Unlike harp seals, harbor seals are not born with a lanugo coat. Most pups are born with a short stiff hair coat typical of adult harbor seals. There are two basic color changes in adult harbor seals. Harbor seals are usually very wary and shy on land and are easily frightened into the water when they feel threatened. They feed on a wide variety of fish, cephalopods, and surface, mid-water, and benthic crustaceans.
Harbor seals are a gregarious species that frequently aggregate on haul-out sites at low tide.
Harbor seals hauled out on rocks or ledges often assume a banana-shaped position that is characteristic of healthy harbor seals. The breeding season is from February to October, and typically occurs in the water. Pupping season peaks between April and July. The average life-span of harbor seals is 30 years, although few harbor seals live longer than 25 years. Predators of harbor seals include sharks and killer whales, eagles and coyotes depending on the region, and humans.