Conservation in action and freshwater pearl mussel species recovery at the FBA Ark
19 February, 2025
Nestled among trees on the shore of Windermere in the Lake District, the FBA Ark may have an unassuming appearance, but did you know that this wooden-framed building is home to about 50,000 freshwater pearl mussels (Margaritifera margaritifera), and is a beacon of species recovery and conservation action?
Once the most abundant bivalve mollusc in ancient rivers around the world, numbers of freshwater pearl mussel are now desperately declining in all countries and the species is nearly extinct in many areas.
Here we catch up with FBA’s Pearl Mussel Assistant, Jodie Warren, to hear about the daily activities at this very special species recovery sanctuary and the freshwater science making a vital contribution towards protecting this vulnerable species.
Tell us a bit about The Ark?
The Ark is a site on the western shore of Windermere where the FBA runs a freshwater pearl mussel captive breeding programme, which was established in 2007. These mussels are largely unheard of, yet they have undergone a 90% decline during the 20th century due to pearl fishing, pollution and habitat degradation.
Did you know… it has been suggested that a desire for pearl mussels may have been one of the leading reasons that the Romans first invaded Britain in 55BC, as Julius Caesar had an admiration for pearls.
Concern for the Margaritifera margaritifera mussel species is so great that it is protected under the EC Habitats Directive and since 1996 has been listed as critically endangered by the International Union for Conservation of Nature (IUCN) and remains on the Red List of Threatened Species. Another issue they face is the decline in fish stocks, as fascinatingly, this mollusc species uses either salmon or trout as part of their life cycle, with the fish acting as hosts for the baby mussel larvae (known as glochidia). Therefore we have several tanks of fish on site, as part of our mussel captive-breeding, and everyone needs checking and feeding every day!
Photo of FBA Ark (left) and view from the Ark looking out to Windermere’s north basin (right)
Tell us a little about the FBA Ark team
There are four of us in the freshwater pearl mussel team who share the responsibility of looking after the pearl mussels on a daily basis. Louise Lavictoire is the head of the team, having been here since the very start of the project she has many years of pearl mussel wisdom which helps us all day-to-day. Ben has been in post as the Pearl Mussel Officer for three years, whilst I have been Pearl Mussel Assistant for two. Sam joined us in May last year and works as part of the team through the LIFE R4Ever Kent project.
FBA Ark team: Samantha Bonny, Jodie Warren and Ben King water safety training in 2024
How many freshwater pearl mussels are you looking after? And roughly how many pearl mussels have you released back into the wild, to date?
At the moment we probably have about 50,000 freshwater pearl mussels on site – but most of them are very very small as they take such a long time to grow. Around 3,500 juvenile mussels have been put back into the river Irt over the last few years, and 350 went into the river Ehen for the first time, last year. Hopefully, there will be many more releases to come in Cumbria, and further afield.
Photos of Louise Lavictoire and Jodie Warren undertaking juvenile mussel releases in the River Irt
Can you give us a flavour of what you do on an average day looking after the freshwater pearl mussels?
Each day starts with daily duties, everyone, mussel and fish, need to be fed, as well as checks of water temperature and flow in all our systems. Once checks are done, jobs really depend upon the time of year, as we focus on different things in different seasons. At the moment we are doing juvenile mussel collections, this means that each day we need to check collection bottles from each fish tank to extract juveniles and put them into our aquariums.
Each juvenile is about 350µm and virtually undetectable by eye, so we need to use microscopes and pipettes to get them out! During spring and summer we spend a lot of time tagging mussels ready for release as well as counting, measuring and moving juveniles between systems to maximise growth. As we care for so many mussels on site, that also means most days we spend time cleaning!
Collecting juveniles using a microscope in the back-lab (left), tagged juveniles in one of our flumes (right)
Photo of juveniles under a microscope
“What I enjoy most is the knowledge that I am helping these mussels at a really critical time. This species is generally not doing well at all in our rivers and without our intervention they are at risk of being completely lost. It is very rewarding placing a little 3cm pearl mussel into some gravel in their native river after 4 to 5 years of being closely cared for and monitored by FBA staff. Especially when you come back a year later with a PIT-tag reader, and the mussels are still there! Hopefully they will remain there for another 100 years or so – well worth all the dedicated hard work at the FBA Ark.”
What is the aim of the species recovery project and what are your hopes for the freshwater pearl mussels that are reared at the Ark?
It is our hope that captive-bred freshwater pearl mussels from the FBA Ark end up thriving in their native rivers. That is what the project set out to do, as well as being a ‘safe house’ for mussel populations that are clinging on, whose rivers are in a really bad way. At the FBA Ark we can hold large numbers of mussels until the time is right for them to be released back into the wild, where they should be.
Once they are nestled back safely in their native rivers, the pearl mussels , as important filter feeders, can continue to contribute to natural river function and enhanced freshwater biodiversity.
Adult freshwater pearl mussels (left), brown trout (right)
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.
