Kaikoura Island Restoration Plans Moving Ahead

Environmental News Issue 9

In a dramatic first for Great Barrier Island a complete island will be totally eradicated of introduced mammalian pests, and further protected against re-infestation—creating an island ark for endangered bird, reptile and invertebrate species.

What’s happening?

The Motu Kaikoura Trust wants to restore the natural environment of Kaikoura Island by removing introduced plants and animals. Rodents (rats and mice), feral cats, pigs, rabbits and deer all have significant impacts on the native animal and plant life of the island. They limit opportunities for native species such as skinks, kaka and brown teal through predation and competition for food and habitat. In the absence of animal pests, species such as black petrel may naturally re-establish and lost species such as giant weta and tuatara could be reintroduced.

Where is Kaikoura Island and why restore it?

Kaikoura or Selwyn Island (564 hectares) is located off the west coast of Great Barrier Island, at the entrance to Port FitzRoy Harbour. Predominantly covered in Manuka and Kanuka forest it also contains some pockets of native broadleaf forest including large trees such as Pohutukawa, puriri and kohekohe, which provide the seed source to expand these forest remnants. The island is also on the ‘flyway’ for species such as Cooks and Black Petrel as they move between Great Barrier and their feeding grounds in the Hauraki Gulf and on the Kaipara Harbour. Bellbirds also move between Great Barrier and Little Barrier.

The removal of animal pests will allow species such as petrels and bellbirds to naturally re-establish and also provide a haven for the reintroduction of a range of species including giant weta and tuatara.

How and when will animal pests be removed?

The deer removal programme commenced in October 2006. Ground hunting with experienced local hunters and trained dogs is proving extremely successful but it may take a couple of years to remove the last animal. Pigs will also be removed using the same techniques. Rabbits and cats will be removed using a combination of ground based techniques.

Rodents will be removed with a combination of an aerial drop using Pestoff 20R a brodifacoum based toxin (the same as that used on Little Barrier Island) and ground based follow up with bait stations and traps. It may take up to 3 years to remove the last one.

Why Pestoff 20R?

Pestoff 20R is a cereal based pellet bait that has been specifically formulated to kill rodents. Brodifacoum is the best poison for eradicating rodents because the combination of a highly palatable bait and the fact that the rodents cannot detect the poison, prevents them from becoming bait-shy thereby increasing the chances that they will consume a lethal dose. The baits are cylinder shaped, about 2cm long and are dyed green to deter birds. A large rat needs about 6 baits to get a lethal dose.

Why does the bait need to be applied from a helicopter?

Trapping and the use of poison baits in bait stations are the most common techniques for control, but because they are labour and cost intensive and do not maximize the chances that every target animal will encounter them, they tend not to be used for eradication in areas as large as Kaikoura.

Aerial baiting removes these issues. It is not limited by terrain or vegetation cover and provides the ability to accurately place bait at very close spacing (within 1-2m of each other compared to 25m to 50m spacing on a bait station grid). Aerial baiting technology has been refined by the Department of Conservation and to date rats have been successfully eradicated from about 50 New Zealand islands using this technique.

What impact does the aerial baiting operation have on the environment?

The operation will have only positive impacts. People will not be impacted in any way. The operation must be undertaken to a rigorous Code of Practice and will only be undertaken on uninhabited islands. Brodifacoum is insoluble in water and is rapidly broken down following rainfall by soil micro-organisms. Extensive monitoring of other similar operations (both on islands and the mainland) has found no traces of brodifacoum in soil or water. This has included analysis of shellfish and marine fish species.

Skywork Helicopters will apply the bait. Skywork is a local company familiar with the islands of the Hauraki Gulf and Kaikoura Island. They have considerable experience in this field. The helicopter will be fitted with an on-board computer navigation system and will utilise custom designed baiting buckets. The combination of the pilots experience and specialised equipment will ensure that bait is only applied to target areas. Because rodents (especially rats) can live down coastal cliffs some baiting will need to be undertaken in these areas. Some bait will fall into the water but will be rapidly broken down by wave action and will not be a threat to marine life.

The Trust is required to submit a resource consent application to the Auckland Regional Council for the aerial baiting part of the eradication. This application requires the preparation of an Assessment of Environmental Effects or AEE which identifies any adverse effects and sets in place strategies to remove or minimise them. It also requires that that all affected parties are consulted. Consultation with locals will occur prior to the application being submitted. This will include commercial fishers, iwi, the Community Board and the Great Barrier Island Charitable Trust as well as the Department of Conservation, owners of adjoining islands and on the closest parts of Great Barrier Is.

How will rats be prevented from returning to Kaikoura?

Rats (and not mice) are known to swim quite large distances (further in salt water because of its buoyancy). Rats from Stewart Island are known to have reinvaded islands at least 200m off its coast and it’s likely that with favourable conditions they can swim a lot further. To stop rats reinvading Kaikoura Island, they will also be eradicated from Motuhaku, Moturako, Nelson and the Grey Islands. Bait stations and some traps will also be installed on the closest peninsulas on the Bracewell and Stellin properties and on some D.o.C land.

The Trust will also undertake an education programme for all visitors to the island to ensure rodents do not come ashore with boats, planes, equipment etc. This will include signs at main entry points and an information pamphlet. Permanent bait stations will also be maintained in main entry points such as the wharf, airfield and Bradshaw Bay.

When will the rodent eradication programme start?

Providing that the resource consent is approved, it is planned to start the programme in winter 2007. This is the best time of the year as natural food supplies are low and rodents are more likely to take the baits. The aerial baiting will involve two drops 4-10 weeks apart depending on weather conditions. The ground based removal of survivors will start once the second drop has been completed.

How does this affect people visiting Kaikoura Island?

People will continue to have free access to the island. The only time that the island will be closed to the public will be when the aerial drops are being undertaken. Notification will be way of signage and public notices in the Barrier Bulletin and the NZ Herald.