Incidental catch in fishing gears is a serious threat to marine megafauna (sea turtles, sharks and marine mammals) at the global scale. In order to manage this threat, it is critical to assess its extent, both spatially and quantitatively. In the southwest Indian Ocean (from 0 to 25째S, from eastern Africa to 60째E), there is a paucity of information on marine mammal bycatch. This report reviews the marine mammal bycatch issue in this region in the following countries: Mozambique, Tanzania (including Zanzibar), Kenya, the Seychelles, the Comoros, Mayotte, Madagascar, Reunion Island and Mauritius. For each country, status of marine mammals, fishing effort, bycatch information and mitigation measures are reviewed. It appears that quantitative information (number of bycaught animals per species, impact on local populations) is limited (except for Zanzibar). However, it is clear that several fisheries incidentally catch marine mammals in the region, most notably gillnets catching dugong (Dugong dugon) and coastal dolphins (Tursiops aduncus and Sousa chinensis), in Zanzibar, southwest Madagascar and probably Kenya. Mitigation measures are limited, particularly efforts to reduce the use of these gears. It is now critical to quantify the extent of bycatch in gillnets and its impact on local marine mammal populations and to implement relevant and effective mitigation measures as necessary.