|Scientific Name:||Halichoerus grypus (Fabricius, 1791)|
|Infra-specific Taxa Assessed:|
Phoca grypus Fabricius, 1791
|Taxonomic Notes:||The taxonomy of the Grey Seal, Halichoerus grypus, has been confusing. Bonner (1981) concluded that there are three populations isolated both geographically and by timing of reproduction. Chapskii (1975) recognized the three populations as separate subspecies, H. g. grypus in the western North Atlantic, H. g. atlantica in the eastern North Atlantic, and H. g. baltica in the Baltic Sea.
Rice (1998) recognized two subspecies, H. g. grypus in the western and eastern North Atlantic and H. g. macrorynchus in the Baltic Sea. However, Boskovic et al. (1996) found large differences in mtDNA between the three breeding areas, with the Baltic and east Atlantic populations much closer to one another than they were to the west Atlantic population. The Society for Marine Mammalogy recognizes two subspecies, the Western Atlantic Grey Seal (H. g. grypus) and the Eastern Atlantic Grey Seal (H. g. macrorynchus) (Committee on Taxonomy 2014). The IUCN Pinniped Specialist Group prefers the common names Northwest Atlantic Grey Seal and Northeast Atlantic Grey Seal, and has assessed those subspecies separately. This assessment combines the subspecies assessments to evaluate the Red List status for H. grypus as a species.
|Red List Category & Criteria:||Least Concern ver 3.1|
|Facilitator/Compiler(s):||Lowry, L., Ahonen, H., Pollock, C.M., Chiozza, F. and Battistoni, A.|
The Grey Seal has the same geographic distribution as in the late 19th century with areas of its range having been recolonized over the past 30-40 years. Their abundance has increased in all regions in the past several decades. Total abundance globally is more than 600,000. Changes in juvenile survival and pup production suggest that some colonies may be approaching a resource ceiling. Grey Seals do not meet IUCN criteria for any threatened category and are listed as Least Concern.
|Previously published Red List assessments:|
|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 the timing of reproduction (Bonner 1981); mtDNA differences are large between these three breeding areas, though the Baltic and Northeast Atlantic populations are much closer to one another than to the Northwest Atlantic population (Boskovic et al. 1996). In the western Atlantic, the population is centered on the eastern Scotian Shelf off northeastern North America, but the Grey Seal ranges from the Gulf of Maine to southern Labrador, including the Gulf of St Lawrence (Lesage and Hammill 2001). The northeast Atlantic population is concentrated around the 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 subpopulation 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).|
Native:Belgium; Canada; Denmark; Estonia; Faroe Islands; Finland; France; Germany; Iceland; Ireland; Latvia; Lithuania; Netherlands; Norway; Poland; Russian Federation; Sweden; United Kingdom; United States
|FAO Marine Fishing Areas:|
Atlantic – northeast; Atlantic – northwest
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Available data on Grey Seal abundance were compiled and reviewed in the 2016 IUCN Red List assessments for the two recognized subspecies. Estimates of the number of mature individuals, and population trend, were as follows: Northeast Atlantic Grey Seal 66,000, increasing; Northwest Atlantic Grey Seal 250,000, increasing. The world-wide population of Grey Seals is estimated to contain about 316,000 mature individuals and the total population size is about 632,000.|
|Current Population Trend:||Increasing|
|Habitat and Ecology:||Grey Seals are a large sexually dimorphic phocid. Northwest Atlantic Grey Seals are significantly larger than Northeast 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 in weight and female pups averaging 14.8 kg (Bonner 1981). Weaning weights average 40 kg for males and 35.8-39.6 kg for females. In the Western Atlantic adult males are on average 2.1 m long and weigh 267 kg, with a maximum of 370 kg (Bowen unpub. data). Adult females average 1.9 m in length and weigh 186 kg with a maximum of 256 kg (Iverson et al. 1993). Newborn pups average 16.6 kg or about 14% of maternal body mass (Mellish et al. 1999). In North America, pups are heavier at birth than pups born in the UK and are 25% heavier at weaning. At the time of weaning, male pups average 56.2 kg and females 51.6 kg, as measured for pups born on the ice near Amet Island (Haller et al. 1996). Male pups weigh 56.6 and females weigh 54.5 kg for those born on land at Sable Island (Bowen et al. 2006). Baltic Grey Seal pups weigh about 12 kg at birth, but weaning mass differs between ice-born pups (48.3 kg) and those born on land (37.4 kg) (Jüssi et al. 2008). Survival to recruitment to the breeding population is positively related to pup size at weaning (Bowen et al. 2015).|
