The Steller sea lion, also known as the northern sea lion, is the largest member of the Otariid (eared seal) family.
Steller sea lions exhibit sexual dimorphism, in which adult males are noticeably larger than females and further distinguished by a thick mane of coarse hair.
Adult males may be up to 10-11 feet (3-3.4 m) in length and can weigh up to 2,500 pounds (1,120 kg). Females are smaller than males, at 7.5-9.5 feet (2.5-3.0 m) in length and weigh up to 770 pounds (350 kg).
The coats of adult males and females are light blonde to reddish brown and slightly darker on the chest and abdomen. The light coloration is still visible when the body is wet, which is different from many pinniped species. Like other pinnipeds, their coat of fur “molts” every year. Both sexes also have long whitish whiskers, or vibrissae, on their muzzle. The flippers and other hairless parts of the skin are black. The fore-flippers are broader and longer than the hind-flippers and are the primary means of locomotion in water. On land, sea lions, unlike “true” seals, can turn their hind flippers forward for walking.
Steller sea lions forage near shore and pelagic waters.They are also capable of traveling long distances in a season and can dive to approximately 1300 feet (400 m) in depth. They use land habitat as haul-out sites for periods of rest, molting, and as rookeries for mating and pupping during the breeding season. At sea, they are seen alone or in small groups, but may gather in large “rafts” at the surface near rookeries and haul outs. They are capable of powerful vocalizations that are accompanied by a vertical head bobbing motion by males.
Steller sea lions are opportunistic predators, foraging and feeding primarily at night on a wide variety of fishes (e.g., capelin, cod, herring, mackerel, pollock, rockfish, salmon, sand lance, etc.), bivalves, cephalopods (e.g., squid and octopus) and gastropods. Their diet may vary seasonally depending on the abundance and distribution of prey. They may disperse and range far distances to find prey, but are not known to migrate.
Steller sea lions are colonial breeders. Adult males, also known as bulls, establish and defend territories on rookeries to mate with females. Bulls become sexually mature between 3 and 8 years of age, but typically are not large enough to hold territory successfully until 9 or 10 years old. Mature males may go without eating for 1-2 months while they are aggressively defending their territory. Females typically reproduce for the first time at 4 to 6 years of age, usually giving birth to a single pup each year.
At birth, pups are about 3.3 feet (1 m) in length and weigh 35-50 pounds (16-22.5 kg).
Adult females, also known as cows, stay with their pups for a few days after birth before beginning a regular routine of alternating foraging trips at sea with nursing their pups on land. Female Steller sea lions use smell and distinct vocalizations to recognize and create strong social bonds with their newborn pups. Pups have a dark brown to black “lanugo” coat until 4 to 6 months old, when they molt to a lighter brown. By the end of their second year, pups are on the same color as adults. Females usually mate again with males within 2 weeks after giving birth. Males can live to be
up to 20 years old, while females can live to be 30.
ESA Endangered – Western Distinct Population Segment
ESA Delisted – Eastern Distinct Population Segment was delisted in 2013
MMPA – like all marine mammals, Steller sea lions are protected throughout their range by the MMPA.
|males: up to 2,500 pounds (1,120 kg)
females: up to 770 pounds (350 kg)
pups: about 35-50 pounds (16-22.5 kg)
|males: about 10-11 feet (3 – 3.4 m)
females: about 7.5 – 9.5 feet (2.5 – 3.0 m)
pups: about 3.3 feet (1 m)
|adults: light blonde to reddish brown and slightly darker on the chest and abdomen
pups: dark brown to black
|variety of fishes (capelin, cod, herring, mackerel, pollock, rockfish, salmon, sand lance, etc.), bivalves, squid, octopus, and gastropods|
|use land habitat as haul-out sites for periods of rest, molting, and as rookeries for mating and pupping;
colonial breeders, adult males (“bulls”) establish and defend territories on rookeries to mate
Steller sea lions prefer the colder temperate to sub-arctic waters of the North Pacific Ocean. Haul outs and rookeries usually consist of beaches (gravel, rocky or sand), ledges, rocky reefs. In the Bering Sea and Okhotsk Sea, sea lions may also haul out on sea ice, but this is considered atypical behavior.
