The California sea lion (Zalophus californianus) is a coastal eared seal found in western North America. It is one of six species of sea lions. Its natural habitat includes areas from southeast Alaska to central Mexico, such as the Gulf of California. California sea lions have different physical traits between males and females. Males are larger than females, have thicker necks, and a bony ridge on the head. They often rest on sandy or rocky beaches but also use manmade places like marinas and wharves. They eat fish and squid, and are hunted by orcas and great white sharks.
During the breeding season, from May to August, male California sea lions claim territories and try to attract females. Females can move between territories and are not forced to stay with one male. Mothers care for their pups while they go to find food. These sea lions use many sounds, such as barks and calls between mothers and their young. When not breeding, they spend most of their time in the ocean but return to land to shed their old skin.
California sea lions are highly intelligent and can be trained to perform tasks. They show little fear of humans if they are used to them. Because of this, they are often displayed in zoos, circuses, and oceanariums. The United States Navy also trains them for military work. The International Union for Conservation of Nature (IUCN) lists the species as Least Concern due to its large population. To protect fish, the states of Oregon and Washington set yearly limits on how many California sea lions can be killed.
Taxonomy
The California sea lion was first described by René Primevère Lesson, a French naturalist, in 1828. It is classified with other sea lions and fur seals in the family Otariidae. Otariids, also called eared seals, have external ear flaps and larger foreflippers and chest muscles compared to true seals. The California sea lion shares its genus, Zalophus, with the Galapagos sea lion and the extinct Japanese sea lion. The name Zalophus comes from Greek words meaning "intensive" and "crest," referring to the raised head crest found in male California sea lions.
In the past, the Galapagos sea lion and Japanese sea lion were considered subspecies of the California sea lion. However, a genetic study in 2007 showed that all three are separate species. The ancestors of the California and Japanese sea lions likely separated about 2.2 million years ago during the Pliocene era. The California sea lion has more differences in size and appearance between males and females than the Galapagos sea lion. The Steller sea lion is the closest living relative of the Zalophus sea lions, sharing a close evolutionary relationship.
Distribution and habitat
California sea lions live along the western coast and islands of North America, from southeast Alaska to central Mexico. In 2009, DNA studies found five different groups of California sea lions: the U.S. or Pacific Temperate group, the Western Baja California or Pacific Tropical group, and the Southern, Central, and Northern Gulf of California groups. The U.S. group mainly breeds on the Channel Islands, though some breeding areas are now found in northern California, and females are often seen there. The Western Baja California group breeds near Punta Eugenia and on Isla Santa Margarita. These groups are separated by the Ensenada Front. The Gulf of California groups live in shallow waters in the north (Northern group), on tidal islands near the center (Central group), and near the entrance of the bay (Southern group). Scientists have not yet studied the status of California sea lions in the deep waters of the central bay.
Some California sea lions travel far from their usual areas, such as the northwestern Pacific, including the Commander Islands. Although some sea lions similar to otariinae have been seen near Japan recently, their exact origins are unknown.
During the breeding season, California sea lions gather on sandy and rocky shores. On warm days, they stay close to the water. At night or during cool weather, they move farther inland or to higher ground. Non-breeding sea lions may gather at places like marinas, wharves, or navigational buoys. California sea lions can also live in freshwater for short periods, such as near Bonneville Dam, about 150 miles (240 km) up the Columbia River. In 2004, a healthy California sea lion was found sitting on a road in Merced County, California, nearly 100 miles upstream from San Francisco Bay and half a mile from the San Joaquin River.
Appearance, physiology, and movement
California sea lions are sexually dimorphic, meaning males and females differ in size, shape, and color. Males can grow up to 2.5–2.7 meters (8.2–8.9 feet) long and weigh about 350 kilograms (770 pounds), while females are typically around 2.1 meters (6.9 feet) long and weigh about 100 kilograms (220 pounds). The heaviest male ever recorded weighed 660 kilograms (1,460 pounds).
Females and young sea lions have tawny brown fur, though they may appear temporarily light gray or silver after shedding old fur. Adult males have fur that ranges from light brown to black, most commonly dark brown. Their faces may have light tan areas. Newborn pups are born with black or dark brown fur.
Although California sea lions have a slender body, adult males have strong necks, chests, and shoulders. They also have a raised crest on their head, giving them a "high, domed forehead" covered in white hairs. Their manes are less developed than those of adult males of other sea lion species. Both males and females have long, narrow muzzles.
As otariids, California sea lions use their front flippers to swim. This method, combined with their streamlined body, helps reduce water resistance. They do not swim continuously; instead, they glide between strokes. Their flexible spine allows them to bend their neck backward to reach their hind flippers, enabling them to turn and stay streamlined underwater. On land, they can move their hind flippers forward and walk on all fours. Their front flippers move side to side rather than forward and backward. They also rely more on head and neck movements than hind flippers for movement on land. California sea lions can swim at speeds of about 10.8 kilometers per hour (6.7 miles per hour), dive to depths of 274 meters (899 feet), and hold their breath for up to 9.9 minutes. Most dives, however, are around 80 meters (260 feet) deep and last less than 3 minutes.
