Corrected Analysis of the Ability to Detect Reductions in Year-Class Strength of the Hudson River White Perch (Morone americana) Population

Abstract

This analysis presents a correction of that presented in Van Winkle et al. (1981; Can. J. Fish. Aquat. Sci. 38: 627–632). An exact solution is obtained based on the noncentral t-distribution to replace the incorrect solution based on the central t-distribution used in our earlier analysis. Our new results, although less pessimistic than before, still are not encouraging. They indicate that variability in baseline data is so great that data from 10 additional years are not adequate for detecting even substantial (> 50%) reductions in mean year-class strength, and that at least 20 years of data collection would be required to detect an actual 50% reduction in mean year-class strength, given a Type II error of 50%.Key words: fractional reduction, impingement, power plant, statistical power, Type I and Type II errors, white perch, year-class strength