Checking one of the rat traps on Ulva Island. Photo: Supplied
The Department of Conservation has triggered an incursion response after a rat was found dead in a trap in one of country's few pest-free, open air sanctuaries.
Ulva Island was first declared pest free in 1997 and sits just under 800 metres off the coast of Rakiura.
Rakiura operations manager Jennifer Ross said they would increase the intensity of biosecurity checks to make sure there were no other rats present as well as more rangers on the ground and more rat detection dog work.
"Given how close Ulva is to the mainland and how many people visit it, incursions are frequent, averaging between one and two incursion events each year," she said.
"Catching rats in traps is a key way we detect invaders and protect the island from rat populations becoming established."
Last winter, they kicked off an eradication programme on the island after a breeding population of rats set up shop there, but there have been no signs of any remaining rats in the months since that happened.
"Since the last incursion, we've upgraded the island's biosecurity system with new tools like trail cameras, more frequent trap checks, and a rearranged grid increasing detection and control devices in the coastal areas where the pests typically first arrive."
Work is underway to figure out if the rat had evaded detection since the eradication or if it was a new arrival.
"As long as rats are present on Rakiura, reinvasion to Ulva is a high risk. Ulva Island is our best local example of Aotearoa as it used to be, and it's absolutely worth defending."