Ghost Fishing

By: Kimmie Riskas

Before the widespread use of synthetics in the 1950s, all fishing gear was made from natural fibers, typically hemp and cotton, and strengthened with a coating of tar or strips of canvas. If lost or discarded at sea, the natural fibers would quickly lose buoyancy, disintegrate, and be chewed into nothingness by marine microbes.

Plastics, however, are durable, lightweight, and cheap, which is why synthetics have almost entirely replaced natural fibers in fishing gear over the last 35 years. Synthetic gear doesn’t break down as readily under prolonged submersion and UV light bombardment as hemp does. Decomposition by algae and colonial invertebrates happens more slowly on synthetic gear, if at all. It’s cheaply mass-produced. If broken or mislaid, synthetic gear is readily dumped overboard, left to drift through the oceans intact. There’s evidence that plastics may last even longer in the ocean, where salinity, temperature, and varying periods of exposure to direct sunlight prolong the plastics’ life far past that of plastic abandoned on terra firma.

All these long-lasting ropes, nets, and lines in the ocean carry unintended consequences for the creatures unfortunate enough to come across them. It’s called ghost fishing, and it’s responsible for the deaths of thousands of seabirds, whales and dolphins, sea turtles, marine mammals, fish and crustaceans every year. Discarded nets and lines quickly accumulate growths of marine algae and fouling colonies of invertebrates (barnacles, crabs, anemones, worms, and the like). Fish predators attracted by this floating buffet meet their death by entanglement. The gear accrues such masses of algae, debris, and dead animals that it sinks under the weight, hovering under the surface at anywhere from twenty to two hundred meters. Once some of this organic load rots away, the ghost nets rise vertically in the water column via buoyant plastic floats, to ensnare more wildlife and being the cycle over again.

A 1997 study by D.W. Laist in the Marine Pollution Bulletin by found that marine debris harms more than 267 species worldwide, including 86% of all sea turtle species, 44% of all seabird species, and 43% of all marine mammal species. In 2000, a single, derelict net recovered in Alaskan waters contained 350 dead seabirds and hundreds of rotting salmon. Sea turtles often mistake floating plastic bags for the diaphanous jellyfish that make up the bulk of turtles’ diets; hundreds of whales and dolphins wash ashore annually whose stomachs and respiratory tracts are choked with plastic sheeting and packaging material. Ghost nets are also destroying coral reef communities, snagging and breaking the very structure of the reef as the nets are dragged along by currents.

In 1975, having completed the transition to synthetic fishing equipment, international fisheries collectively dumped 135,400 tons of plastic gear into the world’s oceans. Although it’s difficult to measure exactly how much of it is floating in the ocean today, expansion of international fisheries and shipping industries since 1975 suggests that the amount of jettisoned fishing paraphernalia has significantly increased as well. The dumping of plastic trash and fishing gear from ships at sea has been banned since 1990 by international shipping regulation MARPOL Annex V. While there is some indication that the amount of discarded flotsam and jetsam has declined slightly in well monitored areas since the ban’s implementation, the vast majority of the world’s oceans are unpatrolled and regulations remain unenforced. An estimated 6.5 million tons of plastic debris are still dumped overboard every year.

Despite the damage caused by ghost fishing in the world’s oceans, discarded fishing gear accounts for a small percentage of marine debris. Litter composition varies by area, reflecting local use of containers, packaging, and fishing equipment. For example, in the eastern China Sea, where fishing is the dominant economic activity, 72% of marine debris originates as nets, ropes, and buoys discarded from fishing vessels. In Jakarta Bay, Indonesia, 42% of marine debris is polythene plastic bags; fishing here has been curtailed as increasing discharge of sewage and industrial effluent from the nearby city poison the water and make commercial fishing unprofitable.


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Filed under Biology, Ecology, Policy

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