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This population of green sea turtles is nearly all female, signalling a major problem

by Daniella Silva /

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The future is female for green sea turtles born along part of Australia’s Great Barrier Reef. Only about 1 percent of juvenile turtles hatching there are male now and that's because of global warming, according to a new study.

In sea turtles, warmer temperatures produce more female hatchlings and cooler temperatures produce more males. Higher temperatures from global warming have made it so “virtually no male turtles are now being produced” in the green sea turtle population in the northern Great Barrier Reef, according to the findings of the study published in Current Biology on Jan. 8.

“That’s really ringing alarm bells for the long-term status of the region,” Dermot O’Gorman, the CEO of World Wildlife Fund Australia, told NBC News. The WWF-Australia helped with the study as part of an initiative looking at turtle health and conservation.

Image: Green Turtle
A green turtle hatchling. Heron Island, Capricorn-Bunker Group, Great Barrier Reef, Queensland, Australia.Auscape / UIG via Getty Images

In turtles that were born on the reef’s warmer northern nesting beaches, 99.1 percent of juveniles, 99.8 percent of sub-adults, and 86.8 percent of adult-sized turtles were female, according to the researchers.

The northern Great Barrier Reef is home to one of the "largest green turtle populations the world," according to the study. Green sea turtles take about 25 years to reach the onset of sexual maturity and they are protected by the Endangered Species Act.

And sea turtles aren't the only reptiles that have their sex determined by the temperature of their nesting environments — most other turtles, as well as alligators, crocodiles and some lizards, fall into that category.

Scientists and conservationists researching climate change and the effects temperatures have on other species say the study has wide-reaching implications and raises the alarm for potentially deadly effects to come.

Image: Green Turtle
A green turtle swims through the pristine waters of the Great Barrier Reef in Queensland, Australia.Grisha Shoolepoff / iStockphoto

“As far as I’m aware, this is one of the first times that kind of our worst fears are coming true and that there are populations that are being exposed to such high temperatures that they are basically unisexual,” said Clare Holleley, a senior research scientist with the Australian National Wildlife Collection.

“That’s been one of the greatest conservation concerns for all of these species,” said Holleley, who researches sex chromosome genomics.

Related: Why climate change may be to blame for dangerous cold

Specifically, Holleley conducts research on how temperature affects the sex of Australia’s bearded dragon lizards. The reptiles have “true, identifiable sex chromosomes” like humans do, she said, but “if you push their incubation temperature too high, the signals from the sex chromosomes can be overridden what would become male normally becomes feminized.”

Image: Central bearded dragon / Inland bearded dragon (Pogona vitticeps) in Tree
Central bearded dragon a in tree, native to Australia.Arterra / UIG via Getty Images

While more data needs to be collected, Holleley said she was seeing hints of female-bias in dragon populations, too.

“Individuals that should be developing as males are developing as females,” she said, adding, “We don’t quite yet have enough data to say that that is increasing over time, but it’s definitely occurring now when it wasn’t before.”

Holleley said that the sea turtle study showed that rising temperatures are “affecting the biology of organisms in real time.”

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“Climate change just doesn’t mean it’s getting hotter and it might be more uncomfortable for me in terms of weather,” she said. “This is affecting the biology, the genome, the very way these [bearded dragons] go about their inherent functioning is being affected."

Nikhil Advani, the lead specialist on climate, communities and biodiversity for the World Wildlife Fund, said the sea turtle study was so concerning because of the extent of the population that was already found to be female.

“It was a really extreme result," he said.

Advani said the notion of a link between climate change and temperature-dependent sex determination in reptiles was first discovered in the mid-90s.

"So, we’ve known about it for quite a while, but I don’t know that we’ve ever seen such a sex bias in a population,” he said.

Image: Central bearded dragon, Pogona vitticeps
Central bearded dragon almost camouflaged while in typical basking position on Bluebush, Maireana in Mungo National Park, far western New South Wales, Australia.Auscape / UIG via Getty Images

Advani added that the study showed just how urgent an issue it is and would continue to be for some species.

Sea turtles “are a really important, keystone species,” O’Gorman said.

The problem isn't just around the Great Barrier Reef. Jeanette Wyneken, a professor of biological sciences at Florida Atlantic University and sea turtle expert, said scientists are seeing it in hatchlings in other turtle populations.

Wyneken said her own research on Loggerhead turtle species showed “high female bias” in recent hatchling populations after “three record warm nesting seasons in a row.” She said nest failure is another major area of concern as evidence shows global temperatures are on still on the rise.

“There’s enough evidence that it’s just going to keep getting warmer and that’s going to push us out of the highly female bias range and into the dead embryo range,” she said.

Related: How to save a sinking island

Hope is not yet lost for green sea turtles, said O'Gorman, as there were still some adult breeding males out there to currently sustain the population, particularly from the southern population and its cooler beaches where the sex bias was 65-69 percent female.

There are also some "practical" intervention methods scientists can take to help relieve the gender bias, such as putting up shade tents around breeding sites or spraying artificial rain to cool sand temperatures, O'Gorman said.

Holleley said that while short-term intervention could help populations, it could also have unintended outcomes and potentially make the population more vulnerable if those intervention methods were suddenly taken away because of funding or changes in administrations.

"You're kind of in a Catch-22, do you intervene and potentially have an adverse outcome as an unintended consequence," she said, "or do you let the population be and see what happens — it's very difficult."

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