Variations in Diet, Daily Ration, and Feeding Periodicity of Pacific Hake (Merluccius productus) and Spiny Dogfish (Squalus acanthias) off the Lower West Coast of Vancouver Island

Abstract

We examined aspects of summer feeding in Pacific hake (Merluccius productus) and spiny dogfish (Squalus acanthias). Euphausiids (Thysanoessa spinifera, Euphausia pacifica) and Pacific herring (Ciupea harengus pallasi) accounted for almost all of the hake diet over all August sampling periods (1983, 1985–89) and the 1988 summer feeding period (June-October). Summer ration estimates were higher for hake feeding on the continental shelf than for fish feeding along the shelf-break. Daily ration declined over summer because the euphausiid ration dropped, even though the herring ration increased. Euphausiids, herring, and hake were the major dogfish prey items. The dogfish ration in August was 1.6 times that of hake. Both predators fed sporadically between dawn and dusk. They evacuated prey linearly over time and digested euphausiids most rapidly. Euphausiids were the most important prey. The size of herring taken varied over time in both predators. Hake took all age-classes of herring whereas dogfish tended not to feed on young-of-the-year (YOY) herring. Herring and predator size relationships were sometimes insignificant, reflecting variation in YOY herring availability. Herring became progressively more important prey as predator size increased.