Essential fish habitat (EFH) map on Potential spawning areas for cod was prepared in PanBalticScope project (co-founded by the European Maritime and Fisheries Fund of the European Union) http://www.panbalticscope.eu/ Cod (Gadus morhua) is represented by three stocks in the Baltic Sea; Eastern Baltic, Western Baltic and Kattegat cod, which is reflected in the map. “Potential spawning areas” were initially delimitated based on Hüssy (2011). In addition, the Gdansk deep as delineated by Bagge et al. (1994) was included as it sometimes contributes to reproduction of Eastern Baltic cod (Hinrichsen et al. 2016). The Gotland basin has ceased to contribute to the reproduction of cod (Hinrichsen et al. 2016). These definitions were applied in the HOLAS II project (HELCOM 2018a) based on approval by all HELCOM Contracting Parties in a review process (there referred to as ‘occasional successful spawning’ and ‘successful spawning’). Following HELCOM (2018b) additional potential spawning areas were identified by environmental thresholds for egg development and survival based on salinity and oxygen conditions (Hinrichsen et al. 2016) during 2011-2016. Separate thresholds were used for Eastern Baltic, Western Baltic and Kattegat cod. Areas denoted “high probability spawning areas” correspond to where the initial delineations (Hüssy 2011, Bagge et al. 1994) achieve the environmental threshold values. Stocks: Kattegat cod: ICES subdivision 21, Western Baltic cod: ICES subdivisions 22-24 Eastern Baltic cod: ICES subdivisions 24 + 25-32 EFH type: Potential spawning areas Approach: Literature review combined with identification of environmental window for spawning based on: salinity and oxygen for Eastern Baltic cod, and on: salinity and depth for Western Baltic Cod and Kattegat cod Variables and thresholds: Eastern Baltic cod: Salinity > 11, Oxygen > 1.5 ml/L (annual average) Western Baltic cod and Kattegat cod: Salinity > 18, Depth >20 m Quality: The Arkona deep is functional for spawning of both the Eastern and the Western Baltic cod and in effect, the definition of the Arcona Basin as a high probability areas in the Arkona basin reflect the result for Eastern Baltic cod. The effective distribution of cod spawning areas is highly dependent on the prevailing hydrological regime, and the presence of spawning also depends on seasonally variable hydrographical conditions, such as temperature, salinity and oxygen. Seasonal differences lead to a progressive spawning season towards the east, typically starting in Kattegat and the Sound in January/February and ending in July/August in the Bornholm area. Fluctuations in temperature can delay the spawning season up to two months. It is difficult to collect egg samples to verify cod spawning, as cod eggs may drift in deep areas, and instead the level of ichthyoplankton is a main source for estimation of good environmental conditions for cod spawning. Modelling based on ichthyoplankton should be validated by comparison with distribution of running adults, to resolve the potential influence of prevailing current speed. The proposed delineations are also influenced by research on the maturity of adults and histology of gonads. The adult and juvenile cod are distributed far outside of the spawning areas depicted in the map. Attribute information: Raster value representing no spawning (0), potential spawning area (0.5) and high probability spawning area (1). References - Bagge, O, F Thurow, E Steffensen, and J Bay (1994) The Baltic cod. Dana 10:1-28 - HELCOM (2018a) State of the Baltic Sea - Second HELCOM holistic assessment 2011-2016. Baltic Sea Environment Proceedings 155 - HELCOM (2018b) Outcome of the regional expert workshop on essential fish habitats, organized by Pan Baltic Scope project and HELCOM (HELCOM Pan Baltic Scope EFH WS 1-2018) - Hüssy, K (2011) Review of western Baltic cod (Gadus morhua) recruitment dynamics. ICES Journal of Marine Science 68:1459-1471 - Hüssy, K, HH Hinrichsen, and B Huwer (2012) Hydrographic influence on the spawning habitat suitability of western Baltic cod (Gadus morhua). ICES Journal of Marine Science, doi:10.1093/icesjms/fss136 - Hinrichsen, HH, A Lehmann, C Petereit, A Nissling, D Ustups, U Bergström, and K. Hüssy (2016) Spawning areas of eastern Baltic cod revisited. Using hydrodynamic modelling to reveal spawning habitat suitability, egg survival probability, and connectivity patterns. Progress in Oceanography 143:13-25 SwAM (2019). Swedish Agency for Marine and Water Management. Symphony Metadata March 2019.whttps://www.havochvatten.se/download/18.67e0eb431695d86393371d86/1552566811384/bilaga-1-symphony-metadata.zip

