Today's trawlers are capable of fishing deep-sea canyons and rough seafloor that was once avoided for fear of damaging nets. To capture one or two target commercial species, deep-sea bottom trawl fishing vessels drag huge nets armed with steel plates and heavy rollers across the seabed, plowing up and pulverizing everything in their path. For a few commercial target species, thousands of tons of coral are hauled up only to be thrown back dead or dying, along with huge quantities of unwanted bycatch. In a matter of a few weeks or months, bottom trawl fishing can destroy what took many thousands of years to create.
Today's trawlers are capable of fishing deep-sea canyons and rough seafloor that was once avoided for fear of damaging nets. To capture one or two target commercial species, deep-sea bottom trawl fishing vessels drag huge nets armed with steel plates and heavy rollers across the seabed, plowing up and pulverizing everything in their path. For a few commercial target species, thousands of tons of coral are hauled up only to be thrown back dead or dying, along with huge quantities of unwanted bycatch. In a matter of a few weeks or months, bottom trawl fishing can destroy what took many thousands of years to create.
Watch the Greenpeace video here:
The mouth of the trawl net is held open by two steel plate doors that help to keep the net on the seafloor. One company markets what it calls 'Canyonbusters', trawl doors that weigh up to five tons each and undoubtedly live up to their name. To protect the net from snagging on rugged seafloors, heavy chafing gear is attached to the bottom of the trawl net. A heavy cable is then strung through steel balls or rubber bobbins ”“ known as roller gear or rockhoppers ”“ that can measure a meter or more in diameter.
Fragile deep-water ecosystems, coral systems in particular, stand no chance against these ruthlessly effective underwater bulldozers. Deep-sea structures are not merely damaged, they are obliterated in a manner akin to clear-cutting a rainforest. After heavy trawling, the surfaces of seamounts are reduced to mostly sand and bare rock or coral rubble.
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Once destroyed, slow-growing deep-sea species are either lost forever or unlikely to recover for decades or centuries. Stable, living habitats such as coral and sponge communities in particular tend to be both the most heavily damaged and the slowest to regenerate. To make matters worse, the deep sea's remarkable array of coral, sponge, fish, crustacean and other species are, to an unusually high degree, undiscovered and endemic. The risk of extinguishing whole species never before seen is, therefore, very high each time a bottom trawler ravages the surface of a seamount.
Considerable damage to deepwater coral communities has been recorded off both coasts of North America, off Europe from Scandinavia to northern Spain, and on seamounts near Australia and New Zealand. In Norwegian waters, for example, an estimated one-third to one-half of the deepwater reefs have been damaged or destroyed by trawling. Photographs document giant trawl scars up to 4 kilometers (2.5 miles) long.
On the high seas south of Australia, in an area known as the South Tasman Rise, observers recorded trawlers bringing up an average of 1.6 tons of coral per hour in their nets in 1997 ”“ the first year of the area's orange roughy seamount fishery. An estimated 10,000 tons or more of coral were brought up in the nets of the 20 or so deep-sea trawlers working in the area. This figure does not include coral that was damaged but not brought up in the nets. By contrast, the catch of orange roughy ”“ the target species in this fishery ”“ in the first year of the fishery was reported to be less than 4,000 tons.
A study in the Gulf of Alaska observed a trawl path that had pulled up one ton of corals. Thirty-one red tree coral colonies had been in the 700-meter trawl path observed. Seven years after the damage, some of the larger colonies that survived the initial trawl tow were still missing 95”“99 percent of their branches. No young corals had replaced the dead ones in the damaged colonies.
Another video from Oceana.org:
Large quantities of 'non-target' species are captured (bycatch) and these are often discarded at sea as a waste product, killing much in the process. For example, according to the United Nations Environment Programme, trawling off the Aleutian Islands in Alaska between 1990 and 2002 produced over 2 million kilograms (4.4 million pounds) of coral and sponge bycatch.
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Visit them at www.oceana.org to learn more.
Other Resources:
Bottom trawling imagery Annotated satellite images from a number of bottom trawling activities around the world
Deep Sea Conservation Coalition Campaign for a ban on deep sea bottom trawling
FAO Gear type fact sheets Gear type fact sheet on various types of bottom trawls
Greenpeace: bottom trawling facts
UNEP: System-Wide EarthWatch Oceans and Coastal Areas On the role bottom trawling plays in global fisheries
