Between-reader bias and variability in the age-determination process

• Published in: Fishery bulletin (Washington, D.C.) Vol. 89; no. 1; pp. 53 - 60
• Main Authors: Kimura, D K, Lyons, J J
• Format: Journal Article
• Language: English
• Published: 01-01-1991
• Subjects: Marine
• ISSN: 0090-0656

At the Alaska Fisheries Science Center, one in five age readings produced for routine stock assessments are re-aged independently by a second age-reader. The Center now has a large database of repeated age readings that covers a variety of groundfish species and years. The purpose of this paper is to point out the problems and utility of interpreting such a database. Data from six marine fish species are used to show the overall levels of between-reader bias, agreement, and variability that have occurred on production age readings. Other uses for these data include objectively ranking the relative difficulty in ageing different species, maintaining quality control, examining between-reader differences in ageing criteria, and evaluating the possible importance of between-reader bias and variability in later analysis and modeling applications.