A 400-gram Norway rat was found on Waiheke Island on Wednesday.
The biggest rat that has been caught so far on Waiheke island: a 400g Norway rat. Photo: Supplied / Te Korowai o Waiheke / Markus Gronwald
The rats are introduced pests in New Zealand and threaten the long-term survival of native species.
Charitable trust Te Korowai O Waiheke is part of the predator-free 2050 movement, a government initiative to help deliver the New Zealand government's ambitious goal of eradicating all possums, stoats and rats by 2050.
Te Korowai o Waiheke rat operation manager Markus Gronwald said this was a world-leading project in a city-like environment.
"Predator-free 2050 was announced in 2016 and its initiative aims at removing all rats, ferrets, stoats, weasels and possums from New Zealand by 2050," Gronwald said.
The funding of predator-free 2050 supports 19 large landscape projects, enabling pest control and eradication projects over 823,000 hectares.
The total project costs add to $75.6 million.
Becoming the world's first predator-free urban island is no small task, there are many challenges in addressing the complete removal of rats from such an urbanised island.
Rat device deployment map in Waiheke. Photo: Supplied / Te Korowai o Waiheke / Markus Gronwald
Te Korowai o Waiheke's rat pilot operational trials are designed to address just that.
In the first week of the Kennedy Point Trail on Waiheke Island, the trapping team collected 280 rats.
"There has been hundreds of rat eradication projects around the world, but Waiheke is a first because it's a highly urbanised island. we have a population of nearly 10,000 people and there are lots of challenges in accessing commercial and industrial places," Gronwald said.
The techniques for eradication on land and forested areas have been tested before, but the complete removal from a highly urbanised environment hasn't yet happened at this scale.
Little is known about how rats use different urban habitats and so eradication techniques must be tested and refined before island-wide eradication can be pursued.
Te Korowai o Waiheke field team members Charlie Thomas and Sam Macpherson. Photo: Supplied / Te Korowai o Waiheke / Markus Gronwald
The biggest urban island rat eradication to date was on Lord Howe Island with a population of 400 people on 1455ha of land.
On the contrary, Waiheke island has 9500 residents on 9200ha of land.
While Waiheke island is more than six times the size of Lord Howe, its urbanisation poses the biggest challenge.
Norway rats are tenacious and will attack native birds that nest on the ground, like kororā / little blue penguins and dotterels.