. The Canadian field-naturalist. Natural history; Sciences naturelles. 5 10 15 Opercle (yr) 20 -,. Figure 1. Comparison of Greater Redhorse opercle-based age estimates with those from scales (top) and pectoral fin rays (bottom). Opercle vs. scale CV (mean ± SE): ± Opercle vs. pectoral fin ray CV: ± from the opercle (Figures 1 to 4). Mean pairwise dif- ferences between scale-based age estimates and those from fin rays and opercles were at least double that between fin rays and opercles (Table 2). Regenerated scales were common. Agreement between age estimates from fin ray


. The Canadian field-naturalist. Natural history; Sciences naturelles. 5 10 15 Opercle (yr) 20 -,. Figure 1. Comparison of Greater Redhorse opercle-based age estimates with those from scales (top) and pectoral fin rays (bottom). Opercle vs. scale CV (mean ± SE): ± Opercle vs. pectoral fin ray CV: ± from the opercle (Figures 1 to 4). Mean pairwise dif- ferences between scale-based age estimates and those from fin rays and opercles were at least double that between fin rays and opercles (Table 2). Regenerated scales were common. Agreement between age estimates from fin rays and opercles was greater than that between scales and the other two structures (Table 2). For all species except Silver Redhorse, there were no significant differences between age estimates from fin rays and opercles. However, the maximum difference between age esti- mates from these two structures was as large as 6 to 11 years. Fin ray based maximum age estimates were also 2 to 4 years less than those from opercles (Table 2). More frequent underestimation of age using fin rays began between ages 12 and 15 (Figures 1-4). For all species except Greater Redhorse, agreement between first and second interpretations of each structure was greater for pectoral fin rays and opercles than for scales (Table 2). JU â 25 / / r 20 ' >, / â â â , â r3 / g Qi 15- â â / c y U. â â / â â / â 10- ⢠J 5 0 â 10 15 20 Opercle (yr) 25 30 Figure 2. Comparison of River Redhorse opercle-based age estimates with those from scales (top) and pectoral fin rays (bottom). Opercle vs. scale CV (mean ± SE): ± Opercle vs. pectoral fin ray CV: ± For Shorthead Redhorse and Siher Redhorse, sam- ple numbers permitted an evaluation of w hether dif- ferences in age estimates among structures were con- sistent across drainages. For Shorthead Redhorse, there was a greater le\'el of agreement among Grand Ri\ er structures (mean pairwise differences: to years


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