Radiometric age validation of Atlantic tarpon, Megalops atlanticus

An improved radiometric aging technique was used to examine annulus-derived age estimates from otoliths of the Atlantic tarpon, Megalops atlanticus. Whole otoliths from juvenile fish and otolith cores, representing the first 2 years of growth, from adult fish were used to determine Pb-210 and Ra-226 activity; six age groups consisting of pooled otoliths and nine individual otolith cores were aged. This unprecedented use of individual otolith cores to determine age was possible because of improvements made to the Ra-226 determination technique. The disequilibria of Pb-210:Ra-226 for these samples were used to determine radiometric age. Annulus-derived age estimates did not agree closely with radiometric age determinations. In most cases, the precision (CV less than or equal to 12%) among the otolith readings could not explain the differences. The greatest radiometric age was 78.0 yr for a 2045-mm-FL female, where the radiometric error encompassed the annulus-derived age estimate of 55 yr by about 4 yr. The greatest radiometric age for males was 41.0 yr for a 1588-mm-FL tarpon, where the radiometric error encompassed the annulus-derived age estimate of 32 yr by I yr. Radiometric age determinations in this study indicated that the interpretation of growth zones in Atlantic tarpon otoliths can be difficult, and in some cases may be inaccurate, This study provides conclusive evidence that the longevity of the Atlantic tarpon is greater than 30 years for males and greater than 50 years for females.