<4.0" (y=1.7236x-0.1513; rM.86; P=<0.001) and for fish >4.0" (y=1.3162x + 

 0.5.5495; R^=OM; P=<0.001). 



Although these regressions demonstrate CPUE to be a predictor of population 

 density, estimates derived from these equations do not have a confidence interval like the 

 actual (depletion) population density estimate, and should be used with caution. For this 

 report, we use only CPUE and actual depletion estimates for tributary assessments. 

 CPUE refers to the number offish collected in a single electrofishing pass and is adjusted 

 per 100' of stream (i.e. CPUE of 8 means 8 fish captured per 100' of sampled stream). 

 Actual population estimates are referred to as density/ 100'. CPUE catch statistics are 

 located in Appendix A and population estimates are in Appendix B. 



Fish were captured using a boat or backpack mounted electrofishing unit. In 

 small streams, we used a battery powered (Smith/Root) backpack mounted DC 

 electrofishing unit. The anode (positive electrode) was a hand-held wand equipped with 

 a 1 -foot-diameter hoop; the cathode (negative electrode), a braided steel wire. On the 

 Blackfoot River, we used an aluminum drift boat mounted with a Coffelt Model WP-15 

 rectifier and 5,000 watt generator. The hull of the boat serves as the cathode and two 

 fiberglass booms, each with four steel cable droppers, serve as anodes. We used direct 

 current (DC) waveform with output less than 1000 watts, which is an established method 

 to significantly reduce spinal injuries in fish associated with electrofishing (Fredenberg 

 1992). Juvenile trout including young-of-the year (YOY) were sampled in the tributaries 

 from August to November. Extra effort was used to sample stream edges and around 

 cover to enable comparisons of densities between years and sampling sections. Captured 

 fish were anesthetized with either tricaine methanesulfonate (MS-222) or clove oil, 

 weighed (g) and measured (mm) for total length (TL). For this report, we converted all 

 weights and lengths to standard units. 



Whirling Disease Sentinel Cage Studies 



Whirling disease surveys involving sentinel fish exposures were undertaken 

 throughout the Blackfoot Watershed in 2004 and 2005. Sentinel cage studies are 

 controlled experiments used to detect levels of whirling disease. Cages consist of an 18 x 

 24" cylindrical screened container placed into a stream site, which allows sfream water to 

 flow through the cage. Each cage contained 50 uninfected rainbow trout or WSCT (35- 

 60 mm) supplied by a state fish hatchery. In specific studies, brook and brown frout were 

 also used to detect levels of whirling disease infection. Timing of field exposure was 

 based on anticipated mean daily temperatures in the 50's (F), which correlates with peak 

 triactinomyxon (TAM) production, and corresponds to peak infection rates in fish 

 (Vincent 2000), except in spring creeks (Kleinschmidt and Nevada Spring Creek) where 

 recent research indicated peak infection occurred in late winter and early Spring 

 (Anderson 2004). The exposure period for each live cage was standardized at 10 days. 

 At the end of the 10-day exposure period, the trout were transferred to Pony, MT, where 

 they were held for an additional 80 days at a constant 50 ° F temperature to insure the 

 WD infection if present would reach its maximum intensity (Vincent 2000). At the end 

 of the holding period, all surviving fish were sacrificed and sent to the Washington State 

 University Animal Disease Diagnostic Laboratory at Pullman, WA. At the lab, the heads 

 were histologically examined using the MacConnell-Baldwin histological grading scale, 

 which ranks infection intensity from (absent) to 5 (severe) (Baldwin et al. 2000). The 



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