A watercourse survey carried out ahead of work to replace culverts has uncovered a previously unknown colony of freshwater pearl mussels in north Highland.
The habitat improvement work – supported with a £170,000 Biodiversity Challenge Fund grant from Scottish Natural Heritage (SNH) and managed by Forestry and Land Scotland (FLS) - will see 8000 native broadleaf trees planted in groups along 6.5km of water course and the removal of six barriers to fish passage from tributaries.
The discovery was made as a survey was being carried out by Alba Ecology's Pete Cosgrove.
Freshwater mussel populations depend upon these fish (Atlantic salmon, brown/sea trout) to support the larval stages of their lifecycle, when they latch on to gill filaments and grow until they detach themselves the following spring. They need to land in clean sand or gravel in order to grow.
Suzanne Dolby, FLS Environment Forester, said: “Our reputation rests mainly on our forestry expertise – but this entails a whole lot more than just knowing about trees. Species conservation is a huge part of what we do and that includes looking after over a quarter of all of Scotland’s pearl mussel watercourses. This is a significant responsibility for a species that has declined by 95 % in central Europe and is classified by the IUCN as being Critically Endangered in Europe. We take practical action to meet these responsibilities and discoveries like this highlight the importance of sustainable forest management and the type of work that we continue to build on to improve in-stream habitat for fish and pearl mussels."
The new culverts restore the natural river bed, allow for a more natural flow of water and allows fish to pass freely along the tributaries to access additional spawning areas on the outskirts of the forest. As the pearl mussels hitch a ride on the gills of young fish, this also allows for larval-stage mussels to colonise new stretches of a watercourse and replenish existing populations.