Waterside Ecology

Independent Ecological Consultancy

Reintroducing freshwater pearl mussels

Client Scottish Natural Heritage


Scotland is a stronghold for the freshwater pearl mussel, containing many of the world’s remaining viable populations of this endangered species. Even here, populations in almost 70% of sites occupied 100 years ago are extinct or no longer viable. Freshwater pearl mussels have an extraordinary life cycle, spending a brief period encysted on the gills of salmon or trout before becoming a free-living mussel. Thus they require healthy fish populations as well as healthy rivers if they are to thrive. One of the aims of the Species Action Plan for the freshwater pearl mussel is to seek ways of restoring populations to water bodies within their historic range.


A team comprising Waterside Ecology and Cosgrove and Hastie Associates has been working with SNH to identify potential sites for pearl mussel restoration and reintroduction. This year, trials were undertaken of two methods of restoration: (a) translocating adult mussels from large donor populations to rivers where they have become extinct; and (b) reintroducing pearl mussel populations by capturing and infecting juvenile salmon and trout with glochidia (larval mussels) and releasing them back into the river.


If successful, it may be possible to replicate these efforts more widely, allowing these fascinating creatures to repopulate streams and rivers where suitable habitat remains. For more information on freshwater pearl mussels please see Life in UK Rivers.