Rat eradication by 2050 will require new technology

Monday, 2 May 2022

With under 30 years to reach the goal of eradicating rats by 2050, experts say new technology is needed for it to work.

As part of the Predator Free 2050 campaign, the Government is aiming to eradicate New Zealand’s main pests and predators in order to give native wildlife a better chance.

Among others, stoats, rats, possums, weasels, ferrets, cats and hedgehogs are on the hit list.

Rats are among the top pests that are a part of the Predator Free 2050 goal. (File photo)

While rat eradication on some of New Zealand’s islands has gone well, the Department of Conservation’s Graeme Elliot thinks the mainland will prove a harder job.

Waiheke Island has just run a large-scale stoat trapping campaign.

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Their cautious nature and ability to breed quickly make rats hard to kill off in the first place, but keeping them from coming back is just as difficult, Elliot said.

On an island there is the natural barrier of water, but killing rats in an area of mainland often sees a population pour back into the area, once the eradication programme has ended.

“We can get about 99% of them, but it’s hard to get that last 1%,” Elliot said.

“It’s generally not worth it either because they just pour back in over the margins”.

Minister for Conservation Kiri Allan said the problem is keeping rats from re-invading.

We know we can get every last rat, Elliot said, but we just can’t keep them out.

The technology doesn’t exist, in a feasible way, to eradicate them on the mainland, he said.

Baited traps and 1080 drops are the main methods of keeping rat populations down. Trialling new technology needs to be balanced with ways we know work, Elliot said, because holding the fort is protecting some species from extinction in the meantime.

“The goal is aspirational, if we get there five years early or five years late it would still [be a success]”.

A rat eradication pilot on Waiheke Island could be a test of how successful a large-scale programme would be.

Te Korowai o Waiheke manager Jenny Holmes said they’ll be trialling different methods in three parts of the island over the next few months to see what works, and what the public will get behind.

The difference between Waiheke and other islands that have become rat-free are the nine thousand people, she said. Understanding those attitudes and how they want to be involved will be a key part of the programme.

“The team at this point are optimistic that they can eradicate from the trial areas and, hopefully, the learning from that will fill their confidence on whether it is possible to do it across the whole island”.

The trial had to be made slightly smaller she said, due to Covid-19 isolations and sicknesses, as rat traps need to be serviced every week for them to be effective.

Minister for Conservation Kiri Allan said the main limiting factor is not the ability to achieve eradication, but rather the ability to defend eradicated areas from re-invasion.

“The Predator Free 2050 Strategy has a strong focus on learning and development for the first phase of the programme. The focus for the next few years will be developing the technologies to address, amongst other things, large-scale rat eradication and defence.”

Eradication of possums, mustelids (stoats, weasels) and rats by 2050 is an ambitious goal, however we are on track to meet this goal, she said.