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Effects of Short Term Exposure to Suspended Sediment on the Behaviour of Juvenile Coho Salmon Berg, Linda 1983

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EEE,ECTS,: OF SHORT-TERM EXPOSURE TO SUSPENDED SEDIMENT ON THE BEHAVIOUR OF JUVENILE COHO SALMON. ( ONCORHYNCHUS KISUTCH ) by LINDA BERG B.Sc, University Of B r i t i s h Columbia, 1979 A THESIS SUBMITTED IN PARTIAL. FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Zoology) We accept th i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA November 1983 © Linda Berg, 1983 I n 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 t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e 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 a n d s t u d y . I f u r t h e r a g r e e 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 o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e h e a d o f my d e p a r t m e n t o r b y h i s o r h e r 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 n o t b e 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 . D e p a r t m e n t o f T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a 1956 Main M a l l V a n c o u v e r , C a n a d a V6T 1Y3 D a t e /JbvxWttA, fQXS D E - 6 (3/81) ABSTRACT The t e r r i t o r i a l and feeding behaviour of juvenile coho salmon was studied in an a r t i f i c i a l stream channel in response to short-term pulses of suspended sediment. Disruption of the soci a l organization of the f i s h resulted at the higher t u r b i d i t i e s tested. Dominance hierarchies were p a r t i a l l y broken down, and t e r r i t o r i e s were no longer defended. Only at lower t u r b i d i t i e s were the hierarchies reformed and t e r r i t o r i e s re-established. Behaviour following water clearance, closely resembled that observed prior to the addition of suspended sediment. The feeding behaviour of the f i s h was affected during the period of exposure to a pulse of suspended sediment. The a b i l i t y of f i s h to capture prey items decreased with an increase in t u r b i d i t y . The disruption of the s o c i a l organization of the f i s h also caused modifications to their feeding behaviour. Rates of g i l l f l a r i n g increased in response to a pulse of suspended sediment and remained elevated following water clearance. Implications of these behavioural modifications are discussed in rel a t i o n to fit n e s s of f i s h populations rearing in streams subjected to frequent short-term pulses of suspended sediment. i i i TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES iv LIST OF FIGURES v ACKNOWLEDGEMENTS v i i i INTRODUCTION 1 LITERATURE REVIEW 4 Sediment and Logging 4 Sediment and Fish 8 METHODS 14 RESULTS 39 Effe c t s on T e r r i t o r i a l Behaviour 39 Effe c t s on the G i l l s 81 Effe c t s on Feeding Behaviour 87 DISCUSSION 100 SUMMARY 109 LITERATURE CITED 112 LIST OF TABLES Table I. Summary of the s o c i a l organization of the "naive" f i s h during the "sudden" pulse experiment 44 Table I I . Summary of the s o c i a l organization of the experienced f i s h during the "sudden" pulse experiment. ..60 Table I I I . Summary of the s o c i a l organization of the "experienced" f i s h during the "gradual" pulse experiment 74 Table IV. Summary of the s o c i a l organization of the "experienced" f i s h during the pre-treatment phase of the "sudden" pulse feeding experiment 88 V LIST OF FIGURES Figure 1. Schematic diagram of the a r t i f i c i a l stream channel 15 Figure 2. Water ve l o c i t y p r o f i l e s in the observation channel 18 Figure 3. Logarithmic grain size d i s t r i b u t i o n of sediment used in the experiments 22 Figure 4. Scanning electron micrograph of sediment p a r t i c l e s less than 0.063mm used in the experiments 24 Figure 5. Regression l i n e for the concentration of suspended sediment measured o p t i c a l l y and gravimetr i c a l l y 27 Figure 6. Summary of the sequence of events in the experimental design of the "sudden" and "gradual" pulse experiments 33 Figure 7. Summary of the sequence of events in the experimental design of the "sudden" pulse feeding experiment. 37 Figure 8. Percent frequency of aggressive acts by the "naive" f i s h during the pre-treatment phase of the "sudden" pulse experiment 40 Figure 9. Cross-sectional diagrams of observation area showing the v e r t i c a l station position of the "naive" f i s h during the "sudden" pulse experiments 42 Figure 10. Total frequency of a l l aggressive acts by each "naive" f i s h during the "sudden" pulse experiments 46 Figure 11. Behavioural repertoires of the "naive" f i s h during the "sudden" pulse experiments 48 Figure 12. Percent frequency of aggressive acts by the "experienced" f i s h during the pre-treatment phase of the "sudden" pulse experiment 58 Figure 13. Cross-sectional diagrams of observations area showing the v e r t i c a l station position of the "experienced" f i s h during the "sudden" pulse experiment. 61 Figure 14. Total frequency of a l l aggressive acts by each "experienced" f i s h during the "sudden" pulse experiment. 63 Figure 15. Behavioural repertoires of the "experienced" f i s h during the "sudden" pulse experiment 65 Figure 16. Percent frequency of aggressive acts by the "experienced" f i s h during the pre-treatment phase of the "gradual" pulse experiment 70 Figure 17. Cross-sectional diagrams of observation area showing the v e r t i c a l station position of the "experienced" f i s h during the "gradual" pulse experiment 72 Figure 18. Total frequency of a l l aggressive acts by each "experienced" f i s h during the "gradual" pulse experiment 75 Figure 19. Behavioural repertoires of the "experienced" f i s h during the "gradual" pulse experiment 77 v i i F i g u r e 20. Mean frequency of g i l l f l a r i n g by a l l f i s h 82 F i g u r e 21. C r o s s - s e c t i o n a l diagrams of o b s e r v a t i o n area showing the v e r t i c a l s t a t i o n p o s i t i o n of the "experienced" f i s h d u r i n g the "sudden" p u l s e f e e d i n g experiment 89 Fi g u r e 22. Mean prey capture success r a t e 91 F i g u r e 23. Mean percent of prey eaten 94 Fi g u r e 24. Mean number of prey captured per f i s h 97 v i i i ACKNOWLEDGEMENTS I would l i k e to thank my supervisor, Dr.T.G. Northcote, for his support and advice, offered throughout th i s study. Special thanks also go to Dr. G.F. Hartman for his strong interest in my study and for his review of the thesis. Other members of my committee, Dr. C C . Lindsey and Dr. J.D. McPhail, are also thanked for their review of the thesis. Gary Birch and Marvin Rosenau are thanked for having supplied the Scheffe Creek f i s h . I am also grateful to Dave Zitten of the Bioscienses Data Center for his tremendous help during the many hours spent in reformating the data and to Kenji Tsumura of the Fish and W i l d l i f e Branch, for brightening up the many cold and dreary days spent at the south campus research uni t. Special thanks go to my family for their patience and moral support. Suppport for the study was provided by the P a c i f i c B i o l o g i c a l Station, Nanaimo (Department of Fisheries and Oceans), D.S.S. 1 INTRODUCTION The acute and chronic e f f e c t s of long-term exposure to suspended sediment on f i s h are well documented ( Conifer et a l . 1978; Crouse et a l . 1981; Gardner 1981; Sigl e r 1980; Noggle 1978; Horkel and Pearson 1976; Vinyard & O'Brien 1976; Sherk et a l . 1974; Rogers 1969; Herbert and Merkens 1961; Wallen 1951). In contrast, surprisingly l i t t l e i s known about the behavioural effects of short-term intermittent exposure. For those species of f i s h using streams in watersheds being logged , the l a t t e r may represent the type of exposure most frequently encountered. North temperate freshwater f i s h , during their evolutionary history, have had to cope with high suspended sediment levels in ri v e r s and streams. This condition, re s u l t i n g from g l a c i a l a c t i v i t y and snow melt water, probably was of regular seasonal p e r i o d i c i t y and consequently in large part predictable. Thus i t seems reasonable to expect that adult and juvenile f i s h in such streams evolved adaptations to minimize deleterious effects of high l e v e l s of suspended sediment. In contrast, the y i e l d of sediment to streams in watersheds subjected to man's a c t i v i t i e s (highway construction, logging, mining) i s recent and often highly unpredictable in seasonal occurrence, magnitude and frequency. Consequently, those species of f i s h that spend a sizeable portion of their l i f e in small streams (trout, some juvenile salmon) may experience adverse ef f e c t s from short-term exposure to suspended sediment. 2 S i g l e r (1980) in competition experiments u t i l i z i n g juvenile coho salmon ( Oncorhynchus kisutch ), showed that f i s h raised in turbid water were less able to establish t e r r i t o r i e s than their counterparts raised in clear water. Noggle (1978), although unable to demonstrate any avoidance of suspended sediment at concentrations normally encountered in nature, showed that at higher t u r b i d i t i e s , juvenile coho salmon have a preference for clear water. Mizunuma (1965), working with a smelt-like f i s h ( Plecoglossus a l t i v e l i s ) and Lawrence and Scherer (1974), working with whitefish and rainbow trout, found similar preferences for non-turbid water. Hence i t seems l i k e l y that with further study additional behavioural e f f e c t s from short-term exposure to suspended sediment might be revealed. The objective of t h i s study was to determine the behavioural effects of short-term exposure to suspended sediment on juvenile coho salmon. Young of t h i s species spend an average of one year in small streams and thus may be more vulnerable to the e f f e c t s of suspended sediment than are species such as pink salmon ( 0. gorbuscha ), that leave the stream environment shortly after emergence. Attention was focussed on the following questions regarding t e r r i t o r i a l and feeding behaviour of the f i s h : 3 1) T e r r i t o r i a l Behaviour: a) do short-term pulses of suspended sediment aff e c t the t e r r i t o r i a l behaviour of juvenile coho? b) i s there any difference in the responses of "naive" f i s h (not previously exposed to suspended sediment) and "experienced" f i s h (previously exposed to suspended sediment)? c) i s the dynamics of a sediment pulse important in a f f e c t i n g t h e i r response? 2) Feeding Behaviour: a) i s the a b i l i t y of f i s h to capture prey from stream d r i f t affected by a suspended sediment pulse? b) i s the s o c i a l feeding pattern of f i s h affected during such a pulse? Coho salmon are important to both the commercial and sports f i s h e r i e s of B r i t i s h Columbia, and as they frequently u t i l i z e streams draining watersheds containing valuable timber stands, they often are exposed to e f f e c t s of logging including short-term suspended sediment pulses. Answers to the above questions may provide valuable information to forestry and f i s h e r i e s managers in areas where the intensive use of forest and/or f i s h e r i e s resources may produce a c o n f l i c t in in t e r e s t . This study was performed in conjunction with a project designed to evaluate the impact of logging on f i s h and their habitats - the Carnation Creek Experimental Watershed Project. 4 LITERATURE REVIEW Sediment and Logging 1) Sediment Production in Logged Watersheds Increased sediment production from logging has been well documented (Cederholm & Salo 1979; Megahan 1975; Swanson & Dyrness 1975; Megahan 1974, 1972; Megahan & Kidd 1972a, 1972b; Anderson 1970; Fredriksen 1970; Dyrness 1967; Belthalamy & Kidd 1966; Fredriksen 1965; Hornbeck & Reinhart 1964; Anderson 1954). The sediment sources are numerous and depend upon factors such as climate, geology, gradient and logging techniques. Common to most studies however i s the recognition of roads as major contributors of sediment (Reid 1981; Cederholm & Salo 1979; Megahan & Kidd 1972a; Anderson 1970; Dyrness 1965; Fredriksen 1970, 1965; Hornbeck 6 Reinhart 1964; Anderson 1954; Hooverl952, 1945). In the H J . Andrews Experimental Forest (Oregon), 72% of the s o i l f a i l u r e s observed following logging were associated with roads (Dyrness 1967). Anderson (1954) attributed 80% of the source of a four f o l d increase in sediment y i e l d after logging to roads. Another watershed study (Megahan & Kidd 1972a) reported a 770 fold increase in erosion rates from roads alone. Increases in suspended sediment levels following road construction and logging has been reported in numerous studies. 