An assessment of freshwater turtle populations at Oak Mountain State Park

Background/Question/Methods

This study assessed the turtle populations at Oak Mountain State Park, Alabama, with an emphasis on temperature-dependent sex determination and nesting habitat temperatures. The purpose of this study was to collect data on the freshwater turtle populations at Oak Mountain State Park (including species diversity, abundance, and an estimate of sex ratios of each species) through direct observation and trapping and to characterize the nesting season (ie. identify the nesting sites, incubation duration, and incubation temperature profiles) to determine if nesting temperatures in the 2013 nesting season result in a balanced Fisherian sex ratio. Headcounts, trapping, and monitoring of nesting habitat temperatures were conducted to assess the populations. Contour density maps were created to determine habitat usage within each study site (i.e. determine which areas were most used by different life stages for foraging, basking, etc.). Nesting temperature data were collected using HOBO temperature data loggers.

Results/Conclusions

Four species were found within the park: Chelydra serpentina, Pseudemys concinna, Sternotherus odoratus, and Trachemys scripta, and variation in size of captured turtles suggested that there has been successful recruitment by some species. Nesting temperatures at all sites monitored were found to be cooler than the pivotal temperature for either T. scripta or S. odoratus, and it was found that vegetation cover influenced the temperatures recorded at nest depth. These data lay a foundation for and will be compared to subsequent nesting seasons at Oak Mountain State Park. Data from multiple years on these populations will be used to estimate population size and structure. Multiple years of nesting temperature data will provide valuable insight on trends in nesting temperature variation and identify whether sex ratios correlate with changes in weather and climate. The results are of importance to the management of these species and lend insight into the future viability of the turtle populations at Oak Mountain State Park.