Project Title: Temperature-Dependant Sex Determination: Implications for the Conservation and Biology of Loggerhead Sea Turtles in Florida
Project Manager: Dr. Thane Wibbels
Organization: University of Alabama at Birmingham (Research and Educational Institute)
Grant Amount: $6,436.00
Completion Date: 2012-11-07
Summary: Sea turtles possess temperature-dependent sex determination (TSD) which has significant implications for their conservation and biology. With previous funding from the Florida Sea Turtle Grants Program we have developed an extensive collaborative network for the simultaneous evaluation of beach temperatures on nineteen loggerhead nesting beaches throughout Florida. This collaborative network provides the unique opportunity to significantly extend our previous findings by addressing two basic questions regarding TSD and sea turtle conservation. First, we will evaluate the effects of beach renourishment on the beach temperatures (using data loggers buried in the beach at nest depth). This study will address an issue being faced by many communities that are artificially renourishing their beaches due to erosion. This will be a collaborative study with Mote Marine Laboratory in which we will evaluate approximately eleven beaches (including control beaches, renourished beaches, and nest relocation areas) ranging from Venice, FL, to Longboat Key, FL. The study will include an evaluation of the beach sand characteristics versus beach temperatures at nest depth. Second, we will continue our collaborations with conservation groups throughout Florida in order to simultaneously monitor nesting beach temperatures. In addition to variation between beaches, our current results suggest year-to-year variations in beach temperatures occur in Florida, thus necessitating the need for multi-year studies. Tropical weather systems have the potential to significantly alter sex ratios. We have yet to record beach temperatures during what might be considered a “typical year” for tropical weather systems affecting Florida. Collectively, the results of the proposed research will provide fundamental knowledge regarding the conservation and biological implications of TSD for loggerhead sea turtles in Florida.
Results: This research sponsored by the Sea Turtle Grants Program provided the foundation for a multi-year project investigating beach temperatures that were simultaneously recorded at nest depth on a wide range of nesting beaches used by loggerhead sea turtles in Florida and in the Southeastern U.S. The results were combined with previous data to provide six continuous years of temperature data collection (2004-2009). The results indicate that temperatures vary significantly between loggerhead nesting beaches. The results also indicate that the spectrum of beaches used by the loggerhead population in the southeastern U.S. include a wide variety of thermal profiles, with potential sex ratios ranging from high female biases to male biases depending on the specific beach. In general, nesting beaches temperatures along the Atlantic coast of Florida (e.g. Melbourne Beach, Juno Beach, Hutchinson Island), where the majority of nesting occurs, were relatively warm suggesting the production of female-biased sex ratios. The histology-based hatchling sex ratio data support the hypothesis that female biases may often be produced on nesting beaches on the Atlantic coast of Florida. In contrast, a few locations (e.g. Cape San Blas on the Florida panhandle) were consistently cooler suggesting the production of a greater proportion of males. However, these locations represented minor nesting beaches compared to those on the Atlantic coast. These finding are consistent with the hypothesis that sex ratio production is beach-specific, but the loggerhead population in the southeastern U.S. is producing an overall female-biased sex ratio. The results provide a basis for suggesting which beaches in the southeastern U.S. are important for the production of female and male loggerheads. The results also indicate that factors associated with beach nourishment projects such as sand type, can significantly influence beach temperature, and thus hatchlings sex ratios. Finally, the results represent a foundation for a temperature database for evaluating potential long-term changes in beach temperatures associated with global climate change. The data indicate that many of the most important nesting beaches for loggerheads are already relatively warm and may be producing strong female biases, thus having little leeway for potential temperatures increases in future years.