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Hitting bottom

As trawling goes into high gear, undersea coastal habitat is being razed to the ground

The Amicus Journal - Winter 1997 (pp 21-25)

by Dick Russell

Imagine diving to the bottom of the ocean at Georges Bank, an extension of the Atlantic continental shelf some 120 miles offshore from the New England coast. Where the sea floor sinks from 50 to 100 meters deep, a vast gravel deposit armors it like pavement, the work of ancient glacial processes and of the winnowing of sand by storms and strong tidal currents. This is no mere sediment; it teems with life. Clams, mussels, and burrowing sea anemones have tunneled into the substrata. Very thin, small, and fragile colonial worm tubes protrude in spherical clumps. Bushy, seaweed-like plants known as hydroids and bryozoans encrust the cobbles and grow over them like vines. In and around these plants live tiny crustaceans and worms. Sponges with life spans as long as a hundred years, filter-feeders in the water column, punctuate the sea floor.

These organisms and dozens more provide a three-dimensional, complexly structured habitat for other species. They offer nursery areas and refuges for juvenile codfish that are otherwise vulnerable to being eaten by larger fishes. The fauna serve as a food source for bottom-dwelling groundfish, such as flounder, cod, and haddock, at many stages of their lives. Adult herring swim down from higher in the water column to attach their eggs to the pebbles. Left undisturbed, a rich, biologically diverse community thrived here for centuries, feeding countless humans with the fish and shellfish it produced.

Now envision, as it churns into these same waters, a hundred-foot-long, steel-hulled trawling vessel powered by a 1,000-horsepower diesel engine the size of a bulldozer's. The combined stench of fuel and dried fish is overpowering. A jumble of cables and winches is sprawled across the cluttered deck, affixed to a large and extremely heavy net. While the boat moves forward, a pair of deckhands lowers the net to the sea floor. Once on the bottom, two iron doors attached to the mouth of the net gouge the seabed, kicking up a plume of sediment that funnels fish into the net. They are known as otter boards, and they weigh a thousand pounds apiece. In front of them drags a cable designed to stir up mud. The net itself and the massive weights attached to it are pulled along behind. In all, the vessel has five different implements that disturb the seabed as the heavy net sweeps across it -- exposing, crushing, scouring, and burying the life forms that support the very codfish and haddock it is harvesting.

Peter Auster, NURC
A lone scallop (lower right) crosses an empty seabed in the wake of a dredge.

In recent years, a growing and increasingly desperate fishing fleet has scraped and plowed the bottom of Georges Bank nearly beyond recognition. Otter trawlers are not the only agents of destruction; scallop dredges also dig down into the bottom, scraping gravel and the sea life attached to it into their chain bags. But the mobile groundfishing draggers, or otter trawlers, are the most destructive, and there are now some 1,000 of them in New England alone. Their effects are sometimes compared to those of such terrestrial activities as plowing a field, clearcutting a forest, or even strip mining. The most apt analogy, however, is to a practice called chaining, in which cattlemen stretch a dragchain between two bull dozers to clear unwanted vegetation as quickly and thoroughly as possible. "That's pretty much what trawlers are doing twenty-four hours a day on our continental shelves," says Dr. Carl Safina, Director of the National Audubon Society's Living Oceans Program.

The waters of Georges Bank cross the U.S.-Canadian maritime boundary. On the American side, overfishing has depleted what was once one of the world's most productive fishing grounds. In the early 1970s, foreign factory trawlers cleaned out the resource so thoroughly they were banned from the area; the fish then started to recover, but, notes NRDC coastal specialist Lisa Speer, "the U.S. fleet was built up with federal subsidies in the late 1970s and early 1980s, and the fish populations plummeted again." A haddock fishery that yielded as much as 50,000 metric tons annually during the 1960s saw catches drop to 880 metric tons by 1993. During the same period, the numbers of cod and yellowtail flounder also fell by more than 80 percent. The National Marine Fisheries Service has since been forced to enact emergency fishing closures in three large areas. In the nearby Gulf of Maine, the haddock were declared commercially extinct in 1995. Populations of sexually mature fish for all three prime offshore New England species currently stand at about one-fifth of what is needed to sustain their numbers in the future, making the importance of viable habitat for juveniles more crucial than ever.

