The walrus (Odobenus rosmarus) is a massive Arctic marine mammal that spends time in the frigid waters of the North Pole, often utilizing ice floes as resting platforms. Their immense size, reaching up to 2,000 kilograms in Pacific males, requires a constant food supply procured from the ocean floor. This dependence on benthic prey necessitates a specialized ability to dive and forage in the shallow continental shelf waters.
Walrus Dive Duration and Depth
Walruses typically make shallow dives compared to other pinnipeds because their primary food source is found close to the seabed in continental shelf regions. A routine foraging dive lasts between five and 20 minutes, usually reaching depths of 70 to 80 meters, corresponding to the location of their preferred prey.
While most dives are short, the animal is capable of far greater feats when necessary. Maximum recorded dive durations have reached nearly 50 minutes. The deepest documented dives exceed 500 meters, though these longer dives are thought to be exploratory or occur during long-distance transits.
Physiological Mechanisms for Extended Immersion
To manage underwater excursions, the walrus employs adaptations known as the mammalian diving reflex. A primary component is bradycardia, an immediate and dramatic slowing of the heart rate upon submersion. This reduction in heart activity decreases the overall rate of oxygen consumption, extending the time the animal can stay underwater.
Another adaptation is peripheral vasoconstriction, restricting blood flow away from tissues tolerant of low oxygen, such as the skin and muscles. This ensures that limited oxygen stores are preferentially supplied to vital organs, namely the brain and the heart. The walrus also possesses high concentrations of the oxygen-binding protein myoglobin in its muscles, which acts as a localized oxygen reserve.
Myoglobin releases its stored oxygen when the surrounding tissue becomes low in oxygen, providing a sustained power source for the muscles even when blood flow is reduced. Walruses also have a larger total blood volume compared to terrestrial mammals, allowing them to carry a greater amount of oxygen bound to hemoglobin. These physiological changes minimize metabolic demand and maximize the efficiency of their internal oxygen supply during a dive.
Underwater Behavior and Foraging
The diving ability of the walrus is primarily used to support its feeding habits. Walruses are benthic foragers, searching for prey that lives on or in the seafloor sediment. Their diet consists almost exclusively of marine invertebrates, particularly bivalve mollusks like clams, sea cucumbers, and worms.
The walrus relies on its sensitive whiskers, known as vibrissae, to locate prey in the dark or turbid waters of the seabed. Once prey is located, the walrus uses its unique, vaulted palate and powerful tongue to create a strong vacuum. This suction allows the animal to suck the soft parts of the mollusk directly out of its shell, leaving the shell behind.
Foraging dives maximize time spent on the bottom, where feeding occurs, with minimal time spent in transit. A walrus can consume up to 60 clams in a single dive, and an adult may require up to 25 kilograms of benthic organisms per day.