"Science, Faculty of"@en . "Zoology, Department of"@en . "DSpace"@en . "UBCV"@en . "Rankin, David Paul"@en . "2010-02-18T11:48:54Z"@en . "1977"@en . "Master of Science - MSc"@en . "University of British Columbia"@en . "A two year study was initiated in 1973 to examine effects of substantial (3.8 fold; from a 1962-66 mean of 39 million to about 150 million in 1973 and 1974) increases in sockeye (Oncorhynchus nerka) Walbaum) fry numbers on zooplankton abundance in Babine Lake. Several lake areas and stationsware sampled for zooplankton bimonthly from May to October during 1973 and 1974 and compared to data gathered between 1958 and 1962 prior to a large scale enhancement program for sockeye stocks. Zooplankton biomass had decreased up to 70% in some areas of the lake during 1973, but only 40% in 1974. Decreases in numbers were also evident. Although seasonal changes in fry diet followed changes in zooplankton species abundance, feeding was selective. The less abundant but larger forms, Daphnia and Heterocope together comprised 70% of the diet during summer, while Cyclops and Diaptomus formed the bulk (87%) of the diet in late fall. Significant decreases in Daphnia and Diaptomus abundance and increases in nauplii-early copepodite abundance had occurred by 1973. The increased 1974 zooplankton abundance relative to 1973 was attributed to decreased mid-summer fry numbers in the lake. Field data suggested low Diaptomus numbers contributed to much higher fry mortality (about double in 1974) compared to 1973.\r\nAn experimental study of species selectivity by sockeye fry indicated that they selected Cyclops and Diaptomus adults. The larger copepods, Heterocope and Epischura, were rejected by fry encountering zooplankton for the first time. Copepodites and nauplii were rejected, but less so when preferred prey were scarce. Prey activity, in my experiments, could not be used to predict predation vulnerability and hence the species selectivity displayed by the fry. Light and temperature had little effect on Cyclops, Dlaptomus and Heterocope activity."@en . "https://circle.library.ubc.ca/rest/handle/2429/20437?expand=metadata"@en . "INCREASED PREDATION BY JUVENILE SOCKEYE SALMON (ONCORHYNCHUS NERKA WALBAUM) RELATIVE TO CHANGES IN MACROZOOPLANKTON ABUNDANCE IN BABINE LAKE, BRITISH COLUMBIA ty DAVID PAUL RANKIN B.Sc, University of Victoria, 1973 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Zoology) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA February, 1977 \u00C2\u00A9 David Paul Rankin In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced deg ree at the 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 ha t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r 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 the Head o f my Depar tment o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Depar tment o f ^-^otp/l06a. s/ The 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 2075 Wesbrook Place Vancouver, Canada V6T 1W5 i ABSTRACT A two year study was initiated in 1973 to examine effects of substantial (3.8 fold; from a 1962-66 mean of 39 million to about 150 million in 1973 and 197*0 increases in sockeye (Oncorhynchus nerka) Walbaum) fry numbers on zooplankton abundance in Babine Lake. Several lake areas and stationsware sampled for zooplankton bimonthly from May to October during 1973 and 197*+ and compared to data gathered between 1958 and 1962 prior to a large scale enhancement program for sockeye stocks. Zoo-plankton biomass had decreased up to 70$ in some areas of the lake during 1973i but only kOf0 in 197^ . Decreases in numbers were also evident. Although seasonal changes in fry diet followed changes in zooplankton species abundance, feeding was selective. The less abundant but larger forms, Daphnia and Heterocope together comprised 70?5 of the diet during summer, while Cyclops and Diaptomus formed the bulk (87$) of the diet in late f a l l . Significant decreases in Daphnia and Diaptomus abundance and increases in nauplii-early copepodite abundance had occurred by 1973. The increased 197^ zooplankton abundance relative to 1973 was attributed to decreased mid-summer fry numbers in the lake. Field data suggested low Diaptomus numbers contributed to much higher fry mortality (about double in 197*0 compared to 1973. An experimental study of species selectivity by sockeye fry indicated that they selected Cyclops and Diaptomus adults. The larger copepods, Heterocope and Epischura, were rejected by fry encountering zoo-plankton for the first time. Copepodites and nauplii were rejected, but less so when preferred prey were scarce. Prey activity, in my experiments, could not be used to predict predation vulnerability and hence the species i i selectivity displayed by the fry. Light and temperature had l i t t l e effect on Cyclops, Dlaptomus and Heterocope activity. i i i . i TABLE OF CONTENTS Page Abstract \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 i Table of Contents \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 i i i List of Figures \u00C2\u00BBv List of Tables i x Acknowledgements x I. Introduction 1 II. Study Area.. 4 A. Babine Lake. 4 B. Spawning Channel Development , 4 C. Sockeye Fry Distribution in Babine Lake......... ..10 III. Materials and Methods 13 A. Lake Program..... 13 Zooplankton Sampling, 1973 13 Zooplankton Sampling, 1974 13 Laboratory Analysis. .13 Analysis of 1973 Stomach Samples 14 Data Analysis. .15 Comparison of Pre- and Postenhancement Data 15 Estimating Heterocope Abundance 17 B. Laboratory Experiments ,18 Electivity 18 Prey Activity i .20 Prey Susceptibility , 23 IV. Results , ,, ,, 24 A. Lake Program 24 Changes in Average Zooplankton Abundance Between Years.24 Iv. Biomass and Numbers. .24 Species Abundance 24 Seasonal Changes in Zooplankton Abundance 34 Biomass and Numbers .34 Taxa. \u00C2\u00AB\u00E2\u0080\u00A2.\u00C2\u00AB.............. .....\u00C2\u00BB\u00E2\u0080\u00A2-. 41 Zooplankton Composition in Sockeye Fry Diets . . . . 5 0 B. Laboratory Experiments. 5? Size Range of Available Prey ..57 Electivity 57 Prey Activity and Susceptibility.. .........66 Activity 66 Susceptibility .66 V. Discussion ....71 A. Lake Program 71 Effects of Fry Predatlon on Zooplankton Abundance .71 Other Causes of Reduced Zooplankton Abundance...........73 Fry Selectivity in Babine Lake 77 Changes in Zooplankton Species Abundance .79 B. Laboratory Experiments..... 80 Electivity 81 Prey Activity and Susceptibility. 82 VI. Conclusions ...85 VII. Management Implications ..87 VIII. Literature Cited 88 IX. Appendices. 92 X. A. Relative Catching Efficiencies of Clarke-Bumpus and Miller Samplers 92 v. LIST OF FIGURES Figure Pag\u00C2\u00A9 1. Babine Lake showing sampling stations and areas....................5 2. Estimated i n i t i a l main arm sockeye fry populations (1962-1976) and resultant smolt output in millions 8 3. Fry distribution within the Main Arm of Babine Lake, based on McDonald (1969). Area locations given in Figure 1....... 