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The Chagos Archipelago.
(Atolls with areas of dry land are named in green)
Salomons Atoll is one of the many above water features of the Chagos Archipelago
The Chagos Archipelago is a hotspot of biodiversity in the Indian Ocean

The Chagos Archipelago (pronounced /ˈtʃɑːɡoʊs/ or /ˈtʃɑːɡəs/; formerly Oil Islands, known as Feyhandheebu Dhivehi, as Phehandweep फेहंद्वीप in Hindi and other North Indian languages, and as Paeikaana Theevukal பேகான தீவுகள் in Tamil) is a group of seven atolls comprising more than 60 individual tropical islands in the Indian Ocean; situated some 500 kilometres (310 mi) due south of the Maldives, on the same submarine ridge along the boundary of the Indian plate joining the African plate, they are roughly halfway between Sri Lanka and Madagascar, or between Tanzania and Java.

The islands and their surrounding waters form a vast oceanic Environment Preservation and Protection Zone (EPPZ) / Fisheries Conservation and Management Zone (FCMZ) of 544,000 square kilometres (210,000 sq mi) – an area twice the size of the UK's land surface.

Officially part of the British Indian Ocean Territory, the Chagos were home to the Chagossians for more than a century and a half until the United Kingdom and the United States expelled them in the 1960s in order to allow the US to build a military base on Diego Garcia, the largest of the Chagos Islands. The deal was sanctioned by the then British Secretary of State for Defence, Denis Healey.

The Chagos group is a combination of different coralline structures topping a submarine ridge running southwards across the centre of the Indian Ocean, formed by volcanoes above the Réunion hotspot. Unlike in the Maldives there is not a clearly discernible pattern of arrayed atolls, which makes the whole archipelago look somewhat chaotic. Most of the coralline structures of the Chagos are submerged reefs.

The Chagos contain the world’s largest coral atoll and the greatest marine biodiversity in the UK by far. It also has one of the healthiest reef systems in the cleanest waters in the world, supporting half the total area of good quality reefs in the Indian Ocean. As a result, the ecosystems of the Chagos have so far proven resilient to climate change and environmental disruptions.




The biodiversity of the Chagos archipelago and its surrounding waters is one of the main reasons it is so special. But this incredible diversity is under threat – at least 60 species that call Chagos home are already on the IUCN Red List of Threatened Species.


The brain coral Ctenella chagius is endemic to the reefs of the Chagos

The reefs host 220 species of coral including the endemic brain coral Ctenella chagius. The coral cover is dense and healthy even in deep water on the steep outer reef slopes. Thick stands of branching staghorn coral (Acropora sp) protect the low lying islands from wave erosion. Despite the loss of much of the coral in a bleaching event in 1998 the recovery in the Chagos has been remarkable and overall coral cover increases year on year.


The reefs are also home to at least 784 species of fish that stay near to the shores of the islands including the endemic Chagos clownfish (Amphiprion chagosensis) and many of the larger wrasse and grouper that have already been lost from over-fishing in other reefs in the region.

As well as the healthy communities of reef fish there are significant populations of pelagic fish such as manta rays (Manta birostris), sharks and tuna. Shark numbers have dramatically declined as a result of illegal fishing boats that seek to remove their fins and also as accidental by-catch in the two tuna fisheries that operate seasonally in the Chagos.


Seabirds nesting on South Brother island in the Chagos Archipelago

Seventeen species of breeding seabirds can be found nesting in huge colonies on many of the islands in the archipelago, and 10 of the islands have received formal designation as Important Bird Areas, by Birdlife International. This means that Chagos has the most diverse breeding seabird community within this tropical region. Of particular interest are the large colonies of sooty terns (Sterna fuscata), brown and lesser noddies (Anous stolidus and Anous tenuirostris) wedge-tailed shearwaters (Puffinus pacificus) and red-footed boobies (Sula sula).


The remote islands make perfect undisturbed nursery sites for nests of green (Chelonia mydas) and hawksbill (Eretmochelys imbricata) turtles. The populations of both species in Chagos are of global significance given the "Critically Endangered" status of hawksbills and the "Endangered" status of green turtles on the IUCN Red List. Chagos turtles were heavily exploited during the previous two centuries, but they and their habitats are now well protected by the administration of the British Indian Ocean Territory and are recovering well.


