A Comparison of Techniques Using Dorsal Spines to Estimate Sauger Age

Abstract

Fish age is useful to fishery managers when evaluating growth rates, mortality rates, and reproduction. Our objective was to determine whether two methods for estimating the age of saugers Sander canadensis using dorsal spines—side illumination and spine sectioning—resulted in similar age estimates at the same efficiency and cost. To do this, we determined whether the coefficients of variation (CV = 100 · SD/mean) differed between age estimates of fish using the two techniques in the Missouri River and a portion of the Kansas River. We found that the CVs did not differ significantly between techniques. While reader agreement did not differ significantly, side illumination took one-half as much time as sectioning. In addition, side illumination displayed outer annuli on older fish better than sectioning and did not require an expensive low-speed saw, microscope slides, or a mounting medium for processing. We conclude that side illumination is the most time- and cost-efficient method for estimating sauger ages from spines.