Island restoration

Islands, due to their isolation, are home to many of the world's endemic species, as well as important breeding grounds for seabirds and some marine mammals.

Since the 1950s several organisations and government agencies around the world have worked to restore islands to their original states; New Zealand has used them to hold natural populations of species that would otherwise be unable to survive in the wild.

As well as displaying greater levels of endemism, island species have characteristics that make them particularly vulnerable to human disturbance.

It began on Cuvier Island, where ecologists removed stock, goats, feral cats and finally, in 1993, Pacific rats.

Trapping is ineffective for rats, given their sheer numbers, and the only method that works is poisoning, which can be delivered into the field by broadcasting (by hand or from the air) or by the maintenance of bait stations.

Invasive vertebrate eradication has many benefits besides conservation of species and has been found to align with 13 UN Sustainable Development Goals and 42 associated targets encompassing marine and terrestrial biodiversity conservation, promotion of local and global partnerships, economic development, climate change mitigation, human health and sanitation and sustainable production and consumption.

[6][7] There are three strategies to reduce the numbers of the introduced animals in order to lighten the problems caused by them: exclusion, control, and eradication.

Control has a meaning of mitigation by reducing the numbers of introduced species down to ecologically and economically less harmful level.

[9] In many cases the removal of introduced species is sufficient to allow a return to a pre-disturbance state, but generally active management, often in the form of replanting native flora and reintroduction of extirpated fauna is needed to achieve restoration goals.

One other important aspect of restoration is prevention, that is, keeping invasive species from returning to a cleared island.

This can be achieved by restricting access to the island in question (reducing possible instances of invasion) to more stringent quarantine methods.

However, as the techniques have improved and larger islands have been restored, most of the initial criticisms from within the field have been dropped, in particular as the costs of eradication are often much lower than continuous pest control.

Outside of the field of conservation there has been some opposition from other interested groups, particularly from the animal rights movement, which contends that the welfare of the pests in question is not adequately addressed in island restoration plans.

Because a broad spectrum of pest removal techniques needs to be used, including leg traps, animal rights campaigners accuse ecologists of cruelty, and indifference to non-targeted species that also take bait or are trapped, and suggest that more humane methods such as capture and sterilization be used instead (something those working in island restoration contend would be too expensive, and potentially ineffective as in Kangaroo Island koalas).

The removal of Eucalyptus trees from Angel Island in San Francisco Bay faced considerable opposition.

[14] These herbivores, along with other factors, such as sporadic logging and frequent cyclones, led to the eventual dwindling of the island's forests and dependent fauna.

In turn, this led to soil erosion by wind and rain, impeding forest regeneration, acting as a positive feedback mechanism that caused rapid deforestation of the island.

In 1957, however, Round Island was officially made a nature reserve, and in 1979 and 1986 was rid of goats (shooting) and rabbits (poisoning), respectively, after several unsuccessful attempts.

This is especially stark for three of the endemic tree species, Latania loddigesii, Pandanus vandermeerschii and Hyophorbe lagenicaulis, which constituted a large portion of the Round Island forest historically.

This has led to six reptile species (five of which were critically endangered) recovering in tandem with the plant community; these are the skinks Leiolopisma telfaririi and Scelotes bojerii, the geckos Phelsuma guentheri, P. ornata and Nactus serpensinsula, and the snake Casarea dussumerii.

[15] The Round Island restoration program represents one of the longest-running projects of its kind in the world, since its conservation status was confirmed in 1957.

Much of the current conservation work on Round Island is conducted by the Mauritian Wildlife Foundation[16] and Durrell Wildlife Conservation Trust[17] and revolves around maintaining soil levels, reforestation of the island, and eradication of remaining invasive plants and invertebrates.

The reduction in seabirds, in turn, had effects on the ecology of the islands, as many of the plants were dependent on the guano from nesting birds acting as a fertilizer.

The poison had to be dropped in the winter, to minimize disturbance to nesting seabirds and reduce the chance of bird strike for the pilots.

Rats, brought to South Georgia Island as stowaways on sealing and whaling ships in the late 18th century,[18] have caused much damage to native wildlife, destroying tens of millions of ground-nesting birds’ eggs and chicks.

[20][21][22] The project was led by zoologist Anthony Martin of The University of Dundee who stated, "This is a man-induced problem and it's about time that man put right earlier errors.

180 tonnes of rat poison, brodifacoum, were dropped over 70% of the island, in what was the world's largest ever operation of this kind.

[25] In June 2015 the eradication programme concluded, apparently successfully, with the island believed "very likely" to be rat free.