by Dr Dan Osmond

You might expect the disappearance of an endangered species to be marked with public outcry, the fear of irrevocable loss, the richness of our environment diminished.

Yet there is a species dangerously close to quietly disappearing in the Westcountry – the Atlantic salmon (Salmo salar).

A fundamental component of the rivers of southwest England, this species has been intertwined with the history and culture of the region for millennia; from Roman fisheries in Exeter to the works of the poet laureate, Ted Hughes, who was one of Westcountry Rivers Trust’s first trustees.

Recent reports suggest that salmon populations in southwest England continue to decline, with the Atlantic salmon placed on the IUCN red list in 2023 as Endangered in Great Britain. The Atlantic salmon is already extinct across much of their historic range in Europe, including Germany and the Netherlands, with the loss of local populations across much of Southern Europe.

Could this also be the fate of Westcountry salmon?

An Atlantic salmon in the River Exe. Photo credit: Charles Fleming

After the last Ice Age, salmon recolonised the newly glacier-free river landscapes across Northern Europe from refuge populations in southern Europe (Finnegan et al., 2013).

In the intervening years, these individual populations have evolved to locally adapt to their environment, with genetically distinct populations living within different rivers (Gilbey et al., 2016).

As a result, analysis has suggested that in populations that have previously been stocked with salmon from other rivers, the higher fitness of the native fish results in low levels of contribution from these stocking events (Finnegan and Stevens, 2008). Crucially, this emphasises the importance of maintaining these locally adapted populations within south west England, as they represent those most likely to succeed in their wild environments.

Returning numbers of adult salmon continue to decline over many rivers across the south west of England, posing the concern that the loss of local populations might be the endpoint of current trajectories. These long-term trends are however complex, with annual weather events and other factors affecting annual recruitment that produce deviation from a long-term pattern.

Environment agency catch stats

Despite this, catch statistics released by the Environment Agency (EA) suggest a trend n continual decline in rod catch, with the lowest reported numbers on record in 2023, with 5,188 across England and Wales. Rod catch data is notoriously fickle, with many factors in addition to the total number of running fish, such as fishing effort, affecting the result.

Despite this, the downward trend is mirrored by fish counter data in rivers where this is available, with an estimated total run of less than 60 salmon in the whole of the Dart in 2023 (Pudwell, 2024). Stock estimates from the EA monitoring at Gunnislake are ongoing, however the initial data suggests lower numbers of returning adult salmon in 2024 compared to 2023, with this prior figure being the second lowest in records for the river.

The low summer flows of 2022 produced conditions unfavourable for the upstream migration of returning adult salmon from the sea, with widespread low fry numbers observed in the summer of 2023 attributed to this limited spawning.

However, 2023 had the sixth wettest July on record and higher-than-average summer rainfall in southwest England. This is more helpful for the migration of adult salmon, particularly in the rain-fed rivers of the Westcountry.

Electrofishing data

Understanding trends across the Westcountry from our electrofishing data is an equally complex picture, given the number of different unique rivers surveyed each year.

What is apparent however is a generally better picture of salmon fry abundance and less restricted presence in 2024 compared to the poor numbers typically observed in 2023.

For example, on the River Teign, we have seen excellent salmon fry numbers on two sites of the South Teign where they were absent in 2023. We have also seen improved results compared to this previous year on many sites of the main Teign. This is encouraging, but it should be seen in the context of a general trend of broad declines across the Westcountry.

Figure 1. Stacked bar chart of individual site classifications for Atlantic salmon fry across the Teign catchment, 2012 – 2024. Data from WRT 5-minute semi-quantitative fry surveys.

Determining the reasons for these declines is notoriously difficult, with multiple stressors impacting  different life stages and difficult to disentangle.

Within England and Wales, scientific consensus suggests that the three most important factors driving declines locally within the freshwater environment are: barriers to migration, excessive nutrient input into freshwaters and the physical modification of lotic systems (Lennox et al., 2021), although other factors also contribute locally and regionally.

Barriers to migration

Across Europe, there is a barrier to migration an estimated average of every 1.3km (Belletti et al., 2020).

