Helcom : Coregonus

Coregonus sp., European whitefish (Coregonidae)

Author: Ronald Fricke, Germany

1. Description of the habitat/autecology of the species

European whitefish is a group of freshwater and sea populations with partly unclear taxonomy. Here are included the anadromous and sea spawning whitefish stocks around the Baltic Sea. This complex includes species and/or populations previously recorded under the names Coregonus balticus and C. maraena, and currently called as C. lavaretus (Säisä et al. 2008). C. oxyrinchus occurs mainly in the North Sea, and not in the Baltic Sea, if not restricted to River Rhine, as Freyhof & Schöter, 2005 suggest. C. lavaretus lives in inshore and coastal waters. In the northern Baltic Sea the anadromous form migrates widely (several hundred km), and is not restricted to river mouths or coastal areas but crosses also the Gulf of Finland and the Gulf of Bothnia; it matures at an age of 2-4 years, and migrates into freshwater for spawning. Spawning time varies from October to November. The eggs are buried in sand or gravel in unguarded nests. Maximum total length is 130 cm (Coregonus maraena /C. balticus) or 46 cm (C. pallasii), maximum weight 10 kg (C. maraena) (Froese & Pauly, 2005). The sea-spawning form spawns in shallow coastal waters.

2. Distribution (past and present)

The species and/or populations in this complex are distributed throughout coastal waters of the HELCOM area, and in adjacent rivers and streams. They are endemic in this area.

3. Importance (sub-regional, Baltic Sea-wide, global)

Due to their potential genetic differentiation, Baltic Sea species and/or populations of this species complex are of global importance according to the definition in HELCOM (2007). It is also an important fish for recreational as well as commercial fishery in the Baltic Sea.

4. Status of threat/decline

In a HELCOM assessment, this species complex is classified as vulnerable (VU) according to IUCN criteria in the HELCOM area and two of the species (C. maraena and C. pallasii) as HELCOM high priority species (HELCOM, 2007). Species/forms included in the complex are listed as vulnerable (VU) to endangered (EN) by various HELCOM member states. The relevant populations are not considered threatened in Sweden. In Finland the anadromous C. lavaretus is classified as vulnerable (VU).

5. Threat/decline factors

Threatened by a variety of factors, including fisheries as a target species, and fisheries as by-catch, eutrophication of the spawning habitats, global warming, construction of dams and weirs in rivers that hampers the spawning migration, and introduction of Coregonus species and populations from other areas as Coregonus specimens readily hybridise. The species in the complex are not rare, but sensitive to human activities; some are considered to be keystone species.

6. Options for improvement

Anadromously migrating Coregonus populations would benefit from a reduction of eutrophication in the spawning rivers, from the construction of fish passes around barriers like weirs, and from a sustainable fisheries management considering the needs of migratory Coregonus.

7. References

Freyhof, J. & Schöter, C. 2005. The houting Coregonus oxyrinchus (L.) (Salmoniformes: Coregonidae), a globally extinct species from the North Sea basin. Journal of Fish Biology 67: 713-729.

Froese, R. & Pauly, D. (eds) 2005. FishBase. Available in: www.fishbase.org, version (11/2005).

HELCOM 2007. HELCOM Red list of threatened and declining species of lampreys and fish of the Baltic Sea. Baltic Sea Environmental Proceedings, No. 109, 40 pp. Available in: http://www.helcom.fi/stc/files/Publications/Proceedings/bsep109.pdf

Säisä M., Rönn J., Aho T., Björklund M., Pasanen P., Koljonen, M-L. 2008. Genetic differentiation among European whitefish ecotypes based on microsatellite data. Hereditas, in press. Doi:10.111/j.2008.0018-0661.02050.x