Doc Rakiura acting operations manager Bridget Carter said yesterday an incursion response started on Ulva Island after a rat was found dead in a trap last week during a routine surveillance.
The team had been checking traps and using lured cameras and rodent detection dogs to determine the extent of rat presence.
“Since the dead rat was found on January 13, rat activity has also been captured on trail cameras,” she said.
“Our plan from here is to continue with increased surveillance and ongoing trapping efforts to monitor for further signs and catch any remaining rats. Toxin may be used sparingly where rats are known to be present but avoid traps.”
She said although detecting rats on the island was disappointing, it did show the biosecurity monitoring system was working as it should.
On average one or two rats managed to find their way to Ulva Island each year due to its proximity to Rakiura where rats were present.
The risk increased when rat numbers were high on the mainland due to warm weather and food availability, she said.
Speaking to the Otago Daily Times, Ms Carter explained they were a big problem on Rakiura, both for wildlife and the community.
Predator Free Rakiura’s aim of eradicating rats as well as possums, feral cats and hedgehogs from both the main island and surrounding isles and rock-stacks was very important, but also a huge challenge.
“This is a massive undertaking, and if achieved will be the largest inhabited island to be eradicated of introduced predators,” Ms Carter said.
The project was planning for the first operational stage, which would trial methods, developed by Zero Invasive Predators (Zip) in South Westland, to see how this could be adapted and applied successfully on Stewart Island.
“Because of the size of Rakiura, the island would need to be tackled in chunks, likely moving from south to north over the course of five to six years.”
Ulva Island was declared rat-free again in early 2024 after a breeding population of rats established on the island in 2023.
Since then the island’s biosecurity system was upgraded with a new network of lured trail cameras, more than double the number of ground-based traps and a 100m-by-100m grid of bait stations throughout the island, Ms Carter said.
“This biosecurity network is focused in coastal areas which is the preferred habitat of Norway [brown] rats.”
She reiterated the commitment to keep the sanctuary free from predators, a status first achieved in 1997.
“Doc and the Rakiura community have worked hard to maintain Ulva Island’s predator-free status and we will continue to respond to any incursion as quickly and effectively as possible.”
