upstream and downstream directions. WD now infects the entire main stem Blackfoot 

 River, as well as the lower reaches of many tributaries (Figure 47), many of which are 

 important spawning and rearing streams for migratory Blackfoot River trout (Pierce et al. 

 2004, this report). Coinciding with WD expansion, declining densities for vulnerable 

 species are now being detected. RBT (fish >6.0") density in the middle Blackfoot River 

 between the North Fork and Clearwater River confluences has declined 52% in 2004 

 compared with the long-term mean (1989-2002). Lower Cottonwood Creek is also 

 highly infected and RBT have declined 50% relative to estimates conducted prior to 

 detection of WD. In this stream, there has been a community-level shift towards brown 

 trout, a WD resistant species. 



For this study, we hypothesize that WD severity will be limited to specific 

 streams based on the physical and biological features of each tributary. Study objectives 

 are to: 1) identify life-history characteristics and relative use of fluvial RBT spawning 

 areas using radio telemetry; 2) determine the timing of RBT emergence and mean grade 

 infection levels at these sites during susceptible (post-emergence) phases; and 3) relate 

 these finding to WD infections in juvenile rainbow trout and the specific habitat 

 parameter in RBT spawning and rearing areas. Ongoing companion studies involve the 

 quantification of stream morphometries and other physical characteristics. Our purpose 

 is to develop methods that help identify and predict environmental conditions conducive 

 to WD in tributaries and help assess the ultimate influence of WD on wild RBT 

 populations of Blackfoot River. Implications relate to: 1) the management of species that 

 may inhabit the open niche if significant RBT declines occur; 2) potential harvest 

 regulations changes for affected species; 3) the development of specific habitat 

 enhancement measures suited to different channel-types and salmonid species; and 4) 

 conservation of WSCT fi-om the perspective of reduced introgression. 



Study Area 



The Blackfoot is \ T/- i 



managed for a diversity of self- ^ ' " v yCieawater River ^;5 



sustaining ''-wild trout" - V / ' 



populations. RBT distribution '•" 4. / ^Moniure creek ."V 



is limited to the Blackfoot _ \ - /^/:V V^ A;^ iv^kl'f; 



River downstream of Nevada .'■ -y.,; ^^^.^l^-NoiihFork ^v^>';:--< 



Creek and the lower reaches of .^_^^' ^" ', ,, ;: .S' 



lower river tributaries. \~~"^----.^^^ ^*'"°"**^'**%-^: '^^^^^ 



Although RBT occupy only n,^^ ^~'~"~-^Goid creek S-j'",^>/;' ■;,; 



-10% of the perennial streams \,., .., , - - Xi^Xr-.'t'' 



^ West Twin -t . > -^ ■ X - 



m the Blackfoot watershed, creek " ' > ■ i t 



they represent the dominant 



game fish in the lower river, 



comprising as much as 70% of 



the total trout community in the 



lower Blackfoot River (Results Part II, Appendix C). RBT thereby provide a large 



segment of the recreational fishery in the lower Blackfoot River. Past studies suggest 



fluvial RBT reproduce primarily in the lower portions of larger south-flowing tributaries 



(FWP unpublished data). Within the range of RBT, this study stratified the lower 



'i:- 



Figure 49. Blackfoot River watershed showing locations of 

 primary RBT spawning tributaries. 



63 



