The satellite image shows a section of the Gulf of Mexico off the coast of Louisiana. The white dots are shrimp trawlers -- fishing boats that drag weighted nets across the ocean floor, a technique that is not only indiscriminate in what it catches but also destroys reefs and the benthic habitat of the ocean floor. By stirring up the organic matter in the sediment, it may even contribute to the formation of so-called "dead zones," such as the giant one that appears annually in the Gulf of Mexico.
Trawling has been likened to hunting game by clearcutting the forest. It's clearly unsustainable and yet it continues at be practiced at all-time record levels. For more on this, read this pdf, or go here to take a Google Earth tour of mudtrails worldwide. Finally, shrimp lovers go here for the 'skinny on shrimp.'