A tropical sea breeze blows as a boat zips around the calm, crystal clear waters of North Queensland, but those on board are not here for a holiday.
Key points:
- Marine turtles are under threat from pollution, nest predation, loss of habitat, environmental damage and climate change
- Scientists are trying to establish a snapshot of Queensland’s turtle populations from Moreton Bay to the Torres Strait
- There is evidence of changes in sex ratios, declines in juveniles and changes in nesting beaches
Beneath the surface, a shadow moves. Suddenly there’s a shout and somebody pointing.
The boat turns and a researcher dives into the shallow water, emerging seconds later, turtle held aloft, its flippers slapping.
“They’re born survivors,” says Ian Bell, a Queensland National Parks researcher.
“They were swimming in the oceans before dinosaurs were walking on the land.”
From Moreton Bay near Brisbane, to the waters just south of Papua New Guinea, Dr Bell and a team of scientists and volunteers are gathering data on Queensland’s turtles.
Six out of seven of the world’s marine turtle species live on the Great Barrier Reef, with green, loggerhead and hawksbill some of the most commonly spotted species.
These scientists want to know more about the populations and threats they face and have ramped up research out of concern for their survival.
After their dramatic capture, the turtles are measured, tagged, weighed and some have DNA and food samples taken.
“With industrialised fishing, coastal development, marine pollution, entanglement and ingestion of marine pollution [and] with feral animal predation of their nests, there’s a whole raft of things that have happened to them,” Dr Bell says.
“And now we’ve got this bowling ball of climate change impacts that we know are likely, but we don’t know exactly what it’s going to look like.”
Out on the ocean
The research requires days on the water at each site as well as skilful and not always successful attempts to capture the turtles from boats in all kinds of weather.
It is a lot more effort than collecting data on nesting turtles, which informs a lot of research, but the scientists say these feeding-ground captures provide a huge amount of extra value.
“Foraging grounds are pretty much where turtles spend a large portion of their lives feeding and growing,” says Queensland Parks and Wildlife Service technical officer Julian Wilson.
Dr Bell says research on feeding grounds also allows scientists to measure juveniles, pubescent turtles and adult males, whereas nesting turtle research largely confines data to adult females.
“We needed to know what’s happening over the greater population,” he says.
While the project is still in its early days, Mr Wilson says there are indications of serious issues in turtle populations.
“We’re not seeing as many juvenile or young turtles as what we’d hoped to or what we have seen in the past,” he says.
“It’s very much raw data … but we’re looking at an 85 per cent skew female to male.”
The sex of turtles is determined by the temperature of eggs in the nest, with warmer nests generating more females.
Low hatchling rate in north islands
Dr Bell says researchers are also mapping DNA against nesting grounds, revealing concerning changes in the origins of turtles, including one of the northern-most islands in the Great Barrier Reef, Raine Island, home to the largest green turtle rookery in the world.
“We’re seeing places like Raine Island not contributing to supplying lots of little juvenile turtles to feeding areas, which is a bit of an early warning alarm bell ringing that Raine Island may not be producing the number of hatchlings that it should be,” he says.
He says there appears to be a general decline in northern green turtle genetic stock, especially compared to southern nesting grounds.
“Maybe the flooding, maybe the nests are too hot, we don’t really know what’s causing it, but it just seems to be a low hatchling production from some of our major nesting beaches,” Dr Bell says.
Turtle stomachs flushed
Once back on land, some turtles also undergo a lavage.
This involves flushing a turtle with water and capturing the contents of its stomach in a sieve to send for analysis.
Researchers say this kind of information is invaluable and a good indicator of their health and food availability.
“If there isn’t enough food around, then the girls aren’t going to put on the fat and then they aren’t going to go into breeding condition and then they might defer their nesting for one or two or three or four or five years,” Dr Bell says.
The proportion of sea grass and algae can also indicate how healthy seagrass beds are.
“Over the last 20 years we’ve been monitoring, we’ve noticed these events where you have a coral bleaching event, a lot of the corals die [and] get smothered with a black film, and that smothers the seagrass,” Dr Bell says.
He says this prompts turtles to switch to an algal diet, which also slows their growth and reproductive rates.
“As we look forward, they’re predicting these coral bleaching events to happen more frequently, so what impact is that going to have on turtle life history?” Dr Bell says.
Dr Bell hopes the weeks on the water and countless hours of measurements will mean a better future for these ancient animals.
“We’re trying to get an idea of what the population looks like, so that we can develop policies and conservation strategies that are going to look after them, for our grandchildren,” he says.
“Having done this for 30 years, even now to stand on a nesting beach and watch a turtle come up and a dig a body pit and then an egg chamber and then lay 120 … and then crawl back to the water again, it still amazes me.”