Estimating the sex ratio of green sea turtles (Chelonia mydas) in Taiwan by the nest temperature and histological methods

• First study on sex ratio of green turtle hatchlings from three nesting sites in Taiwan.
• We combined the nest temperature and histology methods.
• The sex ratios for green turtle populations in Taiwan are female biased.
• Female hatchlings increased with nest temperature during sex determination period.

Sex ratio is an important population characteristic. It is especially important for endangered species with temperature-dependent sex determination, such as sea turtles. As turtle sex ratio at hatching is primarily influenced by the environmental temperature, the ability to estimate sex ratio is crucial to the success of conservation measures. Green turtles (Chelonia mydas) are the only sea turtles that nest in Taiwan. Despite much regional research on the ecology of this species, the sex ratio has not yet been determined in Taiwan. We combined measures of nest temperature during the thermally sensitive period with a histological method to estimate the hatchling sex ratio from three nesting islands in Taiwan from 2010 to 2011. We determined that the sex ratios for green turtle populations in Taiwan were female biased during the study period. In line with that overall trend, Wan-an Island with drier and hotter weather during the nesting season, produced more female hatchlings than the other main nesting island—Lanyu Island. Results of this study stress that differences in sex ratio are important to consider when developing conservation strategies, even among closely located sites such as Wan-an and Lanyu Islands. This is the first study of the hatchling sex ratio of green sea turtles in the East Asian region.