Wildlife Act 1976 / 2000
EU Directive 92/43 Annex V
Bern Convention Appendix III
Key Identification Features
Grey seals are the larger of the two seal species found in Irish waters. Males known as bulls are larger and heavier than the female cows with mature bulls on average measuring up to 2.5 meters in length and weighing up to 300kg. Female adults will grow to 2 meters in body length and can weigh up to 180kg. Grey seal body shape consists of a rounded streamlined torpedo like design with an all over covering of short fur. The coat is moulted once each spring and will appear almost black in colouration when wet but a more grey or greyish brown when dry. There is a high degree of colour variation among individuals with males having less dark patches and spots on their undersides. Females generally have a lighter grey fur colour on the back with a lighter grey colour containing dark areas on the underbelly. Spotted patches for both sexes of grey seals are larger than those of the common seal. Male grey seals have thick muscular necks and shoulders with a flat elongated head and straight parallel nostrils while females have a flatter head profile with a more slender muzzle. The grey seal’s four limbs are each small flippers with each containing five webbed digits. The fore flippers located at the sides of the body have small sharp claws up to 3cms in length at the ends of each digit. Track markings are similar to those of the common seal species but are noticeably wider. On land the grey seal is not very maneuverable and moves in a flopping style but once submerged they become agile swimmers with the ability to dive for long periods. Grey seals have good vision both on land and while submerged. The eyes are large and forward facing with several adaptations which allow for sight in dim underwater conditions, reduction of glare while on land and also protection from sand. Grey seals are a much more vocal species than common seals with a large range of social calls used while hauled out on land ranging from growls, snarls, hisses and barking while at sea they will communicate with a series of grunts, clicks and roars.
In Ireland the grey seal prefers areas of more exposed rocky coastline than that of the common seal species. Haul out sites will be established in areas of rocky coasts or on steep sandbanks. Traditional breeding sites to which individuals will visit every year for the mating and pupping seasons will be found on uninhabited islands, within sea caves or along remote beaches. In Ireland the grey seal will be found along any coastline that will provide access to their traditional breeding sites known as rookeries but their preferred habitats are to be found along the southern and western seaboard. The grey seal species will gather in larger colonies than those of the common seals with bigger rookeries containing several hundred individuals. When outside of the mating and pupping season grey seals will spend most of their time at sea in between periods spent hauled out at favoured resting sites. While at sea the grey seal will spend up to 80% of its time underwater hunting with the remaining 20% of the time spent breathing at the surface.
Food and Feeding Habits
Grey seals are opportunistic carnivorous hunters with a broad diet which will vary with the availability of prey both seasonally and locally. The grey seal usually rests by day at low tide and at sunset at a haul out site while hunting at night and at high tide in the coastal zone up to 80 meters deep although they can dive deeper than 200 meters. They have the ability to dive for long periods into deep waters although in Ireland their hunting dives generally last under ten minutes and are usually conducted in shallow waters not more than one hundred meters deep. During the dive the parallel nostrils will shut tightly with oxygen being stored in the muscles and blood vessels. Seals have twice the amount of blood found in terrestrial mammals of similar size, their muscles can also function with high levels of lactic acid being present. On deeper dives the grey seal has the ability to reduce the blood supply to non-essential areas and can slow their heart rates down to fewer than twenty beats per minute. When hunting bottom dwelling prey items they will catch squid, craustations, flatfish and lobsters. Faster moving fish will be hunted if available including cod, herring, whiting and sand eels. At or near the surface they will hunt mackerel and skate while they have also been known to snatch some resting seabirds. In areas of salmonid rivers grey seals may enter estuaries in search of spawning salmon. This seal species does not feed every day and will fast for long periods on land during the breeding season. In areas of good visibility they will hunt by sight alone but in deeper areas where light levels are poor the seal depends on its underwater directional hearing and sensitive whiskers which pick up movement vibrations. While hunting the grey seal will emit a series of clicking sounds which may have a function in the echolocation of prey similar to that used by dolphin species.
