Gill nets and drift nets
Gill nets and drift nets are fishing tools utilized to capture marine life, but they come with significant ecological concerns. Gill nets are mesh nets that ensnare fish by their gills, designed to target specific fish species while ideally minimizing bycatch—unintended marine animals caught in the nets. However, if not regularly tended, these nets can lead to high rates of bycatch, including vulnerable species like sea turtles, seabirds, and marine mammals. Drift nets, larger and often composed of multiple gill nets, drift freely in the water and can result in even greater bycatch rates. Lost or abandoned drift nets, known as "ghost nets," can continue to trap marine life indiscriminately.
While some measures, like the use of pingers to alert marine mammals, can reduce bycatch, their effectiveness varies across species, and illegal drift netting remains an issue in many areas. Globally, there has been a push to regulate or ban these practices due to their detrimental impact on marine ecosystems. Countries such as New Zealand, Australia, and members of the European Union have taken steps to prohibit drift netting to address these environmental concerns.
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Gill nets and drift nets
DEFINITIONS: Gill nets are mesh nets that ensnare fish by their gills; drift nets are large vertical nets (often made up of multiple gill nets) that are allowed to drift free in a body of water
Although they are made to snare particular types of fish, gill nets and drift nets can trap and kill untargeted types of marine life. Lost drift nets can float in the open sea, killing marine life indiscriminately.
Mesh fishing nets of the type known as gill nets have been used for centuries. Fish swim through the mesh openings of gill nets and become ensnared by their gills when they try to back out. Gill nets are manufactured with specific mesh opening sizes for use in selectively capturing certain fish species without affecting other, untargeted, species. Even if gill nets snare untargeted species, if fishers regularly tend their nets, they can return any entangled untargeted marine life (bycatch) to the sea and guarantee that all targeted fish are removed from the nets before they die so that they are brought to market in the freshest possible condition.
Not all fishers exercise such vigilance, and untended gill nets do kill untargeted marine life. Nylon gill nets, which are quite durable, are almost invisible in the water, and this increases the tendency of untargeted species to swim into them and become entangled. Gill-net bycatches may include sea turtles, seabirds, and marine mammals such as sea otters, seals, dolphins, porpoises, and whales. As of the 2020s, the United States still allows the use of gill nets, but the height of the nets and the size and shape of the mesh are regulated.
Drift nets are very large nets, often made up of several gill nets, that hang vertically in the water; floats attached to the top and weights secured to the bottom keep the nets vertical. Because drift nets are not anchored to the seafloor, they drift with the currents. Drift nets have a high rate of bycatch. One trial use of drift nets to catch skipjack tuna in early 1989 showed that the nets killed one marine mammal for every ten tuna caught, compared with one dolphin per 70 tons of tuna in the eastern Pacific purse-seine tuna fisheries. The loss of drift nets during storms produces “ghost nets,” which continue to catch marine life indiscriminately. It has been estimated that 300,000 dolphins, porpoises, and whales are killed by untended gill nets, drift nets, and ghost nets each year.
Some fishers attach small devices known as pingers, which emit audible signals, to their gill nets or drift nets to warn marine mammals that they are approaching the nets. Several studies have shown that the use of pingers can significantly decrease the bycatch of some marine mammals without affecting fish catches. The responses of different marine species to pingers vary, however. For example, sea lions have been known to become increasingly attracted to pingers over time, and such devices are not a reliable means of reducing bycatch of endangered species.
The United Nations General Assembly passed a resolution in December, 1989, prohibiting the expansion of drift and calling for a gradual phaseout of the practice by 1992. Illegal drift netting continues to occur, however. New Zealand, Australia, and South Africa have prohibited drift netting in their waters. Even Japan, which has one of the largest drift-netting operations in the world, banned large-scale drift netting in its own waters in response to the depletion of marine species that unregulated drift netting caused within Japan’s own exclusive economic zone. The European Union banned the use of drift nets in 2013.
Bibliography
Allsopp, Michelle, et al. State of the World’s Oceans. New York: Springer, 2009.
Barlow, Jay, and Grant A. Cameron. “Field Experiments Show That Acoustic Pingers Reduce Marine Mammal Bycatch in the California Drift Gill Net Fishery.” Marine Mammal Science 19, no. 2 (2003): 265-283.
"Fishing Gear: Gillnets." National Oceanic and Atmospheric Administration, 22 Feb. 2021, www.fisheries.noaa.gov/national/bycatch/fishing-gear-gillnets. Accessed 17 July 2024.
"Illegal Fishing: Driftnets." Oceana, 2024, europe.oceana.org/driftnets/. Accessed 17 July 2024.
Miller, Frederic P., Agnes F. Vandome, and John McBrewster, eds. History of Fishing: Fishing, Gillnet, Trawling, Cod, Trepanging, Fly Fishing, History of Whaling. Beau Bassin, Mauritius: Alphascript, 2009.