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Oysters and a Clear Bay

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					Oysters and a Clear Bay


  INTRODUCTION:
  What aquatic species has been worth its weight in gold in Maryland?
  What aquatic species was the subject of ferocious wars during the late 1800s?
  What aquatic species eats dirt and hangs out in bars?
  If you guessed the oyster, you are
  absolutely right! Beneath the drab and
  lumpy shell of the oyster lies a very color-
  ful history. In addition to its wild popu-
  larity as a tasty meal and its economic
  importance to Maryland, the oyster has
  helped to keep the Bay clean and to pro-
  vide a place for many Bay species to find
  shelter, food, and hiding spots. In this
  activity, you will answer two questions:
  "What has happened to the oyster?" and
  "What does the oyster's scarcity mean for
  the Bay?" To answer these questions, you
  will develop a timeline showing the oys-
  ter's history, investigate the oyster's ability
  to filter, and compare your own filtering
  device to the filtering ability of the oyster.

  MATERIALS:
  Your group will need:
  • Chart: "Maryland Oyster Harvest by
    Season" (attached)
  • 1 sheet of large paper and art supplies
    (magic markers or crayons)
  • Materials for building filters (collect
    from your teacher)
  • Materials for testing filters (collect from
    your teacher)
  • A watch with a second hand
                                                                                     Charles R. Hazard

PROCEDURE:
Part I:
What has happened to the oyster during the past three hundred years? Investigate the color-
ful history of the Chesapeake Bay oyster to answer this question!
1. In your small group, use the data from "Maryland Oyster Harvest by Season" to draw a
   line graph representing one part (assigned by your teacher) of Maryland's oyster harvest



                                                                                  The Catch of the Bay
                                                                                   Section 4, Activity 2 181
   between 1870 and 1993. Your class will combine all of the graphs to form a complete
   timeline.

2. What conclusions can you draw from your class' timeline about the history of Maryland's
   oyster harvest?

      ___________________________________________________________________

      ___________________________________________________________________

      ___________________________________________________________________


3. The following list describes some of the events and regulations that have had an impact
   on oysters during the past 150 years. Plot these events on your class timeline.
   1852: B a l t i m o re & Ohio Railroad reaches the Ohio River, expanding the market for
   oysters westward. People in the western states begin to buy large quantities of oysters.
   1865: The oyster dredge, formerly prohibited in Maryland and Virginia, is legalized after
   the Civil War. Wars between oyster dredgers and oyster tongers continue well into the
   20th century.
   1865:-- present: Dredging flattens high-rise oyster reefs into oyster beds or "bars" on the
   bottom of the Bay. This makes the oysters easier to harvest, but also leaves them susceptible
   to suffocation from sediments.
   1868: The "Oyster Police" form to collect license fees, enforce fishing restrictions, and
   protect private grounds.
   1882: The Oyster Commission is formed to survey oyster beds. They recommend con-
   servation measures and oyster farming.
   1890: The "Cull Law" sets a minimum legal size of three inches for market oysters and
   requires watermen to return shells with spat and young oysters to the oyster bars.
   1972: Hurricane Agnes brings a massive flood of fresh water and sediment (dirt) into
   the Bay.
   1980: Two oyster diseases, MSX and Dermo, enter the Bay. Although they do not harm
   people, the diseases kill oysters as they reach about three inches in size.
   1990s: People all over the world, from the Philippines to Japan to the United States are
   experimenting with raising oysters in hatcheries to meet the growing demand for them
   and supplement the native stocks.

4. Choose two of the events plotted on your class timeline and explain how each has affect-
   ed the oyster harvest. Support your explanations with evidence from the data and any
   prior knowledge you might have.

      a)_________________________________________________________________


       The Catch of the Bay
182    Section 4, Activity 2
       b)___________________________________________________________________

5. List the possible consequences of the trend that your timeline documents. Who and what
   might be affected by the scarcity of oysters in the Bay?

