Sea otters are listed as an endangered species because they are vulnerable to oil spills from ships and coastal tanker traffic. They also have a reduced population size, which puts them in danger of becoming extinct. According to the U.S. Fish and Wildlife Service, sea otters have been protected under the Endangered Species Act since 1977. They are also protected by the Marine Mammal Protection Act.
According to Defenders of Wildlife, a wildlife charity organization, sea otters are endangered because they were nearly hunted to extinction in the 1700s and 1800s. Sea otters once numbered in the hundreds of thousands, but fur traders hunted them in large numbers and, consequently, reduced their population size. The International Fur Seal Treaty of 1911, the Marine Mammal Protection Act and the Endangered Species Act of 1977 helped stop the sea otter population from dwindling. However, the sea otter population has been slow to recover.
In addition to oil spills, sea otters also face other human threats. For example, sea otters sometimes get caught in fishing nets and traps. They eat many of the same types of shellfish that humans like to eat, such as sea urchins, lobsters and crabs. As a result, some fisherman view sea otters as competition and set traps in which they become entangled and drown. These incidents, however, are occurring less frequently due to the various endangered species acts that protect the species.