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Ecology of the leopard dace Rhinichthys falcatus and its ecological relationships with the longnose dace… Gee, John Henry 1961

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ECOLOGY OP THE LEOPARD DACE R h i n i c h t h y s f a l c a t u s AND I TS ECOLOGICAL RELATIONSHIPS WITH THE LONGNOSE DACE R h i n i c h t h y s c a t a r a c t a e b y JOHN HENRY GEE B.. Comm., U n i v e r s i t y of B r i t i s h C o l u m b i a , 1 9 5 9 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS POR THE DEGREE OF MASTER OF SCIENCE i n t h e D e p a r t m e n t of Z o o l o g y 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 the r e q u i r e d s t a n d a r d THE UNIVERSITY OP BRITISH COLUMBIA O c t o b e r , 1 9 6 1 In presenting this thesis in p a r t i a l fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It i s understood that copying or publication of this thesis for financial gain shall not be allowed xvithout my written permission. Department of Zoology  The University of British Columbia, Vancouver 8, Canada. Date Sept. 30, 1961  i i ABSTRACT S y m p a t r i c a l l y o c c u r i n g R h i n i c h t h y s f a l c a t u s and R. c a t a r a c t a e were c o l l e c t e d f r o m f o u r a r e a s of the F r a s e r R i v e r d r a i n a g e s y s t e m . A l i f e h i s t o r y e x a m i n a t i o n of R. f a l c a t u s r e v e a l e d t h a t i t i s an o m n i v o r o u s f e e d e r , s p a w n i n g i n e a r l y J u l y a t age I I I and o l d e r , w i t h some males o f t h i s age d e v e l o p i n g a permanant s p a w n i n g c o l o r . B o t h s e x e s d e v e l o p n u p t i a l t u b e r c l e s a t age I . F e m a l e s a r e h e a v i e r and l o n g e r t h a n m a l e s , t h e g r e a t e s t d i f f e r e n c e s o c c u r i n g a t age I I I and o l d e r . F i e l d c o l l e c t i o n s f r o m a v a r i e t y of d e f i n e d h a b i t a t s showed t h a t R. f a l c a t u s were most numerous d u r i n g d a y l i g h t i n w a t e r v e l o c i t i e s of l e s s t h a n 1.5 f t . / s e c . A d u l t s o c c u p i e d p r i m a r i l y d e p t h s of one f o o t or g r e a t e r , t h e y e a r l i n g and y o u n g - o f - t h e -y e a r f i s h were most numerous i n d e p t h s o f l e s s t h a n one f o o t . R. c a t a r a c t a e were most numerous d u r i n g d a y l i g h t i n d e p t h s o f l e s s t h a n one f o o t , t h e a d u l t s o c c u p y i n g w a t e r v e l o c i t i e s o f g r e a t e r t h a n 1.5 f t . / s e c , w h i l e y e a r l i n g and y o u n g - o f - t h e - y e a r f i s h were d i s t r i b u t e d a l m o s t e q u a l l y i n v e l o c i t i e s b o t h g r e a t e r and l e s s t h a n 1.5 f t . / s e c . B o t h s p e c i e s r e m a i n e d u n c h a n g e d i n t h e i r c u r r e n t d i s t r i b u t i o n a f t e r d a r k b u t some y o u n g - o f - t h e - y e a r and y e a r l i n g f i s h of b o t h s p e c i e s moved o f f s h o r e t o a r e a s d e e p e r t h a n one f o o t w h i l e ad.ult R. f a l c a t u s became more numerous a t n i g h t i n o n s h o r e s h a l l o w s of l e s s t h a n one f o o t i n d e p t h . F i e l d o b s e r v a t i o n s on c u r r e n t d i s t r i b u t i o n of b o t h s p e c i e s were c o n f i r m e d i n l a b o r a t o r y c u r r e n t p r e f e r e n c e e x p e r i m e n t s i n a s t r e a m t a n k . The p r e f e r e n c e of t h r e e s i z e g r o u p s of b o t h i i i s p e c i e s f o r areas of l i t t l e or no c u r r e n t and areas of e i t h e r 1, 2 , 3 , or LL f t . / s e c . w a t e r v e l o c i t y i n the stream tank were t e s t e d I n 30 e x p e r i m e n t s . I n a l l experiments but one, t h e r e was a s i g n i f i c a n t d i f f e r e n c e between the r a t i o of R. f a l c a t u s t o R. c a t a r a c t a e i n the c u r r e n t a r e a s ; R. c a t a r a c t a e were more numerous. Morphology and f u n c t i o n of the a i r b l a d d e r of both s p e c i e s were a n a l y s e d , and d i f f e r e n c e s i n volume were e x p l a i n e d on the b a s i s of d i v e r g i n g h a b i t a t s e l e c t i o n of y e a r l i n g and a d u l t f i s h . The h a b i t a t d i v e r g e n c e between y e a r l i n g and o l d e r R. f a l c a t u s and R. c a t a r a c t a e i s i n accordance w i t h Cause's c o n t e n t i o n . i v TABLE OP CONTENTS Page TITLE PAGE i ABSTRACT i i TABLE OP CONTENTS i v LIST OP FIGURES v i LIST OF TABLES v i i i INTRODUCTION 1 MATERIALS AND METHODS 3 A. C o l l e c t i o n of F i e l d Data 3 B. Method of Stomach A n a l y s i s 5 C. L a b o r a t o r y Experiments 5 1. D e s c r i p t i o n of Experimental S e c t i o n 5 2 . Source of Experimental P i s h 8 3. H o l d i n g of Experimental P i s h 8 I I. S e l e c t i o n of P i s h f o r Experiments . . . . 8 5. Number of Experiments 9 6. Experimental Procedure 11 D. Volume A n a l y s i s of A i r b l a d d e r s 11 RESULTS 14 A. Habits of R. f a l c a t u s 14 1. Age and Growth 4^ 2. Pood X4 3. Reproduction 19 II. P a r a s i t e s 22 Page B. C o m p a r a t i v e E c o l o g y of R. f a l c a t u s a nd R. c a t a r a c t a e . . 22 1. C u r r e n t D i s t r i b u t i o n 22 2. Depth D i s t r i b u t i o n - D a y l i g h t . . • 23 3. D e p t h D i s t r i b u t i o n - N i g h t . 26 ]+. B o t t o m P r e f e r e n c e 26 5. Pood o f R. f a l c a t u s and R. c a t a r a c t a e o f Age 0 and 1 2 ? C. S t r e a m Tank E x p e r i m e n t s 29 1 . R a t i o A n a l y s i s of P i s h i n C u r r e n t Arm 2 9 ( a ) B l o c k r a t i o a n a l y s i s 30 ( b ) E x p e r i m e n t a l r a t i o a n a l y s i s 32 2. P o s i t i o n o f P i s h i n R e l a t i o n t o C u r r e n t Arm 36 D. C o m p a r a t i v e A i r b l a d d e r A n a l y s i s 38 DISCUSSION 1+0 A. L i f e H i s t o r y of R. f a l c a t u s 40 B. E c o l o g i c a l S i g n i f i c a n c e o f E x p e r i m e n t a l and F i e l d D a t a 4 2 C. E c o l o g i c a l S i g n i f i c a n c e of A i r b l a d d e r A n a l y s i s 43 D. B i o l o g i c a l S i g n i f i c a n c e o f H a b i t a t . . S e g r e g a t i o n 44 ACKNOWLEDGMENTS 48 LITERATURE CITED 49 v i L I S T OF FIGURES Page F i g u r e 1. E x p e r i m e n t a l s e c t i o n o f s t r e a m t a n k 7 F i g u r e 2. A p p a r a t u s f o r m e a s u r i n g a i r b l a d d e r volume 13 F i g u r e ?>. L e n g t h f r e q u e n c y o f R. f a l c a t u s c o l l e c t e d on t h e F r a s e r R i v e r b e t w e e n Hope and C h i l l i w a c k , June 2 a n d 5, 1961 • • 15 F i g u r e I I. Growth i n l e n g t h and w e i g h t of R. f a l c a t u s c o l l e c t e d f r o m t h e F r a s e r R i v e r between Hope and C h l l l i w a c k 16 F i g u r e 5» Stomach c o n t e n t s of R. f a l c a t u s c o l l e c t e d f r o m t h e F r a s e r R i v e r b e t w e e n Hope and C h i l l i w a c k . . . 18 F i g u r e 6. Gonad d e v e l o p m e n t o f R. f a l c a t u s c o l l e c t e d f r o m t h e F r a s e r R i v e r b etween Hope a n d C h i l l i w a c k 20 F i g u r e 1. L e n g t h f r e q u e n c y of male R. f a l c a t u s w i t h s p a w n i n g c o l o r , c o l l e c t e d f r o m the F r a s e r R i v e r between Hope and C h i l l i w a c k 21 F i g u r e 8. C u r r e n t d i s t r i b u t i o n o f R. f a l c a t u s and R. c a t a r a c t a e f r o m a l l c o l l e c t i o n a r e a s ( T a b l e I ) . 2LL F i g u r e 9. Depth d i s t r i b u t i o n of R. f a l c a t u s and R. c a t a r a c t a e d u r i n g d a y l i g h t and n i g h t 25 F i g u r e 10. Stomach c o n t e n t s o f R. f a l c a t u s and R. c a t a r a c t a e o f age 0 a n d 1 c o l l e c t e d f r o m the same a r e a s of t h e F r a s e r R i v e r between Hope a n d C h i l l i w a c k 28 F i g u r e 11. F l o w p r e f e r e n c e of R. f a l c a t u s and R. c a t a r a c t a e i n s t r e a m t a n k . 31 F i g u r e 12. Two t y p e s o f c u r r e n t p a t t e r n s o b s e r v e d b e l o w c u r r e n t arm i n e x p e r i -m e n t a l s e c t i o n o f s t r e a m t a n k 35 v i i Page F i g u r e 13. P o s i t i o n o f f i s h i n r e l a t i o n t o c u r r e n t arm, A; i n c u r r e n t arm, B; r e d u c e d c u r r e n t , - i n p o s i t i o n t o e n t e r c u r r e n t arm, C; b a c k - e d d y o f s l i g h t c u r r e n t , Dj n o n - c u r r e n t arm. . . . 37 F i g u r e II4.. C o m p a r i s o n of t h e r e l a t i o n s h i p b e t w e e n volume o f a i r b l a d d e r and w e i g h t o f f i s h i n R. f a l c a t u s and R. c a t a r a c t a e . . . . . . . 