Developing a standard approach for monitoring freshwater pearl mussel (Margaritifera margaritifera) populations in European rivers

Abstract

The freshwater pearl mussel (Margaritifera margaritifera) is an endangered species in Europe, protected nationally and internationally, but with a steadily declining range and abundance owing to pressures such as pollution, river engineering, and illegal exploitation. Despite this, no consistent approaches have been developed around Europe for monitoring pearl mussel populations and their habitats. To address this need, experts on pearl mussel ecology from 11 countries met at a series of workshops in order to develop a protocol for monitoring, published under the auspices of the European Committee for Standardization (CEN). This standard is unique, as it is the first CEN standard dedicated to a single species of conservation concern. The standard is aimed at scientists, conservation bodies, and environmental regulators, and can be used for designing national monitoring programmes as well as reporting on the conservation status of pearl mussel populations under the European Habitats Directive. It contains guidance at the individual site level to determine why populations are failing to recruit, but also addresses the need for a wider‐scale approach to ensure that catchment developments do not have adverse impacts on rivers containing pearl mussels. A pearl mussel monitoring programme needs to investigate the size and viability of populations, as well as the fish hosts (Atlantic salmon, Salmo salar, or brown trout, Salmo trutta) on which pearl mussel larvae depend. Water quality, including variables such as dissolved oxygen, acid–base chemistry, and nutrient levels, is also an essential monitoring component, together with the physical features of the river bed, river flow regimes, and sediment dynamics. It is hoped that this pan‐European approach will improve the ability to compare data across many countries, and will ultimately ensure that the results of monitoring are translated into measures for improving the conservation status of the freshwater pearl mussel throughout its range.

Essay: Making the most of recent advances in freshwater mussel propagation and restoration

“…The amount of demographic detail to be monitored will vary, but should include at least the presence or density of juveniles (to verify that recruitment is occurring), which may require special sampling methods (Strayer & Smith, 2003). To the extent practicable, such monitoring efforts should be harmonized across projects (see Boon et al, 2019 for an example). Care should be taken that the monitoring itself does not harm the mussels.…”

“…First, the goals (e.g., Jones, Neves, & Hallerman, 2012) and design of the project should be quantitatively stated, and as actually implemented. Most projects should monitor the size and demography of the mussel population, over a spatial extent that will depend on the size of the project area and the biology of the mussel and its hosts (see Boon et al, 2019 for an example). The amount of demographic detail to be monitored will vary, but should include at least the presence or density of juveniles (to verify that recruitment is occurring), which may require special sampling methods (Strayer & Smith, 2003).…”

“…For example, surveys should minimize handling time, place mussels promptly back into the site in the streambed from which they were taken, and avoid handling animals at critical times of the year (e.g., during high temperatures or just before glochidia are released) (Strayer & Smith, 2003). To the extent practicable, such monitoring efforts should be harmonized across projects (see Boon et al, 2019 for an example).…”

“…Depending on the goals of the project, and on the specific factors that may affect its performance, it may be worthwhile to monitor additional variables (Boon et al, 2019). Examples include fish populations, concentrations of current or legacy pollutants, or human use of and attitudes about the restoration site or its mussels.…”

Downstream transport and seasonal variation in freshwater pearl mussel (Margaritifera margaritifera) eDNA concentration

“…Freshwater pearl mussels (FPM, Margaritifera margaritifera) were historically distributed across large parts of Europe but have decreased dramatically and are now listed as endangered in the IUCN red list (IUCN, 2017;Lopes-Lima et al, 2017). Freshwater pearl mussels are subject to substantial conservation effort (Geist, 2010) and monitoring programs across Europe (Boon et al, 2019). The species has been studied for its genetic population structure across Europe (Geist & Kuehn, 2005;Geist, Söderberg, Karlberg, & Kuehn, 2010;Stoeckle et al, 2017) which in Northern Europe is linked to host preference (Geist et al, 2018;Karlsson, Larsen, & Hindar, 2014).…”