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"Common seal" redirects here. For the common seal of a company, see Company seal.

Harbor seal
P. v. vitulina off Lismore, Scotland, 2015
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Suborder: Caniformia
Parvorder: Pinnipedia
Family: Phocidae
Genus: Phoca
Species:
P. vitulina
Binomial name
Phoca vitulina
Subspecies

P. vitulina concolor (DeKay, 1842)
P. vitulina mellonae (Doutt, 1942)
P. vitulina richardii (Gray, 1864)
P. vitulina stejnegeri (J. A. Allen, 1902)
P. vitulina vitulina (Linnaeus, 1758)

Harbour Seal Range

The harbor (or harbour) seal (Phoca vitulina), also known as the common seal, is a true seal found along temperate and Arctic marine coastlines of the Northern Hemisphere. The most widely distributed species of pinniped (walruses, eared seals, and true seals), they are found in coastal waters of the northern Atlantic and Pacific oceans, Baltic and North seas.

Harbour seals are brown, silvery white, tan, or grey, with distinctive V-shaped nostrils. An adult can attain a length of 1.85 m (6.1 ft) and weigh up to 168 kg (370 lb). Blubber under the seal's skin helps to maintain body temperature. Females outlive males (30–35 years versus 20–25 years). Harbor seals stick to familiar resting spots or haulout sites, generally rocky areas (although ice, sand, and mud may also be used) where they are protected from adverse weather conditions and predation, near a foraging area. Males may fight over mates under water and on land. Females bear a single pup after a nine-month gestation, which they care for alone. Pups can weigh up to 16 kg (35 lb) and are able to swim and dive within hours of birth. They develop quickly on their mothers' fat-rich milk, and are weaned after four to six weeks.

The global population of harbor seals is 350,000–500,000, but the freshwater subspecies Ungava seal in Northern Quebec is endangered.[1] Once a common practice, sealing is now illegal in many nations within the animal's range.

Description

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Skull of a harbor seal
Skeleton of a harbor seal in the Seal Museum in Iceland

Individual harbor seals possess a unique pattern of spots, either dark on a light background or light on a dark. They vary in colour from brownish black to tan or grey; underparts are generally lighter. The body and flippers are short, heads are rounded. Nostrils appear distinctively V-shaped. As with other true seals, there is no pinna (ear flap). An ear canal may be visible behind the eye. Including the head and flippers, they may reach an adult length of 1.85 m (6.1 ft) and a weight of 55 to 168 kg (120 to 370 lb).[3] Females are generally smaller than males.

Subspecies

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The five proposed subspecies of Phoca vitulina are:

Image Subspecies Common Name Distribution
P. v. vitulina

(L., 1758)

Eastern Atlantic common seal Europe and northwestern Asia.
P. v. concolor

(DeKay, 1842)

Western Atlantic common seal Inhabit eastern North America. The validity of this subspecies is questionable, and not supported by genetic evidence. They might be part of the Eastern Atlantic subspecies.[4]
P. v. mellonae

(Doutt, 1942)

Ungava seal (Lacs des Loups Marins seals) Found in eastern Canada in fresh water
P. v. richardii

(Gray, 1864)

Pacific common seal Western North America.
Phoca vitulina stejnegeri

(J. A. Allen, 1902)

Insular seal Eastern Asia. Currently not recognised as a separate subspecies, but part of P. v. richardii[5]

Population

[edit]
White harbor seal on moss, Alaska

There are an estimated 350,000–500,000 harbor seals worldwide.[1] While the population is not threatened as a whole, the Greenland, Hokkaidō and Baltic Sea populations are exceptions. Local populations have been reduced or eliminated through disease (especially the phocine distemper virus) and conflict with humans, both unintentionally and intentionally. Killing seals perceived to threaten fisheries is legal in Norway, and Canada, but commercial hunting is illegal. Seals are also taken in subsistence hunting and accidentally as bycatch (mainly in bottomset nets). Along the Norwegian coast, bycatch accounted for 48% of pup mortality.[6] Killing or taking seals has been illegal in the United Kingdom since 1 March 2021.[7]

Seals in the United Kingdom are protected by the 1970 Conservation of Seals Act, which prohibits most forms of killing. In the United States, the Marine Mammal Protection Act of 1972 prohibits the killing of any marine mammals, and most local ordinances, as well as NOAA, instruct people to leave them alone unless serious danger to the seal exists.

In North America

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Pacific Coast

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The California population of subspecies P. v. richardii amounted to about 25,000 individuals as of 1984. Pacific harbor seals or California harbor seals are found along the entire Pacific Coast shoreline of the state. They prefer to remain relatively close to shore in subtidal and intertidal zones, and have not been seen beyond the Channel Islands as a pelagic form; moreover, they often venture into bays and estuaries and even swim up coastal rivers. They feed in shallow littoral waters on herring, flounder, hake, anchovy, codfish, and sculpin.[8]

Breeding occurs in California from March to May, with pupping between April and May, depending on local populations. As top-level feeders in the kelp forest, harbor seals enhance species diversity and productivity. They are preyed upon by killer whales (orcas) and white sharks. Haul out sites in California include urban beaches and from time to time they can be seen having a nap on the beach in all of San Francisco Bay, which would include the conurbation of Richmond, Oakland, and San Francisco, the Greater Los Angeles area, which would include Santa Barbara, the city of Los Angeles itself, and Long Beach, and all of San Diego Bay, most famously beaches near La Jolla.[9][10][11][12][13][14]

Considerable scientific inquiry has been carried out by the Marine Mammal Center and other research organisations beginning in the 1980s regarding the incidence and transmission of diseases in harbor seals in the wild, including analysis of phocine herpesvirus.[15] In San Francisco Bay, some harbor seals are fully or partially reddish in colour, possibly caused by an accumulation of trace elements such as iron or selenium in the ocean, or a change in the hair follicles.[16]

