Pacific saury biomass estimated using fishery independent surveys by Japan with special consideration to uncertainties among stratification designs

The present paper discusses different uncertainties associated with Pacific saury biomass estimation using area swept method, calculated based on five stratification designs in terms of survey design and calculation method. This attempt found little difference in Pacific saury biomass among the stratification designs. Therefore, we consider that combination of survey design and calculation method has little effect on estimated biomass. However, due to the limited survey area in 2011 (the easternmost longitude of the survey area were 177 °W in 2011, while 165 °W in other years), the survey data in 2011 was not comparable with those in other years. In conclusion, we recommend the stratification by “latitudinal survey line” as the most appropriate stratification design for biomass estimation, considering the migration model(s) in the future stock assessment which can present spatiotemporal dynamics of Pacific saury.