64 



Food supply also influences the growth differences shown in Figure 14. 



Smith (1973) found a substantial increase in zooplankton immediately below 



the dam and speculated that this increase may provide additional food for 



small fish through the first 6 miles of river below the reservoir. 



Invertebrates also appear more abundant in the upper river. Limited kick 



sampling in October, 1975 showed a greater abundance of invertebrates in 



the riffles of the Hildreth (2), Pipeorgan (8), and Barretts Upstream (15) 



Sections (Table 24). Tipulid larvae primarily accounted for the greater 



volume of invertebrates in the Hildreth (2) and Barretts Upstream (15) 



Sections. 



TABLE 24. Summed results for kick samples collected in a series of study 

 sections in the Beaverhead River on October 22, 1975. Three 

 samples were collected in a riffle in each section. 



No. Invertebrates Vol . Invertebrates 

 Section Collected Collected (ml) 



Hildreth (2) 144 20.3 



Pipeorgan (8) 179 6.8 



Barretts Up. (15) 311 23.4 



Barretts Down. (18) 39 2.6 



Wheat (27) 44 1.3 



Westside Canal (29) 118 3.7 



Anderson Lane (38) 137 4.8 



Blaine (52) 86 1.4 







Comparison of trout populations throughout the study 



All estimates of numbers and biomass of trout for the Pipeorgan (8), 

 Barretts Upstream (15), Wheat (27), and Blaine (52) Sections throughout 

 this study are given in Appendix Tables 25 through 29. It is doubtful 

 estimates in the Wheat (27) and Blaine (52) Sections primarily reflect 

 annual variations in flow. The consistently low estimates of numbers and 

 biomass of total and younger brown trout in the Blaine (52) Section 

 throughout this study suggest that reproduction is a problem. Reproductive 