Although some of the largest harbor seal pupping areas are found in California, they are also found north along the Pacific Coast in Oregon, Washington, British Columbia and Alaska. Large populations move with the season south along the west coast of Canada and may winter on the islands in Washington and Oregon. Pupping is known to occur in both Washington and Oregon as of 2020. People are advised to stay at least 50m (164 ft) away from harbor seals that have hauled out on land, especially the pups, as mothers will abandon them when there is excessive human activity nearby.[17]

A Harbor Seal nursery on ice in front of The Grand Pacific Glacier in Glacier Bay National Park, Alaska

Atlantic Coast

[edit]

Historically, the range of the harbor seal extended from the mouth of the St. Lawrence River and Greenland to the sandy beaches of North Carolina, a distance of well over 1,600 km (990 mi). Evidence of their presence in these areas is consistent with both the fossil record as well as a few landmarks named after them during colonisation: Robbin's Reef, off of Bayonne, New Jersey, gets its name from the Dutch word robben, meaning "seals". On the border between Canada and the US is an island known as Machias Seal Island, a place where today the harbor seal will occasionally visit but is now a sanctuary for puffins. Over the course of hundreds of years, however, the seal was wiped out steadily by being shot on sight by fishermen and by massive pollution. The evidence for this is found in documents all along the coast of New England which put a bounty on the head of every seal shot, as well as the accounts of harbormasters. New York City, when it was founded in the 1640s, was founded on top of an enormous estuary teeming with life that included the harbor seal. Oil in the 1800s started the process of pollution that was later compounded by even more toxic 20th century chemicals that included PCB's and dioxin. By the time of the 1972 Clean Water Act, New York Harbor was almost dead-almost no living thing could survive in it.[18] Approximately 500 km (310 mi) to the north, Boston Harbor was equally polluted. Raw sewage had been dumped in the harbor since the late 1800s and the stench of faecal matter in the Charles River was overpowering, as evidenced by the song "Dirty Water" by the Standells, written in 1966. Flatfish, abundant in the area, had enormous tumors in their livers by the 1980s and the harbor seal was long gone, shot to oblivion.[19]

Harbor seal in Svalbard

As of 2020, however, the seals have returned. They never were extirpated from Canada and certain pockets of the Maine coast, and thus an important mother population was created from whence the species could reclaim the home of their ancestors. Currently, they are sighted as far south as the barrier islands of North Carolina on a regular basis,[20] with Massachusetts being the southernmost point of known pupping areas along the Atlantic Coast.[21] Harbor seals move south from eastern Canadian waters to breed along the coast of Maine, Cape Cod, and the South Shore in Massachusetts in May and June, and return northward in fall. Others will head south from these areas to "vacation" in warmer waters, particularly young seals unable to compete with adults for food and territory; they do not return north until spring.

One park ranger in New York City, which is in the centre of its West Atlantic range, says that "New York is like their Miami resort".[18] This refers to the habit of young seals leaving Cape Cod and even some Arctic waters to inhabit the harbor in winter. In 2018 the New York Post reported that the harbor is now "cleaner than it has been in 110 years",[22] and since the first decade of the 21st century, the harbor seal has found the old turf of its ancestors to be a land of plenty and the water to be livable. Within sight of the New York skyline, known colonies of harbor seals are found on Hoffman[23] and Swinburne Islands[24] as well as portions of Red Hook[25] and Staten Island,[26] readily hauling out every from October until very early May. Known favourite foods of the seal are returning in grand numbers to New York Harbor as well as nearby New Jersey, from Raritan Bay all the way down the entire Jersey Shore, with schools of mossbunker regularly attracting harbor seals, their cousins the grey seals, dolphins and, most recently, whales.[27] Both the northern and southern shores of Long Island have a reliable population of harbor seals as well as greys, where they will take sand lance as well as some species of crab as part of their diet.

Habitat and diet

[edit]
Harbor seals at Point Lobos, California
Harbor seal in the freshwater Connecticut River, following the shad run

Harbor seals prefer to frequent familiar resting sites. They may spend several days at sea and travel up to 50 km in search of feeding grounds, and will also swim more than a hundred miles upstream into fresh water in large rivers in search of migratory fish like shad and salmon. [28] Resting sites may be both rugged, rocky coasts, such as those of the Hebrides or the shorelines of New England, or sandy beaches, like the ones that flank Normandy in Northern France or the Outer Banks of North Carolina.[1] Harbor seals frequently congregate in harbours, bays, sandy intertidal zones,[1] and estuaries in pursuit of prey fish such as salmon,[29] menhaden, anchovy, sea bass, herring, mackerel, hake, cod, whiting and flatfish, and occasionally shrimp, crabs, mollusks, octopus, and squid.[30] Atlantic subspecies of either Europe or North America also exploit deeper-dwelling fish of the genus Ammodytes as a food source and Pacific subspecies have been recorded occasionally consuming fish of the genus Oncorhynchus. Although primarily coastal, dives of over 500 m have been recorded.[31] Harbor seals have been recorded to attack, kill and eat several kinds of ducks.[32]

Behaviour, survival, and reproduction

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Harbor seal swimming
Harbor seal colony in Helgoland, Germany

Harbor seals are solitary, but are gregarious when hauled out and during the breeding season, though they do not form groups as large as some other seals. When not actively feeding, they haul to rest. They tend to be coastal, not venturing more than 20 km offshore. The mating system is not known, but thought to be polygamous. Females give birth once per year, with a gestation period around nine months. Females have a mean age at sexual maturity of 3.72 years and a mean age at first parturition of 4.64.[33] Both courtship and mating occur under water.[34][33] Researchers have found males gather under water, turn on their backs, put their heads together, and call to attract females ready for breeding.[35] Pregnancy rate of females was 92% from age 3 to age 36, with lowered reproductive success after the age of 25 years.[33]

Birthing of pups occurs annually on shore. The timing of the pupping season varies with location,[36] occurring in February for populations in lower latitudes, and as late as July in the subarctic zone. The mothers are the sole providers of care, with lactation lasting 24 days.[37] The single pups are born well developed, capable of swimming and diving within hours. Suckling for three to four weeks, pups feed on the mother's rich, fatty milk and grow rapidly; born weighing up to 16 kg, the pups may double their weight by the time of weaning.

