On the straight and narrow: directed movement by Weddell seals (Leptonychotes weddellii) during on-ice travel

Abstract

Weddell seals (Leptonychotes weddellii) are well adapted to the fast-ice environment of Antarctica, where the majority of their activities are conducted underwater. Little is known about their capacity for terrestrial movement. During a study of their underwater homing ability, we also tracked the on-ice movements of six Weddell seals that had been displaced approximately 10 km from their capture locations along the southwestern coast of Ross Island, Antarctica. Each seal was instrumented with a satellite tag and released into one of the three isolated breathing holes. After at least 2 days in the water, the seal hauled out and traveled freely across the sea ice at a mean rate of 4.4 (± 2.4) km d−1 (maximum 8.3 km d−1). Travel headings, computed from GPS, and Argos positions after seals had traveled 2.1 to 7.5 km, revealed that all seals traveled along remarkably straight paths. Not all seals traveled the same heading, but each seal that was released more than once moved along the same heading, regardless of release location. Most headings traveled by seals were in line with prominent geographic features having high visual contrast, but some seals traveled consistently in directions with no visible landmarks, and other seals moved along their preferred heading during periods when bad weather obscured visual landmarks. These initial data indicate directed terrestrial movement by Weddell seals and invite further studies of the cues they use to maintain consistent headings.