Cuvier Repanga Island Nature Reserve

BARRY SCOTT with ROB CHAPPELL

Cuvier Island, located off the eastern entrance to Colville Channel at the tip of the Coromandel, had a long history of human-induced disturbance but since becoming completely predator and livestock free in 1993 it has become home to many of New Zealand’s endangered wildlife. Rob Chappell from the township of Coromandel has played a key role in the restoration of this island and shares with us some of the history and background to that recovery process.

Introduction

Cuvier/Repanga Island Nature Reserve is the most remote, and second largest (195 Ha) of the predator free offshore islands in the Mercury Island Ecological District. Repanga has special significance for Māori who used the island as a base for catching seabirds and kai moana. The name Cuvier, after Baron Cuvier, was assigned by the explorer D’Urville who passed by the island in 1827. While there is no evidence of pa on the island, archaeological evidence such as midden sites, indicates a long history of Māori presence on the island. Several Hauraki iwi including Ngāti Hei and Ngāti Whaunaunga claim manawhenua over Repanga Island. With the establishment of a lighthouse on the island in 1889, light house keepers and their families settled on the island and stayed from this time through till 1982. Despite its distance from the mainland, the island has had a long history of human-induced disturbance that started with fires and introduction of kiore in pre-European times, followed by further ecosystem degradation with arrival of Europeans including loss of vegetation from grazing livestock and feral goats and loss of native fauna by feral cats. Today after ~60 years of restoration the island has flourishing populations of sea (grey faced, Pycroft’s and diving petrels and fluttering shearwaters) and land birds (tīeke, bellbird, kākāriki and kākā), tuatara, geckos (2 species), skinks (4 species) and other invertebrates, and a flora that is well on the way to recovery thanks to a concerted long term effort by the Wildlife Service, Department of Conservation and volunteers.

Lighthouse

The lighthouse was built as a kitset in England in 1886 comprising a number of cast iron plates that were brought ashore at Landing Bay then hauled by horses and a pulley system up the gully to the assembly site. Two kauri houses were built as kitsets in Auckland assembled at the top of the paddock behind the current house sites. In 1902 heavy rains washed the two houses off their foundations so they were subsequently relocated to their present position as accommodation for the light house keepers.

In 1941 the NZ Navy built three buildings comprising barracks, ablution block and a generator room, on the summit of what was renamed Radar Point to service a radar aerial, which is now lying rusting on the floor of the barracks. There was also a coast watch tower and a pumphouse, which drew water from the creek below. The entire unit was known as Radar Station No.4 and was built during the development of radar in NZ before it was dismantled and sent to England in 1944.

While the lighthouse was initially powered by kerosene it was converted to electricity in 1941 when a generator was installed. All cooking and heating for the houses until this time was provided by coal. All the glass from the original lighthouse unit is currently stored in DOC Pureoroa – all 5 tonnes of it.

Restoration

Restoration of Cuvier began in 1957 following transfer of ownership of the island from Gordon Tizard to the Crown for the sum of 500 pounds. At that time there were livestock on the island to provide meat and milk for the keepers of the lighthouse. A team from the Wildlife Service fenced off the eastern two thirds of the island from stock to form a reserve with the western third retained as a farm. Goats were eradicated by 1961 and feral cats by 1966. However, there was an ongoing issue with lighthouse keepers continuing to bring cats onto the island to control the rats despite their contracts requiring that they be “protectors of the tuatara”. This led to tensions between the Wildlife Service and the lighthouse keepers with one keeper setting fire to the island in 1966 and burning 12 Ha of land above Blanket Bay. The same keeper also destroyed the kiore exclusion enclosure in 1966.