39 v i i i L I S T OP TABLES Page TABLE 1. COLLECTION AREAS AND NUMBER OP PISH COLLECTED . . . . . Ij. TABLE 2. NUMBER AND S I Z E OP PISH USED I N EXPERIMENTS 10 TABLE 3 . EXPERIMENTAL AND BLOCK RATIOS OP R. f a l c a t u s AND R. c a t a r a c t a e IN CURRENT ARM OP STREAM TANK 3k TABLE l i . SUMMARY OP THE COMPARATIVE ECOLOGY OP R. f a l c a t u s AND R. c a t a r a c t a e Lj.1 I INTRODUCTION R h i n i c h t h y a f a l c a t u s ( E i g e n m a n n and Eigenmann) i s a s m a l l r i v e r - d w e l l i n g c y p r i n i d f i s h c o n f i n e d i n i t s d i s t r i b u t i o n t o the P r a s e r and C o l u m b i a r i v e r s y s t e m s . A l t h o u g h i t i s a common f i s h i n b o t h r i v e r s , l i t t l e i s known about i t s l i f e h i s t o r y . A c l o s e l y r e l a t e d s p e c i e s , R. c a t a r a c t a e , a l s o o c c u r s i n b o t h r i v e r s y s t e m s and has b e e n c o l l e c t e d f r o m t h e same a r e a s as R. f a l c a t u s i n t h e l o w e r P r a s e r R i v e r . The s y m p a t r i c o c c u r a n c e of two c o n g e n e r i c s p e c i e s s u g g e s t s a p o s s i b l e c o m p e t i t i v e r e l a t i o n s h i p , o p p o s i n g Gause's c o n t e n t i o n t h a t c l o s e l y r e l a t e d s p e c i e s c a n n o t o c c u p y a s i m i l a r n i c h e w i t h o u t one e l i m i n a t i n g the o t h e r t h r o u g h c o m p e t i t i o n . The p r e s e n t s t u d y was i n i a t e d f i r s t t o d e s c r i b e some o f th e l i f e h i s t o r y f e a t u r e s o f R. f a l c a t u s , and s e c o n d l y , t o ex-amine t h e c o m p a r a t i v e e c o l o g y o f R. f a l c a t u s and R. c a t a r a c t a e i n o r d e r t o e x p l a i n t h e i r a p p a r e n t c o e x i s t e n c e . P u b l i s h e d m a t e r i a l on t h e l i f e h i s t o r y o f R. f a l c a t u s i s s c a n t . E i g e n m a n n and E i g e n m a n n f i r s t d e s c r i b e d t h e s p e c i e s i n 1893. G i l b e r t and E v e r m a n (1895) gave a f u r t h e r m o r p h o l o g i c a l d e s c r i p t i o n w i t h e m p h a s i s on n u p t i a l t u b e r c l e s . A b r i e f and i n c o n c l u s i v e c o m p a r a t i v e f o o d s t u d y o f R. c a t a r a c t a e and R. f a l c a t u s was c o m p l e t e d b y Johannes (1959). The t e r m h a b i t a t w i l l be u s e d i n t h i s i n v e s t i g a t i o n i n r e f e r e n c e t o t h e p h y s i c a l e n v i r o n m e n t o f t h e f i s h , w h i l e e c o -l o g i c a l n i c h e w i l l be u s e d t o d e s i g n a t e t h e p l a c e o f t h e f i s h - 2 -w i t h i n i t s b i o l o g i c a l e n v i r o n m e n t . These d e f i n i t i o n s f o l l o w c l o s e l y t h o s e o f E l t o n (1927) and G r i n n e l l (1928) , as r e -commended by U d v a r d y (1959) . I I MATERIALS AND METHODS A. C o l l e c t i o n o f F i e l d D a t a . R. f a l c a t u s and R. c a t a r a c t a e were c o l l e c t e d f r o m s e v e r a l a r e a s i n the F r a s e r R i v e r d r a i n a g e s y s t e m as shown i n T a b l e 1. F i s h were c o l l e c t e d i n two t y p e s o f s e i n e s . The f i r s t was a common beach s e i n e , 6 f t . wide a n d ij. f t . h i g h w i t h a mesh d i a m e t e r o f 0.1 i n . The s e c o n d t y p e o f s e i n e was e q u i p p e d w i t h a c o d - e n d . I t was 10 f t . w i d e , Ij. f t . h i g h , w i t h a 0.7 i n . mesh d i a m e t e r i n t h e mouth and a 0.3 i n . mesh d i a m e t e r i n t h e c o d - e n d . B o t h s e i n e s were o p e r a t e d b y two men. Two methods o f s e i n i n g were em p l o y e d d e p e n d i n g on the w a t e r v e l o c i t y . I n v e l o c i t i e s o f 2 f t . / s e c . o r g r e a t e r , t h e s e i n e was s p r e a d i n the w a t e r and h e l d I n p o s i t i o n b y one man. The s e c o n d man s t a t i o n e d h i m s e l f 10 t o 15 f t . u p s t r e a m f r o m the s e i n e and t h e n moved as f a s t as p o s s i b l e t o t h e s e i n e w h i l e , a t t h e same t i m e , s c u f f l i n g t h e b o t t o m t o d i s l o d g e f i s h f r o m t h e s p a c e s between s t o n e s . When the s e c o n d man r e a c h e d t h e s e i n e i t was l i f t e d f r o m the w a t e r . The a l t e r n a t i v e method was u s e d i n w a t e r v e l o c i t i e s o f l e s s t h a n 2 f t . / s e c . B o t h men p u l l e d the s e i n e t h r o u g h t h e w a t e r , m oving w i t h the c u r r e n t whenever p r e s e n t . S e i n e h a u l s were made, when p o s s i b l e , i n a r e a s of s i m i l a r w a t e r v e l o c i t y and d e p t h o v e r a homogeneous b o t t o m s o t h a t samples o f f i s h c o l l e c t e d p e r s e i n e h a u l were r e s t r i c t e d t o c e r t a i n p h y s i c a l e n v i r o n m e n t a l b o u n d a r i e s . TABLE I COLLECTION AREAS AND NUMBER OP PISH COLLECTED Number of Pish Collected R. falcatus R. cataractae June 1 -2/60 Praser River , MacAllister, B.C. 38 47 June 3/60 11 11 Quesnel, B.C. 0 2 July 7 - 8 / 6 0 ti 11 Hope> -Chilliwack, B.C. 152 54 July 15/60 ti ti 11 11 83 47 July 2 0 / 6 0 ti 11 11 it 23 49 Aug. 16-18/60 ti it it it 119 109 Aug. 29/60 It it it tt 23 15 Sept. 3/60 II 11 it 11 1003 46 Sept. 25/60 II ti tt ti 12 83 Oct. 18/60 II ti 11 tt 123 86 Nov. 14/60 It ti 11 11 76 0 Mar. 8/61 II ti ti 11 48 0 Apr. 29/61 Baker Creek, Quesnel, B.C. 0 14 May 17/61 11 11 11 0 21 May 18/61 Praser River, MacAllister, B.C. 31 26 May 23/61 Baker Creek, Quesnel, B.C. 0 12 June 25/61 Praser River, Hope-•Chilliwack, B.C. 396 114 B. Method of Stomach A n a l y s i s . P i s h c o l l e c t e d between Hope and C h i l l i w a c k were u t i l i z e d f o r stomach a n a l y s i s . The contents of the a n t e r i o r one t h i r d of the a l i m e n t a r y canal were emptied i n t o a watch g l a s s and i d e n t i f i e d with the a i d of a b i n o c u l a r d i s s e c t i n g microscope. Pood components were c l a s s i f i e d to genus where p o s s i b l e , and f o r each stomach the number of organisms i n each food group was r e c o r d e d and the percent volume that each food group c o n t r i b u t e d to the t o t a l i n d i v i d u a l stomach volume was e s t i -mated. A f t e r i d e n t i f i c a t i o n , stomach contents of each f i s h were d r i e d on a paper towel f o r f i v e seconds and p l a c e d i n a 0. 25 i n . diameter g l a s s tube with one end s e a l e d , and with a mark i n d i c a t i n g a 2 ml. volume. One m i l l i l i t e r of water was added to the g l a s s tube with a graduated s y r i n g e . This washed the stomach contents to the bottom of the g l a s s tube.. The s y r i n g e was f i l l e d with an a d d i t i o n a l m i l l i l i t e r of water which was then added to the g l a s s tube u n t i l the l e v e l reached the 2 ml. mark. Displacement volume of the stomach contents was then c a l c u l a t e d from the remaining volume of water i n the s y r i n g e ; the l a t t e r was c a l i b r a t e d to 0.01 ml. This method a l s o was used to determine the volume of the gonads. C. L a b o r a t o r y Experiments 1. D e s c r i p t i o n of Experimental S e c t i o n L a b o r a t o r y experiments were conducted i n a stream tank, - 6 -d e s c r i b e d by N o r t h c o t e (I960), l o c a t e d a t the U n i v e r s i t y of B r i t i s h Columbia. One p a r t of the stream tank w a s ' m o d i f i e d i n t o an e x p e r i m e n t a l s e c t i o n where a l l e x p e r i m e n t s were con-f i n e d . The b a s i c d e s i g n , s i m i l a r t o t h a t of MacKinnon and Hoar ( 1 9 5 3 ) , w a s t o p r o v i d e areas w i t h and w i t h o u t c u r r e n t , f o r s e l e c t i o n by e x p e r i m e n t a l f i s h . S e l e c t i o n of a c u r r e n t a r e a was t a k e n as an i n d i c a t i o n of c u r r e n t p r e f e r e n c e . The e x p e r i m e n t a l s e c t i o n of the stream tank i s I l l u s t r a t e d i n F i g u r e 1 . The two n o z z l e s , c o n n e c t e d t o w a t e r pumps by f l e x i b l e p l a s t i c p i p e s , c o u l d d i r e c t w a t e r c u r r e n t s i n t o Arm A or Arm B. Two s c r e e n s a t each end of the e x p e r i m e n t a l s e c t i o n s e p a r a t e d i t from the remainder of the stream t a n k , w h i l e a t h i r d removable s c r e e n formed a h o l d i n g a r e a where f i s h were h e l d p r i o r t o each e x p e r i m e n t . An aluminum p l a t e was p l a c e d a g a i n s t the s c r e e n a t the bead of the n o n - c u r r e n t arm t o mi n i m i z e any c u r r e n t s c r e a t e d by wat e r c i r c u l a t i o n i n the s t r e a m tank. The p a r t i t i o n s e p a r a t i n g the two arms housed an o v e r f l o w d r a i n which removed excess w a t e r added i n the n o n - e x p e r i m e n t a l s e c t i o n t o m a i n t a i n a c o n s t a n t water t e m p e r a t u r e . Water temperature remained between 6 . 