Scouring the Ocean Floor Modern fishing boats tow "sweep chained nets with 500 lbs "doors" across the bottom sweeping everything into their net. Illustration courtesy Boston Globe
By Scott Allen, Boston Globe Staff, 08/17/98
Great clouds of mud billow up from the ocean floor as the metal ``doors'' of a fishing net strike bottom, startling fish from their hiding places among the rocks and plants. Between them, a long metal chain scrapes across the sediment, sweeping everything in its path up into the gaping 200-foot-wide net.
That is the modern way of fishing - called dragging - and its ruthless efficiency goes a long way toward explaining why fish populations off New England's shores have plummeted. In 1994, fishermen and scallopers towed their gear across once-bountiful Georges Bank enough to scour every square inch at least three times.
But the full damage from dragging is only now emerging as scientists begin to focus on the seafloor that draggers leave behind, stripped of the blanket of fragile creatures such as sponges and worms that form a vital link in the marine food chain. Not only do the nets take fish, some scientists fear, but they may be damaging the very foundation of life in the ocean.
Before Dragging - Marine life abounds on the seabed of Georges Bank before big fishing nets make their sweep, gathering up everything in their paths. Photo US Geolic Survey / courtesy Boston Globe.
``The reason this has been sort of an ignored problem is that nobody can see it,'' said biological oceanographer Les Watling of the University of Maine, who compares the effects of dragging to stumps left after a forest is cleared. ``One pass of a [dragger] smashes the big things like sponges and large communities... The net acts like sandpaper when it goes over the rocks, and that just chews everything up.''
Draggermen, already pummeled by five years of regulations that have cut their effort nearly in half, believe that more rules to protect the sea floor are premature. They say there is no proof that their work has permanently damaged fish nurseries anyway, noting that cod populations have begun to rebound since parts of Georges Bank closed in 1994.
However, the trend toward more damaging equipment continues as draggers try to compensate for new regulatory limits. ``Street sweepers,'' big wheels of bristles that are attached to the bottom of nets, allow draggers to tow their nets over parts of the sea floor once considered too rocky, thoroughly churning up the bottom in the process.
After Dragging - After an area has been swept by the big nets, the rocky seafloor appears virtually lifeless. It's like clear cutting a forest, scientists say. Photo US Geolic Survey / courtesy Boston Globe.
Though the New England Fishery Management Council has proposed a ban on street sweepers, fishermen who don't use dragging gear already are fed up with the council's slow pace of action. The Cape Cod Commercial Hook Fishermen's Association has filed a lawsuit in Boston against the federal government to force it to take action against destructive fishing gear.
``It was pretty obvious the council wasn't going to address destruction of habitat by fishing methods,'' says Mark Leach, leader of the Cape Cod fishermen who use baited hooks to catch fish. He noted that several council members are draggers themselves, adding, ``It struck too close to home.''
Against the backdrop of the federal lawsuit as well as law changes that require protection of fish habitat, the Conservation Law Foundation of Boston last week published a book that for the first time takes a comprehensive look at the impact of dragging on the seafloor.
Drawing on presentations by both scientists and fishermen, ``Effects of Fishing Gear on the Sea Floor of New England'' describes an astonishingly widespread fishing practice - more than 35,000 square miles were dragged in the Gulf of Maine and Georges Bank annually in the early 1990s - and concludes that it appears to be reducing the variety of plants and animals in the sea.
``Everyone believes that the long term impact is to reduce what's living on the bottom,'' says Eleanor Dorsey at the foundation, who edited the book. ``It's a persistent loss of diversity and of complexity, '' both characteristics that are vital to nurturing commercially important fish, such as the cod.
When fishermen started dragging nets across New England's sea floor in the early 20th century, cod was a cornerstone of the New England economy and few thought much about the impact of the new way of fishing the ocean bottom. Fishermen called the sea cucumbers, sponges and other organisms that came up in their nets ``trash,'' and a 1914 scientific study concluded that dragging did ``not seriously disturb the bottom,'' says University of Rhode Island oceanographer Jeremy Collie.
In those days, dragging was limited to a handful of small boats - compared to the hundreds of larger draggers today - and scientists had no way to see what was happening on the bottom. Only with the advent of underwater video cameras, sonar, manned submersibles and other equipment have researchers been able to see for themselves.
Long line fisherman Mark Leach says sea lemons, or sea squirts are dissapearing from habitat they share with cod. Photo courtesy Boston Globe.
