data collection and problem identification, to development and monitoring of completed 

 projects. Although many restoration projects have been completed in the Blackfoot River 

 watershed, this effort is considered educational at a broad level and is far from complete. 



Fish Population Estimators 



Fish population densities were calculated using single-pass, mark-recapture, or 

 multiple pass-depletion methods. We used mark-recapture in the Blackfoot River and 

 Monture Creek (Appendix C) and depletion estimates (Appendix B) and single pass 

 catch-per-unit-effort (CPUE) in smaller streams (Appendix A). 



Population densities using the mark-recapture method were estimated using 

 Chapman's modification of the Petersen formula (Ricker 1975), and standard equation for 

 calculating variance. For this estimator: 



N= (m+n(c+n -l 



rfl 



V(N) = ((m+n (c+n) Km-r) fc-r)! 



(T+lfiT+l) 



Where: 



N= population point estimate 



m= the number of marked fish .; 



c= the number of fish captured in the recapture sample *•' 



r= the number of marked fish captured in the recapture sample 



V(N) = variance for point estimate 



Confidence intervals (CI) were calculated using the equation N + 1 .96 (V(N))'^ 

 and calculated at the 95% confidence level (Appendix C). 



For fish population estimates in small stream, we used a standard two-pass 

 depletion estimator and standard equations for calculating variance (Leathe 1983). For 

 this estimator: 



N = (ni)! 

 ni - nj 



P = auJQ2 

 n, 

 Where: 



N = point estimate, 



ni = the number of fish collected on the first pass 



n2 = number offish captured on the second pass • ' 



P = probability of capture (>0.5 for N>50 or >0.6 for N <50 for valid estimates) 

 Standard deviation = UiS^j£iJ^^ 



(ni-n2) 



95% confidence interval = N + 1 .96 (Standard deviation). The 95% confidence 

 intervals for these estimates are found in Appendix B. 



For small stream population assessments, we commonly use a single pass catch- 

 per-unit effort (CPUE) method as a simple index of relative abundance (Appendix A). 

 From monitoring sections with both CPUE and depletion estimates, we also recentiy 

 developed linear regressions to help predict densities from CPUE (Pierce et al 2004), 

 These regressions confirm correlations between CPUE and density estimates for fish 



17 



