Their sex is instead determined by environmental factors-in the case of sea turtles, the temperature to which they are exposed in the nest. Eggs laid in sand over 87.8 degrees Fahrenheit will produce females. Green sea turtles from cooler southern nesting beaches were about 65 to 69 percent female, while sea turtles from warmer northern beaches were 86.8 percent female for adult turtles, 99.8 percent for sub-adult turtles, and 99.1 percent for juvenile turtles. Those are both so alarmingly high that green sea turtles are on the endangered species list of the International Union for Conservation of Nature.
The group conducted its research over 16 days in July 2014, plying small boats around the Howick Group of islands in the north Great Barrier Reef - "an absolutely magical place", according to Jensen.
Over the course of the last two decades, temperatures have increased in Australia's northern Great Barrier Reef, which holds some of the largest turtle populations in the world, to the point where there are virtually no male turtles being produced from the nesting beaches.
The proportion of female hatchlings increases when nests are in warmer sands, while cooler temperatures is known to produce more male turtles.
"The disconcerting thing is that we can now see how changes in the climate could affect the longevity of this and other sea turtle populations around the world", Jensen said.
The findings show that the northern population of turtles have been producing primarily females for more than 20 years.
The "pivotal temperature" that creates a 50/50 split of male and female can be passed down from parent to offspring. One population breeds at the southern end and the other nests in the Far North, mostly at Raine Island and Moulter Cay.
The transformation has led scientists to be concerned about the species' future - with just 0.2 per cent of the turtles being male in some areas.
Unlike most animals, genetics don't determine the sex of sea turtles.
David Owens, a professor emeritus from the College of Charleston in SC, was not involved in the new study but said he has dreamed of doing such research for years.
The gender shift has been noticed before by people who study hatchlings, said Jeanette Wyneken, a sea-turtle expert and professor at Florida Atlantic University, who was not involved in the new research.
Green sea turtles are not the only creature to be affected like this.
"Is this species liable to go extinct? Common sense tells you: One male and a hundred females ― that's going to be a very exhausted boy".
For the study, scientists collected blood and skin samples from two genetically distinct populations of green sea turtles, which allowed them to figure out individual sex, in addition to where they were born. It is not a trend backed up by real-world data.
Finding that there are next to no males among young northern green turtles should ring alarm bells, but all is not lost for this important population.
If we don't actively combat climate change, we may lose green sea turtles forever.
The turtles play a crucial role in keeping their habitat healthy. At its worst, it could lead to the collapse of entire fisheries.
Wyneken agrees. "If nothing changes, then it's going to be a problem", she says. The reason, according to the study's authors, has everything to do with rising temperatures.
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