Harbour seals are the smallest and most common seal species and contain five subspecies. Generally, adult males measure 1.4–1.9m (6 ft) in length and weigh 55–170 kg (200–270 lbs), while the slightly smaller adult females measure 1.2–1.7 m (5.5 ft) in length and weigh 45–105 kg (120–200 lbs). The coat consists of thick, short hairs ranging in colour from white with dark spots to black-dark brown with white rings. These patterns are unique to each seal, which helps to identify individuals during observational studies. The short front and rear pectoral flippers have five webbed digits with claws used for scratching, grooming, and defense. The hind flippers also have five digits, but these vary in length. The first and fifth digits are long and wide and the middle digits are short and thin. The hind flippers are used to propel the seal forward using a side-to-side motion. These seals also move by undulating the body on land. Male harbour seals live an average of 20 years of age compared to the female life span of 25–30 years.
World Range and Habitat
Harbour seals are also the most widely distributed pinniped (no external ears; phocid = earless, true seal). They are found in temperate, sub arctic, 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. Harbour seals are found in groups only during haul outs for breeding and molting. Aggressive behaviour is demonstrated by growling and snorting, which only occurs when threatened, waving fore flippers, and thrusting the head. Population estimates are poor, however the global population is estimated at 400,000–500,000.
The five subspecies include:
The eastern Atlantic harbour seal, Phoca vitulina, (a.k.a. the common seal) which 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.
The western Atlantic harbour seal, Phoca vitulina concolor is found from the eastern Canadian Arctic and Greenland down to New Jersey, with individuals occasionally found wandering as far south as Florida.
The eastern Pacific harbour seal, Phoca vitulina richardsi, consists of an estimated 285,000 seals, distributed from the Pribilof and Aleutian Islands in Alaska as far south as Baja California.
The western Pacific harbour seal, Phoca vitulina stejnegeri, (a.k.a. Kuril or insular seal) is a small population of less than 4000 seals, ranging from the western Aleutian and Commander Islands south to the Kuril Islands and Hokkaido.
The Ungava seal, Phoca vitulina mellonae, (a.k.a. Lacs des Loups Marins harbour seal), lives in freshwater lakes and rivers on the Ungava peninsula of northern Quebec.
They generally haul out in small scattered groups, although in protected bays and estuaries, haul outs can number over 1000 individuals. Haul out 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 harbour seals haul out in groups for protection against land predation. The timing of haul outs is often dependent on tidal cycles so that the seals can haul out during low tide. In the absence of tides, the time of day is the major influence on harbour seal haul out behavior. Haul outs 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 (312 miles) to feed. Harbour seals tend to stay within 25 km (15.6 miles) of the shore but individuals are occasionally found 100 km (62.5 miles) or more offshore. Harbour 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 harbour seals is reduced while they are molting, therefore less time is needed foraging for food in the water.
The harbour seal diet varies 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 (8–18 lbs) of food per day. Feeding usually takes place near the shore in shallow water less than 200 m deep (660 ft), most often less than 100 m (330 ft) for periods of a few minutes. However, harbour seals have sometimes been known to dive more than 500 m (1650 ft) for more than 25 minutes.
Most male harbour seals reach sexual maturity at 5–6 years of age at a weight of about 75 kg (165 lbs) Females reach sexual maturity earlier at 2–5 years or 50 kg (110 lbs). Mating season varies, but is 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 one pup is born each year measuring 70–100 cm (3.3 ft) in length and weighing 8–12 kg (26.4 lbs). Unlike other seal species that molt after they are born, many harbour seal pups are born with their adult coat, having shed their light-coloured woolly coat before birth. Harbour seals 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 four weeks during which time they will gain 0.5–.7 kg (1.5 lbs) 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.
Warnings and Comments
Harbour 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. Harbour seals are thought by a few to “compete” with commercial fisheries for food sources and unfortunately this myth results in many harbour seals being killed by humans needlessly. Like other seal species, harbour seals are threatened by entanglement in fishing nets, particularly in gillnet fisheries. Like the gray seal, it is apparently legal to shoot harbour seals to protect fisheries or fish farms in several countries, such as Canada, Norway, and the United Kingdom. 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 are being encouraged. Illegal killing of harbour seals also takes place throughout the species’ range. The species is preyed upon by orca and sharks. Polar bears are known to be predators of Western Atlantic harbour seals. Pups may also be preyed on by coyotes, foxes, and large birds of prey. Harbour seals in the Pacific are known to be killed by Steller sea lions.