Cod, flounder and halibut make delicious seafood, but they're often not sustainably harvested. In fact, they're likely caught with one of the most destructive types of fishing gear: bottom trawls. These large, heavy nets are dragged across large areas of seafloor, and inevitably clear-cut everything in their path. Last month, a group of scientists called for an end to destructive deep sea fishing practices in the journal Science, including bottom trawling -- noting that one-fifth of continental shelves have been trawled at least once, and this has led to both habitat and species loss.
So, how exactly does bottom trawling affect the deep-sea ecosystems?
A new study took a close look at bottom-trawled areas in the Mediterranean, and found that this fishing practice jeopardizes deep-sea sedimentary ecosystems and causes irreversible damage to seafloor communities. The scientists determined that chronically trawled sediments have significantly less biodiversity (by as much as half!) compared to undisturbed areas, and that the presence of worms and other small marine organisms decreased by nearly 80 percent -- posing a threat to marine food chains.
Another recent study on bottom fishing honed in on New England ecosystems, and found that mobile fishing gear -- like bottom trawls and scallop dredges -- cause more damage to ecosystems than stationary gear like traps and gillnets, according to a press release. Additionally, the researchers found that geological formations, like cobbles and boulders, are more susceptible to these destructive fishing practices and take longer to recover than sand and mud habitat -- which, the researchers note, makes sense since it took these geological structures thousands of years to form. The scientists hope their research will aid in developing a framework for fisheries managers, identifying spatial overlap of the most destructive fishing gears and the most vulnerable habitat. Their work is currently being used to construct the fishing closures on Georges Bank and in the Gulf of Maine.
Oceana is working to protect deep sea communities from this destructive fishing practice both domestically and internationally. In U.S. waters, Oceana is campaigning to limit or prohibit bottom trawling in areas known to house corals or deep sea sponges, and Oceana's "freeze the footprint" campaign provides recommendations for fisheries managers. In Europe, Oceana works to classify marine habitats in the Bay of Biscay, Mediterranean Sea and Atlantic Ocean and inform management proposals. Portugal recently closed over two million square kilometers to destructive fishing gears like trawling, and as a result of Oceana's efforts, 180,000 square miles of the Bering Sea are closed to bottom trawling.