Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 8960
Title: Ecosystem dynamics birds and marine mammals, part II:  aspects of the feeding ecology of Bering Sea avifauna
Author/Editor: Gerald A. Sanger, Patricia A. Baird
Publication Year: 1977
Publisher: National Marine Fisheries Service
Contracting Agency: Bureau of Land Management, U.S. Department of the Interior
Contract Number: PO#01-6-208-13424

The authors spent about 65 person-days preparing a report on the birds of the eastern Bering Sea under a subcontract to OCSEAP RU-77 (Ecosystem Dynamics-Birds and Mammals).  The pertinent literature was reviewed on ten species of marine birds which are important in that area either because of their large biomass, or as representatives of the diversity of the pelagic bird community.  Dramatic seasonal changes occur in the abundance of birds in the eastern Bering Sea.  Peak abundance occurs in early spring with the influx of Sooty and Short-tailed Shearwaters from their breeding grounds in the southern hemisphere, and with the staging of Alaskan breeding species prior to nesting. 

During the Alaskan birds' breeding season, the distribution of all species except the shearwaters is strongly oriented toward colonies.  Little is known about the diets of the birds, but the abundant shearwaters and murres appear to consume large quantities of euphausiids, and schooling pelagic and demersal fishes . Prey items range in size from copepods of 7 mm or less (eaten by Least Auklets) to fish of at least 25 cm (eaten by murres).  Glaucous-winged Gulls, Black-legged Kittiwakes, and Northern Fulmars probably benefit greatly from offal produced by Walleye Pollock fisheries.  The fisheries have possibly created an imbalance in the ecosystem which has benefitted planktivorous birds. 

Recommendations to further refine ecosystem data on marine birds include:

  1. More intensive studies on population sizes and the diets of the shearwaters
  2. Better estimates of colony population sizes, and the relationships between numbers of birds on the colonies and numbers at sea
  3. Many more food samples collected systematically throughout the year
  4. Included in the model of the ecosystem should be meroplankton (including ichthyoplankton), copepods, euphausiids, small pelagic fishes, epibenthic macroplankton, and fisheries offal.
Notes: Final report RU-77, Environmental Assessment of the Alaskan Continental Shelf.