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Effect of population densities on survival, growth, and behavior of coho salmon and steelhead trout fry Fraser, Frederick James 1968

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THE EFFECT OF POPULATION DENSITIES ON SURVIVAL, GROWTH, AND BEHAVIOR OF COHO SALMON AND STEELHEAD TROUT FRY by FREDERICK JAMES FRASER B.S c , University of B r i t i s h Columbia, 196^ A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Zoology We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA February, 1968 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h C o lumbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g of t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by the Head of. my Department o r by h i s r e p r e s e n -t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n ' o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . The U n i v e r s i t y oYB Vancouver 8, Canada Depa rtment ABSTRACT The f r y of the very similar salmonids, coho salmon (Oncorhynchus kisutch) and steelhead trout (Salmo g a i r d n e r i ! ) , l i v e i n very close association with each other during t h e i r f i r s t year of l i f e i n fresh water. The present study was designed to measure the eff e c t s of competition between these species. Populations of d i f f e r e n t densities of coho and steelhead f r y i n four i d e n t i c a l a r t i f i c i a l stream-channels were studied. Observations were made on su r v i v a l , growth rates, and some aspects of behavior. Among the various groups of f r y , s u r v i v a l was apparently dependent upon i n t e r s p e c i f i c factors; the presence of another similar species had no observable e f f e c t . Low-density populations survived well, even when another species was present at a high-density. Survival of the f i s h at high-densities was always depressed, even when the companion species was present at low density. Steelhead f r y demonstrated a fa s t e r i n i t i a l growth rate than the coho, enabling them to exceed the coho i n growth despite the l a t t e r * s e a r l i e r hatching and consequent i n i t i a l size advantage. Growth rates were inversely r e l a t e d to density, both i n t e r - and i n t r a s p e c i f i c effects being noticeable. The two species tend to be s p a t i a l l y segregated, coho occupying positions i n the middle and upper layers of the streams, and steelhead remaining close to the bottom. This s t r a t i f i c a t i o n was r e f l e c t e d i n t h e i r feeding behavior and. diet. i i i Emigration a c t i v i t y occurred to a greater degree among the coho than the steelhead. Emigrants of both species were observed, to undergo substantial weight loss subsequent to t h e i r disappearance from the stream-channels. I t was concluded that coho and steelhead f r y l i v e i n close association with one another without experiencing extensive i n t e r s p e c i f i c competition. This i s because of segregation of the species by having d i f f e r i n g habitats, feeding habits, growth and. survival rates, and consequent population dynamics. i v TABLE OF CONTENTS Page TITLE PAGE i ABSTRACT i i TABLE OF CONTENTS i v LIST OF FIGURES v i LIST OF TABLES v i i LIST OF APPENDICES v i i i ACKNOWLEDGEMENTS i x INTRODUCTION 1 DESCRIPTION OF STUDY AREA 3 METHODS AND MATERIALS A. General Procedure h B. Experimental Design 9 C. Emigration and Fry Marking 10 D. C o e f f i c i e n t of Condition 11 E. Instantaneous Growth and Survival Rates 12 F. Feeding Behavior Observations 13 RESULTS POPULATION DYNAMICS A. Survival 1*+ B. Growth 16 C. Biomass Production 18 BEHAVIOR A. Emigration 20 B. Feeding Behavior Observations 25 C. Stomach Content Analysis 29 V TABLE OF CONTENTS (CONTINUED) Page DISCUSSION 32 SUMMARY k ? LITERATURE CITED k9 APPENDICES 52 v i LIST OF FIGURES FIGURE Page 1. The four stream-channels. 5 2. Plan view of the stream-channels showing the d i s t r i b u t i o n of the building-blocks and. shade-covers. 6 3- Stream-channels 3 and h, downstream view. 7 h. An example of pool, r i f f l e , and. marginal t r a n s i t i o n zones. 8 5« The percentage of emigration attempts by the various groups of coho and. steelhead f r y during the experiment. 21 6. Species comparisons of emigration attempts throughout the experiment by the coho and steelhead. f r y i n si m i l a r densities. 22 v i i LIST OF TABLES TABLE Page 1 I n i t i a l numbers of coho and steelhead f r y , and. densities per stream-channel. 10 2 The numbers of coho and. steelhead, f r y present. i n the stream-channels at various times d,uring the experiment. 15 3 The annual su r v i v a l rates for the groups of coho and, steelhead. f r y . 16 k Annual instantaneous growth rates i n length fo r a l l groups of f r y . 17 5 The condition c o e f f i c i e n t s for each group of f r y at the end. of the experiment. 17 6 The regression c o e f f i c i e n t s of growth rate f o r both species of f r y i n a l l density groups. 19 7 The net standing crop of a l l groups of f r y at the end. of the experiment. 19 8 The average d a i l y emigration rates f o r a l l groups of f r y as a percentage of the t o t a l population present. 23 9 The percentage composition of emigrant groups from the stream-channels containing the intermediate and. high-density groups. 2*+ 10 A sample record, of repeater-emigrants showing time and. cumulative percentage weight loss after the i n i t i a l attempt. 25 11 The lengths and, c o e f f i c i e n t of condition of resident and, emigrant f r y from the intermediate and, high-density stream-channels at the end. of the experiment. 27 12 The v e r t i c a l d i s t r i b u t i o n within the stream-channels of the coho and, steelhead. f r y during the feeding behavior observations. 28 13 The percent frequency of invertebrates found, i n the stomachs of coho and. steelhead, f r y from the stream-channels - 1966. 30 v i i i LIST OF APPENDICES APPENDIX Page I Analysis of covariance - su r v i v a l rate comparisons of both species and a l l groups of f r y . 53 II The mean lengths and weights and the c o e f f i c i e n t s of condition (Q) f o r the d i f f e r e n t groups of coho and, steelhead. f r y . 65 III The numbers of f r y emigrating from the stream-channels during the experiment summed f o r each 10-day i n t e r v a l . 66 IV The averaged, emigration data f o r 10-day periods as a percentage of the population, and i t s ar c s i n transformation value. 67 i x ACKNOWLEDGEMENTS I would, l i k e to thank my supervisor, Dr. D. H. Chitty, f o r advice and. guidance during the writing of t h i s t h e s i s . I would also l i k e to thank Drs. N. R. L i l e y , T. G. Northcote and G. F. Hartman f o r c r i t i c a l comments and suggestions which proved to be most h e l p f u l . I am indebted to Dr. P. A. Larkin, Director of the I n s t i t u t e of F i s h e r i e s , for providing f i n a n c i a l support. I would also l i k e to express my appreciation to Dr. J . T. MeFadden, now at the Unive r s i t y of Michigan, f o r assistance i n developing t h i s study and for c r i t i c a l advice i n the preparation of t h i s t h e s i s . The Canada Department of F i s h e r i e s were most generous i n permitting the use of f a c i l i t i e s and. equipment at Robertson Creek as well as for providing f i n a n c i a l support. The F i s h e r i e s Association of B r i t i s h Columbia also provided f i n a n c i a l assistance. Many colleagues of the I n s t i t u t e of F i s h e r i e s were most h e l p f u l i n lending assistance i n f i e l d , work and f r y c o l l e c -t i o n s . Mr. Jack Baker, the resident technician at the Robertson Creek Spawning Channel, provided, valuable assistance. Messrs. Dan Ware, Murray Dingman, and Camil Berube provided very able assistance i n the f i e l d work, and without them t h i s study would not have been possible. Miss Inez S m i l l i e was very h e l p f u l with the laboratory work and data processing. To them a very special thanks. Mrs. Joyce Chubb spent many hours p a t i e n t l y typing manuscripts f o r me. Her assistance i s g r a t e f u l l y acknowledged. X And foremost I would l i k e to dedicate t h i s thesis to the memory of my l a t e wife E l l e n , whose constant support and. i n s p i r a t i o n during my u n i v e r s i t y education made t h i s endeavour possible and worthwhile. INTRODUCTION The sympatric salmonids, coho salmon (Oncorhynchus  kisutch) and steelhead trout (Salmo g a i r d n e r i i ) are a l i k e i n many respects. Milne (19*+8) observed them to be similar i n geographical d i s t r i b u t i o n , systematic counts, spawning locations, breeding changes, feeding habits, and length of time the young spend i n f r e s h water. As ad.ults, both species return to t h e i r n a t a l stream to spawn a f t e r two to f i v e years of ocean l i f e . They d i f f e r s l i g h t l y i n that coho f r y normally remain i n f r e s h water one year, while steelhead may remain up to three years before migrating to the ocean. In t h e i r f i r s t year of l i f e these f i s h are c l o s e l y associated with one another. However, Hartman (1965) reports them t a occupy d i f f e r e n t stream micro-habitats i n the spring and summer, while occurring together i n the f a l l and winter. Peterson (1966) suggests the s p a t i a l segregation to be of a s t r a t i f i e d nature, the coho associated with the stream surface and. the steelhead with the bottom. This close association during the juvenile phase of t h e i r l i f e cycle probably involves competitive i n t e r a c t i o n to some degree. R i l e y (1953) hypothesizes however, that two sim i l a r sympatric species w i l l not occupy the same niche and that t h e i r requirements f o r survival w i l l never be completely i d e n t i c a l . These differences w i l l therefore permit coexistence by l i m i t i n g competition. Furthermore, as Kendeigh (1961) states, the extent of i n t e r s p e c i f i c competition w i l l depend on - 2 -the degree of overlap i n requirements and the shortage of supply from the environment. Competition and t e r r i t o r i a l i t y , and some modifying environmental factors such as temperature, shade, current, bottom type, food, and. time, have been studied i n several salmonids, mostly under laboratory conditions (Boussu, 195^; Brett et a l . 