Halichoerus grypus


Taxonomy [top]

Kingdom Phylum Class Order Family

Scientific Name: Halichoerus grypus
Species Authority: (Fabricius, 1791)
Common Name/s:
English Grey Seal, Gray Seal
Taxonomic Notes: Two subspecies are recognized: Halichoerus grypus grypus in the western and eastern North Atlantic and H. g. macrorynchus in the Baltic Sea. Formerly, there were three subspecies, with the western and eastern North Atlantic populations separated, the latter referred to as H. g. atlantica. The Baltic population was formerly referred to as H. g. baltica (Rice 1998).

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
Assessor/s: Thompson, D. & Härkönen, T. (IUCN SSC Pinniped Specialist Group)
Reviewer/s: Kovacs, K. & Lowry, L. (Pinniped Red List Authority)
Due to its large population, which is increasing in most areas of study, the Grey Seal should be considered to be Least Concern.

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 recommendationContinuing, 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.

Geographic Range [top]

Range Description: Grey Seals have a cold temperate to sub-Arctic distribution in North Atlantic waters over the continental shelf (Hall 2002). There are three populations isolated both geographically and by timing of reproduction (Bonner 1981); mtDNA variations are large between these three breeding areas, though the Baltic and East Atlantic populations are much closer to one another than to the West Atlantic population (Boskovic et al. 1996). In the western Atlantic, the population is centred in north-eastern North America from the Gulf of Maine to southern Labrador, including the Gulf of St Lawrence. The eastern Atlantic population is concentrated around the United Kingdom (UK) and Ireland but is also found around Iceland, the Faroe Islands, and along the European mainland coast from the Kola Peninsula south to southern Norway, and from Denmark to Brittany in France. The Baltic Sea stock is confined to the Baltic Sea (Bonner 1981, Hall 2002). Vagrants are known from as far south as New Jersey in the western Atlantic and Portugal in the eastern Atlantic (Rice 1998).
Belgium; Canada; Denmark; Estonia; Faroe Islands; Finland; France; Germany; Iceland; Ireland; Latvia; Lithuania; Netherlands; Norway; Poland; Russian Federation; Sweden; United Kingdom; United States
Greenland; Portugal
FAO Marine Fishing Areas:
Atlantic – northeast; Atlantic – northwest
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Grey Seal numbers are increasing at most locations, but are declining in a few localities. The Grey Seal population in the UK is one of the most intensively monitored large mammal populations in the world. Pup production of all the major breeding colonies is monitored regularly, annually in the UK and less frequently but regularly in Canada and other range states. However, because of differences in estimation methods and changes in population dynamics it is difficult to estimate the total global population size. For ease of comparison the most recent pup production estimates for all Atlantic populations are given in Table 1 in the linked PDF document, which forms an integral part of this assessment.

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).
For further information about this species, see 9660_Halichoerus_grypus.pdf.
A PDF viewer such as Adobe Reader is required.
Population Trend: Increasing

Habitat and Ecology [top]

Habitat and Ecology: Grey Seals are a large sexually dimorphic phocid. Western Atlantic Grey Seals are significantly larger than eastern Atlantic animals. In the UK, adult males are on average 2 m long and weigh 233 kg, with a maximum of 310 kg. Adult females average 1.8 m and 155 kg. At birth, pups are 90-105 cm, with male pups averaging 15.8 kg and female pups averaging 14.8 kg in weight (Bonner 1981). Weaning weights average 40 kg for males and 35.8 -39.6 kg for females. In the western Atlantic adult males average 2.25 m and 300-350 kg with maximum weights over 400 kg. Adult females average 2 m and 150-200 kg with maximum weights over 250 kg (Mansfield 1988, Hall 2002). Pups are heavier at birth than pups born in the UK and are 25% heavier at weaning. Male pups average 56.2 kg and females 51.6 kg, measured for pups born on the ice near Amet Island (Haller et al. 1996). Male pups weigh 51.6 and females weigh 50.5 kg for those born on land at Sable Island (Baker et al. 1995). Baltic Grey Seal pups weigh about 12 kg at birth, but weaning mass differs between (Jussi et al. 2008) 48.3 (± 8.1 kg) for pups born on ice to 37.4 (± 7.8 kg) for pups on land.

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).
Systems: Terrestrial; Marine

Threats [top]

Major Threat(s): Grey Seals have been important in subsistence harvests in coastal areas within their range throughout history. They have been hunted in the Baltic Sea for more than 10,000 years (Harkonen et al. 2005). Commercial harvesting has been ongoing in many areas for hundreds of years, and at times Grey Seals have been important to local economies (Mansfield 1988). Over-harvesting in the Baltic in the early 20th century led to a large decline; this population once numbered somewhere between 80,000 and 100,000, but was reduced to about 20,000 in the 1940s. A further decline to 1,500-2,000 seals was caused by high loads of PCB (Harding and Härkönen 1999).

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).

Conservation Actions [top]

Conservation Actions: Numerous countries have invoked protective measures to limit Grey Seal harvests, culls, disturbance and by-catch (Bonner 1981, ICES 2005). Pollutant loads in Baltic Grey Seals have declined following regulations banning the use and discharge of toxic pollutants such as DDT and PCBs beginning in the 1970s. Although the prevalence of colonic ulcers has increased over the last decades, the reproductive health of female Grey Seals has improved as has the population level in the Baltic (Bergman et al. 2001). Establishment of coastal marine reserves for seals in Norway have been more effective in protecting harbour seals than Grey Seals because the latter are more likely to travel outside the areas closed to fisheries and become entangled in nets (Bjorge et al. 2002).
Citation: Thompson, D. & Härkönen, T. (IUCN SSC Pinniped Specialist Group) 2008. Halichoerus grypus. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <>. Downloaded on 19 April 2014.
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