Tide turns for crown

Published on Friday 25 March 2011 16:16

ITS most famous catch is the lustrous pearl that became part of the Scottish crown jewels. Now the sensitive waters of the River Ythan - once renowned for the quality of its freshwater mussels - are to be cleaned up as part of a £1.5 million project after decades of pollution.

Scottish Water is to spend the money on improving the quality of the River Ythan, which runs for 39 miles into the North Sea from its source near Huntly to south of Ellon in Aberdeenshire.

Historically, the Ythan was famed for its freshwater pearl mussels and in 1621 the Kelly, or Kellie, pearl, found in a tributary, is believed to be the largest found in Scotland.

It was presented by the Lord Provost of Aberdeen to King James VI and is now part of the Scottish crown, among other pearls, diamonds and rubies.

Persistent poaching led to the species being lost from the river and pollution from the nitrogen in fertiliser from the surrounding farmland has hindered any revival as the threatened species needs clean sand and gravel to thrive.

It is hoped the project to build a new wastewater treatment works at Fyvie will improve water quality and increase the chances of survival of the river's wildlife. It is also home to salmon, trout and the endangered water vole.

David Crawford, construction manager for Scottish Water Solutions, said: "Our investment will benefit the local environment. The existing treatment works at Fyvie is basic in nature and needs upgrading.

"The new plant will improve the level of treatment and reduce the risk of poor-quality effluent going into the sensitive waters of the Ythan."

Fyvie's existing treatment works is located to the south of the village, by the banks of the river. The new works, which will be completed by the end of the year, will use a combination of tanks and filters to produce a much cleaner effluent that can be dispersed in the Ythan with minimal impact on the environment.

The Ythan is regarded as very sensitive due to its limited number of tributaries and extensive farmland along its length. It was the first river in Scotland to be classed as a nitrate vulnerable zone (NVZ) which means farmers and landowners are encouraged to limit the amount of fertiliser they use to reduce the chance of run-off causing pollution.

Mark Andrew, clerk to the Ythan District Fisheries board, said the project is welcome. "It will further improve the water quality which is something for which we have been striving for many years.

"Water quality in itself does not affect fish but it does affect the invertebrates and other things that fish live on and it certainly has had an impact on the type of flora and fauna that grow on the Ythan."

Andrew said it is unlikely freshwater pearl mussels will return to the river."It could not be done by nature as they are not in the river at the moment. They can be reintroduced in a river where they already exist. Where they have entirely died out it's a much more difficult process."

Iain Sime, Scottish National Heritage's freshwater group manager, said the agency's most extensive records for the River Ythan are from the 1990s.

"At the time we concluded that freshwater pearl mussels in the river were close to extinction. This was due to nutrient enrichment and illegal pearl fishing.

"So we welcome the new waste water treatment works. It will contribute to improved water quality and help the biodiversity of the river."

The freshwater pearl mussel, Margaritifera margaritifera, can live for 80-100 years but matures after around 10-15 years so young mussels cannot form a sustainable population. They have been vanishing from Scotland at a rate of two rivers a year since 1970. There are now thought to be only 61 breeding sites left and if the present rate of decline continues, it has been estimated that surviving Scottish populations may only last for another 25 years.

Even so, a meeting of European experts on freshwater pearl mussels last month, concluded that Scotland was the last "stronghold" of the species, making attempts to revive previous habitats more important.

Exploitation of freshwater pearl mussels has taken place since pre-Roman times. The earliest reference in Britain is by Julius Caesar's biographer, Suetonius, who stated that Caeser's admiration of pearls was a reason for the first Roman invasion in 55BC.

In Scotland, the earliest reference dates back to the 12th century when Alexander I, King of Scots, was said to have the best pearl collection of any living man. Commercial exploitation on a much larger scale developed during the 16th century across Britain and Ireland.

Many people worked in the industry up to the 19th century but over-exploitation resulted in stocks being almost wiped out.

Fishing for pearl mussels was made illegal in 1998.