11 4. Observation apparatus used to determine activity rates and conduct predation experiments... 21 5. The prey seizing apparatus (a modified Pasteur pipette) used in zooplankton predation experiments... 21 6. Average seasonal zooplankton biomass and numbers in Babine Lake Areas 1-5 during 1958-'62 and 1973-,7i* (the average represents the area under a seasonal abundance curve divided by the length of the sampling season in days). Vertical bars represent 2 S.E. .......25 7. Average seasonal zooplankton biomass and numbers in Babine Lake Areas 1-5 during 1958-'62, 1973 and 1974. Vertical bars represent 2 S.E. ,, .....27 8a. Average seasonal Cyclops, Diaptomus and Daphnia abundance in Babine Lake Areas 1-5. Vertical bars represent 2 S.E 29 8b. Average seasonal nauplli-early copepodite Heterocope and Bosmlna abundance in Babine Lake Areas 1-5. Vertical bars represent 2 S.E. .,31 v i . 9. Seasonal changes in mean zooplankton biomass in Babine Lake Areas 1, 2, 4 and 5 during i958-'62 and 1973-'74. Vertical bars represent 2 S.E 35 10. Seasonal changes in zooplankton biomass in Babine Lake Areas 2 and 4 during 1958, '60, '62, * 73 and '74 37 11. Seasonal changes in zooplankton numbers in Babine Lake Areas 2 and 4 during 1958, '60, '62, '73 and '74 39 12a. Seasonal changes in Cyclops, Diaptomus and Heterocope numbers in Babine Lake Area 2 during 1958, '60, '62, '73 and '74 42 12b. Seasonal changes in Cyclops, Diaptomus and Heterocope numbers in Babine Lake Area 4 during 1958, '60, '62, '73 and '74 44 13a. Seasonal changes in nauplii-early copepodite, Bosmlna and Daphnia numbers in Babine Lake Area 2 during 1958, '60, \u00E2\u0080\u00A262, '73 and '74 ...46 13b. Seasonal changes in nauplii-early copepodite, Bosmlna and Daphnia numbers in Babine Lake Area 4 during 1958, '60, \u00E2\u0080\u00A262, '73 and 74 48 14. Zooplankton composition of sockeye fry diets in late August and late September of 1967 and 1973 (sample size in brackets). The fry were caught in the Main Arm of Babine Lake , 51 15. Seasonal changes in zooplankton composition of sockeye fry diets in the Main Arm of Babine Lake during 1967 (McDonald 1973)\u00C2\u00BB Carats and numbers indicate sampling dates and sample sizes respectively 53 v i i . 16. The zooplankton composition of sockeye fry diets in different regions of the Main Arm of Babine Lake during late August - early September and late September -early October of 1973 (sample size in brackets).. 55 17. Size frequency distribution of zooplankton species encountered by fry during electivity experiments (n = 40),. 58 18. Mean total zooplankton density at different zooplankton density indices, G =\u00C2\u00BB 1,2 and 4,5 (see methods). Vertical bars represent 95% confidence limits.....,,,.. , 60 19. Electivity values of zooplankton encountered by fed fish at different zooplankton densities. The horizontal scale represents a zooplankton density index increasing from 1 to 5 (see Fig. 18) . . . , 6 2 20. Electivity values of zooplankton encountered by starved fish at different zooplankton densities. The horizontal scale represents a zooplankton density index increasing from 1 to 5 (see Fig. 18) .64 21. Gopepod activity rates at different light intensities and temperatures. Horizontal bars represent 95% confidence limits of log transformed data. Vertical bars indicate range. 22. Zooplankton susceptibility to \" a r t i f i c i a l \" predation. Horizontal bars represent 95% confidence limits; vertical bars, the range , , v i i i , \u00E2\u0080\u00942 23. Relationship between zooplankton biomass (mg. dry wt, m. day ~ ) and primary productivity (mg, G, m. , day ) in several oligotrophic sockeye producing lakes in British Columbia and Alaska (Great Central Lake before and after fertilization; Owikeno Lake (Narver 1969) adjusted according to Stockner and Shortreed (1974); five areas of Babine Lake's Main Arm in 1973) 75 24. Regression of vertical haul biomass (mg. dry wt. m~^ ) on 5 meter-strata biomass (mg. dry wt. m*\"^) in 1973......... 93 25. Regression of vertical haul biomass (mg. dry wt. m~^ ) on 0-5 meter oblique haul biomass (mg. dry wt. m~^ ) in 1974........95 26. Regression of biomass estimates (mg. dry wt. m~^ ) of a Clarke-Bumpus sampler on those of a Miller sampler in 1974 98 27. Regression of Clarke-Bumpus catches (no. L ) on those of the Miller sampler,,... , 100 ix. LIST OF TABLES Table Page 1. Volume contributed by individual Babine Lake macro-zooplankton relative to Diaptomus ashlandi being assigned a unit volume of 1 ....16 X. ACKNOWLEDGMENTS I would like to thank my supervisor, Dr. T. G. Northcote for his assistance and helpful comments during preparation of the thesis, Messrs. F. Jordan, J. Martel, I. Miki and J. Weir of Fisheries and Marine Service provided logistical support and aided in sample collec-tion. Their help was greatly appreciated. The accomodation and support supplied by Messrs. R. M. Ginetz and I. McClean of the Fisheries and Marine Service at Fulton River was greatly appreciated. I would particularly like to thank Mr. A, Facchin for his assis-tance in the field and for processing most of the samples. Mr. S. Borden and Mrs. D. Lauriente of the Biology Data Centre (U.B.C.) provided expert advice on computer programming, I am indebted to Mr, H. D. Smith and Dr. J. G. Stockner for their encouragement, suggestions and criticisms during the study and preparation of the thesis. I would also like to thank my parents for their support during my years in university. This work was supported by a Fisheries and Marine Service grant (65-1621) to Dr. T. G. Northcote... 1. INTRODUCTION Recent studies have shown that both invertebrate and vertebrate predation can alter characteristics of fresh water macrozooplankton communi-ties (Brooks and Dodson 1965; Dodson 1970; Hall 1964; Warshaw 1972; Wells 1970). Invertebrate!predators such as Chaoborus, Diaptomus and Leptodora may reduce zooplankton prey densities, alter size frequency distributions or effect species composition in small lakes through size-selective predation (Sprules 1972). Fish and other aquatic vertebrates (such as salamanders) produce similar but more dramatic results in small lakes (Hutchinson 1971). Analogous changes have been observed in large fresh water lakes. Wells (1970) reported changes in the Lake Michigan zooplankton community resulting from size-selective predation by increased numbers of the alewife, Alosa pseudoharengus (Wilson). Such increases in abundance of a single predator species makes i t relatively easy to account for changes in the prey community. However, interpretation of results may also be confused by inadequate knowledge of fish distribution and feeding (Northcote and Clarotto 1975), effects of competitors or subtle Interactions within the prey community. Increases in planktdvorous sockeye salmon fry (Oncorhynchus nerka Walbaum) have occurred in Babine Lake as a result of a salmon enhancement program (Dill 1968). The annual i n i t i a l fry population was increased from a 1962-66 mean of 39 million to 150 million in 1974. Young sockeye in Babine Lake reside in the pelagic zone for one year where they feed on a variety of zooplankton, chiefly Bosmlna coregoni (Baird), Cyclops scutlfer (Sars), Daphnia longispina (Leydig), Diaptomus ashlandi (Marsh) and Hetero-cope septentrionalis (juday and Muttkowskl) (Johnson 1961; McDonald 1969; Narver 1970). 