UK chalk-stream salmon genetically unique

January 30, 2018

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

The fish are classified as Atlantic salmon (Salmo salar), but research by the University of Exeter and the Game and Wildlife Conservation Trust shows their genes are distinctly different from others of the species.

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.

"Our study provides evidence of the genetic distinctiveness of chalk-stream Atlantic salmon in southern England," said Dr Jamie Stevens, of the University of Exeter.

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

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

Chalk-stream salmon - like other salmon - spend long periods at sea and swim hundreds of miles, but return to breed.

Some salmon return to the exact river where they were born, but Dr Stevens said genetic evidence suggested that may not be the case for chalk-stream salmon.

"We found evidence of quite a bit of mixing of genes between the rivers we studied," he said.

"Rather than coming back to a specific river, they may just home to the chalk rivers generally.

"We can't be sure of that, but the level of similarity suggests that there's ongoing gene flow between these rivers."

Dr Rasmus Lauridsen, of the Game and Wildlife Conservation Trust, said: "Fish research at the Trust is centred around the river lab at East Stoke, Dorset, where we have been monitoring Atlantic salmon numbers in the River Frome since 1973.

"We know that chalk streams are very productive and juvenile salmon in these rivers generally migrate to sea after just one year, whereas young salmon in other river types typically leave freshwater at 2-3 years.

"Chalk-stream salmon are adapted to fast freshwater growth and it is unlikely that they could be replaced if anthropogenic stressors were to drive them to local extinction."

So should chalk-stream salmon be classified as a sub-species?

Dr Stevens says yes.

"They certainly fit the criteria for being a sub-species - they are a genetically unique group with a well-defined distribution, associated with a distinctive habitat," he said.

"About 85 per cent of the world's chalk streams are in the UK, and the fish we studied are in an area of southern Britain that's under massive pressure from human activity.

"These streams begin in agricultural areas, which brings a threat from pollution, and they pass through major urban areas to reach the sea around places such as Southampton, Portsmouth and Poole.

"This is a precarious position for these salmon, and classifying them as a sub-species could aid efforts to protect them."
The paper, published in the Journal of Fish Biology, is entitled: "Atlantic salmon Salmo salar in the chalk streams of England are genetically unique."

University of Exeter

Related Salmon Articles from Brightsurf:

Alaska's salmon are getting smaller, affecting people and ecosystems
The size of salmon returning to rivers in Alaska has declined dramatically over the past 60 years because they are spending fewer years at sea, scientists report.

Chinook salmon declines related to changes in freshwater conditions
A new University of Alaska-led study provides the first evidence that declines in many of Alaska's chinook salmon populations can be attributed in part to climate-driven changes in their freshwater habitats.

Size matters in the sex life of salmon
For Atlantic salmon, size matters when it comes to love.

What does drought mean for endangered California salmon?
Droughts threatens California's endangered salmon population -- but pools that serve as drought refuges could make the difference between life and death for these vulnerable fish.

Salmon provide nutrients to Alaskan streambanks
Nutrient cycling of stream ecosystems dependent on portion of salmons' lifecycle.

Melting glaciers will challenge some salmon populations and benefit others
A new Simon Fraser University-led study looking at the effects that glacier retreat will have on western North American Pacific salmon predicts that while some salmon populations may struggle, others may benefit.

Bigger doesn't mean better for hatchery-released salmon
A recent study in the Ecological Society of America's journal Ecosphere examines hatchery practices in regards to how Chinook salmon hatcheries in the PNW are affecting wild populations over the past decades.

Salmon get a major athletic boost via a single enzyme
A single enzyme anchored to the walls of salmons' blood vessels helps reduce how hard their hearts have to work during exercise by up to 27%.

Salmon are shrinking and it shows in their genes
Male salmon are maturing earlier and becoming smaller, and it shows in their genes.

Young salmon may leap to 'oust the louse'
A study by Simon Fraser University aquatic ecologists Emma Atkinson and John Reynolds reveals that young salmon may jump out of water to remove sea lice.

Read More: Salmon News and Salmon Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to