Unregulated hunting during the 18th and 19th centuries severely reduced otter populations. They typically dive for an average of 2 minutes, but can stay down for up to 4 minutes. To help them do this, the otter's lung is quite large, in fact, otters have the largest lung relative to body size of any mammal. Otters eat lots of sea urchins, which graze on algae such as kelp. The kelp then more easily breaks loose and is washed away, damaging the habitat and exposing the many fish, mollusks, crabs, and other creatures that live in the kelp forest to predation.
Mature females give birth to an average of one pup every one or two years.
Typically the pups are born in the water, but may occasionally be born on the shore and then carried to the water. The mother carries, feeds, and grooms her young on her chest and belly as she floats in the water. The pups begin to dive and collect some of their own food at about two months, but are fed by the mother until they are on average 6 months old. Otters can live up to 10-15 years in the wild. The southern sea otter is the California subspecies that once ranged all along the California coast to Baja California.