Female-biased sea turtle populations

The temperature at which a sea turtle egg incubates determines the sex of the hatchling. Below a pivotal incubation temperature of about 29.0°C the majority of individuals are born male and above that temperature the majority of individuals are born female. This unique process, known as Temperature-Dependent Sex Determination (TSD), is widespread among reptiles.

What will happen to sea turtle populations when air temperatures rise due to climate change? This is a central question of my latest research, the results of which were published in the Journal of Experimental Marine Biology and Ecology this week.

The study was a collaboration between researchers from Swansea University (United Kingdom) and Deakin University (Australia), and conservationists working on the Dutch Caribbean island of Saint Eustatius. We recorded sand temperatures at a turtle nesting beach where leatherbacks, hawksbill and green sea turtles nest. These data were combined  with temperature projections from the Intergovernmental Panel on Climate Change (IPCC) to model how sand temperatures will change in the next 100 years.

The results showed that sand temperatures are relatively high (ranging from 29.1-33.3°C) at this nesting site and that all three species of sea turtles are female-biased: we estimate that for the current populations of hawksbill, leatherback and green turtles the percentage of turtles born male are 36%, 24%, and 16%, respectively. Projecting into the future, it is likely that the female-skew will be intensified due to warming air temperatures. For example, projections indicate that only 2.4% of green turtle hatchlings will be males by 2030, 1.0% by 2060, and 0.4% by 2090.

Nicole Esteban, a Swansea University researcher and former St Eustatius National Parks (STENAPA) manager, who is a lead author of the paper says that “there is a real concern that there will not be enough males born on Saint Eustatius in the future. If there are too few males, the local population is at risk of collapsing. Another concern is that turtle eggs do not develop above a certain temperature. The study highlights the extinction risks of climate change to species whose biology is closely linked to temperature.”

This research underlines that there is real need for effective conservation measures to be put in place to prevent the localised extinction of these turtle populations. Potential conservation strategies include shading turtle nests on the beach or moving nests to a cooler section of a beach such as a protected hatchery.

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A hawksbill turtle swimming near a wreck in Saint Eustatius
(photo courtesy of Frogfish Photography)


Sand temperatures for nesting sea turtles in the Caribbean: implications for hatchling sex ratios in the face of climate change” was published by the Journal of Experimental Marine Biology and Ecology (2016). Authors: Jacques-Olivier Laloë, Nicole Esteban, Jessica Berkel and Graeme C Hays.

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