5 ° C . and 8 . 5>°C. d u r i n g a l l e x p e r i m e n t s . The bottom of each arm was s l o p e d upwards towards the down-current end, t e r m i n a t i n g a t the l i p of the ramp i n a downward s l o p e ( F i g . 1 , s i d e v i e w ) . The upward s l o p e was n e c e s s a r y t o c r e a t e a more u n i f o r m w a t e r v e l o c i t y a l o n g the l e n g t h of the c u r r e n t arm. The bottom of the a r e a I m m e d i a t e l y - 7 -!©© i • 1 " 1 , 1 i .... , ... - — ^ © 1 © ! 1 © -• I \ ®© • t 1 © © © © :© T O P © © i © ! © c : f 5 © © © © © © © © © © © S I D E N O Z Z L E S A R M A A R M B S C R E E N P A R T I T I O N R E M O V A B L E SCR EE N H O L D I N G A R E A PAR TITI ON O V E R F L O W D R A I N LIP O F R A M P A L U M I N U M P L A T E R A M P S U P P O R T F i g u r e 1., Experimental s e c t i o n of the stream tank. -8-below the current arms was marked off into s i x squares to give detailed records on the current d i s t r i b u t i o n of the experimental f i s h . 2. Source of Experimental Fish Experimental f i s h were co l l e c t e d from three locations. A l l R. falcatus of greater fork length than £ 0 mm., and approximately one ha l f of the R. cataractae, were coll e c t e d from the Nicola River at M e r r i t t , B. C , on Dec. 7, i960. The remaining R. cataractae were collected from Brunette Creek at New Westminster, B. C. on Nov. Ii, 1960. R. falcatus of less than 50 mm. fork length were c o l l e c t e d from the Fraser River between Hope and Chilliwack, B. C , on March 8, 1961. 3. Holding of Experimental Fish Experimental f i s h were held i n a single hatchery trough at the same temperature as that used i n the stream tank. There was v i r t u a l l y no current i n this trough although a s l i g h t turbulence occurred at one end where water was i n t r o -duced. Experimental f i s h were fed'Clark's f i s h food" and frozen brine shrimp; they appeared healthy during the course of the experiments. Water temperature i n the hatchery trough varied between £ to 6.5°C. during the time that experiments were ca r r i e d out. 4. Selection of Fish f or Experiments Experimental f i s h were selected from the trough on the basis of fork length, and were measured i n a "V" shaped con-- 9 -t a i n e r s u bmerged i n t h e h a t c h e r y t r o u g h . E x p e r i m e n t s were c a r r i e d out on t h r e e s i z e g r o u p s o f f i s h : 70-95 mm., 50-70 mm., and 30-1+0 mm., f o r k l e n g t h . The number and s i z e o f b o t h s p e c i e s u s e d i n t h e e x p e r i m e n t s a r e shown i n T a b l e I I . The h a t c h e r y t r o u g h was d i v i d e d i n t o t h r e e c o m p a r t m e n t s , w i t h a l l f i s h o r i g i n a l l y h e l d i n t h e f i r s t . P r i o r t o s u b -j e c t i n g any s i z e g r o u p t o e x p e r i m e n t s , f i s h o f t h a t s i z e g r o u p were removed f r o m t h e f i r s t compartment and i s o l a t e d i n t h e s e c o n d . P i s h were s e l e c t e d i n g r o u p s o f t e n f r o m t h e s e c o n d compartment and a f t e r t h e y h a d b e e n s u b j e c t e d t o a c u r r e n t p r e f e r e n c e e x p e r i m e n t , t h e y were r e t u r n e d t o the t h i r d . I f no f i s h i n the s e c o n d compartment r e m a i n e d , and f u r t h e r t e s t s were n e c e s s a r y on t h a t s i z e g r o u p , f i s h were s e l e c t e d f r o m t h e t h i r d compartment and r e t u r n e d t o t h e s e c o n d . A l l f i s h o f t h e 70-95 mm. s i z e g r o u p were u s e d t w i c e and t e n f i s h were u s e d t h r e e t i m e s . P i s h of the 50-70 mm. g r o u p were e a c h u s e d f o u r t i m e s w h i l e f i s h i n t h e 30-Jj.O mm. s i z e g r o u p were u s e d t w i c e . 5. Number of E x p e r i m e n t s Of t h e 1 2 e x p e r i m e n t s t h a t were c o n d u c t e d on t h e 70-95 ™» s i z e g r o u p , t h r e e t e s t s were c o m p l e t e d a t . e a c h o f f o u r w a t e r v e l o c i t i e s ? 1 , 2 , 3> and I4. f t . / s e c . C u r r e n t was m e a s u r e d on t h e l i p o f the ramp w i t h a G u r l y f l o w m e t e r . An e q u a l number of e x p e r i m e n t s a t t h e same v e l o c i t i e s were c o m p l e t e d on t h e 50-70 mm. s i z e g r o u p . F i s h o f t h e 30-1+0 mm. s i z e g r o u p were t e s t e d s i x t i m e s , t h r e e e x p e r i m e n t s a t each o f - 1 0 -TABLE II NUMBER AND SIZE OP PISH USED IN EXPERIMENTS 7 0 - 9 5 mm. Size Group Total number and size of f i s h Pork length (mm.) 7 0 - 7 5 7 5 - 8 0 8 0 - 8 5 8 5 - 9 0 90-95 R. fa lcatus $ $ S $ $ R. cataractae S S 5 ^> ^> Number and s ize of f i s h per experiment R. fa lcatus 1 1 1 1 1 R. cataractae 1 1 1 1 1 5 0 - 7 0 mm. Size Group Total number and s ize of f i s h Pork length (mm.) 5 0 - 6 0 6 0 - 6 5 6 5 - 7 0 7 0 - 7 5 R. fa lcatus 3 3 6 3 R. cataractae 3 3 6 3 Number and s ize of f i sh per experiment R. fa lcatus 1 1 2 1 R. cataractae 1 1 2 1 30-lj-O mm. Size Group Total, number and s ize of f i s h Pork length (mm.) 30-lj.O R. fa lcatus 1 5 R. cataractae 1 5 Number and s ize of f i s h per experiment R. fa lcatus 5 R. cataractae 5 - 1 1 -two v e l o c i t i e s ? 1 and 2 f t . / s e c . Of the group of three experiments completed on a s ize group at any flow, two were made with the current i n one arm while the t h i r d was 'com-pleted with the current i n the opposite arm. 6 . Experimental Procedure P r i o r to each experiment, the water pumps were s tarted and the correct v e l o c i t y was created i n the se lected current arm. Water currents were regulated to minimize surface bubbles and to equal ize , as much as pos s ib l e , water ve lo -c i t y along the length and width of the current arm. A f t e r the required current pattern was es tabl i shed , the removable screen was placed in to p o s i t i o n . Pish were then placed into the holding area of the experimental sec t ion and he ld there for a 30 minute per iod after which the removable screen was l i f t e d out and f i sh were allowed to swim into any preferred area. Observations were made at 30 minute Intervals f or a. ten hour per iod fo l lowing the removal of the screen. Thus 20 observations were r e -corded on the current d i s t r i b u t i o n of the ten experimental f i s h . At the termination of each experiment, the current pat tern was compared to the o r i g i n a l pat tern . D. Volume Analys is of Airbladders Seventy-f ive R. fa lcatus and 73 R. cataractae were taken from a l l f i e l d c o l l e c t i o n s and from museum c o l l e c t i o n s at the U n i v e r s i t y of B r i t i s h Columbia* These f i sh were, however, r e s t r i c t e d to the Praser River drainages. Pish were dr i ed on - 1 2 -a paper towel for 1$ seconds and then weighed on a Mett ler p r e c i s i o n balance accurate to 0 . 1 gm. Weights were estimated to two decimal p laces . The a irbladder was then removed and the outer layer of the anter ior lobe was peeled off . The apparatus used for determining a irb ladder volume i s i l l u s t r a t e d i n Figure 2 . The needle of a 1 ml . syringe was bent at r i g h t angles and passed through a rubber stopper. The a irb ladder was drawn onto the needle with forceps and completely def lated by the syringe. The def lated a i r b l a d d e r , on the other end of the needle, was inserted into the glass tube and he ld i n p o s i t i o n by the rubber stopper. The rubber cap was removed from the overflow tube and water from the syphon tube was allowed to f i l l the glass tube and part of the graduated tube before running over the overflow tube. Water flow from the syphon tube was then ha l ted and the over-flow tube was sealed with the rubber cap. The p o s i t i o n of the rubber cap was then adjusted u n t i l the column of water i n the graduated tube reached a convenient s t a r t i n g mark. The a irb ladder was then i n f l a t e d u n t i l e i ther minute bubbles passed out the pneumatic duct or pressure i n the a i r -bladder forced the plunger of the syringe back when pressure on i t was removed. The displacement volume of the a irbladder was then recorded. The p o s i t i o n of the meniscus i n the graduated tube ( c a l i b r a t e d i n 0 . 