Numbers of spotted-tail quolls in north Queensland have dwindled to critically endangered levels, new research into the threatened marsupials suggests.
Over two years, scientists monitored populations of the north Queensland subspecies of the spotted-tail quoll, Dasyurus maculatus gracilis, which lives in cool regions at high elevation.
The population has halved from previous estimates, of 500 quolls around 25 years ago, to 221 adult quolls – meeting criteria for the subspecies to be listed as critically endangered under the Environment Protection and Biodiversity Conservation Act.
After the Tasmanian devil, the spotted-tail quoll is the second-largest carnivorous marsupial, with adult males growing to several kilograms and females weighing in around 1.5kg. The species preys upon animals including possums, bandicoots, rats and birds.
Study co-author Conrad Hoskin, an associate professor at James Cook University, described the spotted-tail quoll as a “faster, more agile version of a Tassie devil”, which is capable of climbing trees to catch its prey.
Using images captured from bait-activated camera traps, the researchers were able to identify individual quolls from the unique patterns of their spots.
Hoskin said there were six separate groups of northern spotted-tail quolls living in different mountainous regions.
“The compounding problem is that the total [number] is broken up into six small populations that range in size from somewhere around 10 individuals up to about 100 individuals,” Hoskin said.
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A key concern is that these isolated quoll groups are “in the realm of getting into 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.”
The carnivores play a key ecological role, with Hoskin describing the quolls as “the top predator in those mountaintops”.
The researchers are not yet certain about what is driving the population decline. Poisoning from cane toads are a theory, but “cane toads have never been particularly common in the upland of the wet tropics”, Hoskin said. However, he noted that “over the last decade or two, we’ve seen a lot of female toads get … into the higher elevations”.
“The other thing is there’s a lot of fragmentation and traffic in north Queensland, so there are definitely some getting hit on the roads. Climate change could well be impacting them if it’s impacting their prey, like possums and [other] small mammals.
“If you start to get inbreeding effects on top of other threats, you could really drive pretty quick declines.”
The northern subspecies of the spotted-tail quoll is distinct from the northern quoll, a smaller quoll species that is also found in Queensland and is also endangered.
The study was published in the journal Austral Ecology.