Distribution, growth and hatch date of juvenile Pacific bluefin tuna Thunnus orientalis in the coastal area of the Sea of Japan

Mid-water trawl surveys were conducted from late August to late September in 1999 and 2004 in order to investigate the distribution pattern, hatch date, and growth of juvenile Pacific bluefin tuna Thunnus orientalis in the Sea of Japan. Juveniles were collected at the stations where ambient water temperature (mean water temperature from surface to 30 m deep, WT0-30) was 23.4-25.9 degrees C, and most of them were found in waters where WT0-30 was higher than 24 degrees C. Sampled juveniles ranged 108-280 mm fork length. Based on otolith analysis, they were estimated to grow to approximately 180 and 250 mm at 60 and 90 days old, respectively, and showed similar growth to that of Atlantic bluefin tuna in the Mediterranean Sea. The back-calculated hatch date of the samples was mostly in July and most juveniles spawned in the Sea of Japan.