Scale of Scotland's fragmented rivers revealed in Europe-wide study published in Nature

Work by researchers from the Inverness College UHI Rivers and Lochs Institute (RLI) on the fragmentation of Scottish rivers forms part of a study published in this week’s world leading science journal, Nature.

The study, one of the outputs of the European collaborative AMBER (Adaptive Management and Barriers in European Rivers) project, shows European rivers are impacted by more than 1.2 million in-stream barriers and fragmentation in all countries is much higher than expected.

Professor Eric Verspoor, of the RLI based at Inverness College UHI, part of the University of the Highlands and Islands, said: “This study, in which the Scottish component was delivered by the RLI, provides a stark pan-European account of the massive numbers of barriers in Europe’s rivers, including many in Scotland, whose negative impacts on riverine ecology we are only now starting to fully appreciate and mitigate.”

The study found that even Scotland’s relatively pristine river ecosystems are more fragmented by barriers such as dams and weirs than previously believed. Although all major barriers are captured by the existing database curated by the Scottish Environmental Protection Agency, there are still areas within Scotland where knowledge is incomplete, as highlighted by the study.

Barriers, in many cases, can be expected to have significant negative impacts on their fish communities, and especially on the abundance of migratory species like the Atlantic salmon, sea trout and eels. They have historically been constructed to provide energy, water, fishing, access and leisure opportunities, but can also pose potential flood hazards and change freshwater habitats, including impeding or blocking the migration of fish, and changing natural pattens of biodiversity, posing challenges for ecologically sound, sustainable river management.

As part of the broader AMBER project, the RLI team worked in partnership with the Ness District Salmon Fisheries Board and Scottish and Southern Energy to contribute to addressing this challenge, extending work conducted as part of the Upper Garry Salmon Restoration Project on the River Ness. This focused on using new ways of monitoring the impacts of river fragmentation on river biodiversity arising from the presence of hydro dams and Caledonian Canal water diversion weirs and its tributaries, combining areal drone photography and biodiversity assessments based on environmental DNA (eDNA).

Dr Lucio Marcello, of the RLI, explained: “Man-made barriers in rivers are known to often contribute, along with other factors, to the reduced number of salmon produced in Scottish rivers such as the Ness, particularly in upper tributaries such as the River Garry, where hydro dams have resulted in the loss of 36% of previously accessible salmon habitat, hindering fish passage and flooding river stretches.

“This makes it important to work to mitigate such barrier impacts, while taking into account the positive benefits that barriers provide such as hydropower and boat navigation. By more clearly understanding barrier impacts on river ecosystems, we can identify possible ways to deal with existing barrier installations, such as building effective fish ladders, reducing reservoir size behind dams, or by alternative approaches to providing socio-economic benefits.”

The RLI researchers worked with researchers across Europe to collate regional, national, and global datasets to assess the number of individual barriers on rivers to create the first ever comprehensive pan-European barrier inventory - the AMBER Barrier Atlas. More than 2700km of rivers were surveyed across 36 European countries. The lowest barrier densities were recorded in Scotland, Scandinavia and Iceland, with Central Europe showing the highest barrier density.

This research will help inform the implementation actions to restore rivers in Scotland to good ecological status and inform the develop of freshwater management policies, including the EU Biodiversity Strategy, which aims to reconnect at least 25,000km of Europe’s rivers by 2030.

For a broader description of the AMBER research programme, visit: https://amber.international/let-it-flow/ and https://amber.international/magazine/. 

News and Views: Nature, published 16th December

Find out more about the Ness case study