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• Main Authors: Olav Rune Gode, Arill Engas
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: 1981; Halliday; 1986). Swept area abundance indices; Svalbard
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.611.1437; http://journal.nafo.int/j09/godo.pdf

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 depen-dency of wingspread. Assuming that the swept area was linearly related to the wingspread, it was found that the currently applied method relatively underestimates the younger ages of cod (1-3 years) in the Svalbard area. The use of instruments for monitoring trawl geometry during all tows is one way to diminish variability in bottom trawl survey indices.