Sharks and Buoyancy

“What I Gathered from that 150-minute MCAT Class” Pt. 1

When an object is submerged under a fluid, there are two densities at work. The density of the fluid surrounding the object and the density of the object itself. Now if the object’s density is equal to the fluid density, then the buoyancy force (that’s pulling the object up) is equal to the force of gravity pulling the object down. Therefore, these two forces cancel out leaving a net force of zero which means the object is simply “suspended” in the water.

Some fish have an trait called swim bladders that allow them to achieve this suspension despite the varying depths of the ocean. This organ can expand or deflate allowing a fish to stay at a current water depth and conserve energy rather than trying to swim in order to keep from sinking or floating. Which is what evolution is all about – characteristics that allow a species to thrive without expending too many resources.

Now sharks, on the other hand, are much denser and are not equipped with swim bladders. So, as a result, they automatically sink to the floor. To avoid this, sharks are equipped with fins that are used to stay afloat. Which is probably why they are predators – because they need all of that extra energy to move their fins and “just keep swimming”. In some countries, shark fins are highly sought after commodities. However, the rest of the shark is not as profitable, so rather than heaving this giant shark body to shore (and thus, wasting more resources), these “shark finners” skin sharks alive and toss them back in the ocean, fin-less.

Well, because the density of a shark’s body is much greater than the density of the surrounding fluid, the shark ends up sinking to the bottom of the ocean floor. So this great, tremendous predator of the ocean waters is now reduced to nothing more than a loaf of bread, without any means of survival. In the end, these sharks are eaten by other fish or die due to suffocation.

How horrible is that? If I was a shark, I would elect to be taken completely when my fins are removed, rather than being thrown back into the water as a helpless organism. That is not how the great “food chain” works. I think it is absolutely horrible that, out of laziness, we cause another predator – who can easily hunt us down – to be stripped down to nothing. I know it’s a “dog eat dog world” out there, but this isn’t the case. This is, “dog steals another dog’s evolutionary means of survival” and runs away without a second look.

Physics can really get your mind going. What do you think?

– A.


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