But it is the nature of bottom-trawling to destroy the habitat of the juvenile fish as it nets the adults. And as competition has grown and catches have dropped, trawlers have worked the area ever more relentlessly. The entire 16,400-square-mile American side of Georges Bank is estimated to have been completely trawled or dredged three to four times over during every year between 1984 and 1990. Scientists maintain that U.S. draggers also swept the whole floor of the 26,400-square-mile Gulf of Maine every year since 1982. Adds Peter Shelley of the Boston-based Conservation Law Foundation, "With the dearth of fish in those two areas, the same gear is now being used for inshore and coastal estuary habitats. They're going after sea urchins and destroying kelp beds, rockweed, and eel grass in very sensitive places like Jeffrey's Ledge." Nor is the problem confined to these once-abundant Northeastern fishing areas. Tens of thousands of vessels are gouging ocean bottoms across the globe, from small Gulf Coast shrimpers to gigantic factory ships that travel half a world away from their home ports.

"Trawlers are so obviously destructive it's a no-brainer," says Dr. Sylvia Earle, a world-renowned marine biologist whose Deep Ocean Exploration and Research organization is based in Oakland, California. "You don't destroy a forest to catch a few squirrels. The oceans are a life-support system, and we are taking the equivalent of bulldozers to its mechanisms without really understanding how they work."

"The impact of logging pales before the destruction of the ocean," adds Paul K. Dayton, Professor of Marine Ecology at the Scripps Institution of Oceanography. "Yet the ocean is out of sight and poorly understood." Indeed, only in recent years have U.S. marine scientists begun observing the ecosystem changes brought about by dragging. Research vessels now use sonar-scanning methods to map and characterize different portions of the sea floor, then send down video and still cameras attached to robotic vehicles. Sediment samples are carried by dredge back to the ships for analysis. In heavily trawled and dredged areas, the damage is stunning; the seabed is left a flattened wasteland with little sign of life, and the samples show a dearth of organisms.

"It's clear that overfishing is the major cause of the disaster at Georges Bank," says Jeremy Collie, an associate professor of oceanography at the University of Rhode Island who is studying the bank's bottom regions. "But everything we have seen to date supports the fact that the more habitat disturbance there is, the less diversity of species. I don't think the problem is mobile gear per se, but too much use of it."

U.S. Geological Survey
Seabed habitat, ninety meters underwater, in northeastern Georges Bank:
undisturbed, left; disturbed, right.

The European forebears of many New Englanders seem to have known better. As far back as 1366, a petition to outlaw the Wondrychoun -- probably Britain's first bottom-trawler -- was put before the nation's Commons. Not only did this "new craftily contrived kind of instrument" have a mesh size that ensnared fish too small to keep, but "the great and long iron of the Wondrychoun presses so hard on the ground when fishing that it destroys the living slime and the plants growing on the bottom under the water, and also the spat [fry] of oysters, mussels and of other fish, by which the large fish are accustomed to live and be nourished."

It is not known what happened to the Wondrychoun, but a decree passed in Flanders in 1499 banned trawls that "rooted up and swept away the seaweeds which served to shelter the fish" Likewise, the Dutch stopped shrimp trawling in Holland's estuaries in 1583, and France went so far as to make the practice a capital offense the following year. In England, two fishermen daring to use metal chain on their beam trawls were executed. Eventually, as political problems, wars, and pirates demanded these nations' attention, the use of trawls resumed. But the gear of their sailing beam trawlers remained relatively light and was towed at slow speed in shallow water. Not until the advent of the steam trawler early in this century did the size and weight of the gear start to increase. Even so, the primary means of fishing in offshore waters was still sailing schooners using long lines of baited hooks, which disturbed the seabed less.

But by the end of World War II, the era of the trawler had arrived. Diesel-powered boats towing the newly devised otter trawls proved so effective that the schooner fleets could not compete. Only the French, concerned about changes in bottom topography at fishing grounds around Corsica, banned this type of gear in their part of the Mediterranean in the early 1970s. Other countries were not similarly convinced. A 1988 study by the International Council for Exploration of the Sea concluded that, while changes in the "benthic community" of seabed life could be related to fishing, not enough relevant information was available.

Today, with every ocean's species considered at critically low levels due to fishing pressure, the need has escalated to identify all causes and seek all potential remedies. Last June, marine scientists from the United States, Canada, the North Sea, Australia, New Zealand, and elsewhere gathered in Maine to share their studies of bottom habitat. They learned of an experimental scallop dredging program in Scotland that showed major damage to large fauna and concentrations of sand eels. They learned of tremendous increases in the area of the North Sea and other European fishing grounds affected by trawls and dredges since the mid-1970s. They heard about one vessel, fishing with a hydraulic dredge, that retrieved over 4,000 tons of stone and gravel for a yield of three tons of scallop meat; the substrata were sieved on board, and most of the trapped animals died from the heat.

