About a quarter of the ocean's surface is a desert. Hundreds of miles of open water with almost no food in it. So when a big ship crosses one of these empty stretches, it becomes the only interesting thing for miles, and fish start trailing along behind it.Biologists have studied this for decades. Any floating object out there, a log, a clump of seaweed, a drifting coconut, a stray piece of trash, a whole ship, ends up working like a magnet for fish. To something living in all that emptiness, an