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A contribution to the study of the bottom fauna of some portions of the Cowichan river, British Columbia Idyll, Clarence Purvis 1940

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A CONTRIBUTION TO THE STUDY OF THE<BOTTOM FAUNA OF SOME PORTIONS OF THE OOWIOHAN RIYER, BRITISH COLUMBIA by Clarence Purvis I d y l l A Thesis submitted 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 the "Degree of MASTER OF ARTS i n the Department of ZOOLOGY The U n i v e r s i t y of B r i t i s h Columbia October, 1940 '1 j i . Table of Contents Introduction . « 1 Aoknowl edgmen t s 1 Des c r i p t i o n of the r i v e r ........................ 2 Stat i o n s 5 Methods ......................................... 4 L i t e r a t u r e ...................................... 13 Data and r e s u l t s ................................ 15 Rela t i o n of the bottom fauna to f i s h food ....... 21 Conclusions .................... 27 Tables ......... .............................. 28 Bibliography . . ... 47 f i g u r e s 50 A CONTRIBUTION TO THE STUDY OF THE BOTTOM FAUNA OF SOME PORTIONS OF THE COWICHAN RIYER, BRITISH COLUMBIA Introduction In the summer of 1936 an extensive survey of the Cowichan r i v e r system on Vancouver Island, B r i t i s h Columbia, was i n s t i t u t e d by the F i s h e r i e s Research Board of Canada. As part of t h i s survey an examination of the bottom fauna was undertaken. This report summarizes the study of the bottom fauna at c e r t a i n s t a t i o n s i n the upper part of the Cowichan r i v e r and i n a small t r i b u t a r y stream, O l i v e r creek, which enters the Cowichan r i v e r near i t s source, c a r r i e d out during the-'months of May to August, i n c l u s i v e , 1938, 1939 and 1940. The object of t h i s i n v e s t i g a t i o n has been to l e a r n what bottom forms e x i s t i n t h i s area of the r i v e r system, and in what "abundance; and to compare the abundance of the e x i s t i n g forms w i t h organisms taken as food by the f i s h of the system,, Acknowledgment s The valuable assistance and advice of the f o l l o w i n g persons i s g r a t e f u l l y acknowledged by the w r i t e r ; Mr. F e r r i s Neave and Dr. G. G. Garl of the s t a f f of the P a c i f i c B i o l o g i c a l S t a t i o n of the F i s h e r i e s Research Board of Canada, Dr. C. McLean Eraser, former Head of the Department of Zoology of the U n i v e r s i t y of B r i t i s h Columbia, Professor G. J. Spencer of the Department of Zoology of the U n i v e r s i t y of B r i t i s h Columbia, and Dr. W. A. Clemens, former D i r e c t o r of the P a c i f i c B i o l o g i c a l S t a t i o n , and present Head of the Department of Zoology of the U n i v e r s i t y of B r i t i s h Columbia. D e s c r i p t i o n of the r i v e r The Cornelian r i v e r i s about 28 miles long, flowing i n a general eastward d i r e c t i o n from Cowichan lake into Cowichan Bay, on the east coast of Vancouver Island, B r i t i s h Columbia. In general, the r i v e r v a r i e s i n width from one hundred to two hundred f e e t . Except i n l a t e summer and e a r l y f a l l i t c a r r i e s a large volume of water. Just below the lake the r i v e r widens i n t o a large pool, c a l l e d , among other names, the Hatchery'Pool. This pool i s 150 yards across at i t s greatest width, and about 400 yards long. I t has a maximum depth of 30 feet at low water, and about 38 feet at average high water. (Figures 1 to 7 ) . The bottom of the pool con-s i s t s , i n the upper part, of coarse g r a v e l and sand, and elsewhere, of mud, with growth of pond weeds (Potamogeton) i n the shallower p o r t i o n s . Below the pool there i s a short rapids, and below t h i s again a s e r i e s of smaller pools, a l t e r n a t i n g with f a s t e r water. The bottom of the rapids c o n s i s t s mainly of rubble, w i t h some sections of boulders and g r a v e l , and a few patches of moss ( f f o n t i n a l i s ) , grasses and water forget-me-not (Myosotis l a x a ) . 