Atlantic salmon, Salmo salar, are facing increased pressures both sides of the pond. Habitat destruction alongside commercial and recreational fishing has choked salmon numbers on a global scale, as well as local extinction within UK Rivers where they’d once flourished.

Spending up to four years in their natal river, young salmon undergo osmotic development and adapt to more saline waters. After years of fighting against river currents, the salmon ride with the freshwater streams to the sea.

Around a year later, the salmon have grown considerably and are ready to spawn. Atlantic surface currents aid their return to freshwater habitats. Thanks to iron within their lateral line, the salmon utilise the Earth’s magnetic field as a compass to navigate back to their natal rivers, exactly where they’d left a year or so prior.

Did you know? Only ~5% of Atlantic salmon arrives at an alternate river from which they were born. Using both magnetic fields and smell the majority return to their natal river!

As you may know, Wiltshire Wildlife Trust is heavily involved in river restoration projects. The River Avon and its tributaries form one of the most diverse chalk systems within the UK, supporting one of the largest and most diverse wild fish populations. Of course, Atlantic salmon is one of the most significant threatened species within this ecosystem.

More info on the chalk streams project   

The sheer abundance of insects in a pristine chalk stream provides a bountiful food supply for Atlantic salmon and numerous other species. Most significantly, chalk systems provide ideal habitat conditions and protection from predators, with channels and vegetated banks for shelter.

However, there is a long legacy of damaging activities to our chalk streams such as dredging and draining alongside continuous pollution problems. Abstraction of drinking water and extended land management in chalk stream catchments further adds to the damage.

Various techniques have been implemented to restore natural functions and flows, including the bypassing, modification and potential removal of river obstructions. Re-alignment projects have also been highly successful in creating a more natural path and position of the floodplain; see last month’s blog for more info.

So far the results are promising and the River Avon Restoration Project won the 2017 UK River Prize! However, the present issues need constant work and monitoring. Only through this can we make our chalk rivers sustainable and conserve the native populations, such as the Atlantic salmon, successfully. 

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