Ontogenetic changes in the diet of the sevengill shark (Notorynchus cepedianus)

Abstract

The sevengill shark, Notorynchus cepedianus, is a versatile predator capable of feeding on a wide variety of prey species. Stomach content analyses were performed on specimens from California, USA, and southern Africa to investigate whether dietary differences occur in relation to sex and size. Of the 531 specimens examined, 365 (68.7%) contained prey items. The dietary trend with growth and maturity shifted from teleosts to chondrichthyans, with marine mammals becoming increasingly important in the larger size classes of N. cepedianus . Small N. cepedianus (<120 cm total length, TL) fed primarily on teleosts, whereas larger sharks primarily consumed chondrichthyans. Marine mammals made up about one-third of the diet of N. cepedianus >220 cm TL, while teleosts declined to 6% and 13% for male and female sharks, respectively. A decrease was observed in the dietary overlap of each successively larger size class. Ontogenetic changes in the diet of N. cepedianus may provide insight into understanding how adults enhance the survivorship of their young, who are often less experienced at foraging for prey and are more vulnerable to predation.