@prefix vivo: . @prefix edm: . @prefix ns0: . @prefix dcterms: . @prefix skos: . vivo:departmentOrSchool "Science, Faculty of"@en, "Zoology, Department of"@en ; edm:dataProvider "DSpace"@en ; ns0:degreeCampus "UBCV"@en ; dcterms:creator "Prakash, Anand"@en ; dcterms:issued "2012-03-21T20:35:07Z"@en, "1958"@en ; vivo:relatedDegree "Master of Arts - MA"@en ; ns0:degreeGrantor "University of British Columbia"@en ; dcterms:description """Food study based on the stomach content analyses of spring and coho salmon collected from various localities along the southern British Columbia coast during the summer of 1957 revealed that herring followed by Crustacea formed the most important item of the diet of the two species. Coho salmon exhibited more pelagic and varied diet than spring salmon caught in the same area. Definite seasonal fluctuations in the composition of food and feeding intensity were noticed, considerable amounts of Crustacea were taken in early summer months and after that fish assumed importance. July and August mark the period when the feeding activity is intense in both the species. Qualitative and quantitative differences in the feeding conditions on the east and west coasts of Vancouver Island warrant the establishment of two food type areas. The differences in growth of fish on the two coasts as related to feeding conditions are discussed. Although, herring is the major food item of both spring and coho salmon, evidences are presented in support of the hypothesis that a reduction in herring stock abundance due to predation would not affect salmon catches. Based on ova measurements and maturity index values fish have been classified into immature and maturing. It appears that almost all coho salmon available to the commercial fishery are maturing, spring catches on the other hand include large percentage of both immature and maturing fish. Immature and maturing female springs divide at a fork length of 74 cm., cohos do so at an approximate fork length of 52 A volume method for the determination of egg numbers present in the ovary has been developed, the average percentage error between the calculated and actual counts being 5.3. it was found that the absolute fecundity is positively correlated to fish length and negatively to egg size but the magnitude of the effect of fish length on absolute fecundity is about four times greater than that of egg size."""@en ; edm:aggregatedCHO "https://circle.library.ubc.ca/rest/handle/2429/41674?expand=metadata"@en ; skos:note "FOOD AND FEEDING HABITS, MATURITY AND FECUNDITY' OF SPRING SALMON (Oncorhynchus tshawytscha) AND COHO SALMON (Oncorhynchus kisutch) IN SOUTHERN BRITISH COLUMBIA COASTAL WATERS by ANAND PRAKASH B.Sc. (Honours), U n i v e r s i t y of D e l h i , 1952. M.Sc, U n i v e r s i t y of Allahabad, 1954. A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS i n the Department of Zoology We accept t h i s t h e s i s as conforming to the standard required from the candidates f o r the degree of MASTER OF ARTS Members of the Department of Zoology THE UNIVERSITY OF BRITISH COLUMBIA August 1958 i -ABSTRACT Food study based on the stomach content analyses of spring and coho salmon c o l l e c t e d from various l o c a l i t i e s along the southern B r i t i s h Columbia coast during the summer of 1957 revealed that herring followed by C r u s t a c e a formed the most important item of the d i e t of the two species. Coho salmon exhibited more pelagic and varied d i e t than spring salmon caught i n the same area. D e f i n i t e seasonal f l u c t u a t i o n s i n the composition of food and feeding i n t e n s i t y were noticed, considerable amounts of C r u s t a c e a were taken i n early summer months and a f t e r that f i s h assumed importance. J u l y and August mark the period when the feeding a c t i v i t y i s intense In both the species. Q u a l i t a t i v e and q u a n t i t a t i v e d i f f e r e n c e s i n the feeding conditions on the east and west coasts of Vancouver Island warrant the establishment of two food type areas. The differences i n growth of f i s h on the two coasts as r e l a t e d to feeding conditions are discussed. Although, herring i s the major food item of both spring and coho salmon, evidences are presented i n support of the hypothesis that a reduction i n herring stock abundance due to predation would not a f f e c t salmon catches. Based on ova measurements and maturity index values f i s h have been c l a s s i f i e d i n t o immature and maturing. I t appears that almost a l l coho salmpn a v a i l a b l e to the commercial f i s h e r y are maturing, spring catches on the other hand include cm. large percentage of both immature and maturing f i s h . Immature and maturing female springs d i v i d e at a fork length of 74 cm., cohos do so at an approximate fork length of 52 A volume method f o r the determination of egg numbers present i n the ovary has been developed, the average percentage error between the c a l c u l a t e d and a c t u a l counts being 5«3» I t was found that the absolute fecundity Is p o s i t i v e l y c o r r e l a t e d to f i s h length and negatively to egg s i z e but the magnitude of the e f f e c t of f i s h length on absolute fecundity i s about four times greater than that of egg s i z e . In presenting t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree that permission f o r extensive copying of t h i s t h e s i s fo r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s representative. I t i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission. Department of The U n i v e r s i t y of B r i t i s h Columbia, Vancouver 8, Canada. Date - i i i -TABLE OF CONTENTS Page ABSTRACT i INDEX OF TABLES v INDEX OF FIGURES v i ACKNOWLEDGEMENTS v i i INTRODUCTION 1 REVIEW OF THE LITERATURE 2 MATERIALS AND METHODS 6 FOOD AND FEEDING HABITS 8 Treatment of samples for food study 8 COHO SALMON (Oncorhynchus kl^utch). . * . . . 12 Composition fif Food 12 Monthly f l u c t u a t i o n s i n food composition 17 Food type areas 21 Feeding i n t e n s i t y 25 SPRING SALMON (Oncorhynchus tschawytscha). . 27 Composition of food 27 Monthly f l u c t u a t i o n s and feeding i n t e n s i t y . 31 Food type areas 33 Comparison of the food of spring and coho salmon 34 Salmon - herring r e l a t i o n s h i p 37 Discussion 41 - i v -TABLE OF CONTENTS (Cont.) Page MATURITY , 45 Structure of the ovary 46 Stages of maturity 47 Maturation 51 FECUNDITY 6 l Determination of egg numbers . . . . 62 C o r r e l a t i o n between egg number and s i z e of f i s h . 64 Reduction i n absolute fecundity as a fun c t i o n of egg s i z e 70 SUMMARY . • 73 REFERENCES 76 APPENDIX 80 - v -INDEX OF TABLES Table . Page IA - IB. Number of coho and spring salmon samples c o l l e c t e d according to area and month . . . . 1 0 - 1 1 I I . Percentage composition of d i e t constituents of t r o l l - c a u g h t coho salmon 19 I I I . Percentage occurrence of diet constituents of t r o l l - c a u g h t coho salmon 20 IV. Percentage composition of d i e t constituents of t r o l l - c a u g h t spring salmon . 28 V. Percentage occurrence of diet constituents of t r o l l - c a u g h t spring salmon 29 VI. Maturity index - egg diameter r e l a t i o n s h i p . 49 V I I . Percentages of gonads i n d i f f e r e n t stages of maturity i n t r o l l - c a u g h t f i s h according to months 52 V I I I . Percentage of maturing female spring salmon i n each 5 cm. s i z e group 57 IX. Percentage of maturing female coho salmon i n each 5 cm. s i z e group 58 X. Comparison between a c t u a l and ca l c u l a t e d egg counts 65 - v i -INDEX OF FIGURES Figure Page I . Map of southern B r i t i s h Columbia coast showing sampling areas 7 2a - 2b. Food organisms of s p r i n g and coho salmon . . . 1 5 - 1 6 3 . Monthly v a r i a t i o n s i n the volume of f i s h and crustacea eaten by coho and spring salmon on the east and west coasts of Vancouver Island . . . 22 4. Comparison between the east and west coasts of Vancouver Island based on percentage composition of f i s h and crustacea eaten by coho salmon i n d i f f e r e n t years 24 5. Monthly v a r i a t i o n s i n the feeding i n t e n s i t y of spring and coho salmon i n d i f f e r e n t areas . . . 26 6. Food of spring and coho salmon on southern B.C. coast - Percent volume and frequency of occurrence 36 7 . Egg diameter - maturity index r e l a t i o n s h i p . . . . 50 8 . Monthly egg s i z e progression i n spring salmon . . 54 9 . Monthly egg si z e progression i n coho salmon . . . 55 10. Percentage of immature and maturing females for d i f f e r e n t sizes and the s i z e at maturity . . . 59 I I . Egg diameter - egg number r e l a t i o n s h i p 63 12. Egg number - f i s h s i z e r e l a t i o n s h i p 67 13. Relationship beti/een egg diameter and r e l a t i v e fecundity i n spring salmon 71 - v l i -AC KNOWLE D GEME NT S This work was. i n i t i a t e d by the w r i t e r while i n the employ of the F i s h e r i e s Research Board of Canada, P a c i f i c B i o l o g i c a l S t a t i o n at Nanaimo, B.C. i n the summer of 1957* Permission of the F i s h e r i e s Research Board to incorporate the work into t h e s i s form i s g r a t e f u l l y acknowledged. The w r i t e r wishes to extend h i s sincere thanks and gratitude f o r help and guidance which he received from the fol l o w i n g persons: Dr. P. A. L a r k i n , D i r e c t o r , I n s t i t u t e of F i s h e r i e s , The U n i v e r s i t y of B r i t i s h Columbia, f o r guidance and u n f a i l i n g encouragement throughout the course of t h i s study; Dr. D. J. Milne of the P a c i f i c B i o l o g i c a l S t a t i o n , Nanaimo, f o r constructive c r i t i c i s m s , suggestions and pro-v i d i n g background f o r t h i s work; Dr. W. S. Hoar for going through the manuscript and o f f e r i n g his c r i t i c i s m s ; Dr. F e r r i s Neave and Mr. J. I . Manzer f o r providing data c o l l e c t e d by the I n t e r n a t i o n a l North P a c i f i c F i s h e r i e s Commission on the food of coho salmon i n the high seas. Assistance and f a c i l i t i e s provided by the s t a f f of the B i o l o g i c a l S t a t i o n , Nanaimo, i n the various phases of t h i s work i s g r a t e f u l l y acknowledged. The w r i t e r i s p a r t i c u l a r l y indebted to Messrs. L. Ives and R. Lund and many other sport and commercial t r o l l e r s who were responsible f o r the c o l l e c t i o n of samples from the east and west coasts of Vancouver Island. Thanks are also extended to Messrs. K. Muller and E. A. R. B a l l f o r assistance i n c o l l e c t i o n of the Fraser and Fuca samples. - 1 -INTRODUCTION The importance of Spring salmon (Oncorhynchus tshawytscha): and Coho salmon (0^ kisutch) i n the economy of B r i t i s h Columbia can be judged by the f a c t that f o r the l a s t f i v e years the t o t a l catch of these two species of P a c i f i c salmon has con s t i t u t e d about one-fourth of the t o t a l landings and value of the salmon i n B r i t i s h Columbia. The bulk of spring and coho salmon i s caught by commercial and sport t r o l l f i s h -e r i e s while the r e s t i s caught by g i l l net, purse seine and trap f i s h e r i e s . Due to the r a p i d growth of the t r o l l i n g f l e e t i n recent years and increasing e x p l o i t a t i o n of spring and coho salmon stocks much concern has been aroused among the commer-c i a l and sport fishermen about the conservation of both species. The present study formed a part of the general spring and coho i n v e s t i g a t i o n programme of the F i s h e r i e s Research Board of Canada designed to understand more p r e c i s e l y c e r t a i n b i o l o g i c a l aspects e s p e c i a l l y those concerned with food, maturity and fecundity of these two species during t h e i r oceanic existence. The growing b e l i e f among salmon t r o l l e r s on the west coast of Vancouver Island that commercial f i s h i n g f o r herring i s one of the major causes of decline i n salmon f i s h i n g because of decrease i n i t s food supply also prompted attempts to a s c e r t a i n more f u l l y the exact salmon-herring r e l a t i o n s h i p . Another purpose of the