UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

The rearing and feeding ecology of juvenile rainbow trout from a large lake-fed river Irvine, James Richard 1978

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1978_A6_7 I79.pdf [ 6.54MB ]
Metadata
JSON: 831-1.0094391.json
JSON-LD: 831-1.0094391-ld.json
RDF/XML (Pretty): 831-1.0094391-rdf.xml
RDF/JSON: 831-1.0094391-rdf.json
Turtle: 831-1.0094391-turtle.txt
N-Triples: 831-1.0094391-rdf-ntriples.txt
Original Record: 831-1.0094391-source.json
Full Text
831-1.0094391-fulltext.txt
Citation
831-1.0094391.ris

Full Text

THE REARING AND FEEDING, ECOLOGY OF JUVENILE RAINBOW TROUT FROM A LARGE LAKE-FED RIVER •by James Richard I r v i n e •Sc.. (Hon.), U n i v e r s i t y o f B r i t i s h Columbia, 197 A'THESIS SUBMITTED IN PARTIAL FULFILLMENT OF "•. THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department o f Zoology) We accept t h i s , t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA J u l y , 1978 @ James Richard I r v i n e , 197 8 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f i an advanced degree at the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e tha 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 r e f e r e n c e and s t u d y . I f u r t h e r ag ree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . It i s u n d e r s t o o d that c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f Zoology  The U n i v e r s i t y o f B r i t i s h Co lumbia 2075 Wesbrook P l a c e V a n c o u v e r , Canada V6T 1W5 J u l y 25 1978 ABSTRACT J u v e n i l e rainbow t r o u t (Salmo g a i r d n e r i Richardson) from the Lardeau R i v e r i n southeastern B r i t i s h Columbia were s t u d -i e d i n both t h e i r n a t u r a l environment and stream tanks. In the r i v e r , h i g h e s t d e n s i t i e s of r e c e n t l y emerged t r o u t occur-red i n areas w i t h overhanging cover, shallow depth and minimal c u r r e n t . Older, u n d e r y e a r l i n g trout.were g e n e r a l l y found i n regions w i t h s m a l l e r bottom p a r t i c l e s i z e than y e a r l i n g s ; both age c l a s s e s avoided f a s t c u r r e n t areas. Young t r o u t migrated from the Lardeau R i v e r to Kootenay Lake d u r i n g s p r i n g and summer. Except d u r i n g these seasons t r o u t were l a r g e r and more abundant i n the upper versus the lower r i v e r ; t h i s was probably a r e s u l t o f b e t t e r r e a r i n g h a b i t a t and h i g h e r b i o l o g -i c a l p r o d u c t i v i t y i n the upper r i v e r . T rout f e d almost e x c l u s i v e l y on d r i f t i n g organisms. Lake o r i g i n d r i f t was an important food to r i v e r i n e t r o u t d u r i n g summer; kokanee (Oncorhynchus nerka) eggs and f r y were s i g n i f -i c a n t d u r i n g f a l l and s p r i n g r e s p e c t i v e l y . In stream tanks, where i t was p o s s i b l e to manipulate prey p o p u l a t i o n s , l i v e prey were consumed s i g n i f i c a n t l y more than the same s p e c i e s when dead, suggesting t h a t prey body movement was an important prey c h a r a c t e r i s t i c . In both the f i e l d and stream tanks, t r o u t consumed prey w i t h i n a d i s c r e t e s i z e range w i t h l a r g e r f r y g e n e r a l l y consuming b i g g e r prey than s m a l l e r f r y . F u r t h e r work i s suggested which would improve our understanding of the feeding ecology of stream rearing trout. - i v -TABLE OF CONTENTS Page TITLE PAGE i ABSTRACT i i TABLE OF CONTENTS . . .' i v LIST OF TABLES v i LIST OF FIGURES v i i i ACKNOWLEDGEMENTS X I. INTRODUCTION 1 I I . STUDY AREA 5 A. General 5 B. H a b i t a t C l a s s i f i c a t i o n 10 C. Sampling P e r i o d i c i t y 10 I I I . MATERIALS AND METHODS 13 A. F i s h 13 1. C o l l e c t i o n 13 (a) E l e c t r o f i s h i n g 13 (b) D i p n e t t i n g 15 2. Observation 15 (a) S k i n D i v i n g 15 (i) H a b i t a t Information 15 ( i i ) F i s h Feeding 17 3. P r e s e r v a t i o n and Laboratory A n a l y s i s 17 B. I n v e r t e b r a t e D r i f t • 18 1. C o l l e c t i o n 18 2. P r e s e r v a t i o n and Laboratory A n a l y s i s 20 3. Data P r e s e n t a t i o n 21 C. P h y s i c a l Measurements 22 D. Feeding Experiments 22 1. Flow - Through Stream Tanks 22 2. Clo s e d System Stream Tanks 23 (a) Experimental Design 23 (.b) Fry Types 27 (c) Prey Types 27 IV. TROUT REARING IN LARDEAU RIVER 2 9 A. H a b i t a t P r e f e r e n c e s 29 1. Zone 1 29 2. Zones 2, 3, and 4 31 B. Mi g r a t o r y Behaviour •- 37 C. Length and Weight R e l a t i o n s h i p s 3 9 - v -TABLE OF CONTENTS (continued) Page V. FEEDING ECOLOGY 46 A. D r i f t i n g Versus Benthic Prey 46 B. V e r t i c a l S t r a t i f i c a t i o n of I n v e r t e b r a t e D r i f t .... 49 C. Seasonal A v a i l a b i l i t y and U t i l i z a t i o n of D r i f t ... 49 1. Summer 49 2. F a l l 52 3. Winter 52 4. S p r i n g 55 D. Rate of Food Passage 55 E. F i s h S i z e - Prey S i z e R e l a t i o n s h i p s 58 1. F i e l d Evidence 58 (a) Zone 1 . 58 (b) Zones 2, 3, and 4 65 2. Experimental Evidence 65 F. Prey Body Movement - 77 G. P r e v i o u s Feeding Experience 80 VI. DISCUSSION 84 V I I . CONCLUSIONS 99 REFERENCES CITED 102 - v i -LIST OF TABLES Table Number Page 1. T test results of comparisons of fry densities obtained by skin diving i n zone 1 30 2. Mean underyearling trout densities obtained by skin diving i n zone 2 32 3. T test results of comparisons of underyearling trout densities obtained by skin diving i n zone 2 32 4. Mean seasonal densities obtained by e l e c t r o f i s h i n g i n four major habitat types i n zones 2, 3, and 4 .... 33 5. Mean seasonal densities obtained by e l e c t r o f i s h i n g i n zones 2, 3, and 4 according to surface water v e l o c i t i e s and bottom p a r t i c l e sizes 34 6. T test results of comparisons between densities obtained by e l e c t r o f i s h i n g i n zones 2, 3, and 4 according to d i f f e r i n g water v e l o c i t i e s and p a r t i c l e sizes 36 7. Mean lengths and ranges of rainbow trout captured from the upper and lower halves of the Lardeau River by e l e c t r o f ishing 41 8. Logged length-weight functional regression formulae and condition factors for trout captured by el e c t r o -f i s h i n g 43 9. T test results of comparisons of condition factors of trout captured by e l e c t r o f i s h i n g 43 10. T te s t r e s u l t s of comparisons of lengths of trout captured by e l e c t r o f i s h i n g i n the upper and lower halves of the Lardeau River 45 11. Chi-square results of comparisons between feeding s t r i k e d i s t r i b u t i o n s of two groups of trout f r y 48 12. Mean densities of three potential prey types from surface and benthic d r i f t samples i n zone 1 50 13. Mean numbers of three food types per f i s h stomach from rate of food passage experiment 58 - v i i -LIST OF TABLES (continued) 14. Length frequency and range data of f r y d i p n e t t e d i n zone 1 d u r i n g summer 62 15. T t e s t r e s u l t s of comparisons of lengths of f r y d i p n e t t e d i n zone 1 d u r i n g summer 62 16. Mean e l e c t i v i t i e s and s i z e s of zooplankton from the n o r t h e a s t s t a t i o n i n zone 1 64 17. Mean lengths and t h e i r standard d e v i a t i o n s f o r f i s h , d r i f t i n g prey items, and stomach content items from zones 2, 3, and 4 67 18. T t e s t r e s u l t s of comparisons of f i s h l e n g t h s , d r i f t i n g prey l e n g t h s , and stomach content item lengths from zones 2, 3, and 4 68 19. Chi-square r e s u l t s of comparisons of s i z e c a t e g o r i e s of Simulium l a r v a e consumed by three groups of t r o u t f r y 70 20. Mean e l e c t i v i t i e s and s i z e s of zooplankton consumed by three s i z e groups of t r o u t 76 21. R e l a t i o n s h i p between Cyclops d e n s i t y and mean e l e c t -i v i t y f o r t h r e e s i z e groups of t r o u t 7 6 22. Numbers of dead and l i v e prey consumed by two groups of t r o u t and r e s u l t s of c h i - s q u a r e a n a l y s i s on d i f f e r e n c e s found 79 23. Numbers of f r y and food items i n experiment designed to t e s t the e f f e c t of p r e v i o u s f e e d i n g experience ... 81 - v i i i -LIST OF FIGURES F i g u r e Number Page 1. L o c a t i o n of study area 3 2. Mean monthly d i s c h a r g e o f Lardeau R i v e r near Trout Lake (zone 1), Marblehead (zone 4), and Argenta Bridge (zone 4) 6 3. Zone 1 d u r i n g summer showing e x t e n s i v e r e g i o n s of inundated t e r r e s t r i a l v e g e t a t i o n 8 4. Zone 2 d u r i n g summer showing slough h a b i t a t 8 5. Zone 3 d u r i n g summer showing mainstem r i v e r 9 6. Zone 4 d u r i n g summer showing mainstem r i v e r 9 7. Mean monthly water temperatures a t Marblehead (zone 4; 1968-1972) and Argenta B r i d g e (zone 4: 1968-1975) 11 8. Stream d r i f t nets used i n study 19 9. Cl o s e d system stream tank s p e c i f i c a t i o n s 24 10. (a and b ) . Closed system stream tanks i n o p e r a t i o n . 2 5 11. Mean seasonal d e n s i t y estimates of j u v e n i l e t r o u t i n the Lardeau R i v e r 38 12. Mean seasonal . d e n s i t y estimates of j u v e n i l e t r o u t i n the upper and lower halves o f the Lardeau R i v e r .. 38 13. Seasonal l e n g t h f r e q u e n c i e s of rainbow t r o u t captured by e l e c t r o f i s h i n g i n zones 2, 3, and 4 40 14. Logged length-weight r e l a t i o n s h i p , of rainbow t r o u t captured by e l e c t r o f i s h i n g i n zones 2, 3, and 4 ..... 44 15. Mean number of f e e d i n g s t r i k e s i n four r e g i o n s of the water column 47 16. Summer d r i f t d e n s i t i e s of three major prey types i n fo u r r i v e r zones 51 17. Percent occurrence of :six.. food types i n f r y stom-achs from each of fo u r r i v e r zones d u r i n g summer .... 51 - i x -LIST OF FIGURES (continued) F i g u r e Number Page 18. Zooplankton prey d e n s i t i e s a t two l o c a t i o n s i n zone 1 on 8 August 1974 53 19. F a l l d r i f t d e n s i t i e s o f t h r e e major prey types i n four r i v e r zones 54 20. Percent occurrence of seven food types i n e i g h t f r y stomachs from each of t h r e e r i v e r zones d u r i n g f a l l . 54 21. Winter d r i f t d e n s i t i e s of t h r e e major prey types i n f o u r r i v e r zones 5'6 22. Percent occurrence of f i v e food types i n e i g h t f r y stom-,achs from each of three r i v e r zones d u r i n g w i n t e r .... 56 23. S p r i n g d r i f t d e n s i t i e s of three major prey types i n f o u r r i v e r zones 57 24. Percent occurrence o f seven food types i n e i g h t y e a r l i n g stomachs from each of t h r e e r i v e r zones d u r i n g s p r i n g 57 25. Percent occurrence of t h r e e prey types i n d r i f t samples from two s t a t i o n s over two 24 h p e r i o d s i n zone 1 60 26. Percent occurrence of three prey types i n f r y stomachs from two s t a t i o n s over two 2 4 h p e r i o d s i n zone 1 61 27. Length f r e q u e n c i e s of ,fjour_'.size, c a t e g o r i e s of Simulium l a r v a e used i n f e e d i n g experiments 69 28. Length frequency o f Simulium l a r v a e a v a i l a b l e t o ( F i g . 28a), and consumed by ( F i g s . 28b-d), t r o u t f r y . 7 0 29. Mean le n g t h s of Simulium l a r v a e consumed vs:. f i s h s i z e c o n s i d e r i n g a l l f r y e x p e r i m e n t a l l y exposed to f o u r s i z e c l a s s e s of Simulium 7 2 30. Percent occurrence of Simulium l a r v a e and Heptagen-i i d a e nymphs i n t r o u t stomachs and d r i f t from experiment designed to t e s t the e f f e c t of p r e v i o u s f e e d i n g experience 82 - x -ACKNOWLEDGEMENTS Many persons have pr o v i d e d a s s i s t a n c e a t v a r i o u s stages i n the development o f t h i s t h e s i s and i t i s wit h s i n c e r e a p p r e c i a t i o n t h a t I extend my thanks t o them. My super-v i s o r , Dr. T.G. Northcote, p r o v i d e d a d v i c e and encouragement throughout the study. Harvey Andrusak i s g r a t e f u l l y ack-nowledged f o r h i s e n t h u s i a s t i c support. Drs. J.D. McPhail and N.J. Wilimovsky p r o v i d e d h e l p f u l comments on an e a r l i e r d r a f t o f the t h e s i s . A number of i n d i v i d u a l s a s s i s t e d i n the f i e l d and l a b -o r a t o r y and I would s p e c i f i c a l l y l i k e to thank R. C a t h e r a l l , D. Crowley, G. Northcote, L. S c o t t n i c k i and S. S t e e l e f o r t h e i r help. F i n a n c i a l support was pro v i d e d by the F i s h and W i l d l i f e Branch and a N a t i o n a l Research C o u n c i l grant awarded to Dr. T.G. Northcote. F i n a l l y , I would l i k e t o extend s p e c i a l thanks t o Lin d a f o r her continued support, a s s i s t a n c e and encouragement. - 1 -I. INTRODUCTION Researchers have been examining the feeding behaviour of f i s h i n t h e i r natural environment for many years u n t i l , pres-ently, studies of prey s p e c i a l i z a t i o n by f i s h predators have become almost commonplace i n ecology. The feeding of f i s h i n the l o t i c environment, i n p a r t i c u l a r the relationship between juvenile salmonids and invertebrate d r i f t , has been the focus of many of these recent studies (see Waters, 1972; Cadwallader, 1975 for recent reviews). While the experimental approach has proved a successful means of studying f i s h feeding (e.g. Ware, 1972; Bryan, 1973), most studies performed thus far have been conducted on f i s h retained i n aquaria. Fish feeding i n an experimental stream environment has not been examined i n any d e t a i l . The primary aim of t h i s research was to f i l l part of the gap i n our knowledge of the feeding ecology of fishes by considering certain aspects of the feeding behaviour of juvenile rainbow trout i n the stream environment, using both f i e l d and experimental techniques. In p a r t i c u l a r the follow-ing were examined: the importance of d r i f t i n g versus benthic prey; the a v a i l a b i l i t y and u t i l i z a t i o n of invertebrate d r i f t ; the si g n i f i c a n c e to trout of prey body movement; and the relationship between f i s h size and prey size. The f i s h used i n t h i s study were juvenile rainbow trout from the Lardeau River which flows into the north arm of Kootenay Lake, located i n southeastern B r i t i s h Columbia (Fig. - 2 -1). The Lardeau system w i t h i t s p a r t i c u l a r t r o u t p o p u l a t i o n was s e l e c t e d f o r three major reasons. F i r s t , s i n c e the Lardeau R i v e r i s lake f ed, zooplankton predominate i n the stream d r i f t of i t s upper reaches, forming a major p a r t o f the d i e t o f j u v e n i l e t r o u t r e a r i n g there ( I r v i n e , MS 1973). The l o c a t i o n , t h e r e f o r e , p r o v i d e d an o p p o r t u n i t y to examine the importance of lake o r i g i n d r i f t to young rainbow t r o u t , as w e l l as to conduct d e t a i l e d f i e l d analyses of the d i e l r e l a -t i o n s h i p between d r i f t and f r y f e e d i n g . The second c h i e f advantage a l s o concerned the nature of the Lardeau R i v e r . Flowing 65 km to Kootenay Lake, the r i v e r ' s l e n g t h not onl y allows f o r the r e d u c t i o n o f b i o l o g i c a l e f f e c t s from Trout Lake, but changing p h y s i c a l and b i o l o g i c a l c o n d i t i o n s along i t pr e -sented an o p p o r t u n i t y to examine t r o u t f e e d i n g i n a v a r i e t y o f h a b i t a t s . The t h i r d major advantage concerned the f i s h . Juv-e n i l e t r o u t from the Lardeau R i v e r spend t h e i r a d u l t l i v e s i n Kootenay Lake and spawn near the head of the Lardeau R i v e r ( I r v i n e , 197 8). As t h i s l a t t e r area i s known as Gerra r d these f i s h are c a l l e d Gerrard stock t r o u t . Gerrard t r o u t are prob-a b l y g e n e t i c a l l y d i s t i n c t from others i n Kootenay Lake (Cart-wright, 19 61), and are extremely important to the s p o r t f i s h e r y of the lake because they not i n f r e q u e n t l y a t t a i n s i z e s i n excess of 9 kg (Hartman and G a l b r a i t h , 1970). V a r i o u s aspects of the l i f e h i s t o r y of these t r o u t may be important i n determ-i n i n g t h e i r f i n a l l a r g e s i z e i n c l u d i n g t h e i r e a r l y l i f e h i s t o r y . - 2a -F i g . 1. L o c a t i o n of study area. - 3 -- 4 -Unpublished information suggests the p o s s i b i l i t y of faster than normal juvenile growth rates because of exceptionally aggressive feeding behaviour (G.E. Stringer, pers. comm.). Although some research had been conducted on the early ecology of these f i s h p r i o r to thi s thesis (Cartwright, 1961; North-cote, 1969), most had concentrated on th e i r spawning behaviour (Hartman, 1969; 1970; Hartman and Galbraith, 1970). Choosing these f i s h on which to base a study thus provided an excellent opportunity to obtain much needed knowledge on the early l i f e h istory of an important stock of f i s h . In order to carry out the f i e l d feeding portion of the study i t was necessary to know approximately where and for how long f i s h resided i n the Lardeau system. By using a standard f i s h capture technique, information on habitat preferences and migration was obtained. Length and weight s t a t i s t i c s were analyzed..and related to migration patterns and food a v a i l a b i l i t y . Thus, while the feeding ecology of stream rear-ing rainbow trout was the central theme of t h i s study, i n f o r -mation gathered on the early ecology of the Gerrard trout also constituted a s i g n i f i c a n t proportion of the thesis. - 5 -I I . STUDY AREA A . G e n e r a l O r i g i n a t i n g a t T r o u t L a k e i n s o u t h e a s t e r n B r i t i s h C o l u m b i a t h e L a r d e a u R i v e r f l o w s 65L;km t o K o o t e n a y L a k e ( F i g . 