Growth From Birth to 20 Days in the Elephant Seal, Mirounga-Leonina, at Macquarie-Island

Abstract

Recent investigations by members of Australian National Antarctic Research Expeditions to Macquarie I. have revealed a decrease in the elephant seal population there of approximately 50% over the last 36 years. Lower birth weights and/or slower growth during the lactation period might explain this decrease. To test this hypothesis, growth of pups was studied from birth to 20 days during the 1984 and 1985 breeding seasons; these results were compared as far as possible with similar results for the 1956 and 1965 seasons. Average birth weight has not changed significantly over the last 20 years; it is suggested that if food supply were a major factor in the reduction of the elephant seal population, then birth weights in 1985 would have been lower than those in 1956. At birth, male pups were 7% (3 kg) heavier than female pups in 1985. Results from previous years suggest that this is probably normal in this seal. The weight of pups near weaning (20 or 21 days old) is shown to be significantly less in 1984 and 1985 than 1965, but this may be explained by differences in methodology. It is concluded that, on the evidence available, the pattern of pup growth on Macquarie I. has not altered significantly with time, but more work is needed to reach a clear conclusion.