24. Interactions Between Two Sharks: Spiny Dogfish and Sixgill Shark in the Puget Sound/Georgia Basin Ecosystem, Northeast Pacific Ocean
Vincent F. Gallucci and Brian J. Langseth
Abstract.—Predatory interactions of bluntnose sixgill shark Hexanchus griseus and spiny dogfish Squalus acanthias were evaluated as part of a longline tagging study for sixgill sharks in a northeastern Pacific Ocean estuary, the Puget Sound/Georgia Basin (PSGB). This study shows that sixgill sharks will prey upon dogfish. Dogfish were caught in one of three ways: as whole individuals, with parts of their bodies consumed, or as whole individuals with sixgill sharks retained on the hook as well. Bait experiments showed that for one of two sampling periods, hooks baited with dogfish were preferred by sixgill sharks over hooks baited with herring. Analysis of sequential hook data revealed that sixgill sharks were caught on the longline at areas where dogfish were caught in low to intermediate densities, suggesting little preference for the movement of a hooked dogfish. Given that the dogfish population in the PSGB supports a commercial fishery, the importance of the dogfish as sixgill-shark prey may need to be considered in future fishery stock assessments and allowable catch limits may need to be lowered to leave a sufficient source of nutrients for the sixgill-shark population.