INSHORE LAKE MICHIGAN FISH POPULATIONS NEAR THE DONALD C. COOK NUCLEAR POWER PLANT, 1973 By D. J. Jude, F. J. Tesar, J. A. Dorr III, T. J. Miller, P. J. Rago and D. J. Stewart Under contract with American Electric Power Service Corporation Indiana and Michigan Electric Company John C. Ayers, Project Director Special Report No. 52 Great Lakes Research Division The University of Michigan Ann Arbor, Michigan 1975 TABLE OF CONTENTS ACiOSIOWLEDGMENTS v GENERAL INTRODUCTION 1 SECTION A. Experimental Design and Statistical Considerations for Monitoring Fish Populations 3 Introduction .......... 3 Trawls ......................... 4 Gillnets 19 Beach Seines 21 Plankton Nets 22 SECTION B. Spatial and Temporal Distribution, Gonad Condition and Teiaperature-Catch Relationships of Adult and Juvenile Fishes 24 Introduction 24 Methods ............... .... 25 Location of Sampling Stations ............ 25 Gear . 27 Missing Samples . 27 Physical and Limnological Data . 28 Laboratory Analysis of Fish 28 Data Manipulation and Calculations 43 Definitions 44 Results and Discussion 45 Diversity and Distribution of Fish Species in the Study Area 45 Species Catches by Gear Type 51 Most Abundant Species 59 Alewife 59 Spottail Shiner 82 Rainbow Smelt 107 Yellow Perch 129 Trout-Perch 154 Less Abundant Species 179 Johnny Darter ...... 179 White Sucker 181 Lake Trout 185 Unidentified Coregonids . 191 Longnose Sucker 195 Rainbow Trout 200 Sculplns 204 Brown Trout ....... 208 Emerald Shiner ..... ... 209 Longnose Dace 210 Northern Pike 212 Coho Salmon 213 Carp 215 Chinook Salmon ..... 217 Gizzard Shad 219 Nlnespine Stickleback 219 Bluegill , . 220 XXX Channel Catfish 220 Burbot 222 Lake Whiteflsh 222 Black Bullhead 224 Fathead Minnow . .......... 224 Rock Bass 224 Golden Shiner 225 Largemouth Bass 225 Lake Sturgeon 225 Lake Herring ....... 225 QulUback 226 Bowfin . 226 Central Mudminnow 226 Round Whiteflsh 226 SECTION C. Vertical, Diel and Seasonal Distribution of Fish Larvae and Eggs In the Inshore Waters of Southeastern Lake Michigan 228 Introduction ...... . 228 Methods ..... 228 Fish Larvae 229 Fish Eggs 230 Results 230 Fish Larvae 230 Fish Eggs 244 Discussion , 244 SECTION D. Summary of Impingement and Entrainment Data . . . 250 Introduction 250 Methods 250 Impingement 250 Entrainment 250 Results 251 Impingement 251 Entrainment 251 GENERAL SUMMARY 254 LITERATURE CITED 258 XV ACKOWLEDGMENTS To John C. Ayers, who had confidence in our ability, supported our designs and shouldered some .jnpleasant tasks so that we could devote our total efforts toward completion of this report, we extend our grateful appreciation. For the continuing successful completion of our activities at the Cook site we would like to extend special thanks to Jon Barnes. Thomas Bottrell and Ronald Weidenbach, former members of our fisheries group, are acknowledged for their contributions to the study, particularly the field work and data compilation they performed. Sunmer- tifoe assistants James Lee (1973) and Christine Seber (197A) provided invaluable and enthusiastic help. Nancy Thurber deserves thanks for compiling, correcting and organizing figures and tables. We received field assistance from William Yocum, Susan Williams, Erwin Seibel, Bruce Higgins, John Stewart, Donald Robinson, J, C. Ayers, James Roth, Carlos Garcia, Samuel Mozley and Ronald Rossmaan. Robert Purcel of the Bultema Dock and Dredge Go. provided weather data aind use of the tug JAMES EDWARDS. Marvin Demerest and Gary DeYoung assisted with field work and built our present on-site laboratory. We thank operations people, particularly shift engineeirs, for care in handling impinged fish, and Robert Bishoff and Rudy Gordine for providing water circulation data. Captain Edward Dunster and First Mate Earl Wilson of the R/V MYSIS are acknowledged for their help in the completion of trawling activities. Lloyd Mollhagen, Jr. and Larry Rosenthal set gillnets for us during winter months . iSieodore Ladewski deserves special acknowledgment for his suggestions and help in computer programming and data analysis. Edward Johnston, James Kubus and Andrew Schaedel also helped on many occasions. We thank our librarian, Itonald Munro, for his efforts in theses procurement, and Barry Mulder for providing stomach content data. Also deserving thanks is Margaret Everett for reading and editing this report and offering many helpful suggestions on style and form. John C. Ayers and Erwin Seibel also read and criticized the text. We thank H. E. Ayers in a special way for typing the report and Janine Graham for typing many of the tables. We are also indebted to LaRue Wells and Stanford Smith, who read through the manuscript and offered valuable suggestions on subject matter based on their extensive experience in research on Lake Michigan fishes. v GENERAL INTRODUCTION This report concerns preoperational f isb, moiiitoring data gathered during 1973 in the area around the Donald C. Cook Nuclear Plant (2s20C) megawatts) located on the shores of southeastern Lake Michigan near Bridgman, Mich. , in Berrian County. Initial "on-line" status for Unit 1 (1,100 megawatts) is expected during February-March 1975. Fish collection activities during the preoperational year 1973 were directed toward standardizing collection techniques used in 1972,, the first yeai" of fish monitoring, as well as establishing new techniques suggested by previous errors and experience. At present w£; use trawls, seines and gill- nets to collect adult and juvenile fishesj and No. 2 plankton nets to collect fish larvae, from which we hope to establish baseline abundance in- dices, length- frequency histograms and temperature-catch relationships, against which postoperational monitoring data can be compared ^ Soiae data from the first year (1972) of preoperational fish monitoring (Jude at al,. 1973) as well as soiae collected during 1974 are included in the present report to clarify speculative 1973 data or corroborate 1973 findings. In view of the recent disturbances in the complex of fish species in Lake Michigan and their interaction with an ever-changing environment, detecting the effect of yet another input into the ecosystem demands as clear and accurate a picture as can be obtained of the present status of the fish populations, what the natural range of variation in numbers can be, and how fishes found in the inshore environment relate both distributionally and seasonally to other parts of the lake. To do this we have initiated a multi-faceted research effort, directed at fish from egg to adult, to define within the range of present technology the "normal" biology of each species found. Since we could not do lake-wide sampling of fishes, we have supplemented our own experiences and knowledge with extensive literature reviews to fill in the distribution and biology of each species. Postoperational sampling will determine if fish at stations directly off the Cook Plant will be affected by plant operations. Because some stations coincide with the discharge and Intake structures, any possible future pumping effects should be more easily detected. More susceptible species can be determined by comparing field-caught fish with those found on the travelling screens. Sampling at beach stations will detect plume effects, if any, on surf-zone fishes. We have set up control stations (reference locations at Warren Dunes) to detect natural changes in fish populations, so that it will be possible to discriminate between natural and possible plant-induced changes at the plant site during postoperation. This report is divided into four sections plus a general introduction and summary. Each of the four sections was written to be an entity of itself, having an introduction, results, and a methods and discussion section where appropriate. One literature-cited section serves the whole report. Considerable referencing of other sections was done when necessary to corroborate and relate the -various phenomena under investigation within one section. The first section is a statistical design overview and critique of the methods we tried and those eventually used, as well as a discussion of catch data (distribution, zero data, etc.) and problems encountered. It is hoped that others will benefit from our experience. The second section is a discussion of the biology of the 45 fish species (adults and juveniles only) captured during 1973 in the Cook Plant vicinity, including seasonal, dial and horizontal distribution for inferred age groups, spawning times (from our data and literature reviews) and temperature-catch relationships obtained from field data. The third section discusses seasonal, horizontal, vertical and diel occurrence and distribution of fish larvae (fish less than 25.4 mm total length) in the Cook Plant area. Distribution of fish eggs is also included. A discussion of net selectivity, migratory behavior and competition among larvae puts this important life stage into perspective with the adult and juvenile fish biology section. Nursery areas and some indication of spawn- ing times were also obtained from these data. The last section is concerned with impingement (fish entrapped on the intake travelling screens) and entrainment (fish eggs and larvae passed through the travelling screens and condensers and subsequently discharged back into the lake). Since the Cook Plant has not yet gone "on-line," impingement data are scant, but some indication of the species and numbers of fish that might be impinged was obtained from routine test pumping of one of the seven circulating water pumps (9.45 x 10^ 1/min - 2.5 x 10^ gal/min) about once a month. The recent proliferation of nuclear power plants in the United States , and particularly on Lake Michigan, has caused concern on the part of ecologists and the general public alike as to possible effects of these plants. Surprisingly little data, however, have been accumulated regarding actual effects on fish by nuclear power plants — whether by heated discharges, entrainment or impingement. We believe that our studies at Cook will help clarify some of the now cloudy areas of concern and provide actual data, so that possible effects of the plant can be determined. SECTION A EXPERIMENTAL DESIGN AND STATISTICAL CONSIDERATIONS FOR MONITORING FISH POPULATIONS Donald J. Stewart and Paul J. Rago INTRODUCTION The number of years required to evaluate the environmental impact of a thermal discharge plume depends on the magnitude of any possible change, inherent variability of the natural system compounded by sampling error, and the number of observations that it is feasible to make within a given period. Previously, little thought has been given to what quantitative changes in fish populations a particular sampling program might be able to detect; least detectable changes are estimated herein for the Cook Plant study. Need for such information is a recent outgrowth of environmental concern and associated legislation. Studies similar to the Cook Plant study are under way or being planned, and guidelines for design of such studies are now being drafted and may become mandatory through legislation (T. Edsall, personal communication. Great Lakes Fishery Laboratory, U. S. Fish and Wildlife Service, Ann Arbor, Mich.). The objective of this section is to give a critique of the experimental design for the Cook Plant fisheries investigation based on one complete year of field studies. For our benefit, this analysis is intended to identify problems or deficiencies in the existing program which might be corrected as we begin our final year of background studies. It is hoped that others might also benefit from our self-criticism. The focus of this section is on species abundance indices being devel- oped to quantify changes in species populations which might be attributed to Cook Plant thermal discharges. To develop abundance indices for all important species and various life-history stages of each, four different gear — trawls, gillnets, seines and plankton nets — are being used, and the sampling programs are considered below with greatest emphasis on the trawling program. As each sampling gear has its unique biases, data from different gear cannot be directly compared but in fact are overlapping and complementary. Each sampling program should be considered a separate experiment to assess the impact of Cook Plant discharges upon some aspects! of fishes in the thermal plume. Given that abundance indices are used, this study is based on the premise that catch-per-unit-eff ort has a direct linear relationship with fish abun- dance. Standing crops of fish in the study areas are not quantified except for fish larvae from plankton net samples where a known volume of water is sampled. TRAWLS The Cook Plant study trawl data froEi 1973 are better suited for statis- tical analysis than either gillnet samples s, which were too costly to repli- cate in terms of time and manpower available, or beach seine samples , which were technically difficult to replicate exactly at different stations and under varying weather conditions. The basic experimental design for trawls consists of duplicate samples taken both day and night at 6.1 and 9.1-m depths off the Cook Plant (experimental area) and off Warren Dunes (control area) on a monthly basis from April through October. November samples are lacking because of bad weather. In 1973 the above program was completed with only 2 of 112 (56 duplicate) observations missing due to gear problems. Effects of thermal discharges from the Cook Plant could first become evident in 1975. Continuing the above trawling program through 1976 will give 2 years preoperational data and 2 years operational data that, as a minimum, should be adequate to determine acute Impacts of therraai effluents upon the fish community. Thus, the completed experimental design will be a 5-way analysis of variance (ANOVA) with fixed effects (Model I) in a completely crossed design (2 times of day) x (2 depths) x (2 areas) x (7 months) x (4 years) with 2 replicates per cell. Two years of follow-up data are considered herein for discussion only; ultimately, more than 2 years of operational data will be taken. The primary objective of this trawl data analysis is to determine the least detectable true changes in fish populatiorts. Given the existing experimental design and variation inherent in sample estimates, will the sample program accomplish its purpose? There are three secondary objectives of analyzing data at this early stage in the experiment: 1) to examine distributional properties of the trawl data and transformations of the data to determine if a parametric analysis of variance would be valid j 2) to test assumptions of the ANOVA model, and 3) given satisfactory results from the foregoing, to perform an ANOVA to identify biological phenomena which may be worthy of supplementary field effort in our last year of baseline data collection. Statistically significant main effects and interactions between various ANOVA factors might be expected to reflect a chronology of events over the year, such as spawning migrations as well as persistent population differences between areas and diurnal behavior patterns. DISTRIBUTIONAL CHARACTERISTICS OF THE TRAWL SAMPLE DATA The ANOVA model outlined above must be considered for each species sep- arately. Data for a species design matrix, expressed as number of fish per 10~min trawl haul, proved to be extremely skewed to the right for all species considered. A frequency histogram for number of fish per trawl haul is exemplified by that for spottall shiners (Fig. Al); the illustrated density function had the following properties: N = 110 (2 missing observations^, X = 28, s = 40.74 and s2 = 1659.75. The coefficient of dispersion, s2/x = 35, 18,2 109.0 catch Raw data for spottail shiner; April-October, n=112. 13.5 109.0 catch Logio(X+l) transformed data for spottail shiner; April-October, n=112. 5 110.0 catch L6gio(X+l) transformed data for yellow perch April-October, n=112. 10.5 110.0 catch LegloC^"*"!) transformed data for yellow perch; June-October, n=80. FIG. Al. Frequency histograms for trawl catches of spottail shiners and yellow perch from the Cook Plant study areas in 1973, Catches are expressed as number of fish per haul. indicates a contagious distribution (Sokal and Rohlf 1969) , and the co- efficient of variation^ CV = s/X x 100% = 144% ^ is comparable to that for catch-per-trawl-tow data observed in a study of fish populations on Georges Bank (Taylor 1953) . In the latter study the density function was found to conform to a negative binomial distribiitlon, and log (X + K/2) was Indicated as an appropriate transformation to normalize data for analysis of variance. In this case, K is the exponent in the negative binomial function and is a measure of the contagion of the distribution. For the present analysis ^ the customary eiapirical transformation logjo (X + 1) was used to normalize the data (E'ig, Al) and to stabilize error variance. The ongoing analysis of Cook Plant data will eventually include a goodness-of-fit test of the hypothesis that the trawl data are distributed according to the negative binoraial; it would also be valuable to compare results of ANOVAs calculated with the two transformations given above. Parameters comparable to those presented for spottail shiners were cal- culated for four other species — alewife,, rainbow smelt, yellow perch and trout-perch. These four species also had contagious distributions j which for the present analysis are asstmied to be negative binomial (Table Al) . Fish are mobile organisms with complex behavior patterns. Distribution in the study area can change seasonally and perhaps even dlurnally, thereby affecting observed frequency distributions or catch data. To test the possibility that we may not be sampling comparable distributions at different times and places, frequency histograms and coefficients of variation (CV) were examined for various stratifications of the data. Almost without exception frequency distributions were strongly skewed to the right as in Figure Al. For example, when spottail shiner data were stratified by month, depth and area, CVs ranged from 34% to 150% with an average for the 28 strata of 102%. Comparable average CVs for other species considered were alewife 116% ^ rainbow smelt 88%, jj-ellow perch 112% and trout-perch 96%. Observed catch frequencies in ail cases indicated contagious distributions, and the chosen transformation logig (X + 1) , is considered appropriate for all stratifications of the data. Too many zero observations (no fish caught) in the design matrix can cause problems, since log^Q (0 + 1) = and the transformed data might be bimodal with peaks at zero and at the geometric mean of the distribution (Fig. Al). To moderate problems which may arise through violation of the normality assumption of the ANOVA model, only those species with few zeros in their design matrix were included in the analysis. Inspection of frequency histograms of transformed data suggested that more than about 20% zero observations gave a noticeably bimodal distribution. The five most abundant species in the trawl catches had the following percent zeros (N = 112 with two substitutions); alewife 13%, spottail shiner 15%, smelt 9%, yellow perch 28% and trout-perch 21%. Most zero observations for yellow perch and trout-perch occurred during April and May. Deletion of these two months from the ANOVA design matrix for these two species increases confidence in whatever inferences are drawn from the analysis but reduces the scope of the Inferences. The reduced matrices (N = 80 with one substitution) have 14% zeros for both species, and the data more closely approximate a normal TABLE Al. Comparison of distributional properties of 1973 sample data for the most abundant fish species caught in trawls, gillnets, beach seines and plankton nets near the Cook Plant, southeastern Lake Michigan. Standard Coef. of Coef. of % deviation variation dispersion zero Gear N X (s) (s/X) 100 (s2/X) data TRAWL -^ (APR-OCT) Spottail 110 28 40.74 144 59 15 Alewife 110 108 170.34 158 269 13 Rainbow smelt 110 119 245.35 206 507 9 Yellow perch 110 15 22.96 152 35 28 Trout- perch no 29 56.06 195 109 21 GILLNET2 (APR-OCT) Spottail 74 54 67.44 126 85 11 Alewife 74 186 216.64 116 251 10 Rainbow smelt 67 8 18.74 239 45 48 Yellow perch 74 31 48.49 155 75 24 Trout -perch 74 4 10.72 240 26 54 seine'' (APR-OCT) Spottail 83 164 394.73 240 974 14 Alewife 83 1505 5009.60 333 16673 30 Rainboe smelt 83 30 114.31 380 434 70 Yellow perch 83 8 23.08 306 71 71 Trout -perch 83 1 2.94 309 9 82 PI^kNKTON NET (JUN-JUL) Alewife 88 2927 5577.80 191 10630 7 ^ Two missing observations. ^ The basic design matrix has 56 observations; 11 and 18 supplementary gillnet samples are included respectively for smelt and the other four species. Supplementary samples were primarily taken off Cook Plant. ^ One missing observation. distribution as illustrated by the frequency histogram for yellow perch (Fig. Al) . Other fish species were relatively uncommon and only small subsets of their design matrices might be useful for statistical analysis; they are excluded from the present analysis. However, exclusion of uncommon species from statistical analysis at this early stage in the experiment does not preclude their inclusion when more data become available. THE ANALYSIS OF VARIANCE Having narrowed the analysis to include only taxa and months where data can be approximately normalized by transformation, we may proceed with improved confidence that the data are amenable to parametric analysis, but other assumptions of the model remain to be considered below. To summarize the foregoing, the ANOVA factors and their levels to be analyzed are as follows : Factor No. of levels 1. Time of day 2 2. Depth 2 3. Area 2 4. Month 7 5 alewife spottail shiner rainbow smelt yellow perch trout-perch Year Levels Day , night 6.1 m, 9.1 m Cook Plant Warren Dunes April - October June - October Not included in these ANOVAs, since so far only one year of complete data is available (1973) . A four -way ANOVA (Model I) in a completely crossed design was performed using the first four factors for each species. Two computer programs of the UCLA Biomedical series (BMD2V and BMD8V) available through the Statistical Research Laboratory at the University of Michigan were used. Results and discussion of these analyses are presented in Section B of this report under discussions of each species. The ANOVA method that was used can be termed an unweighted means analysis of unbalanced data. This method is appropriate in our case as the missing observations were due to essentially random events (Winer 1971, p. 402). In brief, the method entails running the analysis on the data matrix with cell means substituted for missing values. The computed numerator sums of squares are then adjusted downward through multiplication by the ratio n^/N, which is the harmonic mean cell size divided by the maximum cell size. The number of substitutions is subtracted from the degrees of freedom for the denominator stun of squares. This method is described in a document issued by the Statistical Research Laboratory of the University of Michigan (Fox 1973). The ratio njj/N was 0.966 for alewife, spottail shiner and rainbow smelt (2 missing observations); it was 0.976 for yellow perch and trout-perch (1 missing observation) . ASSUMPTIONS OF THE ANOVA MODEL To test, the assumption of normality of the errors, a frequency histogram of the residuals (eijidm) was examined from the ANOVA of the transformed data for each species. As there were only 2 observations per cell, these distribu- tions were all symmetrical about a mean of zero. The relatively high percent- age of zero or near-zero observations in most cases gave a naticeable peaked- ness (leptokurtosis) to the distribution. Reducing 3'ellow perch and trout- perch to a 5-month data raatrtjc reduced the peakedness for these species. Violation of this assumption has little effect on inference about means (Scheffe 1959). The assumption of equality of variances of the errors was tested by scatter-plottlng residuals against cell means for each species. In all cases this assumption appeared to be met reasonably well. It is interesting to note, however, that for alewife and rainbow smelt high mean values tended to have less variation than intermediate values. This suggests a patchy distribu- tion which is smoothed out by the sample size as fish density increases and is not too unreasonable for schooling fish. The final assumption of the ANOVA model to be considered, and most serious with respect to inferences about means, is statistical independence of the errors (Schef f ^ 1959) . A problem might arise if replicate samples are taken without replacement over exactly the same bottom area. In this case, reduction in numbers of fish caught by the first haul would give a consistently lower catch on the second haul. The same effect might be realized if the boat and net created a disturbance that frightened fish away from the station. Finally;, if too many resident fish are removed from the study area, there could be an unnatural downward trend In catch over months or years. As a test for independence between replicate trawls, each of the 56 pairs was scored a +, or - depending on whether the second trawl haul was greater than, equal to, or less than the first. If the replicates are independent samples from the same population, the ratio of +s to -s should be about 1 to 1. In fact, further analysis has revealed seasonal trends in the data that may be inherent In the trawling methodology and that would mask any effects due to non™ independence between replicates. Most species were found to be onshore-offshore migrants rather than residents of the study areas, so month- to-month sample independence was difficult to test. Given the difficulties of testing the independence-of-errors assumption, the obvious solution is to make a direct effort to avoid sweeping the same area twice. Care should also be taken not to overfish the areas under investigation. SEASONAL TRENDS IN THE TRAWL DATA Pooling the above +:- data by species and station and stratifying by month, seasonal trends in the data were indicated. During April and more so in June, there was a tendency for 4-s. From July through October the tendency was for -s (Table A2) . TABLE A2. Relationship of first to second trawl haul of 56 replicate pairs taken in the Cook Plant study areas from April through October 1973. First hauls were always taken from north to south and second hauls from south to north; +, and - indicate that the second haul was greater than, equal to or less than the first with respect to number of fish caught for each of five species. APR MAY JUN FQL AUG SEP OCT TOTALS SPOTTAIL SHINER Cook Plant Warren Dunes ALEWIFE Cook Plant Warren Dunes RAINBOW SMELT Cook Plant Warren Dunes YELLOW PERCH Cook Plant Warren Dunes TROUT-PERCH Cook Plant Warren Dunes +-0- (h — 04+- 4-+++ +--+0 0-00 ++-+ — hO +-H- +0 — 4+0+ 0+0+ 4+4+ 0-0+ + -0+- total hO -+-0 total 444+ 44+ 0+-0 0-4+ 0-+- +• +++- 000- -+- -04+ 1- 000+ 0-0- -i 1- -4+- +-++ 0+0- 0-0- —0+ total — h_ -04+ 0-00 000+ 0- 0+0- 4-0 -+ -04+ OH — -+ — total — h- +-0+ -04+ +-++ total MONTHLY TOTALS +:-:0 9:15:4 11:10:7 20:25:11 16: 7; 10:14; 26:21:9 15:11:2 8:14:6 23:25:8 9:13:6 4:14:10 13:27:16 9:12:7 13:11:4 C.P. W.D. APR 9: 4: 7 5: 7: 8 MAY 9: 5: 6 5:10: 5 JUN 14: 4: 8: 8: JUL 9: 8: 3 2:13: 5 AUG 7:11: 2 8:12: SEP 7:12: 8: 7: 22:23:11 OCT 1 3:14: 3 5 10: 6: 4 TOTAL 14:11:15 14:15:11 22:12: 6 11:21: 8 15:23: 2 15:19: 6 13:20: 7 10 First and second trawl hauls were always taken respectively going south then north and were taken parallel to shore. Currents, wind and waves are consistently present in the study areas and are especially strong in the fall. As trawl hauls were made for 10 min at a fixed r.p.m., going with the prevail- ing weather and currents would conceivably sample a larger bottom area than going against the currents. If one accepts this premise, then systematic patterns in the relationship of first (to the south) and second (to the north) trawl hauls can be expected when prevailing weather and currents exist. Relative efficiency of the trawl when fished with or against currents of various strengths is unknown. It is known, however, that large fish such as salmon are rarely caught at the trawling speeds used and can probably swim out of the net. As boat and net are slowed by wind, wave and current resistance, escapement should increase. Thus fishing efficiency relative to current direction may compound the disparity between replicates which can result from sweeping different areas of bottom in opposite directions. Pooling the +:- data by species and stratifying by month and area (Cook Plant vs. Warren Dunes), expected patterns emerged. Comparison of monthly +:- ratios for the two study areas (Fig. A2) siuggests that the s SI u 3 « ■a a o o u 3.5 2.0 1.5 1.0 0.5 • 0— Cook Plant Aj — Warren Dunes APR MAY JUN JUL AUG SEP ■OCT FIG. A2. Seasonal changes in the relationship of first trawl to second trawl haul in two areas of southeastern Lake Michigan, first trawl going north to south, second trawl always going south to north. 