Report of the Workshop on Age Reading of Chub mackerel (Scomber Colias) (WKARCM)
The Planning Group on Commercial Catch, Discards and Biological Sampling (PGCCDBS), meeting in February 2014, recommended the realization of a first Workshop on Age Reading of Chub Mackerel to discuss the results of a previous exchange and the development of validation studies in this species (ICES, 2014a). The Workshop on Age Reading of Chub Mackerel (WKARCM, chaired by Andreia Silva, Portugal, and Maria Rosario Navarro, Spain) has been held in Lisbon (Portugal) from the 2–6 November 2015. Three countries took part in this workshop (Portugal, Spain and Italy), with a total of 12 participants. The aim of this workshop was to review the information on age determination, discuss the results of the previous exchange (2012–2013), review the validation methods existing on these species, clarify the interpretation of annual rings, elaborate an age reading protocol and start a reference collection of well-defined otoliths.
This workshop was preceded by two otolith exchanges (2012–2013 and 2015). Three age validation studies, in three different areas (Bay of Biscay, Portugal and Maurita-nian waters) were presented, as well as a compilation of age validation studies of this species in the literature. After the presentation of readings results (mean agreement percentage from 57.5%; mean CV from 29.6%) and the precision of age estimation, the participants identified the sources of bias in the interpretation of the Chub mackerel age. The large number of checks and the position of the first growth ring were identi-fied as the most important problems.
After discussion, a new exercise was made. The precision increased to 60.6% and the mean CV increased to 45.6. Moreover, the number of participants that follow the same age reading criteria increased, although it is still necessary to continue to clarify the age reading interpretation. In consequence, the participants of WKARCM recom-mended studies on validation methods for Scomber colias in all the participating areas and the realization of a new otolith exchange in the following year (2016) to focus on the analysis of exchange results, validation studies and review the age reading protocol for Scomber colias.