Report of the Seabass (Dicentrarchus labrax) Otolith and Scale Exchange Scheme 2013

The ICES Planning Group on Commercial Catch, Discards and Biological Sampling (PGCCDBS) identified the need of a seabass Dicentrarchus labrax) otolith exchange to take place in 2013. It was the second exchange after that’s of 2011. The IFREMER institute coordinated this exchange. A total of 223 fish from the bay of Biscay (ICES area : VIII, N=29), the Eastern English Channel (ICES area : VIId, N=149) and the North Sea (ICES area : IV, N=45) was sampled onboard French research vessels (Gwen-Drez and Thalassa) during 3 international surveys (EVHOE, CGFS and IBTS). The length range of the fish was between 26 and 71 cm, with mean 42.3 cm. For each fish, the Sagittae otoliths and few scales were used to compare the age estimation between the both calcified pieces. Only 3 readers were participated from France (1 reader), Belgium (1 reader) and UK England (1 reader). During the first exchange in 2011, there were only 2 countries (France and UK England). Only images were used during this exchange. The analyses did not show a high mean precision of age estimate for individual fish with Coefficient of Variation (CV) of 9.4% and percent agreement to modal age of 68.6%. Among 223 fish, 84 were read with 100% agreement (37%) and thus a CV of 0%. During this exchange, 2 different calcified pieces (otolith and scale) from the same sampling were analysed. The results showed precision of age estimation from the scales (Agreement = 78.4%; CV=1.4) was better than that’s from the otoliths (Agreement = 55.7%; CV=13.4). However, the size of sampling for the otolith exercise (N=149) is twice as much as that’s of the scale exercise (N=74, Tab. 2). Moreover, 2 readers (France and Belgium) preferred to analyse otoliths and only 1 reader the otoliths of seabass.