Case Study: Steller Sea Lions
What Happened?
Overview:
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.
Objectives:
The students will be able to…- …relate the steps of the scientific method to real research and conservation issues.
- …understand and explain that interactions in an ecosystem are complex.
- …understand that multiple variables can affect the survival of a species.
Materials:
- Research materials on Steller sea lions
Procedure:
- Discuss the importance of marine mammals in arctic ecosystems. What role do they play?
- Research and discuss the needs of Steller Sea Lions.
- 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.
- Conduct a scientific symposium. Have students share their findings with the class. What consensus or connections can be made?
- 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.
More … - 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.
More … - Predation
- 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.
More … - 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.
More … - Disease
- The Steller sea lion population is being reduced by diseases that may
result in mortality or
reduced reproductive output.
More… - Contaminants
- Contaminants from either local or distant sources have had detrimental
physical impacts on Steller sea lions leading to increased mortality or
reduced reproductive output.
More …
*The information in this listing comes directly from the Alaska Fisheries Science Center at http://www.afsc.noaa.gov/stellers/hypotheses.htm
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