Using 210Pb/ 226Ra disequilibrium to validate conventional ages in Scorpaenids (genera Sebastes and Sebastolobus)

Abstract

Age determination of rockfish (genera Sebastes) and thornyheads (genera Sebastolobus) is typically accomplished by counting growth zones in burnt cross-sections of the otoliths. Interpretation of patterns seen in the otolith’s growth zones is often difficult and subjective so age validation is desirable. Unfortunately, age validation has been nonexistent for many of these species. Their biology and life history often make age validation methods used on other species impossible. Therefore, we used radiometric ageing which employs the disequilibrium of 210Pb and 226Ra in the otolith. Two methods were used to obtain material from the otoliths: core samples and whole otolith samples. The 210Pb/ 226Ra ratios generally confirmed ageing criteria used for rockfish, but in some cases there was a bias between growth zone counts and radiometric ages. We investigated two potential sources of bias. First, the initial ratio of 210Pb/ 226Ra as incorporated into the otolith may have been overestimated. Second, the otolith core removal process may have inadvertently left excessive amounts of younger aged material not belonging to the core. Both would cause radiometric ages to be biased low.