Sea turtles have temperature-dependent sex determination (TSD), meaning the sex of an individual turtle is determined by the incubation temperature during embryonic development. That means the temperature surrounding its nesting site on the beach, also known as a rookery. 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.
Of green turtles from warmer northern nesting beaches, 99.1% of juveniles, 99.8% of subadults, and 86.8% of adults were female.
Green sea turtles are considered endangered by the International Union for Conservation of Nature.
A study published today in the journal Current Biology - led by the National Oceanic and Atmospheric Administration (NOAA) in the USA and in conjunction with scientists from Australia - found the group of turtles had primarily produced females for two decades, because of increasing temperatures.
Climate change is causing some troubling new phenomena in the animal kingdom, and is most likely the culprit behind a new study discovering that as much as 99 percent of baby green sea turtles in warm equatorial regions are being born female.
Reseachers have found that nearly entire green sea turtle population living in the northern Great Barrier Reef is now female.
Among adult turtles, 87 percent are female, suggesting there has been a shift in gender ratios during the past few decades. One population breeds at the southern end and the other nests in the Far North, mostly at Raine Island and Moulter Cay.
Sea turtles are the "lawn mowers of the ocean", according to Camryn Allen, an author of the new study and a marine biological researcher with the Joint Institute for Marine and Atmospheric Research - University of Hawaii and located at NOAA in Hawaii.
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The team made this discovery after analyzing hundreds of green turtles (Chelonia mydas) of different ages at their foraging grounds on the Great Barrier Reef. If temperatures continue to rise as a result of climate change, it could lead to a dramatic decline in population.
Researchers warned: "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".
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.
This is extreme - like capital letters extreme, exclamation point extreme. That's so weird, sea turtles. "We won't see the effects of what's happening today for several decades", she said. Common sense tells you: "One male and a hundred females ― that's going to be a very exhausted boy".
"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.
"Sea turtles are sentinels", Allen 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.
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.