Restoration of Atlantic salmon and other diadromous fishes in the Rhine River system

The Rhine River was once one of Europe's important large rivers for diadromous fishes such as Atlantic salmon Salmo salar, sturgeon, and others. Nearly all diadromous fishes disappeared from the river system during industrialization of the 19th and 20th centuries. Severe water pollution and the construction of weirs and dams are considered the major causes of the extinctions. Additional settlement, intense agriculture, and the need for flood prevention degraded river morphology from the upper catchment regions to the delta. Sewage treatment since the 1980s permitted ecological recovery to some extent. Nevertheless, most of the diadromous fishes are still missing or endangered today. However, there are several programs that assist re-establishment of the populations. The Atlantic salmon is the official flagship species of the International RhineAction Program. This species serves as an important indicator organism because the different phases of its life cycle depend on different aspects of the river ecosystem and structure: (a) the morphology of streambeds and catchment area (reproductive phase), (b) the integrity of structural habitat in flowing waters (juvenile phase), (c) impacts on the continuity of downstream migration routes (smolt phase), and (d) barriers that hinder upstream migration (returning adults). Performance of the indicator species and restoration of major habitat factors in several Rhine tributaries are monitored annually. The ambitious Rhine River project demonstrates that fisheries and conservation agencies can act in concert to restore habitat from the upper catchment area to the river mouth.