Fact Sheet
Sea Otter

Threats to Sea Otters

It is estimated that the worldwide population of sea otters once numbered between several hundred thousand to over one million before being nearly hunted to extinction by fur traders in the 1700s and 1800s. Sea otters finally gained protections with the signing of the International Fur Seal Treaty of 1911, and became listed under the Marine Mammal Protection and Endangered Species Acts in the 1970s. Worldwide, numbers have slowly recovered but still stand far below original population numbers. While sea otters are vulnerable to natural predators, their populations are significantly impacted by several human factors as well.

Oil Spills

Oil spills from offshore drilling or shipping are an immense threat to sea otter populations. When sea otters come into contact with oil, it causes their fur to mat, which prevents it from insulating their bodies. Without this natural protection from the frigid water, sea otters can quickly die from hypothermia. The toxicity of oil can also be harmful to sea otters, causing liver and kidney failure as well as severe damage to their lungs and eyes.

A historic example of the impacts oil spills have on sea otters is the 1989 Exxon Valdez oil spill in Alaska’s Prince William Sound, which killed several thousand sea otters. Sea otters are still threatened by events like this because countries around the northern hemisphere continue to ship and drill for oil throughout the Pacific and along coastal areas that sea otters call home. Because their numbers are low and they are located in a rather small geographic area compared to other sea otter populations, the California sea otter is especially vulnerable, and could be devastated by oil contamination.

Shark Attacks

The sea otter habitat range is expanding because of the lack of food in their current range. Unforunately, at the edge of their range, shark-bitten sea otters now account for more than half of the dead animals found. This now exceeds all other causes of mortality combined, and in the last few years, is actually driving a decline in the northern and southern parts of the population. Researchers are not sure why this is happening because there is no record of sea otters ever being food for sharks. 

Conflict with Humans

Direct conflict with humans, such as shootings and entrapment in fishing traps and nets pose a major threat to sea otter populations. Since sea otters eat many of the same shellfish humans like to eat, such as sea urchins, lobster and crab, they often find themselves in the same areas fishermen like to harvest. Some shell fishers view sea otters as competition and a threat to their economic gain. Many fishermen use fishing gear that can entangle sea otters and cause them to drown.

Habitat Degradation

Pollution on land runs off into the ocean, contaminating the sea otters’ habitat. This can jeopardize their food sources, as well as harm them directly. Sea otters are often contaminated with toxic pollutants and disease-causing parasites as a result of runoff in coastal waters. In California, parasites and infectious disease cause more than 40% of sea otter deaths. Hundreds of sea otters have succumbed to the parasites Toxoplasma gondii and Sacrocystis neurona, which are typically bred in cats and opossums. Scientists have also reported the accumulation of man-made chemicals, such as PCBs and PBDEs, at some of the highest levels ever seen in marine mammals.

More on Sea Otter: Defenders in Action »

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In the Magazine
Floating effortlessly on their backs just off the Monterey Bay coast, dozens of dozing sea otters are soaking up the warm southern California sun.
Where We Work
The Golden state is home to millions of wild birds, mammals, amphibians, reptiles and fish that need our help.
Sea otters, © Tony Trupp
Win for Wildlife
Sea otters in California received some great news in September 2011 as Governor Jerry Brown signed legislation re-establishing the California Sea Otter Fund, the main source of funding for sea otter research and conservation efforts in the Golden State.