5 F r e d r i k s e n (1970, 1965) found a 250 f o l d inc rease i n suspended sediment c o n c e n t r a t i o n a f t e r road c o n s t r u c t i o n in an unlogged b a s i n . In a C a l i f o r n i a watershed, Krammer & Burns (1973) and R ice et a l . (1979) repor ted tha t suspended sediment y i e l d s inc reased by 80% over a 4 year p e r i o d f o l l o w i n g road c o n s t r u c t i o n . W a l l i s & Anderson (1965) regressed sediment y i e l d aga ins t bas in c h a r a c t e r i s t i c s ( s l o p e , % area c l e a r c u t ) and found that i f 0.6% of a bas in c o n t a i n s roads , suspended sediment y i e l d s inc rease over n a t u r a l y i e l d s by 24%. G u r t z , Webster & Wal lace (1980) found h igher c o n c e n t r a t i o n s of i n o r g a n i c p a r t i c u l a t e m a t e r i a l s i n streams of logged watersheds in comparison to those i n und is tu rbed watersheds (138 mg/1 & 35 mg/1 r e s p e c t i v e l y ) . Hornbeck & R e i n h a r t (1964) repor ted much higher t u r b i d i t i e s f o l l o w i n g s m a l l to moderate storm events in one logged watershed. Haf ley (1975) and Reid (1981) both t r a c e d plumes of t u r b i d water to mouths of road c u l v e r t s . H a f l e y (1975) found the average c o n c e n t r a t i o n of sediment d i scharge at c u l v e r t mouths to be I000mg/1. Wald (1975) repor ted average sediment c o n c e n t r a t i o n s from 68 c u l v e r t mouths c o l l e c t e d from h e a v i l y used roads to equal 1306 mg/1. The average sediment c o n c e n t r a t i o n from 56 c u l v e r t s of non-used roads e q u a l l e d I00mg/1. Re id (1981) a l s o found s i g n i f i c a n t l y h igher sediment c o n c e n t r a t i o n s in c u l v e r t s d r a i n i n g h e a v i l y used roads . G r e s s w e l l et a l . (1979) repor ted a l a n d s l i d e r a t e i n a c l e a r c u t area of 0 .9 events/km2, whereas i n a nearby und is tu rbed b a s i n , the r a t e was only 0.4 events/km2. S i m i l a r i l y , F i k s d a l (1974, 1973) repor ted road r e l a t e d l a n d s l i d e s to occur 13.3 t i m e s / y r , 6 (70% of the l a n d s l i d e s came i n d i r e c t c o n t a c t with streams) whereas n a t u r a l l a n d s l i d e s o c c u r r e d only 0.3 t i m e s / y r . 2) Sources of Sediment from Roads Reid (1981) concluded that g r a v e l l o g g i n g roads are important sources of sediment i n watersheds of the P a c i f i c Northwest, and looked i n d e t a i l at the s p e c i f i c sources of sediment from l o g g i n g roads. She found that the major c o n t r i b u t o r s were road s u r f a c e s and road r e l a t e d l a n d s l i d e s . S e p a r a t i n g the 2 sediment sources, Reid estimated that of the t o t a l p r o d u c t i o n of sediment from roads, 59% r e s u l t e d from road r e l a t e d f a i l u r e s and 28% from road s u r f a c e e r o s i o n . The l a t t e r was however the major c o n t r i b u t o r of sediments s m a l l e r than 2mm i n diameter. In Christmas Creek b a s i n (Washington), road s u r f a c e e r o s i o n c o n t r i b u t e d 49% of the sediments f i n e r than 2mm in diameter, and road r e l a t e d l a n d s l i d e s 31%. In the Stequaleho b a s i n (Washington), these sources c o n t r i b u t e d 43% and 32% r e s p e c t i v e l y (Reid 1981). The importance of s u r f a c e e r o s i o n to stream s i l t a t i o n i s f u r t h e r i n t e n s i f i e d by the f a c t that these f i n e g r a i n e d sediments, s u s c e p t i b l e to suspension, o f t e n flow d i r e c t l y i n t o c u l v e r t s f e e d i n g streams. The occurrence of suspended sediment i n the a q u a t i c environment i s a l s o a n a t u r a l phenomenon. Many streams c a r r y loads of s i l t d e r i v e d from n a t u r a l slope f a i l u r e s and g l a c i a l meltwaters but the magnitude and frequency of such events are 7 greatly augmented by road construction and logging (pers.comm. H. Klassen). 3) Duration of Suspended Sediment Pulses Logging and/or road induced pulses of suspended sediments are not necessarily long-term (Water Survey of Canada, 1982). The duration of a pulse i s variable, dependant upon the nature of the sediments (size, shape, density etc.) and their o r i g i n . Surface erosional processes such as dry ravel, r i l l i n g and gullying can contribute sediment over long periods of time, but in logged watersheds the pulses are often of a short-term nature. Burns (1972) noted short-term increases in t u r b i d i t y while a bulldozer was working in a stream and Kopperdahl et a l . (1971) noted that following bulldozer a c t i v i t y in one stream, t u r b i d i t y increased to 53 J.T.U.shortly after a l i g h t r a i n . The occurrence of short-term pulses i s probably not only frequent but also unpredictable in streams of logged watersheds, unlike the seasonal p e r i o d i c i t y of natural s i l t a t i o n . Instream yarding, tractor crossings, resuspension of deposited sediments and road related f a i l u r e s produce sediment in highly irregular patterns. B Sediment and Fish The effects of sediment on f i s h are diverse and a f f e c t nearly every stage in t h e i r l i f e cycle. Deposited sediment may inte r f e r e with reproduction ( i e : a v a i l a b i l i t y of suitable spawning habitat, egg and alevin survival rates), decreased food abundance and also valuable habitat. For those species that remain in freshwater for their entire l i f e cycle or only rear in i t for brief periods, the e f f e c t s of suspended sediments may be deleterious. 1) Ef fects on Spec ies Composition and Product ion Rates Streams subjected to prolonged s i l t a t i o n often undergo changes in species composition from game to less desirable species of f i s h (Trautman 1939; Aitken 1936). Trautman (1957) reported that s i l t a t i o n destroyed a whitefish population of the Detroit River. Turbidity re s u l t i n g from a mine drove out a l l fishes from an affected area ( E l l i s 1943). Only when the t u r b i d i t y decreased did f i s h return. Saunders & Smith (1965) reported a 70% decrease of brook trout ( Salvelinus f o n t i n a l i s ) in a stream affected by s i l t a t i o n . In the South Platte River (Colorado), only 15-40% of the number of f i s h occurring above a gravel washing operation were found below the operation where suspended sediments concentrations ranged from 80-100 p.p.m. (Anon. 1967, c i t e d in Gammon (1970)). Burns (1972) reported an immediate decrease in f i s h abundance following s i l t a t i o n from 9 road construction in the logged watershed of South Fork Casper Creek. In a survey of 13 sediment-polluted streams, Jones (1964) found an average of 2-5 fish/130 meters, but in 10 unpolluted streams an average of 16-27 fish/130 meters. Herbert et a l . (1961) found normal trout populations densities at low t u r b i d i t i e s but only 1/7 of normal densities in areas where tu r b i d i t y ranged from 1000-6000 p.p.m. Crouse et a l . (1981) and Gardner (1981) found the production of f i s h to be inversly related to the quantity of fine sediments. The l a t t e r study suggests that t u r b i d i t i e s of greater than 50 J.T.U.significantly af f e c t f i s h production. Gammon(l970) reported that the growth of several species of f i s h was decreased below a gravel washing operation. Buck (1956) noted slower growth of f i s h reared in turbid water (100-180 J.T.U.) in comparison with f i s h reared in clear water. In laboratory studies, Sigler (1981) also noted decreased growth rates of juvenile rainbow trout and juvenile coho in response to suspended sediment. 2) Ef f e c t s on Mortality Direct mortality of juvenile and adult f i s h from exposure to suspended sediment has also been reported. Kemp (1949) attributed a f i s h k i l l in the Potamac River to a flood which produced a t u r b i d i t y of 6000 p.p.m.for 15 days. Wallen (1951) found s i g n i f i c a n t m o r t a l i t i e s at t u r b i d i t i e s of greater than 175,000 p.p.m. Herbert & Merkens (1961) reported that concentrations of diatomacious earth or kaolin clay greater than 10 270 p .p .m.reduced rainbow t r o u t s u r v i v a l over an exposure p e r i o d of 4 to 5 months. N i n e t y - s i x hr LC50 va lues of 28,000 and 55,000mg/l fo r 2 n a t u r a l suspended sediment sources were found fo r chum salmon ( Oncorhynchus keta ) (Smith 1978, as c i t e d in Noggle (1978) ) . Rogers (1969) repor ted 24 hr LC50's ranging from 2.5 g/1 to 300 g/1 fo r 4 e s t u a r i n e s p e c i e s , the value dependant upon s p e c i e s , temperature and the nature of the sediment p a r t i c l e s . Noggle (1978) showed seasonal changes i n the t o l e r a n c e of j u v e n i l e salmonids to suspended sediment. N i n e t y - s i x hr LC50's of l e s s than 150,100 mg/1 and more than 300,000 mg/1 were recorded fo r summer and autumn b ioassays respect i v e l y . Sediment r e l a t e d k i l l s of j u v e n i l e and a d u l t f i s h however, are probably r a r e . The c o n c e n t r a t i o n s and d u r a t i o n s of exposure r e q u i r e d to produce l e t h a l c o n d i t i o n s are r a r e l y encountered in n a t u r e . The b e h a v i o u r a l response of f i s h to s e l e c t i v e l y avo id areas a f f e c t e d by e l e v a t e d suspended sediment c o n c e n t r a t i o n s f u r t h e r decreases the p r o b a b i l i t y fo r d i r e c t m o r t a l i t i e s to occur (Whitman e t . a l . 1982; Noggle 1978; Sumner & Smith 1939). The decreased d e n s i t i e s of f i s h i n t u r b i d water (Burns 1972; Saunders & Smith 1965; E l l i s , 1943) may r e f l e c t such avoidance responses . S i g l e r (1981) repor ted a r e d u c t i o n i n d e n s i t y of s tee lhead and coho f r y in a r t i f i c i a l stream channels exposed to suspended sediments . Most of the emigra t ion occur red w i t h i n the f i r s t two d a y l i g h t pe r iods and the f i r s t n i g h t , suggest ing that even under s h o r t - t e r m exposure to suspended sediment adverse 11 effects are experienced. 3) E f f e c t s on Physiology Indicators of blood physiology further imply that f i s h exposed to suspended sediment experience stress. Sherk et a l . (1974), reported elevated hematocrit lev e l s in several species of f i s h exposed to sub-lethal concentrations of suspended sediments for 5 days, and plasma glucose levels in juvenile coho were increased at sub-lethal concentrations of suspended sediments (Noggle 1978). At the c e l l u l a r l e v e l , damage to the g i l l s from suspended sediments i s frequently observed. C e l l s of the respiratory epithelium were thick (Herbert & Merkens 1961, Noggle 1978) and branchial hemorrhages and anuerysims were observed in g i l l s by Noggle (1978). Herbert & Merkens (1961) noted an increase in f i n rot in f i s h held in turbid water due to lesions to the g i l l s from the abrasive sediment p a r t i c l e s . Clogging of the filaments with sediment p a r t i c l e s results in the production of large quantities of mucus (Noggle, 1978; Herbert & Richards, 1963; Herbert & Merkens, 1961). Consequently, the g i l l lamellae become fused, which in addition to the thick covering of mucus, reduces the surface area for gas exchange and interferes with the ionic exchange of gases across the respiratory epithelium. Horkel & Pearson (1976) reported an increase in v e n t i l a t i o n rates in green sunfish ( Lepomis cyanellus ) following exposure 12 to clay suspensions, and interpreted t h i s increase as a mechanism for compensating for reduced respiratory e f f i c i e n c y . 4) Effects on Feeding The reactive distance of f i s h i s decreased in turbid water (Gardner 1981; Conifer e t . a l . 1978; Vinyard & O'Brien 1976). Noggle (1978) noted a decrease in coho feeding rate to zero at a concentration of 300 mg/1. Garnder (1981), Moore & Moore (1976), Vinyard & O'Brien (1976), Olson, Chase & Hanson (1973), a l l reported decreased feeding rates by f i s h at higher t u r b i d i t i e s . Buck (1956) attributed decreased f i s h i n g success by sportsmen in turbid water to a cessation of feeding by f i s h , possibly due to an i n a b l i l i t y to feed. Decreased food a c q u i s i t i o n combined with the adverse ef f e c t s of s i l t a t i o n on macro-invertebrates,may result in the production of f i s h of poorer quality and hence more susceptible to other stresses associated with suspended sediments. 5) Other Effects on Behaviour The e f f e c t s of suspended sediments on f i s h behaviour were observed i n d i r e c t l y by Sig l e r (1981). In competition experiments, he found that a greater proportion of f i s h held in turbid water moved downstream and out of the channels in comparison with f i s h reared in clear water, and also that they 13 were less able to establish t e r r i t o r i e s . The establishment of t e r r i t o r i e s by stream fishes i s a behaviour evolved to assure adequate food supplies (Kalleberg 1958), and consequently the f i t n e s s of juvenile salmonids may be further decreased by suspended sediment. 