3. O l i v e r creek, an important spawning stream f o r salmon and t r o u t , enters the r i v e r at the f i r s t r i f f l e s below the pool. I t c a r r i e s a small but p e r s i s t e n t volume of water the year round. The bottom c o n s i s t s of sand and g r a v e l , with srome rocks and rubble. The l a t t e r consists of stones and some rock fragment s„ S t a t i o n s Bottom samples were taken at ten s t a t i o n s s i t u a t e d . i n the Hatchery Pool, i n the r i f f l e s immediately below and i n O l i v e r creek. A d e s c r i p t i o n of the s t a t i o n s f o l l o w s . (See Figure 1.) - Pool s t a t i o n s : S t a t i o n 1: "Net-house" s t a t i o n . Near the r i v e r ' s edge; mud bottom; t h i c k growth of Potamogeton r o b b i n s i i ; depth four to six: f e e t ; current very s l i g h t . S t a t i o n 2: "Mid-pool". Mud bottorn, containing sunken bark, leaves, etc.; depth t h i r t y f e e t ; l i t t l e current. S t a t i o n 3: "Gravel;pool" Gravel bar of coarse g r a v e l to sand; depth two to f i v e f e e t ; current moderate. S t a t i o n 4: "Foot of p o o l " Mud bottom; moderate growth of Potamogeton r o b b i n s i i , P. p e r f o l i a t u s , and P. epihydrus; depth eight to twelve f e e t ; current moderate. 4. S t a t i o n 5 r "Edge of pool" Mud bottom; moderate growth of grasses, rushes and water forget-me-not (Myosotis l a x a ) ; sunken bark and leaves; depth one-half to one and one-half f e e t ; current s l i g h t . R i f f l e s s t a t i o n s : S t a t i o n 6: "Rubble, r i f f l e s 1 ' Rubble, with sand substratum; sunken bark; depth one-half, to one. and one-half f e e t ; current moderate to b r i s k . S t a t i o n 7: "Gravel, r i f f l e s " Bar of coarse g r a v e l and sand; depth one-half to one and one-half f e e t ; current moderate. S t a t i o n 8: "Vegetation, r i f f l e s " Thick growth of ffontinalis a n t i p y r e t i c a v a r . p a t u l a (? Myosotis l a x a and rushes; depth .four''to eight inches; current b r i s k . O l i v e r creek s t a t i o n s ; S t a t i o n 9; "Current, creek" R i f f l e s ; coarse- g r a v e l to sand; depth four to ten inches; current b r i s k . S t a t i o n 10; "Pool, creek" Rubble and coarse g r a v e l with sand; depth eight to fourteen inches; current s l i g h t . Methods Bottom samples were obtained by two methods. Where shallowness of the water permitted (that i s , i n a l l the r i f f l e s and creek s t a t i o n s ) , samples were taken with a s p e c i a l l y constructed bottom sampler, which i s described i n d e t a i l elsewhere i n t h i s r eport. (See Figures 2, 3 and 4) Ah Ikman dredge was used i n deep water ( i n c l u d i n g a l l s t a t i o n s i n the pool except #5: the edge of the pool) where i t was not pos s i b l e to employ t h i s sampler. Bottom m a t e r i a l was t r a n s f e r r e d to deep pans and c a r r i e d back to the labo r a t o r y f o r s o r t i n g . This work was done immediately a f t e r the m a t e r i a l was c o l l e c t e d , while the organisms were s t i l l a l i v e . Gravel, sand and mud samples were put on to a screen of galvanized wire n e t t i n g under which was a second screen of f i n e marquisette. Water was poured over the screens repeatedly and the animals were then picked out. Samples containing much vegetation or large rocks were treated s l i g h t l y d i f f e r e n t l y , the vegetation and rocks being washed a piece at a time i n a bucket of water before the sample was poured on to the screens. P i c k i n g over the samples i s a tedious and time-consuming process. In an attempt to cut down the time-involved, a s o r t e r was constructed i n the summer of 1939 a f t e r the plans of H. P. Moon (1935). However, the s o r t e r was found to make l i t t l e d i f f e r e n c e i n e f f i c i e n c y or time, and i t s use was discontinued. In the laboratory the organisms, were counted-and weighed on a t o r s i o n balance to two places of decimals, a f t e r being drained f o r one minute on b l o t t i n g paper. In r e p o r t i n g , weights, that of the s h e l l of molluscs has been deducted* Caddisfly larvae were removed, from t h e i r oases before being weighed. Weights may not be p e r f e c t l y comparable f o r a l l samples since