Territories for breeding grounds are usually on beaches of sand, pebbles, or flat rock. Males prevent females from leaving the beaches until they have mated. Birth occurs from mid December to early February in the year after mating, with the bulk of births during mid January. The gestation period is about 11.75 months. Usually one pup is born at a time, which averages .80 to .85 meters in length and 10 to 15 kilograms in weight.
Male pups tend to be larger than females.
However, since mothers seem to not show any gender based nursing difference, this suggests that the energy spent more in sons than daughters is done during gestation. This investment is important for male reproductive success, as size is important in establishing mating territories. Mothers fast for 5 to 7 days after giving birth in order to nurse their pup. Soon after giving birth mothers enter oestrus and mates again with the male in territory. The mother then leaves her pup behind to find food in the sea.