Tasmania has long been thought of as a stronghold for the tiny and tenacious eastern quoll, but new research shows the species has been in decline in the state for the past 35 years — and researchers do not know why.
Eastern quolls were declared extinct on mainland Australia in 1963 and are carnivorous marsupials, related to the Tasmanian devil.
Calum Cunningham, whose research on quoll populations was recently published in the journal Australian Mammalogy, said the quolls used to occur in such numbers that the first colonial settlers referred to "huge plagues" of the animals.
"It's been long thought that Tasmania had this safeguarded population of quolls … but it doesn't seem to be the case anymore," Dr Cunningham told ABC Hobart's Lucy Braedon.
A patchy decline
Tasmanian Land Conservancy conservation ecologist David Hamilton said the decline of eastern quolls was "very concerning".
What makes the quolls' fate more perplexing is that their decline in Tasmania is patchy.
The animals have disappeared in some areas, but in other places they are still going strong.
"They used to show up on Freycinet regularly … but now we don't see them," Dr Hamilton said.
"[But] if you tell someone in north Bruny Island or the Huon Valley that quolls are decline, they'll look at you like you're crazy."
Why are they disappearing?
Dr Cunningham said the cause of the disappearance was "the million-dollar question".
"As ecologists, we know that the populations are not doing well, but we don't have conclusive evidence on what the causes are," he said.
Dr Cunningham did have two lead suspects however, suggesting they might have been impacted by feral cats and unfavourable weather that had influenced their food supply.
Dr Hamilton said unpicking the exact drivers of the eastern quolls' decline was tricky, but suspected "climate, cats and habitat loss" as possible causes.
Extinction may be on the cards
Australia has the dubious honour of leading the world when it comes to mammal extinctions.
Dr Cunningham was concerned that if dramatic action was not taken to save the eastern quoll, it might go the same way as the 38 other Australian mammals that had become extinct in the past 250 years.
"I'm sad to say it, but it feels like we are in slow motion, watching this species edge closer to extinction," he said.
"While the quoll is probably not going to go extinct in the next few years, it's a very real possibility in the next several decades."
The fact that they were already extinct on the mainland and in areas such as the Freycinet Peninsula suggested to Dr Hamilton that the species was particularly vulnerable to being wiped out.
The quest to save the eastern quoll
Dr Cunningham said scientists urgently need to understand why the species was declining if they were going to be protected.
Eastern quolls are one of the 110 species prioritised in the Threatened Species Action Plan released this month by the federal government.
"Being on that list means quolls are expected to receive about a couple of million dollars in funding, which … is woefully inadequate to turn around this trajectory," Dr Cunningham said.
"It would barely be enough to diagnose the causes of the decline."
While the cause of the decline is still being investigated, there are efforts underway to increase quoll numbers in areas where they are faltering.
Dr Hamilton is involved in an effort to reintroduce captive-bred quolls to Silver Plains, an area in Tasmania's Central Highlands that has experienced a dramatic decline in the species, but not a local extinction.
He said the captive-bred quolls were "doing pretty well" but the effort was still in its early days.
Losing our predators
University of Tasmania ecologist Sofie Nagly said the decline of the eastern quoll was part of a "sad and connected story" in Tasmania, where native predators were in decline or extinct.
"We have already lost the Tasmanian tiger," she said.
She also pointed to the Tasmanian devil, whose population had crashed since the outbreak of devil facial tumour disease in the 1990s.
The fatal disease impacting devils, who are a close relative of both quolls and thylacines, has spread to 90 per cent of the species range.
It has caused population declines of more than 80 per cent where it has spread.
"We are losing our top predators and for any ecosystem that can cause effects all the way down the food chain," Ms Nagly said.
"A great example is the reduction in Tasmanian devils, which has allowed the feral cat population to increase — and that might be impacting the eastern quoll population … so we need to monitor to see what's going on.
"I think it's very important to monitor the situation, because quolls are very important for ecosystem."
