Species of the month

February – Freshwater Pearl Mussel

Few people are fully aware of the significance of the freshwater pearl mussel, a species that lives ‘hidden’ in cold, fast-flowing rivers yet is embedded in our history, culture and biodiversity.

The freshwater pearl mussel is incredibly important as it filters river water, removing tiny particles for nourishment and by doing so helping to clean the water and benefiting other river wildlife.  Each day an adult mussel can filter more water than we use in an average shower.

For reproduction rights contact the Scottish Natural Heritage Image library on Tel. 01738 444177 or www.snh.org.uk

Freshwater pearl mussel feeding. Image (c) Sue Scott/SNH

They can live for more than 100 years, making them one of the longest-lived invertebrates. Freshwater pearl mussels can grow as large as your hand but are rarely seen, partly due to their dark-brown to black colour, but also because they can be completely or partly buried in course sand or fine gravel, making them even less conspicuous.

The species has suffered a catastrophic decline globally and Scotland is now the stronghold of the remaining UK population.  It is the ability to occasionally bear a pearl that was to some extent their undoing.  Some even say that Julius Caeser’s admiration of pearls was a reason for the first Roman invasion in 55BC, whilst others reckon that Alexander I, King of Scots, had the best pearl collection of any man living.  What we know for sure is that the pearl fishing industry was part of our culture sustaining many travelling communities, who would make their summer livelihood from pearl fishing.

Fresh water pearl mussel group

Fresh water pearl mussel group ©Sue Scott/SNH

Over-exploitation by ‘pearl-fishers’ is primarily responsible for the massive decline in freshwater pearl mussels.  There was evidence that pearl mussels became extinct from an average of two rivers every year in Scotland between 1970 and 1998, when they became legally protected.  They also face new pressures from human activities such as water pollution and inappropriate river engineering.

Recently a World Wide Fund for Nature (WWF) award was given in recognition of the successful investigation and prosecution of two contractors and a consultant who, in building a hydro-electric power scheme, allowed large quantities of silt to flow into the River Lyon in Perthshire thus threatening a colony of freshwater pearl mussel.

In August 2010, investigations by SEPA found that considerable quantities of sediment (from the construction of the hydro-electric power scheme) were entering the River Lyon and part of the River Tay (a designated Special Area of Conservation). Investigations by SNH and Police Scotland (formerly Tayside Police) showed that the silt was smothering and killing the vast majority of freshwater pearl mussels in the River Lyon.  This case is the first time there has been a successful prosecution for damaging freshwater pearl mussels.

One of the main, continuing threats to freshwater pearl mussels is illegal pearl fishing and through the ‘Pearls in Peril’ (PIP) LIFE project work is underway to combat this threat. The project is working with the police and fishery managers to implement ‘Riverwatch’ schemes to help prevent the illegal persecution of pearl mussels.

In Scotland a ‘riverwatcher’ is employed seasonally to visit 16 rivers where pearl mussel populations are at risk.  They gather intelligence and visit rivers searching for evidence of pearl mussel crime. A riverwatch scheme was launched on Harris in the Western Isles last summer and more initiatives will be established across Scotland during summer 2014.

A pile of fresh water pearl mussel shells. ©Lorne Gill/SNH

A pile of freshwater pearl mussel shells.
©Lorne Gill/SNH

You can help the freshwater pearl mussel. Keep an eye out for any suspicious activity as we head into spring and summer. Things to look out for include piles of dead shells on the river bank, or anyone using a glass-bottomed bucket and stick to probe around river beds when the water levels are low.  Anything suspicious should be reported to Police Scotland – call 101 (999 if a crime is in progress).

Want to find out more?

Freshwater pearl mussel:


Pearls in Peril project:


Mo the Mussel @twitter:


Children’s factsheet:


Children’s Storey – Maggie the Mussel:


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