Variation in the trophic position of spiny dogfish (Squalus acanthias) in the Northeastern Pacific Ocean: an approach using carbon and nitrogen stable isotopes

Abstract

"Spiny dogfish (Squalus acanthias) are among the most abundant shark species in the Gulf of Alaska (GOA). An increase in relative biomass of spiny dogfish in 2003 and 2007 inspired interest in this species as a commercial resource. However, very little was known about the ecology of this species in the GOA. This study investigated the trophic role of spiny dogfish in the GOA, British Columbia (BC), and Washington using stable isotope analysis of carbon and nitrogen. Specifically, we examined the trophic position (TP) of spiny dogfish in relation to length, sex, and geographic region. Weathervane scallops (Patinopecten caurinus) were used as a stable isotopic baseline organism. Spiny dogfish between 52 to 113 cm length had [delta]¹⁵N values that ranged geographically from 10.8°/₀₀ to 15.6°/₀₀; [delta]¹⁵N was linearly related to length. In contrast, lipid-normalized [delta]¹³C, values ranged from -21.28°/₀₀ to -16.88°/₀₀ and were not linearly related to length. In the GOA, TP of spiny dogfish ranged from 3.3 to over 4.1, with Kodiak having the highest TPs for spiny dogfish of a given length. Our results indicated that size-based ontogenetic changes in TP of spiny dogfish are important and should be incorporated into mass-balance, food-web models such as Ecopath"--Leaf iii.