Freshwater Pearl Mussel (Margaritifera margaritifera)

One of the longest-living invertebrates. Found in pristine, nutrient poor, low-calcium rivers. Incredibly rare and now only found across northern England, Shropshire, and Devon. Scotland is thought to possess functioning populations in many river systems in the highlands. Remains widely distributed in Ireland in suitable river systems and at a limited number of sites in Northern Ireland.

Their shell is large and elongated, typically yellowish-brown in colour when young and darkening with age. Older parts of the shell can appear eroded.

• Avoid stepping into the water – this can stir up sediment, throwing up sediment DNA and any inhibitory molecules present. Sediment may clog the filter and prevent sufficient volumes of water being filtered.
• Freshwater pearl mussels require the presence of substantial populations of a salmonid host species (e.g., Atlantic salmon or brown trout) to thrive. Mussel larvae are released into clouds during reproduction and these are inhaled by the host fish species and attach to the gills. This dispersal method allows them to be transported upstream where they then detach and adhere to the riverbed.
• Freshwater pearl mussels tend to be found exclusively in clear, unpolluted water systems. Juveniles are choked by the accumulation of sediment and this can lead to an ageing population due to juvenile die-off.