some were weighed a l i v e (when possi b l e ) and others a f t e r having been preserved f o r varying 1 engirts. of time (up to. sev e r a l months) i n eight to ten percent, for m a l i n . ; Considerable v a r i a t i o n takes place i n the change i n weight of organisms due to formaldehyde preservation, so no c o r r e c t i o n could be app l i e d . Techniques f o r conducting population studies of the bottom organisms of running waters are s t i l l i n the e a r l y stages, and are as yet imperfect. The problem of making .accurate and comparable population counts i s made d i f f i c u l t by the p h y s i c a l c h a r a c t e r i s t i c s of streams, which render the , taking of s a t i s f a c t o r y samples v i r t u a l l y impossible w i t h present methods and apparatus. Methods used with success i n lakes have a l i m i t e d a p p l i c a t i o n i n dealing with streams. The Ekman dredge, f i r s t designed f o r q u a n t i t a t i v e work on sea-bottom communities, and used w i t h success on mud, sand and f i n e g r a v e l bottoms In lakes,, has proved p r a c t i c a l l y useless i n many streams. This i s due both to the existence of currents which make the dredge d i f f i c u l t to handle, and more, p a r t i c u l a r l y to the type of bottom found most frequently i n streams, i . e . g r a v e l and rubble. The l a c k o f s u i t a b l e apparatus f o r taking stream-bottom samples i s one reason f o r the lag i n the l i m n o l o g i c a l s t u d i e s of running waters. Several methods f o r the taking of stream-bottom samples have been employed by various workers. Bicker {1924), i n h i s study of Ontario streams, took most of h i s samples by scooping up the bottom w i t h a dip-net, measuring the r e s u l t i n g hole. P e r c i v a l and Whitehouse (1929.), studying Yorkshire streams i n England, used a s i m i l a r technique, c a l l i n g t h e i r apparatus a shovel-net. These l a t t e r workers stated t h e i r r e s u l t s to be accurate i n bottoms containing stones up to 7.5 centimeters in'diameter 9 In t h i s same i n v e s t i g a t i o n these men used a sag-net, l i f t i n g l a r g e stones and q u i c k l y s l i p p i n g the net underneath. They also used a moss sampler, which was pushed down i n the vegetation, :a flanged c u t t e r being passed under-neath to, cut o f f the roots. Dr. A. Davidson of the S e a t t l e l a b o r a t o r y of the United States Bureau of F i s h e r i e s , r e c e n t l y designed, a s i m i l a r apparatus to the moss sampler. I t co n s i s t s e s s e n t i a l l y of two brass tubes^ ohe Inside the other. The outer tube i s open at both ends, and the Inner one has i t s bottom perforated by f o u r holes. The sampler Is pushed i n t o the mud or vegetation, and the inner tube given a quarter -turn, c u t t i n g o f f the sample underneath. Nee&ham (1934) designed the. ''square-foot 1' bos, c o n s i s t i n g of an i r o n box, open at both ends, which was pushed into the stream bed, and the enclosed organisms removed with a sieve. Needham, Surber, Davis and Hazzard i n 1934 designed the frame-bottom sampler, which has been i n the most general use i n recent i n v e s t i g a t i o n s . This c o n s i s t s e s s e n t i a l l y of two foot-square brass rod frames, hinged at r i g h t angles. A net i s attached to one frame, and the other i s placed on the stream bed. The area of bottom enclosed by the l a t t e r frame i s ag i t a t e d and the organisms l i v i n g t herein are swept i n t o the net by the current. Leonard (1939) tested the accuracy of t h i s sampler and concluded that ". . . a s regards t o t a l volume of good organisms, considerable r e l i a n c e can be placed on r e s u l t s derived from a s i n g l e c a r e f u l l y handled sample. However, although repeated sampling of - a uniform bottom type w i t h i n a r e s t r i c t e d area y i e l d s very s i m i l a r volumetric values, the f a u n i s t i c e l emen t s vary g r e a t l y i n species composition." This type of sampler i s u n s a t i s -f a c t o r y i n rough g r a v e l and rubble, and i s v i r t u a l l y u s eless i n sections where l i t t