Mystery in Alaska

Why Have All the Sea Lions Gone?

By Frank J. Dinan, Thomas R. Stabler, Renee Larson

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.

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Date Posted

11/03/2009

Overview

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

Subject Headings

Biology (General)

Chemistry (General)

Ecology

Environmental Science

EDUCATIONAL LEVEL

High school, Undergraduate lower division

FORMAT

PDF

TOPICAL AREAS

Scientific method

LANGUAGE

English

TYPE/METHODS

Interrupted