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The role of behavior in the interaction of underyearling coho and steelhead (Oncorhynchus kisutch and… Hartman, Gordon Frederick 1964

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THE ROLE OF BEHAVIOR I N THE INTERACTION OF UNDERYEARLING COHO AND STEELHEAD (ONCORHYNCHUS KISUTCH AND SALMO G A I R D N E R I l ) by ^ GORDON F; HARTMAN B'.A. , 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 , 1954 M.A., 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 , 1956 A THESIS SUBMITTED I N PARTIAL FULFILMENT OF THE REQUIREMENTS OF THE DEGREE OF • DOCTOR OF PHILOSOPHY i n t h e DEPARTMENT OF ZOOLOGY We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e s t a n d a r d r e q u i r e d f r o m c a n d i d a t e s f o r t h e d e g r e e o f DOCTOR OF PHILOSOPHY Members o f t h e D e p a r t m e n t o f Z o o l o g y 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 May, 1964 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y of • B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study,. I f u r t h e r agree that per-m i s s i o n f o r extensive copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . I t i s understood t h a t , c o p y i n g or p u b l i -c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n p ermission, Department of Zoology The U n i v e r s i t y of B r i t i s h Columbia, Vancouver 8, Canada Date May 29, l?6k - i i -ABSTRACT Two s i m i l a r s a l m o n i d s , coho and s t e e l h e a d , c o h a b i t many c o a s t a l r i v e r s o f B r i t i s h C o l u m b i a . F i e l d c o l l e c t i o n s r e v e a l t h a t t h e d i s t r i b u t i o n s o f u n d e r y e a r l i n g coho and s t e e l h e a d a r e s i m i l a r a l o n g t h e l e n g t h o f t h e s e s t r e a m s . However, t h e m i c r o h a b i t a t d i s t r i b u t i o n o f t h e two s p e c i e s i s d i f f e r e n t . I n s p r i n g and summer, when p o p u l a t i o n d e n s i t i e s a r e h i g h , coho o c c u p y p o o l s , t r o u t o c c u p y r i f f l e s . I n autumn and w i n t e r , when numbers a r e l o w e r , b o t h s p e c i e s i n h a b i t t h e p o o l s . N i l s s o n ( 1956) s t a t e d t h a t s e g r e g a t i o n ( s u c h as t h a t shown by coho and t r o u t i n s p r i n g and summer) may be i n d i c a t i v e o f c o m p e t i t i o n r e s u l t i n g f r o m s i m i l a r e c o l o g i c a l demands. To t e s t t h i s h y p o t h e s i s t h e d i s t r i b u t i o n and b e h a v i o r o f coho and s t e e l h e a d were c o m p a r e d i n a s t r e a m a q u a r i u m a t d i f f e r e n t s e a s o n s w i t h g r a d i e n t s o f l i g h t , c o v e r , d e p t h o r d e p t h / v e l o c i t y and i n e x p e r i m e n t a l r i f f l e s and p o o l s . D i s t r i b u t i o n s , and p r e f e r e n c e s o f t h e two s p e c i e s i n t h e e x p e r i m e n t a l e n v i r o n m e n t s were most s i m i l a r i n s p r i n g and summer, t h e s e a s o n s when s e g r e g a t i o n o c c u r r e d i n n a t u r e , and l e a s t s i m i l a r i n autumn and w i n t e r , t h e s e a s o n s when t h e two s p e c i e s o c c u r r e d t o g e t h e r i n n a t u r e . S p r i n g and summer s e g r e g a t i o n i n t h e s t r e a m s i's p r o b a b l y t h e r e s u l t o f i n t e r a c t i o n w h i c h i s p r o d u c e d by e c o l o g i c a l s i m i l a r i t i e s o f t h e s p e c i e s and a c c e n t u a t e d by de n s e p o p u l a t i o n s and i n h e r e n t l y h i g h l e v e l s o f a g g r e s s i v e n e s s . The s p e c i e s do n o t s e g r e g a t e i n s t r e a m s i n w i n t e r b e c a u s e c e r t a i n e c o l o g i c a l demands a r e d i f f e r e n t , numbers a r e l o w e r and i n h e r e n t l e v e l s o f a g g r e s s i v e n e s s a r e l o w . When t h e two s p e c i e s were t o g e t h e r - i i ' i -i n t h e e x p e r i m e n t a l r i f f l e and p o o l e n v i r o n m e n t , t r o u t were a g g r e s s i v e and d e f e n d e d a r e a s i n r i f f l e s .but n o t i n p o o l s ; coho were a g g r e s s i v e i n p o o l s b u t l e s s i n c l i n e d t o d e f e n d s p a c e i n t h e r i f f l e s . T hese d i f f e r e n c e s i n b e h a v i o r p r o b a b l y a c c o u n t f o r t h e d i s t r i b u t i o n o f t r o u t and coho i n n a t u r a l ' r i f f l e s and p o o l s . The d a t a s u p p o r t t h e b a s i c c o n t e n t i o n o f N i l s s d n (1956) and i l l u s t r a t e t h e r o l e o f b e h a v i o r i n s e g r e g a t i o n p r o d u c e d by c o m p e t i t i o n f o r s p a c e . - i v -.TABLE OF CONTENTS . p a g INTRODUCTION . 1 PART I . F I E L D STUDY .... 3 DESCRIPTION OF STUDY AREA 3 A. C h i l l i w a c k R i v e r 3 B. A l o u e t t e R i v e r . 9 C. Sa l m o n R i v e r ••' 13 MATERIALS AND METHODS . 17 RESULTS .. . 19 A. E a r l y L i f e H i s t o r y o f Coho and T r o u t . .. 19 1. L o n g i t u d i n a l d i s t r i b u t i o n i n s t r e a m s ... 19 2. M i c r o h a b i t a t s o f u n d e r y e a r l i n g coho and t r o u t 24 3. S i z e r e l a t i o n s h i p s o f - f i s h I n t h e Salmon R i v e r 26 4. Summary and comments 26 PART I I . EXPERIMENTAL STUDY • ' 31 MATERIALS AND METHODS 31 1. H o l d i n g c o n d i t i o n s and f i s h 31 2. D e s c r i p t i o n o f s t r e a m a q u a r i u m 32 3. D e s c r i p t i o n o f e x p e r i m e n t a l e n v i r o n m e n t s 35 4. E x p e r i m e n t a l p r o c e d u r e 43 5. Scope o f r e s u l t s 47 RESULTS _ 48 1. R e p l i c a t i o n o f e x p e r i m e n t s 48 2. S e a s o n a l c h a n g e s i n d i s t r i b u t i o n 48 3. C o m p a r i s o n o f s p e c i e s i n g r a d i e n t s 52 4. D e s c r i p t i o n o f a g o n i s t i c b e h a v i o r 65 5. A n a l y s i s o f b e h a v i o r 70 -V-Page • RESULTS - c o n t i n u e d 6. D i s t r i b u t i o n i n r i f f l e and p o o l h a b i t a t .. 74 7. A g g r e s s i v e b e h a v i o r i n r i f f l e s and p o o l s . 77 8. Summary o f r e s u l t s 85 DISCUSSION 87 A. B e h a v i o r o f S t e e l h e a d and Coho i n R e l a t i o n t o t h e i r E c o l o g y 87 B. I n t e r a c t i o n o f Young S t e e l h e a d and Coho 91 C. Comments on C o n c e p t s o f C o m p e t i t i o n 94 LITERATURE CITED 97 v i -L I S T OF FIGURES F i g u r e Page 1. L o w e r F r a s e r v a l l e y a r e a i n s o u t h w e s t e r n B r i t i s h C o l u m b i a s h o w i n g A l o u e t t e , C h i l l i w a c k and S a l m o n R i v e r s y s t e m s 4 2. C h i l l i w a c k R i v e r and l o c a t i o n s o f s t a t i o n s 5 3. U p p e r C h i l l i w a c k R i v e r i n a r e a o f l a r g e l o g j a m s , V-36 t o V-38 6 4. C h i l l i w a c k R i v e r i n t h e r e g i o n o f V-17.5 7 5. C h i l l i w a c k R i v e r a t V-5.5 and V-6. N o t e b r a i d e d c h a n n e l and u n s t a b l e g r a v e l b a r s 8 6. A l o u e t t e R i v e r and l o c a t i o n s o f s t a t i o n s 10 7A. A l o u e t t e R i v e r a t A-12, c h a n n e l w i t h l a r g e b o u l d e r s on b o t t o m and w i t h s t r e t c h e s c o n t a i n i n g l a r g e p o o l s 11 B. A l o u e t t e R i v e r a t A-7. N o t e g r a v e l b o t t o m and m o d i f i e d c h a n n e l , • 11 8. A l o u e t t e R i v e r a t A-2 i n meadow and f a r m l a n d ..... 12 9. S a l m o n R i v e r s h o w i n g l o c a t i o n s o f s t a t i o n s 14 10A. S a l m o n R i v e r a t S-9 15 B. R i f f l e and p o o l a r e a s a t S-14 15 1 1 . C o l l e c t i o n o f f i s h w i t h d e t o n a t i n g fuse.. (See s m a l l e x p l o s i o n l e f t f o r e g r o u n d , u p p e r p h o t o g r a p h ) 18 1 2 . D e n s i t y and d i s t r i b u t i o n o f y oung coho and s t e e l h e a d i n t h e C h i l l i w a c k R i v e r . ( D a t a c o m b i n e d f o r p e r i o d f r o m November 1959 t o M a r c h 1962) 20 1 3 . D e n s i t y and d i s t r i b u t i o n o f y oung coho and s t e e l h e a d i n t h e S o u t h A l o u e t t e R i v e r . ( D a t a c o m b i n e d November 1959 t o M a r c h 1962) 21 1 4 . D e n s i t y and d i s t r i b u t i o n o f y oung t r o u t and coho i n t h e S a l m o n R i v e r . ( D a t a c o m b i n e d November 1959 t o M a r c h 1962) 23 - v i i -F i g u r e Page 1 5 . D e n s i t i e s o f y o u n g coho and s t e e l h e a d i n a r e a s where c o v e r ( l o g j a m s ) i s p r e s e n t c o m p a r e d t o a r e a s w here c o v e r i s a b s e n t . D a t a f r o m t h e C h i l l i w a c k R i v e r , November 1959 t o M a r c h , 1 9 6 2 .... 25 16. D e n s i t i e s o f y o u n g t r o u t and coho i n t h r e e t y p e s o f s t r e a m h a b i t a t , r i f f l e , o p e n c h a n n e l and p o o l , d u r i n g s i x p e r i o d s o f t h e y e a r . D a t a f r o m t h e S a l m o n R i v e r , November 1959 t o M a r c h 1962 ... .27 17. S i z e r e l a t i o n s h i p s o f u n d e r y e a r l i n g t r o u t and coho i n the. S a l m o n R i v e r , Smoothed c u r v e s a r e b a s e d on m o v i n g a v e r a g e s o f t h r e e , d a t a b e f o r e s m o o t h i n g was p l o t t e d i n one mm l e n g t h i n t e r v a l s . ' 28 18. L e n g t h f r e q u e n c i e s o f two o r more y e a r c l a s s e s o f t r o u t i n the. S a l m o n R i v e r . D a t a a r e l u m p e d , O c t o b e r t o F e b r u a r y i n c l u s i v e , f o r t h r e e w i n t e r s . 29 19. T e m p e r a t u r e maxima and m i n i m a ( d a i l y ) i n t h e s t r e a m a q u a r i u m d u r i n g t h r e e s e a s o n s i n w h i c h t h e s t u d y was made ( s o l i d l i n e s ) . B r e a k s i n t h e l i n e i n d i c a t e t h a t no e x p e r i m e n t s were i n p r o g r e s s . D o t t e d l i n e s r e p r e s e n t t e m p e r a t u r e maxima and m i n i m a i n h o l d i n g t r o u g h s p l o t t e d f o r two weeks o r more p r e v i o u s t o e x p e r i m e n t s ... 33 20. E x p e r i m e n t a l s t r e a m a q u a r i u m . D e t a i l s o f t h e d r i v e m e c h a n i s m a r e n o t shown 34 2 1 . L a t e r a l and p l a n v i e w s o f c o n t r o l a r r a n g e m e n t and l i g h t , c o v e r , d e p t h and d e p t h and v e l o c i t y g r a d i e n t s . L i g h t and c o n t r o l c o n d i t i o n s a p p e a r s i m i l a r e x c e p t f o r g r a d e d f i l t e r s u s e d t o p r o d u c e l i g h t g r a d i e n t '.. 36 22. V e l o c i t y p r o f i l e i n h o r i z o n t a l and s a g g i t a l p l a n e s i n d e p t h g r a d i e n t . U p p e r f i g u r e shows v e l o c i t i e s 10 cm. above b o t t o m , e x c e p t i n s e c t i o n 1, r i g h t e n d , where p r o f i l e i s . drawn f o r p o s i t i o n 5 cm. above b o t t o m . L o w e r f i g u r e shows c o n d i t i o n s i n s a g g i t a l p l a n e (two c e n t e r r e a d i n g s a v e r a g e d ) . A r r o w s i n d i c a t e d i r e c t i o n o f c u r r e n t , d o t t e d l i n e s r e p r e s e n t s c r e e n s 39 23. V e l o c i t y p r o f i l e i n d e p t h and v e l o c i t y g r a d i e n t . U p p e r f i g u r e shows v e l o c i t i e s 10 cm. above b o t t o m . L o w e r shows v e l o c i t i e s i n s a g g i t a l p l a n e (two c e n t e r r e a d i n g s a v e r a g e d ) . A r r o w s i n d i c a t e d i r e c t i o n o f f l o w , d o t t e d l i n e s r e p r e s e n t s c r e e n s 40 - v i i i -F i g u r e Page 24. H o r i z o n t a l ( u p p e r ) and l a t e r a l v i e w s o f e x p e r i m e n t a l ' r i f f l e and p o o l e n v i r o n m e n t . H o r i z o n t a l a r r o w i n d i c a t e s d i r e c t i o n o f c u r r e n t . V e r t i c a l a r r o w i n d i c a t e s w a t e r s u r f a c e 4 2 25. D i s t r i b u t i o n s o f coho and s t e e l h e a d i n " c o n t r o l " and " c o v e r " g r a d i e n t s , d e s c r i b e d i n t e x t , d u r i n g t h r e e s e a s o n s . D o t s and c i r c l e s r e p r e s e n t mean number o f f i s h p e r s e c t i o n o v e r a one day p e r i o d ( 1 0 - 1 5 o b s e r v a t i o n s ) . V e r t i c a l l i n e s i n d i c a t e r a n g e . S e c t i o n 1 r e p r e s e n t s t h e u p s t r e a m end o f t h e a q u a r i u m , 49 26. D i s t r i b u t i o n s o f coho and s t e e l h e a d i n " l i g h t " , " d e p t h " , and " d e p t h and v e l o c i t y " g r a d i e n t s , as d e s c r i b e d i n t e x t , d u r i n g t h r e e s e a s o n s . C i r c l e s and d o t s r e p r e s e n t mean number o f f i s h p e r s e c t i o n ( 1 0 - 1 5 o b s e r v a t i o n s ) . V e r t i c a l l i n e s r e p r e s e n t r a n g e . S e c t i o n 1 r e p r e s e n t s t h e u p s t r e a m end o f t h e a q u a r i u m , 50 27. D i s t r i b u t i o n o f coho i n c o v e r g r a d i e n t d u r i n g t h r e e s e a s o n s . L o c a t i o n s o f 40 f i s h d u r i n g 10 c o m b i n e d o b s e r v a t i o n s a r e g i v e n . G r o u p s o f d o t s r e p r e s e n t same f i s h o c c u p y i n g same l o c a t i o n r e p e a t e d l y , o r d i f f e r e n t f i s h , i n t h i s and s u c c e e d i n g f i g u r e s o f t h i s t y p e . P o i n t s w i t h i n t h e s t o n e o u t l i n e s r e p r e s e n t f i s h u n d e r s t o n e s . D o t t e d l i n e s r e p r e s e n t s c r e e n s a t ends o f a q u a r i u m i n t h i s f i g u r e and s u c c e e d i n g f i g u r e s o f t h i s t y p e 54 28. D i s t r i b u t i o n o f s t e e l h e a d i n c o v e r g r a d i e n t d u r i n g t h r e e s e a s o n s . L o c a t i o n s o f 40 f i s h d u r i n g 10 c o m b i n e d o b s e r v a t i o n s a r e g i v e n . P o i n t s w i t h i n t h e s t o n e o u t l i n e s r e p r e s e n t f i s h u n d e r s t o n e s , .. 55 29. D i s t r i b u t i o n o f coho i n d e p t h g r a d i e n t d u r i n g t h r e e s e a s o n s . L o c a t i o n s o f 40 f i s h d u r i n g 10 c o m b i n e d o b s e r v a t i o n s a r e g i v e n . Rows o f p o i n t s a t s e c t i o n b o u n d a r i e s r e p r e s e n t f i s h o c c u p y i n g p o s i t i o n s . a l o n g t h e edges o f t h e d e p t h z o n e s ... 58 30. D i s t r i b u t i o n o f s t e e l h e a d i n d e p t h g r a d i e n t d u r i n g t h r e e s e a s o n s . L o c a t i o n s o f 40 f i s h d u r i n g 10 c o m b i n e d o b s e r v a t i o n s a r e g i v e n . Rows o f p o i n t s a t s e c t i o n b o u n d a r i e s r e p r e s e n t f i s h o c c u p y i n g p o s i t i o n s a l o n g .edges o f d e p t h z o n e s . . 59 3 1 . D i s t r i b u t i o n o f c o h o , l a t e r a l v i e w , i n d e p t h g r a d i e n t d u r i n g t h r e e s e a s o n s . L o c a t i o n s o f 40 f i s h i n 10 c o m b i n e d o b s e r v a t i o n s a r e g i v e n .. 60 - i x -F i g u r e Page 3 2 . D i s t r i b u t i o n o f s t e e l h e a d , l a t e r a l v i e w , i n d e p t h g r a d i e n t d u r i n g t h r e e s e a s o n s . L o c a t i o n s o f 40 f i s h i n 10 c o m b i n e d o b s e r v a t i o n s a r e g i v e n . . . . 61 33. R e l a t i o n s h i p o f coho and s t e e l h e a d c o m b i n e d i n d e p t h g r a d i e n t d u r i n g summer c o n d i t i o n s . L o c a t i o n s o f 20 coho p l u s 20 s t e e l h e a d i n 10 c o m b i n e d o b s e r v a t i o n s a r e g i v e n 62 34. R e l a t i o n s h i p o f coho and s t e e l h e a d c o m b i n e d i n d e p t h g r a d i e n t d u r i n g w i n t e r c o n d i t i o n s . L o c a t i o n s o f 20 coho p l u s 20 s t e e l h e a d i n 10 c o m b i n e d o b s e r v a t i o n s a r e g i v e n , 63 35A. Coho, c a 10 months o l d , i n l a t e r a l t h r e a t p o s t u r e . . 66 B. S t e e l h e a d , c a 8 months o l d , i n l a t e r a l p o s t u r e ( s e e f i s h on t h e l e f t ) . F i s h on t h e r i g h t i n f r o n t a l t h r e a t p o s t u r e o f l o w i n t e n s i t y 66 C. Coho, c a 2 months o l d , i n l a t e r a l . t h r e a t p o s t u r e .. 66 36A. Coho, c a 2 months o l d , i n f r o n t a l t h r e a t p o s t u r e o f l o w i n t e n s i t y ( r i g h t ) . Coho, c a 2 months o l d , i n w i g wa.g p o s t u r e ( l e f t ) , , 67 B. Coho, ca 2 months o l d , i n w i g wag ( l e f t ) and l a t e r a l t h r e a t p o s t u r e ( r i g h t ) 67 37. N i p p i n g i n t h e . p a i r o f f i s h on t h e l e f t . P i c t u r e t a k e n a f r a c t i o n o f a s e c o n d b e f o r e t h e f r o n t f i s h was n i p p e d . S e c o n d p a i r o f f i s h ( r i g h t s i d e ) i n c h a r a c t e r i s t i c l a t e r a l p o s t u r e s 69 38. R a t e o f o c c u r r e n c e o f i n d i v i d u a l c o mponents i n t h e a g o n i s t i c b e h a v i o r o f y o u n g coho and s t e e l h e a d . D a t a a r e b a s e d on c o m b i n e d o b s e r v a t i o n s o f f i s h i n t h e f i v e e x p e r i m e n t a l a r r a n g e m e n t s u s e d . See t e x t f o r d e s c r i p t i o n o f b e h a v i o r c o m p o n e n t s 71 39. D i s t r i b u t i o n o f coho and s t e e l h e a d a t f o u r d i f f e r e n t d e n s i t i e s i n r i f f l e and p o o l e n v i r o n m e n t ( J u l y ) . S o l i d d o t s r e p r e s e n t t h e a v e r a g e number o f f i s h p e r s e c t i o n , s p e c i e s s e p a r a t e . C i r c l e s and lkro.ken l i n e s i n d i c a t e t h e a v e r a g e number o f f i s h p e r s e c t i o n , s p e c i e s m i x e d . S c a l e f o r t h e p o i n t s f o r s p e c i e s m i x e d i s h a l f t h a t f o r s p e c i e s s e p a r a t e ( s e e F i g . 24 f o r d e t a i l s o f r i f f l e and p o o l e n v i r o n m e n t ) 75 - X -F i g u r e Page 4 0 . D i s t r i b u t i o n o f coho and s t e e l h e a d a t f o u r d i f f e r e n t d e n s i t i e s i n r i f f l e and p o o l e n v i r o n m e n t ( N o v e m b e r ) . S o l i d d o t s r e p r e s e n t t h e a v e r a g e number o f f i s h p e r s e c t i o n , s p e c i e s s e p a r a t e . C i r c l e s and b r o k e n l i n e s i n d i c a t e t h e a v e r a g e number p e r s e c t i o n , s p e c i e s m i x e d . S c a l e f o r t h e p o i n t s f o r s p e c i e s m i x e d i s h a l f t h a t f o r s p e c i e s s e p a r a t e ( s e e F i g . 24 f o r d e t a i l s o f r i f f l e -p o o l e n v i r o n m e n t ) 76 4 1 . R a t e o f a g g r e s s i v e b e h a v i o r i n r i f f l e and p o o l h a b i t a t s d u r i n g J u l y and November. D a t a b a s e d on o b s e r v a t i o n s made w i t h s p e c i e s s e p a r a t e . C v C i n d i c a t e s coho a t t a c k i n g coho and S v S i n d i c a t e s s t e e l h e a d a t t a c k i n g s t e e l h e a d . Coho o b s e r v e d 390 m i n u t e s i n J u l y and 340 m i n u t e s i n November, s t e e l h e a d o b s e r v e d 380 m i n u t e s i n e a c h p e r i o d 78 4 2 . R a t e s o f a g g r e s s i v e b e h a v i o r i n r i f f l e and p o o l h a b i t a t d u r i n g J u l y and November. D a t a b a s e d on e x p e r i m e n t s i n w h i c h s p e c i e s were m i x e d i n e q u a l numbers and o b s e r v e d 270 m i n u t e s i n J u l y and 250 m i n u t e s i n November. M e a n i n g o f s y m b o l s as f o l l o w s : C v C - coho a t t a c k i n g c o h o , C v S - coho a t t a c k i n g s t e e l h e a d , S v S - s t e e l h e a d a t t a c k i n g s t e e l h e a d , S v C -s t e e l h e a d a t t a c k i n g coho 79 43.- R e l a t i o n , o f r a t e o f a g g r e s s i v e b e h a v i o r , t o d e n s i t y o f f i s h . Coho and s t e e l h e a d c o m p a r e d i n r i f f l e and p o o l h a b i t a t s d u r i n g two s e a s o n s . E a c h d o t o r c i r c l e r e p r e s e n t s 10 m i n u t e s o f o b s e r v a t i o n i n one s e c t i o n o f t h e a q u a r i u m . ( D a t a o b t a i n e d w i t h s p e c i e s s e p a r a t e ) ,., 81 44A. Coho, c a 10 months o l d , i n w i g wag p o s t u r e . F i s h a t l e f t i s d i s p l a y i n g and b e g i n n i n g t o d r o p b a c k t o w a r d f i s h a t r i g h t 83 B. B o t h f i s h d r o p p i n g d o w n s t r e a m and c o m i n g c l o s e r t o g e t h e r 83 C. Coho a t l e f t s t i l l i n w i g wag p o s t u r e , i t s t a i l a l m o s t s t r i k i n g f i s h a t r i g h t . A t t h i s p o i n t t h e f i s h a t l e f t may w h e e l and n i p t h e s e c o n d f i s h o r s e c o n d f i s h may f l e e ,,, 83 4 5 . S m a l l g r o u p o f 8 coho w i t h one d o m i n a n t ( s e c o n d f r o m r i g h t ) and s e v e n s u b o r d i n a t e s . S m a l l f i s h o c c a s i o n a l l y a v o i d e d a t t a c k by r e m a i n i n g s t i l l and r e s t i n g down among t h e s t o n e s , see f o r e g r o u n d . 