Freedom of Information Request - Freshwater Pearl Mussel (FWPM) Reports
Date: 06 November 2025
Our ref: SIR181800/A5543539
Information Request – Freshwater Pearl Mussel (FWPM) Reports
Your Request
'What I would like to know is if NatureScot has commissioned any surveys of FWPM in the last ten years and, if so, could you please supply these surveys and results (i.e. were the populations increasing/decreasing and to what extent, if measurable).
I understand that Peter Cosgrove carried out a survey for NatureScot on the River Spey recently and I would like a copy and the results of this report as well please.'
Our Response
We have discussed your request with our Freshwater and Wetland Team (FW Team), and they have searched the information that they hold on this subject and we can provide you with some of the information that you are requesting.
The full survey reports are confidential, due to the sensitivities of freshwater pearl mussel data, and as a way of protecting this species and to help its survival we can only provide, where possible, summary reports; where we have not been able to provide you with a summary report the FW Team have provided the main points from the surveys undertaken.
In some cases, the name(s) of the specific river(s) have been removed or withheld, due to the sensitivities and to ensure confidentiality. As release of information under the EIRs is a release into the public domain, we do not believe that it is in the public interest to release information that might enable disturbance to the species. We would therefore withhold this information under EIRs Regulation 10(5)(g) – Protection of the environment.
National Survey for freshwater pearl mussel (surveys pre-2015 but published in 2015)
Source: Publication 2015 - SNH Commissioned Report 901 - A national freshwater pearl mussel (Margaritifera margaritifera, L.) survey of Scotland.
Summary report
Inverpolly SAC Site Condition Monitoring 2016
Source: Cosgrove, P.J. 2016. Site Condition Monitoring of freshwater pearl mussels in the Inverpolly Special Area of Conservation. Scottish Natural Heritage Commissioned Report.
No summary report available. The main findings are:
• During October 2016 the six Inverpolly SAC freshwater pearl mussel rivers were surveyed for freshwater pearl mussel using standard methodologies.
• The same 50 m x 1 m transects that were surveyed in 2004 and 2008 were resurveyed in 2016.
• Based on JNCC condition targets, the six Inverpolly SAC freshwater pearl mussel rivers were classified as ‘unfavourable declining’.
• The main threats or issues to the conservation of freshwater pearl mussels in the Inverpolly SAC are (i) illegal pearl fishing, (ii) potential problems with host salmonid populations, and (iii) a suspected but as yet unidentified water quality issue.
• A very large and recent illegal pearl fishing kill was discovered in one of the rivers.
Scottish Natural Heritage Commissioned Report No. - SNH use only - Survey to determine presence of freshwater pearl mussels in a river in Galloway (2017).
There is no summary report available for this survey.
Main findings:
• Freshwater pearl mussels were confirmed to be present in the river, previously un-surveyed for freshwater pearl mussels.
• Habitat survey and electrofishing data have shown that the river is important for salmon and trout spawning and nursery habitats.
• It is recommended that a more detailed survey is completed to detail the extent and health of the freshwater pearl mussel population and clarify whether recruitment is happening.
Scottish Natural Heritage Commissioned Report No. - SNH use only - Monitoring the success of freshwater pearl mussel reintroductions in three rivers - 2018
Source: Watt, J., Hastie, L.C., and Cosgrove, P.J. 2018. Monitoring the success of freshwater pearl mussel reintroductions. Scottish Natural Heritage Research Report No. 956.
Summary report
NatureScot Research Report 1141 - Freshwater pearl mussel survey of a river in the Trossachs - 2020
Source: McDermott, T. & Barry, S. 2020. Freshwater pearl mussel survey of a river in the Trossachs. Scottish Natural Heritage Research Report No. 1141.
Summary Report
NatureScot Research Report 1141 - Freshwater pearl mussel survey of a river in the Trossachs – 2021 – Phase 2
There is no summary report available for this survey
• This project aimed to identify potential habitats and determine habitat quality, survey to locate mussels and record data on their populations size/age structures and identify local and sub catchment-scale pressures which have to potential to negatively influence the distribution and health of freshwater pearl mussel in this system.
• This project found no evidence to suggest functioning populations exist within the upper system.
• Several channels within the survey may have historically hosted pearl mussels.
• Pressures within the channel areas are the impacts of water resource use and enrichment, and lighter land use pressures.
NatureScot Research Report 1210 - Understanding the impact of the 2018 drought on key freshwater pearl mussel populations in Scotland - 2021
Source: Cosgrove, P., Shields, D., Anderson, D. and Massey, K. 2021. Understanding the impact of the 2018 drought on key freshwater pearl mussel populations in Scotland. NatureScot Research Report No. 1210.
