In English, the grey seal is sometimes spelled the gray seal. The earliest description of the this species goes back to the mid-1700's in an account by Cneiff of the seal hunting in the Gulf of Bothnia. Later on in the same century, Olafsen and Povelsen wrote down Icelandic observations of this species. The first systematic name was attributed to Fabricius, who refers to the hooked-nosed seal, Phoca grypus, in his book 'Seals of Greenland' from 1790. Later on, the grey seal was assigned its own genus, Halichoerus, which in greek means sea pig. The complete Latin name currently in use, Halichoerus grypus, meaning 'hooked-nosed sea pig', was given its Latin name by Nilsson in 1820.
The grey seal is one of the larger true seals, and showing more sexual dimorphism than any other phocid except Mirounga. In Northern Europe as well as in North America, this species have been hunted for thousands of years for its fur, blubber and meat, and has thus been a well-known part of the fauna. Skeletal remains at arhcaelogical sites in North America goes as far back as 8500 years B. P. Because of hunting, the number of grey seals were seriously reduced so that in the late 1800s it was regarded as one of the least abundant of northern phocids. Today, after having passed several bottlenecks caused by hunting and environmental polluntants, several grey seal populations have a relatively healthy status both in the Baltic Sea and the Atlantic.
Size, shape and distinctive characteristics
The grey seal is a relatively large phocid seal. It has, as the name indicates, a greyish fur with various darker spots. Colour patterns may vary between grey, brown, black and silver. Usually, male grey seals have a darker emphasis in the coloration, whereas feamale grey seals have a lighter emphasis. Both sexes are darker dorsally and lighter ventrally.
There is a very large sexual dimorphism in this species, with males being almost twice as large as females. Males grow to a weight of 170-310 kg and a length of 2.3 m. Females are smaller (105-186 kg and 2 m). Canadian seals are larger, with males some times weighing over 400 kg. The males have massive shoulders and usually the skin on the chest is heavily scarred and thrown into heavy folds and wrinkles. The nose is long and hook-like, especially in larger males. Adult females ahave a more straight profile to the dorsal surface of their head.
There are two subspecies of gray seals: H. g. grypus is found in the North Atlantic, whereas the H. g. macrorhynchus is found in the Baltic Sea. They differ both in degree of sexual dimorphism and size, but also in behaviour: the Baltic grey seals usually give birth on ice in the winter, whereas the Atlantic populations give birth on rocky or sandy haul-out sites in the early fall.
Grey seals vocalize both in air and under water. During haul-out the almost howling-like seal-song can sometimes be heard from several seals. The function of the song is still unclear.
Grey seals are found in the North Atlantic in Arctic and temperate waters. The haul out sites range in the east Atlantic from Northern Norway and Iceland down to the west coast of France. In the western Atlantic grey seals are concentrated on a major colony of many thousands of individuals on Sable Island off Nova Scotia, and on more dispersed colonies in the Gulf of St Lawrence. In Europe there are larger major populations of grey seals in the Baltic Sea, the German and Dutch coasts, in Norway, Iceland and Scotland.
In older times, grey seal populations were hunted down to small numbers in many parts of the world. The Baltic population was on the brim to become extinct in the 1960 and 1970s, both because of hunting but also because of environmental pollutants. Due to a long period of complete protection and a major improvement for the levels of pollutants in Baltic fish, the Baltic grey seal population in is currently rapidly growing, and a limited hunt is again allowed in the Northern parts of its distribution. In Danish waters, the population of grey seals used to be very numerous and the dominating phocid species until the late 1800s. However, the Danish grey seal was hunted to or close to extinction and replaced by harbour seals. In most parts of the rest of its distribution range, the grey seal populations have experienced declines in periods of excessive hunting, but due to hunting regulations and protection of haul-out sites many populations are currently neither threatened nor declining.
Ecology and Behaviour
The grey seal has adapted to different types of life histories depending on the geographical area. In the Baltic Sea grey seals haul out on rocky islands and sandy shores. In the winter, the seals are adapted to live in the thick Baltic sea ice, maintaining breeding holes and giving birth to their young in late winter. Throughout the rest of its distribution, grey seals give birth in late September. Along the German and Dutch coasts the seals mainly haul out on narrow sand spits, whereas in Scotland and Iceland the seals haul out on rocky shores. On the sandy Sable Island off Nova Scotia there is a major haul-out site for North American grey seals. In some areas grey seals haul out together with harbour seals.
The animals stay on land usually for some days to dry their fur and to relax. Grey seals usually forage nearby the haulout sites but may sometimes also perform longer foraging trips. In such instances foraging excursions may last for several days, and the seals may cover 100s or even 1000s of kilometers.They can dive to 100s meters of depth and stay submerged for over 10 minutes. Grey seals eat all kinds of fish, from smaller-sized fish such as sprat and herring to larger salmonids, gadoids and eels. The diet naturally depends on the season and foraging area.
Grey seals do not perform seasonal migrations, but young individuals may disperse widely. Molting occurs from January to March in the eastern Atlantic, around May in western Atlantic, and around Apral and May on the Baltic ice. The seals eat little or nothing during the molt and spend most of their time on land during this period. The molting haul-out site is not necessarily the same as the breeding haul-out site.
Grey seals give birth to a single pup. In most parts of its distribution the pup is born in September-November. The most pronounced exemption is the Baltic gray seals, giving birth in early March, usually on the ice. The calf is weaned after about three weeks. After weaning mating takes place, usually in the water. The mating behaviour varies in this species. In many areas males gather on land near the nursing colonies of females. Each male tries to control around 6-7 females. The female usually mates with several males. After fertilization, the implantation of the egg is delayed about 100 days, so that active gestation lasts 240 days. The pup is about 70-80 cm long at birth, weighing some 14 kg and covered with creamy white fur. The pup is capable of swiming at brith but usually does not go into the wonter until the first molt. After weaning the female quickly abandon the pup.
Females reaches sexual maturity at and age of 3-5 years, and males at 4-6 years. The females usually have their first pup at an age of 4-5 years. Most males observed during breeding are about 12-18 years. The grey seal can become more than 45 years old, females growing older than males.
Grey seals are opportunistic feeders. They feed on fish of various sizes, ranging from sprat and smaller herring to larger salmonids, eel and gadoids. In some areas they are looked upon as serious competetors to fisherman. Single seals can develop preference to commercially important fish species such as salmon. The major conflict between fisheries and grey seals is because of gear and catch damage caused upon seals feeding on fish caught in stationary traps and gill nets.
Worldwide there are about 380.000 grey seals. Most populations of grey seals are in a rather healthy status because of restrictions or bans on hunting, improvements in the environmental pollutant contents of fish, and because haul-out sites have been protected. However, as with all other marine mammals, many grey seal populations cause concern. In the Baltic sea, it has been discovered that many grey seals suffer from severe ulcers, even though the population is currently in a steady increase.
The gray seal subspecies macrorhynchus is endangered whereas the grypus subspecies is of Least Concern.
Many gray seal haul-out sites are protected from human disturbance by the establishment of seal reserves. In some areas, e.g. the Baltic Sea, there is a very lively conflict between fishermen and grey seals. In some areas there is a limited quota for protective hunting around fishing gear.
Haug, T, M Hammill, D Olafsdottir 2007. The grey seals in the North Atlantic and the Baltic. NAMMCO Scientific Publications Vol. 6, The North Atlantic Marine Mammal Commission, Tromsø.
King, JE 1983. Seals of the World, University of Queensland Press.