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 )
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
Their lifespan ranges from 15 to 25 years, with the oldest recorded wild female grey seal living to be 46 years of age.
Range lifespan
Status: wild: 46 (high) years.
Typical lifespan
Status: wild: 15 to 25 years.
Average lifespan
Sex: male
Status: captivity: 43.0 years.
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
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 )
These seals are also hosts for a parasitic roundworm called cod worm (Pseudoterranova decipiens), that infects cod and other commercially harvested fish.
Commensal/Parasitic Species:
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.
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.
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
Perception Channels: tactile ; chemical
Pollution in the Baltic Sea has led to the declining population of the grey seal. The most dramatic increase in DDT and PCB levels in the Baltic occurred after 1955. Research conducted by Zakharov and Yablokov on skulls of grey seals investigated the notion that these increased pollutants result in skull asymmetry. Their study investigated whether morphological changes could be found in the grey seal population born during the major pollution episode that occurred after 1960. They studied skulls taken from seals born before 1940 and after 1960. It was shown that the pollution group had sharply increased levels of asymmetry in almost all characters analyzed. The findings indicate a dramatic change in the development stability of the Baltic grey seal during the period of heavy pollution after 1960, which could attribute to the rapid decline of the species (Zakharov 1990).
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.
The grey seal (Halichoerus grypus) is found on both shores of the North Atlantic Ocean. In Latin Halichoerus grypus means "hook-nosed sea pig". It is a large seal of the family Phocidae, which are commonly referred to as "true seals" or "earless 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[2] and the horsehead seal.[2][3]
There are two recognized subspecies of this seal:[4]
The type specimen of H. g. grypus (Zoological Museum of Copenhagen specimen ZMUC M11-1525, caught off the island of Amager, Danish part of the Baltic Sea) was believed lost for many years but was rediscovered in 2016, and a DNA test showed it belonged to a Baltic Sea specimen rather than from Greenland, as had previously been assumed (because it was first described in Otto Fabricius' book on the animals in Greenland: Fauna Groenlandica). The name H. g. grypus was therefore transferred to the Baltic subspecies (replacing H. g. macrorhynchus), and the name H. g. atlantica resurrected for the Atlantic subspecies.[6]
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 separate subspecies.[7]
This is a fairly large seal, with bulls in the eastern Atlantic populations reaching 1.95–2.3 m (6 ft 5 in – 7 ft 7 in) long and weighing 170–310 kg (370–680 lb); the cows are much smaller, typically 1.6–1.95 m (5 ft 3 in – 6 ft 5 in) long and 100–190 kg (220–420 lb) in weight.[8] Individuals from the western Atlantic are often much larger, with males averaging up to 2.7 m (8 ft 10 in) and reaching a weight of as much as 400 kg (880 lb) and females averaging up to 2.05 m (6 ft 9 in) and sometimes weighing up to 250 kg (550 lb). Record-sized bull grey seals can reach about 3.3 m (10 ft 10 in) in length.[9][10] A common average weight in Great Britain was found to be about 233 kg (514 lb) for males and 154.6 kg (341 lb) for females whereas in Nova Scotia, Canada adult males averaged 294.6 kg (649 lb) and adult females averaged 224.5 kg (495 lb).[8][11][12] It is distinguished from the smaller harbor seal by its straight head profile, nostrils set well apart, and fewer spots on its body.[13][14] Wintering hooded seals can be confused with grey seals as they are about the same size and somewhat share a large-nosed look but the hooded has a paler base colour and usually evidences a stronger spotting.[15] Grey seals lack external ear flaps and characteristically have large snouts.[16] Bull greys have larger noses and a less curved profile than harbor 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.
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In the United Kingdom and Ireland, the grey seal breeds in several colonies on and around the coasts. Notably large colonies are at Blakeney Point in Norfolk, Donna Nook in Lincolnshire, the Farne Islands off the Northumberland Coast (about 6,000 animals), Orkney and North Rona.[17] 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.[18]
In the Western North Atlantic, the grey seal is typically found in large numbers in the coastal waters of Canada and south to Nantucket 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 is found year-round off the coast of New England, in particular Maine and Massachusetts. Archaeological evidence confirms grey seals in southern New England with remains found on Block Island, Martha's Vineyard and near the mouth of the Quinnipiac River in New Haven, Connecticut.[19] Its natural range now extends much further south than previously recognised with confirmed sightings in North Carolina. Also, there is a report by Farley Mowat of historic breeding colonies as far south as Cape Hatteras, North Carolina.[3]
An isolated population exists in the Baltic Sea,[1] forming the H. grypus balticus subspecies.