present study was to help evaluate the probable e f f i c a c y and f e a s i b i l i t y of - 2 -adopting new minimum*size regulations as applied to spring and coho salmon f i s h i n g . As spring and coho salmon stocks are fished by both the United States and Canada, uniform coastwide regulations were decided upon by the two countries at the Conference on coordination of f i s h i n g regulations i n 1957 i n order that such regulations may lead to a long term u t i l i z a t i o n of these two valuable species of P a c i f i c salmon. The e f f i c a c y of new minimum s i z e regulations depends upon the extent to which small immature f i s h e s can be avoided by commercial t r o l l e r s . I t was, therefore, deemed necessary to determine pertinent f a c t s about maturity of the commercially caught f i s h e s . REVIEW OF THE LITERATURE Food studies of spring and coho salmon on the P a c i f i c coast of North America have been p a r t i c u l a r l y numerous. Chapman (1936) investigated the food of spring and coho salmon off the coast of 'Washington and concluded that p i l c h a r d followed by herring and euphausiids formed the most important food item f o r spring salmon, coho salmon on the other hand subsisted mainly on euphausiids - p i l c h a r d and herring were alter n a t e foods. He pointed out that small f i s h were feeding c h i e f l y on euphausiids, an intermediate group on f i s h and euphausiids while the l a r g e s t f i s h consumed f i s h only. S i l l i m a n (1941) attempted to co r r e l a t e f l u c t u a t i o n s i n the d i e t of spring and coho with the t r o l l catch and stated that - 3 -spring and coho salmon taken o f f Washington between A p r i l and November, 1938? show two feeding phases - a f i s h eating phase and a Crustacea eating phase. He showed that spring and coho salmon of Neah Bay area and Westport area contained p i l c h a r d s , herrings, anchovies, r o c k f i s h , smelt, euphausiids, megalopa larvae, squids, octopus, amphipods and copepods i n t h e i r stomachs. Spring and coho salmon of Puget Sound as reported by Kirkness (1948) were found to subsist l a r g e l y on h e r r i n g , candle f i s h and Crustacea. Coho took a greater v a r i e t y of organisms as food than spring salmon and the e n t i r e d i e t of both species was composed of pelagic organisms. Food of spring and coho salmon taken off the coast of Oregon has been reported by Heg and Van Hyning (195D* They pointed out the di f f e r e n c e s i n food habits of the two species - coho feeding l a r g e l y on small p e l a g i c f i s h , crab larvae, euphausiids and squids, while spring feed mainly on f i s h and euphausiids. Other s i m i l a r studies on either of the two species have been conducted by G i l b e r t (1913), Williamson (1930), Clemens (1934), Senter (1940), Fraser (1946), Foskett (195D, Shapovalov and Taft (1954), Milne ( 1 9 5 5 ) , and Markel (1957). P r i t c h a r d and Tester (1944) studied the food of spring and coho salmon on the B r i t i s h Columbia coast and covered an extensive area from the Queen Ch a r l o t t e t s Islands i n the north to the southern t i p of Vancouver Island. The period of t h e i r study extended from 1939 to 1941 and i t was shown that the food of spring salmon was s i m i l a r i n each of - 4 -the three years; h e r r i n g , p i l c h a r d and sandlance forming the bulk of the f i s h d i e t and euphausiids, amphipods and crab larvae forming the crustacean d i e t . Although t h e i r study has shown c l e a r l y the nature of the food of spring salmon, nothing could be said c o n c l u s i v e l y about the food of coho salmon because of the smallness of the sample studied. A correct a p p r a i s a l of food and feeding habits of a f i s h species depends, besides other things, on a random, non-selective sampling method. The methods adopted by P r i t c h a r d and Tester (1944) for c o l l e c t i n g samples from d i f f e r e n t areas were highly s e l e c t i v e because only those stomachs were taken which contained any food. Such sampling, while good f o r a q u a l i t a t i v e analysis of food Items, prejudices the q u a n t i t a t i v e estimation to a con-siderable extent. The present i n v e s t i g a t i o n may be regarded as f i l l i n g i n some gaps l e f t by e a r l i e r workers and i s l a r g e l y concerned with the food of t r o l l caught spring and coho salmon off the Southern B r i t i s h Columbia coast. The subject of maturity and fecundity of spring and coho salmon su f f e r s from an acute poverty of l i t e r a t u r e . Although such studies have been conducted by several f e d e r a l and p r o v i n c i a l f i s h e r i e s agencies d i r e c t l y concerned with the conservation of these two species, both i n Canada and the United States, there have been r e l a t i v e l y few published records which have dealt with these aspects i n d e t a i l . Notable con-t r i b u t i o n s i n t h i s f i e l d are from G i l b e r t (1913) and R i c h (1925) who studied the maturity of chinook or spring salmon i n the ocean. McGregor ( 1922, 1923) estimated the number of - 5 -eggs i n king salmon and in d i c a t e d a marked di f f e r e n c e i n egg counts of Klamath and Sacramento River races. He also pointed out a possible separation of the r i v e r races of king salmon i n ocean caught f i s h by means of egg count. Heave (1948) presented the average egg count of coho salmon c o l l e c t e d f o r sev e r a l years at Cowichan, Port John, Namu, and the Fraser River. S i m i l a r counts have been reported by Snyder (1921), Foerster and P r i t c h a r d (1936), Hunter (1948), and ?/ickett (195D« Recently Rounsefell (1957) has reviewed the e x i s t i n g l i t e r a t u r e on fecundity of P a c i f i c salmon. MATERIALS AND METHODS Samples f o r the food, maturity and fecundity study were obtained mainly from those areas around Vancouver Island where the commercial f i s h i n g i s most a c t i v e and sampling could be done wi t h s u f f i c i e n t r e l i a b i l i t y . Almost a l l the samples from the east coast and west coast of Vancouver Island were obtained from commercial and sport t r o l l e r s , while those from the Fraser and the S t r a i t of Juan de Fuca areas were c h i e f l y g i l l - n e t and purse-seine caught f i s h . Few samples were obtained from the trap f i s h e r y operating i n the S t r a i t of Juan de Fuca. F i s h i n g areas on the east and west coasts of Vancouver Island included Barkley Sound, Clayoquot Sound, Nootka Sound, Kyuquot Sound, Cape Cook, Courtenay, Departure Bay and the southern p o r t i o n of the Gulf of Georgia (Figure 1.). In order to ensure uniformity i n sampling, each c o l l e c t o r was issued d e f i n i t e i n s t r u c t i o n s (see Appendix A) which were modified from those issued by P r i t c h a r d and Tester (1944). The d e t a i l e d procedures used i n analysing food, maturity and fecundity are given under each section. Figure 1. Map of southern British Columbia ooast showing sampling areas referred to in the text. - 8 -FOOD AND FEEDING HABITS TREATMENT OF SAMPLES FOR FOOD STUDY The present report i s based, on the examination of the stomachs of 659 coho and 551 spring salmon c o l l e c t e d during the period May - October, 1957 (Table I ) . Upon re c e i p t of the samples each stomach was examined f o r i t s contents. Food items were sorted to the lowest catagory to which they could be i d e n t i f i e d . In those stomachs where the food items were found i n an advanced state of d i g e s t i o n , i d e n t i f i c a t i o n was possible only to the generic l e v e l by means of opercle bones, v e r t e b r a l column, o t o l i t h , appendages etc. The q u a n t i t a t i v e a n a l y s i s was done by the volumetric method, i n which the volume of each food item i s expressed as a percentage of the volume of the t o t a l stomach contents (Hynes, 1 9 5 0 ) . Volume of each food item by species was deter-mined by the displacement method i n a measuring c y l i n d e r graduated to 0 . 1 cc. and the percentage c a l c u l a t e d . The prevalence of each item of food i n the d i e t during d i f f e r e n t months was c a l c u l a t e d by the occurrence method (Hynes, 1 9 5 0 ) , i n which the number of f i s h i n which each food item occurs i s expressed as a percentage of the t o t a l number of f i s h examined. From I n d i v i d u a l datum monthly averages were calcu -l a t e d and from these the t o t a l percentage composition by volume or occurrence was determined. - 9 -From the q u a l i t a t i v e and q u a n t i t a t i v e aspects of the food study, t r o l l caught samples were dealt with separately from those caught by-either g i l l net or purse seine. This was done fo r the f o l l o w i n g reasons: (a) F i s h caught by methods other than t r o l l i n g are not cleaned or dressed soon a f t e r t h e i r capture, t h i s brings about a post-mortem d i g e s t i o n and d e t e r i o r a t i o n of the stomach contents. Furthermore, i t i s often seen that purse-seine or g i l l - n e t t caught f i s h e s disgorge t h e i r stomach contents i n t h e i r struggle to release themselves. (b) F i s h i n g i n the S t r a i t of Juan de Fuca and the Fraser River commenced l a t e i n the season and the samples could be procured only a f t e r J u l y (for spring) and August ( f o r coho) from these areas. In the absence of a uniform sampling, i t was considered proper to deal with such samples separately. - 10 -TABLE I. - A Number of samples of coho salmon c o l l e c t e d from various areas In d i f f e r e n t months of 1957. COHO MONTH AREA No. of F i s h Mean Fork Fork length examined Length (cm.) Range (cm.) E.coast V.I. 18 47 43 - 53 W.coast V.I. 2 52 51 - 53 MAY Juan de Fuca — -- — Fraser River — — — —• E.coast V.I. 48 53 46 _ 59 W.coast V.I. 16 58 55 - 64 JUNE Juan de Fuca — — — Fraser River — E.coast V.I. 57 52 40 — 58 W,coast V.I. 41 62 54 - 73 JULY Juan de Fuca _ _ -• Fraser River — — — —• E.coast V.I. 13 57 52 ~ 66 W.coast V.I. 85 64 51 - 74 AUG. Juan de Fuca 129 59 40 - 71 Fraser River — —— E.coast V.I. 5 49 46 _ 52 W.coast V.I. 45 66 56 - 72 SEPT. Juan de Fuca 87 65 45 - 77 Fraser River 32 68 54 — 80 OCT. Fraser River 81 61 53 - 80 SPAWNERS From Adams, Harrison, Vedder, 61 34 79 Robertson, Thatcher, 92 — Cowichan and Eagle Rivers. TOTAL 751 - 11 -TABLE I - B. Number of samples of spring salmon c o l l e c t e d from various areas i n d i f f e r e n t months of 1957. SPRING MONTH AREA No. of F i s h Mean Fork Fork Length ; examined Length (cm.) Range (cm.) E.Coast V.I. 9 63 56 - 79 W.Coast V.I. 35 64 11 - 90 MAY Juan de Fuca — — Fraser River — — E. Coast V.I. 16 64 38 79 W.Coast V.I. 53 71 13 - 103 JUNE Juan de Fuca — __ Fraser River -- — - • E.Coast V.I. 29 54 23 96 W.Coast V.I. 57 76 56 - 108 JULY Juan de Fuca — — Fraser River 64 66 27 - 95 E.Coast V.I. 6 59 30 _ 79 W.Coast V.I. 67 71 33 - 96 AUG. Juan de Fuca 36 66 48 - 90 Fraser River 60 67 46 - 90 E.Coast V.I. 5 26 24 27 W.Coast V.I. 32 76 60 - 96 SEPT. Juan de Fuca 34 81 46 - 106 Fraser River 35 78 55 - 104 OCT. Fraser River 13 81 55 — 99 SPAWNERS From Adams, Harrison, Vedder, ^ , o n Robertson, Thatcher, 10 83 ^ -Cowichan and Eagle Ri v e r s . — TOTAL 561 GRAND TOTAL (coho and spring) - 1312 - 12 -COHO SALMON (Oncorhynchus k l s u t c h Walbaum) COMPOSITION OF FOOD• For the sake of convenience i n the analysis and i n t e r p r e t a t i o n of the d a t a , the stomach contents have been put i n t o three main catagoriesj (1) F i s h , (2) Crustacea, and (3) Miscellaneous. The l a s t mentioned catagory of miscel-laneous organisms consisted of heterogeneous elements of occasional occurrence such as Gastropods, j e l l y - f i s h , plant matter, d e t r i t u s , digested matter, slime. The analysed data of the stomach contents of t r o l l -caught coho are presented by months In Tables I I and I I I and summarized i n Figure 6. The volumetric composition makes i t evident that f i s h and Cr u s t a c e a are the most important food items of coho salmon. The f i s h p o r t i o n of the d i e t was l a r g e l y made up of P a c i f i c herring and sandlance, while Crustacea were represented