CAUFDRNIA
FBH-GAME

■ VOLUME 76

SUMMER 1990

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California Fish and Game is a journal devoted to the conservation and
understanding of fish and wildlife. If its contents are reproduced elsewhere,
the authors and the California Department of Fish and Game would appreciate
being acknowledged.

Subscriptions may be obtained at the rate of $10 per year by placing an
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Complimentary subscriptions are granted on an exchange basis.

Please direct correspondence to:

Robert N. Lea, Ph.D., Editor-in-Chief
California Fish and Game
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\i

VOLUME 76

SUMMER 1990

NUMBER 3

Published Quarterly by

STATE OF CALIFORNIA

THE RESOURCES AGENCY

DEPARTMENT OF FISH AND GAME

—LDA—

STATE OF CALIFORNIA
GEORGE DEUKMEJIAN, Governor

THE RESOURCES AGENCY
GORDON VAN VLECK, Secretary for Resources

FISH AND GAME COMMISSION

ROBERT A. BRYANT. Presider)t
Yuba City

JOHN A. MURDY III, Vice President E. M. McCRACKEN, JR., Member
Newport Beach Carmichael

ALBERT C. TAUCHER, Member BENJAMIN F. BIAGGINI, Member
Long Beach San Francisco

DEPARTMENT OF FISH AND GAME

PETE BONTADELLI, Director

1416 9th Street

Sacramento 98514

CALIFORNIA FISH AND GAME

Editorial Staff

Editorial staff for this issue:

Editor-in-Chief Robert N. Lea, Ph.D.

Editorial Assistant Lisa L. Smith

Inland Fisheries L. B. Boydstun

and Arthur C. Knutson, Jr.

Marine Resources Peter L. Haaker

and Paul N. Reilly

Sturgeon Donald E. Stevens

Wildlife Management Bruce E. Deuel

and Kent A. Smith

131
CONTENTS

Page

Blood Lead Concentrations in Mallards from Delevan and Colusa

National Wildlife Refuges David M. Mauser, Tonie E. Rocke,

John G. Mensik, and Christopher j. Brand 132

Virulence of Four Isolates of Infectious Hematopoietic Necrosis Virus
in Salmonid Fishes and Comparative Replication in Salmonid Fish

Cell Lines Martin F. Chen, Candace M. Aikens,

J. L. Fryer, and J. S. Rohovec 137

The Effects of Different Otolith Ageing Techniques on Estimates of

Growth and Mortality for the Splitnose Rockfish, Sebastes diploproa,

and Canary Rockfish, 5. pinniger Christopher D. Wilson and

George W. Boehlert 146

Crov^'th and Longevity of Golden Trout, Oncorhynchus aguabonita, in

their Native Streams Roland A. Knapp and

Tom L. Dudley 161

Comparison of Efficiency and Selectivity of Three Gears Used to
Sample White Sturgeon in a Columbia River

Reservoir John C. Elliott and

Raymond C. Beamesderfer 174

NOTES

Giant Bluefin Tuna off Southern California, with a New California Size

Record Terry J. Foreman and

Yoshio Ishizuka 181

Bobcat Electrocutions on Powerlines Richard D. Williams 187

BOOK REVIEWS 190

MISCELLANEA 192

132 CALIFORNIA FISH AND CAME

Calif. Fish and Came 76(3) : 1 32-1 36 1990

BLOOD LEAD CONCENTRATIONS IN MALLARDS FROM
DELEVAN AND COLUSA NATIONAL WILDLIFE REFUGES'

DAVID M. MAUSER^

Sacramento National Wildlife Refuge,

Rt. 1 Box 311,

Willows, California 95988

TONIE E. ROCKE

National Wildlife Health Research Center,

6006 Schroeder Rd.,

Madison, Wisconsin 53711

JOHN G. MENSIK

Sacramento National Wildlife Refuge

Rt. 1 Box 311,

Willows, California 95988

and

CHRISTOPHER J. BRAND

National Wildlife Health Research Center,

6006 Schroeder Rd.

Madison, Wisconsin 53711

Blood samples were taken from 181 (108 adult drakes and 73 individuals of mixed
age and sex) mallards. Anas platyrhynchos, from Colusa and Delevan National
Wildlife Refuges during late winter and summer of 1987. The percentage of birds
with elevated lead concentrations was 28.7 for late winter and 16.4 for late summer.
For summer trapped birds, a significantly greater proportion of males than females
contained elevated lead levels. These findings indicate that lead poisoning may be
a year-round event in certain areas of the Sacramento Valley.

INTRODUCTION

Lead poisoning in waterfowl, resulting from ingestion of lead shot, is an issue
that has polarized both biologists and the hunting public for many years. It is
one of the major diseases of wild waterfowl (Friend 1985) with annual losses
estimated to be as high as 2-3 percent of the continent's population (Bellrose
1959). Although large outbreaks have been documented, it is believed that most
losses occur as isolated cases (Sanderson and Bellrose 1986; NWHRC, unpubl.
data). Lead poisoning is usually a chronic, debilitating disease, requiring 3
weeks or longer from ingestion of lead shot to death. Epizootics become
apparent when local predators cannot consume sick and dead birds fast enough
to prevent a visible accumulation of sick or dead birds.

Most studies on lead pellet ingestion and lead poisoning mortality are
conducted during or just after the waterfowl hunting season (Bellrose 1959;
NWHRC, unpubl. data). Few studies have been conducted during the summer
or early fall. We provide information on blood lead concentrations in wild
mallards. Anas platyrhynchos, in California's Sacramento Valley during late
winter and summer.

' Accepted for publication March 1990.

■'Current address: Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon 97331

LEAD CONCENTRATIONS IN MALLARDS 133

STUDY AREA

Samples were collected at Delevan and Colusa National Wildlife Refuges
(NWRs), in Glenn and Colusa counties of California. Both refuges are part of
the Sacramento NWR complex and are administered by the U.S. Fish and
Wildlife Service. Delevan and Colusa NWRs are comprised of 2280 and 1635
ha, respectively, of seasonally-flooded marsh (60%), watergrass fields,
Echinochloa cruzgalli, (10%), permanent ponds (5-7%), rice (<2%) and
uplands (20%). Each area is managed primarily for fall migrant and wintering
waterfowl. Approximately 40% of each area is open to waterfowl hunting.
Non-toxic (steel) shot has been required since the fall of 1986.

METHODS

All birds used in the study were captured opportunistically and thus were not
a random sample of mallards from the study area. In addition, most birds
sampled were captured on previously hunted areas of the refuge (hunted since
1962).

During February 1987, 108 drake mallards were captured with baited funnel
traps. These birds were captured for use as sentinels in a study of botulism on
Sacramento NWR. Birds were bled within 24 hours of capture and placed in
holding pens where they were fed a combination of rice and scratch grains.
Pens were checked daily for sick and dead birds, and cause of death was
determined by necropsy and supporting diagnostic laboratory studies at the
U.S. Fish and Wildlife Service, National Wildlife Health Research Center
(NWHRC) Madison, Wisconsin.

Blood samples were similarly collected from 73 mallards of both sexes
trapped from July through early September, 1987. These birds were banded with
U.S. Fish and Wildlife Service leg bands, to insure that recaptured birds would
not be bled a second time and were immediately released.

Using 21 gauge needles and plastic syringes, blood samples (1.0-2.0 ml)
were drawn from the jugular vein of all birds, placed in heparinized glass tubes
and frozen for later analysis at NWHRC. Blood lead concentrations were
determined with a Perkin-Elmer HGA-400 graphite furnace coupled to a
Perkin-Elmer Model 2380 atomic absorption spectrophotometer set at a
wavelength of 283.3 nm (Fernandes and Hilligoss 1982). Blood lead concen-
trations of 0.2-0.5 ppm were considered to be elevated and > 0.5 ppm were
considered within the range known to be toxic to waterfowl (Friend 1985).
Lead poisoning diagnoses in sick and dead birds was based on pathology and
a toxic concentration of lead in liver ( > 8.0 ppm, wet weight) (Friend 1985).

For summer trapped birds, Chi square analysis was used to test for differences
in the numbers of males and females with elevated blood lead concentrations
( >0.2 ppm; age groupings were consolidated to yield cell expected values of
at least 5).

RESULTS

Of the 108 wild drake mallards captured in February, 15 (14%) had blood
lead concentrations greater than 0.5 ppm, 16(1 5% ) had concentrations ranging
from 0.2 to 0.5 ppm, and 77 (71%) were below 0.2 ppm (background
concentrations) . Within 20 days of capture, 1 2 birds had died, including 8 of 1 5

134 CALIFORNIA FISH AND CAME

birds (53%) that had blood lead concentrations exceeding 0.5 ppm when
initially captured; 2 of 16 birds (12%) with concentrations ranging fronn 0.2 to
0.5 ppm; and 2 of 71 birds (3%) below 0.2 ppm. Lead poisoning was diagnosed
as the cause of death in all 12 birds. Ten of the 12 lead poisoned birds had lead
pellets in their gizzards at the time of death ( ranging from 1 to 52 pellets ) . Two
of the 12 also had lesions associated with avian cholera, and Pasteurella
multocida was isolated from their livers. One additional death occurred from
among the 77 birds with background lead concentrations. Cause of death was
diagnosed as emaciation suspected as a result of parasitism by Echinuria
uncinata.

Of the 73 birds trapped during the summer, 12 (16%) had elevated or toxic
blood lead concentrations. Elevated concentrations were detected in 15% (2 of
13) of birds trapped in July, 11% (5 of 44) in August and 31% (5 of 16) in
September (Table 1 ). A significantly greater proportion of males than females
contained elevated concentrations of lead (X^ = 6.62, p <0.05) (Table 2).

TABLE 1. Distribution of Blood Lead Concentrations of 73 Mallards from Colusa and Delevan
National Wildlife Refuges Captured During July, August, and September 1987.

Percenitige of Totdl

Blood Lead Concentration July August September

Background

(<0.2ppm) 85(11) 89(39) 69(11)

Elevated

(0.2-0.5 ppm) 15(2) 9(4) 12(2)

Toxic

(>0.5ppm) 2(1) 19(3)

TABLE 2. Blood Lead Concentrations by Sex for 71 Mallards Captured During July, August and Sep-
tember 1987 on Colusa and Delevan NWRs

Percentage of Total

Blood Lead Concentration Males Females

Elevated

( > 0.2 ppm) 26 (8) 7(3)

Background

( < 0.2 ppm) 70 (19) 93 (41)

A significantly greater proportion of males had elevated lead concentrations than females
(X- = 6.62, p < 0.05).

DISCUSSION

The most sensitive method of determining lead exposure in live waterfowl Is
the measurement of blood lead concentrations (Anderson and Havera 1985).
Dieter (1979) demonstrated that signs of lead poisoning in canvasbacks, Aythya
valisineria, appeared at blood lead concentrations of 0.2 ppm. At lead
concentrations above 0.5 ppm, 12% of canvasbacks exhibited reduced activity
of delta-aminolevulinic acid dehydratase (ALAD), a key enzyme in the
hemoglobin biosynthetic pathway. Reduced ALAD activity in the brain causes
severe biochemical lesions and cerebellar damage (Dieter and Finley 1979).
The resulting motor disfunction coupled with other pathologic effects of lead
poisoning such as anemia, impaction, and tissue degeneration can eventually
lead to death.

Two male mallards trapped in late winter with background lead concentra-
tions ( <0.2 ppm) that later died of lead poisoning, could have ingested lead
pellets shortly before or on the day of capture. One lead pellet was found in the
gizzard of each bird at necropsy, and thus the lead was not yet detectable in the

LEAD CONCENTRATIONS IN MALLARDS I35

blood. The mortality rates of the birds held in captivity do not necessarily reflect
rates of lead poisoning mortally in free-ranging populations. Nonetheless, the
high lead exposure rate is indicative that lead poisoning is a problem to
waterfowl in these areas.

The percentage of adult male mallards trapped in September with elevated or
toxic blood lead concentrations (27%) was nearly as high as that of males
trapped in February (29%). This was unexpected because most cases of lead
poisoning are reported during the winter (Bellrose 1959; NWHRC, unpubl.
data). The availability of lead shot is thought to be correlated with the amount
of shot deposited on an area during the fall hunting season. However, the heavy
clay soils of the Sacramento NWR complex prevent lead pellets from settling
into the sediments. Thus, pellets are available to birds on these wetlands
year-round. High lead shot ingestion rates have been reported prior to hunting
season in other studies. Zwank et al. (1985) found that lead ingestion rates of
mallards and northern pintails. Anas acuta, were higher before, rather than after,
the hunting season on 2 waterfowl wintering areas in Louisiana. Lead pellet
ingestion and lead poisoning mortality rates were also higher in the fall rather
than in the winter in a study conducted at the Sacramento NWR using sentinel
mallards confined to a heavily hunted wetland (NWHRC, unpubl. data).
Moreover, lead poisoning in the summer and fall may not be easily observed
because summer resident populations are sparse, and sick birds or carcasses do
not persist for long in the environment.

The difference in proportions of males and females with elevated blood lead
concentrations could be due to differences in feeding habits. Male and female
mallards are known to molt at different times (Bellrose 1976). During August
and September, males have generally finished molting flight feathers, whereas
females are just entering the molt (adults only). These differences in physio-
logic condition associated with molt might affect their diet (Heitmeyer 1985).
Diets high in calcium and protein have been found to mitigate the effects of lead
shot ingestion (Sanderson and Bellrose 1986). In addition, females have been
shown to be less susceptible to lead poisoning during the breeding season.
Increased mobilization of calcium from bones for egg laying and a high
metabolic rate apparently decrease the absorption of lead (Finley and Dieter
1978).

Recent conversion to non-toxic shot will not result in immediate major
reductions of lead poisoning in certain habitats. The heavy clay soils of the
Sacramento Valley apparently reduce settling of lead shot into sediment beyond
the reach of feeding waterfowl. Surveys for pellets in wetland sediments at the
Sacramento NWR in 1987 revealed densities of up to 900,000 pellets per acre
in the top 10 cm (NWHRC, unpubl. data). Although the use of steel shot has
been enforced on the National Wildlife Refuges of the Sacramento Valley since
the fall of 1986, lead poisoning in waterfowl continues to be documented
(NWHRC, unpubl. data).

ACKNOWLEDGMENTS

Sincere thanks are extended to M. Smith, National Wildlife Health Research
Center for lead analysis, and E. Collins and P. O'Halloran for permission to
collect samples. F. Weekley, S. Shaeffer, C. Franson, L. Locke, and M. Friend
provided helpful editorial comments and H. Berg provided statistical advice.

136 CALIFORNIA FISH AND CAME

LITERATURE CITED

Anderson, W. L., and S. P. Havera. 1985. Blood lead, protoporphyrin, and ingested shot for detecting lead

poisoning in waterfowl. Wildl. Soc. Bull., 13:26-31.
Bellrose, F. C. 1959. Lead poisoning as a mortality factor in waterfowl populations. Illinois Nat. Hist. Surv. Bull.,

27:235-288.

. 1976. Ducks, geese and swans of North America. Stackpole Books. Harrisburg, Pa. 544 p.

Dieter, M. P. 1979. Blood delta-aminolevulinic acid dehydratase (ALAD) to monitor lead contamination in

canvasback ducks (Aythyd valisineria). Pages 177-191 in F. W. Nielson, G. Migaki, and D. C. Scarpelli, eds.

Animals as monitors of environmental pollutants. Natl. Acad. Sci. Washington, D.C., 421 p
and M. T. Finley. 1979. Delta-aminolevulinic acid dehydratase enzyme activity in blood, brain, and

liver of lead-dosed ducks. Environ. Res., 19:127-135.
Fernandes, F. )., and D. FHilligoss. 1982. An improved graphite furnace method for the determination of lead in

blood using matnx modification and the LVOV platform. Atomic Spectroscopy, 3:130-131.
Friend, M. 1985. Interpretation of criteria commonly used to determine lead poisoning problem areas. U.S. Fish

and Wildl. Serv., Fish and Wildl Leaflet no. 2, Washington, D.C. 4 p.
Sanderson, C. C, and F. C. Bellrose. 1986. A review of the problem of lead poisoning in waterfowl. Illinois Natural

FHistory Survey, Special Publication No. 4. 34 p.
Zwank, P. |., V. L. Wright, P. M. Shealy, and ). D. Newsom. 1985. Lead toxicosis in waterfowl on two major

wintering areas in Louisiana. Wildl. Soc. Bull., 13:17-26.

VIRUS IN SALMONID FISHES I37

Calif. Fish and Came 7b{T,): 137-145 1 990

VIRULENCE OF FOUR ISOLATES OF INFECTIOUS

HEMATOPOIETIC NECROSIS VIRUS IN SALMONID FISHES

AND COMPARATIVE REPLICATION IN

SALMONID FISH CELL LINES'

MARTIN F. CHEN 2

CANDACE M. AIKENS '

). L. FRYER"

AND

J. S. ROHOVEC

Department of Microbiology

Oregon State University, Corvallis, OR 97331-3804

The virulence of low-passage isolates of infectious hematopoietic necrosis virus
(IHNV) obtained from diverse geographic locations was compared in juvenile
Chinook, Oncorhynchus tshawytscha, sockeye (kokanee), O. nerka, and coho, O.
kisutch, salmon, and rainbow (steelhead) trout, O. mykiss. All isolates tested were
pathogenic for sockeye salmon and trout, but two isolates were comparatively
avirulent for chinook salmon. Hybrids of IHNV-resistant coho salmon and suscep-
tible trout appeared to be resistant; however, infection of coho salmon with IHNV
was demonstrated. The infectivity and replication of the IHNV isolates were
compared in cell lines derived from chinook, coho, and sockeye salmon. Infective
dose assays, growth curves, and efficiency of plaquing comparisons showed that the
host preference of IHNV isolates could be demonstrated at the cellular level.

INTRODUCTION

Infectious hematopoietic necrosis virus (IHNV) is a highly destructive
pathogen of juvenile salmonid fishes, while adult fish act as asymptomatic
carriers (Wingfield and Chan 1970). The virus affects different host species
throughout its range on the Pacific Coast of North America. In Alaska,
hatchery-reared sockeye salmon, Oncorhynchus nerka, have experienced
severe outbreaks (Grischowsky and Amend 1976). In California, chinook
salmon, O. tshawytscha, have been killed by the virus. (Wingfield and Chan
1970). Resident and anadromous (steelhead) rainbow trout, O. mykiss, are also
susceptible to IHNV, but coho salmon, O. kisutch, are considered resistant
(Pilcher and Fryer 1980).

in Oregon, epizootics of IHNV have occurred in juvenile steelhead trout at
the Round Butte Hatchery on the Deschutes River, juvenile chinook salmon
reared at the same facility have not been affected. However, outbreaks of IHNV
have occurred in juvenile chinook salmon reared at the Elk River Hatchery on
the Oregon coast (Mulcahy et al. 1980). We compared the virulence of virus
isolates from the Round Butte and the Elk River hatcheries, Oregon, and one
each from an Alaska and California hatchery to determine if the Elk River and
California isolates were unique in their ability to kill juvenile chinook salmon.

' Accepted for publication April 1990.

' Present address: California Departnnent of Fish and Came, Mohave River Hatchery, P.O. Box 938, Victorville,

CA 92393.
' Present address: Cascade Valley Hospital, 330 S. Stillaguamish St., Arlington, WA 98223.
'' To whom correspondence should be addressed.

138 CALIFORNIA FISH AND GAME

We also wished to determine if Round Butte chinook salmon were resistant to
IHNV from the four sample locations. The virulence of the four isolates was also
compared in sockeye salmon and rainbow trout. We found the difference in
virus epizootics at the Elk River and the Round Butte hatcheries was shown to
result from a difference in host preference of the two virus isolates found at
these two hatcheries. Round Butte chinook salmon were not more resistant to
the virus than the other chinook salmon stocks. Rainbow trout and sockeye
salmon were susceptible to all virus isolates tested. Juvenile coho salmon,
although demonstrating resistance, could be experimentally infected by IHNV.
Resistance to IHNV was also shown in F, hybrids of coho salmon X rainbow
trout.

