General · EdgepediaSeptember 17, 20268 min read

Sea lion

A sea lion is a pinniped of the family Otariidae, the group of "eared seals" that also includes the fur seals. Sea lions are distinguished from true seals by external ear flaps, large front flippers, and the ability to bring all four flippers under the body and walk on land; in the water they propel themselves by paddling the front flippers and steer with the rear flippers.¹^•²

Key fact	Detail
Group	Family Otariidae, the eared seals, which includes sea lions and fur seals; pinnipeds also comprise the Phocidae (true seals) and Odobenidae (walruses)¹
Defining traits	External ear flaps, large front flippers used for underwater propulsion, and four-limbed walking on land¹^•²
Evolutionary split	Otariids and odobenids diverged approximately 19 million years ago in the North Pacific³
Largest living species	Steller sea lion (Eumetopias jubatus), an ESA-listed species with two genetically distinct populations⁴
Familiar species	California sea lion (Zalophus californianus), females up to 6 feet and males up to 7.5 feet long⁵
Endangered members	The Galápagos, Australian, and New Zealand sea lions are all assessed as Endangered on the IUCN Red List⁶^•⁷^•⁸
Diving ability	Pinnipeds as a group include species that hold their breath for up to two hours and dive to depths of more than 6,500 feet¹

What separates sea lions from seals

Seals, sea lions, and walruses together form the pinnipeds, a name meaning "fin- or flipper-footed." These animals live in the ocean but come onto land or ice for long periods to rest, molt, mate, and nurse young.¹

The two families most often confused are the Otariidae and the Phocidae. True seals, such as the harbor seal and Hawaiian monk seal, have ear holes but no external ear flaps, small front flippers, and move on land by flopping on their bellies; in the water they sweep their rear flippers back and forth like a fish's tail.¹ Sea lions, by contrast, have visible external ear flaps, which gives the group its "eared seals" nickname. On land they use their large, elongated front flippers together with rear flippers rotated underneath the body to walk, and in the water the roles reverse: the front flippers paddle while the rear flippers act like a boat's rudder.² Sea lions are also generally more vocal and more social in the water than seals, which tend to grunt, growl, or hiss softly.²

Evolution and classification

The oldest definitive pinniped fossils date from approximately 30.6 to 23 million years ago in the North Pacific. Crown pinnipeds comprise the Otariidae (fur seals and sea lions), Odobenidae (walruses), and Phocidae (seals). Both otariids and odobenids are known from the North Pacific, diverging approximately 19 million years ago, while phocids originated later in the North Atlantic or Paratethys region between 19 and 14 million years ago.³ A meta-analytic phylogeny combining 36 recent and 93 fossil taxa found that pinnipeds mostly diversified at constant rates, with walruses the exception, experiencing rapid turnover from 12 to 6 million years ago in which extinction rates ultimately exceeded speciation rates.⁹

Molecular evidence continues to reshape sea lion taxonomy. A genetic analysis of the genus Zalophus showed that the Galápagos sea lion and the California sea lion are separate species, supported by diagnostic SNPs in the mitochondrial and nuclear genomes; the study noted that morphological characters do not necessarily fully reflect rapid divergence at the molecular level.¹⁰

Notable species

Steller sea lion. Eumetopias jubatus is the sea lion of the North Pacific and the species listed as threatened or endangered in part of its range under the U.S. Endangered Species Act.¹ Its two populations differ genetically and morphologically and show contrasting trends.⁴ Steller sea lions are predatory, feeding primarily at night on over a hundred species of fish, including Atka mackerel, walleye pollock, salmon, Pacific cod, and Pacific herring, as well as cephalopods such as squid and octopus; the diet varies across the range and through the year with prey abundance.¹¹ They are large animals: a Steller sea lion nicknamed Chonkers that drew crowds at San Francisco's Pier 39 in 2026 was estimated to weigh between 1,500 and 2,000 pounds (680 and 907 kilograms), surrounded by the much smaller California sea lions that normally occupy the docks.¹²

California sea lion. Zalophus californianus is the trained and display animal most people picture at aquariums and the species hauled out on West Coast docks. NOAA Fisheries divides the population into three stocks, the United States, western Baja California, and Gulf of California stocks, based on the location of major rookeries and the international border. Females reach about 6 feet and males about 7.5 feet. One of the main threats to the species is getting caught in fishing gear.⁵

