Blue shark catches in the Japanese large-mesh driftnet fishery in the North Pacific Ocean from 1973 to 1993
We updated annual catches of blue shark (Prionace glauca) caught by Japanese large-mesh driftnet fishery in the North Pacific Ocean during 1973 and 1993 because the annual catch data contains the same constant values and the calculation/estimation method is not described in the previous literatures. Since Japanese logbook data contains extremely high zero-catch for sharks caught by Japanese large-mesh driftnet fisheries, we estimated the annual catches of blue sharks using the catches in weight of all sharks reported by Japanese statistical yearbook (“Norin-toukei”). Then, Japanese scientific observer data was used to calculate the ratio of blue shark to all sharks because the species-specific shark’s data is not included in the statistical yearbook. The estimated catches in weight of blue shark sharply increased from 1975 to 1977, and subsequently decreased with fluctuations until 1993. Amount of annual catch in weight had a wide range between 1,236.0 and 10,580.7 MT for 1973-1993. We recommend using the estimated catches in this paper for the upcoming stock assessment of blue sharks in the North Pacific Ocean because the values are more reasonable from the view of the annual changes in the trends compared with the unaccountable constant values.