Grey seals feed mainly on mackerel, young cod and other round fish, but also on cephalopods and crustaceans, in contrast to harbour seals which eat more flatfish.
Mammal Species of the World
Grey seals are large and robust.The pelage colour and pattern can differ with age, sex and during moulting. Their colouring can range from grey, tan and brown to orange and reddish (on neck, undersides and flippers) (Jefferson et al, 2008). The top of the coat is usually darker than below, and darker, blotchy pigments usually break up the base colour. Grey seals have an annual moult and prior to this their coats appear paler and duller. Newborn grey seals are creamy white. They have specialised hair that lasts 2–4 weeks before it is replaced with adult hair that has subtle markings (Jefferson et al, 2008).The males are larger and have a thicker neck and broader head than the females, with a large muzzle. It is the distinctive shape of the large, wide muzzle that identifies it from other seal species (Jefferson et al, 2008)
- the species name, grypus, means hook-nosed and refers to the nose profile of the adult male
- Halichoerus means sea pig in Greek (Perrin et al, 2009)
There are 2 sub species of grey seal:
- Halichoerus grypus grypus
- Halichoerus grypus macrorhynchus
The grey seal is often confused with the habour seal as they can share a single haul out site.
Nouveau-né : longueur : 70-100 cm. Poids : 14-17 kg.
Le Phoque gris est un gros phoque au corps puissant et allongé. Le dimorphisme sexuel est marqué par la différence de taille mais aussi par la forme de la tête et du cou. En effet, la tête est en forme de « poire » chez les deux sexes mais avec un profil rectiligne chez les femelles et légèrement convexe chez les mâles. Le museau de ces derniers est plus long et plus large que celui des femelles. De même, le cou et la partie adjacente des mâles sont plus massifs et présentent de nombreux plis pouvant être marqués de cicatrices. Les narines du Phoque gris sont presque parallèles, non jointives à la base et séparées par un pli cutané. Les vibrisses sont longues et le trou auditif, parfois muni d’un petit pavillon, est plus facilement visible que chez le Phoque veau-marin. Ses membres sont en forme de nageoire. Les antérieurs sont courts, recouverts de poils et se finissent par de longues griffes. Les postérieurs se trouvent dans le prolongement du corps et portent chacun 5 doigts reliés par une palmure. La queue est courte. La couleur du pelage du Phoque gris est gris foncé chez les mâles avec des taches pâles et plus clair chez les femelles avec des taches sombres. Les tâches de la tête, caractéristiques de chaque individu, peuvent permettre une reconnaissance individuelle. Il compte 34 ou 36 dents : I3/2, C1/1, PC5/5 ou 6/5.
Le Phoque gris peut se confondre avec le Phoque veau-marin (Phoca vitulina). Ce dernier a un museau plus arrondi, avec un net décrochement entre le front et le museau tandis que le Phoque gris a un museau allongé.
Le Phoque gris part en mer pour se nourrir et revient sur terre pour se reposer, se reproduire et muer. La période de mue a lieu de janvier à mars chez les femelles et de mars à mai chez les mâles. Il se regroupe en colonie pendant la période de reproduction avec un nombre de femelle toujours supérieur à celui des mâles. Etant donné que la composition de la colonie est en perpétuelle changement, dépendant de l’arrivée des femelles gravides et du départ des femelles fécondées, il ne s’agit pas de véritables harems.
La maturité sexuelle est atteinte entre 3 et 6 ans pour les femelles et 7 à 12 ans pour les mâles. L’accouplement peut avoir lieu entre septembre et décembre. La gestation dure 11,5 mois avec une implantation différée, comme chez les autres pinnipèdes, et une croissance de l’embryon qui ne commence que trois à quatre mois après l’accouplement (pendant la mue des femelles). La femelle met bas entre septembre et novembre, sur terre. Elle donne naissance à un jeune tous les deux ans qui va muer au bout de 2 semaines. Le jeune est allaité pendant 3 semaines avant d’être délaissé par sa mère qui entre en œstrus. Ils peuvent vivre jusqu’à 35 ans pour les femelles et 20 pour les mâles.
Opportuniste, le Phoque gris se nourrit d’une grande variété de poissons (saumon, morue, hareng, raies,...) mais aussi de pieuvres et calamars.
Il fréquente les côtes rocheuses bordées de falaises avec quelques petites plages. Mais il se reproduit préférentiellement sur des îles et îlots situées à une certaine distance de la côte. Pour ses sites de repos, il affectionne particulièrement des îlots baignés par des forts courants ou des bancs de sables.
Références : ROBINEAU D. 2004. Phoques de France. Fédération française des sociétés de sciences naturelles, Paris. 196p.
BENSETTITI, F. & GAUDILLAT, V. 2004. Cahiers d'habitats Natura 2000. Connaissance et gestion des habitats et des espèces d'intérêt communautaire. Tome 7. Espèces animales. La Documentation Française. 353p.
Adult males can grow up to 2.3m long and weigh 170–310 kg. Females can grow up to 2m and weigh 105–186 kg. Within the Atlantic subspecies, seals from Canada are slightly larger than European grey seals (Jefferson et al, 2008).
Male grey seals mate with multiple females - they are polygynous - and they will occasionally fight for a mate. They deter other males from accessing the females by threatening them with open mouth displays, hisses and vocalisations which may end up in a fight that can last up to an hour (Perrin et al, 2009).Breeding is on land between late September and early March, and differs through populations and locations. The populations around the British Isles are the earliest to breed and the Canadian populations and those in the Baltic Sea are the last (Jefferson et al, 2008).The female seal gives birth to a single pup that is weaned within 15–20 days. In that time it increases 4-fold in weight. After weaning, it remains on land without eating for 2–4 weeks before venturing into the oceans (Jefferson et al, 2008). The female’s milk is very rich and has a high fat content. The period of maternal care is very short so it is essential that the pup forms a good bond with the mother to obtain the maximum amount of milk before weaning, otherwise the chance of survival is low (Anderson et al, 1979). There is evidence that the survival rate of grey seal pups is related to the density of the population on the haul out sites (Anderson et al, 1979). If a pup is born into a high-density population, the chance of it being separated from its mother is increased. It is therefore more likely to die from being crushed in a fight or from starvation (Cassini, 1999).Female grey seals often go back to the same spot to breed year after year (Boness and James, 1979; Pomeroy et al, 1994). They sometimes return to breed at the site where they themselves were born (Pomeroy et al, 1994).Nearly half the world’s grey seal population breeds around the UK, and 90 percent of these are in Scotland (Special Committee on Seals (SCOS), 2009).