l e current flows. For a q u a n t i t a t i v e study of the bottom fauna of the Cowichan r i v e r , the w r i t e r has designed a sampler combining the features of the square-foot box and the frame sampler, but obviating to some extent the d e f i c i e n c i e s of "these samplers. I t c o n s i s t s of a rectangular wooden box eighteen inches high, s i x t e e n inches wide and seventeen inches long. A t h i r t e e n mesh wire-screen covers the front and a t h i r t y mesh marquisette net i s attached to the back of the box. The box i s strengthened by t r i a n g u l a r blocks set i n t o the corners at the top. These blocks serve a l s o as shelves on which to set the pan. Wooden handles on the sides of the box f a c i l i t a t e the handling of the samples. (See Figures 3, 4 and 5) To operate the sampler i t i s set f i r m l y i n t o the stream bottom, and the m a t e r i a l covering the area thus enclosed i s scooped i n t o deep i r o n pans such as are used to hold Ekman dredge samples. Organisms that are knocked loose while the bottom •'materials are being scooped up are swept i n t o the net by the current i n moving waters. In quiet sections where no current e x i s t s a hand sieve captures such organisms. This sampler works w e l l i n water up to seventeen inches i n depth. I t can be used s u c c e s s f u l l y i n p e r f e c t l y s t i l l water, and. i n quite f a s t current. Being on the same general p r i n c i p l e as the frame sampler i t i s as e f f i c i e n t as the l a t t e r i n ordinary types of bottom.. I t i s s t i l l not e n t i r e l y s a t i s f a c t o r y i n rubble bottom, but i s an improvement over the frame sampler here.. I t s l a r g e r area allows more l a t i t u d e i n choosing a j • • • • - • s u i t a b l e area of the bottom to be sampled, and allows i t to enclose completely more rocks. Also,/rocks and g r a v e l may be banked arotind the sides of the sampler, serving to prevent , the escape of the water due to i r r e g u l a r i t y of the- bottom., This obviates the need f o r placing a net behind the sampler, as i s necessary w i t h the square-foot box. The l a r g e r area enclosed by t h i s sampler i s required to allow room f o r the bottom m a t e r i a l to be scooped out. While greater amounts of m a t e r i a l are thus obtained, making p i c k i n g over a longer task, fewer samples are. necessary f o r accurate r e s u l t s . Thus, while s t i l l imperfect, t h i s sampler i s f e l t to be an improvement over previous types, c h i e f l y on account of i t s somewhat greater accuracy i n rubble bottom, and i n s t i l l water. : 10. Studies of stream bottom populations have long been recognized as being very imperfect. They have recently come under even more serious c r i t i c i s m , p a r t i c u l a r l y from Mottley (1939). The square-foot and s i m i l a r samplers are i n e f f i c i e n t i n several ways. F i r s t , i f the sampler i s not set evenly i n the stream, some organisms are l i k e l y to escape. Secondly, some organisms are missed by a l l the bottom m a t e r i a l i n the sample not being included. I t i s d i f f i c u l t to know how deeply i t i s necessary to dig to capture a l l the organisms present. Mottley p o i n t s out a serious source of e r r o r i n comparing populations of l i k e areas of rubble and sand, f o r example. "The use of a quadrat to compare these two main bottom types i s much l i k e the use of a standard c i t y block to contrast the density of the human population i n blocks of c i t y dwellings w i t h the population i n blocks of apartment houses. The value obtained i s a statement of the t o t a l number of organisms present at a given time, but i t does not d i s c l o s e how densely the various h a b i t a t s w i t h i n the area are populated, l o r instance, a rubble bottom may contain more organisms than a s i m i l a r area of sand, but at the same time the rubble has more h a b i t a t s per u n i t area than the sand owing to the greater habitable surface area w i t h i n the quadrat. A t o t a l count, therefore, gives no i n d i c a t i o n of the density i n each h a b i t a t . A census