Estimating the proportion of Archey’s frogs in the Wharekirauponga mine vibration footprint 23 not significantly different (p>0.05), the estimate from the capture-recapture method should be preferred as capture-recapture methods are more robust and the estimate does not rely on the accuracy of the detection probability estimate. Estimates of the proportion of the Coromandel’s Archey’s frog population in the predicted ≥2 mm sec-1 vibration footprint obtained using the two population estimates are also similar 0.53% (CI95%: 0.33%–0.72%) and 0.58% (CI95%: 0.33%–0.82%). For comparison, the ≥2 mm sec-1 vibration footprint extends over only 0.54% of the 578 km2 area of Archey’s frog’s known distribution range in the Coromandel Peninsula. Obtaining a more reliable estimate of the total population of Archey’s frogs in the Coromandel Peninsula to improve estimates of the proportion of frogs in the predicted vibration footprint would require a well designed study programme with extensive and intensive field work. The first priority for such a programme should be to get better information on the species’ distribution in the Coromandel Peninsula using nocturnal surveys along transects throughout areas of potential frog habitat. This should be followed by work to obtain frog abundance estimates in a representative sample of plots randomly located throughout the species’ distribution range. Although capture-recapture methods provide the most robust method for obtaining population estimates for Archey’s frogs, the method’s cost makes it impracticable over a wider landscape. Also, concern over disturbance to frogs caused by capture and handling during capture-recapture studies means the method is no longer acceptable to the Department of Conservation. Applied hierarchical or N-mixture modelling[23-25] provides an alternative method to obtain robust frog population estimates without capturing and handling frogs. The method uses spatially replicated counts from large numbers of plots. Uncertainty in detection probabilities that compromise the use of simple plot counts is overcomes by modelling the detection process generating observed counts from the actual numbers of individuals present in plots. Although nocturnal surveys for Archey’s frogs, either along transects or in plots, is the method of choice for population studies on Archey’s frogs, because it causes the least disturbance to the frogs and their habitats, planning and managing studies using nocturnal surveys is difficult, because surveys must be undertaken on warm moist nights, which are difficult to predict in advance. Acknowledgements The report was commissioned by Stephanie Hayton of OceanaGold. I would like to thank Emily Hotham for providing original data from her M.Sc. study for reanalysis. Other data used in the report are from field work undertaken by Boffa Miskell staff. Their contribution is greatly appreciated. Katherine Muchna from Boffa Miskell played a crucial role, providing and explaining the data to me and assisting with other background information.
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