Bottom Trawls Create Deserts in the Deep Sea

We already knew that bottom trawl fishing—in which large, heavy nets are dragged along the ocean floor—was damaging to ocean life and marine ecosystems. Numerous studies have shown that trawling damages fragile marine habitats and harms many species because the nets indiscriminately scoop up all animals in their path. But new research shows this type of fishing can have “devastating consequences” for the deep sea floor, creating “highly degraded seascapes.”
Published May 19, the study in the Proceedings of the National Academy of Sciences compared untouched portions of a sea canyon in the Mediterranean with areas that had experienced trawling. The scientists were especially interested in effects on worms and other small creatures in the sediment, many of which play important roles in the seafloor ecosystem. 

The research found that the diversity of species in the trawled areas was cut in half, and overall abundance of the small life forms in the sediment dropped by 80 percent. The trawled areas also had only about half as much organic matter in the sediment compared to the control areas.

The study’s authors reasoned that slower growing life forms in the deep sea (the study areas are in 1,500 to 6,500 feet of water) are especially vulnerable to disruption. They likened the effects of bottom trawling to the “desertification” of farmland, in which overuse from plows or livestock turns arable land to wastes. 

The authors wrote that intensive and chronic bottom trawling will "transform large portions of the continental slope into faunal deserts,” and concluded that trawling “represents a major threat to the deep seafloor ecosystem at the global scale.”

Fisheries managers should take note. As inshore fish populations decline and the technology of industrial-scale fishing advances, many trawling fleets are moving into deeper water. This study indicates we should take a precautionary approach to the seaward expansion of fishing practices known to cause lasting damage.

University of Hawaii, Manoa, biology professor Les Watling, a Pew marine fellow and a renowned expert on deep-sea life, commented in the journal that the study challenges some commonly held assumptions. 

“There has been the sense that trawling on open mud bottoms has little or no impact on the resident species,” Watling wrote, but the study shows otherwise.

Here on the Atlantic coast, the Mid-Atlantic Fishery Management Council is considering restrictions on bottom fishing gear in canyons along the edge of the continental shelf and beyond. The council is rightly concerned about possible damage to fragile deep-sea corals and the animals that live among them. But managers now have solid information that the seafloor itself is also vulnerable, as bottom trawling moves to deeper regions.

Peter Baker directs the Northeast U.S. oceans program for The Pew Charitable Trusts.

Spotlight on Mental Health

Composite image of modern city network communication concept

Learn the Basics of Broadband from Our Limited Series

Sign up for our four-week email course on Broadband Basics

Quick View

How does broadband internet reach our homes, phones, and tablets? What kind of infrastructure connects us all together? What are the major barriers to broadband access for American communities?

Pills illustration
Pills illustration

What Is Antibiotic Resistance—and How Can We Fight It?

Sign up for our four-week email series The Race Against Resistance.

Quick View

Antibiotic-resistant bacteria, also known as “superbugs,” are a major threat to modern medicine. But how does resistance work, and what can we do to slow the spread? Read personal stories, expert accounts, and more for the answers to those questions in our four-week email series: Slowing Superbugs.

Explore Pew’s new and improved
Fiscal 50 interactive

Your state's stats are more accessible than ever with our new and improved Fiscal 50 interactive:

  • Maps, trends, and customizable charts
  • 50-state rankings
  • Analysis of what it all means
  • Shareable graphics and downloadable data
  • Proven fiscal policy strategies


Welcome to the new Fiscal 50

Key changes include:

  • State pages that help you keep track of trends in your home state and provide national and regional context.
  • Interactive indicator pages with highly customizable and shareable data visualizations.
  • A Budget Threads feature that offers Pew’s read on the latest state fiscal news.

Learn more about the new and improved Fiscal 50.