84 - x i -F i g u r e Page 4 6 . D i r e c t i o n o f r e t r e a t o f coho and s t e e l h e a d f o l l o w i n g i n t r a s p e c i f i c a g g r e s s i v e c o n t e s t s ( b a s e d on 248 c o n t e s t s ^ among s t e e l h e a d and 458 among c o h o ) ' '89 - x i i -L I S T OF TABLES T a b l e - Page I . A v e r a g e l i g h t i n t e n s i t y ( L < L U X ) o v e r t h e l e n g t h o f t h e o b s e r v a t i o n f l u m e . T h r e e r e a d i n g s , a c r o s s t h e t a n k , were a v e r a g e d f o r e a c h f i g u r e . R e a d i n g s were t a k e n on t h e b o t t o m w i t h no w a t e r i n t h e a q u a r i u m . S e c t i o n 1 i s a t t h e u p s t r e a m . end o f t h e t a n k 37 I I . D i m e n s i o n s o f s t o n e s ( i n cm) u s e d i n c o v e r g r a d i e n t 3 8 I I I . Number and s p e c i e s o f f i s h u s e d i n e x p e r i m e n t s i n r i f f l e and p o o l e n v i r o n m e n t . I n S e r i e s 1 coho (c) were u s e d a l o n e * i n S e r i e s 2, s t e e l h e a d (S) were u s e d a l o n e and i n S e r i e s 3 t h e two s p e c i e s were c o m b i n e d 46 I V . Numbers o f coho (C) and s t e e l h e a d (S) i n u p p e r and l o w e r h a l v e s o f s e c t i o n s 4 and 5 i n t h e d e p t h g r a d i e n t i n e a r l y summer and w i n t e r ( J u n e and J a n u a r y ) ,. 57 V. A g g r e s s i v e c o n t e s t s p e r f i s h p e r 100 m i n u t e s d u r i n g J u n e and J a n u a r y 1 9 6 3 . S y m b o l s a r e as f o l l o w s : C-coho,. S - s t e e l h e a d , C-C-coho a t t a c k i n g c o h o , C'S-coho a t t a c k i n g s t e e l h e a d , S'»S-steelhead a t t a c k i n g s t e e l h e a d and S * C - s t e e l h e a d a t t a c k i n g coho 64 V I . M i n u t e s o f o b s e r v a t i o n o f coho and s t e e l h e a d i n c o n t r o l and f o u r e x p e r i m e n t a l a r r a n g e m e n t s d u r i n g s p r i n g , , f a l l and w i n t e r 72 - x i i i -ACKNOWL E DGME NT S Many p e o p l e have h e l p e d me d u r i n g t h e c o u r s e o f t h i s w o r k . D r . W.S. H o a r has g i v e n a d v i c e and s t i m u l a t i o n t h r o u g h o u t t h e i n v e s t i g a t i o n . I am p a r t i c u l a r l y g r a t e f u l t o h i m . The s t u d y h a s be e n f u l l y s u p p o r t e d by t h e F i s h and Game B r a n c h o f t h e B.C. G o v e r n m e n t . I am a p p r e c i a t i v e o f t h e e n c o u r a g e m e n t and s u p p o r t g i v e n by R.G. McMynn, f o r m e r C h i e f F i s h e r i e s B i o l o g i s t , S.B. S m i t h , p r e s e n t C h i e f " F i s h e r i e s B i o l o g i s t and D r . T.G. N o r t h c o t e o f t h e F i s h and Game B r a n c h . The wo r k w o u l d n o t have b e e n p o s s i b l e w i t h o u t t h e i r i n t e r e s t . D r . I . Met. Cowan, D r . J . Adams, D r . D. C h i t t y , D r . P. D e h n e l , D r . P. L a r k i n and D r . C.C. L i n d s e y r e a d t h e m a n u s c r i p t and made s e v e r a l v a l u a b l e . . c r i t i c i s m s . I a p p r e c i a t e t h e e x t e n s i v e h e l p g i v e n by C.A. G i l l d u r i n g a l l s t a g e s o f t h e w o r k . F i t . L t . J . B a e h r , K. C a l v e r t , J . Gee, G, H a l s e y , D. H a r v e y , P. K o h l e r , R. K r e j s a , R. L e i g h t o n , B. L i s t e r , J . L o g a n , E. P e t r i e , R. P e t r i e , M. T e r a g u c h i , D. Udy, P. W i c k e t t and D. W i l k i e a l l h e l p e d i n t h e f i e l d w o r k o r some o t h e r p h a s e o f t h e s t u d y . My l a t e b r o t h e r Fay h e l p e d me i n t h e e a r l y s t a g e s o f t h e f i e l d w o r k , I a p p r e c i a t e t h e t i m e he g a v e . I w i s h t o e x p r e s s my g r a t i t u d e t o W. C a u l f i e l d and H. N e a t e who gave h e l p and b r o u g h t good c h e e r a t C o u r t e n a y . F i n a l l y I w i s h t o a c k n o w l e d g e t h e h e l p and t h e p a t i e n c e o f my w i f e H e l e n d u r i n g t h e l a s t t h r e e y e a r s . 1. INTRODUCTION Two s i m i l a r s p e c i e s o f s a l m o n i d s o c c u r t o g e t h e r i n -many o f t h e c o a s t a l s t r e a m s o f B r i t i s h C o l u m b i a . These f i s h - coho s a l m o n ( Q n c o r h v n c h u s k i s u t c h ) , a n d s t e e l h e a d t r o u t (Salmo  q a i r d n e r i i ) - r e s e m b l e e a c h o t h e r i n m o r p h o l o g y , b e h a v i o r and e a r l y l i f e h i s t o r y . On t h e b a s i s o f p r e s e n t c o n c e p t s , t h e y a r e p o t e n t i a l c o m p e t i t o r s . - * -Young coho and s t e e l h e a d c o e x i s t a l o n g t h e l e n g t h s o f s t r e a m s b u t o c c u r i n d i f f e r e n t m i c r o h a b i t a t s ; t h e i r e c o l o g y i s g i v e n more f u l l y i n t h e t e x t . To i n t r o d u c e t h e p r o b l e m , i t i s s u f f i c i e n t t o n o t e t h a t s e g r e g a t i o n i s p r o n o u n c e d i n t h e s p r i n g and b r e a k s down d u r i n g f a l l and w i n t e r . N i l s s o n ( 1 9 5 6) h a s d e v e l o p e d v a l u a b l e c o n c e p t s w h i c h may p r o v i d e an e x p l a n a t i o n f o r t h e s e p a r a t i o n o f coho and t r o u t d u r i n g s p r i n g and e a r l y summer. He p o s t u l a t e s t h a t a l l o p a t r i c p o p u l a t i o n s o f c l o s e l y a l l i e d s p e c i e s , o r s p e c i e s h a v i n g s i m i l a r e c o l o g i c a l demands u t i l i z e t h e f u l l r a n g e o f t h e i r e c o l o g i c a l p o t e n t i a l s u n d e r c o n d i t i o n s o f i n t e n s e i n t r a - s p e c i f i c c o m p e t i t i o n . I n t e n s e i n t e r s p e c i f i c c o m p e t i t i o n i n s y m p a t r i c p o p u l a t i o n s o f s i m i l a r o r c l o s e l y r e l a t e d s p e c i e s f o r c e s e a c h s p e c i e s t o compete o n l y a t i t s " e c o l o g i c a l optimum" i . e . u n d e r t h o s e c o n d i t i o n s t o w h i c h i t i s b e s t a d a p t e d o r where i t has some c o m p e t i t i v e a d v a n t a g e . I t i s t h i s t e n d e n c y o f s p e c i e s t o ^ The m e a n i n g o f c o m p e t i t i o n , when u s e d i n t h i s p a p e r , i s , " T h e demand, a t t h e same t i m e , o f more t h a n one o r g a n i s m f o r t h e same r e s o u r c e s o f t h e e n v i r o n m e n t i n e x c e s s o f i m m e d i a t e supply." ( M i l n e , 1 9 6 1 ) . The m e a n i n g o f n i c h e i s as g i v e n i n De B a c h and Sundby ( 1 9 6 3 ) . 2. u t i l i z e o n l y t h e i r e c o l o g i c a l o p t i m a t h a t r e s u l t s i n s e g r e g a t i o n d u r i n g r i g o r o u s i n t e r s p e c i f i c i n t e r a c t i o n . On t h e b a s i s o f t h i s c o n c e p t one m i g h t a s k i f t h e r e q u i r e m e n t s and b e h a v i o r o f young t r o u t and coho a r e s i m i l a r i n s p r i n g and e a r l y summer b u t d i f f e r e n t d u r i n g f a l l and w i n t e r . T h e r e a r e t h r e e o b j e c t i v e s t o t h i s s t u d y . The f i r s t i s t o o b t a i n and p r e s e n t d a t a f r o m t h e f i e l d s t u d y o u t l i n i n g i n some d e t a i l t h e p e r i o d and n a t u r e o f i n t e r s p e c i f i c s e g r e g a t i o n . The s e c o n d o b j e c t i v e i s t o c o m p a r e , u n d e r p a r t i a l l y c o n t r o l l e d c o n d i t i o n s , t h e e n v i r o n m e n t a l r e s p o n s e s , p r e f e r e n c e s , and b e h a v i o r o f y o u n g coho and t r o u t , and t o d e t e r m i n e i f . s e g r e g a t i o n o c c u r s when t h e s e c o n d i t i o n s a r e most s i m i l a r . E s s e n t i a l l y t h i s i n v o l v e s t e s t i n g N i l s s o n , ; s i d e a s ( N i l s s o n , 1956 and 1963) u n d e r c o n t r o l l e d c o n d i t i o n s . I f t h e s p e c i e s a r e s e g r e g a t e d a t t h a t p e r i o d when r e q u i r e m e n t s a r e s i m i l a r , t h e t h i r d o b j e c t i v e w i l l ' be t o a s c e r t a i n t h e r o l e o f b e h a v i o r i n t h i s i n t e r a c t i o n . Newman ( 1 9 5 6 ) , L i n d r o t h ( 1 9 5 5 a ) , K a l l e ' b e r g ( 1 9 5 8) and N i l s s o n ( 1963) have shown how b e h a v i o r e n t e r s i n t o i n t e r s p e c i f i c c o m p e t i t i o n . I t i s n o t c l e a r h o w e v e r , what t y p e o f b e h a v i o r a l m e c h a n i s m f u n c t i o n s t o g i v e " s p e c i e s A" an a d v a n t a g e i n . o n e s i t u a t i o n and " s p e c i e s B " an a d v a n t a g e i n a n o t h e r . 3. P a r t I . F I E L D STUDY DESCRIPTION OF STUDY AREA T h r e e r i v e r s i n t h e l o w e r F r a s e r v a l l e y o f s o u t h -w e s t e r n B r i t i s h C o l u m b i a were s t u d i e d ( s e e i n s e t s o f t h e C h i l l i w a c k , A l o u e t t e and S a l m o n R i v e r s i n F i g . l ) . A. C h i l l i w a c k R i v e r . The C h i l l i w a c k R i v e r r i s e s i n t h e C a s c a d e Range i n W a s h i n g t o n and d r a i n s n o r t h i n t o C h i l l i w a c k L a k e ( e l e v a t i o n •620 m), t h e n c e i t f l o w s w e s t i n t o t h e F r a s e r R i v e r . F i g u r e 2 shows t h e p o r t i o n o f t h e r i v e r s t u d i e d -and s t a t i o n l o c a t i o n s . The. r i v e r r u n s t h r o u g h a deep v a l l e y i n a s t a b l e r o c k y c h a n n e l f r o m C h i l l i w a c k L a k e t o t h e r e g i o n a t V-28 ( F i g . 2 ) , L a r g e a r e a s o f t h e u p p e r r i v e r a r e c o v e r e d w i t h e x t e n s i v e l o g ja m s ( F i g . 3 ) . I n t h e m i d d l e s t r e t c h e s o f t h e r i v e r (V-28 t o V - 1 3 ) , t h e c h a n n e l b o t t o m i s l e s s s t a b l e and l a r g e l o g jams a r e a b s e n t ( F i g . 4 ) . S e v e r a l l a r g e t r i b u t a r i e s ( S l e s s e , F o l e y , Chipmunk and T a m i h i C r e e k s ) e n t e r t h i s s t r e t c h o f t h e r i v e r . The d i s c h a r g e o f t h e s e t r i b u t a r i e s f l u c t u a t e s c o n s i d e r a b l y ; h e n c e , b e l o w V-13 t h e c h a n n e l i s b r a i d e d and much o f t h e b o t t o m i s u n s t a b l e ( F i g . 5 ) . T h e r e i s one l o g j a m n e a r V-5. The l o w e r m o s t r e g i o n o f t h e r i v e r t r a v e l s a c r o s s f l a t t e r r a i n ; t h e b o t t o m i s composed o f u n s t a b l e s a n d and g r a v e l . Much o f t h e c h a n n e l i s m o d i f i e d and d y k e d ( s e e V-5 t o V - 2 , F i g . 2 ) . The C h i l l i w a c k R i v e r d r a i n s an a r e a o f 1,250 Jcm^. Mean m o n t h l y f l o w s , 1958 t o 1 9 6 2 , i n A p p e n d i x I a r e b a s e d on d a t a f r o m W a t e r R e s o u r c e s P a p e r s 128 and 1 3 1 , and on u n p u b l i s h e d d a t a f r o m t h e W a t e r R e s o u r c e s D i v i s i o n o f t h e D e p a r t m e n t o f F i g . 1. Lower F r a s e r v a l l e y a r e a i n s o u t h w e s t e r n B r i t i s h C o l u m b i a s h o w i n g A l o u e t t e , C h i l l i w a c k and S a l m o n R i v e r s y s t e m s . ft F i g . 2 . C h i l l i w a c k R i v e r and l o c a t i o n s o f s t a t i o n s . 6. F i g . 3 . U pper C h i l l i w a c k R i v e r i n a r e a o f l a r g e l o g j a m s , V-36 t o V-38. 7. Fig.4, Chilliwack River i n the region of V-17.5. F i g . 5 . C h i l l i w a c k R i v e r a t V - 5 . 5 and V - 6 . Note b r a i d e d c h a n n e l and u n s t a b l e g r a v e l b a r s . 9. N o r t h e r n A f f a i r s and N a t u r a l R e s o u r c e s . H i g h e s t m o n t h l y f l o w s o c c u r d u r i n g two p e r i o d s - May t o J u l y and O c t o b e r t o J a n u a r y . O v e r and above s e a s o n a l c h a n g e s , d i s c h a r g e f l u c t u a t e s s h a r p l y d u r i n g p e r i o d s o f one o r two d a y s . Mean m o n t h l y t e m p e r a t u r e s and r a n g e s i n t h e C h i l l i w a c k R i v e r , n e a r V - 1 3 , a r e p r e s e n t e d i n A p p e n d i x I I , B. A l o u e t t e R i v e r The S o u t h A l o u e t t e R i v e r o r i g i n a t e s a t t h e w e s t end o f A l o u e t t e L a k e , I t d r a i n s w e s t i n t o t h e P i t t R i v e r , a t r i b u t a r y o f t h e F r a s e r , F i g u r e 6 shows s t a t i o n s a l o n g t h e p o r t i o n o f t h e r i v e r w h i c h was s t u d i e d . The u p p e r r i v e r (A-16 t o A-9) r u n s down a s h a l l o w v a l l e y t h r o u g h b i g p o o l s and s t r e t c h e s s t r e w n w i t h l a r g e b o u l d e r s ( F i g . 7 A ) , The s t r e a m b o t t o m i s r e l a t i v e l y s t a b l e i n most a r e a s above A-9. From A-9 t o b e l o w A-6 t h e r i v e r p a s s e s t h r o u g h f l a t t e r r a i n i n a c h a n n e l w i t h an u n s t a b l e r o c k and g r a v e l b o t t o m . I n t h i s r e g i o n t h e r i v e r b e d h a s been m o d i f i e d c o n s i d e r a b l y t o p r e v e n t f l o o d i n g ( F i g . 7 B ) . Lowe r s e c t i o n s o f t h e A l o u e t t e (A-3 t o A-0) l i e i n meadowland ( F i g . 8 ) . The s t r e a m b o t t o m i s composed o f f i n e g r a v e l , s a n d and mud. L o g jams a r e a b s e n t a l o n g t h e f u l l l e n g t h o f t h e r i v e r . The A l o u e t t e R i v e r d r a i n s an a r e a o f 205 km^. A p p e n d i x I shows mean m o n t h l y f l o w s f r o m 1958 t h r o u g h 1962. R e c o r d s f o r 1958 and 1959 r e p r e s e n t s p i l l a g e o v e r t h e dam on t h e o u t l e t o f A l o u e t t e L a k e ( d a t a f r o m B.C. H y d r o and Power A u t h o r i t y ) . T hese v o l u m e s do n o t a c c u r a t e l y r e p r e s e n t t h e f l o w i n t h e r i v e r . S e v e r a l s m a l l t r i b u t a r i e s I n c o m b i n a t i o n w i t h g r o u n d s e e p a g e p r e v e n t t h e r i v e r f r o m d r y i n g up, hen c e f l o w s a r e n e v e r z e r o as F i g . 6 . A l o u e t t e R i v e r and l o c a t i o n s o f s t a t i o n s . F i g . 7 A . A l o u e t t e R i v e r a t A - 1 2 , c h a n n e l w i t h l a r g e b o u l d e r s on b o t t o m and w i t h s t r e t c h e s c o n t a i n i n g l a r g e p o o l s , B. A l o u e t t e R i v e r a t A-7, Note g r a v e l b o t t o m and m o d i f i e d c h a n n e l . 12 F i g . 8 . A l o u e t t e R i v e r a t A-2 i n meadow and f a r m l a n d . 13. i n d i c a t e d i n A p p e n d i x I . D i s c h a r g e f r o m A p r i l 1960 t o A p r i l 1 9 6 2 was o b t a i n e d f r o m W a t e r R e s o u r c e s P a p e r No.131 and u n p u b l i s h e d i n f o r m a t i o n f r o m t h e W a t e r R e s o u r c e s D i v i s i o n , T h e se d a t a were r e c o r d e d n e a r t h e town o f Haney and t h e r e f o r e r e p r e s e n t t h e t r u e f l o w o f t h e A l o u e t t e R i v e r . H i g h e s t , mean m o n t h l y d i s c h a r g e s o c c u r d u r i n g December and J a n u a r y . P e r i o d i c s p i l l o f e x c e s s w a t e r a t t h e dam on A l o u e t t e L a k e .'.during h e a v y r a i n s , r e s u l t s ' i n s h a r p f l u c t u a t i o n s o f f l o w a n d damage t o t h e r i v e r f a u n a . A p p e n d i x I I I c o n t a i n s mean m o n t h l y t e m p e r a t u r e s and r a n g e s ( A l o u e t t e R i v e r ) r e c o r d e d n.ear A-9. C. S a l m o n R i v e r The S a l m o n R i v e r r i s e s i n l o w wooded f a r m l a n d , n o r t h -e a s t o f L a n g l e y , B r i t i s h C o l u m b i a , a t an e l e v a t i o n o f a b o u t 100 m. F i g u r e 9 shows t h e l o c a t i o n o f s t a t i o n s a l o n g t h e S a l m o n R i v e r . The u p p e r t r i b u t a r i e s o f t h e r i v e r l i e i n s m a l l v a l l e y s and h a v e s t a b l e c h a n n e l s ( s e e S-12 t o S-19, and S-10 t o S-18, F i g . 9 ) . The m i d d l e s e c t i o n o f t h e r i v e r l i e s i n a l m o s t f l a t s u r r o u n d i n g s i n a sand, and g r a v e l b e d ( F i g . 1 0 A ) . B e l o w S-6 t h e r i v e r m e a n d e r s t h r o u g h meadows i n a mud and s a n d c h a n n e l . The o v e r a l l c h a r a c t e r o f t h e f l o w i s g e n t l e , w i t h much o f t h e r i v e r c o n s i s t i n g o f r i p p l e s and p o o l s l y i n g i n w e l l wooded a r e a s ( F i g . 1 0 B ) . The S a l m o n R i v e r d r a i n s an a r e a o f 83 km . Mean m o n t h l y f l o w s ( A p p e n d i x I , b a s e d on W a t e r R e s o u r c e s D i v i s i o n d a t a ) , r e v e a l a p e a k r u n - o f f b e t w e e n November and F e b r u a r y . D u r i n g w i n t e r l a r g e s h o r t t e r m f l u c t u a t i o n s i n d i s c h a r g e o c c u r , F i g . 9 . S a l m o n R i v e r s h o w i n g l o c a t i o n s o f s t a t i o n s . 1 5 . A B F i g . l O A . B. S a l m o n R i v e r a t S-9. R i f f l e and p o o l a r e a s a t S-14. 16. e.g. f r o m 0.85 m^ on J a n u a r y 23 t o 8.32 m^ on J a n u a r y 2 5 , 1960. A p p e n d i x IV c o n t a i n s mean m o n t h l y t e m p e r a t u r e s and r a n g e s ( S a l m o n R i v e r ) r e c o r d e d a t S-9. The t h r e e r i v e r s s t u d i e d c o n t a i n a v a r i e t y o f t y p e s o f h a b i t a t . T hese h a b i t a t s r a n g e f r o m s m a l l , l o w e l e v a t i o n t r i b u t a r i e s w i t h g e n t l e f l o w s , t o l a r g e r a p i d and t u r b u l e n t r i v e r s . B o t t o m c o n d i t i o n s i n e a c h s t r e a m v a r y f r o m u n s t a b l e s a n d and g r a v e l t o s t a b l e g r a v e l o r b o u l d e r s . 1 7 . MATERIALS AND METHODS Young coho s a l m o n and s t e e l h e a d t r o u t were s t u d i e d i n t h r e e l o w e r m a i n l a n d r i v e r s o f B r i t i s h C o l u m b i a , t h e C h i l l i w a c k R i v e r ( F i g . 2 ) , t h e A l o u e t t e R i v e r ( F i g . 6) and t h e S a l m o n R i v e r ( F i g . 9 ) , T w e l v e t o 16 s t a t i o n s p e r r i v e r were v i s i t e d a b o u t o n c e a month f r o m November, 195 9 , t o M a r c h , 1962. A r o u t i n e c o l l e c t i o n p r o c e d u r e was f o l l o w e d i f c o n d i t i o n s p e r m i t t e d . F i s h were a l w a y s c o l l e c t e d by s e i n i n g i n t h e S a l m o n R i v e r and w h e r e v e r p o s s i b l e i n t h e l a r g e r r i v e r s . I n a d d i t i o n C . I . L . " P r i m a C o r d " , a d e t o n a t i n g f u s e , and e l e c t r i c a l b l a s t i n g c a p s w ere u s e d t o c o l l e c t f i s h among t h e l a r g e b o u l d e r s and u n d e r l o g j a m s . The e x p l o s i v e was d e t o n a t e d i n t h e s t r e a m above a s e t s e i n e n e t ( F i g . l l ) and t h e f i s h d r i f t e d i n t o t h e s e i n e ; t h e b l a s t a r e a ( u s u a l l y s m a l l ) was s e a r c h e d ( F i g . l l ) . R e c o r d s , k e p t on a s t a n d a r d d a t a s h e e t and a s k e t c h map f o r e a c h s t a t i o n , i n c l u d e d number o f f i s h c o l l e c t e d and a p p r o x i m a t e a r e a o f s t r e a m b o t t o m s a m p l e d . T e m p e r a t u r e s were t a k e n . b y W e k s l e r c o n s t a n t t e m p e r a t u r e r e c o r d e r s . S t r e a m v e l o c i t i e s w e r e c a l c u l a t e d f r o m t h e r a t e o f movement o f f l o a t i n g o b j e c t s . T u r b i d i t y and b o t t o m c o m p o s i t i o n were r e c o r d e d on a c r u d e q u a n t i t a t i v e b a s i s . I n a d d i t i o n , d i s t r i b u t i o n d a t a b a s e d on c o l l e c t i o n s , were s u p p l e m e n t e d w i t h a s e r i e s o f d i v i n g o b s e r v a t i o n s i n t h e C h i l l i w a c k R i v e r . I n e a c h d i v i n g c e n s u s t h e number, b e h a v i o r and d i s t r i b u t i o n o f f i s h were r e c o r d e d i n t h r e e s t a n d a r d c e n s u s s t r i p s on t h e s t r e a m m a r g i n a t V-28 and V-30. ,Each s t r i p was 67 m (200 f t . ) l o n g and a b o u t one m e t e r w i d e . t F i g . 1 1 . C o l l e c t i o n o f f i s h w i t h d e t o n a t i n g f u s e . (See s m a l l e x p l o s i o n l e f t f o r e g r o u n d , u p p e r p h o t o g r a p h ) 19. R E S U L T S A. E a r l y L i f e H i s t o r y o f Coho and T r o u t 1. L o n g i t u d i n a l d i s t r i b u t i o n i n s t r e a m s H i g h e s t d e n s i t i e s o f young t r o u t and coho i n t h e C h i l l i w a c k o c c u r r e d i n t h e u p p e r r e a c h e s o f t h e r i v e r ( F i g . 1 2 ) . H i g h d e n s i t i e s r e c o r d e d i n F i g . 