Age Readings of Sebastes mentella Otoliths: Bias and Precision Between Readers by

This study presents comparative otolith-based age readings of pelagic redfish (Sebastes mentella) from the Irminger Sea within an otolith exchange program between institutes in Germany, Iceland and Norway. 213 otoliths were thin-sectioned and read independently in the participating labs. Age reading results were compared between readers in terms of bias and precision, using a set of statistical tests and graphical methods. Significant bias was observed between readers, mainly caused by deviations between age scores in the higher ages (> 20 years). Precision estimates, considering the high longevity of S. mentella, were relatively good compared to age readings of other long-lived species. In contrast, the age dependent percent agreement was poor (< 20%) for a tolerance level of ± 0 years, particularly for the age range 21-40 years, which represents the major fraction of the fished stock. A tolerance level of ± 5 years, however, lead to around 90 % agreement for the age ranges up to 20 years. The fit of age reading scores with the von-Bertalanffy growth curve was relatively good, showing good correspondence between readers. A comparison of growth parameters with age-length relationships reported for demersal S. mentella in shelf areas in the Northeast Arctic, around Greenland and on the Fle mish Cap showed that pelagic S. mentella generally exhibits slower growth. In the age range up to 10 years, however, relatively large fast-growing juveniles seem to be present, probably having recruited from the higher productive shelf area