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, Bowen et al. 2006). Pre-weaning mortality of Grey Seal pups varies widely between colonies; it is usually between 5 and 20% but can be as high as 30% (Bowen et al. 2007, Hammill et al. 2014). 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 (Jüssi et al. 2008). The main predators in this region 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), although this is not observed elsewhere. Mothers typically stay with their pups until weaning (Boness and James 1979), but are rarely more than a few meters away from water at some UK colonies (Twiss et al. 1994). Reproductive performance of adult females varies with age and body mass. Females in their late 20s and older show evidence of reduced reproductive success, caused by senescence (Bowen et al. 2006).
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. 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 Northwest Atlantic lose an average of 75 kg (Haller et al. 1996, Mellish et al. 1999). 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 in Canadian colonies; by the beginning of the next pupping period they again average 210 kg (Beck et al. 2003a).
Adult male Grey Seals come ashore about the time the first pups are born (Boness and James 1979, Bonner 1981). Their average age when first returning to their breeding colonies is 9-10 years at Sable Island (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 (Lidgard et al. 2001). 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, Lidgard et al. 2005, Tinker et al. 1995).
Pupping dates differ significantly between populations: peak dates in the Northwest Atlantic are in January; in the Northeast 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 Northeast Atlantic, and can be born on either ice or land in the Northwest Atlantic and in 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 stay on land from birth until the moult is finished (Noren et al. 2008), 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 mass (Noren et al. 2008). In the United Kingdom, adult females moult from mid-January to mid-February, and males moult from mid-February through early April. In Canada, the moult is later in the spring, with females moulting in May-June and males about a month later (Beck et al. 2003a). 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 shorter than 8 min. (Beck et al. 2003b). Female’s dives are on average slightly longer (5.5 min.) than those of males (4.9 min.), although males tend to dive somewhat deeper (57 m compared to 49 m) (Beck et al. 2003b). On the Scotian Shelf, maximum dives recorded were 412 m for males, and 354 m for females (Beck et al. 2003b). Typically in the UK, dives are shorter and shallower (average 4-10 min., maximum 30 min.). In European waters Grey Seals are primarily demersal feeders, diving to the seabed 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, 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 (Ammodytes sp.), an important part of the Grey Seal’s diet.
Satellite telemetry data from Canada show that Grey Seals there perform much longer foraging trips (averaging 5-12 days) and often travel much larger distances than European Grey Seals (Breed et al. 2009). Foraging trip characteristics differ seasonally and by sex. Females typically fed closer to haulouts than males and spent more time foraging at these patches (Breed et al. 2009). Grey Seals in Canada also exhibit pronounced seasonal sex segregation in foraging distribution (Breed et al. 2006). In the Baltic Sea, Grey Seals make short feeding trips, spending roughly 75% of their time within 50 km of haulout sites (Sjøberg and Ball 2000).
