Australia's crocodiles caned by toads

Barbara McMahon, The Guardian 5 Jun 08;

Poisonous cane toads are responsible for the decline of many native animals in Australia, as well as household pets. Now the dreaded pest, which is marching relentlessly across vast swathes of the country, has found a new species of victim.

Freshwater crocodiles are dying in increasing numbers after coming into contact with the venomous amphibians, according to a leading biologist.

Dr Mike Letnic, of the University of Sydney, says the toads are decimating populations of freshwater crocodiles in the hot, tropical, northern part of the country. According to the biologist, scores of reptiles on the Victoria River district of the Northern Territory have died after eating the toads. "One year [2006] we counted more than 600 crocodiles and the next year we counted less than 400," he said.

"We turned up and there were dead crocs everywhere. Some were floating in the water and other carcasses were rotting on the river bank. The only thing that had changed between our first visit and the next was that cane toads had moved through the river system," he said.

Dr Letnic said examination of the crocodile carcasses showed that the reptiles had eaten cane toads. "Crocs don't ask too many questions when they're looking for a meal," he said.

"They snap at anything that moves past, and we think there have been large concentrations of cane toads congregating on the river, so that's created the problem for the crocodiles."

There are approximately 100,000 freshwater crocodiles and 150,000 saltwater crocodiles in northern Australia. Freshwater crocodiles are smaller than "salties". Dr Letnic, who is presenting his research next week at the Australasian Vertebrate Pest conference in Darwin, said the size of freshwater crocodiles makes them vulnerable. "The weight ratio is important," he said. "The crocs that died were quite young and only about a metre or two long whereas cane toads can weigh more than a kilo."

Cane toads were introduced to Australia from South America in 1932 to combat plagues of beetles infesting sugarcane crops. The toads had little effect but bred prolifically and have been an environmental disaster, with their toxin killing native animals such as goannas and quolls. It is estimated there are now 10 cane toads for every person in Australia.