Trawlers are smoothing the floor of the Mediterranean Sea, much as farmers flattened fields across Europe centuries ago. And it's likely that similar smoothing is occurring wherever bottom trawlers operate across the Seven Seas.

New research published online by Nature on September 5 reveals that bottom trawling—dragging massive nets across the seafloor to catch food such as deep-sea shrimp—is pushing sediment to fill in gaps on a daily basis, resulting in smooth undersea plains. (Scientific American is part of Nature Publishing Group.) "Fishermen are not doing anything different than farmers many decades ago," explains marine scientist Pere Puig of La Agencia Estatal Consejo Superior de Investigaciones Cientificas (CSIC) in Barcelona, who led the research. "Fishing grounds could be seen as farm fields, but there has to be some limitations to avoid the extension of trawling impacts."

Puig and his colleagues started analyzing the impact of bottom trawling after noticing in 2002 that the fishing technique was stirring up and transporting more sediment than natural processes in an area off the coast of Spain. The La Fonera undersea canyon, near the port of Palamos, sees fishing from some 180 bottom trawlers.

The scientists moored an instrument 980 meters deep in the canyon to measure the flow of sediment from both natural processes and bottom trawling. The daily mud slides and their attendant currents, which moved as fast as 38 centimeters per second, transported more than a metric ton of sediment per square meter. All told some 5,378 metric tons of sediment moved this way over the course of 136 days of monitoring—and the fishing technique has been in place since the 1970s.

The researchers also mapped the canyon using sonar pings, revealing "a noticeable smoothing of bottom topography," they write. This smoothing occurred at depths shallower than 800 meters, which corresponds to the deepest trawls undertaken by the fishing fleet. In addition, plotting the navigation tracks of the fleet via global positioning satellite data from 2007 to 2010 showed a match between the fleet's course and the smoothing.

The effects of this smoothing on the creatures that make a home on the seafloor remain unknown, though the activity could conceivably have impacts ranging from a loss of species diversity due to the loss of unique habitats, to changes in how the ecosystem as a whole functions, Puig notes. He adds that the researchers have "no idea" how ecosystem impacts from seafloor smoothing compare with ecosystem impacts from other bottom trawling-related changes, such as the destruction of deep-water corals. But, unlike farmers, fishing fleets tend to "plough" the deep sea almost every day.

Leveling of the seafloor by bottom trawlers is unlikely to be confined to the Mediterranean coast of Spain. Trawling is an important fishing technology in most of the world's most productive fisheries, from the Gulf of Mexico off the coast of Louisiana to the southwestern Pacific Ocean near Australia and New Zealand. "Intensive bottom trawling has also occurred during several decades in continental slopes elsewhere," Puig says. In effect, human reshaping of the bottom of the sea is another unforeseen sedimentary side effect of the dawning geologic era some scientists have dubbed the Anthropocene.

14 Comments

1. 1. rollership 07:07 PM 9/5/12

   Do we have to destroy the final frontier before we even see this magical alien world at the bottom of the ocean? yeah lets just destroy the view for future ocean tourists to ocean cities and kill everything in the ocean, sounds like us.

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2. 2. Unksoldr 07:27 PM 9/5/12

   Why this is news I have no idea. Common sense would tell you that this is exactly what bottom trawling would do.

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3. 3. T1Brit 08:45 AM 9/6/12

   You know what I think? This is spin. It is a Spanish study - the Spanish trawler fleet is the greatest single force for destruction of the deep Ocean in the world. They need some good press badly. So they commission this stupid study which concludes the bleeding obvious, and also adds a slightly rosy image of the seafloor looking like ploughed meadows. The Spanish scientist says 'basically they are doing the same thing as farmers did in Europe' Oh really? I understood that it is more like raping the seafloor and leaving it devastated and barren - not adding anything, not growing any crops - just wiping out every damned living thing like a bombing run. Those scientists are PR men for the Spanish trawler fleet.

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4. 4. dbiello in reply to Unksoldr 09:39 AM 9/6/12

   True, but this is the first empirical proof. And the scale and regularity were somewhat unexpected.

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5. 5. kienhua68 07:32 PM 9/6/12

   I can say that bottom trawling, above all other possible
   insults to the sea, has the longest lasting negative effect on the ocean environment and our food supply.
   
   'Farming' the ocean has never been a concept, fishermen or the fishing industry could accept. Living on Cape Cod I watched as the Draggers scraped away the future of fishing on the Cape. That along with no concern for
   how many fish were taken per trip.
   

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6. 6. Postman1 11:07 PM 9/6/12

   I wonder if bottom trawling could stir up nutrients from the sediment and add to the food supply for krill and other bottom-of-the-food-chain creatures? If so, it wouldn't be an all bad situation.

