A CONTRIBUTION TO THE STUDY OF THEer square foot wet weight i n two successive years. The Cowichan r i v e r i s much below t h i s , y i e l d i n g only 2.28 grams per square foot, wet weight. Table 11 i s a summary of a l l the data i n Tables 1 to 10. I t shows the pool to be more productive than the r i f f l e s by weight, but l e s s productive by number. O l i v e r creek was 21. w e l l below the other two areas i n both weight and number of organisms. S t a t i o n s & and 7 are treated separately, since they represent the type of bottom of which the greatest area of the r i v e r i s composed. Here the y i e l d i s shown to be below the general average f o r a l l s t a t i o n s . Yegetation i s the most productive type of h a b i t a t , followed by mud, rubble and g r a v e l , i n that order. This i s more or l e s s i n accordance with the f i n d i n g s of the m a j o r i t y of workers, except that mud i s some-times stated to have been l e s s productive than rubble (see Moore, e_t a l . , i o c . c i t . ) R e l a t i o n of the bottom fauna to f i s h food The portions of the Gowichan r i v e r studied i n t h i s i n v e s t i g a t i o n support an important number of f i s h . The Hatchery pool and the r i f f l e s below are f a v o r i t e places f o r angling, and O l i v e r creek i s a spawning stream of considerable Importance f o r both salmon and t r o u t . G i l l - n e t catches made i n the pool during June, J u l y and August over a four-year period show that 101 -rainbow, 66 cutthroat, 111 brown t r o u t , and 6 D o l l y Yarden char were captured here. The numbers of trout caught i n course of the i n v e s t i g a t i o n i n d i c a t e that a considerable•population i n h a b i t s the pool during the months i n which the i n v e s t i g a t i o n was c a r r i e d on. The f o l l o w i n g data show the numbers of f i s h which ascended O l i v e r creek to spawn, and the numbers of f r y and l a r g e r f i s h which descended. F i s h ascending the stream included 907 coho salmon, 65 brown 22 * trout and 34 cutthroat t r o u t . Descending f i s h included 1948 y e a r l i n g s and 78,521 f r y of the coho salmon; 5 adults, 26 f i n g e r l i n g and 2 f r y of the brown trout; 15 adults and 978 f r y of the cutthroat t r o u t ; 34 rainbow a d u l t s ; 2 Dolly Varden adults and 15 speckled char a d u l t s . The f i g u r e s are presented with the kind permission of Mr. Neave. Thus an important number of salmon and trout use O l i v e r creek f o r spawning, producing large numbers of young. Data c o l l e c t e d by Mr. Neave by means of a f r y trap near the mouth of the creek show that many of the young f i s h stay i n the creek f o r considerable lengths of time, up to more than a year. This applies to both salmon and t r o u t . The w r i t e r has presented data i n a previous report ( i d y l l , Manuscript, 1939) showing that the young of the rainbow, cutthroat and brown trout feed e x t e n s i v e l y i n O l i v e r creek, taking mostly midges and m a y f l i e s . In a d d i t i o n examination of the stomachs of coho salmon and speckled char show that these species also depend on the organisms i n the creek f o r food. I t i s apparent from these data that the creek supports a f a i r l y large f i s h population.• In a d d i t i o n , q u a l i t a t i v e observation during the summer months in d i c a t e s that large numbers of t r o u t , p a r t i c u l a r l y of y e a r l i n g and smaller s i z e , i n h a b i t the r i f f l e s and feed there. Table 12 shows the percentage occurrence of each of the major groups of bottom forms at each s t a t i o n , with the average percentage f o r a l l s t a t i o n s . The rank of each organism i n percentage of numbers occurring i s deduced from t h i s . The table also shows the numbers of the c h i e f organisms 2«3 « eaten by 561 rainbow, cutthroat and brown trout of a l l s i z e s , caught by various types of gear i n approximately the same area where the bottom samples were taken, with the percentage of the t o t a l which