GROWING SEA TURTLES ON THE NORTHERN GREAT BARRIER REEF

By Melissa Staines, BSc Honours student, The University of Queensland and Turtle Cooling Project Lead

Our trip to the northern Great Barrier Reef started 800km south of the tip of the Cape York. We left from Cairns on 4 January 2019 on a cargo ship heading north at 13 knots. We took a cargo ship because we had a three-month venture ahead – which meant three months worth of food, water and equipment. Almost 40 hours after leaving Cairns we arrived at Milman Island, a remote coral sand cay in the northern Great Barrier Reef. Although only about 25km from the mainland of Australia, the closest township, Horn Island, is a three-hour boat ride north, in good weather conditions.

One of the most fascinating features about Milman Island is that unlike many of the larger turtle rookeries on the northern Great Barrier Reef, it has a dense rainforest. This means the majority of the hawksbills and green turtles that nest there lay their clutches under the shade of a dense canopy. This keeps the nest temperatures cool and potentially produces more male hatchlings. Sadly, in other parts of the northern Great Barrier Reef male green turtles are disappearing as a result of rising sand temperatures.

Vegetated islands like Milman Island, may very likely be the most important male-producing islands for the northern Great Barrier Reef green turtle population and the South Pacific population of hawksbills. Here on Milman Island we are trialling methods to shade green and hawksbill turtle nests. The aim of the project is to re-establish more natural numbers of male and female offspring and find methods that can be rolled out to other more remote locations where feminisation is known to be occurring, like Raine Island.

Turtle tracks on Milman Island © Melissa Staines 

In the northern Great Barrier Reef, soaring temperatures can not only be lethal to incubating clutches but also to us as researchers on the island. We found it very difficult to avoid the humidity and stay hydrated. During the hottest part of the day we sought out shade and a breezy area to sleep. Early mornings, evenings and nights were spent working, and we wouldn’t get to bed until 2 am on the good tides. Sleep deprivation was a very real scenario that hit in the first three days.

My day wouldn’t really start until 3:30 pm. This was when the sun started to lose its sting and we could work on the hatcheries or create experiment plots to relocate the turtle nests. It took us several days to find enough timber for the hatchery, and then several more to put it all together and attach the palm fronds and artificial shade cloth. After some afternoon DIY, we’d cook up dinner. Potato curries and puttanesca became a real crowd favourite (for most). As we’d run out of fresh veggies by day six, most of what we ate came from cans. Each night we’d sit out on the beach and watch the sunset. It was pretty much the only time of the day when you weren’t sweating your entire weight in water or covered head-to-toe in mosquitoes.

Between 5 pm and 7 pm is when we would carry out our routine of watering the sea turtle nests. Six green and six hawksbill nests were irrigated each day with eight litres (~ 21mm per day) of seawater taken straight from the ocean and showered over the nests with watering cans. The idea behind this method is that by watering the nests in the first 35 days of incubation, we were reducing the sand temperature above the nest, thereby keeping the temperature inside the nest lower than 29°C (a male producing temperature). By doing this we hope to grow little male sea turtle hatchlings instead of females - which would most likely be produced in control nests left in the sun. Even in the rain, the nests still had to be watered. When this happened, sometimes it felt a bit fruitless but consistency is key for this experiment.

Melissa irrigating turtle nests with seawater © WWF-Australia / Veronica Joseph

After dinner and watering the nests, it was time to get ready to go out onto the beach for monitoring. Sea turtles typically nest within the first four to six hours after nightfall and two hours either side of high tide. For several nights the high tide was luckily enough to be between 6-9 pm which is when we had the highest density of turtles nesting on the beach.

High tide makes it a bit easier for turtles to get up into the dunes, and the majority of the island is actually inaccessible during low tide. Before I went out each night, I’d first program the data loggers for the clutches that I wanted to relocate into the experiment nests that night. Then I’d pack my kit bag with equipment – measuring tape, data sheets, flipper tags, tag applicators, GPS, pliers, flagging tape and nest pegs. Once I was dressed into my insect-proof(ish) clothes and made sure both head torches were fully charged, it was time to head out onto the beach.

