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Inquiry Lab • Modeling

Chapter 7Overharvesting

Directions: Read the entire lab before doing the procedure and answering the questions.

Problem How does overharvesting affect biodiversity?

Background

Overharvesting

Many animal species face extirpation or extinction because they are overharvested—overhunted, overtrapped, or overfished. If you catch animals faster than they can be replaced by reproduction, populations can be wiped out. Plants, too, can be overharvested. When a forest is clearcut, all species of trees are lost from the area, not just the species that are targeted by the timber industry. To prevent overharvesting, humans must use natural resources sustainably. This means that if we take living things from their ecosystems, we do so in a way that allows the population’s recovery to keep pace with the harvest.

The Fishing Game

In this activity, you will play a game to model the effects of overfishing on biodiversity in a body of water. The desktop will represent a lake or bay. Members of your group are commercial fishers. Each 15-second run will represent a fishing trip in which you will “catch” several species of fish—redbean fish, whitebean fish, pintobean fish, and ricefish. After four trips, you will observe the effects of your fishing. The fork represents a trawl net—a type of fishing gear that is towed through the water to capture aquatic species.

Materials

• 20 red kidney beans / • small jar with lid
• 25 white great northern beans / • small paper cup
• 5 pinto beans / • fork
• 30 rice grains / • stopwatch or clock with second hand
• shallow dish or bowl

Safety

Materials are not safe to eat and may be a choking hazard if swallowed.

Procedure

Step 1Obtain a fork and a jar containing beans representing four populations of “fish.” The types of “fish” are redbean, whitebean, pintobean, and ricefish. Note: Pintobean fish are endangered, and it is illegal to keep them. If you catch any pintobean fish, you will return them to the desktop (water) immediately after you have sorted through the catch, in Step 6.

Step 2Predict what will happen to the four fish populations after four fishing trips. Record your prediction in the space provided (Question 1). Consider the space between the tines of your fork (trawl net) and the sizes of the beans (fish species).

Step 3Assign these roles for your group: timekeeper, data collector, and two alternating fishers. One fisher will catch fish during trips one and three; the other fisher will catch fish during trips two and four.

Step 4Sprinkle the contents of the jar onto your desktop so the beans are in a single layer. Place the paper cup on the desktop.

Step 5Use the fork to lift the beans into the paper cup. Do this for
15 seconds. Keep your other hand under the desktop during your fishing trip.

Step 6When the 15-second fishing trip is over, count the number of fish from each species that landed in the paper cup and record the catch data in the data table. Return all caught pintobean fish to the desktop (water) but place the rest of the catch back in the jar.

Step 7The second fisher should be sure the remaining fish are still arranged in a single layer on the desktop. Replace the empty paper cup on the desktop. Repeat Steps 5 and 6 for the second, third, and fourth fishing trips.

Step 8Put away all materials as directed by your teacher. Wash your hands when you are finished with the lab.

Observe and Collect Data

1.Write your prediction on the lines below.

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2.Fill in the table with the data you collect.

Data Table
Trip / Redbean Fish / Whitebean Fish / Ricefish / Pintobean Fish
1
2
3
4
Total Caught
Original Population

Analyze and Conclude

3.Draw Conclusions Were any of your fish species extirpated? Explain.

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4.Predict Do you predict that any of the fish species will become extinct? Explain.

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5.Compare How did the biodiversity of the body of water compare before and after the fishing trips? Explain.

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6.Infer What would have happened to the pintobean fish if it were not illegal to harvest them?

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7.Apply Concepts Much of commercial fishing involves trawling—dragging large nets behind a boat and capturing both target species and non-target species, also known as bycatch. What did the particular characteristics of your fork (trawl net) mean for the species that lived in the body of water?

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8.Make Generalizations How might trawling result in loss of biodiversity? Consider how bottom trawling (where the net is dragged along the ocean floor) might affect biodiversity compared to midwater trawling (where the net is dragged through the water).

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9.Extension How do you think your results would have been different if you had used forceps to model spear fishing instead of a fork to model trawling? Explain.

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Environmental Science • Lab Manual

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