TAMPA, FLORIDA--Marine researchers appear to have sunk a provocative theory. A new study has found no evidence to support the idea that bottom trawling, a widespread fishing technique, can help boost populations of table fish. The finding, reported here yesterday at a conference on fishing's impact on the sea floor, might end a long-running debate over a possible ecological benefit of trawling, which critics say damages marine habitat.
Trawlers can dramatically shuffle sea-floor communities. The heavy nets often sweep away larger creatures and crush smaller ones. It can take years for some trawled grounds to recover, and critics say the damage hurts fish populations. But trawling captains and some researchers working in Europe's North Sea have argued that trawling might have benefits too: By removing larger, longer lived competitors, frequent trawling could allow smaller, shorter lived organisms to flourish, including marine worms that are a favorite food of commercially valuable flatfish, such as sole. Some have compared trawling to farming, saying that the nets plow the sea floor and "fertilize" growing flatfish.
Three years ago, marine ecologist Simon Jennings and three colleagues at the Centre for Environment, Fisheries & Aquaculture Science in Suffolk, U.K., decided to test the idea. They began studying several hundred square kilometers of fishing grounds in the central North Sea. After picking 27 sites in heavily, moderately, and lightly trawled areas, they took 10 sediment samples from each, counting and weighing every organism they found. Overall, the researchers concluded that trawling had no effect on worm populations. Instead, water depth and sediment type appear to be the major influences, the team concludes in a paper currently in press at Marine Ecology Progress Series.
Jennings says the study undermines not only claims that trawling can boost flatfish prey but also arguments that the nets completely wreck food webs. John Steele, a marine ecologist at the Woods Hole Oceanographic Institution in Massachusetts, says the study should help researchers focus their attention on more important issues, such as ending overfishing. The farming analogy initially "does sound plausible," he says. "But when you really look at it, it seems pretty far-fetched."