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Pouring cool seawater on green turtles鈥� nests may be a simple way to reverse a severe decline in male births that has been linked to global warming.

(Chelonia mydas) that currently hatch on beaches in Australia鈥檚 northern Great Barrier Reef, which is home to one of the largest populations of the turtles in the world, are female.

This is thought to be because rising global temperatures are overheating their nests. The sex of marine turtles is determined by the temperature at which their eggs are incubated, with warmer temperatures producing more females.

鈥淭his extreme feminisation is really concerning because if it continues, and there are very few males left to fertilise the females鈥� eggs, we could see the end of important turtle populations,鈥� says at conservation group WWF Australia.

To try to address this problem, WWF Australia has collaborated with the University of Queensland, the Conflict Islands Conservation Initiative in Papua New Guinea, where there is a similar issue, and other groups to find ways to cool turtle nests down so that enough males are born to sustain the population.

Adult females make nests on beaches by digging a 70-centimetre-deep hole, laying about 100 eggs, then covering them with sand so they can incubate for around 55 days.

The researchers buried temperature loggers in green turtle nests on Heron Island in the southern Great Barrier Reef and Panasesa Island in Papua New Guinea.

They found they could cool the nests by 1.3掳C by pouring 50 litres of seawater onto the sand above using a watering can. The seawater was collected from the shore the day before, allowed to cool overnight, then applied early the next morning.

Previous studies have found that nest temperatures above 28.7掳C (83.7掳F) result in females hatching, but equal males and females develop at 28.1掳C (82.6掳F). That means the small amount of cooling achieved by adding seawater could theoretically be enough to rebalance green turtle populations, says Haskin, who presented the results at the on the country鈥檚 Gold Coast earlier this month.

A separate lab experiment found that a short period of nest cooling 鈥� for about 3 to 7 days 鈥� during the eggs鈥� sex determination period was enough to produce some males.

There were initial concerns that adding seawater to turtle nests would dehydrate the eggs and impair their development, but this turned out not to be the case with the one-off seawater application, says Haskin.

Why climate change is creating more female sea turtles and crocodiles

As the world gets warmer, animals whose sex is determined by temperature are finding cool ways to control their own fate. But can they adapt in time?

at James Cook University in Townsville, Australia, says 鈥渋t is really vital research and I hope that it works鈥�, but 鈥渋t may not be useful as a broad strategy at a beach scale when the clutches in the sand are all at different stages of the incubation cycle鈥�.

Haskin and her colleagues are now speaking to groups that manage important nesting, or rookery, sites in northern Australia to see if they are interested in trialling the cooling procedure on a larger scale.

At the same time, they are using temperature loggers to remotely monitor sand temperatures at other major rookeries around the Asia-Pacific region, in order to identify areas at risk of turtle feminisation where nest cooling may be beneficial.

at the University of Western Australia says nest-cooling strategies may also ultimately be needed for other populations of reptiles that have temperature-dependent sex determination, including the tuatara (Sphenodon punctatus), a unique New Zealand species that has the opposite problem of only producing males at higher nest temperatures.