Guidance Migratory fish
Index section Migratory fish
- Migratory fish: twaite shad in the Westerschelde
- Migratory fish: salmon in the Rijn and Maas
- Migratory fish: the allis shad in the Rijn and Maas
- Migratory fish: the glass eel in the IJsselmeer
Introduction
As migratory fish need fresh water as well as sea water to complete their life cycle, they migrate from the sea to large rivers, and vice versa. Many migratory fish declined in the 20th century. The seven fish species that disappeared from the Netherlands include five migratory species: sturgeon, allis shad, twaite shad, houting and salmon. The reasons for their disappearance are the decline in water quality, the loss of suitable spawning grounds, overfishing and the presence of barriers in estuaries, rivers and brooks (weirs, dams, sluices and hydro power stations). Measures have been taken to improve water quality, fish runs have been installed and landscaping projects to create habitats have been implemented; the result has been that the twaite shad and salmon have recently returned, though they have not yet spawned in the rivers. The allis shad is still absent from Dutch rivers. The eel - also a migratory species - is continuing to decline because of fishing and the decrease in the number of elvers arriving from the Atlantic.
Relevant sections and indicators in the Environmental Data Compendium
Relevant information outside of the Environmental Data Compendium
- More information about biological monitoring in fresh waters can be found at (only in Dutch): www.waterstat.nl
