Freshwater Pearl Mussel

Fast Facts

Latin name: Margaritifera margaritifera

Notable feature: The shells of Freshwater pearl Mussels can grow to 140mm long – that’s the size of your hand!

Conservation Status: Endangered

Where in the UK: Remnant populations in England, Wales and Northern Ireland, the majority of Freshwater Pearl Mussel populations are now found in Scotland.

Freshwater Pearl Mussel (Margaritifera margaritifera) © Joel Berglund

Description:

The Freshwater Pearl Mussel (Margaritifera margaritifera) is a large, native, freshwater mussel which is Critically Endangered in the UK and Endangered globally.

These amazing bivalves live in rivers with exceptionally clean water and lots of healthy wildlife; a healthy population of Freshwater Pearl Mussels shows that a river and all its wildlife are doing well.

Freshwater Pearl Mussels are similar in shape to marine mussels, but grow much larger and are a dull brown colour.

Freshwater Pearl Mussel in hand (Margaritifera margaritifera)

Size: Up to 140mm in length
Life span: Up to 100 years
Diet: Freshwater Pearl Mussels filter tiny particles from the water. They have a pair of siphon tubes one of which takes in water, which after being filtered is expelled through the other siphon.
Reproduction: The Freshwater Pearl Mussel has a fascinating and complex four stage lifecycle. Larvae, called glochidia, are brooded by the females in their gills and released into the water between July and September. The larvae must then be inhaled by salmon or trout and attach to their gills. During this time they will develop into young mussels, before detaching early the next summer, to live independently. They must burrow into the river bed to survive as adults.
When to see: Present in rivers all year round, but strictly protected – it is an offence to disturb or take Freshwater Pearl Mussels from a river.
Population Trend: Declining and Critically Endangered in the UK
Threats: Illegal pearl fishing, water pollution, abstraction, siltation, climate change.
Fun Fact: Freshwater Pearl Mussels are some of our oldest living invertebrates. Large mussels may be as much as 100 years old. The first historical reference in Britain was by Julius Caesar’s biographer around 55BC.

How you can help:

Buglife is working to increase awareness of invertebrates and the Freshwater Pearl Mussel through specific projects and campaigns which have highlighted the damage caused to our freshwater invertebrates through the actions of humans, but we need your help!

Join a recording scheme and log your finds – send any records/sightings to The Conchological Society of Great Britain and Ireland. Also, make sure you report any suspicious behaviour beside rivers, in particular anyone removing mussels from river beds; reports should be made to your local Police Wildlife Crime Officer