of the h a b i t a t s would a l s o be necessary, but t h i s census presents many p r a c t i c a l d i f f i c u l t i e s . As i n the comparison of s i n g l e dwellings and apartment houses the number of 11. i n d i v i d u a l s pep u n i t area of f l o o r space might give a b e t t e r index of. d e n s i t y , so the number of organisms per u n i t of substratum exposed to the water might be a better way of measuring the richness of a. stream." "The quantity of organisms present beneath a square foot of surface of stream bottom, may, therefore, be simply a measure of the density of population with reference to a u n i t area, but i t i s not n e c e s s a r i l y a measure of the r i c h -ness of that area. The richness can only be determined by measuring the density of the population In, each of the n a t u r a l h a b i t a t s . This con s i d e r a t i o n seems to be of fundamental jimportance i n measuring the food grade of streams." Mottley also discusses another source of e r r o r , already mentioned. "The second d i f f i c u l t y i n the use of the quadrat method concerns the e r r o r i nvolved i n determining the ac t u a l boundaries of the area. In t h i s respect t'he 'quadrat i s not at a l l l i k e the c i t y block, which i s a c l e a r - c u t u n i t . The houses do not project, i n t o the s t r e e t s i n the manner i n .which the stones of a rubble bottom extend behind the frame of a sampler. The stones may measure more than an inch or two i n diameter and the boundary may cut across many n a t u r a l u n i t s . I f the stones are brought i n t o t h i s area to remove the organisms c l i n g i n g to them, a considerable e r r o r may be Introduced. I t i s d i f f i c u l t , therefore, to decide how much to Include or exclude In the square-foot sample. In the ordinary sampling method e r r o r s as high as 30 p e r c e n t , or or more may* b'e expected. This l a r g e range of e r r o r throws some doubt on the v a l i d i t y of the quadrat method, p a r t i c u l a r l y f o r rubble bottoms." Further e r r o r i s introduced i n the s o r t i n g of samples. I t i s quite l i k e l y that a considerable number of organisms are missed i n p i c k i n g over the samples, regardless of the care of the work. Also t h i s e r r o r i s greater i n some types of bottom m a t e r i a l (e.g. vegetation) than i n others. Mottley also discusses the question of whether stream bottom sampling can provide an accurate measure of the whole n a t u r a l population. He concludes, "On the b a s i s of a considerable number of samples, s t a t i s t i c a l treatment of the data forces the conclusion that the method does not give a very r e l i a b l e p i c t u r e of the n a t u r a l populations." These c r i t i c i s m s of Mottley's are v a l i d up to a point, a n d " w i l l probably cause a r e c o n s i d e r a t i o n of the value of much work already done on stream bottom'communities. I f accepted completely the c r i t i c i s m s would i n v a l i d a t e a great deal of the i n v e s t i g a t i o n made up to the present on the populations of stream bottoms. Present methods f o r deter-mining the "food-grade" of streams, f o r purposes of gauging the number and s i z e of f i s h to be planted, undoubtedly need to undergo improvements. At the same time, the techniques employed i n the present i n v e s t i g a t i o n serve the purposes f o r which they were designed with some success. The abundance of the bottom forms i s obtained w i t h a degree of accuracy, at l e a s t a minimum f i g u r e heing a r r i v e d a t . 