Harbor Seal (Phoca vitulina): Facts, Diet and Habitat

What does a harbor seal look like?

Harbor seals belong to the true seals, or earless seals (family Phocidae). Like all true seals, they have no external ear flaps, only a small ear opening behind each eye, and short front flippers with strong claws. Their hind flippers point backward and cannot be turned under the body, so on land they move by hunching along on their bellies like a caterpillar. The seal vs sea lion comparison explains how this sets them apart from sea lions.

The head is round, with a short, dog-like snout, large dark eyes, long whiskers and V-shaped nostrils that close tightly underwater. The coat is short and spotted, but the colors vary a lot. Most seals have one of two basic patterns: a light silver, tan or blue-gray background with dark spots, or a dark background with pale rings. Each seal’s pattern is unique, which allows researchers to recognize individuals from photographs. In San Francisco Bay, some harbor seals are partly or fully reddish, possibly because of trace elements such as iron or selenium in the water.

On land, harbor seals often rest with the head and hind flippers raised, in a curved posture that NOAA describes as banana-like. In Europe they are most often confused with the larger gray seal, which has a long, straight “Roman” nose, while the harbor seal has a smaller head with a rounded forehead and a short muzzle.

How big is a harbor seal?

Harbor seals are medium-sized seals. Males are only a little larger than females, and Pacific harbor seals are generally bigger than Atlantic ones. In Alaska, for example, adults average about 82 kg (180 lb).

A newborn pup weighs about 8–16 kg (18–35 lb), usually around 11 kg (24 lb). Weight changes through the year. Seals put on blubber when food is plentiful and lose weight during the breeding season and the summer molt. That layer of fat under the skin keeps them warm in water that is often only a few degrees above freezing.

Where do harbor seals live?

The harbor seal has the largest range of any seal. In the North Atlantic it lives along the coasts of Europe from northern France and the British Isles to Norway, Iceland and Svalbard, where some colonies live at about 78° N, and in the Baltic and North Seas. In the western Atlantic it ranges from Greenland and the Canadian Arctic to New England, and young seals regularly winter as far south as the Carolinas. In the Pacific it is found from Hokkaido in Japan through the Aleutian Islands and Alaska to Baja California in Mexico.

Scientists divide the species into several subspecies, including the eastern Atlantic, western Atlantic and Pacific forms. One unusual population, the Ungava seal, lives year-round in freshwater lakes in northern Quebec, and a small group of harbor seals also lives in Iliamna Lake in Alaska.

Harbor seals stay close to the coast, usually within about 20 km (12 mi) of shore. They haul out on rocky ledges, sandbanks that appear at low tide, mudflats, beaches, harbor floats and, in Alaska, floating ice in glacial fjords. They also swim up estuaries and large rivers. Most adults stay faithful to a few favorite haul-out sites, but tagged seals have traveled several hundred kilometers to follow seasonal food or to give birth.

What do harbor seals eat?

Harbor seals are carnivores that eat mainly fish, usually whatever is common and easy to catch near their haul-outs. Typical prey includes herring, cod, whiting, hake, sand eels, flatfish such as flounder and sole, sculpins, anchovies and salmon. They also take squid, octopus, crabs and shrimp. Diets differ widely from place to place and season to season. A comparison with other seals is in What do seals eat?

Small fish are usually swallowed whole underwater, head first. Seals hunt by sight in clear water, but their sensitive whiskers are just as important. In a famous experiment published in 2001, blindfolded harbor seals followed the invisible wake left by a miniature submarine, showing that their whiskers can track the water movements a swimming fish leaves behind.

Most dives last only a few minutes, typically about 3–7, and many stay in water less than 20 m (65 ft) deep. Harbor seals can go much deeper and longer when needed, with dives to about 500 m (1,640 ft) and of 30 minutes or more recorded. The way they manage this is explained in How long can seals hold their breath?

Behavior: hauling out, resting and calls

Harbor seals spend roughly half their time on land. They haul out to rest, regulate their body temperature, molt, give birth and nurse. At coastal sites their timing follows the tides, with seals gathering on exposed sandbanks and rocks around low tide. Groups can number from a few animals to thousands, but harbor seals are not very social. Resting seals keep some space between them, and in the water they usually travel and feed alone.

They are wary on land. A seal that lifts its head, stares at people or starts moving toward the water is being disturbed, and repeated disturbance can drive seals from a haul-out or separate mothers from pups. In the water, by contrast, they are often curious and may watch people on shore or in boats. Harbor seals can also sleep at sea, floating upright with only the head above the surface or resting underwater and rising to breathe.

