Without island biosecurity pests will rapidly recolonize islands from which they have been eradicated, or worse still colonise islands for the first time. Only with a rigorous audited biosecurity programme can pest-free status be maintained. The gold standard in New Zealand is Nature Reserve islands like Antipodes Island, where quarantine occurs before, during and after arrival, surveillance occurs pre and post border, and incursion response strategies are in place. The New Zealand Department of Conservation operates a robust island biosecurity programme to protect their conservation investments, but it was reported in the news today that last year numbers spiked, including mice, rats, cats and stoats all making it out to islands. Stranger critters such as ferrets and even otters have reached New Zealand’s offshore islands in the past. Unlike the original pest eradications which cleared these islands, and were years in the planning, a response to an incursion must, as DOC manager Andy Cox points out, be as rapid as if a forest fire had broken out. Pest incursions are the biological equivalent of chemical spills, only the agent can keep reproducing.
Unfortunately mice reinvaded Maud Island when they evaded detection in 2013 and DOC had to respond with a $100,000 eradication in 2014. The BBC recently profiled work from the University of Auckland which experimentally demonstrated just how fast mouse invasion of islands can occur, in less than a year. Other research has investigated the optimal balance required between investing in quarantine to prevent incursions, and surveillance to respond to them, but ultimately both are important. Even catching a single incurring rat can be disproportionately difficult, as the case of Razza the rat demonstrated back in 2005. The Treasure Islands programme in the Hauraki Gulf is a great example of such island biosecurity in action, where there has been a 100% success rate intercepting dozens of pest incursions in the Hauraki Gulf over the past decade, with the able assistance of conservation dogs and trialling new methods like caged rats as lures.