Nanda MacLaren, Forest and Bird member and Motutapu volunteer, investigates how Motutapu Island is Becoming Pest Free.
A slightly different version of this article, entitled 'Island Life', was recently published in the August 2009 edition of the Forest and Bird magazine.
http://www.forestandbird.org.nz/

Cradled in the Hauraki Gulf Marine Park, which sprawls on Auckland's doorstep, are several pest free islands and peninsulas. These include the world acclaimed open island sanctuary of Tiritiri Matangi, Motuora, Little Barrier, Motuihe and Tawharanui. Soon to join this list are the combined islands of Rangitoto and Motutapu. At 3,854 hectares these islands are larger than Little Barrier Island or Maungatautari, and 17 times the area of Tiritiri Matangi. This sheer size, combined with the existing and potential wetland areas of Motutapu, means they will become a very significant sanctuary for endangered New Zealand wildlife.

Rangitoto was formed by eruptions approximately 600 years ago. It now hosts a variety of landscapes from bare volcanic lava to mature pohutukawa and rata forest.  Purchased by the Crown in 1854, it was set aside as a scenic reserve in 1890, and has since been a major tourist destination.

Motutapu, a much older island (Jurassic in origin) with a rich archaeological heritage, is joined to Rangitoto by mud flats and a bridge. It was occupied by Maori before and after the eruption of Rangitoto which smothered Motutapu in a deep layer of volcanic ash. There are known to be over 300 sites of Maori interest dating back to the 12^th century. Later European settlement occurred creating a population such that a school was required; farming was the major land use. The island was purchased by the Crown between 1935 and 1944 for defence purposes and many artefacts from that time remain.

Motutapu and Rangitoto are a 30 minute ferry ride away from downtown Auckland. Over 100,000 visitors arrive on their shores annually. Activities include tramping, walking, swimming, fishing, camping and exploration. Both islands are administered by the Department of Conservation (DoC).

Prior to 1990 the pohutukawa forest on Rangitoto was on the brink of collapse due to browsing by wallabies and possums. DoC commenced an eradication operation on both islands. Possums and rock wallabies were targeted with an aerial drop of 1080 laced pellets. The eradication program continued with ground hunters but it wasn't until 1997 that the NZ Herald reported that the program was complete. The forest rapidly recovered.

A vision was born within DoC at this time, that Motutapu and Rangitoto could become a location for genetically self sustaining populations of endangered species. In addition to its sheer size, Motutapu has a unique range of habitats - interior wetlands, exposed coastal forest sites and interior bush and gullies. This will allow it to host not only the more popular species such as kiwi, takahe and tuatara but also plants such as hard beech, tawa, mangeao and mistletoe which are rare in the gulf islands  However, due to the complex history of the island, simply creating a Noah's Ark for wildlife was not an option.

The Motutapu Restoration Project (MRP) was conceived by a group of interested parties including iwi, DoC, biologists and archaeologists, to protect and enhance most archaeological sites whilst providing sufficient habitat to accommodate threatened species. The Motutapu Restoration Trust (MRT) came into being in Feb 1994 to sustain this project. Its mission was to create the financial and support environment to restore the ecological and cultural heritage of Motutapu by raising funds, publicity and volunteers. The planting program that DoC had initiated in 1992 was handed over to the MRT in 2002. The MRT is currently implementing a 10 year plan to plant 180 hectares of pasture, and preserve and protect existing wetland areas and remnant bush. Protection involves the control of several weed species (see fact box).

Birds are currently seen on both islands. In September 2008, a survey by the Ornithological Society of New Zealand (OSNZ) noted 40 species, 27 of which were native. These include NZ dotterel, kereru, grey warbler and Caspian tern.  