1 4 METHODS The approach taken in t h i s study involved monitoring the behaviour of juvenile coho salmon in an a r t i f i c i a l stream channel before, during and after the experimental addition of a short-term pulse of suspended sediment. Experimental Apparatus An oval, plexiglass trough simulating a stream channel was used for observing f i s h behaviour ( f i g . 1). Fish were r e s t r i c t e d to the straight sections of the channel by 1 cm mesh screens at the each end. This provided an observation area 100 x 25 x 25cm. A portable r e f r i g e r a t i o n unit was immersed in the center of the trough and maintained the water temperature in the surrounding stream channel at 10.0 + 0.5 C. There was no exchange of water between the center portion of the trough and the stream channel. Maximum water depth in the channel was 25cm. Two 2.5m fluorescent l i g h t s (Duro-Test-Vita-Lites) suspended above the trough supplied l i g h t . Light intensity, measured with a Li-cor photometer was 3.7, 2.6 and 2.3 microeinstiens/m2/sec at a depth of 0.5, 5 and 12cm, respectively. Water v e l o c i t y was controlled with two submersible pumps and was measured with a Nixon Instruments Streamflow Flowmeter (series 400). Attempts were made to 15 Figure 1. Schematic diagram of the a r t i f i c i a l stream channel. S t i p p l i n g i n d i c a t e s g r a v e l bottom; hatched area i n d i c a t e s upstream and downstream retainment screens; P i n d i c a t e s pumps; R i n d i c a t e s the r e f r i g e r a t i o n u n i t ; arrow i n d i c a t e s d i r e c t i o n of water flow; numbers 1 - 5 i n d i c a t e t u r b i d i t y sampling s i t e s . 16 17 maintain a constant water v e l o c i t y throughout the channel, but the design of the trough resulted in higher v e l o c i t i e s at the upstream end of the observation area and near the center of the channel at mid-depth (fig.2) than in other areas. Nevertheless, water v e l o c i t y p r o f i l e s were similar to those observed in small streams. Airstones kept the oxygen concentration near saturation and water quality was kept within acceptable l i m i t s by a glass-wool activated-carbon f i l t e r . The bottom of the observation area was lined with gravel (2-5cm in diameter) and several large stones (7-1Ocm in diameter), c o l l e c t e d from a stream and washed clean. The experimental trough was enclosed in a curtain of dark p l a s t i c to prevent observer disturbance to the f i s h . Observations were made through a small s l i t in the curtain. Experimental Fish 1) Source of Fish Parents of the "naive" f i s h used in the experiments were obtained from Scheffe Creek (lat.49 48', long.124 78'), Vancouver Island. Eggs were co l l e c t e d and f e r t i l i z e d in the f i e l d and then reared in the laboratory at the University of B r i t i s h Columbia. The "experienced" f i s h were seined as fry from the Salmon River, Langley (lat.49 07', long.122.35'). This river i s frequently subject to s i l t a t i o n and f i s h rearing in this r i v e r were probably exposed to suspended sediment during 18 Figure 2. Water vel o c i t y p r o f i l e s in the observation channel. Top figure shows saggital p r o f i l e , measured at a depth of 10cm; bottom figure shows cross-sectional p r o f i l e , measured at A:1Ocm from the l e f t channel wall; B:10cm from the right channel wall. Hatched l i n e indicates retainment screen; arrows indicate d i r e c t i o n of water flow. 19 i—r*-r 20 10 0 i — r 20 10 RIGHT SIDE LEFT SIDE UPPER END MIDDLE END LOWER END SURFACE BOTTOM WATER VELOCITY (CM/SEC) 20 their developmental history. Scale analysis revealed a l l f i s h to be underyearlings. 2) Fish Handling The naive and experienced f i s h were held in separate 200 l i t e r f iberglass tanks before the experiments. Holding conditions included a flow-through water f i l t e r i n g system, a 12-hour photoperiod and water temperatures of 10-13 C during the spring and summer months, and 7-10 C during the f a l l and winter months. The f i s h were fed twice a day (once at 0730 and again at approximately 1630 hours) on a mixture of frozen brine shrimp and tetra min, supplemented with l i v e r . Before an experiment, the f i s h were anaesthetized with 2-phenoxy-ethanol and their lengths and weights were recorded. A small portion of the caudal f i n of each f i s h was clipped to allow individual i d e n t i f i c a t i o n . The test f i s h were then placed in the observation area and allowed to acclimate at least 5 days. The development of a stable pattern of s o c i a l behaviour was used as the c r i t e r i o n for acclimation. Nature of the Suspended Sediment Pulse 1) Source of Sediment Sediment was coll e c t e d from a s e t t l i n g pond at Jack Cewe Ltd., a gravel company operating alongside the Coquitlam River 21 (lat.49 19', long.122 45'). Logging companies acquire road f i l l materials from such sources, hence th i s sediment i s a reasonable representation of the fine-grained sediment p a r t i c l e s contributed to streams by road construction in logged watersheds. 2) Description of Sediment The p a r t i c l e size d i s t r i b u t i o n of the sediment was determined by f i r s t wet sieving the sample through a 0.063 mm mesh screen. The fra c t i o n greater than 0.063mm was then oven dried at 30 C for 48 hours and shaken in a series of Tyler sieves (1.000, 0.710, 0.500, 0.354, 0.250, 0.177, 0.125, 0.088 and 0.063mm) for 15 minutes. The p a r t i c l e size d i s t r i b u t i o n of the f r a c t i o n smaller than 0.063mm was determined by the hydrometer technique of Day (1965). Nearly 47% of the sediment contained p a r t i c l e s larger than 0.063mm ( f i g . 3 ) . As t h i s f r a c t i o n s e t t l e d rapidly when suspended in water, only sediment smaller than 0.063mm was used to create the suspended sediment s l u r r y . Of t h i s f r a c t i o n , 65% of the sediment p a r t i c l e s were finer than s i l t (0.063mm) and 3.7% were in the size range of clay (<0.002mm). Further analysis of the sediment less than 0.063mm was made with a scanning electron microscope ( f i g . 4 ) . The sediment p a r t i c l e s were angular, measuring 1.5 on a p a r t i c l e roundness scale of 0 to 6, (angular to round, respectively; Blatt e t . a l 1972). 22 Figure 3. Logarithmic grain size d i s t r i b u t i o n of sediment used in the experiments. 23 GRAIN SIZE (MM) 1.8 1.0 0.1 0.01 0.001 0.0001 H i l l I I i l l ! 11 I I I Ul l l I I I I m i I I i I t nil I I I I I I 99.9 -99.8 -89.5 -06 -90 -80 ~ 70 -60 -80 -40 -80 -20 -10 -6 -2 -1 -0 .5 -0.2 -0.1 -o ° 4TTT \ \ \ \ 1.8 T~|—I llll 11 I I I IIIIM » I—I 11II II I I—I llll II I I I T 1.0 0.1 0.01 0.001 0.0001 GRAIN SIZE (MM) 24 Figure 4. Scanning electron micrograph of sediment p a r t i c l e s less than 0.063mm used in the experiments. 25 SCALE 26 Multiple stress fractures due to g l a c i a l scouring were observed on the p a r t i c l e s (pers.comm. L. Veto). 3) Measurement of Turbidity Turbidity was measured by the standard o p t i c a l technique (A.P.H.A. 1975). A Fisher 400 DRT turbidimeter was used to measure t u r b i d i t y in nephelometric t u r b i d i t y units (N.T.U.). This method provides a good estimation of the effect of suspended sediments on l i g h t transmission as i t i s strongly dependant upon the c h a r a c t e r i s t i c s of the sediment p a r t i c l e s (size, shape, number, r e f r a c t i v e index, e t c . ) . In addition the suspended sediment pulse was measured by standard gravimetric techniques (A.P.H.A. 1975). This allowed the derivation of a quantitative relationship between sediment concentration in mg/1 and t u r b i d i t y in N.T.U. ( f i g . 5 ) . The tu r b i d i t y l e v e l s u t i l i z e d in t h i s study (20,30 and 60 N.T.U.) corresponded to sediment concentrations of 13.5, 23.5 and 53.5 mg/1 respectively. 4) Addition of the Suspended Sediment Slurry A slurr y of suspended sediment was created by pre-mixing a subsample of the sediment finer than 0.063mm in a large bucket of water. The slurry was s t i r r e d vigorously, allowed to se t t l e for one half hour and then slowly added to the stream channel 27 Figure 5 . Regression l i n e for the concentration of suspended sediment measured o p t i c a l l y and gravimetrically. 28 0 10 20 30 40 50 60 70 80 90 100 110 CONCENTRATION (MG/L) 29 from a header box equipped with valves. Slurry was added u n t i l the desired t u r b i d i t y was attained. The tu r b i d i t y was measured at 3 depths (0, 12 and 25cm) at each of 4 stations in the channel, selected to prevent disturbance to the f i s h ( f i g . 1 ) . The mean of these t u r b i d i t y values was recorded. Experimental Design 1) Effects on T e r r i t o r i a l Behaviour One group of eight f i s h was used for each experiment and i t s r e p l i c a t e . The experimental f i s h were fed tetra min f i s h flakes, p r i o r to and following the data c o l l e c t i o n periods (0800-1100 and 1330-1 630) . During the morning and afternoon observation periods each f i s h was watched in random order for 2 minutes, for a t o t a l of 5 t r i a l s . At the end of each 2 minute observation period, detailed records on the f i s h studied as well as observations on the other f i s h , were recorded. Four classes of f i s h were recognized within the h i e r a r c h i a l structure: t e r r i t o r i a l , p a r t i a l l y t e r r i t o r i a l , defensive and submissive individuals (table 1). T e r r i t o r i a l f i s h defended their t e r r i t o r i e s against a l l f i s h , whereas p a r t i a l l y t e r r i t o r i a l f i s h only defended their t e r r i t o r i e s against f i s h subordinate to them ( C o l l i a s 1944). Defensive f i s h attempted to 30 displace f i s h from th e i r immediate areas, but were not always successful. Submissive f i s h were "intimidated" by the approach of another f i s h and also by interactions occuring between other f i s h . They frequently hid in the gravel for short periods after an encounter with another f i s h . The behavioural data were c o l l e c t e d on a MORE OS-3 Behavioral Event Recorder. The behaviours recorded included l a t e r a l , threat, fr o n t a l and wigwag displays; nipping, chasing and submission. Preliminary experiments revealed an increase in the frequency of g i l l f l a r i n g following exposure to suspended sediment, so this behaviour was also recorded. Lateral displays, described by Fabricius & Gustafson (1954), Hartman (1965) and Kalleberg (1958) were recognized by the erection of the dorsal f i n and often simultaneous erection of the anal and paired f i n s . Frontal displays described by Fabricius (1958), Hartman (1965) and Kalleberg (1958) were recognized by the compression of the dorsal f i n , s l i g h t arching of the back, and extension of the basihyal. Wigwag displays (Hartman 1965) involved posture similar to that of the l a t e r a l display but the body was in c l i n e d at an angle and the f i s h swam with well accentuated l a t e r a l movements. Threat displays, considered as intentional movements by Hartman (1965), were recognized as a sudden lunge by a f i s h towards another. Nipping included those in which contact with another f i s h was made as well as those, considered by Hartman (1965) as threat nips, in 31 which no contact was made. These two forms of nipping were summed because under turbid conditions i t was sometimes d i f f i c u l t to determine i f contact was made. Submission was recognized by the compression of a l l f i n s and movement away from another f i s h . Submissive f i s h could also be recognized by their darker colouration. The location of each f i s h in the channel was noted at the end of each observation period with the use of a 10x5cm grid placed on the side wall of the observation area. Regarding the t e r r i t o r i a l experiments, the f i r s t two questions asked: i) do short-term pulses of suspended sediment effect the t e r r i t o r i a l behaviour of juvenile coho? i i ) i s there any difference in the reponses of naive f i s h (never exposed to suspended sediment) and experienced f i s h (previously exposed to suspended sediment)? Were addressed simultaneously by testing the response of both naive and experienced f i s h to a short-term pulse of suspended sediment. The t h i r d question: i i i ) i s the dynamics of a pulse important in aff e c t i n g their response? Was addressed by exposing f i s h to two pulses of d i f f e r i n g sediment dynamics. One pulse, the sudden pulse, involved the introduction of sediment to a maximum t u r b i d i t y , therefore there 32 was no r i s i n g limb to the pulse, only a f a l l i n g ; whereas the second pulse, the gradual pulse, involved a gradual increase in tu r b i d i t y to the same maximum t u r b i d i t y as was tested in the sudden pulse experiments. Consequently, the gradual pulse had both a r i s i n g and f a l l i n g limb. The sequence of events occurring throughout the sudden pulse experiments i s shown in figure 6. Days 1 and 2 constituted the pre-treatment phase, and during this period, the tu r b i d i t y was 0 N.T.U. Days 3-5 represented the treatment phase; suspended sediment was added to produce a t u r b i d i t y of 60 N.T.U.at approximately 0830 on day 3, but by the same afternoon the t u r b i d i t y had decreased to 40 N.T.U. V i s i b i l i t y was limited, preventing observation of f i s h behaviour. Data c o l l e c t i o n resumed on the morning of the fourth day, at a tu r b i d i t y l e v e l of 30 N.T.U. By mid-day, i t was necessary to add more sediment slurry in order to maintain the tu r b i d i t y at 30 N.T.U.for the afternoon observation period. The t u r b i d i t y decreased to 20 N.T.U.by the morning of day 5 and was again augmented to maintain t h i s l e v e l for the afternoon data c o l l e c t i o n period. Days 6 and 7 constituted the post-treatment phase; the t u r b i d i t y had decreased to near 0 N.T.U. (4 N.T.U.and 2 N.T.U.on days 6 and 7 resp e c t i v e l y ) . The pre-treatment phase of the gradual pulse experiment was id e n t i c a l to that of the sudden pulse experiment. The treatment phase however spanned a period of 5 days, and involved a gradual 33 Figure 6 . Summary of the sequence of events in the experimental design of the "sudden" and "gradual" pulse experiments. 