Males can live for over 20 years and females can live for over 30 years (SCOS, 2009).
The grey seal is listed in Annex II of the EC Habtats Directive. The Baltic Sea population of grey seal is listed under Appendix II of the Bonn Convention on the Conservation of Migratory Species of Wild Animals. The grey seal population of the British Isles represents about 38% of the world population, of which ca 90% breed in Scotland (Duck, 2002).
The grey seal (Halichoerus grypus) occurs in temperate and subarctic waters on both sides of the North Atlantic ocean resulting in three distinct populations. The western Atlantic population is found in the Canadian maritime provinces located from Cape Chidley on the Labrador coast to Nova Scotia. Grey seals located on the southwestern coasts of Iceland, on the Faeroe Islands and the British Isles comprise the eastern Atlantic population. In addition, the eastern Atlantic population extends further onto the coasts of Norway, northwestern Russia, and even French, Dutch, Gernman and Portugal coasts. The third population is found in the Baltic Sea.
Biogeographic Regions: nearctic (Native ); palearctic (Native ); atlantic ocean (Native )
occurs (regularly, as a native taxon) in multiple nations
Regularity: Regularly occurring
Type of Residency: Year-round
Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Temperate and subarctic regions of the North Atlantic Ocean. Three distinct populations, centered on the Baltic Sea (most common in the northeastern Gulf of Finland, the archipelago separating the Gulf of Bothnia from the Baltic proper, and off southeastern Sweden), eastern North Atlantic (mainly Iceland to northern Norway, with the largest rookeries in the British Isles), and western North Atlantic from Labrador to Massachusetts. In the western North Atlantic, principal breeding/birthing areas are Sable Island, the Basque Islands, Camp Island east of Nova Scotia, Amet Island in Northumberland Strait, Deadman Island in the Gulf of St. Lawrence southwest of the Magdalen Islands, and newly forming pack ice in the eastern portion of Northumberland Strait and between eastern Prince Edward Island and western Cape Breton Island; a few females may give birth south to Muskeget and Tuckernuck islands in Nantucket Sound, Massachusetts, and on Monomoy Island south of Cape Cod (Reeves et al. 1992). Major spring molting sites include Anticosti Island in the Gulf of St. Lawrence and Sable Island. See Reeves et al. (1992) for further details on distribution in the Baltic region and eastern North Atlantic.
At birth, grey seal pups weigh approximately 16 kg and have long, creamy white fur which is shed after the first three weeks of life. They fatten quickly on the rich milk from their mothers, and by moulting age have nearly quadrupled in body mass. At this time the young seals show coat patterns which differentiate the sexes. The female grey seal is silver-grey in colour, with small scattered dark spots, while the males are a dark grey with silver grey spots. The three populations of grey seals differ in exact colorings (grey, brown, silver), however the patterns are similar among the individual sexes -- female grey seals have dark spots on a lighter background while the males have a lighter spotting on a dark background fur, but both sexes in the three populations have a relatively dark back and lighter belly.
In addition to coat markings, the nose of a grey seal can distinguish a male from a female. The male grey seal has a long-arched roman nose which is the basis for its Latin name, Halichoerus grypus, meaning the hooked-nose sea pig. The shoulders of the male are massive with the overall bulk supplemented by a buildup of scar tissue from fighting during breeding seasons. The average adult male reaches his maximum size of 2.2 meters long and 220 kg at 11 years of age. The female is smaller and does not attain full size until approximately 15 years of age, reaching an average weight of 150 kg and length of 1.8 meters (measured from nose to tail). She has a more narrow, short nose and a straight profile to the dorsal surface of the head.
Range mass: 150 to 220 kg.
Range length: 1.8 to 2.2 m.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger; sexes shaped differently
Length: 300 cm
Weight: 290000 grams
Size in North America
Average: 2.3 m males; 2 m females
Range: 2-2.7 m males; 1.6-2.2 m females
Average: 271 kg males; 207 kg females
Range: 240-320 kg males; 150-260 kg females
The habitat of the grey seal differs among each individual group of seals. Some are found along rocky continental coasts, while others are comfortable on isolated islands. There are also many grey seal populations around that haul out on icebergs and ice shelves.
Habitat Regions: temperate ; polar ; terrestrial ; saltwater or marine
Terrestrial Biomes: icecap
Aquatic Biomes: coastal ; brackish water
Habitat and Ecology
Lactation lasts around 15-18 days on average, with ice breeders having slightly shorter lactation periods; weaning is abrupt (Kovacs 1987, Haller et al. 1996). Pre-weaning mortality of Grey Seal pups varies widely between colonies, usually between 5 and 20% but can be as high as 30%. Pup mortality rates are influenced by habitat quality, birth site, quality of maternal care, injuries resulting from male-male aggression and to a lesser extent predation by Greater and Lesser Black-backed Gulls (Larus marinus and L. fuscus) on weakened, unprotected, pups, or pups born on the periphery of a colony (Baker and Baker 1988, Twiss et al. 2003).
In the Baltic pre-weaning mortality is low for pups born on ice, but varies between 5 and 30% on land, depending on pupping density (Jussi et al. 2008). Main predators are White-tailed Eagles (Haliaeetus albicilla) and Greater Black-backed Gulls.
In the UK, females give birth on land and show considerable site fidelity (Pomeroy et al. 1994). Mothers typically stay with their pups until weaning, but are rarely more than a few meters away from water (Twiss et al. 1994). In the Gulf of St Lawrence, lactating females that give birth on the ice spend about 72% of their time hauled out, nursing the pup every 2-3 hours. They are hauled out significantly more in darkness than during daylight hours. From the time of birth until weaning, females lose about 5.7 kg per day (Lydersen et al. 1994). Females in the UK lose an average of 65 kg over the lactation period (Fedak and Anderson 1982), whereas the somewhat larger females in the West Atlantic lose an average of 75 kg (Haller et al. 1996). Females come into estrus around the time of weaning (Boness et al. 1982). Females are at their lowest weight following the moulting period, averaging 126.2 kg; by the beginning of the next pupping period they again average 210 kg (Beck et al. 2000).
Adult male Grey Seals do not typically come ashore until the first pups are born, unlike most other pinnipeds where males arrive before the females (Bonner 1981). Their average age when first returning to their breeding colonies is 9-10 years (Manske et al. 2002). Males spend large amounts of time out of the water fasting during the breeding season. Some males go to sea for periods of 2-3 days while others remain hauled out for the entire breeding season (Lidgard et al. 2003). Males do not defend a fixed territory, but stay near a particular group of females. Breeding age males lose less weight per day than lactating females, but because they are ashore for an average of 36 days, up to an extreme of 57days, they can experience considerable loss of mass (Anderson and Fedak 1985, Tinker et al. 1995).
