Sea otters making a comeback on the California coast

On Sept. 20, the U.S. Geological Survey announced that the southern sea otter population count has risen to 3,272, the highest it has been since 1982.

The population has risen 11 percent since 2013 and may be the highest it has been for 100 years.

The sea otters have quite the comeback story. They used to be hunted incessantly for their soft, thick fur and were thought to be extinct until the 1930’s. In 1977, they became protected by the Endangered Species Act and have been building back up in numbers ever since.

In order to be considered a non-endangered species, the otter population needs to be above 3,090 for three years. If they maintain a high population, then the U.S. Fish and Wildlife Service can remove the southern sea otters from the endangered species list.

This population growth is most likely caused by the wave of disease that has recently hit sea stars. Both sea otters and sea stars eat sea urchins, but since a disease wiped out a large portion of the sea star population, the sea otters have had plenty of sea urchins to snack on.

“The boom in sea urchin abundance throughout northern and central California has provided a prey bonanza for sea otters, and that means more pups and juveniles are surviving to adulthood,” said Dr. Tim Tinker, a research biologist who leads the U.S. Geological Survey’s otter program.

However, the otter population can not expand their range north or south. In fact, the population in the northern and southern region of their geographical range actually decreased. This is because of the presence of great white sharks. Shark bites have become the highest cause of death within otter populations.

Sharks do not look for otters, their food of choice is sea lions. Under the Marine Mammal Protection Act of 1972, killing sea lions and elephant seals was banned, creating an influx in sea lion and elephant seal numbers. Both of these animals are food sources for sharks, therefore, sharks started to hunt in those areas occupied by sea lions, elephant seals, and sea otters.

Lilian Carswell, Southern Sea Otter Recovery Coordinator for the U.S. Fish and Wildlife Service commented, “We do not think sharks eat otters; they just bite them and spit them out because sea otters do not have blubber.”

Nonetheless, the overall otter population is growing and could follow the giant panda in being removed from the endangered species list.

“The population is slowly but steadily recovering and that is good news because sea otters bring ecological benefits,” remarked Tinker.

The otter does indeed present plenty of ecological benefits, being that it is a keystone species of rocky sub-tidal ecosystems. They eat sea urchins, which can destroy kelp beds that provide homes for various species. They also eat crabs, which in turn allows the sea slug population to grow. The sea slugs then eat the algae on sea grass, keeping it healthy so fish can live in it.

Otters also help scientists measure an ecosystem’s health. Otters are usually the first to be exposed to pollutants and indicate to scientists when their ecosystem is being contaminated.

Sea otters are a staple of the marine life community, a sign of a healthy ecosystem, and super adorable. Way to go otters!

–Gianna Ceccarelli 

Sources:

Tinker, Tim, M., and Brian Hatfield B. California Sea Otter (Enhydra Lutris Nereis) Census Results, Spring 2016. Reston: U.S. Geological Survey, 2016. Web. 20 Sept. 2016.