Bycatch of brown trout Salmo trutta in a commercial gillnet fishery targeting whitefish Coregonus lavaretus

The brown trout, Salmo trutta L., population in River Skjern, a major tributary stream to the Danish lagoon Ringkøbing Fjord, is reduced despite various efforts towards its recovery. This study investigated if bycatch of migratory trout in the commercial whitefish, Coregonus lavaretus L., fishery in the lagoon might be a significant cause. Experimental surveys were carried out to examine bycatch levels using different fishing protocols and gear types. Data were also collected through an observer fishery, questionnaires and from a database on local fisheries statistics. Trout occurred as bycatch in low numbers in the observer fishery (mean of 0.2 trout per km gillnet). The whitefish fishing protocols examined in the experimental surveys revealed a significantly lower bycatch of trout when fishing with sinking gillnets than floating gillnets. However, few fishers use floating gillnets in the present-day fishery. The other fishing practices examined revealed no alternatives that would reduce trout bycatch markedly. The results indicated that the whitefish fishery in the lagoon is not the major reason for the lack of recovery of the trout population in River Skjern.