Purposes, outcomes and challenges of eradicating invasive mammals from New Zealand islands: an historical perspective

Context Invasive mammals have been removed from at least 100 offshore islands around New Zealand, covering a total area of around 45 000 ha. Aims To review the outcomes of eradications, the statutory and social environment in which the eradications were conducted, and the lessons provided for future work. Methods Native species to benefit from the eradications were identified, as were the reasons for the eradications and the agencies responsible. Examples are provided using case studies. Key results Three loosely linked work streams were revealed: research into efficient baits and baiting methods, threatened species-led projects nested within priorities for species recovery and supported by legislation, and community-led projects instigated by restoration societies. At least 180 populations of 14 species of invasive mammals were removed. Numerous species of native plants, invertebrates and more than 70 species of terrestrial vertebrates are recovering or are likely to recover as a result of the eradications. Partnerships have been formed with Māori and innovative projects developed with community groups. Conclusions Eradications of invasive mammals are aggressive conservation actions that can have wide benefits for biodiversity but can also be controversial, technically demanding and expensive. Implications Eradications are multi-scale problems. If they are to gain public acceptance, evidence is needed in support. This evidence can include understanding the detrimental effects of invasive species, the likely responses of native biodiversity, and the benefits ensuing from their recovery. However, the way this evidence is gained and communicated will also require deep understanding of nuances in regional political and cultural environments.