EFFECTS OF MINIMUM AND SLOT LENGTH LIMIT REGULATIONS FOR LARGEMOUTH BASS ON THE LARGEMOUTH BASS AND BLUEGILL FISHERIES IN FOUR LAKES IN WISCONSIN

Transcription

1 EFFECTS OF MINIMUM AND SLOT LENGTH LIMIT REGULATIONS FOR LARGEMOUTH BASS ON THE LARGEMOUTH BASS AND BLUEGILL FISHERIES IN FOUR LAKES IN WISCONSIN by Marty E. Lundquist A Thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in Natural Resources (Fisheries) College of Natural Resources UNIVERSITY OF WISCONSIN Stevens Point, Wisconsin June, 199

2 APPROVED BY THE GRADUATE COMMITTEE OF: Dr. Daniel w. Coble, Committee Chairman Professor of Fisheries ~4~ or:fredrfck A. Cop~ Professor of Biology Dr. Richard v. Frie Professor of Fisheries ii

3 ABSTRACT Effects of length limit regulations for largemouth bass (Micropterus salmoides) on the bass and bluegill (Lepomis macrochirus) fisheries in four lakes in southeast Wisconsin were studied from 198 to In 1982 a slot length limit of 35-46mm (12-16 inches) was established on Beulah and Rockland lakes, and a minimum length limit of 46mm was introduced on Pretty and Browns lakes. Angling effort for largemouth bass and bluegills did not change, and some of the expected, desired changes occurred tor both largemouth bass and bluegills. The regulations reduced the harvest rate of protected largemouth bass while the harvest rate of legal bass decreased in one lake and increased in three lakes. Electrofishing catch per effort of larger largemouth bass increased in three lakes, and mean length of protected bass increased in the other, but angler catch rate did not change and relative weight of largemouth bass decreased in three lakes. Relative weight of ~uegills and mean length of harvested bluegills increased. Bluegill electrofishing catch per unit effort increased in two lakes but not the other two, and no change was detected in angler catch rate, or growth rate. iii

4 ACKNOWLEDGEMENTS This study was supported by the Wisconsin Department of Natural Resources, and the Wisconsin Cooperative Fishery Research Unit, University of Wisconsin, Stevens Point. I express my appreciation and special thanks to Dr. Daniel Coble, my committe chairman, for is support, patience, and careful editing of this manuscript. I thank committee members Drs. Fred Copes and Richard Frie for their advice and review of this manuscript. I also express thanks to Dr. Bill Le Grande and Jay Harvey for sharing their knowledge of computers, and Dr. Robert Rogers for his advice on statistical analysis. I am gratefully to Doug Welch and Rick Dueffenbach for scheduling the electrofishing, and creel surveys, and to all DNR personnel who helped conduct the field work. I am also grateful to the work study students who pressed scales. I would like to thank Dorothy Snyder for all her help during this project. My deepest appreciation goes to my parents for their support of my decisions and during my trials and tribulations as a college student aqd for introducing me to nature at a young age. iv

5 TABLE OF CONTENTS ABSTRACT..... iii ACKNOWLEDGEMENTS. LIST OF TABLES. LIST OF FIGURES. LIST OF APPENDICES.... i v.vii. xi.. xvii INTRODUCTION METHODS AND MATERIALS Sampling Creel Survey Length Frequency, Mean Length and, Catch Per Unit Effort From Electrofishing Proportional Stock Density Relative Weight Age, Growth, and Mortality Population Estimates, Standing Stock, and Exploitation RESULTS AND DISCUSSION Creel Survey Fishing Pressure Harvest Rate, Mean Length Harvested, and Catch Rate Largemouth Bass Bluegills Length Frequency, Catch Per Unit Effort, and Mean Length From Electrofishing Samples Largemouth ~. T 37- Bluegills Proportional Stock Density Largemouth Bass Bluegills Relative Weight Largemouth Bass Bluegills Growth Largemouth Bass Bluegills Mort a 1 it y Largemouth Bass Bluegills Population Estimates and Exploitation of Largemouth Bass in Rockland Lake v

6 CONCLUSION... LITERATURE CITED.. APPENDICES vi

7 LIST OF TABLES Table 1. Fish sampling methods in the four lakes with effort in hours for the electroshocker and hours/week for the creel survey Table 2. Minimum stock and quality size {mm) for largemouth bass, bluegills, pumpkinseeds, warmouth, green sunfish, and yellow perch Table 3. Estimated angling effort {hours/hectare) of largemouth bass, bluegills, and all species in 198, 1982, 1984, 1986, and 1988 and results of regression analysis of estimated angling effort versus time in Beulah, Rockland, Pretty, and Browns lakes. + = positively significant, - = negatively significant, and o = not significant at the.5 level of significance Table 4. Estimated mean harvest rate {number/hectare) of largemouth bass of protected, unprotected, and of all sizes in Beulah, Rockland, Pretty, and Browns lakes compared between 198 and {and between 198 and for Rockland Lake) with a Chi-square test {Li 1969; p.458). +=positively significant, - = negatively significant, and o = not significant at the.5 level of significance Table 5. Estimated total number harvested, harvest rate {number/hectare), and percent of each size group of largemouth bass harvested in 198, 1982, 1984, 1986, and Table 6. Estimated mean length {mm) and catch rate {number/hectare) of largemouth bass in 198, 1982, 1984, 1986, and 1988 and results of regression analysis of estimated mean length harvested and catch rate versus time in Beulah, Rockland, Pretty, and Browns lakes. + = positively significant, - = negatively significant, o = not significant at the.5 level of significance vii

