Rehabilitation effort for anadromous salmonids in the river Meuse basin. Achievements and new challenges

Until the end of the 19th century, the Atlantic salmon (Salmo salar) was widespread in the river Meuse basin and salmon fisheries were prosperous in France, Belgium and The Netherlands. The number of salmon and sea trout captures reaches 57000 ind/year in the Dutch Rhine-Meuse delta. Between 1840 and 1950, the building of navigation dams in the river Meuse and its tributaries, as well as the increase of industrial water pollution and the overexploitation of the stock, led to the extinction of all anadromous fish species.
In 1983, the capture of a sea trout (Salmo trutta) in the lower Belgian Meuse brought the problem of the migratory of fish to the surface. Based on scientific advices and feasibility studies carried out from 1983 to 1986, the program Salmon Meuse was launch in 1987. It aims at the restoration of the complete life cycle of migratory salmonids in the international River Meuse Basin.
Important rehabilitation efforts have been progressively done since the beginning of the project to the present 1) Improvement of the general quality of the water 2) Restocking with strains originating from France, Ireland, Scotland 3) Hydromorphological restoration of gravel bed habitats 4) The construction of modern fishways for upstream migration in the Meuse and tributaries 5) Adoption of measures to facilitate downstream migration at hydroelectric sites 6) Development of a salmon hatchery with facilities to realise artificial reproduction using returning adults 7) The establishment of international collaboration network 8) The election of the best strains based on genetics of returning adults and the process of smoltification finally 9) The opening of the Haringvliet sluices in the Estuary of the Meuse in the Netherland in 2018.
In the year 2000, the first adult salmon originating from restocking program was captured in the fishway of Lixhe, and this return of a salmon, more than 50 years of his extinction, was a major ecological event. From 2000 to 2018, the number of returning Atlantic salmon and sea trout progressively increased and reaches n=60 in the best year. This underline partial achievement of the objectives of the project, but the number of returning adult is sill too low to have a natural sustainable population. Supplementary efforts must be undertaken in the future, especially in terms of success of smolts downstream migration and escapement success as well as an optimization of the restocking practices (in terms of quantity and choice of the best development stage).
During our talk, we will synthesise the major key-points of this challenging project whose success requires a balance between the development and maintenance of numerous human activities and the associate preservation of the aquatic environment. We will use examples of results originating from recent scientific research.