Harbor seals are smallish phocids. They have a torpedo-like body shape with little differentiation of neck or hips, with a thick solid appearance. The head is medium-sized, and appears wide across the eyes which, although close-set appear more widely-separated than in the smaller ringed seal, which also has a proportionately smaller rounder head. There are prominent light colored beaded vibrissae above the eyes and on the tapering, moderately wide and thick muzzle. The nostrils are small and terminal, forming a “V” that converges at the bottom. The external ear openings are relatively large and conspicuous, and are set slightly behind and below the eyes. Harbor seals are not obviously sexually dimorphic, and a look at the ventral surface or observing the close association of a pup with its mother are required to separate the sexes. The flippers are relatively short, only about 1/5 to 1/6 of standard length, with long, thin, hooked claws on all digits. The ends of the fore-flippers are pointed, with a longer first digit and successively shorter digits two through five.
The most conspicuous feature of the variably-colored coat is the presence of many fine to medium-sized spots, with smaller numbers of ring-like markings, and some blotches. The markings are usually scattered liberally over the body, with higher densities occurring dorsally than ventrally. Fusion of markings, and the appearance of markings superimposed on other markings impart a confused speckled appearance to the backs of many animals. The most common base color pattern is a light to dark gray, or brown-gray, dorsally, lightening to a paler belly in a counter-shaded pattern. Many dark pelage animals are uniformly dark brown-black above and below, and appear to only have pale rings and ovals. In some localities, a small to moderate proportion of animals have a rust-colored tinge to the head, which in extreme cases can form a hood that reaches the flippers and back. Most pups shed their silvery gray lanugo coat in the uterus before birth. Exceptions to this include pups born early in the breeding season or those born prematurely.
The dental formula is I 3/2, C 1/1, PC 5/5.
Adult males are up to 1.9 m long and weigh 70-150 kg, females 1.7 m and 60-110 kg. At birth, pups are 65-100 cm and 8-12 kg.
Five subspecies are currently recognized: P. v. vitulina of the eastern Atlantic; P. v. concolor of the western Atlantic; P. v. mellonae, of fresh water lakes of the Ungava Peninsula, Canada; P. v. richardii of the eastern Pacific; and P. v. stejnegeri of the western Pacific.
Can be Confused With
Eight other phocids share the range with one or more subspecies of harbor seal. Features for distinguishing harbor seals from northern elephant, gray, hooded, ringed, spotted, harp and ribbon seals are given in their respective species accounts. In the North Pacific, spotted seals pose the greatest identification challenge, and cannot reliably be separated from harbor seals even by most experts.
Elsewhere in Subarctic and Arctic areas, the greatest chance for confusion is between harbor and ringed seals. Details of the coloration and marking patterns, and overall body size and proportions, with harbor seals appearing longer and relatively thinner, are useful. Size and shape of the head and muzzle and relative size of the eyes, which appear smaller and more widely-set apart in harbor seals provide the best clues for distinguishing harbor from ringed seals. Additionally, harbor seals are gregarious when ashore and tend to haul-out on land and locally on glacial ice when consistently available, but not often on sea ice.
Harbor seals are one of the most widespread of the pinnipeds. They are confined to coastal areas of the Northern Hemisphere, from temperate to polar regions. At least four subspecies are recognized: P. v. vitulina occurs in the eastern Atlantic from northern Portugal to the Barents Sea in northwestern Russia, and north to Svalbard; P. v. concolor occurs in the western Atlantic from the mid-Atlantic United States to the Canadian Arctic and east to Greenland and Iceland; P. v. richardii is found in the eastern Pacific from central Baja California, Mexico to the end of the Alaskan Peninsula, and possibly to the eastern Aleutian Islands; and P. v. stejnegeri ranges from either the end of the Alaskan Peninsula or the eastern Aleutians to the Commander Islands, Kamchatka, and through the Kuril Islands to Hokkaido in the western Pacific.
Ecology and Behavior
Harbor seals are mainly found in the coastal waters of the continental shelf and slope, and can be found commonly in bays, rivers, estuaries, and intertidal areas. On land, harbor seals are extremely wary and shy, and it is almost impossible to approach them when they are ashore without stampeding them into the water. In contrast, while in the water, these essentially non-migratory seals can be curious, often craning their necks to peer at people on shore or in boats. Most harbor seal haul-out sites are used daily, based on tidal cycles, although foraging trips can last for several days.
Harbor seals are gregarious at haul-out sites, however they usually do not lie in contact with each other. A hissing rolling growl is one of the few vocalizations made by this seal, and it frequently accompanies foreflipper slapping, batting and scratching of neighboring seals. This is a common occurrence at crowded haul-outs where animals moving and shifting positions bump into or move to close to one another. At sea, they are most often seen alone, but occasionally occur in small groups. Localized aggregations can form in response to feeding opportunities and concentration of prey.
The mating system is promiscuous or weakly polygynous. Mating usually takes place in the water, during the February to October breeding season. Pupping peaks sometime between April and July. In some regions, pupping occurs earlier in more southerly areas.
Feeding and Prey
Harbor seals are generalist feeders taking a wide variety of fish, cephalopods, and crustaceans obtained from surface, mid-water, and benthic habitats. Although primarily coastal, dives to over 500 m have been recorded.
Threats and Status
Many harbor seals live in close proximity to large populations of humans and are exposed to high levels of industrial and agricultural pollutants. Both chronic oil spills and discharges, and episodic large scale spills cause direct mortality, and have long term impacts on harbor seal health and their environment.
Harbor seals live in coastal areas in the middle of some of the most heavily fished waters on earth, and as a result there are entanglement issues as well as effects on the food chains they depend on for their prey. There are also conflicts with smaller localized fisheries, and historically there have been organized population reduction programs and bounties for taking seals
Mass die-offs from viral outbreaks have claimed thousands of harbor seals. In the late 1980s more than 18,000 harbor seals are estimated to have been killed by a phocine distemper virus (morbillivirus). Exposure to diseases from proximity to human populations, and the concentrations of pets and scavenging animals that live with and near them create an increased risk of exposure to communicable diseases. Immunosuppression from chronic exposure to pollutant contaminants probably contributes to harbor seal susceptibility to diseases.
Despite the fact than most harbor seals live in relatively close proximity to humans, their population levels are generally not well know. Combining recent estimates yields a world-wide population of 300,000 to 500,000 animals. P. v. stejnegri of the western Pacific (approximately 7,000), and P. v. mellonae (120-600), of the seal lakes of the Ungava Peninsula, Canada, may be the subspecies most at risk due to low population numbers. Populations in Svalbard and the Baltic Sea, both in the hundreds, are also dangerously low.