What Do Walruses Eat? Clams, Suction Feeding and Whiskers

What foods do walruses eat?

The walrus is a bottom feeder. Studies of stomach contents have recorded more than 60 genera of marine animals in its diet, but bivalve mollusks, especially clams, make up the bulk of it. Typical prey includes truncate softshell clams, Greenland cockles, Macoma clams and Arctic hiatella, along with:

• Snails such as whelks
• Worms, including marine bristle worms, spoon worms and priapulid worms
• Sea cucumbers and tunicates (sea squirts)
• Crustaceans such as shrimp, crabs and amphipods
• Soft corals and other soft-bodied animals
• Occasional fish, such as slow-moving bottom fish and Arctic cod

Exactly what a walrus eats depends on where it feeds, because it takes whatever prey is common on the local seabed. For comparison with other pinnipeds, see What do seals eat?

How do walruses find food?

Walruses usually feed in water too dark or muddy to see much, and their small eyes are suited only to short distances. Instead they rely on touch. A walrus has about 400–700 stiff whiskers, called vibrissae, arranged in 13–15 rows on its broad muzzle. Each whisker is supplied with nerves and blood vessels and can be moved by muscles. Experiments with captive walruses have shown they can tell apart objects only a few millimeters across using their whiskers alone.

To feed, a walrus swims slowly along the bottom with its head down and its muzzle pressed into the sediment, sweeping its whiskers back and forth. In the wild the whiskers are often worn short from this constant use.

Suction feeding: how walruses eat clams

Walruses do not crack clams open with their teeth. A walrus seals its thick lips around the clam and pulls its tongue back sharply inside its arched mouth, working like the piston of a pump. This creates powerful suction that pulls the soft foot and siphon of the clam out of the shell, which is then dropped on the seafloor. When researchers measured this suction in captive walruses, the pressure inside the mouth fell to a small fraction of normal air pressure.

Walruses also use water to uncover prey buried in the sediment. They squirt strong jets of water from the mouth to blast away mud and sand. A study of wild Atlantic walruses observed underwater off northeast Greenland, published in 2003, found that they also waved a front flipper to fan sediment away, and most used their right flipper, a rare example of “handedness” in a wild mammal.

Their famous tusks play no part in digging. Wear marks show the tusks are just dragged along the bottom, as explained in What are walrus tusks for?

How much does a walrus eat?

Walruses need a lot of small prey to fuel their huge bodies. Adults eat roughly 3–6% of their body weight per day. For a 1,200 kg (2,600 lb) bull, that is somewhere around 35–70 kg (75–155 lb) of clam meat and other food a day, and a single feeding session can involve thousands of clams. How much walruses weigh is covered in How big is a walrus?

Food intake changes through the year. Walruses feed most in summer and autumn. Breeding males eat very little during the winter mating season and live off their blubber, while pregnant and nursing females need more food than usual.

Where and how deep do walruses feed?

Walruses feed in shallow water over the continental shelf, usually less than about 80 m (260 ft) deep, and most feeding probably takes place in water 10–50 m (33–165 ft) deep. Feeding dives usually last several minutes, often around 5–10, before the walrus surfaces to breathe. Much deeper dives, beyond 500 m (1,640 ft), have been recorded in a few places, but they are unusual.

Between feeding trips, walruses need a place to rest. Floating sea ice over shallow feeding grounds is ideal, because the herd can rest and drift above its food. As summer ice in the Arctic has shrunk, many Pacific walruses have had to rest on beaches instead, sometimes far from their best feeding areas. That longer commute costs energy and is one of the main concerns for the species’ future.

Do walruses eat seals and birds?

Most walruses eat almost no vertebrates, but there are exceptions. A small number of walruses, mostly big males, regularly kill and eat seals, especially ringed and bearded seals, and there are records of walruses taking seals as large as a 200 kg (440 lb) bearded seal. These seal-eating walruses tend to be large and powerfully built. Walruses also scavenge on dead seals and whales.

Very rarely, walruses have been seen catching seabirds. In the Canadian Arctic, walruses have been observed killing thick-billed murres, also called Brünnich’s guillemots, in the water near a nesting colony.

Walruses as seafloor engineers

Feeding walruses churn up huge areas of the seabed. As they root and blast through the sediment, they leave pits and furrows, release nutrients into the water, and expose buried animals that other scavengers can then eat. Scientists describe this kind of disturbance as bioturbation. Because a single walrus herd can rework a large patch of seafloor, walruses help shape the bottom communities of Arctic seas.