Feeding together: a global diet analysis of twenty-three species of chondrichthyes on a feeding ground area

Abstract

A global analysis of the diet of chondrichthyes (23 species) was conducted during one bottom-trawl research cruise in the region where the highest catches of skates occurred off southwestern Atlantic. The diet was quantified by calculating the percentage frequency of occurrence of each prey. The influence of variables total length, sex, maturity stage, predator species, morphtype (sharks, skates, batoids), and depth on the diet was evaluated by fitting generalized linear models. The diet composition of chondrichthyes consisted mainly of crustaceans, polychaetes, and fish. The study region constituted a feeding ground for the majority of chondrichthyans species analyzed. The diet of chondrichthyes exhibited inter-specific differences sorted into three major trophic guilds and global ontogenetic shift. The consumption of crustaceans and polychaetes decreases with the total length of the chondrichthyes, whereas the consumption of fish increases as the predator grew in size. In addition, prey size of fish and crabs increased with increasing body size of predator, but large chondrichthyes also continued to feed on relatively small crabs. Trophic partitioning and ontogenetic diet shifts may act synergistically, favoring the coexistence of at least 23 species of chondrichthyes at all stages of their life histories, limiting the direct competition for food.