The Moray Firth is home to some of the most iconic salmon rivers in the British Isles and, indeed, the world. Famous names such as the Spey, Deveron, Findhorn, Ness, Conon, Oykel and Shin resonate with the legendary status they hold and the special memories many anglers have of them. It is estimated that the rivers that flow out into the Moray Firth sustain around 20% of the UK’s wild Atlantic salmon population, making it a stronghold for the king of fish.

However, as with salmon populations across the Atlantic, all is not well. Across their North Atlantic range, it is thought that wild salmon numbers have declined by around 70% in the past 40 years. One of the major factors believed to have influenced this decline is a large reduction in marine survival. By this we mean the proportion of young salmon (smolts) that exit their natal rivers to head to their feeding grounds off the coast of Norway and Greenland versus the number that return as mature adults after one or more winters at sea. In the 1970s and 1980s, it’s thought that as many as 25% to 30% of these young fish would have returned to their home rivers to spawn after a year at sea. Now that figure could be as low as 2% to 3%.

With ever more pressures affecting our salmon at sea, from the global impacts of climate change and rising sea surface temperatures to coastal developments such as aquaculture and offshore renewable energy, it was vital for the salmon conservation community to understand more about the movements of our young salmon smolts. The question has been whether identifying migration pathways out into the open ocean would better protect our fish and shepherd them away from danger.

THE MORAY FIRTH TRACKING PROJECT

Each tagged smolt is carefully weighed, measured and recorded – credit Byron Pace

Cue the groundbreaking Moray Firth Tracking Project, launched by the Atlantic Salmon Trust in 2019 in partnership with Fishery Boards and Trusts and with the support of Glasgow University. Spanning seven iconic rivers in the Moray Firth, this monumental three-year study sought to find out exactly where our smolts travelled once they left their home rivers. This was achieved with acoustic telemetry – carefully trapping and implanting salmon smolts with tiny battery-powered acoustic ‘tags’, then laying sets of acoustic receiver ‘arrays’ at various points down the study rivers and out into the Moray Firth itself. Every time one of the implanted fish passed by a receiver unit, the unit would register a high-frequency ‘ping’, logging this location data on a hard drive. By pooling all the pings together, researchers could see how long each fish took to travel down the river and out into the Firth, as well as which routes were taken.

This was no mean feat, particularly when considering that one line of receiver units was laid on the seabed all the way from Berriedale to Spey Bay, a distance of more than 70km. In total, across the study (2019, 2021 and 2022 – 2020 was halted due to the COVID-19 pandemic) the project tagged thousands of salmon smolts and deployed and recovered hundreds of receivers each year. It became the largest project of its kind ever to be undertaken in Europe. This monumental achievement was facilitated by more than 100 volunteers, who dedicated their time to helping trap, tag and release fish in all weather conditions.

A rotary trap used to catch smolts – credit Byron Pace

ALARM BELLS

A discovery in 2019, the first study year, sent alarm bells ringing throughout the angling community, the salmon conservation world and beyond. The project tracked fish out to the furthest receiver arrays in the Moray Firth and demonstrated a number of possible migration routes – although fish appeared to favour a broadly easterly route out of the Moray Firth before heading out into the open sea. What alarmed researchers was how few of these fish were even making it to the saltwater in the first place. On average, half of our fish were going missing before they even made it to the sea.

This suggested that the smolts could be suffering huge losses in the freshwater stage of their migration. The drop in marine survival might be a global problem caused by impacts from a changing climate, but we wondered whether our young salmon were also encountering severe pressures in freshwater. If that was the case, it was possible we might do something about it, something that could inform management strategies to make a real difference to our struggling fish. If we could help more healthy smolts safely out to sea, it made sense that we would have more returning adults. The entire project was reoriented around this new mission: to find out exactly how many of our fish were being lost in freshwater and why.

‘Active Tracking’ on the Spey using a canoe fittted with a receiver to search for tagged fish – credit Ben Etridge

The question for researchers was whether 2019 was an anomaly or had they uncovered something big. Studies in other projects on different rivers were revealing similar findings. The study was repeated to see if this was a recurring pattern, so the second study year in 2021 set out to answer those questions and yielded a similar set of results. A loss rate of 50% in freshwater was common across the study rivers and, most alarmingly of all, on one river the study displayed a staggering 91% loss rate. It was clear that something was going very wrong for salmon smolts in freshwater.

