Overview

California sea lions are the most common pinnipeds along the west coast of the United States, and have recovered dramatically from past human exploitation. While they breed further south in California waters, some California sea lions move up the coast to find good feeding opportunities. They have become common in Puget Sound in non-summer months. While some sea lions get caught in fishing gear, this and other anthropogenic threats do not seem to be severe for the species at this point. The species is not threatened or endangered.

California sea lions are consumers of vast amounts of fish and invertebrates along the coast, and are not well-liked by most fishers. Some individual sea lions have caused major problems for management authorities by stationing themselves near the “pinch points” of locks near Seattle, and taking large numbers of salmon and steelhead that were on their way to spawning areas.

Status, trends, & events

Total population size of the California sea lion may be close to 300,000 animals. While there are no reliable, quantitative trends data for California sea lion numbers in Puget Sound, the overall trend for the population has been a dramatic increase in numbers since the species was protected in 1972. The population size of the US stock reached an estimated 257,600 animals in 2014, a level very close to its estimated carrying capacity (Laake et al. 2018; Carretta et al. 2022). Numbers in inland Washington waters have also clearly been increasing in recent decades, with on average about 450 occurring in Puget Sound proper in spring months, and as many as 3,000 found within the entirety of Washington’s inland waters in spring (Jefferson et al. 2023).

Natural history

Distribution and occurrence

California sea lions are found in continental shelf and slope waters from south of the Gulf of California, Mexico, all along the west coast of North America, and into southern Alaskan waters (Carretta et al. 2022). This species occurs in Puget Sound throughout the year, but numbers in summer are very low. The peak seasons are spring and fall, when California sea lions from California waters move up the coast to feed and invade inland Washington waters (Jefferson et al. 2023).

What do they eat?

Opportunistic feeding is the best way to describe how California sea lions eat. They take a very large variety of food items, but mostly prey on fish (such as Pacific whiting, jack mackerel, Pacific mackerel, blacksmith, rockfish, herring, anchovy, bass, sardines, cusk eels, lanternfish, and salmon/steelhead) as well as cephalopods (market squid and red octopus). In inland Washington, they often target herring, and juveniles of various salmon and steelhead species.

What eats them?

The main predators of this species are large sharks (mainly great white sharks) and killer whales (see Odell 1981). Coyotes and feral dogs may also occasionally kill young sea lions, and in the past, brown bears would likely have been a serious predator.

Biology

California sea lions occupy the core part of their range in Mexico and southern/central California throughout the year. They breed during summer months on islands in Mexico and southern California (the main rookeries are in the Channel Islands), and after the breeding season many animals (particularly males) move north into waters extending from northern California all the way up to southeast Alaska. There are extralimital records both south and northwest of the normal range (Jefferson et al. 2015).

This is a resilient species that has made a dramatic recovery from hundreds of years of relentless exploitation by humans. Especially in the 1800s and 1900s, sea lions were hunted and captured for human and pet food, furs/hides/trimmings, oil, and were killed as target practice, to reduce competition with fishers, and even for sport. Their numbers were reduced to the lowest level (possibly as low as 1,500 animals) in the 19th and 20th centuries. But, since protection in the late 1900s (especially by the US Marine Mammal Protection Act of 1972 (MMPA) and similar legislation in Canada), they have made quite a comeback. It is now believed that they have reached the population’s carrying capacity of around 275,000 individuals (Laake et al. 2018). Within Puget Sound/Hood Canal, aerial surveys conducted between 2013 and 2016 suggest that several hundred may occur during peak seasons of spring and fall, with up to 3,000 found in Washington’s inland waters (including the Strait of Juan de Fuca, and the San Juan Islands area) (Jefferson et al. 2023). They are appearing in places where they have not been seen in recent decades, with some sea lions actually showing up on the porches of coastal residents.

NOAA recognizes five different populations, which are genetically distinct (Carretta et al. 2022). The Pacific Temperate population breeds in US waters and is managed as the US Stock. Other populations occur in Mexican waters. The northern extent of the population’s range has been shifting northwards, as total numbers have increased and climate change results in warming water temperatures. California sea lions now regularly occur in Washington, British Columbia, and Alaskan waters, something that was rare or unheard of in the early 20th century.

California sea lions are probably the most recognizable pinnipeds to most people, as they are the typical “performing seal” found in zoos and oceanaria. The species is highly sexually dimorphic, with males about 1.2 times longer and 3-4 times heavier than females. Adult males also have a large bump on the forehead, which is formed by the bony sagittal crest on their skulls. Bulls (adult males) can be up to 2.4 m long and weigh up to 390 kg, but adult females (sometimes called cows) only reach 2 m in length, and 110 kg in weight. At birth, pups are about 80 cm long and weigh 6-9 kg.

Hauling out usually occurs on islands and rocky substrates, but these animals will also haul out on human-made structures, such as piers, docks, boats, submarines, buoys, porches, etc. Reproduction is highly seasonal, with pupping and mating taking place from May through July. The species is polygynous, with males competing to hold territories on which females congregate. The dominant males aggressively exclude other, more subordinate males from breeding opportunities. After the pup is born, its mother uses a combination of smell and vocal calls to form a mother/pup bond. About a week after birth, the mother will begin making foraging trips to sea, leaving the pup unattended on the rookery for several days at a time. At about 10 months, the pup is weaned, and begins an independent life (see Odell 1981; Melin et al. 2017).

