Chalk-stream salmon could become an official sub-species - University of Exeter

Chalk-stream salmon should be officially classified as a sub-species, new research suggests.

Scientists from the University of Exeter and INRAe (France) carried out detailed genetic testing of salmon from 42 rivers in England, Ireland and France – including fish from chalk streams in southern England and northern France.

They found that salmon from chalk streams are closely related to each other – and genetically distinct from salmon in nearby non-chalk rivers.

The researchers propose that chalk-stream salmon could be formally recognised as a sub-species of Atlantic salmon, with the scientific name Salmo salar calcariensis (meaning Atlantic salmon from a limestone region).

With salmon populations in decline due to multiple factors, the researchers say sub-species status could boost targeted conservation.

“About 85% of the world’s chalk streams are in England, and just six of these contain significant populations of salmon,” said Professor Jamie Stevens, from the University of Exeter. “These streams – the Frome, Piddle, Avon (Hampshire), Stour, Test and Itchen – begin in agricultural areas, which brings a threat from pollution, and pass through major urban areas such as Southampton, Portsmouth, Bournemouth and Poole. Now we know chalk-stream salmon are genetically distinct, we see the vital importance of protecting these habitats, along with chalk streams in northern France.”

Chalk streams – which originate in chalk hills and are generally wide and shallow with clear water – are fed by underground aquifers, have steadier flow rates and more stable temperatures than most other rivers, and are less acidic.