Bomb radiocarbon and lead - radium disequilibria in otoliths of bocaccio rockfish (Sebastes paucispinis): a determination of age and longevity for a difficult-to-age fish

Abstract

Longevity estimates for the bocaccio rockfish (Sebastes paucispinis) using traditional techniques range from less than 20 years to approximately 50 years. Otoliths of bocaccio are difficult to age, and previous attempts to validate ages have been unsuccessful. Because otolith age suggests the bocaccio are reasonably long-lived, lead–radium dating was used in an attempt to independently age bocaccio otoliths. The measured 210Pb and 226Ra activities were among the lowest reported and resulted in poor radiometric age resolution; however, the break-and-burn technique clearly underestimated age in some cases with the longevity of the bocaccio being at least 31 years. To provide better age resolution, the bomb radiocarbon approach was applied to individual otoliths. Based on measured radiocarbon levels relative to a reference time-series, several specimens were aged at approximately 30–40 years. To evaluate these determinations, the remaining otolith of the pair was sectioned and aged blind. The result was an excellent fit to the reference time-series and a validation of the age estimates. The maximum age from growth zone counts was 37 ± 2 years, which is consistent with a reported maximum age of approximately 50 years.