A pup
Pup nursing at Point Lobos in California.

Harbor seals must spend a great deal of time on shore when molting, which occurs shortly after breeding. This onshore time is important to the life cycle, and can be disturbed when substantial human presence occurs.[38] The timing of onset of molt depends on the age and sex of the animal, with yearlings molting first and adult males last.[39] A female mates again immediately following the weaning of her pup. Harbor seals are sometimes reluctant to haul out in the presence of humans, so shoreline development and access must be carefully studied, and if necessary managed, in known locations of seal haul out.[citation needed]

In comparison to many pinniped species, and in contrast to otariid pinnipeds, harbor seals are generally regarded to be more vocally reticent. However, they do use non-harmonic vocalisations to maintain breeding territories and to attract mates during specified times of year,[40] and also during mother and pup interactions.[41]

Annual survival rates were calculated at 0.91 for adult males,[33] and 0.902 for adult females.[42] Maximum age for females was 36 and for males 31 years.[33]

Notable individuals

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  • Andre, rescued and trained by his owner Harry Goodridge, he became an iconic figure in his hometown of Rockport, Maine.
  • Hoover, also rescued from a Maine harbor. Hoover became famous for his ability to imitate human speech, something not observed in any other mammal.
  • Popeye, the official seal of Friday Harbor, Washington, notable for her common sightings up until 2019, when she was presumed to have died. She was identified and named from her cloudy left eye. There is a statue of her in the Port of Friday Harbor.
  • Freddie, a seal pup commonly spotted along the Thames in central London. Named after Freddie Mercury due to his bushy whiskers and playfulness. Freddie was known to travel unusually far into London from the Thames Estuary, and was often sighted as far west as Hammersmith. On 21 March 2021 he had to be put down after he was violently mauled by an out-of-control dog.[43]

See also

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References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Harbor seal

View on Grokipedia
from Grokipedia
The harbor seal (Phoca vitulina), a true seal of the family Phocidae, inhabits coastal waters across the , spanning temperate to regions of the North Atlantic and North Pacific Oceans. It frequents shallow bays, estuaries, and haul-out sites such as rocky shores, sandbars, and intertidal zones, occasionally entering freshwater systems. Adults measure 1.6 to 1.9 meters in length and weigh 60 to 170 kilograms, with males generally larger than females, and possess a short, dense pelage marked by unique individual patterns of spots ranging from gray to brown. Harbor seals are non-migratory opportunistic foragers, primarily consuming fish, cephalopods, and crustaceans through benthic and mid-water pursuits in nearshore areas. They reach at 3 to 7 years, with females giving birth to single pups annually during spring or summer on terrestrial or icy haul-outs, followed by intensive nursing periods of about four weeks. Classified as Least Concern globally by the IUCN due to its broad distribution and stable populations in many areas, the species nonetheless experiences localized declines attributed to factors including , habitat disturbance, and prey scarcity.

Taxonomy and Systematics

Classification and Subspecies

The harbor seal (Phoca vitulina Linnaeus, 1758) is classified in the family Phocidae (true seals), suborder Pinnipedia, order Carnivora, class Mammalia, phylum Chordata, kingdom Animalia. It shares the genus Phoca with the spotted seal (P. largha), distinguished by genetic and morphological differences, including pelage patterns and cranial features. Five subspecies of P. vitulina are commonly recognized, primarily differentiated by geographic isolation, subtle variations in size, coloration, and skull morphology, though some boundaries remain debated due to and limited in certain regions. These include the nominate in , forms in the Atlantic and Pacific oceans, and a potentially distinct landlocked . Taxonomic revisions, such as those based on craniological and analyses, have questioned the validity of some Pacific variants but generally uphold the five-subspecies framework pending further genomic data.
SubspeciesAuthority (Year)Primary Distribution
P. v. vitulinaLinnaeus (1758)Eastern Atlantic, including and
P. v. concolorde la Pylaie (1824)Western North Atlantic, from to
P. v. richardiiJ. A. Allen (1896)Eastern North Pacific, from to
P. v. stejnegeriJ. A. Allen (1902)Western North Pacific, from to (Asia)
P. v. mellonaeDoutt (1942)Ungava Bay, (debated as a distinct freshwater-adapted form)
These subspecies exhibit low intergradation, with Pacific forms showing greater genetic continuity across the than initially proposed, supporting recognition of richardii and stejnegeri as separate despite historical synonymy.

