Sampling locations (solid circles, for details see Table 1) and main circulation features associated with major water masses around the Japanese archipelago.

<p>Broken red lines indicate the location of the three major barriers to gene flow inferred based on the microsatellite data. Broken grey lines delimit the eight coastal regions dividing the country: 1. Hokkaido, 2. Northern Japan Sea, 3. Western Japan Sea, 4. East China Sea, 5. Seto Inland Sea, 6. Southern Pacific, 7. Central Pacific, 8. Northern Pacific.