Name ________________________________
Clark
Science Period ________
Date _____________
LAB6
Counting Turtles
TSWBAT: explain or analyze how organisms interact with each other (food chain, food web, energy pyramid) and
how they obtain and use resources from their ecosystems to develop and thrive in their niches.
Problem:
How can the mark-and-recapture method help ecologists monitor the size of a population?
Materials:
 Model paper turtle population in a brown paper bag
 Calculator
Procedure:
1. The data table shows the results from the first three years of a population study to determine the number
of Hawai’ian sea turtles in the ocean.
2. The paper bag represents the ocean. There is a population of sea turtles that lives in the ocean – 150 of
them have been marked, as shown in the data table, for year 4.
3. “Capture” a member of the population by randomly selecting one turtle. Set it aside.
4. Repeat step 3 nine times. Record the total number of turtles captured.
5. Examine each turtle to see whether it has a mark. Count the number of recaptured (marked) turtles.
Record this number in your data table.
Data Table:
Year
Number marked
(hundreds)
Total number captures
(hundreds)
Number recaptured (with marks)
(hundreds)
1
3.2
2.8
1.5
2
2.5
2.1
1.1
3
2.3
1.9
1.1
4
1.5
Estimated total turtle
population (hundreds)
Analyze and Conclude:
1. Use the equation below to estimate the total turtle population for each year. The first year is done for you
as an example. If your answer is a decimal, round it to the nearest hundredth. Record the population for
each year in the last column of the data table.
Total population = Number marked × Total number captured
Number recaptured (with marks)
Sample (Year 1) Total population = 3.2 × 2.8 = 5.97 or 597 turtles
1.5
2. Graph the estimated total turtle populations for the four years. This graph will be showing change over
time, or the estimated total population for years 1 - 4. Which one goes on the x-axis and which one goes
on the y-axis?
Graph:
Title: The effect of ___________________________________________________________________________
Label each axis with the DV and IV and the units of measurement.
3. Describe how the sea turtle population has changed over the four years of the study. Us evidence or use
quantitative data. Suggest three possible causes for the changes. (Remember what you learned about
things that can affect populations!)
4. Use your graph to predict what the turtle population will be in year 5. Explain your prediction using
evidence (quantitative data).
5. Why is the mark-and-recapture method a useful tool for ecologists? When is this technique the most
useful for estimating a population size? (Compare to a second technique.)