The California Sea Lion is a coastal eared seal native to western North America. It is one of five species of sea lion. Its natural habitat ranges from southeast Alaska to central Mexico, including the Gulf of California. Sea lions are sexually dimorphic—males are larger than females, and have a thicker neck and protruding crest. They mainly haul-out on sandy or rocky beaches, but they also frequent manmade environments such as marinas and wharves. Sea lions feed on a number of species of fish and squid, and are preyed on by killer whales and white sharks.
The California sea lion ranges along the western coast and islands of North America, from southeast Alaska to central Mexico. Mitochondrial DNA sequences in 2009 have identified five distinct California sea lion populations: the US or Pacific Temperate stock, the Western Baja California or Pacific Tropical stock, and the Southern, Central, and Northern Gulf of California stocks. The US stock breeds mainly in the Channel Islands, although some breeding sites may be established in northern California, and females are now commonly found there. The Western Baja California stock mainly breeds near Punta Eugenia and at Isla Santa Margarita. The above mentioned stocks are separated by the Ensenada Front. The stocks of the Gulf of California live in the shallow waters of the north (Northern stock), the tidal islands near the center (Central stock), and the mouth of the bay (Southern stock). The stock status of the sea lions at the deep waters of the central bay has not been analyzed.
Being sexually dimorphic, California sea lions differ in size, shape, and coloration between the sexes. Males are typically around 2.4 m (7.9 ft) long and weigh up to 350 kg (770 lb), while females are typically around 1.8 m (5.9 ft) and weigh up to 100 kg (220 lb). Females and juveniles have a tawny brown pelage, although they may be temporarily light gray or silver after molting. The pelage of adult males can be anywhere from light brown to black, but is typically dark brown. The face of adult males may also be light tan in some areas. Pups have a black or dark brown pelage at birth. Although the species has a slender build, adult males have robust necks, chests, and shoulders. Adult males also have a protruding crest which gives them a "high, domed forehead"; it is tufted with white hairs. They also have manes, which are less developed than those of adult male South American and Steller sea lions. Both sexes have long, narrow muzzles.
California sea lions feed on a wide variety of seafood, mainly squid and fish, and sometimes clams. Commonly eaten fish and squid species include salmon, hake, Pacific whiting, anchovy, herring, rockfish, lamprey, dogfish, and market squid. They mostly forage near mainland coastlines, the continental shelf, and sea mounts. They may also search along the ocean bottom. California sea lions may eat alone or in small to large groups, depending on the amount of food available. They sometimes cooperate with other predators, such as dolphins, porpoises, and seabirds, when hunting large schools of fish. Sea lions sometimes follow dolphins and exploit their hunting efforts. Adult females feed between 10–100 kilometres (6.2–62 mi) from shore. Males may forage as far as 450 km (280 mi) from shore when water temperatures rise. They also have learned to feed on steelhead and salmon below fish ladders at Bonneville Dam and at other locations in the Columbia River.