Variability in Growth Rates of Japanese Jack Mackerel Trachurus japonicus Larvae and Juveniles in the East China Sea – Effects of Temperature and Prey Abundance

Variability in growth rates was examined in relation to the environmental conditions of the surface layer for larvae and early-stage juveniles of Japanese jack mackerel Trachurus japonicus in the East China Sea. The survey waters were assigned into five masses; Kuroshio waters, two mixed waters, and two coastal waters using the temperature–salinity relationship. Growth rates at capture were back-calculated based on otolith daily increments, and relative growth related to the environmental conditions at capture among and within water masses. Among water masses, mean relative growth of larvae and juveniles in the Kuroshio waters was faster than that in the coastal waters, and growth positively correlated with temperature but not with prey abundances. Within water masses, however, in the mixed waters where larvae and juveniles predominantly occurred, mean relative growth of larvae positively correlated with prey abundances but not with temperature. No significant correlation between growth and environmental conditions was found in the other water masses. Since variability of prey abundance in the mixed waters was larger than that in the other water masses, our results demonstrated that prey abundance in the mixed waters strongly affects growth and survival during the larval stage of T. japonicus in the East China Sea.