Reproduction and Life Cycle
The mating season for grey seals in Ireland starts in August and may run until November with large numbers of individuals gathering at rookery sites at this time. Females will give birth to pups during this period with mating occurring on land or while submerged soon after. During this time mature males will become more vocal and aggressive as they attempt to establish mating dominance at the rookery site. Violent fights will occur with the most successful males gaining access to up to ten females per season. During this period most males will not feed for the eight weeks of the breeding season so they will lose a lot of body size and conditioning. Females with pups will become intolerant of other cows and even defend their pups from male aggression. Once mating has occurred the female will leave the breeding site while males will remain on land for most of the breeding season. Once pregnant the grey seal cow will delay gestation of the fetus for three months so as to give birth in more ideal seasonal conditions. True pregnancy will last for eight and a half months with a single pup being born on land at the traditional breeding site in autumn or early winter. When born, pups weigh up to 14kg and will have a pure white foetal coat which will be shed after three weeks. Parental care is given by the female only with feeding occurring regularly every six hours on fatty milk for the first three weeks of the pup’s life, during this time grey seal pups will show a daily average weight gain of up to 2kg while nursing. The grey seal cow will usually not feed during the weaning period and will remain close to the pup until it can swim and hunt for itself. Once the pup is fully weaned the female will mate again with a dominant bull at the rookery site. Female grey seals reach full sexual maturity by their fourth year while males will be fully grown by their sixth birthday although they may not reach the required size to mate and defend territories during the breeding season until they are ten years old. Females can live to 40 years of age while males generally will not survive after 25 years.
Like all seal species the grey seal is believed to have originated from an otter like mammal between 15 and 20 million years ago. The species is now globally widespread with a total worldwide population estimated to be in the region of 350,000 individuals. There are currently three separate populations of grey seals. The western Atlantic population around Canada and Greenland. The eastern Atlantic group which includes seals found around Britain and Ireland and a small Baltic Sea group found near Sweden and Finland. The eastern Atlantic population of which Irish grey seals belong is the largest of the three population groups with individuals traveling north to Iceland and as far south as Spain and Portugal. Total numbers of the eastern Atlantic group are in the region of 125,000 individuals and growing. The species was first scientifically identified in Ireland in 1836 although they have been present in Irish waters for at least 7,000 years. Grey seals are currently found all around the coast but are more concentrated on the rocker north, west and southern coastline.
Grey seals have few natural predators in Irish waters, man is still the cause of most seal deaths. They were for centuries hunted for their fur and meat which resulted in a huge decline in their numbers throughout their range by the 19th century. Seal hunting has been made illegal in most parts of the world but their increasing numbers can bring them into conflict with fishermen who can legally shoot seals which are found close to their nets. Grey seal population increases may be regarded as a threat to the fishing industry as they will take salmon and other commercially important fish species from fixed nets, hunt within salmonid estuaries or target fish farms. Grey seals are very sensitive to any disturbances at their breeding sites which can result in females losing their maternal bond with their pups leading to abandonment and an increase in the already naturally high infant mortality rate.
As grey seals live in large groups natural diseases can spread quickly within a population such as intestinal cod worm parasites and respiratory infections. An outbreak of the viral disease phocine distemper effected the Irish population in the 1980’s. Decreasing water quality of Irish seas may result in a future decline of grey seal numbers as some chemicals like PCBs can accumulate in the environment and effect the population’s reproduction rate. Many natural deaths can occur each year due to the stresses of the mating season with mature male’s territorial fighting and fasting leading to some losses. Pups can be crushed during the mating season particularly in colonies of high population densities or be washed out to sea during severe storms. The mortality rate of newborn grey seals in Ireland may be as high as 50%. The Irish grey seal population should continue to grow since this species has been protected since the 1970’s under international, European and Irish law.