The sea otter (Enhydra lutris) is a distinctive marine mammal native to the coastal waters of the North Pacific Ocean. Unlike most seals and whales, this animal does not possess a thick layer of blubber to insulate itself from the cold ocean temperatures. Instead, the sea otter relies on the densest fur in the animal kingdom, along with an elevated metabolic rate, to generate the necessary body heat. This need for constant internal heat production drives its unique foraging behaviors and specialized diet, making the sea otter one of the most dedicated eaters in the marine environment.
The Sea Otter’s Primary Prey Items
The sea otter is a carnivore that primarily targets a wide range of benthic, or bottom-dwelling, marine invertebrates. Its diet is highly varied and can shift based on local availability, but it consistently includes hard-shelled organisms. Sea urchins are a major and often preferred food source, particularly the large red and purple varieties.
Mollusks feature prominently in the otter’s menu, including various species of clams, mussels, and abalone. They also consume crabs, such as Dungeness and rock crabs, along with smaller invertebrates like snails and fat innkeeper worms. While the diet consists mostly of these shelled creatures, the Northern sea otter subspecies, found in areas like Alaska, is also known to consume fish.
Differences in diet can exist between the subspecies across their wide range. For instance, Southern sea otters focus almost exclusively on invertebrates, while Northern otters may include more fish depending on the region. The otter’s flattened molar teeth are specifically adapted for crushing the hard shells of this diverse prey.
Foraging Strategies and Tool Use
Acquiring the necessary amount of food requires sea otters to be highly efficient and strategic foragers. They locate prey on the seafloor using their sensitive forepaws and whiskers during dives that typically last between one and two minutes. While routine dives occur in shallow nearshore waters, Southern sea otters have been observed to occasionally dive up to 80 feet, though they can reach depths of around 300 feet.
Once prey is captured, the otter uses a loose flap of skin located under each foreleg as a storage pouch to hold multiple items gathered during a single dive. The otter always returns to the surface to consume its meal, floating on its back and using its chest or stomach as a stable, mobile dining platform. This position allows them to process food without diving repeatedly.
The sea otter is also one of the few mammals known to regularly use tools to access food. They select rocks or other hard objects, using them as a hammer to break open the shells of clams, mussels, and abalone against an anvil rock or their own chest. This tool-use behavior is particularly important for females, who often have a smaller bite force, allowing them to access tougher, higher-calorie prey that would otherwise be inaccessible. Using tools also helps reduce the wear and damage to their teeth caused by constantly cracking hard shells.
Energy Needs and Ecological Role
The sea otter’s continuous need for food is directly linked to its exceptionally high metabolic rate. Due to the lack of blubber and the rapid heat loss in cold water, an otter’s resting metabolic rate is approximately three times higher than that of a similar-sized terrestrial mammal. To fuel this internal furnace, an average adult sea otter must consume an amount of food equal to about 20 to 30 percent of its own body weight every day.
This massive caloric requirement means sea otters spend a significant portion of their day, sometimes up to half, actively foraging. The high-volume consumption of invertebrates, especially sea urchins, positions the sea otter as a keystone species in its ecosystem. The otter’s predation on urchins prevents their populations from exploding and overgrazing the kelp forests.
Without the otters to keep the urchins in check, coastal areas can transform into “urchin barrens,” where the kelp is decimated and the overall ecosystem collapses. By controlling these grazing herbivores, sea otters allow the kelp forests to thrive, which in turn provides essential habitat, shelter, and food for countless other marine organisms.