Bottom trawling
Bottom trawling is a method of fishing in which heavily weighted nets towed by boats or ships are dragged across the seafloor. A primary chain agitates fish that then escape into the attached nets. This is an effective fishing method capable of catching not just target species but many other species of fish that are thrown away as by-catch.
Unfortunately these trawls often destroy the habitats covering the seabeds that they scour. Fragile habitats such as corals, sponges, estuary areas and seagrass beds can be destroyed by the weight and sheer power behind these trawling devices. Some habitats are capable of recovering from bottom trawling, given time; Others are permanently destroyed if trawled frequently because they are never allowed to reinstate themselves. Many of these areas are essential fish habitat and their destruction leaves juvenile fish vulnerable to predation and ultimately may reduce fish populations because juveniles aren't surviving. Also repeated trawling manipulates sediments thus increasing levels of turbidity which blocks light to sea floor vegetation.
A hard bottom community off Georgia coast, USA. Photo courtesy of NOAA.
In the open ocean it is often the seemingly featureless areas such as sandy or muddy seabeds that are trawled and subjected to dredging, filling and severe, repeated trawling. However they are extremely biologically diverse structures that can be irreparably effected by continuous trawling pressure.
The world could be trawling at least 20 million km� of the seafloor'an area nearly 2.5 times the size of Brazil. Hence, more and more research is concentrating on the effects of trawling on both the bottom habitat itself and the resident fauna.