0 1 ml . ) was determined with the a i d of a magnifying g lass . -13-(D \J ® © N E E D L E @ RUBBER S T O P P E R (3) SYRINGE ® GLASS TUBE © S Y P H O N TUBE © O V E R F L O W TUBE © RUBBER C A P © G R A O U A T E O T U B E Figure 2. Apparatus for measuring a irbladder volume. I l l RESULTS A. Habits of R. fa lcatus 1 . Age and Growth R. f a l c a t u s , c o l l e c t e d between Hope and Chi l l iwack on June 2 and 5, 1 9 6 1 were aged by length frequency ( F i g . 3)» No obvious differences i n length d i s t r i b u t i o n were found between sexes. Combined length frequencies of both sexes were used i n age determination. Length of f i s h of age I var ied from 18 to 35 mm. fork length, while f i sh of age II v a r i e d from I L 5 - 6 0 mm. Fish of greater length than 6 2 mm. were designated as age I I I and older and were div ided in to two groups; those less than 81 mm., and those greater than 8 0 mm., fork length. Growth i n length and weight by sex i s i l l u s t r a t e d i n F i g . It. F ish of age 0 and age I were not sexed due to the undeveloped state of the gonads. F ish of age I and older were taken from the June 2 and 5 c o l l e c t i o n s , while f i s h of age 0 were c o l l e c t e d on August 15, I 9 6 0 . Female f i s h are heavier and longer than male f i s h ; such differences become more evident among older f i s h . 2 . Food Stomach contents of R. f a l c a t u s , c o l l e c t e d i n the Fraser River between Hope and Chi l l iwack i n June, I 9 6 I and J u l y , i 9 6 0 were s i m i l a r , as c o l l e c t i n g times coincided with the peak spring run-o f f i n both years. Thus the stomach contents 3 0 — > u z 20 uj O UJ ^ IO . A G E I 10 20 3 0 T 4 0 A G E II A G E II1 4- < 81 M M . A G E > 8 0 M M . T 1 5 0 6 0 7 0 8 0 F O R K L E N G T H , M I L L I M E T E R S r 9 0 H CL r o o 110 120 1 vn. 1 Figure 3. Length frequency of R« falcatus collected from Frase"F~RTver between Hope and Chilliwack, June 2 and 5, 1961. -16-A G E Figure I4.. Growth i n length and weight °£ R« fa lcatus from Fraser River between Hope and C h i l l i w a c k . -17-of f i s h c o l l e c t e d i n these two periods were combined. Stomach contents of f i s h c o l l e c t e d i n October and November, i 9 6 0 and March 1961, were also s i m i l a r and were combined as shown i n Figure 5« During the spring run-o f f i n June and J u l y , year l ing (age I) R. fa lcatus fed p r i m a r i l y (by volume) on aquatic insect l arvae ; Ephemeroptera and Diptera were the most predominant forms. Adult (age II and older) R. fa lcatus fed p r i m a r i l y on Lumbricus and aquatic insect larvae . Ephemeroptera "and Diptera again were the dominant forms. Lumbricus i s most ava i lab le as a source of food i n the spr ing . It can be dislodged during f looding or when the ground i n which i t inhabits becomes inundated, the earthworms usua l ly rest with part of t h e i r pos ter ior ends protruding from t h e i r burrows and occas ional ly leave the i r burrows roaming over the s o i l surface (Campbell, 1957). On examin-at ion of a c o l l e c t i o n of R. fa lcatus taken from a f looded pasture, 90$ by volume of the food consisted of Lumbricus. Stomach analysis of c o l l e c t i o n s taken between Hope and Chi l l iwack on September 3, i960 showed that young-of-the-year >• (age 0) R. fa lcatus were feeding exc lus ive ly on aquatic insect l arvae , composed mostly of Diptera ( 9 0 $ ) . Year l ing and adult R. fa lcatus c o l l e c t e d at this time were feeding p r i m a r i l y on t e r r e s t r i a l insects composed exc lus ive ly of winged ants. In October, November, and March, only young-of-the-year R. fa lcatus were c o l l e c t e d i n the Fraser River between Hope AGE O A G E I A G E 2 4-AOUATIC I N S E C T LARVAE TERRESTRIAL I N S E C T S LUMBRICU S A L G A E , DIATOMS, SAND UNKNOWN NEMATODES HYDRACARINA INVERTEBRATE EGGS FI SH AOUATIC INSECT L A R V A E TERRESTRIAL INSECTS ALGAE, DIATOMS, SAND AQUATIC INSECT L A R V A E A L G A E , DIATOMS, SAND NO FISH PRE SENT i SO T " X-LESS THAN 1% T " COLLECT ED IOO 5 0 IOO S O % VOLUME O F TOTAL STOMACH VOLUME JUNE /6I AND J U L Y / 6 0 SEPT ./60 OCT. / 6 0 NO V ./60 AND M A R . / 6 I IOO I J—' CD I Figure 5. Stomach contents of R. fa lcatus co l l ec ted from the Fraser River between Hope and C h i l l i w a c k . - 1 9 -and C h i l l i w a c k . These f i s h fed predominately on aquatic insect larvae , p r i m a r i l y Diptera . 3. Reproduction Gonad volume was used as an i n d i c a t i o n of sexual develop-ment and maturity . Volume determination was not attempted on f i sh of age 0 or I , nor on male f i sh of less than . 8 0 mm. fork length as the gonad volume was too small to be measured. Gonad volume and sexual development i s shown i n Figure 6. Gonads of age III and older female f i s h increased from the June c o l l e c t i o n to the Ju ly c o l l e c t i o n which was followed by a decrease between J u l y a id September c o l l e c t i o n s . A s i m i l a r increase and decrease i s found among age III and older males of greater length than 8 0 mm. The decrease i n gonad volume between J u l y and September may be a t t r i b u t e d to spawning. Young-of-the-year R. fa lcatus were f i r s t c o l l e c t e d between August 16 and 1 8 , i 9 6 0 . These f i sh probably had > hatched some two to three weeks previous to this c o l l e c t i o n date. Gonad development of maturing f i sh and the appearance of young-of-the-year, suggests that the spawning per iod of R. fa lcatus occurs ear ly i n Ju ly . Some of the male R. fa lcatus of age III and older are found with a d i s t i n c t i v e spawning c o l o r a t i o n , as described by C a r l et a l (1959). Not a l l males of this age group have such a c o l o r a t i o n , but there i s a higher percentage of colored males of fork length greater than 8 0 mm. ( F i g . 7 ) This spawning c o l o r a t i o n was observed i n a l l seasons. -20-J U N E J U L Y AUG. SEPT. Figure 6. Gonad development of R. fa lcatus c o l l e c t e d from the Fraser River between Hope and C h i l l i w a c k . S E P T . I 9 6 0 W I T H S P A W N I N G C O L O R > <J 5-Z LU LU cc I 5 H I O -5 -3 5 A G E II I 1 A G E l l l + < 8 I M M . A G E M l + > 8 0 M M . i ' 1 1  IV n H- • • J U N E 1961 A G E II A G E 1 1 1 + < 81 M M . I A G E 1 1 1 + > 8 0 M M . 4 5 5 5 6 5 7 5 8 5 9 5 F O F \ K L E N G T H , M I L L I M E T E R S 105 115 Figure 7. Length frequency of male R. fa lcatus with spawning color c o l l e c t e d from the Fraser River lbetween Hope and C h i l l i w a c k . -22-Age I male and female R. falcatus are found with tubercles„ which occur on the dorsal surface of the head and body as w e l l as the sides of the body, with exception of the f i n s . Gilbert and Everman (1895) ref e r to these as nuptial tubercles and claim they are also present on the dorsal surface of the pectoral f i n rays. Tubercles on this area were not observed on f i s h from the Praser River system. 1+. Parasites Three orders of parasites were represented i n R. falcatus c o l l e c t e d between Hope and G.hilliwack ( G. Gibson, pers. com.). Trematoda were represented by metacercariae of Tetracotyle sp. Six f i s h were heavily invested with plerocercoids of the Cestoda L i g u l a i n t e s t i n a l i s , while Nematoda were represented by three subfamilies. The subfamilies were: Anisakinae (contracacaecum sp.), Dioctophymidae (encysted Eustrongylides sp.), and Spiruridae (Metabronema, sp. and Rhabdochona sp.). Ligula i n t e s t i n a l i s infections appeared to be the only serious cases of parasitism. B. Comparative Ecology of R. falcatus and R. cataractae Numbers of f i s h and corresponding ecological data from a l l c o l l e c t i o n areas (Table I) were u t i l i z e d to describe and compare the ecology of the two species. 1. Current D i s t r i b u t i o n Average numbers of R. cataractae and R. falcatus per seine haul i n v e l o c i t i e s less than 1.5 ft . / s e c . (31+2 seine hauls) were compared to average numbers i n currents greater than 1.5 ft . / s e c . (101 seine hauls). The numbers of each -23-species were recorded by s ize groups ( young-of-the-year - age 0, y e a r l i n g - age I , adult - age II and o lder ) . The difference between average numbers per seine haul of a species s ize group was tested s t a t i s t i c a l l y by a Chi. square tes t ; 0.05 was the accepted l e v e l of s i g n i f i c a n c e . Adul t , y e a r l i n g , and young-of-the-year R. fa lcatus exhib i t a s i g n i f i c a n t di f ference between the two current areas and are most numerous In water v e l o c i t i e s of less than 1.5 f t . / s e c . (P ig . 