Feeding Habits and Daily Ration of Walleye Pollock (Theragra chalcogramma) in the Eastern Bering Sea, with Special Reference to Cannibalism

Abstract

Stomach contents of 3098 walleye pollock (Theragra chalcogramma) collected from the eastern Bering Sea during 1981–83 were examined to (1) describe the diet as influenced by area, season, and fish size, (2) estimate daily ration, and (3) examine the magnitude of cannibalism. Small pollock fed mainly on copepods and shifted to euphausiids and fish with increased size. Stomach contents (percent body weight) were highest in summer and autumn. Laboratory-derived estimates of gastric evacuation rates and age-structured estimates of abundance were used in conjunction with the field data to estimate daily ration of pollock in the eastern Bering Sea. Mean annual daily ration was calculated to be about 0.3% body weight per day. Daily ration was lowest in spring and lower in the northwestern region of the eastern Bering Sea than in the southeastern region. Cannibalism occurred in all seasons, but consumption was highest on age 0 pollock in the southeastern area during autumn. It is estimated that about 400 billion age 0 pollock were consumed annually by larger pollock in the eastern Bering Sea.