The California sea lion (Zalophus californianus) is a coastal eared seal native to western North America.

California sea lions are sexually dimorphic; males are larger than females, and have a thicker neck, and a protruding sagittal crest.

California sea lions feed on a number of species of fish and squid, and are preyed on by orcas and great white sharks.

California sea lions communicate with numerous vocalizations, notably with barks and mother-pup contact calls.

California sea lions are particularly intelligent, can be trained to perform various tasks and display limited fear of humans if accustomed to them.

Because of this, California sea lions are a popular choice for public display in zoos, circuses and oceanariums, and are trained by the United States Navy for certain military operations.

To protect fish, the US states of Oregon and Washington engage in annual kill quotas of California sea lions.

[9] Adult males also have a protruding crest which gives them a "high, domed forehead";[10] it is tufted with white hairs.

[11] The flexibility of its spine allows the California sea lion to bend its neck backwards far enough to reach its hindflippers.

[18] The California sea lion ranges along the western coast and islands of North America, from southeast Alaska to central Mexico.

California sea lions can also live in fresh water for periods of time, such as near Bonneville Dam, nearly 150 miles (240 km) up the Columbia River.

At Monterey Bay, California sea lions appear to be the more common food items for transient mammal-eating orcas pods.

[26] The California sea lions may respond to the dorsal fin of a killer whale and remain vigilant, even when encountering resident fish-eating pods.

After this, the males rely on ritualized displays (vocalizations, head-shaking, stares, bluff lunges, and so on) to maintain their territorial boundaries.

[32] Female California sea lions have a 12-month reproductive cycle, consisting of a 9-month actual gestation and a 3-month delayed implantation of the fertilized egg before giving birth in June or July.

Territorial males are the loudest and most continuous callers, and barks are produced constantly during the peak of the breeding season.

[32] Marine biologist Ronald J. Schusterman and his research associates have studied the California sea lions' cognitive ability.

[37] California sea lions have demonstrated the ability to understand simple syntax and commands when taught an artificial sign language.

[38] In 2011, a California sea lion named Ronan was recorded bobbing her head in synchronization to musical rhythms.

[40] Because of their intelligence and trainability, California sea lions have been used by circuses and marine mammal parks to perform various tricks such as throwing and catching balls on their noses, running up ladders, or honking horns in a musical fashion.

[41] The California sea lion is used in military applications by the U.S. Navy Marine Mammal Program, including detecting naval mines and enemy divers.

[47] Wildlife officials have unsuccessfully attempted to ward off the sea lions using bombs, rubber bullets and bean bags.

[49] Critics have objected to the killing of the California sea lions, pointing out that the level of mortality permitted as a result of recreational and commercial fisheries in the river and as part of the operation of hydroelectric dams pose a greater threat to the salmon.

Many docks are not designed to withstand the weight of several resting California sea lions which cause major tilting and other problems.

Elevated water temperatures reduced the abundance of anchovies, sardines and mackerel, principal components of the California sea lion pup diet during nursery season.

[53] This caused many California sea lion pups to starve, while others died when they took to open waters in search of food at too early an age.

[54] Several months earlier, in the summer of 2014, a large number of Cassin's auklet chicks died during the fledging period due to similar circumstances brought about by elevated water temperatures.

[55] In November 2018, the State of Oregon obtained a permit to kill 93 California sea lions per year below Willamette Falls.

Under a similar program, Oregon and Washington had killed over 150 California sea lions on the Columbia River by January 2019.

In both cases, the purpose was to protect the local populations of fish (such as trout or salmon) from predation by the sea lions.