Improving the conservation status of target species
Sea lamprey, freshwater pearl mussel and thick-shelled river mussel are all endangered species in Sweden. Through the Improve Aquatic LIFE project, concrete actions are now being taken to improve their chances of survival – from restoring habitats and re-establishing reproductive cycles to using innovative methods such as e-DNA and mussel infestation. The work is done in close collaboration with landowners and organizations, with the goal of reversing a negative trend and restoring viable ecosystems.
Three of the project’s target species – Sea lamprey, Freshwater pearl mussel (Margaritifera margaritifera), and Thick-shelled river mussel (Unio crassus) – are currently endangered in Sweden (Red List 2015). Without targeted efforts, these species risk disappearing from our rivers. By creating special habitats for lamprey larvae and infesting host fish with mussel larvae, Improve Aquatic LIFE is actively working to reverse the negative trend.
Background
The sea lamprey, an ancient fish species, has declined sharply and now reproduces in only a few southern Swedish rivers. The threats to the sea lamprey are many. It is prevented from reaching its spawning and nursery grounds by hydropower plants and dams. Channelization, dredging and ditching of rivers destroy larval habitats. In the sea, the lack of sufficient numbers and sizes of host fish is a major problem.
Both the Freshwater pearl mussel and the thick-shelled river mussel are also enangered and their survival is affected by several factors: these mussels depend on specific host fish for reproduction but due to migration barriers and lost habitats, for both the mussels and their host fish, reproduction fails in many populations. Discharges of nutrients and pollutants from agriculture and industry contributes to eutrophication, leading to oxygen depletion and siltation of the riverbeds where mussels live.
What is Improve Aquatic LIFE doing to improve conservation status?
The project implements concrete measures to improve the reproduction and living conditions for these three protected species. The work is carried out in close dialogue with landowners and in collaboration between several organizations.
Sea lamprey from Högvadsån. Photo: Elisabeth Thysell.
Two main focus areas
1. Habitat restoration for the sea lamprey
The goal is to improve habitats for the sea lamprey, and also river lamprey, in Vramsån, River Kävlingeån, Bråån, River Rönne å and River Ätran by recreating nursery habitats for lamprey larvae. By recreating backwater, slow-flowing sections and sediment banks, the young larvae get shelter and food.
Survey of abundance with e-DNA
It is still unclear in which western Swedish rivers the sea lamprey occurs and whether the species manages to reproduce naturally. Therefore, we will use e-DNA analysis – a modern and non-invasive method – to map the species’ presence and identify potential new areas for measures.
2. Infestation of host fish with mussel larvae
To support the reproduction of the freshwater pearl mussel and the thick-shelled river mussel, we will infest suitable host fish with mussel larvae and release them in 17 rivers. This proven method has previously been successfully used in several LIFE projects. Infestation is preceded by thorough field studies to ensure that the correct host fish is infested with the correct mussel in the right environment. Combined with the removal of migration barriers and habitat restoration, these measures will help improve the conservation status of the freshwater pearl mussel and the thick-shelled river mussel.
Results and benefits
The measures improve the conservation status of three of Swedens most endangered freshwater species. When lampreys and mussels regain functional life cycles, important ecosystem functions – such as filtration of particles, uptake of nutrients and stabilization of bottom sediments – are also restored. The project also contributes to new knowledge about these species, which may have implications for species conservation in a broader European context.