The distribution of seabirds and pinnipeds in Marguerite Bay and their relationship

to physical features during austral winter 2001

Erik W. Chapman and Christine A. Ribic

USGS Wisconsin Cooperative Wildlife Research Unit

Dept. Wildlife Ecology, University of Wisconsin, Madison, WI 53706

William R. Fraser

Polar Oceans Research Group

P.O. Box 368, Sheridan, MT 59749

The distribution of seabirds and pinnipeds and their relationship to physical oceanographic variables were investigated within the U.S. Southern Ocean Global Ocean Ecosystems Dynamics (U.S. SO GLOBEC) program for late fall (April-May) and winter (July-August) cruises conducted during 2001. Top predators were surveyed and physical oceanographic variables measured along a study grid near Marguerite Bay on the West Antarctic Peninsula. Sea ice conditions during the cruise provided a unique opportunity to compare the relationship among physical oceanographic variables and species distributions before and after the development of pack ice. Before pack ice development, both ice-affiliated and open water-affiliated species were present in the area. Seabirds were associated with the water column environment, in particular, water mass structure. The birds had higher densities in Inner Shelf Water, particularly near Alexander Island where a strong, coastal current had developed. After the development of pack ice, only ice-associated species were observed. Seabirds were primarily associated with ice characteristics (e.g., ice concentration, ice type) rather than the water column environment. The timing and extent of sea ice development in the fall may have important effects on over-winter predation by seabirds and pinnipeds on zooplankton and fish on the Western Antarctic Peninsula.