2. Babine Lake produces up to 90% of the Skeena River sockeye run which is the second largest in British Columbia. Because sockeye stocks were declining (Shepard and Withler 1968), researchers sought ways of bolstering production. Johnson (MS 1965a) hypothesized that Babine Lake's main arm could support up to four times the average annual numbers of fry existing there during the period 1956-63. Johnson's basic assumptions are para-phrased as follows: 1. Spawning ground availability limited main arm sockeye production. 2. Sockeye fry did not disperse widely but remained in basins adjacent to their natal streams. 3. Sockeye fry densities were five times higher and zooplankton biomass much lower in the North Arm - Nilkitkwa Lake area than those in the main arm, yet no significant differences in fish size existed between these regions. Based on Johnson's work, the Federal Government built three spawning channels to increase spawning ground area. However, fry appeared to feed selectively (Narver 1970) and contrary to the second assumption, moved out of basins adjacent to their natal streams (McDonald 1969). Concentrated predation by fry in certain areas led to a concern that the main arm could not support the increased fry populations. Food limitations could have several effects: increased mortality, decreased size of seaward migrants or increased numbers of two-year migrants (Foerster 1954). Since there appears to be a positive relationship between seaward migrant size and their ocean survival (Johnson 1965c) numbers of returning adults available to the Skeena River fishery could be seriously reduced. Thus i t became necessary to gain an improved estimate of the lake's carrying capacity for 3. juvenile sockeye. To examine possible impacts of sockeye salmon enhance-ment on Babine Lake zooplankton and when or where food availability might limit production, I compared zooplankton biomass, numbers and species composition during pre- and postenhancement periods (1958-62, 1973-74 respectively). If there has been an effect, decreases in zooplankton biomass and species composition changes, related to fry feeding behaviour, might be expected in areas where predation was concentrated. Fry feeding behaviour was examined experimentally for two reasons. First, l i t t l e is known about early phases of fry feeding. Second, Increased fry numbers may induce changes in zooplankton density and in species composi-tion through selective feeding. Therefore experiments were designed to determine how feeding selectivity might vary with changes in zooplankton density and composition. Predator selectivity has been shown to depend on prey density and composition (Chizar and Hindell 1973; Ivlev 1961). As preferred prey density increases selectivity decreases and avoidance of non-preferred forms increases. Selective feeding may also depend on prey activity rates (Czaplicki and Porter 1974; Herzog and Burghardt 1974; Ivlev 196l) and more active prey may be more or less susceptible to predation. There were two objectives to this work} 1. To determine what effect increased sockeye fry numbers had on regional zooplankton abundance and species composition in Babine Lake. 2. To examine experimentally aspects of fry feeding behaviour which might increase the impact of predation on zooplankton. Fry feeding patterns ..in selectivity experiments were 4. compared with those formed in the lake and effects of zooplankton density, size and activity on selectivity were examined, STUDY AREA Babine Lake Babine Lake (Fig, l ) , elevation 711 m,is a large (surface area 491 km ) oligotrophlc lake located about 159 km northwest of Prince George, British Columbia. The lake is divided into three regions based on morphometry, duration of ice cover and productivity. The North Arm and Morrison Arm, which are quite shallow (mean depth 18,7 m and 11.4 m respectively), are ice covered for approxiamtely 6 weeks longer than the rest of the lake. Lower primary productivity occurs in these narrow sheltered regions because of earlier stratification and shallower (< 6 m) mixed layer depth (Stockner and Shortreed 1974). Zooplankton densities are also lower, perhaps a result of higher concentrations of juvenile sockeye (Johnson 196l), lower primary production or both. The Main Arm of the lake (mean depth 68 m) receives more wind induced mixing and upwelling. Stratification occurs later and the mixed layer is much deeper (15-20 m) resulting in increased but regionally variable primary productivity (Stockner and Shortreed 1974), This in turn leads to regional disparities in zooplankton densities. On the basis of sockeye fry distribution (McDonald 1969) the main arm has been subdivided into five areas (Fig. l ) . Spawning Channel Development Three spawning channels were constructed on two tributaries to the main arm (two at Fulton River, one at Pinkut Creek, Fig. l ) . These 5. Figure 1. Babine Lake showing sampling stations and areas. 6. 7. channels were expected to accomodate approximately 240,000 spawning adults and subsequently produce 125 million fry (Dill 1968). The fir s t channel produced fry in 1966 and a l l three were operating by 1968. By 1973 the i n i t i a l fry population had increased to four times pre-1966 levels (Fig. 2). Smolt production, accompanying the increase in fry numbers, rose to approximately 80 million in 1973-74, but declined markedly in 1975 (Fig. 2). 8. Figure 2. Estimated i n i t i a l main arm sockeye fry populations (1962-1976) and resultant smolt output in millions. 9. 10. Sockeye Pry Distribution in Babine Lake Upon entering the lake from Fulton River and Pinkut Greek in the spring of 1966, sockeye fry migrated south (McDonald 1969). By the end of June approximately 70% of the i n i t i a l fry population was concentrated in Areas 4 and 5 (Fig. 1 and 3). This was followed by a period of north-ward dispersal. The fry were distributed evenly between Areas 2, 3 and 4 by the middle of August, but by October most were in Area 2 (Fig. 3). Their distribution patterns from early November until the following May when the majority migrate to sea are.;poorly understood. Although year to year variability is to be expected, patterns observed in 1966 are assumed to represent a general trend. During the summer and early f a l l the fry undergo diel vertical movements, in addition to horizontal migrations (Narver 1970), the former becoming more pronounced as the lake stratifies. Fry ascend to the surface at dusk from below the thermocline (35-55 m in the Main Arm) to feed (McDonald 1973; Narver 1970). This is followed by a night descent to about 12 m and predawn ascent to feed before moving to deeper daytime depths. There is l i t t l e or no feeding by the fish during the day. 11. Figure 3. Fry distribution within the Main Arm of Babine Lake, based on McDonald (1969). Area locations given in Figure 1. Time P e r i o d 1 June 25 - July 27 Time Per iod 2 Aug. 16 - Sept . 