Results of the blue whiting otolith exchange

Abstract

At the Blue Whiting Assessment Working Group, it was agreed to carry out an otolith exchange programme to solve the ageing problems pointed out by ACFM. A sample of 115 otoliths from Division IXa was exchanged, and seven countries are taking part in the exchange, although it has not yet been completed. One otolith from each fish was sectioned and the other preserved in aqueous solution. In the whole otoliths a tendency to lose one or two early rings was observed, and in the sectioned otoliths the presence of false rings was the cause of misreading. A combination of both methods would probably improve the age determinations, but is unfortunately time consuming. The agreement between the readers was in general low, from both sliced and whole otoliths.The ANOVA with a significance level of 5% showed that the mean age of the sample is different for various readers, and the Tukey test showed that there are no significant differences between three readers, at the same significance level. Considering the importance of ageing in the .assessment, new investigations are needed to improve the agreement, and it is suggested that further samples are exchanged, or that an otolith workshop should be convened.