Harbor Seal

About the harbor seal

The harbor seal, also called the common seal, is a true seal found along temperate and Arctic marine coastlines of the Northern Hemisphere, in the northern Atlantic and Pacific oceans as well as the Baltic and North seas. It is the most widely distributed of all pinnipeds, the group that also includes walruses and eared seals. Harbor seals are brown, silvery white, tan, or grey, each individual carrying a unique pattern of spots — either dark markings on a light background or light markings on a dark one. Their bodies and flippers are short and their heads rounded, with distinctive V-shaped nostrils and no visible ear flap, though an ear canal can sometimes be seen behind the eye.

An adult harbor seal can reach 1.85 m (6.1 ft) in length and weigh between 55 and 168 kg (120–370 lbs), with females generally smaller than males. A layer of blubber beneath the skin helps the seal maintain its body temperature in cold water. Five subspecies of Phoca vitulina have been proposed, reflecting the species' broad geographic spread across both sides of the Atlantic and Pacific.

Worldwide, the population is estimated at 350,000 to 500,000 animals. While the species as a whole is not threatened, some regional populations — including those in Greenland, Hokkaidō, and the Baltic Sea — are exceptions, having been reduced by disease, especially phocine distemper virus, and by conflict with humans, both intentional and accidental.

Behavior and diet

Harbor seals are solitary for much of the year but become gregarious when hauled out on shore and during the breeding season, though they don't gather in groups as large as some other seal species. They favor familiar resting sites — rugged rocky coasts, sandy beaches, or estuaries — and generally stay within about 20 km of shore, though they may travel up to 50 km in search of feeding grounds and can swim more than a hundred miles up large rivers chasing migratory fish like shad and salmon. Dives of over 500 m have been recorded, even though the species is primarily coastal.

Their diet centers on prey fish such as salmon, menhaden, anchovy, sea bass, herring, mackerel, hake, cod, whiting, and flatfish, along with occasional shrimp, crabs, mollusks, octopus, and squid; some populations have also been recorded attacking and eating several kinds of ducks. Mating is thought to be polygamous and both courtship and mating happen underwater, with males reported to gather below the surface, roll onto their backs, put their heads together, and call to attract receptive females.

Females give birth once a year after a gestation of around nine months, reaching sexual maturity at a mean age of 3.72 years and giving birth for the first time at a mean age of 4.64 years. Pups are born well developed, able to swim and dive within hours, and weigh up to 16 kg (35 lbs) at birth; they nurse for three to four weeks on rich, fatty milk and can roughly double their weight before weaning. Mothers are the sole caregivers, and lactation lasts 24 days, after which a female mates again almost immediately. Pregnancy rates were measured at 92% between ages 3 and 36, with reduced reproductive success after age 25. Harbor seals are generally more vocally reserved than many other pinniped species, though they do use non-harmonic calls to hold breeding territories, attract mates, and communicate between mothers and pups.

Range and habitat

Harbor seals occur along temperate and Arctic coastlines throughout the Northern Hemisphere, in the northern Atlantic and Pacific oceans and the Baltic and North seas. Along the Pacific Coast, they range the length of California and north through Oregon, Washington, British Columbia, and Alaska, staying close to shore in subtidal and intertidal zones and often venturing into bays, estuaries, and coastal rivers. On the Atlantic Coast, their historical range stretched from the mouth of the St. Lawrence River and Greenland south to North Carolina, more than 1,600 km (990 mi), though hunting and heavy pollution eliminated them from much of the U.S. Northeast by the twentieth century. Since the Clean Water Act era, seals have returned to cleaned-up waters including New York Harbor and Boston Harbor, and they are now regularly sighted as far south as the barrier islands of North Carolina, with Massachusetts marking the southernmost known pupping areas on the Atlantic Coast.

Preferred haulout and resting sites range from rugged rocky coasts to sandy beaches and estuaries, and the species requires places protected from bad weather and predators near a foraging area. Harbor seals must spend significant time onshore for molting shortly after the breeding season, and this onshore time can be disrupted by heavy human presence near known haulout sites.

Conservation status

The harbor seal is rated Least Concern (LC) by the IUCN, with a global population of 350,000 to 500,000, though some regional populations are exceptions to the overall stable trend. The freshwater subspecies known as the Ungava seal, found in Northern Quebec, is considered endangered. Historic threats included widespread commercial and bounty hunting along both U.S. coasts and severe pollution in harbors such as New York and Boston; sealing is now illegal in many nations across the species' range, though killing seals perceived as threats to fisheries remains legal in Norway and Canada. In the United States, the Marine Mammal Protection Act of 1972 prohibits killing any marine mammal, and disease outbreaks, especially phocine distemper virus, along with bycatch in fishing gear, remain ongoing pressures on some populations.