Reflections on Motu Kaikoura

BARRY SCOTT (AGBET Trustee and Environmental News Editor)

In the first week of December 2023 Lotte McIntyre organized a working bee on Motu Kaikoura for the Oruawharo Medlands Ecovision (OME) volunteer group. With an invitation to join them I leapt at the chance so on the first Monday of December ten of us were ferried out to the island from Port Fitzroy by Clint Stannard, Motu Kaikoura Trust ranger on the island. During the two days we were there we cleared vegetation around the cabins and the loop track, dug out and replanted around 70 harakeke, cleared about 60 rat traps along 10 km of tracks, and dealt to some of the wilding pines near Bradshaw Cove.

Motu Kaikoura is a large island (564 ha) off the northwestern coast of Aotea Great Barrier Island. Its location provides a natural physical boundary between the Hauraki Gulf and Aotea, which gives rise to the magnificent, sheltered harbour of Port Fitzroy behind it. After over a century of private ownership, and use for livestock grazing, the island was transferred into public ownership in 2004, principally through funds provided by the government Nature Heritage Fund.  It was gazetted as a scenic reserve with administration of the island ceded to the Motu Kaikoura Trust, a group comprised of representatives from the New Zealand Native Forest Restoration Trust, Friends of Tiritiri Matangi and Ngāti Rehua. Since 2005 it has been an open sanctuary for native flora and fauna, under continuous pest control. It has significant potential as an island for recreation and conservation.

Motu Kaikoura is a large island (564 ha) off the northwestern coast of Aotea Great Barrier Island. Its location provides a natural physical boundary between the Hauraki Gulf and Aotea, which gives rise to the magnificent, sheltered harbour of Port Fitzroy behind it. After over a century of private ownership, and use for livestock grazing, the island was transferred into public ownership in 2004, principally through funds provided by the government Nature Heritage Fund.  It was gazetted as a scenic reserve with administration of the island ceded to the Motu Kaikoura Trust, a group comprised of representatives from the New Zealand Native Forest Restoration Trust, Friends of Tiritiri Matangi and Ngāti Rehua. Since 2005 it has been an open sanctuary for native flora and fauna, under continuous pest control. It has significant potential as an island for recreation and conservation.

The island has a long history of Māori occupation, which started in the late 14th century. By the 15th century the island was occupied by several tribes, collectively known as Ngāti Tai. They are reported to have lived on the island through to the late 17th century when they were overthrown by Ngāti Wai. Many inter-tribal battles occurred over the centuries with Ngāti Rehua being the sole occupiers of the island by the 1800s. Kaikoura along with much of Aotea was sold by Horeta Te Taniwha to Webster, Nagle and Abercrombie in March, 1838(1).

The long period of settler occupation and farming on the island had a serious impact on the flora and fauna of the island. Grazing by pigs, goats and deer, combined with burning, left the island devoid of its original forest vegetation and a soil seriously depleted of organic material and very prone to erosion, particularly on the less sheltered northern and eastern sections of the island. But by 2008 fallow deer, pigs, cats and rabbits had all been eradicated from the island. While an attempt was made to eradicate rats this was unsuccessful as ship rats were detected on the island within 7 months of the toxin drop. Given Man of War Passage is just 80 m in width, ship rats could easily have reinvaded by swimming across this gap.  However, kiore, which are known to be poor swimmers, were also present after the toxin drops, suggesting that the toxin drops did not result in a 100% kill.  Despite this set back rat numbers have been kept relatively low, through an active rat trapping and baiting programme, which has been maintained since 2014 when Clint was appointed Ranger. A goal of the Trust is to maintain rat numbers at a relative abundance index of less than 5%. Currently, there are a total of 843 rat traps over a track network of 29.8 km (16.5 km around the coast) and 572 bait stations. These are serviced once a month. Lotte cleared around 60 of the rat motels, plywood boxes containing two traps and two bait blocks, on the NW section of the island on our first day and also got to see a copper skink in one of the stations as well as several moko skink around the rat motels.

The Management Plan adopted by the Motu Kaikoura Trust is to allow the flora on the island to restore naturally with the only interventions being weed and pest control(2). Regular pest plant surveys by Auckland Council together with control work has helped keep pest plant species on the island relatively low. Council efforts to date have resulted in the eradication of three pest plant species, and ongoing efforts are targeted at eradicating others such as moth plant. The island is free of kikuyu, but has isolated pockets of a number of other weeds, and still a significant number of wild pines (Pinus contorta and P. pinaster). While many of the large pines have been removed some have been retained as they appear to be important as a food source for the kaka population on the island. However, the downside of leaving mature pines on the island are the large number of wilding pines that are now growing across the island. On day two of our visit we removed a couple of hundred of these growing alongside the track that winds through the valley above Bradshaw Cove. But next time we will come armed with electric saws, which should enable more effective removal.

