A comparison of the food habits of juvenile Pacific cod and walleye pollock in the southeast Bering Sea

Abstract

The food habits of juvenile Pacific cod, Gadus macrocephalus, and walleye pollock, Theragra chalcogramma, collected in July and August in 1981 through 1983 in the eastern Bering Sea, were compared in relation to some morphological characteristics. The fishes' gill rakers were counted, the distances between gill rakers were measured, and the stomach tissue weight was measured. The stomach contents were analysed by occurrence, number and volume. It was found that the fishes' gill structures were related to size-selective predation in both fishes. Pollock utilized small zooplankton and cod large zooplankton. Food competition was expected when fishes are smaller than 40 mm TL as indicated by high values in proportional similarity. However, food competition decreases as the fishes grow and develop distinct size-selective predation habits. Prey composition in the stomachs reflected the regional differences of local oceanographic environments.