Comparative analysis of the early growth history of Pacific bluefin tuna Thunnus orientalis from different spawning grounds

This study compared the growth history of young-of-the-year (YOY) Pacific bluefin tuna (PBF) Thunnus orientalis from 3 cohorts (those presumably born in the Nansei Islands area and collected in the Pacific coast of Japan, those presumably born in the Nansei Islands areas and collected in the Sea of Japan, and those presumably born and collected in the Sea of Japan) in 5 year-classes (2011–2015). Growth rates during the larval stage in the Sea of Japan were highly variable compared to those in the Nansei Islands areas, and were not necessarily higher in the former, as expected from the inherent higher primary and secondary productivity of the Sea of Japan. The uncoupling of larval growth rates and food abundance in the Sea of Japan appears to be related to thermal instability and the proximity of winter in relation to the spawning season in this area. Unlike in the larval stage, growth rates during the juvenile and YOY stages were higher in the Sea of Japan compared to those in the Pacific regardless of the natal origin of the fish. This finding is consistent with the higher productivity in this area and also suggests that either the growth rates of older fish are less sensitive to decreasing temperatures or that older fish have lower thermal optima for growth than larvae.