Witham Orb Mussel (Sphaerium solidum)
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: | Sphaerium solidum |
| UKSI Recommended Authority: | (Normand, 1844) |
| 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: | Red list 2014 Critically Endangered in England. Whole of GB population is in England on River Witham and the tidal Great Ouse particularly New Bedford River. It is potentially extinct. |
| Question 2: | Does recovery/ conservation depend on species-specific actions? |
| Response: | Yes |
| Justification: | Re-survey all catchments to establish whether it's still extant. Last surveyed in 2015 when no living specimens were found (Witham catchment and New Bedford river, Great Ouse) |
| 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: | This species would not benefit from untargeted management |
Species Assessment
| Current step on the Species Recovery Curve (SRC): | 4. Autecology and pressures understood |
| Recovery potential/expectation: | Low - Pathogen, hybridisation, INNS |
| National Monitoring Resource: | Structured - insufficient |
| Species Comments: | Strong circumstantial evidence of competitive exclusion due to Asian Clams (Corbicula fluminea). |
Key Actions
Key Action 1
Proposed Action: Re-survey all known previous sites to establish if species is still present or whether it has gone extinct.
Action targets: 3. National Monitoring Plan agreed and implemented
Action type: Targeted monitoring
Duration: 2 years
Scale of Implementation: ≤ 10 sites
High priority sites: Tidal freshwater Great Ouse system, plus the Old West River section of the Great Ouse.
Comments: The whole of the tidal freshwater Great Ouse and Old West river section needs re-surveying and could be completed in 2 field seasons. It should be repeated several times to establish whether its extinct. If eDNA was also used, results more certain. The EAs Lincolnshire Analysis and Reporting Team have began these surveys in 2025, but so far not found any. They were last found alive in 2010.
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.