propulsion. Am. Mus. Novit. 1601, 32 p. GUNTHER, K. 1962. Uber Kieferfunktionen bei Knochenfischen, mit Hinweisen auf die Sardelle iEngraulis encrasicholus) und ihre Regulation-seinrichtung fur die Stromung arteriel- len Blutes. Sitzungb. Ges. Naturforsch. Freunde Berl. (N.F.) 2:135-149. GUTHERZ, E. J., G. M. RUSSELL, A. R. SERRA, AND B. A. ROHR. 1975. Synopsis of the northern Gulf of Mexico industrial and food fish industries. Mar. Fish. Rev. 37(7):1-11. HANSEN, D. J. 1969. Food, growth, migration, reproduction, and abun- dance of pinfish, Lagodon rhomboides, and Atlantic croaker, Micropogon undulatus , near Pensacola, Florida, 1963-65. U.S. Fish Wildl. Serv., Fish. Bull. 68:135-146. HARMIC, J. L. 1958. Some aspects of the development and the ecology of the pelagic phase of the gray squeteague, Cynoscion re- galis (Bloch and Schneider) in the Delaware es- tuary. Ph.D. Thesis, Univ. Delaware, Newark, 84 p. + 80 p. append. Haven, D. S. 1957. Distribution, growth and availability of juvenile croaker, Micropogon undulatus, in Virginia. Ecology 38:88-97. 1959. Migration of the croaker, Micropogon un- dulatus. Copeia 1959:25-30. Herman, S. S. 1962. Spectral sensitivity and phototaxis in the opossum shrimp, Neomysis americana Smith. Biol. Bull. (Woods Hole) 123:562-570. HlLDEBRAND, S. F., AND L. A. CABLE. 1930. Development and life history of fourteen teleostean fishes at Beaufort, N.C. Bull. U.S. Bur. Fish. 46:383- 488. 1934. Reproduction and development of whitings or kingfishes drums, spot, croaker, and weakfishes or sea trouts family Sciaenidae, of the Atlantic coast of the Unit- ed States. U.S. Bur. Fish., Bull. 48:41-117. HlLDEBRAND, S. F., AND W. C. SCHROEDER. 1928. Fishes of Chesapeake Bay. Bull. U.S. Bur. Fish. 43(1), 366 p. HOESE, H. D. 1973. A trawl study of nearshore fishes and invertebrates of the Georgia coast. Contrib. Mar. Sci., Univ. Tex. 17:63-98. HUBBS, C. L., AND K. F. LAGLER. 1964. Fishes of the Great Lakes region. Revised ed. Univ. Mich. Press, Ann Arbor, 213 p. JANNKE, T. E. 1971. Abundance of young sciaenid fishes in Everglades National Park, Florida, in relation to season and other variables. Univ. Miami Sea Grant Program, Sea Grant Tech. Bull. 11, 128 p. JOSEPH, E. B. 1972. The status of the sciaenid stocks of the middle Atlan- tic coast. Chesapeake Sci. 13:87-100. KEAST, A. 1970. Food specialization and bioenergetic interrelations in the fish faunas of some small Ontario waterways. In J. H. Steele (editor), Marine food chains, p. 277-411. Oliver and Boyd, Edinb. KEAST, A., AND D. WEBB. 1966. Mouth and body form relative to feeding ecology in the fish fauna of a small lake, Lake Opinicon, Ontario. J. Fish. Res. Board Can. 23:1845-1874. KUNTZ, A. 1914. The embryology and larval development of Bair- diella chrysura and Anchovia mitchilli. Bull. U.S. Bur. Fish. 33:1-19 LACEPEDE, B. G. E. V. 1803. Histoire naturelle des poissons. Vol. 4, 728 p. MAHOOD, R. K. 1974. Seatrout of the genus Cynoscion in coastal waters of Georgia. Ga. Dep. Nat. Res., Contrib. Ser. 26, 36 p. MARKLE, D. F. 1976. The seasonality of availability and movements of fishes in the channel of the York River, Virgin- ia. Chesapeake Sci. 17:50-55. MASSMANN, W. H. 1962. Water temperatures, salinities, and fishes collected during trawl surveys of Chesapeake Bay and York and Pamunkey rivers, 1956-59. Va. Inst. Mar. Sci., Spec. Sci. Rep. 27, 51 p. 1963. Age and size composition of weakfish, Cynoscion regalis, from pound nets in Chesapeake Bay, Virginia 1954-58. Chesapeake Sci. 4:43-51. MASSMANN, W. H, AND A. L. PACHECO. 1960. Disappearance of young Atlantic croakers from the York River, Virginia. Trans. Am. Fish. Soc. 89:154- 159. MASSMANN, W. H, J. P. WHITCOMB, AND A. L. PACHECO. 1958. Distribution and abundance of gray weakfish in the York River System, Virginia. Trans. 23d. North Am. Wildl. Conf., p. 361-369. McHUGH, J. L. 1967. Estuarine nekton. In G. Lauffl editor), Estuaries, p. 581-620. Am. Assoc. Adv. Sci., Wash., D.C. MERRINER, J. V. 1973. Assessment of the weakfish resource, a suggested management plan, and aspects of life history in North 700 CHAO and MUSICK: LIFE HISTORY OK JUVENILE SCIAENII) FISHES Carolina. Ph.D. Thesis, North Carolina State Univ., Raleigh, 201 p. 1975. Food habits of the weakfish, Cynoscion regalis, in North Carolina waters. Chesapeake Sci. 16:74-76. 1976. Aspects of the reproductive biology of the weakfish, Cynoscion regalis (Sciaenidae), in North Carolina. Fish. Bull., U.S. 74:18-26. MUSIC, J. L., JR. 1974. Observations on the spot (Leiostomus xanthurus ) in Georgia's estuarine and close inshore ocean wa- ters. Dep. Nat. Res., Game Fish Div., Coastal Fish Off., Contrib. Ser. 28, 29 p. MUSICK, J. A. 1972. Fishes of Chesapeake Bay and the adjacent coastal plain. In M. L. Wass et al. (compilers), A check list of the biota of lower Chesapeake Bay, p. 175-212. Va. Inst. Mar. Sci., Spec. Sci. Rep. 65, 290 p. NELSON, W. R. 1969. Studies on the croaker, Micropogon undulatus Lin- naeus, and the spot, Leiostomus xanthurus Lacepede, in Mobile Bay, Alabama. J. Mar. Sci. Ala. 1:4-92. NESBIT, R. A. 1954. Weakfish migration in relation to its conserva- tion. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 115, 81 p. NIKOLSKY, G. V. 1963. The ecology of fishes. (Translated from Russ. by L. Birkett), Academic Press, N.Y., 352 p. NYBERG, D. W. 1971. Prey capture in the largemouth bass. Am. Midi. Nat. 86:128-144. PACHECO, A. L. 1957. The length and age composition of spot, Leiostomus xanthurus, in the pound net fishery of lower Chesapeake Bay. M.S. Thesis, Coll. William and Mary, Wil- liamsburg, Va., 34 p. 1962a. Age and growth of spot in lower Chesapeake Bay, with notes on distribution and abundance of juveniles in the York River system. Chesapeake Sci. 3:18-28. 1962b. Movements of spot, Leiostomus xanthurus, in the lower Chesapeake Bay. Chesapeake Sci. 3:256-257. PARKER, J. C. 1971. The biology of the spot, Leiostomus xanthurus Lacepede, and Atlantic croaker, Micropogon undulatus (Linnaeus), in two Gulf of Mexico nursery areas. Texas A&M Univ., Sea Grant Publ. TAMU-SG-7 1-210, 182 p. Pearson, J. C. 1929. Natural history and conservation of redfish and other commercial sciaenids on the Texas coast. Bull. U.S. Bur. Fish. 44:129-214. 