(LIFE2002NAT/B8590)
The project aims at the long-term conservation of habitats associated last populations of the pearl mussel Margaritifera margaritifera in Belgium. Although this species was widespread in Europe in the past, more than 90% of the population has disappeared since the beginning of this century. In Belgium, the species is found only in one main population (> 1000 specimens) and several smaller populations dispersed mainly in streams with high water quality in the Rulles, Sûre and Our river basins. All known populations are very old (> 40 years). This species is associated to a large of diversity of natural habitats and species concerns by CE 92/43 Directive that will be also concerned by management actions but the project is centred on pearl mussel.
This species of mollusc is characterised by a complex life cycle, as the larvae need to spend several weeks in the gills of Salmonidae (the trout Salmo trutta forma fario) before they metamorphose into small juvenile mussels that settle on the river bed substratum. The onset of reproductive maturity occurs only at the age of 20 years and this species can reach an age of more than 100 years old under perfect ecological conditions. The complexity of its ecological requirements demands actions at multiple levels to answer to five major threats : 1) to avoid volontary destruction of mussels for pearl searching; 2) to avoid the involuntary destruction of mussels and sites, that results from livestock and forestry machines entering the river bed, river bank management, and river bed cleaning; 3) to improve water quality for juvenile stages (larvae, glochidia, juveniles), which are very sensitive to nitrate, phosphate, and oxygen, concentration and to water turbidity (quantity of matter in suspension); 4) to maintain well-balanced fish host populations, with a lot a small trouts, which are preferentially parasited, and 5) to increase local mussel densities, in order to improve the efficiency of reproduction and to re-balance the present age structure.
To respond effectively to these five major demands, actions proposed in the Walloon area are developed on two geographical levels; first, by sensitising and informing potential actors for all of the three orohydrographical basins (60000 ha) to improve water quality, and second, by concrete conservation actions in four large sites designated as SICp (7240 ha), that still shelter pearl mussel populations. Actions developed for all three basins are 1) the sensitising of all actors concerned by using existing structures (natural parks, river contracts, fishing associations) or governmental channels to select priority zones for water quality improvement and definition of an action plan; 2) the identification and comprehensive mapping of major problems in river managing (pollution sources, access of livestock and machine to river beds, water extraction, drainage); 3) a reinforced monitoring of water quality and the initiation of systematic mussel population surveys, and 4) the proposal of specific protective measures for fishing (delaying the season’s opening, restocking constraints) and boating. Concrete conservation actions in sites designated as SICp are 1) a detailed mapping of pearl mussel populations, ecological conditions and problems that need to be solved; 2) the definition of a conservation plan; 3) the launching of immediate managing measures (enclosures, restoration of river banks, control of agricultural and forestry activities) and of less urgent measures (land buying, restoration of river sections, extensive managing of abandoned wet grasslands); 4) a detailed analysis of both mussel and trout population structure and dynamics and 5) the launching of protocols to monitor the project.
Expected results for the tree basins are a significant improvement of water quality, the taking into account of pearl mussel presence in strategic decisions for land use management and an improvement of fish host populations. For the site designated as SICp, the expected results are the restoration of natural habitats of pearl mussel to allow its long-term survival and the conservation of other habitats and species associated concerned by CE 92/43 Directive (152 ha).
This project is developed by the Ministère de la Région Wallonne/ Centre de Recherche de la Nature, des Forêts et du Bois and the partners are Réserves Naturelles RNOB and Parc Naturel Hautes Fagnes Eifel.
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