The 10 Most Dangerous Sharks


Nurse Shark

The nurse shark doing what it does best -- resting.
The nurse shark doing what it does best -- resting.
Wolcott Henry/National Geographic/Getty Images

If the nurse shark were a person, it might have a chip on its shoulder about its name, which isn't nearly as ferocious-sounding as "bull" or "tiger." But while the nurse shark certainly doesn't tend to human beings like an RN, its name is somewhat appropriate insomuch that the shark is generally non-aggressive and typically swims away from people. The species (Ginglymostoma cirratum), which grows to between 8 and 9 feet (2.4 and 2.7 meters) in length, is concentrated in shallow waters in the Caribbean, and off the coast of south Florida and the Florida Keys, but is also found along the Atlantic and Pacific coasts of the Americas [source: Florida Museum of Natural History].

Fortunately, even in the rare instances when a nurse shark does attack a human -- so far, 52 times, with no recorded fatalities -- the bite isn't powerful enough to be lethal [source: International Shark Attack File]. The downside is that the nurse shark's small mouth is attached to a large pharynx that enables it to suck up food and latch onto it. In fact, its grip is so vicelike that, in some cases, rescuers have had to use surgical instruments to free victims.

Fortunately, humans aren't the nurse shark's preferred meal, of course; the species feeds mainly on stingrays, octopi, squids, clams and crustaceans. They're nocturnal animals that rest on sandy bottoms or in caves and crevices during the day, and they often gather in groups of as many as 40. Nurse sharks have rounded, stubby heads with set-back eyes, and long caudal (tail) fins, which account for more than a quarter of their total length. They range from light yellowish tan to dark brown in color, and young nurse sharks have small black spots on their bodies. While nurse sharks are not endangered, their population in Florida has decreased in recent decades. [Source: Florida Museum of Natural History]