Bid to save rare freshwater river mussel in Wales

Media caption,
Mussel power: Bid to save rare shellfish in Wales

One of the most endangered shellfish in Britain could be handed a lifeline by scientists in Wales.

Freshwater pearl mussels are being bred as part of a programme run by Natural Resources Wales (NRW).

So far, 1,300 juvenile mussels have been grown at a Powys fishery.

Conservationists hope the mussels will eventually have a controlled release into Welsh rivers - bringing the species back from the edge of extinction.

"This is an important project because of the threat to the freshwater pearl mussel," explained Dr John Taylor, NRW's fisheries specialist.

"We don't find any baby mussels in our rivers now, the only ones we find are around 50 to 60-years-old. We haven't found any baby mussels for decades now."

The freshwater pearl mussel was once abundant in Welsh waters, but despite legal protection there is now just one stronghold left in Wales, in Gwynedd.

They are one of the longest living invertebrate animals, and can survive for over 100 years.

Image source, Natural Resources Wales
Image caption,
There is just one remaining stronghold for the freshwater pearl mussel in Wales

"We need to do more to help the survival of species threatened by increasing pressure from society and climate change," added Dr Taylor.

They need rivers with clean, well-oxygenated water and stable gravels.

In a good-quality environment pearl mussels can occur in vast beds of 1,000 mussels per square metre, covering extensive areas of the river.

Freshwater pearl mussels: The facts

  • The freshwater pearl mussel (Margaritifera margaritifera) may live for more than 120 years, making them one of the longest-lived invertebrates
  • The species grows to 14cm (5.5in) in length
  • They burrow into sandy substrates, often between boulders and pebbles, in fast-flowing rivers and streams
  • Population declines have been caused by factors such as pearl fishing, pollution and declining salmon stocks

(Source: Defra)

Under the project being run at a hatchery in Brecon, experts have been able to adopt a technique pioneered in places such as Norway and Luxembourg to rear mussels using tubs with sediment and algae.

"Adult mussels are brought into the hatchery in June and settled into a fish tank in a gravel basket," said Dr Taylor.

"In August the mussels release spat, known as glochidia, which latch on to the gills of the trout in the tank, and stay there over winter until they drop off in the following spring.

"At this stage the mussels, about a third of a millimetre in length, are collected in plankton nets and transferred to plastic tubs containing a mixture of organic detritus and commercial concentrated algae.

"The juvenile mussels have now reached 2-3mm and have been transferred to a special rearing trough resembling an artificial river. They are fed a daily diet of algae.

"It is hoped that in a year to 18 months' time, the mussels will be capable of filter feeding and be ready for controlled release."

Those behind the project said they were still working to identify suitable release sites.