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Researchers are lacing corpses of the amphibian with nausea-inducing chemicals to train freshwater crocs not to eat them...

Cane toads are poisoning freshwater crocodiles as they continue their march across Western Australia’s Kimberley region. But in Windjana Gorge, ahead of the front, researchers are gearing up to combat a mass mortality event – lacing cane toad corpses with nausea-inducing chemicals in a bid to train native crocs to stay away from the pests.

As the Kimberley’s dry season progresses through September into October, and rivers shrink to pools, “you get this huge density of crocodiles from the whole river system congregating,” Dr Georgia Ward-Fear, Macquarie University ecologist, explains.

Food portions diminish, crocodiles grow hungrier in the heat, and cane toads begin to seek water as well. When cane toads and crocs overlap, “it becomes the perfect storm”.

“You can potentially get mass mortality events of large proportions of the crocodile population, because they are all there and hungry,” Ward says.

To prevent this, Ward is working with native species at risk and refocusing efforts towards impact mitigation.

She leads a study in Windjana Gorge by Macquarie University, the DBCA and Bunuba rangers, in which researchers are gutting the corpses of euthanised cane toads, injecting them with a non-lethal salt compound, and presenting them as bait for freshwater crocodiles. If crocodiles eat the bait, they experience nausea and learn that cane toads are harmful ahead of the invasion front. This is called conditioned taste aversion.

“It is essentially food poisoning,” Ward says.

“Obviously we know we can’t really clean up all the cane toads,” Marr says. Instead, the trial is a way “of getting the native animals to live among them”.

Nicki Mitchell, an associate professor at UWA who is independent to this study, says adapting behaviours of native animals to avoid cane toad toxins in the future “is an excellent initiative”.

“If this can be rolled out at the right scale, top order predators will naturally be less likely to consume the first toad they see,” she says. “Ideally, what it will do is … [allow] ecosystems to function as they should.”