1 2 , (V-29 t o V - 3 8 ) , were n o t n e c e s s a r i l y r e p r e s e n t a t i v e o f t h e e n t i r e u p p e r r i v e r . However t h e t y p e o f h a b i t a t w h ere h i g h e s t numbers were r e c o r d e d ( l a r g e l o g j a m s ) was c h a r a c t e r i s t i c o f t h e u p p e r p a r t o f t h e C h i l l i w a c k . I n t h i s r e g i o n , t h e r i v e r b e d was more s t a b l e , and o f f e r e d b e t t e r s h e l t e r t o f i s h . F o r t h i s r e a s o n numbers o f f i s h a t s t a t i o n s V - 2 2 , V-28 and V-30 ( F i g . 1 2 ) , where l o g jams were a b s e n t , w e re h i g h e r t h a n t h o s e a t c o m p a r a b l e l o c a t i o n s ( V - 1 7 . 5 , Y-13 and V - 1 0 ) , i n t h e l o w e r h a l f o f t h e r i v e r (See F i g . 1 2 ) . I n t h e d o w n s t r e a m p o r t i o n s o f t h e C h i l l i w a c k ( b e l o w V-10) where t h e b o t t o m was u n s t a b l e and t h e c h a n n e l was b r a i d e d , numbers o f b o t h s p e c i e s w e r e l o w e s t . The r e l a t i v e numbers o f t r o u t and coho and t h e g e n e r a l d i s t r i b u t i o n p a t t e r n was t h e same i n w i n t e r as i n t h e p e r i o d f r o m M a r c h t o S e p t e m b e r ( F i g . 1 2 ) . A t most s t a t i o n s , coho were more a b u n d a n t t h a n s t e e l h e a d . D u r i n g t h e e a r l y summer, young coho were c a p t u r e d f u r t h e r d o w n s t r e a m t h a n s t e e l h e a d ; a s i d e f r o m t h i s , h o w e v e r , t h e two s p e c i e s were d i s t r i b u t e d i n a s i m i l a r f a s h i o n a l o n g t h e l e n g t h o f t h e r i v e r . I n t h e A l o u e t t e R i v e r , g r e a t e s t c o n c e n t r a t i o n s o f coho and t r o u t o c c u r r e d a t s t a t i o n s A-9, A-12, A-14 and A-15, ( F i g . 1 3 ) , a l l o f w h i c h a r e c h a r a c t e r i z e d by a c o v e r o f h e a v y b o u l d e r s ( F i g . 7 A ) . B e l o w A-9 i n a r e a s w i t h mud, s a n d o r u n s t a b l e g r a v e l b o t t o m , ( F i g . 7B and F i g . 8 ) , d e n s i t i e s were l o w ( F i g . 1 3 ) . D u r i n g I S T E E L H E A D D C O H O M A R I — S E P T 3 0 STATION NO F i g . 1 2 . D e n s i t y and d i s t r i b u t i o n o f you n g coho and s t e e l h e a d i n t h e C h i l l i w a c k R i v e r . ( D a t a c o m b i n e d f o r p e r i o d f r o m November 1959 t o M a r c h 1 9 6 2 ) . • 21. I O O -| S T E E L H E A D D C O H O MAR I-SEPT 30 Qm Q - O O O O -P | l 2 2 I 2 | OCT I - F E B 28 UJ _) LAJ I O O -ILJL - IOO - 5 0 O O O or a i rrr 14 15 16, STATION NO 20 KM F i g . 1 3 . D e n s i t y and d i s t r i b u t i o n o f you n g coho and s t e e l h e a d i n t h e S o u t h A l o u e t t e R i v e r . ( D a t a c o m b i n e d November 1959 t o M a r c h 1 9 6 2 ) . 22. t h e w i n t e r , d e n s i t y o f b o t h s p e c i e s was r e d u c e d t o a l o w l e v e l -p r o b a b l y due t o v i o l e n t w i n t e r f r e s h e t s w h i c h s c o u r e d t h e r i v e r p e r i o d i c a l l y . I n t h e p e r i o d M a r c h 1 t o S e p t e m b e r 3 0 , coho f r y were d i s t r i b u t e d f u r t h e r d o w n s t r e a m t h a n s t e e l h e a d . F i g u r e 13 shows t h a t , a l t h o u g h r e l a t i v e numbers o f t r o u t and coho v a r i e d a t d i f f e r e n t s t a t i o n s , b o t h s p e c i e s were d i s t r i b u t e d t o g e t h e r a l o n g much o f t h e r i v e r . H i g h e s t d e n s i t i e s o f y o u n g t r o u t and coho were r e c o r d e d i n t h e u p p e r p a r t o f t h e S a l m o n R i v e r , (S-9 t o S-18) and i n i t s u p s t r e a m t r i b u t a r y , ( S - 1 2 t o S-19, F i g . 14).. T h i s a r e a o f t h e r i v e r was c h a r a c t e r i z e d by s m a l l p o o l s and g e n t l e r i f f l e s ( F i g . 1 0 ) . Much o f t h e s h o r e l i n e was o v e r g r o w n and c o v e r e d w i t h f a l l e n t r e e s . B e l o w S-8 t h e b o t t o m was composed o f u n s t a b l e g r a v e l o r sand and mud; numbers o f coho and t r o u t i n t h i s a r e a were l o w e r ( F i g . 1 4 ) . I n e a r l y summer young coho were d i s t r i b u t e d down t h e S a l m o n R i v e r i n t o t h e mud b o t t o m p o r t i o n s o f t h e s t r e a m a t S-2 and S-3. Coho were more de n s e t h a n t r o u t a t a l l s t a t i o n s , h o w e v e r b o t h s p e c i e s o c c u r r e d t o g e t h e r o v e r most o f t h e l e n g t h o f t h e s t r e a m ( F i g . 1 4 ) , A v a r i e t y o f t y p e s o f p h y s i c a l h a b i t a t were s t u d i e d w i t h i n e a c h o f t h e t h r e e r i v e r s . F u r t h e r m o r e s i z e , b o t t o m and f l o w c o n d i t i o n s d i f f e r e d c o n s i d e r a b l y b e t w e e n t h e s t r e a m s . M e t h o d s o f s a m p l i n g were n o t t h e same i n a l l r i v e r s . I n s p i t e o f s u c h d i f f e r e n c e s i n h a b i t a t and s a m p l i n g t h e two s p e c i e s e x h i b i t e d c o m p a r a b l e d i s t r i b u t i o n p a t t e r n s i n e a c h o f t h e t h r e e r i v e r s ( F i g . 1 2 , 1 3 , and 1 4 ) . T r o u t and coho c o h a b i t e d t h e l o w e r s e c t i o n s o f t h e s t r e a m s i n l o w numbers and o c c u r r e d t o g e t h e r i n h i g h e s t numbers i n t h e more s t a b l e e n v i r o n m e n t s n e a r t h e h e a d - w a t e r s o r 23. I O C H 2 z z o r-< > UI IOCH | TROUT Q COHO APR I - OCT 31 M 5 0 F i g . 1 4 . D e n s i t y and d i s t r i b u t i o n o f young t r o u t and coho i n t h e Salmon R i v e r . ( D a t a c o m b i n e d November 1959 t o M a r c h 1 9 6 2 ) . 24. h e a d - w a t e r l a k e s . 2. M i c r o - h a b i t a t s o f u n d e r y e a r l i n q coho and t r o u t I n t h e C h i l l i w a c k and S a l m o n R i v e r s , young coho and t r o u t e x h i b i t e d s e a s o n a l c h a n g e s i n c h o i c e o f m i c r o h a b i t a t . I n t h e A l o u e t t e R i v e r i t was n o t c l e a r w h e t h e r o r n o t c h a n g e s i n c h o i c e o f m i c r o h a b i t a t o c c u r r e d a t d i f f e r e n t s e a s o n s . R e c e n t l y emerged t r o u t and coho i n t h e C h i l l i w a c k o c c u p i e d t h r e e t y p e s o f m i c r o h a b i t a t : s h a l l o w w a t e r i n s m a l l b a y s a t t h e s t r e a m m a r g i n , s m a l l s h a l l o w r i f f l e s , and s m a l l c r e v i c e s a b o u t t h e i n s h o r e p o r t i o n s o f l o g jams and l a r g e b o u l d e r s . The d i s t r i b u t i o n c h a n g e d d u r i n g summer and e a r l y f a l l . By l a t e f a l l m ost coho were l o c a t e d u n d e r l o g jams o r u n d e r o v e r h a n g i n g b a n k s and b o u l d e r s . S t e e l h e a d , i n l a t e f a l l , o c c u p i e d t h e r o c k y a r e a s , o f t h e s t r e a m m a r g i n and t h e l o g j a m s . F i g u r e 15 shows t h e d e n s i t y o f s t e e l h e a d and coho i n r e l a t i o n t o l o g j a m c o v e r d u r i n g t h r e e s e a s o n s . A p r o n o u n c e d s e a s o n a l r e d u c t i o n i n d e n s i t y o c c u r r e d i n a r e a s where h e a v y l o g c o v e r was a b s e n t . D u r i n g w i n t e r t h o s e f i s h u t i l i z i n g a r e a s where l o g c o v e r was . a b s e n t were f o u n d o n l y u n d e r o r among t h e b o u l d e r s . •In c a s e s where y o u n g coho were f o u n d among t h e l a r g e s t o n e s a t t h e s t r e a m m a r g i n , t h e i r d i s t r i b u t i o n d i d n o t e x t e n d f a r f r o m s h o r e . Young t r o u t on t h e o t h e r h and were s e e n and c o l l e c t e d among t h e b o u l d e r s as much as 8 m f r o m s h o r e . The s t e e l h e a d was a b l e t o o c c u p y a w i d e r v a r i e t y o f m i c r o h a b i t a t s • i n t h e C h i l l i w a c k r i v e r . The s p e c i e s c o m p o s i t i o n i n t h e two m i c r o h a b i t a t s d i s t i n g u i s h e d i n Figur.e 15 was a p p r o x i m a t e l y t h e same a t a l l s e a s o n s . 2 5 , COVER PRESENT ABSENT FISH PER lOO M 2 F i g . 15. D e n s i t i e s o f young coho and s t e e l h e a d i n a r e a s where c o v e r ( l o g j a m s ) i s p r e s e n t c o m p a r e d t o a r e a s where c o v e r i s a b s e n t . D a t a f r o m t h e C h i l l i w a c k R i v e r , November 1959 t o M a r c h 1962. 26. • I n t h e S a l m o n R i v e r r e c e n t l y emerged coho and t r o u t became. s e g r e g a t e d , w i t h r e g a r d t o m i c r o h a b i t a t , d u r i n g t h e f i r s t two months ( F i g . 1 6 ) . T r o u t d e n s i t y was h i g h e s t i n t h e r i f f l e s and l o w e r i n t h e open c h a n n e l h a b i t a t s and p o o l s t h r o u g h o u t M a y i J u n e , J u l y and A u g u s t . I n t h i s p e r i o d coho d e n s i t i e s w e r e h i g h e s t i n t h e p o o l s and l o w e s t i n t h e r i f f l e s . The d e n s i t y o f f i s h d e c r e a s e d t h r o u g h t h e f i r s t 10 months ( F i g . 1 6 ) . I n t h e f a l l and w i n t e r , when numbers o f f i s h were l o w e s t , t h e d e g r e e o f h a b i t a t s e g r e g a t i o n was r e d u c e d . By J a n u a r y and F e b r u a r y coho and t r o u t e x h i b i t e d t h e same p a t t e r n o f m i c r o h a b i t a t d i s t r i b u t i o n ( F i g . 1 6 ) , 3. S i z e . r e l a t i o n s h i p s o f f i s h i n t h e S a l m o n R i v e r Coho b e g a n t o emerge i n l a t e M a r c h , w h i l e t h e f i r s t t r o u t emerged i n e a r l y J u n e . B e c a u s e o f t h i s d i f f e r e n c e i n h a t c h i n g t i m e , coho were l a r g e r t h a n t r o u t i n J u n e and J u l y ( F i g . 1 7 ) . T h i s s i z e d i s c r e p a n c y d e c r e a s e d d u r i n g l a t e summer and autumn u n t i l , by w i n t e r , t h e s i z e r a n g e s were a l i k e ( F i g . 1 7 ) . V i r t u a l l y a l l coho m i g r a t e d o u t o f t h e S a l m o n R i v e r i n May and J u n e , a t age o f a b o u t 14 m o n t h s . T r o u t r e m a i n e d i n t h e r i v e r two y e a r s o r more. W i n t e r s a m p l e s o f , t r o u t ( F i g . 18) c o u l d be s e p a r a t e d i n t o u n d e r y e a r l i n g and " o n e - y e a r p l u s " f i s h u s i n g l e n g t h f r e q u e n c y p l o t s o f a l l t r o u t ( F i g . 19). F i s h o v e r 85 mm were d e s i g n a t e d as one y e a r o r more i n age. 4. Summary and comments F i e l d d a t a show t h a t t r o u t and coho o c c u r t o g e t h e r a l o n g t h e l e n g t h s o f t h e t h r e e s t r e a m s . They a r e h o w e v e r f o u n d i n d i f f e r e n t m i c r o h a b i t a t s w i t h i n t h e s t r e a m s . The d i f f e r e n c e s i n m i c r o h a b i t a t d i s t r i b u t i o n a r e most d i s t i n c t i n t h e s m a l l 27 300 200 l O O 200 IOO-IOO-l O O 50 50 H C O H O • T R O U T M A Y - J U N E J U L Y - A U G S E P T - O C T N O V - D E C J A N - F E B M A R - A P R I L LU —J _ i z -u_ — Z — O < U _1 o o CL 16. D e n s i t i e s o f young t r o u t and coho i n t h r e e t y p e s o f s t r e a m h a b i t a t , r i f f l e , o pen c h a n n e l and p o o l , d u r i n g s i x p e r i o d s o f t h e y e a r . D a t a f r o m t h e Sa l m o n R i v e r , November 1959 t o . M a r c h 1962. 28 1961 -62 TROUT C O H O 6 0 9 0 3 0 F O R K L E N G T H ( M M ) F i g . 1 7 . S i z e r e l a t i o n s h i p s o f u n d e r y e a r l i n g t r o u t and coho i n t h e S a l m o n R i v e r . Smoothed c u r v e s a r e b a s e d on m o v i n g a v e r a g e s o f t h r e e , d a t a b e f o r e s m o o t h i n g was p l o t t e d i n one mm l e n g t h i n t e r v a l s . 2 9 . 3 0 -iP2o-O O 1 0 -O •* i o o in O i O O I O i i FORK LENGTH (MM) F i g . 1 8 . L e n g t h f r e q u e n c i e s o f two o r m o r e . y e a r c l a s s e s o f t r o u t i n t h e S a l m o n R i v e r . D a t a a r e l u m p e d , O c t o b e r t o F e b r u a r y , i n c l u s i v e , f o r t h r e e w i n t e r s . 30. s t r e a m , t h e S a l m o n R i v e r , where t h e two s p e c i e s a r e s e g r e g a t e d i n r i f f l e s and p o o l s i n s p r i n g and summer, b u t , t o a l a r g e d e g r e e , o c c u r t o g e t h e r i n p o o l s i n w i n t e r . T h i s c a s e , where s e g r e g a t i o n o c c u r s a t one s e a s o n b u t n o t a t a n o t h e r , p r o v i d e s a good s i t u a t i o n where N i l s s o n ' s (1956)-c o n c e p t s may be t e s t e d . H o w e v e r , f i s h a r e d i f f i c u l t t o o b s e r v e and e n v i r o n m e n t a l c o n d i t i o n s c a n n o t be c o n t r o l l e d i n t h e n a t u r a l s t r e a m h a b i t a t . F o r t h i s r e a s o n t h e i n v e s t i g a t i o n was b r o u g h t i n t o t h e l a b o r a t o r y where f i s h c o u l d be s t u d i e d i n a s t r e a m a q u a r i u m ; t h e s e c o n d p a r t o f t h i s p a p e r d e s c r i b e s t h e e x p e r i m e n t a l f a c i l i t i e s and t h e m e t h o d s o f c o m p a r i n g t h e d i s t r i b u t i o n and b e h a v i o r o f t h e two s p e c i e s . F i e l d r e s u l t s a r e d i s c u s s e d i n t h e l i g h t o f e x p e r i m e n t a l ' d a t a . 3 1 . P a r t I I . EXPERIMENTAL STUDY MATERIALS AND METHODS 1 . H o l d i n g c o n d i t i o n s and f i s h The e x p e r i m e n t a l s t u d y was c o n d u c t e d b e t w e e n O c t o b e r 1962 and December 1963 i n t h e P u n t l e d g e P a r k H a t c h e r y a t C o u r t e n a y , B r i t i s h C o l u m b i a . The coho s a l m o n were o b t a i n e d f r o m L i t t l e R i v e r , a s m a l l s t r e a m n e a r Comox; t h e s t e e l h e a d were f r o m B i g Q u a l i c u m R i v e r n e a r P a r k s v i l l e . A l l f i s h were c a p t u r e d w i t h s e i n e n e t s . F i s h u s e d i n t h e f i r s t s e r i e s o f o b s e r v a t i o n s (November 1, 1962 t o F e b r u a r y 2 0 , 1963) were c a p t u r e d b e t w e e n O c t o b e r 15 and 2 2 , 1 9 6 2 . Coho u s e d i n e x p e r i m e n t s b e t w e e n A p r i l 19 and O c t o b e r 9, 1963 were s e i n e d A p r i l 11 t o 2 3 , 1 9 6 3 . T r o u t u s e d i n w o r k f r o m J u n e 9 t o O c t o b e r 9, 1963 were o b t a i n e d May 2 5 , 1 9 6 3 . S i z e r a n g e and mean f o r k l e n g t h s o f s a m p l e s o f f i s h , m e a s u r e d a t s e v e r a l i n t e r v a l s d u r i n g t h e w o r k , a r e g i v e n i n A p p e n d i x V. A l l f i s h were h e l d i n r u n n i n g w a t e r i n p a i n t e d p l y w o o d t r o u g h s , 40 cm w i d e and 220 cm l o n g . The t r o u g h s were h o u s e d i n b l a c k p l a s t i c c h a m b e r s and i l l u m i n a t e d w i t h f l u o r e s c e n t l i g h t s . F i s h u s e d i n s p r i n g and f a l l e x p e r i m e n t s were h e l d a t a 12 h r day l e n g t h ( s e e A p p e n d i c e s V I and V I I ; t h o s e u s e d i n : w i n t e r e x p e r i m e n t s were h e l d a t a 12 h r day - s u b s e q u e n t l y r e d u c e d t o 8 h r ( s e e A p p e n d i x V I I I ) . W a t e r u s e d i n h o l d i n g t r o u g h s and s t r e a m a q u a r i u m came f r o m t h e C i t y o f C o u r t e n a y m a i n s . W a t e r t e m p e r a t u r e i n c r e a s e d d u r i n g s p r i n g and e a r l y summer, d e c l i n e d g r a d u a l l y 3 2 . d u r i n g autumn and d r o p p e d t o 5°C o r l e s s i n w i n t e r ( F i g . 1 9 ) , S t r e a m a q u a r i u m t e m p e r a t u r e i n F i g . 1 9 w i l l be r e f e r r e d t o l a t e r i n t h e t e x t . The s h a r p r i s e and t w o - d a y • t e m p e r a t u r e p e a k ( F i g . 1 9 ) o c c u r r e d when a b r e a k i n t h e c i t y w a t e r m a i n f o r c e d t h e u s e o f an a l t e r n a t e s u p p l y . F i s h i n t h e t r o u g h s were f e d a d i e t 2 1 % by w e i g h t l i v e r , 6 5 % d r a i n e d c a n n e d s a l m o n , 8% b r e w e r ' s y e a s t , 6% p a b l u m and s a l t ( c a . one t e a s p o o n f u l f o r 300 g r . o f f o o d ) . T h i s f o o d m i x t u r e was g r o u n d i n t o a p a s t e , f r o z e n f o r s t o r a g e and f e d i n t h e f o r m o f f r o z e n s c r a p i n g s . F i s h were f e d once d a i l y and r e m a i n e d h e a l t h y t h r o u g h o u t t h e s t u d y . 2. D e s c r i p t i o n o f s t r e a m a q u a r i u m The s t r e a m a q u a r i u m was d e s i g n e d t o r e p r e s e n t a s h o r t s e c t i o n o f a s m a l l s t r e a m . D i m e n s i o n s o f t h e u n i t a r e 6.3 m l o n g , 2 m h i g h and 1.2 m w i d e ( F i g . 2 0 ) . The o b s e r v a t i o n f l u m e i s 5 m l o n g , 12 m w i d e and .7 m deep. M o s t o f t h e a q u a r i u m i s made o f 1" ( 2 . 5 cm) p l y w o o d s u p p o r t e d i n a 2" x ^" (5.1 x 0.6 cm) a n g l e i r o n f r a m e ( F i g . 2 0 ) . The windows a r e o f 5/8" (1.6 cm) p l a t e g l a s s . C o n s t r u c t i o n o f t h e a x i a l f l o w pump r e q u i r e d a s t r o n g , n o n - t o x i c r u s t - r e s i s t a n t m a t e r i a l . T h i s p o r t i o n o f t h e a q u a r i u m was t h e r e f o r e made o f 1/8" ( 0 . 3 cm) w e l d e d m i l d s t e e l l i n e d w i t h 1/8" ( 0 . 3 cm) f i b e r -g l a s s r e i n f o r c e d p l a s t i c . C u r r e n t i n t h e s t r e a m a q u a r i u m c o u l d be m a i n t a i n e d a t t h e d e s i r e d v e l o c i t y w i t h a v a r i a b l e s p e e d d r i v e m e c h a n i s m . W a t e r l e v e l was a d j u s t e d w i t h an i n l e t h o s e and a s e r i e s o f d r a i n p i p e s . W a t e r was c i r c u l a t e d f r o m t h e pumps a l o n g t h e t a p e r e d d u c t a t t h e b o t t o m o f t h e u n i t , up a t t h e end o p p o s i t e t h e mo-for 3 3 . C S P R I N G a , n j S U M M E R -i 1 r 1 1 1 1 1 1 T— 7 14 21 28 4 II 18 25 2 9 MAY JUNE JULY 20-IO-F A L L 8 15 SEPT 22 29 — i — 6 DAILY — M AXIMUM—J^ JJJJUJ^  OCT — ^ "—MINIMUM HOLDING TROUGH STREAM AQUARIUM Fi.g.19. T e m p e r a t u r e maxima and m i n i m a ( d a i l y ) i n t h e s t r e a m a q u a r i u m d u r i n g t h r e e s e a s o n s i n w h i c h t h e s t u d y was made ( s o l i d l i n e s ) . B r e a k s i n t h e l i n e i n d i c a t e t h a t no e x p e r i m e n t s were i n p r o g r e s s . D o t t e d , l i n e s r e p r e s e n t t e m p e r a t u r e maxima and m i n i m a i n h o l d i n g t r o u g h s p l o t t e d f o r two weeks o r more p r e v i o u s t o e x p e r i m e n t s . Details of the stream a q u a r l U ™ l + shown.! Experimental * « h a n i s m a r e n o t 35. and a l o n g t h e o b s e r v a t i o n f l u m e b a c k t o t h e pump. The a p p a r a t u s was l i g h t e d f r o m o v e r h e a d by p a r a l l e l f l u o r e s c e n t l i g h t s r u n n i n g t h e f u l l l e n g t h o f t h e o b s e r v a t i o n f l u m e . An o b s e r v a t i o n g a l l e r y o f b l a c k p o l y e t h y l e n e s h e e t i n g p a r a l l e l e d e a c h s i d e o f t h e t a n k . A d j u s t a b l e h o r i z o n t a l s l i t s i n t h e p l a s t i c f a c i n g , t h e a q u a r i u m p e r m i t t e d o b s e r v a t i o n f r o m t h e d a r k e n e d g a l l e r i e s , w i t h o u t d i s t u r b i n g t h e f i s h . 3. D e s c r i p t i o n o f e x p e r i m e n t a l e n v i r o n m e n t s B e h a v i o r and d i s t r i b u t i o n o f f i s h were c o m p a r e d i n a c o n t r o l e n v i r o n m e n t , i n f o u r d i f f e r e n t e n v i r o n m e n t a l g r a d i e n t s and i n a r i f f l e - p o o l e n v i r o n m e n t . The f o l l o w i n g i s a d e s c r i p t i o n o f " t h e s e a r r a n g e m e n t s and some o f t h e c o n d i t i o n s a s s o c i a t e d w i t h them. F i g u r e 21 shows l a t e r a l a s p e c t s and p l a n v i e w s o f c o n t r o l and f o u r g r a d i e n t s . I n t h e c o n t r o l s i t u a t i o n ( F i g . 2 1 a ) t h e d e p t h (28 t o 29 cm), b o t t o m g r a v e l (3 t o 6 cm), v e l o c i t y (22 t o 24 cm/sec) and l i g h t i n g c o n d i t i o n s were u n i f o r m a l o n g t h e l e n g t h o f t h e o b s e r v a t i o n f l u m e . T h e . l i g h t g r a d i e n t ( F i g . 21b) was p r o d u c e d w i t h a s e r i e s o f 10 p l e x i g l a s s s h e e t s . The f i r s t s h e e t was c l e a r , ' t h e r e m a i n i n g 9 s h e e t s were c o a t e d w i t h p r o g r e s s i v e l y more b l a c k p a i n t . L i g h t i n t e n s i t y i n t h e g r a d i e n t was m e a s u r e d w i t h a " p h o t o v o l t " m o d e l 514.M p h o t o m e t e r . T a b l e I shows t h e a v e r a g e l i g h t i n t e n s i t y ( l u x ) a l o n g t h e o b s e r v a t i o n f l u m e . B o t t o m c o n d i t i o n , d e p t h and v e l o c i t y were t h e same as i n t h e c o n t r o l . The c o v e r g r a d i e n t c o n s i s t e d o f f i v e g r o u p s o f s t o n e s ( F i g . 