Objective

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 Acipenser transmontanus. The mark–recapture history information for White Sturgeon allowed for the evaluation of fin rays for age and growth analysis.

Methods

Age was estimated from pectoral fin rays of known‐age White Sturgeon (n = 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).

Result

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.

Conclusion

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.