1958; Chapman, 1962, 1966; Hartman, 1965, 1966; Hoar, 19^2, 1951, 1953; Kalleberg, 1958; Keenlyside and Yamamoto, 1962; Larkin, 1956; MacKinnon and, Hoar, 1953; Newman, 1956; Ruggles, 1966; Smoker, 1953; Stringer and Hoar, 1955)* Few data, however, are available to indicate to what extent i n t e r -s p e c i f i c behavior and. competition a f f e c t s f r y s u r v i v a l and growth under natural conditions. In nature post-emergent salmonid, f r y are normally present i n large numbers. When the f r y of a second similar species emerge the population density within a stream can become very high. I n t e r s p e c i f i c competition may therefore r e s u l t because of high densities of both species, and, the s p a t i a l l i m i t a t i o n s of the stream environment. This competition probably involves, among other things, an excess demand, upon some aspect of the environment such as food, space, or shelter (Chapman, 1966). The end r e s u l t of competitive pressure may be the l i m i t a t i o n of size or numbers of one or both species. To determine to what extent coho and, steelhead, f r y i n t e r a c t , the following hypotheses were tested: ( l ) that growth and survival of each species i s la r g e l y density-dependent and species s p e c i f i c , and (2) that i n t e r s p e c i f i c competition w i l l not be as intense as i n t r a s p e c i f i c competition, and (3) that the species w i l l have certa i n behavioral differences. These hypotheses were tested, with various population densities of coho and. steelhead. f r y i n a simulated, natural stream environment. DESCRIPTION OF THE STUDY AREA This study was c a r r i e d out at the experimental f a c i l i t i e s of the Robertson Creek Spawning Channel ( l a t . If9°20', long. 12 If°59 l ) on the west coast of Vancouver Island. Four "Rearing Channels" ( F i g . l ) were used, f o r t h i s experiment. F a c i l i t i e s at the channels (Lucas, I960) permit control of substrate, water depth, v e l o c i t y , and. entry and. exit of a l l organisms over 3 mnu Each stream-channel was 61.7 m long, 3*1*- m wide and had. an area of 211.0 m2. Gravel of 2.0 cm to 12.0 cm diameter was used, f o r substrate 20.0 cm deep. Cement building-blocks (20.3 cm x 20.3 cm x ^0.6 cm) were placed, throughout the length of each channel ( F i g . 2 and. F i g . 3) providing a nearly complete range of water v e l o c i t i e s ( F i g . h) similar to those found, i n nature. As a r e s u l t , r i f f l e , pool, and. t r a n s i t i o n zones ( v e l o c i t i e s from 0 to 1.1 m/sec) were created. Water depth varied, from 20.0 cm to 100 cm (avg. 30 cm). The water volume entering each channel was maintained, at 0.08 mVsec (2.7 c f s ) . As a further v a r i a t i o n i n the simulated, habitat, shade covers (1.22 m x 2.hk m) were placed above the water surface (0.56 m) at 3.0 m i n t e r v a l s down the length of each channel (Fig. 1). METHODS AMD MATERIALS A. General Procedures Screens and traps were cleaned, and. maintained, throughout the day while water flows into the stream-channels were held, constant. Entry of f i s h into the stream-channels was prevented, by inclined, copper screen (3 mm mesh) traps. The exit of each stream-channel contained an aluminum V-trap i n which a l l emigrating f r y were live-captured, i n a large nylon mesh bag (25 cm diam., 73^5 cm deep; v o l 37«2 l i t r e s ) . Fry were removed, from the exit traps six to eight times d a i l y . To provide a uniform substrate i n a l l stream-channels, a 20.0 cm top-dressing of clean r i v e r - g r a v e l was applied, on 1 May 1966. As a r e s u l t natural productivity was temporarily but s u b s t a n t i a l l y reduced. Supplemental feeding was therefore undertaken when the f r y were introduced s i x weeks l a t e r . For feeding, a two l i t r e mixture of canned, salmon and. f r y food-p e l l e t s was broadcast twice d a i l y . Though natural food, production was reestablished, within s i x weeks, supplemental feeding was maintained, to the end. of the experiment. Fork length of the f r y was measured, to the nearest 0.5 mm. Each f i s h was measured twice to reduce error. Weights were determined, to the nearest 0.01 g and, could, be r e p l i c a t e d within - 0.01 g with 95 percent confidence. Live samples f o r Fig. 1. The four stream-channels used, with building-blocks and shade-covers installed, and the overlooking observation platform. The processing area i s i n the center of the picture. -6--Screen Trops Screen Tfops-- v-Trapsly''"'"' ' iiHJirhfiiiiifinth^iUin^i^ f^l^^^-Fig. 2. Pton view of the Btfeom chonnels showing the distribution of the building - blocks and shade - covers. Fig. 3. Stream-channels 3 and h; downstream view, showing the distribution of the building-blocks. Note the center dividing wall between the stream-channels supporting the shade-covers. The field, laboratory i s i n the background, processing area upper right. F i g . k. An example of pool, r i f f l e , and marginal t r a n s i t i o n zones. length-weight data were obtained from the stream-channels at about monthly i n t e r v a l s . Fry which were removed f o r stomach content analysis were replaced. The d i f f e r e n t emergence times of coho and steelhead made i t necessary to acquire f r y from two sources. The e a r l i e r emerging coho were obtained from the Big Qualicum River, Vancouver Island, B. C , while the steelhead f r y , which were not available there, were acquired l a t e r at the L i t t l e Campbell River, White Rock, B. C. The f r y were seined and transported to Robertson Creek the same day. Upon a r r i v a l they were retained, b r i e f l y i n holding boxes, counted and then released, into the stream-channels. B. Experimental Design The densities x«f f r y i n s t a l l e d i n the stream-channels are shown i n Table I. For easier reference the d i f f e r e n t groups w i l l be r e f e r r e d to i n the text as follows: high densities H C1,2 H S1,2 low densities L C 1 , 2 L ^ l , 2 where the l e t t e r s "H" and "L" represent high and low numbers of f r y respectively. The subscripts 1 and 2 i d e n t i f y the p a r t i c u l a r group. Fry densities were based, upon observations of n a t u r a l l y occurring coho f r y (mean size 35 mm)) i n the channels before access was r e s t r i c t e d and the experiment began. Voluntary residents of each channel averaged 2^0 f r y . R. Peterson (pers. comm.) observed, a similar density for coho f r y i n the L i t t l e Campbell River. He also noted steelhead -10-density to be 0.71 f r y per square meter. I therefore designated 50 f r y to be the low density and 1500 the high density of each species. These population sizes were considered s u f f i c i e n t to demonstrate density e f f e c t s and competitive i n t e r a c t i o n between the species. TABLE I . INITIAL NUMBERS OF COHO AND STEELHEAD FRY, AND DENSITIES PER STREAM-CHANNEL. Group Coho Steelhead Density (No. fry/m2) L C J L S J L 50 50 0 A 7 LC-^HS 50 1500 7.35 HC jLS 2 1500 50 7.35 HC2HS2 1500 1500 lh.22 Natural (Robertson Creek) 2^0 - i.ih Natural (L. Campbell River) - ll+9 0.71 From the various census techniques available I decided. that v i s u a l l y counting the f r y while skin-diving was the most appropriate method. The technique involved slowly swimming upstream and. recording the number of each species. Comparison of i n i t i a l and f i n a l counts shows that these estimates were adequate to reveal population trends. C. Emigration and Fry Marking The experiment was conducted from lh June (Day 1) to 23 November (Day 163) 1966. From Day 1 to Day h8 a l l emigrating f r y were counted and. returned to t h e i r respective stream-channels. From Day ^9 to Day 1^ 6 the emigrants were also cold-branded with -11-numbered dies. A f t e r Day *+9 emigrating f r y were treated as follows. Emigrants from each channel were sorted by species, and. placed i n separate holding aquaria. Fry, i n groups of f i v e , were anaesthetized, with 2-phenoxyethanol, 1 ml per 3«8 l i t r e s ( B e l l , 196^), and. then weighed, measured, and branded i f necessary. The f r y were then placed, i n holding boxes ( F i g . 2) located at the upper end of each stream-channel and. released a f t e r about s i x hours. Dead, f r y could, also be retrieved. From Day 1^ 6 to Day 163 the f r y were simply counted, measured, and, any numbers recorded.. The cold-branding dies were cooled, i n a solution of ethanol and. dry i c e ( -78.25°C). Brand, numbers 2.h mm i n height were placed on the l e f t side of the f r y near the dorsal f i n and. whenever possible above the l a t e r a l l i n e . The mark was e a s i l y observed, on the day following branding and. remained, l e g i b l e up to four months. For data analysis the number of emigration attempts were summed, over 10-day periods to dampen short-term f l u c t u a -t i o n s . The degree of emigration i s relevant only when considered i n terms of percentage of the t o t a l population present. However, these percentage values are often very small i n the l a t t e r h a l f of the experiment and. awkward, to deal with. To compensate therefore, an a r c s i n transformation (Snedecor, 1956) was employed to weight more heavily the smaller percentage values. D. C o e f f i c i e n t of Condition A c o e f f i c i e n t of condition ( N i k o l s k i i , 1963) was used, as an a i d i n determining the general physical condition of the -12-f r y . The usual mode of expression i s the equation W(IQ5) Q = L 3 where W i s the weight (gms)) of the f i s h and L i t s length (mm)]< The f a c t o r 1C-5 brings the value of Q near unity. This c o e f f i c i e n t can be used to indicate seasonal changes i n heaviness of f i s h i n r e l a t i o n to length, and d i f f e r -ences between groups of the same species i n d i f f e r e n t environments. This c o e f f i c i e n t , according to N i k o l s k i i (1963), gives only a f i r s t approximation to the actual condition of the f i s h , but f o r a comparative analysis i t i s quite suitable. E . Instantaneous Growth and Survival Rates Instantaneous growth rates (Ricker, 1958) were determined