2 1 c ) . S t o n e s were e l e v a t e d above s m a l l d e p r e s s i o n s i n t h e 36. 1 W A T E R i S U R F A C E C U R R E N T IrXRECTION 2 d. C O N T R O L • D A R K - - - • • B R I G H T b. L I G H T 1 * r O o O O 0 o o o • o ° a 0 o o o o • « C . C O V E R d. D E P T H * 2 IS — 4 3 S E C T I O N e. D E P T H + V E L O C I T Y F i g . 2 1 . L a t e r a l and p l a n v i e w s o f c o n t r o l a r r a n g e -ment and l i g h t , c o v e r , d e p t h and d e p t h and v e l o c i t y g r a d i e n t s . L i g h t and c o n t r o l c o n d i t i o n s a p p e a r s i m i l a r e x c e p t f o r g r a d e d f i l t e r s u s e d t o p r o d u c e l i g h t g r a d i e n t . T a b l e 1. A v e r a g e l i g h t i n t e n s i t y ( L u x ) o v e r t h e l e n g t h o f t h e o b s e r v a t i o n f l u m e . Three r e a d i n g s , a c r o s s t h e t a n k , were a v e r a g e d f o r e a c h f i g u r e . R e a d i n g s were t a k e n on t h e b o t t o m w i t h no w a t e r i n t h e a q u a r i u m . S e c t i o n 1 i s a t t h e u p s t r e a m end o f .".the t a n k . M e t e r s f r o m U p s t r e a m End o f Tank 4.75 4.25 3.75 3.25 2.75 2.25 1.75 1.25 .75 .25 2.60 10.8 23.8 48.6 85.3 157.7 189.0 201.9 375.8 281.0 ( L u x ) T a b l e I I . D i m e n s i o n s o f s t o n e s ( i n cm) u s e d i n c o v e r g r a d i e n t . S E C T I O N 5 4 3 2 1 Range i n : L e n g t h 22-30 15-17 13-15 10-14 7-12 W i d t h 18-24 12-14 10-11 7-8 5-6 T h i c k n e s s 4-6 4-7 2-4 . 2-5 2-4 1.2- : 2 z i i — .6-: 2 0 2 0 5 .5-Q . U I Q 0 - - " I ' 1 1 ' 1 1 ' 1 1 — 2 0 0 2 0 O 2 0 O 2 0 WATER VELOCITY — CM PER SEC B F i g . 2 2 . V e l o c i t y p r o f i l e i n h o r i z o n t a l and s a g g i t a l p l a n e s i n d e p t h g r a d i e n t . U p p e r f i g u r e shows v e l o c i t i e s 10 cm above b o t t o m , e x c e p t i n S e c t i o n 1, r i g h t e n d , where p r o f i l e i s drawn f o r p o s i t i o n 5 cm above b o t t o m . Lower f i g u r e shows c o n d i t i o n s i n s a g g i t a l p l a n e (two c e n t e r r e a d i n g s a v e r a g e ) . A r r o w s i n d i c a t e d i r e c t i o n o f c u r r e n t , d o t t e d l i n e s r e p r e s e n t s c r e e n s , GO v O 1.2-,-2 z D - 1 ' 1 20 0 1 1 1 2 0 ( i — • — l D _ 20 C ) 20 < i T J 20 0 20 0 ^ • N i -. r- t • 1 ' 1 1 • 1 .5-I r-Q. UJ Q O-2 0 O 20 20 O WATER 2 0 20 O 20 VELOCITY— CM PER SEC B F i g . 2 3 . V e l o c i t y p r o f i l e i n d e p t h and v e l o c i t y g r a d i e n t . U p p e r f i g u r e shows v e l o c i t i e s 10 cm above b o t t o m . Lower shows v e l o c i t y i n s a g g i t a l p l a n e (two c e n t e r r e a d i n g s a v e r a g e d ) , A r r o w s i n d i c a t e d i r e c t i o n o f f l o w , ' d o t t e d l i n e s r e p r e s e n t s c r e e n s . 4^  o 4 1 . g r a v e l so t h a t e a c h h a d a 4 t o 6 cm c a v i t y u n d e r i t . The s i z e o f s t o n e s i n e a c h s e c t i o n v a r i e d somewhat as g i v e n i n T a b l e I I . To p r o d u c e t h e d e p t h g r a d i e n t f o u r s h e e t s o f p l y w o o d were a r r a n g e d s t e p - w i s e i n s e c t i o n s 1,. 2, 3 and 4 ( F i g . 2 1 d ) . S c r e e n s b e t w e e n t h e l e a d i n g and t r a i l i n g e d g es o f t h e s t e p s k e p t f i s h above them, b u t a l l o w e d an even f l o w o f w a t e r so t h a t v e l o c i t i e s were n e a r c o n s t a n t a t a l l d e p t h s ( F i g . 2 2 ) . The b o t t o m was c o v e r e d w i t h t h e same g r a v e l u s e d i n t h e c o n t r o l . I l l u m i n a t i o n was s l i g h t l y h i g h e r i n t h e u p s t r e a m end where t h e f l o o r p a n e l s were e l e v a t e d c l o s e r t o t h e l i g h t s o u r c e . The d e p t h + v e l o c i t y g r a d i e n t was p r o d u c e d by means o f a s l o p i n g f a l s e f l o o r ( F i g . 2 1 d ) . I t was n o t p o s s i b l e t o v a r y v e l o c i t y a l o n g t h e l e n g t h o f t h e o b s e r v a t i o n f l u m e w i t h o u t a l t e r i n g d e p t h o r w i d t h . D e t a i l s o f v e l o c i t y p r o f i l e s i n h o r i x o n t a l and s a g i t t a l p l a n e s a r e shown i n F i g . 23. The b o t t o m was c o v e r e d w i t h t h e same g r a v e l u s e d i n t h e c o n t r o l . L i g h t i n t e n s i t y on t h e r a i s e d u p s t r e a m end o f t h e f a l s e f l o o r was s l i g h t l y h i g h e r t h a n t h e d o w n s t r e a m l e n d . F i g u r e 24 r e p r e s e n t s t h e r i f f l e and p o o l e n v i r o n m e n t . T h i s a r r e n g e m e n t c a u s e d t h e c u r r e n t t o e x h i b i t c o m p l e x f l o w p a t t e r n s w h i c h a r e d e s c r i b e d b r i e f l y b e l o w : P o o l i n S e c t i o n 1, u p p e r 30 cm o f w a t e r c u r r e n t f l o w s d o w n s t r e a m a t a b o u t 20 cm/sec. I n l o w e r 10 t o 12 c m ' c u r r e n t c i r c u l a t e s u p s t r e a m a l o n g t h e b o t t o m a t 4 t o 5 cm/sec. R i f f l e s i n S e c t i o n s 2, 3 and 5, c u r r e n t 28 t o 30 cm/ s e c a t t h e s u r f a c e and 20 cm/sec a l o n g t h e b o t t o m . T e m p e r a t u r e i n t h e a q u a r i u m ( F i g . 19) was g o v e r n e d by s e a s o n a l c h a n g e s i n t h e t e m p e r a t u r e o f t h e w a t e r s u p p l y , F i g . 2 4 . H o r i z o n t a l ( u p p e r ) and l a t e r a l v i e w s o f e x p e r i m e n t a l r i f f l e and p o o l e n v i r o n m e n t . H o r i z o n t a l a r r o w i n d i c a t e s d i r e c t i o n o f c u r r e n t . V e r t i c a l a r r o w i n d i c a t e s w a t e r s u r f a c e . 4 3 . c o n d i t i o n s w i t h i n t h e b u i l d i n g and e n e r g y i n p u t f r o m t h e pump. Tank t e m p e r a t u r e c o u l d u s u a l l y be l o w e r e d by a d d i n g more new w a t e r . I t c o u l d be r a i s e d s l i g h t l y by c u t t i n g t h e i n p u t o f new w a t e r and h e n c e a l l o w i n g t h e p r o p e l l e r t o h e a t t h a t a l r e a d y i n t h e a q u a r i u m . These m e a s u r e s d i d n o t h o w e v e r p r o v i d e f u l l contr.a;!.. D u r i n g p e r i o d s o f f r e s h e t , t h e w a t e r s o u r c e became t u r b i d and c o n s e q u e n t l y new w a t e r c o u l d n o t be r u n i n t o t h e a q u a r i u m . I f t h e a i r t e m p e r a t u r e i n t h e b u i l d i n g was h i g h d u r i n g s u c h f r e s h e t s t h e a q u a r i u m t e m p e r a t u r e w o u l d r i s e . I f i t were l o w t h e a q u a r i u m t e m p e r a t u r e w o u l d f a l l ( s e e O c t o b e r 5 and 6, November 9, 10 and 1 1 , 1962 and J a n u a r y 8, 9, 10, 12 and 1 3 , 1 9 6 3 , F i g . 1 9 ) . T e m p e r a t u r e s w i t h i n t h e a q u a r i u m d e v i a t e d somewhat f r o m t h o s e o f t h e h o l d i n g t r o u g h s e a r l y i n t h e w i n t e r b u t a p p r o x i m a t e d them l a t e r ( F i g . 1 9 ) . D u r i n g t h e s p r i n g and summer e x p e r i m e n t s , w a t e r i n t h e s t r e a m a q u a r i u m r a n g e d f r o m 10° t o 16°C and was g e n e r a l l y warmer t h a n t h a t i n t h e h o l d i n g p o n d s . I n t h e autumn, t e m p e r a t u r e s i n t h e s t r e a m a q u a r i u m f o l l o w e d h o l d i n g t r o u g h t e m p e r a t u r e s and f l u c t u a t e d f r o m 9.4° t o 14,6°.C. F i g u r e 19 shows t h a t s t r e a m t a n k t e m p e r a t u r e s f l u c t u a t e d s e a s o n a l l y and d a i l y . They c o r r e s p o n d e d t o t h o s e o f t h e h o l d i n g t r o u g h s b u t were g e n e r a l l y h i g h e r . 4. E x p e r i m e n t a l p r o c e d u r e Day l e n g t h was m a i n t a i n e d a t 12 h r (06.00 t o 18.00 h r ) i n a l l e x p e r i m e n t s . T h i s p h o t o p e r i o d was n o t c o n s i s t e n t w i t h t h a t o f t h e h o l d i n g t r o u g h s d u r i n g t h e w i n t e r . I t was n e c e s s a r y h o w e v e r t o u s e a 12 h r day i n o r d e r t o g i v e t h e f i s h a 2 h r p e r i o d o f a d j u s t m e n t a f t e r t h e l i g h t s came on s i n c e t h e 4 4 . s u b s e q u e n t 10 h r o b s e r v a t i o n p e r i o d was n e c e s s a r y t o o b t a i n a d e q u a t e r e c o r d s on d i s t r i b u t i o n and b e h a v i o r . I n a l l e x p e r i m e n t s f i s h were h a n d l e d , f e d and o b s e r v e d as c o n s i s t e n t l y as p o s s i b l e . C u r r e n t was s t a r t e d and a d j u s t e d o v e r t h e same t i m e p e r i o d . I n e a c h e x p e r i m e n t , 40 f i s h were p l a c e d i n s t i l l w a t e r betwe'en 20.00 and 22.00 h r . A t 08.00 h r t h e f o l l o w i n g d a y , t h e c u r r e n t was s t a r t e d a t 14 cm/sec and r a i s e d i n two s t e p s t o 23 cm/sec i n c o n t r o l , l i g h t and c o v e r g r a d i e n t . D u r i n g t h e f i r s t day numbers o f f i s h i n e a c h s e c t i o n were r e c o r d e d a t h a l f o r one h o u r i n t e r v a l s . D u r i n g t h e s e c o n d day p o s i t i o n s o f a l l 40 f i s h were p l o t t e d 12 t o 16 t i m e s on o u t l i n e maps o f t h e s t r e a m b o t t o m . B e h a v i o r was r e c o r d e d i n a s e r i e s o f 10 m i n o b s e r v a t i o n s a l o n g t h e l e n g t h o f t h e t a n k . A p r e l i m i n a r y s t u d y r e v e a l e d t h a t t h e two s p e c i e s e x h i b i t e d c o m p a r a b l e components o f a g o n i s t i c b e h a v i o r . These were c o d e d so t h a t a s e q u e n c e o f e v e n t s c o u l d be r e c o r d e d a p p r o x i m a t e l y and q u a n t i f i e d . The f o l l o w i n g i s a l i s t o f b e h a v i o r e l e m e n t s and t h e i r code l e t t e r s , d e t a i l s o f b e h a v i o r w i l l be d e s c r i b e d l a t e r : -L - l a t e r a l d i s p l a y , F - f r o n t a l d i s p l a y , N - n i p , C •- c h a s e , WW - w i g wag d i s p l a y , TN - t h r e a t n i p , IM - i n t e n t i o n movement and F l - f l i g h t . A p r o t o c o l f o r a b e h a v i o r a l s e q u e n c e i s as f o l l o w s : F i s h "A" F i s h " B " "A" " B " L + N L + WW N — F l ; ? «-I n t h i s s e r i e s o f e v e n t s f i s h "A" d i s p l a y s i n l a t e r a l p o s t u r e 4 5 . t h a n n i p s "B". F i s h "B" d i s p l a y s l a t e r a l p o s t u r e t h e n e x h i b i t s a w i g wag d i s p l a y . "A" n i p s "B" a g a i n and "B" f l e e s . The a r r o w u n d e r " F l " i n d i c a t e s t h e d i r e c t i o n o f f l i g h t . F i s h , f e d t w i c e d a i l y i n t h e s t r e a m a q u a r i u m , were g i v e n 8 t o 10 c c o f b r i n e s h r i m p f r o z e n i n t o a b l o c k o f i c e . The f o o d was p l a c e d above t h e s c r e e n i n t h e u p s t r e a m end o f t h e t a n k where i t m e l t e d d u r i n g a p e r i o d o f 20 t o 60 m i n . Many o f t h e b r i n e s h r i m p r e l e a s e d k e p t c i r c u l a t i n g i n t h e c u r r e n t f o r s e v e r a l h o u r s , t h u s e v o k i n g f e e d i n g o v e r a p r o l o n g e d p e r i o d . The p r o c e d u r e f o l l o w e d i n s t u d y i n g f i s h i n t h e r i f f l e -p o o l a r r a n g e m e n t was s l i g h t l y d i f f e r e n t t h a n t h a t u s e d w i t h t h e g r a d i e n t s . Coho and s t e e l h e a d were s t u d i e d s e p a r a t e l y i n two s e r i e s and t h e n o b s e r v e d i n c o m b i n a t i o n i n a t h i r d s e r i e s . T a b l e I I I g i v e s numbers and s p e c i e s o f f i s h u s e d and t h e t i m e s c h e d u l e f o l l o w e d d u r i n g t h e t h r e e s e r i e s o f e x p e r i m e n t s . To b e g i n , e a c h s e r i e s o f f i s h was p l a c e d i n s t i l l w a t e r i n t h e a q u a r i u m a t a b o u t 20.00 h r . The f o l l o w i n g day t h e c u r r e n t was s t a r t e d and i n c r e a s e d s t e p w i s e t o t h e d e s i r e d v e l o c i t y by 09.00 h r . On e a c h s u c c e e d i n g d a y , u n t i l t h e f o u r t h , an a d d i t i o n a l l o t o f f i s h was added a t 08.00 h r . F e e d i n g and r e c o r d i n g s o f d i s t r i b u t i o n and b e h a v i o r were as p r e v i o u s l y d e s c r i b e d . E x p e r i m e n t s on f i s h i n t h e r i f f l e - p o o l a r r a n g e m e n t were c o n d u c t e d i n J u l y and November, 1 9 6 3 , w i t h u n d e r y e a r l i n g f i s h . E x p e r i m e n t s i n t h e c o n t r o l and g r a d i e n t s were done i n t h e s p r i n g , f a l l and w i n t e r . A p p e n d i c e s V I t o V I I I g i v e d e t a i l s o f g r a d i e n t e x p e r i m e n t s . 4 6 . T a b l e I I I . Number and s p e c i e s o f f i s h u s e d i n e x p e r i m e n t s i n r i f f l e and p o o l e n v i r o n m e n t . I n s e r i e s 1 coho (C) were u s e d a l o n e , i n s e r i e s 2, s t e e l h e a d (S) were u s e d a l o n e and i n s e r i e s 3 t h e two s p e c i e s were c o m b i n e d . S e r i e s 1 S e r i e s 2 S e r i e s 3 No. o f No. o f No. o f C S C S C S F i r s t Day 20 - 20 10 10 S e c o n d Day 40 - - 40 20 20 T h i r d Day 60 - - 60 30 30 F o u r t h Day 80 - - . 80 40 40 47. 5. S c o p e o f t h e r e s u l t s E x p e r i m e n t s were c o n d u c t e d so t h a t s e a s o n a l c h a n g e s i n b e h a v i o r and d i s t r i b u t i o n c o u l d be o b s e r v e d i n e a c h s p e c i e s and so t h a t d i f f e r e n c e s b e t w e e n s p e c i e s c o u l d be r e c o r d e d . S e a s o n a l and s p e c i e s c o m p a r i s o n s were made on g r o u p s o f one s p e c i e s o f f i s h a t a t i m e . The i n t e r a c t i o n o f t h e two s p e c i e s was s t u d i e d i n summer and w i n t e r c o n d i t i o n s i n c e r t a i n e x p e r i m e n t a l a r r a n g e m e n t s . D i s t r i b u t i o n a l d a t a a r e b a s e d on g r o u p s o f a n i m a l s . I f i n d i v i d u a l s h a d been t e s t e d s i n g l y , t h e p r e f e r r e d p o s i t i o n s may h a v e b e e n d i f f e r e n t t o t h o s e i n f e r r e d f r o m t h e d i s t r i b u t i o n o f a g r o u p . The maximum number a t a p a r t i c u l a r p o i n t i n a g r a d i e n t may n o t a l w a y s r e p r e s e n t t h e p r e f e r r e d p o s i t i o n . I n s p i t e o f t h i s l i m i t a t i o n h o w e v e r , g r o u p s o f f i s h were u s e d b e c a u s e f i e l d d a t a a r e b a s e d on t h e b e h a v i o r o f a n i m a l s i n g r o u p s . T e m p e r a t u r e s i n t h e h o l d i n g t r o u g h s and s t r e a m a q u a r i u m v a r i e d a t d i f f e r e n t s e a s o n s . These t e m p e r a t u r e s a l s o f l u c t u a t e d w i t h i n e a c h s e a s o n ( F i g . 1 9 ) . The day l e n g t h a t w h i c h f i s h were h e l d was s h o r t e r d u r i n g w i n t e r t h a n d u r i n g s p r i n g and autumn. The e f f e c t s o f v a r i a t i o n s i n t h e s e c o n d i t i o n s c o u l d n o t be f u l l y e v a l u a t e d . H o w e v e r , p h y s i c a l c o n d i t i o n s s u c h as b o t t o m c o n f i g u r a t i o n , b o t t o m g r a v e l , d e p t h , w a t e r v e l o c i t y and l i g h t c o n d i t i o n s were d u p l i c a t e d i n a l l c a s e s ; h e n c e t h e e n v i r o n m e n t was p a r t i a l l y b u t n o t f u l l y c o n t r o l l e d . < 4 8 . RESULTS 1. R e p l i c a t i o n o f e x p e r i m e n t s C e r t a i n e x p e r i m e n t s were r e p l i c a t e d d u r i n g t h e w i n t e r and t h e s p r i n g - s u m m e r s e r i e s . O b s e r v a t i o n s on t h e d i s t r i b u t i o n o f coho i n t h e c o n t r o l e n v i r o n m e n t were made t w i c e i n A p r i l and r e p e a t e d i n June 1963 ( F i g . 2 5 ) . E x p e r i m e n t s w i t h e a c h s p e c i e s i n t h e c o n t r o l , t h e c o v e r g r a d i e n t and d e p t h g r a d i e n t were r e p l i c a t e d u n d e r w i n t e r c o n d i t i o n s ( F i g , 25 and 2 6 ) . I n g e n e r a l , t h e d u p l i c a t e d i s t r i b u t i o n p a t t e r n s were s i m i l a r ( F i g s . 2 5 and 26). D i f f e r e n c e s b e t w e e n s p e c i e s were c o n s i s t e n t i n r e p e a t e d e x p e r i m e n t s i n t h e c o n t r o l and c o v e r g r a d i e n t d u r i n g t h e w i n t e r s e r i e s ( F i g . 2 5 ) . R e p e a t e d o b s e r v a t i o n s i n t h e d e p t h g r a d i e n t p r o d u c e d s i m i l a r d i s t r i b u t i o n p a t t e r n s f o r e a c h s p e c i e s b u t t h e d i f f e r e n c e s b e t w e e n coho and t r o u t i n t h e d e p t h g r a d i e n t were n o t c o n s i s t e n t ( F i g . 2 6 ) . A l t h o u g h r e p e a t e d e x p e r i m e n t s i n t h e d e p t h g r a d i e n t s d i d n o t g i v e d i s t r i b u t i o n s t h a t were i d e n t i c a l , t h e y d i d r e v e a l t h a t e a c h s p e c i e s e x h i b i t e d c h a r a c t e r i s t i c p a t t e r n s . I n t h e c o n t r o l and c o v e r g r a d i e n t t r o u t were d i s t r i b u t e d i n a skewed "U" s h a p e d p a t t e r n , coho i n a s i g m o i d p a t t e r n , u s u a l l y w i t h h i g h e s t means i n t h e f i r s t two s e c t i o n s o f t h e t a n k ( F i g . 2 5 ) . 2. S e a s o n a l c h a n g e s i n d i s t r i b u t i o n C o m p a r i s o n o f t h e d a t a o b t a i n e d d u r i n g t h e t h r e e s e a s o n a l s e r i e s o f e x p e r i m e n t s i n d i c a t e s t h a t numbers o f f i s h were more u n i f o r m a l o n g t h e l e n g t h o f t h e t a n k i n s p r i n g and summer t h a n i n f a l l o r w i n t e r ( F i g s . 25 and 2 6 ) . The g r e a t e s t d i f f e r e n c e s i n s e c t i o n a l a v e r a g e s o c c u r r e d i n f a l l o r w i n t e r . S u c h l a r g e v a r i a t i o n s i n t h e a v e r a g e number o f f i s h p e r s e c t i o n SPRING -SUMMER F A L L COHO STEELHEAD ©-WINTER 5 4 3 2 SECTION 25. D i s t r i b u t i o n s o f coho and s t e e l h e a d i n " c o n t r o l " and " c o v e r " g r a d i e n t s , d e s c r i b e d i n t e x t , d u r i n g t h r e e s e a s o n s . D o t s and c i r c l e s r e p r e s e n t mean number' o f f i s h ' p e r s e c t i o n o v e r a one day p e r i o d ( 1 0 - 1 5 o b s e r v a t i o n s ) . V e r t i c a l l i n e s i n d i c a t e r a n g e . S e c t i o n 1 r e p r e s e n t s t h e u p s t r e a m end o f t h e a q u a r i u m . 50. S P R I N G -S U M M E R FALL W I N T E R 5 4 3 2 S E C T I O N 26. D i s t r i b u t i o n s o f .coho and s t e e l h e a d i n " l i g h t " , " d e p t h " and " d e p t h and v e l o c i t y " g r a d i e n t s , as d e s c r i b e d i n t e x t , d u r i n g t h r e e s e a s o n s . C i r c l e s and d o t s r e p r e s e n t mean number o f f i s h p e r s e c t i o n ( 1 0 - 1 5 o b s e r v a t i o n s ) . V e r t i c a l l i n e s r e p r e s e n t r a n g e S e c t i o n 1 r e p r e s e n t s t h e u p s t r e a m end o f t h e a q u a r i u m 5 1 . were a r e s u l t o f t h e t e n d e n c y o f many i n d i v i d u a l s t o c o n g r e g a t e i n one p o r t i o n o f t h e t a n k u n d e r f a l l o r w i n t e r c o n d i t i o n s . I n s p r i n g b o t h s p e c i e s s c a t t e r e d a c r o s s t h e b o t t o m o f t h e t a n k as w e l l as a l o n g i t s f u l l l e n g t h . Young coho were s c a t t e r e d i n t h e s p r i n g and e a r l y summer b u t i n autumn and w i n t e r t h e y t e n d e d t o f o r m a g g r e g a t e s , w i t h some s o c i a l o r g a n i z a t i o n , n e a r t h e u p s t r e a m end o f t h e a q u a r i u m i n t h e c o n t r o l . a n d t h e c o v e r and l i g h t g r a d i e n t s ( F i g s . 