Winter habitat use and foraging behavior of crabeater seals along the Western Antarctic Peninsula

J.M. Burns^a*, D.P. Costa^b, M. Fedak^c, M.A. Hindell^d, C.J.A. Bradshaw^d, N. Gales^e,

G. McDonald^f, S.J. Trumble^g, D. Crocker^f

^aDepartment of Biological Science, University of Alaska, 3211 Providence Dr., Anchorage, AK 99508 USA

^bDept. of Ecology and Evolutionary Biology, University of California Santa Cruz, 100 Shaffer Road, Santa Cruz, CA 95060 USA

^cSea Mammal Research Unit, Gatty Marine Laboratory, University of St. Andrews, Fife Scotland, KY16 8LB

^dAntarctic Wildlife Research Unit, School of Zoology, University of Tasmania, GPO Box 252-05, Hobart, Tasmania 7001, Australia

^eAustralian Antarctic Division, Channel Highway, Kingston Tasmania 7050, Australia

^fDepartment of Biology, Sonoma State University, 1801 East Cotati Avenue, Rohnert Park, CA 94928 USA

^gSchool of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Fairbanks, AK 99775 USA

We quantified the winter and spring movement patterns and foraging behavior of adult crabeater seals (Lobodon carcinophagus), and the influence of sea ice and bathymetry on their foraging behavior. Thirty-four seals (16 M, 18 F) were outfitted with Satellite Relay Data Loggers (SRDLs) in the Marguerite Bay Region of the Antarctic Peninsula (~67°S, 67°W) during the austral winters of 2001 and 2002. Tags transmitted position and dive information for between 4 to 174 days. Overall, winter activity patterns differed significantly from previously reported data collected during the summer: seals in this study dove deeper (92m ± 0.2m, range 6-713 m) and longer (5.26min ± 0.6, range 0.2-23.6min), hauled out during the night rather than the day, and showed seasonal shifts in foraging patterns consistent with foraging on vertically migrating prey. While these patterns were more pronounced in 2001 than in 2002, there were no strong differences in patterns of habitat use between the two years. While some animals made long distance movements (furthest movements 664 km to northeast, 1147 km to southwest), most seals remained within 300 km of their tagging location. Within the Marguerite Bay/Crystal Sound region, seals appeared to favor foraging locations on the continental shelf within the 50 and 450 m depth range with a tendency to avoid depths of 600m or greater. In both years, seals remained deep within the pack ice throughout the winter, and did not move into regions with less ice cover. Seals were more likely to be located in shallow water where the bathymetric gradients were greatest, and in areas of higher sea ice concentration. In combination, these findings suggest that crabeater seals alter their behavior to accommodate seasonal and/or annual fluctuations in seasonal sea ice and appeared to associate with bathymetric features that are likely to be associated with prey patches.