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First steps to encourage the return of the salmon were introduced by the project Lachs-2000 [Salmon 2000] of the IKSR [Internationale Kommission zum Schutz des Rheins: International Commission for Protection of the Rhine]. This involved importing salmon eggs from abroad and liberating the young fish that hatched out in Rhine tributaries like the River Sieg. Under the auspices of the NRW Migratory Fish Scheme, these measures were intensified to create a comprehensive project for the protection of species. By now over 1400 salmon that have returned from the sea have been registered in the spawning grounds of NRW, and the actual number of fish coming upstream is bound to be more than twice that amount.
So the salmon is the prime mover in NRW’s water development project. As a well-known and popular animal, the species acts as an indicator on behalf of the fish population as a whole. “Where salmon live, the water must be OK”.
Rather by way of a practical experiment, the controlled resettlement of the salmon population is being registered step by step, in order to see where there is still a need for action and what specific steps are still necessary to improve the quality of the water. In view of the steep requirements of its lifecycle, the salmon is an excellent indicator of the different aspects of water protection.
1. In order to reproduce, the salmon needs water of good quality and gravel banks on the bed of the river where there is adequate current. This is a requirement that goes significantly beyond such simple parameters as those of biological water quality Level II, and points to complex interrelationships with the entire catchment area (land use etc.). So what is needed is a holistic view, a systematic approach based on the whole river environment.
2. The young of the salmon (parrs) are dependent on the natural river environment of the trout and grayling regions (to some extent also the barbel region). Broad stretches of water with plentiful variety of structure, like flat gravelbanks and rapids, give them the habitat they need in order to survive. So the young fish can be seen as an indicator of the structural (ecomorphological) quality of the flowing water.
3. On the migratory paths it follows, the salmon is an outstanding indicator of the passability of waterways. Young fish migrating downstream (now known as smolts) are dependent on a safe passage downriver that will enable them to reach the sea. The population reacts in the most sensitive way to interruptions like barrages, or injuries caused by hydropower stations with their turbines. And when the adult salmon, now ready for spawning, return from the sea and swim upriver, they in their turn are dependent on there being a navigable waterway. Weirs and unsuitable fish passages often act as a barrier, and hinder the fish from spawning.
The resettlement of the salmon is therefore being accompanied by scientific control measures to register the success that has been achieved, with reference to all stages of the lifecycle. The survival rates of the salmon young as they emerge into the wild are determined, the downstream migration of the smolts is measured, the return of upriver migrants to the spawning grounds is monitored at the control stations, and finally the success of the salmon in achieving natural reproduction of the species is registered on an annual basis. So on the one hand the development of the population is biologically assessed, and on the other the success of water protection measures can be evaluated as if by a litmus test.
Back to other species protection projects
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