Essential fish habitat (EFH) map on Potential spawning areas for European flounder was prepared in PanBalticScope project (co-founded by the European Maritime and Fisheries Fund of the European Union) http://www.panbalticscope.eu/

European flounder (Platichthys flesus) is a key species in many coastal areas of the Baltic Sea, mainly in the central and southern sub-basins. Adults feed in shallow, coastal areas during summer and move out to deeper areas in winter, where the spawning takes place in spring. European flounder spawns above the sea floor in deep water, in areas with sufficiently high salinity for fertilization and pelagic egg development. ‘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 deeper than 30 m in order to represent pelagic spawning habitat. ‘High probability spawning areas’ were identified as the sub-section encompassing salinity > 10. It should be noted that flounders in the Baltic Sea were recently separated into two species, and that spawning areas of the Baltic flounder (Platichthys solemdali) 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.

Stock: ICES identifies two stocks of European flounder in the Baltic Sea: ICES subdivisions 22-23 (Belt Sea and the Sound), and 24-25 (West of Bornholm and Southern Central Baltic Sea).

EFH type: Spawning areas

Approach: Species distribution modelling combined with identification of environmental salinity window and depth conditions for spawning.

Variables and thresholds: Depth > 30 m, Salinity > 10

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.

Note: the map on European flounder spawning areas is currently missing information for the western Baltic Sea including the Kattegat.

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