Differences have been found in the infectivity of IHNV isolates for salmonid
cell lines (Phillipon-Fried 1980, Fendrick, Groberg, and Leong 1982). To
develop in vitro models of host-specific virulence, the replication of the four
IHNV isolates was compared in cell lines derived from chinook, coho, and
sockeye salmon. Differences among the isolates shown by the in vivo
experiments were also demonstrated in vitro by infective dose assays, growth
curves, and efficiency of plaquing.

MATERIALS AND METHODS
Cell Lines

Chinook, sockeye, and coho salmon embryo cells (CHSE-214, SSE-5, and
CSE-119, respectively, Lannan, Winton, and Fryer 1984) were used in this study.
Cells were grown in Eagle's minimum essential medium (MEM) buffered with
10 mM NaHC03, pH 7.8, supplemented with penicillin (100 lU/ml), strepto-
mycin (100 jLLg/ml) , and 5% fetal bovine serum (MEM-5). Growth of cells and
all incubations of infected cells were carried out at 16°C.

Viral Infectivity Assays

Endpoint dilution assays were performed as previously described (Hedrick,
Leong, and Fryer 1978). Titers were read after 14 d and expressed as the
number of tissue culture infective doses sufficient to infect 50% of inoculated
cultures per ml (TCID5o/ml).

Plaque assays were performed using methylcellulose overlays as previously
described (Hedrick and Fryer 1981 ). Titers were expressed as the average of
triplicate titrations.

Growth Curves

Duplicate, 2-d-old monolayers of CHSE-214 and CSE-119 cells in 25 cm^
flasks were infected with 10"* TCID50 virus in 0.2 ml. After absorption for 1 h,
unattached virus was removed with three washes of MEM, and 6 ml of MEM-5
was added to each flask. At various intervals, 0.1 ml of fluid was removed from
each flask, diluted in 1 ml MEM, centrifuged at 2000^ for 10 min and frozen
at — 70°C. Finally, samples were simultaneously titered by endpoint dilution
assay in CHSE-214 cells.

Viruses

Viruses were received as primary isolates. The Trinity River (TR), California,
chinook salmon isolate was obtained from W. H. Wingfield, California

VIRUS IN SALMONID FISHES 139

Department of Fish and Game, Rancho Cordova, CA. The Elk River (ER)
Chinook salmon isolate and the Round Butte (RB) steelhead trout isolate were
provided by W. J. Groberg, Jr., Oregon Department of Fish and Game and
Wildlife (ODFW), Corvallis, OR. An isolate from adult chinook salmon at
Mendenhall Ponds (MP), Alaska, was received from R. Saft, Alaska Department
of Fish and Game, Anchorage, AK. Second-passage virus produced in CHSE-214
cells were used to infect fish. Cell line infectivity assays and growth curves were
performed using third-passage virus stocks grown in CHSE-214 cells. Virus
harvests were centrifuged at 2000^, pooled, aliquoted and frozen at — 70°C
until used. Each pool was titered after thawing by endpoint dilution assay in
ChHSE-214 cells. Low-passage viruses were used in this study because attenua-
tion and host range adaptation of IHNV has occurred after prolonged serial
passage in cell culture (Fryer et al. 1976, Nims et al. 1970).

Fish

Juvenile fish, eggs, and semen of the four study species of salmonid fishes
were provided by the ODFW: chinook salmon from the Elk, Trask and Round
Butte hatcheries, sockeye salmon from the Wizard Falls Hatchery, steelhead
trout from the Round Butte Hatchery, coho salmon from the Sandy River
Hatchery, and rainbow trout from the Oak Springs Hatchery. The juvenile fish,
eggs, and semen were from adults found to be negative for IHNV at time of
spawning. Juvenile fish were obtained from large lots present in hatching
troughs or ponds. Fish were tested immediately after resorbtion of the yolk-sac,
because susceptibility to IHNV under experimental conditions declines rapidly
with age (Wingfield and Chan 1970). Coho salmon X rainbow trout hybrids
were produced by fertilizing eggs from a single rainbow trout with pooled coho
salmon sperm collected from 10 fish. Eggs from the same rainbow trout were
fertilized with pooled rainbow trout sperm from 10 fish and the pooled coho
salmon sperm was used with coho salmon eggs pooled from three fish to
produce normal rainbow trout and coho salmon, respectively. Production of
true coho salmon X rainbow trout hybrids was verified by liver isoenzyme
assay performed by G.A.E. Gall, Department of Animal Science, University of
California at Davis. All experiments involving live fish were conducted at 12°C
in pathogen-free well water.

Exposure of Fish to Virus

Dilutions of virus were prepared in MEM-5 to achieve concentrations of
10 ^-10^ TCID50 ml when virus was added to containers with 750 ml aerated
water. Each container held 20 juvenile chinook salmon or 30 of the smaller
steelhead trout or sockeye salmon. In each experiment, control fish were
exposed to MEM-5 without virus. After 12-h exposure, the contents of each jar
were placed into a separate 68-1 aquarium receiving single-pass water flowing at
a rate of 1 l/min. Fish were fed twice daily and observed for signs of IHNV
infection for 14 d. Dead or moribund fish were removed daily. The 50% lethal
concentration (LC 50) was calculated from the accumulated mortality according
to the method of Reed and Muench (1938); however, in cases where mortality
was insufficient to determine the LC50, an LC25was similarly calculated. At the
conclusion of each experiment at least 10 control fish were divided into pools
of five fish each and examined for virus as previously described ( Hetrick, Fryer,

140 CALIFORNIA FISH AND CAME

and Knittel 1979) to ensure that the fish were originally free of virus. Five dead
fish were pooled from each dilution series and examined for virus to verify that
virus was present in dead fish exposed to each isolate.

RESULTS
Virulence Testing

Juvenile chinook and sockeye salmon and steelhead trout were exposed to
second-passage TR, ER, RB and MP isolates to determine virulence of the
isolates in each species (Table 1 ). In all three chinook salmon stocks tested, the
TR and ER isolates were more virulent (lower LC,^) than the RB and MP
isolates, while the TR, RB and MP isolates were more virulent in the sockeye
salmon and steelhead trout groups. For the latter two species, the LCso's of TR,
RB, and MP isolates were similar, while the ER isolate was less virulent.
Although RB and MP isolates were virulent for sockeye salmon and steelhead
trout, they were comparatively avirulent for all three chinook salmon stocks.
Virus was recovered from dead or dying fish in each combination of virus
isolate and fish stock, except in the case of Elk River chinook salmon. No Elk
River chinook salmon died after exposure to RB or MP. Virus was not found in
control fish and mortality did not exceed 5% in any control fish group.

TABLE 1. Virulence of Four Isolates of Infectious Hematopoietic Necrosis Virus in Five Oregon Salmonid
stocks. Virulence is Measured by the Logm Virus Concentration (LC) Required to Produce 25%
or 50% Mortality Following a 12-h Exposure.

Virus Source
Fish tested Trinity Elk Round Mendenhall

(size)* River River Butte Ponds

(TR) (ER) (RB) (MP)

Log LC,,, in TCID,o/ml

Round Butte chinook (0.42) 3.3 4.0 5.0 4.8

Trask River chinook (0.54) 2.3 3.2 4.8 4.3

Elk River chinook (0.57) 2.1 4.2 > 5.0 > 5.0

Log LC.,„ in TCID rjm\

Round Butte steelhead (0.23) 2.8 3.5 2.7 2.7

Wizard Falls sockeye (0.18) , 2.4 2.9 2.2 2.0

• Average weight of fish In grams at time of exposure. Variation in weight stemmed from average size differences
at hatching.

Resistance of Coho Salmon-Rainbow Trout Hybrids

Groups of 10 each of coho salmon, rainbow trout, and coho salmon rainbow
trout hybrids were exposed to the TR isolate at concentrations of 10-10^
TCID^o/ml. The small number of fish used in this experiment was due to the
high prehatching and posthatching mortality (98%) of diploid coho salmon
rainbow trout hybrids. Coho salmon and coho salmon rainbow trout hybrids
were more resistant than rainbow trout (Table 2). Virus was recovered from
coho salmon, coho salmon X rainbow trout hybrids, and rainbow trout which
died during the 14-d exposure, and also from surviving coho and hybrid salmon.

VIRUS IN SALMONID FISHES 14]

TABLE 2. Mortality of Rainbow Trout, Coho Salmon, and Rainbow Trout x Coho Salmon Hybrids Ex-
posed to the Trinity River Isolate of Hematopoietic Necrosis Virus.

Mortalities/ W fish

Concentration

Mean
weight
Stock (g) 0' /(?"' 10 ■* 10^ LC,„'

Oak Springs rainbow trout 0.21 0 0 6 8 10''"

Sandy River coho salmon 0.35 0 0 0 6 10""

Coho X rainbow hybrid 0.19 1 1 0 3 lO'^"

■' Control fish were exposed to the virus dilutent, MEM-5.

''Concentration of Trinity River IHNV used in 12-h exposure, expressed in TCIDjo/ml.

' Median lethal concentration expressed in TCIDr,(,/ml.

Infective Dose Determination in Cell Lines

Third-passage virus isolates grown in CHSE-214 cells were titered by the
endpoint dilution assay in three salmonid cell lines to determine if the titer of an
individual isolate varied according to the cell line used (Table 3). The titer of
TR and ER isolates in SSE-5 cells was equal to or less than the titer in CHSE-214
cells. In contrast, the RB and MP isolates produced titers three-to twelve-fold
higher in SSE-5 cells than in CHSE-214 cells. Titers of TR and MP isolates were
much lower in CSE-119 cells than in the other cell lines. The virus-induced
cytopathic effect (CPE) in coho salmon cells was similar to that in the other cell
lines, but appeared 2-4 d later and often did not proceed to completion.

TABLE 3. Titer of Four Virus isolates Determined by Endpoint Dilution Assay in Cell lines Derived
from Chinook (CHSE), Sockeye (SSE), and Coho Salmon (CSE) Embryos.

Virus isolates by chinook salmon stock

Trinity I7J( Round Mendenhall

Cell line River (TR) River (ER) Butte (RB) Ponds (MP)

CHSE-214 lO""'" 10"^ 10'"' 10'"'

SSE-5 10"" lO'"'' 10"' 10'"

CSE-119 10'" nd'' nd 10" ■*

■' Virus titer expressed in TCIDr.o units/ml of undiluted stock virus.
'* nd = not done.

Growth Curves

Replication of IHNV in CSE-1 19 cells was indicated by the appearance of CPE
in the TCID50 assays. To confirm replication, the virus titer was determined after
infection of CSE-119 and CHSE-214 cells (Figure 1 ). An increased titer of virus
was detectable 1 d after infection in both flasks of CHSE-214 cells. Release of
virus from infected CSE-119 cells was demonstrated 2-4 d after inoculation of
virus. Virus titers increased to 10'' TCID5o/ml in both CHSE-214 cultures, but did
not reach 10'' TCIDso/ml in CSE-119 cells. The CPE in the CSE-119 cells did not
reach completion 12 d after inoculation of the virus. The TR isolate appeared to
be capable of only limited replication in coho salmon cells.

Efficiency of Plaguing in Cell Lines

The ratio of the titer in CHSE-214 and SSE-5 cells was determined as an index
of the relative plaguing efficiency of each isolate (Table 4). The CHSE-214:SSE-
5 ratio was 1:1.3 and 1:0.96 for TR and ER, respectively. Ratios for RB and MP
isolates were 1:7.4 and 1:2.8, respectively. Thus, the two isolates which were

142

CALIFORNIA FISH AND CAME

comparatively avirulent in chinook salmon, RB and MP, plaqued less efficiently
in chinook than in sockeye salmon cells, as compared to TR and ER. No clearly
definable plaques were observed when the four isolates were plaqued in coho
salmon cells (CSE-119).

8H

I-

o ■<

-I

3

2'

1>

8H

7-

P

O)

3
2

t

CHSE-214

CSE-119

A 6

Time (days)

10

— r
12

/

CHSE-214

CSE-119

— r-
6

10

12

Tlmo (days)

FICURE 1. Concentration in Log ,„ of infectious virus detected in the supernatant fluids of
CFHSE-214 and CSE-119 cell lines after infection with Trinity River infectious
hematopoietic necrosis virus. Each curve represents the titers determined in one of a
replicate pair of cell cultures.

TABLE 4. Efficiency of Plaquing of Four Virus Isolates in Cell Lines Derived from Chinook (CHSE)
and Sockeye Salmon (SSE) Embryos.

Virus isolate by source
Trinity
Cell line

Trinity

Elk

Round

Mendenhall

River

River

Butte

Ponds

6.2 X lO*'-'

5.3 X 10"

8.0 X 10 '

1.2 X 10'

8.2 X 10"

5.1 X 10"

5.9 X 10"

3.3 X 10'

1:1.3''

1 :0.96

1:7.4

1:2.8

CHSE-214 6.2 X 10 "

SSE-5

■' Virus titer in plaque forming units/ml averaged from three replicate flasks.
'' Ratio of titer in CHSE-214 cells:titer in SSE-5 cells.

DISCUSSION

The IHNV isolates examined in this study could be divided into two types:
those comparatively avirulent in chinook salmon (RB and MP), and those
virulent in chinook salmon, sockeye salmon, and steelhead trout (TR and ER).

VIRUS IN SALMONID FISHES "143

This grouping agrees with the natural occurrence of the disease in chinook
salmon at the sites of isolation. Although the Alaskan isolate (MP) was isolated
from chinook salmon and grown in chinook salmon cells, this isolate possessed
far less virulence for chinook salmon than TR or ER. Isolation of IHNV in
Alaskan chinook salmon is comparatively rare and may result from exposure to
heavily infected sockeye or chum salmon, O. keta (Follett, Thomas, and Hauk
1987). Species-specific virulence of IHNV has been previously reported. Virus
associated with naturally occurring sockeye salmon epizootics possessed little
virulence for chinook salmon experimentally exposed (Rucker et al. 1953,
Wingfield et al. 1970). In contrast, IHNV isolated from Sacramento River
chinook salmon (SRCV) was found to be pathogenic in chinook and sockeye
salmon and steelhead trout (Wingfield and Chan 1970). The TR virus may be
similar to SRCV because of its virulence for all species of fish tested. The ER
isolate was less virulent in sockeye salmon and steelhead trout than the TR.
Strains of IHNV with differing host specificities might act as different agents if
present in the same watershed. For this reason, transfer of fish even between
two areas where IHNV is present should be regarded with caution.

Wertheimer and Winton (1982) reported variation in susceptibility of
chinook salmon stocks to IHNV. Although some variation was found among the
three stocks of chinook salmon tested, the results indicated that the lack of
IHNV-caused mortality in chinook salmon reared at Round Butte Hatchery is a
result of host preference of that strain of virus, rather than an exceptional
resistance of Round Butte chinook salmon to IHNV.

Although coho salmon are considered resistant to IHNV, the virus has been
found in asymptomatic adult coho salmon at the Trinity River Hatchery
(LaPatra et al. 1987). Mortality has not been previously observed following
waterborne exposure of juvenile coho salmon to IHNV (Wingfield and Chan
1970, Wingfield et al. 1970). Injection of juvenile coho salmon with virus from
the Trinity River resulted in a 3% mortality in one study (Hedrick et al. 1987),
but no mortality was observed in other injection experiments (Watson,
Guenther, and Rucker 1954; Parisot and Pelnar 1962). The results here may
differ from previous studies because of different experimental conditions.
Susceptibility to IHNV decreases as the fish grow or the temperature rises
(Pilcher and Fryer 1980). We tested coho salmon at a temperature (12°C)
conducive to IHNV pathogenesis (Amend 1970). Although some mortality was
observed when coho salmon were exposed to very high virus concentrations
(10^ TCID5Q/ml), the coho salmon were more resistant than the rainbow trout.
Further studies using larger sample sizes should be done to confirm that IHNV
can cause disease or mortality in young coho salmon. The TR isolate should be
included in such a study since all reports of virus isolation and mortality in coho
salmon have involved virus from the Trinity River system.

Resistance to IHNV was apparently transferred to rainbow trout eggs by coho
salmon sperm. The use of pooled rainbow trout sperm, pooled coho salmon
sperm, and eggs from one rainbow trout female in this study indicates that the
difference in mortality between rainbow trout and coho salmon x rainbow trout
hybrids was not due to between-family variation. The transfer of IHNV
resistance by coho salmon sperm was also demonstrated by Parsons et al.
(1986) using triploid coho salmon x rainbow trout hybrids. Ord et al. (1976)
conferred resistance to viral hemorrhagic septicemia by fertilizing eggs of

144 CALIFORNIA FISH AND CAME

susceptible rainbow trout with coho salmon sperm. Similarly, the susceptibility
of sockeye salmon to IHNV was decreased by fertilization with sperm from
more resistant sockeye salmon (Mclntyre and Amend 1978). In contrast, coho
salmon sperm did not confer resistance to injected IHNV in coho salmon x
Chinook salmon hybrids, nor were chinook salmon male x coho salmon female
hybrids resistant to injected IHNV (Hedrick et al. 1987). Further studies are
needed to better define the nature of the resistance factor, and the effects of
waterborne or injected virus exposure on hybrid salmonids. Also, future studies
with hybrids should use multiple family groups (Amend and Nelson 1977).
Another possible problem in our hybrid study was that different sizes of fish
were used in the exposure experiments. The fish hatched at different sizes due
to the smaller size of the rainbow trout eggs. Smaller fish are more susceptible
to IHNV than larger ones, as previously noted. We chose to test all species at
a similar stage of maturity: the time of initial feeding.

Evidence for two virulence groups was also found when the four virus isolates
were used to infect salmonid cell lines. The titer of RB and MP was lower in
chinook than sockeye salmon cells in both plaque and endpoint dilution assays,
but TR and ER showed similar titers in cell lines from the two species. Species
specificity was also reported by Nims, Fryer and Pitcher (1970), who found that
a sockeye salmon cell line produced 10-^ — 10^ times more virus than a chinook
salmon cell line after infection by an IHNV isolate from sockeye salmon. Host
specificity of IHNV should be considered in the selection of cell lines for
diagnostic purposes. In areas where the virus is endemic in sockeye salmon or
steelhead trout, the use of CHSE-214 cells may result in reduced chances of
detection of virus. Still, the SSE-5 cell line was highly susceptible to the four
isolates studied.

Wingfield et al. (1970) found no increase in IHNV titer in CSE-119 cells
exposed to an isolate from sockeye salmon, but we found virus titer increased
after CSE-119 cells were inoculated with TR. Some of this increase may have
been due to absorbed virus releasing from the cell surface, but the appearance
of CPE indicates true replication did occur. Possible reasons for the contrasting
results may be in the use of the virulent TR isolate, or that the age of cell
monolayers and temperature of incubation were lower in the present study. No
IHNV plaques were observed by Phillipon-Fried (1980) in CSE-119 cells. We
obtained similar results when the four IHNV isolates were inoculated in CSE-1 19
cells. The limited replication and incomplete CPE seen in infected coho salmon
cells may explain the low mortality in coho salmon experimentally exposed to
IHNV. The relative resistance of CSE-119 cells suggests that the resistance of
coho salmon is in part determined at the cellular level.

ACKNOWLEDGMENTS

This research was supported by the Oregon Department of Fish and Wildlife
under Public Law 89304, Anadromous Fish Act, and also appears as Oregon
Agriculture Experiment Station Technical Paper No. 7956.

