Updated: July 2020
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 2 m in length and 200–400 kg in weight, with males larger than females. In addition to the difference in size between the sexes, 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.
There are estimated to be approximately 650,000 grey seals globally, with the largest numbers found on the east coasts of Canada and the USA.
They are found in temperate waters of the North Atlantic.
Small numbers of grey seals are harvested. This is primarily for their skin, although meat and blubber are also used.
The NAMMCO Coastal Seals Working Group provides scientific advice on stock status and sustainable takes, although management actions are the responsibility of the member countries.
In the most recent assessment (2016) the species is listed as ‘Least Concern’ on the global IUCN Red List as well as on the Norwegian national red list. It is listed as ‘Vulnerable’ on the Icelandic national red list as of 2018.
Scientific name: Halichoerus grypus
Norwegian: Havert, gråsel
English: Grey seal, gray seal
One pup per year, age at maturity 5-7 years
Generalists feeding on a wide variety of prey usually near the sea bottom (demersal and benthic fish)
2m in length and 200-400kg in weight, with males larger than females
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 2 m in length and 200–400 kg in weight, with males being larger than females. In addition to the difference in size between the sexes, 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.
Breeding occurs on islands, isolated beaches, or on pack ice. The grey seal starts breeding in late September and continues until February/March, with peak activity taking place in October/November. The gestation period 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 with a silky white fur that is moulted by the end of the lactation period, which lasts around 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 (NAMMCO 2016c).
Grey seals are generalist predators, consuming a wide variety of species. Their diet varies seasonally and geographically, but the species is considered to be 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 a study conducted in Canada, sandeels and redfish (Sebastes sp.) together accounted for 40-91% of the diet (Bowen & Harrison 1994). Atlantic Cod can also 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).
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 and sandeels are less important in this area (Hammond et al. 1994).
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).
North Atlantic Stocks
Grey seals are only found in the North Atlantic and 3 populations are recognised: the Northeast Atlantic, the Northwest Atlantic and Baltic Sea populations.
The Northeast 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) has noted that genetic studies indicate that the Icelandic grey seals are an isolated population.
The grey seal colony in the Faroe Islands seems to have evolved from UK colonies sometimes after the postglacial period due to geographical isolation. The Faroe Islands appears to have a localised population based on geographic isolation and genetic studies that indicate it 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). This subspecies delineation has been determined by geographical separation and differences in the timing of births (October–January in the Northeast Atlantic, and January–March in the Baltic population)(NAMMCO 2016a).
The Northwest 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 2016a).
A population modelling study has indicated an increase in abundance of the Norwegian grey seal population during the last 30 years, with a total of 8,740 (95% CI: 7,320–10,170) animals estimated in 2011 (Øigård et al. 2012, NAMMCO 2016d). New boat-based surveys carried out in 2014–2015 did, however, show 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 has been used for British grey seal populations. The estimated adult population size in 2014 was 95,200 (95% CI: 76,400–127,500) (Øigård et al. 2012)
The latest aerial census to estimate the status of the grey seal population in Iceland was conducted in 2017. The total population size was estimated to be 6269 (95% CI: 5375–7181) (Granquist & Hauksson 2019).
The present population size of the Faroe Islands is probably on the level of 1,000-2,000 animals (NAMMCO 2016d).
No updated population estimate from Russia is available since the early 1990s, when the total grey seal population was calculated to be about 3,400 (Haug et al. 1994).
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 (NAMMCO 2016d).
In France, the most recent data available was a count of 150 grey seals in 2007 (NAMMCO 2016d).
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 2016d).
In the United States, a survey was conducted in 2016 to estimate pup production and efforts are underway to derive a minimum population estimate and population trend. A survey in 2002 counted a total of around 3,300 seals (Wood et al. 2007).
The last population survey in 2014 indicated around 33,000 seals in the Baltic and an increasing trend (NAMMCO 2016d).
