Evaluation of Dorsal Spines as a Nonlethal Alternative to Otoliths for Estimating Bluegill Ages

Otoliths are considered the most accurate structure for obtaining estimates of fish age for a variety of species, including bluegill (Lepomis macrochirus).  However, removal of otoliths requires fish sacrifice.  Scales offer a nonlethal method to age fish, but scale-based age estimates are often inaccurate and imprecise. Dorsal spines may offer a better nonlethal alternative to otoliths for estimating the age of bluegills, but a previous study indicated that dorsal spines provided consistently lower ages than otoliths for black crappies (Pomoxis nigromaculatus).   Our objective was to determine if ages estimated from dorsal spines and otoliths were similar for bluegills collected from several Wisconsin lakes and to determine if age estimates differed between whole and sectioned dorsal spines. On average, ages estimated from dorsal spines were lower than ages estimated from sectioned otoliths and age estimates from dorsal spines where less precise than those from otoliths.  The extent to which dorsal spine ages differed from otolith ages was not consistent among fish, making development of an age-error matrix difficult. Sectioning of spines appears unnecessary because ages provided from whole spines and sectioned spines were the same.