Commercial Bottom Trawling and Deep Sea Coral - Final

This topic submitted by Craig Voros ( at 11:04 AM on 5/29/06.

Students take a "coral quiz", San Salvador, Bahamas.

Tropical Field Courses -Western Program-Miami University

Craig Voros 5-26-2005
Marine Ecology Paper

Commercial Bottom Trawling and Deep Sea Coral

Corals do exist thousands of feet below the ocean’s surface. Scientists have discovered that some of the largest coral structures in the world are found in waters to deep for sunlight to reach (International Council for the Exploration of the Sea, 2005). These communities and habitats are among the oldest on the planet. Coral reefs are one of the oldest types of living systems on Earth and are critically important for a number of species and for sheries and biodiversity of the oceans (World wildlife Fund, 2003). While the presences of these communities have been known for decades it has not been until recently that their importance is becoming more mainstream (World Wildlife Fund, 2003). Yet as this knowledge grows threats to these communities continue to grow as well. Fishing and resource extraction play a large role in the future of what these ecosystems may look like.
A commercial fishing operation is an industry that has long been regulated by the Federal government. While many there are many commercial fishing methods, bottom trawling is by far the most ecologically devastating to the ocean and sea floor. Fishing boats pull bottom trawl nets across the ocean floor to catch fish, shrimp, and crabs. The sheer size and weight of trawls allow them to capture virtually everything in their path from unwanted fish and mammals, to sea turtles and deep sea corals. A study conducted in 2002 by the National Academy of Sciences found that trawling directly affected about 231,000 square miles of seafloor habitats on the continental shelf and slope off the United States; this area is greater than the state of California (NRC, 2002.).
The problem with commercial trawling and its impact on coral reefs is described by David Griffith, of the International Council for the Exploration of the Sea (ICES);

“Towing a heavy trawl net through a cold water coral reef is a bit like driving a bulldozer though a nature reserve. The only practical way of protecting these reefs is therefore to find out where they are and then prevent boats from trawling over them.” (ICES Press Release, 2005).

Bottom Trawling
Bottom trawling is the practice of dragging huge nets weighted down by trawl doors, chains and rock-hopper gear. These nets are intended to catch groundfish species (rockfish, cod, and sole), shrimp, and crabs. A trawl has a large bag shaped net, wide at the mouth and tapering toward an enclosed end. The net is connected to two large steel doors that can weigh up to 5 tons each. These doors are designed to drag along the seafloor and keep the nets open. The doors are connected to the fishing vessel by long bridles and the distance between the tow large steel doors can be anywhere from 330-650 feet across (Alaska Marine Conservation Council, 2006). A footrope forms the base of the net opening and it is often fixed with rolling disks and metal or rubber bobbins that enable the gear to bounce over the seafloor (Alaska Marine Conservation Council, 2006). On average on a commercial trawling boat can catch an average of fifteen tons of fish in a single haul (Alaska Marine Conservation Council, 2006).
Graphic of a bottom trawling operation. Courtesy of Marine Conservation Biology Institute

Deep Sea Corals
Deep sea corals are very similar to shallow-water corals. They vary greatly in their size, shape, and color, while some are soft and others hard. About 20 of the 703 known species of deep stony corals build reef structures, and most are a part of a larger community of sponges, sea anemones, fish, shellfish and many others. However unlike their tropical relatives, deep sea corals do not get any other their energy from direct sunlight. Instead they feed on microscopic animals from the surrounding water (Oceana, 2003). They also survive at much lower temperatures, as cold as 30 degrees F. Far from the sun these species can live over three miles below the ocean’s surface (Oceana, 2003). Found throughout the world but usually in isolated locations, deep sea corals tend to be found on the edges of the continental shelf or on underwater islands, called sea mounts (Oceana, 2003).
Deep sea corals grow very slowly, typically less than an inch per year. This slow rate of growth and the sheer size of some specimens lead scientists to believe that some species can live to be hundreds if not thousands of years old (Oceana, 2003). Science has just begun to identify the various types of species in these deep sea communities. As technology for manned and un-manned submersibles grows, so too may the knowledge of these unique habitats. While thousands of different types of deep sea coral have been described, including hydrocorals, seam fans, bamboo corals, and black corals, scientist estimate that roughly 800 species of stony corals have yet to be identified (Oceana, 2003). Furthermore the types of fish and other species that live in these communities are so unique that they have yet to be discovered or identified. The importance of these ecosystems is just beginning to emerge. Fish congregate in deep sea coral communities, and that is why fisherman place drag their gear there. Scientific research has shown that a variety of species use corals and sponges in the deep sea as protection from predators, areas of plentiful food, hatcheries for eggs, and nurseries for young fish (Oceana, 2003).

