Characterization of winter foraging locations of Adélie Penguins along the Western Antarctic Peninsula, 2001-2002

Eric S. Erdmann, Christine A. Ribic, Donna L. Patterson-Fraser, and William R. Fraser

In accord with hypotheses driving the Southern Ocean Global Ocean Ecosystems Dynamics (SO GLOBEC) program, we tested the hypthothesis that the winter foraging ecology of a major top predator in waters off the Western Antarctic Peninsula (WAP), the Adélie penguin (Pygoscelis adeliae), is constrained by oceanographic features related to physiography of the region. This hypothesis grew from the supposition that breedign coloinies in the WAP during summer are located adjacent to areas of complex bathymetry where circulation and upwelling processes appear to ensure predicatble food resources. Therefore, we tested the additional hypothesis that these areas continue to contribute to the foraging strategy of this species throughout the non-breeding winter season. We used satellite telemetry data collected as part of the SO GLOBEC program during austral winter 2001 and 2002 to characterize individual penguin foraging locations in relation to bathymetry, sea ice variability within the pack ice, and wind velocity and divergence (as a proxy for potential areas with cracks and leads). We also explored differences between males and female in core foraging area overlap. Ocean depth was the most influential variable in determining foraging location, with most birds focusing their effort in shallow (< 200 m) waters near land and in mixed-layer (200-500 m) waters near the edge of deep troughs. Within-ice variability and wind (as a proxy for potential areas with cracks and leads) were not influential variables, likely due to low resolution satellite imagery and model outputs that were available. Throughout the study period, all indviduals maintained a core foraging area separate from other individuals with very little overlap. However, from a year with light sea ice to one with heavy ice cover (2001 to 2002), we observed an increase in the overlap of individual female foraging areas with those of other birds, likely due to restricted access to the water column, reduced prey abundance, or higher prey concentration. Male birds maintained separate core foraging areas with the same small amount of overlap, showing no difference in overlap between the years. While complex bathymetry was an important physical variable influening Adélie penguin foraging, the analysis of higher resolution sea ice data than was available for this study may help elucidate the role of sea ice in affecting Adélie penguin winter foraging behavior within the pack ice.

STATUS UPDATE

10/05/10: Revision accepted; editor letter sent to corresponding author.