1) . A t a p o i n t 13 km u p s t r e a m f r o m K o o t e n a y L a k e , t h e L a r d e a u a n d D u n c a n R i v e r s y s t e m s j o i n . T h e f l o w o f t h e D u n c a n h a s b e e n r e g u l a t e d s i n c e 1966 b y t h e D u n c a n Dam l o c a t e d s e v e r a l h u n d r e d m e t r e s a b o v e t h e L a r d e a u - D u n c a n c o n f l u e n c e . P h y s i c a l a n d b i o l o g i c a l c o n d i t i o n s v a r y a l o n g t h e L a r d e a u R i v e r a n d f o r t h i s r e a s o n t h e r i v e r h a s b e e n d i v i d e d i n t o f o u r z o n e s ( F i g . 1 ) . Z o n e 1 e x t e n d s 1 km d o w n s t r e a m f r o m T r o u t L a k e t o M o b b s C r e e k ( i n c l u d e s a r e a r e f e r r e d t o a s G e r r a r d ) ; z o n e 2 e x t e n d s 15 km d o w n s t r e a m f r o m M o b b s C r e e k t o R a p i d C r e e k ; z o n e 3 e x t e n d s 2 3 km d o w n s t r e a m f r o m R a p i d C r e e k a n d z o n e 4 t h e r e m a i n i n g 2 6 km t o K o o t e n a y L a k e . A l t h o u g h d e t a i l e d p h y s i c a l c o m p a r i s o n s o f t h e s e d i f f e r e n t r e g i o n s w e r e n o t u n d e r -t a k e n a s p a r t o f t h i s s t u d y , some g e n e r a l c o m p a r i s o n s c a n b e m a d e . T h e i n f l u e n c e o f T r o u t L a k e i s h i g h l y n o t i c e a b l e i n z o n e 1 . T h e l a k e p r o v i d e s r e l a t i v e l y s i l t - f r e e w a t e r t o t h i s z o n e b y a c t i n g a s a s e t t l i n g b a s i n ( 2 0 - 3 0 ppm s u s p e n d e d s e d i m e n t d u r i n g f r e s h e t ) a n d summer w a t e r t e m p e r a t u r e s a r e 1 - . 6 . 5 ° C w a r m e r t h a n 1 . 5 km f u r t h e r d o w n s t r e a m ( H a r t m a n a n d G a l b r a i t h , 3 1 9 7 0 ) . M e a n m o n t h l y d i s c h a r g e r a n g e s f r o m 4 . 6 - 6 6 . 8 m / s ( F i g . 2) w i t h l a r g e d a i l y f l u c t u a t i o n s r a r e . T h e r i v e r i s - 5a -F i g . 2. Mean monthly d i s c h a r g e of Lardeau R i v e r near Trout Lake (<a—<a) (zone 1), Marblehead (o——o) (zone 4) , and Argenta Bridge (• —•) (zone 4) . Zone 1 data c o l l e c t e d 1942 - 1945 (Cartwright, 1961) and zone 4 data 1965 - 197.5 (Inland Waters Branch, Annual Reports) . - 6 -- 7 -ch a n n e l i z e d except d u r i n g f r e s h e t when e x t e n s i v e r e g i o n s of t e r r e s t r i a l v e g e t a t i o n are inundated, p a r t i c u l a r l y along the southwest bank ( F i g . 3). Three l a r g e pools are separated by shallower, f a s t e r c u r r e n t areas of predominantly l a r g e g r a v e l and cobble s u b s t r a t e w i t h l i t t l e s i l t . R i v e r g r a d i e n t i s moderate (-2.2 m/km), p a r t l y the r e s u l t of a n a t u r a l dam . c r e a t e d by an a l l u v i a l fan d e p o s i t e d i n the Lardeau by Mobbs Creek (Hartman and G a l b r a i t h , 197 0). C o o l , t u r b i d g l a c i a l t r i b u t a r i e s e n t e r i n g the Lardeau R i v e r i n zones 2,3, and 4 lower summer water temperatures and i n c r e a s e t u r b i d i t i e s . The r e l a t i v e l y steep g r a d i e n t of zones 2 and 3 (3.4 and 3.6 m/km r e s p e c t i v e l y ) prevents exten-s i v e d e p o s i t i o n o f g l a c i a l f l o u r and s i l t . Sloughs wi t h g r a v e l s u b s t r a t e s are common du r i n g h i g h water p e r i o d s ( F i g . 4) and g r a v e l s u b s t r a t e s a l s o predominate i n the mainstem (F i g . 5). Ri v e r g r a d i e n t has lessened c o n s i d e r a b l y by zone 4 (1.6 m/km) r e s u l t i n g i n the accumulation of heavy d e p o s i t s of g l a c i a l f l o u r and s i l t , e s p e c i a l l y below the Duncan R i v e r c o n f l u e n c e . F i n e g r a v e l and sand are the most common sub-s t r a t e s i n both the main r i v e r and sloughs ( F i g . 6). Discharge and temperature data are a v a i l a b l e from above the Duncan confluence a t Marblehead, and below i t a t the Argenta Bridge ( F i g . 1). Mean monthly d i s c h a r g e s a t Marble-3 3 head range from 13 m /s d u r i n g winter to 227 m /s d u r i n g f r e s h e t ( F i g . 2). Seasonal flow f l u c t u a t i o n s are reduced to - 7a -F i g . 3. Zone 1 d u r i n g summer showing e x t e n s i v e r e g i o n s of inundated t e r r e s t r i a l v e g e t a t i o n . F i g . 4. Zone 2 d u r i n g summer showing slough h a b i t a t . - 8 -- 8a -F i g . 5 . Z o n e 3 d u r i n g summer s h o w i n g m a i n s t e m r i v e r . F i g . 6. Z o n e 4 d u r i n g summer s h o w i n g m a i n s t e m r i v e r . - 10 -some extent below the Lardeau-Duncan confluence by the Duncan Dam ( F i g . 2). The dam a l s o e x e r t s an i n f l u e n c e on water temperature. In the Lardeau River above the Duncan co n f l u e n c e (Marblehead) mean monthly temperatures range between 0.6 -13.6°C. Below the confluence (Argenta Bridge) water tempera-t u r e s are lower than above d u r i n g summer, and h i g h e r the remainder of the year ( F i g . 7). B. H a b i t a t C l a s s i f i c a t i o n Except i n zone 1, p r e c i s e f i s h sampling s t a t i o n s were not e s t a b l i s h e d i n the Lardeau R i v e r due to i t s extreme f l u c t u a -t i o n s i n l e v e l . Rather, many smal l areas of r e l a t i v e l y uniform h a b i t a t were sampled. The h a b i t a t c l a s s i f i c a t i o n scheme was s i m i l a r t o t h a t o r i g i n a l l y proposed by A l l e n (1951). Four h a b i t a t types were d i s t i n g u i s h e d : (1) r i f f l e s - areas of shallow broken water r a p i d l y f l o w i n g over a stony bottom; (2) runs - deeper r e g i o n s of smoother, more g l i d i n g flow and of u s u a l l y slower v e l o c i t y than r i f f l e s which c o u l d be e i t h e r e r o d i n g (a t r u e run) or d e p o s i t i n g (a t r u e f l a t ) ( F r o s t and Brown, 1967); (3) pools - areas w i t h v a r i a b l e depth and sub-s t r a t e composition but n e g l i g i b l e c u r r e n t ; (4) l o g jams -regions where c o n s i d e r a b l e wood d e b r i s had accumulated. C. Sampling P e r i o d i c i t y F i e l d work was concentrated d u r i n g the f o l l o w i n g p e r i o d s : summer - August 1974; f a l l - October 1974; w i n t e r - l a t e Mean m o n t h l y w a t e r t e m p e r a t u r e s a t M a r b l e h e a d ( A — ( z o n e 4 : 1 9 6 8 - 1 9 7 2 ) a n d A r g e n t a B r i d g e (o—o) ( z o n e 4 : 1 9 6 8 - 1 9 7 5 ) . - 12 -December 1974 e a r l y January 1975; s p r i n g - May 1974 and 1975. Data c o l l e c t e d d u r i n g s p r i n g 1974 were s i m i l a r to data from s p r i n g 1975 and have been combined. In a d d i t i o n , some f i s h c o l l e c t e d d u r i n g August 1958 (Cartwright, 1961) have been i n c l u d e d w i t h other summer samples. - 13 -I I I . MATERIALS AND METHODS A. F i s h 1. C o l l e c t i o n (a) E l e c t r o f i s h i n g The most e f f e c t i v e capture technique, and the one most f r e q u e n t l y used to study f i s h h a b i t a t i n zones 2, 3, and 4 was a p o r t a b l e Smith-Root Type V p u l s e d D.C. e l e c t r o f i s h e r . The e l e c t r o f i s h e r was c a r r i e d and operated by one person moving upstream who was f o l l o w e d c l o s e l y by a second i n d i v i d u a l w i t h a s m a l l dipnet.., Since the e l e c t r i c a l i n t e n s i t y a t the pe r i p h e r y of the anode's f i e l d o f t e n o n l y f r i g h t e n s f i s h (Smith-Root I n s t r u c t i o n Booklet, n.d.), the e l e c t r o f i s h e r was turned on and o f f i n t e r m i t t e n t l y when used. Sampling was con-f i n e d to a 1 m s t r i p along the r i v e r bank except where p a r t i c -u l a r h a b i t a t s d i c t a t e d otherwise. Examples of the l a t t e r were r i f f l e s and l o g jams l o c a t e d away from the r i v e r bank. T y p i c a l l y a much wider s t r i p than 1 m would then be e l e c t r o -f i s h e d . Areas e l e c t r o f i s h e d a t one time were approximately 2 2 25 m f o r runs and r i f f l e s and 15 m f o r pools and l o g jams. Changing water ( e l e c t r i c a l c o n d u c t i v i t y , temperature, depth, flow and c l a r i t y ) and weather c o n d i t i o n s make any value assigned as the e f f i c i e n c y o f an e l e c t r o f i s h e r p e r t i n e n t t o one water on one o c c a s i o n only (Cross, 1976). While no attempt was made to q u a n t i f y seasonal changes i n e l e c t r o f i s h i n g e f f i c -i e n c i e s , or d i f f e r e n t e f f i c i e n c i e s among h a b i t a t types w i t h i n i - 14 -any season, some comments are i n order. E l e c t r o f i s h i n g e f f i c i e n c i e s on recently emerged f r y are low and variable (Solomon and Templeton, 19 76) and so summer density estimates of 0+ f i s h i n the Lardeau River were l i k e l y inaccurate. Winter density estimates were probably low because f i s h tended to remain hidden i n the substrate aft e r being electrofished. This was demonstrated on several occasions by disturbing the substrate of an area after e l e c t r o f i s h i n g . After doing t h i s , stunned f i s h frequently floated to.the surface. This did not happen i n other seasons. For a l l seasons, water current i n -creased the e f f i c i e n c y of the e l e c t r o f i s h i n g operation i n runs and r i f f l e s by frequently carrying stunned f i s h into the view of operators. Current was ne g l i g i b l e i n pools and hence could not aid i n f i s h capture but the lack of i t improved f i s h de-tection by increasing v i s i b i l i t y . Capture e f f i c i e n c i e s were probably lowest at a l l times of the year i n log jam areas. In log jam habitats current was frequently minimal and hence l i t t l e aid i n f i s h capture. Wood debris obscured v i s i o n and thereby further reduced capture e f f i c i e n c i e s . Fish captured by e l e c t r o f i s h i n g for stomach content analysis were always taken near mid-day from run habitats immediately adjacent to the r i v e r bank. Surface water v e l -o c i t i e s , measured ~5 cm below the water surface with a Pygmy Gurley flow meter, approximated 0.6 m/s. - 15 -Cb) Dipnetting Dipnetting was the most e f f e c t i v e capture technique for recently emerged fry i n zone 1. To study d i e l feeding pat-terns ~10 fry were dipnetted from two stations at 4 h in t e r v a l s over two 24 h periods i n late July - early August 1974. One station was selected from each side of the r i v e r . The north-east bank station was -12 0 m downstream from Trout Lake and the southwest bank station -14 0 m downstream. Both stations were areas of minimal current < 1 m deep and approximately 4 m i n length and 2 m wide. The chief difference between the two was the amount of overhanging vegetation (more at the southwest s t a t i o n ) . 2. Observation (a) Skin Diving (i) Habitat Information Observations of trout habitat i n zones 1 and 2 during summer were obtained by skin diving. In zone 1 eight stations 2 (either 4 or 8 m i n area) were established -120 m downstream from Trout Lake along a 20 m stretch of the northeast bank. The objective was to assess the importance of overhanging cover, water depth and current v e l o c i t y i n habitat selection by very young f r y . Mean water v e l o c i t i e s within each station were determined by averaging a series of v e l o c i t y measure-ments taken ~5 cm below the water surface using a Pygmy Gurley flowmeter. V e l o c i t i e s too slow for measurement were recorded - 16 -as <7.5 cm/s. F r y d e n s i t i e s a t each s t a t i o n were-determined by s k i n d i v i n g , near mid-day, on e i g h t separate o c c a s i o n s i n l a t e J u l y and e a r l y August 1974. S t a t i o n s were not e s t a b l i s h e d i n zone 2, but r a t h e r , t r o u t d e n s i t i e s were determined i n many areas, and r e s u l t s from s i m i l a r h a b i t a t s combined. Areas sampled approximated 2 20 m . F i s h counts were made by a d i v e r moving upstream, r e c o r d i n g numbers and s i z e s of a l l f i s h observed. In many areas i t was im p o s s i b l e to move f r e e l y through an area due to the s t r e n g t h o f the c u r r e n t . In such i n s t a n c e s a rope was attac h e d to both s i d e s o f the r i v e r and a second, movable rope a f f i x e d to i t , p a r a l l e l to the stream's c u r r e n t . A s e r i e s of l o n g i t u d i n a l t r a n s e c t s were made by p u l l i n g one's s e l f along t h i s second rope, enumerating a l l f i s h i n a 1 m s t r i p beneath i t . E a r l i e r s t u d i e s (Cartwright, 1961; North-cote, 1969), i n c o n j u n c t i o n w i t h t h i s f i e l d program e s t a b l i s h e d approximate s i z e ranges f o r d i f f e r e n t age c l a s s e s ; those t r o u t v i s u a l l y e stimated to be l e s s than 70 mm were c l a s s i f i e d as 0+ and those g r e a t e r than 70 mm as 1+. In zone 2 t r o u t d e n s i t i e s were estimated i n runs and poo l s o n l y . In r i f f l e s , water depths were too shallow and c u r r e n t s too f a s t t o allow a d i v e r to make accurate counts. Among l o g jams, v i s i b i l i t y was g r e a t l y reduced by accumulated wood d e b r i s and d i v i n g was too dangerous. - 17 -( i i ) Fish Feeding During summer, recently emerged fry i n zone 1 and older fry i n zone 2 were observed feeding. Of prime i n t e r e s t was... the number of feeding s t r i k e s i n d i f f e r e n t regions of the water column. The diver positioned himself immediately down-stream from a trout, close enough to observe without disturb-ing the f i s h . A second person, on shore, verbally signalled the s t a r t and f i n i s h of 5 min observational periods during which time the diver recorded, on a sheet of roughened white ple x i g l a s s , numbers of feeding s t r i k e s i n each of the follow-ing four regions: water surface; water surface to f i s h station depth.;, f i s h station depth to bottom; and bottom. At the end of each observation period the following were recorded: f i s h size and depth; bottom p a r t i c l e type and size; water ve l o c i t y , temperature, and depth; and distance from shore. 3. Preservation and Laboratory Analysis Most f i s h captured were measured and released. Those f i s h retained for l a t e r laboratory analysis were k i l l e d , body walls punctured, placed i n 10 percent formalin for several weeks and f i n a l l y stored in, 37 percent isopropanol. In the laboratory a Sauter balance, accurate to 1 mg and Helios d i a l reading c a l i p e r s , accurate to 0.01 mm were used to weigh and measure f i s h a f t e r being blotted dry on paper towel. Stomach contents anterior of the p y l o r i c caecae were counted and - 18 -i d e n t i f i e d at least to family and whenever possible, to species. When invertebrates were measured, the longest possible measurement exclusive of antennae, c e r c i or any extended appendage was taken using an ocular micrometer mounted i n a compound microscope. B. Invertebrate D r i f t 1. C o l l e c t i o n D r i f t samples were co l l e c t e d using nets 1 m i n length with a f r o n t a l opening of 15.2 x 10.2 cm (Fig. 8). To re t a i n early i n s t a r insect larvae and larger zooplankters, nitex netting with a pore size of 130 um was used. Stakes driven into the substrate held the nets i n position. Unless i n d i c -ated otherwise, nets were positioned so that the upper edge of the f r o n t a l opening was about 5 mm above the a i r water i n t e r -face to capture organisms f l o a t i n g on the surface (surface d r i f t sampling). Because of problems with nets clogging, sampling times were usually 5 min but re p l i c a t e samples were always taken. Water v e l o c i t i e s were measured at each location without the net i n position using a Pygmy Gurley flowmeter situated ~5 cm below the water surface. Since i t was desirable to estimate d r i f t densities, the f i l t e r i n g effectiveness of d r i f t samplers was determined over a range of water v e l o c i t i e s . V e l o c i t i e s were measured with a Pygmy Gurley flowmeter just inside the net opening when the net was i n position, and i n the same location without the net. - 18a -Fig. 8. Stream d r i f t nets used i n study. - 19 -> - 20 -The mean of 12 e f f i c i e n c y estimates over v e l o c i t i e s ranging from 0.5 - 0.7 m/s was 80 percent. Using t h i s figure and knowing the net dimensions and water v e l o c i t y , i t was possible to calculate the volume of water f i l t e r e d for each d r i f t sample taken. A comprehensive d r i f t sampling program was undertaken i n zone 1 i n conjunction with the fry dipnetting program des-cribed e a r l i e r [Section I I I . A. 1. (b)]. Replicate 5 min d r i f t samples were taken adjacent to both fry sampling stations during a l l fry c o l l e c t i o n periods. Water depths at d r i f t sampling s i t e s averaged 1 m and v e l o c i t i e s , 0.6 m/s. In addition to regular surface d r i f t samples, r e p l i c a t e ... benthic d r i f t samples, where d r i f t nets were placed immed-i a t e l y above the bottom, were also taken simultaneously with surface d r i f t samples over the f i r s t 24 h period. These samples were taken to assess the importance of v e r t i c a l s t r a t i f i c a t i o n of d r i f t . D r i f t samples taken from each of the four zones were used to assess s p a t i a l and seasonal fluctuations of the d r i f t fauna. A l l samples were coll e c t e d near mid-day ~1 m from shore where water depths averaged 1 m and surface water v e l o c i t i e s 0.6 m/s. 2. Preservation and Laboratory Analysis D r i f t samples were preserved i n 10 percent formalin and la t e r transferred to 70 percent ethanol before laboratory - 21 -a n a l y s i s . Due to l a r g e numbers of organisms and q u a n t i t i e s of s i l t , t o t a l counts were not u s u a l l y made of zooplankton. Samples were thoroughly mixed i n 25 ml of water b e f o r e drawing three 1 ml subsamples. T o t a l counts were made of non-zoo-p l a n k t e r s . I n v e r t e b r a t e s were always i d e n t i f i e d t o f a m i l y and where p o s s i b l e t o s p e c i e s . I n v e r t e b r a t e s were measured as d e s c r i b e d e a r l i e r ( S e c t i o n I I I . A. 3.). 