c h i e f l y by euphausiids, amphipods, and megalopa larvae. The various food items i d e n t i f i e d from the stomach contents are discussed i n the f o l l o w i n g s e c t i o n s : HERRING The P a c i f i c herring (Clupea p a l l a s i i Valenciennes) appeared as the si n g l e food item of outstanding importance to tr o l l - c a u g h t coho. They co n s t i t u t e d 71.6 percent of the t o t a l volume and were present i n 21 percent of the specimens examined (Figure 6.). Although a l l s izes of herring were found i n the stomachs of coho salmon, f i s h measuring 14 to 23 cm i n - 13 -f o r k length were found to be most common. This s i z e range includes f i s h which are i n t h e i r second, t h i r d and f o u r t h year; three and four year old herring make up about 80 to 90 percent of the commercial catch (Taylor, 1955)• Juvenile herring ranging from 2 .5 to 9.0 cm i n fork length were found most commonly i n the stomachs of specimens c o l l e c t e d from the Departure Bay area i n the Gulf of Georgia i n May and June. SAID LANCE These formed the second most important item i n the f i s h d i e t . The species was i d e n t i f i e d as Ammodytes tobianus Girard. They formed 5»L percent of the t o t a l volume of food and occurred i n 6 percent of the stomachs. The occurrence of sand lance i n the stomachs of coho salmon i n c e r t a i n areas, p a r t i c u l a r l y along the north western coast of Vancouver Island as ind i c a t e d by P r i t c h a r d and Tester (1944) could not be established. They were taken by coho salmon i n almost every sampling area on both the east and west coasts of Vancouver Island. OTHER FISHES These included occasional specimens of Rockfish (Sebastodes spp), P a c i f i c Saury (Cololabis s a i r a Brevoort), Stickleback (Gastrosteus aculeatus Linnaeus), u n i d e n t i f i a b l e clupeids and other f i s h remains, forming 3 ' 5 percent of the t o t a l volume of food items taken and occurring i n 18 percent of the stomachs examined. - 14 -EUPHAUSIIDS Euphausiids appeared as the most Important item i n the crustacean d i e t of coho occurring i n 13 per cent of the stomachs and making up 8.6 per cent of the t o t a l volume of food consumed. They were found i n almost a l l areas of the east and west coasts hut were most abundant i n the S t r a i t of Georgia showing d e f i n i t e seasonal trends In t h e i r occurrence. Two types of euphausiids were dis t i n g u i s h e d - a red or pink v a r i e t y and a vuhite v a r i e t y . The red v a r i e t y has been i d e n t i f i e d as Thysanoessa s p i n i f e r a and the white v a r i e t y as Euphausia p a c i f l e a . The l a t t e r was larger than the red and the average s i z e was about 23 m i l l i m e t e r i n length. Most of the stomachs were found to contain the white v a r i e t y . AMPHIPODS These formed a s i g n i f i c a n t p o r t i o n of the crustacean d i e t during e a r l y summer months and l i k e euphausiids were abundant on the east coast of Vancouver Is l a n d . Both Hyperlid and Gammarid amphipods occurred i n the d i e t but the l a t t e r were taken most frequently. Two d i s t i n c t forms of Gammarid amphi-pods were encountered, a purple and an orange pigmented form, the l a t t e r occurring dominantly. Amphipods appeared i n 15.6 per cent of the stomachs forming 5 . 1 per cent of the t o t a l food items taken. MEGALOPA Young crabs and crab megalops const i t u t e d 5*7 per cent of the d i e t of coho salmon and occurred i n 18 per cent of - 15 -P a c i f i c h e r r i n g ( C l u p e a p a l l a s i ) . i S a n d - l a n c e (Ammodytes t o b i a n u s ) . F i g u r e 2 a . F o o d o r g a n i s m s o f s p r i n g and coho s a l m o n . - 16 -E u p h a u s i i d s . A m p h i p o d s . ^ ^ C r a b m e g a l o p s . 2b. F o o d o r g a n i s m s o f s p r i n g and coho s a l m o n . - 17 -the stomachs. Their occurrence, l i k e other crustacean forms, indic a t e d seasonal f l u c t u a t i o n s . D i f f e r e n t types and size s of megalopa larvae were found i n the stomach. Only those belonging to Cancer maglster were i d e n t i f i e d . OTHER CRUSTACEA Occasional forms such as isopods, shrimps, and copepods have been included i n t h i s catagory, none of these items formed a s i g n i f i c a n t p o r t i o n of the d i e t of coho salmon on the east or west coasts of Vancouver Island at any time. They formed 0.1 per cent of the t o t a l volume of food consumed and occurred i n 3*3 per cent of the stomachs examined. MISCELLANEOUS I n c i d e n t a l food items such as Gastropod s h e l l s , j e l l y - f i s h , plant matter, digested matter and slime which are unimportant from the point of view of food have been included i n t h i s catagory. These items occurred i n 4.7 per cent of the stomachs forming 0.3 per cent of the t o t a l food volume. MONTHLY FLUCTUATIONS IN THE FOOD COMPOSITION Monthly f l u c t u a t i o n s i n the amount of various food items consumed are presented i n Table I I . The occurrence of these items during d i f f e r e n t months i s given i n Table I I I . During May and June a large p o r t i o n of the die t of coho salmon was crustacea, whereas f i s h assumed major importance as a food item a f t e r June. This i s i n agreement with S i l l i m a n (1941) who reported two d i s t i n c t feeding phases f o r king (spring) and s i l v e r (coho) salmon taken o f f Washington -an invertebrate feeding phase and a f i s h feeding phase. The analysis of h i s data i n d i c a t e d that the f i s h c o l l e c t e d from Westport and Neah Bay areas subsisted l a r g e l y on a crustacean d i e t during May and June and a f t e r that the salmon depended on f i s h f o r food. S i l l i m a n suggested that although these two phases show considerable overlap, they are d i s t i n c t enough to be r e a d i l y recognized. S i m i l a r seasonal changes i n the com-p o s i t i o n of the food have been reported by Merkel (1957) i n h i s study of the food habits of the king salmon i n the v i c i n i t y of San Francisco. Of the Crustacea, amphipods occupied a dominant place both i n the quantity eaten and i n t h e i r prevalence i n the stomachs. During May and June euphausiids were taken moderately and megalopa larvae formed a s i g n i f i c a n t item i n June only. After June the Crustacea were l a r g e l y replaced by f i s h d i e t c h i e f l y composed of P a c i f i c h e r r i n g which reached i t s peak i n August forming 84.4 per cent of the t o t a l volume of food. In September f i s h formed 74.7 per cent of the t o t a l food but i n the degree of prevalence, euphausiids and megalops equalled the f i s h . Sand lance remained r e l a t i v e l y unimportant and more or less uniform i n the d i e t f o r the e n t i r e period. - 19 -TABLE I I Percentage composition of d i e t constituents of t r o l l - c a u g h t coho salmon from the Vancouver Island area In various months of 1957. Diet Constituents MAY JUNE JULY AUG. SEPT. Herring 50.2 33.7 69.3 84.4 69.I Sandlance — 1.5 2.6 7.5 4 .6 Other Fishes 8.5 4.6 9.6 1.1 1.0 Euphausiids 13.6 21.0 0.5 3.9 22.3 Amphipods 23.9 21.0 6.2 1.6 --Megalops 3.8 18 .0 11.3 1.0 2.5 Other crustacea _ _ 0.1 0.1 0.1 0.2 Miscellaneous -- 0.1 0.4 0.4 0.3 Number of Stomachs T o t a l Vol.(cc) 20 68.2 64 615.8 98 1038.2 98 2252.2 50 782.6 - 20 -TABLE I I I Percentage occurrence of d i e t constituents i n the stomachs of t r o l l - c a u g h t coho -salmon from Vancouver Island area In various months of 1957• Figures i n brackets i n d i c a t e number of stomachs examined. Diet Constituents MAY JUNE JULY AUG. SEPT Herring 19-5 6.4 2 2 . 5 3 4 . 8 3 0 . 8 (8) (10) (34) (39) (16) Sand lance mm mm 3 . 8 4 . 6 12 .5 7.7 (6) (7) (14) (4) Other Fishes 17.1 1 8 . 6 2 8 . 5 9 .8 7 . 7 (7) (29) (43) (11) (4) Euphausiids 9 . 8 13.4 4 . 0 17.9 2 8 . 8 (4) (21) (6) (20) (15: Amphipods 3 9 . 0 2 3 . 7 1 2 . 6 7 . 1 _ » (16) (37) (19) (8) Megalops 12.2 24.4 2 1 . 2 8 . 1 17 .3 (5) (38) (32) (9) (9) Other C r u s t a c e a 2.4 3 . 9 3 . 3 3 . 6 1.9 (1) (6) (5) (4) (1) Miscellaneous 5-8 3-3 6 . 2 5 . 8 (9) (5) (7) (3) - 21 -, FOOD TYPE AREAS Milne (1950) stated that coho salmon taken In the S t r a i t of Georgia are smaller than those caught o f f the west coast of Vancouver Island. These small s i z e d coho are popu-l a r l y known as 'Bluebacks' and are f i s h e d h e a v i l y from June to September w i t h peak catches i n Ju l y and August. On the di f f e r e n c e i n s i z e of i n s i d e and outside coho Milne commented: Past data from tagging, f i n - c l i p p i n g and stream i n s p e c t i o n do not point to the existence of slow growing stocks i n any p a r t i c u l a r stream but rather i n d i c a t e that coho salmon from each stream may go to both i n s i d e and outside waters. Whether these di f f e r e n c e s i n s i z e are due to d i f f e r e n t food con-d i t i o n s or to stocks w i t h d i f f e r e n t growth rates i s open to conjecture. I f d i f f e r e n t feeding conditions are the major f a c t o r , then any d i f f e r e n c e i n the ocean temperatures or n u t r i e n t s a l t s between the two areas may be s i g n i f i c a n t . Accordingly, s p e c i a l emphasis was placed on the c o l l e c t i o n of simultaneous samples from the S t r a i t of Georgia and the west coast of Vancouver Island. Samples obtained from the S t r a i t of Georgia showed that Crustacea remained c o n s i s t e n t l y dominant throughout the period except during May and J u l y . In those months a large number of j u v e n i l e herring increased the per-centage of f i s h consumed to 72 per cent of the t o t a l food volume (Figure 3). Amphipods formed the most important crustacean item of the d i e t of i n s i d e coho, while euphausiids and crab megalops were next i n order of importance. The s i t u a t i o n o f f the west coast, however, was s t r i k i n g l y d i f f e r e n t (Figure 3). F i s h remained dominant throughout the period i n the d i e t of coho salmon and very few Crustacea were taken i n the outside waters. WEST C O A S T S P R I N G C O H O ID IOO-. SO-4 604 40 204 FISH C R U S T A C E A • E A S T C O A S T C O H O f\\j IV) M A Y J U N J U L A U G S E P T M A Y J U N J U L A U G S E P T Figure 3. Monthly variations in the volume of f i s h and Crustacea eaten by coho and spring salmon on the east and west coasts of Vancouver Island. - 23 -For the period as a whole, the east coast coho ate c h i e f l y Crustacea and west coast coho subsisted c h i e f l y on f i s h . The feeding trends showed by coho salmon i n each of these two regions are s u f f i c i e n t l y d i s t i n c t i v e and more or le s s consistent to warrant the establishment of two d i s t i n c t food type areas-. On t h i s basis i t i s p o s s i b l e that the dif f e r e n c e s i n growth of 'Blueback' and west coast coho are r e l a t e d to the differences i n food. The above hypothesis i s further supported by the data c o l l e c t e d during 1950, 1954, and 1956 as a part of the general spring and coho salmon i n v e s t i g a t i o n of the F i s h e r i e s Research Board of Canada. These also show a predominance of Cr u s t a c e a i n the d i e t of coho on the east coast of Vancouver Island as opposed to the west coast where the chief item of food was f i s h (Figure 4 ). S i m i l a r r e s u l t s were reported by Chapman (1936) i n h i s study of the food habits of s i l v e r (coho) salmon o f f the coast of Washington. He found that at Neah Bay the salmon subsisted c h i e f l y on C r u s t a c e a , while off the coast at Westport f i s h formed the dominant food item. Like the east and west coasts of Vancouver Is l a n d , Neah Bay and \"Westport represent two d i s t i n c t oceanographic areas. IOO S O 6 0 4 0 U J 2 0 2 => _ l o 0 > IOO UJ < i — 8o 2 UJ (J 6 C Q : U J 4 0 2 0 O W E S T C O A S T 1 9 5 0 1957 E A S T C O A S T F I S H C R U S T A C E A 1954 1956 1957 Figure 4. Percentage composition of f i s h and crustacea eaten by coho salmon on the east and west coasts of Vancouver Island In d i f f e r e n t years. - 25 -FEEDING INTENSITY To show the f l u c t u a t i o n s i n feeding a c t i v i t y of coho salmon, average volume