San Jose State University SJSU ScholarWorks Master's Theses Master's Theses and Graduate Research Spring 2019 Pond Occupancy by Western Pond Turtles in the Diablo Range of Santa Clara County, California Billy Tu San Jose State University Follow this and additional works at: https://scholarworks.sjsu.edu/etd_theses Recommended Citation Tu, Billy, "Pond Occupancy by Western Pond Turtles in the Diablo Range of Santa Clara County, California" (2019). Master's Theses. 5021. DOI: https://doi.org/10.31979/etd.zr2k-wq38 https://scholarworks.sjsu.edu/etd_theses/5021 This Thesis is brought to you for free and open access by the Master's Theses and Graduate Research at SJSU ScholarWorks. It has been accepted for inclusion in Master's Theses by an authorized administrator of SJSU ScholarWorks. For more information, please contact [email protected]. POND OCCUPANCY BY WESTERN POND TURTLES IN THE DIABLO RANGE OF SANTA CLARA COUNTY, CALIFORNIA A Thesis Presented to The Faculty of the Department of Environmental Studies San José State University In Partial Fulfillment of the Requirements for the Degree Master of Science by Billy Tu May 2019 © 2019 Billy Tu ALL RIGHTS RESERVED The Designated Thesis Committee Approves the Thesis Titled POND OCCUPANCY BY WESTERN POND TURTLES IN THE DIABLO RANGE OF SANTA CLARA COUNTY, CALIFORNIA by Billy Tu APPROVED FOR THE DEPARTMENT OF ENVIRONMENTAL STUDIES SAN JOSÉ STATE UNIVERSITY May 2019 Lynne Trulio, Ph.D. Department of Environmental Studies Rachel O'Malley, Ph.D. Department of Environmental Studies Jessie Bushell, MS Director of Conservation, San Francisco Zoo ABSTRACT POND OCCUPANCY BY WESTERN POND TURTLES IN THE DIABLO RANGE OF SANTA CLARA COUNTY, CALIFORNIA by Billy Tu The loss of natural habitat is one the primary drivers for species decline worldwide. Artificially, created habitat in human-altered landscapes can help supplement or enhance habitat for threatened wildlife populations. The western pond turtle (Emys pallida), a species declining in California, depends on aquatic habitats for its survival, but can use human-created livestock ponds in lieu of natural aquatic habits. This study examined the extent to which western pond turtle used livestock ponds in Santa Clara County, CA, and the importance of key habitat features in the turtle occupancy of livestock ponds. From March 2017 to September 2017, I conducted visual encounter surveys at 78 livestock ponds within the Diablo Range of eastern Santa Clara County. Habitat feature data were collected at 31 ponds. At each site, seven habitat features were evaluated: surface area, pond depth, elevation, number of basking structures, presence of bullfrogs, level of aquatic vegetation, and level of terrestrial tree and shrub cover. Evidence of turtles was found at 13 ponds. Habitat features did not statistically differ between occupied and non- occupied sites, but the number of basking structures and tree and shrub cover may be biologically important. Of 16 previously documented sites, western pond turtles were extant at 12 and likely extant at two. One new documented site was recorded. These results indicate that ponds previously occupied are likely to still contain western pond turtles. To protect western pond turtles, conservation efforts should be directed towards protecting known sites and restoring previously occupied sites. ACKNOWLEDGMENTS The journey to completing this thesis has been a long time coming and would not have been possible without the support and guidance received from my committee, mentors, friends, collaborators, and funders. First, I would like to thank Dr. Lynne Trulio for her continued support throughout this entire process. To my committee members, Dr. Rachel O’Malley and Jessie Bushell, thank you for your guidance and show of support. Secondly, I am grateful for my fiancée, Yen Tran, for sticking by me while I pursued my passion for turtles. To my field assistants (Alec Irwin, Carole Foster, Elisabeth Wilkinson, Emily Moffitt, Huy Vuong, Jim Buskirk, Kendra Mann, Lynea Baudino, Sami Boutros, Sinzee Tran, & Yen Tran), there is no one I would rather spend an afternoon covered in ticks with than you – thank you for your hard work. Much appreciation to the staff at Blue Oak Ranch Reserve, Santa Clara County Parks, San Felipe Ranch, Santa Clara Valley Water District, and Henry Coe State Park for allowing me access and/or shuttling me to my research sites. Dr. Shannon Bros provided much needed statistical analysis advice, while Nicole Catalano help edited this paper. Elisabeth Wilkinson, Mark Seelos, and Colin Kortman helped with GIS. Lastly, I would not have been financially able to complete my thesis and degree without the support from the College of Social Science RSCA grants, Mary Bowerman Science and Research Grant, Mid-Atlantic Turtle & Tortoise Society, San Francisco Zoo Conservation Department, and the John Luckhardt-Kiwanis Memorial Scholarship and the Tricia and Pete Biocini Scholarship Fund, both in the Department of Environmental Studies. v TABLE OF CONTENTS List of Table ...................................................................................................................... vii List of Figures .................................................................................................................. viii Introduction ......................................................................................................................... 1 Literature Review................................................................................................................ 4 Taxonomy ..................................................................................................................... 4 Natural History.............................................................................................................. 5 Aquatic Habitat Use ...................................................................................................... 8 Threats........................................................................................................................... 9 Livestock Ponds .......................................................................................................... 10 Problem Statement ............................................................................................................ 14 Research Questions and Hypothesis ................................................................................. 15 Methods............................................................................................................................. 16 Study Site .................................................................................................................... 16 Study Design ............................................................................................................... 19 Pond Selection ...................................................................................................... 19 Turtle Surveys ....................................................................................................... 22 Data Collection ........................................................................................................... 24 Data Analysis .............................................................................................................. 28 Limitations .................................................................................................................. 29 Results ............................................................................................................................... 31 Discussion ......................................................................................................................... 41 Livestock Ponds Usage by Western Pond Turtle ........................................................ 41 Livestock Ponds and Habitat Features ........................................................................ 42 Recommendations ............................................................................................................. 46 References ......................................................................................................................... 48 vi LIST OF TABLES Table 1. Current Land Use and Size of the Five Study Sites: Rancho Canada de Pala Reserve, Blue Oak Ranch Reserve, Joseph Grant County Park, San Felipe Ranch, and Henry Coe State Park .......................................... 18 Table 2. Ponds Surveyed and Data Collection Sites .............................................. 31 Table 3. Previously Documented Occurrence vs. Survey Results (78 Total Ponds) ....................................................................................................... 32 Table 4. Lakes Surveyed ........................................................................................ 33 Table 5. Range, Mean, Standard Deviation (SD) and MANOVA Results for Pond Occupancy ....................................................................................... 36 Table 6. Pearson Chi-Square Analysis and Likelihood Ratio for Pond Occupancy ................................................................................................ 38 vii LIST OF FIGURES Figure 1. Map of the Five Study Sites in Santa Clara County, California: Rancho Canada de Pala Reserve, Blue Oak Ranch Reserve, Joseph Grant County Park, San Felipe Ranch, and Henry Coe State Park ........ 17 Figure 2. Livestock Pond at Joseph Grant County Park ........................................ 21