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Study of climate impact on wild Scottish salmon begins

Scotland's Rural Affairs Secretary Mairi Gougeon planting a tree to help shade a salmon river in Angus. Photo: Scottish Government.
Scotland's Rural Affairs Secretary Mairi Gougeon planting a tree to help shade a salmon river in Angus. Photo: Scottish Government.

A project to gauge the impact of environmental and climate change on Scotland’s wild salmon population has begun.

Numbers of wild Atlantic salmon returning to Scotland have declined over the last four decades by around 40%, impacting the conservation status of many rivers in the country. Some anglers blame salmon farming, but the Scottish Government and conservationists say there are multiple factors behind the decline.

The £550,000 fund, including £150,000 provided by Crown Estate Scotland, supports sampling of juvenile and adult salmon by local fisheries trusts and boards to collect scales and other biological information from fish captured in rivers throughout the country.

Banking on trees

River temperature is a critical control on Atlantic salmon populations which are adapted to live in relatively cool water, according to Marine Scotland. Salmon tend to prosper when temperatures are in the teens and struggle much above 20°C. Where river temperatures exceed 23°C this can cause thermal stress and behavioural change. At 33°C salmon can no longer survive, even for a few minutes.

During the summer of 2018, it is estimated that around 70% of rivers in Scotland experienced temperatures over 23°C. UK climate change projections provided by the Met Office indicate that summers like these could occur every other year by 2050.

Maximum summer river temperatures can be reduced by increasing the amount of water in the river channel, or reducing the amount of sunlight reaching the water surface by shading the river channel with trees located on river banks.

There are considerable opportunities to increase woodland on river banks in Scotland as it is one of the most sparsely forested countries in Europe. Scotland has around 108,000 km of rivers, of which only 35% are protected by any substantial tree cover.

Read more about the subject here.

Targeted interventions

The scheme will use the data to help target interventions to conserve wild salmon and increase the numbers and size of the fish leaving rivers.

Speaking on a site visit to Glen Clova in Angus, the Scottish Government’s Rural Affairs Secretary, Mairi Gougeon, said: “We take the issue of our declining salmon stocks very seriously, with the reasons for it wide-ranging and complex.

“The investment in monitoring will help us to better understand these pressures.

‘Living parasols’

“We know that high river temperatures during the summer are a pressure on wild salmon and we are identifying priority stretches of waterways to target tree planting, providing living parasols to provide shade and encourage good survival and growth of salmon.

“We are working with landowners and land managers to encourage them to take measures such as tree planting to support salmon conservation.

“However, it is believed that salmon mortality at sea has increased in part due to the effect of climate change on ecosystems and shifts in locations where food is abundant.

“That is why it is vital, especially as we head towards COP26 (the international climate conference in Glasgow) that we continue to address the double challenges of climate change and biodiversity loss.”

Valuable research

Fiona Simpson, asset manager for Crown Estate Scotland, said:  “This funding allows for valuable research to be carried out which will contribute evidence to hopefully lead to a better understanding of some of the reasons behind the decline in Atlantic salmon numbers in Scottish rivers and inform targeted action plans to address current problems”.

As part of the visit, Gougeon planted the first tree in an area earmarked for re-forestation.