This study aimed to determine how spatial and seasonal variations influence the trophic structure of fish assemblages in the eastern Yellow Sea during 2023. Carbon and nitrogen stable isotope analyses revealed significant but spatially variable differences in δ¹³C and δ¹⁵N values among seasons and sites, without consistent overarching trends. These results suggest that phytoplankton-derived organic matter predominantly supports the regional food web, with isotopic niche shifts reflecting local differences in prey availability and hydrographic conditions. The findings contribute to the development of adaptive, ecosystem-based fishery management strategies amid increasing anthropogenic and climatic pressures.