After the eradication of feral cats and goats a series of bird re-introductions commenced first with the transfer of 29 North Island saddlebacks/tīeke (Philesturnus rufusater) from Hen Island to Cuvier Island by Don Merton following the success of a transfer to Red Mercury island in 1964. The birds were released just above North West Bay landing. In 1971 a 10 acre quadrant was set up below the pumphouse in Landing Bay to monitor the bird populations with the wire defining that area still in place; the data from those surveys carried out by Wildlife Service Rangers Dick Veitch and Rob Chappell is currently under analysis by Professor James Russell and students at the University of Auckland. In 1974 30 red crowned parakeets/kākāriki (Cyanoramphus novaezelandiae) bred at the Mt Bruce Wildlife Centre (now Pūkaha National Wildlife Centre) in the Wairarapa were released onto Cuvier. Later it was shown that these birds were hybrids so are considered not suitable for further translocations. Attempts were made to establish stitch birds/hihi (Notiomystis cincta) on Cuvier from Hauturu (Te Hauturu-o-Toi) but without success.

Automation of the lighthouse on the island in 1982 removed the need to have a lighthouse keeper and any livestock to support them so the remaining animals were culled. In 1987 management of the island was transferred from the Hauraki Gulf Maritime Park Board (Dept. of Lands and Survey) to the Dept. of Conservation who established a base in Coromandel town under the leadership of Rob Chappell. More active management of the island followed this transfer of responsibility. A survey for tuatara in 1991 located just 7 survivors, which were transferred to the Auckland Zoo for captive breeding and protection from kiore still on the island at that time. In 1992 a team of students from Whitianga Polytechnic working under the supervision of Rob Chappell demolished the Principal Keeper’s house due to its deteriorating condition and planted 1000 pōhutukawa on the hillside behind using seedlings grown by the Tiritiri Matangi reforestation team. In 1999 the at-risk Calistegia marginata (small-flowered white bindweed) was reintroduced to the island using 210 plants grown by the Auckland Botanical Society from seed collected from the island many years before. Plant pest control was also initiated and is still ongoing in an effort to eradicate the highly invasive moth plant (Araujia sericifera). Restoration of the buildings on the island was also initiated. Archaeologist Neville Richie organised twice yearly working bees of 6 volunteers who stayed for periods of 12 days carrying out building restoration work, track cutting, weed removal, bird surveys and planting.

It was not until 1993 that Cuvier became completely predator free following a brodificoum helicopter drop by Helitranz. This was the first use of GPS tracking for an aerial toxin drop in New Zealand. Since then the science and technology has advanced significantly with a common protocol being toxin free pre-feeding drops followed by the toxin drop, at levels significantly less than previously used. Complete removal of kiore from the island was the real beginning of the restoration of Cuvier. A number of species of bird re-established themselves on the island including fluttering shearwaters (Puffinus gavia) and diving petrels (Pelecanoides urinatrix). Species such as the grey faced petrel (Pterodroma macroptera) increased in numbers as did the tīeke, with current populations around 1000 and 2000, respectively. Further introductions of threatened or at risk species were made. Pycroft’s petrel (Pterodroma pycrofti) chicks that had hatched on Red Mercury Island were relocated as hatchlings to artificial burrows on Cuvier Island in an experiment to see if these chicks could be fledged from that island and further, would they return to the site of hatching or the site of fledging i.e. Red Mercury or Cuvier islands. This experiment was trialed to provide guidance for a proposed threatened species at risk transfer, that of moving Chatham petrel chicks (Pterodroma axillaris) from Rangatira Island to neighbouring Pitt island in the Chathams. At present there are around 100 active burrows on Cuvier Island. The Chatham Island petrel transfer was also a success. Tuatara, from the breeding program at Auckland zoo, and tusked wetas from Mercury Island were also reintroduced to Cuvier in releases from 2001 to 2018. Many bird transfers were also carried out from Cuvier Island including tīeke to Kapiti Island, Tiritiri Matangi, Hauturu, Cape Kidnappers and Boundary Stream, kākāriki to Tiritiri Matangi and bellbirds to Waiheke.

There has also been a strong recovery of plant species following removal of grazing livestock and predators from the island. There has been:

• Increased abundance of species known to be suppressed by kiore including taupata, kohekohe (Dysoxylum spectabile), coastal mahoe, karo, nikau (Rhopalostylis sapida), tawapou, coastal maire (Nestegis apetala), parapara (Pisonia brunoniana) and houpara (Pseudopanax lessoni).

• Increased abundance of large-fruited trees whose seeds are dispersed by kereru, such as tawa and taraire either in situ or from the mainland.

