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Bottom Trawling
Greenpeace documents a Spanish flagged bottom trawler, the Ivan Nores, in the Hatton Bank area of the North Atlantic, 410 miles north-west of Ireland, October 2004. The net contents include the target catch and many species of unwanted 'bycatch'. Scientists are warning that bottom trawling is pushing species to extinction before they are even discovered.
© Greenpeace/Kate Davison
Taken by a fisheries observer on board a NZ bottom trawler NW of New Zealand, this photo shows a giant piece of gorgonian coral being hoisted out of a bottom trawl net. (Note more coral in the net). Coral this size is estimated to be more than 500 years old.
© Ministry of Fisheries NZ
Orange roughy and bycatch being hauled in by the Chang Xing in international waters in the Tasman Sea, 9 June 2004.
© 2004-Greenpeace/Roger Grace
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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.
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.
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.
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.
More information:
Economics & security - why the carnage doesn't make sense
24 Sep 2004
The Destructive Power Of Deep Sea Bottom Trawling On The High Seas
pdf; 2 pages;
531 KB
English | English
US standard | Spanish
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