Behavior Mating Habits Harbor seals congregate on islands and remote mainland coasts or even on the Arctic pack ice to breed. They gather in small to large groups, with females well spaced apart during the birth process. While they do not establish obvious social hierarchies during breeding seasons, there does appear to be competition between males.
Harbor seals give birth to one pup in the spring.
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.