8 LIST OF TABLES (continued) Table 7. Estimated harvest and catch rates (number/hectare) and mean length (mm) of bluegills in 198, 1982, 1984, 1986, and 1988, and results of regression analysis of estimated harvest and catch rates, and mean length harvested versus time in Beulah, Rockland, Pretty, and Browns lakes. + = positively significant, - = negatively significant, o = not significant at the.5 level of significance Table 8. Catch per unit effort (CUE) and mean length of largemouth bass from electrofishing in spring in the four lakes, , and results of regression analysis of CUE and mean length versus time. + = positively significant, - = negatively significant, and o = not significant at the.1 level of significance. Mean in table computed from values in appendix G... 4 Table 9. Catch per unit effort (CUE) and mean length of bluegills from electrofishing in spring in the four lakes, , and results of regression analysis of CUE and mean length versus time. + = positively significant, - = negatively significant, and o = not significant at the.1 level of significance. Mean in table computed from values in appendix H Table 1. Table 11. Proportional Stock Density (PSD %) of largemouth bass and bluegills in 198 to 1989 rrom the four lakes. Number ±rr parentheses represents number of fish of stock size Comparison of mean relative weights of largemouth bass from spring electrofishing I samples between 1988 and and for lakes Beulah, Rockland, and Pretty and between and and for Browns Lake with a t-test (Zar 1974; p.15). The asterisk(*) indicates a significant difference at the.5 level of significance; t values computed from values in appendices I, J. 68 viii

9 LIST OF TABLES (continued) Table 12. Table 13. Table 14. Comparison of mean relative weights of bluegills from spring electrofishing samples between 1988 and and for lakes Beulah, Rockland, and Pretty and between and and for Browns Lake with a t-test (Zar 1974; p.15). The asterisk (*) indicates a significant difference at the.5 level of significance; t values computed from values in appendices L, M Comparison of growth rates and length increments of largemouth bass of various age groups in all lakes from 1979 to F values computed from values in appendix o, (Steele and Torrie 196). +=positively significant, - = negatively significant, o = not significant at the.5 level of significance Comparison of growth rates and length increments of bluegills of various age groups in all lakes from 1979 to F values computed from values in appendix s, (Steele and Torrie 196). +=positively significant, - = negatively significant, o = not significant at the.5 level of significance Table 15. Total annual and instantaneous mortality (A and Z), and survival (S) of largemouth bass, bluegills, and pumpkinseeds (Browns Lake only) for , , and 1988 f1988 l-9-8-s i-n Browns I.ake-h i-s- ~ correlation coefficient. Rates calculated from data from spring electrofishing samples.. 84 Table 16. Comparison of total annual mortality of largemouth bass from spring electrofishing samples between 1988 and and for lakes, Beulah, Rockland, and Pretty and between and and for Browns Lake with a t-test (Zar 1974; p.228). The asterisk(*) indicates a significant difference at the.5 level of significance; t values computed from values in appendix w 85 ix

10 LIST OF TABLES (continued) Table 17. Table 18. Table 19. Table 2. Table 21. Comparison of total annual mortality of bluegills from spring electrofishing samples between 1988 and and for lakes, Beulah, Rockland, and Pretty and between and and for Browns Lake with a t-test (Zar 1974; p.228). The asterisk (*) indicates a significant difference at the.5 level of significance; t values computed from values in appendix w Schnabel population estimate (number/hectare), 95% confidence interval (CI), estimated standing stock, and mean individual weight of largemouth bass in Rockland Lake in Springs Estimated exploitation rate (u) for 198, 1982, 1984, 1986, and Estimated and predicted densities (number/hectare) of largemouth bass ( 2mm) in Rockland Lake compared with a paired t-test (Sokal and Rohlf 1981). Estimated densities based on Chapman-modified Schnable population estimates (Ricker 1975). Predicted densities based on the regression equation, logy= log X (Hall 1986), where Y is the predicted density and X is the spring electrofishing catch per unit effort (CUE) Summary of results of largemouth bass: results of regression analysis, t-tests and Chi-square t-ests - data from -Cr-eel surveys and electrofishing for largemouth bass for the period 198 through "P.to." and "Unpro." indicates largemouth bass of protected and unprotected sizes respectively. "Pre." is pre-regulation years ( ), "Post." represents the time period # = an interpretation of the data. + = positively significant, - = negatively significant, o = not significant Summary of results of bluegill: Results of regression analysis, and t-tests of data from creel surveys and spring electrofishing for bluegills for the period 198 through "Pre." is pre-regulation years { ), "Post." represents the time period # = an interpretation of the data. + = positively significant, - = negatively significant, and o = not significant... 99

11 LIST OF FIGURES Figure 1. Angling effort (hours/hectare) for largemouth bass (LMB) and bluegills (BLG) in Beulah and Rockland lakes in 198, 1982, 1984, 1986, and Figure 2. Angling effort (hours/hectare) for largemouth bass (LMB) and bluegills (BLG) in Pretty and Browns lakes in 198, 1982, 1984, 1986, and Figure 3. Harvest composition (number/hectare) of three size groups of largemouth bass from Pretty Lake in 198, 1982, 1984, 1986, and Figure 4. Harvest composition (number/hectare) of three size groups of largemouth bass from Browns Lake in 198, 1982, 1984, 1986, and Figure 5. Harvest composition (number/hectare) of four size groups of largemouth bass from Beulah Lake in 198, 1982, 1984, 1986, and Figure 6. Harvest composition (number/hectare) of four size groups of largemouth bass from Rockland Lake in 198, 1982, 1984, 1986, and Figure 7. Regression of mean length (mm) of harvested largemouth bass from Browns Lake in 198, 1982, 1984, 1986, and 1988, with regression equation, F value, correlation coefficient (R), and sample size (N). "Sign." indicates a s-i~icant significance. rela~irm at the &.5 level o-f... 3 Figure 8. Estimated numbers of largemouth bass caught and harvested per hectare, and total angling effort (hours/hectare) in Beulah Lake in 198, 1982, 1984, 1986, and Figure 9. Estimated numbers of largemouth bass caught and harvested per hectare, and total angling effort (hours/hectare) in Rockland Lake in 198, 1982, 1984, 1986, and xi

