Food of Pacffic Salrnon and Steelhead Trout in theNortheast Pacific Ocean

Although Pacific salmon (genus oncorhynchus) and steelhead trout(salmo gairdner'i,) in the northeast Pacific ocean have been the subject ofconsiderable study over the past decade, published information on their foodr,'ould appear to be l imited to the spring and summer seasons. This articlereports on observations on the food of salmonids, mainly sockeye (o. nerka)and pinks (o. gorbuscho) caught north of 45oN and east of 1s5"w during theu.inter (January 7 February 8, 1964) and compares these rvith those obtainedduring spring and early summer (]\{ay and June, 1958) reported by LeBrasseur( 1 e66) .

Frc. I . Placesofcaptureand numbers of salmon and steelhead trout examined for feedinshabits, northeast Pacific Ocean, January 7-February g, 7964.

1085

.l . .Ftsu..RB-s. Bo. CANAD.I, 25(5): i085-1089, 196S.Printed in Canada.

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1086 JoURNAL FIsI{ERIES RESEARCH BoARD oF CANADA, voI-' 2s, No 5, 1968

Figure 1 indicates the places of capture and the numbers of f ish of each

species examined. The fish ."vere caught from the Fisheries Research Board

vessel G. B. Reed, using surface longlines. \"Iost of the catches were made at

dawn, but some were also made during approaching dusk. Upon completion

of each haul, data r,vere obtained on size, sex, and age from fish selected at

random from the catch.Organisms consumed.- Stomacfu contents were analysed at sea in the

ship's laboratory. For each fish the total volume of contents was measured

by water displacement in a graduated cylinder. The contents were then placed

in a Petri dish and identif ied according to taxonomic categories, mainly family,

with the aid of a binocular microscope. Volumes of individual categories were

then determined either by direct measurement or by converting visual estimates

of its percentage contribution to the stomach contents into volumetric terms'

The relative importance of eacl'r category in the diet of a particular species

of saln.ron .l l ,as determined from its frequency of occurrence and its percentage

contribution to the combined volume of contents. Parasites and baits were

excluded from the contents. I)ata on nttmbers and sizes of salmon examined

and their food are summarized in 'fable I.

The sockeye examined, r,r,1.ricl 'r according to subsequent scale analyses

had been at sea from a fer,v rnonths up to almost 3 years, fed predominately

on fislr (Lampanyctus le'ucopsal'us and. Tarletonbean'ia crenular'is) of the farnily

Nlyctophidae. Squid (othei than bait) ranked second in importance. Other

T.qsr,n I. Relative importance of various organisms in the rvinter diet of Pacific salmon and

'rt

Species:No. examined:I-ength (fork) range (arz):No. wi t .h food:' fota l

volume of contents ( r r ) :

Sockeve Pinkn 7 ' 2 1

2(r . .5 .59 0 26 0-36 . -5 34 .0 40 .5.!1 1.s 2

2 ( ) 2 . 3 5 2 1 0 . 5

('oho Steelhead4 7

.+4 , 0-7,t .04

1 8 , 0

Organism F a vb

AmphipodPteropodEuphausiidDecapodIsopod

OstracodOctopodSquidFishUnidentifiable

5 0 0< 1 0 015 14 <18 0 0 00 0 00 0 00 1 4 6 00 4 3 2 10 1 4 1 00 1 4 9

420

I J

0U008

I J

T J

1 1253200

t 635

2

< 1< 1< 1

1

< 100

) 7

< 1

97 500 2 51 2 5o 2 50 0

< 1 00 0

< 1 01 0

<1 0

eF : percentage of total fish examined containing food organism in stomach'bV : percentag" *fri.t fu.1i.uf". food n.guni'r'--rnaae" of total volume of combined

stomach contents.

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MANZER: NE PAC OCEAN

organisms included amphipods, pteroof these groups was important.

Of 87 sockeye stomachs examined,from the data in Table I is the fact thsockeye were examined, the percentagef.rom 22 to 94/o. The highest incideof 17) occurred at 48oN, 155"W. T(in weight and fork length) than thosetagging data presented elsewhere (Aof the fish in this locality were probablLeBrasseur (1966) noted significant dimaturing sockeye during spring and sufew feeding fish during winter in this

Pink salmon, r,vhich were in theirexclusively on hyperiid amphipods. Thihaving food in their stomachs. Oteuphausiids, ostracods, f ish and squid.

