Length frequency of shortfin mako (Isurus oxyrinchus) reported in the Japanese observer program between 2011 and 2019

This document paper summarizes the length frequency data of shortfin mako collected by the Japanese observer program between 2011 and 2019. Majority of size data was collected in the area north of 30°N and west of 175° E, which is part of main ground of shallow-set longline fishery targeting swordfish and blue shark. The annual median and quartile percentiles of catch at size of shortfin mako in PCL indicated that remarkable temporal change of body size was not clearly observed and relatively stable in the main fishing ground of offshore shallow-set longline fishery where juvenile dominates. Although coverage of observer data is not high, combined with the abundance index estimated based on shallow-set logbook data and current result, it is suggested that population decrease is unlikely to occur after the last year (i.e., 2016) of stock assessment conducted in 2018.