1932. Winter trawl fishery off the Virginia and North Carolina coasts. U.S. Bur. Fish., Invest. Rep. 10, 31 p. 1941. The young of some marine fishes taken in lower Chesapeake Bay, Virginia, with special reference to the gray sea trout Cynoscion regalis (Bloch). U.S. Fish Wildl. Serv., Fish.' Bull. 50:79-102. Perlmutter, A., W. S. Miller, and J. C. Poole. 1956. The weakfish (Cynoscion regalis) in New York wa- ters. N.Y. Fish Game J. 3:1-43. QASIM, S. Z. 1972. The dynamics of food and feeding habits of some marine fishes. Indian J. Fish. 19:11-28. REID, G. K , JR. 1954. An ecological study of the Gulf of Mexico fish. the vicintiy of Cedar Key, Florida. Bull. Mar. Sci. Gulf. Caribb. 4:1-94. ROELOFS, E. W. 1954. Food studies of young sciaenid fishes Micropogon and Leiostomus, from North Carolina. Copeia 1954:151-153. RoiTHMAYR, C. M. 1965. Industrial bottomfish fishery of the northern Gulf of Mexico, 1959-63. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 518, 23 p. SEGUIN, R. T. 1960. Variation in the middle Atlantic coast population of the gray squeteague, Cynoscion regalis (Bloch & Schneider) 1801. Ph.D. Thesis, Univ. Delaware, Newark, 70 p. +9 p. append. SHEALY, M. H., J. V. MIGLARESE. AND E. B. JOSEPH. 1974. Bottom fishes of South Carolina estuaries, relative abundance, seasonal distribution and length-frequency relationships. S.C. Mar. Resour. Cent., Tech. Rep. 6, 189 p. SPRINGER, V. G., AND K. D. WOODBURN. 1960. An ecological study of the fishes of the Tampa Bay area. Fla. State Board Conserv., Mar. Lab., Prof. Pap. Ser. 1, 104 p. Stickney, R. R., G. L. Taylor, and D. B. White. 1975. Food habits of five species of young southeastern United States estuarine Sciaenidae. Chesapeake Sci. 16:104-114. STRUHSAKER, P. 1969. Demersal fish resources: Composition, distribution, and commercial potential of the continental shelf stocks off Southeastern United States. U.S. Fish Wildl. Serv., Fish. Ind. Res. 4:261-300. SUNDARARAJ, B. I. 1960. Age and growth of the spot, Leiostomus xanthurus Lacepede. Tulane Stud. Zool. 8:40-62. SUTTKUS, R. D. 1955. Seasonal movements and growth of the Atlantic croaker (Micropogon undulatus) along the east Louisiana coast. Gulf Caribb. Fish. Inst., Proc. 7th Annu. Sess., p. 151-158. 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 80 STEEPLES 81 60 45 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 Q 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 B B C C = 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 Zones Zones Zones Zones 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 74 27,135 1970 1,339 4,373 — 11,807 3,534 4,867 1,137 27,057 1971 0 3,346 — 9,642 3,083 4,559 1,349 21,979 1972 0 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 — — — 60 40 — 100 1962 — — — 72 24 — — 96 1963 — — — 89 25 33 — 147 1964 30 — — 81 25 51 (20 t 3D — 187 1965 24 — — 96 25 58(30 + 28) — 203 1966 32 43 — 105 34 67 (28 + 39) — 281 1967 32 58 — 113 50 89 (40 + 49) — 342 1968 35 48 — 134 55 90(53 • 37) — 362 1969 36 63 — 142 51 110(65 + 45) 1 403 1970 25 78 — 162 55 83 (37 + 46) 18 421 1971 — 60 — 160 45 60(18 + 42) 21 346 1972 — 55 — 175 55 60(17 + 43) 25 370 1973 6 42 '40 200 63 68(22 + 46) 24 443 1974 21 39 2NA 202 106 62(16 + 46) 30 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. 78 79 81 AIL ZONES r- 88 70 BROWN PINK-SPOTTED _i— 40 60 PERCENT 80 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 o IT s 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' O O ™ 5.6- 5 5.4' 5.2 z < I 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 O £ 5.4 < 0 5.2 Hi N 7, 5.0- Z < 00 69 70 —f— 71 —1 1 1 1 1 1— 72 73 74 75 76 77 FISHING ZONE 78 —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 *s M»K 1 *PH «ji ■ » si i; 1 1 ! i I . ... IAK > M u ■ |-' u i ■- ! ft |l| 69 70 • • H • • • • • * • - • • ■ • • • • • • • * • • • • • • • ' " • • • • • • • • O . . = . 77 73 75 - • • • • • • * • • • • ■ * • 1 « • • • • • • • • • • e • • 76 • • • • • • • • • • • • • • • • • 77 . . • * • • • • • • - • • • • • • • • • • • ■ • o . o ■ 7a • • * * - - - • • • • • • • - " - • • • • • ' - 79 • • • • • - - - • - - - • • • • • • • e • - 80 • • • • . - - - •r • • • • - - " - • • • • • ' ' " • - HI - • • • • - - • • • • 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 — _ • • • ' ~- _ — — _ O "**» <) • • ~- -^ _ o • ~~~ — ^ • • • • -», • • ■— - _ • """ — - • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • ~~ ■ • -^ • • — O "*• ^ • • • • u o ^v 71 • "^ ^ o 77 v 73 • .... 74 75s • 1* *** m&nP **, ^\ SORt NAM ft RENCt • 77 \ O GUIANA 78 EFFORT: HOURS X 100 >200 ^A 150-2O0 79\ O x O x • • • \ " \ HAZH 80 \ o \ o \ • 81 \ 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 78 I I L_ 20 40 60 PERCENT 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. on 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 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 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 13.8 13.6 13.7 12.9 Zones 78-81 : No. drags 2,975 3,063 1,959 873 91 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 S w Copepod species S W Calanus marshallae c c Metridia lucens2 C C C. tenulcomis u c M. pacifica2 U C. plumchrus R u Lucicuiia flavicornis u U C. cristatus R Candacia columbiae R Rhincalanus nasutus R R C bipinnata R R Eucalanus bungii U U Immature Heterorhabdus Mecynocera clausii U spp. R Paracalanus parvus C C Pleuromamma borealis R Calocalanus styliremis U P. abdominalis R C. tenuis u Centropages abdominalis C U C. sp R Epilabidocera amphitrites U U Pseudocalanus sp.1 C C Acartia clausii C C Microcalanus pusillus U u A. longiremis C C Clausocalanus masti- A. tonsa u C gophorus u A. danae R C furcatus R Eurytemora americana R C. arcuicornis U C Tortanus discaudatus U U C. jobei R Microsetella sp U U C. pergens U C Sapphirina sp. U u C parapergens U Oithona similis C c C. paululus R O. spinirostris C c Ctenocalanus vanus U C Oncaea tenella R R Aetideus pacificus u O borealis R R Immature Gaidius spp. u O conifera R R Gaidius brevispinus R O mediterranea R R Immature Gaetanus spp. R O. dentipes R Gaetanus simplex R O. subtilis R Paraeuchaeta japonica R R O. media hymena R Racovitzanus antarcticas U Corycaeus anglicus R C Scolecithricella minor u U C. amazonicus R 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 17 NH3 2,250 m -3 800 m-3 2.8 8 NH5 1 .550 m -3 530 m-3 2.9 4 NH 10 1 ,000 m "3 365 m-3 2.7 