Steller Sea Lion, Eumetopias jubatus
The Steller sea lion (Eumetopias jubatus) is a species that can be found in the northern Pacific. It is also known as Steller’s sea lion or the northern sea lion and is the only member of its genus, Eumetopias. Its range stretches from Gulf of Alaska to the Sea of Okhotsk and the Kuril Islands in Russia. Its southern range includes Año Nuevo Island near California. Although it once bred as far south as the Channel Islands, it has not been seen there since the 1980’s. Traditionally, populations within this range are separated into different populations known as the eastern and western stocks. It is thought that some populations in Russia hold Asian sea lions and Russian sea lions. This species was named after the naturalist who discovered it in 1741, Georg Wilhelm Steller.
The Steller sea lion is larger than most species in the Pinniped group, which hold walruses and seals. Both males and females grow rapidly in the first five years of life, and males typically continue to grow until eight years of age. Females reach an average body length of 8.2 feet, while males are slightly larger at an average of 9.8 feet. Females weigh between 530 and 770 pounds, while males are significantly heaver weighing between 990 and 2,500 pounds. Males differ in appearance from females in many ways, with thicker necks, larger foreheads, and thicker fur. Adults are typically light yellow to reddish tan in color, while pups are nearly black in color.
The mating season for the Steller sea lion begins in late May, when populations will move further south to breed. Males return to previously used rookeries located on isolated beaches. Older males will mark territories in the rookeries before females arrive about one week later. Occasionally, young that are not able to reproduce will join the females at the rookery. Unlike similar species, males do not force females to stay within their territory, instead letting the females wander wherever they please. Females will mate with many males, which is typical to seals. Territories are separated by natural structures like rocks and water, and those that hold some water are more easily defended and held.
The rookeries are used for rearing young and for giving birth. Females are typically pregnant when arriving at the rookery, and give birth after about one week once there. Breeding occurs shortly after this birth, but females store the sperm until fall in a process known as delayed implantation. One pup is typically produced, although twins do occur. Females will leave periodically to hunt for food during the pup’s first week of life, returning to nurse often. As time goes by, females will leave for longer periods of time, eventually returning to the normal range with the pup. Males do not leave their territories to hunt for food at any point while residing at the rookery, going without food from the months of May to August. Weaning typically occurs at four years of age, but older individuals have been known to continue nursing. Some females have even been recorded nursing from mothers while rearing their own pups.
The diet of the Steller sea lion consists of many types of cephalopods and fish. Some important species that comprise its diet include the Atka mackerel, the Pacific cod, Alaska pollock, and cephalopods like squid. These sea lions prefer schooling fish, but they have been known to eat sea otter pups, northern fur seals, and harbor seals. Because of their large size, they are not often hunted, but they become prey to killer whales and white sharks.
In prehistoric times, the Steller sea lion was an important part of people’s lives in every area of its range. It provided a good source of clothing and food, as well as skins used to line kayaks and baidarkas. In some Alaskan communities, this species is still hunted today, under an order from the government of up to three hundred seals per year. The Steller sea lion has rarely been hunted for commercial purposes, but in the nineteenth century, its whiskers could be sold for a penny each and were used for cleaning tobacco pipes. In modern times, the Steller sea lion is not hunted for any reason, but it is sometimes killed by fishermen to prevent competition for fish stocks. This practice is outlawed in Russia, Canada, and the United Sates, but is still used in Japan as means of protecting fisheries.
Although the primary diet of the Steller sea lion does not contain freshwater fish, it has more recently been spotted moving into the Columbia River during late winter and spring to feed on rainbow trout, white sturgeon, and a few salmon species. Some of these fish species are endangered, so the agencies involved with protected fish have been forced to get involved. Non-violent measures are used to coerce the sea lions away from the fish, including noisemakers and rubber bullets.
Asian and eastern sea lion populations have been found to be stable, but the population of western sea lions, particularly those found near the Aleutian Islands, have declined by seventy to eighty percent since the 1970’s. Because of this, the western populations were classified as “Endangered” and the eastern stock classified as “Threatened” in the Endangered Species Act. It is thought that one cause for this rapid decline might be overfishing of vital species including herring and Alaska pollock. These “lighter” species have become preferred by the sea lions, which once consumed mainly fatty fish like capelin, so storing fat is becoming increasingly more difficult. Another possible cause of the decline is thought to be increased hunting by orcas, which are moving into a different range due to climate changes. More studies are needed to understand exactly why the population numbers of the western sea lions have declined so much. Currently, the Steller sea lion appears on the IUCN Red List with a conservation status of “Near Threatened.”
Image Caption: Steller Sea Lions Eumetopias jubatus, hauled out on rocks in the Southern Gulf Islands of British Columbia. Credit: Yummifruitbat/Wikipedia (CC BY-SA 2.5)