Students use actual data collected by NPPD biologists. The students use technical reading and math skills. They analyze this data and hypothesize a conclusion. 

Students will:

• Utilize charts of data for analysis.
• Hypothesize causes of a real-life situation.

C5, D1, D8, D7, F1, F4 

• Graph paper
• Copies of student background page

Biologists monitor fish populations in reservoirs that have a coal-fired electricity generating stations located nearby. The power stations use water from the reservoir for cooling purposes. Water pumped through the station is warmed up considerably and then discharged back into the reservoir. This process is potentially detrimental to the prized walleye fishery that is supported by the reservoir (if the water that runs through the power station warms the reservoir water temperature to conditions unsuitable for walleye). Therefore, biologists monitor the walleye population on an annual basis to ensure its continued existence and to identify any problems being caused by the power station. 

1. Brainstorm what responsibilities that a biologist might have.
2. Discuss with students how biologists working for Nebraska Public Power District (NPPD) take data on rivers affected by their power generators on these rivers.
3. Give the students copies of the background information.
4. Have the students read and analyze the data.
5. Model graphing the first set of data. (The graph is included in this lesson.)
6. Have the students work in groups to graph the remaining data. Students should graph each set of data (YOY against the other columns) making 5 graphs, plus the first one that was modeled.
7. From these graphs, have students hypothesize a cause. Can anything be done to help remedy the situation? If so, what? Have the groups report to the class their findings.
8. Have the students evaluate each group’s conclusion, and as a class synthesize a group consensus of a possible cause and solution.
9. The probable cause is listed below for teacher information. After the class has made their choice, read this section to them.

Probable cause:

Typically, biologists would use some type of statistical analyses (such as regression) in order to identify which variable(s) were most likely affecting the YOY walleye population. However, we can do much the same by simply plotting the data on an XY scatter graph. Plot the number of YOY walleye (y-axis) against each of the other variable (x-axis) and examine each for consistencies that might suggest a "cause-and-effect" relationship. 

The plots of most of the variables indicate no relationship. That is, the number of YOY present each year varies regardless of the water temperature, flows, etc. However, if you look at the plot of the YOY against the number of predator fish you will see a consistent relationship between the two variables. Notice that in years when predator fish numbers are low the YOY walleye population is high. In years when predator fish numbers are high there are few YOY walleye. This relationship holds true across the range of values observed since 1990. 

Therefore, it appears that the large predator fish population is controlling the YOY walleye population. In recent years there has been an increase in the number of these large predator fish that are present in the lake. Since these large predator fish forage on smaller fish (such as YOY walleye) there has been a decrease in the number of YOY walleye that survive from spawning to the time of the sampling in the fall. 

The biologists can now take this information and determine what actions are needed to correct this problem. 

• Have the NPPD education coordinator come and speak to the class.
• Have the students graph the data using a spreadsheet program.

• Did the students correctly graph the data?
• Did the students find a probable cause and possible solution? 

Biologists monitor fish populations in a reservoir that has a coal-fired electricity generating station located nearby. The power station uses water from the reservoir for cooling purposes. Water pumped through the station is warmed up considerably and then discharged back into the reservoir. This process is potentially detrimental to the prized walleye fishery that is supported by the reservoir (such as if the water that runs through the power station warms the reservoir water temperature to conditions unsuitable for walleye). Therefore, biologists monitor the walleye population on an annual basis to ensure its continued existence and to identify any problems being caused by the power station. 

Gill nets are used each fall to sample young-of-the-year (YOY) walleye. These are the fish that were spawned earlier in the year and have survived over the summer. Knowing how many YOY walleye are present enables the biologists to predict how many larger fish will be present in years to come and how good fishing will be. It also tells the biologists if supplemental stocking of fish from the hatchery will be required to "boost" the population. Sampling these YOY is conducted in exactly the same manner each year (same number of nets in the same locations) to allow comparisons to be made from year-to-year. The relative catch each year will indicate how many YOY are present compared to previous years. For example, if twice as many YOY walleye are captured this year as there were last year we can assume that there are twice as many YOY present in the reservoir this year as there were last year. 

In addition to the gill net sampling, the biologists monitor numerous other variables at the reservoir and the power station in order to relate changes in the walleye population to the conditions that exist. They monitor water temperatures including the temperature of the water that is discharged from the power station and the water temperature in the reservoir during the time period that the walleye spawn. Water flow is monitored, including inflows into and outflows from the reservoir, as well as the volume of water that is pumped through the power station. The number of large predator fish present in the reservoir is also monitored during the annual gill net sampling that is conducted. 

In recent years biologists have noticed that fewer and fewer YOY walleye are captured each year. Therefore, they assume that something is causing the population of YOY walleye to decline. Based upon the information contained in the attached table, try to predict which variable is causing the decline in the YOY walleye population that has been observed.