Comparison of bias and precision of fin rays, otoliths, and scales for ageing Brook Trout (Salvelinus fontinalis), Brown Trout (Salmo trutta), and Rio Grande Cutthroat Trout (Oncorhynchus clarki virginalis)

Abstract

The precision, bias, and accuracy of age estimates from scales, pelvic fin rays, and otoliths were compared for Brook Trout (Salvelinus fontinalis), Brown Trout (Salmo trutta), and Rio Grande Cutthroat Trout (Oncorhynchus clarki virginalis). Calcified structures were collected for each fish and age estimates were obtained by counting the number of annuli by two independent readers. The precision of age estimates was estimated by coefficient of variation (CV), and percent agreement (PA) between readers. Bias and accuracy were investigated through analysis of age-bias plots and Wilcoxon matched pairs rank tests. In all analyses, age estimates of Brook Trout, Brown Trout and the Rio Grande Cutthroat Trout were most precise using otoliths and fin rays. Typically, age estimates of otoliths and fin rays were more accurate than scales particularly for age classes > 4. Age estimates with scales typically underestimated the age of older fish whereas age estimates of fin rays and otoliths were closer in agreement. The differences of age estimates from fin rays, otoliths, and scales found in this study emphasize the importance of validating calcified structures for these species. Additionally, the accuracy and precision of age estimates from fin rays demonstrate that this method is a viable nonlethal alternative to the lethal sampling required for obtaining otoliths.