Harbor Seals

By Barton Creeth

There are an estimated 500,00 harbor seals worldwide distributed throughout the temperate and sub-arctic waters of the North Pacific and North Atlantic. The Pacific harbor seal, one of five recognized subspecies of harbor seals, is found along the Pacific Coast from the eastern Aleutians to Baja California. 40,000 of these Pacific harbor seals live in California waters where an estimated twenty percent breed in the Gulf of the Farallones.

Except for the anomalous red-coated seals of the San Francisco Bay, most harbor seals are silver-tan or dark with scattered rings and spots. Researchers believe that deposits of iron oxide cause the unusual red coats of the San Francisco seals. Pups are born with a naturally colored coat and only acquire the red shade as they mature. The principal source of the iron oxide that causes the discoloration is believed to come from sediments blown into the bay by strong summer winds. More than thirty percent of the seals in the bay have been found with red coats.

Harbor seals are medium sized pinnipeds, which means “fin-foots,” and is the superfamily made up of seals, sea lions, and walruses. Harbor seals weigh up to 300 pounds and reach up to six feet in length—the males being slightly larger than the females. They have multiple layers of blubber that insulate them from the frigid waters of the Pacific Ocean and also provides a significant energy reserve. Often mistaken for seals, the seal-like creatures at Pier 39 are in fact sea lions, identified by their big flippers, earflaps, and their larger, stouter bodies. A “true” seal, like the harbor seal, has ear holes without flaps and much smaller flippers. These ear holes, called pinnae, are openings to the ear canal made of skin and cartilage, and provide harbor seals with a keen sense of hearing while under water.

Harbor seals spend half their time in the water and half their time on land. To maneuver when out of water, harbor seals flop along on their bellies, and are protected from sharp rocks by their thick leathery skin and dense fur. While diving, the heart rates of harbor seals slows from 75 to 120 beats per minute down to only four to six beats per minute, an adaptation that allows for the conservation of oxygen. In comparison to land mammals of the same size, harbor seals have much more blood, which extends their retention of oxygen. They are able to stay underwater for up to forty minutes and dive to depths of up to 1,500 feet. They are also known to take underwater naps.

While curious about humans while in the water, harbor seals are wary of us while on land. They generally only haul out in places where there is little human disturbance. Haul-out locations are generally places with good visibility and immediate access to deep waters. Despite their tendency to congregate in groups, harbor seals rarely interact with one another. When hauled-out they maintain several feet of distance from other individuals. If approached to closely by another seal, they react with loud snorting and aggressive flipper waving. The only exception is the strong bond that exists between mother and pup.

Unfortunately seal pups are orphaned by well meaning people who pick up the seals thinking they have been abandoned. Usually, the mother has gone off hunting or is watching near by. If you find a seal pup on land and it appears to be alone, call the Marine Mammal Center rescue line at (415) 289-SEAL (7325). Human disturbances hinder birth rates and can even cause seals to permanently abandon haul-out sites. SEALS volunteers work to educate the public about the importance of keeping one’s distance to avoid flushing seals. When careful and respectful, seal watching can be a no impact recreational activity.  Some of the best places to glimpse these wonderful creatures are the Point Reyes National Seashore, Fitzgerald Marine Reserve, and Bolinas Lagoon.

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The Marine Mammal Center rescues  and rehabilitates sick and injured harbor seals.>>