This dataset contains data used for the HELCOM Core indicator State of the soft-bottom macrofauna community 2018. Attribute information: "SampleID" = Sample ID "Station" = Station name "Year" = Year of sampling event "Latitude" = Latitude coordinate (WGS84 decimal degrees) "Longitude" = Longitude coordinate (WGS84 decimal degrees) "Depth" = Depth of station (m) "Sentivit" = Sensitivity subset "Sampling_a" = Sampling area (cm2) "Sieve_mesh" = Sive mesh size (microm) "BQI" = Benthic quality index value "Data sourc" = Source of data (national monitoring / other) "Data_origi" = Data providing organization "Country" = Data providing country "Assessment" = HELCOM Level 2 assessment unit where the station resides

This dataset represents the underlying data on core indicator Abundance of sea trout spawners and parr 2018. The indicator evaluates the status of the Baltic Sea area based on sea trout spawning in rivers flowing into the sea. River-specific information provided by ICES WGBAST has been joined with relevant HELCOM Level 3 assessment unit by HELCOM Secretariat. Attribute information: "HELCOM_ID": ID of HELCOM Assessment unit "Country": Country in which the assessment unit resides "level_3" = Name of the HELCOM scale 3 assessment unit "AULEVEL" = Scale of assessment "AU" = Name of the HELCOM scale 3 assessment unit "ICES_AU" = ID of ICES Assessment unit "ICES_SD" = ICES Subdivision "Rivername" = Name of river(s) used in analysis for the assessment unit "Year" = Years covered by the assessment "Data_sourc" = Data source "Data_origi" = Data originator (natonal instiute) "National_m" = National monitoing (YES/NO) "Use_restri" = Use restrictions (YES/NO)

This dataset represents the underlying data on core indicator Population trends and abundance of seals 2018. This dataset contains reported observations for grey seal species. The core indicator evaluates seal distribution to determine whether it reflects good status. Quantitative thresholds are used to evaluate if core indicators status is Good, Not good or Not assessed. Attribute information: "Species" = Species (GS = Grey seal) "Country" = Country (2 digit acronym) "Site" = Name of site "Area" = Area "HELCOM_SUB" = Name of HELCOM Level 2 assessment unit "Latitude" = Latitude (WGS84 decimal degrees) of site "Longitude" = Longitude (WGS84 decimal degrees) of site "N2000_ID" = Natura2000 ID, if the site is located within Natura 2000 site (if available) "Year" = Year of observation "Month" = Month of observation "Day" = Day of observation (if available) "Count" = Number of individuals observed on site "Count_type" = Count type "Age" = Age of individuals (if available) "No_surveys" = Number of surveys "Method" = Method of survey "CV_Estimate" "Estimate_T" = Estimate type: Modelled / minimum (observed) "Source" = Data source

