There are nearly 800 species of fish here, including many species that have already been heavily diminished by over-fishing elsewhere in the world’s oceans.
Many species - including the endemic Chagos clownfish (Amphiprion chagosensis) - linger near the shores of the islands. There are notable populations of open ocean fish such as manta rays (Manta birostris), sharks and tuna, and types of larger wrasse and grouper that cannot be found in other reefs in the region.
The establishment of the Chagos Marine Reserve and the ban on fishing has protected species such as the skipjack (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares). In the past, as many as 25,000 tonnes of these species were caught by international fishing fleets as they passed through the islands’ waters on their year-long migratory journey. Before protection, around 10,000 sharks were caught each year as accidental bycatch by boats fishing around the archipelago. Protection has stopped this, though threats from illegal fishing of tuna, sharks and other species remain an issue.
Among the types of fish that populate the waters around the islands is the bigeye tuna (Thunnus obesus), a deep-water fish that occupies nearly all of the world's oceans within 45-degrees of the equator. It can grow to up to 2.5m in length with up to 200kg of high performance muscle. The bigeye tuna is a one of the most commercially-sought-after species of tuna, and as a result of its overfishing, it has been listed as vulnerable by the International Union for Conservation of Nature (IUCN).
The silky shark (Carcharhinus falciformis) is commonly found near the edges of continental shelves, from the surface to depths of up to 50m. It feeds on bony fishes and cephalopods, and often follows schools of tuna. As a result, the species is frequently caught by tuna longline and purse seine fisheries. It is also hunted for its fins, with many being sold in the Hong Kong shark fin market. The IUCN has designated the global silky shark population as near threatened.
Protection of the seas around the Chagos Archipelago has provided a sanctuary where marine species can rebuild natural populations.