Harbor Seals, Phoca vitulina
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Description & Behavior
Harbor seals, Phoca vitulina (Linnaeus, 1758), are the most common seal species and contain 5 subspecies. Alaskan and western Pacific harbor seals are significantly larger than seals in the Atlantic and southern areas of the eastern Pacific. Generally, adult males measure 1.4-1.9 m in length and weigh 55-170 kg, while the slightly smaller adult females measure 1.2-1.7 m in length and weigh 45-105 kg. The coat consists of thick, short hairs ranging in color from white with dark spots to black-dark brown with white rings on the dorsal side. These patterns are unique to each seal, which helps to identify individuals during observational studies. In the San Francisco Bay area, harbor seals often have reddish coats caused by iron oxide deposits in their coat, the cause for which is unknown.
Their pectoral flippers have 5 webbed digits with claws used for scratching, grooming, and defense. Their hind flippers also have 5 digits, but these vary in length. The 1st and 5th digits are long and wide and the middle digits are short and thin. Their hind flippers are used to propel the seals forward using a side to side motion. These seals also move by undulating their body on land.
Male harbor seals live an average of 20 years of age compared to the female life span of 25-30 years.
World Range & Habitat
Harbor seals are also the most widely distributed pinniped. They are found in temperate, subarctic, and arctic coastal areas on both sides of the North Atlantic and North Pacific oceans. Five separate subspecies have been identified, each common to a specific coastal region.
The 5 subspecies include:
- Eastern Atlantic harbor seals, P. vitulina vitulina (Linnaeus, 1758), (aka the common seal) has an estimated population size of 88,000-93,000 and is found in Svalbard, Iceland, the British Isles, the southwestern Baltic Sea, and on western European coasts from northern Norway to France, including the Kattegat and Skagerrak. A few individuals have been found wandering as far south as Portugal.
- Western Atlantic harbor seals, P. vitulina concolor (DeKay, 1842), is found from the eastern Canadian Arctic and Greenland down to New Jersey, with individuals occasionally found wandering as far south as Florida. There is no reliable population estimate for the small Greenland population, but the American and Canadian populations are thought to total about 60,000-70,000 seals.
- Eastern Pacific harbor seals, P. vitulina richardii (Gray, 1864), consists of an estimated 285,000 seals, distributed from the Pribilof and Aleutian Islands in Alaska as far south as Baja California.
- Western Pacific harbor seals, P. vitulina stejnegeri (Allen, 1902), (aka Kuril or insular seal) is a small population, <4,000 seals, ranging from the western Aleutian and Commander Islands south to the Kuril Islands and Hokkaido.
- Ungava seals, P. vitulina mellonae (Doutt, 1942), (aka Lacs des Loups Marins harbor seal), lives in freshwater lakes and rivers on the Ungava peninsula of northern Quebec. This subspecies feeds exclusively in freshwater and is the only known harbor seal to live in freshwater year round. The number of Ungava seals is unknown but is estimated to be 100-600 individuals.
Harbor seals are found in groups only during haulouts for breeding and molting. Aggressive behavior is demonstrated by growling and snorting, which only occurs when threatened, waving foreflippers, and thrusting the head.
Population estimates are poor, however the global population is estimated at 400,000-500,000 seals.
There is much variation in the appearance, physiology, and behavior of harbor seal species. They generally haulout in small scattered groups, although in protected bays and estuaries haulouts can number over 1,000 individuals. Ungava seals haulout in small groups during spring but alone or in pairs at the end of summer. A variety of habitats are used for hauling out, including rocky shores, reefs, sand and gravel beaches, intertidal mud and sand bars, piers, and, ice floes. Haulout sites are selected for protection from land predators, access to deep water and proximity to food sources, and protection from wind and waves. It is thought that harbor seals haul out in groups for protection against land predation.