• Transition of former pasture to a Muehlenbeckia dominated shrubland of flax, kawakawa, houpara, rangiora, nikau and Coprosma species with occasional forest trees.

• Expansion of Senecio repangae on disturbed, open or fertile sites around seabird colonies.

• Spread of flax and hardy shrubs such as taupata and karo along the coastal areas subjected to wind and salt spray.

Animal species have also made a dramatic recovery. There has been:

• Recovery of land-snail (Rhytida sp.), the paua slug (Schizoglossa sp.), large spiders and large insects such as Mimopeus species, various cicada, centipede and weta species, all likely to have been heavily suppressed by kiore.

• Increased abundance of shore skink (Oligosoma smithi) and egg-laying skink (Oligosomsoma suteri) in coastal areas, Pacific geckos (Hoplodactylus pacificus) common in pōhutukawa forest and coastal flax, moko skink (Oligosoma moco) in open inland sites, and common gecko (Hoplodactylus maculatus) widespread and abundant throughout.

• Tuatara came close to extinction with just 7 individuals remaining before feral cats and kiore were removed but with the captive breeding and reintroduction program they are re-establishing well, especially around seabird burrows.

A Restoration Plan

Since 1960 the ecological restoration of Cuvier has comprised three elements: pest control, natural recovery and species introductions but as discussed above, proper restoration was not possible until the island became totally predator free in 1993. This process has been a combination of both passive (natural recovery) and active intervention to re-establish plant and animal species known to have been formerly present using principles and practices laid out in the DOC Cuvier Restoration Plan (2010-2020)(1) . The vision laid down by this plan was one of maintaining the integrity of ecosystems and preserving the historic heritage of Repanga.

The combined effects of feral cats and kiore resulted in depletion of seabird fauna and lizards to two and six species respectively. Since removal of these predators the resident breeding seabird fauna has increased to eight species, including the re-establishment of colonies of white-fronted terns (Sterna striata striata), red-billed gulls (Larus novaehollandiae), Northern diving petrels (Pelecanoides urinatrix urinatrix), Northern little blue penguins ( Eudyptula minor iredalei), fluttering shearwaters (Puffinus gavia) and Pycroft’s petrels (Pterodroma pycrofti); the latter as a result of reintroductions (2000- 2002). Terrestrial birds were also severely impacted by mammalian predation, with the apparent loss of pied tomtit (Petroica macrocephala toitoi), kākāriki/red-crowned parakeet (Cyanoramphus novaezelandiae novaezelandiae), tīeke, North Island rifleman (Acanthisitta chloris granti), North Island robin (Petroica longipes), whitehead (Mohoua albicilla) and tui (Prosthemadera novaeseelandiae novarseelandiae). Of these, only tui have naturally re-established a permanent population, still in very low numbers, although the North Island rifleman reappeared on the island from 2005 to 2008. Tīeke (1968) and kākāriki/red-crowned parakeet (1974) have been reintroduced, and are now abundant.

One of the challenges with ecological restoration is knowing what was previously present. The very limited fauna and flora records for Cuvier together with the absence of nearby rodent-free islands have made this task even more difficult. Besides readily available records decisions on what to reintroduce have been guided by (i) construction of conceptual models based on knowledge of natural processes operating on neighbouring islands, (ii) analysis of midden sites and (iii) historic data from survey expeditions.

Throughout this long period of ecological restoration and recovery of Cuvier one person’s name keeps appearing and that is former Wildlife Service and DOC ranger, Rob Chappell. Over a period of 50 years Rob has made 63 trips to Cuvier Island. He has many stories to tell of the successes and failures of those early days of restoration efforts on the island involving predator control, animal and bird reintroductions, restoration of buildings, and surveys of the flora and fauna on the island, and the challenges of dealing with lighthouse keepers who were not entirely supportive of their efforts. The current healthy state of the ecology on this island is testament to his mahi. DOC in partnership with mana whenua are continuing the conservation work started by Rob and others.

References:

1. Brandon A and Chappell R (2010). Repanga (Cuvier) Island Restoration Plan 2010-2020. Hauraki Area Office, Department of Conservation. Thames.