A rat has been found dead in a trap on a predator free Southland island, triggering a hunt.

Ulva Island, off the coast of Stewart Island / Rakiura, first became predator-free in 1997 and is a sanctuary for many native species .

Department of Conservation (DOC) acting operations manager for Rakiura, Bridget Carter, said intensive monitoring for rats was underway after the rat was found last week during routine surveillance.

Teams have been checking traps using lured cameras and rodent detection dogs.

"Since the dead rat was found on 13 January, rat activity has also been captured on trail cameras. Further monitoring will tell us if this is a single rat or more," she said.

DOC planned to continue with the ramped up surveillance and trapping efforts to catch any remaining rats, but didn't rule out using toxins if they were avoiding traps.

"Although detecting rats on the island is disappointing, it does show the biosecurity monitoring system is working as it should," she said.

One or two rats manage to get to Ulva Island each year on average, but this risk increases when rat numbers are high on the mainland.

In winter 2023, DOC successfully eradicated a breeding population on the island, which was declared rat-free again early last year.

Visitors are encouraged to report any signs of rat presence on Ulva Island to the DOC Rakiura Office.

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