Name _______________________________________ Date _______________ Per ___
Fish Population Estimates
What is a population?
_________________________________________________________
Formula for estimating the size of a fish population:
N = M · C
R
Formula for % error:
N = estimated population size
measured value – actual value
actual value
M = # of fish marked and released in first
sample
Example: 35 – 42
42
x 100
x 100 = 16.6 % error
C = # of fish (total) in second sample
R = # of marked fish in second sample
* % error = measures the % inaccuracy of
experimental results
Repeat the experiment using different size samples to see what effect that has on your
results. Using the formula above, determine the % error for each sample collection.
M
C
R
N
% error
Pop Size
Prediction
#1
Pop Size
Prediction
#2
Pop Size
Prediction
#3
Conclusions:
Pretend that you are the fishery biologist in charge of estimating the
population of fish in Craig, Montana. Your goal is to estimate as close as you
can to the actual # of fish in the population. How will you do this…what kind
of samples will you try and collect (hint: think size!) Why? What did you
learn about how sample size affects the accuracy of your estimates?