Exploring rivers in the North Vidzeme Biosphere reserve 

The main goal of the project was to investigate and estimate eventual Freshwater Pearlmussel Margaritifera margaritifera rivers in the North Vidzeme Biosphere reserve. There are 59 rivers, 147,3 km investigated. Pearlmussels were not found, but valuable information about localities where pearlmussels have disappeared and about Unio crassus was obtained.

The main goal of the project was to investigate and estimate eventual Freshwater Pearlmussel Margaritifera margaritifera rivers in the North Vidzeme Biosphere reserve. There are 59 rivers, 147,3 km investigated. Pearlmussels were not found, but valuable information about localities where pearlmussels have disappeared and about Unio crassus was obtained.

There are 128 forms filled about the investigated rivers, originals are in the Latvian Fund for Nature, one copy in the Zoological Museum of Latvian University, second copy in the North Vidzeme Biosphere reserve, in Salacgriva. This information is available for all specialists for scientific studies. For mass media this information is available through the organizations mentioned above.

The malacologist Dr.I.Valovirta and 3 professional scuba divers Panu Oulasvirta, Vili Englund, Pekka Tuulenvire from Finland took part in field works. Diving was used in Salaca, Svētupe, Vitrupe and Korģe and allowed to obtain information about mussels in deepest stretches of these rivers. It was a useful experience and helped to approbate the use of divers in Latvian rivers.

Biotopes suitable for Pearlmussels were found in 25 rivers. For survival of Pearlmussels very important is quality of water during a long period of time. The ecosystems of all North Vidzeme Biosphere reserve rivers are influenced by eutrophication. The causes for extinction of Pearlmussels in rivers of the reserve are:
    

     1) wide agricultural lands in basins of all mentioned rivers,
     2) waste waters from towns,
     3) dams and pounds on rivers,
     4) melioration and regulation of rivers.

Mudīte Rudzīte

Pictures are made by:
1) Willem Kolvoort
2) Mudīte Rudzīte