Winter Foraging Movements of Adélie Penguins in the Western Antarctic Peninsula Region

William R. Fraser¹, Christine A. Ribic², Donna L. Patterson¹, and Erik W. Chapman³

¹Polar Oceans Research Group, Sheridan, Montana, USA.

²USGS Wisconsin Cooperative Wildlife Research Unit, Dept. Wildlife Ecology, University of Wisconsin, Madison, Wisconsin, USA.

³Center for Coastal Physical Oceanography, Old Dominion University, Norfolk, Virginia, USA.

Abstract

The transition from summer to winter over the western Antarctic Peninsula (WAP) shelf region is characterized by a substantial and significant decrease in primary production and phytoplankton biomass. This results in a food web that during polar winter is decoupled from the more common summer state of high water column primary production. Despite these conditions, however, a majority of apex predators remain in the WAP during winter, including several species whose numerical abundance alone accounts for much of the regional apex predator biomass. To investigate some of the processes that may sustain these large predator populations during winter, we examined the foraging movements of Adélie penguins (Pygoscelis adeliae) in the U.S. Southern Ocean Global Ocean Ecosystem Dynamics (U.S. SO GLOBEC) study grid near Marguerite Bay. This was done by using Platform Terminal Transmitters (PTTs) attached to penguins during cruises in autumn/winter 2001 and 2002, and tracking their positions using the ARGOS satellite constellation. In 2001, 8 and 12 PTTs were deployed on male and female penguins, respectively. The tags recorded penguin locations for an average of 62 days (s.e. = 34 days) between 8 May and 3 December 2001. In 2002, 21 and 15 PTTs were deployed on male and female penguins, respectively. These tags recorded locations for an average of 73 days (s.e. = 50 days) between 12 April 2002 and 29 January 2003. Winter sea ice conditions were significantly different between the two years and this affected the area over which penguins were able to forage within the study grid. In winter 2001, the ice edge extended north only to about 64 degrees south latitude while in winter 2002, the ice edge extended beyond 61 degrees south latitude, or the northern tip of the WAP. During both winters, penguin foraging locations converged on a large coastal polynya found at the southern end of Adelaide Island, Marguerite Bay. However, during winter 2002 the Adélie penguins, females in particular, were able to extend their foraging to other polynyas within and beyond the SO GLOBEC study grid. Apart from providing open water, these polynyas were in all cases associated with unique, deep bathymetry, higher prey concentrations and large numbers of other top predators. These results suggest that polynyas along the WAP are important winter foraging areas for Adélie penguins and, possibly, other top predators; sea ice is one of the key variables mediating access to regions in the WAP where predictable winter prey concentrations may occur; and female Adélie penguins may be particularly dependent on heavy sea ice conditions to forage successfully.

STATUS UPDATE:

Title, abstract, and author list received on 06/28/05.