Cane toad barrierCane toads have reached the Kimberley and there is no sign that their march of conquest is finished. Their remorseless advance across the Top End makes it seem they are invincible, but CEED researchers Reid Tingley and Darren Southwell believe that the species has an Achilles heel.

Cane toads are a tough, fast, adaptive species with glands that can secrete a cocktail of toxins lethal to native species. Their one weakness is water. Cane toads can travel across dry landscapes like few other amphibians, but even they cannot survive more than 10 days without water. In very dry regions, their spread may be halted by taking away any permanent water sources. If access to enough water sources in the same area can be removed (e.g., by fencing natural water bodies, or minimising leaks in cattle tanks), the last parts of Australia that the toads haven’t yet reached may be walled off. The result would be a break in the landscape – a moat with no water – that toads can’t cross.

The arid Pilbara region is a perfect place to make this last stand. Only a few hundred kilometres from the edge of the advancing wave of toads is an arid corridor where permanent natural water is almost absent. Artificial water points created for pastoralism, and natural springs, dot the corridor, forming a thin strip of suitable toad habitat along the coast.

CEED researchers published a paper in 2013 proposing such a barrier. Reid Tingley and colleagues combined information on toad biology, rainfall and the location of water points to show that the scheme has a good chance of working. A barrier of only a few hundred water points in the right location could stop the invasion dead in its tracks, and prevent toads from occupying more than 260,000 km2 of Western Australia. This is larger than the area of the whole United Kingdom.

The modelling suggested that creating a waterless barrier could work, and conservation organisations and state governments were interested in the proposal. However, Reid and Darren wanted to ask pastoralists and people who know this region firsthand what they thought of the idea. After all, it’s easy to ‘pretend’ to manage water points on a computer by simply deleting them! So they travelled the entire length of the corridor and got feedback on the idea from every local they could find.

Their road trip ended in a meeting in Broome to speak with people who know the country and the reality of getting things done. A wide range of stakeholder groups attended, including academics, NGOs, indigenous groups, and employees from several state and federal government departments. The workshop and trip generated considerable positive feedback about the idea, but perhaps the most promising aspect of the discussions was the realisation that a waterless barrier might create numerous opportunities for ‘win-win’ situations among environmentalists, pastoralists and indigenous communities. For example, this idea could present an opportunity to improve infrastructure and water usage on pastoral stations, while implementing and monitoring a barrier could provide potential employment opportunities for indigenous ranger groups in the area.

The new information gained at the workshop has changed our understanding of how a barrier would work, and where it should go. However, it hasn’t changed the main conclusions of the study – that a waterless barrier could stop the toad advance dead in its tracks, creating a toad-free reserve in the west. In the next few years CEED researchers will continue to collaborate with managers in Western Australia and the federal government to work towards implementation.

Research theme: Environmental policy and management evaluation (A)

Image: A toad barrier surrounding an earth dam (bore water is pumped from underground), by Michael Letnic. When toad barriers are secured around dams, toads cannot get to the water to drink or breed. This will make crossing the desert virtually impossible, because aside from these dams there are very few natural water sources. Because earth dams are managed by people, toad barriers will be easy to include in current and future dam management practices. Photo: Michael Letnic