Fish harvesters drag a large cone-shaped net along the seafloor to catch groundfish such as bluefish, flounder, monkfish, haddock, cod and pollock. The net is sunk and held open by two “otter boards” that look like large, heavy steel or wooden doors. As the net is towed at low speed, hydrodynamic forces push the boards outwards opening the mouth of the net and capturing fish in its path. The net is then hauled to the surface using hydraulic winches and a drum. A single tow can net thousands of fish along with incidental catch.

Also known as “dragging,” bottom trawling uses a large net made of polyethylene to catch fish. Steel or wooden doors spread the net open. Floats are attached to the upper mouth of the net to keep it open vertically and weighted “bobbins” are attached to the lower mouth to sink the net. The bobbins’ design depends on the terrain, varying from small rubber discs for smooth sandy seafloors to large metal balls for rough ground. Known as “rock hoppers,” bobbins lift the net over obstacles on the seafloor.

In New England, many different species are caught in bottom trawls. These include bluefish, Atlantic cod, haddock, pollock, yellowtail flounder, witch flounder, winter flounder, windowpane flounder, American plaice, Atlantic halibut, redfish, ocean pout and white hake. Most trawlers are federally permitted to catch multiple groundfish species. Some trawlers also have state permits to catch allocations in state waters.