Résumé
Tunas are important commercial species that represent a share of about 8 percent of total fish exports. In 2010, the total catch of tuna in three oceans was about 6.6 million tons, 4.3 million tons for the most marketed species, a level roughly stable since 2002 (FAO 2012). Among these tuna species, there are in descending order of capture: skipjack tuna (Katsuwonus pelamis), yellowfin tuna (Thunnus albacares), bigeye tuna (Thunnus obesus), albacore tuna (Thunnus alalunga) and bluefin tuna (Thunnus thynnus). Overall, the biology of albacore stock in the Indian Ocean is not well known and there is relatively little new recent information on albacore stocks. Albacore life history characteristics, including a relatively late maturity, long life and sexual dimorphism, make the species vulnerable to over exploitation. This species is a highly migratory species. It is found around the world in warm, temperate waters and can migrate thousands of kilometers each year across an entire ocean, but the relations between albacore populations across the oceans are uncertain. This species has been studied mainly in the Atlantic and the North Pacific, and very little is known about this species in the southern regions and tropics. In the Pacific and Atlantic oceans there is a clear separation of southern and northern stocks associated with the oceanic gyres that are typical of these areas. In the Indian Ocean, it is thought that there is only one southern stock, distributed from 5°N to 45°S, because there is no northern gyre and low caught in northern regions. This hypothesis needs to be investigated and more particularly the link that does exist between Indian Ocean and south Atlantic. In South African waters, huge numbers of juveniles are observed and the source is still unknown. Determinate this source is of primary concern for Regional Fishery Management Organization which amounts to the question of the relationship between these two oceans (Figure 1).