Production of male hatchlings at a remote South Pacific green sea turtle rookery: conservation implications in a female-dominated world

Sea turtles have temperature-dependent sex determination, with males being produced at low incubation temperatures and females at high temperatures within the thermal range for embryonic development. In the context of climate change, there are concerns that warming temperatures will lead to an increase in female production. If primary sex ratios are extremely skewed, low male production (and subsequent male availability) may threaten long-term population viability. Heightening these concerns is the fact that female-biased sex ratios are already reported at the majority of sea turtle nesting sites across the world. Here, we describe for the first time primary sex ratios at a remote green sea turtle (Chelonia mydas) nesting site in the South Pacific. Nesting surveys were conducted on Tetiaroa, French Polynesia, between the 2007/2008 and 2018/2019 nesting seasons and revealed a trend of increasing annual nest numbers with large inter-annual fluctuations. We deployed temperature loggers to record incubation conditions and estimated hatchling sex ratios. We recorded low incubation temperatures (mean = 28.5 °C, standard deviation = 0.7 °C) and estimated that currently 54% of all hatchlings produced are male. Low incubation temperatures may be linked to light sand color, shading from vegetation behind beaches and heavy rainfall. Since this site will likely continue to produce males in the future, there is reason for cautious optimism for this population of green sea turtles.