Evaluating the influence of environmental factors on the early life history growth of chub mackerel (Scomber japonicus) using a growth and migration model

Chub mackerel is one of the most important fisheries target species worldwide. These fish have large fluctuations in biomass, the mechanism of which remains unclear. This study developed a bioenergetics individual-based model for chub mackerel distributed in the Northwest Pacific and evaluated the dominant environmental factors that affect their early life history. The parameters in the bioenergetics model were obtained or estimated from previous studies, and a migration model with a gradient area search algorithm was coupled. The growth rate of chub mackerel was calibrated to in situ growth data by adjusting the half-saturation constant of consumption (K). During 2002–2016, the growth and migration of chub mackerel were reproduced using the model with satellite-derived forcing. The migration routes and growth were tightly coupled: individuals located to the north of the Kuroshio axis experienced a better prey environment, showed a relatively higher growth rate, and entered a better prey field by self-selected swimming. Years with more high-growth individuals in the model corresponded to observed higher recruitment (R) and recruitment per spawner (RPS). These results support the hypothesis that a higher growth rate in the early stage results in higher recruitment, because individuals with higher growth can migrate into a better prey environment. A negative correlation was found between R and the distance of the Kuroshio axis from the Boso Peninsula, indicating that when the Kuroshio axis was located closer to the Boso Peninsula, the water temperature of the coastal area increased, resulting in an increase in coastal-dominant zooplankton species, which positively affected the growth of chub mackerel in the early life stage. In addition, interannual variations in prey zooplankton species composition and the relative position of the Kuroshio to the spawning grounds partially influenced the early growth of chub mackerel. The results demonstrate the complex mechanisms of ocean currents and prey fields controlling the recruitment of small pelagic species.