Compositional analysis and trophic level study of shrimp trawl by-catch in waters around Lvhua Island, East China Sea

Abstract

Shrimp trawling is a primary fishing method in the East China Sea. Based on survey data from fishery resource monitoring vessels and on-site sampling data collected before and after the 2020 fishing moratorium in the waters around Lvhua Island, East China Sea, we employed statistical and stable isotope methods to analyze the composition and trophic levels of shrimp trawl bycatch. The results revealed diverse species in the bycatch around Lvhua Island, primarily consisting of coastal benthic organisms. The composition structure exhibited significant differences before and after the fishing moratorium, with Sebastiscus marmoratus identified as the dominant species, showing relative importance index percentages (%IRI) of 29.49% and 78.05% before and after the moratorium, respectively. Stable isotope analysis determined carbon and nitrogen isotope values for the shrimp trawl bycatch around Lvhua Island before and after the moratorium, estimating average trophic levels of 3.43 and 3.60, placing the trophic hierarchy at level 3. The distribution of carbon stable isotope ratios indicated noticeable ecological niche overlap among various biological groups in the waters around Lvhua Island.