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The Wetlands: Henderson Island

Used by Permission of Wetlands International
http://www.wetlands.org

[Oeno Atoll] [Henderson Island] [Ducie Atoll] [Wetlands Introduction]

Site descriptions compiled from information provided by J.R. Setterfield (Office of the Governor of Pitcairn Island), M. de L. Brooke and I. Hepburn.

Henderson Island

Location: 24 degrees 22 minutes S, 128 degrees 20 minutes W; in the central South Pacific, 200 km ENE of Pitcairn Island.

Area: Land area, 3,700 ha; area of beaches and reef flats unknown.

Altitude: Sea level to 33 m.

Overview: One of the least disturbed raised coral atolls in the world, with its terrestrial ecosystems virtually intact. The island supports a large breeding population of seabirds, and has four endemic land-birds, one of which is a flightless rail. The beaches and reef flats are important for wintering Bristle-thighed Curlews (Numenius tahitiensis).

Physical features: A raised coral atoll composed of coralline limestone, with a slight depression in the centre considered to be an uplifted lagoon. The island is arid, with no surface fresh water except for some drippings in caves, a few very small fresh to brackish pools at the South End (which appears to be rain-fed and become increasingly saline through evaporation and salt-spray) and small amounts of rainwater trapped in vegetation, such as at the base of Asplenium leaves. Fresh or brackish springs have been located below high tide level at North Beach and Northwest Beach. No readily available source of groundwater has yet been located. The surface of the island is largely reef rubble, with some areas of dissected limestone, especially around the periphery. The island is surrounded by steep cliffs of bare limestone. There is a fringing reef averaging 50-100 m in width around most of the island except in the extreme south and west. In three places, North Beach, Northwest Beach and East Beach, the reef extends up to 200 m offshore, and is backed by a wide, gently shelving coral sand beach over bedrock which is partly exposed. The reef off the East Beach has a poorly developed lagoon; those off the North and Northwest beaches are seawardly sloping reef platforms without a well-defined reef crest. There are two narrow channels through the reef on the north and northwest coasts. Tides are semi-diurnal, with a tidal range at spring tides of about one metre.

The island lies in the Southwest Trades, and probably has a mean annual rainfall of about 1,500 mm. The recorded rainfall during the period February 1991 to January 1992 was 1,620 mm.

Ecological features: Coral cover on the fringing reef is about 5%, dominated by Pocillopora with Millepora becoming dominant at depths greater than 7 m. The top of the island is densely vegetated with tangled scrub and scrub forest, 5-10 m tall, except in the central part of the depression, which is more sparsely vegetated. The tallest trees are screwpine Pandanus tectorius; other trees include the endemic sandalwood Santalum hendersonense, Myrsine hoskau, Celtis paniculata var. viridis, and two shrubby endemic varieties of Bidens hendersonensis. Some coconuts have been planted near the main landing sites, close to which the Pitcairners harvest hardwoods. Otherwise the vegetation is largely undisturbed.

Land tenure: State owned (Crown Land).

Conservation measures taken: Henderson Island has not been declared a protected area as such, although it receives de facto protection from its isolation and various restrictions on possession, occupation and transference of land applied under the Lands and Administration of Estates Ordinance (IUCN, 1991). Access to the island requires a license issued by the Governor following approval by the Pitcairn Islands Council. Henderson Island was inscribed as a World Heritage Site under the Unesco World Heritage Convention in 1988, but no formal management of the site has yet been undertaken. The UK Joint Nature Conservation Committee has recently commissioned the production of a draft management plan for the World Heritage Site.

Conservation measures proposed: Henderson was proposed for listing as an “Island for Science” in 1969 (Elliot, 1973), and recommended as a reserve by the IUCN Threatened Plants Committee (Dahl, 1980). It has also been suggested that the island be declared a Biosphere Reserve under Unesco’s Man and the Biosphere Programme. The draft management plan (Hepburn, in prep) recommends that Local Government Regulations be amended to provide appropriate protection to the World Heritage Site. Hepburn et al. (1992) have recommended that the coastal and inshore marine zones of the island be designated as a Ramsar Site.

Land use: Henderson was apparently colonized by Polynesians between 800 and 1600 AD, but has remained uninhabited in modern times. Pitcairn islanders visit the island roughly once a year, normally for one day, to cut and remove timber (Cordia subcordata and Thespesia populnea) from the woodlands behind the beach. The wood is used for carving handicrafts for sale to visitors. The island is occasionally visited by passing yachts and natural history cruise ships.

