The Steller sea lion (Eumetopias jubatus) is the largest member of the otariid (eared seal) family and the second‑largest pinniped after the elephant seal. Classified in the order Carnivora, suborder Caniformia, it inhabits the temperate and sub‑arctic waters of the North Pacific, ranging from the coasts of Japan and Russia through the Aleutian Islands to central California. Adults occupy offshore rookeries on isolated islands and coastal haul‑outs, while juveniles and non‑breeding individuals use a network of nearshore bays and estuaries. Males can exceed 1,000 kg, dwarfing the 150 kg females, and display a distinctive mane of thick whiskers and a broad, square head. Their thick, water‑repellent fur and a layer of blubber provide insulation against cold currents. The species is socially complex, forming large breeding colonies that can number tens of thousands of individuals. Historically abundant, the Steller sea lion suffered a dramatic decline in the 1970s and 1980s, prompting its listing as “Vulnerable” by the IUCN. Conservation measures, including fishery management and protected areas, have stabilized some populations, but recovery remains uneven across its range.

Steller sea lions are highly gregarious and exhibit a pronounced sexual dimorphism that shapes their social structure. During the breeding season, dominant males establish and defend territories on rookeries, using vocal barks, growls, and visual displays such as flipper slaps to deter rivals. A single male may control a harem of up to 100 females, though most harems are smaller. Females give birth on land and nurse pups for about 11 months, after which the young are weaned and gradually integrate into the colony’s social network. Outside the breeding period, both sexes form large, mixed‑sex aggregations that forage together and engage in play, vocalizations, and synchronized swimming. Individuals maintain home ranges that can extend 200 km from haul‑out sites, and they travel great distances to exploit seasonal prey blooms. Communication relies on a repertoire of barks, grunts, and whistles, each conveying information about identity, reproductive status, or alarm.

Steller sea lions are apex marine carnivores that primarily consume fish and cephalopods. Their diet is dominated by Pacific herring (Clupea pallasii), walleye pollock (Theragra chalcogramma), and various salmon species (Oncorhynchus spp.), which together can comprise up to 70 % of stomach contents in many regions. They also prey on squid, octopus, and occasionally marine mammals such as harbor seals. Daily food intake averages 5–7 % of body mass, meaning a 350 kg male may consume 18–25 kg of prey. Foraging occurs both near the surface and at depths exceeding 200 m, with individuals employing dive cycles of 5–15 minutes followed by surface recovery. Hunting strategies include coordinated group chases, solitary ambushes, and opportunistic scavenging of fish discarded from commercial fisheries. Seasonal shifts in prey distribution drive extensive migrations, and the species’ reliance on high‑energy fish makes it vulnerable to fluctuations in commercial fish stocks.

Females reach sexual maturity at 4–5 years, while males typically do not breed until 7–9 years, when they have attained sufficient size and strength. The breeding season commences in late May and peaks in June, when females give birth after a gestation of 11.5 months, including a 4‑month delayed implantation. Litter size is almost invariably one pup, weighing 30–45 kg at birth. Pups are nursed exclusively on the mother’s rich milk, which contains up to 50 % fat, and they gain an average of 1.5 kg per day. Maternal care lasts about 11 months, after which the juvenile is weaned and begins independent foraging. Males do not participate in parental care; instead, they invest energy in establishing and defending territories, a behavior that drives the pronounced size disparity between the sexes. Annual reproductive success is highly variable and closely linked to prey availability and male dominance hierarchies.

The IUCN classifies the Steller sea lion as Vulnerable, reflecting a 30 % decline in the western population between the 1970s and 1990s. Primary threats include competition with commercial fisheries for key prey such as pollock and herring, which can reduce food availability and lower reproductive rates. Bycatch in gillnets and trawls also causes direct mortality, with estimates of 1,000–2,000 individuals killed annually in the North Pacific. Habitat degradation from coastal development, pollution, and climate‑driven changes in ocean temperature affect haul‑out sites and prey distribution. Although protective measures—such as the Marine Mammal Protection Act in the United States, designated marine protected areas, and fishery management plans—have contributed to population stabilization in the eastern range, the western Alaskan stocks remain below historic levels, with recent surveys estimating fewer than 30,000 individuals. Ongoing monitoring, ecosystem‑based fishery management, and mitigation of bycatch are essential for long‑term recovery.

• Steller sea lions can dive deeper than 200 m and stay submerged for up to 15 minutes.
• Males can weigh more than a ton, making them one of the heaviest eared seals.
• Their milk contains up to 50 % fat, the highest among marine mammals.
• They were named after naturalist Georg Steller, who first described them in 1741.
• Despite their size, they can run up to 25 km/h on land using their foreflippers.