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Climate Change Is Turning Green Sea Turtles Female. That’s a Problem

Over 99 percent of turtle hatchlings in northern Australia are female due to increasing sand and sea temperatures

(mattwicks via iStock)
smithsonian.com

Of all the potential consequences of climate change—rising sea levels, desertification, floods—here’s one that may not be on your radar: climate change is producing an abundance of female turtles. As Helen Davidson at The Guardian reports, according to a new study, warmer sands in a certain section of beach along The Great Barrier Reef have caused more than 99 percent of green sea turtles to hatch as female.

The sex of sea turtle hatchlings is not dependent on the passing down of chromosomes, like in humans. Rather, sea turtle sex is a function of incubation temperature. As Ben Guarino at The Washington Post reports, at roughly 85 degrees Fahrenheit, turtle nests produce equal amounts of males and females. A tad cooler and the clutch leans male. A little warmer and embryos develop as females.

But in a new study in the journal Current Biology, researchers found that recent warming has led to an abundance of female turtles in the northern populations of a major nesting area called Raine Island. Out of a population of about 200,000 turtles, scientists found that 99.1 percent of juveniles were female, 99.8 percent of subadults and 86.8 percent of the entire population was female. Southern populations of turtles in Australia, which live on cooler beaches, show much lower impact. There, researchers found the ratio was about 65 to 69 percent female turtles. 

As Guarino reports, the researchers examined sea and air temperatures recorded in historical data to discern the sand temperatures. Their analysis suggests sand temps have been climbing since the 1960s. 

“Combining our results with temperature data show that the northern GBR 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 authors write in the paper.

Finding out whether a turtle is male or female is harder than it sounds, and is why this type of study hasn't been undertaken before. Without external genitalia, you can’t just flip over a turtle and take a look—and DNA also doesn't provide any clues. So the researchers used two methods to determine the sex of 411 turtles across the age spectrum. First they made a tiny incision to inspect their gonads. They also took blood plasma samples and examined hormones.

While that’s a lot of effort, it’s necessary work and is unveiling the hidden side impact of climate change. Australia isn’t the only place where lady turtles are taking over. As Kavya Balaraman at Climate Wire reports, researchers in Florida have noticed a preponderance of female loggerhead turtles in recent years as well.

Michael Jensen, the study's lead author and a research fellow at NOAAs Southwest Fisheries Center tells Craig Welch at National Geographic that the finding is somewhat counterintuitive. Turtles seem to be thriving in northern Australia. But the sex ratio is something of time bomb, especially since the animals live 60 or 70 years and do not reach breeding age until 25 to 35. 

“You work on one of the biggest turtle populations in the world and everyone tends to think that means things are good,” says Jensen. “But what happens in 20 years when there are literally no more males coming up as adults? Are there enough to sustain the population?” 

As Guarino reports, the population won’t immediately crash. And it’s possible there will be something of a baby bump since one male can fertilize lots of females. But eventually, there may be consequences. “Oh yes, there are a few males remaining, and there will be for decades to come,” sea turtle researcher David Owens, professor emeritus at College of Charleston tells Guarino. “But they will eventually die off. I predict that very soon the [northern Great Barrier Reef] population will start to see reduced fertility at the nesting beach if it is not already happening.”

Dermot O’Gorman, chief executive of World Wildlife Fund Australia tells Davidson that there are some potential quick fixes, like setting up shade cloth to cool beaches and reducing turtle by-catch from fishing fleets to insure breeding-age males stay in the population. But the only sustainable solution is to stop climate change, he says.

This new study is another sign that humans cannot halt the ongoing efforts to protect turtles. A study released last September showed that many populations of the world’s seven species of sea turtles are increasing after decades of conservation work. But any threats to sea turtles are likely threats to entire ocean ecosystems.

“Sea turtles are bellwethers. They’re flagships that we use to tell the story of what’s going on in the oceans,” Roderic Mast, co-chairman of the IUCN Marine Turtle group tells the Associated Press. “That’s why people should care about turtles.”

About Jason Daley

Jason Daley is a Madison, Wisconsin-based writer specializing in natural history, science, travel, and the environment. His work has appeared in Discover, Popular Science, Outside, Men’s Journal, and other magazines.

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