Physical Environment
Parengarenga is the most northern harbour in the North Island. It is formed from a drowned valley system impounded behind a large sandspit. Parengarenga is a large enclosed estuarine harbour with an indented coastline and a narrow entrance bounded by Te Paki Point to the north and Kokota Spit to the south. The harbour area is 6,300 hectares, of which 5700 ha. is exposed at low tide. The intertidal area is mostly firm sandy flats with mudflats in the upper reaches of the tidal arms. Narrow steep-walled channels reach into the intertidal areas. These channels drop in a series of irregular steps to their floors, set into soft sedimentary rock beneath the harbour sand and mud. The substrate in the harbour is predominantly silica-rich white sand, with the sand dunes of the Kokota Spit forming a spectacularly attractive headland at the harbour mouth. Kokota Spit extends approximately 6 km northwards along the coast and is over 3 km wide at its widest point. The northern dunes are flat, with the central dunes high and widening. The sand on Kokota Spit and its ocean beach has an average of 95% quartz, less than 5% feldspar, and less than 1% rock fragments and heavy minerals. This sand is particularly suitable for glass-making. Inside the harbour, the quartz content of the sand reduces to less than 90%, with a corresponding increase in feldspar and heavy minerals (Applied Geology Associates, 1982).
The 30 square kilometres of catchment surrounding the Parengarenga Harbour is predominantly pasture, with plantation forestry to the south.
Parengarenga Harbour is considered internationally important as habitat for migratory waders, and the wetlands and intertidal flats are classified as nationally important as habitat for other bird species, invertebrates and plant associations (DOC, 1990).
Flora & Fauna
The flora and fauna of Parengarenga Harbour have been discussed in the Department of Conservation Coastal Resource Inventory (DOC, 1990) and in the DOC assessment for oyster farming (Fanselow, 1988).
In summary, Parengarenga Harbour has exceptionally high natural value. Eelgrass ( Zostera capricorni ) covers 50% of the intertidal sandflats. Mangroves ( Avicennia marina var. resinifera ) and saltmarsh line the upper reaches of the embayments and form an intertidal fringe in other sheltered areas.
The harbour supports large numbers of edible shellfish including pipi, ( Paphies australis ), Pacific oyster ( Crassostrea gigas ) and cockle ( Austrovenus stutchburyi ). Other edible shellfish that occur are cats-eye ( Turbo smaragda ) mud snail ( Amphibola crenata ) and some scallops ( Pecten novaezelandiae ). The large extent of intertidal seagrass flats with high infaunal biomass provides important feeding grounds for bird and fish populations. Fish species recorded from the harbour include trevally, snapper, kahawai, kingfish, grey mullet, yellow-eyed mullet, eagle ray and school sharks (DOC, 1990).
Parengarenga Harbour is one of New Zealand's major wading bird habitats, and several detailed studies have been carried out on bird use of the area. Over 80 species of bird have been recorded from the harbour and over 20,000 birds including rare and common waders, feed in the intertidal. New Zealand dotterel ( Charadrius obscurus ), variable oystercatcher ( Haematopus unicolor ), fernbird ( Bowdleria punctata vealeae ), and banded rail ( Rallus philippensis assimilis ) use the harbour to breed. Parengarenga supports the largest population of banded dotterels in New Zealand. Birds visiting the harbour which are rarely seen elsewhere include the American whimbrel ( Numenicus hudsonicus ), greenshank ( Tringa nebularia ), grey-tailed tattler ( Tringa brevipes ) and terek sandpiper ( Tringa cinerea ). In late summer-early autumn Parengarenga is the last resting place for the migratory waders flying to the northern hemisphere (DOC, 1990).
The coastal vegetation of the surrounding catchment ranges from pastoral farmland along the western shoreline, exotic plantation forestry in the south, to bush and scrublands on the northeastern margin. The vegetation on Kokota Spit is largely undisturbed native pingao ( Desmoschoenus spiralis ) and toetoe ( Arundo conspicua ). Pingao is an unusual and primitive plant found only in New Zealand and having no close relations anywhere in the world.
References:
Applied Geology Associates. 1982. Coastal sand and shingle resources of Auckland and Northland. Unpublished report to the Auckland Regional Authority, April 1982.
Department of Conservation (1990). Coastal Resource Inventory - First order survey: Northland Conservancy. Compiled by Tim Shaw & Joan Maingay.
Fanselow, R. (1988). Oyster farming: Parengarenga Harbour - an assessment of the opportunities for and constraints on oyster farming. Department of Conservation Northern Region Technical Report.
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