The walrus, Odobenus rosmarus, is an enormous Arctic marine mammal recognizable by its prominent tusks and thick layer of blubber. It is split into two recognized subspecies: the Pacific walrus and the Atlantic walrus, both relying heavily on sea ice for resting and breeding. Their immense size, with Pacific males often exceeding 2,000 kilograms, demands a specialized and efficient foraging strategy. The walrus has developed unique diving capabilities purpose-built for hunting along the ocean floor.
The Maximum Diving Depth and Duration
Walruses are generally considered shallow-water divers compared to other large pinnipeds, as their foraging behavior is tied to the seabed of continental shelves. The vast majority of their dives remain in the range of 20 to 80 meters (66 to 262 feet) deep. However, these animals possess a physiological capacity to go much deeper when necessary, with some Atlantic walruses recorded making isolated dives exceeding 500 meters (1,600 feet) in areas like Smith Sound. While their habitat limits their routine diving, their biology permits far greater depths.
The typical duration of a feeding dive for a walrus averages between five and eight minutes. This timeframe allows them to efficiently search for and consume prey before returning to the surface to breathe. While the maximum recorded dive duration is around 49 minutes, these extremely long dives are rare. Although the Pacific walrus is physically larger than the Atlantic walrus, the observed foraging depths and dive durations for both subspecies are closely aligned, as their feeding habits drive the metrics.
Walrus Foraging Strategy and Preferred Habitat
The walrus is a specialized benthic feeder. Their primary food source is bivalve mollusks, such as clams, along with other invertebrates like sea cucumbers and soft corals. This reliance on bottom-dwelling creatures explains why they prefer the shallow waters of the continental shelf, which are typically less than 80 meters deep and contain the densest populations of their prey.
The search for food in the dark, often turbid water is accomplished not by sight, but through touch. Walruses possess a dense mat of over 400 highly sensitive whiskers, known as vibrissae, which surround their muzzle. These vibrissae are equipped with thousands of nerve endings that allow the animal to detect the minute shapes and movements of buried shellfish in the mud. Once prey is located, the walrus uses a powerful suction technique, drawing the soft body of the clam out of its shell using a piston-like tongue.
Contrary to a common misconception, the walrus does not typically use its tusks to dig for food in the sediment. They are primarily utilized for social displays, establishing dominance, and for helping the massive animal haul its body out of the water onto ice floes or land. The digging and disturbing of the seabed is mostly accomplished through the animal’s flippers and strong jets of water expelled from its mouth.
Physiological Adaptations for Underwater Hunting
To manage the physiological demands of routine diving, the walrus employs a suite of biological mechanisms common to marine mammals. When submerging, the animal triggers the mammalian dive reflex, which includes a dramatic slowing of the heart rate, a phenomenon called bradycardia. This reflex conserves oxygen by reducing the overall metabolic rate of the body.
The walrus initiates peripheral vasoconstriction, which constricts blood vessels in the extremities and skin. This process shunts oxygenated blood away from tissues that are more tolerant of low oxygen levels, redirecting it to the most critical organs, such as the brain and heart. The walrus’s muscles are rich in myoglobin, a protein that stores oxygen directly within the muscle tissue, providing an essential reserve for the duration of the dive.
The animal also possesses specialized pharyngeal muscles in its throat that automatically close the trachea when diving. This mechanism prevents water from entering the respiratory system while the walrus is actively foraging on the seabed. Since walruses typically forage in shallow depths, they do not face the extreme pressure changes that deep-diving species must contend with, lessening the risk of nitrogen narcosis and lung collapse.