Restoring Rangitoto and Motutapu Islands by Des Casey

Environmental News Issue 19 Winter 2009

Rangitoto and Motutapu Islands have sat close to the mainland from long before there was an Auckland, though Rangitoto burst from the sea a mere 600 years ago. Motutapu has been around much longer. Rangitoto is derived from the phrase “Te Rangi i totongia a Tamatekapua” – the day the blood of Tamatekapua was shed. It rises to a height of 260 metres and its lava content measures 2,300 million cubic metres or, if you prefer, 468,000 Olympic-sized swimming pools. Some explosion six centuries ago!

The eruption laid a carpet of ash on nearby Motutapu and transformed this home of many Maori from a hunting and forest resource to a fertile base for gardening and horticulture. Motutapu, “Te Motu tapu a Taikehu”, the sacred island of Taikehu (of the Tainui canoe), has known both Maori and European settlement, and has passed through times of forestation, Maori habitation, European farming, military operations and recreational opportunity.

Over time humans infested both islands with Norway rats, ship rats, mice, possums, wallabies, rabbits, stoats, feral cats and hedgehogs, a pot pouri of intruders that had a devastating impact on fauna and flora. Gradually kiwi, kaka, tuatara, mistletoe, dotterel, kereru, rata and many other species disappeared or were significantly diminished.

A community project to turn this process around and restore Motutapu’s cultural and natural landscape was launched in 1992. Their goal was to replant the forest and restore wetlands, fauna and flora. Since 1994 the Motutapu Restoration Trust has planted in excess of 400,000 trees. The movement has grown, extending in present time to a combined Rangitoto/Motutapu pest eradication project, the first stage of which has just been completed. This has been an exciting development building on earlier successes of eradicating possums and wallabies in 1996, replanting programmes and controlling weeds.

Three aerial applications of rat bait were dropped on both islands in June, July and early August. Auckland Area Manager for the Department of Conservation, Brett Butland, described the effort as “ … a flagship project that Aucklanders can feel proud to be a part of”, a project … “breathing life back into Rangitoto and Motutapu, and creating a large pest-free nature sanctuary right on Auckland’s front doorstep”. Restoration of these two islands will protect the world’s largest pohutukawa forest, and could provide a 3,800 hectare home to some of New Zealand’s most loved wildlife, including kiwi and takahe.

Several helicopters using spreader buckets and GPS technology were complemented by hand laying bait in buildings and covered structures. These aerial drops of brodifacoum, a common rat poison similar to that which can be bought from super-markets and hardware stores, targeted rats and mice. A second stage of removing other pest animals such as stoats, feral cats, hedgehogs and rabbits through trapping, shooting and the use of detection dogs has commenced. Early observations indicate that the rabbit population has been hit hard by rodent bait, with only one rabbit being seen after two weeks of night spotlight searches.

In 1993 Tiritiri Matangi Island was cleared of pests using a similar operation and is now one of New Zealand’s iconic nature sanctuaries. More recently little spotted kiwi, shore skinks and kakariki have been released on Motuihe Island which has been pest free since 2004. Other islands in the Hauraki Gulf Marine Park, such as Kaikoura Island, are undergoing similar processes. Rangitoto and Motutapu can now be added to the list.

During the last few weeks there have been reports of dogs dying after eating something on North Shore beaches. Before the toxin was identified the public and some media suggested that the deaths could be related to the brodifacoum drops. However MAF Biosecurity and other agencies quickly ruled out any link. The Cawthron Institute found the toxin was tetrodotoxin, a naturally occurring substance found in tropical puffer fish. The toxin was also found in sea slugs taken from the beach.

Soon Rangitoto and Motutapu will be following in the footsteps of Tiritiri Matangi and some of our most precious and endangered native treasures will have another base from which to swell their numbers and regain their foothold on life. A next crucial step is the ongoing one of keeping the islands safe. To ensure this care from everyone is crucial. Visitors to the islands, please be vigilant ensuring no stowaways are in bags, among produce or on boats. Check everything before landing, look out for and report rodent and other signs of pest presence, and land only during the day.

On the eve of the final bait drop kayaker Ian Ferguson called on the public to respond: “We all love Rangitoto, so let’s work together to ensure the beautiful, natural environment that we all enjoy visiting in our kayaks and boats stays that way. Make sure you always check your bags and boats for rats, mice and other stowaway pests”. With the pride and enjoyment that places like Tiritiri Matangi bring us, comes the responsibility of enabling such break-throughs to remain strong and healthy.