The River Kent SSSI, SAC and its associated tributaries (Cumbria, England) support vital, UK populations of endangered, white-clawed crayfish (Austropotamobius pallipes) and the freshwater pearl mussels (Margaritifera margaritifera). The Life R4Ever Kent Project is a LIFE funded project aiming to restore and revitalise the River Kent and to ensure future resilience in the system. This involves monitoring the catchment for invasive signal crayfish (Pacifastacus leniusculus) and crayfish plague (Aphanomyces astaci) as well as developing the knowledge of existing populations of white-clawed crayfish and freshwater pearl mussels.
Natural England aims to use this project to provide further field validation for the use of eDNA-based techniques in ecological management and conservation projects and to ensure the sensitivity and reliability of published assays. In 2022, an eDNA survey was conducted in the River Kent catchment. The results indicated the presence of crayfish plague which was not consistent with traditional survey findings and the absence of signal crayfish. Since then, an updated assay has been published by Strand et al. (2023) revealing the original assay used from the 2022 River Kent project (Vrålstad et al. 2009), was amplifying a closely related species, Aphanomyces fennicus. This further calls into question the reliability and accuracy of the 2022 results. To examine these results further, the eDNA surveying of these sites has been repeated.
The overarching aims of the Life R4Ever Kent Project eDNA surveys are:
To use eDNA methods to better determine the presence of white-clawed crayfish across the River Kent SAC and upstream tributaries to aid ark site selection if translocation of white-clawed crayfish populations is required.
To use eDNA-based survey methods to detect the presence of freshwater pearl mussel populations.
To utilise eDNA as a monitoring method to detect the presence of crayfish plague and signal crayfish in selected catchments in Cumbria.
To contribute to further field validation of freshwater invertebrate species assays to understand the key challenges of eDNA application.
Evaluating eDNA results from the original crayfish assay (Vrålstad et al., 2009) and those of the improved assay (Strand et al., 2023) and re-testing sites previously suspected positive for crayfish plague.
During this phase, seven subprojects were conducted across Cumbria with specific aims and project partners. The data provides significant evidence for the stability and extent of white-clawed crayfish populations within the catchment. This study has provided further evidence for several potential, white-clawed crayfish ark sites locations, and we advise that further physiological considerations should be given to these sites before utilisation. Alongside this, we would recommend implementing an early detection monitoring programme for crayfish plague throughout the River Kent SAC, allowing for prompt action to be taken in the event of an outbreak.
eDNA surveys found no evidence of signal crayfish migration from their known locations at Windermere, nor any evidence of crayfish plague within these populations. We advise that these populations are regularly monitored as part of a proactive management strategy to identify their movement early, with the aim of limiting potential damage to surrounding white-clawed crayfish populations. Within this context, we would support an investigation into signal crayfish population control in this area or eradication efforts.
There was a clear distinction in the results at sites surveyed using both crayfish plague assays; positive amplification using the original assay (Vrålstad et al. 2009) and no amplification with the revised assay Strand et al. (2023). This evidence suggests that historical River Kent eDNA results may be attributed to non-target amplification of A.fennicus. We recommend that such results be disregarded as they are likely to be erroneous and unreliable. This project highlighted the importance of continual development of eDNA methodologies in the light of new scientific publications and that any eDNA data should always be considered in conjunction with other contributing factors such as historical presence and traditional survey outcomes. To provide further confirmatory field validation for the Strand et al. (2023) assay, we recommend that it is used as part of an active crayfish plague outbreak investigation. Further studies may benefit from confirming the presence of Aphanomyces fennicus via sequencing using a PCR assay (e.g. Oidtmann et al., 2006).
eDNA surveying also highlighted several potential low-density freshwater pearl mussel populations (River Lune, Liza). Limited knowledge of recent species history at these sampling locations, warrants an investigation into other potential freshwater pearl mussel sites and further validation of the freshwater pearl mussel assay (Carlsson et al., 2017; Mauvisseau et al., 2019). Future eDNA surveys on freshwater pearl mussels would benefit from focusing on potential low-density populations of freshwater pearl mussels to confirm detection accuracy. Further projects may also wish to trial larger pore size filtration methods to obtain greater sample volumes in those areas where filtration is particularly challenging.
Overall, this phase of the Life R4Ever Kent eDNA surveying successfully examined the extent of white-clawed crayfish, signal crayfish, crayfish plague and freshwater pearl mussels across sites across Cumbria. This work has provided vital data to inform further project work, identifying unknown freshwater pearl mussel and white-clawed crayfish locations and evidence for suitable reinforcement/reintroduction sites. Reducing the spread of invasive signal crayfish and remaining clear of crayfish plague should remain a priority and we highly recommend the implementation of a monitoring programme for such a purpose.