Video reveals rodent invasion of ‘pest free’ sanctuary
Efforts to stamp out a growing rat population on a pest-free island sanctuary are failing.
The Department of Conservation has released dozens of videos to Stuff under the Official Information Act, revealing rats on Ulva Island, in Paterson Inlet, about 800m off Rakiura/Stewart Island – an easy swimming distance for rats.
The island achieved predatorfree status in 1997. It is home to many native species, including brown kiwi, kākā, kākāriki, mohua, and tīeke, or South Island saddleback. DOC Rakiura operations manager Ren Leppens said a rat was found in a kill trap on November 9 last year.
A range of detection and surveillance tools were used, including chew sticks, ink cards, trail cameras, rodent detection dogs and checking for signs such as rat footprints on sand. By March, rats of different sizes were increasingly noted on the island.
DOC did not have an estimate of the number of rats on the island but Leppens said there was no evidence of rat predation of eggs or native species. To date, 21 rats had been caught in traps between November 9 last year and May 2 this year.
Rats have re-invaded Ulva Island more than 20 times since 1997, with most incursions successfully thwarted. However, a significant podocarp forest mast (seeding) on the island provided plenty of food which meant the rats had shown little interest in the baits and lures.
‘‘It is disappointing intensive efforts to stamp out the incursion have failed,’’ Leppens said.
Meanwhile, DOC was working with local iwi, the community, landowners and Ulva Island tourism operators, on a strategy to deal with the rats. ‘‘Some possible options include ongoing trapping to maintain lower rat numbers, or once again eradicating rats using ground-based or aerial toxins. If rats are not stamped out, we are facing a loss of some species from the island and impacts on tourism businesses.’’
The issue highlighted the benefits of a predator-free Rakiura, he said. This week a research partnership agreement – worth $2.8 million – was signed to make Stewart Island predator free.
The four-year project involving Manaaki Whenua-Landcare Research and Predator Free Rakiura aims to eradicate major predators – possums, rats, feral cats and hedgehogs – from Rakiura.