Males are generally a dark chestnut brown, although some males do not darken and remain lighter on their head, muzzle, sides, hind and belly. Females and juveniles are usually tan. Both sexes have a sleek, single hair coat, which also distinguishes them from true seals. At about five years of age, males develop a noticeable crest running lengthwise along the top of their skull that creates a high, domed forehead. The fur on this crest usually becomes increasingly lighter in color with maturity. California sea lions lack the "mane" that gives this group of animals their name, having a more slender neck than some species and a rather dog-like head.
California sea lions have many adaptations for their aquatic lifestyle. Their limbs are shortened with the digits elongated and encased in cartilage and connective tissue to form flippers. Their streamlined torpedo-shaped bodies have strong, bulky shoulders and tapers to the tail. Their front flippers are especially long and are used for propelling them through the water. Their back flippers are used as rudders and have three claws for grooming. California sea lions readily move on land by rotating their rear flippers under their body and supporting their body weight on all four flippers. Although California sea lions appear clumsy when moving on land, their movement through the water appears almost effortless. The flexibility of their bodies allows them to make tight, twisting turns as they play or pursue fish. Their speed of 25 to 30 miles per hour (40 to 48 kilometer per hour) can be quickly attained while hunting, avoiding predators or simply playing.
Water conducts heat efficiently, and California sea lions must be able to regulate body temperature. A layer of blubber, or fat, insulates the trunk of their body while their circulatory system can shunt the blood supply to the extremities and the outer surface of the body. A layer of fur traps water next to the skin and warms it to body temperature. California sea lions have a relatively small body surface in proportion to their volume, reducing the amount of heat lost to their surroundings. Overheating can often be a problem for them, and they use behavioral means to cool off. Resting with a flipper in the water, flipping sand over their back or flipper fanning in the water are examples of body temperature cooling methods.
Adult males are about 8 feet (2.4 meters) long, nose to tail, and weigh an average of 600 pounds (272 kilograms), though in preparation for the breeding season their weight often increases up to 1,000 pounds (454 kilograms). Adult females are significantly smaller and slimmer than the males and are about six feet (1.8 meters) in length and weigh an average of 220 pounds (100 kilograms).
There are three species of California sea lion, divided by geographical divisions: Pacific coast, Gulf of California and the Galapagos Islands. California sea lions are currently found in the eastern North Pacific from British Columbia to Baja California, the Gulf of California, and in a separate population on the Galapagos Islands. The population in Japan is now extinct. The United States population of California sea lions is estimated at 210,000. Population estimates in other areas are considered unreliable.
California sea lions have numerous vocalizations used not only on land, but underwater as well. Males typically patrol their aquatic and terrestrial territories and bark or roar to warn intruders away—sometimes even barking underwater. During these patrols, males display to all other males that are in the vicinity. These behaviors are vital to maintaining a territory, and include barking, head shaking, oblique stares and lunges at the opponent's flippers.
Females use specific calls to identify their pups. Following birth, the cow and pup spend time nuzzling and vocalizing to each other. This process imprints on their memories exactly what one another smells and sounds like. While the calf is still nursing, the cow alternates between feeding her pup and hunting for food. When a cow enters the water to hunt, her pup joins with other pups in the pod. Once back from her feeding trip, the mother calls her offspring using a pup attraction call and the pup answers with its own unique bleat. The mother then confirms her pup by smell, leads it to a sheltered spot and nurses it.
As social animals, California sea lions spend much time communicating with each other. From alarm barks to growls, bleats to roars, California sea lions are one of the noisiest pinniped species. Visual signals are an important part of their non-vocal communication. Vibrissae are used for whisker greeting one another as well as in conjunction with smell when bulls check the sexual receptivity of cows. Bulls produce strong smells when in rut, presumably important in breeding behavior.
California sea lions, being predators, have excellent senses. Their eyesight is particularly well developed since they spend much time underwater with reduced light levels. But the surface environment is completely different with its brightness and glare, so their pupil can contract to a tiny pinhole to protect their sensitive retinas. Their external earflaps are greatly reduced for streamlining, yet they can hear quite well both above and below the surface. Their ears are also valvular and close when in water.
California sea lions often vocalize underwater and are able to locate sound sources easily. Sensitive vibrissae, the whiskers on the face, can be rotated forward, enabling California sea lions to capture prey in total darkness. They can detect the slight movements of fish swimming nearby. California sea lions seem to have an acute sense of smell. Their nostrils are closed at rest and have to be opened to take a breath.
They are generalist feeders, taking fish (such as herring, anchovies, rockfish), krill and invertebrates such as squid and octopus.
At the Smithsonian's National Zoo, they receive thawed frozen squid, capelin, herring, butterfish and mackerel. They get vitamin supplements daily to replace any nutrients lost in the food during the freezing process.
Females give birth to a single pup and are protective of them for several days, moving the pups around with them. Females then begin to leave their pups for increasing lengths of time. Within two weeks, females come into estrus and solicit attention from bulls. After copulation, the fertilized egg develops into a blastocyst, remaining dormant for several months before attaching to the uterine wall. This delayed implantation ensures that birthing occurs at the right time each year.
Pups are about 2.5 feet (75 centimeters) long, nose to tail tip, and weigh about 18 pounds (8 kilograms) at birth, and are chestnut brown in color. Young pups suckle at frequent intervals throughout the day, but by three weeks are left alone for increasing amounts of time. Pups gather in groups, called colonies and spend their time resting, exploring the rookery, or playing in tide pools. Pups nurse anywhere from six months to a year, until the arrival of the next pup. Females reach sexual maturity at 4 or 5 years, males at 5 to 6 years in human care.
California sea lions live 15 to 20 years in the wild and average 25 to 30 years in human care.
California sea lions' natural predators are sharks and orcas. Disease, parasites and the weather system, El Nino, also take their toll. California sea lions are protected under the Marine Mammal Protection Act, which makes it illegal to harm them. Still, fishermen who regard the animals as competition and a threat to the fishermen's livelihood kill a number each year. Entanglement in and ingestion of plastics in the ocean is another serious threat to these animals. Habitat destruction, pollution and diminished food supply through overfishing are hazards faced by marine life in general. Toxic algae blooms fed by agricultural run-off and other pollution can lead to the poisoning of marine mammals by a chemical called domoic acid, which can cause brain damage.
Water quality is vital to a sea lion's well being, as blubber can hold pollutants along with the body fat. Many studies are showing concentrations of pollutants such as DDT and PCBs incorporated within the bodies of fur seals and sea lions. The levels of these toxins increases with age in males, but drops sharply after maturity in females. This suggests the transfer of these pollutants during lactation to offspring.
One male sea lion named Jetty, three adult female California sea lions named Sidney, Summer, Calli, and Catalina, a female born June 2016, live on American Trail. Calli and Summer are not related, but they have similar stories. Both sea lions were orphaned as young pups: Calli’s mother died shortly after she was born, and Summer was abandoned by her mother. In June 2005, Pacific Marine Mammal Center in Laguna Beach, California, rescued Calli and Summer. There, animal care staff hand-raised them.