Island Invasives Conference

Recent progress in techniques for the eradication of invasive species on inhabited islands.  By John Ogden

Island Invasives Conference. 2010 started off well, and ended even better! In January there was a conference in Auckland entitled “Island Invasives: Eradication and Management”. This conference was organised jointly by the Centre for Biodiversity and Biosecurity of the University of Auckland, and Invasive Species Specialist Group of the International Union for Conservation of Nature. About 240 people attended, from 26 countries all over the world. Fifty papers were presented in concurrent sessions over two days, and some of these were particularly relevant to the Trust’s vision for a pest-free Great Barrier. In particular, in the session entitled “Social and Economic Dimensions of Eradications” there were sixteen presentations, including one from the GBICT outlining our experiences in attempting to promote our vision. Also in that session there were two other papers specifically addressing eradications on inhabited islands: Lord Howe (Ian Wilkinson) and Tristan da Cunha (Karen Varnham). Neither of these has yet been successfully completed, but neither have they tried and failed. In both cases, as on Great Barrier, it is an on-going process of convincing a minority of the population that the risks can be mitigated and are far outweighed by the long-term economic and conservation benefits. In the same session there was also a paper outlining the successful use of volunteer hunting for the control of pigs on Oahu, Hawaii. Most of these papers, including the paper presented by the Trust, have been reviewed and accepted for publication and will become available in 2011.

Tristan da Cunha - a volcanic peak in the remotest South Atlantic
- the local community are scoping a rat eradication.

Key Paper. November saw the publication of a key review paper: “Eradication of Invasive Mammals on Islands Inhabited by Humans and Domestic Animals”, by Steffen Oppel, three other members of the Royal Society for the Protection of Birds, and Brent Bevan, of the Department of Conservation, Stewart Island Field Centre. The paper is a review of all the relevant literature on the topic – with about 70 papers referred to. An abstract is given below:

Non-native invasive mammal species have caused major ecological change and species extinctions on many islands. While eradications from uninhabited islands have been well documented, there is very little to go on when considering inhabited islands. This paper addresses the challenges associated with campaigns to eradicate invasive mammals from islands inhabited by humans and domestic animals.

On inhabited islands, detailed analyses of the social, cultural, and economic costs and benefits of eradication are required to increase the probability of local communities supporting the eradication campaign. The ecological benefits of eradication (e.g., improvement of endemic species’ probability of survival) are difficult to trade-off against social and economic costs due to the lack of a common currency. Local communities may oppose an eradication campaign because of perceived health hazards, inconvenience, financial burdens, religious beliefs, or other cultural reasons. Besides these social challenges, the presence of humans and domestic animals also complicates eradication and biosecurity procedures (measures taken to reduce the probability of unwanted mammals re-colonizing an island). For example, houses, garbage-disposal areas, and livestock-feeding areas can provide refuges for rats and therefore can decrease the probability of a successful rat eradication campaign. Transport of humans and goods to an island increases the probability of inadvertent reintroduction of invasive mammals, and the establishment of permanent quarantine measures is required to minimize the probability of unwanted re-colonization after eradication. The authors recommend a close collaboration between island communities, managers, and social scientists from the inception of an eradication campaign to increase the probability of achieving and maintaining an island permanently free of invasive mammals.

Lord Howe Island - subtropical and idyllic but ship rats
pose a grave threat to indigenous species.

The paper discusses the ‘Conditions for Successful Eradication Campaigns’ under four main headings: Social Acceptabilty; Costs and Benefits of Eradication; Reducing the Probability of Invasion to Near Zero, and Increasing the Probability of Eliminating all Individuals. The last two headings seem at first to overlap, but one deals primarily with biosecurity, while the other deals with getting the last rat or feral cat, and how we know when we’ve got it!

Finally, the ‘Recommendations’ are highly pertinent. The first point made is that ecosystem restoration (i.e. pest eradication) on inhabited islands is essentially a social activity, and concern for the urgency of an eradication cannot preclude the importance of community control over the associated decisions and project activities. Regular public review and consultation is part of the process. A fair and transparent decision-making process may be more important to a community than technical details or even specific outcomes. Engaging the community at all stages of the project, from information gathering, to consultation, to decision making, to on-the-ground eradication work, and to final evaluation of the results is important. Such a programme avoids a ‘top-down’ approach and is most likely to generate public ownership of the eradication project. If members of the community see it as their project and take pride in it, complicated tasks such as maintaining high biosecurity standards, are more likely to be carried out and enforced by the community. Links to other ecological and economic benefits, such as the potential to use the project in tourism businesses will also be recognised. “Ultimately, eradication projects yield long-term benefits for native island species only if the benefits for human inhabitants are strongly linked to biological gains and are economically and socially sustainable.”

A thoroughly good read. It is published in ‘Conservation Biology’ and can be obtained by contacting:  or