The hooded seal is so-named because of the adult male's large elastic nasal cavity, or 'hood', that extends from the nostrils to the forehead. It is used for display and as a warning during the breeding season.

These large mammals are uncommonly aggressive for a seal. Males occasionally exceed 3 m (10 ft.) in length and 400 kg (880 lb.) in weight. Females average about 2 m (6.5 ft.) and usually weigh about 160 kg (352 lb.). They have been reported to live for as long as 30 to 35 years.

The hooded seal population is distributed in the North Atlantic from Russia to Canada. In early spring they travel down around the Maritimes on the pack ice in order to breed and have their pups. The hooded seal has the shortest lactation period of any mammal. The pups nurse for less than 4 days, during which time they double their birth weight of about 24 kg (53 lb.).

The hooded seal diet consists of mussels, starfish, squid, shrimp, herring and cod. Aside from humans, who hunt them for their skin, their principal predator appears to be the killer whale.