What's next in controlling predators?

More native wildlife has returned to suburban gardens in Wellington as a result of predator-control efforts at the ...
MATT DUNCAN

More native wildlife has returned to suburban gardens in Wellington as a result of predator-control efforts at the Zealandia sanctuary.

If this winter's mouse eradication on remote Antipodes Island is successful, New Zealand can tick another predator-free island off the to-do list. But what is the future for predator control? SARAH-JANE O'CONNOR reports.

Spare a thought for the small team of eradicators spending the winter on remote, subantarctic Antipodes Island trying to rid the island of the invasive mice thought to be damaging invertebrates, plants and birds.

While their work is difficult and required years of planning, there's a pretty good chance that, if they're successful, mice won't return to the island. All it takes is a rigorous quarantine process for the handful of scientists and hardy tourists who make the journey across the Southern Ocean.

The late Sir Paul Callaghan, who called for a "predator-free New Zealand".
KEVIN STENT

The late Sir Paul Callaghan, who called for a "predator-free New Zealand".

It's a different story for islands closer to mainland New Zealand, or even the mainland itself. But if the Antipodes is checked off as another pest-free offshore island, conservationists are starting to run out of obvious places to focus their efforts on next. Perhaps it's time to seriously ask how we take this island model of conservation and apply it to the islands that we live on.

When so much time and money goes into getting rid of rodents from islands and reserves, it seems counter-productive to be releasing animals back into those areas.

But that's exactly what University of Auckland conservation biologist James Russell and his research students have been doing as they figure out the best ways to track and trap invading rodents. Their findings, Russell says, point to a key conclusion: reinvasions are inevitable, but don't mean a complete failure of the eradication.

Zero Invasive Predators chief executive Al Bramley says inevitable reinvasion is part of the challenge his team is trying to address. Instead of a traditional eradication - like that done on islands - they are working on a "remove and protect" model.

From late 2014, they've worked to rid the 400-hectare Bottle Rock Peninsula, in Queen Charlotte Sound, of rats and possums. To stall the invasion front, they maintain a "virtual barrier" across the two-kilometre neck of the peninsula. Six defence lines, 100 metres apart, contain an array of control tools spaced every 10m.

Eighteen months down the track, Bramley says the trial has been "remarkably successful", with over 95 per cent of the rats and possums that tried to get through the barrier being caught or killed.

One day, he imagines a frontier of detectors attached to a satellite network that will ping his team to let them know a rat or possum was hanging around. Perhaps, soon, it will be possible to send a drone within hours to drop a targeted toxin in the area the predator was detected. The idea is that the few animals that make it through the virtual barrier will be picked up and dispatched quickly, with minimal labour required.

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Without even moving to drones, technology is already playing a part in how we capture predators.

Wellington-based company Goodnature has developed a self-setting trap, powered by a gas canister and triggered when an unsuspecting mammal pokes its head into the trap. Landcare Research scientists are developing pheromone-based lures for possums and hope to extend the technique to stoats.

It was technological leaps like this that stood out to Russell when he recently led a symposium to mark 50 years of island eradications in New Zealand, "although, at the time, research can seem slow and painful over the typical three- or four-year funding timeframe".

"Ten years ago we were very concerned about a single rat getting back to an island, and now…we are comfortable enough that we took all pests off Rangitoto Island, which has daily traffic. Indeed, half the Hauraki Gulf is now free of introduced mammals.

"When you look back over each decade over the last 50 years, it's just been: problem identified, problem solved. There was the scale issue, which helicopters solved. There was the biosecurity issue, and now we've identified the next issues, which is these inhabited islands.

"I'm confident that within 10 years we'll be much further ahead of where we are today in doing eradications on large, inhabited islands."

Shortly before he died, physicist Sir Paul Callaghan strayed from his own field to make a national call for a "predator-free New Zealand". It was ambitious, perhaps audacious, but it could be done, he said.

Four years have passed and there are obvious examples of some of the big picture projects Callaghan thought New Zealand's version of an Apollo mission would include.

In Wellington, it's Zealandia and the "halo effect", which sees more native wildlife returning to backyards around the city. Auckland's Waitakere Ranges have Ark in the Park and Hawke's Bay has Cape to City - 26,000ha of predator control and ecological restoration between Hastings and Cape Kidnappers.

Predator Free New Zealand (PFNZ) spokeswoman Jessi Morgan said Callaghan's goal was "completely feasible" and helped to rally citizens around a common goal. There were two main challenges, she said: finding the right tools, and getting New Zealanders to "take up arms and help make it a reality".

"This isn't the preserve of the government agencies. If the PFNZ goal is to become a reality, we need predator control to be something that we all do. If every house had a trap, it would make a huge difference."

 - Stuff

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