Steller sea lion

May 13, 2011, 10:00 am
Content Cover Image

Also Northern sea lion, Sea king, Stellar sea lion, and Steller's sea lion. The Steller Sea Lion (Scientific name: Eumetopias jubatus) is one of 16 species of marine mammals in the family of Eared seals which include sea lions and fur seals. Together with the families of true seals and Walruses, Eared seals form the group of marine mammals known as pinnipeds.

The Steller Sea Lion is found on the North Pacific coasts. Steller's Sea Lions are not often found in captivity. This is due to their belligerent nature. They are thought to be dangerous to have in zoos, and untrainable for circuses.

Eared seals differ from the true seals in having small external earflaps and hind flippers that can be turned to face forwards. Together with strong front flippers, this gives them extra mobility on land and an adult fur seal can move extremely fast across the beach if it has to. They also use their front flippers for swimming, whereas true seals use their hind flippers.

The world population of Steller's sea lions has been undergoing a mysterious decline; since 1980, numbers have dropped from over 300,000 individuals to fewer than 100,000. Despite this well-documented and worrying decline, the causes are still being debated.

 

caption Stellar Sea Lion. Source: Tom Early/BioLib/Encyclopedia of Life

 

 Conservation Status

 

Scientific Classification

Kingdom: Anamalia (Animals)
Phylum:--- Chordata
Class:------ Mammalia (Mammals)
Order:-------- Carnivora (Carnivores)
Family:-------- Otariidae (Eared Seals)
Genus:----------Eumetopias
Species:------------ Eumetopias jubatus (Schreber, 1776)

Physical Description

Steller's sea lion is the largest of the eared seals (members of the family Otariidae), a group that includes fur seals and sea lions.

The impressive adult males are two and a half times the size of the females; they have large necks, and shoulders covered with a mane of long, coarse hair.  The length of the average male is 282 centimeters, while the length of the average female is only 228 centimeters. The weight of the average male is 566 kilograms, while the weight of the average female is only 263 kilograms.

Both sexes are a a yellowish buff color, and a coat of short coarse hair that lacks a distinct undercoat, whilst pups are originally black, moulting to the adult coat after three to four months.

Newborn pups are about 100 centimeters long, weigh 16-23 kilograms, and have a thick, dark brown pelage that molts to lighter after six months. After 2-3 years their color changes again, this time to the adult color.

The common name of the species comes from the German naturalist who first described these seals in 1741, George Wilhelm Steller.

Reproduction

Steller's sea lions breed in massive, noisy rookeries common to most eared seals.

The males arrive at the haul-out sites in spring and establish their territory on the limited space of the beach. Male Steller Sea Lions (bulls) are extremely aggressive and territorial. They are large animals and often fight for mates. They do this by throwing their huge bodies up against one another and biting. The strongest bull is the male with the largest harem. They usually do not feed throughout the breeding season, as they cannot afford to relinquish their hard-won position.

Females arrive in mid-May to late June and give birth to a single pup; only four days later the female is ready to mate again and the most successful males will aggressively guard, and mate with, up to 30 females.

Sixty to sixty seven percent of all females are impregnated every year.

Implantation of the fertilized egg is delayed for three months giving Steller's Sea Lion a twelve month gestation period.

Around nine days after giving birth the female will resume foraging trips to the sea. The new pups are fed by their mother for a minimum of three months, but a mother may continue to suckle her young for up to two or three years. 

The pups are able to swim after one month, and can catch food after approximately three months.

The breeding season draws to an end in early July but these sea lions maintain their social lifestyle, being commonly seen on shore throughout the year in groups of tens to hundreds of animals.

The age of maturity is 3-6 years for females, and 3-7 years for males, but males are unlikely to breed successfully until their eighth to tenth year due to the fierce competition at rookeries.

Lifespan/Longevity

On average, females live 30 years. Males, subject to injury in violent encounters with other males, typically live only 18 years.

Behavior

Steller's Sea Lions are not often found in captivity. This is due to their belligerent nature. They are thought to be dangerous to have in zoos, and untrainable for circuses.

They acquire their food by diving into the ocean. The deepest recorded dive by one of these huge beasts was 120-160 yards. This particular animal was found caught in a net, so this number could be slightly inaccurate.

Sea Lions are also known for their "sun bathing" (basking). They are most often viewed by boaters and tourists as they lay in the sunshine on the rocks.

Studies are now being done on the communication of Steller Sea Lions. They are believed to make certain clicking noises when hunting and swimming and can produce a low roaring sound similar to that of a lion.