0 UJ o < io- I - I969 i I I I I i i i - I 970 • N H 1 I97I • I972 \ 1 1 1 \ l\ - * ^ — < f \ • A • • * • \ » \ ► s I \ / \ ' * I I I iiii i i i CD < CD O _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 O < a 2 io3 m < 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 UJ O 2 < Q QQ < CD io3 O 10' ■ 1969 • 1970 » 197 I • 1972 ' , A"\. *A / v? 4 \ ■ 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 Q 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 - *° ° »« 10 1969-70 J I L 25 30 35 o LJ cr z> < rr LU Q_ UJ I 5 1970-71 °o°° o o o orf> 8 o 25 30 35 10 % ° 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_ " 18 27 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° - i ^ i Revil agiged 18 3S IS 0 39 r c <. Chpp 7 ■rton 1 no 32 110 257 70 14 27 20 "^ 1 7 l 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 i 19721 1973 1974 1975 All years Month2 Males Females Males Females Males Females Males Females Males Females Males Females Males Females Males Females Total Jan. 1 2 2 11 9 12 23 24 85 104 163 170 283 323 606 Feb. 20 15 15 135 128 230 209 68 72 453 439 892 Mar. 11 35 79 78 26 18 32 31 148 162 310 Apr. 52 55 25 15 50 53 41 30 9 25 177 178 355 May 6 12 1 7 1 3 16 13 24 35 59 June 3 19 21 19 24 43 July 2 16 25 18 25 43 Aug. 3 1 12 12 15 13 28 Oct. 10 7 7 7 17 33 34 47 81 Nov. 35 39 49 45 19 27 12 9 115 120 235 Dec. 6 11 3 3 9 14 23 Total 52 55 3 2 63 76 61 96 347 345 405 395 364 411 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) r\ DEC I97I (7) JAN I972 (9) r^ln -^ MAR 1972 (10) l-H r-n-H APR 1972 (28) P^L P 5- 0 — JAN 1974 (100) MAR 1974 (28) 1974 (I) P- NOV -M H-rLjV1 -— i — —— l n — I (41) J 1974 (3) rs n p— i r-p a JAN 1975 (173) H FEB 1975 (73) 00 125 150 175 200 LENGTH (cm) MAY -P =■ ■^1 . K 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 -- 12 o c o t 10 o a. o a. en 08 CO iii Z V o Ob 04 - (245) 02 ^HHHHHHkfj^HHkn- (23) (44) (28) (68) 183) (212) (174) (109) (2461(244) _ J ! I I I 1 8 10 LAYER (no) 12 16 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 80 E ^ GO X h- tD LU |5 40 o h- 20 ~ oc 0 o _ Ave lencjUi at birth • I • • • • • 1 . 1 • • • • • • . • - • : • • • • - i • • - • • •• • • • • 1 1 ! 1 10 20 JAN 10 20 FEB 1974 28 10 20 MAR 30 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 13 ^ • I A 5° • n° a J / Galopogos Is tJo o* 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 1 l l 1 JANUARY JO° 30" \ C\ 1 l 1 FEBRUARY 1 1 \ bV :<■ 1975 20° 20° l! h 1975 -20° H Revil ogiged OS Is # • « ^-"w-U tf <; Revi lagiged os is m \ X b^ ^ iO,J Chpp erton 1 • • • • IG° 10° Chpp srlon 1 >. ( • y W W' • ^i! \ • *^_ *s ■ * / / 0° 0° \ 0° Galapagos Is. ^ 1 i / Galapagos Is. ^ I 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° M ,JP V 1 1 1 1 l 1 MARCH '■•'• VJ> \ APRIL ' \ W ?.' 1975 20° ^ \ 1975 ^ < 20° n N Revil ogiged • « \^6 £ <; Revil agtged 3S Is « • • • • • Clipperton Is _ • / Clipperton Is m 10° \< \ ^ 3° 1 / 0° c° V 0° Galapagos is 9 l i / Galapagos Is W I i 1 I 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 - o o 0 Average length at birth • • • • • • • • — •• • • • • • • • • • • • • • • . '• : i • • • i 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> o 10 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 ) 23 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 x S? 400 < (X. in 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- 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. 38 90.1 65 100 Feb. 107 83.3 20 100 Mar. 42 88.3 30 100 Apr. 13 81.1 50 100 May 9 89.9 67 100 Aug. 3 98.0 94 100 Oct. 7 71.1 47 100 Nov. 26 83.6 44 100 Dec. 5 94.0 73 91 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 z UJ (n UJ £ 60 100 40 - o o < rr a. C/5 20 - 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)/ 1 1 ,' . >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 T -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 SD <94 &94 3150 3400 594 356 230 81 108 160 160 162 192 195 195 190 176.0 175.8 174.1 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 1 /ou 600 500 • • 400 300 200 • * 100 • • % . . — - •*•** »••• -•- ^. , . — '• ;■ ~- • ■ 1 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) I 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 (%) 1 41 92.7 7.3 — 2 51 78.4 9.8 11.8 3 50 92.0 2.0 6.0 4 43 90.7 2.3 7.0 5 56 91.1 3.6 5.3 6 53 86.8 11.3 1.9 7 60 85.0 15.0 0.0 8 39 82.1 10.3 7.6 9 26 80.8 11.5 7.7 10-11 63 73.0 19.0 8.0 12-15 55 41.8 1.8 56.4 16-19 13 23.1 0.0 76.9 20-26 6 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 = ci 22 20 £ 16 < a. o a. ir o < or < > o 14 10 D|«'f| "I 10 II 14 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 UJ -I o in UJ 4 o or < a: UJ < 3 - 2 - - ' ® ® # ® ® ® © ® ® «® ® p ® ® © ©@° ®%> 1 0 , - -v* J. *■ 1 / . 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 o h- CE O Q. O or 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. % No. % No. % No. °o No. % No. % 13 33.3 14 30.4 29 20.6 60 37.3 49 32.9 165 30.8 23 59.0 20 43.5 83 58.9 75 46.6 74 49.7 275 51.3 0 0 0 0 1 0.7 2 1.2 1 0.7 4 0.7 0 0 4 8.7 3 2.1 5 3.1 3 2.0 15 28 3 7.7 8 17.4 24 17.0 16 9.9 22 14.8 73 13.6 0 0 0 0 1 0.7 3 1.9 0 0 4 0.7 39 100.0 46 100.0 141 100.0 161 100.0 149 100.0 536 100.0 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.) 39 46 140 158 149 532 Pregnancy (months) 10.6 10.6 10.6 10.6 10.6 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 I II and III Feb. 1973 41 139 1.83 14.6 16.0 Mar. 1973 18 133 1.52 12.2 12.2 Jan. 1974 23 124 1.16 9.3 9.3 Feb. 1974 42 118 0.97 7.7 7.7 Jan. 1975 33 132 1.48 9.4 9.4 Feb. 1975 12 120 1.03 8.2 8.2 Year: 1973 91 128.5 1.33 10.6 10.6 1974 81 124.5 1.18 9.4 9.4 1975 88 127.0 1.27 10.2 10.2 Pooled 260 126.7 1.26 10.1 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. r 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. % No. % (M^F) Fetuses >15 126 49.0 65 51.6 61 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) (140) (690) (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) (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) (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) (447) (2,262) (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 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 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 No 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. 