Comparative Demography and Habitat Use of Western Pond Turtles in Northern California: The Effects of Damming and Related Alterations by Devin Andrews Reese B.A. (Harvard University) 1986 A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Integrative Biology in the GRADUATE DIVISION of the UNIVERSITY of CALIFORNIA at BERKELEY Committee in charge: Professor Harry W. Greene, Chair Professor Mary E. Power Professor Reginald Barrett 1996 The dissertation of Devin Andrews Reese is approved by: University of California at Berkeley 1996 Comparative Demography and Habitat Use of Western Pond Turtles in Northern California: The Effects of Damming and Related Alterations Copyright © 1996 by Devin Andrews Reese 1 Abstract Comparative Demography and Habitat Use of Western Pond Turtles in Northern California: The Effects of Damming and Related Alterations by Devin Andrews Reese Doctor of Philosophy in Integrative Biology University of California at Berkeley Professor Harry W. Greene, Chair Despite their tenure in California for more than two million years, a period including extreme changes in the landscape, western pond turtles (Clemmys marmorata) are now declining. Survival and viability of populations are impacted by a range of factors, including damming, residential development, agricultural practices, introduced predators, and direct harvest. Some of the few remaining large populations occur in the Klamath River hydrographic basin. From 1991-1995, I examined demography and habitat associations of western pond turtles on a dammed tributary (mainstem Trinity River) and an undammed tributary (south fork Trinity) using mark-recapture techniques and radiotelemetry. In addition, radiotracking of turtles in a set of agricultural ponds in Santa Rosa provided an assessment of movements in a fragmented aquatic landscape. Although both Trinity River populations were sparse compared to large, extant populations in lower order streams, the mainstem population was more sparse and 2 significantly more adult-biased. Riverine western pond turtles were associated with basking sites of low slope in areas of deep, pooled waters that provided aquatic refugia. Lewiston Lake, the reservoir formed by the dam, supports a small, adult-biased population of turtles. Modifications of the river channel for fisheries enhancements are too shallow and exposed to improve conditions for turtles. Small wetlands adjacent to the river, including vernal pools, play a significant role in the life cycle of western pond turtles. The riverine sites and agricultural ponds host a complex set of terrestrial movements for nesting, overwintering, estivation, basking, and travel between multiple bodies of water. The relatively low densities of western pond turtles in the Trinity River system may be attributable to a more diffuse distribution of resources in higher order streams. However, the adult-biased age structure indicates possible recruitment declines along the dammed mainstem. Dam-induced changes, including filling of pools with sediment, increased water velocities along the shoreline, and lowered water temperatures, are probably deleterious to turtles. Restoration attempts geared towards recreating a wide, braided channel should include recovery of warm, pooled areas with structural complexity. Management efforts throughout the range of this species must take place at the landscape scale, including protection of suitable upland habitat and maintenance of aquatic connectedness. Chair Date iii DEDICATION to my father Thomas S. Reese for the example he set as a research scientist and to my mother Anne H. Reese for her dedication to humanitarian work and to the hundreds of western pond turtles who unwittingly participated in these studies iv TABLE OF CONTENTS LIST OF FIGURES ix LIST OF TABLES xii LIST OF APPENDICES xv ACKNOWLEDGEMENTS xvi CHAPTER l: INTRODUCTION 1 CHAPTER 2: METHODS OVERVIEW Study Sites 8 Field Methods 12 Statistical Analyses 14 CHAPTER 3: DEMOGRAPHY OF WESTERN POND TURTLE POPULATIONS IN THE TRINITY RIVER IN THE CONTEXT OF DAM-INDUCED ALTERATIONS. ABSTRACT 16 INTRODUCTION 17 METHODS Field Methods Mark-recapture 18 Float Surveys 20 Data Analysis Population Size A. Mark-recapture 21 B. Remaining mainstem reaches 26 Population Density 26 Population Structure 27 RESULTS Population Size A. Mark-recapture 29 B. Remaining mainstem reaches 36 Population Density 38 Population Structure 38 DISCUSSION 41 v CHAPTER 4: SITE CHARACTERISTICS AND BASKING BEHAVIOR OF WESTERN POND TURTLES IN THE MAINSTEM TRINITY RIVER ABSTRACT 46 INTRODUCTION 47 METHODS Study sites 48 Field Methods 49 Data Analysis Examination of basking intensity 52 Comparison of turtle basking site used to availability 54 Analysis of lifestage differences in basking