Mystery in Alaska

Why Have All the Sea Lions Gone?

Co Authors:	Frank J. Dinan Department of Chemistry & Biochemistry Canisius College dinan@canisius.edu Thomas R. Stabler Department of Chemistry and Biochemistry Canisius College stabler@canisius.edu Renee Larson Biology Department Canisius College
Abstract:	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.
Objectives:	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.

Teaching Notes

Case teaching notes are intended to help teachers select and adopt a case. They typically include a summary of the case, teaching objectives, information about the intended audience and how the case may be taught, a case analysis or answer key, and references.

Download Teaching Notes

Answer Key

Answer keys provide answers to the questions posed in a case study. Since these questions are intended to be answered by students and are often graded, answer keys are password-protected and access to them is limited to registered instructors.

Name:
Email:
Department:
Institution:
City State:
Comments:
	Enter Security Code:

Username
Password

	Register \| Lost Your Password?