Northern Ireland's Priority Species

Phoca vitulina – common seal

Phoca vitulina

Phoca vitulina L. 1758
Family: Phocidae

The common seal, or harbour seal as it is also known, is found all around the coastline of Northern Ireland and is seen regularly hauled out on rocky shores and sandbanks. In 1988 the European common seal population was decimated by a viral disease, phocine distemper virus (PDV) – it is estimated that around 18,000 seals died, about 50% of the total population. Eventually the population recovered and numbers increased but an outbreak of the disease in 2002-2003 killed a further 22,500 seals. In Northern Ireland around 350 seals died during the two disease outbreaks.

In brief

  • Found all around the coast of Northern Ireland – Strangford Lough, County Down holds the largest breeding colony in Ireland

  • Prefers to haul out in sheltered inshore bays and estuaries - habitat varies from rocky shores to mudflats and sandbars usually close to deep water and good feeding areas

  • Mostly seen from July to September at haul out sites

  • Declining and scarce with Northern Ireland being the Irish stronghold

  • Main threats to the population are disease and pollution.

Species description
The common seal has a streamlined body covered with a thick layer of fat (blubber) under the skin which helps keep the animal warm. The fur is brownish-grey with small dark spots giving the coat a mottled appearance. The limbs have been modified into flippers for swimming. The head is rounded with a short muzzle and large eyes. Males can grow up to 1.8m in length; females are smaller, up to 1.5m. When hauled out on the shore common seals often lie in a head up, tail up position.

Life cycle
Female seals can breed when they are 3 to 4 years old; males become sexually mature a little later at 5 to 6 years old. Mating takes place in late summer and a single pup is born the following year in June or July. The pup is well developed and can swim and dive within a few hours of birth. The pup is fed on very rich milk (45% fat) and grows quickly; it is weaned after about four weeks and must then learn how to fend for itself. Common seals eat a wide variety of different fish such as plaice, flounder, herring, mackerel, whiting, etc and may swim long distances (up to 50km) from their haul out sites to find food. Much of their time is spent alone in the sea, feeding, and they are only found in groups at haul out sites (places where they rest, mate, give birth and moult). Seals moult their fur coats once a year in July/August when the breeding season is over. The moult normally lasts around 3-4 weeks and the seals spend most of this time ashore. Seals can live for up to 30 years; females usually live longer than males.

Similar species
The common seal and the grey seal are both found around the N. Ireland coast. The common seal is the smaller of the two species and has a more rounded head with a short muzzle. The nostrils of the common seal meet together and form a V shape while those of the grey seal are nearly parallel and do not meet. Grey seal pups are born with white fur and do not usually swim until they shed this coat at 3 to 4 weeks. Common seal pups are grey/brown at birth and can swim within an hour of being born.

How to see this species
Common seals can be seen all around the coast of Northern Ireland, but most are found on the County Down coastline – Strangford Lough holds the largest population in Ireland. The best time to see seals is in July and August when they spend a lot of time hauled out on the shore.

Current status
The common seal is widely distributed in the Northern Hemisphere and there are at least four subspecies. Only the eastern Atlantic subspecies is found in European waters. The UK holds 50% of the European population, around 50,000 animals.

An aerial survey carried out in 2002 found 1248 common seals around the coastline of Northern Ireland – only animals on land at the time of the survey were counted. Strangford Lough, County Down holds the largest colony and is the most important breeding site for the common seal in Ireland.

  • Protected under schedule 5 in the Wildlife (Northern Ireland) Order 1985

  • Listed under Annex II and V of the EU Habitats directive

  • Listed under Appendix III of the Bern Convention.

Why is this species a priority in Northern Ireland?

  • Declining and scarce with Northern Ireland being the Irish stronghold.

The UK holds around 45% of the world population of the European sub-species.

Threats/Causes of decline

  • Chemical pollution – in particular organochlorines that may interfere with seal reproduction

  • Oil pollution

  • Disease – phocine distemper virus.

Conservation of this species

Current action

  • The main site for this species, Strangford Lough, has been designated an ASSI and a SAC

  • In 2002, a Northern Ireland seal survey was carried out by the Sea Mammal Research Unit (St. Andrews)

  • Seal surveys are carried out by EHS on a regular basis.

Proposed objectives/actions

  • Maintain the number of viable populations of the common seal

  • Maintain the range of the common seal

  • Provide specific protection, where appropriate, for the breeding and hauling out sites of the common seal from undue disturbance or changes resulting, directly or indirectly, from human activities.

What you can do
To report common seal sightings contact CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Co. Down, BT18 0EU, Tel: 028 9039 5264, [at]

Further information

The Wildlife (Northern Ireland) ) Order 1985.

Exploris – the N. Ireland Aquarium

Mammal Society Common Seal Fact Sheet

MarLIN – Common Seal

EHS – Designated Sites – Strangford Lough Part 1

EHS – Designated Sites – Strangford Lough Part 2

EHS – Designated Sites – Strangford Lough Part 3

Northern Ireland's Mammals, Amphibians & Reptiles


Text written by:
Angela Ross, Curator of Vertebrates, Ulster Museum

iNaturalist: Species account : iNaturalist World Species Observations database