Coconut crabs are the world's largest terrestrial arthropod and live in one of the most undisturbed populations in the Chagos

The coconut crab (Birgus latro) is the world’s largest terrestrial arthropod, reaching over one metre in leg span and 3.5-4 kilos in weight. As a juvenile it behaves like a hermit crab and uses empty coconut shells as protection but as an adult this giant crab climbs trees and can crack through a coconut with its massive claws. Despite its wide global distribution, it is rare in most of the areas it is found. It is primarily threatened by over-collection for food, but also as ornaments for sale to tourists and as bait for fish traps. Demand for coconut crabs as souvenirs is strong, and other threats include habitat destruction and predation from introduced species such as rats. The coconut crabs on Chagos constitute one of the most undisturbed populations in the world. An important part of their biology is the long distances their young can travel as larvae. This means the Chagos coconut crabs are a vital source for replenishing other over-exploited populations in the Indian Ocean region.


The Chagos Islands have been colonised by plants since there was sufficient soil to support them – probably less than 4,000 years. Seeds and spores arrived on the emerging islands by wind and sea, or from passing sea birds. The native flora of the Chagos Islands is thought to comprise forty-one species of flowering plants and four ferns as well as a wide variety of mosses, liverworts, fungi and cyanobacteria.

Today, the status of the Chagos Islands’ native flora depends very much on past exploitation of particular islands. About 280 species of flowering plants and ferns have now been recorded on the islands, but this increase reflects the introduction of non-native plants by humans, either accidentally or deliberately. Because some of these non-native species have become invasive and pose a threat to the native ecosystems, plans are being developed to control them. On some islands, native forests were felled to plant coconut palms for the production of copra oil. Other islands remain unspoiled and support a wide range of habitats, including unique Pisonia forests and large clumps of the gigantic fish poison tree (Barringtonia asiatica). Unspoiled islands provide us with the biological information that we need in order to re-establish the native plant communities on heavily altered islands. These efforts will ultimately help to improve the biodiversity of the Chagos Islands.


The entire land area of the islands is a mere 63.17 km², with the largest island, Diego Garcia, having an area of 27.20 km². The total area, including lagoons within atolls, however, is more than 15,000 km², of which 12,642 km² are accounted by the Great Chagos Bank, the second largest atoll structure of the world (after the completely submerged Saya de Malha Bank). The shelf area is 20,607 km², and the Exclusive Economic Zone, which borders the corresponding zone of the Maldive Islands in the north, has an area of 636,600 km² (including territorial waters).

The largest individual islands are Diego García (27.20 km²), Eagle (Great Chagos Bank, 2.45 km²), Île Pierre (Peros Banhos, 1.50 km²), Eastern Egmont (Egmont Islands, 1.50 km²), Île du Coin (Peros Banhos, 1.28 km²) and Île Boddam (Salomon Islands, 1.08 km²).

The number of atolls in the Chagos Islands is given as four or five in most sources, plus two island groups and two single islands, mainly because it is not recognized that the Great Chagos Bank is a huge atoll structure (including those two island groups and two single islands), and because it is not recognized that Blenheim Reef has islets or cays above or just reaching the high water mark.

In addition to the seven atolls with dry land reaching at least the high water mark, there are nine reefs and banks, most of which can be considered permanently submerged atoll structures. They are listed in the table from north to south:

