Grey seal

Updated: June 2018

The grey seal (Halichoerus grypus) is a coastal or continental shelf marine mammal species, inhabiting the temperate areas of the North Atlantic. Grey seals haul out on exposed reefs or on beaches of undisturbed islands. They are relatively large, around 2m in length and 200-400kg in weight, with males larger than females. Besides the difference in size between the two genders, there are differences in shape as well. The snout of the adult male is elongated with a convex outline giving it an appearance like a horse head. The body colour of the adults may vary from entirely black to almost creamy-white, with males tending to be darker than females.

Grey seal assessment table

ABUNDANCE

Roughly 650,000, with the largest numbers on the east coasts of Canada and USA

DISTRIBUTION

Temperate waters of the North Atlantic

RELATION TO HUMANS

Small numbers taken mainly for skin, although meat and blubber are also used.

CONSERVATION AND MANAGEMENT

Management is the responsibility of the countries. The NAMMCO Coastal Seals Working Group provides scientific advice on stock status and sustainable takes.

© Amy Bishop

© Pixabay

Latin: Halichoerus grypus
Faroese: Láturkópur
Greenlandic: Sigguttooq
Icelandic: Útselur
Norwegian: Havert, gråsel
Danish: Gråsæl
English: Grey seal, gray seal

Lifespan

35-40 years

Productivity

One pup per year, age at maturity 5-7 years

Feeding

Generalists feeding on a wide variety of prey usually near the sea bottom (demersal and benthic fish)

Size

2m in length and 200-400kg in weight, with males larger than females

© Amy Bishop

General Characteristics

The grey seal (Halichoerus grypus) is a coastal or continental shelf marine mammal species, inhabiting the temperate areas of the North Atlantic. Grey seals haul out on exposed reefs or on beaches of undisturbed islands. They are relatively large, around 2m in length and 200-400kg in weight, with males larger than females. Besides the difference in size between the two genders, there are differences in shape as well. The snout of the adult male is elongated with a convex outline giving it an appearance like a horse head. The body colour of the adults may vary from entirely black to almost creamy-white, with males tending to be darker than females.

Reproduction

© Amy Bishop

Breeding occurs on islands, isolated beaches or on the pack ice. The grey seal starts breeding in late September with its maximum activity in October/November and continues until February/March. The gestation period of the female Grey seal is 11.5 months, including a 3-month delay in the implantation of the fertilised egg. Grey seals give birth to a single pup, in the autumn. Pups are born in a silky white fur which is moulted by the end of the lactation period, which lasts about 15-20 days. Pupping sites are usually on isolated skerries or uninhabited islands. In Canada, and also in the Baltic, spring-breeding seals may give birth on sea ice as well (“Report of the Committee on Hunting Methods” 2016).

Molting grey seal pup © Sandra Granquist

Foraging

Grey seals are generalist predators, consuming a wide variety of species. Their diet varies seasonally and geographically, but the species is considered as largely demersal or benthic feeders (Bowen et al. 1993).

The grey seal is a large consumer of sandeel (Ammodites spp.), which at times can be over 50% of their diet (Bowen & Harrison 1994, Hammond et al. 1994, Beck et al. 2007). In Canada sandeels and redfish (Sebastes sp.) together accounted for 40-91% of the diet (Bowen & Harrison 1994). Atlantic Cod can be an important part of the diet in some areas and seasons (Hammill et al. 2014). There is ongoing debate about the possible negative impacts of seal predation on certain groundfish populations. One factor contributing to this debate is the growth in grey seal populations in eastern Canadian waters over the past five decades and the concurrent decline, or in some cases collapse, of several groundfish populations in the 1990s (Hammill et al. 2014, Link 1).

In the Eastern Atlantic Stock, the most important prey are gadids, sandeel and wolffish (Anarchichus spp). (Prime & Hammond 1990, Hauksson & Bogason 1997, Mikkelsen et al. 2002). In the Outer Hebrides, UK, gadids account for 40% or more of the diet, sandeels are less important in this area (Hammond et al. 1994).

