The Steller sea lion (Eumetopias jubatus), also called Steller's sea lion or the northern sea lion, is a large animal that is at risk of becoming endangered. It lives mainly in the coastal ocean areas of the northeast Pacific Ocean and the Pacific Northwest regions of North America, from northern California to Oregon, Washington, British Columbia, and Alaska. Its range also includes the Northern Pacific, the Aleutian Islands, and areas near Kamchatka, Magadan Oblast, and the Sea of Okhotsk, as far south as the northern coast of Honshu. It is the only animal in the genus Eumetopias and the largest of the eared seals (Otariidae). Among all pinnipeds, only walruses and two types of elephant seals are larger. The species is named after Georg Wilhelm Steller, a naturalist and explorer who first described it in 1741. In recent years, Steller sea lions have drawn a lot of attention from scientists and the public because their numbers have dropped a lot in parts of their northern range, especially in Alaska, and the reasons for this decline are not fully understood.
Description
Adult sea lions are lighter in color than most sea lions, ranging from pale yellow to tawny and sometimes reddish. Steller sea lion pups are born nearly black, weighing about 23 kg (51 lb), and stay dark for several months. Female sea lions reach sexual maturity between four and six years of age, while males reach maturity between three and eight years of age. Both males and females grow quickly until they are five years old. After that, female growth slows significantly. Adult females are 2.3–2.9 m (7.5–9.5 ft) long, with an average length of 2.5 m (8.2 ft), and weigh 240–350 kg (530–770 lb), averaging 263 kg (580 lb). Males continue to grow until their secondary sexual traits develop between their fifth and eighth years. Males are slightly longer than females, growing to about 2.82–3.25 m (9.3–10.7 ft) long, with an average length of 3 m (9.8 ft). Males have broader chests, thicker necks, and a larger upper body. Males weigh between 450–1,120 kg (990–2,470 lb), with an average weight of 544 kg (1,199 lb). Males are also distinguished by broader and higher foreheads, flatter snouts, and a thick, coarse mane of hair around their large necks. Their Latin name means "maned one with the broad forehead."
Range
The Steller sea lion lives in an area that starts on the north side of Honshu, Japan, and goes north to the Gulf of Alaska. It also extends south to Año Nuevo Island near central California. These sea lions used to breed as far south as the Channel Islands, but they have not been seen there since the 1980s. Scientists have divided the global Steller sea lion population into two main groups based on genetic studies and migration patterns. These groups are separated by a line at 144°W longitude, which runs through the middle of the Gulf of Alaska. New research shows that sea lions in Russia’s Sea of Okhotsk and Kuril Islands form a third group in Asia, while those on the eastern coast of Kamchatka and the Commander Islands belong to the western group.
During summer, Steller sea lions often move their range slightly south. Although there are no breeding areas in Japan, they gather at several regular sites around Hokkaidō during winter and spring. Some individuals have been seen in the Yellow Sea, Bohai Gulf, and along the coasts of the Korean Peninsula and China. The oldest known fossil of this species was discovered near Kanazawa, Japan, and is about 800,000 years old, from the late Early Pleistocene period.
Ecology
Steller sea lions live in the coastal waters of the subarctic because the area has a cooler climate. Like all otariids, Steller sea lions are amphibious, meaning they spend time in water and on land. They spend most of their time in the water hunting for food but go onto land to reproduce, care for their young, shed their fur, and rest. Steller sea lions often gather on isolated islands because these places are ideal for living on land. These islands are preferred because they help sea lions avoid land predators, stay cool with wind, and reach food in the ocean more easily. Some land areas, called rookeries, are used mainly for reproduction, while other areas are used for activities like molting. However, both living things (biotic factors) and non-living things (abiotic factors) can affect how much time Steller sea lions spend on land. The number and location of haul-out sites depend on factors like food availability, predator numbers, tide levels, and weather.
