- Extensive assessments of a species distribution, its variation in density and demographic status across environments are crucial to develop successful conservation efforts.
- The freshwater pearl mussel (Margaritifera margaritifera) is considered one of the most endangered freshwater bivalves with many recovery efforts continuing throughout its geographic range. The distribution and conservation status of M. margaritifera are not well documented in the Iberian Peninsula. Galicia (NW Iberian Peninsula) represents nearly 70% of the historical distribution of the species in the southern limit of its European range.
- An extensive field survey was conducted in two phases at 2436 locations. The presence and density of M. margaritifera was determined at 555 sampling points spread across 54 rivers that belong to 23 drainage basins in Galicia. The present work has more than doubled the number of rivers known to provide habitat for this endangered species in the Iberian Peninsula.
- In Galicia the species is heterogeneously distributed with a highly variable density of individuals within and between rivers. For example, within the River Camba density ranged from 0.02 to 47.8 ind m-2. The maximum density detected in a sample was 332 ind m-2. Twelve rivers in Galicia are thought to have more than 5000 individuals, and small individuals were found in 11 rivers.
- High rates of decline and extinction of M. margaritifera populations are known in some areas and the main threat to unionoid bivalves is a lack of natural recruitment. Thus, Galician populations are important for providing new opportunities for conservation of the species in Europe because it is vitally important to find the reasons for recruitment failure.
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