Bycatch and discard of longline fisheries in the Atlantic Ocean: its implication on marine ecosystem conservation and management

Taking ICCAT (International Convention for the Conservation of Atlantic Tuna) as an example, the management and conservation measures of regional fisheries management organization were mainly focus on major tuna, billfish and... [ view full abstract ]

Taking ICCAT (International Convention for the Conservation of Atlantic Tuna) as an example, the management and conservation measures of regional fisheries management organization were mainly focus on major tuna, billfish and sharks. However, the bycatch/discard of other species were less attention. For understanding the impact on marine ecosystem, onboard observer data of Taiwanese large scale tuna longline fleets from 2009-2017 were used to analyze the spatial-temporal distribution of all species caught. Not like that seven species were accounted 97% of total catch from logbook, the results showed the recorded species were ranged from 43 for temporal operating albacore-targeting vessels to 46 species for tropical operating bigeye tuna-targeting vessels. The species diversity was higher in the tropical area. The discard rates significantly different by fleet, species, and area. Long snouted lancetfish, Crocodile shark, cookie cutter shark, and pomfrets were the major discard species. Among commercial species, blue shark and swordfish discard rates were over 40%. For swordfish, the discard rates were higher in the last quarter and when the catch rates were higher. These were due to quota limitation.  It is suggested to consider full utilization on those discard species and take those number into the consideration for stock assessment.