As temperatures rise, male sea turtles disappearing from Australia’s Great Barrier Reef

A sea turtle’s sex is determined by its nesting environment. The gender shift suggests climate change is having a significant effect on one of the biggest green-turtle populations in the world.

Male sea turtles are disappearing from Australia’s Great Barrier Reef.

A new study of gender ratios found that 99 percent of immature green turtles born in the northern part of the reef are female. Among adult turtles, 87 percent are female, suggesting there has been a shift in gender ratios during the past few decades.

A sea turtle’s sex is determined by its nesting environment. As sands warm, more females will hatch relative to males; if the sand temperature tops 84.7 degrees during incubation, only females will emerge.

The gender shift suggests climate change is having a significant effect on one of the biggest green-turtle populations in the world, said Michael Jensen, lead author of the new study, published in Current Biology.

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“We’re all trying to wrap our heads around how these populations are going to respond to those changes,” said Jensen, a marine biologist with the National Oceanic and Atmospheric Administration (NOAA) in San Diego.

At what biologists call the pivot temperature, turtles hatch as a mixture of males and females. For green sea turtles, this temperature is 29.3 degrees Celsius (85 Fahrenheit). A few degrees below 29.3 C, all the sea turtles are born male. Heat up the eggs, and only females are born.

“That transitional range, from 100 percent males to 100 percent females, spans a very narrow band of only a couple of degrees,” Jensen said.

The gender shift has been noticed before by people who study hatchlings, said Jeanette Wyneken, a sea-turtle expert and professor at Florida Atlantic University, who was not involved in the new research.

But it was not clear until this study that the shift was so dramatic and happening in such a large population across time, she said.

“This is the first paper that’s shown this multigenerational effect,” influencing the gender of juveniles, older adolescents and adults, Wyneken said.

It takes 35 to 40 years for a green sea turtle to reach sexual maturity, she said.

“These animals are teenagers for an awfully long time. We won’t see the effects of what’s happening today for several decades,” she said.

David Owens, a professor emeritus from the College of Charleston in South…

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