Common or Harbour Seals (Phoca vitulina) are true seals of the Northern Hemisphere. Having the widest range of all pinnipeds, Common Seals are found in coastal waters of the northern Atlantic and Pacific Oceans as well as those of the Baltic and North Seas.
With an estimated 400,000-500,000 individuals, the total population of Common Seals is not threatened as a whole. Local populations have been reduced or eliminated through outbreaks of disease and conflict with humans, both unintentionally and intentionally. While it is legal to kill seals which are perceived to threaten fisheries in the United Kingdom, Norway and Canada, commercial hunting is illegal; the seals are also taken in subsistence hunting and accidentally as bycatch in fishing nets.
With each individual possessing a unique pattern of fine, dark spots, Common Seals vary in colour from brownish black to tan or grey; underparts are generally lighter. The body and flippers are short, with a proportionately large, rounded head. The nostrils appear distinctively V-shaped; as with other true seals, the ears are not visible.
Including the head and flippers, Common Seals may reach an adult length of c. 185 centimetres and a weight of 130 kilograms. Females are smaller than males.
Habitat and diet
Characterized as being habitual in their choice of resting sites, Common Seals may spend several days at sea and travel up to 50 kilometres in search of feeding grounds. Resting sites may be both rugged, rocky coast such as that of the Hebrides, or sandy intertidal zones; some seals may also enter estuaries. The seals frequently choose to congregate in harbours, lending the animals their other common name.
The feeding habits of Common Seals have not been studied closely; they are known to prey primarily upon fish such as menhaden, sea bass, herring, whiting and flatfish, and occasionally upon shrimp and squid. Common Seals are thought able to remain submerged for up to 10 minutes, reaching depths of 50 metres or more.
Behaviour and reproduction
While not forming groups as large as most other pinnipeds, Common Seals are gregarious animals. When not actively feeding, the seals will haul themselves out of the water and onto a preferred resting site. The seals tend to hug the coast, not venturing more than 20 kilometres offshore. Both courtship and mating occurs underwater.
Birthing of pups occurs annually on shore, beginning in February for populations in lower latitudes, and as late as July in the subarctic zone. The mothers are the sole providers of care; males occupy themselves with fights between other males. The pups are born singly and well developed, capable of swimming and diving within hours. Suckling for 3-4 weeks, pups feed on the mothers' rich milk and grow rapidly; born weighing up to 16 kilograms, the pups may double their weight by the time of weaning.
Common Seals expend a great deal of time on shore whilst moulting, which the seals undergo shortly after breeding. A female will mate again immediately following the weaning of her pup.