Food habits of Pacific cod and walleye pollock in the northern Gulf of Alaska

Abstract

Seasonal variations in the diets of Pacific cod Gadus macrocephalus and walleye pol- lock Theragra chalcogramma were examined from fish collected during 5 sampling periods from August 1998 to June 1999 in the Kodiak Island area in the Gulf of Alaska. Both species were shown to be generalist predators, eating a wide variety of fish and invertebrates. Pollock, which are limited to pelagic prey, can be considered more specialized than cod. Cod consumed 78 prey items, and pollock consumed 45 prey items, with 28 items shared by both species. Individual pol- lock, however, typically concentrated on a single prey item, while individual cod stomachs con- tained a wider variety of prey. The principal prey of Pacific cod was Tanner crab Chionoecetes bairdi, comprising >28% of the cod diet by weight. The most common prey item for walleye pol- lock was the euphausiid Thysanoessa. Over the 5 sampling periods, the prey evenness and niche width occupied by the 2 species were similar, but seasonal differences were evident.