The same methods were used to estimate the sauger population. 



WATER TEMPERATURE 



Water temperatures were monitored at stations la. Ilia, and Vc with 

 Taylor 30-day recording thermographs. The recording sheets were changed 

 monthly. All water temperatures were recorded in Fahrenheit degrees. 

 Daily maximum and minimum temperatures were tabulated and are given in 

 appendix B. 



IMPACTS OF WATER WITHDRAWALS 



Impacts were assessed by flow period. The year was divided into three 

 segments corresponding to the life-history phases of the important fish 

 species in the Tongue River: migration, spawning, and rearing (Stalnaker 

 and Arnette 1976). Since incubation periods of warm-water fishes are short, 

 incubation is ignored as a biological phase. It is generally agreed that 

 depth and velocity are the most important limiting factors during these 

 life history stages. 



Depth is significant in maintaining suitable passage requirements 

 and in supplying the necessary wetted areas for spawning and food production. 

 In prairie stream ecosystems, Bovee (1975) suggested that if passage 

 (migration) requirements were met, spawning requirements would also be met. 

 Rearing, as a life stage, generally encompasses those times of the year 

 when fish are not engaged in migration or spawning. Therefore, rearing 

 flows are those which will maintain the habitat necessary for sustenance 

 of the fish species present. 



The fall flow period encompasses the months of August (late summer) 

 through November. These flows coincide with late irrigation with late 

 irrigation withdrawals and are accompanied by warm water temperatures. 

 Temperature and water-quality requirements must be met during this time. 

 A reduction in flow during these months may elevate water temperatures 

 above tolerable limits and result in degraded water quality. 



Winter (December, January, and February) is also a critical low-flow 

 period. Dewatering results in accelerated freeze-up of riffles and 

 depleted oxygen levels. It is during this time that fish population levels 

 are reduced. Fall and winter are considered rearing phases. 



Spring (March through May) is the migration and spawning season for 

 most warm-water species. If adequate flows are maintained to ensure passage, 

 it is assumed that adequate water will be available for spawning. 



The peak run-off period, May through July, is also important for 

 passage, spawning, and rearing. Additionally, spring peaks scour the 

 channel, cleansing the substrate interstices for food production and 

 successful reproduction. 



17 



