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Method
Students will explore the methods biologists use to study fish populations through a simulation
activity.
Objectives:
Students will be able to:
- Learn why monitoring fish populations is important.
- Be able to describe three methods scientists use to sample fish.
Materials Needed:
Background:
Fisheries biologists have a variety of methods they use to study different species of fish in
different areas. The population estimates they obtain are used to set fishing quotas and
harvest regulations. The goal of fisheries research is to allow the largest harvest possible
while assuring enough fish escape and spawn to maintain the population.
The following are some research techniques used by fisheries biologists:
Aerial surveys:
Biologists fly over a river system, estimate the number of fish present, and extrapolate the total
number of fish spawning in the river from this number. This is cost-effective way
to sample many rivers in a large area. The draw-back is that this method is very inaccurate
and weather dependant.
Counting Tower:
This method is used in clear, narrow, and shallow spawning streams. An observer sits in a
tower and counts the fish as they pass. This is a much more accurate counting system compared to aerial surveys.
Equipment costs are low.
Weir:
This method is also used in clear, fairly narrow and shallow spawning streams. Floating panels are
placed across a spawning stream which allow fish to swim downstream, but block their upstream passage.
The center of the weir has a chute with a gated holding pen.
A biologist counts and identifies the species and sex of the fish as they pass through the gate.
This method is very accurate but costs more for salaries and equipment.
Sonar:
This method is useful in larger muddier river systems where you can't actually see the passing
fish.The sonar equipment is extremely expensive.
Preparation:
Set up the overhead projector and draw two parallel lines on it to represent a river. Cut out
paper masks to represent each research method.
Procedure
Turn on the projector and place some beans in the river drawing to indicate spawning fish. Tell the students
that fisheries biologists monitor the numbers of salmon spawning in streams across the state each year.
Having a good idea of the total populations of spawning fish helps biologists predict the numbers of new fish that might
be expected to hatch and return in subsequent years.
Tell the students that they have been given the task of estimating how many fish are spawning in all the rivers in a big portion of the state, and that they only have a few days to do it. Have them brainstorm methods they could use to accomplish this task. When a student suggests using aerial surveys, discuss the pros and cons of this research method. Put some torn pieces of paper over the
beans to indicate partial cloud cover, and discuss weather and visibility problems associated with aerial surveys.
Now, tell the students that you need to have a more accurate count of how many fish are
spawning in a clear, narrow, and shallow spawning stream. After sharing and discussing
ideas, demonstrate how a counting tower and weir works by putting the paper cut-outs on the
overhead projector.
Next, tell the students that you need to have an accurate count of how many fish are traveling
in
a large and muddy river system. Discuss ideas on how to accomplish this. Use the projector
and beans to demonstrate how sonar works.
Wrap up by discussing the pros and cons of each research method.
Extensions:
-
Follow up with the Fisheries Management activity. Have the students develop a hypothetical
management plan for their area using these research methods to study their fish populations.
-
Invite a fishery biologist into your class to discuss their work.
-
Build a scale model of some of these research methods.
Text and graphics by USFWS staff
Last modified 4, March, 2009
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