This species is usually solitary, the only social cohesion being between the mother and her nursing pup. Adults and juveniles form strong linear hierarchies based on size and sex, adult males being dominant. Many individuals may gather at a favorite "hauling out" site for sleeping, birthing and resting. Harbor seals are strong swimmers using black flippers in a side to side motion and can leap completely out of the water or stay submerged 20-43 minutes. Metabolism slows to allow this. They are non-migratory and make only limited movements in connection with foraging and breeding. Enemies include sharks, killer whales, bears, walruses and, in the case of the young, eagles.