by the following formula: l o g e L l - l o g e L o § L = ; where g-^  = annual instantaneous rate of growth i n length L Q = length of f i s h at time o Lj^ = length of f i s h at the end of the experiment t = time Annual survival rates were determined by using the following formula: N l — = e~ and rearranging N o l o g e N l - l8fe No - i = t -13-where N Q = number present i n i t i a l l y = number present at end of time period i = instantaneous mortality rate t = time e = base of natural logarithms. Ricker (1958) provides an appendix table of exponential functions and derivatives. For a p a r t i c u l a r i value the corre-sponding annual s u r v i v a l rate (s) can be obtained. Covariance analyses of survival rates were c a r r i e d out and s i g n i f i c a n t differences were determined, by F-tests at the 5 percent p r o b a b i l i t y l e v e l . F. Feeding Behavior Observations Underwater observations were conducted, on feeding behavior to determine s p a t i a l d i s t r i b u t i o n s and. differences between the species. Canned, salmon was used, to encourage a maximum feeding response. This food, was presented, at various depths from the surface to the bottom of the stream-channels by means of a 50.0 cm. x 0.95 cm, diameter glass tube syringe. Observations i n each stream-channel consisted, of 15-minute periods, 5 minutes before feeding and for 10 minutes during feeding. Observations on post-feeding behavior were also carried out. Before and during food, presentation, the species, numbers present, and v e r t i c a l d i s t r i b u t i o n s of the f r y were recorded. _1L_ G. Stomach Content Analysis Stomach content analysis was performed on random samples of both species from a l l four stream-channels. This analysis was performed to detect any evidence of dietary differences between the species. Where possible, stomach contents were c l a s s i f i e d to Family while a general d i v i s i o n between t e r r e s t r i a l and aquatic invertebrates was maintained. In determining r e l a t i v e quantities of items from the food--spectrum a percent frequency basis was employed. RESULTS  POPULATION DYNAMICS A. SURVIVAL The numbers of f r y present at ce r t a i n times during the experiment are shown i n Table 2. Precise counts were made at the beginning and end of the experiment. Intervening counts are the estimates made by skin-diving which are considered s u f f i c i e n t l y r e l i a b l e to provide an i n d i c a t i o n of the trend of survival f o r the groups. Paired comparisons were tested by covariance analysis to determine differences i n survival rates. The following comparisons were found to be s i g n i f i c a n t l y different;(Appendix I ) : H C - L and. H S X H C 2 and H S J L HC X and HS 2 HC 2 and HS 2 -15-TABLE 2. THE NUMBERS OF COHO AND STEELHEAD FRY PRESENT IN THE STREAM-CHANNELS AT VARIOUS TIMES DURING THE EXPERIMENT. DAY Group 1 18 h9 66 9 2 • I63 L C J L 50 ^7 1+6 ^5 ¥f L S J L - 50 ±7 tf8 ^5 ^9 L C 2 50 k8 kd k 7 H S X - 1500 1250 895 725 331 H C J L 1500 1330 1161 107^ 612 L S 2 - 50 k8 h7 k8 H C 2 1500 1210 950 836 h79 H S 2 - 1500 1150 871 653 31^ At the same time the sur v i v a l rates f o r each species i n the groups LC^S^ and HCjLS 2 are also d i f f e r e n t . In t h i s case however, analysis was not necessary to confirm these differences. Comparisons of su r v i v a l rates of the following groups revealed them to he not s i g n i f i c a n t l y d i f f e r e n t : LCi and LS X L C 2 and. L S 2 LCL and L S 2 LC X and L C 2 L C 2 and, LSj^ L S X and L S 2 HC X and. HC 2 H S J L and. HS 2 -16-A l l low-density groups had sur v i v a l rates which were not s i g n i f i c a n t l y d i f f e r e n t from one another. The high-density i n t e r s p e c i f i c comparisons indicated s u r v i v a l rates to be s i g n i -f i c a n t l y y d i f f e r e n t , while the i n t r a s p e c i f i c comparisons ( i . e . HCi and. HC 2 ; H S l and HS 2) were not. Table 3 contains the annual s u r v i v a l rates of both species and a l l density groupings, based on the term of the experiment. The table shows that i n the low-density situations the steelhead. (LSi and. LS2) rates of sur v i v a l were greater than those of the coho i n si m i l a r circumstances (LC X and. L C 2 ) . On the other hand the high-density coho (HC X and HC 2) had higher s u r v i v a l rates than did the steelhead i n comparable situations (HSj. and HS 2). TABLE 3. THE ANNUAL SURVIVAL RATES FOR THE GROUPS OF COHO AND STEELHEAD FRY. GROUP Species L C i L C 2 HCi HC2 Coho 0.756 0.87^ 0.107 0.062 L S i HSi* L S 2 HS 2 Steelhead. 0.951 0.015 0.902 o.om B. GROWTH Detailed growth data and condition c o e f f i c i e n t s of the f r y at various times during the experiment are shown i n Appendix I I . Annual instantaneous growth rates f o r length are given i n Table and the condition c o e f f i c i e n t s f o r a l l groups at the end of the experiment are i n Table 5» -17-TABLE h. ANNUAL INSTANTANEOUS GROWTH RATES IN LENGTH F O R A L L G R O U P S O F F R Y . G R O U P Species L C J L L C 2 H C - L H C 2 Coho 1.19 1.08 0.90 LSj_ HSj. L S 2 H S 2 Steelhead 2.50 1.77 1.33 1.3^ T A B L E 5- T H E C O N D I T I O N C O E F F I C I E N T S F O R E A C H F R Y A T T H E E N D O F T H E E X P E R I M E N T . G R O U P O F G R O U P Species L C X L C 2 HCj_ H C 2 Coho l.lh 1.21 1.18 1.13 L S i HSi L S 2 H S 2 Steelhead 1.21 1.20 1.20 1.15 In each stream-channel the steelhead exceeded the companion coho f r y i n annual instantaneous growth. The f r y i n the low-density grouping (LCjLSi) demonstrated the highest instantaneous growth rates f o r each species. The f r y i n the high-density grouping (HC 2HS 2) had the lowest growth rate, p a r t i c u l a r l y the coho, while the steelhead had. annual instan-taneous growth equal to that of the intermediate-density group (HSi). -18-The high-density f r y of the intermediate groupings ( L C 2 H S 1 and H C 1 L S 2 ) had, growth rates which were also intermediate i n nature, with the steelhead, (HS X) again demonstrating the greater amount of instantaneous growth. Table 5 indicates that the c o e f f i c i e n t s of condition f o r a l l groups of f r y were approximately the same,. ranging between 1.13 and 1.21. On the average, the coho had s l i g h t l y lower c o e f f i c i e n t s than the steelhead. Both species i n the high-density grouping had, the lowest values. However, a l l groups had values ;which f a l l between the a r b i t r a r i l y set norm of 1.1 to 1.2 (B. L i s t e r , pers. comm.). Growth rate regression c o e f f i c i e n t s of a l l f r y groups are contained i n Table 6. The regression values were calculated f o r two time periods; the i n i t i a l growth period (Day 1 to Day 3*+), and the f i n a l growth period. (Day 35 to Day 163). In the i n i t i a l growth period the regression c o e f f i c i e n t values (bi) of the two species are a l l s i g n i f i c a n t l y d i f f e r e n t from each other, except for the H C 1 L S 2 group. In every other case the steelhead had. a higher rate of growth. In the f i n a l growth period C^)? the slope values of a l l groups are not s i g n i f i c a n t l y d i f f e r e n t from one another (except f o r the LCjLSi group). In t h i s period the growth rates f o r .""both species are similar. C. BIOMASS. PRODUCTION Terminal net standing crop (Table 7) was calculated f o r a l l groups of f r y by determining the product of the mean weight, and numbers of survivors i n each stream-channel at the -19-TABLE 6. THE REGRESSION COEFFICIENTS OF GROWTH RATE FOR BOTH SPECIES OF FRY IN ALL DENSITY GROUPS. THE COEFFICIENT b i INCLUDES THE GROWTH PERIOD FROM DAY 1 TO DAY 3*f, WHILE b 2 REPRESENTS THE GROWTH PERIOD FROM DAY 35 TO DAY 163. LC]_ L S i LC 2 HS ^  HC1 LS 2 HC 2 HS 2 0.606 1.61 0.3^3 0.995 0.127 0.286 O.13I+ 0.79^-b 2 0.12*+ O A 3 8 o.r+3 0.159 0.192 0.068 0.131 0.092 end of the experiment. I n i t i a l values were subtracted from the terminal values to obtain the net standing crop. TABLE 7. THE TERMINAL NET STANDING CROP OF ALL GROUPS OF FRY AT THE END OF THE EXPERIMENT. THE FIGURES ARE GRAMS OF FISH (BIOMASS) PER STREAM-CHANNEL. GROUP Species LCjLS! LC 2^S j_ HC j^ LS 2 HC 2HS 2 Total Coho 179.98 153.62 9^5.63 59.1^ 1338.37 Steelhead W3.78 875.58 77-58 231.0*4- 1667.98 Total 663.78 1029.20 1023.21 290.18.;. The high-density f r y of the intermediate groups ( i . e . HCj_ and HSj[) produced the greatest amount of biomass. In the high-density grouping, biomass production was sub s t a n t i a l l y lower. In t h i s case, the coho (HC 2) biomass was minimal, amounting to approximately one-quarter of that produced by the companion steelhead. ( H S 2 ) , and, less than seven percent of that - 2 0 -produced. by the s i m i l a r coho group (HCj_) i n the intermediate-density. The biomass produced by the steelhead (HS2) i n the high-density group i s about 37 percent of that produced, by the steelhead. (HS^) of the intermediate group. The low-density steelhead. (LS^) produced, a r e l a t i v e l y large amount of biomass i n comparison to that of the companion coho (LCj[). The other low-density steelhead group, from the intermediate-density, produced, a biomass which amounted to only 16 percent of the LS^ group's production. The low-d.ensity coho groups (LCj. and. L C 2 ) produced approximately equal amounts of biomass. The t o t a l biomass produced by each species i s also given i n Table 7» Though both species l i v e d i n the same physical environment, d i f f e r e n t amounts of biomass were elaborated. In t h i s case the steelhead. f r y produced approximately 330 grams more biomass than did, the coho. Biomass production on a group basis i s also provided, i n Table 7. The two intermediate-density groupings (LCpHS^ and H C _ L and L S 2 ) have very s i m i l a r net-production f i g u r e s . The low-density group produced, the next highest biomass while the high-density group had the lowest production rate of the four groups. BEHAVIOR A. EMIGRATION Fr y emigration rates from the various stream-channels are shown i n Figure 5» Comparisons of emigration by each species i n the various groups are shown i n Figure 6. Emigration i s -22-Fig. 6 Spsclss comparisons of •migration attempts throughout th« tipQrlrrwnt