each main group c o n s t i t u t e d , with i t s consequent rank. In the l a s t column the average percentage of occurrence of each organism i n the trout stomachs i s given. No attempt has been made to separate the data f o r the food of .pool, r i f f l e s and creek t r o u t . There i s no evidence to i n d i c a t e that trout feed e x c l u s i v e l y i n any one of these three areas at a l l times. On the contrary, i t i s probable that considerable movement takes place between pool and r i f f l e s . A c t u a l tagging records substantiate t h i s view. Also, f i s h move out of O l i v e r creek Into the r i v e r and would probably move i n the other d i r e c t i o n as w e l l i f passage were'not blocked by an experimental f i s h trap on the creek. This table reveals, f i r s t of a l l , that f o r the area as a whole c a d d i s f l i e s rank f i r s t In point of numbers occurring, j u s t i f y i n g once more the a s s e r t i o n that the Trichoptera i s the dominant group i n the r i v e r . I f r e l a t i v e areas were compared t h i s dominance would ajopear even more marked. In fact the whole r e l a t i o n s h i p of the various groups would probably undergo some s h i f t . Computations of the r e l a t i v e area that each type of bottom made up of the whole r i v e r bottom were not p o s s i b l e with any degree of mathematical exactness i n t h i s i n v e s t i g a t i o n . Crustacea are seen to occur i n the next l a r g e s t numbers, followed by midges, molluscs, and m a y f l i e s , i n that order. There i s a gap between mayflies and the next most numerous group, the b l a c k f l i e s . The l a t t e r are probably present i n greater numbers than any other group i n part of A p r i l , May and June, but are scarcer at other times- of the year. 3" A comparison of the occurrence of the various organ-isms i n the Bottom fauna with t h e i r importance as f i s h food (as revealed by numbers eaten and percentage of occurrence i n the f i s h stomachs) shows that there i s not an exact c o r r e l a t i o n between the numbers of organisms present and the numbers of organisms and frequency with which they were eaten. The closes t c o r r e l a t i o n i s i n the case of c a d d i s f l i e s , which are the most numerous organisms present, occur oftenest i n the stomachs, and are eaten i n the second l a r g e s t numbers, and midges, which rank t h i r d i n a l l three^categories. M a y f l i e s rank f i f t h i n numbers present i n the fauna and numbers eaten, but second i n percentage occurrence i n the stomachs. The other grou.ps show greater d i s p a r i t y , i n varying degrees. The greatest gap between numbers of organisms present and numbers u t i l i z e d as food occurs i n the fresh-water shrimps which rank as the second most numerous organism In the fauna but which are not used as food by the tr o u t to any s i g n i f i c a n t * S p e c i f i c determinations of the various groups has not been attempted by the w r i t e r . The f o l l o w i n g a u t h o r i t i e s have k i n d l y agreed to make determinations and specimens have been sent to them. A report of t h e i r f i n d i n g s w i l l be made i n due course. Plecoptera: Mr. IFerris_Neave; Odonata: Dr. E. M. Walker; Ephemeroptera: Dr. ]?. P. ide; Hirudinea: Dr. E. H. Gordero; Kydracarina: Dr. 'Ruth M a r s h a l l ; P l a n a r i a : Dr. Libby Hyman; Oligochaeta: Dr. H. W. Olson; Trichoptera: Dr. Donald Denning; Ghironomidae: Dr. J. G. Rempel. 