PROJECT DESCRIPTION
BACKGROUND
According to the most recent Article 17 report of the Habitats Directive, the conservation status of the thick shelled river mussel (Unio crassus) (UC) is “unfavourable – bad” in both Denmark and the wider Continental biogeographical area. Until recently, the species was considered to be extinct in Denmark. However, in 2004, it was discovered in the water course (Odense Å) and more recently (2007) in the Torpe Kanal, a tributary to the Suså river system.
Currently, the Suså river system is unfavourable to the river mussel due to several threats such as poor physical conditions and a lack of continuity. In addition, the host fishes common Minnow (Phoxinus phoxinus) and Bullhead (Cottus gobio), for larvae (glochidiae) are not present in the water course. The river mussel and its host fish, Minnow, are nevertheless present in the Odense å River, but the condition is negatively impacted by a weir in Odense city.
OBJECTIVES
The main objective of the UC LIFE Denmark project was to contribute to achieving a favourable conservation status of the thick shelled river mussel in Denmark and in the Continental biogeographic region.
This was accomplished by increasing the number of available habitat areas for the species and by reintroducing it into the Suså river system.
At a secondary level, the project also benefitted endangered habitat types (Annex I-listed) of the EU Habitats Directive, such as water courses of plain to montane levels and Hydrophilous tall herb fringe communities. Also the Annex II-listed fishes brook lamprey (Lampetra planeri) and spined loach (Cobitis taenia) benefitted – hence the designation of the Suså site within the Natura 2000 network.
RESULTS
The project has completed all actions foreseen in the Grant agreement (GA) with the changes approved in the amendment no 2 to the GA.
In the River Suså, 10.6 km of the river have been restored (compared to 6.7 km foreseen in the GA), resulting in the improvement of the conservation status of the habitat 3260. The populations of the Unio crassus host fish, Minnow and European Bullhead have been strengthened, with the latter species being reintroduced in Denmark. It is estimated that the release of glochidia infested Minnows has resulted in 10 000 young UC.
In the Odense River system, a major migration obstacle has been removed, resulting in establishing of passage for fish and creation of a 3.1 km path of free-flowing river (3.6 km foreseen in the GA).
The population of UC in the Salling å system has been strengthened via release of 7 000 infested minnows.
All in all, the project has reached its objective of improving the conservation status of the UC, its host fish and its habitat.
