The role of Lake IJsselmeer, a closed-off estuary of the River Rhine, in rehabilitation of salmonid populations

After many technical measures and restocking activities in the River Rhine, there are now signs of salmonids being able to complete their anadromous life cycle. In Lake IJsselmeer, a former estuary of the River Rhine, the large effort associated with professional fisheries has been used to collect bycatch data on rare, migratory fish. To clarify the function of the lake for salmonids, catch data collected throughout the year between 1995 and 1999 were related to various possible migratory strategies known for these species. Species‐specific differences were found in timing, length–frequency distribution and maturity stage reflecting different behaviour of Atlantic salmon, Salmo salar L. (n=249) and sea trout, S. trutta L. (n=3962). There was evidence that salmon exhibited traditional anadromous behaviour and use the lake only as a corridor. By contrast, sea trout appears to use the lake both as a corridor and as feeding habitat.