of food per stomach was c a l c u l a t e d f o r each month from May to September. The f i n a l f i g u r e s were corrected f o r length and were c a l c u l a t e d as the volume of food per 10 cm of f i s h length. Monthly averages f o r the east and west coasts which represent two d i f f e r e n t feeding areas were ca l c u l a t e d separately and the r e s u l t s are shown i n Figure 5* Considerable d i f f e r e n c e s i n the feeding i n t e n s i t y of east and west coast coho salmon are apparent. F i s h caught i n the Gulf of Georgia showed an increased feeding during June which took a downward trend t h e r e a f t e r . West coast coho on the other hand, exhibited a progressive increase i n the feeding a c t i v i t y from May to August a f t e r which there was a sudden drop i n the amount of food eaten. Feeding i n t e n s i t y as revealed by the average volume of food per 10 cm. of f i s h length was also c a l c u l a t e d f o r samples obtained from the S t r a i t of Juan de Fuca and the Fraser River i n the l a t e season. A decline i n feeding a f t e r August was apparent. From the data a v a i l a b l e i t i s clear that coho salmon on the west coast feed most a c t i v e l y i n August. This increased feeding i s probably associated w i t h the accelerated maturity during the same period which w i l l be discussed i n the second secti o n of t h i s paper. About 95 per cent of t r o l l caught coho both from Inside and outside waters belong to age group 3>0 ( P r i t c h a r d , 1940) - 26 -Figure 5. Monthly variations in the feeding intensity of spring and coho salmon in different areas. Solid lines : mean volume of food per stomach. Dotted lines : mean volume of food per 10 cm. of fish length. - 27 -and are on t h e i r spawning migration. Reference to Figure 5 w i l l show that there i s a marked decrease i n the rate of feeding as the f i s h move from the east and west coasts of Vancouver Island towards inland f r e s h water streams. The S t r a i t of Juan de Fuca samples show further decrease i n feeding and f i n a l l y when i n October the f i s h enter the Fraser River as spawners there i s a complete cessation of feeding. The contention that the west coast coho show slack feeding a f t e r August i s further supported by the increasing number of empty stomachs i n the samples. I t appears that t h i s decline i n feeding a c t i v i t y i s more a f u n c t i o n of some inherent p h y s i o l o g i c a l a c t i v i t y of the f i s h at the commencement of maturity than that of n o n a v a i l a b i l i t y of s p e c i f i c food Items. SPRING SALMON (Oncorhynchus tshawytscha Walbaum) COMPOSITION OF FOOD The a n a l y s i s and i n t e r p r e t a t i o n of the data f o r spring salmon food and feeding habits f o l l o w s very c l o s e l y the l i n e s adopted f o r the food study of coho salmon. The food of spring salmon seems e s s e n t i a l l y s i m i l a r i n i t s general nature to that of coho, except f o r a somewhat r e s t r i c t e d nature of d i e t of the spring as opposed to a varied d i e t of coho. The analyses of the stomach contents during various months are presented i n Tables IV and V. Percentage composition and occurrence of d i f f e r e n t food items f o r the enti r e period May - September are shown i n Figure 6 . - 28 -TABLE IV Percentage composition of d i e t constituents of t r o l l - c a u g h t spring salmon from Vancouver Island area i n various months of 1957. Diet MAY JUKE JULY AUG. SEPT. Constituents Herring 21.9 46.1 81.8 79.1 98.3 Sand Lance 57.0 18.2 12.2 6.4 Other Fishes 1.2 6.0 1.6 3.2 1.0 Euphausiids 18.3 25.0 4 .1 10.7 0.2 Amphipods Megalops 0.8 4 . 0 0.1 - - 0.1 Other crustacea 0.1 0.7 0.1 0.2 0.2 Miscellaneous 0.7 -- 0.1 0.4 0.2 Number of 44 69 86 73 37 Stomachs To t a l Vol (cc) 680.4 1064.9 1939.4 2155.5 1180.6 - 29 -TABLE V. Percentage occurrence of d i e t constituents i n the stomach of t r o l l caught spring salmon from Vancouver Island area i n various months of'1957. Figures i n brackets i n d i c a t e number of stomachs examined. Diet MAY JUNE JULY AUG. SEPT, Constituents Herring 7.9 26.6 38.2 46.1 62.1 (4) (25) (34) (30) (18) Sand lance 23-5 13.8 19.1 20.0 (12) (13) (17) (13) Other Fishes 11.8 22.3 15.7 9.2 10.3 (6) (21) (14) (6) (3) Euphausiids 33.3 12.8 11.2 6.2 3.5 (17) (12) (10) (4) (1) Amphipods Megalops 5.9 16.0 3.4 -- 3-5 (3) (15) (3) (1) Other C r u s t a c e a 7.8 7«5 4.5 6.2 10.3 (4) (7) (4) (4) (3) Miscellaneous 9.8 1.0 7.9 12.3 10.3 (5) (1) (7) (8) (3) - 30 -Spring salmon tend to subsist l a r g e l y on f i s h w i t h s p e c i a l emphasis on herring and sand lance. P a c i f i c herring (Clupea p a l l a s i i ) was the most important s i n g l e item of food c o n s t i t u t i n g 69.2 per cent of the t o t a l volume of food con-sumed. Percentage occurrence of herring i n the stomach of spring salmon as shown i n Figure 6 i s much greater than that i n coho salmon. The s i z e of herring eaten by the spring salmon ranged from 4.5 to 23.7 cm. i n fork length but the s i z e range most commonly taken was 17 to 23 cm. No trace of p i l c h a r d was found i n any of the stomachs examined, e a r l i e r i n v e s t i g a t o r s have reported p i l c h a r d as an important item of diet of spring salmon (Chapman, 1936, P r i t c h a r d and Tester, 1944). The next most important food item a f t e r P a c i f i c herring was sand lance (Ammodytes tobianus) which formed 17 per cent of the t o t a l food volume and occurred i n 16.8 per cent of the stomachs. Sand lance ranging from 6 to 21 cm. i n t o t a l length were found i n the spring stomachs. Usually equal sized f i s h were found i n i n d i v i d u a l stomachs. There was no i n d i c a -t i o n of the abundance of sand lance i n any of the sampling areas as evident from the stomach contents. P r i t c h a r d and Tester (1944) reported an abundance of sand lance along the north-western coast of Vancouver Island. Other miscellaneous f i s h such as P a c i f i c saury (Cololabis s a i r a ) , Rockfish (Sebastodes spp), Gray cod (Gadus macrocephalus T i l e s i u s ) , Sand f i s h (Trichodon trichodon T i l e s i u s ) , u n i d e n t i f i e d clupeids and other f i s h remains formed 3.3 per cent of the t o t a l food eaten and occurred i n 15.2 per - 31 -cent of the stomachs. Crustacean d i e t was composed of euphausiids, young crabs and crab megalops and miscellaneous forms. Euphausiids were the dominant item i n crustacean d i e t , while there was a complete absence of amphipods i n the d i e t of the spring throughout the period May - September. Euphausiids represented by Euphausia p a c i f i c a , and Thysanoessa s p i n i f e r a constituted 9 per cent of the t o t a l food volume and were found i n 13.4 per cent of the stomachs. Young crabs and megalops of Cancer magister formed 0 . 9 per cent by volume of the t o t a l food and occurred i n 6 .7 per cent of the stomachs. Other crustacea, c h i e f l y isopods, occurred i n 6 .7 per cent of the stomachs and formed 0 . 3 per cent of the t o t a l volume. The catagory of miscellaneous items represented by gastropod s h e l l s , digested matter and slime contributed only 0 . 3 per cent to the t o t a l volume of food and occurred i n 7*3 per cent stomachs. A general lack of food items l i k e squids, j e l l y - f i s h and other off shore f i s h e s was noticed. These items have been reported by e a r l i e r workers. MONTHLY FLUCTUATIONS MP FEEDING INTENSITY Tables IY and V give monthly f i g u r e s which show seasonal trends i n the d i e t composition of spring salmon. Con-siderable q u a n t i t i e s of f i s h , p a r t i c u l a r l y P a c i f i c herring were eaten throughout the period of i n v e s t i g a t i o n . September marked the peak period both i n t h e i r prevalence i n the diet and the - 32 -amount eaten. Sand lance dominated the d i e t of spring salmon only i n May and e s p e c i a l l y i n those samples which were obtained from Barkley Sound. -A gradual reduction i n the amount of sand lance eaten was noticed a f t e r May and herring assumed consider-able importance, reaching i t s peak i n September when 9 8 . 3 per cent of the d i e t was composed of herring. Euphausiids appeared to be the most important item i n the crustacean p o r t i o n of the d i e t . Considerable amounts were taken during May and June but a f t e r that a reduction both i n percentage volume and percentage prevalence was noticed. Crab megalops and other Crustacea did not contribute much to the d i e t as a whole and no appreciable seasonal trends i n t h e i r occurrence and composition were noticeable. In contrast to the coho, the spring salmon from the east and west coasts of Vancouver Island showed no trace of amphipods i n t h e i r stomachs i n any month. This f a c t probably suggests a d i f f e r e n t feeding behaviour of the two species. The feeding i n t e n s i t y of 538 specimens as c a l c u l a t e d on the basis of average volume of food per stomach and per 10 cm. of f i s h length i s presented i n Figure 5 . As the mean s i z e range of the specimens examined from May to September was small, the curves f o r average volume of food per stomach for the whole period did not show any appreciable change even a f t e r adjusting f o r length of the f i s h . From these curves i t i s evident that large q u a n t i t i e s of food were taken o f f the west coast of Vancouver Island as compared to the east coast. Spring salmon i n the Gulf of Georgia show a s l i g h t downward - 33 -trend i n feeding a c t i v i t y from May to J u l y . After that the feeding Is intense and i s , perhaps, due to the abundance of young herring i n the 'gulf. August marks the period when the feeding i n t e n s i t y reaches i t s peak both f o r the east and west coast spring. In September a considerable drop i s seen on both the coasts. Samples obtained from the mouth of the Fraser i n J u l y , August and September also show a d e c l i n i n g feeding trend a f t e r J u l y which becomes more pronounced i n August and September. From the evidence a v a i l a b l e i t appears that August marks the period of maximum feeding off the southern coast of B r i t i s h Columbia and a s i g n i f i c a n t decline i n feeding i n t e n s i t y follows t h e r e a f t e r . FOOD TYPE AREAS The stomach analyses of the samples c o l l e c t e d from the east and west coasts of Vancouver Is l a n d , S t r a i t of Juan de Fuca and the Fraser give no s u f f i c i e n t l y d i s t i n c t i v e Indica-t i o n s to warrant the establishment of food type areas. As discussed e a r l i e r i n the case of coho salmon, the east and west coasts of Vancouver Island represent two d i s t i n c t areas which d i f f e r both q u a l i t a t i v e l y and q u a n t i t a t i v e l y with regard to food. In the case of spring salmon, however, only q u a n t i t a t i v e differences i n the amount of food a v a i l a b l e on the two coasts are evident (Figure 5) and there i s hardly anything to i n d i c a t e that the food of spring salmon on the two coasts d i f f e r s q u a l i t a t i v e l y a l s o . - 34 -Samples obtained from the Fraser River showed a predominance of sand lance i n t h e i r d i e t with p r a c t i c a l l y no case of herring being found i n the stomachs. Crustacea on the other hand formed a very small p o r t i o n of the d i e t . Juan de Fuca springs were found feeding l a r g e l y on herring and crustacea (mainly euphausiids) w i t h no trace of sand lance. In view of a rather u n s p e c i f i c d i e t of spring salmon i n a p a r t i c u l a r area, i t i s hard to e s t a b l i s h food type areas as could be done w i t h coho salmon of the east and west coasts. There are however d e f i n i t e evidences that l i k e coho, the spring salmon i n the Gulf of Georgia are smaller In average s i z e than those on the west coast and i t seems reasonable to assume that t h i s s i z e d i f f e r e n c e might be r e l a t e d to the amount of food a v a i l a b l e i n the two areas. COMPARISON OF THE FOOD OF SPRING AND COHO SALMON Because both the commercial and sport t r o l l f i s h e r i e s catch spring and coho salmon almost e x c l u s i v