A longitudinal study of growth of southern elephant seals,
Mirounga leonina, during their first foraging trip was
undertaken at Macquarie Island. On average, body mass increased by 75%
while foraging at sea, with individuals growing at 0.34 ± 0.12 (s.d.)
kg day-1 (n = 64), and
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, rather than increases in gross body size. This may be in response
to the functional 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 negatively related to
departure mass for females, and this is hypothesised to be related to sex
differences in body composition, as well as intrasex differences in foraging
skills, diving ability and food- conversion efficiency. Despite this, there
was no detectable age-specific sexual dimorphism in the first year of life.
Animals that were at sea longer tended to return in better body condition.
Interspecific comparison suggests that southern elephant seals grow more than
do northern elephant seals, Mirounga angustirostris, and
this difference may be related to prey abundance and distribution.
