Fifteen years of annual Norwegian–Russian cod comparative age readings

Determining the population age structure of important fish species with high accuracy and precision is fundamental to age-based fish stock assessment. Otoliths sampled for independent age reading by Russian and Norwegian specialists have routinely been exchanged twice annually since 1992. In total, 6386 pairs of otoliths were exchanged during 1992–2006; to verify techniques, 1331 of these were read repeatedly by experts attending annual joint age readers’ meetings. Important lessons have been learned during these 15 years of collaborative, regular, and systematic age reading. Consistency between the two laboratories in reading cod ages appears to have increased. The scientific, biological, and hence economic effect, of this work is easily observed. The need for regular meetings to tune and coordinate age-reading procedures is ongoing.