3. Data P r e s e n t a t i o n Organisms captured i n d r i f t nets were c l a s s i f i e d as e i t h e r prey s p e c i e s or non-prey s p e c i e s depending on whether they were r e g u l a r l y consumed by young t r o u t . Prey were group-ed i n t o three c a t e g o r i e s : zooplankton; immature a q u a t i c i n s e c t s ; and t e r r e s t r i a l i n s e c t s . Zooplankton prey ( t y p i c a l l y l a c u s t r i n e o r i g i n ) were c h i e f l y Daphnia g a l e a t a mendotae, Ep i s h u r a nevadensis and Bosmina l o n g i r o s t r i s ; immature a q u a t i c i n s e c t s ( t y p i c a l l y r i v e r i n e o r i g i n ) were mainly d i p t e r a n pupae, p l e c o p t e r a n and ephemeropteran nymphs, chironomid, t r i c h o p t e r a n and Simulium l a r v a e ; t e r r e s t r i a l i n s e c t s were l a r g e l y d i p t e r a n and non-dipteran a d u l t s but a l s o i n c l u d e d some non-aquatic immature i n s e c t s . Non-prey were of two c a t e g o r i e s : non-prey zooplankton - s p e c i e s such as K e l l i -c o t t i a T o n g i s p i n a and Cyclops b i c u s p i d a t u s ; other non-prey - forms such as Hydra and i n s e c t exuviae. Throughout the t h e s i s , whenever seasonal i n f o r m a t i o n i s given, summer data are presented b e f o r e s p r i n g . T r o u t emerge - 22 -and f i r s t feed and seek h a b i t a t s d u r i n g t h a t season. C. P h y s i c a l Measurements ' At a l l f i s h and i n v e r t e b r a t e d r i f t sampling s i t e s c u r r e n t v e l o c i t y was measured ~5 cm below the water s u r f a c e w i t h a Pygmy Gurley flow meter. Average p a r t i c l e s i z e ( e x c l u d i n g s i l t ) and.water c l a r i t y were v i s u a l l y estimated and water depth, temperature and presence o f overhanging cover recorded. D. Feeding Experiments 1. Flow-Through Stream Tanks . An attempt was made to estimate r e l a t i v e food passage r a t e s of d i f f e r e n t n a t u r a l food types u s i n g flow-through stream tanks. Two tanks, 2.4 m long , 2 5 cm wide, and 30 cm deep were c o n s t r u c t e d out of plywood. Two movable screens a t f r o n t (1.25 mm and 130 um diameter mesh) and one a t back (1.25 mm diameter mesh) prevented food items from e n t e r i n g and f r y from l e a v i n g . To simulate the n a t u r a l s u b s t r a t e , rocks were p l a c e d on the bottom. In August, 1974 the tanks were p l a c e d i n Gerrard Creek ( F i g . 1) and 65 r e c e n t l y emerged f r y captured from the.-northeast s t a t i o n i n zone 1 [ S e c t i o n I I I . A. 1. (b)] in t r o d u c e d . The s u r f a c e water v e l o c i t y i n the tanks was approximately 10 cm/s and the temperature 13°C. Over the next 4 8 h, f i v e f i s h were removed every 4 h f o r l a t e r stomach content a n a l y s i s i n the l a b o r a t o r y . The experiment assumed t h a t a l l f i s h began wi t h s i m i l a r l y f u l l stomachs wi t h food a t - 23 -about the same stage o f d i g e s t i o n . 2. C l o s e d System Stream Tanks (a) Experimental Design With one ex c e p t i o n f e e d i n g experiments were conducted a t Meadow Creek ( F i g . 1) i n two octagonal p l e x i g l a s s stream tanks ( F i g . 9). The f o l l o w i n g d i s c u s s i o n a p p l i e s to these e x p e r i -ments. Minor design d i f f e r e n c e s i n the experiment which was not performed a t Meadow Creek w i l l be d i s c u s s e d s e p a r a t e l y . Stream tank temperature f l u c t u a t i o n s were minimized i n two ways. F i r s t , a plywood r o o f prevented d i r e c t s u n l i g h t from s t r i k i n g the tanks d u r i n g the h o t t e s t p a r t of the day ( F i g . 10a). As w a l l s were not i n c l u d e d , a c o o l i n g flow of a i r was allowed. Second, each stream tank was i t s e l f immersed i n a l a r g e r wooden tank ( F i g . 10b). Cool Meadow Creek water (10.5 - 12°C) c o n t i n u a l l y pumped i n t o these o u t e r tanks and allowed to overflow back i n t o Meadow Creek helped c o n t r o l stream tank temperatures. Temperatures ranged from 11 - 13°C, depending on the experiment. P r i o r to each experiment, c l e a n water was added t o the stream tanks. The water was obtained from a nearby n a t u r a l s p r i n g and s t r a i n e d through f i n e n i t e x n e t t i n g (130 um) to remove any p o t e n t i a l food items. Rocks, s i m u l a t i n g a n a t u r a l s u b s t r a t e , were scrubbed v i g o r o u s l y and r i n s e d c l e a n b e f o r e being p l a c e d on tank bottoms. U s u a l l y about 30 f i s h were i n t r o d u c e d to the tanks approximately 40 h bef o r e an e x p e r i -- 23a -Fig. 9. Closed system stream tank s p e c i f i c a t i o n s . - 24 -105.5 cm-•92.5 cm-~ " f 17.0 cm A - 24a -F i g . 10. (a a n d b ) . C l o s e d s y s t e m s t r e a m t a n k s i n o p e r a t i o n . - 26 -merit. F i n e mesh screens (1.25 mm diameter) p l a c e d over the tanks reduced the p o s s i b i l i t y o f a i r - b o r n e i n s e c t s a c c i d e n t a l -l y e n t e r i n g and ensured t h a t f i s h c o u l d not jump out. S e v e r a l hours a f t e r i n t r o d u c i n g f i s h to the tanks, water c u r r e n t was i n i t i a t e d by submersible e l e c t r i c pumps and a s u r f a c e water v e l o c i t y of approximately 10 cm/s maintained throughout the experiment. F i s h were l e f t unfed u n t i l approx-i m a t e l y 1 h be f o r e experiments began. T h i s allowed p r e v i o u s l y consumed food to become d i g e s t e d and a l s o reduced i n d i v i d u a l v a r i a t i o n s i n hunger l e v e l . A t t h i s time approximately 1.5 g Chinook Mash (hatchery food) were p l a c e d i n the tanks to reduce hunger l e v e l s to a more n a t u r a l s t a t e , s i n c e i t was f e l t u n s a t i a t e d f i s h may e x h i b i t a t y p i c a l f e e d i n g behaviour. For each experiment, prey items were i n t r o d u c e d i n approximately equal numbers i n t o four s e c t i o n s o f the tanks through funnels ( F i g . 10b). To reduce v a r i a b i l i t y i n l i g h t i n t e n s i t i e s , a l l experiments were performed near mid-day. F i s h were fed a t 5 min i n t e r v a l s f o r 1 h. While prey d i d s e t t l e out d u r i n g t h a t p e r i o d , some were always c i r c u l a t i n g at any given time and f r y continued to feed throughout the experiments. At the end of each experiment, f r y were removed from the stream tanks, body w a l l s s l i t and f r y preserved i n 10 percent f o r m a l i n . A f t e r most experiments tank water was s t r a i n e d through 130 um n i t e x n e t t i n g to gather uneaten prey items which were a l s o p r eserved i n 10 percent f o r m a l i n . - 27 -The only experiment not conducted a t Meadow Creek was performed i n an environmental c o n t r o l chamber a t U.B.C. (Vancouver, B.C.). Water temperatures of 13°C and 12 h day-lengths were maintained throughout this experiment.;. Water was s t r a i n e d through 130 um n i t e x n e t t i n g to remove any p o t e n t i a l food items. Other design d e t a i l s were i d e n t i c a l to Meadow Creek experiments. (b) F ry Types With one e x c e p t i o n , a l l experiments were performed on Gerrard stock f r y . The experiment conducted a t U.B.C. was performed on c l o s e l y r e l a t e d Duncan R i v e r stock t r o u t . Gerrard stock f r y were of fou r types: (1) young r i v e r  f r y - r e c e n t l y emerged rainbow d i p n e t t e d f r o n zone 1; (2) o l d e r r i v e r f r y - o l d e r ( l a r g e r ) rainbow f r y e l e c t r o f i s h e d from zones 2 or 3; (3) naive hatchery f r y - f r y r a i s e d i n i n c u b a t i o n boxes (eggs taken from t r o u t spawning a t Gerrard) and used immediately upon emergence (no f e e d i n g e x p e r i e n c e ) ; (4) o l d e r hatchery f r y - of same o r i g i n as naive hatchery f r y only r a i s e d e x c l u s i v e l y on hatchery food (no p r e v i o u s e x p e r i -ence w i t h n a t u r a l food t y p e s ) . Hatchery Duncan f r y were a l s o r a i s e d e x c l u s i v e l y on hatchery food. (c) Prey Types B l a c k f l y l a r v a e (Simulium spp) were ob t a i n e d from r i f f l e areas of the Lardeau R i v e r near the o u t l e t o f Trout Lake. - 28 -Large numbers were gathered by scraping rocks to which they were attached. The larvae were separated into d i f f e r e n t size categories by flushing them through a series of graded sized sieves (0.25 - 1.25 mm diameter mesh). Heptageniidae (ephemeropteran) nymphs were obtained c h i e f l y from Meadow Creek (Fig. 1). Using a spade, one person s t i r r e d the substrate immediately upstream from a second person holding a fine mesh (2.5 mm diameter mesh) pole seine. Invertebrates and debris captured by the net were l a t e r sorted manually i n the lab. Only the one family of nymphs was used to minimize v a r i a b i l i t y within t h i s prey category. Zooplankton used i n the experiments performed at Meadow Creek originated from Trout Lake. Using the d r i f t samplers described e a r l i e r (Section I I I . B. 1. ), organisms (largely zooplankton) were captured i n the Lardeau River immediately downstream from Trout Lake. Collections were taken just p r i o r to experiments to ensure that a large proportion of the plankton was a l i v e . Daphnia rosea and Ceriodaphnia sp used in the U.B.C. experiment were obtained from Loon Lake, U.B.C. Research Forest and the Library Pond, U.B.C. campus, respect-i v e l y . Invertebrates were measured as described e a r l i e r (Section II I . A. 3.). - 29 -IV.- TROUT REARING IN LARDEAU RIVER A. ; H a b i t a t P r e f e r e n c e s 1. Zone 1 Skin d i v i n g was used to determine r e c e n t l y emerged f r y d e n s i t i e s a t e i g h t s t a t i o n s d u r i n g summer. S t a t i o n s 1 and 2, and s t a t i o n s 3 and 4, were chosen to determine the s i g n i f i c a n c e of overhanging v e g e t a t i o n . Both s t a t i o n p a i r s were adjacent to each other, and very s i m i l a r except f o r the presence, or absence, of overhead s h e l t e r . Higher f r y d e n s i t i e s were ob-t a i n e d a t the s t a t i o n s w i t h overhanging cover: Over- Mean Mean Mean Range i n S t a t i o n hanging Water Depth F r y F r y Number Cover V e l o c i t y (cm) Dens i t y D e n s i t y (+ or -) (cm/s) (no/m2) (no/m2) 1 + <7.5 24 0.5 0.0 - 1.5 2 - <7.5 30 0.3 0.0 - 1.0 3 + <7.5 20 1.9 0.8 - 3.3 4 <7.5: 12 0.8 0.3 - 1.8 D e n s i t i e s a t s t a t i o n 3 were s i g n i f i c a n t l y g r e a t e r than a t s t a t i o n 4 (Table 1) . The c h i e f d i f f e r e n c e between s t a t i o n s 2 and 4 was water depth. D e n s i t i e s at the shallower s t a t i o n (4) were s i g n i f -i c a n t l y g r e a t e r than a t the deeper s t a t i o n (2) (Table 1). - 30 -S t a t i o n p a i r s 5 and 6, and 7 and 8 were s i m i l a r except f o r c u r r e n t v e l o c i t y : Over- Mean Mean Mean Range i n S t a t i o n hanging Water Depth F ry Fry Number Cover V e l o c i t y (cm) D e n s i t y D e n s i t y (+ or -) (cm/s) (no/m2) (no/m2) 5 6 7 8 <7. 5 67 <7.5 45 63 70 36 35 1.0 0.0 1.1 0.1 0.0 0.0 0.4 0.0 1. 8 0.0 1.6 0.3 D e n s i t i e s a t the slower c u r r e n t s t a t i o n p a i r s (5 and 7) were s i g n i f i c a n t l y g r e a t e r than a t the f a s t e r c u r r e n t s t a t i o n s (6 and 8) (Table 1). In summary, the r e s u l t s demonstrate the importance of areas with overhanging cover, shallow water and minimal cur-... r e n t to very young t r o u t . Table 1. T t e s t r e s u l t s of comparisons of f r y d e n s i t i e s ob-t a i n e d by s k i n d i v i n g i n zone 1. S t a t i o n s t t Compared c a l c df . 05 1 vs. 2 1.16 12 1.78 3 vs. 4 3.33 15 1.75 2 vs. 4 2.05 13 1.77 5 vs. 6 2.52 14 1.76 7 vs. 8 6.25 8 1.86 - 31 -2. Zones 2, 3, and 4 Underyearling trout habitat was studied i n zone 2 during summer by skin diving. Densities were obtained i n run and pool habitats (Table 2). Densities i n pools were s i g n i f i c a n t l y higher than i n runs (Table 3). Faster water v e l o c i t i e s i n runs apparently limited trout numbers. Trout were s i g n i f i c a n t -l y more abundant where surface water v e l o c i t i e s were less than 45 cm/s than where v e l o c i t i e s were faster (Table 3). Trout densities i n pools with overhanging cover were s i g n i f i c a n t l y higher than i n pools without. Densities were also signif-.. i c a n t l y greater i n areas where water depths averaged less than 4 0 cm compared to deeper areas. Densities were greater i n .. areas where mean bottom p a r t i c l e size was less than 40 cm than i n areas of larger p a r t i c l e size but differences were not s i g n i f i c a n t . Trout densities were also obtained from zones 2, 3, and 4 by e l e c t r o f i s h i n g . Densities are given for habitat types (Table 4) and by mean surface water v e l o c i t y and bottom p a r t i c l e size (Table 5). Small sample sizes and large var-i a b i l i t y are common i n the data i n Table 4. Therefore, i t i s not surprising that one way analyses of variance for each season and age class considering d i f f e r e n t habitats f a i l e d to r e j e c t the n u l l hypothesis that the sample means for the di f f e r e n t habitats came from the same population. S i m i l a r l y , results of t tests comparing densities of d i f f e r e n t p a r t i c l e size and v e l o c i t y regions were frequently not s i g n i f i c a n t - 32 -Tab.le 2. Mean underyearling trout d e n s i t i e s obtained by skin d i v i n g i n zone 2. Category d a n b S C Runs 0.17 46 0.35 Pools 0.60 11 0.67 V e l o c i t y < 45 cra/s 0.35 39 0.51 V e l o c i t y > 45 cm/s 0.02 18 0.07 P a r t i c l e s i z e <_ 20 cm 0.26 40 .0.41 P a r t i c l e s i z e > 20 cm 0.19. 17 0.50 Depth < 40 cm 0.46 25 0.56 Depth > 40 cm 0.09 32 0.26 Pools with overhanging cover 0.77 7 0.77 Pools without over-hanging cover 0.00 4 0.00 a 2 Mean Density (nos./m ). Number of times category sampled. Standard deviatxon of the mean. Table 3. T t e s t r e s u l t s of comparisons of underyearling trou t d e n s i t i e s obtained by skin d i v i n g i n zone 2. Comparison Being Made c a l c . df t.os Runs vs. pools 2.11 11 1.79 V e l o c i t y < 4 5 cm/s vs. > 45 cm/s . 3 . 9 4 41 1.68 P a r t i c l e s i z e < 20 cm vs. > 20 cm 0.55 55 1.67 Depth <_ 40 cm vs. > 40 cm 3.02 32 1.70 Pools with overhanging cover vs. pools without 1.96 9 1.83 Table 4. Mean seasonal densities obtained by el e c t r o f i s h i n g i n four major habitat types i n zones 2, 3, and 4. Season Age Class d a Runs b n s c d a R i f f l e s b n s c d a Log Jams b n s c d a Pools b n s c Summer 0+ 0.18 13 0.35 0.05 16 0.11 0.13 2 0.18 0. 12 5 0.08 F a l l 0 + 0. 31 15 0. 35 0.17 2 0. 24 0.18 3 0. 28 0.49 7 0. 54 Winter 0+ 0.13 15 0.16 0. 05 3 0. 08 0.00 3 0. 00 0.19 8 0.17 Spring 1+ 0. 04 42 0. 06 0. 04 20 0.14 0.05 15 0.10 0.11 18 0.16 Summer 1+ 0.02 13 0.04 0. 02 16 0. 03 0.06 2 0. 09 0. 00 5 0. 00 F a l l 1+ 0. 09 15 0.08 0.01 2 0. 08 0.07 3 0.09 0. 02 7 0.06 Winter 1+ 0.10 15 0.11 0. 01 3 0. 01 0.00 3 0. 00 0. 01 8 0.03 Spring 2 + 0.02 42 0.03 0.01 20 0. 03 0.03 15 0. 09 0. 01 18 0.02 'Mean density (nos./m ). 'Number of times habitat sampled. Standard deviation of the mean. - 34 -Table 5. Mean seasonal densities obtained by electro-f i s h i n g i n zones 2, 3, and 4 according to surface water v e l o c i t i e s and bottom p a r t i c l e a sxzes . Season Class C l a s s i f i c a t i o n d n S Summer 0+ Velocity < 45 ' cm/s 0. 14 26 0. 26 Summer 0+ Velocity > "45 cm/s 0. 02 8 0. 04 Summer 0 + P a r t i c l e size < 20 cm 0. 15 11 0. 36 Summer 0 + P a r t i c l e size > 20 cm 0. 09 23 0. 13 Summer 1+ Velocity < 45 cm/s 0. 02 26 0. 03 Summer 1+ Velocity > 45 cm/s 0. 02 8 0. 04 Summer 1* P a r t i c l e size < 20 cm 0. 02 11 0. 04 Summer 1+ P a r t i c l e size > 20 cm 0. 02 23 0. 03 F a l l 0+ Velocity < 45 cm/s 0. 41 18 0. 43 F a l l 0+ Velo c i t y > 45 cm/s 0. 17 6 0. 27 F a l l 0+ P a r t i c l e size < 20 cm 0. 44 7 0. 58 F a l l 0+ P a r t i c l e size > 20 cm 0. 32 17 0. 32 F a l l 1+ Velocity < 45 cm/s 0. 07 18 0. 08 F a l l 1+ Velocity- > 45 cm/s 0. 05 6 0. 09 F a l l 1+ P a r t i c l e size < 20 cm 0. 00 7 0. 00 F a l l 1+ P a r t i c l e size > 20 cm 0. 15 17 0. 25 Winter 0 + Velocity < 45 cm/s 0. 14 23 0. 16 Winter 0+ Velocity > 45 cm/s 0. 05 3 0. 08 Winter 0 + P a r t i c l e size < 20 cm 0. 20 5 0. 28 Winter 0 + P a r t i c l e size > 20 cm 0. 12 21 0. 12 Winter 1+ Velocity < 45 cm/s 0. 07 23 0. 10 Winter 1+ Velocity > 45 cm/s 0. 00 3 0. 00 Winter 1+ P a r t i c l e size < 20 cm 0. 01 5 0. 03 Winter 1+ P a r t i c l e size > 20 cm 0. 07 21 0. 10 Spring 1+ Velocity < 45 cm/s 0. 