trawl

Trawl fishing is a method in which a large fishing net, the trawl, is towed behind a vessel to harvest fish and other marine life. Trawling can be bottom trawling, in which the net is dragged along the seabed, or pelagic trawling, in which the net operates in the mid-water column above the bottom.

The trawl net has a wide mouth that is kept open by otter boards (also called doors) as it is pulled through the water. The net consists of the mouth, a body, and a codend where the catch collects. Ground gear such as a ground rope and protective bobbins helps the net slide along the seabed; tickler chains may be used to disturb fish along the bottom and guide them into the net. A separation line and sweeps may be used in some designs to improve sorting and reduce bycatch. The catch is discharged from the codend at the stern.

Operation and scope vary with target species and habitat. Tow duration, speed, and depth depend on fishing conditions and regulatory limits, and the gear is often operated by one or more vessels through winches and tow wires.

Environmental and regulatory considerations are central to modern trawling. Bottom trawling can damage seabed habitats and cause non-target species bycatch, while pelagic trawling can affect mid-water ecosystems. Many regions implement gear restrictions, area closures, seasonal bans, and catch limits to manage stocks and minimize environmental impact.

History and development: trawl fishing emerged in the early modern period and expanded with steam-powered and later motorized vessels, becoming a dominant method in many fisheries. Net design and towing technology have continued to evolve, shaping the scale and efficiency of modern trawl fleets.