Use of post-bomb radiocarbon dating to validate estimated ages of Pacific bluefin tuna, Thunnus orientalis, of the North Pacific Ocean

摘要

Estimation of the age of Pacific bluefin tuna (PBF), Thunnus orientalis, is one of the most important processes involved in assessment of its stock biomass. Recently, the ages of PBF have been estimated by analyzing otolith thin sections. However, the accuracy of this estimated age has not yet been confirmed. In this study, the estimated ages of PBF were validated by a novel use of post-bomb radiocarbon dating. The analysis was based on a metric of the abundance of C-14 relative to C-12 (Delta C-14) in the core portion of the otoliths of PBF. The Delta C-14 of the otolith core portion was measured by accelerator mass spectrometry and compared with reference values of corals in the western Pacific. The decrease of the Delta C-14 of the whole otoliths of PBF that were 0-2-years of age from 1982 to 2010 coincided with the decrease of Delta C-14 reference values. This result suggests that post-bomb radiocarbon dating can be used"to estimate ages of adult PBF. The Delta C-14 of the otolith core portions of fish estimated to be 2-27-years of age gradually declined as birth year approached the present day. This trend was consistent with the trend of the reference values and 10%. lower. The portions of the otolith formed after 2-years of age remained on the surface of the adult otolith core; these portions would dilute the Delta C-14 values of the otolith cores of adults and provide an explanation for the depletion. These results support the use of otolith thin sections to estimate PBF ages. (C) 2016 Elsevier B.V. All rights reserved.