1) Host-fish mapping. The thick shelled river mussel (Unio crassus) is a threatened mussel species (EN), dependent on functioning host fish populations. In Sweden, the host fish species is largely unknown. As the larger scope of this 4.9 M € UC4LIFE-project is to restore depressed riverine habitats and re-introduce Unio crassus in rivers where the mussel have become extinct, we need to identify the functional host fish species at those sites subjected to restoration. The objective is therefore primarily to identify functioning host fish species in seven rivers along a southern-to-northern-gradient within the Unio crassus distribution range in Sweden. Artificial infection by glochidia larvae at potential host fish in aquariums will serve as an additional method to evaluate host fish utilization rate during laboratory conditions. This will be performed by catching fish and fertilized female mussels before their larvae have been released. At the point when the mussels release their glochidia larvae, fish will be introduced to the aquariums and infected with glochidia larvae. By studying subsequent survival rates of the glochidia larvae for each of the fish species, we can identify the most suitable host fish for the mussel, and then relate those results from those obtained from the molecular method.
2) River restoration. The main objective is to restore parts of the 267 km long stretches at the twelve project sites. The total river length (distributed amongst the twelve project sites) that will be positively affected (hydrologically and ecologically) by this action is, however, much longer. The major restoration efforts (ie the size of the measures and related costs) will be conducted in River Klingavälsån and River Fyleån as the entire flood plain will be subjected to re-meandering measures. Site specific, in-river restoration efforts will be made at all project sites and removal of obstacles and building by-pass channels (six sites), will improve habitat quality and affect accessibility by organisms positively, increasing dispersal and migration rates in those fragmented rivers. The restoration actions are focusing on mechanisms driving the river dynamics (meandering, structures, substrate and connectivity), meaning that once implemented, the effects will not only be maintained by natural mechanisms, but also reinforced with time.
3) Re-introduction of Unio crassus. The primary objective is to reintroduce juvenile Unio crassus at two project sites (in the River Klingavälsån and River Fyleån) after artificial infestation. We will both release juvenile mussels and infected host fish, since a combination of the two methods will most likely increase the survival rates of re-introduced mussels. Re-introduction success may also differ between different rivers, which is an additional reason to use both methods described. The re-introductions will occur in areas with a historical record of Unio crassus presence and at areas that are considered to have the physical and chemical conditions to harbour enough numbers of host-fish species and Unio crassus. In addition, we believe that the restoration action will create even better physical and chemical conditions for the mussels and related host fish species.
The re-introduction phase will start by artificial infections of host fish with glochidia larvae in laboratory conditions. Gravid mussels will be collected from the selected rivers and placed in aquarias. Analyses of infection rates and the size of the glochidia larvae will be measured repeatedly for every fish species. When the juvenile mussels are being released from the host fish, they will be introduced at the mussel channels and parts of the river that have been specially designed (by substrate and cover) for high survival rates by mussels
Information and education by stakeholders and the public goes alongside with the river restoration activities. Part of the information activities includes practical “hands-on” activities for local kids and their families, meetings and happenings. These actions will utilize the local Water Councils infrastructure and the project information campaigns will cover the villages and schools around the project sites during the project phase.
5) Monitoring. The aim is tostudy and quantify the effectiveness of the project’s conservation actions compared to the initial situation and predicted results. Evaluating and learning how river restoration affects different habitat qualities for aquatic organisms is important to predict the outcome of restoration and to develop future restoration schemes. Until recently, most river restoration work have focused on lotic habitats (water habitats with fast water velocity), here we are dealing with semi-lentic habitats (water habitats with slower water velocity), and the results gained from the restoration actions proposed will be novel in several perspectives. Thus, the monitoring results will be important for future river restoration world-wide. Moreover, the experiences gained by the monitoring program will also provide us with vital information about the mussel activities and how host fish mapping can be performed in a cost efficient way and on a larger scale. In addition, the results from the monitoring action will bring novel information about how host fish species (utilized by freshwater mussels) can be sampled, analysed and mapped at a larger scale.