Estimating the proportion of Archey’s frogs in the Wharekirauponga mine vibration footprint 8 Estimates of Archey’s Frog Abundance Published Estimates There are several estimates of Archey’s frog abundance obtained using a variety of methods (Table 5). These estimates include: counts of the numbers frogs found during daytime searches of potential refuge sites along transects[7-10]; minimum numbers alive estimated from the number of toe clipped individuals found during daytime searches of refuges in a 10x10 m plot[11]; capture-recapture estimates of plot population size using toe clipped individuals found during daytime searches of frog refuges in a 10x10 m plot[12]; and capture-recapture estimates of plot population size using photographic identification of individuals found during night-time searches of a 10x10 m plot in Whareorino, west Waikato[13]. Counts of frogs found during daytime searches provide population indices, which can be used for comparative purposes. However, in the absence of information on detection probabilities simple counts can be misleading even for comparisons and are not useful for population estimation. Minimum number alive estimates from the total numbers of uniquely identified individuals in plots are also confounded by lack of information on detection probabilities. Capture-recapture methods are the most effective method for obtaining robust population estimates for animals like Archey’s frogs that are difficult to observe[14]. Results from a long-term (1984–2002) capture-recapture study of Archey’s frog in a single 10x10 m plot on Tapu Ridge in the Coromandel Peninsula (Figure 7) showed an 88% decline in the plot population between around 1996 presumed to be a result of an outbreak of the fungal disease chytriodiomycosis[15]. The means of plot population estimates during the periods 1984–1994 and 1996–2002 were 433 frogs (SE ±32) and 53 frogs (SE ±8) respectively, giving density estimates (Table 5) of 43,300 ha-1 (CI95%iv: 37,028–49,572 ha-1) and 5,300 ha-1 (CI95%: 3,732–6,868 ha-1). The study was undertaken using toe clipping to identify individual frogs found during repeated daytime searches of frog refuges in the plot. The plot is in mixed podocarp-hardwood forest (N3a) in the ≥400<500 m altitude band. Its location was selected because Archey’s frogs were known to be locally abundant; consequently density estimates from the single plot are unlikely to be representative of the wider area. A capture-recapture study of Archey’s frogs in Whareorino forest, west Waikato[13] used photographic identification of individuals found during night-time searches of a single 10x10 m plot. The plot was in mixed podocarp-hardwood forest in the ≥300<400 m altitude band and was selected because of known frog abundance. The published plot population estimate is 103.7 (SE ±16.5), giving a population density estimate of 10,370 ha-1 (CI95%: 7,136– 13,604 ha-1). Again, density estimates from a single plot chosen for its abundant frog population are unlikely to be representative of the wider area. iv CI95% ~ the 95% confidence interval. The interval with a 95% probability of enclosing the actual value of the parameter being estimated.
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