Lost and abandoned fishing nets, crab pots and marine debris killing marine wildlife and choking the oceans.
Gillnet washed up in northern Australia with dead shark (no species ID). Credit FAO
Fishing gear and marine debris - 6.5 million tonnes every year May 2009. Large amounts of fishing gear lost at sea or abandoned by fishers are hurting the marine environment, impacting fish stocks through "ghost fishing" and posing a hazard to ships, according to a new report jointly produced by the UN Food and Agriculture Organization (FAO) and UN Environment Programme (UNEP).
Problem is getting worse According to the study, the problem of abandoned, lost or otherwise discarded fishing gear (ALDFG) is getting worse due to the increased scale of global fishing operations and the introduction of highly durable fishing gear made of long-lasting synthetic materials.
10% of marine litter The report estimates that abandoned, lost or discarded fishing gear in the oceans makes up around 10 percent (640,000 tonnes) of all marine litter. Merchant shipping is the primary source on the open sea, land-based sources are the predominate cause of marine debris in coastal areas.
Most fishing gear is not deliberately discarded but is lost in storms or strong currents or results from "gear conflicts," for example, fishing with nets in areas where bottom-traps that can entangle them are already deployed.
The main impacts of abandoned or lost fishing gear are:
Continued catches of fish - known as "ghost fishing" - and other animals such as turtles, seabirds, and marine mammals, who are trapped and die.
Alterations of the sea-floor environment; and - the creation of navigation hazards that can cause accidents at sea and damage boats.
Gill nets, fishing pots and traps are most likely to "ghost fish," while longlines, are more likely to ensnare other marine organisms and trawls most likely to damage sub-sea habitats.
Ghost net recovered by Scottish trawler in the North Sea. Credit FAO.
Gill nets are the major problem - 10 kilometres long In the past, poorly operated drift nets were the prime culprits, but a 1992 ban on their use in many areas has reduced their contribution to ghost fishing.
Today, bottom set gill nets are more often-cited as a problem. The bottom edge of these nets is anchored to the sea floor and floats are attached to their top, so that they form a vertical undersea wall of netting that can run anywhere from 600 to 10,000 metres in length. If a gillnet is abandoned or lost, it can continue to fish on its own for months - and sometimes years - indiscriminately killing fish and other animals.
Crab and lobster pots Traps and pots are another major ghost fisher. In the Chesapeake Bay of the United States, an estimated 150,000 crab traps are lost each year out of an estimated 500,000 total deployed. On just the single Caribbean island of Guadeloupe, about 20,000 of all traps set each year are lost each hurricane season - a loss rate of 50 percent. Like gill nets, these traps can continue to fish on their own for long periods of time.
Islands of garbage
The total input of marine litter into the oceans per year has been estimated at approximately 6.4 million tonnes annually, of which nearly 5.6 million tonnes (88 percent) comes from merchant shipping.
Some 8 million items of marine litter are thought to enter the oceans and seas every day, about 5 million (63 percent) of which are solid waste thrown overboard or lost from ships.
It has been estimated that currently over 13,000 pieces of plastic litter are floating on every square kilometre of ocean. In 2002, 6 kg of plastic was found for every kilogram of plankton near the surface of a gyre point in the central Pacific, where debris collects.
Mass concentrations of marine debris in high seas accumulation areas, such as the equatorial convergence zone, are of particular concern. In some such areas, rafts of assorted debris, including various plastics; ropes; fishing nets; and cargo-associated wastes such as dunnage, pallets, wires and plastic covers, drums and shipping containers, along with accumulated slicks of various oils, often extend for many kilometres.
Solutions - Inventing "smarter" gear
Work is underway to explore durable gear that incorporates bio-degradable elements. This approach is already used in some countries for fish traps and pots, which are constructed with a biodegradable "escape hatch" that disintegrates when left under water too long, rendering the trap harmless.
Fledgling efforts are under way to develop biodegradable and oxy-degradable plastics for wider using in the fishing industry.
The use of passive acoustic pingers on nets can help prevent cetacean entanglement when fishing and remain active if gear is lost. Experimentation is also underway in the addition of sound-reflecting substances to netting material, with the same goal.
Designs are being developed that incorporate pieces of cord to nets that function normally during fishing but which break when trapped large animals begin to thrash, freeing them.
The addition of magnets to gear can deter sharks from approaching too closely.