34 S • 0 - 1 40 to o -OBSERVATtON PERIOD SUDDEN PULSE X —X„ •X-X- •x-x K-X-PHASE - £ PRE-TREATMENT TREATMENT . P O S T - T R E A T M E N T ^ BEHAVIOUR - £ FULL REPERTOIRE SCHOOLING —V— X-FULL REPERTOIRE^ -1 1 1 1 1 1 1 1 1 1 1 1 1 r~ 12 24/0 12 24/0 12 2470 12 24/0 12 24/0 12 24/0 12 24 HOURS 1 2 3 4 6 6 7 DAY 6 0 - | 9 t-' t Q 2 0 -0 -PHA8E. OBSERVATION PERIOD -x-x-GRADUAL PULSE x—x, .X—X ,x«*r-•x—X X — X -PRE-TREATMENT — X - TREATMENT- POST-TREATMENT — BEHAVIOUR- £ FULL REPERTOIRE - SCHOOLING ' T J ^ J R X — FULL R E P E T O W E — > ~ l 1 1 1 1 1 1 1 1 1 —1 1 I I I I I I 12 24/0 12 24/0 12 24/C 12 . 24/0 12 24/0 12 24/0 12 24/0 12 24/0 12 24 HOURS 6 DAY 35 i n c r e a s e i n t u r b i d i t y from 0 to 20 to 30 and to 60 N.T.U, on days 3,4 and 5 r e s p e c t i v e l y ( f i g . 6). When necessary, the d e s i r e d t u r b i d i t i e s were a r t i f i c a l l y maintained f o r the after n o o n o b s e r v a t i o n p e r i o d s . The dynamics of the pul s e was such that by days 6 and 7, the t u r b i d i t y f e l l to 30 and 20 N. T . U . r e s p e c t i v e l y , and on days 8 and 9, c o n s t i t u t i n g the post-treatment phase, to n e a r l y 0 N.T.U. (4 and 2 N . T . U . r e s p e c t i v e l y ) . 2) E f f e c t s on Feeding Behaviour The fe e d i n g experiment i n v o l v e d the use of two groups of f i v e "experienced" f i s h . In each r e p l i c a t e , the t e s t f i s h were t r a i n e d to feed on p u l s e s of a d u l t b r i n e shrimp ( Artemia sp. ). A l l f i s h were observed to feed when many b r i n e shrimp were used, but with the i n t r o d u c t i o n of s i n g l e prey items, as many as 4 of the 5 f i s h never consumed prey. Presumably t h i s was due to the presence of a dominance h i e r a r c h y . Consequently, t o a l l e v i a t e any i n t e r f e r i n g v a r i a b l e s such has l e v e l of hunger between the f i s h , the f i s h were fed i n excess at the end of each day throughout the fe e d i n g experiment. P r e l i m i n a r y experiments a l s o r e v e a l e d i r r e g u l a r f e e d i n g h a b i t s by coho f o l l o w i n g the i n g e s t i o n of more than 30 prey items by any one f i s h . Hence, durin g the a c t u a l experiment, only 10 prey items were introduced per t r i a l t o avoid the problem of s a t i a t i o n . Two s i z e c l a s s e s of b r i n e shrimp were i n t r o d u c e d upstream 36 of the f i s h in alternate order. Attempts were made to introduce the prey items at di f f e r e n t positions in the water column (surface, mid-water, near-bottom), but the design of the channel resulted in most prey items following a trajectory along the center of the channel at a depth of 10 cm at the upstream end, 6-10 cm near the center of the tank and 1-2 cm at the downstream end of the observation area. T r i a l s were run twice d a i l y on each day, one at 0900, the second at 1500. A t o t a l of 5 t r i a l s were run at each treatment l e v e l . The sequence of events occuring during the experiment i s shown in figure 7. The data co l l e c t e d from each t r i a l included: a) position of each f i s h p rior to prey introduction b) position at which the prey was captured c) identit y of the captor d) number- of strikes per prey by the captor e) feeding movements by the other f i s h , regardless of prey acqui s i t i o n Prey items which were not ingested by any of the f i s h were colle c t e d in a net immediately downstream from the observation area. The capture e f f i c i e n c y of the net was 100%. 37 Figure 7. Summary of the sequence of events in the experimental design of the "sudden" pulse feeding experiment. 38 60-40-20-0-PHASE OBSERVATION PERIOD " X — x - x — x - x \ X ~ X — X - X — X . X - X - X - X - * \ •X—X—X-X—X TREATMENT X - x — X - X - , _ y POST- Sw, ^ TREATMENT ' T~ 1 1 1 1 1 1 1 1 1 1 1 1 0 24/0 24/0 24/0 24/0 24/0 24/0 24/0 24/0 24/0 24/0 24/0 24/0 24 HOURS 6 e 10 11 12 13 DAY 39 RESULTS E f f e c t s on T e r r i t o r i a l Behaviour 1) Sudden Pu lse a) Naive F i s h i ) P r e - t r e a t m e n t Phase L a t e r a l , t h r e a t , f r o n t a l and wigwag d i s p l a y s as w e l l as chas ing and n i p p i n g by the j u v e n i l e coho salmon were observed ( f i g . 8). The behaviour of each f i s h was dependant upon i t s s o c i a l s t a t u s , but a l l p a t t e r n s were i n v o l v e d i n the format ion and maintenance of the dominance h i e r a r c h y , as w e l l as i n t e r r i t o r y de fense . L a t e r a l , t h r e a t and wigwag d i s p l a y s and n ips were the only behaviours which occur red o f t e n enough to a l l o w s t a t i s t i c a l a n a l y s i s of the t o t a l frequency of these behaviours by a l l f i s h d u r i n g the p r e - t r e a t m e n t phase. A l l f i s h h e l d s t a t i o n s i n the water column, the dominant upstream of the s u b o r d i n a t e s , the subdominant downstream of the former and the subord inates d i s p e r s e d even f u r t h e r downstream ( f i g . 9 ) . In both r e p l i c a t e s , a s t a b l e dominance h i e r a r c h y , e s t a b l i s h e d d u r i n g the a c c l i m a t i o n phase, e x i s t e d fo r the d u r a t i o n of the p r e - t r e a t m e n t phase ( t a b l e 1 ) . Dominant-subord inate r e l a t i o n s h i p s were determined through t h r e a t and 40 Figure 8. Percent frequency of a g g r e s s i v e a c t s by the "naive" f i s h d u r i n g the pre-treatment phase of the "sudden" pulse experiment. L = l a t e r a l d i s p l a y ; T=threat d i s p l a y ; N=nip; W=wigwag d i s p l a y ; F = f r o n t a l d i s p l a y ; CH=chase; S=submission. REPLICATE 1 L T N W F BEHAVIOUR i 1 I CH S 100T BO-SCH 40A REPLICATE 2 20^ 0-L T T N ~ i — W F —I —T~ CH S BEHAVIOUR 42 Figure 9. Cross-sectional diagrams of observation area showing the v e r t i c a l station position of the "naive" f i s h during the "sudden" pulse experiments.a=pre-treatment phase; b=60 N.T.U.treatment phase; c=30 N.T.U.treatment phase; d=20N.T.U.treatment phase; e=post-treatment phase; here and elsewhere hatching indicates degree of t u r b i d i t y . REPLICATE 1 REPLICATE 2 Table I. Summary of the social organization of the llnaive" f i s h during the "sudden" pulse experiment. Replicate 1 FISH SIZE 5.5 5.0 4.9 4.7 4.7 4.7 4.9 4.7 2.01 1.49 1.2. .1.3 1.2 1.1 1.2 1.1 PRE-TREATMENT EXPERIMENTAL PHASE 30 N.T.U. 20 N.T.U. LG(cm)WT(gm) RANK. BEHAV. H A N K BEHAV. RANK BEHAV. 1(d) 2(sd) 3 3 4 4 4 5 t Pt Pt Pt d d d 8 1(d) 2(sd) ac sc 8C BC 8C BC BC SC Kd) 3 3 2(«d) 3 3 3 3 t nt nt Pt nt nt nt nt POST-TREATMENT RANK Kd) 2< d) BEHAV. t d Pt Pt a d d • Replicate 2 5.8 2.6 5.4 1.9 5.1 1.5 5.1 1.8 5.1 1.6 5.0 1.4 5.0 1.5 4.7 1.3 Kd) t s ( 8 d ) pt 3 pt 4 d 4 d 5 8 5 8 5 8 1(d) BC 2(sd) sc 3 BC 3 BC 3 ac 3 sc 3 8C 3 sc Kd) t 2(sd) nt 3 nt 3 nt 3 nt 4 nt 4 nt 4 nt Kd) t 2 ( 8 d ) pt 3 Pt 3 Pt 5 8 4 d 4 d 5 a * H l e r a r c h l a l rank: 1 - 5 highest to lowest s o c i a l rank ** Behaviour Observed: I - t e r r i t o r l i t ; p t - p a r t i a l l y t e r r i t o r i a l ; d- defensive; 8 - submissive sc- schooling; nt- n o n - t e r r i t o r i a l 45 threat-nip interactions, and size was an important factor in organizing the hierarchy (table 1). In both r e p l i c a t e s , one f i s h dominated a l l others. The movement of the despot downstream of i t s t e r r i t o r y into the area of the subordinate f i s h , resulted in the l a t t e r f leeing their t e r r i t o r i e s and / or positions, to school in one of the channel corners. When the despot returned to i t s t e r r i t o r y , the subordinate f i s h too returned to their former t e r r i t o r i e s and / or positions. A second f i s h (the subdominant), submissive to the despot, dominated the other f i s h . These f i s h , the subordinates, held a s o c i a l status at 1,2 or 3 l e v e l s below that of the subdominant. In both repl i c a t e s , the t o t a l frequency of aggressive behaviour by the t e r r i t o r i a l and p a r t i a l l y t e r r i t o r i a l f i s h was s i g n i f i c a n t l y greater than by either defensive or submissive f i s h (p<0.05; Mann-Whitney U Test; f i g . 10). The l a t t e r e l i c i t e d aggression only infrequently. In the repertoires of the despots, l a t e r a l displays occurred s i g n i f i c a n t l y more frequently than threat displays (p<0.05 Mann-Whitney U Test). Threat displays occurred 17.0% and 47.8% as often as l a t e r a l displays, (replicates 1 and 2 respectively, fig.11). S i m i l a r i l y , the behavioural repertoires of the subdominant f i s h were also dominated by l a t e r a l displays. Again the difference was s i g n i f i c a n t (p<=0.05, Mann-Whitney U Test; f i g . 11). Lateral displays were used by the despots and subdominants to deter other f i s h from entering their t e r r i t o r i e s . If a l a t e r a l display alone did not discourage a potential intruder, threat 46 Figure 10. Total frequency of a l l aggressive acts by each "naive" f i s h during the "sudden" pulse experiments.a=pre-treatment phase; b=30 N.T.U.treatment phase; c=20 N,T.U.treatment phase; d=post-treatment phase. (+ 1 standard error shown). 47a MEAN FREQUENCY OF AGGRESSIVE ACTS / 2 MIN. o - * r o o > - f c o i o > - v i c o < o o 1_ I I I I 1 ,_ ! 1 1 1 JJ -I oo-to "Tl -D CO GO 77} H 11 y ? t r -\ \ \ \ "Tl (p a 2 s £ » -03 3 fgo s I* S I 3= 30 m 5 rrf 47b MEAN FREQUENCY OF AGGRESSIVE ACTS / 2 MIN. G > - * r o c o - ^ ( n c h > j 0 3 C O o • i i i i 1 1 1 1 1 3 o % Ol ZD CP f° , 05 x -n g P> i "TI •. m <B a-3 -2 S T \ \ \,\. 33 m TJ o > H m ro 48 Figure 11. Behavioural repertoires of the "naive" f i s h during the "sudden" pulse experiments.a=pre-treatment phase; b=30 N.T.U.treatment phase; c=20 N.T.U.=treatment phase; d=post-treatment phase; L=lateral display; T=threat display; N=nip; W=wigwag display. (+1 standard error shown). 49 i •E -E { J - i \ i I * A A i < i i A A~T , u > « m m ~ i l A A A — 1 — I — I — r - 1 -i " i « « i ! ! i " i " { I I j l l j l l 50 displays and sometimes nips, were then e l i c i t e d . The lower-ranking p a r t i a l l y - t e r r i t o r i a l f i s h in r e p l i c a t e 2 also showed a behavioural repertoire similar in both form and function to that of the dominant and sub-dominant f i s h . In the f i r s t r e p l i c a t e however, the repertoires of these f i s h d i f f e r e d ( f i g . 11). Threat displays dominated in their repertoires, l a t e r a l displays occurred 25.6% and 60.0% as frequently ( f i s h 3 and 4 respectively). The behaviour of the defensive and submissive f i s h was strongly influenced by the a c t i v i t y of the dominants, consequently their repertoires did not conform to any patterns as occurred in the t e r r i t o r i a l f i s h ( f i g . 