Flathead flounder (Hippoglossoides dubius) are found in the Sea of Japan and Northern part of the Pacific. It is determined that the Japan Sea stock is regarded as an individual subpopulation according to the stock condition of the fishing area by Japan Government. Therefore the Japan Sea subpopulation of flounder is assessed individually and managed separately from the pacific stock. It was determined that a western group and northern group existed in the Japan Sea subpopulation. These two groups divide near the Noto from the results of tag and release experiments (Bates et al. 2008).