07 54 0. 13 Spring 1+ Velo c i t y > 45 cm/s 0. 02 26 0. 04 Spring 1+ P a r t i c l e size < 20 cm 0. 05 38 0. 11 Spring 1+ P a r t i c l e size > 20 cm 0. 06 43 0. 11 Spring 2 + Velocity < 45 cm/s 0. 02 53 0. 03 Spring 2 + Velocity > 45 cm/s 0. 01 27 0. 02 Spring 2+ P a r t i c l e size < 20 cm 0. 01 35 0. 02 Spring 2 + P a r t i c l e size > 20 cm 0. 02 45 0. 03 Data from log jam habitats not used i n ca l c u l a t i o n of densit-ies . 3D 2 Mean density (nos./m ). Number of times c l a s s i f i c a t i o n sampled. Standard deviation of the mean. - 35 -(Table 6 ) . Nevertheless, b i o l o g i c a l l y meaningful trends can s t i l l be observed. For in s t a n c e , water v e l o c i t y had a n o t i c e -able e f f e c t on h a b i t a t s e l e c t i o n by underyearling t r o u t . During summer, underyearling d e n s i t i e s were s i g n i f i c a n t l y higher i n areas where surface water v e l o c i t i e s were l e s s than 45 cm/s compared to f a s t e r current areas (Table 6 ). R i f f l e s were the l e a s t densely populated h a b i t a t during t h i s season (Table 4 ) . D e n s i t i e s were always highest i n slow cu r r e n t regions (Table 5) although d i f f e r e n c e s were only s t a t i s t i c a l l y s i g n i f i c a n t f o r s p r i n g (Table 6 ) . Pool h a b i t a t s , where water currents were slowest, had the highest d e n s i t i e s during f a l l , w i n t e r and s p r i n g (Table 4 ) . Bottom p a r t i c l e s i z e had l e s s e f f e c t on h a b i t a t s e l e c t i o n by underyearling t r o u t . While d e n s i t i e s were u s u a l l y g r e a t e s t i n regions of small p a r t i c l e s i z e (Table 5 ) , these d i f f e r e n c e s were not s t a t i s t i c a l l y s i g -n i f i c a n t . D e n s i t i e s of ol d e r t r o u t (Tables 4 and 5) were lower and l e s s meaningful than of younger t r o u t . Except during summer, y e a r l i n g rainbow were c h i e f l y captured i n regions where sur-face water v e l o c i t i e s were l e s s than 45 cm/s. These t r o u t were most abundant i n areas of l a r g e r bottom p a r t i c l e s i n f a l l , w i n t e r and s p r i n g (Table 5) and d i f f e r e n c e s were s t a t -i s t i c a l l y s i g n i f i c a n t i n f a l l and winter (Table 6 ) . In summary, areas w i t h overhanging cover, shallow depth and slow c u r r e n t were favoured by underyearlings during summer. Slow curren t areas continued to be important to underyearlings - 36 -Table 6. T test results of comparisons between densities obtained by e l e c t r o f i s h i n g i n zones 2, 3, and 4 according to d i f f e r i n g water v e l o c i t i e s and p a r t i c l e .sizes. Water v e l o c i t i e s compared were <_ 45 cm/s vs.;- > 45 cm/s and p a r t i c l e sizes, < 2 0 cm vs. >2 0 cm. Age Season Class Comparison calc. .:df t.05 Summer 0+ Ve l o c i t i e s 2. 28 28 1. 70 Summer 0+ P a r t i c l e sizes 0. 52 11 1. 79 Summer 1+ Ve l o c i t i e s 0. 41 32 1. 69 Summer 1+ P a r t i c l e sizes 0. 23 32 1. 69 F a l l 0+ V e l o c i t i e s 1. 29 22 1. 72 F a l l 0 + P a r t i c l e sizes 0. 52 8 1. 86 F a l l 1+ V e l o c i t i e s 0. 33 22 1. 72 F a l l 1+ P a r t i c l e sizes 1. 58 22 1. 72 Winter 0+ V e l o c i t i e s 1. 00 24 1. 71 Winter 0+ P a r t i c l e sizes 0. 61 4 2. 10 Winter 1+ V e l o c i t i e s 1. 24 24 1. 71 Winter 1+ P a r t i c l e sizes 2. 31 22 1. 72 Spring 1+ V e l o c i t i e s 2. 68 71 1. 66 Spring 1+ P a r t i c l e sizes 0. 49 79 1. 66 Spring 2 + Ve l o c i t i e s 1. 31 69 1. 66 Spring 2+ P a r t i c l e sizes 1. 96 77 1. 66 - 37 -throughout the year with highest densities found i n pool hab-i t a t s during f a l l , winter and spring. Older 11+ and 2+) trout were also most abundant i n areas of slow v e l o c i t y . There appeared to be a p a r t i a l segregation of age classes according to bottom p a r t i c l e size with older trout most frequent i n areas of large p a r t i c l e s and younger trout more common i n areas of small p a r t i c l e s . B. Migratory Behaviour Most fry emigrate from zone 1 shortly a f t e r emerging. Only three fry were seen during a skin diving survey along both r i v e r banks of zone 1 on 21 August 1974. Two li n e s of evidence are suggestive of a spring emigra-tion from zones 2, 3, and 4. F i r s t , mean density estimates indicate a d e f i n i t e reduction between f a l l and summer (Fig. 11). In Figure 11 mean seasonal densities are the average of density estimates i n runs and pools since these were the most numerous habitat types. Skin diving density estimates were used for summer 0+ f i s h since e l e c t r o f i s h i n g e f f i c i e n c i e s on newly emerged fry are low and variable (Solomon and Templeton, 1976). Winter density estimates were l i k e l y low because, as explained e a r l i e r , f i s h tended to remain hidden i n the sub-strate a f t e r being electrofished. Two factors l i k e l y contributed to the reduction i n f i s h density between f a l l and summer (Fig. 11). The f i r s t was f r y mortality and the second migration out of the Lardeau system. - 37a -F i g . 11. Mean s e a s o n a l d e n s i t y e s t i m a t e s o f j u v e n i l e t r o u t i n t h e L a r d e a u R i v e r . A r e a s s a m p l e d 2 (m ) i n d i c a t e d by numbers in b r a c k e t s . F i g . 12. Mean s e a s o n a l d e n s i t y e s t i m a t e s o f j u v e n i l e t r o u t i n t h e u p p e r (i) and l o w e r (+) h a l v e s 2 o f t h e L a r d e a u R i v e r . A r e a s s a m p l e d (m ) i n d i c a t e d by numbers i n b r a c k e t s . - 38 -0.4 0.3 JZ 0.2 to h (H40) 0.1 (280) (295) (1320) (400) Season SUMMER FALL WINTER SPRING SUMMER .Age Class 0+ 0+ 0+ 1+ 1 + cu Q. 0.5 0.4 0.3 JC i i 0.2 0.1 (26%35) (130) (150) (160) (135) (565) (755) H Season SUMMER FALL WINTER SPRING Age Class 0+ 0+ 0+ l+ - 39 -The second l i n e of evidence suggesting a spring migration re s u l t s from a comparison of f i s h densities i n the upper and lower halves of the Lardeau River. Numbers were not high enough to consider each r i v e r zone separately. Averages of densities i n pools and runs obtained by e l e c t r o f i s h i n g were used (Fig. 12). Summer densities were similar i n both regions of the r i v e r , perhaps because fry were s t i l l adjusting t h e i r longitudinal d i s t r i b u t i o n i n the r i v e r . Underyearling trout were more abundant i n the upper half of the r i v e r during f a l l and winter but yearlings during spring were not (Fig. 12). This i s suggestive of a general downstream migration being i n progress during spring. C. Length and Weight Relationships During summer, length frequencies of f r y and older juv-eniles were d i s t i n c t (Fig. 13). Fry ranged between 26.0 -62.8 mm with an average of 40.2 mm (Table 7). Fish larger than this range were almost e n t i r e l y 1+. Of scales examined from 17 juveniles ranging from 80 - 161 mm, 16 were from 1+ f i s h and one from a two-year old. The length frequency method was s t i l l useful i n distinguishing age classes i n f a l l (Fig. 13). One hundred and forty f r y ranged from 41.2 - 92.4 mm with a mean length of 62.0 mm (Table 7). Larger f i s h were once again shown to be almost exclusively 1+. By winter, the length frequency method was no longer always successful i n separating 0+ and older f i s h (Fig. 13). Scales were examined -39a -Fig. 13. Seasonal length frequencies of rainbow trout captured by e l e c t r o f i s h i n g i n zones 2, 3, and 4 (n = number of f i s h ) . - 40 -24 -| 21 • CY 18 -Z UJ no 15 -Ul OC 12 • u. t-z 9 -Ul o or UJ 6 -0. 3 -0 L S U M M E R ( n - 2 0 2 ) 15 3 0 4 5 6 0 75 9 0 105 120 13J 150 165 180 F O R K L E N G T H (mm> 2 2 -j 2 0 -18 ->• o z 16 -UJ 3 14 -o UJ <c 12 -ti. 10 -t-z 8 -UJ o cc UJ 6 -0. 4 -2 -0 F A L L < n « 1 5 9 ) "hrrrfpfiril 15 3 0 4 5 6 0 7 5 9 0 105 120 135 150 165 180 F O R K L E N G T H ( m m ) 13 • 1 2 -II -•:i 8 7 • 6-ii 2 1 W I N T E R (n = 1 4 6 ) ir —i—r 15 3 0 4 5 6 0 75 9 0 105 120 135 150 165 180 F O R K L E N G T H ( m m ) 14 13 12 11 i o H 9 8 II 5 4 2 1 S P R I N G ( n - 161 ) 1  | " h 0 1 r - 15 3 0 4 5 6 0 75 9 0 105 120 135 150 165 180 F O R K L E N G T H ( m m ) - 41 -Table 7. Mean lengths and ranges of juvenile trout cap-tured from the upper and lower halves of the Lardeau River by e l e c t r o f i s h i n g . Mean Length Range Fish Population n (mm) (mm) Total Summer 0+ 261 40. 2 26 . 0 - 62. 8 Summer 0+ upper half 97 36. 7 26. 0 - 56.3 Summer 0+ lower half 164 42. 3 28. 2 - 62. 8 Total F a l l 0+ 140 62. 0 41. 2 - 92.4 F a l l 0+ upper half 107 63. 6 42. 2 - 92.4 F a l l 0+ lower half 33 56. 8 41. 2 - 77.3 Total Winter 0+ 112 70. 0 40. 9 - 100.5 Winter 0+ upper half 48 76. 2 45. 1 - 100.5 Winter 0+ lower half 64 65. 4 40. 9 - 98.9 Total Spring 1+ 142 70. 0 44. 3 - 109. 3 Spring 1+ upper half 51 71. 3 44. 3 - 102.0 Spring 1+ lower half 91 69. 3 49. 0 - 109.3 Total Summer 1+ 53 102. 4 75. 5 - 160. 8 Summer 1+ upper half 12 124. 1 75. 6 - 160. 8 Summer 1+ lower half 41 96. 0 75. 5 - 132. 0 Total f a l l 1+ 19 132. 3 102. 2 - 168. 0 F a l l 1+ upper half 10 136. 9 102 . 2 - 161.3 F a l l 1+ lower half 9 127. 1 105. 2 - 168.0 Total Winter 1+ 34 132. 1 101. 9 - 175.0 Winter 1+ upper half 10 136. 7 101. 9 - 175.0 Winter 1+ lower half 24 130. 2 103. 7 - 174. 0 Total Spring 2+ 19 135. 5 111. 3 - 171. 6 Spring 2+ upper half 11 139. 3 111. 3 - 171.6 Spring 2+ lower half 8 130. 3 111. 4 - 145. 0 - 42 -from 21 f i s h ranging between 98 - 157 mm. Three f i s h were interpreted to be i n t h e i r f i r s t winter, 15 i n t h e i r second and three i n t h e i r t h i r d . It was concluded that most f i s h less than 100 mm were i n t h e i r f i r s t winter, while most greater than 100 mm were i n t h e i r second. During spring, length frequencies of d i f f e r e n t age classes again overlapped (Fig. 13). Of scales examined from f i s h during spring, a l l those from f i s h less than 110 mm indicated the completion of only one annulus, while most of those from larger f i s h had completed two. It was therefore concluded that most f i s h less than 110 mm had completed one winter while most larger f i s h had completed two. As would be expected, most growth took place between spring and f a l l . Yearlings grew an average of 12.5 mm per month over this period; t h e i r instantaneous growth rates were 0.0143 and 0.0043 per day (weight and length respective-ly) -The logged length-weight regression for a l l f i s h (Fig. 14) reveals two growth stanzas, one above and one below 4 0 mm. Length-weight regressions were performed for each age class by season (Table 8). Since the slope of the f i t t e d l i n e for each regression (b) was always close to three, growth was 3 assumed isometric. Condition factors (K = W/L ) were computed for each f i s h , seasonal averages for the d i f f e r e n t age classes being included i n Table 8. Some caution must be exercised i n the interpretation of these data since summer caught f r y had - 43 -Table 8. Logged length-weight functional regression formulae and condition factors (K) for trout captured by e l e c t r o f i s h i n g . Fish Population Y Slope Intercept (b) n K Summer 0+ - 5.85 3.52 181 0. 91 F a l l 0+ - 5.21 3.14 121 1.11 Winter 0+ - 5.54 3.32 76 1.10 Spring 1+ - 4.73 2.89 54 1.17 Summer 1+ - 5.28 3.17 37 1.16 F a l l 1+ - 4.92 3. 02 10 1. 32 Winter 1+ - 4.77 2.93 21 1.20 Spring 2+ - 5.68 3. 35 10 1.14 A l l f i s h < 40 mm - 6.42 3.89 122 0. 87 A l l f i s h > 4 0 mm - 5. 26 3.17 388 1.12 Table 9. T test results of comparisons of condition factors of trout captured by e l e c t r o f i s h i n g . Populations Being Compared calc. df:-. .05 Summer 0+ vs. f a l l 0+ 13.43 300 1.65 F a l l 0+ vs. winter 0+ 0.54 195 1.65 Winter 0+ vs. spring 1+ 3.28 128 1.66 Summer 1+ vs. f a l l 1+ 3.85 45 1.68 F a l l 1+ vs. winter 1+ 2.54 29 1.70 Winter 1+ vs. spring 2+ 1.18 29 1.70 - 43a -Fig. 14. Logged length-weight r e l a t i o n s h i p of rainbow trout captured by e l e c t r o f i s h i n g i n zones 2, 3, and 4. - 44 -a s i g n i f i c a n t l y d i f f e r e n t length-weight r e l a t i o n s h i p than other f i s h . 50.0 r °> io.o4-f x 5 2 ' 0 . : 0.14-20 FORK LENGTH (mm) S i g n i f i c a n t increases i n condition occurred from summer to f a l l for both age classes, and from winter to spring for the youngest age class (Table 9 ) . Condition factors for yearlings decreased s i g n i f i c a n t l y from f a l l to winter. Length-weight and length frequency data were examined from trout c o l l e c t e d along the r i v e r ' s length. Length-weight data did not vary along the r i v e r . However, except for under-yearlings during summer, rainbow trout from the upper half of the r i v e r were always longer than trout from the lower half (Table 7). These differences were s t a t i s t i c a l l y s i g n i f i c a n t - 45 -for f a l l and winter f r y , and summer yearlings (Table 10). Table 10. T test results of comparisons of lengths of trout captured by e l e c t r o f i s h i n g i n the upper and lower halves of the Lardeau River. Populations Being Compared ca l c . df ...0.5. Summer 0+ upper vs. lower 5. 99 259 1. 65 F a l l 0+ upper vs. lower 3. 38 138 1. 66 Winter 0+ upper vs. lower 3. 90 110 1. 66 Spring 1+ upper vs. lower 0. 85 140 1. 66 Summer 1+ upper vs. lower 3. 35 13 1. 78 F a l l 1+ upper vs. lower 1. 18 17 1. 74 Winter 1+ upper vs. lower 0. 74 12 1. 78 Spring 2+ upper vs. lower 1. 02 17 1. 74 - 46 -V. FEEDING ECOLOGY A. D r i f t i n g Versus Benthic Prey The following n u l l hypothesis was tested: "There i s no difference between d r i f t i n g organisms and benthic organisms as prey to young rainbow trout." Observations were conducted on two groups of f r y feeding i n the Lardeau River: x Size Range Group n Location (mm) (mm) Small f r y 24 Zone 1 28 25 - 35 Large fry 26 Zone 2 54 45 - 65 D r i f t i n g organisms were attacked much more frequently than benthic organisms (Fig. 15), thereby r e j e c t i n g the above hypothesis. Strike patterns for both f i s h groups d i f f e r e d s i g n i f i c a n t l y from what would be expected i f feeding s t r i k e s had been d i s t r i b u t e d equally among the four water column regions (Table 11). Both groups of f ry fed most frequently from that portion of the water column between the surface and thei r station. Feeding attack d i s t r i b u t i o n s d i f f e r e d s i g n i f -i c a n t l y between fry groups (.Table 11) . While the second most favoured feeding zone of small f r y was the surface, that for large f ry was between the i r station and the r i v e r bottom. - 46a -Fig. 15. Mean number of feeding s t r i k e s i n four regions of the water column. - 47 -S M A L L F R Y L A R G E F R Y w 12-t-D Z > l i . tr w o. w ui 10H 8H LL o LU m 5 z z < LU BOTTOM TO STATION STATION TO SURFACE BOT TOM TO STATION STATION TO SURFACE - 48 -Small fry from zone 1 had a s i g n i f i c a n t l y higher prey attack rate than large fry from zone 2 tt , = 5.04 > t n = c a l c . .U D 1.65). Because of the size difference between fry groups, .., small fry were presumably younger and had less experience feeding than large f r y . It i s possible that small fry con-sumed smaller and less energetically p r o f i t a b l e food items than large fry and hence one might expect small fry to have a higher attack rate. However, i t also appeared that small fry were less selective i n t h e i r feeding behaviour. Although i t was not possible to obtain quantitative r e s u l t s , observa-tions suggested that small fry were s t r i k i n g at, and r e j e c t i n g , non-food items more frequently than large and presumably more experienced f r y . Table 11. Chi-square r e s u l t s of comparisons between feeding s t r i k e d i s t r i b u t i o n s of two groups of trout f r y . 2 2 X X Comparison calc. df .05 Small f r y feeding d i s t r i b u t i o n vs. expected d i s t r i b u t i o n 446.9 3 7.8 Large fry feeding d i s t r i b u t i o n vs. expected d i s t r i b u t i o n 292.4 3 7.8 Small fry feeding d i s t r i b u t i o n vs. large fry feeding d i s t r i b u t i o n 80.8 3 7.8 - 49 -B. V e r t i c a l S t r a t i f i c a t i o n of D r i f t In simultaneous surface and benthic d r i f t samples from zone 1 zooplankton were always numerically dominant, followed by immature aquatic insects and t e r r e s t r i a l insects (Table 12). No consistent differences between pairs of surface and benthic d r i f t samples could be seen. Therefore, i t was concluded that differences between surface and benthic d r i f t samples were more l i k e l y the r e s u l t of sampling error than representative of v e r t i c a l s t r a t i f i c a t i o n of d r i f t . C. Seasonal A v a i l a b i l i t y and U t i l i z a t i o n of D r i f t 1. Summer Zooplankton were the most abundant mid-day d r i f t i n g prey type (Fig. 16). Surprisingly, t h e i r densities were lowest i n zone 1, the station farthest upstream. This i s p a r t l y explain-ed by d i e l patterns of zooplankton abundance i n zone 1. Zoo-plankton prey species during summer exhibited a marked d i e l p e r i o d i c i t y i n d r i f t (Fig. 18). Densities during mid-day were lower than at night. This was probably the consequence of v e r t i c a l zooplankton migration i n Trout Lake. V e r t i c a l migra-tion brings more zooplankters at night than during the day into that portion of the lake where the p r o b a b i l i t y of being swept away by the outlet r i v e r i s highest. Mid-day d r i f t sampling i n the lower three r i v e r zones captures plankton o r i g i n a t i n g from Trout Lake at times other than mid-day when densities are higher. Highest plankton densities were found Table 12. Mean densities (nos./m ) of three potential prey types from surface and benthic d r i f t samples in zone 1. Station and Sample Prey 0300 0700 1100 1500. 