Updated: June 2018
Harbour seals are small phocid seals (“true seals”), averaging around 150 cm in length and 70-100 kg in weight, with the males being generally larger than the females. The colour pattern of their coat is very variable, but usually silvery and darker on the back and creamy or lighter-grey on the belly and flanks, with dark spots covering the entire body. Pups can occasionally carry a fluffy white coat at birth, but this is usually shed in the uterus, before birth. Most of the times pups are born in their adult-pattern coat (Bjørge et al. 2010).
About 200,000 in the North Atlantic.
Temperate to sub-Arctic waters along the eastern and western coasts of the North Atlantic. Svalbard is also home to the northernmost population of harbour seals.
Hunted in Norway and Iceland for meat and skin.
Scientific advice on management is provided by NAMMCO and management is the responsibility of each country.
Latin: Phoca vitulina
Danish: Spættet sæl/Spraglet sæl
English: Harbour seal, common seal
Females, 30-35 years; males, 20-25 years
One pup per year
Generalist predators, with an overall preference for small to medium sized fish including cod, herring, sandeel, and flatfishes
Around 150 cm in length and 70-100 kg in weight, with the males being generally larger than the females
The harbour seal (Phoca vitulina) is a coastal, non-migratory species, distributed in the temperate and subarctic waters of the northern hemisphere. Four marine subspecies are recognised (only the first two are in the NAMMCO area):
Eastern North Atlantic (P. v. vitulina; Linnaeus 1758) – distributed throughout Svalbard, Norway, Russian Federation, Iceland, Denmark, Sweden, Germany, Poland, United Kingdom, Ireland, Netherlands, Belgium, France
Western North Atlantic (P.v. concolor; DeKay 1842) – distributed from Labrador in Canada to Virginia in USA and in Greenland
Eastern North Pacific (P. v.richardii; Gray 1864) – distributed through Alaska, some Russian islands, west coasts of Canada and USA
Western North Pacific (P.v. stejnegeri; Allen 1902) – distributed from eastern Siberia in the Russian Federation to northern Japan. This subspecies is sometimes treated as a separate species, Phoca kurilensis or Phoca insularis (Bjørge et al. 2010).
In addition, there are some landlocked harbour seals in lakes and connecting rivers in the Ungava Peninsula, Northern Quebec, Canada (Smith et al. 1996). These seals are recognized as a fifth sub-species: the Ungava seal P.v. mellonae (Doutt 1942).
Harbour seals are small phocid seals, averaging around 150 cm in length and 70-100 kg in weight, with the males being generally larger than the females. The colour pattern of their coat is very variable, but usually silvery and darker on the back and creamy or lighter-grey on the belly and flanks, with dark spots covering the entire body. Pups can occasionally carry a fluffy white coat (called lanugo) at birth, but this is usually shed in the uterus, before birth. Most of the times pups are born in their adult-pattern coat (Bjørge et al. 2010).
Harbour seals show strong site fidelity. They move between haul sites out and feeding areas, but rarely show seasonal migration. They haul out, give birth and nurse their young on beaches, sandbanks and rocks, usually in the intertidal zone along the coast, and forage in close proximity of the coast. They can dive deeper than 200 m, but perform on average much shallower dives, within 60-100 m depth, mainly as a consequence of their habitat choice (Sharples et al. 2012, Ramasco 2015). Recently, the occurrence of resting dives, similar to the typical drift dives performed by other phocid seals (Crocker et al. 1997), was documented in harbour seals (Ramasco et al. 2013).
Harbour seals are opportunistic feeders, more benthic (bottom of the sea) than pelagic (in the water column). They use different underwater feeding techniques, depending on prey type, including ambush, active search or digging with final pursuit (Bowen et al. 2002). They are highly social animals. They mostly feed independently, but gather to rest at haul out sites on a regular basis, usually timed with low tide in areas where the tidal cycle strongly impacts the geography of their habitat (Cronin et al. 2009).
Life history and Ecology
The annual reproductive cycle of most seal species is characterized by a tight synchrony of births, ensuring that pups are born at the optimal time of year (Boyd 1991). Across their range harbour seals give birth to one pup per year between February and July, depending on the environmental conditions and population status, with lower latitudes and populations in good conditions breeding earlier (Reijnders, Brasseur, & Meesters 2010). Lactation lasts about three-four weeks, but the pup is able to swim already few minutes after birth. Male harbour seals come into breeding areas toward the end of lactation and perform underwater displays to attract females and mate (Van Parijs et al. 1997). Female harbour seals mate in this period but have delayed implantation with about eight months long pregnancy.
