Sharks are trash fish. The biggest enemy to sharks is man. Sharks are a critical part of marine ecosystems, a source for knowledge to help the human condition, and the basis of a valuable fishery. Sharks' eyes, which are equipped to distinguish colors, employ a lens up to seven times as powerful as a human's, and some shark species can detect a light that is as much as ten times dimmer than the dimmest light the average person can see. Some sharks can respire by pumping water over their gills through opening and closing their mouths while at rest on the bottom.
Great whites are relatively uncommon large predators that prefer cooler waters.
In some parts of their range, great whites are close to being endangered. Whale sharks, which are the largest fish that ever lived, are plankton feeders like the great whales, thus the name. The more than 350 species all differ in habitat, lifestyle and body form. Although there have been some reports of people being poisoned by shark meat, the meat from the majority of sharks is edible and delicious when properly handled and prepared. Sharks' relatively large and complex brains are comparable in size to those of supposedly more advanced animals like mammals and birds.