Revision of fleet definition of size data of blue shark (Prionace glauca) collected by Japanese commercial longline fishery and longline research program in the North Pacific.
In the Shark Working Group in 2021, the size data of blue shark (Prionace glauca) caught by Japanese fishery and research cruise was summarized, based on the several data sources. In this summarization, size data from several sources was aggregated based on the gear configuration (e.g., night and shallow-setting or daytime and deep-setting). However, this kind of aggregation could lead to poor fitting of Stock Synthesis (SS) to the observed size data, due to the gap of operation area among sources. In this context, operation pattern including area,time period, target were re-examined for size data from Kinkai-shallow fleet (Fleet 4) and the fleet definition for the size data from Kinkai-deep (Fleet 5) and Enyo-deep (Fleet 7) was also checked. Fleet 4 size data consists of three sources (1. shallow-set research, 2. observer data on Kinkai-shallow commercial vessel, and 3. port sampling data for the catch of commercial Kinkai-shallow vessel). The operation area of shallow-set research data (1999-2021) partly overlaped with that of commercial vessel and thus usage of this data only as representative of Kinkai-shallow fleet would bias the result. Research data between 1978 and 1982 also overlapped with commercial fishing ground after 1994, but the effort was concentrated in the northern area with targeting salmon shark and blue shark, and then shifted to the eastern area outside of Kinkai-shallow fishing ground. Size data collected from observer data was overlapped with the port sampling data. Thus, only port-sampling data for Kinkai-shallow was suggested to be representative of Fleet 4.