The timing of haulouts is often dependent on tidal cycles so that seals can haulout during low tide. In the absence of tides, the time of day is the major influence on harbor seal haulout behavior. Haulouts are most common during warmer months. Individuals of the species tend to stay in the same area all year round, however juveniles are known to travel long distances up to 500 km to feed. Harbor seals tend to stay within 25 km of the shore but individuals are occasionally found 100 km or more offshore.
The time of year and duration for molting varies between populations and subspecies, and also varies within populations with individuals of varying age, sex, and reproductive status. Harbor seals haul to molt for an average of 12 hours each day compared to 7 hours per day when they are not molting. The metabolism of harbor seals is reduced while they are molting, therefore less time is needed foraging for food in the water.
Feeding Behavior (Ecology)
Harbor seal diets vary seasonally and regionally. They primarily feed on crustaceans, mollusks, squid, and fish. The food is torn into chunks and swallowed whole. The molars crush shells and crustaceans for swallowing, but food is generally not chewed. Adults consume 5-6% of their body weight or 4.5-8.2 kg of food per day. The diet of Ungava seals has not been well studied, but they are known to prey on salmonids such as small brook trout. Feeding usually takes place near the shore in shallow water <200 m deep, most often <100 m for periods of a few minutes. However, harbor seals have sometimes been known to dive more than 500 m for more than 25 minutes.
Most male harbor seals reach sexual maturity at 5-6 years of age at a weight of about 75 kg. Females reach sexual maturity earlier at 2-5 years or 50 kg. Mating season varies between subspecies, but generally in the warmer months. Females are ready to breed about 6 weeks after they give birth. The gestation period lasts between 9-11 months, and usually only 1 pup is born each year measuring 70-100 cm in length and weighing 8-12 kg.
Unlike other seal species that molt after they are born, many harbor seal pups are born with their adult coat, having shed their light-colored woolly coat before birth. Some pups however, most often pups of younger mothers, are born with their pre-natal coat and molt shortly after birth.
Harbor seal can crawl and swim almost immediately after they are born, often within an hour of birth, which is useful for pups born in intertidal areas. Pups are nursed mostly on land but also in water for about 4 weeks during which time they will gain 0.5-0.7 kg per day. The mother makes short feeding trips while she is nursing, for longer periods of time as she begins to wean, which is either abrupt or gradual. After weaning, pups disperse often traveling long distances like other seal pup species.
Unlike other seal species, mating takes place primarily in the water. Adult males gather in potential breeding areas and compete by performing aquatic displays, underwater vocalizations, and fighting takes place as demonstrated by neck wounds commonly seen during the breeding season. Some researchers believe that the males maintain underwater territories. Males lose up to 25% of their body weight during the breeding season from the energetic requirements of competing and breeding.
Pupping and Molting seasons:
- Eastern Atlantic - Pupping: June to mid-July. Molting: June-September.
- Western Atlantic - Pupping: mid-May to July. Molting: July-August.
- Eastern Pacific - Pupping: February-March in Mexico, March-June in California, and progressively later northwards up to British Columbia and Washington (June-September). May-July in Alaska. Molting: May-October, progressively later for northern populations. July-August in Alaska.
- Western Pacific - Pupping: mid-May to July.
- Ungava seals - Pupping: mid-April to mid-May.
Conservation Status & Comments
Harbor seals are hunted primarily for their skins, oil, and meat. Their tendency to remain in the same area year-round puts them at greater risk for hunting. The Lake Ontario population was exterminated by the early 1800s, and the Greenland, Hokkaido, and Baltic Sea populations are currently under severe threat. In the Gulf of Alaska, populations have declined dramatically during the last 20-30 years.