by tht coho and sttslhsad fry In similar densities. Tht psrcsntagt valuss havs undargons arcsln transformation. presented i n terras of percentage values which have undergone ar c s i n transformation. Emigration data, summed for 10 day periods are i n Appendix I I I , while the percentages of emigration f o r each group, and t h e i r a r c s i n transformation are i n Appendix IV. Immediately following introduction into the stream-channels, a l l groups of f r y (except the LS X steelhead) had high rates of emigration which subsequently declined, to low e q u i l i -brium l e v e l s . The lower rates of emigration were then maintained u n t i l the end of the experiment. Table 8 shows the differences i n pre* and post-equilibrium emigration. The pre-equilibrium emigration rates were much higher than those of the post-equilibrium period. A f t e r equilibrium was established, the coho f r y of a l l groups maintained average d a i l y emigration rates which were higher than those of the steelhead. TABLE 8. THE AVERAGE DAILY EMIGRATION RATES FOR ALL GROUPS OF FRY AS A PERCENTAGE OF THE TOTAL POPULATION PRESENT. THE RATES ARE SHOWN FOR BOTH BEFORE AND AFTER THE ESTABLISHMENT OF EMIGRATION EQUI-LIBRIUM. LCj_ L S X L C 2 HS X L S 2 HC 2 HS 2 Pre-13.7^ equilibrium ^.93 0.20 6.55 10.85 25.25 10.99 rates Post-equilibrium 0.18 0.09 rates 3-38 1 A 6 1.1+8 0.51 2.76 1.97 Comparisons show that f r y of the high-density group (HC 2HS 2) had. higher emigration rates than those of the -2h-intermediate groups ( i . e . HCj_ and. HS^). The low-density groups had. minimal emigration rates. Any discrete group of f r y emigrating from a stream-channel would he composed, of both f i r s t - t i m e emigrants and. those who had emigrated, two or more times. Table 9 shows that from 55 percent to 70 percent of a l l emigration, depending on the group, was performed, by repeaters. Some f r y were noted, to emigrate several times. TABLE 9- THE PERCENTAGE COMPOSITION OF EMIGRANT GROUPS FROM THE STREAM-CHANNELS CONTAINING THE INTERMEDI-ATE AND HIGH DENSITY GROUPS Percentage of Group emigrant group being repeaters HCj_ 55.5 HC 2 69. H S J L 61.6 HS 2 71.1 Average 6*fA Table 10 i s a sample record of repeater-emigrants showing time of each emigration attempt a f t e r the i n i t i a l emigration, and the cumulative percentage change i n weight. S i x f r y of each species were chosen as representative of the emigrant population from the HC 2HS 2 group, wherein the largest amount of emigration took place. TABLE 10. A SAMPLE RECORD OP REPEATER-EMI GRANTS SHOWING TIME AND CUMULATIVE PERCENTAGE WEIGHT LOSS AFTER THE INITIAL ATTEMPT. THE FRY WERE CHOSEN FROM THE HC 2HS 2 GROUP. THE DATA IS ALSO SUMMARIZED. THE DAYS IN THE TABLE ARE THE TIMES AFTER THE FIRST EMIGRATION ATTEMPT. No. of Emigr. Attempts Day Cum % Day Cum % Day Cum % Day Cum % Dav Cum % Day Cum % Coho 2 k 6.1 16 5-3 1+9 27.8 8 if. 2 5 12.6 26 18.2 3 23 17.2 25 2k. 5 60 51.5 17 10.2 11 17.8 32 23.2 k 29 27.6 32 32.2 70 51.5 28 21.2 38 29.0 3h 37-0 5 35 29-3 ^0 36 A 73 51.5 30 21.7 39 31-0 35 39.2 6 38 33-6 7 39 33.6 Steelhead 2 k 8.6 62 3^.0 3 3.1 13 16.2 27 21.0 5 13.8 3 35 Ik.7 65 37.5 23 10 A 72 37-7 33 31.0 lk 21.0 k k2 20.6 66 37-5 58 33.0 80 39-7 >+5 23.8 21 33.6 5 59 37.6 22 29.1 SUMMARY Coho Steelhead. Average time to second emigration 18 days 2k days Average weight loss at second emigration 12 .kfo 16.1ft. Average time to l a s t emigration Average weight loss at l a s t emigration k2.7 days 35.6^ 51.7 days 30.0$ -26-Table 10 shows that a l l the emigrants l o s t weight over the course of time. In most cases, the majority of emigration attempts take place af t e r an i n i t i a l period (e.g. between an average of 18 and 2h days fo r coho and steelhead. r e s p e c t i v e l y ) . The repeaters, i n most cases, then emigrated, several times within a short period, and, were seen no more. Table 10 also shows that the coho (on the average) spent a shorter time i n the stream-channel than did the s t e e l -head, before the second, as well as the l a s t emigration attempt. The coho also experienced, a greater loss i n body weight. Two of the steelhead. f r y showed a reveral i n the trend by recovering some of the l o s t weight. This did not occur among the coho. F i n a l lengths and. condition c o e f f i c i e n t s for both resident and emigrant f r y of the high-density groups are contained, i n Table 11). The data show that differences i n size and. condition exist between resident and. emigrant f r y of each group. However, only the coho ( H C J L ) of the intermediate-density group have differences which are s i g n i f i c a n t l y d i f f e r e n t on the basis of t - t e s t s . . The condition c o e f f i c i e n t f o r a l l emigrants i s approxi-mately 1.05 as compared, to the average of 1.17 for the residents. B. FEEDING OBSERVATIONS Underwater observations on the feeding behavior of the two species were conducted i n the stream-channels. General observations made pr i o r to feeding showed, the coho f r y to be -27-TABLE 11. THE LENGTHS (mm) AND COEFFICIENT OF CONDITION (Q) OF RESIDENT (Res) AND EMIGRANT (Em) FRY FROM THE INTERMEDIATE AND HIGH DENSITY STREAM-CHANNELS AT THE END OF THE EXPERIMENT. HS^ H S 2 HC X H C 2 Res Em Res Em Res Em Res Em 70.2^- 65.30 58.95 61.52 66.76 61.07 61.69 60.68 13.70 9.18 9-55 8.65 11.90 1 0 A 7 8.83 5.68 100 38 100 i+9 100 100 100 100 1.20 1.06 1.15 1.0k 1.18 1.07 1.13 1.05 Mean length (mm) Std. Error Sample size Q-value located, predominantly near the surface, while the steelhead. restricted, t h e i r a c t i v i t i e s to the stream-bottom. The r e s u l t s of the feeding studies support the above observations on species s t r a t i f i c a t i o n . The data compiled, i n Table 12 shows the coho to be surface and subsurface feeders while the steelhead. r e s t r i c t e d t h e i r feeding a c t i v i t i e s to the bottom. I t i s also shown that on the average, 22.3 percent of the coho present at the surface descended to feed, among the steelhead, whereas none of the l a t t e r would, ascend, to the surface (approximately 35 cm) i n response to the food. Food, presented, at the surface appeared to create a c o n f l i c t i n motivation f o r the steelhead. This c o n f l i c t may have developed, because surface-food, provided a strong stimulus, while an equally strong reluctance to leave the stream-bed. persisted. This c o n f l i c t was manifest by the steelhead,'s focus TABLE 12. THE VERTICAL DISTRIBUTION WITHIN THE STREAM-CHANNELS OF THE COHO AND STEELHEAD FRY DURING THE FEEDING BEHAVIOR OBSERVATIONS No. of Observations Surface Feeding Bottom Feeding of Grazing To t a l m A c t i v i t y Observation Coho @\ Coho @,Stlhd. Q Stlhd@Coho @ Coho @ Stlhd. @ Stlhd. § Date Time (hr.) Surface Bottom Surface Bottom Surface Bottom Surface Bottom Coho Stlhd July 13 2 38 3 0 18 35 6 0 22 0 11 July 18 2 kk 0 0 Ik * f l 9 0 18 0 l l f Aug. 5 2 77 I f 0 17 65 15 0 31 0 7 Aug. 22 2 31 2 0 21 27 9 0 33 0 5 Sept. k 2 29 0 0 27 31 k 0 h? 0 12 Sept.19 2 38 3. 0 26 39 6 0 2k 0 17 T o t a l 12 257 12 0 123 238 ^9 0 175 0 66 Average if - 2 . 8 2.0 0 20.5 36.7 8.17 0 29.17 0 11 Std Error 17.56 1.68 0 5.17 9.18 1.58 0 1.31 0 k.k3 -29-of attention on the food, passing overhead, and. the appropriate intention movements to s t a r t pursuit. Some steelhead. f r y were observed starting pursuit of a surface food item but would, then quickly return to the bottom af t e r ascending l e s s than halfway to the surface (20 cm). There were no observed, instances wherein a bottom oriented, steelhead, f r y would, intercept a surface presented, food, p a r t i c l e even though the food, presented, caused, a very strong feeding reaction among both species. Grazing i s shown by Table 12 to be a d i s t i n c t s t e e l -head, feeding behavior. Grazing behavior involved, nipping items such as invertebrates and. algae from the gravel substrate. Grazing was never observed to occur among the coho. Post-feeding observations did. not reveal any notice-able a l t e r a t i o n i n behavior or increase i n i n t e r a c t i o n between or among the species. G. STOMACH CONTENT ANALYSIS The r e s u l t s of stomach -content analysis on rand.om f r y samples from a l l stream-channels are contained, i n Table 13. Generally the data show that d i s t i n c t differences often exist between the food selected, by the two co-existing species. Examination of the 13 July 1966 stomach samples, indicate that the two species have d i f f e r i n g diets. The food, items i n the surface oriented, coho f r y had. the following percentage composition: simulids 5h.60 percent, tend.ipeds 1^.50 percent, and, t e r r e s t r i a l organisms 27*60 percent. At TABLE 13. THE PERCENT FREQUENCY OF INVERTEBRATES FOUND IN THE STOMACHS OF COHO AND STEELHEAD FRY FROM THE STREAM-CHANNELS - 1966 Sample Other aquatic T e r r e s t r i a l Date Size Simulidae Tendlpedidae Trichoptera invertebrates organisms Ju l y 13 Coho 17 5>+. 60 A . 