The pouch on the heads of mature male hooded seals explains their name. It can be expanded to about twice the size of a football.
Hooded seals rarely approach land, preferring to spend their whole lives among the ice floes in the cold Arctic Ocean, diving deeply in search of fish and squid, which are their main food source. Apart from during the breeding season, hooded seals live alone. They dive down to depths of more than 180 m (590 ft) to feed on shoaling fish and bottom-living creatures.
When the breeding season arrives in spring, the seals congregate on wide ice floes. The females take up widely spaced positions on the ice, preparing to give birth to the young conceived the year before. Meanwhile, males compete for access to small groups of females. The victors stay near the females as they nurse their new-born calves, chasing away any intruders while inflating their nasal balloons.
Hooded seals are so named because the males possess elastic sacs, or hoods, on the tops of their heads. The hoods are connected to their noses and can be inflated with air to amplify their calls while sparring with rival males. Female seals also have hoods, but their hoods are not inflatable like those of the males.
The growth of the young pups is truly phenomenal. Hooded seal pups are suckled for only four days - the shortest time of any mammal - after which the mothers abandon them. This is achieved thanks to the richness of their mother’s milk, which is of about 65 per cent fat. Pups are born in March on ice floes and are suckled for between 7 and 12 days. Their coats are bluish-grey at first and they moult at 14 months old. Males also visit the nursery grounds at this stage, and will mate with the females once their pups are weaned.
Distribution: North Atlantic, but makes regular migrations as far as Norway. May also travel further afield, being recorded from Alaska, Guadeloupe and the Canary Islands.
Habitat: Drifting ice floes.
Weight: 350 - 450 kg (771 - 992 lb); males are heavier.
Length: 200 - 300 cm (79 - 118 in).
Maturity: Females 3 - 6 years; males 5 - 7 years.
Gestation Period: 341 - 365 days.
Breeding: 1; weaning occurs within 4 days - the shortest period of any mammal.
Diet: Piscivorous, hunting fish including herring and cod, as well as squid, starfish and shellfish, depending on their locality.
Lifespan: 30 - 35 years.
The eyes are relatively large, and help to alert the seals to possible danger.
This is only present in male hooded seals, developing from the age of four.
These are held back against the sides of the body when the seal is resting on land.
The spotted markings on the coat are highly individual.
This swelling results from a membrane normally kept within the nostrils, which can be inflated as a threat, like the hood.
Hooded seals dive to depths of 1000 m (3280 ft), and can stay submerged for over 50 minutes.