(alternate name)
type Area (km²) number
of islands
Land Total
0 unnamed bank submerged bank 3 04°25′S 72°36′E / 4.417°S 72.6°E / -4.417; 72.6
1 Colvocoresses Reef submerged atoll 10 04°54′S 72°37′E / 4.9°S 72.617°E / -4.9; 72.617 (Colvocoresses Reef)
2 Speakers Bank unvegetated atoll >0 582 1) 04°55′S 72°20′E / 4.917°S 72.333°E / -4.917; 72.333 (Speakers Bank)
3 Blenheim Reef (Baixo Predassa) unvegetated atoll 0.02 37 4 05°12′S 72°28′E / 5.2°S 72.467°E / -5.2; 72.467 (Blenheim Reef)
4 Benares Shoals submerged reef 2 05°15′S 71°40′E / 5.25°S 71.667°E / -5.25; 71.667 (Benares Shoals)
5 Peros Banhos atoll 13 503 32 05°20′S 71°51′E / 5.333°S 71.85°E / -5.333; 71.85 (Peros Banhos)
6 Salomon Islands atoll 5 36 11 05°22′S 72°13′E / 5.367°S 72.217°E / -5.367; 72.217 (Salomon Islands)
7 Victory Bank submerged atoll 21 05°32′S 72°14′E / 5.533°S 72.233°E / -5.533; 72.233 (Victory Bank)
8a Nelsons Island parts of mega-atoll
Great Chagos Bank
0.81 12642 1 05°40′53″S 72°18′39″E / 5.68139°S 72.31083°E / -5.68139; 72.31083 (Nelson Island)
8b Three Brothers (Trois Freres) 0.37 3 06°09′S 71°31′E / 6.15°S 71.517°E / -6.15; 71.517 (Three Brothers)
8c Eagle Islands 2.63 3 06°12′S 71°19′E / 6.2°S 71.317°E / -6.2; 71.317 (Eagle Islands)
8d Danger Island 0.66 1 06°23′00″S 71°14′20″E / 6.3833333°S 71.23889°E / -6.3833333; 71.23889 (Danger Island)
9 Egmont Islands atoll 4 29 7 6°40′S 71°21′E / 6.667°S 71.35°E / -6.667; 71.35 (Egmont Islands)
10 Cauvin Bank submerged atoll 12 06°46′S 72°22′E / 6.767°S 72.367°E / -6.767; 72.367 (Cauvin Bank)
11 Owen Bank submerged bank 4 06°48′S 70°14′E / 6.8°S 70.233°E / -6.8; 70.233 (Owen Bank)
12 Pitt Bank submerged atoll 1317 07°04′S 72°31′E / 7.067°S 72.517°E / -7.067; 72.517 (Pitt Bank)
13 Diego Garcia atoll 30 174 42) 07°19′S 72°25′E / 7.317°S 72.417°E / -7.317; 72.417 (Diego Garcia)
14 Ganges Bank submerged atoll 30 07°23′S 70°58′E / 7.383°S 70.967°E / -7.383; 70.967 (Ganges Bank)
15 Wight Bank 3 07°25′S 71°31′E / 7.417°S 71.517°E / -7.417; 71.517 (Wight Bank)
16 Centurion Bank 25 07°39′S 70°50′E / 7.65°S 70.833°E / -7.65; 70.833 (Centurion Bank)
Chagos Archipelago Archipelago 63.17 15427 64 04°54' to 07°39'S
70°14' to 72°37' E
1) a number of drying sand cays
2) main island and three islets at the northern end

The deep oceanic waters around the Chagos Islands, out to the 200 nautical mile limit, include an exceptional diversity of undersea geological features (such as 6000m deep trenches, oceanic ridges, and sea mounts). These areas almost certainly harbour many undiscovered and specially adapted species. Although the deepwater habitats surrounding the islands have not been explored or mapped in any detail, work elsewhere in the world has shown that high physical diversity of the sea floor is closely linked to a high diversity of species.


The main natural resources of the area are coconuts, and fish and the licensing of commercial fishing provides an annual income of about two million dollars for the British Indian Ocean Territory authorities.[1]

All economic activity is concentrated on the largest island of Diego Garcia, where joint UK-US military facilities are located. Construction projects and various services needed to support the military installations are done by military and contract employees from the UK, Mauritius, the Philippines, and the US. There are currently no industrial or agricultural activities on the islands. All the water, food and other essentials of daily life are shipped to the island. An independent feasibility study led to the conclusion that resettlement would be "costly and precarious". Another feasibility study, commissioned by organisations supporting resettlement, found that resettlement would be possible at a cost to the British taxpayer of £25 million. If the Chagossians return, they plan to re-establish copra production and fishing, and to begin the commercial development of the islands for tourism.

