Cottus gobio Linnaeus, 1758, Miller’s thumb (Cottidae)

Author: Ronald Fricke, Germany

1. Description of the habitat/autecology of the species

This species inhabits gravel and rock bottoms in streams, rivers and lakes, in estuaries and in brackish waters in the Baltic Sea. It feeds on small bottom invertebrates, like insects and crustaceans. The eggs are attached in clumps underneath larger stones. In freshwater habitats this species migrates over short distance only. Dispersal in fresh water mainly occurs by larvae and juveniles carried downstream with the current; in the sea, little dispersal observed. Maximum total length 18.0 cm, usually smaller; maximum individual age 5 years.

2. Distribution (past and present)

Distributed in coastal areas in brackish water of less than 10 per mille from the Bay of Mecklenburg northward and eastward to the Gulf of Bothnia and Gulf of Finland. In Poland, however, it is replaced by C. microstomus (Freyhof et al, 2005).  Outside the HELCOM area, C. gobio is distributed throughout most of Europe, south to northern Spain, northern Italy and Macedonia, excluding Ireland.

3. Importance (sub-regional, BalticSea-wide, global)

Due to its high genetic diversity, this populations in the HELCOM area are of global importance. The species is not considered as rare in the HELCOM area, but it is sensitive to human activities. Its decline status is unknown.

4. Status of threat/decline

In a HELCOM assessment, this species is classified as vulnerable (VU) according to IUCN criteria in the HELCOM area (HELCOM, 2007). The species was listed as extinct (EX) for marine waters by Denmark and Germany, as endangered (EN) by Russia, and as near threatened (NT) by Estonia. It is considered to be a common species in coastal and freshwater areas in Finland and Sweden and is classified as least concern (LC).

5. Threat/decline factors

Threatened by eutrophication, as the species needs clean water and sediments, especially for spawning, egg deposition, and larval habitats. Cottus gobio is also threatened by gravel extraction, and by barriers to dispersal and migration (like weirs) in its freshwater habitats.

6. Options for improvement

Populations of this species would benefit from a reduction of eutrophication and restriction of gravel extraction in their habitats. Hence, the species would benefit from protected areas. For barriers in their freshwater habitats, fish passes could be constructed.

7. References

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

Freyhof, J., M. Kottelat and A. Nolte. 2005. Taxonomic diversity of European Cottus with description of eight new species. Ichthyological Exploration of Freshwaters, 16: 107-172.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