1975. Report of the Meeting on Smaller Cetaceans, Montreal, April 1-11, 1974. In E. D. Mitchell (editor), Review of biology and fisheries for smaller cetaceans, p. 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. 749 FISHERY BULLETIN: VOL. 75, NO. 4 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 42 40 39 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 0 1 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 99 0.30 386 234 782 92 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 84 47 124 182 0.53 909 845 274 0.50 6 0 40 220 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 '0 1 2 3 4 1 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 0 1 2 3 Sum 0 1 2 3 Sum 1968 Summer 0 346 0 0 346 (57) 207 42 0 249 ( 8) Winter 147 277 65 14 503 (74) 0 802 659 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) 0 773 0 0 773 (21) 1971 Summer 262 0 0 0 262 (55) 645 133 0 778 (27) Winter 86 128 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 0 1 2 3 4 month L W L W L W L W L W Clubhouse Springs: April 126 19 176 55 229 127 September 105 13 166 49 212 105 276 238 Hoglot Springs: April 107 10 150 31 199 72 241 136 September 88 6 130 26 178 56 226 118 Maxwell Springs: April 106 12 154 38 203 89 264 172 September 89 7 147 34 200 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. on 15 Sept. Apr-Sept. Mean trout biomass (kg/ha) of: Age 0 0 -0.62* -0.59 Age 1 -0.86" -0.72* Ages 0 and 1 -0.85** -0.76" Age 1 1 -0.08 0.38 -0.61* -0.53 All ages 0.13 -0.66" -0.72" 0.59* Age 2 2 0.04 -0.81" -0.79" -0.62* All ages 0.14 -0.72" -0.68' -0.48 Age 3 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 -0.78* -0.84" Age 1 -0.67* -0.64* Ages 0 and 1 -0.82" -0.85" Age 1 1 0.01 -0.57 -0.70* -0.62 All ages 0.01 0.66* -0.77" 0.63* Age 2 2 006 -0.87" -0.86" -0.68* All ages 0.17 -0.71** -0.69' 0.46 Age 3 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 19 15 o AGE 1 G CLUBHOUSE SPRINGS A HOGLOT SPRINGS □ O MAXWELL SPRINGS "~^nq^ □ O r = -066* A A "W o ^^\ o ? 22 u ^3 O o AGE 2 m ann. Si 20 in z o LENGTH 65 A A AA \o z < r = -072" 29 l 27 25 23 2H AGE 3 O r = -0 82" \o O 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; K * 0 CLUBHOUSE SPRINGS A A HARVEST HOGLOT SPRINGS A .:. 2 3. MAXWELL SPRINGS 1969 MAXWELL SPRINGS 1970 A i\ i \ / \ ; \ \ / ^ \l ^ ' \ \ ' \ \ \ \ ' \ \ 1 1 \ A \ N. \ 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. 25 3 20 o 1.0 tr o 2 to O i2 0.5 V) z O TOTAL ▲ NATURAL □ FISHING 171'- - 1 5+ 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 95 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 o □ CLUBHOUSE SPRINGS ^ s A HOGLOT SPRINGS ~ 300- O MAXWELL SPRINGS »- _l < 3 Q a z 120 -i 100 80 60 p 40 o 3 a o £ °- 20 z 20 40 60 MEAN BIOMASS OF INDIVIDUAL COHORTS (kg/ha) 80 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 z 2 o i- o 3 O o Q- MAXWELL SPRINGS HOGLOT SPRINGS .— age I* CLUBHOUSE SPRINGS " -age 0 < < 5 300 200 '00 1250 2500 MEAN DENSITY OF SPRING YEARLINGS (No /ha) MAXWELL SPRINGS HOGLOT SPRINGS CLUBHOUSE SPRINGS _ age I*- age 0- s " 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 P (kg/ha) 6 (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 o o 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 (D 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 85 Hoglot Springs: 1969-70 27.0 89.0 116 0 54.6 61.4 47 1970-71 8.8 114.5 1233 25.4 97.9 21 Maxwell Springs: 1969-70 87.9 200.3 288.2 71.8 216.4 25 1970-71 57.8 188.2 246.0 39.7 206.3 16 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 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 cr LLl a. 5 u 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 z -0 50 0.25 0.00 -0.25 D \ A/\.~^n/\/\ A~ /\ j\l\ r\ t \/\ \/\ /Ya AAA /V- /" A^ \ 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 cc>o's"^"-"C7icb»bif>croojed — oo^OT(TiQO©QdKf^^Ku>^^U)U>o^u^ioo^ir>^^^^^^^^^^^fOiofOiOfOfOroifOioroiOfOiOfOifl-ou>cMcnt^inioct^ioioi^'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 a. 2 o 50- tr. 3 < -1.00 JAN JUNE MONTHS JAN 15 .10 - .05 - E o < to -05 ! I ! 1 1 B 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 < 0. 5 -0.2 -0.4 -0.6 -0.8 1 I ! 1 1 ! 1 1 1 ! - \ i / ''~~\ - // \\ \ \ V i \ \ l\ \ \ / •• ' 1 ' J / ; \ \ .-•" 1 I ''■■■ ' /"' '•• \ * \ / t '■■ ' I •••....V \ '■■ / / v....,/ *■■ 1 k / / \ / / V/ / \ \ / J y \ / V. ^.y - 1 1 i 1 1 i 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 29 Id Q. 2 1 ! I I I I I I ' ! I i 'I 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 < X p-H Q Z w cu co C o • I— t o C a c o pH u a c cd •iH u tt> o o C CO en ju "be 03 CD CO 03 XI Oh 00 l> I O t> 3 03 O 03 CD o .J* O co" 0) 03 CO c 03 CO CD u B 03 Sh CD a CD CD O CO I 03 CD CO i CO o + + II CO e _ l CO 03 (N CD CO 03 CD XI O 03 0 03 CO Sh CD be C • I— I c c be CD CO © t> Cn 0) X o o a s A) 3 00 03 9) >- c CD £ o o T3 C es CO >> _4) 03 13 e 3 • i-H 03 0) -C s CU •P-t 1 -t-> 1—1 CD H X, 3 +-> m CO • pi < *» < X a z w CU a. < i/i D tu -J J < o ■> 2 1 < z OJ 01 < X a. 00 o 0> C> oj 0J ■u — « • • • • •9 •9 9 o D 1 pp eg CO rg C0 r- O o r-. f> • • • • ■9 o oj ^ r- co 1 r- I — o — - CM I GO CO I w* T~ •* r^ fO -• cO i 9 1 9 I 0> n 9 oj r- o m ru. • • • • 0* o IS r- 00 1 i ■9 1 i<7 o r» cr •9 05 ao oj • • • • as m r- o in i in i rg 00 •o o o o> o rn • • • • r- X9 m nl r-- * CO CO CM o 1 Cf co 1 CM • •o o • >0 0> • r- « * D co i 05 9 N. o C >u N o — rg rn (^ s f- t"- cr> o* c* cr UJ en U III _> 3 r- J p- < -1 -> a 5 z *4 CO N pi rg « -1 « N o o O O • • • • o o 1 o o o in « 00 (0 CO »g o N o fg <* o o o o • • • • o o 1 o 1 o r*l m4 O rg « CO r<1 1*1 0 in 05 rn 0 c o o o o • • • • o 1 o O 1 o 1 -0 CO CO rr rv in pi •o <0 i*l K) it) o pi CJ o • • • • o o i o 1 o r* c o o n & pp JT o OJ eg CO pi o o o • • • • o 1 o o o 0> CM rv >0 pi o pi 00 r-> r) n o o o o • • • • o 1 o o 1 o 1 «r in ^ r- v0 If] r*- c0 r^ in o N n CJ PI O PI • • • • o 1 o o o 1 o r^ m o 0> pi o o in V c 0J n n rg o • • • • o o o i o 1 rg co o in rg ■9 Op' >n M CO pi eg 00 rn r^ o o 9 »n gj m pi o r> o O o o o o o o • • • • CJ 1 o 1 o o o rn ■9 & « 0*> rn « H rn in co Ifj r>- •9 r^ • • • • in 9 9 m rg CO rg rg o _ rg rn r>- N r^ r. 0- 0- &» o 780 SECKEL and YONG: SEA-SURFACE TEMPERATURES AND SALINITIES 00 © X o o co 0> CO 03 4) O t, 3 01 i CO cu CO a a o u -o c CO M C CO CO 01 CO CM w « < E- 3 z u Oh Cm < o z < UJ in < I a -0 in o CO K N in 0< • • • • <\l ro * AJ 1 St 1 I r*> m » •0 K in co 0> • • • • pH >o * o IM n r\j UJ r* -. ph \0 !NJ cO -0 • • •o r> I •0 1 o «;> 0> — . - a r~ o ~ 1*1 1 i cm 1 •» o t n -- r- • • • >n in PH m I 1 n t O -* vO • • • o * rvi O CM r- N (\J I 10 •» n o • • o r* in rO "M n m o CO ^0 in o • • » • 10 i0 CO o i r> r- 1 n . « in » r\j in C\) CM • • • • o o ph CM r^ in CC a o CM to < r- s r- s UJ 0> o 0> C7> > w> < UJ > in co n -H o o pH o o o o • • • • o 1 o 1 o 1 o m h- 0> 0 -H CM CO — o o PH o o o o • • • • o 1 o 1 o o 1 & ff nj on in CO in _ o o o o o o o o • • • ■ o o 1 o 1 o 1 1*1 c"> in r>- O -H •-■ C\l O o o o • • • • o o 1 o o 1 CM .0 n> PH o CM "M o o PH PH fvj o o o o •» >o iC o cm !