Mouse management on Ōtamahua/Quail Island—lessons learned

Ōtamahua/Quail Island is an 85 ha Recreation Reserve in Lyttelton Harbour, New Zealand. It is being ecologically restored and cats, hedgehogs, rabbits, mustelids and rats have been eradicated. However, the house mouse (Mus musculus) survived two eradication attempts, a bait station operation in 2002 and an aerial operation in 2009. Data on aerial bait deposition, bait degradation, mouse resurgence and non-target mortalities were collected. Brodifacoum bait deposition in many areas was considerably lower than the prescribed rate of 8 kg/ha. Mouse sign was simultaneously detected at seven sites around the island 6 months after the aerial operation. Tails were collected from trapped mice on Quail Island, the adjacent mainland and on the stepping-stone island (King Billy) to undertake DNA analysis. Little genetic discrimination was observed between samples obtained after the 2009 aerial bait operation, and samples from before or outside of the bait drop. By contrast, samples taken from a location 15 km distant were genetically distinguishable. Intensive trapping was also trialled in a 2 ha area as a possible strategy to regulate the mouse density using two trap designs and three bait types. Mouse trapping data indicated that abundance was highest in May and lowest in January. The results are discussed in terms of mouse eradication and management.