Boulders brought back to River Wye in bid to boost salmon survival

Nation.Cymru staff

Boulders are being returned to a seven-kilometre stretch of the River Wye to improve habitats for salmon and other wildlife.

Natural Resources Wales’ Upper Wye Catchment Restoration Project is carrying out the work at Llangurig, where boulders removed over generations are being reintroduced.

Surveys found abundant salmon fry in the area, but poor survival into the next stage of development, known as parr. The project team believes a lack of boulder cover and varied habitat may be limiting the fish’s ability to feed, shelter and grow.

Writing in an NRW blog, project managers Brendan and Henry said: “Boulders are a natural feature of upland rivers such as the Upper Wye. Over time, many were removed from the river, leaving some sections with a lack of flow variety and fewer of the natural features that provide habitat for fish and other wildlife.”

The team spent two years carrying out baseline surveys and reviewing monitoring data before work began, examining fish, aquatic invertebrates and the river channel to identify where boulders could provide the greatest benefit.

The boulders have been placed in an irregular pattern to mimic natural conditions, creating a mixture of faster and slower flows, pools, shallow stretches of turbulent water and quieter areas.

“Boulders create areas of shelter from strong currents and predators, as well as deeper pockets of water and different feeding opportunities,” the project managers said.

The work aims to improve conditions for trout and Atlantic salmon, one of the species for which the River Wye is designated a Special Area of Conservation.

A more varied riverbed also provides habitats for aquatic invertebrates, which are an important source of food for fish and other wildlife.

The team has also been working with farmers and landowners around Llangurig on riverside fencing, buffer strips and tree planting.

These measures are intended to protect riverbanks, reduce the amount of soil and pollutants entering the water and provide shade as trees mature.

Offcuts

At nearby Tarenig Forest, forestry offcuts are being used in drains and ditches to slow the movement of water through the landscape during heavy rainfall.

Monitoring will continue to assess changes in fish populations, aquatic invertebrates and the river channel, with particular attention to whether more young salmon survive to become parr.

The Upper Wye Catchment Restoration Project covers the river from its source to Hay-on-Wye. It is funded by the Welsh Government’s Nature and Climate Emergency Fund as part of the Water Capital Programme.

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