Whole or sectioned otoliths? Choosing the best method for aging bluemouth, Helicolenus dactyloterus (Delaroche, 1809)

• Sectioned and whole otoliths are compared using the same bluemouth individuals.
• Bias and precision are analyzed.
• The results indicate that both methods can be used for aging bluemouth.

Several studies on bluemouth age and growth have been published over the last two decades, but they show inconsistent differences in maximum age estimates, suggesting interpretation differences in reading whole or sectioned otoliths. In order to clarify this issue, the present study was carried out to assess bias and precision of age reading between three age readers using three aging procedures (the ventral face of sectioned otoliths, the ventral face of whole otoliths, and the posterior region of whole otoliths) in the same individuals of the same statistical sample covering a wide total body length range (10–44 cm). Good precision between – reader comparisons and aging procedures was detected with coefficients of variation and average percent errors below 6.70% and 4.17%, respectively. The lowest total agreement between readers was obtained for the ventral face of sectioned otoliths (40.00%) and the highest for the posterior region of whole otoliths (64.17%) increasing to 83.48% and 88.33%, respectively, within ±1 year. The percentage of agreement within ±1 year between aging methodologies was above 90%. No systematic disagreement between readers was detected (p > 0.05) as also no significant differences between readers (U, p > 0.82) and aging procedures (U, p overall = 0.92, p by 5 cm length class >0.55). The results of this study indicate that both sectioned and whole otoliths can be used for aging bluemouth across its length range.