PROJECT DESCRIPTION
BACKGROUND
Many thick shelled river mussel (Unio crassus) populations have become extinct in Sweden. Remaining populations of this endangered species have become fragmented (at some 140 sites), with distribution confined to south-eastern Scandinavia. This decline is linked to habitat degradation (e.g. fragmentation, dredging and channelisation of watercourses) and the resulting scarcity of host fish. Declining host fish abundance leads to small mussel populations in which recruitment of young mussels cannot be maintained, so ageing populations slowly die out. Other problems concern drainage; historical water legislation requires landowners to dredge and clean rivers and streams, but at sites with populations of Unio crassus this conflicts with current EU legislation designed to protect rare species and vulnerable habitats. In addition, cutting down shading trees causes high water temperatures, homogenous habitat and increased amounts of suspended material, which negatively affects mussel and fish populations.
OBJECTIVES
The objective of the UC4LIFE project was to strengthen the conservation status of thick shelled river mussel (Unio crassus), which is classified as ‘unfavourable’ under the EU Habitats Directive, and improve the ecological status of the rivers where it is found in Sweden. The project selected 12 sites (3 where mussels are already extinct) in which to identify and map host fish to ensure successful conservation actions (7 sites); to recreate natural river dynamics by restoring structures and processes beneficial for Unio crassus and host fish species (12 sites); and to rear and reintroduce juvenile mussels and glochidia-infected host fish to build up populations (2 sites) and to reallocate adult mussels to more favourable habitat (6 sites). The project also aimed to raise awareness for future river management at the 12 project sites through the platform of local water councils.
RESULTS
UC4LIFE developed methods for rearing and reintroducing thick shelled river mussel (Unio crassus) into rivers where it has become extinct, for the first time in Scandinavia. The project identified and mapped host-fish species, and undertook large-scale restoration activities to create conditions favourable for the mussel and its host fish. Taking an integrated approach, the project combined conservation work with information activities and socio-economic modelling.
The project demonstrated innovative techniques for the rearing of thick shelled river mussel, to obtain the numbers needed for re-introducing the species into rivers, including the use of a re-circulation pump system in the rearing units and specially designed boxes for re-introductions. The mussel breeding facility at Hemmestorp Mill, built by the project, will continue to serve as a basis for future mussel breeding and reintroduction work in Sweden.
An evaluation of which fish species Unio crassus uses as hosts was conducted, by electrofishing over 168 km of river and laboratory identification. This showed that 13 of the 17 fish species caught had gills infested with glochidia (the larval stage of the mussel). Of these, the project team identified three species as the most-suitable host fish species for re-introduction activities. A total of 484 infested host fish were released into rivers, resulting in about 170 000 juvenile mussels released from the fish; 6 783 juvenile mussels obtained from laboratory fish were released into rivers; and 790 gravid adult mussels were reallocated to more suitable habitats in the project sites. These actions resulted in around 12 million glochidia being released in Fyleån Creek and about 13 million in Klingavälsån River, successfully reintroducing populations to these sites where the species had gone extinct.
Reintroductions and reallocations were directly linked to the implementation of large-scale restoration activities that improved environmental conditions for both the mussel and its host-fish species. These involved the recreation of habitat structures, including gravel river beds at two sites, the addition of boulders and woody debris, the planting of shading trees alongside streams, and the re-meandering of rivers at two sites. Various habitat improvements were achieved at all 12 project sites (totalling 267 km of river length). The project team also constructed two side channels, and removed or by-passed eight major migration barriers to increase connectivity in six rivers, which is important for host-fish movement.
Post-restoration monitoring confirmed an overall positive outcome for other biotic variables in the rivers (e.g. invertebrates and fish). The combined results from the restoration work, the host-fish mapping, reintroductions and reallocation studies showed that the project significantly contributed to an overall increase in biodiversity as a consequence of the restoration efforts at the project sites. In addition to the direct conservation benefits, the restoration work has contributed to a more varied environment and an increase in connectivity. The results developed in the project can be easily replicated and have been already taken up by several initiatives.
The project conducted a widespread public engagement process, which achieved a high level of recognition in Sweden for both the mussel and for its habitats. The project directly contributed to the implementation of the Water Framework Directive and the Habitats Directive, by improving water quality and the conservation status of Unio crassus.
A holistic and integrated approach was undertaken, which combined the conservation work with information activities and socio-economic modelling. The project beneficiaries undertook an assessment of the socio-economic value of the restoration work at one of the project sites (Fyleån), which concluded that the restoration contributed to the recreational quality of the area.
Further information on the project can be found in the project's layman report and After-LIFE Conservation Plan (see "Read more" section).