e l y , samples obtained from the S t r a i t of Georgia, Barkley Sound, Clayoquot Sound, Nootka Sound, Esperanza I n l e t , Kyuquot Sound and Quatsino Sound areas included both coho and spring salmon which were c o l l e c t e d more or le s s i n the same period i n these areas. This f a c t has not only helped i n the appraisal of the food and feeding habits of the two species i n a p a r t i c u l a r area i n i t s proper perspective but a l s o can be u t i l i z e d to assess how much these two species d i f f e r from each other i n t h e i r - 35 -food and feeding habits. As mentioned e a r l i e r , the basic d i f f e r e n c e between the d i e t of spring and coho salmon l i e s i n the f a c t that while coho tend to depend on a large v a r i e t y of food items spring salmon shows quite conservative t a s t e . S i m i l a r trends have been reported by P r i t c h a r d and Tester (1944), Kirkness (1948), Heg and Van Hyning ( 1 9 5 D . Both the spring and coho salmon depend l a r g e l y on f i s h as food. Nevertheless, there are d e f i n i t e i n d i c a t i o n s that C r u s t a c e a forms an important part of coho's d i e t and t h i s i s p a r t i c u l a r l y true of the east coast 'Blueback' whose main food i s Crustacea. While enough has been brought to l i g h t concerning differences i n food and feeding habits of the coho and spring salmon, the reasons for these differences are s t i l l obscure. Whether these differences are due to s e l e c t i v i t y on the part of f i s h or due to a v a i l a b i l i t y of s p e c i f i c items of food can only be confirmed by further d e t a i l e d work. Based on the data i n hand i t seems reasonable to a t t r i b u t e these differences to the depth which the two species i n h a b i t . Associated with the coho tagging programme of the F i s h e r i e s Research Board of Canada, preliminary i n v e s t i g a t i o n s on the depth of occurrence of spring and coho salmon i n r e l a t i o n to temperature and s a l i n i t y con-d i t i o n s were conducted at Barkley Sound i n 1953 (Milne, 1 9 5 5 ) . I t was found that the spring migrate at greater depths and are seldom caught at the surface. Most of them are taken by t r o l l l e s s than 10 miles from the shore and around 15 fathoms. Coho salmon on the other hand, are caught around 5 fathoms and l e s s than 20 miles from the shore thereby showing a more pelagic existence. P E R C E N T O F T O T A L V O L U M E Figure 6. Food of spring and coho salmon on southern B r i t i s h Columbia coast. So l i d bars indioate per cent volume, plai n bars indicate frequency of occurrence. - 37 -SALMON - HERRING RELATIONSHIP The data presented i n t h i s paper as w e l l as the various accounts of food and feeding habits of spring and coho salmon published by e a r l i e r workers make i t clear that P a c i f i c herring forms a very important item of t h e i r d i e t . This i s p a r t i c u l a r l y true of spring salmon. In view of t h i s f a c t i t i s pertinent to examine c r i t i c a l l y the salmon-herring r e l a t i o n s h i p since i t i s of greatest concern to salmon t r o l l fishermen who have expressed fear that a decline i n herring stocks due to excessive e x p l o i t a t i o n might lead to a decline i n o v e r a l l salmon catch on B r i t i s h Columbia coast. I t was possible In most cases to record the exact length of the herring which had not been digested. In cases where a p a r t i a l d i g e s t i o n bad taken place, f i s h lengths were estimated from the v e r t e b r a l columns which were usually recovered i n t a c t . The anal y s i s of the data reveals that 14 to 23 cm. fork length c o n s t i t u t e d the most vulnerable s i z e range. This s i z e range includes herring few of which are i n t h e i r 2nd year and a majority i n t h e i r 3 r d and 4th years. Three and four year old herring form a s i g n i f i c a n t p o r t i o n of the commercial catches. Taylor and Milne (1954) i n t h e i r memorandum regarding the possible r e l a t i o n s h i p between the abundance of herring and the abundance of spring salmon off the west coast of Vancouver Island mentioned that i n Jul y 1953) the si z e of herring consumed off Barkley Sound ranged from 15 to 19 cm. i n standard length. - 38 -They concluded that the abundance of spring salmon i s u n l i k e l y to be affected by the decline i n the supply of herring because the herring used as food belong to those age groups which have not been r e c r u i t e d to the winter f i s h e r y . Present i n v e s t i g a t i o n reveals that the spring and coho salmon took mostly large s i z e d herring which probably belong to age groups I I I and IV and to a l e s s e r extent to age group I I . In southern waters of B r i t i s h Columbia the recruitment to the herring f i s h e r y occurs l a r g e l y at age I I I and to a le s s e r extent at age IV. The dominant age group i n the commercial catches i s formed by three year old f i s h (Taylor, 1955)• I t i s therefore evident that the spring and coho salmon on the southern B r i t i s h Columbia coast depend l a r g e l y on that s i z e of herring which forms a dominant p o r t i o n of the commercial catches. On the basis of the above f a c t , i t i s n a t u r a l to suspect that a decrease i n the supply of herring might lead to d r a s t i c • e f f e c t s on the salmon population abundance but a c r i t i c a l i n s i g h t of the observations made so far on the food and feeding habits of spring and coho salmon makes the possib-i l i t y of the above contention somewhat untenable. Coho salmon, as shown by several studies made so f a r , i s not s p e c i f i c i n i t s d i e t and shows a more or less omnivorous behaviour. Therefore, from the point of view of salmon-herring r e l a t i o n s h i p coho does not seem to play a very s i g n i f i c a n t r o l e . Spring salmon on the other hand has been found to subsist l a r g e l y on herring. Williamson (1926) studied the food of spring salmon on the west coast of Vancouver Island and found that sand lance formed the - 39 -p r i n c i p a l food, whereas, p i l c h a r d , h e r r i n g , euphausiids and megalops made up the rest of the d i e t . Chapman (1936) found that p i l c h a r d followed by herring were the most important s i n g l e item i n the d i e t of spring salmon caught o f f the coast of \"Washington. Merkel (1957) i n his study of the food habits of king salmon i n the v i c i n i t y of San Francisco reported that Northern anchovy (Engraulis mordax) and Rockfish (Sebastodes spp) formed the dominant item of d i e t i n 1955* From these studies i t i s evident that the food of salmon changes w i t h l o c a l i t y and time (season). I t seems therefore, that the d i e t of spring and coho salmon i s more a fun c t i o n of the a v a i l a b i l i t y of s p e c i f i c food items than that of preference or s e l e c t i o n on the part of the f i s h . These f i s h would feed on any acceptable food organism which i s a v a i l a b l e to the f i s h at the time and place of t h e i r occurrence. Judging by the p l a s t i c i t y of d i e t i n spring and coho salmon, i t may be concluded that although herring forms an important item of the die t at present, i t does not nec e s s a r i l y c o n s t i t u t e the only food on which the spring and coho salmon are dependent. The herring f i s h e r y f l u c t u a t e s and there i s at present no i n d i c a t i o n of i t s decline due to ove r f i s h i n g . Salmon t r o l l catches on the other hand also have not shown d e c l i n i n g trends f o r the l a s t few years on B r i t i s h Columbia coast. I t i s therefore hard to comprehend the possible r e l a t i o n s h i p between salmon and herring abundance. I f for a moment we suppose that herring i s the only food on which the salmon i s dependent f o r i t s growth, then the reduction i n the supply of t h i s s p e c i f i c - 40 -food w i l l show up i n part i n the gross poundage of the commercial catch and retarded growth rate of the f i s h i n general. Furthermore, we have no conclusive evidence that there have been changes i n the a v a i l a b i l i t y of salmon i n the absence of abundant stocks of herring. - 41 -DISCUSSION In food studies of a f i s h species, the importance of a p a r t i c u l a r food item i s u s u a l l y judged by the amount consumed and also by the'number of stomachs containing i t . I f large number of stomachs contain that item, i t i s assumed that e i t h e r there i s an abundance of that p a r t i c u l a r item or a s e l e c t i o n on the part of f i s h . The data presented i n t h i s paper as w e l l as the findings of e a r l i e r i n v e s t i g a t o r s lead to the conclusion that although spring and coho salmon are e s s e n t i a l l y piscivorous l a t e i n l i f e , they do e x h i b i t consider-able p l a s t i c i t y i n t h e i r feeding habits and t h e i r piscivorous behaviour i s not confined to one or two species of f i s h . There are i n d i c a t i o n s that the food of spring and coho salmon changes with the area and with the time i n the same area. These f l u c t u a t i o n s seem to be more a function of changes In a v a i l a b i l i t y than a possible s e l e c t i o n on the part of the f i s h . I t i s usually assumed that the extent to which an organism i s eaten by a f i s h i s contingent upon i t s a v a i l a b i l i t y at the time and place where the predator e x i s t s . This does not i n any way preclude the p o s s i b i l i t y of s e l e c t i o n exercised by the f i s h . S e l e c t i o n of a food item i s dependent d i r e c t l y on i t s s^ize, shape, smell and taste and i n d i r e c t l y on the behaviour of the predator. The food habits of the east coast coho may be interpreted to some extent i n t h i s l i g h t . As already shown, coho salmon on the east coast of Vancouver Island subsisted c h i e f l y on crustacea, while spring salmon - 42 -i n the same area were found feeding on small f i s h . I t i s therefore very probable that due to l i m i t s imposed by the s i z e of coho on the past coast, the f i s h preferred C r u s t a c e a ^ and not large f i s h . With the exception of t h i s case, i t can be concluded that the changes i n food are r e l a t e d l a r g e l y to changes i n a v a i l a b i l i t y and the a v a i l a b i l i t y of a food item i n i t s turn i s dependent on i t s r e l a t i v e density at a p a r t i c -u l a r time and place. Evidence In support of the above comes from the studies conducted on the food of coho salmon i n 1956 as a part of the I n t e r n a t i o n a l North P a c i f i c F i s h e r i e s Commission's programme of i n v e s t i g a t i o n s . Preliminary obser-vations have revealed that squids form an important item of the d i e t of coho salmon i n the high seas followed by euphausiids A l l f i s h samples having squids i n t h e i r stomachs were taken f a r out i n the sea and those with euphausiids were caught close to the coast. I t has already been shown that the east and west coasts of Vancouver Island represent two feeding areas which are probably d i f f e r e n t so f a r as the amount of food a v a i l a b l e i s concerned. The west coast i s characterised by uniform low temperature, high s a l i n i t y and richness of the nutrient s a l t s and plenty of food. The east coast on the other hand presents quite converse conditions, v i z . high summer temperature, low s a l i n i t y and les s food. The differences i n the p r o d u c t i v i t y # Chapman (1936) and Milne (1955)' have reported that large f i s h tend to depend on a f i s h diet mostly, whereas small f i s h show a preference f o r C r u s t a c e a . - 43 -on the two coasts seem l a r g e l y to be influenced by ocean-ographic conditions. Northwest winds i n summer on the west coast of Vancouver Island r e s u l t i n upwelling nutrient r i c h water to the surface ?;hich could be expected to cause higher p r o d u c t i v i t y . On the east coast on the other hand, r e l a t i v e l y high f r e s h water inflow during summer months r e s u l t s In marked v e r t i c a l s t a b i l i t y i n the water