Eradication of stoats ( Mustela erminea ) from Secretary Island , New Zealand

Stoats (Mustelia erminea) are known to be good swimmers. Following their liberation into New Zealand, stoats reached many of the remote coastal islands of Fiordland after six years. Stoats probably reached Secretary Island (8140 ha) in the late 1800s. Red deer (Cervus elaphus) are the only other mammalian pest present on Secretary Island; surprisingly, rodents have never established. The significant ecological values of Secretary Island have made it an ideal target for restoration. The eradication of stoats from Secretary Island commenced in 2005. Nine-hundred-and-forty-five stoat trap tunnels, each containing two kill traps, were laid out along tracks at a density of 1 tunnel per 8.6 ha. Traps were also put in place on the adjacent mainland and stepping-stone islands to reduce the probability of recolonisation. Pre-baiting was undertaken twice, first in June and then in early July 2005. In late July, the traps were baited, set and cleared twice over 10 days. Ninety-five stoats were captured in this period. Subsequent trap checks have taken place three times each year: in November, February and between May-July. Forty-four stoats were caught in February 2006, with successive captures decreasing to between 0 and 9 each trapping period, with most caught in autumn. Genetic analysis of stoats captured to June 2008 indicates that these stoats were a mixture of residents and a few immigrants. A significant stoat plague event during summer 2006-2007 may have increased the likelihood of new stoats subsequently arriving on Secretary Island. While eradication has not yet been achieved, many of our conservation objectives are being met. The experimental nature of this programme has opened the door for testing new ground in the field of island eradications and challenging some of the previously held views of what should and should not be attempted.