Fact vs. Fiction: Sharks Part 1/3

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VS.™

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At one point in our lives we have seen at least one thriller, science fiction, or horror movie that stars an animal of monstrous proportions and attitude. The most well-known example of this is the shark nicknamed Bruce from the Jaws franchise. Jaws is your standard sci-fi thriller, where a creature is making a small town’s beach its feeding ground, and it is the duty of only three people – a police officer, a sailor and a scientist — to combat the creature and stop it. Even though in real life sharks are relatively harmless, it is human nature to stretch the truth or take things too literally, which makes situations very bad when we know so little about it to begin with. As humans, we have a history of fearing the unknown, and anything that scares us we try to hide from, eliminate, or separate from us.

Sharks are fish that have no bones, only cartilage. Their jaw is not fused to the braincase, which is the part of the skull that protects the brain,  allows them to eat very large prey whole. Sharks have no swim bladder for buoyancy (like the bony fishes) and use an oily liver to aid in buoyancy (Stewart). Sharks have an advanced electroreceptive system that detects slight electrical fields such as a fish in distress or something making large vibrations in the water. Furthermore, the teeth and skin are also modified placoid scales. They are  easily replaceable when they’ve broken or worn out as the teeth are lined up in a way that it resembles the teeth are waiting in line for their turn.

Moving up to swimming, while a shark is like a giant fish, and have different morphologies for different habitats. Some sharks (like the great white shark) swim by propelling itself through the water using its tail. The fins are only used for balance. Other sharks, like the whale shark, move their bodies from side to side to propel themselves through the water. Some species can move fast such as the Shortfin Mako shark (also known as the fastest shark) that can gain burst of speed to up to 42 mph, which is suited for open ocean hunting. Other species are slow swimming, like the Greenland shark (the slowest shark), which moves at a rate of less than 1 mph, and uses this as a ‘slow and steady’ strategy to hunt for prey.

The morphology of a shark is vastly different from a fish although and limits how it is able to swim the way it does. The shark’s morphology prevents them from being able to stop or swim backwards like a fish can do. Their pectoral fins cannot bend upward (like fish can), which only allows a shark to swim forward, not backwards (Donley). The oil in the liver is lighter than water and gives the shark some buoyancy, but it is still heavier than water and will sink if it doesn’t actively swim. However, they can use gravity (as they sink) to help them move backwards instead of swim if they needed to. Their bodies also limit them to swerve to the side in order to avoid obstacles- they cannot simply stop. Like a machine they only need to eat, swim, and reproduce.

The book, Jaws, written by Peter Benchley, was about a Great White Shark that started to hunt people that wandered into the water in a small island town. Benchley regretted writing the book as he spoke to in an interview for Animal Attack Files in 2000, “What I now know, which wasn’t known when I wrote Jaws, is that there is no such thing as a rogue shark which develops a taste for human flesh–No one appreciates how vulnerable they are to destruction’’ (BBC News). Sharks may be scary to most, even terrifying at their strength and many rows of sharp teeth. However, some large shark species certainly do attack humans—about 10 people a year are killed, usually by great white, bull and tiger sharks. Rarely though are the victims actually eaten by said shark, but they often die from the trauma and blood loss of the wound.

Even in films, the questions of a shark being able to achieve what the shark (Bruce) could do fictionally and realistically to its prey. For example, one scene of Jaws, the shark was shot with a harpoon tied to three air barrels to keep him close to the surface and tire him out. Unbelievably, in the movie, the shark was still able to dive. This incredible feat was brought to the attention of a popular show on the Discovery Channel, Mythbusters, which set out to see what myths about the famous shark were fact or fake. After a series of tests with a shark of similar size and weight to the one portrayed in the film, they scientifically determined that it is plausible for a shark like that to have enough force to pull the barrels underwater, but impossible for it to be held under there constantly. It would eventually tire out in a matter of minutes rather than the span of hours in the movie. It would also be the same for when the boat was dragged after they tied the rope of the barrels to the back of the boat, it does not have enough energy to maintain that amount of force constantly. Another popular myth tested was a little bit after the story of the USS Indianapolis, as told by Quint when he was in the Navy in WWII, a character from the film. Drunk and tired from the three character’s first encounter, Quint was distracted and began to sing shanties as the barrels and tag emerge from the water. The shark charges, and punctures the wooden boat on in the hull, which causes a short circuit. Now this myth was proven plausible, but only for a wooden boat, like in the one in the film, but other cases have not been reported. It can, however, tear a shark cage apart under the right circumstances, but overall, a shark’s strength has its limits and is not the ‘beast’ we were led to believe. Whether a shark has enough strength to do so, it would take too much energy for it to even attack and destroy a vessel, and to them, and it’s just not worth it for them.

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Jaws Myth: Boat Ram Scene

Video: https://www.youtube.com/watch?v=2PyDqdT4t-E

Mythbusters: Jaws Myths, Plausible, Busted, Confirmed

NOTE: Some Myths were deleted as they had no need to be on the list on why sharks are not like the shark in the movies

A Great White Shark can pull barrels underwater and hold them there.

BUSTED: The force a shark can generate in a continuous pull is insufficient to keep the barrels underwater for a significant amount of time.

A Great White Shark can ram a dive cage with enough force to damage or destroy it.

CONFIRMED: The “ShaRammer”, a machine designed to simulate the force of a Great White Shark, penetrated the cage with enough force to rip a significant part of it loose and carry it away on its body. The cage was completely destroyed.

A Great White Shark can ram a boat with enough force to punch a hole in it.

PLAUSIBLE: A Great White has enough power to punch a hole in the side of a wooden boat under the right circumstances, but an example of this happening has never been documented.

A Great White Shark can pull a boat backwards with great enough speed that waves break over the rear end.

BUSTED: The same reason why the shark cannot hold the barrels underwater continuously.

References:

Donley, J., Sepulveda, C., Konstantinidis, P. (2004). et al. Convergent evolution in mechanical design of lamnid sharks and tunas. Nature 429, 61–65  doi:10.1038/nature02435

Ritter, D. E. (1999). Fact Sheet: Tiger Shark. Shark Info. Retrieved from www.sharkinfo.ch

Stewart, K., E., D., & Thomson. (2015). Body Form and Locomotion in Sharks. Retrieved from https://academic.oup.com/icb/article/17/2/343/163516.

(2015). How Jaws Misrepresented the Great White. BBC News. Retrieved from www.bbc.com/news/magazine-33049099.

(1993). Inner Ear and Lateral Line. In A. Popper. The Physiology of Fishes. CRC Press.

(2005). MythBusters Special 8: JAWS Special. MythBusters Results. Retrieved from www.mythresults.com/special8.

Images:

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