Three-dimensional movements and swimming activity of a northern elephant seal

We attached a video system and data recorder to a northern elephant seal to track its three-dimensional movements and observe propulsive strokes of th e hind flippers. During 6 h of recording, the seal made 20 dives and spent 90% of the time submerged. Average dive duration, maximum depth and swimmin g speed were 14.9 min +/- 6.1 S.D., 289 m +/- 117 S.D. and 1.1 m s(-1) +/- 0.12 S.D., respectively. The distance swum during a dive averaged 925 m +/- 339 S.D., and the average descent and ascent angles were 41 degrees +/- 18 S.D. and 50 degrees +/- 21 S.D., respectively. Dive paths were remarkably straight suggesting that the seal was navigating while submerged. We identi fied three modes of swimming based on the interval between propulsive strok es: continuous stroking; stroke-and-glide swimming; and prolonged gliding. The seal used continuous stroking from the surface to a mean depth of 20 m followed by stroke-and-glide swimming. Prolonged gliding started at a mean depth of 60 m and continued to the bottom of dives. For dives to depths of 300 m or more, 75% of the descent time was spent in prolonged gliding and 1 0% in stroke-and-glide swimming, amounting to 5.9-9.6 min of passive descen t per dive. Average swimming speed varied little with swimming mode and was not a good indicator of propulsive effort. It appears that the seal can us e prolonged gliding to reduce the cost of transport and increase dive durat ion. Energetically efficient locomotion may help explain the long and deep dives that routinely exceed the theoretical aerobic dive limit in this spec ies. (C) 2001 Elsevier Science Inc. All rights reserved.