Known less for their pretty faces and more for their ability to invade millions of square kilometres of Australia, the cane toad has prompted researchers to figure out ways to stop them in their tracks.
Credit: AFP
SYDNEY: Fencing off dams or replacing open water storages with enclosed tanks could reduce the cane toad population and stop them from invading arid Australia, researchers have reported.
Flooding rains are helping cane toads invade Australia’s desert regions, and thousands of dams made for livestock provide toads with a refuge in the normally parched landscape. This has allowed the introduced pests to colonise areas where they would otherwise perish due to scarcity of water.
“Our research looks to exploit the toads’ thirst for water as a way to stop it from spreading, and suggests fencing or controlling access to permanent sources of water in semi-arid areas of Northern Australia could reduce the final range of the cane toad in Australia by 38%,” said lead author Mike Letnic from the School of Natural Sciences at the University of Western Sydney.
Strongholds near water sources
Since their introduction to Australia in 1935, cane toads (Bufo marinus) have colonised millions of square kilometres. Concerted and costly efforts to control cane toads - particularly over the last three decades – have failed.
“They have caused strong population declines of some of Australia's endangered small mammals, a population crash in freshwater crocodile numbers by up to 70% in some of Australia's northern rivers and have caused extensive population declines in snakes and our big predatory native lizards, the goannas,” said one of the researchers Tim Dempster from the University of Melbourne.
Like a bushfire that spots ahead of the fire front, cane toads establish strongholds around permanent water sources, like dams. While this has helped toads spread far, it's also a weakness the researchers believe can be exploited - literally stopping them dead in their tracks.
All fenced-off toads died
The team experimented with cane toads which were placed near nine artificial water points during the dry season in the Victoria River District of the Northern Territory, publishing their findings in Proceedings of the Royal Society B: Biological Sciences.
Some of the water points were unfenced but others were surrounded by cloth netting 60 cm high that also extended along the ground to stop the large toads from burrowing underneath. The netting was secured by wire and metal posts at least two metres from the water's edge.
All 21 toads placed near fenced-off water points died, and most of them expired within 12 hours. Of the 20 toads with unfettered access to water, all survived except for one, which was killed by a predatory bird.
Removing the stepping stones
"The introduced cane toads require constant access to surface water and do not have the physiological adaptations of many native frogs which allow these species to survive the long dry season of Northern Australia," said Letnic.
“Basically, step by step, toads use these water points to invade the dryer regions of Australia. By stopping toads from using these water points, we are removing their 'stepping stones' in the landscape,” said Dempster.
“If we remove enough of these stepping stones so that they cannot make it between them, we can halt further invasion.”
Costly, but not disruptive solution
Changing the way water is stored will be costly, but not incompatible with running cattle in the outback, according to Letnic.
"Livestock will continue to drink from troughs - as they do now - but the water storage would no longer be accessible to toads. Our research also shows native animals will not be adversely affected by the changes,” he said.
“The trial fences did not prevent large native animals from accessing the dams and all animals indigenous to Northern Australia have evolved to survive the dry season without artificial water sources," said Letnic.
According to the researchers, it’s probably too late to completely eradicate cane toads in Australia, especially in the wet tropics and warm eastern seaboard. But they said their research demonstrates that there is an opportunity to stop toads pushing into biologically diverse and relatively untouched semi-arid regions.
With the University of Western Sydney