Steller sea lions are skilled and opportunistic predators, eating many types of fish and squid. Important parts of their diet include walleye pollock, Atka mackerel, halibut, herring, capelin, flatfish, Pacific cod, rockfish, sculpins, Pacific salmon, sand lance, and squid and octopus. They often eat schooling fish and hunt near the shore and on the continental shelf. They gather in groups of up to twelve where food is plentiful. They are sometimes found near fishing boats, eating leftover fish from the boats. Most information about their hunting habits comes from studies near Alaska; less is known about their behavior in other areas.
The food Steller sea lions eat changes with the seasons and location. As opportunistic predators, they focus on the most common prey in their area. In addition to the ocean, they sometimes enter estuaries and eat brackish-water fish like sturgeon. Rarely, they hunt other animals, such as northern fur seals, ringed seals, harbor seals, and sea otter pups. Evidence suggests that the variety of animals they eat has increased over time.
Steller sea lions are top predators in their environment but are hunted by killer whales. Shark species, such as sleepers and great whites, may also prey on young sea lions.
Behavior and life history
In the spring, mature male sea lions gather on traditional breeding areas, usually on beaches of isolated islands. Larger, older males claim and defend specific areas on these sites. A week later, adult females arrive, sometimes with young, non-reproductive offspring, and form loose groups across the breeding area. Like other otariids, Steller sea lions are polygynous, meaning males have multiple mates. However, unlike some species, they do not force females into harems but instead control areas where females can move freely. Steller sea lions use aquatic, partially aquatic, and land-based territories. Males with partially aquatic areas are most successful in defending them. Territory boundaries are marked by natural features like rocks or ridges, and these areas can remain stable for about 60 days. Though male sea lions usually tolerate pups, one male on Medny Island in Russia was recorded killing and eating several pups, the first known case of cannibalism in this species. Researchers do not know the reason for this behavior, but the male may have had an unusual personality.
Pregnant females give birth shortly after arriving on breeding sites. Mating usually happens one to two weeks after birth, but the fertilized egg does not implant in the uterus until fall. The fertilized egg may stay in a waiting state for up to three months before implanting and developing. Twins are rare. After nursing their pups for about a week, females begin longer foraging trips, leaving their pups behind. Eventually, both mother and pup leave the breeding area together. This pattern of care is common in otariids. As pups grow older, mothers spend more time foraging at sea. This continues until pups reach a weight and energy level that allows them to eat independently. A study by the University of California, Santa Cruz found that male pups typically consume more milk than females. This may be due to the size differences common in otariids. Male sea lions fast during the breeding season, often avoiding water from mid-May to August, when breeding sites begin to break apart and animals leave for the open ocean.
The age at which pups stop nursing varies greatly; some stay with their mothers for up to four years. Rarely, mothers have been seen feeding their own daughters while the daughters care for their newborns. A 1983 study at Año Nuevo found that the time females spend with their pups depends on the pup's growing energy needs and how efficiently the pup suckles. On average, females spend 21 hours on land and 36 hours at sea with their pups. As pups age, females spend more time at sea. At six weeks after birth, the mother's time at sea decreases by 30 percent. There is no connection between the pup's activity or physical movement and their suckling time, age, or sex. Studies using labeled water showed that pups who drink more milk are heavier. These findings suggest that the time females spend with their pups depends on the pup's ability to suckle and their energy needs.
In the past, low pup survival has been linked to poor nutrition in females, which contributed to the decline of Steller sea lions in Alaska.
Steller sea lions are the largest of the eared seals and swim as fast as smaller California sea lions. Their speed during gliding has been measured at 2.9–3.4 meters or 1.2–1.5 body lengths per second, close to the optimal speed for California sea lions. A 2007 study found that most of the force used to swim comes from the forward movement of the front flippers. Earlier research suggested that force was generated during the outward motion or final drag phase of the flippers, but the 2007 study found little force during those phases. Sea lions adjust their swimming performance by changing the duration and intensity of movements without altering the order of actions. Steller sea lions' ability to turn is similar to other eared seals, better than whales, and worse than many fish.
To dive for long periods, Steller sea lions hold their breath, slow their heart rate, and narrow blood vessels in their limbs. These adaptations help them store oxygen and forage efficiently. Their thick blubber and fur also keep them warm during dives.
