Adult sea otters may grow up to 5 feet in length. The males weigh 80–100 pounds but can weigh more than 100 pounds. The females are smaller, weighing 50–70 pounds.
Female sea otters reach sexual maturity at 2–5 years of age. Males become sexually mature at 4–6 years of age. Sea otters breed throughout the year, but in Alaska most pups are born in the late spring. Female otters give birth to one pup at a time. Pups are 3–5 pounds at birth and light brown in color. The pup generally rides on the mother’s chest as she swims on her back. A mother sea otter will not leave her pup unaccompanied except to dive for food. The pup is weaned after 3-6 months. By this time, it weighs approximately 30 pounds and appears almost as large as its mother.