Evolutionary History

The family Phocidae, to which the harbor seal (Phoca vitulina) belongs, originated in the North Atlantic region during the late to early , approximately 27–20 million years ago, with crown-group phocids emerging around 30–24 million years ago. evidence and molecular phylogenetic analyses indicate that early phocids diversified initially in the North Atlantic and Mediterranean, adapting to marine environments through modifications such as reduced hind limbs and enhanced forelimb propulsion for swimming. The subfamily , comprising northern true seals including Phoca, diverged after the (southern seals and monk seals), with phocine radiation linked to cooling climates and expansion in the -Pliocene transition. The genus Phoca first appears in the fossil record during the late , around 3–5 million years ago, with ancestral forms giving rise to modern harbor seals in the . These early Phoca fossils, primarily from and , exhibit morphological traits like a streamlined body and dental adaptations for grasping , consistent with the predatory niche occupied by extant species. The Pliocene-Pleistocene transition marked further diversification, driven by glacial cycles that facilitated dispersal across Atlantic and Pacific basins via the . Molecular data reveal a deep phylogenetic split between North Atlantic and North Pacific P. vitulina lineages, likely predating the Pleistocene, with finer-scale structure among subspecies reflecting post-glacial recolonization and isolation. Within Phocinae, Phoca clusters closely with genera like Pusa (ringed seals) and Halichoerus (gray seals), showing minimal genetic divergence and supporting a recent common ancestry in the late Miocene to Pliocene. Genetic studies of isolated populations, such as those in Iliamna Lake, Alaska, indicate ongoing evolutionary divergence through landlocking, potentially accelerating local adaptations but without altering the broader genus phylogeny.

Physical Description

Morphology and Adaptations

The harbor seal (Phoca vitulina) possesses a streamlined fusiform body, tapered at both ends to reduce drag and enhance hydrodynamic efficiency during swimming. Its dense pelage of short hairs varies from silver-gray to black, marked by irregular dark spots that are more numerous on the dorsal surface, aiding in camouflage against benthic substrates. The rounded head features forward-facing eyes with flattened corneas and rounded lenses, adaptations that facilitate acute vision in air and underwater by compensating for refractive differences between media. External pinnae are absent, but enlarged middle ear ossicles support effective sound transmission and localization in aquatic environments. Nostrils converge in a V-shaped configuration capable of sealing watertight during dives, minimizing water entry while allowing rapid upon surfacing. Foreflippers are short, broad, and equipped with robust claws for terrestrial maneuvering, whereas elongated hindflippers with flexible generate primary via lateral undulations of the trunk and tail. A subcutaneous layer, reaching up to 10 cm in thickness, provides against cold coastal waters, maintains neutral for energy-efficient , and stores as a metabolic reserve during periods such as molting or pup rearing. Sensory adaptations include mystacial vibrissae with follicles encircled by blood sinuses and dense innervation, enabling detection of prey-generated water disturbances through hydrodynamic signatures, even in low-visibility conditions. These integumentary structures feature specialized overlapping skin lobes that protect against abrasion while preserving tactile acuity in frigid temperatures via localized vascular countercurrent heat exchange. Collectively, these traits reflect evolutionary convergence on phocid morphology, prioritizing propulsion efficiency, sensory acuity, and metabolic resilience in dynamic nearshore habitats.

Size Variation and Sexual Dimorphism

Harbor seals exhibit modest sexual dimorphism, with adult males generally larger than females in both length and mass, though the difference is less pronounced than in many other phocid species. Adult males typically measure 1.5 to 1.9 meters in length and weigh 70 to 170 kilograms, while females range from 1.2 to 1.7 meters in length and 50 to 110 kilograms. This size disparity arises from sexual selection pressures associated with aquatic mating, where larger males may gain competitive advantages in defending territories or accessing females, yet harbor seals show lower dimorphism overall compared to more polygynous pinnipeds. Geographic variation in size follows latitudinal gradients, with individuals from higher latitudes and Pacific populations attaining greater dimensions than those in the Atlantic, potentially reflecting adaptations to thermal environments via increased volume for insulation as predicted by ecogeographic principles. In the eastern Pacific (subspecies P. v. richardii), adults average around 1.5 to 1.8 meters in length and up to 129 kilograms, with males exceeding females by approximately 10-20% in mass. Atlantic populations (P. v. vitulina and related ) are smaller on average, with adults around 1.5 meters and 70 to 100 kilograms, and similarly slight male bias in . Such intraspecific variation underscores the influence of regional prey , oceanographic conditions, and across ocean basins.
Region/SubspeciesMale Length (m)Male Mass (kg)Female Length (m)Female Mass (kg)
Eastern Pacific (P. v. richardii)1.5–1.980–1701.2–1.750–110
Atlantic (P. v. vitulina)~1.570–100Slightly smallerSlightly less

Distribution and Habitat

Geographic Range

The harbor seal (Phoca vitulina) occupies coastal waters throughout the , ranging from temperate to regions in both the North Atlantic and North Pacific Oceans, with the broadest distribution among species. Its range extends as far north as 78° N latitude, encompassing areas from to polar environments along continental margins. Southern limits include in the eastern Pacific, northern in the eastern Atlantic, and temperate zones in . Five subspecies are recognized, each with distinct regional distributions reflecting historical isolation and adaptation. P. v. vitulina inhabits the eastern North Atlantic from northern northward to the and northwestern . P. v. concolor occurs along the western North Atlantic coast, from the southward to , with vagrant occurrences farther south. P. v. richardsii, the eastern Pacific subspecies, ranges from north to the . P. v. stejnegeri is found in the western Pacific, from the and to northern . P. v. mellonae, a debated subspecies, is restricted to the Ungava Bay region in northern . Harbor seals generally remain near haul-out sites, with limited migrations tied to seasonal prey availability and pupping grounds rather than extensive latitudinal shifts.