8 ) . Adult R. cataractae show a s i g n i f i c a n t d i f ference i n numbers between the two current areas, as they were more numerous i n water v e l o c i t i e s of greater than 1.5 f t . / s e c . There was no s i g n i f i c a n t di f ference i n the numbers of year l ing and young-of-the-year of this species between the two current areas. These resu l t s indicate that R. cataractae i n i t s f i r s t year or ear ly i n i t s second year, changes i t s current d i s t r i b u t i o n by se l ec t ing an increased water v e l o c i t y . This may account for the s i m i l a r i t y i n numbers of these two age groups i n the two current areas. 2. Depth D i s t r i b u t i o n - Daylight The analys is used for current d i s t r i b u t i o n was also used for depth d i s t r i b u t i o n ( P i g . 9)» One hundred and t h i r t y -f ive seine hauls were made In depths less than 1 f t . , while 125 seine hauls were made i n depths greater than 1 f t . Adult R. fa lcatus were more numerous i n depths greater than 1 f t . , although the di f ference i n numbers per seine haul between the two depth areas was not s i g n i f i c a n t . Year l ing R. fa lcatus were d i s t r i b u t e d i n almost equal numbers between the two depth A G E F L O W FT. / S E C . R. C A T A R A C T A E R . F A L C A T U S 2 + > | l / 2 < 1 1/2 ] ] 1 > | l / 2 < 1 1/2 ] O > l 1/2 < 1 1/2 1 1 I 1 1 I O .5 O .5 I O I.S 2 . 0 2.5 A V E R A G E N U M B E R O F F I S H P E R S E I N E H A U L Figure 8 . Current d i s t r i b u t i o n of R. fa lcatus and R. cataractae from a l l c o l l e c t i o n areas (Table I ) . A G E D A Y L I G H T D A R K N E S S 2 + x D E P T H G R E A T E R T H A N 1 F O O T - Q D E P T H L E S S T H A N 1 F O O T - • H.ACTA 1 X V//A < I 3 i -< O <£ O za X X 2 +• i </> t-< / V / / V I u _ l 1 1 < d. O 3 5.6 1 i i i i i O I 2 O I 2 3 A V E R A G E N U M B E R O F F I S H P E R S E I N E H A U L Figure 9. Depth d i s t r i b u t i o n of R. fa lcatus and R. cataractae during dayl ight arid at night (x-'less than 0.1). - 2 6 -areas while the young-of-the-year of this species were more numerous i n depths of 1 f t . or l e s s . This difference was s i g n i f i c a n t . Adult, yearling, and young-of-the-year R. cataractae were more numerous i n depths of less than 1 f t . , but only the yearling f i s h showed a s i g n i f i c a n t difference i n this comparison. 3. Depth D i s t r i b u t i o n - Night Only a small number of after-dark seine hauls were applicable to depth d i s t r i b u t i o n analysis (27 seine hauls In depths greater than 1 f t . , 28 seine hauls i n depths less than 1 f t . ) , thus only indications can be drawn from the data. Some young-of-the-year R. falcatus move offshore to depths deeper than 1 f t . , but a larger number per seine haul were taken i n shallow water. Yearling R. falcatus also ex-h i b i t an offshore movement to deeper depths, while adults, i n contrast, show an onshore movement to depths of less than 1 f t . (Pig. 9). Young-of-the-year R. cataractae, c o l l e c t e d a f t e r dark, x^ rere too few i n number to permit analysis. Yearling of this species exhibited a similar offshore movement to the yearling R. fa l c a t u s . Depth d i s t r i b u t i o n of adult R. cataractae did not appear to vary between day and night. ij-. Bottom Preference Ec o l o g i c a l data on the d i s t r i b u t i o n of f i s h over d i f f e r e n t types of bottom was not analysed as gravel areas were usually confined to areas of water v e l o c i t y and sand or s i l t bottoms - 2 7 -were confined to areas of l i t t l e or no current . R. f a l c a t u s , observed i n the Nico la River on December 7, I 9 6 0 , were found between rocks ( 2 - 6 i n . diameter) i n pool areas of the r i v e r . At this time, the water was c l e a r , with bottom areas c l e a r l y v i s i b l e from shore. R. f a l c a t u s , i n the Fraser R i v e r , were c o l l e c t e d p r i m a r i l y on sand or s i l t bottoms i n turb id water (water v i s a b i l i t y I4.-II4. i n . ) . In the hatchery trough, R. fa lcatus and R. cataractae showed a preference for darkened areas. I f one h a l f of the trough was covered with a plywood sheet, a l l f i sh would se lect the darkened area under the plywood. Thus i t i s l i k e l y that R. fa lcatus may se lect bottom cover or darkness i n c l ear water which would r e s u l t i n i t s presence i n gravel spaces i n areas of l i t t l e or no current . In turb id water this species may not require cover or darkness. F i e l d observations indicate that R. cataractae found i n r i v e r areas of fast water v e l o c i t i e s , occupied spaces between stones i n both c l ear and turbid water, and could be d i s -lodged only by d i s turbing the gravel bottom. Such a bottom s e l e c t i o n may be necessary to inhabit a p o s i t i o n i n fast water v e l o c i t i e s , as th is species does not remain d i r e c t l y i n the current . 5. Food of R. fa lcatus and R. cataractae of age 0 and I . — . . . ._ _ _ . . . -_. — -Stomach contents of R. fa lcatus and R. cataractae of age 0 and I , both c o l l e c t e d from the same areas In the Fraser River between Hope and C h i l l i w a c k , are i l l u s t r a t e d i n Figure 10. Both species of age 0 were c o l l e c t e d together only i n R. F A L C A T U S R . C A T A R A C T A E A Q U A T I C I N S E C T L A R V A E A L G A E , D I A T O M S , S A N D H Y D R A C A R I N A D I P T E R A L A R V A E T R I C O P T E R A L A R V A E P L E C O P T E R A N Y M P H S E P H E M E R O P T E R A N Y M P H S U N I D E N T I F I E D A Q U A T I C I N S E C T L A R V A E • Z i T E R R . E S T F U A L I N S E C T S A L G A E , D I A T O M S , S A N D N E M A T O D E S p L U M B R I C U S U N K N O W N D T E R R E S T R I A L I N S E C T S A Q U A T I C . I N S E C T L A R V A E P A L G A E , D I A T O M S , S A N D B 4 FISH II FISH =1 • J 26 FISH tO FISH S O V O L U M E I O O O F T O T A L S O S T O M A C H - I [ — I O O V O L U M E A G E O S E P T / 6 0 A N D O C T / 6 0 A G E I J U N E / 6 I A N D J U L Y / 6 0 A G E I S E P T . / 6 0 Figure 10. Stomach contents of R. fa lcatus and R. cataractae of age 0 and I from the same areas of the Fraser River between Hope and C h l l l i w a c k . September and October, I 9 6 0 . Pood taken i n each month by these f i s h was s i m i l a r and thus combined. Diet of the two species was also s i m i l a r ; both r e l i e d on aquatic insect larvae as a major food source. Diptera formed 96% of the diet of R. falcatus and Q2% of R. cataractae. Yearling f i s h (age I) of both species fed predominately upon aquatic insect larvae during June, 1961 and July, I 9 6 0 at the peak of the spring run-off. Diptera and Ephemeroptera were the most important food items, but were taken i n differing amounts by each species. Stomach analysis of yearling f i s h i n September, i 9 6 0 c o l l e c t i o n s showed a complete divergence i n diet. R. falcatus fed p r i m a r i l y on t e r r e s t r i a l insects, while R. cataractae fed p r i m a r i l y on aquatic insect larvae. This divergence i n diet i s concurrent with the divergence i n habitat selection which commences i n the f i r s t year (age 0) and i s complete i n the second (age I ) . C. Stream Tank Experiments Experiments, designed to test flow preference indicated by f i e l d ecological data were completed on three size groups of f i s h according to the previously described method. Ex-periments commenced on January l i , 1961 and terminated on March 17, 1961. 