The use of Pb-210/Ra-226 and Th-228/Ra-228 dis-equilibria in the ageing of otoliths of marine fish

Naturally-occurring isotopes of radium are ideally suited as tracers for chemical uptake in the calcified tissues of marine organisms since radium is a water soluble, bio-geochemical analogue for calcium. Assays designed to exploit this uptake mechanism can be used to determine the longevity of certain species of fish. Measurements of Pb-210/Ra-226 disequilibria in the otoliths of redfish have revealed that this species of fish can live to ages in excess of 75 years in coastal waters off Nova Scotia, Canada. Measurements of the Th-228/Ra-228 disequilibria in the otoliths of the much shorter-lived silver hake and flying fish may provide estimates of longevity on time scales of 0-10 years, which could then be used to evaluate the accuracy of currently-used ageing models based on otolith annulus counts. Age determinations of fish based on natural radioisotopes can result in significant improvements in the assessment and management of certain fisheries resources. (author)