Diving classification and behavior of free-ranging female southern elephant seals based on three-dimensional movements and video-recorded observations

The goal of this study was to classify dives of free-ranging female southern elephant seals Mirounga leonina from Península Valdés, Argentina, during their 2 mo post-breeding migration. Classifications were based on 3-dimensional movements and video-recorded observations from 13 797 dives obtained by attaching video and data recorders to the backs of 8 seals. We inferred behavioral functions for the dive classes based on video-recorded observations. Three dive types were identified: foraging, resting, and transit. Most (98%) prey captures occurred during foraging dives, and primary prey were pencil smelt and myctophids. Over deep water, foraging dives were deep (maximum depth 553 ± 258 m, mean ± SD), long in duration (21.5 ± 5.8 min), and meandering with bursts of speed, steep descent and ascent angles, and vertical head movements associated with prey capture. Resting dives were shallower (maximum depth 375 ± 114 m) but lasted longer (22.6 ± 6.2 min), with lower stroking rates and speeds and greater variation in pitch and roll angle during descent. Transit dives were shallower (maximum depth 307 ± 171 m), shorter (19.9 ± 6.6 min), and more linear, with higher swim speeds and stroking rates, shallower ascent angles, and farther straight-line distances traveled. Seals exhibited several strategies to reduce the energetic cost of foraging, including gliding during descent, swimming at optimal speeds for energy savings during foraging dive ascents, ascending at the most cost-effective angles during transit dives, and resting preferentially during daytime hours when prey are deepest and foraging dives are less efficient.