Too hot for turtle guys: Great Barrier Reef is dangerously warm for male green sea turtles

In the largest green sea turtle colony, a lopsided majority of newborn babies are female. Male turtles hatch from just one percent of the eggs around the Great Barrier Reef. Researchers now fear for the survival of the species.

When sea turtles first lay their eggs, it's not initially clear whether male or female young ones will hatch. That's determined by the temperature of their surroundings. The hotter the sand, the higher the probability that babies will be female. From 29.9 degrees Celsius upward, there won't be little turtle boys. And because of global warming, this benchmark is exceeded more and more frequently.

It's difficult to determine a sea turtle's sex. You can only tell for sure once the animal is fully grown - and that takes at least 20 years. That is probably why the surplus of females has gone unnoticed for so long. One way to tell the sexes apart: Male turtles have a longer tail and longer claws.

Now, researchers from the US and Australia have developed a method to determine the sex of green sea turtles via DNA and blood tests while the animals are still young. What they didn't expect is that today already, 90 percent of green sea turtles at the Great Barrier Reef are female.

The small number of males is not the only challenge for green sea turtles. They are only sexually mature at 15, and even then, they only have sex every three years on average. Evolutionary speaking, a small female surplus in populations is nothing out of the ordinary. But the turtles cannot survive entirely without men.

Female sea turtles return to the beach where they hatched to lay their own eggs again and again. On Raine Island's beach, the largest nesting ground for green sea turtles in the Pacific, you can find up to 18,000 animals during high season. After the eggs have been warmed by sun and sand long enough, the babies hatch, make their way into the sea and only return once it's their time to lay eggs.

Researchers believe there's a lack of male sea turtles across the world. That's why they're examining the effect that rising temperatures have had on green sea turtle populations along the coasts of Hawaii and on the island of Saipan in the western Pacific. The early gender detection method could lead to surprising results there as well.

The results of the Australian study are bad news for other animals as well. Other reptiles, like crocodiles or lizards, also develop their sex due to temperature. With alligators, things work in exactly the opposite way as they do with sea turtles: If it gets too hot, only male babies hatch from their eggs.