In the world of salmon, there is certainly no shortage of opinions and theories as to the cause of the decline, and those who spend their lives living and working on our rivers have long identified several of the pressures facing our fish. Debates around predator management and licensing have been raging for years. We argue about the effects of agricultural run-off, afforestation, changing weather patterns and flow rates, hydroelectric dams and other barriers to migration without really knowing which of these factors have the biggest impact. There was a need for more robust scientific evidence to identify the main cause of freshwater smolt loss. This would enable river managers to take targeted steps to solve the problem. There were many ‘suspects’ but the key was finding the prime suspect.

Deploying an acoustic receiver in a freshwater loch – credit Ben Etridge

Seeing a need to look at the loss rates in higher resolution to determine this, the project team placed a much higher density of receiver units in-river in 2022, the final year of the project. This would enable them to pinpoint any zones in our rivers that were seeing higher than ‘background’ loss rates, thus identifying the cause.

At the time of writing, the complete results from the Moray Firth Tracking Project are being analysed in detail, so the full findings will be revealed this spring. But early results are giving us a view at what the prime suspect might be. The rivers in the study featured a mix of free-flowing, ‘natural’ rivers and rivers that had been highly modified with dams, weirs, locks and canalised sections. While the free-flowing rivers exhibit a steady rate of downstream loss, the human-modified rivers with barriers to migration are seeing a dramatic and instant drop in smolt survival in the immediate area of the barrier.

PINCH POINTS AND PREDATORS

Barriers to migration and their negative effects on fish have long been known, but the project’s early results have begun to draw a fascinating connection between these ‘pinch points’ and the issue of predator management. Such pinch points, by altering smolt schooling behaviour, slowing down and disrupting their migration, and by changing environmental cues, could be giving predator species access to an easy meal. Perhaps then, time and energy spent fighting government agencies for predator control licensing changes could be far more effectively focused on removing the root cause of the issue? Maybe if we solve the pinch points we can address the predation issue.

Salmon smolts caught in the trap – credit Byron Pace

In tandem with the acoustic salmon smolt tagging work in year three, researchers also tagged predatory fish, such as large brown trout and pike, to monitor their movements around the pinch points, and conducted DNA sampling of scats left by fish-eating birds and mammals before, during and after the smolt run. By combining these studies, researchers hope to have a clearer picture than ever before of the relationship between pinch points and predator interaction, helping to give a renewed focus to salmon restoration and management strategies.

Early results are also pointing to flow rate as one of the main causes of smolt loss. Changing climate and weather patterns have transformed many of our systems from snow-fed rivers to spate rivers, and dry spells during the smolt run can have a severe impact on their survival. Many of our rivers are heavily abstracted or are impounded with hydroelectric dams that control flow rates, those too affecting the survival of our precious salmon smolts.

We have long thought of barriers to salmon migration within the context of returning adult fish, constructing elaborate fish passes to try to help adult salmon overcome these great obstacles on their way upstream. Now, the Moray Firth Tracking Project is shining a glaring light on a piece of the puzzle that we have been missing. It is becoming ever clearer that we need a total rethink of how we manage barriers and flow regimes to allow young salmon to navigate downstream safely.

But there is good news. Pinch points and flow regimes can be fixed. With the right evidence behind us, and with the right support for fishery managers, this is something tangible that a passionate salmon community can work with. Salmon are one of nature’s great survivors but it is up to us to give them the conditions they need to do more than that. Our great fish shouldn’t simply survive, they should thrive. We must be ambitious and look to remove barriers to migration altogether or, at the very least, ensure that fish passes are fit for purpose and flow regimes are protecting that downstream migration adequately. In an ever-changing and challenging world, with many dangers to salmon on the high seas, by safeguarding them in the early stages of their lives we can endeavour to have more of them coming home.

Jonathon Muir is head of communications at the Atlantic Salmon Trust