25. extent. Molluscs also appear not to "be used i n proportion to t h e i r incidence i n the population, but the diff e r e n c e i s not so marked here as with the•Crustacea. There are probably three main reasons f o r t h i s lack of c o r r e l a t i o n between the numbers present and the numbers used as trout food. The f i r s t i s the f a c t that "numbers present" do not a c t u a l l y represent the r e l a t i v e numbers f o r the whole area, since the areas of the various bottom h a b i t a t s are not taken i n t o account. The second i s the fa c t that "numbers present" do not n e c e s s a r i l y mean numbers a v a i l a b l e as food. This f a c t o r probably accounts to a large extent f o r the very small importance of such groups as the annelids, flatworms and Anodonta i n the f i s h food. Groups such as the c a d d i s f l i e s and ma y f l i e s , which are both numerous and r e a d i l y a v a i l a b l e as food due to s i z e and h a b i t s , w i l l - n a t u r a l l y make up a large proportion of the food. The last- f a c t o r i n f l u e n c i n g the importance of an organism as food f o r trout i s p o s s i b l e s e l e c t i v i t y . In a previous report ( I d y l l , Manuscript, 194.0) the w r i t e r has shown that there appears to be a d e f i n i t e d i f f e r e n c e i n the s e l e c t i v i t y of the three species of trout (rainbow, cutthroat and brown) In the Gowichan r i v e r system, as revealed by d i f f e r e n c e s i n the food of these three species under s i m i l a r feeding o p p o r t u n i t i e s . While the present r e s u l t s do not provide s t a t i s t i c a l proof i n support of t h i s content ion that trout s e l e c t t h e i r food, they may point t e n t a t i v e l y to such a conclusion. I t Is d i f f i c u l t to evaluate properly the s i g n i f i c a n c e of the f a c t o r s 26. of true r e l a t i v e numbers of organisms present and of numbers of organisms a v a i l a b l e , i n explaining why some forms are not eaten i n proportion to t h e i r incidence i n the population, and i t may be that these two f a c t o r s are s u f f i c i e n t to account f o r the d i s p a r i t y between numbers of organisms present i n the fauna and numbers eaten by the f i s h . However, t h i s does not seem to account e n t i r e l y f o r the d i f f e r e n c e i n the case of some of the groups, p a r t i c u l a r l y the shrimps. These animals are present In large numbers and are r e a d i l y a v a i l a b l e , yet do not form a s i g n i f i c a n t part of the trout food. Some other groups show a l e s s s t r i k i n g but s t i l l apparent d i s p a r i t y . There has been much controversjr on t h i s p o i n t . Two opinions are quoted as i l l u s t r a t i n g the opposite viewpoints on t h i s question. W e i l l (1958) made a study ,of brown tr o u t food i n r e l a t i o n to the bottom fauna i n England. This w r i t e r says: "The t r o u t feeds on the whole range of animals present i n whatever type of habitat i t f i n d s I t s e l f , to an extent dependent on t h e i r degree of a c c e s s i b i l i t y and the extent of t h e i r r epresentation i n the fauna. This i s s u f f i c i e n t to account f o r the nature of i t s stomach contents without invoking d i s c r i m i n a t i o n on the part of the f i s h . " In contrast, A l l a n ( 1938), who reported the food of brown trout from Windermere, England, says: "Percentages which the most important food animals-make up of the food are probably very much greater than are t h e i r percentages i n the fauna at the same time, i . e . the f i s h are performing a d e f i n i t e s e l e c t i o n i n t h e i r food." A great deal of f u r t h e r research w i l l be necessary before a f i n a l d e c i s i o n can be made. Conclusions (1) The port i o n s of the Cowichan r i v e r studied i n t h i s i n v e s t i g a t i o n are poor i n bottom fauna. The Hatchery pool y i e l d e d an average wet weight of 20.86 grams per square yard and an average number of organisms of 623 per square yard. The r i f f l e s y i e l d e d 12.21 grams and 887 organisms per square yard and O l i v e r creek y i e l d e d 6.90 grams and 448 organisms per square yard. (2) The Hatchery pool i s more productive than the r i f f l e s below on the basis of weight of organisms, but l e s s productive on the basis of numbers. O l i v e r creek i s l e s s productive than the other two areas. , (3) Vegetation i s the most productive type of habitat i n t h i s r i v e r , followed h j mud, rubble and gravel, bottom, i n that order. 