Thegrey seal (Halichoerus grypus) is a largeseal of thefamilyPhocidae, which are commonly referred to as "true seals" or "earless seals". The only species classified in thegenusHalichoerus, it is found on both shores of the NorthAtlantic Ocean. InLatin,Halichoerus grypus means "hook-nosed sea pig". Its name is spelledgray seal in theUnited States; it is also known asAtlantic seal[2] and thehorsehead seal.[2][3]
There are two recognized subspecies of this seal:[4]
Image
Subspecies
Distribution
Halichoerus grypus grypusFabricius, 1791
Baltic Sea
Halichoerus grypus atlanticaNehring, 1886
western North Atlantic stock (eastern Canada and the northeastern United States), the eastern North Atlantic stock (British Isles, Iceland, Norway, Denmark, the Faroe Islands, and Russia)[5]
The type specimen ofH. g. grypus (Zoological Museum of Copenhagen specimen ZMUC M11-1525, caught in 1788 off the island ofAmager, Danish part of theBaltic 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 inOtto Fabricius' book on the animals in Greenland:Fauna Groenlandica). The nameH. g. grypus was therefore transferred to the Baltic subspecies (replacingH. g. macrorhynchus), and the nameH. 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]
A juvenile grey seal swims in the Farne Islands, UK.
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 inGreat Britain was found to be about 233 kg (514 lb) for males and 154.6 kg (341 lb) for females whereas inNova 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 smallerharbor seal by its straight head profile, nostrils set well apart, and fewer spots on its body.[13][14] Winteringhooded seals can be confused with grey seals as they are about the same size and somewhat share a large-nosed look. They can be distinguished by the fact that the hooded seal 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.
Besides these very large colonies, many much smaller ones exist, some of which are well-known tourist attractions, despite their small size. Such colonies include one on theCarrack rocks,Cornwall.
During the winter months, grey seals can be seenhauled 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; their primary predator would be theorca or killer whale, but certain large species of sharks are known to prey on grey seals inNorth American waters, particularlygreat white sharks andbull sharks but also, upon evidence, additionallyGreenland sharks. Some grey seal carcasses have washed ashore with visible "cookie cutter" bite marks, a telltale sign of attack by a Greenland shark (also called the sleeper shark).[21][22] In the waters ofGreat Britain, grey seals are a fairly common prey species forkiller whales.[23][24] In the Baltic, grey seal pups are prey forWhite-tailed eagles, andGreat black-backed gulls.[1]
A short video on monitoring and conservation of grey seals at Skomer IslandCaptive grey seal being fed, showing snout shape
The grey seal feeds on a wide variety offish, mostlybenthic ordemersal 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 othergadids,flatfish,herring,[26]wrasse[27] andskates[28] are also important locally. However, it is clear that the grey seal will eat whatever is available, includingoctopus[29] andlobsters.[30] 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 likeharbour seals andharbour porpoises.[31][32][33] In 2014, a male grey seal in theNorth 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 thatcannibalism andinfanticide 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.[34][35]
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 behaviour 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 behaviour. They were astonished at how loud these marine mammals were able to clap underwater, but it is logical for the reasons they do this.[36]
Grey seals are capital breeders; they forage to build up stored blubber, which is utilised when they are breeding and feeding 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 do not provide parental care but they defend females against other males for mating.[37] The pups are born at around the mass of 14 kg.[38] 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.[38] 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.[39] 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.[40] andCanada[41] there have been calls for a seal cull.
