OSLO Lost or abandoned nets in the oceans can keep on "ghost fishing" for years in a growing threat to marine stocks, a U.N. report said Wednesday.
About 640,000 tonnes of discarded fishing gear gets added to the oceans yearly, or 10 percent of the world total of marine debris, according to the study by the U.N. Food and Agriculture Organization (FAO) and U.N. Environment Program (UNEP).
Fishing gear "will continue to accumulate and the impacts on marine ecosystems will continue to get worse if the international community doesn't take effective steps to deal with the problem of marine debris as a whole," Ichiro Nomura, an FAO assistant director-general, said in a statement.
The study recommended measures such as cash incentives for fishing fleets to bring broken nets to port, better mapping of subsea hazards to avoid losses or new designs such as nets that dissolve if left in the water too long.
Nets sometimes snap in storms, get snagged on coral reefs or can get entangled in other fishing gear.
They can then start what the report termed "ghost fishing" -- pointlessly ensnaring fish or creatures such as turtles, seabirds or whales for years or even decades.
The report did not estimate overall damage to the oceans or economic losses to fishing fleets from gear littering seabeds from the South China Sea to the Mediterranean.
"It's very difficult to estimate the impact," said David Osborn, coordinator of UNEP's Global Program of Action on land-based sources of marine pollution.
"But we know that it's affecting fish take and it also represents a problem in terms of navigational hazards, like by fouling propellers," he told Reuters.
A 1992 ban on drift nets helped curb some problems, the study said. But gill nets, anchored to the seabed, can form a vertical wall between 600 metres and 10,000 metres (2,000 and 33,000 ft) long and can start ghost fishing if they break loose.
In Chesapeake Bay in the United States, an estimated 150,000 crab traps are lost every year of an estimated 500,000 deployed.
UNEP chief Achim Steiner said discarded gear was one of many threats to the seas along with over-fishing or acidification from greenhouse gases. He said all were damaging "ghosts in the marine environment machine."
Among recommendations, the report said fishing crews could be paid to report losses of nets or bring damaged gear to port. Marking nets could help identify offenders and track reasons for accidents.
New technologies can help. In some countries pots and traps have a biodegradable top that dissolves if it is in the water too long. Some nets for catching fish are designed to let turtles swim out.
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(Editing by Janet Lawrence)