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This Sea Turtle Population Is Almost All Female, Thanks To Climate Change

One population of green sea turtles in Australia’s Great Barrier Reef is nearly entirely female thanks to climate change, according to a new scientific paper published this week.

Unlike most other animal species whose sex is determined during the fertilization period, a green sea turtle’s sex is influenced by the temperature surrounding the developing egg. That means the temperature surrounding its nesting site on the beach, also known as a rookery.

Turtle eggs incubated below 81.86 degrees Fahrenheit will hatch as male, while those incubated above 87.8 degrees will be female, according to the National Oceanic and Atmospheric Association.

The new study, published in the journal Current Biology this week, found that 99 percent of juvenile sea turtles born in the northern part of the Great Barrier Reef are female. The study’s authors also found that females made up 99.8 percent of sub-adult turtles and 86.8 percent of adult turtles.

Green sea turtles are considered endangered by the International Union for Conservation of Nature.

For the study, researchers with NOAA, California State University and Worldwide Fund for Nature Australia examined two populations of green sea turtles living in the northern and southern part of the Great Barrier Reef.

“Combining our results with temperature data show that the northern [Great Barrier Reef] green turtle rookeries have been producing primarily females for more than two decades and that the complete feminization of this population is possible in the near future,” the study’s co-authors wrote.

The new study suggests that climate change and the rising of ocean and air temperatures are having a dramatic effect on one of the largest populations of green sea turtles in the world, in the northern Great Barrier Reef.

The ratio of that population is one male for every 116 females, the study found.

“This is extreme ― like capital letters extreme, exclamation point extreme,” Camryn Allen, marine biologist and co-author of the study, told National Geographic.

“We’re talking a handful of males to hundreds and hundreds of females. We were shocked.” 

On the southern end of the reef, where temperatures have not increased as significantly as in the north, the population had a better ratio. For every one male, there are two females, according to the new research.

The study’s authors believe that their research points to a dim future for this population of north Great Barrier Reef turtles. If temperatures continue to rise as a result of climate change, it could lead to a dramatic decline in population.

“With warming global temperatures and most sea turtle populations naturally producing offspring above the pivotal temperature, it is clear that climate change poses a serious threat to the persistence of these populations,” the study’s authors wrote.

Biologist David Owens, a professor at the College of Charleston who was not involved in the study, agrees.

Climate change is clearly the culprit,” Owens told The Washington Post.

This is extreme — like capital letters extreme, exclamation point extreme.
Camryn Allen, study co-author

Jeanette Wyneken, a turtle biologist at Florida Atlantic University who was not involved in the study, told HuffPost that the study’s findings do not mean that the entire species will soon become extinct. However, she says it could be the start of a decline in green sea turtle populations. 

“Is this species liable to go extinct? Not yet,” Wyneken told HuffPost. “If this happens everywhere, we’ll probably see a slow decline. Common sense tells you: One male and a hundred females ― that’s going to be a very tired boy.”

Wyneken was confident that other green sea turtle populations are experiencing the same thing.

“I’m virtually positive this is happening elsewhere,” she said.

Marine biologists have noticed that green sea turtle populations have been shifting to become more female, but, according to Wyneken, this study is one of the first to look at multiple generations of turtles, which take up to 40 years to reach sexual maturity. 

“It’s one of those really important studies that puts together several different types of data that answers a question that has been standing out for a long time,” said Wyneken.

But the only way to find that out is to do the same study for different turtle populations, which sea turtle biologist Kate Mansfield says is necessary to protect conservation efforts for the animal.

“Generally, this is very important work that needs to be replicated among other major rookeries,” Mansfield, who works at the University of Central Florida’s marine turtle research group, told HuffPost. 

“We’ve made so much progress with many sea turtle populations in the last 30-plus years … that it would be heartbreaking to lose the ground we have gained through conservation actions over the decades.”

Mansfield told HuffPost that it’s not clear yet how sea turtles will adapt to climate change, but she pointed out that the rate at which their habitats are changing is unprecedented.

“The degree of temperature and habitat change that has happened is likely unprecedented due to how quickly these changes are happening now with the rapid warming of the earth,” she told HuffPost in an email. “We don’t know how resilient sea turtle species are when faced with such rapid changes in climate, habitat availability, and developmental pressure.”

Sea turtles play an important role in maintaining a healthy ecosystem in the ocean. 

“Green turtles feed on sea grass, eat on algae, and those are the base of the food chain” in the ocean, Wyneken told HuffPost. Without the turtles’ grazing, seabeds become unhealthy, which affect all other animals higher on the food chain.

“At the very best, the ecosystem becomes less diverse,” Wyneken added. At its worst, it could lead to the collapse of entire fisheries.

“We could lose so much,” Wyneken said.

To find out how the study’s authors completed their research, read the full scientific paper here

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