Stream Salmonids on the Cormorant (Phalacrocorax carbo) Menu

Predation from endemic predators is a natural regulating factor for fish species in rivers and lakes, but recently there has been a great increase in the populations of some of these predators, and predation is now threatening particularly populations of Atlantic salmon (Salmo salar), brown trout (Salmo trutta), North Sea houting (Coregonus oxyrhynchus), and grayling (Thymallus thymallus) throughout Europe. Especially the increased numbers of great cormorant (Phalacrocorax carbo sinensis) have resulted in a significant increase in predation pressure in Danish rivers, and a substantial decrease in numbers of salmonids and other river fish. The increased predation has led to intense conflicts between conservation of wild fish stocks and protection of predators, and given incentive to study the basis of the conflicts: Do cormorants significantly reduce fish populations? Despite decades of conflicts and political focus on the issue, only few scientific studies have focused on the results of these increased predation rates. In this chapter, we will describe the current situation and present some of the published and unpublished studies on predation from cormorants, and we will focus on the effects of cormorant predation on brown trout, Atlantic salmon, and grayling in Denmark.