Southern Hemisphere and Australasian species. The Galápagos sea lion (Zalophus wollebaeki) coexists with the Galápagos fur seal as one of two endemic pinnipeds of the Galápagos archipelago¹³ and qualifies for listing as Endangered under IUCN criterion A2ab.⁶ The Australian sea lion (Neophoca cinerea) is the only pinniped species endemic to Australia. Males reach 185 to 225 centimeters in length and 180 to 250 kilograms in weight, while females reach 130 to 185 centimeters and 65 to 100 kilograms.¹⁴ The New Zealand sea lion, known in Māori as pakake or whakahao, is one of the rarest sea lion species in the world, with a population of about 10,000 confined to New Zealand, and is listed as Nationally Endangered in New Zealand and Endangered on the IUCN Red List.⁸

Biology and behavior

Throughout the breeding season, sea lions depend on peaceful terrestrial habitat where they can rest, molt, socialize, mate, deliver their young, and nurse small pups.¹¹ Foraging behavior varies widely within a species. In the non-breeding season, some adult female Steller sea lions spend long periods foraging well off the continental shelf while others forage much nearer to terrestrial sites, and the animals forage both near and offshore, in benthic and pelagic zones.¹¹

The Australian sea lion shows the most distinctive breeding system in the family: it is the only pinniped species with a non-annual breeding cycle, with intervals of 17 to 18 months between pupping seasons. Its breeding seasons are protracted, lasting 4 to 9 months, and are asynchronous between colonies, so different colonies breed at different times of year.¹⁴ Females become sexually mature at 4.5 to 6 years of age, nurse their pups for 15 to 18 months, and show high natal site fidelity, breeding only at the site where they were born.¹⁴

Diving physiology has been studied most thoroughly in Steller sea lions through controlled studies with trained animals diving in the open ocean, work designed to determine the physiological limitations and trade-offs that marine mammals face while diving under varying environmental and nutritional conditions.¹⁵

Conservation

All seals and sea lions in United States waters are protected under the Marine Mammal Protection Act, and seven species, including the Steller sea lion, are also listed as threatened or endangered in part of their range under the Endangered Species Act.¹ For the Steller sea lion, historical culling and commercial harvests in Alaska before the Act, competition with fisheries for prey, incidental take, entanglement, and legal and illegal shooting all adversely affected the species; intentional killing is now illegal with narrow exceptions, including non-wasteful subsistence take by coastal Alaska Natives.⁴ Internationally, the species is protected in Canada as a Species of Special Concern and listed as endangered under Russian legislation.⁴

Climate-driven events now register clearly in population data. During the 2014–2016 North Pacific marine heatwave, fewer pups were produced from 2015 to 2017 in the central and eastern Gulf of Alaska, fewer adult females survived in the eastern Aleutian Islands, Southeast Alaska, and the Gulf of Alaska, and non-pup numbers then fell across the whole Gulf of Alaska in 2019, ending a trend that had been rising.⁴

Fisheries bycatch is a recurring pressure across the family. In Australia, demersal gillnet fisheries have been a primary threat to the Australian sea lion; mortality in Commonwealth fisheries off South Australia was estimated at 3.9 percent of the overall female population per breeding cycle before management measures introduced from 2010, including spatial closures and 100 percent observer coverage, reduced mortalities to fewer than 4 per breeding cycle, with 21 total mortalities over 2010 to 2019.¹⁴ The species was moved from Vulnerable to Endangered under Australia's EPBC Act in December 2020, a change attributed to new information and a more rigorous synthesis rather than a genuine deterioration in status.¹⁴ The New Zealand sea lion faces threats including commercial and recreational fisheries, human disturbance, vehicle collisions, disease, and shark predation, and its main breeding colony is in decline.⁸

Because the Australian sea lion's long, non-annual breeding cycle slows recovery after direct or indirect mortality, and because most colonies are very small, even low levels of mortality in a given location are a concern; once a colony is extirpated, it is unlikely to re-establish due to high female site fidelity.¹⁴

References

Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 21, 2026 · Edited: Sep 30, 2026; Oct 21, 2026