28th January 2025
Fresh Water Pearl Mussels
The mysterious Freshwater Pearl Mussel, its contents highly prized but itself invaluable beyond measure, spends all of its life hidden amongst the sand and gravel of the riverbeds of Europe. The importance of the freshwater pearl mussel lies not in its ability to, on the rare occasion, produce a pearl but by its very presence and the way in which it feeds.
Mussels feed by drawing in river water and ingesting the fine particles of organic matter contained therein. This filters and improves the quality of the water for the other fish and mammals in and around the river system. A single adult freshwater pearl mussel filters around 50 litres of water a day which is more water than the average person uses in a shower. They are, however, very sensitive and vulnerable to water pollution and habitat disturbance. Their very presence therefore indicates good water quality. The lack of presence of a colony or an unhealthy colony could conversely indicate poor water quality.
Scottish rivers once boasted healthy populations of Margaritifera margaritifera but ravaged during the Victorian era when Queen Victoria made the wearing of freshwater pearl popular, and further decimated by poor river quality, modern agricultural practices, illegal fishing and now climate change this long living mollusc is in crisis.
The Freshwater Pearl Mussel is listed as endangered by the International Union for the Conservation of Nature. It is protected under the Wildlife and Countryside Act 1981. It is illegal to kill, take or disturb the freshwater pearl mussel or its habitat. It is also illegal to possess any freshwater pearls collected since 1998 and no pearls may be sold or advertised for sale unless under licence from the Scottish Government.
While poaching is still a concern the biggest threat facing these animals today is climate change. Mussels have a short parasitic larval phase in which they attach themselves to the gills of salmon and trout.Very little is known about the relationship between the two species but clearly the long term viability of the mussel depends on both the availability and health of their host. Climate change can cause rivers to heat up to dangerous levels which in turn reduces oxygen levels and the health and reproductive ability of salmon and trout.
One effective way of mitigating the effects of climate change is tree cover. Shading of rivers helps to lower the temperature of the water as the planet heats up. The roots of the trees help to shore up river banks as flooding becomes more prevalent and the habitat they create introduces both a greater range and number of insects and other species resulting increased availability of food sources for aquatic animals. Planting projects aimed at increasing tree coverage are already being introduced across Scotland and this includes Balnagown.
The estate to date has planted hundreds of hectares of trees and hundreds more are planned with most of this reforestation will be with native species and take place on the northern part of the estate . This will include both riparian and montane planting and will take place in particular around the Oykel catchments which have historically been heavily fished for pearl mussels.
Peatland restoration is another effective way to help combat climate change and support the freshwater pearl mussel. Peatlands are capable of both locking in and storing vast amounts of carbon and will sequester more each year. According to the IUCN the worldwide, “remaining near natural peatland sequesters 0.37 gigatonnes of carbon dioxide a year’. The storing of water helps to reduce peak flows, reducing flooding and the subsequent scouring of the riverbed while also helping to reduce drought by releasing water slowly into the rivers and streams. Balnagown has already restored 340 hectares of Peatland and plans to restore over 600 hectares more over the next two and a half years.
The hope is that on Balnagown as well as all over Scotland that if the habitat is corrected that pearl mussels will return. Already Scotland is seeing a small improvement in current colonies due to the measures being taken. Balnagown does have areas with freshwater pearl mussels, and it is hoped with these improvements that the colonies will stretch and reinhabit more areas. Going forward the estate will continue to take measures to improve and protect the natural environment and we will keep you updated on our progress.
