How climate change is turning green turtle populations female in the northern Great Barrier Reef

A new study reveals rising temperatures are turning green turtle populations almost completely female in the northern Great Barrier Reef. 

More than 200,000 nesting females—one of the largest populations in the world—call the northern Great Barrier Reef home. But this population could eventually crash without more males, according to the study published in Current Biology

How does climate change impact sex?
Because incubation temperature of turtle eggs determines the animal’s sex, a warmer nest results in more females. Increasing temperatures in Queensland’s north, linked to climate change, have led to virtually no male northern green sea turtles being born.

For the study, scientists caught green turtles at the Howick Group of islands where both northern and southern green turtle populations forage in the Great Barrier Reef.  Using a combination of endocrinology and genetic tests, researchers identified the turtles’ sex and nesting origin.

Of green turtles from warmer northern nesting beaches, 99.1% of juveniles, 99.8% of subadults, and 86.8% of adults were female. Turtles from the cooler southern reef nesting beaches showed a more moderate female sex bias (65%–69% female).

Lead author Dr. Michael Jensen, from the National Oceanic and Atmospheric Administration, says northern Great Barrier Reef green turtle nesting beaches have been producing primarily females for more than two decades resulting in “extreme female bias”.

The scientific research was facilitated through the Great Barrier Reef Rivers to Reef to Turtles project, led by WWF-Australia. WWF’s Marine Species Project Manager Christine Hof was also a scientific researcher in the study.  

Great Barrier Reef: On the frontline of climate change
The Great Barrier Reef is one of the world’s richest ocean environments. It’s home to more than 1,500 species of fish, six of the world’s seven species of threatened marine turtles, and more than 30 species of marine mammals. Today, it faces the impact of mass coral bleaching and now a growing threat to its northern green sea turtles.

“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.,” said WWF-Australia CEO Dermot O’Gorman

Scientists and wildlife managers are seeking practical ways to help the turtles. One possibility is a shade cloth erected over key nesting beaches that could help lower nest temperatures to produce more males.

More ambitious climate change targets must also be adopted and enforced in order to save the Great Barrier Reef, its natural treasures and unique wildlife.