9 Memorandum : Vibration effects on amphibians (Leiopelmatid frogs) 64524 Vibration effects_memorandum (15 June 2022)_Final Rev 0 until 1998, when it was closed due to falling gold prices. The mining licence required CGNZL to maintain rigorous environmental standards and undertake regular environmental monitoring. Hochstetter’s frog (L. hochstetteri) was chosen as a species to monitor because of the high conservation concern for this species and the sensitivity of frogs as indicator species for the ‘health’ of the environment (Whitaker, 1999). The population of Hochstetter’s frog in the vicinity of the Golden Cross mining operation was surveyed and monitored between 1991 and 1998, which included a baseline survey in 1989 (prior to mining) and monitoring over subsequent years of mining activity (Slaven, 1992; Slaven, 1994; Whitaker, 1996; Whitaker, 1999). Key findings of this long-term study indicated that: • The relative abundances and densities of frogs within the study streams varied markedly over the nine-year (1989-1998) period and these variations were most likely the result of sampling bias rather than changes in actual numbers of frogs. • The population structure (i.e., the proportion of frogs in each size class) changed significantly over the study period. Initially, the decline in the proportion of juvenile frogs and increasing proportion of adult frogs was interpreted as evidence for of declining recruitment and an increasingly aging population (Slaven, 1994; Whitaker, 1996). However, Whitaker (1999) subsequently reported an increased proportion of sub-adults in the final 1998 survey, suggesting that the observed changes in age structure were the result of actual (natural) fluctuations in recruitment (possibly the result of regional climatic variations) rather than consequences of mining activities or monitoring methodology. • Whitaker (1996) dismissed vibration effects on frog populations as a result of mining operations as being irrelevant. • Whitaker (1999) concluded that no evidence was detected that the activities of the mining operation affected Hochstetter’s frog populations or frog habitat in the study streams. What can be drawn from this study is that Hochstetter’s frog populations at the Golden Cross mine study sites fluctuated naturally over the period of mining operations and that frog populations persisted in the vicinity of mining operations, which included activities such as drilling and blasting, between 1991 and 1998. More recent records of Hochstetter’s frog from 2008, from areas in the vicinity of the original frog monitoring sites, indicate that Hochstetter’s frogs continued to persist in the general location post-mine closure. Furthermore, Archey’s frog is also known from the same locations. Archey’s frog was first recorded there in 1986 and subsequently recorded in 2004 and again in 2011 (DOC Herpetofauna database). These records indicate that Archey’s frog persisted at the site, and by inference were subjected to the same mining disturbances, alongside Hochstetter’s frog over the duration of the mining operations. However, there is no information on the population trends of Archey’s frog between 1991 and 1998 because this species was not monitored as part of the mining licence. More recently, Heilig & Partners (2020) assessed the surface vibration effects associated with blasting at the historical Golden Cross mine. They modelled magnitude distribution curves and vibration contours associated with production blasting (open pit and underground mine) and vibration contours were
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