Habitat Preferences and Microhabitats

Harbor seals (Phoca vitulina) primarily occupy coastal marine habitats in temperate and regions of the , favoring nearshore environments such as bays, estuaries, lagoons, and river mouths where water depths are generally shallow to moderate. These seals exhibit a strong affinity for areas with ready access to both terrestrial haul-out sites and productive grounds, often within 30 kilometers of primary haul-out locations. Haul-out preferences include a variety of substrates, encompassing sandy and beaches, rocky shores, intertidal mudflats, reefs, and man-made structures like piers, with selections influenced by factors such as protection from wave action, predator avoidance, and needs. In some populations, offshore islands are preferentially used for hauling out due to proximity to deeper waters and reduced terrestrial disturbance. Microhabitats for hauling out are selected based on site-specific characteristics that optimize energy balance and safety; for instance, seals in the Dutch show elevated densities near haul-out sites in waters approximately 30 meters deep with low mud content, indicating a for substrates that facilitate easy access and minimal entanglement risks. microhabitats vary regionally but commonly include shallow beds, subtidal reefs, and deeper basins up to 150–200 meters, where seals exploit benthic and pelagic prey concentrations; average dive depths reach 91 meters, though maximums exceed 400 meters in areas like submarine canyons. In high-Arctic settings, such as , seals utilize floes and coastal terrestrial sites for resting, adapting to seasonal dynamics while maintaining fidelity to established haul-out areas along western coasts. Overall, use reflects a balance between haul-out site availability—prioritizing low-disturbance, sun-exposed microsites for pupping and molting—and adjacent marine zones rich in prey, with seals demonstrating behavioral plasticity to exploit heterogeneous coastal mosaics.

Diet and Foraging Behavior

Prey Species and Feeding Strategies

Harbor seals (Phoca vitulina) are generalist carnivores whose diet consists primarily of , supplemented by crustaceans, cephalopods, and occasionally small mammals or seabirds, with prey selection driven by local abundance and availability. In Alaskan populations, common prey include (Gadus chalcogrammus), (Gadus macrocephalus), (Clupea pallasii), (Thaleichthys pacificus), (Mallotus villosus), sand lance (Ammodytes hexapterus), (Oncorhynchus spp.), sculpins (Cottidae), and flatfishes (Pleuronectiformes). In the , seals preferentially target silver hake (Merluccius bilinearis), (Sebastes fasciatus), and (Clupea harengus). European populations emphasize gadoids such as (Melanogrammus aeglefinus), (Pollachius pollachius), (Pollachius virens), and (Gadus morhua), alongside . Invertebrates like , crabs, and constitute a smaller proportion, often increasing in benthic foraging zones, while dietary diversity reflects opportunistic exploitation of schooling and demersal species. Feeding strategies emphasize benthic and nearshore , with seals conducting dives ranging from shallow (under 50 m) to deeper profiles (up to 100-200 m) to pursue prey, adapting tactics based on and prey . As central-place foragers hauling out at coastal sites, they minimize travel costs by targeting productive patches, switching between area-restricted search in prey-dense areas and transit dives during offshore excursions. Harbor seals detect prey using sensitive mystacial vibrissae () that sense hydrodynamic trails, enabling efficient in low-visibility conditions; they typically prey whole or in large pieces without , relying on gular maneuvers to manipulate items. Foraging is predominantly solitary and opportunistic, with seals adjusting dive durations (1-7 minutes) and depths to match prey distribution, though prey profitability influences tactic selection, favoring energy-rich, easily captured items like clupeids over more evasive species. Seasonal shifts occur, with higher consumption in summer and increased intake in winter, reflecting prey migrations and seal energy demands.

Trophic Interactions

Harbor seals (Phoca vitulina) occupy a mid-to-upper trophic position in coastal marine food webs, functioning as generalist mesopredators that exert top-down control on and populations while remaining vulnerable to apex predators. Their diet, dominated by fishes and cephalopods, positions them as key consumers in nearshore ecosystems, where they can influence prey abundance through density-dependent predation; for example, increased harbor seal biomass correlates with reduced availability for fisheries due to enhanced exploitable biomass removal via trophic cascades. isotope analyses confirm their averages around 4.0–4.5, reflecting consistent piscivory across populations, though intrapopulation diet variation occurs based on local prey density. As prey, harbor seals face predation primarily from transient (mammal-eating) killer whales (Orcinus orca), which account for the majority of documented attacks in regions like the and , targeting both adults and pups during haul-outs. Sharks, including (Carcharodon carcharias) and Greenland sharks (Somniosus microcephalus), pose significant threats in temperate and subarctic waters, with predation rates elevated during seasonal migrations. Other marine predators include Steller sea lions (Eumetopias jubatus) and, in Arctic locales, polar bears (Ursus maritimus), while terrestrial carnivores such as wolves (Canis lupus), coyotes (Canis latrans), and bears opportunistically prey on pups at rookeries; avian scavengers like bald eagles (Haliaeetus leucocephalus), (Corvus corax), and gulls also target neonates. Harbor seal predation imposes measurable impacts on lower trophic levels, particularly salmonids; in the , seals consumed an estimated 46–59% of juvenile (Oncorhynchus kisutch) annually from 2004 to 2016, potentially contributing to declines amid overlapping pressures. Similarly, their consumption of Chinook (O. tshawytscha) and supports hypotheses of compensatory dynamics in altered food webs, where seal population recoveries post-1970s culls have intensified competition with sympatric like grey seals (Halichoerus grypus), exhibiting up to 70% trophic niche overlap in shared habitats. These interactions underscore harbor seals' role as bioindicators of , with shifts in their body condition linked to prey during rapid warming events, as observed in Alaskan populations from 1975 to 2014.