50 1.20 2.10 27.60 Steelhead 12 7 A 0 90.30 0.50 0.30 1.50 Aug. 12 Coho 11 99.30 0 A 0 0.01 0.20 0.09 Steelhead 9 98.50 I .30 0.06 0.00 O.lh Sept.12 Coho 6 5.13 ^2.21 50.10 0.00 2.56 Steelhead 6 7-50 22.20 62.70 0.10 7.50 Oct. l*f Coho 7 8k.20 0.00 15-50 0.30 0.00 Steelhead 7 0.00 O.83 99-17 0.00 0.00 -31-the same time steelhead stomachs contained 7 A 0 , 90.30 and. 1.50 percent of the same items respectively. The 12 August 1966 sample analysis shows both species to be preying almost e n t i r e l y on the large numbers of simulid. larvae. Analysis showed coho to have 99.3° percent and. s t e e l -head. 98.50 percent of the stomach items consisting of simulid.s. At t h i s time t e r r e s t r i a l organisms constituted, a very small portion of the diet. The portion of simulid.s i n the 12 September 1966 analysis of both species i s s u b s t a n t i a l l y reduced. In t h i s sample a wider choice from the food spectrum i s demonstrated. Trichopterans provide about h a l f the diet for both species while tendipeds amount to ^2.21 and 22.20 percent for the coho and steelhead. respectively. In the 1*+ October 1966 sample, the second, generation simulids represent 8k. 2 percent of the coho diet and. 0 percent f o r the steelhead. At the same time trichopterans are an important constituent of the steelhead d i e t , representing 99.17 percent of the t o t a l contents as compared, to only 15*50 percent of the coho. I t i s not possible to state with certainty that an invertebrate was d r i f t or benthic at the time of ingestion by f r y . However, underwater examination of the stream-channel bottom determined habitat l o c a t i o n of some of the major food, organisms. For example, colonies of simulid. larvae were associated, with f a s t water areas such as the small w a t e r f a l l at the entrance to each stream-channel, and. the various -32-r i f f l e zones. Subsequent observations revealed that such high v e l o c i t i e s (up to -1.1 m/sec) i n the r i f f l e s were too f a s t for f r y to swim f o r more than a few seconds before being swept into slower water. As a consequence i t can be i n f e r r e d that invertebrates such as colonies of simulids were l a r g e l y inaccessible to predation by f r y as long as they remained, i n t h e i r benthic habitat. Other invertebrates such as the trichopterans were observed to be crawling upon the rocks of the streamjebed. i n much slower water (0 to O A m/sec). DISCUSSION The four stream-channels used for th i s experiment were constructed so that a l l f r y groups would, be exposed to the same physical environment. The only variable was the di f f e r e n t combinations of f r y . The d i f f e r e n t f r y densities tested the hypothesis that growth and survival of each species i s l a r g e l y density-dependent and, species-specific. The various s u r v i v a l rates among the d i f f e r e n t groups suggests that there are important species differences. For example, the similar s u r v i v a l of the low-density groups, regardless of the density of the companion species, reveals the existence of differences separating, to some extent, one species from the other. The steelhead, i n both intermediate and high-density groupings, had. survival rates which were very si m i l a r to one another, regardless of the numbers of coho present. - 3 3 -At the same time, the high-density coho groups had su r v i v a l rates i n both situations which were higher than those of the steelhead, and also d i f f e r e n t from each other. The intermediate coho f r y had. a higher s u r v i v a l rate than did. the high-density group, and. perhaps t h i s difference may be more than density-dependent. The differences were not s i g n i f i c a n t s t a t i s t i c a l l y , but b i o l o g i c a l l y they quite l i k e l y are. I t can only be postulated, but t h i s difference may be the r e s u l t of i n t e r s p e c i f i c influence, wherein the presence of steelhead. may have a depressing e f f e c t on the coho (Stringer, 1952). The differences i n s u r v i v a l between the species could, also be due to an innate a b i l i t y of the coho to occupy a wider niche, as suggested by the feeding studies. The absence of steelhead. may have permitted greater e x p l o i t a t i o n of the environment by the high-density coho i n the intermediate group. On the other hand, the s t r i c t e r l i m i t a t i o n s of the steelhead. niche, as also suggested, by the feeding studies, may not have permitted, these f r y to take advantage of the absence of coho. The differences i n survival rates of each species i n the intermediate-density groups, suggest that the survivorship of one species i s l a r g e l y unaffected, by the presence of another. I f the species differences were small, the mortality should, be si m i l a r with both groups having a common sur v i v a l rate. The experimental r e s u l t s do not support t h i s idea. The high-density group experienced, twice the density pressure than did the intermediate groups. In t h i s case, greater differences i n survival between these and. the intermediate -3k-species groups might be expected. However, the s i m i l a r i t y of s u r v i v a l among each species further points out that the differences between the species are s u f f i c i e n t to reduce the e f f e c t of population density pressures on s u r v i v a l , almost e n t i r e l y , to one of i n t r a s p e c i f i c o r i g i n . The mortality of the high-density f r y groups may be at t r i b u t a b l e to several f a c t o r s . One f a c t o r causing mortality could be the physiological stress (Brown, 1957) which may develop due to crowding. Another factor which.might have had an adverse e f f e c t on the s u r v i v a l of emigrants was the experi-ence of being captured and. subjected, to the experimental procedure. Because most emigrants were repeaters, i t may be that cumulative e f f e c t s , due to emigration, depressed s u r v i v a l . However, i t i s suggested, that mortality rates were a r e f l e c t i o n of more natural influences rather than the p o s s i b i l i t y of i t being an experimental a r t i f a c t . Predation i s a natural factor which should, be considered. In t h i s p a r t i c u l a r s i t u a t i o n however, i t i s not thought to be of importance i n the s u r v i v a l of these f r y . Predation from birds and mammals was reduced to minimal l e v e l s due to a continuous predator-control program. Predation and, cannibalism by f r y i n the stream-channels was observed, to take place on rare occasions. However, among these salmonids, i t i s considered, to be a factor of reduced, importance (Le Cren, 1965; Lowry, i n Chapman, 1965)? p a r t i c u l a r l y within a single age-class group. - 3 5 -There i s no d i r e c t evidence pointing to a single f a c t o r which explains mortality. I f the numbers adjustment i s not being caused by disease, predation, emigration or cannibal-ism then the question as to what i s the cause remains unanswered. Evidence does show that those f r y who emigrated, more than one time underwent substantial weight l o s s . This weight loss took place over a reasonably long period, of time and the tempo of emigration f o r an i n d i v i d u a l increased near, presumably, the end. of the f r y ' s l i f e . The weight loss appears to begin before emigration occurs, and. i t therefore i s not l i k e l y an experi-mental a r t i f a c t , but probably r e f l e c t s some form of stress being exerted, from within the group. I t i s suggested, that some form of psychological stress i s a normal component of the f r y ' s environment. The exact cause of t h i s stress i s not known, but the ef f e c t i s apparently d.eath by starvation. Perhaps some form of psychological i n h i b i t i o n blocks the feeding behavior. The fa c t that the majority of emigrants l o s t substan-t i a l amounts of body weight by the l a s t emigration attempt tends to suggest that a physical weakness may be the underlying fa c t o r causing emigration. I t i s possible that these f r y were no longer p h y s i c a l l y able to r e t a i n a p o s i t i o n i n the stream-channels and. to thri v e as did. the residents. One qualifying f a c t o r regarding i n d i v i d u a l emigrants i s that they could not be identified, u n t i l Day 50 when the marking program began. As a consequence i t i s not possible to state when an i n d i v i d u a l f i r s t emigrated. Quite l i k e l y any - 3 6 -p a r t i e u l a r i n d i v i d u a l emigrated at l e a s t once, p a r t i c u l a r l y during the i n i t i a l period of i n s t a b i l i t y . I t should therefore be kept i n mind that the time indicated i s a c t u a l l y i n addition to the unknown period p r i o r to marking. Many species of f i s h have variable growth rates which often r e f l e c t the environment within which they l i v e (Lindstrom and. Nilsson, 1962; Nilsson, I960; and Larkincand. Smith, 195^)• For example, the low density groups, i n response to the optimum environmental conditions, demonstrated, the greatest increase i n growth. The medium and high-density populations of f r y demonstrated, lesser growth rates. When the growth rates were calculated, for two time periods, differences between the species became apparent i n the i n i t i a l growth period, while i n the f i n a l growth period, both species with one exception, were simi l a r . I n i t i a l l y the steelhead, which were very small at introduction, had. growth rates which were much higher than those of the coho. In the f i n a l growth period, after the sizes of the species within each density group became approximately equal, the two then had, similar growth rates. The growth of the f r y i n the various groups indicate that growth rate'ois density-dependent rather than species s p e c i f i c , when dealing with f i s h of equal si z e . However, even though low densities of f r y survived very well i n the presence of a high-density companion species, they did. not grow equally as well, although they too had. a high growth rate during the i n i t i a l time period. This reduced, rate of growth could, be due to a number of f a c t o r s . I t i s possible -37-that food i t s e l f , or interference i n obtaining food, l i m i t e d growth at high-density, p a r t i c u l a r l y when the sizes of the f i s h were simi l a r . I t i s also possible that the higher densities p r e c i p i t a t e an increased rate of behavioral i n t e r -action (Keenlyside et a l . 