Protocol to assessing impact of fish migration barriers

How to assess the impact of obstacles to flow on the movement of the main fish species in continental France

OMENA has published a book that assesses the impact of fish migration barriers in contintental France. You will be able to view the document from this link. To view some of our other resources from the Platform follow this link. 


Biodiversity is currently undergoing one of the most intense and rapid crises of mass extinction that the planet Earth has ever known and humanity is, without any doubt, the essential cause of the drastic losses. Among the many factors are chemical pressures in the form of water, soil and air pollution as well as in the form of climate change, excessive use of natural resources (hunting, fishing, cutting of forests, etc.), and physical pressures such as the destruction or loss of access to the habitats required by numerous species for their survival. The impact of physical pressures and in particular the fragmentation of habitats is today better understood and has been amply demonstrated. The international community has progressively acknowledged this issue and responded with a number of legal texts. In the European Union, the Water framework directive (WFD) is a prime example. The objective of the texts is generally to preserve and to restore ecological continuity and ecological corridors in order to slow or to stop at least part of the loss of biodiversity now taking place. Before taking action in favour of ecological continuity, it is necessary to assess the degree to which natural areas have been modified and to identify the situations creating the greatest problems. In aquatic ecosystems, hydraulic structures are one of the main causes of degraded ecological continuity, particularly for fish whose survival depends on their freedom of movement. An assessment of the impact of structures on the movement of fish is a prerequisite to determining the seriousness of problems in the field and identifying the priorities for action. To date, these assessments have generally been carried out by a small number of highly specialised experts. However, the massive (yet often unsuspected) numbers of transverse obstacles on rivers (over 70 000 obstacles have already been inventoried in France thanks to the characterisation reports for the WFD) created a pressing need for a simple, robust and standardised method for assessments that could be used by a large number of persons active in the environmental and territorial-planning fields. Onema responded to the challenge and coordinated the development of a protocol to assess the impact of obstacles to flow on the movement of the main fish species in continental France