Rare Pearl mussels continue to grow in Northumberland

[Editor]

Pearl mussels in North Tyne have ended their reproductive drought by breeding for the second year in a row.

Environment Agency officers released 11,000 sea trout at the top of the River Rede last Friday. The fish were carrying mircoscopic pearl mussel larvae, each of which is around a tenth of a millimetre in size.
Using the 'host fish'

The breeding programme mirrors what should happen in the wild, using trout as ‘host fish’ for the mussels. The process involves male mussels releasing sperm into water, which is then filtered by the females.

The sea trout were bred at the Environment Agency’s Kielder Hatchery, where they were deliberately ‘infected’ with pearl mussel larvae from a captive pearl mussel population in the hatchery’s artificial stream. Around 20 percent of the fish are expected to be carrying the larvae.

The fish were released in part of the River Rede where pearl mussels haven’t been seen for 50 years.



Environment Agency ecologist Anne Lewis said: “We’ve been working hard to get the right breeding conditions in the hatchery since 2004. It’s a really exciting time as the mussels have continued to breed for a second year.

“Mussels are not breeding in the wild and will become extinct in Northumberland if we cannot find ways to support the species.

“In the past, pollution, dredging and poaching have all taken their toll on the population nationally but our rivers are now the healthiest they have been for 20 years. The work we and our partners are doing to improve habitat in the North Tyne and Rede for the pearl mussel is also great for other iconic river wildlife, such as salmon and trout.”

Pearl mussels has been in British rivers since the end of the Ice Age and they were recorded at the time of the Roman invasion.

Long way to go

After fertilisation the eggs ripen in the female’s breeding pouch before being released as larvae, which must attach themselves to the gills of young fish in order to develop into tiny mussels, ready to lead an independent life.

Anne said: “From here it’s a slow growing process for the mussels. They’ll be with the sea trout until spring next year, by that time they will just visible to the naked eye. They then drop off the fish and continue grow in the river bed for about 20 years before they are ready to breed.”

Kielder hatchery assistant David Kirkland said: "Stocking our first batch of host fish was a proud moment and a big step forward in our efforts to keep pearl mussels in the Tyne, we're learning all the time and hope to achieve a higher rate year on year."

Once established in the region’s rivers, the young pearl mussels will grow to about 130mm and live to around 100 years-old.



Pearl mussel facts

• They would prefer to be packed together in dense beds, sometimes in the thousands but now in England and Wales they are much more spread out.
• Pearl mussels are very sensitive to river pollution and there have been cases where dredging riverbeds for gravel has damaged mussel populations.
• There are still thousands of mussels in a handful of rivers in the North of England – 50,000 are thought to be in the Rivers North Tyne and Rede
• In ‘Lives of the Caesars’ the biographer Suetonius tells of Julius Caesar’s taste for pearls. He suggests their occurrence in Britain was an important factor in the first Roman invasion of 55 BC.
• Pearl mussels can live between 80 to100 years in Britain and can grow up to 15 cm in length.
• Pearl mussels are internationally recognised as an endangered species. It is illegal to disturb the mussels or their habitat.
• There are still wild breeding populations in Ireland and Scotland.
• Although an internationally protected species, the illegal practice of pearl fishing has been cited as one factor in reducing the mussel population density, with the resulting decimation leading to current breeding problems