Published: Sun, January 14, 2018
Research | By Raquel Erickson

Warm Temperatures Turning Sea Turtle Population Almost Entirely Female

Warm Temperatures Turning Sea Turtle Population Almost Entirely Female

Researchers previously determined the sex of individual hatchlings through anatomical exams at nesting beaches, providing only a snapshot in time from only a few nests. Increasing temperatures in Queensland's north, linked to climate change, have led to virtually no male northern green sea turtles being born.

After collecting 411 for analysis and release, they found a "moderate female sex bias" in turtles from beaches in the cooler, southern Great Barrier Reef, where about 65-69 per cent were female.

"Knowing what the sex ratios in the adult breeding population are today and what they might look like five, 10 and 20 years from now when these young turtles grow up and become adults is going to be incredibly valuable".

"This has given us an important new window into demographic changes in these populations over the last several decades, which have gone undetected until now", said Michael Jensen, a research biologist at NOAA Fisheries.

"This is extreme, like capital letters extreme, exclamation point extreme", says Camryn Allen, a scientist from the National Oceanic and Atmospheric Administration in Hawaii. 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.

Since figuring out the sex of buried eggs is too hard, researchers made a decision to catch sea turtles and use genetic tests to find out where they'd come from. Heat up the eggs, and only females are born.

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

"This research is so important because it provides a new understanding of what these populations are dealing with".

Green turtles are in fact remarkably widespread, and are found in tropical, subtropical and temperate waters around the world.

"These animals are teenagers for an awfully long time". "If this happens everywhere, we'll probably see a slow decline".

Biologist David Owens, a professor at the College of Charleston who was not involved in the study, agrees. He praised the way the study team - which included a wide range of expertise - was able to link temperature with turtle gender.

WWF-Australia CEO Dermot O'Gorman said Australians, and many people around the world, would be concerned at yet another climate change impact on the nation's most popular icon. Given that the warmer temperatures seen in northern Australia have been distributed around the globe, experts predict that other sea turtle populations in warm regions are also following the same trend. For every one male, there are two females, according to the new research. 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. Without male members, the colonly could not sustain itself and may disappear forever.

With warming global temperatures and most sea turtle populations naturally producing offspring above the pivotal temperature [14], it is clear that climate change poses a serious threat to the persistence of these populations.

For the study, scientists caught green turtles at the Howick Group of islands where both northern and southern green turtle populations forage in the Great Barrier Reef.

That'll be why they call sea turtles the "polar bears of the south", then.

Allen said the reasons for the gender bias were still a mystery.

A unusual phenomenon is occurring in one population of green sea turtles in Australia's east coast, where up to 99 percent of the endangered sea turtles that hatch are female.

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