Impacts of Trawling
Bottom trawling reduces the complexity, productivity, and biodiversity of seafloor habitats (NRC, 2002). In addition, stable living habitats, such as sponge and coral communities are among the most heavily damaged and the slowest to recover from trawling (NRC 2002). Trawling is the single largest threat to slow-growing seafloor animals such as corals and sponges (Freiwald, 2004).
The most obvious affects of trawling on deep sea coral reefs is the mechanical damage caused by the gear itself. The equipment breaks up the reef and their delicate structures. The heavy gears can directly kill corals, break up reef structure, and bury corals through increase sedimentation (Rogers, 1999). When trawling fishing gear is dragged along sea floors, species are uprooted and destroyed. This method, results in habitat that takes centuries to recover, if it does at all (Oceana, 2005). More importantly there are few legal protections for these organisms resulting in areas where corals previously thrived being barren. Other species that depended on these crucial coral habitats are facing serious population declines.
Deep sea trawling is likely to cause widespread ecological changes and reductions in the diversity of life at all depths (Cryer, 2002). Other species depend on deep sea corals and sponges for habitat. After tropical rainforests, coral reefs are the most biodiverse habitats in the world. More importantly bottom trawls do not distinguish between target and non-target species. Although deep sea corals and sponges are not desired species in fishing industry, when bottom trawl nets are retrieved from the ocean floor, non target fish, sponges, and corals are all discarded in large quantities (Oceana, 2005). Continual bottom trawling activity in an area can permanently damage sea floor habitats.

Important Legislation
In response to this problem Congress has introduced Senate Bill, S.1635 and in the House of Representatives, H.R. 3778; otherwise known as the ‘Bottom Trawl and Deep Sea Coral Act’. This Act was enacted to establish areas where bottom trawling is permitted, to protect deep sea corals and sponges, and for further research of their ecosystem. In general, the Act will allow fishermen to use bottom trawls in areas that, traditionally, have been fished using bottom trawls and that do not contain deep sea coral and sponge ecosystems (S. 1635, and H.R. 3778, 2005). It is intended to provide long-term protection for deep sea coral and sponge ecosystems, particularly in regions that have not been traditionally fished with bottom trawls (S. 1635, and H.R. 3778, 2005). Also, the Act will be used to identify, map, and assess deep sea coral and sponge ecosystems to create a balanced policy for maintenance of fishing and protection of deep sea ecosystems (S. 1635, and H.R. 3778, 2005).
The Bottom Trawl and Deep Sea Coral Act was introduced to the Senate by Frank Lautenberg on September 8, 2005, it was read twice and then referred to the Committee on Commerce, Science, and Transportation. The bill was also introduced to the House of Representatives September 14, 2005 by E. Clay Shaw, and on September 26 of the same year it was referred to the Subcommittee on Environment, Technology, and Standards. Currently no hearings in either branch of Congress have been held concerning this legislation.
This legislation is necessary because the problem affects a large number of people, and has broad consequences. In this situation there are two major conflicting groups, those that oppose the destruction of living coral and sponge ecosystems, and those who have traditionally fished and maintained a living through bottom trawling. Government intervention is necessary because both parties will be unable to come to a resolution on their own. This problem can be divided among the needs of the economic parties versus the needs of the environmental parties. The decisions and solutions generated will affect numerous people. However it is important to note that the destruction of fish habitat will ultimately decrease the economic benefits of fishing.
The fishing industry and the economic perspectives are represented by groups such as the Maine Lobstermen’s Association, The National Fisheries Institute, United Fisherman of Alaska, Western Fishboat Owner’s Association, GroundFish Forum, Fisheries Marketing Association, United Salmon Association, and the At-Sea Processors Association, to name a few. The environmental perspective is represented by groups such as Oceana, International Council for the Exploration of the Sea, Marine Conservation Biology Institute, Greenpeace, Earth Friends, Conservation International, Pacific Fisheries Management Council, National Coalition for Marine Conservation and the Deep Sea Conservation Coalition to name a few.
It is important for this legislation to be passed. It meets the minimum requirements necessary to ensure the future survival of deep sea coral and sponge habitats, while permitting limited bottom trawling. This policy would prevent future areas from being destroyed, while also allowing important ecological areas to be conserved, regardless if they are located in traditional fishing grounds. This policy is equal and fair for all the interested parties; it does not ignore the needs of any one of the interested groups over another, and does not place blame. I think both parties will be able to live with this legislation because it will not limit the economic needs of the fishing industry or conclude that sea coral and sponge habitats are not important. This policy will protect viable fish populations and help the fishing industry, by protecting habitat that is used as nursing grounds.