Grey Seals are generalist predators, consuming a wide range of species, although typically fewer than 10 species comprise most of the diet (Bowen and Siniff 1999). Grey Seal diet varies by seasonally and location, though they are largely demersal or benthic feeders (Bowen et al. 1993, Hall 2002). At times in Canada and the North Sea, the food consumed by Grey Seals can be over 50% Sandeels, although several dozen species are eaten (Bowen and Harrison 1994, Hammond et al. 1994, Beck et al. 2007). 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) account for 56% of the diet by weight. Grey 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, the dominant prey species consumed by Seals differs by season, sex, and age-class; however, Sandeels and Redfish (Sebastes sp.) together accounted for 40-91% of the diet in all seasons, sexes, and age-classes (Bowen and Harrison 1994). Pollock (Pollachius virens), and flounders (Turbot Reinhardtius hippoglossoides, Witch Glyptocephalus cynoglossus, and Yellowtail Limanda ferruginea) account for more than 10% of the diet in some demographic groups within seasons (Beck et al. 2007). Atlantic Cod can be an important part of the diet in some areas and seasons (Hammill et al. 2014).
|Continuing decline in area, extent and/or quality of habitat:||No|
|Generation Length (years):||16.5|
|Movement patterns:||Not a Migrant|
|Congregatory:||Congregatory (and dispersive)|
|Use and Trade:||
Grey Seals have been important in subsistence harvests in coastal areas within their range throughout history. Grey Seals are protected in the USA under the Marine Mammal Protection Act and in Canada under the Fisheries Act. Nevertheless, there is a management plan that permits commercial harvesting of Grey Seals in Canadian waters, although relatively few Seals are taken each year. Grey Seal pups were taken in Orkney until the early 1980s, partly for commercial exploitation and partly as a population control measure. Large-scale culls of Grey Seals in the North Sea, Orkney, and Hebrides were carried out in the 1960s and 1970s as population control measures.
In Norway, hunting quotas are set within the context of a Grey Seal management plan and bounties have also been paid to reduce numbers in areas where there are conflicts with fisheries (Nilssen and Haug 2007). Hunting of Grey Seals is also permitted in Iceland (Hauksson 2007). In the Faroe Islands, licenses to kill Grey Seals are issued for the purpose of protecting marine fish farming (Mikkelsen 2007).
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 (Härkönen 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 economics of some fisheries (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, primarily juveniles less than a year old, which represented 7% of the tagged animals in the region (Bjørge 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. More recent photographic analysis of Grey Seals at haulout sites on Cape Cod, Massachusetts revealed 5-8% of Seals exhibited signs of entanglement (Sette et al. 2009). Finally, in the US commercial fisheries there was an average annual mortality of 853 Grey Seals reported for the period 2006-2010 (Waring et al. 2013). For the period 2008-2012, the total estimated human caused mortality (and serious injury to) Grey Seals was 4,533 per year of which about 1,000 were taken in US observed fisheries, about 400 in the Canadian hunt, 90 taken by the Department of Fisheries and Oceans Canada (DFO) in scientific collections, and about 3,000 were killings of nuisance animals in Canada (DFO 2011).
Grey Seals are known carriers of phocine distemper virus (PDV), in all populations (Ross et al. 1992, Duignan et al. 1995, Härkönen et al. 2006). However, they have suffered almost no mortality from the disease, in marked contrast to Harbour Seals. Härkönen 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 Seals haulout with Harbour Seals in the Wadden Sea and are known to travel more widely than the more 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 (Härkönen 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 Seals have a relatively high rate of colonic ulcers associated with hookworm infestations, which are sometimes fatal. This condition is not found elsewhere (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 Grey 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 those mortalities are attributable to contact with oil (St. Aubin 1990).
|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 (Bjørge et al. 2002).|
Anderson, S. S. and Fedak, M. A. 1985. Grey seal males: energetic and behavioural links between size and sexual success. Animal Behavior 33: 829-838.
Baker, J.R. and Baker, R. 1988. Effects of environment on grey seal (Halichoerus grypus) pup mortality. Studies on the Isle of May. Journal of Zoology (London) 216: 529-537.
Baker, S. R., Barrette, C. and Hammill, M. O. 1995. Mass-Transfer during lactation of an ice-breeding pinniped, the grey seal (Halichoerus grypus), in Nova-Scotia, Canada. Journal of Zoology (London) 236: 531-542.
