The species and latin name of the Hooded Seal (Cystophora cristata) refer to the truncated nose and secondary balloon-like sac, or nasal membrane, on the head of the male seals. They are described as plumed (cristata) as well as “bladder-bearing” (cystophora, which originates from a Greek word). The purpose of these unusual features is acoustic display and sexual posturing. The species is mainly found in the northern Atlantic from Canada across to Svalbard, and the Arctic Ocean, however individuals have been found roaming further afield. C. cristata are classified as Vulnerable by the IUCN, although data is not conclusive, and some studies indicate their situation could be even more serious. Estimated population size = 675,000.
C. cristata are a large true seal (males ♂ up to 3 m long/ 400 kg, females ♀ up to 2.4 m/ 300 kg). They have fairly short, rear-facing flippers, and large, broad heads (with sexual appendages in the males as described in the paragraph above). The hood, which is actually a nasal cavity, can inflate and deflate, creating sound underwater, and the pink nasal membrane protrudes from the left nostril, and can also be shaken to create different noise signals. These appendages signal the individual’s status to other males, as well as advertise their sexual prowess to available females. Because of this, male C. cristata are easily recognisable. Females, by comparison, show just a blunt snout, with an occasional short proboscis. Their robust bodies are white to grey or silver in colour, with black patches all over.
C. cristata feed on a wide variety of fish and invertebrates, concentrating their efforts where there is high productivity and favouring prey rich in lipids and fatty acids. Males and females have been shown to have differing preferences, and an array of different dive depths have been recorded for both, from 100 to 1000 m. Examples of prey types include amphipods, krill, halibut, cod, herring, redfish, squid, octopus and mussels.
Sexual maturity – males ♂ 5-7 years old/ females ♀ 3-6 years old.
Male C. cristata compete, call and display aggressively for access to females, usually mating in the water when pups have been weaned. Delayed implantation of around 4 months means the female will give birth again a year later. The colonies are thought to have a mostly polygynous structure but some males will remain with and defend just one female instead of breeding with multiple. Metre long pups, also called bluebacks, are born in March and April, getting their nickname from their blueish grey fluffy coats, which they will keep for the first year. C. cristata have the shortest nursing time of any mammal, with pups being weaned after just 4 days. This is beneficial for the adults who do not lose much weight during lactation, unlike many other phocids, and the pups themselves will double their size in this time, owing to a combination of their own fatty tissue, and the high (60%) fat content of the milk provided. After weaning, adults will travel out to sea to feed, before returning to the ice once more in July to moult. Pups will remain on the ice for severaldays or weeks, living off their reserves, until they venture into the water to start learning to forage. The rest of the time the species is fairly solitary. Life expectancy for C. cristata is 30-35 years.
There are no recognised subspecies of C. cristata, though they are often referred to in terms of two separate populations in the northeast and northwest Atlantic. Perhaps owing to their migratory nature, they may mate with partners from any of the breeding areas.