In the “Ecosystem restoration on Mainland New Zealand”
Cuvier Island (170 ha) was formed about 12,000 years ago as sea levels rose around a coastal mountain, trapping the remnants of its mainland fauna and flora. In the early nineteenth century Cuvier Island was inhabited by Maori (at least periodically), and Pacific rats were apparently the only introduced mammals present. In the late 1880s the island became a lighthouse reserve and about one quarter of its area was used as a farm. By 1957 the place was a mess. Wandering stock (cattle and sheep), introduced in 1889, and wild goats had reduced the forest to an open woodland that lacked an understorey. Some previously reported plants were extinct on the island, and scrub on coastal faces was reduced to eroding grassland.
Predation, largely by cats, had eliminated North Island saddleback, pied tit, tui, and red-crowned parakeet (Merton 1972). Burrowing seabirds were reduced to two species breeding on the island (sooty shearwater, and grey-faced petrel), and tuatara were reduced to seven adults (references in Towns et al. in press).
Restoration of the island began over 30 years ago with eradication of goats in 1961, a new boundary fence for the lighthouse settlement was completed in 1963, excess stock were destroyed, feral cats were removed by 1964 and domestic cats banned from the island from 1970. At the time these removals of goats and cats were major advances. But removal of the huge population of rats was beyond us.
Even while the rats were still present some natural regeneration and restoration were possible. Rapid regeneration was recorded following removal of goats as grassland beneath scattered pohutukawa trees developed a dense woody understorey. Other palatable species spread from plants confined to cliffs (Merton 1972).
In 1968 saddleback from the last remaining population of the species were reintroduced to Cuvier Island, followed by red-crowned parakeets in 1974. These were significant events. The return of species to part of their former range was hitherto unheard of in New Zealand. More was to follow. With the development of new rodenticides, special bait spreaders for use under helicopters, and satellite navigation systems to ensure complete coverage with baits, the eradication of Pacific rats from Cuvier Island was completed by Department of Conservation staff in 1993 (Towns et al. 1995).
The last tuatara, rescued from the island before removal of the rats, are now breeding in captivity and when their numbers are high enough will be returned to the island. This enhancement of the tuatara population may represent their first increase in numbers after 1000 years of decline. Some challenges remain. Despite 30 years free of predation by cats, most of the burrowing seabirds have not returned even though they are present in huge numbers on islands nearby. Since the guano from seabirds acts as a nutrient driver for the entire system, restoration of this island ecosystem will require further innovations to encourage seabirds to return.
This project helped to fundamentally change the status of saddleback, and the island should eventually support many thousands of tuatara. Just as importantly, removal of cats and rats from islands like Cuvier is enabling a resurgence of less visible species such as invertebrates and lizards, now lost or declining on the mainland.
The Cuvier project has been one of several testing grounds where Department staff learned techniques for pest eradication and restoration. A second testing ground, with even higher stakes, was on Mangere Island in the Chatham Islands.