SALMON from the chalk streams of southern England are genetically unique, researchers have discovered.

The fish are classified as Atlantic salmon but research by the University of Exeter and the Game and Wildlife Conservation Trust shows their genes are distinct from others.

The researchers studied five chalk streams in Hampshire and Dorset, habitats they said were under “massive pressure” from human activity.

Classifying chalk-stream salmon as a separate sub-species could make it easier to protect them.

Jamie Stevens, of the University of Exeter, said: “Our study provides evidence of the genetic distinctiveness of chalk-stream Atlantic salmon in southern England. They are as different from their non-chalk cousins as the salmon of the Baltic are, and people have suggested the Baltic fish should be classified as a sub-species. While we found distinct differences between chalk and non-chalk salmon, we found little genetic differentiation within chalk-stream populations.”

Chalk streams are fed by underground aquifers and have steadier flow rates and more stable temperatures than most other rivers.

Of the 161 rivers classified as chalk streams by the Environment Agency, only five contain significant populations of salmon, the Frome, Piddle, Avon, Test and Itchen.