The dark-colored pups can be born on land or in the water, and the nursing period lasts about six weeks. After nursing is complete, the adult seals mate. Pregnancy lasts nine months, but the fertilized egg does not begin to develop for three months, aligning birth dates to the same time each year. The coats of harbor seal pups are the same color as adults, and they are ready to swim almost immediately. They also produce sounds by slapping the surface of the water with their front flippers.
Mothers feed shrimp and other small prey items to their newly weaned pups.
A mother conducts her pup into the sea and spends considerable time nurturing it, holding the pup to her with a flipper if danger threatens. If disturbed by humans or dogs, mothers will temporarily leave their pup alone on the beach. The young should not be disturbed since the mothers usually watch from the water, returning to their young as soon as they feel secure. Nursing is over in six weeks when the pups disperse and the adults mate again to begin the yearly reproductive cycle. Migration Harbor seals are not migratory.