The pest-free open sanctuary has been the subject of a month-long incursion response after a rat was found dead in a trap in February.
Department of Conservation (Doc) Rakiura operations manager Jennifer Ross said after more than four weeks of increased surveillance, intensive trap checks and comprehensive monitoring work across the island, there have been no further rodent detections.
"This means we’re winding down our incursion response and returning to normal surveillance measures. Normal surveillance doesn’t mean we’re taking our foot off the pedal; far from it. Having an intensive network in place round the clock means when we do get a detection — like we did in February — we can act quickly and scale up," she said
Ulva Island is one of the few pest-free open sanctuaries in New Zealand. It is home to vulnerable native species like tieke/South Island saddleback, mohua/yellowhead, titipounamu/rifleman, and South Island kākā.
Since February 20, Doc staff have checked over 225,000 trail camera images, walked more than 110km of trap lines, travelled more than 180km by dinghy, and completed over 2750 trap checks. Two rodent detection dogs also scoured the island.
"Given how close Ulva is to mainland Rakiura — just 780m at its closest point, and how many people visit it, incursions are frequent, averaging between one and two incursion events each year. "Catching rats in traps is a key way we detect and remove invaders and protect the island from rat populations becoming established."
The island was first declared pest-free in 1997. In winter 2023 a breeding population of rats established on the island sparking an intensive re-eradication programme. In the months since the eradication took place, monitoring had not shown any sign of rats on the island, until one was found in February.
The island’s biosecurity system was upgraded with more trail cameras, more frequent trap checks and a rearranged grid increasing detection control devices in the coastal area where rodents usually arrive.
Keeping Ulva Island pest-free will continue to be a challenge as long as there are pests on Stewart Island.