12 LIST OF FIGURES (continued) Figure 1. Figure 11. Figure 12. Figure 13. Figure 14. Figure 15. Figure 16. Estimated numbers of largemouth bass caught and harvested per hectare, and total angling effort (hours/hectare) in Pretty Lake in 198, 1982, 1984, 1986, and Estimated numbers of largemouth bass caught and harvested per hectare, and total angling effort (hours/hectare) in Browns Lake in 198, 1982, 1984, 1986, and Regression of mean length (mm) of harvested bluegills from Beulah and Rockland lakes in 198, 1982, 1984, 1986, and 1988, with regression equation, F value, correlation coefficient (R), and sample size (N). "Sign." indicates a significant relation at the.5 level of significance Regression of mean length (mm) of harvested bluegills from Browns Lake in 198, 1982, 1984, 1986, and 1988, with regression equation, F value, correlation coefficient (R), and sample size (N). "Sign." indicates a significant relation at the.5 level of significance Spring electrofishing catch per unit effort of largemouth bass in 1-mm length groups, sample (N), and Proportional Stock Density (PSD) from Beulah Lake in 198 to Slot length limit represented by dashed vertical lines RegressiDn a spring el~trmishing catch per unit effort of largemouth bass longer than 35mm from Beulah and Rockland lakes in 198 to 1988, with the regression equation, F value, correlation coefficient (R), and sample size (N) for each lake. "Sign." indicates a significant relation at the.1 level of significance Spring electrofishing catch per unit effort of largemouth bass in 1-mm length groups, sample (N), and Proportional Stock Density (PSD) from Rockland Lake in 198 to Slot length limit represented by dashed vertical lines xii

13 LIST OF FIGURES (continued) Figure 17. Figure 18. Figure 19. Figure 2. A: Regression of mean length (mm) of largemouth bass longer than 35mm from spring electrofishing samples from Rockland Lake in 198 to B: Regression of mean length (mm) of protected largemouth bass from spring electrofishing samples from Pretty Lake in 198 to 1988, with the regression equation, F value, correlation coefficient (R), and sample size (N) for each lake. "Sign." indicates a significant relation at the.1 level of significance.. 45 Spring electrofishing catch per unit effort of largemouth bass in 1-mm length groups, sample (N), and Proportional Stock Density (PSD) from Pretty Lake in 198 to Minimum length limit represented by dashed vertical line A: Spring electrofishing catch per unit effort of protected largemouth bass from Browns Lake in 198 to B: Spring electrofishing catch per unit effort of unprotected largemouth bass from Browns Lake in 198 to 1989, with the regression equation, F value, correlation coefficient (R), and sample size (N) for each lake. "Sign." indicates a significant relation at the.1 level of significance Spring electrofishing catch per unit effort of largemouth bass in 1-mm length groups, sample (N), and Proportional Stock Density (_psnj from _Brmms Lake in 198_ to 19ft9 ~ Minimum length limit represented by dashed vertical line Figure 21. Spring electrofishing catch per unit effort of bluegills in 1-mm length groups, sample (N), and Proportional Stock Density (PSD) from Beulah Lake in 198 to Quality size is represented by the solid vertical 1 ine Figure 22. Spring electrofishing catch per unit effort of bluegills in 1-mm length groups, sample (N), and Proportional Stock Density (PSD) from Rockland Lake in 198 to Quality size is represented by the solid vertical line xiii

14 LIST OF FIGURES (continued) Figure 23. Figure 24. Spring electrofishing catch per unit effort of bluegills in 1-mm length groups, sample (N), and Proportional Stock Density (PSD) from Pretty Lake in 198 to Quality size is represented by the solid vertical 1 ine Spring electrofishing catch per unit effort of bluegills in 1-mm length groups, sample (N), and Proportional Stock Density (PSD) from Browns Lake in 198 to Quality size is represented by the solid vertical line Figure 25. Figure 26. Figure 27. Figure 28. Figure 29. Spring electrofishing catch per unit effort of all bluegills from Beulah Lake in 198 to 1988, and from Browns Lake in 198 to 1989, with the regression equation, F value, correlation coefficient (R), and sample size (N) for each lake. "Sign." indicates a significant relation at the.1 level of significance Spring electrofishing mean length (mm) of all bluegill from Browns Lake in 198 to 1989, with the regression equation, F value, correlation coefficient (R), and sample size (N) for each lake. "Sign." indicates a significant relation at the.1 level of significance Proportional Stock Density (PSD %) of largemouth bass and bluegills from Beulah and Rockland lakes in 198 to Points are connected in chronological order. --- Solid squares represent 198 and 1988 values.. 6 Proportional Stock Density (PSD %) of largemouth bass and bluegills from Pretty in 198 to 1988, and Browns Lake in 198 to Points are connected in chronological order. Solid squares represent 198 and 1988 or 1989 values Relative weight of largemouth bass from , , and 1988 in 1-mm length groups in Beulah and Rockland lakes.. 66 xiv

