Creature Feature: California Sea Lions

Above: California sea lions sunning themselves at Fisherman’s Wharf in San Francisco. Photo: Bill Lim, Flickr CC. Below: Closeup of a male California sea lion. Photo: Amy the Nurse, Flickr CC.
Above: California sea lions sunning themselves at Fisherman’s Wharf in San Francisco. Photo: Bill Lim, Flickr CC.

If you live in Humboldt, you’ve probably spotted the California sea lion (Zalophus californianus) on docks, jetties, beaches, or in the ocean. California sea lions belong to the genus Zalophus, derived from the Greek words za, “intensive,” and lophus, “crest.” These intelligent mammals are native to western North America and range from Vancouver Island, British Columbia, to central Mexico. They belong to the family Otariidae along with other sea lions and fur seals. Unlike true seals, Otariids have external ear flaps (true seals only have ear holes) and larger foreflippers. They can also rotate their hindflippers underneath their bodies and “walk” on land. Sea lions are named for their lion-like manes and barks, characteristics that are exemplified by South American and Steller sea lions. California sea lions, however, lack manes.

California sea lions are closely related to Galapagos sea lions and the extinct Japanese sea lions. Galapagos and Japanese sea lions were once thought to be subspecies of the California sea lion. However, a 2007 study found they were actually separate species. California and Japanese sea lions probably diverged around 2.2 million years ago in the late Pliocene Epoch, and the California sea lion has greater sexual dimorphism than the Galapagos sea lion.

Closeup of a male California sea lion. Photo: Amy the Nurse, Flickr CC.
Closeup of a male California sea lion. Photo: Amy the Nurse, Flickr CC.

A group of sea lions is called a “colony” when on land, and a “raft” when in water. Sea lions sometimes jump out of the water (called “porpoising”) to increase their speed and “surf” breaking waves. California sea lions “flap” their foreflippers to propel themselves through water and use their hindflippers to steer. With top speeds of 25 to 30 mph, California sea lions are faster than other sea lions and seals.

California sea lions “haul-out” (temporarily leave water) on protected beaches and artificial structures for rest, reproduction, thermoregulation (the regulation of body temperature), and social activity. Sea lions often have problems with overheating. To cool off, they may stick a foreflipper in the water or splash sand on their backs.

Sea lions use their whiskers (called vibrissae) to sense motion in water and to orient themselves by touching objects. Vibrissae are used for whisker greeting, part of a sea lion’s nonvocal communication. Sea lions also use their vibrissae to feel out crab and squid on reefs.

California sea lions forage near the coast, the continental shelf, and seamounts (underwater mountains). Squid and fish are their primary diet, but they also eat octopus, herring, rockfish, small sharks, and Pacific whiting. They are also prey for orca whales and great white sharks.

California sea lions are sexually dimorphic, meaning males and females differ in size, color, and other characteristics beyond their sex organs. At 850 pounds and seven feet long, males are at least twice as large as females, who weigh 220 pounds and grow up to
six feet long. Males are dark brown with tan spots on their faces, and females are tan. Males also develop a bony ridge that runs lengthwise across the top of their skull, called a sagittal crest. Females have lower, smoother foreheads.

The main breeding range for California sea lions is from the Channel Islands in southern California to central Mexico. Their breeding colonies, called rookeries, are located on quiet islands. From May to August, males establish territories via barking and aggressive displays. Males that secure waterfront properties (territories that include beach and extend into water) are likely to attract the most females. Pups are born from June to July and weigh 13 to 20 pounds. Mothers and pups recognize each other amidst crowded rookeries by unique scent and vocalization.

Sea lions are protected under the Marine Mammal Protection Act (MMPA) of 1972 which prohibits hunting, killing, capture, and harassment of marine mammals. As a result of the MMPA, the California sea lion population increased 5.4 percent annually between 1975 and 2008 and has hovered under carrying capacity since 2008. The International Union for Conservation of Nature (IUCN) lists them as “least concerned” due to their large and increasing population.

The California sea lion’s success means they increasingly conflict with beachgoers, fishers, and endangered fish. Dams have reduced the salmon population in the Columbia River, forcing them to move 100 miles upriver from the coast in search of prey. Male sea lions in particular like to munch on endangered salmon and steelhead that congregate below fish ladders. One of their favorite sites is Bonneville Dam, which is located 40 miles east of Portland and spans Oregon and Washington.

In March 2008, Oregon, Washington, and Idaho received federal authorization to kill up to 93 sea lions per year at Bonneville Dam, and in October 2017, Oregon Department of Fish and Wildlife Federal Wildlife (ODFW) requested permission to do the same at Willamette Falls. Both Republican and Democrat members of the U.S. House of Representatives recently approved the “Endangered Salmon and Fisheries Predation Prevention Act” which, if signed into law, would allow fishermen and tribes to kill ten times as many sea lions (up to 920) in the river annually. The removal of males has not been shown to have a significant impact on the population, as California sea lions are now more numerous than ever and have exceeded their historic range.