Spring . The low level of development would have little impact on the 

 fishery of the lower Tongue River. July would be the month of the highest 

 impact, with inadequate flows two out of three years. Low flows during 

 this period would result in excessive water temperatures which would be 

 detrimental to sturgeon egg hatching. Predicted flows for May and June would 

 have little or no negative impact. For sauger spawning, flows in March would 

 be inadequate one out of two years and April flows would be inadequate 

 67 percent of the time. The impact during these months would probably be 

 minimal . 



At the intermediate level of development, July flows would be inadequate 

 83.3 percent of the time, resulting in high water temperatures, reduction in 

 egg survival, and loss of spawning habitat. Impacts would be minor in May 

 and June. April flows would be inadequate 76.7 percent of the time (23 of 

 30 years). This flow reduction would result in loss of habitat, loss of 

 wetted perimeter, and loss of depth and velocity needed for sauger to spawn. 

 The impacts during March would be similar to those of March under the low 

 projection. 



The effect of the high level of development during the spring spawning flows 

 would be similar to that of the intermediate level with the exception of July. 

 During July, flows would be insufficient 90 percent of the time, with impacts 

 similar to those described previously. This would seriously affect shovelnose 

 sturgeon spawning in the lower Tongue River. 



Summary of Impacts . With the low level of agricultural development, 

 there would be little impact except during fall. With the intermediate and 

 high levels of development, there would be severe impacts on the fishery 

 during the entire year, resulting in the loss of spawning and rearing flows 

 necessary to maintain the sauger and channel catfish fishery. There would 

 be a severe loss of spawning habitat for the shovelnose sturgeon during the 

 spring (runoff) flows. 



Industry Projection 



A summary of possible impacts associated with each development level is 

 presented in table 21 . 



No major impact associated with the low level of development could be 

 predicted to occur on the Tongue River. 



Impacts predicted for the intermediate level of development would be 

 greatest during the spring, when an estimated 500,000 m^ (5.4 million ft^) of 

 potential spawning habitat would be lost downstream from the T&Y Diversion. 

 Winter flows less than 2.5 m3/sec (90 cfs) would result in icing on riffles 

 and, therefore, invertebrate losses (Bovee 1976). This would occur about 

 20 percent of the time at this level of development. These flows would 

 adversely affect the fishery. 



The intermediate development level, even with 60 percent of NGPRP 

 instream flows (NGPRP 1974) guaranteed, would still have high impact. In many 

 years there would be little or no flow in the river during the fall, and 



69 



