4 December 2012

The fox and the devil

The waves of extinctions that swept across mainland Australia 100 years ago are poised to strike again, this time on the island wilderness of Tasmania. The fate of dozens of unique animals now depends on the delicate dance of the Tassie devil and the European red fox.
red fox eradication on Tasmania

European red foxes may be on the verge of becoming established irreversibly in Tasmania, and a massive up-scaling of the eradication program is needed to stop the invasion. Credit: iStockphoto

Many Australians were deeply alarmed by the unusual transmissible cancer spreading through populations of the Tasmanian devil. Not only is the iconic devil linked to cinema heroes Errol Flynn and Walt Disney, but it is also a top predator in an ecosystem that includes many species that are either extinct or rare on the mainland. Indeed, the devil was formerly a mainland species, as was the now extinct Tasmanian tiger.

The loss of the devil, a top predator, is likely to have significant flow-on effects through the network of species with which it either competes with or predates upon. The government and research response to the appearance of the facial tumour disease has been swift, focused and impressive with quality science seemingly matched with an educated debate and widespread public support.

As devil populations decline, there has been growing evidence of European red foxes (Vulpes vulpes) on the island – ever since a fox was seen leaving a container ship docked at the port of Burnie, in northwest Tasmania, in 1998. The evidence for foxes now includes more than 2,000 sightings, four road kills, and DNA evidence from predator faecal material and even blood. Evidence points to a series of isolated introductions, but the populations have not yet become fully established.

Foxes represent a major threat to Australia’s last, relatively intact vertebrate communities, yet their presence and the threat they pose is little known outside of the island state, and their eradication a topic of ongoing controversy within the Tasmanian community. Foxes are a top predator in many ecosystems, and the introduction of foxes to the Australian mainland has been linked with the contraction in range of many taxa and the extinction of over 20 species of mammal. Should the fox become established in Tasmania, are some 78 vertebrate species would be at risk, not to mention impacts on agricultural production, so its presence is a matter of grave concern.

The Tasmanian government recognised this threat by establishing the Fox Free Tasmania Taskforce (later to become the Fox Eradication Program) in 2001, and charging it with the responsibility of assessing the extent of the problem and then overseeing the eradication. That program has continued uninterrupted since then, but amid much local public debate and with closure threatened at least once. A quick search for ‘fox’ on blogs and forums, such as the Tasmanian Times, will give you a feel for how such online forums can generate opposition on this topic, much of which revolves around skepticism about even the presence of foxes.

The source of the controversy (and much misunderstanding) concerning the program to eradicate foxes are difficult to isolate, yet the contrast between the early engagement of the academic community around the two problems (devil decline and fox introduction) is stark. I think the difference lies, at least in part, in the nature of the two problems. The first involves clear, definable, biologically interesting questions about a problem that is immediately and clinically obvious. The second, although superficially simple – Where are foxes and how do we kill them? – is much harder to define and study because in this case the animal is rare, highly cryptic and very difficult to detect. While, ecologically, fox eradication represents considerable challenges, it seems at times that dealing with sparse data is more like a challenge for detectives than for scientists. Yet the need for good science is overwhelming. Much revolves around how to distinguish between true and false occurrences of individuals at any given location while research is critical to determining how all free-living foxes can be placed at risk of early death via control operations.

Invasions into new and vulnerable ecosystems by species that are likely to be detrimental must be subject to prompt and rigorous action. Designing a successful invasive species eradication program requires among other things a science base, exposure of all individuals to eradication techniques, no risk of reinvasion, methods that can detect the last survivors, and a monitoring phase to ensure that eradication has been achieved. The last two points are especially difficult to implement effectively for recently introduced species which are usually rare and difficult to detect and exacerbated by the huge scale of the task in Tasmania. Successful eradications also require widespread public support because eradication invariably involves the use of lethal techniques that are often controversial.

This week, the Journal of Applied Ecology published the results of a broad survey for fox presence in Tasmania conducted by myself and colleagues from the University of Canberra, Arthur Rylah Institute, NSW Department of Primary Industries and the Tasmanian Fox Eradication Program. We used molecular approaches that target the DNA found on the surface of predator faeces (scats) to determine whether faeces collected systematically across eastern Tasmania contained traces of fox DNA. Canid scats can persist in nature for weeks or even months, and several species, including foxes, tend to leave them in prominent places. We found that 56 of over 9,500 scats collected before 2011 contained fox DNA. When combined with carcasses and other hard evidence, there is strong support for the presence of foxes in the central north, midlands, and in isolated areas of the northeast and southeast. Although widespread, the distribution appears fragmented into eight clusters and our modelling shows that they have not yet spread to all areas of suitable habitat.

Our data suggest that foxes may be on the verge of becoming established irreversibly in Tasmania. It is conceivable that the moment may even have passed; although now is not the time to stop – quite the reverse. Given the widespread distribution, the current approach of broad-scale baiting in a sweep across the island converging from the northwest and the southeast, is appropriate but it will need to be completed rapidly and thoroughly. The baiting sweeps will also need to be repeated and their effectiveness assessed. A massive up-scaling of effort is likely to be required to achieve this. Furthermore, to be successful, this eradication is going to require widespread community support because it involves the use of 1080, a poison that is controversial in Tasmania for reasons unrelated to fox baiting. That, along with the widespread scepticism about even the presence of foxes, presents a real challenge to the Tasmanian government and community.

Failure to ensure fox eradication in Tasmania will have far reaching consequences. That the arrival of a top mammalian predator is coincident with the decline of another top predator, the devil, is a double whammy for Tasmanian wildlife. The cascading effects of such loss and gain are very hard to predict, but they are likely to herald big changes in the interactions and even persistence of much of Tasmania’s fauna. A worst case scenario is that devils cease to be ecologically relevant and foxes become established as the top mammalian predator in Tasmania. It is scary to think that the extinction dynamics that played out on the Australian mainland 100 years ago could be repeated this century – and soon.

Stephen Sarre is a professor in wildlife genetics at the Institute for Applied Ecology, University of Canberra, in Australia.

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