Migratory fish: salmon in the Rijn and Maas
The salmon disappeared from the Netherlands in the mid 20th century. Thanks to the improved water quality in the large rivers, it has recently returned.
Trends until 1957
In bygone days large numbers of salmon swam up the Rijn and Maas, to spawning grounds in the upper and middle courses of these rivers. Salmon used to be fished commercially in these rivers until the 1950s. But catches dwindled (see left-hand figure) and from 1957 the salmon was designated as extinct in the Netherlands. The main causes of its extinction were the worsening water quality and the physical obstacles that prevented it from reaching its spawning grounds (dams, weirs, sluices and hydropower stations). Also important were overfishing and the destruction of suitable spawning grounds by the dredging of sand and gravel.
Trends since 1994
Thanks to improved water quality, the construction of fish passages and various proactive habitat creation projects along the rivers, salmon catches in the Rijn and Maas have been increasing since 1994 (see right-hand figure). Important in habitat creation has been the creation of backwaters which offer shelter during the salmon run because here the current is slow.
The salmon caught are probably almost all fish that were released upstream in tributaries in Germany and in the Ardennes as juveniles and are now returning to the Rijn from the sea. These salmon swimming upstream are found mainly in channels of the Rijn, and in far fewer numbers in the Maas. These individuals are probably not yet breeding. At the end of 2002, adult salmon were observed in the Belgian Maas.
Technical note
The historical data on the salmon supply have been compiled from sales of salmon at auction. The data are from the RIVO archives and from various fisheries statistics. The recent data are from four locations scattered along the Maas and Rijn, where for two 6-week periods a number of commercial fishermen recorded the catches in nine special coarse-grid hoop nets like those that used to be used for river fishing. The trapped salmon were measured and then released, to continue their migration. The 600 salmon trapped since 1994 are only a fraction of the total number of fish that swam up the river.
The salmon is on the Red List of freshwater fishes.
References
- Departement van Economische Zaken (1932-1940). Jaarcijfers over de visscherij gedurende het jaar 1932 (etc.) Departement van Economische Zaken. Afdeeling Visscherijen. Directie Visscherijen. 's-Gravenhage.
- Departement van Landbouw, Nijverheid en Handel (1921-1938). Verslag over de visscherij gedurende het jaar 1921 (etc.) Departement van Landbouw, Nijverheid en Handel. Afdeeling Visscherijen. Directie Visscherijen. 's-Gravenhage.
- Nie, H.W. de, en G. van Ommering (1998). Bedreigde en kwetsbare zoetwatervissen in Nederland. Toelichting op de Rode Lijst. IKC Natuurbeheer. Wageningen.
- Visscherijinspectie (1911-1920). Jaarverslag der Visscherijinspectie. IV. Verslag betreffende den staat der binnenvisscherij. Mededeelingen en Verslagen van de Visscherijinspectie. 's-Gravenhage.
- Winter, H.V., E.M. Hartgers, J.A.M. Wiegerinck en H.J. Westerink (1999). Biologische monitoring zoete rijkswateren; samenstelling van de visstand in 1999 op basis van vangsten met fuiken en zalmsteken. RIVO rapport C010/00. IJmuiden.
- Winter, H.V., J.A.M. Wiegerinck en H.J. Westerink (2001). Jaarrapportage passieve vismonitoring zoete rijkswateren: trends en samenstelling van visstand in 2000 op basis van vangsten met fuiken en zalmsteken. RIVO rapport C035/01. IJmuiden.
- Winter, H.V., J.A.M. Wiegerinck en H.J. Westerink (2002). Jaarrapportage passieve vismonitoring zoete rijkswateren: samenstellen van visstand op basis van vangsten met fuiken en zalmsteken 2001. RIVO rapport C019/02. IJmuiden.