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7. 7. spinylumpsucker 03:42 PM 9/7/12

   It isn't news that trawling is destructive - to ocean biodiversity, fish habitats, etc. I guess the news here is that it's also fundamentally reconstructing the topography of our ocean floor. There's very little video footage of trawlers in action, but there is this one, which is pretty horrifying:
   
   http://youtu.be/cVHRsRQ-UIo

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8. 8. Deweye 04:05 PM 9/8/12

   Almost as horryfying in all this is that, still, our human perception and awearness are so focused on our own, imagined,land-based biosphere, when we out to realize that there is really just one integreated biosphere; dramatic changes in one part of it will ultimately have consequences on the other parts. Where is the united human effort to stop bottom trawling?

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9. 9. Quinn the Eskimo 01:31 AM 9/9/12

   I didn't realize, David, that the sea mounts had been so eroded by fishing. The distinguished Bob Ballard had declared the sea floor large mud flats. Perhaps, with all this damage, we should ban the restaurants that are called Red Lobster from offering sea food?

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10. 10. Ian St. John 01:19 PM 9/10/12

    I agree with the article in terms of making some areas off limits to fishing, but it should be selected 'nursery habitat' mostly and it should encompass a large proportion of the total fishable seabed. 60 to 80% in my opinion. Couple this with elimination of species and catch quotas in the open areas so that the 'restricted' areas provide the nursery for generations of fish, while the open areas provide the catch without dumping of 'bycatch' so that we can utilise almost all of the fish we catch. The 'regulation' of fisheries would be 'automatic' as fish move from the regulated to the unregulated areas (from population pressure) ensuring a good population of mature fish to maintain spawning. Also, the size of the fish would go down a bit (the largest fish are the best spawners) which would help to ensure a stable and efficient production of new spawn. Taking the largest fish ONLY is counter productive.

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11. 11. HubertB 08:04 PM 9/10/12

    The most productive fish nursery is a mangrove swamp. An extremely large of the world's mangroves have been cut down (Miami Beach). The second most productive fish nursery is a salt marsh. Many of those are now sports arenas (meadowlands), airports (JFK), houses, warehouses. etc. We are probably allowing trawlers to destroy another great fish nursery. We are eating our seed corn.

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12. 12. IslandGardener 03:44 AM 9/11/12

    'Fishermen are not doing anything different than farmers many decades ago... Fishing grounds could be seen as farm fields' says Pere Puig.
    
    This sounds horribly like the argument used by biologist Thomas Huxley (who should have known better) in the 19th century when deciding whether to do anything about trawling. He ignored the protests of non-trawling fishermen.
    
    I learnt this recently by reading the excellent 'The Unnatural History of the Sea' by marine biologist Callum Roberts. It's a heartbreaking read, because the destruction he describes is so terrible, and has been going on so long, that we can barely even imagine the riches we have destroyed.
    
    But he ends more positively, with evidence that marine conservation (including banning trawling from almost everywhere) can restore much of that richness.
    
    http://www.york.ac.uk/res/unnatural-history-of-the-sea/
    
    And anyway farm fields are not such a great example of being environmentally friendly. We've destroyed natural habitats and turned the carbon in soil organic matter into carbon dioxide.
    
    If we want to see how we could get food from the sea in ethical and sustainable ways with a good land analogy it'd be better to think of something like forest gardening and other forms of agroforestry.
    http://en.wikipedia.org/wiki/Agroforestry
    Then we'd be more likely to think it was stupid to reduce the structural diversity of the seafloor and to destroy all the habitats which used to be there. If there's no habitat for fish fry to live in or feed from when they're at their smallest and most vulnerable then how can they grow to be the fish which we then want to catch?
    
    I wonder what the Marine Stewardship Council make of all this...
    http://www.msc.org/

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13. 13. lennysupak@live.com in reply to rollership 09:49 PM 9/12/12

    Been there done "that". It may be too far gone already. If you would like a tour of the Bering Sea go ahead. While you can. It is a rather unforgiving and fascinating area. It would be
    "nice" to save something, beautiful. In USA inc. I agree.

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14. 14. BuckSkinMan 11:40 PM 9/12/12

    Keeping humans from food - especially from the more delectable kinds - seems to be a rather overly optimistic endeavor. ;-)
    
    While this article deals only with a limited example (reminding one of the oh-so simple minded use of desert island metaphores), it fails to address what is being done to improve the methods like bottom trawling. Like we've never seen prior examples: nets which release turtles and other protected species, etc.
    
    Dragging out the crayons and construction paper, lets draw a diagram for those who find this idea challenging. 1. examine a technological method which produces successful harvests. 2. look for and study any deleterious side effects. 3. come up with new designs to continue the successful harvesting while eliminating damage to the environment. Rinse and repeat.

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