Walruses prefer molluscs - mainly bivalves such as clams. They also eat many other kinds of benthic invertebrates including worms, gastropods, cephalopods, crustaceans, sea cucumbers, and other soft-bodied animals. Walruses may occasionally prey on fishes such as polar cod.
Walruses may eat the carcasses of young seals when food is scarce.
There are some rare but habitual seal-eating walruses. Their diet consists mainly of ringed and bearded seals. These are usually male walruses, recognizable because they are usually larger than other males, with powerful shoulder and chest muscles. Their skin may become grease-stained from the blubber of the seals they prey on.
Adult walruses eat about 3% to 6% of their total weight per day.
Adults may eat as many as 3,000 to 6,000 clams in a single feeding session.
Observations of feedings indicate that walruses usually fill their stomachs twice daily.
In the summer months, and during the southward migration in the fall, walruses spend most of their day foraging. They eat less on their northward migration in the spring. Food intake for mature male walruses dramatically decreases during the breeding season and probably for a shorter time for females in estrus. Pregnant females increase food consumption about 30% to 40%.
Methods of Collecting and Eating Food
Walruses usually forage on the bottom within 80 m (262 ft.) of the surface. Most feeding probably takes place between 10-50 m (33-164 ft.).
Because visibility is poor in deep and murky waters, walruses rely on their vibrissae to locate food. A walrus moves its snout along the bottom, rooting through the sediment and using its vibrissae to help detect prey. Abrasion patterns of the tusks show that they are dragged through the sediment, but are not used to dig up prey.
In addition, researchers have seen foraging Atlantic walruses rapidly waving a foreflipper to uncover prey from the sediment. The walruses that were observed, preferentially used their right flipper when foraging this way.
Evidence shows that walruses may take in mouthfuls of water and squirt powerful jets at the sea floor, excavating burrowing invertebrates such as clams.
Walruses do not chew their food, but they do sometimes crush clam shells.
Soft-bodied invertebrates are usually not crushed or torn. A walrus sucks off the foot and the fleshy siphon of a clam and swallows it whole.
The cheek teeth do get worn, but this is probably from abrasion by minute particles of sand that walruses inadvertently take into their mouths and not from crushing clam shells.
Researchers have found numerous pebbles and small stones in the stomachs of walruses. These are thought to be ingested while feeding.