Improving catch efficiency by changing ground gear design: Case study of Northeast Atlantic cod (Gadus morhua) in the Barents Sea bottom trawl fishery

The aim of this study was to determine if catch efficiency for cod (Gadus morhua L.) in the Barents Sea bottom trawl fishery could be improved by replacing the conventional rockhopper ground gear with a new type of ground gear called semicircular spreading gear (SCSG). Based on experimental fishing conducted in 2014 and 2015, we quantified the escape rate of cod beneath the fishing line of the trawl for each of the two ground gears and thereby obtained a measure for the ground gears’ catching efficiency. Fish escapees were collected in a retainer bag attached to the fishing line of the trawl and behind the ground gear, and its catches were compared with those in the trawl codend. A significant improvement in the catch efficiency was found for the SCSG relative to the rockhopper gear for cod between 56 and 105 cm, as significantly fewer cod escaped under the trawl equipped with the new ground gear. The results demonstrated that ground gear efficiency was length dependent for both ground gear types, as both showed increasing efficiency with increased fish length. The average catch efficiency for cod above 56 cm increased 9.19%–22.4% (depending on the herding efficiency) with the SCSG compared to the rockhopper, which corresponds to a reduction in the escape rate of 57.1%–61.73% (depending on the herding efficiency). This study demonstrates that improved catch efficiency can be obtained by substituting the conventional rockhopper gear with the newly developed SCSG without increasing trawl dimensions.