Iceland and the Faroe Islands
The Icelandic grey seal population increased from the 1960s until 1982, then 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. This means that there has not, as yet, been a population assessment performed on grey seals in the Faroe Islands. Irregular observations around the islands indicate that the Faroese population has not seen a rapid increase, as has been evident for colonies around Britain and in West Atlantic (Bowen et al. 2003). 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. They also generally suffer high pup mortality due to the breeding grounds being exposed to intense fall storms (Mikkelsen 2007). For the relatively small population of grey seals in the Faroes, removal of a significant number of animals around fish farms, together with high pup mortality, has the potential to significantly impact the size and development of the population (NAMMCO 2016d).
UK, North Sea and mainland Europe
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 stabilise during the 1990s and has remained so since then. Pup production at colonies in Orkney and in the North Sea has continued to increase, although in recent years the rate of increase has declined. This may imply that the UK grey seal population is encountering some density dependent factors that are limiting its size (Duck & Thompson 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. As a result of an extermination campaign, the last breeding populations disappeared in tthe Wadden Sea the 16th century, as well as in the Kattegat-Skagerrak and the Southwestern Baltic before 1900. No regular pupping occurred along mainland Europe until the end of the 1970s. Tracking of movements indicates 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 is now establishing itself further in the Wadden Sea area and northwards (NAMMCO 2016a).
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 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 had a negative impact on the breeding success of pagophilic species (species preferring ice), including grey seals. On the other hand, the populations on Sable Island have 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 most recent assessment of Canadian grey seals was completed in 2014. A population model incorporating estimates of reproductive rates up to 2012 was fitted to pup production estimates up to 2010 to describe the dynamics of the grey seal population in Atlantic Canada. Combining all three herds, the model estimated a total 2014 grey seal pup production in Atlantic Canada of 93,000 (95% CI: 48,000–137,000) animals, with an associated total population of 505,000 (95% CI: 329,000–682,000). The model indicates that population size in all three management areas continues to grow (NAMMCO 2016d).
The establishment of the grey seal population in US waters is recent and little information is available to describe its status and trends. Efforts are, however, underway to derive a minimum population estimate and trend for the portion of the grey seal stock in US waters, based on aerial surveys conducted in Massachusetts from 2005–2015 during grey seal moulting periods. In addition, the use of fixed-wing and rotary drones, as well as manned aircraft, was used to conduct surveys in 2016 over the grey seal breeding grounds in the US. It is planned to use these data together with those collected by Department of Fisheries & Oceans Canada (DFO) in 2016 to estimate pup production over the entire range of the stock (NAMMCO 2016d).
The grey seal population in the Baltic Sea went through a depression in the 1970s, with numbers as low as 3,000 individuals. The population is now recovering after a century of bounty hunting and 3 decades of low fertility rates caused by environmental pollution. The grey seal population is monitored by counting the hauled out proportion of the animals during the annual moult. The counts are based on aerial photography and monitoring effort is synchronised between countries to reduce double counting. Population increase is calculated from the counts and reached 10–12% per annum during the early 2000s, but has slowed to about 6% in recent years (NAMMCO 2016d). Counted numbers fluctuate annually due to weather and other factors, however clear increasing trends in populations can be observed in all parts of the Baltic Sea. The growing population has led to increased interactions with fisheries and demands are now being made for a 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).
Management plans for coastal seals in Norway were adopted and implemented by the Ministry of Fisheries and Coastal Affairs on 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 stabilised to ensure that at least 1,200 pups are recorded annually. Quotas for removals 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). The administration of hunting licenses and hunting statistics is undertaken by the county authorities (NAMMCO 2016a).
In 2006, the Icelandic government published a management plan where a target grey seal population size of 4,100 was recommended (NAMMCO 2006). Management actions should be initiated if the population dropped appreciably below that number, although no specific population regulating method is mentioned.
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 2004).
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 carrying capacity, to allow breeding seals to expand to suitable distribution in all areas of the sea, and attaining a health status that secures the continued existence of the populations. The population target limit is defined by the ecological carrying capacity (NAMMCO 2016a).
The Canadian grey seal population is managed by the governmental organisation 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, and; the Target Reference Point, the level that industry and management would like the population to remain.
In 2012, the Canadian Standing Senate Committee on Fisheries and Oceans 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 reduce the level of the grey seal impact on groundfish.
