RESULTS 



Standing Crop and Flow Relationships 



The standing crop and flow data collected in past years 

 for the Madison, Beaverhead, Gallatin and Big Hole Rivers are 

 discussed by river reach in this section. The flow recommen- 

 dations derived from this data are summarized and referenced 

 to the monthly hydrograph for each reach in later sections. 

 These recommendations will serve as the standard for evaluat- 

 ing the reliability of the flow recommendations generated by 

 the four instream flow methods. 



Relatively wide confidence intervals were obtained for 

 the standing crop estimates to be presented in this section. 

 The narrow confidence intervals advocated for research are 

 im.practical if not impossible to obtain for population esti- 

 mates on the larger waterways such as those in this study. 

 The standing crop comparisons in this paper are based entirely 

 on differences in point estimates rather than statistical dif- 

 ferences. The confidence intervals are presented solely for 

 the benefit of the reader. ^ 



■ .' ' Madison River - Reach #1 r." > .- :. - 



Flows in the Madison River are primarily regulated by 

 Hebgen Reservoir which stores water for downstream hydro- 

 electric generation. Before 196 8, the Montana Power Company 

 began storing water in Hebgen Reservoir in late February 

 to early March prior to the onset of spring runoff. This 

 policy resulted in extremely low flows in the Madison River 

 during late winter and early spring. In 1968, Montana Power 

 agreed to start storing water when runoff begins in late 

 April to early May. This change resulted in higher flows in 

 the river from February to May. , _. 



The estimated standing crops of trout in a 4-mile sec- 

 tion of reach #1 in spring 1967, prior to the flow increases, 

 and in the spring of 1968, 1969, 1970, and 1971, after flows 

 were increased, are given in Table 5. In 19 71, three years 

 after the policy change, the numbers and biomass of age II 

 and older trout were 171 and 124%, respectively, of those in 

 1967. 



» 



It is assumed that the reduced winter flows prior to 

 1968 were the major factor limiting the trout populations in 

 reach #1 and the population increases between 1967 and 1971 

 primarily reflect the higher flows following the change in 

 storage policy. In recent years, fishing pressure and ele- 

 vated svuniner water temperatures resulting from the thermal 

 heating of Ennis Reservoir are known to affect trout popu- 

 lations in this reach. While these limiting factors were 

 probably operating prior to 1971, flow is assumed to be the 

 overriding factor. - . l:T .^i \- ^ . ^ .j h, 



27 