2 5 and 2 6 ) . I n t h e d e p t h g r a d i e n t t h e s e a s o n a l t r e n d e x h i b i t e d by coho was a s h i f t t o t h e d e e p e s t s e c t i o n o f t h e t a n k d u r i n g w i n t e r . I n s p r i n g and e a r l y summer young s t e e l h e a d were s c a t t e r e d and d i s t r i b u t e d a l o n g t h e t a n k i n a s i m i l a r f a s h i o n t o t h e c o h o . I n f a l l and w i n t e r many t r o u t were a c t i v e , i . e . m o v i n g a b o u t i n t h e c o n t r o l , as w e l l as t h e c o v e r and l i g h t g r a d i e n t s ( A p p e n d i c e s V I I and V I I I ) . These f i s h were u s u a l l y m o v i n g and s e a r c h i n g a b o u t t h e s c r e e n i n s e c t i o n 1. The a p p a r e n t s e a s o n a l s h i f t i n t o t h e u p s t r e a m r e g i o n o f t h e a q u a r i u m i s i n d i c a t i v e o f w a n d e r i n g and s e a r c h i n g i n t h e u p s t r e a m e n d , r a t h e r t h a n a p r e f e r e n c e f o r i t . The numbers o f s t a b l e s t e e l h e a d p o s i t i o n s i n t h e u p s t r e a m s e c t i o n was u s u a l l y h a l f , o r l e s s , o f t h e numbers shown i n F i g u r e s 25 and 26 i n t h e c o n t r o l , d e p t h g r a d i e n t and l i g h t g r a d i e n t . C o n s i d e r i n g t h i s movement, i t a p p e a r s ' t h a t s t e e l h e a d w h i c h a r e n o t r o a m i n g assume a more s c a t t e r e d d i s t r i b u t i o n t h a n coho a l o n g t h e t a n k i n t h e c o n t r o l and t h e l i g h t g r a d i e n t . A c t i v i t y a c c o u n t s f o r t h e a p p a r e n t s e a s o n a l s h i f t o f f i s h i n t o s e c t i o n 1 i n t h e c o v e r g r a d i e n t . H o w e v e r , t h e h i g h numbers o f f i s h i n s e c t i o n 5 . 52. r e p r e s e n t s a p r e f e r e n c e f o r p o s i t i o n s u n d e r o r a r o u n d t h e l a r g e s t o n e s . S t e e l h e a d , l i k e c o h o , show a s t r o n g w i n t e r p r e f e r e n c e f o r t h e d e e p e s t s e c t i o n o f t h e d e p t h g r a d i e n t . T r o u t e x h i b i t e d . no s e a s o n a l change i n d i s t r i b u t i o n i n t h e d e p t h + v e l o c i t y g r a d i e n t ( F i g . 2 6 ) . 3. C o m p a r i s o n o f s p e c i e s - i n g r a d i e n t s I n e x p e r i m e n t s c o n d u c t e d u n d e r s p r i n g and summer c o n d i t i o n s , t h e d i s t r i b u t i o n s o f coho and s t e e l h e a d were s i m i l a r i n e a c h o f t h e f i v e e x p e r i m e n t a l c o n d i t i o n s ( F i g s . 2 5 and 2 6 ) . H owever, i n autumn and w i n t e r e x p e r i m e n t s , t h e d i s t r i b u t i o n d i f f e r e n c e s b e t w e e n t h e s p e c i e s were g r e a t e r . E n v i r o n m e n t a l p r e f e r e n c e s , as i n f e r r e d f r o m e x p e r i m e n t a l d i s t r i b u t i o n s , were most s i m i l a r i n s p r i n g and e a r l y summer, t h e s e a s o n i n w h i c h s e g r e g a t i o n was most p r o n o u n c e d i n t h e S a l m o n R i v e r . D i s t r i b u t i o n s and i n f e r r e d p r e f e r e n c e s were d i v e r g e n t d u r i n g f a l l and w i n t e r ( F i g s . 25 and 2 6 ) , t h e s e a s o n s i n w h i c h p o p u l a t i o n s o v e r l a p p e d most i n t h e S a l m o n R i v e r ( s e e F i g . 1 6 ) . D u r i n g t h e s e a s o n when l a b o r a t o r y d i s t r i b u t i o n s a r e s i m i l a r t h e two s p e c i e s meet and i n t e r a c t i n t h e n a t u r a l s t r e a m e n v i r o n m e n t . I n t h e s e a s o n s when e x p e r i m e n t a l d i s t r i b u t i o n s a r e d i f f e r e n t , t h e two s p e c i e s a r e more c o m p a t i b l e i n t h e n a t u r a l s t r e a m e n v i r o n m e n t . D i f f e r e n t e n v i r o n m e n t a l r e s p o n s e s i n t h e l a b o r a t o r y , ( i . e . r e s p o n s e t o c o v e r and d e p t h , F i g s . 27, 28, 31 and 3 2 ) , a r e i n d i c a t i v e o f t h e m e c h a n i s m s t h a t a l l o w t h e two s o e c i e s t o c o e x i s t i n c l o s e p r o x i m i t y i n f a l l and w i n t e r . I n t h e c o v e r and d e p t h g r a d i e n t s y oung f i s h u t i l i z e d s t o n e s and p o o l s p a c e i n a s i m i l a r f a s h i o n i n s p r i n g and summer b u t n o t i n w i n t e r . Coho, 6 t o 8 weeks o l d , s c a t t e r e d among t h e 5 3 . s t o n e s w h i c h f o r m e d t h e c o v e r g r a d a t i o n ( F i g . 2 7 ) . D u r i n g s p r i n g a b o u t one t h i r d (126 o f a t o t a l o f 412) o f t h e p o s i t i o n s t a k e n by coho were i m m e d i a t e l y d o w n s t r e a m f r o m stones'. Many p o s i t i o n s r e c o r d e d were among t h e s t o n e s . I n w i n t e r 126 o f 390 p o s i t i o n s o c c u p i e d were i m m e d i a t e l y d o w n s t r e a m f r o m t h e s t o n e s . F i s h were h o w e v e r r e c o r d e d a t f e w e r p o s i t i o n s among t h e r o c k s ( F i g . 27) i n t h e w i n t e r . Those t h a t were n o t i n t h e s h e l t e r o f s t o n e s were a t p o s i t i o n s a t t h e s i d e s o f t h e t a n k . S t e e l h e a d , 3 t o 5 weeks o l d , d i s t r i b u t e d t h e m s e l v e s i n t h e same p a t t e r n as t h e 6 t o 8 week coho ( F i g . 2 8 ) . D u r i n g s p r i n g , one t h i r d o f t h e s t e e l h e a d p o s i t i o n s were i m m e d i a t e l y d o w n s t r e a m f r o m s t o n e s . As i n t h e c a s e o f c o h o , t h e o t h e r p o s i t i o n s were s c a t t e r e d among t h e s t o n e s , and none was u n d e r them ( F i g . 2 8 ) . D u r i n g t h e f a l l , a l a r g e number o f young t r o u t were a c t i v e and r e m a i n e d i n t h e u p s t r e a m end o f t h e a q u a r i u m ( F i g . 2 8 ) . One s i x t h o f t h e p o s i t i o n s r e c o r d e d were i m m e d i a t e l y d o w n s t r e a m f r o m s t o n e s , o n l y s i x p o s i t i o n s w e r e u n d e r them ( F i g . 2 8 ) . I n w i n t e r o n e - f o u r t h o f t h e p o s i t i o n s r e c o r d e d were u n d e r s t o n e s and a p p r o x i m a t e l y o n e - e i g h t h were d o w n s t r e a m f r o m them ( F i g . 2 8 ) . I t i s e v i d e n t t h a t t h e d i s t r i b u t i o n s o b s e r v e d i n t h e s p r i n g c o n d i t i o n w o u l d r e s u l t i n a h i g h d e g r e e o f c o n t a c t b e t w e e n s p e c i e s i f t o g e t h e r i n a c o v e r g r a d i e n t . H o w e v e r , i n Howe v e r , i n w i n t e r t h e t e n d e n c y o f t r o u t t o h i d e u n d e r s t o n e s w o u l d , t o a d e g r e e , i s o l a t e them f r o m coho w h i c h do. n o t do so ( F i g s . 27 and 2 8 ) . A s e c o n d c a s e o f t r o u t and coho u s i n g t h e same s p a c e i n a d i f f e r e n t manner, i n w i n t e r , o c c u r s i n t h e d e p t h g r a d i e n t . C O H O MAY 28 OCT 3* H JAN 25 1CCVER GRADIENT — P L A N VIEW 0 j 0 ' • ::.0 'O-.-'- ;:vO..V-^  >..oV. DIRECTION OF FLOW <= e: •a ' •;• P. •o • ,. .• • vQ ... • ; aO • \ • • •%Q *£>•••: ' '•.[ la » — . . ,€>:• SECTION F i g . 2 7 . D i s t r i b u t i o n o f c o h o : i n c o v e r g r a d i e n t d u r i n g t h r e e s e a s o n s . L o c a t i o n s o f 40 f i s h d u r i n g 10 c o m b i n e d o b s e r v a t i o n s a r e g i v e n . G r o u p s o f d o t s r e p r e s e n t same f i s h o c c u p y i n g same l o c a t i o n r e p e a t e d l y o r d i f f e r e n t f i s h , i n t h i s and s u c c e e d i n g f i g u r e s o f t h i s t y p e . P o i n t s w i t h i n t h e s t o n e o u t l i n e s r e p r e s e n t f i s h u n d e r s t o n e s . D o t t e d l i n e s r e p r e s e n t s c r e e n s a t ends o f a q u a r i u m i n t h i s f i g u r e and s u c c e e d i n g f i g u r e s o f t h i s t y p e . STEELHEAD !• -77-1 •••;>• 10 MAY 30 - . v — 1 • '• v—' U;"C ;o "O ] C O V E R GRADIENT j — P L A N VIEW •o SEPT 29 j ^ ;o : 0 • D ' ' 0 . • 0 • • 0 =.Q •• . a - ":. 1% IP • CP ••• • 0 . ; . i—: -J • : : , ••• r : , JAN 27 • Q CD G3 CD • o r= :—:—:—•• • •i-.s • $ • • • - o •o • j • , • ; • -'••-•••5 SECTION F i g . 2 8 . D i s t r i b u t i o n o f s t e e l h e a d i n c o v e r g r a d i e n t d u r i n g t h r e e s e a s o n s . L o c a t i o n s o f 40 f i s h d u r i n g 10 c o m b i n e d o b s e r v a t i o n s a r e g i v e n . P o i n t s w i t h i n t h e s t o n e o u t l i n e s r e p r e s e n t f i s h u n d e r s t o n e s . 56. F i g u r e s 29 and 30 show t h a t t h e h o r i z o n t a l d i s t r i b u t i o n s o f coho and s t e e l h e a d a r e s i m i l a r i n s p r i n g , b u t d i f f e r e n t i n w i n t e r . T a b l e I V shows t h a t i n J u n e t h e r e i s a s i g n i f i c a n t d i f f e r e n c e i n t h e numbers o f young coho and t r o u t i n t h e u p p e r and l o w e r h a l v e s o f s e c t i o n s 4 and 5 ( C h i - s q u a r e t e s t s ) . S e g r e g a t i o n i s h o w e v e r more p r o n o u n c e d d u r i n g w i n t e r . T h i s i n c r e a s e i n s e g r e g a t i o n i s p r i m a r i l y due t o a change i n t h e b e h a v i o r o f s t e e l h e a d . V e r t i c a l d i s t r i b u t i o n o f b o t h s p e c i e s ( F i g s , 31 and 32) c o n s i d e r e d i n c o n j u n c t i o n w i t h h o r i z o n t a l d i s t r i b u t i o n s ( F i g s . 29 and 30) show t h a t i n t h e w i n t e r most s t e e l h e a d were s p r e a d o v e r t h e b o t t o m i n t h e deep s e c t i o n . On t h e o t h e r h a n d most coho were d i s t r i b u t e d a t t h e e d g e s n e a r t h e b o t t o m o r i n l o o s e a g g r e g a t i o n s up e a c h s i d e o f t h e d e e p e s t s e c t i o n . I n d i v i d u a l s o f b o t h s p e c i e s d e f e n d e d a r e a s a l o n g t h e d o w n s t r e a m edge o f e a c h d e p t h z o n e . A l a r g e amount o f i n t r a s p e c i f i c f i g h t i n g o c c u r r e d i n t h e s e a r e a s . When t h e two s p e c i e s were p l a c e d t o g e t h e r d u r i n g summer ( F i g . 33) i n e q u a l numbers t h e amount o f i n t r a s p e c i f i c and i n t e r s p e c i f i c a g g r e s s i o n was h i g h ( T a b l e V ) . D u r i n g w i n t e r when t r o u t and coho were p l a c e d i n t h e d e p t h g r a d i e n t t o g e t h e r ( F i g . 34) t h e y were s e g r e g a t e d s p a t i a l l y as a l r e a d y , d e s c r i b e d . I n t r a s p e c i f i c and i n t e r s p e c i f i c a g g r e s s i o n were l o w e r t h a n u n d e r summer c o n d i t i o n s ( T a b l e V ) . I n t e r s p e c i f i c f i g h t i n g was n o t d i s p r o p o r t i o n a t e l y l o w e r as e x p e c t e d on t h e b a s i s o f s p a t i a l s e g r e g a t i o n - . However p r a c t i c a l l y a l l i n t e r s p e c i f i c c o n t e s t s o c c u r r e d a t t h e d ownstream edges o f d e p t h z o n e s i n s e c t i o n s 3 and 4. Few a g g r e s s i v e c o n t e s t s were r e c o r d e d b e t w e e n t h e coho i n a g g r e g a t i o n s a t t h e s i d e o f ..the deep s e c t i o n and t r o u t on t h e b o t t o m . 57. T a b l e I V . Numbers o f coho (C) and s t e e l h e a d . (S) i n u p p e r and l o w e r h a l v e s o f s e c t i o n s 4 and 5 i n t h e d e p t h gradient.': i n e a r l y summer and w i n t e r (j.uhe and J a n u a r y ) . J u n e J a n u a r y C S C S U p p e r h a l f 124 75 168 24 L ower h a l f 103 145 161 281 COHO DEPTH GRADIENT — PLAN VIEW JUNE 26 OCT 3 JAN IO DIRECTION OF FLOW < e : F i g . 2 9 . D i s t r i b u t i o n o f coho i n d e p t h g r a d i e n t d u r i n g t h r e e s e a s o n s . L o c a t i o n s o f 40 f i s h d u r i n g 10 c o m b i n e d o b s e r v a t i o n s a r e g i v e n . Rows o f p o i n t s a t s e c t i o n b o u n d a r i e s r e p r e s e n t f i s h o c c u p y i n g p o s i t i o n s a l o n g t h e edges o f t h e d e p t h z o n e s . STEELHEAD JUNE 22 OCT 5 JAN 12 3 SECTION DEPTH GRADIENT — PLAN VIEW DIRECTION OF FLOW « 30.. D i s t r i b u t i o n o f s t e e l h e a d i n d e p t h g r a d i e n t d u r i n g t h r e e s e a s o n s . L o c a t i o n s o f 40 f i s h d u r i n g 10 c o m b i n e d o b s e r v a t i o n s a r e g i v e n . Rows o f p o i n t s a t s e c t i o n b o u n d a r i e s r e p r e s e n t f i s h o c c u p y i n g p o s i t i o n s a l o n g edges o f d e p t h z o n e s . C O H O JUNE 26 DEPTH GRADIENT — L A T E R A L VIEW OCT 3 JAN IO V — -i DIRECTION OF FLOW < e i S E C T I O N F i g . 3 1 . D i s t r i b u t i o n o f c o h o , l a t e r a l v i e w , i n d e p t h g r a d i e n t d u r i n g t h r e e s e a s o n s . L o c a t i o n s o f 40 f i s h i n 10 c o m b i n e d o b s e r v a t i o n s a r e g i v e n . S T E E L H E A D JUNE 22 -asDEPTH GRADIENT — L A T E R A L VIEW OCT 5 JAN 12 4" '•• DIRECTION OF FLOW < €1 SECTI ON F i g . 3 2 . D i s t r i b u t i o n o f s t e e l h e a d , l a t e r a l v i e w , i n d e p t h g r a d i e n t d u r i n g t h r e e s e a s o n s . L o c a t i o n s o f 40 f i s h i n 10 c o m b i n e d o b s e r v a t i o n s a r e g i v e n . J U N E 2 8 COHO DEPTH GRADIENT — P L A N VIEW STEELHEAD COHO STEELHEAD >—— 3 SECTION — LATERAL VIEW DIRECTION OF FLOW < €1 -I Fig.33. . R e l a t i o n s h i p o f coho and s t e e l h e a d c o m b i n e d i n d e p t h g r a d i e n t d u r i n g summer c o n d i t i o n s . L o c a t i o n s o f 20 coho p l u s 20 s t e e l h e a d . i n 10 c o m b i n e d o b s e r v a t i o n s a r e g i v e n . JAN 17 COHO STEELHEAD DEPTH GRADIENT — P L A N VIEW COHO STEELHEAD L A T E R A L VIEW DIRECTION OF FLOW < €1 3 SECTION Fig.34. R e l a t i o n s h i p o f coho and s t e e l h e a d c o m b i n e d i n d e p t h g r a d i e n t d u r i n g w i n t e r c o n d i t i o n s . L o c a t i o n s o f 20 coho p l u s 20 s t e e l h e a d i n 10 c o m b i n e d o b s e r v a t i o n s a r e g i v e n . 64. T a b l e V. A g g r e s s i v e c o n t e s t s p e r f i s h p e r 100 m i n u t e s d u r i n g J u n e and J a n u a r y 1963. S y m b o l s a r e as f o l l o w s : C - c o h o , S - s t e e l h e a d , O C - coho a t t a c k i n g c o h o , OS- - coho a t t a c k i n g s t e e l h e a d , S»S - s t e e l h e a d a t t a c k i n g s t e e l h e a d and S«C - s t e e l h e a d a t t a c k i n g c o h o . D a t e N u m b e r o f F i s h C o n t e s t s M i n u t e s _ • - C S O C O S S'S S'C O b s e r v a t i o n J u n e 28 20 20 12.7 6.1 6.3 1.3 90 J a n u a r y 17 20 20 4.4 1.3 2.4 0.9 90 65. 4. D e s c r i p t i o n o f a g o n i s t i c b e h a v i o r Young coho and s t e e l h e a d d i s p l a y u s i n g a number o f s i m i l a r p o s t u r e s and movements. These d i s p l a y s and movements a r e l i s t e d i n t h e " M a t e r i a l s and M e t h o d s " . B e f o r e any c l a s s i f i c a t i o n and q u a n t i f i c a t i o n o f t h e b e h a v i o r components a r e a t t e m p t e d , i t i s e s s e n t i a l t o u n d e r s t a n d t h e b a s i s o f t h e c l a s s i f i c a t i o n . E a c h o f t h e d i f f e r e n t c omponents a p p e a r s i n a v a r i e t y o f f o r m s w h i c h a p p e a r t o be r e l a t e d t o t h e i n t e n s i t y o f t h e b e h a v i o r . I n t h e f o l l o w i n g d e s c r i p t i o n o f b e h a v i o r e a c h component i s d e s c r i b e d and t h e v a r i a b i l i t y i n d i c a t e d . I t i s a c k n o w l e d g e d t h a t t h i s t y p e o f f i s h b e h a v i o r c o u l d be c l a s s i f i e d on a more r e f i n e d s c a l e by q u a n t i f y i n g i n t e n s i t y o r d u r a t i o n o f c o m p o n e n t s . S u c h was n o t f e a s i b l e i n t h i s s t u d y b e c a u s e o f t h e number o f f i s h t h a t were o b s e r v e d and t h e r a p i d i t y o f t h e a c t i o n . L a t e r a l d i s p l a y was d e s c r i b e d by F a b r i c i u s ( 1 9 5 3 ) and K a l l e b e r g ( 1 9 5 8 ) . T h i s v a r i e d f r o m a s i m p l e e r e c t i o n o f t h e d o r s a l f i n , l a s t i n g one o r two s e c o n d s t o a p r o l o n g e d e r e c t i o n o f d o r s a l , and p a i r e d f i n s and a l o w e r i n g o f t h e b a s i h y a l a p p a r a t u s f o r 10 o r 15 s e c o n d s ( F i g . 3 5 ) . The d o r s a l l i n e o f t h e b ody was e i t h e r s t r a i g h t o r s l i g h t l y r e c u r v e d . The c r i t e r i o n f o r a l a t e r a l d i s p l a y was t h e e r e c t e d d o r s a l f i n and t h e l i n e o f t h e b a c k . L a t e r a l d i s p l a y s were s i m i l a r f o r t h e two s p e c i e s , a l t h o u g h t h e d i s p l a y was u s u a l l y more o b v i o u s i n coho w h i c h possess., l a r g e m e d i a n f i n s w i t h l o n g , c o l o r e d e d g es ( F i g . 3 5 C ) . The f r o n t a l d i s p l a y , d e s c r i b e d by F a b r i c i u s (1953) and K a l l e b e r g ( 1 9 5 8 ) v a r i e d f r o m a p o s t u r e i n w h i c h t h e b a c k was s l i g h t l y a r c h e d , t h e d o r s a l f i n c o m p r e s s e d and t h e b a s i h y a l e x t e n d e d f o r one o r two s e c o n d s ( F i g . 3 6 A ) , t o a p o s t u r e i n w h i c h 6 6 . F i g . 3 5 A . Coho, c a 10 months o l d , i n l a t e r a l t h r e a t p o s t u r e . B. S t e e l h e a d , c a 8 months o l d , i n l a t e r a l p o s t u r e ( s e e f i s h on t h e l e f t ) . F i s h on t h e r i g h t i n f r o n t a l t h r e a t p o s t u r e o f l o w i n t e n s i t y . C. Coho, c a 2 months o l d , i n l a t e r a l t h r e a t p o s t u r e . 67 i g . 3 6 A . Coho, c a 2 months o l d , i n f r o n t a l t h r e a t p o s t u r e o f l o w i n t e n s i t y ( r i g h t ) . C o ho, c a 2 months o l d , i n w wag p o s t u r e ( l e f t ) . B. Coho, c a 2 months o l d . i n w i g wag ( l e f t ) and l a t e r a t h r e a t p o s t u r e ( r i g h t ) . 1 68. t h e b a c k was s t r o n g l y a r c h e d , t h e d o r s a l f u l l y c o m p r e s s e d and t h e b a s i h y a l w e l l e x t e n d e d f o r l o n g e r ( u n m e a s u r e d ) p e r i o d s . I n t h e w i g wag d i s p l a y f i s h a d o p t e d a l a t e r a l p o s t u r e , u s u a l l y w i t h m e d i a n and p a i r e d f i n s w e l l e x t e n d e d , and swam w i t h a c c e n t u a t e d l a t e r a l movements w i t h t h e h e a d down and t h e body a t a 20 t o 30 d e g r e e a n g l e f r o m h o r i z o n t a l ( F i g . 3 6 B ) . I n t h i s d i s p l a y t h e amount o f f i n e r e c t i o n v a r i e d . The a n g l e o f body i n c l i n a t i o n and t h e a m p l i t u d e o f swimming movement was l o w i n d i s p l a y s t h a t were o f s h o r t d u r a t i o n . I n w i g wag d i s p l a y s ( i n f e r r e d t o be o f h i g h i n t e n s i t y ) t h e f i n s were e r e c t e d f u l l y , t h e a n g l e o f i n c l i n a t i o n was s t e e p ( n e a r 30 d e g r e e s ) and l a t e r a l movements were a c c e n t u a t e d . The c r i t e r i o n f o r a w i g wag d i s p l a y was t h e e r e c t e d f i n s , t h e i n c l i n e d p o s t u r e and a c c e n t u a t e d swimming movements. As i n t h e c a s e o f t h e l a t e r a l d i s p l a y , t h e w i g wag was more s t r i k i n g i n coho t h a n t r o u t b e c a u s e o f d i f f e r e n c e s i n f i n s h a p e and c o l o r . C h a s i n g i n v o l v e d c h a s e and f l i g h t . I f one f i s h d a r t e d a f t e r a n o t h e r and p u r s u e d i t p a s t t h e p o i n t f r o m w h i c h i t f l e d i t was d e s i g n a t e d as c h a s i n g . P u r s u i t s r a n g e d f r o m s l o w s h o r t e x c u r s i o n s o f 20 o r 30 cm t o l o n g c h a s e s o f 2 o r 3 m. N i p s were t h o s e b i t e s i n w h i c h t h e r e a p p e a r e d t o be a d e f i n i t e c o n t a c t ( F i g . 3 7 ) . ' I n some i n s t a n c e s f i s h o n l y "mouthed" t h e i n d i v i d u a l a t t a c k e d . I n o t h e r c a s e s t h e b i t e s w ere so h a r d t h a t t h e a n i m a l s seemed t o be b r i e f l y s t u c k t o g e t h e r . T h r e a t n i p s were n i p s w h i c h were a i m e d a t o t h e r f i s h . S u c h b i t e s a p p e a r e d t o be i n h i b i t e d and h e n c e m i s s e d c o n t a c t by as much as 20 o r 30 cm. I n some c a s e s a f i s h swam a s h o r t F i g . 3 7 . N i p p i n g i n t h e p a i r o f f i s h on t h e l e f t . P i c t u r e t a k e n a f r a c t i o n o f a s e c o n d b e f o r e t h e f r o n t f i s h was n i p p e d . S e c o n d p a i r o f f i s h ( r i g h t s i d e ) i n c h a r a c t e r i s t i c l a t e r a l p o s t u r e s . 70. d i s t a n c e and n i p p e d i n t h e d i r e c t i o n o f a n o t h e r . I n o t h e r s i t u a t i o n s t h e y t u r n e d t h e i r h e a d s and n i p p e d i n t h e d i r e c t i o n o f a n e i g h b o u r i n g f i s h . I n t e n t i o n movements were r e s p o n s e s i n w h i c h a f i s h o n l y t u r n e d i t s h e a d q u i c k l y t o w a r d a n o t h e r o r made a s h o r t l u n g e a t i t . No t h r e a t n i p was i n v o l v e d . T hese movements, w h i c h were b r i e f , v a r i e d as d e s c r i b e d and were o f t e n d i f f i c u l t t o d i s t i n g u i s h f r o m n o n - s o c i a l b e h a v i o r and t h r e a t n i p s . An e x a m p l e o f an a g g r e s s i v e b o u t i n v o l v i n g s e v e r a l o f t h e d e s c r i b e d a g g r e s s i v e components was g i v e n i n t h e m a t e r i a l s and methods s e c t i o n . Some c o n t e s t s were s h o r t and i n v o l v e d o n l y two o r t h r e e b e h a v i o r a l c o m p o n e n t s , o t h e r s were l o n g and i n v o l v e d s e r i e s o f b i t e s and d i s p l a y s i n t e r s p e r s e d among e a c h o t h e r and r e c i p r o c a t e d b e t w e e n i n d i v i d u a l s . 