For an animal of such size, the walrus feeds on organisms that are relatively low in the food chain, preferring the small invertebrates that inhabit the ocean floor to the highly mobile fish and crustaceans taken by most other pinnipeds (2). By far the greatest proportion of its diet is comprised of bivalve molluscs such as clams, cockles, and mussels, but it will also take various shrimps, crabs, worms, octopuses, sea cucumbers, slow moving fish and, very rarely, seals (1) (2) (5) (7). In order for such a large, bulky animal to sustain itself on a diet dominated by relatively small organisms, it needs to be a highly efficient forager (2). Diving to depths of up to 180 metres for up to 24 minutes at a time, it uses its highly sensitive whiskers and snout to locate food, which it then excavates using the tough edges of its nose, and by squirting jets of water from its mouth (2) (5) (7), and creating water flow with its foreflippers (6).
Male and female walruses typically spend little time together outside of the breeding season, but being a highly gregarious species, both sexes haul out on land or ice in large numbers. In these largely sexually segregated herds, the animals lie in close physical contact, sometimes piled on top of each other (2) (8). Walrus society is extremely hierarchical, with the largest individual, with the largest tusks, commanding the best positions at the haul out sites. Usually the dominant walrus can displace subordinates with the minimal of posturing, but similar sized/tusked adults may put up a fight, in which case a stabbing duel may ensue, until one aggressor accepts defeat and retreats to less coveted territory (2) (7). Although these fights do take place between both sexes, the most violent encounters occur between bulls during the breeding season (4) (7).
In the harsh winter, males and females congregate for the mating season, between January and April (2) (4) (7). Whilst the females haul out on ice floes, the males compete for nearby aquatic territory through a combination of vocalisation, physical displays, and, if necessary, intense fighting (1) (4). The female chooses a mate from the competing males and usually copulates in the water, with the most dominant bulls siring offspring with multiple females (2) (4). After a gestation period that lasts 15 months, including a four to five month period of delayed implantation, the female gives birth to a single calf. The calf is able to swim immediately but is typically only weaned during its second year, and usually remains within the extremely protective care of its mother for several years (2) (5). While most females become sexually mature at 7 years of age, and give birth for the first time at around the age of nine years, most males only become sufficiently physically and socially mature to mate at around 15 years, despite reaching sexual maturity between 7 and 10 years (2) (7).
The seasonal movements of the walrus, and in particular of the females, calves and most of the juveniles in the Pacific, are typically governed by the movements of the pack ice. However, in the summer in the Atlantic, walruses of all sexes and ages commonly haul out on land relatively far from the pack ice (1) (4).