International Council for the Exploration of the Sea
Report of the 2017 3.a Sprat Age Reading Exchange.pdf (562.22 kB)

Report of the 2017 3.a Sprat Age Reading Exchange

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posted on 2022-11-14, 11:14 authored by Julie Coad Davies

In 2016 a pre-workshop sprat exchange took place for the North Sea (4) and Celtic Seas Ecoregion (Divisions 7 (excl. 7.d, e) and 6) stocks. The initial intention was to include samples from the 3.a (Skagerrak and Kattegat) stock but this was not possible due to problems with WebGR. WKARSPRAT (the Workshop for the Age Estimation of Sprat) took place in November 2016. At the workshop the 3.a exercise was partially completed by those readers who were present but time restraints did not allow for all samples to be examined (see ICES, 2016 for results). Much time was spent discussing samples in plenary, the general opinion of the members was that there are regional differences in the readability of the otoliths from the three sprat stocks, with those from 3.a being the most difficult to interpret. Correct age determination of sprat is confounded by the presence of faint translucent rings which are not true annuli and a lack of contrast between the true summer and winter rings (wr), the later feature being most apparent in otoliths from 3.a sprat. Results were discussed during the workshop and a timetable for completion of the 3.a exchange was drafted. An updated age reading protocol and an agreed age image reference collection was compiled by the members of the workshop. Readers were instructed to follow this protocol when completing the rerun of the 3.a exchange. The results here are based on all 100 samples and 10 readers from 6 institutes (Denmark Norway, Sweden, Northern Ireland, Ireland and Germany) who participated, only 4 of whom (from Denmark and Sweden) routinely read 3.a sprat.



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