Net Loss: Trawling Critiqued

WASHINGTON, D.C.--A group of marine scientists lobbed a warning shot across the bows of the world's trawling fleets today, charging that sweeping the seafloor with heavy nets in search of food causes more environmental damage than logging. The damage estimate, included in a suite of seven papers in the current Conservation Biology, adds to an increasingly acrimonious debate over whether governments should establish trawling-free reserves in some heavily fished waters.

The most controversial of the new papers, by University of Maine biologist Les Watling and Eliot Norse of the Marine Conservation Biology Institute, based in Redmond, Washington, equates the undersea habitat damage caused by trawling with clear cutting. 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, Watling and Norse say. They estimate, based on scant industry records, that trawlers worldwide drag up to 15 million square kilometers each year--150 times the area logged. "With the possible exception of agriculture, we doubt that any other human activity physically disturbs the biosphere to this degree," the pair concludes.

Another of the new studies, led by Jonna Engel of the Moss Landing Marine Laboratory in California, 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 significantly fewer species than the lightly fished stretch. The researchers 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 shellfish.

But some trawling industry officials note that the seabed shuffle isn't all bad: it benefits some economically important fish by churning up food for organisms at the bottom of the food chain. As a result, "there isn't anything approaching a consensus on the effects--positive or negative--of [trawling]," claims industry consultant Nils Stolpe of Bucks County, New Jersey.

In light of the uncertainty, policy-makers will want more specific information before closing waters to trawling, says National Marine Fisheries Service official Andy Rosenberg. "The science is still spotty and too inconclusive," he maintains.