POPULATION STRUCTURE, LIFE HISTORY, AND TERRESTRIAL MOVEMENTS OF WESTERN POND TURTLES (ACTINEMYS MARMORATA) IN LENTIC HABITATS ALONG THE TRINITY RIVER, CALIFORNIA

HUMBOLDT STATE UNIVERSITY

by Leah Marie Sloan

A Thesis Presented to The Faculty of Biological Sciences

In Partial Fulfillment Of the Requirements for the Degree Master of Science In Biological Sciences

May 2012

POPULATION STRUCTURE, LIFE HISTORY, AND TERRESTRIAL MOVEMENTS OF WESTERN POND TURTLES (ACTINEMYS MARMORATA) IN LENTIC HABITATS ALONG THE TRINITY RIVER, CALIFORNIA

HUMBOLDT STATE UNIVERSITY

by Leah Marie Sloan

We certify that we have read this study and that it conforms to acceptable standards of scholarly presentation and is fully acceptable, in scope and quality, as a thesis for the degree of Master of Science: ________________________________________________________________________ Dr. Sharyn Marks, Major Professor Date ________________________________________________________________________ Dr. Hartwell Welsh, Committee Member Date ________________________________________________________________________ Dr. Erik Jules, Committee Member Date ________________________________________________________________________ Dr. Kristine Brenneman, Committee Member Date _______________________________________________________________________ Dr. Michael Mesler, Graduate Coordinator Date ________________________________________________________________________ Dr. Jená Burges, Vice Provost and Dean of Graduate Studies Date

ABSTRACT

POPULATION STRUCTURE, LIFE HISTORY, AND TERRESTRIAL MOVEMENTS OF WESTERN POND TURTLES (ACTINEMYS MARMORATA) IN LENTIC HABITATS ALONG THE TRINITY RIVER, CALIFORNIA Leah Marie Sloan

As populations of a species decline, an understanding of habitat use and regional variation in population health can aid in focusing conservation efforts. Western Pond Turtle (Actinemys marmorata) populations have declined throughout much of their range as a result of habitat loss, overexploitation, introduced species, and water course alterations. The Trinity River, in northwestern California, has been modified from its natural state by damming and flow regulations; these alterations have decreased river quality for turtles. I investigated the health of Western Pond Turtle populations in lentic sites adjacent to the Trinity River and its tributaries using four indicators of population health: 1) age structure, 2) size structure, 3) body size, and 4) growth rate of young turtles. Of six lentic sites sampled, four were biased towards large, old turtles. These sites had prolific Bullfrog populations, while the other two sites lacked Bullfrogs. Given that Bullfrogs will eat hatchling turtles, Bullfrogs likely are inhibiting turtle recruitment. The four lentic sites with Bullfrogs also had turtles with faster growth rates and larger sizes, likely a result of warmer water temperatures. I also used radio telemetry to monitor the terrestrial movements of turtles within a complex of lentic habitats along the Trinity

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River. The majority of turtles used multiple aquatic resources within a year, indicating that their home range can include multiple water bodies separated by upland habitat. Overall, conservation efforts should focus on creating or preserving aquatic habitats free of Bullfrogs, and terrestrial corridors for turtles to move between them.

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ACKNOWLEDGEMENTS

First and foremost I would like to acknowledge the organizations and people that provided the funding and equipment that made this project possible. Most especially, I thank the U.S. Bureau of Reclamation's Trinity River Restoration Program (Interagency agreement number # R10AC20019) for incorporating my project into their restoration efforts and for providing me with funding and support throughout my study; B. Gutermuth was particularly instrumental in ensuring that I had all the necessary resources to successfully complete my project. I also thank the US Fish and Wildlife Service, particularly C. Chamberlain and J. Bettaso, for providing the majority of the equipment for this project and for funding my summer field assistants. A. Baker and A. Desch of the HSU Biology and Wildlife stockrooms were extremely helpful in providing me with additional equipment. I am grateful to the Bureau of Land Management for providing a campsite near my study site. I also thank the HSU Department of Biological Sciences for awarding me a Master’s Student Grant. Numerous people lent their assistance and expertise to this project; I am profoundly grateful to you all! I especially thank my major advisor, S. Marks, for her patience, kindness, and dedication throughout this study and the many preliminary drafts of this thesis. Her guidance and assistance have been invaluable. In addition, I thank the members of my graduate committee, K. Brenneman, H. Welsh, and E. Jules, for lending me their advice and expertise. I am very grateful to J. Bettaso, D. Ashton, and C. Bondi v

for sharing with me their vast knowledge and experience with Western Pond Turtles and all the members of the HSU Herpetology Group for lending me their support, guidance, and friendship throughout my time at HSU. I also thank R. van Kirk for his statistical guidance and A. Scheiff for downloading my temperature data. I am particularly obliged to the private landowners who allowed me access to their property and ponds; it would have been impossible to complete this study without their assistance and generosity. This project could not have been completed without the tireless work of many people in the field. I thank my summer field assistants, J. Brown (2010) and J. Carlson (2011), for spending their summers chasing turtles and mucking around in anoxic, leechinfested ponds. I am also profoundly grateful to I. Zacher for volunteering countless hours to this project, from rescuing my car out of the snow to picking insects out of mud in the pouring rain. I also thank many others who came camping with me in Weaverville in order to volunteer with fieldwork: N. O’Brien, C. Brady, A. Pesqueda, J. Cresswell, J. Ponte, J. Paget-Seekins, H. Kurkjian, S. Hedrick, H. Hedrick, C. Bube, G. Leech, T. Richards, and K. Wright. Lastly, I most sincerely thank my parents for being wonderful naturalists and teaching me to love, cherish, and protect the natural world. I have become the biologist I am today because of your support, encouragement, and inspiration. Thank you!

