An Evaluation of the Accuracy of Age Estimation Methods for Southern Lake Michigan Alewives

Abstract

An evaluation of otoliths, scales, vertebrae, and opercles taken from southern Lake Michigan alewives Alosa pseudoharengus was conducted to identify the best structure for estimating age. Based on percent agreement and coefficient of variation analyses, ages estimated from otoliths were significantly more precise than ages estimated from other structures. Mean frequency counts of annuli on scales, vertebrae, and opercles tended to overestimate the relative abundance of young fish and underestimate the relative abundance of older fish more than those of otoliths. Length frequency histogram analysis of alewives collected in 2003 corroborated the accuracy of otolith age estimates. The mean time necessary to estimate alewife ages did not differ significantly between structure types. Based on their precision, accuracy, and time efficiency, otoliths are recommended for estimating ages of southern Lake Michigan alewives.