Search the SPREP Catalogue

Following the incursion of rats (Rattus rattus) on Taukihepa (Big South Cape Island; 93.9 km²) off southern New Zealand in 1963, and the subsequent extirpation of several endemic species, the New Zealand Wildlife Service realised that, contrary to general belief at the time, introduced predators do not reach a natural balance with native species and that a safe breeding habitat for an increasing number of ‘at risk’ species was urgently needed. Off shore islands offered the best option for providing predator free habitat but there was a limited number of predator-free islands available and most were very small. Eradicating rodents on larger islands to provide a wider range and greater area of habitats was required and hand treating these larger areas using trapping and hand application of toxicants, the only methods available at the time, proved problematic and often impossible. Helicopters had been used to distribute bait for the control of rabbits and brushtail possums in the past but eradication of any particular predator species was considered ‘not feasible’. The development of a GPS-based aircraft guidance system, a suitable bait product, specialised bait delivery systems and second-generation anti-coagulant toxicants changed that. Now islands as large as South Georgia (3,900 km²) have been treated using this method

The impacts of house mice (Mus musculus), one of four invasive rodent species in New Zealand, are only clearly revealed on islands and fenced sanctuaries without rats and other invasive predators which suppress mouse populations, influence their behaviour, and confound their impacts. When the sole invasive mammal on islands, mice can reach high densities and influence ecosystems in similar ways to rats. Eradicating mice from islands is not as difficult as previously thought, if best practice techniques developed and refined in New Zealand are applied in association with diligent planning and implementation. Adopting this best practice approach has resulted in successful eradication of mice from several islands in New Zealand and elsewhere including some of the largest ever targeted for mice; in multi-species eradications; and where mouse populations were still expanding after recent invasion. Prevention of mice reaching rodent-free islands remains an ongoing challenge as they are inveterate stowaways, potentially better swimmers than currently thought, and prolific breeders in predator-free habitat. However, emergent mouse populations can be detected with conventional surveillance tools and eradicated before becoming fully established if decisive action is taken early enough. The invasion and eventual eradication of mice on Maud Island provides a case study to illustrate New Zealand-based lessons around mouse biosecurity and eradication.

Attempts to eradicate invasive terrestrial arthropods are often regarded as gambles. They o?er the possibility of long term freedom from a pest but are usually confronted with substantial uncertainty and come with a range of technical, economic, environmental, social and political risks. Few guidelines are available for evaluating eradication attempts against terrestrial arthropods. Here, we build on scienti?c literature, including six criteria previously developed to evaluate the feasibility of vertebrate eradications, and our own experiences to de?ne nine criteria that are intended to both assist experts to evaluate proposed arthropod eradication attempts and guide attempts that are underway. The criteria are straight forward and easily interpreted, though evaluating them for a particular programme relies on expert group assessment that will often benefit from rigorous supporting statistical and/or modelling analyses.

Pieris brassicae, large white butter?y, was ?rst found in New Zealand in Nelson in May 2010. The Ministry for Primary Industries (MPI) responded with a monitoring programme until November 2012 when the Department of Conservation (DOC) commenced an eradication programme. DOC was highly motivated to eradicate P. brassicae by the risk it posed to New Zealand endemic cress species, some of which are already nearly extinct. DOC eliminated the butter?y from Nelson in less than four years at a cost of ca. NZ$5 million. This is the ?rst time globally that a butter?y has been purposefully eradicated. Variation in estimates of bene?ts, costs, the e?cacy of detection and control tools, and the probability of eradication success all contributed to uncertainty about the feasibility. Cost bene?t analyses can contribute to assessing feasibility but are prone to inaccurate assumptions when data are limited, and other feasibility questions are equally important in considering the best course of action. Uncertainty does not equate to risk and reducing uncertainty through data gathering can inform feasibility and decision making while increasing the probability of eradication success.

Breeding success of 5 Cory’s shearwater Calonectris diomedea sub-colonies of Lavezzu Island (Lavezzi Archipelago, Corsica) was checked annually for 25 consecutive years from 1979 to 2004. Between 1989 and 1994, 4 ship rat Rattus rattus controls were performed in several subcolonies. In November 2000, rats were eradicated from Lavezzu Island and its 16 peripheral islets (85 ha) using traps then toxic baits. We compare cost (number of person-hours required in the field) and benefit (Cory’s shearwater breeding success) of control and eradication. The average breeding success doubled when rats were controlled or eradicated (0.82) compared to the situation without rat management (0.45). Moreover, the average breeding success after eradication (0.86) was significantly (11%) higher than after rat controls (0.75). Furthermore, the great variation in breeding success recorded among sub-colonies both with and without rat control declined dramatically after eradication, suggesting that rats had a major impact on breeding success. The estimated effort needed to perform eradication and checking of the permanent bait-station system during the year following eradication was 1360 person-hours. In contrast, rat control was estimated to require 240 or 1440 person-hours per year when implemented by trained and untrained staff, respectively. Within 6 yr, eradication cost is lower than control cost performed by untrained staff and confers several ecological advantages on more ecosystem components than Cory’s shearwater alone. Improved eradication tools such as hand or aerial broadcasting of toxic baits instead of the fairly labour-intensive eradication strategy we used would dramatically increase the economic advantage of eradication vs. control. Therefore, when feasible, we recommend eradication rather than control of non-native rat populations. Nevertheless, control remains a useful management tool when eradication is not practicable.