Reducing Seabed Impact of Trawling Through Technical Innovations

Otter trawls and beam trawls may alter physical and biological structures of the seabed through their contact with the seabed and benthic organisms though the degree of impact may vary with diversity, sensitivity and natural disturbance of the seabed. While research is continuing to quantify the various impacts of different fishing gears used in different fisheries under different fishing ground conditions, fishing gear technologists have made great effort to reduce seabed impacts in various fisheries. This paper illustrates some recent effort in this area. Alternative gears with less seabed contact, such as pelagic or semi-pelagic trawls, may be used instead of traditional bottom-tending gears in some fisheries where herding of target species by sand clouds is less critical. Gear modifications which have less seabed impact include designs with less contact area or contact points, lower weight of groundgear and doors, use of more efficient and high aspect ratio trawl doors, provision of dropout openings in beam trawls, adoption of "sweepless" trawls (without groundgear), and "wheeled" or "rollerball" groundgear replacing rockhoppers. Electrical stimuli have been tested in beam trawls to replace or reduce traditional heavy tickler chains in some fisheries or to selectively stimulate target species. Some novel gears have potential for reducing seabed impact, including the "Active Trawl" system, the "Auto-trawl" system, and the use of "soft" door, and footgear depressors in trawls, though they are in very early stages of development.