LITERATURE CITED

Amend, D. F. 1970. Control of infectious hematopoietic necrosis virus disease by elevating the water temperature.
). Fish. Res. Bd. Canada, 27:265-270.

VIRUS IN SALMONID FISHES 145

Amend, D. F., and ). R. Nelson 1977. Infectious hematopoietic necrosis: variation in susceptibility of sockeye
salmon (Oncorhynchus nerka) to disease. ). Fish. Biol., 11 (6):567-573.

Fendrick, |. L., W. |. Groberg, Jr., and |. C. Leong. 1982. Comparative sensitivity of five fish cell lines to wild type
infectious haemotopoietic necrosis virus from two Oregon sources. J. Fish Dis., 5:87-95.

Follett, ). E., ). B. Thomas, and A. K. Hauck. 1987. Infectious haemotopoietic necrosis virus in moribund and dead
juvenile chum Oncorhynchus keta (Walbaum), and chinook, O. tshawytscha (Walbaum), salmon and
spawning adult chum salmon at an Alaskan hatchery, j. Fish Dis., 10:309-313.

Fryer, J. L., J. S. Rohovec, C. L. Tebbit, J. S. McMichael, and K. S. Pilcher. 1976. Vaccination for control of
infectious diseases in Pacific salmon. Fish Pathol., 10:155-164.

Crischowsky, R. S., and D. F. Amend. 1976. Infectious hematopoietic necrosis virus: prevalence in certain Alaskan

sockeye salmon, Oncorhynchus nerka. ). Fish. Res. Bd. Canada, 33:186-188.
F^edrick, R. P., J. C. Leong, and J. L. Fryer. 1978. Persistent infections in salmonid fish cells with infectious

pancreatic necrosis virus (IPNV). ). Fish Dis., 1:297-308.

Hedrick, R. P., and J. L. Fryer. 1981. Persistent infection of three salmonid cell lines with infectious pancreatic
necrosis virus (IPNV). Fish Pathol., 15:163-172.

Hedrick, R. P., S. E. LaPatra, ). L. Fryer, T. McDowell, and W. H. Wingfield. 1987. Susceptibility of coho
Oncorhynchus kisutch and chinook Oncorhynchus tshawytscha salmon hybrids to experimental infections
with infectious hematopoietic necrosis virus (IHNV). Eur. Ass. Fish Pathol., Bull., 7:97.

FHetrick, F. M., j. L. Fryer, and M. D. Knittel. 1979. Effect of water temperature on the infection of rainbow trout
5<3/mo ^<?//'c//7er/ Richardson with infectious hematopoietic necrosis virus. J. Fish Dis., 2:253-257.

Lannan, C. N., J. R. Winton, and ). L. Fryer. 1984. Fish cell lines: establishment and characterization of nine cell
lines from salmonids. In Vitro., 20:671-676.

LaPatra, S. E., ). L. Fryer, W. Wingfield, and R. P. Hedrick. 1987. Transmission of infectious hematopoietic necrosis
virus (IHNV) between adult species of salmon: management strategies for anadromous broodstock. Fish
Health Section, Am. Fish. Soc. Newsletter, 15(2):7.

Mclntyre, J. D., and D. F. Amend. 1978. Heritability of tolerance for infectious hematopoietic necrosis in sockeye
salmon Oncorhynchus nerka. Am. Fish. Soc, Trans., 107:305-308.

Mulcahy, D. M., G. L. Tebbitt, W. ). Groberg, Jr., ). S. McMichael, |. R. Winton, R. P. Hedrick, M. Philippon-Fried,
K. S. Pilcher, and ). L. Fryer. 1980. The occurrence and distribution of salmonid viruses in Oregon. Oregon
State University Sea Grant College Program, Corvallis, ORESU-T-80-004:1-71.

Nims, L., J. L. Fryer, and K. S. Pilcher. 1970. Studies of replication of four selected viruses in two cell lines from
salmonid fish. Proc. Soc. Exp. Biol. Med., 135:6-12.

Ord, W. M., M. LeBerre, and P. de Kinkelin. 1976. Viral hemorrhagic septicemia: comparative susceptibility of
rainbow trout Salmo gairdneri and hybrids 5. gairdneri x Oncorhynchus kisutch to experimental infection. J.
Fish. Res. Board Canada, 33:1205-1208.

Parsons, J. E., R. A. Busch, G. H. Thorgaard, and P. D. Sheerer. 1986. Increased resistance of triploid rainbow trout
x coho salmon hybrids to infectious hematopoietic necrosis virus. Aquaculture, 57:337-343.

Parisot, T. J., and j. Pelnar. 1962. An interim report on Sacramento River chinook disease: a virus-like disease of
chinook salmon. Prog. Fish Cult., 24:51-55.

Phillipon-Fried, M. 1980. Partial characterization of six established salmonid cell lines. M.S. Thesis. Oregon State
University, Corvallis. 58 p.

Pilcher, K. S. and ). L. Fryer. 1980. The viral diseases of fish: a review through 1978, part I: diseases of proven
etiology. Crit. Rev. Microbiol., 7:287-364.

Reed, L. J. and H. Muench. 1938. A simple method of estimating fifty percent endpoints. Am. j. Hygiene,
27:493-497.

Rucker, R. R., W. J. Whipple, J. R. Parvin, and C. A. Evans. 1953. A contagious disease of salmon possibly of virus
origin. U.S. Fish Wildl. Serv. Fish. Bull., 54:35^6.

Watson, S. W., R. W. Guenther, and R. R. Rucker. 1954. A virus disease of sockeye salmon: interim report. U.S.
Fish Wildl. Serv. Spec. Sci. Rep., 138:1-36.

Wertheimer, A. D., and J. R. Winton. 1982. Difference in susceptibility among three stocks of chinook salmon,
Oncorhynchus tshawytscha, to two isolates of infectious hematopoietic necrosis virus. NOAA Tech. Memo.,
Nat. Mar. Fish. Serv., F/NWC-22:1-11.

Wingfield, W H., and L. D. Chan. 1970. Studies on the Sacramento River chinook disease and its causative agent.
in S.F. Snieszko (ed.), A symposium on diseases of fishes and shellfishes. Am. Fish Soc. Spec. Publ.
Washington, D.C., 5:307-318.

Wingfield, W. H., L. Nims, ). L. Fryer, and K. S. Pilcher. 1970. Species specificity of the sockeye salmon virus
(Oregon strain) and its cytopathic effects in salmonid cell lines, in S.F. Snieszko (ed.), A symposium on
diseases of fishes and shellfishes. Am. Fish. Soc. Spec. Pub. Washington, D.C., 5:319-326.

146 CALIFORNIA FISH AND CAME

Calif. Fish and Game 76 ( 3 ): 1 46- 1 60 1 990

THE EFFECTS OF DIFFERENT OTOLITH AGEING

TECHNIQUES ON ESTIMATES OF GROWTH AND

MORTALITY FOR THE SPLITNOSE ROCKFISH, SEBASTES

DIPLOPROA, AND CANARY ROCKFISH, 5. PINNIGER

CHRISTOPHER D. WILSON '

Department of Fisheries and Wildlife

Oregon State University, Corvallis, OR 97331

and

GEORGE W. BOEHLERT

Southwest Fisheries Center Honolulu Laboratory

National Marine Fisheries Service, NOAA

2570 Dole St., Honolulu, HI 96822-23%

and Joint Institute of Marine

and Atmospheric Research,

University of Hawaii, Honolulu, HI 96822

Different ageing techniques affect not only the estimates of length at age but also
estimates of population growth and mortality rates. This study considers these
effects for the splitnose rockfish, Sebastes diploproa, and canary rockfish, S.
pinniger, based on ages determined from the surfaces and sections of otoliths
collected during a trawl survey off the west coast of North America in 1980.
Estimates of growth based on surface rather than section ages were nearly identical
for S. diploproa but were higher for S. pinniger; slightly different whole otolith
ageing techniques are suspected of producing these interspecific differences. For
both species, however, estimates of mortality were reduced by more than half when
section rather than surface ages were used.

INTRODUCTION

Ages of fish are needed to estimate two vital parameters of exploited fish
populations, namely growth and mortality rates. Many fish species typically are
aged by interpreting rings on the otolith, as is the case for rockfishes (Sebastes)
for which the otolith is the preferred ageing structure (Six and Norton 1977,
Chilton and Beamish 1982). Various techniques have been developed to
facilitate the detection and the interpretation of otolith patterns used in age
determination (Chilton and Beamish 1982). Two methods to determine ages
are counting the number of rings or annuli viewed on the exterior of the whole
otolith (surface ages) or on a lateral cross section of the otolith (section ages).
Section ages are often greater than surface ages for older specimens of many
long-lived, slow-growing species (Beamish 1979a, 1979b, Boehlert and Yoklav-
ich 1984), and recent evidence demonstrates that the section ages represent the
true ages of fish (Bennett et al. 1982, Leaman and Nagtegaal 1987, Campana et
al. in press).

Because present evidence supports the validity of section ages for older fish,
important biological and management implications could result if many
demersal fish stocks are underaged due to the more common surface ageing

Accepted for publication April 1990.

Present Address: Southwest Fisheries Center Honolulu Laboratory, National Marine Fisheries Service, NOAA,
Honolulu, HI and Department of Oceanography, Uniyersity of Hawaii, 1000 Pope Road, Honolulu, HI 96822.

ROCKFISH AGEING TECHNIQUES 147

technique. Archibald et al. (1981) found that estimates of instantaneous
mortality (Z) were reduced by as much as 50% when the otolith sections were
used to age 10 species of rockfishes. Even for fishes that are not long lived, age
length data without older fish affect the estimation of von Bertalanffy growth
parameters (Hirschhorn 1974). Because population size, growth, and mortality
are the basic data required for most production modeling, systematic bias in age
determination may lead to serious errors in determining stock production
estimates (Le Cren 1974). In the present study, we determine whether
significant differences in the estimates of growth and mortality rates are affected
by the method of otolith age determination for two species of Sebastes — the
splitnose rockfish, 5. diploproa, and canary rockfish, 5. pinniger.

MATERIALS AND METHODS

Otoliths from 5. diploproa and 5. pinniger were collected during a 1980 trawl
survey conducted off the west coast of North America (lat 36° 49' to 50° OO'N).
Gear, sampling design, and catch processing generally followed the procedures
in Dark et al. (1983). Several differences in the collection and care of otoliths
have been described by Boehlert and Yoklavich (1984). Otoliths used in the
present study were initially collected for other work; therefore, fish comprising
the age subsample were systematically chosen until a predetermined number
for each size class was attained. When mortality rates were estimated in the
present study, the original age subsample was applied to a simple random
sample of length-frequency data to remove any potential sampling bias (Dark
1975) which may have been introduced during sample collection.

The length-frequency data were chosen for each species in the following
manner. For 5. pinniger, the limited length-frequency data from the 1980 survey
were combined with length-frequency data collected in 1980 by the Washing-
ton Department of Fisheries and the Oregon Department of Fish and Wildlife.
For 5. diploproa, the length-frequency sample was restricted to fish from lat 40°
26' to 48° 47' N, where 76% of the fish in the age sample were collected. This
was done because Boehlert and Kappenman (1980) detected increases in
growth rate with latitude for 5. diploproa when specimens were compared from
this and two other geographic regions (i.e., lat 34°-37°, 37°-40°, 40°-48° N).
Thus, all 5. diploproa otoliths were analyzed as a single stock, even though 24%
were collected south of 40° N, in order that the effects of using surface versus
section ages could be evaluated with as large an age sample as possible.
Resulting growth curves would most likely represent fish from the northernmost
strata (40°^8° N) described by Boehlert and Kappenman (1980).

Ageing

Ages were determined from the same whole and sectioned left sagittal otolith
of 5. diploproa and 5. pinniger by one of three readers from the same
laboratory. The variability in ageing the otolith data set within and between
readers is presented in Boehlert and Yoklavich (1984). Surface ages for both
species were derived from whole otoliths by the method of Boehlert and
Yoklavich (1984). The otolith was read from the focus to the dorsal edge or, in
the case of older individuals, from the focus to the posterodorsal region (Figure
1A, IB). Otoliths from many older specimens, particularly 5. diploproa, possess
posterior projections. Pairs of translucent and opaque bands in these regions

■|48 CALIFORNIA FISH AND CAME

were included in the counts for 5. diploproa but not for S. pinniger;
methodology for the latter species follows the general technique in Six and
Norton (1977).

FICURE 1. External surface of the whole otolith from (A) a 32 cm fork length (FL) female Sebastes
diploproa with a surface age of 22 years and a section age of 25 years, and (B) a 52 cm FL
male 5. pinniger with a surface age of 18 years and a section age of 19 years. (C) anterior,
(D) dorsal, (F) focus, (P) posterior, (V) ventral, (W) posterior projection.

Dorsoventral otolith sections (0.4 mm thick; Figure 2) were obtained with a
double-bladed diamond saw; each section was mounted on a microscope slide
and polished to remove surface artifacts (Nichy 1977, Boehlert 1985). The
otolith section was read (30X or 100X) from the focus to the dorsal edge. For
older individuals, the reader began counting toward the dorsal tip, then
followed a distinct ring from the dorsal region of the section into the internal
dorsal quadrant and continued counting towards the section edge (Figure 2).

In many species of rockfishes, surface and section ages tend to agree for
younger individuals (Beamish 1979b, Shaw and Archibald 1981, Boehlert and
Yoklavich 1984). For example, C. Boehlert and M. Yoklavich (unpub. data)
systematically subsampled every fourth otolith pair from 5. diploproa and every
third otolith pair from 5. pinniger used in this study and found mean differences
between surface and section ages of < 2 years for 5. diploproa females aged
< 1 2 and males < 1 7 years and 5. pinniger females < 7 and males < 8 years. For
this reason, we assigned a section age equal to the surface age for all remaining
otoliths with surface ages less than or equal to the values listed above. Thus, an
otolith from an 5. pinniger male with a surface age of 6 years was given a section
age of 6 years if the otolith had not been included earlier in the subsample. This
procedure allowed an increased sample size.

ROCKFISH AGEING TECHNIQUES 149

FIGURE 2. Dorsoventral cross section of the left otolith from a 31 cm fork length (PL) Sebastes
diploproa with a surface age of 28 years and a section age of 39 years. (D) dorsal, (F)
focus, (E) external surface, (I) internal surface, (V) ventral. Surface ages were
determined by counting rings on the external side of the otolith from the focus
towards the dorsal edge.

Mortality and Growth Rates

Total instantaneous mortality rates (Z) were estimated by calculating the
slope of the descending right side of the age-frequency distribution (catch
curve) by simple linear regression (Ricker 1975). Total instantaneous mortality
rates were compared by using an f-test (Meter and Wasserman 1974).

Individual length at age data were fit to the von Bertalanffy growth model
(Ricker 1975) by a nonlinear regression routine (Dixon 1981 ). Von Bertalanffy
growth curves were compared by using the chi-square test for homogeneity of
individual parameters (Rao 1973) and by the method developed by Gallucci
and Quinn (1979) in which the von Bertalanffy growth function is reparame-
terized with the introduction of a new parameter (w). Results of all statistical
tests were considered significant at P < 0.05.

RESULTS
Sebastes pinniger

Otoliths were collected from a total of 363 female and 516 male S. pinniger
specimens between latitudes 43° 11' and 49° 16' N. Females had maximum
surface ages to 22 years and section ages to 34 years (Table 1). Differences
between the two methods were greater for males; maximum surface and
section ages were 25 and 60 years, respectively (Table 1 ).

Fitted growth curves for males based on each ageing method are more similar
than growth curves for females. Estimates of Loo for both sexes based on
surface ages significantly exceeded those based on section ages (by nearly 6 cm
fork length (fl) for females and 4 cm fl for males, Figure 3). The difference in
growth estimates between treatments apparently occurs beyond the region of
the curve where statistical tests on cu are most powerful (Gulland 1983).

150 CALIFORNIA FISH AND GAME

TABLE 1. Mean Fork Lengths at Age (FL in Centimeters) and Standard Deviation (SD) for Female

and Male Sebastes pinniger Based on Surface and Section Ages. S Indicates the Number of
Otoliths.

Surface Section

Age

1

2

3

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

33 — — — — —

34 — — — 1 50.00

Males

2 3 16.00 1.73 2

3 5 21.80 1.30 4

4 3 25.00 3.61 4

5 4 35.25 4.92 3

6 3 35.33 1.53 6

7 20 38.70 3.63 13

8 24 40.42 2.47 22

9 18 43.61 3.45 9

10 29 45.24 2.89 18

11 42 47.00 2.85 20

12 70 48.49 1.85 35

13 69 49.59 2.02 28

14 55 50.22 1.90 22

15 47 51.55 1.77 23

16 52 51.79 2.05 13

17 25 52.84 1.65 23

18 24 53.46 1.82 24

19 9 53.33 1.32 27

20 6 53.67 2.25 27

21 3 53.33 0.58 27

22 4 54.25 0.96 22

23 _ _ _ 12

24 — _ — 12

25 1 57.00 — 12

N

FL

SD

Females

N

FL

SD

4

15.50

0.58

3

15.67

0.58

—

—

—

1

15.00

—

3

30.00

4.36

3

30.00

4.36

4

31.75

0.50

2

32.00

—

11

37.27

3.55

8

36.38

3.50

6

37.67

1.86

5

36.80

3.70

18

41.28

2.70

9

41.00

7.63

13

44.08

4.52

16

43.50

3.20

18

46.11

3.43

20

46.10

3.65

37

49.27

2.91

28

46.71

4.47

64

49.92

2.69

50

49.50

3.70

57

52.23

2.49

47

50.64

3.59

38

53.97

2.83

34

52.53

2.26

33

54.48

2.58

18

52.22

3.14

23

55.52

2.13

21

53.90

3.06

14

56.00

1.84

16

54.06

2.64

15

57.00

1.60

13

55.46

2.96

2

59.50

2.12

15

54.80

2.51

2

61.50

3.54

11

55.00

1.73

—

—

—

6

53.83

2.64

1

59.00

—

4

54.75

1.71

—

—

—

8

56.38

2.39

—

—

—

5

57.20

2.49

—

—

—

5

56.60

2.19

—

—

—

5

57.40

6.07

—

—

—

4

57.00

4.83

—

—

—

1

50.00

—

—

—

—

3

58.33

1.15

—

—

—

1

58.00

—

15.50

2.12

20.25

2.50

24.25

3.30

33.00

8.72

34.17

3.31

39.31

3.86

40.36

2.61

43.78

3.03

43.06

4.08

45.05

3.75

47.09

2.73

47.79

2.77

47.45

3.69

47.83

2.37

50.46

2.26

49.13

1.89

50.71

1.90

49.89

1.97

50.48

2.59

51.33

2.11

50.32

2.06

51.50

1.83

50.42

1.83

50.58

3.68

(Conti

nued)

ROCKFISH AGEING TECHNIQUES 151

TABLE 1— Continued

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 — — — 1 56.00

57 — — — — —

58 — — — — —

59 — — — 1 55.00

60 — — — 1 56.00

14

52.07

2.23

8

52.50

2.14

7

52.14

2.34

2

51.00

1.41

5

52.60

1.82

10

52.30

2.63

3

51.67

0.58

8

52.50

1.85

3

54.00

1.00

6

52.83

1.17

3

54.33

4.62

2

52.50

2.12

10

52.80

1.99

1

52.00

—

6

52.67

1.86

2

54.00

1.41

2

53.50

0.71

1

53.00

—

1

52.00

—

4

53.25

1.89

1

50.00

—

1

48.00

—

1

52.00

—

2

52.00

1.41

1

53.00

1

53.00

Catch curves constructed from surface and section ages of 5. pinniger dearly
differed (Figure 4). Regardless of the ageing technique used, however, both
sexes were fully recruited to the fishery by age 12. Estimates of Z derived from
surface and section ages significantly differed for both sexes: Z values estimated
from section ages were 61% less for females and 78% less for males than those
calculated from surface ages (Table 2).

