Ryan S. Hardy Sean Wilson Michael C. Quist Courtnie L. Ghere 2024 <p>Objective </p><p><span>Successful conservation and management of fishes require an understanding of their age and growth. However, methods for estimating the age and growth of long-lived fish species are difficult to validate. The Kootenai River basin has a decades-long mark–recapture program for endangered White Sturgeon&nbsp;</span><i>Acipenser transmontanus</i><span>. The mark–recapture history information for White Sturgeon allowed for the evaluation of fin rays for age and growth analysis.</span></p><p>Methods </p><p>Age was estimated from pectoral fin rays of known‐age White Sturgeon (<i>n</i> = 162) to evaluate ageing accuracy and precision. Lengths were back‐calculated using four models and measurements obtained from two fin ray transects (i.e., lateral and posterior). </p><p>Result </p><p><span>Between-reader agreement for White Sturgeon ages was 58.7%. Consensus age agreement with known ages was poor (30.7%) and decreased with age. Among the four back-calculation models, the Fraser–Lee model provided the lowest root mean square error and percent error. Estimates of mean back-calculated lengths at age derived from the Fraser–Lee model were similar between the two measurement transects. Back-calculated lengths at age were similar to known lengths at age.</span></p><p>Conclusion </p><p><span>Ageing of White Sturgeon using fin rays was unreliable, and accuracy decreased with fish age. Back-calculated lengths at age were accurate using measurements from fin rays of known-age fish. Length estimates from the two measurement transects were similar when using the Fraser–Lee method, suggesting that they may be used interchangeably.</span></p> application/pdf 10.1002/nafm.11021 en Wiley Evaluation of techniques for estimating the age and growth of known‐age White Sturgeon article