Diet Variation and Predatory Impact of Spiny Dogfish (Squalus acanthias) in North Carolina Waters

Spiny dogfish (Squalus acanthias) are small sharks that are highly abundant in North Carolina waters from November through March.  There has been much interest in the trophic ecology of spiny dogfish due to suspected predatory and competitive interactions with species important to commercial and recreational fisheries.  The stomach contents of 399 spiny dogfish were collected during trawl surveys conducted in North Carolina waters in February and March, as well as size and sex data for the sampled sharks.  Data on depth, water temperature, and relative abundance of other species were also collected at each sampling station.  Stomach contents were identified to the lowest possible taxa and prey species were assigned to broad prey groups by taxonomic classification.  Spiny dogfish diet was found to be highly piscivorous, with teleost fishes making up 94% of the diet by weight in February and 61% in March.  The amount of fish prey was related to dogfish size, with large sharks consuming mostly fishes while crustaceans and other invertebrate species became more important with decreasing size.  Abundance of smaller sharks was positively correlated with depth and temperature, and males occupied significantly deeper and warmer stations than females.  The most important fish species consumed in February was Atlantic menhaden (Brevoortia tyrannus) while sharks sampled in March consumed a variety of species.  Striped bass (Morone saxatilis) showed high spatial overlap with adult female dogfish and made up about 2.4% by weight of teleosts consumed in February, which may indicate competitive and predatory interactions between these two species.  These results suggest that the tendency of spiny dogfish to segregate by size and sex may significantly influence their trophic interactions with other species in North Carolina waters.