Chatham Islands wetlands

Dune lakes, Chatham Islands

Wetlands are extensive and diverse on the Chatham Islands, where around 8.5 percent of New Zealand's threatened freshwater fish are found.

Although the annual rainfall is relatively low (500–1500 mm at Waitangi) the land is of low relief, rising to just 299 m and with gently rolling slopes, so that drainage is poor.

Peat development is encouraged by the climate being cloudy, cool, coastal, humid, and windy. About 60 percent of the land surface is covered with peat (to about 10 m deep in places) or peaty soils. Bogs occur on elevated peat surfaces where they are nourished only by rainfall, and are therefore quite infertile. Small valleys carry moving groundwater and a certain amount of nutrients from mineral soils, and these are occupied by fens and swamps.

Lakes, ponds, and pools of many sizes are common, some associated with peatland and others enclosed by sand dunes. These provide further wetland habitats, especially shallow freshwater aquatic ones, and marshes around their margins.

Close to the coast, the strong influence of sea salts produce distinctive wetland communities: seepages with coastal wetland plants, damp turf vegetation on headlands and on shallow peats overlying rock, and small estuaries with tidal marshes.

Te Whanga Lagoon shore
vegetation zones

The wetland interface between land and sea is especially well represented around the margin of Te Whanga, a huge shallow coastal lagoon that occupies a fifth of the area of Chatham Island. Te Whanga is valued as a source of inanga, patiki, swan eggs, and cockles. Its marginal zones of mudflats, shell ridges, saltmarsh turf, and rushlands are important for many coastal, freshwater, and migrant wading birds.

Habitat degradation has contributed to the extinction of some bird species associated with freshwater habitats including brown teal, Chatham Island fernbird, and Chatham Island rail. Game birds such as black swan and ducks are present on several water bodies.

Of the 10 known species of indigenous freshwater fish found on the Chathams, one species Galaxias rekohua (discovered in 1995) is endemic to the Chatham Islands.

The Chatham Islands have 42 endemic flowering plants, 17 of which grow partly or wholly in wetlands. Two of these are notable for their functional role as predominant peat-formers: the forest tree tarahinau, and the Chatham island bamboo rush.

Many Chatham islands wetlands have been affected by fire, livestock, and wild animals (especially cattle, sheep, and pigs), but compared with mainland New Zealand they are less impacted upon by nutrient enrichment and weeds. Freshwater aquatic habitats of lakes and rivers, for example, have so far escaped invasion by the many potentially troublesome aquatic weeds.

The Department of Conservation is working with Chathams landowners to protect and restore freshwater ecosystems. They are currently not formally protected on the Chathams, other than a small amount of habitat on conservation land. 

back to top