Seal is a common name given to a diverse group of aquatic, generally marine, mammals of the order Pinnipedia in 2 distinctive groups: eared and earless. All have streamlined bodies, limbs developed into flippers, eyes adapted for vision both underwater and in air and valved nostrils.
Seal is a common name given to a diverse group of aquatic, generally marine, mammals of the order Pinnipedia in 2 distinctive groups: eared and earless. All have streamlined bodies, limbs developed into flippers, eyes adapted for vision both underwater and in air and valved nostrils. The respiratory, circulatory and excretory systems are adapted to life without fresh water and to breath-hold diving.
Eared seals in Canadian seas are northern fur seal (Callorhinus ursinus), the smallest species, unique in its dense coat of fur that keeps the skin dry and thus protects the animal from cold water; northern (or Steller) sea lion (Eumetopias jubatus), the largest species, males to 3 m long and 900 kg weight, females less than half that; and California sea lion (Zalophus californianus). Sea lions lack an underfur and have blubber for cold protection.
The bodies of eared seals are streamlined for high speed swimming which is done with oarlike action of large, hairless, fore flippers, using hind flippers for manoeuvring. On land they walk or lope using both fore and hind flippers. They have a small, external ear (pinna). Adult males are much larger than females (in northern fur seal, male to 320 kg, female to 60 kg).
Six species of earless seals regularly inhabit Canadian waters: harbour (Phoca vitulina), ringed (P. hispida), harp (P. groenlandica), bearded (Erignathus barbatus), hooded (Cystophora cristata) and grey (Halichoerus grypus). The northern elephant seal (Mirounga angustirostris) is an infrequent visitor.
The ears of earless seals are openings on the side of the head with no pinna. They swim by side-to-side movements of the hind flippers that are permanently rotated backward; fore flippers are short with terminal claws; all flippers are haired. On land they drag themselves with the fore flippers or undulate caterpillarlike. Males, except in grey and elephant seals, are only slightly larger than females.
Earless seals are excellent breath-hold divers. Ringed seals may stay submerged for 45 minutes and elephant seals for as long as 2 hours; most other species dive for shorter periods. Elephant seals feed along the edge of the continental shelf where they regularly dive to depths of 800 m.
They occur in Canadian waters of all 3 oceans: harbour in both Pacific and Atlantic; bearded and ringed in the Arctic; harp and hooded in the North Atlantic and parts of the Arctic; and grey in the Atlantic from Labrador south to New England. The northern elephant seal migrates north from its breeding grounds in Mexico and California to occur infrequently along the BC coast.
Harp seals have an annual migration of some 3200 km from the Arctic Ocean in the summer months to Newfoundland and the Gulf of St Lawrence in the late winter and spring. Hooded seals also make long migrations. Ringed and bearded seals may move long distances between summer and winter in order to stay with ice; grey and harbour seals are more sedentary.
Harbour seals in Canada are estimated at 50 000 on the Pacific coast, with no estimate for the Atlantic coast; bearded, 300 000-400 000; ringed, 1.5 million; harp, 4.8 million and increasing at about 5% per year; hooded, 400 000; grey, 144 000 and increasing at 8-13% per year.
Reproduction and Development
In most species, age at first breeding in females is 3-6 years and males the same or slightly older. Except for elephant and grey seals, animals are dispersed during the breeding season and a male may service only one to a few females; elephant seals have harem breeding. A single pup is born annually after a gestation period of 11-12 months, including a period of delayed implantation.
Season of birth is variable: ringed, bearded and hooded seals give birth on the ice in March and April; harp, mid-February to mid-March; grey, mid-January; and harbour, during the summer. Young are relatively large at birth (a 180 kg hooded seal may give birth to a 27 kg pup) and can swim well soon after (except the elephant seal). The period of nursing is short, from 3-5 days in hooded to about a month in harbour seal. After weaning, the pup is independent.
Diet consists of fish, squid, shrimp, crab, varying with the species and the locality. Ringed use polar cod, shrimp and large plankton; Atlantic species take polar and Atlantic cod, capelin, flatfish, sculpins; harbour eat a varied diet including bottom fish, cod, rock fish, herring, salmon, crabs and octopus.
Relationship with Humans
The harbour seal in BC and the several species of the Atlantic are believed to be competitors with humans for commercially valuable fish species, but there is little evidence yet that decreasing the pelagic seals increases the available fish catch. Harbour seals may cause serious losses to local salmon runs by concentrated feeding on migrating salmon in river mouths; to salmon AQUACULTURE; or by taking salmon directly from gill nets. The grey seal is the most important alternate host of a parasitic worm that caused commercially important losses to the Atlantic cod industry.
Ringed and bearded seals are a major resource to the INUIT as food, saleable pelts and, formerly, many other useful products. Harp and hooded seals have been a source of food and saleable hides for coastal people of the ATLANTIC PROVINCES.
The commerce in the pelts of newborn harp seals (whitecoats) has been the focus of a major confrontation involving organized groups who, on ethical grounds, oppose the killing of animals for commercial purposes, and those who saw the large numbers of seals as a resource to be used wisely. The kill was managed by Canada as a commercial fishery with concern for conservation and humane practices.
The strategy of the anti-killing groups was to destroy the market for the pelts of all seals. The consequence to those who used seals for food and income was widespread hardship. Reduction of the harvest has been followed by increases in the seal numbers and increased concern that the seals are part of the problem in the collapse of the Atlantic COD industry.
The market for seal products is slowly reviving, but pups are no longer taken. In the face of a rapidly increasing population of harbour seals on the BC coast, questions are being raised as to their impact on commercial and sport fisheries.
Eared seals in Canadian waters are confined to the Pacific Ocean. The northern fur seal breeds on Pribilof and Bogoslof Islands off Alaska, Commander Islands, Russia and San Miguel Island, California; in winter it is found along the BC coast. The northern sea lion is resident on rocky islets from Washington to Alaska and occupies 2 large breeding colonies in BC. The California sea lion invaded Canadian waters (the coast of VANCOUVER ISLAND) as a winter visitant about 1970, but only males occur.
Northern fur seal numbers in BC waters are unknown but estimated at over 1 million; northern sea lions in Canadian waters in 1913 numbered 11 000-14 000 and in 1985 about 5000; California sea lions number about 5000.
Reproduction and Development
Sea lions have a harem organization, with the strongest adult males controlling the breeding access to 1-2 to as many as 60 females. One pup is born annually after a gestation period of 11-12 months. The pups do not swim when young and have a long nursing period: 4 months (northern fur seal) to more than a year (sea lion). Though both sexes are capable of breeding at ages between 3-5 years, males are unable to secure a mate until 7 or more years old.
All 3 species are fish eaters (herring, pollock, salmon, octopus, etc), and sometimes consume SEABIRDS.
Relationship with Humans
The pelts of the northern fur seal have been much sought after by the fur trade. Canadian sealers participated in pelagic hunting of this seal between the 1890s and 1911 that reduced the population from some 4.5-5 million to about 300 000. In 1911 a North Pacific Fur Seal Convention between the US, Great Britain (for Canada), Japan and Russia provided conservation and the population gradually increased to about original numbers. An overkill of females from the mid-1950s to late 1960s as well as the development of the pollock fishery again reduced numbers. Since 1984, the northern fur seal has been protected under US law.
The northern sea lion was hunted by native people for its hide, meat and oil. There was a small commercial harvest between 1913 and 1940, but the decline in numbers resulted from killings on rookeries from 1936 to 1967 to protect fisheries. It is considered a threatened species (1990) in the US. Sea lions are tourist attractions.