Gill nets are panels of diamond-shaped mesh netting used for catching fish. When fish attempt to swim through the net their gill covers get caught and they cannot back out. Depending on the target species , different mesh sizes are available for use. The top line of the net has a series of floats attached for buoyancy, and the bottom line has lead weights to hold the net vertically in the water column.
Gill nets have been in use for many years. They became popular in commercial fisheries in the nineteenth century, evolving from cotton twine netting to the more modern nylon twine netting and monofilament nylon netting. As with many other aspects of commercial fishing , the use of gill nets has developed from minor utilization to a major environmental issue. Coupled with overfishing , the use of gill nets has caused serious concern throughout the world.
Because gill nets are so efficient at catching fish, they are just as efficient at catching many non-target species , including other fishes, sea turtles , sea mammals, and sea birds. Gill nets have been used extensively in the commercial fishery for salmon and capelin (Mallotus villosus ). Dolphins , seals , and sea otters (Enhydra lutris ) get tangled in the nets, as do diving sea birds such as murres, guillemots, auklets, and puffins that rely on capelin as a mainstay in their diet. Sea turtles are also entangled and drown.
The problem has gotten worse over the last decade with the introduction and extensive use, primarily by foreign fishing fleets, of drift nets. Described as "the most indiscriminate killing device used at sea," drift nets are monofilament gill nets up to 40 mi (64 km) in length. Left at sea for several days and then hauled on board a fishing vessel, these drift nets contain vast numbers of dead marine life, besides the target species, that are simply discarded over the side of the boat. The outrage expressed regarding these "curtains of death" led to a United Nations resolution banning their use in commercial fisheries after the end of 1992. Commercial fishermen who use other types of nets for catching fish, such as the purse seines used in the tuna fishing industry and the bag trawls used in the shrimping industry, have modified their nets and fishing techniques to attempt to eliminate the killing of dolphins and sea turtles, respectively. Unfortunately, such modifications of gill nets are nearly impossible due to the nets' design and the way these nets are used.
See also Turtle excluder device
[Eugene C. Beckham ]
Norris, K. "Dolphins in Crisis." National Geographic 182 (1992): 2–35.