The workshop's co-organizer was Elliott A. Norse, who left his position as chief scientist at the Center for Marine Conservation earlier this year to found a new Marine Conservation Biology Institute in Redmond, Washington. According to Norse, trawling and dredging have other ecological effects besides the obvious scarring of the ocean floor: "An enormous amount of sediment gets re-suspended into the water column, where it makes the water very turbid-a problem not only for marine animals that hunt with sight, but for photosynthesizing organisms that need light. This also causes filter-feeding creatures a lot of trouble, because all these non-nutritive particles get sucked in by mussels, clams, oysters, and sponges that must then get rid of them. And when the sediments do eventually settle, they cover over many organisms."

Les Watling, a benthic ecologist at the University of Maine's Darling Marine Center, has observed vast amounts of trawl-generated mud settling over the rocks and burying sponges in the Gulf of Maine. "We don't know anything about the life histories of these particular sponges," Watling says, "but you can't go clean them off because then you break up the animals. We can't say for sure whether we're losing species because of sediment-loading, but these sponges may not make it." Other evidence supports Watling's concerns. A 1992 New Zealand study of seabed trawling revealed that turbidity was killing scallop larvae, eliminating slow-growing deep-water coral, and destroying bryozoan beds that served as fish nurseries. One Gulf of Maine species appears to have completely vanished in waters raked by scallop dredges -- a marine worm whose unusually large nerve axion once made it a valuable subject for neurological research. As Watling notes, "There maybe other species out there on those banks that could be useful in some way, which are being lost as biodiversity goes."

Biodiversity has been going much faster since the latest advance in trawling technology entered the picture. In the mid-1980s, thousands of vessel owners began installing roller gear, or "rockhoppers." Until then, many uneven, rocky areas were avoided by fishermen, lest their nets get caught on the rough bottom. "If you saw a three-foot-diameter boulder in your depth-finder," as Watling puts it, "you tended to stay away from places like that." But the rockhoppers are equipped with rollers on the front, much like automobile tires, that allow them to move right over any obstructions. These are allterrain-vehicles; using them, fishing vessels can trawl the only places where the bottom habitat had remained pristine. "In 1987, we visited four or five of these areas in the Gulf of Maine, and there was no evidence of trawling," says Watling. "When I went back to one of these places in 1993, it looked like the land when it's been clearcut. The boulders were all turned over, and it couldn't have been from storm effects because that can't occur below a 70-meter depth. There just wasn't anything left standing. In my opinion, rockhopper gear puts the final nail in the fisheries coffin."

The effect of rockhoppers was also detected last summer during a research cruise to an area of the Gulf of Alaska where, in depths as great as 700 meters, 80 percent of the bottom was seen to have been recently trawled. And rockhoppers are proliferating in hard-bottomed sectors of the Gulf of Mexico, where the sight of the underwater "flower garden" banks, festooned with extraordinary varieties of coral, sponges, and other species is, in Norse's words, "like visiting another world." In fact, says Scripps' Professor Dayton, "The recent development of so-called 'rockhopper' gear is eliminating the last of the bottom communities."

Peter Auster, NURC
Ocean floor data are collected by a remote-controlled robot.

Yet trawling is not the only available means of catching bottom-dwelling fish. Mark Leach is president of the Cape Cod Commercial Hook Fishermen's Association, which represents a small-vessel fleet of about a hundred boat owners who operate primarily within 50 miles of the New England shoreline. They continue to use the old method, a series of 200 to 1,000 baited hooks set on longlines, which sustained the region's ground-fishermen for 300 years. The longline method is far from environmentally perfect; longlines can catch and kill unwanted fish that are simply discarded, as well as other wildlife, and they can bounce off the seabed and do some limited damage. But the practice is much less destructive than trawling. If no fish take the lines that sink to the bottom, within about an hour the baits are nibbled off by sea fleas, crabs, or lobsters, and the habitat remains undisturbed.

Leach is well aware, from firsthand experience, that "there is precious little habitat left, to the point where a lot of areas we consider critical are so smoothed down that it's becoming easier and easier for mobile gear to tow across it." What Leach and his counterparts are looking for, as he wrote in a guest column last February for the Commercial Fisheries News, is "permitting only the use of rationally managed fixed gear in most areas until less-destructive types of mobile gear are developed."

