Case study:Improving the Conservation Status of Freshwater Pearl Mussel Targeting the Clun SAC and Upstream Waters

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Location: 52° 27' 20", -3° 12' 51"
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Project overview

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Status In progress
Project web site
Themes Environmental flows and water resources, Fisheries, Habitat and biodiversity, Hydromorphology, Land use management - agriculture, Land use management - forestry, Monitoring, Social benefits, Water quality
Country England
Main contact forename Mike
Main contact surname Kelly
Main contact user ID
Contact organisation Shropshire Hills AONB Partnership
Contact organisation web site
Partner organisations Natural England, Environment Agency, CSFI, Land Life and Livelihoods, local farmers and landowners
Parent multi-site project
This is a parent project
encompassing the following
Newly created buffer strip on River Clun © Shropshire Hills AONB

Project summary

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- To restore the Clun SAC to favourable Condition
- Riparian habitat restoration/creation by stock exclusion, control of Phytophthora alni by coppicing, tree planting, provision of sustainable livestock watering, improvements in stock crossings
- Surveys and scoping studies to inform conservation activity

The River Clun and tributaries are located in Shropshire, England, with the lower Clun and most of the Special Area of Conservation (SAC) being located in Herefordshire. The catchment is important for ecology due to the underlying geology of sandstone and mudstones. Clun SAC was designated in 2004 for it population of Freshwater pearl mussels (Margaritifera margaritifera) demonstrating the European and UK government commitment to its protection. The SAC is in unfavorable condition - Pearl mussels are indicators of excellent water quality, requiring oligotrophic water for their survival. Recruiting populations of pearl mussels help maintain good water quality, as individuals they are able to filter up to 50 litres of water per day to help maintain habitat for other freshwater wildlife (including host salmonids). Pearl mussels are keystone species and are model species to deliver catchment wide conservation strategies; by protecting the pearl mussel, river habitats will be improved for a range of other species.

Reasons for the project
Freshwater pearl mussels are dependent on low sediment and nutrient levels, fast flows of cool water, clean gravels and fringing shade. They also rely on the presence of juvenile salmonids for part of their life-cycle. It is thought that the decline in the population has been occurring for a number of decades, age profiles indicate a population that has failed to recruit juveniles probably since the 1960’s. Recruiting populations are usually numbered in the hundreds of thousands, the Clun population is now estimated at just over 1000 individuals, considered to be permanently stressed and in rapid decline they are in danger of imminent extinction.

Works include: Control of Phytophthora alni by coppicing.

Monitoring surveys and results

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Lessons learnt

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Significant lineage of riprian buffers established and multiple resourse protection measures implemented. As of February 2014, the project has established/protected approximately 25,000m of riparian buffer. Surveys and scoping studies undertaken. This is ongoing work in collaboration with EA, NE and CSFI and complements HLS and CSFI capital works in the Clun Catchment.

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Catchment and subcatchment


River basin district Severn
River basin Teme


River name R Clun - conf R Unk to conf R Teme
Area category 100 - 1000 km²
Area (km2)
Maximum altitude category 200 - 500 m
Maximum altitude (m) 453
453 m
0.453 km
45,300 cm
Dominant geology Calcareous
Ecoregion Great Britain
Dominant land cover Improved grassland
Waterbody ID GB109054043990


Name Clun, Clunton, Clungunford, Leintwardine, Bishops Castle, Newcastle
WFD water body codes GB109054043990
WFD (national) typology
WFD water body name R Clun - confluence R Unk to confluence R Teme
Pre-project morphology
Reference morphology
Desired post project morphology
Heavily modified water body No
National/international site designation EU - Special Area of Conservation
Local/regional site designations
Protected species present Yes
Invasive species present Yes
Species of interest Protected - Freshwater pearl mussel (Margaritifera margaritifera); Invasive - Phytophthora alni
Dominant hydrology
Dominant substrate
River corridor land use
Average bankfull channel width category
Average bankfull channel width (m)
Average bankfull channel depth category
Average bankfull channel depth (m)
Mean discharge category
Mean annual discharge (m3/s)
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)

Project background

Reach length directly affected (m)
Project started
Works started 2011/08/01
Works completed
Project completed
Total cost category 100 - 500 k€
Total cost (k€) 374
374 k€
374,000 €
Benefit to cost ratio
Funding sources SITA Trust, Natural England, Defra

Cost for project phases

Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
Investigation and design
Stakeholder engagement and communication
Works and works supervision
Post-project management and maintenance

Reasons for river restoration

Mitigation of a pressure
Hydromorphology Quantity & dynamics of flow, Substrate conditions, Width & depth variation
Biology Fish
Physico-chemical Nutrient concentrations
Other reasons for the project Freshwater Pearl Mussel


Structural measures
Bank/bed modifications
Floodplain / River corridor Riparian habitat restoration, Tree planting, Cut back of trees
Planform / Channel pattern
Other Livestock access
Non-structural measures
Management interventions Livestock exclusion, Sustainable livestock watering
Social measures (incl. engagement)


Hydromorphological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Biological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Physico-chemical quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Any other monitoring, e.g. social, economic

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Monitoring documents

Additional documents and videos

Additional links and references

Link Description Freshwater Pearl Mussel Conservation in the Shropshire Hills (January 2010) Hydrological Investigations of Potential Re-Location Sites for the Freshwater Pearl Mussel in the River Clun (Shropshire) River Clun Restoration Strategy - summary page

Supplementary Information

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