About The Species
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.
State-financed bounty hunters once hunted harbor seals in Washington and Oregon because they were considered competitors of fishermen. This hunting program ended in 1960.
Harbor seals, like all marine mammals, are protected under the Marine Mammal Protection Act.
In the United States, NOAA Fisheries has identified five stocks of harbor seals: Alaska, California, Oregon-Washington coastal, Washington inland, and western North Atlantic. Each stock has experienced different population trends over the past 30 years. Along the West Coast, stocks are stable and some are even increasing. The population in New England is also increasing. Breeding and molting colonies can number in the thousands in these areas.
Most stocks in Alaska are also stable or slightly increasing, but the Gulf of Alaska stock is small today compared to the 1970s and 1980s. This stock may be continuing to decline.
- Throughout Its Range
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, or a dark background with light rings.
Behavior and Diet
Harbor seals haul out (rest) on rocks, reefs, beaches, and drifting glacial ice at night and during the day. They haul out to regulate their body temperature, molt, interact with other seals, give birth, and raise their pups. They 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. Instead, they move by undulating in a caterpillar-like motion. This 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. Mother harbor seals 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. They occur on the U.S East and West coasts. On the East Coast, harbor seals are found from the Canadian Arctic to New York and occasionally as far south as the Carolinas. Harbor seals are found all along the West Coast of North America, from California to the Bering Sea. They have long been considered non-migratory and typically stay within 15 to 31 miles of home, but telemetry data have shown they sometimes travel 62 to 249 miles from their tagging location.
Lifespan & Reproduction
Harbor seals reach sexual maturity between 3 and 7 years old and mate in the water. While females usually give birth during the spring and summer, the pupping season varies by location. 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 coast of Washington.
Females are pregnant for about 10 months. Pups weight about 24 pounds at birth and are ready to swim within minutes. They are nursed for 4 to 6 weeks on milk that is 50 percent fat. Like adults, seal pups haul out on shore to rest and regulate their body temperature. Mothers and pups group together in nurseries to protect themselves from predators.
Harbor seals can become entangled in fishing gear and other types of marine debris, either swimming off with the gear attached or becoming anchored. They can become entangled in many different 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 and swim with attached gear for long distances, ultimately resulting in fatigue, compromised feeding ability, or severe injury, which may lead to reduced reproductive success and death.
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 disturbance, can degrade important nursery areas for harbor seals. Increased vessel traffic can also cause altered behavior, increased energetic expenditures, and increased exposure to stress. In Alaska, vessel traffic can also displace seals from ice floes, putting pups at risk from increased time spent in cold water and separated from their mothers.
Harbor seals are susceptible to habitat destruction and degradation. This can range from physical barriers that limit their access to important migration, breeding, feeding, or pupping areas, to activities that destroy or degrade their habitats. Physical barriers may include shoreline and offshore development (oil and gas exploration, dredging, pile driving) and increased boat traffic. Recreational use of marine areas, including resort development and increased boat traffic, may displace seals that would normally use those areas.
Contaminants enter ocean waters from many sources, including oil and gas development, wastewater discharges, urban runoff, and other industrial processes. Once in the environment, these substances move up the food chain and accumulate in predators near the top of the food chain such as harbor seals. Because of their blubber stores, harbor seals accumulate these contaminants in their bodies, threatening their immune and reproductive systems.
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 ship traffic.
Harbor seals are protected under the Marine Mammal Protection Act. In the United States, NOAA Fisheries works to protect all populations of harbor seals.
NOAA Fisheries is committed to the protection of harbor seals. Targeted management actions taken to secure protections for these seals include:
Harbor seals are vulnerable to chemical contaminants because they are near the top of the food chain. NOAA's Damage Assessment, Remediation, and Restoration Program, which cleans up existing contamination, has several active projects in the Pacific Northwest and California.
Educating the Public
Some harbor seals haul out in public areas. Together with the West Coast Marine Mammal Stranding Network, we have developed programs to educate the public about how to “Share the Shore” with harbor seals, as well as prohibitions against capturing, harming, or harassing them.
Implementing Oil Spill Response Plans in the Event of a Spill
Harbor seals are at risk of harm in the event of an oil spill. To reduce the risk of a spill, Washington’s Department of Ecology created the Spill Prevention, Preparedness, and Response Program. To minimize the effect of a potential spill on harbor seals, NOAA developed the Marine Mammal Oil Spill Response Guidelines.
