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Freshwater pearl mussel

The freshwater pearl mussel is an important part of our biodiversity and has an important place in our cultural heritage. However the species is one of the most critically endangered molluscs in the world. Part of the reason pearl mussels are rare in Scotland is due to ongoing, illegal pearl fishing and they need your help.

Scotland contains many of the world's most important remaining populations. But even in Scotland there has been a dramatic decline in the number of rivers that continue to support freshwater pearl mussels. Over the last 100 years more than one third of the rivers that used to contain freshwater pearl mussels no longer do so. A further third only contain old freshwater pearl mussels, with no sign of reproduction. They are witness to our rivers' deteriorating status and need urgent conservation action.  Our work on this iconic species includes the 'Pearls in Peril external site ' project to save and restore populations in 21 sites across Scotland, England & Wales. 

What can I do to help?

To help counter criminal threats the pearl mussel very much needs your help. If you see any suspicious activity in or near a river that may contain pearl mussels, please contact the police external site as soon as possible. Further information about how to help is available in a leaflet  PDF document . If you are planning to work in a river that may contain pearl mussels, please be aware it is a crime to damage pearl mussels. 

What are freshwater pearl mussels?

Freshwater pearl mussels are similar in shape to common marine mussels but grow much larger and live far longer than their marine relatives. Incredibly, they can live for more than 100 years, making them one of the longest-lived invertebrates. They can grow to as large as your hand and are dark brown to black in colour. They live at the bottom of clean, fast-flowing rivers, where they can be completely or partly buried in course sand or fine gravel. They feed by drawing in river water and filtering out fine particles. Each day an adult is able to filter more water than we use in an average shower.  They have a complex lifecycle and, in their first year, they harmlessly live on the gills of young salmon or trout.

Why are they endangered?

Their place in our history comes from the fact that they very occasionally bear a pearl. In some ways this has led to their downfall, with over-exploitation by 'pearl-fishers' primarily responsible for massive declines in their numbers and range. But as filter feeders, freshwater pearl mussels are also extremely vulnerable to water pollution and engineering work in rivers such as the construction of weirs or deepening of pools. The effect of these threats means that the survival of the species in Scotland is not assured. As such, the freshwater pearl mussel is fully protected  making it illegal to disturb, injure, take or kill a freshwater pearl mussel. Despite this protection, the threat continues and the freshwater pearl mussel is a UK wildlife crime conservation priority.

Their place in our cultural heritage

Exploitation of freshwater pearl mussels has taken place since pre-Roman times. The earliest reference in Britain is by Julius Caesar's biographer, Suetonius, who stated that Caeser's admiration of pearls was a reason for the first Roman invasion in 55BC. In Scotland, the earliest reference dates back to the 12th Century when Alexander I, King of Scots was said to have the best pearl collection of any man living. The medieval poem 'The Parl' which dates from the late 14th Century is another early reference to freshwater pearl mussels in Scotland.

There are further references in later centuries that indicate a growing exploitation of Scottish pearl mussels. By the 18th century the first references to a decline in pearl mussel numbers can be seen. This decline accelerated during the 20th century, such that more recently there was evidence that pearl mussels became extinct from an average of two rivers every year in Scotland between 1970 and 1998 (when the species gained full legal protection).

Given the freshwater pearl mussel's place in our cultural history it is important that the final chapter in that history is not to see the species become extinct in our rivers. Rather, with action, its history will remain alongside its continued place as an important component of our biodiversity.

Last updated on Friday 27th November 2015 at 11:16 AM. Click here to comment on this page