Very much like a large sandbank and only 7 metres (23 ft) high at its highest point, Tromelin is about 1,700 metres (1.1 mi) long and 700 metres (0.43 mi) wide, with an area of 80 ha (200 acres), covered in scrub dominated by Octopus Bush and surrounded by coral reefs. There are no harbours or anchorages, so that access by sea is difficult. A 1,200-metre (3,900 ft)airstrip provides the island's link with the outside world.
The island has been identified as an Important Bird Area (IBA) by BirdLife International because of its significance as a seabird breeding site. Both Masked (with up to 250 pairs) and Red-footed Boobies (up to 180 pairs) nesting there. Sulidae populations have seriously declined in the western Indian Ocean with those on Tromelin among the healthiest remaining. The island’s Masked Boobies are of the western Indian Ocean subspecies (Sula dactylatra melanops), of which Tromelin is a stronghold. The Red-footed Boobies constitute the only polymorphic population in the region, indicating its biogeographical isolation. Both Great and Lesser Frigatebirds used to nest on the island but have subsequently become extinct as breeders, though they continue to use the island for roosting. There are no resident landbirds.
The island was first recorded by a French navigator, Jean Marie Briand de la Feuillée, in 1722 and initially named Île des Sables.
In 1761 the French ship Utile, carrying slaves from Madagascar to Mauritius, ran onto the reefs of the island. The crew reached Madagascar in a raft, abandoning some 60 slaves on the desert island. Fifteen years later in 1776, Bernard Boudin de Tromelin (from whom the island takes its name), captain of the French warship La Dauphine, visited the island and rescued the survivors—seven women and an eight-month-old child.
French claims date back to 1810. However, from the 19th century until the 1950s, Tromelin was a dependency of the British colony of Mauritius. In 1954, by an agreement between the British and the French, France constructed a meteorological station and a landing strip on the island. It is a matter of dispute whether the agreement transferred sovereignty of Tromelin from one to the other, and Mauritius claims the island as part of its territory on the grounds that sovereignty was not transferred to France and the island was thus part of the colony of Mauritius at the time of independence. Indeed, as early as 1959, even before independence, Mauritius informed the World Meteorological Organization that it considered Tromelin to be part of its territory. France and Mauritius reached a co-management treaty in 2010.
^Marriner, N.; Guérout, M.; Romon, T. (2010). "The Forgotten Slaves of Tromelin (Indian Ocean): New Geoarchaeological Data". Journal of Archaeological Science37 (6): 1293–1304. doi:10.1016/j.jas.2009.12.032.