1900 . 2300 Date Type Type hrs hrs hrs hrs hrs hrs Surface 1 37.03 34.30 74.02 31.61 6.63 8.60 2 0.75 0.34 0.62 0.86 0.37 0.52 Northeast D r i f t 3 0.11 0.31 0.06 0.08 0. 09 0.07 Benthic 1 37.63 39.67 56.54 36.60 11.90 20.98 2 0.72 0.26 0.07 0.67 0.35 0.98 D r i f t 3 0.02 0.00 0.03 0.04 0. 01 0.03 Surface 1 5.62 10.83 3.70 1.67 4.78 4.91 2 0.26 0.26 0.68 0.02 0.20 0.74 Southwest D r i f t 3 0.00 0.00 0.0.4 0.03 0.03 0. 04 Benthic 1 17.77 26.93 2.27 1.91 2.76 4.83 2 0.64 0.30 0.55 0.56 0.37 0.65 D r i f t 3 0.00 0.00 0.08 0.00 0.06 0.00 1 = zooplankton. 2 = immature aquatic insects. 3 = t e r r e s t r i a l insects. - 50a -Fig. 16. Summer d r i f t densities of three major prey types i n four r i v e r zones. Means and ranges given. Zone 1 n = 12 samples analyzed, zone 2 n = 2, zone 3 n = 4, zone 4 n = 2. Fig. 17. Percent occurrence of six food types i n f r y stomachs from each of four r i v e r zones during summer. Zone 1 n = 80 stomachs, zone 2 n = 254, zone 3 n = 39, zone 4 n = 40. - 51 -620 470 320 E O 170 to 20 CL CD E Z J 10 8 6 4 2 II til ft River Zone 1 2 3 4 Prey Type ZOOPLANKTON m 1 1 I5! A m. IMMATURE AQUATIC INSECTS 1 2 3 4 TERRESTRIAL INSECTS o c <u l_ r> o CJ O c CU o cu 0_ 80 70 60 50 -| 40 30 20 10-I JL LJ3_ JQ-CLXL River Zone 12 3 4 :r2 3 4 i n 4 l 2 3 4 l 2 ^ Prey Type Z O O P L A N I < T O N INSECT CHIRO. DIPT. T E R R E S T N Y M PHS L A R V A E PUPAE INSECTS ILU_a_n_ 12 3 4 MISC. - 52 -i n zone 4 (Fig. 16). During summer, water leve l s are s u f f i c -i e n t l y high, and slack water areas numerous enough, to allow some natural plankton production to occur i n the side channels and backwaters of t h i s r i v e r region. Zooplankton were the most frequently consumed food item from the upper two r i v e r regions, chironomid larvae from zone 3 and dipteran pupae and t e r r e s t r i a l insects from zone 4 (Fig. 17) . 2. F a l l D r i f t densities of prey types were generally highest, further upstream (Fig. 19). Trout were only captured from the lower three r i v e r zones.and hence feeding patterns can only be compared for these. Immature aquatic insects c o n s t i -tuted the majority of food types consumed but d i s t i n c t s p a t i a l feeding patterns were lacking (Fig. 20). The consumption of kokanee eggs i s probably important to the trout population since these eggs presumably have a high energetic content. Underyearlings and older trout u t i l i z e d kokanee eggs. Of 295 food items found i n the stomachs of 10 f a l l caught yearlings, 199 or 6 7 percent were kokanee eggs. 3. Winter Again trout were only captured from the lower three r i v e r zones. Immature aquatic insects constituted the majority of d r i f t i n g prey items from these r i v e r zones and accounted for - 52a -F i g . 18. Zooplankton prey d e n s i t i e s a t two l o c a t i o n s i n zone 1 on 8 August 197 4. Means and ranges of r e p l i c a t e samples given. - 53 -to E o CD CL tn (D JQ E 700 600 c 500 o -•— D 400 55 -•— CO o 300 <Dsz 200 o 100 Jl A 0300 0700 1100 1500 1900 2300 1400 1200 § 1000 55 800 S 600 t 4 0 0 o CO 200 0300 0700 1100 1500 T i m e (hours) 1900 2300 - 53a -F i g . 1 9 . F a l l d r i f t d e n s i t i e s o f t h r e e m a j o r p r e y t y p e s i n f o u r r i v e r z o n e s . M e a n s a n d r a n g e s g i v e n . Z o n e 1 n = 2 s a m p l e s a n a l y z e d , z o n e 2 n = 2 , z o n e 3 n = 4 , z o n e 4 n = 2 . F i g . 2 0 . P e r c e n t o c c u r r e n c e o f s e v e n f o o d t y p e s i n e i g h t f r y s t o m a c h s f r o m e a c h o f t h r e e r i v e r z o n e s d u r i n g f a l l . - 54 -to E O CL CD JQ E 3 45 40 35 30 25 15 <P 12 9 River Zone 1 2 3 4 Prey Type ZOOPLANKTON M i IMMATURE AQUATIC INSECTS _ f i ra r-i_ 1 2 3 4 TERRESTRIAL INSECTS c u o c CD i — L. Z3 O o O c CD o 1_ c u 801 70 60 50 40 30 20 10 1 1 I River Zone 234 234 234 234 234 234 234 Prev Tvoe I N S E C T  r r y 1 N Y M P H S CHIR0. SIMULIUM TRICH0P. DIPT. LARVAE LARVAE LARVAE PUPAE TERREST. K0KANEE INSECTS EGGS a l l prey consumed (Figs. 21. and 22). T r i c h o p t e r a n l a r v a e were most h e a v i l y u t i l i z e d f u r t h e r upstream and chironomid l a r v a e , f u r t h e r downstream. 4. Spr i n g Trout were again absent from zone 1. Immature a q u a t i c i n s e c t s were the predominant p o t e n t i a l prey type from the '. lower three zones ( F i g . 23). I n s e c t nymphs and t r i c h o p t e r a n l a r v a e made up the m a j o r i t y of food items and kokanee f r y were consumed by some f i s h ( F i g . 24). Kokanee f r y were a l s o of importance to o l d e r f i s h s i n c e two o f nine 2+ t r o u t had fed upon kokanee. D. Rate of Food Passage Estimates of r e l a t i v e r a t e s o f food passage of d i f f e r e n t food types were crude s i n c e d i f f e r e n t f r y had consumed d i f f e r -ent food p r i o r to the experiment. R e s u l t s d i d show t h a t food passage was v i r t u a l l y completed by 32 h s i n c e no i d e n t i f i a b l e organisms were found a f t e r t h i s p o i n t (Table 13). Zooplankton were d i g e s t e d q u i c k e s t , f o l l o w e d by a q u a t i c i n s e c t l a r v a e and t e r r e s t r i a l i n s e c t s . On the b a s i s o f these r e s u l t s i t was decided t h a t f o r f u t u r e experiments u s i n g c l o s e d system stream tanks, a p e r i o d of 40 h would be s u f f i c i e n t to ensure a l l p r e v i o u s l y consumed food had passed through the d i g e s t i v e system. - 55a -Fig. 21. Winter d r i f t densities of three major prey-types i n four r i v e r zones. Means and ranges given. Four samples analyzed per zone. Fig. 22. Percent occurrence of f i v e food types i n eight f r y stomachs from each of three r i v e r zones during winter. - 56 -24 to 21 E O 18 i ~ a> 15 Cl-io 12 X I e 9 Z3 6 River Zone 1 2 3 4 Prey Type ZOOPLANKTON A 2 3 4 IMMATURE AQUATIC INSECTS I 3 4 TERRESTRIAL INSECTS 70 h CD g 60 ^ 50 O 4 0 § 30 o aj 20 CL ioh River Zone Prey Type 2 3 4 INSECT NYMPHS JLtL 2 3 4 CHIRO. LARVAE 2 3 4 SIMULIUM LARVAE 2 3 4 TRICHOP. LARVAE 2 3 4 MISC. - 56a -F i g . 23. S p r i n g d r i f t d e n s i t i e s of three major prey-types i n f o u r r i v e r zones. Means and ranges given. Zone 1 n = 2 samples analyzed, zone 2 n = 4, zone 3 n = 2, zone 4 n = 2. F i g . 24. Percent occurrence of seven food types i n e i g h t y e a r l i n g stomachs from each of three r i v e r zones d u r i n g s p r i n g . - 57 -to E O CD Q. CU XI E 3 10 9 8 7 6 5 4 3 2 River Zone 1 2 3 4 Prey Type ZOOPLANKTON 2 3 4 IMMATURE AQUATIC INSECTS 1 2 3 4 TERRESTRIAL INSECTS cu o c CD 60 50 40 3 O o O 30 c CO o V -cu 0_ 20 10 River Zone Prey Type JL JL 2 3 4 2 3 4 2 3 4 2 3 4 2 3 4 2 3 4 2 3 4 INSECT CHIR0. SIMUL/UMJR\ZH0P. DIPT. TERR. KOKANEE NYMPHS LARVAE LARVAE LARVAE PUPAE INSECTS FRY - 58 -Table 13. Mean numbers of three food types per f i s h stomach from rate of food passage experiment. Aquatic Time Insect T e r r e s t r i a l (h) Zooplankton Larvae Insects 0 22.5 2.6 3.4 4 11. 5 0.9 7.1 8 3.1 0.6 3.0 12 0.0 0.8 1.9 16 0.0 0.4 0.5 20 0.0 0.0 0.3 24 0.0 0.0 0.3 28 0.0 0.0 0.2 32 0.0 0.0 0.0 36 0.0 0.0 0.0 E. Fish Size - Prey Size Relationships The following n u l l hypothesis was tested: "When exposed to similar prey populations, d i f f e r e n t sized f r y w i l l consume similar sized prey." 1. F i e l d Evidence (a) Zone 1 Information pertaining to the above hypothesis i s avail-able from concurrent d r i f t and f ry sampling i n zone 1 CFigs. 25 and 26). Since the format of these figures i s unusual, - 59 -they are e x p l a i n e d . The o r d i n a t e axes are l o g a r i t h m i c and v a l u e s f o r prey types a d d i t i v e . As an example, a t the n o r t h -e a s t s t a t i o n , on J u l y 26 a t 0300 hours, approximately 9 8 percent of d r i f t i n g prey types were zooplankton, 1.1 p e r c e n t immature a q u a t i c i n s e c t s and 0.17 percent t e r r e s t r i a l i n s e c t s ( F i g . 25). For the J u l y d r i f t r e s u l t s , means of r e p l i c a t e p a i r s of b e n t h i c and s u r f a c e d r i f t samples were averaged f o r each time p e r i o d . For the August d r i f t r e s u l t s , means of r e p l i c a t e p a i r s of s u r f a c e d r i f t r e s u l t s o n l y were averaged f o r each time p e r i o d . Zooplankton, the s m a l l e s t of the t h r e e p o t e n t i a l food types, were a l s o the most abundant, w h i l e t e r r e s t r i a l i n s e c t s were g e n e r a l l y the l e a s t frequent ( F i g . 25). Fry stomach content and d r i f t sample r e s u l t s from the n o r t h e a s t s t a t i o n on J u l y 26 were very s i m i l a r . For both, zooplankton were always most numerous f o l l o w e d by immature a q u a t i c i n s e c t s . T e r r e s t r i a l i n s e c t s were r e l a t i v e l y r a r e . At the same l o c a t i o n on August 8, zooplankters were n u m e r i c a l l y the most important food type 50 percent o f the times, being r e p l a c e d by immature a q u a t i c and t e r r e s t r i a l i n s e c t s a t other times. T h i s p a r t i a l s h i f t i n prey may have been the r e s u l t o f i n c r e a s e d f i s h s i z e (Table 14). Those f r y captured a t the n o r t h e a s t s t a t i o n on August 8 were s i g n i f i c a n t l y l a r g e r than those f r y captured there 13 days e a r l i e r (Table 15). Fry captured from the southwest s t a t i o n on J u l y 26 u t i l -i z e d zooplankton h e a v i l y d u r i n g one time p e r i o d o n l y ( F i g . 26). - 59a -Fig. 25. Percent occurrence d r i f t samples from periods i n zone 1. of three prey types i n two stations over two 24 h - 60 -N O R T H E A S T S T A T I O N JULY 2 6 100-i N O R T H E A S T S T A T I O N A U G U S T 8 100: LU O z UJ cc cc o o o z UJ o cc LU a 10 • i.o 4 0300 0700 1100 1500 1900 2300 TIME (hours) S O U T H W E S T STATION J U L Y 2 6 0300 07C0 1100 1500 1900 2300 TIME (hours) S O U T H W E S T S T A T I O N A U G U S T 8 0300 0700 1100 1500 1900 2300 TIME (hours) TIME (hours) Z O O P L A N K T O N I M M A T U R E Q A Q U A T I C I N S E C T S T E R R E S T R I A L I N S E C T S - 60a -Fig. 26. Percent occurrence of three prey types i n f ry stomachs from two stations over two 24 h periods i n zone 1. Number of stomachs analyzed indicated by numbers i n brackets. - "61 -100: LU o z UJ cc DC D O O o H Z LU o CC LU 0. 10H N O R T H E A S T STATION J U L Y 26 da) . . iis! M , . x (is2 N O R T H E A S T STAT ION A U G U S T 8 0300 0700 1100 1500 TIME (hours) 1900 2300 S O U T H W E S T STATION J U L Y 26 03) Jii, (6) J§i (12) 0300 0700 1500 1900 TIME (hoursj Z O O P L A N K T O N 0300 0700 1100 1500 1900 2300 TIME (hours) S O U T H W E S T S T A T I O N A U G U S T 8 M fo) (10) 0300 0700 1900 2300 TIME (hours) •I M M A T U R E n m - r r-r,r,r-„T„ A O i . A x i r P/^ T E R R E S T R I A L A Q U A T I C I N S E C T S I N S E C T S - 62 -Table 14. Length frequency and range data of f r y dip^-netted in zone 1 during summer. Mean Size Size Range Location Date . n. . . (mm) (mm) Northeast station July 26 75 30. 9 27.2 - 36. 9 Northeast station Aug 8 65 31.6 27.7 - 41. 7 Southwest station July 26 43 34.2 27.8 - 49. 0 Southwest station Aug. 8 35 35. 5 27.4 - 48. 9 Table 15. T tes t results of comparisons of lengths of fry dipnetted i n zone 1 during summer. Populations being compared calc. df .05 Northeast July 26 vs. southwest July 26 4.96 116 1.66 Northeast July '26 vs. northeast August 8 1.94 139 1.66 Northeast August 8 vs. southwest August 8 4.33 100 1.67 Southwest July 26 vs. southwest August 8 0.97 77 1.67 Southwest July 26 vs. northeast August 8 3.29 107 1.66 Northeast July 26 vs. southwest August 8 6.11 109 1.66 - 6 3 -A t a l l o t h e r t i m e s t h e y f e d p r i m a r i l y o n t h e s e c o n d m o s t n u m -e r o u s p r e y t y p e . F r y c a p t u r e d f r o m t h i s s i t e o n A u g u s t 8 n e v e r c o n s u m e d z o o p l a n k t o n b u t a l w a y s f e d h e a v i e s t o n t h e n e x t m o s t a b u n d a n t f o o d s o u r c e . T h i s a p p a r e n t a v o i d a n c e o f z o o -p l a n k t o n a s a f o o d s o u r c e w a s a g a i n l i k e l y a c o n s e q u e n c e o f i n c r e a s e d f i s h s i z e . S o u t h w e s t f r y w e r e a l w a y s s i g n i f i c a n t l y l a r g e r t h a n n o r t h e a s t f r y ( T a b l e s 1 4 a n d 1 5 ) . The d a t a d o n o t s u p p o r t t h e h y p o t h e s i s . A l l g r o u p s o f f r y w e r e e x p o s e d t o s i m i l a r p r e y p o p u l a t i o n s , z o o p l a n k t o n b e i n g t h e m o s t a b u n d a n t p r e y t y p e i n a l l c a s e s . T h o s e g r o u p s o f f r y f e e d i n g o n z o o p l a n k t e r s w e r e s m a l l e r t h a n t h o s e f r y f e e d i n g o n n o n - z o o p l a n k t e r s . I t i s p o s s i b l e , h o w e v e r , t h a t f a c t o r s o t h e r t h a n f i s h s i z e may h a v e b e e n i m p o r t a n t i n c a u s -i n g t h e o b s e r v e d f e e d i n g s h i f t s . D a t a f r o m t h e n o r t h e a s t s t a t i o n w e r e e x a m i n e d i n m o r e d e t a i l t o d e t e r m i n e w h e t h e r f r y s e l e c t i v e l y f e d o n l a r g e r z o o p l a n k t e r s . E l e c t i v i t y c o e f f i c i e n t s " ' " ( I v l e v , 1 9 6 1 ) w e r e c o m p u t e d f o r t h e f o u r m a j o r z o o p l a n k t o n t y p e s ( T a b l e 1 6 ) a v a i l a b l e t o f r y . The p r o p o r t i o n o f C y c l o p s a n d B o s m i n a i n f i s h s t o m a c h s was l e s s t h a n t h e i r p r o p o r t i o n i n t h e d r i f t (E<0) w h i l e t h e p r o p o r t i o n o f D a p h n i a a n d c a l a n o i d c o p e p o d s was g r e a t e r i n f i s h s t o m a c h s t h a n d r i f t ( E > 0 ) . P r e y s i z e ( T a b l e 1 6 ) o f f e r s a n e x p l a n a t i o n f o r t h e l a c k o f p r e d a t i o n .. 1. E = R .-. P 1 1 w h e r e R . = r e l a t i v e c o n t e n t i n t h e d i e t a n d R 1 + P P n = r e l a t i v e c o n t e n t i n t h e e n v i r o n m e n t - 64 -Table 16. Mean e l e c t i v i t i e s (xE) and sizes of zooplankton from the northeast station i n zone 1. Zooplankter xE E Range x Length Range (mm) (mm) Cyclops 3 -0. . 83 -1. . 00-- -0 ;;47 . 0. 44 0. ,42 -- 0. , 45 Bosmina3, -0. ,88 -1. .00 - -0 .37 0. .21 0. .20 -- 0. , 22 Daphnia 3 0. . 89 0. . 84 - 0. 96 0. .42 0. ,34 -- 0. ,53 Calanoids 0. .59 -0. . 05 - o. 94 0. , 85 0. .64 -- 1. ,18 Cyclops -0. . 88 -1. , 00 - -0 . 68 0. , 45 0. ,36 -- 0. , 48 Bosmina^5 -0. .45 -0. , 72 - -0 . 02 0. .29 0. .22 -- 0. .34 Daphnia^ 0. , 63 0. , 07 - 0. 83 0. .48 0. ,34 -- 0. , 67 Calanoids* 3 0. ,86 0. , 37 - 0. 99 0. .78 0. ,67 -- 0. , 90 326 July, ^8 August. c _ . . . Mean of six time periods. ^ n = 25 i n each case. - 65 -on s m a l l Bosmina and the s e l e c t i v i t y f o r l a r g e c a l a n o i d copepods but does not e x p l a i n the p r e f e r e n c e f o r Daphnia over Cyclops. (b) Zones 2, 3, and 4 Measurements were made of food items i n g e s t e d by e i g h t f r y from each of zones 2, 3, and 4 d u r i n g each of the fou r seasons. As w e l l , subsamples of organisms from d r i f t samples (excl u d i n g zooplankton) from each of zones 2, 3, and 4 were measured d u r i n g each of the fou r seasons. D r i f t i n g organisms t h a t were never consumed by f r y were not measured. Mean lengths of f r y used i n t h i s a n a l y s i s i n c r e a s e d s i g -n i f i c a n t l y from one season to the next (Tables 17 and 18). Mean lengths of d r i f t i n g prey items ranged s e a s o n a l l y between 1.44 - 2.88 mm (Table 17). Mean lengths of stomach content items were always l a r g e r than d r i f t i n g prey items f o r t h a t season (Table 17); these d i f f e r e n c e s were s t a t i s t i c a l l y s i g n i -f i c a n t d u r i n g summer, winter, and s p r i n g (Table 18). Stomach content items were s i g n i f i c a n t l y l a r g e r i n f a l l than summer and l a r g e r i n s p r i n g compared t o winter. The r e s u l t s do not support the hypothesis s t a t e d a t the beginning of S e c t i o n V.E. As f r y grew they tended t o s e l e c t l a r g e r prey items. 2. Experimental Evidence The r e l a t i o n s h i p between f i s h s i z e and prey s i z e was examined e x p e r i m e n t a l l y i n c l o s e d system stream tanks. F i f t y - 66 -of each .of four size groups of dead Simulium larvae were fed at 5 min int e r v a l s for 1 h to three groups of underyearling trout: Fish Food Items Popula- H2O Mean Fish Introduced tions Temp. No. Size (Nos./5 min) Tested Date °C Fish mm g 14/8/75 13 31 29 0.21 28/7/75 13 34 31 0.21 Older r i v e r f r y 27/8/75 12 30 41 0.78 200 dead Simulium of 4 size classes Naive hatchery fry Young r i v e r fry Young r i v e r . f r y were s i g n i f i c a n t l y larger than naive hatchery f r y and older r i v e r f r y s i g n i f i c a n t l y larger than young r i v e r f r y : Populations Being Compared t c a l c . df t.05 Young r i v e r f r y vs. naive hatchery f r y 2.27 63 1.67 Older r i v e r fry vs. young r i v e r f r y 16.61 62 1.67 The size ranges of the four classes of dead Simulium larvae fed to the three groups of underyearlings overlapped (Fig. 27) producing a bimodal prey d i s t r i b u t i o n (Fig. 28). - 67 -Table 17. Mean lengths (x) and th e i r standard deviations (.S) for f i s h , d r i f t i n g prey items, and stomach content items from zones 2, 3, and 4. x n (mm) S Summer fry 24 45. 0 5. 8 F a l l f r y 24 56. 9 11. 0 Winter fry 24 63. 2 13. 