HEART-RATE, SWIMMING SPEED, AND ESTIMATED OXYGEN-CONSUMPTION OF A FREE-RANGING SOUTHERN ELEPHANT SEAL

Heart rate, swimming speed, and diving behaviour were recorded simulta neously for an adult female southern elephant seal during her postbree ding period at sea with a Wildlife Computers heart-rate time depth rec order and a velocity time depth recorder. The errors associated with d ata storage versus real-time data collection of these data were analys ed and indicated that for events of short duration (i.e., less than 10 min or 20 sampling intervals) serious biases occur. A simple model fo r estimating oxygen consumption based on the estimated oxygen stores o f the seal and the assumption that most, ii not all, dives were aerobi c produced a mean diving metabolic rate of 3.64 mL O-2 kg(-1), which i s only 47% of the field metabolic rate estimated from allometric model s. Mechanisms for reducing oxygen consumption while diving include car diac adjustments, indicated by reductions in heart rate on all dives, and the maintenance of swimming speed at near the minimum cost of tran sport for most of the submerged time. Heart rate during diving was bel ow the resting heart rate while ashore in all dives, and there was a n egative relationship between the duration of a dive and the mean heart rate during that dive for dives longer than 13 min. Mean heart rates declined from 40 beats min(-1) for dives of 13 min to 14 beats min(-1) for dives of 37 min. Mean swimming speed per dive was 2.1 m s(-1), bu t this also varied with dive duration. There were slight but significa nt increases in mean swimming speeds with increasing dive depth and du ration. Both ascent and descent speeds were also higher on longer dive s.