Besides these very large colonies, many much smaller ones exist, some of which are well known as tourist attractions despite their small size. Such colonies include one on the Carrack rocks in Cornwall.
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.
Grey seals are vulnerable to typical predators for a pinniped mammal. Large sharks are known to prey on grey seals in Canada, particularly great white sharks but also, upon evidence, additionally Greenland sharks.[20][21] In the waters of Great Britain, grey seals are a fairly common prey species for killer whales.[22][23] Apparently, grey seal pups are sometimes taken alive by white-tailed eagles, as well.[1]
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,[25] wrasse[26] and skates[27] are also important locally. However, it is clear that the grey seal will eat whatever is available, including octopus[28] and lobsters.[29] 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.
Recent observations and studies from Scotland, The Netherlands, and Germany show that grey seals will also prey and feed on large animals like harbour seals and harbour porpoises.[30][31][32] In 2014, a male grey seal in the North Sea was documented and filmed killing and cannibalising 11 pups of his own species over the course of a week. Similar wounds on the carcasses of pups found elsewhere in the region suggest that cannibalism and infanticide may not be uncommon in grey seals. Male grey seals may engage in such behaviour potentially as a way of increasing reproductive success through access to easy prey without leaving prime territory.[33]
While it was originally understood that marine mammals communicate vocally, new research conducted by researchers at Monash University shows that grey seals clap their flippers as another form of communication. They clap their flippers underwater to deter a predator from attacking. If done during the mating season, the clapping can be used as a way to find a potential mate. The Monash researchers point out that seals are typically known for clapping, so this behavior may not be a surprise, but the clapping we know typically occurs in captivity. Clapping seals are associated with aquariums and zoos, but were never observed in the wild for this behavior. They were astonished at how loud these marine mammals were able to clap underwater, but it is logical for the reasons they do this.[34]
Grey seals are capital breeders; they forage to build up stored blubber, which is utilised when they are breeding and weaning their pups, as they do not forage for food at this time. They give birth to a single pup every year, with females' reproductive years beginning as early as 4 years old and extending up to 30 years of age. All parental care is provided by the female. During breeding, males don't provide parental care but they defend females against other males for mating.[35] The pups are born at around the mass of 14 kg.[36] They are born in autumn (September to December) 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.[36] Grey seal pups are precocial, with mothers returning to the sea to forage once pups are weaned. Pups also undergo a post-weaning fast before leaving the land and learning to swim.[37] 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 the U.S.[38] and Canada[39] there have been calls for a seal cull.
Seal pup first-year survival rates are estimated to vary from 80 to 85%[40][41] to below 50%[42] depending on location and conditions. Starvation, due to difficulties in learning to feed, appears to be the main cause of pup death.[42]
After near extirpation from hunting grey seals for oil, meat, and skins in the United States, sightings began to increase in the late 1980s. Bounties were paid on all kinds of seals up until 1945 in Maine and 1962 in Massachusetts.[43] One year after Congress passed the 1972 Marine Mammal Protection Act preventing the harming or harassing of seals, a survey of the entire Maine coast found only 30 grey seals.[43] At first grey seal populations increased slowly but then rebounded from islands off Maine to Monomoy Island and Nantucket Island off of southern Cape Cod. The southernmost breeding colony was established on Muskeget Island with five pups born in 1988 and over 2,000 counted in 2008.[44] According to a genetics study, the United States population has formed as a result of recolonisation by Canadian seals.[44] By 2009, thousands of grey seals had taken up residence on or near popular swimming beaches on outer Cape Cod, resulting in sightings of great white sharks drawn close to shore to hunt the seals.[45] A count of 15,756 grey seals in southeastern Massachusetts coastal waters was made in 2011 by the National Marine Fisheries Service.[46] Grey seals are being seen increasingly in New York and New Jersey waters, and it is expected that they will establish colonies further south.
Human noise pollution continues to affect marine-life communication but remains an understudied facet of marine conservation efforts. In more recent years, the potential negative effect of human noise has been highlighted with the discovery of seals using clapping as a form of communication.[34]
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 drowning in fishing gear.[47]
Grey seals have proved amenable to life in captivity and are commonly found in zoo animals around their native range, particularly in Europe. Traditionally they were popular circus animals and often used in performances such as balancing and display acts.
{{cite journal}}: CS1 maint: DOI inactive as of December 2022 (link) The grey seal (Halichoerus grypus) is found on both shores of the North Atlantic Ocean. In Latin Halichoerus grypus means "hook-nosed sea pig". It is a large seal of the family Phocidae, which are commonly referred to as "true seals" or "earless 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.
