An invasion of the North Sea by blue-mouth,Helicolenus dactylopterus(Pisces, Scorpaenidae)

Blue-mouth (Helicolenus dactylopterus) is one of four species of the Scorpaenidae which may be caught in the North Sea. It is known as a typical deep water fish which lives along the shelf edge. Reports from the North Sea have been rare. An invasion of blue-mouth in the northern North Sea that took place in the winter 1990/91 is described. Blue-mouth have spread over a considerable area since and, recently, catches were even reported from the southern North Sea. Length distributions are given as well as age/length information from fish collected in the North Sea and at Rockall.