Physical Environment
Ninety Mile Beach is the exposed sandy coastline extending between Ahipara and Scott Point on the western coast of the Aupouri Peninsula. Ninety Mile Beach is composed of clean quartz based sand, which is firmly compacted with little or no silt or clay. The quartz content of the sand is high (averaging about 56% of the sediment with the shell removed), and the heavy mineral content low (about 5%) (Applied Geology Associates, 1982). The beach is very mobile, particularly during a storm event, when vast quantities of sand are moved on and off the beach area. South-westerly wave conditions prevail, and since the west coast of the Peninsula sweeps around to the north-west, the south-westerly swell approaches nearly normal to the coast. This means that long-shore drift of sediment up the beach (i.e. northwards) is reduced, so that sediment brought into the area exceeds that moving out, resulting in an overall deposition of sand on the beach. About two thirds of the way north along the beach is the Bluff, a low rocky headland. Extensive dune fields back the coast and are largely planted in forestry with areas of exotic sand binders and pasture. Ninety Mile Beach and adjacent dunes are of national importance as habitat with high natural values.
Flora & Fauna
The flora and fauna of Ninety Mile Beach is typical of exposed northern sand beaches. On very mobile exposed sandy beaches like Ninety Mile Beach, the intertidal animals are robust and capable of moving quickly to avoid smothering by sand or dislodgement. Species diversity is comparatively low and usually dominated by small crustacea, (i.e. amphipods and occasionally isopods), and by bivalve molluscs.
Common on the upper beach are the sand hopper, Talorchestia quoyana and the sea slater Scyphax ornatus . The dominant shellfish on Ninety Mile Beach, tuatua ( Paphies subtriangulata ) and toheroa ( Paphies ventricosa ), are located in the mid to low inter-tidal. Both species are patchy in their distribution and local knowledge is usually necessary to locate the denser beds. Historically, the toheroa has been exploited to such an extent that harvesting is highly restricted, but tuatua, which occurs lower on the beach, are still present in numbers that make the species attractive to gather.
Ninety Mile Beach is a feeding area for a number of threatened NZ birds including the variable oystercatcher ( Haematopus unicolor ), New Zealand dotterel ( Charadrius obscurus ) and the Caspian tern ( Hydroprogne caspia ).
The surrounding catchment has been highly modified, and much of the dunefield has been planted in pasture, pine forest, marram grass or lupins. Coast forest remnants are present near the Bluff and on Matapia Island near the northern end of the beach. Matapia Island is described by the Department of Conservation (DOC) (1990) as a site of international significance. The island has no rats, supports a varied lizard population, is an important nesting site for sea birds including black-winged petrel ( Pterodroma nigripennis ), and is a winter haul-out area for fur seals ( Arctocephalus forsteri ).
The dune lakes and swamps behind Ninety Mile Beach are considered to have high natural environment value as they are habitats for a variety of bird species including the banded dotterel (Charadrius bicinctus ) and rare plants (e.g. Hydatella inconspica ).
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.
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