Trawl Ropes and Nets: Understanding Their Impact on Marine Life

Trawl Ropes and Nets

Trawling is one of the most common commercial fishing methods used around the world. A trawl is a large fishing net that is pulled along the seafloor, either along coastal waters or in the open ocean. Trawlers use heavy ropes called trawl ropes to tow large trawl nets behind fishing vessels. There are a few main types of trawling gear configurations in use.

Beam Trawl Ropes and Nets

Beam trawls utilize a metal or wooden beam that extends horizontally from the back of the fishing boat. Heavy ropes called trawl ropes are attached to each end of this beam to help keep the net open. The beam ensures the mouth of the net stays fully open as it's dragged along the bottom. Beam trawls are particularly used for flatfish like sole and plaice in shallow coastal waters. The beam can vary in width but averages around 8-10 meters wide. The trawl ropes are very thick, usually 5-8 cm in diameter, to withstand the heavy weights and forces of dragging the net.

Otter Trawl Ropes and Nets

Trawl Ropes And Nets are one of the most widespread trawling methods globally. They utilize large wooden or metal otter boards attached via thick trawl ropes near the front of the net opening. These otter boards, also called trawl doors, help keep the mouth of the net fully open in a horizontal position as it's towed behind the boat. Otter trawls are often used offshore or in deeper coastal waters to target species like cod, haddock, and shrimp. The otter boards can range from 2-10 meters wide depending on the target species and fishing grounds.

Pair Trawling

In pair trawling, two fishing boats work together to tow one larger trawl net between them using system of thick trawl ropes and winches. This allows them to fish a wider section of seafloor at once. Pair trawling is commonly used in Scandinavian waters and the Barents Sea to catch cod and haddock. The pair of vessels work closely coordinated to control the movements of the shared net.

Environmental Impacts of Trawl Ropes and Nets

Heavy Seafloor Disturbance

The most significant environmental impact of Trawl Ropes And Nets is the physical disturbance caused to seabed habitats as the bottom-dragging gear is towed along. The heavy weights of the trawl nets, doors, and ropes can plow furrows in soft sediments, crush corals and sponges, and uproot seagrasses. Studies have shown trawling can flatten underwater topography, stirring up large clouds of sediment that smother bottom-dwelling organisms. This damage impacts ecosystem structure and the availability of habitats and prey for many marine species. Repeated trawling of the same areas intensifies this physical destruction of benthic environments.

Bycatch and Discard Mortality

Due to the non-selective nature of bottom trawls, a large quantity of unintended catch, known as bycatch, is brought up in the nets along with the target species. This bycatch can include juvenile commercial fish, sharks, sea turtles, marine mammals, and many invertebrate species. Most of this bycatch is discarded at sea, either because it is an undersized or prohibited species. However, studies show high rates of mortality for many discarded bycatch animals that do not survive being returned to the water. This unobserved and undocumented mortality impacts the sustainability of fisheries and ecosystems.

Ghost Fishing

Lost or abandoned fishing gear also poses environmental dangers. When trawl nets, ropes, and other gear becomes detached from fishing vessels, it can continue "ghost fishing" by indiscriminately capturing marine life. Ghost gear becomes deadly marine debris, ensnaring and killing fish, mammals, and turtles for extended periods as it drifts on the seafloor or at the surface. Derelict fishing gear has been documented entangling and killing endangered species like whales, damaging ecosystems long after active fishing has ceased. Better management is needed to prevent gear loss and recover ghost fishing gear.

Alternative Trawling Methods

While bottom trawling significantly impacts benthic habitats and bycatch rates, some fisheries are exploring modifications to reduce these environmental effects. For example, some fleets have incorporated certain types of bycatch reduction devices into trawl nets to allow non-target species to escape. Lighter roller-rigged trawls that "roll" over hard sediments instead of plowing may cause less physical damage to corals and sponges compared to conventional trawling methods. Industry-wide implementation of vessel monitoring systems and closed areas for bottom fishing can also help protect vulnerable habitats from repeated disturbance. Overall, more sustainable management practices are still needed to balance fisheries productivity with reducing trawling impacts on marine ecosystems and biodiversity.

Trawl fishing using heavy nets, otter boards, and thick ropes is a globally widespread method of commercial fishing. However, bottom trawling extracts a significant ecological cost through physical seafloor destruction and high rates of non-target bycatch mortality, as well as risks from ghost fishing gear. While fisheries aim to use improved trawl technologies and marine protected areas to moderate these effects, bottom trawling will likely continue altering benthic communities and ecosystems if left unchecked. Greater regulation and fishing restrictions may be required to rebuild depleted fish stocks and maintain biodiversity within our oceans.

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