GROWTH OF SOUTHERN ELEPHANT SEALS, MIROUNGA-LEONINA, DURING THEIR FIRST FORAGING TRIP

A longitudinal study of growth of southern elephant seals, Mirounga le onina, during their first foraging trip was undertaken at Macquarie Is land. On average, body mass increased by 75% while foraging at sea, wi th individuals growing at 0.34 +/- 0.12 (s.d.) kg day(-1) (n = 64), an d spending 182 +/- 51 days (n = 64) at sea. Relatively smaller changes in body length were recorded during the same period, suggesting that growth was composed primarily of adjustments to body composition, rath er than increases in gross body size. This may be in response to the f unctional demands of pelagic life. Body size established early in life (birth mass and departure mass) positively influenced body mass upon return from the first foraging trip. Growth rate, however, was negativ ely related to departure mass for females, and this is hypothesised to be related to sex differences in body composition, as well as intrase x differences in foraging skills, diving ability and food-conversion e fficiency. Despite this, there was no detectable age-specific sexual d imorphism in the first year of life. Animals that were at sea longer t ended to return in better body condition. Interspecific comparison sug gests that southern elephant seals grow more than do northern elephant seals, Mirounga angustirostris, and this difference may be related to prey abundance and distribution.