Videos reveal rodent invasion
Efforts to stamp out a growing rat population on a precious pest-free island sanctuary are failing, with motion-activated cameras capturing footage of the pests mating.
The Department of Conservation has released dozens of videos to The Press under the Official Information Act, revealing the presence of rats on Ulva Island, in Paterson Inlet, about 800m off Rakiura/Stewart Island, and an easy swimming distance for rats.
The clips show male and female rats at various locations on the island, which achieved predator-free status in 1997 and was praised as a ‘‘conservation jewel’’ by Prince Harry in 2015.
The sanctuary is home to many native species, including brown kiwi, ka¯ka¯, ka¯ka¯riki, mohua, and t¯ıeke, or South Island saddleback.
DOC Rakiura operations manager Ren Leppens said a rat was found in a kill trap on November 9, 2021 through proactive surveillance checks.
The cameras were checked daily during the main period of the incursion, then less frequently once rats were no longer being caught in traps or seen on the cameras, he said.
By March, rats of different sizes were increasingly noted on the island, with several released clips showing them mating before the cameras.
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, 2021 and May 2, 2022, with more recent data yet to be collated.
‘‘Rats can breed from a very young age, and the population can multiply rapidly,’’ he said.
Rats have re-invaded Ulva Island more than 20 times since 1997, with most incursions successfully thwarted.
DOC is working with local iwi, the community, landowners and Ulva Island tourism operators on a strategy to deal with the rats and protect wildlife on the island.