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 The sex of sea turtle hatchling is determined by the temperature when the eggs incubate. A higher temperature produces more females, with males produced by lower temperatures. 

The increase in sea temperatures is leading to more female sea turtles. Some populations are showing up to a 90% bias towards female hatchlings, with potential impacts for population viability. High sand temperatures also cause reduced hatching success.

The study, published in the Journal of Applied Ecology, shows the potential for two interventions to reduce nest incubation temperatures and stabilise sex ratios in a nesting loggerhead turtle population in the Eastern Atlantic Ocean. 

Dr Leo Clarke, marine biologist at 91����� and lead author of the study explained: 

“Previous work has tested various techniques to reduce nesting temperatures in sea turtles, including sprinkling and shading of the nests and moving eggs to labs for incubation

“However many of these techniques require significant resource and manpower. Turtle nesting sites or ‘rookeries’ are often in remote locations and ideal solutions need to be simple and cheap.

“We tested two interventions: nest shading, and a new technique that we call nest “splitting”. This involved halving the number of eggs in a nest, hopefully reducing the amount of metabolic heat that the eggs generate as they incubate and reducing temperatures.”

Both techniques reduced nest temperatures compared to natural nests. Shaded nests were on average 1.1°C cooler and split nests were 0.5°C cooler, resulting in hatchling sex ratios that were 1.5% female and 45% female, compared to 69% females produced in natural nests. 

Importantly, neither technique affected the fitness of the hatchlings, which can also be affected by nest temperatures.