Report of the Roundnose grenadier (Coryphaenoides rupestris) Otolith Exchange Scheme 2011

The roundnose grenadier (Coryphaenoides rupestris) Otolith Exchange 2011 was a second one after the exchange of 2007. It was composed by 2 sets of otoliths from VIa(western Scotland ; n=64, the same as the exchange 2007 used one) sampled from January to June 2006 and otoliths from IIIa (Skagerrak ; n=63) sampled from January 2011. 6 readers participated from Spain (3 readers), UK England (1 reader), Norway (1 reader) and France (1 reader). Only images of otoliths sections were used during this exchange. The set of otoliths from VIa showed Coefficient of Variation of 14.9% and percent agreement to modal age of 29.3%. The set of otoliths from IIIa showed Coefficient of Variation of 22.6% and percent agreement to modal age of 30.7%. These results from both areas were very close to those from 2006. For the roundnose grenadier in the western Scotland (VIa) and in the Skagerrak (IIIa), there was an important bias between the readers and the modal age. In the western Scotland, with the same sampling between 2007 and 2011, the level of precision was very close in the 2 exchanges (2007 and 2011) but there was a certainly bias between both modal ages and between 2 readings of each reader. The sample from the Skagerrak was composed by younger fish than those of the sample from the western Scotland but the results showed the same bias. Sections of these otoliths remain definitively very difficult to interpret.