While several flora and fauna surveys have been carried out across the island there has not been any systematic ecological study to monitor the changes that have occurred since the removal of goats, pigs and fallow deer since 2008, but Clint shared with us that he has seen dramatic changes in the 10 year period he has spent on the island. A good example was the site on the southern coast where we collected the harakeke, which was once just exotic grasses but is now covered in dense clusters of harakeke. The most marked vegetation changes are in the sheltered valleys where there is better retention of moisture and reduced impact of wind, allowing the native vegetation to successfully regenerate, as in the lower reaches of the valley where we removed the wilding pines. The flora on the island can be arbitrarily divided into the kanuka woodlands of the southern, northern and western slopes of the island – the predominant type; the broadleaf forest of the southwest region; and the kauri associated forest that grows east of Houseboat Bay.

While there is a ‘no intervention’ policy for restoration of the vegetation, it was clear that for some species such as kauri, where the number of trees is very low, it will take many years for them to fully re-establish on the island. I could not help but contemplate whether some judicious planting of seedlings of some of the bigger trees, especially those whose seeds are not distributed by kererū, might accelerate the restoration process and also help restore greater numbers of birds and invertebrates.  While removing the wilding pines on the track through the valley above Bradshaw Cove we spotted a few small kauri, a single miro, and two large mature towhai in flower. Where there is serious erosion along the top of the island near the airstrip and along the northern coast, restoration is a much slower process. Unfortunately, these are open sites that are rapidly occupied by weed species such as gorse, prickly hakea and wilding pines. With more working bees like ours, and armed with a better array of gear, the wilding pines could be removed across large areas of the island before they become much larger and more difficult to remove.

Motu Kaikoura like most of the islands around Aotea would once have been teeming with seabirds. While Cooks Petrels are regularly heard flying across the island at dusk, no active burrows for petrels or shearwaters have been found on the island. It would be interesting to see how this might change if both kiore and ship rats were totally eradicated (mice are absent from the island). Maybe even then some intervention might be required to get some of these species re-established on the island. It is clear looking at a topo map of Aotea that the weak link in keeping islands like Motu Kaikoura and the Broken Islands rodent free, is the large peninsula between Wairahi and the Hauraki Gulf, which will remain as a ‘rodent feeder’ until such time as this area or the whole island is free of predators.

At least four species of skink are known to be present on Motu Kaikoura – moko, copper, shore and ornate skink. The latter was recently found at several sites during a biodiversity survey by the Motu Kaikoura Trust and highlights the value of ongoing rodent control(3). But which species of geckos are on the island is less clear, although Clint did spot what was probably a Pacific gecko in December 2021. In addition, the Trust is compiling a list of insects known to be present on the island with the help of veteran entomologist Peter Maddison. To date, a total of 75 different species have been recorded and will soon be listed on their web site.  The status of short tailed and long tailed bats on the island is also not known.

The two days on the island was a great opportunity for everyone to become much more familiar with the flora and fauna of the island, its history, and the impacts of introduced mammalian pests. It also provided a wonderful opportunity to see how we could contribute to the restoration of the flora and fauna of the island. Removal of wilding pines is an obvious one. Dealing to the ship rats and kiore is the same challenge as it is on Aotea Great Barrier Island.

It was interesting to hear from Clint that besides the Man of War Passage the other main reinvasion site for the island is the small channel that separates Motu Kaikoura from Nelson Island and in turn from Motuhaku, where there is currently little rat control. It would be great if Tū Mai Taonga could persuade the owner of these two islands to have them eradicated of rats. This would help reduce the population of rats on Motu Kaikoura significantly and better restore all three islands as safer havens for the seabirds of the Hauraki Gulf to nest and breed.

One major impediment for those wanting to visit, walk, explore, volunteer or carry out research on the island is transport. At present there is no regular water taxi service from Port Fitzroy to Motu Kaikoura so you either need to have your own boat or find someone willing to take you out to the island (and back). This is a great pity as there is good accommodation there to stay with several cabins and the recently completed (2019) solar powered lodge for communal meals and gatherings – and a pretty good library of books.

Since the working bee I have once again visited and stayed on the island for two nights after kayaking up the western coast from Whangaparapara through Bowling Alley and the Broken Islands. On the second day, we did a complete circumnavigation of Motu Kaikoura, Nelson Island and Motuhaku where we enjoyed a totally different perspective and experience of the island. Paddling alongside a flock of no less than 300 fluttering shearwaters by the passage between Motu Kaikoura and Nelson Island, exploring all the little bays and coves around the three islands and looking at the dramatic geology of the volcanic coastline, were all highlights. Looking through the clear blue waters at the fish and beautiful red, brown and green algae growing around the coastline brought home to me once again what is at stake with the spread of exotic caulerpa through these waters. Stopping the spread through Ports Abercrombie and Fitzroy is really something worth fighting for.

We were Lotte McIntyre, Raoul Stuart, Clara Safioti, Jennifer Neads, Kim Bannister, Frances McClure, Peter Jemmett, Margaret Jemmett, Prue Smith and Barry Scott

Acknowledgements

We thank Clint, Jacinda and family for hosting us on Kaikoura, sharing their accumulated knowledge over a 10 year period and transporting us to and from the island.

References

1. Andy Dodd and Vanessa Tanner. (2006) Kaikoura Island Archaeological Survey. Department of Conservation Report

2. Motukaikoura Scenic Reserve Management Plan (2020)

   https://motukaikoura.org/wp-content/uploads/2023/04/ManagementPlan2020.pdf

3. Motu Kaikoura newsletter, January 2024