1. Ratio Analysis of Fish i n Current Arm Only the r a t i o of the numbers of R. falcatus to R.  cataractae i n the current arm were analysed. Observed ratios of the two species i n the current arm at any one time i s c a l l e d an observation r a t i o . A one hour time per iod between observation r a t i o s ensured independence between observations. The sum of the seven observation ra t ios taken for analys is from each experiment i s c a l l e d an experimental r a t i o . The sum of the three experimental r a t i o s of a s ize group at any flow is c a l l e d a block r a t i o . (a) Block r a t i o analys is Figure 11 i l l u s t r a t e s the average number of f i sh i n the current arm per observation. The v e r t i c a l bars on th is graph are proport iona l i n area to the block r a t i o s and thus d i f f i -c u l t i e s of i l l u s t r a t i n g ra t ios with zero numbers are avoided. The s t a t i s t i c a l procedure i n the analysis of block r a t i o s consisted of f i r s t a test of homogeneity on the 21 observed r a t i o s composing the block r a t i o . Homogeneity was found i n a l l block r a t i o s . Homogeneity permitted a pooled Chi-square test to be ca l cu la ted on the block r a t i o s . The accepted l e v e l of s ign i f i cance was 0.0$. A s i g n i f i c a n t di f ference was found between the numbers of R. cataractae and R. fa lcatus of the 70-95 mm. s ize group at flows of 1, 2, and 3 f t . / s e c . R. cataractae were more numerous i n the current arm. The block r a t i o at the 1+ f t . / s e c . v e l o c i t y was not subjected to a Chi-square test as. only one R. cataractae was observed. Attempts to enter the current arm at th is flow were recorded during every other h a l f hour per iod throughout the three experiments. An attempt was r e -corded i f a f i sh could swim up to the l i p of the current arm ramp or f u r t h e r . There was a s i g n i f i c a n t dif ference i n the number of attempts made by the two species to enter the -3V-i cc < 2 LU W u 5 -4 ~ 3 -I -2 O H < > cc LU m 0 3 O ct ID CL I in 5 -4 -2 -I -a Ui CD 2 D Z LU O < Ct UJ > < 2 -_E3 • R FALCATUS R. CATARACTAE 7 0 - 95 M M . SIZE GROUP 50 — 7 0 M M . SIZE GROUP 30 — 4 0 M M . S I Z E G ROUP I 2 I 3 I FLOW — F E E T PER S E C O N D Figure XI. Flow preference of R. fa lcatus and R. cataractae i n stream tank. -32-c u r r e n t arm at the I4. f t . / s e c . v e l o c i t y . R . c a t a r a c t a e made 53 a t t e m p t s w h i l e R . f a l c a t u s made o n l y 18. S i g n i f i c a n t d i f f e r e n c e s were f o u n d between the two s p e c i e s w i t h the 5 0 - 7 0 mm. s i z e group a t v e l o c i t i e s of 1 and 3 f t . / s e c . R . c a t a r a c t a e were more numerous a g a i n i n the c u r r e n t arm. A t 2 f t . / s e c . w a t e r v e l o c i t y , R . c a t a r a c t a e were more numerous, b u t the d i f f e r e n c e was not s i g n i f i c a n t . A t the I I f t . / s e c . w a t e r v e l o c i t y , one R . c a t a r a c t a e was n o t e d i n t h r e e o b s e r v a t i o n s w h i l e R . f a l c a t u s n e v e r e n t e r e d the c u r r e n t arm. Attempts were not r e c o r d e d at t h i s v e l o c i t y . E x p e r i m e n t s were completed on the 3 0 - l i 0 mm. s i z e group at v e l o c i t i e s of 1 and 2 f t . / s e c . A s i g n i f i c a n t d i f f e r e n c e was found at the v e l o c i t y of 1 f t . / s e c , R . c a t a r a c t a e were more numerous i n the c u r r e n t arm. No f i s h were obser v e d i n the c u r r e n t arm a t the v e l o c i t y of 2 f t . / s e c . A t t e m p t s , r e -c o r d e d a t both v e l o c i t i e s , showed t h a t f o r e v e r y attempt made by R . f a l c a t u s t o e n t e r the c u r r e n t arm, R . c a t a r a c t a e made t e n . T h i s r a t i o , a t both v e l o c i t i e s , was s i g n i f i c a n t l y d i f f e r e n t . (b) E x p e r i m e n t a l r a t i o a n a l y s i s The p r e s e n t a t i o n of da t a on b l o c k r a t i o s has o b s c u r e d some v a r i a t i o n i n the observed numbers of f i s h which becomes apparent when the e x p e r i m e n t a l r a t i o s are compared. A t e s t of homogeneity on each of the t h r e e e x p e r i m e n t a l r a t i o s com-p o s i n g each b l o c k shows t h a t t h e s e groups of e x p e r i m e n t a l r a t i o s a r e h e t e r o g e n e o u s , v a r y i n g by more tha n chance ( w i t h e x c e p t i o n of one b l o c k - 7 0 - 9 5 mm. s i z e group a t 3 f t . / s e c ) . -33-This v a r i a t i o n is apparent i n Table I I I . Two experimental r a t i o s , one from each arm i n a l l blocks were subjected to a homogeneity tes t ; a l l were homogeneous. Therefore, the most var iab le r a t i o i n a block appears to be the remaining r a t i o which is one of the p a i r of r a t i o s i n the same arm. As the two r a t i o s conducted i n the same current arm were a l ternated between arm A and B, the cause of the v a r i a b i l i t y cannot be a t t r i b u t e d to e i ther arm i n the exper i -mental sec t ion , but i s common to both arms. The cause of the v a r i a t i o n i s unknown. That condi t ioning i n the hatchery or the method of se l ec t ing experimental f i s h p r i o r to each experiment could cause such v a r i a t i o n seems u n l i k e l y . Differences i n current patterns below the l i p of the ramp could cause such v a r i a b i l i t y . During the l a s t exper i -ment, such differences were noted. The manner i n which water passed over the l i p of the ramp caused v e r t i c a l differences i n the flow pat tern as I l l u s t r a t e d i n Figure 12. Water, on passing over the l i p of the ramp, could e i ther continue along the surface (Type A) or fol low the bottom contour (Type B) . This would af fect the approach of the f i sh In t h e i r attempts to enter the current arm. Both species remained i n contact with the bottom while swimming. With Type A current pat tern , R. cataractae would not be able to detect the source of current and R. fa lcatus could be f a l s e l y a t t rac ted to the current arm. I f fur ther experimental .work was to be done on a s i m i l a r basis as the previous experiments, one of two improved methods could be used. The f i r s t of these two methods would TABLE III EXPERIMENTAL AND BLOCK RATIOS OP R. fa lcatus AND R. cataractae IN CURRENT ARM OP STREAM TANK Plow Size Ratio group 70-95 E x p e r i -m e n t mental Block 50-70 E x p e r i -mm. mental Block 30-ij.O E x p e r i -mm. mental Block 1 f t . / s e c . Current Species arm R . f . j R . c . A . 0 28 A 21 35 B 0 35 21 98 A 27 35 B 21 33 B 6 21 54 89 A 5 33 B 0 2 C 0 0 5 35 2 f t . / s e c . urrent Species arm R. f. :R. c. A 17 25 A 12 10 B 8 25 37 60 A 28 7 A 17 35 B 10 23 55 63 A 0 0 B 0 0 B 0 0 0 0 3 f t . / s e c . Current Species arm R. f. :R. c. A 0 11 B 0 8 B 0 11 0 30 B 0 5 B 0 6 B 6 10 6 21 Figure 12. Two types of current patterns observed below the current arm i n experimental sect ion of stream tank. -36-be to introduce experimental f i s h and after the passage of a certain time period, a count could be made on t h e i r d i s t r i b u -t i o n . Then f i s h could be removed from t h e i r preferred areas and placed i n a central area, to be released for a second time period. The second alternative method would be to introduce experimental f i s h and then change the current to the opposite arm a f t e r a count was made. This method would res u l t i n a complete reversal of preferred areas. 2. P o s i t i o n of Fish i n Relation to Current Arm Di s t r i b u t i o n of f i s h i n a l l parts of the experimental section also i l l u s t r a t e s the difference i n current preference between the two species. During the experiments, f i s h were found predominately i n four areas; A - the current arm, B - the base of the current arm, C-- the base of the non-current arm, and D - the non-current arm (Fig. 13). There was a c i r c u l a r current over the unpartitioned section below the two arms. Fish, i n order to swim from D to A had to move against the current as shown by the dotted arrows i n Figure 13. As v e l o c i t y was increased, the numbers of f i s h i n the four areas were forced back i n thei r p o s i t i o n from A to D. R. cataractae i n this analysis again exhibited a greater preference for faster water v e l o c i t i e s than did R. falcatus. The number of R. cataractae moving out of the faster water v e l o c i t y areas of A and B to the l i t t l e or non-current areas of C and D were very few, when water v e l o c i t i e s i n the current arm were increased. With high water v e l o c i t i e s , -37-7 0 - 9 S MM. A B C O A B C D U UJ A B C D A B C D U O 3 _i ui > t t = L A B C D A B C D SIZE GROUP 50-70MM. A B C D A B C D A B C D A B C D JX1 A B C D A B C D 30 - 40 MM. r A B C D A B C D A B C D A B C D -4 -3 Z g - 2 - | < > a. LU «/> m o -4 - 3 DC Ul -2 0. - 1 I i/i LL u. o - 4 cc - 3 Ul ID - 2 2 ~ 1 Z Ul O < OC - 4 ul > - 3 < - 2 - 1 51 A B C D A B C D A B C D A B C D R. FALCATUS R. CATARACTAE • v/////As///?y/Jzmz/, TOP VIEW OF EXPERIMENTAL SECTION SOLID ARROWS REPRESENT DIRECTION OF CURRENT BROKEN ARROWS INDICATE PATH O F FISH IN M O V I N G FROM D TO A Figure 13. P o s i t i o n of f i sh In r e l a t i o n to current arm, A; i n current arm, B; reduced current , i n p o s i t i o n to attempt to enter current arm, C; back-eddy of s l i g h t current , D; non-current arm. -38-R. falcatus was most numerous In the l i t t l e or non-current areas of C and D. D. Comparative Airbladder Analysis Airbladder volume of both species is similar for fish of approximately 0.3 gm. in weight or less (Pig. Ii;). As R. cataractae increases in body weight, the airbladder volume shows l i t t l e increase and appears