Harbor Seal
Phoca vitulina

With one of the largest territories of any seal, the harbor seal will visit the Chesapeake Bay region during the winter for warmer weather and access to fish.

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Harbor seals rest near the Chesapeake Bay Bridge-Tunnel in Virginia on Dec. 13, 2018. (Photo courtesy of Jaime Gormley, taken under NMFS permit 19826-03 issued to Deanna Rees/NAVFAC Atlantic)

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Appearance

Harbor seals are a true seal, unlike fur seals and sea lions. One of the most noticeable characteristics of true seals is that they lack ear flaps and have an exposed hole for an ear. True seals also have fused pelvic bones which impacts how they move on land and in water. True seals will scrunch their body like caterpillars to move on land, and in the water they use their back flippers for power and their front flippers for steering. This differs from fur seals and sea lions, which use all four flippers to move on land and use all four flippers to propel themselves in water.

Harbor seals can have widely varying colors but most are light tan or gray with dark brown or black spots. Harbor seals have a “dog-like” head and V-shapes nostrils.

Feeding

Harbor seals are opportunistic feeders, with diets that includes a range of fish, shellfish and crustaceans. They can dive for up to 30 minutes in search of food. In preparation for an extreme dive, harbor seals will slow their heart rate to 3 to 4 beats per minute.

Predators

Orca whales, sharks and polar bears are all predators of the harbor seal. But one of the top threats to harbor seals is interference from humans. Until the 1970’s, harbor seals were hunted for interfering with fishermen. Seals can suffer deadly injuries from entanglement in fishing equipment and accumulating chemical contaminants present in polluted waterways. Harbor seals are also losing their breeding grounds to development. A growing threat to the harbor seal population has been humans attempting to rescue harbor seals pups and accidentally separating pups from their mothers.

Voice

Although not as loud as other seals and sea lions, the harbor seal will use vocalizations to signal a warning, mating and territory disputes.

Reproduction and life cycle

Harbor seals reach sexual maturity at 3-7 years old at which point they will join a group of seals during mating season and mate in the water. The gestation period is 10 - 11 months. In the spring, seals will birth a single pup which is weaned for 4-6 weeks. A harbor seal will travel the most in its lifetime during the juvenile stage after being weaned and before sexual maturity.

Did you know?

  • Harbor seals can sleep underwater for 30 minutes at a time.
  • Harbor seals milk is almost 50% fat.
  • During the winter, a harbor seal’s blubber layer can be 30% of its total body mass.
  • Harbor seal pups can swim almost immediately after birth.

Sources and additional information

Fisheries: Harbor Seal Fact Sheet - Maryland Department of Natural Resources
Species Directory: Harbor Seal - NOAA Fisheries
Animals: Harbor Seal - Smithsonian Zoo & Conservation Biology Institute
Creature Feature: Harbor Seal - Natural Resources Council of Maine

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