Melissa monitoring a hawksbill turtle ©Melissa Staines

A typical night for me involved walking laps of the island with buckets of eggs. Normally I wouldn’t have to travel any further than a kilometre, since we had turtle nestings in almost every sector of the island and lots of volunteers to help bring the eggs back. To me, every turtle had her own personality and tolerance. Most turtles (particularly hawksbills) were quite comfortable with researchers working around them while they’re laying, but quite often you can tell if a turtle was more timid by her nesting behaviour. Of course, the biggest difficulty with sea turtle monitoring is that the majority of the time you’re in complete darkness and it takes a lot of experience to be able to recognise by listening for what stage of the nesting process the turtle is in. The early stages of emerging, body pitting and egg chambering is the most sensitive period for the turtle, as she’s very aware of her surroundings and any sudden movements or changes in lighting can trigger her to stop nesting and crawl back into the ocean.

Relocating eggs added a whole other level of difficulty to monitoring turtles. Since we don’t want to disturb the turtles while laying, we found that catching the eggs as they fell into the chamber meant we could relocate clutches faster. Most nights I was able to relocate 4-7 clutches with the help of the other researchers. The whole process of relocating is very intensive – eggs cannot be rotated after two hours as the embryos are fragile and can rupture from sudden motion changes. The last step in the relocation process is to build the new nest hole. This is extremely important, as it determines if the eggs will survive. Nests must be deep enough that the entire clutch can fit and be protected from the sun’s heat. The largest clutch that we relocated had 216 eggs from a single female hawksbill (the average is around 120 eggs).

Melissa holding the eggs of a hawksbill (left) and green (right) turtle ©Melissa Staines

By 2 am it was time for bed. If there was to be a high tide around sunrise, then another researcher would wake up at 4:30 am to try and find any turtles making their way back after nesting. One morning, I came across the largest green turtle I’d ever seen. She had made a 3x3m ‘crater’ body pit and was just hind-flipper filling – meaning that she would’ve just finished laying within the last 5-10 minutes. Our timing couldn’t have been better. Her carapace (shell) was a mammoth 113cm and her flippers were almost as long as my leg. She also laid 120 eggs (what an egg machine). When we weighed her, she was a staggering 165kg of pure muscle, bone and fat. By the time she was heading back to the ocean, the sun had risen and she dived straight into the crystal blue water of the northern Great Barrier Reef.

In the final days of our first leg of the trip, we’d heard news from correspondence over the satellite phone that a tropical low was crossing over the Cape and that in a few days there was the potential of it forming a cyclone. When the day arrived for us to head home, the winds were absolutely howling from the north. At 3 pm, we heard the sound of the charter boat cracking through the waves. The boat was delivering a second team to continue turtle monitoring. As we spoke to the skipper over the VHF radio, his boat (although big) was being rolled in six foot waves. I swallowed my tongue… four hours of hellish northerly winds and we were going to have to go straight through it. Once we were on board, there was a full safety induction before we began our journey. Thud after thud, the boat was body slamming the ocean. At one point my bag flew a metre up into the air. Cringing at the thought that my laptop being smashed and broken, I was gripping the post of the boat so tight that my knuckles turned white. Making wraps for lunch on board was like watching toddlers eat – coleslaw and cheese was being thrown everywhere! When we got closer to the mainland, the water was light blue and shallow and the swell died down.

The best feeling that night was sinking into a good pub dinner, an ice cold drink and the cosiest hotel bed. You really learn to appreciate a freshwater shower and toilet facilities when you’re deprived of them for three weeks on an uninhabited island. I’ll be interested to see how much I look like Tom Hanks after five weeks of playing Castaway when returning to Milman island in late February and March to continue the project. The other thing I have to figure out is how to get an ice machine on the island – I think that would really boost my motivation to get some data entry done in the middle of the day in 90% humidity.

Learn more about the Turtle Cooling Project.