Males may mate with more than one female during the season. Females are capable of giving birth every year but usually do so at greater intervals. If a litter does not survive, the female may experience a postpartum estrus. Females are known to adopt and nurse orphaned pups. Reports of the period of pregnancy range from 6.5 to 9 months, and delayed implantation is probably involved.
Births probably occur most often in the water.
There is normally a single offspring. About 2 percent of births are multiple, but only one young can be successfully reared. The pup weighs 1.4-2.3 kg at birth. While still small, it is carried, nursed, and groomed on the mother's chest as the mother swims on her back. The pup begins to dive in the second month of life.