Comparing Scale and Otolith-Based Aging Methods for Age Estimation of Hornyhead Chubs
Calcified structures such as otoliths and scales are frequently used to age fishes. Scales can be read to age fishes which does not require specimens to be destroyed, but the accuracy of ages derived from scales can vary due to scale reabsorption or damage during the life of a fish. Otoliths, calcium carbonate structures found in the inner ear, aren’t reabsorbed and are more accurate for estimating ages than scales. However, otoliths require practice to consistently remove and specimens are severely damaged in the process. Scales may be used to assess age demographics of understudied fishes like Hornyhead Chubs, but without directly comparing scale-based ages to age estimates from otoliths, differences in data collected from scales and otoliths are unknown. This study compared estimates from Hornyhead Chub scales and otoliths to fish length to quantify variation within length-at-age data sets based on each structure. Otoliths and scales from dorsal and pectoral regions were extracted from Hornyhead Chubs of varying lengths. Age estimates were obtained by counting annuli in otoliths and scales, and the standard length of each fish was measured. Ford-Walford plots were generated for each structure and used to calculate Von Bertalanffy growth curve variables. Ages collected from dorsal scales formed a growth curve with a larger asymptotic growth (L∞) and growth constant (K) than otoliths, while pectoral scale ages created a curve with smaller L∞ and K values in comparison to otoliths. Both scale-based length-at-age data sets had higher standard deviation for each age than ages derived from otoliths. These results demonstrate that using scales to age Hornyhead chubs can lead to increased data variability, which should be accounted for when assessing age demographics of Hornyhead Chub populations with scales.