Walrus (Odobenus rosmarus)
The walrus has a very distinctive feature: two large external tusks, which can grow to be a metre long and weigh 5 kg. Walruses have a disjointed circumpolar distribution. Two subspecies are recognized, one in the Pacific and the other in the Atlantic. In the North-East Atlantic, walruses are distributed in shallow coastal areas along eastern Greenland, the Svalbard and Franz Josef Land archipelagos, and in the southern Barents and Kara Seas.
The walrus’s most distinctive feature is the external tusks, which are possessed by both males and females. Tusks can grow to be a meter long and weigh 5 kg in large bulls. Walruses are cinnamon brown in colour. They can appear white after diving or even pink when they are warm, due to them varying the blood supply to the periphery of the body under different circumstances. They have a small head with a flat, broad muzzle that bears many short, sturdy, colourless whiskers. Walruses have no external ear flaps, similar to the true seals, but they can bring their hind legs up under their bodies, similar to the fur seals and sea lions, so they can walk on all-fours on land. Walruses have extremely thick leather, which is heavily wrinkled and covered with tubercles in males, particularly on the neck. Males are proportionally more massive in the neck and shoulders than females and are much larger overall. Adult males are 3-3.5 m long and weigh approximately 1500 kg, while females are about 2.5 m long and weigh around 900 kg. Calves are born weighing about 85 kg and are about 1.3 m long. The calves are chocolate brown with darker, almost black, flippers.
Walruses have a disjointed circumpolar distribution. Two subspecies are recognized, one in the Pacific and the other in the Atlantic. In the Northeast Atlantic walruses are distributed in shallow coastal areas along eastern Greenland, the Svalbard and Franz Josef Land Archipelagos, and in the southern Barents, Pechora and Kara Seas. Svalbard’s walruses are part of a joint population (genetically indistinguishable) with animals on Franz Josef Land. In Svalbard in recent decades, most all the walruses are males; the females and calves in the Barents Sea walrus population are mostly found in the eastern part of the range towards Franz Josef Land. However, in recent years, more and more females with calves have been sighted in Svalbard, as the animals are expanding further into their former range. Walruses reside year-round in Svalbard waters.
There are approximately 200,000 Pacific walruses and some 20,000-30,000 Atlantic walrus. Walruses are extremely social animals. They haul out in tight groups when on land or ice and usually travel at sea in groups as well. There is significant sexual segregation outside the breeding season. Solitary individuals can be seen on occasion on the ice or in the water; these are usually adult males. Walruses have a narrow ecological niche that limits their distribution.
They depend on:
- the availability of large areas of shallow water with suitable bottom substrate to support a productive bivalve community
- the presence of reliable open water over rich feeding areas, particularly in winter when access to many feeding areas is limited by ice cover
- the presence of haul out areas in reasonably close proximity to feeding areas.
Haul out platforms are usually ice pans although terrestrial haul out sites are used in the summer and autumn. Because they feed in shallow, coastal areas walruses usually perform only relatively shallow, short dives. Most dives recorded in Svalbard are shallower than 50 meters; though the maximum dive recorded in the region is over 450 meters and the maximum duration measured to date is 37 minutes.
The walrus’s main prey is bivalve molluscs (clams of various types) that they search for using their sensitive whiskers on or in bottom substrates. They clear soft substrates away from food using their front flippers and then suck the clams from their shells, leaving the shells on the bottom. Thousands of clams can be consumed in a single meal. Some walruses prey on birds and other marine mammals, eating a variety of seal species. The mammal-eating walruses are usually large males and they can be identified by the amber coloured stains on their tusks and chest from the blubber of their prey.
Polar bears and killer whales attack walruses, mainly taking calves. However, predators of walruses meet valiant defences by mothers on land and in the water the whole group will defend against an attack.
There are approximately 200,000 Pacific walruses and some 20.000–30,000 Atlantic walrus. The Svalbard population is thought to include about 2000 animals.
Life history and reproduction
Walruses give birth in May. Just prior to parturition, pregnant females separate from the herd and give birth to their offspring alone on pack ice. New mothers remain on the ice fasting for the first few days postpartum, relying on stored body energy accumulated prior to parturition. Subsequently, females and their young return to the herd and the female recommences foraging. Walrus pups suckle for between two and three years on relatively low-fat milk, with weaning taking place much more gradually than among most other seals. The mothers are always with their dependent young, taking their calves with them to sea on foraging expeditions. Walrus calves are able to nurse at sea, hanging upside-down in the water, cradled by their mother’s front flippers. Dependent youngsters are always attended on the surface by some members of a group when their mothers dive to forage. But, by the age of about five months, the calves are strong enough to dive and they begin to feed on benthic organisms and likely gain valuable foraging experience from their mothers over the remainder of lactation. Female walruses mate about nine months after the birth of their pup, with about 16 months of feeding of their youngster still to go. Breeding takes place in December and January. Males display in small groups along ice edges where females are hauled out, with each male defending a small territory in the water and performing vocal and visual displays. Copulation takes place in the water. Males are very aggressive with one another and injuries are not uncommon during mating battles. When a calf is weaned, female offspring are assimilated into the mother’s herd, whereas male offspring join male groups. Females give birth for the first time when they are about 10 years old. Males also reach sexual maturity by this time, but generally do not get the chance to mate until they are about 15. Walruses live to an age of over 40 years.
Management status and monitoring
Walruses were once very abundant in the Svalbard Archipelago. However, they were hunted virtually to extinction in Svalbard during three and a half centuries of heavy commercial exploitation. Ivory was a valuable trade item and walrus haul out sites were very easily exploited. Walruses became protected 1952 inSvalbard, when it is likely that only a few hundred remained. Despite 50 years of protection, walrus numbers are still low in Svalbard and they remain on the Norwegian National Red List. However, walrus numbers are increasing and they are starting to haul out in sites on land that have not been used for many decades. In August 2006 a survey was conducted of all known (past and present) haul-out sites within Svalbard. Together with information from a satellite-tagging programme, which allowed for the calculation of an adjustment factor that accounted for the proportion of animals that were out swimming when the photographic survey of haulouts took place, the Svalbard subpopulation was estimated to be 2,500 walruses.
MOSJ indicators (Environmental Monitoring of Svalbard and Jan Mayen):
Awaiting results from MOSJ…