which i n h i b i t s replenishment of n u t r i e n t s i n upper layers and thus reduce the general p r o d u c t i v i t y . These di f f e r e n c e s are r e f l e c t e d In part i n the growth of spring and coho salmon on the two coasts. Spring and coho salmon off the east coast of Vancouver Island are usually smaller than t h e i r counterparts on the west coast (Table I ) . Jensen (1948) also reported s i z e differences of s i l v e r and Chinook salmon remaining i n Puget Sound and o f f the coast. He suggested that t h i s may be due to lack of feed In the sound. S i m i l a r i n d i c a t i o n s are seen i n Chapman's (193&) account of the food habits of coho off the coast of Washington. Milne (1955) suggested that effectiveness of c e r t a i n types of lures used i n t r o l l i n g i s probably c l o s e l y associated with the s i z e and type of food eaten by the f i s h at the time of capture. Present i n v e s t i g a t i o n has shown quite conclusively that both spring and coho salmon on the east and west coasts show a greater consumption of crustacea i n May and June than i n any other month. Based on Milne's observations i t would be reasonable to i n f e r that during crustacea eating phase, t r o l l i n g l ures which are small and resemble moving crustacea. would be more e f f e c t i v e , whereas during the f i s h eating phase the use _ 44 -of large plugs and spoons might be advantageous. S i l l i m a n (1941) has also indicated the p o s s i b i l i t y of a c o r r e l a t i o n between the salmon t r o l l catch and the amount of f i s h eaten. - 45 -MATURITY The maturity study i s based on d e t a i l e d examination of ovaries and testes from 751 coho and 561 spring salmon. After the r e c e i p t of the samples, gonads were cleaned of the attached t i s s u e , weighed, and t h e i r volume determined by displacement method. The maturation of the female spring and coho salmon was studied by the measurement of ova diameters. The use of ova diameter measurements to demonstrate the developmental changes that take place i n the ovaries p r i o r to spawning was introduced by Thompson (1915) In h i s study of the P a c i f i c h a l i b u t . Other i n v e s t i g a t o r s have also used t h i s method i n maturity studies of several other marine species (Rich, 1925; C l a r k , 1925, 1929, 1934; Schaefer, 1936; Olsen and Merriman, 1946). As the ma t e r i a l for the present study was formalin-preserved, the ova i n many cases were somewhat d i s t o r t e d from t h e i r s p h e r i c a l shape. To avoid any possible s e l e c t i o n or bias i n measuring the ova and to compensate f o r the d i s t o r t i o n due to preservation, a procedure s i m i l a r to that adopted by Vladykov (1956) and Rich (1925) was employed. The diameters of 20 ova from d i f f e r e n t regions of the ovaries, along whichever axes they lay side by side i n a row over a V-shaped measuring trough graduated i n millimetres were taken. Pre-lim i n a r y observations revealed that the development of ova In d i f f e r e n t regions of the ovary i s uniform as evident by remarkable uniformity i n the s i z e of the ova throughout the e n t i r e length of the ovary. - 46 -STRUCTURE OF THE OVARY The ovaries of the spring and coho salmon are located just above the alimentary canal i n the abdominal c a v i t y . The two ovaries are us u a l l y asymmetrical i n length as w e l l as g i r t h . The r i g h t ovary i s usual l y somewhat larger and with more eggs than the l e f t one. A c r i t i c a l examination reveals t h a t , although there i s a remarkable uniformity i n the s i z e of the ova throughout the length of the ovary, there are two types of small eggs which stand out among the maturing ova. The f i r s t type i s di s t i n g u i s h e d by a few very small, sometimes microscopic deep orange-coloured bodies present i n between the maturing eggs i n the i n t e r - o v a r i a n t i s s u e . These have been noticed i n almost a l l maturing ovaries i n varying numbers e s p e c i a l l y near the terminal end of the ovary where they occur i n c l u s t e r s . The second type are small maturing ova which have undergone a t r e s i a and have stopped further development and occur as w h i t i s h , i r r e g u l a r l y scattered eggs. These seem to be more common i n the ovaries which have reached an advanced state of maturity. Vladykov (1956) noticed s i m i l a r eggs i n w i l d speckled trout ovaries and c a l l e d the smaller bodies \"Recruit-ment stock\" and w h i t i s h eggs ' A t r e t i c eggs'. Ho attempt has been made i n the present study to investigate or elucidate the probable r o l e of these small eggs. Regarding a t r e t i c eggs Vladykov mentioned that the number -of such eggs varies consid-erably with the season, l o c a l i t y and food. An attempt was - 47 -made to i n v e s t i g a t e the possible v a r i a t i o n s i n the number of such eggs according to areas and the type of food eaten by the f i s h but the r e s u l t s did not show any evident r e l a t i o n s h i p . STAGES OF MATURITY The gonads of spring and coho salmon have been c l a s s i f i e d i n t o three stages of maturity on the basis of t h e i r r e l a t i v e degree of development. In females, the degree of development i s r e a d i l y determined as the ova diameter measurements af f o r d easy and p r a c t i c a l c r i t e r i a of the state of maturity. In the case of males, however, no quantitative measure which would provide reasonably accurate estimates of r e l a t i v e maturity could be found. Although a r e l a t i o n e x i s t s between the s i z e of the f i s h and the weight of the te s t e s , v a r i a t i o n s i n the si z e or weight of the testes among the f i s h examined were so great that no precise d e l i n e a t i o n of t h e i r growth change could be obtained. For t h i s reason the degree of maturity was determined by c a l c u l a t i n g the \"Maturity index (K)\" for each f i s h . K i s an expression of the r a t i o between the weight of the gonad and the weight of the whole f i s h , and i s expressed by the formula W K = § W f where W represents the weight of the gonad i n grams and Wf i s the weight of the dressed f i s h i n pounds. The use of K as an index of the state of maturity - 48 -i s based on the premise that as the maturity advances, the value of K increases proportionately. Such a trend can be seen i n maturity index - egg s i z e r e l a t i o n s h i p (Figure 7 and Table V I ) . The three d i f f e r e n t stages of maturity show con-siderable gradation i n the degree of development of the gonads and are as f o l l o w s : STAGE I. Immature. Testes elongate, slender, occupying the whole length of the body c a v i t y i n the form of t h i n bands. (Upper l i m i t of K f o r males 1.0) Ovaries having a granular appearance, eggs small i n s i z e not more than 2.0 mm. diameter. I I . Maturing. Testes moderately enlarged, usually creamy-white i n colour. (K for males over 1.0) Ovaries enlarged with uniform-sized eggs over 2.0 mm. diameter. I l l , Mature. Testes greatly enlarged, usually pale white i n colour, f i l l i n g most of the body c a v i t y . Ovaries f u l l y enlarged with large ova f i l l i n g the e n t i r e abdominal c a v i t y . (This stage i s distinguished from Stage I I by the f a c t that the f i s h are e i t h e r i n f r e s h water zone or very close to i t - t h i s would mean that a l l the f i s h i n Stage I I I w i l l spawn the same year.) Because of the a r b i t r a r y nature of-the above c l a s s i f i c a t i o n i t i s hard to determine with c e r t a i n t y when a f i s h passes - 49 -TABLE VI. Rela t i o n s h i p between female maturity index (K) and egg diameter COHO SPRING Maturity index (K) Maturity index (K) Egg Diam. group (mm) Mean Range Mean Ran ge 1 . 1 - 1 . 5 3 . 9 3 . 2 - 5 . 2 2 . 0 1 . 1 - 3 . 8 1 . 6 - 2 . 0 4 . 6 3 . 6 - 7 . 0 2 . 9 2 . 0 - 4 . 2 2 . 1 - 2 . 5 6 . 7 4 . 7 - 1 1 . 0 4 . 6 3 . 6 - 6 . 0 2 . 6 - 3 . 0 1 1 . 2 6 . 7 - 1 8 . 3 7 . 6 3 . 9 - 1 0 . 3 3 . 1 - 3 - 5 1 4 . 2 1 0 . 3 - 1 9 . 7 9 . 4 7 . 0 - 1 1 . 3 3 . 6 - 4 . 0 2 1 . 0 1 2 . 4 - 3 0 . 6 1 3 . 3 8 . 8 - 2 0 . 6 4 . 1 - 4 . 5 2 8 . 8 1 3 - 7 - 3 7 . 0 1 8 . 5 1 1 . 0 - 2 5 . 4 4 . 6 - 5 . 0 3 6 . 3 2 8 . 2 - 4 8 . 7 2 5 . 7 1 6 . 6 - 3 2 . 8 5 . 1 - 5 . 5 4 7 . 5 3 5 . 1 - 6 6 . 1 3 1 . 4 2 1 . 5 - 4 2 . 0 5 . 6 - 6 . 0 5 8 . 2 4 2 . 4 - 7 9 . 6 4 0 . 6 3 2 . 9 - 4 4 . 7 6 . 1 - 6 . 5 6 2 . 8 4 6 . 8 - 7 6 . 7 4 6 . 0 3 0 . 5 - 4 . 6 . 2 6 . 6 - 7 . 0 — — 5 6 . 7 3 4 . 5 - 7 4 . 6 7 . 1 - 7 . 5 -- — 6 0 . 1 4 7 . 9 - 7 4 . 5 - 50 o o o • SPRING COHO -i r 1 1 1 1 2 3 4 5 6 7 E G G D I A M E T E R M M . Figure 7. Relationship between egg diameter and maturity index of female spring and ooho salmon. - 51 -from one stage of maourity to the other. However, the methods employed to assess the maturation trends i n males and females appear to he adequate for a close approximation. A l l males with testes immature enough to be considered as of stage I never exceeded 1 .0 as t h e i r maturity index and f o r t h i s reason 1 .0 was taken as the upper l i m i t of K for immature males. S i m i l a r l y by observing monthly egg-size progression of female springs i t vims found that f i s h w i t h egg diameters over 2 . 0 mm. are i n a process of maturation and w i l l probably spawn the same year. On t h i s basis 2 . 0 mm. was taken as the upper egg diameter l i m i t f o r immature females. These c r i t e r i a do not apply so r i g i d l y to coho salmon because a l l of commercially caught f i s h are i n stages I I and I I I . Table VII shows the percentages of males and females i n d i f f e r e n t stages of maturity i n t r o l l catches according to months. In May, large numbers of coho salmon were immature but as the season advanced the percentage of mature fishes gradually increased and during August almost 100 per cent of the f i s h were mature. The s i t u a t i o n i n the case of spring salmon was d i f f e r e n t , immature f i s h e s were taken by the t r o l l f i s h e r y throughout the period from May to September - with the exception of July when 53 per cent of maturing females and 67 per cent of maturing males were taken. MATURATION The growth of ripening ova was studied by means of egg-size progression and frequency of d i s t r i b u t i o n of ova of - 5 2 -TABLE V I I . Percentages of gonads i n d i f f e r e n t stages of maturity i n t r o l l - c a u g h t f i s h according to months. Figures i n brackets r e f e r to number of f i s h observed. MONTHS C 0 H 0 S P R I N G Female Male Female Male Stage I Stage I I Stage I Stage I I Stage I Stage I I Stage Stage I I I MAY 100 (13) — 57 (4) 43 (3) 64 (14) 36 ( 8 ) 100 (16) JUNE 74 ( 2 3 ) 2 6 ( 8 ) 1 5 (4) 85 ( 2 3 ) 57 (20) 4 3 ( 1 5 ) 7 6 24 (22) (7) JULY 18 (7) 82 (33) — 100 ( 5 7 ) 4 7 (17) 5 3 (19) 33 67 (14) (28) AUGUST 3 (2) 9 7 ( 6 0 ) — 100 (34) 6 0 (21) 40 (14) 7 0 3 0 (14) (6) SEPT. 5 (2) 9 5 ( 3 5 ) — 100 ( 1 1 ) 8 3 ( 1 5 ) 17 (3) 69 31 (9) (4) - 53 -349 coho and 220 spring salmon by months. As the samples from the east and west coasts of Vancouver Island were c o l l e c t e d In more or less the same time, the samples of these two areas have been combined and t h e i r egg-size pro-gression i s shown i n Figures 8 and 9. From the frequency polygons two things are apparent: 1. A progressive increase i n ova diameter with the advancing season. 