In the early 1990s, conservationist and TV personality Steve Irwin and his father Bob discovered a new species of turtle in the Burdekin River catchment in North Queensland.
Irwin’s tortoise, as it was named, is a short-necked, yellowish creature about 30 centimeters long. He can breathe through his cloaca – his buttocks – to stay underwater longer.
This, added to a few other habits, makes it a difficult turtle to spot: while Elseya Irwini was recorded in other waters, no one had seen it in the lower Burdekin River for 25 years.
Now, thanks to the still-young method of eDNA sampling, researchers have been able to confirm that Irwin’s tortoise is still hanging out below Burdekin Falls Dam, which opened in 1987.
“Until this rediscovery, we had no official documentation proving that Irwin’s tortoise was still living in the lower reaches of the Burdekin River, and that river has changed a lot since the construction of the Burdekin Falls Dam,” explains the Professor Damien Burrows, Director of the Center for Tropical Waters and Aquatic Ecosystems Research (TropWATER) at James Cook University, and co-author of a paper outlining the research, published in BMC Ecology and evolution.
“It’s reassuring to know that they still live there.”
Environmental DNA analysis, or eDNA analysis, is the process of finding DNA fragments of a species in a given environment – often water.
The researchers took water samples from the Burdekin, Bowen and Broken River watersheds and tributaries, analyzing each sample for fragments of turtle DNA.
“We sampled 37 sites throughout the watershed for the current survey and had positive detections at 18 of them,” Burrows says.
“eDNA may not be evenly distributed in a given water body, so at each site we take five water samples, each from a slightly different part of the water body or site.”
Although they haven’t seen the turtle in person in much of its historic range, this DNA shows proof that it is there.
“It used to be very difficult to sample Irwin’s tortoise because they only live in places where there are crocodiles or in upland tributaries that are very difficult to access,” Burrows says.
“They don’t easily fall into traps and the water they live in in the Burdekin isn’t clear, so you can’t set up underwater cameras to see them.
“But now with eDNA, all we had to do was take a water sample and analyze their DNA.”
Unfortunately, eDNA cannot give researchers a clear idea of how many species are present or how old they are.
But lead author Dr Cecilia Villacorta-Rath, research fellow at TropWATER, says their presence means the Burdekin Dam hasn’t damaged turtle populations as much as feared.
“We don’t know anything about the demographics of this population, but the fact that we found their eDNA now, despite the construction of the dam in the 1980s, may indicate that adult Irwin’s tortoises are able to survive in these harsh conditions. more turbid water,” says Villacorta-Rath.
This also has implications for the proposed dam construction on Broken River – another Irwin’s turtle hotspot.
“These turtles prefer running, well-oxygenated water,” says Burrows.
“The Broken River and its tributaries have a permanent flow of water and thus provide favorable habitat for the turtle. The water held back is deep and still, so it is not considered good habitat for these turtles.
“To assess the effect of any dam project on the turtle, we need to better understand their distribution and abundance across their range.”
Burrows says eDNA can help with that.
“Now that we have demonstrated that this technique works and is powerful, we intend to use this technique at other sites in the Broken River watershed in the near future. This information will help communities and government make decisions about any dam project. »