Bottom trawling impacts, clearly visible from space

February 15, 2008

Bottom trawling, an industrial fishing method that drags large, heavy nets across the seafloor stirs up huge, billowing plumes of sediment on shallow seafloors that can be seen from space.

As a result of scientific studies showing that bottom trawling kills vast numbers of corals, sponges, fishes and other animals, bottom trawling has been banned in a growing number of places in recent years. Now satellite images show that spreading clouds of mud remain suspended in the sea long after the trawler has passed.

But what satellites can see is only the “tip of the iceberg,” because most trawling happens in waters too deep to detect sediment plumes at the surface, say scientists speaking a symposium session called Dragnet: Bottom Trawling, the World's Most Severe and Extensive Seafloor Disturbance at the American Association for the Advancement of Science 2008 Annual Meeting. The session was organized by Marine Conservation Biology Institute.

Speakers at the session include Dr. Elliott Norse, President of Marine Conservation Biology Institute in Bellevue WA; John Amos, President of SkyTruth in Shepherdstown WV, Dr. Les Watling, Professor of Zoology at the University of Hawaii in Manoa HI; and Susanna Fuller, Ph.D. Candidate in Biology at Dalhousie University, Halifax NS.

“Bottom trawling is the most destructive of any actions that humans conduct in the ocean,” said Dr. Watling. “Ten years ago, Elliott Norse and I calculated that, each year, worldwide, bottom trawlers drag an area equivalent to twice the lower 48 states. Most of that trawling happens in deep waters, out of sight. But now we can more clearly envision what trawling impacts down there by looking at the sediment plumes that are shallow enough for us to see from satellites,” he said.

Dr. Watling will show startling video and images of the seafloor comparing untrawled and trawled ecosystems. They are available at

“Bottom-trawling repeatedly plows up the seafloor over large areas of the ocean” said Mr. Amos. “Until recently, the impact was basically hidden from view. But new tools – especially Internet-based image sites, like Google Earth – allow everyone to see for themselves what’s happening. In shallow waters with muddy bottoms, trawlers leave long, persistent trails of sediment in their wake.”

To see a gallery of satellite images, and take a Google Earth “virtual tour” of trawl-caused sediment plumes, go to and navigate to the “Trawling Impacts” image gallery.

Susanna Fuller studies impacts of trawling on sponges in the Northwest Atlantic Ocean. “Seafloor animals such as glass sponges are particularly vulnerable to bottom trawling,” said Ms. Fuller, a graduate student of Professor Ransom Myers. Dr. Myers, who died last year, had published a series of papers showing that overfishing has eliminated 90 percent of the world’s large predatory fishes and is devastating marine ecosystems.

“What is amazing is the level of damage these types of animals have suffered, after the cod fishery in Canada was closed. We immediately started trawling deeper with no restrictions, and continue to do so,” she said. “There are ways to catch fish that are less harmful to the world’s vanishing marine life. We need to start protecting the seafloor by using fishing gear, besides bottom trawls, especially in the deep sea. It’s the only thing left,” she said.

“For years marine scientists have been telling the world that fishing has harmed marine biodiversity more than anything else,” said Dr. Norse. “And it’s clear that trawling causes more damage to marine ecosystems than any other kind of fishing. Now, as the threats of ocean acidification and melting sea ice are adding insult to injury, we have to reduce harm from trawling to have any hope of saving marine ecosystems,” Dr. Norse said.

Scientific findings about trawling impacts have led to increasing restrictions on this industrial fishing method. In 2005, the General Fisheries Commission for the Mediterranean banned trawling in the Mediterranean Sea below depths of 1,000 meters, and the United States closed vast deep-sea areas off Alaska to bottom trawling. In 2006, the United Nations General Assembly began deliberations on a trawling moratorium on the high seas, which cover 45% of the Earth’s surface, and South Pacific nations effectively put an end to trawling in an area amounting to 14 percent of the Earth’s surface.

There are tens of thousands of trawlers worldwide. They fish for shrimp and finfishes. Some bottom trawling operations catch 20 pounds of “bykill” for every pound of targeted species.

Source: SeaWeb

Explore further: Conservationists push for Atlantic's 1st national monument

Related Stories

Conservationists push for Atlantic's 1st national monument

September 13, 2015

Undersea ravines deeper than the Grand Canyon, submerged mountains rising thousands of feet from the ocean floor and forests of kelp and coral would become the first marine national monument in the Atlantic if conservationists ...

Trawling is changing seafloor habitats: study

September 5, 2012

Bottom trawling is dramatically altering the ocean floor and harming habitats, similar to the way that farming has permanently changed the landscape, a study said on Wednesday.

Deep-sea fish in deep trouble

September 7, 2011

A team of leading marine scientists from around the world is recommending an end to most commercial fishing in the deep sea, the Earth's largest ecosystem. Instead, they recommend fishing in more productive waters nearer ...

Cliffhanging corals avoid trawler damage

January 20, 2012

Bottom trawling fishing boats have devastated many cold water coral reefs along the margin of the North East Atlantic Ocean. Now, researchers have found large cold water coral colonies clinging to the vertical and overhanging ...

Conservationists call for increased focus on coastal ecosystems

November 8, 2011

The world's coastal marine ecosystems are being overlooked, both in terms of their ecological importance and their potential as a rallying point for conservation. Writing in Aquatic Conservation: Marine and Freshwater Ecosystems ...

Recommended for you

Can Paris pledges avert severe climate change?

November 26, 2015

More than 190 countries are meeting in Paris next week to create a durable framework for addressing climate change and to implement a process to reduce greenhouse gases over time. A key part of this agreement would be the ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.