Atlantic cod
Atlantic cod
Sandeel
Redfish

Distribution and Habitat

Grey seals are distributed in the temperate waters of the North Atlantic. They usually move in specific corridor areas to travel between their foraging areas offshore and their haul-out sites on land (Jones et al. 2015). Satellite telemetry data from Canada show that West Atlantic grey seals perform much longer foraging trips (averaging 5-12 days) and often travel much larger distances than East Atlantic grey seals (Breed et al. 2009).

Grey seal populations in the North Atlantic. Iceland has been noted to be genetically different than the other Northeast Atlantic grey seals (Frie 2009).

North Atlantic Stocks

Found only in the North Atlantic, 3 populations of grey seals are recognized: the Northeast Atlantic, the Northwest Atlantic and Baltic Sea.

The North East Atlantic population is centred around the British Isles, ranging from Iceland, eastward along the coast of France, and north to Norway and the Kola Peninsula, Russia (Haug et al. 1994). Frie (2009) also noted that genetics studies indicate that the Icelandic grey seals are an isolated population.

The grey seal colony in the Faroe Islands seem to have evolved from UK colonies sometimes after the postglacial period due to geographical isolation. The Faroe Islands appears to have a localized population based on geographic isolation and genetics that is significantly different from Norwegian grey seals (Klimova et al. 2014). Movements of UK grey seals to the Faroe Islands have been documented (Mcconnell et al. 1999, Matthiopoulos et al. 2004), but the intensity or influence of such a migration is not known.

Norwegian populations are, on the other hand, connected to the UK and Russian populations (Henriksen et al. 2007).

The Baltic Sea population is concentrated in the central Baltic area, bounded by Sweden, Finland and Estonia (Harding et al. 2007)

The Baltic grey seal (Halichoerus grypus macrorynchus) is a recognised subspecies of the Atlantic grey seal (H.g.grypus). motivated by geographical separation and difference in birth timing (Oct. –Jan. in East Atlantic, Jan. – March in the Baltic , “NAMMCO SC/23/Report” 2016).

The North West Atlantic population is found from the north eastern United States to Cape Chidley at the northern tip of Labrador (60° N), with the largest concentration around Sable Island, off the Nova Scotia coast. Canadian grey seals form a single genetic population that is divided into three groups for management purposes based on the location of breeding sites. Most pups (81%) are born on Sable Island (Sable), while 15% are born in the Gulf of St Lawrence (Gulf) and 4% are born along the coast of Nova Scotia (CNS) (“NAMMCO SC/23/Report” 2016)

Grey seal populations in the North Atlantic. Iceland has been noted to be genetically different than the other Northeast Atlantic grey seals (Frie 2009).

North East Atlantic

A recent population modelling study indicated an increase in abundance of the total Norwegian grey seal population during the last 30-years, suggesting a total of 8,740 (95% CI 7,320-10,170) animals estimated in 2011 (Øigård et al. 2012). New boat based surveys carried out in in 2014-2015 showed a significant decrease in the grey seal pup production compared with the counts in the period 2007-2008, likely due to high levels of by-catch in the monkfish fishery.  Bayesian state-space modelling methodology for British grey seal populations. Estimated adult population size in 2014 was 95,200 (95% CI 76,400-127,500). The most recent abundance estimate of grey seals in Iceland is of 4,200 (95% CI: 3,400-5,000) animals in 2012. The present population size of the Faroe Islands is probably on the level of 1,000-2,000 animals (“NAMMCO SC/23/Report” 2016). On the other hand, no updated population estimate is present since the early 1990s (Haug et al. 1994) from Russia, when the total grey seal population were calculated to be about 3400. Following a remarkable increase in 2014, the total number of grey seals in the Wadden Sea (Danish, German and Dutch coasts) was 4,521 during the moulting period in spring. In France, the most recent data available was a count of 150 grey seals 2007 (“NAMMCO SC/23/Report” 2016).

North West Atlantic

The most recent assessment of Canadian grey seals was completed in 2014. the model estimated a total grey seal pup production in Atlantic Canada of 93,000 (95% CI=48,000-137,000), with an associated total population of 505,000 (95% CI=329,000-682,000). The model predicts that population size in all three management areas continues to grow (“NAMMCO SC/23/Report” 2016).

