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

Perch (Perca fluviatilis) is a key species in many Baltic coastal areas. It is of freshwater origin and spawns predominantly in freshwater tributaries, close to the coastline, or in enclosed bays. Species distribution modelling have shown the importance of suitable environmental conditions for perch reproduction. Young perch has limited dispersal from its spawning area, and tagging studies have shown that most (50-95 % of the recaptures of perch are made up to 20 km from tagging site (Johnsson 1978, Böhling and Lehtonen 1985, Veneranta et al. 2011, Saks et al. 2020). Due to lack of coherent data on perch spawning and nursery areas across the Baltic Sea countries, environmental variables were used in delineating potential recruitment areas for perch. The map was originally developed within the HOLAS II project (HELCOM 2018) when it was approved by all HELCOM Contracting Parties in a dedicated review process. Potential perch recruitment areas were delineated as areas with suitable condition of depth, wave exposure and salinity. Thresholds were obtained from literature, and selected to rather overestimate than underestimate the recruitment area. For the Finnish coastline, a national model was used. The map was subsequently considered by the Pan Baltic Scope project, who proposed adjustments to thresholds for some areas in Russian waters, and corrections to Estonian and German waters.

Stock: Several, undefined

EFH type: Recruitment areas

Approach: Environmental window, national modelling approach in Finnish waters, supplemented with corrections to Estonian, German and Russian waters based on national validation with monitoring data.

Variables and thresholds: Depth < 4 m (for Danish waters < 3 m), Logged exposure < 5 (For Koporo Bay and Narva Bay in Russian waters < 5.23), Salinity < 10. Based on the model for the Finnish coastline, perch recruitment areas were defined as: Unsuitable for reproduction: P(catch larvae) < 0.5, Suitable for reproduction: P(catch larvae) > 0.5, Important for reproduction: the smallest area where the expected cumulative larval abundance is 80% of the total expected abundance over study area.

Quality: Recruitment area here refers to essential habitats for young-of-the-year perch (based on inventory data from spawning until the end of the first summer). The map is based on literature and environmental variables, derived from inventory data. The species distribution modelling studies, where the thresholds values for environmental variables have been obtained, are from the northern Baltic Sea. Here, the same thresholds have been applied in the southern Baltic. Also, the data layers on environmental variables are based on modelling. Due to these constraints, the data layer should be considered as a rough estimation.

Attribute information: Raster value representing the potential occurrence of perch recruitment area (either 0 or 1).

References

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- Böhling, P, and H Lehtonen (1985) Effect of environmental factors on migrations of perch (Perca fluviatilis) tagged in the coastal waters of Finland. Finnish Fisheries Research 5: 31-40

- HELCOM (2018) State of the Baltic Sea - Second HELCOM holistic assessment 2011-2016. Baltic Sea Environment Proceedings 155

- HELCOM (2020) Essential fish habitats in the Baltic Sea – identification of potential spawning, recruitment and nursery areas

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- Johnsson, T (1978) Dispersal area of perch, Perca fluviatilis, tagged in a stream flowing into the Bothnian Sea. Aquilo, Series Zoologica 18: 62-64

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- Sundblad, G, Bergström, U, Sandström, A, and P Eklöv (2014) Nursery habitat availability limits adult stock sizes of predatory coastal fish. ICES Journal of Marine Science 71:672-680

- Veneranta, L, L Urho, A Lappalainen, and M Kallasvuo (2011) Turbidity characterizes reproduction areas of pikeperch (Sander lucioperca (L.)) in the northern Baltic Sea. Estuarine, Coastal and Shelf Science 95:199-206