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Aquatic Respiration
Chemistry of Oxygen Solubility
Data Interpretation
Diel Temperature Variation in Lakes
Effect of pH
Effect of Photosynthesis and Respiration on Aquatic Chemistry
Fish Stocking Decisions
Heat Budgets of Lakes
Increased Conductivity
Modeling Water Quality
Properties of Water
Rain Storms, Landuse and Lake Turbidity
Sustaining Life Under
the Ice
Thermal Stratification
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  Investigating Fish Stocking Decisions

The issue of stocking a lake can be volatile. Anglers, local residents, and business owners may believe that a certain lake should be stocked with lake trout. After all, it may improve fishing in the lake, which can have a positive effect on the local economy. Like many issues faced by natural resources personnel, the issue of stocking is not that clear-cut. Before stocking a lake, natural resources personnel must determine if lake trout can succeed in a given lake. Like all animals, lake trout depend on specific environmental conditions for their survival. In this lesson, you will decide whether the temperatures and oxygen concentrations of Ice Lake can support lake trout.

Knowledge Base
Consider what you know about the needs of lake trout. What water qualities are necessary for lake trout to survive in a given lake? What factors need to be considered before stocking a lake? What social and economic issues are related to stocking? What can happen if a lake is "incorrectly" stocked?

Lake trout require specific environmental conditions for their survival. They seek out water temperatures of about 9–13° C during the summer. In the cool, relatively unproductive lakes that lake trout commonly inhabit, oxygen concentrations are near saturation. If summer temperatures exceed approximately 20° C or if oxygen concentrations fall below about 8 mg/l conditions are not ideal for the survival of adult lake trout.

Experimental Design
As a Minnesota Department of Natural Resources fisheries biologist you need to determine whether or not to stock Ice Lake with lake trout. Your decision will be based primarily on dissolved oxygen (DO) and temperature - two very important water quality measures for fish survival.

Think about how to efficiently approach answering the question of whether or not to stock lake trout. You know you have the temperature and DO data available from WOW. How many sampling times and different days do you feel you will have to analyze? How will you organize and analyze this data so you can make your decision?

Data Collection
Make sure you have an organized way to record your DO and temperature data before you visit the "Data" area of the WOW website.

Data Management and Analysis
You may want to construct a graph(s) of temperature and oxygen concentrations in Ice Lake. If you do, be sure to label axes and include titles and legends on your graphs.

Interpretation of Results
Explore the lake survey data of the Minnesota Department of Natural Resources ( Consider the common physical characteristics of Clearwater, Greenwood, Saganaga, and Seagull Lakes (all in Cook County). These lakes all support healthy lake trout populations. Lake trout lakes are most common in Northeastern Minnesota, but even there lake trout are near the southern edge of their range.

According to your data, can lake trout succeed in Ice Lake? How would you explain your reasoning to area anglers?

Reporting Results
You need to make a presentation to the DNR and concerned local citizens about the ability of lake trout to survive in Ice Lake. The data and your analysis should provide most of the information you need to complete the report. Your teacher will specify the format: a written paper, an oral presentation, a poster, or multi-media presentation. Be prepared to answer any questions about your research findings.


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date last updated: Friday October 08 2004