International Council for the Exploration of the Sea
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Report of the Seabass (Dicentrarchus labrax) Otolith and Scale Exchange Scheme 2011

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posted on 2022-11-10, 11:07 authored by Kélig Mahé, Alison Holmes, Jerome Huet, Karine Sevin, Romain Elleboode

For seabass (Dicentrarchus labrax), Otolith and Scale Exchange Scheme  2011 was the first exchange. A total of 155 fish from Eastern English  Channel (ICES area : VIId) was sampled on-board French research vessels  (Gwen-Drez and Thalassa) during 2 international surveys (Channel Ground  Fish Survey and International Bottom Trawl Survey). The length range of  the fish was between 17 and 74 cm, with a mean length at 46.99 cm. For  each fish, the Sagittae otoliths and few scales were used to compare the  age estimation between both calcified pieces. 4 readers were  participated from UK England (1 reader) and France (3 readers). Only  images were used during this exchange. There were noted by the readers  that it was very difficult to obtain an image of the scale with the same  quality on its whole surface. On 4 readers, 2 readers used transmitted  light for the otoliths and 2 readers used reflected light. There was no  preference to the type of light. The analyses did not show a high mean  precision of age estimate for individual fish with Coefficient of  Variation (CV) of 13.1% and percent agreement to modal age of 54.1%.  Among 155 fish, only 2 were read with 100% agreement (1.3%) 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 the  same precision of age estimation from the otolith (percent agreement =  60.1 ; CV = 12) or the scale (percent agreement = 62.3 ; CV = 12).  However, this exchange showed that the age estimation from the otoliths  was different than this from the scales. 



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