Estimating Black Crappie Age: An Assessment of Dorsal Spines and Scales as Nonlethal Alternatives to Otoliths

Abstract

Otoliths generally provide more accurate and precise age estimates for crappies Pomoxis spp. than do scales, but sacrificing crappies for otolith removal may not be desirable in all situations. We evaluated the use of dorsal spines and scales as nonlethal alternatives to otoliths for estimating the ages of black crappies P. nigromaculatus using 111 fish collected from two Minnesota lakes. Among-reader precision was similar for ages estimated from scales and dorsal spines (coefficients of variation [CVs] = 10–14%), but the precision associated with both structures was substantially lower than that observed for otoliths (CVs = 0.12–1.3%). Complete reader agreement (i.e., all three readers agreed on age) for dorsal spines (44–51%) and scales (33–36%) was substantially lower than that observed for otoliths (87–98%). Partial agreement (i.e., at least two of three readers agreed on age) was 100% for both otoliths and dorsal spines and between 79% and 89% for scales. Scale ages assigned by individual readers agreed with consensus otolith ages less than 70% of the time; agreement of individual spine ages with consensus otolith ages was 33% or less. Mean scale ages were usually similar to consensus otolith ages for crappies between the ages of 2 and 6 years, while mean spine ages were consistently lower than consensus otolith ages. Thin-sectioning dorsal spines did not significantly change the number of annuli detected by individual readers. Our results suggest that dorsal spines are not a useful alternative to scales for estimating black crappie age in a nonlethal manner. A conspicuous lumen located in the center of each dorsal spine partially or fully obscures at least one annulus. When otolith removal is not desirable, use of scales and multiple readers may provide mean age estimates that are similar to consensus otolith ages, but we suggest that otolith analysis remains the most reliable method for estimating black crappie age, regardless of latitude.