Sea lions and fur seals are members of the family of eared seals. They differ from true seals in that they have external ear flaps, a flexible neck, and hind flippers that can be turned forward for walking on land.
The Steller’s sea lion, also known as the northern sea lion, is one of the largest species of sea lion. Males may grow up to 13 feet (4 meters) in length and weigh as much as 2,200 pounds (1,000 kilograms). Females are much smaller, weighing about half as much. The sea lion’s thin coat of short, coarse hair is tawny brown in color.
Steller’s sea lions feed primarily on fishes, squids, octopi, and crustaceans (shellfish such as shrimp and crabs). They hunt in relatively shallow waters, but can make 20–minute dives down to depths of about 650 feet (198 meters).
During the spring breeding season, the sea lions gather in large groups called rookeries. The Aleutian Islands, a chain of volcanic islands curving in an arc about 1,200 miles (1,931 kilometers) west off the Alaska Peninsula, are one of the animals’ principle gathering places.
Males come ashore first and stake out their individual territories, occasionally through fighting. They will try to mate with females that pass through their territory. A dominant male who is able to defend his territory successfully may mate with as many as 30 females over a two–month period.
Females arrive on the islands shortly after the males. They first give birth to pups that had been conceived during the previous breeding season. A few weeks later, they are ready to mate again. The pups remain dependent on their mothers for about a year.
Habitat and current distribution
Steller’s sea lions inhabit the coastal waters around rocky islands. They occasionally come on shore to rest and sun themselves on the beaches. Their range extends from the Aleutian Islands west into the Bering Sea and down the Asian coast to northern Japan, and east into the Gulf of Alaska and down the Canadian and American coasts to southern California.
History and conservation measures
In 1972, the U.S. Congress passed the Marine Mammal Act, which prohibited the hunting of sea lions in U.S. territorial waters. The Steller’s sea lion received further protection in 1990 when it was placed on the Endangered Species List.
The National Marine Fisheries Service has acted to protect breeding spots from shipping and to reduce the number of accidental deaths of sea lions during commercial fishing operations.
Despite these protective measures, the population of Steller’s sea lions continues to decline. Disease, pollution, predators, habitat destruction, and other possible causes have all been investigated. Not one of these has proven conclusive. Scientists remain baffled as to the reason. If the decline continues unchecked, the Steller’s sea lion may soon disappear from most of its range.