Critical habitat has been defined for Steller sea lions as a 20 nautical mile buffer around all major haul-outs and rookeries, as well as associated terrestrial, air and aquatic zones, and three large offshore foraging areas (50 CFR 226.202 on Aug. 27, 1993).
Steller sea lions are distributed mainly around the coasts to the outer continental shelf along the North Pacific Ocean rim from northern Hokkaiddo, Japan through the Kuril Islands and Okhotsk Sea, Aleutian Islands and central Bering Sea, southern coast of Alaska and south to California. The population is divided into the Western and the Eastern “distinct population segments” (DPSs) at 144° West longitude (Cape Suckling, Alaska). The Western DPS includes Steller sea lions that reside in the central and western Gulf of Alaska, Aleutian Islands, as well as those that inhabit the coastal waters and breed in Asia (e.g., Japan and Russia). The Eastern DPS includes sea lions living in southeast Alaska, British Columbia, California, and Oregon.
For management purposes, Steller sea lions inhabiting U.S. waters have been divided into two DPSs: the Western U.S. and the Eastern U.S. The differentiation is based primarily on genetic and physical differences, but also on differing population trends in the two regions.
Threats to Steller sea lions include
- boat/ ship strikes
- contaminants/ pollutants
- habitat degradation
- illegal hunting/ shooting
- offshore oil and gas exploration
- interactions (direct and indirect) with fisheries
*Direct fishing impacts are largely due to fishing gear (drift and set gillnets, longlines, trawls, etc.) that has the potential to entangle, hook, injure, or kill sea lions. They have been seen entangled in fishing equipment with what are considered “serious injuries.”
*Indirect fisheries impacts include having to compete for food resources and possible modifications to critical habitat by fishing activities
Historically, threats included:
- hunting for their meat, fur hides, oil, and various other products (in the 1800s)
- killing and placing bounties on this species, which fishermen blamed for stealing fish from them (in the early 1900s)
- killing to limit their predation on fish in aquaculture facilities (fish farms), but intentional killing of Steller sea lions has not been permitted since they were protected under the Marine Mammal Protection Act (MMPA) and listed under the ESA (not since 1972)
Protective zones, catch/harvest limits, various procedures and other measures have been implemented around major haul-outs and rookeries in order to safeguard their critical habitat. The IUCN Red List of Threatened Species considers this species to be “Endangered.”
Subsistence harvests by natives in Alaska and Canada (150-300 taken a year) also occur.
The Steller sea lion was listed under the ESA as threatened throughout its range on December 4, 1990. This listing included animals from Alaska, California, Oregon and Washington in the U.S., as well as Canada, Japan, and Russia.
On June 4, 1997, the population west of 144° W longitude was listed as an endangered DPS (the Western DPS) under the ESA; the population east of 144° W remained listed as threatened as the Eastern DPS. The Western DPS declined by 75% between 1976 and 1990, and decreased another 40% between 1991 and 2000 (the average annual decline during this period was 5.4%) leading us to divide the species into the two distinct population segments (DPS) and listing the Western DPS as endangered.
Critical habitat has been designated (50 CFR 226.202 on Aug. 27, 1993) for Steller sea lions as a 20 nautical mile buffer around all major haul-outs and rookeries, as well as associated terrestrial, air, and aquatic zones, and three large offshore foraging areas. We also designated no-entry zones around rookeries (50 CFR 223.202). We implemented a complex suite of fishery management measures designed to minimize competition between fishing and the endangered population of Steller sea lions in critical habitat areas.
A recovery plan was developed for Steller sea lions in 1992. A revised recovery plan, which discusses separate recovery actions for the threatened and endangered populations, was issued in 2008.
The Eastern DPS of Steller sea lions was delisted on November 4, 2013 due to recovery, a great success story of the conservation benefits provided by Endangered Species Act protections.
- Potential Financial Assistance Program for Pinnipeds off Alaska
- The Eastern Steller sea lion has recovered and no longer ESA-listed.
- Steller sea lions’ impressive low-frequency vocalizations sound more like a roar when compared to California sea lions, which sound more like a bark.
- Steller sea lions are named for the German surgeon and naturalist George Wilhelm Steller. In 1742, he observed and described these large pinnipeds.
- Steller sea lions are the fourth largest pinniped in the world, behind the northern elephant seal, southern elephant seal, and walrus.