Distribution and Habitat
The harbour seal (which is known in the British Isles as the common seal) resides in North Pacific, North Atlantic, and Arctic waters. There are five named subspecies: P.v. concolor, P.v. mellonae, P.v. vitulina, P.v. stejnegeri, and P.v. richardii. While P.v. mellonae is the only harbour seal restricted to freshwater habitats (in northern Quebec), all harbour seals will enter estuaries and the lower reaches of rivers throughout their range.
The colour and pattern of the harbour seal coat may vary between regions and even between individuals in a populations. Most conspicuous are the spots, rings and blotches, which are generally more numerous on the back than on the belly. Males range from 1.4-1.9 m, and weigh from 70-130 kg; females are slightly smaller. Harbour seals are often found alone or in small groups at sea, but are gregarious at haul-out sites. Females reach sexual maturity at approximately 3-5 years of age, males between 5 and 6. A single pup is born each year, from January to October, depending on location. Mating takes place after the pups are weaned at about 4 weeks. Harbour seals are opportunistic feeders and their diet varies with season, location, and prey availability.
Population estimates of harbour seals are imprecise for many areas: P.v. concolor 40,000-100,000; P.v. mellonae 100-600; P.v. richardsi 380,000; P.v. vitulina 70,000; P.v. stejnegeri 4,000.
Threats to the Species
Because harbour seals are a coastal species, they are easily affected by habitat disturbance and alteration. Some populations are threatened by pollution, which may affect seal health and reproduction. Unknown numbers are caught incidentally in fishing gear, and some populations (e.g. P.v. stejnegeri in Japan) are significantly affected by interactions with fishing gear. The freshwater harbour seal (P.v. mellonae) may be potentially vulnerable because of its small population size, restricted range and susceptibility to disturbance. Bounties and culling programs have been initiated at various times throughout the last century. As recently as 1997 a culling program was undertaken in British Columbia, Canada, because of predation of declining salmon stocks. In recent years, a substantial decline in the Sable Island population off eastern Canada in the Northwest Atlantic has occurred, the cause of which is still unknown.
Jefferson et al. 1994. Marine mammals of the world. FAO and UNEP. 320pp.
Reijnders, P. et al. 1993. Seals, Fur Seals, Sea Lions, and Walrus. Status Survey and Conservation Action Plan. IUCN Seal Specialist Group. Gland, Switzerland. 87pp.