Seal pup a few days after birth
Seal pup first-year survival rates are estimated to vary from 80 to 85%[42][43] to below 50%[44] depending on location and conditions. Starvation, due to difficulties in learning to feed, appears to be the main cause of pup death.[44]
Male grey seals engage in aggressive sexual behaviour, which can lead to severe injuries and even death for the female. Sometimes they will also target females from other seal species.[45] In theNorth Sea, multiple cases were recorded of pregnant harbour seals dying as a result offorced copulation with male grey seals.[46]
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 inMaine and 1962 inMassachusetts.[47] One year after Congress passed the 1972Marine Mammal Protection Act preventing the harming or harassing of seals, a survey of the entire Maine coast found only 30 grey seals.[47] At first grey seal populations increased slowly but then rebounded from islands off Maine toMonomoy Island andNantucket Island off of southernCape Cod. The southernmost breeding colony was established onMuskeget Island with five pups born in 1988 and over 2,000 counted in 2008.[48] According to a genetics study, the United States population has formed as a result of recolonisation by Canadian seals.[48] By 2009, thousands of grey seals had taken up residence on or near popular swimming beaches on outer Cape Cod, resulting in sightings ofgreat white sharks drawn close to shore to hunt the seals.[49] A count of 15,756 grey seals in southeastern Massachusetts coastal waters was made in 2011 by theNational Marine Fisheries Service.[50] Grey seals are being seen increasingly inNew York andNew 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.[36]
In the UK seals are protected under theConservation of Seals Act 1970; however, it does not apply toNorthern 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 theBaltic Sea 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 inSweden andFinland, with 50% of the quota being used. Otheranthropogenic causes of death include drowning in fishing gear.[51]
Grey seals have proved amenable to life in captivity[citation needed] and are commonly found as 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.
^Boskovic, R.; et al. (1996). "Geographic distribution of mitochondrial DNA haplotypes in grey seals (Halichoerus grypus)".Canadian Journal of Zoology.74 (10):1787–1796.Bibcode:1996CaJZ...74.1787B.doi:10.1139/z96-199.
^Hall, Ailsa; Thompson, David (2009). "Grey Seal (Halichoerus gryphus)". In Perrin, W. F.; Würsig, B.; Thewissen, J. G. M. (eds.).Encyclopedia of marine mammals. Academic Press. pp. 500–502.ISBN978-0-08-091993-5.
^Schuster, Marreno; Glen, Megan (2011).Marine Science: The Dynamic Ocean. US Satellite Laboratory: Pearson. p. 107.ISBN978-0-13-317063-4.
^Waters, Joseph H. (February 1967). "Gray Seal Remains from Southern New England Archeological Sites".Journal of Mammalogy.48 (1):139–141.doi:10.2307/1378182.JSTOR137818.
^Hillmer, Angelika (16 February 2015). "Kegelrobben mit großem Appetit auf Schweinswale" [Grey seals with a great appetite for porpoises].Hamburger Abendblatt (in German).
^Bubac, Christine M.; Coltman, David W.; Don Bowen, W.; Lidgard, Damian C.; Lang, Shelley L. C.; den Heyer, Cornelia E. (June 2018). "Repeatability and reproductive consequences of boldness in female gray seals".Behavioral Ecology and Sociobiology.72 (6): 100.Bibcode:2018BEcoS..72..100B.doi:10.1007/s00265-018-2515-5.ISSN0340-5443.S2CID46975859.
^ab"Homepage".Friends of Horsey Seals. Retrieved19 March 2021.
^Wilson, Susan C. (1975). "Attempted Mating between a Male Grey Seal and Female Harbor Seals".Journal of Mammalogy.56 (2):531–534.doi:10.2307/1379389.JSTOR1379389.
^abBarbara Lelli; David E. Harris & AbouEl-Makarim Aboueissa (2009). "Seal Bounties in Maine and Massachusetts, 1888 to 1962".Northeastern Naturalist.16 (2):239–254.doi:10.1656/045.016.0206.S2CID85652019.
^abWood, S.A.; Frasier, T.R.; McLeod, B.A.; Gilbert, J.R.; White, B.N.; Bowen, W.D.; Hammill, M.O.; Waring, G.T.; Brault, S. (2011). "The genetics of recolonization: an analysis of the stock structure of grey seals (Halichoerus grypus) in the northwest Atlantic".Canadian Journal of Zoology.89 (6):490–497.Bibcode:2011CaJZ...89..490W.doi:10.1139/z11-012.
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