This method of increasing the spawning capacity of the river 

 might be carried out in three general types of operation: 



1* A minimum flow sufficient to accommodate the maximum 

 population could be maintained throughout the year * — ^A ml nimum 

 flow would call for the least administration, supervision, 

 construction, and maintenance of fish retaining and counting 

 structures. This method would be least hazardous for spawning 

 fish, as it would guarantee adequate water at all times. The 

 minimxfltt flow required would be 300 cubic feet per second. To 

 maintain such a flow, 217,200 acre-feet of water would be needed 

 and most of this water would be derived from storage. When 

 spawning, egg incubation and migration were not in progress, some 

 of this water would not be necessary and its flow downstream might 

 be construed as wastage. This plan has the greatest biological possi- 

 bilities, but due to its relatively large water demand, it will probably 

 be the least desirable to the constructing agency. 



2* A fixed flow schedule could be established to accommodate 

 the salmon life history and what is presumed to be the maximum spawning 

 migration .— A fixed flow schedule would prescribe water releases througji- 

 out the year designed to accommodate the life history phenomena of the 

 salmon as known at the present time (Figure 12). This schedule would 

 not vary from year to year, but would remain the same regardless of 

 the numbers of spawning salmon. It would require a minimum of admin- 

 istration and construction. Some maintenance and operation of fish 

 retaining and counting structures would be necessary. 



A fixed spawning flow of 300 cubic feet per second during November 

 would make available the estimated 9,897 salmon nesting sites between 

 Lewiston dam site and North Fork (Table 19). Approximately 5,600 of 

 these nesting areas are normally occupied, and the additional 4,300 

 spawning areas available could accommodate 11,200 spawning salmon, 

 using the established sex ratio of 1 female to 1.63 males. Adequate 

 spawning area for the greatest number of salmon actually counted at 

 Lewiston during 1944 and 1945 would result from this flow. However, 

 observations in the fall of 1946 when no count was made, definitely 

 indicate that a g reater population of spawning salmon was present and 

 may have been crowded under the conditions of this plan. The amount 

 of crowding on spawning beds which can occur without reducing repro- 

 ductive efficiency has not been determined, but certainly scsne could 

 ooour* Furthermore, it is almost certain that the spawning capacities 

 fixed by survey are conservative. 



Populations of spawning salmon are known to vary in number over 

 very wide limits. Studies in California's Central Valley and elsewhere 

 demonstrate variations between years and between cycles which exceed 

 500 percent. The provision of a slight margin is available nesting 



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