In the United States, a survey was conducted in 2016 to estimate pup production in and efforts are underway to derive a minimum population estimate and population trend. A survey in 2002 counted a total of around 3300 seals (Wood et al. 2007).

Baltic

The last population survey in 2014 indicated around 33,000 seals in the Baltic and an increasing trend (“NAMMCO SC/23/Report” 2016).

© Amy Bishop

North East Atlantic

In the UK, between the early 1960s and the early 1990s, grey seal pup production progressively increased. At colonies in the Inner and Outer Hebrides, production appeared to stabilize during the 1990s and has remained so. Pup production at colonies in Orkney and in the North Sea has continued to increase but in recent years the rate of increase has declined. This may imply that the UK grey seal population is incurring in some density dependent factors, limiting its size (Duck & Thompson 2007).

The Icelandic grey seal population has increased from the 1960s until 1982, then has likely decreased by about 3% (95% CI 1% – 5%) annually from 1982 to 2002. After 1990 the rate of population decline was probably more rapid at about of 6% per year, causing a marked decline since the mid-1990s (Hauksson 2007).

For the Faroe Islands, the present biological knowledge on grey seals is very limited, largely due to their inaccessible nature. These seals have most likely been hunted since the early human settlements on the islands in the 8th century. This has probably prevented the population from increasing above a certain threshold. In addition, since the establishment of aquaculture in the islands in late 1970s, seals have been subject to removals around salmon sea farms, and generally suffer high pup mortality, due to the exposed breeding grounds (Mikkelsen 2007).

In mainland Europe the grey seal was a common species during the Stone Age (8,000-5,500 BC). Along the North Sea coast populations started to decline substantially during the 11th century as a result of excessive hunting. The last breeding populations disappeared in the 16th century in the Wadden Sea, and before 1900 in the Kattegat-Skagerrak and the Southwestern Baltic as a result of an extermination campaign. No regular pupping occurred along mainland Europe until the end of the 1970s. Tracking of movements indicate these seal groups to be linked to the larger populations in the UK (Härkönen et al. 2007). It seems that the grey seal population is currently increasing in this area and establishing itself further in the Wadden Sea area and northwards (“NAMMCO SC/23/Report” 2016)

North West Atlantic

The part of the population in the Gulf of St. Lawrence increased from 15,500 (95% CI = 14,600-16,300) animals in 1970 to 62,700 (95% CI = 49,800-67,800) animals by 1996 and then declined to 22,300 (95% CI = 17,200-28,300) animals in 2000. On Sable Island the population has increased from 4,800 (95% CI = 4,700-4,900) animals in 1970 to 212,500 (95% CI = 159,600-276,200) in 2000. Overall there has been a deterioration in ice conditions since 1996, which is supposed to have a negative impact on breeding success of the pagophilic species, including grey seals. On the other hand, the populations on Sable Island has experienced a different trajectory, with a continuous growth. This difference can be due to the higher mortality rates in the Gulf, and partially to a net movement of animals from one area to the other (Hammill et al. 2007).

The establishment of the grey seal population in US water is recent and little information is available to describe its status and trends.

Baltic

The grey seal population in the Baltic Sea went through a depression in the 1970s with numbers as low as only 3,000 individuals. The population is recovering after a century of bounty hunting and 3 decades of low fertility rates caused by environmental pollution. A conservative estimate of the population size in 2003 was 19,400 animals, and available data suggest an annual rate of increase of 7.5% since 1990. The growing population has led to increased interactions with the fishery, and demands are being raised for the re-introduction of the hunt. Due to a potential risk of quasi-extinction, the overall recommendation is that hunting should be kept to a minimum, carefully documented and accompanied by close population monitoring (Harding et al. 2007).

© Pixabay
© Pixabay

Norway

Management plans for coastal seals in Norway were adopted and implemented by the Ministry of Fisheries and Coastal Affairs on the 5th November 2010. The goal of the management plans is to ensure viable populations of harbour and grey seals within their natural distribution areas. Grey seals are monitored by counting pups and the government decided that the population should be stabilized so that 1,200 pups can be recorded annually. The quotas are based on scientific advice in accordance with the management plan. Three geographical Management Units (MU) for grey seals are used, based on biological evidence (the Southern MU from Lista to Stad; the Central MU from Stad to Lofoten; and the Northern MU from Vesterålen to Varanger). However, the administration of hunting licenses and hunting statistics is undertaken by the county authorities (“NAMMCO SC/23/Report” 2016).

