Walruses, large marine mammals of the Arctic, are often seen in and around icy waters. While they cannot breathe underwater, like all mammals, walruses breathe air and must periodically return to the surface. Despite this fundamental biological fact, they possess an array of specialized adaptations that allow them to spend significant time submerged, making them highly efficient aquatic inhabitants of their cold environment.
Walrus Diving Physiology
Walruses possess adaptations enabling them to hold their breath for extended periods. Their bodies are equipped with a high concentration of oxygen-binding proteins, such as myoglobin in their muscles and hemoglobin in their blood, allowing for efficient oxygen storage and transport. During a dive, a walrus can significantly slow its heart rate, known as bradycardia. This adaptation conserves oxygen by reducing its consumption and redirecting blood flow to organs like the brain and heart.
Specialized pharyngeal muscles also play a role in preventing water from entering the trachea when a walrus opens its mouth underwater. Walruses possess a thick layer of blubber, which not only provides insulation against the frigid Arctic waters but also aids in buoyancy regulation during dives. Their lungs, while similar in structure to those of terrestrial mammals, demonstrate a higher degree of flexibility, facilitating effective air exchange upon surfacing.
Underwater Foraging and Dive Limits
While submerged, the primary activity for walruses is foraging for food, predominantly benthic invertebrates found on the seafloor. Their sensitive whiskers, known as vibrissae, are particularly developed for this purpose, allowing them to detect prey such as clams and other mollusks in murky or low-visibility waters. Once prey is located, walruses use a powerful suction technique to extract the soft tissues from shells.
Walrus dives are optimized for feeding, making them shorter and shallower than their maximum capabilities. They can hold their breath for up to 30 minutes, though common foraging dives might last between 5 to 8 minutes. Walruses forage in waters around 10 to 80 or 90 meters deep, corresponding to the distribution of their preferred food sources. Although studies have recorded exceptional dives exceeding 500 meters, these are less frequent, with the majority of their time spent in shallower, prey-rich areas.
Surfacing and Recovery
After a period of underwater activity, walruses must return to the surface to replenish their oxygen supply and expel carbon dioxide from their bodies. They take several rapid breaths upon breaking the surface to quickly re-oxygenate their blood. Following these initial breaths, walruses continue to breathe at the surface for about a minute before initiating another dive.
Walruses use ice floes or land as haul-out sites for resting and recovery between diving bouts. These resting periods conserve energy and allow their bodies to recover from the physiological demands of diving. Their prominent tusks, which are elongated canine teeth, are used to help them pull their large bodies out of the water onto ice or land. This allows them to rest, socialize, and nurse their young in a more stable environment.