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Freshwater Pearl Mussel

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(Courtesy of the Northumberland Biodiversity Partnership)

The freshwater pearl mussel (Margaritifera margaritifera) is found on the North Tyne and River Rede and these populations make up one of the two remaining significant populations in England. A breeding programme for freshwater pearl mussel is currently being implemented at Kielder hatchery with a view to infecting the fish stock for the North Tyne and Rede to try and address the decline in the species.

The freshwater pearl mussel is a bivalve mollusc that lives in fast flowing, nutrient poor rivers with clean sandy and stony bottoms. They are filter feeders, extracting fine organic particles from the water. Their shell is oval and elongated and is dark brown or blackish in colour. They can grow up to 15cm long and have a natural life span of up to 80 to 100 years, making them one of the longest lived known invertebrates. As the name suggests they can produce pearls and have been exploited for these since Roman times. During reproduction females inhale male sperm from the water, producing tiny bivalve larvae called ‘glochidia' from the fertilised eggs. Each female is able to shed about 3 million of these in late summer. The species is dependent on the presence of salmonid fish as the larvae lodges on their gills.

It is estimated that only 0.1% survive this stage of the life cycle. In spring the juvenile mussels fall off their host gills and try to find a suitable location in clean sand or gravel. There is further massive mortality at this stage as juvenile mussels are eaten by fish. Those that are successful grow quite rapidly reaching 2cm in 4-5 years. Adult mussels are known to be eaten by otters and also avian predators if they are stranded by low water. The freshwater pearl mussel is a rare, globally threatened species that had been lost from all but seven rivers in England. Many of the UK populations may not have produced young for over 30 years, creating a fragile aging population.

To find out about TRT's collaboration with the FBA, EA and NWL Ltd; the Tyne Freshwater Pearl Mussel Project click here.