Exclusive, 12 September 2014
Millions of freshwater pearl mussels have been killed by sewage pollution of the River Spey in northeast Scotland over the last 15 years, according to scientific reports released under freedom of information law.
Experts from the James Hutton Institute in Aberdeen have revealed that the number of mussels in the river has halved from 10 million in 1998-9 to five million in 2013. They blame high levels of phosphorus and other pollutants in sewage discharges for the decline, along with other factors.
Freshwater pearl mussels, a globally endangered species that can live for more than 100 years, are among the UK’s most protected wildlife. They hide at the bottom of clean, fast-flowing rivers and have long been victims of illegal fishing for the pearls they sometimes produce.
But the mussels are also under threat from pollution, the scientists warn. In detailed draft reports for the Cairngorms National Park Authority in May and June, they argue that the environmental standards set for the Spey are far too lax.
Concentrations of phosphorus in the Spey "are generally too high and of greatest immediate concern,” they say. Standards under the European Union’s water framework directive "have been set considerably higher than they should be, possibly by 1-2 orders of magnitude”.
The phosphorus comes from detergents, fertilisers and human waste. Levels of other sewage pollutants like suspended solids and dissolved oxygen are also “some cause for concern”, the scientists say.
The worst pollution comes from the sewage works at Aviemore, they say. But they add that discharges from four other works at Carrbridge, Nethy Bridge, Dulnain Bridge and Grantown are also affecting water quality.
“Water quality issues combined with low flow periods may have played a part” in the massive losses of freshwater pearl mussels, the scientists conclude. They recommend more stringent standards and more intensive monitoring.
The 60-page reports, written by Susan Cooksley and Leah Jackson Blake from the James Hutton Institute, were obtained by a local wildlife group, the Badenoch and Strathspey Conservation Group. It is campaigning against plans for up to 2,000 new houses in the Cairngorms National Park, which it says will increase pollution of the Spey.
“It looks alarmingly as if the Spey’s pearl mussels are in free fall,” said the group’s convenor, Dr Gus Jones. “Pollution levels are already exceeding safe limits and yet thousands more houses are planned in Strathspey, further impacting on water quality."
He called for pollution standards to be immediately tightened up. “We hope this timely report will be a wake-up call that radical action is urgently needed if Scotland is to save the Spey’s pearl mussels,” he added.
The Cairngorms National Park Authority (CNPA) defended its house-building plans, which it argued were broadly backed by a public inquiry report published this week. “We are of course concerned about the conservation status of the freshwater pearl mussel,” said the park’s conservation director, Hamish Trench. “We await the full survey results so that we can get a clear picture of the issue we're facing and what practical steps we can take.”
The 2013 Spey mussel survey quoted in the released reports was carried out by the government’s wildlife agency, Scottish Natural Heritage. “We completed the survey this year and are analysing the information ahead of a survey report next month,” said the agency’s policy manager, Iain Sime.
“There are several potential issues likely to be affecting the pearl mussels. We will be discussing those with the CNPA and others in the weeks ahead with a view to identifying conservation measures to help the species.”
Scottish Water, which operates sewage works on the Spey, pointed out that there were also private septic tanks in the area. It had made significant investments to improve its plants in recent years, said a company spokeswoman. “All our assets in this area are performing to a high level and meet compliance levels as set out by the environmental regulator.”
This story was followed up by the BBC.