s • 



Figure 4: --Growth history of white crappie in 

 Lewis and Clark Lake during the first 7 years 

 of impoundment. Solid lines connect points rep- 

 resenting average lengths of age groups (Roman 

 numerals) at time of capture (June -August) 

 Number of fish aged in parenthesis . 



Figure 5: --Growth history of sauger in Lewis 

 and Clark Lake during the first 7 years of im- 

 poundment. Solid lines connect points represent- 

 ing average lengths of age groups (Roman 

 numerals) at time of capture (June-August) 

 Number of fish aged in parenthesis . 



species during the remainder of the period. 

 Reasons for poor reproduction and growth after 

 1957 are unknown, but they may be related to the 

 rapid exchange of water, increased turbidity, or 

 to the pattern of reservoir water level fluctuation 

 as suggested by Shields 6/. 



Lewis and Clark Lake is a re -regulating 

 type reservoir and water levels can be expected 

 to fluctuate from 1 to 2 feet each week, April 

 through November. Seasonal water level fluctu- 

 ation, primarily for flood control, requires that 

 the reservoir be maintained at the maximum 

 level (1,208 feet) until April and then drawn down 

 to the minimum level (1,204 feet) until the end of 

 of July. In 1956 the water level in the reservoir 

 reached planned operational stage (1,205 feet) 

 in February. During the latter part of March 

 there was a drawdown of 15 feet to allow com- 

 pletion of certain construction phases of the 

 project. By the end of June construction was 

 completed, and between June 15 and July 1 the 

 reservoir was restored to normal operating 

 pool (1,204 feet). 



TTie pattern of water level fluctuation which 

 occurred in 1956, the year in which reproduction 

 and growth were good for most fishes, has not 

 been duplicated. This suggests that rising water 

 levels during the month of June may be beneficial 

 for reproduction of most species . Shields 6/ 

 suggested that the production of fish food orga - 

 nisms and hence fish growth could be increased 

 by maintaining the water level at minimum pool 

 (1,204 feet) until about mid-June and then raising 

 the level to maximum pool (1,208 feet) until 

 September. This might encourage terrestrial 

 vegetation in the shallow flood plain and possibly 

 increase growth of rooted aquatics beneficial 

 for production of aquatic organisms . 



Another factor related to water level fluctu- 

 ation which may effect reproduction and growth 

 is surface wind . High wind combined with low 

 water levels increases the effect of wave action 

 in littoral areas and increases turbidity. Wave 



6/Shields, James T. 1958. Report of fisheries 

 investigations during the third year of impound- 

 ment of Gavins Point Reservoir, South Dakota, 

 1957. Dingell -Johnson Project F-l-R-7, 48 pp. 

 (Mimeo . ) 



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