All sea turtle hatchlings recorded in Florida this year were female, a turtle hospital said.
Climate change is heating up the beaches, which skews the gender balance towards more women.
Experts disagree about what that means for the survival of sea turtle species.
A Florida turtle hospital said all the turtles it has tested in the past four years have been female, a worrying trend it attributes to climate change.
The temperature of the sand where the eggs are buried affects the sex of sea turtles.
Males are already a small minority of sea turtles – outnumbering 10 to 1 – and as the sand gets warmer, fewer and fewer males develop.
Experts disagree about the effect of this trend on the survival of sea turtle species. Climate change is putting a lot of pressure on the endangered animals anyway, an expert told Insider.
Female sea turtles are made in warm sand
“There are seven species of sea turtle, and all of them produce more females as it gets warmer,” said Lucy Hawkes, an ecologist from the University of Exeter who has been studying the phenomenon since 2007.
“All of them have heavily female-biased gender ratios,” she said in an email to Insider.
Sea turtle eggs incubated in sand warmer than 88.8° Fahrenheit (31° Celsius) will be female, according to the US National Oceanic and Atmospheric Administration.
The past four summers have been the hottest on record, Bette Zirkelbach, director of Turtle Hospital in Marathon, a city in the Florida Keys, told Reuters.
“Researchers studying sea turtle hatchlings and eggs have found no male sea turtles, only female sea turtles for the past four years,” she said.
The phenomenon has been observed all over the world. A 2018 study found that 99% of the turtles in eastern Australia were also female.
Running out of men?
Experts are divided about what this could mean for sea turtle populations.
Biologist David Owens, professor emeritus at the College of Charleston told The Washington Post in 2018 that within a few decades to a century, “there won’t be enough males in sea turtle populations.”
Having fewer males could lead to unsustainably poor genetic diversity among sea turtles, Melissa Rosales Rodriguez, a sea turtle keeper from the Miami Zoo, told Reuters.
However, Hawkes told Insider that it’s probably more complicated than that.
It is unclear what the “optimal” gender balance should be, she said.
It is common for a group of sea turtle nests to hatch about 90% female, and evidence suggests that only a few males are needed to fertilize all the eggs.
So it’s possible, for example, that “having lots of females could be an evolutionary adaptation to increase the population from being endangered,” she said.
A few studies have also suggested that males can still be produced from a warm nest if the eggs are wet.
“If you ran out of all the males, it would threaten the population – but we don’t think that’s going to happen any time soon,” she said.
In any case, there is no doubt that climate change is putting pressure on sea turtles.
That causes more storms, which can wipe out thousands of brooding nests at once, and sea-level rise that floods the nest and kills the eggs, she said.
“The biggest thing we can do in this regard is to limit the development of sheltered beaches, so reduce the number of new hotels etc being built behind the beach,” Mr Hawkes said.
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