Estimation of isoscapes, trophic positions, and trophic niches of demersal fishes and squids in the East China Sea inferred from stable isotope ratios

Stable isotopes facilitate the comparison of isotope niches across populations, allow for the estimation of community metrics related to dietary preferences, enable the integration of diet over various time scales, and assist in identifying functional groups as well as isotopic niche overlap among populations. Tagging programs are commonly used to study the habitats and migration patterns of fish. However, the diversity of demersal fish species is high, and archival tagging instruments are expensive. Isoscapes of stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) in demersal species were generated using 1802 measured values of demersal species in the East China Sea. We then used generalized additive models (GAMs) to assess explanatory variables, such as feeding habits, body form, and season. The high values of δ¹³C and δ¹⁵N areas were observed in the central East China Sea due to the Changjiang River plume. These isoscapes can be used to estimate habitats and migration of demersal species. High trophic niche overlap ratios (> 0.5) were observed among crustaceans, fish, benthos, gelatinous, and plankton feeders, which were separated from other groups. The species with the highest trophic position was the Longtooth grouper (TP = 4.4; Epinephelus bruneus), and the lowest was Okamejei acutispina and Psenes maculatus (TP = 3.2). Such trophic niche overlap ratios and trophic positions are useful for the construction of ecosystem-based fishery management.