Auckland Island, the fifth largest island in New Zealand, is the only island in New Zealand's subantarctic region where introduced mammalian pests remain (pigs, Sus scrofa; mice, Mus musculus; cats, Felis catus). The island has unique biodiversity and is a key site for progressing New Zealand's goal to be free of several introduced predators by 2050. Recent island eradication successes have rekindled interest in eradicating pests from Auckland Island, and for the first time considering all three pests in one project. Over a 3-year period, we tested the feasibility of eradicating pigs, mice and cats by looking at what it would take to succeed, rather than what we could practically deliver with the tools we currently have. We proposed adaptations to current methods and used an evidence-based approach by undertaking large-scale field trials to test uncertainties and emerging technologies in-situ. We gathered data and evaluated proposed methods against five established principles of eradication while considering the logistics and infrastructure requirements of the project. Eradicating pigs, mice and cats from Auckland Island is worthwhile and feasible but dependent on further development of emerging technologies and capabilities for efficient delivery with an acceptable level of risk. Three eradication operations are required with specific sequencing and timing, supported by initial establishment of infrastructure. The project needs a large investment spread over 8 to 10 years to yield permanent and internationally important benefits with low ongoing cost to sustain. The feasibility study exposed the project's scale and was used to inform decision makers, who postponed the work in 2020 in response to the economic impacts of COVID-19. The study focusses future preparations on identified planning issues and dependencies to progress project readiness in anticipation of it being launched when economic conditions allow.
Since their liberation in 1807, feral pigs (Sus scrofa) have negatively impacted ecosystem health and processes on subantarctic Auckland Island, New Zealand. Eradication of invasive alien species is often critical to restoration programmes and preventing species extinctions. Eradication programmes utilising multiple techniques have allowed feral pig eradications on large islands. Protracted eradication programmes can have a higher risk of failure due to factors such as biological, logistical, social, and funding support. A temporary local pig eradication pilot study was successfully implemented on a densely vegetated fenced 951 ha peninsula on Auckland Island, emulating the principles set out during the Santa Cruz Island (California, USA) eradication. We applied multiple techniques, each delivered at the appropriate pig population density and within a finite period, to reduce the inherent risk of eradication failure. Aerial hunting was used to reduce the pig population before systematic ground hunting by a team using specially trained dogs removed survivors and validated eradication success. The deployment of a high specification thermal or forward-looking infrared (FLIR) camera in a particular manner greatly improved the efficiency of aerial hunting during this pilot study. The use of passive trapping, Judas pigs and division of the island into smaller fenced units are supplementary methods proposed for the Auckland Island eradication to enhance eradication efficiency as the methods implemented here are scaled up.
This investigation suggests new techniques to calibrate estimators of variance. Estimators of the variance of simple mean, ratio and regression estimators under different sampling schemes are shown to be special cases of the proposed calibration techniques. The approach has more practical use due to recent advances in programming techniques and computational speed. An empirical study has been carried out to address the properties of these proposed strategies.
House mice (Mus musculus) are an invasive species on Auckland Island in the New Zealand subantarctic and planning for their eradication is underway. Mast seeding events cause rodent populations to irrupt, though little is known about this phenomenon in snow tussock grass (Chionochloa spp.) systems on Southern Ocean islands. The aim of this study was to understand population fluctuations of mouse abundance on Auckland Island for the 2 years following a mast event, and with which tools to monitor abundance, to inform planning of bait application for eradication. Mouse populations were studied using kill and live trapping at two sites on Auckland Island, and mouse density was estimated using spatially explicit capture-recapture models. Mouse population density was highest during summer mast seeding of Chionochloa antarctica and then declined the following winter and subsequently remained low for the following year. Breeding remained seasonal, with a pulse in early summer and a very low level continuing through winter in both years, regardless of mast conditions. These results are similar to those from other cool temperate Southern Ocean islands where seasonal resource availability appears to drive breeding. Throughout the study the capture probability of mice was generally higher when population density was lower, which highlights that conclusions about population trends could be misleading if abundance indices are not calibrated to measures of population density. Mouse eradication should preferentially take place outside of a mast event but would likely still succeed during and following a mast event. Our work fills a key knowledge gap about rodent population trends during mast events for Southern Ocean islands, which is particularly important where eradications are planned.
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