11 two areas are influenced by different current patterns which prevail in opposite directions. Further, both systems seem to reverse their direction in August while maintaining their antagonistic relationship. Further indications of the trends just mentioned are evident when one examines the original +, 0, - matrix (Table A2) for strings of consecutive +s or -s. Spottails off Cook Plant bad all +s in June and almost all -s from August through October. Alewife showed a string of +s off Cook Plant in June and July with opposing -s off Warren Dunes during the same months. It might be noted that these more consistent patterns occurred during spawning seasons when the density of adult fishes is highest in the study areas, suggesting that seasonal trends (Fig. A2) could be even more evident if all species were always present at spawning time densities. As with alewife, smelt showed a string of +s off Cook Plant during their spawning period, April and May, with opposing -s off Warren Dunes in May. Yellow perch showed a string of -s off Warren Dunes in July and August, Trout - perch, the species which was overall least abundant of those considered, had no noticeable trends. If in fact trawling with the current gives larger catches, then it might be concluded that the area off Cook Plant is influenced by prevailing south to north currents in April through June and increasing north to south currents from August through October. The pattern for Warren Dunes would be just the opposite. Currents are emphasized here because wind and wave direction are likely to be similar in both study areas for a given sample period. STATISTICAL IMPLICATIONS OF THE TRENDS What are the implications of these seasonal trends and area differences for the validity of inferences drawn from the experimental design? Seasonal trends in the relation of first to second haul catches are believed due to always taking first and second trawls going south then north. It is thought that trawling speed and perhaps differential fishing efficiency give larger catches when going with the current. Moreover, stronger currents should give relatively greater disparity between catches in replicate trawls. As long as one trawl haul is made in each direction, average bottom area swept and average fishing efficiency would be approximately the same for all stations and months. Thus Inferences drawn from the ANOVA model, which compares means, will still be valid, but the error variance will be increased somewhat by the non-independence of the replicate catches. A normal approximation to the binomial distribution (Zar 1974, p. 287-290) was used to test for the hypothesized 1:1 ratio of +s to -s. Data were stratified by species (area and month pooled). The test showed no significant deviations (p<.01) from the 1:1 ratio for all species tested. Far yellow perch, however, the ratio +:- was 13:27. The test statistic Z was 2.194, which was greater than Z.05(= 1.96) and close to the critical value Z,oi (= 2.576). This suggests that other factors may be influencing the ratio of first to second trawls. For yellow perch there was a strong tendency for the second trawl haul to be less than the first, especially off Warren Dunes. Given the small size of the net, 5.8 m footrope, and normal drift of the boat, the probability is considered low that the observed effect is due to sweeping 12 the disturbed area on the replicate trawl. If equal bottom areas could be swept with equal fishing efficiency, variation in the system would be reduced to that of the fish themselves and statistical decision-making power would be improved. Added variance from methodology probably contributed to skewness of the raw-data density function (Fig. Al) as well as leptokurtosis of residuals calculated from log- transformed data. Variation due to replicate trawl hauls sweeping different bottom areas could be eliminated by always trawling a known distance in a fixed time interval ^ i.e., at a fixed real speed relative to the bottom. This could be accomplished by using radar reflectors on shore or on anchored buoys. It is more difficult to correct for relative fishing efficiencies with and against a current if current speeds vary seasonally and spatially. Efficiency is best averaged by taking replicates in opposite directions. Given that there now exists i yr of data based on 10-mln trawls, the value of making the above methodological changes is reduced as there would be no way to accurately relate 1973 data to new data. From the fore- going it shoud be evident that, given the objectives of this study, the trawling procedure in use can give reasonably accurate results whereas single obseirvatioas or duplicate timed trawl hauls taken in the same direc- tion can give erroneous results, at least in the ar«jas currently under study. STATISTICAL POWER TO DETECT CHANGES IN FISH POPULATIONS At this stage in the experiment it is important to evaluate the eiq)erimental design to determine if enough samples are being taken to accomplish the primary objective of the study — assessment of environmental impact of Cook Plant thermal discharges. Using the standard deviation (s) from the ANOVAs of trawl catches, it is possible to compute minimal popula- tion changes that can be detected when the thermal regime is altered. Yellow perch are used to exemplify the computations „ Least detectable true changes (LDTC) were calculated using a formula derived from Sokal and Rohlf (1969). A least detectable true difference, 6, between two means of transformed data is given b^? the following equation, 2 "^ " ^ n ^""-[v] ^ ^2(1-P:i[v]^ 6 = within-cell error standard deviation of an ANOVA comparing preoperational and operational data; this is the square root of the error mean square n = number of observations in each of the two groups being compared a = significance level 13 t = Student's t V = degrees of freedom P = power (the probability that a true difference will be judged significant by the test) The degrees of freedom, v, are the same as those for the mean square error term for the factorial ANOVAs used in this study. For any factorial ANOVA, the error degrees of freedom are a function of the number of levels of each of the factors. For example if l\ Q, R and S are the factors in an exper- imental design and p, q, r, and s are their respective numbers of levels, then the error degrees of freedom for that ANOVA are pqrs(n-l), where n is the number of replicates. Thus in our study the number of error degrees of freedom per year will be 56 for the species in group A and 40 for the species in group B; Group A (alewlfe, spottails, rainbow smelt) (2 areas) x (7 months) x (2 depths) x (2 times of day) x (2 replicates - 1) = 56 Group B (yellow perch, trout-perch) (2 areas) x (5 months) x (2 depths) x (2 times of day) x (2 replicates - 1) - 40 Procedures for an unweighted means analysis of unbalanced data indicate that 1 error degree of freedom must be subtracted for each missing observation. In the 7-month data matrix there were 2 missing obseirvations and in the 5-month data matrix there was 1 missing observation. Consequently there were 54 error degrees of freedom for group A species and 39 for group B species. In calculating the least detectable true differences, however, it was assumed that there were no missing observations. Hence 56 and 40 error degrees of freedom were used in Tables A3-7 . Each of Tables A3-7 consists of two comparisons. The first is a com- parison of 1 yr of preoperational abundance indices with 1 yr of operational abundance indices; the second compares 2 preoperational yr with 2 operational yr. Although both Cook Plant and Warren Dunes data were used for estimating the error variance and the degrees of freedom, for purposes of the LDTC calculation only Cook Plant data were considered in making preoperational to operational comparisons of the mean abundance. Thus n, the number of observations in each of the two groups being compared, will be exactly half the number of observations from which the error standard derviation is calculated. As an illustration of the above, consider the 1973 yellow perch data. The value of s calculated from the 5-month ANOVA was 0.31112 with 39 degrees of freedom. Details of this ANOVA appear in the part of Section B on yellow perch. Again note that 1 degree of freedom was subtracted for a missing observation, giving 39 rather than 40. The number of observations n at the Cook Plant in 1973 was 40. An equal ntmber of observations were made at Warren Dunes, giving a total of 80 for the two areas. Thus on the left side of Table A3 n = 40 is used. Forty error degrees of freedom are 14 TABLE A3. Least detectable true changes in geometric mean abundance of yellow perch at Cook Plant. These are the values of the ratios 10°, where 6 is the least detectable true change of the transformed variable. It is givejn as a function of « and P. Two alternatives are included, one with 2 yr of sampling and one with 4 yr of sampling (based on the assumption that the within-cell error standard deviation remains the same as it was in 1973), Each change is expressed as the ratio of the operational value to the pre- operational value of the quantity "mean number per trawl plus one." =/P Comparison of 1 pre- operational yr with 1 operational yr; n = 40, V = 80. .90 .95 1.88 1.99 1.77 1.88 1,69 1.80 1.61 1.71 Comparison of 2 pre- operational yr with 2 operational yr; n = 80, V = 160. 90 .95 ,01 ,025 ,05 ,10 1.55 1.61 1.49 1.55 1.44 1.50 1.39 1.45 TABLE A4. Least detectable true changes in geometric mean abundance of spottail shiners. See Table A3 for explanation. c/p Comparison of 1 pre- operational yr with 1 operational yr ; n = 56, V = 112. .90 .95 1.53 1.59 1.47 1.53 1.43 1.49 1.38 1.43 Comparison of 2 pre- operational yr with 2 operational yr ; n = 112. 224. .90 .95 1.35 1.38 1.31 1.35 1.28 1.32 1.25 1.29 ,01 .025 .05 .10 15 TABLE A5. Least detectable true changes in geometric mean abundance of alewife. See Table A3 for explanation. 7P Comparison of 1 pre- operational yr with 1 operational yr; n = 56, V = 80. ,90 ,95 Comparison of 2 pre- operational yr with 2 operational yr; 112, V = 224. n .90 .95 .01 .025 .05 .10 1.79 1.70 1.63 1.56 1.90 1.81 1.73 1.65 1.51 1.45 1.41 1.36 1.57 1.51 1.47 1.42 TABLE A6. Least detectable true changes in geometric mean abundance of rainbow smelt. See Table A3 for explanation. =/P Comparison of 1 pre- operational yr with 1 operational yr; n = 56, V = 112. Comparison of 2 pre- operational yr with 2 operational yr; n = 112, V = 224. .90 .95 .90 .95 1.62 1.69 1.40 1.44 1.54 1.62 1.36 1.40 1.49 1.56 1.32 1.37 1.44 1.50 1.30 1.33 .01 .025 .05 .10 16 TABLE A7, Least detectable true changes in geometric mean abundance of trout-perch. See Table A3 for explanation. 7P Cosnparison of 1 pre^ operational yr with 1 operational yr ; n = 40, V = 80. Comparison of 2 pre^ operational yr with 2 operational yr ; n = 80, V = 160. .90 .95 ,.90 .95 1.86 1.98 1.54 1.60 1.76 1.87 1.48 1.55 1.68 1.78 1.44 1.50 1.60 1.69 1.39 1.45 .01 .025 .05 .10 contributed by each year, giving a total of v = 80, On the right side of the table, 2 yr of preoperational data are compared to 2 yr of operational data. In each 2-yr period there will be 80 observations at the Cook Plant; hence n =80. As before, 40 degrees of freedom will be contributed to the error standard deviation per year; hence v = 160. The computation of this last value can be summarized: 2 areas x 5 month x 2 depths x 2 times of day X 4 years x (2 replicates - 1) = 160. An exactly analogous procedure is used to derive the values of n and v for the 7-Tnonth data matrix used to analyze alewife., spottails and smelt. To return from the transformed difference 5 to the original data, the following derivation is needed. Let fx be the true preoperational mean abundance in fish per trawl; its transform is gj = log (f ^ + 1) . The operational mean abundance is f2; its transform is g2 = log(f2 + 1). Let 1) = g2 ~ gj^ be the difference between the two transformed quantities. Next, form the ratio of f2 + 1 and fi + 1 and take its logarithm; log f2 + 1 f^ + 1 = log (f ^ + 1) - log (f.i + 1) g2 = gi = D Thus (f2 + l)/(fi + 1) = 10^. This is an identity that holds no matter how large the change may be. Next, we ask what values the ratio (f2 + 1)/ (fj^ + 1) must assume in order that the transformed quantity D will exceed the least detectable true difference S, Since the test is two-tailed, the change will be detectable whenever the relation lDi:>, ■y 6 holds, that is. whenev€>r (f2 + l)/(fx + 1) > 10^ or < 10"'^, Thus the test can detect either an Inci-ease or a decrease in the abundance after opesration starts. If one adheres to the 0.01 significance level (6) as was chosen for 1973 data and sets P = .95, a single year of data after start of thermal 17 discharges from Cook Plant (1975) should be sufficient to detect approxi" mately a two-fold increase or a 50% decline in relative abundance of yellow perch, expressed as geometric mean number per trawl haul, near the Cook Plant (Table A3). The other four species have IDTCs ranging from 1.59 to 1.98 (Tables A4-7). When a second year of operational data (1976) is added to the design matrix, LDTCs become even smaller. If variability of the data remains about the same as it was in 1973 ^ the existing experimental design should be able to detect changes as small as a 1.61-fold increase or a 1/1.61-fold decrease in yellow perch abundance near the Cook Plant (°^ = .01, P = .95, Table A3) or even finer differences if one accepts a lower «; and P. Again, all other species considered had smaller LDTCs than yellow perch; the LDTC of 1.38 for spottail shiners is the smallest value estimated for an «: = .01 and P = .95 (Table A4). Such comparisons of Cook Plant operational data will ultimately be made with both Cook Plant preoperational data (the temporal control) and Warren Dunes data (the spatial control) . Comparable calculations made with the completed data matrix may give slightly different values for the LDTCs. The LDTCs presented above are considered to be reasonable approximations. Results of the foregoing analysis are most encouraging and support the contention that the experimental design is adequate, at least, to detect acute impacts of Cook Plant discharges upon fish populations. However, someone or some agency must decide what constitutes a damaging change in a fish species population. There are no quantitative guidelines in the latest draft of proposed guidelines for administration of the 316(a) regu- lations, which are meant to decide which particular thermal discharges are not harmful to fishes (U. S. Environmental Protection Agency 1974). Apparently, detected changes in a population will be judged when found, and ultimately a legal precedent will be established. In the meantime, the least detectable true changes computed herein (1.38-1.61) can be judged. If they are determined to be inadequate, the Cook Plant sample program can be either intensified or extended to hopefully meet the desired criteria. However, as noted earlier, intensification is limited by a desire to avoid overfishing and depletion of the fish community being studied. JUSTIFICATION OF AjNOVA FACTORS The ANOVA factor AREA, which provides the primary spatial control for detecting impacts of Cook Plant heated effluents, was the only factor not entering into significant interactions for all the species considered. AREA had no interactions for yellow perch (Table A8) and main effects re- lated to AREA were insignificant (P<0,01) for all species except alewife; this is indicative of the generally small differences between Cook Plant and Warren Dunes. Thus when the Cook Plant begins operation, the factor AREA should provide a reasonably sensitive test of fish population changes in the study areas. 18 TABLE A8. Comparison of the highest order of significant (p>0.01) inter- action between ANOVA factors for the 5 raost abundant species in 1973 trawl catches for Cook Plant study areas « Values are based on 4-way ANOVA' s, results of which are presented elsewhere in this report. ANOVA FACTOR (and highest order of interaction) SPECIES Spottail Alewif e Smelt Yellow perch Trout-perch AREA MONTH DEPTH TIME 3rd 3rd 3rd 3rd 2nd 2nd 2nd 2nd 3rd 3rd 3rd 3rd none 1st 1st 1st 2nd 2nd 2nd 2nd The ANOVA factor MOOTH is necessary, as most species were found to make large-scale seasonal migrations in and oxit of the study areas, and different species of fish utilized the study areas during different months. Like- wise the factor DEPTH is necessary; variation in the system from onshore- offshore movements and depth preferences was often considerable, and to ignore differences between samples taken in 6.1 and 9,1-m depths would increase least detectable changes. The value of the ANOVA factor TIME is best exemplified by trout-perch, a nocturnal species; samples taken only in the day would greatly under- estijnate trout^-perch abundance. Interactions of TIME with other ANOVA factors can result from daily activity cycles of various species and it is useful to consider resulting variation in the system. The ANOVA factor YEAR, which has only one level, 1973, complete, is needed as it Is known that fish populations can undergo large changes from year to year. It is necessary to factor out variation due to natural fish population changes from that which might result from Cook Plant heated effluents. To accomplish the goal of assessing Impact of Cook Plant oper- ation. It is imperative to evaluate main effects and interactions for both YEAB. and AREA. GILLNETS Gillnets are passive fishing gear which are selective for certain species and sizes of fish (Carlander 1953; Heard 1962). Several factors are responsible for bias that analysis of glllnet catches will necessarily entail. Most importantly, two Interacting mechanical considerations largely determine a catch: 1) size range of mesh sizes along a particular 19 net, and 2) morphology of fishes that inhabit an area. Many papers in the literature have dealt with the effect of mesh size on selection of fish. Catch in any particular mesh size is correlated most closely with girth of the fish (Berst 1961; McCombie and Fry 1960). Average sizes of our gilled fish were greater than sizes of fish caught in other gear types used in the study. No YOY of any species were caught in our gillnets. Morphology is another determinant of the catch from gillnets (ctenoid fish, e.g. yellow perch, Bagenal 1972), and heavily toothed species, such as trout, smelt and salmon are particularly susceptible to gillnets due to easier entanglement in the gillnet mesh. Spinous rays on carp and catfish also result in greater catch rate. Behavioral characteristics are other variables which influence the catch from gillnets. Movement of fish and the associative pattern of grouping of individuals of any species or assemblage of species will determine the quantity of each species caught (Heard 1962; Van Oosten 1935). Our gill- nets, 2-m deep, are set on the bottom; thus we might expect a greater abundance of demersal fish in the catch if they are of sufficient size and morphology to be gilled. Species with strong pelagic tendencies such as the alewife will be captured in bottom-set gillnets in numbers which under- estimate their actual abundance. Although bottom-set gillnets caught many alewives in our study area, data from Point Beach demonstrated that surface gillnets in shallow areas caught nearly twice as many alewives as did bottom sets (Wis. Elec. Power Co. and Wis. Mich. Power Co. 1973). Catches in gillnets set obliquely surface to bottom in deeper areas off Saugatuck show that the vertical distribution of alewives is highly variable, but that at times the species is rather uniformly distributed at all levels in the water column (unpublished data, Great Lakes Fishery Lab., U. S. Fish and Wildlife Service). Gillnet catches also depend upon fish mobility and the nature of these movements. Mobility is influenced by temperature. During very cold periods most fish move slowly, if at all, and we can infer that an individual fish has a lower probability of being captured when it is relatively immobile. Very high temperatures most likely have a similar diminishing effect with respect to mobility. Standard series gillnets were all set parallel to shore and thus detect more effectively onshore-offshore movements than longshore migrations. The one perpendicular set, station A, did illustrate that longshore movement, especially in salmonids, does occur. Larger fish may move more than smaller ones due to greater foraging requirements, which results in proportionally larger catches (increased selectivity) of these larger fish (Latta 1959) . Watt (1956) noted that increased movement as a function of length should be considered in setting up models involving different age classes. Pulling and setting of the nets may overlap peak, activity periods of crepuscular fish, e.g. yellow perch (Herman et al. 1969) and spottails (Griswold 1963). Thus any inferences pertaining to day vs. night abundance in the Cook Plant area may be tenuous for certain gillnetted species. Finally, schooling patterns of fish influence gillnet catches; highly contagious distributions result in greater variability of catch data (Moyle and Lound 1960; Bagenal 1972). From these considerations it is obvious that inferences concerning species composition and their relative size composition would be In serious 20 error if not supplemented with trawling and seining data. Despite the bias of gillnets, they are valuable indicators of the presence of larger fish in the area. Trawls and seines of the sizes used in this study are notoriously inefficient in the capture of larger fish, particularly salmonids , Since gillnet sets were not replicated in this study, catch data are not generally amenable to parametric analysis of vai'iance without pooling or using an interaction mean square as the denominator of calculated F values,, both of which require assuiaptions. Bagenal (1972) demonstrated that many replicate gillnet sets are required to obtain reliable raean catches. In his example six gillnet sets would be needed for pike to obtain geometric mean catches with confidence iiiterv^al limits of the mean times 2 and the mean divided by 2 at the 0.05 «; level. Thus in terms of our study, to test for differences between Cook Plant and Warren Dunes we would need to pool day and night gillnet sets and/or 6,1-m and 9=l-m sets to get an estimate of error variance. However, both pooling strategies require; the assximption that there are no differences between day and night catches or between 6.1 m and 9.1 m. At the present., such assumptions are unwarranted. If at a future date we decide that pooling is justified, pariaiaetric AKOVAs may be included in next year's report. As a first approximation in our analysis of gillnet data, two non- parametric tests were used to test for differences between areas. Moyle and Lound (1960) concluded that nonparametric tests were of greater value when the number of net sets is small and fish of a particular species are most often taken in the nets. The Mann-Whitney TJ test for two sample cases and the Kruskal-Wallis test (a further development of the Mann- Whitnej'' tests for K samples) were used. Both tests assume that samples are randomly selected from their respective populations and that each observation in a sample, as well as between samples., is independent (Conov€;r 1971) . No tests were made between day and night because day and night codes were not provided for the data matrix. These tests will be included next year. BEACH SEINES Beach seines sample the most variable habitat of the inshore regions (the inmiediate beach zone) . Like gillnets there are a number of biases attributable to gear selectivity, but none of these contributes as much to the variability as habitat variability and differential use of the beach zone bj' the species assemblage in the study areas. Habitat variability encompasses all those factors which affect size of the area swept by the seine. High winds, waves and current alter beach habitat as well as efficiemcy of beach seines. Resultant shifting of nearshore sand bars due to these effects alters maximum distance from shore which can be effectively sampled by seining. Differing temporal use of the beach zone for spawning and recruitment of larval fish not only illustrates the com- plex ecology of the beach zone but also introduces "noise" into the data. Although the experimental design was intended for parametric analysis, excessive zeros in the data matrix give high skewness and kurtosis values 21 to the catch frequency distributions. These distributions violated the normality assumptions of parametric statistics; consequently the Kruskal- Wallis test was used to analyze the data. PLANKTON NETS Based on the experiences and advice of L, Wells (personal communication. Great Lakes Fishery Lab., U. S. Fish and Wildlife Seirvice) , nylon No. 2, 1/2-m diameter plankton nets were used to monitor fish larvae populations in the Cook Plant study area. Ease of handling and catch efficiency were the major criteria in selecting the i/2-m diameter net. A larger diameter net would be too long and cumbersoHje for both the beach zone and for use from the R/V MYSIS. Smaller nets filter less water and thus are undesirable. Efficiency of a plankton net (percent of the water that passes through the net) is a function mainly of its mesh size- Size of larval catches depends on current velocity, planktonic concentrations and behavior characteristics of fish larvae. The No, 2 net has 351 njicron openings (0.351 tum) which should prevent most larvae and eggs from escaping. Spottail shiner eggs (0.6 to 1.0-mm diameter) were the smallest eggs observed for any species common to the study area, thus the No. 2 net should be adequate. Decreasing mesh size poses problems of clogging. A No. 5 net, used in our 1972 sampling, often clogged with algae preventing filtering of water. Similarly, a large algal bloom in October 1973 resulted in net clogging in our No, 2 net. Should this problem worsen, a larger mesh size may be required. Differing behavior characteristics of fish species in the inshore zone cause bias in plankton net catches. Numbers of demersal species such as spottails, sculpin and trout-perch were probably grossly underestimated in 1973. Extensive sled tow sampling was performed in 1974 to overcome this discrepancy. Another confounding factor concerns diel differences in numerical abundance. We have found that at least two species, smelt and alewife, exhibited diel vertical and possibly horizontal migrational patterns. Thus day sampling, when larval smelt are in the lower strata, would greatly underestimate their abundance. As fish length increases, avoidance reactions to the plankton net increases (gear efficiency varies inversely as fish mature) . Few fish are caught beyond a certain species' specific critical length. For species whose spawning periods are short (e.g. smelt), this poses no problem, since most of the larvae will be within a certain size range, then when smelt larvae are no longer caught one can conclude that the species' critical length has been reached by that year class of smelt, beyond which they are seldom caught in plankton nets. However, for species whose spawning period is more than a month (e.g. alewife) there are problems associated with varying size classes, and possibly an underestimation of total numbers of fish larvae results. This occurs because the net is only sampling the newly hatched and smaller of the total population of alewife larvae present. Interpretation problems then follow. Net avoidance results in an interim length interval where alewives are large enough to avoid plankton nets yet too small to be captured by other gear types. 22 Extensive sampling was also performed in the beach zone (0-2 m) in 1973. This highly variable habitat has not been sampled adequately in the past, and knowledge of its usage by fish laxrvae may prove valuable when plant operation commences. Strong current effects are particularly pro- nounced in the beach zone where results of strong winds are eventually felt. As volume of water sampled is a function of both current and velocity of the net in the water, we chose to do two larvae tows in opposite directions in 1973 to average gear efficiency effects due to current. In 1974 approximate current velocity was determined using a drift bottle and simultaneous duplicate tows were made against the current, permitting us to control effects due to current over the sampling season. This is in contrast to trawling methodology where current is not known and replicates are taken in opposite directions. Fish larvae samples were not replicated on the E./V MYSIS due to time and cost constraints. Limited statistical testing can be performed by pooling depths, and sometimes stations, to determine various treatment effects. Seasonal abundance changes of fish larvae necessitated deletion of months when few or no larvae were present for accurate statistical test- ing. Finally, flowmeter methodology presented numerous problems but proved invaluable In quantification of numbers. The large range and high variabil- ity in flowmeter readings (12-1900) in these 5-min tows necessitates use of the flowmeter for standardizing tow volumes. Alternative methods of measuring volume sampled require sophisticated and costly equipment. Whereas if one is willing to accept upper level contamination by fish lar^rae in tows performed at lower depths (a problem easily corrected by calculation) 5 a reliable, consistent and repeatable result can be obtained. 23 SECTION B SPATIAL AND TEMPORAL DISTRIBUTION, GONAD CONDITION AND TEMPERATURE-CATCH RELATIONSHIPS OF ADULT AND JUVENILE FISHES Frank J. Tesar, David J. Jude, Timothy J. Miller, John A. Dorr III and Paul J. Rago INTRODUCTION Our first step in monitoring the biology of fishes in Lake Michigan was establishment of appropriate sampling stations in the vicinity of the Cook Plant and at the reference location Warren Dunes. To establish a data base- line during the preoperational period, selected station fishing data were designated as the standard series, other netting was termed supplementary, and when all fishing activities were combined this was called total fishing efforts or total samples. These stations were established to determine the spatial and temporal distribution of fish populations in the vicinity of the Cook Plant. From 1973 on, the stations will be sampled extensively in an attempt to detect any changes in the numbers and species of the resident and migratory populations. The objective of this section is to provide data to which pos toper at ional data can be compared. It includes a discussion and elaboration of the biology of each species established from our data and literature reviews conducted to date. The section utilizes results and statistical tests discussed in Section A. Our results are organized into four major parts. The first part discusses the number of species we captured and compares this with other species lists from nearby areas. It also attempts to depict the broader aspects of fish movement, distribution and occurrence in the inshore zone of Lake Michigan, with emphasis on species complexes. The second part is an elaboration of what species are and are not caught by our various gear, and points out that because of the great selectivity of these various nets, different net types are needed to delineate species assemblages. The last two parts concern individual fish species. First is a detailed discussion of the five most abundantly caught species. Included are statistical analyses of the seasonal, spatial and diel distribution, length-frequency histograms, temperature-catch relationships from field- caught fish, gonad development data, spawning times and some comments on disease. The last part discusses briefly the remaining less abundant species, including sizes of fish caught, seasonal, spatial and diel be- havior patterns, gonad development and spawning times if possible, and any diseases noted. 24 We have attempted to characterize the "normal" distribution, behavior and abundance of fish populations in the area as well as to note any abnormalities, such as diseases in fish or aberations, natural or unnatural, in station catches, so that our ability to detect possible differences in the postoperational phase will be maximized. Such future sampling will help clarify just how fruitful our efforts in the preoperational phase have been. METFxODS LOCATION OF SAMPLING STATIONS Seven permanent sampling stations were established in Lake Michigan off the Cook Plant (experimental area) and off Warren Dunes State Park (control area) (Fig. Bl) . Routine samples taken at these stations are referred to in this report as the standard series. At the Cook Plant there were two beach seining stations (A, B) , one north and one south of the plant, and two offshore stations (C, D) at 6.1-m (20 ft) and 9,1-m (30 ft) depths where trawl and gillnet samples were taken. At Warren Dunes there were one beach seining station (F) and two offshore stations (G, H) at 6.1-m and 9.1-Hi depths for trawl and gillnet samples. Offshore stations at 6.1-m (C, G) and 9.1-m (D, H) were established to correspond to location of the Cook Plant's three intake structures, 671 m (2200 ft) offshore in 9.1 m of water and the two discharge structures 354 m (1160 ft) offshore in 6.1 m of water. Although the standard series had priority, occasionally there was time to take supplementary trawl or gillnet samples at the standard stations or at other stations (E, M, L; Fig. Bl) established for this purpose. All methods used at supplementary stations were identical to those used at standard series stations except the setting of gillnets perpendicular to shore at station A in 1,5-3.0 m (5-10 ft) of water. Substrate at seining stations A and F during 1973 was sand with some gravel, which is typical of beaches in southeastern Lake Michigan. Distinct sand bars parallel to shore were present during most sampling months. Station B, just south of Cook Plant, differed from the other two seining stations in lacking a well-developed sand bar; the bottom was flat and shallow for a considerable distance due to the sand replenishment program south of the safe harbor which had been carried on by the qompany. Fish catches at station B reflected this difference. Substrate at all offshore stations — Gj, D, G. H — was sandy with coarser sands at Warren Dunes (see Seibel and Ayers 1974 for a detailed discussion of substrates in the area) . Slope of the bottom off Cook Plant was steeper than off Warren Dunes, thus trawl and gillnet samples from Warren Dunes v/ere taken further offshore. 25 ST. JOSEPH RIVER LAKE MICHiGAM BEACH SEINE STAT80NS A,B,F 6.1 M GILLNET AND TRAWLING STATIONS C,G S.IM GILLNET AND TRAWLING STATIONS D,H SUPPLEMENTARY STATIONS S GILLNET AND TRAWLING) A,£,M,L ST. JOSEPH iiir BENTON "ARBOR oSTEVENSViLLE ^QgRAND 86"30' ^^ DONALD C. COOK ■^i> NUCLEAR POWER PLANT .• J (UNDERWATER INTAKE AMD DISCHARGE STRUCTURES SHOWN) ,WECO BEACH BRIDGMAN MICHIGAN V/ARREN DUNES STATE PARK METERS H 1 1 1- — « 5000 FIG, Bl . Map of the Cook Plant and Warren Dunes study areas in southeastern Lake Michigan 1973 j only schemata of underwater structures are shown . 