Conservation programme releases 5000 freshwater mussels in effort to save species from extinction
23 July, 2025
This week the Freshwater Biological Association reached a crucial milestone in our efforts to save the freshwater pearl mussel (Margaritifera margaritifera) from extinction in England.
On 23 July 2025 in the River Kent (Cumbria), we released our 5000th juvenile mussel from our conservation breeding programme, the Freshwater Pearl Mussel Ark, boosting the population in the River Kent from fewer than 10 individuals to over 100. As part of the EU LIFE funded R4ever Kent project, population reinforcements of 4000 mussels are planned over the next few years to bring this population back from the brink of extinction.
About the Freshwater Pearl Mussel Ark
Initiated in 2007 and funded by Natural England and the Environment Agency, the Freshwater Pearl Mussel Ark was set up to breed freshwater pearl mussels from priority populations in England, with the aim of releasing juveniles from each population back in to the rivers where their parents originated.
The freshwater pearl mussel is a long-lived (>100 years!), slow growing mussel which takes between 6 – 9 years to reach sizes large enough for release back into the wild. At the same time as the Ark commenced, a wide range of partners committed to carrying out catchment-scale restoration activities in these priority rivers in order to restore and improve habitats, ready for juveniles when they were large enough to be released.
One of our longest-running and most successful collaborations has been with West Cumbria Rivers Trust, who have spearheaded restoration works on the River Irt. Over 4000 juvenile mussels have subsequently been released in to the river since 2021, with monitoring playing a key role in ensuring that release strategies are refined and improved for maximum juvenile survival.
The freshwater pearl mussel is a long-lived (>100 years!), slow growing mussel which takes between 6 – 9 years to reach sizes large enough for release back into the wild.
Preparing to release freshwater pearl mussels in the River Kent, Cumbria, July 2025.
Update on juvenile freshwater pearl mussel population reinforcements
To date, FBA have carried out juvenile population reinforcements on three mussel rivers in England, two of which are designated as Special Areas of Conservation for the species. Our breeding programme now boasts around 50,000 juvenile mussels of various ages and sizes from seven different priority populations in England and Wales.
In England, there are only around a dozen rivers containing populations of freshwater pearl mussels and all except one is not recruiting sustainably (or at all!). For those populations failing to recruit new juveniles, the youngest individuals are commonly over 70 years old and so the population is slowly and silently heading for extinction as the oldest individuals die of old age.
Conservation breeding and population reinforcements are necessary in the short-term to safeguard these populations, while habitat improvements and catchment-scale restoration offer the longer-term solution needed not only for the freshwater pearl mussel, but a wider range of freshwater species.
The 5000th freshwater pearl mussel tagged at the FBA Ark, July 2025, ready for release.
Safeguarding the future survival of freshwater pearl mussels
Whilst this is an important and exciting milestone, we cannot rest on our laurels. We have many thousands of individuals in a wide variety of rearing systems at the FBA which will soon become large enough for release and we must ensure the habitat is good enough to receive them and that they have a high chance of survival.
On a personal note, I’d like to thank the fantastic team at the FBA, both past and present, who have contributed to this wonderful achievement. Ben, Jodie and Sam, current members of the pearl mussel team work tirelessly 365 days of the year to ensure our precious juveniles are well cared for and will be robust when it comes to their time for release. I’d also like to acknowledge the unwavering work of our fantastic external partners and funders with whom we have worked with for almost 20 years to safeguard this species.
They say it takes a village to raise a child… Imagine raising 50,000! I’m very proud of our ‘village’ of supporters, advocates, partners, funders, land managers and members of local communities who have all played their part in saving this vital keystone species.
Louise Lavictoire and Ben King preparing to release freshwater pearl mussels, bred at the FBA Ark, into the river.
Watch the release of our 5000th freshwater pearl mussel!
“I’d like to thank the fantastic team at the FBA, both past and present, who have contributed to this wonderful achievement. Ben, Jodie and Sam, current members of the pearl mussel team, work tirelessly 365 days of the year to ensure our precious juveniles are well cared for and will be robust when it comes to their time for release. I’d also like to acknowledge the unwavering work of our fantastic external partners and funders with whom we have worked with for almost 20 years to safeguard this species.”
Interested in discovering more?
Read: Avoiding extinction: Conservation breeding and population reinforcement of the freshwater pearl mussel, 20 May, 2024 By Louise Lavictoire & Chris West
Find out more about FBA's Freshwater Pearl Mussel Ark
Established in 2007, the Freshwater Pearl Mussel Recovery project is an ongoing partnership project between the Environment Agency, Natural England and the Freshwater Biological Association.