1962). Perhaps a high-density of one species has a depressing e f f e c t upon the normal behavior of another companion species (Stringer, 1952). At any rate, growth appears to be c l o s e l y related, to the environment, r e f l e c t i n g the influence of both i n t e r -and. i n t r a s p e c i f i c population densities. Le Cren (1965) concurs, stating that growth rate appears to depend, upon environmental influences though genetical factors can play some part. With but one exception, the lengths of both resident and. emigrant f r y of each stream-channel were found, to be similar at the end. of the experiment. At the same time, i n every case, the condition c o e f f i c i e n t s were lower for the emigrants. This s i t u a t i o n may indicate that mortality had, by the end of the experiment, removed, most of the unstable members of the populations, while some emigrants managed, to become residents. The reversal i n weight l o s s , as demonstrated, by some steelhead, may indicate that i t i s possible f o r emigrants to overcome whatever barrier there i s , to become a member of the stable population. Carlander (1955) states that differences i n the standing crops (biomass) of any one species i n the presence of another species may give some clues as to the extent of competition. He cautions however, that analysis of standing -38-crop may not give proof of competition, but can aid i n deter-mining where the competition may be suspected. I f the accumulation of biomass within a species group i s a parameter by which i n t e r s p e c i f i c competition i s to be appraised, then the res u l t s of t h i s experiment suggest that the high-density members of the intermediate groups had the greatest biomass production. However, i t i s obvious that the low-density group, p a r t i c u l a r l y the steelhead, produced, the greatest amount of biomass f o r the fewer f i s h involved. In t h i s Situation, competition for the nec e s s i t i e s of l i f e must have been minimal. There i s no apparent reason why the steelhead, of t h i s group were able to elaborate such a large amount of biomass, however t h i s could, be a natural response to the environment which i s a genetic f a c t o r not possessed, by the coho. Both high-density species of the intermediate groups produced approximately equal biomass. This equality of biomass production may indicate the extent of competition, however there were twice as many coho involved, than steelhead. The significance of these r e s u l t s are not apparent, but i t i s commonly observed, i n nature (B. L i s t e r , pers. comm.). The species i n the high-density group produced a very small amount of biomass. The coho production i n p a r t i c u l a r was minimal. This s i t u a t i o n could, be due at least to one of two f a c t o r s . F i r s t l y , the conditions, as created i n the stream-channels, could, have permitted, competition i n i t s most extreme form so that the f i s h were forced, to r e l y on t h e i r - 3 9 -species s p e c i f i c survival a b i l i t y , while adjusting to an adverse environment by reducing biomass elaboration. Secondly, i t i s possible that the environment i n the stream-channels was saturated, with f r y and i t s carrying capacity severely over-taxed, and consequently f r y suffered from i n s u f f i c i e n t food. The end r e s u l t s however, do not support such a suggestion. I t i s also thought that mortality i n t h i s l a t t e r case would, have made the necessary population adjustments to minimize environmental stress, and. i f such was the case, then the outcome should, have been subs t a n t i a l l y d i f f e r e n t from the intermediate groups. Therefore i t i s concluded, that the high density groups demonstrated, the highest degree of competition by elaborating the least amount of biomass. Survival and. growth observations suggest that niche segregation occurs with s u f f i c i e n t d i s t i n c t i o n to permit a species' population dynamics to occur, without any serious degree of reaction to the presence of another similar species. N i k o l s k i i (1962) quotes S. A. Severtsov's observation that ". . . the population dynamics of a species could, be called, a focus at which a l l i t s p e c u l i a r i t i e s were re f l e c t e d ; they were the r e s u l t of a l l aspects of i t s ecology which i n turn are determined, by the adaptation of the species." My experimental r e s u l t s tend to agree with Severtsov's observations, by demonstrating the fact that there are some s i g n i f i c a n t differences between these two sympatric salmonids. These differences are s u f f i c i e n t to permit very AO-close association with one another without any pronounced, degree of i n t e r a c t i o n . The differences i n emergence time of the coho and steelhead, f r y and, concomitant size differences may be an adaptation of extreme importance to both species. This temporal difference may explain i n part the f a s t e r growth rate demonstrated, by the steelhead. i n the i n i t i a l growth period. Chapman (1962), states that during emergence of coho f r y , those f i s h emerging f i r s t appear to enjoy an ecological advantage. In the same vein, the e a r l i e r emergence of coho f r y , i n r e l a t i o n to the steelhead, may also be providing the l a t t e r with an ecological advantage. For example, the s t e e l -head. f r y , because of t h e i r l a t e r emergence, may occupy the niche recently vacated, by the larger coho. This l a t e r emergence, and. consequent smaller si z e , may tend to minimize dire c t food, competition with the larger coho. Competition f o r food, by f r y of a cer t a i n size range, may also involve food organisms of a c e r t a i n size which i s related, to mouth size (Lindstrom, 1955; Hartman, 1958; Gee and Northcote, 1962). Therefore, smaller steelhead. may be occupying a niche d i f f e r e n t from that of the coho, on the basis of size. This size-related, aspect of competition may be the reason for the f a s t e r growth by the steelhead. i n the i n i t i a l growth period. In other words, the steelhead. f r y may have avoided competition by exploiting a special category of the food, resource which was no longer being used, by the larger coho. By l a t e summer the steelhead f r y had eliminated, the size differences, both i n t h i s experiment and. i n nature (G. F. Hartman, pers. comm.). This development could poten-t i a l l y create strong competitive i n t e r a c t i o n between the species, p a r t i c u l a r l y between certa i n food items, except f o r the subsequent change i n ecological requirements which occurs i n response to the forthcoming winter conditions. During the winter period, general a c t i v i t y and food requirements of both species are much lower, so that competitive i n t e r a c t i o n i s probably reduced even though both f r y are very c l o s e l y associated. In the following spring, the coho emigrate to the ocean, leaving behind, most of t h e i r p o t e n t i a l competitors. The steelhead who remain, are then i n a size range which reduces competition to one of an i n t r a s p e c i f i c nature, even when the new crop of coho f r y emerge. This f i n a l separation of the two species may be completely analogous to the f i r s t year of l i f e together. I n i t i a l l y , these similar f i s h occupied, d i f f e r e n t microhabitats i n f r e s h water presumably to avoid, intensive i n t e r s p e c i f i c competition. As t h e i r sizes become equal, i t i s possible that competition could, increase substantially, p a r t i c u l a r l y i n the following spring, when they become more active again. To avoid, t h i s p o s s i b i l i t y the coho smolts emigrate to the ocean consequently assuring the avoidance of a competitive confronta-t i o n . - 3 + 2 -Certain aspects of f r y behavior were examined to reveal any behavioral differences between the two species. For example, the emigration patterns of the f r y showed that the coho were more active than the steelhead. I t was shown that the coho not only had. rates of emigration which were consistently higher than the steelhead, but also made a s i g n i f i c a n t l y greater number of emigration attempts. This higher rate of a c t i v i t y by the coho could well be a species s p e c i f i c behavior pattern. This a c t i v i t y may have s i g n i f i c a n t survival value i n nature by dispersing the species to a l l possible habitat locations whenever density pressures are great. I f the coho do have a wider habitat,or a greater t o l e r a t i o n to environmental v a r i a b i l i t y , as indicated, by t h i s study, then higher a c t i v i t y patterns may be s i g n i f i c a n t and have s u r v i v a l value. On the other hand, the higher rate of a c t i v i t y may be one f a c t o r responsible, to some degree, for the lesser growth rate. The energy expended i n greater locomotor a c t i v i t y may have sacrificed, growth po t e n t i a l . Stringer (1952) observed, i n an aquarium experiment, that coho,nip coho more than trout (Salmo g a i r d n e r i i ) , and. the nipping i n t e n s i t y i s accelerated, by the removal of the l a t t e r . He also noted that trout were the dominating species, and that the presence of one species suppressing the a c t i v i t y of another was not an uncommon observation. I f the higher emigration rates are a r e f l e c t i o n of the coho's reaction to the presence of steelhead, then perhaps psychological stress i s the major A3-cause. However, even coho of the low-density group had a much higher rate of emigration, where presumably stress would be minimal. Feeding behavior observations provided evidence to suggest that s t r a t i f i c a t i o n by the two species occurs within the stream-channels. These observations also suggested that the coho possess a wider tolerance of habitat type (Chapman, 1966) than do the steelhead. This occupation of a more diverse habitat was manifest by the one-way overlap into the steelhead niche by some coho during, the feeding observations, as well as t h e i r greater reliance on t e r r e s t r i a l organisms (Peterson, 1966). Nevertheless t h i s type of s t r a t i f i c a t i o n , p a r t i c u l a r l y f o r the steelhead, may be the device proposed, by Kendeigh (1961) which reduces i n t e r s p e c i f i c competition so that an overlap i n species' requirements i s minimized.. The post-feeding behavior observations (which were not formally quantified.) indicated, that l i t t l e or no change i n behavior of either species of f r y took place following feeding, such as an increase i n agonistic behavior. Many hours of observation served to convince me that feeding i s a dominant behavioral pattern which occupies the majority of the f r y ' s time. Newman (1956), and Keenlysid,e et a l . (1962), as well as many other workers, have reported, on the basis of laboratory studies, that a d i r e c t r e l a t i o n s h i p exists between feeding and aggression. Chapman (1962) also noted, that aggression usually ceased during feeding ( a r t i f i c i a l l y present-ed.) and resumed, when food ceased, to d r i f t downstream. My observations from nature do not support t h i s r e l a t i o n