Distribution

Steller sea lions (Eumetopias jubatus) live in the North Pacific Ocean and consist of two distinct populations separated at 144° W longitude (near Cape Suckling, just east of Prince William Sound, Alaska). The National Marine Fisheries Service listed the Steller sea lion as threatened rangewide under the Endangered Species Act in April 1990. The decline has continued for the western population in Alaska, which was declared endangered in 1997. The eastern population remains listed as threatened. Source: NOAA

Steller's Sea Lion is found on the North Pacific coasts. The countries included are Russia, Japan, Canada, and part of the United States. More specifically it is found from the sea of Japan at 43 degrees N, north to the Pacific rim at 66 degrees N, and then south down to the North American Pacific coast to San Miguel Island at 34 degrees N.

Habitat

Found in the cool waters of the northern Pacific Ocean, hauling out on beaches and rocky coastline.

Food Habits

Steller's Sea Lions are known to be true carnivores. They feed on both commercial and non-commercial fish, walleye pollock ([[Theragra chalcogramma]]), Atka mackerel ([[Pleurogrammus monopterygius]]) and Pacific herring ([[Clupea harengus]]), and also on cephalopods (octopus and squid). Commercially exploited walleye pollack is an important part of their diet. This selective diet is a major cause of the Sea Lions' diminishing population, due to competition with humans for this favorite. Stellar sea lions are known to prey of other pinnipeds at times, including Harbor seals, Bearded seals, ringed seals, Spotted seals and young Pribilof fur seals.

Conservation Status

These animals are a threatened species. The Steller sea lion was placed on the Endangered Species list in 1990. The Western Alaskan population was reclassified as Endangered in April 1997.

The world population of Steller's sea lions has been undergoing a mysterious decline; since 1980, numbers have dropped from over 300,000 individuals to fewer than 100,000. Despite this well-documented and worrying decline, the causes are still being debated; various hypotheses cite pollution, bycatch, parasites and disease, rookery disturbance and predation by killer whales. Research into dietary factors have revealed that Steller's sea lions in the northeast Pacific have suffered a decrease in the diversity and energy content of their diet since the mid 1970s, corresponding to changes in fish species available due to natural climatic changes. A diet dominated by low energy fish (such as pollock) can cause sea lions to lose condition, and can result in reduced pregnancy rates and increased susceptibility to disease or predation. This may be one of the major causes of the population decline. 

Thousands were once killed each year in the nets of fishermen in Alaska. Changes in fishing techniques and gear in 1984 reduced the number killed.

An unknown number are shot each year during commercial fishing because this species is seen as a pest to the industry. The Steller Sea Lion eats a variety of commercial fish. The intense commercial fishing of pollock, a major food source, has decreased the Alaskan population from 175,000 animals in 1962 to 40,000 in 1992. They are also caught in plastic trash, which usually leads to death. This species is also hunted on a small scale for subsistence and for trade.

The Commonwealth of Independent States (CIS) is proposing to add the species to the "red" species list. 

The United States National Marine Fisheries Service (NOAA) has established a number of protection measures relating to fishing bans around major rookeries and feeding areas, in an attempt to slow the decline in population numbers. A consortium of North Pacific Universities is carrying out ongoing research into the causes of the perplexing population decline. The battle to understand the factors involved in the decline in Steller's sea lion numbers may also provide better understanding of the complex marine ecosystem and the effects of fish stock changes (by both natural and man-made causes) on other marine mammals and sea birds.

Classified as Endangered (EN) on the IUCN Red List 2007. 

Economic Importance for Humans

Profit from meat, hides, and blubber. Ecotourism benefits greatly from sea lions because humans think that they are "cute".

They are a primary source of food for inhabitants of the Aleutian Islands. Their skins were used for boat coverings, clothing, and their whiskers for cleaning of Chinese opium pipes. Since the passage of the Marine Mammal Protection Act (1972), the use of these sea lions has declined.

Eats many commercial fish that humans exploit.

Further Reading 

  1. Eumetopias jubatus (Schreber, 1776) Encyclopedia of Life (accessed April 7, 2009)
  2. Eumetopias jubatus, Gonder, M., 2000, Animal Diversity Web (accessed April 9, 2009)
  3. Steller sea lion, Seal Conservation Society (accessed April 9, 2009)
  4. The Pinnipeds: Seals, Sea Lions, and Walruses, Marianne Riedman, University of California Press, 1991 ISBN: 0520064984 
  5. Encyclopedia of Marine Mammals, Bernd Wursig, Academic Press, 2002 ISBN: 0125513402
  6. Marine Mammal Research: Conservation beyond Crisis, edited by John E. Reynolds III, William F. Perrin, Randall R. Reeves, Suzanne Montgomery and Timothy J. Ragen, Johns Hopkins University Press, 2005 ISBN: 0801882559
  7. Walker's Mammals of the World, Ronald M. Nowak, Johns Hopkins University Press, 1999 ISBN: 0801857899 
  8. Steller sea lion, MarineBio.org (accessed April 9, 2009)
Glossary

Citation

Life, E. (2011). Steller sea lion. Retrieved from http://www.eoearth.org/view/article/156250

0 Comments

To add a comment, please Log In.