The Chagos group is a combination of different coralline rock structures topping a submarine ridge running southwards across the centre of the Indian Ocean, formed by volcanoes above the Réunion hotspot.

Until October 2010, Skipjack (Euthynnus pelamis) and yellowfin tuna (Thunnus albacares) were fished for about two months of the year as their year-long migratory route takes them through Chagos waters.

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.

December through February is considered the rainy season (summer monsoon); typical weather conditions include light west-northwesterly winds and warmer temperatures with more rainfall.

Although the Portuguese navigator Pedro de Mascarenhas (1470 – 23 June 1555) is credited with having encountered the islands during his voyage of 1512–13, there is little corroborative evidence; cartographic analysis points to 1532 or later.

[24] The earliest and most interesting description of the Chagos, before coconut trees grew widely on the islands, was written by Manoel Rangel, a castaway from the Portuguese ship Conceição which ran aground on the Peros Banhos reefs in 1556.

Between 1967 and 1973, the population was forcibly removed from the islands and moved to Mauritius and the Seychelles to make way for a joint United States–United Kingdom military base on Diego Garcia.

[42] On 18 March 2015, the Permanent Court of Arbitration unanimously held that the marine protected area (MPA) which the United Kingdom declared around the Chagos Archipelago in April 2010 violates international law.

Anerood Jugnauth, Prime Minister of Mauritius, pointed out that it is the first time that the United Kingdom's conduct with regard to the Chagos Archipelago has been considered and condemned by any international court or tribunal.

[45] The issue of compensation and repatriation of the former inhabitants of several of the archipelago's atolls, exiled since 1973, continued in litigation, and in 2010 it was submitted to the European Court of Human Rights by a group of former residents.

Diego Garcia was a preferred location due to existing infrastructure, with Ile du Coin and Boddam also being provisional initial candidate sites.

[4] United Nations' resolutions on self-determination deprecated the parcelling up of imperial territories before independence, without its endorsement and local support, mindful of the Partition of India which provided the strong governments sought by the separate factions but failed to ensure a relatively peaceful transfer of power in many places.

Maldives states that the UK's claim to a 200 nautical mile Exclusive Economic Zone around the Chagos Archipelago is invalid as the islands are considered uninhabited.

[clarification needed][54] A subsidiary issue is the Mauritian opposition to the 1 April 2010 UK Government's declaration that the BIOT is a Marine Protected Area with fishing and extractive industry (including oil and gas exploration) prohibited.

During the debate, the Mauritian Prime Minister, Sir Anerood Jugnauth, described the expulsion of Chagossians as "akin to a crime against humanity," while the United Kingdom continued to assert that it had no doubt about its sovereignty over the archipelago.

[68][69] Whereas these talks included the resettlement of expelled Chagossians, Cleverly's successor as British foreign secretary, David Cameron, later ruled out a return of the islanders.

[citation needed] Some Chagossians fear that their interests might not be prioritised under Mauritian sovereignty, possibly leading to further marginalisation or lack of support for their right to return to and resettlement on the islands.

Legal actions like those initiated by Bernadette Dugasse against the UK government for failing to include Chagossians in sovereignty talks further underscore their opposition to decisions made without their input.

The UK considers it an Overseas territory of the United Kingdom, and the Government of the BIOT consists of a Commissioner appointed by the King on the advice of the Foreign and Commonwealth Office.

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 used to operate seasonally in the Chagos.

[citation needed] The coconut crab (Birgus latro) is the world's largest terrestrial arthropod,[91] reaching more than a metre in leg span and 3.5–4 kilos in weight.

The native flora of the Chagos Islands is thought to consist of forty-one species of flowering plant and four ferns, as well as a wide variety of mosses, liverworts, fungi and cyanobacteria.

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).

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 extending 200 nautical miles from the islands.

Leaked US cables have shown the FCO suggesting to its US counterparts that setting up a protected no-take zone would make it "difficult, if not impossible" for the islanders to return.

[102] On 18 March 2015 the Permanent Court of Arbitration unanimously held that the marine protected area (MPA) that the UK had declared around the Chagos Archipelago in April 2010 violated international law.

Anerood Jugnauth, Prime Minister of Mauritius, pointed out that it was the first time that the UK's conduct with regard to the Chagos Archipelago had been considered and condemned by any international court or tribunal.

He qualified the ruling as an important milestone in the relentless struggle, at the political, diplomatic and other levels, of successive governments over the years for the effective exercise by Mauritius of its sovereignty over the Chagos Archipelago.

The Tribunal also found that the United Kingdom's undertaking to return the Chagos Archipelago to Mauritius when no longer needed for defence purposes was legally binding.

WikiLeaks published a cable from the US embassy in London to Washington stating: HMG would like to establish a marine park or reserve providing comprehensive environmental protection to the reefs and waters of the British Indian Ocean Territory (BIOT), a senior Foreign and Commonwealth Office (FCO) official informed Polcouns on May 12.