15 LIST OF FIGURES (continued) Figure 3. Relative weight of largemouth bass from , , and 1988 ( in Browns Lake) in 1-mm length groups in Pretty and Browns lakes Figure 31. Relative weight of bluegills from , , and 1988 in 1-mm length groups in Beulah and Rockland lakes Figure 32. Relative weight of bluegills from , , and 1988 ( in Browns Lake) in 1-mm length groups in Pretty and Browns lakes Figure 33. Regressions of instantaneous growth rate by age group of largemouth bass in Beulah Lake from 1979 to Figure is a representation of table 8, minus age groups 8-9, 9-1. Values used to calculate regressions are in appendix o Figure 34. Total length (mm) at age of years , , and 1988 of largemouth bass in Beulah and Rockland lakes; and the southeastern Wisconsin average (Druckenmiller 1972) Figure 35. Total length (mm) at age of years , , and 1988 ( in Browns Lake) of largemouth bass in Pretty and Browns lakes; and the southeastern Wisconsin average (Druckenmiller 1972) tfo'-'ti-t"!gmure ~6 'Pot-al length {mm-} at age o-f yeafb 19& , , and 1988 of bluegills in Beulah and Rockland lakes; and the southeastern Wisconsin average (Druckenmiller 1972) Figure 37. Total length (mm) at age of years , , and 1988 ( in Browns Lake) of bluegills in Pretty and Browns lakes; and the southeastern Wisconsin average (Druckenmiller 1972) XV

16 Figure 38. Figure 39. Figure 4. Figure 41. Figure 42. Catch curve from spring electrofishing samples from , , and 1988 for largemouth bass in Beulah and Rockland lakes. Natural logarithm of numbers caught versus age Catch curve from spring electrofishing samples from , , and 1988 ( in Browns Lake) for largemouth bass in Pretty and Browns lakes. Natural logarithm of numbers caught versus age Catch curve from spring electrofishing samples from , , and 1988 for bluegills in Beulah and Rockland lakes. Natural logarithm of numbers caught versus age Catch curve from spring electrofishing samples from , , and 1988 ( in Browns Lake) for bluegills in Pretty and Browns lakes. Natural logarithm of numbers caught versus age Regression of population estimates from spring electrofishing samples in Rockland Lake from 198 to 1988, with the regression equation, F value, correlation coefficient (R), and sample size (N). F value computed from values in appendix X, (Steel and Torrie 196). "Not sign." indicates no significant relation at the.5 level of significance.. 92 xvi

17 LIST OF APPENDICES Appendix A. Appendix B. Appendix C. Common and scientific names of species caught by electrofishing (E), and angling (A) during spring 1988 to spring 1989 in the four study lakes Location of the four study lakes in three counties in southeast Wisconsin Hydrographic maps of Beulah, Rockland, Pretty, and Browns Appendix D. Length - frequency distributions of largemouth bass in electrofishing samples in spring and fall of 1988 in all lakes and spring of 1989 in Browns Lake Appendix E. Appendix F. Appendix G. Appendix H. Length-frequency distributions of bluegills, pumpkinseeds, yellow perch, green sunfish, and warmouth in electrofishing samples in spring and fall of 1988 in all lakes and spring of 1989 in Browns Lake Bluegill and prey weighted Proportional Stock Densities (PSD %) from 198 to 1985 and 1988 ( in Browns Lake) in the study lakes. Prey weighted PSD was not calculated when number of stock size fish or prey species was less than 3 because Novinger and Legler (1978) suggested 3 as a minimum number of fish to determine PSD Length frequency distributions of largemouth ba~ in spring e~refishing samples in 198 to 1988 (198 to 1989 in Browns Lake) from the study lakes. These data are plotted in figures 14, 16, 18, and 2 as number per hour Length frequency distributions of bluegills in spring electrofishing samples in 198 to 1988 (198 to 1989 in Browns Lake) from the study lakes. Subsample size is the number of fish measured to determine length distribution of the entire sample (total). These data are plotted in figures as number per hour xvii

18 LIST OF APPENDICES (continued) Appendix I. Mean Relative Weight (Wr%) of largemouth bass in 1-mm length groups from and 1988 { in Browns Lake) from spring electrofishing samples in the study lakes. Sample means compared with a t-test (Sokal and Rohlf 1981; section 9.4). All statistical tests were at the.5 level of significance data from Mayers (1988) Appendix J. Appendix K. Appendix L. Appendix M. Mean Relative Weight (Wr%) of largemouth bass in 1-mm length groups from and 1988 ( in Browns Lake) from spring electrofishing samples in the study lakes. Sample means compared with a t-test (Sokal and Rohlf 1981; section 9.4). All statistical tests were at the.5 level of significance data from Mayers (1988) The Wr regression equation of largemouth bass (> 1mm) from Pretty Lake in 1988 and a t-test of the significance of the slope (Sokal and Rohlf 1981; p.473). The period exhibited a significant negative slope at the.5 level of significance. Wr values are from appendix I, J and are plotted in figure Mean Relative Weight (Wr%) of bluegills in 1-mm length groups from and 1988 ( in Browns Lake) from spl."i-ng eleg~l;'g ishing samples in ~ s~udy lakes. Sample means compared with a t-test (Sokal and Rohlf 1981; section 9.4). All statistical tests were at the.5 level of significance data from Mayers (1988) Mean Relative Weight (Wr%) of bluegills in 1-mm length groups from and 1988 ( in Browns Lake) from spring electrofishing samples in the study lakes. Sample means compared with a t-test (Sokal and Rohlf 1981; section 9.4). All statistical tests were at the.5 level of significance data from Mayers (1988) xviii

19 LIST OF APPENDICES (continued) Appendix N. Appendix. Appendix P. Appendix Q. Appendix R. Appendix s. The Wr regression equation of bluegill (> 8mm) from Beulah Lake and a t-test of the significance of the slopes (Sokal and Rohlf 1981; p.473). All three periods exhibited a significantly negative slope at the.5 level of significance. Wr values are from appendix L, M and are plotted in figure , and data from Mayers (1988) Instantaneous growth (G) and length increments (mm) of largemouth bass in the study lakes. Values determined from last two annuli on scales for all years except 1986, in which the first and second annuli from the scale edge were used. Number in parenthesis represents sample size for instantaneous growth and length increments. 156 Comparison of instantaneous growth rates of largemouth bass, bluegills, and pumpkinseeds (Browns Lake) of various age groups in all lakes between 1988 and pre-regulation ( ) years, with a t-test (Zar 1974; p.15). The asterisk (*) indicates a significant difference at the.5 level of significance; t values computed from values in appendix o, s..16 Total length (mm) at age of largemouth bass and bluegills in the four study lakes, and pumpkinseeds (Browns Lake) for , , and 1988 ( for Browns Lake} '&-ime pe-z-48-; and the southeaswrn Wisconsin average (Druckenmiller 1972) , and from Prendergast (1984) and Mayer (1988) respectively Back calculated total lengths (mm) of largemouth bass in some lakes Instantaneous growth (G) and length increments (mm) of bluegills in the study lakes, and pumpkinseeds (Browns Lake). Values determined from last two annuli on scales for all years except 1986, in which the first and second annuli from the scale edge was used. Number in parenthesis represents sample size for instantaneous growth and length increments xix

