Testing assumptions of otolith radiometric aging with two long-lived fishes from the northern Gulf of Mexico

In this study, we evaluate the assumptions for estimating ages with radiometric and elemental analyses of otoliths of red snapper (Lutjanus campechanus) and red drum (Sciaenops ocellatus) from the northern Gulf of Mexico. In whole otoliths of both red snapper and red drum, 226Ra activity was inversely correlated with the otolith mass increase with age, validating the assumption that 226Ra accumulation in otoliths occurs at a rate proportional to that of Ca. 222Rn emanation from otoliths decreased as otolith mass increased. 222Rn loss occurred in all red snapper otolith samples ([Formula: see text]4.1%) and, to a lesser extent, in red drum otolith samples ([Formula: see text]0.6%) and decreased with increasing size (age) of the otolith. For red drum, the assumption that the initial activity ratio of 210Po to 226Ra in otoliths is essentially zero was indirectly validated with elemental analyses of Pb and Ba. Radiometric age estimation of shallow-water fishes from the northern Gulf of Mexico holds great promise, considering that 226Ra activities observed in this study are some of the highest recorded to date for species to which the 210Pb/226Ra dating technique has been applied.