Skipjack (Euthynnus pelamis) and yellowfin tuna (Thunnus albacares) are fished for about two months of the year as their year-long migratory route takes them through Chagos waters. While the remoteness of the Chagos offers some protection from extractive activities, legal and illegal fishing have had an impact. There is considerable poaching of turtles and other marine life. Sharks, which play a vital role in balancing the food web of tropical reefs, have suffered sharp declines from illegal fishing for their fins and as bycatch in legal fisheries. Sea cucumbers, which cleanse sand, are poached to feed Asian markets.


Tropical oceanic climate; hot and humid but moderated by trade winds. Climate is characterised by plenty of sunshine, warm temperatures, showers and light breezes. December through February is considered the rainy season (summer monsoon); typical weather conditions include light west-northwesterly winds and warmer temperatures with more rainfall. June to September is considered the drier season (winter), characterised by moderate south-easterly winds, slightly cooler temperatures and less rainfall. The annual mean rainfall is 2600 mm (100 inches), varying from 105 mm (4 inches) during August to 350 mm (14 inches) during January.


Detailed map of the Chagos Archipelago

The ancient Sanskrit phrase Lakshadweepa referred to the Islands of Laccadives, Maldives and the Chagos Archipelago as well. The Chagos islands were ruled from India originally, although never settled.

Maldivian mariners knew the Chagos Islands well. According to Southern Maldivian oral tradition, traders and fishermen were occasionally lost at sea and got stranded in one of the islands of the Chagos. Eventually they were rescued and brought back home. However, these islands were judged to be too far away from the Maldives to be settled permanently by Maldivians. Thus for many centuries the Chagos were ignored by their northern neighbours. [2] In Maldivian lore Diego Garcia is known as Fōlhavahi or Hollhavai (the latter name in the Southern Maldives Adduan dialect of Dhivehi) and Feyhandheebu is the Divehi name for Chagos.

The first European explorer to spot the Chagos was Vasco da Gama in the early 16th century. Portuguese seafarers named the group and some of the Atolls, but they never made these islands part of their seaborne empire. They judged this lonely and isolated group to be economically and politically uninteresting. Peros Banhos Atoll was discovered in 1513 by Afonso de Albuquerque. The earliest and most interesting description of the Chagos, before coconut trees grew on the islands, was written by Manoel Rangel. He was a castaway from the Portuguese ship Conceição which ran aground on the Peros Banhos reefs in 1556.[3]

The French were the first to lay a claim on the Chagos after they settled Réunion and Ile de France (later renamed Mauritius).

On 27 April 1786 the Chagos Islands and Diego Garcia were claimed for Britain. However, the territory was ceded to the United Kingdom by treaty only after Napoleon's defeat, in 1814. On 31 August 1903 the Chagos Archipelago was administratively separated from the Seychelles and attached to Mauritius.

The islands were retained as part of the British Indian Ocean Territory when Mauritius gained independence. Since 1976, the archipelago has been coterminous with the British Indian Ocean Territory, but it is also claimed by Mauritius.[4]

The archipelago's first inhabitants arrived in the 18th century. These were the lepers of Ile de France (Mauritius) who were brought there in the second half of the 1700s. Soon after, a plan was drawn up by the French to settle the Chagos and make them profitable. Workers for a massive French project to establish coconut plantations and produce oil were sent from Ile de France (Mauritius) and settled in some of the largest islands. Consequently, in some maps of the time the Chagos are known as the "Oil Islands". Most of these workers were of African origin, but it is likely that there were also a few South Indians among them. The supervisors of the plantations were probably Frenchmen and the workers were probably little more than slaves, but very little has been recorded about conditions on the islands during that time.

By the mid-20th century the oil plantations had largely failed, but the original workers and their families had settled some of the largest islands and survived there. The islanders were known as the Ilois (one French Creole word for "islanders") and they numbered almost 2,000. They were of mixed African and South Asian descent and lived very simple, spartan lives in their isolated archipelago. Few remains of their culture have been left, except for the ruins of a few dwellings and a stone church that can still be seen in Diego Garcia.

Suddenly, between 1967 and 1971, the entire population was forcibly removed from the islands and relocated to Mauritius to make way for a joint United States-United Kingdom military base on Diego Garcia. Apparently, the displaced people received an initial funding of some £650,000 for their rehousing from the British Government, but individual islanders saw little of those funds and ended up living in a slum in Mauritius.

