Learn More About These Fascinating Animals
The southern sea otter (Enhydra lutris nereis) is found along the California coast from Half Moon Bay to Coal Oil Point near Santa Barbara. The animals live in the kelp forest in water as cold as 35˚ to 60˚ F (2˚ to 16˚C). As mammals, sea otters nurse their young and are warm-blooded. They hunt, mate, groom, give birth, play, rest, and sleep entirely at sea, where the animals lounge at the water’s surface and on kelp beds.
The Alaskan and Asian sea otters are two other subspecies. The Alaskan sea otter is found along Alaska’s Aleutian Islands to Prince William Sound and Southeast Alaska, and off the coasts of British Columbia and Washington. The Asian sea otter is found in the Commander and Kuril Islands in Russia and along the eastern coast of the Kamchatka Peninsula. Members of the Mustelidea family, sea otters are related to river otters, skunks, and weasels.
Sea otters, the smallest of the marine mammals, are the only ones that do not have blubber to keep them warm in the cold ocean water. In order to stay warm, sea otters have to eat a lot. Dr. Tim Tinker, a research wildlife biologist with the Western Ecological Research Center of the U.S. Geological Survey and an adjunct professor in the department of ecology and evolutionary biology at the University of California Santa Cruz, says a sea otter is essentially a “swimming furnace.” The animals eat 25 to 30 percent of their body weights each day and convert food into energy to fuel their high metabolisms. An adult male sea otter can eat as much as 15 pounds of food in one day. Abalone, squid, sea urchins, clams, snails, and many other invertebrates are part of their diet.
Sea otters are a keystone species, meaning that the presence or absence of sea otters has an inordinately large effect on the health and balance of its ecosystem.
When otters are plentiful, sea urchins, a favorite food item, are kept in check. When sea otters are scarce, sea urchins can consume too much giant kelp and other algae, reducing the kelp canopy and the species of fish and shellfish living in it. Sea otter populations help increase the abundance of kelp.
Sea otters are a valued sentinel species because they are highly visible and easy to study. Researchers can tag the animals, making them easy to follow and collect detailed information on their activities. For example, by collecting information about the sea otter’s eating habits and their health, Tinker and colleagues are learning which types of shellfish carry pollutants or parasites that cause health problems for otters. By identifying those behaviors, diets, or feeding locations that are associated with health problems, the scientists pinpoint risk factors and work upstream to correct those problems.
Sea otters spend a large part of the day hunting for food. They forage on the ocean floor, generally in waters less than 60 feet deep (although they occasionally dive as deep as 300 feet), and dive for one to three minutes at a time. Sea otters have sensitive whiskers that can help them find food in dark or murky water. Sea otters always eat at the surface, carrying their food in folds of skin under their front arms called pockets. Extremely resourceful, they will use rocks and shells as tools to help them break open the shells of their catch. At the surface, a sea otter will lie on its back, take out one piece of food at a time, open it by banging it against a rock, and use its chest as a dinner table.
When food is abundant, most sea otters eat energy-rich prey such as abalone and red urchins. When food is scarce, individual sea otters will adapt to the shortage by specializing on certain kinds of prey. One otter may eat mostly clams and worms; another may prefer crabs and sea stars; yet another may feed on mussels and marine snails.
Scientists have observed multiple and very different diets among otters living in the same habitat. Specializing on one type of prey makes an otter a more efficient predator.
Sea otters learn to hunt from their mothers, so different individuals will have different hunting skills and different favorite foods. These diverse food preferences might explain why so many sea otters can share a particular habitat.
When sea otters are not searching for food or eating, they are grooming. Sea otters have very dense fur to keep them warm and keep their body temperatures at 100˚ F (38˚C) in the cold ocean water. Sea otters have the densest fur of any animal on the planet. In just one square inch, a sea otter has 800,000 to one million hairs, more than enough to cover an entire adult dog or cat. This lush coat makes grooming a vital and an almost constant activity. The animals are very limber and their skeletons are loosely jointed, meaning they can easily reach and groom every single part of their bodies.
In addition to their thick fur, sea otters rely on an insulating layer of air to stay warm. You have probably seen the Aquarium’s sea otters roll at the surface of the water. They are busy trapping a layer of air inside their fur. This air layer keeps the water from touching the otter’s skin. Sea otters spend four to six hours a day maintaining the protective layer of air and keeping the coat spotless. It is vital that an otter keep its fur clean so that the undercoat stays dry. If the undercoat gets wet, it might cause fatal hypothermia.
The sea otter’s lush coat once put its pelts in high demand. The sea otter’s natural curiosity made the animals easy to hunt and kill, and widespread hunting almost led to their extinction. It is estimated that thousands of southern sea otters once existed off the California coast. In the 19th century, hunting left as few as 50 otters off the California coast. Now protected, sea otters are making a slow comeback. Federal protection has brought their numbers back up to 2,800, but their gradual recovery is currently stalled. Tinker said scientists consider the population stable, but still in a depleted state. The U.S. government lists sea otters as a threatened species, and the animals are protected by the California Endangered Species Act, the U.S. Endangered Species Act, and the Marine Mammal Protection Act of 1972.
California’s small sea otter population has a few natural predators, such as great white sharks and killer whales, but human activity is a great threat to these animals. Fertilizers and other contaminants are washed into the ocean from land, bringing chemicals and parasites that can cause disease and death in otters and other marine species. Disease-causing pathogens that originate on land can reach the marine environment through storm sewers, sewage outflow, surface run-off, and polluted waterways. Once in the marine environment, sea otters can ingest these pathogens and harmful toxins by way of their food.
Marine debris, such as fishing nets and long lines, can entangle and harm the animals. Oil spills are especially harmful to sea otters because the oil coats their dense fur, destroying its waterproofing and insulating capabilities. The otter ends up freezing to death or being poisoned from ingesting the oil while trying to clean its fur. California’s sea otters are concentrated in a relatively small area, and a major oil spill of the central coast could wipe out the entire population. Overfishing is another threat to sea otters. When stocks of their favorite foods are depleted, sea otters have to rely on poorer quality foods, which in some cases carry dangerous parasites. When food is very scarce, otters lose weight and spend more time feeding, and because they are nutritionally stressed, they are more susceptible to disease. Emerging threats such as climate change and ocean acidification will pose additional challenges for the species.
Newborn sea otters are dependent on their mothers for at least six months. Mothers teach their babies how to forage, swim, and groom, things that are essential for survival. Babies that are separated from their mothers have slim odds for survival.
In some cases, baby sea otters that are found stranded can be successfully rehabilitated, reared by “surrogate mother” sea otters in captivity, and eventually returned to the wild population. In other cases, young sea otters are judged incapable of surviving in their natural environment, and they are sent to zoos and aquariums where they serve as ambassadors for their brethren in the wild. All of the Aquarium’s sea otters were found stranded soon after their births.
California’s sea otter population is struggling, but a caring public can make a difference in its recovery. Be sure to visit the Northern Pacific Gallery to learn more about these animals and to find out how you can help.