Pupping dates differing significantly between populations: peak dates in the western Atlantic are in January; in eastern Atlantic peak dates vary between September and December in different subpopulations; and in the Baltic Sea peak pupping is in late February to early March, which coincides with the annual maximum ice coverage. The differences in pupping seasons probably keep the groups reproductively isolated (Bonner 1981). Pups are born on land in the eastern North Atlantic, and can be born on either on ice or land in the western North Atlantic and the Baltic (Bonner 1981, Baker et al. 1995). Pups are born with a woolly white lanugo that is moulted around the time of weaning. Pups usually stay on land from birth until the moult is finished, although some pups on small exposed beaches often swim for short periods even before moulting (Kovacs 1987). During the post weaning fast pups lose up to 25% of their body weight (Mansfield, 1988). In the United Kingdom, adult females moult from mid-January to mid-February, and males moult from mid-February through until early April. In Canada, the moult is later in the spring (Bonner 1981). Peak moulting season for Baltic seals is the last week of May to the second week in June.
Grey Seals are shallow, short-duration divers. Most adult diving is shallower than 120 m and less than 8 min. Females dives are on average slightly longer (5.5 min.) than those of males (4.9 min.), although males tend to dive a little bit deeper (57 m compared to 49 m). In the Gulf of St Lawrence, maximum dives recorded were 412 m for males, and 354 m for females (Beck et al. 2003). Typically in the United Kingdom, dives are shorter and shallower (average 4-10 min., max. 30 min.). In European waters gray seals are primarily demersal feeders, diving to the sea bed during most dives (usually 60 m, but down to 200 m in some areas; Thompson et al. 1991).
Grey Seals are not long-distance migrants. In Europe, they often haulout on land, especially on outlying islands and remote coastlines exposed to the open sea. Tracking of individual seals has shown that they can feed up to several hundred kilometres offshore during short foraging trips lasting 2.3 days on average (McConnell et al. 1999). Individual Grey Seals, based at specific haulout sites, often make repeated trips to the same region offshore but will occasionally move to a new haulout and begin foraging in a new region. Movements of Grey Seals between haul-outs in the North Sea and the Shetland Isles, Outer Hebrides and Faeroe Islands have been recorded. During foraging trips Grey Seals often target areas with fine gravel/coarse sandy sea-bed sediments, which are the preferred habitat of sandeels, an important part of the Grey Seal’s diet. Satellite telemetry data from Canada shows that Grey Seals there perform much longer foraging trips and often travel much larger distances than European seals. In the Baltic Sea, Grey Seals make short trips, spending roughly 75% of their time within 50 km of haulout sites (Sjoberg and Ball 2000).
Grey Seal diet varies by location, though they are largely demersal or benthic feeders, (Hall 2002). In some areas, the food consumed can be over 70% sandeels (Ammodytes sp.). In Iceland, where 15 species make up the majority of the diet, the most common stomach contents by weight are Atlantic Cod (Gadus morhua) 24%, sandeels 23%, catfish (wolf-fish, Anarhichas lupus) 15%, and saithe (Pollachius virens) 11% (Hauksson and Bogason 1997). At the Faroes, adults feed on cod and catfish, subadults feed on sandeels and saithe and juveniles consume sandeels (Mikkelsen et al. 2002). In the United Kingdom, sandeels, cod and Dover Sole (Solea solea) accounted for 56% of the diet by weight. Gray seals also eat other flatfish, including Dab (Limanda limanda), Flounder (Platichthys plessus) and plaice (Pleuronectes platessa) (Prime and Hammond 1990). In the Outer Hebrides, gadids account for 40% or more of the diet (ling (Molva molva), Atlantic Cod and Whiting (Merlangius merlangus)); sandeels are less important in this area (Hammond et al. 1994). In Canada, 15 species of fish occur regularly in the diet (Mansfield 1988). Atlantic Cod, Herring (Clupea herringus) and Capelin (Mellotus villosus) account for 72% of prey by weight (Murie and Lavigne 1992).
Habitat Type: Marine
Comments: Generally in coastal waters off rocky shores. Also often in estuaries. Rests ("hauls out") on exposed rocky coasts and remote islands. Spends much time on land during spring molt. Young are born on rocky mainland shores, small offshore islands, sand bars, land-fast ice, or sea caves. The largest colonies tend to be on remote uninhabited islands.
Water temperature and chemistry ranges based on 1658 samples.
Depth range (m): 0 - 27
Temperature range (°C): 0.718 - 21.498
Nitrate (umol/L): 0.748 - 10.275
Salinity (PPS): 31.182 - 35.521
Oxygen (ml/l): 5.180 - 8.784
Phosphate (umol/l): 0.241 - 0.855
Silicate (umol/l): 0.987 - 5.009
Depth range (m): 0 - 27
Temperature range (°C): 0.718 - 21.498
Nitrate (umol/L): 0.748 - 10.275
Salinity (PPS): 31.182 - 35.521
Oxygen (ml/l): 5.180 - 8.784
Phosphate (umol/l): 0.241 - 0.855
Silicate (umol/l): 0.987 - 5.009
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Stellwagen Bank Pelagic Community
The species associated with this page are major players in the pelagic ecosystem of the Stellwagen Bank National Marine Sanctuary. Stellwagen Bank is an undersea gravel and sand deposit stretching between Cape Cod and Cape Ann off the coast of Massachussets. Protected since 1993 as the region’s first National Marine Sanctuary, the bank is known primarily for whale-watching and commercial fishing of cod, lobster, hake, and other species (Eldredge 1993).
Massachusetts Bay, and Stellwagen Bank in particular, show a marked concentration of biodiversity in comparison to the broader coastal North Atlantic. This diversity is supported from the bottom of the food chain. The pattern of currents and bathymetry in the area support high levels of phytoplankton productivity, which in turn support dense populations of schooling fish such as sand lance, herring, and mackerel, all important prey for larger fish, mammals, and seabirds (NOAA 2010). Sightings of many species of whales and seabirds are best predicted by spatial and temporal distribution of prey species (Jiang et al 2007; NOAA 2010), providing support for the theory that the region’s diversity is productivity-driven.
