Understanding the impact of the 2018 drought on key freshwater pearl mussel propulations in Scotland.
The report aims to quantify, wherever possible, the impact of the prolonged period of dry weather in 2018 on selected pearl mussel (Margaritifera margaritifera) populations in Scotland. The survey evaluated the status of pearl mussels in 6 rivers in Scotland. There is clear evidence of large-scale detrimental impacts (pearl mussel mortalities) from the 2018 drought on several of these Scottish rivers. Other rivers which were not rigorously studied at the time of the drought do not show such clear evidence of direct, quantifiable impacts attributable to the 2018 drought, although overall pearl mussel population decline was evident in some/all watercourses studied. Regular monitoring work needs to be conducted on more pearl mussel rivers, if the required before, during and after studies are going to be available to provide the much needed evidence in future drought years.