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 almost entirely focussed on seal pups, which are taken mainly for their skin but the meat, blubber and the flippers have also played an important role for human consumption in the past. The grey seal pups’ skins are tanned for the leather industry and are a very strong material. The meat is used fresh, salted or smoked. 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.
Traditional seal hunting has virtually ceased in the Faroe Islands since the late 1960s with new weapon regulations that baned the use of the rifle as a hunting weapon. In the early 1980s, fish farms were introduced and this lead to problems with seals’ interaction with the farmed fish. Farmers with a licence were then given permission to possess and use rifles as a weapon. All shot animals must be reported to the governmental authorities. There is no longer any tradition to utilise seal meat, blubber or skin in the Faroe Islands (NAMMCO 2016c).
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, although it was 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. Since the water is not very clear, retrieval of sunken seals is 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 (NAMMCO 2016c).
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 (TAC) for 2016 was 60,000 animals. All commercial seal license holders are required to complete a mandatory training program.
REPORTED CATCHES IN NAMMCO MEMBER COUNTIES
|Norway||2020||Finnmark - Lofoten||4||140|
|Norway||2020||Lofoten - Stad||0||0|
|Norway||2020||Stad - Rogaland||12||60|
|Norway||2019||Finnmark - Lofoten||22||140|
|Norway||2019||Lofoten - Stad||0||0|
|Norway||2019||Stad - Rogaland||40||60|
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Other human impacts
The most important anthropogenic sources of mortality for grey seals (other than hunting) are by-catch during fishing operations, removal during interactions with fish farms, and pollution.
Although it is known that there is a degree of grey seal mortality due to by-catch in commercial fisheries (particularly gillnet fisheries), estimating the exact level is challenged by the potential for misidentification of seal species in logbook and inspector reports. This is particularly the case for young seals, where grey and harp seals can be misidentified and reported as harbour seals. There are now attempts underway in some countries to minimise this misidentification through the use of photos and analysis of DNA samples.
In Norway, the levels of by-catch of grey seals in fishing operations have been estimated using a range of data sources over the years, including: mark recapture data, data from the Coastal Reference Fleet (CRF) (a monitored segment of the coastal fishing fleet), and modelling of population trajectories. Using data from the CRF (scaled up to the whole fleet using national landing statistics) is currently the preferred data source for by-catch estimates. Although analysis remains ongoing and improvements in precision are still being made, preliminary estimates suggest a by-catch of grey seals in the low hundreds each year in Norwegian gillnet fisheries (Moan & Bjørge 2020). The by-catch of grey seals in Norway appears to be at a level similar to the annual hunt and therefore is important to include in population assessments. It is also likely that the level of by-catch 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 main fisheries of concern for grey seal by-catch are the gillnet fishery for cod and lumpsuckers. In a report from 2019, just below 1000 grey seals were reported to be caught annually in lumpsucker gillnets between 2014–2018 (Marine and Freshwater Research Institute 2019). The most reliable by-catch data for cod gillnets comes from the March-April research survey and from the reports of fisheries observers (1% coverage of the fleet and representative geographical spreading). However, estimating by-catch in cod gillnets remains difficult due to a lack of data outside of April.
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 marine mammals, including grey seals (NAMMCO 2016a).
There is an increasing problem with interactions between seals and commercial fisheries in the Baltic, and herring gillnet fishery is particularly vulnerable to this (NAMMCO 2016c).
In Canadian waters in the Northwest Atlantic, no data are available on incidental catches in fishing operations, although the numbers are thought to be small (NAMMCO 2016a).
Until recently, the most significant human-grey seal interaction in the Faroe Islands was in connection with salmon farming. The practice of culling grey seals interacting with fish farming installations is, however, banned by law since 14 May 2020 (National Progress Report Faroe Island 2020). Before this, the total numbers of grey seals removed at aquaculture farms in the Faroe Islands were estimated to be around 150-250 grey seals annually. These removal levels were around 10-20% of the approximate estimate of the population size (NAMMCO 2016a).
