Hatch date and early growth of juvenile Japanese jack mackerel Trachurus japonicus caught in the Uwa Sea.

Development and growth rate variations during early life are important for understanding the mechanisms of recruitment dynamics. We examined the larval growth rate and age at the onset of metamorphosis (d ) of juvenile Japanese jack mackerel recruited to a population in the Uwa Sea, Japan. Otolith microstructure analyses revealed that the hatch date of juveniles ranged from February to April in 2011-2015, and that their d were 25.5-30.5 days and mean growth rates at the larval stage (G ) were 0.30-0.34 mm day . Among d and G , d showed significant negative correlations with juvenile abundance. Moreover, the hatch date did not coincide with the spawning period of this species in the Uwa Sea, and the hatch date and mean growth rate at the larval stage were comparable to those of Japanese jack mackerel juveniles sampled in the East China Sea (ECS). These findings suggest that most juvenile Japanese jack mackerel originated in other waters, including the ECS, and that larval stage duration influenced their recruitment abundance in the Uwa Sea.