Sea level rise threatens island turtle hatchery

Every nest laid at the world's largest green turtle rookery off Queensland could soon be swamped by rising seas, scientists warn.

Raine Island, on the northern tip of the Great Barrier Reef, is world's oldest known sea turtle rookery.

For more than 1000 years, green turtles have been returning to their birthplace to lay their own clutches of eggs in the sand.

But a new study suggests that could change within the next 25 years, as climate change pushes sea levels higher and higher.

Ecologists have modelled what's likely to happen to important turtle breeding grounds around the world, under various climate change scenarios.

Currently the world is on a high-emissions pathway but even under moderate climate change scenarios, Raine Island is predicted to suffer 100 per cent nest flooding.

That's also true for another very important site - Saona Island in the Dominican Republic where protected leatherback, green and hawksbill turtles nest.

Other nesting grounds dotted around the globe are not as badly affected but impacts will still be severe, according to the new modelling published by Spain's University of Cadiz with input from the Queensland government.

The study warned "climate changes might be too rapid for sea turtles to respond through their ability to disperse or colonise new habitats".

It said there is an urgent need to develop conservation plans for the most vulnerable populations while the opportunity remains to save them.

Owen Coffee, a marine ecologist with Queensland's environment department, spent three years working on Raine Island, says the emerging threat has been evident for some time.

Millions of dollars have already been spent on the island's ongoing recovery project, with one of the primary goals to tackle the issues driving the rookery's declining productivity.

A large chunk of that money was spent moving 40,000 cubic metres of sand from the base of the beach near the water, up and over the highest parts of the beach where nests are often laid.

The re-profiling was about preventing sea water inundation. Turtle embryos need oxygen to develop and prolonged immersion prevents oxygen from entering the porous eggs.

"It approximately doubled ... the habitat, those areas that are now higher than the inundation levels," Dr Coffee said.

"There's a lot more regions on the island where it's possible for a turtle to nest where those nests are not at risk of being inundated."

There's no doubt green turtles - which are listed as vulnerable in Australia but endangered globally - need all the help they can get given climate change is also skewing the gender balance on Raine Island.

"Greater than 95 per cent, I think its closer to 98 per cent, of the hatchlings produced in any given nesting season on Raine are emerging as females," he said.

That's because warmer nests tend to produce females, a problem that has spawned another set of interventions in the form of nest cooling projects on Raine and other reef islands where they lay their eggs.

Dr Coffee said there is no doubt green turtles need human care and attention in the face of climate threats, including inundation.

"The distance between Raine and other suitable habitat is not insignificant," he said.

"And we need to identify what islands are going to be more resilient to that sea level rise if we're going to consider whether the population has the capacity to move, and whether we have the capacity to assist that."

The study has been published in the journal Scientific Reports.