Southern Sea Otters

Raft of southern sea otters

The Monterey Bay Aquarium's Sea Otter Program has been studying the threatened southern sea otter since 1984 with the aim of understanding threats to the population and promoting its recovery. We also rescue, treat and release injured otters; raise and release stranded pups through our surrogate program; and seek homes for sea otters that can't return to the wild.

Sea Otters Under Siege

Southern sea otters (Enhydra lutris nereis) once ranged from Baja California to the Pacific Northwest. But, by the 1920s, they were almost extinct due to intensive hunting. They were listed as threatened under the Endangered Species Act in 1977. We and our partners have contributed to the protection of the sea otter population in California.

Recent research by the U.S. Geological Survey and the Aquarium suggests that the sea otter population growth rate is limited by food availability. Meanwhile, the risk of a major oil spill remains a serious threat.

Why Are Sea Otters Important?

Sea otters are an iconic species, representing the beauty and diversity of life in Monterey Bay. They're also a keystone species, determining the kinds and health of species in nearshore environments. They eat sea urchins and other invertebrates that graze on giant kelp. Without sea otters, urchins prevent kelp forests from forming important habitats for many animals. Similarly, their consumption of crabs in estuaries reduces predation on snails. The snails graze algae that otherwise choke eel grasses.

Sea otters are also good indicators of ocean health. Since they are a top predator of invertebrates along the California coast, changes in their health can make scientists aware of variations in the ocean environment itself.

Sea Otter Recovery

By 1911, when sea otters gained protection under the North Pacific Fur Seal Treaty, a small group of perhaps 50 otters survived along the remote Big Sur coast. Since then, they've slowly expanded their range and grown in number to nearly 3,000. As of 2014, their range extends from south of Half Moon Bay in the north to south of Point Conception in the south—only a small part of their historic range.


Sea Otters in Big Sur later 1900s (Photo © William L. Morgan/California Views Photo Archives)
Sea Otters in Big Sur, Circa 1938
(Photo © William L. Morgan/California Views Photo Archives)

In 1750, as many as 15,000 sea otters lived and foraged along the California coast. Then fur hunters began killing them for their warm, luxurious pelts. By the early 1900s, only about 50 otters along the isolated Big Sur coast had escaped the slaughter. Today's southern sea otters are descendants of those few survivors.

With conservation efforts, California's sea otter population has slowly grown to around 3,000. But in recent years, the population has not increased. Scientists are trying to understand why.

What Threatens Sea Otters Today?

The sea otter population in California remains small and vulnerable. Parasites, such as intestinal worms, and infectious disease cause a significant percentage of otter deaths. Protozoal diseases are often fatal to marine mammals. Wild sea otters acquire many infectious diseases because of high pathogen and contaminant pollution levels in coastal ocean waters.

The greatest threat to the sea otter population is an oil spill. Because their numbers are low and they are located in a rather small geographic area, the California otter population could be devastated by oil contamination. Oil ruins the insulating property of an otter's fur, causing many oiled otters to die of hypothermia, while others die from ingesting the oil or inhaling petroleum fumes. Prevention of oil spills is the best strategy, since rehabilitating oiled otters is quite difficult.


Sea Otter Research and Conservation program at the Monterey Bay Aquarium

Southern sea otters are dying at a high rate, and our scientists are trying to find out why. They study how sea otters live, the risks they face and how they become sick or injured. Although we focus on the southern sea otter, our Sea Otter Program staff and volunteers collaborate with the U.S. Geological Survey and other scientists to study sea otters from Russia and Alaska to southern California.

We Study Sea Otters in the Wild

We help conduct a variety of sea otter research projects along the California coast. We capture and tag dozens of sea otters in the wild, and then we track and monitor them—some from birth to death—in an effort to understand how they live and what's causing their sluggish recovery. These multi-year studies are performed with research colleagues at the U.S. Geological Survey, the California Department of Fish and Wildlife, and the University of California.

For instance, we're currently studying how sea otters are using estuarine habitat in Elkhorn Slough.

We Count Sea Otters

Every spring and fall, our scientists and colleagues fan out across 400 miles of California coast to count sea otters as part of the U.S. Geological Survey annual census. These counts provide a critical measure of whether the struggling population is rebounding or declining. See USGS sea otter survey results.

