Report of the Workshop on the Age Reading of Blue Whiting
The workshop on age reading of blue whiting (WKARBLUE) was held in Bergen, Norway, from the 10th to the 14th of June 2013. The meeting was co-chaired by Jane A. Godiksen (Norway) and Manolo Meixide (Spain), and included 19 age readers from 11 countries, where one country participated by web-camera.
The objectives of this workshop were to review, document and make recommendations on current methods of aging blue whiting (Micromesistius poutassou).
This workshop was preceded by an otolith exchange, which was undertaken using WebGR in the months prior to the workshop. The exchanged otolith collection included 158 images from the previous exchange, 50 of these, along with 100 new otoliths, were also read during the workshop after establishing guidelines for reading. The overall agreement with modal age of the pre-workshop exercise was 56.6%, with a precision of 13.2% CV. The three sets of otoliths read during the workshop had an agreement ranging between 54.5% and 74.1% with a precision ranging from 13.4% to 40.5% CV. The collection with the highest agreement and highest CV was a collection from the Faroe Islands including many young fish, which are easier to read than older specimens.
The main issues during this workshop were identification of the position of the first annual growth ring, false rings and interpretation of the edge. These issues are the same as has been mentioned in previous reports, and thus a reoccurring problem among age readers. A reference collection of images from the workshop will be made and placed in WebGR, this will hopefully be helpful when running into these issues during reading.
Bias in age readings is an issue that would strongly affect the stock assessment. The results of this workshop show that the readers, who submit blue whiting age compositions to the Working Group on Assessment of Widely Distributed Stocks (WGWIDE) presented null or low bias in three of the four samples used. Strong bias was observed in the last sample among both experienced and new readers, and that particular sample was considered by all readers as very difficult to age.
Published under the auspices of the following ICES Steering Group or Committee