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Conservation as the catch of the day for trawl nets
31st July 2003

New York Times - Science

For more than six centuries, the wide-mouth bottom-scraping nets called trawls have been praised as the ultimate fishing device and cursed as a wasteful destructive scourge on the seas.

In 1376, just six years after the nets were first tried in British waters, fishermen complained to King Edward III that trawls, then called wondyrechauns, were "destroying the flowers of the land beneath the water there, and also spat of oysters, mussels and other fish upon which the great fish are accustomed to be fed and nourished."

The document even includes what appears to be the first description of what is now called bycatch, captured fish that are unmarketable because they are too small or the wrong species.

The petitioners said the trawlers "take such quantity of small fish that they know not what to do with them; and they feed and fat their pigs with them, to the great damage of the Commons of the Realm and the destruction of the fisheries."

Today, thousands of ocean going trawlers are set up like floating factories, with slanting platforms astern where bulging nets are drawn up and assembly-line operations where the catch is sorted and flash frozen.

Nets have evolved from crude mesh bags barely wider than the sailboats that dragged them into $100,000 fish-harvesting systems, some broader than a football field and equipped with electronic sensors that detect approaching obstacles.

On "rockhopper" trawls, first deployed in the 1980's, large rollers were added along the bottom edge of the net that allowed hauling over rocky or coral-crusted areas of seabed without snags.

That innovation opened vast new regions to fishing, not only further depleting stocks, but also ravaging the corrugated places on the bottom that provide habitat for fish and the small animals and plants they depend on.

Until recently, every innovation was aimed at catching more fish, with little regard for the ecological consequences. That began to change a decade ago, after biologists started tallying the loss of seabed ecosystems crushed by repeated towing and the vast unintended toll of sea turtles and unwanted fish swept into the gaping bags.

Fishermen, too, began to recognize that in capturing fish of all sizes they were undermining the health of the resource.

Since then, under tightening laws, fleets in North American and European waters have begun to shift to designs and practices that curb the bycatch and ecological effects.

For more than six years, the United States has required that trawled shrimp, whether imported or caught in American waters, come just from nets equipped with special grates called turtle exclusion devices that let shrimp in but divert sea turtles. American shrimp fleets are also increasingly installing grates and escape holes that cut the unwanted fish harvest in shrimp nets.

A sign that times have changed can be seen in the net research under way in a 70-foot-long glass-walled tank of flowing water at Memorial University in St. John's, Newfoundland. Until recently, the tank was used almost entirely to find ways to catch more fish.

Now, 99 percent of the work there is aimed at making fishing less environmentally harmful, said Glenn Blackwood, director of the Center for Sustainable Aquatic Resources at the university.

Scale models of new trawl designs are tested in the tank, and they incorporate escape holes, various mesh styles and other features, all aimed, Mr. Blackwood said, at catching the right fish, not just more fish.

Other designs glide a yard or two off the seabed without scraping it.

"Historically, we just fished and caught whatever was in the swept area," he said. "Now the focus has to be on surgically removing fish from the ocean.” Still, environmentalists and many marine scientists voice complaints that sound very much like that 1376 petition to Edward III — though in modern language and on an incomparably vaster scale.

Last year, the National Research Council of the National Academies reported that the complexity of American marine ecosystems was being reduced by towed bottom gear. The council called for a mapping program to add habitat types to coastal charts that now show just topography. And the group recommended reducing overall fishing activity, diverting trawling from the most vulnerable places and changing net design to reduce bycatch.

Other experts recently estimated that trawling now affected stretches of the sea bottom equalling the combined area of Brazil, Congo and India. And the trawled spots are almost all concentrated in the most productive, biologically rich places, the continental shelves and the tops of the underwater mountains called seamounts.

A survey of fishermen, scientists and other experts published in May by the Marine Conservation Biology Institute, a research and advocacy group in Redmond, Wash., found consistent agreement that bottom trawling was the most harmful commercial fishing method, with damage to the seabed judged worse than the damage to the bycatch.

The report, called "Shifting Gears" and online at, noted that 98 percent of marine species lived in, on or just above the sea floor.

"Our research indicates that shifting to more selective, environmentally friendly gear could mean the difference between having plenty of fish to go around and ecological and economic disaster," said Dr. Ratana Chuenpagdee, a researcher at the Virginia Institute of Marine Science in Gloucester Point, Va., and an author of the report.

But it is clear from history and the continuing spread of technology that trawling will be around as long as humans continue to harvest fish in the wild. Improvements in design may reduce ecological damage but will never prevent it entirely.

For that reason, Dr. Callum Roberts, a fisheries scientist at the University of York in Britain, recently urged in a report to the European Union that the only way to continue to trawl and still have something worthwhile catching was to put substantial parts of the oceans off limits.

"Yes, we should have the underwater equivalent of intensive agriculture — the muddy seabed ploughed by trawls," Dr. Roberts wrote. "But give us wilderness, too, the nature reserves and national parks."

Without them, he concluded, "the seas will become a sorry shadow of their former abundance and the giants that we once hauled from them creatures of imagination alone."