2 Spring yearlings 24 69. 3 8. 7 Summer d r i f t i n g prey 130 1. 57 1. 07 F a l l d r i f t i n g prey 125 2. 88 2. 99 Winter d r i f t i n g prey 202 1. 67 0. 89 Spring d r i f t i n g prey 149 1. 44 0. 50 Summer stomach content items 420 2. 21 1. 63 F a l l stomach content items 314 3. 34 1. 56 Winter stomach content items 274 3. 40 1. 45 Spring stomach content items 186 5. 67 4. 08 - 68 -Table 18. T test r e s u l t s of comparisons of f i s h lengths, d r i f t i n g prey lengths and stomach content item lengths from zones 2, 3, and 4. Comparisons. Being Made cal c . df .0.5 Summer fry vs. f a l l f r y 4.72 4 6 1.6 8 F a l l fry vs. winter fry 1.80 4 6 1.6 8 Winter fry vs. spring yearlings 1.90 46 1.68 Summer d r i f t vs. summer stomach contents 5.22 330 1.65 F a l l d r i f t vs. f a l l stomach contents 1.63 152 1.65 Winter d r i f t vs. winter stomach contents 16.16 461 1.65 Spring d r i f t vs. spring stomach contents 14.02 192 1.65 Summer stomach contents vs. f a l l stomach contents 9.51 689 1.65 F a l l stomach contents vs. winter stomach contents 0.5 6 5 84 1.65 Winter stomach contents vs. spring stomach contents 7.27 217 1.65 - 68a -Fig. 27. Length frequencies of four size categories of Simulium larvae used i n feeding experi-ments (n = 50 i n each case). - 69 -Length (mm) - 69a -Fig. 28. Length frequency of Simulium larvae a v a i l -able to (Fig. 28a), and consumed by (Figs. 28 b-d), trout f r y (n = 200 for a, 285 for b, 573 for c and 931 for d). - 70 -Length (mm) - 71 -The size d i s t r i b u t i o n of prey consumed by each group of trout (Figs. 2 8 b-d) d i f f e r e d s i g n i f i c a n t l y from the pot e n t i a l prey d i s t r i b u t i o n and the prey d i s t r i b u t i o n of older r i v e r f r y was d i f f e r e n t from both young r i v e r and naive hatchery f r y (Table 19). Mean prey sizes consumed by naive hatchery f r y , young r i v e r f r y and older r i v e r f r y were 3.0, 2.9, and 3.9 mm re-,, spectively. When mean prey size was plotted against f i s h size for a l l f i s h (Fig. 29) i t was seen that larger f r y generally consumed larger prey (r = 0.60). Table 19. Chi-square results of comparisons of size cat-egories of Simulium larvae consumed by three groups of trout f r y . 2 2 Comparisons Being Made X , df X n_ C.ctJ-.C. • • .U.I) Naive f r y prey vs. poten t i a l prey 129.3 8 15.5 Young fry prey vs. potential prey 4 77.4 8 15.5 Older f r y prey vs. poten t i a l prey 544.8 8 15.5 Naive f r y prey vs. older f r y prey 95.3 7 14.1 Young trout prey vs. older f r y prey 3 03.4 7 14.1 The data r e j e c t the hypothesis. Older r i v e r f r y were s i g n i f i c a n t l y larger than both young r i v e r and naive hatch-ery fry and consumed s i g n i f i c a n t l y larger prey. The size difference between young'/ r i v e r and naive hatchery f r y was - 71a -Fig. 29. Mean lengths of Simulium larvae consumed vs. f i s h size considering a l l fry experimentally exposed to four size classes of Simulium (n = 97). - 72 -FISH UEH5TH OvfvlJ - 73 -appar e n t l y not s u f f i c i e n t to produce d i f f e r e n c e s i n prey s i z e s consumed. Both the s i z e d i s t r i b u t i o n of prey consumed by o l d e r r i v e r f r y and the p o t e n t i a l prey d i s t r i b u t i o n were bimodal w i t h i d e n t i c a l peaks ( F i g . 2 8a and d ) . T h i s suggested t h a t prey d e n s i t y a f f e c t e d the f e e d i n g p a t t e r n s o f rainbow f r y as w e l l as prey s i z e . To f u r t h e r study the r e l a t i o n s h i p between f i s h s i z e and prey s i z e and the importance o f prey d e n s i t y , three d i f f e r e n t s i z e groups o f f i s h were exposed to s i m i l a r s p e c i e s compositions of l i v e zooplankton. Zooplankton were i n t r o d u c e d a t 5 min i n t e r v a l s to t r o u t i n c l o s e d system stream tanks: Food F i s h H2O Mean F i s h Items P o p u l a t i o n s Temp. No. ...Size. Introduced Tested Date °C F i s h mm g A s s o r t e d Naive l i v e Hatchery Zooplank-. Fry 17/8/75 12 30 29 0.17 ton Older Hatchery Fry 17/9/75 12 32 35 0.40 Older R i v e r Fry 29/9/75 13 33 43 0.73 Numbers of zooplankters i n t r o d u c e d every 5 min were those captured i n 5 min d r i f t samples taken a t the o u t l e t of Trout Lake. Two e x t r a d r i f t samples, taken a t the begi n n i n g and end of d r i f t sampling p e r i o d s were preserved and l a t e r - 74 -analyzed i n the laboratory to determine species compositions and numbers of zooplankters introduced for each experiment. Water v e l o c i t i e s at d r i f t sample s i t e s were always 0.7 m/s 3 and water volumes f i l t e r e d , ~250 m . .An e f f o r t was made to keep zooplankton a l i v e since i t was found that i n d r i f t samples that had been frozen, plankters had a tendancy to become clumped together and with b i t s of plant material and detritus and then s e t t l e out quickly i n stream tanks. There-fore, a l l d r i f t samples were taken immediately p r i o r to the experiments. Fish size varied s i g n i f i c a n t l y during the three experi-ments : Populations Being Compared t c a l c . df t . 05 Naive hatchery fry vs. older hatchery f r y 13.48 60 1.67 Older hatchery fry vs. older r i v e r f r y 10.17 63 1.67 Unfortunately, zooplankton numbers were not consistent i n the three experiments. The r o t i f e r , K e l l i c o t t i a longispina was the most common zooplankter i n each case but because i t was never consumed, i t was ignored i n the analysis. The t o t a l avoidance of K e l l i c o t t i a was apparently due to i t s small size (x length = 0.06 mm). E l e c t i v i t y values demonstrated that, whenever present, Bosmina and Cyclops were consumed less, and Daphnia and Diaptomus consumed more than proportionately to - 75 -their abundance i n the d r i f t (Table 20). The small size of Bosmina, and the large size of Diaptomus may explain t h e i r avoidance and selection as prey items, respectively. The widely contrasting e l e c t i v i t i e s between Cyclops and Daphnia are i n t e r e s t i n g , p a r t l y because the two species were sim i l a r sized (Table 20), but also because the r e s u l t s were very sim i l a r to the f i e l d r esults from zone 1. In zone 1, Cyclops were rarely fed upon and similar sized Daphnia s e l e c t i v e l y fed upon (Table 16). Behavioural differences between these two prey species presumably are important factors influencing f i s h feeding but prey density also may play a r o l e . E l e c t i v -i t y values for Cyclops increased with both absolute (nos. per experiment) and r e l a t i v e (percent composition of total) densities (Table 21). Densities were l i k e l y also important for other species but because of d i f f i c u l t i e s i n d i s t i n g u i s h -ing between the e f f e c t s of prey size, density and other variables, r e s u l t s were inconclusive. In conclusion, d i f f e r -ent sized fry did not select d i f f e r e n t sized zooplankton, presumably because a l l prey species were smaller than optimal. Zooplankton were always smaller than Simulium selected by similar sized trout (Fig. 28). Prey size appeared important i n determining whether some species were selected but offered no explanation for others, especially Cyclops. - 76 -Table 20. Mean e l e c t i v i t i e s (x E) and sizes of zoo-plankton consumed by three size groups of trout. _ S i z e a Fish Plankton _ x Size Range Population Genus x E (mm) (mm) Naive Hatchery Fry Older Hatchery Fry Older River Fry Bosmina  Daphnia  Cyclops Daphnia  Cyclops  Diaptomus Bosmina  Daphnia  Cyclops Diaptomus -0.89 0.70 •0.71 0.75 •0.49 0.89 •0.54 0.80 •0.20 0.97 0.15 0.26 0.27 0. 34 0.28 0.51 0.15 0.29 0. 32 0.53 0.12 0.22 0.24 0.28 0.22 0.42 0.12 0.24 0.28 0.48 0.20 0. 30 0. 30 0.42 0.36 0. 66 0.20 0.88 0.38 0. 60 n = 15. Table 21. Relationship between Cyclops density and mean e l e c t i v i t y (x E) for three groups of trout. Fish Population x E Naive Hatchery Fry Older Hatchery Fry Older River Fry 975 8780 14,6000 77.6 93. 8 96.9 -0.71 -0.49 -0.20 d a= absolute density (mean no. organisms/5 min). 3d = r e l a t i v e density (percent of t o t a l prey introduced). - 77 -F. Prey Body Movement The following n u l l hypothesis was tested using closed system stream tanks: "Prey body movement i s not an important c h a r a c t e r i s t i c in the feeding behaviour of trout i n moving water." Different groups of trout were exposed to l i v e and dead prey items: Food Items Introduced (Nos./5 min) Fish Populations Tested Date H 20 Temp, °C Mean Fish No. Size Fish mm g 25 0 dead Simulium + 25 0 dead Heptaqeniidae 250 l i v e Simulium + 250 dead Heptageniidae 2 25 dead Ceriodaphnia + 225 dead Daphnia rosea 225 l i v e Ceriodaphnia + 225 dead Daphnia rosea Young River Fry Hatchery Duncan Fry 17/7/75 11 31 23/7/75 12 31 14/7/76 13 32 14/7/76 13 32 30 0.22 30 0.23 31 0.21 35 0.31 It was assumed that the chief difference between l i v e and dead prey was body movement. In the f i r s t experiment Simulium larvae were the second largest size group of e a r l i e r experiments [Fig. 27(c)] rang-- 78 -ing in size from 3.5 - 6.5 mm. Heptageniidae nymphs were handsorted to be within the same size range. In the second experiment Daphnia averaged 2.0 mm and ranged between 1.6 -2.3 mm while Ceriodaphnia averaged 1.2 mm and ranged between 1.0 - 1.5 mm (n = 25 i n both cases). Unfortunately, because of d i f f i c u l t i e s i n obtaining and keeping s u f f i c i e n t quantities of Heptageniidae nymphs and Daphnia a l i v e , i t was not possible to perform the reverse of these experiments ( i . e . feed f i s h l i v e Heptageniidae nymphs and dead Simulium larvae or l i v e Daphnia and dead Ceriodaphnia). In many respects dead prey seemed favoured over l i v e prey. Presumably dead prey were easier to catch because of t h e i r lack of escape behaviour. Live Simulium s e t t l e d out much more rapidly and frequently than dead Simulium because of the former's tendancy to attach themselves. Trout were never observed feeding o f f the bottom. S e t t l i n g out was much less important i n the experiment using the two cladocera species but individuals of both species were sometimes retained i n the surface tension. Non-living and l i v i n g organisms were caught in the surface tension at approximately the same rate. In both experiments, s i g n i f i c a n t l y more l i v e prey than dead, of the same species, were consumed (Table 22). The n u l l hypothesis was rejected and i t was concluded that the s p e c i f i c kinds of body movements exhibited by l i v e prey organisms were important c h a r a c t e r i s t i c s i n the feeding behaviour of trout in moving water. Table 22. Numbers of dead and l i v e prey consumed by two groups of trout and r e s u l t s of chi-square analyses on differences found. a Total Prey Consumed Total Prey Consumed Trout No. Dead Population Fish Simulium Dead Hepta-geniidae No. Fish Live Simulium Dead Hepta-geniidae X calc, X' 05 Young River Fry Hatchery Duncan Fry 31 113 250 Dead Dead Ceriodaphnia Daphnia 26 152 102 31 262 132 Live Dead Ceriodaphnia Daphnia 34 574 184 228 73 3.8 3.8 Ho = Live Simulium (Ceriodaphnia) and dead Heptageniidae (Daphnia) should be consumed proportionately to dead Simulium (Ceriodaphnia) and dead Heptageniidae (Daphnia). - 80 -G. Previous Feeding Experience The following experiment had a two-fold purpose: to determine i f trout fry would select f a m i l i a r i n preference to novel food; and to determine i f increasing the proportion of a novel food i n the fishes' environment would at some point cause a switch i n feeding patterns with trout consuming the novel food disproportionately to abundance. F i f t y older hatchery f r y (no experience with natural prey types), averag-ing 35 mm, were transferred to a closed system stream tank on 29 August 1975. They were fed 300 sim i l a r sized Simulium larvae [3.5 - 6.5 mm; Fig. 27 (c)] every 5 min for 1 h each morning for 4 days (Table 23). In addition, 8 h a f t e r each feeding the tank was s t i r r e d , reintroducing s e t t l e d larvae into the d r i f t ; these e s s e n t i a l l y being additional feedings. After this 4 day period, the prey composition was altered d a i l y to include a progressively larger proportion of Hepta-geniidae nymphs (handpicked to range between 3.5 - 6.5 mm) and a smaller proportion of Simulium larvae. On the eighth day, twice as many Heptageniidae as Simulium were introduced (Table 23). After each of these l a t t e r 4 days, eight f r y were s a c r i f i c e d for stomach analysis and the next day, feed-ing portions reduced proportionately. A shortage of prey items prevented t h i s experiment from being performed on untrained f r y . Fry fed proportionately to prey abundance (Fig. 30). There was no evidence of either a t r a i n i n g bias for the - 31 -Table 23. Numbers of fry and food items i n experiment designed to test the e f f e c t of previous feed-ing experience. (Nos./5 min) Before After Day Feeding Feeding Simulium Heptageniidae 1 50 50 300 2 50 50 300 3 50 50 300 4 50 42 300 5 42 34 208 42 6 34 26 134 68 7 26 18 75 75 8 18 - 36 67 - 81a -Fig . 30. Percent occurrence of Simulium larvae (prey type 1) and Heptageniidae nymphs (prey type 2) i n trout stomachs (O) and d r i f t (•) from experiment designed to test the e f f e c t of previous feeding experience. Percent Occurrence ,1... „ , • „„ co -ro T K f. W " * U M • n g r v i - r m i v v n u - n — m j i . - 38 -- 33' -Simulium (upon which f i s h were trained) or a consequent s h i f t to the alternate prey species. The results are i n contrast to an e a r l i e r experiment. In the previous experiment, young r i v e r f r y , exposed to equal numbers of si m i l a r sized dead Simulium larvae and Heptageniidae nymphs, selected a greater proportion of Heptageniidae (Table 22). The d i f f e r e n t feeding h i s t o r i e s of the two f i s h stocks o f f e r an explanation for these patterns. The fry used i n the e a r l i e r experiment had experience preying on a wide variety of d i f f e r e n t shaped and sized organisms i n the Lardeau Rive'r, while the fry used i n t h i s experiment were raised exclusively on hatchery food p r i o r to t h e i r t r a i n i n g period. The young r i v e r f r y may have developed a preference for mayflies, while the hatchery fry were accustomed to feeding randomly on a l l d r i f t i n g prey items provided they were within a p a r t i c u l a r size range. While a longer t r a i n i n g period may have caused a feeding preference for Simulium, i t i s not known whether switching to a novel prey i n response to varying prey densities would have taken place. - 84 -VI. DISCUSSION The Lardeau River i s an important rearing area for juvenile Gerrard rainbow trout. Early habitat requirements, as documented i n zone 1 (Section IV. A. 1.), are sim i l a r to those reported i n the l i t e r a t u r e for other salmonid f r y . Hartman (1965), L i s t e r and Genoe (1970), Mundie (1974) and others have reported the importance of slower water along the margins of streams to recently emerged fr y . Features suggest-ed by Boussu (1954) and'Mundie (1969) for optimal salmonid rearing i n streams - shallow depth, numerous marginal back eddies, copious overhanging vegetation, banks permitting hiding places,'and high b i o l o g i c a l productivity - are preva-lent i n zone 1 during summer. In zones 2, 3, and 4, age classes were p a r t i a l l y segre-gated into regions of d i f f e r e n t bottom p a r t i c l e size and cur-rent v e l o c i t y (Section IV. A. 2.). More complete segregations of age classes have been shown i n other studies. For example, compared to 1+ steelhead (Salmo gairdneri) Everest and Chapman (1972) found 0+ steelhead i n summer commonly chose areas of slower current (< 15 cm/s vs. 50 - 100 cm/s) and shallower depth (< 15 cm vs. 60 - 75 cm). Pearlstone (1976) also found a segregation of year classes of summer rearing steelhead with 0+ f i s h i n shallower regions of the stream (30 cm vs. 53 cm) over smaller substrate ( 1 - 10 cm vs. 5 - 2 0 cm) than 1+ steelhead. Pearlstone did not fin d focal point - 85 -v e l o c i t i e s to vary with f i s h size even though f i s h moved to higher v e l o c i t y regions of the stream as they grew. Everest and Chapman (1972) and Pearlstone (1976) measured microhabitat c h a r a c t e r i s t i c s for i n d i v i d u a l f i s h while this study deter-mined trout densities i n r e l a t i v e l y large areas and then c l a s s i f i e d the habitat of these areas. The microhabitat approach obtains more precise habitat information and i s , therefore, a superior method when time and study conditions permit. The habitat information obtained i n t h i s study by skin diving was generally more informative than that obtained by e l e c t r o f i s h i n g . Emigration from the Lardeau River to Kootenay Lake occurs during two d i s t i n c t time periods; trout densities i n the r i v e r and length and weight s t a t i s t i c s can be related to these periods. A survey conducted during summer 1966 demon-strated summer to be an important migratory period (Irvine, 1978). Fry migrating downstream began appearing i n nets at Marblehead (Fig. 1) on July 4 with numbers increasing rapidly to peak on July 14. A steady decline occurred u n t i l the end of July. During August numbers captured were small but r e l a t i v e l y constant. Results (Figs. 11 and 12) suggested spring to be a second important downstream migratory period. This l a t t e r period concurs with work done on other populations of stream rearing Salmo gairdneri. For example, Stauffer (1972) found