California sea lions can see colors in the blue-green range of the spectrum. This ability likely helps them survive in marine coastal environments. They have good underwater hearing, able to detect sounds from 0.4 to 32 kHz. They use their whiskers, or vibrissae, to sense touch and vibrations in water. Compared to harbor seals, California sea lions have smoother, less specialized vibrissae that are less effective at tracking hydrodynamic trails but still perform well.
Ecology
California sea lions eat many types of seafood, including octopus, squid, and fish, and sometimes clams. Common fish and squid they eat are salmon, hake, Pacific whiting, anchovy, herring, rockfish, lamprey, dogfish, and market squid. They usually search for food near mainland coastlines, the continental shelf, and underwater mountains called seamounts. They may also look for food along the ocean floor. California sea lions hunt alone or in small to large groups, depending on how much food is available. They sometimes work with other predators, like dolphins, porpoises, and seabirds, to catch large groups of fish. California sea lions may follow dolphins and use their hunting efforts to find food. Adult female sea lions hunt between 10–100 km (6.2–62.1 mi) from shore. Adult males may search for food as far as 450 km (280 mi) from shore when water temperatures increase. They have also learned to eat steelhead and salmon that swim below fish ladders at Bonneville Dam and other places where fish must wait to pass through dams and locks.
California sea lions are hunted by orcas and large sharks. In Monterey Bay, California sea lions are often eaten by orca pods that hunt mammals. California sea lions may notice the dorsal fin of a killer whale and stay alert, even when near orca pods that eat fish. California sea lions are also prey for great white sharks. They have been found with scars from attacks by great white sharks and shortfin mako sharks. Sharks attack California sea lions by surprising them while they rest at the ocean surface. California sea lions that are attacked on their hindquarters are more likely to survive and reach the shore.
Life history
California sea lions breed together from May to August when they gather at their breeding areas called rookeries. When creating a territory, male sea lions try to stay on the rookery for as long as possible to increase their chances of reproducing. During this time, they do not eat and rely on a thick layer of fat called blubber for energy. Larger males can store more blubber and wait longer to defend their territory. A male usually keeps his territory for about 27 days. Female sea lions give birth over a long period, so males do not establish territories until after females have given birth. Most fights between males happen during this time. After this, males use behaviors like vocalizations, head shaking, and bluff lunges to keep their territory boundaries. Because temperatures can reach over 30 °C (86 °F), males must include water in their territories. Some territories are underwater, especially near steep cliffs. Sea lions that fail to establish a territory are driven out to sea or gather at nearby beaches.
Before mating, females gather in groups of 2 to 20 individuals. These groups may include females mounting each other and males. As females begin to mate, these groups break apart. The way California sea lions breed is similar to a system where females choose mates by moving between territories. They avoid males that are too aggressive or energetic. Males cannot stop females from leaving their territories, especially in water. Mating may happen outside rookeries between non-territorial males and females as they move to and from mating areas. In some places, a few males may mate with many females, while in others, a single male may father no more than four pups.
Female California sea lions have a 12-month reproductive cycle. This includes 9 months of pregnancy and 3 months of delayed implantation of the fertilized egg before giving birth in June or July. The time between births is long for this species, lasting 21 days for sea lions near California and over 30 days for those in the Gulf of California. After giving birth, females stay with their pups on land for 10 days and nurse them. Then, females go on foraging trips lasting up to three days, returning to nurse their pups for up to a day. Pups left on land often gather in nurseries to play. When returning from trips, females call their pups with unique sounds, and the pups respond with similar calls. Mothers and pups can recognize each other’s calls. At first, mothers lead reunions, but as pups grow older, they help with reunions. Older pups may sometimes join their mothers during foraging trips. Adult male sea lions do not care for pups but are more involved than males of other otariid species. They have been seen helping protect swimming pups from predators. Pups are weaned by one year but may continue to nurse for another year.
California sea lions use many sounds to communicate. The most common is their bark. Territorial males make the loudest and most continuous barks, especially during the breeding season. Males bark rapidly when excited. Barks of territorial and non-territorial males sound similar, though territorial males’ barks are deeper. Males may bark when threatening other males or during courtship. The only other sound made by territorial males is a "prolonged hoarse grunt" when startled by a human. This sound is also made by non-reproductive males.
Female sea lions are less vocal. Their barks are high-pitched and short, used in aggressive situations. Other sounds females make include "squeals," "belches," and "growls." The sound females use to call their pups is called a "pup-attraction call," described as loud and noisy. Pups respond with a "mother-response call," which is similar. Pups also make sounds like bleats or barks when playing or in distress. California sea lions can make sounds underwater, including "whinny" sounds, barks, buzzings, and clicks.
