Complejos de seguridad

Richard Henry’s employment as caretaker of Resolution Island, Fiordland, is arguably New Zealand’s first concerted effort to conserve native species for their intrinsic value. During 1895 to 1907 hundreds of kākāpō, little spotted kiwi (Apteryx owenii) and South Island brown kiwi (Apteryx australis) were translocated in the Fiordland sounds. Unfortunately, much of his work proved futile once stoats invaded many of the islands around 1900. Despite this, his work was the start of conservation efforts as we know them today (Miskelly & Powlesland, 2013; Berry, 1998; Saunders & Norton, 2001; Taylor, 2007).

The New Zealand Wildlife Service developed translocation techniques for forest birds, and initiated the eradication of cats from offshore islands. The 1930’s were the start of pest-control efforts to attempt to restore habitats to pre-predator invasions (Saunders & Norton, 2001; Powlesland, et al., 2009). From 1964, the number of translocations increased dramatically, with many successes. This rapid increase in conservation activity was in part motivated by the rapid loss of three endemic species (Bush wren (Xenicus longipes), South Island snipe (Coenocorypha iredalei) and the greater short-tailed bat (Mystacina robusta)) and the near extinction of the South Island saddleback (Philesturnus carunculatus) on Big South Cape (Taukihepa) Island in 1964 following the arrival of ship rats. The increases in effort and success were facilitated by improved techniques, especially the use of newly-developed mist nets, and developments in island pest eradications (Miskelly & Powlesland, 2013).

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The Department of Conservation (DOC) came into force with the passing of the Conservation Act 1987. The Act included a merger between several governmental agencies such as the New Zealand Wildlife Service, the Department of Land and Surveys, the New Zealand Forest Service and the National Parks Authority. During this time, methods to eradicate rats from offshore islands were developed (Miskelly, 2009). Today, pest control operations in New Zealand include one-off pest specific operations (e.g. Tiritiri Matangi Island) as well as longer term continuous trapping or pulsed poison operations (e.g. Ark in the Park) (O'Donnell & Hoare, 2012).

The Department of Conservation administers approximately 80,000km² of publicly owned land

in New Zealand in the form of national parks, conservation parks and reserves. In addition to the public land managed by the Department of Conservation there is an increasing number of sites that are managed by community conservation groups (Miskelly, 2009). Some of the public and private sites have predator proof fencing and are focussed on ecosystem restoration rather than single species re-establishments (Leech, et al., 2008; Miskelly & Powlesland, 2013).

Major success stories for New Zealand re-establishments include the Malherbe’s parakeet (Cyanoramphus malherbi) to Maud Island, Red-fronted parakeet (Cyanoramphus novaezelandiae) to Tiritiri Matangi Island (Soorae, 2010) and North Island kākā to Zealandia in Wellington. One of the internationally renowned conservation stories is how the Chatham Island black robin (Petroica traversi) was saved from the brink of extinction when only five birds (one female and 4 males) remained in 1980. Today around 250 birds make up the black robin population, all descendants from the one female. This population continues to struggle; however, this is mainly due to their poor genetic diversity (Department of Conservation, 2017).

Genetic diversity allows a population to adapt to a changing environment or to be buffered against stochastic events such as harsh weather or disease outbreaks. Genetic diversity has been an important consideration in the development of management strategies for threatened populations around the world. In New Zealand, however, species recovery programmes have tended to focus on increasing population size at the expense of decreasing genetic diversity (e.g. by using over-represented founders) (Jamieson, 2009). To ensure that re-establishments can lead to self-sustainable populations it is crucial to incorporate sound population management as part of all restoration projects in New Zealand.

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1.14.1 Island re-establishments

The potential of New Zealand’s offshore islands as conservation management sites has been recognised for over 100 years. Despite the inability to protect the birds on Resolution Island, the process of translocating birds to this offshore island proved that ‘securing’ vulnerable species on predator-free islands was a key to averting further extinctions (Saunders & Norton, 2001).

With the increased ability to remove pests from offshore islands (especially those up to 2,000ha in size), came the opportunity to translocate vulnerable species to these islands to establish new populations (Saunders & Norton, 2001). Species such as takahē are managed on a large number of islands, to continue to grow their population while maintaining proper genetic management.

Department of Conservation records show that 17 species of vertebrates (15 mammals and two bird species) have been successfully eradicated from 140 islands around the New Zealand coast (Saunders & Norton, 2001). The following nine islands are now considered to be free of all species of introduced mammals: 1) Little Barrier Island; 2) Raoul Island; 3) Kermadec Islands; 4) Kapiti Island; 5) Whale Island; 6) Codfish Island; 7) Breaksea Island; 8) Mana Island and 9) Campbell Island. These islands are internationally important sites for biodiversity conservation and restoration (Miskelly, 2009).

Again, it is important to consider the fact that population genetics is also very important for island populations where reduced genetic diversity can occur due to limitation of immigration. The North Island kākā population on Kapiti Island is suffering from reduced genetic diversity because of a recent bottleneck (Sainsbury, et al., 2006). When the island was almost completely deforested in the 1840s, the carrying capacity for kākā was severely reduced. The subsequent invasion of the introduced brushtail possum from the 1890s, until their eradication in the 1980s, kept the kākā population size low over a prolonged period (Beggs & Wilson, 1991). Low genetic variation is linked to a reduction in reproductive fitness and hatching success (Moorhouse, 1997; Sainsbury, et al., 2006).

1.14.2 Mainland Islands

The term ‘mainland island’ was coined to describe mainland sites that are managed as if they are islands. Some of these “islands” are forest islands in a “sea” of farmland, but others are embedded within large expanses of contiguous forest. The island metaphor refers to traps,

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toxins, and/or pest-proof fencing creating a barrier to pest re-invasion analogous to the protection provided by the sea around a true island (Miskelly, 2009). The first predator-proof fence around a mainland sanctuary was completed in 1999 at a 252ha site called Karori Sanctuary (now Zealandia) in Wellington (Innes, et al., 2010). Mainland island pest control regimes are more intensive and have been maintained for longer periods than has normally been the case previously in New Zealand (Saunders & Norton, 2001).

During 1995 and 1996 the Department of Conservation initiated six mainland island projects. Three of these (Trounson Kauri Park, Boundary Stream Reserve and Paengaroa Reserve) are ‘habitat islands’ involving isolated forest remnants in essentially modified landscapes dominated by farmland. The other three (Northern Te Urewera National Park, Rotoiti Nature Recovery Project and Hurunui River) are ‘habitat complexes’ featuring core management areas within a larger complex of similar habitats. These mainland island projects have ecosystem-focused restoration goals. Management objectives include rehabilitating habitats, enhancing particular plant and animal populations, and informing stakeholders of activities and progress. The development of sustainable management regimes by which critical pests can be effectively controlled and their re-invasion limited to acceptable levels is a priority activity at these sites (Saunders & Norton, 2001; Adams, et al., 2008).

Besides the six mainland “islands” managed by the Department of Conservation, there are an increasing number of community projects (over 8,000ha) which follow similar restoration goals (Berry, 1998; NatureSpace, 2016; Innes, et al., 2010). Mainland island projects are relatively expensive and it may take many years before restoration goals can be assessed (Saunders & Norton, 2001). Despite this, the number of successful reintroductions of forest bird species (including North Island kākā) suggest that mainland sites can provide a suitable habitat for species, and in some cases become fully self-sustainable populations.

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