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Report2014

Report of the Benchmark Workshop on Baltic Flatfish Stocks (WKBALFLAT), 27–31 January 2014, Copenhagen, Denmark.

Willestofte Berg, Casper; Bergenius, Mikaela; Brooks, Liz; Degel, Henrik; Drevs, Tenno; Eero, Margit; Florin, Ann-Britt; Fowler Fowler, Mark; Hemmer-Hansen, Jakob; Hollowed, Anne

Abstract

The Benchmark Workshop on Baltic Flatfish Stocks (WKBALFLAT) 2014 was convened between 26 November 2013 and 31 January 2014. It included an initial three days data compilation workshop (DCW) 26-28 November 2013 and a five day benchmark meeting 27-31 January 2014. The process started with a data call in October 2013 for which all member states were requested to upload data to relevant ICES databases and provide information to the stock coordinators. The group worked by correspondence between the two physical meetings. The DCW was chaired by two ICES chairs: Margit Eero (Denmark) and Mikaela Bergenius (Sweden). The benchmark meeting in January was chaired by Liz Brooks (USA) with the assistance of the two ICES chairs. Two independent scientists from outside the ICES community reviewed the work conducted and provided comments and input during the discussions: Anne Hollowed (USA) and Mark Fowler (Canada). This benchmark workshop considered the assessment units, data availability for assessment and the assessment methods for Dab and Flounder in Subdivisions 22-32 in the Baltic Sea. Concerning stock units, the starting point was one assessment unit for Dab in Subdivisions (SD) 22-32 and one for Flounder in SDs 22-32 (based on Advice 2013). In 2013, both stocks were assessed according to the ICES data-limited approach for advice. As an outcome of WKBALFLAT, the Flounder stock was separated into four assessment units: Flounder SD 22-23 Flounder SD 24-25 Flounder SD 26 and 28 Flounder SD 27, 29-32These units were derived based on earlier work by ICES/HELCOM workshops, WKFLABA (ICES, 2010) and WKFLABA2 (ICES, 2012a) and recommendations by SIMWG (ICES, 2012). For dab, one stock unit in SD 22-32 was maintained. However, there are some indications that SD 21 could potentially be merged with dab in SD 22- 32 and future work is recommended to solve the issue of dab stock ID in this region. Both dab and flounder are mainly caught as bycatch species in cod or other flatfish fisheries in the Baltic Sea. Therefore one of the main data issues for these stocks is related to discards. The amount of discard of flatfish in the Baltic is significant and often of a similar magnitude as the flatfish landings. The discard behaviour for bycatch species is rather complex and unpredictable because it varies independent of factors directly connected to the abundance of flatfish stocks. Large efforts were made by the group to compile discard information from different countries for Flounder stocks in SD 22-23, SD 24-25 and SD 26&28 and for dab in SD 22-32. The discard compilation was carried out using the facilities of ICES database InterCatch. During this process several issues were identified related to incomplete sampling and limitations for discard extrapolation possibilities in the standard software. Thus, the present discard estimates were considered too uncertain to be used as a basis for catch advice. Therefore, providing only landings advice for both dab and all flounder stocks was recommended. Both short-term and long-term solutions were developed to allow improvement of discard estimates in future. 2 | ICES WKBALFLAT REPORT 2014 Another common issue for the stocks considered by WKBALFLAT is the lack of age information both for commercial catches and surveys. Age readings, carried out by approved methods, are currently available only for a few recent years. Length distributions are available and methods to convert these to ages were explored, with promising results. However, proper validation of the resulting age distributions, for example with real age readings, was not possible to conduct during WKBALFLAT. Therefore, more work on this aspect is needed before age based stock assessment methods could be used as a basis for advice for these stocks. Exploratory analyses with production models and the age-based stock assessment model SAM were carried out. Due to the issues mainly with discards and age information described above, the conclusion of WKBALFLAT was to use survey based trend assessments as a basis for advice (ICES category 3.3.) for all flounder and dab stocks in the Baltic. However, significant progress was made by WKBALFLAT towards developing analytical assessments for most of these stocks. It was emphasized that this work should be taken further to WGBFAS where improving the input data and exploratory analyses with analytical assessment models should be continued, in parallel with survey based assessment to be used for advice. This could facilitate possible transition to analytical assessments for some of these stocks in future.

Published in

ICES CM 2014
2014, number: ACOM:39
Publisher: ICES