Climate Change Turned 99.8% of These Sea Turtle Babies into Girls

A photo provided by the Australian government shows baby sea turtles crawling toward the surf on Raine Island. Credit: Credit: State of Queensland

The climate is changing, and so are the turtles.

A study published yesterday (Jan. 8) in the journal Current Biology about green sea turtles that nest along island beaches near Australia’s Great Barrier Reef found that turtles born in areas most heated by climate change are 99.8 percent female. Turtles born farther south, along a cooler beach, are only about 65 percent female.

The result isn’t surprising if you know a bit about turtle biology, but it is alarming. Sea turtles, like these green sea turtles (Chelonia mydas), don’t have genetically determined sexes, the way mammals do. Instead, the researchers wrote, “In sea turtles, cooler temperatures produce more male hatchlings while warmer temperatures produce more females.”

An egg in hot sand is more likely to produce a female turtle, and an egg in cool sand is more likely to produce a male. [In Photos: Tagging Baby Sea Turtles]

The pivot temperature where a population will turn out 50 percent females and 50 percent males is based on genetics and varies with species and even individual nesting groups, the researchers wrote. Turtles  seem to target their breeding periods to times when the sand is slightly warmer than their pivot temperatures, resulting in populations moderately skewed female. But shift the temperature of that period just a few degrees and the resulting baby turtles will be not just a bit female — instead, hardly a male will appear in the whole group.

Due to climate change, Raine Island — the site of the key breeding ground in this study — has warmed significantly since the 1990s, the researchers wrote, likely accounting for the hard female skew.

This photo shows Raine Island, where the turtles lay their eggs.

Credit: Credit: State of Queensland

So, the researchers developed a new technique: Studying the turtles’ hormones.Proving that the increasing temperatures actually changed the turtle population proved challenging, though. Turtles don’t wear signs of their sex as obviously as humans; researchers can’t tell just by looking between their legs. And the easiest method — cutting them open — isn’t really an ethical way to approach an endangered turtle population.


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