20 LIST OF APPENDICES (continued) Appendix T. Appendix U. Appendix V. Appendix w. Appendix X. Appendix Y. Comparison of instantaneous growth rates and length increments of pumpkinseeds of various age groups in Browns Lake from 1979 to F values computed from values in appendix S, (Steel and Torrie 196). + = positively significant, - = negatively significant, and o = not significant at the.5 level of significance Comparison between length at age in 1988 of largemouth bass, bluegills, and pumpkinseed (Browns Lake), with the southeast Wisconsin average (Druckenmiller 1972) with a paired t-test (Zar 1974; p.121). All statistical tests were at the.5 level of significance. Where significant changes occurred, the southeast Wisconsin average had the larger value Back calculated total lengths (mm) of bluegills in some lakes Number of largemouth bass, bluegills, and pumpkinseeds (Browns Lake) in each age class from , , and 1988 ( in Browns Lake) from spring electrofishing samples, and the regression equations used for the catch curves shown in figures Estimated population density (number/hectare) of largemouth bass from electrofishing in spring in Rockland Lake, _9~ and results of regression analysis of estimated population density versus time. "No" indicates not significant at the.5 level of significance Results of regression analysis from spring electrofishing samples of largemouth and bluegills in the four study lakes. "Pro." and "Unpro." indicates protected and unprotected size largemouth bass respectively. + = positively significant, - = negatively significant, and o = not significant at the.5 level of significance. Duplicate of relative abundance and mean length by electrofishing tests in table XX

21 1 INTRODUCTION The Wisconsin Cooperative Fishery Research Unit and the Wisconsin Department of Natural Resources began this study to determine what effect length limit regulations on largemouth bass (Micropterus salmoides) would have on the largemouth bass and bluegill (Lepomis macrochirus) fisheries of four lakes in southeast Wisconsin. The goal of the study was to improve the bass and bluegill fishing in the four lakes. It was thought that overharvest of largemouth bass had resulted in too little predation on panfish: bluegill, pumpkinseed, yellow perch, black crappie, warmouth, and green sunfish (Appendix A). All four lakes were considered out-of-balance before length limit regulations were imposed (Michaelis 1982). It was believed that the regulations would improve the bass fishery through protection of certain sizes of largemouth bass and result in larger bluegills because of increased predation by the greater numbers of bass. Data described below were collected from 198 to The fishing season for largemouth bass extended from the first Saturday in May to March first, and the possession limit was 5. From 198 to 1982 there was no length limit on largemouth bass. On May 1, 1982, length limit regulations were added: a 35-46mm (12-16 inch) slot length limit was placed on largemouth bass in two lakes, and a 46mm minimum length limit was imposed on two lakes. Largemouth bass of

22 2 lengths within the slot in the two lakes, or shorter than 46mm in the other two lakes, were to be released alive immediately. Bass of other sizes could be harvested. If anglers abide by the regulations, high minimum length limits protect large fish and also small fish, which is valuable if recruitment is low or irregular. Slot length limits protect large fish, but allow small fish to be harvested, which may be appropriate if recruitment is consistently high. Michaelis (1982) described the fisheries before regulations were imposed. Prendergast (1984) and Mayers (1988) described the fisheries one and three years, respectively, after regulations were imposed. Objectives of my portion of the study were to describe changes in the fisheries in lakes Beulah, and Rockland (slot length limit lakes) and Pretty and Browns (minimum length limit lakes) through 1988 for the first three lakes and through spring 1989 for Browns Lake. Electrofishing and fyke nets were used to sample the -----r-f-riss-hh ~la~ien-s, and -Jteel SUEveys we~e used t-g a-ssess angling. Characteristics used to describe the largemouth bass and panfish (mostly bluegill) fisheries were: 1, length frequency, catch per unit effort, and mean length; 2, Proportional Stock Density (Anderson 1976); 3, Relative Weight (Wege and Anderson 1978); 4, growth rate; and 5, total annual mortality rate from the electrofishing sampling; and 6, fishing pressure (hours/hectare), catch rate, and harvest rate (number/hectare) from the creel

23 3 surveys. Also population density (number/hectare) was calculated for largemouth bass in Rockland Lake for every year , and exploitation rate was calculated for every other year. Lake Beulah (338 ha) is in Walworth County, Lake Pretty (26 ha) is in Waukesha County, Rockland (16 ha) and Browns (16 ha) are in Racine County (Appendices B, C). Rockland, Pretty and Browns are hardwater seepage lakes; Rockland and Browns have an outlet; Pretty has none. Lake Beulah was originally five lakes that were made into one by the damming of the outlet stream in 184. Beulah is also a hardwater lake. Shoreline development is greater on Pretty and Browns lakes, intermediate on Beulah, and Rockland Lake is mostly undeveloped. Aquatic vegetation occurred in all lakes, but was spare in Pretty Lake. Vegetation was most abundant in Browns Lake, where plants grew to the surface throughout the lake in summer except for an approximate 3 hectare area.(-"-'m=i=cnaelis 1982). Aquatic wee~ hary_esting machines wo~rked throughout the summers on Browns and Beulah lakes. Browns Lake was chemically treated in September of 1971, to remove carp and stunted panfish (Schumacher and Rebicek 1977). In 1987 and 1988, 18,687 panfish and 961 bullheads (Ictalurus sp.) weighing a total of 5,313 kilograms were caught by fyke nets and seine and removed from Browns Lake and transferred to Lac La Belle in Waukesha County. In May 1977, and 1978, panfish were removed from

