FY 1997

Feeding habits and daily ration of juvenile walleye pollock, Theragra chalcogramma, in the western Gulf of Alaska

Merati, N., and R.D. Brodeur

In Ecology of Juvenile Walleye Pollock, Theragra chalcogramma, NOAA Tech. Report NMFS 126, Papers from the workshop "The Importance of Prerecruit Walleye Pollock to the Bering Sea and North Pacific Ecosystems", Seattle, WA, 28–30 October 1993, 65–79 (1996)

The stomach contents of age-0 walleye pollock, Theragra chalcogramma, collected in the western Gulf of Alaska during September of 1990 were examined to determine diel feeding patterns and variations in feeding habits with respect to time of day, fish size, and geographic area. Most (90%) of the 549 fish examined (length range 49-113 mm standard length) had food in their stomachs, with an overall median fullness of 1.6% body weight (BW). Juvenile pollock fed mainly at night, with stomach fullness and prey condition declining throughout the daylight hours. Daily ration was estimated to range from 7.4% to 8.5% BW/d based on the diel trajectory of stomach content weight. The dominant prey by number were larvaceans and copepods (copepodites and adults), whereas euphausiids were the dominant prey by weight, constituting >80% of the total biomass consumed. Despite some apparent trends in the diet with size of predator (i.e., copepods gradually decreased and larvaceans and euphausiids increased in importance with increasing size of pollock), there did not appear to be an abrupt ontogenetic shift in the diet of these juveniles. However, there were major changes in the diet depending on geographic area. Stomach samples collected near Kodiak Island contained mainly euphausiids, whereas those collected in the western part of the study area contained large numbers of larvaceans. There was no discernable pattern in the type of prey consumed at different times of day.