Estimating the proportion of Archey’s frogs in the Wharekirauponga mine vibration footprint 21 Published density estimates for Archey’s frogs from other capture-recapture studies (Table 5) are considerable higher (43,300 ha-1, 5,300 ha-1 10,370 ha-1) than either the 931 ha-1 average density estimates for the Coromandel, or our highest density estimate for any single habitat (1,902 ha-1) and if used to estimate the total Coromandel Archey’s frog population would result in much higher population estimates. Although our total population estimate of 54.8 million Archey’s frog in the Coromandel is the best estimate that can be achieved with available data, it is based on sparse data and untested assumptions, and is unlikely to be accurate. Density estimates for the seven habitats are derived from a relatively small sample of one hundred and thirty-one 10x10 m plots spread between five sites (Figure 7) within an estimated 578 km2 distribution range. The exact area of the species distribution range is uncertain, because its boundaries have not been established with certainty. Sparse sampling with plot locations concentrated at sites with relatively easy access means the plots are probably not a representative sample of abundance throughout the species’ distribution range. Although, plots in areas with historical Archey’s frog sightings could have biased the population estimates upwards, there are few accessible areas in the species distribution range without historical Archey’s frog sightings (Figure 1). It is not known whether frog density estimates in the seven habitats and the detection probability estimate used to obtain most of the density estimates are valid over the wider landscape, or whether there are major regional variations in frog densities and detection probabilities as a result of regional differences in habitat structure or localised contingencies such as local disease outbreaks, pest eruptions, pest control operations, or habitat disturbance histories. Despite these caveats around the accuracy of our population estimates of 54.8 million Archey’s frog in the Coromandel, it is far more reliable than the previously published estimate of 5,000–20,000 mature frogs for the entire Archey’s frog population[1, 27, 28], which is not supported by any data and is almost certainly wrong, probably by three orders of magnitude. Our population estimate is likely to be an underestimate of the total Coromandel population because the estimate is restricted to frogs inhabiting the main block of native habitat ≥200 m a.s.l. on the Coromandel Peninsula’s axial mountain range (Figure 1), but Archey’s frogs almost certainly occur outside of this area. Relatively high densities of frogs encountered during plot surveys close to and below 200 m a.s.l. (Tables 6 & 8) show that the species does occur below 200 m a.s.l. in areas with suitable habitat. Also frogs may inhabit habitat patches not contiguous with the main block of native habitat ≥200 m a.s.l.. Areas of the habitat types used for estimating the Coromandel Archey’s frog population were obtained from the vegetation layer in the NZ Land Resource Inventory spatial database Version 3 (NZ LRI) (https://lris.scinfo.org.nz/layer/48055-nzlri-vegetation/). Information in the database on vegetation types was derived from stereo aerial photograph interpretation, field verification and measurement, undertaken between 1973 and 1983[2, 33]. Land Cover Database version 5.0 (LCDB v5.0) (https://lris.scinfo.org.nz/layer/104400-lcdb-v50-landcover-database-version-50-mainland-new-zealand), which was last corrected during summer 2018–19, is the most recent spatial database for vegetation types in the Coromandel. Satellite imagery is the primary data source for classify vegetation classes in LCDB v5.0. Information from the older NZ LRI spatial database was used in preference to information from LCDB, because in the LCDB database there are only three classes of indigenous woody vegetation
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