downstream rainbow trout migration of a Lake - 86 -Michigan tributary began i n late A p r i l and extended to l a t e July; Shapovalov and Taft (1954) found most downstream migration i n Waddell Creek, C a l i f o r n i a took place from 1 A p r i l - 21 July; Moring and Lantz (1975) reported the heaviest downstream migration i n Deer Creek, Oregon occurred between February and June. Underyearling trout were more abundant i n the upper than the lower Lardeau River during f a l l and winter but not during the migratory seasons summer and spring (Fig. 12). Also, f a l l and winter underyearlings i n the upper r i v e r were s i g -n i f i c a n t l y larger than underyearlings i n the lower r i v e r , while summer fry and spring yearlings were not (Tables 7 and 10). Higher densities and larger sizes of f i s h i n the upper r i v e r during non-migratory periods r e s u l t from the upper r i v e r being b i o l o g i c a l l y more productive than the lower r i v e r and possessing better physical habitat. Cartwright (1961) found almost twice as many aquatic invertebrates i n the poorest of his benthic samples from the upper r i v e r compared to the best of his samples from the lower r i v e r . D r i f t i n g prey densities found i n t h i s study were generally higher i n the upper versus the lower r i v e r zones (Figs. 16, 19, 21, and 23). Changes i n condition (Table 8) appear related to food abundance and a v a i l a b i l i t y , which are r e s t r i c t e d when high trout densities reduce t e r r i t o r y sizes. Other workers (Mason - 87 -and Chapman, 1965; McFadden, 1969; Slaney and Northcote, 1974), have demonstrated a po s i t i v e relationship between food abundance and t e r r i t o r y size, and Kalleberg (1958) has proposed that non-reproductive t e r r i t o r i a l i t y evolved as a mechanism for ensuring an adequate food supply. In the Lardeau River, condition of yearlings d i d not increase from spring to summer, and condition factors of summer f r y were low, suggesting a l i m i t i n g environmental factor during summer. This leads to the hypothesis that high trout densities, the consequence of recent f r y emergence, produce r e l a t i v e l y small t e r r i t o r i e s , l i m i t i n g food.. From summer through f a l l , condition factors of both age groups increased (Table 8). This may have resulted from larger t e r r i t o r i e s caused by f r y mortality and emigration, combined with increased food abundance (especially kokanee eggs). Since underyearling condition factors did not decline between f a l l and winter, food may not have been l i m i t i n g during the l a t t e r season. However, condition of yearlings declined from f a l l to winter. The increase i n condition between winter and spring for the younger cohort was s i g n i f i c a n t (Table 9). This may have re-sulted from emigration and mortality combining to increase t e r r i t o r y sizes, and hence, increasing food a v a i l a b i l i t y . As well, improved environmental conditions may have been p a r t i a l l y responsible. - 88 -As discussed i n greater d e t a i l elsewhere (Irvine, 1978), further work should be i n i t i a t e d to improve our understanding of the Gerrard f i s h and the importance of the Lardeau River as a rearing area to them. A tagging operation of juvenile trout within the r i v e r should take place, preferably using a magnetic nose-tagging machine (in conjunction with f i n c l i p s ) . At a l a t e r date, trout entering the sport fishery i n Kootenay Lake, as well as f i s h spawning at Gerrard (zone 1), would be examined for the presence of these markings. In addition, a detailed examination of scales from known Gerrard spawners could also be undertaken. The early c i r c u l i pattern would be examined, and compared with scales from Lardeau River juveniles for further information on t h e i r early l i f e history. These techniques would not only establish the importance of the Lardeau system for rearing but would also provide valuable growth data and make i t possible to d i s t i n g u i s h between r i v e r resident trout and juvenile stream rearing Gerrard f i s h . If the majority of large trout spawning at Gerrard do u t i l i z e . the Lardeau for rearing i t i s l i k e l y that the amount of rearing habitat i n the r i v e r l i m i t s t h e i r population s i z e . Some means of enhancing the rearing capacity of the Lardeau system should be considered. An a r t i f i c i a l rearing channel has been suggested as the best possible method (Irvine, 1978). Many authors have attempted to relate the feeding behav-iour of juvenile salmonids i n the l o t i c environment to - 89 -invertebrate d r i f t . While the role of benthic organisms consumed o f f the bottom has been a somewhat contentious issue (Chaston, 1968; Jenkins, Feldmeth, and E l l i o t , 1970), only occasionally (Keenleyside, 1962; Jenkins, 1969; G r i f f i t h , 1974) has any attempt been made to observe f i s h feeding i n t h e i r natural habitat, and rarely has the r e l a t i o n s h i p been examined quantitatively. Observations of juvenile trout i n the Lardeau demonstrated that juvenile trout fed almost exclusively on d r i f t i n g organisms (Fig. 15). Because of t h i s , the ensuing study of the r e l a t i o n s h i p between f i s h feeding and invertebrate d r i f t was j u s t i f i e d . In the l o t i c environment, energy requirements are high and to survive salmonid fry must obtain food energy by the most p r o f i t a b l e means available. Juvenile trout are t e r r i t -o r i a l and i t i s u n l i k e l y that s u f f i c i e n t quantities of benthos exist within t h e i r t e r r i t o r i e s to keep them a l i v e (Chapman, 1966), so they are forced to r e l y on d r i f t . Since a very precarious energy balance between su r v i v a l and death exists for many stream rearing salmonids (Mundie, 1969), food optimization i s e s s e n t i a l . The quantity of stream d r i f t passing any given point i s c h i e f l y dependent upon water v e l o c i t y , and the faster the v e l o c i t y , the greater the energy expenditure necessary for maintenance of position. I t seems l i k e l y that a tradeoff exists between these two variables. While i t i s advantageous for trout to locate i n - 90 -f a s t moving areas because g r e a t e r q u a n t i t i e s of d r i f t i n g i n v e r t e b r a t e s are present, above a c e r t a i n c u r r e n t speed the energy r e q u i r e d to h o l d p o s i t i o n w i l l exceed the energy d e r i v e d . T h i s study demonstrated t h a t j u v e n i l e t r o u t avoided f a s t c u r r e n t areas (Tables 2 and 5). Most o f t e n u n d e r y e a r l i n g t r o u t i n the Lardeau River rose i n the water column to feed ( F i g . 15). T h i s i m p l i e s they were l e a v i n g m i c r o h a b i t a t s near the stream bottom where c u r r e n t was reduced (due to the f r i c t i o n a l e f f e c t of the s u b s t r a t e ) , and moving up i n t o areas where d r i f t r a t e s were higher. A f t e r s t r i k i n g at an o b j e c t , f r y would g e n e r a l l y r e t u r n to t h e i r s t a t i o n . While i n v e r t e -b r a t e d r i f t i n zone 1 was not v e r t i c a l l y s t r a t i f i e d (Table 12), d r i f t i n deeper r i v e r r e g i o ns may be. D e t a i l e d micro-h a b i t a t s t u d i e s are needed measuring c u r r e n t i n areas where f r y l o c a t e and feed. In c o n j u n c t i o n , d r i f t should be s t u d i e d to determine whether d r i f t d e n s i t i e s , as w e l l as r a t e s , are h i g h e r i n f a s t e r , s u r f a c e water. Observations of f r y f e e d i n g i n the Lardeau suggested t h a t l e a r n i n g p l a y e d an important r o l e i n t h e i r f e e d i n g be-haviour. Larger j u v e n i l e s appeared to s t r i k e l e s s f r e q u e n t l y at i n e d i b l e o b j e c t s than d i d s m a l l e r f i s h ( F i g . 15) and hence wasted l e s s energy. I t i s p o s s i b l e t h a t many f r y p e r i s h because they do not l e a r n upon what to feed. F u r t h e r o b s e r v a t i o n s of j u v e n i l e salmonids f e e d i n g i n t h e i r n a t u r a l environment are r e q u i r e d . The importance of - 91 -d r i f t i n g organisms as food no doubt varies among d i f f e r e n t species, c e r t a i n l y among d i f f e r e n t size classes, and even within size classes of the same species, both seasonally and d i e l l y . It i s surprising that while considerable e f f o r t has been expended studying stream d r i f t and fry feeding very l i t t l e has been spent observing f i s h i n t h e i r natural environ-ment." Zooplankton were the most important food item for summer fry i n r i v e r zones 1 and 2 (Fig. 17). These r e s u l t s conform to those reached e a r l i e r (Irvine, MS 1973) where zooplankton of Trout Lake o r i g i n constituted 41 percent of the organisms consumed by fry i n zone 1. Lake o r i g i n d r i f t i s v i t a l l y important to recently emerged fry in two ways; directly, as a food source and i n d i r e c t l y , as an abundant source of nourishment • to the l o t i c benthic fauna which are i n turn fed upon by f r y . The large numbers of kokanee eggs and fry consumed by juvenile trout (Figs. 20 and 24) are important. During most years spawning kokanee (and hence kokanee eggs) are present i n the Lardeau River from late August u n t i l early November. Downstream migrating kokanee fry are probably present i n the r i v e r from early A p r i l u n t i l l a te June. These two food re-sources may serve the valuable function of increasing the growth rate of juvenile trout. McCart (1966) found rainbow trout from the upper Babine River to have a faster growth rate than trout from ..the north arm of Babine Lake and suggest-ed t h i s may have been due to the greater a v a i l a b i l i t y of - 92 -salmon eggs and fry to the r i v e r trout. Density independent exploitation by f i s h of natural foods has long been known to occur. It appears that, to maximize energy gains, juvenile trout feed s e l e c t i v e l y . Of the various sensory systems possessed by f i s h , the v i s u a l system appears to be the most important for trout i n prey detection and recognition. Prey c h a r a c t e r i s t i c s which f i s h can v i s u a l l y d i s t i n g u i s h include size, form, contrast, motion, and colour (Hyatt, 1978). Other prey properties l i k e l y to be of importance include density and p a l a t a b i l i t y . Certain properties of the predator are also important i n s e l e c t i v e feeding; most important are siz e , hunger state, and previous feeding experience. The importance of several of these char-a c t e r i s t i c s i n the sele c t i v e feeding of young stream dwelling trout were examined i n t h i s study. Prey movement i s one of the most important prey charact-e r i s t i c s to many v i s u a l predators. Its importance has been demonstrated for toads (Ewert, 1974) and birds (Smith, 1976), and Woodhead (1966) concluded i t l i k e l y important to many fishes. Nonpredatory f i s h have been shown to react strongest to baits of average v e l o c i t y and vermiform movements while predatory f i s h react to baits of more rapid v e l o c i t y and exhibiting jerky movements, simulating a diseased or weakened f i s h (Protasov, 1970). Rimmer and Power (1978) showed that A t l a n t i c salmon alevins i n s t i l l water consumed zooplankton - 93 -only i f prey were moving. Both Ware (1973) and Bryan (1973) have experimentally demonstrated the importance of prey move-ment to rainbow trout, but since t h e i r work was conducted i n standing water aquaria, t h e i r results are not necessarily relevant to stream dwelling trout. Movement i s an obvious feature of d r i f t i n g organisms and i t i s i n t e r e s t i n g to consider the importance of small scale body movement by prey organisms within d r i f t . The experimental re s u l t s of t h i s study suggested prey body move-ment i s important (Table 22). While r e p l i c a t i o n of these results i s necessary, one can speculate upon the su r v i v a l importance of cueing i n on prey body movement. In the stream environment f i s h are presented with a great many objects within the approximate size range upon which they can feed. Many of these provide l i t t l e or no n u t r i t i o n a l benefit (eg. inorganic material). A major distinguishing c h a r a c t e r i s t i c between energetically p r o f i t a b l e and unprofitable objects i s movement. Therefore, i t seems l i k e l y that the survival rate of young salmonids feeding upon active and hence gener-a l l y n u t r i t i o n a l food types would be greater than those .. feeding on non-moving items. It i s f a i r l y obvious that for a l l predators, prey org-anisms w i l l l i e within a discrete size range. Below a threshold size predation i s n e g l i g i b l e because prey are too small either to be seen or to be energetically p r o f i t a b l e to consume. Above t h i s size threshold predation increases - 94 -with increasing prey size (Hall et a l . , 1976) u n t i l some c r i t i c a l prey size i s reached above which physical l i m i t a t i o n s of the predator prevent prey ingestion. In some cases i t i s worthwhile to determine these size ranges, both for a better understanding of f i e l d feeding data, and also for possible improvement of a r t i f i c i a l rearing and feeding habitats. The relationship between prey size and predator size i s not so inherently obvious since i t i s not immediately clear why prey size should increase as predators grow. Juvenile rainbow trout i n the stream environment were shown to be size s e l e c t i v e predators, with larger fry con-suming bigger prey than smaller f r y . K e l l i c o t t i a longispina, presumably because of th e i r very small siz e , were never con-sumed by fry i n zone 1. In experiments, larger Simulium were avoided by young r i v e r and naive hatchery f r y , although consumed by older r i v e r fry (Fig. 28) and mean prey size increased with f i s h size (Fig. 29). F i e l d r e s u l t s (Fig. 26 and Table 17) showed a gradual size increase i n prey items over time, concurrent with f i s h growth. D i f f e r e n t i a l selec-tion, on the basis of prey size, by d i f f e r e n t sized juveniles probably serves to reduce competition among d i f f e r e n t sized members of the same species. In both the f i e l d (Table 16), and experimental work (Table 20), posit i v e e l e c t i v i t i e s were obtained for large calanoid copepods and Daphnia and negative e l e c t i v i t i e s for - 95 -smaller Bosmina. This i s as expected of size s e l e c t i v e predators. However, Cyclops were also rarely consumed and t h e i r sizes were similar to Daphnia. Other workers have shown that body size i s not the only important c r i t e r i o n i n f i s h feeding. Brooks (1968) found Alosa pseudoharenga con-sumed a l l Daphnia catawba before feeding on larger Epischura  nordenskioldi and Ivlev (1961) reported Bosmina was consumed more frequently than larger Diaptomus. For t h i s study, a number of possible explanations concerning the lack of feed-ing on Cyclops e x i s t . For example, Cyclops may have a better escape response than other plankters. Brook and Woodward (1956) and Schroder (1967) have shown Cyclops to have p o s i t i v e rheotactic behaviour. A l t e r n a t i v e l y t h e i r p a l a t a b i l i t y may be less than the s i m i l a r sized and yet more frequently con-sumed Daphnia. Or, Daphnia may be n u t r i t i o n a l l y more bene-f i c i a l . A number of authors have found a general preference for cladocerans over copepods i n f i s h feeding (Galbraith, 1967; Brooks, 1968; Craddock et a l . 7 1976). The hypothesis that Cyclops are rarely consumed because of t h e i r escape behaviour could be tested using a si m i l a r design to experiments of t h i s study. One group of fry could be fed dead zooplankton and a second group l i v e zooplankton (both prey populations consisting partly of Cyclops) and feeding patterns of the two fry groups compared. If dead Cyclops are consumed s i g n i f i c a n t l y more than l i v e , movement - 96 -i s l i k e l y an important c h a r a c t e r i s t i c reducing prey suscepti-b i l i t y for t h i s species. A good understanding of the role of prey density was not obtained. As r e l a t i v e and absolute densities of Cyclops increased, so did e l e c t i v i t i e s (Table 21). Rankin (MS 1977) found a si m i l a r relationship for sockeye salmon with e l e c t i v -i t i e s of preferred prey increasing with absolute densities. Ivlev (1961), working with Cyprinus carpio, found when dens-i t i e s of a l l prey species increased concurrently, e l e c t i v i t i e s of avoided forms decreased. Different results were obtained when numbers of only one prey species were varied (i.e.. absolute numbers of a l l other species remained the same). If the species whose numbers were varied were a preferred prey item, as t h e i r numbers increased, e l e c t i v i t y decreased but i f they were an avoided prey item, as numbers increased, so did e l e c t i v i t y (Ivlev, 1961). The experiments described in t h i s study were not s u f f i c i e n t to determine whether juv-enile trout i n the stream environment would react s i m i l a r l y to density a l t e r a t i o n s . The experiment examining previous feeding experience was designed to determine whether trout f r y could be trained to disproportionately attack an abundant prey species u n t i l that species became rare, at which time the greater propor-t i o n of attacks would be switched to an alternate prey which had meanwhile become more abundant (Table 23). Murdoch - 97 -(1969) has c o n s i d e r e d consequences of such s w i t c h i n g and Murdoch e t a l . (1975) have demonstrated i t f o r the guppy, P o e c i l a r e t i c u l a t u s . In t h i s study, t r a i n i n g b i a s e s a p p a r e n t l y were not formed and s w i t c h i n g d i d not occur. Prey consumption was d i r e c t l y p r o p o r t i o n a l to prey abundance ( F i g . . 