Technical Abstract: Population abundance is a fundamental parameter of fisheries science. Accuracy of estimation of population size based on removal methods depend upon on the relationship between catch per effort, cumulative catch and specific underlying assumptions. A study was conducted to determine if increasing the length of interval between electrofishing passes reduce bias in estimates of population size. Four stream reaches were repeatedly sampled by electrofishing at 15, 30, 60 or 120 minute intervals. Electrofishing was followed by a population census in order measure total numbers and biomass of fish present. Percent differences in estimated and measured numbers and weights of fish were calculated for each sampling interval. The 15 minute interval sampling resulted in percent differences between observed biomass and estimated fish biomass that were significantly higher than all other sampling schemes. The high 15 minute interval average difference was followed by a lower difference for the 30, 60, and 120 minute intervals as might be expected if fish "forgot" the electrofishing experience as time increased between runs.