Drift nets are free-floating nets used in oceans to snare fish by their gills. Each net can measure up to 50 feet (15 meters) deep and 55 miles (89 kilometers) long. Because drift nets are not selective, many fish and marine mammals are trapped in them. Those unwanted by fishermen, such as sharks, turtles, seabirds, and dolphins, are removed from the nets and thrown back, dead, into the ocean. Drift nets are an extraordinarily destructive fishing technology.
Drift nets are used in all of the world's major fishing regions, and the snaring of unintended marine species is always a serious problem. This is especially true in the commercial fishing of swordfish, tuna, squid, and salmon. During the late 1980s, drift nets were estimated to have killed as many as one million dolphins and porpoises annually. In addition, millions of seabirds, tens of thousands of seals, thousands of sea turtles, and untold numbers of sharks and other large species of fish were accidentally snared and killed.
Great lengths of drift nets and other fishing nets are lost at sea every year, especially during severe storms. Because the nets are made of materials that do not degrade or break down easily, they continue to snare fish and marine mammals underwater for many years. It is unknown how many are killed as a result of these so-called "ghost nets."
In response to mounting concerns about the harmful nature of drift nets, the United Nations banned the use of those nets longer than 1.5 miles (2.5 kilometers) in 1993. Although this regulation would not eliminate the snaring of unintended species, it would reduce the amount killed by as much as two-thirds. Unfortunately, there has been a great deal of resistance from the fishing industry and fishing nations to this regulation. Many fisheries continue to use much longer nets.