Somewhere along their journey, our wild salmon are disappearing

Out of every 100 young salmon that leave our rivers for the sea, less than 5 return to breed as adults.

We have lost nearly 70% of the population in 25 years.

If this decline continues, the iconic wild Atlantic salmon could disappear in our lifetime.

The Moray Firth Tracking Project, launched in 2019, aims to find out what is happening to our salmon on this journey, so we can take steps to inform river managers and policymakers on how best to implement practical management solutions to protect wild Atlantic salmon and sea trout across their entire range. Our salmon are a key indicator species for wider ecosystem health and their decline is a wake-up call. We must solve the twin crises of climate change and biodiversity loss, not only for salmon, but for all the other plants and animals that share their world.

Something needed to be done.

Why are fewer and fewer adult salmon returning to our rivers? Image credit: Chris Conroy

Solving the mystery of our missing salmon

When we launched it, the Moray Firth Tracking Project was the largest, most ambitious acoustic tracking project to be undertaken in Europe. Importantly though, we wanted the findings from this project to be applicable to salmon populations and salmon rivers far and wide, not just in the Moray Firth itself. Our research findings would be fed directly into the Likely Suspects Framework for the benefit of salmon ecosystems everywhere.

We selected the Moray Firth as our study area as it is home to around 20% of all UK salmon, making it an excellent place to research fish from a number of important river systems. Iconic rivers like the Spey, Deveron and Findhorn were amongst them. The project used acoustic telemetry to track young salmon (or ‘smolts’) through our rivers, estuaries, and out into the sea so we could learn more about what was going wrong.

What is ‘acoustic tracking’ and how does it work?

Acoustic tags are small, battery-powered devices, about the size of a bean, which emit a high frequency ‘ping’ which can be detected by an acoustic receiver unit placed within a river, an estuary or on the seabed. By inserting these tags into young salmon smolts at the beginning of their downstream migration to the sea, we can learn more about their behaviour and the threats they face along the way.

So how do we get one of these acoustic tags into a fish?

We do this by trapping and anaesthetising salmon smolts in their home rivers, before carefully implanting them with an acoustic tag which sits harmlessly within their belly cavity. This procedure is conducted by highly trained and licensed professionals to ensure our young fish are all fit and healthy when we release them and send them on their way. After the young salmon have recovered, they are carefully released back into the river to carry on their journey, their newly-fitted tags pinging away and sending us data whenever they pass by one of our acoustic receiver units. This research will help us find out:

  • The migration pathways of our salmon so we can better protect them on their journey.
  • The ‘likely suspects’ contributing to their decline so we can take measures to improve their numbers.
  • How to improve their chances of returning safely to our rivers, both in the Moray Firth and across the UK.

The Moray Firth Tracking Project Activity

Year 1 – 2019: What did we discover?

During Year 1, our team of scientists and volunteers took a positive leap towards discovering what was happening to our salmon.

Our initial aim to study migration pathways for young salmon heading out to sea yielded some interesting findings, notably that most of the smolts from the study area favoured a southerly migration route out into the North Sea before heading north to their feeding grounds off Norway and Greenland. However, we discovered something alarming was happening to our young salmon before they even made it to the saltwater. Initial results suggested that around half of our smolts were dying during their downstream migration, before they even reached the sea. This was the first time we had any idea that in-river losses could be this significant.

Whilst these results were concerning, we were encouraged to know that we had begun to build strong evidence that could guide focussed and effective solutions to the problems facing wild salmon. As we planned our second study year, we sought to repeat our work from Year 1 to make sure this loss rate wasn’t an anomaly.

We found that half of our young salmon were dying before they even made it to the sea…

Year 2 – 2021: What next?

After being forced to put our plans on hold due to the COVID-19 pandemic in 2020, year two of the Moray Firth Tracking Project was conducted in spring 2021, designed to focus in on identifying the causes, or suspects, of smolt loss that we discovered in the first year. We looked for year-to year variation on how smolts migrate downriver, through our estuaries and out into the Moray Firth, homing in on areas of high mortality.

