Results of Japanese fishery independent surveys for Pacific saury conducted in 2016 and 2017, and verification in biomass estimating method

To estimate the biomass of Pacific saury in the North Pacific, fishery independent surveys by Japanese scientific research vessels were conducted in 2016 and 2017 as with the previous years. The biomass calculation method was modified to reduce uncertainty in the estimated biomass. The biomass of Pacific saury sharply decreased, especially in 2017. The survey results in 2016 and 2017 suggest that the current stock status of Pacific saury decreased abruptly despite being concluded to be at a healthy level in the NPFC’s stock assessment in 2017. The biomass estimates by modified method tend to be slightly more than those by previous one, but there were no clear changes in their trend. The surveyed areas widely covered the inferred distribution range of Pacific saury. This result suggests that the Pacific saury biomass estimates based on the Japanese fishery independent surveys are indispensable data to the stock assessment.