Checking one of the rat traps on Ulva Island. Photo: Supplied
The Department of Conservation (DOC) has declared Ulva Island rodent-free again.
A rat was found dead in a trap on the pest-free open sanctuary in February.
As a result, DOC launched an incursion response - but four weeks of intensive surveillance and monitoring failed to uncover any further rats.
Ulva Island, declared pest-free in 1997, is just 780 metres from Rakiura/Stewart Island at its closest point.
Rakiura operations manager Jennifer Ross said as a result, rodent incursions occurred once or twice a year, and DOC was now returning to normal monitoring.
"Normal surveillance doesn't mean we're taking our foot off the pedal, far from it. Having an intensive network in place round the clock means when we do get a detection - like we did in February - we can act quickly and scale up."
Ulva Island was one of New Zealand's few pest-free open sanctuaries and was home to vulnerable native species like tieke/South Island saddleback, mohua/yellowhead, titipounamu/rifleman, and South Island kākā.
Since 20 February, the department had checked over 225,000 trail camera images, walked more than 110km of trap lines, travelled more than 180km by dinghy and completed more than 2750 trap checks. Two rodent detection dogs also scoured the island multiple times.
Last winter, a breeding population of rats established on the island, sparking an intensive re-eradication programme.
In the months since, monitoring - including trap checks, motion sensitive camera surveillance, and the use of rodent detection dogs - had not shown any sign of rats remaining on the island, until one was found in February.
As part of last year's re-eradication response, the island's biosecurity system was upgraded with more trail cameras, more frequent trap checks and a rearranged grid increasing detection control devices in the coastal area where rodents usually arrive.
But keeping Ulva Island pest-free remained a challenge as long as there were pests on Rakiura.
"That's why initiatives such as Predator-Free Rakiura are so important, and everyone has their part to play," Ross said.
"We'd like to extend our thanks to everyone for doing their part and continuing to be extra vigilant when visiting Ulva Island. Special mention to the Ulva Island Charitable Trust, who have offered to donate $5000 to the response."
If visitors saw anything suspicious on Ulva Island they should take photos, record the location accurately and report it to the DOC Rakiura office, Ross said.
