Hooded Seals are a markedly sexually dimorphic phocid seal species. Adult males average 2.5 m in length and weigh an average of 300 kg (Kovacs and Lavigne 1986), with large animals reaching over 400 kg (Kovacs et al. 1996). Adult females are smaller, averaging 2.2 m and 236 kg (ranging up to over 300 kg) (Kovacs and Lavigne 1992).

Hooded Seals are a strongly ice-associated species that breeds and moults in loose herds on heavy drift ice (Lavigne and Kovacs 1986, 1998). They spend a lot of time in ice-filled waters outside the breeding season, but they also undertake extensive migrations within the North Atlantic, sometimes occupying pelagic areas without sea ice during the summer (Vacquié-Garcia et al. 2017, Hamilton et al. 2022). They are largely solitary outside the breeding and moulting seasons although food aggregations can result in small clusters during their pelagic phases (Storrie et al. 2018, Bengtsson et al. 2021).

Hooded Seals give birth on drifting pack ice in late March and early April. They choose the heaviest available floes in quite dense ice areas (Kovacs 2018). Females are spaced out on the ice with several hundred meters between mother pup pairs. The breeding season for this polygynous (serially monogamous) species is very short, usually lasting about two to three weeks in total within a population (Kovacs 1990). Females, with their “blueback” pup are normally attended by a male. Males use their inflatable hood and septum to display to females and in contests with other males. If displays do not sort out who is remaining on site with a given female, males will fight violently. Mating takes place in the water once the female has weaned her pup. This species has the shortest lactation period for any mammal with most pups being weaned within four days (Bowen et al. 1985). During the nursing period pups grow extremely rapidly, gaining 7 kg per day and doubling their birth mass by the time of weaning (mean weaning mass 47 kg, Kovacs and Lavigne 1992). This amazing growth is achieved by drinking an average of 10.4 kg of milk daily, with very high efficiency of transfer of energy from maternal blubber through milk and into pup tissue with 73.2 ± 7.7% of the ingested energy as body tissue. (Lydersen et al. 1997). This species is likely on the edge of mammalian physiological limits, with pups running a slight “fever” they are growing so quickly (Lydersen et al. 1997).

Hooded Seals are extreme divers. Although most dives are from 100–600 m deep and last 5–25 minutes, very deep dives to over 1,500 m and dives lasting almost an hour have been recorded for adult animals of both sexes (Folkow and Blix 1999, Folkow et al. 2010, Andersen et al. 2013b, Vacquie-Garcia et al. 2017). Age and sex classes show somewhat different foraging habitat preferences that result in somewhat different movement and diving patterns (Andersen et al. 2009, 2013a,b; Bajzak et al. 2009; Vacquie-Garcia et al. 2017). Hooded Seals feed on a wide variety of fish and invertebrates including Greenland Halibut, gadid fishes such as Atlantic Cod (Gadus morhua) and Polar Cod (Boreogadus saida), Redfishes (Sebastes spp.), Herring (Clupea harengus), Capelin (Mallotus villosus), Atlantic Argentine (Argentina silus), Squid (Gonatus fabricii), amphipods and shrimps (Pandalus borealis) (Haug et al. 2004, 2007, Tucker et al. 2009).

A study of movement patterns over the last three decades for Hooded Seals in the Northwest Atlantic shows that their foraging areas have shifted northward, resulting in them remaining in similar oceanographic conditions throughout the decades (Vacquie-Garcia et al. 2024). This sort of range shifting is expected for highly mobile megafauna as a first response to climate change, but Arctic animals are limited in how far north they can shift and remain in productive areas (Gilg et al. 2012). Tracking set temperature and salinity values is likely the result of the preferences exhibited by their invertebrate and fish prey species. Animals from the Gulf and Front displayed somewhat different temperature preferences, which might provide some resilience at the species level.

Greenland Sharks (Somniosus microcephalus), Polar Bears (Ursus maritimus) and Killer Whales (Orcinus orca) are known to prey on Hooded Seals (Leclerc et al. 2012, Foote et al. 2013, McKinney et al. 2013, Øigård et al. 2014, Kovacs 2018). Longevity is normally 25–30 years (Kovacs 2018). The generation length is estimated to be 12.8 years (Pacifici et al. 2013), giving a three-generation length period of 38.4 years.

Ice conditions in the areas used for breeding and moulting have been deteriorating for decades. Sea ice losses have been extreme in the breeding areas used by the European population of Hooded Seals during the last three generations (57% thickness reduction, reduction in extent of ca 40%), and projections for the future suggest the declining trend will continue (Estathiou et al. 2022, Sumata et al. 2022). Sea ice conditions are also declining in the Northwest Atlantic, throughout the breeding range of hooded seals, with the Gulf of St Lawrence experiencing complete ice failures much more often in recent decades, putting hooded seals at risk of reproductive failure in this region already (Johnston et al. 2005, Stenson and Hammill 2014).