Behavior and Social Ecology

Daily and Seasonal Patterns

Harbor seals (Phoca vitulina) display diel activity patterns characterized by alternating periods of at and haul-out on or , with haul-out peaks typically occurring from midday to late afternoon, influenced by tidal stage and solar exposure for . Low facilitate greater haul-out participation, as seals prefer exposed substrates for resting, reducing predation risk and energy expenditure while allowing pups to nurse and adults to socialize. bouts, often benthic and targeting or , predominate during high or nocturnal hours, with seals diving to depths of 50-100 meters for 3-5 minutes per dive, though patterns vary regionally due to prey availability and disturbance factors like vessel traffic. These daily cycles result in seals spending approximately 40-50% of their time hauled out on average, though this shifts with environmental cues such as weather, where calmer conditions promote extended rest periods. Seasonally, harbor seal behavior aligns with reproductive and physiological demands, featuring heightened haul-out activity from spring through summer during pupping (typically May-July in northern populations like , or March-June in ) and subsequent molting (June-August), when seals remain ashore up to 12 hours daily to minimize water exposure that could hinder hair regrowth and heat retention. Pupping occurs on secure haul-outs, with females giving birth to single precocial pups after a 9-11 month gestation, followed by 3-4 weeks of that synchronizes with peak land use; males exhibit territorial defense underwater but aggregate ashore post-breeding. Autumn and winter mark a transition to increased aquatic time for , with reduced haul-outs as energy demands rise for fat accumulation ahead of the next cycle, though non-migratory habits limit movements to <50 km from core sites. Molting, a post-pupping process lasting 2-3 months, elevates metabolic rates and restricts diving, reinforcing seasonal haul-out maxima observed in counts up to 2-3 times higher than winter baselines. Regional variations, such as earlier pupping shifts by 25 days in some North Sea populations linked to climate influences, underscore adaptive flexibility in these cycles.

Predators and Anti-Predator Defenses

Harbor seals (Phoca vitulina) face predation primarily from transient killer whales (Orcinus orca), which are stealthy marine mammal specialists that hunt seals in coastal waters across much of their range. Great white sharks (Carcharodon carcharias) and other large sharks, including salmon sharks (Lamna ditropis) and Pacific sleeper sharks (Somniosus pacificus), opportunistically prey on seals, particularly in Pacific regions where seals aggregate at haul-out sites. Steller sea lions (Eumetopias jubatus) and, in some areas, California sea lions (Zalophus californianus) also attack harbor seals, especially juveniles and during competitive interactions at shared haul-outs. In Arctic and sub-Arctic populations, polar bears (Ursus maritimus) target seals on ice or shore, while grey seals (Halichoerus grypus) have been documented preying on them in the North Atlantic, though such events remain infrequent. To counter these threats, harbor seals rely on behavioral adaptations centered on habitat use and sociality. Hauling out on land, rocks, or ice serves as a primary defense against aquatic predators like killer whales and sharks, as seals on shore are inaccessible to submerged hunters; in areas like Hood Canal, this strategy correlates with lower encounter probabilities during peak predation periods. Seals select haul-out sites with topographic features that enhance safety, such as steep drops into deep water for rapid escape dives, and exhibit site fidelity patterns indicative of predator avoidance. Social grouping further bolsters defenses by distributing vigilance costs; seals in larger haul-out aggregations spend less time alert to aerial or terrestrial threats, such as bald eagles (Haliaeetus leucocephalus) targeting pups, compared to solitary individuals. Terrestrial clustering specifically functions to deter opportunistic land-based predators and improve collective detection of approaching dangers. In water, seals employ maneuverability and bottom-oriented foraging to evade surface-ambushing predators, while their mottled pelage provides crypsis against rocky seabeds and substrates during rest or evasion. Increased human presence near haul-outs can blunt these responses, leading to reduced flushing toward water upon predator cues, though baseline anti-predator behaviors persist in less disturbed areas.

Reproduction and Life Cycle

Mating Systems

Harbor seals (Phoca vitulina) exhibit an aquatic mating system, with copulation occurring exclusively underwater, typically shortly after females give birth on land during the breeding season, which varies by subspecies and latitude but often spans late spring to fall. Males compete for access to receptive females through underwater vocalizations known as roars, produced during brief dives (lasting 20-60 seconds) at frequencies around 78-2300 Hz, serving as advertisement displays to attract and assess potential mates. These acoustic signals peak in intensity during the mating period, correlating with female presence in haul-out areas, and show individual variation that may aid in mate recognition or rival deterrence. The system is polygynous, with dominant males achieving multiple copulations per season by aggregating in "hotspots"—underwater or nearshore areas frequented by females passing through foraging routes—rather than defending fixed terrestrial territories like some otariids. Polygyny levels remain low relative to terrestrial pinniped species, with genetic studies indicating most males sire 1-2 pups annually, though a few achieve higher success via prolonged residency (up to 40 days) and agonistic interactions such as chasing, neck-biting, and flipper-grasping to herd or isolate females. Male body size and condition influence competitive ability, as larger individuals better sustain energy demands of continuous underwater displays and pursuits while fasting during the breeding period. Elements of lek-like behavior have been observed, wherein males perform competitive displays in communal aquatic arenas without exclusive resource defense, prioritizing female traffic over territory exclusivity; however, some males exhibit temporary spatial fidelity to high-traffic zones, suggesting a hybrid strategy balancing advertisement and mild territoriality. Female choice appears influenced by male vocal quality and persistence, with receptive females approaching callers for precopulatory interactions, though coercion via herding occurs; post-mating, females exhibit delayed implantation, allowing embryonic diapause that aligns with optimal pupping conditions. Overall, the system favors males with superior endurance and signaling, but high energetic costs limit prolonged male tenure, contributing to moderate variance in reproductive success.

