Green Sea Turtle Population Is Nearly All Female

Pat Wise
January 12, 2018

How to Save the Sea Turtles?

There's something odd happening with green sea turtle populations in Australia's Great Barrier Reef, and now scientists believe they have figured out why.

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

The study authors, from NOAA's Marine Mammal and Turtle division in La Jolla, California, analyzed sea turtle populations on beaches at the northern and southern ends of Australia's Great Barrier Reef.

If temperatures to continue to rise, some turtle populations are at risk of becoming "completely feminized", which could, in turn, wipe out the population over the course of a few decades. With average global temperature predicted to increase by approximately 2.6 degrees Celsius by 2100, many sea turtle populations are now in severe danger of dying out.

Unfortunately, Dr Michael Jensen of the National Oceanic and Atmospheric Administration has found things are more serious for the endangered green sea turtles (Chelonia mydas) of the Great Barrier Reef. These data show that while the now-adult turtles would have been hatched in temperatures close to 29.3?C (the temperature at which the sex ratio is 1:1), in more recent decades, when the now-juveniles and sub-adults hatched, temperatures were consistently higher. Turtles from the cooler southern reef nesting beaches showed a more moderate female sex bias (65%-69% female).

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

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.

"We could lose so much", Wyneken said. "If this happens everywhere, we'll probably see a slow decline".

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

"We've had little pieces of this story come out before, but this is the first time anyone's been able to orchestrate the whole story to bring in global climate change along with feminization", Owens said.

Increasing temperatures, linked to climate change, are being blamed because the incubation temperature of eggs determines the sex of turtles with a warmer nest resulting in more females.

So strong is this fidelity to home that populations of turtles from different origins are thought to only rarely interbreed. At about four years of age, the turtle then heads to feeding grounds, such as a reef, where it remains until reaching sexual maturity (approximately 25 years of age). If they are lost, other species that depend on the same habitat will also be harmed. "I sure hope so and I'm sure there will be", Ms Allen said. "They're telling us something is going on in the oceans and we need to pay attention".

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The research, that was facilitated by the Rivers to Reef to Turtles project and led by WWF Australia, was published in the journal. "The exact mechanism is not well understood", she said.

"We're talking a handful of males to hundreds and hundreds of females".

Without the new study, he said, scientists might not have recognized the gender skewing in the north for decades - perhaps missing the window to make a difference.

The results are correlative rather than definitive, says Jensen, but are nonetheless "worrying". "But now we know and can focus our research on the right questions and start thinking about what can be done".

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