- 6.1 Impacts on indigenous species due to changes in predator/prey relationships and induced predator/prey imbalances. Impacts on weeds.
- 6.2 Impacts on domesticated rabbits and laboratory colonies.
- Conclusion
6. The likely success and costs of measures which can be employed to ameliorate negative impacts of RCD
If RCD is introduced into New Zealand measures must be available to minimize the direct and indirect effects. The most important of these are the direct effects on valued rabbits and the indirect effects on predators following a decline in rabbit numbers.
6.1 Impacts on indigenous species due to changes in predator/prey relationships and induced predator/prey imbalances. Impacts on weeds.
| The Application recognises that there are potential risks for native and introduced flora and fauna, both directly and indirectly, and outlines measures to minimise them. It also makes the point that: | |
| "Many of the perceived ecological effects are not specific to RCD, whether or not they prove to be net gains or losses for the environment, but result simply from a long-term reduction in rabbit populations by any means, natural or induced." | |
A large number of submitters stressed the necessity for intervention to take place if a release of RCD virus were to go ahead. DoC considers that before any approval of the current application could be given, appropriate institutional arrangements should be in place to ensure the release of RCD in New Zealand is complemented by risk management measures that are appropriately funded and supported by appropriate research. Reviewers and submitters have called for either a national or a strategic predator control strategy.
National predator control strategy
Fordham proposes the institution of a national predator control strategy. Eradication of all predators would be unattainable, but the establishment of an over-arching strategy for predator control would be ecologically very sensible. It could coordinate national and regional programmes rigorously targeted at appropriate species, places and times.
A national predator control strategy could be developed whether or not RCD virus is released. But the links between rabbits and predators suggest that coordination of the use of RCD or 1080 would produce more effective anti-predator planning and, consequently, better management of New Zealand ecosystems.
Strategic predator control
DoC supports a strategic predator control programme linked to the potential release of RCD which would require an integrated and co-ordinated approach.
If RCD is released in New Zealand, institutional arrangements should be in place so that strategic predator control for vulnerable species is carried out as required at appropriate sites. Strategic predator control would consist of trapping (and other measures) in order to lessen the risk of predation increases due to prey switching, predator guild changes and predator movements (DoC).
Ecosystems point out that control of mustelids (stoats, weasels and ferrets) and cats has been traditionally by trapping, but this method is expensive, time-consuming, short-term and only partially effective. Methods of direct and indirect poisoning are under development, but safe and proven poisoning methods are not currently ready. Trapping predators, particularly stoats is not always effective and might not provide adequate protection for native wildlife in some circumstances.
To lessen the effect of prey switching and predator movements, predator control would have to be carried out at appropriate sites whenever RCD epidemics caused rabbit numbers to drop. Mitigation of predator guild effects might require intensive, widespread and long-term predator control to manipulate the relative and absolute numbers of predator species within the guilds.
Predator control would have to take place at sites where fauna would be vulnerable to the predation increases that rabbit declines could bring. DoC is currently identifying sites where action would be required if species were to be protected.
Monitoring rabbit density
There do not appear to be any mechanisms currently in place to ensure that the monitoring of rabbit densities at sites identified as containing at-risk fauna is funded and carried out. If RCD is released, such monitoring would be desirable in order to ensure that predator control is carried out at the appropriate times (DoC).
Monitoring spread of RCD
There does not appear to be a mechanism currently in place to ensure that monitoring of the spread and re-occurrence of RCD in rabbits throughout New Zealand is funded and carried out. Such monitoring would be necessary so that predator control actions can be instigated to mitigate the anticipated increases in predation pressure (DoC).
Monitoring of native fauna and flora before and after rabbit declines
Before RCD is released, an overall programme should be set up for the monitoring of native fauna and flora before and after rabbit declines. Such monitoring, for all species identified as vulnerable, is necessary to ascertain the effectiveness of management interventions. It would also provide data for predator/prey models that could be used to refine management interventions in the future (DoC).
Identification of and commitment to other measures necessary to mitigate risk
Before any approval of the proposal is given there need to be arrangements in place to ensure any other measures identified (by suitable research - see below) as necessary to mitigate the risks of an RCD introduction are implemented. These measures might include suitable weed control measures to protect species identified as vulnerable to any growth in weeds resulting from decreased rabbit grazing. Other measures could include the training of staff necessary to carry out the numerous actions considered necessary to mitigate the risk of an RCD introduction (DoC).
Research into new predator control techniques is underway and funded, with results expected over the next two years. This research is proceeding as quickly as practicable (DoC).
Research into modeling of predator/prey systems is being undertaken by Landcare Research. It is expected that the results of this research will help refine management interventions and identify other measures necessary to mitigate the risk of an RCD introduction - such as complementary rabbit control to minimise rabbit fluctuations and hence (possibly) prey switching (DoC).
Recommendations of DoC
DoC recommends that before RCD virus is introduced:
- vulnerable species (and the sites that need to be managed to protect these species) should be identified and agreements reached on responsibility for predator control.
- measures for predator control over extensive areas must be available and resourcing mechanisms for the short and long term funding.
- for the monitoring of rabbit densities at sites identified as containing at-risk fauna should be agreed and funding issues sorted out.