Today, researchers know that the ocean floor is a world unto itself, an array of undersea peaks and valleys, mud and rock, that supports a wide array of life: starfish and sponges, dense beds of horse mussels, anemones that look like little palm trees, worms peaking out of delicate calcium towers, and more.
Far from ``trash,'' the plants and animals at the bottom of the sea, known as the benthic community, are a major fraction of life in the ocean and a key source of food for commercially valuable fish such as flounder and cod. Just as important, certain types of sea bottom serve as nurseries for the next generation. Juvenile cod, scallops and haddock, for example, thrive in sediment with the consistency of a gravel driveway.
Underwater photographs of a gravel seabed taken by the US Geological Survey reveal that repeated dragging strips away the worms, hydrozoans, and other creatures, leaving the bare stones behind. ``There are lots of attached organisms in gravel,'' explained the survey's Page Valentine. Draggers ``knock them off and they don't come back right away,'' though there are signs of recovery two and a half years after dragging ceases.
For years, the saving grace for bait-and-hook fishermen was limiting where the draggers could go. When Mark Leach, now 41, started fishing in the 1970s, the rocky and uneven seabed off the elbow of Cape Cod was too treacherous for draggers. If they tried, their nets would often snag on boulders, tearing the net and taxing the boat's engine.
So cod fishermen out of Chatham and Harwich continued to catch fish much the way it was done by the 19th century dorymen made famous by painter Winslow Homer, using long lines with hundreds of baited hooks attached. Though they couldn't catch as many fish as their dragging counterparts, the long liners could work in rich fishing areas where the draggers couldn't go.
But the march of technology swept across the fishing industry in the 1970s and 1980s, bringing bigger, more powerful boats and innovations in the nets that allowed draggers to catch more fish or scallops and go just about anywhere. They attached rubber wheels or disks called cookies or rockhoppers to their chains, allowing nets to jump over rocks up to three feet in diameter.
Leach and other long linemen protested the draggers' intrusion to their fishing grounds, arguing that they were doing irreversible damage. They said that ``sea lemons,'' lemon-shaped invertebrates that congregate in the same areas as cod, were fast disappearing, suggesting that the draggers were taking both the cod and their habitat. Long liner Fred Bennett dropped a 100-pound roller onto a vase of flowers to demonstrate the damage done by dragging at a 1995 hearing of the New England Fishery Management Council.
/ Scallop boats typically drag two 13-15 foot-wide dredges along the seabed, using sweepchain to gathher catch. Illustration courtesy Boston Globe.
But draggers accused Bennett and other long liners of playing into the hands of regulators who were trying to crack down on over-fishing, and they called for unity among fishermen. ``I thought I came to a public hearing, not a public hanging,'' said Jim Kendall of the New Bedford Seafood Coalition, according to the Cape Cod Chronicle's account of the meeting. Draggers still argue that the impact of their gear has been exaggerated by people who don't understand. Frank Mirarchi, a Scituate dragger, explains that, although dragging of New England waters is extensive, it is concentrated in certain areas rather than blanketing the entire seabed. Moreover, Mirarchi has found that the best fishing areas are ones that he drags the most, suggesting that dragging doesn't do long-term harm, at least on soft surfaces where he drags. Likewise, scallopers believe that periodic disturbances from their dredges actually improve scallop habitat, a view that Dorsey of the Conservation Law Foundation says may have merit.
Over time, however, repeated dragging or dredging for scallops is like a force of evolution, scientists say, eliminating softer organisms such as shrimp and sponges, and favoring the survival of tough scavengers such as hermit crabs. Watling of the University of Maine suggests that, even when the dragging stops, the recovering seafloor is less diverse - and less life-sustaining - than it was before, much like a prairie after the land has been converted to growing wheat. ``The prairie produces wheat, but it doesn't have very much biodiveristy compared to what it was like before people grew wheat,'' said Watling. ``It's the same thing with the sea. Are we interested in those kinds of monocultures in the sea?'' That question is squarely before the Fishery Management Council as it grapples with changes in federal fisheries law that require them to protect ``essential fish habitat.'' The 17-member council just finished mapping these sensitive areas, but has not decided how to protect them.
US District Judge Richard Stearns in Boston has delayed the Cape Cod long line fishermen's suit until fall to give the council time to take action on gear damage, but the long liners' lawyer says he will press the suit if the council doesn't do better than it has so far. Draggers and scallop dredgers ``are strip-mining the seafloor,'' declared attorney David Farrell, Jr. of Chatham. ``Who's surprised that the fisheries are depleted?''