In year two our teams tagged 761 salmon smolts at 8 sites and deployed 245 receivers.
The results of our second year found that the number of smolts surviving their downstream journey and making it to the sea was similar to that of 2019, with 51% of smolts recorded
leaving the river mouths and 34% being detected on the Spey Bay-Brora marine array. When smolts reached the marine environment, they displayed a greater range of distribution in the Moray Firth compared to 2019, when a predominantly southerly clustering was observed. Importantly though, to start to focus in on the suspects for smolt mortality and how we can begin to develop management actions to combat them, 2021 saw us install a higher concentration of in-river receivers, enabling rivers to begin to identify exactly how and where our smolts were going missing.

Watch our short film which documented the groundbreaking work carried out in Spring 2021 for Year 2 of the Moray Firth Tracking Project.

A key finding from year two was the identification of our prime suspect – the in-river ‘pinch point’. Our results started to show that sections of river with blockages to migration pathways, such as dams, weirs and canalised areas, could delay migration by physically holding back smolts and inducing behavioural changes. Pinch points can also come in the form of areas of low flow due to abstraction or low rainfall, or excessive sedimentation which causes a shallowing or slowing of the river. Importantly too, the pinch points appeared to be upsetting the natural predator/prey balance. Could predatory species which feed on young salmon be gaining an unnatural advantage from the human-made changes to our rivers?

Year 3 – 2022:

Prime Suspect Identified – Pinch Points

The aim of year three, our 2022 study year, was to further investigate the causes of smolt loss throughout the freshwater environment, with greater focus on the human-made pinch points and the effects of predation in some of these zones. We concentrated our pinch point identification efforts in four rivers: the Oykel, Ness, Spey and Deveron.

In addition to our in-river receivers, and to begin to take an even closer look at predator interactions, further receivers were deployed within two grid arrays in a loch within the Oykel catchment and Loch Oich in the Ness catchment, as part of piscivorous predator behaviour studies. This study will compare the effects of trout and pike predation in a natural, unimpeded loch (Oykel catchment) with a loch that features a hydro dam, a lock system and then a canal system (Loch Oich). These receiver grids will enable us to accurately track predatory fish movements, simultaneously with smolt movements through the two lochs. This study includes the use of ‘predator tags’ which change ‘ping’ frequency if the smolt is consumed by a predator. As part of the predator behaviour studies large trout and pike have been tagged with acoustic transmitters to monitor their movements.

Ness Catchment Predator eDNA Project

Collecting an eDNA sample from cormorant scat

Environmental DNA, or eDNA, originates from cellular material shed by organisms into the environment and we have developed our own project using eDNA collection and analysis to deepen our understanding of the effects of predation on migrating salmon smolts. After the success of a ‘proof of concept’ trial in 2021, this year we launched a full study in the Ness catchment where the Moray Firth Tracking Project had identified considerable smolt losses.

The aims of our eDNA project are:
• To learn which predatory birds and mammals are feeding on smolts throughout the catchment.
• To understand predator diets before, during and after the smolt run.
• To measure the proportion of salmonids to other prey species in scat samples.
• To find out if a number of individuals are eating smolts, or if certain individuals are ‘smolt specialists’.

We employed a seasonal sampler from February to June 2022 to collect scat samples, of which nearly 500 were collected. These samples came from species including goosander, cormorant, mink and otter and have been sent to University College Dublin for analysis. This data will enable us to understand which predators our smolts are encountering and the locations where most of this predation takes place. As ever, our efforts are focussed on providing evidence-based science to generate meaningful management recommendations for salmon managers everywhere.

Credit: Richard Davies

Why we need this information 

We need sound, science-based solutions to make a real, impactful change for this iconic species. Our mission is to influence policy change for the better protection of wild fish by providing this science and ensuring it reaches policymakers. Through this work, we are making important discoveries about how our fish migrate out to sea, whilst identifying the risks that they face along the way.

What happens next?

Our scientific work will be fully analysed by our team of researchers and then, importantly, it will go through the peer review process before the final findings and conclusions are published. In the meantime, the preliminary results will form the basis of management recommendations which will be communicated to fishery managers.

Support our salmon

To continue this vital work, we need your support. Your donations will go towards solving the mystery of our missing salmon, and will help to secure a sustainable future for this remarkable species.

Make your donation here.

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