Meeting Abstract
Most activities of Weddell seals occur during dives that extend hundreds to thousands of meters in distance and require the seals to hold their breath for 20 minutes or more. In the fast-ice environment of Antarctica, holes in the ice where seals can surface to breathe are scarce. Consequently, seals must return to a previous breathing hole or locate a new one to avoid drowning; how they navigate underwater with such precision is not known. This study used field experiments to test multiple hypotheses concerning the sensory cues and tactics Weddell seals may employ to navigate underwater in this challenging environment, with special attention to their possible use of geomagnetic cues. An archival data logger was fitted to each of 10 adult seals, which were released at three locations that differed in the orientation of the geomagnetic field, and allowed to perform voluntary dives. Analysis of three dimensional dive tracks demonstrated that outbound paths of dives in a given direction progressively increased in distance from the breathing hole. Seals returned home from long distance dives on remarkably straight homeward paths, or they traveled directly to a frequented route then turned toward home, which is consistent piloting by landmarks. Seventy-five percent of the frequented routes were directly below known linear disturbances in the snow on the top of the sea ice, indicating that Weddell seals primarily used overhead visual cues (pilotage by landmarks and waypoints) to navigate under ice cover. They were able to do so during both daylight and surface twilight, presumably due to exceptional visual sensitivity in low light environments. We did not find evidence that seals used geomagnetic or hydrodynamic cues when returning to a breathing hole under these conditions.