26 GEAR Duplicate 10-min bottom tows were taken monthly both day and night at the four offshore stations (C, D, G, H) , using a semi-balloon, nylon trawl having a 4.9-m (16 ft) headrope and a 5.8-m (19 ft) foo trope. The body and cod end of the net were composed respectively of 3.8-cm (1.5 in) and 3.2-cm (1.25 in) stretch mesh, while the cod end interliner was 1.27-cm (0.5 in) stretch mesh. All trawl hauls were made at an average speed of 4.8 km/hr (3 mph)>i.e., at a fixed rpm using the University of Michigan's R/V MYSIS. The trawl was towed parallel to shore following Stl^-m and 9.1-m depth contours; one replicate was taken from south to north and the other north to south. Nylon experimental gillnets 160.1 m x 1.8 m (525 ft x 6 ft) were set at the offshore stations (C, D, G, H) at least once per month for about 12 hr during daylight and 12 hr during the night. Nets were composed of 12 panels of netting as follows: 7.6-m (25 ft) sections of each of the following mesh sizes (bar measure) — 1.3 cm (0.5 in), 1.9 cm (0.75 in) and 2.5 cm (1.0 in); 15.3-m (50 ft) sections of mesh sizes 3.2-7.6 cm (1.25-3.0 in) by 0.3-cm (0.25 in) intervals; and a final 15.3-m section of lO-cm (4 in) mesh. All gillnets were set parallel to shore on the bottom, except supple- mentary sets at station A which were set perpendicular to shore. Beach seining was conducted during periods of reduced wave height and current using a nylon seine 38.0 m x 1.8 m (125 ft x 6 ft) with a 9.1-m (30 ft) bag; the entire seine had 0.5-cm (0.25 in) bar mesh. The seine was first stretched perpendicular to the shoreline and then pulled parallel to shore a distance of 61 m (200 ft). Duplicate, non- over lapping samples were taken in this manner both day and night once each month at seining stations (A, B, F) . The seine was pulled against the current or southerly when no current was detectable. When the current was too strong to seine against, seining was done with the current. MISSING SAMPLES In summary, the standard monthly sample series consisted of 16 trawl hauls, 8 gillnet sets and 12 beach seine hauls. While it was hoped that standard series fishing could be performed every month of the year, this was not always possible due to equipment failure, inclement weather and ice. Following is a summary of samples missing from the standard series in 1973 (missing observations in parentheses) : 1. January - all trawls (16), gillnets (8), seines (12) 2. February - all trawls (16), day and night gillnet sets at G and H, day gillnet sets at C and D (6), night seines at A, B, F, day seines at F (8). 3. March - all trawls (16), day seine at B (1) day and night seines at F (4) 4. April - day trawl at G (1) 27 5. July - day seine at F (1) 6. September - night trawl at G (1) 7. Ncwember - all trawls (16), night gilinet sets at G and H (2), night seines at F (2) 8. December - all trawls (16), all gillnets except night gilinet at C (7), all seining (12) PHYSICAL AND LIMNOLOGICAL DATA Each time a particular fishing gear was used at a station, weather and other physical parameters were recorded (Tables Bl-4) , Wind direction and speed were obtained using an anemometer when aboard the R/V MYSIS and estimated at other times. Wave direction and height were estimated visually. Water temperatures for trawl, gilinet and seine samples were taken at the surface and fishing depth using a battery-operated telethemnometer . A glass mercury thermometer was sometimes used during beach seining. Current at beach stations was estimated by measuring the time it took a neutrally buoyant object to travel 3.1 m (10 ft). Secchi disc readings were taken during daytime each time a fishing gear was used, LABORATORY ANALYSIS OF FISH Fish from seines, gillnets and trawls were processed fresh when time permitted, and otherwise put in plastic bags and frozen at the Cook Plant as soon as possible (usually within 2 hr) and stored in freezers. Trawl catches were frozen immediately on board the R/V MYSIS. At the laboratory, bags of fish were thawed as needed, separated by species, then grouped according to size classes. When large numbers of a particular size class were present, a subsample was randomly selected and a mass weight of the remaining group taken. Total length (to nearest mm, fin pinched), weight (to nearest 0.1 g using a PIOOO Mettler balance), sex, gonad condition, fin clips, lamprey scars, evidence of disease and parasites were recorded for all fish except those mass weighed. Large fish and fish in mass weights (>1000 g) were weighed with a hanging scale spring balance (K023G Chatillon) to the nearest 25 g. Gonad condition was described according to five stages of development: 1) underdeveloped, 2) moderately developed — for females, eggs discernible but not fully ripe, 3) ripe, 4) ripe-running — sex products exiting with application of moderate pressure, 5) spent. Other categories included: 6) fish decomposed or mutilated (traveling screen catches at times) so that sex was impossible to determine, 7) unable to ascertain sex on an adult fish, 8) immature. Scale samples were also taken from selected species (alewlfe, rainbow smelt, perch, coho, chinook, lake trout) but have not yet been analyzed. All fish were identified to species using Hubbs and Lagler (1964) , Trautman (1957) and Eddy (1957), when necessary with the exception of the genera Coregonus (subgenus Leuaiahthys) and Cottus. 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To confound the problem, it has been suggested that various species may be introgressing (Wells and McLain 1973). The only adult Leua-iahthys that could be identified positively was the lake herring, C. avted-l. Other adult Leuoiahthys and juveniles under 150 mm were pooled as unidentified coregonids (code XC) . This latter group was probably made up of C. hoyi (bloater) and a few juvenile C artedij, as these are the most abundant species of Leuaiehthys in southeastern Lake Michigan (L. Wells, personal communication. Great Lakes Fishery Lab., U. S. Fish and Wildlife Service). Difficulties were encountered distinguishing between Cottus oognatus and Cottus bairdi, due in large degree to inexperience on the part of the identifiers. Presently, with better identification references (McAllister 1964; D. Rottiers, personal communication, Great Lakes Fishery Lab., U. S. Fish and Wildlife Service), study of identified specimens and greater experience, identification difficulties have been eliminated. It is probable that of the specimens originally identified as C, hai-vdiy the majority were actually C. oognatus, as this is the predominant species in samples taken from the study areas. DATA M^JIIPULATION AM) CALCULATIONS Data from fish captured by seine, gillnet and trawl were recorded directly on a 75-column coding form. For each fish the following information was recorded, one fish per line: date and time of sample, type of gear, night or day series, station, water temperature at fishing depth where gear is used, a species code, a unique incrementing number, length, weight, sex and gonad condition. Special subsampling columns were used to designate the fish sampled from a larger group as well as coltmms to record the total weight of fish not examined (mass weight) . A program was written to search the data for subsampled lots and then calculate the number of fish processed, the mean weight of those fish, and the number of fish present in the mass of fish not examined. The number of unsampled fish was assigned to length intervals proportionally, based on the number of measured fish found in len^jth intervals. Fish were divided visually into many size classes when originally subsampled, to minimize error associated with this reconstruction of sample length-frequencies. Fish data were keypunched, verified and then read onto disk files and tapes. For the bulk of our numerical analysis we used the Michigan Inter- active Data Analysis System (MIDAS) which was developed by the Statistical Research Laboratory at the University of Michigan. MIDAS has very efficient programs for collating data, calculating statistics and depicting graphical relationships (Fox and Guire 1973). From MIDAS, we obtained summary statis- tics and histograms on sex ratios, seasonal gonad conditions, temperature- catch relationships, length-frequency histograms and length-frequency histo- grams of stomach-sampled fish. It should be made clear that length-frequency histograms for the five major species included all fish captured. Thus for trawls and seines the 43 numbers of fish in each inteirval represent the combined numbers from both replicates, while for gillnets the numbers represent the corrected number per 12 hr in each interval. Other graphs usually depict mean catch, so that to compare these with length-frequency histograms their numbers should be doubled. Months when no or very few fish were caught were sometimes eliminated from length-frequency histogram figures. Seining and trawling data were replicated (two hauls per station) ; in cases where only one of the two replicates was present, catch was doubled to facilitate comparisons. Gillnet catches were adjusted to approximate numbers caught per 12 hr by making the assumption that catch was a linear function of time. In the field, nets were set for as close to 12 hr as possible, but the range for length of time the standard series gillnets were set was from 2.0 (storm came up) to 17.9 hr and averaged 9,5 ± 0.41 hr (N = 72). It is known that the foregoing assumption is not completely valid as gillnet catches per- unit-time might be expected to decrease as the net fills with fish, but the increased accuracy probably could not justify the cost of determining a precise relationship for each species. Temperature-catch statistics for individual species were stratified by gear type (standard series only) and averaged over the number of stations. Standard error also was calculated and shown on the figures. The output consisted of frequency histograms of the mean mnnber of fish caught by gear type over 2 C intervals. Water temperature used was recorded from the bottom where the particular gear was used. The following numbers of trawls, gillnets and seines were used: 110, 98 and 84 respectively in this evalua- tion. One should note that inferences drawn from these histograms are confounded not only by gear selectivity but also by seasonal presence of size classes. For example, adult smelt are generally present in the area only during spring, when water temperatures are relatively cold, approxi- mately 8 C. Later in summer, when water temperatures are around 20 C, large numbers of young-of-the-year are recruited. Since the histograms are not stratified by size class, one should be careful when evaluating temperature relationships for each species. Numbers of fish caught within each temper- ature interval is a function of the biology of each species: age, temper- ature preference and acclimation temperature (Cherry et al. 1974). Present refinements in data analysis will permit temperature-catch histograms to be further stratified by size class and month. DEFINITIONS For purposes of this report a number of definitions were made. Fish larvae were arbitrarily designated as any fish 2.54 cm or smaller in total length, so that all fish greater than this will be treated in the adult and juvenile section. Young-of-the-year was abbreviated as YOY and refers to newly hatched fish in their first year of life. In this same context, age class is sometimes used in discussions of the literature and is synonymous with YOY. Age classes 0, I, II, III etc. are mentioned occasion- ally and refer respectively to fish in their first year of life, second 44 year of life, etc. Fish change year classes in January, Other ambiguous terms used in this report are: offshore - usually refers to water depths greater than 9,1 m. In some instances when discussing seine catches, offshore indicates water depths greater than 2 m. Inshore - usually refers to water depths less than 9.1 m to shore. Beach zone = surf zone - water depths from 2 m to shore, Diel - refers to the 24-hr day. Diurnal - activity by daylight, occurring every day; opposite of nocturnal. RESULTS AND DISCUSSION DIVERSITY AND DISTRIBUTION OF FISH SPECIES IN THE STUDY AREA Between May 1972 and January 1974, 45 fish species representing 16 families were captured from Lake Michigan in the vicinity of the Cook Plant (Table B5) , Five of these species were captured only in 1972, seven other species were first encountered in 1973, and 32 species were captured during both years. Five species of fish have been taken only from the traveling screens from Cook Plant's intake system, including one encountered for the first t:une in January 1974. Species composition of samples in the vicinity of the Cook Plant appears to be more diverse than numbers of species sampled near the following power generating facilities on Lake Michigan: Ludington Pumped Storage Project, 24 sp. (May 1973); Bailly Generating Station, 17 sp, (April 1973) and Zion Station, 24 sp, (December 1973). Fifty-five species were caught near Palisades Nuclear Power Plant (December 1973) , Pooling our data with that from other studies, we estimate that the actual ntmiber of species occurring in the area of Lake Michigan near the Cook Plant is about 70 or 75, but some are extremely rare or transients that normally inhabit streams, inland lakes or protected bays. Patterns of species movements as reflected by standard series catches (Table B6) illustrate the complexity of a natural system. Spatial and temporal fish migrations cause differential utilization of the study area throughout the year. As samplers of mobile animal populations, we are faced with the inherent problem of making inferences about population dynamics that are derived from static samples. Hopefully, our extensive sampling program of trawls, gillnets and beach seines will strengthen our inferences on adult fish movements. Coupled with our fish larvae sampling, we should be able to characterize the biology of many of the species inhabit- ing the Cook Plant area. The following discussion will attempt to typify the seasonal distribution of species associations that variously inhabit the study area (Table B6) . To avoid redundancy with the ensuing individual species accounts, only broad generalizations will be made on species distributions and factors influencing these distributions. Four major factors contributed to the patterns of species association observed throughout the year — temperature, spawning activity, diel activity and upwelling. Temperature may be the most imjjortant environmental parameter affecting our sampling. Since fish are poikilotherms, their behavior is dominated and liimited by water 45 TABLE B5. Scientific name, common name and abbreviations for all species of fish captured from Cook Plant study areas in southeastern Lake Michigan from May 1972 through January 1974. Fish were taken with netting gear unless other- wise noted. Names assigned according to Bailey et al. 1970. An X denotes presence in that year. Scientific and common name Abbreviation 1972 1973 Acipenseridae Aevpenser fulvesaens Rafinesque Lake sturgeon LG X Amiidae Amia aalva Linnaeus-^ Bowf in BF Clupeidae Alosa pseudohaTengus (Wilson) Alewif e Dovosoma aeped-ianum (Lesueur) Gizzard shad AL GS X X X X Salmonidae Coregonus artedii Lesueur^ LH Lake herring or Cisco Coregonus alupeaformis (Mitchill) LW Lake whitefish Coregonus hoyi (Gill)^ BL Bloater Prosopium oyl-indraaeum (Pallas) RW Round whitefish Onoorhynohus kisutoh (Walbaum) CM Coho salmon Onoorhynahus tshawytsoha (Walbaum) CH Chinook salmon Salmo gairdneri Richardson^ RT Rainbow trout Salmo trutta Linnaeus BT Brown trout Salvelinus namayaush (Walbaum) LT Lake trout X X X X X X X X X X X X X X X X X Osmeridae Osmevus mordax (Mitchill) Rainbow smelt SM X Umbrldae Umbra timi (Kirtland)^ Central mudminnow MM X Esocldae Esox tuoius Linnaeus Northern pike NP X 46 TABLE B5 continued. Scientific and common name Abbreviation 1972 1973 Cyprinidae Couesius ptumbeus (Agassiz) LC Lake chub Cyprinus oarpi-o Linnaeus CP Carp Notemigonus opysoleuaas (Mitchill) GL Golden shiner Notropis athevinoides Rafinesque ES Emerald shiner Notropis hudsonius (Clinton) SP Spottail shiner Pimephates pvomelas Rafinesque PP Fathead minnow Rhiniohthys Qataraotae (Valenciennes) LD Longnose dace X X X X X X X X X X X Catostomidae Cavpiodes oypr-inus (Lesueur) Quillback Catostomus aatostomus (Forster) Longnose sucker Catostomus cormer'soni (Lacepede) White sucker Moxostoma maarolep-Cdotvim (Lesueur) Shorthead redhorse QL LS WS SR X X X X X X X Ictaluridae Ictalwms metas (Rafinesque) Black bullhead latalupus natat-ts (Lesueur) -^ > ^ Yellow bullhead latatupus punatatus (Rafinesque) Channel catfish BB YB CC X X X Percopsidae Pevcopsis om-isaomayous (Walbaum) Trout-perch TP X X Gadidae Lota lota (Linnaeus) Burbot BR X X Gasterosteidae Pungitius pungitius (Linnaeus) Ninespine stickleback NS X X 47 TABLE B5 continued. Scientific and common name Abbreviation 1972 1973 Centrarchidae Ambloplites rupestris (Rafinesque) RB X Rock bass Lepomis ayanellus Rafinesque GN X X Green sunfish Lepomis gibbosus (Linnaeus) ^ PS XX Pumpkins eed Lepomis maaroohirus Rafinesque BG X Bluegill Miaroptevus dotomieui Lacepede SB X Smallmouth bass Mioroptevus salmoides (Lacepede) LB X Largemouth bass Pomoxis nigromaaulatus (Lesueur)^ BC XX Black crappie Percidae Etheostoma nigrum Rafinesque JD XX Johnny darter Pevaa ftavesoens (Mitchill) YP XX Yellow perch Stizostedion vitvevm vitvewn (Mitchill) WL X Walleye Cottidae Cottus baivdi Girard^ MS X X Mottled sculpin Cottus Gognatus Richardson^ SS XX Slimy sculpin 1 Obtained only from the 1.5-cm (3/8 in) mesh basket which receives fish and other materials impinged on the traveling screens during periods of pumped water circulation. 2 Some difficulties in identification were experienced (see text). 3 Two phenotypes present. 4 Captured in January 1974. 48 U X3 C CO 0) CO Oi c ■•H CO CO en •r-l u 01 to ■■o to •t3 C to cn e o • 't-( CO 60 en iH S 60 O o o. til 60 3 3 a 3 •-2 m,-I^Or~•tMr^C^OOO^O^OOvOCT>r-^OOCNCS3^D(»^O^vOr^ 00 o vD m tn •a- CM r-l i-tvOtNCMCMCMrMi-i >-lp-lf»1<7>CNrHOOOO-3--3--3--*rO(MC^CNIr-|.-trHi-lt-l r^vDln0^00■-lr^>-^OOOOOOOOOOOOOO ooooooooo VO O 00 r-i rH V V V V V V V o,-iooooooooooooooooooooooooooooo moomj^noOi-ioo tS I-! CM CM VO m,-<0cMi-ir-i000cM00>nm0000F-(00 c 0) •H ^ J-l to 3 ^-3 •« C AJ 1-1 ,c 0) oc AJ 3 CO to CO G 01 s: ,C jj CO d •H o iw CD in U-< o o tc CD M H (U 0) ,Q ■w e to 3 IS :a n-3-,-(oonOr-4 r-lr^r-lr^vO^^r-l-a^r-IOCMCri OOOrHCMOOOOOOO CM m r-l CT> Pvl r-l ^O ■3-rMO-JrvifnmcMn cy« lA "-a" C7N lO 0> CM 03 \Dr^ino-a-r»r-»oooo>£>ooocMnoo tn— 4— |CMr-4\OC»*) r-l CM r* CM *o r-* cn rH r-inOOOOOOOr-lf-IOOO CMrHmf-^U-lOOCOCMsOmrOCOCOr-lcnCMr^-^vOOlACMCnr-ICMr-IOOt-lOO OcMm<7^^0mc^i CMr-lr-l n r-l 00 -^ cy* *^ to vO r». rH r-l rHsTro-a-r-r^mcNcMooo-a-vOvo^j-oocMinoeMncMOOr-iOr-tOOO mJr-i rHcnr-l rH t-i CM CO CO r-l P^v0CM^0r^C^C0r-IOOlA-*CMr-ltMOC<^CMCMOr-l<3^OOS^-JXi-IPi(flmwafe;UOOtJZS«CJFq^pqpjCdOrJ 1^ en rH e o o o I rH u-1 c CM o cr. c oc cr> c CM •H " 00 r-l cn V£> Q, C r-t e o to •H CO 4J to «3 "TD •H VO CO r-l 4J •H CD E -Q •H X r-l to c CD 00 Q) a) r- x: •r^ S CJ to (X in — ( CM 49 temperature. Many differences in abundance between Cook Plant and Warren Dunes are probably due to differences in local temperature, which in conjunction with Instinctive behavior patterns regulate the timing and extent of spawning activity. Spawning activity accounted for rauch of the monthly variation in numbers of rainbow smelt, trout-perch, perch and alewlfe. Many of the interactions in ANOVA were directly traced to spawning. In general, fish which wintered in the offshore zone began to move inshore in spring. After spawning they generally dispersed more widely into warmer x^ater and with the onset of winter moved back into deeper water. The sequence of spawning appeared to be: April-May, smelt and sculpins; late June-early July, alewife, yellow perch and spottail; July-August, trout -perch, spottail and alewlfe. Ripe lake trout were found in the area in the fall, but no evidence of success- ful natural recruitment has been found anywhere in the entire lake (Wells and McLain 1973). Intertwined with spawning behavior is die! activity which is undoubtedly related to feeding activity. Nocturnal behavior by trout-perch and to some extent by alewlfe and spottail, crepuscular activity of yellow perch and diurnal activity of YOY of most species illustrate the wide variation in temporal activity. Although upwellings are a temperature phenomenon, they are also a mechanical phenomenon. In late summer, large bodies of cooler water displacing the inshore water caused many fish to leave the area (alewife, spottail, trout -perch and to some extent yellow perch) and at least four species to enter (smelt, lake trout, bloater and sculpin) . These four factors overlap in their effects, and determining relationships proved very difficult. Poor weather conditions during December, January -and February limited our sampling to gillnets and a few beach seines. While more extensive sampling would have undoubtedly increased catches, sets that were fished indicate low numbers of fish present during winter. The immediate beach zone is very cold, and fish movement, particularly warm-water species, is very slow when temperature is low. Thus gillnets, which depend on fish movements, and beach seines underestimate fish numbers in winter. Spottails comprised the bulk of the winter catch along with a few suckers, rainbow trout, burbot and smelt. Spottails probably inhabit the study area the entire year. The spring catch was heavily influenced by influx of adult fish seeking warmer water and suitable spawning areas. No trawling was done in March, so our estimates of numbers of smaller fish in the offshore area are probably too low. Few fish were caught in beach seines, probably due to the cold water. Alewife, spottails and smelt respectively were the most abundant species in March. By April the spawning run of smelt was evident from seining and trawling catches. In May, water temperatures had increased and the total body of warm water was larger. Numbers of adults of all prominent species were moderate, indicating dispersal through the warm-water area. Smelt move back into deeper water following spawning. Spottails did not disperse as much as the other species. During June, July and August the bulk of spawning took place and many YOY were recruited, especially In August. The total ntraiber of fish caught 50 in June was third highest for the year. Spawning adults of warm-water species such as the alewife, spottail, yellow perch, trout-^perch and johnny darter crowded within the 9.1-m contour. For most of these species, spawning activity was probably normally distributed about June, extending from May through July. In July most species declined in numbers from the;ir June peaks. Apparently after spawning, adults began to disperse and were not as concentrated in shallower waters. The peak number of coregonids (XC) in July is unexplalnable, but corresponds with the findings of Wells (1968) . The overall high catch of all abundant species in August was influenced by two components. First, newly recruited YOY of alewives, yellow perch and spottail shiners were very abundant in the beach zone. Second, a cold-water upwelling (Selbel and Ayers 1974) apparently forced large numbers of both adult and juvenile smelt into the trawling zone. These combined effects resulted in the highest monthly catches of the year. We concluded that because of the massive effects of upwellings on fish movements, it will be imperative to have continuous accurate water temper- ature data at the Cook Plant. As water temperature declined in the fall (September, October, Novem- ber), most species began their offshore movement into deeper water. In contrast to August and October, beach seining in September caught very few YOY alewife or spottails. High wind and waves decreased the effectiveness of our seining and probably made the beach zone inhospitable for YOY. In conjunction with the Inclement weather during sampling, an ongoing up- welling was forcing the warmer water farther out into the lake. The majority of adults and juveniles probably followed the wann-water body, accounting for the low overall catch. Smelt, a cold-water species, was the most abundant fish caught in September. While some of the formerly most abundant species were caught in low numbers in September, some less abundant species were at their yearly peaks in September. Largest catches of white suckers, emerald shiners and longnose daces were taken in September. Lake trout spawn in late fall and would be expected in great numbers then. White suckers were caught mainly in gillnets and trawls. Emerald shiners and longnose dace were caught in seines during the warmer part of the month. Their presence in abundance in the surf zone is un- exjjlainable, but may be related to the upwelling that occurred. October and November temperatures were more typical of the overall do;imward trend expected in fall. Typical, however, is a precarious word for fall, due to frequent upwellings which introduce high variability in fall temperatures. Nimibers of warm-water species declined from summer peaks because of adults moving offshore, and natural mortality had lowered the numbers of YOY. Lake trout numbers were still high, reflecting the numbers of ripe adults seeking shallow areas for spawning. Alewife numbers declined drastically in November. Apparently the bulk of the population had moved offshore into deeper waters or farther south in the lake. Appearance of gizzard shad in November may be due to southern migrations to warmer waters. SPECIES CATCHES BY GEAR TYPE As with most fishing methods, sampling is biased by degree of efficiency 51 of the gear. Gear we used varied widely in its ability to catch fish. Seines and trawls (active fishing gear) were more effective in catching smaller fish of a given species; larger fish can usually avoid these nets. Gillnets (passive fishing gear) were effective in catching all sizes of fish except very small individuals, but susceptibility is dependent on fish movements, fish morphology and probably time of day. Relative effectiveness of the three types of gear in capturing differ- ent species at Cook Plant and Warren Dunes stations was compared (Tables B7, B8) . Efficiency varied considerably in capturing a given species. Because all sizes are included in the tables, little can be said about gear selectivity for different size groups of a species. Some gear selec- tivity is mentioned in the discussion of individual species. Since a complete standard series of nets was not obtained (see Methods Section, Missing Samples) , some bias toward warmer month catches was unavoidable but not thought to change overall conclusions to any significant degree. Because there was one more seining station at the Cook Plant, actual numbers of fish captured at Cook and Warren Dunes (Tables B7, B8) cannot be compared directly. However, if gear selectivity and efficiency were the same at all stations (there appears to be no reason to refute this) then percentages can be compared and will be discussed below. There were no major differences in percentages of fish caught using the three gear tjrpes during day and night between Cook and Warren Dunes stations (Tables B7, B8). The various gear were equally efficient at catching a given species at the two different areas. Small species (i.e., alewife, spottail, smelt, trout-perch, johnny darter, emerald shiner, longnose dace, gizzard shad and fathead minnow) were caught mainly by seining and to a lesser degree by trawling. Smaller individuals of larger species (i.e., juveniles of rainbow trout, yellow perch and brown trout) were also caught by seining. Larger species (yellow perch, white and longnose sucker, lake trout and burbot) were caught mainly by gillnets. Overall, more species were caught at night than during the day. Prob- ably the fishing gear is more efficient at night, because fish are less able to sense nets and are usually more active at night (depending on species) . Fish may also be more randomly distributed at night than during the day because of spaxjning and foraging activities. Several differences between day and night catches of certain species were quite evident. More alewives were caught during the day than at night, which is especially pronounced in seine data. More spottails were caught in seines during daytime than during night at Cook stations. At Warren Dunes stations more spottails were caught by all gear at night than during the day. More trout-perch were caught at night than during the day, indicating pronounced nocturnal behavior. To show overall composition and predominant fishes caught with the three gear types at Warren Dunes and the Cook Plant, standard series day and night catches were pooled over months (Figs. B2-4) , Alewives 52 0) r-l U 0) 4-1 ^ CO c cfl C (-( CO 4-i Tl tu CO ,C OJ CD 60 •H CO <4-i C to 0) 4-1 o CI) u c cu fl< CD CU C ^J CO OJ CO CD CU CO T3 Z CO 4-1 COt pq w PQ <: H CU C CO 60 •H XI e c a> u u 0)1 Cil -Hi cjI u XI H z ? ai >-' e 3 vO CT^ ty» •-( »o o \0 *a- 1*1 %x> *^ io O O ,-( ON -^ ON O r-4 fNj CNJ QO v£> O p«^ m »X) On rj o* .-H sr m o » m ^7 NO vO CO O .-4 00 r^ O r-l CO r^ On en »A O r^ O u-i O O O en o O O O NO O r~ o r-l o m ON m CO CO iTHO NO CO .-( CJN r-~ tn i-l CM in r^ *^ ^ m CM O O O O o o CNi r*- NO CNj in m r O o^ -^r j-i OJ -Y-l VI E J3 -H ^ f-4 ts C 4) ai a 3 c 0) o kl a e) c Bm Ui Hi s s: a OJ -rl O 0) o. m -3- r-l CO r- -o- r-i m o rH O r-l NO n r-t la in 00 00 CM rn rsi »n rH ON rH O O ^ CTN rH CM »n CO CO CM rH «3- .3^ rH 00 rH «n -J O -3- O CO CM r^ NO rH NO On in rH rH en CM rH rH -a- CM -3 CO CM in en 000 CO o o o o O tr\ O O NO O NO 3 u 01 a a. tu m U O UH C o o tH C u -H ■H C 4J -H a UH C (U iH»^S3x-)SwtaWrJZOooo25:iacJcorJiap< CM U LO NO w u JJ i-H 0) at r-t >j a a 0) 0) t3 rJ u tu 01 LO en H -• CM 53 r-H •? ca C M !-i •u 0) 4-1 13 CO C ca tfl (!J CO 4-1 4-i a 0) o c CO iH rH m •H o 60 CO r. M cn 0) QJ +J C ca •H ? dJ CO 0) c o •H cn ■u c ^ •H 00 •H 4000CSlCN*COCM in CM r~- m CO o fH moo r^ O CM o o Tl O LO M3 VO O CM -^ CNJ \o o n lo o m t-H CNj r^ !■ ^ C?V CM Cs| CM O O^ r^ f^ rH CM in rH CS CN CM rH CO rH CO m rH \£) o rH r- T-H CM O 0^ (X) CTn M3 i -^ iri vo rv» o CO cn r-l O rH rH VO tS rH CO O vO r^ -a- o m m CO •o u a o o c CD o o 4J in o to u-1 cn mc^i.^^OCOCT^^».^O^JO^rl ^OCMCMa\l^ir»,^^m^y^ incN pM \D cn CO CJ^ cn oo 001-~COvD00cnCMCM>OCM >0, a\ a^ \£3 CO 00 o\ rH cn tvl O CJ^ CM CO O >i5 csl VD •3- CM «Z3 m <3N O 1-H pH C7\ C7N 00 -^ CO O CM in ^T CM C\ o O O CM .-) CM rH CM -)3JX.-!aSwpaWrJ a,3:tncntoocj bJScocu lOOcjzZcao caJcopL. i O rJ cn CM o CM o H D. 03 E C 3 o CD -H •O (8 B >^ ■H J3 i-t JD c a a s: a » -H O CQ 01 m 4-1 ^ kg (4.9 x 10^ lb) in 1967 (Weils and McLain 1973)-, In addition to commercial utilization by man^ alewives are important forage fish. Larger piscivorous fishes such as burbot and lake trout prey upon alex^'ives (Scott and Grossman 1973) and we have found that large yellmv' perch fed heavily upon large adult alewives during spring and early stancier, FroiB su:r/eys at the Finger Lakes, Odell (1934) reported alewives in stomachs of walleye ^ northern pike, bass, pickerel , Cisco, lake trout, rainbow trout, eel and yellow perch. In Lake Michigan, Wagner (1972) found that when alewives were abundant they were preyed upon heavily by northern plke^ s-mallmouth bass, walleye, burbot and bowfin. The abundant supply of alewives, upon which salmon prey, has made possible the successful salmon stocking programs In Lake Michigan in recent years (Wells and McLain 1973) o Alewives constituted the vast majority of the catch from our fishing efforts in 1973 (Table B6) . Alewives were collected during spring, summer and fall by all fishing gear employed (Tables B7, B8) . Records indicate that alewives utilize all depths in southeastern Lake Michigan during their annual movements (Weils 1968; Bromi 1972). They are found in deeper water in the winter, migrate inshore in spring, disperse widely in warm sunmer waters and return to deeper water in fall. This seasonal migration closely follows seasonal water temperature changes. Statist-loal Analysis of Alewife Catch Trawls. Results of ANOVA (Table B9) for trawl catches of alewives Illustrate the highly complex pattern inherent in sampling an abundant pelagic fish species. Four highly significant (P = <.005) first-order interactions and two significant (P = <.01) second-order interactions were present. Since these confounded interpretation of main effects, higher order interactions must be examined and analyzed in terms of a suit- able biological analogue. Unfortunately, a satisfactory explanation or confirmation of these interactions as a distinct biological pattern must await at least another year of preoperational data. As a first approximation, most of the interactions can be attributed to the general inshore migration of alewives commencing in April, continuing through June, and vertical migration of schooling fish which at various times remove alewives from the trawling depths, particularly at 9.1 m. Greater catches at 6.1-m depth than at 9.1 m, high catches in the seines, and personal observations of surfacing fish at night tend to support activity in the upper water strata. One echo-recording trace of this phenomenon on 13 May 1974 detected schooling fish between 2.1 and 5.2 m on the 6.1-m contour at the Cook Plant, Additional echo soundings would prove helpful in confirming or rejecting this phenomenon, Gillnet studies at the Point Beach Nuclear Plant also indicated vertical variation and surface activity (Wis. Elec. Power Co, and Wis. Mich. Power Co. 1973). In contrast to our bottom-set gillnets, both surface and bottom gillnets were fished by Point Beach researchers. They found that surface gillnets 60 TABLE B9- Sunmary of analysis of variance for dlewives caught in trawls in the Cook Plant study area from April through October 1973. Source of variation df Adjusted mean square-^ F-statistic AREA 1 3.20860 26.91 MONTH 6 2.58857 21.71 DEPTH 1 2.23550 18.75 TIME of day 1 1.11313 9.34 AxM 6 1.54793 12.98 AxD 1 .06744 .57 AxT 1 4.13170 34.65 MxD 6 .22304 1.87 MxT 6 5.91008 49.57 DxT 1 .97695 8.19 AxMxD 6 .27586 2.31 AxMxT 6 .46255 3.88 AxDxT 1 .02288 .19 MxDxT 6 .68968 5.78 AxMxDxT 6 .15731 1.32 Within cell error 54"^ .119235 <.01 <.01 <.01 <.01 <.01 NS^ <.01 NS <.01 <.01 <.053 <.01 NS <.01 NS ^ Mean squares were multiplied by harmonic cell size/maximum cell size (n, / N = .966) to correct for 2 missing observations where the cell mean was substituted. 2 Not significant (P >.05). 3 Not significant (.01

