TUSKED SEALS

Walrus (Odobenus rosmarus)

The Walrus (Odobenus rosmarus) is the only species of the family Odobenidae in the world. In the past there were numerous other species but they are all long since extinct. The historical origin of the word Walrus is an interesting one with several different theories on how the word came about. One thought is that it originates from an Old Norse word for ‘whale-horse’, owing to the ‘neighing’ sound emanating from a large colony of Walrus’ during an expedition to the Arctic. Another is that it evolved from the Dutch words ‘wal’ and ‘reus’, meaning shore giant. The latin name has also a descriptive origin, with Odobenus translating from Greek to mean walking (benus) with teeth (odo), in reference to them using their large tusks to drag their bodies out of the water, and rosmarus referring to the pink or rosy colour of the animal (ros) and the fact that they are marine (marus). The species, found in the North Pole region, are classified overall by the IUCN as Vulnerable. Estimated population size = 225,000.
O. rosmarus is a large and somewhat bulky tusked pinniped (males up to 3.6 m long/ 1,900 kg, females up to 3 m/ 1,200 kg). Neither a true nor eared seal, they have characteristics of both, but as stated earlier, they are an entirely different family group of their own. Their rear flippers are hefty and webbed, and similar to that of the true seals, though notably, they are capable of rotating forwards as in the eared seals, in order to walk on all fours. The fore flippers are broad and square, and more like those of the Otariids in length, though during swimming they are mostly held by the animal’s sides, in a manner characteristic of the Phocids. Their heads are round and broad with a square shaped face, and with the thick neck hide and enormous body bulk, they appear inordinately small and somewhat part of the body. The most distinguishing feature is the long, heavy tusks (or elongated canine teeth) which are present in both males and females, and can grow up to a metre in length. The tusks have several uses, including: male dominance and display, quarrelling, dragging the body out of the water, and maintaining holes in the ice. Also on the face, are two small black eyes, two flattened nostrils, and a frontal whisker pad with long, pale, stiff vibrissae. Again, akin to the Phocidae species, they lack external ear flaps. The skin of a Walrus is thick and heavy with creasing and folds all over, a thin coating of fur, and an extremely thick layer of blubber underneath. Usually colouration is brown to grey (much paler in water when blood vessels contract to conserve warmth), but in males particularly there is a tendency to look pinker in later life as the fur thins, as per the latin name. When the animal is out on land in warmer weather, the blood vessels dilate to increase circulation and regulate the temperature of the blood, this gives them their pink or even red hue. The final characteristics of O. rosmarus are an air sac under the throat to aid in buoyancy, and skin nodules, or ‘bosses’ in just the mature males, around the neck and shoulders, presumed to be a secondary sexual characteristic.
Feeding behaviour:
O. rosmarus use their sensitive whiskers to forage for prey in soft sediment on the seafloor. Their principle diet choice is bivalve molluscs, but they will also commonly eat worms, snails, shrimps, sea cucumbers, and various marine invertebrates. Molluscs are sucked from their shells using a powerful suction action from the mouth. Sometimes O. rosmarus will hunt slow swimming fish, and periodically, they have been recorded taking seabirds and even smaller seals when the opportunity presents. Foraging dives are usually fairly shallow.
Breeding behaviour:
Sexual maturity – males 7-10 years old/ females 5-7 years old.
O. rosmarus are polygynous breeders with males establishing aquatic territories where they display and vocalise and defend their harems. Courtship and mating occur in water during winter, and after a gestation of around 15 months (including delayed implantation), young are born from April to June the following year. These calves are not born with a lanugo, and instead have a dark coat which enables them to swim immediately. With mothers only giving birth at maximum every 2 years, parental care and investment in the Walrus is very high, and can last 2 years or more itself. Nursing takes place mostly in water and continues for at least the first 6 months of the youngster’s life, before it may start to learn to forage. Typically the calves live in the female group until the arrival of a younger sibling. O. rosmarus moult inconspicuously in the summertime. Life expectancy for this species is around 40 years.
Despite a past distinction between three sets of Walrus populations, in recent years it has been decided that only two of the populations represent a genuine subspecies. These are:
Atlantic Walrus – (Odobenus rosmarus rosmarus)
Pacific Walrus – (Odobenus rosmarus divergens)

Photo: Mike Dunn/ NOAA

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