A study of fish behaviour in the extension of a demersal trawl using a multi-compartment separator frame and SIT camera system

A rigid separator frame with three vertically stacked codends was used to study fish behaviour in the extension piece of a demersal trawl. A video camera recorded fish as they encountered the separator frame. Ten hauls were conducted in a mixed species fishery in the northern North Sea. Fish behaviour was analysed using the camera observations from several of these hauls by assigning seven descriptive attributes and also using catch data. Gadoids, in particular haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), and saithe (Pollachius virens), were caught in the upper codend, whereas Nephrops (Nephrops norvegicus) were caught in the lower codends. Catches of flatfish were more uniformly distributed among the three codends. Unlike the flatfish, gadoids reacted to the presence of the separator frame. The camera method and the separator frame yielded different information about fish behaviour within the trawl, and together the two methods provided a more complete picture of the catching process. Behavioural observations, vertical distribution, and the methodology are discussed, as is the potential for improving species separation in demersal trawls.