Pearl Rivers Project
This partnership project was set up to help improve water quality along the River Mole for the benefit of wildlife, including the critically endangered freshwater pearl mussel, by involving farmers and the local community.
The pilot project focussed on approximately 15km of the River Mole, along with the surrounding two sub-catchments, near South Molton, as shown in purple on the MAP.
The pilot project was completed in March 2012. It is hoped that further funding will be found to expand the project to cover the whole of the Mole and Bray catchments.
To find out more about the project contact Tom Hynes at NDBS on 01271 388534.
Article in UK Biodiversity News published by the UK Government's Joint Nature COnservation Committee (page 39)
The Freshwater Pearl Mussel
- Is classified as endangered in the UK
- Is a legally protected species
- Is one of the longest lived invertebrates known, living for up to 100 years.
- Its numbers have declined particularly rapidly over the last 50 years due to over-collection, pollution and a fall in fish numbers.
- Is found in a handful of clean fast flowing rivers across northern England with outlying populations in Shropshire and Devon.
- The fourth largest colony in the UK is within North Devon's Biosphere Reserve but these mussels have not bred since the 1960s because of a combination of nutrients and soil run-off into rivers.
"The freshwater pearl mussel is a fascinating species with a really unusual lifecycle. Because it needs good quality rivers it can be used as an indicator of the environment as a whole. When rivers are good enough for freshwater pearl mussels then the whole environment must be in a good condition for wildlife". Richard Knott, from the Environment Agency.
The young Pearl Mussel larvae, called glochidia, are released in summer and attach themselves to the gills of young salmon or trout. They then stay with the fish until the following spring when they drop off onto suitable gravel beds where they begin maturing. A river that is good for salmon and trout has potential to be good for freshwater pearl mussels whereas one that is poor for fish will also be poor for the mussels.
12 farmers were given one-to-one advice and a follow-up report by Creedy Associates to help identify potential diffuse pollution problems and to identify important wildlife habitats on the farm. Advice was also offered on how to resolve problems and potential sources of grant aid were suggested. The project also had a capital grant scheme which was used to help tackle the most important issues identified. Some of the grant was for keeping stock out of the rivers and streams and some used for setting up alternative supplies for watering stock.
The areas managed by the farmers invited was 2,365 acres of which 56% was grassland, 39% arable and fodder crops and around 3% woodland.
Five farms were mixed (arable and livestock), 3 were beef and sheep, 2 small scale mixed, 1 arable and only 1 dairy.
42 soil samples were taken in the target area. The mean pH was 5.7 (generally between 5.6 and 5.3). The mean phosphate index was 2 with the mode being 3. The majority of fields were at or slightly above the optimum phosphate index.
Several nutrient management plans were produced by the project for farms because the application of phosphate and potash to grazing ground was above crop recommendations. It is thought that this was largely because the understanding of grazing ground nutrient requirements were not well understood.
The project involved the local community in Habitat Walkover Suveys which were run by Westcountry Rivers Trust. Following a training workshop, 17 volunteers recorded information on the condition of the 15 km of the River Mole in the pilot project area. The surveys looked at the channel habitat (glide, parr, pool or fry) bankside habitat and land use, channel modifications and evidence of pollution, invasive plants and wildlife. Because of the pearl mussel's dependance on its salmonoid host the survey recorded the potential suitability of the river habitat for both pearl mussels and salmonoids.
The surveys also trialled the use of underwater digital photography to evaluate the suitability of the river substrate for freshwater pearl mussels. Images were analysed using the Digital Gravelometer Software designed by Loughborough University. Although the analysis was unsuccessful during the project, the software is still being developed and it is hoped that future trials will have success at analysing the substrate without removing it from the river thereby reducing the risk of damage to freshwater pearl mussels.
"The project was very successful at getting a small team of volunteers to carry out the surveys. Everyone learnt a lot and some wonderful wildlife was seen during the surveys. This work could not have happened without the support of the riparian landowners. We know much more about the condition of the Mole which should help identify what needs to be done to help the survival of this endangered species." Tom Hynes, Biodiversity Officer with the North Devon Biosphere Service.
"We are very pleased to be involved with this project that works with farmers, the public and with one of North Devon Biosphere Reserve's most interesting and endangered species. In the past, the freshwater pearl mussel was a flourishing species but over-collection, pollution and a fall in fish numbers have caused a catastrophic decline in the population size". Derrick Spear, chairman of the Tarka Country Trust.