Warming Climate Is Making Almost All Baby Sea Turtles Born Girls

Written by Dana Sanchez
sea turtle
The gender balance of sea turtles is out of whack globally due to climate change. Female hatchlings outnumber males dramatically — bad news for Cape Verde. Sea turtle hatchlings. Photo: Terry Ross/Flickr/Creative Commons

All over the world, the gender balance of sea turtles has been thrown out of whack by climate change, and female hatchlings are expected to outnumber males in increasing proportions.

Scientists blame the rising temperature of beach sand, where momma turtles have been coming ashore for millions of years to dig their nests and deposit their eggs.

The past five years have been the hottest on record. About 10 percent of Earth has warmed more than 3.6 Fahrenheit, according to a Washington Post analysis.

The gender of hatchlings depends on the temperature where they are in the nest, known as the “pivotal temperature,” according to SeeTurtles.org. If the temperature is 83-to-85 degrees Fahrenheit, embryos in a nest develop into a mix of males and females. Temperatures above this range produce females and colder temperatures produce males.

The sea turtle survival rate to adulthood is low at the best of times. When the babies emerge from the nest, they’re preyed on by ghost crabs, birds, raccoons and dogs as they head to the ocean. If they make it, they become food for fish. An estimated one in 1,000 hatchlings will survive to adulthood.

As the earth gets hotter, turtle hatchlings worldwide are expected to skew dangerously female, scientists predict, making the ancient animals an unwitting gauge for the warming climate, Washington Post reported.

The West African island nation of Cape Verde is home to the third-largest nesting loggerhead population in the world. Eighty-four percent of hatchlings are now female, researchers from Britain’s University of Exeter said in a July report. As the Earth gets hotter, sex ratios could reach more than 99-percent female by 2100.

This is bad news for Cape Verde, where the economy is tied to the 30,000 sea turtles that swim there to nest each year. Tourism accounts for 15 percent of Cape Verde economic growth.

Sea turtle populations in Florida and Australia are also showing dramatic sex imbalances, raising fears that these animals, which outlasted dinosaurs, are headed for extinction.

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Female turtles that hatched in Australia before the early 1990s outnumbered males by a ratio of 6 to 1. That’s when the temperature started climbing and the gender chasm in Australia started widening, according to U.S. agency NOAA, the National Oceanic and Atmospheric Administration.

After years of hotter nesting seasons, sea turtles tested in Southern California have gone from 65 percent to 78 percent female, according to a 2015 report.

And hatchlings on Boca Raton beaches are at least 90 percent female these days, according to an estimate by researchers at Florida Atlantic University.

“All over the world, the sea turtle gender balance is being thrown way out of whack,” said Lucy Hawkes, the English ecologist who led the study on Boa Vista, Cape Verde.