24 4 Pretty Lake. Michaelis (1982) gave a more complete description of the lakes and their past management. Harvest regulations for species other than largemouth bass were no closed season and a possession limit of 5 panfish in aggregate for all lakes. The fishing season for northern pike extended from the first Saturday in May to March 1 for all four lakes, with five being the bag limit on Pretty Lake, and a bag limit of two on the other three lakes.

25 5 METHODS AND MATERIALS SAMPLING Fish were captured in 1988 and 1989 by electrofishing and angling {Table 1). Electrofishing was conducted with a boat-mounted boom electroshocker {Novotny and Priegel 1974). Lakes Beulah and Browns were electrofished on two nights in spring and fall, Rockland Lake was also electrofished in 1988 two nights in fall, but four nights in spring so that a multiple census population estimate of largemouth bass could be calculated. Pretty Lake was electrofished two nights in 1988 in spring, but not in fall because of low water. The only electrofishing in 1989 was in spring, in Browns Lake. One complete circuit of the shoreline was electrofished on Browns and Rockland lakes each night. Because of its size, only the shoreline of the southwest portion of Lake Beulah vas e-leeu-e-fished {Appendix ~}. In ~t.y La-ke, twa circuits of the lake were completed each night, one along the shoreline, and another along the weed line at a depth of about 2 meters. Captured fish were held in a holding tank. Largemouth bass {Appendix D), northern pike, and walleye were measured to the nearest 2.54mm {one-tenth of an inch), weighed to the nearest grams {half ounce), scale samples were collected, and the fish, released. Panfish were netted

26 Table 1. Fish sampling ~ethods in the four lakes with effort in hours for the electroshocker and hours/week for the creel survey. BEULAH ROCKLAND PRETTY BROWNS ~ YEAR GEAR TOTAL EFFORT DATES S~PLED TOTAL EFFORT DATES SAMPLED TOTAL EFFORT DATES SAMPLED TOTAL EFFORT DATES SAMPLED ' ELECTROFISHING , 25 MAY , 19, 26 MAY;1 JUNE MAY 2 JUNE I 24 MAY CREEL SURVEY MAY- 31 AUG. 2 7 MAY- 11 SEPT MAY- 31 AUG. 2 7 MAY- 11 SEPT. ELECTROFISHING 3.5 5, 12 OCT , 1 OCT , 11 OCT ELECTROFISHING , 22, 23 MAY

27 7 from the holding tank without regard to size and placed in a 19-liter jug containing 1 percent formalin. Panfish were added until the jugs were full, and they constituted a subsample (Appendix E). The rest of the panfish were counted by species and released. Panfish in the jugs were later measured, weighed, and a scale sample was collected. Prendergast (1984) considered samples from the spring electrofishing of 1982 to form part of the pre-regulation data because they were obtained 12 days after regulations were imposed. All electrofishing samples after spring, 1982, form post-regulation data. CREEL SURVEY Creel surveys were conducted on the lakes in 1988 as well as 198, 1982, 1984, and Rockland and Browns lakes were surveyed in 1988 from 7 May (the opening of bass season) through 11 September. Beulah and Pretty lakes were surveyed from 28 May through 31 August. All weekends, holidays, and three weekdays selected at random, were censused in two periods: 6-14 hours and hours. The early and late periods were randomly selected for each survey day. One creel clerk worked on Rockland and Browns lakes. The creel clerk surveyed each lake 2 hours per week, half of each survey day on each lake. I surveyed Beulah and Pretty lakes. Beulah was surveyed for 24 hours each week, 8

28 8 hours on one weekday, 4 hours on each of the other weekdays, and 4 hours on both weekend days. Pretty Lake was surveyed 16 hours a week, 4 hours on each of two weekdays, and 4 hours on each of both weekend days. Instantaneous counts of boat and shore anglers were obtained every other hour, including immediately when a clerk arrived at a lake and immediately before the clerk left a lake. Clerks counted from one or two vantage points on Rockland, Pretty, and Browns lakes, and while traversing a transect entirely across Lake Beulah. Anglers were interviewed from a boat between instantaneous counts or on shore at the completion of their trip. About 5% of the interviews were from completed trips. Information recorded included: mode of fishing (boat or shore), number in party, time spent fishing, species sought (if more than one, the percent applied to each species was recorded), and the number of each species caught and released. When a creel clerk found an angler with an illegal ba-ss, the fish was released, but. counted as a harvested fish because it was assumed the angler would have kept the fish if not stopped by the clerk. Creeled fish, with the permission of the angler, were counted, measured, weighed, and a scale sample was collected from largemouth bass. When time did not allow for measuring all fish, a sample of panfish was selected without regard to size. Estimated catch and harvest rates were calculated by

29 9 dividing catch (number of fish released or kept) or harvest (number of fish kept) from interviews by total effort from instantaneous counts (Hoey and Redmond 1974). Because Beulah and Pretty lakes were not surveyed for the whole month of May, estimates of fishing pressure, catch, and h~rvest for the surveyed period, 28 May - 31 May, were extrapolated to cover the period 7 May - 27 May, by the proportion: Est. for the last 4 days in May for Browns and Rockland lakes Est. for entire month of May in Browns and Rockland lakes = Est. for the last 4 days in May for Beulah and Pretty lakes Unknown estimate for entire month of May for Beulah and Pretty lakes LENGTH FREQUENCY, MEAN LENGTH AND, CATCH PER UNIT EFFORT FROM ELECTROFISHING I evaluated changes in size composition of the l-a-rgemouth bass and bluegill populations by comparing length frequencies from spring electrofishing samples from 198 to 1988 (1989 in Browns Lake). I also assessed changes in size by linear regressions (Steel and Terrie 196) of mean length of each species in spring electrofishing samples versus time for the course of the study. I calculated regressions separately for all largemouth bass and for largemouth bass longer than 3mm for the slot length limit lakes (Beulah and Rockland) and for protected bass, those shorter than 4mm, from the minimum length limit lakes.

