17 hours ago
River Usk project tracks salmon migration barriers
Known as 'smolt' at this life stage, the juvenile fish migrate to the sea to mature and free movement between river and sea is vital for their life cycle.
The Natural Resources Wales (NRW) River Usk Smolt Telemetry Project, established in 2021, track the fish's journey along the catchment area.
The project tags up to 100 smolts annually with small acoustic transmitters.
Around 55 static acoustic listening devices set up along the river document the fish's movements.
The data reveals that as the smolts journey towards the sea in spring, they struggle to navigate man-made barriers like weirs, especially in low river flow conditions.
These obstacles cause significant delays, exacerbated by low water levels during dry years.
The study found that only 24 per cent of tagged smolts reached the sea in a dry season, compared to 67 per cent in a wet one.
These numbers don't just reflect a decrease in successful migrations during dry seasons, but also a significant delay, with some smolts taking five weeks longer to leave the river.
Aquaculture officer leading the project for NRW, Oliver Brown, said: "The project has evolved over the last couple of years and is giving us a good indication of what's happening to these fish at a critical point in their life cycle."
The study's findings are instrumental in shaping improvements on the River Usk under the Four Rivers for LIFE project.
The project is building a new smolt pass on the weir, creating a more accessible pathway for migrating smolts.
Four Rivers for LIFE manager, Susie Kinghan, said: "The smolt tracking research has been of significant importance to us as a project.
"The fish-pass work we are doing on the weir will help salmon and other species to move freely downstream, helping to increase their dangerously low numbers."
