Salmon populations in the River Frome, Dorset, have reached their lowest levels in 40 years, according to the Game and Wildlife Conservation Trust (GWCT).

Last year, GWCT researchers tagged and measured approximately 10,000 juvenile salmon before they migrated to sea, but this year the count fell sharply, with fewer than 4,000 tagged.

This reflects what the trust describes as a “continued steep decline” in salmon numbers in UK rivers.

Since 2005, GWCT has been monitoring salmon in the Frome, tagging juveniles each autumn as they mature in the river. These young salmon, or smolts, are recorded via tag readers and fish traps as they migrate to the North Atlantic in spring.

After feeding at sea for one or two years, survivors return to the river, where they’re recorded again as they swim past the monitoring stations.

GWCT data reveals a stark contrast between past and present return rates. In the 1970s and 80s, 15-20% of salmon would return as adults, but today this rate has dropped to just 4-5%.

In 2023, only 443 adult salmon returned to spawn in the River Frome, a significant drop from the 4,000 per year recorded in the 1980s.

Senior research assistant Will Beaumont described 2024’s results as “the worst we’ve ever had.”

“We have failed to hit 10,000 parr [juveniles] in the past on several occasions but usually it’s not this far off,” he continued.

Previous low counts, such as the 4,988 in 2016, were linked to winter warmth and spring droughts.

The trust points to multiple causes for the salmon’s decline, including agricultural runoff, climate-driven warmer seas and rivers, and nutrient pollution from sewage and septic systems, which all degrade river habitats essential for the salmon’s lifecycle.

Dylan Roberts, GWCT’s head of fisheries, said: “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.”

He highlighted the effect nutrients from sewage treatment discharge and septic tanks can have on river 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,” he continued.

 

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