Beck, C.A., Bowen, W.D. and Iverson, S.J. 2003a. Seasonal energy storage and expenditure in a phocid seal: evidence of sex-specific trade-offs. Journal of Animal Ecology 72: 280-291.
Beck, C.A., Bowen, W.D., McMillan, J.I. and Iverson, S.J. 2003b. Sex differences in the diving behaviour of a size-dimorphic capital breeder: the grey seal. Animal Behavior 64: 1-13.
Beck, C. A., Iverson, S.J., Bowen, W.D. and Blanchard W. 2007. Sex differences in grey seal diet reflect seasonal variation in foraging behaviour and reproductive expenditure: evidence from quantitative fatty acid signature analysis. Journal of Animal Ecology 76: 490-502.
Bergman, A., Bergsrand, A. and Bignert, A. 2001. Renal lesions in Baltic grey seals (Halichoerus grypus) and ringed seals (Phoca hispida botnica). Ambio 30: 397-409.
Bjørge, A., Oien, N., Hartvedt, S., Bothun, G. and Bekkby, T. 2002. Dispersal and bycatch mortality in gray, Halichoerus grypus, and harbor, Phoca vitulina, seals tagged at the Norwegian coast. Marine Mammal Science 18: 963-976.
Boness, D. J., Anderson, S. S. and Cox, C. R. 1982. Functions of female aggression during the pupping and mating season of grey seals, Halichoerus grypus (Fabricius). Canadian Journal of Zoology 60: 2270-2278.
Boness, D.J. and James, H. 1979. Reproductive behaviour of the grey seal, Halichoerus grypus (Fab.), on Sable Island, Nova Scotia. Journal of Zoology, London 188: 477-500.
Bonner, W.N. 1981. Grey seal Halichoerus grypus Fabricius, 1791. In: S. H. Ridgway and R. Harrison (eds), Handbook of marine mammals, Vol. 2: Seals, pp. 111-144. Academic Press.
Boskovic, R., Kovacs, K. M., Hammill, M. O. and White, B. N. 1996. Geographic distribution of mitochondrial DNA haplotypes in grey seals (Halichoerus grypus). Canadian Journal of Zoology 74: 1787-1796.
Bowen, W.D. and Harrison, G.D. 1994. Offshore Diet Of Grey Seals Halichoerus grypus Near Sable Island, Canada. Marine Ecology Progress Series 112: 1-11.
Bowen, W.D., and Siniff, D.B. 1999. Distribution, population biology, and feeding ecology of marine mammals. In: J.E., Reynolds, III and S.A. Rommel (eds), Biology of Marine Mammals, pp. 423-484. Smithsonian Press, Washington, D.C.
Bowen, W.D., den Heyer, C.E., McMillan, J.I., and Iverson S.J. 2015. Offspring size at weaning affects survival to recruitment and reproductive performance of primiparous gray seals. Ecology and Evolution 5: 1412-1424.
Bowen, W.D., Iverson, S.J., McMillan J.I. and Boness, D.J. 2006. Reproductive performance in grey seals: age-related improvement and senescence in a capital breeder. Journal of Animal Ecology 75: 1340-1351.
Bowen, W.D., Lawson, J.W. and Beck, B. 1993. Seasonal and geographic variation in the species composition and size of prey consumed by grey seals (Halichoerus grypus) on the Scotian shelf. Canadian Journal of Fisheries and Aquatic Science 50: 1768-1778.
Bowen, W. D., McMillan, J. I. and Blanchard W. 2007. Reduced population growth of gray seals at Sable Island: evidence from pup production and age of primiparity. Marine Mammal Science 23(1): 48–64.
Breed, G.A., Bowen, W.D., McMillan, J.I. and Leonard, M.L. 2006. Sexual segregation of seasonal foraging habitats in a non-migratory marine mammal. Proceedings of the Royal Society B 273: 2319-2326.