never to exceed a volume of 0.1 ml. in fish of over 2i| gms. in weight. The airbladder volume of R. falcatus increases greatly with increasing weight of fi s h , exceeding 0.I4. ml. in fish of 11 gms. body weight. Regression lines were calculated for both series of points. The regression in both cases was significant (p less than .005)• The correlation coefficient (r) for R. falcatus was 0.95 and for R. cataractae, O.I4I4.. Figure I L L . Comparison of the r e l a t i o n s h i p between volume of a irb ladder and weight of f i s h In R. fa lcatus and R. cataractae. IV DISCUSSION A. L i f e H i s tory of R. fa lcatus A comparative summary of the ecology and some aspects of the l i f e h i s t o r y of R. fa lcatus and R. cataractae appears i n Table IV. The sexual, dimorphism i n growth rate as found i n R.  fa lcatus i s also common to R. atratulus meleagris . Raney (191+0) found that female f i s h were larger than males. Spawning time of R. fa lcatus and R. cataractae i s very close and i t i s poss ible that some overlap i n spawning time occurs. Spawning R. cataractae have been c o l l e c t e d i n the mouth of the Coquiha l la River near i t s entrance to the Fraser River at Hope on J u l y 3, 1956. Spawning habi tats of both species remain unknown. The funct ion of the tubercles i n R. fa lcatus remains unknown. Tubercles are not, however, uncommon among species of the genus Rhinichthys . Male R. cataractae develop tubercles over most of the body and on the pectora l f i n rays , but only at spawning time (Hankinson, 1 9 2 3 ) . Raney (191+0) and Schwartz (1958) have described tubercles on male f i s h among three sub-species of R. a t ra tu lus . Raney (I9I4.O) suggests that the tubercles on the caudal peduncle of R. a tratulus meleagris may ass i s t the male i n holding himself against the female during the spawning act . The development of spawning c o l o r a t i o n i n male R.  fa lcatus most l i k e l y functions i n sex recogni t ion as i t de-velops at the same age as sexual maturity . Spawning c o l o r a t i o n -CI-TABLE IV SUMMARY OP THE COMPARATIVE ECOLOGY OP R. fa lcatus AND R. cataractae. R. fa lcatus R. cataractae Food; Age 0 Age I and older Current t P r i m a r i l y Diptera larvae P r i m a r i l y Diptera larvae T e r r e s t r i a l insects and Bottom organisms bottom organisms Age 0, F i e l d 0-1.5 f t . / s e c . Lab. 0-0.5 f t . / s e c . Age 1, F i e l d 0-1.5 f t . / s e c . and Lab. 0-2 f t . / s e c . older Depth : Day - Age 0 1 0-1 f t . 0-1 f t . Deeper than 1 f t . and older Night - Age 0 0-1 f t . 1 Deeper than 1 f t . 2 0-1 f t . and older Airb ladder volume: V a r i a b l e , 0-3 f t . / s e c . 0.3-1 f t . / s e c . Greater than 1.5 f t . / s e c . 1-3 f t . / s e c . 0-1 f t . 0-1 f t . 0-1 f t . Deeper than 1 f t . 0-1 f t . Age 0 1 and older S i m i l a r for both species Increase i n volume proport iona l to increase i n body weight. L i t t l e increase i n volume with increas ing body weight. -1+2-among males i s common to the three subspecies of R. atratulus (Schwartz, 1958). B. E c o l o g i c a l S igni f icance of Experimental and F i e l d Data Experimental and f i e l d data show that the s e l e c t i o n of d i f f e r i n g water v e l o c i t i e s resu l t s i n the habi ta t divergence between y e a r l i n g and adult f i sh of each species . The habitat divergence i s complete when the f i s h is approximately a year o l d , and the respect ive habitats of each species draw further apart as the f i s h mature. R. cataractae se lects fas ter water v e l o c i t i e s with age as shown by the current preference ex-periments, while R. fa lcatus remains i n slow or non-current areas. I t i s d i f f i c u l t to determine at which time i n the f i r s t year the habi tat divergence becomes complete. Poss ib ly R. cataractae begin to se lect s l i g h t water v e l o c i t i e s w i th in one or two months fo l lowing hatching but many s t i l l overlap the habi tat of age 0 R. f a l c a t u s . Approximately one month af ter hatching R. cataractae were taken In v e l o c i t i e s from 0-1 .5 f t . / s e c , while R. fa lcatus of the same age at the same time were i n non-current areas. Stream tank experiments on the 30-1+0 mm. s ize group which were approximately eight months old showed s i g n i f i c a n t differences i n the current preferences of the two species . Thus both species , s h o r t l y after hatching, may begin to diverge i n t h e i r habi ta t optima probably with considerable overlap i n numbers between the two hab i ta t s . The overlapping i n numbers could r e s u l t from the var iab le current preference of the young -43-R. cataractae , as many were c o l l e c t e d from non-current areas with R. fa lcatus of the same age (age 0 ) . When both species reach the end of the i r f i r s t year, the divergence i n habi tat optima have increased r e s u l t i n g i n decreased overlapping of habitat ranges. As the d ie t of young-of-the-year of both species is s i m i l a r , competition i n those areas where R. cataractae over-laps the habitat of R. fa lcatus could be severe. Competition cannot be assessed, however, as abundance of food i s not known. S t a r r e t t (1950) found that when species of minnows entered in to severe competit ion, the optimal food was replaced by an a l t ernat ive source, One could not, however, conclude from th i s that competit ion for food does not occur when both species feed on a s i m i l a r food source, as the a v a i l a b i l i t y of a l ternate food sources i s unknown. Competition between f i s h of both species i s r e s t r i c t e d to the area of overlap as those f i s h i n t h e i r respect ive habitat optima, even though feeding on s i m i l a r types of food, are feeding i n d i f ferent areas. C. E c o l o g i c a l S igni f icance of Airb ladder Analys is The p r i n c i p a l funct ion of the a irb ladder i s hydrostat ic (Harden-Jones, 1957). As the volume of the a irb ladder i n -creases, the volume of the f i s h increases and hence the density decreases. Thus, freshwater f i s h with we l l developedairbladders of 7-10$ of t h e i r t o t a l volume are able to swim e a s i l y i n mid-water (Tay lor , 1921; Harden-Jones, 1951). Both R. fa lcatus and R. cataractae have an a irbladder volume less than "7% and -kk' i t i s l i k e l y that both species remain near or i n contact with the bottom much of the time. It would be an advantage for a bottom dwell ing f i s h i n fast water to have as great a densi ty as poss ib le i n order to maintain p o s i t i o n . The low a irb ladder volume of R. cataractae has aided this species to occupy such a hab i ta t . As R.  cataractae increases i n weight, the densi ty of the f i sh also increases . The increase i n density i s p a r a l l e l e d by an i n -crease i n preference for fast water v e l o c i t i e s as the f i s h be-come l a r g e r . Airb ladder volume of age 0 f i sh of both species i s s i m i l a r i n accordance with the i r habitat s i m i l a r i t i e s . The larger a irb ladder volume of year l ing and adult R. fa lcatus per-mit i t to feed on the water surface , u t i l i z i n g t e r r e s t r i a l insec t s . Adult and y e a r l i n g R. cataractae have not been known to feed on t e r r e s t r i a l insects (Johannes, 1958; C a r l et a l , 1959; Beckman, no date) . D. B i o l o g i c a l S igni f icance of Habitat Segregation The b i o l o g i c a l s ign i f i cance of habi tat segregation can be i l l u s t r a t e d by Gause's contention (1931)-) that c l o s e l y r e -la ted species cannot coexist In a s i m i l a r niche without one species e l iminat ing the other through competit ion. This Contention takes i t s roots from a statement made by Darwin (1859, from Harper et a l , 1961). Darwin s tates , "It i s the most c l o s e l y a l l i e d forms - v a r i e t i e s of the same and re la ted genera - which, from having near ly the same s truc ture , c o n s t i t u t i o n , and h a b i t s , general ly come into the severest competition with each other; consequently each new v a r i e t y or species , during the progress of i t s formation, w i l l general ly press hardest on i t s nearest kindred and tend to exterminate them." Hutchinson (191+8) has added two r e s t r i c t i o n s to Gause's -1+5-content ion: I . external factors can act to l i m i t the mixed populat ion of coex i s t ing species occupying s i m i l a r n iches , and 2. chance o s c i l l a t i o n s of environmental condit ions can con-t i n u a l l y reverse the d i r e c t i o n of competit ion. Lack (191+9) hypothesized that such external