Steller sea lions are the largest eared seals and the fourth largest pinniped (a group of aquatic carnivorous mammals) in the world. Male Steller sea lions are noticeably larger than the females and have a thick mane of coarse hair. Males can weigh up to 1,120 kilograms (2,500 pounds); whereas, females weigh up to 350 kilograms (770 pounds). Pups range from 16 to 22.5 kilograms (35 to 50 pounds). Males can reach lengths up to 3 to 3.4 meters (10 to 11 feet), while females reach 2.3 to 2.9 meters (7.5 to 9.5 feet). The color of adult Steller sea lions ranges from light blonde to reddish brown, their chest and stomach are slightly darker. Unlike other pinnipeds, when Steller sea lions get wet, their light colored fur is still visible. Similar to other pinnipeds, Steller sea lions molt their winter coat each year. (Bickham, et al., 1996; Gelatt and Lowry, 2012; NOAA Fisheries, 2012)
Steller sea lions are found in the cold waters of the North Pacific Ocean and typically stay near land. They are mostly found along the northern California coast, Alaska, and the coasts of Russia and Japan. Steller sea lions are considered endangered in some areas (west of the 144º W latitude) and threatened in others (east of 144º W latitude). (Bickham, et al., 1996; Gelatt and Lowry, 2012; NOAA Fisheries, 2012)
Steller sea lions are found in the cold waters of the Pacific Ocean on rookeries (breeding grounds) and near haul outs (non-breeding grounds). Within these areas, there is a 37 kilometer (20 nautical miles) radius where Steller sea lions typically are found. These areas are protected by the species recovery plan. Steller sea lions are able to dive as far as 400 meters (1,312 feet) and can stay under water for up to two minutes. (Gelatt and Lowry, 2012; NOAA Fisheries, 2012)
In populations of Steller sea lions, a dominant male mates and guards up to 30 females per breeding season. However, younger males may sneak onto breeding grounds and try to mate with the females without the dominant male noticing. Females begin mating between the ages of 3 to 6 years. Steller sea lions have one pup at a time and give birth between mid-May and July. Females are able to breed again 2 weeks after their pup is born. (Gelatt and Lowry, 2012; NOAA Fisheries, 2012; Sinclair and Zeppelin, 2002)
Steller sea lions breed, give birth and nurse pups on remote islands called 'rookeries'. Females are pregnant for a year, after which, they have a single pup. Pups generally nurse for a year, but in some cases, they may nurse up to three years. At birth, pups weigh between 16 to 23 kilograms (35-50 pounds) and are about 1 meter (3.3 feet) long. Both male and female Steller sea lions are ready to breed between the ages of 3 to 6 years; however, due to competition with other males, most males will not breed successfully until they are 8 to 10 years old. Dominant males, females, and new pups live on rookeries during the summer when breeding occurs. Older pups do not stay on rookeries as long because they cannot breed. After the breeding season ends in August, females and their young move to non-breeding areas, known as 'haul outs'. Steller sea lions are very social and continue living with each other after the breeding season has ended. (Gelatt and Lowry, 2012; NOAA Fisheries, 2012; Sinclair and Zeppelin, 2002)
Female Steller sea lions provide care for their young for as long as three years. They nurse their young for up to a year, but some will let their young nurse longer. Male Steller sea lions do not provide much parental care for their young; however, males will guard all the females that they impregnated. After female Steller sea lions give birth, they forage around the rookery and onshore, mostly at night, and may be gone for as long as a day. After finding a food source, they return and nurse their pup. (Gelatt and Lowry, 2012; Horning and Mellish, 2012; NOAA Fisheries, 2012)
Male Steller sea lions can live up to 20 years; whereas, females can live up to 30 years. Their lifespan in captivity has not been reported. The main cause of death for Steller sea lions is old age. They are sometimes killed by fisherman because they interfere with fishing nets and fish hatcheries. (Gelatt and Lowry, 2012)
