Distribution of the freshwater pearl mussel Margaritifera margaritifera (Linnaeus 1758) in Latvia Margaritifera margaritifera (Linnaeus 1758) in Latvia Margaritifera margaritifera in relation to water quality

The aim of the present work was to update the distribution of the freshwater pearlmussel Margaritifera margaritifera in Latvia. From 1999 to 2003 a total length of about 610 km was surveyed in 163 rivers. The distribution of the species in Latvia is about 40 km of river-parts in eight rivers, with a mussel population of about 25,000 individuals. In six rivers only shells and parts of shells were found indicating that populations occurred here previously and had become extinct. All the Latviaʼs pearl mussel populations are aging, but the pearl mussels are healthy and able to reproduce. Chemical analyses of water samples showed that the quality of water in Latvian pearl mussel rivers is considerably worse than in other countries where viable populations are found. Therefore, we can expect a rapid population decline and loss during the next 10 - 50 years. The populations could be maintained if the conditions in the rivers were improved for the survival of young pearl mussels.