Importance of spatio-temporal data for predicting the effects of climate change on marine turtle sex ratios

Species with temperature-dependent sex determination (TSD) are likely to be impacted by climate change. There is a paucity of data on the contemporary sex ratios of offspring produced by regional marine turtle populations. The lack of such information inhibits the ability of researchers to accurately predict how future meteorological and climate-driven changes may affect turtle populations. Moreover, these data are integral for the development of regional and global recovery plans for declining turtle populations. We estimate offspring sex ratios for the loggerhead turtle Caretta caretta at a range of beaches on the Mediterranean island of Cyprus over a 10 yr period (1997 to 2006; 40 beaches, 628 clutches, 29402 hatchlings). Based on hatchling sex determination, we found the pivotal incubation temperature (the temperature at which a 50: 50 sex ratio occurs) to be 28.9 degrees C, and the pivotal incubation duration to be 56.3 d. From the incubation durations of over 628 in situ clutches laid on different beaches, we estimate that 89% of the offspring produced from these clutches were female. There was, however, both inter-annual (74 to 95% female) and inter-beach (58-98% female) variability in mean offspring sex ratios. These findings highlight the need for wide-scale, long-term monitoring of primary sex ratios in order to accurately predict the likely impacts of climate change. Despite spatial and temporal variation in offspring sex ratios produced, male hatchlings are certainly in the minority in Cyprus. It is therefore highly likely that beaches producing males will become increasingly critical habitats for successful clutch incubation in the face of predicted rising temperatures.