Something Fishy

Download PDF Lesson | Get Acrobat
A Printable version of this lesson is available in PDF format.
This requires a free plug-in, Adobe Acrobat Reader.
You can find out if you need it by clicking on the PDF link.


Students will estimate the size of a large population by applying the concepts of ratio and proportion through the capture-recapture statistical procedure.

Overview of the Lesson

Students are introduced to a problem involving an environmental issue: scientists have determined that the number of fish in the Chesapeake Bay has decreased. Assuming that this is true, scientists must have counted the number of fish and noted the change. How did they count the fish? Groups are formed to explore a wide range of possible strategies. Students are introduced to the capture-recapture method which involves capturing fish, tagging them, returning them and recapturing another sample. In groups, students are given containers (the bay) and an unknown number of fish-shaped cheese crackers to use in simulating the capture-recapture method. Students net the fish-shaped cheese crackers and substitute fish-shaped pretzels to simulate tagged fish. Groups then take samples and record the number of tagged fish and the total number of fish. After several samples are taken, results from each group are recorded. Students apply their knowledge of proportion to arrive at the total fish population.