LEBLANC, A.M.*; ROSTAL, D.C.; WIBBELS, T.; Georgia Southern University; Georgia Southern University; University of Alabama at Birmingham: Natural Pivotal Temperature and Sex Ratios of Loggerhead Sea Turtles (Caretta caretta) Nesting on Two Georgia Barrier Islands

Temperature-dependent sex determination was studied in loggerhead sea turtles (Caretta caretta) nesting on two Georgia barrier islands during the 2000-2003 nesting seasons. Both in situ (n = 60) and relocated (n = 78) nests were studied on Blackbeard Island and Wassaw National Wildlife Refuges. Nest temperatures were monitored with temperature data loggers to estimate pivotal temperature and to predict hatchling sex ratios. Nests were monitored throughout the nesting season to examine seasonal changes in sex ratios. Ten hatchlings were sampled from each of ten nests and their gonads were histologically examined to determine sex. Temperature data from these nests were correlated with the histologically determined sex ratios to estimate pivotal temperature and transitional range of temperatures. The estimated pivotal temperature based on temperature regimes in natural nests was similar to previously published pivotal temperature for on Atlantic loggerheads based on constant incubation temperatures. These data were then used to predict sex ratios produced in other nests that contained data loggers. Our results show that nests laid during the first third of the nesting season (May 1 – June 4) produced the highest percentage of males, in comparison to nests laid during the remainder of the season (June 5 – August 10) which produced predominantly females. The results indicate that both male and female hatchlings were produced on these Georgia barrier islands, but overall a significant female bias was predicted.