AUSTRALIA is considering building an exclusion fence in an effort to stop the northward advance of one of the country鈥檚 most devastating pests, the cane toad.
The fence would be built across the neck of the Cobourg peninsula north-east of Darwin, part of the Gurig national park. No more than 9 kilometres long, it would be dwarfed by the 1600-kilometre rabbit fence erected in Western Australia. But if it keeps the poisonous toads out of the national park, it would be a major achievement, says Delia Lawrie, chair of the Northern Territory鈥檚 environment and sustainable development parliamentary committee. 鈥淚t would make the Cobourg peninsula the only intact biodiverse mainland area in the top end of Australia.鈥�
Cane toads were introduced into Queensland in 1935 and have steadily spread north and west, advancing at a rate of about 30 kilometres a year. In the past few years, they have taken hold in Kakadu national park, one of the few areas of Australia that had been relatively untouched by introduced species. Lawrie reckons if the fence is not built by the end of the year, the toads could easily reach Darwin and the peninsula by the end of the wet season in March.
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Cane toads cannot jump, so the fence would only need to be around 60 centimetres high. But they can burrow, so it would have to penetrate about 30 centimetres into the ground. The National Parks and Wildlife Service would decide the best location for the fence, determining its length and cost. Lawrie accepts that some toads would swim around the fence, or be carried in by cars and people. Monitoring inside the park would be needed to spot and kill intruders.
But Ross Alfred, a biologist at the James Cook University of North Queensland in Townsville, thinks the project is doomed. While a good fence and monitoring programme could minimise the number of toads that make it to the peninsula, the project would be expensive and probably futile. The toads multiply rapidly and have no natural predators; so even if only a few make it across, they will eventually colonise the region, he says.