Results Part II: Blackfoot River Trout Populations 



In June 2002, we completed bi-annual fish population surveys at two long-term 

 monitoring sections (Johnsrud and Scotty Brown Bridge) of the lower Blackfoot River. 

 We also established a new population survey site - the Wales Creek section - in the 

 middle Blackfoot River 



downstream of Nevada Creek Density/1000' (+95% CI) 

 between river mile 60.0 and 67.0 



Johnsrud Section 



The 2002 trout species 

 composition (% of total catch) in 

 the Johnsrud section was 64.3% 

 rainbow trout (n=617), 20.5% 

 brown trout (n=197), 11.4% 

 WSCT (n=109) and 3.8% bull 

 trout (n=37). Compared with 

 2000, this represents a relative 

 increase in brown trout and bull 

 trout, a decline in rainbow trout 

 and no change in WSCT. Based 

 on the total trout point estimate, 

 the overall trout (> 6.0") density 

 decreased 23% from 171 to 132 

 fish/ 1000' between 2000 and 

 2002. This decline occurred 

 primarily within the small-to- 

 intermediate rainbow trout size 

 classes (Figure 16). The 2002 

 point estimate for small rainbow 

 trout (5.0-9.9") decreased from 99 

 to 67.4 fish/1 000'. Rainbow trout 

 in the intermediate (10.0-11.9") 

 size class also decreased from 

 27.0 to 19.5 fish/ 1000' between 

 2000 and 2002. Larger rainbow 

 trout (> 12.0") increased from 

 17.9 to 32.2 fish /1 000' (Figure 

 16). 



From 2000 to 2002, the 

 combined densities of WSCT, 

 bull trout and brown trout (> 6.0") 

 remained generally stable. For 

 native WSCT (> 6.0"), densities 

 decreased slightly from 17.4 to 



fi 



ND NDrhND 



F^ 



11 



25 



20 



Figure 14. Estimated densities (Fish>6.0") of bull trout 

 (top), WSCT (middle) and brown trout (lower) in the 

 Johnsrud section. 1989-2003. 



29 



