Credit: AnnaMargittai, Flickr
Sharks and humans have a tortured relationship. But underneath the fearsome killer instinct and razor-sharp teeth is an ultra-sensitive machine that nature has tuned to perfection. A shark's body is bristling with sensory organs, listening, feeling and responding to an underwater world humming with activity. Their famed ability to detect even a whiff of blood is just the beginning. Sharks have ears and eyes similar to humans, as well as electrical receptors that can detect a struggling fish or Earth's magnetic field. A line of pressure-sensitive cells runs down each side of their body as well, letting them know if anything stirs in the waters nearby.
Sharks' electric sense perception deserves its spooky abbreviation, “ESP.” Sharks' ampullae of Lorenzini (pictured) are little tubes that are extremely sensitive to the electrical signals emitted by struggling, wounded fish – or even from a single muscle twitch. This allows them to hone in on struggling fish, or prey that may stir while buried in the sand. Electroreceptors first appear early on in the development of shark embryos (inset), recent research found, developing out of the same stem cells that shape humans' head and facial features. The finding suggests that electro-sensing was probably common in our ancient ancestors until they came ashore and lost the ability.
“And, you know, the thing about a shark... he's got lifeless eyes. Black eyes. Like a doll's eyes. When he comes at ya, doesn't seem to be living...” -- Jaws, 1975 Like most pop culture references to sharks, this famous quote from Steven Spielberg's Jaws is overstated. The shark is famous for its empty stare, but erroneously so -- sharks have pupils just like humans that can expand and contract to control the amount of light they let in. Their eyes even have color (pictured). Sharks can see very well in low-light conditions common underwater, but their eyes don't have lenses and so can't reolve shapes.
Nostrils of Death
Just like a human's, the shark's nose picks up chemicals mixed into the surrounding environment. But since this all occurs underwater, the nose needs to be able to channel water across its feathered-shaped olfactory organs - called lamellae - and scan for a hint of something good to eat.
The Sounds of Supper
Sharks' sense of hearing and taste are both linked to touch – they literally feel their way to their next meal. While sharks are able to detect sound through an organ in the utriculus portion of the inner ear, they primarily rely on small hairs in the ears to feel changes in the water. Taste is similar -- sharks often bite their prey once before deciding whether or not to dive in for a meal. This behavior is mostly based on how the quarry feels in the shark's mouth; sharks don't exactly taste their "snack," so much as feel how soft, hard and potentially nutritious it will be.
Feeling the Pressure
A shark's lateral line is essentially a pressure meter: as any solid body moves through the water, it sends out pressure waves. Sharks both detect that movement and sense direction, feeling from which direction the pressure waves came as if they were touching the object itself. Humans have no sense comparable to the lateral line.
Like most animals, sharks are eating, mating machines. And as the dominant predators of the seas, sharks have the ability to inspire fear and encourage us to keep our distance. But they are also marvels of natural engineering, able to function effectively in the often dark, murky and confusing underwater environment. They are streamlined, beautiful, nearly perfect; as the dominant species on the planet, we still have much to learn from them.
Guest commentator Debbie Salamone is Communications Manager at the Pew Campaign to End Overfishing in the Southeast.
There's nothing like a good shark attack story. I should know. I was a journalist for 21 years near Volusia County, Florida — the shark bite capital of the world. I even made sure someone phoned my newspaper to report my own shark attack as I was pumped full of morphine and wheeled into the operating room.
Sharks always seem to be taking the rap as man-eating villains –- in the media, movies and books. So let's get a little perspective. Your chances of being attacked by a shark are just one in 11.5 million, according to the University of Florida's International Shark Attack File.
On average, there are about 65 shark attacks worldwide each year; a handful are fatal. You are more likely to be killed by a dog, snake or in a car collision with a deer. You're also 30 times more likely to be killed by lightning and three times more likely to drown at the beach than die from a shark attack, according to ISAF.
Even digging a sand hole is more dangerous…
The New England Journal of Medicine reported that from 1990 to 2006, 16 people died by digging until the sand collapsed and smothered them. ISAF counted a dozen U.S. shark deaths in the same period. Clearly, you'd be safer in the water, with the sharks.
Still not convinced? Consider another ISAF statistic: In one year in the U.S., sharks injured just 13 people while nearly 200,000 were hurt in accidents involving ladders, toilets and chainsaws.
And in an older, but memorable study by the Consumer Product Safety Commission, researchers tracked vending machine deaths from 1977 to 1995. Thirty-seven people were killed when they toppled a vending machine to get a reluctant quarter or cola — an average of about two per year, or twice the number killed by sharks in the US. Just when you thought it was safe to get a Dr. Pepper…
You get the picture.
Even when they do happen, most shark attacks are “hit and run" — the shark takes a bite, realizes it made a mistake and moves on to something more delicious. That's what happened to me. Devastating injuries and brutal attacks are much more unusual.
Sharks may not appear as the most cuddly creatures on Earth, but they are worth saving for the health of the entire ocean ecosystem. Learn more about the threats to sharks and the importance of preserving them at www.pewsharks.org. And if you're still afraid to go back in the water, more comforting statistics on the risk of shark attacks are available at ISAF.