Swimming

Fact vs Fiction: How Sharks Hunt and ‘Feel’ (2/3)

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Disclaimer: I do not own any images displayed or material presented. This is purely for educational purposes

Image result for surfer and sealImage result for surfer and seal

 Nelson, G. for  (2015). Researchers examine why sharks mistake surfers for their intended prey. Daily Mail Australia. Retrieved from https://www.dailymail.co.uk/news/article-3031958/Researchers-examine-sharks-mistake-surfers-intended-prey.html.
Norén, L. (2009). Seeing Sharks. Retrieved from https://thesocietypages.org/graphicsociology/2009/page/3/.

While shark attacks rarely kill humans, in contrast, we annually kill about 20-30 million sharks in the fishing industry or for sport, according to the Florida Museum of Natural History’s Department of Ichthyology. Sharks are animals, they act on instinct, they do not just attack or hold grudges as seen in many shark movies. When humans are jumping and swimming around the water, it signals the shark of potential prey, much like a fish in distress. Contrary to popular belief, sharks don’t actually mistake us – people – for the seals that they normally eat. The way a shark hunts is mainly to test if it is worth their energy to try and kill an individual prey, they do a hit-and-run tactic to ‘test’ the prey to determine if it is food. Shark’s eyes are keen, but some images that they normally do not see, like a human, may confuse them. They simply might not know what it is they are looking at. Even though they can see a human, “sometimes that’s not enough for a shark, they want to feel what it is. When this happens, the shark will place its jaws over the object, scientists call this ‘mouthing’. The shark clamps down with the same bite force as a human, hardly anything to a shark. The reason for this is to get an idea of what the object is, and if it’s worth pursuing further interest” (Drift). Such an incident is called an attack for record-keeping purposes but compared to what sharks can and routinely do to seals makes an incident like this actually pretty tame in contrast.

Eye
Godknecht, A. (2004) Sharks Are Masters of Seven Senses. Shark Foundation – Foundation for Research and the Preservation of Sharks, Shark Foundation / Hai-Stiftung. Retrieved from https://www.shark.ch/Information/Senses/index.html.

Seeing under water is only possible from 0 to ~50 meters, depending on the water conditions. In addition, colors are absorbed more strongly with increasing water depth. Under these circumstances the advantage lies with whomever has better eyesight, be it predator or prey. Sharks have developed methods of amplifying light in their eyes which make them more efficient than such night-hunting mammals as cats, foxes or wolves, and yet we perceive that sharks mistake surfers for seals.

RA Martin, Neil Hammerschlag, and Ralph Collier from the ReefQuest Center for Shark Research argue that a “shark’s vision is too good and its sense of smell too sophisticated to confuse us [people] with a seal. These are supreme ocean predators and are highly unlikely to make clumsy and possibly costly mistakes.” (BBC News). The first blood draws a shark, but now we see that sharks are much more complex than we thought. Sharks have senses not available to most other animals.

Pressure-sensitive pores scattered over their head and down the body mean they detect the slightest changes in pressure, enabling them to discern the smallest of movements even when other senses are restricted—such as their sight in murky water. They also possess sophisticated electroreceptors which help them home in on the tiny electrical fields present around all living things, even creatures buried in sand. So, when we swim, they can detect that we are in the water and where the most activity can be felt. Such highly-tuned animals are not likely to misidentify something as large as a human being, hence why they ‘hit-and-run’ a human.  It is implied by most scientists today that sharks such as Great Whites see humans as other predators that could compete with them for food.

Generally, when sharks attack people they are not interested in eating the people, they want the people to leave the area. Scientists “Martin, Hammerschlag and Collier have studied many shark attacks and say that prior to targeting a human, they show aggressive postures as a warning, and when that message is ignored they take action”, which is why sharks usually let go after the first bite, and the victims is left with a missing limb or a chunk of flesh missing (BBC News). It has been a little over 40 years since Jaws changed our perception of the ocean, and slowly but surely its grip is relaxing. There is an increase in concern for shark welfare and a greater understanding of the creatures as fascinating and impressive predators. The calls for their protection are getting louder and although most people find it hard to love them, sharks are garnering more respect. We are less likely to criminalize them and more prone to accept their presence.

TBC in Part 3: https://u.osu.edu/kociba.5/2019/09/25/fact-vs-fiction-reality-of-sharks-and-their-future-3-3/

References:

Choi, C.  (2010). How ‘Jaws’ Forever Changed Our View of Great White Sharks. Live Science. Retrieved from www.livescience.com/8309-jaws-changed-view-great-white-sharks.html.

Godknecht, A. (2004) Sharks Are Masters of Seven Senses. Shark Foundation – Foundation for Research and the Preservation of Sharks, Shark Foundation / Hai-Stiftung. Retrieved from https://www.shark.ch/Information/Senses/index.html.

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

Martin, R. A. (2012).Biology of Sharks and Rays: Vision and a Carpet of Light. ReefQuest Centre for Shark Research. Retrieved from www.elasmo-research.org

Meyer, C.G. (2004). Sharks can detect changes in the geomagnetic field. Journal of the Royal Society. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/16849172

Mislinski, P. (2014). Why Do Sharks Attack? Discovery, Oceana. Retrieved from www.discovery.com/tv-shows/shark-week/about-this-show/why-do-sharks-attack/.

Nelson, G. for  (2015). Researchers examine why sharks mistake surfers for their intended prey. Daily Mail Australia. Retrieved from https://www.dailymail.co.uk/news/article-3031958/Researchers-examine-sharks-mistake-surfers-intended-prey.html.

Norén, L. (2009). Seeing Sharks. Retrieved from https://thesocietypages.org/graphicsociology/2009/page/3/.

Phillips, T. (2017) Why Do Sharks ‘Attack’ Humans? More than Just Mistaken Identity… Drift Surfing. Retrieved from www.driftsurfing.eu/why-do-sharks-attack-humans-more-than-just-mistaken-identity/.

 

 

Fact vs. Fiction: Sharks Part 1/3

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Disclaimer: I do NOT own the images they are for educational/reference purposes ONLY

Warning: Some images may be violent

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.

PLAUSIBLE: A shark’s maximum striking force is great enough to pull the barrels under.

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.

Punching a shark in the nose, eyes, or gills will cause it flee or at least back off briefly.

PLAUSIBLE: The sharks punched by both a specially modified Buster and Jamie were driven off briefly and were hesitant about making repeated approaches. Strikes to the gills were noted to be more effective than strikes to the nose.

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Given how movies can exaggerate an animal’s strength, a lot of these scenes are for entertainment purposes and do not serve as factual information. As all movies of fiction, it was to spice things up for audience. This however created a negative drawback when Jaws premiered in 1975. We knew little to nothing about sharks then, and we are still scratching the surface of the species. Not just the Great White, but for all types of sharks.

TBC in Part 2: https://u.osu.edu/kociba.5/2019/09/25/fact-vs-fiction-how-sharks-hunt-and-feel-2-3/

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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