The radiometric ageing technique was used in an attempt to validate annulus-derived age estimates from otoliths of the Atlantic tarpon, Megalops atlanticus. Whole juvenile otoliths and otolith cores from adults, representing the first 2 years of growth, were used to determine the validity of age estimates derived from otolith annulus counts and to validate longevity. Fifteen otoliths samples were processed to determine 210Pb and 226Ra activity. Six of the samples were age-groups consisting of pooled otoliths, and nine were individual otoliths. This unprecedented use of individual otoliths cores was made possible because of improvements to the 226Ra assessment technique. The disequilibria of 210Pb:226Ra for these samples were used to determine radiometric age. Annulus-derived age estimates did not closely agree with radiometric age determinations. In most cases, low level of precision among the otoliths readings could not explain the differences. The greatest radiometric age was 82.1 yr for an individual female which was 27 years greater than the annulus-derived age estimate for this fish. The greatest radiometric age for males was 43.7 yr which was slightly greater than the annulus-derived age estimate for this fish (32 yr). Von Bertalanffy growth parameters were calculated from the radiometric age estimates and compared favorable with annulus-derived estimates. Because the radiometric ageing technique has improved and numerous studies support its validity, the radiometric ages determined in this study may be more accurate than annulus-derived age estimates. Based on radiometric age estimates the longevity of the Atlantic tarpon was confirmed to be at least 33.3 yr for males and 53.2 yr for females, but may exceed 43.7 yr for males and 82.1 yr for females.
Funding: This work was supported in part under funding from the Department of the Interior, U.S. Fish and Wildlife Service, Federal Aid for Sportfish Restoration Project Number F-59.
1Florida Marine Research Institute
Department of Environmental Protection
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