To better understand habitats of larval Pacific bluefin tuna (PBT; Thunnus orientalis) in the nursery grounds, the vertical distribution of larval PBT was collected using a 1-m² Tucker trawl and a 3.14-m² ring net at depths of 0, 10, 20, and 30 m during the spawning seasons of 2016 and 2017. Most of the larvae in the Japan Sea (756 of 938 individuals) were collected from the surface layer using a ring net, while similar numbers were collected from 0 to 20 m depth in the Nansei area. The temperature at ≥20 m depths in the Japan Sea was cooler than the optima temperature, and the thermocline was steep at 10 m depth, and the cold subsurface water was suggested to make the PBT larvae aggregate near the surface. A weak ontogenetic and diel migration was observed; the body size at 10 m depth during the day and 0 m at night were significantly larger than those at 0 m during the day in the Japan Sea. These results suggested that some small larvae sink to 10 m and/or large larvae move to the surface at night. Our results showed that the larval PBT habitat is strongly controlled by water temperature, and that global warming would have a positive effect on PBT larvae in the Japan Sea, which was evidenced by the higher density of PBT larvae after 2010 compared to before 1990.

为了更好地了解育苗场中的太平洋蓝鳍金枪鱼幼体（PBT；Thunnus Orientalis）的栖息地，使用1-m ²塔克拖网和3.14-m ²收集幼虫PBT的垂直分布。在2016年和2017年的产卵季节中，在0、10、20和30 m深度的环网。日本海中的大多数幼体（938个个体中的756个）是使用环网从表层收集的，而相似的收集了南塞地区0至20 m深度的数字。日本海中≥20 m深度处的温度比最佳温度要低，而温跃层在10 m处的温度则较陡，建议用低温地下水使PBT幼虫聚集在水面附近。观察到较弱的个体发育和diel迁移。在日本海中，白天10 m深处和晚上0 m深处的体形明显大于白天0 m处的体形。这些结果表明，一些小的幼虫沉到10 m处，和/或大的幼虫在晚上移到地表。