New handbook on fish age estimation

Cooperative Research Report (CRR) No. 346 Handbook of fish age estimation protocols and validation methods now available.
Published: 8 May 2019

​​ICES ​latest CRR​ presents age estimations methodologies for all major commercial fish stocks in European waters.

Data on age and growth of fish are essential for understanding vital traits of fish species and populations (lifespan, age at recruitment, age at sexual maturity, reproduction periods, migrations, mortality, etc.), the study of population demographic structure and its dynamics (e.g. age-based stock assessment). The age profile of a fish stock can be indicative of its general health, with a broader range of ages signaling a healthier population.

Fish aging is commonly carried out by counting the natural growth rings in fish otoliths – the tiny calcium carbonate ear stones buried behind a fish's brain. In order to review age reading practices and methods, ICES organizes international age reading calibration workshops and exchanges within its community, coordinated by the Working Group on Biological Parameters (WGBIOP).  As a response to the need for greater standaradization of methods, age-reading experts from Europe, the US, and Canada have collaborated to write this CRR.

The resulting report is a comprehensive manual on the methodology of age estimation and validation. It represents a collation of the state-of-the-art scientific work on the methods and validated age estimation of commercially exploited fish species across Europe. Lotte Worsøe Clausen, co-editor, notes that the availability of the latest methodologies by species grouping will also facilitate rapid and quality-assured development of methods suitable for new species.

Standardizing current methods will promote an increase in the quality of data. While the authors would have liked to include a web-based library of validated age-estimations based on mark-recapture fish, they hope what is presented helps experts involved in age estimations as well end-users of age-aggregated data. It will also be of interest to other users, both in terms of the statistical methods for handling biological data and getting insights to the wide range of life histories of fish, their growth, and biology.

Upcoming age reading workshops​

ICES Working Group on Biological Paramenters (WGBIOP) focuses on accuracy in life history parameter estimations to support stock assessment. WGBIOP reviews life-history parameters and monitors potential changes in biological processes, such as growth rate, onset of maturity, and maturity and fecundity at size/age at a national, regional, and stock level, providing a bridge between the data collectors and the end users that has often been lacking in the past. Their ultimate objective is to stimulate the achievement of a higher level of quality within, and integration among European institutes concerning fish age estimation

For upcoming workshops, please refer to the latest WGBIOP report or SmartDots list of events (updated regularly). All past calibration workshop reports can be found on WGBIOPS Data Quality Assurance Repository.  


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​Transversal section of the right otolith of a black scabbardfish at 118 cm TL. The estimated age for this specimen is 12 years. Figure 5.9 in CRR No. 346.

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New handbook on fish age estimation

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