Harbour seals are known to be generalist predators, with an overall preference for small to medium sized fish (Ramasco 2015). They feed commonly on codfish (Gadidae), sandeel (Ammodytes sp.), herring (Clupea harengus) and flatfishes (Pleuronectidae) depending on their surrounding habitat (Härkönen 1987, Olsen & Bjørge 1995, Bowen & Harrison 1996, Tollit et al. 1998). Differences in their diet, with seasonal and interannual variability, are documented across their geographical range (Härkönen 1987, Pierce et al. 1991, Hall et al. 1998). The shifts in diet with time are often linked to changes in the most abundant prey to be found in their preferred size group (Ramasco, in press). Harbour seals have been observed to respond to different prey pulses, such as seasonal increased concentration of herring or salmon (Middlemas et al. 2006, Thomas et al. 2011).
Distribution and Habitat
Harbour seals are distributed from temperate to sub-Arctic waters along the eastern and western coasts of the North Atlantic and the North Pacific Oceans (Bjørge et al. 2010). They primarily use areas close to the coastline (within 50 km, Jones et al. 2015), and generally do not perform seasonal migrations. In certain areas, for example where ice cover limits food or habitat accessibility during part of the year, the species shows small-scale seasonal migrations (Lesage et al. 2004).
North Atlantic stocks
Andersen & Olsen (2010) reviewed the genetic studies made on harbour seals populations in the North Atlantic and identified twelve distinct populations: USA/Canada, Iceland, west coast of Norway, Ireland-Scotland, English east coast, Channel area, Wadden Sea, Limfjord, Skagerrak, Kattegat, West Baltic, and East Baltic/Baltic proper. A subsequent study additionally compared the Greenland and Svalbard populations to the geographically closest ones, in mainland Norway and Iceland, and found them to be distinct (Andersen et al. 2011). Most of the genetic studies reviewed do not investigate potential population differences within each country, suggesting that the number of genetically distinct harbour seals populations is likely higher than 14.
Current Abundance and Trends
The estimated world population of harbour seals is of approximately 610,000 – 640,000 individuals, including both the Atlantic and Pacific stock (Bjørge et al. 2010). Updated estimates of each population together with population trends can be found in NAMMCO SC/23/Annex 2 (page 117). Harbour seals seem to be increasing in southern Scandinavia, and UK, with the exception of local areas in Scotland; and seem stable in Norway. In the other areas of occurrence, the trends are uncertain.
Harbour seal abundances have fluctuated widely in the Northeast Atlantic in recent decades, mainly due to local outbreaks of the Phocine Distemper Virus (PDV). A first epidemic in 1988 killed about 50% of the harbour seals in Skagerrak-Kattegat, the Wadden Sea and the Wash in the UK, with the subsequent very rapid recovery of about 13% increase per year, and even higher growth rates observed regionally (Härkönen et al. 2006, Reijnders, Brasseur, Tougaard, et al. 2010, Olsen et al. 2010). A new PDV epizootic struck the same populations in 2002 with mortality similar to, or in some areas less than, in 1988. A number of animals gaining immunity during the first epizootic may still be part of the population in 2002, and thus contributed to less mortality.
Differently to most other areas affected by the 2002 epizootic, the population in the Wash (UK) has continued to decline since. A decline in harbour seal abundance since the late 1990s is also observed in Orkney, Shetland, and, but to a lesser extent, in the Outer Hebrides and east Scotland. The abundance in West Highlands has continued to increase (Thompson et al. 2010).
The reasons behind the rapid decrease of several populations of harbour seals is still unknown, but several possible causes have been identified, such as shifts in spatial distribution, or timing of the moult, mass mortality due to illnesses, unreported anthropogenic removal, predation by killer whales (Orcinus orca), and severe competition with grey seals (Halichoerus grypus). Most of the aforementioned causes would have been detected, since they involve large numbers of animals, leaving the competition hypothesis as the most probable. Pup production in grey seals has increased since the 60s by fivefold, and levelled off in the last 2 decades indicating that the population is approaching carrying capacity. At the same time, the North Sea sandeel (Ammodytes ssp.) stock has drastically dropped at the end of the 90s possibly enhancing the competition between harbour and grey seals. A combination of reasons can be likely (Bjørge et al. 2010).
