Sea turtles that hatch on a vital breeding ground off the coast of Africa are already overwhelmingly female — and by the end of the century, there could be no males at all, a new study finds.
That’s because egg incubation temperature determines the sex of loggerhead sea turtles, and the nesting ground is getting hotter. About 83 percent of turtles born on the Cape Verde islands in the Atlantic Ocean today turn out to be female, but that share could rise so high that only 0.14 percent of new hatchlings will be male by 2100 thanks to climate change. And that’s in a scenario where humans cut planet-warming emissions to limit global warming, University of Exeter researchers said in a news release on their findings.
The situation is even more bleak in middle-of-the-road and high emissions scenarios, under which “hatching of male loggerheads could cease entirely,” according to researchers. It’s not just males at risk, either: By the end of the century, “lethally high temperatures” could roast more than 90 percent of the eggs on the islands — killing them before they even hatch.
“Under all three climate change scenarios in our study, by 2100 more than 99% of hatchlings would be female — and under mid and high-emissions scenarios there could be no males at all,” Dr. Lucy Hawkes, a study author from the University of Exeter, said in a statement.
But what kind of impact does that have beyond the Cape Verde islands?
“Cape Verde hosts one of the largest nesting populations of loggerhead turtles in the world — up to 15% of the global nesting total,” Hawkes said, making the archipelago the world’s third-largest nesting haven.
Researchers published their findings this month in the journal Marine Ecology Progress Series, writing in their abstract that the Cape Verde turtles are particularly at risk because “most of the population cannot move to nest on cooler islands.”
The study relied on projections from the Intergovernmental Panel on Climate Change (IPCC), hatchling data and current island temperature numbers, researchers said.
“What surprised us was how even the low emissions scenario has detrimental effects for this population,” lead author Claire Tanner said in a statement. “What this shows is that now is the time to act on climate change — before it is too late to prevent the estimations seen in this paper.”
It’s possible the turtles could adapt to changing conditions by nesting sooner in the year when it’s less hot — a behavior natural selection would encourage, researchers said. But Hawkes said that fast-moving climate change likely means the turtles won’t be able to adapt quickly. What’s more, around 85 percent of the turtle nests on the Cape Verde islands are already in the coolest spot, meaning that finding less hot conditions on the islands themselves isn’t a solution.
What happens if or when there are no more male hatchlings? Researchers said the reproductive lifespan of male turtles isn’t known, “so older males may continue breeding for many years after new males stop being hatched.”
Loggerheads are found in oceans around the world, including from Newfoundland down to Argentina on the western edge of the Atlantic Ocean, and from Alaska to Chile on the Pacific Ocean’s eastern rim, according to the National Wildlife Federation. The Endangered Species Act listed the animals as threatened in 1978, the wildlife group said.
The turtles commonly nest in Oman, the United States and Australia. U.S. nests are primarily “on beaches from North Carolina through southwest Florida, and minimal nesting extends westward into the Gulf of Mexico to Texas and northward to southern Virginia” — with roughly 80 percent of the southeastern U.S. nesting along Florida’s central Atlantic coast, the National Wildlife Federation said.