       ___________________________________________________________________

       ___________________________________________________________________

       ___________________________________________________________________

       ___________________________________________________________________

Part I1:
In this section, you will attempt to out-filter the oyster with your own filtering device!
1. One of the most important functions of the oyster is its ability to filter sediments and
   pollutants out of the water. Your teacher will either conduct a filtering demonstration
   using live oysters or will show you video footage of oysters filtering dirty water. If you are
   using live oysters, you can time them. Start timing when the oysters open their shells and
   stop timing when the water is clear. Record the time it takes for the oysters to filter the
   water and the rate at which they filter.
   Amount of water in the tank _________________________
   Time taken to completely filter the tank _____________________________
   Rate that oysters filtered tank ______________________________liters/hour

2. While your oysters filter their aquarium water, your group will build the best filtering
   device possible using the materials provided by your teacher. Your device will be compared
   to the oyster in terms of effectiveness (how clean it makes the water) and speed. You can
   build your machine in whatever way you think is best, but you must follow the guidelines
   listed below:
   • You must draw a plan or "blueprint" of your device before you begin to build it
   • Your device must have a name
   • Your device must be designed to clean dirty water that is poured through it as quickly
        and effectively as possible
   • Your device does not need to use all of the materials provided
   • You may test your device once before the final exhibition and make impro v e m e n t s
        if necessary
   • You must choose one member of your group to serve on the judging committee

3. When you are finished building your device, mix the ingredients for the dirty water in an
   empty 250 ml graduated cylinder or beaker:
   • Fill your container 3/4 full of water


                                                                          The Catch of the Bay
                                                                           Section 4, Activity 2 183
   •   Add one tablespoon of each type of sediment (dirt and silt)
   •   Stir to mix thoroughly
   •   Add algae water (if available) or other water until the container is full

4. Your group will pour the dirty water mixture over your filtering device, into a container.
   Use the watch to determine how long it takes for the water to pass through the device.
   Start timing as soon as you start to pour and stop timing when the time between drips
   slows to five seconds.
   One round takes approximately__________________________minutes.

5. Your group should decide whether you want to clean your water as quickly or as
   effectively as possible. Continue pouring the water back and forth through the device
   until the water is as clear as you want it to be. Keep track of how many rounds it takes.
   When you are finished, answer the following questions:

   a) How long did you take to filter the full 250 ml of water? If you chose to do multiple
      rounds, calculate the total time it took to filter.




   b) Describe the clarity (clearness) of your water. Explain why your device did, or
      didn't, filter well.

       ___________________________________________________________________

       ___________________________________________________________________

       ___________________________________________________________________

       ___________________________________________________________________




       The Catch of the Bay
184    Section 4, Activity 2
Part Il1:
Use what you have learned from the first two sections of this activity to compare your
filtering device to the oyster.

1. Fill in the chart below to compare an oyster and your filtering device.




2. In 1800, the oysters in the Chesapeake Bay could filter the entire Bay in three to six
   days. However, it takes today's remaining oysters a year to do the same job. The
   Chesapeake Bay contains approximately 17,000,000,000,000 (17 trillion) gallons of
   water. How many devices would it take to filter all the water in the Bay in three to
   six days?



                                                                       The Catch of the Bay
                                                                        Section 4, Activity 2   185
3. Many people around the state think that the oyster is the ultimate filtering device! After
   watching oysters filter and building your own filtering device, explain why you agree or
   disagree with this assertion.

       ___________________________________________________________________

       ___________________________________________________________________

       ___________________________________________________________________

       ___________________________________________________________________

       ___________________________________________________________________

4. Even though oysters still face many problems, people around the Bay are finding ways to
   help bring oysters back to their former abundance by restoring oyster reefs and raising
   oysters in hatcheries and oyster gardens. Turn back to the timeline that you constructed
   in Part I of this activity and add the years 1995 - 2000. Considering the efforts to restore
   oysters, but also the problems that oysters continue to face, draw an extension to the
   timeline that predicts oyster levels until the year 2000. If your class has chosen to do an
   oyster project, add it to your timeline as well.

5. Explain the extension you drew on your timeline using your knowledge of the oyster's
   history. If your prediction shows a rise in the oyster population, explain what brought
   about the increase. If your prediction shows a further decline in oysters, explain what
   brought about the decrease. What would happen to oysters, watermen, and the Bay if
   your prediction came true?

       ___________________________________________________________________

       ___________________________________________________________________

       ___________________________________________________________________

       ___________________________________________________________________

       ___________________________________________________________________

       ___________________________________________________________________

       ___________________________________________________________________

       ___________________________________________________________________



       The Catch of the Bay
186    Section 4, Activity 2
The Catch of the Bay
 Section 4, Activity 2 187

				
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