Outside the breeding season, males move to the northern parts of their range to feed, while females stay near breeding areas. California sea lions can stay at sea for up to two weeks, making continuous dives and returning to the surface to rest. They may travel alone or in groups and rest on land between trips. Adult females and juveniles molt in autumn and winter, while adult males molt in January and February. Sea lions in the Gulf of California do not migrate and stay there year-round.
Intelligence and trainability
Marine biologist Ronald J. Schusterman and his team have studied the cognitive abilities of California sea lions. They found that these animals can recognize relationships between things based on how they function or relate to each other, not just because of shared features. California sea lions can learn simple commands using an artificial sign language. However, they usually do not use the signs in a meaningful or logical way. In 2011, a California sea lion named Ronan was recorded moving her head in time with music. This ability, called "rhythmic entrainment," was previously observed only in humans, parrots, and other birds that can mimic sounds.
Because of their intelligence and ability to learn, California sea lions are used in circuses and marine parks to perform tricks, such as balancing balls on their noses, climbing ladders, or honking horns in a musical way. Trainers give fish as rewards to encourage these behaviors. For example, during ball-balancing training, a trainer might toss a ball so the sea lion accidentally balances it on its nose, helping it understand the task. A California sea lion may take a year to learn a trick for public display. However, it can remember the behavior even after three months of not performing. Some groups, like the Humane Society of the United States and World Animal Protection, oppose using sea lions for entertainment, arguing that the tricks are exaggerated versions of natural behaviors and distract audiences from the animals' unnatural living conditions.
The U.S. Navy uses California sea lions in military operations through the Navy Marine Mammal Program. These animals help detect naval mines and enemy divers. In the Persian Gulf, they can swim behind divers approaching a naval ship and attach a clamp with a rope to the diver's leg. Navy officials claim this can happen in seconds, before the enemy notices. Groups like PETA believe these operations risk the animals' safety. However, the Navy states that the sea lions are removed from the mission area once their task is complete.
Status
The IUCN lists the California sea lion as Least Concern because "its large and increasing population size." The estimated population is between 238,000 and 241,000 for the U.S. or Pacific Temperate stock, between 75,000 and 85,000 for the Western Baja California or Pacific Tropical stock, and 31,393 for the population in the Gulf of California. Along the Pacific coast of the United States, California sea lions are so numerous that they are near the maximum number that can live in the area. However, the population in the Gulf of California decreased by 20% by 2008. California sea lions may be killed when they conflict with fishermen, by poaching, or by becoming caught in human-made garbage. They are also threatened by pollutants like DDT and PCB, which build up in the marine food chain.
In the United States, the California sea lion is protected by the federal Marine Mammal Protection Act (MMPA), passed in 1972, which makes it illegal to hunt, kill, capture, or harass the animal. In 1994, an amendment to the Act allowed limited killing of pinnipeds that prey on endangered salmon if the predation was shown to harm the recovery of salmon populations. Applications were granted to remove some California sea lions at Ballard Locks and the Bonneville Dam, where up to 92 sea lions could be killed each year for five years. Wildlife officials tried using bombs, rubber bullets, and bean bags to scare the sea lions away, but these methods were not effective. Some people have criticized the killing of sea lions, noting that fish deaths from fishing and hydroelectric dams may pose a greater threat to salmon than sea lion predation.
These animals use human-made environments, such as docks, as places to rest. Many docks are not built to support the weight of large numbers of sea lions, causing them to tilt or break. Wildlife managers have used various methods to control the animals, and some city officials have redesigned docks to better handle the weight.
In January and February 2015, 1,450 malnourished or sick California sea lion pups were found along the California coast, with estimates suggesting more pups had died. Scientists believe unusually warm Pacific coastal waters, linked to the Pacific decadal oscillation and El Niño, caused this event. Warmer water reduced the number of anchovies, sardines, and mackerel, which are key foods for sea lion pups during their nursery season. This led to many pups starving, while others died after entering the ocean too early to find food. Earlier, in the summer of 2014, many Cassin’s auklet chicks died due to similar conditions caused by warm water.
In November 2018, the State of Oregon received permission to kill 93 California sea lions each year below Willamette Falls. Under a similar program, Oregon and Washington had killed more than 150 sea lions on the Columbia River by January 2019. These actions aimed to protect local fish populations, such as trout and salmon, from sea lion predation. In August 2020, the federal government allowed Oregon, Washington, Idaho, and six regional tribes to kill up to 540 California sea lions and 176 Steller sea lions over five years to protect endangered fish in the Columbia River basin. Between 2020 and April 2023, Oregon killed 99 sea lions as part of this program.