The effect of poisoned and notional vaccinated buffers on possum (Trichosurus vulpecula) movements: minimising the risk of bovine tuberculosis spread from forest to farmland
R. Pech A B , A. Byrom A , D. Anderson A , C. Thomson A and M. Coleman AA Landcare Research, PO Box 40, Lincoln 7640, New Zealand.
B Corresponding author. Email: pechr@landcareresearch.co.nz
Wildlife Research 37(4) 283-292 https://doi.org/10.1071/WR09161
Submitted: 20 November 2009 Accepted: 24 March 2010 Published: 28 June 2010
Abstract
Context. Vaccination of brushtail possums (Trichosurus vulpecula) has been proposed as a cost-effective alternative to lethal control for preventing potentially bovine tuberculosis (Tb)-infected possums from crossing forested buffer zones that abut farmland.
Aim. Evaluation of these two management option requires an estimation of the buffer width required to reduce the risk of disease spread to an acceptable level.
Methods. The movements of two groups of adult and subadult possums were monitored for up to 12 months in the Kaimanawa Range, North Island of New Zealand, using GPS technology. One group was in untreated forest immediately adjacent to a recently poisoned forest buffer, and the second group was 2 km further into untreated forest, which mimicked a vaccinated buffer with no reduction in possum abundance.
Key results. Close to the poisoned buffer, where the initial population density was 0.49–1.45 ha–1, adult possum home ranges averaged 10.2 ha in the summer immediately after control and 9.5 ha in the following winter. Two kilometres into the untreated forest, where the density was >3 ha–1, the corresponding values were only 3.5 ha and 2.8 ha. Over the first 6 months of monitoring, a ~350-m wide poisoned buffer would have contained 95% of movements by adult possums, as well as movements by most individuals, but a ~150-m wide vaccinated buffer would have been as effective. Equivalent results for the subsequent 6-month period were ~450 m and ~200 m for poisoned and vaccinated buffers, respectively. Movements by possums were not biased in the direction of the population ‘vacuum’ created by the poisoning operation. When subadult possums were included in the analysis, buffer widths of ~500–600 m for both poisoning and vaccination would be required to contain 95% of new den site locations.
Conclusions and implications. Detailed data on possum movements provide a means for agencies managing Tb to specify the width of a buffer, subject to an acceptable level of risk that it could be breached by a potentially infected possum. As well as depending on the width of a treated buffer, the final cost-effectiveness of vaccination compared with poisoning will depend on the relative cost of applying the two control techniques, and the frequency of application required either to prevent Tb from establishing (in the case of vaccination) or to suppress possum density (in the case of lethal control).
Acknowledgements
This project was contracted by the Animal Health Board (Project R-10699). Funding for GPS collars was provided by Landcare Research. The research was approved by the Landcare Research Animal Ethics Committee (AEC approval no. 07/09/03). Mandy Barron ran the computer simulations using the spatial model for possum population dynamics. Technical support was provided by C. Brausch, D. Clarke, K. Drew, S. Hough, D. Richards and J. Williamson. Hawke’s Bay Regional Council and Epro Ltd provided possum monitoring data and valuable assistance in selecting the study area. Thanks to various hunters for returning radio-collars from possums killed in this popular hunting area. Access was permitted by the Department of Conservation, and the Bay of Plenty District Health Board approved the use of toxins for retrieving collared possums at the end of the study. Thanks to Dan Tompkins, Phil Cowan and Graham Nugent for comments on the manuscript.
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