Marine turtles’ male drought has scientists seriously concerned about risk of population decline

You may have heard of the “man drought” in Australia, but in the animal world it’s becoming an existential threat.

Turtles are facing a male drought of their own, as hotter sand temperatures, due to climate change, produce far more female hatchlings than males.

And it has scientists seriously concerned.

“In certain places, where the temperatures have risen quite considerably in recent years, it’s estimated that over 95 per cent of the hatchlings being born on beaches are female,” said Monash University PhD candidate David Adams.

Life is already tough for these marine creatures.

Only one in 1,000 hatchlings make it to adulthood. Now climate change is making it even harder for the turtle population.

Turtles have what is called temperature-dependent sex determination (TDSD), so the warmer the sand, the more likely feminisation occurs.

“It’s a fair bet that if you have 100 times as many females, it could come to the point where there are so few males available that we start to see the population begin to decline,” Mr Adams said.

The researcher has spent the past three months on Heron Island, a breeding ground for green turtles and endangered loggerheads off the central Queensland coast.

His pilot study is building on previous Australian research that found a single application of seawater could make a difference. 

“They had good results, so my study is an investigation into whether it can be scaled up to include nests that are irrigated more often and at different intervals,” Mr Adams said.

It has been a labour-intensive endeavour.

Each night and into the dawn, Mr Adams – armed with a bucket – has walked the coral cay’s perimeter multiple times, searching for signs of nesting turtles. 

As soon as he spots the newly laid eggs, he collects them and the surrounding sand and moves them to his experiment site.

“I like to keep as much of the sand that’s been … soaked with [birthing] fluid in the nest when I relocate them, because we don’t know what that fluid does,” he said.

In each hatchery plot — a series of wooden, rectangular frames at the top of a sand dune — he has relocated 10 nests and left enough space between each, so they won’t interact with each other.

The number of eggs varies. One nest has only 33 eggs, but one moonlit evening, Mr Adams hit the jackpot when he found a nest with 150 eggs.

Once the nests are set up, Mr Adams measures the amount of oxygen and water surrounding the eggs to find what impact seawater would have on them.

“With turtle rookeries anywhere in the world, in general, there isn’t a lot of fresh water available, especially in the quantities that would be needed to irrigate a section of beach that’s full of nests, like Heron Island,” he said.

It is a delicate balance.

Research, Mr Adams said, had found that when eggs were inundated with seawater in the first week, it was bad for them. 

“We’re trying to strike a balance between frequent enough watering to reduce temperature and keep it low enough to create males, but not so much that it’s so moist and salty that the eggs can’t take on water,” he explained.

As part of his research, Mr Adams is studying the embryonic development of the eggs.

Each day, he takes one egg from the nest and places it in the refrigerator, where development halts at that stage.

The incubation period for turtles is between 60 and 70 days, so he will end up with that many eggs.

He extracts the embryo and is able to take a snapshot of their development.

If all goes well, the results from this study could be used on managed beaches around the world to create more males.