Among the major sources of mortality are by-catch, predation by killer whales (Orcinus orca), competition, or viral outbreaks. The impact of predation by killer whales is unknown. In Norway, during winter, killer whales follow the over wintering herring and may move closer to seal colonies and have been reported to eat harbour and grey seals. In Scotland, killer whale predation on harbour seals seems to be on the increase. Grey seals may also be a source of mortality for harbour seals, either as predators or as competitors. In various areas where harbour seals and grey seals overlap, the population growth rate of harbour seals is usually lower. This has been seen in the Baltic Sea, Sable Island (Canada), Scotland, and New England (US) (“NAMMCO SC/23/Report” 2016).
The council of NAMMCO requested an assessment of the species in the North Atlantic. As a result, the Scientific Committee convened a Working Group to review the status of harbour seals throughout the North Atlantic, which resulted in NAMMCO’s Scientific Publication series, volume 8, 2010. The working group met again in 2016, and noted that harbour seals appear to be declining in many areas, especially where grey seals are increasing, although there are little data to indicate if grey seals could have any impact on the harbour seal populations.
Harbour seals in Norway suffered a severe decline prior to the 1960’ due to unregulated hunting (Øynes 1964). Regulatory measurements were introduced in 1973 in part of the country. A new management regime was finally implemented in 1997 with the aim to secure viable stocks. The most recent survey period (2011-2015) revealed a minimum total population of 7,642 harbour seals along the mainland Norwegian coast. This last estimate is close to the counts of 6,938 animals in 2003-2006 and 7,465 in 1996-1999, revealing a stable population trend since the 90’s (“NAMMCO SC/23/Report” 2016).
A distinct population of around 1000 individuals is to be found in Svalbard (Lydersen & Kovacs 2010).
The Icelandic harbour seal population was considerably larger in the early 19th century than at present, with about 60,000 (90% CI:40-100) animals. Aerial surveys conducted since 1980 indicate that the population has declined from 33,000 (90% CI:26,000-44,000) animals in 1980 to about 12,000 (90% CI:9,000-16,000) animals in 2006. Since 2003, total removals have decreased and the population decline appears to have ceased (Hauksson & Einarsson 2010). During the latest full census in 2016, the population was estimated to be about 7,700 animals (Þorbjörnsson et al. 2017), which is a decrease of 30% since 2011. The reasons for the decline are not known, but could include hunting, by-catch (seals caught in fishing nets), ecosystem changes related to climate change, and disturbance from tourism. These issues are currently being investigated by researchers at the Marine and Freshwater Institute in Iceland, and the Icelandic Seal Center.
Southern Scandinavia (Kattegat, Skagerrak, Western Baltic, Limfjord)
The harbour seal population in Southern Scandinavia has experienced repeated declines caused by hunting and epizootics. Harbour seals have disappeared from haulout areas along the Danish shores of Kattegat and in the westernmost part of the Baltic Sea, where they were previously numerous. In the 1920-30s, when abundance was at its lowest, the population is estimated to have been only a fraction of its original size. Following 30 years of protection the population is currently approaching historic abundance and seems to have reached the carrying capacity in some areas, showing a decrease in population growth rates, possibly caused by density dependent effects (Olsen et al. 2010).
The small population of harbour seals in the east Baltic (also called Baltic proper) was hunted close to extinction in the beginning of the 20th century and experienced a severe bottle-neck minimum numbers in the 1970s. Protective measures, in the form of banned hunting and establishment of protected areas, have improved the situation, and the hauled-out moulting population size in 2008 was 588. Despite the conservation measures the population is not expected to reach favourable conservation status within foreseeable future (Härkönen & Isakson 2010).
Mainland Europe (Wadden Sea)
The Wadden Sea harbour seal population has been severely depleted by hunting in the first half of the 20th century. After hunting was stopped in the mid-1970s the population recovered gradually. This recovery was twice interrupted by PDV outbreaks in 1988 and 2002. These epizootics reduced the population by 57% and 50% respectively. They also lead to changes in age and sex structure of the population, which gradually returned to stability (Reijnders, Brasseur, Tougaard, et al. 2010). After the outbreaks the population showed a strong recovery with a growth rate close to the considered maximum possible for this species, with a constant increase until 2013. Recent growth rates show that the overall increase of the population has slowed down, suggesting it has reached carrying capacity (“NAMMCO SC/23/Report” 2016).
The UK holds approximately 40% of the European harbour seal population, with the majority found around the coasts of Scotland (Thompson et al. 2010). The last survey in 2011 counted 28,161 individuals in Great Britain, and 948 in Northern Ireland, for a total of 29,109 (“NAMMCO SC/23/Report” 2016). A general decline has been observed in most harbour seal colonies around Scotland. The populations along the north and northwest mainland coast were an exception, with numbers appearing to be stable. The widespread declines, ranging from Shetland to the Wash, suggest that the causes, still unknown, may have been present over a large part of the North Sea and waters off western Scotland (Thompson et al. 2010).