Harbor seals are thought by a few to "compete" with commercial fisheries for food sources and unfortunately this myth results in many harbor seals being killed by humans needlessly. Like other seal species, Harbor seals are threatened by entanglement in fishing nets, particularly in gillnet fisheries. Like the gray seal, it is apparently legal to shoot harbor seals to protect fisheries or fish farms in several countries, such as Canada, Norway, and the United Kingdom. Reporting shootings is not required in the United Kingdom under the "Fisheries Defence Clause" of the Conservation of Seals Act and therefore the scale of shootings in the U.K. is uncertain. Official statistics show that more than 60 harbor and gray seals were "legally" shot by Scottish fishery boards during the year 2000, the most in more than a decade. The estimates by conservationists, however, number several thousand seals shot under the Fisheries Defence Clause each year in Scotland. Conservation groups are also promoting the development and use of humane non-lethal seal deterrents such as anti-predator nets on fish farms for this species as well. In addition, the transition from open sea cage fish farms to land-based closed loop systems is being encouraged. Illegal killing of harbor seals also takes place throughout the species' range.
Like other seal species, harbor seals are also blamed for reduced fish stocks and culls are requested. Culling of seal populations has not been proven effective given the complexity of the marine food web and would likely have the opposite effect. Overfishing, habitat destruction, and marine pollution are the more likely candidates to blame for reduced fish stocks. In fact, many harbor seal populations are only recently recovering from bounty schemes and culling operations that ended in the 1970s.
Like other seal species, harbor seals are threatened by environmental contaminants such as organochlorine pesticides which harm their immune systems and decrease reproductive capacity. Oil and hydrocarbon contamination is also significant in harbor seal populations. Harbor seals have also been killed by being trapped in the intake pipes of power plants in the United States.
Diseases also threaten some harbor seal populations. Brucellosis has been documented in harbor seals in both California and Washington State. A new virus that was similar to a bovine pneumonia was also reported in harbor seals in Point Reyes, California following the sudden death of over 100 seals during a 3-month period in 1997. The eastern Atlantic harbor seal experienced an epizootic (an outbreak of disease affecting many animals of one kind at the same time) of phocine distemper virus (PDV) in 1988. A virus similar to canine distemper virus killed more than 18,000 seals from the Kattegat to the North Sea, through the Wadden Sea, because of secondary infections, particularly bacterial pneumonia. It is thought that the virus was transmitted to harbor seals by harp seals. In New England between 1979-1980, about 445 harbor seals, mostly juveniles, died of acute pneumonia due to an Influenza A virus of avian origin.
Human activity has also caused problems in harbor seal populations near coastal areas where activities such as vessel traffic, development, and recreation take place. Pup mortality can increase in such areas because of separation or abandonment, and haulouts that experience disturbance may be abandoned completely.
Hunting of harbor seals still takes place in Iceland and Norway. The Baltic Sea population was severely depleted in the 20th century by hunting, pollution, and the PDV virus. In 1998, a survey estimated only 580 harbor seals were left in the Baltic Sea, with no detectable increase in the population size since 1994. The eastern Atlantic harbor seal is listed as an Appendix III species under the Bern Convention, and the subpopulations in the Baltic and Wadden Seas are listed as an Appendix II species under the Bonn Convention. The species is also listed as a protected species under Annex II and Annex V of the European Community's Habitats Directive, and several important sites for the harbor seal have been proposed in EC member countries as Special Areas of Conservation.
Western Atlantic harbor seals: Fisheries and aquaculture-related mortality of this subspecies is high. An estimated average total of 873 seals were killed each year by fisheries in the United States between 1994 and 1998 by entanglement in nets in the Gulf of Maine. In Canada, harbor seals are entangled in nets of groundfish and salmon gillnet fisheries. A number of seals have also been entangled in nets of the Spanish deep water trawl fishery off Canada. When the Greenland salmon gillnet and Atlantic Canada cod trap fisheries ended in 1993, the number of entanglements decreased. The Canadian government has implemented a pilot program to allow aquaculture installations to shoot seals. Inuit natives also kill small numbers of seals in Canada.
The seal population in Greenland is also vulnerable to hunting and disturbance. Populations there are declining even in protected areas. The harbor seal is prized by locals for its meat and fur, and in fact, harbor seal skin is part of Greenland's national costume.