Breed, G.A., Jonsen, I.D., Myers, R.A., Bowen, W.D. and Leonard, M.L. 2009. Sex-specific, seasonal foraging tactics of adult grey seals (Halichoerus grypus) revealed by state--space analysis. Ecology 90(11): 3209-3221.
Chapskii, K.K. 1975. Obosnavanie dvukh novykh podvidov nastoyashchikh tyulenei semeistva Phocidae. Trudy Zoologischeskogo Instituta Akademii Nauk SSSR 53: 282-333.
Committee on Taxonomy. 2014. List of marine mammal species and subspecies. Society for Marine Mammalogy. Available at: https://www.marinemammalscience.org/species-information/list-of-marine-mammal-species-subspecies/. (Accessed: 4 February 2014).
DFO. 2011. Stock assessment of Northwest Atlantic grey seals (Halichoerus grypus). Department of Fisheries and Oceans Canada Canadian Science Advisory Secretariat Science Advisory Report 2010/091.
Duignan, P. J., Saliki, J. T., S. Aubin, D. J., Early, G., Sadove, S., House, J. A., Kovacs, K. M. and Geraci, J. R. 1995. Epizootiology of morbillivirus infection in North American harbor seals (Phoca vitulina) and gray seals (Halichoerus grypus). Journal of Wildlife Diseases 31: 491-501.
Fedak, M. A. and Anderson, S. S. 1982. The energetics of lactation: accurate measurements from a large wild mammal, the grey seal (Halichoerus grypus). Journal of Zoology (London) 198: 473-479.
Hall, A. 2002. Gray seal Halichoerus grypus. In: W. F. Perrin, B. Wursig, J. and G. M. Thewissen (eds), Encyclopedia of Marine Mammals, pp. 522-524. Academic Press, San Diego, California, USA.
Haller, M.A., Kovacs, K.M. and Hammill, M.O. 1996. Maternal behaviour and energy investment by grey seals (Halichoerus grypus) breeding on land-fast ice. Canadian Journal of Zoology 74: 1531-1541.
Hammill, M.O., Stenson, G.B., Swain, D.P. and Benoit, H.P. 2014b. Feeding by grey seals on endangered stocks of Atlantic cod and white hake. ICES Journal of Marine Science 71: 1332-1341.
Hammond, P. S., Hall, A. J. and Prime, J. H. 1994. The diet of grey seals in the Inner and Outer Hebrides. Journal of Applied Ecology 31: 737-746.
Harding, K. C. and Härkönen, T. J. 1999. Development in the Baltic grey seal (Halichoerus grypus) and ringed seal (Phoca hispida) populations during the 20th century. Ambio 28: 619-627.
Härkönen, T., Dietz, R., Reijnders, P., Teilmann, J., Harding, K., Hall, A., Brasseur, S., Siebert, U., Goodman, S. J., Jepson, P. D., Rasmussen, T. D. and Thompson, P. 2006. A review of the 1988 and 2002 phocine distemper virus epidemics in European harbor seals. Diseases of Aquatic Organisms 68: 115-130.
Härkönen, T., Harding, K. C., Goodman, S. J. and Johannsson, K. 2005. Colonization history of the Baltic harbor seals: Integrating archaeological, behavioral, and genetic data. Marine Mammal Science 21(4): 695-716.
Hauksson, E. 2007. Abundance of grey seals in Icelandic waters, based on trends of pup-counts from aerial surveys. In: T. Haug, M.O. Hammill, and D. Olafsdottir (eds), Grey seals in the North Atalntic and in the Baltic, pp. 85-98. NAMMCO Scientific Publications, Tromso.
Hauksson, E. and Bogason, V. 1997. Comparative feeding of grey (Halichoerus grypus) and common seals (Phoca vitulina) in coastal waters of Iceland, with a note on the diet of hooded (Cystophora cristata) and harp seals (Phoca groenlandica). Journal of Northwest Atlantic Fishery Science 22: 125-135.