152

CALIFORNIA FISH AND GAME

0
0
0
0
0
0
0
0

K

K

to

U)

Surface

63.40

0.13

0.46

8.09

Section

57.70

0.16

0.14

9.37

363

10

20

30 40

Age (years)

50

60

FIGURE 3. Fitted von Bertalanffy growth curves, parameter estimates (see text for explanation),
and mean lengths at age based on surface (closed circles) and section ages (open
circles) of otoliths from (A) female and (B) male Sebastes pinniger. Points
representing single individuals are not shown. N indicates sample size.

ROCKFISH AGEING TECHNIQUES

153

E

3
Z

•

o

A

A

//, V , ,

/v

B

/\.

A

C

/ , , , , lA , . . ,

/'^'"K. ,

D

/ —

H{\hA

10

20 30

40

SO 60

Age (years)

FIGURE 4. Catch curves based on (A, C) surface and (B, D) section ages of otoliths from (A,
B) female and (C, D) ma\e Seb^stes pinniger.

Sebastes diploproa

Otoliths from 1,131 female and 922 male 5. diploproa were collected
between lat 36° 49' and 48° 47' N. Both sexes of 5. diploproa reached much
greater ages than those attained by 5. pinniger. Female 5. diploproa attained
ages similar to males and had surface ages to 55 years and section ages to 81
years compared with 46 and 84 years, respectively, for males (Table 3). Growth
curves of either sex based on surface and section ages were essentially identical,
and parameter estimates and co were not significantly different (Figure 5).

Catch curves constructed from surface and section ages of 5. diploproa
clearly differed (Figure 6). In all cases, particularly among females, substantial
variation occurred between year classes, with a succession of weak year classes
between ages 10 and 20. Therefore, Z was determined for fish older than 21
years. As with 5. pinniger, significant differences were found between estimates
of Z derived from surface and section ages for both sexes; estimates based on
section ages were 55% less for females and 76% less for males than those based
on surface ages (Table 2).

154

CALIFORNIA FISH AND CAME

TABLE 2. Estimates of Total Instantaneous Mortality (Z) for Sebssles pinniger and 5. diploproa.
Range Indicates Ages Over Which Z Was Determined.

Surface Section

Sex Z Range Z Range

Sebasles pinniger

Female 0.452 12-22 0.178 12-34

Male 0.405 12-25 0.089 12-60

5. diploproa

Female 0.109 25-48 0 049 22-71

Male 0.130 23-40 0.031 26-75

50
40
30
20

101-

0
50

•

A

*^

^^j^^Sotio

f .-p^7QA^03:^rQrft^o„

o

■e^^"'" o

/

I^ K t.

u

f

Surface

34.54 0.10 -4.34

3.39

Section

34.08 0.10 -4.45

3.37

.... 1

... 1 .... 1 . ,

n = 1131

.. 1 .... 1 .... 1 .... 1

... 1 ... .

40

B

r^^^^

^^J*'^

-^

TT-O

K

K

t.

w

Surface

30.00

0

16

-1.97

4.79

Section

29.87

n

0

16
922

-2.01

4.75

I ■ ■

I ■■ ■ ■ I .... I .... I

10

20

30

40

50

60

70

80

Age (years)

90

FIGURE 5. Fitted von Bertalanffy growth curves, parameter estimates (see text for explanation),
and mean lengths at age based on surface (closed circles) and section ages (open
circles) of otoliths from (A) female and (B) male Sebastes diploproa. Points
representing single individuals are not shown. N indicates sample size.

ROCKFISH AGEING TECHNIQUES

155

10 20 30 40 50 60 70 80

FIGURE 6.

Age (years)

Catch curves based on (A, C) surface and (B, D) section ages of otoliths fronn (A,
B) female and (C, D) male Sebastes diploproa.

DISCUSSION
Differences in Growth

The effects of changing the methodology of fish age determination can vary
from a minor error to major differences. Estimates of maximum age in the genus
Sebastes have changed markedly in recent years (Beamish 1979b; Bennett et al.
1982; Leaman and Nagtegaal 1987); thus, one would expect similarly remark-
able differences in estimates of growth within a species. For 5. pinniger,
estimates of the Loo were significantly lower when section rather than surface
ages were used although the increase in the growth completion rate (von
Bertalanffy's k) for both sexes (Figure 3) was not significant. Therefore, when
surface ages are used, errors in ageing incorrectly place older, larger individuals
into younger age groups, thus inflating their mean lengths at age (Wilson 1985).
This results in lower mean lengths at age for many of these section age groups
relative to surface age groups, and a corresponding decrease in Loo based on
section ages.

Another explanation to account for the differences between growth curves
constructed from surface and section ages in 5. pinniger is that a curve fitting
problem occurs, particularly for females. Thus, Loo may be overestimated when
data are available for only the ascending limb of the von Bertalanffy growth
function (Knight 1968, Gallucci and Quinn 1979, Vaughan and Kanciruk 1982).
Note that the estimate of Loo is typically greater than the maximum observed
length in our study (Table 1, Figure 3). Because surface ages have a lower range
than section ages and are more concentrated on the ascending limb of the
growth curve, they may fail to adequately estimate the upper portion of the

156 CALIFORNIA FISH AND GAME

curve, which represents Loo. For example, the large differences between
estimates of L oc for female 5. pinniger may occur because their surface ages are
more concentrated on the ascending portion of the curve than are those of
males (Table 1). This situation is analogous to fitting growth curves with
incomplete representation of the range of ages (Hirschhorn 1974).

Unexpected results of our study were the similarities in estimated growth
parameters for 5. diploproa based upon section and surface ages (Figure 5)
despite the much higher maximum section ages (Table 3). This difference from
5. pinniger is likely due to our surface ageing methodology. We suggest that the
surface ageing technique for 5. diploproa has changed over several years to
provide older age estimates. Boehlert (1980), for example, used surface ages
and observed only 0.5% of all specimens in excess of 25 years of age compared
with 18.9% in the present study. Earlier surface ages for 5. diploproa were
assigned without rolling or tilting the otoliths, thus preventing the enumeration
of additional annuli on the posterior "winglike" projections (Figure 1A). More
recently, annuli located on posterior projection (present in older individuals of
many species of Sebastes) have been included in surface age counts in order
that surface ages more closely represent section ages (Chilton and Beamish
1982, Boehlert and Yoklavich 1984). In the present study, surface ages for 5.
pinniger were assigned using standard criteria for this species (Six and Norton
1977) without including these counts (which are typically less well developed
on otoliths of 5. pinniger); the counts were included in assigning surface ages
to 5. diploproa. Thus, while maximum ages increased, counts including the
posterior projection resulted in surface ages closer to section ages and
minimized the higher mean length estimates for ages on the ascending arm of
the growth curve as seen in the surface ages of 5. pinniger (Figures 3, 5). Had
the age estimates from Boehlert (1980) or the "other agency" readers in
Boehlert and Yoklavich (1984) been used, it is likely that differences in growth
parameters similar to those for 5. pinniger would have been observed for 5.
diploproa.

TABLE 3. Mean Fork Lengths at Age (FL in Centimeters) and Standard Deviation (SD) for Female
and Male Sebastes diploproa Based on Surface and Section Ages. N Indicates the Number
of Otoliths.

Surface Section

Age

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

N

FL

SD

Females

N

FL

SD

8

13.00

1.31

7

12.86

1.35

12

14.83

1.53

14

14.93

1.54

24

16.54

1,38

16

16.50

1.54

36

18.47

2.09

32

17.72

2.04

68

20.40

2.31

76

20.38

2.23

119

22.59

2.02

117

22.60

2.03

125

23.22

2.02

117

23.15

2.04

119

24.97

2.21

130

24.97

2.14

82

25.71

1.92

75

25.73

2.05

61

26.48

2.47

60

26.30

2.68

25

26.56

1.45

30

26.63

1.43

20

27.15

3.28

21

27.00

2.66

13

26.46

2.50

12

25.50

3.53

8

27.50

1.69

4

27.50

1.73

2

28.00

1.41

6

27.17

2.64

11

29.36

2.42

5

28.60

2.07

10

29.30

1.77

7

29.14

1.57

7

29.71

1.60

11

29.45

0.93

(Continued)

ROCKFISH AGEING TECHNIQUES 157

TABLE 3— Continued

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

76

77

78

79

80

81

13

30.15

15

30.13

10

30.00

21

30.71

18

31.33

17

31.53

25

31.80

18

31.33

14

32.21

23

32.22

20

33.30

21

33.19

14

33.07

9

33.33

17

33.47

7

34.29

17

34.53

15

35.53

12

35.58

15

34.47

10

35.50

6

34.33

8

35.00

5

34.60

4

34.00

7

35.57

2

36.50

4

36.50

5

34.80

2

35.50

2

36.50

2

38.00

1.68 7

1 .06 11

2.45 11

1.55 27
1.88 19
2.37 15
1.91 17
1.97 9

2.46 14
2.19 9
1.81 9
1.57 3
2.40 8
3.16 1
2.15 9

2.56 7
2.53 9
1.60 9
1.73 12

2.50 7
1.90 13
1.86 4
2.14 8

2.51 5
1.41 7
1.13 4
0.71 11
1.00 11
1.64 6
0.71 7
0.71 3
1.41 10

_ _ 4

_ — 4

_ — 5

_ — 8

36.00 1.00 2

_ — 6

_ — 4

_ _ 6

_ — 3

_ — 5

_ — 2

_ — 3

_ _ 4

Males

1 12 11.33 1.61 11

2

8 14.87 0.99 6

29.57

2.15

30.36

1.80

30.36

1.75

30.81

1.49

30.37

1.67

30.80

0.94

30.59

1.37

31.22

1.99

30.79

2.12

31.89

2.15

30.56

2.01

32.67

1.53

32.25

1.75

37.00

—

33.44

2.30

33.43

1.72

34.22

2.17

33.56

1.51

32.58

1.73

32.57

1.90

33.77

2.86

34.25

2.36

34.38

2.39

33.87

2.00

36.00

1.15

34.50

1.29

33.09

1.97

35.33

3.30

33.29

2.73

33.29

2.43

35.33

0.58

34.50

2.68

34.50

1.91

36.00

1.41

36.00

1.22

35.37

2.45

34.50

2.12

35.83

1.94

34.25

3.10

34.67

2.34

32.00

2.65

35.80

1.92

35.50

0.71

36.33

2.08

35.50

1.29

35.50

1.41

35.00

1.41

35.75

1.71

38.00

—

34.67

2.08

35.00

—

30.00

z

39.00

34.00

—

36.00

34.00

—

36.00

—

35.50

3.54

11.09

1.45

15.00

1.10

(Continued)

158

CAI

LIFORNIA Fl

SH AND C/

TABLE 3— Continued

Surface

Age

N

hL

i/J

3

27

16.15

2.16

4

47

17.70

1.92

5

86

19.98

2.02

6

100

21.87

1.86

7

128

23.23

1.82

8

114

24.32

1.91

9

62

24.69

2.05

10

30

24.23

2.16

11

15

25.53

3.20

12

16

25.81

1.83

13

7

26.43

1.72

14

8
9

27.63
28.22

2 07

15

0.83

16

7

27.57

1.27

17

11

27.64

1.43

18

9

28.56

1.51

19

5

28.00

1.22

20

13

28.92

1.12

21

9

28.44

1.67

22

9

29.56

2.13

23

29

28.93

2.20

24

16

29.44

1.71

25

20

29.15

1.31

26

15

29.73

1.10

27

17

30.41

1.84

28

13

30.46

1.39

29

16

29.94

1.18

30

16

30.19

2.48

31

9

30.11

1.90

32

6

31.00

0.89

33

4

29.75

2.22

34

5

30.40

0.55

35

5

30.80

0.84

36

3

30.33

1.15

37

7

30.43

1.27

38

1

30.00

—

39

2

29.50

3.54

40

4

30.50

1.29

41

42

43

1

31.00

—

44

45

46

1

31.00

—

47

—

—

—

48

—

—

—

49

50

51

52

53

54

55

56

57

58

59

60

61

—

—

—

—

—

—

62

63

64

65

—

—

—

Section

""AT

27

48

79

101

124

119

61

32

21

14

11

6

8

5
10

6

3

9
14
12
14
13
14
15

6

6

5

4

4

6

S

1

2

6

1

1

4

4

2

2

3

4

5

8

5

6

6

2

1

2

1

3

1

6

2

2

2

1

2

2

1

2

1

hi

Si)

16.48

2.08

17.63

2.05

19.77

2.25

21.71

1.96

23.16

1.83

24.12

2.11

24.90

1.79

24.28

2.25

25.52

3.12

25.57

1.70

25.82

2.96

27.67

2.42

27.63

1.30

28.40

1.67

28.50

1.27

27.17

1.17

29.67

1.15

28.67

1.41

28.64

1.08

28.92

1.24

28.32

1.50

29.31

1.18

29.43

1.40

29.13

0.99

27.67

3.88

29.50

0.84

30.20

1.10

28.25

2.50

29.25

0.96

29.33

1.75

30.00

0.71

30.00

—

30.00

2.83

29.83

0.98

30.00

—

26.00

—

30.25

2.63

30.75

1.71

28.50

0.71

29.50

2.12

30.00

2.00

30.25

0.50

29.80

0.84

30.50

1.51

30.20

1.92

29.83

2.86

28.67

1.63

30.50

2.12

31.00

—

31.50

0.71

30.00

—

31.33

2.52

30.00

—

31.50

0.84

30.50

0.71

31.50

0.71

30.00

—

30.00

—

29.50

2.12

30.50

0.71

29.00

—

29.50

0.71

32.00

—

(Continued)

3

32.00

1.73

2

31.50

0.71

1

36.00

—

1

31.00

1

32.00

1

33.00

ROCKFISH AGEING TECHNIQUES ^59

TABLE 3— Continued

66 — — —

67 — — —

68 — — —

71 — — — 1 32.00

73 — — —

74 — — —

75 — — —

80 — — — 1 35.00 —

82 — — — — — —

84 — — — 1 30.00 —

Mortality

The results of this study demonstrate that total mortality (Z) is significantly
less when section rather than surface ages are used for slow-growing, long-lived
fishes such as 5. pinniger and 5. diploproa (Table 2). As evident in the larger
reduction in Z for males versus females, the problem is more pronounced in
males, possibly because their slower growth increases the difficulty of assigning
accurate surface ages. This may explain why Z is higher in male 5. diploproa
than in females when surface ages are used and lower when section ages are
used. The absence of older 5. pinniger females also contributed to the smaller
decrease in Z when section ages were used.

This study has documented important differences in estimates of growth and
mortality which result solely from differences in otolith ageing methodology. It
is hoped that subsequent research will incorporate these estimates into various
stock assessment models to evaluate the effect that these different otolith ageing
techniques have on models designed to evaluate yield and production
characteristics of long-lived, slow-growing fish stocks.

ACKNOWLEDGMENTS

This work was supported by a cooperative agreement (number 80-ABH-
00049) and contract (number 81-ABC-00192-PR6) from the Northwest and
Alaska Fisheries Center, Seattle, Washington.

LITERATURE CITED

Archibald, C. P., W. Shaw, and B. M. Leaman. 1981. Growth and mortality estimates of rockfishes (Scorpaenidae)
from B.C. coastal waters, 1977-1979. Can. Tech. Rep. Fish. Aquat. Sci. 1048, 57 p.

Beamish, R. ). 1979a. Differences in the age of Pacific hake (Merlucclus productus) using whole otoliths and
sections of otoliths. ). Fish. Res. Board Can., 36; 141-151.

Beamish, R. ). 1979b. New information on the longevity of Pacific ocean perch (Sebastes alutus) . |, Fish. Res.
Board Can., 36: 1395-1400.

Bennett, ). T., C. W. Boehlert, and K. K. Turekian. 1982. Confirmation of longevity in Sebastes diploproa (Pisces:
Scorpaenidae) from ^'° Pb/"'' Ra measurements in otoliths. Mar. Biol. (Berl.), 71: 209-215.

Boehlert, C. W. 1980. Size composition, age composition, and growth of canary rockfish, Sebastes pinniger, and
splitnose rockfish, 5. diploproa, from the 1977 rockfish survey. Mar. Fish. Rev., 42(3^); 57-63.

1^ CALIFORNIA FISH AND CAME

Boehlert, G. W. 1985. Using objective criteria and multiple regression models foi age determination in fishes. Fish.

Bull., 83: 103-117.
Boehlert, C. W., and R. F. Kappenman. 1980. Variation of growth with latitude in two species of rockfish (Sebastes

pinniger and S. diploproa) from the northeast Pacific Ocean. Mar. Ecol. Prog. Ser., 3: 1-10.
Boehlert, C. W., and M. M. Yoklavich. 1984. Variability in age estimates in Sebastes as a function of methodology,

different readers, and different laboratories. Calif. Fish and Came, 70(4); 210-224.
Campana, S. E., K. C. T. Zwanenburg, and |. N. Smith. In press. -'" Pb/"'' Ra determination of longevity in redfish.

Can. J. Fish. Aquat. Sci.
Chilton, D. E., and R. ). Beamish. 1982. Age determination methods for fishes studied by the Groundfish Program

at the Pacific Biological Station. Can. Spec. Publ. Fish. Aquat. Sci. 60, 102 p.
Dark, T. A. 1975. Age and growth of Pacific hake, Merluccius productus. Fish. Bull., 73: 336-355.
Dark, T. A., M. E. Wilkins, and K. Edwards. 1983. Bottom trawl survey of canary rockfish (Sebastes pinniger),

yellowtail rockfish (5. flavidus) , bocaccio (5. paucispinis) , and chilipepper (5. goodei) off Washington

—California, 1980. U.S. Dep. Commer., NOAA Tech. Memo. NMFS F/NWC-48, 40 p.
Dixon, W. |. 1981. BMDP statistical software. Univ. Calif. Press, Berkeley, 726 p.
Gallucci, V. F., and T. |. Quinn II. 1979. Reparameterizing, fitting, and testing a simple growth model. Trans. Am.

Fish. Soc, 108: 14-25.
Culland, ). A. 1983. Fish stock assessment. A manual of basic methods. John Wiley and Sons, New York, 223 p.
Hirschhorn, C. 1974. The effect of different age ranges on estimated Bertalanffy growth parameters in three fishes

and one mollusk of the northeastern Pacific Ocean. Pages 192-199 in T. B. Bagenal (ed.) The ageing of fish.

Unwin Brothers, Surrey, Engl.
Knight, W. 1968. Asymptotic growth: An example of nonsense disguised as mathematics. |. Fish. Res. Board Can.,

25: 1303-1307.
Leaman, B. M., and D. A. Nagtegaal. 1987. Age validation and revised natural mortality rate for yellow tail

rockfish. Trans. Am. Fish. Soc, 116: 171-175.
Le Cren, E. D. 1974. The effects of errors in ageing in production studies. Pages 221-224 In T. B. Bagenal (ed.)

