Workshop on Age reading of Horse Mackerel, Mediterranean Horse Macke-rel and Blue Jack Mackerel (Trachurus trachurus, T. mediterraneus and T. picturatus) (WKARHOM3), 5–9 November 2018. Livorno, Italy.

Based on the previous work of WKARHOM2 (2015), the Working Group on Biological Parameters (WGBIOP 2017) identified the need for a new otolith exchange followed by an age reading Workshop. The Workshop on Age reading of Horse Mackerel, Medi-terranean Horse Mackerel and Blue Jack Mackerel (Trachurus trachurus, T. mediterraneus and T. picturatus) (WKARHOM3) was held in Livorno (Italy) from the 5th to the 9th No-vember 2018. The meeting was co-chaired by Alba Jurado-Ruzafa (Spain), Kélig Mahé (France) and Pierluigi Carbonara (Italy), and included fifteen age readers from nine countries. The objectives of this workshop were to review the current methods of age-ing Trachurus species, to evaluate the new precision of ageing data of Trachurus species and to update guidelines, common ageing criteria and reference collections of otoliths. The exchange results showed a low value of percentage of agreement from 45.1% to 59.1% for the three Trachurus species. The Coefficient of Variation was lower for T. trachurus (17.3–32.2) than for the other Trachurus species (60.1-73.4) because the sampled specimens were older for this species than for the two other species. With feedback from the readers present at the exchange and the discussion during the WKARHOM3 meeting, the main cause of age determination error for T. trachurus was identified as otolith preparation techniques (whole/slice). However, for the three Trachurus species, there are several difficulties in age determination: identification of the first growth an-nulus, presence of many false rings (mainly in the first and second annuli) and the interpretation and identification of the edge characteristics (opaque/ translucent). The second reading was performed during the workshop with 50 images per each species. Each reader read only the images of the species that is read in their laboratory. The percentage of agreement between readers increased to 70.6% with a CV of 18.4 for T. trachurus and to 67.8% with a CV of 31.7 for T. mediterraneus. Finally, this group reached an agreement on defining an ageing guideline and a reference collection presented in this report and the aim is to employ these tools for all laboratories