.05) interaction terms were pooled into the error term. All significant terms in the original ANOVA were unchanged by this pooling strategy. Pooling interaction sums of squares into the error term should be avoided, since not much is known about the operating characteristics of such procedures. Wiiile pooling increases degrees of freedom in the test statistic, it can lead to Incorrect results if the interactions are in- correctly assumed to be zero^ since there is an increase in the expected mean square, hence decreasing sensitivity of the tests (Scheff^ 1959), Here again need for an additional year*s data is illustrated. 62 o H H a H H o H CD S 3 O ^ +J Oli • d a; ro •H ^ r^ M j_i a\ =) r-* T3 W) a r\ U) •H c rH J-J cfi P 3 W) nJ Tt •H x: rC Tl CJ rH ri •H 15 tti s ■I-' ^ r!xS o >^ aj iH /3 4J Pm CO t3 0) 0) C O -1-1 •H o 3 P. O ■M cfi O •H 3 & -H O r^ ^~, Cfl 4J 0) cn C > 0) o •r^ C § _5i P 1>^ ri '^ >+H ^ 0) O M rH tfl o >^ C2 O 0) P. rP T3 6 S 2 3 cfl CO C 5 to si II o 4 ■"^■^-^ OOO OOOOOOOo 8 00 0000000 o> t^ «> lo ■* K> «i "" IHOnVO HSU 'ON a o 6 Pu Q> O o 60 •H d C3 >^ cd X( 0/ 4-1 C 00 60 c ■::! •H rC u o Id S 4-1 a) 0) r^ CO cti c a) ■H CS 60 5J •H 3 O j_i t» 6C C 3 -H O f^ CO OS 0) i-i •H M « s O O !-i ^ 0) 60 •5 => S O 3 H 4-1 3 : ^^ O JD M 0) 65 o (A O .05); month effects were highly significant (P < .05). Seasonal Distribution by Age-size Class Alewives utilize all depths of Lake Michigan during at least some part of the year and consequently affect many other species in the lake (Smith 1968) . In midwinter they are concentrated en the bottom in the deepest portions (Wells 1968) . By late winter and early spring they move shoreward into the mid-depth region also occupied by the bloater. During late spring and summer alewives concentrate inshore. In fall, offshore movement to mid-depth regions takes place. Apparently this seasonal migration follows the pattern of annual water temperature changes. Our data can only partially substantiate the observed seasonal pattern, since only inshore regions were sampled. Length-frequency histograms of alewives TABLE Bll. Summary of nonparametric analysis of alewife beach seine data (April - October 1973) from southeastern Lake Michigan. NS = not signifi- cant; S = significant at the 0.05 level. Factor Kruskal-Wallis statistic (and levels) df ^^-^^^ p Station (A, B, F) 2 0.59356 (.74) NS Area (Cook, A, B; Dunes F) 1 0.00399 (.95) NS Month 6 24.5850 ,0004 S 67 caught in standard series nets were compileii by gear type (Figs, B8-10) . These histograms have to be viewed in total because of size selectivity of the various gear. Because very few juveniles were collected by our inshore sampling (they reside at mid'-depths further out into the lake — Brown 1972), only seasonal distribution of young-of-the-year (YOY) and adults will be discussed below. Young-of-the-Yeav. Young-of-the-year were first caught in limited numbers in July through day seining in the Cook Plant vicinity (Fig. B8) . Lack of YOY in day seine catches at Warren Dunes may be related to school- ing behavior (i.e-^ patchy distribution) of this species. No YOY were caught by trawling (Fig. BIO) 5 indicating these fish probably remain in- side the 6.1-m contour, although small size of YOY alewife may have made them less susceptible to trawling. Seined YOY were 20-30 mm and probably hatched 3-4 weeks prior to the date of capture^ indicating June to be the month when spawning occurred. In August, YOY catch increased enormously; conversely catch of adults diminished noticeably. Modal length of YOY was approximately 40 mm. Numbers of YOY caught by day seining were high at all stations. At night YOY apparently moved to deeper water, since few were seined while numerous YOY were caught in trawls at Warren Dunes. Some YOY were caught by day trawl- ing at 6.1 m off Warren Dunes, indicating these fish range out to this depth during the day. Absence of YOY in night trawls at the Cook Plant is puzzling. Young-of-the-year may be following daily temperature changes to a greater extent than adults. YOY were not caught by seining in September. During sampling, weather conditions were poor and high waves may have made beach-zone condi- tions adverse for these fish. Trawling, which took place a week later during an upwelling, indicated that limited numbers of YOY were in deep water (6.1 and 9.1 m) during the day but were scarce at night. By October, YOY were again present in the beach zone. Modal length had increased to about 50-60 ram. This agrees well with 1962-66 and 1970 observations in southeastern Lake Michigan (Brown 1972). It is, however, well below the 80-90 mm average length in 1968-1969. Wells (1968) found average length of young alewife to increase consistently with increasing distance from shore. Thus our estimates of average length may be biased downward. Young-of-the-year utilized the beach zone during the day in October, which may be Interpreted as either temperature preference behavior or acquisition of the adult behavioral pattern evidenced in spring. Trawl catch in October showed that YOY were at 6.1 and 9.1 m during the day, but were not present in as great numbers as was found at night. No YOY were caught by seining in November and December. These fish had apparently left inshore waters with the remaining alewife population, although we could not verify this because trawling was not performed. However, modest numbers of YOY alewife were captured during November 1974 trawling activities, indicating at least part of their numbers were still inshore. 68 STATION A CO H O W 750- 1*50 A 150-] P ° R "0' "♦SO. 150- Q r-T- STATION B 'J "T ' ' I' ' r ' I 1 i STATION r SQ 100 150 200 50 100 150 200 750- <*50- M A Y 150- 750- i»5Q- 150- ■^ -» ' I ' J ' I "' SO 100 150 200 -T — i — 1 — r-r- j—i J— T 50 100 150 200 7 5 0- i»50- J 150- U N 7S0 USO- iSO_ r-r-i-^t-nr-r-V-T-nH 50 100 15. 200 ''~T~T-^ r J I I - r- 50 100 ISO 200 LejGffl ItfllR'/ft. (iM) J 50 100 150 200 i— J- - LLLL ioiio 150 ' 260 n? 50 100 150 200 FIG. B8 . Length-frequency histograms for alewives caught in standard series seining during 1973 in the Cook Plant study area of southeastern Lake Michigan. 69 STATION A STTATION B STATION F 750- 1.50- J J50- u °- K50_ 150- n . T L D A Y N I G H T > 1 1 1 • 1 < 50 100 150 i ' ' 1 ' 1 1 I 1 1 » »-l ' 1 ' 1 ' 200 50 100 150 200 50 100 150 1 ' 200 PC M o w m 750- <.5D- A ISC- U 0. G 7S&- 1.50- 153- T 1 IS ! • "T 1 D A Y N I G H T ' 1 ' 1 • 1 50 100 150 j • • t ' 1 1 1 • 1 ' ' J ' J ' J ' 200 50 100 150 200 50 100 150 260 750- MSO- 150- c °- T 750- KSO- 15D_ III f " • D A Y If 1 '5] 1 N I G H T l' 11 i ' 1 50 100 150 ' i ' 200 ' 1 ' 1 ' 1 ' 50 100 150 200 i 1 ' ' 50 100 150 ' 1 ' 200 LfNCTH IffTEKv'AL O-ti) FIG. B8 continued. 70 Q <>- — e) X 1- ao- ," o x h- o ; 2: o i UJ en ■ u - 7- ■ C) i~ CO a ■H 4-) c ,d CO W) 61) :i •H CD rC c; a •H CO S CIJ > (U •H Ai rs cfl 0) i-J t-l crt c u 0) n J-) o en <+-( en OJ en .c 6 ■u cd 3 u o bt) en O ■M y-i CO o •H 43 efl a) >. u a cfl c 0) !>N 3 13 cr 3 - O IC 1- a <>• z ^ tD re }- 2: o (- 10 . a z o < o — - ! ' 1 ' 1 " r ' i ' 1 13 o o ON' S <3 >H *^ C3 Z O H HSI5 JO raawnN 72 Q <>- Z — C3 X I— o<>- ■O XI- X o C/5 CD 2: q < o y CJ 2: o X i 1 — r~r i ' I >-) 1=) i-J - z — o a: t- oo ;-< o 3: 1- X o f: to (S> I O CO p •H o O pq OT W P-l O O H O M HSM KO HaaRM 74 Q<:>- 2: — ts X h- Q <>- , Q r 2: ■ en <: PM Pi g <3 >H J' -" Wl a •H M s x) 00 c •H rH IS c« U » ■U /-•^ cd rn 4-1 (11 Cd •H T3 U fl> 03 a X) II M cfl Q T5 2 C *w^ nJ j-j rn c td C 60 •H •H ^ 4-1 ^ •H bOS S trt CU r) Ai td en i-l i= •H u s (LI <1) 4J rH to (rt cd 0) )-l 43 4-1 4-1 3 M to § M-l VJ Wl CO ■u (U 0) !-i •H cd X3 >> >.•« 3 C ■w 0) to 3 o- 4-1 0) C M Cd M-l r-l 1 P^ i u A! ar C 01 U tJ fe r-l HSIi 50 HaaKON 75 a <>■ 2: — 13 X 1- ao- 2: — O 3; 1— . -= ?- l- < fc5 UJ - _. ■ • 2: CO '^ i ' i ' r i ' s • 1 J- ^* >-5 & 2; -r •-) & ij O o O H HSI5 50 ^aSHflN 76 Q< >- ' Q o t CO M en -1 — t-r J- »-« T3 (U 3 a •H 4-1 C O O O H e W3 W PM o H HSU m ^wmm. 77 Q <>- h: — • tn X !— Q <>- : —• to X i a 2: i to • 1 r-i ■''■■' i ■J - i i ' i J -« O O H t3 0) •H 4-1 C O a o rH H HSI5 10 ^aawriN 78 YCPi apparently move to offshore regions and remain there until reach- ing full sexual maturity. It is unlikely that they grow enough during winter to be mistaken as adults the following spring. Small numbers of alewives in the 50" 100 mm range caught in April, May and June are probably a mixture of small adults due to size segregation and occasional sampling of the fringes of a predominantly pelagic population of 1 and 2-yr old fish located mainly outside the traveling zone (Wells 1968; Brown 1972) . More extensive sampling studies (e.g. Brown 1972) have shown that after their first summer alewives are predominantly pelagic remaining primarily at mid-depths until their third summer. Adzitts. Adults first moved into our study zones in March. These were large fish in the 140«-200 mm range (Fig. B9) . Other studies (Rothchild 1965; Wells 1968) also found larger fish leading the inshore migration. By April much more of the adult population had reached the inshore regions. Once again, these were large numbers of individuals in the 150-200 mm range, probably the III, IV and V age groups (Brown 1972; Norden 1967a). Adults were also caught in the beach zone at night in April. The adult population was now exploiting all depths of the inshore waters. Numbers of adults caught in May decreased, probably a result of warming of inshore waters. As an increasing area of the lake was heated to preferred temperature levels alewives were able to disperse more widely, thus reducing their numbers inshore. Large numbers of ripe, ripe-running and spent alewives caught in June and July indicate a June- July spawning period (Tabic; B12) , Landlocked alewives spawn primarily on shallow beaches (Scott and Grossman 1973) and by migrating up rivers (Edsall 1964; Brown 1972) . Further support for a June- July and some of August spawning period is provided by presence of alewif e eggs and I'-day old larvae in the area during these months (see Section C) . Spawning continued through July but apparently at a diminished rate. Adults captured were still in a length range of 160-200 mm. Slow growth of alewives in Lake Michigan (Smith 1970) makes it difficult to detect any pattern of increasing modal length for adults over a single growing season. Very few adults were caught by beach seining after June. Evidently they do not return to this area after spawning. Some adults were caught by gillnetting and trawling at 6.1-m and 9.1-m stations after July and into fall., but numbers were low compared to spring and early summer catches. In Nov«2mber only five small alewives (45-63 mm) were caught in beach-zone seining activities, the vast majority of the population having left inshore waters., Temperature-Catah Retationships Graham (1956) estimated that alewives acclimated to 10, 15 and 20 C approached their upper incipient lethal temperatures at just above 20 C, just below 22.8 C and about 22.8 C, respectively. On 28 July 1964 Wells 79 TABLE B12. Monthly gonad conditions of 6lewives as determined by inspection and classification of the state of development of ovaries and testes. Fish were captured during 1973 in southeastern Lake Michigan. All fish examined in a month were included except immature and poorly received specimens. Gonad condition Feb Mar Apr May Jun Jul Aug Sep Oct Nov ^Dec Females Poorly dev. Mod. dev. Well dev. Ripe-running Spent 50 97 12 21 190 270 25 103 253 1 2 224 184 9 2 35 21 Males 1 3 1 45 25 22 13 38 1 5 Poorly dev. Mod . dev . Well dev. Ripe- running Spent 38 104 13 20 267 140 28 1 132 8 1 165 244 153 243 173 Unable to dist 11 74 inguish 40 5 44 59 1 13 2 1 4 3 1 20 3 19 3 4 1 1 Includes or dy imp inged fish. (1968) found most alewives in water temperatures from 11-16 C even though a complete range of temperatures were available spatially to them. Our temper- ature-catch data for alewives (Fig. Bll) indicate to some extent the inshore preference range of adults and YOY. Adults were captured primarily by trawling and gillnets, although many were caught some months in seines. The lower range, 4-12 C, where one peak catch occurred is probably representative of temperatures recorded at the time when adults were captured in spring. Adults appear to prefer the 16-22 C temperature range. Most YOY were caught at 16-20 C and 24-28 C with a probable preference for the upper end of this range . Other Considerat-ions Alewives were observed on numerous occasions by SCUBA divers working in the vicinity of the Cook Plant during 1973-1974. Fish were seen both in the riprap area and at control stations north and south of the riprap. Although 80 3000 ALEWIFE NF - SEINE - GiLLNET - TRAWL - NOT FISHED 25001- o z? fi W 3 CO Q J C. a> B !-« U r-f 33 • ffi --CC on P-' c o •H 0] 4J i-l (U CO j: C -u >> M 3 CO « -H o , Q 2 on 0) g u U .H 33 . 3 o o c o •H U cd iJ u 4J C OT x: « >^ 00 ^ 1 CO -H o. a z; O .-H on o • CJ »o a; x: u c bO !-4 c N IHOnVO HSU *0N IHSnVO HSU • Xi PQ M O 88 As was seen in the trawl catch, night yields firom gillnets were generally higher than day catches for both areas. However, while trawl catches showed a change to higher day catches in July and August followed by higher night catches in September and October, no such pattern was evident in gillnet catches. In November and December catches were low, but some spottails were still present in the area. Comparisons between day and night activity derived from gillnet data must be tempered by evidence that spottails feed just before sundown (Griswold 1963). Setting of the day-night gillnets probably overlaps this peak activity period which would tend to diminish validity of inferences. Consequently no statistical tests V7ere performed to test for differences in catch between day and night. The only apparent difference between the Cook Plant and Warren Dunes areas occurred in August and September when Warren Dunes had consistently higher day and night catches at both depths. These apparent area differ- ences, when tested by non-parametric statistics (Table B15) , were not significant. In addition, neither non-parametric test used indicated significant differences between depths. Of course, differences in catch among months were highly significant (P = . 008) . Seines. In terms of spottails caught, seines were by far the most productive gear. Most seined fish were captured during the day, although the general pattern was high night catches in April and May and high day catches in June and August (Fig. B15) . Other studies have shown that spottail shiners are more easily caught by night seining (Scott and Grossman 1973). The Kruskal-Wallis test (Table B16) showed no significant differences among the three stations nor between the two study areas. Apparently spottails are uniformly distributed in the beach zones of the two study areas, demonstrating the homogeneous quality of the; southeastern Lake Michigan beach zone. As expected, there were highly significant (P < 0.001) effects related to seasonal changes. Temporal changes in spottail distribution will be discussed below. TABLE B15. Summary of nonparametric analyses of spottail shiners caught in standard series gillnets in Cook Plant study areas from April through October 1973. NS = not significant, S = significant at the 0.05 level. Factor (and levels) df Kruskal-Wallis Value statistic P Mann-Whitney Value U statistic P Month (Apr-Oct) 6 17.319 .0082 S Depth (6.1 m, 9.1 m) 1 .021363 .8838 NS 669.0 .8837 NS Area (Cook Plant, Warren Dunes) 1 .029845 .8628 NS 628.5 .8627 NS 89 o < 1 1 0) 0) C C •H 3 o cd c OJ ct! W IS H < Ul O o o o in O O lO o in CM aqSnBO qsTj •ou UBan 0) c •u •H C cu to CO Pi XI <; o ^ rt o <: , 60 to -H o z o < 1 I I ■^-^ L O o o O o x: C CO ^ to ^^ 3 5- 0) to c 01 i-> tr. to a> x: i-i O to x: CO •H y-i CO cu •H to 00 to r^ <-> cr. CO -^ •H ^ to S x; 3 O x: cu XI S 3 C to t " M M!i.iNUi-i 10 '♦C 70 100 13C 160 10 1,0 70 100 13C 160 la 1.0 70 100 130 160 SCC_ -pv-r-f r-i-H-^ t ■ ■! 1 ! ■ 1 J ._ >■ ■ >il .■ U'i ii 10 <*0 70 100 130 160 10 '♦0 70 IOC 130 260 10 WO 70 100 130 160 LjENGIK interval (m) FIG. B16, Length-frequency histograms for spottall shiners caught in standard series seining during 1973 in the Cook Plant study area of southeastern Lake Michigan. 92 en H O Pi w J U L A U G STATION A 500- . 300- 100- I 1 I. soo- . 300_ - 100- j STATION 3 STATION F ' ti ' ' t ' ' I ' ' i ' ' ' ' ' * 10 UO 70 100 130 160 10 i»o 70 100 130 160 10 WO 70 100 IJO 150 500. • 300_ . 100_ 1 500_ . 300- . 100- 111,1 1 1 . 1,1 1 J I . 1 ij JLL III iL. 10 ".C 70 IOC 130 150 10 <.0 70 100 130 160 Itt 1.0 70 100 13p 160 N I G H IT C T 500. 30C. 100- 500- 300_ 100- I ' ■ t ' ' t ■ ' I ' ' 1 ' ' t T ' 'l I ■ I J I 1 I 1 { ! I I I I t I » ■> I ' ' I ' * t ' ' I' ■ r 10 i«0 70 100 130 160 10 i*0 70 - 100 130 160 10 '♦0 70 100 IJO ISO LENGTH INTERVAL 0-m) FIG. B16 Continued. 93 Q <>■ O CO Q<>- :2 — o a: 1— O < I— to _ o a o I C/5 "T — ' — ' — " r~^ — I — * — \r~* — r in ui in ^ in i/i tn tM r«. c< CM r, P4 fa W « a <3 cts M C •H u w -i o o M-l to , tJOtJ o 3 4.J 4-) 0) to •H ,fi 4J C P^ to o rH c fl4 ■ Z — iO a <>- Z — O X 1- ■ — - - 2: — us x o <: >- O Xh- 1-3 !=> a f-j C3 H-3 g ■H U o u r-l m o H p4 HSM dO HaaHIlN 96 a <>■ a<>- o X 1- — f to 2: — a o < .. O O CO J) O J) <| !Z) U us o W W PM ^ o •13 a) 3 fi •H J-i c o o H pq H HSI5 50 ^aawiiN 97 Q <;^ . 13 ~ o i - Q -z. O < fc5 o to ^ ~ irt O O U H _ i- - ^ O > 0) C •H 4J C o •a M HSM 50 HaawM 98 o < >- Z >- O XK- Q < V Z -- O X H — ~t J-° 2 ^ o - ^ - 1 i- — r- r I 1 1 • 1 1 1 ■« H M C ■H rH ^ tn M 4-) cn ^^ (U cd •H 4-> (-1 Cd . O T5 w 3 0) U •H cn 43 ■u >. C CJ cd d i-l 0) PM rM - Z --lO X}~ Q < >- ■ O T r j' 1 • - o o i5 V— en _ U3 f r- ^ I J-2 tjj 7" g <; o o CO w ^ 0) C •H a o u 00 H HSi^ io HagMiN 101 o _ o l-° ^ Q 9 O O H 13 O > T3 QJ 3 C •H •u C O o 00 pp O M P4 HSI5 io ^aawnN 102 Based upon a literature search, our YOY appear to grow noticeably slower than in other studies (Table B17) . Average length of YOY in this study was about 50 ram, while in other studies lengths ranged from 54 imn (Wells and House 1974) to 77 nam (Griswoid 1963), At the end of their second season of growth our fish approximate the size of those found in other habitats. Our spottails then grow to average lengths that are probably greater than reported elsewhere. We would expect our spottails to grov? at least as fast as those in other habitats, since food appears to be abundant and water temperatures are high. Slower growth in early stages of development and increased growth later in life, growth campensation, may be linked to two interact- ing factors. First, the large sizes that our fish attain are probably related to absence of predation by larger salmonids. We found very few spottciils in stomach contents of larger saimonids. Some documented predators of spottail shiners such as walleye (Smith and Kramer 1964) are rare in the study area. Prominent piscivorous saimonids may ignore spot- tail shiners in preference for other prey, particularly alewife. Wells and House (1974) have speculated that spottails are not important forage fishes in Lake Michigan. Factors causing decreased growth of YOY are less clear. Niche over- lap with the alewife is suggested as the major factor. In an extensive study of stomach contents of more than 100 spottails from Lower Red Lake, Minn., Smith and Kramer (1974) noted a distinct change in food preference with increasing length. Crustacea, particularly cladocerans and copepods, were major items in diets of spottails between 7 and 69 mm in length. Beyond this size range, insects comprised the bulk of stomach contents. In this study, concentrations of YOY alewife and spottails in the beach zone, both of which are selectively feeding on zooplankton, indicate at least a partial niche overlap. Later, when spottails begin to feed more on benthic organisms, the competitive inhibition from alewives is mitigated and spottails grow at a faster rate. Basch (1968) found that adult spot- tails and adult alewives did not compete for food in Little Bay de Noc, Mich. Of course, these hypotheses must await analysis of stomach samples. Juveniles. Juveniles 1-yr old were caught in April along with adults. Throughout our sampling, they appeared to associate with adults in their spatial and temporal ranging. "Juvenile" is a somewhat arbitrary classifi- cation for spottails because some fish mature at 1 yr old. Wells and House (1974) found in Lake Michigan 53% of the males and 40% of the females of age I, and all fish of age II were mature (adults). Some juveniles utilized the beach zone along with YOY in August, but for the most part the majority were found offshore with adults. In April, juveniles were 30-70 mm, approximately the same length as YOY captured in October. By July, spottail juveniles were 40-80 mm and in August this range had increased to 90 mm. A few spottails which may have been yearlings in the lOO-mm size range were caught in September trawls and gillnets. Annual growth appears to be complete by September. Wells and House (1974) speculated that all age groups had stopped growing by mid-October in southeastern Lake Michigan during 1964. L03 TABLE B17 Summary of calculated total length in millimeters at each annulus of spottail shiners at various ages. Data are from several habitats. F = female, M = male. . _.- — ^ Age class Source I F M II F M III F M IV F M V F M McCann 1959 (Clear L. , Iowa) 77I 98 108 Smith & Kramer 196A (Lower Red L. , Minn.) 58 56 90 85 106 100 113 103 Basch 1968 (Northern L. Mich.) 59 57 87 86 105 106 117 Wells & Bouse 1974^ (Southeastern L. Mich.) 63 62 97 95 114 108 123 117 131 129 (Kalamazoo River, Mich.) 56 54 80 79 94 93 105 106 -^ Sexes combined. 2 Length at the end of each year of life. Adults. Adults were caught throughout the entire sampling period. The first significant occurrence of adults was in March, primarily at the 9.1-m contour (Fig. B17). Apparently larger adults lead the inshore migration. Size range was from 80-140 ram with an average length of 120 mm. These fish were probably 3-5 yr old, although very few spottail shiners have been found to live more than 4 yr (Carlander 1969) . A 120-mm average is similar to the averages calculated by House and Wells (1974) for 4-yr olds (at the end of their fourth year) found in southeastern Lake Michigan (Table B17). Four-year olds averaged 108 mm for males and 114 mm for fe- males in Lower Red Lake (Smith and Kramer 1964) , but this may have been the result of gear selectivity — only seines and trawls were used. Basch (1968) reported 4~yr old females averaged 117 mm, which agrees reasonably well with our data. Our longest spottail was a 150-mm female, which is slightly larger than has been reported elsewhere (Trautman 1957; Scott and Grossman 1973). Adults remained abundant in the study area through June. Gonad exam- inations (Table B14) Indicated that spawning occurred in June and early July. Our SCUBA divers observed spottail shiners spawning on the intake cribs on 17 June 1973. They saw 500-1000 spottalls swimming above and into patches of 1 1/2-in thick Ctadophora. Many of the fish appeared swollen, and when captured and squeezed they exuded eggs and milt. Several females were observed to deposit eggs into the Cladophora but subsequent fertiliza- tion by males was not observed. In dives on 13 and 26 June spottail shiner 104 egg;s were collected and reared. From this It was concluded that 1) spot- tails will use Ctadophora as a spawning substrate to which eggs are firmly attached, and 2) the spawning period may be 3-4 weeks with a noticeable peak occurring in a matter of days. Spawning for an entire population may possibly occur in as short a period as 1 day. In a study on Nemeiben Lake, Saskatchewan, all spottails caught before 10 July were ripe while all those caught after 11 July were spent (Peer 1966). Spawning generally takes place over sandy shoals (Scott and Grossman 1973). After spawning, adults in our study areas began to disperse from the beach zone and into deeper, offshore water (6.1 and 9.1 m) . Large numbers of specimens were caught at night in September in trawls, indicating that spottails occupied the same zone in fall as was found in spring. During the coldest months (November, December, January and February) spottails were present in the inshore waters, but numbers caught were low. We believe spottails were present in the inshore waters at the 6.1-m and 9.1-m contours during this period, but a combination of factors caused low catches. Only gillnetting and seining were performed during some of these months. With water temperatures between and 10 C fish movements are at a minimum, and gillnets are ineffective when fish do not move. Apparently spottails do not enter the beach zone during the colder months, since seining produced few fish. Undoubtedly trawling during colder months would have produced more spottails from the 6.1-m and 9.1-m depths. Tvawl catches from southeastern Lake Michigan during November and February indicated that spottails were present in low numbers at 6.1 and 9.1 m and out to 31 m (Wells 1968). Temperature-Catoh Relationships Wells (1968) found maximum concentration of spottails on 28 July 1964 to be at 16-22 C. Our temperature-catch data also (Fig. B19) indicate to some extent temperatures selected by spottails. There appear to be two peaks of maximum, catch one between 6-12 C and the other at 16-22 C. Apparently during cooler seasons, spring and fall, fish utilize the warmer waters, which probably accounts for the 6-12 C peak. In summer, spottails were caught most often in 16-22 C tempetatures . YOY, which were caught primarily by seining, apparently preferred the warmest temperatures, up to 28 C in summer. Other Considerations During examinations of spottails caught in 1973, a diseased condition on some fish was noted. Approximately 50-100 fish were found to have an infection of the abdomen. This infection is being analyzed by fish disease specialists and will be reported, with incidence numbers, in the 1974 fish report. Incidence of this disease suggests that spottails may be reaching a population peak in the study area. Future computing refine- ments of disease incidence plus computation of condition factors and length-weight regression may lend support to this theory. A possible pop- ulation decline could result if this disease increases in future years. 105 SPOTTAIL SHINER S- SEINE 113- GILLNET - TRAWL NF - NOT FISHED 9 II 13 15 J7 19 TEMPERATURE RANGE C FIG. B19. Mean catch and standard error of spottall shiners at a given 2 C temperature interval in gillnets, seines and trawls during 1973 In southeastern Lake Michigan. Midpoint of temperature Interval is given. 106 Population declines caused by disease are not uncommon. The dramatic di€;-off of smelt in the early forties was attributed to a bacterial or viral infection (Van Oosten 1947), Rainbow Smett Rainbow smelt is an introduced marine species in Lake Michigan. The present population originated from an initial planting in Crystal Lake, Mich,, in 1912 (Van Oosten 1937) and entered Lake Michigan via a small drainage stream about 1922 (MacCallum and Regier 1970). They spread rapidly after entering the lake; the first catch of smelt in commercial nets occurred near Frankfort, Mich, in 1923. By 1924 these fish had entered Green Bay and by 1936 had occupied the entire lake (Wells and Mc- Lain 1973). Commercial catch of smelt rose steadily from 3.9 x 10^ kg (8.6 X 10"^ lb) in 1931 to 2.2 x 10^ kg (4.8 x 106 lb) in 1941. The smelt population suffered a catastrophic collapse in winter 1943, such that by 1944 production of smelt was only 2.3 x 10^ kg (5 x 10^ lb). Apparently these smelt died of a viral infection (Van Oosten 1947) • The population rebounded quickly, however, and commercial yield peaked in 1958 with a 4.1 X 10° kg (9.1 X 10^ lb) catch. Since that time, production has been largely determined by market demand. In addition to commercial fishing, sport fishing by dipnetting in streams and beach areas has been a sizable recreational activity in Michigan every spring (Wells and McLain 1973). Smelt are preyed upon by a variety of creatures-'-lake trout, land- locked salmon, brook trout, burbot, walleye, perch, gulls, crows and their own species (Scott and Crossman 1973). In Lake Michigan, smelt have been found to be an important item in the diet of lake trout (Wright 1968) , but in the Cook Plant area we have found that alewife are by far the most important forage fish for larger salmonids, at least in the inshore zone. Statisti-oal Analysis of Smelt Catch Trawls. Results of the analysis of variance (ANOVA) (Table B18) for trciwl catches showed highly significant (P < .01) main effects due to MONTH, DEPTH and TIME of day; no significant differences were detected between study areas. There were four significant first-order interactions which confounded interpretation of main effects. Before considering these interactions in detail (Fig. B20) , the biological phenomena underlying the results of ANOVA should be considered. In particular, the spatial and temporal uses of the inshore zone, in this case 9.1 m, by smelt are particularly relevant. Adult and yearling smelt are normally found in the inshore zone only during the spring spawning run. Smelt may also follow the cold-water mass of upwellings inshore; during summer months, however, upwellings and the subsequent presence of smelt inshore are essentially brief and randomly occurring events. Following spawning or as inshore water temperatures rise, adult smelt return to deeper, cooler offshore waters of the lake. Smelt larvae remain too small to be captured in our trawl mesh until August, at which time they are caught in abundance. Thus two factors, spring spawning and late summer recruitment of YOY, account for much of the significance of the interactions. 107 TABLE B18. Summary of analysis of variance for smelt caught in trawls in the Cook Plant study areas from April through October 1973. Source of Adjusted variation df mean squares" F-statistic P AREA 1 0.34881 4.39 <.052 MONTH 6 4.42583 55.68 <.01 DEPTH 1 5.88228 74.00 <.01 TIME of day 1 1.25386 15.77 <.01 AxM 6 1.15233 14.50 <.01 AxD 1 0.80302 10.10 <.01 AxT 1 0.02334 0.29 NS3 MxD 5 1.56289 19,66 <.01 MxT 6 1.39539 17.55 <.01 DxT 1 0.28181 3.55 NS AxMxD 6 0.10304 1.30 NS AxMxT 6 0.24387 3.07 <.05 AxDxT 1 0.00166 0.02 NS MxDxT 6 0.12616 1.59 NS AxMxDxT 6 0.24557 3.09 <.05 Within cell error 54'+ 0.0794938 1 Mean squares were multiplied by harmonic mean cell size/maximum cell size (n, /N = 0.966) to correct for two missing observations where the cell mean was substituted. Not significant Not significant (.01 < P < .05) (P > .05). Two degrees of freedom were subtracted to correct for two missing observations where the cell mean was substituted. 108 -9 J / o H 2: P-i o < < - VD o --0 t3 • a CJN ca f^.Tj 4-1 cC c c t3 cd cfl rH iw rH CL, • ^ (U a 4J •a Cd u 4-1 x) 01 13 C x: c cd • ■u cd m ^— \ r^ 4-) w .a C3^ nJ cd i-> iH (U a M M C rH cd a •H 3 v^' tfl >^ C! ^ a ^ Cd 60 rH >H t3 •H & • cu x; cd CJN rH >-i •H +j T) s C O. cu td ^ cd CD to rCl ^^-^ 3 TJ 4-1 •H 4J 0) ^ I-l rH (50 ^— ^ Q) •H Cd g CI cu CO A. )-i T) cd ~, C! Cd cd u T} ! > 0) MH cd -2 13 a 13 3 CU i X z I I o o (0 o u CD c o B u 0) p. cu o d o M •H C C CO 60 n c •H 40 ^ OJ o CD iH CO w 0) iH iJ •H C M H OJ C -U •H CO Ct) 4-1 0) 60 4-1 3 3 - ci3 o U CO B en CO r^ O CU tU XI ^ B B o ^ M X. CO CO -H >: G Q Z X 0) fc< U U O <3 CO n <; g < o in o o O ^qSneo qsxj -ou ueaw CU C iJ •H c 0) CO u en r-l x: a. >, 00 jC <: ta -H o j-i Q z CO o< CU OH o <1 CQ cLj tn .