PRESENT STATUS OF THE SALMONIDS ATLANTIC SALMON AND SEA-TROUT IN THE DUTCH PART OF THE RIVER RHINE

In the past, the anadromous salmonids, Atlantic salmon (Salmo salar) a nd sea-trout (Salmo trutta), have formed natural populations in the ri ver Rhine. From the beginning of the nineteenth century onwards, the g reater part of the drainage area of the river has been gradually alter ed from a more or less rural and agricultural area, into a highly indu strialised one with subsequent industrialisation, river-engineering an d heavy pollution. These developments are considered to be the major c ause for the disappearance of the populations of anadromous salmonid f ish in the 1950s. The water quality has recovered significantly during the past 25 years. From about 1975 onwards, this process gave rise to a recovery of the anadromous trout population. Results of recent stud ies of the sea-trout migration pattern are presented. They reveal that nowadays these salmonids can complete their up- and downstream migrat ions from the North Sea to places, situated at hundreds of kilometres upward the river and vica versa. The numbers of recorded Atlantic salm on and catch locations in inland waters are presented. They show a sig nificant increase since 1989. These phenomena can be understood as pro mising signs of the recovery of the Rhine aquatic ecosystem.