Marine Species Project Manager
In early 2019 we travelled to Milman Island to commence an innovative trial on methods to cool turtle nests. The sex of a turtle is determined by the temperature of the sand incubating its eggs. Hotter temperatures produce females, while cooler temperatures produce males. Rising temperatures due to climate change has upset the natural gender balance, and it’s possible in the future that sea turtles will be completely female.
Six weeks later, we returned to the island to see our hatchlings emerge and then our researchers began the lengthy process of analysing the data from the nests. Now, the results from the trials are in! Let’s dive into what all this means...
Shade and irrigation is the solution
During our first visit to Milman Island researchers tested various methods to cool the sand with the hopes of producing more males. The sand temperature of nests dictates the sex of hatchlings, with hotter temperatures producing mostly females.
Researchers tested cooling nests by covering them with palm fronds, man-made artificial shade cloth, seawater, and tree shade. The aim was to see which cooling method would produce the most males and help re-establish a more even gender ratio?
And the winner is… palm fronds and artificial shading, combined with rain, were the most successful in cooling nests and producing more male hatchlings!
The data shows that these two methods, with rain, produced more than 80% male turtles — a huge and exciting win for conservation and will help us be able to ensure balanced populations of turtles in the future.
The need for speed
After our turtles hatched, our researchers put them through a series of performance tests to examine their speed and agility. Hatchlings need peak performance when they emerge from their sandy nests. Their journey from nest to ocean and beyond is a gauntlet fraught with challenges and threats. Sea birds and crabs await to pick them off the beach, and once in the water other predators lurk — not to mention the addition of man-made threats like fishing nets and plastic.
The faster and more agile the turtle, the better their chances of survival. Science tells us that only 1 in 1,000 hatchlings survive. So, if they’re unable to run down the beach fast enough or evade predators, sadly they won’t be able to contribute to a population already in decline. That’s why we want to find cooling methods that produce the most energetic hatchlings.
Scientists tested the hatchlings’ running and swimming speed, as well as their ability to ‘self-right’. This involved placing the turtle on its back and timing how long it took them to flip over.
With all the data quickly collected, the turtles were then released to make their journey to the water. In the meantime, scientists retrieved data loggers which were placed in the turtle nests and began the long process of analysing all their data to see what solution worked best.
What the results mean
After months of analysis, our researchers found that palm fronds and artificial shading, combined with rain, were the most successful in cooling the nests and producing more males. In addition, hatchlings from these nests were faster and more active, which means they had a greater chance of surviving their first 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.
Natural rainfall actually proved to be the most effective way of reducing nest temperatures and producing more male hatchlings. However, with climate change affecting the frequency and intensity of these important rainfall events, this cannot be relied on to re-establish natural gender ratios and interventions like palm fronds, artificial shading and irrigation are now needed to guarantee the future of sea turtles.
Research like this is really important and provides us with the most effective techniques and scalable solutions that we can roll out to other locations and hopefully recover sea turtle populations.
WWF-Australia and its partners will launch phase two of the project this November. In phase two we hope to gain greater insights including, how many males we need, the window of time where temperature determines gender, and when and where these interventions are needed most.
Stay tuned to find out what comes next!
View the full report here.
Learn more about the turtle cooling project.
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