Disturbances and threats: Goats and pigs were intorduced to the island in the early part of this century but did not survive. Introduced Polynesian Rats (Rattus exulans) are, however, still present, and cause devastating predation on the chicks of three species of gadfly petrel, Pterodroma neglects, P. heraldica and P. ultima. The terrestrial vegetation is still largely pristine, with very few exotics, although there are two substantial coconut groves at the principal landing sites. A proposal in 1982/83 by an American millionaire to settle on Henderson was given serious consideration by the British authorities. The development would have included clearance of forest in order to graze cattle, the building of an airfield, and the introduction of other farm stock. The proposal was finally rejected on environmental and technical grounds. There has been some anchor damage to the coral reefs. Reef blasting to improve the landing passage would be detrimental, as would the introduction of any alien plants or animals.

Hyrdological and biophysical values: None known.

Social and cultural values: Miro trees (Thespesia populnea) and Toa (Cordia subcordata) are of value to the Pitcairn islanders as a source of wood for carving.

Noteworthy fauna: The beaches and reef flats are used by a wintering population of some 40-50 Bristle-thighed Curlews (Numenius tahitiensis), most of which arrive in early September and depart in April. Small numbers of Wandering Tattlers (Heteroscelus incanus), and Sanderlings (Calidris alba), also occur on the beaches. The island is very important for its large breeding population of seabirds, estimated at 50,000-80,000 pairs. These include 10,000-20,000 pairs of Kermadee Petrels (Ptedodroma neglecta), 30,000 pairs of Herald Petrels (P. heraldica), several thousand pairs of Murphy’s Petrels (P. ultima), 200-300 pairs of Red-tailed Tropicbirds (Phaethon rubricauda), 50-60 pairs of Masked Boobies (Sula dactylatra), a few hundred pairs of Red-footed Boobies (S. Sula), 100 pairs of Great Frigatebirds (Fregata minor), 100 pairs of Brown Noddies (Anous stolidus), small numbers of Black Noddies (A. minutus), possibly ten pairs of Blue-grey Noddies (Procelsterna cerulea), and very large numbers of Fairy Terns (Gygis alba), (Hepburn, in prep). The island has three endemic species of land-birds, the Henderson Island Rail (Porzana (Nesophylax) atra), Henderson Island Fruit-Dove (Ptilinopus insularis), and Stephen’s Lorikeet (Vini stepheni), as well as an endemic subspecies of the Pitcairn Reed Warbler (Acrocephalus vaughani taiti). The rail is primarily a forest bird, foraging in the leaf litter for insects and molluscs. Although still common, this flightless and tame species would be at considerable risk from introduced predators and is therefore listed as threatened in the IUCN Red Data Book (Collar & Andrew, 1988). The total population was estimated at about 4,700 pairs in 1991/92(Hepburn, in prep). The lorikeet appears to be rather uncommon, and is also listed as threatened.

The only mammal present is the introduced Polynesian Rat (Rattus exulans). Green Turtles (Chelonia mydas) nest on East Beach, where up to 30 scrapes were reported in 1991/92. There is one species of skink (Emoia cyanura), which appears to be abundant throughout the island, and two species of gecko, one of which (as yet unidentified) may be endemic. Coconut Crabs (Birgus latro) are present. Possibly all of the island’s 14 or so species of small land snail and about 30% of the island’s 170 species of insect are endemic. The proportion of endemic species in some other invertebrate groups is given by Hepburn (in prep). The coral reefs support a diverse mariena fauna, although fish species are relatively few (UNEP/IUCN, 1988).

Noteworthy flora: Henderson supports a rich and almost undisturbed terrestrial flora, with 72 species of vascular plants, ten of which are endemic to the island. The two endemic varieties of the shrub Bidens hendersonense are of particular botanical interest.

Scientific research and facilities: A number of scientific expeditions have visited the island, including the Whitney South Sea Expedition in 1922 and the Mangarevan Expedition in 1934. A multi-disciplinary scientific expedition (the Pitcairn Islands Scientific Expedition) was based on the island from January 1991 to March 1992. The major results of this expedition are likely to be available in 1994.

