Spatial and temporal variability in feeding and condition of age-0 walleye pollock (Theragra chalcogramma) in frontal regions of the Bering Sea

Abstract

Dietary composition, feeding intensity, and condition index of age-0 walleye pollock (Theragra chalcogramma) were examined for variations related to time of day, location, size of predator, and year. Stomach contents of pollock collected at a hydrographic front near the Pribilof Islands during September 1994 through 1996 were compared with those collected on either side of the front. Diets were dominated in all regions by small zooplankton, mainly copepods, pteropods, euphausiids, and chaetognaths, but fish and some epibenthic crustaceans were also consumed. Copepods and pteropods dominated the diet in all years and areas by number, but the diet was more mixed by weight with chaetognaths, euphausiids, and fish (small pollock) also being important. No significant diel differences in the gravimetric composition of major prey taxa were noted. Stomach fullness was highly variable by year and habitat and no significant differences were observed. Stomach fullness peaked at around sunset for fish <50 mm and at night for the larger fish, implying that feeding chronology changed with ontogeny. Pollock condition factor (Fulton's K) varied from 0.45 to 1.20 (mean=0.77; s.d.=0.09). Year was not found to be an important factor relating to condition, although location with respect to the front was important with offshore fish having a significantly higher condition than those fish found inshore of the front. (C) 2000 International Council for the Exploration of the Sea.