Faroe Islands and Greenland
The harbour seal was exterminated as a breeding species in the Faroe Islands in the mid-19th Century. For the last 40 years the harbour seal has only been positively identified twice in the Faroe Islands, in 2001 and 2005 (Mikkelsen 2010).
The total number of harbour seals in Greenland according to these estimates was about 3,000 in 1950 and fewer than 1,000 in 2007. The number of harbour seals in the southernmost part of Greenland has increased significantly in recent years, while historically used haulout locations along the west coast have gradually been abandoned after the 1950’s (Rosing-Asvid 2010).
A bounty harvest as well as subsistence and commercial hunting probably lead to a decline in the population from 1949 to the early 1970s. The bounty was removed in 1976, and harbour seals, in the southern parts of their range have been protected since then. At that time the total population south of Labrador was estimated to be 12,700 (Boulva and McClaren 1979). Since then, research has been limited to specific areas and there is little information available on total abundance and trends. Urban development resulting in habitat degradation is probably the most important factor affecting harbour seal populations in Atlantic Canada (Hammill et al. 2010).
Atlantic United States
The harbour seal is the most abundant and widespread seal species in this area. The number of harbour seals observed during the pupping season in this region has increased from about 10,500 animals in 1981 to 38,000 animals in 2001 (uncorrected counts, Waring et al. 2010). The corrected estimate of harbour seal abundance in 2001 was of 99,340 animals (CV=0.09) (Gilbert et al. 2005), this was higher than the most recent one in 2012, which was of 75,834 animals (CV=0.15, Waring et al. 2015a), indicating a slight decrease. Currently there is some uncertainty in the patterns of harbour seal abundance and distribution in the Northeastern US. Johnston et al. (2015) document a decline in stranding and by-catch rates of harbour seals, providing support for an apparent decline in abundance.
The hunt has been regulated by quotas since 1997, and in 2003 the quotas and bounties were increased. After a decade with high quotas and a declining population of harbour seals, a management plan for harbour seals was implemented in 2010. Since 2011 quotas were based on scientific advice and since there have been decreases in the yearly reported catches. Management units for Norwegian harbour seals are defined by county limits, however raise concerns that there may be population subdivision within counties. Harbour seals are regularly counted along the entire Norwegian coast at known haulout sites during the moulting period from mid-August to early September. The government decided that the harbour seal population should be stabilized at a level where 7,000 moulting seals can be recorded. The government has been suggested to balance the desire for the preservation of large seal populations against damage on fisheries and aquaculture in the coastal zone.
In 2006, the Icelandic government published a management plan where a minimum population size of 12,000 harbour seals was recommended (NAMMCO annual report, 2006). The management plan states that management actions should be initiated if the population dropped appreciably below that number, but no specific population regulating method was 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] Special Committee on seals. Scientific advice on matter related to the management of seal populations: 2004”). Harbour seals are regularly monitored through aerial surveys of animals hauled out during the annual moult in early August. The Scottish and English east coast populations mainly haul out in tidal estuaries and are surveyed annually, using fixed wing aircraft and digital photography. Populations in north and west Scotland often haul out on rocky shores and are surveyed less frequently, using helicopters fitted with thermal imagers (Thompson et al. 2010).
The department of Fisheries and Oceans Canada has published an Integrated Fisheries Management Plan for Atlantic Seals for the period 2011-2015 (see Grey seals). In this plan hunt is regulated for most of the Atlantic seals in Canadian waters. Commercial harvesting for harbour seals is not permitted under this management plan.
Hunting and Utilisation
Despite their widespread presence, harbour seals are at present hunted only in Norway and Iceland, as a regulated hunt. In Atlantic Canada they are hunted only by indigenous people.
In Norway hunting is non-commercial and occurs from land. Ideally seals are shot when they are hauled out. If seals are shot in the water, they need to be retrieved or sink otherwise. Hence this hunt often occurs in shallow waters or with the use of a small vessel as support. The use of rifles with expanding bullets is mandatory.
Seal hunting in Iceland is focused 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. Net hunting around the river mouths is the most common method for hunting the harbour seal pup. The hunting takes place in the spring. No specific quota system has been established. Seal hunting from land and shallow waters is managed by land owners and there are no special protected areas or protected periods. Annual takes range from 200 – 400 harbour seal pups. Harvests have declined in recent years because of the low market price of the skins. For a very long time before 1980 the catch was 4000 – 6000 harbour seal pups.
