[A-OS12] Marine ecosystems and biogeochemical cycles: theory, observation and modeling

[AOS12-14] Evaluating the influence of environmental factors on the early life history growth of chub mackerel (Scomber japonicus) using a growth and migration model

*Chenying Guo¹, Shin-ichi Ito², Yasuhiro Kamimura³, Peng Xiu¹ (1.South China Sea Institution of Oceanology, Chinese Academy of Sciences, 2.Atmosphere and Ocean Research Institute, the University of Tokyo, 3.Japan Fisheries Research and Education Agency)

Keywords:chub mackerel, Scomber japonicus, Individual-based model, Bioenergetics model, Northwest Pacific

Chub mackerel is one of the most important fisheries target species worldwide, showing large fluctuations in biomass, the mechanism of which is still unclear. This study developed a bioenergetics individual-based model for chub mackerel distributed in the Northwest Pacific and evaluated dominant environmental factors that affect their early life history. 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 by the model with satellite-derived forcing. The migration routes and growth were tightly coupled: the 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 supported the hypothesis that higher growth rate in the early stage results in higher recruitment since individuals with higher growth can migrate into a better prey environment. A negative correlation was found between R and the relative 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 and positively affecting the growth of chub mackerel at the early life stage. In addition, interannual variations of 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 demonstrated complex mechanisms of ocean currents and prey fields controlling the recruitment of small pelagic species.