As if a single stoat on Great Barrier Island was not bad enough, conservationists believe at least two of the highly-destructive pests may have found their way to the previously stoat-free island.

Photo: 123RF

Two specialist stoat-sniffing dogs are forming part of a large-scale operation by the Auckland Council and the Department of Conservation (DOC) to find the creatures.

Incident controller Jonathan Miles said the sighting on 3 January at Medlands Beach was being treated seriously.

A worst-case scenario was if it was a breeding pair.

"We are taking this extremely seriously because Great Barrier Island has never had stoats on it and certainly we do not want stoats on there because they are a major predator to the bird population."

If confirmed, the stoats were likely stowaways on a boat.

"Because of where the island is in distance from the mainland, really the only way that a stoat will get there is, in a way, human assisted. So yeah, a boat."

That was a reminder of why it was important for visitors to the Hauraki Gulf island to check their gear and vessels for pests, he said.

"Stoats, ferrets, weasels, plague skinks and even Argentine ants rely on people to transport them to our islands, so it's up to people to make sure they are not unwittingly introducing these devastating pests by thoroughly checking their gear and vessels before they leave the mainland."

The island has significant populations of endangered birds which would be easy prey for them and with the speed stoats could cover the ground, Mr Miles said it was vital to get on their trail as early as possible.

A member of the public said they saw the stoats at Medlands Beach on 3 January and reported them the following day.

DOC and the Auckland Council have set up a network of trail cameras, tracking tunnels and traps which, along with the dogs, will try to confirm and eradicate any stoats.