Freshwater Pearl Mussel

Freshwater Pearl Mussels (Margaritifera margaritifera) are rare and getting rarer. There is only one population in England and that is in Cumbria. They are more numerous in Scotland but are declining. They require pristine water to survive and have a complex life cycle in which the larvae attach themselves to the gills of Salmonid fish for ten months. The fish also require pure water. Apart from pollution one reason for their decline is because people have been collecting them for their pearls. The Pearl is a natural defence when grit or some other foreign gets into the soft parts. The mussel secretes the smooth pearl around the sharp grit. Some pearls can be large because the mussel can live for up to one hundred years.

On leaving the shelter of the fishes gills the larva at first feeds by grinding algae off stones and then later it becomes a filter feeder and the adult can filter 50 litres of water a day. The mussel helps to purify the water but in doing so is at risk from pollution.

While canoeing (two man Canadian canoe) down the river Tay from Kenmore to Aberfeldy my companion, a retired vet with a great affinity for water, swam on the surface of shallow sections of the river with a snorkel mask and checked for freshwater mussels to be seen on the river bed. I’m glad to say that he found them. This is a testament to the purity of the water in the Tay.

At Loch Leven near Kinross I have seen discarded mussel shells where evidently someone had been collecting the mussels for their pearls. The Freshwater Pearl Mussel is protected in law and should be left strictly alone.

Creative Commons - credit Joel Berglund

Read more on the Scottish Natural Heritage website - SNH website - Freshwater Pearl Mussels