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Climate change is turning some sea turtle populations 99% female

From CBC - January 9, 2018

About 99 in 100 newly hatched turtle babies are female at one of the biggest sea turtle nesting sites in the world and warming temperatures are to blame for the lack of male babies, a new study suggests.

That's because the sex of young sea turtles (and alligators, crocodiles and some other kinds of turtles) is determined by the temperature at which their eggs are incubated, with warmer temperatures producing females, and cooler temperatures producing males.

Because of the role of water temperature in the sex of offspring,scientists have been worried for some time that climate change, which has caused a rapid increase in the average global temperature in recent decades,could push the sex ratios of some populations of those animals to skew female.

A study published Monday in the journal Current Biology shows that's already happening, and has been for about two decades, at nesting sites at Raine Island and Moulter Cay in the northern Great Barrier Reef "such that virtually no male turtles are now being produced from these nesting beaches." That area, off the coast of Australia, has experienced very warmtemperatures, leading to a range of other problems such as deadly coral bleaching.

The researchers expressed concern that in the future, the lack of malescould leave many females unable to find a mate and "eventually impact the overall fertility of females in the population."

Great Barrier Reef nesting area

That's aconcern because the northern Great Barrier Reef is one of the biggest sea turtle nesting areas in the world, where about 200,000 females go to lay their eggs, reported the scientists from the U.S. National Oceanic and Atmospheric Administration Fisheries Department and the Queensland Department of Environment and Heritage Protection.

They made the discoveryafter they caught and examined 400 green sea turtles of various ages feeding off the Howick Group of Islands in the Great Barrier Reef off the coast of Queensland in Australia, studyingwhich were male and which were female. They then used genetic analysis to trace each turtle to the beach where itoriginally hatched, as the turtles almost always return to lay eggs at the beach where they were born. That means their birthplace can be determined using DNA from their maternal lineage.

Among turtles from the southern Great Barrier Reef, about 65 to 69 per cent of turtles were female.

But among those from the northern Great Barrier Reef, 99.1 of juvenile, 99.8 per cent of subadult and 86.8 per cent of adult turtles were female.

Since the 1990s

When the researchers looked at sand temperatures from those beaches, they found the green sea turtle nests in those areas have been incubated above the temperature that produces a balanced sex ratio since the early 1990s. The higher proportion of femalesamong younger turtles shows the problem has been getting worse.

'It bears noticing'

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