-<-'" ON o o o o (M u -. (Tl CO «>0 13 -H ,c tm r) a •H •H ?: ^4 3 CU TJ ^ CO -a H-J CU j:: G en u •H CU l4-i j-i cn cn CO a; U-( o o z L4 x: OJ 00 XI 3 s O 3 t-i C X u C CO >> OJ M z 00 3 U • U3 OJ :< « x: • u O C l-l o i^ a :iq3nBO qsxj 'ou ueap^ aqSriBo qsTj -ou uHa^ 113 TABLE B20. Summary of nonparametric analysis of smelt caught in standard series beach seines in Cook Plant study areas April and May 1973. NS = not significant; S = significant at the 0.05 level. Factor (and levels) df Kruskal-Wallis statistic Value P Station (A, B, F) Area Cook (A, B); Dunes (F) Month (April, May) 2 1 1 .2738 .2709 3.7408 .87 NS .60 NS .05 S TABLE B21. Average length of several year classes of rainbow smelt as found in the literature. Location Age (year class) Mlramichi-^ River , Canada Lake Huron Lake Superior Gull Lake,l Michigan — . — 602 1 663 150 II 137'+ 1175 151 163 III 156 155 190 188 IV 176 183 211 198 V 194 228 186 •^ These lengths are the averaged lengths of males and females. 2 Burbldge 1969. 3 Bailey 1964. '^ McKenzie 1964. 5 Baldwin 1950. 114 STATION A STATION B STATiaf F PC fn o Pi r ■ — 1"^ 30 90 150 210 270 30 90 150 210 270 30 90 150 210 270 300 180- M 60- A Y 300. 180, 60, H- T — ■ — I — « — r > — I — < — I — I — r — » — 1 » r -T J l—f-T-i j i [- 30 90 150 210 270 - 30 30 150 210 270 30 90 150 210 270 300 180. J 60, U N 300 180 60 . — ] . J ■> 1 J 1 r— J 30 90 150 210 270 30 90 150 210 270 J 1 — I — ] — r— I — r 30 30 150 —J r— I I 2!0 270 LBJ6TH mmi^L (fr.) FIG. B23. Length- frequency histograms for smelt caught In standard series seining during 1973 in the Cook Plant study area of southeastern Lake Michigan. 115 a<>- 2 — to xi~ Ci- 2:'— O XH- in g i y _o O to CM 60 •S t>o •H +-1 4-1 0) C! • t-( ^v rH nJ •H 4J 60 nj CO •H M >w 3 O CD CD Vj o 60 O CO 4-) -i CO <4-l iH i:^ 4-1 J^ 60 O c o . 4J pij W pq s - 'i3:ni~ a<>- : — • C3 X J— to o t »— « 1— g — ^ y o o ■ - en - 1 ' 1 ' 1 J ' ■ J ' I r T r— r Id C C o o H C5 H Hsi^j dO ^aawfiN 117 a<:>- 'C3 3: t- C}<; ^ z -- e>xi- o g 2: o 1— to 1— LU y o o CO tn !=> IZ 1-3 C3 l-J -a Q) 3 C •H 4J C O U - 2: 1-1 15' 3: 1— o p < t-f- I UJ To ^ y o 2: o CO - Z-- O X h- -s i "T — r 3 s •H 4-1 e o o ■ O H HSU ao HasHriN 120 o<>- e> X H- o<>- o 3: 1- CM o ■ •p- o - >- - - < fe — - Q to o to "JT ■r— r IT) lA O CO r-- CTi rH hf) C •H W S 13 6n (3 •H rH s « ^1 4-1 • /'*V to cfi 0) 4J ■H cd tJ Tl (U CO O fl TS U II cti -a g n) V— ' 4J rn c C tfi •H on •rl 4-1 rC ^ o I'm •H 3 S ca c; flj ,i<5 w CO rH 1-1 (U e C to ;-! 01 !-i 4-t O to MH cfl a) to ^ s 4J td 3 u O bt) W o 4-1 MH to O •H ^ ^ (U >. ^J O c« C d) >-. 3 Tl cr 3 0) 4-1 n to m 1 4J 43 C 4-1 tn bO rH C Pli OJ 1-4 ri^ o o • o m (N (U PQ xi H H S |x< -H HSI5 d;o ^aawfiN 121 a<>- iD 3Z\— a<.>- CD 3; 1— ID 2: O < I i s '-n n Z 1-) tJ hJ 0) 3 G •H 4J d o o m CM m H HSM do mmim 122 oo Z" O OII- X •!' ■ O 1- ' < . fe (s - ''fl _i > ■ _ A ■ ao 2: ^ o 3: H- Is Q r— , -■ s LU 3 < & o c/: W P^ OJ 3 S •H C o o in og pq H HSIi iQ HaawiiN 123 o<>- :z ■— tD x: 1— Q O ■O X H- !3 • 13 P is O U H a o > T3 0) •H c o o in PQ H HSM AO HaawriN 124 standard series catches. Our data appear to approximate most closely average lengths reported by McKenzie (1964) from the Miramichi River. Young-of-the-Year. Spawning in the Cook Plant vicinity takes place primarily in the beach zone and at the mouths of two small streams, one neiar Weco Beach and one at Warren Dunes. Spawning has been reported to occur in deeper water (9-22 m) in Lake Erie (MacCallum and Regier 1970). Pe;ak spawning occurred during the last 2 weeks of April in 1973 and in 1974 extended into May. Larvae remained In the inshore area for a short time, then appeared to migrate to deeper (6.1 and 9.1 m) waters. A vertical migration of YOY smelt off the bottom at night is hypothesized (see Section C) . A similar migration was documented for adults in Lake Erie by Ferguson (1965). Our sled tows to collect fish larvae, performed in May, June and July 1974, documented that in the inshore zone near the 6.1-m and in particular the 9.1-m contour at least some, if not all, the YOY remain on the bottom. Few were taken in shallower waters, and since sled tows in our studies were not performed deeper than 9.1 m, smelt YOY may extend to deeper contours. In eastern Lake Erie, Ferguson (1965) re'ported YOY smelt frequented shallow, epillmnial waters and at times were highly concentrated near shore. Our first major catches of YOY in standard series trawls occurred in August (Fig. B25) . Modal length of YOY then was 40 mm. They were captured at all stations during this period, indicating their wide distribution during this time of the year. YOY did not occupy the beach zone, none were caught in seines, and since an upwelling occurred during this period they were apparently little affected by it. In September YOY were again caught in trawls at all stations; more were caught during the day. Modal length at this time was approximately 45 mm. In October, YOY smelt had grown to a modal length of 54 mm and were still present in the inshore zones, as evidenced by their appearance in all trawl catches at every 6.1-m and 9.1-m station. Yearli-ngs. In April and May, yearlings with a length of approximately 65 mm were present in modest numbers at all stations, with diurnal catches generally largest (Fig. B25) . Yearlings were seined at night in May, suggesting this size class extended its activities into the beach zone. This was the only time yearlings were seined, therefore use of the beach zone may be limited to this brief period of the year. In June and July, yearlings apparently moved outside the 6.1-m contour area, as few were captured at this depth whereas many were taken both during the day and night at 9.1 m. August and September catches of yearlings were sparse, although a few fish were taken at nearly every station fished. Modal length of yearlings had increased from 65 mm in April to about 90 mm in September. It appears that yearlings began to migrate from the study area in August and September, completing their departure by October since none were trawled then. Wells (1968) recorded appreciable numbers of young smelt in trawl catches taken from Lake Michigan on 14 October and 125 again on 4 November 1964. Most were found in 18-22 m of water, confirm- ing the fall movement of yearling smelt to deeper water. Adults. Two adult smelt were taken in a gillnet in February (Fig. B24) . The bulk of the adult population is concentrated in deeper water at this time (Wells 1968) , but this catch indicates that a few smelt range into inshore waters during winter. In March, smelt were caught in modest numbers at all 6.1~m and 9.1~m stations, though none were seined at the two Cook Plant stations. Apparently smelt were moving inshore to spawn; however, as of March, none had entered the beach zone. In April our seining corresponded with the spawning peak of smelt. At this time gonad data (Table B22) indicate spawning was indeed in progress, as many ripe-and-running males and females were recorded in seine catches particularly, but also in gillnet catches. The general pattern of diel movement was an onshore movement at night, followed by the actual spawning act, and an offshore movement during the day. This diel pattern is evidenced by higher nighttime than daytime catches in seines, and by the fact that April gillnet catches were highest during the day although smelt were also caught In night sets. This pattern, however, was not entirely consistent as large daytime seine catches were recorded at station B, Our only explanation is that apparently the sheltered nature of station B and the shallow shoal area attracted smelt to such a degree that they remained in the area during the day rather than moving offshore as they did in other areas. Trawl catches of adult smelt were negligible in April and the remainder of the year, suggesting that adults often avoid the trawl. During May, June and July few adult smelt were taken within the 9.1-m contour. After spawning they moved to deeper, cooler waters and remained there during warmer months. Incidental catches of smelt in gillnets and trawls occurred during upwellings when fish apparently followed cold- water masses inshore. Such an upwelling was recorded in August and September, at which time small catches of smelt were taken in gillnets. Wells (1968) showed that after spawning in April smelt moved offshore to deeper water; they were present out to 18 m in early May to 27 m by late May through August, and were dispersed throughout deeper parts of the lake in October and November. Ferguson (1965) also noted that smelt avoided warm inshore waters. Ferguson (1965) found that Lake Erie adult smelt begin moving toward the surface in late afternoon, remain there at night (though feeding did not occur) , then return to the bottom in late morning, at which time maximum feeding occurred. After September, adult smelt in the Cook Plant vicinity were scarce; however, a few individuals were caught at almost all stations in October and November, indicating that at least part of the population ranged into inshore waters during the fall. Temperature-Catah Relationships Preferred temperature for adult smelt was reported by Ferguson (1965) 126 TABLE B22. Monthly gonad conditions of rainbow smelt as determined by inspec- tion cind classification of the state of development of ovaries and testes. Fish v/ere captured during 1973 in southeastern Lake Michigan. All fish examined in a month were included except Immature and poorly received speci- mens. Gonad condition Feb Mar Apr May Jun Jul Aug Sep Oct Nov Poorly dev. Mod. dev. 3 Well dev. 18 79 201 4 Ripe- running 57 1 Females 3 21 13 3 1 6 6 3 Spent 30 6 A9 12 Males Poorlv dsiv. 2 1 Hod. dev. 1 11 20 1 Veil dev. 6 26 188 1 2 Ripe— ininnin g 17 4 35 8 1 5 23 7 1 Spent 26 11 13 1 31 13 .^ Unable to distinguish 12 4 33 6 109 45 to be 6.1 C; Wells' (1968) data show 6-14 C as preferred temperatures for smelt. The majority of trawl-caught smelt in our study, mostly YOY and yearlings, were taken at temperatures between 12 and 14 C (Fig. B26). To adequately delineate temperature-catch relationships for adults, gillnet data are used inasmuch as few adults were caught in trawls. Maximum numbers of smelt were caught in gillnets when temperatures were between 6 and 8 C. The suggested temperature preference of 6-8 C agrees well with the 6.1 C and 7.2 C preferred temperatures reported by Ferguson (1965) and Hart and Ferguson (1966) respectively. Although seines caught adults exclusively, these catches were not considered in the determination of temperature preference since the majority of these fish were spawning adults with accompanying behavior modifications. Peak catches occurred at 8-10 C. Scott and Grossman (1973) stated that smelt do not spawn until water reaches 8.9 C. Summarizing, three temperature regimes were apparent: 1) yearling and YOY smelt were most frequently caught at 12-14 C, 2) a temperature of maximum catch 127 SMELT S - SEINE ^ - GILLNET - TRAWL NF ~ NOT FISHED _ It «. «. •- «. B. r^ z :i 2 2 ^/z 23 25 27 29 TEMPERATURE RANGE C FIG. B26. Mean catch and standard error of smelt at a given 2 C temperature interval in gillnets, seines and trawls during 1973 in southeastern Lake Michigan. Midpoint of temperature interval is given. 128 between 6-8 C is indicated for adults, and 3) spawning appeared to peak when water temperatures reached 8-10 C, Other Consider ations Smelt were commonly found in stomachs of salmonids during certain times of the year, indicating smelt to be an important forage fish along with sculpins and trout-perch, in the event alewife populations should ever become decimated. Because they are fed upon by salmonids, which feed throughout the water column; it may also be suggested that smelt spend more time off the bottom (documented by Ferguson 1965) than does the more demersal spottail for example, which is seldom eaten by salmonids. However, there may be other reasons why spottails are not preyed upon significantly. We did not record any external or internal diseases or abnormalities in smelt. Yellow Ferah Yellow perch and Eurasian perch, similar species, combined have an almost circumpolar distribution in fresh waters of the northern hemisphere (Scott and Grossman 1973). Today yellow perch occur throughout most of North America, having been introduced in many areas. They inhabit waters of moderate temperatures from large lakes to ponds or quiet rivers and reach greatest abundance in rather fertile waters with large plankton crops and rich bottom fauna. Large bays of the Great Lakes are typical of such waters, and Green Bay in Lake Michigan has been an excellent habi- tat for yellow perch. Yellow perch have been an important sport and commercial fish in Lake Michigan, with annual commercial harvests averaging 1.1 x 10^ kg (2.4 x 10^' lb). Since catch records were begun in 1889 (Wells and McLain 1973), yellow perch yields have fluctuated widely, and in the early 1960's a production peak crashed coincident with and paralleling spread of alewives in Lake Michigan. Following the drastic decline of the alewife population in 1967-68, yellow perch responded with a strong 1969 year class. Because of its commercial and recreational importance, there is con- siderable literature on various aspects of the life history of yellow perch (Scott and Grossman 1973), which will not be dealt with here. In Lake Michigan several studies have been performed in and around Green Bay on yellow perch distribution, growth and food habits (Hile and Jobes 1942; Mraz 1952; Joeris 1957; Toth 1959; Dodge 1968). Although yellow perch are common in the rest of the lake we could find only two investi- gations pertaining to yellow perch in southern Lake Michigan (Wells 1968; Brazo 1973). More documentation is needed concerning the niche of this important fish in Lake Michigan, to better understand its economic and ecological value. 129 Statistiadl Analysis of lellow Ferah Catch Trawls, Analysis of variance of 1973 trawl catches of yellow perch (Table B23) indicates no significant difference (P > .01) between popula- tions off Cook Plant and those off Warren Dunes. However, two of the first-order interactions— MONTH x DEPTH and MONTH x TIME of day (Table B23) — were highly significant (P < .01) Explanation of the interactions will be attempted through examinations of seasonal migrations of yellow perch as demonstrated by plotting the monthly geometric mean values of numbers of perch caught by depths, 6.1m and 9.1 m, and pooled over stations and time (day and night) (Fig. B27). We will attempt to discuss interactions by pointing out discrepancies and irregularities in observed trends. Yellow perch were scarce at all trawl stations in April and May but appeared in abundance at 6.1-m stations in June. Failure to catch many yellow perch at 9.1 m in June suggests that most of the perch populations had migrated to shallow waters, within the 9.1-m contour, between May and June. Yellow perch remained concentrated inshore during June and July, and analysis of gonad conditions (Table B24) clearly revealed that they spawned in early June. These results are in close agreement with observations that yellow perch in Lake Michigan near Ludington migrate en masse to the littoral zone in late May (water temper- ature = 7 C) , and spawn in June at water temperatures near 11 C (Brazo 1973). Whether or not yellow perch spawn in the vicinity of the Cook Plant is as yet unconfirmed. Peak offshore (9.1 m) trawl catches in August and September suggest a general offshore migration, which was completed before the October sample period. This shift from higher inshore (6.1 m) catches in August to higher offshore (9.1 m) catches in September probably contributes much to the significance of the MONTH x DEPTH interaction. In the absence of extensive orthogonal contrasts and/or multiple comparison tests, one can roughly index the contribution of each cell to the interaction by the following formula: X. . = M. . - M . + M.. 13 13 -3 where: X.. = interaction effect (see Cohen 1969) 13 M. . = cell mean of the ith row and jth column ^J (Eq. 1) M. = ith row mean 1 M . = ith column mean •3 M. . = grand mean of all cells. This simple procedure indicates that the greatest interaction effect occurred in September, followed by another high interaction effect in June. Similar conclusions may be drawn through examination of Figure B27 . The general picture of seasonal migrations indicated by the MONTH x DEPTH interaction agrees with earlier trawl studies in southeastern Lake Michigan. It has been found that yellow perch are offshore at about 20 m 130 TABLE B23. Summary of analysis of variance for yellow perch caught in trawls in the Cook Plant study areas from June through October 1973. Source of variation df Adjusted mean square-^ F-Statistic AREA 1 .00428 0.04 MONTH 4 .84163 8.70 DEPTH 1 1.52628 15.77 TIME of day 1 .06315 .65 AxM 4 .08685 .90 AxD 1 .14712 1.52 AxT 1 .39739 4.10 MxD 4 1.12924 11.67 MxT 4 2.89516 29.91 DxT 1 .02140 .22 AxMxJD 4 .16485 1.70 AxMxT 4 .22534 2.33 AxDxT 1 .03864 .40 MxDxT 4 .03729 .39 AxMxDxT 4 .05215 .54 Within cell error 39'* .096793 NS^ <.01 <.01 NS NS NS <.053 <.01 <.01 NS NS NS NS NS NS Mean squares were multiplied by harmonic cell size/maximum cell size (n^^/N = 0.976) to correct for 2 missing observations where the cell mean was substituted. 2 3 k Not significant (P>.05). Not significant (.01

J 4-i u- o q5 , h- Wuj I z q: -J tr-S cr> 5co I-- >" C£> o o 10 w j,H9nvo X <^ h- o Z -DAY -NIGH l^s^T i. B cu o cu a cu a 60 o u X u 00 CM PQ IHOnVO HSld 'DN u d • M 60 X> •H CU 135 of setting and pulling nets, night gillnet sets probably overlap the early morning activity period and day glllnets may be removed from the water before the evening activity period commences. Observations by our SCUBA divers indicate that yellow perch were generally inactive at night, either resting on the bottom or suspended in the bottom 2 m of the water column. Since non-moving fish have a low probability of being gilled, this appears to confirm that most night catches were biased upward by net times over- lapping crepuscular activity periods. Seines. Yellow perch were abundant in the beach zone only during June, with mostly yearlings captured; seining February through May yielded no yellow perch. In July and August a few small individuals were captured (Fig. B29) , and in October about 50 TOY and yearlings were taken at Warren Dunes at night. Nonparametrlc tests for differences between the beach stations (A, B and F) , and between the Cook Plant and Warren Dunes study areas were carried out using the Kruskal-Wallls test (Table B26) . June was the only month for which there were sufficient data to make such tests , and neither test was significant (P > .05). Although a test was not made, there did not appear to be noticeable differences between day and night catches In the beach zone, except in October at Warren Dunes as previously noted. Seasonal Distri-but-ion by Age-Size Class In addition to changes in abundance parameters, subtle effects of the Cook Plant thermal discharges may be detected through analysis of growth rates and temporal and spatial distributional patterns of various size classes. Scale samples for analysis of growth rates of yellow perch from study areas have been taken but not yet analyzed. To facilitate the ensuing discussion, average sizes of yellow perch at the end of each growth season were compiled (Table B27) . As a preliminary approximation of seasonal growth, monthly composite length-frequency histogram summaries were compiled using data from both standard series and supplementary samples (not shown) . Length modes Indicated in our standard series length-frequency histograms for YOY and yearlings (Figs. B30, 31, 32) are generally distinct, whereas discrete length modes for larger classes (older fish) are frequently difficult to distinguish. Therefore the extent to which length modes are confounded by segregation according to size rather than age is unknown; a definitive answer must await scale analysis, but our data will suffice for the pres- ent discussion. It should also be pointed out that length modes greater than 100 mm may be biased upward slightly by Inclusion of gillnet data. loung-of-the-IeoJ'. YOY yellow perch first appeared in July in beach seine samples at sizes of about 25 mm (Fig. B30, Table B28) . This is consistent with our deduced June spawning, an incubation period of 8-10 days (Herman et al. 1969, Lake Mendota, Wis.) and an approximate first 136 o o 4-1 X O < '*'Cl_ o 03 _-■ z:::::^:^ =.=— *-^ Month C! C ^^^^^'=="^=-=^==-=r-=r^^ •r^ a 0) o <^ >< C 2 c^) Vj «< Q) CO H U- pa IS w J J -3 O o o 6 6 o in ^ f^ CM — •*c: n) » T-1 Ph ^ <: O ^ n) o <; (U o H M u w 1 O O m <51- 3q3nBO qsxj 'ou ubbr O to O CM O Oi CJ c o •u 4= OiO •H fl -a R aj >i c« • Tl G n) M W) C H •H x: M a 3 iH TJ g t3 0) (U ^ .C nj IC hJ •H 4J C M •H cfl a> !U to rC 4-1 C ;:3 •H O to 4J j: d m •H P « ro o r- o^ x: r-) a !-i 0) u (X Qi X 3 e o CD rH > X Xi JJ g >^ c w n1 (-1 r3 m M m ^ S u 0) CD 0) 0) IJ-1 o t3 C 0) 0) u i-i • G. 0) C O ^ r-4 O il O U g (D £ iH cfl c 6 -H 0) U-l X j-i II M C fj-i 0) tH •* 0) ■H .-1 rt to 4J g o u 11 ^w' S 0) N •H • to to c C o ta •H m 4J g to o •V o d) iH u n to •-{ a V O o •H r-^ M to Cfl o > M • O r-~ U-l CN PQ 0) in W •H ►J 1-1 m <: U-l H o 00 CO o o CO c o •H AJ to o o o en (T) 0^ U O en csi ro 00 £N CM O ^ VD 00 S P^ #v CM u c 0) CO > (30 •H CO CM •H Pri tH a) Xi C •H o ^ u u •H 4J o w S to U-l g •H (U 0) 5 iH a: A! rH to to CO i^ O h4 r-1 00 o 00 CM in rH (N in CN CN rH CN rH m IN IT) CN cn o in 0^ CM in ro C3^ rH CN CN rH o . ^ -a- rH rH CO in vo in ID . • 4= X C- a. AJ 4.1 60 oc #. 9' C c 00 r^ a; tu rH rH 0) O rH .H »- w -C J2 >> >< to (S o o H H f- >H IT) If) IV 03 CN CN CN o CM c in in Q) •U CTi c^ 4-1 to to rH rH to ^ Vj O u 3 to to O cO CO XI J- u 0) 00 N cr. ,!»: rH o Xi C •<1- 1 m K r- o o to a\ rH CJN to CSN o •-3 > rH (U rH PL, rH m a\ •o m m C e H P^ CO CO C m o Q) Vj •H > 3 >-i to W W c •H (U .-H PS o «S S 10 pq S-i 0} 0) 0) c 00 Ji 9 c •H 0) o -H pq h-a rJ S C 0) to rH i — ' j < 1 — ' — I — ' — I — ■■ — i — t—y -fTT — r~> — T'T- <.0 120 200 280 360 4 120 200 280 350 "^ " 120 200 2 lo36C J u N 30. 10. 50- 30- ili L. -J — . — p /2Z T ~i — '— T UL_xi- i»0 120 200 280 ;£3 '•0 120 200 280 350 ^D 120 200 280 360 J U L r -j r^ 1 1 1 |— I r i»0 120 200 280 360 'tO 120 200 280 35 C U^OTH I^fyf:R\'AL Ov^) I [— T 1 > 1 » 1 ' i UO 120 200 280 360 FIG B30 . Length-frequency histograms for yellow perch caught in standard series seining during 1973 in the Cook Plant study area of southeastern Lake Michigan. 140 STATION A STATION B STATION F M o ai w P5 50. 30- A 10. u G 50. 3 0- 10-5 "T r-n ' i ■ f— T I — ' « — 1 — • — i — " — I — ' — I — > — 1 ' > — I ■ — I — ■ — i — ' — rr^TT i»0 120 200 28 360 i*0 120 200 280 350 '*0 120 200260 :ibO so- so. s 10- K 50- P ■ 30-. 10- — -_ — _— -, ,- — J, 1 , , 1*0 120 200 280 3S0 — . J 1 i . — i I -j- kC 120 200 280 360 i* 120 200 230 360 -j I —i :^ 1 1 I 1 r 50- 30, 10, c T 50 30 IC- 1*0 120 200 280 360 — j r— j < j r- , T- -J— "•O 120 2 00 280 350 L£NGTH INTERVAL (rv-i) Hill UO 120 200 2S0 350 FIG. B30 continued. 141 o<>- z — • o 3: i- Q <>- z — • to XI— i5 •-^i o g o o n T — ' — r~' — I — «— J — • — i — ' — r O O OOCJ o oo Pi^ W PQ -J r-i — I — I — I — r O O O C3 c» u^ (n r-< m a ^<+H O u o CO IW ^ u Tl M 3 o 4J 4-J CO CO •H 4-1 43 C CO >,rH O Pm a Q) ^ 3 o cr* o 0) o u M-l cu 1 J3 ^ u 4J on c a •H cu hJ m r^ i-i CO OS rH m Wl C • •iH o U M 3 (H T3 HSii io •aaswiiN 142 a < >- z: — CD 3: 1- Q<>- ■CD XI- o g —'^ I- <: — CD CM J^ > o g hS!±i g t/1 T — f— r 000 -J — I — r t3 0) d •H ■U C o u <; P^ 0:5 s <: >H o M HSI5 KO ^aaHTiN 143 cxo- : — o XI- a<.>- ' o X I- o ■ • - -f o i - o ^ 1- ■V r---r— .— , — 1 ■ ■ • »~ J t 1 I i; - ' i-s i=: ^ t-) t3 eJ •X} 3 C O a o M HSI5 50 ^aawfiN 144 ca <:>- Z"0 X I- a o - 1 :E. tr> -- 1/1 <; p o > ' 1 en w PM 'a c •H c o CJ rH - ■ QD X h- o<>- Z-^OXH- I -o o i UJ g ^00 o T — « — r ^^ ut O U H 3 O > T3 C •H 4J C O o M HSII 10 EaSHflN 146 n<>- ' e) X (- o <>- 2: -- d x 3: ^ ^* in <3 Ph 0!j s <; >-' 60 c •H M S T3 SO C •H t-H ;s 03 U ■P Cfi 0) cd •H 4-1 ^< Cd (U r0 CO -d C3 u cd II TJ cd & 4-1 CO a ■ •H c td JJ GO ^ -H ^ Mrc: 1: 3 CJ cd -H "^^ S ^ OJ -> ^ cc: u cd LiJ 0) |J t— Ph P! * ' 15 M — T — OJ 1— iH AJ CO rH to -i: ^ 00 cd > xi >. 3 CJ -u C CO Q) 3 J-" cr c (U cd n ^ m PM i^ 4J 60 fi 0) i-J tu ^ . -P <^ _ (T) G pq -H • en C3 r- H CTv |i< H HSM JO Hasai>inN 147 DO- Z — > O X H a<>- z-- o xt— C5 O a ■z. o < UJ •"> m 1-) t3 Z I-) CO hJ c o a en pq o M HSU d:o yaewriN 148 oo- 2: — O X H 00- z: ^ w X h- i a ii 1 2: o -r-j h O O CD o CO W Pm T3 g •H 4-1 C O O CO M HSM JO ^aawfiN 149 2: — o X 1— a - o a: h- O u H ^ a > C •H ■U C o o rH pq O H Hsid do Haap^N 150 TABLE B28. Growth of 1972 and 1973 year class yellow perch (modal total length-mm) during 1973 as deduced from monthly composite length-frequency histograms. April through October data were based mostly on standard series samples, January through March and December on impingement samples only, and November on gillnet samples only. — - class Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 1972 65 65 70 65 70 80 110 140 140 150 160 1973 • — 25 65 80 90 105 70 concentration in the beach zone in June, July and perhaps including August, and a gradual offshore dispersal in late summer. Adults. Virtually all adult yellow perch are in deep water during winter, in contrast to the more widely dispersed yearlings. A few perch were taken in April and May, but June marked the most significant influx into our area, when large numbers were caught at 6.1'-m stations. This large catch was associated with large gillnet catches at station A, 1-3 m deep, observed in 1973 (see Table B-41) and again, in particular, 1974. Concurrently, catches at 9.1-m stations were low, indicating the bulk of the adult perch population was in 1-6 m of water during this period. Few adults were taken in June seine hauls, which suggests adult perch may not utilize or enter to any great extent the shallow, less than 1-m, beachwater zone, even during periods of maximum inshore abundance. Gonad data (Table B24) show that 651 of 729 (89.3%) yellow perch captured in June were spent. To determine that we did not simply fail to fish during the period in 1973 when ripe-running perch may have been in the study area, we conducted two series of gillnet sets in 1974, one supplementary set in early June, and a standard series set in late June. Very few fish were caught in the early sets and those captured in the late sets were all spent, as were the fish caught in 1973. SCUBA divers have been able to squeeze eggs and milt from a few perch captured while diving in the study area; however, spawning and egg masses have never been observed. We have tentatively concluded that yellow perch are spawning outside the 9.1-m contour or elsewhere in the lake, and only enter the inshore zone around the Cook Plant when most are spent. From June through August, daytime locus of the perch population occurred at 6. 1-m stations. For remaining months perch were migrating offshore, since in August and September perch were most often captured at 9.1-m stations at night, indicating the initiation of the fall-winter offshore migration which was complete by October. After August, daytime locus of the perch population appeared to remain in the vicinity of the 6.1 to 9.1~m contour until the seasonal offshore migration of perch was complete. Mraz (1952), in an early May tagging study of yellow perch 151 from Green Bay, showed that 79.5% (101 of 127 recaptured) of the fish were recaptured at the release site, 19.4% were taken within 38 km, 6.5% between 38-76 km and 1.9% between 76-92 km of the release site. Eighty-six of these fish were recaptured In late May, 21 In June and July, and one in September. Throughout the months we observed two types of migrational patterns: 1) the seasonal pattern of onshore-offshore movement just discussed, 2) a diel pattern of nocturnal shoreward movement followed by a diurnal retreat to deeper water. It Is possible that this second migration- al pattern may represent primarily crepuscular behavior; however, since an attempt was made to separate day and night fishing efforts we have little data taken during the crepuscular periods. Tempevature-Catah Relationships According to Fry (1964) , yellow perch cannot acclimate to temperatures above 32 C and have a final preferendum of 24 C. Final preferendum is defined as that temperature range in which fish will ultimately congregate in an infinite gradient (Fry 1947). Fry also found that laboratory deter- mined thermal preferences, especially for warm-water species, were several degrees higher than those deduced from field observations. YOY yellow perch taken from Lake St. Clair and acclimated to 24 C in October and November selected temperature ranges from 23-24 C and 20-21 C respectively (McCauley and Read 1973). Adults from the Grand River acclimated to 24 C in June preferred temperatures of 18-20 C; those from Lake St. Clair acclimated to 24 C in October preferred 16-19 C. Scott and Grossman (1973) postulate a similar temperature preference and suggest that perch follow the 20 G iso- therm in their seasonal movements. Our data (Fig. B33) suggest two separate peaks of maximum catch for yellow perch. The first range for small and medium-size fish may be deduced from numbers caught in seines and trawls. Larger perch are in- frequently caught in seines and trawls, thus these gear reflect temperature preference for smaller fish. Yellow perch were caught in trawls between 8 and 24 C with peak catches between 22 and 24 C. Seining data suggest that smaller fish, mostly yearlings, were caught in water temperatures from 20-24 C, which agrees fairly well with Ferguson's (1958) determination of 23.5 C. A second range for medium and larger-size perch can be deduced from gillnet data. Most gillnet-captured perch were taken between 16 and 22 C. Other Cons-iderat-Cons Yellow perch were observed by SCUBA divers on several occasions during the day and once at night at the Cook Plant in the period between June and September 1973. Perch were seen only in areas adjacent to the intake and discharge structures, never in areas outside of the riprap (i.e., natural, undisrupted areas), which might indicate either positive attraction to the structures as a source of shelter, protection or as a better forage area or that these fish are more easily frightened from, and therefore not as 152 X o < o X CO O d < 7 9 II 13 15 17 19 TEMPERATURE RANGE C FIG. B33. Mean catch and standard error of yellow perch at a given 2 C temperature Interval in gillnets, seines and trawls during 1973 in southeastern Lake Michigan. Midpoint of temperature interval is given. 153 frequently observed in open parts of the lake. Perch were seen most fre- quently during the warmest period of the diving season, June through August, which correlates with periods of maximum abundance (Table B6) . Differences between diurnal and nocturnal behavior of these fish were noted. During the day, perch were seen to be actively swimming throughout the lower half of the water column in the areas near the crib structures. Fish did not rest on or swim along the bottom riprap. Schooling behavior was not noted, although dispersal was uneven. At night, perch in the area of the structures were inactive, either resting on the bottom or suspended in the bottom 2-m portion of the water column. Fish could be captured bare- handed. More fish were observed at night (maximum observation 100) than during the day (maximum observation 10) . The heightened Incidence of ob- servance nocturnally may be due to the fact that the fish are less easily frightened from the area when they are inactive. During a night dive on 17 June 1973 in the area adjacent to the south intake structure, 60-75 (150-250 mm) and 15-20 (250-350 mm) perch were observed over a 71~min period. Water temperature was 18.5 C. More perch were seen during this dive than on any other occasion, the majority were inactive or resting on the riprap surrounding the intake structure. Spawn- ing activity was not observed. Work from Neill (1969) on Lake Monona, Wis., which receives a heated effluent, showed that perch were taken most often during the day with electro-shocking gear. Neill described perch as heat-intolerant species which seldom occupied the outfall area. He found through mark and recapture experiments that perch did not remain in the effluent for very long and that yellow perch were more abundant in the reference than in the effluent area. In the Cook Plant vicinity considerable value is placed on yellow perch by local sport fishermen. During the summer, local residents fish for perch from boats and piers at St. Joseph and along the lake shore. In summer of 1974, on some days 10-20 boats were observed off the Cook Plant, the fisher- men probably seeking yellow perch. Apparently the underwater structures and riprap attract yellow perch which in turn concentrate fishermen in the area. TTout-PeTch Trout-perch are widely distributed in lakes and streams throughout central and northern North America (Scott and Crossman 1973). In the United States it is a common native species in the Great Lakes but is relatively rare further south. Its commercial and sport fishing value is negligible. Although of little economic importance, trout-perch are a significant compo- nent of the aquatic food chain. In some northern lakes they are Important forage fish for lake trout and walleye. Because trout-perch feed at night in the shallows and move into deeper water during daylight, they may serve as nutrient transporters (McPhail and Lindsey 1970) . 