Hooded Seals are found throughout the North Atlantic, extending into drift ice areas within the Arctic Ocean (Kovacs 2018). Animals from the Greenland Sea stock reside in the Northeast Atlantic, ranging from mid-Norway in the south almost to the North Pole outside the breeding and moulting seasons (Folkow and Blix 1995, Folkow et al. 1996, Vacquié-Garcia et al. 2017, Hamilton et al. 2022). During breeding the whole adult population normally has concentrated in areas of drift-ice in the vicinity of the island of Jan Mayen and during moulting the whole 1+ population congregated to the north of the breeding area (Lavigne and Kovacs 1988). Recently, available ice at the time of breeding and moulting for this population is only present in areas close to the coast of East Greenland (Øigård et al. 2014).

Northwest Atlantic Hooded seals breed in the Gulf of St Lawrence, on the Front (north of Newfoundland) and in the Davis Strait, where they aggregate in loose herds (Lavigne and Kovacs 1988). Following breeding these groups disperse to feed and then form aggregations once again on the heaviest available first-year drift ice in Southeast Greenland to undertake their annual moult. Following the moult, traditionally they leave the Greenlandic coast and spread through waters of Baffin Bay, Davis Strait and West Greenland (Andersen et al. 2009, 2013a). Little is known about the distribution patterns followed by animals from the Davis Strait, but it is assumed that their summering areas primarily are in waters west of Greenland and in the Eastern Canadian Archipelago, similar to the other Northwest Atlantic breeding groups. A new study on movement patterns suggests that Northwest Atlantic Hooded Seals are dispersing further to the north for summer feeding than they did in the past (Vacquié-Garcia et al. 2024).

Some Hooded Seals wander widely (particularly young animals), and vagrants have been registered along European coastlines as far south as Portugal and the Canary Islands, which are likely animals from the Greenland Sea population. Vagrants have been registered in North America from New England south into the Caribbean; several Pacific occurrences have also been reported, as far south as California (Mignucci-Giannoni and Haddow 2002, Harris and Gupta 2006). During years with little sea ice strandings in the St Lawrence River area are common; this phenomenon seems to be increasing (Truchon et al. 2013). The North American observations of vagrant Hooded Seals likely stem from animals the breed in the Northwest Atlantic.

The species is listed on Annex V (animal and plant species of community interest whose taking in the wild and exploitation may be subject to management measures) of the EU Habitats Directive (Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora - consolidated version 01/01/2007) and on Annex III (protected fauna species) of the Bern Convention (the Convention on the conservation of European wildlife and natural habitats).

Numerous conservation measures, international management plans, harvest quotas and restrictions, as well as agreements and treaties, have been developed for the conservation of Hooded Seals dating back to the 1870s (Sergeant 1976). Hunting was banned in the Gulf of St Lawrence in 1964, and quotas were placed on the rest of the Canadian harvest beginning in 1974; blue-back harvesting became prohibited in 1987 in Canada (Ronald and Lavigne 2006). Total Allowable Catch (TAC) was 10,000 animals in Canadian waters prior to 2007 but was reduced to 8,200 because the stock was considered to be data deficient and increasing Greenlandic hunts had to be taken into account within the Canadian Atlantic Seal Management Strategy (Hammill and Stenson 2007, 2009). From 2016 onward no quotas were set in Canada, but subsidies had been removed, allowing the market to determine financial reward of the harvest; few Hooded Seals are harvested within this regime.

In European waters, harvest quotas were implemented at Jan Mayen in 1971, and complete cessation of the commercial harvest was enacted in 2007 (2008 hunting season closure) for the Greenland Sea stock. The ICES/NAFO/NAMMCO Working Group on Harp and Hooded seals (WGHARP) models population numbers from surveys and provides advice for management. Based on surveys conducted in 2022 and new biological parameter data, zero quota was reiterated as being the recommended level for Greenland Sea Hooded Seals (ICES 2023).

The EU ban on the import of seal products in 2009 markedly affected the market for Hooded Seal pelts, with the result that harvests decline. But this Regulation was amended in 2015 to allow for trade of hides from Indigenous harvests, opening the market for Greenland in particular (EU 2015).

Hooded Seals were classified as Vulnerable on the IUCN Red List in 2016 (Kovacs 2016). The European population is currently classified as Endangered on the Norwegian Red List (Eldegard et al. 2021). The European Red List for 2025 classifies hooded seals as regionally Vulnerable (Kovacs 2025), because the decline in the Greenland Sea population has recently slowed; this population might be stable at a new lower level (or still declining slowly - ICES 2023).

Global assessment of population structure would help in the assessment process. More robust N1+ population estimates are needed for all stocks. Ongoing survey efforts are required to track impacts of climate change and population trends.