Hooded Seal

The hooded seal (Cystophora cristata) is a large seal of the cold North Atlantic and Arctic waters. Males have an inflatable nasal hood and a reddish nasal membrane they balloon out in display. Pups are born on drifting pack ice and weaned in just a few days, one of the shortest nursing periods of any mammal.

Hooded seals (Cystophora cristata) are largely solitary, ice-associated pinnipeds that spend most of the year dispersed across the deep, cold waters of the North Atlantic and Arctic Ocean basins. They are cathemeral, active at any hour, with diving activity often continuing round the clock during foraging bouts at sea. Outside of the breeding and molting seasons, hooded seals are among the most pelagic of northern phocids, ranging widely and diving repeatedly to great depths in search of prey, only returning to pack ice for pupping, mating, and molting.

Social organization is minimal for most of the year, but seasonal aggregations occur on drifting pack ice during the breeding season (March) and again during molting (June–July), when large numbers of individuals may gather on the same ice floes without forming true colonies or harems in the way many otariids do. Males compete aggressively for access to receptive females, and dominant males may guard a female and her pup for the brief nursing period, but this does not constitute long-term pair bonding or classic harem structure. Home ranges are enormous, with satellite tracking showing migrations spanning thousands of kilometers between Arctic Canada, Greenland, Svalbard, and the Barents Sea.

The species is renowned for its extraordinary communicative and physical adaptation: the inflatable nasal septum (“hood”) of adult males and the associated red nasal membrane balloon can be inflated as a visual and acoustic display used in male-male competition and possibly female attraction. Vocalizations, low-frequency underwater calls, and physical displays substitute for scent marking, which is of limited use in a marine, ice-based environment. Hooded seals also exhibit remarkable diving physiology, including bradycardia and peripheral vasoconstriction, enabling dives exceeding 1,000 meters and lasting up to an hour.

Hooded seals are opportunistic, deep-diving carnivores that prey primarily on cephalopods (particularly squid) and a variety of fish species including Greenland halibut, redfish, capelin, cod, and herring. Foraging occurs mostly in deep offshore waters and along continental slopes, where seals perform long, deep dives—often 100 to over 1,000 meters—to access prey associated with the deep scattering layer. Their hunting strategy relies on stealth, excellent low-light vision, and highly sensitive vibrissae capable of detecting prey movement in dark or turbid water.

Metabolically, hooded seals possess a thick blubber layer and elevated blood volume and myoglobin concentrations that support extended breath-holding and cold tolerance, key adaptations for exploiting prey resources unavailable to shallower-diving predators. Diet composition shifts seasonally and geographically, tracking prey availability, migrations, and ice conditions; individuals in the Davis Strait and Greenland Sea populations show different prey emphases based on regional productivity. As marine mammals, hooded seals meet their water needs metabolically and through prey consumption, and they do not require fresh water.

Breeding takes place in a highly compressed window during March on drifting pack ice, primarily in well-defined whelping areas such as the “West Ice” near Jan Mayen, the Davis Strait, and the Gulf of St. Lawrence (though the latter population has declined sharply). The mating system is polygynous/promiscuous, with males competing for proximity to receptive females via aggressive displays involving hood inflation and vocalizations. Gestation lasts approximately 8 months (including delayed implantation), and females give birth to a single pup per year; twinning is exceptionally rare.

Hooded seals hold the record among mammals for the shortest lactation period, nursing pups for just 3 to 4 days on extremely fat-rich milk (up to 60% fat), during which pups may double their birth weight. Weaning is abrupt, and pups are left to fend for themselves shortly thereafter, entering the water independently within days. Females mate again almost immediately after weaning their pup. Sexual maturity is reached at approximately 2–5 years in females and slightly later, around 4–6 years, in males, though full social/behavioral maturity in males may take longer given the intense competition for mates.

Hooded seals face mounting threats primarily linked to climate change and the loss of stable pack ice required for pupping and molting. Because they are highly ice-dependent for reproduction, reduced sea ice extent and earlier ice breakup in the North Atlantic and Arctic have led to increased pup mortality from premature separation and ice collapse. Historically, the species suffered severe population declines due to commercial sealing for pelts and blubber, particularly in the Northwest Atlantic (Davis Strait/Gulf of St. Lawrence populations), with some stocks reduced by more than 90% from historic levels.

Natural predators include polar bears, killer whales, and Greenland sharks, which opportunistically target pups and vulnerable adults on or near ice edges. Bycatch in commercial fisheries, pollution (including persistent organic pollutants that bioaccumulate in blubber), and reduced prey availability due to overfishing and shifting ocean conditions compound the pressures on the species. The IUCN currently lists the hooded seal as Vulnerable, and conservation actions include harvest quotas and monitoring under Canadian and Norwegian fisheries management authorities, NAMMCO (North Atlantic Marine Mammal Commission) scientific assessments, and CITES Appendix II trade regulation, alongside ongoing research into population trends via satellite tagging and aerial surveys.

• The Inflatable Hood: Adult males possess an elastic nasal cavity that inflates into a balloon-like “hood” over the head, and can also blow a bright red membrane out of one nostril—used in dominance displays and mate competition.
• Shortest Lactation of Any Mammal: Hooded seal pups nurse for just 3–4 days, the shortest recorded lactation period among all mammals, fueled by milk containing up to 60% fat.
• “Bluebacks”: Newborn hooded seal pups are called “bluebacks” due to their striking blue-gray natal coat, which they molt after several months.
• Deep-Diving Champions: Hooded seals can dive over 1,000 meters (nearly 3,300 feet) and remain submerged for up to an hour, among the deepest and longest dives recorded for any phocid seal.
• Ice-Obligate Breeders: Unlike many seals, hooded seals almost exclusively use drifting pack ice—not landfast ice or beaches—for pupping, mating, and molting, making them acutely vulnerable to sea ice loss.
• Transatlantic Wanderers: Vagrant hooded seals have been recorded far outside their normal range, including sightings off Florida, the Caribbean, Portugal, and even inland in Europe, likely reflecting long-distance dispersal behavior.
• Distinctive Coat Pattern: Adults have a striking silvery-gray coat covered in irregular black blotches, giving them a distinctive “spotted” appearance that differs markedly from the pup’s coloration.