Fish Story: Researchers Say Trawling Not So Destructive After All

A new study contradicts conventional wisdom, showing how bottom trawling can have minimal impacts on the ocean floor.
(Photo: Chris Furlong/Getty Images)
Feb 26, 2015· 1 MIN READ
Katharine Gammon has written for Nature, Wired, Discover, and Popular Science. A new mom, she lives in Santa Monica.

For decades, trawling—pulling a net along the seafloor to catch fish—has been denounced as one of the most environmentally destructive practices in the fishing industry. But researchers now say trawling may not be so bad after all and could even be transformed into a more benign way of fishing.

That sounds like heresy, given global campaigns to ban trawling, which scours the seabed. A new study published this month in the journal Fishery Bulletin, however, uncovers a different story.

Researchers tested an area of soft-bottom ocean near Morro Bay, California, keeping some areas untouched and trawling others up to eight times. Using underwater robots, they photographed the areas two weeks, six months, and one year later. The results showed minimal damage to the areas, confirming what fishers had said for years.

Those findings surprised the study’s authors.

“I expected to find more impacts than we did,” said Mary Gleason, lead scientist for the Nature Conservancy’s California Oceans Program and coauthor of the report. “We did have some scour marks from the steel doors at the bottom, but other than that, we didn’t see any changes in the seafloor communities.”

Ocean-floor communities are surprisingly dynamic, the researchers found. After a year, they didn’t find the density of seafloor life significantly different between trawled and untrawled areas.

That’s not to say trawling doesn’t have significant effects on other ocean environments— particularly rocky-bottomed seabeds.

“The nature of the impact is going to depend on the type of equipment, the type of habitat, and the intensity of trawling,” said Gleason. She added that regulations around trawling need to be balanced with the science and that sole and other are flatfish caught by trawlers are important parts of local economies.

Groundfish populations are rebounding, and trawled fish recently joined the list of those considered sustainable to eat by Monterey Bay Aquarium’s Seafood Watch.

Even some soft-bottomed areas may react differently to being trawled. The area the researchers tested is representative of about 85 percent of the continental shelf off the coast of California, but other environments may not fare as well, said Gleason.

In the future, it may be possible to balance trawling with smart fishery management. James Lindholm, a coauthor of the study and a marine scientist at California State University, Monterey Bay, is studying the effects of newer, lighter equipment on the ocean floor. Typically, heavy steel doors scrape the floor in a trawl operation. But the new equipment floats just above the ocean bottom, which not only protects marine life but also allows fishers to travel faster and use less fuel.

“It’s so important to be working with the fishing community to address the key management questions that are out there,” said Gleason. “A lot of times we just rely on scientists and management agencies, and it’s really important to do that more collaboratively.”