•) o o a r^ £ PH 0> O PH o PH o o o o • • • • o 1 o o 1 o N » n N O o n ,n *m r* PH o o o o o • • • • o o o 1 o 1 "1 CO a in r- o o r*> o 0J » o o o o OX o o o «\l o o o iD H m PH 0- •H o <» PH pH -o n o o o o • • • • o o o o _ o ■9 o ■» in <\l in — o n CM o o o o • • • • o 1 o o o CM <\] r» m CO n o PH ■» -H CO CM o o o O • • • • o 1 o 1 o 1 o ^^ in co o c? «H f) 1) « — cO o o — — o PH in c PH "M CM CM "1 n o ■C "M (0 o o O • • p • 1- 25 < , 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. I 2 3 A 5 6 7 19" 1971 1972 1973 1 1 2. 44 -6.13 -16.78 -23. 7 3 -2.18 6.9 1 1 *.58 2 -22. 31 1 7.61 7. 60 1 4. 33 ".98 1 3. 05 -6.74 3 -22.04 -10.25 - 16. 75 26.25 29.57 9.s i 1(J. 38 4 26. 63 -22. 46 -18.15 -13.17 25.9: 1^.12 3.83 1 -9.01 1 8.72 ". 88 -23.22 -19.97 23. 73 2' . ?1 2 - 14.62 -1 1 .07 -2^. 19 - 1 9. 3? 1 8. 78 -28. C 3 12. 39 3 -3. 95 -4. ''A 8. 41- - 1 3. 99 -2.6" -6.' 5 -2C ,C5 A -7. 34 24. 95 -13. 18 3.2 1 1 1. 7b - 16.66 25. 18 1 7. 99 -27.53 -29.51 - 1 4 . 94 -26. 1 A 1 2. «5 -22. *4 2 -7.77 -27.22 2 0 . C 6 4. 35 -1.33 21.18 1 "".69 3 -6.13 -If. 93 - 1 5. 60 2Q.25 23. 39 21.23 1 ° . 5 3 A 1.16 2 1 . 36 11.98 1 .52 24. 55 0.57 - 19 .27 1 28. 56 26. 13 9. 53 -4. 76 -15.17 26. 74 24 .63 2 2S. 96 21.19 12. ce 25.17 -8. 93 -2^.7" -13.43 3 23. 99 - 1 8.26 7. 15 - 1 1 .40 -2". 1 1 -13.69 16.43 A 17.68 26.83 -28. 86 27.12 - 1 9. 7a -21.2 1 13. C 1 AMPL I TUOES N-VALUES VEAP QU. K B 1 2 3 4 5 6 7 197? 1971 1972 1973 1 26.8641 P .0 034 r. . "85 1 -0. 1 98 3 - ".."75 3 - i . 2552 -0.1641 '. .0452 - .C599 2 2ft. 8841 - : . o c 4 i -(. .4763 r . 3681 o . 16 "9 ' - . 0 8 24 -<~ .0936 - " . 1 r 1 1 -' . "466 3 2 5.7091 -r. -C49 -o . 4564 - 0.2126 ".1819 -" . 075A r . 1993 '" . ". 043 " . 16 64 4 24. 16 13 0. - 033 0 . 36 38 - C . 1039 -C. 1 390 -".0981 -, . 1 2 S 9 - - . '1722 - '.-893 1 23.91 e>5 0." 176 0. I«T1 u.CKc 0.1309 - 0 . 1 C 2 4 -C . "435 - . " ' JJ . 1 "56 2 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 3 26.31 06 -t . 0098 -C .5 171 0. 202 1 o .047? ".1281 - " . 27?o - ? . '. 9 c r -0. "912 4 24.66^2 0. }G9 1 -0. 2 184 0.211' C.-76 j -•:•• 1 34 6 -0.r573 : .: 33" -r . '7 1 7 1 25.C3 DS 0.0 133 "."496 -C . ""632 -".^819 0 . 1725 '.'"f >l - C . C 9 1 8 -0 . 1 1 2<~ 2 26.5641 C .0038 -0.1173 C .24 1"= -0.1913 0 .r 57fc : . 2' T 5 - :. 1676 0. 1233 3 27. 3256 3. : 12'. -0.291 A -0.5543 0 .5779 - 'i . 2 5 ' 6 " . 723" - .1923 -" . 6557 4 29. 50 1 3 -0. '0 1 9 -*">. 3996 0. 1060 -r . -,9 35 .1P» ".1171 - :. 1484 r . 1 364 1 27.2621 0 . " C 1 7 C.6704 0 .3264 ".2433 "."114 -T . 1 570 :.25T ". 926 2 27.3407 - 0 . C 22 3 -0. 150.9 -C . 321 2 -C.0S33 -J. 2 38 1 C . 1 7 3 4 -" .1 ^7* 0. J9 1 3 3 24.6561 -C.^C33 C .6 202 -0.2669 0 .24 38 -0. 2662 -".1172 -o. 1539 -C . "6 32 4 23. 0?,1 0 .0092 0. 5485 0.2358 ".1139 ■ . 297" -'.1569 t' . i :39 C. 243 783 FISHERY BULLETIN: VOL. 75, NO. 4 A C o CI) CO ^ V CO !h -t-> CO > 0) -t-> T3 CD CO CJ > T> c CO „Q CO o — CO X -t-» +j Ui £ CO «l-H co CO CD >> > CO 3 C CJ CO -a u C -i-> o Q fe s •— X CO CO Q o t> 05 Z -u w a. Oh i—l < CO CO CO CO 0) CO 0) CO O •C c -C cu U S of X cu CO u aj •/. o C3 ■9, c ,a o c tt-H T^ '"^ S.S-S :°£ D ^ f! CO CO g > >', (t ' + -.; * * *i ■ J' ('< . 7 ; i * + t t >J ' - * < ^v « + • i < 1 . - *\ , ft , • \ 05 (Do) 3aruva3dW31 V3S 784 SECKEL and YONG: SEA-SURFACE TEMPERATURES AND SALINITIES Oo)3aniva3dW3i V3S 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 1 2 3 4 5 6 7 8 9 10 11 12 13 1970 0.41 0.32 0.32 0.30 0.29 0.28 0.26 0.25 0.24 0.24 0.23 022 0.22 1971 0.37 026 0.25 0.23 0.22 0.22 0.21 0.21 0.18 0.18 0.18 0.18 0.18 1972 0.35 0.29 0.28 0.26 0.23 0.23 0.22 0.22 022 0.22 0.21 0.21 0.21 1973 0.29 0.29 0.28 0.26 0.24 0.24 0.23 0.23 022 0.22 0.22 0.21 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. n -values Year 1 2 3 4 5 6 7 8 9 10 11 12 13 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 n ■values Year Quarter n-values Year 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1970 1 0.35 0.32 0.31 0.25 0.23 0.22 0.22 1972 1 0.36 0.35 0.35 0.33 0.32 0.32 0.31 2 0.46 0.37 0.35 0.35 0.34 032 0.32 21 3 0.50 0.47 0.46 0.45 0.43 0.43 0.42 3 ? Data sets incomplete or missing 4 0.39 0.38 0.36 0.35 0.34 0.33 0.33 4J 1971 1 0.30 0.30 0.28 0.27 0.27 0.27 0.26 1973 1 0.64 0.60 0.59 0.59 0.58 0.55 0.55 2 0.30 0.29 0.27 0.26 0.25 0.25 0.24 2 0.71 0.68 0.69 0.66 0.65 0.64 0.58 3 0.42 0.39 0.38 0.37 0.33 032 0.32 3 0.53 0.49 0.46 0.42 0.41 0.40 0.39 4 0.34 0.31 0.30 0.29 0.28 0.28 0.27 4 0.46 0.43 0.43 0.37 0.35 0.34 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 1 2 3 4 5 6 7 8 9 0 0.5478 -0.1755 -0.1397 0.1131 An 0.0279 -00538 0 0263 0.0583 00782 00245 10 0.0174 00760 0.0642 0.0401 0.0905 0.0168 00439 0.0641 -0.2483 00055 20 0.1262 0 0126 -0.0035 -0.0263 0 0408 0.0211 0.0253 0 0235 0.0576 00279 30 -0.0428 00019 -0 0060 00497 -0.0114 0.0191 0.0134 0.0348 -00041 0.0258 40 0 0332 0 0042 -0.0024 0.0502 0.0274 0.0056 00239 0 0040 -0.0171 -0.0274 50 0.0377 -0.0436 0.0015 00116 -0.1030 0.0298 0.0257 0.0154 -0.0007 0 0068 60 0 0162 -0.0113 -0.0050 -0.0267 00202 0 0202 0.0231 00107 0.0145 -00234 70 0.0174 00117 -0 0067 Bn 0 0305 0 _ 0 0887 0.2135 0.1425 0 0989 0.0023 0.0552 0.0418 0.0052 10 0 1329 0 0093 0 0696 0 0044 0.0437 -0.0274 0.0195 0 0056 -1.4540 0.0197 20 00262 00509 0.0531 0.0198 0 0676 0.0572 -0.0049 0.0035 0.0105 0.0409 30 -0.0313 0.0422 -0.0177 - 0.0767 -0.0058 0.0373 - 0.1468 -0.0175 00347 0.0226 40 00519 0.0306 0.0078 -0.0188 -0.0288 0.0258 0.0207 -0.0533 00105 00327 50 0.0151 -0.0145 00652 -0.0230 -0.0113 0.0283 -0.0074 0.0238 0.0050 0.0090 60 0 0188 -0.0138 0 0200 0.0272 -0.0316 -0.0222 0.0053 -0.0254 0.0177 -0.0083 70 0.0011 -0.0167 -0.0020 APPENDIX F TABLE 2.