UC Santa Cruz

The yellowtail rockfish, Sebastes flavidus, is a widespread and abundant mesopredator in the California Current Large Marine Ecosystem. We utilized stomach content and stable isotope analyses to investigate the trophic ecology of this species at three sites off central California just before (August-October 2013) and during (August and October 2014) a marine heat wave. Sebastes flavidus largely consumed pelagic prey (zooplankton and micronekton). Diets were dominated by tunicates (salps and pyrosomes), pelagic crustaceans (euphausiids, hyperid amphipods, larval decapods), and fishes, with the relative contribution of these prey taxa varying spatially (sample location, longitude, depth) and temporally (year, month), based on complementary multivariate analyses. Prey-specific indices demonstrated that individual S. flavidus diet composition typically was dominated by one of these prey groups, and that prey switching occurred based on the relative availability of prey and their energetic importance. Stable isotope analysis of δ15N indicated that the S. flavidus populations sampled in 2014 had been feeding at an elevated trophic position and more variable prey spectrum relative to 2013, probably as a consequence of greater piscivory and the incorporation of temporal changes in diet composition. Because its opportunistic feeding behavior reflects the dynamism and heterogeneity of the pelagic forage preyscape, S. flavidus may be an important ecosystem indicator species. For example, the novel incorporation of pyrosomes as a large portion of the diet of S. flavidus during 2013-2014 directly related to the massive increase in pyrosome abundance in the California Current during the 2014 marine heat wave.