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| Ecology and Behavior |
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. |
| Feeding and Prey |
| 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. |
| Threats and Status |
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. |
| Links |
For current information on the conservation status of this species, please consult the following websites:
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| References |
HALL, A. 2002. Gray Seal Halichoerus grypus. Pp. 522-524 in W. F. Perrin, B. Wursig, 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. |
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