California Sea Lion

About the California sea lion

The California sea lion is a coastal eared seal native to western North America, one of six species of sea lion alive today. It was first described in 1828 by the French naturalist René Primevère Lesson and is grouped with other sea lions and fur seals in the family Otariidae. Eared seals differ from true seals in having visible ear flaps and proportionately larger foreflippers and pectoral muscles, which they use to propel themselves through the water. Along with the Galapagos sea lion and the extinct Japanese sea lion, it belongs to the genus Zalophus; genetic work from 2007 confirmed that all three are separate species rather than subspecies of one another, with the California and Japanese lineages splitting roughly 2.2 million years ago.

The species is strongly sexually dimorphic. Males grow to 8.2–8.9 feet (2.5–2.7 m) and around 770 pounds (350 kg), with the heaviest recorded individual weighing 1,460 pounds (660 kg). Females are considerably smaller, around 6.9 feet (2.1 m) and 220 pounds (100 kg). Adult males develop a thick neck, robust chest and shoulders, and a protruding sagittal crest tufted with white hair that gives them a domed forehead — the feature that gives the genus its name, from Greek words meaning "intensive crest." Females and juveniles have tawny brown fur, while adult males range from light brown to dark brown or black. Pups are born with black or dark brown coats.

In the wild, California sea lions range along the western coast and islands of North America from southeast Alaska to central Mexico. Genetic studies have identified five distinct populations, including a U.S. stock that breeds mainly in the Channel Islands and stocks within the Gulf of California. During the breeding season they gather on sandy and rocky shores, moving closer to the water on warm days and farther inland in cooler weather. Outside the breeding season they spend much of their time at sea, hauling out at marinas, wharves, and even navigational buoys, and coming ashore mainly to molt.

Behavior and diet

California sea lions feed on a wide variety of seafood — mainly fish and squid such as salmon, hake, Pacific whiting, anchovy, herring, rockfish, and market squid, along with octopus and occasionally clams. They forage near mainland coastlines, the continental shelf, and seamounts, sometimes searching along the ocean bottom, and may hunt alone or in groups depending on how much food is available. They sometimes cooperate with dolphins, porpoises, and seabirds when working a large school of fish, and have learned to feed on salmon and steelhead queued below fish ladders at dams such as Bonneville. Adult females typically forage within 6–62 miles (10–100 km) of shore, while adult males may range up to 280 miles (450 km) offshore when water temperatures rise. Orcas and great white sharks are their main predators; sea lions attacked in the hindquarters are more likely to survive an encounter and reach shore.

Breeding is polygynous and gregarious, running from May to August. Males establish territories on the rookeries and fast for as long as they can hold them — about 27 days on average — relying on stored blubber for energy while they defend their space with vocalizations, head-shaking, stares, and bluff lunges. Females move freely between territories and are not coerced by males; they gather in "milling" groups before mating begins and appear to choose their partners as they move through the rookery, a pattern researchers have compared to a lek mating system.

Female California sea lions carry a 12-month reproductive cycle made up of a nine-month gestation and a three-month delayed implantation, giving birth in June or July. A mother stays onshore nursing her pup for about 10 days, then leaves on foraging trips of up to three days, returning to nurse for up to a day at a time; mothers and pups recognize each other's distinctive calls. Pups gather in nurseries to socialize while their mothers are away and are weaned by a year old, though some continue to nurse for a second year. Adult males take no direct role in raising pups but have been observed helping shield swimming pups from predators. The species communicates through a range of vocalizations, most notably a bark that territorial males produce almost constantly during the height of the breeding season.

Range and habitat

California sea lions occur along the Pacific coast and islands of North America, from southeast Alaska to central Mexico, including the Gulf of California. Within that range, researchers recognize five separate populations, sometimes divided by geographic features such as the Ensenada Front, including a U.S. stock that breeds mainly in California's Channel Islands and stocks confined to the shallow northern waters, tidal islands, and mouth of the Gulf of California. Vagrant individuals have turned up as far away as Russia's Commander Islands.

The species is flexible about habitat, hauling out on both sandy and rocky shorelines as well as manmade structures such as marinas and wharves. It can also tolerate fresh water for extended periods — sea lions have been recorded nearly 150 miles up the Columbia River near Bonneville Dam, and one was even found on a road in California's Central Valley, roughly a hundred miles from the coast.

Conservation status

The IUCN lists the California sea lion as Least Concern, reflecting the species' abundance across its range. That status has not stopped conflict with people: because sea lions congregate below dams and fish ladders to feed on migrating salmon and steelhead, the U.S. states of Oregon and Washington carry out annual kill quotas aimed at protecting those fish runs. The species' intelligence and trainability — it can be taught to perform tasks and shows limited fear of humans once accustomed to them — has also made it a fixture of public display in zoos, circuses, and oceanariums, and the U.S. Navy trains California sea lions for certain military operations.