British Indian Ocean Territory

About the territory

The British Indian Ocean Territory (BIOT) covers about 640,000 km2 of ocean, including the reefs and islands of the Chagos Archipelago. The land area of the islands is around 60 km2 and they lie between 4o and 8o South and 70o and 75o East. There are also 4,000 km2 of near-surface coral reefs. The nearest land is the Maldive Islands 500 km to the North. There are five atolls: Chagos Bank, Peros Banhos, Salomon, Egmont and Diego Garcia and ten reefs and submerged shoals. Annual rainfall is between 250 and 400cm. Average temperatures range between 24C and 31C.

The Islands were uninhabited when first discovered in the 16th century and the French assumed sovereignty over them in the late 18th century. At the Treaty of Paris 1814 the French ceded Mauritius and its dependencies, which included the Chagos Archipelago, to the United Kingdom. In 1965 the islands were detached from the colony of Mauritius in order to form the British Indian Ocean Territory. The population was relocated to Mauritius and the Seychelles so that the islands could be set aside for UK and US defence purposes. Since then UK and US military personnel and civilian contract employees have been the only inhabitants. In February 2012 these numbered approximately 2, 800 people, all on Diego Garcia.


The biodiversity of BIOT has been fairly extensively studied as a result of a number of scientific expeditions. There are very few endemics but they include one marine alga, one brain coral and a gastropod. According to the Kew database there are about 280 species of flowering plants and ferns. However, the original native flora is considered to comprise only 41 species of flowering plants and four species of ferns, the remainder having been introduced. There is also a wide variety of mosses, liverworts, fungi and cyanobacteria. There are no endemic plant species.

There are over 384 species of mollusc and the 1996 Expedition identified 95 insect species. Two endemic species of butterfly, (Jamonia villida) and (Hypolimnus bolina), and an endemic subspecies of the hawkmoth (Macroglossum corythus) were also recorded along with six species of damselflies and dragonflies.

Three species of fish are endemic: an anemone fish (Amphiprionchagosensis), a goby (Trimmatom offucius) and a worm fish (Paragunellichthys fehlmani). An undescribed razorfish may also be endemic.

There are no terrestrial amphibians or reptiles.

Policy/Strategy background

There is no specific legislation regarding invasive species.

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