Ontogenetic shifts in diet and trophic position of walleye pollock, Theragra chalcogramma, in the western East Sea (Japan Sea) revealed by stable isotope and stomach content analyses

We determined the dietary composition and trophic position (TP) of walleye pollock in the western East Sea (Japan Sea), based on the δ13C and δ15N values of this species, sympatric dominant fish and invertebrates, and their putative food sources in winter. A broad range of the consumer δ13C′ (lipid-corrected) values reflected clear distinctions between benthic and pelagic feeders, differentiating benthic vs. pelagic trophic pathways. The intermediate δ13C′ and δ15N values of pollock fell between those of benthic and pelagic feeders, indicating their trophic links through both pathways. Increases of their isotopic values with increasing body length suggest an ontogenetic change in dominant diets from pelagic to benthic prey as confirmed by stomach content analysis. Their ontogenetic pattern in resource utilization might be associated with deeper migration range with size, increasing TP during ontogeny.