Increased sightings of various seal species, including harbor seals, have recently been reported along the eastern seaboard of the United States possibly due to a cleaner habitat and/or reduced hunting. Increased commercial fishing may also be forcing seals to migrate further south in search of food. A number of seals in need of rescue were reported, mostly undernourished pups and injured adults.
Eastern Pacific harbor seals: There has been a significant decline in the harbor seal population in the Gulf of Alaska and the Aleutian Islands since the 1970s. Tugidak Island and Prince William Sound populations have decreased by 90%. The cause for this decline is unknown, and is suspected to be associated with decreases in the Steller's sea lion and northern fur seal populations in the region. The Bering Sea population is thought to be declining, however populations from California to Washington are either stable or increasing slightly.
The species is preyed upon by orca (killer whales) and sharks. Polar bears are known to be predators of Western Atlantic harbor seals. Pups may also be preyed on by coyotes, foxes, and large birds of prey. Harbor seals in the Pacific are known to be killed by Steller's sea lions.
El Niño events can decrease food availability which impacts harbor seal populations. For example, reproductive activity was reduced by half in Point Reyes, California during the 1997-98 event.
Alaskan native subsistence hunting of harbor seals is estimated at more than 2,500 seals each year. Northwest Indian tribes are developing regulations for the ceremonial and subsistence killing of harbor seals, and plans for commercial hunting of the species was reported by one tribe.
In 1999, the U.S. federal National Marine Fisheries Service recommended that the Marine Mammal Protection Act be amended to authorize state and federal wildlife managers to kill harbor seals preying on endangered fish species in Washington, Oregon, and California. Authority to kill seals that pose a threat to public safety and property at locations such as docks and marinas was also recommended as well as authority for commercial fishermen to kill seals that destroy their catch or gear, a policy that was withdrawn in 1994. Conservation groups argue that effective and humane non-lethal deterrence methods should be developed and that the problem of overfishing should be addressed.
The Exxon Valdez oil spill in Prince William Sound, Alaska killed an estimated 33% of the harbor seal populations using haulout sites contaminated by the oil spill. The seals were coated with oil and suffered from the inhalation of volatile substances and oil absorption into seal tissue resulting in abnormal behavior and pathological brain damage.
In March 2001, the California Coastal Commission approved an application by the San Diego City Council to renew the 0.4 hectare Seal Rock Marine Mammal Reserve established in 1994 in La Jolla for another five years. The California Coastal National Monument was created in 2000 providing federal protection to the species' habitat on thousands of islands, rocks, exposed reefs, and pinnacles up to 19 km offshore along the California coast.
The harbor seal population in Mexico is fully protected under the Ley General de Vida Silvestre NOM-059-ECOL-1994 which forbids the killing, collecting or possession of the species or any part or product obtained from the species. Unfortunately, harbor seals are still killed as bait for sharks by long-line fishermen in Baja California.
Western Pacific harbor seals: Due to entanglement in fishing nets, particularly salmon trap nets, the small population in Hokkaido, estimated at 300-400 seals, is threatened by a mortality rate that exceeds the birth rate. Pollution is also a problem.
Ungava (harbor) seals: Ungava harbor seals are cited as Vulnerable by the Committee on the Status of Endangered Wildlife in Canada, which describes them as a "unique endemic subspecies of Harbor seals with limited range and low numbers, making it vulnerable to human impact and natural catastrophic events." The population currently has minimum legal protection in Canada and none of its habitat is protected, but fortunately the Québec government is considering legal protection for part of the habitat. The Ungava seal is listed as Lower Risk on the IUCN Red List.
References & Further Research
Seal Conservation Society (SCS): Harbour Seal, Phoca vitulina
Alaska Harbor Seal Census - Feature Article OND1999
Coastal Research and Education Society of Long Island
David Hall's Encounters in the Sea
Sable Island Green Horse Society
Research Phoca vitulina » Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library [audio / video] ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS
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