MOTU-MANAWA / POLLEN ISLAND
DRAFT MANAGEMENT PLAN - POLLEN ISLAND CARE GROUP - date required
1. CONTEXT
1.1 Plan Objective
The purpose of this Management Plan is to provide guidelines for the effective management and protection of the island,
The permitted use of the land, for the purpose of protecting and preserving the ecological associations, plant and animal communities, soils and geomorphology and other matters of special interest, for scientific study, research, education and amenity.”
1.2 Location
Thousands of motorists pass Pollen Island Scientific Reserve as they drive on the North West motorway. It is located a few hundred metres from MHWS at the end of the Rosebank Peninsula, in the Waitemata Harbour, Auckland, at 36 degrees 52 minutes South and 174 degrees 40 minutes East (Map Reference NZMS 260 Sheet R11 595805). Access is through the Pollen Island Marine Reserve.
1.3 Legal Description and Legal Protection
The legal description is "An uninhabited island A1 93 DP NA Pollen Island, Avondale 1007, Rating Group K".
The Department of Conservation (DoC) now own and manage the island as declared as a Scientific Reserve under Section 14 of the Reserves Act. The Pollen Island Care Group as agreed with the Department of Conservation to help keep free of all noxious pests (including rabbits, possums and rats). It also requires that access to the land be restricted to groups approved by the Pollen Island Care Group and/or Northern Conservation Officer, and that no fires shall be lit on the land. Also of importance are the restrictions imposed on all areas adjacent to the island by the Marine Reserves Act 1971 and Marine Reserves Regulations of 1993.
1.4 General Characteristics and Use
One of the few remaining unmodified areas in the Waitemata Harbour, the shellbank and associated shrubland comprising Pollen Island cover some 13 hectares above sea level. The exposed eastern side is less than a metre above high tide level and is being actively eroded. It is surrounded by tidal flats, saltmarsh and mangroves and deep channels and muddy conditions discourage predators such as dogs and cats but both Norway and ship rats have been identified as present. These deep channels also significantly restrict certain weed access. The sheltered western side is contiguous with the extensive saltmarsh of glasswort and low mangroves, including small vegetated islets covering about 50 hectares between the island and the motorway.
1.5 Ecological Values
Aided by its isolation and being relatively predator free it has a significant population of fernbirds and small numbers of the nationally threatened New Zealand dotterel are present. Marine invertebrates such as shellfish, worms and crabs provide food for bird and fish species and this nursery area plays a vital role in sheltering juvenile fish which later move out into the Hauraki Gulf. Insect life is also significant as one of the world's rarest creatures, an undescribed native Bactra moth (Bactra sp.), has been found only on the island. A 2mm shore bug (Saldula stuneri) is known only from tidal pools on this site and two other localities. Three other rare moths are also present. The area is a nationally important locality for the study of strand island stability, formation of inter-tidal mudflats, and subfossil pollen studies. There is currently virtually no humus layer and therefore the island is unsuitable for most plant species but given time this situation will gradually change and allow a more suitable environment for plant establishment.
The area around the island is classified in the Draft Regional Plan Coastal for the highest level of protection as Coastal Protection Area 1. The land boundaries of the Marine Reserve and Pollen Island itself are classified as Outstanding Landscape and the site of the limeworks on the island is listed for protection under the Cultural Heritage Schedule.
1.6 Historical and Cultural Heritage
The Ngati Whatua and Te Kawerau a Maki have traditional claims and links to this part of the Auckland region. They used the upper harbour and surrounding lands for gardens and seasonal food gathering. In the mid-1800s several brickmaking industries began using west Auckland clays. Lime was required and the shell from Pollen Island shellbanks was a readily obtainable source. Dr Daniel Pollen was the first European owner and the island remained in the Pollen family until 1918 when it came into public ownership.
1.7 History of Threats and Conservation Measures
1967 - A reclamation authorisation was granted over the area by the Auckland Harbour Board (AHB) between Pollen Island and the tip of Rosebank Peninsula.
1983 - The New Zealand Wildlife Service classified the entire Waitemata Harbour as a Site of Special Wildlife Interest (SSWI).
1986 - Waitemata Harbour Maritime Planning Scheme sent mixed signals. The ecological value of the area was recognised by conservation and habitat zonings. A special Pollen Island zone to the landward side of the island recognised the exceptional conservation value of the area but still allowed the possibility of future port development.
1988 - Auckland Regional Planning Scheme. 6 October 1988, AHB and POA agreed to a “Port Plan”. Central Auckland F&B sent letters of objection to the Minister of Conservation, Helen Clarke.
1989 - 4 September, the first public notice of the F&B application to the Director General of Conservation for a 500 hectare marine reserve in the tidal waters around Pollen Island and Traherne Island. There was a two month period for submissions, with 319 being received.
1989 - Transit NZ proposed a major motorway interchange at Rosebank/Patiki Road. Objections were made by the Auckland Regional Council (ARC), DoC, F&B and other environmental groups and the battle to save the inter-tidal mudflats from the impact of the motorway interchange began. By December 1989 an option that avoided significant impact on the seabed and was second lowest in capital cost had survived the prescreening process.
