44 



TABLE 9. Correlation coefficients for the multiple linear relationships 



between the spring estimates of numbers of age II and older 



rainbow trout and mean fall to spring flows in the Hildreth 

 Section of the Beaverhead River. 



Partial Correlation Coefficients 

 No. of I & Older 

 Rainbow Trout Mean Flow Multiple 

 Dependent Variable Previous Fall Fall -Spring Correlation (r) 



No. of II & Older , , ,. ,, 



Rainbow Trout - Spring .9658 1 ' .8510 1 ' .971 2— 7 



1/ Indicates significance at 5% level. 



Limited evidence suggested spawning flows influenced numbers of 

 yearling rainbow trout. The number of yearlings in turn determined the 

 number of age II rainbow trout one year later. Numbers of age IV and 

 older rainbow trout were influenced by the magnitude of mean flows during 

 the nonirrigation season. 

 Biomass of Trout (Hildreth Section) 



Brown Trout 



Spring and fall biomass estimates of brown trout by age groups are 

 given in Table 11. Spring biomass estimates of age II and older brown 

 trout are compared in Figure 5. Biomass decreased between 1967 and 1968, 

 remained relatively stable between 1968 and 1975, then increased in 1976. 

 The decrease between 1967 and 1968 reflects an elevated mortality of 

 age III and older brown trout. Strong 1973 and 1974 year classes 

 primarily account for the increase in 1976. 



The biomass of the 1965 through 1973 year classes are shown for an 

 18-month period in Table 12. Significant relationships between the 

 magnitude of mean flows during the irrigation and nonirrigation seasons 



