Link #45: Most Sharks Will Drown If They Stop Swimming!

Link #45: Most Sharks Will Drown If They Stop Swimming!

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Link #45: Most Sharks Will Drown If They Stop Swimming!

Great White Shark
Great White Shark. Image credit: Elias Levy cc2.0

In our last post, we described how humans produce enough saliva in their lifetime to fill two Olympic-size swimming pools. While our capacity to produce saliva is inbuilt, swimming is something that we have had to learn. One animal for which swimming comes naturally is the shark.

In fact, most sharks actually need to continue swimming to be able to survive. If they don’t swim all the time then they will end up drowning. Sounds like an awful lot of work, doesn’t it? For most of us who like to plop ourselves on our couches off and on, it would seem that way. However, it’s perfectly true.

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Will a Shark Drown If It Stops Swimming?

Shark Cage Diving in Hermanus
Image credit: Hermanus Backpackers cc2.0

There are two ways you can look at the term ‘drowning’ here, and both of them are valid. The obvious meaning is to be unable to breathe, but some people may see it as sinking.

For most sharks, both are true. This means that if they’re not constantly swimming then they will be unable to breathe and drown. Similarly, if they don’t move around constantly then they’ll sink after a while.


Why Will a Shark Drown If It Stops Swimming?

Gills of whale shark
The gill slits of a whale shark flaring as it expels water from its pharyngeal cavity. Image credit: Jaontiveros GFDL

You already know that fish breathe through their gills which allow them to draw oxygen from water. Most fish have a system by which they push water through their gills.

Unfortunately, most species of sharks don’t have this mechanism. Instead, these sharks swim to push water through their mouths and into their gills where oxygen is extracted. These types of sharks are known as ram ventilators.

As a result, if a shark stops moving then its gills stop getting water and it stops getting oxygen. This is why a shark will drown if it stops swimming.


Why Will a Shark Sink If It Stops Swimming?

Fins typical function
Fins typically function as foils that provide lift or thrust, or provide the ability to steer or stabilize motion in water. PD image

In order to understand why a shark will sink if it doesn’t swim, you need to understand how other fishes keep floating even when they stop swimming. Fish that have bones, possess a balloon-like apparatus inside their bodies known as swim bladder.

The swim bladder is filled with gas which provides buoyancy and allows a fish to float. When the fish wants to dive, it deflates the swim bladder with muscles that are located around it.

Now, sharks are not bony fishes. Instead, they have cartilage which makes them much more flexible. Most sharks have a huge liver which is filled with oil. In fact, the liver is so large that it accounts for about 30 percent of the shark’s body mass.

However, this isn’t the only thing that sharks use to remain afloat in water. A key component to their ability to float is their fins. Their fins work on the same principle as that of an airplane’s wings.

The water flowing over the fin has to go faster than the water flowing below it because it has to cover a greater distance. The fins are curved on top. When the water flows faster above and slower below the fin, it generates lift which keeps the shark floating.

Hence, if the shark stops swimming then the water stops flowing around its fins and the shark sinks slowly.




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Sources:

http://en.wikipedia.org/wiki/Shark
http://animals.howstuffworks.com/fish/sharks/shark-drown.htm
http://animals.pawnation.com/can-sharks-not-float-sink-8238.html
http://www.sharky-jones.com/Sharkyjones/Slow/QandA/QA7%20-%20swimming.html
http://www.discovery.com/tv-shows/shark-week/about-this-show/can-sharks-drown/

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