Neonatal growth and organ allometry of Northwest Atlantic harp seals (Phoca groenlandica)

Abstract

Growth and organ allometry of neonatal harp seals (Phoca groenlandica) were monitored during the first 6 weeks of life from 1982 to 1984. At birth, pup mass was 9.9 ± 1.7 (1 SD) kg. After their 1st day of relatively slow growth, pups gained mass rapidly, increasing 2 kg/day throughout the remainder of the ~12-day nursing period. Two-thirds of this mass gain was accumulated as a layer of subcutaneous blubber. Pups lost mass at a rate of ~0.5 kg/day during the postweaning fast, utilizing energy stores from the viscera, muscles, and limited amounts of blubber. In neonates, liver mass fluctuated in conjunction with total body mass gain and loss. The liver of adult harp seals was large relative to terrestrial mammals of similar size, but relatively small compared with other pinnipeds. The heart of harp seals grew slowly in pups and did not lose mass during fasting, and in adults it was of similar size relative to other mammals. The spleen of neonates was large and grew quickly during nursing. Spleen mass was quite variable among postweaning animals. As would be expected for a large-sized, precocially born, relatively advanced mammalian neonate, pups are born with large brains that grow very slowly. Adult brain mass, in relation to body mass, was similar to that of other mammals.