Postweaning duration and body composition changes in southern elephant seal (Mirounga leonina) pups at King George Island

Weaning mass in southern elephant seals is highly variable, the heaviest pu ps being three times as heavy as the lightest ones. After weaning, pups und ergo an extensive postweaning period in which they draw on their reserves. To quantify the energy expenditure during the postweaning period, changes i n mass, body composition, and postweaning duration were measured in souther n elephant seals at King George Island, South Shetland Islands, Antarctica. Overall, mean pup weaning mass was 154 +/- 26 kg (n = 117) and did not dif fer between sexes. Mean minimum postweaning duration was 42.5 +/- 7.5 d. He avier animals at weaning had lower mass-specific mass loss rates than light er ones, and a faster depletion of body reserves was associated with a shor ter postweaning period. The proportion of body mass represented by fat at w eaning was 37% +/- 4% (n = 47) and did not differ between sexes. Of these p ups, 36 were recaptured after a mean period of 36 d after weaning. On avera ge, total mass loss measured in these animals (39 kg) was composed of 39% w ater, 47% fat, and 12% protein. The composition of mass loss was not signif icantly different between sexes and was not related to weaning mass or tota l body energy reserves. However, fatter animals at weaning lost more fat pe r kilogram lost than thinner ones. Late in the fast, males and females appe ared to be in a similar body condition. Nevertheless, the overall proportio n of body mass represented by fat at this time was lower than that presente d by the same animals at weaning. We estimated that during the postweaning period pups lost, on average, 30% of their mass at weaning. This comprised approximately 35% of the energy and 32% of the fat in the pup's body.