Lead-radium dating - Pacific cod
SHORT LIFESPAN for Pacific Cod
Published with Marine and Freshwater Research 2016
Lead-radium dating of Pacific cod (Gadus macrocephalus) - validation of the young-fish scenario
ABSTRACT: Age readers disagree on the age reading interpretation of otolith growth patterns for the Pacific cod (Gadus macrocephalus). One interpretation describes a young-fish scenario with a life span near 10- 12 years, whereas another interpretation describes an old-fish scenario at more than 30 years. In this study, lead- radium dating was performed on Pacific cod otoliths to test the validity of the old-fish age reading scenario. Radiometric ages revealed that the young-fish scenario was valid because the actual age of the two oldest adult groups was more than 20 years younger than estimated by the old-fish scenario.
Publication: Andrews 2016
Plot of Pb-210:Ra-226 ingrowth curve with measured activity ratios for Pacific cod otolith samples plotted relative to two time scenarios (solid line = direct ingrowth, dashed line = core-age corrected). The young-of-the-year sample (circle) was in agreement with the predicted ingrowth for the total age of the sample (4.7 years, including storage time), providing an indication that measurements made from adult core material will provide valid estimates of age. The adults are initially plotted (squares) at the old-fish scenario age estimate for each group, providing an indication that age estimates were not accurate by up to ~20 years (offset from ingrowth curve to the right). Projection of these age estimates (arrows) to the ingrowth curve (A) indicates the corresponding Pb-210:Ra-226 activity ratio for these older ages would be well beyond any analytical uncertainties. Projection (arrows) of the measured Pb-210:Ra-226 activity ratios to the ingrowth curve (B) provides valid estimates of age that are much younger than can be accounted for in the old-fish scenario (Table 2). Error bars for age reading were removed because the uncertainty is no longer applicable once projected to ingrowth curve for an independent age estimate.
