We are facing a crisis from the changing climate with nine of the ten warmest years occurring since 2002, and seven of the ten wettest since 1998. Climate change could see summers in Scotland up to 4.8 degrees warmer and 40% drier. Wild Atlantic salmon are threatened by climate change both at sea and in freshwater.
Survival of salmon and sea trout during their marine migration phase has fallen over the last 40 years. Some of this reduced survival can be explained by changes in sea surface temperature and subsequent contraction of feeding grounds as a consequence of climate change.
In rivers, the optimum temperature range for Atlantic salmon is thought to span 6-20°C, within which maximal growth occurs at 16-17°C. Atlantic salmon exhibit thermal stress at approximately 23°C with mortality at approximately 33°C. Temperatures recorded during the summer of 2018 show that 69% of Scottish rivers experienced temperatures that cause thermal stress for salmon on one or more days. River temperature is an important control on the health of fish populations. Under climate change it is expected that river temperatures will rise with potentially devastating consequences for fish and invertebrate populations.
What are we doing?
One of the most effective interventions is the planting of native trees beside rivers in order to provide dappled shade and reduce river temperatures. Over one million trees have now been planted in Scotland for this purpose, but given the scale of the issue, many more trees are required. Fisheries Management Scotland are advocating for changes to the Forestry Grant Scheme, and other funding mechanisms to help facilitate the planting of native trees beside those rivers which Marine Scotland Science has identified as vulnerable to damaging temperature rises. In September 2021, Mairi Gougeon visisted the South Esk to learn more about the work undertaken by the Esk Rivers and Fisheries Trust to improve habitat and plant riverbank trees.
Through the Missing Salmon Alliance, we contributed to the installation of an inspirational artwork project – Salmon School – in the blue zone at COP26. The centre piece of Salmon School is a stunning art installation of more than 300 glass salmon by renowned artist Joseph Rossano, which was displayed at COP26 in recognition that our iconic wild salmon are on a path to extinction. As an integral part of the migration phase of Salmon School, the Clyde River Foundation worked with pupils from 26 primary schools across the Clyde catchment area to inspire future stewards of rivers to learn more about the amazing life cycle of salmon and the challenges they face. In October 2021, Màiri McAllan, Minister for Environment, Biodiversity and Land Reform joined staff and pupils from Underbank Primary School to celebrate this inspirational project and learn more about Salmon School. By placing wild salmon at the forefront of twin crises of climate change and biodiversity loss, our aim is to make the case for a range of measures that will reduce or eliminate the impact climate change is having on wild salmon.