In a study at the University of British Columbia's Open Water Research Station, trained Steller sea lions from the Vancouver Aquarium were released into the ocean to study their diving behavior. Their dives are more energy-intensive if they make multiple dives in a row. Their ability to dive without oxygen depends on their nutritional state and feeding habits.
Like most otariids, Steller sea lions make sounds on land. Mature males use a range of vocalizations, such as growls, snorts, and hisses, to warn others during territorial disputes. Both males and females also make underwater sounds, like clicks and barks. These sounds are used for social communication. Sonogram readings show that Steller sea lions produce short, low-frequency pulses underwater, similar to the male "belching" sounds made on land. These underwater sounds occur about 20–30 times per second.
Vocalizations are important for mother-pup pairs, as mothers must locate their pups in crowded breeding areas after foraging. Mothers and pups use unique calls, like names, to identify each other. Their sounds are similar to sheep bleats and loud bellows.
Because Steller sea lions differ in size between males and females, their hearing sensitivity also differs. Females may have better hearing for high-frequency calls, possibly to hear their pups. Their hearing range also allows them to detect underwater calls from one of their main predators, the killer whale.
Interactions with humans
Steller sea lions were hunted by ancient people for food, clothing, and other goods wherever their habitat overlapped with human communities. In addition to food and clothing, their skin was used to cover boats called baidarkas and kayaks. Today, some Native communities in Alaska still hunt a small number of sea lions, usually fewer than 300, for subsistence.
Historically, Steller sea lions had little commercial value. For example, in the 19th century, their whiskers were sold for one penny each to be used as cleaners for tobacco pipes.
Sometimes, fishermen intentionally kill Steller sea lions because they are seen as competitors for fish. Killing sea lions is illegal in the United States and Russia. However, in Japan, a limited number are still harvested each year, supposedly to protect fish populations. In Canada, commercial hunting is not allowed, but some First Nations communities may be granted permits to hunt a small number of sea lions. Limited hunting may also occur if animals are harming fish farms.
In recent years, Steller sea lions have been spotted in the Columbia River estuary, where they eat white sturgeon, several types of salmon, and rainbow trout. Some of these fish are protected under the U.S. Endangered Species Act. Steller sea lions are present in the Columbia River nearly all year, except during early summer, and they swim as far upstream as Bonneville Dam. Although they are not as common as California sea lions, their presence concerns fish managers because Steller sea lions are protected by the Marine Mammal Protection Act. Managers are required to use non-harmful methods, such as rubber bullets or bullhorns, to deter them. The public is not allowed to interfere with sea lions because it can stress the animals and disrupt their behavior. Additionally, Steller sea lions are large and can be aggressive, so disturbing them is illegal and may result in fines, court appearances, or jail time.
In Hokkaido, Japan, Steller sea lion meat is used in curry and sold as a souvenir, often in cans. In Rausu, their meat is used in local dishes.
The populations of eastern and Asian Steller sea lions appear stable, but the western population, especially near the Aleutian Islands, has declined by 70–80% since the 1970s. In 1997, the western population was listed as endangered, and the eastern population was listed as threatened under the U.S. Endangered Species Act. Since then, the species has been studied extensively and has sparked political and scientific debate in Alaska.
One possible reason for the decline is the overfishing of fish such as Alaska pollock and herring in the Gulf of Alaska. This has led to a theory called the "junk-food hypothesis," which suggests that sea lions eat less nutritious fish like pollock and flounder instead of fatty fish like herring and capelin, making it harder for them to store fat. Other theories include increased predation by orcas and sharks, changes in prey availability due to climate shifts, disease, or contaminants, and shooting by fishermen. The decline is likely caused by multiple connected factors that are still being studied.
Another theory suggests that the lack of food causes stress, which affects the population. Female sea lions that do not get enough nutrients may not complete their pregnancies.
In October 2013, the eastern Steller sea lion was removed from the U.S. Endangered Species List after its population increased significantly in recent years.