Freshwater Pearl Mussel (Margaritifera margaritifera)
Key Details
| Taxonomic Groups: | Invertebrate > mollusc > Mollusc (non-marine) |
| Red List Status: | Critically Endangered (Not Relevant) [CR(nr)] |
| D5 Status: | Included in the baseline Red List Index for England (Wilkins, Wilson & Brown, 2022) |
| Section 41 Status: | (not listed) |
| Taxa Included Synonym: | (none) |
| UKSI Recommended Name: | Margaritifera (Margaritifera) margaritifera |
| UKSI Recommended Authority: | (Linnaeus, 1758) |
| UKSI Recommended Qualifier: | (none specified) |
| Red List Citation: | Seddon et al., 2014 |
| Notes on taxonomy/listing: | (none) |
Criteria
| Question 1: | Does species need conservation or recovery in England? |
| Response: | Yes |
| Justification: | This species is critically endangered in England having been lost or reduced to a few old, non-breeding individuals in most formerly occupied rivers. It is the subject of numerous well-funded conservation initiatives. The species has declined hugely or become extinct in most English river systems due to a complex combination of factors including: (1) formerly pearl fishing, (2) sedimentation, (3) water pollution, (4) inappropriate river channel management, (5) a decline in salmonoid fish necessary to harbour the mussel's glochidia larva and (6) low water flows due to land drainage and over-abstraction. |
| Question 2: | Does recovery/ conservation depend on species-specific actions? |
| Response: | Yes |
| Justification: | The majority of populations in England are now facing rapid declines in numbers and with no recent recruitment will likely lead to local extinction in the next ten years. We have identified that urgent population reinforcement/captive rearing is needed to address this situation in the short term and, whilst improving water quality and catchment land use is a long-term commitment, ensuring that genetic material is available to restock rivers in the future is our top priority. This will buy us time for our remaining populations while we continue to improve catchments in order to create the right habitat and water quality conditions to sustain populations in the long-term. |
| Question 3: | At a landscape scale, would the species benefit from untargeted habitat management to increase habitat mosaics, structural diversity, or particular successional stages? |
| Response: | No |
| Justification: | The species will benefit from improvements in water quality, pollution, water flows and sedimentation in rivers. |
Species Assessment
| Current step on the Species Recovery Curve (SRC): | 7. Best approach adopted at appropriate scales |
| Recovery potential/expectation: | Low - Combination or other (detail in comments) |
| National Monitoring Resource: | Opportunistic - insufficient |
| Species Comments: | The mussels are long-lived slow breeders with >10 years required to reach breeding status. Climate change risks are expected to increase over the coming decades. Further impacts on river habitat and on mussel / host salmonid populations through increased storms/flooding/droughts and increase in water temps. There is no structured monitoring for FWPM in England. We need to prioritise restoring natural river flows and improving in-river habitat so that populations are more resilient to low flow/storm events/climate change etc. This can be achieved through addressing land drainage/management, water abstraction (for water supply/industry) and removing physical barriers/structures (weirs). The above does require a strategic catchment approach alongside other actions to address diffuse pollution - nutrients and sediments. |
Key Actions
Key Action 1
Proposed Action: Expand the captive breeding of individuals to further English populations for release to suitable rivers.
Action targets: 7. Best approach adopted at appropriate scales
Action type: Ex situ conservation
Duration: >10 years
Scale of Implementation: National
High priority sites: Priority populations for captive rearing/reintroduction to be agreed between local catchment partnerships and NE, EA and FBA.
Comments: Captive rearing is being undertaken by Freshwater Biological Association, Natural England, Environment Agency and Natural Resources Wales.
Key Action 2
Proposed Action: Reintroduction of species into suitable rivers identified by Natural England, EA and Freshwater Biological Association. Monitoring of introduced populations will be used to gauge success of individual projects.
Action targets: 6. Recovery solutions trialled
Action type: (Re-)introduction
Duration: >10 years
Scale of Implementation: ≤ 50 sites
High priority sites: Priority populations for captive rearing/reintroduction to be agreed between local catchment partnerships and NE, EA and FBA.
Comments: We are now at the stage where we have sufficient captive bred juvenile mussels for some of our most threatened populations to reintroduce back at identified recovery sites. We have trialled the reintroduction of juvenile mussels in west Cumbria and this will help inform other reintroductions across the country.
Key Action 3
Proposed Action: Targeted habitat restoration for the species at prioritised sites where there is high recovery potential. This will protect remaining threatened mussel populations and/or help identify receptor sites for reintroduction. The work may involve a site prioritisation exercise.
Action targets: 6. Recovery solutions trialled
Action type: Habitat management
Duration: >10 years
Scale of Implementation: ≤ 50 sites
High priority sites: Priority sites to be agreed between local catchment partnerships and NE, EA and FBA.
Comments: Until the water quality and habitat is improved, identifying sites to act as “recovery sites” should be given a high priority.
Acknowledgment:
Data used on this website are adapted from Threatened species recovery actions 2025 baseline (JP065): Technical report and spreadsheet user guide (Natural England, 2025). Available here.