s h i p . The feeding experiment i n p a r t i c u l a r and other behavioral observations i n general, produced no evidence of aggression either during or af t e r feeding. This discrepancy i s probably due to differences existing between the aquarium and. the natural environment. In the aquarium environment, the ease of conditioning f i s h to routines and patterns i s well documented. (Hoar, 1958; B u l l , 1957). For example, the a r t i f i c i a l feeding regime often involves the sudden, but anticipated, appearance of food, which assures a maximum feeding response from hungry f i s h , who could, very e a s i l y demonstrate a consequent higher rate of i n t e r a c t i o n . In nature, an e n t i r e l y d i f f e r e n t s i t u a t i o n occurs with regard, to the feeding behavior pattern. Many workers (Peterson, 1966; Ruggles, 1966; Muller, 1963, 195*+; Waters, 1962) have studied, the invertebrate d r i f t i n streams. The species composition of t h i s d r i f t f luctuates on a diurnal basis such that invertebrate food organisms are nearly always available at any p a r t i c u l a r time. The point i s that natural food, i n a stream i s present on a f l u c t u a t i n g but continuous basis. The f r y feed, or mouth-test a l l d r i f t items (e.g. d e t r i t u s , wood, p a r t i c l e s , f e c a l material and. food) continuously throughout the day (with perhaps a diurnal rhythm). This continuous feeding a c t i v i t y , assures that f i s h do not normally experience extreme states of hunger. This lack of hunger and. unnatural conditioning, probably reduces the necessity for any extensive behavioral +5-i n t e r a c t i o n . Continuous aggressive i n t e r a c t i o n would, involve a serious waste of time and. e f f o r t on the part of the f r y , and, i t i s suggested, that t h i s food-aggression phenomena occurs only during special situations. Stomach content analysis, though based, on small samples, revealed, that dietary differences occurred, at times between the species. I f cer t a i n invertebrates are a r b i t r a r i l y defined, as indicator species, further substantiation may be provided, f o r the concept of species s t r a t i f i c a t i o n . A food source indicator i s defined, as an invertebrate which, i f eaten, would indicate with a f a i r degree of r e l i a b i l i t y , the l o c a t i o n within a stream where i t was most l i k e l y ingested. The food, item would, thus provide an insight into the feeding ecology of the f r y . No proof i s offered, for t h i s d i s t i n c t i o n but i t i s suggested, by observations. The benthic simulid.s, who are considered, to be d r i f t organisms which have become d.etached. from their fast-water habitat, i l l u s t r a t e t h i s idea. Two other examples are the tendipeds and. trichopterans, which normally crawl upon the substrate i n other habitat areas, and. are thuso c l a s s i f i e d , as benthic epifauna. The components of the f r y stomach contents thus contribute to the characterization of each species. The dietary differences between the species can be explained, to some d.egree i f one accepts the above c l a s s i f i c a -t i o n . In addition the grazing by the steelhead, as well as the feeding behavior observations, when correlated, with the higher incidence of d r i f t and. benthic organisms i n t h e i r -1+6-stomach, adds further evidence to the suggestion of s t r a t i f i -cation. I f these f r y are opportunists within t h e i r niche (Larkin, 1956) taking whatever food item i s most abundant, then when two such c l o s e l y associated, species have diets which d i f f e r , i t may be reasonable to assume that t h i s i s due to some degree of niche d i f f e r e n t i a t i o n . Chapman (1962) reported the frequent occurrence of redirected aggression by both dominant and. subordinate coho f r y i n connection with aborted aggressive interactions. This a c t i v i t y i s described as the picking up of a l g a l t u f t s or bottom p a r t i c l e s and r e j e c t i n g them. Chapman's description of redirected aggression i s very s i m i l a r to my description of grazing by the steelhead. f r y . In view of the f a c t that t h i s a c t i v i t y was not observed to occur among t,he coho while i t was c l e a r l y evident among the steelhead, combined, with the f a c t that the aggressive i n t e r a c t i o n , which pr e c i p i t a t e d t h i s redirected a c t i v i t y , was not observed, leads me to conclude that even though the descriptions are similar, the functions attributable to the act are considerably d i f f e r e n t . These two species of salmonids are considered, to have a very close evolutionary r e l a t i o n s h i p . Milne's (19^8) work, as well as the r e s u l t s of more recent biochemical systematics (Tsuyuki, et a l . 1962; Tsuyuki, et a l . 1965) tend to confirm that of a l l the North American salmonids, these two species, with the possible exception of cutthroat trout (Salmo  c l a r k i i ) , have the closest phylogenetic r e l a t i o n s h i p . -1+7-Evolving together has caused these two species to develop important, although subtle differences, such as d i f f e r i n g f r y emergence time, smolt transformation time, and. niche preference which permits coexistence within a stream without one being a serious threat to the s u r v i v a l of the other. Le Cren (1965) also studied, two salmonids which are very s i m i l a r . In a study of survival during the egg-to-fry stage of salmon (Salmo s a l a r ) , and, trout (S. t r u t t a ) , he found, that trout mortality was species-specific and. density-dependent on trout alone, while the salmon mortality was proportional to the number of both salmon and, trout present. I t appeared, that the trout f r y were dominant to the salmon f r y . Evidently these two species have not evolved, the necessary mechanisms to reduce the effects of coexistence to the same degree as have coho and. steelhead. SUMMARY Survival of both species of f r y appeared, to be s p e c i e s - s p e c i f i c . S urvival of low-densities of one species was not influenced, by the presence of large numbers of another. Steelhead. f r y demonstrated, a f a s t e r i n i t i a l growth rate than did. the coho, who o r i g i n a l l y enjoyed, an ecological advantage. Both species had. similar growth rates i n the f i n a l growth period. Growth rate i s considered, to be mostly density dependent. The two species have c e r t a i n behavioral differences which tended, to s t r a t i f y the species. The steelhead were - i f 8 -always associated, with the bottom while the coho generally occupied, the surface areas. The coho demonstrated, greater emigration a c t i v i t y . Various causes of mortality were discounted, and, the suggestion made that und.er these p a r t i c u l a r circumstances, some form of psychological stress may play an important role i n the control of population numbers. The increase i n aggression following feeding, as reported, i n the l i t e r a t u r e , was not observed. On the basis of t h i s research i t i s concluded that growth i s l a r g e l y density-dependent while s u r v i v a l i s species s p e c i f i c . At the same time i n t e r s p e c i f i c competition i s much less intense than i n t r a s p e c i f i c competition. 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(eds.) Blackwell. Oxford. 265-282. NIKOLSKII, G.V. 1963. The ecology of Fishes. Academic Press. London & New York, 352 pp. NILSSON, N.A. I960. Seasonal fluctuations i n the food, segregation of trout, char, and. whitefish i n lh north-Swedish lakes. Rept. Inst. Freshw. Res. Drottningholm. *+lt 185-205. PETERSON, G.R. 1966. The relationship of invertebrate d r i f t abundance to the standing crop of benthic organisms i n a small stream. M.Sc. Thesis, Dept. Zool. Univ. B r i t i s h Columbia, 39 pp. RICKER, W.E. 1958. Handbook of computations for b i o l o g i c a l s t a t i s t i c s of f i s h populations. B u l l . F i s h . Res. Bd. Canada, No. 119, 300 pp. RILEY, G.F. 1953. Theory of growth and competition i n natural populations. J. F i s h . Res. Bd. Canada, 10:211-223. RUGGLES, C P . 1966. Depth and. v e l o c i t y as a factor i n stream rearing and. production of juvenile coho salmon. Can. F i s h . Cult. 3L £ : 3 7 - 5 3 . SMOKER, W.A. 1953* Stream flow and. s i l v e r salmon production i n Western Washington. Wash. Dept. F i s h . Res. I.A-12. SNEDEC0R, G.W. 1956. S t a t i s t i c a l methods. 5th Ed. The Iowa State Univ. Press. Iowa. 53*+ PP« -52-STRINGER, G.E. 1952. An experimental study of some v i s u a l l y released, behaviour patterns i n young coho salmon and. Kamloops trout. M.A. Thesis. Dept. Zool. Univ. B r i t i s h Columbia, 36 pp. STRINGER, G.E. and M.S. HOAR. 1955* Aggressive behavior of underyearling Kamloops trout. Can. J. Zool. 33:13+8-160. TSUYUKI, H., and E. ROBERTS. 1962. Species differences of some members of Salmonidae based, on t h e i r muscle myogen patterns. J . F i s h . Res. Bd. Canada, 20:101-103+. TSUYUKI, H., E. ROBERTS, and. M.E. VANSTONE. 1965- Comparative zone electropherograms of muscle myogens and. blood hemoglobins of marine and freshwater vertebrates and, t h e i r a p p l i c a t i o n to biochemical systematics. J. F i s h . Res. Bd. Canada, 22:203-213. WATERS, T.F. 1962. Diurnal p e r i o d i c i t y i n the d r i f t of stream invertebrates. Ecology, 3+3:316-320. APPENDICES APPENDIX 1 ANALYSIS OF COVARIANCE 1. LOW DENSITY COHO AND STEELHEAD SURVIVAL ( L C j L S j . ) Group Sx' 1 XV 2yf D e v i a t i o n f rom R e g r e s s i o n R e g r . Sums o f Mean C o e f . f S q u a r e s Squa re Coho ( L C p S t e e l h e a d ( L S X ) W i t h i n R e g r e s s i o n C o e f . Common A d j . Means T o t a l 5 16 .8066 -0.3971 0.1523 -0.0236 h 0.13+30 0.0357 k 2 . 6 8 7 5 - 0 . 0 2 5 0 0 . 0003 - O y X ) ^ 3. 0.0001 0 . 0 0 0 0 3 7 0.13+31 0.0201+ 1 0 . 0006 0 . 0 0 0 6 9 19A9i+i -0.3+221 0.1526 -0.0216 8 0.13+25 10 Mean Squa re f o r R e g r e s s i o n C o e f f i c i e n t 0 . 0 0 0 6  F = Mean Squa re W i t h i n Samples = 0.0203+ = 0 . 0 2 9 T a b u l a t e d F (1,7) P o f 5% = 5.53+ . L C i and. L S i s u r v i v a l r a t e s a r e n o t s i g n i f i c a n t l y d i f f e r e n t . 