Abstract

The breeding process in Mirounga leonina (L.) at Macquarie and Heard Islands is described in detail on the basis of records made by A.N.A.R.E. men of branded seals 4-8 years old, daily counts, and observations. These natural populations are contrasted with the exploited one at South Georgia, where the bulls are now fewer and younger. At Macquarie Island the largest harems contain over 1000 cows and are shared by the strongest bulls. The activities of each male age class are described, also the establishment of the harem by the cows and its subsequent development, including parturition and pup growth. Onset of maturity in the male begins at 6 years old at Macquarie Island and 4 years old at South Georgia. About one-third of the females at Macquarie Island are pregnant in the fourth year, and about one-quarter defer first pregnancy until the seventh year; all third-year cows at South Georgia are pregnant. The former seals also grow more slowly, and it is suggested that pressures within this population that is at its natural limit, operating among females as well as males, retard development and breeding. The effects of continuous sealing at South Georgia may have resulted in a population still below its potential size.