Hiby, L., Lundberg, T., Karlsson, O., Watkins, J., Jüssi, M., Jüssi, I. and Helander, B. 2007. Estimates of the size of the Baltic grey seal population based on photo-identification data. NAMMCO Scientific Publications 6: 163-175.
ICES. 2005. Report of the working group on marine mammal ecology (WGMME), 9-12 May 2005, Savonlinna, Finland. ACE:05. 137 pp..
IUCN. 2016. The IUCN Red List of Threatened Species. Version 2016-1. Available at: www.iucnredlist.org. (Accessed: 30 June 2016).
Iverson, S.J., Bowen, W.D., Boness ,D.J., and Oftedal, O.T. 1993. The effect of maternal size and milk energy output on pup growth in grey seals (Halichoerus grypus). Physiological Zoology 66: 61-88.
Jüssi, M., Härkönen, T., Jüssi, I. and Helle, E. 2008. Decreasing ice coverage will reduce the reproductive success of Baltic grey seal (Halichoerus grypus) females. Ambio 37: 80-85.
Kovacs, K M. 1987. Maternal behaviour and early behavioural ontogeny of grey seals (Halichoerus grypus) on the Isle of May, UK. Journal of Zoology (London) 213: 697-715.
Lesage, V. and Hammill, M.O. 2001. The status of the grey seal, Halichoerus grypus, in the Northwest Atlantic. Canadian Field-Naturalist 115(4): 653-662.
Lidgard, D.C., Boness, D.J., and Bowen, W.D. 2001. A novel mobile approach to investigating mating tactics in male grey seals (Halichoerus grypus). Journal of Zoology 255: 313-320.
Lidgard, D.C., Boness, D.J., Bowen, W.D. and McMillan, J.I. 2003. Diving behaviour during the breeding season in the terrestrially breeding grey seal: implications for alternative mating tactics. Canadian Journal of Zoology 81: 1025-1033.
Lidgard, D.C., Boness, D.J., Bowen, W.D. and McMillan, J.I. 2005. State-dependent male mating tactics in the grey seal: the importance of body size. Behavioral Ecology 16: 541-549.
Lydersen, C., Hammill, M. O. and Kovacs, K. M. 1994. Activity of lactating ice-breeding grey seals, Halichoerus grypus, from the Gulf of St Lawrence, Canada. Animal Behavior 48: 1417-1425.
Mansfield, A. W. 1988. The grey seal. Underwater World. Canadian Department of Fisheries and Oceans, Ottawa, Canada.
Manske, M., Stobo, W.T. and Schwarz, C.J. 2002. Estimation of age-specific probabilities of first return and annual survival rates for the male gray seal (Halichoerus grypus) on Sable Island, from capture-recapture data. Marine Mammal Science 18(1): 145-155.
McConnell, B. J., Fedak, M. A., Lovell, P. and Hammond, P. S. 1999. Movements and foraging areas of grey seals in the North Sea. Journal of Applied Ecology 36: 573-590.
Mellish, J-A.E., Iverson S.J., and Bowen W.D. 1999. Variation in milk production and lactation performance in grey seals and consequences for pup growth and weaning characteristics. Physiological and Biochemical Zoology 72: 677-690.
Mikkelsen, B. 2007. Present knowledge of grey seals (Halicheorus grypus) in Faroese waters. In: T. Haug, M.O. Hammill, and D. Olafsdottir (eds), Grey seals in the North Atlantic and in the Baltic, pp. 79-84. NAMMCO Scientific Publications, Tromso.
Mikkelsen, B., Haug, T. and Nilssen, K. T. 2002. Summer diet of grey seals (Halichoerus grypus) in Faroese waters. North Atlantic Marine Science 87: 462-471.
Nilssen, K.T. and Haug, T. 2007. Status of grey seals (Halichoerus grypus) in Norway. In: T. Haug, M.O. Hammill, and D. Olafsdottir (eds), Grey seals on the North Atlantic and in the Baltic, pp. 23-31. NAMMCO Scientific Publications, Tromso.
