Ensuring pet cats and dogs and native birds do not accidentally die during trapping or poisoning has been identified as one of the major challenges of an ambitious plan to remove predators from a swathe of Stewart Island/Rakiura.
All domestic cats would need to be de-sexed, collared and micro-chipped before the project began and would need to be kept indoors, in outdoor enclosures or taken off the island altogether during the predator-removal phase of up to two years, a technical report says.
All dogs would need to be muzzled when outdoors while trapping or poisoning was under way.
The risk of ground-dwelling birds such as kiwi and weka and kaka becoming caught in traps was considered to be low, but native birds such as gulls, morepork, weka and falcons were at risk of dying from eating the carcasses of poisoned rats or possums.
Three technical reports were commissioned by the Department of Conservation (Doc) on behalf of the Predator Free Rakiura Governance Group. They contain a wealth of detail about the scale of the project, the cost, and the challenges.
If eradication took place from the larger area of the island, 19,700 bait stations and 24,7000 traps would be used, requiring several hundred people to check them regularly, one report said.
Eradicating rats from the Oban township, home to about 400 people, ''poses a unique set of planning challenges'', the report said.
Bait would have to be laid in, around and, ideally, under all buildings, while all sheds, boats and vehicles would also need to be treated.
The technical reports have been released for public consultation.
Drop-in sessions are being held at the island's community centre on October 5-6 where the report's authors will answer questions and listen to feedback, while people are also being encouraged to comment in writing.
Group member and Stewart Island resident Sandy King said the scenarios were designed to stimulate discussion.
''None of the options are set in stone. No decisions have yet been made.''
The experts' predictions for the cost of the project had been an ''eye-opener'' for group members and would be for the public and potential funders as well, she said.
''At the upper end it could be well over $30 million. It's too soon to say whether the project is a goer or not, but it is fair to say the cost would make funders stop and think.
''But they spend $30 million on stadiums in Auckland and Wellington so why not $30 million on Stewart Island?''
The idea of a predator-free Stewart Island/Rakiura was first raised in 2013 by millionaire philanthropist and environmental campaigner Dr Gareth Morgan, who offered to help fund it via his Morgan Foundation.
Dr Morgan and Doc have funded the investigation phase.
Ms King said she believed Dr Morgan would follow through and fund the project, ''but not all of it'', while Doc would fund ''in kind''.
The backing of island residents, the general public, iwi and funders would be required before the project could be confirmed, and that would take time, Ms King said.
''As far as I am concerned, the sooner this happens the better, but I am personally open to the fact it could take decades,'' she said.
At a glance
Predator Free Rakiura Project's goals
• Plan to remove predators including rats, possums, feral cats and hedgehogs from part of Stewart Island/Rakiura, including the Oban township and to build a predator fence to keep the area pest-free.
• Two options being considered, one covering 2150ha with a 7.2km-long, 1.8m-high fence, the other covering 4800ha with an 8.8km-long fence.
• Four options for predator removal being considered, including a combination of leg-hold and cage traps, laying poisons in bait traps, and hunting feral cats at night. Aerial poison drops ruled out because of public resistance.
• Projected capital costs range from $9.05 million to $32.9 million, with ongoing annual costs of $1.38 million-$2.04 million.
• Up to 1500 people required during main predator removal phase.
- Source: Predator Free Rakiura Project technical reports
