Scientists' Salvation for Crocs: 'Food Poisoning'

It's a hard life as a freshwater crocodile in Australia, where death can come with a single bite. "It's not pretty," Georgia Ward-Fear, a Macquarie University conservation scientist who's witnessed crocodiles dying from literal poison, tells NPR. "They go into seizures. And death is fairly quick and probably very painful because it's essentially a massive cardiac arrest." The culprit? Poisonous cane toads, brought to the continent in the 1930s to deal with troublesome sugar cane beetles. They have since grown to a population of 200 million and, during the dry season, converge on the same water sources visited by crocodiles. Within weeks, "we see these mass-mortality events of crocodiles," says Ward-Fear. As a result, some populations of the protected reptiles have fallen by more than 70%.

Remarkably, however, Ward-Fear and colleagues have been able to drastically reduce crocodile mortality rates with a unique teaching method described Wednesday in Proceedings of the Royal Society B. In four gorge systems across Western Australia's northern Kimberley region, they set out dead cane toads that had most of their toxic parts removed but were injected with lithium chloride, a strong salt that induces nausea in crocodiles, per the Guardian. "It's essentially food poisoning," Ward-Fear tells NPR. The unpleasantness is temporary. What isn't temporary is the crocs' aversion to cane toads after tasting an altered one. "It's encoded deep in the brain," as NPR reports.

In the Danguu Geikie gorge, where cane toads had arrived two years earlier, researchers were able to reduce crocodile mortality rates by 95%, "whereas in the nearby control area where we had not done any intervention, the mortalities just kept raging unabated," Ward-Fear tells NPR. In the three other gorges, where cane toads arrived for the first time only after the bait was left, "we saw no mortalities ... which was really exciting," she tells the Guardian. "It was a huge success," she adds, per NPR. Indigenous rangers and wildlife management agencies have already adopted the approach, known as a behavioral intervention. It's "a lot easier to implement and more ethical than culling the invasive species," Ward-Fear tells NPR. (More crocodiles stories.)