Annual Salmon Count Shows Lowest Number of Juveniles for More Than 20 Years

The annual counting and tagging of juvenile wild Atlantic salmon on the River Frome in Dorset have yielded the lowest number of fish in more than 20 years of monitoring, which is hugely concerning for the scientists running the project.

It follows the recording of the lowest ever number of adults returning from sea to spawn last year – further confirming the continued steep decline of salmon in our rivers.

Numbers of wild Atlantic salmon in our rivers have crashed by some 80% over the past 40 years. Rivers which had tens of thousands of salmon in the 1980s now only have a few hundred in them. They are now classified as endangered in the UK and on the IUCN Red list along with other threatened species like elephants, pandas and polar bears.

In a bid to try to identify what is causing this and what can be done to reverse it, MSA member, the Game & Wildlife Conservation Trust’s (GWCT) Fish Research team spend four weeks in late summer in the river catching, weighing, measuring and micro-chipping the juvenile salmon, known as parr, that have hatched in the spring.

Based at the River Lab near Wareham, they head out every morning to a different section of the river Frome, trying to cover as much of the juvenile salmon habitat within the 35-mile-long river as possible.

The aim every year is to tag 10,000 salmon parr, but this year the team did not even manage to catch half of that – only 3,813 salmon were caught and tagged.

GWCT fisheries Senior Research Assistant Will Beaumont is leading the Fieldwork work, which took place between 22 August and 20 September and forms part of a ‘Core Salmon Rivers’ research programme in partnership with the Atlantic Salmon Trust and the Missing Salmon Alliance.

He says: “We have failed to hit 10,000 parr in the past on several occasions, but usually it’s not this far off. This year has been the worst we’ve ever had.”

“Why that is, is hard to say. Water levels are high, which made it hard to fish some sections, and the rain and floods during the winter are likely to have affected egg survival. We will be going through our data to try to identify the cause, but we don’t know yet.

“But the fact remains that salmon is such a fast-declining fish, that finding so few parr this year is concerning. We have seen this downward trend for years, but this is a record low.”

Image: Game & Wildlife Conservation Trust

Fifty years of data

Dr Sophie Elliott, GWCT Senior Fisheries Scientist who analyses the data, says: “In 2023 an estimated 443 salmon returned to the river to spawn, compared to over 2,500 a year in the 1980’s. This year’s parr are the surviving offspring of those 2023 adult salmon which will help explain the very low numbers of parr.”

To try to identify what is causing the continuing decline in wild Atlantic salmon, the GWCT’s Fish Research Centre has been studying the health and lifecycle of this iconic species since 1973 and therefore have data going back more than 50 years, making the Frome monitoring programme one of the longest running and most comprehensive of its kind in Europe. Since 2005 they have caught and tagged salmon parr every autumn and are using this data to try to find solutions to help fish populations recover.

The team not only catch and tag the juveniles in the autumn, but each surviving individual salmon is then recorded by tag readers and fish traps in the river as they migrate out to sea the following spring as ‘smolts’. When the survivors return to the river after having spent a year or two feeding in the North Atlantic, the survivors are again recorded as they pass the readers in the river.

By monitoring both smolts leaving the river and adults returning the scientists can separately estimate freshwater production and marine mortality and therefore separate the effect of events happening at sea and in rivers that affect the population.

Causes for the decline

A number of factors are behind the decline of wild Atlantic salmon in our rivers, with some the biggest problems being run-off from agricultural land and climate change causing warming seas and rivers.

Dylan Roberts, GWCT’s Head of Fisheries, says: “We know that excessive sediment in rivers caused by run-off from agricultural land reduces the survival of salmon and trout eggs and the Frome has a lot of sediment in the gravel.

“There has been huge expansion in the past 20 years of growing maize as biofuel, after the introduction of government grants for this. It is also grown to feed the expanding dairy herds that are kept indoors for part of or the whole year. Maize is harvested in late autumn, leaving the fields brown over winter and when exposed to heavy rain the dirty water runs straight into the river.

“Nitrogen and phosphorus, along with similar nutrients from sewage treatment discharge and septic tanks end up in the water. This causes excessive growth of algae which suffocates the riverbed, shades and reduces the growth of plants, like water crowfoot, that provide crucial habitats for juvenile salmon and the insects they feed on.

“While there are ways in which we can help salmon in our rivers, such as cleaning the gravel and cutting back the vegetation to encourage the river plants to grow, this needs to happen on a whole catchment-wide scale. Working together with farmers, which is what the GWCT are doing, is key to achieving this.”

Sophie Elliott further adds: “It is much harder to help salmon at sea given their long migration to Icelandic waters and the poor recording of salmon as bycatch. Here we need a change in policy to recognise wild Atlantic salmon as a marine, as well as freshwater species, and give them more protection not only in their natal rivers, but through estuaries where mortality is high, and during their marine migration for which they can stay out at sea for up to four years.”

The GWCT is currently running a Save Our Salmon Appeal in a bid to raise £20,000 desperately needed for our Fish Research Centre and their vital monitoring work, which is largely privately funded whereas other monitored salmon rivers are publicly funded

Much of the centre’s equipment needs replacing and PIT (passive integrated transponder) tags used to tag parr need to be purchased. This money would enable us fit even more fish with tags, fund crucial equipment such as an electro-fishing generator and help us to further study the fish and the impact conservation measures, such as gravel cleaning, has on populations. Only then can we better understand how these fish migrate up and downstream, the challenges they face, and how best to help them.

Salmonid electrofishing and parr tagging – how it is done:

Every August/September the GWCT Fish Research Centre team set out to capture and tag 10,000 juvenile salmon and 3,000 brown trout.

Fisheries scientists, volunteers and students make up two teams of six or seven and head out daily for four weeks to cover most of the River Frome, fishing sections at a time. The tagging work is undertaken in a mobile riverbank laboratory.

At least three people get in the river and walk upstream in waders with a metal loop (called an anode) which is moved through the water to create a slight electric current in the water to slow the fish’s movement to be able to capture them.

The fish are then put in a bucket and handed over to the lab team on the riverbank to be weighed, measured, anesthetised and tagged with microchips - PIT tags (passive integrated transponder) which is what a vet will use in cats and dogs. A few scales are also taken to help age and undertake genetic analysis on the fish.

After recovering in a bucket of oxygenated water the fish are returned unharmed to the same 100m section of the river from where they were caught.