9 Time P e r i o d 3 O c t . 6 - Oct . 25 Year 13. MATERIALS AND METHODS LAKE PROGRAM Zooplankton Sampling, 1973 Samples were collected bimonthly (May-October) from ten depths (0.5, 1.5, 7.5, 12.5. 18.0, 22.0, 26 .0, 31.0, 36.0, 42.0m) at each of several stations (see Fig. 1) along the main axis of the lake using modified Miller samplers, with #10 (153yW ) mesh nets, towed at 1.5 m/sec. The samplers with mouth diameters of 12 cm, were enlarged versions of that described by Miller (1961). Sampling depths were confirmed using a Furuno FUG 400W echo sounder. The barge and equipment used in sample collection was described by Anderson and Narver (1968). Tow length varied between 3 and 6 minutes depending on zooplankton and algae abundance (later in the season nets became rapidly clogged with algae, predominantly Tabellaria fenestrata Kiitz). In addition to the ten horizontal strata sampled a vertical haul was taken from a depth of 40 m or the lake bottom i f the lake was shallower. Three percent formalin was used to preserve samples. Zooplankton Sampling, 1974 Samples were collected at 19 stations southeast of Fulton River (see Fig. l ) . Sampling technique differed from that of 1973 in that an oblique haul from the surface to 5 m (most of the zooplankton was in the upper gimeters) replaced horizontal tows. The depth of the sampler was increased by 1 m increments while being towed at 1.5 m/sec. Two length varied between 3 and 6 minutes. Sucrose was added to the formalin to prevent body distortion of cladocerans (Haney and Hall 1972). Laboratory Analysis Each sample was split several times in a Folsom plankton splitter. One half of the sample was used :for zooplankton dry weight determination and the remainder was subdivided (generally between a 1/128 and a 1/256 split) until the sub-sample contained sufficient plankters to be counted in 20 minutes (generally about 500 - 600 organisms). The following dominant types were enumerated: Bosmina coregoni Cyclops scutifer*, Daphnla longispina, Dlaptomus ashlandi*, Epischura nevadensls (Lilljeborg), Heterocope septentrionalis, Holopediuia gibberum (Zaddach) and copepod nauplii. A more complete species l i s t of Babine Lake zooplankton is provided by Johnson (1965b). The fractions used for dry weight were filtered onto pre-ashed, pre-weighed 4.25 cm Reeve-Engel GFC filters and dried at 65\u00C2\u00B0C for 48 hr, then weighed on a Mettler H 18 balance. Each sample was then ashed at 600\u00C2\u00B0C for four hours. Ash free dry weights were calculated using Johnson's (1964) formula. Analysis of 1973 Stomach Samples Juvenile sockeye salmon (samples available, were taken during August - October in Areas 1-5) were supplied by J. G. McDonald of the Pacific Biological Station and had been preserved in 10$ formalin for approximately 14 months. The wet weight and fork length of each fish was recorded prior to dissection. Stomachs removed from the fish were divided into cardiac and pyloric sections at the major fold. Each section was weighed intact, then weighed again with contents removed to determine wet weight of the latter. The contents were immersed in 37$ isopropyl alcohol for 24 hrs. to break up binding mucoid material. Zooplankton 1. Adults and copepodites counted separately. 15. types were enumerated as previously described and total volume of each estimated using a technique modified from Hellawell and Abel (1971). A grid was placed under the glass slide and the number of squares counted instead of using a micro projector. Percent composition by volume was calculated using the volume estimates given in Table I. Mean percent abundance of each zooplankton taxon was determined after an angular trans-formation to achieve normal distribution of the data (Sokal and Rolf 1969). In order to compare diets during pre- and postenhancement periods the results of a 1967 fry stomach analysis (McDonald 1973) are presented along with the 1973 fry stomach analysis. Data Analysis Comparison of Pre- and Postenhancement Data Clarke-Bumpus and Miller samplers, used during study periods 1958-'62 and 1973-'7*+ respectively, were compared to determine their relative sampling efficiency (Appendix A). A conversion factor, applied to the 1973_,74 biomass data, allowed comparison of biomass levels during the two periods. Changes in zooplankton abundance were determined, in part, by comparing integrated areas under seasonal biomass curves, averaged over several stations in each region during the pre- and postenhancement study periods (l958-'62, 1973-'74). Seasonal total zooplankton and species abun-dance curves were treated in a similar fashion. In addition, 1958-'62 values represent five year means since the among year variability was needed to make the comparisons. Areas divided by sampling season length (days), which varied from year to year, gave estimates of average abundance per day. Each zooplankton type was graphed separately and ordinate scales were varied depending on abundance levels. 16. Table I. Volume contributed by individual Babine Lake macrozooplankton relative to Dlaptomus ashlandi being assigned a unit volume of 1. Species Relative Relative Volume (1) Volume (2) Bosmina coregoni 1.5 1.4 Cyclops scutifer 1.5 .7 Daphnia longisplna 2.5 2.5 Dlaptomus ashlandi 1.0 1.0 Epischura nevadensis - 4.1 Heterocope septentrionalis 12.0 16.2 Holopedium gibberum - 7.0 (1) from Narver (1969) (2) Calculated from 1973 zooplankton and stomach samples using a method adapted from Hellawell and Abel (1971). 