Potential male leatherback hatchlings exhibit higher fitness which might balance sea turtle sex ratios in the face of climate change

Sea turtles are vertebrates with temperature-dependent sex determination. Rising temperatures due to climate change cause female-biased sex ratios. We have assessed the influence of nest depth and shading conditions on nest temperatures and hatchling fitness of the leatherback sea turtle (Dermochelys coriacea). We relocated 48 leatherback clutches into a hatchery in 2013, 2014 and 2015, respectively. Of these, 24 clutches were placed under shade conditions and 24 were placed under unshaded (sun) conditions at three depths (50, 75, 90 cm). Fitness (as measured by greater carapace length, carapace width and hatchling weight) and locomotion performance (faster crawling and shorter righting responses) were better in leatherback hatchlings from the cooler, shaded nests than in those from the warmer, unshaded nests. In 2013, in clutches at a depth of 50 cm, hatching success was higher for the shaded clutches (79.68% +/- 15.32%) than for the unshaded clutches (38.39% +/- 34.35), while in clutches at deeper depths unshaded clutches had higher hatching success (35.58% +/- 24.01%) than shaded clutches (60.62% +/- 12.21%). Our results show that shaded conditions produced hatchlings with a higher fitness and a higher likelihood of being male. Therefore, our results can be used to provide conservation policies with a tool to decrease the current female-skewed sex ratio production caused by rising temperatures at most nesting rookeries around the world.