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The Workshop on methods to develop a swept-area based effort index (WKSABI) was held at ICES HQ, Copenhagen, on 8–9 January 2019 under the co-chairmanship of Kai Wieland, Den-mark, and Henrik Degel, Denmark. The workshop was attended by 12 participants representing seven different countries.The objectives of the workshop were to adopt and agree on swept-area based effort indices for trawl surveys available in DATRAS and define and describe MFSD indicators using these swept-area based indices. Surveys considered where the North Sea International Bottom Trawl Survey, the Northeast Atlantic International Bottom Trawl Surveys and the Baltic International Trawl Survey. MFSD indicators considered were Marine Litter and the Large Fish Indicator (LFI).In total, eight presentations were given addressing the Terms of References of the workshop. Based on the initial presentations on data availability, quality check and swept-area based results for the different surveys and MFSD indicators, caveats were described, and methodological strat-egies to overcome existing data issues were defined.Swept-area based survey indices require tow-by-tow information of towed distance and door or wing spread from all survey participants. For several reasons, this information is not always available and missing values have to be estimated. The level of data availability for this purpose differed considerably between the surveys. Despite the use of standardized survey trawl, gear geometry between countries or within countries between years can vary substantially and it was therefore concluded that algorithms for estimating missing values should be as specific as pos-sible for a given survey, vessel, country, and year combination. This is important in order to minimize bias and variability when including the imputed values for the calculation of swept-area. After these requirements are met and datasets have been completed, further analysis on the potential of swept-area based indices for abundance and its use in stock assessment can be un-dertaken. Since door spread has been much more often observed than wing spread and is usually measured with a low variability than wing spread, swept are based on door spread is preferred if indices rather than absolute estimates are required.The calculation of the MFSD indicators Marine litter and LFI require the availability of swept-area and this is then usually based on wing spread. Since direct observations of wing spread area missing for the majority of surveys and years, generic models across years and vessels have been used for estimating the missing values. This may be appropriate when trends rather than partic-ular year effects are needed. Although estimates of MFSD indicators suffer of the problems men-tioned above, missing checks of data quality on marine litter submissions or the application of ‘global’ length-weight relationships for species for which no specific observations are available in the calculation of e.g. LFI may be more important here.

The International Council for the Exploration of the Sea (ICES) Baltic International Fish Survey Working Group (WGBIFS) met in the Marine Research Institute, Klaipeda University in Kaipeda, Lithuania, on 25–29 March 2019. A total of 21 participants, representing all countries around the Baltic Sea, attended in the meeting (see Annex 1). Olavi Kaljuste, Sweden chaired the group.The main aim of the WGBIFS is the planning, coordination, and implementation of demersal trawl surveys and hydroacoustic surveys in the Baltic Sea. It compiles results from, coordinates and plans the schedule for the Baltic International Acoustic Survey (BIAS), the Baltic Acoustic Spring Survey (BASS), and the Baltic International trawl Surveys (BITS) in the 1st and 4th quarter on an annual basis. The group provides the herring, sprat and cod abundance indices for theBaltic Fisheries Assessment Working Group (WGBFAS) to use as tuning fleets. The common survey manuals are also updated according to decisions made during the meeting.Survey results from 2018 and the first half of 2019 were compiled. The schedule for surveys in the second half of 2019 and the first half of 2020 were planned and coordinated. All Baltic fish stocks assessment relevant surveys were internationally coordinated. The area coverage and the number of control hauls in the BASS and in the BIAS in 2018 were considered to be appropriate for the calculation of tuning indices and the data can be used for the assessment of Baltic herring and sprat stocks. The number of valid hauls accomplished during the 4th quarter 2018 and 1st quarter 2019 BITS were considered by the group as appropriate for tuning series and the data can be used for the assessment of Baltic and Kattegat cod and flatfish stocks.Data from the recent BITS has been uploaded to ICES DATRAS database. Tow-Database which allows planning the spatial distribution of hauls in the areas, where the seabed is suit-able for safety trawling, was corrected and updated. Access-databases for aggregated acoustic data were updated. ICES database of acoustic-trawl surveys for disaggregated data was updated as well.All countries also registered collected litter materials to the DATRAS database.Inquiries from other ICES expert groups were discussed and addressed.