sea otter

Sea Otter Project

Sea Otter Project

The Karen C. Drayer Wildlife Health Center's faculty, affiliates and collaborators have ongoing studies on the health and conservation of sea otters and other marine mammals in California. In addition to research, our team organizes outreach and education opportunities for K-12 students.

Threats to Sea Otters & Other Marine Mammals

Fecal pathogens - Toxoplasma gondii

Some fecal pathogens that can affect marine mammals are Toxoplasma gondii, sarcocystis neospora, crypto sporidium, giardia and a host of bacterial pathogens. Our teams have worked on all of these issues and more, but Toxoplasma gondii research in particular has been foundational for the Karen C. Drayer Wildlife Health Center. One major threat to sea otters is Toxoplasma gondii, which is a tiny parasite that lives in the bodies of many people and animals. Most people with Toxoplasma gondii (Toxo) never show any symptoms of illness, but if you do get sick, you may be ill for about 2 weeks and have fever, head and muscle aches, sore throat and swollen neck, and difficulty seeing.

You should worry about Toxo if your immune system is compromised, such as if you have AIDS or are taking drugs that suppress your immune system. Your body’s defenses may not be able to ward off the spread and the parasites may cause brain disease. You should also worry about Toxo if you’re pregnant, because infection of an unborn child can cause birth defects, blindness and brain damage.

If you think you have been exposed to Toxoplasma, especially if you are pregnant, talk to your doctor.

Spread from cats

Although cats are the hosts that spread Toxo, they never show symptoms of the illness. 

How does that happen?

Even though lots of animals, including birds, have Toxo, only cats (pet cats, feral cats, mountain lion, bobcats, etc.) shed Toxoplasma gondii “eggs” (called oocysts) in their poop. They can shed millions of oocysts for 7-14 days the first time they get infected. The oocysts live in the soil and water, are spread by earthworms, flies and beetles, and are picked up by other animals. Cats pick up Toxo when they eat small wild animals. The parasites spread throughout the body to places like the lung, eye, and brain, and remain in the body for a long time.
How are Sea Otters Being Killed by Toxo?
Those Toxo oocysts are making their way into the ocean, but we don't know exactly how sea otters are becoming infected. We do know that the only way to prevent them from being infected is to reduce cat poop in the environment. 

You could ingest Toxo by: 

  1. Eating raw or undercooked meat or shellfish
  2. Drinking water that contains Toxoplasma oocysts
  3. Getting soil with Toxoplasma oocysts in your mouth
  4. Getting infected cat poop from your hand into your mouth after cleaning its litter box
  5. Being infected before you were born, if your mother got Toxoplasma while she was pregnant

You can protect yourself by: 

  1. Cooking shellfish well and meat until it is no longer pink
  2. Using hot, soapy water to wash knives and cutting boards used to prepare meat
  3. Washing dirt off vegetables before eating
  4. Avoiding drinking water from rivers and streams
  5. Washing your hands after gardening and removing dirt from under your nails

You can protect sea otters by

  1. Not flushing kitty litter down the toilet—sewage treatment may not kill Toxo oocysts
  2. Putting cat poop in plastic bags and dropping them in your trash can
  3. Keeping your cats indoors 
  4. Removing cat poop from your yard. Toxo oocysts last for months in soil and can move into rivers and oceans during the rainy season

Harmful algal blooms

Algae – microscopic, single-celled plants – that live in the ocean sometimes “bloom” or multiply so quickly that they appear in dense patches on the sea’s surface. Although most are harmless, some species produce toxins that move up through the food web and can kill shellfish, fish, birds, marine mammals and even humans.

Why is domoic acid such a concern?

Occasionally along the California coast the diatom Pseudonitzschiablooms and produces a neurotoxin called domoic acid. No one knows what sets off the glass-shelled algae to bloom or produce so much domoic acid. This toxin can cause seizures and even death in otters who eat contaminated shellfish. Many otters develop inflammation of heart muscle and heart failure after being exposed to domoic acid. Heart disease is responsible for 13% of sea otter deaths. 

Is domoic acid dangerous to people?

Humans who eat shellfish or fish tainted with domoic acid can start twitching and feel nauseous. The toxin can permanently destroy a part of the brain that controls short-term memory and, in severe cases, causes death.

Other diseases

Tiny acanthocephalan, or thorny-headed, worms kill about 14% of sea otters. Otters become infected after eating sand crabs and spiny mole crabs that harbor the intermediate life stage of these worms. In heavily infected otters, the worms burrow through the walls of the otters’ intestines, set off a painful inflammation that ties the intestines in knots, and the otters die. This disease is most common in juveniles. Sea otters also succumb to a variety of bacteria and a fungus, Coccidioides immitis, that causes valley fever or coccidioidomycosis. Otters are infected the same way that humans are – by inhaling fungal spores in dust from the state’s dry interior valleys.


In California, great white sharks are sea otters’ primary predators. In Alaska, killer whales seem to be eating more sea otters, perhaps because their usual prey (seals and sea lions) are becoming more scarce. Stellar sea lions, coyotes, bears and eagles have also been known to feed on sea otters.

What about humans? 

Humans kill sea otters unintentionally -- by hitting with them with boats or entangling them in fishing gear -- and intentionally, by shooting them.


Many pollutants - from sources such as agricultural runoff, sewage plants, marinas and boat yards - become concentrated in shellfish and other otter prey. Organochlorine chemicals, polychlorinated biphenyls (PCB’s), mercury, and other pollutants can affect otters in many ways. They can damage otters’ nervous systems, affect pregnancy and fetal health, and lower the otters’ immune system defenses against diseases.

Oil pollution is also a major threat to otters. When their fur becomes matted by oil, otters can’t maintain their body heat, and they can die from hypothermia. Oil can also damage otters’ internal organs.

Can these pollutants also affect people?

Yes. If pollutants are making otters sick, it’s likely that humans may be at risk for some of the same health problems. Because otters are near the top of the food chain, they eat many of the same shellfish that humans eat. Since humans share the near-shore environment as otters, the marine mammals serve as a good sentinel species for problems in a healthy ecosystem.