Given the season here in the U.S. and elsewhere in the Northern Hemisphere, I’m sure many readers of this blog are heading to the beach. So in the interest of scientific inquiry (certainly not to scare you), I thought it might be timely to look at a favorite subject of beachgoers everywhere—sharks; specifically, given the focus of this blog, how well these fearsome denizens of the sea see.
For many years, scientists believed that sharks did not have very acute vision—that they relied primarily on their other highly developed senses to track their prey. But recent research indicates that some shark species have very highly developed vision that matches or surpasses that of human beings.
The anatomy of a sharks’ eye is much like ours. Like us – and unlike most fish – sharks have the ability to open and close their pupils to accommodate different light situations. Most sharks also have a cornea, iris, lens and a retina complete with rod and cone cells, which means they can see color and detail. And, like cats, sharks’ eyes have a mirror-like layer in the back of the eye called the tapetum lucidum, which enhances their light sensitivity, making it ten times better than ours.
But not all sharks are the same—or see the same way. According to the United Nations Food and Agricultural Organization, there are 354 species of sharks, ranging in length from six inches to 49 feet, and their vision varies according to differences in the size, focusing ability and eye strength.
Its unmistakably shaped head makes the hammerhead shark perhaps the most distinctive shark in the world. And that unique head, which provides great distance between each eye, provides hammerheads with excellent stereovision and depth perception, which scientists think helps them make quick work of prey like fast-moving squid.
Another familiar species of shark – particularly to movie fans and viewers of “Shark Week” – is the great white. While many sharks have nictitating membranes, which protect their eyes while they are hunting or when they are being attacked, great whites do not. Instead, their eyes roll backwards in those situations. (That doesn’t help make them seen any less scary, does it?)
The bottom line: current research indicates sharks have terrific vision. And that great vision, coupled with their ability to detect even small amounts of electric current or vibrations and chemical changes in the water (not to mention those many rows of big, sharp teeth) helps make them highly effective hunters.
All this information about how well sharks see needn’t change your beach plans. While they are fearsome predators, keep in mind that the odds of being attacked by a shark are extremely rare: about 1 in 11.5 million, according to the National Shark Attack File. Far more humans are killed or injured by dogs, bees, snakes and a whole host of other animals than by sharks.
But sharks can be dangerous, and the easiest way to avoid being attacked is to not get in the water with them (of course!). Here are more commonsense tips for avoiding shark attacks and fending them off in the unlikely event you attract their interest.
Have a great summer!