Hydrographic features and seabird foraging in Aleutian Passes
Strong tidal currents crossing over the abrupt topography of the Aleutian Passes result in regions with high horizontal property gradients. These frontal regions vary with the tidal cycle and form the boundary between vertically mixed and stratified regions. Concentrations of seabirds were associated with convergence zones in the mixed water (MW) and with the front between North Pacific (NP) water and MW. Species that were foraging by picking at prey from the surface were associated with surface convergences that appeared to be associated with Langmuir circulation cells or tidal features (all fulmar aggregations) in the central passes (Samalga, Seguam). In contrast, subsurface foraging puffins and small alcids were mostly observed in areas of turbulent, well-mixed water near the shallow regions of the passes. Short-tailed shearwater flocks that were plunge-diving for prey were associated with the front between the NP water and MW in the passes. On our transects, we observed no significant aggregations of seabirds associated with Bering Sea water or NP water away from the frontal zones. The interaction of strong currents with bathymetric features results in zones of vertical advection, mixing, and surface convergences that make island passes attractive foraging regions for seabirds. Deep passes lacking these features, such as many of the passes in the western Aleutian Archipelago, are not as likely to facilitate trophic transfer to top predators as shallow passes, such as those found in the eastern Aleutian Islands.
Keywords: Aleutian Islands; Aleutian Passes; Fulmarus glacialis; Puffinus tenuirostris; convergences; northern fulmar; seabird foraging; short-tailed shearwater; tidal fronts; trophic transfer; zooplankton
Document Type: Research Article
Affiliations: 1: Ecology and Evolutionary Biology Department, University of California Irvine, Irvine, CA 92697-2525, USA 2: Institute of Marine Science, University of Alaska Fairbanks, Fairbanks, AK 99775-7220, USA 3: Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, WA 98195-4235, USA
Publication date: 01 November 2005