Of four cohoes (O. kisutch\ examiDecapod crustaceans were the most im

Four of the seven steelheads examiJudging from occurrence, the most im

The stomach contents of the single cbeyond recognition.

Seasonal diferences in feertingof sockeye and pink salmon in the nortby comparing data collected during Janfor May and June, 1958. LeBrasseur 's dgil lnets during hours of darkness. F-romtl'reir stomachs LeBr:rsseur (1966) postulactively in the early morning. Results orvould support this vier,t' because sockeat dawn. Thus, despite the use of differin the two seasons, presumably the operiods within their diurnal feeding cycaction of the two gears for feeding fishof this paper, for the sizes of f ish availablin selectivity is assumed.

The numbers of sockeye and pinks widuring these two seasons and the meanonly on fish with food, are presented inJanuary are in cubic centimeters and thunits are considered equal measures ofvalues are unadjusted for f ish size sisignificantly correlated with fish size (682 ; f o r p i nks , r : 0 .17 , n l g7 . ) .

& TRour FooD 1087

, euphausiids, and isopods but none

3 were devoid of food. Undiscernibleat f ishing sites where nine or more

fish with entpty stomachs rangedof fish with empty stomachs (16fish, on the average, were smaller

en elsewhere. From age, size, and1966), a large fraction, if not all,their penultimate year. Although

nces in feeding of immature andr, no explanation of the relatively

ality can be offered.al year of l i fe, were feeding almostitem lvas present in 10 of 15 fish

r orsanisms encountered included

, two had food in their stomachs.rtant items found.contained food in their stomaclis.

tant organisms were squid.um (O. keta) (42.5 cm) were digested

- Seasonal differences in the foodast Pacific Ocean were determinedry with those of LeBrasseur (196.5)

ta are from catches made by surfacethe proportions of f ish with food inted that sockeye and pinks fed nrostlonglining at different t imes of day

and pinks took bait most readilynt f ishing methods to catch salmonrvations on feeding are for similarUnknown. however. is the selective

n different seasons. For the purposeto each gear, no significant difference

l r and wi t l rout food in thei r s tomachsuantity of ingested material, basedable IL Al though mean values forfor N{ay June are in grams, these

pacity. Also, for each species, thesethe quantity of contents was notgth) (for sockeye, r : 0.25, n :

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1088 JOURNAL FISHERIES RESEARCH Bo.{RD oF C-\ \ADA, vol .25' No s ' 1968

T.rsLr I [ . Percentages of feeding sockel 'e and _pink salmon and mean Quant i ty of stomach

contents dur ing s inte"r and ear ly Jum-er. Dara for . ear ly summer are f rom LeBrasseur (196. i ,1." (Numbers of fish examined given in parentheses')

Species

/o with food Mean quantity (fish with food)

\\Iinter Early summer \\Iinter (cc) Early summer (g)

SockeyePink

s0 (87)62(24)

Two points emerge from a comparison of the data in Table II. First, on

the basis of chi-square tests for homogeneity, for each species the numbers of

feeding fish in the trvo seasons differed significantly (for sockeye, Xz :63.15'

P < 0.01; for p inks, x2 : 14.64, P 1 0.01) . Second, on the average, f ish in

early summer contained almost tu,ice the quantity of food in their stomachs

as fish in r,vinter. Thus, it can be concluded that sockeye and pinks feed more

intensively in early summer than in $,inter. Whether this reflects seasonal

differences in availabil ity or abundance of food or in relative activity of the

salmon cannot be anslvered by these data.Andrievskaya (1957) and Allen and Aron (1958), studying food of salmon

in the north'nvest Pacific Ocean in spring and summer, showed for the three

major species - sockeye, pink, and chum - qualitative differences in the

diet of f ish inhabiting different areas. LeBrasseur (1966) in his studies also

showed spatial differences in the relative importance of food organisms in the

summer diet of salmon in the northeast Pacific Ocean, but further pointed

out that these differences were largely associated lvith oceanographic domains.

