Report of the Workshop on Age estimation of Blue Whiting (Micromesistius poutassou) (WKARBLUE)
The workshop on age reading of Blue whiting (WKARBLUE2) took place at IPMA, Lisbon, from the 6th to the 9th of June 2017. The meeting was chaired by Patrícia Gonçalves (IPMA) and Jane A Godiksen (IMR) and included 17 readers from 8 institutes.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 year prior to the workshop. The actual otoliths were also sent round to all participating institutes. The exchanged otolith collection included 245 images. The overall agreement with modal age of the pre-workshop exercise was 64.1%.There were no clear signs of seasonal misinterpretations, but the Mediterranean and most northern areas (ICES area XIVb and NAFO 1C) proved to be quite difficult.
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 with annotations from the work-shop is available in an annex of this report. It will be uploaded to SmartDot as soon as it is up and running on the ICES server. This reference collection of annotated images will hopefully be helpful when running into these issues during future age reading.
Different methods to help age readers determine a zone were discussed during the workshop. The burning of otoliths showed some potential in interpreting the inner ring, but is not to be used as a routine. The sliced technique is time consuming and does not help with interpretation and may introduce misinterpretation of ageing.
During the workshop some of the otoliths from the exercise were polished, to help readers in the cases where the age rings were not so evident, completely absent, or showing a growth pattern different from the expected. The polished results proved useful for ring interpretation and helped during the plenary discussion, although we do not recommend this technique to be used as routine procedure, as it is very time consuming. A Plug-in for ImageJ which can detect variation in opacity in the otolith was presented. Also, a table with possible otolith ring diameters from an IPMA study was tested during the workshop. The table showed potential, but a larger dataset is still needed before it can be adopted as a guideline.
The results from the pre-workshop exchange and from the exercises conducted during the workshop reveal some difficulties on interpreting the blue whiting age rings. Based on those results we further recommend the implementation of daily ring studies and validation of the 1st ring for blue whiting across areas.
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