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Mystery in Alaska

Why Have All the Sea Lions Gone?

Co Authors:

Frank J. Dinan
Department of Chemistry & Biochemistry
Canisius College

Thomas R. Stabler
Department of Chemistry and Biochemistry
Canisius College

Renee Larson
Biology Department
Canisius College


This interrupted case study highlights the importance of energy considerations within food chains by examining the population decline of Steller sea lions along the western Alaskan coast. A ban on commercial fishing of pollock in the 1970s caused a shift in the availability of the sea lions’ prey. Sea lions have an overall negative net energy balance when consuming pollock, but an overall positive net energy balance when consuming the fattier, easier to catch and digest herring. Could an increase in pollock and a decrease in herring be responsible for sea lion decline? Originally designed for an environmental science course, the case could easily be adapted for an introductory level chemistry or biology course by stressing quantitative, energy balance aspects.

  • Infer that the problem with the Steller population is due to the nutritional and energy needs of these sea lions.
  • Interpret data from graphs and other visuals and apply them to a real-life situation.
  • Recognize the special vulnerability of sea lion pups and the key role they play in maintaining the population.
  • Do calculations that allow them to determine the contribution that fats, proteins, and carbohydrates make to sea lions’ diets when eating pollock and herring.
  • Recognize the importance of proper energy balances within elements of a food chain.
  • Explain why the Western stock of Steller sea lions is decreasing while the Eastern stock is increasing.
Keywords: Sea lion; marine mammal; herring; pollock; fish; population ecology; ecological energetics; food chain; predation; predator-prey; Alaska; experimental design
Topical Area: Scientific method
Educational Level: High school, Undergraduate lower division
Formats: PDF
Type/Method: Interrupted
Language: English
Subject Headings: Environmental Science   Ecology   Biology (General)   Chemistry (General)  
Date Posted: 11/03/09
Date Modified: N/A
Copyright: Copyright held by the National Center for Case Study Teaching in Science, University at Buffalo, State University of New York. Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work.

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Thanks for a great case. This is really useful for IB biology when looking at energy in the food chain.

Christian Moore


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