Working together along our rivers to save our salmon
By Eleanor Williams, Game & Wildlife Conservation Trust
The rivers and waterways of Britain are the veins and arteries of our rural landscape, and the species that inhabit them are crucial to the riverine ecosystem. As spring turns into summer, a species of fish that has been inhabiting this unique underwater world for six million years begins its perilous 2,000-mile journey into the Atlantic.
Wild Atlantic Salmon hatch in our rivers in early spring and spend a year, or occasionally two, living here before starting their migration.
With numbers having declined sharply by some 80% over the past 40 years, wild Atlantic salmon is a species in crisis. It is classified as ‘endangered’ in the UK and on the IUCN Red list along with other threatened species like elephants, pandas and polar bears.
If the decline in salmon continues it could disappear from our UK rivers in the next 30 years.
In a bid to understand the health and lifecycle of wild Atlantic salmon, the sharp decline in numbers and what can be done to reverse it, the Game & Wildlife Conservation Trust’s (GWCT) fish research department closely monitors tracks the salmon population in the Frome.
The team, based at the River Lab near Wareham in Dorset, consists of scientists, ecologists and data experts. Our data goes back more than 50 years, making it the longest running and most comprehensive salmon monitoring project in the UK, perhaps even in Europe.
This process can be divided into the three main phases of work:
Parr tagging
During late summer each year, 10,000 juvenile salmon are caught using electro-fishing – where a current is sent through the water to incapacitate them - before they are netted, weighed, measured and tagged with microchips - PIT tags (passive integrated transponder) - by the fisheries research team, in partnership with CEFAS.
Teams of scientists and volunteers head out daily for four weeks to cover the entire stretch of the river, fishing sections at a time. The tagging work is done in a mobile riverbank laboratory set up next to where the team is fishing.
Two teams of 7 people, including students and volunteers, head out daily and students under supervision of our fisheries scientists.
Each fish is caught from a known 100m section then passed to the tagging team who operate the mobile river bank lab where they are anesthetised, tagged, have length and weight noted and finally a small scale sample taken before being returned to the same 100m section unharmed. To mark that they are tagged, part of a small fin is removed, which does not affect their survival or ability to swim.
Electro-fishing on the River Frome
Redd counts
In January the team walk along the river to check how many redds – nests for spawning - the salmon had been preparing in the gravel.
Salmon are finding this increasingly difficult to do find good spawning sites due to the sediment that builds up along the bottom and suffocates the eggs.
In 2025 the team counted just 41 redds – that figure is expected to be around four or five times higher.
Smolt Trap
During spring, from March and through to April, smolts - young salmon that have hatched the previous year are caught, weighed and measured as the pass the River Lab on their way out to sea. These will include some of parr that were PIT-tagged the previous summer (and others we missed). This will give us an idea of how many have survived the winter and how well they have grown.
We use a specially designed trap on the river which we check every 30 minutes, day and night for about two months.
Years of experience of both tag detections and running of this trap has shown that the bulk of the migration happens during the hours of darkness. Operating the trap when the smolts are moving means night-time work. As the GWCT Fisheries is a small department, we bring in volunteers to help with this project.
We always have two people working at night, one of which is a staff member who holds the correct Home Office certification and experience, and one volunteer.
Most fish stop moving during dawn and dusk, presumably to avoid first light and high activity of predators such as pike, but some also move during the day.
The later in the season it gets, we might see more fish moving during the day as they feel it’s warming up and they need to ‘get a move on’ and not miss the opportunity to head out to sea.
The trap is checked very half hour and all fish are then taken inside a nearby building for processing, when biometric data is taken from each fish. Afterward they are released further downstream to continue their migration.
This entire monitoring process helps us follow the salmon in the Frome through their lives through a system of tag readers in the river that detect the young fish as they leave in spring for their 2,000-mile return journey to the North Atlantic and the numbers that return after one to three years at sea.
It also enables us to measure how many of the juveniles in the river that make it to sea, and how many return to their native river to spawn.
Issues for salmon
Our research tells us that much of the problem lies at sea, with declining marine survival and growth rates. However, we believe that some of the issues for salmon at sea begin in the river and two significant problems are declining water quality and physical habitat - together these are producing juvenile salmon which are less fit to survive in the ocean.
The main problems for salmon are:
Run-off from agricultural land, causing excessive sediment
Climate change causing warming seas and rivers
Nitrogen and phosphorus, along with similar nutrients from sewage treatment discharge and septic tanks that cause excessive growth of algae which ‘suffocates’ the river bed, shades and reduces the growth of plants, like water crowfoot, that provide crucial habitats for juvenile salmon and the insects they feed on
By-catch at sea (poor recording of and little protection from)
Declining marine survival and growth rate at sea
Working together on a catchment scale
To tackle these problems and improve river conditions for salmon we need to work together.
The GWCT works with farmers and private land managers on a landscape scale, and by bringing them and other stakeholders along the river together, we are starting to take steps in the right direction.
Dylan Roberts, GWCT Head of Fisheries, said:
“If you go back to the early and mid-19th century, salmon were so abundant that they were harvested in their hundreds of thousands, excess was fed to pigs and used as fertilizer on the land. Staff at country estates insisted that it was written into their contracts that they should only be fed wild salmon four times a week. But what has happened?
“Having monitored and researched the population of wild Atlantic salmon in the river Frome in Dorset for many years, we have seen first-hand the changes to the physical nature of the river. In recent years, we have seen a huge growth of algae between spring and autumn which smothers the riverbed, shades and then reduces the growth of plants like water crowfoot, which are crucial habitats for juvenile salmon and the insects upon which they feed.
“Excessive algae, also reduces the amount of oxygen available to fish in rivers at night and especially during the warmer months, this can stress, reduce the growth of and even kill fish. The algae grows excessively due to high levels of nutrients - nitrate and phosphate which are released into rivers from sewage and septic tank discharges and running off agricultural land.
“Our published research shows that where water plants are abundant, we find more juvenile salmon and also larger juvenile salmon. Being larger is crucial to increase their chance of survival at sea, where our research also tells us that the larger juvenile salmon when entering the sea are three times more likely to return as adults. So juvenile salmon in the Frome need the river full of clean water and healthy plants.
“The GWCT’s farmer cluster approach and the Environmental Farmers Group (EFG) are great ways of bringing together all those of farm and work along the river to address this issue.
“Rivers are the spawning and nursery areas for our wild Atlantic salmon, they need clean gravel to spawn and diverse physical habitats, and in the case of a lowland rivers like the Frome this means abundant aquatic plants.
“If we work together, and all make an effort to reduce run-off and implement mitigating measures such as protecting river banks from heavy grazing, we might yet stand a chance of saving our wild salmon.”