— Coefficients for Koko Head salinity, a = 35.0141, b = 0.0001. 0 1 2 3 4 5 6 7 8 9 0 -0 1228 0.0366 0.0685 -0.0653 An -0.0894 0.0441 -0 0034 -0.0048 00165 0.0163 10 00286 -0.0017 0.0109 -0.0128 -0.0156 0.0024 0.0043 0 0093 0.0903 -0.0020 20 -0 0004 -0.0095 0 0032 -0.0127 0.0017 -0.0035 0 0020 -0.0101 -0.0034 0.0028 30 0.0020 0.0117 -0.0043 -0.0097 -0.0132 -00023 -0.0091 0.0094 -0.0067 -0.0039 40 -0.0057 0.0085 0.0070 0.0040 -0.0136 -0.0098 -0.0035 0.0041 0.0030 -0.0053 50 -00031 -0.0062 0 0070 00130 -0.0002 -0.0092 -0.0053 -0.0002 0.0064 0.0046 60 -0.0006 -0.0048 -0 0039 -0.0021 00013 -0.0008 -0.0063 0.0002 0.0014 0.0022 70 00089 -00016 00028 Bn 0 0206 0 0.0663 -0.0287 -0.0063 0.0174 -0.0532 0.0026 -0.0221 00006 10 -0.0372 -0 0034 -0.0095 -0.0047 0.0268 -0.0041 0.0007 -0.0199 0.0085 0 0034 20 -0.0099 -0.0050 -00075 -0.0012 -0.0108 0.0020 0.0058 0.0075 0.0131 0 0026 30 00109 0 0028 0 0088 0.0086 -0.0105 -0.0095 0.0021 0.0126 0.0043 0.0138 40 -00050 -0.0067 -0.0039 00158 -0.0005 -0.0121 -00124 0.0064 0.0125 0.0092 50 -0 0002 0.0028 0.0037 00001 0.0050 0.0003 00001 -0.0089 -0.0003 0.0000 60 0 0074 0.0108 -0.0071 -0.0070 0.0059 -0.0028 0.0028 0.0049 -0.0011 00007 70 0.0072 -0.0021 0.0015 APPENDIX F TABLE 3.— Coefficients for Christmas Island temperature, a = 26.1443, b = -0.0054. 0 1 2 3 4 5 6 7 8 9 0 1 5694 -0.2024 -0.3409 -0.1310 An 0.1924 0.3505 -0.1455 -0.4605 -0.1400 -0.2839 10 0.1658 -0.3162 0.0228 -0.2507 -0.0381 0.1309 0.2614 0.0088 -0.0257 0.0569 20 -0.4204 -0.0517 -0.0635 0.0676 0.0431 0.0179 0.0014 -0.0727 -0.0298 -0.0637 30 0.0295 -0.0316 -0.0583 -0.0133 0.0264 0.0040 0.0073 -0.0021 -0.0587 -0.0397 40 0.1025 -0.0243 -0.0049 0.0496 -0.0108 0.0176 0.0054 -0.0458 0.0351 -0.0144 50 00100 0.0321 0 0211 -0.0272 0.0145 -0.0076 00085 0.0031 -0.0410 0.0141 60 0.0369 -00001 0.0292 -00495 -0.0385 -00080 -0.0065 00232 -00204 0.0170 70 0.0134 00126 -0.0021 -0.0141 0.0203 -0.0178 -0.0085 0.0325 0.0144 0.0445 80 00022 Bn 0 -0.8028 -0.2146 -0.6457 -0.4963 -0.3942 -0.3880 0 1339 -0 1839 0.0969 10 -0.1253 0.1038 0.1556 -0.0039 00555 0.2400 0 1030 0.1198 -0.0589 0.1246 20 00883 0.0041 0.0403 -0.1501 -0.0233 0.0791 -0.0622 -0.0063 0.0252 0.0138 30 00456 0.0172 00133 -0.0420 -0.0357 0.0625 0.0097 0.0054 0.0347 -0.0026 40 -0 1791 -0.0090 00979 -0.0668 -0.0407 0.0247 0.0003 -0.0241 0.0154 -0.0151 50 00073 0 0230 0.0144 0.0196 -0.0277 -0.0250 0.0374 -0.0110 0.0054 00258 60 -0.0250 00336 -0.0219 -0.0223 -0.0124 -0.0314 0.0035 -0.0044 0.0041 0.0267 70 -0.0323 0.0071 -00183 -0.0084 0.0289 -0.0417 0.0431 -00055 00038 0.0022 80 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 J 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 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° V 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 1 1 : i 1 • 1 \ X LMAY 23-JULY 10, 1972 a • • • • castor a 45° X X X X X X • • • • CATCH/150 LINE HOURS / x No Catch o L- «S C BLANCO ' ^ • 6-50 \ • 51-100 X X • • £ 101-200 > C MENDOCINO 40° o m o o X X o • X o • o C • o • • • • X \ A 201-300 - o • • 0 • o • • 35° •X • X o .' o OXO >' • • ° < • • • <-> • 1 — IfT CONCEPT'ON • ° x • ■ o 0 X o • x x X X • X o X ^^ *f SAN OiEGO o X X X X X X X X c \ - X X ° L 30° _ X X X X X X X X X X » X i X x X X X oco i , X ' ,— ' i ' 150 48° 45= 45° 40° 35° 50 25 145° 140° . 35° .. MAY 10-JULY 16,1973 • X • 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° )H 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- _ _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 <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 P w 400 uj u. i 600 I- a. ill Q 800 1000 31 30 29 28 1972 27 26 25 mm' Along I37°30' W. tr 100 £ 200 d300 3I°N 32°N 38°N 39°N 40°N 200 - 400 600 a 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 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° v. 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 2E 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 X No Catch o 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 O i- 2 • 3- -20 • 21 -40 MEM • 41 -80 m 81 -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 - A 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 ARON, W. 1962. The distribution of animals in the eastern North Pacific and its relationship to physical and chemical con- ditions. J. Fish. Res. Board Can. 19:271-314. BROCK, V. E. 1943. Contribution to the biology of the albacore (Germo alalunga) of the Oregon coast and other parts of the North Pacific. Stanford Ichthyol. Bull. 2:199-248. Callaway, R. J., and J. w. McGary. 1959. Northeastern Pacific albacore survey. Part 2. Oceanographic and meteorological observations. U.S. Fish. Wildl. Serv., Spec. Sci. Rep. Fish. 315, 133 p. CAREY, F. G. J. M. TEAL, J. W. KANW1SHER, K. D. LAWSON, AND J. S. BECKETT. 1971. Warm-bodied fish. Am. Zool. 11:135-147. CHRISTENSEN, N., AND O. S. LEE. 1965. Sound channels in the boundary region between eastern North Pacific central water and transition wa- ter. Proc. 2d U.S. Navy Symp. Mil. Oceanogr. 11:203-225. Clemens, h. b. 1961. The migration, age, and growth of Pacific albacore (Thunnus germo), 1951-1958. Calif. Dep. Fish Game, Fish Bull. 115, 128 p. 1962. The distribution of albacore in the North Pacif- ic. Pac. Mar. Fish. Comm., Annu. Rep. 14:44-47. Craig, w. l., and j. j. Graham. 1961. Report on a co-operative, preseason survey of the fishing grounds for albacore (Thunnus germo) in the east- ern North Pacific, 1959. Calif. Fish Game 47:73-85. FLITTNER, G. A. 1963. Review of the 1962 seasonal movement of albacore tuna off the Pacific coast of the United States. Commer. Fish. Rev. 25(4):7-13. 1964. Review of the movement of albacore tuna off the Pacific coast in 1963. Commer. Fish. Rev. 26(12):13-19. Graham, J. J. 1957. Central North Pacific albacore surveys, May to November 1955. U. S. Fish. Wildl. Serv., Spec. Sci. Rep. Fish. 212, 38 p. 1959. Northeastern Pacific albacore survey. Part 1. Biological observations. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 310, 33 p. 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 population. In Radioactive contamination of the marine environment, p. 263-276. Int. At. Energy Agency, Vienna. JAPANESE FISHERIES AGENCY. 1975. Report of tuna tagging for 1974. [In Jap.] Pelagic 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. JOHNSON, M. W., AND E. BRINTON. 