We Develop New Technologies

We work with medical and engineering experts to develop ways to track and monitor sea otters that cause less stress to the animals and provide us with better information. New technologies under development include smaller implantable transmitters and time-depth recorders, new physiological sensors, improved data-retrieval systems and improved surgical techniques.

We Study Stranded Sea Otters

After rescuing otters that have been stranded along the shore, we perform many of the same diagnostic tests used by human doctors, and we keep extensive medical records for each animal. Tracking sea otter health helps us understand what a "normal" sea otter looks like so we can determine when one in our exhibit or in the stranding program is ill and how to treat it. We also conduct various behavioral and physiological studies with the animals during their time at the Aquarium.

We Retrieve and Help Analyze Sea Otter Carcasses

Of all the southern sea otters that die, an extraordinarily high percentage die from shark bites or succumb to some form of infectious disease. To keep track of these trends, we respond to calls about dead sea otters and collect these animals for post-mortem analysis by pathologists with the California Department of Fish and Wildlife in Santa Cruz.

We take blood and other samples from each dead sea otter to use in research projects on disease, contaminants, physiology, metabolism and genetics, and we store some of these samples for future research.

We Raise and Release Stranded Pups

Since 2005, our Sea Otter Program has used the Aquarium's female exhibit otters to rear stranded pups. The females bond with the pups and provide maternal care while the pups grow and develop survival skills. We then track and monitor these pups in the wild, from release through adulthood, to observe their survival and reproduction. Our data has shown that surrogacy is a viable way to raise and release stranded sea otter pups.

Rescue & Care

Behind the scenes care of a sea otter pup

Our Sea Otter Program works with other aquariums and wildlife rescue facilities to respond to every sea otter that comes ashore in distress along the California coast. We rescue and care for sea otters that wouldn't survive without our help.

We aim to return these sea otters to the wild. When we receive a report of a stranded sea otter, we go to the scene and determine whether the otter needs help. If necessary, we capture and transport it to the Aquarium for care. Although we handle sea otters of all ages, a significant number of the rescued animals are pups that have become separated from or have been abandoned by their mothers.

Over the past 30 years, over 700 sea otters—adults and pups—have come through the Sea Otter Program, and the Aquarium's staff and veterinarians have developed diets and care protocols that have resulted in a high survival rate. Until the Aquarium began caring for stranded sea otter pups in 1984, no one knew how to keep pups alive once they became separated from their mothers.

Stranded pups rescued by our staff are introduced to one of our non-releasable exhibit sea otters, who rotate duties as surrogate mothers behind the scenes. Staff monitor young animals once they are released, and they may recapture sea otters that aren't foraging or navigating well. Recaptured animals return to the Aquarium to rest and gain weight in preparation for re-release. It sometimes takes three or four releases before the young sea otters adapt to life in the wild.

We Share What We Know

We have a responsibility to share our veterinary and husbandry expertise with other zoos and aquariums. To improve the health and longevity of sea otters in captivity and during field research, we host and train veterinarians and caregivers from other facilities, work to improve standards for sea otter veterinary care and medicine, and offer support and assistance with sea otter care and research activities whenever we can.

Our Sea Otter Program is a recognized leader in management programs for sea otters in zoos and aquariums. We coordinate a global network of institutions that house sea otters or have an interest in sea otter conservation. This network is crucial for improving programs related to general care, veterinary science, cooperative research and conservation.

Report a Stranded Otter

Wild southern sea otter pup

Sea otters are protected under federal law. They're protected by the Marine Mammal Protection Act of 1972 and the Endangered Species Act of 1973. Only authorized wildlife professionals—like our Sea Otter Program staff—are allowed to catch or move them.

Follow these steps if you come across a sea otter you think is ill, injured or abandoned.

  1. Don't touch it or try to catch it—doing so is illegal, and sea otters can bite.
  2. Keep people and pets away from the otter. Don't wrap a stranded otter in a blanket—it will overheat very quickly.
  3. Call one of the agencies listed below to report a sea otter in distress. Wildlife specialists will come and determine whether the otter needs help. If it does, they'll capture it and take it in for care.

Print out a flyer with tips for reporting stranded otters (PDF).

To report a stranded sea otter, contact one of the following agencies:

In Central California:
Monterey Bay Aquarium
(831) 648-4840
(sea otter 24-hour emergency line)

The Marine Mammal Center
(415) 289-7325

Shark Research Bluefin Tuna Research