The ageing in fish. Unwin Brothers, Surrey, Engl.
Neter, |., and W. Wasserman. 1974. Applied linear statistical models. Regression, analysis of variance, and

experimental designs. Richard D. Irwin, Inc., Homewood, III.
Nichy, F. 1977. Thin-sectioning fish ear bones. Fish age determination aids pollution control research. Sea

Technol., Feb., p. 27.
Rao, C. R. 1973. Linear statistical inference and its implications. 2nd ed. )ohn Wiley and Sons, New York, 625 p.
Ricker, W. E. 1975. Computation and interpretation of biological statistics of fish populations. Bull. Fish. Res. Board

Can. 191, 382 p.
Shaw, W., and C. P. Archibald. 1981. Length and age data of rockfishes collected from B.C. coastal waters during

1977, 1978, and 1979. Can. Data Rep. Fish. Aquat. Sci. 289, 119 p.
Six, L. D. and H. F. Horton. 1977. Analysis of age determination methods for yellow tail rockfish, canary rockfish,

and black rockfish off Oregon. Fish. Bull., 75: 405-414.
Vaughan, D. S., and P. Kanciruk. 1982. An empirical comparison of estimation procedures for the von Bertalanffy

growth equation. ). Cons. Cons. Int. Explor. Mer, 40: 211-219.
Wilson, C. D. 1 985. The effects of different otolith ageing techniques on estimates of growth and mortality for two

species of rockfishes, Sebastes pinniger and Sebastes diploproa. M.S. Thesis, Oregon State Univ., Corvallis,

107 p.

GROWTH AND LONGEVITY OF GOLDEN TROUT 161

Calif. Fish and Game 76 ( 3 ): 1 61 -1 73 1 990

GROWTH AND LONGEVITY OF GOLDEN TROUT,
ONCORHYNCHUS AGUABONITA, IN THEIR NATIVE

STREAMS '

ROLAND A. KNAPP

AND

TOM L. DUDLEY
Department of Biological Sciences and

Marine Science Institute

University of California
Santa Barbara, California, U.S.A. 93106

Golden trout, Oncorhynchus aguabonita, from 17 streams in the Kern Plateau
region of the Sierra Nevada, California, were aged using otoliths, and growth rates
were determined using length-age and weight-age relationships. Growth rates,
condition factors, and densities of trout were correlated with site-specific biological
and physical factors using stepwise multiple regression techniques. These stream
populations were highly stunted, and individuals attained quite old ages (9 years).
Densities were usually low and high density had a significant negative effect on
growth ( P < 0.001 ) . In addition, growth was positively affected by amount of aquatic
vegetation, amount of bank vegetation, stream channel stability, and elevation.
While site-specific factors such as trout density may influence trout growth, the low
growth rates throughout the study area were probably due to the low productivity
of these unstable montane streams and the short growing period at high elevations.

INTRODUCTION

Golden trout, Oncorhynchus aguabonita, formerly Salmo aguabonita, have
been widely introduced throughout the United States of America and other
parts of the world, but are endemic to only two watersheds, both in the
southern Sierra Nevada mountains of California (Fisk 1983). There are two
subspecies of the golden trout; O. a. aguabonita is native to the headwaters of
the South Fork Kern River and Golden Trout Creek and O. a. whitei is native to
the Little Kern River, Tulare County. Golden trout were initially thought to be
most closely related to cutthroat trout (Jordan 1892), but are now understood
to belong to the rainbow trout series (Berg 1987).

Although the golden trout is the official California state fish, its natural history
in native habitats is poorly understood. What is known of golden trout natural
history is primarily based on introduced populations of lake-dwelling fish (Fisk
1 983 ) . In these populations, spawning is typically initiated in June and continues
through July. Eggs hatch in 29 to 50 days, and after 2-3 weeks in the gravel the
fry emerge and grow rapidly during the first summer. They reach approximately
4.5 cm by age one year, 12 cm at two, and 19 cm at three years of age
(Needham and Vestal 1938, Fisk 1983). Lake fish reach reproductive maturity
at three years of age and may survive to spawn as many as three times. The
maximum recorded age is six years. Golden trout from streams rarely achieve
lengths greater than 18 cm and ages of such populations are unknown (Fisk
1983). Factors which influence growth rates of stream populations are also
unknown.

Accepted for publication April 1990.

152 CALIFORNIA FISH AND CAME

Growth rates of trout can vary markedly in relation to temperature, food
ration, and density (Elliott 1982). In many cases, the differences within a species
may be greater than those between species. Under good conditions, non-
anadromous trout in streams may achieve a length greater than 40 cm after only
three years (Carlander 1969). Growth is often retarded at higher elevations, due
to lower temperatures and a shorter growing season. Purkett (1951 ) reported
that three-year old rainbow trout, Oncorhynchus mykiss, formerly Salmo
gairdneri, averaged 29 cm at 1,600 m and 24 cm at 1,850 m, and a 24-year old
brook trout, Salvelinus fontinalis, reached only 24 cm at 3,322 m in a low
productivity Sierra Nevada lake (Reimers 1979). If higher elevation habitats
have lower fish densities than lower sites, however, reduced competition at
higher sites may result in faster growth rates (McAfee 1966).

In this paper, we report on ages, growth, and population densities of golden
trout, O. a. aguabonlta, from 12 of its native streams in the Golden Trout
Wilderness, Inyo National Forest. Five additional study streams contained
populations introduced from nearby native populations around the turn of the
century. These included three sites on the eastern edge of the Golden Trout
Wilderness and two sites in Kings Canyon. Several populations in the Golden
Trout Wilderness have been the subject of an intensive management project to
preserve the native habitat and gene pool of the golden trout (Fisk 1983).
Brown trout, Salmo trutta, had been introduced to the South Fork Kern River
drainage, and these predators and competitors were removed by California
Department of Fish and Game biologists from 1976 to 1982. Golden trout were
transplanted extensively during this operation, though trout were not trans-
planted into any of our study streams. Our objective was to provide information
on golden trout ages and growth rates from stream populations and to
determine what biological and physical factors affected trout growth rate,
condition, and density.

STUDY SITES

The 17 study streams all originate on or near the Kern Plateau of the southern
Sierra Nevada (Inyo and Tulare counties, California; Figure 1). Most are
tributaries of the South Fork Kern River or Golden Trout Creek, both within the
Golden Trout Wilderness. Three streams flow eastward into the Owens Valley
and two are tributaries of the Kings River in the southern portion of Kings
Canyon National Park and drain into the Central Valley.

The southern portion of the Sierra Nevada was largely unaffected by the
Pleistocene glaciation which shaped the valleys north of the Kern Plateau (jahns
1954). Consequently, most of the stream valleys in this region consist of broad
alluvial flats separated by low granitic ridges sparsely vegetated with lodgepole,
Pinus contorta, and foxtail, P. balfouriana, pines. The meadows range in
elevation from 2,300 to 3,200 m, and are composed of relatively unconsolidated
granitic sands and fine sediments. They are more subject to erosion and
degradation than meadows in the glaciated Sierra Nevada (Albert 1982).

Characteristics of the individual streams are provided in Table 1. The streams
of this region are typically of low gradient and stream bottoms consist of
unstable sand and occasional gravels and cobble. Meanders are common in the
unconfined meadow flats, and most streams are relatively wide and shallow.

GROWTH AND LONGEVITY OF GOLDEN TROUT

163

Discrete riffle-pool sequences are largely absent. The banks are generally
steep-sided, rarely densely vegetated, and active erosion sites are common. True
riparian vegetation is absent, except for mesic herbs and occasional willow
shrubs, Salix spp. In-stream cover which can be used by trout is rare. As a
consequence of stream openness, summer stream temperatures fluctuate
greatly, ranging daily from 3° to 22°C. Golden trout are the only fish species
inhabiting the study streams.

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FIGURE 1. Map of California showing study sites on the Kern Plateau. Study sites are numbered
and correspond to numbers in Table 1. The two study sites in Kings Canyon
National Park (16, 17) are not shown.

MATERIALS AND METHODS

Sampling occurred during the summers of 1983 and 1984. At each site, a 100
m linear transect was established along a representative stream section, and all
samples were taken from this section. The section was mapped three-
dimensionally to assess geomorphological characteristics such as meander
patterns, width /depth relationships, and pool /riffle ratios. Two bottom substrate
cores (15 cm deep x 8 cm diam) were taken and partitioned into five sediment
size classes with sieves (mesh sizes = 2.0, 1.0, 0.5, and 0.1 mm — particles
larger than 2 cm were hand separated from the 2 mm sieve). The three largest
size classes were weighed in the field and the two smallest size classes were
returned to the laboratory for more accurate weighing.

Invertebrates were collected with a 30 cm x 30 cm modified Hess sampler.
The sampler was pushed approximately 10 cm into the substrate and the
substrate within the sampler was vigorously stirred by hand. Any suspended

164

CALIFORNIA FISH AND GAME

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GROWTH AND LONGEVITY OF GOLDEN TROUT I55

organisms and other organic material was washed into a 330 jitm mesh net
attached to the downstream end of the sampler. Samples were preserved in
70% ethanol for size partitioning and species identification in the laboratory.
Four samples were collected from riffles at each site.

Bank condition was characterized every meter along one randomly chosen
100 m section of stream bank within the study site. At each point, we noted the
type of vegetation, whether or not the stream edge was bare, the presence or
absence of aquatic vegetation (macrophytes and algae), and whether or not the
bank was undercut. If the bank was undercut, the extent of undercutting was
measured.

The Pfankuch stream stability rating was calculated for each site (Pfankuch
1975). This index is based on a visual assessment of subjective measures related
to stream channel stability, including bank condition, substrate type, vegetative
cover, width-depth ratio, and pool-riffle ratio. Stream channel stability is
negatively correlated with the index value. For example, narrow, deep streams
with overhanging banks and substrates composed mostly of cobble and gravel
receive a lower score than wide, shallow streams with highly eroded banks and
substrates composed mostly of sand and silt.

Fish were collected by electroshocking (Smith-Root Model 11 Electrofisher).
Three passes were conducted at each site in order to obtain a regression
estimate for population size (Seber and LeCren 1967). However, this method
was not appropriate for the study streams, since the first pass often produced
fewer fish than the second and third passes. Because of the limitations of
population estimates based on the regressions, the data were used to estimate
minimum densities within the stream sections. Fish were retained in buckets
until all passes were completed and then measured.

The standard lengths (sl) of all captured fish were measured to the nearest
mm on a measuring board. We estimated weights by immersing the fish in a
graduated cylinder containing a known volume of water and recording the
volume of water displaced. We assumed, and verified in the laboratory, that the
specific density of fish tissue was similar to that of water ( 1 .0 g/ml ) . Therefore,
a fish that displaced 50 ml of water was recorded as weighing 50 g. Ten fish
from each site, representing a range of sizes, were sacrificed and preserved in
95% ethanol and returned to the laboratory for age determinations. Smaller
samples were preserved from three streams which contained few fish. In
addition, 10 juveniles ( <1 year of age) were collected from each site where
they were present. Since electroshocking did not effectively capture juveniles,
they were instead collected using handnets.

Both scales and otoliths (sagittae) were used for age determination; annuli
and presumed daily growth increments of otoliths were examined at 100-400X
in oil immersion under a light microscope (Campana and Neilson 1985).
Otoliths from fish > 3 years old were first ground with carborundum 600 grit to
enhance transparency, while otoliths from younger fish were viewed directly.

We investigated the importance of 24 biological and physical site character-
istics in determining golden trout growth, condition (K), and density. Site
characteristics included riparian stream cover, substrate size composition, bank
condition, gradient, elevation, suspended particulates, stream surface area,
stream width /depth ratios, pool /riffle ratios, watershed area, abundance of
bank and instream vegetation, fish density, stream channel stability, and aquatic

156 CALIFORNIA FISH AND CAME

insect abundance. Data were analyzed using stepwise multiple regression
procedures. The effects of stream channel stability on trout growth, condition,
and density were analyzed separately since the stability index incorporated
many of the other independent variables.

In stepwise multiple regression procedures in which fish growth (SL/age,
weight/age) or condition were included as dependent variables, each fish was
a separate observation. When fish density was entered as the dependent
variable, each stream was a separate observation. Proportional data were
arc-sine square root transformed. The required significance level for inclusion in
the regression model was p < 0.1 5. Only those fish more than one year old were
used in the analyses since young of the year were present in only five of the
study streams when collections were made in 1983.

RESULTS

A total of 376 fish from 17 streams were weighed and measured during 1983.
Of these, 176 fish from 15 streams were preserved for age determinations. In
1984, an additional 20 fish were preserved from two streams from which no
samples had been collected in 1983.

Scales were unsuitable for age determination since annuli were non-existent.
In contrast, annuli were easily counted on nearly all otoliths, possibly due to the
large and discrete differences in seasonal temperature cycles (Campana and
Neilson 1985). Based on annuli counts, golden trout frequently lived more than
five years; the oldest was nine years old. We did not validate annulus formation,
but are confident that our age estimates are accurate, since otoliths accurately
reflected ages of fish up to 23 years old in an extremely stunted brook trout
population (Reimers 1979).

Inter-annular increments were present on all otoliths and were assumed to be
produced daily. Daily increment production has been verified in several fish
species closely related to golden trout including steelhead trout (Campana
1983), Chinook salmon (Neilson and Geen 1982), and sockeye salmon
(Marshall and Parker 1982). The number of increments between successive
annuli ranged from 90-120. Although it is not known for golden trout whether
growth ceases when increment formation stops, the increment counts suggest
a period of rapid growth of between three and four months per year
(June-September). Growth at other times of the year is probably very slow.

Otoliths from young-of-year trout always showed a distinct discontinuity,
after which increments were clearly reduced in width (Figure 2). We believe
this represents the date at which alevins emerged from the gravel after depletion
of the yolk sac. Similar discontinuities were reported from otoliths of sockeye
salmon (Marshall and Parker 1982) and correspond to the date of first feeding.

Lengths of golden trout for all age classes are shown in Figure 3. First year
growth was rapid, after which fish grew at a slower rate, especially after the fifth
year. The length of golden trout for ages 1-9 was fitted to an equation of the
form y,| = 7.30 + 4.02 In x.,^^ (R^ = 0.51, p< 0.0001, n = 138; Table 2).
Weight followed a pattern similar to length, but was more variable (Figure 4).
The weight of trout of ages 1-9 was fitted to an equation of the form
y^, = 2.85 + 19.90 In x^ge (R^ = 0.30, p< 0.0001, n = 138; Table 2). When fit

GROWTH AND LONGEVITY OF GOLDEN TROUT

167

to a logarithmic equation, the length-weight relationship for all trout was [In
w = -3.59 + 2.70 In I] (R^ = 0.90, p< 0.0001, n = 343).

FIGURE 2. Otolith from a 2.5 cm golden trout. Arrow points to suggested emergence mark. Scale
bar = 100 jam.

Age-length data was also fitted to a Von Bertalanffy growth function
(FISHPARM computer software— Prager et. al. 1987). The Von Bertalanffy
equation for all collected fish was I, = 15.5(1 -exp (-0.42[t + 0.54])). The
asymptotic length for this sample of golden trout was 15.5 cm.

The effects of site characteristics on trout growth (measured as SL/age) were
evaluated for 95 fish from 12 streams using stepwise multiple regression. The
remaining 43 fish were eliminated because their associated stream variables
contained missing values. Fish age accounted for most (62%) of the variation
in trout growth explained by the model (Table 3). The percent of stream
length covered with aquatic vegetation also added significantly to the model and
explained 2% of the variation in trout growth. Fish density (number of
fish/m^)did not vary much between sites (Table 1) and did not explain a
significant amount of the variation in trout growth.

168

CALIFORNIA FISH AND CAME

20-

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AGE (years)

FIGURE 3. Golden trout lengths by age class. Sample sizes for age classes 1-9 are given in Table
2. N = 58 for age 0.

TABLE 2. Actual and Predicted Standard Lengths and Weights of Trout of Ages 1-9. See Text for
Equations.

AC£ CLASS (YEARS)

12 3 4 5 6 7 8 9

n 10 27 47 28 10 10 5 0 1

preclictod length (cm) 7.3 10.1 11.7 12.9 13.8 14.5 15.1 15.6 16.1

actuallength (cm) 7.1 9.8 11.8 13.2 15.0 13.1 14.2 — 16.1

predicted weight (g) 2.9 16.6 24.7 30.4 34.9 38.5 41.6 44.2 46.6

actual weight (g) 6.4 14.0 23.9 31.7 47.3 33.2 33.2 — 55.0

TABLE 3. Results of Stepwise Multiple Regression Analysis of Trout Growth Measured As SL/age

(n = 95). Variables Are Listed As They Entered The Model. See Text for Definition of Inde-
pendent Variables.

Variable Slope P R'

fish age -0.76 0 0001 0.62

% stream vegetated 0.95 0.005 0.02

fish density (#/m-') -3.53 >0.10 0.01

When growth was measured as weight/age, regression analysis for 87 fish
from 11 streams indicated that golden trout density explained the largest
amount of the variation in growth (21%; Table 4). Elevation did not vary much
between sites (Table 1 ), but still explained 8% of the variation in trout growth.
The percent of the bank covered by vegetation explained an additional 7% of
the variation.

GROWTH AND LONGEVITY OF GOLDEN TROUT l 59

TABLE 4. Results of Stepwise Multiple Regression Analysis of Trout Growth Measured as Weight/Age
(n = 87). Variables are Listed as they Entered the Model. See Text for Definition of Inde-
pendent Variables.

Variable Slope P R'

fish density (#/100 m) -0.19 0.0001 0.21

elevation (m) 0.01 0.0001 0.08

% bank vegetated 7.99 0.004 0.07

Condition factors ranged from 1.16 to 1.47, with a nnean of 1.34 ± 0.11 S.E.
(Table 1 ). Although 106 fish were used in the model, none of the site-specific
stream variables satisfied the minimum significance level for entry into the
regression model.

Multiple regression analyses using fish density (measured as the number of
fish per 100 m of stream and as the number of fish per m ) as the dependent
variable resulted in none of the site variables satisfying the minimum required
significance level for entry into the regression model. Four streams were
eliminated from the analysis because of missing values.

The Pfankuch stream stability rating was significantly correlated with fish
growth measured as weight/age (r=— 0.35, p = 0.0001, n = 138), but not as
SL/age (r=— 0.09, p>0.30, n = 138). The correlation between the stream
stability rating and fish density measured as the number of fish/ 100 m was
marginally significant (r = 0.44, p = 0.08, n = 16), but the stream stability rating
and fish density measured as the number of fish/m ^ were not significantly
correlated (r = 0.05, p>0.50, n = 16). Trout condition was also not significantly
correlated with the stream stability rating (r=— 0.07, p>.15, n = 343).

DISCUSSION

Scales proved unsatisfactory for aging golden trout in this study. Reimers
(1958) experienced similar difficulties with scales taken from brook trout from
an alpine Sierra Nevada lake. Otoliths, however, proved highly suitable for age
determinations. The oldest fish sampled was 16.1 cm SL and was in its tenth
year of growth, making it the oldest golden trout on record. Six and seven year
old fish were common. Other species of trout occasionally attain similar ages in
streams (O. mykiss — 7 years, Greeley 1933; O. clarkii — 10 years, Oregon State
Game Comm. 1950; 5. trutta — 8 years, Sigler 1952). Most other records of
salmonids near 10 years of age or greater are from lake populations (Fenderson
1954, Sumner 1948) or are sea-run individuals (Sumner 1962).

The exceptionally low productivity of streams occupied by golden trout may
be a factor in their longevity as well as their retarded growth. In one remarkable
case, Reimers (1979) found that introduced brook trout, Salvelinus fontinalis,
survived for up to 24 years of age in a high altitude, low productivity Sierra
Nevada lake. Reimers accounted for their exceptional age by their minimal
energetic costs. Activity was reduced by low temperatures in conjunction with
extreme food depletion. These fish became highly stunted and did not
reproduce until age 16, when population densities declined and allowed food
levels to increase and make reproduction possible. Considerable evidence
correlates stunting due to reduced food ration and low temperature with
enhanced longevity (McCay et al. 1956, Comfort 1963). Golden trout were
clearly stunted, suggesting that their increased longevity may be the result of an
analogous situation.

