To reproduce, freshwater pearl mussels require clear and flowing waters, which are now rare in the south of Finland. The project will involve breeding and rearing specimens in their early stages, to get them past the most critical phases of their lives. This photograph was taken in the clear freshwater pearl mussel waters of northern Finland. Photo: Jari Ilmonen.

The known freshwater pearl mussel populations in rivers in southern Finland mainly consist of elderly individuals incapable of reproduction. This is an endangered species which will become extinct unless extraordinary measures are undertaken, despite the populations currently hanging on in the north of Finland.

We conduct diving surveys in order to investigate the status and distribution of freshwater pearl mussels in the rivers Mustionjoki, Ähtävänjoki and Kiskonjoki. We collect glochidia larvae from the populations in the rivers Mustionjoki and Ähtävänjoki and send them to a Norwegian hatchery that specialises in freshwater pearl mussels. The larvae are first grown in the gills of salmon fish and then, for almost two years, in artificial channels within gravel. The tiny young mussels are then transferred back to their home waters, initially in breeding boxes to allow continuous monitoring for a couple of years. When the mussels are eventually released into the target water bodies, they are around 7–20 mm in diameter.

This is the first ever attempt to breed freshwater pearl mussels within Finnish populations. In addition to the Norwegian hatchery, we will transfer a small number of larvae to Central Finland, where the aim is to develop breeding and rearing methods for future purposes.

If successful, the rearing, transfer and transplantation of freshwater pearl mussels probably represents the only way to save the species from extinction in Southern Finland. Today, the major threat to the mussels is posed by the destruction of habitats due to the incoming load from catchment areas and the absence of the host fish, required by the larval stages of the species, in the water system. We also aim to counter these threats through other measures, described in detail in the relevant pages.

Last updated 22 May 2020