Summary report
River Dee Site Condition Monitoring 2022-2023
Source: Cosgrove, P., Massey, K., Shields, D., Picton, J., Cosgrove, C., Towers, M., and Tree, A. 2024. Site Condition Monitoring of freshwater pearl mussel in the River Dee 2022–2023. NatureScot/CNPA Research Report 1353.
NatureScot Research Report 1315 - Life in our Lochs - are there freshwater pearl mussel populations in our lochs as well as our rivers? - 2023
Source: O’Leary, D., Robinson, G., Cooksley, S., McDermott, T. 2023. Life in our Lochs - are there freshwater pearl mussel populations in our lochs as well as our rivers? NatureScot Research Report No. 1315.
Summary report
River Spey Site Condition Monitoring 2024
Source: Cosgrove P., Shields, D and Massey K. 2024. Site Condition Monitoring of freshwater pearl mussel on the River Spey SSSI/SAC and River South Esk SAC 2024. NatureScot Research Report.
We do not have a summary report available yet. The main findings are:
• There has been a c. 12% overall increase in terms of like-for-like SCM 50 x 1 m transect relative abundance comparisons with previous SCM. There has also been a substantial increase in the proportion of juvenile pearl mussels in a section of the River Spey SAC.
• Based on the number of favourable condition targets that have not been met, and an overall 12% increase, the condition of the pearl mussel feature in the River Spey SAC is considered likely to be ‘unfavourable, no change’.
• The biggest threat to the River Spey SAC pearl mussel population, is considered to be upper catchment range reduction, water crowfoot and associated drivers of detrimental change such as illegal pearl fishing.
River South Esk Site Condition Monitoring 2024
Source: Cosgrove P., Shields, D and Massey K. 2024. Site Condition Monitoring of freshwater pearl mussel on the River Spey SSSI/SAC and River South Esk SAC 2024. NatureScot Research Report.
We do not have a summary report available yet. The main findings are:
• In 2024 a total of 352 pearl mussels were recorded in River South Esk SAC during SCM.
• There has been a c. 91 % overall decline in terms of like-for-like SCM 50 m x 1 m transect relative abundance comparisons with previous SCM in the River South Esk. The reasons for this apparent decline are likely related to the impact and knock-on effects of extreme flooding, associated with Storm Babet in 2023.
• Based on the number of favourable condition targets that have not been met, and the c. 91 % decline in the population since it was last assessed in 2009, the condition of the pearl mussel feature in the River South Esk SAC is considered likely to be ‘unfavourable declining’.
• The biggest threat to the River South Esk SAC pearl mussel population is considered to be climate change, and the associated increase in flood events combined with current and historic catchment land management practices, such as muirburn and drainage ditch cutting.
Ongoing Surveys in 2025
• A further survey of the River South Esk is taking place in 2025. No findings or reports are yet available for release. We hope to have some information available by April 2026 so at the moment we are exempting this information under 10(4)(d) (Material in the course of completion)
• Surveys of three potential freshwater pearl mussel rivers in Scotland. This work is currently ongoing. No findings/reports are yet available for release, and we are not releasing the names of the three rivers at this time as these are new areas/rivers being surveyed. We hope to have some information available by the late April 2026 so at the moment we are exempting this information under 10(4)(d) (Material in the course of completion)
How We Handled Your Request
We believe you have asked for environmental information as defined in the Environmental Information (Scotland Regulations 2004 (‘the EIRs’), so we are dealing with your request under those regulations. To be able to use the EIRs, we must apply an exemption under section 39(2) of the Freedom of Information (Scotland) Act 2002 (‘FOISA’). The Scottish Information Commissioner’s guidance recommends that public authorities apply this exemption to environmental information and handle request under the EIRs.
If you would like to find out more about the access to information legislation, there is a guidance booklet available on the Scottish Information Commissioner’s website.
Review and Appeal
I hope this information meets your requirements, but if you are dissatisfied with how we have responded to your information request, please write to us within 40 working days explaining your concerns. You can contact us at Battleby, Redgorton, Perth, PH1 3EW or email us at [email protected]. We will carry out a review of our response and contact you with our findings within 20 working days.
If you are not satisfied following this, you can make an appeal to the Scottish Information Commissioner within 6 months. The Scottish Information Commissioner can be contacted at:
Scottish Information Commissioner
Kinburn Castle
Doubledykes Road
St Andrews
Fife
KY16 9DS
Telephone: 01334 464610
Yours sincerely
FOI Officer,
NatureScot