Gestation, Birth, and Pup Rearing

Harbor seals exhibit a gestation period of 9 to 11 months, incorporating delayed implantation lasting 1.5 to 3 months, during which the embryo remains viable but does not develop until attachment to the uterine wall. Active fetal growth spans approximately 8.5 months following implantation. Females typically produce a single pup after this period. Birth timing varies latitudinally, occurring as early as February in southern populations like Baja California and extending to July in northern European locales, with peak pupping in May to June across many regions including the northeastern United States. Pups are born on accessible terrestrial sites such as beaches, rocky shores, or ice floes, without confinement to designated rookeries, reflecting the species' flexible habitat use. Newborns weigh 11 to 16 kg and measure 75 to 100 cm in length, possessing lanugo fur and the immediate ability to swim and dive. Postnatal care involves intensive lactation for 4 to 6 weeks, during which mothers provide milk with high fat content (up to 40-50%), delivered in brief sessions of about one minute every 3 to 4 hours, either on land or in water. Females alternate nursing with foraging bouts at sea, leaving pups unattended on haul-out sites and relocating them via vocal cues upon return. Weaning follows abruptly, after which pups achieve independence, rapidly learning to capture prey independently despite minimal post-weaning maternal oversight. Females often ovulate and mate shortly after weaning, facilitating annual reproductive cycles.

Population Dynamics

Global and Regional Estimates

The global population of harbor seals (Phoca vitulina) is estimated at 610,000–640,000 individuals, encompassing both North Atlantic and North Pacific stocks, though some assessments cite lower figures of 350,000–500,000 based on earlier surveys. These discrepancies arise from varying survey methods, haul-out correction factors, and incomplete coverage across subspecies ranges, with more recent syntheses favoring the higher range due to updated regional data. The species remains classified as Least Concern by the IUCN, reflecting overall stability despite localized declines. Regional estimates vary by ocean basin and subspecies, with the North Pacific supporting the majority. The North Atlantic population totals approximately 200,000, including the northwestern subspecies (P. v. concolor) and northeastern (P. v. vitulina). In European waters, P. v. vitulina numbers around 83,000 as of 2008 assessments, with the UK component at about 43,750 in 2020. U.S. waters in the western North Atlantic host roughly 61,000 individuals based on 2018 surveys.
Region/SubspeciesEstimated PopulationYear/Source Notes
North Pacific (overall, incl. P. v. richardsii and P. v. stejnegeri)>300,000Recent syntheses; includes eastern Pacific stocks.
(U.S.)156,000 (141,000 non-glacial + 15,000 glacial)2020s trend data from aerial surveys.
(Canada)~105,000 (95% CI: 90,900–118,900)Most recent coast-wide estimate.
California (U.S.)~34,0002009 survey; stable but dated.
P. v. mellonae (Ungava, freshwater)50–600Endangered subspecies; low numbers persist.
Pacific populations, particularly in and , drive the global total, while Atlantic stocks show mixed trends with recoveries in some areas offset by declines in others, such as (~10,000 in 2020). Comprehensive worldwide censuses remain challenging due to the seals' wide distribution and seasonal haul-out behaviors. Harbor seal populations underwent severe depletion due to commercial and government bounties from the through the mid-20th century. In the , bounties persisted until 1960 in Washington and , reducing numbers to historic lows before recovery commenced post-cessation. Protections under the U.S. of 1972 facilitated rebounds, with similar restrictions in the 1970s across and enabling from depleted states in regions like the Kattegat-Skagerrak, where numbers recovered from over- lows estimated around 16,500 in 1890. In Swedish and Danish waters, the metapopulation expanded from approximately 2,500 individuals to 25,000 over four decades following these measures. Recent trends exhibit regional divergence, with many recovering populations stabilizing and others declining amid potential density-dependent factors like prey scarcity. In Washington State, stocks grew markedly from 1977 onward—the Southern Puget Sound increasing 14-fold to 2,529 seals by 2023, and the Washington Coast quadrupling to around 19,561—but leveled off by the 2000s, with no significant growth in areas like Hood Canal. Conversely, the Aleutian Archipelago saw a 67% overall drop from 1977–1982 to 1999, including 86% in the western sector, alongside a 70% reduction in islands hosting over 100 seals. Iceland's population halved in the 1980s due to human removals before a further decline to 10,319 (95% CI: 6,733–13,906) by 2020, a 69% total reduction from 33,327 in 1980. Declines along Scotland's west coast reached 20% from to 2023, the first notable drop after decades of stability or growth. Observations of reduced somatic growth across multiple populations indicate nutritional stress, potentially from localized prey depletion following post-protection expansions. Global estimates hover at 610,000–640,000, but without unified monitoring, overarching trends remain indeterminate amid these heterogeneous regional signals.

Conservation Status and Threats

The harbor seal ( vitulina) is assessed as Least Concern by the International Union for Conservation of Nature (IUCN) on the global Red List, reflecting its broad distribution across northern temperate and coastal waters and generally stable or recovering populations in many areas following historical exploitation. This classification accounts for an estimated global population exceeding 600,000 individuals, with no evidence of widespread decline meeting IUCN criteria for higher categories, though regional variations exist. assessments differ; for instance, the Ungava (P. v. mellonae) is due to limited data, while eastern Atlantic populations remain Least Concern. Localized s, such as in the where populations are Critically Endangered from past overhunting and epizootics, do not alter the species-level status. Harbor seals receive legal protections primarily through national legislation rather than international treaties like , under which the species is not listed owing to its non-threatened status and minimal unregulated trade. , the Protection Act (MMPA) of safeguards all harbor seals by prohibiting hunting, harassment, capture, or disturbance, with exceptions only for permitted scientific research, subsistence use by , or incidental take in fisheries under strict quotas. This act has contributed to population recoveries since its enactment, though enforcement addresses issues like vessel disturbance and intentional feeding. In , protections vary by region; the species overall is not listed federally as at risk, but the eastern subspecies (P. v. concolor) is designated Endangered under the Species at Risk Act since , mandating recovery strategies amid observed declines. In the , the Conservation of Seals Act 1970 bans most killing, with closed seasons from June to December and licenses required for any to protect fisheries. Across , the EU affords strict protection, prohibiting deliberate capture or exploitation while requiring . Despite these measures, derogations for fishery conflict management persist in some jurisdictions, highlighting tensions between conservation and economic interests.

