Bycatch in the tuna purse-seine fisheries of the western Indian Ocean

The magnitude of bycatch in the western Indian Ocean (WIO) tuna purse-seine fishery is unknown, perhaps because there is no tuna-dolphin association and the fishery has not attracted attention. Catches of associated species by tuna purse seiners in the WIO were estimated based on scientific observations from aboard Soviet purse seiners from 1986-92. More than 40 fish and marine animal species were recorded, of which only the yellowfin and skipjack tuna were target species. Average levels of bycatch per set and per 1000 t of target species, non-recorded annual bycatch of the major fish groups, turtle and whale bycatch, and other statistics are summarized. Gaps in recording data hinder assessment of tuna fishery impacts on the WIO ecosystem. Further monitoring by scientific observers on board tuna purse-seine and longline vessels fishing in the WIO is recommended.