Commercial fishermen all around Sweden declare that cormorants’ are predating in and around there fishing tools and that leads to damage and sometimes death among the fishermen’s catch. This brings an economic loss when fish disappear or become severely damaged and therefore unsuitable to sell. This complex of problems is known from Denmark, the east coast of Sweden and since 10-15 years in Swedish lakes. The commercial fishing of vendace (Coregonus albula) in, for example Lake Vänern, is one of several types of net fishing that have had predation problems under a longer period of time. There are also problems with the fishing which is performed with hoop nets. In this type of fishing, it is often the eel (Anguilla anguilla) and the whitefish (Coregonus spp) that become most exposed for injuries. The cormorant population have been gone from lake Vänern for a long period of time and the recolonization of cormorants in Lake Vänern started 1989 on the island Ruskskär near Lurö. My main purpose with this project was to see whether P.c. sinensis have a negative or positive effect on the commercial fishing in Lake Vänern. This investigation was divided into two parts. The first part dealt with predation in nets that catch vendace. Second part treated predation in hoop nets and the attempt to reduce damage and predation. The studies of damage on the vendace become complicated because of the applyed method. The situation gave no reliable information about the problem. Material that I received in journal form from five places around Lake Vänern showed no connection between the numbers of cormorant and the catch of fish. When it came to predation and damage frequencies in hoop nets, the eel and whitefish became most exposed. An attempt to decrease the damage was done in 2004 by frighten the cormorants with a decoy. This attempt didn’t give any clear answers. There was a large catch of whitefish and eel 2004 compared with 2003. I can’t say if this has to do with the appearance of a decoy, there are many more factors that can affect the results. The whitefish shows a damage frequency of 10 % and the eel between 20-39 %, the remaining fish species showed very few damage sign. Statistical test of the cormorant’s preference for size on the whitefish and eel has shown no significance between attacked fish and its length.