Pollutants have been problematic over a period of several decades, especially for the Baltic grey seal population. In a long term study, Bergman (1999) reported reduced a reproductive ability, reduced pregnancy rate, and lesions on the female reproductive organs, as well as a disease complex in adult individuals of both sexes. This, together with hunting, was seen to be the major contributor to the population decrease in the 1970s.
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 (NAMMCO 2001). 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).
A programme for estimating the abundance of grey seals in the Faroe Islands started in summer 2018, visiting all islands except Suðuroy and using both boats and drone footage (National Progress Report Faroe Islands 2018). During the summer of 2019, the total shoreline of the archipelago was surveyed by boat (with the exception of the east side of Suðuroy), and all seals hauled-out and in the water were counted. Each island was visited 1–3 times and in high-density areas, footage captured by drone was used to improve accuracy (National Progress Report Faroe Islands 2019).
In July 2020, two grey seals in Vestmannasund were tagged in an effort to study the potential disturbance from ocean turbines recently installed in this narrow strait. Land-based observations of marine mammal occurrences in the area were also performed between June and August. Both of the tagged seals were found to move within the strait for a significant proportion of the time. Several longer-distance trips were also made, but the seals never made any offshore movements (National Progress Report Faroe Island 2020).
In 2021, there are plans to expand the summer census to include camera traps and satellite tracking, in order to study grey seal behaviour and to further improve the accuracy of the abundance estimate (National Progress Report Faroe Island 2020).
The latest aerial census to estimate the current status of the Icelandic grey seal population was conducted in 2017, with the analyses published in 2019 (Granquist & Hauksson 2019). The total population size was estimated to be 6269 (95% CI: 5375–7181). Breiðafjörður was the most important pupping area in Iceland, with 58% of the total pup production in 2017.
In Iceland in October 2016, five grey seal pups were tagged with satellite tags to map habitat use (National Progress Report Iceland 2018). The results of this research were published in 2019 (Baylis et al. 2019).
A study of Icelandic grey seal genetics was initiated in 2016, in cooperation between the Marine and Freshwater Institute (MFRI), the Icelandic Seal Center (ISC), the Natural History Museum of Denmark and Main University. Analysis is ongoing (National Progress Report Iceland 2019).
A project investigating environmental toxicants in seals in Icelandic waters was initiated by MFRI in 2017 and analysis is ongoing (National Progress Report Iceland 2019). The focus of the project is to investigate the contents of new contaminants of concern in marine mammals, including new brominated flame retardants and PFAS (per- and polyfluoroalkyl substances). The project is an international cooperation between Sweden (Naturhistoriska Riksmuséet and Stockholm University), Greenland (Grönlands Naturinstitut) and MFRI (Iceland). A paper on fluorine mass balance and suspect screening in marine mammals from the Northern Hemisphere was published in 2020 (Spaan et al. 2020).
Efforts to estimate by-catch of grey seals in fisheries are also ongoing at the MFRI.
Research has been conducted by the Norwegian Institute of Marine Research and UiT the Arctic University of Norway to obtain knowledge of feeding habits and prey consumption of grey seals. During 1999–2010, prey items were determined from 182 grey seal gastrointestinal tracts and 199 faecal samples collected in Finnmark, Nordland and Rogaland counties. The most important prey were revealed to be saithe (Pollachius virens), cod (Gadus morhua) and wolffish (Anarchichus spp). Wolffish was mainly eaten by seals ≥ five years old. Otherwise, the data did not suggest important temporal or spatial variations between the main prey items in the grey seal diet. However, capelin (Mallotus villosus) was eaten during spring in Finnmark suggesting that seasonally abundant pelagic fish species could be regionally important (National Progress Report Norway 2019).
Total annual grey seal consumption of various species has also been estimated using bio-energetic modelling. The input variables were seal numbers, energy demands, diet composition in terms of biomass, and energy densities of prey species. Assuming the observed grey seal diet composition in the sampling areas was representative for the diet along the Norwegian coast, the mean total annual consumption by 3850 grey seals was estimated to be 8084 tons in Norwegian waters; saithe (3059 tons), cod (2598 tons) and wolffish (1364 tons) (National Progress Report Norway 2019).
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Institute of Marine Research (Norway) – Grey seal (in Norwegian)