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
provide some of the basic physical conditions required to support lake
trout.
Knowledge
Base
Imagine
the Ice Lake Association asked you if lake trout would survive if they
were stocked in Ice Lake. You plan to investigate this question by looking
up summer and winter temperature and oxygen levels in a typical Northeastern
Minnesota lake that does support lake trout.
Before you
begin, consider what you know about the water quality needs of lake
trout.
- 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?
Experimental
Design
A natural
resources technician has provided you with the following information
(see Table 1) for a typical good lake where lake trout flourish.
- Construct
a graph of the concentration of oxygen at each depth for each season
and describe the pattern you see. Now add the temperature data to
the graphs you have constructed.
- Do you
observe declining oxygen levels with increasing temperature in any
of your graphs?
Table
1
Mackinaw Lake
|
|
Winter
|
Summer
|
Depth (m)
|
O2 (mg/l)
|
Temperature (°C)
|
O2 (mg/l)
|
Temperature (°C)
|
0
|
14.0
|
0
|
8.3
|
23
|
2
|
13.5
|
2
|
8.3
|
23
|
4
|
13.0
|
3
|
8.6
|
21
|
6
|
13.0
|
3
|
10.1
|
13
|
8
|
13.0
|
3
|
11.8
|
7
|
10
|
12.8
|
4
|
12.1
|
6
|
12
|
12.7
|
4
|
12.7
|
4
|
14
|
12.7
|
4
|
12.7
|
4
|
16
|
12.7
|
4
|
12.7
|
4
|
18
|
12.7
|
4
|
12.7
|
4
|
The technician
reminds you that lake trout seek out water temperatures of about 913°
C in the summer. 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.
You know
Mackinaw Lake supports lake trout. Now you need to collect data from
Ice Lake to see if it can support lake trout. You will organize and
analyze your data in the same way you have just reviewed the data
from Mackinaw Lake. You need to begin by collecting data from one
sampling period in each of the seasons: spring, summer, and fall.
Data
Collection
Collect
the temperature and DO data for Ice Lake on three different dates.
Record the data in Excel or another spreadsheet program.
Data
Management and Analysis
- Create
graphs for each season showing the temperature and dissolved oxygen
profiles.
Interpretation
of Results
- Based
on the data you have collected, would lake trout succeed in Ice Lake?
Explain how you have arrived at your conclusion.
- If you
found habitat limitations for lake trout because of low oxygen levels
or temperatures that are too high, would you expect these conditions
to persist through times of the year for which you do not have data?
Why or why not?
- Explain
why you would or would not recommend the Ice Lake Association should
attempt to stock lake trout?
Reporting
Results
Turn your
answers and your graphs in to your teacher. Check to see if other groups
got similar results. Your group may be asked to make a presentation
of your findings to the class.
|