PASSAGE AND SPAWNING FLOWS 



Sauger are found moving out of the Yellowstone into the Tongue from 

 March to June. According to Bovee (1974), the spawning depth criteria 

 for sauger is 1.2-1.5 m (3.9-4.9 ft). Since it is assumed that if passage 

 criteria are met then spawning criteria are also met, the converse was also 

 assumed to be true. Therefore, only one flow level is recomnended to meet 

 the needs for both passage and spawning. Based on predicted flow conditions 

 from the WSP program, flows ranging from 19.8 to 48.9 m^/sec (700-1725 cfs) 

 would provide adequate passage and spawning depths. The minimum sustaining 

 discharge is defined as 75 percent of optimum (Bovee 1974). The recoimended 

 minimum passage and spawning flow for sauger for the months of March through 

 June is 14.9 m^/sec (525 cfs). 



The spawning migration of the shovelnose sturgeon cotmences around the 

 first of May. Depth requirements for shovelnose sturgeon are reported as 

 0.3-0.9 m (1 to 3 ft) (Bovee 1974). Sampling of shovelnose in the lower 

 Tongue River revealed that nearly 80 percent of the fish sampled were taken 

 in depths ranging from 0.6 to 1.0 m (2 to 3.3 ft). Based on WSP predicted 

 flows, discharges of 23 to 62 m^/sec (800-2200 cfs) are required to meet 

 shovelnose sturgeon criteria. The recomnended flow for shovelnose sturgeon 

 during May, June, and half of July is 17 m^/sec (600 cfs). 



Channel catfish spawn at temperatures ranging between 23.9 and 29.5°C 

 (75-85°F). Water temperatures in the Tongue River generally reach these levels 

 during June, July, and August. Therefore, requirements for this species 

 are established for this time period. Spawning depths for catfish have not 

 been determined, but Bovee (1974) reported depth preferences ranging from 

 0.31 to 1.53 m (1.0 to 5.0 ft). Using WSP predicted flows for pool areas, 

 flow ranges of 8.5 to 21 m^/sec (300 to 750 cfs) were established. Based on 

 75 percent of optimum, the recommended flow for channel catfish is 6.4 m-^/sec 

 (225 cfs). 



REARING FLOWS 



Rearing flows are needed during the remainder of the year. Dewatering 

 will more severely affect areas of shallow, fast water than areas of deep, 

 slow water. If these shallow areas are maintained, then the stream will 

 be protected. Rearing flow recommendations are based upon the assumption 

 that rearing is proportional to food production, which is in turn assumed 

 proportional to wetted perimeter (White and Cochnauer 1975). Wetted perimeter 

 was determined for several transects based on WSP predicted flows. Starting 

 at zero discharge, wetted perimeter increases rapidly for small increases in 

 discharge up to the point where the river nears its maximum width. Beyond 

 this inflection point, wetted perimeter increases slowly while discharge 

 increases rapidly. The optimum quantity of water for rearing is selected 

 near this inflection point (figure 27). Optimum flow value for the Tongue 

 is 7 m3/sec (250 cfs), so the recommended minimum flow value (75 percent of 

 optimum) is 5.4 m3/sec (190 cfs). Bovee (1975) suggested using the stonecat 

 as a rearing flow indicator species. The stonecat was selected for its 

 preference of fast, shallow water areas. Stonecats sampled by Bovee in the 

 Tongue River showed a marked depth preference ranging between .30 and .60 m 



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