11). If a dominant approached a defensive f i s h , while i t attempted to displace another f i s h from i t s area, both the defensive and intruding f i s h f l e d in submission to the dominant. The aggression e l i c i t e d by the submissive f i s h was never instigated by them but was evoked in r e t a l i a t i o n to aggression directed at them by others. i i) Treatment Phase Upon the addition of suspended sediment to produce the highest t u r b i d i t y tested, a l l f i s h showed an "alarm" reaction. When the sediment pulse reached the observation area, the f i s h l e f t t heir t e r r i t o r i e s and / or holding positions to "investigate" the leading edge while d r i f t i n g downstream in a 51 group along the t u r b i d i t y front u n t i l they were stopped by the lower screen. Then, upon being confined to turbid water, the f i s h c l e a r l y became "alarmed". Some swam in sporadic spurts throughout the observation area, moving from one end to the other and from the surface to the bottom. Others buried themselves in the gravel where some remained for several hours, whereas others frequently s h i f t e d their position within the substrate. Some individuals underwent prolonged periods (20-60 minutes) of l a t e r a l displaying, regardless of whether or not another f i s h was nearby. Observations on the few f i s h v i s i b l e under high t u r b i d i t y conditions suggested that neither a dominance hierarchy nor t e r r i t o r i a l i t y existed during t h i s treatment phase. The "alarm" reaction of the f i s h at the onset of high t u r b i d i t y , lasted at least 3 hours. Approximately 4 hours after sediment introduction, the f i s h seemed to "calm down" and only infrequently e l i c i t e d the sporadic outbursts of a c t i v i t i e s evoked at the start of the sediment introduction. The few f i s h which were v i s i b l e remained in the gravel for 45 minutes of the fourth hour of observation. During the 4 hours of observation at t h i s high t u r b i d i t y , r e l a t i v e l y few interactions between the f i s h were witnessed (16 in r e p l i c a t e 1 and 12 in repl i c a t e 2). Also, in contrast to the pre-treatment phase, aggression was not s i t e - s p e c i f i c ( t e r r i t o r y and/or position defense) but rather in response to a direct 52 encounter of a f i s h with another in the turbid water. Quantification of the s o c i a l behaviour of the f i s h resumed when the tu r b i d i t y decreased to 30 N.T.U. At thi s t u r b i d i t y l e v e l , the f i s h could be accurately i d e n t i f i e d and followed throughout the observation area. V i s i b i l i t y in the water was approximately 7-10cm. During this phase, the f i s h no longer seemed "alarmed" by the suspended sediment and several moved out of the gravel. Five and 4 of the 8 f i s h (replicate 1 and 2 respectively) were positioned in or on top of the gravel, the remaining f i s h (3 and 4, re p l i c a t e 1 and 2 respectively), were positioned in the water column ( f i g . 9 ) . They did however frequently s h i f t their positions. In each r e p l i c a t e , the dominance hierarchy was composed of 3 level s in contrast to 5 in the pre-treatment phase (table 1). The despots and subdominants were the only f i s h to retain their s o c i a l status, and no dominant-subordinate r e l a t i o n s i p s could be detected between the subordinate f i s h . A similar s o c i a l status of these f i s h was assumed. The dominance of the despot and subdominant was however weak and they were often observed to tolerate subordinate f i s h d i r e c t l y beside them. Consequently, no f i s h could by considered as t e r r i t o r i a l during this phase (table 1). In 11 of 16 instances, the t o t a l frequency of aggressive behaviour e l i c i t e d by individual f i s h was lower than 53 that in the pre-treatment phase ( f i g . 10 and 11). This decrease was s i g n i f i c a n t for the despot of re p l i c a t e 2 and both subdominants in replicates 1 and 2 (p<0.05; Mann-Whitney U Test). The aggression e l i c i t e d by the formerly t e r r i t o r i a l f i s h was not associated with defense of any one area, and l a t e r a l and threat displays were e l i c i t e d at other f i s h when they were encountered in the turbid water. On occassions when a f i s h r e t a l i a t e d , nips and/or wigwag displays were evoked. A further decrease in t u r b i d i t y to 20 N.T.U.resulted in an increase in water transparency to approximately 20cm. During th i s phase a l l f i s h in both re p l i c a t e s moved out of the gravel, but most continued to remain in close association with the bottom ( f i g . 9). A few f i s h (two in replicates 1 and one in replicate 2) were positioned up in the water column. The structure of the dominance hierarchy in replicate 1 was more complex than i t was during the 30 N.T.U.treatment phase, but the previously subdominant f i s h lost i t s status to another formerly subordinate f i s h (table 1). In the second r e p l i c a t e , several stable dominant subordinate relationships were established, forming a 4-tiered hierarchy (table 1). The establishment of a t e r r i t o r y was successful for the despot and subdominant f i s h in r e p l i c a t e 1 and the dominant f i s h in r e p l i c a t e 2 (table 1). The subordiante f i s h continued to be non defensive of their immediate areas. 54 The t e r r i t o r i a l f i s h in replicate 1 did not show any increase in frequency of aggressive behaviour as was expected due to their t e r r i t o r i a l nature, but rather an i n s i g n i f i c a n t decrease ( f i g . 10). This may be because the subordinate f i s h were very quiet and rarely s h i f t e d their positions. Consequently, t e r r i t o r i a l defense may not have been required as frequently as during the pre-treatment phase. In replicate 2, where the hierarchy was more defined, the subordinate f i s h were less submissive and hence more l i k e l y to intrude upon the t e r r i t o r i e s of the other f i s h . Therefore an increase in aggression by the t e r r i t o r i a l f i s h was noted (fig.10). Lateral displays dominated in the behavioural repertoire of the despot (replicate 1), and were used each time a f i s h approached i t s t e r r i t o r y . Threat displays, were for the most part unassociated with t e r r i t o r y defense, but directed at other f i s h in order to assert dominance ( f i g . 11). In contrast, both l a t e r a l and threat displays were used by the despot and subdominant of re p l i c a t e 2 for t e r r i t o r y defense. The subordinate f i s h in r e p l i c a t e 1 were less aggressive than those in r e p l i c a t e 2, consequently the dominant and subdominant f i s h in the l a t t e r r eplicate were required to e l i c i t threat displays in addition to l a t e r a l displays. The repertoires of the non-t e r r i t o r i a l f i s h were varied, and in those that had obtained dominance ( f i s h 3,4 and 5, re p l i c a t e 2), their behaviours were associated with the assertion of their dominance. Aggression 55 displayed by submissive f i s h was always in response to aggression directed at them by dominant f i s h . i i i ) Post-Treatment Phase The behaviour of the f i s h during t h i s phase, clo s e l y resembled that observed during the pre-treatment phase. A l l f i s h were positioned in the water column, and only the most submissive f i s h remained in close proximity with the bottom ( f i g . 9). The structure of the dominance hierarchy in both replicates d i f f e r e d only s l i g h t l y from those of the pre-treatment phase (table 1). Most f i s h regained th e i r s o c i a l status, but some s h i f t s in s o c i a l rank occurred. Both hierarchies were stable for the duration of t h i s phase. Within these stable hierarchies, 3 and 4 f i s h (replicate 1 and 2 respectively) defended t e r r i t o r i e s (table 1). Two f i s h in each r e p l i c a t e were submissive to a l l f i s h , whereas the remaining were defensive. The t e r r i t o r i a l and p a r t i a l l y t e r r i t o r i a l f i s h a l l e l i c i t e d aggression more frequently than the n o n - t e r r i t o r i a l f i s h ( f i g . 10), s i g n i f i c a n t l y so in 5 of 7 cases (r e p l i c a t e 1 and 2 combined; p<0.05; Mann-Whitney U Test). In 4 of 5 instances the p a r t i a l l y t e r r i t o r i a l f i s h were more aggressive than the 56 dominant-territorial f i s h , s i g n i f i c a n t l y so for 3 of the f i s h (p<0.05; Mann-Whitney U Test). Lateral displays dominated the behavioural repertoire of both despots and were adequate to displace t e r r i t o r y intruders ( f i g . 11). Threat displays were used only infrequently on t e r r i t o r y intruders but were e l i c i t e d when they d r i f t e d downstream amongst the subordinates. Presumably these displays asserted their dominance. The subdominant f i s h in r e p l i c a t e 1 had more d i f f i c u l t y in displacing t e r r i t o r y intruders than did the despots. Consequently threat displays were used s i g n i f i c a n t l y more frequently than l a t e r a l displays (p,0.05; Mann-Whitney U Test; fig.11), and nips were commonly associated with the threats. S i m i l a r i l y , threat displays were important for the defense of the t e r r i t o r y of the subdominant in replicate 2 but this f i s h appeared to have had a stronger dominance over the subordinates than did the subdominant in r e p l i c a t e 1. This was reflected by the higher r e l a t i v e frequency of l a t e r a l displays to threat displays. The dominance of f i s h 3 and 4 (replicate 2) were also well established, but they too required threat displays in addition to l a t e r a l displays to assert their dominance. Fish 4, in r e plicate 1 defended i t s t e r r i t o r y primarily with threat displays ( f i g . 11). The behavioural repertoires of the defensive f i s h were 57 simple ( f i g . 11). Lateral displays dominated in each of their repertoires and were used in defense of their area but as well as aft e r a confrontation with a dominant. Aggression in submissive f i s h always followed an interaction with a dominant f i s h . b) Experienced Fish i) Pre-treatment Phase During t h i s phase, the behaviour of the experienced f i s h was similar to that of the naive f i s h . Their behavioural repertoire was comprised of the same behaviours ( f i g . 12), and they too established a stable dominance hierarchy and some t e r r i t o r i e s , both of which persisted throughout t h i s phase (table 2). A l l f i s h were positioned in the water column ( f i g . 13) and the l e v e l of aggression ( f i g . 14) and form and function of the behavioral repertories of individual f i s h ( f i g . 15), resembled those of the naive f i s h of similar s o c i a l status. Exceptions in the behaviour of the f i s h were however noted, just as they were between the replicates of the naive f i s h . Presumably, these are attributable to the r e l a t i v e strength and structure of the individual hierarchies. i i) Treatment Phase The experienced f i s h exhibited an "alarm" reaction i d e n t i c a l to the naive f i s h , following the introduction of e 12. Percent frequency of aggressive acts by the "experienced" f i s h during the pre-treatment phase of the "sudden" pulse experiment.. L=lateral display; T=threat display; N=nip; W=wigwag display; F=frontal display; CH=chase; S=submission. 100 n 80H 60-40-f 20A L T N —r-W T" F CH S BEHAVIOUR Table I I . Summary of the social organization of the "experienced" fish during the "sudden" pulse experiment. EXPERIMENTAL PHASE FISH SIZE PRE-TREATMENT 30 N.T.U. 20 N.T.U. POST-TREATMENT * ** LG(cm)WT(gm) RANK BEHAV. RANK BEHAV. RANK BEHAV. RANK BEHAV. 5.9 2.3 Kd) t Kd) sc Kd) t Kd) t 5.8 2.4 2(sd) Pt 2(sd) sc 2(sd) Pt 2(sd) Pt 5.5 1.9 3 Pt 3 sc 3 nt 3 Pt 5.3 1.6 4 d 3 sc 3 nt 4 d 5.5 1.8 4 d 3 sc 4 nt 6 s 5.5 1.7 4 d 3 sc 3 nt 4 d 5.1 1.5 5 s 3 sc 4 nt 5 d 5.1 1.5 5 8 3 sc 4 nt 5 d Hierarchial Rank: 1 - 5 highest to lowest social status Behaviour Observed: t= t e r r i t o r i a l ; pt= partially t e r r i t o r i a l ; d= defensive; 8= submissive sc= schooling; nt= non-territorial 61 Figure 13. Cross-sectional diagrams of observations area showing the v e r t i c a l station position of the "experienced" f i s h during the "sudden" pulse experiment.a=pre-treatment phase; b=60 N.T.U.treatment phase; c=30 N.T.U.treatment phase; d=20 N.T.U.=treatment phase; e=post-treatment phase. 63 Figure 14. Total frequency of a l l aggressive acts by each "experienced" f i s h during the "sudden" pulse experiment.a=pre-treatment phase: b=30 N.T.U.treatment phase; c=20 N.T.U.=treatment phase; d=post-treatment phase. (+1 standard error shown). 64 65 Figure 15. Behavioural repertoires of the "experienced" f i s h during the "sudden" pulse experiment.a=pre-treatment phase; b=30 N.T.U.treatment phase; c=20 N.T.U.treatment phase; d=post-treatment phase; L=lateral display; T=threat display; N=nip; W=wigwag display. (+1 standard error shown). 4 »—• s-l 12 4 -~*+rfi H o o*. 2. 1-O RSH 5 4-C O M . 3-0 . ~" 4-M J . 1-0 RSH 7 4-».•* 3 1-O-RBH 8 4' to* j . • 2-1-0-L T N W~ • p " 71 r h LTJ±t±i J ± l t b • i p h • a L T H W b L T N W - i 1 1 i L T N W 67 suspended sediment. The few v i s i b l e f i s h were i n the g r a v e l ( f i g . 