Australia is facing a growing crocodile problem. In the last two decades, attacks have increased dramatically following a population boom. While authorities are stepping up safety messaging and increasing the number of permitted crocodile kills, experts are skeptical about the effectiveness of these measures due to the highly mobile nature of crocodiles. One killed, another will swiftly take its place. However, a groundbreaking approach is emerging, offering a stealthy way to prevent attacks. This new technology leverages the genetic fingerprints of crocodiles, allowing for the identification of areas where these predators lurk.
Harnessing the power of environmental DNA (eDNA), wildlife officials will be able to test waterways and alert swimmers, boaters, and campers to avoid areas where crocodiles are present or have recently been. The crocodile problem is a bittersweet consequence of a conservation success story. In the early 20th century, overhunting drove the Australian crocodile population to a mere 3,000. Thankfully, protection measures introduced in the 1970s resulted in a remarkable population surge, reaching an estimated 100,000 crocodiles inhabiting waterways across the country. This population explosion, however, has unfortunately led to an increase in both crocodile attacks and retaliatory attacks by humans.
The most recent incident, on August 3, saw 40-year-old David Hogbin succumb to a 16-foot-long saltwater crocodile (Crocodylus porosus) in the Annan River of Queensland. The crocodile was later killed by wildlife officials. In 2023, a 13-foot crocodile was found beheaded on a beach, and a few months later, a 40-year-old female crocodile was also discovered dead, having been butchered with only her head and spine remaining. These acts highlight the escalating tension between humans and these apex predators.
One major challenge in avoiding crocodile attacks is their ability to be the ultimate ambush predators. These creatures can lie completely still underwater for up to eight hours, waiting patiently for unsuspecting prey to pass by before striking. From the surface, the water may appear devoid of crocodiles, but the Northern Territory Government advises assuming their presence in all waterways. This is where the groundbreaking eDNA technology comes into play. Researchers are developing tests that will reveal the presence of crocodiles without ever needing to see them.
Elise Furlan, a molecular ecologist with the University of Canberra (UC) who leads this program, explains, “Environmental DNA (eDNA) relies on detecting trace amounts of DNA that all living organisms leave behind…things like hair, skin cells, feces, or urine.” To test for eDNA, the team collects water samples and filters them. In the lab, they extract any detectable DNA, amplify it, and search for evidence of crocodile DNA. To ensure accuracy, the team tested eDNA in water from crocodile-holding ponds at a Queensland Department of Environment, Science and Innovation (DESI) facility and compared the results with water that had never housed crocodiles. They then removed the crocodiles from the pond and tested the water to determine how quickly the DNA degrades. This experiment will reveal how long a crocodile needs to be in a body of water for the tests to detect its presence and how long its traces remain after it leaves the area.
While the program is still in its early stages, with current samples needing lab analysis, the researchers are optimistic about developing a real-time spot test to detect crocodiles. Although the tests are not 100% accurate and may produce false negatives, they offer a significant improvement over traditional detection methods. The hope is that eDNA tests will be used in conjunction with other attack-prevention measures, such as public safety messaging. The team plans to sample rivers and other water bodies in Queensland where crocodiles are present to validate the tests’ effectiveness in real-world environments. “This research absolutely has the potential to have a very practical application,” Furlan concludes.
