Great Barrier Island and four other New Zealand offshore havens could play a big role in helping save some of the world's most threatened species, a major global study has found.

A team of international researchers found that wiping out invasive mammals on 107 islands around the planet would help protect 80 threatened species and help reach a United Nations goal to halt biodiversity loss.

Of nearly 170 islands identified by the study, 107 could have eradication projects launched by next year, and five of those were in New Zealand.

The islands were Great Barrier Island and Kawau Island in the Hauraki Gulf, Motukawanui Island in Northland, Slipper Island in Coromandel, and the subantarctic Auckland Island.


None of those five had yet been swept of pests, although about a third of New Zealand's 345 islands were now considered free of mammalian predators.

University of Auckland conservation biologist Dr James Russell, who was among researchers from 40 institutions who contributed to the report, said it was already known that islands were crucial to conservation.

But the study offered a bigger picture – and narrowed down where the most progress could be made, he said.

"One of the study's most important aspects is that it not only assesses the feasibility of eradicating predators on these islands but assesses how feasible this work would be from a political and socio-economic point of view."

Restoring islands by eradicating damaging, non-native invasive mammals such as rats, cats, goats and pigs had repeatedly proven to achieve results and make a major contribution towards stemming the global extinction crisis.

Initiating restoration projects on 107 islands with a total land area of 1623sq km could save 151 populations of 80 threatened species, the study found.

More than 1,200 projects to eradicate invasive mammals have been attempted on islands worldwide with an average success rate of 85 per cent.

Russell said New Zealand was one of the most experienced countries in the world in island pest eradication and has lent expertise to a wide range of island projects from Mexico to the Pacific.


"New Zealand has been offering support to other countries for some time and is seen as a global leader in this area with our own ambitious targets such as pest-free Auckland Island and Predator Free New Zealand."

The researchers used biological and geographic data compiled for 1,279 islands with 2,823 populations of 1,184 bird, reptile and mammal and amphibian species listed as critically endangered or endangered by the IUCN Red List of threatened species.

The study identified 107 islands where eradication of predators could be started by 2020 and a further 62 islands where work could begin by 2030, to benefit 9.4 per cent of the world's threatened island species in total.

Worldwide, islands currently supported about 36 per cent of bird, mammal and amphibian and reptile species classified as critically endangered.

The new study came as the Department of Conservation this week announced that three islands in the Abel Tasman National Park were once again predator free, after a 2017 operation successfully eradicated all mice.

DOC urged people visiting those islands - Adele/Motuareronui, Fisherman/Motuareroiti and Tonga – to ensure they kept mice, rats and other pests away.