57 



(38) Sections. Growth, in addition to numbers of trout, influenced the 



differences in biomass between years. Mean weights at capture, as 



indicated by age II brown trout, were lower in all sections in Spring, 



1976 (Figure 14). Greater densities of trout in 1976 may explain the 



lower mean weights in the Hildreth Extended (2), Barretts Upstream 



Extended (15) and Barretts Downstream (18) Sections. However, densities 



were similar in the lower four sections in both years. The consistency 



of the weight decreases throughout the river would suggest that the 



exceptionally high flows occurring between Spring, 1975 and 1976 retarded 



growth. High flows may affect growth by lowering both water temperatures 



and the availability of food. 



TABLE 22. Relationship between annual rates of population decrease (%) 

 of age II and older brown trout and mean flows (cfs) in a 

 series of study sections in the Beaverhead River between 

 spring, 1975 and spring, 1976. Range of average daily flows 

 in parenthesis. 



