Queen Mary University of London shows the benefits of a classic chalk river plant, the water crowfoot (Ranunculus)
The plant Ranunculus is an aquatic member of the buttercup family and is often found in clean gravelly lowland watercourses such as chalk rivers. Water crowfoot is particularly vulnerable to low water flows, pollution and physical loss from leisure activities, weed cutting and swan grazing.
Dr Jessica Marsh’s research at the Game and Wildlife Conservation Trust (GWCT) shows that a high coverage of water crowfoot is associated with more and better-growing young salmon. With salmon populations declining, Dr Marsh’s findings recommend a solution: restoring high coverage of water crowfoot at least in lowland salmon rivers to tackle the depletion of this magnificent fish.
Jessica explained: “The populations of wild Atlantic salmon are in decline throughout most of their range, and the rivers of southern England are no exception. Brown trout are also declining due to predation, habitat degradation, pollution and warming water temperatures.
“It’s therefore important to ensure that young fish have the best possible habitats in which to grow and thrive. Our research identified that instream aquatic vegetation has benefits for juvenile salmon and to a lesser extent, trout, and demonstrates that river restoration aims for lowland rivers might be achieved through the promotion and even enhancement of naturally occurring Ranunculus beds to improve the production of both young salmon and trout.”
Jessica’s experiment took place in the River Frome in Dorset where water crowfoot plants were physically redistributed to make areas of low, medium and high plant cover. Over two years of monitoring, these sites were investigated for the effects of water crowfoot cover on the abundance, growth rates, feeding opportunities and competition between salmon and trout.
Across three published scientific papers, Jessica has revealed how young salmon and trout benefit directly from the physical shelter that water crowfoot provides, as well as indirectly through enhancement of prey provision and in depth and flow.
Previous GWCT research has suggested that larger salmon smolts or young salmon or trout moving from freshwater to the sea – are more likely to survive their Atlantic migration and return to breed. The river habitat and resources in the fishes’ first summer are important to achieve good body condition and size, with Jessica’s research finding that water crowfoot abundance influences these outcomes.
Dr Rasmus Lauridsen, Head of Fisheries Research at GWCT and supervisor of the study said: “Wild salmon populations have declined dramatically, in some areas by as much as 70 – 80% in the last 30 years. The GWCT has been monitoring salmon numbers in the River Frome, at our Salmon & Trout Research Centre since 1973, creating one of the most comprehensive records of salmon movement and survival in England and Wales.
“As a wildlife conservation organisation with an internationally recognised research centre for salmon and trout, we strive to support research that is both scientifically robust and has practical applications. Dr Marsh’s study illustrates how habitat quality impacts production of juvenile salmon and trout and the findings have clear management applications for river restoration techniques in lowland rivers.”
Professor John Iwan Jones, Head of the River Communities Group at Queen Mary University of London and supervisor of the study, said: “This research has shown that by promoting the naturally occurring Ranunculus beds that are so characteristic of our lowland rivers we can improve conditions for other threatened species, such as salmon and trout. Lowland chalk streams suffer from many pressures: this work has implications for how best to restore these important rivers and the species that live in them”.