Biology and Management of Dogfish Sharks

22. Stable Isotopic Variability Along Spiny Dogfish Spines: Implications for Retrospective Ecological Studies

Susan Hazlett, Nicole Misarti, Alexander G. Andrews, Gordon A. McFarlane, and Matthew J. Wooller


Abstract.—Spiny dogfish Squalus acanthias are an abundant and commercially important species of fish off both the Atlantic and Pacific coasts of North America. They are opportunistic feeders and have a varied diet that can include many fish species, especially small forage fish such as herring, capelin, and sand lance as well as crustaceans, worms, euphausiids, gelatinous zooplankton, and cephalopods. The purpose of our present study is to investigate the utility of the second dorsal spine in providing multiyear information on the feeding habits of dogfish using stable isotope (C and N) analysis. The outer dentine and enamel layers of a spine from three dogfish (caught off the coast of British Columbia) were analyzed to obtain their stable nitrogen and carbon isotope composition (δ15N and δ13C, respectively). Each sample had annuli from multiple years, allowing possible seasonal migrations to be averaged over samples. The δ15N ranged from a low of 11.6‰ to a high of 14.9‰ over the three spines and δ13C ranged from –11.5‰ to –18.4‰. The variable isotopic signatures along the spine indicate that the method may be used to assess ecological changes. Stable isotope measurements of dogfish spines could be a valuable means of determining long-term changes in habitat usage and feeding ecology.