Age reading just got smarter

The new SmartDots tool aims at making the process of reading fish age smoother.
Published: 5 March 2018

​​​​​​​​​​​​​​​​​​Determining the age of fish underlies the estimation of life history parameters such as growth rates and mortality, as well as catch at age, which are vital for stock assessment. Aging is commonly done 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, co-ordinated by the Working Group on Biological Parameters (WGBIOP). Exchanges are done for quality assurance: they involve multiple readers and a set of otoliths and ensure that agreement exists between readers. 

Over the last ten years there has been a gradual shift to image- based age reading, mostly for the purposes of exchanges but also where institutes are creating their own otolith image reference libraries. Images are now being annotated, meaning there is a record of which growth structures are being identified as the countable rings (known as annuli) as opposed to earlier years when it was only the ages of the fish which were logged. Having a collection of annotated images makes it easier to train new readers.  

Connecting the dots

The ICES Data Centre together with the Flanders Research Institute for Agriculture, Fisheries and Food (ILVO) and the Danish National Institute for Aquatic Resources (DTU Aqua) has developed a new tool, SmartDots, to make the age reading process more streamlined. It enables age readers to annotate otolith images following standardized protocols. It also serves as a database to store annotated images and associated metadata, and to carry out statistical analysis and reporting of results of age reading exchanges and workshops. 

SmartDots has an integrated measuring tool which can be used for both otolith micro and macrostructure increment width analysis, which can potentially support age validation and stock affiliation studies. In the near future the tool will be developed so that it can be used for maturity staging calibration exercises. 

Julie Coad Davies, Chair of WGBIOP and a scientist at DTU Aqua in Denmark, sees the tool as a great improvement for age readers:  

“SmartDots is a huge improvement to the way things have been done before. Previously, the tool being used was not so user intuitive, and its functionalities were limited. We now have a package which combines an age reading tool, an otolith database, and an integrated reporting procedure”, she explained. 

Ensuring quality​​

Coad Davies thinks that the tool will make huge improvements in the overall quality assurance procedures needed when providing biological data. 

“A large part of my work at DTU Aqua is centred on quality assurance of the age data which we provide to ICES. This is used as input for fish stock assessments and will ultimately form the basis of stock management. We need to ensure that bias in age data is kept to a minimum and identify errors resulting from incorrect ageing practices. This needs to be co-ordinated internally at our institute and also internationally. SmartDots helps us with this process. As well as this and its user-friendliness, the tool has great potential for further development in both otolith related and a wider range of biological studies.”

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​Cod otolith; photo - Audrey Geffen​, University of Bergen

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Age reading just got smarter

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