After negotiations in the late 1970s and early 1980s, the Government agreed to pay a further £4 million to the Chagossians. The Government says the total sums paid to the Chagossians amounts to £14.5 million in today's prices. Attempts by the Chagossians to secure additional compensation to this were dismissed by the High Court and Court of Appeal in 2003 and 2004.[5] It later became clear that the Chagossians had been fraudulently reclassified as 'migrant workers' in order to facilitate the American military occupation of their home. The High Court had repeatedly found in favour of the Chagosians and it was only by means of a Royal Decree that the UK government was able to overturn the decision.

The court found that the Chagossians, as British dependent Citizens, had been unlawfully dispossessed and ordered that they be allowed to return to their home. It was only by means of the executive order that this was presented. The British government went so far as to commission a (widely discredited) report in which it suggested that the islands were uninhabitable despite currently being home to hundreds of American military personnel.

In the Chagos, the houses the Chagossians had abandoned fell slowly into ruin. Now the vegetation has taken over and in some islands it is difficult to discern where the village once had been. Yachtsmen passing through the archipelago often try to find the ruins and are unsuccessful.

Currently, the only human structures on the islands are located in the joint defence and naval support facility on Diego Garcia. Other uninhabited islands, especially in the Salomon group, are common stopping points for long-distance yachtsmen travelling from Southeast Asia to the Red Sea or the coast of Africa, although a permit is required to visit the outer islands.

For more information on the expulsion of the islanders and the court case, see the following 'Politics' section and the separate article on Diego Garcia.


The British Indian Ocean Territory flag flies over Chagos Archipelago

The most high profile aspect of Chagos Island politics relates to the continued uncertainty as to the future of the former inhabitants of the islands who were evicted in the 1960s and 1970s as part of an arrangement between the United Kingdom and the United States to establish a military establishment on the island of Diego Garcia. The islanders' plight has been well documented, including a documentary produced by investigative journalist John Pilger, entitled "Stealing a Nation", which won the British Royal Television Society Best Documentary Award in 2004.

In 2000, the English High Court ruled that a local Ordinance made by the Commissioner of the British Indian Ocean Territory exiling the islanders was unlawful,[6] a decision which was accepted by the British Foreign Secretary, Robin Cook. Subsequent efforts by the Chagossians to obtain further compensation payments were dismissed by the High Court and Court of Appeal, who held that the compensation paid had been fair and lawful. Following the conclusion of the compensation cases, the British Government attempted to achieve the same objective through use of Orders in Council enacted under the royal prerogative, which is the only means short of an Act of Parliament by which legislation can be enacted for the Territory. These Orders in Council were found in part to be unlawful by the High Court[7]. The UK government appealed the ruling, but on 23 May 2007 the Court of Appeal dismissed the appeal saying that the methods used to stop the Chagos families to return to the islands were "unlawful" and "an abuse of power".[8] The Government has been granted leave to appeal to the House of Lords on the condition that they undertook to pay the costs of the respondents. On 22 October 2008 the UK Law Lords upheld the UK Government's bid to stop Chagossians from returning to their homeland.[9] The Chagossians may now take their legal battle to the European Court of Human Rights.[10]

Despite the Law Lords ruling, the long term future of the archipelago still appears uncertain. In the medium term the US-UK joint use of Diego Garcia for defence purposes is by treaty currently set to expire in 2016, although both Governments have the option of extending the lease for another 20 years if considered necessary.

Conservation efforts


The Chagos is one of the few marine locations in the world where there are almost no ongoing, direct human impacts over almost all of its areas. Designating the Chagos as a marine reserve would, among other things, allow the area to serve as a reference site for global scientific research to aid in understanding of such things as climate change, tropical marine ecosystems and the impacts of commercial fisheries.