170 CALIFORNIA FISH AND GAME

In streams, golden trout growth rates are much lower than the rates reported
from lake populations (Needham and Vestal 1938, Curtis 1934, McAfee 1966).
This agrees with considerable information regarding other species of trout
(Carlander 1969), and may be due to several factors. In lakes, fish have access
to zooplankton and large prey items not available in streams. This is particularly
true following introduction of new populations (including O. aguabonita) to
fishless lakes, before the prey community composition has been altered
(Needham and Vestal 1938). Fish feeding behavior is different in lakes and
streams; in streams, fish must expend energy maintaining position and feeding
in fast currents (Jenkins 1969, Smith and Li 1983), reducing energy available for
growth.

Regression analyses suggested that several factors may influence the growth
of golden trout in our study streams. When growth rate was measured as
standard length/age, most of the variation was explained by age (Table 3);
younger age classes grew more rapidly than older age classes. The amount of
the stream covered with aquatic vegetation was positively correlated with trout
growth. Aquatic vegetation often provides important habitat for invertebrates
and may promote higher invertebrate abundance and diversity (Dudley et al.
1986). Thus, aquatic vegetation may increase the amount of food available to
golden trout.

Weight at each age class showed much more variation than size at each age
class ( Figures 3 and 4) . Since weight can be modified over a shorter time period
than length, growth rates based on weight may have been more sensitive to the
effects of the site variables used in the analyses than growth rates based on
length. Growth rates measured as weight/age were affected by numerous site
variables (Table 4). Sites with higher fish density (number of fish/m')
contained fish with significantly slower growth rates. Increased fish density may
result in decreased growth rates by decreasing per capita food availability or by
increasing competition for foraging sites or cover (Chapman 1966, Chapman
and Bjornn 1969, Elliot 1984). Such competition could force fish to expend
energy on agonistic interactions instead of on growth.

Density measured as the number of fish/ 100 m may be a better predictor of
growth rates than density measured as the number of fish/m' if these trout
populations are limited more by the availability of cover than by foraging sites.
Nearly all cover in the study streams occurred along the banks and was heavily
utilized by fish. Foraging sites were generally in mid-stream and may not have
been in short supply in the study streams, since individuals often changed sites
without interactions from conspecifics.

Fish from higher elevation streams had higher growth rates than those from
lower elevations. McAfee (1966) suggested that if higher elevation habitats
have lower fish densities than lower sites, reduced competition at higher sites
may result in faster growth. However, our analyses should have removed any
density effect and we are thus unable to provide a satisfactory explanation for
this relationship.

There was a positive relationship between the amount of streambank
vegetation and trout growth. Overhanging vegetation provides cover for fish
and may increase the number of terrestrial insects available to trout.

GROWTH AND LONGEVITY OF GOLDEN TROUT

171

100-

•

90-

•j-

■

80-

r

3 70-

■

,_ 60-

UJ 40-
^30-

(

1

1 I

i

•

20-
10-

!

'—I f 1

-

1

0 123456789

AGE (years)

FIGURE 4. Golden trout weights by age class. Samples sizes for each age class are given in
Table 2.

The negative correlation between the Pfankuch stream stability rating and
trout growth (weight/age) suggests that trout from streams with higher channel
stability gained weight faster than those from streams with lower channel
stability. Similar effects of channel stability on fish growth have been found for
rainbow trout (Van Velson 1979) and brown trout (Dahlem 1979) and were
suggested to result from increased food and cover.

Condition factors for 343 trout ranged from 0.90 to 2.16. Despite this
variability, our calculated mean K was 1.34, which is similar to K values
estimated for lake populations of golden trout (K = 1.315 in Needham and
Vestal 1938, 1.34 in Curtis 1934). Apparently, populations of golden trout
achieve quite similar condition relationships, even in very different habitats. K
values of other trout species vary considerably among habitats, but it appears
that trout in montane streams have K values similar to those of golden trout,
ranging from 1.15 to 1.63 (Carlander 1969). This uniformity in condition even
among different trout species may explain why none of the measured site
characteristics affected trout condition in our analysis.

Trout density was not affected by any of the measured site characteristics
used in the regression analysis. This analysis should be interpreted with caution,
however, as each stream was considered as a separate observation and only 13
streams were used in the analysis. Thus, even if any site characteristics (e.g.
amount of suitable spawning gravel or aquatic insect biomass) did affect trout
density, the analysis may have lacked the power to detect such effects. The
marginally significant correlation between trout density (number of fish /1 00m)

172 CALIFORNIA FISH AND CAME

and the Pfankuch stream stability rating suggests that less stable stream channels
support higher densities of fish. Although we are unable to provide an
explanation for this relationship, it may suggest that fish grew more slowly in
streams with lower channel stability because of higher trout densities.

In summary, several site variables affected trout growth. Trout density, trout
age, and the Pfankuch stream stability rating were negatively correlated with
trout growth while the amount of aquatic vegetation, the amount of bank
vegetation, and elevation were positively correlated with trout growth. Differ-
ences between sites in stream stability, trout density, bank vegetation, and
aquatic vegetation may all influence trout growth by increasing or decreasing
the amount of available food or cover. Small increases or decreases in the
availability of food or cover may be important in these low productivity streams.
However, the low growth rates of golden trout throughout the study area were
probably a result of the low productivity of these unstable montane streams and
the short period of time available each year for rapid trout growth.

ACKNOWLEDGMENTS

We thank many people for their assistance in organizing and conducting this
research, including Scott Cooper, Jon Diehl, Jim Killiam, the other Scott Cooper,
and Caria D'Antonio of the University of California, Ralph Giffen and Robin
Hamlin of the U.S. Forest Service, and Steve DeBenedetti of the National Park
Service. We also thank William Hayden for supplying us with the FISHPARM
software and Bill Berg for clarifying the systematics of golden trout. We
particularly appreciate the guidance, enthusiasm and philosophical wisdom of
Phil Pister of California Fish and Game. The people of Cottonwood Pack Station
did an admirable job of figuring out where we were. Research was in part
funded by California Water Resources Center Grant No. W628 and National
Science Foundation Grant No. BSR83-05837.

LITERATURE CITED

Albert, C. P. 1982. A survey of factors influencing the condition of the stream zone in the Golden Trout

Wilderness. MA. Thesis, Sonoma State University, California. 65 p.
Berg, B. 1987. Evolutionary genetics of rainbow trout, Parasalmo gairdneri (Richardson). Unpublished Ph.D.

dissertation, U.C. Davis. 184 p.
Campana, S. E. 1983. Feeding periodicity and production of daily growth increments in the otoliths of steelhead

trout iSa/mo gairdneri) and starry flounder (Platichthys slellatus). Can. ). Zool., 61: 1591-1597.
Campana, S, E. and J. D. Neilson. 1985. Microstructure of fish otoliths. Can ). Fish. Aq. Sci., 42: 1014-1032.
Carlander, K. D, 1969. Handbook of Freshwater Fishery Biology. Iowa State University Press, Ames, Iowa. 752 p.
Chapman, D. W. 1966. Food and space as regulators of salmonid populations in streams. Am. Nat., 100: 345-358.
Chapman, D. W. and T. C. Bjornn. 1969. Distribution of salmonids in streams, with special reference to food and

feeding. Pages 153-177 in T. C. Northcote, ed. Symposium on salmon and trout in streams. University of

British Columbia, Vancouver, B.C.
Comfort, A. 1963. Effect of delayed and resumed growth on the longevity of a fish Uebistes reticulatus Peters)

in captivity. Gerontologia, 8(2); 150-155.
Curtis, B. 1934. The golden trout of Cottonwood Lakes (Salmo aguabonita Jordan). Amer. Fish. Soc, Trans., 64:

259-265
Dahlem, E. A. 1979. The Mahogany Creek Watershed— with and without grazing. Pages 31-34 in O.B. Cope, ed.

Forum on grazing and riparian/stream ecosystems. Trout Unlimited, Inc.
Dudley, T. L., S. D. Cooper, and N. Hempill. 1986. Effects of macroalgae on a stream invertebrate community.

N. Amer. Benthol. Soc, )., 5: 93-106.
Elliott, ). M. 1982. The effects of temperature and ration size on the growth and energetics of salmonids in

captivity. Comp. Biochem. Physio., 73(1): 81-91.

GROWTH AND LONGEVITY OF GOLDEN TROUT I73

Elliot, ). M. 1984. Numerical changes and population regulation in young migratory trout Salmo trutta in a Lake
District stream, 1966-1983. |. Anim. EcoL, 53; 327-350.

Fenderson, C. N. 1954. The brown trout in Maine. Maine Fish Bull., 2: 16 p.

Fisk, L. 1983. Golden trout of the High Sierra. Calif. Fish and Came, 16 p.

Greeley, ). R. 1933. The growth rate of rainbow trout from some Michigan waters. Amer. Fish. Soc, Trans., 63:

361-378.
)ahns, R. H. 1954. Geology of Southern California. California Division of Mines and Geology, Bulletin 170.

Jenkins, T, M. 1969. Social structure, position choice and microdistribution of two trout species (Salmo trutta and
5. galrdneri) resident in a mountain stream. Anim. Behav. Monogr., 2: 57-123

Jordan, D. S. 1892. Description of the golden trout of Kern River. Bien. Rept. St. Bd. Fish. Comm., Calif., 5: 62-65.

Marshall, S. L. and S. S. Parker. 1982. Pattern identification in the microstructure of sockeye salmon
(Oncorhynchus nerka) otoliths. Can. J. Fish, and Aquat. Sci., 39: 542-547.

McAfee, W. R. 1966. Golden trout. Pages 216-221 in A. Calhoun, ed. Inland Fisheries Management. Calif. Dept.
Fish and Came.

McCay, C. M., F. Pope, and W. Lunsford. 1956. Experimental prolongation of the life span. Pages 29-39 in R. L.
Craig, ed. Problems of aging, 28th Grad. Sympos. New York Acad. Medicine, 1955. George Eliot Books, New
York. 221 p.

Needham, P. R., and E. H. Vestal. 1938. Notes on growth of golden trout (Salmo agua-bonila) in two High Sierra
lakes. Calif. Fish and Game, 24(3): 273-279.

Neilson, J. D. and C. H. Geen. 1982. Otoliths of chinook salmon (Oncorhynchus tshawytscha): daily growth
increments and factors influencing their production. Can. J. Fish. Aquat. Sci., 39: 1340-1347.

Oregon State Came Commission. 1950. Annual report. Fishery Division, 1951. 238 p.

Pfankuch, D. 1975. Stream reach inventory and channel stability evaluation. USDA Forest Service, Northern
Region. 26 p.

Prager, M. H., S. B. Saila, and C. W. Recksiek. 1987. FISHPARM: A microcomputer program for parameter
estimation of nonlinear models in fishery science. Old Dominion University Research Foundation. Technical
Report 87-10.

Purkett, C. A., Jr. 1951. Growth rate of trout in relation to elevation and temperature, Amer. Fish. Soc, Trans., 80:
251-259.

Reimers, N. 1958. Conditions of existence, growth, and longevity of brook trout in a small, high altitude lake of
the eastern Sierra Nevada. Calif. Fish and Game, 44: 319-333.

Reimers, N. 1979. A history of a stunted brook trout population in an alpine lake: A lifespan of 24 years. Calif. Fish
and Game, 65: 196-215.

Seber, G. A. F., and E. D. LeCren. 1967. Estimating population parameters from catches large relative to the
population. J. Anim. EcoL, 36: 361-643.

Sigler, W. F. 1952. Age and growth of the brown trout, Salmo trutta fario Linnaeus, in Logan River, Utah. Amer.

Fish. Soc, Trans., 81: 171-178.
Smith, |. J. and H. W. Li. 1983. Energetic factors influencing foraging tactics of juvenile steelhead trout, Salmo

galrdneri. Pages 173-180 in L. G. Noakes et al., eds. Predators and prey in fishes. W. junk Publ., The Hague,

Netherlands.

Sumner, F. H. 1948. Age and growth of steelhead trout, Salmo gairdnerii Richardson, caught by sport and
commercial fishermen in Tillamook County, Oregon. Amer. Fish. Soc, Trans., 75: 77-83.

Sumner, F. H. 1962. Migration and growth of the coastal cutthroat trout in Tillamook County, Oregon. Amer. Fish.
Soc, Trans., 91(1): 77-83.

Van Velson, R. 1979. Effects of livestock grazing upon rainbow trout in Otter Creek. Pages 53-55 in O. B. Cope,
ed. Forum — Grazing and Riparian/Stream Ecosystems, Trout Unlimited, Inc.

174 CALIFORNIA FISH AND CAME

Calif. Fish and Came 76 ( 3 ): 1 74- 1 80 1 990

COMPARISON OF EFFICIENCY AND SELECTIVITY OF

THREE GEARS USED TO SAMPLE WHITE STURGEON IN A

COLUMBIA RIVER RESERVOIR'

JOHN C. ELLIOTT

AND

RAYMOND C. BEAMESDERFER

Oregon Department of Fish and Wildlife

17330 S. E. Evelyn St.,

Clackamas, Oregon 97015

We compared the efficiency and size selectivity of setlines, gillnets, and angling
to select a cost-effective means of capturing a large number of adult and subadult
white sturgeon, Acipenser transmontanus, unharmed while minimizing size selec-
tivity and catch of non-target game fish. Setlines provided the greatest catch rate
per sampling week (61.4), followed by gillnets (49.4) and angling (34.4). Setlines
also captured a wider size-range of sturgeon than gillnets or angling. No other game
fish were caught with setlines or angling while gillnets caught other game fish
including salmon and steelhead, Oncorhynchus spp.

INTRODUCTION

White sturgeon, Acipenser transmontanus, is a valuable resource along the
Pacific Coast of North Annerica (Pycha 1956, Semakula and Larkin 1968,
Kohlhorst 1980, Cochnauer 1983, Oregon Department of Fish and Wildlife
1988). In the Colunnbia River, white sturgeon support recreational, commercial,
and tribal fisheries (Galbreath 1985) . With the decline of anadromous salmonid
fisheries (Raymond 1988), the white sturgeon fishery has rapidly increased in
importance. Total effort and landings have increased several-fold since 1970
(Oregon Department of Fish Wildlife 1988), and effort by recreational white
sturgeon anglers now exceeds effort by recreational salmon anglers down-
stream from Bonneville Dam (Hess and King 1988).

The status of white sturgeon varies within the Columbia River basin. Although
the population below Bonneville Dam has supported a harvest of over 50,000
fish annually in recent years, populations in the Snake and Kootenai rivers
(Columbia River tributaries) have diminished to the point where no harvest is
allowed. Populations have declined in tributaries, possibly for several reasons:
(i) migration of white sturgeon into the upper basin has been blocked by the
construction and operation of hydroelectric dams (Bajkov 1951, Lukens 1981 );
(ii) habitat, including food availability, flow, and temperature has been altered
by the creation of reservoirs formed by these dams (Bajkov 1951, Coon et al.
1977, Haynes et al. 1978, Lukens 1981); (iii) other biological and physical
factors such as predation and the level of pesticides also may have changed
(Bosley and Gately 1981).

We needed a gear that would collect a large sample of white sturgeon
unharmed to evaluate effects of dam construction and operation on white
sturgeon and to design management strategies to optimize yield (Rieman et al.
1987). Other considerations included sampling efficiently to minimize the cost

Accepted for publication )une 1990.

GEAR SELECTIVITY FOR WHITE STURGEON

175

of sampling hundreds of kilometers of river, gear size selection which might bias
representation of the population ( Beamesderfer and Rieman 1988), and
incidental catch of other game fish. Hence, the objective of this report is to
describe the most effective gear for capturing subadult and adult white stureon
unharmed while minimizing size selectivity and catch of other game fish.

STUDY AREA

We selected The Dalles Reservoir, a mainstem impoundment of the Columbia
River (Figure 1 ), for our gear analysis because this reservoir is relatively small
compared with other impoundments in the Columbia River and access to all
parts of the reservoir is good. The Dalles Reservoir is located between The
Dalles and John Day dams (river kilometer 308 to 347). It was formed in 1957
with the closure of The Dalles Dam, a U.S. Army Corps of Engineers
hydroelectric, navigation, and flood control project. At mean operating level,
the reservoir has a surface area of 3,800 hectares, water elevation of 48.2 m
above mean sea level, and depth as great as 61 m. The upper reservoir is
riverine, and measurable current exists throughout the reservoir. Average daily
inflow and outflow ranges from 3,000 to over 12,000 m^/s.

Snake River

McNary Dam

Portland

John Day Dam

'Bonneville The Dalles Dam
Dam

FIGURE 1. Location of The Dalles Reservoir.

METHODS

We chose setlines, gillnets, and angling as potential ways to collect white
sturgeon based on review of the literature and discussions with commercial
fishermen. We sampled from March through September, 1987. Effort of each
gear was evenly distributed throughout the reservoir and the period of sampling.

Setlines consisted of a 182-m long mainline of 6.4 mm diameter nylon rope,
along which 40 hook lines (gangions) were equally spaced. Each gangion
consisted of a removable, spring-loaded snap attached to a 0.5-m length of
parachute cord by a swivel, with a hook attached to the other end of the cord.
Each setline included 10 each of size 10/0, 12/0, 14/0 and 16/0 circle hooks.
Circle hooks have the point bent at a 90° angle to the shaft to better retain
hooked fish for long periods of time. Each end of a setline was held in place by

176

CALIFORNIA FISH AND CAME

a 15-20 kg anchor. Each anchor ws also attached to a buoy with rope identical
to the mainline. Lines were set for 4-48 h in depths from 3 to 50 m. Hooks were
baited with 2.5- to 5-cm long cross-section slices of adult pacific lamprey,
Entosphenus tridentatus, or 2.5- to 10-cm^ pieces of adult coho salmon,
Oncorhynchus kisutch, with skin attached. Only one bait type was used on
each line. Setlines were deployed and retrieved from a 7 m figerglass skiff
equipped with a hydraulic pot hauler.

Gillnets were sinking type and set stationary and perpendicular to the current.
Each net was 45.6 m long and consisted of six, equal length, alternating panels
of 5.1 cm, 8.3 cm and 11.4 cm bar mesh. Net panels were constructed from
multifilament and cable nylon. Each panel was hung with 4.6 m deep mesh on
a framework with a 3-m long vertical slacker lines attached to the float and
leadline at 3.8 m intervals along the length of the net. Gillnets were held in place
by 4.5-20 kg anchors depending on current. A buoy marked each anchor.
Gillnets were fished for 1^ h in depths from 3 to 35 m. Nets were deployed and
retrieved by hand from the boat.

<

60

30

0
60

30

SETLINE
N = 765

GILLNET

N = 182

ou

ANGLING

30

N = 30

0

1

100 200

FORK LENGTH (CM)

300

FIGURE 2. Length-frequency distributions of white sturgeon collected with various gear in The
Dalles Reservoir of the Columbia River, 1987.

Angling gear consisted of a medium heavy action rod with a sensitive tip, a
bait casting reel with 18 kg breaking strength monofilament line and 7/0 or 9/0
J-type hooks. Rods were closely attended. Hooks were baited with Pacific
lamprey pieces, coho salmon pieces, whole eulachon, Thaleichthys pacificus,

GEAR SELECTIVITY FOR WHITE STURGEON

177

whole juvenile coho salmon or pickled herring, Clupea sp. We fished from an
anchored boat for durations of 1/2 to 3 h in depths from 15 to 45 m.

We measured fork length of captured white sturgeon to the nearest
centimeter. Hook size and bait type were recorded for all sturgeon caught by
setlines and angling. We also identified and counted the catch of other fish
species.

30 n

10/0

20

— , N - 167

10

0
30 1

,

1

hn ^^/°

% ''

N = 197

g 10-
Z 0-

J

~l — ■ . .

^ 30n

\~1 ^*/°

5 20
5 10.

o

oJ

30 1

N = 181

1

y-^

t~n ^^/°

20

N = 186

10

1

nj

1 t=i

100 200

FORK LENGTH (CM)

300

FIGURE 3. Length-frequency distributions of white sturgeon collected with various hook sizes on
setlines in The Dalles Reservoir of the Columbia River, 1987.

