Variation in groundfish predation on juvenile walleye pollock relative to hydrographic structure near the Pribilof Islands, Alaska

Abstract

Walleye pollock (Theragra chalcogramma) are an important forage fish in the eastern Bering Sea ecosystem. As part of an ongoing study of the processes affecting juvenile walleye pollock recruitment in the eastern Bering Sea, a concentrated effort has been focused on the hydrographic fronts near the Pribilof Islands, Alaska, as important nursery areas for these juveniles. Diel variation in the consumption of age-0 pollock by arrowtooth flounder (Atherethes stomias) was examined from a series of collections at a station at the tidal front located north of St Paul Island, Alaska. Age-0 pollock were the primary prey of arrowtooth flounder throughout the day, but they were least digested in the late day, indicating a diurnal feeding pattern. A similar diurnal pattern was not seen in the vertical distribution of age-0 pollock, suggesting that the feeding pattern exhibited by arrowtooth flounder was based on their diel migratory behavior. Lengths of age-0 pollock consumed by arrowtooth flounder were similar to those sampled with midwater trawls. Walleye pollock cannibalism was examined along a transect that included samples collected at the front and offshore of the front. Age-0 fish were the primary prey (by weight) at all locations. Adjacent cohort cannibalism was prevalent (age-0 pollock were 79% of the diet by weight) at the frontal region. Estimates of age-0 pollock cannibalism rates were highest at the front for age-1 pollock and offshore for the adults. Prey selectivity analysis indicated that age-0 pollock were more highly selected offshore than at the front.