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
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.
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
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
“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.
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
Cod otolith; photo - Audrey Geffen, University of Bergen