After expert elicitation: The importance of evidence-based conservation assessments to close knowledge gaps for threatened species conservation

As more species are listed as threatened and conservation statuses deteriorate, competition for resources to protect these species intensifies. Effective allocation of limited funding is crucial and should be based on robust evidence to reduce uncertainty. Evidence-based methods are key to producing reliable conservation outcomes, from initial conservation assessments to evaluating policy and management. However, urgency often drives conservation assessments before adequate surveys are conducted, or funding is contingent on an already elevated threat ranking. In such cases, expert elicitation is a necessary and pragmatic tool. Where feasible, subsequent empirical evaluation is important to ensure conservation rankings remain evidence-based and biologically plausible, as improper assessments can lead to lost opportunity costs. In 2014, the Western Ringtail Possum, one of Australia's most imperilled species, was assessed as Critically Endangered based on estimated decline. The population was thought to be 3400 and declining, but this estimate relied on disparate survey methods or indices that lacked standardisation and did not account for detection probability. Using distance sampling across 41 sites and 1236 km of transects we provide a robust abundance estimate of 21,811 individuals (95 % CI: 19,162–26,192). When approximating mature individuals, the estimate is 18,023 (95 % CI: 14,902–21,797), quintupling the previous estimate. Our survey, which excluded stronghold populations in urban and peri-urban areas, covered 112,965 ha, more than double the previously estimated area of occupancy. This robust survey method allows for future evaluation of management interventions through formal experimental design and underscores the importance of evidence-based methodologies in threatened species conservation. • Evidence-based methods are key to producing reliable conservation outcomes . • Elicited population estimates require field verification to justify expenditure. • Verification surveys guided by strategy documents maximise synergistic outcomes. • Robust empirical data supports decisions on further conservation funding and management strategies .