Mark-and-Recapture Activity by J0h22E

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```									Name: _______________________                                              Date: ___________
Mark-and Recapture Activity

Mark-and-Recapture Activity
Read the paragraphs below and then scan the table. Answer the questions that follow.

A population is a group of organisms of the same species that live in a particular area. It
is important for scientists to monitor the populations of animals such as sea turtles
closely, since many such species are endangered. It would be difficult, if not impossible,
for scientists to find and count each sea turtle in the Peconic Bay. Instead, they must use their
knowledge of math to estimate the total population. One option for doing so is the mark-and-
recapture method. As you might guess from its name, this method involves capturing and
marking (or tagging) members of a selected animal species and then releasing them back to the
wild. Shortly thereafter, a second “roundup” is held in which a second group of the same species
is captured. Some organisms captured in this second group were previously marked; others were
not. The total number of animals in this second group and the number that are tagged are counted.
With this information, it is possible to estimate the total population of a species in a particular
region using the following equation:

N = M n/m

where N = the total number of a selected animal species in a particular area, M = the total
number of animals captured in the first roundup, then marked and released, n = the total
number of animals captured in the second roundup, and m = the total number of animals
captured in the second roundup that has marks. Scientists have been collecting sea turtle
population data once a year for five years. They always collect this data at the same time of year,
making the second roundup within a few days of the first. The table below summarizes the data
collected.

Sea Turtle Data Summary

APES                                             1                                         Mr. Clark
Bethpage HS
Name: _______________________                                         Date: ___________
Mark-and Recapture Activity

Analysis Questions:

1. Use the equation discussed on the previous page to calculate the estimated population
for years 1-5. Round your answers to the nearest animal and enter them in the table.

2. Graph your results for question 1 on a separate sheet, leaving room to add the results
for Year 6 at a later time. Be sure to label the axes and add a title. What trend does your
graph show?

3. Calculate the ratio of m to n for Year 1. Explain in words the relationship between this
ratio and the estimated total population (N).

4. Using your graph, make a prediction for Year 6. Explain your reasoning.

5. Now try out the mark-and-recapture method yourself to develop an estimate for Year

6. Your teacher will provide you and a partner with a box filled with pieces of paper that
represent sea turtles. Twenty of these “turtles” have been previously marked with an X.
Now, without looking at the paper, recapture 15 of the “turtles” from the box. Examine
these turtles to see how many are marked. Record your data for Total Sea Turtles
Captured in 2nd Roundup and Total Sea Turtles Captured in 2nd Roundup With Marks in
the Year 6 row of the Sea Turtle Data Summary table on the previous page. Then use
this data to estimate the population of turtles in the region in Year 6 and record your
estimate in the table 6. Compare your results with five other groups. Write down the
other group’s results below. How do they compare with your own? Calculate the mean,
median and mode for the six groups (your own plus the other five) and record them
below.

7. Why is it important that the data in the table was gathered at the same time each year?

8. Why do you think it was important that the second roundup of sea turtles each year
took place just a few days after the first?

APES                                          2                                     Mr. Clark
Bethpage HS

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