15 June 2021


By Caitlin Smith, Marine Species Conservation Officer, WWF-Australia

Climate change is causing the “feminisation” of green turtle populations in Far North Queensland. This is because the sex of a sea turtle is determined by the temperature of sand incubating the eggs. Warmer temperatures, of 29.1 degrees Celsius and above, produce females, and cooler temperatures produce males.

WWF-Australia and the University of Queensland scientists supported by furniture company Koala are investigating simple but effective ways to cool sand temperatures and re-establish more natural gender numbers of offspring - potentially reversing the man drought experienced by the species.

WWF-Australia’s Marine Species Conservation Project Officer, Caitlin Smith takes us behind the scenes of the Turtle Cooling research project on Heron Island. 

Turtle cooling project - relocating eggs
Turtle cooling project - relocating eggs © WWF-Australia

In December 2020, we set up an experiment to determine if seawater could lower sand temperatures. We collected 16 clutches of eggs from 16 nesting green turtles and moved them into experimental tests that we dug ourselves. During our time on Heron Island, the sand was so dry due to the lack of rain. This meant we had to use buckets with the bottom cut out to hold the sand in place as we relocated the eggs to our experiment site, otherwise the sand kept collapsing. It was somewhat like a reverse sand castle! The dry sand is an enormous issue to overcome, and not just for us researchers. Nesting females have to come back night after night trying to dig egg chambers that keep collapsing due to the lack of rain. They will do this until they are either successful or they can no longer expend energy and expel their eggs into the ocean. Therefore, climate change and lack of rainfall not only affects incubating eggs, but the nesting female’s capacity to even lay them. 

Once the bucket had done its job of securing the sand, it was removed and the eggs were approximately 70cm below the surface of the sand. These clutches were then irrigated almost a month later with seawater to lower sand temperatures at nest depth. 

Larissa Young working on the Turtle Cooling Project
Larissa Young working on the Turtle Cooling Project © WWF-Australia

Fieldwork is not always as glamorous as you’d think. Working in the tropics, means tropical storms. It’s rather hard to hold an umbrella and relocate eggs, so unfortunately, if it rains, we still need to go out and get the work done. Luckily, we work with some amazingly positive people and even rain can’t put a dampener on our day. 

Larissa Young and Caitlin Smith - researchers on Turtle Cooling Project, Heron Island
Larissa Young and Caitlin Smith - researchers on Turtle Cooling Project, Heron Island © WWF-Australia

Larissa and I (Caitlin) are collecting hatchlings to bring back to the Heron Island Research Station lab to sample. Our experiment site is on the far eastern side of Heron Island nicknamed ‘Shark Bay’ due to the large presence of reef sharks and stingrays. Here, we built a fortress made of logs and sticks (as you can see behind me) to protect our incubating clutches from other nesting green turtles as they often dig up other eggs in an attempt to lay their own. We’ve had a few cheeky females break through our fortress this season, but fortunately they didn’t uncover any of our clutches. Our sampling technique will be able to tell us whether the hatchling Larissa is holding is male or female. 

Hatchlings from Turtle Cooling Project
Hatchlings from turtle cooling project © WWF-Australia

These green turtle hatchlings just emerged from their nest and are being transported back to Heron Island Research Station to have a small blood sample taken to determine the sex ratio of the clutch. From this we can see if our method of irrigating the nest to cool the sand temperature was successful in producing more males, compared to our control clutches that were not irrigated and were subject to natural conditions. In this picture you can really see their sharp little nose, called a caruncle. 

Chris Hof, Turtle Cooling Project
Chris Hof, Turtle Cooling Project © WWF-Australia

Did you know that before 2020, the only way that you could tell the sex of a marine turtle hatchling was to euthanise them and look at their gonads under a microscope? In this experiment, we’re testing whether seawater irrigation can lower sand temperatures to produce male hatchlings. Within this we’re validating a method that doesn’t require the euthanisation of hatchlings, and instead uses a small blood sample. Here I am taking the blood sample from the hatchling’s neck. This does not hurt the turtle and is a very quick process. We use syringes that are similar to daily insulin injections. 

Heron Island - home of Turtle Cooling project
Heron Island - home of Turtle Cooling project © WWF-Australia

This photo is taken from the bar on Heron Island where we like to kick back after a hard day's work of watering nests, sampling hatchlings and digging nests. Here, you can just relax and watch the life of the reef swim by including black tip reef sharks, eagle rays and parrot fish. This is my favourite spot on the island because of the way the sunlight reflects off the crystal blue water. It never gets old! The gantry, pictured on the left, was used to transfer people and cargo before the channel was built. Did you know that Heron Island used to be a turtle soup factory in the 1920s? It sure has come a long way since then, becoming a hot spot for researchers to further the conservation of turtles and many other marine organisms. 

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. Read the project report and watch the video above to learn more about this project.