Henderson Island, United Kingdom

Published: October 8, 2008, 3:58 pm

Topics:

Ecology (main) Geography (main)

Geographical Location

Henderson Island (24°22'S, 128°20'W), a World Heritage Site, is the largest island in the Pitcairn Island group, one of the remotest groups of islands in the South Pacific, with no major landmass within a 5,000 kilometer (km) radius. The group comprises four islands, with Henderson lying 200 km east-north-east of Pitcairn, 200 km east of Oeno and 360 km west of Ducie. Only Ducie, and the Chilean islands of Rapa Nui (Easter Island) and Sala y Gomez lie further to the east within Polynesia.

Date and History of Establishment

• 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 lands applied under the Lands and Administration of Estates Ordinance.
• Some wildlife protection is provided by part IV of the Local Government Regulations.

Area

Henderson Island caves, UK. (Source: Pacific Union College)

Land area 3,700 hectares (ha).

Land Tenure

The Pitcairn Island group is a Dependent Territory of the United Kingdom, and Henderson is Crown Land.

Altitude

Up to a maximum of 33 meters (m).

Physical Features

Henderson is an elevated coralline limestone ("makatea") island which rises as an isolated conical mound from a depth of about 3.5 km, and is presumably a reef-capped volcano. The surface of the island is in large part reef-rubble interspersed with areas of dissected limestone, surrounded by steep limestone cliffs undercut on all sides except to the north. There are three main beaches, to the north, north-west and north-east. Tidal range at spring tides is probably about 1 m, and tides are semidiurnal. The central depression is considered to be an uplifted lagoon. Freshwater is almost completely absent, only occurring as drippings in caves, and as a spring below high tide level in the north (flow and permanence unknown). The geology of the island is summarized by Fosberg et al. (1983), who conclude that the limestones are of late Tertiary age. It is also suggested that much of the inland topography may be karst features.

There is a fringing reef at least 200 m wide to the north, north-west and north-east sides of the island, backed by a wide beach. Reefs off the north and north-east beaches are seawardly sloping reef platforms without reef crests, and are not typical fringing reefs. Coral cover is about 5%, dominated by Pocillopora with Millepora becoming dominant at depths greater than 7 m. Submassive Acropora colonies are also present on the buttresses and solid substratum. In total, 19 genera and 29 species of coral were collected in 1987. There are two narrow channels through the reef on the north and north-western coasts.

Climate

Henderson lies in the south-east trades, and total recorded rainfall for the period from February 1991 to January 1992 was 1623 millimeters (mm). Average monthly maximum temperature, during the same period, ranged from 29.6°C (February) to 24.2°C (June); average monthly minimum temperature ranged from 22.2°C (February) to 15.7°C (June).

Vegetation

The vegetation of the island has not been modified to any significant extent, and most of the surface of the island is densely vegetated with tangled scrub and scrub forest 5 m-10 m tall. The central part of the depression is more sparsely covered. The flora is described by St John and Philipson (1962), Fosberg et al. (1983) and Flenley et al. (1987). The island has a high degree of endemicity for its size, out of a total of 51 native flowering plant taxa, ten are endemic. The tallest trees are screw-pine Pandanus tectorius, and other trees include the endemics Santalum hendersonense, Myrsine hoskae, Celtis paniculata var. viridis, and two endemic varieties of Bidens hendersonensis. The last named species, which is listed by the International Union for the Conservation of Nature and Natural Resources (IUCN) as rare or possibly endangered (IUCN Red List Criteria for Endangered), is of particular botanical interest as a woody member of a mainly herbaceous genus, and also because of its isolation from related genera within the Compositae. Hardwoods, miro Thespesia popuinea and toa Cordia subcordata also occur.

