Freshwater pearl mussel

Freshwater pearl mussels are found mainly in fast-flowing rivers with stony beds. They are dependent on the presence of salmonid fish as hosts for their larvae. Freshwater pearl mussels are still present in several of the Cairngorms National Park's rivers, including the Spey and the Dee. From 1980 onwards there are records in 14 10-km squares.

The species is still abundant in the Spey. Mussels are also found in the Rivers Dee and South Esk.

Mussels are now scarce where they were once abundant, and have disappeared from many rivers outwith the Park.

The main causes of the decline are:

  • overfishing, due to a continued market for their pearls - they have been fished for centuries and illegal fishing is still a threat;
  • changes in water quality – from land uses within the catchment, e.g. enrichment from agricultural runoff, erosion and siltation from overgrazing banks, acidification from forestry;
  • decline in salmonid stocks;
  • inappropriate river engineering works – damaging or disturbing the river bed.

Freshwater pearl mussels are now fully protected under the law – it is an offence to remove or disturb them. In theory, pearl fishing should no longer pose a threat, but isolated incidents are reported each year.