|The precision of otolith radiometric ageing of fish and the effect of within-sample heterogeneity|
Francis, R.I.C.C. (2003). The precision of otolith radiometric ageing of fish and the effect of within-sample heterogeneity. Can. J. Fish. Aquat. Sci. 60(4): 441-447
In: Canadian Journal of Fisheries and Aquatic Sciences = Journal canadien des sciences halieutiques et aquatiques. National Research Council Canada: Ottawa. ISSN 0706-652X, more
Aging; Marine fish; Otoliths; Marine
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Ageing of fish using radiometric methods applied to otoliths is a widely accepted and valuable technique for validating annulus counts. Initially, whole otoliths were analysed, but it is now more frequent, and requires less stringent assumptions, to analyse otolith cores. Data from published studies were used to calculate typical ageing errors, assuming linear growth in otolith mass. These errors increase with increasing age, are much smaller if an improved method for measuring 226Ra is used, and, for older ages, are greater when cores are used (nevertheless, the use of cores, rather than whole otoliths, is recommended because the stronger assumptions required for the latter are hard to justify or verify). It is common to use more than one otolith per sample (sometimes more than 100) so as to provide sufficient sample mass, and to assume no within-sample heterogeneity in otolith age and mass-growth rate. A simulation experiment was carried out to determine whether any violation of this assumption was likely to have a significant effect on the accuracy of estimated ages. Plausible levels of heterogeneity were found to produce only a negligible decrease in precision and small bias (<10%).