Rodent eradication on Lord Howe Island: challenges posed by people, livestock, and threatened endemics

Like many oceanic islands, World Heritage listed Lord Howe Island (LHI), 760 km north-east of Sydney (Australia), has populations of invasive rodents. The house mouse (Mus musculus) probably arrived around 1860, and the ship rat (Rattus rattus) in 1918. Both species have significantly reduced the island’s biodiversity. Rats are implicated in the extinction of at least 20 species (or subspecies) of birds, invertebrates and plants. Exotic rodents remain a threat to many endemic species, so much so that predation by ship rats on LHI is listed as a Key Threatening Process under New South Wales and Australian environmental legislation. A feasibility study in 2001 concluded that eradication of rats and mice was technically feasible. A cost-benefit study in 2003 demonstrated that costs of the eradication would be quickly offset by discontinuation of the current rat control programme and increased yields of commercial palm seed. A plan to eradicate exotic rodents on LHI was prepared in 2009. Technical challenges include: the presence of numerous threatened endemic species, several of which could be placed at risk during the eradication; a permanent human population of approximately 350, their pets and livestock; and a well-developed tourist industry. Several species of threatened fauna will be housed in captivity for the duration of the operation to mitigate the risk of primary and secondary poisoning. The presence of a large human settlement requires customary eradication strategies to be modified. Within uninhabited areas, bait will be aerially broadcast, whereas within the settlement, bait will be hand broadcast or placed in bait stations. Livestock will either be eliminated from the island before the eradication or aggregated into small enclosures. Community support is vital to the success of the operation, and extensive consultation is a major component of the eradication programme.