Energy saving trawl in Mediterranean demersal fisheries

This study aimed at the development of demersal trawl design, for the Mediterranean fisheries, with reduced fuel consumption. The new design include the use of a new high strength material and the use of larger meshes in net areas where no negative effect on the catching power is foreseen. It is essential that the new design combine the features of large headline height and good contact between the footrope and the seabed, with a low towing resistance. A typical trawl, commercially used in Italy, was selected as a basis for the development of the new design. This trawl became the reference to which the changes introduced in the new design were compared throughout the study. To reduce the netting area of the experimental trawl, a high strength Dyneema fibre was tested. The intention was to reduce the mesh twine diameter while keeping the netting strength constant. Dyneema was used in the wing section of the experimental trawl. Sea trials were made on a research vessel to measure the engineering performance of the trawls. During these tests a towed underwater camera was used to make a visual inspection of the trawls. The results from the sea trials show that it is possible to design trawls with up to 30% less fuel consumption and up to 40% more headline height, when larger mesh sizes, new high strength materials and reshaped wings are introduced. An inspection of the Dyneema netting after the commercial tests on the experimental trawl showed that the stability of the knots in this type of netting was not sufficient to keep the meshes rightly shaped. Further product development is necessary before such material could be commercially used in the Mediterranean fisheries.