New insights into the life of Freshwater pearl mussels

Penny Lawson - October 3, 2019

They may not be one of the most glamorous wildlife sights, but Freshwater Pearl Mussels are an increasingly rare find, and the Spey is one of only a few remaining Scottish rivers where they are hanging on. Populations in the lower river are thought to be reasonably stable, but there is deep concern that the mussels are failing to breed and therefore declining in the upper catchment. Ecologist Kieran Leigh-Moy was brought in by SNH last year on a graduate placement to try to find out more.

Kieran’s many hours of field work confirmed that mussel densities in the upper catchment were indeed very low with no evidence of juveniles being present. The good news is that a previously unknown population was discovered in one tributary, the furthest upstream juveniles mussels have been found by approximately 20 miles.

The research found out useful information about the type of habitat mussels need and which tributaries have the potential to support them. Habitat survey work also suggested that the decline in populations may be linked to low oxygen levels in the river bed due to deposition of increased amounts of fine sediment, and changes seen in the shape of the mussel’s shells show that climate change factors may be affecting their health. Further research on fine sediment sources and deposition in the upper catchment is being carried out in the next few months by a research team commissioned by SNH.