Biosecurity threatened after campers take selfies of pet cat ashore K'gari/Fraser Island

The cat owners had documented their trip on social media, which was reported to authorities by Fraser Coast locals.   (Supplied: Department of Environment and Science)

A seemingly innocent post to social media of a family's pet cat on Queensland's heritage-listed K'gari/Fraser Island has outed the travellers as being behind a "major breach of quarantine", with authorities warning of the seriousness of the misdemeanour. 

When campers posted photos online of their pet ginger cat on the island, it was not long before keen-eyed social media users alerted authorities.

Queensland Parks and Wildlife Service (QPWS) Compliance Manager Mark Devery says the relatively harmless pet posed a huge threat to the island's natural wildlife.

"If a cat survives out there, they can always become a problem and the department certainly puts a lot of energy into controlling feral cat populations. So, we certainly don't want to add to them."

Authorities say the campers have since left the island, but they are working to identify those responsible. (Supplied: Department of Environment and Science)

But Mr Devery said the biggest threat the cat posed was on the island's most protected species.

"This is a major breach of quarantine, as domestic animals including cats, birds and dogs are not permitted in Queensland's national parks," he said.

"On K'gari there's always the possibility of a domestic animal carrying a disease or virus that could negatively impact the important wongari [dingo] population."

The ranger said there was more than one reason pets were not allowed on the heritage parkland.

"The wongari is the apex predator on K'gari. If it saw the cat as a potential food source then you could have an adverse interaction between the cat, the wongari and the owner, which is highly undesirable," Mr Devery said.

The cat's owners also documented their travels to Bribie Island on social media. (Supplied: Department of Environment and Science)

Cat owners have moved on

Further investigation of the social media account led authorities to believe the cat's owners were no longer on the island.

"The images indicate that the particular family with the cat may be moving around Queensland or possibly moving around Australia, so we no longer think they are on K'gari," he said.

But QPWS's compliance team were working to track down the campers.

"When people post these things which clearly are not lawful within the locations they are in, they thereby encourage others to do the same which is the problem," Mr Devery said.

"Of course, anyone can always bring a certified assistant dog, but otherwise no domestic animals.

"The fine for an unauthorised domestic animal is $137."

The owner of this cat was fined earlier this year for taking their pet to K'gari. (Supplied: Department of Environment and Science)

These particular cat owners were not the first to breach the island's biosecurity this year.

"But the implications are not just a fine."

"If you come to any of these locations and you're discovered with a domestic animal, you're not going to be able to stay and you will be asked to leave."