The ‘Unlocking the Severn’ LIFE project has reconnected 158 miles of shad and sea lamprey habitat through the creation of fish passes at four weirs on the river Severn. Such reconnection schemes in river systems can lead to changes in the fish community. This project aimed to generate biodiversity data using eDNA metabarcoding to investigate wider ecological effects of restoring river connectivity in the river Severn. Specifically, to map the distribution of shad (Alosa spp.) eDNA in relation to weirs in the Severn and investigate the possible presence of shad in the Thames. It also aimed to provide semi-quantitative data on fish community structure in the Severn and Thames; compare 2022 fish community data with data from previous metabarcoding surveys in 2021 and 2018 in the river Severn; and provide data on invertebrate diversity and community composition in the Severn and Thames respectively.
eDNA samples were collected at five sites in the river Severn and two sites in the river Thames. Samples were filtered and sent to the laboratory for DNA extraction and sequencing using PCR with two different primer sets; fish specific primers targeting the mitochondrial (mt) 12S region and invertebrate specific primers targeting a section of the generic mt COI barcoding region. Raw sequencing data were analysed using a reproducible metabarcoding bioinformatic protocols established at UHI Inverness. Shad DNA was detected above the Lincomb weir during the 2022 shad spawning run indicating that the shad are accessing the reconnected habitat in their first spawning event following reconnection.