DURATION OF LACTATION AND POSTWEANING CHANGES IN MASS AND BODY-COMPOSITION OF HARBOR SEAL, PHOCA-VITULINA, PUPS

We studied changes in body mass and body composition of harbour seal pups from weaning to 5-6 weeks postweaning in June-August 1988 and 1989 on Sable Island, Canada. Known-age pups (n = 52) were captured at 3-day intervals from late lactation through about 40 days postweaning. Pups were weaned, on average, at 24.1 +/- 0.44 days (mean +/- SE) postpartum at a body mass of 24.9 +/- 0.45 kg. There were no significant differences between years or sexes in the age and mass at weaning or in the rate of mass loss during the postweaning period. The duration of the postweaning fast averaged from 15-17 days as assessed by stomach lavage. The rate of mass loss was independent of weaning mass. At weaning, pups contained an average of 47.7% water and 32.8% fat, based on deuterium oxide dilution. During the first 14 days postweaning, the estimated body composition of pups did not change, despite the loss of body mass. Over the next 26 days, the estimated percent body water increased to about 63% and body fat declined to about 12%. The average energy density of harbour seal pups at weaning was low (16.3 kJ/g) compared with that of other phocids (17.7-22.2 kJ/g). This low energy density at weaning may reflect the highly aquatic and precocial development of harbour seal pups.