Fauna

Masked Booby Sula dactylatra. (Source: CalPhotos)

Fauna recorded from the island are listed in Fosberg et al. (1983), and variously commented on by other visitors. There are no native species of land mammal. All four of the island's land birds are endemic, flightless Henderson rail Nesophylax ater, Stephen's lorikeet Vini stepheni (R), Henderson fruit dove Ptilinopus insularis, and Henderson warbler Acrocephalus vaughani taiti. Very little information is available on either the ecology or the status of these four birds. Fifteen seabirds have been recorded, at least nine of which are thought to breed on the island; Murphy's petrel Pterodroma ultima, phoenix petrel P. alba, herald petrel P. arminjoniana, Kermadec petrel P. neglecta, shearwater Puffinus pacificus, masked booby Sula dactylatra, red-tailed tropicbird Phaethon rubicauda, brown noddy Anous stolida, blue-grey noddy Procelsterna caerulea, and fairy tern Gygis alba. Bourne and David (1983) provide a species list with detailed annotation. Other terrestrial species are also poorly recorded and understood (including lizards and skinks as well as invertebrates), and it is likely that the invertebrate fauna is much larger, including several more endemics. For example, a new species of hawk-moth was identified in 1986, which is significantly different from any described hawk-moth.

Various records of the marine and littoral fauna have been made by Paulay (1987), and by Broodbakker (in litt., 1981; 1987) and Richmond (in litt., 1987), and a list of marine molluscs recorded from Henderson is given in Fosberg et al. (1983). Species of particular note include coconut crab Birgus latro (R) (identified from remains collected in 1987), at least two coenobite species (one of which was found to be the commonest crustacean on the island in 1987), and spiny lobster Panulirus penicillatus (CT). Green turtle Chelonia mydas (E) occasionally nests on the island (Fosberg et al., 1983). Collections of marine molluscs and sponges and of as yet unidentified caridean shrimps (mostly Alpheids, probably comprising 5-8 species), were made in 1987. There is a diverse (Species diversity) echinoderm fauna. An unidentified holothurian is common on the northern reef flats, and an echinoid Heterocentrotus sp. (possibly H. trigonarius) is locally abundant on the sloping marginal reefs and shallow reef flat of the northern beach. Fish are sparse, with Caranx lugubris being the most common and obvious species. A more comprehensive account of the corals is given in UNEP/IUCN (1988).

Cultural Heritage

The history of the island, which has been uninhabited apart from occasional visitors, is described in Fosberg et al. (1983). Recently discovered archaeological remains suggest that Henderson was colonized by Polynesians between the 12th and 15th centuries, but their impact would appear to have been slight, although there is some disagreement over this.

Local Human Population

The island is visited by Pitcairn islanders once or twice each year, chiefly to cut "miro" Thespesia populnea and tao from which carvings are made for sale to visitors to Pitcairn, and sandalwood Santalum hendersonense.

Visitors and Visitor Facilities

Cruise ships visit occasionally.

Scientific Research and Facilities

Fosberg et al. (1983) summarize scientific expeditions to the island, of which the two most important were the Whitney South Sea Expedition in 1922 and the Mangarevan Expedition of 1934. They also summarize the published information, and provide nearly 100 references. The island was visited by Operation Raleigh in spring 1987 and by an expedition from the Smithsonian Institution in the same year, and by the Sir Peter Scott Commemorative Expedition in 1991-1992.

Henderson is the world's best remaining example of an elevated coral atoll ecosystem and is thought to be of outstanding value in this regard. This is particularly so because of the relatively low level of disturbance in comparison with other raised coral atolls. The importance of the island was indicated by the International Biological Programme and by a resolution of the 15th Pacific Science Congress, as well as by individual scientists.

Conservation Value

Henderson remains in an undisturbed state, largely as a result of its remoteness, and its inhospitable nature. Unlike other oceanic islands, it has suffered little human modification, and few exotic species (Alien species) exist.

Conservation Management

Access to Henderson requires a license issued by the Governor following approval by the Pitcairn Island Council. A discussion document on the conservation and management options for the Island has been drawn up by the Foreign and Commonwealth Office. This was handed to the Pitcairn Island Council by the Governor in May 1995, and subject to the Pitcairn Islanders' views, will form the basis of a management plan for Henderson Island. Management objectives outlined in this document include: establishment of a management authority comprising representatives of the various interested parties; avoid further degradation of the coastal miro and toa woodland; prevent the introduction of exotic flora and fauna; ensure that visitors do not damage the island in any way; and the introduction of a significant fee for stopping at Henderson.