Essential fish habitat (EFH) map on Potential spawning areas for herring was prepared in PanBalticScope project (co-founded by the European Maritime and Fisheries Fund of the European Union) http://www.panbalticscope.eu/ Herring (Clupea harengus) is widely distributed in the Baltic Sea and is common in all sub-basins. Herring feeds in the pelagic, mainly on zooplankton, and is an important prey for cod, other fish, and marine mammals. In fisheries management, herring in the Baltic Sea is sub-divided into several stocks. Herring spawns in coastal areas or offshore shallows. It has demersal eggs, which are attached to the substrate. Spawning may occur both in spring and autumn, depending on population, but spring spawning dominates today. Spawning areas of herring were identified by main habitat associations, based on existing observations of herring spawning grounds in the Baltic Sea. ‘Potential spawning areas’ were delineated based on the distribution of any of the following: modelled photic zone, photic hard bottom, charophytes, Fucus spp, Furcellaria lumbricalis, and Zostera marina, several data layers were combined due to uncertainty in the coverage of some of them, ‘High probability’ spawning areas were identified as areas where the modelled photic zone overlaps with any of the other layers. The habitat variables were identified by other existing HELCOM data layers. Stock: Herring in ICES subdivisions 22-24 (spring spawning), subdivisions 25-27, 28.2, 29 and 32, subdivision 28.1 (Gulf of Riga), subdivisions 30-31. EFH type: Spawning areas Approach: Habitat associations combined with manual corrections to eastern Gulf of Finland (Neva inlet), Curonian lagoon, Szczechin lagoon, Vistula lagoon and German waters Variables and thresholds: Distribution of Photic zone, Photic hard bottom, Charophytes, Fucus spp., Furcellaria lumbricalis, Zostera marina. The resulting data layer was corrected by removing recruitment areas in eastern Gulf of Finland (Neva inlet), Curonian lagoon, Szczechin lagoon and enhancing that of the Vistula lagoon. Quality: The data layer is mainly developed based on main habitat associations as identified from scientific literature, not actual data on herring spawning. The delineations are based on other data layers (benthic and habitat-related ecosystem components) for which mapping is not exhaustive and sampling density may vary between countries. Underlying data layers on vegetation (Fucus, Furcellaria, charophytes, Zostera) are based on inventory data and species distribution models. Information on the distribution of Furcellaria is lacking from Russia. Herring preferably spawns in shallow areas. However, the layer does not include depth as a variable, as some known spawning areas offshore would not be included if the depth restriction is used. Due to constraints in the resolution of the underlying data layer, the map also identifies areas shallower than one meter as potential spawning areas of Baltic herring. However, spawning of Baltic herring does not usually occur in such shallow depth. The map represents potential spawning areas. In addition, behavioral components and hydrographic factors influence on the actual chose of spawning site at a certain occasion. Due to these constraints, the data layer on Baltic herring spawning habitats should be considered as a rough estimation. Attribute information: Raster value representing no spawning (0), potential spawning area (0.5) and high probability spawning area (1). References - Fey, DP (2001) Differences in temperature conditions and somatic growth rate of larval and early juvenile spring spawned herring from the Vistula Lagoon, Baltic Sea manifested in the otolith size to fish size relationship. Journal of Fish Biology 58: 1257–1273 - Fey, DP, AM Lejk, P Margonski, L Szymanek, I Psuty, T Nermer, F Lempe, HV Strehlow, P Polte, D Moll, N Stybel, A Hiller, and M van Laak (2014a) Herring. An analysis of spawning ground management, ecological conditions and human impacts in Greifswald Bay, Vistula Lagoon and Hanö Bight. NMFRI, Gdynia, 177 pp. - Fey, D, A. Szkudlarek-Pawelczyk, and A. Wozniczka (2014b) Abundance and distribution of larval herring, Clupea harengus (Actinopterygii: Clupeiformes: Clupeidae) in the Pomeranian Bay, Baltic Sea as an indicator of spawning sites. Acta Ichthyologica et Piscatoria 44: 309–317 - HELCOM (2018a) HELCOM Map and Data service. Layers: mean slope and bottom currents. https://maps.helcom.fi/website/mapservice/. Accessed March 2019 - HELCOM (2018b) HELCOM Map and Data service. Layers: Seabed sediment polygon (BALANCE), Fucus distribution, Furcellaria lumbricalis distribution. https://maps.helcom.fi/website/mapservice/ Accessed 29 October 2018 - Kanstinger P, J Beher, G Grenzdörffer, C Hammer, KB Huebert, D Stepputtis, and M Peck (2018) What is left? Macrophyte meadows and Atlantic herring (Clupea harengus) spawning sites in the Greifswalder Bodden, Baltic Sea. Estuar Coast Shelf Sci 201:72-81) - Krasovskaya, N (2002) Spawning of Baltic herring in the Vistula Lagoon: Effects of environmental conditions and stock parameters. Bulletin of Sea Fish. Inst. No. 1 (155), Gdynia: 3–25 - Popiel, J (1984) On the biology of the Baltic herring. Reports of the Sea Fisheries Institute, Gdynia, vol. 19, 8-16.

This dataset represents the underlying data on core indicator in Abundance of key coastal fish species 2018. The core indicator evaluates the abundance of typical species of fish, such as perch and flounder, in the coastal areas of the Baltic Sea, to assess environmental status. Quantitative thresholds are used to evaluate if core indicators status is Good, Not good or Not assessed. As a rule, good status is achieved when the abundance is above a set site and species-specific threshold value. This dataset displays the result of the indicator in HELCOM Assessment Scale 3 (Division of the Baltic Sea into 17 sub-basins and further division into coastal and offshore areas). Attribute information: "COUNTRYID" = Country code "ORGANIZATI" = Data provider "AREANAME" = ICES area "Assessment" = Name of scale 3 HELCOM assessment unit "IndicatorI" = Name of the indicator (abbreviation) "SpeciesId" = Species "IndicatorV" = Result value for the indicator "MethodId" = Catch method "GearType_N" = Gear type of catch "Season_NAM" = Season

This dataset represents the underlying data on core indicator Seasonal succession of dominating phytoplankton groups 2018. The core indicator evaluates phytoplankton community structure to determine whether it reflects good environmental status. Quantitative thresholds are used to evaluate if core indicators status is Good, Not good or Not assessed. Attribute information: "Code"= ID of HELCOM level 2 assessment unit "Assessment" = Name of HELCOM level 2 assessment unit "Station" = Name of station "Lat" = Latitude of station in WGS 84 decimal degrees "Lon" = Longitude of station in WGS 84 decimal degrees "Data_avail" = Data availability period (years) "Reference" = Reference period (years) "Data_provi" = Data provider organisation "Country" = Data provider country "Station_na" = Station name "Date" = Sampling date and time "Year" = Year of sampling "Month" = Month of sampling "Cyano" = Cyanobacteria "Dino" = Dinoflagellates "Diatoms" = Diatoms "Meso_rub" = Mesodinium rubrum "CyanoIn" = "DinoIn" = "DiatomsIn" = "MesoRubIn" =

This dataset represents the underlying data on core indicator Diatom/Dinoflagellate ration 2018. The core indicator evaluates phytoplankton community structure to determine whether it reflects good environmental status. Quantitative thresholds are used to evaluate if core indicators status is Good, Not good or Not assessed. Attribute information: "Station" = Name of station "Date" = Sampling date and time "Assessment" = Name of HELCOM level 2 assessment unit "Biomass_of" = Biomass of all diatoms "Biomass_1" = Biomass of all dinoflagellates (autotrophic and mixotrophic) "Data_origi" = Data originating organization "Use_restri" = Data use restrictions (YES/NO). Restricted data is not included.