While many of these locally are not totally impassable, the cumulative impact builds: if 10% of fish fail to pass each barrier, over 10 barriers only 35% of the total population passes upstream to spawning habitat.

In addition, such barriers create artificial hotspots for predation, with delays to downstream migrating smolts in particular leaving them more vulnerable to a higher risk of predation at these sites (Mensinger et al., 2024).

Even for species that do not need access to the sea to complete their life history, barriers fragment populations and leave them vulnerable, as has been observed in brown trout (Salmo trutta) (Osmond et al., 2024). In southwest England, many of these weirs and dams were historically created for milling and other industrial purposes, and are now largely redundant. These concerns are not new, some of the earliest legislation passed to limit the damage caused by barriers is written into the Magna Carta in 1215, yet as populations decline further, limiting these losses is all the more vital.

Westcountry Rivers Trust has been dedicated to improving access for fish migration since our formation 30 years ago. In most cases, the removal of barriers entirely provides the least expensive option with the greatest gains for fish migration and wider restoration of natural river system functioning.

Keybridge Weir where work has been undertaken to support migratory fish

In recent years, we have partnered with the EU-funded Water For Growth program to remove Grogley and Keybridge weirs in the Camel catchment. We are now working towards the delivery of removing another major barrier, Dunmere Weir, in 2025.

In some scenarios, removing barriers is unfeasible, due to infrastructure constructed around these with an ongoing purpose. In these cases, we have worked to deliver fish passage solutions, such as the construction of rock ramps as seen at Head Weir on the River Mole, in the Taw catchment.

In this case, migratory shad has been observed to be passing upstream in recent years. They have faced large declines in distribution due to poor ability to pass barriers. Despite these gains in habitat availability for migratory fish, many barriers remain and we are actively seeking opportunities for improvement, such as through our Strategic Exe Weirs and Strategic Teign Barriers projects.

Water Pollution

Pollution has become an increasingly live issue in public perception of our rivers, with increasing scrutiny placed on the practice of combined sewer overflows (CSOs).

This is an issue that is particularly relevant in south west England, with Cornwall having the highest number of pollution incidents recorded in England.

This effluent is problematic for our rivers primarily due to the excessive nutrients that it contributes, leading to eutrophication that strips essential oxygen out of the water. At best, this limits the diversity of aquatic life that salmon feed and are dependent on, at worst this can cause acute fish-kill events.

Though less apparent than the point sources of pollution from CSOs, agriculture is a higher contributor to pollution than water industry sources in England, particularly within the Westcountry (The Rivers Trust, 2024).

Soil health

Run-off of fertilisers applied to crops, improper storage of slurry from cattle, and farming on sensitive soils are all sources of this pollution, with rivers paying the price for poor land management. A report from the EA in 2022 suggested that two-thirds of cattle farms in north Devon were actively polluting rivers (McKay, 2022).

An additional risk to fish populations from land management is soil erosion. As with nutrients, agriculture is also a major contributor to the sediment pollution in rivers.

Dairy farming has historically been a major driver of this sedimentation in south west England, due to cattle eroding banksides and accessing rivers (Wilson and Everard, 2018).

More recently, maize production has increased dramatically, with grave consequences for the health of our rivers. Data from the Soil Association show an increase in growth of this crop across the UK from 8000 hectares in 1973 to 183,000 hectares in 2014, with farming groups continuing to lobby for the expansion of this highly profitable crop (Farnworth and Melchett, 2015).

Maize poses a high risk of soil erosion, due to the late cropping season leaving soils bare over peak rainfall periods in winter and heavy machinery at these times increasing soil compaction and thereby run-off.

Choking rivers

While this soil erosion might sound somewhat benign, the input of sediment into rivers chokes life-giving oxygenating flows in gravels, killing developing fish eggs and reducing the biodiversity of sensitive aquatic insects. Within many of the rivers impacted by this soil erosion, our electrofishing surveys show previously productive habitats to support few, if any juvenile salmon.

