Tasmanian tigers could have lived much later than experts have always believed, into the 1980s and beyond, new research led by a University of Tasmania professor suggests.
UTAS professor of environmental sustainability Barry Brook said the research team used uncertainty modelling and sensitivity analysis to work out that "extinction likely occurred within four decades of the last capture, so around the 1940s to 1970s".
"But we found, through further analysis, that extinction might have been as recent as the late 1980s to early 2000s, with a very small chance that it still persists in the remote south-western wilderness areas."
The research team, which included scientists from the US, the UK and France, re-examined a database of 1,237 Tasmanian tiger sightings from 1910 and later, with an eye to plausibility rather than whether they were backed by physical evidence.
Some accounts, around the time the last tiger died in captivity in 1936 or shortly after, included physical evidence like an image or pelt, but visual sightings continued long after that.
"In terms of physical evidence, there's formal modelling you can do from the last observed animal in the species that tells you how long you'd expect to wait [until the species was extinct]," Professor Brook said.
"If you take that hard approach to evidence, it comes to the unsurprising conclusion that they were probably gone by the early 1940s.
"But if you take a more lenient definition of evidence, after the bounty period … they were often recorded but not captured, so we know they were around. With that type of evidence, you have to ask, how plausible is it that some of those records are valid?
"There are some cases that seem, on the face of it, to be extremely plausible, like Hans Naarding from 1982."
Naarding was a park ranger at Togari, in Tasmania's far north-west, who parked his car one night in the pouring rain at a remote crossroads.
He reported that he observed a fully grown male thylacine for about a minute but did not have a camera, so there was no photo. The sighting sparked a year-long search by Parks and Wildlife, which ultimately proved fruitless.
"You could say, 'Well, that was a delusion, and that's possible, but it's also possible he saw a thylacine," Professor Brooks said.
At the other end of the scale were "highly implausible" accounts from tourists reporting "dog-like" animals seen by the side of the road.
"Based on the relative plausibility of some of these records, the thylacine probably persisted into the 1960s and maybe into the 1980s, and, with some extremely slight possibility, maybe even longer than that," Professor Brooks said.
So is there even the remotest chance that Tasmanian tigers survive, to this day, in the state's wild and rugged south-west?
"I don't think it is possible," Professor Brook said.
"It's a wild, vast area, and there aren't many people or much activity, that's true.
"But the thylacine was a large, wide-ranging predator and there have been enough cameras out there, especially over the last 10 years, to say it's just not there.
"You could have entertained that hypothesis 10 or 15 years ago when there hadn't been much scientific effort out there, but there has been now, and we still haven't found any trace."
The chance is not zero though. Professor Brook said the state's south-west could maintain a thylacine population because there's plenty of food.
"There's enough game and habitat, plenty of places to hide," Professor Brook said.
"So there's a tiny possibility, but my probability estimate would be that it's 99 per cent likely they're extinct now."
The research was published in the journal Science of the Total Environment.
'Hearsay not highly valued'
Wildlife biologist Nick Mooney said the study used a method and modelling that were "perfectly alright".
"The problem is that the original data is very fragile," he said.
"That's just hearsay, essentially.
"So the quality of the original information that this is based on is the problem, not the study itself."
In former roles with Tasmania's parks and wildlife services, Mr Mooney has himself investigated some of the more credible reported thylacine sightings in the state.
"The trouble is you can't cross-examine the people who actually made those reports, and there's a problem with that anyway — with modified memory," he said.
"In fact, the reality of those reports is that they're almost never as credible as they sound or look like on a form. That's why hearsay evidence is not highly valued.
"Any sighting is prone to the possibilities of the person being right, the person being wrong, the person having some strange delusion, or the person lying."
He did not dispute that there was the possibility that thylacine might have existed past the 1930s.
"There's a remote possibility, I think, that the animal might still be there, but it's very unlikely and diminishing as we speak."
The research was published in the journal Science of the Total Environment.
