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.
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
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
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.
Who can I get further information from?
Rod Miller – Motu Kaikoura Trustee
firstname.lastname@example.org Phone/Fax: (09) 4255612