In Greenland all hunting on this species was banned in 2010. In Nunavut (Atlantic Canada) harbour seals are hunted by Inuk people. There are currently no restrictions on the seasons or numbers of seals that can be harvested (“Report of the Committee on Hunting Methods” 2016).
Other Human impacts
By-catch during fishing operations and removals near fish farm are the major factors negatively impacting harbour seals populations in the North Atlantic. In Norway, a coastal reference fleet (CRF) for the coastal gillnet fishery for cod and monkfish reports by-catch data and landings. Fisheries of concern are assumed to only be the gillnet fishery for cod & monkfish, with species of concern being harbour and grey seals and harbour porpoises. The estimated by-catch of harbour seals for the period 1997-2014 was of an average of 555 harbour seals per year. The by-catches in the cod fishery peak in February-April while the higher levels seen in the monkfish fishery occur from July-December. 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 fisheries of most concern are assumed to only be the gillnet fishery for cod & lumpsucker (“NAMMCO SC/23/Report” 2016). In US waters, the total human caused mortality and serious injury to harbour seals for the period 2008-2012 was estimated to be caused by US commercial fisheries on 97 % of the cases (Waring et al. 2015b).
In Iceland and Norway fish farmers are allowed to remove seals near the farms by shooting. In Iceland interactions between seals and fish farms are reduced by the use of double-netting. However, there are some interactions between harbour seals and the salmon fishery around the river mouths, but removals are thought to be low, about 2-3 per year. In Norway reporting is mandatory, but little to no reports are provided to the government, therefore the extent of the problem is not known (“NAMMCO SC/23/Report” 2016).
Commercial ship and vessel-based tourism are an antropogenic source of disturbance for harbour seals colonies, causing potential shifts in local distribution and population decline (Jansen et al. 2015). Similar consequences can be due to habitat degradation caused by increased urbanization (Reijnders 1994).
In the UK between 2008 and 2010, several harbour seals were found stranded with peculiar injuries consisting of a single continuous curvilinear skin laceration spiralling down the body. Similar injuries were observed previously in Canadian waters. After some investigation the cause of death was found to be a traumatic event, with the seal being drawn through the ducted propellers of marine vessels (Bexton et al. 2012).
Pollutants are well known to negatively impacting marine mammals. The levels of pollutants in harbour seals are regarded as low and do not constitute a health threat (Drescher et al. 1977). However, some environmental contaminants, in particular persistent organic pollutants and mercury, are known to affect the immune system and might play a role in rendering marine mammal populations vulnerable to disease through immunotoxicity (Mos et al. 2006).
Research on harbour seals in Norway includes regular counts for abundance along the entire coast of Norway, but also studies on diet, behaviour, and harbour seal’s role in the ecosystem.
A recent study by scientists at the Institute of Marine Research on harbour seals in Porsangerfjord investigated diving, movements, and diet (Ramasco 2016). This study identified that harbour seals perform “resting dives”, which is a behaviour that has not been seen previously by this species. Ramasco (2016) also found that harbour seals mainly forage during the day in the autumn and spring in Porsangerfjord. When comparing the seals diving behaviour to the presence of certain possible prey in the area, it is likely that seals are preferring small fish close to where the seals haul out, but their diet likely changes with the seasons as different prey become available, and when the sea ice forms.
Research in Iceland has focused recently on getting updated abundances, diet and prey selection, and movements and foraging behaviour in estuaries.
The most recent survey for harbour seals was conducted in 2016, and indicated that the population is declining. The full results of the study can be found here. The potential causes of the decline are not known. It is possible that hunting and by-catch (seals being caught in fishing nets) could be contributing to the decline, but the numbers of hunted and by-caught seals is not well known. Other factors that could be affecting harbour seals are the changes being seen in the ecosystem around Iceland, such as the warming of the water, and the associated northward movement of an important prey species, the sandeel. Another potential factor in the decline of harbour seals is disturbance from tourism. These factors, and potentially the combination of them all, are being investigated further by researchers in Iceland at the Marine and Freshwater Institute and the Icelandic Seal Center. Additionally, the NAMMCO By-Catch Working Group is working towards obtaining reliable estimates of seal by-catch.
There are very few harbour seals in Greenland, likely less than 100 in a few haulout areas. In 2009 and 2010, researchers from the Greenland Institute of Natural Resources tagged 6 harbour seals with satellite tags. These seals mostly stayed near where they were tagged, which is likely a breeding site.
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