2. LOW DENSITY COHO AND STEELHEAD SURVIVAL (LC XLS 2) Group 2x< 1 xy 1yc Deviation from Regression Regr. Sums of Mean Coef. f Squares Square Coho (LCi) Steelhead (LS 2) Within Regression Coef. Common Adj. Means To t a l 5 16.3066 -O.3971 0.1523 -0.0236 1+ 2.6875 -0.0533 0.0010 -0.0198 3 7 1 1 9 . ^ 1 -0.h50h O.1533 -0.0231 8 10 Mean Square f o r Regression C o e f f i c i e n t 0.0003 F = Mean Square Within Samples = 0.0205 = 0.01*+6 Tabulated F (1,7) P of % = 5-5k LC X and L S 2 s u r v i v a l rates are not s i g n i f i c a n t l y d i f f e r e n t . 0.11+30 0.0357 0.0002 0.0000 0.11+32 0.0205 •0.0003 0.11+29 3. LOW DENSITY COHO AND STEELHEAD SURVIVAL (LCgLSp Group 2x' 2XV Deviation from Regression Regr. Sums of Mean Coef. f Squares Square Coho (LC 2) Steelhead "(ESj.) Within Regression Coef. Common Adjusted Means 5 16.8066 -0.6377 0.1028 -0.0379 h k 2.6875 -0.0250 0-0003 -0.0093 3 7 1 9 19. ^ 1 -0.6627 0.1031 -0.031+0 8 10 9 Mean Square f o r Regression C o e f f i c i e n t 0.0018 F = Mean Square Within Samples = 0.0113 = 0.159 Tabulated F (1,7) P of % - 5-5^ L C 2 and L S _ L s u r v i v a l rates are not s i g n i f i c a n t l y d i f f e r e n t . O.O787 0.0197 0.0001 0.00003 0.0788 0.0113 -0.0018 -0.0018 0.0806 h. LOW DENSITY COHO AND STEELHEAD SURVIVAL (LC 2LS 2) Group 1xc Deviation from Regression Regr. Sums of Mean Coef, f Squares Square Coho (LC 2) Steelhead (LS 2) Within Regression Coef. Common Adjusted Means Tota l 5 16.8066 -0.6377 0.1028 -O.0379 h O.0787 0.0197 2.6875 -0.0533 0.0010 -0.0198 ^ 0.0002 0.00006 7 0.0789 0.0113 1 0.000k O.OOOU, 19.h9hl -O.6910 O.1038 -O.0351+ 8 O.0793 10 0.000*+ Mean Square f o r Regression C o e f f i c i e n t  F = Mean Square Within Samples = 0.0113 = 0.035 Tabulated. F (1,7) P of % = 5.5^ L C 2 and L S 2 survival rates are not s i g n i f i c a n t l y d i f f e r e n t . 5. LOW DENSITY COHO SURVIVAL (LCjLCg) Deviation from Regression Regr. Sums of Mean" Group f 1xd 2xy 1 y 2 Coef. f Squares Square Coho (LCj_) 5 16.8066 -0.3921 0.1523 -0.0233 0.13+32 0.0358 Coho (LC 2) £ 16.8066 -0.6377 0.1028 -0.0379 it 0-°787 0.0197 Within 8 0.2219 0.0277 Regression Coef. 1 0.0023 0.0023 Common 10 33-6132 -1.0928 0.2551 -0.0325 9 0.2196 Adjusted Means To t a l 11 10 Mean Square f o r Regression C o e f f i c i e n t 0.0023  F = Mean Square Within Samples = 0.0277 = ° - o 8 3 0 Tabulated F (1,8) P of 5% = 5-32 . LC X and L C 2 s u r v i v a l rates are not s i g n i f i c a n t l y d i f f e r e n t . 6. LOW DENSITY STEELHEAD SURVIVAL (LSjLS 2) Group 1x< 2 xy 2J£l Deviation from Regression Regr. Sums Mean Coef. f Squares Square Steelhead. (LSj^) Steelhead (LS 2) Within Regression Coef. Common Adjusted Means To t a l h 2.6875 -0.0250 -0.0003 -0.0093 }+ 2.6875 -0*0533 0.0010 -0.0198 8 5.3750 -O.0783 0.0013 -0.011+5 3 1 6 1 7 8 F = Mean Square f o r Regression C o e f f i c i e n t 0.0001 Mean Square Within Samples = 0.00005 = 2 , 0 0 Tabulated. F (6,1) P of 5% = 5-99 LS^ and L S 2 s u r v i v a l rates are not s i g n i f i c a n t l y d i f f e r e n t . 0.0001 0.00003 0.0000 0.0000 0.0003 0.00005 -0.0001 0.0001 0.0002 7. HIGH DENSITY COHO AND STEELHEAD SURVIVAL (HC,HS,) Deviation from Regression Regr. Sums of Mean Ixv 2 y 2 Coef. k Squares Square Coho (HCj.) 5 16.8066 -2.0911 0.5*+80 -0.12¥+ h 0.2879 0.0959 Steelhead. (HS^ h 2.6875 -1.7656 1.3866 -0.6591 1 0.2228 0.07^2 Within 7 O.5107 0.0729 Regression Coef. 1 O.6953 0.6953 Common 9 1 9 . W l -3.8567 i . 9 3 1 ^ 0.0992 8 1.2060 Adjusted Means Tota l 10 9 Mean Square f o r Regression C o e f f i c i e n t 0.6953  F = Mean Square Within Samples = 0.0729 = 9.53 Tabulated. F (1,7) P of 5% = 5*59 . . HCj. and HSi survival rates are s i g n i f i c a n t l y d i f f e r e n t . 8. HIGH DENSITY COHO AND STEELHEAD SURVIVAL (HCjHS2) Deviation from Regression P Regr. Sums of Mean Group f 2x^ Sxy l y Coef. f Squares Square Coho (HCp 5 16.8066 -2.0911 0.5>+80 -0.12^ h 0.2879 0.0959 Steelhead. (HS 2) ± 2.6875 -1.83.82 l . W l -0.6863 1 0.1866 0.0622 Within 7 0.1+7^ 5 0.0677 Regression Coef. 1 0.7293 0.7293 Common 9 1 9 . W l -3.9293 1.9961 -0.2017 8 1.2038 Adjusted. Means Total 10 Mean Square f o r Regression C o e f f i c i e n t 0.7293  F = Mean Square Within Samples = 0.0677 = 10'77 Tabulated F (1,7) P of 5% = 5.59 . . H C J L and, HS 2 survival rates are s i g n i f i c a n t l y d i f f e r e n t . 9. HIGH DENSITY COHO AND STEELHEAD SURVIVAL ( H C ^ S ^ Group 1Y' Deviation from Regression Regr. Sums of Mean Coef. f Squares Square Coho (HC 2) Steelhead (HSi_) Within Regression Coef. Common Adjusted Means Total 5 16.8066 -2.973k 0.9304- -O.1769 k O.kOkk 0.1011 k 2.6875 -1.7656 I.3866 -0.6591 1 0.2228 0.07^2 7 0.6272 0.0896 1 0.5372 0.5372 9 19.^9^1 -*+.7390 2.3170 -0.2k32 8 l.l6kk 10 Mean Square f o r Regression C o e f f i c i e n t 0.5372 F = Mean Square Within Samples = O.O896 = 5*996 Tabulated. F (1,7) P of 5% = 5-59 HC 2 and. H S J L s u r v i v a l rates are s i g n i f i c a n t l y d i f f e r e n t . 10. HIGH DENSITY COHO AND STEELHEAD SURVIVAL (HC 2 and HS 2) Group 2x< 1vc Deviation from Regression Regr. Sums of Mean Coef. f Squares Square Coho ( H C 5 ) Steelhead (HS 2) Within Regression Coef. Common Adjusted Means To t a l 5 16.8066 -2.973^ 0.930'+ -O.1769 h O.hOkh 0.1011 it 2.6875 - I .8382 l . ¥ + 8 l -0.6863 3 0.1866 0.0622 7 0.5910 0.08M+ 1 0.5993 0.5993 9 19.h9hl -h.8116 2.3785 -0.2^+69 8 I.1903 10 9 Mean Square f o r Regression C o e f f i c i e n t 0.5993  F = Mean Square Within Samples = 0.08¥f =7.10 Tabulated, F (1,7) P of 5% = 5-59 HC 2 and HS 2 are s i g n i f i c a n t l y d i f f e r e n t . 1 ON 1 11. HIGH DENSITY COHO SURVIVAL (HCjHCg) Group I X 2 Ixy 2 y 2 Regr. Coef. f Sums of Sauares Mean Square Coho (HCJL) 5 16.8066 -2.0911 0.5U,80 - 0 . 1 2 ^ k 0.2879 0.0959 Coho (HC 2) 5 16.8066 0.9301+ -0.1769 k 0.i+0¥+ 0.1011 Within • > " 8 0.6923 0.0865 Regression Coef. 1 0.0230 0.0230 Common 10 33-6132 -5.06^5 1.1+781+ -0.1507 9 0.7156 Adjusted Means Total 11 10 Mean Square f o r Regression C o e f f i c i e n t 0.0230  F = Mean Square Within Samples = 0.0865 = -°«2658 Tabulated F (1,8) P of % = 5.32 EC 1 and HC 2 are not s i g n i f i c a n t l y d i f f e r e n t . 12. HIGH DENSITY STEELHEAD SURVIVAL (HSjHS 2) Group f 2 x 2 IXY 2y2 Regr. Coef. f Sums of Sauares Mean Square Steelhead. (HS X) h 2.6875 -1.7656 1.3866 -0.6591 3 0.2228 0.073+2 Steelhead (HS 2) 2-6875 -1.8382 1.1+3+81 -O.6863 1 0.1866 0.0622 Within 6 OA093+ 0.0682 Regression Coef. 1 O.OO36 O.OO36 Common 8 5.3750 -3.6038 2.833+7 -0.670*+ 7 0.3+130 Adjusted Means Total 9 8 Mean Square f o r Regression C o e f f i c i e n t 0.0036  F = Mean Square Within Samples = 0.0682 = °*°53 Tabulated F (1,6) P of % - 5-99 HS X and HS 2 are not s i g n i f i c a n t l y d i f f e r e n t . - 6 5 -APPENDIX II THE MEAN LENGTHS AND WEIGHTS AND THE COEFFICIENT OF CONDITION (Q) FOR THE DIFFERENT GROUPS OF COHO AND STEELHEAD FRY COHO LCj_ L C 2 HC X HC 2 Time (Davs) No. L (mm) S.E. Wt (g) S.E. Q No. L (mm) S.E. Wt (g) S.E. Q No. L (mm) S.E. Wt (g) S.E. 0. No. L (mm) S.E, Wt (g) S.E. Q 1 50 1+1.09 2.0k 0.81 0.29 1.16 50 i+1.09 2.01+ 0.81 0.29 1.16 50 1+1.09 2.0i+ .0.81 0.29 1.16 50 1+1.09 2.01+ 0.81 0.29 1.16 lk 61.00 0.59 3 A 5 0.80 1.51 16 52.1+2 7 - 9 L 1.00 0.61 0.69 8k 15 72.60 6.31 if. 89 1.16 0.96 27 5k. 89 6.68 1.86 0.72 1.12 50 51.66 8.57 1.75 0.91+ 1.27 50 51.3^ 8.27 1.5^ 0.60 1.13 U 6 3 ^3 77-75 6.98 5-36 1.35 1.11+ 1+6 70.21 9.56 1+.22 l.i+7 1.21 100 66.79 11.90 3.53 1.78 1.18 100 61.69 8.83 2.66 1.23 1.13 STEELHEAD LS X HSJL L S 2 HS 2 18 50 3^.5^ 2.58 0.3k 0.13 0.80 50 3h.?k 2.58 0.3^ 0.13 0.80 50 3^.5^ 2.58 0.3k 0.13 0.80 50 2.58 0.3^ 0.13 0.80 3^ 9 60.22 5.ko 2.78 0.87 1.27 50 50. ^ 6 6.21+ 0.79 0.13 0.61 50 if7. 25 11.80 0.93 0.60 0.88 8k ik 69-36 7.56 k.23 1.11 1.26 50 53-26 5.13 1.87 0.97 1.23 10 53 AO 8.30 1.78 1.01 1.16 50 50.91+ 10.95 1.55 0.7^ 1.16 163 k9 9k.kh 20.91+ 10.22 5.00 1.21 100 70.2i+ 13.70 1+.18 2 A 9 1.20 1+8 58.81 10.31 2 A 6 1.3^ 1.20 100 58.95 9.55 2.36 1.18 1.15 - 6 6 -APPENDIX I I I . THE NUMBERS OF EMIGRATION ATTEMPTS FROM THE STREAM-CHANNELS DURING THE EXPERIMENT SUMMED FOR EACH 10-DAY INTERVAL. Time (days) LCi L S i L C 2 HSi HCi L S 2 HC 2 HS 2 1-10 >+5 2 61+28 1713 11-20 11 1* 17 1+3+8* 1051+ * 22 722 591* 21-30 6 1 23 961 76 57 263+3+ 2288 31-3+0 36 1 81 51+2 76 12 1076 1619 3+1-50 1 1 36 98 81 1 888 625 51-60 1 1 39 103 108 7 160 83 61-70 1 0 17 151+ 3+7 7 161 325 71-80 0 0 19 66 70 3+ 172 13+0 81-90 1 1 7 95 13+0 0 292 156 91-100 2 0 5 79 li+6 0 151 166 101-110 0 1 11 87 239 15 23+5 152 111-120 0 0 6 59 118 0 207 115 121-130 0 0 6 70 91 0 105 89 131-13+0 2 0 63 51 283+ 0 263+ 63+ li+1-150 2 0 23+ 3+5 151+ 0 236 36 151-160 0 0 3 20 120 0 2 23+ 68 Total 108 7 359 2878 9232 125 9260 6517 *Three day t o t a l APPENDIX I V . THE AVERAGED EMIGRATION DATA FOR 10 DAY PERIODS AS A PERCENTAGE OF THE POPULATION, AND ITS ARCSIN TRANSFORMATION VALUE. L C X L S X L C 2 HS X HCj^ L S 2 HC 2 H S 2 Time (d a v s ) % A r c i A r c % A r c % A r c % A r c i A r c % A r c % A r c ' 1-10 9.00 17.5 0.1+0 3.6 1+3.2 1+1.1 10.51 18.9 11-20 2.20 8.5 0.20* 2.6 2.60 9.3 16.2* 23-7 7-3 15-7 19-3* 26.1 12.62 12.1+ 8.79* 17-2 21-30 1.20 6.3 0.20 2.6 3.90 11.1+ 5-kh 13.1+ O.51+ 1+.2 10.0 18.1+ 18.20 25-2 21.20 27 A 31-1+0 7.30 15-7 0.20 2.6 16 .90 21+.3 2.12 8.3 0.1+2 3-7 2.1+0 8.9 7-10 1 5 A 11.30 19.6 1+1-50 0.20 2.6 0.20 2.6 7-35 15-7 5-03 5-0 0.61 1+.5 0.20 2.6 6.37 1^. 5 1+.58 12.3 51-60 0.20 2.6 0.20 2.6 8.10 16.5 0.88 5.1+ 0.85 5-3 l A O 6.8 0.65 ^.6 O.51+ 1+.2 61-70 0.20 2.6 0 0 3.51+ 10.8 1.75 7.6 O.i+O 3.6 1.50 7-0 0.99 5-7 2.68 9.1+ 71-80 0 0 0 0 1+.00 11.5 0.83 5.2 0.62 1+.5 0.83 5.2 1.52 7.0 1.1+8 6.9 81-90 0.20 2.6 0.20 2.6 1.50 7.0 1.28 6 A 1.25 6.1+ 0 0 3.22 10.3 2.00 8.1 91-100 0.1+1 3.7 0 0 1.00 5.7 1.03 5.8 1.1+1 6.9 0 0 1.85 7.8 2.37 8.8 101-110 0 0 0.20 2.6 1.20 6.3 1.1+0 6.8 2.11 8.3 0.80 5.1 1.28 10.1+ 2.37 8.8 111-120 0 0 0 0 I . 3 0 6.6 1.01+ 5.8 1.33 6.6 0 0 2.76 9-5 2.15 8.1+ 121-130 0 0 0 0 I . 3 0 6.6 l . l + l 6.8 1.15 6.1 0 0 1.62 7-3 1.68 7.1+ 13I-II+O 0.1+1+ 3.8 0 0 13.1+O 21.5 1.11 6.0 3.57 10.8 0 0 I+.1+7 12.2 1.70 7.5 11+1-150 0.66 1+.7 0 0 5.1 13.O 1.11 6.0 2.29 8.7 0 0 2.98 9.9 0.86 5.3 151-160 0 0 0 0 0.60 1+.6 0.56 1+.3 1.93 7.9 0 0 i+.l+O 12.1 1.85 7-8 161-163 0 0 0 0 1+.25 11.9 0.89 5 A 3-69 11.1 0 0 7.1+O 15.8 1.35 6.6 *3-day average 

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