Stellwagen Bank is utilized as a significant migration stopover point for many species of shorebird. Summer visitors include Wilson’s storm-petrel, shearwaters, Arctic terns, and red phalaropes, while winter visitors include black-legged kittiwakes, great cormorants, Atlantic puffins, and razorbills. Various cormorants and gulls, the common murre, and the common eider all form significant breeding colonies in the sanctuary as well (NOAA 2010). The community of locally-breeding birds in particular is adversely affected by human activity. As land use along the shore changes and fishing activity increases, the prevalence of garbage and detritus favors gulls, especially herring and black-backed gulls. As gull survivorship increases, gulls begin to dominate competition for nesting sites, to the detriment of other species (NOAA 2010).
In addition to various other cetaceans and pinnipeds, the world’s only remaining population of North Atlantic right whales summers in the Stellwagen Bank sanctuary. Right whales and other baleen whales feed on the abundant copepods and phytoplankton of the region, while toothed whales, pinnipeds, and belugas feed on fish and cephalopods (NOAA 2010). The greatest direct threats to cetaceans in the sanctuary are entanglement with fishing gear and death by vessel strikes (NOAA 2010), but a growing body of evidence suggests that noise pollution harms marine mammals by masking their acoustic communication and damaging their hearing (Clark et al 2009).
General threats to the ecosystem as a whole include overfishing and environmental contaminants. Fishing pressure in the Gulf of Maine area has three negative effects. First and most obviously, it reduces the abundance of fish species, harming both the fish and all organisms dependent on the fish as food sources. Secondly, human preference for large fish disproportionately damages the resilience of fish populations, as large females produce more abundant, higher quality eggs than small females. Third, by preferentially catching large fish, humans have exerted an intense selective pressure on food fish species for smaller body size. This extreme selective pressure has caused a selective sweep, diminishing the variation in gene pools of many commercial fisheries (NOAA 2010). While the waters of the SBNMS are significantly cleaner than Massachusetts Bay as a whole, elevated levels of PCBs have been measured in cetaceans and seabird eggs (NOAA 2010). Additionally, iron and copper leaching from the contaminated sediments of Boston Harbor occasionally reach the preserve (Li et al 2010).
Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: No. No populations of this species make annual migrations of over 200 km.
Does not make distinct, long-distance migrations. Juveniles especially may disperse widely after breeding season.
See Lavigueur and Hammill (1993) for information on seasonal movements in the Gulf of St. Lawrence.
Halichoerus grypus is an opportunistic feeder consuming between four and six percent of its body weight in one feeding per day. The diet consists of a large variety of fish and the occasional crustaceans and mollusks. According to King, at least 29 different species of fish have been recorded as being eaten by these seals. Fish taken include nearly any species found at pelagic and midwater levels as well as bottom dwelling fish at depths of seventy or more meters.
The feeding methods of the grey seal vary among populations, however they are most often social feeders. Social feeding reduces the opportunity for the prey to escape thereby increasing the feeding efficiency. When small fish are caught by the seal, they are usually consumed underwater and are swallowed whole. However, when large fish are captured, they are brought to the surface and held in the prehensile front flippers. The fish head is then bitten off and discarded, while the remainder of the fish is broken into small pieces able to be swallowed.
Animal Foods: fish; mollusks; aquatic crustaceans
Primary Diet: carnivore (Piscivore )
Comments: Feeds opportunistically on various fishes (herring, cod, capelin, pleuronectids, skates, etc.) and smaller quantities of crustaceans and molluscs (chiefly squid and octopus). In the Gulf of St. Lawrence, the average size of fishes eaten is about 18 cm. Young and adults have similar diets, though newly weaned young often eat shrimp and crabs. Fasts during breeding season. Feeds little or not at all during spring molt. Forages on the bottom at depths of up to at least 70 m.
These seals are also hosts for a parasitic roundworm called cod worm (Pseudoterranova decipiens), that infects cod and other commercially harvested fish.
- cod worm (Pseudoterranova decipiens)
Diseases and Parasites
Studies at Sable Island in Nova Scotia and other locations imply that the breeding season can be an important time for spread of the codworm parasite. It is thought that pups lack resistance to this parasite, and their concentrations in breeding areas are correlated with incidence of marine transmission to certain fisheries. For example several thousand pups may be born at Sable Island annually and the subsequent incidence of cod worm is correlated temporally with dispersal patterns of the pups, with the seal breeding grounds at the epicenter, according to Anderson.
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 81 to >300
Comments: Difficult to estimate because preferred areas continually change due to ocean currents and storms.
10,000 to >1,000,000 individuals
Comments: Total population in the early 1990s was close to 200,000, with nearly half breeding in Great Britain (Reeves et al. 1992). In Canada, pup production was estimated as more than 12,000/year in the mid-1980s; in 1990, more than 11,000 were born on Sable Island; total population in the western north Atlantic is 85,000-115,000 (Reeves et al. 1992).
Gregarious on land when molting. After weaning, young become somewhat nomadic.
The worldwide population of grey seals is estimated at about 380,000 (Jefferson et al, 2008). The Atlantic population is healthy and growing. This is partly due to the human over-exploitation of an Atlantic shark species which is a predator to the seal. This has enabled the population to grow. However the Baltic seal population is still recovering from hunting in the early 1900s (Jefferson et al, 2008). In the UK, seal populations are monitored by aerial photography and direct counts from boats or the shore (Sea Mammal Research Unit, 2010).
Life History and Behavior
Perception Channels: tactile ; chemical
Grey seals use almost the whole water column to obtain their food - they feed from the ocean floor to the surface and in between. The seals even take seabirds. Their prey includes:
- molluscs (Jefferson et al, 2008)
Comments: Intermittently active day/night.
Their lifespan ranges from 15 to 25 years, with the oldest recorded wild female grey seal living to be 46 years of age.
Status: wild: 46 (high) years.
Status: wild: 15 to 25 years.
Status: captivity: 43.0 years.
Lifespan, longevity, and ageing
An interesting case demonstrates a breeding difference between populations. Land-breeding gray seals are polygynous, with males competing to monopolize matings with as many as 7 females. Ice-breeding seals do not appear to be polygynous. Due to the instability of the early January ice, little is known of their habits. However, initial research indicates that a more monogamous system exists.
