Foraging of Planktivorous Seabirds and Hydrographic Processes in the Aleutians

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A multidisciplinary study will be conducted to test the hypothesis that planktivorous seabirds will concentrate their foraging where tidal and sub-tidal currents, interacting with bathymetry, transport and concentrate zooplankton near the surface in spatially predictable upwellings and fronts. It is hypothesized that quasi-permanent fronts, caused by horizontal gradients in mixing associated with gradients in tidal velocity and bottom depth, will be of importance to the birds. Physical processes and plankton distributions in both shallow (100 m) and deep (600 m) passes near Buldir Island will be compared, as will avian responses to concentrations of prey in both the horizontal and vertical dimensions. Advanced technologies including an Acoustic Doppler Current Profiler (ADCP), an integrating echosounder, multiple opening-closing nets (MOCNESS) and computerized data entry and real-time analyses of results to optimize use of the ship will be employed. The study provides a unique opportunity to combine the benefits of new technologies for investigating how physical processes affect the distribution and concentration of plankton that support higher trophic levels. The study will be one of the few to examine simultaneously physical processes, zooplankton distributions and abundance, and the foraging ecology of marine birds in the western Aleutians. This suite of information will permit comparison of the marine ecology of seabirds on oceanic islands with that of seabirds on nearby continental islands studied previously.