initiative. Landovsoiers are encouraged to participate in all project phases from fish 

 population data collection, to 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 

 (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+1)(C+1) -1 

 R+1 



V(N) - (M+n (C+1) (M-R) (C-R) 

 Where: 



(R+1)\R+2) 



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 -n2 



P = n 1 - n? 

 ni 

 Where: 



N = point estimate, 



ni = the number of fish collected on the first pass 



n2 = number of fish captured on the second pass 



P = probability of capture (>0.5 for N>50, >0.60 for N <50 for valid esfimates) 



Standard deviation = n^n? (n^+n?)"'^ 

 (ni-n2)^ 



22 



