Estimating the proportion of Archey’s frogs in the Wharekirauponga mine vibration footprint 20 a) b) Figures 10 a & b. Locations of capture-recapture plots (a), red discs, and simple count plots (b), blue discs, in the predicted vibration footprint. Counts from sixty-eight 10x10 m plots spread across the ≥2 mm sec-1 vibration footprint (Figure 10b) provide a second density estimate of 1,003 frogs ha-1 (SE ±190) in the vibration footprint (Table 8). Using the frog density estimate from the capture-recapture study gives an estimated 289,887 (CI95%: 202,373–373,364) Archey’s frogs in the 315 ha of the predicted ≥2 mm sec-1 vibration footprint and 149,932 (CI95%: 104,669–193,107) in the 163 ha of the predicted ≥4 mm sec-1 vibration footprint (Table 12), which are respectively 0.53% (CI95%: 0.33%–0.72%) and 0.27% (CI95%: 0.17%–0.37%) of the estimated 54.8 million Archey’s frogs on the Coromandel Peninsula. Using the alternative density estimate from simple counts adjusted by a detection probability estimate, the estimated number of Archey’s frogs within the ≥2 mm sec-1 vibration footprint is 315,917 (CI95%: 198,909–432,925), or 0.58% (CI95%: 0.33%–0.82%) of the estimated Archey’s frog population on the Coromandel Peninsula. Discussion On first consideration, our estimate of 54.8 million Archey’s frog in the Coromandel seems surprisingly large, especially in comparison with the previously published estimate of 5,000– 20,000 for the entire Archey’s frog population[1, 27]. However, our population estimate corresponds to an average frog density of 931 ha-1, or 9.3 frogs per 100 m2 plot. Assuming a detection probability of 0.322, this will result in an expected count of 2.05 Archey’s frogs during nocturnal survey of a single 10x10 m plot. This is consistent with observations during nocturnal plot surveys. By contrast a total Coromandel population estimate of 20,000 mature frogs would result in 0.003 mature frogs in a 10x10 m plot and expected plot counts of 0.001 mature frogs. As 80% of frogs found during our surveys were adults, a population 20,000 mature frogs would result in an expected count of 0.0013 all-age frogs in a 10x10 m plot. This expected count is orders of magnitude below observed average plot counts from numerous nocturnal plot surveys over wide areas.
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