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

Abstract

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°C, and most of them were found in waters where WT0-30 was higher than 24°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.

Otolith δ18O of Pacific bluefin tuna Thunnus orientalis as an indicator of ambient water temperature

“…These 2 areas have different temperatures and salinities. The seawater in the western Pacific is influenced by the Kuroshio Current, which is characterized by high salinity and enriched water δ In contrast, breeders probably spawn in the coastal waters of the southern Sea of Japan based on larval appearance frequency (Nishikawa et al 1985, Tanaka et al 2007. As explained by Shiao et al (2010), water δ O value of the 32.5 psu surface water in the East China Sea, which connects with the Sea of Japan, is −0.16 ‰.…”

“…This difference was also observed in Pacific bluefin tuna spawning in the northwest region of the Philippine Sea, between eastern Taiwan and Ryukyu Islands located in the southern part of Japan (roughly the western North Pacific) from late April to June (Bayliff 1994, Chen et al 2006, Tanaka et al 2006, Shiao et al 2010 and in the southern Sea of Japan in late July to August (Tanaka et al 2007, Itoh 2009). These 2 areas have different temperatures and salinities.…”

The relationship between fishing characteristics of Pacific bluefin tuna (Thunnus orientalis) and ocean conditions around Jeju Island

“…According to Fig. 8, T. orientalis has two spawning grounds that are located in the northern area of Kuroshio axis in the Taiwan Sea and the East Sea (Bayliff 1994;Okiyama 1974;Chen et al 2006;Tanaka et al 2007). Therefore, the fishing ground around Jeju Island is regarded as the path for migrating northward of immature T. orientalis which was spawned in the Taiwan Sea.…”

“…Harada (1980) stated that spawning of T. orientalis occurs at the age of about 5 years when it reaches around 150 cm in FL and 60 kg in weight. Two main spawning grounds of T. orientalis had been identified to be in the southwestern North Pacific, one off east Taiwan and one in the south of the East Sea (Okiyama 1974;Chen et al 2006;Tanaka et al 2007), but currently, there is no evidence for any local stocks in both spawning regions (Shimose et al 2009). T. orientalis is a highly migratory species occurring throughout the North Pacific Ocean ranging from the East Asian coast to the western coast of North America and is also recorded as a visitor to the South Pacific (Collette 1999;IUCN 2014).…”

Rapid ontogenetic shift in juvenile Pacific bluefin tuna diet

“…PBT spawn from April to June in spawning grounds located between the Philippines and the Ryukyu Islands of Japan, and in August in the Sea of Japan (e.g. Okiyama 1974, Chen et al 2006, Tanaka et al 2007). After being transported by sea currents to Japanese coastal areas (e.g.…”