Protected under Schedule 5 of the UK Wildlife and Countryside Act (1981) and the Wildlife (Northern Ireland) Order 1985, the freshwater pearl mussel is also listed on annexes II and V of the EU Habitats Directive and Appendix III of the Bern Convention. It is included on the IUCN Invertebrate Red List, where its status is described as Vulnerable (IUCN 1990). Classified as a priority species by the UK Biodiversity Steering Group, a national Species Action Plan has been prepared to encourage measures for its survival.

The freshwater pearl mussel is distributed from the arctic and temperate regions of western Russia through Europe to the north eastern seaboard of North America. Recent studies have revealed that there have been dramatic declines throughout its Holarctic range. Substantial populations with active recruitment are now found on fewer than 50 rivers in Canada, northwest Russia and northeast Scandinavia, with a handful of sites in Bavaria, the Czech Republic and Austria.

Formerly widespread and abundant in areas of England and Wales, recent surveys revealed most former populations to be virtually extinct, with very little active recruitment. There have been major declines in Northern Ireland, with recent survey work again showing population declines and scant recruitment, including the rare hard-water form, Margaritifera margaritifera durrovensis (Phillips) which is unique to Ireland.

Originally widely distributed throughout Scotland, a comprehensive survey from 1996 to 1999 revealed that the freshwater pearl mussel is now extinct in most of the lowlands and scarce everywhere except for a handful of Highland rivers. If the present rates of extinction continue, it has been estimated that surviving Scottish populations may only persist for a further 25 years. Up to half the world’s known remaining populations with active recruitment now occur in Scotland.

The early causes of decline were undoubtedly pearl fishing and industrial pollution. The current lack of recruitment may be due to a number of factors, including increasing siltation and eutrophication of rivers. The recent declines in stocks of migratory salmonid fish upon which the larvae are dependent are also giving cause for concern. River engineering for hydro-schemes, flood defence purposes and fishery improvements continues to pose a serious localised threat. Forestry operations, acidification, effluent from fish farms and chemical sheep dip are further threats to the declining populations.

Actions taken within the UK will have a direct consequence for the global survival of this species.

Ecology of the Freshwater Pearl Mussel, Magaritifera margaritifera

Monitoring the Freshwater Pearl Mussel

Developing a Monitoring Protocol for the Freshwater Pearl Mussel

Conservation of the Freshwater Pearl Mussel:
        1 Captive Breeding Techniques
        2 Relationship with salmonid fish