Report of the Workshop on Age reading of Horse Mackerel, Mediterranean Horse Mackerel and Blue Jack Mackerel (Trachurus trachurus, T. mediterraneus and T. picturatus) (WKARHOM2)
The Workshop on Age reading of Horse Mackerel, Mediterranean Horse Mackerel and Blue Jack Mackerel (Trachurus trachurus, T. mediterraneus and T. picturatus) (WKARHOM2) was held in Santa Cruz de Tenerife (Canary Islands, Spain) 26–30 October 2015. The meeting was co-chaired by Kélig Mahé (France) and Pierluigi Car-bonara (Italy), and included twelve age readers from six institutes (five countries). The objectives of this workshop were to review, document and make recommenda-tions on current methods of ageing Trachurus species.This workshop was preceded by otolith exchanges in 2014, which were undertaken using WebGR. A total of 550 fish was sampled from the Atlantic Ocean (Eastern Channel, Celtic Sea, Bay of Biscay, Azores, Portuguese waters and Tenerife) and the Mediterranean Sea (Alboran Sea, South Adriatic Sea and Ligurian Sea). 19 readers from 8 countries (France, Germany, Spain, Ireland, Italy, Portugal, Netherlands and Norway) participated to this exchange. Among three Trachurus species, all data showed a very low precision with the percentage of agreement between 47 and 56% and a CV from 29 to 69%. The precision analysis showed the same level of precision between otolith sections and whole otoliths from the Ligurian Sea.The workshop achieved quite a lot in terms of ironing out, through discussion and calibration, of some of the major difficulties in ageing otoliths of Trachurus species. The results of the comparison between different ageing techniques on the same set of fish, showed a bias intra-reader and so it is recommended to use only one ageing technique by each reader. Moreover, the precision of reading is the same between slices and whole otoliths and so there is not a best ageing technique for T. trachurus. The progress of reading showed a percentage of agreement close to 65% for T. trachu-rus and Trachurus picturatus. However, the percentage of agreement for Trachurus mediterraneus remained to 44.4% with a CV to 40. In fact, the next exchange must be target Trachurus mediterraneus as a priority. Finally, this group reached an agreement on a definition of an ageing guideline and a reference collection presented in this report and the aim is to employ these tools for all laboratories.
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