The Atlantic salmon of Scotland are hardy and determined animals. Each spring and summer, they return from the North Atlantic Ocean to breed in Scotland’s shallow rivers, leaping up waterfalls and over weirs, propelling themselves upstream in a Herculean effort. Some fail, others triumph, but today they face yet another challenge.
During the mid-1980s, there were between eight and ten million salmon swimming around Scotland’s Atlantic coast; that number has now dropped to two to three million. There’s evidence of rising at-sea mortality as climate change warms and acidifies oceans, reducing the availability of the salmon’s prey. New research suggests climate change is also bearing down on rivers.
Across Atlantic streams, average temperatures increased by 0.22°C annually between 2000 and 2009, and under business-as-usual scenarios, August stream temperatures are projected to increase by 2.5°C by the 2080s, which is bad news for salmon. Adapted to life in cold water, salmon experience stunted growth and demographic changes at high temperatures. Heat influences their cardiovascular health and reduces their resistance to disease and parasites. ‘Now salmon are struggling to cope with the rising temperatures. There are recent records of 27°C in the upper reaches of the Dee catchment,’ says Peter Cairns, director of SCOTLAND: The Big Picture, an environmental charity. He adds that in 2018, when Scotland recorded the lowest rod catch for salmon since records began, freshwater temperatures across 70 per cent of Scotland’s rivers were too warm for salmon survival on at least one day of the summer period.
Evidence suggests that the degraded quality of river catchments compounds the impact of our changing climate. ‘Atlantic salmon evolved using river systems in Scotland that were once way more forested and therefore shaded,’ says Cairns. Yet Scotland is today one of the least wooded countries in Europe, with just three PLIGHT OF THE SALMON per cent of its native woodland intact. Scientists from Marine Scotland have found that just 35 per cent of rivers in Scotland have adequate tree cover for salmon survival. ‘We’ve seen situations where the temperatures on rivers are getting critical for salmon,’ says Alan Wells, director of Fisheries Management Scotland. ‘It will get worse. We need to grow trees now to create that cooling shade.’
A movement to get trees back on riverbanks is gathering pace. Fisheries managers on the River Dee in Aberdeenshire have already planted 250,000 saplings of native tree species along key tributaries and plan to plant a million more by 2035. ‘Broad-leaf trees close to the bank can reduce the light that enters the water,’ explains fisheries scientist Anthony Hawkins in a recent paper in the Journal of Earth Science and Climatic Change.
A new initiative called Riverwoods – led by the Scottish Wildlife Trust and supported by Scottish Water and several other government and regulatory bodies – aims to create a network of riparian woodlands along Scotland’s riverbanks, and has already received a number of large grants. ‘River health is complex, but tree planting is one of the most basic things we can get started with right away,’ says Cairns. To raise awareness of the issue, his organisation has produced a documentary: Riverwoods. The film will premiere in London in May at a fundraising event hosted by the European Nature Trust, with funds being directed to tree-planting initiatives for salmon and river health. ‘It’s just one example of where the public and private sectors are coming together on this issue.’