With less than 30 years to reach the goal of eradicating rats by 2050, experts say new technology is needed to make it work.
As part of the Predator Free 2050 campaign, the government aims to eradicate major pests and predators from New Zealand to give native wildlife a better chance.
Among others, stoats, rats, opossums, weasels, ferrets, cats and hedgehogs are on the list of victims.
While the eradication of rats on some New Zealand islands has gone well, Graeme Elliot of the Department of Conservation thinks the mainland will prove a tougher job.
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Their cautious nature and ability to reproduce quickly make rats difficult to kill 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 the mainland often sees a population returning to the area, once the eradication program is complete.
“We can get around 99% of it, but it’s hard to get the last 1%,” Elliot said.
“It’s usually not worth it either, because they just trickle down the margins.”
We know we can catch every last rat, Elliot said, but we just can’t keep them out.
The technology does not feasibly exist to eradicate them on the continent, he said.
Baited traps and 1080 drops are the primary methods of maintaining rat populations. Trials of new technologies must be balanced with the methods we know, Elliot said, because holding the fort protects some species from extinction in the meantime.
“The goal is ambitious, if we get there five years early or five years later, it would still be [be a success]”.
A pilot rat eradication project on Waiheke Island could be a test of the success of a large-scale program.
Te Korowai o Waiheke director Jenny Holmes said she will test different methods in three parts of the island over the next few months to see what works and what audiences get.
The difference between Waiheke and the other islands that have become rat-free are the nine thousand people, she said. Understanding these attitudes and how they want to be involved will be a key part of the program.
“The team at this stage are optimistic that they can eradicate the test areas and hopefully the lessons learned from this will fulfill their confidence that it can be done island-wide.”
The trial had to be scaled back slightly, she said, due to Covid-19 isolations and illnesses, as rat traps need to be serviced weekly for them to be effective.
Conservation Minister Kiri Allan said the main limiting factor is not the ability to achieve eradication, but rather the ability to defend eradicated areas from reinvasion.
“The Predator Free 2050 strategy places a strong emphasis on learning and development for the first phase of the program. Over the next few years, the focus will be on the development of technologies allowing, among other things, the eradication and large-scale defense of rats.
Eradicating opossums, mustelids (stoats, weasels) and rats by 2050 is an ambitious goal, but we are on track to achieve this goal, she said.