THESE ISLANDS NEAR AUSTRALIA ARE GIVING HOPE FOR TROPICAL MARINE TURTLES FACING A “MAN DROUGHT”

New research indicates Papua New Guinea’s Conflict Islands are producing balanced sex ratios of green and hawksbill turtle hatchlings– a situation scientists describe as “likely rare in the global context”.

The sex of a turtle embryo is determined by the nest temperature – hotter nests produce more females, while cooler nests produce more males.

Sea turtle populations globally face the threat of “feminisation” due to human-induced climate warming that is increasing sand temperatures at nesting sites.

The new study, published today in the scientific journal Global Change Biology, estimated from long-term climate models that over the past 60 years sand temperatures in the Conflict Islands have increased by about 0.1°C per decade. 

Despite this increase, the average modelled hatchling sex ratio has likely been relatively balanced over this same period (46.2% female +/- 10.7%). But the hatchling sex ratio is expected to increase to become more female biased over the next 80 years (76-87% female).

The balanced sex ratio in the Conflict Islands of Papua New Guinea is “starkly different” to Queensland’s Raine Island – the largest green turtle rookery in the world. For several decades, the sex ratio of Raine Island’s green turtle hatchlings has been more than 99% female.

“Nesting locations that are still producing balanced hatchling sex ratios are likely very scarce. Importantly, nesting sites like the Conflict Islands that continue to generate significant numbers of male hatchlings may be critical to the survival of future populations both in the Coral Sea and globally,” said lead author, University of Queensland PhD candidate, Melissa Staines.

The Conflict Islands and Raine Island are similar distances from the equator so why is the hatchling sex ratio so different?

“Many factors can influence sand temperature such as rainfall, beach orientation and shade from vegetation, and we made some novel approaches to accounting for these factors in our analyses,” said Ms Staines.

“The reason for cooler sand temperatures within the Conflict Islands is likely due to high rainfall and the dense tropical forest that fringes the dunes where the turtles lay their eggs, meaning natural nests are shaded for most of the day. In contrast, Raine Island has no trees, so all nests are exposed to full sun every day,” she said.

Hayley Versace, a co-author and manager at Conflict Islands Conservation Initiative said: “Through this research, we found no immediate threat that climate warming will lead to extreme feminisation of the green and hawksbill turtle populations nesting in the Conflict Islands."

"This was an important step in better understanding the threats facing these beautiful and near-pristine islands of remote Papua New Guinea. Our conservation efforts can be focused on more immediate threats such as sea level rise and the take of eggs and turtles."

“The need for constant monitoring and protection of these islands and turtles has importance on a global scale," said Ms Versace.

The Conflict Islands research is part of the Turtle Cooling Project, which is investigating ways to cool sand temperatures and re-establish more natural gender numbers of offspring where needed.

Including the Conflict Islands, sand temperature data loggers and weather stations have been deployed at important nesting beaches for green and hawksbill turtles across a number of Asia Pacific sites.

Deakin University researchers are providing in-kind support for analyses and overall project design for data collection at these nesting beaches.

The Turtle Cooling Project is a partnership between the World Wide Fund for Nature-Australia, The University of Queensland, and the Conflict Islands Conservation Initiative with funding support from furniture company Koala.

Already, the Project has shown that a one-off application of sea water can produce a short-term drop in nest temperature by 2°C, enough to generate more male hatchlings. 

Those findings were published last month in leading ecological journal Marine Ecology Progress Series, with support from the James Fairfax Foundation and Koala.

Unlike freshwater, sea water is abundant at all nesting sites and sea water irrigation may be a strategy for turtle rookeries facing extreme feminisation.  

WWF-Australia is leading the Turtle Cooling Project because to regenerate nature by 2030, and ensure no future extinctions, innovative interventions to help our species adapt to warming will be increasingly needed.

For more on the Turtle Cooling Project go to:  https://wwf.org.au/what-we-do/species/green-turtle/green-turtles-and-climate-change/