Estimates of Food Consumption by Marine Mammals in the Eastern Bering Sea

One important aspect of the management of commercial fisheries in an ecosystem context involves understanding the diet and consumption rates of fish species by their natural predators. Such knowledge allows for comparison of commercial fish catches with consumption through predation by species groups such as marine mammals. For the Bering Sea, the limited data available only allows a preliminary assessment of food consumption by marine mammals. Estimates of food consumption for this study were based on marine mammal population and diet data reported in the literature. Where direct consumption data were not available, consumption was estimated from population data and energy requirements. Food consumption by marine mammals (except walrus) in the eastern Bering Sea and Aleutian Islands region was estimated at 3.21 x 10 metric tons (t) per year. Fish comprised 42% of food consumed, an estimated 1.34 x 10 t of fish eaten per year. Pinnipeds ate 65% of the estimated annual consumption of fish. Marine mammals ate an estimated 3.2% of the standing stock of all fish species occurring in the eastern Bering Sea and Aleutian Islands region. Accounting for variations in population size over time of marine mammals in the Bering Sea, the estimated historical consumption of fish by all marine mammals was 0.44 x 10 t to 3.04 x 10 t, which represents 1.0% to 7.3% of the standing stock of all fish species. Commercial groundfish fisheries during the period 1988-90 caught about 7.1% (1.79 x 10 t) of the stock of commercially important groundfish species each year, whereas, at present, marine mammals annually consume an estimated 2.0% (0.45 x 10 t) of the standing stock of those fish species. This is 75% lower than the average commercial catch. THIS PAGE INTENTIONALLY LEFT BLANK