2. D i f f e r e n t i a l growth of ova i n the f i s h which w i l l spawn the same year and those which w i l l not. In order to compare the r e l a t i v e growth of maturing ova, ovary samples of spawners were obtained from the Fraser, Adams, Harrison, Vedder, Eagle and Thatcher Rivers which had ova i n t h e i r ultimate spawning s i z e . By t r a c i n g the development of the modes and f o l l o w i n g the growth of maturing ova, i t was p o s s i b l e to d i s t i n g u i s h between immature and maturing females. Frequency d i s t r i b u t i o n of ova diameters of spring salmon c o l l e c t e d from the east and west coasts of Vancouver Island, the S t r a i t of Juan de Fuca and the f r e s h water streams reveals that the stock a v a i l a b l e to the f i s h e r y s p l i t s i n t o immature and maturing groups at an average egg diameter of 2.1 - 2.5 mm. (Figure 8) . Studies conducted by Rich (1925) and Milne (1954) on the maturity of spring salmon also point out s i m i l a r separation. Based on observa-ti o n s made on 220 spring salmon taken off Barkley Sound and from the Fraser River g i l l - n e t f i s h e r y , Milne showed that a - 54 -•I I. I l l -O C T O B E R (13 ) III. FRESH WATER I-OCEAN S E P T E M B E R (39 ) A U G U S T ( 5 9 ) J U L Y (S2) J U N E ( 3 5 ) M A Y (2 2) i D O L O O L D o i D o m o m o t f i o m 1 1 1 1 1 11 11 11 1 1 1 i ^ H < 0 < H < O r H < O r - t - £ > r H < O r H t O ( - H < 0 < - t E G G D I A M E T E R M M . Figure 8. Monthly egg size progression in 220 spring salmon taken in 1957. Figures in brackets refer to number of f i s h examined each month. t£> o m o m o m o 10 o ^ o 10 * • • • • • • •h qq oj to co - >-cc. < > O u. O u o cc UJ Q. d Z o UJ 60CH 500-AOOA 3 0 0 -200-J IOCH ON t 4 EGG D I A M E T E R M M . Figure 11. Relationship between the diameters of eggs of spring and cftho salmon and their number per cubic centimetre of ovary volume. Based on egg counts of 603 spring and coho salmon. - 64 -To check the accuracy of t h i s method actual counts were made of ova from 11 f i s h which included large and small females. These counts were then compared with those obtained by the above method. The calculated t o t a l s d i f f e r e d from the actual counts by amounts varying from 1.5 per cent to 10 .1 per cent. The average percentage error was 5»3 (Table .X). Although the egg diameter - egg number r e l a t i o n s h i p curve gives s u f f i c i e n t l y accurate estimation of the t o t a l number of eggs present i n the ovaries, i t i s , however, l i m i t e d i n i t s a p p l i -c a t i o n when we are dealing with ova larger than 5 m i l l i m e t r e . This i s due to the fact that beyond 5 mm. l e v e l the curve tends to become asymptotic. To obtain counts of ova over 5 mm. i n diameter, i t would be necessary to transform t h i s curve i n t o a logarithmic one. •CORRELATION BETWEEN EGG NUMBER AND SIZE OF FISH Several i n v e s t i g a t o r s have shown that the number of maturing eggs has a p o s i t i v e c o r r e l a t i o n with the size of f i s h . Such a c o r r e l a t i o n can be seen i n the case of spring and coho salmon (Figure 1 2 ) . The values obtained from 25 sets of observations i n the case of coho and 15 sets of observations f o r spring were u t i l i z e d and by the method of least squares, the equation which best expresses the r e l a t i o n between length and fecundity was cal c u l a t e d . The r e l a t i o n s h i p seems to be of the type Y = a +. bX and the regression equations for spring and coho salmon were found to be: - 65 -TABLE X. Comparison between actual and calculated egg counts of 11 spring and coho females. Egg diam. Actual Calculated fo (mm) count count difference 1.5 3582 3332 n r: i 0 J 1.7 2804 2714 3 . 3 2 . 3 3885 3705 4 . 7 2 . 8 2970 2790 5.7 3 . 0 2601 2499 4.1 3 . 6 3074 3180 3 . 3 3 . 9 4237 4175 1.5 4 . 1 5250 ' 5020 4 . 6 4 . 8 3412 3625 5 .9 4 . 9 5219 4740 10.1 5 . 0 5136 5564 7.7 Mean 3834 3758 5.3 - 66 -Y - 184.42X - 7203 and Y = 101.9X - 3057 r e s p e c t i v e l y , where Y i s the egg number and X represents fork length of the f i s h . The number of eggs i n coho salmon varied from 2064 to 5670, with an average of 3635 eggs. Spring salmon had a greater number of eggs varying from 3025 to 10,121 with an average of 5604 eggs. Foerster and P r i t c h a r d (1936) estimated the average egg count of coho c o l l e c t e d i n 1934 to be approximately 3000. To compare with other species of P a c i f i c salmon they reduced the egg counts to a common denominator, i . e . the number of eggs per inch of f i s h or per pound of f i s h and concluded that even w i t h i n a species there i s a s i g n i f i c a n t v a r i a t i o n i n egg number according to si z e and that egg number - f i s h size r e l a t i o n s h i p may be d i f f e r e n t from year to year. Packer (1932) i n his study of brook trout Salvelinus f o n t i n a l i s stated that the r e l a t i o n s h i p between number of eggs and length of f i s h i s c u r v i l i n e a r instead of l i n e a r . The l a t t e r i s obtained only when the logarithms of egg numbers and logarithms of lengths are u t i l i z e d . Scott (1956) advocated t h i s logarithmic trans-formation of the data to cancel out the e f f e c t of correlated mean and variance and thus change the r e l a t i o n s h i p into a l i n e a r form which i s e a s i l y handled by the method of lea s t squares. In the present study, however, the logarithmic trans-formation of the data does not seem to serve a useful purpose because the values on which Figure 12 i s based are obtained only from maturing f i s h representing a narrow range of f i s h lengths. - 68 -Now the question worth considering i s how a regression equation can be u t i l i z e d i n p r e d i c t i n g egg number for d i f f e r e n t f i s h lengths? Several i n v e s t i g a t o r s have pointed out that the egg count f o r the f i s h of same lengths may vary s i g n i f i c a n t l y according to races, l o c a l i t y , year and so on and as such, the slope of the l i n e representing egg number - f i s h length r e l a t i o n -ship may s h i f t i t s p o s i t i o n accordingly. Furthermore, the ef f e c t of egg s i z e on egg number i n a p a r t i c u l a r species as shown i n the next section may be a s i g n i f i c a n t f actor i n s h i f t i n g the slope. In order to appraise the u t i l i t y of a regression equation for p r e d i c t i n g egg number f o r various f i s h lengths i t would be necessary to take into account the factors determining egg number and f i s h length. Reference has already been made to ovarian f o l l i c u l a r regression as a fac t o r deter-mining the egg number. Rounsefell ( 1 9 5 7 ) using Foerster and Pritchard's ( 1 9 4 1 ) data f o r pink salmon t r i e d to show by means of s t a t i s t i c a l treatments that sea temperature i s the p r i n c i p a l factor i n c o n t r o l l i n g average length of the f i s h and that the annual differences i n mean egg count i n pink salmon are a function of sea temperature. Scott ( 1 9 5 6 ) In his study of the ef f e c t of food on the fecundity of Kamloops trout provided experimental evidence that s t a r v a t i o n may cause suppression of maturation i n l a t e r years of growth and thus a f f e c t fecundity. Age of the f i s h may a l s o be an important factor a f f e c t i n g fecundity. R a i t t ( 1 9 3 3 ) reported that fecundity i n haddock depended mainly on the size of the f i s h but the older f i s h of the same length had larger number of eggs. Recently - 69 -Nagasaki (1958) i n his study of the fecundity of P a c i f i c herring (Clupea p a l l a s l ) i n B r i t i s h Columbia coastal waters reported that fecundity depended mainly on body length and to a lesser extent on age, independently of i t s e f f e c t on body length. He also found that fecundity of herring of same body length and the same age was s i g n i f i c a n t l y higher i n northern B r i t i s h Columbia than i n southern. In short i t i s reasonable to assume that egg number i n a f i s h i s an ever f l u c t u a t i n g e n t i t y and the degree of f l u c t u a t i o n depends upon the s e v e r i t y of the stress imposed by environmental factors w i t h i n c e r t a i n l i m i t s . I t i s therefore u n l i k e l y that egg number - f i s h s i z e r e l a t i o n s h i p equation would be the same for d i f f e r e n t years, l o c a l i t i e s , races, etc. - 70 -REDUCTION IN ABSOLUTE FECUNDITY AS A FUNCTION OF EGG SIZE As the number of eggs per cm. of f i s h length i s , besides other f a c t o r s , dependent on the s i z e of the eggs (Figure 13), r e l a t i v e fecundity was u t i l i z e d f o r a correct a p p r a i s a l of the e f f e c t of egg s i z e on the absolute fecundity. In p l o t t i n g the number of eggs per cm. of f i s h length against egg diameters, a negative r e l a t i o n s h i p was found to e x i s t between the two v a r i a b l e s , i n other words as the egg diameter increased there was a decrease i n r e l a t i v e fecundity. Reference to s i m i l a r reduction i n the number of eggs as a function of egg s i z e has been made by Vladykov (1956) and Scott (1956) i n other species. In order to evaluate the mutual r e l a t i o n s h i p between fecundity, f i s h length and egg s i z e more thoroughly, analysis of m u l t i p l e regression (Snedecor, 1957) was done by taking 25 sets of observations which covered the e n t i r e range of f i s h lengths and egg diameters i n spring salmon. The r e l a t i o n s h i p between the three v a r i a t e s i s expressed as Y = a • b y l > 2 X - l * b y 2 # 1 X 2 where Y - number of eggs (absolute f e c u n d i t y ) , Xj_ = f i s h length and X 2 = egg diameter, byx.2 = regression c o e f f i c i e n t i n standard measure of Y on X-^ independent of X 2 and b y 2 ^ = regression c o e f f i c i e n t i n standard measure of Y on X 2 independent of X-j_. IOO E G G D I A M E T E R (mm) Figure 13. Relationship between eg« diameter and number of eggs per eentiaetre of fish length. Data based on 169 spring salmon, eaoh dot indicates ayerage egg number for each 0.5 mm. diameter group. - 72 -The m u l t i p l e regression equation was found to be Y * 1892 f 59.76 X x - 228.0 X 2 which i n d i c a t e s that a p o s i t i v e c o r r e l a t i o n e x i s t s between the number of eggs and f i s h length, while egg number i s negatively corre l a t e d with egg s i z e . In order to estimate the r e l a t i v e importance of X^ and Xg with regard to t h e i r independent effect on Y, the standard p a r t i a l regression c o e f f i c i e n t s ( b ^ a n <^ b ' y 2 q) were ca l c u l a t e d and compared. I t was revealed that the r e l a t i o n s h i p between f i s h length and egg number i s about four times greater than the e f f e c t of egg s i z e on egg number independent of f i s h length. I t can therefore be concluded that fecundity i n spring salmon and also i n coho salmon depends mainly upon the body length and to a lesser extent on egg s i z e independent of body length. - 73 -SUMMARY 1. The stomach contents of spring and coho salmon c o l l e c t e d during the summer of 1957 from commercial and sport f i s h e r i e s operating i n southern B r i t i s h Columbia c o a s t a l waters V\\/ere analyzed. F i s h , c h i e f l y P a c i f i c herring and Crustacea formed the most important items of the d i e t of spring and coho salmon. 2. Coho salmon appear to accept a wider v a r i e t y of food items, p a r t i c u l a r l y those of the pelagic habitat and feed on whatever acceptable food item i s a v a i l a b l e i n the area at the time. 3. D e f i n i t e seasonal changes i n the composition of food of coho were observed. In the early part of the summer (May and June), C r u s t a c e a formed the dominant food but l a t e r f i s h replaced Crustacea. Both i n quantity eaten and prevalence In the stomachs, amphipods appeared to be of outstanding importance. 4. The east and west coasts of Vancouver Island repre-sent two d i s t i n c t food type areas with respect to the amount of food a v a i l a b l e to coho and spring salmon and the type of food items occurring. Crustacea formed the dominant food of coho salmon on the east coast, while f i s h was the dominant food on the west coast. These d i f f e r e n t feeding conditions as a f f e c t i n g the growth of east and west coast coho are discussed i n d e t a i l s . 