Rising ocean temperatures are putting the survival of sea turtle populations at risk by heating up their nesting sites on beaches around the world, according to a study published Wednesday by The Royal Society Open Science Journal.

Of the seven extant sea turtle species, six are already on the IUCN Red List of Threatened Species, two of which - the hawksbill and Kemp's turtle - are critically endangered.

Turtles are all the more threatened because unlike other species, such as birds and butterflies, they have a longer reproductive cycle and take longer to adapt to changes.

Thus, the beaches where they come to lay their eggs - which according to an immutable cycle are the same as those where they were born - are increasingly degraded by the rise in sea level or erosion but also by climate change which warms the sand in which these reptiles come to bury their pregnant offspring.

And this is not without consequences for the long-term survival of the species.

Newly hatched turtles reach the sea, on the beach of Punta Chame, Panama, November 13, 2022 © Luis ACOSTA / AFP/Archives

Indeed, the determination of the sex of future turtles depends not on the chromosomes but on the temperatures during the incubation period: the hotter it is, the more females there will be.

A previous study conducted on green turtles in 2019 had shown that between 76 and 93% of turtles would be female by 2100, hampering the possibility of finding a partner to reproduce.

Not to mention the risks of incubation failure which would be increased with the rise in mercury.

Wednesday's study, which is based on modeling, looked at whether sea turtles could shift their breeding season to cooler times of the year to lower nest temperatures.

Of the 58 nesting sites studied around the world, the researchers found that such adaptation only mitigated rising temperatures in 55% of cases.

And this, if global warming is limited to 1.5 degrees by the end of the century, a scenario that many now consider unrealistic.

According to the study's lead author, Jacques-Olivier Laloe, these findings highlight the "really worrying" possibility that local extinctions could occur, especially for sea turtles that live around the Equator where temperatures vary. less and where earlier laying will therefore have little effect.

"In reality, it is likely that sea turtles have less ability to adapt to climate change" than according to this "rather optimistic" study, he said.

© 2023 AFP