DECLINES in adult salmon on the River Frome in Dorset witnessed in recent years show no sign of subsiding, according to the latest figures in a fisheries report.

Leading UK conservation science charity the Game & Wildlife Conservation Trust (GWCT) carries out all its research into salmon on the River Frome - which runs through Evershot and Maiden Newton - near Wareham. Their latest Fisheries Research Review, published this week, shows that a low number of adult fish returned to the river last year. It was hoped that a good number of smolts - young salmon leaving the river for their marine journey - in 2018 would boost these numbers, but far fewer returned to the river than expected.

One factor that might have contributed to this is size, with smolts leaving the river for the sea at Poole harbour in 2018 being the smallest ever recorded by the Trust – four per cent smaller than the 10-year average. 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. The low number of smolts that left the river in 2017 will also have had an impact.

Fisheries ecologists are working to understand the declines. Despite the impact of Covid-19, the fisheries team enlisted their families to ensure that the River Frome was perhaps the only river in Britain to have full monitoring through lockdown. This dedication avoids a two-year gap in the data, as this year’s smolt will be monitored when they return as adults over the next two years.

Much of this work is part of SAMARCH, a multi-million-pound project that will provide evidence to strengthen the management and protection of salmon and sea trout at sea over five years (2017 to 2022).

David Mayhew, chairman of GWCT fisheries research steering committee, said: “Our fisheries team spent more time in the field last year than probably any other year in the last 10 years. Furthermore, two of our PhD students, Jessica Marsh and Jessica Picken, submitted their theses on the importance of instream vegetation for salmonids and the effect of low flows on salmonid ecosystems, respectively. A remarkable achievement.”

It is hoped that Jessica Marsh’s work will offer rare optimism for salmon numbers. She found that with increasing coverage of Ranunculus (the aquatic plant often known as water-crowfoot) not only did the density of salmon parr go up but so did their growth rate.

Rasmus Lauridsen, head of GWCT Fisheries Research, is encouraged by the findings: “This work illustrates how important juvenile freshwater habitat is”, he said. “It could provide us with a management tool to increase not only the production of juvenile salmon but also their growth rate in lowland rivers”

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

To support our fisheries research, visit www.gwct.org.uk/fishing/