Compared with sea lions, harbor seals are quiet. They grunt, growl, snort and slap the water with their flippers. During the breeding season, males make low roaring calls underwater to attract females and warn rivals, and pups call to their mothers with a bleating cry. Harbor seals are also one of the few mammals with clear evidence of vocal learning. The most famous example was Hoover, a harbor seal at the New England Aquarium in Boston in the 1970s and 1980s, who imitated human phrases in a strong Maine accent.

Breeding, pups and lifespan

The pupping season depends on location. Pups are born from about February to April in Baja California and southern California, in May and June in New England, and in June and July in Britain and the Wadden Sea. Pups are born on land or on sandbanks and, unusually among seals, can swim within minutes to hours of birth, often following their mother into the water at the next high tide. Most pups shed their white woolly baby coat before birth, so they arrive with a coat much like an adult’s.

The mother nurses her pup for about 4–6 weeks with milk that is about 50% fat, and the pup roughly doubles its weight. She often feeds at sea during this time and leaves the pup on the beach to wait for her. People who find these pups often think they have been abandoned, as explained in Is a seal pup alone on the beach abandoned?

Mating takes place in the water soon after the pups are weaned. The fertilized egg does not implant for about two months, so the whole pregnancy lasts about 10–11 months and the next pup arrives at the same season a year later. Females usually mature at 3–4 years old and males at 4–5 years.

Harbor seals usually live 20–30 years in the wild, and females outlive males. The oldest wild females on record were about 35–36 years old and the oldest males about 31.

Predators and threats

The main natural predators of harbor seals are orcas and sharks. In the Pacific Northwest and Alaska, mammal-eating orcas take many harbor seals, and great white sharks hunt them off California and, increasingly, off Cape Cod in Massachusetts. In the North Sea and around Scotland, large male gray seals have been found attacking and killing harbor seals.

Disease has caused the biggest sudden losses. Phocine distemper virus, a relative of the measles and canine distemper viruses, killed about 18,000 harbor seals in northern Europe in 1988 and about 21,700 seals, mostly harbor seals, in a second North Sea outbreak in 2002, around half of the local population. In New England, distemper was linked to a large seal die-off in 2018–2020, and bird flu (H5N1) killed harbor and gray seals there in 2022.

People cause other problems:

• Bycatch and entanglement. Seals drown in gillnets and other fishing gear or get caught in packing bands and lost nets.
• Pollution. Chemicals such as PCBs build up in seals, which feed near the top of the food chain.
• Disturbance. Boats, walkers, drones and dogs can flush seals off haul-outs. In Alaska’s fjords, vessel traffic can push mothers and pups off the ice.
• Conflict with fisheries. Seals are still killed legally in some countries to protect fish farms and fisheries, and illegally in others.
• Habitat change. Coastal development and the shrinking of tidewater glaciers remove resting and pupping sites.

Conservation status

The IUCN Red List classifies the harbor seal as Least Concern. Estimates of the world population range from about 350,000 to 500,000 or more animals. Many populations have grown since bounty hunting and commercial sealing ended. In the United States, state-paid bounties on harbor seals ended in 1960, and the Marine Mammal Protection Act of 1972 made it illegal to kill or harass them. Harbor seals have since returned to places they had vanished from, including New York Harbor, where they are again a regular sight in winter.

The overall picture hides some local declines. Numbers in parts of Scotland, including Orkney and the Firth of Tay, have fallen steeply since the early 2000s for reasons still being studied. Populations around Greenland, Hokkaido and the Baltic Sea are small, and the freshwater Ungava seal of Quebec, possibly fewer than 100 animals, is considered endangered in Canada.

Harbor seals and people

Harbor seals are among the easiest marine mammals to see in Europe and North America. Well-known viewing sites include the Wadden Sea coasts of the Netherlands, Germany and Denmark, The Wash and Norfolk coast in England, Iceland’s glacier lagoons, Point Reyes and La Jolla in California, and many harbors in Washington, British Columbia and Maine. They appear in guides such as wild mammals of the UK.

The best way to watch them is quietly, from a distance and with binoculars. NOAA recommends staying at least 50 yards (46 m) away from seals in the United States, and similar codes of conduct apply in Europe. Keep dogs on a leash near haul-outs, never feed seals, and report a seal that looks sick or injured to a local marine mammal stranding network or rescue group instead of approaching it.