Update of Japanese annual catches for blue shark caught by Japanese offshore and distant water longliner in the North Pacific Ocean from 1994 to 2020
This working paper provides update of Japanese annual catches of blue shark (Prionace glauca) caught by Japanese offshore and distant-water longline fisheries in the North Pacific Ocean for 1994-2020. Since the landings of sharks is frequently underestimated due to the lower market value than any other teleost species such as tunas and billfishes, total annual catches including retained and discard/released catches were estimated using a product of standardized annual CPUEs and the total fishing efforts. The estimation methods of catches were substantially changed due to the changes in the CPUE standardization methods. Since the spatio-temporal models provide only the CPUEs scaled by the mean value, the scaled CPUEs was converted to absolute CPUEs using an average value of nominal CPUE. Then the catch number was estimated using the CPUEs and fishing effort. The calculations were separated by the shallow- and deep- sets longline fisheries. The annual catch number for shallow-set longline fishery was estimated using the season-year CPUEs of Japanese offshore and distant water shallow-set longline fishery with the fishing efforts of the shallow-set fishery, while those for deep-set longline fishery was estimated using the annual CPUEs of Japanese research and training vessels with the fishing efforts of the deep-set fishery. Further, the annual catch number for each fishery was converted to annual catch weight using an average weight of blue sharks caught by the fishery. The estimated annual catch weight showed a continuous decreasing trend in a gradual decline of the total fishing effort. The total catches in recent five years were varied between 6,674 and 9,240 MT.