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The annual stage and temperature hydrographs, such as figure 11, were analyzed in reference to characteristics related to the cuing of the pallid sturgeon and for the spawning and the nesting of the least tern and piping plover.

1929 'NATURAL' HYDROGRAPH FOR THE MISSOURI RIVER AT SIOUX CITY

12

10

8

Gage Height (feet

6

4

2

0

3/1/1929

3/8/1929

3/15/1929

3/22/1929

3/29/1929

4/5/1929

4/12/1929

4/19/1929

4/26/1929

5/3/1929

5/10/1929

5/17/1929

5/24/1929

5/31/1929

6/7/1929

6/14/1929

6/21/1929

6/28/1929

7/5/1929

7/12/1929

7/19/1929

7/26/1929

8/2/1929

8/9/1929

8/16/1929

8/23/1929

8/30/1929

9/6/1929

9/13/1929

9/20/1929

9/27/1929

Gage Height

Temperature

Figure 11. 1929 'natural' hydrograph for the Missouri River at Sioux City. Gage height and temperature values are calculated.

Figure 11 shows that the Missouri River stage was greater than 7 feet from about June 11 through July 22. Similarly water temperature first exceeded 18o C on June 25.

C) DISCUSSION AND CONCLUSIONS

The possible factors that might cue a fish, such as a pallid sturgeon, to spawn are numerous. These factors are both endogenous and exogenous. There are many observations on the exogenous factors including characteristics of the spawning sight that might be initiate spawning. In reference to the Missouri River, the author is not aware of any observation of a pallid sturgeon or shovelnose sturgeon spawning in the Missouri River main stem. However, the range of the pallid sturgeon before the creation of the reservoirs included the entire main stem of the Missouri River. It is sometimes stated that shovelnose sturgeon, which is considered a surrogate for the pallid sturgeon, spawn in the non-channeled Missouri River near Vermillion, South Dakota. These statements generally are in

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    5.00

Temperature (deg. C

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