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Bibliography A l l a n , K. R. (1938), "Some Observations on the Biology the Trout (Salmo t r u t t a ) i n Windermere." Jour, of Animal Ecology, V o l . 7, No. 2. Carpenter, K. E. (1927), "Eaunistic Ecology of some Cardiganshire Streams." Jour, of Ecology, V o l . 18 I d y l l , C. P. (1940), "The Pood of the Trout i n the Cowl chan River System." (MS. ) ' Ke n d a l l , W. 0. and Dence, W.A. (1927), "A Trout Survey of the Allegany State Park." Roos. Yfold L i f e B u l l . , V o l . 4, No. 3. Leonard, J. W. (1939 ), "Comments on the Adequacy of Accepted Bottom Sampling Technique." Proc. N. Am. Wild L i f e Con., 1939. Moon, II. P. (1935), "Methods and Apparatus S u i t a b l e f o r an I n v e s t i g a t i o n of the L i t t o r a l Region o f Ol i g o t r o p h i c Lakes." I n t . Rev. der gesam. Hydrobiol. u. Hydrogr., Band 32, Heft 4-/5. Moore, E., e_t a l . (1927 ), "A B i o l o g i c a l Survey of the Genessee River System". State of N.Y. Cons. Dept., Supp. to 16th Ann. Report. Mottley, C. McC., et. a l . (1938), "The Determination of the Food Grade of Streams". Trans. Am. F i s h , Soo., Vol . 68. Muttkowski, R. A. (1929), "The Ecology of Trout Streams i n Yellowstone N a t i o n a l Park," Roos. Yfild L i f e Annals, V o l . 2, No. 2. 4 a , Needham, P. R. (1934), "Quantitative Studies of Stream Bottom Foods/' Tr ans. Am. F i s h . Soc., V o l . 64. Needham, P. R. (1938), "Trout Streams", Comstock Pub. Col, Ithaca, N.Y. Needliam, P. R. and Hanson, H.A. (1934), "A Stream Survey of the Waters of the S i e r r a N a t i o n a l Forest, C a l i f o r n i a , " U. S. Dept. of Comm., Bur, of F i s h e r i e s . (Mimeogr. ) Needham, P. R., Davis, H. S., Hazaard, A. S., and Surber,E.W. (1935), "Quantitative Net f o r C o l l e c t i n g Bottom Animals i n Streams," U.S. Dept. of Comm., Bur, of F i s h e r i e s . (Mimeogr.) N e i l l , R. M. (1938), "The Food and Feeding Habits of the Brown Trout (Salmo t r u t t a L.) i n Re l a t i o n to the Organic Environment," Trans. Royal Soc. Edinburgh, V o l . LIX, pt. I I . P e r c i v a l , E. and Whitehead, H. (1929), "A Quantitative Study of the Fauna of some Types of Stream Bed," Jour, of Ecology, V o l . 17. -(1930), " B i o l o g i c a l Survey of the River Wharfe: Report on the Invertebrate Fauna," Jour, of Ecology, V o l . 18. Richardson, R. E. (1925), " I l l i n o i s R iver Bottom Fauna i n 1923," B u l l . 111. Div. of Nat. H i s t . Survey, V o l . X V . , A r t i c l e VI. (1928), "The Bottom Fauna of the Middle I l l i n o i s R iver, 1913-1925," B u l l . State of 111. Div. Nat. H i s t . Survey, V o l . XVII, A r t i c l e X I I . Ricker, W. S. (1934), "An E c o l o g i c a l C l a s s i f i c a t i o n of Certain Ontario Streams," Pub, of the Ont. F i s h . Research Lab., Wo. 39. Smith, 0. R. and Needham, P. R. (1935), "A Stream Survey of the Mono and Inyo National Forests, C a l i f o r n i a , " U.S. Dept. of Comm., Bur, of F i s h e r i e s . (Mimeogr.) S u l l i v a n , K. 0. (1929), "Notes on the Aquatic L i f e of . the Niagara River, Arkansas, w i t h S p e c i a l Reference to Aquatic Insects," Ecology, V o l . X, No. 3. Surber, E. W. (1936), "Rainbow Trout and Bottom Fauna Production i n One M i l e of Stream", Trans. Am. F i s h . Soc., V o l . 66. Taft, A. C., and Shapovalov, Leo (1935), "A B i o l o g i c a l Survey of the Streams and Lakes of the Klamath and Shasta N a t i o n a l Forests of C a l i f o r n i a , " U.S. Dept. of Comm., Bur, of Fisheries.(Mimeogr.) Wiebe, A. H. (1927), " B i o l o g i c a l Survey of the Upper M i s s i s s i p p i R iver w i t h S p e c i a l Reference to P o l l u t i o n , B u l l . U.S. 'Bur, of F i s h e r i e s , V o l . X L I I I , Pt. I I . Ide, F. P. (1939), "Quantitative Determination of the Insect Fauna of Rapid Water," Univ. Tor. Stud. B i o l . Serv. No. 47, Pub. Ont. F i s h . Res. Lab:., No. 59. 50. / Figure 1 Figure 2 The sampler being used at S t a t i o n 10. Figure 5 General view of the R i f f l e s . 52. Figure 7 View of the Hatchery pool, l o o k i n downstream from S t a t i o n 2 towards S t a t i o n 1.