Commission Decision of 25 February 2016 setting up a Scientific, Technical and Economic Committee for Fisheries, C(2016) 1084, OJ C 74, 26.2.2016, p. 4–10. The Commission may consult the group on any matter relating to marine and fisheries biology, fishing gear technology, fisheries economics, fisheries governance, ecosystem effects of fisheries, aquaculture or similar disciplines. This report is the fourth of a suite of STECF EWG reports dedicated to the fishing effort regime in the Western Mediterranean Sea, following EWG reports 18-09, 18-13 and 19-01. The group wasrequested toprogress on an operational mixed-fisheries model for Effort Management Unit 1 (i.e. GSAs 1-2-5-6-7), to update mixed fisheries models and F-E analyses with the most recent data and the most recent stock assessments., and to draft amixed-fisheries advice including relevant scenarios and displays. In EMU 1, good progresses were achieved in combining effort and catch data from both France and Spain into the bioeconomic multifleet model IAM. The model is now able to run and perform management simulations on the stock of hake (combined assessment in GSAs 1-2-5-6-7). Time did not allow to include additional stocks at this stage, but the required elements are now in place and adding these should be fairly straightforward in the future.The updates of the F-E analyses performed in EWG 18-09 and 18-13 with the most recent time series did not change the perception of the lack of relationship between fishing effort and fishing mortality. For many stocksand fleet segments, the relationship using effort expressedas fishing days has no obvious slope, indicating that the limited reduction of effort observed in the recent years did not have any visible effect on reducing fishing mortality yet.Supplementary analyses were performed using effort expressed in hours instead of days, which improved the relationship to some extent. This is consistent with previous statements in previous reports that fishing effort would be best expressed and managed in terms of fishing hours than fishing days:Extended simulation work was performed regarding management scenarios, especially in EMU 2 (GSAs 8-9-10-11). The multi-fleet BEMTOOL model was updated and extended, and 6 scenarios involving effort reductions, sometimes combined with spatial closures, were simulated in a stochastic approach. Also, the individual-based spatial model SMART was updated, and the outcomes of the spatial closures scenarios was used to parameterise the spatial scenarios in BEMTOOL. Finally, the simpler NIMED model was also updated and run, but its results were not compared to the two other models. In EMU 1, the IAM model (hake alone) was used to perform 3 runs of effort reduction, one of them including a French proposal for a spatial closure in the Gulf of Lion. Finally, a 3-pages synthetic advice is proposed, summarising the key findings of the simulations. A key outcome is that the proposed closure of the coastal zone down to 100 m deep, max 6nm from the shore, is unlikely to contribute to reducing hake catches. Rather, it can have an adverse effect if the fleets reallocate their effort further away where important concentrations of juvenile exists. In the light of the F-E relationships analyses, all results presented in this report are considered to be overoptimistic since they assume a true reduction in F if effort decreases, which may in reality be limited during the first years of effort reductions

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