Mating System: monogamous ; polygynous
The breeding season of the grey seal varies greatly, occurring anywhere from mid-December to October, depending upon the location of the population. Breeding rookeries are formed on various types of habitat including sandy beaches, rocky islands, coasts, caves, and ice. During the months prior to the breeding season, seals actively feed. The females do so to grow for the future developing fetus and to build the fat reserves which will sustain them and the calf for the fasting which follows the birth, usually lasting for three weeks. The males also actively feed, because they too will fast for the breeding season, however their fasting will typically last for up to six weeks. The males ordinarily enter the rookeries once the females give birth and try to gain sole access to groups of females. Territory-related fighting occurs during the breeding season, although it is relatively minor compared to other seal species. Fighting in grey seal communities differs among populations, but generally increases as does the density of females. The successful males are able to mate with up to ten females, depending upon locality and density of the females.
Sixteen percent of female grey seals are sexually mature on their third birthday and give birth to their first young one year later. This figure rises to seventy-one percent by the fourth year and eighty-nine percent by the fifth year of life. The males also become sexually mature at age three, but due to competition for females, rarely mate before they are eight years old.
Once impregnated and following a gestation period of eleven months, females usually give birth a day after coming ashore at the rookery. Grey seals are attentive mothers and defend their pups against predation and intrusion. The pup is nursed for approximately 2 weeks after it is born, gaining around 1.5 kg per day. Once the pup is weaned, the female mates with one or more males and then leaves the pup at the rookery. The pup will remain on land, living off of its blubber reserves until it has fully molted, at which point it will feed at sea. The young seals generally disperse in many different directions from the rookery and are known to wander to distances of over 1,000 km.
Breeding season: The breeding season of the grey seal varies greatly, occurring anywhere from mid-December to October.
Average number of offspring: 1.
Average gestation period: 11 months.
Average weaning age: 14 days.
Average time to independence: 14 days.
Range age at sexual or reproductive maturity (female): 3 (low) years.
Range age at sexual or reproductive maturity (male): 3 to 8 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous
Average birth mass: 14000 g.
Average gestation period: 240 days.
Average number of offspring: 1.
Western Atlantic: single pups are born during late December-early February, with a peak in mid-January. In the British Isles, most births occur in fall. Young are weaned in 2-3 weeks. Weaned pups may fast on land or ice for 1-4 weeks before beginning to feed at sea. Mates around time of weaning. Bulls may monopolize 4-6 cows if cows are not widely dispersed. Gestation lasts about 1 year, including delayed implantation period of 3-4 months. Most females are sexually mature at 5 years (Can. J. Zool. 70:1604), sometimes a year or two sooner. Males become sexually mature at 4-8 years but, because of social interactions with dominant older males, are not likely to breed successfully until at least 10 years old. Few live longer than 30-35 years. Recent genetic data from North Rona Island off Scotland indicate a surprisingly high level of mate fidelity (in 30% of cases, pups born in consecutive years to a particular female were full siblings); resident dominant males sired relatively few of the pups (Amos et al., 1995, Science 268:1897-1899).
Molecular Biology and Genetics
Barcode data: Halichoerus grypus
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Statistics of barcoding coverage: Halichoerus grypus
Public Records: 3
Specimens with Barcodes: 48
Species With Barcodes: 1
The grey seal species as a whole is under no special conservation status. In fact, many countries allow either monitored or unlimited hunting of the seals. For nearly a decade, from 1982 until 1993, Norway, Iceland and Canada offered bounties and local culls for the grey seal. Many fisherman believe that this species competes with them for fish, and seals damage nets and traps. Recently the species has been given great legal protection in Europe, and fewer culls are being authorized.
The Baltic Sea population of this species is much smaller than the two Atlantic population, probably due to hunting and pollution of its habitat. It has greater legal protection.
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: least concern
IUCN Red List Assessment
Red List Category
Red List Criteria
IUCN Evaluation of the Grey Seal, Halichoerus grypus
Prepared by the Pinniped Specialist Group
A. Population reduction Declines measured over the longer of 10 years or 3 generations
A1 CR 90%; EN 70%; VU 50%
Al. Population reduction observed, estimated, inferred, or suspected in the past where the causes of the reduction are clearly reversible AND understood AND have ceased, based on and specifying any of the following:
(a) direct observation
(b) an index of abundance appropriate to the taxon
(c) a decline in area of occupancy (AOO), extent of occurrence (EOO) and/or habitat quality
(d) actual or potential levels of exploitation
(e) effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
Age-structure data from Grey Seal populations in the late 1970s indicated a generation time of approximately 14 years. Abundance is well known as all major populations are monitored regularly. Subpopulations in the Gulf of St Lawrence and Iceland have declined over last decade but by less than 50%. However, the three main sub populations globally (East Atlantic, West Atlantic, Baltic) have all increased over the past 30 years.
A2, A3 & A4 CR 80%; EN 50%; VU 30%
A2. Population reduction observed, estimated, inferred, or suspected in the past where the causes of reduction may not have ceased OR may not be understood OR may not be reversible, based on (a) to (e) under Al.
A population reduction of Grey Seals has not been observed, estimated, inferred, or suspected in the past 30 years.
A3. Population reduction projected or suspected to be met in the future (up to a maximum of 100 years) based on (b) to (e) under A1.
At present there are no indications that the Grey Seal population is likely to decline in the future. The continued growth of the Canadian and North Sea populations during periods of intense over fishing of several of their important prey species suggests that the populations are robust. Major regime shifts in the north Atlantic could lead to population declines.
A4. An observed, estimated, inferred, projected or suspected population reduction (up to a maximum of 100 years) where the time period must include both the past and the future, and where the causes of reduction may not have ceased OR may not be understood OR may not be reversible, based on (a) to (e) under A1.
A population reduction of Grey Seals has not been observed, estimated, inferred, or suspected in the past 30 years and there are no indications that a decline is likely.
B. Geographic range in the form of either B1 (extent of occurrence) AND/OR B2 (area of occupancy)
B1. Extent of occurrence (EOO): CR
The EOO of Grey Seals is 1,500,000 km².
B2. Area of occupancy (AOO): CR
The AOO of Grey Seals is 1,500,000 km².
AND at least 2 of the following:
(a) Severely fragmented, OR number of locations: CR = 1; EN
The Grey Seal population is not severely fragmented and number of breeding locations 10.
(b) Continuing decline in any of: (i) extent of occurrence; (ii) area of occupancy; (iii) area, extent and/or quality of habitat; (iv) number of locations or subpopulations; (v) number of mature individuals.
No recorded declines in (i),(ii),(iii),(iv), overall increase in (v) with local declines in Iceland and possibly in Gulf of St Lawrence.
(c) Extreme fluctuations in any of: (i) extent of occurrence; (ii) area of occupancy; (iii) number of locations or subpopulations; (iv) number of mature individuals.
