7 Sept 2019


A combination of shade and irrigation could be a way to cool sea turtle nests enough to produce more male hatchlings, according to research conducted on Milman Island in Queensland’s far north.

It’s calculated that shaded nests, which were additionally cooled by prolonged rain, produced more than 90% male hatchlings, according to temperatures recorded in the nests.

In another boost, hatchlings from the shaded nests moved and swam faster than other hatchlings – increasing their chances of survival.

The nest cooling project is a partnership between The University of Queensland, the Queensland Government, Conflict Island Conservation and the World Wide Fund for Nature-Australia and is supported by Australian furniture company Koala and Sea Turtle Foundation.

It was prompted by fears for the future of sea turtles after research indicated that more than 99% of green turtles being born in the northern Great Barrier Reef are female.

A sea turtle’s sex is determined by the incubation temperature of eggs with higher temperatures producing more females. Scientists say hotter sand, linked to global warming, is causing the decrease in male hatchlings.

The Milman Island trial, conducted in January and February this year, was impacted by the record rainfall that flooded Townsville and was described as a "one-in-1,000 year" event.

“The good news is that the unprecedented rain event has produced much-needed male turtle hatchlings in Queensland’s north. But we can’t rely on freak weather for the survival of the species, we must do further research on how best to help turtles cope with climate change,” said Dr David Booth, School of Biological Sciences, University of Queensland.

The key findings from the Milman Island trial include:

  • Natural palm-frond & artificial shading, combined with rain, were successful in cooling nests and producing more male hatchlings.
  • This implies a combination of irrigation and shaded hatcheries could maximise male hatchling production.
  • Hatchlings from shaded nests were faster and more active, which means they have a greater chance of survival 48 hours after emerging from their nests.
  • Heavy rainfall meant the use of seawater irrigation as a stand-alone nest cooling method could not be properly assessed and more research is needed.

The initial field work on Milman Island has revealed crucial research opportunities for the next stage of the project, which gets underway in November with support from Koala.

“At Koala sustainability and conservation work is embedded in our mission. As a business we want to take the opportunity to support WWF projects to have a positive impact. With our sofas, we wanted to contribute to another animal. The Great Barrier Reef is a national icon that's in a lot of trouble at the moment. So we chose the Reef and the green sea turtle,” said Koala founder Mitch Taylor.

“If we’re going to help turtles survive climate change we need the right information. At Koala we want to contribute to a solution. We hope this research will help nail down the most practical ways to ensure these magnificent creatures continue to enthral us all,” he said.

Melissa Staines, University of Queensland, was project lead for stage one on Milman Island. Next she will try to crack a mystery.

“How many males do we need for a healthy population? Is 10% enough or do we need a lot more than that? Answering that question will give us a target to ensure sea turtles survive a warming planet,” Ms Staines said.

WWF-Australia Marine Species Project Manager Christine Madden Hof said further irrigation trials will focus on mimicking heavy rain.

“The amount of seawater applied on Milman was the equivalent of a shower. We now suspect more seawater needs to be poured on nests to replicate the cooling effect of a heavy downpour,” she said.