This dataset represents the underlying data on core indicator in Abundance of key coastal fish species. The core indicator evaluates the abundance of typical species of fish, such as perch and flounder, in the coastal areas of the Baltic Sea, to assess environmental status. Quantitative thresholds are used to evaluate if core indicators status is Good, Not good or Not assessed. As a rule, good status is achieved when the abundance is above a set site and species-specific threshold value. This dataset displays the result of the indicator in HELCOM Assessment Scale 3 (Division of the Baltic Sea into 17 sub-basins and further division into coastal and offshore areas). Attribute information: "COUNTRY" = Country code "DATAPROVID" = Data provider "AREANAME" = ICES area "A_unit" = Name of scale 3 HELCOM assessment unit "IND_VALUE" = Result value for the indicator "METHOD" = Catch method "GEARTYPE" = Gear type of catch "SEASONID" = Season

Essential fish habitat (EFH) map on Potential spawning areas for Baltic flounder was prepared in PanBalticScope project (co-founded by the European Maritime and Fisheries Fund of the European Union) http://www.panbalticscope.eu/ Baltic flounder (Platichthys solemdali) is a key species in many coastal areas of the Baltic Sea. It is the only endemic fish species of the Baltic Sea. Baltic flounder spawns in shallow coastal areas and on offshore banks, with eggs developing on the sea floor. Successful spawning may be expected at salinities down to around 5-7 (Nissling et al. 2002). ‘‘Potential spawning areas’ were initially delineated by a species distribution model (Orio et al. 2017) developed based on years 1993-1997 to consider a period with relatively better oxygen conditions, but applied with more recent data (2011-2014). The area was further delineated to encompass only areas shallower than 30 m in order to represent the demersal spawning habitat. ‘High probability spawning areas’ were identified as the sub-section encompassing salinity > 6. It should be noted that flounders in the Baltic Sea were recently separated into two species, and that spawning areas of the European flounder (Platichthys flesus) are described separately. The two data layers do not overlap and can be combined to obtain a map on spawning areas for both flounder species taken together. Stocks: ICES identifies two stocks of Baltic flounder: ICES subdivisions 26, 28 (East of Gotland and Gulf of Gdansk), and 27, 29-32 (Northern Central Baltic Sea and Northern Baltic Sea). EFH Type: Spawning areas Approach: Species distribution modelling combined with identification of environmental salinity window and depth conditions for spawning, supplemented with additional information from monitoring in Estonian waters. Variables and thresholds: Depth < 30 m, Salinity > 6 Quality: The data layer is based on species distribution modelling focusing on mature flounder at the spawning stage and should be considered a rough estimation. The data layers on environmental variables are based on modelling. Other variables than those tested in the model may also be influential. The studies from which the thresholds values for environmental variables have been obtained are based on publications conducted before the separation of Baltic flounder from European flounder but have taken the specific characteristics of the separate spawning ecotypes into account. Attribute information: Raster value representing no spawning (0), potential spawning area (0.5) and high probability spawning area (1). References: - Momigliano, P, GP Denys, H Jokinen, and J Merilä (2018) Platichthys solemdali sp. nov. (Actinopterygii, Pleuronectiformes): a new flounder species from the Baltic Sea. Frontiers in Marine Science 5:225 - Nissling, A, L Westin, and O Hjerne (2002) Reproductive success in relation to salinity for three flatfish species, dab (Limanda limanda), plaice (Pleuronectes platessa), and flounder (Pleuronectes flesus), in the brackish water Baltic Sea. ICES Journal of Marine Science 59:93-108 - Orio, A, U Bergström, M Casini, M Erlandsson, R Eschbaum, K Hüssy, A Lehmann, L Ložys, D Ustups, and A-B Florin (2017a) Characterizing and predicting the distribution of Baltic Sea flounder (Platichthys flesus) during the spawning season. Journal of Sea Research 126:46-55 - Seifert, T, F Tauber, and B Kayser (2001) A high resolution spherical grid topography of the Baltic Sea -2nd edition. Baltic sea Science Congress, Stockholm 25-29 November 2001, Poster #147