Mariana and colleagues from Brazil have recently published an article at the Journal of Experimental Marine Biology and Ecology that determines the primary sex ratio of loggerhead hatchlings produced in Brazil during the last 25 years. Sea turtles have temperature dependent sex determination, with warmer temperatures producing more females. Therefore concern exists that global warming will cause a feminization of sea turtle populations. This study came from the need to understand the current sex ratio being produced at loggerhead nesting grounds to establish baseline parameters as climate change progresses and to identify beaches that produce a higher proportion of males.
Concern over the potential impacts of increased temperature on marine turtles, which have temperature dependent sex determination, has resulted in an increase in research that predicts the sex ratio of marine turtle hatchlings under various scenarios of climate change. To accurately understand the projected impacts from global warming, it is necessary to understand the sex ratio baseline in advance of climate change. To address this, the primary sex ratio of loggerhead hatchlings, Caretta caretta, was estimated from incubation duration of 27,697 in situ nests from 21 nesting beaches used by two subpopulations of loggerhead turtles in Brazil over the last 25 years. A strong female bias (94%) was observed in all the areas used by the northern loggerhead stock, Sergipe (SE) and Bahia (BA), whereas a more balanced sex ratio (53% female) was estimated at the regions used by the southern loggerhead stock, Espirito Santo (ES) and Rio de Janeiro (RJ). Both inter-annual (SE: 83% to 99%, BA: 79. % to 98%, ES: 33% to 81%, RJ: 18% to 81%) and inter-beach variabilities (SE: 91% to 98%, BA: 89% to 96%, ES: 47% to 69%, RJ: 28% to 55%) in mean female offspring were observed. These findings provide evidence of persistent female bias in Brazil, and importantly identify male producing beaches and months, which will guide management decisions.
Full reference: Marcovaldi, M. A., López-Mendilaharsu, M., Santos, A. S., Gustave, G. L., Godfrey, M., Tognin, F., Baptistotte, C., Thome, J. C., Dias, A. C. C., Castilhos, J. C., & Fuentes, M. M. P. B. (2016). Identification of loggerhead male producing beaches in the south Atlantic: Implications for conservation. Journal of Experimental Marine Biology and Ecology, 477, 14-22. doi:0.1016/j.jembe.2016.01.001