A stoat that seemingly swum to predator-free Oruawairua/Blumine Island has been caught in a trap, showing the value of permanent trap networks on predator-free islands.
The Marlborough Sounds sanctuary island is home to rare and vulnerable bird species including kākāriki karaka/orange-fronted parakeet, mohua and tīeke/saddleback, as well as the nationally vulnerable giant snail Powelliphanta hochstetteri.
DOC Picton Biodiversity Ranger Amy Brunsden says quickly catching the stoat in the permanent trap network is the best result we could hope for.
"This shows the value of having the trapping and surveillance network on the island, despite its predator-free status. It means we can respond quickly and catch any predators before they become established and start breeding.
"Critically endangered kākāriki karaka nest and roost in tree holes so they're extremely vulnerable to predation and even one stoat could do lots of damage. They are only found in five sites in the wild and each is vital for the species' recovery.
A trail camera captured an image of a stoat in July and DOC became aware of it in mid-August during a monthly review of the images. The cameras are set up to monitor for incursions like this.
"Stoats can swim surprising distances; they have been recorded swimming as far as 5 km. This one most likely swum across from nearby Arapaoa Island, which has stoats in low numbers, and is only 400 m away at the closest point," Amy says.
"Once DOC became aware of the stoat, rangers went out to check the island's permanent trapping network and were thrilled to find a stoat had been caught.
"To be sure it was only one stoat, we've also put out extra trail cameras and tracking tunnels which detect introduced predators. A trained stoat detection dog will also check the island."
The additional measures will be in place until DOC is certain only one stoat made the swim, Amy says.
Amy says we know from other island incursions it can be tough to remove stoats in low numbers so it's vital to detect any intrusions and respond quickly.
While the trapped stoat likely got to Oruawairua under its own steam, it's a reminder predator-free islands count on people to play their part to keep them that way, Amy says.
"New Zealand's animals and plants are different and predator-free islands like Oruawairua are a chance for people to go naturing in these ecosystems as they once were.
"We're privileged a sanctuary like Oruawairua is open to the public, but with this comes a responsibility for visitors to follow quarantine procedures and make sure they don't accidentally introduce pests or predators. Everyone has a role in protecting nature.
"Thoroughly check your boat or kayak and equipment for pests like rodents, insects like ants, and unwanted seeds. Make sure it's had a thorough clean, and keep any bags tightly closed ahead of your visit. There's more info on quarantining in the DOC website."
Visiting pest free islands: Know before you go
Background information
Oruawairua was declared predator-free in 2008 following a DOC eradication programme for rats and stoats in 2005.
Before this incursion, a stoat was last detected on the island 10 years ago, which was also caught in a trap.
DOC has permanent traplines and trail cameras set up across the island which are checked monthly as a first line of defence against any possible incursion.
The Nelson Marlborough Institute of Technology trainee ranger course and the Untouched World Foundation both visit the island annually to carry out crucial maintenance on tracks and traps.
The Arapaoa Kiwi Trust runs a trapping programme which aims to eradicate stoats from nearby Arapaoa Island.
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