17. Differences ln analytical technique between study periods necessi-tated combining the 1973-74 Cyclops and Diaptomus adult and copepodite counts prior to comparing data of these periods. In addition, copepodite counts for these two genera were combined with copopod nauplii counts. Seasonal abundance patterns in 1958. I960 and 1962, representing years of high and low abundance, in Areas 2 and 4 were compared to patterns observed in 1973 and 1974. Areas 2 and 4 were sampled in both study periods and patterns were generally similar to those in Areas 1 and 5 respectively (Johnson 1965b), although densities in these regions were lower than in Area 2 and 4. Seasonal abundance patterns compared to seasonal changes in sockeye fry diets in 1967 and 1973t gave a rough measure of feeding selectivity. Estimating Heterocope Abundance Daytime samples from the surface were not representative of the food complex encountered by fry at night. One of the major food species, Heterocope migrates from a daytime depth of 20 - 30 m to the surface at dusk (Narver 1970). Thus a technique was required whereby abundance of Heterocope sampled during the day could be expressed in terms of the abun-dance of other zooplankton in the upper 5 m at night. Since sampling techniques varied between study periods, methods of estimating Heterocope abundance also had to be modified. During the 1958-'62 period zooplankton were caught during the day by a series of oblique hauls as deep as 80 m (Johnson 1965b). Heterocope concentrations were estimated by summing the concentrations from oblique hauls taken between 10 and 80 m at each station. Heterocope percent abundance was then calculated by comparing summed concentrations to that of other 18. zooplankton in the upper five meters. In 1973-74 Heterocope abundance was determined by applying 40 m vertical haul concentrations to estimates of total abundance obtained from 0-5 meter oblique hauls in 1974. Since no oblique hauls were taken ln 1973\u00C2\u00BB i t was necessary to assess abundance in the 0-5 mtstrata by some other means. Total abundance calculated from 40 m vertical hauls (1974) was regressed on total abundance estimated by 0-5 m tows taken in 1974, giving the following relationship: Y - .50(X) + 1.14, r - .93, n - 50 where Y \u00E2\u0080\u00A2 vertical haul estimate of total abundance (no. l i t e r \" 1 ) X \u00C2\u00BB oblique haul estimate of total abundance (no. l i t e r \" 1 ) Vertical haul abundance estimates (1973) were then converted to oblique haul estimates and 1973 Heterocope relative abundance calculated based on derived estimates. LABORATORY EXPERIMENTS Electivity A random sample of the 1974 Fulton River sockeye fry (mean weight \u00C2\u00BB .15 gmf mean length =\u00C2\u00BB .30 cm) run was subdivided into two groups. Group 1 fish, kept in filtered (5 ^ Aquapure filter) Fulton River water, were fed frozen Babine Lake zooplankton every 24 hours and were referred to as fed fish. Group 2 fish, kept in unfiltered Fulton River water, fed on material entering from the river. The amount of food, of a size suitable for fry to feed on, entering Group 2 tanks was negligible. These fry were referred to as starved fish. 19. Prior to the start of an experiment (at approximately 2030 hrs PST) several 19 l i t e r tanks were f i l l e d with filtered river water. One fish (either fed or starved) was placed in each tank and allowed to acclima-tize for two hours. Fed fish had been without food for 24 hours and starved fish had empty stomachs when the experiments were started based on stomach analysis of control fish. During the experiments fry were unable to see each other and were fed either littoral or limnetic plankton. The two plankton groups were chosen for the following reasons. First, young sockeye fry appeared to spend some time in the littoral zone of the lake (McDonald 1969) and second, i t was thought that the litt o r a l species composition might be different from that in the limnetic zone. A sample of either limnetic or litt o r a l plankton was inspected to determine species composition. Samples, approximating Diaptomus concentrations of 20, 50, 75$ 100 or 500 per l i t e r (represented by the zooplankton density index, 1-5), were then added to each tank. These produced mean total zooplankton concentrations ranging from about 100 to 6,200 per li t e r . Diaptomus was chosen as a zooplankton density Indicator because of its abundance, conspicuousness and importance as a food organism in the lake. Two tanks containing fish but no food were used as controls. The fish were allowed to feed for 15 minutes then killed and preserved in 10% formalin. In total, 20 combinations of fish group (fed or starved), zooplankton group (limnetic or littoral) and food density (c 1T5) were used, each replicated three times. Specimens of each zooplankton species were measured, using an ocular micrometer on a dissecting microscope, to determine length frequency distributions. Gopepods were measured from the rostrum to the distal ends 20. of the caudal setae and cladocerans from the head to the distal end of the posterior spine(s). Experimental fish were weighed (mean wt, - .15 g\"0 and, stomach contents analysed as outlined above except that only the cardiac: section of the stomachs were examined. Zooplankton volume corrections (see column 3, Table i ) were then applied to the counts. Electivity coefficients (ivlev 1961) were calculated for each prey genus from mean values of replicates (angular transformation) ln each experimental combination . Values of g range from +1 (denoting positive selection) through 0 (no selection) to - 1 (negative selectivity or avoidance). Data analysis was facilitated by combining the results involving the limnetic and litt o r a l zooplankton groups. This was done because the two plankton groups differed l i t t l e in species composition, and recent evidence suggested most fry spent l i t t l e time in the litt o r a l zone (K. Simpson personal communication). In addition only the feeding results involving the significantly different low (C \u00C2\u00BB 1,2) and high (C = 4,5) zooplankton densities were analized. Prey Activity Live Cyclops, Dlaptomus and Heterocope were placed in separate 250 ml beakers and acclimated at 4, 8 and l6\u00C2\u00B0C for four hours. They were then placed in separate petri dishes under an observation apparatus and observed through a magnifier (Fig. 4) . The number of \"starts\" (commencement after cessation of swimming activity) per minute was recorded for ten 2. Electivity Index (E) -where r is the proportion of a particular prey type in the diet p is the portion of a particular prey type in the environment 21. Figure 4. Observation apparatus used to determine activity rates and conduct predatlon experiments. Figure 5. The prey seizing apparatus (a modified Pasteur pipette) used in zooplankton predatlon experiments. 22. Reducer (Dis =1.1 cm) B u l b Volume * 2 m l Bulb Volume wi th S p h e r e - U r n f 10:4mm (Heterocope 10 :1.2mm. fcyclop^ Diaptomus) 23. i n d i v i d u a l s of each species a t the three d i f f e r e n t acclimation temperatures and three l i g h t i n t e n s i t i e s (220, 350 and 560 lux- 3). Prey S u s c e p t i b i l i t y Zooplankton used i n predation experiments were sorted i n t o f i v e 4 4 groups: C. s c u t l f e r , D. ashlandi , and H. s e p t e n t r i o n a l i s . Samples were acclimated i n darkness a t l6\u00C2\u00B0G f o r four hours. Each species was then placed separately i n an observation apparatus ( F i g . 