Precision of Smallmouth Bass Age Estimates from Sectioned Otoliths and Pectoral Fin Rays

Previous research has indicated that sectioned pectoral fin rays are a suitable non-lethal alternative to otoliths for age estimation in many fish species, although fin rays may underestimate age for relatively old fish.  However, no published studies have evaluated precision of sectioned otoliths and pectoral fin rays for estimating age of smallmouth bass (Micropterus dolomieu).  Smallmouth bass (125-483 mm total length) were collected from five lakes and rivers in Illinois by electrofishing.  Sagittal otoliths and pectoral fin rays were removed from 72 fish, embedded in epoxy, sectioned, and examined by three independent reading pairs (two readers per pair).  Age-bias plots of within-reading pair, among-structure comparisons showed minimal bias; age estimates from otoliths and pectoral fin rays agreed within one year 73% of the time within reading pairs.  Ages assigned by the three independent reading pairs agreed within one year 86% of the time using otoliths and 78% of the time using pectoral fin rays.  Coefficients of variation for age estimates obtained from otoliths and pectoral fin rays were not statistically different from one another (P > 0.05), and length had no significant influence on the coefficient of variation of age estimates for either aging structure (P > 0.05).  Mean otolith and pectoral fin ray age estimates for individual fish were highly correlated (r² = 0.81, P < 0.05).  Our results indicate that precision of age estimates is comparable among these two structures and suggest that pectoral fin rays may provide non-lethal alternative to otoliths for estimating age of smallmouth bass.