Recreation and tourism: The island is occasionally visited by passengers from cruise ships, with groups of up to 100 people landing at a time.

Management authority and jurisdiction: Pitcairn Islands Council in conjunction with the British Consulate-General in Auckland (New Zealand).

References: Collar & Andrew (1988); Dahl (1980, 1986); Elliot (19730; Hay (1985); Hepburn (in prep); Hepburn et al. (1992; IUCN (1991); St. John & Philipson (1962); UNEP/IUCN (1998).

Reasons for inclusion: 1a, 2a, 2b, 2c, 2d. Henderson is of outstanding value as the world’s best remaining example of a raised coral atoll ecosystem. The reef flats and beaches support an internationally significant wintering population of Bristle-thighed Curlews.

Source: J.R. Setterfield, I. Hepburn and references.

[Oeno Atoll] [Henderson Island] [Ducie Atoll] [Wetlands Introduction]

REFERENCES

Brooke, M. de L., Spencer, T. & Benton, T. (1991). Pitcairn Islands Scientific Expedition: Interim Report, Cambridge: PISE.

Collar, N.J. & Andrew, P. (1988). Birds to Watch: The ICBP World Checklist of Threatened Birds. ICBP Technical Publication No. 8. ICBP, Cambridge, U.K.

Dahl, A.L. (1980). Regional Ecosystems Survey of the South Pacific Area. SPC Technical Paper No. 179. South Pacific Commission, Noumea, New Caledonia.

Dahl, A.L. (1986). Review of the Protected Areas System in Oceania. UNEP & IUCN Commission on National Parks and Protected Areas, Gland, Switzerland.

Elliot, H. (1973). Pacific Oceanic Islands Recommended for Designation as Islands for Science. In: South Pacific Commission Regional Symposium on Conservation of Nature - Reefs and Lagoons, 1971. Part II: Working Papers: 287-305. South Pacific Commission, Noumea, New Caledonia.

Hay, R. (1985). Bird Conservation in the Pacific Islands. SPREP Topic Review No. 25 (ICBP Study Report No. 7). South Pacific Commission, Noumea, New Caledonia. (ICBP, Cambridge, U.K.).

Hepburn, I. (in prep). Henderson Island World Heritage Site. Draft Management Plan. Prepared by NaturData for the Joint Nature Conservation Committee.

Hepburn, I., Oldfield, S. & Thompson, K. (1992). UK Dependent Territories Ramsar Study: Stage 1. Report submitted to the Department of Environment, European and International Habitat Branch, by the International Waterfowl and Wetlands Research Bureau and NGO Forum for Nature Conservation in UK Dependent Territories.

IUCN (1991). IUCN Directory of Protected Areas in Oceania. Prepared by the World Conservation Monitoring Centre. IUCN, Gland, Switzerland and Cambridge, U.K.

Philipson, W.R. & St. John, H. (1960). List of the Flora of Oeno Atoll, Tuamotu Archipelago, South-Central Pacific Ocean. Trans. Royal Society of New Zealand 88: 401-403.

Pratt, H.D., Bruner, P.L. & Berrett, D.G. (1987). A Field Guide to the Birds of Hawwaii and the Tropical Pacific. Princeton University Press, Princeton, U.S.A.

Rehder, H.A. & Randall, J.E. (1975). Ducie Atoll: its history, physiography and biota. Atoll Research Bulletin 183: 1-55.

St. John, H. & Philipson, W.R. (1962). An account of the flora of Henderson Island, South Pacific Ocean. Trans. Royal Society of New Zealand 1: 175-194.

UNEP/IUCN (1988). Coral Reefs of the World. Volume 3: Central and Western Pacific.

UNEP Regional Seas Directories and Bibliographies. IUCN, Gland, Switzerland, and Cambridge, U.K./UNEP, Nairobi, Kenya.

Weisler, M., Benton, T.G., Brooke, M. de L., Jones, P.J., Spencer, T. & Wragg, G. (1991). The Pitcairn Islands Scientific Expedition (1991-1992): First results; future goals. Pacific Science Association Information Bulletin 43: 4-8.

Williams, G.R. (1960). The Birds of the Pitcairn Islands, Central South Pacific Ocean. Ibis 102: 58-70.

Wetlands International

[Oeno Atoll] [Henderson Island] [Ducie Atoll] [Wetlands Introduction]


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