Bottom trawlers decried as ocean clearcutters
By Environmental News Network staff
(ENN) -- An extremely common industrial fishing method, known as bottom trawling, has the same devastating impact on the ocean bottom as clearcutting forests has on the Earth's surface, according to a series of reports published in the December issue of The Journal from the Society for Conservation Biology.
Trawling vessels drag huge nets for thousands of miles along estuaries, bays and the continental shelves, pulling tons of marine creatures, rocks and mud. Les Watling of the University of Maine in Walpole and Elliott Norse of the Marine Conservation Biology Institute in Redmond, Wash., estimate that trawlers scrape nearly 6 million square miles a year, the equivalent of half the world's continental shelves. This is twice the area of the lower 48 United States and about 150 times larger than the area of forests clearcut each year.
And on top of that, fishermen trawl pretty much wherever and whenever they want because there are very few government restrictions in place -- the frontier mentality still reigns in high-seas fisheries, according to the report.
The damage left behind by trawling is immense. Many of us retain in our mind's eye the storybook picture we had as kids of the bottom of the ocean as one vast wet sandy desert. The truth is that the bottom of the ocean is a complex series of ecosystems, made up mud, seagrass beds, coral reefs, rocky reefs and cobbles. Each sea bed type supports a different community of sea life, and provides protection from predators, food and a safe place to raise young.
Bottom trawling rips all that up. The nets take everything in their paths and the weighted lines dragging the ocean floor crush, bury and expose any remaining wildlife. By leveling the ocean floor, the food chain is disturbed, the hiding places have been removed and conditions favorable to faster growing species take over.
Seafloor recovery could take centuries. Many seafloor inhabitants are slow growing and long lived and are therefore slow to repopulate and rebuild their structures in areas that have been disturbed. Some species of sponges can reach 50 years old, some clams can live for more than 200 years and individual gorgoinan corals have been estimated to live 500 years or more. Some tube-dwelling species can only rebuild homes during an early stage in their development and are therefore left permanently exposed by trawl gear.
Bottom trawling also causes abnormally high nutrient levels in the ocean by stirring up the sediment. Most continental shelf environments typically get half their nutrients from the steady influx of organic material decaying in the sediment. But by stirring up the sediment, bottom trawling releases a huge pulse of nitrogen and other nutrients into the water.
Cynthia Pilskaln of the University of Maine in Orono and her colleagues estimate that re-suspending as little as a tenth of an inch of sediment could more than triple nutrient levels in the sea water.
Higher nutrient levels could increase noxious phytoplankton such as those in red tides, notorious for causing mass fish kills, and shift the balance of plankton populations, which in turn could shift the balance of the fish and other marine life that feed on them.
While the federal government has jurisdiction over eight times as much sea as land, only a tiny area of the ocean is protected from commercial fishing -- the 110-square-mile Florida Keys National Marine Sanctuary. Commercial fishing is permitted in the other 11 national marine sanctuaries. This lack of protection is attributable to opposition from the fishing industry and lack of public awareness, says Tatiana Brailovskaya of the Nereus Project in Newcastle, Maine.
Continued unregulated bottom trawling will eventually lead to more severe collapses of worldwide fisheries, say many of the scientists who contributed to Conservation Biology's special report issue. In shrimp trawls in some parts of the world, 90 percent of the catch is bycatch, thrown back dead or dying. Also, as preferred fish become fewer, the boats are fishing for species which were formerly not considered marketable, further depleting the ocean.
The Marine Conservation Biology Institute and American Oceans Campaign announced the publication of the findings Monday and are calling for the creation of true reserves where fishing is banned.
Why has it taken so long to notice the destruction of sea floor ecosystems?
"The oceans, unlike forests, still look like oceans even after we've removed their contents," says James Carlton of Williams College-Mystic Seaport in Mystic, Conn.
The majority of work presented in The Journal of Conservation Biology was financially supported by the NOAA Regional Marine Research Program.
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