Assessing the Contribution of Purse Seine Fisheries to Overall Levels of Bycatch in the Indian Ocean

Principle 2 of the Fishery Improvement Project run by the Producers’ Organization OPAGAC contains actions intended to assess the environmental impacts of OPAGAC’s purse seine fleet in the three oceans, which include the evaluation of the contribution of purse seine fisheries to overall levels of bycatch mortality in the Indian Ocean with a focus on endangered, threatened and protected species. This study represents a first attempt at evaluating impacts in the Indian Ocean in recent years. A broad and diverse range of fisheries operate in the Indian Ocean for which, in addition, data on bycatch are very poor quality or completely lacking. This study used a wide range of data sources to produce estimates for the major bycatch stocks identified by the IOTC, including sharks, marine turtles and marine mammals. According to the estimates from this study the purse seine fishery in the Indian Ocean is responsible for just 0.15% of the fishing mortality of sharks, 0.16% of whale sharks, nil of marine mammals, and 0.3% of marine turtles. By species, the silky shark is the most important bycatch species for purse seiners, although levels of fishing mortality are still very low, at 1.3% of the total. On the contrary, gillnet, driftnet, freshtuna and deep-freezing longline fisheries are responsible for most of the bycatch mortality of the three groups. However, the uncertainty of estimates for longline and gillnet fisheries, mainly for whale, sharks, marine mammals and marine turtles, is high due to nil or very poor levels of observer coverage in many fleets, insufficient reporting requirements, poor data quality, and little information available from other sources. The IOTC needs to urgently address those issues to be able to ensure bycatch stocks are assessed within reasonable levels of uncertainty and management advice leads to informed management decisions in the future.