Noren, S.R., Boness, D.J., Iverson, S.J., McMillan, J. and Bowen W.D. 2008. Body condition at weaning affects the duration of the postweaning fast in gray seal pups (Halichoerus grypus). Physiological and Biochemical Zoology 81: 269-277.
Pacifici, M., Santini, L., Di Marco, M., Baisero, D., Francucci, L., Grottolo Marasini, G., Visconti, P. and Rondinini, C. 2013. Generation length for mammals. Nature Conservation 5: 87–94.
Pomeroy, P. P., Anderson, S. S., Twiss, S. D. and McConnell, B. J. 1994. Dispersion and site fidelity of breeding female grey seals (Halichoerus grypus) on North Rona, Scotland. Journal of Zoology (London) 233: 429-447.
Prime, J. H. and Hammond, P. S. 1990. The diet of grey seals from the southwestern North Sea assessed from analyses of hard parts found in faeces. Journal of Applied Ecology 27: 435-447.
Rice, D.W. 1998. Marine Mammals of the World: Systematics and Distribution. Society for Marine Mammalogy, Lawrence, Kansas.
Ross, P. S., Visser, I. K. G., Broeders, H. W. J., van de Bildt, M. W. G., Bowen, W. D. and Osterhaus, A. D. M. E. 1992. Antibodies to phocine distemper virus in Canadian seals. Veterinary Record 130: 514-516.
Sette, L.A., Waring, G.T., Touhey, K., Sharp, S., Sharp, B. and Landry, S. 2009. Photographic surveys of entanglement occurrence at grey seal (Halichoerus grypus) and harbor seal (Phoca vitulina) haul-outs on Cape Cod, Massachusetts. Poster presentation, 18th Biennial Conference on the Biology of Marine Mammals.
Sjoberg, M. and Ball, J. P. 2000. Grey seal, Halichoerus grypus, habitat selection around haulout sites in the Baltic Sea: bathymetry or central-place foraging? Canadian Journal of Zoology 78: 1661-1667.
St. Aubin, D. J. 1990. Physiologic and toxic effects on pinnipeds. In: J. R. Geraci and D. J. St. Aubin (eds), Sea mammals and oil: confronting the risks, pp. 103-127. Academic Press, New York, USA.
Thompson, D., Hammond, P. S., Nicholas, K. S. and Fedak, M. A. 1991. Movements, diving and foraging behaviour of grey seals Halichoerus grypus. Journal of Zoology (London) 224: 223-232.
Tinker, T. M., Kovacs, K. M. and Hammill, M. O. 1995. The reproductive behaviour and energetics of male grey seals (Halichoerus grypus) breeding on a landfast ice substrate. Behavioral Ecology and Sociobiology 36: 159-170.
Twiss, S. D., Duck, C. and Pomeroy, P. 2003. Grey seal (Halichoerus grypus) pup mortality not explained by local breeding density on North Rona, Scotland. Journal of Zoology (London) 259: 83-91.
Twiss, S. D., Pomeroy, P. P. and Anderson, S. S. 1994. Dispersion and site fidelity of breeding male grey seals (Halichoerus grypus) on North Rona, Scotland. Journal of Zoology (London) 233: 683-693.
Waring G.T., Josephson E., Maze-Foley K., Rosel, P.E., editors. 2013. U.S. Atlantic and Gulf of Mexico Marine Mammal Stock Assessments, 2012. NOAA Technical Memorandum NMFS NE 223. National Marine Fisheries Service, Woods Hole, MA.
Woodley, T. H. and Lavigne, D. M. 1991. Incidental capture of pinnipeds in commercial fishing gear. International Marine Mammal Association Technical Report 91-01: 35 pp.
|Citation:||Bowen, D. 2016. Halichoerus grypus. The IUCN Red List of Threatened Species 2016: e.T9660A45226042.Downloaded on 24 February 2018.|