FBA Ark supporting conservation breeding of the freshwater pearl mussel population in the River Irfon Catchment
17 March, 2026
In 2018, a collaborative project commenced between Natural Resources Wales (NRW), the Freshwater Habitats Trust (FHT) and the Freshwater Biological Association to begin conservation breeding of the Afon Irfon freshwater pearl mussel population.
As with all Welsh populations, the Afon Irfon population is small, thought to consist of fewer than 200 individuals, and vulnerable to extinction. There has been no juvenile mussel recruitment in the Irfon for several decades due to poor-quality habitat conditions, brought about by catchment modifications and intensive land use in the wider catchment. The population required immediate intervention to avoid extinction.
Background on the River Irfon freshwater pearl mussels at the FBA Ark
Adult mussels are held at the NRW hatchery, and in 2018, thirty adult mussels were also transferred to the FBA’s Species Recovery Centre, based on the shores of Windermere, with the aim of propagating a healthy population of juvenile mussels from this broodstock. Initially, the FBA conducted host fish trials on the Irfon broodstock, exposing their glochidia to both Atlantic Salmon and brown trout, to see which species they could successfully encyst on. The results showed that the Irfon mussels have a host-preference for brown trout - since then, the FBA has been conservation breeding from the Irfon broodstock, encysting juvenile trout with Irfon glochidia and collecting the juvenile mussels that drop off after metamorphosis.
The broodstock was rotated in 2022, returning the original adult mussels to the River Irfon, and bringing 30 more adults to the SRC; this serves to maximise genetic diversity.
Afon Irfon freshwater pearl mussels nestled into their home at the FBA Ark, in the Lake District, Cumbria.
Partnership working to support conservation of Afon Irfon freshwater pearl mussel populations
In this partnership, the FBA are responsible for the care of the existing adult broodstock as well as maintaining, cleaning and feeding the juvenile mussels. The team regularly communicates with the NRW and FHT, providing updates and annual and interim reports to keep a record or progress.
“We are glad to be involved in this partnership and help to provide much-needed juvenile freshwater pearl mussels for the Arfon Irfon. These mussels, combined with those reared at the Natural Resources Wales hatchery will hopefully help to fill the gap of the missing juvenile cohorts that have failed in recent years, and with the help of the Natural Resources Wales and Freshwater Habitats Trust catchment restoration works, will successfully grow into adult mussels that may populate the river over the next 100+ years.”
Current cohorts of Irfon juveniles at the FBA Ark
Staff at the FBA currently maintain three cohorts of Irfon juveniles which were collected each year from 2023-2025, totalling approximately 700 individuals, some of these are over 20mm in length at only 3 years old – fast growth for a freshwater pearl mussel.
After a good season of collections this year, there are a further 8,000 being maintained in aquariums from the 2026 cohort. It is intended that these propagated juveniles will eventually be reinforced into the River Irfon, once conditions and habitat improve. Mussels would be released once they grow to >15mm to balance a trade-off between the increased mussel resilience with age and the associated time, energetic and financial resource investment into their maintenance.
Afon Irfon freshwater pearl mussel conservation in action at the FBA Ark, in the Lake District, Cumbria.
Film: Freshwater Pearl Mussels in the River Irfon Catchment
Before he left, Ben King liaised with FHT to support video production and update the project with the progress of our breeding activities. Working in collaboration on both catchment management and conservation breeding will give this population of freshwater pearl mussels the best chance of recovery and we're very proud to be part of that!
FHT: Protecting one of Britain's best freshwater landscapes
The Irfon catchment in mid-Wales is a Special Area of Conservation designated for its exceptional freshwater biodiversity, which includes one of the few remaining UK freshwater pearl mussel populations. Sadly, exposure to multiple pressures means the catchment is currently failing to meet Habitats Directive and Water Framework Directive targets.
The River Irfon in Wales is an important freshwater habitat for freshwater pearl mussels.
Find out more about the River Irfon Catchment project on the Freshwater Habitats Trust website.
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.
