Age readings of Sebastes marinus otoliths: bias and precision between readers and otolith preparation methods

摘要

This study presents a comparative age reading on Sebastes marinus from the Icelandic shelf within an otolithexchange program between institutes in Germany, Iceland and Norway. Out of a series of 212 otolith pairs, oneotolith of each pair was prepared by the break-and-burn technique, while the other otolith was used for crosssections.Age reading results are compared between readers and otolith preparation methods in terms of bias andprecision, using a set of statistical tests and graphical methods. Significant bias was observed for both thecomparison between readers and between methods, mainly caused by deviations between age scores in thehigher ages ( 20 years). Precision estimates, involving the high longevity of redfish, were relatively goodcompared to previous age reading comparisons using other species. In contrast, the age dependent percentagreement was poor ( 30%) for a tolerance level of ± 0 years, particularly for the age range 21-30 years. Atolerance level of ± 3 years, however, lead to around 90% agreement for the age range up to 20 years. The fit ofage reading scores with the von-Bertalanffy growth curve was relatively good, providing growth parameterscomparable to S. marinus from the Norwegian shelf. The observed problems in bias and precision of agereadings should to be improved by continuing with similar Sebastes otolith exchange programs and setting up afurther age reading workshop to harmonise the interpretation of growth structures.