Warming warning over turtle feminization

Up to 93% of green turtle hatchlings could be female by 2100, as climate change causes « feminisation » of the species, new research suggests.

The sex of turtle hatchlings is determined by temperature, and at present about 52% of hatching green turtles — one of seven species of sea turtle — are female.

But a study by the University of Exeter and the Marine and Environmental Sciences Centre (Portugal) shows that in warmer temperatures predicted by Intergovernmental Panel on Climate Change (IPCC) scenarios, 76-93% of hatchlings would be female.

The figures are specific to the study site in Guinea-Bissau, West Africa, but researchers say they expect a similar picture globally.

They say the changing gender ratio would initially lead to more females nesting, increasing the population, before by a decline « as incubation temperatures approach lethal levels. »

They also predict rising sea levels will submerge 33-43% of current nesting areas used by green turtles on the beaches where the study was carried out.

« Green turtles are facing trouble in the future due to loss of habitats and increasing temperatures, » said Dr Rita Patricio, of the Centre for Ecology and Conservation on the University of Exeter’s Penryn Campus in Cornwall.

« Our results suggest the nesting population of green turtles the Bijagós Archipelago, Guinea-Bissau, will cope with the effects of climate change until 2100.

« Cooler temperatures, both at the end of the nesting season and in shaded areas, will guarantee some hatchlings are male.

« Although rising temperatures will lead to more female hatchlings — and 32-64% more nesting females by 2120 — mortality in eggs will also be higher in these warmer conditions.

« As temperatures continue to rise, it may become impossible for unhatched turtles to survive. »

The research team, which included the Institute of Biodiversity and Protected Areas of Guinea-Bissau, say nesting sites submerged by rising seas may not simply « move » inland.

« Beach retreat may be OK in some areas, but the turtles we studied were nesting on a small island (Poilão Island) so there is a limit to how far the beach can go, » Dr Patricio said.

« In other places there may be natural barriers or human constructions that stop beaches moving inland. »

The Bijagós Archipelago is the most important nesting place for green turtles in Africa, and the main breeding ground for the species in the South Atlantic.

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