Successive UK governments, both Labour and Conservative, have supported environmental conservation of the Chagos. They have committed to treat the whole area as a World Heritage site. In 2003, the UK government established an Environment (Protection and Preservation) Zone under Article 75 of the UN Convention on the Law of the Sea. This zone extends 200 nautical miles from the islands. On eastern Diego Garcia, the largest island of the Chagos and the site of a UK–US military facility,[11] Britain has designated the very large lagoon and the eastern arm of the atoll and seaward reefs as a “wetland of international importance” under the Convention on Wetlands of International Importance (the Ramsar Convention).[12]


An effort led by the The Chagos Environment Network[13], a collaboration of nine leading conservation and scientific organisations seeking to protect the rich biodiversity of the Chagos Islands and its surrounding waters, currently urges the UK Government to declare the Chagos archipelago and waters, out to its 200 mile Environmental Preservation and Protection Zone, a full no-take marine reserve in which extractive activities such as fishing would be prohibited.[13] The Chagos Environment Network cites several reasons for supporting a protected area:

The Chagos no-take marine reserve would maintain the pure and unpolluted waters of Chagos, providing a safe refuge for its rich marine life, including many threatened species, such as turtles and sharks. Seabirds and nesting turtles too will benefit from the additional conservation measures that a protected area will bring. Both groups are recovering from severe depredations of the past in a way that is not possible in most places.
World fish stocks have declined catastrophically because of destructive and unsustainable fisheries practices. The Indian Ocean has been badly affected in this regard, given its heavily populated rim of countries. A large ‘no-take’ protected area would assist fish population recovery, potentially increasing fish numbers over a much wider area. The protected area would also provide a temporary refuge for migratory species, such as tuna, from exploitation.
In the long-term, a Chagos no-take marine reserve would contribute to a richer ocean and would benefit people living in and around that ocean, such as the coastal countries of East Africa and elsewhere. In regards to the displaced Chagossian people, whatever the outcome of legal challenges brought by Chagossian groups against the UK government, the Chagos Environment Network believes that the Chagos need conservation now and that this will be beneficial to everyone under all future legal scenarios. The Chagos Environment Network urged that the Chagos Islands and their surrounding waters be designated as a no-take marine reserve "without prejudice” to the outcome of the legal process. This designation would mean that the Chagos Islands and their resources would remain healthy no matter what the future holds, but that conservation arrangements could be modified if necessary in the light of a change in circumstances.
The Chagos is one of the few marine locations in the world where there are almost no ongoing, direct human impacts over almost all of its areas. The marine reserve can serve as a reference site for global scientific research to aid in our understanding of such things as climate change, tropical marine ecosystems and the impacts of commercial fisheries.
Deep ocean 
The deep oceanic waters around the Chagos Islands, out to the 200 nautical mile limit, include an exceptional diversity of undersea geological features (such as 6000m deep trenches, oceanic ridges and sea mounts). These areas almost certainly harbour many undiscovered and specially adapted species.
UK international commitments 
The creation of the Chagos Protected Area would be an important contribution by the UK to at least seven international environmental conventions. It would also contribute to the UK’s global commitments, such as halting the decline of biodiversity by 2010, establishing marine protection networks by 2012, and restoring depleted fish stocks to sustainable levels by 2015.

The UK government has opened a three-month public consultation set to end on the 5th of March 2010 about conservation management of the Chagos Islands and its surrounding waters. [14]

Among the three options under consideration, Option I would provide the best means to preserve one of Earth's last unspoiled tropical island, reef and deep-sea ecosystems in that it would “Declare a full no-take marine reserve for the whole of the territorial waters and Environmental Preservation and Protection Zone (EPPZ)/Fisheries Conservation and Management Zone (FCMZ).” [14] This option would establish the largest marine reserve in the world, a conservation legacy almost unrivalled in scale and significance. It would also establish the United Kingdom as a world leader in marine conservation for the benefit of all nations.


The inhabitants of Chagos were speaking Ilois creole, a French Creole which has not been properly researched from the linguistic point of view.

The island names are a striking combination of Portuguese, French, English and Creole names.

See also



  • Pilger, John (2006). Freedom Next Time. Bantam Press. ISBN 0593055527.  Chapter 1: Stealing a Nation pp19 – 60
  • Rao, Padma, "Der Edikt der Königin", Der Spiegel 5 December 2005, pp. 152–4.
  • Xavier Romero-Frias, The Maldive Islanders, A Study of the Popular Culture of an Ancient Ocean Kingdom. Barcelona 1999, ISBN 84 7254 801 5

Coordinates: 6°00′S 71°30′E / 6°S 71.5°E / -6; 71.5


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