LONG-TERM CHANGES IN POPULATION STATISTICS OF FRESHWATER DRUM ( APLODINOTUS GRUNNIENS ) IN LAKE WINNEBAGO, WISCONSIN, USING OTOLITH GROWTH CHRONOLOGIES AND BOMB RADIOCARBON AGE VALIDATION by Shannon L. Davis-Foust A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Biological Sciences At The University of Wisconsin-Milwaukee August 2012 LONG-TERM CHANGES IN POPULATION STATISTICS OF FRESHWATER DRUM ( APLODINOTUS GRUNNIENS ) IN LAKE WINNEBAGO, WISCONSIN, USING OTOLITH GROWTH CHRONOLOGIES AND BOMB RADIOCARBON AGE VALIDATION by Shannon L. Davis-Foust A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Biological Sciences at The University of Wisconsin-Milwaukee August 2012 Major Professor Dr. Rebecca Klaper Date Graduate School Approval Date ii ABSTRACT LONG-TERM CHANGES IN POPULATION STATISTICS OF FRESHWATER DRUM ( APLODINOTUS GRUNNIENS ) IN LAKE WINNEBAGO, WISCONSIN, USING OTOLITH GROWTH CHRONOLOGIES AND BOMB RADIOCARBON AGE VALIDATION by Shannon Davis-Foust The University of Wisconsin-Milwaukee, 2012 Under the Supervision of Dr. Rebecca Klaper Estimating fish population statistics such as mortality and survival requires the use of fish age data, so it is important that age determinations are accurate. Scales have traditionally, and erroneously, been used to determine age in freshwater drum (Aplodinotus grunniens ) in the majority of past studies. I used bomb radiocarbon dating to validate that sagittal otoliths of drum are the only accurate structure (versus spines or scales) for age determinations. Drum grow slower and live longer than previously recognized by scale reading. Drum otoliths can be used not only to determine age, but also to estimate body length. I examined archaeological drum otoliths dated to the 1830's and older from around the Winnebago system. Maximum body length attained by modern drum had not significantly changed over time; however, longevity is reduced and growth rates have increased in modern drum. The changes in these demographic statistics could be due to several environmental factors that have changed in the Lake Winnebago system since European settlement, and in particular the effects from the removal trawling program that iii removed large quantities of drum annually from 1936 to 1990. Disentangling growth responses to environmental factors such as climate and trophic interactions is a major goal of ecology. Annual growth rates measured from otoliths have frequently been reported to correspond to temperature, but not to food abundance. I constructed growth chronologies of drum using a linear mixed model that separates endogenous and exogenous growth effects. Diet analysis of drum revealed an adult length-related diet shift. The growth rates of large drum from 2001 to 2008 were significantly greater than small drum, which coincided with the arrival of zebra mussels (Dreissena polymorpha ) in the Lake Winnebago system. The increase in growth rates of large drum were positively correlated to, but departed from, regional temperatures compared to small drum. The increased growth rates of large drum post zebra mussel establishment were corroborated by improved in body condition of large drum. Zebra mussels provide a significant source of nutrition to drum, which is unique because most effects of dreissenids are reported at lower trophic levels. Major Professor Dr. Rebecca Klaper Date iv © Copyright by Shannon L. Davis-Foust 2012 All Rights Reserved v TABLE OF CONTENTS LIST OF FIGURES ......................................................................................................... viii LIST OF TABLES............................................................................................................. xi PREFACE......................................................................................................................... xii DEDICATION................................................................................................................. xiii ACKNOWLEDGEMENTS............................................................................................. xiv CHAPTER ONE: INTRODUCTION TO USING A BIOLOGICAL CHRONOMETER TO GAUGE ENVIRONMENTAL CHANGE....................................................................1 Background of the Lake Winnebago System ..............................................................4 Background of Freshwater Drum ..............................................................................11 Ecological Roles of Freshwater Drum.......................................................................14 Historical Management of Lake Winnebago Freshwater Drum................................18 CHAPTER TWO: AGE VALIDATION OF FRESHWATER DRUM USING BOMB RADIOCARBON ..............................................................................................................24 Introduction................................................................................................................24 Methods .....................................................................................................................27 Results........................................................................................................................32 Discussion..................................................................................................................40 CHAPTER THREE: LONG-TERM CHANGES IN THE DEMOGRAPHY OF A FRESHWATER FISH CORRESPONDING TO ANTHROPOGENIC DISTURBANCES46 Introduction................................................................................................................46 Methods .....................................................................................................................48 Results........................................................................................................................54 Discussion..................................................................................................................63 CHAPTER FOUR: FRESHWATER DRUM RESPONSE TO THE INTRODUCTION OF ZEBRA MUSSELS IS REFLECTED IN THEIR OTOLITH GROWTH CHRONOLOGY................................................................................................................69 vi Introduction................................................................................................................69 Methods .....................................................................................................................72 Results........................................................................................................................77 Discussion..................................................................................................................84 CHAPTER FIVE – CONCLUSIONS: LINKING IMPACTS OF ROUGH FISH REMOVAL AND OTHER CHANGING ENVIRONMENTAL FACTORS TO THE FRESHWATER DRUM POPULATION IN LAKE WINNEBAGO ...............................87 APPENDICES ...................................................................................................................93 Appendix A: Area Swept Population Estimate of Lake Winnebago Freshwater Drum94 Appendix B: The Linear Mixed Effects Model.........................................................97 Appendix C: The Lake Winnebago Freshwater Drum Growth Chronology Index.101 Appendix D: Length Distribution Trends of Lake Winnebago Freshwater Drum from 1986-2011 ...........................................................................................................103 Appendix E: Year Class Strength of Lake Winnebago Freshwater Drum ..............104 Appendix F: Stock Recruitment Analysis of Lake Winnebago Freshwater Drum..105 LITERATURE CITED ....................................................................................................107 CURRICULUM VITAE..................................................................................................121 vii LIST OF FIGURES Figure 1.1. Lake Winnebago is part of the Fox-Wolf Watershed, which covers approximately 17% of the land area of Wisconsin (map modified from Wisconsin Department of Natural Resources 1989). The map on the left depicts the Fox River (dotted area) and the Wolf River basins (striped area). ...................................................... 5 Figure 1.2. Approximate timings for major anthropogenic disturbances to Lake Winnebago since the impoundment of the lower Fox River in 1850. ................................ 7 Figure 1.3. “Molars” in the freshwater drum pharynx, which are adapted for crushing mussel shells. .................................................................................................................... 13 Figure 2.1. Otolith core ∆ 14 C chronologies for freshwater drum (triangles), Arctic char and lake trout (small squares; Campana et al. 2008), black drum from Chesapeake Bay (plus signs; Campana and Jones 1998), gray snapper from the Gulf of Mexico (large squares; adapted from Fischer et al. 2003), together with the atmospheric values from the Western Hemisphere (times signs; adapted from Nydal 1993). The ∆ 14 C values are fitted with locally weighted least-square regressions................................................................. 34 Figure 2.2. Catch per unit effort (CPUE) of age-0 freshwater drum from experimental trawl assessments, Lake Winnebago, 1962–1984............................................................. 35 Figure 2.3. Age frequency histograms for freshwater drum sampled in