site characteristics 56 Assessment of underwater habitat use 57 RESULTS Examination of basking intensity 58 Comparison of turtle basking site used to availability 60 Analysis of lifestage differences in basking site characteristics 62 Assessment of underwater habitat use 62 DISCUSSION Examination of basking intensity 65 Comparison of turtle basking site use to availability 69 Analysis of lifestage differences in basking site characteristics 70 Assessment of underwater habitat use 70 ACKNOWLEDGEMENTS 71 CHAPTER 5: HABITAT USE BY WESTERN POND TURTLES IN AN ALTERED SYSTEM, THE TRINITY RIVER BASIN OF NORTHWESTERN CALIFORNIA ABSTRACT 72 INTRODUCTION 73 MATERIALS AND METHODS Study Sites 77 Field Methods 77 Data Analysis Comparison of available habitat on mainstem and south fork 81 Comparison of turtle habitat use to availability 82 vi RESULTS 84 Comparison of available habitat on mainstem and south fork 85 Comparison of habitat use to availability on the mainstem 88 Comparison of habitat use to availability on the south fork 91 DISCUSSION 97 ACKNOWLEDGEMENTS 103 CHAPTER 6: INVESTIGATION OF WESTERN POND TURTLE POPULATIONS IN LEWISTON LAKE ABSTRACT 104 INTRODUCTION 105 METHODS AND ANALYSIS Study Site 107 Surveys 107 Aquatic Habitat Analysis 112 Nesting Searches 114 RESULTS Surveys 116 Aquatic Habitat Analysis 117 Nesting Searches 119 DISCUSSION 123 ACKNOWLEDGEMENTS 126 CHAPTER 7: HABITAT QUALITY OF ARTIFICIAL SIDE CHANNELS AND BANK FEATHERED EDGES FOR WESTERN POND TURTLES IN THE TRINITY RIVER ABSTRACT 127 INTRODUCTION 128 STUDY AREA 132 METHODS Surveys 134 Aquatic Habitat Comparisons and Evaluations 135 vii ANALYSIS Surveys 136 Aquatic Habitat Comparisons 136 Aquatic Habitat Evaluations 138 RESULTS Surveys 139 Aquatic Habitat Comparisons 141 Aquatic Habitat Evaluations 144 DISCUSSION 148 ACKNOWLEDGMENTS 150 CHAPTER 8: MOVEMENTS AND MICROHABITAT USE OF HATCHLING AND JUVENILE WESTERN POND TURTLES IN THE TRINITY RIVER BASIN ABSTRACT 151 INTRODUCTION 152 METHODS Field Methods Juvenile Searches 154 Radiotelemetry 155 Habitat Measurements 157 Data Analysis Juvenile Searches 159 Habitat Measurements 160 Radiotelemetry 161 RESULTS Juvenile Searches 162 Habitat Measurements 164 Radiotelemetry 168 DISCUSSION 171 ACKNOWLEDGEMENTS 176 viii CHAPTER 9: USE OF THE TERRESTRIAL AND AQUATIC LANDSCAPES BY WESTERN POND TURTLES: A COMPARISON OF THREE LOCALES ABSTRACT 177 INTRODUCTION 178 METHODS Study Sites 181 Field Methods 183 Data Analysis 187 I. Terrestrial Movements A. Overview 188 B. Overwintering: Behavior 189 C. Overwintering: Timing 190 D. Overwintering: Distance 191 II. Aquatic Movements 193 RESULTS I. Terrestrial Movements A. Overview 195 B. Overwintering: Behavior 206 C. Overwintering: Timing 208 D. Overwintering: Distance 214 II. Aquatic Movements 218 DISCUSSION 222 ACKNOWLEDGEMENTS 232 CHAPTER 10: DISCUSSION 234 LITERATURE CITED 241 ix LIST OF FIGURES Figure Number and Title Page 2-1 Location of study reaches along the mainstem Trinity River, Trinity County, California. 9 2-2 Location of study reaches along the south fork Trinity River, Humboldt and Trinity Counties, California. 10 2-3 Diagram of marking and measuring techniques for western pond turtles. Adapted from Holland 1994. 13 3-1 Percent of captured turtles that were adults and juveniles at each of three sites. 40 4-1 Proportion of captured turtles that were sighted basking prior to capture along the mainstem Trinity. 59 4-2 Distribution of turtle-use perches and potential perches across substrate types at the mainstem Trinity. 64 5-1 Graph of the first two principal components for habitat measurements from mainstem and south fork random quadrats. 87 5-2 Distribution of random habitat quadrats at the mainstem and south fork study sites across shoreline vegetation types. 90 5-3 Distribution of turtle habitat quadrats and random habitat quadrats across shoreline vegetation types at the mainstem site. 93 5-4 Distribution of turtle habitat quadrats and random habitat quadrats across shoreline vegetation types at the south fork site. 96 5-5 Depiction of favorable habitat for western pond turtles. 102 6-1 Map depicting the location of Lewiston Lake in relation to the Central Valley Project. From USDI Bureau of Reclamation 1992. 108 6-2 Diagram of baited trap used to capture turtles in Lewiston Lake. 109 6-3 Map of Lewiston Lake showing trap stations and locations of ponds. 111 x Figure Number and Title Page 6-4 Plot of classification error rates across threshold values for logistic regression of turtle presence against habitat characteristics. 121 7-1 Schematic profile of side channel sites before and after construction. 130 7-2 Schematic profile of bank feathering sites before and after construction. 131 7-3 Side channel and feathered edge sites