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  • Behavior of organisms (9-12)

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  • Saving Sturgeon

    Atlantic sturgeon have survived since the age of the dinosaurs. Centuries ago, these giant fish were abundant in Virginia rivers. Today, these fish are struggling to stay off the endangered species list. How could such an immense species that has survived for millions of years become nearly extinct in a few short centuries?

    Sturgeon are unusual fish that have changed very little since prehistoric times. Instead of scales, sturgeon have five rows of bony plates or “scutes." They have a long snout with barbels to help them detect prey on the river bottoms. Their protractible, toothless mouth extends out, sucking up food items like a vacuum-cleaner. They can live to be 60 years old and up to 14 feet in length. They can be found along the Atlantic coast from Canada to Florida and become reproductively active anywhere from age 5 to age 20. Adult sturgeon migrate upriver in the spring to spawn.

    Sturgeon were an important food source for Native Americans and were harvested using nets, spears, weirs, and even lasso. Sometimes the Native Americans didn’t even need fishing gear as the jumping sturgeon occasionally landed directly in their canoe. The meat, oil and roe of the fish were all consumed. As colonists arrived in North America, the plentiful sturgeon became important to them as well. Legend has it that there were so many sturgeon in the James River during colonial times that one could cross a river by walking on their backs. Like the Native Americans, colonists relied on the sturgeon for food especially during those first lean years and found sturgeon to be a profitable export back to Europe.

    By the end of the 1800s, harvesting of sturgeon reached its peak. At the same time, our growing nation was wreaking havoc with sturgeon habitat and migration routes. Dams and water wheels blocked the path to spawning grounds. The build up of industry and dredging of waterways destroyed important habitat. To make matters worse, sturgeon were often caught as bycatch from other fisheries such as shad. These colossal fish with their bony scutes damaged fishing gear and disgruntled fishermen killed the “useless" fish. Overfishing, habitat loss and bycatch mortality combined with the late age of reproductive maturity of sturgeon caused the stocks to plummet by the early 1900s.

    Management efforts were implemented to help increase sturgeon populations. A law was passed in 1929 making it illegal to take sturgeon less than 4 feet in length (approximately 10 years old). Stocks still were not recovering, so in 1974 Virginia declared a moratorium on sturgeon fishing. The rest of the east coast followed suit in 1998. Along with the moratorium, the Atlantic States Marine Fisheries Commission (ASMFC) outlined a plan to increase populations to sustainable levels over the next 40 years. The plan calls for the following actions:

    Data Activity

    Scientists at the Virginia Institute of Marine Science (VIMS) are conducting research experiments on sturgeon interaction with gill nets, a common type of fishing gear that can entangle sturgeon. Gill nets are long fishing nets that are stretched across a body of water. Fish swim into these nets and their gills become entangled in the mesh. Sturgeon, though not a targeted species, can get their bony scutes entangled in the nets. By observing the interaction of sturgeon with gill nets of varying net height, twine size and hang ratio (how taut or slack the net is), scientists are hoping to identify which combination of these are less likely to result in sturgeon becoming entangled and taken as bycatch.

    In the following activity, we will look at the VIMS sturgeon data to see which variables are less likely to entangle sturgeon. First, here are some definitions explaining terms from the research experiment.


  • Twine Size – Thickness of the string used to make the net
  • Hang Ratio – Describes how tight or slack the net webbing is hung. The larger the hang ratio, the tighter the net is hung resulting in a more open webbing.
  • Net Height – The distance between the top float line and the bottom lead line of the net
  • Interaction – Occurs when a sturgeon comes within 6" of the net
  • Entangled – When a sturgeon is stuck in the net for any length of time
  • Retained – When a sturgeon becomes stuck in the net and remains there for 30 minutes

    Using the following VIMS Sturgeon Gear Interaction data, we will compare the percentage of fish entangled and retained.

    To do this activity in Microsoft Exel, click here to download an Excel spreadsheet of the data.

  • For each data row, calculate the percentage of fish that interacted and were entangled ([Entangled divided by Interacted] x 100). Enter these values in the first empty column.
  • For each data row, calculate the percentage of entangled fish that were retained ([Retained divided by Entangled] x 100). Enter these values in the second empty column.

    Twine Size
    Hang Ratio
    Net Height (inches)
    # of Fish Interacted
    # of Fish Entangled
    # of Fish Retained
    % Entangled
    ( E / I )
    % Retained
    ( R / E)

    To evaluate the entangled and retained percentages based on the three net variables (twine size, hang ratio and net height), we will combine all values for a given variable and enter in the chart below.

    Example: Let's separate the data by Twine Size variable. From the table above, add the Total Interacted (Column 4) for all of the 0.4 Twine Size data (Row 1 + Row 4). So you will be adding 35 + 31 = 66. Repeat for Total Entangled (Column 5) and Total Retained (Column 6). Enter these sums in the table below. Now, using the same formula as in Table 1, calculate the percent entangled ([Entangled divided by Interacted] x 100) and the percent retained ([Retained divided by Entangled] x 100). Repeat this for 0.52 Twine Size (Row 2 + Row 3 + Row 5 + Row 6). Enter the values in the table below.

    Do the same procedure with the Hang Ratio and the Net Height.

    Combined Individual Variables
    Total Interacted
    Total Entangled
    Total Retained
    % Entangled
    ( E / I )
    % Retained
    ( R / E )
    0.4 Twine Size            
    0.52 Twine Size            
    0.5 Hang Ratio          
    0.625 Hang Ratio          
    30" Net Height            
    45" Net Height            


    For each variable type (twine size, hang ratio and net height), graph the percent entangled and percent retained and answer the following discussion questions. (See sample graph.)

    1. Looking at Twine Size, is there a difference in the percent entangled between the 0.4 mm and 0.52 mm? Is there a difference in percent retained?
    2. Looking at Hang Ratio, is there a difference in the percent entangled between the 0.5 and 0.625? Is there a difference in percent retained?
    3. Looking at Net Height, is there a difference in the percent entangled between the 30" and 45"? Is there a difference in percent retained?
    4. Based on your data analysis, what type of net would be best at reducing the number of sturgeon entangled in gill nets?
    5. Look at the original VIMS data table. Which net had the lowest percentage of sturgeon retained? Does this match up with the net type you described above?

    If you have questions about this Data Tip or have suggestions for a future data tip, contact Lisa Ayers Lawrence.

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