Workshop on Ageing Validation methodology of Mullus species (WKVALMU)
The Working Group on Biological Parameters (WGBIOP) meeting in 2016 (ICES, 2016) recommended a Workshop of Ageing Validation methodology for Mullus species (WKVALMU). This workshop (Co-chairs: Kélig Mahé, France; Pierluigi Carbonara, Italy and Chryssi Mytilineou, Greece) has been held in Conversano (Italy) from 15 to 18 May 2017. Five countries took part in this meeting (Italy, Spain, Greece, France, Croatia) for a total of 16 participants. This meeting was organized to try to clarify the rules which are applied on the ageing of mullet species (Mullus surmuletus and M. barbatus). At the beginning of the workshop, a lot of presentations were discussed focusing on the used ageing methodologies by each institute and all ageing validation studies. A synthesis of validation methods was conducted during the workshop aiming to identify a) the first false ring coinciding with the demersal check formation for both species (for the fish around 5 cm of total length), b) the period with opaque edge in otoliths (from May to October) and c) the mean length at the first age groups derived from the length distribution analysis. Various schemes for the age interpretation are used by the readers. This is a source of bias in the readings. As a consequence, schemes for the age interpretation have been discussed. Two main age interpretation schemes were decided to be applied on a set of 40 images. These otoliths had also been used in the 2011 exchange. The bias between the two age interpretation schemes was estimated. According to this, the bias between readers was smaller for the scheme 1 (birthdate: 1st January) than scheme 2 (birthdate: 1st July). Differences in ageing were detected during the first semester. Moreover, these results showed the low agreement between readers for each interpretation scheme. Comparing the modal age obtained by each interpreta-tion scheme, a significant difference was observed. For stock assessment and management purposes, it would be desirable that all countries use the same age interpretation scheme. Based on several discussions on the age interpretation results of this exercise, a new age interpretation scheme was proposed during this workshop. The WKVALMU proposed recommendations for the next exchange which will be organ-ised in 2018. In 2019, the new workshop (WKCAM3; Split; co-chairs: P. Carbonara, It-aly; K. Mahé, France; D. Medvesek, Croatia) will focus on the analysis of the new exchange results, validation studies and will formalise guidelines on the ageing of Mul-lus surmuletus and M. barbatus. During the present workshop, it was noted that the difficulty and the low agreement in age interpretation makes necessary the development of a European project on age validation methods. Consequently, a draft proposal has started to be written during this workshop.
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