No extreme fluctuations in any of: (I),(ii), (iii) or (iv)
C. Small population size and decline
Number of mature individuals: CR
Annual pup production is approximately 100,000 indicating an adult female population 100,000.
AND either C1 or C2:
C1. An estimated continuing decline of at least: CR = 25% in 3 years or 1 generation; EN = 20% in 5 years or 2 generations; VU = 10% in 10 years or 3 generations (up to a max. of 100 years in future) — N/A
C2. A continuing decline AND (a) and/or (b):
(a i) Number of mature individuals in each subpopulation: CR or
(a ii) % individuals in one subpopulation: CR = 90–100%; EN = 95–100%; VU = 100% — N/A
(b) Extreme fluctuations in the number of mature individuals. — N/A
D. Very small or restricted population
Number of mature individuals: CR AND/OR restricted area of occupancy typically: AOO
The number of mature individuals is certainly 100,000. AOO is 1,500,000 km² and the number of locations is 50.
E. Quantitative Analysis
Indicating the probability of extinction in the wild to be: Indicating the probability of extinction in the wild to be: CR 50% in 10 years or 3 generations (100 years max.); EN 20% in 20 years or 5 generations (100 years max.); VU 10% in 100 years
Long- term continuing increases in total population and most subpopulations suggest very low likelihood of extinction within 3 generations.
Listing recommendation — Continuing, well documented increases in overall population and most subpopulations, low levels of localized hunting and widespread conservation measures in most range states and current population size based on pup production estimates is 400,000. Continued declines in Icelandic waters give cause for concern, but globally, Grey Seals should be classified as Least Concern.
National NatureServe Conservation Status
Rounded National Status Rank: N4 - Apparently Secure
Rounded National Status Rank: N1 - Critically Imperiled
NatureServe Conservation Status
Rounded Global Status Rank: G4 - Apparently Secure
Reasons: Wide distribution in the North Atlantic Ocean; relatively high population estimates, but apparently declining in some parts of range; local threats from over-exploitation.
Grey seals are listed as being of least concern on the International Union for Conservation of Nature (IUCN) red list of threatened species (IUCN, 2010).Grey seals are now protected, although controlled hunting still occurs in some areas. Regular counts of grey seal populations suggest they are increasing (Perrin, 2009).Under the Conservation of Seals Act 1970, the Natural Environment Research Council is under obligation to the UK government to provide advice on the British seal populations (Special Committee on Seals, 2009).
Grey seals face several threats.Historically, populations of grey seals have suffered pressures from hunting and poaching. Some Atlantic populations were targeted because they were thought to be damaging commercial fishery stocks, either directly or indirectly (Jefferson et al, 2008). Grey seals can also become entangled in fishing nets.
Another danger of being a coastal species is the threat from industrial and agricultural pollutants appearing in the food chain. These can affect the seals' immune systems and within the Baltic populations has been linked to decline in reproduction (Jefferson et al, 2008). Phocine distemper virus (PDV) is carried in all grey seal populations, although they are not significantly affected (Harkonen et al, 2006; Barrett et al, 1995) by the disease and are less sensitive than harbour seals. Grey seals make a more efficient antibody response than harbour seals to virus proteins (Duignan, 1997). However, grey seals may contribute to transporting the disease to harbour seal populations as they often share the same haul out sites (Harkonen et al, 2006).
Baltic Grey Seals alternate between land- and ice-breeding, and the proportion of pups born on land vary from 5% to 95%, so it is not easy to use typical pup production counts to enumerate Grey Seals in the Baltic. Surveys in the Baltic count the number of seals hauled out during peak moulting season (late May-to early June), which represents approximately 80% of total population size (Hiby et al. 2007). Counted numbers hauled out in 2007 was estimated at 22,000.
Pup production figures can be used to derive approximate total population estimates. In Canada the “all age” population is approximately 250 000 divided into two main herds, one largely located in the southern Gulf of St Lawrence and the other at Sable Island (DFO 2006). The Sable Island colony has been increasing at a rate of 13% per year, but has recently showed signs of slowing (Bowen et al. 2007). The Gulf of St Lawrence population is decreasing (Hammill et al. 2007). In the UK the different subpopulations show differing dynamics (SCOS 2006). In the Hebrides and Northern Isles pup production has stabilized while in the central and Southern North Sea production is still increasing exponentially. The total population is estimated to be between 117,000 and 171,000 at the start of the breeding season, i.e. excluding pups. Overall the UK population is increasing at approximately 2.5% p.a. (SCOS 2007).
Total population estimates for other regions are: USA - 7,300 – increasing (Waring et al. 2005); Iceland – 11,600 – declining (Hauksson 2007); Norway - 3,100 – trend unknown (Wiig 1986); Ireland - 2,000 – increasing; Russia - 1,000-2,000- unknown; Baltic Sea - 22,000- increasing (2007, Helcom portal).
Government culls, bounties and licensed kills for protection of fishing gear have been put into effect in many countries and continue to be used to control Grey Seal numbers and reduce their impact on commercially important coastal fisheries (i.e. salmonid fisheries). Grey Seals feed on a number of commercial species, and by damaging nets and traps they are in direct conflict with fisheries. They also are vectors for parasites that can have an impact on the economy of some fisheries (see ICES 2005).
Entanglement in commercial fishing nets causes by-catch mortality in most parts of the Grey Seals’ range (Woodley and Lavigne 1991). By-catch levels are approximately 300 per year in Swedish fisheries in the Baltic (ICES 2005). A Norwegian study from 1975-1998 reported the death of 259 seals, representing 7% of the tagged animals, primarily juveniles less than a year old (Bjorge et al. 2002). Among 528 deaths of tagged seals in the UK, 148 were attributable to fishing nets. However, this may overestimate the rate of entanglement-related mortality due to the high rate of tag returns from fisheries. Woodley and Lavigne (1991) suggested that 1-2% of animals less than a year old die in fishing gear. Finally, in the United States’ Northeast sink-gillnet fishery there was an average annual mortality of 141 Grey Seals reported for the period 1999 to 2003 (Waring et al. 2005).
Grey Seals are known carriers of the morbillivirus, known as phocine distemper virus (PDV), in all populations (Ross et al. 1992, Duignan et al. 1995, Harkonen et al. 2006). However, they have suffered almost no mortality from the disease, in marked contrast to Harbour Seals. Harkonen et al. (2006) report Grey Seal mortality of approximately 230 (equal to 1% of the harbour seal mortality) in the 1988 epizootic in Europe and the death of 30 Grey Seal pups in the Baltic were attributed to PDV. Because Grey Seal haulout with Harbour Seals in the Wadden Sea and are known to travel more widely than the sedentary Harbour Seal, it is presumed that they had a role in the outbreak and spread of the 2002 epizootic of PDV in Harbour Seals (Harkonen et al. 2006).
