Hokanson (1977) listed a range of sauger spawning temperatures 

 from 4 to 14.4°C. Mean water temperature in the Tongue River was 

 generally about 2.5° warmer than the Yellowstone River. 



Water temperatures during the time when sauger were collected 

 in the Powder River ranged from 1 to 17°C during 1976-1980 (Table 

 23). Mean water temperature during April ranged from 7.8 to 10.9°C 

 during 1976 to 1980; an average of 1.6°C colder than mean April 

 temperatures in the Tongue River. 



During April, water temperatures usually peaked from noon to 

 3 p.m. in the Yellowstone and declined to a minimum between 

 midnight and 6 a.m. In the Tongue and Powder rivers, however, the 

 cycle was reversed; water temperatures did not peak until midnight 

 and then declined to minimums between noon and 3 p.m. This makes 

 the difference in water temperature between the tributaries and the 

 mainstem even greater (a mean difference of 5°C warmer in the two 

 tributaries) during the time of day when sauger migration is 

 probably greatest (evening and night) . 

 Streamf lows 



Sauger spawn when flows are relatively stable in the Tongue 

 River - the period after peak lowland runoff and before mountain 

 runoff. Flows in the Tongue River during 1976-1979 (years when 

 numbers of mature male sauger entering the Tongue River were 

 similar) ranged form 370 to 720 cfs and was generally above 440 cfs 

 (Table 22, Figures A-23, A-24, A-25, and A-26) . The discharge 



95 



