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Resource Ecology & Ecosystem Modeling Program

Fish Stomach Collection and Lab Analysis

During the second quarter of 2011, Resource Ecology and Ecosystem Modeling (REEM) Program staff began focusing their efforts on analyzing stomach contents from the Gulf of Alaska. The contents of 2,706 stomach samples from 26 species were analyzed from the Gulf of Alaska, and 925 stomach samples from 3 species were analyzed from the Bering Sea. Detailed analysis, with high taxonomic resolution of prey types and enumeration of all prey items, was performed on walleye pollock samples collected during a 2010 hydroacoustic survey for a Bering Sea Integrated Ecosystem Research Program (BSIERP) project. This quarter, 825 euphausiid prey from these stomach samples have been measured and will be used in a future comparison with net-caught euphausiids. Tissue samples of muscle and liver from arrowtooth flounder, Pacific cod, and walleye pollock have been dried, ground, and tinned (160, 276, and 137, respectively) in preparation for stable isotope analysis. Fishery observers returned stomach samples from 133 arrowtooth flounder, 97 walleye pollock, and 15 Pacific cod from Alaskan fishing grounds. In total, 8,272 records were added to the REEM food habits database.

Stomachs are being collected this spring and summer during the AFSC’s hydroacoustic survey of the Gulf of Alaska, the bottom trawl survey of the Gulf of Alaska, and the groundfish and crab survey of the eastern Bering Sea. Shipboard analysis of stomach contents is also being conducted on board one of the Gulf of Alaska bottom trawl survey vessels.

By Troy Buckley, Geoff Lang, Mei-Sun Yang, and Richard Hibpshman

Summer Food Habits of Arctic Cod in the Eastern Bering Sea

The Arctic cod (Boreogadus saida) is an ecologically important inhabitant in Arctic waters that extends its distribution southward into the eastern Bering Sea during colder years. The Arctic cod, known to be a predator of a variety of zooplankton and a prominent prey for many birds, marine mammals, and other fishes, is a nodal species in the Arctic marine foodweb. Arctic cod are caught during the AFSC groundfish and crab surveys in the eastern Bering Sea, especially during colder summers. Stomach samples have been collected from them during previous surveys on an ad hoc basis over the years but were targeted during the 2010 surveys, yielding 320 samples.

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Figure 1. Summer diet composition of 6- to 26-cm FL Arctic cod in the eastern Bering Sea.

Most of the Arctic cod stomach samples analyzed to date were sampled prior to 2010. These 253 Arctic cod ranged in length from 6 to 26 cm fork length (FL), with the large majority of the stomach samples obtained from fish between 10 and 18 cm FL. The diet of these Arctic cod consisted mostly of small crustaceans in all the size categories examined, but some differences in diet with predator length were seen (Fig. 1). Chaetognaths tended to decrease in importance with increasing size of Arctic cod. Fishes (Teleostei) and slightly larger crustaceans (Decapoda; shrimp and crabs) were consumed primarily by Arctic cod over 15 cm. A consistent, more general trend with increasing size was the gradual decrease in pelagic prey (chaetognaths, copepods, euphausiids, and hyperiid amphipods) and the gradual increase in more benthically oriented prey (gammarid amphipods, mysids, cumaceans, and decapod crustaceans). When analyzed, the stomach samples collected in 2010 may provide some geographically interesting results, as the majority of them were collected in the northern Bering Sea between Saint Matthew Island and the Bering Strait.

By Troy Buckley, Caroline Robinson, and Kimberly Sawyer.

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