MAF Says No To RCD As Rabbit Control in New Zealand

2 July 1997

The Ministry of Agriculture delegated Decision-maker, Dr Peter O'Hara, has decided not to permit rabbit calicivirus disease (RCD) to be imported into New Zealand as a biological control agent for rabbits. This means that the virus will continue to be classified as an unwanted organism in terms of the Biosecurity Act 1993.

Dr O'Hara said there were three principal reasons for deciding not to permit the introduction of the RCD virus:

  1. the poor understanding of the epidemiology of the RCD virus and the disease it produces;
  2. the significant uncertainty as to the likely effectiveness of the virus as a biocontrol agent (as proposed by the Applicant Group) or even to act cost-effectively as a biocidal agent;
  3. the inadequacy of the biological control management programme proposed by the Applicant Group to deal with the uncertainties and risks which are now apparent, and the legal basis for management of the virus.

Expanding on these reasons, Dr O'Hara made the following points:

  • the epidemiology of the virus and the disease in feral rabbits is poorly understood. Methods of spread and persistence are still only postulated. In most countries, the information about the disease relates to domestic rabbits;
  • recent information from Australia raises questions about the likely behaviour of RCD in NZ and about the ability of humans to manipulate the virus to initiate disease outbreaks;
  • the behaviour of the disease in NZ can not be predicted. The mode of action proposed by the Applicant Group is now much more uncertain. Unless RCD behaves as proposed, it is doubtful that the benefits will exceed the costs;
  • unlike other biological control agents released to date, trialing the virus in NZ is not an option because of the difficulty of containing a virus. We have to depend on experience in other countries.
  • the management programme proposed by the Applicant Group was subject to considerable criticism in the consultation process;
  • the management programme is not adequate to deal with current uncertainties;
  • the legal and financial basis for the management of RCD and its consequences have not been established.

Dr O'Hara said other issues and matters of concern were raised by the consultation process and four issues stood out above the others in terms of the level of interest. Those issues are outlined below, along with Dr O'Hara's assessments of them.

  • the risk of RCD to humans.
  • a low but not zero risk which would not add to the background risk which is already accepted.
  • the risk of RCD to species other than the rabbit.
  • the Australian testing programme plus other published work plus lack of field evidence indicate the risk of clinical disease to be very low. Sub-clinical infections not ruled out. Recent published evidence of sub-clinical infections in dogs and foxes.
  • the potential of the RCD virus to mutate and initiate an adverse epidemiological event.
  • RNA viruses are well known for the instability of their nuclear material but mutations which result in adverse events such as host change or increased virulence are very rare.
  • the risks associated with prey switching by rabbit predators and the potential for changes in predator guilds.
  • prey switching by predators is a manageable problem but DoC will need additional resources which have not been earmarked.

Dr O'Hara acknowledged that some commentators might not agree with his assessments, but he had concluded that these issues were not in themselves reasons for not permitting the importation of the RCD virus.

"I recognise that my decision will disappoint and even anger many people who are struggling to deal with rabbits using current technology," Dr O'Hara said in his report. "I can empathise the sense of futility they feel that, even when they have achieved a good rabbit kill through an expensive primary poisoning operation, they have regained a plateau position for their farming operation which will be eroded by the prolificacy of the remaining rabbits.

"It is important to note that if the original timetable for the joint Australia - New Zealand research programme could have been followed, this decision would not have been taken until 1998. Our current lack of understanding of RCD as a tool for biological control is a serious impediment to rational decision making."

Dr O'Hara highlighted the non-sustainability of present "user-pays" rabbit control policies.

"For more than one hundred years (1887-1995), the rabbit problem in New Zealand was considered to be sufficiently significant to warrant subsidisation of control costs. There can be little doubt that taxpayer and ratepayer funds have made a major contribution to confining the rabbit problem to a relatively small area of New Zealand's land mass," he said.

"The cessation of subsidies for rabbit control with the completion of the Rabbit and Land Management Programme in 1995 and the introduction of 'user-pays' pest control by regional councils in their regional pest management strategies, has shifted the costs for rabbit control to land-holders. On rabbit-prone land, these costs represent a major financial burden and, for many, it is not a sustainable burden.

"In my view, current rabbit control policies can only contribute to further degradation of rabbit-prone land with loss of productive, ecological, environmental, amenity and heritage values. The fundamental problem is the high cost of currently available rabbit control technology."

He said there was also a pressing need for a new technological approach to rabbit control.

"Throwing dollars at the problem will help as it has done in the past, but current technology based on primary poisoning with 1080 reinforced by secondary control measures does not achieve a permanent solution. New technology is required," Dr O'Hara said. "RCD might still be a candidate for biological control if we can learn to manage it and answer some of the epidemiological questions discussed in the Chief Veterinary Officer's report."

Both the Decision-maker's report and that of the Chief Veterinary Officer have been sent to all reviewers and to all those who made submissions. These documents are also on the MAF Internet site: www.maf.govt.nz.

  

 

Last Updated: 09 September 2010

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