Harbour seal
Introduction
The harbour seal (Phoca vitulina), also known as the common seal, is a species of pinniped found along temperate and Arctic marine coastlines of the Northern Hemisphere. As one of the most widely distributed seal species, it inhabits coastal waters of the North Atlantic and North Pacific Oceans, as well as the Baltic and North Seas. Harbour seals are part of the family Phocidae, commonly referred to as the true seals or earless seals, characterized by their lack of external ear flaps and their ability to move efficiently in water.
Taxonomy and Evolution
Harbour seals belong to the order Carnivora, suborder Caniformia, and family Phocidae. The species Phoca vitulina is divided into five recognized subspecies: P. v. vitulina (Eastern Atlantic), P. v. concolor (Western Atlantic), P. v. stejnegeri (Western Pacific), P. v. richardii (Eastern Pacific), and P. v. mellonae (Ungava Seal, found in freshwater lakes of Canada). The evolutionary history of harbour seals traces back to the late Miocene epoch, approximately 10 to 5 million years ago, when they diverged from other pinnipeds.
Physical Characteristics
Harbour seals exhibit a robust and streamlined body, with adult males typically measuring 1.4 to 1.9 meters in length and weighing between 55 to 170 kilograms. Females are slightly smaller, ranging from 1.2 to 1.7 meters and weighing 45 to 105 kilograms. Their coats are spotted, with a color palette ranging from silver-gray to dark brown or black. These spots provide effective camouflage against the rocky and sandy substrates of their habitats.
Behavior and Ecology
Habitat
Harbour seals are predominantly coastal, preferring sheltered bays, estuaries, and intertidal zones. They are known to haul out on sandy beaches, mudflats, and rocky outcrops, which they use for resting, thermoregulation, and breeding. Their distribution is influenced by the availability of prey and suitable haul-out sites.
Diet
As opportunistic feeders, harbour seals have a varied diet that includes a wide range of fish, crustaceans, and cephalopods. Common prey species include herring, cod, mackerel, and flatfish. Their foraging behavior is adapted to local prey availability, and they are known to dive to depths of up to 500 meters in search of food.
Reproduction
Harbour seals are polygynous, with males establishing territories during the breeding season to attract females. Mating typically occurs underwater, and after a gestation period of about 11 months, females give birth to a single pup. Pups are born with a soft, lanugo coat, which is shed within a few weeks. They are capable of swimming and diving shortly after birth, and weaning occurs at around four to six weeks of age.
Communication and Social Structure
Harbour seals are generally solitary animals, although they can be found in groups during the breeding season and at haul-out sites. They communicate using a range of vocalizations, including grunts, growls, and barks, particularly during mating displays and when defending territories. Their vocal repertoire is less complex than that of some other pinniped species, such as the California Sea Lion.
Conservation Status
The International Union for Conservation of Nature (IUCN) classifies the harbour seal as a species of Least Concern, due to its wide distribution and large population size. However, certain subspecies and regional populations face threats from habitat degradation, pollution, entanglement in fishing gear, and climate change. Conservation efforts focus on habitat protection, pollution control, and the establishment of marine protected areas.
Human Interactions
Harbour seals have historically been hunted for their fur, oil, and meat. While commercial hunting has largely ceased, they are still subject to bycatch in fisheries and are sometimes perceived as competitors for fish stocks. In some regions, they are protected by national and international legislation, which regulates interactions and ensures sustainable management of their populations.