International Council for the Exploration of the Sea
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Report of the Workshop on Age Reading of Saithe (Pollachius virens) (WKARPV)

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posted on 2015-01-01, 00:00 authored by ICESICES

The workshop on age reading of Saithe (Pollachius virens) (WKARPV) was held in Boulogne-sur-Mer, France, from 26 to 29 May 2015. The meeting was co-chaired by Kélig Mahé (France) and Jane A. Godiksen (Norway), and included eight age readers from four countries.The objectives of this first workshop were to review, document and make recommendations on current methods of aging saithe (Pollachius virens).This workshop was preceded by an otolith exchange in 2013, which was undertaken using WebGR. Participants who hadn’t taken part in the exchange were asked to annotate the images in the months prior to the workshop, however, due to problems with accessing WebGR only a limited amount of the readers managed to do this in time. The otolith collection included 298 images from the North Sea and the Barents Sea. The overall agreement with modal age of the pre-workshop exercise was 85.9%, with a precision of 6.2% CV. The images were analysed and the differences discussed and guidelines were established from this discussion. To test the guidelines a set of 50 otoliths from the Barents Sea was read during the workshop. These were read both with reflected and transmitted light and had an agreement ranging between 79.2% and 82.3% with a precision ranging from 3.7% to 4.6% CV. There was clear bias be-tween the individual readers using the two different light sources. Width measure-ment analysis of the 50 otoliths was carried out in plenary after agreeing on the ages of 48 of the 50 otoliths to determine the continuity of the position of the growth rings.

In general, the understanding of the annual rings was high between the readers, and there was little disagreement, however, since the otolith preparation is different among institutes, there was discussion especially about the perception of the edge. Readers used to reading broken otoliths found it difficult to read the edges of the image of the slides. Therefore, we recommend that both broken and slides are com-pared during the next saithe exchange along with images on WebGR.


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Recommended citation

ICES. 2015. Report of the Workshop on Age Reading of Saithe (Pollachius virens) (WKARPV), 26-29 May 2015, Boulogne-sur-Mer, France. ICES CM 2015\SSGIEOM:15. 43 pp.