Interannual variations in rates of larval growth and development of jack mackerel (Trachurus japonicus) in the East China Sea: implications for juvenile survival

Abstract

Interannual variability in somatic growth rate during the larval stage and age at the onset of metamorphosis as a proxy for the development rate of jack mackerel (Trachurus japonicus) were examined in relation to habitat conditions during 2005 to 2010 in the shelf break region of the East China Sea (ECS). Habitat conditions were assessed in the February to March and the April surveys, which corresponded with the early hatching period in the spawning grounds and the main sampling period in the larval nursery grounds, respectively. Relationships between the growth and development rates and juvenile abundances in the near-bottom layer in May to June during the six consecutive survey years were explored. Annual mean growth rates during the late larval stage of pelagic juveniles were faster in years with higher concentrations of Paracalanidae and Oncaeidae copepodites as the main food item for larval T. japonicus in April following the surge of chlorophyll a concentrations. Juvenile abundance in the near-bottom layer was better related to the annual mean growth rate during the late larval stage than to the growth rate during the early larval stage and the development rate. These results suggest that preferred prey conditions due to higher phytoplankton productivity enhance the growth rate during the later larval stage and hence survival during the habitat transition from the surface to the near-bottom layer for T. japonicus in the ECS.