The influence of body size on dive duration of underyearling southern elephant seals (Mirounga leonina)

The dive duration of 16 underyearling (6-12 months old) southern elephant s eals Mirounga leonina during their second trip to sea was investigated usin g geolocating time-depth recorders. Underyearling seals had a lesser diving ability, with respect to duration and depth, than adult southern elephant sea:is. Individual underyearlings dived for average durations of up to 20.3 min and depths up to 416 m compared to durations and depths of 36.9 min an d 589 m, respectively for adults. Dive duration was positively related to t heir body mass at departure, indicating that smaller seals were limited to shorter dive durations, perhaps as a result of their lesser aerobic capacit y. All seals often exceeded their theoretical aerobic dive limit (average o f 22.1 +/- 18.1%). The number of dives exceeding the theoretical aerobic di ve limit was not related to mass, suggesting that factors other than mass, such as foraging location or prey availability, may have been responsible f or differences in diving effort. Foraging ability, indicated by the ability of the seals to follow vertically moving prey, was positively related to s eal mass, indicating that small mass restricted foraging ability. The short er dive durations of the smaller seals inferred that they had shallower div e depths in which to search for prey, thus restricting foraging ability. Al though foraging ability was restricted by size, foraging success was found to be inversely related to mass, the smaller seals gaining a higher proport ion of blubber than larger seals during their foraging trips. Thus, despite smaller seals being restricted to shallower depths and shorter durations, their foraging success was not affected.