England chalk stream heat threatens salmon and trout

Record summer heat and drought are warming England’s rare chalk streams, reducing river flows and putting salmon and trout under stress, wildlife and fisheries officials said.

On a branch of the River Itchen near Winchester in Hampshire, Robert Wellard, director of fisheries at the Piscatorial Society, measured the water at 17C. Kathryn Boler, who manages the Freshwater Programme for the Hampshire and Isle of Wight Wildlife Trust, said August temperatures should be closer to 12C or 13C.

The Itchen reached 21.7C in July, according to Environment Agency figures. Boler said water above 19C puts extra stress on salmon and trout because it reduces oxygen in the water while increasing the fish’s physiological needs.

Chalk streams are fed by underground springs filtered through porous chalk bedrock and are known for clear, cool, mineral-rich water. The Wildlife Trust says 85 percent of the world’s 200 recorded chalk streams are in England.

Several angling clubs, which mainly practise catch-and-release fishing, have temporarily limited activity to reduce stress on fish.

Lower flows in drought conditions also expose fish to predators. Paul Vignaux, who heads a local association for landowners and anglers on the Itchen, said Atlantic salmon were more trapped in low-flow conditions and more vulnerable to harbour seals and cormorants.

Vignaux said 180 salmon came to spawn in the Itchen in 2022. Preliminary figures for last year counted 250, which he said was 32 percent of the threshold considered necessary for the species’ conservation.

The Environment Agency said in its July salmon count for the Itchen and the nearby Test that young freshwater salmon were far below usual levels in abundance and size.

An Environment Agency model projects that the average temperature of rivers where brown trout live in England will exceed the tolerable limit at most sites by 2070. It projects the critical threshold for salmon will be exceeded in half of their habitats by 2080.

Scientists say climate change is increasing the frequency and intensity of heatwaves, drought and other extreme weather. Environmentalists and anglers are calling for river restoration, reduced water extraction and more tree planting to increase shade.