Chub mackerel (Scomber japonicus) is a pelagic species that is widely distributed in coastal waters of the Pacific in both northern and southern hemispheres (Froese and Pauly 2019)(IUCN 2009). In the NW Pacific this species ranges throughout Japan’s EEZ to the north and extends into the South China Sea to the south.  Some genetic studies suggest variation between fish in various parts of this region (Zeng et al. 2012),(Zhu et al. 2016), (Cheng et al. 2015) but the most recent and comprehensive study found a high degree of genetic homogeneity (Cheng et al. 2018). Pacific chub mackerel is a transboundary and straddling species and has been identified as a priority by the North Pacific Fisheries Commission (NPFC 2019)(NPFC 2019). Japan conducts separate annual assessments for the Pacific coast and Tsushima Current fisheries.