The calibration exercise of age determination of Antarctic Toothfish from Subarea 48.6 by Japanese and Spanish aging laboratories

Japanese and Spanish laboratories have conducted a calibration exercise of ageing work by exchanging sample images of otolith obtained in each fishery at Subarea 48.6 before the 3rd Age determination Workshop for toothfish (WS-ADM3). This exercise aimed to identify differences in aging and readability score level between two laboratories and evaluate whether age datasets provided by the Spanish laboratory last year can be used as input data for the Casal2 model. This paper compares estimated age data using images of two different methods (‘thin section’ and ‘bake and embed’) by Japanese and Spanish laboratories respectively. The result shows that while the Japanese laboratory had good consistency of aging work between two readers using images prepared by both methods, an inconsistency of age estimations was observed when comparing age estimation results of Japanese and Spanish readers, regardless of the two different preparation methods. This result suggests that it is unlikely that the age data provided by the Spanish laboratory can be used as input data for Casal2 as it is. This paper recommends the use of an updated CCAMLR reference list in case Japanese and Spanish laboratories do aging work using different methods. The ‘thin section’ method is intended to be initiated by Spanish labs if possible. In that case, readers participating in the aging workshop will discuss with other readers in other laboratories or an additional calibration exercise between Japan and Spain is recommended.