Freshwater pearl mussels discovered in Scottish lakes

Using remote-controlled underwater drones and snorkel gear, small numbers of pearl oysters have been spotted in two lakes in Sutherland and the Trossachs.

The survey was conducted by NatureScot and funded by the Scottish Government’s Central Research Fund.

The mussels likely got into the lakes by clinging to the gills of a host fish, either a young trout or a salmon. They spend the first year of their life attached harmlessly to the fish before dropping off to live independently.

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Freshwater pearl mussels are rare in Scotland, largely due to ongoing illegal pearling, poor water quality and habitat degradation. Centuries of overexploitation of the mussel and intensification of land use are the main reasons for the massive historical decline in their numbers and range.

As filter feeders, freshwater pearl mussels are also extremely vulnerable to water pollution and river engineering. The impact of these threats means the species is critically endangered in some rivers in Scotland.

NatureScot, Scotland’s conservation agency, is spearheading efforts to conserve the iconic species.

NatureScot’s Iain Sime, who led the latest project, said: “Other mussel species, including the much more widespread swan and barnacle mussels, are known to live and breed in Scottish lakes, but until now we had no evidence that pearl mussels routinely do so as well.

“This project has been an exciting first step in exploring our lakes and we are very keen to conduct further research to learn more about this critically endangered species. We don’t yet know if they can breed in lakes, and we’d like to learn more about the relationship of a pinhole pearl mussel to its host fish.

“As a result of the research, we will extend our conservation management advice for freshwater pearl mussels to lakes and rivers.”