30 1 Similarly, I evaluated changes in relative abundance for each species from linear regressions of catch per unit effort in spring electrofishing samples versus time. I calculated regressions separately for bass longer than 3mm in the slot length limit lakes and for both protected (< 4mm) and unprotected (>4mm) largemouth bass in the minimum length limit lakes. The regulations were stated in inches: inch slot and 16 inch minimum length. Because their metric equivalents did not coincide with 1-mm size groups, I considered 3mm equivalent to 12 inches and 4mm equivalent to 16 inches. PROPORTIONAL STOCK DENSITY Proportional Stock Density (PSD) is the percentage of quality sized fish in a stock (Anderson 1976) and is defined as: number of fish> minimum quality size PSD = X 1 number of fish> minimum stock size I used the quality and stock sizes (Table 2) defined by Anderson and Gutreuter (1983). Proportional Stock Density has been used to evaluate community and population structure (Anderson and Weithman 1978). PSD ranges for largemouth bass of 4 to 6 percent

31 11 Table 2. Minimum stock and quality size (mm) for largemouth bass, bluegills, pumpkinseeds, warmouth, green sunfish, and yellow perch. SPECIES Stock - size Quality - size Largemouth bass 2 3 Bluegill 8 15 Pumpkineed 8 15 War mouth 8 15 Green sunfish 8 15 Yellow perch 13 2

32 12 have been considered satisfactory (Reynolds and Babb 1978), and PSD's of 2 to 4 percent have been considered satisfactory for bluegills (Novinger and Legler 1978) when angling for largemouth bass and bluegills is important. I calculated PSD for largemouth bass and bluegills and also a prey community PSD by weighting the PSD of each prey species by its relative abundance (Anderson and Weithman 1978). Because the weighted PSD's were so similar to bluegill PSD's (Appendix F), I used bluegill PSD's for all analyses. I calculated largemouth bass, bluegill and weighted PSD's only if there were at least 3 fish longer than stock size in a sample, as recommended by Novinger and Legler (1978). I did not calculate weighted PSD's for predators because largemouth bass were virtually the only predator caught. Community structure can be evaluated by plotting prey PSD as a function of predator PSD in a tic-tac-toe graph (Anderson 1976; Anderson and Weithman 1978). Parallel lines o reeommended PSD range-s result in a eenter panel which is the recommended area for a balanced fish community.

33 13 RELATIVE WEIGHT I used a Relative Weight (Wr) index developed by Wege and Anderson (1978) to evaluate weight-length relations of largemouth bass longer than 1mm and bluegills longer than 8mm. Wr compares the actual weight (W) of a fish to a standard weight (Ws) for a fish of the same length and species: Wr = W/Ws x 1. Mean Relative Weight, standard deviation, and 95% confidence intervals were calculated for every 1~mm length group of largemouth bass and bluegills captured during spring electrofishing. Regression equations used to calculate standard weights were: largemouth bass, log weight (g) = log length (mm) (Wege and Anderson 1978); and bluegills, log weight (g) = log length (mm) (Hillman 1982). Wege and Anderson (1978) considered a Wr of 95-1% as satisfactory for largemouth bass in late summer and early fall, and Legler (1977) considered 95-1% to be satisfactory for bluegills. Hil.lman (19B2), Michaelis (1982), Prendergast (1984), and Mayers (1988) judged these ranges too narrow for diverse fish communities, concluding that Wr's of 9-15% were satisfactory for largemouth bass and bluegills. I agree with their assessment that 9-15% is a satisfactory range of Wr values for largemouth bass and bluegills in diverse fish communities.

34 14 AGE, GROWTH, AND MORTALITY Scales from largemouth bass and bluegills were used to determine age and growth statistics in all lakes. If there were more than 12 scales in a 1-mm length group, 1 were selected randomly from the group; otherwise, all scales were read. I cleaned scales by scrubbing with a toothbrush, then pressed them on an acetate slide with a hand roller press. I used a tri-simplex projector to magnify the image of the scales 3X, and a digitizer to record measurements from the focus to each annulus and to the scale edge along the anterior scale radius. The most legible scale image of several on a slide was measured. Back calculations from scales were obtained by the program developed by Frie {1982). I estimated instantaneous growth rate {G) from back calculated lengths at annulus formation using the length-weight relationship {ln weight = ln u + v ln length) of a functional regression {Ricker 1975). Then I calculated regressions of instantaneous growth rates for each age versus time from 1979 to To detect changes in instantaneous growth rate, I compared slopes of the regressions of instantaneous growth rates for each age {Steel and Torrie 196), and I also compared instantaneous growth rates with a t-test {Zar 1974) for each age group between the pre-regulation and the 1986 to 1988 time periods.