Grey Seals are exposed to agricultural pollutants through the food chain in their coastal ranges. PCBs and DDT contaminant loads are extremely high in Baltic Grey Seals, despite the fact that tissue burdens have declined since the 1970s. Analysis of samples collected from 1996 to 1998 indicated that Grey Seals still have a very heavy load of contaminants when compared to other seals outside the Baltic (ICES 2005).
Health effects on Grey Seals have been suggested to be linked to their high exposures to PCBs and DDT. Baltic Grey Seal have a relatively high rate of colonic ulcers associated with hookworm infestations, which are sometimes fatal. This condition occurs in Baltic Ringed Seals as well, but is not found elsewhere in either species (ICES 2005). Uterine stenosis and a host of other pathologies in other organs have been attributed to long-term exposure to environmental toxics, particularly in older Baltic Grey Seals. These are specifically linked to reproductive and population declines for this subspecies and are conditions not seen in other populations (Bergman et al. 2001). However, no negative effects have been attributed to heavy metal contaminants in Baltic Grey Seals (Bergman et al. 2001, ICES 2005).
Grey Seals live close to human population centres and shipping lanes and spend much of their time in the vicinity of favourite haulout locations. Spilled oil from vessel accidents and other sources have fouled gray seal sites since at least the 1940s (St. Aubin 1990). Despite numerous records of oiled animals and occasional reports of dead animals coated in oil, or animals having ingested oil, it has not been determined whether these mortalities are attributable to contact with oil in this species (St. Aubin 1990).
Grey Seals are generalist predators and their population has increased in recent decades during periods of declines of some commercial fish stocks that are important Grey Seal prey. The risks of over-fishing induced declines of fish stocks on gray seals are unclear at this time. One potential threat is the risk of a demand for larger culls and control of Grey Seal populations to help rebuild fisheries stocks that are affected by, or are presumed to be affected by, Grey Seals.
The potential effects of climate change on Grey Seals are not well known. Although not a high Arctic species, some Grey Seals pup on ice and are seasonally associated with ice in parts of their range (Bonner 1981). It is unknown how decreases in sea-ice cover might affect Grey Seals, although Learmonth et al. (2006) identify the Grey Seal as a species that will probably undergo a decrease in its range because of climate change. Since Baltic Grey Seal pup mortality on land breeding sites is considerably greater compared with pups born on ice, and weaning weights much lower on land, a scenario with less ice will reduce the mean long-term growth rate in this population (Jussi et al. 2008).
Degree of Threat: B : Moderately threatened throughout its range, communities provide natural resources that when exploited alter the composition and structure of the community over the long-term, but are apparently recoverable
Comments: Baltic population is much smaller than it was in the early 1990s, due to overexploitation and slow recovery caused in part by pollution-related reproductive declines (see Reeves et al. 1992). In many areas, entanglement in fishing nets results in mortality, especially of juveniles. Some hauling-out habitat has been lost to development.
Biological Research Needs: Life-history information; determine the amount of competition between its associated species.
Global Protection: Unknown whether any occurrences are appropriately protected and managed
Comments: Individuals protected by the Marine Mammal Protection Act.
Needs: Protect from hunting; land purchase of hauling out areas.
Relevance to Humans and Ecosystems
Grey seals are widely believed by commercial fisherman to be a pest. They may remove fish from nets, become tangled in nets, damage traps, and feed on farmed fish. These seals are also hosts for a parasitic roundworm called codworm (Pseudoterranova decipiens), that infects cod and other commercially harvested fish.
There is some dispute about the large-scale impacts of grey seals on the Atlantic fisheries, but they are at least occasionally a problem in local situations.
In the past, grey seal pups were killed and harvested on a large commercial scale for their skins. There have been no recent large-scale hunts.
Comments: Perceived to compete with fisheries for commercially valuable fishes (e.g., cods, herrings, salmon). May remove or mutilate fishes in nets and traps, often damaging gear in the process. May interfere with lobster trapping by opening traps and eating the bait. Serves as primary reservoir of codworm, the removal of which increases the cost of producing marketable cod and other fishes. Population control measures through bounty and culling schemes continue to be advocated by fishermen.
Has been exploited intensively (commerical and subsistence use) throughout the range (see Reeves et al. 1992). In Canada, bounty kills and culls of perhaps 2000 seals/year occurred from the 1960s to the 1980s. Commonly displayed in zoos and aquaria. Has been used in important studies of diving physiology and sleep.
The grey seal (Halichoerus grypus, meaning "hooked-nosed sea pig") is found on both shores of the North Atlantic Ocean. It is a large seal of the family Phocidae or "true seals". It is the only species classified in the genus Halichoerus. Its name is spelled gray seal in the US; it is also known as Atlantic seal and the horsehead seal.
It is a large seal, with bulls reaching 2.5–3.3 m (8.2–10.8 ft) long and weighing 170–310 kg (370–680 lb); the cows are much smaller, typically 1.6–2.0 m (5.2–6.6 ft) long and 100–190 kg (220–420 lb) in weight. Individuals from the western Atlantic are often much larger, males reaching 400 kg (880 lb) and females weighing up to 250 kg (550 lb). It is distinguished from the harbor seal by its straight head profile, nostrils set well apart, and fewer spots on its body. Bull Greys have larger noses and a less curved profile than common seal bulls. Males are generally darker than females, with lighter patches and often scarring around the neck. Females are silver grey to brown with dark patches.
Ecology and distribution
In the United Kingdom and Ireland, the grey seal breeds in several colonies on and around the coasts. Notably large colonies are at Donna Nook (Lincolnshire), the Farne Islands off the Northumberland Coast (about 6,000 animals), Orkney and North Rona. off the north coast of Scotland, Lambay Island off the coast of Dublin and Ramsey Island off the coast of Pembrokeshire. In the German Bight, colonies exist off the islands Sylt and Amrum and on Heligoland.
In the Western North Atlantic, the grey seal is typically found in large numbers in the coastal waters of Canada and south to about New Jersey in the United States. In Canada, it is typically seen in areas such as the Gulf of St. Lawrence, Newfoundland, the Maritimes, and Quebec. The largest colony in the world is at Sable Island, NS. In the United States it's found year round off the coast of New England, in particular Maine and Massachusetts, and slightly less frequently in the Middle Atlantic States. Its natural range extends south to Virginia.
