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New Zealand has many invasive vertebrate species that adversely affect native biota, compete with livestock, and spread diseases. Large-scale management of the most critical pests is achieved mainly by lethal control. This includes aerial application of the controversial toxin sodium fluoroacetate (1080), despite vociferous opposition from those concerned about potential non-target deaths, environmental contamination, and animal welfare impacts. We have borrowed a framework from animal welfare science, namely the ‘3Rs’ (reduction, refinement, and replacement), to address some of the concerns about the use of aerial poisoning while sustaining its cost-efficiency. The first aim was to reduce the amount of toxin used so that undesirable nontarget impacts are minimised. A range of projects have: 1) developed a method to identify the high-risk habitat within a landscape that needs to be targeted and, equally importantly, the low-risk habitat over which toxic bait does not need to be sown; and 2) optimised the combinations of prefeeding, sowing rate, and bait distribution to achieve the desired percentage kills at the lowest cost and lowest sowing rate of poison bait. To address the second aim, refining toxin use, we have improved target specificity by developing repellents to minimise unintended bykill of non-target species such as deer, and by identifying long-term strategies that minimise the total number of animals killed. The final aim, replacement of 1080, focuses on the search for alternatives, such as fertility control. It also involves development of complementary tools, such as tuberculosis vaccines, that may reduce the frequency or need for repeated use of 1080. This integrated ‘3Rs’ approach has quickly led to changes to operational practice by management agencies, with some operations now using up to 92% less toxic bait than usual, and other operations switching from aerial 1080 poisoning to ground-based non-1080 approaches for ongoing control. Looking forward, the ‘3Rs’ approach offers a framework for continuous improvement in the use of control tools for a wide range of species, whilst also providing a clear pathway to complementary or alternative approaches.

Strategic management of brushtail possum populations in New Zealand is presently dependent on the use of a standardized trap-catch procedure for monitoring population trends. Where this has been used in the first few months after control, calculated rates of increase often far exceed known reproductive and dispersal rates, suggesting that trapping-based population indices immediately following control are biased low. We are investigating the problem by genotyping DNA extracted from possum fecal pellets and using matching genotypes in the ear tissue of trapped possums as a measure of trappability. We have used quantitative polymerase chain reaction (PCR) to determine the threshold of possum DNA required from fecal samples in order to obtain an accurate genotype (>99%) from field samples. This has enabled the removal of “allelic dropout” as a source of error in obtaining accurate genotypes from such noninvasive DNA samples. Validation tests were conducted on fecal samples collected from caged (i.e., identifiable) possums, and fecal pellets and ear tissue from trapped possums in the field. The tests confirmed that the sample collection and preservation procedures used resulted in accurate identification of possums from both types of sample material, although fecal pellets older than about 7 days were unlikely to yield sufficient DNA for amplification and genotyping. Genotyping of a large quantity of sample material collected before control, and at 1, 4, and 9 months after control, in 2 replicated field trials is proceeding and revealing information on the trappability of possums that survive control, and the contribution of immigration to the populations after control.

The ongoing use of 1080 toxin for the control of mammal pests in New Zealand remains highly contentious. Several reviews over the last 25 years identified information gaps and areas of concern, both social and scientific. In this paper these areas of concern are discussed and the extensive scientific and social research that has been undertaken to clarify and address them is reviewed. Although there has been a major national investment in research aimed at finding an alternative to 1080, that has not yet been fully achieved because of low or inconsistent efficacy and/or low cost-effectiveness of alternatives, regulatory difficulties in obtaining approval for aerial delivery of any alternative, and toxic residue concerns. Finding an alternative that has similar efficacy while satisfying the demands for species-selectivity, no residues, and humaneness is a continuing challenge. The most promising prospect appears to be through understanding the genome of the target animals and opportunities for genetic manipulation, either by developing species-specific designer lethal toxicants based on genome mining, or by gene editing to develop non-lethal technologies. Both will require considerable time and funding for research, and considerable effort and engagement to address social and regulatory hurdles. [ABSTRACT FROM AUTHOR]