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TABLE OF CONTENTS

Page ABSTRACT...................................................................................................................... iii ACKNOWLEDGEMENTS .............................................................................................. v TABLE OF CONTENTS ................................................................................................ vii LIST OF TABLES............................................................................................................. x LIST OF FIGURES ......................................................................................................... xii LIST OF APPENDICES................................................................................................... xv CHAPTER 1………………….……………………………………………………….…..1 INTRODUCTION........................................................................................................ 1 METHODS .................................................................................................................. 6 Study Area …......................................................................................................... 6 Turtle Sampling...................................................................................................... 9 Marking and Morphometrics.................................................................................. 9 Population Health…………….............................................................................. 10 Pond Characteristics……….................................................................................. 11 Data Analysis ....................................................................................................... 12 RESULTS .................................................................................................................. 15 Proportion of Young to Old Turtles...…………................................................... 15 Proportion of Small to Large Turtles ………….........………………………..… 15 Body Size………………...................................................................................... 16 vii

Growth of Young Turtles….................................................................................. 21 Environmental Variables ..................................................................................... 23 Bullfrog and Fish Presence ………………...……………………………………26 DISCUSSION ............................................................................................................ 28 Age and Size Structure ………………………………...……………..………….29 Growth Rate and Body Size ………………………………………..……………34 REFERENCES .......................................................................................................... 37 CHAPTER 2 …………………………………………………………………………….44 INTRODUCTION…………………………………………………………………...44 METHODS ……………………………………………………………………….....48 Study Area………………………………………………………………….……48 Turtle Capture, Marking, and Morphometrics……………………………….…..51 Radio Telemetry ………………………………………………………………....51 Pond Characterizations ……………………………………………………….…52 Data Analysis ………………………………………………………………..…..54 RESULTS …………………………………………………………………………...56 Terrestrial Movements ……………………………………………………….….59 Terrestrial Movements among Aquatic Habitats …………………………….….62 Overwintering Behavior …………………………………………………………63 Terrestrial Movements Associated with Reproduction ………………………….64 Environmental Characteristics ………………………………………………..…65 DISCUSSION ……………………………………………………………………….73 Use of an Aquatic Habitat Complex by Turtles……………………………….…73 viii

Proportion of Active Turtles ………………………………………………….…75 Terrestrial Distances …………………………………………………………….76 Overwintering ………………………………………………………………..….77 Nesting Movements ………………………………………………………..……78 Conservation Implications …………………………………………………..…..78 Conclusions ………………………………………………………………..…….80 REFERENCES …………………………………………………………….………..82 APPENDICES ………………………………………………………………………87

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LIST OF TABLES

CHAPTER 1 Table

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1. Ponds where Actinemys marmorata were trapped in six sites along the upper Trinity River and its tributaries .................................................................................. 8 2. Candidate models for the comparison of the proportion of old (≥ 10 years) to young (< 10 years) Actinemys marmorata in six lentic sites near the Trinity River using logistic regression on binary data ................................................................... 19 3. Candidate models for the comparison of the proportion of large (carapace length ≥ 125 mm) to small (< 125 mm) Actinemys marmorata in six lentic sites near the Trinity River using logistic regression on binary data .............................................. 19 4. Mean maximum carapace lengths (CL), standard error (SE), and sample size (n) for large (≥ 125 mm carapace length) Western Pond Turtles in two lotic sites and six lentic sites along the Trinity River. * indicates data from Ashton et al. 2011 .... 20 5. Mean weight (WT), standard error (SE), and sample size for large (≥ 125 mm carapace length) male and non-gravid female Western Pond Turtles in six lentic sites along the Trinity River .................................................................................... 20 6. Estimated carapace lengths (mm), based on growth curves (Fig. 4), for young Actinemys marmorata in lentic habitats along the Trinity River, CA ....................... 22 7. Presence or absence of Lithobates catesbeianus (American Bullfrog), Micropterus salmoides (Largemouth Bass), and other fish in the ponds at six lentic sites in Trinity County, CA ................................................................................................. 27

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CHAPTER 2 Table

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1. Weight, carapace length, age (10+ represent turtle ≥ 10 years), sex (M = male, F = female), number of relocations, and duration and dates tracked for radio-tagged Actinemys marmorata. * turtles that were retagged after their initial transmitters failed ....................................................................................................................... 57 2. Presence (1) or absence (0) of amphibians and fish in minnow traps set on five different occasions in the five permanent ponds at Lowden Ranch throughout 2010 and 2011. ........................................................................................................ 72 3. Numbers of aquatic insects found in each of the permanent ponds at Lowden Ranch in the summer and fall of 2010. Numbers given for the five most prevalent insect orders. Samples from three 0.5 meter kick-net sweeps. .................. 72

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LIST OF FIGURES

CHAPTER 1 Figure

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1. The upper Trinity River, Trinity County, CA from Lewiston (just below the Lewiston Dam) to Junction City. The approximate locations of the six sites are shown in bold; each site has from one to ten ponds .................................................... 7 2. Percent of young (