Since 1950 the freshwater pearl mussel has been recorded from 151 ten km squares in Britain and 14 ten km squares in Northern Ireland. The British range is to the north and west of a line running from Scarborough in Yorkshire to Beer Head in Devon. Many populations may not have produced young for over 30 years as site records are often based on observers only finding dead shells. In Ireland the mussel occurs throughout the country, being widespread in the south and west. It has, however, declined in the east, and recruitment rates are not known for most populations.
The species is dependent on the presence of salmonid fish as hosts for its larvae.
This mussel is classed as Vulnerable on the IUCN/WCMC RDL. It is listed on Annexes II and IV of the EC Habitats Directive and Appendix II of the Bern Convention and is fully protected under Schedule 5 of the WCA 1981 and the Wildlife Order (Northern Ireland) 1985.
Current factors causing loss or decline
Poor water quality, including nutrient enrichment (which also affects the numbers of host fish).
Habitat removal and alteration through development, drainage schemes, flow regulation and fisheries management.
A decline in populations of host fish.
Conifer planting, exacerbating the effects of river acidification.
Amateur pearl fishing, aided by improved accessibility.
Poor land management in the catchment (e.g. overgrazing leading to sedimentation from soil erosion).
SNH have commissioned and received advice on the feasibility of conducting a national survey and developed a methodology for monitoring key sites around Scotland. Some surveying was undertaken at key sites in 1994 and 1995. A project investigating threats to pearl mussels began in 1995, supported by SNH and the University of Aberdeen.
NE and the NRA have completed a survey of sites in England in 1995.
NE has prepared a species action plan.
CCW surveyed the River Wye in 1992/93.
Action plan objectives and targets
Maintain the size of all viable populations.
Increase the size of all viable populations.
Encourage re-colonisation of this species into at least 10 suitable former areas by 2005.
Proposed actions with lead agencies
Policy and legislation
Identify water quality requirements for the species and seek to ensure that these form the basis for setting Statutory Water Quality Objectives, including Special Ecosystem Standards for sites occupied by the pearl mussel. (ACTION: DoE, DoE(NI), NRA, RPBs, SOAEFD, WO)
Seek to ensure that catchment management plans, flood defence activities, water level management plans and freshwater fisheries management take account of the requirements of this mussel, where populations still occur. (ACTION: DoE(NI), IDBs, NRA, MAFF, RPBs, SOAEFD, WOAD)
Encourage favourable land management within catchments where the river supports major populations of the mussel, through appropriate land management and grant schemes. (ACTION: DANI, FA, MAFF, SOAEFD, WOAD)
Site safeguard and management
Consider designating centres of large, self-sustaining populations as SSSI/ASSI, and designate SACs for the most important ones. (ACTION: CCW, DoE, DoE(NI), SOAEFD, WO)
Species management and protection
Review the protection given to the species under the WCA 1981. (ACTION: DoE, JNCC)
Consider re-introduction into formerly occupied areas if conditions become ecologically suitable, using appropriate stock to maintain regional genetic variation. (ACTION: CCW, NE, SNH)
Review the protection given to the species under the Wildlife (Northern Ireland) Order 1985.
Provide advice to river and land managers, water bailiffs and local police in relevant areas on the presence and legal status of this species, and appropriate methods of management for its conservation. (ACTION: CCW, DoE(NI), NE, NRA, RPBs, SNH)
Future Research and Monitoring
Identify catchments where there is the best chance of re-establishing this species. (ACTION: CCW, DoE(NI), NE, NRA, RPBs, SNH)
Carry out research to investigate key threats; fish hosts; life cycle and life history in different places; tolerance to variation in acidity; genetic variation; viability of re-seeding populations, and the effects of commercial exploitation. (ACTION: CCW, NE, DoE(NI), NRA, RPBs, SNH)
Establish the current status of populations throughout the UK. (ACTION: CCW, DoE(NI), NE, SNH)
Encourage regular monitoring of known populations and seek to identify further threats to the species. (ACTION: CCW, DoE(NI), NE, SNH)
Pass information gathered during survey and monitoring of this species to JNCC or BRC so that it can be incorporated in national databases. (ACTION: CCW, DoE(NI), NE, SNH)
Provide information annually to the World Conservation Monitoring Centre on the UK status of the species to contribute to maintenance of an up-to-date global red list . (ACTION: JNCC)
Communications and Publicity
Promote awareness of the threats to the species and publicise the legal protection afforded to it. (ACTION: CCW, NE, DoE(NI), NRA, RPBs, SNH)
Consider convening a conference on the conservation of freshwater mussels in the UK, to promote co-ordination of effort. (ACTION: JNCC)
Links with other action plans
Originally published in: Biodiversity: The UK Steering Group Report - Volume II: Action Plans (December 1995, Tranche 1, Vol 2, p162)