Variation in catch composition in offshore fishing boats and motivation toward flotsam-associated fishing in the Indian Ocean: implications for management

Regional fisheries management organizations are mandated to reduce impacts of commercial fishing activities on non-target species. This is particularly important because fishing associated with natural drifting objects and artificial fish-aggregating devices across the oceans poses adverse impacts on non-target species, including juveniles of tuna species. In the Indian Ocean off Sri Lanka, deep-sea fishing boats are engaged in fishing with gillnets, longlines, and encircling nets associated with natural floating objects. The present study aimed at investigating whether target species and bycatch species in the catches of fishing methods can be differentiated to introduce effective management to the fisheries and to perceive driving forces in terms of the nature of fishing strategies with a view to recognizing appropriate management measures. From the boats operated from four fishery harbors of southern Sri Lanka from February 2018 to December 2020, species compositions of landings of 1915 fishing operations consisting of gillnetting, longlining, flotsam-associated ring netting, and a combination of ring netting with gillnetting and longlining were analyzed separately for each fishing method. Also, cost components of individual fishing operations and corresponding net revenues, gleaned from logbook records of boats, were scrutinized. This analysis underscored that there was a noticeable difference in species caught in the five types of fishing boats, consisting of large tuna and tuna-like species in the landings of longlines and drift gillnets. Landings of flotsam-associated ring netting were dominated by shade-loving species and juvenile tunas. As fuel cost is considerably lower in ring net fisheries than in gillnet and longline fisheries due to shorter trip duration and as there is higher net revenue from the fishing operations, there is an increasing trend of ring netting associated with floating objects. Under the existing legal framework, this fishery can be restricted by introducing high seas licenses.