A second rat incursion on predator free Ulva Island this year highlights the value of the island's strong biosecurity surveillance network.
Department of Conservation staff on Stewart Island/Rakiura have scaled up an incursion response following at least two further rat detections on the island, coming after two months of no detections.
DOC Operations Manager Jennifer Ross says thanks to the earlier investment in the island's biosecurity and trapping network, the rats were able to be detected quickly.
"Quick detections are a vital part of an incursion response. The sooner we know about an incursion, the sooner we can act, maximising our chances at returning the island to a predator free haven for vulnerable native species."
In January, a dead rat was found in one of the island's traps, sparking an incursion response. Increased surveillance over the next two months, including thorough searches by a pest detection dog, did not find any further signs of rats, and the response was wound down in early March.
A further rat was then detected by an AI-equipped trail camera located toward the eastern end of Ulva Island on Friday, 13 March.
Once the report was confirmed, the team were able to respond quickly and scale up an incursion response, which had been wound down just days before.
Since then, two rats have been trapped.
"While we never want to see a rat on Ulva Island, this shows our biosecurity network is working exactly as intended. Previously, it could have taken up to four weeks to discover another new arrival. Now, we detect incursions quickly and are able to scale up our response straight away," Jennifer says.
The intensive incursion response includes weekly checking of all traps, reviewing all trail camera footage, and inspecting for signs of rat activity. Bait stations have also been opened, and a rodent detection dog is on hand to support the response.
The island's network of trail cameras was upgraded in 2024 to boost the island's defences against rats making the short swim or hitching a ride in people's gear from mainland Rakiura. On average, one or two rats reach Ulva Island each year.
Jennifer Ross says the ongoing risk to Uva Island showcases the importance of the Predator Free Rakiura vision.
"Removing rats from Rakiura once and for all will dramatically reduce the risk to Ulva Island and other vulnerable ecosystems. Achieving a predator free Rakiura will be a gamechanger for native species and the future of conservation here."
Visitors are asked to support Ulva Island's biosecurity by checking bags and footwear thoroughly for soil, seeds and vegetation and reporting any signs of rodents.