5. A n a l y s i s o f b e h a v i o r By r e c o r d i n g b o u t s i n t e r m s o f i n d i v i d u a l b e h a v i o r c o m ponents i t was p o s s i b l e t o exa m i n e t h e r a t e o f . o c c u r r e n c e o f i n d i v i d u a l a g g r e s s i v e c o mponents as w e l l as c o m p l e t e c o n t e s t s . The b r e a k d o w n o f a g o n i s t i c b e h a v i o r i n t o a l l i t s c o m p o n e n t s made i t p o s s i b l e t o compare q u a l i t y and q u a n t i t y o f a g g r e s s i v e n e s s i n d i f f e r e n t s e a s o n s and s p e c i e s . F i g u r e 38 r e p r e s e n t s b e h a v i o r r e p e r t o i r e s o f coho and s t e e l h e a d d u r i n g t h r e e s e a s o n s . D e t a i l s o f o b s e r v a t i o n t i m e a r e g i v e n i n T a b l e V I . The d i a g r a m s i n t h e f i g u r e show o n l y t h e r a t e o f o c c u r r e n c e o f e a c h component, ..they do n o t show how t h e s e may be r e l a t e d t o e a c h o t h e r d u r i n g a g g r e s s i o n . T h e r e a r e t h r e e m a i n p o i n t s i l l u s t r a t e d i n F i g u r e 38. F i r s t , t h e r e p e r t o i r e s o f t h e two s p e c i e s d i f f e r a t a l l s e a s o n s . S e c o n d , 71 COHO L STEELHEAD M WW SPR ING — C S U M M E R FALL HS z 2 O O cc UJ a. IO ^ cc 5 iu a. •O L U I-< CC W I N T E R L " LATERAL W W " WIG WAG F"FRONTAL C " CHASE N " NIP TN "THREAT NIP I M" INTENTION MOVEMENT 38. R a t e o f o c c u r r e n c e o f i n d i v i d u a l c o mponents i n t h e a g o n i s t i c b e h a v i o r o f young coho and s t e e l h e a d . D a t a a r e b a s e d on c o m b i n e d o b s e r v a t i o n s o f f i s h i n . t h e f i v e e x p e r i m e n t a l a r r a n g e m e n t s u s e d . See t e x t f o r d e s c r i p t i o n o f b e h a v i o r c o m p o n e n t s . 7 2 . T a b l e V I . M i n u t e s o f o b s e r v a t i o n o f coho and s t e e l h e a d i n c o n t r o l and f o u r e x p e r i m e n t a l a r r a n g e m e n t s d u r i n g s p r i n g , f a l l and w i n t e r . Coho S t e e l h e a d S e a s o n 750 410 S p r i n g 390 440 F a l l 890 720 W i n t e r 7 3 . w i t h i n e a c h s p e c i e s t h e amount o f a g g r e s s i v e b e h a v i o r d e c r e a s e s s e a s o n a l l y f r o m s p r i n g t o w i n t e r . T h i r d , t h e q u a l i t y o f b e h a v i o r e x h i b i t e d by e a c h s p e c i e s c h a n g e s s e a s o n a l l y . The most o b v i o u s s p e c i e s d i f f e r e n c e s were t h e r e l a t i v e l y s t r o n g n i p p i n g and c h a s i n g c o mponents o f t h e t r o u t as o p p o s e d t o s t r o n g w i g wag, t h r e a t n i p and i n t e n t i o n movement components o f co h o . The l a t e r a l d i s p l a y , w h i c h o f t e n p r e c e d e d t h e w i g wag, was s t r o n g e r i n t h e coho t h a n i n t h e s t e e l h e a d d u r i n g s p r i n g and autumn ( F i g . 3 8 ) . L e v e l o f a g g r e s s i v e b e h a v i o r among coho was h i g h i n s p r i n g , summer and f a l l , i t d e c r e a s e d d u r i n g w i n t e r . Among t r o u t a g g r e s s i v e n e s s d e c r e a s e d p r o g r e s s i v e l y f r o m s p r i n g t o autumn and w i n t e r . D u r i n g s p r i n g and summer l a t e r a l d i s p l a y s , n i p p i n g and c h a s i n g were f r e q u e n t i n b o t h s p e c i e s . N i p p i n g and. c h a s i n g c o m ponents were v e r y s t r o n g i n t h e s t e e l h e a d ( F i g . 3 8 ) , d u r i n g s p r i n g and summer. B e h a v i o r c o m p o s i t i o n o f t h e two s p e c i e s was m o s t . s i m i l a r i n t h e s p r i n g , by autumn i t . h a d d i v e r g e d . By w i n t e r t h e l a t e r a l d i s p l a y c o mponents were g r e a t l y r e d u c e d and e q u a l l e d by t h r e a t n i p s and w i g wag e l e m e n t s i n t h e co h o . The most e v i d e n t s e a s o n a l change i n t h e s t e e l h e a d c o n f i g u r a t i o n was t h e r e d u c t i o n o f t h e c h a s e component. A h i g h e r f r e q u e n c y o f e l a b o r a t e d i s p l a y s and n o n -c o n t a c t b e h a v i o r was e v i d e n t i n t h e c o h o . The m a i n b e h a v i o r e l e m e n t s o f t h e t r o u t were l a t e r a l d i s p l a y s , b i t i n g and c h a s i n g . H a r t m a n (1963) showed t h a t young brown t r o u t (Salmo t r u t t a Linn,} d i s p l a y e d f r e q u e n t l y , b u t n i p p e d l e s s a t l o w w a t e r v e l o c i t i e s (8 t o 9 c m / s e c ) . A t h i g h e r v e l o c i t i e s (18 t o 19 cm/sec and 74. 28-30 cm/sec) t h e y n i p p e d r e l a t i v e l y more and d i s p l a y e d l e s s . The m e c h a n i c a l d i f f i c u l t y o f h o l d i n g p o s i t i o n i n t h e c u r r e n t w i t h m e d i a n and p a i r e d f i n s e x t e n d e d a p p e a r e d t o be t h e m a i n r e a s o n t h a t a g o n i s t i c b e h a v i o r t o o k on a d i f f e r e n t c h a r a c t e r a t h i g h e r w a t e r v e l o c i t i e s . A c o m p a r i s o n o f b e h a v i o r p a t t e r n s o f c o h o . a n d s t e e l h e a d w i t h brown t r o u t , s u g g e s t s t h a t s t e e l h e a d b e h a v i o r , i n v o l v i n g p r i m a r i l y l a t e r a l d i s p l a y s , n i p s and c h a s e s , i s more a d a p t e d t o r h e o c r e n e c o n d i t i o n s t h a n t h e b e h a v i o r o f coho w h i c h i n v o l v e s more w i g wag d i s p l a y s and l e s s n i p p i n g . R e s u l t s o f f i e l d and l a b o r a t o r y s t u d i e s s u g g e s t t h a t t h e d i f f e r e n c e s i n b e h a v i o r o f coho and s t e e l h e a d a r e r e l a t e d t o t h e i r e c o l o g y . 6. D i s t r i b u t i o n i n r i f f l e , and p o o l h a b i t a t The m a j o r d i f f e r e n c e i n d i s t r i b u t i o n o f t r o u t and coho i n t h e f i e l d was r e l a t e d t o r i f f l e and p o o l h a b i t a t s . I n t h e l a b o r a t o r y c e r t a i n b e h a v i o r f e a t u r e s o f e a c h s p e c i e s a p p e a r e d a d a p t i v e t o p a r t i c u l a r c u r r e n t c o n d i t i o n s and an a t t e m p t was made i n t h e l a b o r a t o r y a n a l y s e s t o d e t e r m i n e w h e t h e r t h e r e were b e h a v i o r c h a r a c t e r i s t i c s w h i c h c o n f e r r e d a d v a n t a g e s on t r o u t i n r i f f l e s and coho i n p o o l s . D i s t r i b u t i o n s i n r i f f l e and p o o l h a b i t a t s ( F i g s . 39 and 40) i n d i c a t e t h a t b o t h s p e c i e s p r e f e r r e d p o o l s o r t h a t some e n v i r o n m e n t a l r e g u l a t i o n o f b e h a v i o r a l l o w e d more i n d i v i d u a l s t o r e m a i n i n t h e p o o l s . B o t h t r o u t and coho h a d s i m i l a r d i s t r i b u t i o n s i n t h e r i f f l e and p o o l h a b i t a t s when t h e s p e c i e s were s e p a r a t e . S t e e l h e a d , h o w e v e r , were more numerous i n t h e r i f f l e a r e a s ( F i g s . 39 and 4 0 ) , When coho and s t e e l h e a d were m i x e d i n J u l y e x p e r i m e n t s , d e n s i t y o f s t e e l h e a d was r e d u c e d F i g . 3 9 . D i s t r i b u t i o n of c»h» and s t e e l h e a d a t f o u r d i f f e r e n t d e n s i t i e s i n r i f f l e and p o o l e n v i r o n m e n t ( J u l y ) . S o l i d d o t s r e p r e s e n t t h e a v e r a g e number o f f i s h p e r s e c t i o n , s p e c i e s s e p a r a t e . C i r c l e s and b r o k e n l i n e s i n d i c a t e t h e a v e r a g e number o f f i s h p e r s e c t i o n , s p e c i e s m i x e d . S c a l e f o r t h e p o i n t s f o r s p e c i e s m i x e d i s h a l f t h a t f o r s p e c i e s s e p a r a t e , ( s e e F i g . 2 4 f o r d e t a i l s o f r i f f l e and p o o l e n v i r o n m e n t ) . 7 5 . COHO STEELHEAD 2 0 F I S H 4 0 FISH 6 0 F I S H 8 0 F I S H 2 1 5 4 SECTION 3 2 I F i g . 4 0 . D i s t r i b u t i o n o f coho and s t e e l h e a d a t f o u r d i f f e r e n t d e n s i t i e s i n r i f f l e and p o o l e n v i r o n m e n t ( N o v e m b e r ) , S o l i d d o t s r e p r e s e n t t h e a v e r a g e number o f f i s h p e r s e c t i o n , s p e c i e s s e p a r a t e . C i r c l e s and b r o k e n l i n e s i n d i c a t e t h e a v e r a g e number p e r s e c t i o n , s p e c i e s m i x e d . S c a l e f o r t h e p o i n t s f o r s p e c i e s m i x e d i s h a l f t h a t f o r s p e c i e s s e p a r a t e , ( s e e Fig.24 f o r d e t a i l s o f r i f f l e - p o o l e n v i r o n m e n t ) . 76. 2 0 F I S H 4 0 F I S H 6 0 F ISH 8 0 F ISH uJ UJ 00 to UJ u IO £ 2 0 to z O l -o UJ to a UJ a I O H 3 0 n O z UJ 3 2 0 T IO COHO STEELHEAD T r O UJ X to UJ o z O o UJ a UJ -I 1 :—I r 5 4 3 2 1 5 4 3 2 1 SECTION 77. ( i n r e l a t i o n t o t h e s i t u a t i o n where t h e s p e c i e s was a l o n e ) i n 6 o u t o f 8 c a s e s i n t h e p o o l h a b i t a t , and i n c r e a s e d i n 8 o u t o f 12 i n s t a n c e s i n t h e r i f f l e h a b i t a t . Coho d e n s i t y , was r e d u c e d ( i n r e l a t i o n t o ' t h e s i t u a t i o n where t h e s p e c i e s was a l o n e ) i n 9 o u t o f 12 c a s e s i n t h e r i f f l e s and i n c r e a s e d i n 5 o u t o f '8 i n s t a n c e s i n p o o l s . Upon m i x i n g , coho d e n s i t i e s i n c r e a s e d i n t h e p o o l s and d e c r e a s e d i n t h e r i f f l e s , and s t e e l h e a d d e n s i t i e s c h a n g e d i n t h e o p p o s i t e d i r e c t i o n i n more c a s e s t h a n e x p e c t e d by c h a n c e (P = .05, C h i - s q u a r e t e s t ) . . D u r i n g w i n t e r t h e e f f e c t s o f i n t e r s p e c i f i c m i x i n g were n o t c l e a r ( F i g , 4 0 ) , I n e x p e r i m e n t s where t h e s p e c i e s were m i x e d , s t e e l h e a d d e n s i t i e s d e c r e a s e d i n t h e p o o l i n s e c t i o n 1, and i n c r e a s e d i n t h e t h r e e r i f f l e s e c t i o n s i n a l l b u t one i n s t a n c e . However d e n s i t y o f s t e e l h e a d , i n m i x e d g r o u p s , was h i g h e r i n t h e p o o l i n s e c t i o n 4 a l s o . Changes i n r e l a t i v e d e n s i t y o f coho showed no c o n s i s t e n t r e l a t i o n t o t h o s e o f s t e e l h e a d as o c c u r r e d i n J u l y ( F i g . 3 9 ) . 7. A g g r e s s i v e b e h a v i o r i n r i f f l e s and p o o l s L e v e l s o f a g g r e s s i v e n e s s were h i g h e r i n r i f f l e h a b i t a t • t h a n i n t h e p o o l c o n d i t i o n s when t h e s p e c i e s were s e p a r a t e ( F i g . 4 1 ) . An e x c e p t i o n t o t h i s was t h e c a s e o f s t e e l h e a d u n d e r w i n t e r c o n d i t i o n s . F i g h t i n g and d i s p l a y i n g . o c c u r r e d more f r e q u e n t l y i n summer- t h a n i n w i n t e r i n t h e r i f f l e and p o o l e n v i r o n m e n t as was o b s e r v e d i n t h e e x p e r i m e n t a l g r a d i e n t s . I n t e r s p e c i f i c m i x i n g r e v e a l e d an e n v i r o n m e n t a l e f f e c t on b e h a v i o r w h i c h may i n a l a r g e d e g r e e e x p l a i n why t r o u t m a i n t a i n e d t h e m s e l v e s i n t h e r i f f l e s e c t i o n s o f t h e a q u a r i u m and a c t u a l l y r e d u c e d u t i l i z a t i o n o f - t h i s s p a c e by coho.- F i g u r e 4 2 7 8 . 2 0 -O -z 1 0 -2 0 -POOL • J U L Y H N O V RIFFLE C v C SvS .41. R a t e o f a g g r e s s i v e b e h a v i o r i n r i f f l e and p o o l h a b i t a t s d u r i n g J u l y and November. D a t a b a s e d on o b s e r v a t i o n s made w i t h s p e c i e s s e p a r a t e . C v C i n d i c a t e s coho a t t a c k i n g c o h o , and S v S i n d i c a t e s s t e e l h e a d a t t a c k i n g s t e e l h e a d . Coho o b s e r v e d 390 m i n u t e s i n J u l y and 340 m i n u t e s i n November, s t e e l h e a d o b s e r v e d 380 m i n u t e s i n e a c h p e r i o d . 7 9 . Z 2 I O o o cc UJ Q. I CO cr ui a to I -UJ 5-O ° 5-j IO-POOL • J U L Y N O V C v C CvS SvS SvC RIFFLE F i g . 4 2 . R a t e s o f a g g r e s s i v e b e h a v i o r i n r i f f l e and p o o l h a b i t a t d u r i n g J u l y and- November. D a t a b a s e d on e x p e r i m e n t s i n . w h i c h s p e c i e s were m i x e d i n e q u a l numbers and o b s e r v e d 270 m i n u t e s i n J u l y and 250 m i n u t e s i n November. , M e a n i n g o f s y m b o l s as f o l l o w s : C v C coho a t t a c k i n g c o h o , C v S - coho a t t a c k i n g s t e e l h e a d , S v S - s t e e l h e a d a t t a c k i n g s t e e l h e a d and S v C - s t e e l h e a d a t t a c k i n g c o h o . 8 0 . shows t h a t coho d i s p l a y e d a h i g h l e v e l o f i n t e r s p e c i f i c and i n t r a s p e c i f i c a g g r e s s i v e n e s s w i t h i n p o o l s . A g g r e s s i v e n e s s o f t r o u t was c o r r e s p o n d i n g l y l o w i n t h e p o o l s ( F i g . 4 2 ) . ( C h i -s q u a r e v a l u e s i n d i c a t e t h a t d i f f e r e n c e s i n r a t e s o f a g g r e s s i v e n e s s o f t r o u t and coho i n r i f f l e s and p o o l s i s s i g n i f i c a n t . P . 0 1 ) . I n t h e r i f f l e h a b i t a t o f t h e a q u a r i u m coho were n o t c o m b a t i v e , s t e e l h e a d on t h e o t h e r h and were p a r t i c u l a r l y a g g r e s s i v e ( F i g . 4 2 ) . I n a d d i t i o n t o b e i n g more a g g r e s s i v e , s t e e l h e a d t e n d e d t o d e f e n d t e m p o r a r y t e r r i t o r i e s . A c o m p a r i s o n o f F i g u r e s 41 and 42 i n d i c a t e s t h a t m i x i n g t h e two s p e c i e s i n a r i f f l e and p o o l e n v i r o n m e n t h a d t h e e f f e c t o f r e d u c i n g t h e l e v e l o f coho a g g r e s s i v e n e s s i n r i f f l e s and i n c r e a s i n g i t i n p o o l s . The d e g r e e o f a g g r e s s i v e n e s s o f s t e e l h e a d i n r i f f l e s was i n c r e a s e d i n m i x e d g r o u p s . I n m i x e d g r o u p s s t e e l h e a d f i g h t i n g was more f r e q u e n t i n t h e p o o l s i n November t h a n i n J u l y , s u c h was n o t t h e c a s e when t h e s p e c i e s were s e p a r a t e ( s e e F i g s . 41 and 4 2 ) . H i g h r a t e s o f a g g r e s s i v e b e h a v i o r i n t h e r i f f l e s ( s p e c i e s u n m i x e d ) r e s u l t e d i n l o w d e n s i t i e s o f f i s h i n s u c h a r e a s . B e h a v i o r d i f f e r e n c e s , w h i c h were r e l a t e d t o t h e e n v i r o n m e n t , a c c o u n t e d f o r t h e s t r i c t d e n s i t y r e g u l a t i o n i n r i f f l e s . S t r o n g c u r r e n t i n d u c e s more d i s t i n c t t e r r i t o r i a l t e n d e n c i e s as h a s p r e v i o u s l y b e e n d e m o n s t r a t e d ( K a l l e b e r g , 1 9 5 8 ) . I n a d d i t i o n t h e p r e s e n c e o f r e f e r e n c e o b j e c t s i n d u c e s f i s h t o e s t a b l i s h and d e f e n d t e r r i t o r i e s ( H a r t m a n , 1 9 6 3 ) . I n t h e r i f f l e s e c t i o n s c u r r e n t was f a s t and t h e r e were r e f e r e n c e o b j e c t s , i . e . l a r g e s t o n e s . A g o n i s t i c a c t i v i t i e s i n t h e s e a r e a s were e a s i l y ' i n d u c e d , h e n c e i n F i g u r e 4 3 r a t e s o f a g g r e s s i o n were h i g h at' l o w d e n s i t i e s . H i g h d e n s i t i e s o f f i s h d i d n o t o c c u r b e c a u s e 81. P O O L R I F F L E JULY • O NOV 30-z UJ g 1 0 < o o o °o » • ^ c y # gF» o 9-2 0 4 0 2 0 STEELHEAD C O H O 4 0 FISH PER SECTION (l.2 M ) F i g . 4 3 . R e l a t i o n o f r a t e o f • a g g r e s s i v e b e h a v i o r t o d e n s i t y o f f i s h . Coho and s t e e l h e a d • com p a r e d i n r i f f l e and p o o l h a b i t a t s d u r i n g two s e a s o n s . E a c h d o t o r c i r c l e r e p r e s e n t s 10 m i n u t e s o f o b s e r v a t i o n i n one s e c t i o n o f t h e a q u a r i u m . ( D a t a o b t a i n e d w i t h s p e c i e s s e p a r a t e ) . 8 2 . i n c r e a s e d f i g h t i n g l e d t o d i s p l a c e m e n t s o f f i s h . I n t h e p o o l s h o w e v e r a g g r e s s i v e n e s s d e c r e a s e d w i t h an i n c r e a s e i n f i s h d e n s i t y ( F i g . 4 3 ) . K e e n l e y s i d e and Yamamoto (1 9 6 2 ) d e m o n s t r a t e d a l m o s t t h e same e f f e c t w i t h A t l a n t i c s a l m o n ' i n s m a l l s t i l l w a t e r a q u a r i a . R e d u c t i o n i n r a t e o f a g g r e s s i o n w i t h i n c r e a s e i n numbers was p a r t i c u l a r l y e v i d e n t i n coho ( F i g . 4 3 ) . C e r t a i n b e h a v i o r f e a t u r e s p r o b a b l y a c c o u n t f o r t h i s phenomenon i n g r o u p s o f c o h o . I n a g r o u p o f c o h o , c o m p e t i t i o n was s t r o n g e s t f o r p o s i t i o n s n e a r t h e f r o n t . I n f i g h t i n g f o r p o s i t i o n s , f i s h o f t e n swam p a r a l l e l t o e a c h o t h e r i n l a t e r a l t h r e a t p o s t u r e . A f t e r swimming p a r a l l e l f o r a s h o r t d i s t a n c e one f i s h , u s u a l l y t h e d o m i n a n t i n d i v i d u a l , d a r t e d a h e a d o f t h e s e c o n d and p e r f o r m e d a w i g wag d i s p l a y i n w h i c h i t d r o p p e d b a c k w a r d d o w n s t r e a m t o w a r d t h e s e c o n d f i s h ( F i g s . 44A, B and C ) . I n many c a s e s t h e u p s t r e a m f i s h e nded b y , l i t e r a l l y b r u s h i n g i t s o p p o n e n t b a c k w i t h i t s t a i l ( F i g . 4 4 C ) . I f t h e d i s p l a c e d f i s h r e m a i n e d b e h i n d t h e v i c t o r , l i t t l e more f i g h t i n g o c c u r r e d . The wig.- wag t h r e a t was c l o s e l y a s s o c i a t e d w i t h t h e f o r m a t i o n o f s t a b l e s o c i a l g r o u p s w i t h one t o t h r e e d o m i n a n t s a t t h e f r o n t and s e v e r a l s u b o r d i n a t e s b e h i n d them as i l l u s t r a t e d i n F i g u r e 4 5 , S t e e l h e a d d i d n o t e s t a b l i s h s t a b l e s o c i a l g r o u p s as d i d c o h o . I n J u l y o b s e r v a t i o n s a g g r e s s i v e n e s s d e c r e a s e d w i t h i n c r e a s e i n numbers o f s t e e l h e a d . S u c h a change t o o k p l a c e b e c a u s e as numbers went up many s t e e l h e a d s e t t l e d t o t h e b o t t o m and became q u i e t w h i l e o t h e r s b e g a n t o roam a b o u t . These f i s h were n o t o f t e n a t t a c k e d . T h e r e were u s u a l l y l a r g e , p o t e n t i a l l y d o m i n a n t t r o u t , t h e y d i d n o t o f t e n e x h i b i t t h e w i g wag t h r e a t 83 F i g . 4 4 A . Coho, c a 10 months o l d , i n w i g wag p o s t u r e . F i s h a t l e f t i s d i s p l a y i n g and b e g i n n i n g t o d r o p b a c k t o w a r d f i s h a t r i g h t . B. B o t h f i s h d r o p p i n g d o w n s t r e a m and c o m i n g c l o s e r t o g e t h e r . C. Coho a t l e f t s t i l l i n w i g wag p o s t u r e , i t s t a i l a l m o s t s t r i k i n g f i s h a t r i g h t . A t t h i s p o i n t t h e f i s h a t l e f t may w h e e l and n i p t h e s e c o n d f i s h o r s e c o n d f i s h may f l e e . F i g . 4 5 . S m a l l g r o u p o f 8 coho w i t h one d o m i n a n t ( s e c o n d f r o m r i g h t } and s e v e n s u b o r d i n a t e s . S m a l l f i s h o c c a s i o n a l l y a v o i d e d a t t a c k by r e m a i n i n g s t i l l and r e s t i n g down among t h e s t o n e s , s e e f o r e g r o u n d . 85,. and d i d n o t h o l d t h e f r o n t p o s i t i o n s i n any s t a b l e g r o u p s . 8. Summary o f r e s u l t s F i e l d o b s e r v a t i o n s r e v e a l e d s e a s o n a l c h a n g e s i n t h e d i s t r i b u t i o n r e l a t i o n s h i p s o f y o u n g coho and t r o u t . C o n c o m i t a n t w i t h t h e s e were c h a n g e s i n w a t e r t e m p e r a t u r e , and p o p u l a t i o n d e n s i t y . L a b o r a t o r y e x p e r i m e n t s p o i n t e d t o f e a t u r e s o f e n v i r o n m e n t a l and s o c i a l , b e h a v i o r w h i c h were r e l a t e d t o c h a n g e s o c c u r r i n g i n n a t u r e . F i e l d and l a b o r a t o r y r e s u l t s a r e s u m m a r i z e d b r i e f l y b e l o w as an i n t r o d u c t i o n t o t h e D i s c u s s i o n . F i e l d o b s e r v a t i o n s a p p l y p a r t i c u l a r l y t o t h e S almon R i v e r . 