INTRODUCTION:

Sometimes the people responsible for managing wildlife populations need to count the total number of animals in a population. It is impossible to count these animals directly, so naturalists use ingenious capture-recapture methods. The method used in this activity is the simplest type of capture-recapture method. If a researcher were trying to determine the deer population, the person might capture a group of deer, tag them, release them, and recapture a group of deer. The total population size would be estimated from the proportion of tagged deer to untagged deer in the recaptured sample.

Example:

In 1970, naturalists wanted to estimate the number of pickerel fish in Dryden Lake in central New York State. They captured 232 pickerel, put a mark on their fins, and returned the fish to the lake. Several weeks later, another sample of 329 pickerel fish were captured. Of this second sample, 16 had marks on their (Chaterjee in Mosteller et al. Statistics by Example: Finding Models).

Let N be the total of pickerel fish in the lake. Because the proportion of marked

fish in the population should be approximately equal to the proportion of marked

fish in the sample, we can write the following equation.

Number of marked pickerel fish in the population		Number of marked pickerel fish in the sample
__________________________	=	__________________________
Total number of pickerel fish in the population (N)		Number of pickerel fish in the sample

Then we can estimate N by solving this equation. Thus in Dryden Lake.

232		16
_____	=	_____
N		329

16N = (232)(329)

N	=	(232)(329)
		_________
		16

(The estimate for the number of pickerel fish in the lake is 4771)

N = 4770.5

INVESTIGATION:

1. Obtain a container from your teacher.
2. Remove a sample from the container.
3. Mark the sample and record the total.
4. Put the marked sample back in the container and mix it up.
5. Take another sample from the container.
6. Count the number of marked specimen and unmarked specimen in this sample. Record this information and the total in the sample.
7. Repeat steps 5 and 6 as many times as the time allows.
8. Input the data for each trial into the following equation and determine the estimated population for each sample.

   Number of marked specimen in the population		Number of marked specimen in the sample
   ______________________	=	_______________________
   N		Total number of specimens in sample

9. Find the mean of all of the N values determined in step 8.
10. Make a scatter-plot graph showing the N value for each trial versus the trial number.
11. Draw a horizontal line on the graph showing the mean of all the N values (step 9 ).
12. Obtain the exact count in your container to check your mean estimate ( Step 9 ).
13. Determine the density in each container

• Calculate the volume of the container
• Determine the density by dividing the actual number of specimen by the volume
• Repeat steps a and b for each container

1. Find the mean density for each container by using the data of the other groups.

ASSIGNMENT:

1. Do the practice exercises attached.
2. Write a lab report to report the results of this investigation

Lab Report:

Purpose: A paragraph explaining the reason for doing the investigation.

Procedure: An explanation of how the investigation was done.

Data: A copy of all the data from the investigations recopied neatly.

Calculations: Calculations should be shown neatly and clearly. Graph should be included here also.

Results: Explain the conclusion of the investigation. Be sure to support your conclusions with facts

and statements that you have determined from your calculations.

Evaluation: Explain why your estimated values are not the same as the

actual number.

Next Page

Project Home Page

Go to the CD-ROM Table of Contents

© 1998 Elmwood Jr/Sr High School