13) and although i n t e r a c t i o n s were few, those that o c c u r r e d , suggested the absence of a dominance h i e r a r c h y ( t a b l e 2). No f i s h defended t e r r i t o r i e s nor t h e i r immediate areas ( t a b l e 2), and the l e v e l of a g g r e s s i o n was low. The manner i n which the v a r i o u s a g g r e s s i v e behaviours were employed by the formerly t e r r i t o r i a l f i s h a l s o s h i f t e d from e x p l o i t a t i v e to i n t e r a c t i v e . P r e v i o u s l y , a g g r e s s i o n was used to defend a resource, i e : space, food; whereas d u r i n g t h i s treatment phase, the a g g r e s s i o n was a s s o c i a t e d p r i m a r i l y with s i t u a t i o n s where another f i s h was encountered. The response of the experienced f i s h to the decrease i n t u r b i d i t y to 30 N.T.U.treatment phase was s i m i l a r to that of the naive f i s h . F i v e of the 8 f i s h moved out of the g r a v e l but continued to remain i n c l o s e a s s o c i a t i o n with i t ( f i g . 13), the others remained i n the g r a v e l . Only a weak and simple s t r u c t u r e d dominance h i e r a r c h y e x i s t e d and no f i s h defended t e r r i t o r i e s ( t a b l e 2). Consequently, aggression was e l i c i t e d l e s s f r e q u e n t l y than d u r i n g the pre-treatment phase by the four f i s h having h e l d the top s o c i a l ranks i n the l a t t e r phase ( f i g . 14). T h e i r b e h a v i o u r a l r e p e r t o i r e s were a l s o much simpler, fewer forms of aggression were e l i c i t e d ( f i g . 15) and the manner i n which they were employed was i n t e r a c t i v e and not e x p l o i t a t i v e . With a subsequent decrease i n t u r b i d i t y t o 20 N.T.U., the 68 f i s h were p o s i t i o n e d higher i n the water column ( f i g . 13), had developed a more complex dominance h i e r a r c h y , and e x h i b i t e d t e r r i t o r i a l i t y ( t a b l e . 2). The despot and subdominant f i s h , having r e - e s t a b l i s h e d t h e i r t e r r i t o r i e s , showed s i g n i f i c a n t i n c r e a s e s i n frequency of e l i c i t a t i o n of a g g r e s s i o n , as d i d s e v e r a l of the n o n - t e r r i t o r i a l f i s h ( f i g . 14), attempting to defend or e s t a b l i s h a t e r r i t o r y , (most notably f i s h 3). The aggression e l i c i t e d by these f i s h was a s s o c i a t e d with t e r r i t o r y defense but due to the i n s t a b i l i t y of the s o c i a l s t r u c t u r e , (dominant subordinate r e l a t i o n s h i p s were s t i l l being e s t a b l i s h e d d u r i n g t h i s phase), both l a t e r a l and t h r e a t d i s p l a y s were necessary to deter t e r r i t o r y i n t r u d e r s ( f i g . 1 5 ) . The r e p e r t o i r e s of the subordinate f i s h were i n response to aggression d i r e c t e d at them by the dominants and a l s o the establishment of dominant-subordinate r e l a t i o n s h i p s . i i i ) Post-Treatment Phase The behaviour of the f i s h was very s i m i l a r to that observed i n the pre-treatment phase and a l s o to that of the naive f i s h . A l l f i s h were p o s i t i o n e d i n the water column ( f i g . 13) and a s t a b l e dominance h i e r a r c h y almost i d e n t i c a l to that observed d u r i n g the pre-treatment phase was p r e s e n t . A l l f i s h p r e v i o u s l y t e r r i t o r i a l regained t h e i r t e r r i t o r i e s ( t a b l e . 2) and defended them i n a s i m i l a r manner, with the exception of f i s h 2 ( f i g . 15). Threat d i s p l a y s were necessary f o r the e x e r t i o n of both dominance and t e r r i t o r i a l r i g h t s of t h i s f i s h and dominanted i t s 69 behavioural repertoire (p<0.05; Mann-Whitney U Test). Fish 2 received challenges much more frequently from f i s h 3 than i t had in the pre-treatment phase. Its persistence may have been att r i b u t a b l e to the unsuccessful but perseverent attempts of f i s h 5 to acquire a t e r r i t o r y , which in turn "aggravated" f i s h 3. The remaining subordinate f i s h e l i c i t e d aggression in response to the other t e r r i t o r i a l f i s h . 2) Gradual Pulse a) Experienced Fish i) Pre-Treatment Phase The behaviour of the f i s h during the pre-treatment phase did not d i f f e r from the groups of f i s h tested in the previous experiments (fig.16). A l l were positioned in the water column ( f i g . 17). A stable dominance hierarchy, more linear than in the previously tested groups, was present and four t e r r i t o r i e s were established (table 3). The t e r r i t o r i a l f i s h showed more aggression than the n o n - t e r r i t o r i a l f i s h , although the difference was not s i g n i f i c a n t , and the most submissive f i s h e l i c i t e d the least amount of aggression ( f i g . 18). Lateral displays were used by the three highest s o c i a l l y ranked f i s h primarily for t e r r i t o r y defense ( f i g . 19). Threat displays were used to exert their dominance. Use of these behaviours by the subordinate f i s h was variable, probably because of interference from the a c t i v i t i e s of the dominants. 70 Figure 16. Percent frequency of aggressive acts by the "experienced" f i s h during the pre-treatment phase of the "gradual" pulse experiment.. L=lateral display; T=threat display; N=nip; W=wigwag diaplay; F=frontal display; CH=chase; S=submission. 71 100-j 80-60-g 40-20H L T N W T -F I i CH S BEHAVIOUR 72 Figure 17. Cross-sectional diagrams of observation area showing the v e r t i c a l station position of the "experienced" f i s h during the "gradual" pulse experiment.a=pre-treament phase; b = i n i t i a l 20 N.T.U.treatment phase; c = i n i t i a l 30 N.T.U.treatment phase; d=60 N.T.U.treatment phase; e=final 30 N.T.U.treatment phase; f=final 20 N.T.U.treatment ph g=post-treatment phase. Table I I I . Summary of the s o c i a l organization of the "experienced" f i s h during the "gradual" pulse experiment. EXPERIMENTAL PHASE FISH SIZE PRE-TREATMENT 20 N.T.U. 30 N.T.U. 30 N.T.U. 20 N.T.U. POST-TREATMENT LG(cm)WT(gm) RANK BEHAV. RANK BEHAV. RANK BEHAV. RANK BEHAV. RANK BEHAV. RANK BEHAV. 6.0 2.8 Kd) t Kd) t Kd) sc Kd) sc Kd) t Kd) t 5.8 2.8 2(sd) Pt 2(sd) Pt 2 sc 2 sc 2(sd) Pt 2(sd) Pt 5.8 2.2 3 Pt 3 Pt 2 sc 2 sc 3 Pt 3 pt 5.7 2.2 4 Pt 4 Pt 2 sc 2 sc 4 d 4 Pt 5.6 2.0 5 d 5 d 2 sc 2 sc 4 s 5 d 5.4 1.7 6 s 6 8 2 sc 2 sc 4 s 6 s 5.3 1.7 6 s 6 s 2 sc 2 sc 4 s 6 s 5.3 1.8 6 s 6 s 2 sc 2 sc 4 s 6 s * H i e r a r c h i a l Rank: 1-5 highest to lowest s o c i a l rank ** Behaviour Observed: t= t e r r i t o r i a l ; pt= p a r t i a l l y t e r r i t o r i a l ; d= defensive; s= submissive 8 c = schooling; nt= n o n - t e r r i t o r i a l 75 Figure 18. Total frequency of a l l aggressive acts by each "experienced" f i s h during the "gradual" pulse experiment,a=pre-treatment phase; b = i n i t i a l 20 N.T.U.treatment phase; c = i n i t i a l 30 N.T.U.treatment phase; d=final 30 N.T.U.treatment phase; e=final 20 N.T.U.treatment phase; f=post-treatment phase. (+1 standard error shown). 76 311 -»•> i CL [ \ V v 35 -E L \ \ \ \ \ \ \ V r — I 1 1 1 T 1 1 1 r - . o o e o K • «o ^ n «t »- o t o CM 0 a. 3 2 TW Z I S10V 3AJSS3UDQV JO A0N3nO3Ud NV3M e 19. Behavioural repertoires of the "experienced" f i s h during the "gradual" pulse experiment,a=pre-treatment phase; b=30 N.T.U.treatment phase; c=20 N.T.U.treatment phase; d=post-treatment phase; L=lateral display; T=threat display; N=nip; W=wigwag display. (+1 standard error shown). POH a 6 4-4-j » * 1 : ^ I k fete t • nTn 4-» • t : V, & 4, ^ I K . 4-3-M _ J % V • • • 4-3-•t, link E \ \ 4-a-w • • 4-»• 3-:. $ n 4-»• 3-1-0-^ 1 i I i i i i i I ^ I i 1 I 1 J . ' ! ' I I ' . ' »M r •.OM. L T NI L T M W b L T N I c I T N W d EXPB»«34TM. PHUE 79 i i ) Treatment Phase The small increase in t u r b i d i t y to 20 N.T.U.did not result in an "alarm" reaction as occurred with the f i s h exposed to a sudden increase. No s h i f t in either v e r t i c a l or horizontal positioning of the f i s h occurred ( f i g . 17), nor was there any disturbance to the dominance hierarchy (table 3). A l l f i s h continued to defend their t e r r i t o r i e s in a manner very similar to that during the previous phase and no changes in the behavioural repertoires of the f i s h were noted ( f i g . 19). In contrast,increase in t u r b i d i t y to 30 N.T.U.resulted in a major disruption of the s o c i a l organization of the f i s h but no "alarm" reaction was observed. The f i s h moved closer to the gravel, and two positioned themselves in the substrate ( f i g . 17). The linear hierarchy broke down (table 3), and a simple two leveled hierarchy existed. None of the previously t e r r i t o r i a l and/or p a r t i a l l y t e r r i t o r i a l f i s h defended their areas. The f i s h seemed "quiet" and "wary" of their surroundings, and this trend was r e f l e c t e d in a lower t o t a l frequency of aggression by a l l f i s h (fig.18) and also in the s i m p l i c i t y of their repertoires ( f i g . 19). At the maximum t u r b i d i t y tested, no "alarm" reaction was observed. The behaviour of the f i s h was similar to the 30 N.T.U.phase and to that where f i s h were exposed to a sudden 80 pulse of suspended sediment. A l l f i s h v i s i b l e during the 30 N.T.U.treatment phase were buried in the substrate, and very few interactions (0.5 per 10 minutes) occurred. The small amount of aggression which did occur was due to interactive and not e x ploitative competition. When the t u r b i d i t y decreased from 60 to 30 N.T.U.,, a few f i s h moved out of the gravel bottom and onto i t s surface ( f i g . 17) but l i t t l e change in their behaviour occurred. The dominance hierarchy was similar to that observed during the previous 30 N.T.U.treatment phase (table 4)and no t e r r i t o r y defense occurred. The l e v e l of aggression was low ( f i g . 18) and the behavioural repertoires were extremely simple ( f i g . 19). Aggression was s t i l l i n teractive and not e x p l o i t a t i v e . The response of the f i s h to a decrease in t u r b i d i t y to 20 N.T.U.closely resembled that observed in the previous tests. Fish positioned themselves higher in the water column ( f i g . 17) and the frequency of interactions was increased by a l l but one f i s h ( f i g . 18). Several dominant-subordinate relationships were established, and three of the four previously t e r r i t o r i a l and/or p a r t i a l l y t e r r i t o r i a l f i s h re-established t e r r i t o r i e s in conjunction with their dominance. The defence of their t e r r i t o r i e s d i f f e r e d only s l i g h t l y in comparison with that during the pre-treatment phase ( f i g . 19). This was probably attributable to the i n s t a b i l i t y of the s o c i a l organization, due 81 to the re-establishment of dominant-subordinate relationships. i i i ) Post-Treatment Phase During t h i s phase, the behaviour of the f i s h was similar to that observed during the pre-treatment phase and also to that of the other f i s h tested (naive and experienced), following exposure to the sudden pulse. A l l f i s h were positioned in the water column ( f i g . 17). A dominance hierarchy, i d e n t i c a l to that established prior to the pre-treatment phase was in effect and a l l of the previously t e r r i t o r i a l f i s h regained their t e r r i t o r i e s (table 3). Their method of defense was also similar to that observed in the pre-treatment phase ( f i g . 18 and 19). Effects on the G i l l s 1) Sudden Pulse a) Naive Fish During the pre-treatment phase, only one of 16 f i s h showed any evidence of i r r i t a t i o n to the g i l l s ( f i g . 20), so the mean rate of g i l l f l a r i n g was very low (0.01 fl a r e s / 2 minures). Following the introduction of the suspended sediment pulse to a t u r b i d i t y of 60 N.T.U., the f i s h v i s i b l e in the highly turbid water showed an immediate response to the e f f e c t s of the sediment on their g i l l s . A pronounced f l a r i n g of the g i l l s in 82 Figure 20. Mean frequency of g i l l f l a r i n g by a l l f i s h . . "Sudden" pulse: a=pre-treatment phase; b=30 N.T.U.treatment phase; c=20 N.T.U.treatment phase; d=post-treatment phase; "gradual" pulse: a=pre-treatment phase; b = i n i t i a l 20 N.T.U.treatment phase; c = i n i t i a l 30 N.T.U.treatment phase; d=final 30 N.T.U.treatment phase; e=final 20 N.T.U.treatment phase; f=post-treatment phase. (+1 standard error shown). 83 84 conjunction with a small forward thrust of the body was observed but was not quantifiable. Quantification of the frequency of g i l l f l a r i n g by the f i s h during the 30 N.T.U.phase revealed a s i g n i f i c a n t increase by a l l f i s h (replicates 1 and 2; p<0.05; Mann-Whitney U Test; f i g . 20). The magnitude of the response by each f i s h was variable, ranging from 0.2 to 1.6 f l a r e s / 2 minutes, but the mean rate of f l a r i n g by a l l f i s h was greatly increased (0.7 fl a r e s / 2 minutes) from that evident in the pre-treatment phase. Despite the decrease in t u r b i d i t y to 20 N.T.U, the mean frequency of g i l l f l a r i n g continued to increase to 1.0 f l a r e s / 2 minutes, ( f i g . 