4) at l6\u00C2\u00B0G and 5&0 lux, and the time I required, a c t i n g as a l i g h t adapted \"experienced\" predator, to remove ten i n d i v i d u a l s with a modified pipe t t e ( F i g . 5) was recorded. Each experiment was r e p l i c a t e d ten times f o r each species. The sequence of experiments was chosen a t random to minimize the e f f e c t of immediately previous experience a t catching that species i n determining my subsequent success as a predator. The dimensions of prey s e i z i n g apparatus, a c l e a r ' Pasteur pipette, are given i n FigineS. The pipe t t e mouth diameter was adjusted depending on prey s i z e (1.2 mm f o r Cyclops and Diaptomus, 4 mm f o r Heterocope). Suction bulb volume was reduced from 2 ml to 1.3 ml to lower the chances of capturing prey not near the pipe t t e mouth. 3. Approximate l i g h t i n t e n s i t y was measured with a Photovolt Corp. F200 meter s e n s i t i v e between 300 and 650 with a peak at 375. 4. With and without eggs. 24. RESULTS LAKE PROGRAM Changes in Average Zooplankton Abundance Between Years Biomass and Numbers Average biomass levels, calculated from integrated areas under seasonal biomass curves (see methods), were significantly lower in 1973^ ?4 than 1958-162 (Pig. 6)^ The most significant decreases 70%) were observed i n Areas 1, 2 and 4. Average numbers were also lower in 1973-*74 than 1958-'62 (except i n Area 5) (Pig. 6) . The 1973 and 1974 biomass and numbers considered separately, differed i n a similar manner from 1958-'62 (Fig. 7). Biomass levels i n 1973 were considerably lower (Ci60%) than i n 1958-'62;(and 1974), particularly i n Areas 1, 2 and 5. Numbers were also lower in 1973 (Fig. 7). In 1974 biomass levels were significantly lower than in 1958-'62 (Fig. 7). Decreased biomass (*2k0%) was most evident in Areas 2 and 4. Although generally lower, numbers in 1974 were not s i g n i f i -cantly different from 1958-'62, Species Abundance The abundance of Cyclops, Daphnia, Diaptomus, Heterocope and nauplii-copepodites of a l l stages differed most between study periods (Fig. 8a, b). Cyclops abundance was significantly lower i n Areas 2'and 4 during 1973 than i n 1958-'62. There was l i t t l e difference between 1974 levels and those of 1958-'62 and the trend for Cyclops numbers to increase from north to south observed i n 1958-62 was also more apparent i n 1974 than 1973 (Fig. 8at). 5. Two years separated by a dash Indicate data averaged over more than one season (year). Data points with non-overlapping confidence intervals were considered significantly different. 25. Figure 6. Average seasonal zooplankton biomass and numbers in Babine Lake Areas 1-5 during 1958-'62 and 1973-'74 (the average represents the area under a seasonal abundance curve divided by the length of the sampling season in days). Vertical bars represent 2. S.E. 125-r 1 0 0 -7 5 -5 0 -2 5 -o 50-40-30-20-10-0 o i 2 3 4 Lake Areas (Fig.l) 1 9 5 8 - 6 2 (\u00E2\u0080\u00A2) 1973-74 (O) 27. Figure 7. Average seasonal zooplankton biomass and numbers in Babine Lake Areas 1-5 during 1958-'62, 1973 and 1974. Vertical bars represent 2. S.E. 125 1 0 0 -7 5 -50 - -2 5 -i A _ l _ A I O A i 50 r 4 0 -3 0 -2 0 -1 0 -0 -o A 5 2 3 4 Lake A r e a s (Fig.1) 1 9 5 8 - 6 2 , 1973 1974 ( A ) (o) 29. Figure 8a. Average seasonal Cyclops. Diaptomus and Daphnia abundance in Babine Lake Areas 1-5. Vertical bars represent 2 S.E. Cyclops scutifer 30. 3 0 T 2 0 I 10 f I . i - i i i i i i \u00E2\u0080\u0094J i i_ -J L l _ _ l 1 L. . . o E 3 0 - r 2 0 Diaptomus ashlandi 10+ * i _ l I L_ 4-r 2 f Daphnia longispina i \u00E2\u0080\u00A2 J i i_ J i _i i i_ Lake Areas 1958- 62 (\u00E2\u0080\u00A2) 1973 (A) 1974 (o) 31. Figure 8b. Average seasonal nauplii-early copepodite, Heterocope and Bosmlna abundance in Babine Lake Areas 1-5. Vertical bars represent 2 S.E. 10 + 5 + Naup l i i copepodites _ l I I I I I 1 1 L . T o 1 - 1 \u00E2\u0080\u0094 I \u00E2\u0080\u0094 \u00C2\u00AB -32. E Z3 .15-.10 .06 Heterocope septentrionalis 1 i 5 _l__k I I I I 1 L . \u00E2\u0080\u00A2 _ J 1_ A 9 - j \u00E2\u0080\u0094 i \u00E2\u0080\u0094 3 + B o s m i n o c o r e g o n i Q \u00E2\u0080\u00A2 j i i_ 5 Lake Areas 1958 - 62(\u00C2\u00BB) 1973 (A) 1974 (O) 33. Diaptomus, which was more (70$ abundant than Cyclops in 1958-'62, was reduced to a greater (40%) degree than Cyclops in 1973, particularly ln Areas 1, 2 and 4 (Fig. 8a). Average 1973 Diaptomus abundance in most areas was only slightly higher than Cyclops. Diaptomus increased in 1974 and observed values were not significantly different from those in 1958-'62. As with Cyclops, the trend for numbers to increase from north to south evident in 1958-'62 was more pronounced in 1974 than 1973 (Fig.8a). Daphnia, which was less abundant than either Cyclops or Diaptomus, was also significantly lower in 1973 than 1958T'62 (Fig. 8a). Its abundance increased in 1974 relative to 1973, but was s t i l l lower than in 1958-'62 although the difference was not significant. Unlike previous groups examined, nauplii-early copepodite abun-dance had generally changed l i t t l e in 1973 relative to 1958-'62. In 1974 nauplii-copepodite numbers were significantly higher than in 1958-'62 or 1973. Heterocope and Bosmlna abundance varied less between periods (Fig, 8b), Heterocope, which was much less abundant than the other zoo-plankters mentioned above, was more numerous in Area 1 in 1973 than 1958-'62 but tended to be lower in Areas 4 and 5. In 1974, Heterocope abun-dance in Areas 2 and 3 was lower than in 1973, but relative to 1958-'62, lower in a l l regions (particularly Area 2; Fig. 8b). Bosmlna showed l i t t l e significant variation in 1973 relative to 1958-'62 except in Area 1 (Fig. 8b). Concentrations in 1974 generally were significantly higher than those of 1973. but differed l i t t l e from 1958-S2 except in Area 5. Bosmlna concentrations in Area 5 during 1974, were considerably higher than in 1958-62 or 1973. 34. Seasonal Changes in Zooplankton Abundance Seasonal changes in zooplankton abundance during 1958-/62 and 1974 were compared to determine when zooplankton were most abundant and to see i f there have been major changes in seasonal patterns between study-periods. Biomass and Numbers Biomass generally peaked in July and August, but reached maxima earlier in the southern than northern areas during the five year period, 1958-'62 (Fig. 9). Year to year variation in biomass levels was greater in northern than southern areas. In the 1973-'74 period there was no evidence of a seasonal progression in timing of biomass peaks from south to north. May - mid June biomass in 1973-'74 appeared lower than in 1958-'62 (particularly in Areas 2 and 4) and biomass tended to peak later in the season than observed previously (Fig. 9). During 1958, I960 and 1962 biomass levels on the average were 20% higher in Area 4 than in Area 2 (Fig. 10). A similar trend was observed in 1973, \"but not 1974. Relatively stable and high biomass levels in Area 2 during 1974 contrasted with the fluctuating lower levels of 1973. Numbers peaked earlier than biomass due to the presence of large numbers of juveniles (Fig. 11). Seasonal changes in numbers were similar in a l l areas during 1958, '60, '62 and '73, but generally peaked later in 1974 than the other years mentioned and remained relatively high through late summer (Fig. 11). Numbers in Area 2 during early June of 1974 were lower than in 1973 and the decline in numbers in mid-June of 1974 paralleled that of the biomass seen in Figure 10. 