Using Environmental DNA to detect a dangerous carnivore

Negative human-wildlife interactions can be better managed by early detection of the wildlife species involved. However, many animals that pose a threat to humans are highly cryptic and detecting their presence before the interaction occurs can be challenging. Here we describe a method whereby the presence of a dangerous animal, the estuarine crocodile (Crocodylus porosus) was detected using traces of DNA shed into the water, known as environmental DNA (eDNA). C. porosus is present in waterways throughout South-East Asia and Oceania and has been responsible for over a thousand attacks upon humans in the past decade. A critical factor in the crocodile's capability to attack humans is their ability to remain hidden in turbid waters for extended periods, ambushing humans that enter the water or undertake activities around the waterline. Using our eDNA technique in an experimental setting, we could correctly discriminate C. porosus from a closely related sympatric species that does not pose a threat to humans, the freshwater crocodile (Crocodylus johnstoni). Further, we could detect the presence of C. porosus within an hour of its entry and up to 72 hours after it exited. We conclude that eDNA could be a valuable tool for reducing human-wildlife conflict through early detection of the species in question.