Harbor seals in Chatham MA - Photo: NOAA Fisheries
Harbor seals in Chatham MA - Photo: NOAA Fisheries
About the Species
Harbor seals in Chatham MA - Photo: NOAA Fisheries
Harbor seals in Chatham MA - Photo: NOAA Fisheries
Harbor seals are one of the most common marine mammals along the U.S. West and East Coasts. They are commonly seen resting on rocks and beaches along the coast and on floating ice in glacial fjords with their head and rear flippers elevated in a “banana-like” position. They feed primarily on fish in marine and estuarine waters, but also in rivers and freshwater lakes. Harbor seals are important indicators of a clean and healthy coastal marine ecosystem. They are a nutritional and cultural resource for Alaska Native communities, and are one of many natural attractions that draw visitors and commerce to US coastal states.
State-financed bounty hunters once hunted harbor seals in Alaska, Washington, Oregon, Massachusetts, and Maine because they were considered competitors of the fishing industry. This hunting program ended in 1960. Since ending of those programs, along with passage of the Marine Mammal Protection Act in 1972, many harbor seal populations in the US have seen positive growth.
Harbor seals, like all marine mammals, are protected under the Marine Mammal Protection Act, with other species also protected under the Endangered Species Act.
Population Status
In the United States, NOAA Fisheries has identified 18 stocks of harbor seals. Twelve of these stocks are in Alaska, and the others include California, Oregon-Washington coastal, three stocks within Washington inland waters, and the eastern USA/Canada stock (which is part of a complex North Atlantic population structure). In Alaska, there are the Aleutian Islands, Pribilof Islands, Bristol Bay, Cook Inlet/Shelikof Strait, SouthNorth Kodiak, NorthSouth Kodiak, Prince William Sound, Glacier Bay/Icy Strait, Lynn Canal/Stephens Passage, Sitka/Chatham Strait, Dixon/Cape Decision, and Clarence Strait stocks. The Bristol Bay stock in Alaska includes a small population of freshwater harbor seals that live in Iliamna lake, located in Southcentral Alaska.
Each stock has experienced different population trends over the past 30 years. Along the West Coast, stocks either show some fluctuations with no obvious trend or are growing ; the population in New England appears to be stable. Individual breeding and molting colonies can number in the thousands in some of these areas. While most of the 12 harbor seal stocks in Alaska were stable or increasing over the 8 years between 2011 and 2018, seals in the Aleutian Islands, Glacier Bay, and Icy Strait regions likely declined. There is a small but apparently stable population of less than 500 harbor seals in the Pribilof Islands.
Learn more about our estimates for population size in our stock assessment reports
Appearance
Harbor seals are part of the true seal family. All true seals have short forelimbs, or flippers. They also lack external ear flaps and instead have a small hole (opening to the ear canal) on either side of their head.
Harbor seals weigh up to 285 pounds and measure up to 6 feet in length. Males are slightly larger than females, and seals in Alaska and the Pacific Ocean are generally larger than those found in the Atlantic Ocean.
Harbor seals have short, dog-like snouts. The color of each seal’s fur varies but there are two basic patterns: light tan, silver, or blue-gray with dark speckling or spots, and a dark background with light rings. Harbor seals molt (shed hair) in the mid to late summer for 1-2 months, spending more time out of the water.
Behavior and Diet
Harbor seals haul out (rest) on rocks, reefs, beaches, and drifting glacial ice when they are not traveling and/or foraging at sea. They haul out to regulate their body temperature, molt, interact with other seals, give birth, and nurse their pups. These seals also haul out in groups to avoid predators and spend less time being watchful for predators than those that haul out alone.
Harbor seal pelvic bones are fused, preventing them from moving their hind flippers under their pelvis to walk on land like sea lions. Instead, they move by undulating in a caterpillar-like motion. If you observe this behavior, it does not mean they are injured.
Harbor seal pups can swim at birth. They can also dive for up to 2 minutes when they are only 2 to 3 days old and by the end of their first month of life embark on journeys of over 100 miles from their natal area. Mother harbor seals sometimes raise their pups in nurseries—groups of mothers and their young—that help protect the seals from predators.
The harbor seal’s diet consists mainly of fish, shellfish, and crustaceans. Harbor seals complete both shallow and deep dives while hunting, depending on the availability of prey. They can sleep underwater and come up for air once every 30 minutes.
