Top predators in relation to bathymetry,
ice, and krill during austral winter in Marguerite Bay, Antarctica
Dr. Christine A. Ribic, USGS Wisconsin Cooperative Wildlife Research Unit, Dept. Wildlife Ecology, University of Wisconsin, Madison, WI
Erik W. Chapman, Center for Coastal Physical Oceanography, Old Dominion University, Norfolk, VA
Dr. William R. Fraser, Polar Oceans Research Group, Sheridan, MT
Gareth Lawson, MIT/Woods Hole Oceanographic Institution Joint Program in Oceanography, Woods Hole, MA
Dr. Peter Wiebe, Woods Hole Oceanographic Institution, Woods Hole, MA
ABSTRACT
The winter distribution of seabirds and pinnipeds and their relationship to physical and biological features were investigated as part of the U.S. Southern Ocean Global Ocean Ecosystem Dynamics (U.S. SO GLOBEC) field program along a study grid centered around Marguerite Bay on the west Antarctic Peninsula during July-August 2001 and August-September 2002. During the cruises, the pack ice had developed well north and west of the study area and all of the survey transects were within the pack ice. As a result, the most common seabird species were ice-affiliated species: snow petrel (Pagodroma nivea, 1.2 individuals km-2), Antarctic petrel (Thalassoica antarctica, 0.3 individuals km-2), and Adelie penguin (Pygoscelis adeliae, 0.5 individuals km-2). The most common pinniped was crabeater seal (Lobodon carcinophagus, 0.7 individuals km-2). Top predators were patchily distributed throughout the study area. In 2001, when the ship was able to survey within Marguerite Bay, the common species occurred primarily near Alexander Island and the northern section of inner Marguerite Bay while offshore concentrations of top predators occurred south of Alexander Island. In 2002, all surveys occurred outside of Marguerite Bay due to the ice conditions; snow petrel, Antarctic petrel, and Adelie penguin were observed off of Adelaide Island while crabeater seals were seen primarily off of Alexander Island. Milling snow petrels and Antarctic petrels were associated with lower sea ice concentrations in both years. Adelie penguins were associated with Marguerite Trough in both years. Crabeater seal occurrence was associated with area of lower chlorophyll concentration away from Marguerite Trough; these were the ice-covered areas near and south of Alexander Island. On lines where concurrent measurements of krill and top predators were available, crabeater seals coincided with deep krill concentrations, Adelie penguins were associated with both krill and zooplankton concentrations, while snow petrels had the least consistent associations. The interaction of physical and biological features appears to be important for understanding how top predators exploit their food resources.
STATUS UPDATE:
03/16/07: Received final version with assigned U.S. GLOBEC contribution number (517).