Camera-trapping density estimates suggest critically low population sizes for the Wet Tropics subspecies of the spotted-tailed quoll (Dasyurus maculatus gracilis)

Abstract

Accurate estimates of distribution and population density are critical for the management of threatened species. This is particularly pertinent for mammalian predators, whose generally low population density, elusive nature, and large home range requirements make it difficult to detect declines. We aimed to refine population estimates of the northern spotted-tailed quoll (Dasyurus maculatus gracilis) in the Wet Tropics bioregion, to estimate the total number of adults, the likely size of subpopulations across the known distribution of the subspecies, and its associated conservation status. We performed targeted upland camera-trapping surveys from June 2017 to May 2019. To calculate population densities, we used a combination of the number of individuals identified from each survey and the mean maximum distance moved from three life history stages. We then extrapolated these estimates to modelled suitable habitat areas, refined by the camera-trapping surveys. Population sizes for the six defined subpopulations were estimated, and ranged from approximately 5 to 105 individuals. The total population was estimated to be 221 individuals. This total population estimate, and the estimates for each of the subpopulations, are lower than previous published estimates and are cause for concern. Given the low population estimates presented here and unresolved threats driving declines in some subpopulations, we suggest elevation of this subspecies to Critically Endangered under the EPBC Act.