The greatest threat to sea otters is human activity. Although it is illegal today, sea otters were once hunted in large numbers for their pelts. Massive fur hunting began in the 18th century.

The species was saved by the enforcement of a Treaty for the Preservation and Protection of Fur Seals, signed by the United States, Russia, Japan, and Great Britain in 1911. It is estimated that when the treaty was signed, there were only about 1,000 to 2,000 otters left alive in the wild.