Swept area variation with depth and its influence on abundance indices of groundfish from trawl surveys

Abstract

Norwegian stratified-random bottom trawl surveys are carried out under the assumption that a constant area is swept by the trawl during a standard haul to generate abundance indices. Results from measurements of trawl geometry during a trawl survey in the Svalbard area, showed that there was a considerable depth dependency, and to a lesser extent, area/bottom stratum dependency of wingspread. The currently applied method relatively underestimates the younger ages of cod Gadus morhua (1-3yr) in the Svalbard area. -from Authors