The Freshwater Pearl Mussel is classified as Endangered on the IUCN Red List of Endangered Species however, there is a significant population established within the North Devon catchment. A survey conducted into the age of these populations concluded that the youngest population was 40 years old. The suggestion that they have not been able to successfully reproduce since the 1960s is concerning and prompted investigation into possible reasons the population is failing.
Westcountry Rivers Trust was commissioned by their partners Devon Area of Outstanding Natural Beauty (Devon AONB), The Biosphere Reserve, The Environment Agency and Tarka Country Trust conduct surveys into possible reasons the population of Freshwater Pearl Mussels have gone into decline. With the help of enthusiastic volunteers, walkover surveys were conducted on the River Mole in order to identify and report on the various types of habitat found.
Two key elements that the larval stages of the Freshwater Pearl Mussels depend on for survival are the presence of Salmon (Juvenile Mussels attach themselves to the gills), and clean, coarse sand to burrow in. The results of the walkover survey indicted the presence of otter, kingfishers and dippers, this suggests that the river is sufficiently healthy enough to support predators. High levels of bank erosion were reported, as well as a distinct lack of riparian vegetation. Both of these issues will cause sediment to enter the river and clog any potential breeding grounds for both the Salmon and the Freshwater Pearl Mussels. This can be remedied by simple measures such as allowing the riparian vegetation to return and act as buffer strip, as well as gravel cleaning and reintroduction. Hopefully once these areas have been addressed the river will return to a good ecological standard capable of supporting and sustaining juvenile Freshwater Pearl Mussels.