We evaluated gear based on harm caused to white sturgeon, sampling
efficiency, size selectivity, and catch of other game fish. Harm was evaluated by
the number of dead white sturgeon in the catch by gear. Sampling efficiency
was evaluated by comparing catch-per-u nit-effort (CPUE) among gears. We
standardize CPUE of gear by calculating mean catch per crew week (40 hours
of sampling by a crew using the gear) based on 13.4 crew weeks of setlining,
3.7 crew weeks of gillnetting and 0.9 crew weeks of angling. We evaluated size
selectivity by comparing length-frequency distributions of catch among gears.
We assumed size selectivity was least where the range of lengths sampled was
greatest. Statistical differences in length frequencies of fish captured among
gears were identified with chi-square tests. We also used chi-square analysis to
test for the selectivity associated with hook size and bait type used while
setlining.

1 78 CALIFORNIA FISH AND GAME

TABLE 1. Summary of white sturgeon effort and catch in The Dalles Reservoir, 1987.

Number of Crew Catch per 40

Gear Observations hours Catch crew hours

Selline 233 538 826 61.4

Cillnet 87 149 184 49.4

Hook and line 25 36 31 34 4

RESULTS

All three gear sampled white sturgeon essentially unharmed. Direct mortality
was only one fish for each gear.

Setlines were the most productive gear (Table 1 ). Catch per crew week with
setlines was 1.24 times catch with gillnets and 1.78 times catch by angling.

TABLE 2. Incidental catch of fish other than sturgeon in The Dalles Reservoir, 1987.

Hook

and

Species Set line Cillnet Line

Carp, Cyprinus carpio 0 4 0

Qhar\r[e\ Q&\i\sh, Ictalurus punctatus 0 1 0

Chinook salmon, Oncorhynchus tshawytscha 0 1 0

Largescale sucker, Catostomus macrocheilus 0 6 0

Northern squawfish, Plychocheilus oregonensis 19 14 0

Sockeye salmon, Oncorhynchus nerka 0 3 0

Steelhead, Oncorhynchus mykiss 0 10 0

Walleye, Stizostedion vitreum 0 2 0

Different gear caught different sizes of fish (Figure 2) and differences were
significant between setlines and gillnets (X*^ = 340.7; df = 7; p <0.01).
Setlines captured white sturgeon over a much wider range of lengths and fish
of a greater length than gillnets. Sample sizes from angling were inadequate to
statistically compare length distribution differences with other gears.

Differences in length-frequency distributions were significant for white
sturgeon captured by various hook sizes (X^ = 88.3; df = 18; p < 0.01)
(Figure 3). Larger hooks took larger fish and fish over a wider range of fork
lengths. White sturgeon greater than 90 cm fork length appeared fully recruited
to all setline hook sizes.

No significant difference in length-frequency distributions was detected
between bait types (X^ = 5.2; df = 5; p = 0.389).

Gillnets frequently caught fish other than sturgeon including several game
species (Table 2). Setlines caught only the nongame northern squawfish. No
other fish were caught while angling for sturgeon.

DISCUSSION

We concluded that setlines were the best available gear for our study. Setlines
caught more white sturgeon per crew hour than the other gears and did not
catch any other game fish. Setlines also appeared to take the most represent-
ative sample of white sturgeon over 90 cm based on length-frequency
distributions of catches. We were primarily concerned with white sturgeon 90
cm and larger, corresponding to lengths harvested in the fisheries, and the
reproductive stock (fish longer than 183 cm, the maximum legal length limit).

GEAR SELECTIVITY FOR WHITE STURGEON 179

The gillnets had many drawbacks and few advantages over setlines. Whereas
white sturgeon mortality was low in gillnets, the nets captured fish other than
sturgeon, particularly adult salmon and steelhead, often with a substantial
mortality rate. This restricted use of gillnets to areas and times where salmon
and steelhead were absent. Gillnets also captured white sturgeon from a
narrower range of lengths than did setlines, and much of the catch consisted of
fish under 90 cm fork length.

Angling was also inferior to setlines. Although mortality was low, the effort
per fish was high. The length range of white sturgeon captured with hook and
line fell within that captured by setlines, although a similar distribution might be
expected with a greater sample size.

We will only sample with setlines for the remainder of the study. However,
we have made a few modifications to address the efficiency and selectivity of
our setlines. We are discontinuing using 10/0 hooks for the following reasons:
(i) they required more crew hours to use because they were harder to sharpen
and bait and required more frequent replacement; (ii) the white sturgeon they
captured were within the range of those captured with 12/0 hooks; and (iii)
these hooks were often straightened out or snapped off, apparently unable to
hold larger fish. We will only use 136-kg test gangions because of the number
of broken 68-kg test gangions observed.

Finally, we will only use Pacific lamprey for bait. Pacific lamprey slices appear
to be an attractive bait for white sturgeon for more than one day. Coho salmon
pieces often fell apart within 24 hours. Further, Pacific lamprey is relatively easy
to obtain and minimizes preparation and gear deployment time.

ACKNOWLEDGMENTS

We thank Doug Engle and Ray FHartlerode for assistance with field sampling.
Bruce Rieman guided this project through its early stages. Wayne Burck, Mary
Buckman, and Tony Nigro provided constructive editorial comments on early
drafts of this manuscript. The Bonneville Power Administration provided
funding for this work under Contract DE-AI79-86BP63584.

LITERATURE CITED

Bajkov, A. D. 1951. Migration of the white sturgeon Acipenser transmontanus in the Columbia River. Fish
Commission of Oregon Research Briefs, 3(2):8-21.

Beamesderfer, R. C, and B. E. Rieman. 1988. Size selectivity and bias in estimates of population statistics of

smallmouth bass, walleye, and northern squawfish in a Columbia River reservoir. No. Am. ). Fish. Mangt.,

8:505-510.
Bosley, C. E. and C. F. Cately. 1 981 . Polychlorinated biphenyls and chlorinated pesticides in Columbia River white

sturgeon Acipenser transmontanus. U.S. Fish and Wildlife Service, Marrowstone Field Station, Nordland,

Washington. Unpublished report.

Cochnauer, T. C. 1983. Abundance, distribution, growth and management of white sturgeon Acipenser
transmontanus in the middle Snake River, Idaho. Doctoral dissertation. University of Idaho.

Coon, ). C, R. R. Ringe, and T. C. Bjornn. 1977. Abundance, growth, distribution and movements of white
sturgeon in the mid-Snake River. Water Resources Research Institute, Research Technical Completion Report,
Project B-026-IDA. University of Idaho. Moscow. 63 p.

Calbreath, ). 1985. Status, life history, and management of Columbia River white sturgeon, Acipenser
transmontanus. Pages 119 to 126 in F. P. Binkowski and S. I. Doroshov, eds. North American sturgeons. Dr.
W. Junk, Dordrecht, The Netherlands.

Haynes, |. M., R. H. Cray, and ). C. Montgomery. 1978. Seasonal movements of white sturgeon (Acipenser
transmontanus) in the mid-Columbia River, Trans. Am. Fish. Soc, 107:275-280.

180 CALIFORNIA FISH AND GAME

Hess, S. S., and S. D. King. 1988. The 1987 lower Columbia River (Bonneville to Astoria) and estuary salmon
(buoy 10) recreational fisheries. Oregon Department of Fish and Wildlife Report. 62 p.

Kohlhorst, D. W. 1980. Recent trends in the white sturgeon population in California's Sacramento-San Joaquin
Estuary. Calif. Fish and Game, 66:210-219.

Lukens, j. R. 1981. Snake River Sturgeon Investigations (Bliss Dam Upstream to Shoshone Falls). Idaho
Department of Fish and Came Report to Idaho Power Company. 33 p.

Oregon Department of Fish and Wildlife. 1988. Columbia River fish runs and fisheries, 1960-87. Portland. 105 p.
Pycha, R. L. 1956. Progress report on white sturgeon studies. Calif. Fish and Game, 42:23-35.
Raymond, H. L. 1988. Effects of hydroelectric development and fisheries enhancement on spring and summer
Chinook and steelhead in the Columbia River basin. No. Am. ). Fish. Mangt , 8:1-24.

Rieman, B. E., ]. C. Elliott, and A. A. Nigro. 1987. Appendix A. Pages 7-24 in Status and habitat requirements of
white sturgeon populations in the Columbia River downsteam from McNary Dam. Bonneville Power
Administration, Annual Progress Report, Portland, Oregon. 60 p.

Semakula, S. N., and P. A. Larkin. 1968. Age, growth, food and yield of the white sturgeon (Acipenser
Iransmontanus) of the Fraser River, British Columbia. ). Fish. Res. Bd. Can., 25:2589-2602.

NOTES 181

Calif. Fish and Game 76 ( 3 ) 1 990

NOTES

GIANT BLUEFIN TUNA OFF SOUTHERN CALIFORNIA,
WITH A NEW CALIFORNIA SIZE RECORD

Most of the Pacific bluefin tuna, Thunnus thynnus orientalis (Temminck and
Schlegel, 1844), landed by purse seiners in the eastern Pacific weigh 5 to 25 kg,
but fish weighing over 50 kg are not uncommon. Exceptionally large bluefin tuna
were caught, mostly in November and December, 1988, by a fleet of small
purse seiners based in San Pedro, California. During the period of 28 October
1 988 to 4 January 1 989, 1 5 boats made 56 trips to areas just south of the east end
of Santa Rosa Island, northwest of San Nicolas Island, and to Tanner and Cortes
banks (Figure 1 ). They captured an estimated 987 fish weighing from about 50
to 458 kg; the total weight was about 139 mt and the average size was about 141
kg. These fish are of special interest because bluefin tuna of this size are of great
value on the Japanese sashimi market, no bluefin of this size had been caught
previously in such quantities in the eastern Pacific, and many of these were
larger than any bluefin caught previously in California.

Meristic characters and morphology were used to verify identification. Gill
raker count on a 242-cm specimen was 13 + 23 = 36, and the ventral surface
of the liver was striated in several specimens, which, coupled with the extreme
size, indicate these fish were not yellowfin tuna, T. albacares. The caudal keels
were usually black or dark grey, indicating that these were not southern bluefin,
T. maccoyii. The pectoral length, as a percentage of fork length, was 16.8% for
the record fish, indicating it was a Pacific bluefin tuna (Gibbs and Collette
1967).

Yukinawa and Yabuta (1967) fitted a von Bertalanffy growth curve to age
data derived from scales of bluefin up to 7 years old from the western Pacific
and extrapolated lengths-at-age to 20 years. From their equation, bluefin of this
size are estimated to be from 5 to 17 years old. Bluefin of the same size from
the Atlantic are estimated by analysis of otoliths (Hurley and lies 1983) to be
7 to 24 years old, although significant variation in age exists among individuals
of the same length and between sexes.

The largest fish (Figure 2) was caught at ca. 0200 h on 18 December 1988,
at San Nicolas Island, by the 21 -m purse seiner SEA QUEEN. It weighed 457.7
kg and measured 271.2 cm fork length (FL). It exceeded the previous California
record (Dotson and Graves 1984) by 220.7 kg, although there is an unsubstan-
tiated record of a 408-kg fish taken in a net in Monterey Bay early in the 20th
century (Holder 1913). The fish was male, appeared robust, and its position
relative to the length-weight curve was well above the rest of the values used
for fitting it (Figure 3).

Large bluefin were initially sighted around 15 October, but were over deep
water and no successful sets were made. On 27-30 October several vessels
caught ca. 63 tons of smaller bluefin (50-70 kg), mostly around Tanner and
Cortes banks. On 30 October, a favorable report from spotter aircraft sent the

182

CALIFORNIA FISH AND CAME

boats north to the relatively shallow (less than 50 fm) area south of East Point
on Santa Rosa Island. As the fish were wild and not catchable during the day,
the boats, assisted by the spotter aircraft, set at night on visible trails caused by
movement of the fish through bioluminescent plankton. The nets of most
vessels in the fleet normally fish at 45-50 fm maximum depth, and unless the
schools were in shallower water, the fish usually escaped underneath or
otherwise evaded the net. Sets were made in water as shallow as 18 fm and as
deep as 100 fm. Catches of the large fish were first made on 31 October and
continued sporadically through December with the last catch occurring on 3
January 1989. Most of the sightings were made between Santa Rosa Island and
Begg Rock.

r ' ' I I ' I ' ' I I '

FIGURE 1 . Areas of catches (crosshatched) of large bluefin tuna captured during November and
December 1988.

Schools such as these are conspicuous during both night and day when near
the surface, and with the aid of fairly constant spotter aircraft activity in previous
years, were seen sporadically in 1986 and 1987, although less frequently than in
1988. Schools were reported from the Sixtymile Bank northwest to the
Rodriguez Seamount but few, if any, were caught. Prior to this season (1988),
spotter aircraft may have ignored large fish in small schools (1-5 fish) because
they were either misidentified as pods of marine mammals or judged unprof-
itable in tonnage. As prices rose dramatically due to interest shown by Japanese
buyers, the spotters and vessels alsobecame interested in the small schools of
larger fish.

NOTES

183

FIGURE 2. The California record bluefin tuna.

Drift gill-net vessels also reported the large fish, although offshore and over
deeper water (greater than 1000 fm), during October-December of 1986, 1987,
and 1988, but caught no bluefin greater than about 50 kg, as the larger fish tore
holes in the nets. During this period of 1988, a gill-net vessel set its gear in the
Santa Rosa Flats area, and the pilot of a spotter aircraft observed a school of
bluefin swim through the net. Subsequent examination of the net revealed
the large holes similar to those evident after fishing in the offshore areas.

The mean weight of the fish caught mostly at Santa Rosa Island during
November (194 kg) was much greater than that of those caught during
December (100 kg), when fishing shifted to San Nicolas Island and Tanner and
Cortes banks. The greatest mean size of fish and smallest number of fish per
successful set (Table 1 ) were captured during the latter half of November,
when a total of 79 fish (6.6 per set) averaged 260 kg for the 2-week period of
18 November-1 December. Calkins (1982) presented length-frequency data by
year for surface-caught bluefin in the eastern Pacific Oceanwhich showed few
instances of fish approaching these sizes.

184

CALIFORNIA FISH AND GAME

500
450

t

w

- T 1 1

-9.02408
eight - e

r^ = .96

2.6767
Length

1 1

T 1

*

-

400

-

n = 38

9^

~

-5^350

^ 300

^250
III

200

-

° .8«r^

CD a^
D

y^

-

150

-

^.^4^°

~

100
en

1

1 1 1

1 1 1

1 1

1 1

160 180 200 220

LENGTH (cm)

240

260

280

FIGURE 3. The length-weight relationship for 38 bluefin tuna captured during Novennber and
December 1988 off Southern California. Record fish indicated by star.

TABLE 1.

Summary of South

ern

California Land

ngs (in Kg)

of Large

Bluefin Tuna Captured Between

28 October 1988 a

nd 3 January

1989.

Week

Total no.

Mean no

Mean wt.

Total

Mean

ending

Area

Trips

offish

of fish

per fish

landings

catch

Nov 3

Tanner, Cortes
banks, Santa Rosa 1.

6

56

9.3

150

8.404

1,401

Nov 10

Santa Rosa 1.

10

189

18.9

178

33,744

3,374

Nov 17

"

5

103

20.6

197

20,284

4,057

Nov 24

"

5

34

6.8

272

9,230

1,846

Dec 1

"

7

45

6.4

251

11,318

1,617

Dec 8

Tanner Bank

5

84

16.8

52

4,385

877

Dec 15

Tanner Bank,
San Nicolas \.

9

287

31.9

126

36,208

4,023

Dec 22

San Nicolas,
Sta. Barbara 1.

5

36

7.2

170

6,107

1,222

Dec 29

—

0

0

—

—

—

—

)an 5

Tanner Bank

4

153

38.3

59

9,072*

2,268*

56

987

17.6

141

1 38,753

2,478

TOTAL
* estimated

According to records of the Inter-American Tropical Tuna Commission
(lATTC), catches of large bluefin in the eastern Pacific are rare. During
August-December 1977, fish of about 50 to 110 kg were caught off northern
Baja California by purse seiners. In October 1986, one vessel caught 45 mt of
bluefin in shallow water off Santa Rosa Island, about half of which were
exceptionally large. Fifty of these were measured by the lATTC; their lengths
ranged from 180 to 200 cm (ca. 109 to 145 kg). On 7 December 1981, a single
fish weighing 237 kg was caught in a drift gill-net 12 mi south of Anacapa Island
(Dotson and Graves 1984). The record for bluefin tuna captured in California
waters by a sport angler stood at 113.9 kg from 1899 to 4 October 1983, when
a 164.9-kg fish was captured at Osborn Bank (S.J. Crooke, Calif. Dept. of Fish

NOTES 185

and Game, Long Beach; pers. comm.). Large bluefin tuna are known to occur
in Baja California waters around Guadalupe Island (lat 29°irN, long 118°17'W).
On 21 July 1982, an angler captured a 126.5-kg bluefin and on 22 September, of
that year, a diver speared a 180.5-kg fish at this locale.

Bluefin weighing more than 225 kg occur frequently in Japanese longline
catches in the central and western Pacific. The largest bluefin recorded by the
Far Seas Fisheries Research Laboratory of Shimizu, Japan, weighed about 555 kg
(ca. 3 m). It was caught during April 1986, about 300 mi south of Kyushu Island,
Japan. Large Pacific bluefin also occur occasionally in the southwest Pacific
(Collette and Smith 1981 ). Bluefin between 225 and 450 kg are caught regularly
in the Atlantic, and fish between 450 and 680 kg are sporadically encountered
there (Hisada and Suzuki 1982).

lATTC employees collected biological samples from 62 of the fish and made
abstracts of the logbook records of all the vessels. The mean sea-surface
temperature (for those boats recording it) was 14.rC. Gross examination of
stomach contents during processing revealed that when captured the fish had
been feeding primarily on chub mackerel. Scomber japonicus, and small (10
cm) market squid, Lollgo opalescens, indicating feeding near the surface.

The gonads of 45 fish were examined; all were males. No studies of sex ratios
in large ( > 100 cm) bluefin tuna in the eastern Pacific appear in the literature,
but Yamanaka et al. (1963) note that females predominated in fish sampled by
longline during May and June in the area east of Formosa (Taiwan), and males
in fish sampled around Sanriku during June through August. Rivas ( 1 975 ) found
a preponderance of females in Atlantic bluefin tuna caught in the Straits of
Florida and near the Bahama Islands during April and May, and a preponder-
ance of males in the Gulf of Maine and off Nova Scotia and Newfoundland in
July through October. Although there is an indication of segregation by sex in
these large fish in the eastern Pacific, lack of data from other geographical areas
precludes further speculation.

The reason for the appearance of these exceptionally large fish in the eastern
Pacific is unknown. Immature Pacific bluefin are trans-Pacific migrators
(Orange and Fink 1963, Clemens and Flittner 1969, Bayliff 1980), with a portion
of the population migrating from the western Pacific after the first or second
year of life and staying in the eastern Pacific for up to 2 years or more, before
returning to the western Pacific. Bluefin tagged in the eastern Pacific and
recaptured in the western Pacific were at liberty for a minimum of 22 months
(Clemens and Flittner 1969, Bayliff 1988). There is no evidence of spawning,
e.g. presence of larvae or juveniles or reproductively-active adults, in the
eastern Pacific (Bell 1963). First maturity occurs at 3 to 4 years (Hirota, et al.
1976), and fish older than that (50 to 150 kg) occur in the eastern Pacific at
irregular intervals, especially late in the year around offshore banks, but not
nearly as frequently as do the younger ones. It is not known whether these large
fish were recent arrivals form the western Pacific or had spent several years in
the eastern Pacific.

