Grey seals Halichoerus grypus depend on the sea for their food but also have a need for safe areas of land to haul out to rest, give birth and moult. They are shy aquatic mammals that frequent remote and exposed rocky coasts and islands and may desert a locality if subjected to disturbance. The grey seal is the larger of the two species found in UK waters; the average weight of males is 230 kg and length 207 cm.

Grey seals tend to form large breeding aggregations on remote rocky shores and islands during the breeding season, where they stay ashore for the duration of the pupping and mating period. In the west coast of Scotland breeding generally occurs between October and November when a single pup is produced and weaned after 16 – 21 days. The main UK breeding colonies are located in the Inner and Outer Hebrides, Orkney, Shetland, the mainland coast of north and north-east Scotland, the Isle of May, the Farne Islands and west Wales. The largest breeding colonies, based on pup production, are candidate SACs. Currently the Sea Mammal Research Unit (SMRU) monitor each discrete breeding site in the Inner and Outer Hebrides, Orkney and the Isle of May between 3 to 6 times every year during the breeding season. This is when the seals spend the largest proportion of their time on land and are therefore visible to be counted in the surveys. The survey methods used do contain considerable uncertainties, as there will be an unknown number of animals in the water at the time of survey.

The estimated size of the UK grey seal population at the start of the 2001 pupping season was 130,100 individuals. Taking account of uncertainty, this could range from less than 112,000 to as many as 147,000 seals. 91.5% of which are associated with Scottish breeding sites. Approximately 9,000 grey seals breed in the Inner Hebrides of which the greatest concentration is found at the Treshnish Isles.

The UK grey seal population represents around 40% of the world population and more than 95% of the EU population of the species. Unlike common seals Phoca vitulina who are found throughout the whole of the northern hemisphere, grey seals are only found in the North Atlantic and in the Baltic Sea. Within continental Europe, the grey seal is extremely rare and the UK is an important stronghold for the species. Consequently, the UK has international obligations with respect to conservation of the species.

The two species of seal found in UK waters, grey and common Phoca vitulina, are both listed in Annex II of the Habitats Directive.

Sources:
Joint Nature Conservation Committee
Scottish Executive