Destructive Trawling FAQ
Why are healthy seafloor environments important?
More than 40 percent of U.S. "lands," (land plus ocean seafloor) are on the seafloor of our exclusive economic zone (three miles to 200 miles off the shore). Beneath the surface, the seafloor consists of a mosaic of habitats including smooth sand, mud, rocky ridges, deep-sea canyons, and seamounts. The incredible biodiversity of the oceans is especially concentrated around complex habitats of geologic structures (e.g., gravel, boulders, crevices, rock pinnacles, overhangs) and biogenic structures, which are created by animals such as sea anemones, sponges and deep sea coral. The marine food web and healthy marine ecosystems rely on diverse, relatively undisturbed, complex seafloor habitats.
What is bottom trawling and what does it do to the seafloor?
Bottom trawling is a specific type of fishing gear that destroys marine biodiversity and threatens commercial and non-commercial fish species. Bottom trawling is an indiscriminate method of fishing using large, heavy nets that drag along the ocean floor smashing into everything in their path, including fragile deep-sea corals and anemones, and catching a wide array of fish species of all ages and other marine species.
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Mounting scientific evidence shows that trawling is one of the most destructive types of bottom fishing because it (1) removes species that live on the seafloor, (2) homogenizes the habitat by smoothing the sediment and breaking down any complex structures, and (3) reduces overall habitat complexity.
What is bottom trawling gear?
Bottom trawls have a footrope (the bottom lip of the net) that can span over 150 feet in width and can be lined with heavy rollers or rockhoppers more than 30 inches in diameter. The larger trawls can drag over a half-acre swath with each pass over an area. The damage done by even a single pass of a trawl can be very extensive. Trawls with heavy, large-diameter rollers and rockhoppers have been shown to displace 19 percent of boulders (some weighing 25 tons each).
The size of trawl gear and frequency of its use in an area can increase the severity of the damage. Before the mid-1980s, rocky, complex habitats were relatively undamaged, because fishermen kept bottom trawls out of areas where structures such as corals, boulders or pinnacles might snag the trawl net. Large, heavy roller and rockhopper gear, in combination with more powerful fishing boats and other technical innovations, now allow bottom trawls to access virtually all areas of the continental shelves and deeper continental slopes, including areas with structurally complex habitat.
Won't the seafloor environment and marine life repair itself?
Frequent bottom trawling with large roller and rockhopper gear can change the species that live in the area. Habitat-forming species such as corals, sponges, and fish that dig burrows or build mounds no longer thrive in areas where trawling has reduced the structural complexity of the seafloor. In an experiment off Alaska, 67 percent of vase sponges and 55 percent of sea whips (a type of deep-sea coral) that were damaged by one pass of a trawl still had not recovered after a year of no further trawling.
DESTRUCTIVE BOTTOM TRAWLING IS THE BIGGEST HUMAN THREAT TO DEEP SEA CORALS AND SPONGES
What are deep sea corals and sponges?
Deep sea corals and sponges, some of the oldest animals on Earth, grow at the rate of just a few millimeters each year and live for thousands of years. In recent years NOAA and other scientific organizations worldwide have discovered that the majority of the coral species found in the world's oceans live in deep or cold waters. Deep sea corals are typically found along continental margins, seamounts, undersea canyons and ridges. Some individual corals grow together to form small bushes or fans; others form larger colonies such as reefs or great trees. Sponges are single animals. Two thirds of all coral species are deep-sea corals.
Why are deep-sea corals and sponges important?
Deep sea corals and sponges are essential to the ocean's health because they preserve ocean biodiversity and long-term sustainability of commercial and recreational fish species. Deep-sea corals can form reefs and gardens that are essential to numerous oceanic species - including fish - by providing shelter, protection from strong currents, protection from predators, nurseries for young fish, feeding areas, spawning areas, resting areas, and breeding areas for a host of other marine life. They also provide important clues for the study of global climate change and are under study as sources of new biomedical compounds for medical treatment of disease.
