Shark bycatch in the Japanese high seas squid driftnet fishery in the North Pacific Ocean

Abstract

From the late 1970s to 1992, large-scale pelagic driftnet fisheries in the North Pacific targeted flying squid ( Ommastrephes bartrami), tunas and billfishes. In the late 1980s, cooperative multinational scientific observer programs began on Japanese, South Korean, and Taiwanese driftnet fleets fishing in international waters. These programs resulted in some of the most comprehensive data on the distribution and abundance of epipelagic species in the North Pacific transition region. Eleven elasmobranch taxa were sighted by observers in the Japanese flying squid driftnet fishery. Blue sharks accounted for 93.7% of the elasmobranch bycatch in 1990 and 1991. In 1991, observers collected biological data on a limited number of shark and fish species, including blue shark ( Prionace glauca) and salmon shark ( Lamna ditropis). Canada experimented with a flying squid driftnet fishery in coastal waters near British Columbia beginning in 1979 but it was terminated in 1987 because of unacceptable levels of bycatch. Blue shark and salmon shark CPUEs were an order of magnitude higher in the coastal Canadian experimental driftnet fishery than in the high seas squid driftnet fishery. The average size of blue sharks in coastal catches was larger than sharks caught in the high seas fishery. The seasonal pattern of CPUE in the Japanese squid driftnet fishery was consistent with the seasonal location of the fleet and the subtropical–subarctic ecological gradient that polarizes salmon and blue sharks. Errors-in-variables regression equations are provided to convert among total length, eye-fork length, and precaudal length measurements.