Report of the Benchmark Workshop on Flatfish (WKFLAT). 1–8 February 2011, Copenhagen, Denmark

WKFLAT 2011 met from 1st to 8th February 2011 at ICES headquarters in Copenha-gen. The meeting was chaired by Rob Scott (JRC) and the ICES co-ordinator was Jean-Claude Mahé (France). Chris Legault (USA) and Chris Francis (New Zealand) par-ticipated in the meeting as invited external experts. A total of 16 participants from seven countries were in attendance. Stakeholder representatives were in attendance for part of the meeting. The main goals and objectives of the meeting were to evaluate the appropriateness of stock assessment data and methods for five flatfish stocks. These included sole in VIIa, sole in VIIIab, plaice in VIIa, plaice in VIIfg and megrim in IV and VI. For each stock the preferred stock assessment method was determined and the stock annexes updated with the agreed procedures for generating and collating the input data to the stock assessment and the methods for estimating stock status. Much of the work dur-ing the meeting focused on data quality issues. Issues relating to assessment method-ology were considered only later in the meeting. Alternative assessment approaches were investigated for all stocks although in some cases time constraints allowed only for preliminary investigations to be conducted. The main results of the meeting were: Sole in VIIIab (Bay of Biscay): Two new cpue series were calculated for French commercial vessels and were investigated for inclusion in the stock assessment. The existing assessment method (XSA) was retained with virtually no modifications to parameter settings, but including the two new tuning-series. Sole in VIIa (Irish Sea): Alternative methods for raising the international catch-at-age matrix were investigated in order to reduce the impact of recent changes in sampling levels that have occurred at the national level. The existing assessment method (XSA) was retained with only minor modifications to the parameter settings. Plaice in VIIa (Irish Sea) and Plaice in VIIfg (Celtic Sea): Several alternative methods were investigated to explore options for incorporating a short time-series of discard observations into the assessment. None of the approaches examined proved to be entirely satisfactory. The group concluded that the Aarts and Poos (2009) method, developed initially for North Sea plaice, could be used as a trends only assessment for the provision of management advice but could not be used as a basis for predict-ing future catch options. Megrim in VI and IV: Only very limited data were available to WKFLAT. The group considered the basis for the stock definition and concluded that there was little evi-dence that megrim in Subdivisions VI and IV comprise separate stocks. WKFLAT applied several assessment methods to the data but was unable to recommend a pre-ferred assessment for this stock