Interaction between the vertical distribution of juvenile walleye pollock Theragra chalcogramma in the eastern Bering Sea, and cannibalism

Abstract

In autumn 1984 the interaction of vertical migration of age-0 walleye pollock Theragra chalcogramma m the eastern Bering Sea, and cannibalism was examined. Patterns of verhcal migration were Inferred from acoushc observations, midwater trawls, and occurrence of juveniles in the stonlachs of adults caught in bottom trawls. Generally, most age-0 pollock were distnbuted in the near-surface layer at night. Dunng the day larger individuals moved through the thermocline into the bottom layer. Vanations in rmgratory patterns were observed and are discussed in relation to the thermocline, zooplanktan abundance, growth, and size. Age-0 juveniles from 50 to 60 mm ate n~ostly large copepods. At 3 stations the growth of juveniles, as inferred from otohth increment widths for the 10 d prior to capture, increased with zooplankton abundance. Of 1503 adult pollock stomachs, 29 contained juvenile pollock, all of which were age-0 fish, 20 to 100 mm in length. Adult pollock contained an average of 3.0 juveniles per stomach. The size composihon of juveniles in adult stomachs and the diurnal pattern of adult pollock feeding on juveniles indicated that cannibalism occurred mostly in daytime and was closely coupled with verhcal distribution patterns of juveniles.

Vertical Distribution and Prey of Walleye Pollock in the Northern Japan Sea

“…*1 Cannibalism by walleye pollock occurs near Funka Bay,31) off the eastern coast of Hokkaido,32) and the eastern Bering Sea. 15,22,33) In the southwestern Okhotsk Sea, where walleye pollock have a higher growth rate than in the northern Japan Sea,2) adult pollock feed exclusively on euphausiids, while immature pollock feed mainly on amphipods.34) Walleye pollock feed mainly on zooplankton, and do not consume fishes (including juvenile pollock) in this study area (this study and Kooka et al6)). The low growth rate of walleye pollock in the northern Japan Sea might be affect ed by the vertical distribution pattern and food utilization.…”

Shifting control of recruitment of walleye pollock Theragra chalcogramma after a major climatic and ecosystem change

“…The abundance of Age 0 juveniles in August was interpolated from values in the iife table for the number of juveniles in September and the mortality between June and September for each year. Late summer appears to be the period when Age 0 juvenile pollock become vulnerable to groundfish predators (Bailey 1989).…”

Linking northern fur seal dive behavior to environmental variables in the eastern Bering Sea

“…Evidence from scat analysis suggests that juvenile pollock of year-class 0 and 1 (2-20 cm) are preferred by foraging fur seals , which are smaller than the .40 cm adults taken by the commercial fishery (Ianelli et al 2007). As adult walleye pollock are known to prey on age-0 juveniles of their own species (Bailey 1989), it is reasonable to suggest that the link between the distribution of commercially harvested adult pollock and northern fur seals may be confounded due to their sharing of a common prey resource. Alternatively, Gudmundson et al (2006) investigated diet overlap at a breeding rookery with commercially targeted year-classes of walleye pollock using prey remains in spews, and found significant overlaps with the fishery.…”