RESOURCE ECOLOGY & FISHERIES MANAGEMENT (REFM) DIVISION
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RESOURCE ECOLOGY & ECOSYSTEMS MODELING PROGRAM

Laboratory analysis was performed on 4,483 groundfish stomachs from the eastern Bering Sea and 983 from the Gulf of Alaska. A total of 1,484 stomachs were collected from the eastern Bering Sea. Stomach samples taken by 23 observers in the eastern Bering Sea were returned during this period.
 

Groundfish Food Habits and Predation on Commercially Important EBS Prey Species, 1993-96

An AFSC Processed Report summarizing the diet composition and size, distribution, and amounts of important prey consumed by eastern Bering Sea groundfish from 1993 through 1996 is nearing completion. Estimates of predation by major groundfish species -- walleye pollock (Theragra chalcogramma), Pacific cod (Gadus macrocephalus), yellowfin sole (Limanda aspera), flathead sole (Hippoglossoides elassodon), rock sole (Lepidopsetta bilineatus), Alaska plaice (Pleuronectes quadrituberculatus), Greenland turbot (Reinhardtius hippoglossoides), arrowtooth flounder (Atheresthes stomias), Pacific halibut (Hippoglossus stenolepis), and skates (Rajidae) -- on commercially important prey during the main feeding period of May through September are provided in this report. Diet information on butterfly sculpin (Hemilepidotus papilio) and marbled (Lycodes raridens), wattled (L. palaeris), and shortfin (L. brevipes) eelpouts is also presented.

Figure 1.  Estimated number at-age of snow crab, Tanner crab, and walleye pollock consumed by groundfish during months 5 to 9 from 1984 to 1996 in the Eastern Bering Sea. (There was no cannibalism estimate for walleye pollock in 1984.)

Estimated number-at-age of snow crab (Chionoecetes opilio), Tanner crab (C. bairdi), and walleye pollock consumed by groundfish predators are presented in Figure 1 above. Pacific cod was the main predator, in terms of biomass, on Tanner and snow crab in the eastern Bering Sea. Walleye pollock cannibalism was the most important source of groundfish predation on age-0 walleye pollock. Total numbers of age-0 snow crab consumed were small for 1993-96 compared to 1990-92. However, age-1 consumption was large relative to previous years and may indicate increased recruitment from the 1993-96 year classes. Consumption of Tanner crab of all age groups in 1993-96 was low relative to previous years, a potential indication of low recruitment. Age-0 pollock consumption by groundfish was relatively high in 1994 and 1996. However, we know from survey and fishery data that the 1996 year class of walleye pollock was above-average, while the 1994 year class was below average. Investigations are continuing to better understand the time and space distribution of cannibalism and the eventual effects of cannibalism on recruitment into the fishery.

Smelts (Family Osmeridae) were consumed by several groundfish species in 1993-96 including arrowtooth flounder, flathead sole, Pacific cod, Pacific halibut, skates and walleye pollock. Consumption of smelts by these predators was much higher in 1993 than in any other year sampled from 1984 to 1996.

Estimated amounts of fish processing offal consumed by predators during the 4 years was relatively stable across years and was approximately half the amounts seen in the 1990-92 period.

Butterfly sculpins exhibited a diverse, primarily benthic diet by weight composed of amphipods (10%), polychaete worms (15%), shrimp (12%), echiurid worms (7%), walleye pollock (7%), and larvaceans (24%). Little dietary variation was seen with predator size for butterfly sculpins. Wattled, marbled, and shortfin eelpouts also consumed benthic organisms such as polychaete worms (20%-30%), amphipods (10%-40%), brittle stars (25%) and miscellaneous fish(3%-15%) including sculpins, pricklebacks, Pacific herring (Clupea pallasi), snailfish, capelin (Mallotus villosus) and walleye pollock. Polychaete worms were more important by weight to smaller eelpouts while fish prey became more important with increasing eelpout size.

By Geoff Lang.

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AFSC Quarterly
Research Reports
Oct.-Dec. 2002