Abstract
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.
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Acknowledgements
The Direction de l’Environnement en Polynésie Française issued all permits and authorizations to carry out this work. JOL thanks Air Tahiti NUI for supporting his travel to French Polynesia. JM and MG acknowledge the support of the Virtual Data initiative, run by LABEX P2IO and supported by Université Paris-Sud, for providing computing resources on its cloud infrastructure. CG and the Te Mana O Te Moana team thank the Direction de l’Environnement en Polynésie Française, The Brando resort and Tetiaroa Society for their long-term support of this research, as well as the Fondation Albert II de Monaco, Van Oord, Vilebrequin, Esri, Air Tahiti Nui, IFBD, Hinerava and Mireille and Richard Bailey for their financial support. JS acknowledges the BHP–CSIRO Ningaloo Outlook Marine Research Partnership for providing funding and was supported by an Australian Government Research Training Program Scholarship at The University of Western Australia. The authors thank the Te Mana O Te Moana team and the numerous volunteers who helped with data collection.
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CG initiated the turtle monitoring project. CG, MT, and QG and many volunteers completed all the fieldwork and compiled the nesting survey and nest temperature data. JOL designed the long-term sand temperature experiments and collected the sand temperature data. GCH, JOL, and JM conceived the manuscript. JM led the data analysis with contributions from MG, JOL and JS. MG built the mathematical models and implemented them in R packages. JOL, JM and GCH led the writing of the manuscript with contributions from all authors. JOL and JM are joint first-authors.
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Laloë, JO., Monsinjon, J., Gaspar, C. et al. Production of male hatchlings at a remote South Pacific green sea turtle rookery: conservation implications in a female-dominated world. Mar Biol 167, 70 (2020). https://doi.org/10.1007/s00227-020-03686-x
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DOI: https://doi.org/10.1007/s00227-020-03686-x