Bournemouth Water teamed up on a project designed to protect a critically endangered species.
They collaborated on highly successful tests for a new eel pass design using natural gravel substrate instead of existing plastic alternatives.
European eels are listed as critically endangered on the IUCN Red List of Threatened Species, with their population dropping by 90–95% since the 1980s.
A test facility – built by Fishtek Consulting – was installed at Knapp Mill on the Hampshire Avon, which is owned by Bournemouth Water.
The tests compared eel passage rates across existing plastic-based eel passed with the new natural gravel design.
Ellie Strudwick, a University of Exeter student, undertook the work for her dissertation after spending a placement year at Fishtek.
She explained: “Juvenile eels (elvers) are small and vulnerable when they begin their upstream migration into freshwater, as they are immediately faced with river obstructions, such as weirs, dams and hydropower stations.
“These artificial barriers prevent elvers from migrating upstream to resource-rich habitat and have been a major cause of European eel population decline.
“The test facility comprised a series of channels lined with different eel substrates that led to a trap box divided into three sections. I controlled the flow rate via an electric pump to ensure an even flow in each section and checked the trap box daily. The trapped elvers were counted and photographed so they could be measured on the computer using software. I then released the elvers upstream.”
Fishtek Technical Director Adam Fryer explained that barrier removal is vital in eel conservation. Where a barrier cannot be removed, eel passes are often installed to allow elvers to ascend upstream.
He said: “There is a range of off-the-shelf substrates, usually formed from plastic, that can be installed on an existing barrier or in a trough or channel that bypass a barrier and provide the right conditions to allow eels to ascend upstream. However, these substrates are not always effective, and they risk leaching microplastics into the watercourse.
“Overall, we found that gravel substrate was as effective as the widely used bristle substrate, while readily used peg type tile substrate proved to be relatively ineffective for elver passage. I concluded that eel tile spacing was too high and that elvers were likely able to ascend only because of algae growth on the tiles.”
Adam said: “This study has given us a huge amount of information that can inform our eel pass design.
“It also provides a framework to show how a collaborative approach among industry, academia, a water utility and the regulator can advance the field of fish passage research and optimise outcomes when designing and installing environmental mitigation.”
Environment Agency Senior Technical Specialist (National Fisheries Technical Team) Dr Adrian Fewings said: “This collaborative approach allows all participants to progress improvements in eel pass design based on sound field observations.”
The tests were a partnership between Bournemouth Water, RSK Group company Fishtek Consulting, and the University of Exeter’s Department of Earth and Environmental Sciences.
