The walrus, Odobenus rosmarus, is a massive marine mammal inhabiting the Arctic and subarctic waters of the Northern Hemisphere. Adult males of the Pacific subspecies can weigh over 2,000 kilograms, making them one of the largest pinnipeds. This animal is known for its unique feeding habits, which distinguish it from most other marine carnivores in its icy environment. Its specialized diet is adapted to the shallow continental shelf waters where it spends its time.
The Direct Answer: Krill vs. Benthic Invertebrates
Walruses do not consume krill, which are small, shrimp-like crustaceans found throughout the water column. The walrus is primarily a benthic forager, meaning it feeds almost exclusively on the seafloor. Krill, conversely, are largely pelagic, dwelling in the open water, making them incompatible with the walrus’s lifestyle.
The walrus diet is overwhelmingly dominated by benthic invertebrates, constituting up to 97% of its food intake. Their preferred prey are bivalve mollusks, particularly various species of clams. Because these prey items are small, a walrus must consume a massive quantity to sustain its large body mass. A single walrus can ingest 3,000 to 6,000 clams during one feeding session.
Specialized Benthic Feeding Mechanisms
To locate and consume prey buried in the dark, murky sediments, the walrus relies on highly developed sensory and feeding structures. Its most sensitive tools are its 400 to 700 stiff, bristle-like whiskers, known as vibrissae, which cover its muzzle. These vibrissae are equipped with nerves and blood vessels, making them sensitive enough to detect objects as small as two millimeters wide buried in the seafloor.
Once prey is located, the walrus uses a powerful suction technique rather than chewing. It creates a vacuum by sealing its muscular lips around the clam shell. By rapidly withdrawing its piston-like tongue into its highly vaulted palate, the strong negative pressure extracts the soft body of the mollusk directly from the shell, which is then discarded.
The prominent tusks, which are elongated canine teeth, play no direct role in hunting or digging up food. This is a common misconception. The tusks are primarily used as tools for hauling the walrus’s bulk onto ice floes or rocky shores. They also serve to maintain breathing holes in the ice and are used in dominance displays and social interactions.
Secondary Prey and Opportunistic Behavior
While clams are the dietary staple, the walrus is an opportunistic feeder that consumes a variety of other bottom-dwelling organisms. Secondary prey includes a wide range of soft-bodied invertebrates. These items include marine worms, sea cucumbers, snails, and various crustaceans like shrimp and crabs.
Walruses occasionally target small, slow-moving fish, though this is not a primary food source. In rare instances, usually involving large, older males, they have been observed preying on other marine mammals, most notably ringed or bearded seals. This predatory behavior is considered opportunistic, occurring when preferred benthic food is scarce.