1995, 10 July - A ten year lease of the island was granted by the POA to F&B.
1995, 9 October - The Pollen Island/Motu Manawa Marine Reserve was gazetted.
1995, 9 November - The Marine Reserve was formally opened by the Minister of Conservation
1996, February - Transit NZ started work on the Rosebank Road Northwestern motorway interchange.
Ports of Auckland land transfer the Department of Conservation.
Pollen Island Care Group formally takes over the general maintenance of Pollen Island.
Pollen Island gazette as a Scientific Reserve.
1.8 Relationship between Pollen Island and the Marine Reserve
Pollen Island and the marine area surrounding it, in particular the marine reserve, are inextricably linked. The island was formed by natural marine processes, and is continually modified by those processes. Erosion and shellbank accretion are assisted by spring tides and storm action. The island also forms an excellent example of an ecotone from mangrove through salt meadow to terrestrial vegetation. It is difficult to put a line where marine life stops and terrestrial life commences. Perhaps there is no line. The island and the marine reserve are therefore ecologically and geologically linked.
Laid on top of this contiguous natural ecosystem are human lines. Marine reserves are administered by the Department of Conservation. Pollen Island is managed by the Pollen Island Care Group. These two “titles” are separated by the mean high water springs line (MHWS).
The Pollen Island/Motu Manawa Marine Reserve was gazetted on 9 October 1995. This reserve complements Pollen Island and extends the protected area around the island. The marine reserve, whilst being an important reserve in its own right, will also act as a buffer area for the island.
Given the inter-relationship of both the island and the marine reserve both the Department of Conservation and the Pollen Island Care Group must ensure that activities occurring in each area do not compromise the values of that area or of the adjacent area.
Management of the marine reserve is undertaken under the provisions of the Marine Reserves Act 1971 and the Marine Reserves regulations 1993. This management is also subject to the objectives and policies of the Conservation Management Strategy.
Section 19 of the Act lists those activities which are offences within marine reserves, see appendix 2. Since MHWS is difficult to determine "on the ground", the Pollen Island Care Group will need to ensure that their activities do not conflict with Section 19.
2.0 NATURAL VALUES
2.1 Geology
Geological Setting of Pollen Island
Pollen Island is a narrow, low, vegetated bank protecting an extensive area of high tide glasswort salt meadow, salt marsh and low mangrove flats. These ecosystems are established in a thin veneer (1 - 10 centimetres thick) of sandy mud or soil deposited over a terrace of stiff Pleistocene sediments. The seaward side of the island is eroding, with 0.3 - 1 meter high banks of stiff Pleistocene sediments along most of its length. The island probably extended much further eastwards a few thousand years ago and has since been eroded back to its present narrow form.
The subsurface composition of Pollen Island has been investigated to a depth of 1.5 - 2 metres through the sinking of approximately 100 bore holes in the 1950s (Chapman and Ronaldson 1958). The island is composed of 0.1 - 1 meter thick partly weathered blue-grey mud overlying a peat deposit. Attempts to radiocarbon date the peat in the 1950’s suggested that it is older than 20 000 years. The 0.5 - 1 meter thick peat in turn overlies further weathered mud.
The peat is inferred to have accumulated in a freshwater swamp environment at a time of lower sea level during one of the glacial episodes. The mud above and below it were possibly deposited in an inter-tidal environment during interglacial periods when sea levels were close to the present.
Recent drillhole exploration by the ARC and the University of Auckland on the Rosebank Peninsula side of the motorway indicates that the stratigraphy seen on Pollen Island is the upper part of a much thicker (?50m) sequence of the Pleistocene alluvial, marine and ash sediments (NZ Herald 27 September 1995). Almost all of Rosebank Peninsula is underlain by this sedimentary sequence which accumulated in a deep valley or basin over the last million years. Weathered early Miocene Waitemata Sandstone forms the small hill at the south end of the motorway bridge over the Whau and is exposed in the inter-tidal channels draining the Pollen Island mangrove swamp in that vicinity.
The best known examples in New Zealand of three-dimensional fossilised, limonite-cemented casts of network burrows protrude from the inter-tidal mud off the southeast corner of Pollen Island. They are eroding out of the blue grey mud that overlies the peat and are inferred to have been made by burrowing callianassid, alpheid or mantid shrimps (Grenfell and Hayward, 1995).
Shell banks are actively accumulating and migrating off the seaward side of both the north and south ends of Pollen Island. The banks are largely composed of shells of the cockle (Austrovenus stutchburyi) which live on the adjacent inter-tidal flats.
Issues: Marine erosion is actively removing parts of the seaward side of Pollen Island. At times this erosion, coupled with rare storm surges is destroying parts of the coastal fringe vegetation.
The mobile shell banks periodically advance into and through established mangrove forest killing the trees and destroying the habitat.
