Historically western pond turtles (WPT) existed along the West Coast (The range of the western pond turtle extends from the Puget Sound lowlands in Washington south to Baja California). The oldest known western pond turtle fossils are from the Pliocene Epoch, approximately 2 million years ago. Western pond turtles may be found in both aquatic and terrestrial landscapes; terrestrial habitats are used for nesting, overwintering, and thermoregulation, and they utilize aquatic habitats for feeding, breeding, and basking.
Western pond turtles may live for 50-70 years. Being such a long-lived species they do not reach reproductive maturity for approximately 10 years.
Once extremely abundant throughout their range, their numbers have declined precipitously over the last few decades. Early losses of WPT: Tens of thousands of turtles were taken from California waterways each year in the late 1800’s for the restaurant industry. The Sonoma County population has never completely recovered from this devastating reduction. Current factors effecting WPT: The combination of slow juvenile growth and low hatchling survivorship is another major hurdle to the restoration of the species. Populations also struggle with introduced predators, illegal collection for food or the pet trade, and drastic habitat loss and fragmentation caused by urban and agricultural development.
In order to slow their decline and contribute to the scientific understanding of the species, we (Dr. Geist and his lab) have initiated studies to help the conservation of our local population. Through financial support and interest provided by the Sonoma County Fish and Wildlife Commission we were able to monitor a local population of turtles during the nesting season. As females were observed nesting, data was collected. We then carefully collected the eggs and brought them into the lab for incubation and observation. By removing the eggs, they were protected from nest predators such as skunks and foxes during incubation. This also allowed us to investigate the critical temperatures that determine WPT gender during incubation. This research is of value because in WPTs, like most turtles, sex ratios are determined by the temperature of the eggs during incubation (Temperature-Dependent Sex Determination or TSD). Better understanding of TSD is essential for the conservation of the species.
As populations are imperiled, the role of reproductive females becomes especially valuable for species recovery. Determining the critical temperatures of TSD will allow for potential manipulation to female biased sex-ratios in lab raised turtles. An additional benefit for lab rearing turtles is that hatchlings can enter a head-starting program. Head starting is an effort to grow organisms in a protected environment, under ideal conditions for survivorship, before reintroducing them to the wild. Hatchling WPTs are extremely vulnerable to introduced predators (e.g., bullfrogs and bass) due to their small size and weakly ossified shells. Once WPTs grow to a size too large to be consumed by these predators, their survivorship increases dramatically. Our goal is to have the hatchlings reach this size threshold in an abbreviated amount of time. By using light cycles and temperature regimes that emulate a perpetual summer, WPTs are allowed to grow continuously, avoiding periods of dormancy they experience in the wild. This allows our head-started WPTs to reach the size of wild 2 to 3-year-old WPTs in only 10 months. Partners in this AZA CEF-funded conservation effort include the Oakland Zoo and San Francisco Zoos. The Woodland Park Zoo in Seattle and the Oregon Zoo have utilized head-starting to bolster Washington’s WPT population for more than 10 years with extraordinary success.