13. . The r e l a t i v e abundance i s shown f o r each organism and the p r o d u c t i v i t y of the various types of bottom may be compared with s u f f i c i e n t accuracy to make the r e s u l t s a valuable i n d i c a t i o n of conditions. L i t e r a t u r e A considerable and growing„literature e x i s t s on the limnology of lakes and standing waters i n general. Much l e s s work has been done on the limnology of/streams. Richardson i n 1925 published a report of the bottom fauna of the I l l i n o i s r i v e r , i n reference to tolerance of d i f f e r e n t animals to p o l l u t i o n . Wiebe published In 1927 a s i m i l a r report f o r the upper M i s s i s s i p p i r i v e r . Moore _et a l . (1927) reported f o r the Genessee r i v e r that stream bottoms wi t h considerable vegetation (water cress or ffontinalis) was most productive of organisms. Rubble and f l a t rocks produced an abundance of bottom forms, muck or s i l t bottom supported an average population, while f i n e sand contained very few organisms and f i n e .to~ coarse g r a v e l very few more. Richardson (1928), published, a f u r t h e r report on the I l l i n o i s p o l l u t i o n study. S u l l i v a n (1929) l i s t s the organisms a v a i l a b l e as f i s h food i n the Niagara r i v e r , Arkansas. P e r c i v a l and Whitehead (.loo. c i t . ) show vegetation (moss and Potamogeton) to support the greatest population, w i t h stones having a growth of Gladophora next. Muttkowski (1929) l i s t s the animals In the streams of Yellowstone N a t i o n a l Park. 14. P e r c i v a l and Whitehead (1930) reported on the invertebrate fauna of the River Wharfe. Packer (1934) l i s t s the species and abundance of organisms i n c e r t a i n trout streams of Ontario. P. R. Needham (1934) found that rubble supported the l a r g e s t invertebrate faunal population i n Waddell creek, with coarse and f i n e g r a v e l supporting smaller. P. R. Needham and Hanson (1935) reported that the streams of the S i e r r a N a t i o n a l Forest were poor i n food organisms, y i e l d i n g an average of only 143 organisms per square foot of bottom. Smith and P. R. Needham (1934) showed an average of 370 organisms per square foot inhabited the streams of the Mono and Inyo N a t i o n a l Forests, C a l i f o r n i a . Taft and Shapovalov (1935) showed that the average number of organisms supported by streams of the Klamath and Shasta N a t i o n a l Forests was'380. Surber (1936) found the average wet weight production of Big Spring Greek was 5.047 and 6.695 grams per square foot- i n two succeeding years. Needham (1938) i n h i s book "Trout Streams" makes a good a n a l y s i s of bottom sampling and r e s u l t s . He summarizes data obtained by himself (quoted above) and by Pate (quoted here under "Moore, et. a l . ) . This shows t h a t , i n r i f f l e s , rubble produces the most p o t e n t i a l f i s h food, y i e l d i n g 1.84 per square foot, while coarse and f i n e g r a v e l are f a i r l y r i c h , and sand, hard pan and bed rock poor i n food. In slow-moving water, s i l t produces 3.47 gm per square foot, w i t h muck and sand y i e l d i n g much l e s s . 15. Data and r e s u l t s The f o l l o w i n g t a b l e s show the number and weight of organisms from the -various types of bottom i n the r i v e r and creek. The average number of organisms per square yard i s taken to the nearest whole number of organisms. Table 1 represents the data obtained from 14 samples at S t a t i o n 1 (pool; mud bottom; t h i c k growth of Potamogeton; depth 4-6 f e e t ; very s l i g h t c u r r e n t ) . I t shows that molluscs were the most numerous organisms, while midges occurred i n the greatest number among•the i n s e c t s . Fresh-water shrimps (mostly H y a l e l l a a z t e c i ) were present i n large numbers. Other important groups were Odonata, Nematoda, Annelida and Trichoptera. Table 11 shows that S t a t i o n 1 was the most productive of any of the ten, ranking f i r s t by weight of organisms and second by number ( f o l l o w i n g the vegetation s t a t i o n i n the r i f f l e s i n t h i s l a t t e r ) . Table 2 summarizes the f i n d i n g s from 19 samples from S t a t i o n 2 (mid-pool; mud bottom with sunken bark, leaves, e t c .; depth 25 to 30 f e e t ; l i t t l e c u r r e n t ) . Here again molluscs are predominant by numbers, and midges come nest. Annelida and Trichoptera are the other outstanding groups. Table 11 shows S t a t i o n 2 to rank second by weight, but only seventh by number of organisms. Numbers of the large clam Anodonta cause the weight of samples from t h i s area to be proportion-a t e l y l a r g e r than the number of organisms would seem to warrant. Thus the productiveness