A study reveals that endangered Spotted-tailed Quolls in North Queensland might in fact be critically endangered, with numbers down to fewer than 250 individuals in a handful of small and declining populations.

The research collaboration between the University of the Sunshine Coast (UniSC) and James Cook University (JCU) is the first to estimate the number of northern Spotted-tailed Quolls in all surviving populations.

The researchers used remote camera traps to find Spotted-tailed Quolls (Dasyurus maculatus gracilis), the second largest carnivorous marsupial in Australia after the Tasmania Devil.

“This project involved many days of rainforest trekking while deploying and collecting camera traps all over the mountains of the central and northern Wet Tropics,” said UniSC Masters graduate and lead author of the study, Jesse Rowland.

“We built a catalogue of images of individual quolls, using their spot patterns, and then went through all the photos to see which quolls have visited each camera. That gave us the data we needed to estimate the population size and demographic make-up of each population.”

JCU’s Associate Professor Conrad Hoskin, a co-author, says this is a landmark study of one of Australia’s rarest creatures.

“The north Queensland subspecies of the Spotted-tailed Quoll is only found in six mountainous areas, all in the Wet Tropics, and it’s very rarely seen. This new population estimate is backed by the best quality data to date, and the results are alarming.”

The study, published in the journal Austral Ecology, estimated that the total population is around 221 individuals.

The populations range in size from about five adults in the smallest group, up to around 105 adults in the largest. The researchers found that the three populations in the north (in the Daintree region) are relatively numerous, but the three southern groups (in the Atherton Tablelands region) are small in size, and at least one of these populations may disappear in the near future.

“Our estimate is half a previous estimate of over 500 quolls, made about 25 years ago,” Mr Rowland said.

“These new results are very much cause for concern, and we suggest the status of the subspecies should be elevated to critically endangered under the Environment Protection and Biodiversity Conservation Act.”

Dr Scott Burnett, a co-author of the study, said the quolls’ scarcity, combined with their extensive range, and their extremely rugged habitat in the Wet Tropics, makes spotted-them very difficult to study.

“Accurate population estimates are so important for gauging the effects of many threats which limit quolls – including human activities and climate change – and for measuring the success of conservation efforts,” he said.

“Our latest analysis has returned worryingly low population estimates in most of the surviving populations.”

Associate Professor Conrad Hoskin worries that the small size and isolation of the remaining populations compounds the extinction risk to northern Spotted-tailed Quolls.

“When populations become this small, inbreeding can become an issue that threatens the short and longer-term survival of the species. We need to work out the genetics of the remaining populations and factor that into conservation decisions moving forward.” 

Meanwhile a recent study led by UniSC on another endangered quoll species has found male Northern Quolls are giving up sleep in favour of having more sex – and it could be killing them.

The study investigated why male Northern Quolls (Dasyurus hallucatus) – who usually mate themselves to death in one season – do not survive to breed again while females can live and reproduce for up to four years.