The Department of Conservation will consult with the Rakiura/Stewart Island community on plans to deal with a rat incursion on predator-free Ulva Island/Te Wharawhara.
An incursion response after a rat was detected in February, has failed to remove all rats, which have now spread to other parts of the island.
Ulva Island is within Paterson Inlet, 800 m off Rakiura/Stewart Island – an easy swimming distance for rats. It first achieved predator-free status in 1997 and has since become a sanctuary for many native species, including brown kiwi/tokoeka, kākā, kākāriki, yellowhead/mohua, tieke/South Island Saddleback, and many more.
DOC Rakiura Operations Manager Ren Leppens says it’s disappointing intensive efforts to stamp out the incursion have failed, and the priority now is to make a plan with the Rakiura community.
“DOC will be working with local iwi, the community, landowners and Ulva Island tourism operators, to come up with a strategy to deal with the rats and protect precious wildlife on the island.”
Some possible options include ongoing trapping to maintain lower rat numbers, or once again eradicating rats using ground-based or aerial toxins.
“Until rats are eradicated from the Rakiura mainland, Ulva Island will need to be continuously defended,” says Ren Leppens.
“Despite ongoing trapping efforts, at least one rat a year has infiltrated the island since 2012, most likely swimming over, although they may also have arrived on visitors’ boats or stowed away in gear.
“If rats are not stamped out, we’re facing a loss of some species from the island, and impacts on tourism businesses that operate there. Our team on Rakiura is highly motivated to protect this special place, as are the locals.
“The issue with ongoing rat invasions on Ulva Island highlights the benefits of a Predator Free Rakiura, as once rats have been eradicated from the Rakiura mainland, Ulva Island will be significantly more secure as a sanctuary for our treasured biodiversity.
Rats have reinvaded Ulva Island more than 20 times since 1997, with most incursions successfully thwarted. In 2010 an incursion resulted in a breeding population on the island and an eradication operation was undertaken to restore its predator-free status.
DOC’s technical advisors are currently reviewing options to suppress rats on Ulva Island to keep the population at a low level to protect the most vulnerable native species. However, this approach won’t provide the same level of long-term protection as a rat-free island sanctuary.