Study: Bottom trawling damages fish populations

GRANTS PASS, Ore. — Scientists taking a new look at old videotapes of the muddy seafloors off southern Oregon found that places showing tracks from the nets of fishing trawlers had fewer numbers and kinds of fish than areas that were undisturbed.

Other studies worldwide have documented the damage that bottom trawling does to seafloor habitats, but this is the first to look at fish numbers and diversity on muddy seafloors on the West Coast's Continental Shelf, where bottom trawlers do much of their work, the study authors said.

A review of videotapes taken in 1990 from a manned submersible in an area known as the Coquille Bank off southern Oregon found that in areas showing roller tracks in the mud from bottom-trawling nets, there were 20 percent fewer fish, 30 percent fewer species of fish and six times fewer invertebrates, such as crabs.

"We are not suggesting trawling be banned," said Mark Hixon, a professor of marine biology at Oregon State University and lead author of the study published in the Journal of Experimental Marine Biology and Ecology.

"The question must be asked whether we want to sacrifice these ecological communities, not even knowing what the long-term effects of bottom trawling might be, or whether some mud areas of the Continental Shelf deserve permanent protection," he said.

The areas disturbed by fishing tended to have more scavengers, such as sea stars, hermit crabs and hagfish, which may have been attracted by burrowing organisms exposed by the trawling gear, Hixon added.

Two years ago, federal fisheries managers banned bottom trawling on 300,000 square miles off the West Coast to protect coral beds, kelp forests, rocky reefs and other essential fish habitat. But there have been no efforts to protect the muddy seafloor that covers most of the Continental Shelf, scientists said. Some areas of the shelf are temporarily off-limits to bottom trawling until rockfish populations rebuild from overfishing.