A breeding programme is set to boost a critically endangered species.
About 120 young freshwater pearl mussels are being released into a Gwynedd river to help the species.
The mussels were raised at Natural Resources Wales’s (NRW) captive-rearing facility near Brecon.
They will be released into the river following extensive habitat restoration works in 2022.
The location is protected to prevent poaching and is one of the last remaining pearl mussel populations in Wales.
The species is classified as functionally extinct due to the small numbers and age of the mussels left.
In 2022, more than 1,000 tonnes of boulders, cobbles, and fresh gravel were re-introduced into the river to increase valuable habitat for pearl mussels.
The mussels are initially placed into the river in purpose-built concrete silos with filters to allow them to draw water.
Release locations are carefully chosen to protect the mussels from both low and high flow conditions to maximise their chances of survival.
NRW will undertake a regular monitoring programme to assess how the mussels are growing and surviving in natural conditions.
John Taylor from NRW, who has overseen the captive breeding work, said: "Freshwater pearl mussels have a complex lifecycle, and begin their development as parasites on the gills of fish, before dropping off and burying in the gravel of river beds.
"Research has shown that it is this first stage of the life cycle where the mussels are struggling to survive.
"The captive breeding programme is essential in the short term as it will allow us to prevent the extinction of this species in Wales and provide a much-needed boost to dwindling, old populations which are not viable."
Thomas Doherty-Bone, NRW’s freshwater pearl mussel recovery officer, said: "Releasing our captive-bred pearl mussels is a big step, but critical for the future survival of the species.
"Sadly, in Wales, there has been no evidence of young mussels surviving in the wild for the last 40 years, so both habitat restoration and rearing programmes are now essential."
The pearl mussel project is funded by the Welsh Government’s Water Capital Programme.
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