Where are deep-sea corals and sponges found?
Scientists know that deep-sea corals grow off every coast, from Maine to Texas, Alaska to California and around Hawaii. However, most of the deep-sea corals off the U.S. coasts have not even been located, let alone studied. They remain largely unprotected as a result.
What is the difference between tropical, shallow-water corals and deep-sea corals?
Shallow and Dee-Sea Coral Comparisons
Shallow | Deep | |
Geographic range | Narrow band around the equator, close to shore | All oceans from Arctic to Antarctic, national waters and also on seamounts in high seas |
Depth range | 160 feet generally, 700 feet where the water is very clear | To 4 miles |
Feeding | Directly from sunlight through symbiotic relationship with photosynthetic algae | Organic matter and nutrients captured from sea water |
Shape and color | Many, from great reefs and gigantic crimson trees to soft hand-sized and thimble-sized ivory cups. Some hard to the touch, others soft and sway with the current. | Same |
Variety of life | One of the greatest on Earth | Some reefs (Lophelia, Oculina) have as high a diversity as shallow water reefs |
Threats | Climate change (bleaching, sea level change), over fishing of reef fish (changing ecology, cyanide and dynamite fishing), pollution (disease, algal growth, blocking sunlight) | Biggest is trawling, others include other fishing methods, possibly oil and gas development, cable laying |
What are the threats to deep sea corals and sponges?
Deep sea coral habitats are subject to growing human impacts, particularly from deep sea trawl fisheries into deep water regions. The National Research Council, the U.S. Commission on Ocean Policy, and the Pew Oceans Commission have found that bottom trawling can destroy deep sea coral habitats. Even a single pass of a bottom trawl can flatten centuries of growth.
What have other countries done to protect deep sea corals?
The European Union, Australia, Ireland, New Zealand, Canada and Norway have already prohibited the use of mobile bottom-tending fishing gear in some areas containing deep sea coral ecosystems.
What are seamounts and why should they be protected from bottom trawling?
Recent science has shown us that large seafloor hills or "seamounts" are actually often mounds resulting from thousands of years of coral growth. When such slow-growing animals are damaged or killed, the years, decades or centuries needed for the corals to recover can open the door for flat-bottom species to take over and push out species that prefer structured habitats. Numerous studies have found that heavily trawled areas suffer biodiversity crashes, particularly in complex habitats. Scientists do not yet fully understand how the trawling-induced impacts on one species will affect other species. The longer we allow bottom trawling to occur in these habitats, the more likely we will lose species that are important for the marine ecosystem, food, medicines, and technological advances.
How does destructive bottom trawling affect the commercial and recreational fishing activities?
Some commercially and recreationally important fish and crustaceans have shown greater survival rates in the healthy, structurally complex habitats. Lingcod use high-relief bottom to lay their eggs. Juvenile Atlantic cod show far greater survival rates where the seabed is complex and offers protection from predators and strong currents. Adult haddock and most groundfish rely on seafloor life found in complex habitats as their major source of food. Without complex habitats, populations of the fish that depend on structured habitats may suffer population declines or may take longer to recover from other threats such as overfishing.
How will restricting bottom trawling help commercial and recreational fishermen?
Restricting bottom trawling in complex habitats promotes sustainable fisheries. The issue is not whether to stop fishing, but whether to allow use of a type of gear as destructive as large roller and rockhopper trawls. The same fish may be caught by hook and line or by fish trap without causing the widespread flattening of habitat or changes in species composition that bottom trawling can lead to. Unlike some areas of sand and mud, areas of three-dimensional, structurally complex habitat do not remain productive after decades of trawling.
It is critical that remaining pristine areas of structurally complex habitat be protected from damage by large rollers and rockhoppers. Stopping trawling in areas that have already been altered will allow for recovery to begin. Protecting structurally complex habitat would result in more fish for both fishermen and fish consumers, a richer diversity of species, and a healthier marine ecosystem.
