The difference a photo makes is interesting.
Out of Sight, Out of Mind: Loving Our Oceans to Death has a Landsat satellite image of the Gulf of Mexico

The cloudy water that you see is the direct result of commercial bottom trawlers dragging large, heavy nets across the seafloor, denuding it of all life in their quest for a few marketable fish and shrimps. Unfortunately, most bottom trawlers destroy as much as 20 pounds of “bycatch” — unmarketable corals, sponges, fishes and other animals — for every pound of commerically valuable “seafood” that they retrieve, while they leave behind huge, choking clouds of mud and sediment that take weeks or longer to settle.
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“Until recently, the impact was basically hidden from view,” he continued. “But new tools — especially Internet-based image sites, like Google Earth — allow everyone to see for themselves what’s happening. In shallow waters with muddy bottoms, trawlers leave long, persistent trails of sediment in their wake.”
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What can you do to reduce this enviromental destruction? Until the industrial fishing industry proves that they are acting in a more environmentally responsible manner, you can boycott eating orange roughy, Chilean sea bass (Patagonian toothfish), and all shrimps. (Keep in mind that those shrimp species that are not caught by trawling are usually farmed in shallow coastal mangroves, which also leads to tremendous, and possibly irreversible, environmental damages).

But don’t just stop buying trawler-caught seafood – tell your supermarket or fishmonger why you’ve stopped buying it. Your consumer action can make a huge difference.