Data quality statement: This data product has undergone rigorous quality checking, as outlined in the supporting documentation (Moriarty et al, 2017; Greenstreet et al 2017). It is suitable for supporting OSPAR fish community assessments and additional indicator research and development. Data source: Data was sourced on the Database of Trawl Surveys (DATRAS) housed by ICES, this data is traditionally used for stock assessments and fish community studies by the ICES community and public users. The ICES data have to pass an extensive quality check. Collection methods: The data was collected by the Wageningen Marine Research during their North Sea Beam Trawl Survey coordinated by the working group on Beam Trawl Surveys. Data processing methods: While DATRAS has an integrated quality check, it was necessary to do a more extensive quality check and estimate certain values when data was not originally collected. The processing methods are fully outlined in Moriarty et al (2017). Data Interoperability: Sampling Information Field -Unit- Description HaulID - - Unique haul identifier (SurveyAcronym/Ship/Year/HaulNo) (H) Survey-Acronym - - Unique survey identifier (SubregionCountryGearTypeQuarter: e.g. GNSNedBT3) Ship - - Unique vessel identifier (e.g. SCO3: Scotia III) GearType - - Unique gear type code (BT = Beam Trawl, OT = Otter Trawl) Gear - - Unique gear code (e.g. GOV = Grande Oerverture Verticale) YearShot - - Year that gear was shot MonthShot - - Month that gear was shot DayShot - - Day that gear was shot TimeShot -GMT- Time that gear was shot (in format HHMM) HaulDur(min) -Min- Duration of fishing operation ShootLat(decdeg) -Deg.- Latitude in decimal degrees of the haul shoot position ShootLong(decdeg) -Deg.- Longitude in decimal degrees of the haul shoot position ICESStSq - - ICES statistical rectangle where gear was shot SurvStratum - - Stratum tag for stratified surveys Depth(m) -m- Depth tag assigned to the haul Distance(km) -km- Tow distance (dH,TOW) WingSpread(m) -m- Mean distance between the wings during fishing operation(dH,WING) DoorSpread(m) -m- Mean distance between the doors during fishing operation (dH,DOOR) NetOpen(m) -m- Mean head-line height above seabed during fishing operation (dH,HEIGHT) WingSwptArea(sqkm) -km2 - Area of seabed swept by the net (AH,WING = dH,TOW x dH,WING) WingSwptVol_CorF - - Multiplier (1 / dH,HEIGHT): converts to ‘density by wing-swept volume DoorSwptArea_CorF - - Multiplier (dH,WING / dH,DOOR): converts to ‘density by door-swept area DoorSwptVol_CorF - - Multiplier (dH,WING / (dH,DOOR x dH,HEIGHT)): converts to ‘density by door-swept volume Biological Information There are two Biological Information data products, ‘BaseLine’ and ‘KNN’. In ‘Baseline’ the k-NN procedure has not been applied, so densities-at-length of species complexes (e.g. genus, family or order taxonomic resolution level identifications codes) have not been resolved to the complexes constituent species, densities of a species where length data are not provided have not been resolved to their constituent length categories, and destinies of species complexes have not been resolved to their constituent species and length categories. In ‘KNN’ the k-NN procedure has been applied to address these three type of problem. Consequently the ‘KNN’ data product will have more records that the ‘Baseline’ data product and some fields are not relevant to the ‘Baseline’ data product. The ‘KNN’ data product will have the following structure. Field -Unit- Description HaulID - - Unique haul identifier (SurveyAcronym/Ship/Year/HaulNo) (H) SpeciesSciName - - Unique species name for each species sampled across the NE Atlantic (S) FishLength(cm) -cm- Integer numbers indicating fish length to the ‘cm below’ (L) IndivFishWght(g) -g- Estimated weight of individual fish of specified species and length (WS,L) Number - - Total number of fish of specified species and length in the catch (NS,L,H) DensAbund(N_sqkm) -km-2- Abundance density estimate (Dnos,S,L,H = NS,L,H / AH,WING) DensBiom(kg_Sqkm) -kg km-2- Biomass density estimate (Dbiom,S,L,H = (NS,L,H x WS,L)/ AH,WING) The ‘BaseLine’ product will not include the fields IndivFishWght(g) and DensBiom(kg_Sqkm), and the field SpeciesSciName will simply be called SciName. The two fields are excluded because with uncertain species identities it would not be possible to consistently include data for the field IndivFishWght(g), and in addition with uncertainty regarding length category, estimation of appropriate reliable values for the field DensBiom(kg_Sqkm) would also not always be possible. The ‘BaseLine’ data product was included because of feedback from data providers and potential data users, who stated that they would prefer having access the “real” data, rather than rely on estimated values to fill in where information was missing.