Iceland

In 2006, the Icelandic government published a management plan where a target grey seal population size of 4,100 was recommended (NAMMCO annual report, 2006). Management actions should be initiated if the population dropped appreciably below that number, but no specific population regulating method was mentioned.

United Kingdom

Under the Conservation of Seals Act 1970, the UK Natural Environment Research Council (NERC) has a duty to provide scientific advice to the government on matters related to the management of seal populations. NERC has appointed a Special Committee on Seals (SCOS) to formulate this advice. Formal advice is given annually based on the latest scientific information provided to SCOS by the Sea Mammal Research Unit (“[SCOS] Special Committee on seals. Scientific advice on matter related to the management of seal populations: 2004”).

Baltic

Given the continuous distribution of the species and free movement of individuals in the Baltic Sea the species is treated as a single management unit, and the grey seal management principles are defined by the HELCOM 2006 Seal Recommendation. The long term objectives are: to allow population growth towards the carrying capacity, to allow the breeding seals to expand to suitable distribution in all areas of the sea, and attaining health status that secures continued existence of the populations. The population target limit is defined by the ecological carrying capacity (“NAMMCO SC/23/Report” 2016).

Canada

The Canadian grey seal population is managed by the governmental organization Fisheries and Ocean Canada. Currently the Canadian grey seal is considered a data-rich species, with three or more abundance estimates over a 15-year period, with the most recent estimate obtained within the last five years. Information (≤5 years old) on fecundity and/or mortality is also required in order to determine sustainable levels of exploitation.

All Canadian Atlantic seal populations are managed under a precautionary approach. Three types of reference points are identified: the Critical Limit, which is the level below which a population is considered to have likely experienced serious and irreversible harm, and below which, all human induced removal should be stopped; the Precautionary Reference Point, above which the population is considered to be healthy and conservation is not considered to be of greatest concern; the Target Reference Point, the level at which industry and management would like the population to remain.

The Canadian Standing Senate Committee on Fisheries and Oceans has in 2012 recommended to the Department of Fisheries and Oceans to implement for a period of four years, starting in 2013, a targeted removal program in the southern Gulf of St. Lawrence to hopefully reduce the level of the grey seal impact on groundfish.

North East Atlantic

Norwegian and Icelandic catch data for Grey seals between 1993 and 2015, from CSWG (2016) and National Progress Reports.

Norwegian grey seals are subject to a non-commercial hunt. Hunting is usually performed by shooting the animal from land and retrieving it in the water with the support of a small boat.

Seal hunting in Iceland is focussed almost entirely on seal pups, mainly for the skin; but the meat, the blubber (fat) and the flippers played an important role for human consumption in the past. Pups are taken when they are a few weeks old, just towards the end of lactation. Annual takes are less than 400 pups. The grey seal pups are almost entirely caught in the whelping areas, using either a seal club or a rifle from a very short distance. For hunting of adult grey seals a rifle is used. The grey seal pups’ skins are tanned for the leather industry, and this is a very strong leather material. The meat is used fresh, salted or smoked.

Traditional seal hunting virtually ceased in the Faroe Islands since the late 60’s with the new weapon regulations, banning the use of rifle as hunting weapons. In the early 1980’s, fish farms were introduced and with them the problems of seals’ interaction with the farmed fish. Farmers were then given permission to possess rifles and are not required to keep hunting logbooks or to retrieve the shot animals. There is no longer any tradition to utilise seal meat and blubber or the fur in the Faroe Islands (“Report of the Committee on Hunting Methods” 2016).

Baltic

The Baltic grey seal population is now recovering after commercial over-harvesting in the first half of the 20th century. Seal hunting was stopped entirely in Sweden in 1975 and in Finland in 1982, and only recently restarted in 2001 and 1997 respectively. Seal hunting is now strictly regulated in both countries. Hunting from boats is not permitted. During the spring period seals are hunted on the ice. Seals sink quickly in the Baltic because the salinity of the water is very low. Also the water is not very clear, which makes retrieval of sunken seals difficult. Therefore, hunters prefer areas of shallow water where sunken seals can be retrieved more easily. Hunting is forbidden in seal reserves, which include all the major resting-places for seals in the Baltic (“Report of the Committee on Hunting Methods” 2016).

