Spot-tailed quoll numbers in northern Queensland have declined to critically endangered levels, according to new research on endangered marsupials.
For two years, scientists monitored populations of the North Queensland subspecies of the spotted-tailed quoll, Dasyurus maculatus graciliswhich lives in cool regions at high altitudes.
The population has halved from previous estimates, from 500 quolls around 25 years ago, to 221 adult quolls – meeting the criteria for the subspecies to be listed as critically endangered under the law on environmental protection and biodiversity conservation.
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After the Tasmanian devil, the spotted-tailed quoll is the second largest carnivorous marsupial, with adult males reaching several kilograms and females weighing around 1.5 kg. The species feeds on animals including opossums, bandicoots, rats and birds.
Study co-author Conrad Hoskin, an associate professor at James Cook University, described the spot-tailed quoll as a “faster, more agile version of a Tassie devil”, capable of climbing trees to catch its prey.
Using images captured from bait-activated camera traps, researchers were able to identify individual quolls from the unique patterns of their spots.
Hoskin said there were six distinct groups of northern spot-tailed quolls living in different mountainous regions.
“The compounded problem is that the total [number] is divided into six small populations ranging in size from about 10 individuals to about 100 individuals,” Hoskin said.
A major concern is that these isolated quoll groups are “on the verge of entering a downward spiral based on genetic issues”, he said. “If you only have 10 or 20 individuals, you can’t avoid related individuals breeding with each other.”
Carnivores play a key ecological role, with Hoskin describing quolls as “the best predator on these peaks”.
Researchers are not yet sure what is causing the population decline. Cane toad poisoning is a theory, but “cane toads have never been particularly common in the highlands of the humid tropics,” Hoskin said. However, he noted that “over the past decade or two we have seen many female toads ascending…into the higher elevations”.
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“The other thing is there’s a lot of fragmentation and traffic in North Queensland, so there’s definitely some collisions on the roads. Climate change may well impact them if it impacts on their prey, such as opossums and [other] small mammals.
“If you start having inbreeding effects on top of other threats, you could really lead to some pretty rapid declines.”
The northern subspecies of the spotted-tailed quoll is distinct from the northern quoll, a smaller species of quoll that is also found in Queensland and is also endangered.
The study was published in the journal Austral Ecology.