Feeding habits of Trachurus japonicus in the East China Sea

A total of 453 Trachurus japonicus specimens with a fork length (FL) of 46-250 mm were sampled in the seasonal light seine net surveys in the East China Sea in May, August, and November, 2008 and in February, 2009. The stomach contents of the specimens were analyzed, and the seasonal and ontogenetic variations in the feeding habits of the T. japonicus were examined by the Kruskal-Wallis test, chi-squared test, and cluster analysis. There were 124 prey species (including not identified) ingested by the T. japonicus, among which, planktonic crustaceans and small-scale marine fish made up the dominant prey groups. According to the percentage index of relative importance (IRI%), Bregmaceros macclellandi was the most dominant prey, accounting for 39.2%, followed by Macrura mysis larva (18.4%), brachyura zoea larva (7.6%), and Euphausia pacifica (6.6%). The feeding intensity of the T. japonicus varied significantly with its FL and season, being the highest for the T. japonicus with a FL of 140-159 mm, higher for the T. japonicus juveniles with a FL of 45-99 mm, while lower for the T. japonicus of other size classes, and the highest in spring and the lowest in winter. Cluster analysis revealed there was an abrupt change in the diet composition for the T. japonicus with a FL of about 100 mm FL. The average trophic level of the T. japonicus in four seasons was 3.51, indicating that the T. japonicus in the East China Sea was of low-level carnivores feeding on plankton and nekton.