20). There was no s i g n i f i c a n t difference between th i s and the rate during the previous phase. G i l l f l a r i n g , during the post-treatment phase, continued to occur at a l e v e l s i g n i f i c a n t l y greater than that observed during the pre-treatment phase ( f i g . 20; p<0.05; Mann-Whitney U Test). The mean rate of f l a r i n g (0.9 f l a r e s / 2 minutes)was not s i g n i f i c a n t l y d i f f e r e n t from the rate observed during the previous treatment phase (fig.20). b) Experienced Fish In contrast to the naive f i s h , 6 of the experienced f i s h (previously exposed to suspended sediment), exhibited some g i l l 85 i r r i t a t i o n p r i o r to the addition of suspended sediment ( f i g . 20). The mean rate of g i l l f l a r i n g was 0.1 f l a r e s / 2 minutes. This difference may be due to the fact that the naive f i s h were reared from eggs to fry in the same water source, (Vancouver c i t y water), whereas the experienced f i s h were only exposed to th i s source source shortly before experimentation. Presumably, the residual chlorine, not removed by the dechlorinator, i r r i t a t e d the g i l l s . Following the addition of the suspended sediment pulse, the experienced f i s h exhibited a response similar to that of the naive f i s h . Quantification at 30 N.T.U.revealed a s i g n i f i c a n t increase in g i l l f l a r i n g by a l l f i s h , fron 0.1 flares/2minutes to 0.9 flares/2 minutes ( f i g . 20; p<0.05; Mann-Whitney U Test). The l a t t e r mean rate of f l a r i n g was not s i g n i f i c a n t l y d i f f e r e n t from the rate observed by the naive f i s h . With a decrease in t u r b i d i t y to 20 N.T.U., a l l but 1 f i s h showed a decrease in g i l l f l a r i n g but only in 1 instance was the decrease s i g n i f i c a n t ( p<0.05 Mann-Whitney U Test). The l a t t e r mean rate of g i l l f l a r i n g not s i g n i f i c a n t l y d i f f e r e n t from the previous phase. Seven of the 8 f i s h continued to e l i c i t g i l l f l a r e s at frequencies s i g n i f i c a n t l y increased from the pre-treatment phase ( p<0.05; Mann-Whitney U Test), and the average rate (0.5 fla r e s / 2 minutes) was not s i g n i f i c a n t l y d i f f e r e n t from the rate 86 observed by the naive f i s h during t h i s phase (fig.20). 2) Gradual Pulse a) Experienced Fish Only 3 of the 8 f i s h showed any appreciable rates of g i l l f l a r i n g during the pre-treatment phase ( f i g . 20). The mean rate of f l a r i n g was 0.02 f l a r e s / 2 minutes. The small increase in t u r b i d i t y to 20 N.T.U.significantly increased the pre-treatment rate of g i l l f l a r i n g to 0.22 f l a r e s / 2 minutes (p<0.05, Mann-Whitney U Test;fig.20), and the following increase in t u r b i d i t y caused a further s i g n i f i c a n t increase to 0.8 fl a r e s / 2 minutes (p<0.05, Mann-Whitney U Test; although not quantifiable, the rate of g i l l f l a r i n g appeared to remain at an increased rate during the 60 N.T.U.treatment phase. A decrease in t u r b i d i t y to 30 and 20 N.T.U.did not result in a s i g n i f i c a n t change in the rate of g i l l f l a r i n g (1.0 and 0.9 respectively; f i g . 20). Although the rate of g i l l f l a r i n g did decrease during the post-treatment phase to 0.5 f l a r e s / 2 minutes (fig.20), i t was s t i l l s i g n i f i c a n t l y increased from the rate observed during both the pretreatment and the i n i t i a l 20 N.T.U.treatment phase. 87 Effects on Feeding Behaviour The s o c i a l organization of the f i s h during the pre-treatment phase i s shown in table 4. The location of the individual f i s h in each replicate i s shown in figure 21. In each r e p l i c a t e , the despots held their t e r r i t o r i e s upstream of the subordinate f i s h , the subdominants d i r e c t l y behind the despot. The remaining f i s h were confined in a small area further downstream. The response of the f i s h to a suspended sediment pulse was very similar to that of the f i s h tested previously. A disruption of their s o c i a l organization occurred and the re-establishment of a stable dominance hierarchy and t e r r i t o r i e s resulted following water clearance. The introduction of two d i f f e r e n t size classes of prey produced no s t a t i s t i c a l l y s i g n i f i c a n t difference in either the capture or success rate per s t r i k e . Consequently, the data obtained for each size class were pooled. 1) Success Rate / Strike Prey a c q u i s i t i o n declined with increased t u r b i d i t y ( f i g . 22). The success rate increased s i g n i f i c a n t l y during the 20 N.T.U.treatment phase, and again during the post-treatment phase. It i s possible that the success rate at 60 N.T.U.was Table IV. Summary of the social organization of the "experienced" f i s h during the pre-treatment phase of the "sudden" pulse feeding experiment. REPLICATE 1 REPLICATE 2 FISH SIZE RANK* BEHAV.** FISH SIZE RANK* BEHAV. LG(cm)WT(gm) LG(cm)WT(gm) 6.4 2.9 Kd) t 6.3 2.8 Kd) t 6.0 2 .7 2(sd) 5 .9 2 .6 2(sd) Pt 5 .9 2 .3 3 6 5 .7 2 .0 3 d_ 5 .9 2 .1 3 - s 5 .7 1 .7 4 6 5 .4 1 .8 3 s 5 .6 1 .6 4 6 * Hierarchial Rank: 1 - 4; highest to lowest social rank ** Behaviour Observed: t=t e r r i t o r i a l ; pt=partially t e r r i t o r i a l ; d=defensive; 6=submissive. 89 Figure 21. Cross-sectional diagrams of observation area showing the v e r t i c a l station position of the "experienced" f i s h during the "sudden" pulse feeding experiment.a=pre-treatment phase; b=60 N.T.U.treatment phase; c=30 N.T.U.treatment phase; d=20 N.T.U.treatment phase; e=post-treatment phase. REPLICATE 2 91 Figure 22. Mean prey capture success rate.a=pre-treatment phase; b=60 N.T.U.treatment phase; c=30 N.T.U.treatment phase; d=20 N.T.U.treatment phase; e=post-treatment phase; 1=replicate 1; 2=replicate 2. (+1 standard error shown). 93 greater than that during the 30 N.T.U.treatment phase, due to a smaller v i s u a l f i e l d during t h i s phase and consequently, a shorter reactive distance. As the f i s h could only see within a limi t e d distance, they only had to lunge out and capture the prey whereas during the 30 N.T.U.phase, ( v i s i b i l i t y was increased), there was a greater distance in which the f i s h could make errors. 2) Capture Rates Prey capture rates of the juvenile coho salmon also decreased in turbid water ( f i g . 23). A s i g n i f i c a n t decrease during the 60 N.T.U.phase was noted but capture rates at a tu r b i d i t y of 30 N.T.U.did not change s i g n i f i c a n t l y with respect to the 60 N.T.U.treatment phase. Capture rates increased s i g n i f i c a n t l y with a further reduction in t u r b i d i t y to 20 N.T.U. Post-treatment capture rates (0 N.T.U.) increased s i g n i f i c a n t l y from the rates observed in the turbid phases, but 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 the pre-treatment rates. 3) Capture Sites During the pre-treatment phase, 98.9% of the prey were captured at positions upstream of the capturer (replicate 1 and 2 pooled), whereas only 16.3%, 10.8% and 16.2% of the prey were captured at postions upstream of the capturer in water of a tu r b i d i t y of 60, 33 and 20 N.T.U., respectively. These values 94 Figure 23. Mean percent of prey eaten.a=pre-treatment phase; b=60 N.T.U.=treatment phase; c=30 N.T.U.=treatment phase; d=20 N.T.U.treatment phase; e=post-treatment phase; 1=replicate 1; 2=replicate 2. (+1 standard error shown). 95 100 90-80-70-60-50 40-30-20-10 ' " H i 1 T T e 1 2 a 1 2 b n c EXPETOMENTAL PHASE 1 2 d 96 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 those of both the pre- and post-treatment phases, but not from each other. The post-treatment value of 52% was s i g n i f i c a n t l y d i f f e r e n t from that of the pre-treatment phase. Presumably, t h i s i s due to the presence of the less stable dominance hierarchy during the post-treatment phase. Fish, although having established a hierarchy were s t i l l somewhat stressed from having undergone exposure to the sediment pulse. 4) Prey Acquistion by Individual Fish The disruption of the s o c i a l organization of the f i s h following the addition of suspended sediment also occured in these experiments. This had a large effect upon the a b i l i t y of the individual f i s h to capture prey items. In the pre-treatment phase, when a stable dominance hierarchy was present, and several f i s h defended t e r r i t o r i e s , the despots consumed the majority of the prey items captured ( f i g . 24). Following the disruption of the s o c i a l organization by the addition of sediment to a maximum t u r b i d i t y of 60 N.T.U., the subordinates were capable of capturing a greater portion of the t o t a l number of prey items caught. A further, but i n s i g n i f i c a n t decrease in capture rates by the despots occurred at a t u r b i d i t y of 30 N.T.U.but then increased s i g n i f i c a n t l y during the 20 N.T.U.treatment phase during the post-treatment phase. Again, as with the capture s i t e s , the involvement of the despots with t e r r i t o r i a l defense often resulted in them not noticing a prey 97 Figure 24. Mean number of prey captured per fish.a=pre-treatment phase; b=60 N.T.U.treatment phase; c=30 N.T.U.=treatment phase; d=20 N.T.U.treatment phase; e=post-treatment phase. (+1 standard error shown). 8 £ 71 6-i 4 " u. O ^ z REPLICATE 1 %n M? lei f f i rh r i • i " i • i 1 2 3 4 5 J+L I ' r r I ' I 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 T 1 I I I 1 2 3 4 5 10 -, 3 -° ' i ' i i i * r 1 2 3 4 5 FISH a REPLICATE 2 Hi f] 1 2 3 4 5 FISH rfi 4 I'i 1 ' i' i' 1 2 3 4 5 FISH i i i i 1 2 3 4 5 FISH I I I t 1 2 3 4 5 FISH c d EXPERIMENTAL PHASE 99 item, thereby allowing i t to be available for consumption by other f i s h . 100 DISCUSSION These laboratory experiments show that both t e r r i t o r i a l and feeding behaviour of juvenile coho salmon are affected by exposure to short-term pulses of suspended sediment. In doing so, they suggest that the fi t n e s s of f i s h rearing in streams subjected to logging may be reduced. Most species of salmon and trout show t e r r i t o r i a l behaviour in streams. Hierarchial rank, achieved through agonistic bouts, i s p o s i t i v e l y correlated with growth and the genetic f i t n e s s of an individual (Li and Brocksen 1977). Fish which achieve behavioural dominance gain the advantage of a greater feeding opportunity through the establishment of a t e r r i t o r y (Chapman 1962; Symons 1968; Fenderson et a l . 1968; Jenkins 1969). T e r r i t o r i a l i t y has long been recognized as a mechanism for l i m i t i n g the density of stream dwelling salmonids, and as a c h a r a c t e r i s t i c evolved as a food-linked s p a t i a l requirement (Kalleberg 1958; Allen 1969; Chapman and Bjornn 1969; Jenkins 1969; McFadden 1969; Slaney and Northcote 1974). Chapman (1962) and Mason and Chapman (1965), found that t e r r i t o r i a l f i s h were larger than n o n - t e r r i t o r i a l f i s h , and D i l l , Ydenberg and Fraser (1981) showed that f i s h possess a behavioural response allowing them to adjust 101 t e r r i t o r y size to l o c a l food abundance. Slaney and Northcote (1974) showed that t e r r i t o r y size and frequency of aggression vary inversly with prey abundance. S i m i l a r i l y , Gass (1979), Kodric-Brown and Brown (1978), Lance (1978) and Myers et a l . (1979), found for a number of other animals, that home ranges were smaller when food was abundant. The advantage of t e r r i t o r i a l i t y reaches beyond the acquirement of a food resource however, but also encompasses energy costs, susceptability to predation, and movement to less favorable habitats. L i t t l e v a r i a t i o n occurred between the behavioural patterns of the individual groups of f i s h tested during the pre-treatment phase (naive versus experienced), and any d i s s i m i l a r i t i e s were attri b u t a b l e to differences in the aggressiveness of individuals, which strongly influences the degree of s o c i a l integration ( C o l l i a s 1944). The behaviour of the f i s h during the pre-treatment phase clos e l y resembled that described by others for young coho and other salmonid species, both in the laboratory and in the f i e l d (Mason 1966; Chapman 1962; Mason and Chapman 1965; Hartman 1965; Kalleberg 1958; Jenkins 1969). An i n i t i a l period of schooling, leading to fixed positioning and a period of active f i g h t i n g , as was observed for several species of f i s h and chickens (Braddock 1942; as c i t e d in C o l l i a s 1944) and brown and rainbow trout (Jenkins 1969) preceded a period of s o c i a l s t a b i l i t y which prevailed 102 for the duration of the