World Fish Migration Day – Barriers to Fish Migration
Man-made weirs (known as barriers to fish passage) cause a major impact on migratory fish around the Forth. The map below shows that impact visually based on barrier locations with section of the rivers colour coded based on accessibility to migratory fish.
Red shows parts of river catchments which are not accessible to migratory fish such as salmon, sea trout and sometimes eels and lamprey. The barrier is considered impassable due to its height or design, cutting off potential spawning habitat upstream of the obstacle.
Orange shows parts of the catchments which are only partially accessible to migratory fish. This might mean that the barrier is passable at times due to flow conditions going over the weir but the majority of the time impassable. It also takes into account weirs which have existing fish passes but deemed not optimal.
Green shows either free flowing rivers with little or no barriers on them or if a barrier has a working fish pass which is deemed optimal for most migratory fish.
The map is reflective of where migratory fish are found around the Forth. The majority of the Forth’s salmon population is found in the western rivers of the Forth basin (areas highlighted in green on the map). The lack of barriers in this area and full access to spawning habitat is a key factor in the success of salmon in this area. Areas in red have no sustainable salmon populations due to inaccessible habitat and areas coloured orange still have some salmon populations but it is massively reduced on what it could be if they had full access to the habitats available in the catchments.
Caveats need to be made with the map. We have mainly used barrier information from SEPA along with our own local knowledge but from experience, there will be barriers we don’t know of and we know SEPA’s data does not hold all barriers around the Forth either. It also doesn’t take into account natural barriers such as waterfalls (which might prevent total access to the top parts of some catchments), something we hope to adapt and include in the map in the future.
It is SEPA’s duty to regulate these barriers and ensure that there is appropriate mitigation where they cannot be removed. SEPA also controls the Water Environment Fund which can help owners undertake works. Despite this, over 60 barriers in the Forth are un-regulated and projects lead by SEPA to resolve fish passage issues are constantly delayed. If we are protect and conserve our iconic Atlantic salmon, sea trout, eels and lamprey then this work needs to be escalated to ensure their survival for future generations.