35. Figure 9. Seasonal changes in mean zooplankton \"biomass in Babine Lake Areas 1, 2, k and 5 during 1958-'62 and 1973-'?2*. Vertical bars represent 2 S.E. ART A I 300-p 00 + 20 + 10 May J i r* J J y . Ai^usJ Seprentier October 1958 - 62 1973 -'74 A R E A 2 W\u00C2\u00B0T T 37. Figure 10. Seasonal changes in zooplankton \"biomass in Babine Lake Areas 2 and 4 during 1958,'60, '62, '73, and '74. 1 0 0 0 1 S 1 0 0 t Area 2 Area 4 M o n t h s I958 (\u00E2\u0080\u00A2) I960 (A) I962 (O) 1973 (A) 1974 10) CO 39. Figure 11. Seasonal changes in zooplankton numbers in Babine Lak Areas 2 and 4 during 1958, '60, '62, 73 and 1 9 5 8 ( \u00E2\u0080\u00A2 ) I 9 6 0 (A) (962 (O) M J J A S 0 1 9 7 3 ( A ) 1 9 7 4 (O) 41. Taxa Cyclops was most abundant in June during 1958, '60 and '62 \"but small f a l l peaks also occurred in Areas 2 and 4, (Pig. 12a, b). Both spring and f a l l blooms were prolonged in Area 4. Similar patterns were not as evident in 1973 and 1974, since spring blooms were apparently prolonged. Although 1974 Cyclops abundance was higher than in 1973, in mid-June of 1974, Area 2 numbers had apparently declined sharply from early June levels (Pig. 12a). Seasonal changes in Diaptomus abundance patterns had altered somewhat between study periods in that adults appeared more abundant in mid-summer in the latter period (Fig. 12a, b). While early summer and f a l l blooms were recorded in Area 2, only a single late June bloom was observed in Area 4 during 1958, '60, and '62. In 1973 and 1974, single blooms in late July were observed in Areas 2 and 4. Area 2 Diaptomus was considerably lower in spring of 1974 than 1973* although higher during the rest of the season. Heterocope, which was less abundant than Cyclops or Diaptomus, was most numerous in July - August but blooms were also observed in September - October during 1958 and 1962. In Area 2 the 1973 summer peak was prolonged and in 1974, absent. However, in Area 4 both peaks were present but occurred somewhat earlier than in 1958-'62 (Fig. 12a, b). Nauplii-early copepodites were most abundant in June of 1958, *60 and '62 but smaller f a l l peaks were also observed in September - October (Fig. 13a, b). In 1973 and 1974, spring peaks were more prolonged in both areas than in 1958, '60 or '62. The 1973 and 1974 f a l l blooms apparently were larger and occurred earlier in Area 4 than in Area 2. Both cladocerans, Bosmlna and Daphnia, showed similar fluctuations 42. Figure 12a. Seasonal changes i n Cyclops, Diaptomus and Heterocope numbers i n Babine Lake Area 2 during 1958, '60, '62, '73 and '74. 44. Figure 12b. Seasonal changes in Cyclops. Diaptomus and Heterocope numbers in Babine Lake Area 4 during 1958, '60, '62, '73 and '74. 1 9 5 8 I960 I 9 6 Z (\u00E2\u0080\u00A2) (O) 1 9 7 3 (a ) 1 ! I M (O) 46. Figure 13a. Seasonal changes in nauplii-early copepodite, Bosmina and Daphnla numbers in Babine Lake Area 2 during 1958, '60, \u00E2\u0080\u00A262, '73 and '74. 48. Figure 13b. Seasonal changes in nauplii-early eopepodite, Bosmina and Daphnia numbers in Babine Lake Area 4 during 1958, '60, '62, '73 and '74. 50. in abundance being most numerous in July - August during 1958, '60 and \u00E2\u0080\u00A262 (Fig. 13a, b). Similar patterns were observed in 1973-74, however Daphnia was greatly reduced, particularly in Area 4 during 1973. Zooplankton Composition in Sockeye Fry Diets A comparison of the late August and late September diets of fry between 1967 and 1973 indicate that significant changes in composition have occurred (Fig. 14). In late August of 1973, Daphnia and Dlaptomus had increased in dietary importance relative to 1967. Epischura and Heterocope, which together formed \ % of the diet in 1967, were present only in small proportions in 1973. Changes in the early f a l l diet between 1967 and 1973 were more striking than those observed in late August, Daphnia, Epischura and Heterocope which together dominated the late September diet of 1967 were almost completely superseded by Dlaptomus and Cyclops in 1973. McDonald (1973) indicated Daphnia and Heterocope formed the bulk of the diet during the 1967 sampling season (Fig. 15). Heterocope dominated fry diets in early summer and f a l l ( Cg 60%), During late summer Daphnia replaced Heterocope as the major food organism ( C\u00C2\u00A3 1%) in the diet. The other cladoceran, Bosmina, was utilized to a limited extent ( CL %) in early summer and f a l l . Of the two numerically dominant zooplankters in the lake,(see Fig. 8a, b), Dlaptomus was utilized to a limited extent, particularly later in the June - October period, while Cyclops was not. Examination of fish taken from different areas in late August of 1973 indicates the prevalence of Daphnia in the diets was fairly wide spread in the main arm, (Fig. 16). However, Dlaptomus formed a large proportion of the diet in Areas 1 and 2. By late September, Dlaptomus dominated the diet in a l l areas of themain arm. The other numerically dominant 51. Figure 14. Zooplankton composition of sockeye fry diets in late August and late September of 1967 and 1973 (sample size in brackets). The fry were caught in the Main Arm of Babine Lake. 52. Iqte - August late - Septe mber 100 c o o a. 6 o O c a> o v_ CL. 5 0 4-0 * * * \u00E2\u0080\u00A2 * \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00C2\u00AB t- < * \u00E2\u0080\u00A2 * * \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 4- 4 i. 4 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2\u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 * \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 4 \u00E2\u0080\u00A2 * \u00C2\u00AB\u00E2\u0080\u00A2 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 4 4 W W n j i n u 1973 (3 2) B o smino Cyc lops Daphnia Diaptomus E p i s c h u r a Hete rocope P a r t i a l l y d i g e s t e d m a t e r i a l 53. Figure 15. Seasonal changes in zooplankton composition of sockeye fry diets in the Main Arm of Babine Lake during 196? (McDonald 1973). Carats and numbers indicate sampling dates and sample sizes respectively. 54. 1 0 0 55. \u00E2\u0080\u00A2 * Figure 16. The zooplankton composition of sockeye fry diets in different regions of the Main Arm of Babine Lake during late August -early September and late September - early October of 1973 (sample size in brackets). 