The Future of Deep Sea Corals
It is easy to relate how devastating bottom trawling can be on these relatively fragile deep sea coral ecosystems. As commercial fishing boats get bigger and engines larger, areas that were once inaccessible to fishermen will soon feel the effects of their industry. As fish populations dwindle and move farther out to sea this industry will be forced to follow them and use the most economically convenient way to make a living. For the flatfish, shrimp, and crabbing fishing industries, bottom trawling does seem to be the answer. However this method can be highly destructive on ocean health, and must be limited in some fashion. The Bottom Trawl and Deep Sea Coral Act is one way to limit this destructive fishing practice. It is important that scientists be able to study how vital these habitats are and map their full extent across the globe. If we can identify areas where these habitats are, then legislation can be written to protect those crucial areas. If these unique habitats are going to survive then work must be done now to protect it.
Alaska Marine Conservation Council. Accessed 5/26/2006. “Our Work: Bottom Trawling Fact Sheet”. Available at

Bottom Trawl and Deep Sea Coral Habitat Act, S. 1635, H.R. 3778, 109th U.S.C., (2005)

Cryer, M., B. Harthill, S. O’Shea. 2002. “Modification of marine benthos by trawling: toward a generalization for the deep ocean?” Ecological Applications 12(6): 1824-1839

Freiwald, A., J.H. Fossa, A. Grehan, T. Koslow, J.M. Roberts, J.M. 2004. “Cold-water coral reefs.” UNEP-WCMC, Cambridge, United Kingdom

International Council for the Exploration of the Sea, ICES. 2005. Accessed 5/26/2006. “Coral reefs in the Nortah atlantic?” Available at

International Council for the Exploration of the Sea, ICES. 2005. Accessed 5/26/06. “Press Release: Close Europe’s cold-water reefs to fishing.” Available at

National Research Council. 2002. “Effects of trawling and dredging on seafloor habitat.” Committee on Ecosystem Effects of Fishing: Phase 1—Effects of Bottom Trawling on Seafloor Habitats, National Research Council

Oceana. 2003. “Deep Sea Corals: Out of sight but no longer out of mind.” Accessed 5/26/2006. Available at

Oceana, Marine Conservation Biology Institute, 2005. “Justification of the bottom trawling and deep sea coral habitat act of 2005.” Available at

Roberts, C.M. 2002. “Deep impact: the rising toll of fishing in deep seas.” TRENDS in Ecology and Evolution 17(5): 242-245

Rogers, A.D. 1999. “The biology of Lophelia pertusa and other deep-water reef-forming corals and impacts from human activities.” International Review in Hydrobiology 84: 315-406

World Wildlife Fund. 2003. “Norweigan coldwater coral protection.” Gift to the Earth #86. June 11, 2003

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