Since sockeye and pinks in the northeast Paci6.c Ocean differ seasonally

in their geographic distribution (Anon., 1964; }danzer et al., 1965) and' de-

pending on the tinie of year, may inhabit more than one domain, seasonal

differences in the diet of these species were determined by comparing stomach

contents of f ish from similar domains (Table III). The domains considefed

are subarctic for sockeye and transitional for pinks, since in winter virtually

all f ish of the respective species were caught in these domains (Manzer and

Dodimead, MS, 1965; Anon., 1966).Notable qualitative differences in the diet of these species in winter and

early summer are also indicated. For sockeye, fish were dominant in winter,

accounting ior 7l/6 of the total food ingested. In early summer, in contrast,

squid were most important. With pinks, amphipods were most important in

winter, constituting almost all of the stomach contents. In early summer'

euphausiids were most important (447d, followed by ampl'ripods (347d'

From the foregoing it can be concluded that the food ingested by sockeye

and possibly pink salmon in rvinter and in early summer differed both in

quantity and quality.

86 (601)eo(17s)

+.6(44)3 s (1s )

8. s (s17)8 . 3 (1s8)

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MANZER; NE PAC OCEAN SALMON & TROUT FOOD 1089

T.eeLB.I I I . .Percentage.composi t ion of food of sockeye salmon in the subarct ic domain andplnk salmon ln the transltional domain in the northeasl Pacific during winter and early summer

seasons. Data for early summer are from LeBrasseur (1966).

Organism

Sockeye Pink

Winter Early summer Winter Early summer

AmphipodCopepodEuphausiidPteropodSquidFishMiscellaneous f

unidentified

No. of fish examined

I

< 1

:2 l

7 l

< 1< 1

884

t 6 t

97

1

a;T

34n

A . l

7

2

9

1 6

< 1

21

1

87

The author acknowledges the assistance of the Nanaimo Station's scaleReading and computer Service Groups and Messrs c. E. Turner and L. w.Barner, who carried out, frequently under diff icult physical conditions, thevarious field routines rvhich lvere part of this study. Dr R. R. parker andMr R. J. LeBrasseur helpfully commented on the manuscript.

Fisheries Research Board of CanadaBiological Station, Nanaimo, B.C.

J. I . MaNznn

Receiaed for publicat'ion January 9, 1968.

REFERENCES

Ar-r-er, G. H.. er.m. W. AnoN. 1958. Food of salmonid fishes of the western North PacificOcean. U.S. Fish Wildlife Serv., Spec. Sci. Rept. No. 237. 11 p.

ANonlnv564_ve, L. P: !217_. [The fgod of Pacific salmon in the northwestern Pacific Ocean.]Materialy po Biologii Morskovo Perioda Zhigni Dalnevostochnykh Lososei. p. O+-Zj.-- iitiRussian.j (Transl.

-Fish. Res. Bd. Canada,

-No. Si2.)

ANoN. 1964. International North Pacific Fisheries Commission, Annual Report for 1962.1966. International North Pacific Fisheries Commission, Annuai Report for 1964.

'

LnBrussrun, 8.,J. 1?q5. Stomach contents of salmonids caught in the northeastern pacificocean - 1958. Fish. Res. Bd. canada, Pacific Biol. sta. ciic., Statist. s".., No.-is.-

--- --

1966. Stomach contents of salmon and steelhead trout in the northeastern PacificOcean. J. Fish. Res. Bd. Canada, 23(1): 85-100.

MANznn, J. I., ann A. J. Doorltaao. MS, 1965. Winter distribution of salmon in the north-east..Pacific 9g9un J"Tt?.y^ 7-F.ebruary_7, l9g!, wit!' some reference to oceanographiccondit ions. Fish. Res. Bd. Canada, MS Rept. (Biol.) , No. 824. t6 p.

MaN_znn,^J. I . , T. Isnloa, A. E. PnmnsoN, eNo M. G. HaNeveN. 1965. salmon of the Northraclhc Ucean - Part V. Offshore distribution of salmon. Bull. Intern. North PacificFish. Comm., No. 15. 452 p.

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