Factors controlling spatiotemporal variations in stable nitrogen isotopes of Trachurus japonicus larvae and juveniles in the East China Sea

To clarify the factors that affect spatiotemporal isotopic variations in fishes, we examined stable carbon and nitrogen isotope ratios (δ13C and δ15N) of Japanese jack mackerel Trachurus japonicus larvae and juveniles sampled in the shelf break region of the East China Sea (ECS) in April during six consecutive surveys (2005–2010). The δ13C values in fish tissues were similar between northern and southern ECS, while δ15N values were higher in the southern ECS, probably because of lower nitrogen fixation and the presence of fish with larger body size occupying a higher trophic level. Interannual variations in δ15N of T. japonicus juveniles might be mainly contributed by the variation in the abundance of the main diet such as Oncaeidae copepodites and Corycaeus. The isotopic overlaps between epipelagic T. japonicus larvae and other dominant mesopelagic fish larvae were negligible, suggesting lesser competition for food resources. Knowledge regarding spatiotemporal variation in stable isotope ratios of T. japonicus can be applied to understand the feeding habits and migrations of fishes in the ECS.