Freshwater pearl mussels: advice for making planning decisions
How to assess a planning application when there are freshwater pearl mussels on or near a proposed development site.
Applies to England
This is Natural England’s ‘standing advice’ for freshwater pearl mussels. It is a material planning consideration for local planning authorities (LPAs). You should take this advice into account when making planning decisions. It forms part of a collection of standing advice for protected species.
Following this advice:
- avoids the need to consult on the negative effects of planning applications on freshwater pearl mussels in cases outside designated sites where you have not sought specific advice from Natural England
- can help you make decisions on development proposals
You may need a qualified ecologist to advise you on the planning application and supporting evidence. You can find one using either the:
- Chartered Institute of Ecology and Environment Management (CIEEM) directory
- Environmental Data Services directory
How freshwater pearl mussels are protected
Freshwater pearl mussels are protected by the Wildlife and Countryside Act 1981.
It is an offence to intentionally:
- kill, injure or take them
- possess or control them (alive or dead)
It is also an offence to intentionally or recklessly:
- damage or destroy a structure or place used for shelter or protection
- disturb them in a place used for shelter or protection
- obstruct access to a place used for shelter or protection
The developer must comply with the legal protection of freshwater pearl mussels.
You should consider if the developer has taken appropriate measures to avoid, mitigate and, as a last resort, compensate for any negative effects on freshwater pearl mussels.
The developer may need a wildlife licence to carry out their proposed activity.
When to ask for a survey
You should ask for a survey if:
- historical or distribution records show that freshwater pearl mussels may be present - you can search the National Biodiversity Network Atlas by species and location
- the development proposal affects clean, fast-flowing rivers across northern England, Shropshire or Devon - the habitat for freshwater pearl mussels
Absence of a record does not mean there are no freshwater pearl mussels. It could mean there is no survey data available for that location.
You must check if the ecologist is qualified and experienced to carry out surveys for freshwater pearl mussels. CIEEM publishes advice on the valid age of data
The ecologist should also follow the Biodiversity code of practice for planning and development (BS 42020:2013) available on the British Standards Institute website. These documents may not be accessible to assistive technology.
Assess the effect of development on freshwater pearl mussels
The proposal needs to show how likely it is that freshwater pearl mussels will be affected by any development work.
Freshwater pearl mussels are sensitive to pollution and depend on salmon and trout. Proposals that affect either of these will harm the species.
Harmful activities include:
- disturbing the mussel beds
- intensive land-use near water courses
- river engineering or works, such as dredging river shingle, sand and gravel
- storing materials in the water
- using machinery and vehicles in the water
- removing (abstracting) water and changing river flow
Activities may also be harmful if they:
- reduce water quality, for example, discharged chemicals or nutrients that lower oxygen levels
- lead to a decline in populations of salmon or trout (the mussels’ host fish)
- lead to a decline in habitat conditions, such as loss of tree cover that provide shade for mussels
- pollute the water or cause silt and sediment deposits (siltation)
Avoidance, mitigation and compensation measures
Look for examples of avoidance, mitigation or compensation plans in the development proposal.
To avoid possible effects on freshwater pearl mussels, developers could redesign the proposal to:
- avoid disturbing the river bed
- alter the timing of works, doing work outside of sensitive periods
- change the methods of working
Where this is not possible, mitigation should include how the developer will:
- protect the species population and distribution
- protect the river bed and the habitat immediately around it
- consider how other species, such as the mussels’ host fish could be affected by the mitigation
Mitigation measures can include:
- doing work in small sections
- reducing disturbance to the river bank
- reducing the area affected
- preventing any sediment from being released into the water
- preventing water pollution including silt
If the proposal cannot mitigate for harm, then compensation measures must be in place to:
- improve the size and quality of the mussel habitat
- fix any broken connections to the mussels’ habitat
Compensation measures can include:
- supporting captive breeding and reintroduction programmes
- providing habitat to replace any that will be lost
- improving existing habitat in terms of its quality
The developer can improve existing habitats if they:
- reduce the effect of sediment upstream of the mussel beds by fencing off river banks, creating buffer zones or shoring up banks by managing or planting new trees
- stop nutrients and sediment from entering the river from sources of pollution such as ditches, cattle drinking points, roads and farms
- control non-native and invasive plant species
- carry out in-channel works to maintain water flow and improve river bed composition by removing weirs or other structures
- improve the survival of fry and juvenile mussels by cleaning and adding river gravel or boulders
- install large woody debris to improve habitat conditions for host fish
For more information on mitigation plans and compensation measures, read the planners guide for protected species and development.
Planning and licence conditions
If the proposal is likely to affect freshwater pearl mussels, the developer must apply for a wildlife licence.
Before you can grant planning permission, you must:
- make sure any mitigation or compensation conditions you impose are not likely to conflict with the requirements of a wildlife licence
- be confident that Natural England will grant a wildlife licence
You can find more information in the guidance on protected species and development: advice for local planning authorities.
For freshwater pearl mussels, Natural England will only issue a licence if the proposal enhances the species’ habitats and helps to conserve them.
Enhance biodiversity
To meet your biodiversity duty, you should suggest ways for the developer to:
- create new or enhanced habitats on the development site
- achieve a net gain in biodiversity through good design, such as green roofs, street trees or sustainable drainage
Site management and monitoring
You should consider the need for site monitoring and management. These measures are likely to be needed by protected species licences.
A site management and monitoring plan should make sure:
- water quality is good
- water flow is maintained
- populations remain healthy
- water bodies are free from non-native species
- there’s no interference to habitat after development
- gravel bed habitat and woody debris is maintained
This can include additional survey work to check that mitigation measures are working as intended, followed by remedial work if needed.
Updates to this page
Last updated 25 October 2023 + show all updates
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Page updated because of new requirements for protected species mitigation licences for animals and plants in schedule 5 and schedule 8 of the Wildlife and Countryside Act 1981 (brought in by the Environment Act 2021).
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First published.