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Grey seal Halichoerus grypus (Fabricius, 1791)

The males of this species are 195-230 cm long and weigh 170-310 kg. Females have a length of 165-195 cm and a weight of 95-105 kg. Pups are at birth 95-105 cm long and weigh 11-20 kg. This is the seal species with the most pronounced sexual dimorphism. Males are dark with light patches and have an elongated snout with a wide heavy muzzle. Females are light colored with dark spots. Pups are born with a white lanugo and moult after 2-3 weeks.

Distribution

There are three different stocks. The West Atlantic stock ranges from Cape Chidley in the north of Labrador, through Newfoundland, Nova Scotia and the Gulf of St. Lawrence to Nantucket, RI. The East Atlantic stock can be found on Iceland, the Faroe Islands, in Norway from Møye to North Cape, around the British Isles (where the majority of the seals can be found around the Hebrides) and some in the Wadden Sea, along the continental North Sea coast and in Brittany, France. The Baltic stock is located in the Gulf of Bothnia, the Gulf of Finland and along the Baltic coasts of Poland and Germany.

Feeding

The grey seal feeds on local inshore fish species, cephalopods and crustaceans. Bonner (1982) estimated a daily consumption of 7½-12½ kg. Prime and Hammond (1988) investigated the diet of the grey seal population of Donna Nook (UK). They found the diet to consist predominantly of flounder, sole, sand eel, cod and whiting. They estimated the total annual consumption of that population at 863,500 kg.

Population dynamics and life history

Females become mature at ages 4 to 7 and males at ages over 10 years. Gestation lasts 11½ months including a delay of implantation of 3 months. The pregnancy rate is assumed to be between 80 and 90%. The longevity for females is 46 years and for males 26 years. Adult female mortality ranges from 6 to 13½%. First year mortality is, depending on the location, 34-60%.

Trophic relations

There may be some competition for food with the harbor seal, Phoca vitulina. The killer whale can be a predator in some areas.

Interactions

Many of the fish species in the grey seals' diet are commercially exploited, so there is competition for resources with the fisheries. Grey seals have been seen to raid the nets of fishing boats and completely empty them. They also do damage to set nets. Consequently some seals drown in the nets or are shot by the fishermen. Another concern relating to the fisheries is that the grey seal acts as a vector of the cod worm, Phocanema. Since the life cycle of the cod worm is a complex one, the importance of the grey seal therein is hard to determine.

Population size

Several censuses have been carried out of grey seal populations, using land, boat and aerial counts. The West Atlantic stock is estimated at 30,000 animals, of which 17,900 are located in the Gulf of St. Lawrence and 9,400 at Sable Island.