Good quality in-stream and riverbank habitat plays a fundamental role in the health of our native fish populations. In recent years fisheries managers have placed a significant focus on ensuring that the environment on which the fish rely – aquatic and riparian – is optimal. In doing so, assessing the quality and quantity of in-stream and riverbank habitat is a key consideration.
Loss of riverbank vegetation
Native riverbank vegetation plays an important role in healthy aquatic ecosystems. Native vegetation maintains the structure and function of the watercourse and acts as a buffer to help filter nutrient and sediment input. Healthy native riparian vegetation helps to reduce stream erosion and maintain stable channels, as well as providing shade. Native vegetation will also support a range of terrestrial invertebrates which is an important component of the diet of juvenile Atlantic salmon.
Canalisation, dredging & boulder removal
Modifications to rivers have occurred over many decades to improve drainage of agricultural land and prevent flooding of fields. Such changes compromise the natural riverbed morphology and can have an impact on salmon production, due to lack of in-stream and riparian cover for fish and damage to spawning substrate.
Loss of sediment transfer
Man-made dams and other artificial structures in rivers prevent the natural downstream movement of sediments. Such obstructions can trap a high percentage of moving sediment. This can reduce the availability of quality spawning gravel downstream. Below such obstructions, erosion can also be exacerbated as the river recaptures sediment from the bed and banks. The eroded riverbed will not provide the optimal habitat for spawning fish or invertebrates and may therefore limit salmon production.
Lack of large woody structures
Juvenile salmon rely on complex and varied habitats within rivers. This complexity is often provided by large woody habitat, arising from fallen trees and often added to rivers by fisheries managers. This provides additional habitat for fish, and helps provide shade, shelter from high velocity flows, sites for feeding, spawning and nursery areas as well as refuges from predators.
Large woody structures also add complexity to the channel, helping to create pools and gravel beds and they support invertebrate life by trapping nutrients for key species groups such as mayflies, stoneflies and caddis species.
Non-native conifer afforestation
Poorly planned plantations of species such as Sitka spruce can degrade fish habitat by over-shading if they are planted too close to the watercourse or if natural seeding is not controlled. Water quality at catchment scale may be affected both through increased acidification as well as increased sedimentation due to the loss of peatland and increased drainage of the catchment. These factors will all have an impact on Atlantic salmon productivity and survival.
What are we doing?
Fisheries Management Scotland are working with our members to protect and improve habitat at significantly greater pace and scale. At a national level, we are working through SEPA’s Fish and Fisheries Advisory Group to ensure that the protection of in-stream and riverbank habitat is prioritised, and that regulated activites do not lead to further deterioration. Finally, we are working to ensure that public funding is available and prioritsed towards management activities that will help address the wild salmon crisis.