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Papers Posit Grave Impact of Trawling

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Science  18 Dec 1998:
Vol. 282, Issue 5397, pp. 2168
DOI: 10.1126/science.282.5397.2168b

WASHINGTON, D.C.– A group of marine scientists has lobbed a rhetorical warning shot across the bows of the world's trawling fleets. In a press conference this week, they presented evidence that dragging heavy nets across the seafloor causes far more environmental damage than does the more visible clearing of forests. Some trawlers are returning fire, however, saying that the scientists have overstated their case and that some fishing grounds have remained productive despite more than a century of trawling. Caught in the crossfire are government fisheries officials, who believe the new findings will fuel but not settle an increasingly rancorous debate over whether to curtail trawling in some heavily fished waters.

Net loss.

A patch of seafloor off Swan's Island, Maine, before (left) and after the area was swept by a scallop dragger.


The latest battle over sustainable fishing was triggered by a suite of seven papers released on Monday* and by a flotilla of results discussed last week at a conference in the United Kingdom.** Some seafloor researchers and the American Oceans Campaign, a Washington, D.C.-based environmental group, hope the findings will prompt an outcry against the largely invisible impact of trawling, a technique traditionally confined to shallow coastal seas that has recently extended its reach into waters up to 2 kilometers deep. At the press conference, which included Hollywood star Ted Danson, scientists and environmentalists called on governments to establish more marine reserves where trawling—but not all fishing—is banned. “We cannot continue to allow the use of trawling on such a broad scale if we are going to sustain fish habitat and marine biodiversity,” said biologist Peter Auster of the University of Connecticut, Avery Point, author of one of the papers.

The most controversial paper, by Les Watling, a biologist at the University of Maine, Orono, and Elliott Norse of the Redmond, Washington-based Marine Conservation Biology Institute, equates the habitat damage caused by trawling with forest clear-cutting—long denounced by biologists as a major threat to biodiversity. Both techniques, the researchers argue, transform structurally complex habitats supporting many kinds of life into relatively flat, uniform environments that shelter fewer species. But trawlers cover far more ground than loggers, say Watling and Norse. Their estimate, based on scanty industry records, is that the worldwide fleet of trawlers drag up to 15 million square kilometers annually—an area 150 times greater than the forest cleared each year. Unlike loggers, however, some trawlers may sweep the same seafloor patches many times in a single year, leaving little time for slow-growing organisms to regain their toeholds. Trawling's long reach “was not previously appreciated,” the pair concludes. “With the possible exception of agriculture, we doubt that any other human activity physically disturbs the biosphere to this degree.”

Another of the new studies, led by Jonna Engel of the Moss Landing Marine Laboratory in California, is among the first to document the change in biodiversity from trawling. Using sonar, video images taken from submarines, and samples of seafloor life, it compared a repeatedly trawled seabed 180 kilometers off the central California coast with a nearby swathe that was dragged less often. Engel's team found that the heavily trawled area was flatter and harbored fewer species than the lightly fished stretch. They also found that increased trawling reshuffled sea life communities: smaller, rapidly reproducing creatures—such as nematode worms—tended to replace larger, longer-lived organisms, such as some shellfish. Other studies suggest the ecological changes can persist for months or longer after trawling ends.

The idea that trawling produces undersea winners and losers also surfaced at last week's conference in Wales, which featured work in European waters. Dutch researchers, for instance, found that a century of trawling may have reshaped parts of the North Sea's floor into perfect habitat for Dover sole, a sought-after catch, and swept away less adaptable creatures, such as delicate anemones. “It's ironic that destructive fishing activity appears to have created just the kind of flat, homogenized habitat that sole prefer,” says conference organizer Michel Kaiser of the University of Wales in Bangor.

Fishing industry officials point to such results in arguing that policy-makers need more information before establishing trawl-free zones. Trawlers and marine biologists agree that “some gear does impact some bottom types during some fishing operations,” says Nils Stolpe of the New Jersey Seafood Harvester's Association in Bucks County, New Jersey. But “there isn't anything approaching a consensus on the effects, positive or negative.”

And even some ocean protection advocates are uneasy about tarring trawling with clear-cutting's reputation. The analogy is “inaccurate at best and incendiary at worst,” says Dery Bennett, head of the American Littoral Society, a coastal protection group based in Highlands, New Jersey. Trawled areas, he believes, generally recover far more quickly than clear cuts if left alone. In addition, he says, the comparison may poison the atmosphere for scientists and fishermen working together to ban trawling in particularly sensitive areas such as coral reefs and nursing grounds for young fish.

The United States has already taken limited steps toward protecting reefs and some nursing grounds, notes National Marine Fisheries Service deputy director Andy Rosenberg. But he says policy-makers will want more specific information before closing more waters to trawling. “The science is still spotty and too inconclusive,” he says. The new studies, he adds, “should really help the policy debate move forward.”

  • * Conservation Biology, December 1998.

  • ** “Effects of fishing on non-target species and habitats: Biological, conservation and socio-economic issues,” Baumaris, Anglesey, Wales, 7 to 10 December 1998.

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