of t h i s deep part of the pool on the 16. basis of fish, food i s probably over emphasized by t h i s table since Anodonta has p r a c t i c a l l y no value as trout food. This applies i n a somewhat l e s s e r degree to the weight r e s u l t s obtained from Stations 1, 4 and 6 as w e l l , where specimens of Anodonta were found i n varying numbers. The data from 18 samples from S t a t i o n 3 (pool; g r a v e l ; 2 to 5 feet deep; moderate current) are shown In Table 3. Here- mayflies are by f a r the l a r g e s t group of a rather sparse population. Midges, s t o n e f l i e s , shrimps and c a d d i s f l i e s were present i n smaller numbers. According to Table 11 t h i s s t a t i o n ranked f i f t h by number and l a s t by weight, so that i t was one of the l e a s t productive areas examined. However, the con d i t i o n i s probably somewhat exaggerated by t h i s data, since samples here had to be taken with the Ekman dredge, due to the depth of the water. I t i s c e r t a i n that the dredge i s hot as e f f i c i e n t as the bottom sampler i n t h i s type of m a t e r i a l , so t h a t . a l l the organisms from the area were probably not brought up i n the samples from t h i s s t a t i o n . Table 4- i s a -summary of the data from 16 samples from S t a t i o n 4 (pool; mud bottom; moderate growth of Potamogeton; depth 8 to 12 f e e t ; current moderate). Here molluscs lead i n point of numbers and shrimps are not f a r behind. Midges are the dominant i n s e c t s w i t h c a d d i s f l i e s and mayflies making up an important part of the population. The d i f f e r e n c e s between the conditions at t h i s s t a t i o n and those at S t a t i o n 1 are not great, being d i f f e r e n c e s i n depth and current 17. p r i n c i p a l l y . Table 11 shows t h i s area to rank high i n r e l a t i v e productiveness, being t h i r d i n both point of numbers and weight of organisms. Data from 18 samples from S t a t i o n 5 (edge of pool; mud bottom; grasses and rushes, decaying vegetation; depth s i x to eighteen inches; current s l i g h t ) are shown by Table 5. Here shrimps are the predominating organisms, no others occurring i n large numbers. Molluscs are the next l a r g e s t numerical group. Annelid worms (other than leeches, which were counted separately) rank ahead of any insect group. M a y f l i e s were the most numerous i n s e c t s , but t h e i r numbers were small. Table 11 reveals that t h i s s t a t i o n ranks next to l a s t , both as regards weight and number of organisms. This puts i t l a s t in.productiveness, which Is perhaps somewhat s u r p r i s i n g , considering the e c o l o g i c a l c o n d i t i o n s . Table 6 summarizes the data, from 18 samples from S t a t i o n 6 ( r i f f l e s ; rubble; depth s i x to eighteen inches; current moderate to b r i s k ) . At t h i s s t a t i o n Trichoptera were present i n the greatest numbers by f a r , no other group approaching them i n s i z e of population. M a y f l i e s were the next most numerous, • with molluscs f o l l o w i n g them. F'latwarms, midges and shrimps were the other important groups. This s t a t i o n i s shown by Table 11 to rank rather f a r down (eighth) by number, and only f o u r t h by weight, so that i t i s somewhere i n the middle i n r e l a t i v e productiveness. This i s an important s t a t i o n since a large proportion of the r i v e r bottom as a 18 . whole i s composed of rubble. Thus c a d d i s f l i e s are the dominant forms i n the r i v e r , mailing up the l a r g e s t population of the bottom dwellers. The f i n d i n g s from 20 samples from S t a t i o n 7 ( r i f f l e s ; gravel;' depth s i s to eighteen inches; moderate current) are represented by Table 7. Here again c a d d i s f l i e s are the most numerous forms by a large majority. Since the part of the general r i v e r bottom that i s not rubble i s composed of g r a v e l f o r the most part, t h i s emphasizes again the dominance of Trichoptera i n the Cowichan r i v e r . M a y f l i e s , s t o n e f l i e s , aquatic beetles and shrimps are the other prominent groups. Leeches and flatworms also f i g u r e i n the