56. Lat* August - Early September B o s m i n a C y c l o p s Daphnio D iaptomus E p i s c h u r a par t ia l l y d i g e s t e d m a t e r i a l H e t e r o c o p e 57. zooplankton, Cyclops, was a more fimporfcantfood organism in late September than late August. The dietary importance of Cyclops varied between Areas, being generally more important in the northern main arm than in the south. LABORATORY EXPERIMENTS Size Range of Available Prey The size range of prey, available to fry, was bounded by the small ( .8 mm) Dlaptomus and Cyclops copepodites and Bosmina, and by the large copepod, Heterocope (x = 4.3 mm, Fig. 17). Adult Dlaptomus and Cyclops f e l l within the range bounded by their copepodites and the medium sized (x \u00E2\u0080\u00A2\u00C2\u00BB 2.57 mm) Daphnia. Epischura (J? =\u00C2\u00BB 2.84 mm) was one of the larger prey available to fry during feeding experiments (Fig. 17). Electivity The mean total zooplankton densities (represented by zooplankton density indices 1, 2, 4 and 5; see methods) which each predator theoretically encountered are shown in Figure 18. Both predator groups, (fed and starved), encountered similar densities although starved fish encountered a greater range of densities than fed fish. Significant differences in density did not exist within zooplankton groups 1, 2, and 4, 5; however, low (1, 2) and high (4,5) densities were significantly ;different. There was a consistent predatlon pattern in a l l electivity experiments (Fig. 19,20). Adult Cyclops and Dlaptomus were selected (E> 0), while other forms were avoided. Because Bosmina and Daphnia were not abundant, electivity was not related to total prey density and these species are not represented in the figures. Fed fish generally showed increased electivity for Cyclops and Dlaptomus adults and Cyclops copepodites as total prey density rose. Electivity of Dlaptomus copepodites decreased while a l l other forms (nauplii, Heterocope, Epischura) were avoided ( E = -1), 58. Figure 17. Size frequency distribution of zooplankton species encountered by fry during electivity experiments (n = 40). 59. 12 8 4 B. COREGONI X=88 DAPHNIA LONGISPINA X = 2.57 i n=40 r-i , n-40 1 I I I 1 ! r 0 5 10 20 30 40 D. ASHLANDI X-1.12 CD -O e \u00E2\u0080\u00A2 c >. u c; 0). CT 0) 24 22 18 14 12 8 4 X-.80 + n=40 0 5 n=40 10 20 E. NEVADENSIS X=2.84 i n=40 ao H. SEPTRIONALIS X=4.30 40 n-50 50 14 12 8 4 I-C'SCUTIFER X=.84 X=1.87 n-40 0 5 / / / 10 20 | | adult copepodite Size (mm) 6o. Figure 18. Mean total zooplankton density at different zooplankton density indices, C = 1, 2 and k, 5 (see methods). Vertical bars represent 95% confidence limits. 61. 20,000 10, 000 4-Fed Fish in c ' Q c o <=, o QL O O N O H . c o C D 2 I ooo Starved F ish OO-L | 1 H-2 4 5 Z o o p l a n k t o n D e n s i t y I n d e x 62. Figure 19. Electivity values of zooplankton encountered by fed fish at different zooplankton densities. The horizontal scale represents a zooplankton density index increasing from 1 to 5 (see Fig. 18). C scutifer D. ashlandi (adults) (adults) Copepod H. septentrionalis E. nevadensis naupl i i 64. Figure 20. E l e c t i v i t y values of zooplankton encountered by starved f i s h at d i f f e r e n t zooplankton d e n s i t i e s . The h o r i z o n t a l scale represents a zooplankton density index in c r e a s i n g from 1 to 5 (see F i g . 18). C. sculifer D. oshlandi (adultt) (adultt) Ul ON 66. Starved f i s h displayed increased selectivity for Cyclops and Dlaptomus adults as total prey density rose. Electiveties of Cyclops and Dlaptomus copepodites fluctuated below 0 but were generally lowest when their relative abundance was highest. Nauplii, Heterocope and Epischura (in most cases) were avoided (E \u00C2\u00BB - l ) . Prey Activity and Susceptibility Activity Cyclops and Heterocope were much more active than Dlaptomus (Fig. 21). Cyclops' characteristic horizontal movements were punctuated by short periods of \"rest\", hence a high ac t i v i t y rate. No significant variations l n Cyclops activity were noted except at 4\u00C2\u00B0C where activity was lower between 350 and 560 lux and at 560 lux where activity increased with temperature (see Fig. 21), Heterocope activity, similar to that of Cyclops, was reduced at 350 lux and 8\u00C2\u00B0C. Dlaptomus, unlike Cyclops and Heterocope, moved vertically and long periods of \"rest\" were punctuated by bursts of activity, resulting in low ac t i v i t y rates. There were no significant light or temperature induced variations in Dlaptomus act i v i t y . Susceptibility Predatlon susceptibility to the pipette differed l i t t l e among genera and between individuals with or without eggs (Fig. 22), except for egg bearing Cyclops which were 1.4 times more susceptible to predation than Cyclops without eggs. The apparent differences in Dlaptomus with and without eggs were not significant. Vulnerability of the much larger Heterocope was similar to that of the other genera, however the increased pipette aperature size may have affected results. According to Bernoulli's principle, increased aperature size should reduce intake velocity at the pipette mouth. Reductions in velocity could reduce capture success. 67. Figure 21. Gopepod activity rates at different light intensities and temperatures. Horizontal bars represent 9% confidence limits of log transformed data. Vertical bars indicate range. 68. 560 ^ -C yd ops Heterocope Diaptomus 220 lux 1 5 0 T Temp. 100 50 1 6 ' C i 1 , 1 : 1 8 C 150 -r 1 0 0 -50+1 .1 4 350 150 100 50 _4 y- _| 1- -\ \ 16 C 150-100-50 + -I r 200 000 400 500 600 L i g h t I n t e n s i t y ( L u x ) 560 150 100 50 5 10 15. T e m p e r a t u r e ( 0 C ) 20 69. Figure 22. Zooplankton susceptibility to \" a r t i f i c i a l \" predation. Horizontal bars represent 95% confidence limits; vertical bars, the range. 2 0 0 Cyclops Diaptomus Heterocope r\u00E2\u0080\u0094 1 i 1 -1 5 0 eggs no 1 0 0 \" eggs no o rH O Y=0.23 + 0.-68*X n-15. r=0.93 w . ZO* P< 6 3 | a nJ rH U Q) tr 10 \u00E2\u0080\u00A2H co 3 6 O \u00E2\u0080\u00A2+\u00E2\u0080\u00A2> P. y-q.40 + o.70*x n-15, r=0.98 Cyclops/Litre ( M i l l e r ) Diaptomus/Litre ( M i l l e r ) Y=0.03 + 0.71*X 'n-15, r=0.85 a PP I eu U rt rH O CD U -P \u00E2\u0080\u00A2H C \u00E2\u0080\u00A2H 6 W O FP Y\u00E2\u0080\u00940.11 + 0.96*X n-14, r=0.89 Daphnia/Litre ( M i l l e r ) d- 3- 1- \u00C2\u00BB\u00E2\u0080\u00A2 6- 7 . t- j. Bosmina/Litre ( M i l l e r ) "@en . "Thesis/Dissertation"@en . "10.14288/1.0094068"@en . "eng"@en . "Zoology"@en . "Vancouver : University of British Columbia Library"@en . "University of British Columbia"@en . "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en . "Graduate"@en . "Increased predation by Juvenile Sockeye Salmon (Oncorhynchus Nerka Walbaum) relative to changes in Macrozooplankton abundance in Babine Lake, British Columbia"@en . "Text"@en . "http://hdl.handle.net/2429/20437"@en .