In June of this year (2009), DoC began what they describe as the most complex island pest eradication ever attempted anywhere in the world. It will rid Rangitoto and Motutapu of animal pests that eat birds, reptiles and invertebrates or compete with them for food. Helicopter aerial drops using spreader buckets and GPS technology will cover both Rangitoto and Motutapu dispersing brodifacoum bait. In conjunction with hand laying of bait in buildings and other structures protected from the aerial drop (such as lava tunnels on Rangitoto) the bait should reach all target pests. Rats and mice will eat the bait and be eliminated by this operation.  The island's rabbit population will also be knocked back. Follow up work including trapping, shooting and the use of specially trained dogs for detecting pests will be used to eliminate stoats, hedgehogs and feral cats. It is hoped the islands can be declared pest-free in July 2011.

The complexity arises from the difficulty of the terrain (lava rocks, caves and tunnels on Rangitoto, a large number of buildings), the farming activities (all farming stock is removed from the islands for several months during bait laying), and the large number of visitors. The island has to be closed to all visitors for a ten day period over each of three bait laying operations. DoC, a world leader in island pest eradications with experience of more than 50 successful island pest eradications in New Zealand, is confident that this eradication will be successful and that the existing and newly planted forest will flourish as a result.

The MRT, who have been busy raising funds, building and running an island based nursery to raise locally collected seed, and planted approximately 400,000 native seedlings through an efficient volunteer program, noted the implementation of the pest eradication plan and paused to consider the implications.

Until now, most native reafforestation programs had focussed on creating pioneer forest from plants grown in root trainers, and on Motutapu the same plan was being followed.  However, post-pest removal there will be a translocation plan for introducing expanding bird, invertebrate and reptile populations. Birds in particular will require a wide variety of fruiting trees for all year round sustenance.  Thus, with the guidance of Dr Shane Wright (biogeographer), the programme is moving away from dense planting of a basically kanuka/manuka  sward  and changing to more open plantings of broadleaf pioneers (for example wharangi, mahoe and taupata).  Then, wherever appropriate, final stage species will be introduced (for example totara, pohutakawa, mangeao, kohekohe and puriri).  This new approach could advance the growth of diverse old-growth forest by several decades.

Another huge implication of the pest eradication is the need for ongoing biosecurity.  The constant movement of large numbers of people, farm animals and equipment provides opportunities for rats and mice to re colonise the islands. Advocacy and education will be key components of the biosecurity plan with signs at key departure points and all landing points. Widely dispersed tracking tunnels and traps around access points will monitor for re-colonisers

This is a flagship project that all New Zealanders can feel proud to be a part of but with that pride comes responsibility, and all visitors are expected to help to ensure that the islands remain pest-free.

Fact Box

Rangitoto has the largest Pohutakawa forest in the world.

Winter is chosen for pest eradication when food is scarce and pest numbers low.

More than 100,000 visitors to the island P/A.

1400 volunteers working P/A

25,000 trees planted P/A.

Rangitoto means Blood Red Sky.

Motutapu means Sacred Island or the full name is Te Motutapu a Taikehu, "The sacred island of Taikehu", Taikehu being an ancestral tohunga of Ngai Tai.

Approximately 145 tonnes of bait will be dropped.

It can take around 4 days to kill a Norway rat following ingestion of brodifacoum.

Brodifacoum can stay active up to 4 months but the baits break down quickly after rain.  The toxin is bound to the soil where it is broken down by micro-organisms.

Between 200 and 300 helicopter flights will be required.

The pest eradication program price tag is around $3,000,000.

The most extensive pest eradication project was Campbell Island (11300ha) completed in 2001.

The 7 target pest species are ship rats, Norway rats, feral cats, mice, rabbits, stoats and hedgehogs.

Ship rats, mice, rabbits and hedgehogs have never been targeted for eradication on such large islands.

Hedgehogs don't hibernate during Motutapu winters.

Current plant pests include: woolly nightshade, moth plant, apple of Sodom, rhamnus, wattle, Selaginella.

How You Can Help

Become A Volunteer:  the planting program depends on volunteers to collect seeds, propagate them in the nursery, plant the saplings in the winter and protect the growing forest with weed control. Volunteer days are first, third and fifth Sunday of the month all year.

Become a Friend or a Sponsor or Make a Donation: The Trust depends on your generosity to enable the ecological restoration of the island.

Acknowledgements:

Bridget Winstone
Russell Greenwood
Richard Griffiths
The MRT