1. SPRING AND EARLY SUMMER F i e l d o b s e r v a t i o n s 1. S p e c i e s l a r g e l y s e g r e g a t e d i n d i f f e r e n t m i c r o - h a b i t a t s . 2. Coho i n p o o l s , t r o u t i n r i f f l e s . 3. P o p u l a t i o n d e n s i t y p e r u n i t o f a r e a i s h i g h . 4. Coho r e l a t i v e l y l a r g e c o m p a r e d t o t r o u t . 5. T e m p e r a t u r e o f w a t e r 8.3° - 17.2°C, ( t i m e p e r i o d c o r r e s p o n d s t o l a b o r a t o r y p e r i o d ) . L a b o r a t o r y o b s e r v a t i o n s 1. B o t h s p e c i e s have s i m i l a r d i s t r i b u t i o n s i n e x p e r i m e n t a l g r a d i e n t s . t 2. B o t h u t i l i z e s p a c e i n p o o l s and c o v e r i n t h e same manner. 3. B o t h s p e c i e s e x h i b i t h i g h l e v e l o f a g g r e s s i o n w h i c h i n v o l v e s much b i t i n g and c h a s i n g . 4. T e m p e r a t u r e 10° t o 16°C. 5. Body and f i n c o l o r s v i v i d . 86 v 2 . F A LL F i e l d o b s e r v a t i o n 1. S p e c i e s p a r t i a l l y s e g r e g a t e d i n e a r l y f a l l , c o m i n g t o g e t h e r more i n l a t e f a l l . 2. Coho i n p o o l s , t r o u t d e n s i t y a b o u t e v e n i n r i f f l e s and p o o l s . 3. P o p u l a t i o n r e d u c e d i n p o o l s , r e d u c e d more i n r i f f l e s . 4. T r o u t s i z e r a n g e a p p r o x i m a t i n g t h a t o f coho, 5. T e m p e r a t u r e o f w a t e r 7,2° t o 12.5°C. L a b o r a t o r y o b s e r v a t i o n 1. S t e e l h e a d and coho h a v e d i f f e r e n t d i s t r i b u t i o n s i n e x p e r i m e n t a l g r a d i e n t s . 2. S p e c i e s u t i l i z e s p a c e and c o v e r i n a b o u t t h e same manner. 3. Coho a g g r e s s i o n h i g h , b u t l e s s b i t i n g and c h a s i n g i s e x h i b i t e d . S t e e l h e a d a g g r e s s i o n l o w e r t h a n i n ; s p r i n g , r e l a t i v e l y l e s s c h a s i n g . 4. T e m p e r a t u r e 9° t o 14.5°C. 5. Body and f i n c o l o r s l e s s v i v i d . WINTER 1. S p e c i e s e x h i b i t no m i c r o h a b i t a t s e g r e g a t i o n . 2. H i g h e s t d e n s i t y o f b o t h s p e c i e s i n t h e p o o l s . 3. P o p u l a t i o n d e n s i t y r e d u c e d f u r t h e r i n p o o l s , v e r y l o w i n r i f f l e s . 4. T r o u t s i z e r a n g e a p p r o x i m a t i n g t h a t o f c o h o s . 5. T e m p e r a t u r e o f w a t e r 0.3° t o 7°C. 1. S p e c i e s have d i f f e r e n t d i s t r i b u t i o n s i n e x p e r i m e n t a l g r a d i e n t s . 2. They u t i l i z e s p a c e i n p o o l s and a r o u n d c o v e r i n d i f f e r e n t m a n n e r s . 3. A g g r e s s i o n v e r y l o w i n b o t h s p e c i e . s . Coho d i s p l a y c omponents a r e s t r o n g , v e r y l i t t l e b i t i n g and c h a s i n g . S t e e l h e a d show o n l y two components s t r o n g l y ; s i m p l e d i s p l a y s and b i t i n g . 4. T e m p e r a t u r e 0.5° t o 7.5°C. 5. Body and f i n c o l o r s l e s s v i v i d t h a n i n s p r i n g and f a l l . 8 7 . DISCUSSION An a n i m a l ' s b e h a v i o r i s a d a p t e d t o i t s e n v i r o n m e n t j u s t as i s i t s m o r p h o l o g y and p h y s i o l o g y . A c c o r d i n g l y t h e r e a r e b o t h e n v i r o n m e n t a l and s o c i a l r e s p o n s e s o f coho and t r o u t w h i c h r e l a t e t o t h e i r e c o l o g y . C e r t a i n a s p e c t s o f t h e e c o l o g y and b e h a v i o r o f coho and t r o u t w i l l now be c o n s i d e r e d b e f o r e e n t e r i n g t h e m a i n body o f t h e d i s c u s s i o n , w h i c h w i l l d e a l more d i r e c t l y w i t h i n t e r s p e c i f i c i n t e r a c t i o n . A. B e h a v i o r o f S t e e l h e a d and Coho i n R e l a t i o n t o t h e i r E c o l o g y U n d e r n a t u r a l c o n d i t i o n s coho were most f r e q u e n t l y d i s t r i b u t e d i n g r o u p s w h i c h were r e s t r i c t e d t o c e r t a i n t y p e s o f h a b i t a t . T r o u t were more s c a t t e r e d and a p p e a r e d c a p a b l e o f u t i l i z i n g a w i d e r a r r a y o f s t r e a m h a b i t a t s . U n d e r e x p e r i m e n t a l c o n d i t i o n coho were b e s t a d a p t e d t o m a i n t a i n i n g p o s i t i o n s i n p o o l s , and t r o u t t o h o l d i n g p o s i t i o n s i n r i f f l e s . T hese d i f f e r e n c e s , w h i c h a r e most e v i d e n t d u r i n g s p r i n g and summer, p r o b a b l y a c c o u n t f o r d i f f e r e n c e s i n p o p u l a t i o n s t a b i l i t y o f t h e two s p e c i e s i n s m a l l c o a s t a l s t r e a m s . D u r i n g May and J u n e l a r g e numbers o f y o u n g coho were d i s p l a c e d d o w n s t r e a m i n t h e S a l m o n R i v e r . Chapman ( 1 9 6 2 ) h a s shown t h a t s u c h d i s p l a c e m e n t i s t h e r e s u l t o f a g g r e s s i o n and c o m p e t i t i o n f o r s p a c e . The ...emigration o f y o u n g coho f r o m s t r e a m s o c c u r r e d a t a s e a s o n when l e v e l s o f a g g r e s s i o n were h i g h e s t and when b e h a v i o r was l e a s t r i t u a l i z e d . D o w n s t r e a m d i s p l a c e m e n t o f t r o u t d i d n o t o c c u r e v e n t h o u g h d e n s i t y and r a t e o f a g g r e s s i o n were h i g h . K a l l e b e r g ( 1958) showed t h a t t e r r i t o r y s i z e d e c r e a s e d w i t h i n c r e a s e d p o p u l a t i o n d e n s i t y o f A t l a n t i c s a l m o n f r y . T r o u t i n t h e S a l m o n 88. R i v e r may accommodate f o r c h a n g e s i n numbers by c h a n g i n g t e r r i t o r y s i z e . Coho, w h i c h a r e r e s t r i c t e d t o p o o l s , may d i s p l a c e s u r p l u s i n d i v i d u a l s o u t o f t h e p o o l s . E x p e r i m e n t a l d a t a i n d i c a t e d t h a t s u c h i n d i v i d u a l s w o u l d be u n a b l e t o m a i n t a i n p o s i t i o n s a g a i n s t t r o u t i n t h e r i f f l e s . As a r e s u l t c o h o , p u s h e d o u t o f p o o l s , w o u l d move d o w n s t r e a m t o u n u s e d p o o l s p a c e o r . b e d i s p l a c e d c o m p l e t e l y . The d i r e c t i o n o f r e t r e a t f o l l o w i n g combat may be i m p o r t a n t i n a c o n s i d e r a t i o n o f t h e m a t t e r o f d o w n s t r e a m d i s p l a c e m e n t . R e t r e a t i n g t r o u t i n t h e e x p e r i m e n t a l s t r e a m a q u a r i u m t e n d e d t o move u p s t r e a m o r l a t e r a l l y , Coho on t h e o t h e r h a n d moved d o w n s t r e a m o r l a t e r a l l y , ( F i g . 4 6 ) . These d i f f e r e n c e s a r e c o n s i s t e n t w i t h d i f f e r e n c e s i n amount o f d o w n s t r e a m d i s p l a c e m e n t a n d . w i t h t h e t y p e o f a g g r e s s i v e b e h a v i o r e x h i b i t e d by coho and t r o u t . D u r i n g w i n t e r coho a r e u s u a l l y f o u n d i n dense g r o u p s . The t e n d e n c y t o f o r m s u c h g r o u p s i s u s u a l l y r e f l e c t e d i n t h e w i n t e r d i s t r i b u t i o n s ( F i g s . 25 and 2 6 ) . I n w i n t e r no d o w n s t r e a m e m i g r a t i o n o c c u r r e d i n t h e Sa l m o n R i v e r . L a b o r a t o r y s t u d i e s -r e v e a l e d s e v e r a l b e h a v i o r a l phenomena w h i c h w o u l d f a c i l i t a t e s t a b i l i t y o f g r o u p s i n r e s t r i c t e d a r e a s o f t h e s t r e a m d u r i n g t h e w i n t e r . L e v e l s o f a g g r e s s i v e n e s s were l o w e r i n b o t h s p e c i e s . The amount o f b i t i n g and c h a s i n g was l o w i n p r o p o r t i o n t o n o n -c o n t a c t a g g r e s s i v e n e s s . The w i g wag d i s p l a y o c c u r r e d f r e q u e n t l y i n l a b o r a t o r y c o n d i t i o n s and was e x h i b i t e d i n c o n t e s t s f o r p o s i t i o n n e a r t h e f r o n t o f a g r o u p . F i s h w h i c h were d i s p l a c e d by o t h e r s u s i n g t h e w i g wag t h r e a t were p u s h e d b a c k i n t o t h e g r o u p o f s u b o r d i n a t e s b u t were n o t d r i v e n e n t i r e l y o u t o f t h e g r o u p . ESI C O H O • S T E E L H E A D cn 4 0 -I-< UJ CC H UJ cc u_ 2 0 j O L A T E R A L I D O W N S T R E A M U P S T R E A M D I R E C T I O N O F R E T R E A T .46. D i r e c t i o n o f - r e t r e a t o f coho and s t e e l h e a d ( b a s e d ' o n w^'+'H" a 9 ^ e s s i v e c o n t e s t s i s s u i n g c'oho)? S S t S ' ^ a n d 90. D u r i n g w i n t e r , t r o u t d i d n o t o c c u r i n t i g h t g r o u p s as d i d c o h o . B e h a v i o r components ( t h r e a t n i p s and w i g wag d i s p l a y s ) w h i c h were e v i d e n t i n t h e g r o u p b e h a v i o r o f coho were e x h i b i t e d i n f r e q u e n t l y i n l a b o r a t o r y g r o u p s o f t r o u t . H i d i n g b e h a v i o r shown by t r o u t u n d e r w i n t e r c o n d i t i o n s h a s a d a p t i v e v a l u e i n p r o t e c t i n g them f r o m " s c o u r i n g " and p r e d a t i o n . C o a s t a l r i v e r s o f B r i t i s h C o l u m b i a a r e f r e q u e n t l y s u b j e c t t o f r e s h e t s ; h e n c e , h i d i n g b e h a v i o r , e i t h e r i n l o g j ams o r u n d e r s t o n e s , i s a d v a n t a g e o u s i n m a i n t a i n i n g p o s i t i o n . L i n d r o t h ( 1 9 5 5 b ) has shown t h a t m e r g a n s e r s c a n t a k e a h e a v y t o l l on t r o u t p a r r p o p u l a t i o n s . L i n d r o t h and B e r g s t r o m ( 1 9 5 9 ) d e m o n s t r a t e d t h a t m e r g a n s e r s c o u l d e a s i l y see f i s h i n open w a t e r and c h a s e d them t e n a c i o u s l y . The b i r d s e v e n s e a r c h e d a c t i v e l y u n d e r t h e s t o n e s f o r t h e t r o u t p a r r . I t may be assumed t h a t f i s h i n p o s i t i o n s u n d e r l a r g e s t o n e s w o u l d g a i n c o n s i d e r a b l e p r o t e c t i o n f r o m s u c h p r e d a t i o n . I n most c a s e s h i d i n g t r o u t i n t h e C h i l l i w a c k R i v e r were u n d e r r o c k s 20 t o 40 cm i n d i a m e t e r . Many h i d i n g f i s h were f o u n d w e l l down among t h e s t o n e s r a t h e r t h a n n e a r t h e s u r f a c e . The h a b i t o f s e e k i n g s h e l t e r i s i m p o r t a n t i n t h e e c o l o g y o f y o u n g s t e e l h e a d b e c a u s e i t o f f e r s p r o t e c t i o n f r o m w i n t e r f r e s h e t s and f r o m p r e d a t i o n t o many f i s h w h i c h a r e d i s t r i b u t e d a l o n g t h e s t r e a m m a r g i n s - i n o t h e r w i s e u n p r o t e c t e d l o c a t i o n s . The f o r e g o i n g comments have p o i n t e d o u t some d i f f e r e n c e s i n t h e b e h a v i o r and e c o l o g y o f t h e two s p e c i e s . A l t h o u g h t r o u t o c c u p y a w i d e r v a r i e t y o f s t r e a m h a b i t a t s t h a n coho ( p a r t i c u l a r l y i n t h e l a r g e s t s t r e a m ) t h e two s p e c i e s o v e r l a p t o a l a r g e d e g r e e i n s p a c e u t i l i z a t i o n . The r e l a t i o n s h i p o f s i m i l a r s p e c i e s s u c h 91. as t h e t r o u t and coho m a k i n g demands on t h e same r e s o u r c e l e a d s t o a f u n d a m e n t a l i n t e r e s t i n e c o - b i o l o g y . B. I n t e r a c t i o n o f Young S t e e l h e a d and Coho S e g r e g a t i o n o f n a t u r a l p o p u l a t i o n s o f young coho and t r o u t o c c u r r e d a t t h e s e a s o n i n w h i c h e x p e r i m e n t s i n d i c a t e d g r e a t e s t s i m i l a r i t y o f e n v i r o n m e n t a l p r e f e r e n c e s . S e p a r a t i o n i n t h e w i l d was l e a s t p r o n o u n c e d d u r i n g w i n t e r m o n t h s , when e x p e r i m e n t s i n d i c a t e d d i f f e r e n c e s i n p r e f e r e n c e s . T hese two o b s e r v a t i o n s c o n s i d e r e d t o g e t h e r s u p p o r t t h e b e l i e f t h a t i n t e r s p e c i f i c c o m p e t i t i o n may be m a n i f e s t e d i n s e g r e g a t e d r e s o u r c e u s e ( N i l s s o n 1 9 5 6 , 1 9 6 3 ) . I n t e r a c t i o n , w h i c h o c c u r r e d i n s p r i n g and summer b e c a u s e b o t h s p e c i e s h a d s i m i l a r demands, was a c c e n t u a t e d by t h r e e f a c t o r s . P o p u l a t i o n d e n s i t i e s were h i g h e s t i n s p r i n g and summer ( F i g . 1 6 ) . L e v e l s o f a g g r e s s i v e n e s s were h i g h e s t e a r l y i n t h e y e a r ( F i g . 3 8 ) . I n a d d i t i o n t o t h i s t h e a g g r e s s i v e n e s s shown i n v o l v e d much b i t i n g and c h a s i n g . S i z e d i f f e r e n c e s may h a v e c o n t r i b u t e d t o t h e e f f e c t o f s e g r e g a t i o n . Coho were l a r g e r t h a n t h e t r o u t i n s p r i n g and summer ( F i g . 17) and c o u l d h a v e d i s p l a c e d them f r o m p o o l s . I n d i r e c t o p p o s i t i o n t o t h e above s i t u a t i o n , w i n t e r p o p u l a t i o n s o f coho and t r o u t c o e x i s t e d t o a l a r g e e x t e n t i n t h e p o o l s . T h r e e m a i n f a c t o r s c o n t r i b u t e d t o t h i s i n t e r s p e c i f i c c o m p a t a b i l i t y . F i r s t , s p a t i a l d i s t r i b u t i o n and p r e f e r e n c e s o f t h e two s p e c i e s , i n t h e s t r e a m a q u a r i u m , were d i f f e r e n t i n w i n t e r . S e c o n d , s t r e a m p o p u l a t i o n d e n s i t i e s were l o w e r i n w i n t e r ( F i g . 1 6 ) , T h i r d , l e v e l s o f a g g r e s s i v e n e s s were l o w e r i n w i n t e r ( F i g . 3 8 ) . These t h r e e f a c t o r s must c o n t r i b u t e s u b s t a n t i a l l y t o t h e w i n t e r c o e x i s t e n c e o f coho and t r o u t . 9 2 . T h e r e i s an a p p a r e n t p a r a d o x i n t h e f a c t t h a t w i l d p o p u l a t i o n s o f b o t h t r o u t and coho o c c u p y p o o l s a t a s e a s o n when e x p e r i m e n t s i n d i c a t e d i f f e r e n c e s i n p r e f e r e n c e s . I t s h o u l d be p o i n t e d o u t t h e r e f o r e , t h a t b o t h s p e c i e s showed a p r e f e r e n c e f o r t h e d e e p e s t s e c t i o n o f t h e d e p t h g r a d i e n t , w h i c h was c o m p a r a b l e t o a p o o l ( F i g . 2 6 ) . However t r o u t and coho u t i l i z e d t h i s p o o l s p a c e d i f f e r e n t l y , coho f o r m e d g r o u p s i n open w a t e r above b o t t o m , and t r o u t s c a t t e r e d a c r o s s t h e b o t t o m ( F i g s . 31 and 3 2 ) . I n t h e c o v e r g r a d i e n t t r o u t o c c u p i e d s p a c e u n d e r s t o n e s b u t coho o c c u p i e d s p a c e b e s i d e t h e s t o n e s o r d o w n s t r e a m f r o m them ( F i g s . 27 a n d ' 2 8 ) . I n a s t r e a m d u r i n g t h e w i n t e r b o t h s p e c i e s may make a demand on p o o l s p a c e . However s m a l l b u t i m p o r t a n t d i f f e r e n c e s i n t h e u s e o f s p a c e and c o v e r s u c h as t h o s e d e s c r i b e d , c o u l d p e r m i t c o e x i s t e n c e o f b o t h s p e c i e s i n a p o o l w i t h i n a f e w i n c h e s o f e a c h o t h e r . As a l r e a d y s t a t e d , s u c h c o e x i s t e n c e w o u l d be f a c i l i t a t e d b e c a u s e l e v e l s o f a g g r e s s i v e n e s s i n b o t h s p e c i e s a r e l o w d u r i n g w i n t e r . The p r e v i o u s d i s c u s s i o n e x p l a i n s some o f t h e r e a s o n s why coho and t r o u t s e g r e g a t e s p a t i a l l y i n s p r i n g and summer b u t o c c u r t o g e t h e r i n w i n t e r . However one i m p o r t a n t q u e s t i o n s t i l l r e m a i n s . How do t h e s e two s p e c i e s r e m a i n i n e q u i l i b r i u m i n t h e two d i s t i n c t i v e n a t u r a l m i c r o h a b i t a t s , r i f f l e s and pools'? To g a i n b e t t e r u n d e r s t a n d i n g o f t h i s p r o b l e m i t may be v a l u a b l e t o c o n s i d e r t h e e f f e c t o f e n v i r o n m e n t on t h e b e h a v i o r o f young brown t r o u t . H a r t m a n ( 1 9 6 3 ) showed t h a t young brown t r o u t c o u l d be i n d u c e d t o t a k e up and d e f e n d p o s i t i o n s i f p r e s e n t e d w i t h s i m p l e v i s u a l r e f e r e n c e p o i n t s . I f t h e s t r u c t u r a l c o m p l e x i t y o f t h e s e r e f e r e n c e p o i n t s was i n c r e a s e d , t h e r a t e o f o c c u p a n c y was 93. i n c r e a s e d . K a l l e b e r g ( 1 9 58) showed t h a t t h e d e f e n c e o f t e r r i t o r i e s by young brown t r o u t and s a l m o n was i n i t i a t e d by r u n n i n g w a t e r . T e r r i t o r i a l b e h a v i o r o f young brown t r o u t was. r e l e a s e d by c e r t a i n s t i m u l i , t h e e f f e c t o f w h i c h c o u l d be r e i n f o r c e d by o t h e r s . The b e h a v i o r o f c h o o s i n g and d e f e n d i n g t e r r i t o r i e s a p p e a r s t o be a r e a c t i v e t y p e o f b e h a v i o r w h i c h i s g o v e r n e d by a c o m p l e x o f e n v i r o n m e n t a l s t i m u l i . P r e s u m a b l y y o u n g s t e e l h e a d i n t h e r i f f l e e n v i r o n m e n t r e c e i v e d more s t i m u l i w h i c h e l i c i t e d a g g r e s s i v e b e h a v i o r and t e r r i t o r y d e f e n c e , t h a n t h e y r e c e i v e d i n t h e p o o l s . The r e s p o n s e s o f young coho t o v a r i o u s s t i m u l i were d i f f e r e n t ; h e n c e , t h e y were more s t r o n g l y m o t i v a t e d t o d e f e n d s p a c e i n p o o l s and l e s s , so i n r i f f l e s . S u c h a d i f f e r e n t i a l r e s p o n s e t o e n v i r o n m e n t a l c o n d i t i o n s i s i n d i c a t e d by t h e d i f f e r e n c e s i n a g g r e s s i v e n e s s i n r i f f l e and p o o l h a b i t a t s ( F i g . 4 2 ) . S e g r e g a t i o n i n t h e S a l m o n R i v e r i s p r o b a b l y m a i n t a i n e d b e c a u s e o f d i f f e r e n c e s i n m o t i v a t i o n a l s t a t e s o f t r o u t and coho i n t h e t h r e e m i c r o - h a b i t a t s o f t h e s t r e a m . I f i t w ere n o t f o r . t h i s d i f f e r e n t i a l a g g r e s s i v e n e s s , coho d i s p l a c e d f r o m p o o l s w o u l d be a b l e t o e l i m i n a t e t h e s m a l l e r t r o u t f r o m t h e r i f f l e s , t h u s s h i f t i n g t h e b a l a n c e , i n t h e w h o l e s t r e a m , i n f a v o r o f one s p e c i e s . I n c o n c l u d i n g t h e comments on t h e e c o l o g i c a l r e l a t i o n s h i p o f t h e s e two s p e c i e s i t i s e m p h a s i z e d t h a t c h a n g e s i n s o c i a l b e h a v i o r a c c o u n t , i n a l a r g e way, f o r t h e s e a s o n a l c hange i n s e v e r i t y o f i n t e r a c t i o n . D i f f e r e n c e s i n a g g r e s s i v e n e s s i n r i f f l e and p o o l e n v i r o n m e n t s a c c o u n t f o r t h e s e g r e g a t i o n and t h e e q u i l i b r i u m o f coho and t r o u t i n t h e two m i c r o h a b i t a t s , 94. C. Comments on C o n c e p t s o f C o m p e t i t i o n A number o f i n v e s t i g a t o r s have r e p o r t e d i n s t a n c e s i n w h i c h c o m p e t i t i o n o r i n t e r a c t i o n b e t w e e n s p e c i e s i s m a n i f e s t e d i n s e g r e g a t i o n ( s e e Beaucharnp and U l l y o t t , 1932; M a c a n , 1961; and C o n n e l l , 1 9 6 1 ) . S e g r e g a t i o n p r o d u c e d by c o m p e t i t i o n among f i s h h a s been r e c o r d e d by N i l s s o n ( 1 9 5 5 , 1958, 1960 and 1 9 6 3 ) . M u i r a ( 1 9 6 2 ) r e v i e w e d s e v e r a l c a s e s ' i n w h i c h i t o c c u r r e d i n c o m p e t i n g s p e c i e s o f J a p a n e s e f i s h . L i n d r o t h ( 1 9 5 5 a ) , K a l l e b e r g ( 1 9 5 8 ) and S a u n d e r s and Gee (1964) d e a l w i t h s e g r e g a t i o n o f c o m p e t i n g s p e c i e s o f s t r e a m d w e l l i n g s a l m o n i d s . I n most o f t h e p r e c e d i n g c a s e s e a c h s p e c i e s h a s a s l i g h t m o r p h o l o g i c a l , p h y s i o l o g i c a l o r b e h a v i o r a l a d v a n t a g e o v e r t h e o t h e r i n some p a r t o f t h e e n v i r o n m e n t . I t i s n e c e s s a r y t o p o i n t o u t t h a t s i m i l a r , c o m p e t i n g s p e c i e s s e g r e g a t e and come i n t o e q u i l i b r i u m i n n a t u r e , s i n c e many l a b o r a t o r y i n v e s t i g a t i o n s on c o m p e t i t i o n , c a r r i e d o u t i n homogeneous c o n t r o l l e d e n v i r o n m e n t s , w o u l d i n d i c a t e o t h e r w i s e ( r e v i e w s by C r o m b i e , 1947; de B a c h and S undby, 1 9 6 3 ) . G r i n n e l l ( 1 9 0 4 ) , Gause ( 1 9 3 4 ) and De B a c h and Sundby (1963) have i n d i c a t e d t h a t s p e c i e s h a v i n g t h e same n i c h e c a n n o t o c c u r t o g e t h e r w i t h o u t one e l i m i n a t i n g t h e o t h e r . De B a c h and Sundby (1963) have r e c o r d e d a c a s e i n w h i c h one s p e c i e s o f A p h y t i s e l i m i n a t e s . a n o t h e r and i s s u b s e q u e n t l y d i s p l a c e d by a t h i r d s p e c i e s . They s u g g e s t t h a t t h e d i s p l a c e m e n t m e n t i o n e d above i l l u s t r a t e s " t h e c o m p e t i t i v e d i s p l a c e m e n t h y p o t h e s i s " , i . e . s p e c i e s w i t h i d e n t i c a l e c o l o g i c a l n i c h e s c a n n o t c o e x i s t l o n g i n t h e same h a b i t a t . B e c a u s e o f t h e way.'the h y p o t h e s i s h a s b een s t a t e d and b e c a u s e o f t h e v a r i a t i o n s i n i t s i n t e r p r e t a t i o n , t h e c o m p e t i t i v e d i s p l a c e m e n t c o n c e p t has b e e n c o n t r o v e r s i a l ( H a r d i n , 95. 