Ex-vessel price for the vessel owners who sold their catches outright was
$15.40 to $26.40 per kg, although other owners opted to receive a share of the
profits from the sale of the fish in Japan, where prices ranged from $35.20 to
over %77 per kg.

186 CALIFORNIA FISH AND CAME

ACKNOWLEDGMENTS

We thank Bruce B. Collette of the National Museum of Natural History and
W. H. Bayliff of the lATTC for their reviews of the manuscript, Liz Palmer and
Ed Everett for collection of data, and Kurt Schaefer for identification of stomach
contents. We also thank John Huelman, of Ventura, for information on spotter
aircraft activity; Sal Ciaramitaro and John Mattera for anecdotal fishing
information; the staff of United Food Processors of Terminal Island, and the
crews of the San Pedro purse-seine fleet for their cooperation in allowing
collection of catch and biological data.

LITERATURE CITED

Bayliff, W. H. 1980. Synopsis of biological data on the northern bluefin tuna, Thunnus thynnus (Linnaeus, 1758),

in the Pacific Ocean. Inter-Am. Trop. Tuna Comm., Spec. Rep., 2:262-293.
Bell, R. R. 1963. Synopsis of biological data on California bluefin tuna Thunnus saliens Jordan and Evermann 1926.

FAO, Fish. Rep., 6(2):380-^21.

Calkins, T. P. 1982. Observations on the purse-seine fishery for northern bluefin tuna (Thunnus thynnus) in the

eastern Pacific Ocean. Inter-Amer. Trop. Tuna Comm., Bull., 1 8(2) :1 23-225.
Clemens, H. B., and C. A. Flittner. 1969. Bluefin tuna migrate across the Pacific Ocean, Calif. Fish and Game,

55(2);132-135.
Collette, B. B., and B, R. Smith. 1981. Bluefin tuna, Thunnus thynnus orientalis, from the Gulf of Papua. )apan. ).

IchthyoL, 28(2):166-168.
Dotson, R. C, and J. E. Graves. 1984. Biochemical identification of a bluefin tuna establishes a new California size

record. Calif. Fish and Game, 70(1);58-64.
Gibbs, R. H., )r., and B. B. Collette. 1967. Comparative anatomy and systematics of the tunas, genus Thunnus. U.S.

Fish Wildl. Serv., Fish. Bull., 66(1 ):65-130.
Hirota, H., M. Morita, and N. Taniguchi. 1976. An instance of the maturation of 3 full years old bluefin tuna

cultured in the floating net. )ap. Soc. Sci. Fish., Bull., 42(8):939.
Hisada, K., and Z. Suzuki. 1982. Catch, fishing effort and length composition of the Atlantic bluefin caught by the

Japanese longline fishery. Int. Comm. Cons. All. Tunas, Coll. Vol. Sci. Pap., 17(2);307-314.
Holder, C. F. 1913. The game fishes of the world. Hodder and Stoughton, New York. 411 p.
Hurley, P. C. F., and T. D. lies. 1983. Age and growth estimation of Atlantic bluefin tuna, Thunnus thynnus, using

otoliths. Pages 71-75 in E. D. Prince and L. M. Pulos, eds. Proceedings of the international workshop on age

determination of oceanic pelagic fishes: tunas, billfishes, and sharks. U.S. Dept. of Commerce, NOAA Tech.

Rep. NMFS 8.
Orange, C. J., and B. D. Fink. 1963. Migration of a tagged bluefin tuna across the Pacific Ocean. Calif. Fish and

Came, 49(4):307-309.
Rivas, L. R. 1975. Variation in sex ratio, size differences between sexes, and change in size and age composition

in western north Atlantic bluefin tuna ( Thunnus thynnus.) Int. Comm. Cons. Atl. Tunas, Coll. Vol. Sci. Pap.,

5(2):297-301.
Yamanaka, H., et al. 1963. Synopsis of biological data on kuromaguro Thunnus orientalis (Temminck and

Schlegel) 1842 (Pacific Ocean). FAO, Fish. Rep., 6(2):180-217.
Yukinawa, M., and Y. Yabuta. 1967. Age and growth of the bluefin tuna Thunnus thynnus (Liinnaeus) in the North

Pacific Ocean. Rep. Nankai Reg. Fish. Res. Lab. 25:1-18.

— Terry J. Foreman, Inter-American Tropical Tuna Commission, c/o Scripps
Institution of Oceanography, La jolla, California 92093, and Yoshio Ishizuka,
National Research Institute of Far Seas Fisheries, Shimizu, Japan. Accepted for
publication May 1990.

NOTES 187

BOBCAT ELECTROCUTIONS ON POWERLINES

Powerline electrocution of birds has been well documented in the scientific
literature (Anderson 1933, Dilger 1954, Harrison 1963, Boeker and Nickerson
1975, Kothman and Litton 1975, Switzer 1977, Pomeroy 1978, Benson 1981,
Olendorff et al. 1981, Dedon and Colson 1987, Williams and Colson 1989).
However, published accounts of electrocutions of other vertebrate taxa are
extremely rare. Edison Electric Institute (1980) noted that snakes, mice, tree
squirrels, Sciurus spp.; flying squirrels Glaucomys spp.; raccoons;, Procyon
lotor, and black bears, Ursus americanus; occasionally come in contact with
energized electrical equipment and, therefore, are subject to potential electro-
cution. Among wild mammals, squirrels are the most frequent victims of
electrocution because of their penchant for chewing on energized wires
(Commonwealth Edison 1975, Pacific Gas and Electric Company [PG&E]
unpubl. data). There is some evidence that interactions between black bears
and power lines are increasing in number as civilization encroaches on the
species' habitat. In Albuquerque, New Mexico, for example, a tranquilized
black bear that had climbed a power pole to escape capture suffered a non-fatal
electrical burn as it fell into a 7,200-volt powerline (W. R. Pilz, Public Service
Company of New Mexico, pers. comm.). To my knowledge, powerline
electrocutions have not been reported in the literature for any other mammalian
species. This note documents the electrocution of two bobcats. Fells rufus, on
PG&E power poles in north-coastal California.

The carcass of an adult female bobcat was discovered by a PG&E line crew
on 19 September 1988, approximately 8.5 km northwest of Inverness, at Point
Reyes National Seashore. The animal was draped over a transformer attached
to a pole supporting a 12,000-volt powerline (Figure 1). Maggots had infested
the carcass, suggesting that the animal had died several days prior to being
discovered. PG&E linemen reported that a similar bobcat electrocution oc-
curred in the late-1970s, approximately 16 km southwest of Inverness, near the
Point Reyes Light Station. However, no additional details are available on this
earlier mortality.

Bobcat electrocution appears to be an extremely unusual and random event,
as evidenced by the absence of published accounts of powerline interactions.
These animals often climb trees when threatened, or occasionally while hunting
(Chapman and Feldhamer 1982). Where trees are absent, as in the coastal
scrub habitat covering much of Point Reyes National Seashore, it is reasonable
to assume that bobcats will climb utility poles to escape danger or pursue prey.
I speculate that the animals in question may have climbed power poles to
escape the pursuit of dogs originating from the local ranches. This behavior
would be consistent with the well-documented "treeing" response displayed
by bobcats and other felids when pursued by trained hunting dogs. After an
animal climbs a power pole, simultaneous contact with two energized wires or
a wire and a grounded object (e.g., a transformer) would normally be sufficient
to cause a "flashover" of electricity and electrocution of the animal.

I gratefully acknowledge W. Crawley, T. j. McMorrow, and B. E. Perron for
providing background information on the bobcat electrocutions. E. W. Colson,
M. F. Dedon, T. Silver, and B. F. Waters reviewed the manuscript.

188

CALIFORNIA FISH AND CAME

FIGURE 1. Carcass of an adult female bobcat on a 12,000-volt powerline transformer.

LITERATURE CITED

Anderson, A. H. 1933. Electrocution of purple martins. Condor, 35:204,

Benson, P. C. 1981. Large raptor electrocution and power pole utilization: a study in six western states. Raptor

Res., 14:125-126.
Boeker, E. L., and P. R. Nickerson. 1975. Raptor electrocutions. Wildl. Soc. Bull., 3:79-81.
Chapman, |. A., and G. A. Feldhamer. 1982. Wild mammals of Nortfi America. The John Hopkins Univ. Press,

Baltimore MD. 1147 p.
Commonwealth Edison. 1975. Chewing squirrels foiled at Commonwealth Edison. Public LJtilities Fortnightly, Sept.

11, p. 90.
Dedon, M, F., and E. W. Colson. Investigation of bird-caused outages in the Pacific Gas and Electric Company

service area. Pages 34-45 in W. R. Byrnes and H. A. Holt, eds. Proc. fourth symposium on environmental

concerns in rights-of-way management. Purdue Univ., West Lafayette, Ind.
Dilger, W. C. 1954. Electrocution of parakeets at Agra, India. Condor, 56(2):102-103.
Edison Electric Institute. 1980. Compatibility of fish, wildlife, and floral resources with electric power facilities.

Edison Electr. Inst., Washington, DC. 130 p.
Harrison, J. 1963. Heavy mortality of mute swans from electrocution. Wildfowl Trust Ann. Rep. 14:164-165.

NOTES 189

Kothman, C. H., and C. W. Litton. 1975. Utilization of man-made roosts by turkey in west Texas. Pages 159-163
in K. Halls, ed. Proc. of the third national wild turkey symposium.

Olendorff, R. R., A. D. Miller, and R. N. Lehman. 1981. Suggested practices for raptor protection on power lines;

the state of the art in 1981. Raptor Res., Rep. 4. Ill p.
Pomeroy, D. E. 1978. The biology of Marabou storks in Uganda; II. Breeding biology and general review. Ardea,

66:1-23.

Switzer, F. 1977. Saskatchewan Power's experience. Blue lay, 35:259-260.

Williams, R. D., and E. W. Colson. 1989. Raptor associations with linear rights-of-way. Pages 173-192 in Proc.
western raptor management symposium and workshop. Natl. Wildl. Fed., Washington, D.C.

— Richard D. Williams, Technical and Ecological Services, Pacific Cas and
Electric Company, 3400 Crow Canyon Rd., San Ramon, CA 94583. Ac-
cepted for publication June 1990.

190 CALIFORNIA FISH AND CAME

BOOK REVIEWS

MARINE POPULATIONS: AN ESSAY ON POPULATION REGULATION AND SPECIATION

by Michael Sinclair. 1988. University of Washington Press, Seattle, WA. 260 p. $25.00 cloth,
$15.00 paper.

The oceans are a highly dynamic environment. Anyone who has studied planktonic life forms
sooner or later is confronted with the question of "How do these organisms maintain populations
in regions that are conducive to their life history?" Plankton are subjected to currents transporting
them from areas optimal for growth and reproduction to areas that may preclude growth, increase
mortality rates, and not allow for recruitment of these organisms or their progeny back to the
originating population. This question not only relates to phytoplankton and invertebrate zooplank-
ton, but to fishes that have a planktonic life stage. It is this question and its implications that the
author examines in this book.

We know a good amount about the life history of Atlantic herring and the author uses these
populations to show that self-sustaining populations exist in areas of the ocean in which ocean
dynamics can be used to ensure that some portion of the planktonic larval stages will recruit back
to the originating population. In response to ocean dynamics, populations of herring have spawning
periods timed to take advantage of seasonal changes in currents, spawning in the proximity of bays
and estuaries, or the migration of spawning adults to areas in which larval stages will have maximal
survival to a size at which they are capable of returning to the spawning areas. Those that are
carried to regions from which they cannot contribute to the population are lost from the gene pool.

Following this analysis, the author defines the "member/vagrant hypothesis". This hypothesis
leads to several tenants. Populations (which have a planktonic life stage) are found in
"geographical settings . . . within which the species' life cycle is capable of closure". Population
size for the most part is limited by the geographical area that allows for closure — those animals
spawned outside of the area (or time period) are lost to the population. For such organisms food
may seldom be a limiting factor. Likewise intraspecific competition may seldom come into effect.
Recruitment success or failure becomes primarily a function of ocean dynamics. A weakening of
currents may result in high recruitment despite lower productivity because more larvae remain in
the geographical area that allows closure. Conversely stronger currents with higher net productivity
may increase larval survival but if most of these are carried away never to recruit back to the
population we have recruitment failure. Once populations become limited to specific geographical
areas by ocean dynamics, a mechanism for speciation becomes apparent. We now have isolated
spawning groups.

The author goes on with further examples of populations, both fishes and invertebrates, in which
the hypothesis is apparently working. The more I read, the more excited I became. In the last
several chapters, the author questions a number of ecological generalizations (food is a limiting
factor, etc). Likewise certain aspects of evolutionary theory, primarily that populations are
self-regulating and therefore competition is a strong factor in natural selection, are not applicable
to animals whose populations are controlled by ocean dynamics.

If any of these statements pique your curiousity, by all means read this book. I hope that the
arguments put forth here are given serious thought. All too often we tend to sit back and assume
an understanding of phenomena because a theory exists or a simple explanation is given, i.e., that
factor is density dependent, when in fact we do not really know the underlying relationships.
Perhaps this is why a number of fisheries today are in trouble. If many of our pelagic fisheries are
limited by ocean dynamics, then it comes as no surprise that our population dynamics models have
not served us well.

The next question then becomes "What do we do now?" Hopefully this work will lead to
advances in fishery management as well as a re-examining of ecological and evolutionary
mechanisms when the old explanations fail. I would hope that anyone interested in population
dynamics and certainly students now taking such courses would read this book.

— John j. Geibel

BATTLING THE INLAND SEA: American Culture, Public Policy, & the Sacramento Valley,

1850-1986

By Robert Kelley. 1989. University of California Press, Berkeley, CA, 416 p., $35.00

This book presents an excellent history of flood control efforts in the Sacramento valley primarily
from the 1850's through 1920, when the present flood control system had been adopted and its

BOOK REVIEWS igi

implementation was well underway. Events from 1920 through the flood of 1986 are described
briefly. The author describes the interrelationships between flood control, swampland reclamation
and hydraulic mining. It is a story of repeated failures but eventually largely successful conclusion,
as the largest flood of record was contained with minimal harm.

The author is a historian, and an important feature of the book is how he has interwoven flood
control activities with the underlying social and political events. Among the latter is the evolution
from a constitutional requirement that governmental actions be prescribed in detail in law to the
acceptance of laws delegating considerable discretion to the executive branch to act within broad
policy. Also of interest, are the shifts back and forth between populist driven local control and
centralized professional management, depending primarily on whether the Democrats or Repub-
licans controlled government.

In the Preface the author acknowledged that reclamation of the valley "ended in the destroying
of a large natural environment". He, however, makes no attempt to describe the resources which
were lost. Nevertheless, those interested in the evolution of our present society in the Sacramento
valley will find the book worth reading.

— Harold K. Chadwick

ARIZONA GAME BIRDS

By David E. Brown. 1989. The University of Arizona Press, Tucson, AZ. 307 p., illustrated.

$19.95 cloth.

I have been an avid consumer of information about upland game birds for over twenty years, as
both a hunter and researcher. Unfortunately, good books about western upland game birds have
been few and far between. I am most pleased to report that this is a good one and will no doubt
become a standard for personal libraries.

The author uses his experience as a wildlife manager with the Arizona Department of Came and
Fish, a naturalist, and a hunter to provide the reader with an informed and insightful treatment of
Arizona game birds. Each chapter covers the distribution, habitat, life history, management history,
population dynamics, and hunting of one of the thirteen game birds. The material is detailed enough
to be of value to the professional, yet not so detailed as to be laborious to read. The text is well
referenced, although the literature is only effectively cited up to 1985. However, it still provides an
efficient and easy way to enter the scientific literature. The book was interesting to read and I
recommend it highly.

— Sonke Mastrup

192 CALIFORNIA FISH AND CAME

MISCELLANEA

The following excerpts are from early issues of California Fish and Game:

Forests, water power, and wild game are three of California's greatest resources. They are ours
to use but not destroy.

— from cover of Volume I, Number 7 — October 1914

The writer has been observing the fisheries of southern California for nearly thirty years. In that
time the supply has dropped off to a menacing extent, due to lack of laws, lack of protection, and
over-fishing where fishes should be protected.

— Charles Frederick Holder, Volume 1, Number 1 — October 1914

Students of natural history have become fully aware that as the country is settled marked changes
take place in its bird life. A few of our species, such as the linnet and mockingbird, have become
more numerous than they were in the early days. But many more have become noticeably scarcer;
some have disappeared altogether. Bird life as a whole has diminished in quantity to an alarming
degree.

— Joseph Grinnell, Volume 1, Number 1 — October 1914

Everyone owns a share in the natural resources of this state. The protection and conservation of
game is, therefore, to the interest of every citizen.

— /-/. C Bryant, Volume 1, Number 3— April 1915

Only a little study of the conservation situation in America is sufficient to show we have allowed
certain parties at interest to take more than their rightful share of the resources of wild nature which
as a matter of simple justice belong, not only to all the people now living, but also to the generations
of the future indefinitely.

—W. P. Taylor, Volume 1, Number 4— July 1915

Two sea otters were seen basking in the sun in the kelp beds off Del Monte wharf on October
22, 1916. They were apparently an old and young one, and the theory is that the old one came back
to look for one of her young which was caught in a sea bass net last year.

—P. H. Oyer, Volume 3, Number 2— April 1917

The sea urchin, which is quite abundant on our coast, will some day be an article of economic
importance. A few are gathered and the meat eaten by Japanese in California and by natives in
Alaska.

— John N. Cobb, Volume 3, Number 3 — July 1917

INSTRUCTIONS TO AUTHORS

EDITORIAL POLICY

California Fish and Game is a technical, professional, and educational journal
devoted to the conservation and understanding of fish and v/ildlife. Original manu-
scripts submitted for consideration should deal with the California flora and fauna
or provide information of direct interest and benefit to California researchers and
managers. Authors should submit the original manuscript plus two copies, including
tables and figures.

MANUSCRIPTS: Authors should refer to the CBE Style Manual (Fifth Edition) and
a recent issue of California Fish and Game for general guidance in preparing their
manuscripts. Some major points are given below.

1. Typing — All text submitted, including headings, footnotes, and literature cited
must be typewritten doublespaced, on white paper. Papers shorter than 10
typewritten pages, including tables, should follow the format for notes. Letter
quality computer print-out is acceptable.

2. Citations — All citations should follow the name-and-year system. The "library
style" is used in listing literature cited.

3. Abstracts — Every article must be introduced by a concise abstract. Indent the
abstract at each margin to identify it.

4. Abbreviations and numerals — Use approved abbreviations as listed in the CBE
Style Manual. In ail other cases spell out the entire word.

TABLES: Each table should be typewritten with the heading margin left justified.
Tables should be numbered consecutively beginning with "1" and placed together
in the manuscript following the Literature Cited section. Do not double space tables.
See a recent issue of California Fish and Game for format.

FIGURES: Consider proportions of figures in relation to the page size of California
Fish and Game. The usable printed page is 1 17 by 191 mm (4.6 by 7.5 in.). This must
be considered in planning a full page figure, for the figure with its caption cannot
exceed these limits. Photographs should be submitted on glossy paper with strong
contrasts. All figures should be identified with the author's name in the upper left
corner and the figure numbers in the upper right corner. Markings on figures should
be made with a blue china marking pencil. Figure captions must be typed on a
separate sheet headed by the title of the paper and the author's name.

PROOF: Galley proof will be sent to authors approximately 60 days before publi-
cation. The author has the ultimate responsibility for the content of the paper and
is expected to check the galley proof carefully.

PAGE CHARGES AND REPRINTS: All authors will be charged $35 per printed page
and will be billed before publication of manuscripts. Reprints may be ordered
through the editor at the time the proof is submitted. Authors will receive a reprint
charge schedule along with the galley proof.

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