Here's the good news: You don't have to worry about a blue shark stalking you while you frolic in the waves a few yards from your beach blanket. This aquatic predator, who can grow in excess of 12 feet (3.6 meters) in length, prefers to remain in waters at least 1,150 feet (350 meters) deep. That's where it finds its dinner: small bony fishes, like herring and sardines, and invertebrates, like squid, cuttlefish and octopi. It's also been known to scavenge on dead marine animals and steal from fishermen's nets.
And that brings us to the bad news: Although blue sharks aren't known to be particularly aggressive -- especially compared to their nastier cousins the bull sharks -- they won't always turn their noses up at a potential meal of human flesh, either, if you happen to be shipwrecked or floating on your seat cushion after surviving a plane crash. Reportedly, blue sharks have circled unfortunates bobbing around in their feeding grounds, and have been known to take exploratory bites [source: Florida Museum of Natural History]. That said, between 1580 and 2010, there've only been 32 (just 32!) reported blue shark attacks, including four unprovoked attacks that resulted in fatalities [source: International Shark Attack File].
In reality, blue sharks (Prionace glauca) have far more to fear from people. An estimated 10 to 20 million of them are killed by humans each year. Many blue sharks are killed when they become entangled in fishermen's nets and others are slaughtered for their fins, which are sold on Asian markets for making shark fin soup, a delicacy [source: Florida Museum of Natural History].