154 As with most forage fish species, definitive works on trout-perch are rare. Kinney (1950) made the first extensive investigation of age, growth, reproduction and food habits of trawled trout-perch in western Lake Erie, While investigating the biology of a cestode, Lawler (1954) made observations on reproduction and age of stream-trapped trout«.perch from Heming Lake, Manitoba. Magnuson and Smith (1963) performed the most comprehensive study to date of trout-perch from Lower Red Lake, Minn. Age, growth, population structure and reproduction of 10,511 seined and trawled fish were intensively studied. From fish collected by trawling, Bostock (1967) studied the ecology of trout-perch from Lake Superior. House and Wells (1973) described age composition, growth rate, fecundity and spawning season of trawled trout- perch from southeastern Lake Michigan. Although much is known on the life history of this fish, more studies are needed on relationships between trout-perch and other species in the Great Lakes as well as information on spawning habits and distribution of larval trout-perch. Stat-istiaal Analyses of Trout-Perah Catch Tvccwts. Results of the ANOVA revealed highly significant (P < 0.01) main effects due to MONTH, DEPTH and TIME of day (Table B29) . Differences between areas was not significant (0.01 level). The test statistic was very close to zero, indicating very little difference between study areas. The value of this finding is reduced, hovrever, since AREA entered into interac- tions with MONTH, DEPTH and TIME of day. However, it is probable that trout-perch populations are similar at the Cook Plant and Warren Dunes areas. This attests to the homogenous quality of the inshore waters along the coast of southeastern Lake Michigan and helps establish a baseline for detecting population differences between trout-perch at the control site and the plant site once the Cook Plant becomes operational. In the ANOVA there were significant (P < 0.01) second-order interactions among MONTH, AREA and DEPTH and among MONTH, AREA and TIME (day-night) (Table B29) . Since higher-order interactions tend to mask main effects, it became necessary to examine the two interactions in detail. Both interactions are inextricably linked to the following factors: 1) general inshore spawning activity commencing in June, 2) climatic (physical) factors occurring during sampling, such as an August upwelling, and 3) high variability inherent in trawl samples. Area effects in the interaction terms are the most difficult to explain. Conceivably, different behavior patterns are occurring between trout-perch at the Cook Plant and Warren Dunes, but unless different physical substrate characteristics are present or a distinct biological pattern becomes apparent in subsequent sampling, it is unwarranted to consider that there are actual differences between study areas. The MONTH x DEPTH x AREA interaction (Fig. B34) is probably the result of high June catches at the 9.1-m stations, which were probably somewhat related to spawning although spawning is thought to continue through July. After June, 9.1-m catches at Warren Dunes were either equal to or greater than 6.1-m catches. Catches at Cook 6.1-m stations, probably partially 155 TABLE B29- Summary of analysis of variance for trout- perch caught in trawls in the Cook Plant study area from June through October 1973. Source of variation df Adjusted mean square 1 F-Statistic AREA 1 .01518 MONTH 4 1.05937 DEPTH 1 2.98711 TIME of day 1 8.30979 AxM 4 .38472 AxD 1 .00372 AxT 1 .31215 MxD 4 .77185 MxT 4 .79715 DxT 1 4.38239 AxMxD 4 .45518 AxMxT 4 .49765 AxDxT 1 .00390 MxDxT 4 .12307 AxMxDxT 4 .31117 Within cell error 39^ .0946524 .16 11.19 31.56 87.79 4.06 .04 3.30 8.15 8.42 46.30 4.81 5.26 ,04 1.30 3.29 NS2 <.01 <.01 <.01 <.01 NS <.01 <.01 <.01 <.01 <.01 <.01 NS NS <.053 ^ Mean squares were multiplied by harmonic cell size/maximum cell size (n, /N 0.976) to correct for two missing observations where the cell mean was sub- stituted. 2 Not significant (P>.05). 3 Not significant (.01 <.05). k One degree of freedom was subtracted to correct for one missing observation where the cell mean was substituted. 156 Area x Month x Depth Interaction 100 3 CO u (U Cu js a u CD ! f 1 <^c: o o X ^ O 2 K. o <• h- — , jr- OOtD O CO o <0 o 'J- o CVJ O o IHSnVO HSU 'ON 64 (£2 <3-=:--ri <►-:> U- o o o 4» o o o IHSnVO HSU *0N IHOnVO HSld 'ON X Q < -7 ^ "<^ Lu o-cn do — CD 00 I- " i I O i VO >-. r'l u W cfl 3 • !-( rCl IHOnVO HSU 'ON M 0) 160 u-1 CO c 3 P a 0) u cd (U c •H (U CO J2 O cfl *feC. n e o < ■•^> <( ■i) m M ^" ~'C'__ O O to -^ bO ja < CO tH o Q 2 CO <; J< O ^-' CJ <. ^ cu a ^^•s* •H ^S« CD 4-1 ^ n) 13 60 • C B •H CO Vj 60 3 -H t3 x; Td -H Q) S ^ CO cu •H ^ 14-1 CO h4 cn 0) G a ^ •r-l 0) 0) 4J CO cn CO C Q) •H jr; u 4J 3 ^ 60 CO 3 CO S CJ -H ^ ro r^ 2 P. 1 1 4J >-l 3 CU CO ,a 4-1 OJ < > iw IS 4_) . < (U »-i s « 3 s >-i u. B37. Feb JZ -3 si Ix. 2 161 TABLE B30. Simmary of nonparametric analyses of trout-perch caught in standard series glllnets from Cook Plant study areas April through October 1973. NS = not significant. Factor (and levels) Kruskal-Wallis statistic Mann-Whitney U statistic •3^ Value P Value P Month (May-Oct) 5 3.3460 Depth (6.1 m, 9.1 m) 1 .60421 Area (Cook Plant, Warren Dunes) 1 .67204 .6468 NS — — .4370 NS 482.00 .4123 NS 442.50 .4086 NS .3834 NS nonparametric Kruskal-Wallis test was used to test for differences between stations and study areas; no significant difference was found (Table B31) . Insufficient data existed to test differences between months. Seasonal Distribution by Age-Size Class Length-frequency histograms for trout-perch caught in standard series nets were compiled by gear type (Figs. B38, 39, 40). These histograms must be examined in total to delineate movement patterns because of size selectivity of the various gear. We can discuss with confidence only the seasonal ranging of young~of-the-year, yearlings and adults. Beyond this categorization inferences become less valid. Young-of-the-Year. YOY with a modal length of about 25 mm first appeared in September sampling (Fig. B40) . Because the majority of spawning activity probably occurred from June to August, although some spawning may have occurred in May and September (Table B32) , YOY trout-perch should have been taken in samples before September, Either YOY were not present in the study area from June through August or, as appears to be the case, fish were present and our sampling gear did not collect them. Assuming YOY trout-perch were present in the study area before September, probably the mesh of the trawl net was too large to retain small specimens. Another possible explana- tion for the failure to capture YOY prior to September may be that their distribution is very spotty. Also, we suspect that most or all life stages of trout-perch are associated closely with the bottom. YOY were not captured by seining, indicating that at this life stage utilization of the beach zone does not occur. In October many YOY, 25 to more than 40-mm size range, were caught by trawling (Fig. B40) , which again lends support to a July spawning peak. YOY were captured during the day and night, and apparently do not exhibit a tendency towards extensive nocturnal horizontal movements as do adult fish. By November YOY had presumably moved offshore as did the bulk of the adult trout-perch population. 162 M O W g STAT 1 Of i A 10 6 . A P R 10 2 - 20 EO 100 litO 180 10. 6- M 10- 6- I I — T — < r-^ — ; ' i — ■• — f— 20 60 100 mo ISO STATION B — I . [ -T f ■ , ■ p- 20 60 100 mo 180 — T < — 1 — »-■ " r 1 ' t — r— i— 20 so 100 IWO J£.C STAT10»J F -I — I — t — I — t — ■ — I — « — I — 20 60 100 mo lao 20 T — t— I — I- ■ i "I — J — I — r~ :0 60 100 mo 180 10 - 6 . 2 _ U 10 J L 6 2 - r 20 — , -I I — r , — I — r- Eo 100 mo 160 "T ' — I ' — T-> — I — ■ — 1— 20 60 100 \^a ISO -| — 1 — t— r~I — ' — i — ■ — r 20 60 100 I'iO 180 liMGIK INTERVAL (f-w) FIG. B38. Length-frequency histograms for trout-perch caught in standard series seining during 1973 in the Cook Plant study area of southeastern Lake Michigan. ND = no data. 163 STATlOri A STATION B STATION F 10. 6- A 2- U G 10- 6- 20 60 100 mo 130 20 60 100 i>*0 180 20 60 l(5o mO 180 H O t — 1 — I — I— I — I — I — i—TT— r 20 60 100 lUO 18W -1 ■ I *— J—i — J — ■ j- 20 60 100 mo 180 10- 6- N IC 5- 2- -j — i — i I 1 < I — r— T T — '—I — > — r~T — t — ' — r 'I'll T • 1 ■ « ■ J ■ ' — I • — f 20 60 100 1<<0 180 ND 20 60 100 mo ISO 20 60 100 l'«0 18D 20 60 1 Ao 1<«0 ISO A • A '^io'.*.* i_ Lfl^[jm INTERVAL (mi) FIG. B38 continued. 164 ao- |(J3 Xh- Q<>- 3: o i o CO Q o p CO o o p 00 o in -4; PU Pi Wl .s ■u 4-1 -j cd -. u T) Wl 3 4-1 4J CO CO •H 4-1 ^ C cd >^rH PH c cu >: 3 cr Q) C_) U "4-1 cu 1 ^ XI 4J 4J tx a c •H (U h-i rO r^ • CT\ ay <-i en M 60 C • •H CJ ^4 t- 3 (^ TJ g H HSU .io ^aawfiN 165 QO- :z — i33:i- QO- Z ■— O 3H— I cr> S a o CO i fe •-1 C3 2 o in i-I 13 hJ 13 a> 3 o o en PQ o M HSM 10 ^aaHON 166 Q<>- MJ OTh- o 1 UJ Q o 1" 00 O I CO CN — « g •H C o o pq O H P4 <| tD o w W Pm HSM io HaawfiN 167 o<>- 2>->0 XH- i 1:^ fe a z o 1- o o < I— CO T — < — r m 1/1 CD -J 1 1 1 1 1 J r- in C3 un Q) P a •H 4-) C o o n m O O H S O > Hsii 10 HaawiiN 168 Q<>- Z — O X t— X ■y . o J- < fe - Q<>- '13 X H- t = <3 -s ^ ccr Q o < O z o CO H 60 C •H H 3 •13 nn C •H rH ? cd u +J to OJ •H CS >-i ■U 0) to to la T! o M c n) T) II C 4-1 g CO c •H a CO JU 60 ^ •H 60 J2 3 a crt •H o S ,G QJ c; ^ M to O •u u to 4J to (1) M ,c o •u IM 3 o M CO ^ IH !-j o 60 O to JJ (U CO M •H CO A >, 1>,'0 U 3 c ■U) 0) to JJ (U fl l-l to <4-l rH 1 PM ^ 4J ^ 60 o c o - ■O X H- Q<>- Z-- ej X H I' C3 ■z. o . - » (- fe - ►n & Z •-) P h4 t3 0) B •H c o CJ o - Z — O XI- r x - - o i - a <>- 'O X I- ■ '- a: o I- o to T — r- I C o a o - 2:-- CO n::!- 00- •iOZCh- i p Q !5 1- 1: p i P O U H IZ o f> ^3 g •H +J c o o o H HSIl 50 ^aSMlN 172 TABLE B31. Summary of nonpar ametric analysis of trout-perch beach seine data collected from Cook Plant study areas 1973. NS = not significant. Factor Kruskal-Wallis statistic (and l€>vels) ^f Val ue P Stations (A, B, F) 2 .20192 .9040 NS Area (Cook Plant, Warren Dunes) 1 .11538 .7341 NS No trout-perch larvae, fish less than 25 mm, were captured during 1973 (see Sec. C) . Again assuming that spawning occurs in the study area, the suspected benthic behavior of these larvae and our failure to sample effec- tively at this strattun may explain why no larvae were captured. Benthic sled tows initiated in 1974 should help to verify or disprove whether trout- perch larvae are present in the area and whether demersal behavior is occurring. Yearlings. Yearling trout-perch first appeared in limited numbers in April trawl samples (Fig. B40) ; modal length was approximately 40 mm, Additional yearlings were collected in May and June at which time modal length was more than 45 mm. By July this length had increased to 50 mm, which compares favorably to findings of House and Wells (1973) , who calculat- ed total length of southeastern Lake Michigan trout-perch to be 49 mm at the end of their first year of life. Growth of yearlings from Lake Michigan appears to be slower than yearlings studied in Lower Red Lake, Minn, by Magnuson and Smith (1963), whose calculated average lengths for females and males in June (time of annulus formation) was 51.4 and 50.8 mm respectively. Yearlings were caught in April and May more frequently during night than day trawling (Fig. B40) , but differences between numbers were not as pro- nounced as with adult trout-perch, which were caught at night. Evidently yearlings do not migrate beyond the 9.1-m contour as do adults. Only one yearling was caught by beach seining in May (Fig. B38) , indicating that yearlings rarely enter the beach zone. We concluded that yearlings in the spring during both day and night are distributed from 2 to at least 9 m. During June, July and August, differences between day and night catches of yearlings were more pronounced, with greater catches occurring at night. Apparently at this stage yearlings are following the nocturnal migrational pattern exihibited by adults to a greater extent than in April and May. In April and May there was little difference in catches between stations; however in June, July and August catches of yearlings at the 6.1-m stations were greater at night than during the day. The obvious pattern is that yearlings remain at the 9.1-m contour and probably deeper water during the day and migrate inshore at night to the 6.1-m contour and possibly even shallower water. They must not migrate into the beach zone at night since no yearlings were caught by night beach seining. Reasons for this nocturnal migration 173 TABLE B32. Monthly gonad conditions of trout-perch as determined by- inspection and classification of the state of development of ovaries and testes. Fish were captured during 1973 in southeastern Lake Michi- gan. All fish examined in a month were included except immature and poorly received specimens. Gonad coodition Feb Mar Apr Hay Jun Jul Aug Sep Oct Nov Dec Females Poorly dev. 1 1 4 14 86 1 Mod. dev. 5 3 1 38 10 38 1 Well dev. 18 55 198 117 55 12 1 Ripe-running 3 1 7 Spent 53 53 Males 71 34 9 1 Poorly dev. 2 1 4 6 22 55 3 Mod. dev. 1 10 19 9 21 14 16 1 Well dev. 10 47 111 56 53 6 Ripe- running Spent 1 1 20 33 34 21 1 Unable to distinguish 1 2 11 11 9 3 4 are probably related to feeding behavior; future analysis of stomach samples may help clarify this behavioral pattern. In September a few yearling trout-perch were caught at 9,1-m stations during the day and at all stations at night. By October no yearlings were caught during the day, but many were caught with adults at 6.1 and 9.1-m stations, indicating that inshore nocturnal migrations from farther out were still occurring in October. Adults. Due to considerable variation of length within each age class (Bostock 1967) , ages of trout-perch are generally difficult to determine accurately. From age-group length distributions determined by House and Wells (1973) , It appears that fish 80-140 mm long could range from 2-7 yr old. As a first approximation of age-classes, we compiled a composite length-frequency histogram consisting of standard series and supplementary nettings, and examined it by month (histogram not shown). Local modes of trout-perch lengths appeared to corroborate the findings of House and Wells (1973). Two- and 3-yr olds are probably 50-100 mm total length. Fish 100-140 mm are probably 4-6 yr old. Trout-perch from 140-170 mm may be 7-9 yr old. Trout-perch undoubtedly grow to greater lengths in southeastern Lake Michigan than has been reported elsewhere in the Great Lakes. The largest specimen House and Wells (1973) captured was a 152-mm female. Scott and Grossman (1973) indicate an identical maximum length for a specimen 174 from Lake Ontario. In the southern boundaries of their range, trout- perch grow to their greatest reported lengths, occasionally to 200 mm (McPhail and Lindsey 1970). Our largest specimen was a 168-mm (T.L.) female weighing 38.8 g. Several other fish were well over 150 mm. The large size attained by trout-perch in southeastern Lake Michigan may be related to lack of predation. Stomach contents of large salmonids captured during our fishing efforts seldom contained trout-perch. No trout-perch were caught during our limited fishing efforts in January and February (Table B6) . Like alewife, trout-perch sought deeper waters in Lake Michigan during winter months. Wells (1968) found most trout-perch at 37 to 61 m in winter. Bostock (1967) found trout-perch in Lake Superior were confined to waters deeper than 64 m during the winter and early spring. Our catches indicated they were still scarce inshore in March, In April, adult trout-perch began to appear in about equal numbers in our catches at both study areas (Fig. B40) . All size classes were repre- sented. Apparently the total population migrated inshore in spring, in contrast to some other species (e.g. alewife) where larger individuals migrated Inshore first. Most trout-perch were caught at night at 9.1 m. An analogous pattern continued into May, but overall catch was higher. Night catches continued to be higher in both study areas but there was no apparent preference for either 6,1 or 9,1-m depths. Evidently fish were outside the 9.1-m contour during the day in April and May and migrated inshore at night. May was also the first month of the year when trout-perch were captured in the beach zone, during night seining (Fig. B38) . At night apparently at this time of year these fish extended their range into the beach zone, which was possibly associated with feeding behavior or thermal preferences. Scott and Grossman (1973) indicate that trout-perch move into shallows of lakes to feed in the evenings and retreat to deeper water with approach of dawn. June marked the first major influx of adult frout'-perch into the inshore area (Fig. B40) . Very high night catches characterized the yield at each station with the exception of the 6.1-m station at the Cook Plant. All size classes were represented in the catches, indicating that a complete cross-section of the adult trout-perch population was inshore at this time. Day catches in June were relatively large compared v/ith previous months ' catches, and subsequent gonad examination (Table B32) suggested that initiation of spawning activity may have been responsible. Ripe adults were found in the study area from May through August (Table B32) , and spent adults were found in increasing numbers from June through August. House and Wells (1973) found trout-perch spawning from late June to September in southeastern Lake Michigan. They apparently spawned later in southeastern Lake Michigan in 1973 than has been reported from other areas: Hemlng Lake, Manitoba (May — Lawler 1954); Lower Red Lake, Minn. (May to August — Magnuson and Smith 1963); Lake Erie (May to July — Fish 1932). Kinney (1950) found trout-perch spawned from June to August in Lake Erie, later than reported by Fish CI 932). Although ripe fish in an area does not necessarily prove spai/ming is occurring, presence of many ripe and several ripe'-running speci- mens in our samples Indicates that some spawning must have occurred in study areas. General accounts from the literature (McPhall and Linsey 1970; Scott 175 and Grossman 1973 j Magnuson and Smith 1963) revealed that spawning takes place at night in shallow water (0-1.3 m) in slow moving streams or along lake beaches. Eggs are small, 1.5 to 1.9 mm in diameter, adhesive, and hatch in about 1 week. House and Wells (1973) found that sexual maturity is attained by few 1-yr old fish, 84% of 2-yr old males, 50% of 2-yr old females, and all 3-yr olds. Trout-perch mortalities of dieoffs following spawning have occasionally been reported (Magnuson and Smith 1963) , however we observed none in our study area to date. In July, differences in catch between depths and areas were not as great as in June, and nocturnal behavior was again suggested. Day catch exceeded night catch for the first and one of the only times at the Cook Plant in August, whereas the usual pattern of greater night catch was true for Warren Dunes. Considerably more trout-perch were caught during the day at the 6.1-m Cook station than in any other month at that station. This apparent irregularity appeared to be caused by an upwelling which occurred during trawling. It is hypothesized that this cold water mass "forced" fish into shallower water. Effects of the upwelling were apparently greatest at the Cook Plant, since more fish at Warren Dunes were caught at 9.1 m than at 6.1 m. (See Seibel and Ayers 1974 for a discussion of up- wellings in the study area) . Number of adult troutr-perch caught in September decreased noticeably from summer peaks. Fish had apparently begun to move into deeper water. The familiar pattern of highest night catches in deeper, 9.1-m, waters returned . In October, as in most past months, the same general pattern of heighten- ed nocturnal activity continued. October night catches of trout-perch at both study areas were much higher than their respective nighttime September yields. Presence of fish in the seine catch at night indicated trout-perch were again utilizing the beach zone as they did in May. Very few fish were caught in November and December; however, no trawling was performed and possibly a few more would have been caught if trawling had been done. Wells (1968) found the majority of trawled trout-perch were in water deeper than 13 m in November, although a few fish were caught at 5.5 and 9.1 m. Apparently by November the majority of the trout-perch population in the study area had migrated to deeper water for the winter. The fall migration was evidently somewhat prolonged during 1973 in our study area. Wells (1968) captured all of his October specimens beyond the 9.1-m contour in southeastern Lake Michigan in 1964 when bottom temperatures were 11.7 to 12.3 C, while we caught large numbers of trout-perch when bottom temperatures were 13.7-15.7 C in October. By November bottom temper- atures were below 12 C in our study area and we caught few trout-perch. Bostock (1967) found the return to deeper water occurred by late September and early October in Lake Superior. Temperature-Catch Relat-ionships Any conclusions from our study about temperature preference of trout- perch must be cautious generalities for the following reasons: 1) extensive 176 trawling by Wells (1968) suggests that except for June through August the bulk of the trout'-perch population resides outside the 9.1-m contour, 2) preferred temperatures may reflect spawning temperature preferences rather than temperatures most often selected during the non-spawning period of the year. Most of our trout-perch were caught in trawls when water temperature was from 14-20 C (Fig. B41) ; peak catch occurred between 16-18 C. This corresponded well with the upper range of temperature preferences, 10-15 C, found by Wells (1968). Othev Cons'tdevat'Lons The large size attained by trout-perch and their abundance in the study area is thought to be related to lack of predation. We seldom found trout- perch in stomachs of piscivorous fishes — yellow perch, northern pike, lake, rainbow and brown trout, chinook and coho salmon. However, available liter- ature reveals that most of the above species do prey on trout-perch in other habitats (Lawler 1954; Magnuson and Smith 1963; Scott and Grossman 1973). Evidently extremely abundant alewives supply piscivores in our study area with an ample food supply and act as a buffer species for the trout-perch at least. Alewives were a common and apparently preferred or available prey of the piscivores in our study areas. Since trout-perch are abundant in the study area, we hypothesize that the demersal behavior of trout-perch makes them a less available prey than the ubiquitous alewife. A similar situation may exist with spottail shiners, which are also extremely abundant in the study area, yet seldom preyed upon. Absence of predation by lake trout on trout-perch is difficult to explain, since lake trout in the study area preyed upon other bottom-dwelling fish such as sculpins. If for some reason alewife numbers were to decrease drastically in southeastern Lake Michigan, spottails and trout-perch might serve as food for lake trout. Walleye, which prey on trout-perch and are usually found in waters with trout-perch, were not found in the study area; one walleye was captured in 197 2. Magnuson and Smith (1963) found walleye to be the most significant single predator on trout-perch in Red Lakes, Minn. Scarcity of walleye in the study area is an enigma. Possibly absence of spawning areas prevents this species from developing a population capable of sustaining itself. We suggest that it might be advisable to stock walleye in southeastern Lake Michigan, where sufficient prey exists for this species. Although there is presently a stocking program of other piscivores, lake trout and salmon, in Lake Michigan, addition of another valuable sport fish may be warranted in view of the abundance of food. 177 40 TROUT-PERCH - SEINE - GILLNET - TRAWL - NOT FISHED o H c_> (1) • !-i vO O • J^ #^ CD CO u C 0) o o > •H 4J •H •P PS CO 1-1 +J to X w -H D. 3 0) >^ o CO U •H o CO Ti >~> 4J a c 0) • cu D. 4J g >-i CO S (U t-H & 0) P. Xi (X 4-1 u 3 (U CO CD u to ? to OJ C 00 CO rH c 4-1 .-H •H 0) •H ^ c 60 > fH CO rH U Vi t4 O 4J 60 M-i •n C 4J a ■H 0) to to ■ 0\ 4-1 B x: M 60 x: ro S O CM O vO O r~l OO < CM 00 <; c^ oJ to a r-l td in > o o z: o 3 CM < CM c 3 O ►-3 CM U •l 00 ol cB CM II I! II r— -it rH r- en CO 00 O O rH O n rH CM CM . CO rH rH rH CM CM X •H Ql CM ~3- rH rH rH CO m rH ^ OO CH in i-H U-1 CM CM CO 00 rH CO rH in CO rH CM lO CO rH CM CM CM (^ CM 0> <■ \0 r-i vr CO mm CO m 00 r-» 00 o ~3- r^ rH vt- *^ rH CO ^ rH -* rH r-t m C3\ -* O vO O rH CM <3^ 00 CM CM rH U rO CO CO (U •H CJ 0) ft CO 14-1 o CO c o •H 4J •r( a •H M-l tu T3 U O x> 188 unlikely that observed nocturnal activity could be attributed to feeding, as approximately 85% of the fish caught at this time had empty stomachs. Martin (1970) also noted a cessation of lake trout feeding activity during the spawning period, September through October. Lake trout were captured more frequently at 6.1"-m than at 9.1-m stations (Table B40) . Supplementary netting (Table B41) supports the con- clusion that longshore movements are more pronounced for lake trout than for most other non-salmonid species. All glllnets were set parallel to shore except those at station A, which were set perpendicular to shore. Catches from the perpendicular sets were higher for lake trout and other salmonids than catches from 6.1 and 9.1 m on the same day. Largest catch of lake trout occurred in station A nets during October (Table B41) , Examination of gonads (Table B42) showed an increase in ripeness of ovaries and testes beginning late In the summer and peaking during Septem- ber vd.th spent females first appearing in October. Observed gonad condi- tions and inferred September through November spawning period agreed well with the accepted classification of lake trout as fall spawners. Length-frequencies of lake trout with various fin-clips were compiled (Table B43), and these data point out the preponderance of fish 550-800 mm TABLE B42. Monthly gonad conditions of lake trout as determined by inspection and classification of the state of development of ovaries and testes. Fish were captured during 1973 in southeastern Lake Michigan. All fish examined in a month were included except immature and poorly received specimens. Gonad coDdition Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Females ?oorly dev. 1 Hod. dp-v. 1 6 13 Well dev. 1 1 Ripe-running Spent 2 11 6 8 21 31 1 2 6 Males Poorly dev. 3 1 Mod. dev. 1 7 19 35 Well dev. 1 9 15 4 Kipe-ninning 4 SpiBnt 1 13 1 Unable to distin?>uish 189 ^ o o u • s - s •H • cn r^ o o> • v« • F-O rH « *• 9 « 03 bO Ma fl 4 ft « •H «fr » 8 • « _ • « ?. n* • « T) »•» « 4-1 • •• •• 9 o - o ^ « * « ,. « r^ 00 • •• * •*""» m 3 s W • » •^ *».»»»- • • . • • ■u •a -•• % • .. A • 3 « «sv* o 9. «• M « • o ■P « • • t£3 dJ • ^ 03 r-H tt " 'd (1) p- O p. _o •H ■ m iH a • •H « LH . c u-4 nj O 60 •H C3 C Xi o cj •H -H •u S 3 • ~ ^ a) ■H ^ M « ■U fJ o en — CD ■H a fO na ^J 0) >, 4-1 a en ,« C rt 0) 0) 3 ^ cr 4-1 C3 dj 3 _o M o c 4J kJ ij O O o o u o c o c ca C9 (U 01 > 01 ■H > >^ iJ IX u > o. p. o. o. > > > 3 3 . ^^- :§ . 3 . a o o .a . , . pj . • ^ • • -] 1 o! Pi 1 ,J o5 « H CM Eh O W ano-KiJ ^0 NOixVooi 190 long that occur in the Cook Plant vicinity. No attempt was made to assign ages based on clips for this report, although it was noted that a consider- able range of potentially overlapping lengths were present for a given clip. Problems in assigning ages are anticipated. Our catch data were compared with that for lake trout caught near Ludington (Chiotti 1973; Fig. B42) , and good agreement was found between length ranges and modal sizes of fish captured. We caught more fish less than 300 mm, which we attribute to more extensive trawling during which time we caught six lake trout ranging from 130-158 mm, the only fish less than 300 mm. No adult lake trout were cap- tured in trawls, probably because these larger fish were able to avoid the net. Lake trout were caught most often in the temperature range 6-18 C (Fig. B43). Maximum catch occurred at 12-14 C, which agrees closely with preferred temperatures recorded in the literature (12 C, Ferguson 1958; 10 C, Daly et al. 1969). Scott and Grossman (1973) reported a spawning temperature preference range from 8.9-13.9 C. It may be that temperature preferences recorded to date are primarily a reflection of preferred spawning temperatures. To determine if there are differences between spawn- ing and non-spawning temperature preferences, more temperature and catch data are needed for lake trout on a monthly basis, particularly during non- spawning months. Unidsntif-ied Covegonids As previously discussed in this section, difficulty was experienced in separating small lake herring (Coregonus artedii) and other rarer species of deep-water chubs from bloaters (Coregonus hoyi) . However, since we believe probably all were bloaters, discussion below will be concerned with this species. Historically the "chubs" comprised a seven-species complex, the small- est of which was C. hoyi (Smith 1964) . A considerable commercial fishery operated throughout the period of first catch record (1879-1908). This fishery was quite exploitive. Implementing many gear and mesh size changes. The largest two of the seven species became extinct in the 1950' s and the next four largest species declined drastically between 1930 and 1961. Bloaters, the smallest of these species, increased in numbers over this same period due to reduced competition from larger chub species, which suffered from over-fishing and lamprey predation, and to reduced predation from lake trout, which also were a victim of the sea lamprey and perhaps over-fishing. Since 1960-61 the bloater has been by far the dominant chub, and Wells (1966) has suggested that hybridization between bloaters and the remaining rare, larger species has occurred, confounding species identification pro- blejns. Bloaters increased in average length between 1954-55 and 1960-61, at which time they were also becoming more abundant (Smith 1968). Indications are that this length increase began prior to 1954 and has continued on a yearly basis to the present. Bloaters reached maximum abundance during 191 668-0Q8 X X CO CD U- Li_ \- o h- < Q. lEL ^ O O 3 o _J o e I- •z. bJ _1 O O o o o o 00 o o o to o o JO o cvj o o o 4J 60 c •H 3 5-1 n3 (U C tfl 60 •H o •H S I 5-1 o AS t-l M-l O CO C o •H 4-1 •H M CO •H . TS CO cd o c a !^ OJ 3 M 4J m CO I ^ u ■u a 60 rt (U PM (U O ^ o •U C_) 14-1 o c o CD % M-l CO CO Ph '— > 6 CO O r-~ CJ C7> O NUMBER OF TROUT •H +J o ■H J! 192 X CD 13 ^ c (1) •H :* x: ^ o Cfi •H •H ^ U-l s o wo »-i Cm rvi -a *-« g X o ■-< ^ 196 TABLE B45. Monthly gonad conditions of bloaters (unidentified corego- nids) as determined by inspection and classification of the state of development of ovaries and testes. Fish were captured during 1973 in southeastern Lake Michigan. All fish examined in a month were included e: H-l U-( QJ 1! • jn CO *J P^ r~- a^ n »« E r-) Cfl Q) ^ 01 H 60 60 CO ,_t e B m •H IH > M o 3 II u (D Id (D IS C ex -T-* •u >^ »v JZ ,C u 13 iJ 60 0) u 3 t3 60 c cfl c >-H U CO •H CX u-t en X s C (U •H 4J •H en c d. II •rH tH CI 3 • w 1 O CO •0 CO J-) #v (U 4-i H CO 0) o ■ l+-( iH rH X ^ iH 0) (U CO ■H M rH 60 rQ C 13 CO -H II (U w c -n (3 •H !>^ OJ e O ^J *\ ^-1 C 3 rH 0) OJ i-) g ■u 3 P^ s cr cfl M T3 QJ CJ i-> C U 3 M-( ^ II i CO T3 Xi -H H C J-l 14-i Cfl 60 ^ C U-i OJ 0) OJ O c >-j r-i •H 3 CO CU 4-1 <: t-< CO CO tu g ,ja 11 ^ • e •H o-l 3 w "1 C Cfl PQ (U rH • -tJ W CO C 3 i-J 3 cu iH PQ 4-) > <3: CJ •H c H cfl 60 •H {oj r4 «£} «n j-l O ♦-4 *-* *.3- CM CM 10 > -^ -^ »H .H fsi »n .iH I WWW w w H r~ H tt H .