Feature

Rabbit Wrangles

The myxomatosis debate tends to bring out extremes. One report insists on the immediate introduction of myxomatosis to control rabbits. Not surprisingly, it was commissioned and written by South Island high country farmers. Animal rights people protest equally vociferously that the virus is not acceptable because of the suffering it causes.

Myxomatosis takes 10-16 days to work, causing multiple skin lesions and weeping tumors. It's not a pretty death, but it's an effective one, with claimed kill rates as high as 100%. However, myxomatosis in Australia and Britain has done little to provide on-going control of rabbits, as virus-resistant breeds have appeared. It now takes only five years for selection out of virulent strains to occur, rendering myxomatosis ineffective.

Myxo advocates have made much of the development of an Australian strain which is said to kill quickly without physical symptoms. However, ecologists in contact with Australia's DSIR-equivalent, the CSIRO, say that there is no such "rabbit-friendly" strain at present. Parliamentary Commissioner of the Environment, Helen Hughes, is also dubious about such claims.

There is an attenuated recombinant strain under development which would piggy-back a rabbit sterilizing gene on a harmless strain of myxo. The CSIRO says that five years of trialling are needed before such an approach is ready, and that the recombinant virus would still have to compete with existing strains.

Viral haemorrhagic disease (VHD) is also suggested as a quick killer. However, immunity to this can be built up rapidly, requiring reinfection. DSIR ecologist John Flux sees it as a better alternative to myxomatosis, but considers VHD a killing tool, not a control tool.

"It's the flyspray approach -- VHD will knock them down and then they're back up the next year, so you have to do it forever," he says. "People want something which'll blast the rabbits. They find it difficult to sit back and let the cats manage the problem."

Hughes is wary of focusing on predator control techniques. She cites a relative lack of research into rabbit population structures and breeding patterns in the affected areas. John Robertshaw, of MAF Tech's Semi-Arid Lands Research Group in Alexandra, is also keen to see better knowledge of how the rabbits interact with the environment. He sees it as vital that scientists look at everything from predator/prey relations to physical and climatic components.

Henrik Moller, director of Otago University's Wildlife Management Diploma, is hunting for funding for a variety of research programmes that would provide that information. He hopes to gain funds to take a more comprehensive look at rabbit predators, at ways of reducing rabbit population booms and at public attitudes towards biological control techniques.

Good research takes time, and many high country farmers feel that they have already run out of it. However, as Moller points out, the release of a biocontrol agent -- such as myxomatosis -- is irreversible, and "we would live with any mistakes forever".

It's not all straight debate, even amongst scientists. The DSIR's predator control suggestion has been dismissed by one biologist based in the high country as "pontification from suitcase scientists in Wellington".

Vicki Hyde is the editor of New Zealand Science Monthly.