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.] Okeanologiya 5:325-337. (Transl. in Oceanology 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. 75:867-870. LAURS, R. M. 1973. Requirements of fishery scientists for processed oceanographic information. Proc. World Meteorol. Or- 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 alalunga, in relation to ocean features as indicated by ultrasonic tracking and oceanographic sampling. Fish. Bull., U.S. 75:347-355. LAVEASTU, T., AND I. HELA (editors). 1970. Fisheries oceanography. Coward and Gerrish Ltd., Bath, Engl., 238 p. MCGARY, J. W., J. J. GRAHAM, AND T. OTSU. 1961. Oceanography and North Pacific albacore. Calif. Coop. Oceanic Fish. Invest. Rep. 8:45-53. MCGARY, J. W., AND E. D. STROUP. 1956. Mid-Pacific oceanography, Part VIII, middle 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. Exp. Mar. Biol. Ecol. 12:187-217. MEEHAN, J. M., AND L. H. HREHA. 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 Gulf of Alaska regions. J. Fish. Res. Board Can. 17:221- 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. OWEN, R. W., JR. 1968. Oceanographic conditions in the northeast Pacific Ocean and their relation to the albacore fishery. U.S. Fish Wildl. Serv., Fish. Bull. 66:503-526. PANSHIN, D. A. 1971. Albacore tuna catches in the northeast Pacific dur- ing summer 1969 as related to selected ocean condi- tions. Ph.D. Thesis, Oregon State Univ., Corvallis, 110 p. PEARCY, W. G., AND J. L. MUELLER. 1970. Upwelling, Columbia River plume and albacore tu- na. Proc. 6th Int. Symp. Remote Sensing Environ. Univ. Michigan, Ann Arbor, p. 1101-1113. PINKAS, L. 1963. Albacore scouting in the eastern North Pacific Ocean. FAO Fish. Rep. 6:1343-1353. 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. POWELL. D. E. 1950. Preliminary report on 1950 North Pacific albacore tuna explorations of the John N. Cobb. Commer. Fish. Rev. 12(12):l-7. 1957. North Pacific albacore tuna exploration by the M/V John N. Cobb— 1956. Commer. Fish. Rev. 19(6):l-9. 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. POWELL, D. E., AND H. A. HlLDEBRAND. 1950. Albacore tuna exploration in Alaskan and adjacent waters— 1949. U.S. Fish Wildl. Serv., Fish. Leafl. 376, 33 p. REID, J. L., JR. 1962. On circulation, phosphate-phosphorus content, and zooplankton volumes in the upper part of the Pacific Ocean. Limnol. Oceanogr. 7:287-306. RODEN, G. I. 1970. Aspects of the mid-Pacific Transition Zone. J. Geophys. Res. 75:1097-1109. 1972. Temperature and salinity fronts at the boundaries of the subarctic-subtropical Transition Zone in the western Pacific. J. Geophys. Res. 77:7175-7187. 1975. On North Pacific temperature, salinity, sound veloc- ity and density fronts and their relation to the wind and energy flux fields. J. Phys. Oceanogr. 5:557-571. SCHAEFERS, E. A. 1953. North Pacific albacore tuna exploration, 1952. Commer. Fish. Rev. 15(9):l-6. SETTE, O. E., AND J. D. ISAACS (editors). 1960. The changing Pacific Ocean in 1957 and 1958. Calif. Coop. Oceanic Fish. Invest. Rep. 7:14-217. SHARP, G. D., AND R. C. DOTSON. 1977. Energy for migration in albacore Thunnus alalunga. Fish. Bull., U.S. 75:447-450. . SHOMURA. R. S., AND T. OTSU. 1956. Central North Pacific albacore surveys, January 1954-February 1955. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 173, 29 p. 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. UDA, M. 1973. Pulsative fluctuation of oceanic fronts in association with the tuna fishing grounds and fisheries. J. Fac. Mar. Sci. Technol., Tokai Univ. 7:245-265. VENRICK, E. L., J. A. MCGOWAN, AND A. W. MANTYLA. 1973. Deep maxima of photosynthetic chlorophyll in the Pacific Ocean. Fish. Bull., U.S. 71:41-52. YAMANAKA, H., J. MORITA, AND N. ANRAKU. 1969. Relation between the distribution of tunas and water types of the North and South Pacific Ocean. Bull. 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 2 3 4 5 6 7 8 Male: 2 44 3.3:5:0.3 3 51 3.2 ±0.3 4.2 ±0.3 4 23 3.2 ±0.3 4.2 ±0.3 4.9±0.2 5 11 3.2±0.2 4.2 ±0.2 4.9 ±0.3 5.4 ±0.3 7 1 3.0 4.3 4.8 5.6 6.1 6.4 Female: 2 50 3.4±0.2 3 71 3.4 ±0.2 4.6 ±0.3 4 36 3.3 ±0.3 4.6±0.3 5.5±0.3 5 22 3.3 ±0.3 4.6±0.4 5.4 ±0.4 6.0 ±0.4 6 4 3.4 ±0.1 4.7 ±0.2 5.6 ±0.3 6.4 ±0.4 7 1 ±0.4 7 3 3.2 ±0.1 4.3±06 5.3 ±0.5 6.2 ±0.4 7.1 ±0.7 7.9±0.8 8 3 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 1 2 3 4 5 6 7 8 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 1 2 3 4 5 6 7 8 9 2 50 301 ±21 3 71 280±19 383 ±21 4 36 279 ±25 389 ±24 465 ±25 5 22 289 ±20 399 ±24 470 ±22 526 ±22 6 4 273 ±23 379 ±33 450 ±21 512±22 568 ±25 7 3 252±12 332 ±48 412±34 484 ± 5 553±16 612±19 8 3 289 ±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 Ld tut ID □_ n i n 25 30 35 40 45 50 55 60 65 70 75 h. 5 Z in <* 4 - 3 - 2 - 1 - MALE tin. JZL _L _L 25 30 35 40 60 65 70 75 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 SD Mean SD Mean SD Mean SD Mean SD 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 56 0.6 16.5 0.9 N.C. (1) 89.0 2.7 68.4 2.6 41.3 05 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. N.C. Del. Ches. I M.C. N.C. Del. Ches. N.C. N.C. Location Bay Bay (1) (2) (3) Bay Bay (2) (3) Bay 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 II Stage Megalopa 1 st crab South Carolina 15°C-30%« 36 12 27 (') 20°C-30%o 36 7 12 (') 25°C-15%. 