In 2004, NPWS began monitoring, or surveillance, of the freshwater pearl mussel under Article 11 of the Habitats Directive. The methods have been developed by freshwater pearl mussel experts and have evolved over time. Information on monitoring methods can be found in the monitoring report to the Sub-basin Management Plan project and basic survey methodologies are presented in Irish Wildlife Manual number 12 (2004), however both are now somewhat out-of-date. It is intended to update IWM 12 to incorporate baseline and routine monitoring methods. The European Committee for Standardization (CEN) is also developing a standard for freshwater pearl mussel monitoring.
The species occurs in more than 160 rivers in 104 catchments or sub-catchments across 14 Irish counties (NPWS, 2013c). Monitoring is undertaken at ‘population’ scale, which coincides with the catchment/sub-catchment scale, as a population is defined “as a group of mussels occupying an area of a catchment that are capable of genetic exchange, either through sexual reproduction or through transportation of glochida on host fish” and (Moorkens et al., 2007). Full baseline monitoring, in which the distribution and abundance of the species in a catchment or sub-catchment is mapped, has been completed for 13 populations. NPWS aims to conduct routine monitoring, in which the viability of the population and the condition of its habitat are measured, of a representative sample of 30 or more populations once every three years. The monitored populations cover a broad geographical range and a wide variation in population size and viability. While populations outside of SACs are monitored, the programme generally concentrates on the SAC populations.
Owing to the risk of pearl-fishing, the policy is not to make detailed data on the location and abundance of freshwater pearl mussels publicly available, hence monitoring reports are not on the website. A full list of NPWS monitoring reports and other NPWS freshwater pearl mussel surveys and research are available on this site. These can be requested, for bona fide users, via the data request form.