1960; C o l e , 1960; P a t t e n , 1 9 6 1 ; V a n V a l e n , 1960; M c i n t o s h , 1 9 6 1 ) . The c o n c e p t m i g h t have b e e n more a c c e p t a b l e i f i t had s t a t e d L t h a t - i n a d m p a t r i c p o p u l a t i o n s o f s i m i l a r s p e c i e s t h e l e v e l o f c o m p e t i t i v e i n t e r a c t i o n w i l l i n c r e a s e w i t h t h e d e g r e e o f e c o l o g i c a l and b e h a v i o r a l s i m i l a r i t y . T h i s does n o t l e a d t o the-d i f f i c u l t y o f d i s c u s s i n g d i f f e r e n t s p e c i e s w i t h i d e n t i c a l n i c h e s , a l t h o u g h i t does s t i l l l e a v e t h e p r o b l e m o f q u a n t i f y i n g e c o l o g i c a l and b e h a v i o r a l s i m i l a r i t y . I t i s I m p o s s i b l e t o s a y how s u c h i n t e r a c t i o n w i l l be m a n i f e s t , b e c a u s e c o m p e t i t i o n may a l t e r t h e n u m b e r s , t h e g r o w t h r a t e o r t h e n i c h e o f an a n i m a l i n a p a r t i c u l a r h a b i t a t . T e m p e r a t e f r e s h w a t e r f i s h a r e i n g e n e r a l u n s p e c i a l i z e d and f l e x i b l e ( L a r k i n , 1956) and h e n c e can a l t e r t h e i r n i c h e , as y o u n g t r o u t and coho a r e p r e s u m e d t o do. T h i s , on t h e o t h e r h a n d , may n o t be t r u e o f f i s h i n t h e o l d f r e s h w a t e r e n v i r o n m e n t s s t u d i e d by F r y e r ( 1 9 5 9 ) . H i g h l y s p e c i a l i z e d a n i m a l s s u c h as t h e p a r a s i t i c wasps (De B a c h and S u n d b y , 1 9 6 3 ) , may be v i r t u a l l y i n c a p a b l e o f o c c u p y i n g an a l t e r e d n i c h e ; t h u s , e l i m i n a t i o n o f one s p e c i e s i s t h e n e c e s s a r y outcome o f c o m p e t i t i o n when no a d d i t i o n a l f a c t o r s c o n t r o l t h e numbers o f b o t h c o m p e t i n g s p e c i e s . I t i s r e a s o n a b l e t o assume t h a t t h e amount o f s p e c i a l i z a t i o n as w e l l as t h e d e g r e e o f s i m i l a r i t y o f s p e c i e s w i l l d e t e r m i n e t h e e f f e c t s o f c o m p e t i t i o n . These e f f e c t s may i n v o l v e d i s p l a c e m e n t i n s p a c e , d i s p l a c e m e n t o r s e g r e g a t i o n i n f o o d h a b i t s , s e p a r a t i o n i n some g r a d i e n t o f e n v i r o n m e n t a l c o n d i t i o n s , c h a n g e s i n g r o w t h r a t e s , o r t h e c o m p l e t e e l i m i n a t i o n o f one s p e c i e s . S p e c i e s i n t e r a c t i o n n e e d n o t be m a n i f e s t e d i n one t y p e o f end r e s u l t o n l y . 96:. I n t h e f i e l d o f e c o l o g y , h y p o t h e s e s c a n o f t e n be p o s t u l a t e d much more e a s i l y t h a n t h e y can. be t e s t e d - . The p r e s e n t r e s e a r c h does n o t d e m o n s t r a t e t h a t t h e c o n c e p t s p u t f o r w a r d by N i l s s o n (1956 and 1963) a p p l y i n a l l c a s e s , a l t h o u g h i t does d e m o n s t r a t e t h a t s u c h c o n c e p t s p r o v i d e a v a l u a b l e f r a m e w o r k f o r i n t e r p r e t i n g c e r t a i n s i t u a t i o n s i n n a t u r e and i n t h e l a b o r a t o r y . M o r e o v e r t h e w o r k p r o v i d e s f u r t h e r s u p p o r t f o r t h e c o n c e p t t h a t s p e c i e s t e n d t o be s e g r e g a t e d i n t h e i r u s e o f a p a r t i c u l a r r e s o u r c e when i t i s i n s h o r t s u p p l y . I n a d d i t i o n , t h e s t u d y h a s e m p h a s i z e d t h e r o l e o f b e h a v i o r i n t h e e c o l o g i c a l r e l a t i o n s h i p s o f t h e two s p e c i e s and d e m o n s t r a t e d a s t r o n g b e h a v i o r a l b a s i s f o r t h e m a r k e d s e g r e g a t i o n w h i c h t h e y show. 97. LITERATURE CITED Beauchamp, R.S. and P. U l l y o t t . ' 1932. C o m p e t i t i v e r e l a t i o n s h i p s b e t w e e n c e r t a i n s p e c i e s o f f r e s h - w a t e r t r i c l a d s . J . E c o l . 20 ( 1 ) : 200-208. Chapman, D.W, 1962, A g g r e s s i v e , b e h a v i o r o f j u v e n i l e coho s a l m o n as a c a u s e o f e m i g r a t i o n . J . F i s h . R e s . Bd. C a n a d a , 19(6): 1 0 4 7 - 1 0 8 0 . C o l e , L.C. 1960. C o m p e t i t i v e e x c l u s i o n . S c i e n c e ' , 132 ( 3 4 2 3 ) : 3 4 8 - 3 4 9 . C o n n e l l , J.H. 1 9 6 1 . The i n f l u e n c e o f i n t e r s p e c i f i c c o m p e t i t i o n and o t h e r . f a c t o r s on t h e d i s t r i b u t i o n o f t h e b a r a n c l e C h t h a m a l u s s t e l l a t u s . E c o l o g y , , 4 2 ( 4 ) : 7 1 0 - 7 2 3 . C r o m b i e , A.C. 1947. I n t e r s p e c i f i c c o m p e t i t i o n . J . A n i m a l E c o l . . 1 6 ( 1 ) : 4 4 - 7 3 . De B a c h , P. and R.A, S u n d b y . 1963. C o m p e t i t i v e d i s p l a c e m e n t b e t w e e n e c o l o g i c a l h o m o l o g u e s . H i l g a r d i a , - 3 4 ( 5 ) : 1 05-166. F a b r i c i u s , E. 1953. A q u a r i u m o b s e r v a t i o n s on t h e s p a w n i n g b e h a v i o u r o f t h e c h a r , Salmo a l p i n u s . R e p t . I n s t . F r e s h w a t e r R e s . D r o t t n i n g h o l m , 34: 14-48. F r y e r , G. 1959, The t r o p h i c i n t e r r e l a t i o n s h i p s and e c o l o g y o f some l i t t o r a l c o m m u n i t i e s o f L a k e N y a s a w i t h e s p e c i a l r e f e r e n c e t o t h e f i s h e s , and a d i s c u s s i o n o f t h e e v o l u t i o n o f a g r o u p o f r o c k - f r e q u e n t i n g C i c h l i d a e . P r o c . Z o o l . S o c . L o n d o n , 1 3 2 ( 2 ) : 1 5 3 - 2 8 1 . G a u s e , G.F. 1934. The s t r u g g l e f o r e x i s t e n c e . The W i l l i a m s and W i l k i . n s Co., B a l t i m o r e . 163 p. G r i n n e l l , J . \ 1904.' The o r i g i n and d i s t r i b u t i o n o f t h e c h e s t n u t -b a c k e d c h i c k a d e e . Auk, 21: 3 6 4 - 3 8 2 . H a r d i n , . G. 1960. The c o m p e t i t i v e e x c l u s i o n p r i n c i p l e . S c i e n c e , 131 ( 3 4 0 9 ) : 1 2 9 2 - 1 2 9 7 . H a r t m a n , G.F. 1963. O b s e r v a t i o n s on b e h a v i o r o f j u v e n i l e brown t r o u t i n a s t r e a m a q u a r i u m d u r i n g w i n t e r and s p r i n g . J . F i s h . R e s . Bd. C a n a d a , 2 0 ( 3 ) : 7 6 9 - 7 8 7 . 98. K a l l e b e r g , H. 1958. O b s e r v a t i o n s i n a s t r e a m t a n k o f t e r r i t o r i a l i t y and c o m p e t i t i o n i n j u v e n i l e s a l m o n and t r o u t (Salmo s a l a r L. and S. t r u t t a L . ) . R e p t . I n s t . F r e s h w a t e r R e s . D r o t t n i n g h o l m , 3 9 : 5 5 - 9 8 . K e e n l e y s i d e , M.H. and F.T. Yamamoto. 1962. T e r r i t o r i a l b e h a v i o u r o f j u v e n i l e A t l a n t i c s a l m o n (Salmo s a l a r L. ). B e h a v i o u r , 19 ( 1 - 2 ) : 139-169. L a r k i n , P.A. L i n d r o t h , A. 1956. I n t e r s p e c i f i c c o m p e t i t i o n and p o p u l a t i o n c o n t r o l i n f r e s h w a t e r f i s h . J . F i s h . R e s . Bd. C a n a d a , 1 3 ( 3 ) : 3 2 7 - 3 4 2 . 1 9 5 5 a . D i s t r i b u t i o n t e r r i t o r i a l b e h a v i o u r and movements o f s e a t r o u t f r y i n t h e R i v e r I n s a l s f i l v e n . R e p t . I n s t . F r e s h w a t e r R e s . D r o t t n i n g h o l m , 3 6 : 1 0 4 -119. , 1955b, M e r g a n s e r s as s a l m o n and t r o u t p r e d a t o r s i n t h e R i v e r I n d a l s & l v e n , R e p t . I n s t . F r e s h w a t e r R e s . D r o t t n i n g h o l m , 36: 1 2 6 - 1 3 2 . , and E. B e r g s t r B m . 1959. N o t e s on t h e f e e d i n g t e c h n i q u e o f t h e g o o s a n d e r i n s t r e a m s . R e p t . I n s t . F r e s h w a t e r R e s . D r o t t n i n g h o l m , 4 0 : 1 6 5 - 1 7 5 . M a c a n , T.T. 1961. F a c t o r s t h a t l i m i t t h e r a n g e o f f r e s h w a t e r a n i m a l s . B i o l . Rev. 36: 151-198. M c i n t o s h , R.P, 1 9 6 1 . C o m p e t i t i v e e x c l u s i o n p r i n c i p l e . S c i e n c e , 1 3 3 ( 3 4 5 0 ) : 3 9 1 . M i l n e , A. 1961. D e f i n i t i o n o f c o m p e t i t i o n among a n i m a l s . S y m p o s i a , S o c . E x p t l . B i o l . 15: 4 0 - 6 1 . M i u r a , ' T,. 1962. E a r l y l i f e h i s t o r y and p o s s i b l e i n t e r a c t i o n o f f i v e i n s h o r e s p e c i e s o f f i s h i n N i c o l a L a k e , B r i t i s h ' Columbia. Ph.D. T h e s i s , D e p t . Z o o l . U n i v . B r i t i s h C o l u m b i a , .133 p. Newman, M.A. 1956. S o c i a l b e h a v i o r and i n t e r s p e c i f i c c o m p e t i t i o n i n two t r o u t s p e c i e s . P h y s i o l . Z o f l l . 2 9 ( l ) : 6 4 - 8 1 . 1955. S t u d i e s on t h e f e e d i n g h a b i t s o f t r o u t and c h a r i n N o r t h S w e d i s h l a k e s . R e p t . I n s t . F r e s h w a t e r R e s . D r o t t n i n g h o l m , 36: 163-225. 1956. Om k o n k u r r e n s e n i n a t u r e n . Z o o l o g i s k R e v y , 1956: 4 0 - 4 7 . N i l s s o n , N.A. » 1958. On t h e f o o d c o m p e t i t i o n b e t w e e n two s p e c i e s o f C o r e g o n u s i n a N o r t h - S w e d i s h l a k e . R e p t . I n s t . F r e s h w a t e r R e s . D r o t t n i n g h o l m , 39: 1 4 6 - 1 6 1 . 99. N i l s s o n , N.A. 1960. S e a s o n a l f l u c t u a t i o n s i n t h e f o o d s e g r e g a t i o n o f t r o u t , c h a r and w h i t e f i s h i n 14 N o r t h -S w e d i s h l a k e s . R e p t . I n s t . F r e s h w a t e r R e s . D r o t t n i n g h o l m , 4 1 : 1 8 5 - 2 0 5 . , 1963. I n t e r a c t i o n b e t w e e n t r o u t and c h a r i n S c a n d i n a v i a . T r a n s , Am. F i s h e r i e s S o c . 9 2 ( 3 ) : 2 7 6 - 2 8 5 . P a t t e n , B.C. 1961. C o m p e t i t i v e e x c l u s i o n . S c i e n c e , 1 3 4 ( 3 4 9 0 ) 1 5 9 9 - 1 6 0 1 . S a u n d e r s , R.L, and J.H. Gee. 1964. Movements o f y o u n g A t l a n t i c S a l m o n i n a s m a l l s t r e a m . J . F i s h . R e s . Bd. C a n a d a , 2 l ( l ) : 2 7-36. Van V a l e n , L. 1960. F u r t h e r c o m p e t i t i v e e x c l u s i o n . S c i e n c e , 1 3 2 ( 3 4 4 0 ) : 1 6 7 4 - 1 6 7 5 . W a t e r R e s o u r c e s P a p e r No. 128. 1958-1959. D e p t . N o r t h . A f f a i r s and N a t u r a l R e s o u r c e s , W a t e r R e s o u r c e s B r a n c h . S u r f a c e W a t e r S u p p l y o f C a n a d a , P a c i f i c D r a i n a g e . 388 p. No.131. 1 9 5 9 - 1 9 6 0 . D e p t . N o r t h . A f f a i r s and N a t u r a l R e s o u r c e s , W a t e r R e s o u r c e s B r a n c h , S u r f a c e W a t e r S u p p l y o f C a n a d a , P a c i f i c D r a i n a g e . 4 0 2 p. A p p e n d i x I . Mean m o n t h l y d i s c h a r g e i n M J p e r s e c o n d , f o r t h e C h i l l i w a c k R i v e r a t V e d d e r . C r o s s i n g , t h e A l o u e t t e R i v e r a t 1 4 t h S t r e e t b r i d g e and f o r t h e S a l m o n R i v e r a t S p r i n g b r o o k Road b r i d g e (1958 t o 1 9 6 2 ) , J a n . 1 Feb. Mar, A p r . May J u n e J u l y Auq. S e p t . O c t . Nov. Dec. C h i l l i w a c k R.. 1-1958 56.9 52.1 40.5 46.7 130. 5 103.9 4 5 . 3 25.4 34.2 65.4 70.8 95.7 1959 70.5 32.3 32.8 72.2 91. 4 135.5 110.4 43.5 68.8 74.2 82.7 4 8 . 9 1960 22.7 37.6 22.2 47.3 ..65. •4 105.3 73.9 35.1 28.0 36.8 56.3 62.0 1961 73.9 75.0 47.0 55.2 8 1 . 4 183.7 95.4 57.7 27.8 49.8 4 5 . 6 4 4 . 2 1 9 6 2 88.9 70.5 22.9 57.6 — . — — — — — — -A l o u e t t e R. 1958 " 7,9 0.0 0.0 0.0 0. 0 0.3 3.7 0.0 0.0 0.0 2.0 1.4 1959 0.6 0.0 0.0 0.0 0. 0 0.0 10.5 2.2 2.2 0.0 0.0 0.0 1960 - - - 2.3 1. 7 ' 1.1 0.4 0.6 0.7 1.9 2.4 2.1 1961 9,8. 5.2 3.1 1.6 1. 3 0.6 0.4 0.3 0.4 2.1 3.5 7.0 1962 5.2 2.2 1.1- . 1.5.. — — — — — — — S a l m o n R. 1958 - -. - - - *.28 * . 2 3 *.40 — — _ 1959 - - - - *.14 *.38 . *.31 -' ±1-. 64 — I 9 6 0 .,5.10 3.20 1.40 1.40 1. 40 .50 .28 .23 .27 1.50 2.70 3.14 1961 4.67 5.97 3.70 1.47 1. 27 .33 .33 .25 .21 .86 1.67 3,40 1 9 6 2 3.51 1.98 1.50 1.61 1. 34 .54 .24 .29 .33 .94 3.26 3.93 1958-59 A l o u e t t e R i v e r d a t a f r o m B.C. H y d r o & Power A u t h o r i t y - s e e t e x t . * M i s c . s i n g l e r e a d i n g s Water R e s o u r c e s D i v i s i o n . + A v e r a g e o f two e s t i m a t e s by a u t h o r . A p p e n d i x I I . Maximum, minimum and mean m o n t h l y t e m p e r a t u r e (°C) o f t h e C h i l l i w a c k R i v e r , (*mean b a s e d on l e s s t h a n 20 day's d a t a , **mean b a s e d on l e s s t h a n 10 d a y s d a t a ) . 1 9 6 0 1 9 6 1 1 9 6 2 Max. M i n . Mean Max. M i n . Mean Max. M i n . Mean J a n u a r y ~ 5.9 -2.0 2.8 6.0 2.0 4.2 3.7 -1.0 2.0 F e b r u a r y 6.0 -2.0 4.2* 5.2 3.0 4 . 1 * 5.0 -1.0 2.3** M a r c h 8.0 -1.0 4.3 . 6.0 2.0 3.6* 7.5 -0.5 3.0 A p r i l 10.1 4.3 6.2 8.8 2.5 5.9 11.5 2.0 6.2 May 10.3 5.9 7.5* . 10.6 4.5 6.9 11.7 5.5 8.1 J u n e 12.0 5.8 8.6 12,2 6.5 9.3 J u l y 17.0 8.4 12.4 15.8 8.2 11.9 A u g u s t • 17.5 10.0 13.0 16.0 9.0 13.0 S e p t e m b e r 13.8 9.0 11.2 - - -O c t o b e r 12.1 6.6 9.1 10.0 5.5 7.5 * November 8.1 4.5 6.2 4.1 -1.0 2.4* December ~6.0 '3.4 4,8 4.0 0.0 2.2 A p p e n d i x I I I . Maximum, minimum and mean m o n t h l y t e m p e r a t u r e (°C) o f t h e A l o u e t t e R i v e r , • .(*mean b a s e d on l e s s t h a n 20 days d a t a , * * b a s e d on l e s s t h a n 10 d a y s d a t a ) . 1 9 6 0 1 9 6 1 1 9 6 2 Max. M i n . Mean Max. M i n . Mean Max. M i n . Mean J a n u a r y 6.4 • 0.7 4.2* 6.5 0.0 2.8 F e b r u a r y 7.2 1.7 5.4* • 7.4 4.2 6.1* M a r c h 10.3 5.0 6.3* 10.6 1.5 5.5 A p r i l 11.1 5.0 8.4* 13.4 ' 5.2 ' 8.9 May 20.5 6.1 12.0 • 15.0 6.9 10.5 J u n e 23.4 10.5 1 5 . 2 * 25.0 11.2 1 7 . 8 * .; 20.6 9.6 14.3 J u l y 27.8 ..1.2.8 2 0 . 8 * 27.1 13.1 20.1 A u g u s t 27.8 12.2 1 5 . 6 * 23.8 12.1 1 8 . 0 * * S e p t e m b e r 13.7 10.0 1 1 . 3 * * 15.0 11.1 1 3 . 2 * * O c t o b e r 11.6 6.6 9.1 15.0 3.4 1 0 . 2 * * November 8.8 2.1 5.3 5.5 4.5/ 5.2** December 6.1 0.0 2.5 5.0 3.0 4.0** A p p e n d i x I V . Maximum, minimum and mean m o n t h l y t e m p e r a t u r e (°C) o f the' S a l m o n R i v e r . 1 9 6 0 1 9 6 1 1 9 6 2 Max. M i n . Mean Max. M i n . Mean-- Max. M i n . Mean J a n u a r y 7.2 0.6 3.7 6.4 0.0 3.2 F e b r u a r y 7.8 3.6 5.5. 9.2 -0.5 5.4 M a r c h 10.3 3.1 "6.8 10.3 0.3 5.0 A p r i l 11.7 5.0 8.1 11.7 5.9 8.7 14.7 5.9 9.5 May 11.7 7.2 9.0 15.3 8.6 11.2 14.2 7.3 10.6 J u n e 13.4 8.6 10.8 . 17.5 11.4 14.0 17.8 9.5 12.9 J u l y 16.4 10.0 '13.0 20.3 10.0 15.5 A u g u s t 17.0 9.2 12.1 • 18.4 10.0 15.2 S e p t e m b e r 13.1 8.9 11.2 15.9 8.6 11.7 O c t o b e r 12.0 7.2 9.5 " 12.2 5.6 8.7 November 9.2 3.9 6.4 8.4 2.8 5.3 • December 7.6 0.6 3.8 6.7 1.1 3.7 A p p e n d i x V, Mean f o r k l e n g t h and r a n g e o f s a m p l e s o f f i s h u s e d i n e x p e r i m e n t s , O c t o b e r 3 0 , 1962 t o November 23, 1963. (* - m e a s u r e m e n t s made on p r e s e r v e d m a t e r i a l ) . Coho - C, S t e e l h e a d - S. D a t e p r e s e r v e d o r m e a s u r e d P e r i o d when u s e d S p e c i e s Mean F o r k L>.. r inl'ram'.: Range i n mm.. S a m p l e S i z e . O c t . 1 9 - 2 0 , 1962 Nov.1, 1962- F eb.20,1963 C 58.3 ' 40--95 13 -* II it II II S 50.9 38- -72 20 J a n . 1 0, 1963 •i II II c 68.6 52- -97 73 II ti II S • 60,7 50- -75 40 J a n . 19, ti II II n c 6 6 . 2 47- -88 40 II II n s 61.7 47- -76 40 A p r i l 2 5 , ii II u n c 67.5 51- -99 57 n n II s 59.3 49- -67 40 * May 1, 1963 May 7 t o Nov.23, 1963 C 37.9 3 5 - 4 2 15 -* May 2 5 , " n II II s 33.5 26-42 22 #• J u n e 8, " II ti n c 43.4 40-47 16 -* J u n e 12, " ti ti ii s 39.7 29-49 62 -* J u l y 1 9, " II ii ti c 52.1 38-64 65 II II ti ii ii s 42.7 35-56 64 S e p t . 2, " II ti ti c 66.4 ' 50-89 60 ti II II ti ii s 5 6 . 2 39-80 74 O c t . 8, " ti ti ti c 73.1 52-104 65 II tt ii ti II s 72.7 5 4 - 1 0 2 36 N o v . 2 3 , 1963 n II II c 76.7 62-93 30 * ti ti II II II s 7 3 . 2 4 7 - 1 1 2 35 * A p p e n d i x V I . D e t a i l s o f s p r i n g and e a r l y summer e x p e r i m e n t s c o m p a r i n g b e h a v i o r and d i s t r i b u t i o n o f coho and s t e e l h e a d . A r r a n g e m e n t S p e c i e s . T e m p e r a t u r e Day L e n g t h i n A v e r a g e number D a t e and Y e a r i n A q u a r i u m (40 f i s h ) Range °C H o l d i n g Pond m o v i n g  1963 A p r i l 1 9-21 C o n t r o l Coho 6.5-8.3 12 1.8 " 21-23 it it 8.5-9.2 12 2.7 J u n e 7-9 II it 11.7-12.0° 12 3.9 " 9-11 II S t e e l h e a d 14.0-14.3° 12 6.0 May 26-28 C o v e r Coho 10.0-11.2 12 3.7 " 28-30 II S t e e l h e a d 13.0-13.3 12 2.2 June' 11-13 L i g h t Coho 13.0-13.5 12 ' 4.1 11 13-15 n S t e e l h e a d 13.4-14.0 12 1.9 J u n e 22-24 D e p t h S t e e l h e a d 15.2-15.6 12 4.8 " 24-26 it Coho 14.0-15.9 1 2 4.1 J u n e 3 0 - D e p t h & S t e e l h e a d 14.0-14.5 12 9.8 J u l y 2 V e l o c i t y J u l y 2-4 it ti Coho 14.9-15.4 12 8.4 A p r i l 28-30 C o v e r Coho 7.1-7.5 12 2.5 " • 24-26 it II 7.1-8.4 12 1.1 J u n e 16-18 D e p t h II 15.0-16.0 12 3.5 1--o (Jl A p p e n d i x V I I , D e t a i l s o f f a l l e x p e r i m e n t s c o m p a r i n g b e h a v i o r and d i s t r i b u t i o n o f young s t e e l h e a d and c o h o . D a t e and Y e a r 1963 S e p t . 19-21 " 21-23 S e p t . 27-29 S e p t . 29-O c t . 1 S e p t . 23-25 11 25-27 O c t . 1-3 " 3-5 O c t . 5-7 •i 7_9 A r r a n g e m e n t i n A q u a r i u m C o n t r o l II C o v e r S p e c i e s T e m p e r a t u r e (40 f i s h ) Range °C L i g h t D e p t h D e p t h & V e l o c i t y S t e e l h e a d Coho S t e e l h e a d Coho Coho S t e e l h e a d Coho S t e e l h e a d Coho 12.7-13.3 13.2- 13.4 12.3- 13.1 14.2-14.5 12.7-13.5 13.6-14.2 12.5 - 13.0 1 1 . 6 - 12.1 10.1-10.6 S t e e l h e a d 10.8-11.0 Day L e n g t h i n H o l d i n g Pond 12 12 12 12 12 12 12 12 12 12 A v e r a g e number m o v i n g  7.9 3.0 11.5 2.6 3.5 11.6 3.9 7.2 6.2 7.5 A p p e n d i x V I I I . D e t a i l s o f w i n t e r e x p e r i m e n t s c o m p a r i n g d i s t r i b u t i o n and b e h a v i o r o f y o u n g s t e e l h e a d and c o h o . A r r a n g e m e n t S p e c i e s D a t e and Y e a r i n A q u a r i u m (40 f i s h ) 1 9 6 2 - 1 9 6 3 Nov. 5-7 C o n t r o l Coho II 1 9 - 2 1 '• Dec. 4-6 11 " Nov. 11-13 C o n t r o l S t e e l h e a d " 17-19 • • " « Dec. 6-8 " " " Nov.30-Dec.2 L i g h t Coho Dec. 2-4 L i g h t S t e e l h e a d i D e c . 1 7 - 1 9 D e p t h & V e l o c i t y Coho D e c . 1 9 - 2 1 D e p t h & V e l o c i t y S t e e l h e a d J a n . 1 9 - 2 1 C o v e r Coho " 23-25 " 11 J a n . 2 1 - 2 3 C o v e r S t e e l h e a d " 25-27 " " J a n . 8-10 D e p t h Coho II 1 2 _ 1 4 " J a n . 6-8 D e p t h S t e e l h e a d " 1 0 - 1 2 11 " T e m p e r a t u r e Cay L e n g t h i n A v e r a g e number Range °JC H o l d i n g P o n d m o v i n g  6.9-7.1 1 2 8.7 7.2-7.8 9 6.3 4.7-4.9 8 7.0-7.1 1 2 18.3 6.2-7.2 12 17.7 5.2- 5.7 8 19.7 2.7- 3.2 9 2.2 ,3.1-4.0 9 7.4 5.0-5.3 8 . 5 . 0 5.3- 5.6 8 10.6 2.0-2.4 8 1.1 2.4- 2.8 8 2.1 3.0-3.1 8 7.0 2.8- 2.8 8 8.1 1.7-2.5 8 2.3 0.5-1.0 8 0.6 3.9- 4.4 8 0.7 0.8-1.0 8 0.9 

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