Atlantic gray seal - Halichoerus grypus

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Gray seals are robust and sexually dimorphic; males grow noticeably larger, with a proportionately larger and broader head. The most distinctive features are the muzzle and head. The muzzle is particularly long, and wide at the end, with a fleshy mystacial area. In adult males, the top of the muzzle is convex. In adult females and subadults, the top of the muzzle is variable and can be flat, slightly convex (as in adult males), or slightly concave; the last case produces a barely noticeable forehead. The shape of the head has led to the locally-used common name “horsehead.” The nostrils are widely separated and almost parallel to each other, forming a “W” pattern as opposed to the “V” of seals of the genus Phoca. The eyes are small in proportion to the size of the head, widely-separated, and due to the length of the muzzle, proportionately farther back from the nose than on other phocids that share the gray seal’s range. The fore flippers are short, and on adult males wide and relatively thick. Adult males are also thicker through the neck than females.

Pelage color and pattern are variable between the sexes and age classes. Most gray seals are shades of gray, slightly darker above than below. There are usually numerous irregular dark blotches and spots on the back and sometimes a few below, although some females with very few spots appear to be solid grayish cream color. Males darken with age, becoming dark brown to blackish, with a variable number of lighter blotches and spots. Orange to reddish coloration can be seen on the neck, undersides, and flippers of some animals. Gray seals appear paler and duller in coloration just prior to the annual molt. Newborns have a silky, creamy-white lanugo, occasionally with a grayish tinge. The lanugo is molted in 2-4 weeks, and is replaced by a pelage like that of the female, but with more subtle markings.

Adult males are up to 2.3 m long and weigh 170-310 kg, females average 2 m and 105-186 kg. Pups are 90-105 cm and 11-20 kg at birth.

The dental formula of adults is I 3/2, C1/1, PC 5-6/5.

Two subspecies are recognized: H. g. grypus from the western North Atlantic east, including Greenland and Iceland, to western Russian, south to the British Isles and France; and H. g. macrorhynchus from the Baltic Sea.

Five phocids share the gray seal’s range. The gray seal is larger, with a relatively larger head and longer muzzle, widely-separated eyes and eyes set far back from the end of the muzzle. They also have distinctly different pelage markings than harbor, harp, and ringed seals. The shape of the head, nose, and muzzle, placement of the eyes, and overall color and markings also facilitate separation of gray seals from similar-sized bearded and hooded seals.

Gray seals have a cold temperate to subarctic distribution in the North Atlantic. There are three somewhat isolated stocks: a western Atlantic stock centered in northeastern North America; an eastern Atlantic stock split between Iceland, the Faroe Islands, Norway, the United Kingdom, and Ireland; and a Baltic Sea stock. At sea, gray seals generally spend their time in coastal waters. When out of the water they haul-out on isolated beaches and rocky ledges of islands, and will also haul-out and give birth on shore-fast and pack ice.

Gray seals are polygynous, but males do not defend territories or herd females. They actively compete for access to females using vocalizations, threat gestures, and occasional fighting. Pupping and breeding occur between late September and early March, depending on location. Gray seals breed earliest in the British Isles, followed by those in Norway and Iceland, and finally by those off Canada, and in the Baltic Sea. The single pup is usually attended continuously by its mother and weaned in 15-20 days, at which time many have quadrupled their birth weight of 11-20 kg. After weaning the pups remain ashore fasting for two to four weeks before dispersing to sea and wandering widely.

Many, but not all gray seals disperse from their rookeries during the non-breeding season, but gather again at traditional sites to haul-out for the annual molt. They are usually quite gregarious at haul-outs with groups of 100 or more being common, and they will share haul-outs with harbor seals. When ashore gray seals do not lie in contact with each other.

At sea they are usually solitary, or found in small dispersed groups. They will rest at the surface in a vertical “bottle” position, treading water with only the head and upper neck exposed. The maximum depth of dives is approximately 300 meters and up to 30 minutes. Most dives are from one to ten minutes, and to 60 meters or less.

Gray seals feed on a wide variety of benthic and demersal prey in coastal areas. They also feed on schooling fish in the water column, and occasionally take seabirds. Prey species taken include: sand lance, whiting, saury, smelt, various kinds of skates, capelin, lumpfish, pollock, cod, haddock, saithe, plaice, flounder, salmon, and a variety of cephalood and molluscan invertebrates. Cannibalism by adult males on pups has been reported.

At present, most gray seal populations are healthy and growing, and the worldwide population is estimated at about 220,000. A notable exception is the Baltic Sea population, which once numbered 100,000 and is now only a few thousand, having never recovered from sealing and poaching in the early 20th century. Most gray seal populations experienced similar hunting pressures during this period, largely because of the payment of government-sponsored bounties to hunters. Bounties were established to control gray seal populations that were deemed to directly (through feeding) or indirectly (as a vector for seal, or cod worm, a destructive parasite) damage important commercial fisheries. Prior to bounty and commercial hunting, gray seals were locally important in subsistence harvests throughout the history of their contact with humans.

Gray seal mortality has also been attributed to distemper virus outbreaks that caused severe mortality in harbor seals. As a coastal species, gray seals are exposed to and ingest industrial and agricultural pollutants through the food chain. This may have an effect on their immune system and other aspects of health and reproduction. Entanglement in fishing nets is another source of mortality. Interestingly, human over-exploitation of North Atlantic sharks may have had the effect of helping gray seal populations grow and recover by increasing survival, particularly of newly weaned pups and juveniles.

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Hall, A. 2002. Gray seal Halichoerus grypus. pp. 522-524 in W.F. Perrin, B. Würsig and J.G.M. Thiewissen, eds. Encyclopedia of marine mammals. Academic Press.

Lavigueur, L. and M.O. Hammill. 1993. Distribution and seasonal movements of grey seals, Halichoerus grypus, born in the Gulf of St. Lawrence and eastern Nova Scotia shore. Canadian Field-Naturalist 107(3): 329-340.

Murie, D.J. and D.M. Lavigne. 1992. Growth and feeding habits of grey seals (Halichoerus grypus) in the northwestern Gulf of St. Lawrence, Canada. Canadian Journal of Zoology 70:1604-1613.

Pomeroy, P.P., S.S. Anderson, S.D. Twiss and B.J. McConnell. 1994. Dispersion and site fidelity of breeding female grey seals (Halichoerus grypus) on North Rona, Scotland. Journal of Zoology, London 233:429-447.

Twiss, S.D., P.P. Pomeroy and S.S. Anderson. 1994. Dispersion and site fidelity of breeding male grey seals (Halichoerus grypus) on North Rona, Scotland. Journal of Zoology, London 233:683-693.

Vincent, C., L. Meynier and V. Ridoux. 2001. Photo-identification in grey seals: Legibility and stability of natural markings. Mammalia 65(3):363-372.