5. Unlike coho, spring salmon appear to be more conser-vative i n t h e i r feeding habits. The differences i n the - 74 -di e t of spring and coho salmon are perhaps due to the diff e r e n c e s of depth which these two species i n h a b i t ; coho being more pelagic i n i t s feeding migration. Both spring and coho salmon, p a r t i c u l a r l y those of the west coast show intense feeding a c t i v i t y during l a t e J u l y and August. After August the feeding i n t e n s i t y take a d e c l i n i n g trend. There i s evidence that part of herring on which spring and coho salmon feed belong to that age group which forms a major p o r t i o n of the commercial catches but the past h i s t o r y reveals that spring and coho salmon do feed on alternate foods i n the absence of herring. There i s no conclusive evidence to show that reduction i n herring abundance due to pradation would lead to a reduction i n salmon catches. Three types of ova were found i n the maturing ovary: (a) Maturing eggs which are quite uniform i n s i z e through out the ovary and are destined to be spawned, (b) A t r e t i c eggs which are dead maturing eggs occurring as w h i t i s h i r r e g u l a r l y scattered eggs, and (c) Recruitment stock represented by very small deep orange coloured y o l k l e s s bodies attached to int e r - o v a r i a n t i s s u e . Females have been c l a s s i f i e d as immature, maturing and mature on the basis of egg size - ova diameter of 2.0 mm. separates immature and maturing f i s h . In the case of males the d i s t i n c t i o n between immature and maturing i s based on whether or not the maturity index value - 75 -(gonad wt/dressed f i s h wt) i s over 1.0. 10. Immature and maturing female springs divide at a for k length of approximately 74 cm., while coho do so at an approximate length of 52 cm. 11. A volume method has been developed for determination of egg numbers present i n the ovary. The ca l c u l a t e d t o t a l s and act u a l counts of eggs show an average percentage error of 5*3-12. By s t a t i s t i c a l treatments i t has been shown that the absolute fecundity i s p o s i t i v e l y correlated with f i s h length but negatively to egg s i z e . The magnitude of the e f f e c t of f i s h length on absolute fecundity i s about four times greater than that of egg s i z e . - 76 -REFERENCES Chapman, W.M. 1936 The p i l c h a r d f i s h e r y of the state of \"Washington i n 1936 with notes on the food of the s i l v e r and Chinook salmon off the Washington coast. Dept. F i s h . , State of Wash., B u l l . (36 C) : 1-20. Cla r k , F. N. 1925 The l i f e h i s t o r y of Leuresthes tenuisan - an atherine f i s h w ith t i d e c o n t r o l l e d spawning habits. C a l i f . F i s h and Game Comm. F i s h . B u l l . No.10. 51 pp. 1929 The l i f e h i s t o r y of the C a l i f o r n i a Jack smelt. Atherinopsis c a l i f o r n i e n s i s . C a l i f . F i s h and Game Comm. F i s h . Bui 1 i No. l6T~23 pp. 1934 Maturity of the C a l i f o r n i a sardine (Sardina caerulea) determined by ova diameter measurements. C a l i f . Div. F i s h and Game. F i s h . B u l l . No.42. 49 pp. Clemens, W. A. 1934 The food of spring salmon i n Shuswap Lake. Can. F i e l d . N a t u r a l i s t . 48(9) : 142. Foerster, R. E. and P r i t c h a r d , A. L. 1936 The egg content of P a c i f i c salmon. Progr. Rept. Pac., 2 8 . : 3-5« F i s h . Res. Bd. Can. Foskett, D. R. 195L Young salmon i n the Nanaimo area. F i s h . Res. Bd. Can., Prog. Rept. P a c , 86. : 18-19. Fraser, C. McLean. 1946 Food of f i s h e s . Trans. Roy. Soc. Canada. Series 3 . 4(5) : 33-39. G i l b e r t , C.H. 1913 Age of maturity of the P a c i f i c coast salmon of the genus Oncorhynchus. B u l l . Bur. F i s h . U.S., 1 9 1 2 . , 3 2 : 1-22. 1913 The salmon of Swiftsure Bank and the Fraser River sockeye run of 1912. Rept. Comm'er F i s h . , 1912, Prov. B r i t . Col. 14-24. Heg, R. and J. Van Hyning. 1951 Food of the chinook and s i l v e r salmon taken o f f the Oregon coast. Oregon F i s h . Comm. Res. B r i e f s , v o l . 3, No.2, : 32-40. - 77 -Hunter, J . G. 1948 Natural propogation of salmon i n the Central c o a s t a l area of B r i t i s h Columbia. F i s h . Res. Bd. Can., Prog. Rept. Pac. 77 : 105-106. Hynes, H. B. N. 1950 The food of the f r e s h water sticklebacks (Gastrosteus aculeatus and Pygosteus pungitius) with a review of methods used i n studies of the food of f i s h e s . J . Anim. E c o l . London. 19 :26-58. Jensen, H.M. 1948 Puget Sound salmon i n v e s t i g a t i o n . Dept. F i s h . State Wash., Annual. Rept. 1948. : 3 3 . Kirkness, W. 1948 Food of chinook and s i l v e r salmon of Puget Sound. Dept. F i s h . State. Wash., Annual. Rept. 1948. : 2 8 - 3 2 . McGregor, E. A. 1922 Observations on the egg y i e l d of Klamath River King salmon. C a l i f . F i s h & Game. 8 (3) : I 6 O - I 7 6 . 1923 A possible separation of the r i v e r races of king salmon i n ocean caught f i s h by means of anatomical c h a r a c t e r i s t i c s . C a l i f . F i s h & Game. 9 (4) : 138-150. Merkel, T. J . 1957 Food habits of the king salmon, Oncorhynchus tshawytscha (Walbaum), i n the v i c i n i t y of San Francisco, C a l i f o r n i a . C a l i f . F i s h & Game. 43 (4) : 249-270. Milne, D. J . 1950 The difference i n the growth of coho salmon on the east and west coasts of Vancouver Island i n 1950. F i s h . Res. Bd. Can., Prog. Rept. Pac. 85 : 80-82. 1954 T r o l l salmon. F i s h . Res. Bd. Can., Pac. B i o l . Stn., Annual Rept. 1954. 1955 S e l e c t i v i t y of t r o l l i n g l u r e s . F i s h . Res. Bd. Can., Prog. Rept. Pac. 103 : 3 - 5 . Nagasaki, F. 1958 The fecundity of P a c i f i c herring (Clupea p a l l a s l ) i n B r i t i s h Columbia coastal waters. J. F i s h . Res. Bd. Can. 15 (3) : 313-330. Neave, F. 1948 Fecundity and m o r t a l i t y i n P a c i f i c salmon. Trans. Roy. Soc. Canada., Ser 3 , 42 (sect 5) : 97-105. - 78 -Olsen, Y. H. and D. Merriman 1946 Studies on the marine resources of southern New England. TV. The biology and economic importance of the ocean pout Macrozoarces americanus. Bingham. Oceanogr. C o l l . B u l l . 9. Art 4. : I E 4 . P r i t c h a r d , A. L. 1940 Studies on the age of the coho salmon (Oncorhynchus kisutch) and the spring salmon (0. tshawytscha) i n B r i t i s h Columbia. Trans. Roy. Soc. Canada. Ser 3, 34 (sect V) : 99-120. P r i t c h a r d , A. L. and A. L . Tester. 1944 Food of spring and coho salmon i n B r i t i s h Columbia. B u l l . F i s h . Res. Bd. Can., 65 : 1-23. R a i t t , D. S. 1933 The fecundity of haddock. F i s h . Res. Bd. Scotland., S c i . Invest., 1932. No. 1 : 3-42. Rich, W. H. 1925 Growth and degree of maturity of Chinook salmon i n the ocean. B u l l . U.S. Bur. F i s h . , 41 : 67 -110. R i c k e r , W. E. 1932 Studies of speckled trout (Salvellnus f o n t i n a l l s ) i n Ontario. Pub. Ont. F i s h . Res. Lab., 44 : 67-110. Rounsefell, G. A. 1957 Fecundity of North American salmonidae. U.S. F i s h & Wild L i f e Service. F i s h . B u l l . 122. V o l . 57- » 451-468. Schaefer, M. B. 1936 Cont r i b u t i o n to the l i f e h i s t o r y of the surf smelt (Hypomesus pretiosus) i n Puget Sound. Wash. Dept. F i s h . B i o l . Rept. 35B. : 1-45. Scott, D. P. 1956 E f f e c t of food quantity on the fecundity of Kamloop trout Salmo g a l r d n e r l kamloops. Jordan. Ph.D. Thesis. Dept. of Zool. Univ. B r i t . C o l . Senter, V. E. 1940 Observations on the food of P a c i f i c salmon. P a c i f i c Fishermen. V o l . 38 (4) : 26. Shapovalov, L. and A. 0. Taft 1954 The l i f e h i s t o r i e s of the rainbow trout (Salmo g a l r d n e r l galrdnerl) and s i l v e r salmon (Oncorhynchus kisutchX\"with s p e c i a l reference to Waddell creek, C a l i f o r n i a , and recommendations regarding t h e i r management. C a l i f . F i s h & Game. F i s h . B u l l . , 98 : 1-375. - 79 -S i l l i m a n , R. P. 1941 Fl u c t u a t i o n s i n the d i e t of chinook and s i l v e r salmons o f f Washington as r e l a t e d to the t r o l l catch of salmon. Copeia. 2 : 80 -87 . Snedecor, G. W. 1957 S t a t i s t i c a l methods. The Iowa State College Press. Snyder, J. 0 . 1921 How many eggs does a salmon lay? C a l i f . F i s h & Game. 7 : 6-3-64. Taylor, F. H. C. 1955 The P a c i f i c herring (Clupea p a l l a s i ) along the P a c i f i c coast of Canada. Internat. North. Pac. F i s h . Comm. B u l l . No. 1 : 105-128. Taylor, F. H. C. and D. J. Milne. 1954 The possible r e l a t i o n s h i p between abundance of herring and the abundance of spring salmon off the west coast of Vancouver Island. Memorandum (Unpublished). F i s h . Res. Bd. Can. Pac. B i o l . Stn. : 1 -8 . Thompson, W. F. 1915 A preliminary report on the l i f e h i s t o r y of the h a l i b u t . Rept. Commsr. F i s h . B. C. for 1914. : N76-N99. Vladykov, V. D. 1956 Fecundity of w i l d speckled trout (Salvelinus f o n t i n a l i s ) i n Quebec lakes. J. F i s h . Res. Bd. Can7~13 (6) : 799-841. Wickett, W. P. 1951 The coho salmon population of N i l e creek. F i s h . Res. Bd. Can. Prog. Rept. P a c , 89 : 8 8 - 8 9 . Williamson, H. C. 1930 Notes on food of spring salmon. Canadian. F i e l d . N a t u r a l i s t . 44 (9) : 203-204. - 80 -APPENDIX A INSTRUCTIONS ,FOR THE COLLECTION OF STOMACHS AND GONADS OF SPRING AND COHO SALMON Each c o l l e c t o r i s being provided with k i t s made up of one l i v e r can, one quart of formalin, and 25 numbered bags. Upon re c e i p t of t h i s shipment, the bags should be removed and kept separately, the formalin emptied into the l i v e r can and the can f i l l e d to approximately one half I t s capacity with s a l t or f r e s h water. In order to have a representative sample, i t i s suggested that they should be spread throughout the period of f i s h i n g by taking eit h e r 5 or 10 samples a week. Fishermen are asked to c o l l e c t stomachs and gonads i n an unbiased and random way. In large f i s h remove the U-shaped stomach by severing the g u l l e t immediately behind the mouth and the i n t e s t i n e immediately behind the f i n g e r - l i k e sacs ( p y l o r i c caeca), also remove each reproductive organ (gonad) making c e r t a i n that each stomach and gonad i s complete. In small f i s h remove en t i r e gut and complete contents of the body cav i t y and place them In the bag, t i g h t e n the draw s t r i n g and t i e i t around the top of the bag. In the book provided record the l a b e l number, date of capture, the f i s h i n g l o c a t i o n , the fork length In centimetres and at l e a s t 5 scales from the l e f t side of the f i s h , and any other remarks. - 81 -Insert the bag and contents into the formalin s o l u t i o n i n l i v e r can. The k i t . should be considered f u l l when there Is s t i l l enough formalin l e f t to cover the bags. At t h i s time close the l i d t i g h t l y - and ship the package f r e i g h t or express c o l l e c t . t o the B i o l o g i c a l S t a t i o n , Nanaimo, B. C. Please mark on the re t u r n address so that further equipment and cheque to cover 25 cents payment for each sample may be deli v e r e d . Your c o n t r i b u t i o n i s only part of a program through-out B r i t i s h Columbia. The analyses of these should serve as a basis f o r determining: (1) The a c t u a l food of spring and coho salmon taken i n the commercial catches. (2) The r e l a t i v e value of herring and shrimp i n the food r e l a t i o n s h i p . (3) The degree of maturity for d i f f e r e n t sizes of f i s h caught. The i n v e s t i g a t o r s would welcome any data from log books or other records which have been co l l e c t e d In the past. Credit w i l l be given f o r such data and they w i l l be treated as s t r i c t l y c o n f i d e n t i a l . PLEASE NOTE: (a) Separate marked cans should be used f o r spring and coho salmon. (b) M a i l the envelope provided to B i o l o g i c a l Station with information as to when each k i t i s despatched. (c) I f f i s h i s undersized and small enough to go into the bag, make a small s l i t i n the underside and include the whole f i s h as the sample. "@en ; edm:hasType "Thesis/Dissertation"@en ; edm:isShownAt "10.14288/1.0106784"@en ; dcterms:language "eng"@en ; ns0:degreeDiscipline "Zoology"@en ; edm:provider "Vancouver : University of British Columbia Library"@en ; dcterms:publisher "University of British Columbia"@en ; dcterms:rights "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en ; ns0:scholarLevel "Graduate"@en ; dcterms:title "Food and feeding habits, maturity and fecundity of spring salmon (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) in southern British Columbia coastal waters"@en ; dcterms:type "Text"@en ; ns0:identifierURI "http://hdl.handle.net/2429/41674"@en .