Volunteers in Par collecting water samples

Westcountry Rivers Trust has been working to better understand this pollution through our Westcountry Citizen Science Investigations program, to allow us to understand the level of threat and potential sources.

We also deploy continuous sensors and carry out point monitoring at strategic locations. At a practical level, our experienced farm advisors actively assist farmers through projects to enable practices that lead to less costly loss of nutrients and farm run-off.

Our Upstreaming Thinking program has enabled us to work with farmers across Cornwall and Devon to incentivise land management practices that reduce and mitigate these pressures on our rivers. These include initiatives to fence rivers away from cattle access and create wide riparian buffers, identify sources of pollution, and work with farms in grant-funded infrastructure improvements to address these sources and provide soil-specific management plans and other advice.

We have also worked with landowners to trial under-sowing strategies with maize, to provide a winter cover crop during the vulnerable wet season. The reality of the situation is however sobering; many of our rivers continue to fail to meet ecological and chemical targets due to land use.

Achieving improvement requires cooperation from all.

Physical modification

Across millennia, we have physically altered the paths and hydrological dynamics of our river systems.

This modification includes the drainage and disconnection of rivers from their floodplains, straightening and dredging from their naturally meandering paths and entombing water in featureless concrete channels. .

Physical modification can have several negative impacts on fish populations. . These include the loss of habitat to support diverse ecosystems, leaving ecology less resilient to environmental stress (such as water pollution or climate change) and lacking the physical characteristics to give suitable habitat to different life stages of migratory fish – such as deep pools and refuge habitat for adult fish, and the coarse gravel riffles required for juveniles.

Restoration of physical habitat is vital, particularly for the juvenile in-river living stages of salmon.

Previous studies have shown that higher quality and complexity habitat supports both increased numbers of juvenile salmon and also increases growth rates (Marsh et al., 2022).

Westcountry Rivers Trust has been actively improving river habitat across our catchments through several projects to bolster freshwater ecosystems.  Reversing these physical changes to our rivers to restore them to biodiverse functioning ecosystems sometimes requires an appreciation of that which is beyond human memory and our shifting baselines.

Reconnection

One such area is the natural course and shape of rivers. Reconnection of rivers with their floodplains helps to alleviate peak spate flows, filter pollutants from the water and create more ecologically favourable hydrological conditions.

Our charity has been involved in many projects to deliver wetland scrapes, slowing water flows and reconnecting rivers with their floodplains, such as the river Fal in Cornwall.

Beavers

One promising development in the restoration of modified ecosystems is the reintroduction of European beavers to some of our rivers.

These ecosystem engineers offer radical landscape-scale restoration of functions they would naturally have played within our river systems, through wetland creation.

We are working with local organisations to understand more the impact this reintroduced species can have on our rivers and the risks and benefits they might have for our migratory fish.

Climate Change induced pressures

Anthropogenic climate change is a worldwide concern for the balance of many of our ecosystems, as the rate of change and potential to pass earth-system tipping points leaves species unable to adapt to these rapid changes.

Within south west England, changes to our climate are producing wetter, milder winters and warmer drier summers.

Amongst this trend, the likelihood of previously extreme weather events will increase, resulting in summer drought heat stress events and winter flooding becoming more frequent (Met Office, 2022).

This has relevance to salmon populations, as water temperatures are regularly reaching the upper thermal limit of salmonid growth during the summer, reducing growth and, in extreme cases, may cause mortality.

Additionally, higher water temperatures in winter result in the early emergence of fry and lower survival rates of these developing juveniles (Jonsson and Jonsson, 2009). Across the native range of salmon populations, spawning time depends on local adaptation and temperature experienced, suggesting some plasticity to acclimate to changing winter temperatures.

Further research has demonstrated adaptation to warmer climates between populations of other salmonids (Chen et al., 2018) and has suggested that exposure to warmer temperatures as a developing egg confers higher heat-stress tolerance later in life (Warriner et al., 2020).

Resilience

This offers hope of resilience within this species, which has historically persisted through large environmental changes, through maintenance of diversity and alleviating other stressors is required to enable the possibility of adaptation.

