The amount of young salmon leaving the River Frome is the highest in eight years, with numbers up by 40 per cent in 2020 on the 10-year average.

However, the Fisheries Research Review from the Game and Wildlife Conservation Trust (GWCT), which detailed the numbers, also warned that climate change is having an impact on them.

According to the latest figures, an estimated 13,062 salmon smolts left the River Frome, showing signs of hope for their long-term future in Dorset’s River Frome.

Time will tell how many of these fish return to the river from the North Atlantic in 2021 and 2022, but experts say signs are as positive as they have been for some time.

Rasmus Lauridsen, head of GWCT Fisheries Research, said: “As well as the high number of smolts (young salmon heading off on their marine journey) leaving the river, it’s encouraging that they were larger than average too, making them better equipped for life at sea.”

Previous research by the GWCT has shown that larger smolts are more than three times more likely to return from the sea than smaller ones, so it is hoped there will be more adult salmon passing through the Wareham-based monitoring station on their return.

He added: “The past three years have seen below-average numbers of adult salmon returning to the Frome, although our monitoring in 2020 showed a surprisingly good number of the smolts leaving in 2018 returning, having spent two years at sea.”

However, further research says a combination of warm winters and cool springs has negatively impacted juvenile salmon in the mainly groundwater-fed river.

This builds on previous GWCT research on the predominantly rainwater-fed rivers of Wales where similar impacts of temperature highlighted how freshwater conditions in contrasting river-types can significantly affect population dynamics.

These insights will be pivotal in planning future conservation measures, with the GWCT, one of the founder members of the Missing Salmon Alliance, a group of organisations fighting to reverse the devastating collapse in wild Atlantic salmon around the UK.

The review can be downloaded for free at www.gwct.org.uk/fisheriesreport.