-3- vo n w - . CTX W W CJ - H f-1 H H *o */^ w tH -3- r^ c^ - r-f »0 H - u-> CO U U b] t>} O . r^ xn P^ >H rH t-^ W3 H H CO H iH 10 CM H H C9 H f-" ^ iH f-< CM xtxo xfMO xf^o satiuo x:^ox»uo spxo x^uo xi^o xcmo c J5 5 >% S 13 01 u O > o 9S 206 TABLE B5A. Monthly gonad conditions of sculpins as determined by inspection and classification of the state of development of ovaries and testes. Fish were captured during 1973 in southeastern Lake Michigan. All fish examined in a month were included except immature and poorly received specimens. Gonad condicion Feb Mar Apr Hay Jun Jul Aug Sep Oct Nov Dec Poorly dev. Hod. dev. Well dev. Ripe- running Spent Poorly dev. Mod. dev. Well dev. ajLpe— running Spent 11 12 47 12 3 1 10 36 Females Males Unable to distlnguiah 10 that slimy sculpins were distributed over a wide depth range in winter, moved inshore, then abandoned shallow areas in spring as soon as warming was signi- ficant; greatest numbers at 6 m (depth of shallowest samples) were in mid- April. They continued a gradual movement away from shore through suimner and fall. Rottlers (1965) stated spawning probably occurred in southeastern Lake Michigan from before 5 May 1964 when 66% of his specimens were spent, until 23 May when almost all were found to be spent. Peak spawning was between 31 and 82 m early in the season and somewhat deeper later. Sculpins were one of the more abundant species collected from traveling screens (impinged) during 1973. From these limited data (see Section D) and observation made by project divers, the presence of a local population of sculpins near the intakes is indicated. Sculpins have been observed by SCUBA divers on numerous occasions in the vicinity of the Cook Plant. They and johnny darters are the species most consistently observed by divers in the riprap area, Sculpins were not seen in areas outside the riprap. It is quite likely that riprap may afford demer- sal fish such as sculpln sufficient protection to allow development of an inshore population in areas normally too harsh for continual habitation. Contrasting day versus night impingement catches and diving observations appear to verify the nocturnal activity of this species. 207 Rottiers (1965) states that the majority of slimy sculp ins in Lake Michi- gan appear to prefer cold water, 6 C or less, except for short periods during fall overturn. Wells (1968) found the temperature preference of trawl-caught sculpins to be 4-5 C. Sculpins were caught in water temperatures ranging from 6-22 C (Table B55) with greatest catch at 6-8 C. TABLE B55. Temperature-catch relationships of slimy sculpins inferred from mean catch over 2 C temperature intervals in seines (S) , gillnets (G) and trawls (T) . Standard error is also given. Dash means no fishing was done and blanks indicate no fish were caught at that temperature. Mld-polnc of 2 C c«mper«cure interval H 13 15 17 19 21 23 25 27 .5^.5 .4-. 2 — .1^.1 — 3-.5 .8-. 2 .4*. 2 .7-. 3 .2-.1 .4-. 3 A high incidence of spiny-headed worms {Aoanthocephala) was observed in the lower intestinal tract of sculpins, up to seven in some of the larger specimens . Brown Trout Brown trout were stocked in Lake Michigan in 1883, and several hundred- thousand browns have been stocked in Lake Michigan since the mid-1960' s (Wells and McLain 1973). These fish have provided a very successful sport fishery and, judging from the large size of some we caught, they are growing very well in Lake Michigan. In 1971, fishermen in the seven counties around the Cook Plant (District 12, Tody 1973) caught 42,480 brown trout, although many of these may have been taken from inland streams. Our data (Table B56) suggest fall spawning, but more adults are needed to judge adequately. Water temperature for spawning is listed as 6.7-8.9 C (Scott and Grossman 1973). They also noted that some brown trout spawned on rocky reefs along shore in Lake Superior. During 1973, 76 brown trout, 0.04% of the total, were captured in stand- ard series fishing (Table B6) . Peak numbers were taken in June (33) and July (18). Twenty were caught during the day, 56 at night. Sixty-eight were caught while seining, seven by gillnet and one by trawl. There appeared to be little difference between numbers caught at Cook Plant and Warren Dunes. Range in size (standard and supplementary fishing) was 106 mm, 15 g, seined at station A in October, to 682 mm, a 4070-g male caught at night in a gillnet at station A. Browns from all fishing efforts in March and April were large, 267-543 mm; most were captured with gillnets from deeper water. In May, large 208 TABLE B56. Monthly gonad conditions of brown trout as determined by inspection and classification of the state of development of ovaries and testes. Fish were captured during 1973 in southeastern Lake Michigan. All fish examined in a month were included except immature and poorly received specimens. Gonad condition Feb Mar Apr Mjty Jun Jul Aug Sep Oct Nov Dec Females Poorly dev. 1 12 Mod. dev. 3 1 Well dev. 1 1 Ripe-running Spent 8 12 Males Poorly dev. Hod. dev. Well d ev . Ripe- running Spent Unable to di sting uish fish were again taken by gillnet, but a number of smaller trout 106-202 mm were captured in beach-zone waters with seines. In June and July, months of largest catches of brown trout, all were small and were caught by seines in beach-zone waters, indicating that smaller fish reside in these waters during the spring and summer months, and that larger browns probably move from warmer inshore waters to cooler, deeper waters of the lake during late spring and summer. In August and September, small fish were caught in seines and three larger fish in gillnets. The same pattern was seen for fish caught in October , indicating the movement of large brown trout back into the now cooler inshore waters. Temperature optimum for brown trout was reported to be 18.3-23.9 C (Scott and Grossman 1973). Final temperature preference for age class II brown trout was reported as 12.4-17.6 C (Ferguson 1958), Our gillnet data (Table B57) , which involve mostly larger specimens, suggest 6-16 C as temperatures most commonly frequented. Smaller fish were caught almost exclusively by seine, in water temperatures from 4-26 C, with indications that these fish preferred a higher temperature range than older adults. Emerald Shiner The emerald shiner, a minnow native to Lake Michigan, has undergone dramatic changes In its populations in recent years with the increase of alewife in the lake. In earlier years it was the most abundant inshore forage fish 209 TABLE B57. Temperature-catch relationships of hrovm trout inferred from mean catch over 2 C temperature intervals in seines (S) , gillnets (G) and trawls (T) . Standard error is also given. Dash laeans no fishing vas done and blanks indicate no fish were caught at that temperature. md-potnc of 2 C temperature Interval 1 3 5 ? 9 11 13 15 17 19 21 23 25 27 5 - .5^.5 .06^.06 .zt.i ,2-. 2 — .8-.8 .2-.2 .9^.* .6^.3 C .*^.2 .3^.3 .2-.2 .li.2 _ _ - - .ll.l but has almost disappeared since the 1960's (Wells and McLain 1973). It is postulated that emerald shiners, which feed mainly on zooplankton, were deci- mated because of their inability to compete with alewife young and adults which inhabit the same areas of the lake inshore during spring and midsummer. Commercial utilization of emeral shiners has been as bait, both fresh and pickled. In our standard series sampling we caught 49 individuals, 0.03% of the total, all in seines (Table B7 and B8) . Monthly catches of emerald shiners remained low but constant for most of 1973, The only peak in monthly catches was in August and September. Emerald shiners were caught almost exclusively at station B south of Cook. Stations A and F both accounted for only five individauls, while station B accounted for 39. This is thought to be related to the sheltered nature of station B afforded by the sand replenishment pro- gram initiated to curtail erosion south of the former safe harbor. Length range for the emerald shiner was 43-96 mm, average length 64 - 1.8 mm (S. E.). Examination on a Ttionthly basis showed a relatively constant length regime from month to month. Gonad data are scanty because of difficulties in sexing these fish. Emerald shiners were caught in water 4-28 C with greatest catches in temperatures of 26-28 and 18-20 C (Table B58) , indicating that they are eurythermal with a definite preference for higher temperatures. It might be hypothesized from regular occurrence in seine catches as well as broad temper- ature tolerance that shiners occupy the beach-zone waters during most of the year. None have been collected from traveling screen catches to date, also indicating a beach-zone distribution. Longnose Dace Spawning habits of longnose dace have not been studied to any extent, but it is thought that spawning occurs in May, June or early July in riffles and on gravelly bottoms (Scott and Grossman 1973. 210 TABLE B58. Temperature-catch relationships of emerald shiners inferred from mean catch over 2 C temperature intervals in seines (S), gillnets (G) and trawls (T) . Standard error is also given. Dash means no fishing vas done and blanks indicate no fish were caught at that tcanperature. Kld-polnc of 2 C tomperaCure Interval 11 13 15 IJ 19 Jl 23 25 27 .3±.5 .li.l .it.os .si.2 .2t.2 - iti .5i.3 .6±.3 .uU ,U t ~ Longnose dace accounted for 0.02%, 41 fish, of the total number captured in standard series fishing (Table B6) . They appeared only in seine hauls, with 36 caught at station B south of Cook. Seining at station A and F accounted for three and two respectively. The vast majority of station B catches were taken at night. This station was just beyond the area where large mounds of sand were located for sand replenishment because of the safe harbor and as a result was broad and shallow. As found with emerals shiners, this feature is thought to contribute to the larger catches. Occurrence of longnose dace was relatively constant for all months except September when 22 were collected, all but two at night. Length range was 30-80 mm, average length 49+1.6 mm (S. E.). Examination of monthly length ranges showed an increase in size of individuals for June through July, how- ever the number caught was small. Longnose dace were caught in water temperatures from 2--26 C, with greatest catch at 22-24 C (Table B59). greatest TABLE B59. Temperature preference of longnose dace inferred from ToT^nTllZTm ^-^--"-•^— is in seines (S) . giufS fi.hw ZTi \ standard error is also given. Dash means no fishing was done and blanks indicate no fish were caught at that temperature. "&'•>- ot- lu^l Mid-point of 2 C temperature Interval I 3 5 7 9 11 13 15 17 19 21 23 25 27 s — .5i.5 .s!.5 .li.08 .4^.2 _ .5^.2 1^.7 .«i.3 c — T ~ — — 211 Northern Pike Northern pike were captured regularly although in low numbers during our sampling. They are a warm'-water species and probably enter Lake Michigan as YOY or adults from rivers and lakes and from areas like Green Bay, Wis., where sizable populations exist. Annual production of northern pike averaged 2.9 x 104 kg (46,000 lb) from 1899-1970 (Wells and McLain 1973). They are sight feeders and most active during daytime. They spawn in the spring in April to early May when water temperatures are 4.4-11.1 C, almost invariably in areas of flooded vegetation or in marshes or shallow weedy bays (Scott and Grossman 1973). In standard series efforts, 38 were captured, 15 in October (Table B6). They were taken in 5 of the 11 months fished. More northerns were caught during the day (22) than at night (16), 31 from gillnets, five small fish (age class I) in seines, and two in trawls. Range in size of fish captured was from 98-815 mm (5.2-4150 g) . Most fish were 300-500 mm long (about 2-4 yr old — -Scott and Grossman 1973). No adult fish were caught during spawning, so ability to corroborate known spawning times is limited. Data (Table B60) suggest, however, that spawning occurs sometime after March; northern pike gonads were poorly developed from August through December. These fish were most frequently caught at temperatures of 8-24 C (Table B61). TABLE B60. Monthly gonad conditions of northern pike as determined by inspection and classification of the state of development of ovaries and testes. Fish were captured during 1973 in southeastern Lake Mich- igan. All fish examined in a month were included except immatures and poorly received specimens. Gonad condition Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Females Poorly dev. 12 8 2 1 Mod. dev. 1 Well dev. 2 Ripe-runriing Spent Males ?oorl;y dev. 6 11 Mod. dev. 3 11 Well dev. Ripe-running Spent 1 Unable to distinguish 212 TABLE B61. Temperature-catch relationships of northern pike inferred from mean catch over 2 C temperature intervals in seines (S), gillnets (G) and trawls (T) . Standard error is also given. Dash means no fishing was done and blanks indicate no fish were caught at that temperature. Mid-point of 2 C cempcrature Interval 11 13 15 17 19 21 23 25 27 .1^.08 si. 2 .8^.8 it. 6 li.i .it.l .2-. 2 .1-.06 1^1 Coho Salmon Introduction of coho salmon into Lake Michigan began in 1966 with re- lease of 66O5OOO yearlings (Wells and McLaln 1973). A total of 10.3 million have been stocked through 1970. A considerable sport fishery is nov7 enjoying the results of those efforts as anglers in Michigan waters caught an estimated 500,000 coho in 1970. Catch rates tended to be greatest in statistical districts MM-5 (Grand Traverse Bay area) through MM'-8, which includes the Cook Plant vicinity (Tody 1973) . Spring salmon fishing is concentrated almost exclusively in the MM-8 district. Adult coho salmon weighed an average of 4,313 g (9.5 lbs) in the spawning runs of 1967-69. Average weight of Lake Michigan coho has been reported as 500-900 g for 1-yr olds (age group II) and 4000 g for 2-yr olds (age group III) during 1968-70 (Parsons 1973). Coho (smolt-age group I) were planted in the St. Joseph River in 1969 and 1970, 100,000 each time (Parsons 1973). Coho were reported by Engel and Magnuson (1971) to be inshore in spring and fall and in the theriQOcline during late summer in a small lake in Wisconsin. Anadromous coho spawn in the fall in rivers and streams, and much natural reproduction has occurred in Lake Michigan (Parsons 1973; Tody 1973). Our gonad data in- directly substantiate fall spawning, as most fish from March through June had poorly dejveloped gonads (Table B62) . It is assumed salmon became gravid in the fall. Eggs are laid deep in gravel from October to November, and fry emerge from beds around April, remaining in streams for varying lengths of time (Hart 1973) . Wells and McLain (1973) stated that introduction of the salmonids has probably had little effect on native fish stocks, but their main effect may be through their probable reduction of alewife populations. We caught 32 coho salmon during standard series fishing, 0.02% of the total number of fish taken. Since the Cook Plant is not close (within 18 km) to any rivers or major streams (there are intermittent streams, one about 3 km north, an outlet from Grand Mere Lake, and one about 1.6 km south near Weco Beach) coho salmon do not concentrate to any extent in the area. This is probably the reason for our low catch of these salmonids. Coho do travel 213 TABLE B62. Monthly gonad conditions of coho salmon as determined by inspection and classification of the state of development of ovaries and testes. Fish were captured during 1973 in southeastern Lake Michi- gan. All fish examined in a month were included except immature and poorly received specimens. Gonad condition feh Mar Apr May Jun Jul Aug Sep Oct Nov Dec Females Poorly dev. 11 1 Mod. dev. 5 3 A Well dev. 1 Ripe- running Spent 9 Males Poorlv dev. 5 8 1 Mod. dev. 1 1 Well dev. 4 Ripe-running Spent 1 Unable to distineuish occasionally with the longshore currents during certain seasons. They are quite abundant in and around the mouth of the St. Joseph River, about 18 km north of the Cook Plant. Most coho in standard series catches were taken in May and June, none during February, July, August, November and December. More (23) were caught during the night than during the day (9). More were caught with gillnets than with seines, none were taken with trawls (Table B7, 8). Coho captured, total fishing efforts, ranged from 73-845 mm (3.7-4610 g). During March, April and May most fish caught were large, from 350-550 mm long. In June all coho caught except one 483-mm specimen caught with a gillnet, were taken with seines at all three seining stations. These six fish ranged from 73-95 mm, indicating small coho are probably inhabiting beach-zone waters during June. A slight possibility exists that these coho may have been naturally produced since Parsons (1973) states that coho are planted at about 101-152 mm during March through May. No small coho were caught in July through December. In September, October and December, coho taken were longer, ranging from 500-845 mm. The only gillnet set in December was a supplementary set at station A. Coho salmon was one of three species captured (burbot and rainbow trout were the others) , indicating coho may be in the vicinity of the Cook Plant inshore waters at least during early winter. Temperature preference of coho is listed as 11.6 C by Tody (1973) and 12-14 C by Brett (1952) ; he also found upper lethal temperature for coho fry 214 to be 25.1 C. Our gillnet data for larger fish show maximum catch at 10-12 C, with a range from 2-18 C (Table B63) , Seining data represent the small fish captured as 73-95 mm, and apparently they prefer considerably warmer tempera- tures as most were taken at 20-24 C, very near their upper lethal maximum. Some also were captured at 8-10 C. TABLE B63. Temperature-catch relationships of coho salmon inferred from mean catch over 2 C temperature intervals in seines (S) , gillnets (G) and trawls (T) . Standard error is also given. Dash means no fishing was done and blanks indicate no fish were caught at that temperature. Mld-poiot of 2 C temperature Interval 9 11 13 15 17 19 21 23 25 S — .5-. 2 i-.a Carp Carp is one of several introduced exotic species in Lake Michigan. It was first recorded in the commercial catch of 1893, with annual averages of 5.8 X 10-' kg (2.3 million lb) in 1966-70 (Wells and McLain 1973), All carp captured were large individuals with a range from 134-832 mm (50-10,200 g) . Most were adults 400-700 mm long. They were captured from April through October, most in June (19). They were most frequently captured with gillnets; seines were second in effectiveness. None were captured while trawling, indicating they can apparently avoid the trawl during both day and night. Considering just standard series data (Table B6) , 14 carp were caught during June out of a total of 28 for the season. They represented 0.01% of the total number of fish captured. Carp were captured about equally at Cook and Warren Dunes during the day. More were captured at night at both locations, with 17 captured at Cook and only four at Warren Dunes. Carp probably do not spawn in Lake Michigan in the vicinity of the Cook Plant. Gonad development data (Table B64) showed that a few ripe-running individuals were present in May and June; spent fish were present in August. However, a local resident near Grand Mere Lakes revealed that carp "during spawning season" oftentimes would be washed up on the beach if waves were high that day, where they could be easily speared. Swee and McCrimmon (1966) reported that spawning of carp in the Great Lakes is intermittent depending on temperatures and may extend from May through August. Scott and Grossman (1973) and others state that carp spawn in early spring and summer as the waters warm. Spawning does not begin In earnest until water temperatures 215 TABLE B64. Monthly gonad conditions of carp as determined by inspection and classification of the state of development of ovaries and testes. Fish were captured during 1973 in southeastern Lake Michigan. All fish examined in a month were included except immature and poorly received specimens . Gonad condition Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Females Poorly dev. 3 3 Mod. dev. 1 112 Well dev. 13 3 Ripe- running Spent 1 Males Poorly dev. 1 13 1 Mod. dev. 3 7 5 3 Veil dev. 1 2 4 11 13 11 Ripe-running 1 1 Spent 1 Unable to distinguish are at least 17 C (McCriramon 1968). Except a recent specimen about 125 mm long from a seine haul April 1974, we have never caught any of their young, which leads us to believe that at least in the Cook Plant area large carp either come from other areas in Lake Michigan or enter the Cook Plant vicinity from inland lakes, rivers and streams. Perusal of temperature-catch data (Table B65) shows that carp were caught at a wide range of water temperatures from 8-24 C, with most caught at higher temperatures. Pitt et al. (1956) gave a final preferred temperature greater than 30 C for carp. We observed large concentrations of carp in the thermal effluent in Lake Michigan at Big Rock Nuclear Plant in Charlevoix during June 1973 suggesting that carp may also concentrate in the thermal effluent of the Cook Plant. However, the Big Rock discharge is in a canal on ^hore, while the Cook discharge is at 6.1 m (20 ft) and utilizes jet diff users which should dissipate the waste-water more quickly. Similarly, tagging studies on 13 and 15 June 1973 at the Palisades Plant, which also has an onshore discharge canal, showed high concentrations of carp in the thermal plume (Consumers Power Co. 1972). The local population of carp was estimated to be between 1000 and 3000 in the areas of the discharge on any one day in late June while the thermal effluent was present. This estimate is thought to be low, since hundreds of carp were seen and not marked. Nowhere else in the immediate 216 TABLE B65. Temperature-catch relationships of carp Inferred from mean catch over 2 C temperature Intervals in seines (S) , gillnets (G) and trawls (T) . Standard error is also given. Dash means no fishing was done and blanks indicate no fish were caught at that temperature. Mld-polnc of 2 C temperature Interval 1 3 5 7 9 11 13 15 17 19 21 23 25 27 S — .li.08 .li.l — jt.3 .iX.l .5i.6 .ll.2 2^1 area of Palisades were carp as abundant as in the discharge. Chinook. Salmon Chinook salmon were stocked in Lake Michigan in 1967; by the end of 1970, 4.. 1 million fingerlings had been released (Wells and McLain 1973). The sport fishery harvested 170,000 of these fish in 1970. Growth of chinook in Lake Michigan is estimated as follows: age II ranged from 61.2-64.0 cm (24.1-25.2 in); age III, 86.9-98.8 cm (34,2-38,9 in); age IV 98.6-98.8 cm (38.8-38.9 in) (Tody 1973). Chinook salmon, age 0, are planted in the spring when they are 51-76 mm long and 4-5 months old (Parsons 1973) . Spawning runs that develop are usually composed of II- and Ill-yr old fish. Rarely do chinook reach age V, We caught 26 chinook salmon in standard series fishing efforts (Table B6), most during May (5) and June (6). None were captured in February, November and Dec(2mber. Most were caught in gillnets and seines, one in a trawl. During the night (18) were caught, during the day eight. Range in size of all chinook caught was from 69-934 mm (2.7-8640 g) , with the 200-mm size group being most abundant. Small fish 69-96 mm were seined during May and June only, with one small fish captured in a trawl. Thus, like coho, which were most abundant in the beach zone in June, some small chinook also prefer inshore waters during late spring. Our gonad data (Table B66) are inadequate to show spawning, but it is known that chinook salmon spawn in the fall usually in rivers. It is thought that the St. Joseph River, about 18 km north, attracts most chinook salmon in the area during the spawning season. Preferred temperature of YOY and yearling chinook salmon is 11.7 C (Ferguson 1958). Considering our field data, adults were captured over the range 4-16 C, with 12-16 C having highest catch (Table B67). Smaller fish 69-96 mm caught in seines were taken at 6-8, 10-12 and 20-24 C, indicating a broader range of temperature tolerance than indicated in the literature. 217 TABLE B66. Monthly gonad conditions of chinook salmon as determined by inspection and classification of the state of development of ovaries and testes. Fish were captured during 1973 in southeastern Lake Michigan. All fish examined in a month were included except immature and poorly received specimens. Gonad condition Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Females Poorly dev. Mod. dev. Well dev. Ripe-running Spent Poorlv dev. Mod. dev. Well dev. Ripe- running Spent 2 1 Males 2 1 2 Unable to distinguish TABLE B67. Temperature preference of chinook salmon inferred from mean catch over 2 C temperature intervals in seines (S) , gillnets (G) and trawls (T) , Standard error is also given. Dash means no fishing was done at that temperature. Mld-polnc of 2 C temperature Interval 11 13 15 17 19 21 23 25 27 .3-.1 .1-.07 4- + -{- + + + C .2-.1 .2-. 2 .l-.l .2-. 2 .5-. 2 .5-. 3 T - - - .it.l 218 Gizzcayd Shad As a result of their migratory habits, gizzard shad entered Lake Michigan possibly through the Chicago River Canal and were first noted in 1953 (Miller 1957). They are a common species in Lake Erie (Scott and Crossman 1973; Parkhurst 1971). Shad reach the northern limit of their range in the Great Lakes, being much more common and abundant in rivers and large reservoirs farther south. Spawning occurs in spring and early summer and was specifically recorded by Bodola (1964) in Lake Erie on a sandy, gravelly bar in temperatures of 17.2-22.8 C. Following spawning, fish return to deeper water. Eggs hatch In 95 hr at 16.7 C (Miller 1960). Females averaged the following standard lengths at respective years of age in Lake Erie: age I, 140 mm; II, 285 mm; III, 335 mm; IV, 366 mm; V, 390 mm (Bodola 1964), Gizzard shad are abundant in Lake Erie where they far outnumber alewiyes, and their abundance in Lake Michigan appears to be increasing from our limited s<-nnpling in 1972 (one was caught) „ They may be another Indicator of the increasing eutrophication of Lake Michigan which, as in Lake Erie, might favor gizzard shad survival over alewife. In standard series fishing we caught 23 gizzard shad, all from seines, one in October and 22 in November. Of these, 6 were caught during the day, 17 at night. They ranged from 52-130 mm (1.1-23.5 g) . According to Lake Erie standards (Bodola 1964) these fish were probabl}^ YOY and appear to be quite abundant along the entire shoreline relative to previous year's data when only one fish was caught (Jude et al. 1973). In total fishing we caught 40 individuals, one in January, one in March and the rest from September to November. Sex ratio of the unadjusted stan- dard series catch was 13 females to 3 males with 3 undetermined. The largest of these was a 494-mm (1500-g) female. The largest catch of shad in supple- mentary fishing came from a gillnet set at station C in September, when five females ranging from 415-450 mm were captured. A similar catch at station A, also supplementary fishing, was recorded during October, when five females ranging from 356-445 mm were taken. These fish were almost 100 mm longer than Lake Erie shad (Bodola 1964) ; Trautman (1957) cited 521 mm as maximum size of fish captured in Ohio. Gillnetted fish were caught at the 6.1-m stations, indicating a preference for inshore waters. Shad were taken from 8-18 C, with maximum catch (lio.5) at 10-12 C, tlinesp-ine Sti-aklebaak The ninespine stickleback is found throiighout the northern hemisphere in both fresh and salt water. Freshwater forms are scaleless, marine forms have small bony plates over portions of their bodies. The ninespine stickle- back spawns in fresh water during the summer and has been reported to spawn more than once per season (Scott and Crossman 1973) , It has an interesting reproductive behavior in that the male builds a nest of sticks and leaves and cares for the eggs and young. Maturity is gained by most individuals in their first year (Jones and Hynes 1950) . They also reported the following length ranges per year class: age class I, 38-46 mm; II, 45-48 mm; III, 48-55 nmi. Long<5vity is about 3.5 yr. Since they are scaleless, aging is done through use of otoliths. While not being of any direct use to man, they are reported 219 to be an important prey in areas where they have a high population (Dymond 1929). Dryer (1966) reported large numbers of ninespine sticklebacks occur- ring in Lake Superior. This abundance led to the supposition that their im- portance as a forage fish has been neglected. Wells and McLain (1973) in- dicate that ninespine sticklebacks have increased in abundance in southern and east central Lake Michigan in the past few years. In our studies ninespine sticklebacks accounted for 0.01% of the total standard series catches for 1973. Total number caught was 19, with a range of 60-78 mm. Most fish were caught during May and June, 12 and five respec- tively. One fish was caught during March and April; none were caught in remaining months. Almost equal numbers of Individuals, 11 and eight respectively, were caught at Cook and Warren Dunes stations. There was, however, a difference in the numbers caught per fishing gear. Cook stations accounted for eight fish in seines and three in trawls as opposed to two in the seine and six in the trawl for Warren Dunes (Tables B7,8). None were captured in gillnets. Examination of catches on a day-night basis showed only one fish caught during the day, at station D in a trawl, and 18 at night. Examination of seine haul catches revealed little difference among stations. A comparison of offshore stations showed the majority of the catches were taken at 9.1 m. Four individuals were caught at station D, five at station H; 6.1-m stations accounted for one specimen. Gonad data are sparse in terms of numbers of fish examined (Table B68) . They do suggest an increase in the state of maturity toward summer, conforming to the reported general spawning season. The ninespine stickleback was almost completely absent from the sampling areas during the day. No information on their movement was found in the literature; we suspect they may move offshore during the day and inshore at night. It is also possible that net avoidance during the day may play a role in catch differences. Bluegill Bluegills are a common inhabitant of inland lakes and ponds and have ready access to Lake Michigan via streams and rivers. They apparently do not adapt or fluorish in the ologotrophic lake environment as they were infre- quently caught. In standard series operations 11 were taken during May through August and November (maximum catch of five). Nine were caught at night, two during the day, nine with the seine and two with the trawl. Range in size of fish caught was from 33-95 mm (0-5-16.3 g) • Two were females, the rest were Immature. Channel Catfish The channel catfish Is a freshwater species with a large natural range, extending over east and central North America from extreme southern Canada to northern Mexico (Scott and Grossman 1973). Introductions have been made west 220 o u 1+-I ^ -r) 0) 0) H T) 0) u S o 0) o <4-< Q) ^1 II /'-^ fi< CD to C ■H O W • •H 1) c 4-1 x: ct) •H u or 13 c •H C (V x: O ^J u o cfl •H P^S t3 cfl C QJ •H ^ o S-' tl) W) 4:; M-l o fi o cd H 0) 0) c 4J o 4-1 CO •H O CO 4-1 OJ •H u ■£ d OJ 4J •H ,Q 3 m Q) ^ CD 13 a rt U 0) >1 O ^ 4-1 H-l ■tJ •H S CD xt •H 13 c a O Cd •H rC > •u c 0) o w e •H d J-i cfl 0) •H iH OJ TJ |Xi CD C o rM »\ u O X o ai 13 u CD nJ C cu '13 o £ Q) M 4J S TJ s g d •H ^ cfl 0) ^ ■u X CD cu 0) •H 'C3 CD >4-l 3 01 13 ^ cu II H !-i 3 r-^ 4J P< ■ CD 00 fX r. vO O a> PQ r-i S to W O e ►J 13 Pfl r-{ II <; Ql H CD >3 o o > o 53 o o to 00 s fs 1-1 in CM m 04 X u-i vn in X vi-1 p^ CM r» c fc. X Z X 3 •'^ y^ x-N ^*S •^ T-t CM .-1 r-l s_^ v-' v-^ v^ CM >. b. 03 "'^ S >-i 2 Pw lA P>^ 11 CM l>4 s .