Monitoring results are aided by the fact the spotted tail quoll carries a unique identifier on its body: the pattern of spots on its back is as unique as a human fingerprint or a zebra's stripes.

Now, survey efforts have identified 52 individual quolls in the Barren Grounds Nature Reserve, which is the highest number since monitoring began five years ago, the NSW Government said.

Quoll expert James Dawson from the Department of Planning, Industry and Environment said this survey and photo monitoring results indicate that this quoll population, one of four monitored across NSW, is stable and could be increasing.

Read more: Meet a few of the Illawarra's most endangered species

This came as particularly good news after attempts to reintroduce quolls into the wild at Booderee National Park appeared to have failed with none being seen by May.

"Every June the team undertake a two-week trapping survey where we catch quolls, weigh them, give them a quick health check, a microchip and photograph their unique spot patterns," Mr Dawson said.

"In the most recent survey young and old males and females were caught, showing that the population is a robust resident breeding population.

"It's particularly encouraging to see young females that are the nucleus of the future population."

Mr Dawson said nearly 30 motion sensor cameras have been in place at different sites around Barren Grounds Nature Reserve and adjacent Budderoo National Park.

"Some of the photos we got this year are quite extraordinary, not only because they tell us where and how active these animals are but also because we saw many individuals on multiple cameras," he said.

"This is very encouraging as it demonstrates that this area between the Illawarra and Southern Highlands has a spreading breeding population that is possibly increasing in their geographical range.

A highly elusive carnivorous marsupial, the spotted tail quoll has become particularly susceptible to predators - primarily the fox - as habitat loss from human development of bushland has caused populations to become fragmented.

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