During warm summer periods, salmonids have been shown to seek out cooler oxygenated refuges within rivers (Jonsson, 2023).

Enabling this thermal refuging requires open connected river systems where fish can migrate to cooler tributaries and deeper pools, emphasising the importance of previously mentioned projects to remove barriers to migration.

River restoration strategies have been demonstrated to buffer temperature increase risk to salmon populations. Complex heterogeneous habitats and reducing over-widening from bank instability have been shown to limit water temperature increases (Justice et al., 2017), while restoration of native riparian woodland cover can offer cooling effects for rivers (Thomas et al., 2015).

Westcountry Rivers Trust has been active in projects to restore trees to our riversides for the benefits that they give in habitat creation and buffering climate impact. These include the Water for Woodlands project, where we have supported the creation of woodland along the river Deer in the Tamar headwaters, and pocket planting of native trees to the headwaters of the Barle this winter through the Natural England Species Recovery project.

At Sea

Being an anadromous fish, the freshwater life of Atlantic salmon is only part of their story.

There is increasing evidence of the risks experienced by Atlantic salmon at sea. Marine survival rates are now typically an order of magnitude below their historic level, typically below 5% (Gillson et al., 2022) and most recently estimated at 4.19% for salmon of all age classes in the Tamar (Baycock et al., 2024).

Many threats affect this marine survival rate, from bycatch in commercial fisheries, disease from aquaculture, and shifting plankton and prey fish distribution with climate change.

Conservation of wild Atlantic salmon populations to reduce this marine mortality rate will require international cooperation and management beyond the scope of local intervention.

Smolt to Adult Supplementation

In the immediate term, we are exploring the viability of smolt to adult supplementation (SAS) schemes to increase the marine survival rate. This is a newly developing practice whereby smolts leaving rivers are captured and reared in a marine facility to be released as adults into rivers. This is a more direct intervention on populations than we have previously considered. It overcomes some of the limitations of traditional hatchery approaches as it still allows for natural selection and free mate choice in a wild environment, while directly addressing the unnaturally high at-sea mortality.

SAS will require close monitoring to understand the effects on populations and clearly defined targets of what purpose the intervention serves and when to exit this strategy. This is intended as a short-term support to the viability of populations. Only measures that directly address the drivers of increased mortality will provide long-term solutions.

Alongside this, the quality of smolts heading to sea, a function of the health of their river habitat, has a positive impact on the survival of salmon at sea (Gregory et al., 2019) – giving ecological restoration of freshwater habitats benefits beyond their in-river stages, highlighting the importance of creating healthy river ecosystems.

Looking ahead

Across our biosphere, species diversity and abundance are declining.

No group of animals has declined so rapidly within this as freshwater migratory fish (Deinet et al., 2020).

Understanding the multiple stressors responsible for these declines is complex. Atlantic salmon are exposed to different factors throughout their life history – from increased sediment load impacting in-gravel egg survival, barriers to migration increasing predation rates to emigrating smolts, and regime shifts in marine ecosystems impacting the growth and survival of adult fish at sea.

Exposed to such a range of environmental pressures across their life cycle, salmon represent not only an important species in their own right but also reflect a measure of the overall health of our aquatic ecosystems.

The current downward trajectory of salmon populations, representing a risk of local extinction for some populations, reveals a concerning picture of the state of our rivers.

Once common throughout our large rivers, the European sturgeon is now functionally extinct in the UK.

In the thinning of life, is the once prolific Atlantic salmon also fated to be a mere memory within our rivers?

History has demonstrated the resilience of Atlantic salmon, recolonising post-industrial rivers after improvements to water quality and after the removal of impassible barriers, showing that there is hope yet for wild Westcountry salmon.

Commitment

Westcountry Rivers Trust is committed to better quantifying and understanding risks to freshwater ecosystems. Our staff continue to be the boots on the ground and waders in the water for the region’s freshwater environments, enabling the most appropriate evidence-led interventions.

This crisis point for our salmon populations highlights the scale and pace of action now required.

Westcountry Rivers Trust remains ready to keep bringing rivers to life for all who depend on them.

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