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Redistributions of Cetaceans in the Southeast Bering Sea Relative to Anomalous Oceanographic Conditions during

By The El Niño and Cynthia T. Tynan

Abstract

The distributions of foraging whales typically reflect the productivity of their pelagic and coastal environments (Tynan, 1998; Croll et al., 1998). Whales can therefore serve as important integrators of the regional biomass of their principal prey: euphausiids, copepods and schooling fish. Redistributions of whales can also serve as important indicators of change in the ecosystem. In order to consider how the distribution of whales in the southeast Bering Sea may have changed relative to the anomalous oceanographic conditions of 1997 and 1998, it is first necessary to review the historical distributions of whales relative to the mean circulation. The general circulation consists of a cyclonic gyre over the deep basin, with the Kamchatka Current forming the western boundary and the Bering Slope Current forming the eastern boundary of the gyre. A 0.5 m sea-level difference between the Bering Sea and the Arctic Ocean drives the mean northward transport through Bering Strait (Coachman, 1993). The circulation and hydrographic structure of the Bering Sea is highly variable on interannual and decadal time scales. Transport in the gyre can vary by as much as 50 % due to changes in the Alaskan Stream inflow or alteration in the winddriven circulation (Schumacher and Stabeno, 1998). The Bering Slope Current is primarily an extension of the Alaskan Stream water which enters through the passes along the Aleutian Chain. This flow turns eastward along the northern side of the Aleutian Chain as the North Aleutian Slope Flow and then continues to the northwest over the slope at mean speeds of 3–15 cm s –1 as the Bering Slope Current (Schumacher and Reed, 1992). The nutrient-rich waters of the Bering Slope Current help to create one of the most productive ecosystems in the world. Approximately half of the Bering Sea consists of the broad continental shelf, which is more than 500 km wide in the eastern portion (Coachman, 1986). The circulation over the eastern shelf is sluggish, with current speeds on the order of 1–5 cm s –

Year: 2013
OAI identifier: oai:CiteSeerX.psu:10.1.1.360.348
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