A spatial analysis of trophic composition: a case study of hairtail (Trichiurus japonicus) in the East China Sea

Abstract The spatial distribution of fish on feeding grounds is an important factor in determining their prey composition. Of the factors that may influence the spatial distribution on the feeding ground and sub-sequent diet composition is the fish maturation stage. Using hairtail (Trichiurus japonicus) as an example, we evaluated the impacts of gonad development stage on diet composition. Hairtail supports one of the most valuable and largest fisheries in the East China Sea. As one of the top predators, it plays an important role in the ecosystem. We analyzed hairtail stomach samples collected on their feeding grounds from a fisheries-independent survey program in September 2005. Our analyses suggest that females in their third maturity stage tended to feed more intensively. Fish were the most important preys for hairtail, accounting for 72.6% of the total stomach contents in weight. The four most important fish species were juvenile hairtail (25.2%), Japanese scad (11.4%), Japanese jack mackerel (7.7%), and small yellow croaker (5.9%), suggesting strong cannibalism. A cluster analysis suggests that hairtail could be divided into three groups in their spatial distribution based on their diets: one group with similar percentages of fish and crustacean preys mainly distributed in the south of East China Sea far from the coast; one group mainly consuming fish and distributed over the north of East China Sea near the coast; and the third group consuming mainly crustacean species mainly distributed in the open sea. We hypothesize that gonadal development stage of hairtail may deter-mine their movement from spawning ground to feeding ground, and subsequently spatial distribution on the feeding ground, which in turn results in different feeding intensities and prey compositions