Distribution, abundance and population demography of the northern spotted-tailed quoll (Dasyurus maculatus gracilis)

Jesse Rowland

doi:10.25907/00124

Monitoring the distribution, abundance and population demography of threatened species is important for their management and guiding conservation outcomes. These factors are crucial in order to detect declines, particularly for mammalian carnivores which are generally elusive, exist at low population densities and have large home ranges. The spotted-tailed quoll (Dasyurus maculatus) is the largest marsupial carnivore on mainland Australia. The species has been described as comprising two subspecies. Dasyurus m. maculatus occurs across Tasmania and along the east coast of mainland Australia as far north as south-east Queensland. Dasyurus m. gracilis is endemic to the Wet Tropics bioregion of north Queensland. The northern subspecies is listed as Endangered under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 and the Queensland Nature Conservation Act 1992, and primarily occurs in upland rainforest. The main threats to survival are habitat loss and fragmentation, competition with introduced predators (e.g., feral cats) and ingestion of cane toads. To date, this subspecies has been surveyed using methods such as live-trapping and radiotelemetry to estimate population numbers, and more recently, using camera traps. Between June 2017 and May 2019, camera trapping surveys were undertaken at each of the six defined subpopulations where the subspecies persists; Carbine Tableland, Windsor Tableland, Thornton Peak Uplands, Lamb Range, Bellenden Ker Range and the South Johnstone area of Wooroonooran National Park. I compared two bait station techniques (bait bags versus bait canisters) for determining the sex and identifying individual quolls using images taken by camera traps at two locations, Windsor Tableland and Mt Lewis. We developed the raised bait canister method as a novel technique to encourage quolls to stand on their hind legs and reveal their ventral surface to the camera. Population densities were derived for each subpopulation using a combination of the minimum number known to be alive from each survey, and the mean maximum distance moved (MMDM) values from three life history stages for D. m. gracilis. Density estimates were then extrapolated to suitable habitat extents in the respective survey areas to derive subpopulation size estimates. Higher detections of quolls were found using the bait bag method, while the bait canister method proved significantly better for determining the sex of individuals (with 81% of identified quolls being confidently assigned a sex). Quoll densities were found to be strongly linked to elevation, with higher densities found above 1000 m than below it for all subpopulations, except South Johnstone. Results also indicated that D. m. gracilis is most common in three upland rainforest regional ecosystems and that terrestrial prey activity (derived from numbers of camera trap detections) may be a driving factor in the distribution and density of the subspecies. The total population of the northern spotted-tailed quoll is estimated to be 221 (127.6–461.4) individuals. This population estimate is much lower than previous published estimates. Northern subpopulations at Carbine Tableland, Windsor Tableland and Thornton Peak Uplands are surviving in higher densities than the remaining southern populations, in the central and southern Wet Tropics, where numbers are concerningly low. Monitoring of key populations is critical. Incorporating novel survey techniques such as the elevated bait station developed here could provide additional demographic data on individual quolls whilst limiting the need for more invasive live-trapping methods. Elevating this northern subspecies to critically Endangered under both Federal and state legislation is recommended, given the low population estimates and unresolved threatening processes playing significant roles in the declines of some populations.

Distribution, abundance and population demography of the northern spotted-tailed quoll (Dasyurus maculatus gracilis)

Files and links (1)

Abstract

Details

Metrics