Early Growth and Milk-Composition in Southern Elephant Seals (Mirounga-Leonina)

Abstract

Growth rates and changes in body composition of pups were monitored during the 3-week lactation period of southern elephant seals at Macquarie Island. Despite a slight decrease in weight in the first days post-partum, pups attained a mass of 114+/-16.6 kg (mean+/-s.d.) at weaning, representing an average growth rate of 3.53+/-0.80 kg day-1 over the entire lactation period. The proportion of body mass represented by fat was less than 3% at birth, increasing to 40.8+/-12.7% at weaning. Lean tissue mass altered little for most of the lactation period, but did show an increase in the last four days. The fat content of the milk reflected these changes, starting at 16.1+/-6.98% on Day 1 of lactation and increasing to 39.5+/-15.2% about the time of weaning. Fat content of the milk was, however, highly variable and at weaning ranged from 7% to 55%. Although the growth rate of the pup was correlated with mass lost by its mother during lactation, there was no relationship between maternal mass and weaning weight of pups. It is suggested that growth rates may be related to maternal condition and not simply mass, and, further, that differences in growth rates between populations of southern elephant seals are related to maternal energy reserves.