Validation of scale-reading estimates of age and growth in a brown trout Salmo trutta population

In this study, we validated a scale-reading method estimating age and growth in brown trout Salmo trutta in wild, landlocked, stream-dwelling populations from mountain headwaters in the Elbe catchment area of the Czech Republic. The values estimated from scale reading were compared with measured values, collected using a mark-recapture program over eight consecutive years. The age-corrected absolute percentage error was 10.71%, primarily because the ages of the oldest individuals according to scale reading were underestimated, and the ages of juvenile individuals were slightly overestimated. The back-calculated length was slightly underestimated (the mean error was ?4.60 mm), but it was not significantly different from the real measured length. This study suggests that in cold mountain headwaters, scale reading is a sufficiently accurate method for age and growth estimation in juvenile brown trout; however, the results for adult individuals must be taken with caution.