Case Study: Steller Sea Lions

What Happened?


Students will research and discuss the various factors affecting Steller sea lion populations and will discuss the processes and methods scientists use to gather and analyze data.


The students will be able to…



  1. Discuss the importance of marine mammals in arctic ecosystems. What role do they play?
  2. Research and discuss the needs of Steller Sea Lions.
  3. Analyze the different hypotheses scientists are currently investigating to discover the reason behind the Steller Sea Lion population decline. Assign groups of students to investigate each one.
  4. Conduct a scientific symposium. Have students share their findings with the class. What consensus or connections can be made?
  5. What conclusions can be made? What actions are recommended for the future?

*Hypotheses Listing:

Fisheries Competition
Commercial fisheries potentially cause or contribute to nutritional stress in the western stock of Steller sea lions by reducing either the abundance of prey at scales relevant to foraging sea lions or by disturbing prey patches so as to reduce their availability. In turn, nutritional stress is manifested in the population as increased mortality or lowered reproductive output.
Environmental Change
Environmental conditions in areas inhabited by Steller sea lions may have changed since the 1970s in ways that reduced the availability of prey for Steller sea lions and precipitated nutritional stress. The changes may have either reduced the abundance of important prey items or altered their distributions.
Predation of Steller sea lions by killer whales and sharks has increased as a function of a) their increased population size, b) their increased per capita consumption, or c) remained constant over time, but with increasing effects as the Steller sea lion population has diminished over time.
Anthropogenic Effects
One or more sources of anthropogenic activity, including incidental mortality (e.g. entanglement), direct mortality (e.g. shooting), commercial harvesting, subsistence harvesting, and harassment have contributed to the decline in the Steller sea lion population. Such effects would include both those over the past decades since the decline began and those that may be ongoing.
The Steller sea lion population is being reduced by diseases that may result in mortality or
reduced reproductive output.
Contaminants from either local or distant sources have had detrimental physical impacts on Steller sea lions leading to increased mortality or reduced reproductive output.

*The information in this listing comes directly from the Alaska Fisheries Science Center at

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