The female, however, savagely keeps the male at bay until her pup is weaned and she enters estrus, about 4 weeks after giving birth. The male then becomes aggressive and forces the mother and pup apart. Mating takes place from October to December and occurs on the ice, rather than in the water as in most polar phocids. The male and female remain in close contact for a few days, then break up. As a result of fights with both males and females, the old males are heavily scarred about the head and neck.
Agonistic interaction is accompanied by hissing and blowing sounds.
Births occur from September to November, with a synchronized peak in early to mid-October. Total gestation lasts about 11 months and probably includes a period of delayed implantation. The single pup is about 150 cm long and has a soft, woolly, grayish brown coat. In the 4-week period of lactation it grows from 25 to 120 kg. The young are nearly full grown after 2 years, but some growth continues for years afterwards.