Sea Otter Biology and
Natural History

The southern sea otter is a carnivore. Sea otters grow to approximately four feet in length, with the male weighing approximately 65 pounds and females about 45 pounds.

The sea otter is one of the few animals to use tools. Sea otters use rocks, other shellfish, or man-made objects to pry prey from rocks. They also use tools as hammer or anvil.

Unlike other marine mammals, sea otters do not have a thick layer of blubber and rely upon their dense fur for insulation. The average person has about 600,000 hairs on their head; the sea otter has two million hairs per square inch.The fur is sensitive to soiling from oil or other contaminants. Soiling of the fur by oil generally results in death.

Sea otters feed on a wide variety of marine invertebrates including clams, mussels, urchins, snails, crabs, and abalone and use a variety of strategies for finding their food.

Sea otters eat the equivalent of 20 to 30 percent of their body weight per day to maintain their body heat.

Adult female otters give birth to a single pup nearly every year. Pups have long black or brown hair and are so buoyant that they can not dive underwater. Pups are often seen bobbing beside or resting upon mothers.

In California, sea otters spend between 17 to 38 percent of their time foraging and 50 to 68 percent of their time resting. Sea otter populations at carrying capacity (Amchitka Island, AK) spend 51 to 58 percent of their time foraging and 32 to 34 percent of their time resting.

From evidence found in the fossil record, sea otters and their ancestors have been a component of California's ecosystem for the past five million years.

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