A significant effort is underway in the United Kingdom to rescue the endangered freshwater pearl mussels from the brink of extinction. This summer, hundreds of young pearl mussels will be released into a secret location in a river in north Wales as part of a conservation project aimed at preserving these rare aquatic creatures.

The breeding of juvenile mussels has taken place at a hatchery situated in the scenic Brecon Beacons of southern Wales. These carefully nurtured molluscs will then be transported to a river in Gwynedd, which has been restored to create an environment conducive to their growth and survival.

While pearl mussels have an astonishing lifespan of over a century, with some adults in the hatchery tanks potentially having been alive during Queen Victoria’s reign, the successful maturation of young mussels in the wild has been rare in Wales for many decades. This decline can be attributed to several factors, including habitat loss, pollution, the climate crisis, and historical human exploitation. These mussels have been harvested for their occasional pearl production since the Roman era.

Experts from Natural Resources Wales (NRW) will survey the unnamed river in the coming weeks to assess its suitability for the mussel release. Once the necessary permits are obtained, the first batch of mussels will be introduced into their new habitat. To ensure the protection of these vulnerable creatures, the location is being kept secret, as there is a concern that individuals may break the laws put in place to safeguard the mussels and search for pearls. However, the chances of finding pearls among these mussels are incredibly slim.

“They are fabulous things,” said Tristan Hatton-Ellis, a freshwater ecologist with NRW. “We are hoping that putting back the riverbed will be massive not just for the pearl mussels but for salmon, trout and invertebrates.”

Currently, only about 1,000 aging adult pearl mussels survive in the wild in Wales. These adults can grow up to 14 centimetres in length and prefer clean, fast-flowing water. They reproduce by producing glochidia, the larval stage, which attach themselves to the gills of salmon or trout. Afterward, the juveniles spend up to a decade buried in river gravels, but recent years have seen no successful maturation of young mussels.

The complex life cycle of pearl mussels necessitates the presence of rivers with diverse water flows. Unfortunately, human activities such as dredging, embankment construction, and land drainage have resulted in the degradation of the features crucial for the mussels’ thriving population.

To restore the river in Gwynedd, an extensive revitalisation project has been undertaken. Over the course of six months, more than 850 tonnes of boulders and cobbles were meticulously placed back into the river, accompanied by 330 tonnes of fresh gravel. Embankments were dismantled to reconnect the river with its floodplain, and drainage ditches, previously cutting through peatland, were filled in. Fencing has been erected along the riverbanks to prevent livestock from accessing the area, and trees have been planted to provide shade, benefiting both the river ecosystem and the potential mussel beds.

Simultaneously, NRW has been improving its Brecon hatchery, one of two specialist freshwater pearl mussel breeding facilities in the UK, the other being located in Cumbria, in north-west England.

By undertaking these comprehensive conservation measures, including the release of juvenile mussels into a restored river and enhancing breeding facilities, conservationists and experts hope to reverse the decline of freshwater pearl mussels in Wales. This endeavour represents a significant step towards safeguarding the future of these rare and extraordinary aquatic creatures for generations to come.

Katie Fincken-Roberts, a biodiversity specialist from NRW, said there were currently about 32,000 juveniles in the hatchery. She said: “We need them to grow to a certain size, about 25mm, before we think they’d be robust enough to be released. We have a couple of hundred that would potentially go back this year and then the following year there would be pushing a thousand and hopefully it will ramp up.”

 

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