54 (1) 25oC-20%« 54 3 8 C) 25°C-30V 54 3 6 14 25°C-40%o 54 3 7 (') 25°C-45%o 54 4 8 n 30°C-30%o 36 (1) Rhode Island 15°C-30%o 60 (2) 20°C-30%« 60 5 8 14 25°C-30%« 60 4 (') 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 reared samples Zoea 1* x (mm) '0.75 10.78 0.775 SD (mm) 0.019 0.020 0.028 N 10 10 13 Zoea II x (mm) 0.94 0.94 0.96 SD (mm) 0.02 0 038 0 035 N 7 14 11 Megalopa x (mm) 1.16 1.21 1.20 SD (mm) 0.049 0064 0001 N 4 3 4 '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, second maxilliped, (C> antennule, 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 L 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 on each side, pointing margin ending in short hook posteriorly posteriorly Zoea II Same as zoea I Same as in zoea I, but Same as in zoea I, but 8 setae on ventrolateral with pair of pleopod with pair of pleopod margin buds per somite buds per somite L 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 L erinacea Same as in zoea I, but with pair of pleopod buds per somite No setation on ventro- lateral margin L 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 with pair of pleopod lateral margin buds per somite buds per somite L emarginata Zoea I Single, long, slightly curved posteriorly Same as in L. dubia 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 N SV vs. SL' P 1 40.7 54.8 0.30 0.19 0.97 0.97 11 8 HL2 vs. SV P 1 -1.95 -1.02 0.29 0.28 0.95 0.98 15 15 Depth at pelvics vs. SV P 1 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 P 1 -0.39 5.16 0.20 0.20 0.92 0.97 15 15 Depth at caudal base vs. HL P 1 -0.13 0.65 0.02 0.03 0.95 0.78 11 8 Orbit diameter vs. HL P 1 0.05 0.09 0.40 0.36 0.97 0.98 14 15 Eye length vs. HL P 1 -0.52 -0.46 0.38 0.33 0.96 0.99 14 14 Snout vs. HL P 1 -1.19 -1.50 0.38 042 0.99 0.93 15 15 Maxillary length vs. HL P 1 0.65 0.44 0.37 0.38 0.99 0.99 15 15 Maxillary width vs. HL P 1 -2.27 -2.81 0.34 0.34 0.96 0.96 15 15 Interorbit vs. HL P 1 0.31 -0.56 0.23 0.26 0.96 0.71 13 15 Pectoral-pelvic origin vs. HL P 1 4.10 8.07 0.25 0.23 0.97 0.75 15 14 Pectoral length vs. HL P 1 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 4 5 Caudal rays 6 7 8 9 10 X D. polystictum D. lorum Species 1 1 23 5 8 1 9 1 Total pectoral rays 24 25 26 27 1 X 7.9 5.8 D. polystictum D. lorum 2 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 18 19 20 21 22 23 24 25 X O. polystictum 1 3 3 19.3 D. lorum 2 Preanal 6 9 2 2 22.8 Species 37 38 39 40 41 42 . 46 47 48 49 50 51 X D. polystictum 1 3 1 1 — 1 38.5 D. lorum 3 5 Total — 5 3 1 48.2 Species 71 72 73 74 . . . 106 107 108 109 110 X D. polystictum 4 2 1 71.7 D. lorum 2 — 2 2 2 108.5 850 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. z LU > 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 >- < < CO 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 75 >50 y>5of 50 75^ 50 J <£5( D \ 1 ^50^ oc — 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. Q in LU o 25 -i X C9 o X W 25 — | o en CO 20 — _i § 20- 19 < "3 15 — 13 I CD Z> 15 -z. u. o 10 o 2 5 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 Clemens, h. b. 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 D. L. Alverson (editors), The Columbia River estuary and 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« J I I I I I I I 1 T I t I T I T I I I | n-^^^t^1 LA «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 L D L D L D June 9-10 0 0 849 951 0 0 10-11 890 1.838 2,315 1,103 0 0 11-12 87 11 2,435 848 0 0 13-14 4 364 0 14 0 0 14-15 51 354 355 0 63 719 15 650 — 0 — 206 — Total 1,682 2,567 5,954 2,916 269 719 Periods called 5 4 4 4 2 1 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 0 ll||||||||||.|,...|.| ... V ■ .li-.a.i.. -H ■ - • i ^"^T 1 5 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 25 E E. i t— : 20 w 10 < < Q. • 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). LU LU 50 • 45 • • • 40 O o • • • • • • 35 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 5n CO o O 4 LU o to 3- F = . 9857 L 3 95S HOWEL L B KESL ER r - . 885 —i — i— i — | — i — i — i—i — | i i — i—i — | — i — i — i — i— | — i— i — i i | — i— i — n — pi 25 30 35 40 45 50 55 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- o 3- r =812 F » 2O550 A ' PITT (1971) 10 "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 5i CO CD O 4 fe ■ CO 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 2- 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 10 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 N genesis regression regression descence Jan. 5 0 0 60 40 Feb. 8 50 0 12 38 Mar. 12 75 0 8 17 Apr. 10 100 0 0 0 May 13 100 0 0 0 June 4 75 25 0 0 July 3 0 100 0 0 Aug. 6 0 0 100 0 Sept 7 0 0 100 0 Oct. 10 0 0 100 0 Dec. 7 14 0 14 72 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' — 25 100 Oct. 1974 Coho 1 + OMP 100.000 100 90 Oct. 1974 Coho 1 + OMP 100,000 100 76 Oct. 1974 Coho 1 + OMP 100,000 165 90 Oct. 1974 Chinook 0 + OMP 100,000 157 89 July 1975 Chinook 0 + OMP 50,000 250 90 Aug. 1975 Sockeye 1 + OMP 450 39 85 Sept 1975 Coho 1 + OMP 250 160 93 Nov. 1975 Coho 1 + OMP 164 164 85 Nov. 1975 Coho 1 + Dry2 9,000 600 0 Dec. 1975 Chinook 2 + OMP 40 40 0 Dec. 1975 Coho 2 + OMP 94 94 0 Dec. 1975 Coho 3 Natural 25 25 0 Dec 1975 Coho 1 + OMP 500 200 0 Jan. 1976 Coho 1 + SC3 400 40 0 Jan. 1976 Coho 1 + OMP 66,000 60 99 Oct. 1976 Coho 1 + OMP 1,600 120 75 Oct. 1976 Coho 0 + OMP 1,000 100 0 Oct. 1976 Coho 0 + OMP 4,000 180 38 Aug.-Oct. 1976 Coho 1 + Dry 100,000 + 114 37 Net pens: South Puget Sound Net pen: Central Puget Sound Net pen: Central Puget Sound Net pen: Central 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: 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 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 s n 10 5 10 5 15 10 5 " r^ rp K N DEC (43) AW, _2 8_S_ i r r~~A r~M f»./ T A, 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_ 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— 30 5*20 1-5 CD ~ < 10 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 43 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 i 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 91 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 23 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 703 703 415 561 465 405 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 INFORMATION FOR CONTRIBUTORS TO THE FISHERY BULLETIN Manuscripts submitted to the Fishery Bulletin will reach print faster if they conform to the following instructions. These are not absolute requirements, of course, but desiderata. CONTENT OF MANUSCRIPT The title page should give only the title of the paper, the author's name, his affiliation, and mailing address, including Zip code. The abstract should not exceed one double- spaced page. In the text, Fishery Bulletin style, for the most part, follows that of the U.S. Government Printing Office Style Manual. 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Quast, Scientific Editor Fishery Bulletin Northwest and Alaska Fisheries Center Auke Bay Laboratory, National Marine Fisheries Service, NOAA P.O. Box 155, Auke Bay, AK 99821 Fifty separates will be supplied to an author free of charge and 100 supplied to his organiza- tion. No covers will be supplied. 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