Marine Conservation Biology Institute Marine Conservation Biology Institute
Marine Conservation Biology Institute

Disturbance of the Seabed by Mobile Fishing Gear: A Comparison with Forest Clear-Cutting

Elliott's paper made cover story in "Conservation Biology" in 1998  

In 1998, MCBI President Dr. Elliott Norse co-authored a widely cited paper in "Conservation Biology" comparing bottom trawling to forest clear-cutting. Download Disturbance of the Seabed by Mobile Fishing Gear: A Comparison with Forest Clear-Cutting. [PDF]


Bottom trawling and use of other mobile fishing gear have effects on the seabed that resemble forest clear-cutting, a terrestrial disturbance recognized as a major threat to biological diversity and economic sustainability. Structures in marine benthic communities are generally much smaller than those in forests, but structural complexity is no less important to their biodiversity. Use of mobile fishing gear crushes, buries, and exposes marine animals and structures on and in the substratum, sharply reducing structural diversity. Its severity is roughly comparable to other natural and anthropogenic marine disturbances. It also alters biogeochemical cycles, perhaps even globally. Recovery after disturbance is often slow because recruitment is patchy and growth to maturity takes years, decades or more for some structure-forming species.

Trawling and dredging are especially problematic where the return interval is shorter than succession to the ecosystem's original structure; extensive areas can be trawled 100-700% per year or more. Their effects on biodiversity are most severe where natural disturbance is least prevalent, particularly on the outer continental shelf and slope, where storm-wave damage is negligible and biological processes (including growth) tend to be slower. Recent advances in fishing technology (e.g., rockhopper gear, global positioning systems, fish finders) have all but eliminated what were de facto refuges from trawling. The frequency of trawling (in percent of the continental shelf trawled per year) is orders of magnitude higher than other severe seabed disturbances, annually covering an area equivalent to perhaps half of the world's continental shelf, or 150 times the land area that is clear-cut yearly. Mobile fishing gear can have large and long-lasting effects on benthic communities, including young stages of commercially important fishes, although some species benefit when structural complexity is reduced.

These findings are crucial for implementation of "Essential Fish Habitat" provisions of the US Magnuson-Stevens Fishery Conservation and Management Act that aim to protect nursery and feeding habitat for commercial fishes. Using the precautionary approach to management, modifying fishing methods, and creating refuges free of mobile fishing gear are ways to reduce effects on biological diversity and commercial fish habitat.

untrawled trawled
Groupers were abundant on deep-sea Oculina coral reefs off Florida's Atlantic Coast before trawling began; legal and illegal trawling has nearly eliminated the corals and large fishes in this ecosystem. (Untrawled photo by Dr. R. Grant Gilmore, Dynamac Corporation; trawled photo by Lance Horn, National Undersea Research Center/University of North Carolina at Wilmington)





What We Do - MCBI works to stem "marine clear-cutting" on multiple fronts. Learn how we protect the seafloor habitat through scientific research and advocacy, here in the US and on the high seas.