10 Facts You Didn't Know About Sharks

Sharks inspire our curiousity and our fear of the unknown. They rule the watery depths where 95% of the Earth's oceans remain unexplored by humans. Here are some fast facts to pique your interest in these fascinating creatures. Read the full transcript here: http://bit.ly/1OhUoJk

Sabrina Stierwalt, PhD
4-minute read
Episode #153

This week marks a very important summer holiday observed by many who value exploration and risk-taking in order to triumph over the fear of the unknown. No, I’m not talking about Independence Day in the United States. I’m talking about the pop culture phenomenon known as Shark Week, a week of entirely shark-based television shows on the Discovery Channel. This year marks the event’s 28th installment, making Shark Week the longest running cable program in history.

So, why are we so obsessed with sharks? Perhaps we want to understand these creatures that are bigger, faster, and stronger than we are. Maybe our fascination with sharks reflects our desire to know more about the mostly uncharted ocean. By some metrics, we have explored even less of the Earth’s oceans than we have of outer space.

Geologists and oceanographers have mapped the entire ocean floor, but only to a resolution of 5 kilometers or about 3 miles. That means that in most areas of the sea floor, we can only see structures larger than 3 miles across. Anything smaller, like a potential shipwreck or deep blue marine habitat, remains unseen.

In space, we have a much more detailed picture of our planetary neighbors. NASA’s Magellan mission mapped 98% of Venus at a resolution of 100 meters. A full coverage map of Mars made by the Mars Odyssey spacecraft obtained similar resolution, while the European Space Agency has mapped ~60% of the Martian surface at 20 meters resolution. So, we may not be sure of the true extent of our universe, and we have yet to send probes outside of even our own solar system. However, in the areas of space that we have the technology to explore, we have made far more progress than in the depths of the ocean.

The deepest known part of the ocean, the Marianas Trench in the Pacific, reaches nearly 11,000 meters. The water pressure at the bottom of the Trench reaches over 1,000 times that at sea level or over 15,000 psi. Only three people have made it to the bottom of the Trench, including two engineers in 1960 and the movie producer James Cameron roughly 50 years later. In contrast, although humans have not traveled into space beyond the Moon, a mere 380,000 kilometers away, 12 people have made that trip.

Perhaps we look to sharks, the rulers of the deep, to tell us more about the uncharted depths where they can travel easily but we, and our probes, cannot. Since Shark Week has evolved from strictly factual documentaries to include lots of shark fan fiction, here are ten true and very interesting facts about sharks.

1. Sharks glide through water much like airplanes move through the air.

A shark’s tail forces water to flow over its fins much like a propeller creates airflow over the wings of a plane. Their infamous dorsal fins are used for added stability.

2. Most species of shark won’t drown if they stop moving.

Using the muscles around their mouths, ancient sharks could pump water over their gills so that oxygen could be absorbed. Present day sharks often breathe differently by instead using fast swimming motions to force water over their gills. When they want to stop to rest, they return to the muscle-based breathing method that doesn’t require motion. Although a few shark species don’t have strong enough muscles to revert to the more ancient breathing method, scientists have observed them taking breaks, although how they are dealing with such a strong dip in oxygen is unknown.

3. Sharks don’t get cavities.

Several shark species have teeth that are coated in fluoride thus helping their pearly whites stay strong and cavity-free.

4. Sharks have some of the largest fish brains.

We usually think of a shark as a lone hunter prowling the ocean solo, but many are actually social creatures and travel in herds with established hierarchies.

5. Sharks can track their prey via their heartbeats.

Sharks can track the electrical pulses associated with a heartbeat via electricity-sensing nodules on their noses called ampullae of Lorenzini.

6. Sharks don’t actually like the taste of humans.

If you are unlucky enough to be bit by a shark, the shark will not likely come back for a second taste when she or he realizes that you are not, in fact, a marine mammal.

7. You are more likely to be bitten by another person than by a shark.

You are even less likely to die from a shark bite than you are to be bitten. Of the 30 to 50 shark attacks reported each year, only 5 to 10 are fatal. So, while being bitten by a shark is rare, dying from a shark bite is even rarer.

8. The dens of goblin sharks are too deep for humans to explore.

The pink, long-nosed goblin shark lives along continental shelves and underwater mountain ranges in dwellings more than 100 meters deep.

9. The largest known whale shark was longer than a four story house.

Whale sharks are the biggest living species of fish. The largest known whale shark was just over 40 feet long and 47,000 pounds.

10. Sharks are vulnerable.

Between 20-30% of shark species are believed to be close to extinction, mostly due to being hooked by accident at commercial fisheries.

Until next time, this is Sabrina Stierwalt with Ask Science’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Ask Science on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com.

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About the Author

Sabrina Stierwalt, PhD

Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.