Estimating Chub Mackerel Migration Using Light Element Isotope Ratios in the Eye Lens

Abstract

Fish otoliths and eye lenses retain the isotopic and trace elemental composition of the food consumed and the surrounding seawater at the time of their formation. The method called iso-logging that reconstructs the migration history of organisms between regions with different isotopic compositions by utilizing the time-series isotopic information preserved in such accumulative tissues has recently attracted attention. In this study, we conducted the estimation of nitrogen stable isotope ratios and the measurement of radiocarbon isotope ratios from lens samples of adult chub mackerel (Scomber japonicus) reported by Harada et al. (2022). For the spatial distribution of marine nitrogen isotope ratios, we used the monthly isoscape data by Yoshikawa et al. (2024) to construct a spatiotemporally continuous nitrogen stable isotope dataset. We developed a state-space model that integrates these isotopic data, and estimated the migratory pathways of chub mackerel. Radiocarbon measurements showed distinct changes during the later growth stages, when variations in nitrogen isotope ratios become smaller, suggesting that multi-elemental constraints may contribute to improving the accuracy of migration path estimation.