35 15 My back calculated lengths at age were determined from scales from fish from combined electrofishing samples from fall and the following spring. All fish captured in fall were assumed to have formed an annulus; hence, their length at age was comparable to length at age of fish captured the following spring. I also compared length at age for largemouth bass and bluegills with the southeast Wisconsin average (Druckenmiller 1972) with at-test (Zar 1974). Total annual and instantaneous mortality (A and Z) and survival (S) rates were calculated from catch curves (Ricker 1975). POPULATION ESTIMATES, STANDING STOCK, AND EXPLOITATION I used Chapman's modification of the Schnabel formula (Ricker 1975; equation 3.17) to estimate the size of the largemouth bass population in Rockland Lake. I calculated population estimates for fish larger than the minimum size, 13 Omm, t-hat both Mayer-s t ) and- I ~h~ht; was 't-he size effectively captured by electrofishing. I also calculated populations estimates for fish larger than the minimum size harvested by most anglers, i.e. 2mm. Largemouth bass were marked by clips of the caudal fin on four nights of electrofishing in a 2 week period every spring from 198 to Electrofishing was used for both marking and recapture of fish. Approximate confidence limits (95%) were estimated by treating R (recatures) as a Poisson variable (Ricker 1975; p.97).

36 16 The exploitation rate of largemouth bass in Rockland Lake in 198, 1982, 1984, 1986, and 1988 was calculated by division of the estimated harvest (from creel surveys} by ~population estimates (Ricker 1975; p.264}. Separate exploitation rates were calculated from population estimates based on minimum length of fish harvested by anglers and from minimum length of fish in electrofishing samples. Hall (1986} found a positive linear relation between electrofishing catch per hour of largemouth bass and the estimated number of largemouth bass longer than 199mm in 12 Ohio lakes. I used Hall's regression equation, log 1 (number per hectare) = log 1 (electrofishing catch per hour) , to calculate predicted densities of largemouth bass longer than 199mm ir. Rockland Lake. Then I used a paired t-test (Zar 1974; p.121) to assess the difference between my estimated densities (from Schnabel population estimates) and the predicted densities (from Hall's equation) of largemouth bass longer than 199mm.

37 17 RESULTS AND DISCUSSION CREEL SURVEY Fishing Pressure The length limits probably did not affect fishing pressure. Angling effort (hrs/ha) did not change for largemouth bass and bluegills in any lake (Table 3). Effort varied considerably from year to year making significant trends impossible to identify (Figures 1, 2). Effort for all species combined decreased in Browns Lake (Table 3). I do not know if this decrease was related to abundance of species other than largemouth bass and bluegills or to anglers' perceptions of chances for successful fishing trips. HARVEST RATE, MEAN LENGTH HARVESTED, AND CATCH RATE Largemouth bass The length limits affected the harvest of largemouth bass, as one might predict. I would expect harvest rate to decrease after imposition of the length limit regulations in the minimum length limit lakes because of the release of large numbers of protected largemouth bass. In the slot length limit lakes, the harvest rate should decrease for

38 Table 3. Estimated an~ling effort (hours/hectare) for largemouth bass, bluegills, and all species in 198, 1982, 1984, 1986, and 1988 and results of regression analysis of estimated angling effort versus time in Beulah, Rockland, Pretty and Browns lakes. + = positively significant, - = negatively significant, and o = not significant at the.5 level of significance. SPECIES LAKE EFFORT (HRS/HECT} YEAR F VALUE SIGNIFICANT,_. LARGEMOUTH BASS BEULAH ROCKLAND PRETTY BROWNS BLUEGILLS BEULAH ROCKLAND PRETTY BROWNS ALL SPECIES BEULAH ROCKLAND PRETTY BROWNS

39 , <( J: (f) 188 a:, ::r: 88. ~ l- 68 a: f2 48 u.. UJ m 19 BEU.LA H LAKE.. ~ LMB.a- BLG ~ r ~m~----~ YEAR, <( I U) _a:...~ I..._, l a: ROCKLAND LAKE ~ GJ o------~o ~ LMB.a- BLG u u.. w ~------~ ~------~------~ YEAR Figure 1. Angling effort (hours/hectare) for largemouth bass (LMB) and bluegills (BLG) in Beulah and Rockland lakes in 198, 1982, 1984, 1986, and 1988.

40 2, <! I1.-oe '-... (J) 88 a: J: 68 '-.../ I- 48 a: 28 LJ.. LJ.. w 8 PRETTY LAKE ~ YEAR ~ LMB.a- BLG ~128 <! I 188 ' (J) 88 -tr- I 68 '-.../ f- 48 a: 28 LJ.. u.. w BROWNS LAKE. 1988'' 1982' YEAR 1988' ~ LMB.a- BLG Figure 2. Angling effort (hours/hectare) for largemouth bass (LMB) and bluegills (BLG) in Pretty and Browns lakes in 198, 1982, 1984, 1986, and 1988.

41 21 fish within the slot, but the harvest rate for bass of all sizes could decrease or not depending on the harvest of fish smaller than the slot. The harvest rate decreased in the minimum length limit lakes (Pretty, Browns) for fish of protected sizes << 4mm), and therefore for all largemouth bass (Table 4; Figures 3, 4). The pattern of harvest in Browns Lake was as one might expect: bass of legal size continued to be harvested from 1982 to 1988 and the illegal harvest was small (Figure 4; Table 5). In Pretty Lake there appeared to be a substantial illegal harvest in 1982 and 1984, and no largemouth bass were observed in the creel in Still, the harvest of largemouth bass decreased (Table 4). Novinger (1987) found a decrease in largemouth bass harvest rates after a 381mm length limit was imposed for bass in the James River and Long Creek arms of Table Rock Reservoir, Missouri. In both Pretty and Browns lakes the harvest rate of -----rl~e~g~al bass increased aft~ the regulations were imposed (Table 4}, a suggestion that the regulations effected an increase in survival of largemouth bass to larger sizes. In the slot length limit lakes, the harvest rates of protected largemouth bass (about 3-399mm) decreased in Lake Beulah after imposition of the regulations, but not in Rockland Lake if data for 1988 are included in the analysis (Table 4; Figures 5, 6). There appeared to be a substantial illegal harvest of protected bass in 1988 in Rockland Lake