The body with the authority to create such a system is the New England Fishery Management Council, charged with enacting and enforcing regulations for its region, as first mandated by Congress in the 1976 Magnuson Fishery Conservation and Management Act. The law specifically states: "If manmade environmental changes are contributing to the [decline of spawning stocks or average annual recruitment of fishes] ... councils should recommend . restoration of habitat." However, the New England Council is dominated by commercial trawling interests, and its newly amended Northeast Multispecies Fishery Management Plan failed to emphasize habitat protection. And so, this past June, Leach's organization filed suit against the Commerce Department and its National Marine Fisheries Service, which oversees the regional councils. The suit charged that the New England Council's Amendment 7 "fails to incorporate the differential impact of fishing gear types on habitat and catch selectivity." It notes a lack of any proposed restrictions, for example on the size of rockhoppers, and cites the Council's reasoning that further habitat studies are needed as a delaying tactic. In response, the Council's manager have characterized the hook fishermen's lawsuit as a simple "gear conflict" issue.

The New England Council would do well to take a cue from its counterpart in the South Atlantic region The pace-setter in habitat protection the South Atlantic Council prohibited rockhopper bottom trawling in 1988 off North Carolina, South Carolina, Georgia, and the eastern Florida coast including the Keys. The Council subsequently prohibited al fish traps in hard-bottom areas and this summer, banned rock-shrimp trawls off Florida's southeastern coast-to protect a unique, fragile area of oculina coral whose spiring pinnacles rise to heights well over 75 feet. "Our most recent video showed fairly significant damage to this spectacular branching coral," says Roger Pugliese, the South Atlantic Council's fishery biologist. "That whole area serves as a very vital habitat to many of the species in our Snapper/Grouper Fishery Management Plan. This is probably the most significant action taken so far anywhere in the Atlantic to protect an area from the impact of fishing gear. Our Council is also developing policy statements on dredging and dredge disposal, and submerged aquatic vegetation."

Ken Hinman, director of the Washington-based National Coalition for Marine Conservation, believes that similar actions should be taken by the Gulf Council. "There are 15,000 shrimp boats dragging seasonally down there, the bulk of them in nearshore waters and other sensitive areas. The effects these may be having on the bottom nursery areas tend to get overshadowed by the fishery's problems with bycatch [of unwanted species that are discarded]."

Once action is taken, what are the prospects for recovery? The research to date shows that these things take time, as summarized in a 1992 report by the New Zealand Ministry of Agriculture and Fisheries: "The greater the frequency of gear impact on an area, the greater the likelihood of permanent change. In deeper water where the fauna is less adapted to changes in sediment regimes and disturbance from storm events, the effects of gear take longer to disappear. Studies indicate that in deep water ... the recovery time is probably measured in decades."

Still, scientists are seeing hopeful signs at a fairly extensive area of Georges Bank that underwent an emergency fishing closure in 1994. "What we've noticed preliminarily, in going back two years later to this heavily impacted region, is some initial recovery of attached organisms going on," says Page Valentine of the U.S. Geological Survey. "Of course, nobody knows how long it will take the bottom to recover to its natural state, probably some years."

The signs of resilience, however, bode well for an idea that Peter Auster of the National Undersea Research Center has put forward in two recent papers. Auster and many other experts believe that fishery managers must establish "nonextractive areas," closed to the harvest of any living resources, as well as less restrictive marine reserves where no mobile fishing gear would be allowed. Within these protected areas, undersea wildlife and fish populations could live and reproduce undisturbed. And Auster cites data showing that rigorously protected areas can also serve as a source of re-colonization for surrounding regions, since most species spray their eggs into the water column and the eggs and fry in their early life stages are swept along by the currents for, sometimes, hundreds of kilometers. Finally, Auster adds, "These regions could also serve as reference sites, so we can know more about what humans are doing to the sea floor habitat and biodiversity. What we want to figure out is if there are any thresholds below which complexity does not make a difference to survivorship -- in other words, find out where it's okay to drag and where you shouldn't."

This much is becoming increasingly evident: what high-tech fishing gear is doing to the natural systems of the living oceans constitutes an ecological crisis of its own within the larger, worldwide crisis of overfishing. The loss of sea-floor diversity not only endangers the populations of fish we depend on for our food, but could also threaten the biological processes that maintain the stability of the planet itself. Humans are still profoundly ignorant about the invisible realms that constitute 70 percent of the earth's surface. Who knows whether the seemingly incidental effects scientists are now observing-the broken coral, the disappearance of small marine species, the flattened and empty seabeds -- may not turn out to have fundamental implications for the other life inhabiting the seas, and ultimately for the life that inhabits dry land?

In 1995, a workshop convened by the National Research Council identified fishing as the most ubiquitous agent of change in marine biodiversity. That should send a clear enough signal to policymakers, managers, fishermen, and the public: we must recognize that we are both destructive and ignorant about what we are destroying, and begin to act with more respect.

Peter Auster and Paul Donaldson, NURC
A juvenile cod finds no shelter from predators in a trawled seascape.


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