Bycatch of Taiwanese Tuna Longline Fisheries in the Pacific Ocean

Forty-three trips of observed data on Taiwanese large scale tuna longline fishing vessels in the Pacific Ocean from 2004 to 2007 were used to analyze the scale of bycatch. Albacore, bigeye, and yellowfin tuna were the most commonly caught species, and the composition were varied by fleets. The bigeye accounted for over 44% of the catches by the tropical bigeye fleets, while the albacore accounted for over 85% and 72% of the catches by the northern and southern albacore fleets respectively. The major bycatch were swordfish, blue marlins, blue sharks, and silky sharks. As for the discards, 2.59-3.1 % albacore, 1.6-4.8% of bigeye tuna, 0.5-3.9 % of yellowfin tuna were discarded because of their smaller sizes or depredation by sharks or dolphins. The depredation percentage of tuna was around 0.3% - 0.7 % by cetaceans, and 0.5%- 0.6% by sharks. Regarding to other ecological related species, 31 species of seabirds, four species of sea turtles, and five species of cetaceans were sighted during these observations. Three hundred and sixty one seabirds and seventy six sea turtles were bycatch, which the major species were black-footed albatross and Laysan albatross in North Pacific Ocean and Olive Ridley turtles in tropical areas. No cetaceans were bycatch in these trips.