population to an important extent. Table 11 shows t h i s type of bottom to be r e l a t i v e l y l e s s productive than any other of those sampled except the edge of the pool,, Table 8 summarizes data from 6 samples from S t a t i o n 8 ( r i f f l e s ; t h i c k growth of moss and other vegetation; depth four to eight inches; current b r i s k ) . The outstanding feature of t h i s s t a t i o n i s the- very large number of b l a c k f l i e s (Simuliidae) which g r e a t l y outnumber other groups. One sample y i e l d e d over 9,000 b l a c k f l i e s per square yard. This compares with f i g u r e s given by Ide (1939) who found that a square yard of bottom of a stream i n Ontario y i e l d e d approximately 4,000 to 13,000 adult b l a c k f l i e s during periods of about four months. The enormous number of Simuliidae caused t h i s s t a t i o n to be ranked f i r s t i n point of numbers (although only f i f t h by weight). 19. This over-emphasizes the importance of t h i s type of bottom from the point of view of f i s h food, since these very large populations of b l a c k f l i e s b i g enough to provide food f o r f i s h are very seasonal, occurring f o r r e l a t i v e l y short periods during the year. Ide states the peak of the b l a c k f l y emergence to have come between May 27 and June 7 i n the streams he studied. However, during the time they are large enough to be eaten, as shown by stomach analyses ( I d y l l , Manuscript, 1940), M a y f l i e s , shrimps, midges, molluscs and c a d d i s f l i e s occurred i n important numbers at t h i s s t a t i o n , along with the b l a c k f l i e s . The water f e l l too low to take more than s i x samples at s t a t i o n 8 so that the data here are l e s s complete than at the other s t a t i o n s . Data from 13 samples from S t a t i o n 9 (creek; r i f f l e s ; coarse g r a v e l to sand; depth four to ten inches; current b r i s k ) are summarized i n Table 9. Here mayflies and midges occurred i n about equal numbers, to take f i r s t place i n the population. C a d d i s f l i e s also occupy an important place w i t h b l a c k f l i e s , c r a n e f l i e s and s t o n e f l i e s occurring l e s s frequently, but s t i l l i n s i g n i f i c a n t numbers. Table 11 shows that by number t h i s s t a t i o n ranked f o u r t h , by weight s i x t h . Table 10 summarizes the data from 12 samples from S t a t i o n 10, (creek; pool; rubble and coarse g r a v e l ; depth eight to fourteen inches; current s l i g h t ) . Midges are again the most numerous type of organism, but c a d d i s f l i e s here exceed mayflies i n numbers, i n contrast to the l a s t s t a t i o n . 20. These three groups are much the most important with c r a n e f l i e s and annelid worms showing a smaller though important popu-l a t i o n . Table 11 shows t h i s s t a t i o n to rank s i x t h both by weight- and number of organisms. The greater weight, i n comparison with the l a s t s t a t i o n , i s due to the presence of la r g e - s i z e d c a d d i s f l y larvae. A f u r t h e r study of Table 11 shows the r e l a t i o n s h i p of the three main areas to each other, and the p r o d u c t i v i t y of the r i v e r bottom as a whole. The average wet weight of organisms f o r the whole area i s 20.48 grams per square yard, and the average number Is 667 organisms per square yard. Thus the Cowichan r i v e r Is shown to be poor i n bottom forms. Needham and Hanson ( l o c . c.it. ) designate the streams of the S i e r r a N a t i o n a l Forest as "poor i n foo^d organisms" since they y i e l d only 143 per square foot as compared w i t h 370 and 380 per square foot i n the streams of the Mono and Inyo and the Shasta and Klamath National Forests r e s p e c t i v e l y . On the basis of the square foot the Cowichan r i v e r produces an average of only 74 bottom organisms', or about h a l f the production of the "poor" streams of the S i e r r a Forest. Surber ( l o c . c i t • ) shows h i s experimental stream to y i e l d an average of 5.047 and 6.695 grams j>er 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. 

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