Radio Tagging Atlantic Salmon

In the Scottish Highlands

For the winter 2019 rewilding impact project vote, our focus turned to the Scottish Highlands, where we work with Alladale Wilderness Reserve, a rewilding estate working to bring wilderness back to the Highlands. Here, our members were given the choice between radio tagging wild Atlantic salmon for monitoring salmon migration, translocating mountain hares and building eagle nest platforms. Our members voted for the mountain hare project, but we were able to secure funding for the eagle nest platforms and Atlantic salmon tagging through our wonderful business partners Inlumi.


Project Timeline

April 2021

Due to the COVID-19 pandemic the project activities are put on hold for 2020. Work begins to catch and tag salmon with radio tags as they move into the intervention area and up stream to spawn. Monitoring of the salmon migration also begins.

August 2021

Tagging ceases as Atlantic salmon reach their spawning sites. Salmon migration tracking continues until December when salmon return back to sea.

December 2021

Data is analysed.

January 2022

Results and recommendations are presented.

Learn more about why we are monitoring Atlantic salmon migration

Why are salmon important to the ecosystem?

Every year in Autumn, Scotland's crystal clear salmon rivers and streams are transformed into a frenzy of fish leaping and swimming their way upstream to spawn in freshwater gravel beds, before returning to sea. In doing so, salmon help bring nutrients from the ocean ecosystem upstream into freshwater environments. Through excretion, spawning, death and decay, salmon directly affect the ecology of their freshwater environments and increase nutrient availability for algae, invertebrates and young salmon. 

Salmon themselves are an important food source for an abundance of aquatic and terrestrial wildlife, such as otters, waterfowl and eagles. At sea, salmon are predated on by some of the ocean's top predators, such as sharks, dolphins and seals. They also have an interesting symbiotic relationship with a priority species in the UK Biodiversity Action Plan, the freshwater pearl mussel (Margaritifera margaritifera). Adult mussels filter water, improving the water quality and reproductive conditions for salmon, and salmon return the favour by providing a safe environment for mussel larvae to develop within their gills.

A Difficult Journey

According to the Atlantic Salmon Trust, for every 100 wild Atlantic salmon (Salmo sala) that leave Scotland’s rivers for the sea, fewer than five return. This represents a decline of nearly 70% in 25 years. There is no single cause of this decline in migration, but a complex web of anthropogenic activities, including climate change. On the River Carron, which runs through our reforestation area at Alladale Wilderness Reserve, a unique situation exists. Water from the uppermost reaches of the river is re-routed to another catchment for hydro-electric power generation via a tunnel. Consequently, migrating juvenile salmon would be likely to head down this pipe and be “lost” to the Carron system. The historic solution was to put a dam immediately downstream to prevent adult salmon from spawning in this area and retain their offspring in the Carron system.

A river and dam on a misty day in Scotland. Dams can cause problems for wild Atlantic salmon migration
Atlantic salmon face significant challenges as they migrate to their spawning sites in Scotland's rivers

Identifying The Threats

For a number of years, salmon have been reported above the dam. For several consecutive seasons, salmon/trout hybrids and some full juvenile salmon have been caught above this dam. This implies that salmon are circumventing the dam and spawning there, but the exact mechanism is unknown. One of the ways salmon could be getting over the damn is swimming through the scour valve when it is opened for a few hours in the autumn. In partnership with the Kyle of Sutherland Fisheries Trust, we are supporting efforts to radio track the salmon and identify the way in which salmon are ascending the dam by funding the purchase of 10 radio tags. This will help provide the Trust with vital information for the conservation of wild Atlantic salmon in the River Carron.

A researcher releases an adult wild Atlantic salmon back in a calm river
Monitoring samon as they migrate to their spawning sites will help identify the threats they face during this challenging part of their lives
Heart Image

the team behind the project

Team Member

Hannah Kirkland, Conservation Biologist at Mossy Earth

Team Member

Dr Keith Williams, Director at Kyle of Sutherland Fisheries Trust

Team Member

Sean Robertson, Science & Mitigation Officer at Kyle of Sutherland Fisheries Trust

Learn more about migratory fish, their threats & conservation

Tiago, our conservation biologist, sat down with Jaakko Erkinaro. A renowned researcher, Jaakko's fields of research cover both freshwater and marine phases of salmonid fishes, for which he has published over one hundred peer-reviewed scientific articles. Together they discussed threatened freshwater ecosystems, the problems migratory fish face, and the conservation of such watercourses.

Sources & further reading

Peer Reviewed Research Section
  1. A Manifesto for Rewilding the World - George MonbiotExternal link
  2. Rewilding Success Stories - The GuardianExternal link
  3. Rewilding abandoned landscapes in Europe - Springer Link PublishingExternal link
  4. Factors affecting the within-river spawning migration of Atlantic salmon, with emphasis on human impacts - Springer Link PublishingExternal linkIcon Peer Review