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A FULL CIRCLE MOMENT
Most of us dream about leaving home: chasing new opportunities, exploring the world, making our mark.
Salmon do something surprisingly similar. They hatch in a river, then develop a restless urge to head out into the vast, unknown ocean. They grow, explore, and survive in a world completely different from the one they were born in. But no matter how far they roam, something inside them always calls them back. After years at sea, they swim thousands of miles against currents and obstacles to return to spawn, in the exact river where their journey began.
It’s a story of adventure, courage, and an unbreakable bond with home, reminding us that sometimes, the greatest journey isn’t just about leaving, but about coming back.
This journey has been honoured in a conference led by the Atlantic Salmon Trust and The Tweed Foundation, called From Headwater to Headland. Amid the rapidly changing conditions in the North Atlantic, these organisations focus on maximising the number of young and healthy salmon (smolts) leaving the river to boost adult salmon survival at sea and protect returning populations. Since 2006, Atlantic salmon populations have declined by 30-50% in Great Britain1 and survival rates from smolt to salmon have dropped by 5%, reclassifying this fish as endangered and signalling biodiversity loss.
So how can we improve the way we conserve salmon?
POTHOLES ON THE PATH
Before salmon ever reach the ocean, their journey is already being reshaped. As smolts they undergo smoltification (yes, that is a real scientific term!), a series of biological changes that allow them to survive in saltwater. But climate change and chemical pollution are altering the cues that trigger this transformation.
Research presented in From Headwater to Headland shows that across northern European rivers, smolts are migrating earlier by almost three days per decade, as rising river temperatures speed up their development. Entering the sea earlier often means they are smaller. Using a 20-year dataset on the length of young salmon in the Burrishoole catchment in Ireland, one study projected that as river temperatures rise over the next few decades, salmon could reach smoltification as much as three months earlier, at a length that is 5-6cm smaller than the usual smolt size.
Early smoltification means that smolts are likely to be smaller and less fit, threatening their survival at sea. Using statistical models to describe seasonal changes in salmon length with water temperatures, research suggests that larger fish are stronger swimmers2 and therefore better able to tackle environmental challenges such as predators.
When they aren’t fighting off bigger fish, earlier timing and reduced size may also mean smolts reach the ocean when conditions aren’t optimal, further decreasing their likelihood of survival and return from the big blue.
Chemical pollution adds another layer of risk. Research has shown that low concentrations of the agricultural herbicide atrazine (used to stop weed growth among crops), can leak into waterways from land, inducing additional stress3 and disrupting the physiological changes smolts need to tolerate saltwater. Because these changes begin in the river, pollution can weaken fish long before their ocean journey truly begins.
ROADBLOCKS AND HUNGRY PREDATORS
For smolts, the journey to sea is full of obstacles. With only a third of the world’s longest rivers unrestricted by dams or reservoirs4, many freshwater habitats are fragmented by physical structures such as barrages, weirs and hydropower schemes, which can all delay migration and increase exposure to predators
Even short delays matter, because smolts must reach the ocean during a narrow “window” when conditions are right5 (think of it like trying to avoid rush hour!). With every delay, comes the possibility of fewer adult salmon making the journey back home.
On the River Dee in North Wales, researchers tagged 94 smolts and tracked them using fixed electronic receivers to see how they passed through a sluice gate system (a sliding plate used to control water flow in rivers). While 91.5% successfully migrated downstream, 6.6% failed to pass at all, and 3.2% were delayed for more than four days. Smolts moved faster when river flow was higher but travelled more slowly through the sluices themselves. Even small slowdowns can leave fish vulnerable at critical moments.
Vulnerability means predation. In Denmark, a study on tagged smolts during the 1990s revealed that as many as 40–60% of smolts were predated during the few weeks of their migration, especially at bottlenecks like dams where fish are forced to slow down, allowing larger predators to aggregate and ambush their prey.
THE SALMON SCENE
When you step back, a pattern emerges. Climate change, pollution, barriers and predators aren’t isolated problems: they overlap, interact and amplify one another during the most vulnerable stage of a salmon’s life. A delayed smolt at a sluice gate may face higher predation. A smaller fish, shaped by warming rivers, may be less resilient if injured or stressed.
Scientists are already improving long-term monitoring, using tracking technology that follows individual fish through rivers and out to sea (tools such small electronic tags that send signals to underwater receivers) to see where and when numbers begin to drop.
But gaps remain. Many rivers lack consistent monitoring across the entire migration route, and survival in the vast marine ecosystem is still harder to measure than in freshwater. To truly protect salmon, data must follow them from headwaters to open sea, and conservation strategies must respond to the full picture, not just one stretch of water.
What we do know is that salmon conservation cannot treat rivers and oceans as separate worlds. The freshwater and marine stages are tightly connected, and what happens upstream ripples far beyond the river.
HOW TO FIND ANOTHER WAY
Salmon recovery is about whole ecosystem recovery, which can be improved through supporting river restoration projects, engaging with local conservation groups and even staying informed through organisations like the Atlantic Salmon Trust (check out their blue book series for more resources like From Headwater to Headland)
The more we recognise how connected these pressures are, the better chance salmon have of completing the journey that has defined them for thousands of years- and of returning home once more.
WANT TO KNOW MORE?
Wild Atlantic Salmon: Restoring the Run– a film by YETI exploring the many ways we are connected with wild Atlantic salmon.
Saving Salmon– A podcast by Atlantic Salmon Federation, filled with tales of wild Atlantic salmon and the people who fight to protect them
Creatures of Light collection– a meaningful and symbolic art project led by actor and activist Jim Murray, to raise awareness on Atlantic salmon populations in the UK. Each piece was essentially painted by the rivers!
Article written by Charlene Deouza
References:
Primary paper:
Barry, J. et al. (2017) Atlantic Salmon Trust and the Tweed Foundation: From Headwater to Headland: Improving smolt survival in rivers and estuaries, Blue Book Series, Atlantic Salmon Trust. Available at:
https://atlanticsalmontrust.org/wp-content/uploads/2017/12/TAST-Blue-Fisheries-Book.pdf (Accessed: 21 February 2026).
Other sources:
- Game and Wildlife Conservation Trust (2023) ‘IUCN Classifies Atlantic Salmon
in Great Britain as Endangered’. Available at:
https://www.gwct.org.uk/news/news/2023/december/iucn-classifies-atlantic-
salmon-in-great-britain-as-endangered/ Gregory, S.D. et al. (2017) ‘Patterns on a Parr: Drivers of long‐term salmon Parr length in u.k. and French rivers depend on geographical scale’, Freshwater Biology, 62(7), pp. 1117–1129. Available at: https://onlinelibrary.wiley.com/doi/10.1111/fwb.12929
Waring, C.P. and Moore, A. (2004) ‘The effect of atrazine on Atlantic salmon (Salmo salar) smolts in fresh water and after sea water transfer’, Aquatic Toxicology, 66(1), pp. 93–104. Available at: https://pubmed.ncbi.nlm.nih.gov/14687982/
Gramling, C. (2019) ‘Only a third of Earth’s longest rivers still run free,’ Science News. Available at: https://www.sciencenews.org/article/only-third-longest-rivers-run-free-earth.
Russell, I.C. et al. (2012) ‘The influence of the freshwater environment and the biological characteristics of Atlantic salmon smolts on their subsequent marine survival’, ICES Journal of Marine Science, 69(9), pp. 1563–1573. Available at: https://academic.oup.com/icesjms/article/69/9/1563/634513?login=false
