Milman Island is an uninhabited, picturesque sandy quay in the northern Great Barrier Reef. It’s one of the largest nesting sites for hawksbill turtles and is also home to green turtles, which is why WWF-Australia and our partners Koala, University of Queensland, the Queensland Department of Environment and Science, and the Sea Turtle Foundation have been working here to trial methods to cool nest temperatures to combat the effects of climate change.
I had the opportunity to visit Milman Island twice - first to document the nesting process and secondly to see the hatchlings emerge. This is what we got up to...
A very long journey
Milman Island isn’t the easiest place to get to. From Sydney, we flew into Cairns and then to Horn Island. From there, we took a three hour (100km) boat ride to reach Milman Island’s sandy shores. As Milman is an uninhabited island we had everything in tow - tents, sleeping bags (which were completely unnecessary in 38 °C weather), mattresses, wetsuits and emergency snacks. Thankfully our research team already on the island was equipped for a three-month stay and had plenty of (canned) food awaiting our arrival.
Midnight turtle patrol
Field work is hard work! Don’t let the white, sandy beaches fool you. Milman Island, with its 36 °C days and 80 per cent humidity, doesn’t ease up all that much at night. And night time is when the bulk of the work happens. Turtle nesting depends on the tides, which during our visit meant around 8 pm to 2 am! Each night we headed out to patrol the beach, armed with plenty of mosquito repellent, head torches, walkie-talkies and clipboards for collecting data. We patrolled different sections of island to find nesting green and hawksbill turtles. Turtles are very fussy nesters. They emerge from the ocean and make their way up dunes or under trees to begin nesting. They then begin ‘body-pitting’ by excavating the area with their rear flippers. Green turtles will sometimes body-pit several times before deciding on a place to nest. After body-pitting, then they dig downward to build their egg chamber and deposit their eggs. On average sea turtles will lay a clutch of 120 eggs. Once finished, they then cover their eggs and return to the ocean. Field work requires great patience. This whole process can take hours. Thankfully, there are lots of turtles at different stages of nesting up and down the beach to check on.
Once the turtles finish nesting, the researchers carefully relocate eggs to the experimental nests (pictured above in daylight). Here, they were cooled with either shade cloth or palm fronds, shaded under a tree or irrigated with seawater or rainwater. More on these results shortly...
Before moving the eggs into the experimental nests, we documented the number of eggs in each clutch and their weight. Green turtles can weigh up to 150 kg and their eggs look like a large ping-pong ball, weighing roughly 50 grams. Hawksbill turtles grow to a maximum of 80 kg so their eggs were smaller and averaged 25 grams each. After recording the data we helped dig new nests. For green turtles, nests must be 65 cm deep while hawksbill nests are 55 cm deep. Both have a bowl-like base. Eggs are carefully placed into the new nest along with a data logger to record temperatures and then covered up with sand.
Welcome to the world!
On my second visit to Milman Island, things were a little different. Returning six weeks after the first visit, it was now time for the turtles to hatch from the experiment nests. The hatchlings have incredible intuition. They emerged from their deep, sandy nests and confidently made their way to the ocean as if they had done this a million times - and indeed sea turtles are an evolved group of reptiles that have existed on Earth and travelled our seas for the last 100 million years, so this is second nature to them.
The need for speed
Before the hatchlings could begin their journey to the ocean, the researchers put the hatchlings through a series of speed tests. The hatchlings were placed on an almost three-metre guttering and the time it takes to run from one end to the other was recorded. The same was done for their swimming speed. The hatchlings were also placed on their backs and their speed for ‘self-righting’ themselves or flipping themselves back over was recorded. The hatchlings were put through these speed tests as they need peak performance once they break the sand. Their journey to the ocean and beyond is rife with predators and other threats. The faster and more agile they are, the better their chance of survival. Our researchers hypothesise that hatchlings in cooler nests will be much more energetic and faster than hatchlings exposed to direct sunlight, who they predict will be more lethargic.
The journey to the ocean
A turtle’s entry into the world is a bit of a baptism by fire. Born buried alive, they must dig their way out a deep sandy nest. They start running for their life moments after it begins, evading predators as they make a dash from the nest to the ocean. If they make it that far, they then face threats lurking in the oceans which are ever-present throughout adulthood. It’s no easy ride. Now the threat of climate change and feminisation is also facing sea turtles. Thankfully projects like this have the potential to help decimated sea turtle populations recover...
The results are in!
And on that note, finally, the results are in! After the hatchlings emerged the researchers began the process of analysing the data to determine how many of the hatchlings from the experimental nests, compared to the nests exposed to sunlight were male and how many were female. Natural palm fronds and artificial shade have been found to be most successful in cooling turtle nest and producing males. Cooler nests also produce more energetic hatchlings. This is really important. As we’ve seen, hatchlings need peak performance upon emerging from their nest, and to avoid predators as they dash to the ocean. Now, armed with the knowledge of which shading solution is most efficient, we will be rolling these methods out in other nesting sights including Raine Island, the biggest green turtle rookery in the world.
Learn more about the turtle cooling project and results.