Steller sea lions are generally social within their populations and can be found in large groups in rookeries or on beaches. Steller sea lions are usually found in groups ranging from one to twelve, but have been seen with as many as a hundred individuals on a beach. (Gelatt and Lowry, 2012; NOAA Fisheries, 2012)
Steller sea lions are typically found along California and further north on the west coast of North America. Likewise, they may also be found in Alaska, Japan, the Gulf of Alaska, and the Bering Strait. Young Steller sea lions usually travel farther than adults, because they are unable to mate they will go farther for food. (Bickham, et al., 1996; Gelatt and Lowry, 2012; NOAA Fisheries, 2012; Sinclair and Zeppelin, 2002)
Steller sea lions produce sounds similar to a roar to communicate with each other. Their close relative, California sea lions, also communicate this way, but they produce a barking sound. (Gelatt and Lowry, 2012; NOAA Fisheries, 2012)
Steller sea lions look for food along shorelines. They eat a variety of fish, including walleye pollock, Atka mackerel, Pacific salmon, and Pacific cod. Their main food source is Atka mackerel, but during the winter they primarily eat walleye pollock and Pacific cod. They will also eat octopus, squid, bivalves, and gastropods. Steller sea lions have also been known to kill other animals, such as harbor seals and ringed seals, along with younger northern fur seals. (Gelatt and Lowry, 2012; NOAA Fisheries, 2012; Sinclair and Zeppelin, 2002)
Salmon sharks, killer whales, and Pacific sleeper sharks are some of their known predators. Their population size is more strongly related to the number of predators around them than to the amount of food available for them. Great white sharks have been known to kill and consume Steller sea lions if their territories happen to cross. Humans may also prey on Steller sea lions.
Steller sea lions are thought to deplete fish stocks and eat fish out of hatcheries, so they are often killed or hunted. (Gelatt and Lowry, 2012)
Historically, Steller sea lions were hunted for their meat, fur, and oil; this played a part in the decrease of their population. Incidental population destruction has also occurred due to fishing nets, ship strikes, pollutants and diseases. (Bickham, et al., 1996; Gelatt and Lowry, 2012; NOAA Fisheries, 2012)
Throughout most of its range (west of the 144º W latitude), Steller sea lions are considered endangered, while in other parts (east of 144º W latitude), they are considered threatened. Populations of Steller sea lions are declining due largely to culling by fisherman. Historically, Steller sea lions have also been harvested for their fur, blubber, and meat. (Gelatt and Lowry, 2012)
Danielle Keranen (author), Michigan Technological University, Amy Schrank (editor), Michigan Technological University, Leila Siciliano Martina (editor), Animal Diversity Web Staff.
Bickham, J., J. Patton, T. Loughlin. 1996. High Variability for Control-Region Sequences in a Marine Mammal: Implications for Conservation and Biogeography of Steller Sea Lions (Eumetopias jubatus). Journal of Mammalogy, Volume 77/ Issue 1: 95-108.
Horning, M., J. Mellish. 2012. Predation on an Upper Trophic Marine Predator, the Steller Sea Lion: Evaluating High Juvenile Mortality in a Density Dependent Conceptual Framework. PloS One, Volume 7/ Issue 1: 1-10.
Kenyon, K., D. Rice. 1961. Abundance and Distribution of the Steller Sea Lion. Journal of Mammalogy, Volume 42/ Issue2: 223-234.
NOAA Fisheries, 2012. "Steller Sea Lion (Eumetopias jubatus)" (On-line). NOAA Fisheries Office of Protected Resources. Accessed November 19, 2012 at http://www.nmfs.noaa.gov/pr/species/mammals/pinnipeds/stellersealion.htm.
Sinclair, E., T. Zeppelin. 2002. Seasonal and Spatial Differences in Diet in the Western Stock of Steller Sea Lions (Eumetopias jubatus). Journal of Mammalogy, Volume 83/ Issue 4: 973-990.