Overseeing Marine Mammal Health and Stranding Response
We work with volunteer networks in all coastal states to respond to marine mammal strandings. When stranded animals are found alive, NOAA Fisheries and our partners assess the animal’s health. When stranded animals are found dead, our scientists work to understand and investigate the cause of death. Although the cause often remains unknown, scientists can sometimes identify strandings due to disease, harmful algal blooms, vessel strikes, fishing gear entanglements, pollution exposure, and underwater noise. Some strandings can serve as indicators of ocean health, giving insight into larger environmental issues that may also have implications for human health and welfare.
Reducing Vessel Strikes
Collisions between harbor seals and vessels can injure or kill seals. The most effective way to reduce vessel disturbance is for vessels to stay away from seals. If this is not possible, the second-best option is for vessels to follow voluntary approach guidelines.
In Alaska, for example, we have issued voluntary approach guidelines to reduce the disturbance of harbor seals in glacial fjords. Tidewater glacier areas provide essential habitat for harbor seals, especially when nursing pups and molting. Scientific research indicated that previous marine mammal approach measures (voluntary guidelines to avoid approaching within 100 yards) were not adequately protecting harbor seals from disturbance in Alaska’s glacial fjords. Because glaciers in Alaska are experiencing unprecedented rates of ice loss, harbor seals are already coping with reduced ice cover at some tidewater glaciers, which makes them more sensitive to other impacts.
For these reasons, NOAA developed the Alaska Harbor Seal Approach Guidelines in Glacial Fjords (PDF, 2 pages). The guidelines suggest that all vessels (from kayaks to cruise ships) should:
- Strive to maintain 500 yards from seals without compromising safe navigation.
- Make an approach plan to avoid surprising seals.
- Be equally as cautious to reduce disturbance when departing the fjord as arriving.
- Minimize wake, avoid abrupt changes in course or engine pitch, and avoid loud noises (such as collisions with ice) near seals.
- Try to avoid traveling through thick ice, as the absence of seals on the ice does not mean the area is not being used.
- Time visits when feasible to minimize overlap with the peak numbers of seals hauled out midday and minimize the chances of disturbance.
Providing Sustainable Harbor Seal Subsistence
As the primary consumptive users of Alaska harbor seals, Alaska Natives are committed to a long-term, sustainable harvest of harbor seals for food and handicrafts. Their long history of self-regulation coupled with their rich oral tradition and day-to-day contact with Alaska harbor seals gives them special insights into and knowledge of this important marine mammal.
Key Actions and Documents
Incidental Take Authorization: Astoria Waterfront Bridge Replacement Project in Astoria, OR (Phase 2, 2019)
Incidental Take Authorization: U.S. Army Corps of Engineers North Jetty Maintenance and Repairs Project, Coos Bay, Oregon
Incidental Take Authorization: Skipjack Offshore Energy, LLC Marine Site Characterization Surveys off of Delaware and Maryland
NOAA Fisheries conducts various research activities on the biology, behavior, and ecology of harbor seals. The results of this research are used to inform management decisions for this species.
In the Aleutian Islands of Alaska, NOAA Fisheries scientists and their collaborators track location data from satellite tags deployed on harbor seals to determine their movement and distribution, as well as their diving and haul-out behavior.
In Washington, NOAA Fisheries conducts observational studies to understand the life history and population dynamics of harbor seals in Puget Sound. Our scientists have continually monitored this population since 1993.
Determining the size of harbor seal populations helps resource managers determine the success of conservation measures. Our scientists collect population information and present the data in annual stock assessment reports.
Monitoring Population Abundance and Distribution
Scientists observe harbor seals to record their numbers and distribution. By comparing numbers collected over multiple years, scientists can look for trends—i.e., whether the population is increasing, decreasing, or remaining stable during a given period.
Alaska Fisheries Science Center Harbor Seal Research
The Cook Inlet and Kodiak Marine Mammal Disaster Response Guidelines (CIKMMDRG) build upon the…
This summary will provide an update on NOAA-AFSC’s latest research on seal-vessel interactions…
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NOAA Fisheries is not operating the Alaska Marine Mammal Observer Program (AMMOP) due to a lack of available resources to fund additional observations of the southeast Alaska salmon drift gillnet fishery. We will reassess future AMMOP activities as