-( rH « JD cy o u o CO a! 03 (J in o to Pi J3 lU 3 e •o U -O IB S " 3 -H O A Pi » g y-\ PI u W 18 C A fl «l m a gj u e -H 2 ID 221 of the Rocky Mountains, The channel catfish is an excellent gamefish which is often overlooked in its northern range- In its southern range it is widely fished and prized for its flesh. It is also an excellent species for pond culture and is extensively fanned In southern United States, Our standard series of nets accounted for 11 channel catfish making up 0.01% of the total catch. Three fish were caught in seines, seven in gill- nets and one in a trawl. Total length ranged from 163'-651 mm. Two individuals were taken during the day and nine at night. Channel catfish axe known to be more active during the night than the day. Gonad data show spent males and females occurring in June, August and September (Table B68) . Scott and Grossman (1973) report the spawning season from late spring to summer. Burbot Burbot have never been important commercially in the Great Lakes (Wells and McLain 1973). Reduction of burbot to very low numbers by the late 1960's has been attributed to sea lamprey predation; with control of lampreys they are increasing. Burbot spawn from January to March in Canada (Scott and Grossman 1973). Our gonad data confirm winter spawning, as the two males and one female caught in December (Table B68) at station A were ripe, and burbot eggs were found in beach fish larvae tows in January 1974. Scott and Cross- man (1973) note there is circumstantial evidence that burbot spawn in deep water in some areas, but the spawning site is usually in 0.3-1,2 m of water over sand or gravel bottom in shallow bays or gravel shoals 1,5-3.0 m deep. Our data support shallow-water spawning. The actual spawning activity is said to take place in a writhing ball (10~12 individuals) only at night. Temperature is usually 0.6-1.7 C. Eggs hatch in 30 days at 6.1 C; young appear in late February to June. Maximum size in Canada is 937 mm fork length. In Canada and the Great Lakes the burbot is a resident of deep waters of lakes during summer, coming inshore only to spawn and sometimes remaining until late spring. In standard series fishing (Table B6) we caught six individuals; three additional ones were caught in supplementary gillnets set at station A (Table B41) . They ranged in size from 343-579 mm (254-1225 g) ; most were 400-500 mm long. All burbot were caught in gillnets. except one taken with a trawl at station G. Four were caught in April, two in June and three in December, Optimum temperature for this species is 15.6-18.3 G with 23.3 C being its upper limit (Scott and Grossman 1973) . Our gillnetted specimens were caught in water temperatures of 4-8 C and 16-18 C, the trawl-caught specimen in 18-20 C (Table B69). Lake Whi-tefish Lake whitefish stocks have been exploited in Lake Michigan for well over a hundred years. In the early years of maximum abundance they were captured using gillnets and beach seines. Decline of lake whitefish populations is reported to have started as early as 1850 (Wells and McLain 1973) and has 222 CJ Q) !-i fM 3 Vj 1 CM 4J O rvl trj U u U di 0) O r>4 O t3 r-i S g II cfl AJ o Se w o 1 M-l 05 U-l e — < •H m '^ >. C o •H 4J t-> CO r •'-' -s.^ •H > t t^ > " 4J ^ ^ £3 ,£3 •-H ct) • 1 a n-i ^ p- 4J M (0 U O (U (1 ! 5 c s o •H 4J {%; •IJ 4= 4-1 ^:: •H o •S^ o ■xj « -S w u (fl 1 O 2 -catch m caue to (U H O I CO Temperature- r some seldo .. C iH (U S > CS •H )-i (>0 u •u o 1! H (0 •H M •H i o V. cn o u-< 4-1 tu ^ • 0) J3 03 C •IJ ^ M rH c m cs rH m > •H !-i w u M les were immediately preservejd in 10% formalin. A flowmeter attached to the center opening of the net indicated volume of w,ater sampled. Flowmeters were calibrated by four people pulling a 1/2-m ring horizontally with and without the net 13.3 m four times each in an indoor swimming pool. Efficiencies (ratio of volume of water filtered with the net to volume of water filtered without the net) were calculated to be 84 and 92% for the two meters used. Each revolution of the flowmeter was calculated to represent 0.0170 m3 or 17.0 Z of water filtered by the net per revolution of the flowmeter. Volume of water filtered at beach stations ranged from 1.7-6.6 m3; for deepwater stations water filtered ranged from 0.8-32.4 m^. Numbers of larvae captured were adjusted to number per 1000 m^ by calculation to agree with published reports (Wells 1973) and to avoid reporting less than whole numbers of larvae. The flowmeter was unavailable for some beach station tows. In these cases an aver,age value of 3,96 m^ (233 t 10 revolutions, N = 28) was used. In one instance during deepwater tows, an average value was used (14.0 m^ - 826 i 36.8 revolutions, N = 63) because a leaf had been caught in the meter. During April and May the 1000' s indicator was missing from the flowmeter. Flowmeter readings for June and July were averaged, and two standard deviations on either side of the mean were calculated to be 242 and 1410 (iE = 826) . From these data we concluded that all readings less than 242 in April and May should have had a 1000 appended to them, and this was done for nine flowmeter readings. Numbers of larvae captured in the steptow represent an "average value" for the various depths over which the net was towed and are comparable to values obtained from the 0, 1 and 2-m tows, since the net was towed for 5 min as was done with the other tows. Because the net when brought from lower levels passed through the water column above, total numbers captured per 229 steptow were adjusted by calculation to compensate for this upper strata contamination. Through swimming pool tests, towing the net vertically in 2.6 m of water, we determined that the net filtered 0.476 m^ (28 i 0.52 revolutions) of water or 0.18 m^ for each meter of water through which the net passed. Numbers of fish larvae that would have been captured if 0.18 m3 were filtered at each of the depths were calculated. Then nximbers of fish larvae caught at 1 m, 2 m, and the steptow were adjusted by subtraction to account for larvae caught while passing through upper layers, then multiplied by a factor to get the catch in terms of numbers per 1000 m3. Only alewives were depicted in length-frequency histograms for fish larvae since they were most frequently caught and presented enough data, A computer program was written to plot length-frequency histograms which used intervals of 0.5 mm, i.e., 1.6-2.0 mm, 2.1-2.5 mm, etc. Since duplicate tows were made for beach stations A, B, F, mean number of larvae in each length interval was plotted. Then one average, the nximber of fish per length interval averaged over each meter of water, was desired for comparison with deepwater stations C, D, G and H. For 6.1-m stations this was accomplished by summing from each length interval the number of fish caught in m, 1 m, 2m and three times the number found in the steptow to represent 3, 4 and 5 m. In one case (station C June, the l^o depth tow) 86 fish larvae were captured but lost before measuring. In this case we assumed the length distribution was the average of that found at the other three depths sampled. This appeared to be the case from examining length distributions over depths for other stations. For 9-m stations, numbers in each length interval were summed by adding those caught in m, 1 m, 2 m and six times those caught in the steptow to represent 3, 4, 5, 6, 7, 8m, Numbers obtained were then divided by six or nine depending on station depth, and plotted, the numbers of larvae represent- ing the average number of fish per 1000 m^ averaged over the entire water column. Analysis of variance, after a log + 1 transformation more closely approximated homogeneity of variance and normality, was used to test differen- ces in catch of alewife fish larvae. Time of day, month, depth and station where the fish were caught were the main effects (treatments) . See Section A for further discussion of techniques used. FISH EGGS Data on fish eggs came from two main sources — fish larvae tows and benthic ponar grab samples. Some samples were obtained also by SCUBA divers. Eggs from tows have not been identified to date, but identifications were inferred from spawning runs of adults where feasible. They are presented as numbers per 1000 m3 using the same flowmeter methodology as discussed for fish larvae. Ponar samples will be analyzed at a future date. RESULTS FISH LARVAE Fish larvae were most abundant during June and July; April and August 230 were months of lesser abundance (Table CI) . No fish larvae were captured during March, October and November, A few smelt and alewife larvae were caught in May and September respectively. Smelt were most abundant during April, the same month during which large numbers of spawning adults were captured in seine hauls at inshore beach stations. Interestingly no smelt larvae were captured at any beach station during April. Since we did capture some during 1974 studies in May it is believed that they do occur there just after hatching and probably migrate to deeper water where they grow larger. They were common at all open-water stations but were caught only during the night and were most abundant at 6.1 m, Warren Dunes. These larvae ranged in length from 4.1-7,1 mm total length with a mean of 5.8 ± 0.05 (N = 75). They were judged to be fairly young, since 1-day old specimens which we reared in the laboratory at 9 C were around 5.1 mm (N = 10). Since weather, water temperature and other conditions were similar, aijd samples for these open-water stations were taken on the same day, the fact that no larvae were caught during the day must be attributed to either daytime net avoidance or some other behavior making smelt more susceptible to netting at night. Net avoidance seems unlikely since smelt were captured at deeper water stations, though in low nvmibers, and at beach stations during the day by us and by Wells (1973). At this time in May, smelt would be most likely to avoid a net. Larvae probably exhibit some type of vertical migration, being on the bottom during the day and near the surface at night in response to light or perhaps feeding behavior. If larvae were near or on the bottom during periods of daylight, our day tows would capture no smelt. Evidence for such behavior was obtained from our 1974 sled tows taken on the bottom during the day in May, when moderate numbers were found in samples. Also our diurnal 1974 entrainment sampling appeared to verify this hypothesis. Nuiabers of smelt collected during April at stations C, D and H at all depths were similar, while numbers caught at station G, 6.1 m, Warren Dunes, were consistently higher. Little difference was seen among numbers of smelt caught at the various depths at a given station. For the remaining months, a few smelt were captured in May at stations A, C and D, in June at station B and in August at stations D and F. Yellow perch were first captured in a night 1 m and steptow during April at 6.1 m, Warren Dunes. They were also captured at night during May at the north beach station at the Cook Plant. Our data indicate that peak spawning of yellow perch in the Cook Plant vicinity occurred within a very short t:Lme span, 1.5 weeks, starting around mid-June.. Wells (1973) explained similar early occurrences of yellow perch larvae in Lake Michigan as having been hatched from spawnings 3.n inland lakes and somehow entering Lake Michigan. In our samples, remaining yellow perch larvae were captured only in June and only at Cook Plant stations. They were captured in highest numbers at beach stations and were caught almost exclusively at night,, No patterns in vertical distribution were evident at deep-water stations. Our inability to capture large numbers of yellow perch during the day was unejcpected in view of those captured by Wells (1973) during June. In April, two perch larvae were caught, both 6.9 mm long. In May the only perch caught was 7.3 mm long. Mean length of the 19 caught in June was 6.0 ± 0.2 mm, range 4.4-7.5 mm. Thus it can be 231 TABLE CI. Number of fish larvae (<25.4 mm total length) per 1000 m^ captured during 1973 in the Cook Plant and Warren Dunes vicinity. S = smelt, T"= yellow perch, A = alewife^ SP == spot tail shiner, X = unidentified, ST = steptow, dash indicates no sampling was done. March April May Station Depth (in) Day Night Day Night Day Night At 286S ± 286 *253S ± *L26Y ± 12( B+ F-t- - C „ _ **147S 1 _ 62S ***71S 2 - 77S ST - - D _ _ **285S 85S 1 - — 273S 2 - **L02S ST - - 143S G _ **336S 1 _ **753S - - ** 54Y 2 _ ** 1214S ST _ **425S - ** 56Y H _ _ 1 _ 258S 2 - 146S ST - - 70S E 1 ~ - - - - 2 ST - - - - - M _ _ — « 1 - - - 2 _ - - ST _ _ - - 232 TABLE CI continued. June July Station Depth (m) Day Night Day Night At Bt '^614A ± 5134 *3036A + 506 *L265Y + 126 *L771A ± 506 *L898A ± 126 *1134Y ± 567 *506SP ± 506 *630SP ± 315 *126S ± 126 *3036A ± 759 '*2150A ± 126 *2898SP±1012 *3795A ± 1518 *26818A ± 20243 '^222A ± 633 *630SP ± 630 *6451A ± 1139 *630SP ± 630 *3795A ± 253 *L0246A ± 1898 *256SP ± 256 M 3290A 5 08 2 A 1590A 77Y 1 9822A 1925A 2682A 2 1897A 4079A 343A 2415A 164SP ST 83 OA 5356A 96 5A 193A 153Y 153SP 64 9A 217 6A 2200A 1 6535A 1146A 1061A 255Y 69Y 2 1754A 1612A 560A 817A 213Y ST 148A 653A 606A 346A 210SP 954A 8946A 83A 528A 142X 1 444A 4592A 983A 267A 65X 2 52 6A 2853A 47 6A 623A ST 1264A 3037A 914A 480A 504A 1612A 720A 168A 1 ***309A 902A 133A 2 289A 907A 186A 661A ST 313A 1637A 424A 68A _ 480A _ 1 87A - - 2 669A - 109A - ST 42A - 448A - - - _ _ 1 - - _ — 2 - - _ _ ST — — _ 233 TABLE CI continued. August Sep t ember October Station Depth (m) Day Night Day Night Day Night At 6463A ± 4077 1323A ± 385 B+ 2820A ± 516 375A ± 375 F + *14294A ± 4428 829A ± 406 *126A ± 126 123SP + 123 C 1 2 ST D 1 68S 2 ST G 372A 1 72A 2 52A ST H 1 13 3 A 2 552A ST 148A E 99A — - - - 1 345A - - - - 2 - - - - ST — — — — M — - - - - 1 - - - - - 2 - - - - - ST - - - - - 234 TA;BLE Cl continued. November December Station Depth (m) Day Night Day Night At - Bt - Ft _ C 1 _ - 2 ST - - D 1 - - 2 ST : : ■" ■"■ G 1 - _ 2 ST — ~* - H 1 - - A. 2 — -~ — — ST - - E - - _ _ 1 - - - 2 - - _ ST - - M — — _ _ 1 - - - 2 _ — _ ST — "- — — t represents the mean and standard error of duplicate samples. * = mean value of 3. '96 m^ for amount of water filtered was used. ** = 1000 was added to flowmeter reading. *** = mean value of 14.0 m'^ for amount of water filtered was used. 235 concluded that perch probably spawn through latter June in waters around the Cook Plant. Spottail shiner larvae proved to be very difficult to identify and in the past were confused with yellow perch. Recently discovered distinguishing characteristics have ameliorated the problem. Spottail larvae were captured June through August, with June the month of maximum abundance. Since we believe spottail larvae spend most of their time on the bottom, their numbers here are undoubtedly underestimated. Our 1974 sled tow samples confirmed this, as large numbers of spottails were caught at night, particularly at most beach stations. In June, spottails with a mean length of 5,7 i 0.1 mm (range 4.9-7.6 mm, N = 35) were caught exclusively at Cook stations in night step- tow and 2-m samples at 6.1 and 9.1-m stations. They were most abundant during day and night at the Cook south beach station, where the shallow nature of this habitat must have been favorable to spottails as a nursery area. In July, spottails captured were 7.0 t. 0,9 mm (range 4,4-13.0 mm, N = 12), larger than those captured in June. However, presence of small larvae (4.4 mm) indicates hatching through July. Larvae were taken only at night from beach stations, and were more abundant at Cook than at the Warren Dunes station. In August one larva, 6.1 mm, was taken at night from the beach station at Warren Dunes . Unidentified fish larvae (4.9 and 6.3 mm, N = 2) were caught at 6.1 m, Warren Dunes from the surface tow at night and the 1-m tow during the day. We caught no trout-perch larvae in our larvae tows, although our unident- ified larvae had some of the characteristics of trout-perch. Clarification must await laboratory rearing of specimens, which we hope to accomplish during 1975. We did capture 14 trout-perch in our trawling efforts on 26-27 October at stations C (6.1 m. Cook) and H (9,1m, Warren Dunes) , indicating that re- production had occurred. These fish were YOY ranging from 12-18 mm and prob- ably, like spottails, reside on the bottom and may be missed by our normal fish larvae sampling techniques. Sculpin larvae were taken only incidently in a trawl haul at 20,4 m, station E, on 19 June 1973. Water temperature was 7.2 C. These larvae were just hatched, since eggs, eyed embryos and larvae were all in the same sample. It is not known what species these were, but most probably they were slimy sculp ins. The spoonhead sculpin {Coitus rioei) was rarely caught by U. S. Fish and Wildlife Service personnel (Rottlers 1965) , and the deepwater sculpin {Myoxooephalus quadviaomis) is usually found in much deeper water. Neither fish has been captured during our sampling efforts. Spawning in riprap areas around intake and discharge structures in 1974 was also recorded by SCUBA divers (see Sec. B, sculp ins) . Rottlers (1965) has suggested that there may be two peaks in spawning by slimy sculplns, one in early spring by fish in shallow water, around 15 m or less, and another later on in the year in deeper water. Alewlf e larvae were captured June through September, with June the month of maximum abundance. In all months, larvae were more numerous at beach stations than deeper-water stations. This was particularly evident 236 during August when larvae, mostly alewlves, were highly concentrated in Inshore waters. More alewlves were caught during the day in August than at night. However, an analysis of variance (ANOVA) on data from the beach sta- tions during June through August indicated there was no difference in numbers of alewife larvae caught between stations among months or between day and night. For offshore stations, an ANOVA for June and July showed a significant difference between catches of alewlves at Warren Dunes and Cook locations , with the Dunes' stations having more alewife larvae (calculated F = 5.27; Tabular Fq o5» (1,32) = 4.15). No difference between numbers caught during day and night may be related to the fact that larvae are small and probably still l£ick sufficient ability to actively escape a net, because they are newly heitched in June (Fig. CI). They would be equally susceptible to netting during day and night if they exhibited no vertical migratory behavior. There appears to be a limited vertical migration upward by alewife larvae at night at stations C and D (not observed at G and H) , since no larvae were caught in the upper layer, 0-1 m, during the day and yet that same night record high abundances were recorded at those depths (Fig, C2) . It may be due also to the patchy distribution of this species. Few alewlves were caught at deeper-water stations in August, and no consistent patterns with regard to stations, depth or day-night variations were evident. Alewife larvae captured during day and night sampling at beach stations in June (Fig. CI) were the same size. More larvae were caught during the day than at night, although this difference was not statistically significant. All small larvae caught in June at the beach stations were less than 10 mm (early post-larvae stage according to Norden 1967b), indicating they were still fairly young. Mansueti and Hardy (1967) stated that an alewife larva 5.15 mm T. L. was 5 days old. One can conclude that a large hatch of alewlves, and thus spawning, occurred in early June in or near the beach area as hatch- ing can occur within 3 days of spawning (Mansueti and Hardy 1967). Wells (1973) caught alewife larvae as early as 28 May in Lake Michigan off Saugatuck, but none in the Cook Plant vicinity. Greatest ntunbers of alewives were caught during the day in June at sta- tion A, north of the plant; similar sizes but fewer fish were caught during the night. A similar pattern was observed at other stations. We concluded that net avoidance by these fish was negligible at this time. Mean size of larvae captured during the night was consistently smaller than that of larvae caught during the day at most stations, and many of the smallest individuals were caught only during the night. This suggests that perhaps newly hatched larvae stay on the bottom during the day and come to the surface only at night during the first early period of their lives. However, this pattern for small larvae was inconsistent in July. In July, greatest numbers of alewife larvae were caught at station B during the day. At stations B and F few larvae greater than 8 mm were caught during the night whereas quite a number were collected during the day, indicating some type of diel movement by these larger larvae. In contrast, newly hatched larvae 2.5-6 mm were caught in approximately equal numbers during the day and night except at station F, where relatively large numbers of these small larvae were captured at night (2000-4000/m3) compared with day 237 ■T3 2 CO 03 « g CO "r! cu (1) -^^ S ** CO o u •H H to Cti CO ^ t% CO -H rH td C 0) CO O CO (U M-l U-l ,fl -H B O ^ CO CB (U 60 ,Q CO O 4J -U •« CO cd CO •H C ^ CO -. O i-J tH _^ 60 » 1:3 • - . >- a I X L.JI. t ,» I ,1 «- est O n 1 X CD It IX <3\ II IX o eg 1^3 ■-* f— r CO «J *''*'*'*''' g •H 4J O u d3 H P4 240 .—I LU CD i t— I u5 CD I m m n *''■'■'■'■ I . I t ' o 2- u-i S fe o s: I IX .i ' ' ' ' ' ' ■ ' f 1 I f . I . t I I , f - {" 0001 / HSU JO iGa-rw p 00 X) 13 C S ^ 03 •H 0) 4J CO CO ^ to 4J to 2! f^ 3 o CO C M-l U O C 4J o -H a 3 to ^j !-< -W 4-1 60 CO O CO ■u B ^ CO w •H rH M ^ • C >> rH T3 s e (u a) co iw 3 -H CTt-H S M vO <4-l 1 AJ ,C to 0) to CO c CJ 4J (U CD P, 3 CO 60 3 +J <; ^ 60 O '3 3 M C CO fa tO O 60 CO (U o\ CM CJ) 241 en i CD i-H >- eD g C3 ^:: CD i cr> CJ oo in g II IX ON I X >- ■ t X « ■ ' • I ' ' « t ' ' ■ t. 1 I I . a fe : CD . > - •^ a: D - r^ LU I X II I X o vO - U3 2 » ' ' ' ' ' ■ ■1 — ■''*'«•'■ I . c-4 CM UJ 31 1- O z^ f .i Xl 0) 3 c •H 4J a o u 04 ^ 0001 / HSU dO HBHlrfTN o H 242 \?. g CD •a: g en g 5- o « I X o CM tf I X is I ' I » 1 1 1 1 1 1 1 I 1 1 1 I 1 1 1 1 1 1 1 1 1 1 1 1 . 1 , 1 . 1 . t CO CM O CM I X O CM II IX fe o CM c. : r-l 5 -I d: UJ ...1 J I. t ^-^ s CD : 1^ r ro^^ z - r-i r <» r^^ UJ E fe — c» •— « » .-t ' ^ t- -52 rW OOOT / HSU JO yBflijriN CM CM ,<— <^ g ay—y ^ -s tP LU 2 fe? ^ O i— « •u CD o u «o ^ 3 • Cvl CN U o H |i4 243 catches (500/m^). Larvae in these large catches at beach stations in July were very small (Fig. CI) and could have hatched that same evening or the day before. In August, alewife larvae captured were generally larger than those caught in previous months (Figs. CI, C2); however a few newly hatched larvae less than 6 mm were captured at station A, indicating that alewives have a prolonged spawning period lasting from June through August, a fact supported by examination of adult gonad data. At all stations, far more alewife larvae were captured during the day than at night, the same type of phenomenon observed in June and July, again indicating that net avoidance is probably not significant for alewives less than about 18 mm in length and that alewives are probably moving either outward or downward at night, Since few were caught at any depth at deeper water stations, one might conclude a downward migration was occurring during the night, at least at the inshore beach stations. FISH EGGS Fish eggs were observed in samples from April through September (Table C2) . No eggs were collected in March, October and November. Eggs were almost al- ways more abundant in beach station samples in a given month than at the deeper-water stations. This is probably related to the greater wave and current activity inshore but could be associated also with more spawning in beach-zone waters. In April and May eggs were found only in beach station.- tows. They were collected in high concentrations at station A, 17,457/m3, during April in both day and night samples and were present at all beach stations during the night tows. These were probably smelt eggs, as we captured large numbers of gravid fish in seine hauls during April. Eggs collected around 15 May were probably smelt eggs also, since Wells (1973) stated his earliest collection of alewife larvae was on 28 May, thus probably ruling out eggs collected in May as alewife. In June through September very large numbers of eggs were recorded, probably most alewife. It was observed that yellow perch were eating large numbers of eggs during July, and that during one storm when wave height was about 1-4 m during larvae tows the highest concentrations of eggs were obtained. This indicates that a large concentration of alewife eggs probably lies on the bottom at least during July. In June most eggs were again collected at beach stations, though quite a number were collected from most depths towed at stations C, G (6.1 m) and H (9.1 m) . In July, August and September, eggs were caught only at beach stations, except for two minor occurrences at deep-water stations. It would appear that these were mostly alewife eggs, and it is probable that by latter August and September most eggs were dead. DISCUSSION Net avoidance by fish larvae is an important consideration when evaluat- ing distribution and occurrence data. Young alewife larvae did not appear to avoid the net to any great extent. For alewives greater than 10 mm there was a definite trend toward more being caught during the day than at night, suggesting that net avoidance is also minimal for these fish and that some 244 TABLE C2- Kumber of fish eggs per 1000 m^ collected with horlzonal Ko. 2 plankton net tows during March through November, 1973 in the vicinity of the Cook Plant and Warren Dunes. March April Station Depth (m) Day Night Day Night *17457 ± 17457 *1392 + 1392 *506 + 506 - - *253 ± 253 - - - - - - - - - - - - - - - - - - - - At Bt F+ C 1 2 ST G 1 2 ST H 1 2 ST E 1 2 ST M 1 2 ST 245 TABLE C2 continued. Maz June • tion Depth (m) Day Night At *1138 ± 632 Bt 14282 ± 9316 Ft C 1 2 ST D 1 2 ST G 1 2 ST H 1 2 ST E _ — 1 - - 2 - - ST - - M 1 2 ST Day Night *25300 ± 22517 *53003 ± 33776 *8982 ± 3162 770 660 164 128 170 42600 195 6000 9595 93 8662 1235 445 _ - - — 246 TABLE C2 continued. July Station Depth (m) Day Night August Day Night A+ Bt M 1 2 ST I 2 ST 1 2 ST 1 2 ST 1 2 ST 1 2 ST *2656 ± 2150 *90700 ± 11006 *1012 ± 1012 *2150 + 126 *2530 ± 759 *4029152 ± 982788 244 ± 244 139 ± 139 550 ± 550 *380 + 126 353 ± 141 174 ^ - 193 - - „ - - — 247 TABLE C2 continued, : , ' ' ' — — . . September October November Station Depth (m) Day Night Day Night Day Night A+ *2777 ± 2777 Bt *253 ± Ft *5313 ± 5313 C _ 1 — _ 2 _ _ ST - D _ 1 _ „ 2 — _ ST - G _ 1 _ _ 2 _ _ ST - H _ 1 — _ 2 — _ ST - E — — ^ _ 1 - - — _ 2 - ~ — — ST - — - M _ — .^ _ 1 - - — _ 2 - - - _ ST — — - - ^represents the mean and standard error of duplicate samples. * = mean value of 3.96 m^ for amount of water filtered was used, 248 sort of dlel vertical migration was occurring. We seldom caught larvae over a certain species' specific size, suggesting that larvae rapidly attain the ability to detect and avoid a net, which Hogman (1971) discussed for whitefish larvae. An alternate hypothesis for explaining lack of larger smelt and perch in net catches is a demersal existence by these fish after they attain a certain size. The largest yellow perch and smelt caught were 8.0 and 7.1 mm respectively. A few odd catches of larger smelt, 17,6 and 23.8 mm, were made in June and August, Maximum size of spottail shiners in June was 7.6 mm, in July 13.0 mm. Any conclusions with regard to migratory behavior either vertically or horizontally must be made in view of the above considerations. Larger alewife larvae were caught more often during the day than at night. This could be a phototactic response or related to feeding. Our 1974 sled tow data should clarify whether it does occur. Smelt were more common in the upper reaches during the night and apparently more toward or on the bottom during the day. We hypothesized that trout-perch, slimy sculpin and to a certain extent spottail larvae probably stay on the bottom for most of their early existence, since they were rarely or never caught in our larval tows. The much discussed competitive influence of alewives on yellow perch (Smith 1970; Wells and McLain 1973) is a distinct possibility considering the great abundance of alewife larvae and adults at the time yellow perch larvae were also present, Alewife larvae were most abundant during June, July and August, particularly in beach-zone waters. Perch larvae were most abundant in inshore beach-zone waters during June. Smelt larvae occurred earlier in the year, before alewife larvae invaded inshore waters. Spottails and trout-perch spawn later in the spring and summer, the latter probably in deeper water. Spottail shiners are considerably more numerous than the once abundant emerald shiner (Wells and McLain 1973) and appear not to be adversely affected by the alewife, since spottails were the second most abun- dant species in the vicinity during 1973. 249 SECTION D SUMMARY OF IMPINGEMENT AND ENTRAINMENT DATA David J. Jude and John A. Dorr III INTRODUCTION The plant's circulation pumps were operated very little during 1973 be- cause of difficulties in construction of the intake and discharge pipes as well as with various aspects of the pumps and associated equipment. Most pumping that was done was for testing equipment and for keeping the pumps from rusting and/or malfunctioning from disuse. Some difficulties in the mechanism for fish collections were encountered, so that fish were not con- sistently collected after pumping occurred. Pumping was performed with only one pump of seven, and the amount of water circulated was only a fraction of the eventual total water circulation. Therefore data collected were at best an indication of some of the amounts of species that might be encountered had continuous pumping occurred. Limited entrainment sampling for fish larvae and eggs occurred only during February 1973, again due to the infrequent operation of the plant's circula- tion pumps. METHODS IMPINGEMENT Cook Plant personnel presently separate fish from debris collected from the traveling screens, place the fish in a plastic bag, then tag and freeze them. Fish are thawed at the laboratory and processed in the same way as other fish, with an additional notation on the physical condition and degree of putrificatlon. ENTRAINMENT A 303 il/min (80 gal/min) diaphragm pump (actual capacity is 208 £/min) with a hose extended to different depths in the intake forebay (1.5, 3.0, 4.6 and 9.1 m) was used to ptunp water into a 1/2 m No, 2 plankton net suspended in a 208 I (55 gal) drum. Water flow through the drum was measured with a flowmeter. On one occasion a 1/2 m. No. 2 plankton net was suspended directly in the intake forebay. Samples were preserved with 10% formalin. No samples were taken from the discharge forebay. Sampling was performed primarily for the purpose of testing sampling equipment and procedures. 250 RESULTS IMPINGEMENT Of the 426 fish we processed during 1973, six species comprised 93% of the total number captured (Table Dl) . Slimy sculpin made up 29.6% of those captured, probably due to the fact that all pumping occurred during January, Februar^r, March, April, October, November and December— months when water temperatures were low. Our temperature data suggest slimy sculpin prefer temperatures less than 16 C. This, associated with the sculpin' s natural attraction to rocky and dark places for concealment and spawning, apparently makes the species susceptible to this type of entrapment. Yellow perch comprised 25.8% of those caught and were almost all less than 100 Tnm. Spot- tail shiner, 13.4%, and smelt, 13.8%, were the next two most abundant species impinged. Alewife, 7.7%, and black bullhead, 2.8% (12 specimens), were the other fairly common species caught. Black bullheads are apparently more susceptible to pumping impingement than to our sampling methods, since we were able to capture only four during all our field sampling in 1973. Perhaps they are also attracted to the intake area like sculpins. Twenty species were impinged, which is less than half as many as we captured during our regular field sampling activities. Bowfin, black crappie, pumpkinseed sunf Ish and mudminnow were four new species captured this year, taken es:clusively from traveling screen catches. ENTKii.INMENT A total of 16 diaphragm pump samples and one suspended net sample were obtained (Table D2) . Upon laboratory examination no samples were found to contain either fish eggs or larvae. All samples were relatively free of algae s sand and organic debris. From consideration of the fish larvae and egg data (Sec, C) which are given in terms of numbers per 1000 m3, it can be seen that if an adequate sample is desired for determining entrainment effects, at least 10 m3 for a sample of 10 larvae during months of maximum abundance should be filtered. For months of lesser abundance of common species of larvae and of rarer species, 200 m^ or more should be sampled. 251 CD 'O Ml a 3 ro CO t-» ty> tfl p. >- o -u rH •~i ai o ,n St. ^ OJ rH '^ ^ CD ^ 0) •H (d CO r-i 03 0) cci rH tn j C4 •n *n o !o 1 cr- o i-H r^ m ^3- fn r- ^ \D -^U 33 » CN r^ * h 1-^ * * K * CD 13 1 1 r^ CU D, cfl CO ■O r~i m iM ■NI CN n iH ^ -n .-i M E-i CU CU a* ^ r-l rH f-i .-( rH f-t T-f rH r-l -H r~l ~i ^ .-t < * [* * * K ■K . c J2 XI J3 Vj • U ^', i> ti O i) ■ o n W pei < X 1 c ^ in tn c^J in CT\ o 1 in rH