North West Atlantic

A commercial juvenile grey seal hunt usually runs from early February until early March, mainly along the Eastern Shore of Nova Scotia and in the Southern Gulf of St Lawrence. The grey seal Total Allowable Catch for 2016 is 60,000 animals. All Commercial Seal license holders are subject to complete a mandatory training.

Other human impacts

The most important anthropogenic sources of mortality for grey seals, other than hunt, are by-catches during fishing operations, removal during interactions with fish farms and pollution.

By-catches

In Norway, the levels of by-catch of grey seals in fishing operations are estimated using three different sources: mark recapture data, data from the Coastal Reference Fleet (a monitored segment of the coastal fishing fleet), and from modelling population trajectories. For grey seals this resulted in an estimate of total by-catch of 8,379 animals for the period 1997-2014, with an annual by-catch of 466 grey seals. The by-catch of grey seals is about twice the annual hunt (240 seals). It is likely that the level of by-catches has been increasing in recent years north of 62°N due to an increase in fishing effort with large mesh gill nets, particularly in the monkfish fishery.

In Iceland, the most reliable by-catch data originate from the March-April cod gillnet research survey and with fisheries observers (1% coverage of the fleet and representative geographical spreading). The main fisheries of most concern are assumed to only be the gillnet fishery for cod & lumpsucker, with species of concern being, respectively, harbour porpoise and harbour and grey seals.

In the Faroe Islands, the use of pelagic or semi-pelagic trawl fishery with very high vertical opening and herring set gillnet is source of mortality for several marine mammals, including grey seals (“NAMMCO SC/23/Report” 2016).

There is an increasing problem with interactions between seals and commercial fisheries in the Baltic, and herring gillnet fishery is particularly vulnerable to this (“Report of the Committee on Hunting Methods” 2016).

In the Western Atlantic (Canadian waters), no the other hand, no data are available on incidental catches in fishing operations, but the numbers are thought to be small (“NAMMCO SC/23/Report” 2016)

Fish farming

In the Faroe Islands, the most significant human-grey seals interaction is in connection with salmon farming. The total numbers of grey seals removed at aquaculture farms in the Faroe Islands are estimated to be around 150-250 grey seals annually. These removal levels (150-250 seals) are around 10-20% of the rough estimate of population size (“NAMMCO SC/23/Report” 2016).

Pollutants

Pollutants have been problematic especially for the Baltic grey seal populations during several decades. Bergman (1999) reported, in a long term study, earlier, reduced reproductive ability with lesions of the female reproductive organs and rate of pregnancy, as well as a disease complex in adult individuals of both sexes. This, together with hunting, was the major contributor of the population decrease in the 1970’s.

Abundances

In 2001, NAMMCO’s Scientific Committee noted that the abundance of grey seals around Iceland had declined sharply, while there were apparent increases in grey seal abundance in other areas. Grey seals had been assessed by NAMMCO in 1997 and 1998. In 2003, a working group on grey seals was sponsored, resulting in the publication of a volume assessing the status of grey seals in the North Atlantic (Haug, Hammill, & Ólafsdóttir 2007).

Grey seal abundances are often evaluated by determining the number of pups born in a season, usually using aerial surveys. This can either be used as an index of total population abundance or the latter can be estimated from pup production via numerical modelling. Ongoing research has been addressing the best way to obtain viable population estimates from pup counts, for example using a Bayesian model approach (Øigård et al. 2012).

Diet

Because of the potential impact that grey seals may have on fish species of economic interest, a large amount of studies focuses on mapping the diet of this predator. The variation between time periods and geographical areas does not allow for a wide generalization across systems, therefore management decisions need to be based on individual assessment of local diets.

Movements

Grey seals habitat usage maps are important information to focus conservation efforts and enable spatial management of human activities. Because of this, grey seals movement is another common topic of research, which has increased widely in the last decades with the introduction of telemetry methods (Matthiopoulos et al. 2004).

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