The distinctive bark of the California sea lion is immediately recognizable to many residents of coastal California. It is loud and can be heard from several kilometers away, when conditions are right. Although it has been suggested that sea lions may have a simple form of echolocation, this has not been proven. California sea lions are not particularly deep divers, with the deepest dives of only about 275 m and 10 minutes. Most feeding dives are much shallower and shorter. These animals are quite opportunistic and often feed in association with human activities (such as commercial and sport fishing operations), and with other species of marine mammals (such as humpback whales and dolphins).

Although their diet is highly varied, the tendency of California sea lions to feed on threatened stocks of salmon and steelhead has gotten them into conflicts with fishers, and wildlife managers. Deterrence methods and even relocations to other areas have not been particularly successful, and as a result lethal removal methods have sometimes been employed. Obviously, such extreme measures are very controversial.

What threatens them?

Threats to the species include commercial fisheries interactions (esp. with trawl, purse seine, and gillnet fisheries), marine debris entanglement, poaching, disease outbreaks, and contamination by pollutants. Other causes of occasional mortality (e.g., oil exposure, dog attacks, vessel strikes, injuries incidental to research activities, noise disturbance, power plant entrapment, and shooting/hooking by recreational fishers) are not thought to cause population level declines. Diseases include paralytic shellfish poisoning and infections from pathogens, such as Pseudo-nitzschia, a diatom genus which produces the neurotoxin domoic acid leading to amnesia, and the bacteria that cause leptospirosis. It is also thought that climate change may be limiting population growth in the California Current ecosystem (see Carretta et al. 2022).

California sea lions are frequent stranding victims along their coastal range, with disease and injury causes highly varied. Rehabilitation by marine mammal rescue organizations is often successful, and many times these animals can be relocated back into the wild after being treated.

The legal status of all marine mammals in US waters provides them with a high level of protection from hunting and other potential threats. The US MMPA has been in effect since 1972, and was a major reason for the remarkable recovery of this species, from depleted levels to numbers that now appear to be at the carrying capacity of their environment. The US stock is considered to be within its optimum sustainable population, and is not considered Threatened or Endangered under the US Endangered Species Act, nor “depleted’ under the MMPA. The population is healthy and is in no danger of extinction (Carretta et al. 2022).

Data sources & gaps

Monitoring and information gaps for this species in Puget Sound are many. There are no regular monitoring efforts to estimate numbers or examine trends in the Sound, and efforts to determine exactly how California sea lions use these waters and their impacts on other species (including on threatened fish stocks) are limited.

Methods & statistics

The abundance time series graph above was constructed from data on annual pup counts, survivorship from mark-recapture studies, and estimates of human-caused mortality. The logistic growth curve uses 95% bootstrap confidence intervals to evaluate variability (from Laake et al. 2018). The distribution map was compiled from all available data sources (from Jefferson et al. 2015). The data on numbers in Puget Sound and inland Washington waters are from a paper by Jefferson et al. (2023) recently published in Aquatic Mammals.

References

The scientific name of the species is Zalophus californianus. In Mexico, they are known as “lobo marino” (Spanish).

Carretta, J. V., E. M. Oleson, K. A. Forney, M. M. Muto, D. W. Weller, A. R. Lang, J. Baker, B. Hanson, A. J. Orr, J. Barlow, J. E. Moore and R. L. Brownell Jr. (2022). U.S. Pacific marine mammal stock assessments: 2021. NOAA Tech. Memo. NMFS-SWFSC, 663.

Jefferson, T. A., M. A. Smultea, and E. J. Ward. 2023. Distribution and abundance of California (Zalophus californianus) and Steller (Eumetopias jubatus) sea lions in the inshore waters of Washington, 2013-2016. Aquatic Mammals 49:366-381.

Jefferson, T. A., M. A. Webber and R. L. Pitman. (2015). Marine Mammals of the World: A Comprehensive Guide to Their Identification. Academic Press/Elsevier.

Laake, J. L., M. S. Lowry, R. L. Delong, S. R. Melin and J. V. Carretta. (2018). Population growth and status of California sea lions. Journal of Wildlife Management 82(3):583-595. 2018. https://wildlife.onlinelibrary.wiley.com/doi/10.1002/jwmg.21405

Melin, S. R., F. Trillmich, and D. Aurioles-Gamboa. (2017). California, Galapagos, and Japanese sea lions, Zalophus californianus, Z. wollebaeki, and Z. japonicus. Encyclopedia of Marine Mammals (Third Edition). Würsig, B., J. G. M. Thewissen and K. M. Kovacs, eds. (Pages 153-157). Academic Press.

Odell, D. K. (1981). California sea lion Zalophus californianus (Lesson, 1828). In S. H. Ridgway and R. J. Harrison (Eds.), Handbook of Marine Mammals, Volume 1: The walrus, sea lions, fur seals and sea otter. (Pages 67-97). Academic Press.

Acknowledgments

The authors thank the Puget Sound Partnership for funding the analysis of species data in inland Washington waters. Funding for this article was provided by the University of Washington Puget Sound Institute with support from the U.S. Environmental Protection Agency and the Puget Sound Ecosystem Monitoring Program. 

Licensing & attribution

Data and products from the PSEMP Marine Mammal Work Group are governed by a Creative Commons BY-NC-SA license. Attribution should be to: “PSEMP Marine Mammal Work Group” with the link: https://psemp.net/mmwg.