Management Constraints

Goats and pigs were introduced to the island early in the century, but have fortunately not survived (and the keeping of goats on Henderson is now prohibited). Introduced rats are still present, although this is the Polynesian rat Rattus exulans, rather than black or brown rats. The terrestrial vegetation is still largely pristine, with very few [[exotic]s], although there are two substantial coconut groves at the principal landing sites, and Cordyline terminals and Aleurites moluccana have also been deliberately introduced, and Achyranthes aspera accidentally.

In 1982/1983 the island was potentially under severe threat as a result of a proposal by a wealthy American to build a house, landing facilities and airstrip. A resolution at the 15th Pacific Science Congress in 1983 urged the British Government not to permit the proposed development before a detailed biological survey had been carried out and an assessment of the impacts made. The proposal was opposed by scientific and conservation bodies who petitioned the British Government to deny permission to carry out these plans. This they subsequently did. Had such plans gone ahead, the terrestrial fauna and flora would undoubtedly have been severely damaged, with likely resulting impacts on the [[reef]s].

Staff

None.

Budget

None.

IUCN Management Category

Natural World Heritage Site - Criteria iii, iv.

Further Reading

• Bourne, W.R.P. and David, A.C.F. (1983). Henderson Island, Central South Pacific, and its birds. Notornis 30: 233-252.

• Bourne, W.R.P. and David, A.C.D. (1986). Henderson Island. Letter to Nature 322: 302.
• Brooke, M. de L. (1992). Sir Peter Scott Commemorative Expedition to the Pitcairn Islands 1991-1992. Expedition Report. 52 pp.
• Flenley, J., Parkes, A. and Johnson, M. (1987). Vegetation survey of Henderson Island. Unpublished report to Operation Raleigh, London.
• Foreign and Commonwealth Office (1988). Nomination of Henderson Island for inclusion in the World Heritage List. Submitted by The Secretary of State for Foreign and Commonwealth Affairs, United Kingdom. Prepared by S. Oldfield. Produced by the Nature Conservancy Council. 21 pp.
• Foreign and Commonwealth Office (1995). Henderson Island Management Discussion Document: May 1995. 8pp.
• Fosberg, F.R. (1984). Henderson Island saved. Environmental Conservation 11(2): 183-184.
• Fosberg, F.R. and Sachet, M.-H. (1983). Henderson Island threatened. Environmental Conservation 10(2): 171-173.
• Fosberg, F.R., Sachet, M.-H. and Stoddart, D.R. (1983). Henderson Island (south-eastern Polynesia): summary of current knowledge. Atoll Research Bulletin 272. 53 pp.
• Oldfield, S. (1987). Fragments of Paradise. Pisces Publications, Oxford. 192 pp. ISBN: 0950824550
• Paulay, G. (1987). Comments on the Pitcairn Islands. Unpublished report. 2 pp.
• St John, H. and Philipson, W.R. (1962). An account of the flora of Henderson Island, South Pacific Ocean. Transactions of the Royal Society of New Zealand 1: 175-194.
• Serpell, J., Collar, N., Davis, S. and Wells, S. (1983). Submission to the Foreign and Commonwealth Office on the future conservation of Henderson Island in the Pitcairn Group. Unpublished Report, WWF-UK, IUCN, ICBP. This report has 24 letters annexed to it in support of the report's conclusions that settlement on the island would be inappropriate.
• Sinoto, Y.S. (1983). Analysis of Polynesian migrations based on archaeological assessments. J. Soc. Océanistes 39: 57-67.
• Steadman, D.W. and Olson, S.L. (1985). Bird remains from an archaeological site on Henderson Island, South Pacific: Man-caused extinctions on an "uninhabited" island. Proceedings of the National Academy of Science, USA 82: 6191-6195.
• UNEP/IUCN (1988). Coral reefs of the world. Volume 3. Central and Western Pacific. IUCN, Gland, Switzerland and Cambridge, UK/UNEP, Nairobi, Kenya. 329 pp. ISBN: 2880329582
• Williams, G.R. (1960). The birds of the Pitcairn Islands, Central Pacific Ocean. Ibis 102: 58-70.

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Citation

M, U. (2008). Henderson Island, United Kingdom. Retrieved from http://editors.eol.org/eoearth/wiki/Henderson_Island,_United_Kingdom