Natural erosion and shell bank migration are part of the natural order and are generally uninfluenced by human activities.
Policy: Natural physical process will be allowed to continue unimpeded. No erosion retardation structures will be constructed.
2.2 Vegetation and Flora
Vegetation
The vegetation of the island and associated saltmarsh was mapped in the 1950’s by Chapman and Ronaldson (1958) and commented on by Cameron (1990). Marsh ribbonwood (Plagianthus divaricatus) and oioi (Leptocarpus similis), 1-1.3m tall, form the main vegetation of the island. On the slightly higher land flax (Phormium tenax)(up to 2m tall) and Olearia solandri (up to 3m tall) locally form taller vegetation. A few Sydney golden wattles (Acacia longifolia)(up to 4.5m tall) are the tallest plants on the island. Manuka (Leptospermum scaparium), mapou (Myrsine australis) and karamu (Coprosma robusta) occur locally in small numbers and are all present in the best developed shrubland with Olearia solandri at the north end of the island. The eastern side of the island is being actively eroded by storms and here flax frequently dominates. Usually oioi and marsh ribbonwood form a thicket behind the flax.
At the narrowest point of the island, the vegetation is low and open. Unlike the shrublands on either side, this area (c. 25m long) is dominated by herbaceous weeds. It lacks the shrub-oioi cover here because there is no slightly raised surface present for its establishment.
The island’s sheltered margin is fringed with a zone of sea rush, which is usually narrow. The extensive sheltered tidal flats between the motorway and the island are almost entirely covered in low open vegetation of mangrove (Aricennia marina) and glasswort (Sarcocornia quinqueflora). The zonation of the vegetation is controlled by land level in respect to sea level. At the lowest level are mangroves (inundated twice a day); glasswort (only inundated twice a day by the larger tides); sea rush (more or less high-water spring); marsh ribbonwood/oioi/needle tussock (Stipa stipoides); flax/Olearia solandri (only very occasionally reached by the sea).
Flora
The specialised habitat of salty, wet mud or loose shell, all exposed by some degree to saltwater, is suitable for only a narrow range of species. Ninety vascular plant species have been recorded for the island (Cameron 1990, 1991) although many of these are represented by few individuals. Although a large percentage (64%) of the flora is adventive, most of these are annuals and are scarcely visible for much of the year. Tall fescue (Festuca arundinacea) was the only widespread adventive species on the island. A creeping native buttercup (Ranunculus acaulis) which grows locally on the exposed eastern muddy bank is now a very scarce species in the Waitemata Harbour.
Issues: The strong marine influence and tide levels govern the zonation patterns and low species diversity. Erosion and accretion of soil and shell destroys existing sites and/or creates new sites for vegetation colonisation.
The vegetation and flora of Pollen Island is the best remaining example of this type close to Auckland.
Policy: Planting is prohibited on the island except where specific management of threatened species requires it, but this will be subject to approval from the Pollen Island Management committee.
2.3 Birds
Fernbird
Vegetation along the shore of Pollen Island contains an established population of fernbirds. The site is regionally significant for this species and critical for its preservation in Auckland. The population consists of an estimated 15-20 pairs and appears to have been stable at this level for some years (Taylor 1995).
Other Land Birds
The coastal habitat is suitable for banded rail and occasional reports support the likely continued presence of this species. The site attracts a range of common species. (An asterisk indicates probable nesting). Harrier, kingfisher, skylark, welcome swallow, blackbird*, song thrush*, grey warbler*, fantail, silvereye*, chaffinch*, greenfinch, house sparrow, starling, common myna, Australian magpie.
Wading Birds
The shell banks contiguous with Pollen Island are used for nesting by New Zealand dotterel (2 or 3 pairs). This species is highly threatened throughout the Auckland region.
The spur-winged plover frequents the northern shore and probably nests in grassy areas of the Te Atatu peninsula. Adjacent tidal flats provide the main feeding grounds of the Upper Waitemata Harbour for other wading birds, particularly bar-tailed godwit, knot, pied oystercatcher, pied stilt, banded dotterel and wrybill. These species form high-tide roosting flocks, often containing several hundred birds, which take advantage of the shore and shell banks of Pollen Island according to season and tidal height. Pollen Island has an important role in sheltering these roosts and feeding areas.
Gulls and Terns
Most years Pollen Island has a nesting colony of black-backed gulls (typically 10 - 20 pairs). These gulls threaten and may predate any New Zealand dotterel nests. Caspian terns have been recorded nesting, visiting the upper harbour and roosting among the wader flocks. Red-billed gulls and white-fronted terns feed in the waters adjacent to the island.
Other Shore Birds
Other birds which regularly feed and roost on or near Pollen Island include shags, herons and ducks. The particular species involved are pied shag, little black shag and little shag (the nearest nesting colony of these three species is at Western Springs), white-faced heron (common), white heron (rare visitor), paradise shelduck, mallard and grey duck. Pukeko are present, and probably nest in the immediate vicinity.