It is a matter of dispute whether the building agreement transferred sovereignty of Tromelin from one to the other, and Mauritius claims the island as part of its territory, on the grounds that France has not retained its sovereignty over island in 1814 which was "de facto" 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. A co-management treaty was reached by France and Mauritius in 2010, but has not been ratified.