pre-treatment phase. Two forms of aggression were recognized, one for dominance and one for t e r r i t o r i a l i t y , but they were not mutually exclusive. Tension was greatest between the closest ranked individuals ( C o l l i a s 1944; Noble 1939; Lorenz 1931, as c i t e d in C o l l i a s 1944), and the l e v e l of aggression was highest amongst the highest ranked i n d i v i d u a l s . Most f i s h were susceptable to aggression by ^ the dominants whereas the subordinates aggression was in h i b i t e d by h i e r a r c h i a l formation (Jenkins 1969; Fenderson and Carpenter 1971; Noble 1939; Lorenz 1931). The s o c i a l organization of both naive and experienced f i s h was markedly affected by the addition of a sudden pulse of suspended sediment, and there were no recognizable differences in their reactions. Fenderson and Carpenter (1971), and Dickson and MacCrimmon (1982) also found no q u a l i t a t i v e differences between the behaviour of hatchery and wild juvenile A t l a n t i c salmon ( Salmo salar ). The similar response of both populations of f i s h tested, suggest that the behavioural response of f i s h to a suspended sediment pulse i s not acquired through experience, at least not during the time scale of the fresh water phase of the l i f e cycle of coho salmon. It i s possible that through evolutionary time, a favourable response to suspended sediment has evolved ( i e : avoidance of turbid streams by adult f i s h ; Saunders & Smith 1965; 103 preference for non-turbid water; Bisson and Bilby, 1983; Whitman et a l . , 1982), but t h i s was not tested herein. The dynamics of the pulse appeared to be important in c o n t r o l l i n g the i n i t i a l response of the f i s h to suspended sediment. The increase in t u r b i d i t y to only 20 N.T.U.caused no a l t e r a t i o n to the behaviour of the f i s h . With subsequent increases in t u r b i d i t y however, a similar reaction to that observed of the f i s h exposed to a sudden pulse resulted. This difference suggests that the absolute l e v e l of t u r b i d i t y is important in causing the reactions witnessed, and that juvenile coho may be capable of t o l e r a t i n g low suspended sediment concentrations but higher leve l s (39 and 60 N.T.U.) produce behavioural a l t e r a t i o n s . The reaction of the f i s h to suspended sediment i s due to a number of possible factors acting independantly or s y n e r g i s t i c a l l y . Visual i s o l a t i o n from conspecifics plays an important role in t e r r i t o r i a l behaviour, (Fabricius and Gustafson 1954; Kalleberg 1958; D i l l 1978b). The presence of a f i s h within the v i s u a l range of another constitutes a threat in i t s e l f (Jenkins 1969). In these experiments, the t u r b i d i t y provided the necessary v i s u a l i s o l a t i o n to disrupt the s o c i a l integration. A decrease in v i s i b i l i t y was implied from the results of the feeding experiments, from the difference in the i n i t i a l reactions of the f i s h to the dynamics of the two pulses and also from the s h i f t in 104 the station positions closer to the gravel. The greater the v i s u a l i s o l a t i o n , the smaller the e f f e c t dominance and t e r r i t o r i a l i t y may have in providing a competitive advantage by allowing a greater feeding opportunity through the reservation of a larger proportion of the food supply (Magnuson 1966). The extent to which the resource i s shared depends upon a variety of factors including v i s u a l i s o l a t i o n and fluctuations of any one of the factors can change the competitive advantage derived from dominance (Magnuson 1966). Consequently, the temporary suppression of dominant-subordinate relationships and t e r r i t o r i a l behaviour at higher t u r b i d i t y l e v e l , may be a mechanism evolved to minimize energy costs during unfavourable environmental conditions. The suppression of dominant-subordinate relationships during s t r e s s f u l situations has been shown to occur in other animals as well ( Cooper 1942; as c i t e d in C o l l i a s 1944). The disruption of the s o c i a l organization of the f i s h may also be attributed in part to both physiological and psychological stress. The work of Noggle (1978) and Sigler (1980) support the hypothesis that f i s h are stressed in turbid water. Elevated plasma glucose concentration were observed in coho held in turbid water at sub-lethal concentrations of suspended sediment (Noggle 1978) and growth was supressed in coho and steelhead fry reared in turbid water (Sigler1980). Several other researchers have 105 shown through c l i n i c a l indices of stress that an inverse relationship exists between s o c i a l rank and stress (Eijke and Schreck 1980; Noakes and Leatherland 1977; Delventhal 1978; Peters et a l . 1980; and Scott and Currie 1980). Subordinate f i s h tend to have less body fat, smaller spleens, larger interrenal c e l l s , fewer leucocytes, higher plasma glucose, and lactate concentrations, lower hepatic glycogen levels and high adrenocorticol a c t i v i t y in comparison with dominant f i s h . Stress can also be inferred from changes in the coloration of the f i s h . Fenderson et a l . (1968) showed that the pattern of f i s h coloration i s i n d i c a t i v e of s o c i a l stress. Dominant f i s h are l i g h t and non-descript whereas subordinate f i s h are darker and have a mottled pattern. There was a change in color from the normal dominant-subordinate colouration which existed during the pre-treatment phase when a stable dominance hierarchy was present, to an apparent darkening by a l l v i s i b l e f i s h following the introduction of suspended sediment. This observation suggests that the f i s h were stressed by suspended sediment. In birds, physiological changes induced by the environment have been shown to increase intragroup aggression and decrease s o c i a l integration (Nice 1937). Alterations to the "internal d i s p o s i t i o n " of f i s h may be further affected by the effects of suspended sediment on their physiology. Damage to the g i l l s of f i s h exposed to suspended sediment may i n f l i c t p hysiological stress. Noggle (1978) and Herbert and 106 Merkens (1961), both reported g i l l lesions and fusion of g i l l lamellae in salmonids held in highly turbid conditions. This could interfere with respiratory processes as was noted by Horknel and Pearson (1976). In the experiments reported herein, an increase in the frequency of g i l l f l a r i n g following the addition of suspended sediment, suggests that even short-term exposure to suspended sediment can interfere with normal respiratory processes. Thus, i t seems l i k e l y that the effects of exposure to suspended sediment on the behaviour of the juvenile coho, is due to a combination of vi s u a l i s o l a t i o n , physiological and psychological stress. The effects of suspended sediment on the feeding behaviour of juvenile coho may further induce stress through starvation. The decreased a b i l i t y of f i s h to feed as e f f i c i e n t l y as in non-turbid water may lower their resistance to b i o l o g i c a l and physical stress and interfere with their e f f i c i e n t assimulation of food. Noggle (1978) found feeding by coho to decrease as t u r b i d i t y increased, as did Olsen et a l . (1973) for rainbow trout, and Vinyard and O'Brien (1976) for sunfish. Coho are d r i f t feeders and rely primarily on their v i s u a l a b i l i t i e s to capture prey. Hence i t seems l i k e l y that the decrease in reactive distance observed by f i s h in turbid water i s important in t h i s response. 107 The consumption of the majority of the prey items by the dominant f i s h during both the pre and post-treatment phases of the experiment was mediated by i t s a b i l i t y to supress the a c t i v i t y of the subordinates. Fenderson et a l . (1968) working with A t l a n t i c salmon, found that dominant f i s h consumed twice the amount of food eaten by subordinates, and that when the dominant was removed , prey a c q u i s i t i o n by the subordinate f i s h increased. In the feeding experiment reported herein, removal of the dominant f i s h was mimicked by the suppression of i t s dominance through the effect of suspended sediment on the s o c i a l structure of the f i s h . This resulted in an increase in feeding by the subordinates during the i n t e r v a l in which the s o c i a l intergration was decreased. Jenkins (1969) also showed a competitive advantage of dominance in surface feeding by rainbow trout and brown trout. He found no rela t i o n s h i p between food volume and rank for organisms scattered amongst f i s h of a l l ranks, but with respect to free d r i f t i n g forms, the dominant consumed more prey items that did the subordinate f i s h . In the assessment of the implications of the effect of suspended sediment on the feeding behaviour of juvenile coho salmon, i t should be recognized that these results are s p e c i f i c to the laboratory condition in which they were obtained, and can only in part be applied to f i e l d conditions. The results of these and other experiments 108 suggest that subordinate f i s h feed more e f f e c t i v e l y in turbid water, but in the f i e l d , prey items are not confined within the small area defined by the experimental apparatus. Consequently the feeding rates of subordinate f i s h may actually be further supressed in turbid water. In the f i e l d , the s p a t i a l dimension of the feeding environment is much larger and hence the p r o b a b i l i t y of prey d r i f t i n g within the limited v i s u a l range of the f i s h in turbid water is poor. In the laboratory prey invariably followed a trajectory which placed them close to i f not within the v i s u a l range of at least one f i s h . Consequently, the b e n i f i t s gained by subordinates feeding in turbid water, may not necessarily be experienced in the f i e l d . \ 109 SUMMARY Short-term exposure to suspended sediment a f f e c t s the behaviour of juvenile coho salmon. T e r r i t o r i a l behaviour i s altered through: i) a decrease in s o c i a l integration, i i ) a disruption of the dominance hierarchy, i i i ) a suppression of t e r r i t o r i a l i t y , iv) a change from exploitative to interactive aggression. . Feeding behaviour i s altered through: i) a change in the s o c i a l feeding pattern, i i ) a decrease in feeding a b i l i t y . Short-term exposure to suspended sediment also induces physiological stress. This was inferred from the increase in rate of g i l l f l a r i n g following sediment exposure. Although no difference exists in the response of naive and of experienced f i s h to a pulse of suspended sediment, the dynamics of a sediment pulse has important a f f e c t s on their behavioural response. This i s suggested by: i) a sudden increase in t u r b i d i t y to the maximum tested produces an "alarm reaction" by the f i sh. i i ) a small increase to 20 N.T.U., does not affect their s o c i a l organization. 110 i i i ) a subsequent increase from 20 to 30 N.T.U.disruptes the s o c i a l organization of the f i s h , but does not produce an "alarm reaction" iv) the descending phases of the sudden and gradual t u r b i d i t y pulses a f f e c t behaviour in a similar manner Several factors are important in producing the above behavioural responses: 1) Visual I s o l a t i o n : t h i s was inferred to have occurred from the feeding experiments and was also supported by the observation of a lowering of station position closer to the gravel by f i s h in turbid water, and also by the decrease in distance at which they were observed to react to each other. 2) Physiological and Psychological Stress: the darkening of body colour in conjunction with the effect of sediment on the g i l l s indicates that f i s h experience some form of physiological stress in turbid water. This may in turn a l t e r the "internal d i s p o s i t i o n " of the f i s h , producing psychological stress. The l a t t e r may be accentuated further by the v i s u a l i s o l a t i o n of the f i s h from conspecifies, food and reference points for positioning. Together, physiological and psychological stress may act to further decrease the s o c i a l integration of the f i s h . The above responses, in conjunction with others not 111 within the scope of th i s study, imply that exposure to short-term pulses of suspended sediment may be deleterious to the fitness of f i s h populations. The accumulative ef f e c t s of exposure to short-term but frequent pulses of suspended sediment ( i e : as occurs in streams of watersheds exposed to logging) may lower survival rates of f i s h , through direct mortality or through a decrease in resistance to other physical or b i o l o g i c a l factors. 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