Influence of timing of fishing on trophic levels and diets of typical fish and invertebrate species in the Bohai Strait over a single year based on carbon and nitrogen isotope analysis

•The trophic level variations of typical fishes and invertebrates were evaluated according to δ15N values.•Changes in the diet compositions of typical fishes and invertebrates were assessed by δ13C values.•Four sampling cruises over a year were launched corresponding to the beginning and the end of the closed fishing season in the Bohai Sea.