Walruses feed on animals that reside on the surface of the bottom of the ocean, or in the sediments that coat the bottom. Their main diet includes mussels, snails, echinoderms, and crabs. Walrus foraging dives usually last 2-10 minutes at depths of 10-50 m. They swim headfirst along the ocean bottom, rooting about with their stiff beard bristles in a piglike fashion. Softbodied organisms are swallowed whole. Two theories on how walruses eat bivalves have been proposed, and it appears that walruses employ both methods. Walruses crack mollusk shells between their flippers and then eat the soft part. More often, walruses hold the shelled organisms in their lips and ingest the fleshy parts by powerful suction, discarding the shells. Occasionally, walruses also prey on fish, seals, and young whales. Walruses are capable of holding down seals and small whales with their flippers and tearing them apart with their tusks. In the winter, when accompanying the females and young, the bulls apparently eat very little. It was once believed that walruses used their tusks to dig up food, but this notion is false (Nowak 1991, Parker 1990).