A river pearl was well known in Europe relatively recently. It was picked out from a mollusc – freshwater pearl mussel, Margaritifera margaritifera. A remarkable feature of this mussel consists in the fact, that it reproduces by means of salmonid fishes: its larvae live and develop on the gills and fins of Atlantic salmon (Salmo salar) or brown trout (Salmo trutta). It is considered that mussel larval infection is not harmful for fish. Probably, the presence of pearl mussel makes positive influence on salmon populations, because these molluscs purify water in the places, where salmonids breed and where their juveniles live. Moreover, molluscs congestions contribute to creation of numerous micro-habitats suitable for young fishes.

Pearl mussels’ populations are declining rapidly in Europe. Many populations have been disappeared. The condition of salmonid populations is not perfect too. Salmonid fisheries management and mussel restoration actions are not well coordinated.

Now many populations of pearl mussel are represented only by very old individuals, which did not breed successfully over many years because of the absence of salmon. However, the possibility to mussel population restoration in such conditions still exists, because this mollusc is capable to live more than 100 years without losing the reproduction capacity.

The project focuses on the populations of south-eastern edge of Baltic Sea basin (Veliky Novgorod region). They have never been explored by scientists, and remain unknown for the local administration. It is just known that the trout rivers were numerous there, and the pearl was collected there in 19th century and earlier. At least some rivers remained in relatively good condition, that is why mussels could survive there. The project aims to study current state of these populations and to raise actively the problem of their conservation or restoration.

The project originated from research and conservation activities concerning pearl mussels in the neighbour territory – Saint-Petersburg region, which were supported by the Rufford Small Grants Foundation.