factors as predat ion and paras i t i sm could act i n such a way as to l i m i t competition of coex i s t ing species . Ut ida (1953) has demon-s trated experimental ly that paras i t i sm can act i n such a manner. Gause (1931+) experimented with two species of c l o s e l y r e l a t e d c i l i a t e d protozoans, Paramecium caudatum and P. a u r e l i a . When these two species were kept i n separate c u l t u r e s , both populations exhib i ted a sigmoid growth curve and maintained a constant populat ion l e v e l . When both protozoans were kept In the same c u l t u r e , P. a u r e l i a e l iminated P. caudatum. When a t h i r d protozoan, P. b u r s a r i a , was placed i n the same cu l ture with P. caudatum, both were able to survive and reach a state of equ i l ibr ium even when feeding on the same food. P. bursar ia occupied a d i f f erent part of the cul ture when It could feed on bac ter ia without competing with P. caudatum. Other experiments by Crombie (191+7), and Park (191+8), i n add i t ion to those prev ious ly mentioned, have j u s t i f i e d Gause's contention. E l t o n (191+6) has summarized this con-tent ion for f i e l d condi t ions . E l t o n conducted a survey of eco log ica l studies with c l e a r l y defined habitats and found that i n a community there was a high percentage of genera repre-sented by only one species . In animal communities, 86$ of the genera found were represented by only one species and i n plant -46-communities, 84$. Opposition to Gause's contention (Diver , 1936 and Co le , i960) i s concerned mainly with eco log ica l terminology and a p p l i c a t i o n of mathematical models rather than with the b io -l o g i c a l basis of the p r i n c i p l e . In late J u l y , at the probable time of hatching of both species , the Praser River i s near i t s maximum year ly discharge. Part of the surrounding land of the lox^er Praser V a l l e y becomes flooded at this time provid ing increased non-current areas over flooded land and gravel bars. The water i s turb id (Ii-6 inches v i s a b i l i t y ) at th is time of year and the increase i n water l e v e l and f looding could provide addi t iona l food sources. Such r i v e r condit ions appear su i table for the sur-v i v a l of newly hatched f i s h . I t i s poss ible at th i s time, with an excess of food, cover, and non-current areas, that young-of-the-year R. fa lcatus and R. cataractae can coexist i n a s i m i l a r niche for the i r f i r s t month (August). However, as the water l e v e l begins to drop from August u n t i l A p r i l , such favorable environmental condit ions for coexistence would become scarce and i n t e r -s p e c i f i c competition would r e s u l t and increase through the winter months. Such increased competition would re su l t i n an increas ing divergence i n habi tat optima between the two species; as each would attempt to u t i l i z e i t s e co log i ca l potency (Ka l l eberg , 1958), and reduce the area of habi tat overlap. Thus, the r e s u l t i n g near-complete habi tat divergence at the end of the f i r s t year, allows these two congeneric species , -47-whose ranges overlap and occur i n the same r i v e r areas, to exis t without entering into severe competition for those r e -sources of the i r environment that are essent ia l f or the i r existence. The poss ib le coexistence of young-of-the-year R. fa lcatus and R. cataractae i n s i m i l a r niche suggests an addi t iona l exception to Gause's contention. That i s , sympatr ica l ly occuring species may occupy a s i m i l a r niche for a short per iod of t h e i r l i f e cycle when essent ia l environmental resources are i n excess of the demand for them. ACKNOWLEDGMENTS I am indebted to the B. C. Pish and Game Branch of the Department of Recreation and Conservation for the p r i v i l e g e of c o l l e c t i n g data and the use of vehic les and equipment while employed by the Branch. The wr i t er i s also grate fu l to Dr. C. C. Lindsey, Dr. W. S. Hoar, Dr. G. G. Scudder and p a r t i c u l a r l y Dr. T. G. Northcote for t h e i r advice, c r i t i c i s m s and encouragement. I also wish to acknowledge Mr. G. Gibson for the i d e n t i f i c a t i o n of parasites, and Messers. C. A. G i l l , D. W. Wi lk ie and M. Teraguchi who p a r t i c i p a t e d i n f i e l d c o l l e c t i o n s . LITERATURE CITED Bookman, W. C , (no date) . Guide to the f ishes of Colorado. U n i v e r s i t y of Colorado Museum, 110 pp. Campbell, R. N . , 1957. The effect of f looding on the growth rate of brown trout i n Loch Tummel. Freshwater and Salmon Fisher ies Research, 3 , 7 pp. C a r l , G. C , W. A. Clemens, and C. C. Lindsey, 1958. The fresh-water f ishes of B r i t i s h Columbia. B. C. Prov. Museum, Dept. of Educat ion. Handbook No. 5»» 192 pp. Cole , L . C , I960. Competitive exc lus ion. Science, 132 (31+23): 348-49 . Crombie, A. C , 1947* In terspec i f i c competit ion. J , Anim. E c o l . , 16 ( 1 ) : 44-73-Diver , C , 1936. The problem of c l o s e l y re la ted species and the d i s t r i b u t i o n of t h e i r populat ions . Proc. Roy. Soc. B r . , B 121 : 62-65 Eigenmann, C. H . , and R. S. Eigenmann, 1893. Agosia f a l c a t i a . Amer. Nat . , 2 7 : 153. E l t o n , C. S . , 1927. Animal ecology. Sedgwick and Jackson, London, 209 pp. E l t o n , C. S . , 1946. Competition and the s tructure of eco-l o g i c a l communities. Jour. Anim. E c o l . , 15 : 54 -68 . Gause, G. F . 1934« The struggle for existence. Will iams and W i l k i n s , Balt imore, I63 pp. G i l b e r t , C. H . , and B. W. Everman, l 8 9 5 « A report upon investigation i n the Columbia River basin with de-s c r i p t i o n of four new species of f i shes . B u l l . - 5 0 -U. S. P i s h . Comm., 1891+, 11+: 169-201+. G r i n n e l l , J . , 1928. The presence and absence of animals. Univ. C a l i f . Chron . , 30: 1+29-1+50. Hankinson, T. L . , 1923. The creek f i s h of western New York. Copeia, 11.5: 31 . Hardin-Jones, P. R . , 1 9 5 l « The swimbladder and the v e r t i c a l movements of Teleostean f i shes . Jour. Exp. B i o l . 2 8 : 553-566. 1957. The swimbladder. The physiology of f i shes . V o l . 2. Academic press , New York, 305-322. Harper, J . L . , J . N. Clatworthy, I . H. McNaughton, and G. R. Sagar, I 9 6 I . The evolut ion and ecology of c l o se ly re la ted species l i v i n g i n the same area. E v o l u t i o n , 15: 209-227. Hutchinson, G . , 1948. C i r c u l a r causal systems i n ecology. Ann. N. Y. Acad. S c i . , 50: 221-21+6. Johannes, R. E . , 1959. The feeding re la t ionsh ips of Rhinichthys  fa lcatus and Rhinichthys cataractae i n B r i t i s h Columbia. B. A. Thes is , U n i v e r s i t y of B r i t i s h Columbia Dept. of Zoology. 11 pp. K a l l e b e r g , H. 1958. Observations In a stream tank of t e r r i -t o r i a l i t y and competition i n juveni le salmon and trout . Ins t i tu te of Freshwater Research, Drot tn ing-holm Rept. 3 9 : 55-98. Lack, D. , 191+9• The s ign i f i cance of eco log ica l i s o l a t i o n . Genetics, paleontology, and evo lut ion . Princeton Univers i ty press , Pr ince ton: 299-308. - 5 1 -MacKinnon, D . , and W. S. Hoar, 1953. Responses of coho and chum salmon f r y to current . Jour. Pish Res. Bd. C a n . , 10 ( 8 ) : 523 -539. Northcote, T. G. , i960. Migratory behavior of juveni le r a i n -bow trout Salmo g a r r d n e r i , i n out let and i n l e t streams of Loon Lake, B r i t i s h Columbia. Ph.D. Thesis , U n i v e r s i t y of B r i t i s h Columbia, Dept. of Zoology. lh.6 pp. Park, T. , I9I4.8. Experimental studies of i n t e r s p e c i f i c com-p e t i t i o n . 1. Competition between populations of f l our beet les , Tribol ium confusan Duval , Tribol ium  castaneum Herbst. E c o l . Mongr., 1 8 ; 265-308. Raney, E . C , 19k0. Comparison of the breeding habits of two subspecies of black-nosed dace, Rhinichthys atratulus (Herman) Amer. Midland Nat . , 23 (2): 399-1+03. Schwartz, P. J . , 1958. The breeding behaviour of the southern blacknose dace, Rhinichthys atratulus obtusus Agass iz . Copeia, 1958 (2): l k l - k 3 . S t a r r e t t , W. C , 1950. Pood re la t ionsh ips of the minnows of the Des Moines River , Iowa. Ecology 31 (2): 216-233. Taylor , H. P . , 1921. A irb ladder and spec i f i c g r a v i t y . B u l l . U. S. Bur. P i s h . , 38: 121-26. Udvardy, M. D. P . , 1959. Notes on the eco log ica l concepts of h a b i t a t , biotope and niche. Ecology, kO ( k ) : 725-28. U t i d a , S. 1953. I n t e r s p e c i f i c competition between two species of bean weevi l . Ecology 3k (2): 301-307. 

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