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The Atlantic salmon (salmo salar) is an anadromous migratory fish that spawns in the upper reaches of NRW’s gravelly waterways (the grayling and trout regions, and to some extent the upper barbel region as well) in November and December. The young fish emerge from the spawning trenches at the end of April or beginning of May. In our latitudes, they then spend one to two years growing in the river as a ‘parr’. In spring or early summer (from the end of March to the beginning of June) the fish return to the sea as ‘smolts’, having now attained a length of around 15 cm. On reaching the sea, the salmon visit their preferred feeding grounds in the North Atlantic (off the coasts of Norway, Iceland, Greenland and Ireland). They remain here for one or two years, and in view of the plentiful supply of food increase enormously in weight. As ‘grilse’ (fish that have spent one winter in the sea, with a length of 50-75 cm and weighing 1.5 to 4 kg) or multi-sea-winter salmon (with a length of 80-100 cm and a weight of 5-10 kg), the fish return, now ready for spawning, to the home waters where they were first hatched out. Larger fish that have seen three or more sea-winters may measure up to 100-150 cm and weigh as much as 30 kg, but these are very rare nowadays, as the longer a fish remains at sea, the more likely it is that it will be caught.
After spawning most of the fish die. Only a few salmon, now known as ‘kelts’, return to the sea again, and of these only a fraction will come back upstream to spawn once more. Up to the end of the 19th century, professional fishermen used to catch as many as 250,000 salmon in the Rhine every year. The original stock of salmon in the Rhine may have resulted in the annual upriver migration of several million fish. As a result of the progressive regulation of waterways, the construction of barrages and increasing pollution of the rivers, the original Rhine salmon died out in the first half of the 20th century. The resettlement of the species in NRW today is being carried on with the help of salmon eggs that have been imported from other European countries (Ireland, Scandinavia and France).
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