Garrard GE, SA Bekessy, MA McCarthy and BA Wintle (2014) Incorporating detectability into environmental impact assessment for threatened species. CONSERVATION BIOLOGY 29(1):216-225

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Environmental impact assessment (EIA) is a key mechanism for protecting threatened plant and animal species. Many species are not perfectly detectable and, even when present, may remain undetected during EIA surveys, increasing the risk of site-level loss or extinction of the species. Numerous methods now exist for estimating detectability of plants and animals. Despite this, regulations concerning survey protocol and effort during EIAs fail to adequately address issues of detectability. Probability of detection is intrinsically linked to survey effort and thus minimum survey effort requirements are a useful way to address the risks of false absences. We describe two methods for determining appropriate survey effort requirements during EIA surveys and demonstrate their application for Pimelea spinscens subsp. spinescens, a critically endangered grassland plant species in Melbourne, Australia. We demonstrate how minimum survey effort requirements change with suboptimal survey conditions and shifting burden of proof (ie. from determining presence to demonstrating absence of the species). In our study, P. spinescens was detected in only half of the surveys undertaken at sites where it was known to exist. Modelled estimates of the survey effort required to detect the species or demonstrate its absence with any confidence are much higher than the effort traditionally invested in EIA surveys for this species. We argue that minimum survey requirements be established for all species listed under threatened species legislation and hope that the work presented here will provide extra impetus for collecting, compiling and synthesizing quantitative detectability estimates for a broad range of plant and animal species.