Sea lions are mammals that cannot breathe underwater and must return to the surface for air. They have developed specialized abilities to hold their breath for extended periods and manage the pressures of deep-water diving. Their successful existence in marine habitats relies on these unique physiological and behavioral adaptations.
How Sea Lions Dive
When a sea lion prepares to dive, it exhales a significant portion of air from its lungs, which helps reduce buoyancy and allows for easier descent. Underwater, their nostrils naturally close, preventing water entry. Sea lions can hold their breath for 3 to 8 minutes, with some dives extending up to 20 minutes for deeper foraging excursions.
Sea lions are capable of diving to considerable depths, ranging from 135 to 272 meters (450 to 900 feet). Some species, like the New Zealand sea lion, can reach up to 550 meters. These sustained periods underwater are supported by internal mechanisms that regulate their oxygen use.
Amazing Adaptations for Underwater Life
A primary adaptation for oxygen conservation during a dive is bradycardia, where their heart rate slows considerably. It can decrease from around 95 beats per minute at the surface to 6-10 beats per minute during deep dives, lowering oxygen consumption. Peripheral vasoconstriction complements this by redirecting blood flow from non-essential organs and tissues to prioritize the brain and heart. This strategic redistribution ensures oxygen is primarily supplied to the organs most sensitive to oxygen deprivation.
Sea lions possess an increased capacity to store oxygen compared to land mammals. They have a higher blood volume and elevated concentrations of hemoglobin, which binds and transports oxygen. Their muscles also contain a high concentration of myoglobin, a protein that stores oxygen directly in the muscle tissue, providing a localized oxygen reserve for muscular activity during a dive.
To manage pressure changes at depth and avoid decompression sickness, sea lions exhibit lung collapse. Their flexible rib cages and lungs compress under pressure, pushing air out of gas-exchange areas into stronger, non-exchange airways. This mechanism limits nitrogen absorption into the bloodstream, reducing “the bends” risk. During prolonged dives, sea lions may also rely on anaerobic metabolism, allowing muscles to function without oxygen and tolerating lactic acid buildup.
Underwater Activities and Behavior
Underwater, sea lions engage in various activities essential for their survival. Their agile, streamlined bodies, propelled by powerful front flippers, allow them to swim efficiently at speeds up to 40 kilometers per hour (25 miles per hour). They are skilled hunters, feeding on fish species like herring, anchovies, and rockfish, as well as squid, octopus, and krill. Their keen underwater vision helps them locate prey in low-light conditions.
Sea lions utilize their highly sensitive whiskers, known as vibrissae, to detect movements and vibrations in the water. These whiskers are useful for sensing prey, navigating murky waters, or even in complete darkness. Underwater, sea lions may exhibit social behaviors, including communication through vocalizations. They also use the underwater environment for resting, sometimes sinking to the bottom or floating with their noses just above the surface.