Anthropogenic Impacts

Harbor seals experience significant mortality from in commercial fisheries, particularly gillnet operations. In , an estimated 555 individuals drown annually in gillnets, representing a substantial portion of local populations. In the Northwest Atlantic, recovering populations of vitulina vitulina face ongoing incidental captures in sink-gillnet fisheries, with bycatch informing dietary overlaps with commercially targeted fish species. Contaminants such as polychlorinated biphenyls (PCBs) accumulate in harbor seals through in prey, posing risks to , immune function, and thyroid regulation. In the northwest Atlantic, PCBs remain the dominant in seals, with concentrations linked to elevated toxicity thresholds despite regulatory bans since the . In the , PCB levels in seals declined 71–98% from 1983 to 2003, yet persist at levels correlated with health impairments in and Washington populations. Human disturbance from vessel traffic, , and coastal development disrupts haul-out, , and behaviors, elevating stress and energetic costs. Pacific harbor seals exhibit heightened vigilance and reduced site occupancy near areas of frequent boat activity, with repeated exposure degrading nursery and molting habitats. Land-based anthropogenic in sites like , has contributed to localized declines in colony abundance, as documented through community monitoring from 2015 onward. In the , seals' central-place amplifies to such disturbances, potentially reducing prey and pup .

Natural and Environmental Factors

Harbor seals (Phoca vitulina) experience substantial natural mortality from infectious diseases, with phocid herpesvirus-1 detected in 18.9% of necropsied cases from 2007 to 2021, reaching a peak prevalence of 30.8% in 2019. Fungal pathogens, including Cryptococcus gattii causing pulmonary mycosis, accounted for isolated deaths, alongside bacterial bronchopneumonia and cachexia as leading pathologies in stranded individuals. Parasitic burdens, dominated by metastrongyloid lungworms such as Otostrongylus circumlitus and Parafilaroides gymnurus, frequently infect seals, often co-occurring with one or two species per host and exacerbating , particularly in juveniles where they contribute to morbidity and elevated death rates. Helminth infections in Pacific harbor seals include acanthocephalans, cestodes, and nematodes, with associated pathologies like verminous noted in stranded animals from regions like the . Environmental variability affects haul-out patterns and physiological stress; seals exhibit reduced on-land presence during warmer temperatures, higher wind speeds, and cloudy conditions, which can impair and efficiency, with juveniles showing heightened vulnerability to . In tidewater glacial habitats, natural fluctuations in ice availability and conditions influence abundance and , independent of human presence. Shifts in diet, potentially driven by natural prey variability tied to oceanographic processes, underscore dependencies that alter nutritional outcomes and resilience.

Management and Recovery Efforts

Management of harbor seal (Phoca vitulina) populations primarily involves monitoring, regulatory protections, and threat mitigation rather than formal recovery plans, as the species is classified as Least Concern globally by the IUCN and not listed as endangered or threatened under the U.S. Act. In the United States, the Marine Mammal Protection Act (MMPA) of provides core protections by prohibiting unauthorized take, harassment, or killing, while allowing limited exceptions for subsistence harvest by and incidental fishery under quotas derived from Potential Biological Removal (PBR) levels. NOAA Fisheries conducts biennial stock assessments for U.S. stocks, using aerial photographic surveys—such as those tallying over 30,000 seals in in 2019—to track abundance and trends, informing allowable incidental take authorizations for fisheries. These assessments revealed stable or increasing populations in most Pacific stocks post-1972 protections, which reversed historical declines from commercial hunting that reduced numbers by up to 90% in some regions by the mid-20th century, though certain Alaska stocks (e.g., ) have declined 5-6% annually since the 1990s, prompting targeted research into prey declines and environmental factors without triggering endangered listing petitions, as a 2016 review of seals deemed them warranting no such status. Bycatch reduction remains a key effort, with NOAA implementing gear modifications like pingers and time-area closures in gillnet fisheries, which have lowered harbor seal entanglement rates from historical highs; for example, observed in fisheries averaged 300-500 seals annually in the 1990s but stabilized below PBR thresholds through these measures by the 2010s. Rehabilitation centers, such as those operated under MMPA strandings networks, treat thousands of stranded pups yearly—e.g., over 1,000 in alone in peak years—releasing survivors to bolster local recruitment and yielding data on and , though post-release survival rates hover at 50-70% based on tagging studies. In Native communities, co-management agreements under the MMPA allocate subsistence quotas, such as 755 seals harvested in 2018 across managed stocks, balancing cultural needs with sustainability assessments showing harvests below sustainable yields. In , particularly the —a site hosting ~20% of the global population—trilateral cooperation among , , and the via the Seal Expert Group coordinates annual synchronized counts (e.g., 23,000 seals in 2022) and the Wadden Sea Seal Management Plan (2023-2027), which emphasizes habitat protection, pollution reduction, and disturbance minimization over active recovery, as populations have naturally rebounded from phocine distemper virus (PDV) epizootics in 1988 (killing ~50% of seals) and 2002 through immigration and density-dependent regulation rather than culling bans alone. This plan sets thresholds for "favorable " under EU , including maintaining pup production above 90% of , and restricts shooting to verified problem animals, contributing to a post-2002 recovery to ~25,000 individuals by 2015 despite regional variations driven by juvenile dispersal. Genetic studies support delineating management units to prevent overharvest in isolated subpopulations, as in Norwegian and Icelandic stocks where quotas are set based on viability models. Overall, recovery from anthropogenic declines has been achieved primarily through legal prohibitions on commercial exploitation since the 1960s-1970s, enabling populations to approach pre-industrial levels in protected areas (e.g., eastern Pacific stocks estimated at 150,000-200,000 by ), with ongoing management focusing on adaptive responses to emerging threats like climate-driven prey shifts rather than species-wide interventions.

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