- should be reached as to who would do the monitoring of the distribution of RCD throughout New Zealand, how it would be done and how it would be funded.
- should be reached as to who would do the monitoring of native fauna and flora (a community level impact) before and after rabbit declines throughout New Zealand, how it would be done and how it would be funded.
- should be reached as to who would do the assessment of environmental impacts and mitigation of any other undesirable effects on the conservation estate, such as the likely invasion of weeds.
- measures for weed control must be available and resourcing mechanisms for the short and long term funding must be identified.
- must be ascertained whether it would be appropriate or possible to put more resources into modeling of predator/prey systems in order to get results of current research earlier rather than later.
Effectiveness of management intervention in mitigating increased predation pressure
The management interventions outlined above are unlikely to counter all the unintended effects that could flow from an RCD introduction.
It is unlikely that all the areas at risk from increased predation would be identified, and inaccessible sites would not be subject to management intervention. Local extinction of constituent native fauna is therefore a possibility. Likewise, attempted mitigation of any negative effects of weed growth is unlikely to counter all potential problems (DoC).
Cost of mitigation
Twenty nine threatened species at 59 sites have been presently identified by DoC as requiring protection from an increase in predation or weed competition in the event of an RCD-induced decrease in rabbit numbers. In addition there are up to ten high profile sites where protection would be required. Species at these sites, such as the yellow eyed penguin and albatross, do not meet the species-based criteria but are at locations classed as high profile sites.
DoC’s current estimated cost of mitigating the effects of reduced rabbit numbers due to RCD on key threatened species are:
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$670 000 |
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$270 900 |
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$2, 900 000 - 3, 150 000 |
The estimated total cost is $3, 840 900 - 4, 090 900 per year for 3-5 years. Depending on the persistence and dynamics of RCD in New Zealand, DoC believes that significant funding is likely to be needed on a long term basis.
Whilst DoC have a major concern about RCD it undertakes only limited monitoring and predator control when current applications of poison are made.
The recommendations of DoC are made on the basis that the precautionary principle should apply as there is uncertainty over how RCD would behave in New Zealand (see section 5.2.2). DoC believes that these recommendations should be implemented before the virus is imported. Close monitoring of the impacts of RCD would then determine the extent and duration of mitigation measures.
Weed control should be the responsibility of the land holder as this would be a consequence of effective rabbit control whatever the tool.
6.2 Impacts on domesticated rabbits and laboratory colonies.
Many submitters who own rabbits as pets object to the threat that RCD creates and allude to the distress that they would experience if their pets die from the disease. Several point out that, since rabbits are relatively inexpensive to buy and keep, they provide a lifelong hobby for many people; a hobby, it is claimed, which is their right to enjoy.
Some rabbits have a high individual value as pets or show animals and some play an integral role in research and industry. The costs associated with the prevention of RCD are of concern to rabbit owners.
The Application points out that two inactivated vaccines with a history of high effectiveness are registered for use in New Zealand and would be available if the virus is introduced. Capucci (pers comm) claims the vaccine to be effective in controlling the disease in farmed rabbits in Italy. The manufacturers recommend annual vaccination but the cost of vaccination/quarantine for domestic and laboratory rabbit owners has not been calculated. In Australia costs for vaccination (including veterinary fees) range from $A8 to $A80, with an average of $A20 (BRS, 1996). Vaccines can have side effects and are not 100% effective even when used precisely as recommended. The Application does acknowledge that there have been a few instances of untoward local skin reactions following vaccination of rabbits but there has been no substantiated cases of losses in productivity or of animals dying as a result of the vaccination.
Vaccination is not recommended in very young rabbits and if vaccination is performed at under ten weeks a repeat dose is recommended. There is little evidence to support a life-long immune response to the vaccine and contact with the disease to boost immunity cannot be relied upon.
There would be some situations where vaccination of valued rabbits is not practicable or desirable, e.g. where rabbits must be free of antibodies to RCD virus. Quarantine measures can be applied to reduce the chance of infection. These are strategies which attempt to isolate the valued rabbits from sources of infection and include the use of physical barriers and hygiene practises that prevent direct and indirect contact with the virus, infected rabbits and their products. Potential sources of infection include; vectors of the virus, contaminated rabbit handlers, equipment, bedding, food and cages etc. This is not discussed in the Application.
Measures can be taken to protect rabbits from RCD. Vaccination is the most reliable method and two vaccines are registered and able to be used in New Zealand if needed. Quarantine and hygiene measures that reduce the chance of exposure of the rabbit to the virus may also be advisable.
Conclusion
The mitigatory measures recommended by DoC must be considered by the decision maker. Clarification of the costs and the funding sources for mitigation needs to be resolved before the RCD virus could be released.
Without doubt an introduction of RCD virus would mean that owners of valued rabbits (pets, farmed rabbits, and those used in research and industry) would face increased costs in protecting their rabbits from infection. These costs have not been quantified.
Contact for Enquiries
Manager, Strategic Science Team
MAF Biosecurity New Zealand
PO Box 2526
Wellington
NEW ZEALAND
Phone: +64 4 894 0115
Fax: +64 4 894 0731
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