The sea otter (Enhydra lutris) is a highly specialized marine mammal that spends its entire life in coastal Pacific waters. Unlike seals and whales, it is one of the smallest marine mammals and lacks a thick layer of blubber for insulation, relying instead on its dense fur to survive the cold ocean. Since sea otters must consume a large quantity of food daily—up to 25 percent of their body weight—diving to the seafloor to forage is a continuous necessity for survival. The ability to perform deep, repeated dives allows these animals to access the diverse array of invertebrates.
The Maximum Diving Depth
While a sea otter typically forages in relatively shallow coastal areas, its maximum diving capability is significantly greater than its routine depth. Most of their foraging occurs in waters less than 30 meters (approximately 100 feet) deep, as this depth requires less time and energy to reach the sea floor. However, when prey is scarce or they are hunting larger, deeper-dwelling species, they can push their limits considerably.
The extreme depth capacity for an adult sea otter can reach up to 100 meters (about 330 feet), with some observations noting dives as deep as 183 meters (600 feet). Studies have shown that adult male sea otters tend to exhibit deeper maximum foraging dives than females, averaging depths of over 80 meters. These deeper dives are only undertaken when the potential caloric reward outweighs the physical demand.
Duration and Foraging Strategy
The time a sea otter spends underwater is directly tied to the success of its foraging dive and the type of prey it is pursuing. Most routine dives in shallow water last between one and three minutes, which is enough time to locate and retrieve small invertebrates. The sea otter can hold its breath for much longer when necessary, with maximum reported durations extending up to five minutes, and occasionally reaching seven or eight minutes.
Sea otters are benthic foragers, meaning they hunt along the ocean floor for prey like sea urchins, crabs, clams, and mussels. They use their highly sensitive forepaws and whiskers to locate prey hidden in crevices or buried in the sediment. A unique aspect of their strategy is the use of tools, as they are one of the few mammals known to use rocks to dislodge prey like abalone or to crack open hard shells while floating on the surface. The duration of the surface interval between dives is also important, as it allows the otter to process the captured prey and replenish its oxygen supply before the next dive bout begins.
Physiological Adaptations for Deep Dives
The sea otter’s ability to dive is supported by a unique set of physical and physiological characteristics. Unlike most other marine mammals, the sea otter’s primary insulation is its incredibly dense fur, which can have up to a million hairs per square inch. This fur traps an insulating layer of air against the skin, though this layer compresses significantly under the pressure of a deep dive, reducing its effectiveness. The large lung capacity relative to their body size results in significant positive buoyancy, meaning the otters must actively expend energy to swim downward and stay submerged.
To manage the oxygen demands of diving, sea otters exhibit specific physiological responses. When a dive commences, the animal utilizes oxygen-conserving mechanisms, reflected in a metabolic rate during a single dive that is only slightly higher than their resting rate. This careful rationing of stored oxygen, alongside a high oxygen storage capacity in their blood, allows the sea otter to maximize its time at the sea floor.