When farmers or ranchers want to clear an area of unwanted brush, small trees, or other vegetation, they sometimes attach a heavy chain between a pair of tractors or bulldozers. That, in essence, is what many scientists say happens to the ocean floor when fishing vessels engage in bottom trawling or dredging. Reports published this week in the journal Conservation Biology document the extent and impact of what is being called the underwater equivalent of forest clearcutting. After trawling, the sponges and mussels, the tube-dwelling worms and amphipod crustaceans that live in undisturbed areas are almost all gone. Boulders formerly covered with marine animals are almost lifeless from being rolled around by nets or dredges.
Nothing humans do to the sea has more physical impact than bottom trawling.
Elliott Norse, president of the Marine Conservation Biology Institute in Redmond, Wash., estimates there are 89,000 trawling vessels around the world, and their largely unregulated operations cover an area twice the size of the contiguous 48 states every year. The result, says Norse, is long-term damage to plant and animal habitat that harms the biodiversity essential to maintaining a healthy marine environment. Pushed to the Limits, and Beyond Nearly 70 percent of the world's marine fish species are overfished or fished to the limit of sustainability, according to the United Nations Food and Agriculture Organization. Still, NMFS officials this week cautioned that there are many factors other than trawling behind the decline in fisheries. For its part, the fishing industry dismisses charges that trawling is as environmentally harmful as critics say it is.