NOAA Technical Memorandum
NMFS-AFSC-36
Variations in mean stomach content weights of walleye pollock, Theragra chalcogramma, in the eastern Bering Sea
Abstract
Variations in mean stomach content weights (as percentage of body weight) of walleye pollock, Theragra chalcogramma, collected in the eastern Bering Sea from 1981 to 1987 were analyzed. The results of a one-way analysis of variance (ANOVA) showed that bottom depth and prey type explained the highest proportions of the total variation in stomach content weights (5.7% and 4.6%, respectively), followed by season and year with 3.8% and 2.8% of the total variation, respectively. Time of day and predator length were not important factors. They explained only 1% and 0.04% of the total variation, respectively.
In general, the mean stomach content weights were low in the continental slope area and high in the continental shelf area. Because this phenomenon does not reflect the abundance of zooplankton, and because the percentage of empty stomachs increases as the bottom depth increases, it is suggested that undetected regurgitation played an important role in the variation of the stomach content weights.
Walleye pollock that ate both fish and invertebrates had significantly higher stomach content weights than those that ate only invertebrates. Prey type or size, therefore, is probably one of the determinants of the gastric evacuation rate.
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