Estimation of annual catch for blue shark caught by Japanese high seas squid driftnet fishery in the North Pacific Ocean from 1981 to 1992
This working paper provided annual catches of blue shark (Prionace glauca) caught by Japanese high seas squid driftnet fishery in the North Pacific Ocean for 1981-1992. Since the logbook data from 1981 to 1992 have no speciesspecific information about sharks, the annual catches of blue shark was predicted using statistical model (a generalized linear model and a generalized additive model) with scientific observer data in 1990 and 1991 as well as the information about the logbook data from 1981 to 1992. The coefficients of explanatory variables estimated from four models (different model structures from simple to complex) with scientific observer data, and then the relevant information about factors of logbook data were used to predict the catches. The predicted catches in number of blue sharks by different models were aggregated to calculate the annual catches. The annual catches had increased since the early 1980s and peaked in 1988, and subsequently decreased sharply. Annual catches in weight converted from the catch in number using an average weight of individuals were widely ranged from 645 to 20,268 MT. We recommend that the estimated catches will be used for the upcoming stock assessment of blue sharks in the North Pacific Ocean because the estimated catches are more reasonable from the view of the annual changes in the trends compared to the unaccountable constant catches used in the previous stock assessment.