There are not many creatures in the world that are as effective at hunting as the shark. When asked what makes them great hunters, people answer "because they're fast" or "because they are stealthy." Yes, sharks can swim fast at short bursts like the Shortfin Mako (Isurus oxyrinchus) shark, which exceeded a burst speed of more than 40 mph, or the Great White (Carcharodon carcharias) at more than 25 mph. Yes, sharks are stealthy. Their torpedo-shaped body is covered in tiny toothlike plates called dermal denticles. This "skin-teeth" perfects the animal's hydrodynamic design by reducing drag and enabling it to swim through its environment in utter silence.
Though speed and stealth help the shark to catch its prey, a great hunter must also find its next meal. Having roamed Earth's oceans for the last 450 million years, this animal has been perfecting its hunting technique. There are more than 400 species of sharks identified and found worldwide, except in the Arctic and Antarctic. Some are large, like the whale shark species at 60 feet long, while others are small, like the 10-inch-long Pygmy shark (Euprotomicrus bispinatus). Big or small, fast or not, sharks have developed into what seems to be the perfect hunter.
Typically hunting at dawn and dusk, they take advantage of the low light because they have a membrane, tapetum lucidum, which reflects light within the eye. Many people know it as eye shine. While swimming, they move their head side to side expanding their field of vision noticing anything moving within 50 feet. Sharks are also keen listeners hearing sounds from as far away as hundreds of miles. Since sound travels five times faster in water, flow over the smooth skin of a dolphin or the scaly body of a fish produces sound that radiates through the water. Sound powerful enough is felt along the shark's nerve-packed lateral line that extends alongside its body from head to tail.
Sharks are keen listeners, able to hear sounds from hundreds of miles away. Sound powerful enough is felt along the shark’s nerve-packed lateral line which extends alongside their bodies from head to tail.
DAVID FLEETHAM photo
Sharks can even detect trace amounts of blood by sniffing the water. Not only can sharks smell blood in the water, they can determine which direction it came from. Great White sharks are said to be able to detect a single drop of blood in an Olympic-sized swimming pool. Upon finding a possible meal, the shark will inspect it and may taste it by test biting. It's like having a meal presented to you and everything on your plate is unknown. You cautiously and conservatively taste before digging in. You need to be sure it won't hurt you and that it's really food.
In murky or dark conditions where other senses may not be useful, sharks can detect electricity. Every living organism produces electricity each time muscles move, including beating hearts. Electroreceptive organs called Ampullae of Lorenzini are located on the shark's snout. Research has found that a shark can detect electricity at levels as low as millionths of a volt!
Sharks are awesome hunters, and the role they play in keeping our oceans clean and beneficial by removing the dead, dying and weak ensures there will be healthy fish for the rest of us. Hawaii is home to at least 41 identified species of shark and since new species are still being discovered, we need to respect them and their environment. It is indisputable that we need sharks in the ocean and they need our help. The simplest way you can help is to choose sustainable seafood and refrain from supporting any industry responsible for harming or killing sharks.
* Erin Iberg is the community education manager at the Maui Ocean Center. "Ka Mo'olelo Moana," or "The Ocean Story," is a monthly column submitted by the Maui Ocean Center, which is open from 9 a.m. to 5 p.m. daily in Maalaea. For more information, call 270-7000.