3 0 ) . S i n c e Bryan (1973) was able to produce t r a i n i n g b i a s e s i n hatchery r e a r e d rainbow t r o u t i t appears t h a t the t r a i n i n g program f o l l o w e d here was not s u f f i c i e n t . I t i s of i n t e r e s t t h a t w i l d t r o u t s e l e c t e d f o r mayfly nymphs over b l a c k f l y l a r v a e (Table 22) while hatchery r e a r e d t r o u t e x h i b i t e d no p r e f e r e n c e ( F i g . 3 0 ) . I t i s p o s s i b l e t h a t the a r t i f i c i a l l y r e a red t r o u t had become accustomed to f e e d i n g randomly on d r i f t i n g p a r t i c l e s , p r o v i d e d they were w i t h i n a p a r t i c u l a r s i z e range. The w i l d t r o u t may have developed prey p r e f e r e n c e s based perhaps on n u t r i t i o n a l b e n e f i t s of one prey s p e c i e s over another. These prey p r e f e r e n c e s might i n f e r s u r v i v a l advantages on w i l d versus hatchery r e a r e d t r o u t which c o u l d be of i n t e r e s t to those i n v o l v e d i n s t o c k i n g a r t i f i c i a l l y r e a r e d t r o u t i n t o n a t u r a l systems. T h i s study has concentrated on the f e e d i n g behaviour of one stock of stream r e a r i n g rainbow t r o u t . Feeding r e s u l t s from the f i e l d and stream tanks were g e n e r a l l y c o n s i s t e n t . F i s h f e d p r i m a r i l y on d r i f t i n g organisms; prey c h a r a c t e r i s t i c s s i g n i f i c a n t i n t r o u t f e e d i n g were body movement, s i z e and d e n s i t y . These should be c o n s i d e r e d e x p e r i m e n t a l l y i n g r e a t e r - 98 -d e t a i l ; the importance of prey colour, contrast and shape needs also to be examined. Results of t h i s study implied previous feeding experience influenced feeding behaviour. Future experimental studies should consider species s p e c i f i c feeding patterns as well as the e f f e c t on feeding of d i f f e r e n t l i f e history patterns. For example the feeding behaviour of trout that spend a l l t h e i r l i v e s i n the l o t i c environment could be compared to trout that spend part of t h e i r l i v e s i n the l e n t i c environment. The study was one of the f i r s t to examine salmonid feed-ing using stream tanks and somewhat unusual among experimental feeding studies since only natural prey organisms were used. Stream tanks are a useful means of studying feeding and i t i s hoped that they w i l l be used i n the future to further improve our understanding of the feeding ecology of stream rearing salmonids. - 99 -V I I . CONCLUSIONS 1. The L a r d e a u R i v e r i s a n i m p o r t a n t r e a r i n g a r e a f o r G e r r a r d t r o u t t h r o u g h o u t t h e y e a r . S t u d i e s c o n s i d e r i n g t h e p o s s i b i l i t y o f e n h a n c i n g t h e r e a r i n g c a p a c i t y o f t h e L a r d e a u s y s t e m s h o u l d be i n i t i a t e d . 2. H a b i t a t s w i t h o v e r h a n g i n g c o v e r , s h a l l o w d e p t h , a n d s l o w c u r r e n t s u p p o r t e d h i g h e s t d e n s i t i e s o f u n d e r y e a r l i n g t r o u t d u r i n g summer. S l o w c u r r e n t a r e a s c o n t i n u e d t o be i m p o r t a n t t h r o u g h o u t t h e y e a r . Age c l a s s e s s e g r e g a t e d , i n p a r t , a c c o r d i n g t o b o t t o m p a r t i c l e s i z e w i t h o l d e r t r o u t m o s t f r e q u e n t i n r e g i o n s o f l a r g e p a r t i c l e s a n d y o u n g e r t r o u t more common i n r e g i o n s o f s m a l l p a r t i c l e s . A l l t r o u t a v o i d e d f a s t c u r r e n t r e g i o n s . 3 . D o w n s t r e a m m i g r a t i o n s f r o m t h e L a r d e a u R i v e r t o K o o t e n a y L a k e o c c u r r e d d u r i n g s p r i n g a n d summer. E x c e p t d u r i n g t h e s e s e a s o n s u n d e r y e a r l i n g t r o u t w e r e l a r g e r a n d more a b u n d a n t i n t h e u p p e r v e r s u s t h e l o w e r L a r d e a u R i v e r . T h i s was p r o b a b l y due t o b e t t e r r e a r i n g h a b i t a t a n d h i g h e r b i o l o g i c a l p r o d u c t i v i t y i n t h e u p p e r r i v e r . 4. T r o u t c o n d i t i o n was r e l a t e d t o f o o d a b u n d a n c e and a v a i l -a b i l i t y , c o n d i t i o n b e i n g l o w e s t when h i g h t r o u t d e n s i t i e s l i m i t e d f o o d a v a i l a b i l i t y by r e d u c i n g t e r r i t o r y s i z e s . 5. J u v e n i l e t r o u t i n t h e L a r d e a u R i v e r f e d a l m o s t e x c l u s i v e l y o n d r i f t i n g o r g a n i s m s . L a r g e r j u v e n i l e s h a d a l o w e r - 100 -s t r i k e frequency than s m a l l e r f i s h , i m p l y i n g h i g h e r f e e d i n g e f f i c i e n c i e s . F u r t h e r o b s e r v a t i o n s of j u v e n i l e salmonids f e e d i n g i n the stream environment are needed. The importance of d r i f t i n g organisms as food t o d i f f e r -ent s i z e s and s p e c i e s of f i s h should be s t u d i e d . Foods somewhat a t y p i c a l f o r r i v e r i n e f i s h f r e q u e n t l y c o n s t i t u t e d s i g n i f i c a n t p r o p o r t i o n s of the d i e t of t r o u t r e a r i n g i n the Lardeau R i v e r . Zooplankton were the most important food f o r summer f r y from the upper r i v e r and kokanee eggs and f r y were important food t o j u v e n i l e t r o u t d u r i n g f a l l and s p r i n g r e s p e c t i v e l y . Experimental r e s u l t s suggested prey body movement was an important c h a r a c t e r i s t i c s i n c e l i v e organisms were con-sumed s i g n i f i c a n t l y more than the same s p e c i e s when dead. F u r t h e r experiments should be undertaken t o v e r i f y these r e s u l t s . F i e l d and l a b o r a t o r y r e s u l t s demonstrated j u v e n i l e t r o u t consumed prey w i t h i n a d i s c r e t e s i z e range w i t h l a r g e r f r y g e n e r a l l y s e l e c t i n g b i g g e r prey than s m a l l e r f r y . S e l e c t i v i t y f o r Daphnia was g r e a t e r than f o r s i m i l a r s i z e d Cyclops. T r a i n i n g b i a s e s were not formed i n an experiment designed t o . t e s t p r e v i o u s f e e d i n g experience. Because of t h i s , i t was not determined i f s w i t c h i n g from one prey type to another would occur. - 101 -10. Wild trout selected mayfly nymphs over b l a c k f l y larvae while hatchery reared trout exhibited no preference. This implies that hatchery trout may become accustomed to feeding randomly on d r i f t i n g p a r t i c l e s provided they are within a p a r t i c u l a r size range while wild trout develop prey preferences. This could partly explain higher survival rates of wild compared to stocked hatchery trout. 11. Further feeding experiments using stream tanks should be undertaken. The importance of prey colour, contrast and shape needs to be examined. Experiments should also be performed to consider species s p e c i f i c feeding patterns and genetic e f f e c t s of d i f f e r e n t l i f e history patterns on feeding. - 102 -REFERENCES CITED All e n , K.R. 1951. The Horokiwi stream. New Zeal. Mar. Dept., Fish. B u l l . 10, 231 p. Boussu, M.F. 1954. Relationship between trout populations and cover on a small stream. J. Wildl. Mgmt. 18: 227-239. Brook, A.J. and W.B. Woodward. 1956. Some observations on the e f f e c t s of water inflow and outflow on the plankton of small lakes. J. Animal Ecology 25: 22-35. Brooks, J.L. 1968. The eff e c t s of prey size selection by lake planktivores. Syst. Zool. 17: 272-291. Bryan, J.E. 1973. Feeding history, parental stock, and food selection i n rainbow trout. Behaviour 45: 123-153. Cadwallader, P.L. 1975. Feeding habits of two f i s h species i n r e l a t i o n to invertebrate d r i f t i n a New Zealand River. New Zeal. J. of Mar. and Freshwat. Res. 9(1): 11-26. Cartwright, J.W. 1961. Investigations of the rainbow trout of Kootenay Lake, B r i t i s h Columbia with special reference to the Lardeau River. B.C. Fish and Wildl. Branch, Mgmt. Publ. 7, 46 p. Chapman, D.W. 1966. Food and space as regulators of salmonid populations i n streams. Amer. Nat. 100: 345-357. Chaston, I. 1968. A study on the exploitation of invertebrate d r i f t by brown trout (Salmo t r u t t a L.) i n a Dartmoor stream. J. Appl. Ecol. 5: 721-729. - 103 -Craddock, D.R., T.H. Blahm, and W.D. Parente. 1976. Occur-rence and u t i l i z a t i o n of zooplankton by juvenile chinook salmon i n the lower Columbia River. Trans. /Amer. Fish. Soc. 105(1): 72-76. Cross, D.G. 1976. A method of comparing the e f f i c i e n c i e s of e l e c t r i c f i s h i n g operations. J. Fish. B i o l . 9: 261-265. Everest, F.H. and D.W. Chapman. 1972. Habitat selection and s p a t i a l i n t e r a c t i o n by juvenile chinook salmon and s t e e l -head trout i n two Idaho streams. J. Fish. Res. Bd. Canada 29(1): 91-100. Ewart, J.P. 1974. The neural basis of v i s u a l l y guided be-havior. S c i . Amer. 230: 34-42. Frost, W.E. and M.E. Brown. 1967. The trout - the natural history of the brown trout i n the B r i t i s h I s l e s . C o l l i n s Clear-Type Press: London, Great B r i t a i n , 316 p. Galbraith, M.G., J r . 1967. Size-selective predation on Daphnia by rainbow trout and yellow perch. Trans. Amer. Fish. Soc. 96(1): 1-10. G r i f f i t h , J.S., J r . 1974. U t i l i z a t i o n of invertebrate d r i f t by brook trout (Salvelinus f o n t i n a l i s ) and.cutthroat trout (Salmo c l a r k i ) i n small streams i n Idaho. Trans. Amer. Fish. Soc. 103(3): 440-447. H a l l , D.J., S.T. Threlkeld, Carolyn W. Burns, and P.H. Crow-ley. 1976. The s i z e - e f f i c i e n c y hypothesis and the size structure of zooplankton communities. Ann. Rev. Ecol. Syst. 7: 177-208. - 104 -Hartman, G.F. 1965. The role of behaviour i n the ecology and int e r a c t i o n of underyearling coho salmon (Oncor-hynchus kisutch) and steelhead trout (Salmo gair d n e r i ) . J. Fish. Res. Bd. Canada 22(4): 1035-1081. Hartman, G.F. 1969. Reproductive biology of the Gerrard stock rainbow trout. In: T.G. Northcote (ed.) Symposium on salmon and trout i n streams, H.R. MacMillan Lectures i n Fisheries, Univ. of B r i t i s h Columbia: 53-67. Hartman, G.F. 19 70. Nest digging behavior of rainbow trout (Salmo gairdneri). Can. J. Zool. 48: 1458-1462. Hartman, G.F. and D.M. Galbraith. 1970. The reproductive environment of the Gerrard stock rainbow trout. B.C. Fish and Wildl. Branch, Mgmt. Publ. 15, 51 p. Hyatt, K.D. 1978. Factors a f f e c t i n g the a c q u i s i t i o n of natural foods by f i s h . In: W.J. Hoar and D.J. Randall (eds.), Fish physiology (in press). Inland Waters Branch. Annual Reports for the Years 1965-1975. Surface water data for B r i t i s h Columbia. Department of the Environment. Water Survey of Canada. Ottawa, Canada. Irvine, J.R. 1973. The significance of lake-origin d r i f t organisms as an energy source to young rainbow trout i n outlet stream rearing areas. Univ. of B r i t i s h Columbia B.Sc. Thesis (MS). - 105 -Irvine, J.R. 1978. The Gerrard rainbow trout of Kootenay Lake, B r i t i s h Columbia - A discussion of t h e i r l i f e history with management, research, and enhancement recommendations. B.C. Fish and Wildl. Branch, Mgmt. Rep. 72 f 58 p. Ivlev, V.A. 1961. Experimental ecology of the feeding of fishes. Yale University Press, New Haven, Conn. 302 p. Jenkins, T.M., J r . 1969. Social structure, position choice and microdistribution of two trout species (Salmo t r u t t a and S. gairdneri) resident i n mountain streams. Anim. Behav. Monogr. 2: 57-123. Jenkins, T.M., J r . , CR. Feldmeth, and G.V. E l l i o t t . 1970. Feeding of rainbow trout (Salmo gairdneri) i n r e l a t i o n to abundance of d r i f t i n g invertebrates i n a mountain stream. J. Fish. Res. Bd. Canada 27: 2356-2361. Kalleberg, H. 1958. Observations i n a stream tank of t e r -r i t o r i a l i t y and competition i n juvenile salmon and trout. Rept. Inst. Freshwat. Res. Drottningholm 39: 55-98. Keenleyside, M.H.A. 1962. Skin-diving observations of A t l a n t i c salmon and brook trout i n the Miramichi River, New Brunswick. J. Fish. Res. Bd. Canada 19(4): 625-634. L i s t e r , D.B. and H.S. Genoe. 1970. Stream habitat u t i l i z a -t i o n by cohabiting underyearlings of chinook (Oncorhyn-chus tshawytscha) and coho (.0. kisutch) salmon i n the Big Qualicum River, B r i t i s h Columbia. J. Fish. Res. Bd. - 106 -Canada 27(7): 1215-1224. McCart, P. 1966. Behaviour and ecology of sockeye salmon f r y i n the Babine R i v e r . J . F i s h . Res. Bd. Canada 24(2): 375-428. McFadden, J.T. 1969. Dynamics and r e g u l a t i o n of salmonid p o p u l a t i o n s i n streams. In: T.G. Northcote (ed.), Symposium on salmon and t r o u t i n streams, H.R. MacMillan L e c t u r e s i n F i s h e r i e s , Univ. of B r i t i s h Columbia: 313-329. Mason, J.C. and D.W. Chapman. 1965. S i g n i f i c a n c e of e a r l y emergence, environmental r e a r i n g c a p a c i t y , and b e h a v i o r a l ecology of j u v e n i l e coho salmon i n stream channels. J . F i s h . Res. Bd. Canada 22: 173-190. Moring, J.F. and R.L. Lantz. 1975. The A l s e a watershed study: e f f e c t s of l o g g i n g on the a q u a t i c resources of three headwater streams of the A l s e a R i v e r , Oregon. P a r t 1 — b i o l o g i c a l s t u d i e s . Oregon W i l d l . Comm. F i s h . Res. Rep. No. 9, 66 p. Mundie, J.H. 1969. E c o l o g i c a l i m p l i c a t i o n s of the d i e t of j u v e n i l e coho i n streams. In: T.G. Northcote (ed.), Symposium on salmon and t r o u t i n streams, H.R. MacMillan L e c t u r e s i n F i s h e r i e s , Univ. of B r i t i s h Columbia: 135-152. Mundie, J.H. 1974. O p t i m i z a t i o n of the salmonid nursery stream. J . F i s h . Res. Bd. Canada 31: 1827-1837. - 107 -Murdoch, W.W. 1969. Switching i n ge n e r a l p r e d a t o r s ; e x p e r i -ments on predator s p e c i f i c i t y and s t a b i l i t y o f prey p o p u l a t i o n s . E c o l . Monogr. 39: 335-354. Murdoch, W.W., S. Avery, and M.E.B. Smyth. 197 5. Switching i n predatory f i s h . Ecology 56: 1094-1105. Northcote, T.G. 1969. Lakeward m i g r a t i o n o f young rainbow t r o u t (Salmo g a i r d n e r i ) i n the upper Lardeau R i v e r , B r i t i s h Columbia. J . F i s h . Res. Bd. Canada 26: 33-45. P e a r l s t o n e , P.S.M. 1976. Management i m p l i c a t i o n s o f summer h a b i t a t c h a r a c t e r i s t i c s of j u v e n i l e s t e e l h e a d t r o u t (Salmo g a i r d n e r i ) ...in the B i g Qualicum R i v e r . B.C. F i s h and W i l d l . Branch, Mgmt. Rep. No. 67, 13 p. Protasov, V.R. 1970. V i s i o n and near o r i e n t a t i o n of f i s h . I s r a e l Program f o r S c i e n t i f i c T r a n s l a t i o n s , Jerusalem, 1970. Rankin, D.P. 1977. Increased p r e d a t i o n by j u v e n i l e sockeye salmon (Oncorhynchus nerka Walbaum) r e l a t i v e t o changes i n macrozooplankton abundance i n Babine Lake, B r i t i s h Columbia. Univ. o f B r i t i s h Columbia, M.Sc. T h e s i s (MS). Rimmer, D.M. and G. Power. 1978. Feeding response o f A t l a n t i c salmon (Salmo s a l a r ) a l e v i n s i n f l o w i n g and s t i l l water. J . F i s h . Res. Bd. Canada 35: 329-332. Schroder, R. 1967. V e r h a l t e n von Cyclops abyssorum i n der Stromung. Arch. H y d r o b i o l . Suppl. 33(1): 84-91. - 108 -Shapavalov, L. and A.C. Taft. 1954. The l i f e h i s t o r i e s of the steelhead rainbow trout (Salmo g a i r d n e r i i gairdnerii) and s i l v e r salmon (Oncorhynchus kisutch) with special reference to Waddell Creek, C a l i f o r n i a , and recommenda-tions regarding t h e i r management. C a l i f . Dept. Fish and Game, Fish. B u l l . 98, 375 p. Slaney, P.A. and T.G. Northcote. 1974. Ef f e c t s of prey abundance on density and t e r r i t o r i a l behavior of young rainbow trout (Salmo gairdneri) i n laboratory stream channels. J. Fish. Res. Bd. Canada 31: 1201-1209. Smith, Susan M. Predatory behaviour of young Turquoise-browed Motmots, Eumomota superciliosa. Behaviour 56: 309-320. Smith-Root Instruction Booklet. n.d. Preliminary i n s t r u c t i o n manual. Type V e l e c t r o f i s h e r . 14 p. (MS). Solomon, D.J. and R.G. Templeton. 197 6. Movements of brown trout Salmo t r u t t a L. i n a chalk stream. J. Fish. B i o l . 9: 411-423. Stauffer, T.M. 1972. Age, growth, and downstream migration of juvenile rainbow trout i n a Lake Michigan tributary. Trans. Amer. Fish. Soc. 101(1): 18-28. Ware, D.M. 1972. Predation by rainbow trout (Salmo ga i r d n e r i ) : the influence of hunger, prey density, and prey si z e . J. Fish. Res. Bd. Canada 29: 1193-1201. - 109 -Ware, D.M. 1973. Risk of e p i b e n t h i c prey to p r e d a t i o n by rainbow t r o u t (Salmo g a i r d n e r i ) . J . F i s h . Res. Bd. Canada 30: 787-797. Waters, T.F. 1972. The d r i f t o f stream i n s e c t s . Ann. Rev. Entomol. 17: 253-272. Woodhead, P.M.J. 1966. The behaviour of f i s h i n r e l a t i o n t o l i g h t i n the sea. Oceanogr. Mar. B i o l . Ann. Rev. 4: 337-403. 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0094391/manifest

Comment

Related Items