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Steller Sea Lions

About AquaFacts: AquaFacts are a resource for students who are looking for information on the animals at the Aquarium or other Aquarium-related topics. Here, we’ve compiled some of the most frequently asked questions that we’ve received about Steller sea lions. The answers come from our biologists and from reputable sources that we reference at the end of this page. If you have a question about Steller sea lions that’s not addressed in this page or the references below, please feel free to email our librarian.

Steller Sea Lions Credit: Andrew Trites

Questions & Answers

Where do Steller sea lions live?

Steller sea lions range throughout the Pacific Rim (from northern California to Northern Honshu in Japan, and to the Bering Strait). About 70 percent of the Steller sea lion population resides in Alaska. Steller sea lions are highly gregarious and they use traditional haul out sites (an area used for resting) and rookeries (an area used for breeding and rearing young) on remote and exposed islands. These sites can be rock shelves, ledges, boulders, and gravel or sand beaches.

stellers-on-rock.jpgstellers-swimming.jpg

 

 




Photos: Andrew Trites

What do Steller sea lions eat?

Adult Steller sea lions eat a wide variety of fishes, including Pacific herring, pollock, salmon, cod, and rockfishes. They also eat octopus and some squids. On average, an adult Steller sea lion eats about six percent of its body weight each day.

Who eats Steller sea lions?

The main predators of Steller sea lions are killer whales, sharks and humans.

How do Steller sea lions reproduce?

Steller sea lions mate and give birth on land. Births occur mid-May to mid-July and peak in June. In May, dominant males (nine years and older) establish their breeding territories on rookeries, and maintain them for approximately 40 days without eating. During this time, the males establish a group of females (harem) and mate with many females on their territories, demonstrating their polygamous nature. Mating occurs soon after the birth of the previous year's pups. The pups are fed on their mother's milk, and they enter the water at four to six weeks of age. Some pups will nurse for 1 to 3 years, but most are believed to wean before they are 1 year of age. Females give birth to one pup only, and may not give birth every year. Pups are able to crawl and swim soon after birth. Females accept only their pups, recognizing their pup's vocal and olfactory cues. Pups will approach other females, but are often bitten or thrown by females who have their own pups. Males defend territories for an average of 2 years. Pups are sometimes killed or injured from: a storm washing them away from a rookery; by adults tossing, biting, or crushing them; or by abandonment and disease.

Are Steller sea lions always in the water?

Steller sea lions are mammals, so they need to come to the surface to breathe air. They spend a portion of their time on the land and venture out in the water to hunt for food. Steller sea lions appear to prefer the coastal shelf region within 45 km of the shore, although they can be found over 100 km from the shore in waters exceeding 2,000 m deep. They do not migrate like some pinnipeds, but they do move seasonally to different feeding and resting areas.

Are Steller sea lions endangered?

Since 1980, more than 80 percent of the Steller sea lion population has disappeared, leaving the current wild population with less than 75,000 individuals. In 1990, Steller sea lions were listed as "threatened" under the United States Endangered Species Act. In 1997, the U.S. National Marine Fisheries Service reclassified some populations of Steller sea lions in Alaska as "endangered".

Why are Steller sea lions disappearing?

Scientists are currently researching why Steller sea lion populations are declining. Possible reasons for this include an increase in parasites, disease, predation by killer whales, environmental factors and nutritional stress caused by natural changes in the abundance or quality of key prey species, or by competition with other species, including humans, for food.

What is the Vancouver Aquarium Marine Science Centre doing to help solve the puzzle of the disappearing Steller sea lions?

In 1993 the Aquarium, in partnership with the North Pacific Universities Marine Mammal Research Consortium, began to study the declining population of Steller sea lions. Aquarium researchers have undertaken a combination of field and lab studies with training Steller sea lions for research. The studies emphasize the effects of changes in types of prey on sea lion condition, health and energy balance. You can learn more about the Consortium by visiting their website at www.marinemammal.org

What are the differences between Steller sea lions and harbour seals?

Steller sea lions are larger and have longer flippers. They are very vocal and can be aggressive while defending their territory. Sea lions are also able to support themselves on their front two flippers and can pull their hind flippers under their bodies to walk. Sea lions swim with their front flippers, while seals swim with their hind flippers. Seals have a smaller and sleeker torpedo shaped body, rarely vocalize and tend to be quite shy. Seals do not use their flippers to support their bodies on land and move by sliding or shuffling.

Who are the Steller sea lions at the Aquarium?

Rogue, Willo, Izzy and Ashby



Facts & References

Key Facts

  • Males have a higher mortality rate than females. By ten years of age, there is a 3:1 ratio of females to males.
  • It is very difficult to study Steller sea lions in the wild, because Steller sea lions are extremely skittish, especially in the winter.
  • Stones are commonly found in Steller sea lions' stomach from pebbles to stones up to 12 cm in diameter! Scientists are not certain if these rocks are swallowed by accident or if they serve a useful function. It is speculated that they might help grind up fish, or act as a ballast when diving, or might help ward off hunger pangs when the animals are fasting on shore.
  • The deepest dive recorded for a Steller sea lion is 424 m.

References

  1. Haley, Delphine (Editor), Roger L. Gentry and David E. Withrow. 1986. "Steller Sea Lion," in Marine Mammals. 2nd Edition. Seattle, Pacific Search Press.
  2. Personal communication with The North Pacific Universities Marine Mammal Research Consortium. University of British Columbia: Vancouver, B.C. 2005.

Permission is granted by the Vancouver Aquarium Marine Science Centre for classroom teachers to make copies for non-commercial use. This permission does not extend to copying for promotional purposes, creating new collective works, or resale.

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