Where They Live
Harbor seals live in temperate coastal habitats along the northern coasts of North America, Europe, and Asia, occurring as far north as 78° N. They occur in the U.S. East and West coasts. On the eastern North America Coast, harbor seals are found from the Canadian Arctic to the Mid-Atlantic. Harbor seals are found all along the West Coast of North America, from Baja California, Mexico to the Bering Sea. They have long been considered non-migratory and typically stay within 15 to 31 miles of their natal area, but tracking data have shown they sometimes travel 62 to 486 miles from their tagging location, often to exploit seasonally available food or give birth to pups.
World map providing approximate representation of the harbor seal range
Lifespan & Reproduction
Harbor seals reach sexual maturity between 3 and 7 years old. While females usually give birth during the spring and summer, the pupping season varies by location. Along the West Coast, pups are born earlier in the south than in the north. The only exception is harbor seals in the inland waters of Washington, which are born 2 months later than seals along the outer coast of Washington.
Harbor seals mate in the water. Females are pregnant for about 10 months, though a viable embryo exists for about 2 months prior to implantation and growth. Pups weigh about 24 pounds at birth and are ready to swim within minutes. They nurse for 4 to 6 weeks on milk that is 50 percent fat. Like adults, seal pups haul out to rest and regulate their body temperature. Adult females forage during lactation.
Threats
Entanglement
Harbor seals can become entangled in fishing gear, either swimming off with the gear attached or becoming anchored. They can become entangled in many different fishing gear types, including gillnets, trawls, purse seines, or weirs. Once entangled, seals may drown if they cannot reach the surface to breathe, or they may drag attached gear for long distances as they swim, ultimately resulting in fatigue, compromised feeding ability, or serious injury, all of which may lead to reduced reproductive success and even death. Other types of marine debris, such as packing bands, may be encountered on shore, leading to entanglement around the head and neck, which may cause serious injury and death from wounds, additional energy expenditure, and drowning.
Illegal Feeding and Harassment
Illegal feeding of harbor seals can lead to many problems including habituation, aggression, negative impacts to fisheries, entanglement, injury, and death. Harassment, including repeated exposure to vessel traffic and other disturbance, can degrade important nursery, molting, and haul out areas for harbor seals. Increased vessel traffic can also cause altered behavior, increased energetic expenditures, and increased exposure to stress. For example, in Alaska, vessel traffic can displace seals from glacial ice, putting pups at risk from increased time spent in cold water and separation from their mothers.
Learn more about the Alaska harbor seal approach guidelines in glacial fjords (PDF, 2 pages)
Habitat Degradation
Harbor seals are susceptible to habitat loss and degradation. Physical barriers, which may include shoreline and offshore structures for development (e.g., for oil and gas, dredging, pile driving), can limit access to important migration, breeding, feeding, molting, or pupping areas. Oil and gas development, commercial and recreational development (including resort development), and increased vessel traffic may displace seals or their prey that would normally use those areas. Seals that rest, rear pups and molt on glacial ice in Alaska’s fjords are vulnerable to unprecedented loss of glacier mass and diminishment of their essential floating ice habitat.
Chemical and Microplastic Contaminations
Contaminants enter ocean waters from many sources, including oil and gas development, wastewater discharges, agricultural and urban runoff, and other industrial processes. Once in the environment, these substances move up the food chain and accumulate in top predators such as harbor seals. Many of these chemicals and microplastics do not degrade, degrade very slowly, or degrade into more harmful compounds. Harbor seals accumulate contaminants, which threaten their immune and reproductive systems, in their blubber, blood, and organs (for example, liver or brain). These chemicals and microplastics can be passed from mothers to pups during pregnancy and in milk. In addition to direct effects on seal health, these contaminants may have implications for humans that rely on seals for subsistence.
Vessel Collisions
Inadvertent vessel collisions can injure or kill harbor seals. Harbor seals are vulnerable to vessel collisions throughout their range, but the risk is much higher in some coastal areas with heavy vessel traffic.
Scientific Classification
| Animalia |
Chordata |
Mammalia |
Carnivora |
Phocidae |
Phoca |
vitulina |
Last updated by NOAA Fisheries on 04/18/2025
