10 Quick Facts about Sharks

10 Quick Facts about Sharks

The proper way to celebrate Shark Week

1. The Great White isn’t the biggest.

Photo Credit: Zac Wolf via Wiki Commons

Photo Credit: Zac Wolf via Wiki Commons

Now that Shark Week is here, the Great White is sure to garner a lot of attention, but many people incorrectly label it as the largest shark in the world. It might be the largest predator, but the whale shark holds the record for largest living shark (or any other fish, for that matter). It can grow up to 40 ft (12 m) in length and weigh up to 47,000 lbs (21.5 tons). However, it’s pretty docile and has even been reported to allow divers to catch a ride on its fins. There’s also no chance of one eating a human as it is a filter feeder like certain species of whale (hence the name).

2. They have an extra sense.

Sharks have electroreception which is the ability to detect natural electrical stimuli through electroreceptor organs called the ampullae of Lorenzini. Although many animals have this ability on a certain level, sharks have the greatest sensitivity to electricity. They can use it to detect animals even if they are still, hidden or buried in sand.

3. They have a lot of teeth.

Shark teeth

This is pretty obvious as soon as one opens its mouth, but you are still not seeing all of them. This is because sharks have several rows of teeth and when they start losing teeth on the front row, the next one moves forward like a conveyor belt. This is an ongoing process that takes place their entire lives. In some species a row of teeth is replaced in several months while in others it only takes a few days. This leads to certain species having over 50,000 teeth during their lifetime.

4. We know very little about how they reproduce.

Over the last decade or so, we observed several cases of something we never knew sharks were even capable of – parthenogenesis. This is a form of asexual reproduction where the embryo develops normally without being fertilized beforehand. This process was observed in captivity in several species of shark where it would have been impossible for the females to have any kind of contact with males.

5. Speaking of shark reproduction, most species of shark are ovoviviparous.

Photo Credit: Albert Kok via Wiki Commons

Photo Credit: Albert Kok via Wiki Commons

This means that they breed by laying eggs like other fish, but that the eggs hatch inside the mother’s body in the oviduct. They continue to be nourished inside until they finally exit their mother’s body alive and functional. However, many species engage in ovophagy. This literally means “egg eating” and it involves the more developed embryos eating the eggs of their unfortunate siblings.

6. What happens if sharks stop swimming?

They’ll die, obviously, because they can’t breathe. You’ll find this bit of trivia repeated very often and, actually, there is a bit of truth to it. The shortest answer is that this is true, but not for all species. There are two methods that sharks use to breathe. One of them is called ram ventilation which is the technique where they move forward in order to force water through their gills. The other is buccal pumping where muscles in the mouth are strong enough to pump water into their bodies. Buccal pumping allows shark to remain stationary without any problem. As it turns out, most sharks that use ram ventilation are also capable of using buccal pumping every now and then so they can also stop without repercussions. There is a small group, though, called forced ram ventilators which contains species that cannot breathe through buccal pumping. These species, which include the Great White and the whale shark, would indeed die if they stopped swimming.

7. So how do they sleep?

Photo Credit: Jim Winstead via Flickr

Photo Credit: Jim Winstead via Flickr

Actually, there is a lot about shark sleep we still don’t know. When it comes to species that can stop swimming, they will remain inactive and relatively motionless, but they keep their eyes open and they track movement around them. Species that need to swim continuously go into a process called sleep swimming where they keep moving although they are basically unconscious. In this case, it is the spinal cord which is actually guiding the movements and not the brain.

8. Can they be trained?

Actually…yes. Although don’t expect to have your very own performing shark anytime soon, sharks in captivity have been trained to react to certain stimuli such as lights and noises.

9. Does this mean they are smart?

Sharks and divers

Not necessarily, but they are certainly not as dumb as people make them out to be. Again, another bit of trivia passed around is that sharks have a brain the size of a golf ball or even smaller, furthering their label as “primitive killing machines”. However, studies have shown that their brain mass to body mass ratio is comparable to that of birds and even most mammals.

10. So are they dangerous?

Obviously, you shouldn’t go poking sharks for fun, but the fearsome reputation they have is more of a product of Hollywood, particularly Jaws. Sharks cause around 5 fatalities per year. Several factors can cause that number to spike in certain years but, overall, they produce far fewer fatalities than bees, ants, hippos, jellyfish, dogs and even deer (yes, deer, they cause a lot of car accidents).



Featured image courtesy of Jeff Kubina via Flickr.