In recent years, the number of grey seals has been on the rise in the west and in Canada there have been calls for a seal cull.
During the winter months grey seals can be seen hauled out on rocks, islands, and shoals not far from shore, occasionally coming ashore to rest. In the spring recently weaned pups and yearlings occasionally strand on beaches after becoming separated from their group.
The grey seal feeds on a wide variety of fish, mostly benthic or demersal species, taken at depths down to 70 m (230 ft) or more. Sand eels (Ammodytes spp) are important in its diet in many localities. Cod and other gadids, flatfish, herring and skates are also important locally. However, it is clear that the grey seal will eat whatever is available, including octopus and lobsters. The average daily food requirement is estimated to be 5 kg (11 lb), though the seal does not feed every day and it fasts during the breeding season.
The pups are born at around the mass of 14 kg. They are born in autumn (September to November) in the eastern Atlantic and in winter (January to February) in the west, with a dense, soft silky white fur; at first small, they rapidly fatten up on their mothers' extremely fat-rich milk. The milk can consist of up to 60% fat. Within a month or so they shed the pup fur, grow dense waterproof adult fur, and leave for the sea to learn to fish for themselves. In recent years, the number of grey seals has been on the rise in the west and in the U.S. and Canada there have been calls for a seal cull.
In the United States grey seal numbers are increasing rapidly. Up until 1962, Maine and Massachusetts had bounties on seals so that only a few isolated colonies of grey seals remained in Maine. Then in 1972 Congress passed the Marine Mammal Protection Act that prevented harming or harassing seals, and grey seal populations rebounded. For example there is a large breeding colony near Cape Cod, Massachusetts, where pups rebounded from a handful in 1980 to more than 2,000 in 2008. By 2009, thousands of grey seals there had taken up residence on or near popular swimming beaches when great white sharks started hunting them close to shore. Also grey seals are seen increasingly in New York and New Jersey waters, and it's expected that they will establish colonies further south.
In the UK seals are protected under the Conservation of Seals Act 1970, however it does not apply to Northern Ireland. In the UK there have also been calls for a cull from some fishermen, claiming that stocks have declined due to the seals.
The population in the Baltic Sea has increased about 8% per year between 1990 and the mid-2000s with the numbers becoming stagnant since 2005. As of 2011 hunting grey seals is legal in Sweden and Finland with 50% of the quota being used. Other anthropogenic causes of death include the drowning in fishing gear.
There are two recognized subspecies of this seal:
- Halichoerus grypus grypus (North Atlantic), synonymously known as H. g. atlantica
- Halichoerus grypus macrorhynchus (Baltic Sea), synonymously known as H. g. balticus
Molecular studies have indicated that the eastern and western Atlantic populations have been genetically distinct for at least one million years, and could potentially be considered as separate subspecies.
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- Mowat, Farley, Sea Of Slaughter, Atlantic Monthly Press Publishing, First American Edition, 1984.
- Gray Seal (marine mammals) . what-when-how.com
- Stewart, J.E., et al. (2014). "Finescale ecological niche modeling provides evidence that lactating gray seals (Halichoerus grypus) prefer access to fresh water in order to drink". Marine Mammal Science 30 (4): 1456–1472. doi:10.1111/mms.12126.
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- Stenman, Olavi (2007). "How does hunting grey seals (Halichoerus grypus) on Bothnian Bay spring ice influence the structure of seal and fish stocks?". International Council for the Exploration of the Sea. Retrieved 20 November 2011.
Analysis of fish otolithes and other hard particles in the alimentary tract showed clearly that the herring (Clupea harengus) was the most important item of prey.
- Savenkoff, Claude; Morissette, Lyne; Castonguay, Martin; Swain, Douglas P.; Hammill, Mike O.; Chabot, Denis; Hanson, J. Mark (2008). "Interactions between Marine Mammals and Fisheries: Implications for Cod Recovery". In Chen, Junying; Guo, Chuguang. Ecosystem Ecology Research Trends. Nova Science Publishers. p. 130. ISBN 978-1-60456-183-8.
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- Bidggod, Jess (16 August 2013) Thriving in Cape Cod’s Waters, Gray Seals Draw Fans and Foes. New York Times
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- Once again, coastal waters getting seals’ approval Boston Globe. 3 October 2009.
- Bäcklin, Britt-Marie; Moraeus, Charlotta; Kunnasranta, Mervi; Isomursu, Marja (2 September 2011). "Health Assessment in the Baltic grey seal (Halichoerus grypus)". HELCOM Indicator Fact Sheets 2011. HELCOM.
- Wozencraft, W. C. (2005). "Order Carnivora". In Wilson, D. E.; Reeder, D. M. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. ISBN 978-0-8018-8221-0. OCLC 62265494.
- Boskovic, R., et al. (1996). "Geographic distribution of mitochondrial DNA haplotypes in grey seals (Halichoerus grypus)". Canadian Journal of Zoology 74 (10): 1787–1796. doi:10.1139/z96-199.
|Wikimedia Commons has media related to Halichoerus grypus.|
- BBC Wales Nature: Grey Seal video clips
- Grey Seals on pinnipeds.org
- ARKive – images and movies of the grey seal from Atlantic (Halichoerus grypus)
- images of the grey seal from North Sea (Halichoerus grypus)
- Grey Seal Conservation Society (GSCS)
- The first filming of the grey seal in Eastern Crimea, Ukraine
Names and Taxonomy
Comments: Boskovic et al. (1996) examined mtDNA variation among seals from the Gulf of St. Lawrence, Sable Island, Nova Scotia, Norway, and the Baltic Sea. They found no shared haplotypes between the western Atlantic group and the eastern Atlantic group. MtDNA data indicated little or no geogrpahic separation between animals breeding in the Gulf of St. Lawrence and those breeding on Sable Island.
A cladistic analysis of mtDNA data yielded three clades among northern seals: Phoca-Pusa-Halichoerus, Cystophora-Pagophilus, and Erignathus (Perry et al. 1995). Each clade may be regarded as a tribe of the subfamily Phocinae. The magnitude of the differences among Phoca, Pusa, and Halichoerus was on the same order as that between species and subspecies within the genus Odocoileus. Because Cystophora is the closest relative of Pagophilus, the latter cannot be regarded as congeneric with Phoca; the differences between the two are great enough to justify placing them in separate genera (Perry et al. 1995).
Mouchaty et al. (1995) examined the cytochrome b gene and found a close phylogenetic relationship between P. hispida and Halichoerus grypus, which, they noted, merits further study.